Biodegradation potential of MTBE in a fractured chalk aquifer under aerobic conditions in long-term uncontaminated and contaminated aquifer microcosms.

PubMed

Shah, Nadeem W; Thornton, Steven F; Bottrell, Simon H; Spence, Michael J

2009-01-26

The potential for aerobic biodegradation of MTBE in a fractured chalk aquifer is assessed in microcosm experiments over 450 days, under in situ conditions for a groundwater temperature of 10 degrees C, MTBE concentration between 0.1 and 1.0 mg/L and dissolved O2 concentration between 2 and 10 mg/L. Following a lag period of up to 120 days, MTBE was biodegraded in uncontaminated aquifer microcosms at concentrations up to 1.2 mg/L, demonstrating that the aquifer has an intrinsic potential to biodegrade MTBE aerobically. The MTBE biodegradation rate increased three-fold from a mean of 6.6+/-1.6 microg/L/day in uncontaminated aquifer microcosms for subsequent additions of MTBE, suggesting an increasing biodegradation capability, due to microbial cell growth and increased biomass after repeated exposure to MTBE. In contaminated aquifer microcosms which also contained TAME, MTBE biodegradation occurred after a shorter lag of 15 or 33 days and MTBE biodegradation rates were higher (max. 27.5 microg/L/day), probably resulting from an acclimated microbial population due to previous exposure to MTBE in situ. The initial MTBE concentration did not affect the lag period but the biodegradation rate increased with the initial MTBE concentration, indicating that there was no inhibition of MTBE biodegradation related to MTBE concentration up to 1.2 mg/L. No minimum substrate concentration for MTBE biodegradation was observed, indicating that in the presence of dissolved O2 (and absence of inhibitory factors) MTBE biodegradation would occur in the aquifer at MTBE concentrations (ca. 0.1 mg/L) found at the front of the ether oxygenate plume. MTBE biodegradation occurred with concomitant O2 consumption but no other electron acceptor utilisation, indicating biodegradation by aerobic processes only. However, O2 consumption was less than the stoichiometric requirement for complete MTBE mineralization, suggesting that only partial biodegradation of MTBE to intermediate organic metabolites occurred. The availability of dissolved O2 did not affect MTBE biodegradation significantly, with similar MTBE biodegradation behaviour and rates down to ca. 0.7 mg/L dissolved O2 concentration. The results indicate that aerobic MTBE biodegradation could be significant in the plume fringe, during mixing of the contaminant plume and uncontaminated groundwater and that, relative to the plume migration, aerobic biodegradation is important for MTBE attenuation. Moreover, should the groundwater dissolved O2 concentration fall to zero such that MTBE biodegradation was inhibited, an engineered approach to enhance in situ bioremediation could supply O2 at relatively low levels (e.g. 2-3 mg/L) to effectively stimulate MTBE biodegradation, which has significant practical advantages. The study shows that aerobic MTBE biodegradation can occur at environmentally significant rates in this aquifer, and that long-term microcosm experiments (100s days) may be necessary to correctly interpret contaminant biodegradation potential in aquifers to support site management decisions.

Effect of process parameters and operational mode on nitrous oxide emissions from a nitritation reactor treating reject wastewater.

PubMed

Pijuan, Maite; Torà, Josep; Rodríguez-Caballero, Adrián; César, Elvira; Carrera, Julián; Pérez, Julio

2014-02-01

Nitrous oxide (N2O) and methane emissions were monitored in a continuous granular airlift nitritation reactor from ammonium-rich wastewater (reject wastewater). N2O emissions were found to be dependent on dissolved oxygen (DO) concentration in the range of 1-4.5 mg O2/L, increasing within this range when reducing the DO values. At higher DO concentrations, N2O emissions remained constant at 2.2% of the N oxidized to nitrite, suggesting two different mechanisms behind N2O production, one dependent and one independent of DO concentration. Changes on ammonium, nitrite, free ammonia and free nitrous acid concentrations did not have an effect on N2O emissions within the concentration range tested. When operating the reactor in a sequencing batch mode under high DO concentration (>5 mg O2/L), N2O emissions increased one order of magnitude reaching values of 19.3 ± 7.5% of the N oxidized. Moreover, CH4 emissions detected were due to the stripping of the soluble CH4 that remained dissolved in the reject wastewater after anaerobic digestion. Finally, an economical and carbon footprint assessment of a theoretical scaled up of the pilot plant was conducted. Copyright © 2013 Elsevier Ltd. All rights reserved.

Molecular dynamics simulations of the surface tension of oxygen-supersaturated water

NASA Astrophysics Data System (ADS)

Jain, S.; Qiao, L.

2017-04-01

In this work, non-reactive molecular dynamic simulations were conducted to determine the surface tension of water as a function of the concentration of the dissolved gaseous molecules (O2), which would in turn help to predict the pressure inside the nanobubbles under supersaturation conditions. Knowing the bubble pressure is a prerequisite for understanding the mechanisms behind the spontaneous combustion of the H2/O2 gases inside the nanobubbles. First, the surface tension of pure water was determined using the planar interface method and the Irving and Kirkwood formula. Next, the surface tension of water containing four different supersaturation concentrations (S) of O2 gas molecules was computed considering the curved interface of a nanobubble. The surface tension of water was found to decrease with an increase in the supersaturation ratio or the concentration of the dissolved O2 gas molecules.

Influence of dissolved organic matter on photogenerated reactive oxygen species and metal-oxide nanoparticle toxicity.

PubMed

Li, Yang; Niu, Junfeng; Shang, Enxiang; Crittenden, John Charles

2016-07-01

The effect of humic acid (HA) or fulvic acid (FA) on reactive oxygen species (ROS) generation by six metal-oxide nanoparticles (NPs) and their toxicities toward Escherichia coli was investigated under UV irradiation. Dissolved organic matter (DOM) decreased OH generation by TiO2, ZnO, and Fe2O3, with FA inhibiting OH generation more than HA. The generated OH in NPs/DOM mixtures was higher than the measured concentrations because DOM consumes OH faster than its molecular probe. None of NPs/FA mixtures produced O2(-). The generated O2(-) concentrations in NPs/HA mixtures (except Fe2O3/HA) were higher than the sum of O2(-) concentrations that produced as NPs and HA were presented by themselves. Synergistic O2(-) generation in NPs/HA mixtures resulted from O2 reduction by electron transferred from photoionized HA to NPs. DOM increased (1)O2 generation by TiO2, CuO, CeO2, and SiO2, and FA promoted (1)O2 generation more than HA. Enhanced (1)O2 generation resulted from DOM sensitization of NPs. HA did not increase (1)O2 generation by ZnO and Fe2O3 primarily because released ions quenched (1)O2 precursor ((3)HA*). Linear correlation was developed between total ROS concentrations generated by NPs/DOM mixtures and bacterial survival rates (R(2) ≥ 0.80). The results implied the necessity of considering DOM when investigating the photoreactivity of NPs. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dissolved organic matter and aluminum oxide nanoparticles synergistically cause cellular responses in freshwater microalgae.

PubMed

Ye, Nan; Wang, Zhuang; Wang, Se; Fang, Hao; Wang, Degao

2018-06-07

This study investigated the impact of dissolved organic matters (DOM) on the ecological toxicity of aluminum oxide nanoparticles (Al 2 O 3 NPs) at a relatively low exposure concentration (1 mg L -1 ). The unicellular green alga Scenedesmus obliquus was exposed to Al 2 O 3 NP suspensions in the presence of DOM (fulvic acid) at various concentrations (1, 10, and 40 mg L -1 ). The results show that the presence of DOM elevated the growth inhibition toxicity of Al 2 O 3 NPs towards S. obliquus in a dose-dependent manner. Moreover, the combination of DOM at 40 mg L -1 and Al 2 O 3 NPs resulted in a synergistic effect. The relative contribution of Al-ions released from Al 2 O 3 NPs to toxicity was lower than 5%, indicating that the presence of the particles instead of the dissolved ions in the suspensions was the major toxicity sources, regardless of the presence of DOM. Furthermore, DOM at 10 and 40 mg L -1 and Al 2 O 3 NPs synergistically induced the upregulation of intercellular reactive oxygen species levels and superoxide dismutase activities. Analysis of the plasma malondialdehyde concentrations and the observation of superficial structures of S. obliquus indicated that the mixtures of DOM and Al 2 O 3 NPs showed no significant effect on membrane lipid peroxidation damage. In addition, the presence of both DOM and Al 2 O 3 NPs contributed to an enhancement in both the mitochondrial membrane potential and the cell membrane permeability (CMP) in S. obliquus. In particular, Al 2 O 3 NPs in the presence of 10 and 40 mg L -1 DOM caused a greater increase in CMP compared to Al 2 O 3 NPs and DOM alone treatments. In conclusion, these findings suggest that DOM at high concentrations and Al 2 O 3 NPs synergistically interrupted cell membrane functions and triggered subsequent growth inhibition toxicity.

Effects of increased inspired oxygen concentration on tissue oxygenation: theoretical considerations.

PubMed

Lumb, Andrew B; Nair, Sindhu

2010-03-01

Breathing increased fractional oxygen concentration (FiO2) is recommended for the treatment of tissue ischaemia. The theoretical benefits of increasing FiO2 on tissue oxygenation were evaluated using standard physiological equations. Assuming constant oxygen consumption by tissues throughout the length of a capillary, the oxygen content at 20 arbitrary points along a capillary was calculated. Using mathematical representations of the haemoglobin dissociation curve and an iterative approach to include the dissolved oxygen component of oxygen content, the oxygen partial pressure (PO2) profile along a capillary was estimated. High FiO2 concentrations cause large increases in PO2 at the arteriolar end of capillaries but these large PO2 values, caused by the extra dissolved oxygen, rapidly decline along the capillary. At the venular end of the capillary (the area of tissue most likely to be hypoxic), breathing oxygen causes only a modest improvement in PO2. Increasing FiO2 to treat tissue hypoxia has clear benefits, but a multimodal approach to management is required.

Influence of under pressure dissolved oxygen on trichloroethylene degradation by the H2O2/TiO2 process.

PubMed

Hoseini, Mohammad; Nabizadeh, Ramin; Nazmara, Shahrokh; Safari, Gholam Hossein

2013-12-20

The widespread use of trichloroethylene (TCE) and its frequent release into the environment has caused many environmental and health problems. In this study the degradation of TCE at different micromolar concentrations was investigated in a stainless steel reactor with various concentrations of H2O2 and TiO2 at different oxygen pressures and three different pHs. To examine the synergistic effect of under pressure oxygen on TCE degradation, the concentrations of H2O2 and TiO2 as well as pH were first optimized, and then the experiments were performed under optimal conditions. Gas chromatography with a flame ionization detector (FID) was used to measure TCE concentrations. Results showed that the percentage of TCE degradation without pressurized oxygen was low and it increased with increasing pressure of oxygen at all initial concentrations of TCE. The degradation percentages without oxygen pressure were 48.27%, 51.22%, 58.13% and 64.33% for TCE concentrations of 3000, 1500, 300 and 150 μg/L respectively. At an oxygen pressure of 2.5 atmospheres (atm) the percent degradation of TCE reached 84.85%, 89.14%, 93.13% and 94.99% respectively for the aforementioned TCE concentrations. The results of this study show that the application of dissolved oxygen under pressure increases the efficiency of the H2O2/TiO2 process on the degradation of TCE and can be used along with other oxidants as an effective method for the removal of this compound from aqueous solutions.

Influence of under pressure dissolved oxygen on trichloroethylene degradation by the H2O2/TiO2 process

PubMed Central

2013-01-01

Background The widespread use of trichloroethylene (TCE) and its frequent release into the environment has caused many environmental and health problems. In this study the degradation of TCE at different micromolar concentrations was investigated in a stainless steel reactor with various concentrations of H2O2 and TiO2 at different oxygen pressures and three different pHs. Methods To examine the synergistic effect of under pressure oxygen on TCE degradation, the concentrations of H2O2 and TiO2 as well as pH were first optimized, and then the experiments were performed under optimal conditions. Gas chromatography with a flame ionization detector (FID) was used to measure TCE concentrations. Results Results showed that the percentage of TCE degradation without pressurized oxygen was low and it increased with increasing pressure of oxygen at all initial concentrations of TCE. The degradation percentages without oxygen pressure were 48.27%, 51.22%, 58.13% and 64.33% for TCE concentrations of 3000, 1500, 300 and 150 μg/L respectively. At an oxygen pressure of 2.5 atmospheres (atm) the percent degradation of TCE reached 84.85%, 89.14%, 93.13% and 94.99% respectively for the aforementioned TCE concentrations. Conclusions The results of this study show that the application of dissolved oxygen under pressure increases the efficiency of the H2O2/TiO2 process on the degradation of TCE and can be used along with other oxidants as an effective method for the removal of this compound from aqueous solutions. PMID:24359702

Greenhouse gases dissolved in soil solution - often ignored, but important?

NASA Astrophysics Data System (ADS)

Weymann, Daniel; Brueggemann, Nicolas; Puetz, Thomas; Vereecken, Harry

2014-05-01

Flux measurements of climate-relevant trace gases from soils are frequently undertaken in contemporary ecosystem studies and substantially contribute to our understanding of greenhouse gas balances of the biosphere. While the great majority of such investigations builds on closed chamber and eddy covariance measurements, where upward gas fluxes to the atmosphere are measured, fewest concurrently consider greenhouse gas dissolution in the seepage and leaching of dissolved gases via the vadose zone to the groundwater. Here we present annual leaching losses of dissolved N2O and CO2 from arable, grassland, and forest lysimeter soils from three sites differing in altitude and climate. We aim to assess their importance in comparison to direct N2O emission, soil respiration, and further leaching parameters of the C- and N cycle. The lysimeters are part of the Germany-wide lysimeter network initiative TERENO-SoilCan, which investigates feedbacks of climate change to the pedosphere on a long-term scale. Soil water samples were collected weekly from different depths of the profiles by means of suction cups. A laboratory pre-experiment proved that no degassing occurred under those sampling conditions. We applied the headspace equilibration technique to determine dissolved gas concentrations by gas chromatography. The seepage water of all lysimeters was consistently supersaturated with N2O and CO2 compared to water equilibrated ambient air. In terms of N2O, leaching losses increased in the ascending order forest, grassland, and arable soils, respectively. In case of the latter soils, we observed a strong variability of N2O, with dissolved concentrations up to 23 μg N L-1. However, since seepage discharge of the arable lysimeters was comparatively small and mostly limited to the hydrological winter season, leached N2O appeared to be less important than direct N2O emissions. In terms of dissolved CO2,our measurements revealed considerable leaching losses from the mountainous forest and grassland soils, based on concentrations up to 24 mg C L-1 and high seepage discharge. Such losses turned out to be similarly important like soil respiration, particularly during winter when temperature-dependent soil respiration declined. In conclusion, the results of the first year of our measurements provide evidence that dissolved greenhouse gases should be considered in studies which aim to assess full greenhouse gas balances, particularly in ecosystems where hydrological conditions favour microbial activity and high leaching losses.

Investigation of the noble gas solubility in H 2O-CO 2 bearing silicate liquids at moderate pressure II: the extended ionic porosity (EIP) model

NASA Astrophysics Data System (ADS)

Nuccio, P. M.; Paonita, A.

2000-12-01

A semi-theoretical model is proposed to predict partitioning of noble gases between any silicate liquid and a H 2O-CO 2 gas phase with noble gas as a minor component, in a large range of pressures (at least up to 300 MPa). The model is based on the relationship between the concentration of dissolved noble gas and ionic porosity of the melt, found by Carroll and Stolper [Geochim. Cosmochim. Acta 57 (1993) 5039-5051] for H 2O-CO 2 free melts. It evaluates the effect of dissolved H 2O and CO 2 on the melt ionic porosity and, consequently on Henry's constants of noble gases. The fugacities of the noble gases in the H 2O-CO 2-noble gas mixtures are also considered in our equilibrium calculations of dissolved gas by using a modified Redlich-Kwong equation of state for the H 2O-CO 2-noble gas system. The formulated model (referred to as the extended ionic porosity model) clearly predicts a positive dependence of noble gas solubility on dissolved H 2O in melt, which becomes negligible when water concentration is higher than 3 wt%. Oppositely, noble gas solubility decreases as a consequence of increasing CO 2 in both basaltic and rhyolitic melts. The increase of noble gas solubility as a consequence of H 2O addition to the melt grows exponentially with the increase of the noble gas atomic size. As a result, although xenon solubility is much lower than the helium solubility in anhydrous melts, they become almost comparable at several percent of dissolved H 2O in the melt. On this basis, an exponential augmentation of the number of large free spaces in silicate liquid can be inferred in relation to increasing dissolved H 2O. Comparison between our predicted values and available experimental data [A. Paonita et al., Earth Planet. Sci. Lett. 181 (2000) 595-604] shows good agreement. At present, the EIP model is the unique tool which predicts how the main volatiles in magmatic systems affect the noble gas solubility in silicate melts, therefore it should be taken into account for future studies of noble gas fractionation in degassing natural magmas.

[Distributions and air-sea fluxes of dissolved nitrous oxide in the Yangtze River estuary and its adjacent marine area in spring and summer].

PubMed

Wang, Lan; Zhang, Gui-ling; Sun, Ming-shuang; Ren, Jing-ling

2014-12-01

Distributions and air-sea fluxes of nitrous oxide (N2O) in the seawaters of the Yangtze River estuary and its adjacent marine area were investigated during two cruises in March and July 2012. Dissolved N2O concentrations in surface waters ranged from 9.34 to 49.08 nmol x L(-1) with an average of (13.27 ± 6.40) nmol x L(-1) in spring and ranged from 7.27 to 27.81 nmol x L(-1) with an average of (10.62 ± 5.03) nmol x L(-1) in summer. There was no obvious difference between surface and bottom N2O concentrations. N2O concentrations in both surface and bottom waters decreased along the freshwater plume from the river mouth to the open sea. High values of dissolved N2O were found in turbidity maximum zone, which suggests that maximal turbidity enhances nitrification. Temperature had dual effects on dissolved N2O concentrations. N2O saturations in surface waters ranged from 86.9% to 351.3% with an average of (111.5 ± 41.4)% in spring and ranged from 111.7% to 396.0% with an average of (155.9 ± 68.4)% in summer. N2O were over-saturated at most stations. The sea-to-air fluxes of N2O were estimated to be (3.2 ± 10.9), (5.5 ± 19.3) and (12.2 ±52.3) μmol x (m2 x d)(-1) in spring and (7.3 ± 12.4), (12.7 ± 20.4) and (20.4 ± 35.9) μmol x (m2 x d)(-1) in summer using the LM86, W92 and RC01 relationships, respectively. The annual emissions of N2O from the Yangtze River estuary and its adjacent marine area were estimated to be 0.6 x 10(-2) Tg x a(-1) (LM86), 1.1 x 10(-2) Tg x a(-1) (W92) and 2.0 x 10(-2) Tg x a(-1) (RC01). Although the area of the Yangtze River estuary and its adjacent marine area only accounts for 0.02% of the total area of the world's oceans, their emission of N2O accounts for 0.06% of global oceanic N2O emission, indicating that the Yangtze River estuary and its adjacent marine area is an active area to produce and emit N2O.

Assessment of online monitoring strategies for measuring N2O emissions from full-scale wastewater treatment systems.

PubMed

Marques, Ricardo; Rodriguez-Caballero, A; Oehmen, Adrian; Pijuan, Maite

2016-08-01

Clark-Type nitrous oxide (N2O) sensors are routinely used to measure dissolved N2O concentrations in wastewater treatment plants (WWTPs), but have never before been applied to assess gas-phase N2O emissions in full-scale WWTPs. In this study, a full-scale N2O gas sensor was tested and validated for online gas measurements, and assessed with respect to its linearity, temperature dependence, signal saturation and drift prior to full-scale application. The sensor was linear at the concentrations tested (0-422.3, 0-50 and 0-10 ppmv N2O) and had a linear response up to 2750 ppmv N2O. An exponential correlation between temperature and sensor signal was described and predicted using a double exponential equation while the drift did not have a significant influence on the signal. The N2O gas sensor was used for online N2O monitoring in a full-scale sequencing batch reactor (SBR) treating domestic wastewater and results were compared with those obtained by a commercial online gas analyser. Emissions were successfully described by the sensor, being even more accurate than the values given by the commercial analyser at N2O concentrations above 500 ppmv. Data from this gas N2O sensor was also used to validate two models to predict N2O emissions from dissolved N2O measurements, one based on oxygen transfer rate and the other based on superficial velocity of the gas bubble. Using the first model, predictions for N2O emissions agreed by 98.7% with the measured by the gas sensor, while 87.0% similarity was obtained with the second model. This is the first study showing a reliable estimation of gas emissions based on dissolved N2O online data in a full-scale wastewater treatment facility. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dissolved oxygen: Chapter 6

USGS Publications Warehouse

Senn, David; Downing-Kunz, Maureen; Novick, Emily

2016-01-01

Dissolved oxygen (DO) concentration serves as an important indicator of estuarine habitat condition, because all aquatic macro-organisms require some minimum DO level to survive and prosper. The instantaneous DO concentration, measured at a specific location in the water column, results from a balance between multiple processes that add or remove oxygen (Figure 6.1): primary production produces O2; aerobic respiration in the water column and sediments consumes O2; abiotic or microbially-mediated biogeochemical reactions utilize O2 as an oxidant (e.g., oxidation of ammonium, sulfide, and ferrous iron); O2 exchange occurs across the air:water interface in response to under- or oversaturated DO concentrations in the water column; and water currents and turbulent mixing transport DO into and out of zones in the water column. If the oxygen loss rate exceeds the oxygen production or input rate, DO concentration decreases. When DO losses exceed production or input over a prolonged enough period of time, hypoxia ((<2-3 mg/L) or anoxia can develop. Persistent hypoxia or anoxia causes stress or death in aquatic organism populations, or for organisms that can escape a hypoxic or anoxic area, the loss of habitat. In addition, sulfide, which is toxic to aquatic organisms and causes odor problems, escapes from sediments under low oxygen conditions. Low dissolved oxygen is a common aquatic ecosystem response to elevated organic

A Dissolved Oxygen Threshold for Shifts in Bacterial Community Structure in a Seasonally Hypoxic Estuary.

PubMed

Spietz, Rachel L; Williams, Cheryl M; Rocap, Gabrielle; Horner-Devine, M Claire

2015-01-01

Pelagic ecosystems can become depleted of dissolved oxygen as a result of both natural processes and anthropogenic effects. As dissolved oxygen concentration decreases, energy shifts from macrofauna to microorganisms, which persist in these hypoxic zones. Oxygen-limited regions are rapidly expanding globally; however, patterns of microbial communities associated with dissolved oxygen gradients are not yet well understood. To assess the effects of decreasing dissolved oxygen on bacteria, we examined shifts in bacterial community structure over space and time in Hood Canal, Washington, USA-a glacial fjord-like water body that experiences seasonal low dissolved oxygen levels known to be detrimental to fish and other marine organisms. We found a strong negative association between bacterial richness and dissolved oxygen. Bacterial community composition across all samples was also strongly associated with the dissolved oxygen gradient, and significant changes in bacterial community composition occurred at a dissolved oxygen concentration between 5.18 and 7.12 mg O2 L(-1). This threshold value of dissolved oxygen is higher than classic definitions of hypoxia (<2.0 mg O2 L(-1)), suggesting that changes in bacterial communities may precede the detrimental effects on ecologically and economically important macrofauna. Furthermore, bacterial taxa responsible for driving whole community changes across the oxygen gradient are commonly detected in other oxygen-stressed ecosystems, suggesting that the patterns we uncovered in Hood Canal may be relevant in other low oxygen ecosystems.

Dissolved oxygen as a factor influencing nitrogen removal rates in a one-stage system with partial nitritation and Anammox process.

PubMed

Cema, G; Płaza, E; Trela, J; Surmacz-Górska, J

2011-01-01

A biofilm system with Kaldnes biofilm carrier was used in these studies to cultivate bacteria responsible for both partial nitritation and Anammox processes. Due to co-existence of oxygen and oxygen-free zones within the biofilm depth, both processes can occur in a single reactor. Oxygen that inhibits the Anammox process is consumed in the outer layer of the biofilm and in this way Anammox bacteria are protected from oxygen. The impact of oxygen concentration on nitrogen removal rates was investigated in the pilot plant (2.1 m3), supplied with reject water from the Himmerfjärden Waste Water Treatment Plant. The results of batch tests showed that the highest nitrogen removal rates were obtained for a dissolved oxygen (DO) concentration around 3 g O2 m(-3) At a DO concentration of 4 g O2 m(-3), an increase of nitrite and nitrate nitrogen concentrations in the batch reactor were observed. The average nitrogen removal rate in the pilot plant during a whole operating period oscillated around 1.3 g N m(-2)d(-1) (0.3 +/- 0.1 kg N m(-3)d(-1)) at the average dissolved oxygen concentration of 2.3 g O2 m(-3). The maximum value of a nitrogen removal rate amounted to 1.9 g N m(-2)d(-1) (0.47 kg N m(-3)d(-1)) and was observed for a DO concentration equal to 2.5 g O2 m(-3). It was observed that increase of biofilm thickness during the operational period, had no influence on nitrogen removal rates in the pilot plant.

Isotopic Clues on Factors Controlling Geochemical Fluxes From Large Watersheds in Eastern Canada

NASA Astrophysics Data System (ADS)

Rosa, E.; Helie, J.; Ghaleb, B.; Hillaire-Marcel, C.; Gaillardet, J.

2008-12-01

A monitoring and monthly sampling program of the Nelson, Ottawa, St. Lawrence, La Grande and Great Whale rivers was started in September 2007. It provides information on the seasonality and sources of geochemical fluxes into the Hudson Bay and the North Atlantic from watersheds covering more than 2.6 106 km2 of the eastern Canadian boreal domain. Measurements of pH and alkalinity, analyses of major ions, strontium and dissolved silica, 2H and 18O of water, concentrations and isotopic properties of dissolved organic and inorganic carbon (13C) and uranium (234U/238U) were performed. Lithology more than latitudinal climatic gradients controls the river geochemistry. Rivers draining silicate terrains show lower dissolved U concentrations but greater 234U/238U disequilibria than rivers draining carbonates (average of 1.38 vs. 1.23). Groundwater supplies might exert some control on these U- isotope signatures. No clear seasonality is observed in 234U/238U ratios, but U concentrations are correlated to dissolved organic carbon (DOC) concentrations in most rivers. Rivers draining carbonates present higher total dissolved carbon concentrations and higher 13C-contents in dissolved inorganic carbon (DIC), in response to the dissolution of soil carbonates. DOC/DIC ratios above 2.4 are observed in rivers draining silicates; their lower 13C-DIC content directly reflects the organic matter oxidation in soils. Total dissolved solids are one order of magnitude or more greater in rivers draining carbonates, showing the strong difference in chemical weathering rates according to the geological setting. The stability in chemical fluxes and water isotopic compositions in the La Grande River, which hosts hydroelectric reservoirs covering more than 12 000 km2, indicates that it is the most buffered hydrological system among the investigated watersheds. Seasonal fluctuations are observed elsewhere, with maximum geochemical fluxes during the spring snowmelt. 2H-18O content of river water appears to be the only parameter presenting a strong latitudinal and climatic gradient (independent of lithology).

Electrodeposition of crystalline GaAs on liquid gallium electrodes in aqueous electrolytes.

PubMed

Fahrenkrug, Eli; Gu, Junsi; Maldonado, Stephen

2013-01-09

Crystalline GaAs (c-GaAs) has been prepared directly through electroreduction of As(2)O(3) dissolved in an alkaline aqueous solution at a liquid gallium (Ga(l)) electrode at modest temperatures (T ≥ 80 °C). Ga(l) pool electrodes yielded consistent electrochemical behavior, affording repetitive measurements that illustrated the interdependences of applied potential, concentration of dissolved As(2)O(3), and electrodeposition temperature on the quality of the resultant c-GaAs(s). Raman spectra indicated the composition of the resultant film was strongly dependent on both the electrodeposition temperature and dissolved concentration of As(2)O(3) but not to the applied bias. For electrodepositions performed either at room temperature or with high (≥0.01 M) concentrations of dissolved As(2)O(3), Raman spectra of the electrodeposited films were consistent with amorphous As(s). X-ray diffractograms of As(s) films collected after thermal annealing indicated metallurgical alloying occurred only at temperatures in excess of 200 °C. Optical images and Raman spectra separately showed the composition of the as-electrodeposited film in dilute (≤0.001 M) solutions of dissolved As(2)O(3)(aq) was pure c-GaAs(s) at much lower temperatures than 200 °C. Diffractograms and transmission electron microscopy performed on as-prepared films confirmed the identity of c-GaAs(s). The collective results thus provide the first clear demonstration of an electrochemical liquid-liquid-solid (ec-LLS) process involving a liquid metal that serves simultaneously as an electrode, a solvent/medium for crystal growth, and a coreactant for the synthesis of a polycrystalline semiconductor. The presented data serve as impetus for the further development of the ec-LLS process as a controllable, simple, and direct route for technologically important optoelectronic materials such as c-GaAs(s).

The impact of four decades of annual nitrogen addition on dissolved organic matter in a boreal forest soil

NASA Astrophysics Data System (ADS)

Rappe-George, M. O.; Gärdenäs, A. I.; Kleja, D. B.

2012-09-01

Addition of mineral nitrogen (N) can alter the concentration and quality of dissolved organic matter (DOM) in forest soils. The aim of this study was to assess the effect of long-term mineral N addition on soil solution concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the Stråsan experimental forest (Norway spruce) in Central Sweden. N was added yearly at two levels of intensity and duration: the N1 treatment represented a lower intensity, but a longer duration (43 yr) of N addition than the shorter N2 treatment (24 yr). N additions were terminated in the N2 treatment in 1991. The N treatments began in 1967 when the spruce stands were 9 yr old. Soil solution in the forest floor O, and soil mineral B, horizons were sampled during the growing seasons of 1995 and 2009. Tension and non-tension lysimeters were installed in the O horizon (n=6) and tension lysimeters were installed in the underlying B horizon (n=4): soil solution was sampled at two-week intervals. Although tree growth and O horizon carbon (C) and N stock increased in treatments N1 and N2, the concentration of DOC in O horizon leachates was similar in both N treatments and control. This suggests an inhibitory direct effect of N addition on O horizon DOC. Elevated DON and nitrate in O horizon leachates in the ongoing N1 treatment indicated a move towards N saturation. In B-horizon leachates, the N1 treatment approximately doubled leachate concentration of DOC and DON. DON returned to control levels but DOC remained elevated in B-horizon leachates in N2 plots 19 yr after termination of N addition. Increased aromaticity of the sampled DOM in mineral B horizon in both the ongoing and terminated N treatment indicated that old SOM in the mineral soil was a source of the increased DOC.

Geographic and seasonal variation of dissolved methane and aerobic methane oxidation in Alaskan lakes

DOE PAGES

Martinez-Cruz, K.; Sepulveda-Jauregui, A.; Walter Anthony, K.; ...

2015-08-04

Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH 4) produced in lakes. Aerobic CH 4 oxidation depends mainly on lake CH 4 and oxygen (O 2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH 4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcelymore » reported in the literature. In the present study, we measured CH 4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH 4 and O 2 concentrations. Here, we found that in the winter, aerobic CH 4 oxidation was mainly controlled by the dissolved O 2 concentration, while in the summer it was controlled primarily by the CH 4 concentration, which was scarce compared to dissolved O 2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH 4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH 4 cycling.« less

Geographic and seasonal variation of dissolved methane and aerobic methane oxidation in Alaskan lakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez-Cruz, K.; Sepulveda-Jauregui, A.; Walter Anthony, K.

Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH 4) produced in lakes. Aerobic CH 4 oxidation depends mainly on lake CH 4 and oxygen (O 2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH 4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcelymore » reported in the literature. In the present study, we measured CH 4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH 4 and O 2 concentrations. Here, we found that in the winter, aerobic CH 4 oxidation was mainly controlled by the dissolved O 2 concentration, while in the summer it was controlled primarily by the CH 4 concentration, which was scarce compared to dissolved O 2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH 4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH 4 cycling.« less

A Dissolved Oxygen Threshold for Shifts in Bacterial Community Structure in a Seasonally Hypoxic Estuary

PubMed Central

Spietz, Rachel L.; Williams, Cheryl M.; Rocap, Gabrielle; Horner-Devine, M. Claire

2015-01-01

Pelagic ecosystems can become depleted of dissolved oxygen as a result of both natural processes and anthropogenic effects. As dissolved oxygen concentration decreases, energy shifts from macrofauna to microorganisms, which persist in these hypoxic zones. Oxygen-limited regions are rapidly expanding globally; however, patterns of microbial communities associated with dissolved oxygen gradients are not yet well understood. To assess the effects of decreasing dissolved oxygen on bacteria, we examined shifts in bacterial community structure over space and time in Hood Canal, Washington, USA−a glacial fjord-like water body that experiences seasonal low dissolved oxygen levels known to be detrimental to fish and other marine organisms. We found a strong negative association between bacterial richness and dissolved oxygen. Bacterial community composition across all samples was also strongly associated with the dissolved oxygen gradient, and significant changes in bacterial community composition occurred at a dissolved oxygen concentration between 5.18 and 7.12 mg O2 L-1. This threshold value of dissolved oxygen is higher than classic definitions of hypoxia (<2.0 mg O2 L-1), suggesting that changes in bacterial communities may precede the detrimental effects on ecologically and economically important macrofauna. Furthermore, bacterial taxa responsible for driving whole community changes across the oxygen gradient are commonly detected in other oxygen-stressed ecosystems, suggesting that the patterns we uncovered in Hood Canal may be relevant in other low oxygen ecosystems. PMID:26270047

The combined effect of dissolved oxygen and nitrite on N2O production by ammonia oxidizing bacteria in an enriched nitrifying sludge.

PubMed

Peng, Lai; Ni, Bing-Jie; Ye, Liu; Yuan, Zhiguo

2015-04-15

Both nitrite [Formula: see text] and dissolved oxygen (DO) play important roles in nitrous oxide (N2O) production by ammonia oxidizing bacteria (AOB). However, few studies focused on the combined effect of them on N2O production by AOB as well as the corresponding mechanisms. In this study, N2O production by an enriched nitrifying sludge, consisting of both AOB and nitrite-oxidizing bacteria (NOB), was investigated under various [Formula: see text] and DO concentrations. At each investigated DO level, both the biomass specific N2O production rate and the N2O emission factor (the ratio between N2O nitrogen emitted and the ammonium nitrogen converted) increased as [Formula: see text] concentration increased from 3 mg N/L to 50 mg N/L. However, at each investigated [Formula: see text] level, the maximum biomass specific N2O production rate occurred at DO of 0.85 mg O2/L, while the N2O emission factor decreased as DO increased from 0.35 to 3.5 mg O2/L. The analysis of the process data using a mathematical N2O model incorporating both the AOB denitrification and hydroxylamine (NH2OH) oxidation pathways indicated that the contribution of AOB denitrification pathway increased as [Formula: see text] concentration increased, but decreased as DO concentration increased, accompanied by a corresponding change in the contribution of NH2OH oxidation pathway to N2O production. The AOB denitrification pathway was predominant in most cases, with the NH2OH oxidation pathway making a comparable contribution only at high DO level (e.g. 3.5 mg O2/L). Copyright © 2015 Elsevier Ltd. All rights reserved.

Riverine N2O concentrations, exports to estuary and emissions to atmosphere from the Changjiang River in response to increasing nitrogen loads

NASA Astrophysics Data System (ADS)

Yan, Weijin; Yang, Libiao; Wang, Fang; Wang, Jianing; Ma, Pei

2012-12-01

This study investigated the variations of dissolved N2O and emissions over diurnal and seasonal temporal scales in 2009, as well as the time series of riverine N2O export to estuary and emission to atmosphere in response to increasing anthropogenic nitrogen loads in the Changjiang River. For the diurnal study, N2O concentrations ranged from 0.26 to 0.34 and from 0.44 to 0.52 μg N-N2O L-1 in August and October 2009, respectively. The dissolved N2O was supersaturated with a mean value of 197%. Studies on N2O emissions, also taken in August and October, ranged from 2.67 to 11.6 and from 6.72 to 15.2 μg N-N2O m-2 h-1, respectively. For the seasonal study (June through December 2009), N2O concentrations ranged from 0.34 to 0.72 μg N-N2O L-1 and were supersaturated in all the samples (average 212%). N2O emissions ranged from 1.87 to 40.8 μg N-N2O m-2 h-1. Our study found no significant differences in diurnal patterns of N2O saturation but detected significant difference in seasonal patterns of N2O saturation: higher during summer while lower during autumn and winter. We found a significant relationship between dissolved N2O and river nitrate, which can predict the variation of N2O concentrations in the River. The net production of N2 ranged from 0.01 to 0.47 mg N-N2 L-1. These excess N2 values were significantly correlated to the N2O production and are suggestive of denitrification in the river. Applying the Global News model to the river system using measures taken during the 1970 to 2002 period, we estimated N2O emissions to atmosphere increased from 330 to 3650 ton N-N2O yr-1. During that same 1970-2002 period, N2O exports to estuary increased from 91 to 470 ton N-N2O yr-1. Taken together, the findings reported here suggest that both the river N2O concentrations and emissions would increase in response to rising anthropogenic nitrogen loads. Our study showed that the mean emission factor based on the ratio of the total N2O flux to NO3- flux is four times greater than the value of 0.0025 obtained with the methodology recommended by the Intergovernmental Panel on Climate Change. Thus, our findings reflect the open river channel rapid exchange of gases with the atmosphere.

Equilibrator-based measurements of dissolved nitrous oxide in the surface ocean using an integrated cavity output laser absorption spectrometer

NASA Astrophysics Data System (ADS)

Grefe, I.; Kaiser, J.

2014-06-01

Dissolved nitrous oxide (N2O) concentrations are usually determined by gas chromatography (GC). Here we present laboratory tests and initial field measurements using a novel setup comprising a commercially available laser-based analyser for N2O, carbon monoxide and water vapour coupled to a glass-bed equilibrator. This approach is less labour-intensive and provides higher temporal and spatial resolution than the conventional GC technique. The standard deviation of continuous equilibrator or atmospheric air measurements was 0.2 nmol mol-1 (averaged over 5 min). The short-term repeatability for reference gas measurements within 1 h of each other was 0.2 nmol mol-1 or better. Another indicator of the long-term stability of the analyser is the standard deviation of the calibrated N2O mole fraction in marine air, which was between 0.5 and 0.7 nmol mol-1. The equilibrator measurements were compared with purge-and-trap gas chromatography-mass spectrometry (GC-MS) analyses of N2O concentrations in discrete samples from the Southern Ocean and showed agreement to within the 2% measurement uncertainty of the GC-MS method. The equilibrator response time to concentration changes in water was from 142 to 203 s, depending on the headspace flow rate. The system was tested at sea during a north-to-south transect of the Atlantic Ocean. While the subtropical gyres were slightly undersaturated, the equatorial region was a source of nitrous oxide to the atmosphere, confirming previous findings (Forster et al., 2009). The ability to measure at high temporal and spatial resolution revealed submesoscale variability in dissolved N2O concentrations. Mean sea-to-air fluxes in the tropical and subtropical Atlantic ranged between -1.6 and 0.11 μmol m-2 d-1 and confirm that the subtropical Atlantic is not an important source region for N2O to the atmosphere, compared to global average fluxes of 0.6-2.4 μmol m-2 d-1. The system can be easily modified for autonomous operation on voluntary observing ships (VOS). Future work should include an interlaboratory comparison exercise with other methods of dissolved N2O analyses.

C-O volatiles in Apollo 15 and Apollo 17 picritic glasses

NASA Technical Reports Server (NTRS)

Rutherford, Malcolm J.; Fogel, Robert A.

1993-01-01

A15 and A17 primitive picritic glasses have been examined by FTIR for the presence of dissolved C-O species to determine the role of C-O gasses on driving lunar fire-fountains. A15 green and yellow glasses were extensively studied and found to be free of dissolved C species down to FTIR detection limits (10-100 ppm; species and sample specific). Preliminary data on A17 orange glasses are similarly devoid of FTIR detectable C-O species. Re-analyses of the C-O driving mechanism theory for mare volcanism demonstrates the need to determine the fO2 of the lunar interior; the factor that most critically determined the role of C gasses in the fire-fountaining events. Oxygen fugacities equivalent to IW-0.5 and above imply dissolved CO3(=) in the primitive glasses at levels above FTIR detection. The f02's below IW-0.5 imply concentrations of CO3(=) below FTIR detection. Recent data suggesting lunar mantle fO2's of IW-2 or less, strongly mitigate against finding FTIR measurable dissolved CO3(=) consistent with the findings of this study.

Cellular partitioning of nanoparticulate versus dissolved metals in marine phytoplankton.

PubMed

Bielmyer-Fraser, Gretchen K; Jarvis, Tayler A; Lenihan, Hunter S; Miller, Robert J

2014-11-18

Discharges of metal oxide nanoparticles into aquatic environments are increasing with their use in society, thereby increasing exposure risk for aquatic organisms. Separating the impacts of nanoparticle from dissolved metal pollution is critical for assessing the environmental risks of the rapidly growing nanomaterial industry, especially in terms of ecosystem effects. Metal oxides negatively affect several species of marine phytoplankton, which are responsible for most marine primary production. Whether such toxicity is generally due to nanoparticles or exposure to dissolved metals liberated from particles is uncertain. The type and severity of toxicity depends in part on whether phytoplankton cells take up and accumulate primarily nanoparticles or dissolved metal ions. We compared the responses of the marine diatom, Thalassiosira weissflogii, exposed to ZnO, AgO, and CuO nanoparticles with the responses of T. weissflogii cells exposed to the dissolved metals ZnCl2, AgNO3, and CuCl2 for 7 d. Cellular metal accumulation, metal distribution, and algal population growth were measured to elucidate differences in exposure to the different forms of metal. Concentration-dependent metal accumulation and reduced population growth were observed in T. weissflogii exposed to nanometal oxides, as well as dissolved metals. Significant effects on population growth were observed at the lowest concentrations tested for all metals, with similar toxicity for both dissolved and nanoparticulate metals. Cellular metal distribution, however, markedly differed between T. weissflogii exposed to nanometal oxides versus those exposed to dissolved metals. Metal concentrations were highest in the algal cell wall when cells were exposed to metal oxide nanoparticles, whereas algae exposed to dissolved metals had higher proportions of metal in the organelle and endoplasmic reticulum fractions. These results have implications for marine plankton communities as well as higher trophic levels, since metal may be transferred from phytoplankton through food webs vis à vis grazing by zooplankton or other pathways.

Relative contributions of copper oxide nanoparticles and dissolved copper to Cu uptake kinetics of Gulf killifish (Fundulus grandis) embryos

USGS Publications Warehouse

Jiang, Chuanjia; Castellon, Benjamin T.; Matson, Cole W.; Aiken, George R.; Hsu-Kim, Heileen

2017-01-01

The toxicity of soluble metal-based nanomaterials may be due to the uptake of metals in both dissolved and nanoparticulate forms, but the relative contributions of these different forms to overall metal uptake rates under environmental conditions are not quantitatively defined. Here, we investigated the linkage between the dissolution rates of copper(II) oxide (CuO) nanoparticles (NPs) and their bioavailability to Gulf killifish (Fundulus grandis) embryos, with the aim of quantitatively delineating the relative contributions of nanoparticulate and dissolved species for Cu uptake. Gulf killifish embryos were exposed to dissolved Cu and CuO NP mixtures comprising a range of pH values (6.3–7.5) and three types of natural organic matter (NOM) isolates at various concentrations (0.1–10 mg-C L–1), resulting in a wide range of CuO NP dissolution rates that subsequently influenced Cu uptake. First-order dissolution rate constants of CuO NPs increased with increasing NOM concentration and for NOM isolates with higher aromaticity, as indicated by specific ultraviolet absorbance (SUVA), while Cu uptake rate constants of both dissolved Cu and CuO NP decreased with NOM concentration and aromaticity. As a result, the relative contribution of dissolved Cu and nanoparticulate CuO species for the overall Cu uptake rate was insensitive to NOM type or concentration but largely determined by the percentage of CuO that dissolved. These findings highlight SUVA and aromaticity as key NOM properties affecting the dissolution kinetics and bioavailability of soluble metal-based nanomaterials in organic-rich waters. These properties could be used in the incorporation of dissolution kinetics into predictive models for environmental risks of nanomaterials.

No effect of H2O degassing on the oxidation state of hydrous rhyolite magmas: a comparison of pre- and post-eruptive Fe2+ concentrations in six obsidian samples from the Mexican and Cascade arcs

NASA Astrophysics Data System (ADS)

Waters, L.; Lange, R. A.

2011-12-01

The extent to which degassing affects the oxidation state of arc magmas is widely debated. Several researchers have examined how degassing of mixed H-C-O-S-Cl fluids may change the Fe3+/FeT ratio of magmas, and it has been proposed that degassing may induce either oxidation or reduction depending on the initial oxidation state. A commonly proposed oxidation reaction is related to H2O degassing: H2O (melt) + 2FeO (melt) = H2 (fluid) + Fe2O3 (melt). Another mechanism by which H2O degassing can affect the iron redox state is if dissolved water affects the activity of ferrous and/or ferric iron in the melt. Although Moore et al. (1995) presented experiments showing no evidence of an affect of dissolved water on the activity of the ferric-ferrous ratio in silicate melts, other experimental results (e.g., Baker and Rutherford, 1996; Gaillard et al., 2001; 2003) indicate that there may be such an effect in rhyolite liquids. It has long been understood that rhyolites, owing to their low total iron concentrations, are more sensitive than other magma types to degassing-induced change in redox state. Therefore, a rigorous test of whether H2O degassing affects the redox state of arc magmas is best evaluated on rhyolites. In this study, a comparison is made between the pre-eruptive (pre-degassing) Fe2+ concentrations in six, phenocryst-poor (<5%), fresh, glassy obsidian samples with their post-eruptive (post-degassing) Fe2+ concentrations. Near-liquidus co-precipitation of two Fe-Ti oxides allows the pre-eruptive oxygen fugacity and temperature to be calculated in each rhyolite using the oxygen barometer and thermometer of Ghiorso and Evans (2008). Temperatures range from 793 (± 19) to 939 (± 15) °C, and ΔNNO values (log10fO2 of sample - log10fO2 of Ni-NiO buffer) range from -0.4 to +1.4. These ΔNNO values allow the ferric-ferrous ratio in the liquid to be calculated, using the experimental calibration of Kress and Carmichael (1991), which relates melt composition (not including dissolved water), oxygen fugacity and temperature to melt ferric-ferrous ratios. With temperature known, the plagioclase-liquid hygrometer of Lange et al. (2009) was applied and maximum melt water concentrations range from 4.2 to 7.5 wt%. Both the oxidation state and water concentration are known prior to eruption, at the time of phenocryst growth. After eruption, the rhyolites lost nearly all of their volatiles, as indicated by the low loss on ignition values (LOI ≤ 0.7 wt%). In order to test how much oxidation of ferrous iron occurred as a consequence of that degassing, we measured the ferrous iron concentration in the bulk samples by titration, using the Wilson (1960) method, which was successfully tested again three USGS and one Canadian Geological Survey standards. Our results indicate no detectable change within analytical error between pre- and post-eruptive FeO concentrations, with an average deviation of 0.09 wt% and a maximum deviation of 0.15 wt%. Our results show that H2O degassing has no effect on the redox state of rhyolite magmas, which requires that dissolved water has no resolvable affect on the activity ratio of the iron oxide components in melt.

Proper interpretation of dissolved nitrous oxide isotopes, production pathways, and emissions requires a modelling approach.

PubMed

Thuss, Simon J; Venkiteswaran, Jason J; Schiff, Sherry L

2014-01-01

Stable isotopes ([Formula: see text]15N and [Formula: see text]18O) of the greenhouse gas N2O provide information about the sources and processes leading to N2O production and emission from aquatic ecosystems to the atmosphere. In turn, this describes the fate of nitrogen in the aquatic environment since N2O is an obligate intermediate of denitrification and can be a by-product of nitrification. However, due to exchange with the atmosphere, the [Formula: see text] values at typical concentrations in aquatic ecosystems differ significantly from both the source of N2O and the N2O emitted to the atmosphere. A dynamic model, SIDNO, was developed to explore the relationship between the isotopic ratios of N2O, N2O source, and the emitted N2O. If the N2O production rate or isotopic ratios vary, then the N2O concentration and isotopic ratios may vary or be constant, not necessarily concomitantly, depending on the synchronicity of production rate and source isotopic ratios. Thus prima facie interpretation of patterns in dissolved N2O concentrations and isotopic ratios is difficult. The dynamic model may be used to correctly interpret diel field data and allows for the estimation of the gas exchange coefficient, N2O production rate, and the production-weighted [Formula: see text] values of the N2O source in aquatic ecosystems. Combining field data with these modelling efforts allows this critical piece of nitrogen cycling and N2O flux to the atmosphere to be assessed.

FIELD MEASUREMENT OF DISSOLVED OXYGEN: A COMPARISON OF METHODS

EPA Science Inventory

The ability to confidently measure the concentration of dissolved oxygen (D.O.) in ground water is a key aspect of remedial selection and assessment. Presented here is a comparison of the commonly practiced methods for determining D.O. concentrations in ground water, including c...

Pressure, O2, and CO2, in aquatic Closed Ecological Systems

NASA Astrophysics Data System (ADS)

Taub, Frieda B.; McLaskey, Anna K.

2013-03-01

Pressure increased during net photosynthetic O2 production in the light and decreased during respiratory O2 uptake during the dark in aquatic Closed Ecological Systems (CESs) with small head gas volumes. Because most CO2 will be in the liquid phase as bicarbonate and carbonate anions, and CO2 is more soluble than O2, volumes of gaseous CO2 and gaseous O2 will not change in a compensatory manner, leading to the development of pressure. Pressure increases were greatest with nutrient rich medium with NaHCO3 as the carbon source. With more dilute media, pressure was greatest with NaHCO3, and less with cellulose or no-added carbon. Without adequate turbulence, pressure measurements lagged dissolved O2 concentrations by several hours and dark respiration would have been especially underestimated in our systems (250-1000 ml). With adequate turbulence (rotary shaker), pressure measurements and dissolved O2 concentrations generally agreed during lights on/off cycles, but O2 measurements provided more detail. At 20 °C, 29.9 times as much O2 will distribute into the gas phase as in the liquid, per unit volume, as a result of the limited solubility of O2 in water and according to Henry's Law. Thus even a small head gas volume can contain more O2 than a larger volume of water. When both dissolved and gaseous O2 and CO2 are summed, the changes in Total O2 and CO2 are in relatively close agreement when NaHCO3 is the carbon source. These findings disprove an assumption made in some of Taub's earlier research that aquatic CESs would remain at approximately atmospheric pressure because approximately equal molar quantities of O2 and CO2 would exchange during photosynthesis and respiration; this assumption neglected the distribution of O2 between water and gas phases. High pressures can occur when NaHCO3 is the carbon source in nutrient rich media and if head-gas volumes are small relative to the liquid volume; e.g., one "worse case" condition developed 800 mm Hg above atmospheric pressure and broke the glass container. Plastic screw cap closures are likely to leak at high pressures and should not be assumed to seal unless tested at appropriate pressures. Pressure can be reduced by having larger head-gas volumes and using less concentrated nutrient solutions. It is important that pressure changes be considered for both safety and closure, and if total O2 is used as the measure of net photosynthesis and respiration, the O2 in the gas phase must be added to the dissolved O2.

Lifetime and dissolution kinetics of zinc oxide nanoparticles in aqueous media

NASA Astrophysics Data System (ADS)

Wang, Ning; Tong, Tiezheng; Xie, Minwei; Gaillard, Jean-François

2016-08-01

We have assessed the persistence and lifetime of ZnO nanoparticles (ZnO-NPs) by performing dissolution experiments in three different aqueous media. These experiments were performed at ZnO-NP concentration levels close to the solubility of zincite (˜8 μM or 650 μg l-1 of ZnO)—a concentration that is orders of magnitude higher than current estimated relevant environmental concentrations. The kinetics were followed by voltammetry, while maintaining the pH at about 7.5 using a CO2/N2 gas mixture to remove di-oxygen interference. Our results show that, under these conditions, ZnO-NPs readily dissolve with a lifetime expectancy that does not exceed 90 min. Water chemistry, especially the presence of dissolved organic matter (DOM), plays an important role in ZnO-NP dissolution. Dissolution rates significantly increase in the presence of strong chelating agents, EDTA and L-cysteine, while the addition of polymeric DOM, such as sodium alginate, has the opposite effect. Our results suggest that ZnO-NPs are unlikely to persist in natural aqueous media and that the toxicity should be primarily related to the released Zn2+ ions rather than effects commonly associated to the presence of nanoparticles.

ABIOTIC O{sub 2} LEVELS ON PLANETS AROUND F, G, K, AND M STARS: POSSIBLE FALSE POSITIVES FOR LIFE?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harman, C. E.; Kasting, J. F.; Schwieterman, E. W.

2015-10-20

In the search for life on Earth-like planets around other stars, the first (and likely only) information will come from the spectroscopic characterization of the planet's atmosphere. Of the countless number of chemical species terrestrial life produces, only a few have the distinct spectral features and the necessary atmospheric abundance to be detectable. The easiest of these species to observe in Earth's atmosphere is O{sub 2} (and its photochemical byproduct, O{sub 3}). However, O{sub 2} can also be produced abiotically by photolysis of CO{sub 2}, followed by recombination of O atoms with each other. CO is produced in stoichiometric proportions. Whethermore » O{sub 2} and CO can accumulate to appreciable concentrations depends on the ratio of far-ultraviolet (FUV) to near-ultraviolet (NUV) radiation coming from the planet's parent star and on what happens to these gases when they dissolve in a planet's oceans. Using a one-dimensional photochemical model, we demonstrate that O{sub 2} derived from CO{sub 2} photolysis should not accumulate to measurable concentrations on planets around F- and G-type stars. K-star, and especially M-star planets, however, may build up O{sub 2} because of the low NUV flux from their parent stars, in agreement with some previous studies. On such planets, a “false positive” for life is possible if recombination of dissolved CO and O{sub 2} in the oceans is slow and if other O{sub 2} sinks (e.g., reduced volcanic gases or dissolved ferrous iron) are small. O{sub 3}, on the other hand, could be detectable at UV wavelengths (λ < 300 nm) for a much broader range of boundary conditions and stellar types.« less

Popping rocks from the Mid-Atlantic Ridge: Insights into mantle volatile concentrations and degassing dynamics

NASA Astrophysics Data System (ADS)

Jones, M.; Soule, S. A.; Kurz, M. D.; Wanless, V. D.; Le Roux, V.; Klein, F.; Mittelstaedt, E. L.; Curtice, J.

2016-12-01

During a 1985 cruise, the Mid-Atlantic Ridge (MAR) near 14°N yielded an unusually vesicular mid-ocean ridge (MOR) basalt that popped upon recovery from the seafloor due to the release of trapped volatiles. This `popping rock' has been inferred to be representative of primitive, undegassed magmas from the upper mantle due to its high volatile concentrations. Thus, the sample has been used to constrain CO2 flux from the MOR system, upper mantle volatile concentrations, and magma degassing dynamics. However, the lack of geologic context for the original popping rock raises questions about whether it truly reflects the volatile content of its mantle source. Here, we present results from a 2016 cruise to the MAR aimed at characterizing the geologic context of popping rocks and understanding their origins. The newly recovered samples display differences in volatile concentrations and vesicularities between popping and non-popping rocks. These differences may be related to geologic setting and eruption dynamics with potential implications for mantle volatile concentrations. Volatile concentrations in the outer quenched margin of new samples were measured by ion microprobe to elucidate degassing systematics, brine/magma interactions, and popping rock formation. The large variability in dissolved H2O (0.05-0.77 wt%) can be attributed to spatially variable brine contamination. Dissolved CO2 concentrations (153-356 ppm) are likely controlled by initial volatile concentrations and variable degrees of degassing. The subset of popping samples display low dissolved CO2 concentrations (161-178 ppm) and moderate dissolved H2O concentrations (.44-.50 wt%) and are at equilibrium with their eruption depth based on solubility calculations. X-ray microtomography reveals vesicularity in newly collected popping rocks exceeding 19%, making these samples the most highly vesicular recovered from the MAR. The total gas contents in the basaltic glasses are inferred from dissolved volatile concentrations and vesicularity. These calculations are aided by analysis of gas contents in vesicles by confocal Raman spectroscopy and vacuum crushing experiments. The preliminary results and seafloor observations allow an evaluation of the origins of popping rocks and their implications for mantle volatile concentrations.

Geochemical modeling of iron, sulfur, oxygen and carbon in a coastal plain aquifer

USGS Publications Warehouse

Brown, C.J.; Schoonen, M.A.A.; Candela, J.L.

2000-01-01

Fe(III) reduction in the Magothy aquifer of Long Island, NY, results in high dissolved-iron concentrations that degrade water quality. Geochemical modeling was used to constrain iron-related geochemical processes and redox zonation along a flow path. The observed increase in dissolved inorganic carbon is consistent with the oxidation of sedimentary organic matter coupled to the reduction of O2 and SO4/2- in the aerobic zone, and to the reduction of SO4/2- in the anaerobic zone; estimated rates of CO2 production through reduction of Fe(III) were relatively minor by comparison. The rates of CO2 production calculated from dissolved inorganic carbon mass transfer (2.55 x 10-4 to 48.6 x 10-4 mmol 1-1 yr-1) generally were comparable to the calculated rates of CO2 production by the combined reduction of O2, Fe(III) and SO4/2- (1.31 x 10-4 to 15 x 10-4 mmol 1-1 yr-1). The overall increase in SO4/2- concentrations along the flow path, together with the results of mass-balance calculations, and variations in ??34S values along the flow path indicate that SO4/2- loss through microbial reduction is exceeded by SO4/2- gain through diffusion from sediments and through the oxidation of FeS2. Geochemichal and microbial data on cores indicate that Fe(III) oxyhydroxide coatings on sediment grains in local, organic carbon- and SO4/2- -rich zones have localized SO4/2- -reducing zones in which the formation of iron disulfides been depleted by microbial reduction and resulted in decreases dissolved iron concentrations. These localized zones of SO4/2- reduction, which are important for assessing zones of low dissolved iron for water-supply development, could be overlooked by aquifer studies that rely only on groundwater data from well-water samples for geochemical modeling. (C) 2000 Elsevier Science B.V.Fe(III) reduction in the Magothy aquifer of Long Island, NY, results in high dissolved-iron concentrations that degrade water quality. Geochemical modeling was used to constrain iron-related geochemical processes and redox zonation along a flow path. The observed increase in dissolved inorganic carbon is consistent with the oxidation of sedimentary organic matter coupled to the reduction of O2 and SO42- in the aerobic zone, and to the reduction of SO42- in the anaerobic zone; estimated rates of CO2 production through reduction of Fe(III) were relatively minor by comparison. The rates of CO2 production calculated from dissolved inorganic carbon mass transfer (2.55??10-4 to 48.6??10-4mmol l-1yr-1) generally were comparable to the calculated rates of CO2 production by the combined reduction of O2, Fe(III) and SO42- (1.31??10-4 to 15??10-4mmol l-1yr-1). The overall increase in SO42- concentrations along the flow path, together with the results of mass-balance calculations, and variations in ??34S values along the flow path indicate that SO42- loss through microbial reduction is exceeded by SO42- gain through diffusion from sediments and through the oxidation of FeS2. Geochemical and microbial data on cores indicate that Fe(III) oxyhydroxide coatings on sediment grains in local, organic carbon- and SO42--rich zones have been depleted by microbial reduction and resulted in localized SO42--reducing zones in which the formation of iron disulfides decreases dissolved iron concentrations. These localized zones of SO42- reduction, which are important for assessing zones of low dissolved iron for water-supply development, could be overlooked by aquifer studies that rely only on groundwater data from well-water samples for geochemical modeling.

Illuminating Geochemical Controls of Methane Oxidation Along a Gradient of Permafrost Thaw

NASA Astrophysics Data System (ADS)

Perryman, C. R.; Kashi, N.; McCalley, C. K.; Malhotra, A.; Giesler, R.; Varner, R.

2017-12-01

Increases in annual mean temperature in the subarctic have accelerated the thaw of organic-rich permafrost peatlands, exacerbating methane (CH4) production from microbial decomposition of peat deposits and subsequent CH4 emissions. Methanotrophic bacteria may oxidize/consume upwards of 90% of produced CH4 in some settings, pending substrate availability and environmental conditions. Redox chemistry may also control the rate of CH4 oxidation in thawing permafrost areas, particularly redox potential (Eh) and the availability of oxygen (O2) and other terminal electron receptors. We investigated potential CH4 oxidation rates across a permafrost thaw gradient in Stordalen Mire (68°21'N,18°49'E) near Abisko, Sweden. Methane oxidation rates for sites from thawing and collapsed palsa, semi-wet Sphagnum, and open-water sedge sites were determined through laboratory incubations. Peat cores were extracted from two depths at each site and incubated at in situ temperatures and CH4 concentrations. Headspace samples were collected over a 48-hour period and analyzed for CH4 concentration using flame ionization detection gas chromatography (GC-FID). Dissolved O2, Eh, and dissolved CH4 were measured in sites with porewater. Oxidation rates ranged from <0.1 to 19 μg of CH4 per gram of dry biomass per day. Eh remained positive (41.6 to 316.8 mV) with available dissolved O2 (0.3 - 5.2 mg/L) in all measurement locations down to 20cm, indicating in situ aerobic CH4 oxidation is viable across these environments. Potential CH4 oxidation rates increased with increasing dissolved CH4 concentration. Highest potential CH4 oxidation rates were found in open-water sedge sites. Eh and dissolved O2 were lowest at these sites, suggesting that methanotrophs with low-O2 demand may populate sedge areas. Furthermore, potential CH4 oxidation rates were higher at depth than at the surface in thawing palsa, suggesting CH4 oxidation may mitigate CH4 production triggered by warming in these actively thawing environments. Forthcoming elemental analyses of peat and pore water will further elucidate trends and geochemical controls of CH4 oxidation rates in thawing permafrost areas.

Comparative effects of zinc oxide nanoparticles and dissolved zinc on zebrafish embryos and eleuthero-embryos: importance of zinc ions.

PubMed

Brun, Nadja Rebecca; Lenz, Markus; Wehrli, Bernhard; Fent, Karl

2014-04-01

The increasing use of zinc oxide nanoparticles (nZnO) and their associated environmental occurrence make it necessary to assess their potential effects on aquatic organisms. Upon water contact, nZnO dissolve partially to zinc (Zn(II)). To date it is not yet completely understood, whether effects of nZnO are solely or partly due to dissolved Zn(II). Here we compare potential effects of 0.2, 1 and 5mg/L nZnO and corresponding concentrations of released Zn(II) by water soluble ZnCl2 to two development stages of zebrafish, embryos and eleuthero-embryos, by analysing expressional changes by RT-qPCR. Another objective was to assess uptake and tissue distribution of Zn(II). Laser ablation-ICP-MS analysis demonstrated that uptake and tissue distribution of Zn(II) were identical for nZnO and ZnCl2 in eleuthero-embryos. Zn(II) was found particularly in the retina/pigment layer of eyes and brain. Both nZnO and dissolved Zn(II) derived from ZnCl2 had similar inhibiting effects on hatching, and they induced similar expressional changes of target genes. At 72hours post fertilization (hpf), both nZnO and Zn(II) delayed hatching at all doses, and inhibited hatching at 1 and 5 mg/L at 96 hpf. Both nZnO and Zn(II) lead to induction of metallothionein (mt2) in both embryos and eleuthero-embryos at all concentrations. Transcripts of oxidative stress related genes cat and Cu/Zn sod were also altered. Moreover, we show for the first time that nZnO exposure results in transcriptional changes of pro-inflammatory cytokines IL-1β and TNFα. Overall, transcriptional alterations were higher in embryos than eleuthero-embryos. The similarities of the effects lead to the conclusion that effects of nZnO are mainly related to the release of Zn(II). Copyright © 2014 Elsevier B.V. All rights reserved.

In situ iron activated persulfate oxidative fluid sparging treatment of TCE contamination--a proof of concept study.

PubMed

Liang, Chenju; Lee, I-Ling

2008-09-10

In situ chemical oxidation (ISCO) is considered a reliable technology to treat groundwater contaminated with high concentrations of organic contaminants. An ISCO oxidant, persulfate anion (S(2)O(8)(2-)) can be activated by ferrous ion (Fe(2+)) to generate sulfate radicals (E(o)=2.6 V), which are capable of destroying trichloroethylene (TCE). The property of polarity inhibits S(2)O(8)(2-) or sulfate radical (SO(4)(-)) from effectively oxidizing separate phase TCE, a dense non-aqueous phase liquid (DNAPL). Thus the oxidation primarily takes place in the aqueous phase where TCE is dissolved. A bench column study was conducted to demonstrate a conceptual remediation method by flushing either S(2)O(8)(2-) or Fe(2+) through a soil column, where the TCE DNAPL was present, and passing the dissolved mixture through either a Fe(2+) or S(2)O(8)(2-) fluid sparging curtain. Also, the effect of a solubility enhancing chemical, hydroxypropyl-beta-cyclodextrin (HPCD), was tested to evaluate its ability to increase the aqueous TCE concentration. Both flushing arrangements may result in similar TCE degradation efficiencies of 35% to 42% estimated by the ratio of TCE degraded/(TCE degraded+TCE remained in effluent) and degradation byproduct chloride generation rates of 4.9 to 7.6 mg Cl(-) per soil column pore volume. The addition of HPCD did greatly increase the aqueous TCE concentration. However, the TCE degradation efficiency decreased because the TCE degradation was a lower percentage of the relatively greater amount of dissolved TCE by HPCD. This conceptual treatment may serve as a reference for potential on-site application.

Sulfur formation by steady-state continuous cultures of a sulfoxidizing consortium and Thiobacillus thioparus ATCC 23645.

PubMed

Alcántara, S; Velasco, A; Revah, S

2004-10-01

The elemental sulfur formation by the partial oxidation of thiosulfate by both a sulfoxidizing consortium and by Thiobacillus thioparus ATCC 23645 was studied under aerobic conditions in chemostat. Steady state was attained with essentially total conversion to sulfate when the dissolved oxygen concentration was 5 mgO2 l(-1) and below a dilution rate (D) of 3.0 d(-1)for the consortium and 0.9 d(-1) for T thioparus. The consortium formed elemental sulfur in steady state under oxygen limitation. Fifty percent of the theoretical elemental sulfur yield was obtained with a dissolved oxygen concentration of 0.2 mgO2 l(-1). Growth of T thioparus was negatively affected with a concentration below 1.9 mgO2 l(-1). Consortium yield from batch cultures was 2.1 g(-1) (protein) mol(-1) (thiosulfate), which was comparable with the values obtained in the chemostat at dilution rates of 0.4 d(-1) and 1.2 d(-1). The consortium showed a maximum degradation rate of 0.105 g(thiosulfate) g(-1) (protein) min(-1) and a saturation rate for S2O3(2-) of 1.9 mM.

In Situ Natural Abundance 17 O and 25 Mg NMR Investigation of Aqueous Mg(OH) 2 Dissolution in the Presence of Supercritical CO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Mary Y.; Deng, Xuchu; Thanthiriwatte, K. Sahan

We report the development of an in situ high pressure NMR capability that permits natural abundance 17O and 25Mg NMR characterization of dissolved species in aqueous solution and in the presence of supercritical CO 2 fluid (scCO 2). The dissolution of Mg(OH) 2 (brucite) in a multiphase water/scCO 2 fluid at 90 atm pressure and 50 C was studied in situ, with relevance to geological carbon sequestration. 17O NMR spectra allowed identification and distinction of various fluid species including dissolved CO 2 in the H 2O-rich phase, scCO 2, aqueous H 2O, and HCO 3 -. The widely separated spectralmore » peaks for various species can all be observed both dynamically and quantitatively at concentrations of as low as 20 mM. Measurement of the concentrations of these individual species also allows an in situ estimate of the hydrogen ion concentration, or pCH + values, of the reacting solutions. The concentration of Mg 2+ can be observed by natural abundance 25Mg NMR at a concentration as low as 10 mM. Quantum chemistry calculations of the NMR chemical shifts on cluster models aided in the interpretation of the experimental results. Evidence for the formation of polymeric Mg 2+ clusters at high concentrations in the H 2O-rich phase, a possible critical step needed for magnesium carbonate formation, was found. The approach and findings enable insight into metal carbonation reactions associated with geological carbon sequestration that cannot be probed by ex situ methods.« less

Mega-solubility of quartz resulting from highly alkaline fluids produced by dissolved albite in H2O at deep crustal conditions

NASA Astrophysics Data System (ADS)

Makhluf, A. R.; Manning, C. E.

2017-12-01

Models of H2O-rich fluids equilibrated with rocks at high P and T fail to predict the high solubilities observed experimentally, chiefly because thermodynamic data for the most abundant solutes is lacking. We investigated the effects of dissolved albite (Ab) on the solubility of quartz (Qz) at 1.0 GPa and 675-900 °C using a piston-cylinder apparatus to quantify possible mineral buffering or enhancement effects. We found a very large enhancement effect on the solubility of Qz when dissolved in dilute aqueous Ab solutions. SiO2 concentrations are similar to Qz solubility in strongly alkaline KOH solutions. At the highest temperature of 900 °C, we found that the solubility of Qz in 1.0 molal Ab solution increases by of factor of 4.5 over that in pure H2O, which corresponds to 10.7 molal SiO2. The nearly identical solubility of Qz in KOH(aq) and Ab solutions of the same concentration, P, and T, strongly suggest that NaOH(aq) liberated from NaAlSi3O8 in H2O fluids effects SiO2 solubility in a similar manner to that of KOH(aq). The deprotonated silica dimer was found to be a key species responsible for the high solubility of Qz in KOH(aq) and is likely responsible for the high solubility of Qz in Ab solutions. While the binaries Qz-H2O, Ab-H2O, and Qz-Ab are well known at 1.0 GPa, little data exists on the ternary system. The new results help quantify the ternary relations in the Ab-Qz-H2O system, which can be used as a simple model for liquid-vapor immiscibility granitic magmas. In addition, these highly alkaline solute-rich aqueous fluids suggest a mechanism for Ab-Qz metasomatism in subduction zones, such as in the Catalina schist (Bebout and Barton 1993), which provides an alternative to high P-T magmas. Our results show that subduction zone and metasomatic fluids may be much more alkaline and have significantly higher dissolving power than previously thought.

Aquifer geochemistry at potential aquifer storage and recovery sites in coastal plain aquifers in the New York city area, USA

USGS Publications Warehouse

Brown, C.J.; Misut, P.E.

2010-01-01

The effects of injecting oxic water from the New York city (NYC) drinking-water supply and distribution system into a nearby anoxic coastal plain aquifer for later recovery during periods of water shortage (aquifer storage and recovery, or ASR) were simulated by a 3-dimensional, reactive-solute transport model. The Cretaceous aquifer system in the NYC area of New York and New Jersey, USA contains pyrite, goethite, locally occurring siderite, lignite, and locally varying amounts of dissolved Fe and salinity. Sediment from cores drilled on Staten Island and western Long Island had high extractable concentrations of Fe, Mn, and acid volatile sulfides (AVS) plus chromium-reducible sulfides (CRS) and low concentrations of As, Pb, Cd, Cr, Cu and U. Similarly, water samples from the Lloyd aquifer (Cretaceous) in western Long Island generally contained high concentrations of Fe and Mn and low concentrations of other trace elements such as As, Pb, Cd, Cr, Cu and U, all of which were below US Environmental Protection Agency (USEPA) and NY maximum contaminant levels (MCLs). In such aquifer settings, ASR operations can be complicated by the oxidative dissolution of pyrite, low pH, and high concentrations of dissolved Fe in extracted water.The simulated injection of buffered, oxic city water into a hypothetical ASR well increased the hydraulic head at the well, displaced the ambient groundwater, and formed a spheroid of injected water with lower concentrations of Fe, Mn and major ions in water surrounding the ASR well, than in ambient water. Both the dissolved O2 concentrations and the pH of water near the well generally increased in magnitude during the simulated 5-a injection phase. The resultant oxidation of Fe2+ and attendant precipitation of goethite during injection provided a substrate for sorption of dissolved Fe during the 8-a extraction phase. The baseline scenario with a low (0.001M) concentration of pyrite in aquifer sediments, indicated that nearly 190% more water with acceptably low concentrations of dissolved Fe could be extracted than was injected. Scenarios with larger amounts of pyrite in aquifer sediments generally resulted in less goethite precipitation, increased acidity, and increased concentrations of dissolved Fe in extracted water. In these pyritic scenarios, the lower amounts of goethite precipitated and the lower pH during the extraction phase resulted in decreased sorption of Fe2+ and a decreased amount of extractable water with acceptably low concentrations of dissolved Fe (5.4??10-6M). A linear decrease in recovery efficiency with respect to dissolved Fe concentrations is caused by pyrite dissolution and the associated depletion of dissolved O2 (DO) and increase in acidity. Simulations with more than 0.0037M of pyrite, which is the maximum amount dissolved in the baseline scenario, had just over a 50% recovery efficiency. The precipitation of ferric hydroxide minerals (goethite) at the well screen, and a possible associated decrease in specific capacity of the ASR well, was not apparent during the extraction phase of ASR simulations, but the model does not incorporate the microbial effects and biofouling associated with ferric hydroxide precipitation.The host groundwater chemistry in calcite-poor Cretaceous aquifers of the NYC area consists of low alkalinity and moderate to low pH. The dissolution of goethite in scenarios with unbuffered injectate indicates that corrosion of the well could occur if the injectate is not buffered. Simulations with buffered injectate resulted in greater precipitation of goethite, and lower concentrations of dissolved Fe, in the extracted water. Dissolved Fe concentrations in extracted water were highest in simulations of aquifers (1) in which pyrite and siderite in the aquifer were in equilibrium, and (2) in coastal areas affected by saltwater intrusion, where high dissolved-cation concentrations provide a greater exchange of Fe2+ (FeX2). Results indicate that ASR in pyrite-beari

Neptunium(V) and neptunium(VI) solubilities in synthetic brines of interest to the Waste Isolation Pilot Plant (WIPP)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novak, C.F.; Nitsche, H.; Silber, H.B.

1996-12-31

The solubility of Np(V) and Np(VI) has been measured in three synthetic Na-K-Mg-Cl brines in the presence of CO{sub 2}(g). Experiments were prepared from oversaturation by adding an excess of NpO{sub 2}{sup +} or NpO{sub 2}{sup 2+} to the brines and allowing the neptunium solids to precipitate. Vessels were maintained in contact with fixed CO{sub 2}(g) partial pressures at constant pH and 24 {+-} 1 C. Dissolved Np(V) concentrations decreased several orders of magnitude within the first 100 days of the experiment, while dissolved Np(VI) concentrations decreased initially but then remained relatively constant for more than 400 days. The solidmore » phases formed in all experiments were identified by X-ray powder diffraction as KNpO{sub 2}CO{sub 3}{center_dot}xH{sub 2}O(s). Steady state concentrations for Np(V) are similar to those observed for Pu(V) in the same brines under the same conditions, where Pu occurs predominantly as Pu(V). Similarly, steady state concentrations for Np(VI), which was not reduced over a two year period, compare well with measured Pu(VI) concentrations in the same brines before the Pu(VI) was reduced to Pu(V).« less

The impact of four decades of annual nitrogen addition on dissolved organic matter in a boreal forest soil

NASA Astrophysics Data System (ADS)

Rappe-George, M. O.; Gärdenäs, A. I.; Kleja, D. B.

2013-03-01

Addition of mineral nitrogen (N) can alter the concentration and quality of dissolved organic matter (DOM) in forest soils. The aim of this study was to assess the effect of long-term mineral N addition on soil solution concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in Stråsan experimental forest (Norway spruce) in central Sweden. N was added yearly at two levels of intensity and duration: the N1 treatment represented a lower intensity but a longer duration (43 yr) of N addition than the shorter N2 treatment (24 yr). N additions were terminated in the N2 treatment in 1991. The N treatments began in 1967 when the spruce stands were 9 yr old. Soil solution in the forest floor O, and soil mineral B, horizons were sampled during the growing seasons of 1995 and 2009. Tension and non-tension lysimeters were installed in the O horizon (n = 6), and tension lysimeters were installed in the underlying B horizon (n = 4): soil solution was sampled at two-week intervals. Although tree growth and O horizon carbon (C) and N stock increased in treatments N1 and N2, the concentration of DOC in O horizon leachates was similar in both N treatments and control. This suggests an inhibitory direct effect of N addition on O horizon DOC. Elevated DON and nitrate in O horizon leachates in the ongoing N1 treatment indicated a move towards N saturation. In B horizon leachates, the N1 treatment approximately doubled leachate concentrations of DOC and DON. DON returned to control levels, but DOC remained elevated in B horizon leachates in N2 plots nineteen years after termination of N addition. We propose three possible explanations for the increased DOC in mineral soil: (i) the result of decomposition of a larger amount of root litter, either directly producing DOC or (ii) indirectly via priming of old SOM, and/or (iii) a suppression of extracellular oxidative enzymes.

Method for dissolving plutonium oxide with HI and separating plutonium

DOEpatents

Vondra, Benedict L.; Tallent, Othar K.; Mailen, James C.

1979-01-01

PuO.sub.2 -containing solids, particularly residues from incomplete HNO.sub.3 dissolution of irradiated nuclear fuels, are dissolved in aqueous HI. The resulting solution is evaporated to dryness and the solids are dissolved in HNO.sub.3 for further chemical reprocessing. Alternatively, the HI solution containing dissolved Pu values, can be contacted with a cation exchange resin causing the Pu values to load the resin. The Pu values are selectively eluted from the resin with more concentrated HI.

Dissolution Behaviour of Hazardous Materials from Steel Slag with Wet Grinding Method

NASA Astrophysics Data System (ADS)

Hisyamudin Muhd Nor, Nik; Norhana Selamat, Siti; Hanif Abd Rashid, Muhammad; Fauzi Ahmad, Mohd; Jamian, Saifulnizan; Chee Kiong, Sia; Fahrul Hassan, Mohd; Mohamad, Fariza; Yokoyama, Seiji

2016-06-01

Steel slag is a by-product from steel industry and it contains variety of hazardous materials. In this study, the dissolution behaviour and removal potential of hazardous materials from steel slag with the wet grinding method was investigated. The slag was wet ground in the CO2 atmosphere and the slurry produced was filtered using centrifugal separator to separate the liquid and solid sediments. Then, the concentrations of dissolved metal elements in the liquid sediment were analyzed by ICP-MS. The changes of pH during the grinding were also investigated. It was found that the pHs were decreased immediately after the CO2 gas introduced into the vessel. The pHs were ranging from 6.8 to 7.6 at the end of grinding. The dissolved concentration of Zn and Cr were ranging from 5~45 [mg/dm3] and 0.2~2.5 [mg/dm3] respectively. The ratios of Zn removal for stainless steel oxidizing and reducing slag were very high, but those from normal steel oxidizing and reducing slag were very low. It is assumed that the Zn dissolved as ZnOH+ from Zn(OH)2 that formed due to the reaction between ZnO and water. Dissolution of Cr also occurred but in very low quantity compared to the dissolution of Zn. The dissolution of Cr occurred due to the grinding process and small amount of Cr(OH)3 was formed during the grinding. This small formation of Cr(OH)3 resulted to the low dissolved concentration of Cr in the form of Cr(OH)2+. According to the XRD analysis, the Cr mostly existed in the slags as Cr(IIl) in the form of MgCr2O4 and FeCr2O4.

Impact of the excess sludge modification with selected chemical reagents on the increase of dissolved organic substances concentration compounds transformations in activated sludge.

PubMed

Zawieja, Iwona; Lidia, Wolny; Marta, Próba

2017-07-01

Submission of excess sludge initial disintegration process significantly affects the efficiency of anaerobic stabilization process. Expression of increasing the concentration of organic matter in dissolved form is to increase sludge disintegration. As a result of chemical modification is an increase of the chemical oxygen demand and the concentration of volatile fatty acids. The aim of this study was to determine the impact of the disintegration process with selected chemical reagents to increase the concentration of organic substances in dissolved form. The process of chemical disintegration of excess sludge was treated using the following reagents: Mg(OH) 2 , Ca(OH) 2 , HCl, H 2 SO 4 , H 2 O 2 . The modification was carried out at ambient temperature for 2, 6 and 24h. During sludge disintegration it was noticed the growth of indicators values that confirmed the susceptibility of prepared sludge to biodegradation. Copyright © 2017 Elsevier Inc. All rights reserved.

Biogeochemical controls on diel cycling of stable isotopes of dissolved 02 and dissolved inorganic carbon in the Big Hole River, Montana

USGS Publications Warehouse

Parker, Stephen R.; Poulson, Simon R.; Gammons, Christopher H.; DeGrandpre, Michael D.

2005-01-01

Rivers with high biological productivity typically show substantial increases in pH and dissolved oxygen (DO) concentration during the day and decreases at night, in response to changes in the relative rates of aquatic photosynthesis and respiration. These changes, coupled with temperature variations, may impart diel (24-h) fluctuations in the concentration of trace metals, nutrients, and other chemical species. A better understanding of diel processes in rivers is needed and will lead to improved methods of data collection for both monitoring and research purposes. Previous studies have used stable isotopes of dissolved oxygen (DO) and dissolved inorganic carbon (DIC) as tracers of geochemical and biological processes in streams, lakes, and marine systems. Although seasonal variation in δ18O of DO in rivers and lakes has been documented, no study has investigated diel changes in this parameter. Here, we demonstrate large (up to 13‰) cycles in δ18O-DO for two late summer sampling periods in the Big Hole River of southwest Montana and illustrate that these changes are correlated to variations in the DO concentration, the C-isotopic composition of DIC, and the primary productivity of the system. The magnitude of the diel cycle in δ18O-DO was greater in August versus September because of the longer photoperiod and warmer water temperatures. This study provides another biogeochemical tool for investigating the O2 and C budgets in rivers and may also be applicable to lake and groundwater systems.

Occurrence of nitrous oxide in the central High Plains aquifer, 1999

USGS Publications Warehouse

McMahon, P.B.; Bruch, B.W.; Becker, M.F.; Pope, L.M.; Dennehy, K.F.

2000-01-01

Nitrogen-enriched groundwater has been proposed as an important anthropogenic source of atmospheric nitrous oxide (N2O), yet few measurements of N2O in large aquifer systems have been made. Concentrations of N2O in water samples collected from the 124 000 km2 central High Plains aquifer in 1999 ranged from < 1 to 940 nM, with a median concentration of 29 nM (n = 123). Eighty percent of the N20 concentrations exceeded the aqueous concentration expected from equilibration with atmospheric N2O. Measurements of N2O, NO3-, and 3H in unsaturated-zone sediments, recently recharged groundwater, and older groundwater indicate that concentrations of N2O in groundwater increased over time and will likely continue to increase in the future as N-enriched water recharges the aquifer. Large concentrations of O2 and NO3- and small concentrations of NH4+ and dissolved organic carbon in the aquifer indicate that N2O in the central High Plains aquifer was produced primarily by nitrification. Calculations indicate that the flux of N2O from the central High Plains aquifer to the atmosphere from well pumping and groundwater discharge to streams was not a significant source of atmospheric N2O.Nitrogen-enriched groundwater has been proposed as an important anthropogenic source of atmospheric nitrous oxide (N2O), yet few measurements of N2O in large aquifer systems have been made. Concentrations of N2O in water samples collected from the 124000 km2 central High Plains aquifer in 1999 ranged from < 1 to 940 nM, with a median concentration of 29 nM (n = 123). Eighty percent of the N2O concentrations exceeded the aqueous concentration expected from equilibration with atmospheric N2O. Measurements of N2O, NO3-, and 3H in unsaturated-zone sediments, recently recharged groundwater, and older groundwater indicate that concentrations of N2O in groundwater increased over time and will likely continue to increase in the future as N-enriched water recharges the aquifer. Large concentrations of O2 and NO3- and small concentrations of NH4+ and dissolved organic carbon in the aquifer indicate that N2O in the central High Plains aquifer was produced primarily by nitrification. Calculations indicate that the flux of N2O from the central High Plains aquifer to the atmosphere from well pumping and groundwater discharge to streams was not a significant source of atmospheric N2O.Water samples were collected from 92 domestic wells, 16 monitoring wells and 15 public-supply wells in the High Plains Aquifer in 1999, and concentrations of nitrous oxide were measured. The groundwater concentrations ranged from less than 1 to 940 nM. Concentrations expressed as a percent of saturation in water ranged from less than 10 to 9690%. A significant decrease was noted in N2O concentrations with increasing depth of the well screen below the water table, and a significant positive correlation was found between the concentrations of N2O and nitrate. The small area-averaged N2O emission rate for the aquifer indicated that it was not an important component of the atmospheric N2O budget, but the importance could increase as groundwater N2O concentrations increase.

Influence of dissolved oxygen concentration on the start-up of the anammox-based process: ELAN®.

PubMed

Morales, N; Val del Río, A; Vázquez-Padín, J R; Gutiérrez, R; Fernández-González, R; Icaran, P; Rogalla, F; Campos, J L; Méndez, R; Mosquera-Corral, A

2015-01-01

The anammox-based process ELAN® was started-up in two different sequencing batch reactor (SBR) pilot plant reactors treating municipal anaerobic digester supernatant. The main difference in the operation of both reactors was the dissolved oxygen (DO) concentration in the bulk liquid. SBR-1 was started at a DO value of 0.4 mg O2/L whereas SBR-2 was started at DO values of 3.0 mg O2/L. Despite both reactors working at a nitrogen removal rate of around 0.6 g N/(L d), in SBR-1, granules represented only a small fraction of the total biomass and reached a diameter of 1.1 mm after 7 months of operation, while in SBR-2 the biomass was mainly composed of granules with an average diameter of 3.2 mm after the same operational period. Oxygen microelectrode profiling revealed that granules from SBR-2 where only fully penetrated by oxygen with DO concentrations of 8 mg O2/L while granules from SBR-1 were already oxygen penetrated at DO concentrations of 1 mg O2/L. In this way granules from SBR-2 performed better due to the thick layer of ammonia oxidizing bacteria, which accounted for up to 20% of all the microbial populations, which protected the anammox bacteria from non-suitable liquid media conditions.

Coupled biotic-abiotic oxidation of organic matter by biogenic MnO_{2}

NASA Astrophysics Data System (ADS)

Gonzalez, Julia; Peña, Jasquelin

2016-04-01

Some reactive soil minerals are strongly implicated in stabilising organic matter. However, others can play an active role in the oxidation of organic molecules. In natural systems, layer-type manganese oxide minerals (MnO2) typically occur as biomineral assemblages consisting of mineral particles and microbial biomass. Both the mineral and biological fractions of the assemblage can be powerful oxidants of organic C. The biological compartment relies on a set of enzymes to drive oxidative transformations of reduced C-substrates, whereas MnO2 minerals are strong, less specific abiotic oxidants that are assumed to rely on interfacial interactions between C-substrates and the mineral surface. This project aims to understand the coupling between microbial C mineralization and abiotic C oxidation mediated by MnO2 in bacterial-MnO2 assemblages. Specifically, under conditions of high C turnover, microbial respiration can significantly alter local pH, dissolved oxygen and pool of available reductants, which may modify rates and mechanism of C oxidation by biotic and abiotic components. We first investigated changes in the solution chemistry of Pseudomonas putida suspensions exposed to varying concentrations of glucose, chosen to represent readily bioavailable substrates in soils. Glucose concentrations tested ranged between 0 and 5.5mM and changes in pH, dissolved oxygen and dissolved organic and inorganic carbon were tracked over 48h. We then combined literature review and wet-chemical experiments to compile the pH dependence of rates of organic substrate oxidation by MnO2, including glucose. Our results demonstrate a strong pH dependence for these abiotic reactions. In assemblages of P. putida - MnO2, kinetic limitations for abiotic C oxidation by MnO2 are overcome by changes in biogeochemical conditions that result from bacterial C metabolism. When extrapolated to a soil solution confronted to an input of fresh dissolved organic matter, bacterial C metabolism of the labile fraction may lower solution pH into a regime that favours abiotic oxidation of recalcitrant C by MnO2. This project demonstrates that the co-occurrence of mineral particles with metabolically active cells provides a direct link between the C and Mn cycles.

Long-term limnological data from the larger lakes of Yellowstone National Park, Wyoming, USA

USGS Publications Warehouse

Theriot, E.C.; Fritz, S.C.; Gresswell, Robert E.

1997-01-01

Long-term limnological data from the four largest lakes in Yellowstone National Park (Yellowstone, Lewis, Shoshone, Heart) are used to characterize their limnology and patterns of temporal and spatial variability. Heart Lake has distinctively high concentrations of dissolved materials, apparently reflecting high thermal inputs. Shoshone and Lewis lakes have the highest total SiO2 concentrations (averaging over 23.5 mg L-1), apparently as a result of the rhyolitic drainage basins. Within Yellowstone Lake spatial variability is low and ephemeral for most measured variables, except that the Southeast Arm has lower average Na concentrations. Seasonal variation is evident for Secchi transparency, pH, and total-SiO2 and probably reflects seasonal changes in phytoplankton biomass and productivity. Total dissolved solids (TDS) and total-SiO2 generally show a gradual decline from the mid-1970s through mid-1980s, followed by a sharp increase. Ratios of Kjeldahl-N to total-PO4 (KN:TP) suggest that the lakes, especially Shoshone, are often nitrogen limited. Kjeldahl-N is positively correlated with winter precipitation, but TP and total-SiO2 are counterintuitively negatively correlated with precipitation. We speculate that increased winter precipitation, rather than watershed fires, increases N-loading which, in turn, leads to increased demand for TP and total SiO2.

Study on Enhancement Principle and Stabilization for the Luminol-H2O2-HRP Chemiluminescence System

PubMed Central

Yang, Lihua; Jin, Maojun; Du, Pengfei; Chen, Ge; Zhang, Chan; Wang, Jian; Jin, Fen; Shao, Hua; She, Yongxin; Wang, Shanshan; Zheng, Lufei; Wang, Jing

2015-01-01

A luminol-H2O2-HRP chemiluminescence system with high relative luminescent intensity (RLU) and long stabilization time was investigated. First, the comparative study on the enhancement effect of ten compounds as enhancers to the luminol-H2O2-HRP chemiluminescence system was carried out, and the results showed that 4-(imidazol-1-yl)phenol (4-IMP), 4-iodophenol (4-IOP), 4-bromophenol (4-BOP) and 4-hydroxy-4’-iodobiphenyl (HIOP) had the best performance. Based on the experiment, the four enhancers were dissolved in acetone, acetonitrile, methanol, and dimethylformamide (DMF) with various concentrations, the results indicated that 4-IMP, 4-IOP, 4-BOP and HIOP dissolved in DMF with the concentrations of 0.2%, 3.2%, 1.6% and 3.2% could get the highest RLU values. Subsequently, the influences of pH, ionic strength, HRP, 4-IMP, 4-IOP, 4-BOP, HIOP, H2O2 and luminol on the stabilization of the luminol-H2O2-HRP chemiluminescence system were studied, and we found that pH value, ionic strength, 4-IMP, 4-IOP, 4-BOP, HIOP, H2O2 and luminol have little influence on luminescent stabilization, while HRP has a great influence. In different ranges of HRP concentration, different enhancers should be selected. When the concentration is within the range of 0~6 ng/mL, 4-IMP should be selected. When the concentration of HRP ranges from 6 to 25ng/mL, 4-IOP was the best choice. And when the concentration is within the range of 25~80 ng/mL, HIOP should be selected as the enhancer. Finally, the three well-performing chemiluminescent enhanced solutions (CESs) have been further optimized according to the three enhancers (4-IMP, 4-IOP and HIOP) in their utilized HRP concentration ranges. PMID:26154162

Study on Enhancement Principle and Stabilization for the Luminol-H2O2-HRP Chemiluminescence System.

PubMed

Yang, Lihua; Jin, Maojun; Du, Pengfei; Chen, Ge; Zhang, Chan; Wang, Jian; Jin, Fen; Shao, Hua; She, Yongxin; Wang, Shanshan; Zheng, Lufei; Wang, Jing

2015-01-01

A luminol-H2O2-HRP chemiluminescence system with high relative luminescent intensity (RLU) and long stabilization time was investigated. First, the comparative study on the enhancement effect of ten compounds as enhancers to the luminol-H2O2-HRP chemiluminescence system was carried out, and the results showed that 4-(imidazol-1-yl)phenol (4-IMP), 4-iodophenol (4-IOP), 4-bromophenol (4-BOP) and 4-hydroxy-4'-iodobiphenyl (HIOP) had the best performance. Based on the experiment, the four enhancers were dissolved in acetone, acetonitrile, methanol, and dimethylformamide (DMF) with various concentrations, the results indicated that 4-IMP, 4-IOP, 4-BOP and HIOP dissolved in DMF with the concentrations of 0.2%, 3.2%, 1.6% and 3.2% could get the highest RLU values. Subsequently, the influences of pH, ionic strength, HRP, 4-IMP, 4-IOP, 4-BOP, HIOP, H2O2 and luminol on the stabilization of the luminol-H2O2-HRP chemiluminescence system were studied, and we found that pH value, ionic strength, 4-IMP, 4-IOP, 4-BOP, HIOP, H2O2 and luminol have little influence on luminescent stabilization, while HRP has a great influence. In different ranges of HRP concentration, different enhancers should be selected. When the concentration is within the range of 0~6 ng/mL, 4-IMP should be selected. When the concentration of HRP ranges from 6 to 25 ng/mL, 4-IOP was the best choice. And when the concentration is within the range of 25~80 ng/mL, HIOP should be selected as the enhancer. Finally, the three well-performing chemiluminescent enhanced solutions (CESs) have been further optimized according to the three enhancers (4-IMP, 4-IOP and HIOP) in their utilized HRP concentration ranges.

Escherichia coli avoids high dissolved oxygen stress by activation of SoxRS and manganese-superoxide dismutase.

PubMed

Baez, Antonino; Shiloach, Joseph

2013-03-12

High concentrations of reactive oxygen species (ROS) were reported to cause oxidative stress to E. coli cells associated with reduced or inhibited growth. The high ROS concentrations described in these reports were generated by exposing the bacteria to H2O2 and superoxide-generating chemicals which are non-physiological growth conditions. However, the effect of molecular oxygen on oxidative stress response has not been evaluated. Since the use of oxygen-enriched air is a common strategy to support high density growth of E. coli, it was important to investigate the effect of high dissolved oxygen concentrations on the physiology and growth of E. coli and the way it responds to oxidative stress. To determine the effect of elevated oxygen concentrations on the growth characteristics, specific gene expression and enzyme activity in E. coli, the parental and SOD-deficient strain were evaluated when the dissolved oxygen (dO2) level was increased from 30% to 300%. No significant differences in the growth parameters were observed in the parental strain except for a temporary decrease of the respiration and acetate accumulation profile. By performing transcriptional analysis, it was determined that the parental strain responded to the oxidative stress by activating the SoxRS regulon. However, following the dO2 switch, the SOD-deficient strain activated both the SoxRS and OxyR regulons but it was unable to resume its initial growth rate. The transcriptional analysis and enzyme activity results indicated that when E. coli is exposed to dO2 shift, the superoxide stress regulator SoxRS is activated and causes the stimulation of the superoxide dismutase system. This enables the E. coli to protect itself from the poisoning effects of oxygen. The OxyR protecting system was not activated, indicating that H2O2 did not increase to stressing levels.

Escherichia coli avoids high dissolved oxygen stress by activation of SoxRS and manganese-superoxide dismutase

PubMed Central

2013-01-01

Background High concentrations of reactive oxygen species (ROS) were reported to cause oxidative stress to E. coli cells associated with reduced or inhibited growth. The high ROS concentrations described in these reports were generated by exposing the bacteria to H2O2 and superoxide-generating chemicals which are non-physiological growth conditions. However, the effect of molecular oxygen on oxidative stress response has not been evaluated. Since the use of oxygen-enriched air is a common strategy to support high density growth of E. coli, it was important to investigate the effect of high dissolved oxygen concentrations on the physiology and growth of E. coli and the way it responds to oxidative stress. Results To determine the effect of elevated oxygen concentrations on the growth characteristics, specific gene expression and enzyme activity in E. coli, the parental and SOD-deficient strain were evaluated when the dissolved oxygen (dO2) level was increased from 30% to 300%. No significant differences in the growth parameters were observed in the parental strain except for a temporary decrease of the respiration and acetate accumulation profile. By performing transcriptional analysis, it was determined that the parental strain responded to the oxidative stress by activating the SoxRS regulon. However, following the dO2 switch, the SOD-deficient strain activated both the SoxRS and OxyR regulons but it was unable to resume its initial growth rate. Conclusion The transcriptional analysis and enzyme activity results indicated that when E. coli is exposed to dO2 shift, the superoxide stress regulator SoxRS is activated and causes the stimulation of the superoxide dismutase system. This enables the E. coli to protect itself from the poisoning effects of oxygen. The OxyR protecting system was not activated, indicating that H2O2 did not increase to stressing levels. PMID:23497217

Gas Transfer Controls Carbon Limitation During Biomass Production by Marine Microalgae.

PubMed

Tamburic, Bojan; Evenhuis, Christian R; Suggett, David J; Larkum, Anthony W D; Raven, John A; Ralph, Peter J

2015-08-24

This study presents the first in-depth analysis of CO2 limitation on the biomass productivity of the biofuel candidate marine microalga Nannochloropsis oculata. Net photosynthesis decreased by 60% from 125 to 50 μmol O2 L(-1)h(-1) over a 12 h light cycle as a direct result of carbon limitation. Continuous dissolved O2 and pH measurements were used to develop a detailed diurnal mechanism for the interaction between photosynthesis, gas exchange and carbonate chemistry in the photo-bioreactor. Gas exchange determined the degree of carbon limitation experienced by the algae. Carbon limitation was confirmed by delivering more CO2 , which increased net photosynthesis back to its steady-state maximum. This study highlights the importance of maintaining replete carbon concentrations in photo-bioreactors and other culturing facilities, either by constant pH operation or preferably by designing a feedback loop based on the dissolved O2 concentration. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Concentration dependences of the density, viscosity, and refraction index of Cu(NO3)2 · 3H2O solutions in DMSO at 298 K

NASA Astrophysics Data System (ADS)

Mamyrbekova, A. K.

2013-03-01

Physicochemical properties (density, dynamic viscosity, refraction index) of the DMSO-Cu(NO3)2 · 3H2O system are studied in the concentration range of 0.01-2 M at 298 K. The refraction index of a solution of copper(II) nitrate in dimethylsulfoxide (DMSO) is measured at 288-318 K. The excess and partial molar volumes of the solvent and dissolved substance are calculated analytically.

Geochemical evolution of acidic ground water at a reclaimed surface coal mine in western Pennsylvania

USGS Publications Warehouse

Cravotta,, Charles A.

1991-01-01

Concentrations of dissolved sulfate and acidity in ground water increase downflow in mine spoil and underlying bedrock at a reclaimed surface coal mine in the bituminous field of western Pennsylvania. Elevated dissolved sulfate and negligible oxygen in ground water from bedrock about 100 feet below the water table suggest that pyritic sulfur is oxidized below the water table, in a system closed to oxygen. Geochemical models for the oxidation of pyrite (FeS2) and production of sulfate (SO42-) and acid (H+) are presented to explain the potential role of oxygen (O2) and ferric iron (Fe3+) as oxidants. Oxidation of pyrite by O2 and Fe3+ can occur under oxic conditions above the water table, whereas oxidation by Fe3+ also can occur under anoxic conditions below the water table. The hydrated ferric-sulfate minerals roemerite [Fe2+Fe43+(SO4)4·14H2O], copiapite [Fe2+Fe43+(SO4)6(OH)2·20H20], and coquimbite [Fe2(SO4)3·9H2O] were identified with FeS2 in coal samples, and form on the oxidizing surface of pyrite in an oxic system above the water table. These soluble ferric-sulfate 11 salts11 can dissolve with recharge waters or a rising water table releasing Fe3+, SO42-. and H+, which can be transported along closed-system ground-water flow paths to pyrite reaction sites where O2 may be absent. The Fe3+ transported to these sites can oxidize pyritic sulfur. The computer programs WATEQ4F and NEWBAL were used to compute chemical speciation and mass transfer, respectively, considering mineral dissolution and precipitation reactions plus mixing of waters from different upflow zones. Alternative mass-balance models indicate that (a) extremely large quantities of O2, over 100 times its aqueous solubility, can generate the observed concentrations of dissolved SO42- from FeS2, or (b) under anoxic conditions, Fe3+ from dissolved ferric-sulfate minerals can oxidize FeS2 along closed-system ground-water flow paths. In a system open to O2, such as in the unsaturated zone, the aqueous solubility of O2 is not limiting, and oxidation of pyrite by O2 and Fe3+ accounts for most SO42- and Fe2+ observed in acidic ground water. However, in a system closed to O2, such as in the saturated zone, O2 solubility is limiting; hence, ferric oxidation of pyrite is a reasonable explanation for the observed elevated SO42- with increasing depth below the water table.

Hybrid method for numerical modelling of LWR coolant chemistry

NASA Astrophysics Data System (ADS)

Swiatla-Wojcik, Dorota

2016-10-01

A comprehensive approach is proposed to model radiation chemistry of the cooling water under exposure to neutron and gamma radiation at 300 °C. It covers diffusion-kinetic processes in radiation tracks and secondary reactions in the bulk coolant. Steady-state concentrations of the radiolytic products have been assessed based on the simulated time dependent concentration profiles. The principal reactions contributing to the formation of H2, O2 and H2O2 were indicated. Simulation was carried out depending on the amount of extra hydrogen dissolved in the coolant to reduce concentration of corrosive agents. High sensitivity to the rate of reaction H+H2O=OH+H2 is shown and discussed.

Comparing Measures of Estuarine Ecosystem Production in a ...

EPA Pesticide Factsheets

Anthropogenic nutrient enrichments and concerted efforts at nutrient reductions, compounded with the influences of climate change, are likely changing the net ecosystem production (NEP) of our coastal systems. To quantify these changes, scientists monitor a range of physical, chemical, and biological parameters sampled at various frequencies. Water column chlorophyll concentrations are arguably the most commonly used indicator of net phytoplankton production, as well as a coarse indicator of NEP. We compared parameters that estimate production, including chlorophyll, across an experimental nutrient gradient and in situ in both well-mixed and stratified estuarine environments. Data from an experiment conducted in the early 1980s in mesocosms designed to replicate a well-mixed mid-Narragansett Bay (Rhode Island) water column were used to correlate changes in chlorophyll concentrations, pH, dissolved oxygen (O2), dissolved inorganic nitrogen, phosphate, and silicate concentrations, cell counts, and 14C carbon uptake measurements across a range of nutrient enrichments. The pH, O2, nutrient, and cell count measurements reflected seasonal cycles of spring blooms followed by late summer/early fall respiration periods across nutrient enrichments. Chlorophyll concentrations were more variable and rates of 14C productivity were inconsistent with observed trends in nutrient concentrations, pH, and O2 concentrations. Similar comparisons were made using data from a well-mixe

Effects of dissolved oxygen and pH on nitrous oxide production rates in autotrophic partial nitrification granules.

PubMed

Rathnayake, Rathnayake M L D; Oshiki, Mamoru; Ishii, Satoshi; Segawa, Takahiro; Satoh, Hisashi; Okabe, Satoshi

2015-12-01

The effects of dissolved oxygen (DO) and pH on nitrous oxide (N2O) production rates and pathways in autotrophic partial nitrification (PN) granules were investigated at the granular level. N2O was primarily produced by betaproteobacterial ammonia-oxidizing bacteria, mainly Nitrosomonas europaea, in the oxic surface layer (<200μm) of the autotrophic PN granules. N2O production increased with increasing bulk DO concentration owing to activation of the ammonia (i.e., hydroxylamine) oxidation in this layer. The highest N2O emissions were observed at pH 7.5, although the ammonia oxidation rate was unchanged between pH 6.5 and 8.5. Overall, the results of this study suggest that in situ analyses of PN granules are essential to gaining insight into N2O emission mechanisms in a granule. Copyright © 2015 Elsevier Ltd. All rights reserved.

Degassing history of water, sulfur, and carbon in submarine lavas from Kilauea Volcano, Hawaii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixon, J.E.; Stolper, E.M.; Clague, D.A.

1991-05-01

Major, minor, and dissolved volatile element concentrations were measured in tholeiitic glasses from the submarine portion (Puna Ridge) of the east rift zone of Kilauea Volcano, Hawaii. Dissolved H{sub 2}O and S concentrations display a wide range relative to nonvolatile incompatible elements at all depths. This range cannot be readily explained by fractional crystallization, degassing of H{sub 2}O and S during eruption on the seafloor, or source region heterogeneities. Dissolved CO{sub 2} concentrations, in contrast, show a positive correlation with eruption depth and typically agree within error with the solubility at that depth. The authors propose that most magmas alongmore » the Puna Ridge result from (1) mixing of a relatively volatile-rich, undegassed component with magmas that experienced low pressure (perhaps subaerial) degassing during which substantial H{sub 2}O, S, and CO{sub 2} were lost, followed by (2) fractional crystallization of olivine, clinopyroxene, and plagioclase from this mixture to generate a residual liquid; and (3) further degassing, principally of CO{sub 2} for samples erupted deeper than 1,000 m, during eruption on the seafloor. They predict that average Kilauean primary magmas with 16% MgO contain {approximately}0.47 wt % H{sub 2}0, {approximately}900 ppm S, and have {delta}D values of {approximately}{minus}30 to {minus}40%. The model predicts that submarine lavas from wholly submarine volcanoes (i.e., Loihi), for which there is no opportunity to generate the degassed end member by low pressure degassing, will be enriched in volatiles relative to those from volcanoes whose summits have breached the sea surface (i.e., Kilauea and Mauna Loa).« less

Enhanced Indirect Photochemical Transformation of Histidine and Histamine through Association with Chromophoric Dissolved Organic Matter.

PubMed

Chu, Chiheng; Lundeen, Rachel A; Remucal, Christina K; Sander, Michael; McNeill, Kristopher

2015-05-05

Photochemical transformations greatly affect the stability and fate of amino acids (AAs) in sunlit aquatic ecosystems. Whereas the direct phototransformation of dissolved AAs is well investigated, their indirect photolysis in the presence of chromophoric dissolved organic matter (CDOM) is poorly understood. In aquatic systems, CDOM may act both as sorbent for AAs and as photosensitizer, creating microenvironments with high concentrations of photochemically produced reactive intermediates, such as singlet oxygen (1O2). This study provides a systematic investigation of the indirect photochemical transformation of histidine (His) and histamine by 1O2 in solutions containing CDOM as a function of solution pH. Both His and histamine showed pH-dependent enhanced phototransformation in the CDOM systems as compared to systems in which model, low-molecular-weight 1O2 sensitizers were used. Enhanced reactivity resulted from sorption of His and histamine to CDOM and thus exposure to elevated 1O2 concentrations in the CDOM microenvironment. The extent of reactivity enhancement depended on solution pH via its effects on the protonation state of His, histamine, and CDOM. Sorption-enhanced reactivity was independently supported by depressed rate enhancements in the presence of a cosorbate that competitively displaced His and histamine from CDOM. Incorporating sorption and photochemical transformation processes into a reaction rate prediction model improved the description of the abiotic photochemical transformation rates of His in the presence of CDOM.

Production of NO2/-/ and N2O by nitrifying bacteria at reduced concentrations of oxygen

NASA Technical Reports Server (NTRS)

Goreau, T. J.; Kaplan, W. A.; Wofsy, S. C.; Mcelroy, M. B.; Valois, F. W.; Watson, S. W.

1980-01-01

The influence of oxygen concentration on the production of NO2(-) and N2O by nitrifying marine bacteria of the genus Nitrosomonas is investigated. Pure cultures of the ammonium-oxiding bacteria isolated from the Western Tropical Atlantic Ocean were grown at oxygen partial pressures from 0.005 to 0.2 atm, and concentrations of N2O in the air above the growth medium and dissolved NO2(-) were determined. Decreasing oxygen concentrations are observed to induce a marked decrease in NO2(-) production rates and increase in N2O evolution, leading to an increase of the relative yield of N2O with respect to NO2(-) from 0.3% to nearly 10%. Similar yields of N2O at atmospheric oxygen levels are found for nitrifying bacteria of the genera Nitrosomonas, Nitrosolobus, Nitrosospira and Nitrosococcus, while nitrite-oxydizing bacteria and a dinoflagellate did not produce detectable quantities of N2O. Results support the view that nitrification is a major source of N2O in the environment.

Uranium biogeochemistry across the redox transition zone of a permanently stratified fjord: Framvaren, Norway

USGS Publications Warehouse

Swarzenski, P.W.; McKee, B.A.; Skei, J.M.; Todd, J.F.

1999-01-01

During August 1995, the vertical concentration profile of dissolved and particulate uranium exhibited strong non-conservative characteristics in the upper 30 m of Framvaren Fjord. There was a pronounced peak in both particulate (> 0.2 ??m; 1.09 nM) and dissolved (< 0.2 ??m; 17.06 nM) uranium in the finely stratified waters at the O2/H2S interface which is positioned well within the euphotic zone at about 20-21 m. Such concentration maxima at the redox boundary are also observed for dissolved organic carbon (DEC), Sr and Ba. Dissolved U levels seen in the water column from 18 m down to 30 m exceeded the high salinity (salinity = 35) U concentrations (13.63 ?? 0.84 nM; Chen, J.H., Edwards, R.L., Wasserburg, G.L., 1986. 238U, 234U and 232Th in seawater. Earth Planet Sci. Lett. 80, 241-251.) observed uniformly in the open ocean. A prolific population of S microbes (e.g., Chromatium, Chlorobium sp.) flourishes at the O2/H2S interface. The source of elevated U at the redox boundary must be due to microbial uptake and subsequent release processes rather than dilution from oceanic uranium. Uranium oxidation state determinations in waters from 1, 22 and 30 m depth reveal that reduced U(IV) is not present in significant abundance, and that the chemical and/or biological reduction of hexavalent uranium is largely inhibited. Our results suggest that U and other trace constituents such as DOC, Sr, Ba, Fe(II), Mn(II) are greatly modified by direct and indirect microbial transformation reactions which are most concentrated across the redox transition zone in Framvaren Fjord.

Occurrence of greenhouse gases in the aquifers of the Walloon Region (Belgium).

PubMed

Jurado, Anna; Borges, Alberto V; Pujades, Estanislao; Hakoun, Vivien; Otten, Joël; Knöller, Kay; Brouyère, Serge

2018-04-01

This work aims to (1) identify the most conductive conditions for the generation of greenhouses gases (GHGs) in groundwater (e.g., hydrogeological contexts and geochemical processes) and (2) evaluate the indirect emissions of GHGs from groundwater at a regional scale in Wallonia (Belgium). To this end, nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ) concentrations and the stable isotopes of nitrate (NO 3 - ) and sulphate were monitored in 12 aquifers of the Walloon Region (Belgium). The concentrations of GHGs range from 0.05μg/L to 1631.2μg/L for N 2 O, 0μg/L to 17.1μg/L for CH 4 , and 1769 to 100,514ppm for the partial pressure of CO 2 (pCO 2 ). The highest average concentrations of N 2 O and pCO 2 are found in a chalky aquifer. The coupled use of statistical techniques and stable isotopes is a useful approach to identify the geochemical conditions that control the occurrence of GHGs in the aquifers of the Walloon Region. The accumulation of N 2 O is most likely due to nitrification (high concentrations of dissolved oxygen and NO 3 - and null concentrations of ammonium) and, to a lesser extent, initial denitrification in a few sampling locations (medium concentrations of dissolved oxygen and NO 3 - ). The oxic character found in groundwater is not prone to the accumulation of CH 4 in Walloon aquifers. Nevertheless, groundwater is oversaturated with GHGs with respect to atmospheric equilibrium (especially for N 2 O and pCO 2 ); the fluxes of N 2 O (0.32kgN 2 O-NHa -1 y -1 ) and CO 2 (27kgCO 2 Ha -1 y -1 ) from groundwater are much lower than the direct emissions of N 2 O from agricultural soils and fossil-fuel-related CO 2 emissions. Thus, indirect GHG emissions from the aquifers of the Walloon Region are likely to be a minor contributor to atmospheric GHG emissions, but their quantification would help to better constrain the nitrogen and carbon budgets. Copyright © 2017 Elsevier B.V. All rights reserved.

Recycling Titanium and Its Alloys by Utilizing Molten Salt

NASA Astrophysics Data System (ADS)

Okabe, Toru H.; Taninouchi, Yu-ki

It is commonly believed that the deoxidation of titanium (Ti), or the direct removal of oxygen (O) dissolved in metallic Ti, is practically impossible when magnesium (Mg) is used as the deoxidizing agent. In recent years, it has been experimentally demonstrated that O dissolved in Ti can be directly removed using MgCl2 molten salt electrolysis. By the electrochemical deoxidation technique, Ti wires containing 0.12 mass% O were deoxidized to less than 0.02 mass% O. In some cases, the concentration of O in the Ti wires was reduced to the level of 0.01 mass% O, which cannot be attained using the current Kroll process. The possible application of this deoxidation technique to practical industrial recycling processes is also discussed.

Light–dark O2 dynamics in submerged leaves of C3 and C4 halophytes under increased dissolved CO2: clues for saltmarsh response to climate change

PubMed Central

Duarte, B.; Santos, D.; Silva, H.; Marques, J. C.; Caçador, I.; Sleimi, N.

2014-01-01

Waterlogging and submergence are the major constraints to which wetland plants are subjected, with inevitable impacts on their physiology and productivity. Global warming and climate change, as driving forces of sea level rise, tend to increase such submersion periods and also modify the carbonate chemistry of the water column due to the increased concentration of CO2 in the atmosphere. In the present work, the underwater O2 fluxes in the leaves of two abundant Mediterranean halophytes were evaluated at different levels of dissolved CO2. Photosynthetic enhancement due to increased dissolved CO2 was confirmed for both Halimione portulacoides and Spartina maritima, probably due to high tissue porosity, formation of leaf gas films and reduction of the oxygenase activity of Rubisco. Enhancement of the photosynthetic rates in H. portulacoides and S. maritima was concomitant with an increase in energy trapping and transfer, mostly due to enhancement of the carboxylation reaction of Rubisco, leading to a reduction of the energy costs for carbon fixation. Transposing these findings to the ecosystem, and assuming increased dissolved CO2 concentration scenarios, the halophyte community displays a new ecosystem function, increasing the water column oxygenation and thus reinforcing their role as principal primary producers of the estuarine system. PMID:25381259

Dissolution process for ZrO.sub.2 -UO.sub.2 -CaO fuels

DOEpatents

Paige, Bernice E.

1976-06-22

The present invention provides an improved dissolution process for ZrO.sub.2 -UO.sub.2 -CaO-type pressurized water reactor fuels. The zirconium cladding is dissolved with hydrofluoric acid, immersing the ZrO.sub.2 -UO.sub.2 -CaO fuel wafers in the resulting zirconium-dissolver-product in the dissolver vessel, and nitric acid is added to the dissolver vessel to facilitate dissolution of the uranium from the ZrO.sub.2 -UO.sub.2 -CaO fuel wafers.

Enhanced Al and Zn removal from coal-mine drainage during rapid oxidation and precipitation of Fe oxides at near-neutral pH

USGS Publications Warehouse

Burrows, Jill E.; Cravotta, Charles A.; Peters, Stephen C.

2017-01-01

Net-alkaline, anoxic coal-mine drainage containing ∼20 mg/L FeII and ∼0.05 mg/L Al and Zn was subjected to parallel batch experiments: control, aeration (Aer 1 12.6 mL/s; Aer 2 16.8 mL/s; Aer 3 25.0 mL/s), and hydrogen peroxide (H2O2) to test the hypothesis that aeration increases pH, FeII oxidation, hydrous FeIII oxide (HFO) formation, and trace-metal removal through adsorption and coprecipitation with HFO. During 5.5-hr field experiments, pH increased from 6.4 to 6.7, 7.1, 7.6, and 8.1 for the control, Aer 1, Aer 2, and Aer 3, respectively, but decreased to 6.3 for the H2O2 treatment. Aeration accelerated removal of dissolved CO2, Fe, Al, and Zn. In Aer 3, dissolved Al was completely removed within 1 h, but increased to ∼20% of the initial concentration after 2.5 h when pH exceeded 7.5. H2O2 promoted rapid removal of all dissolved Fe and Al, and 13% of dissolved Zn.Kinetic modeling with PHREEQC simulated effects of aeration on pH, CO2, Fe, Zn, and Al. Aeration enhanced Zn adsorption by increasing pH and HFO formation while decreasing aqueous CO2 available to form ZnCO30 and Zn(CO3)22− at high pH. Al concentrations were inconsistent with solubility control by Al minerals or Al-containing HFO, but could be simulated by adsorption on HFO at pH < 7.5 and desorption at higher pH where Al(OH)4− was predominant. Thus, aeration or chemical oxidation with pH adjustment to ∼7.5 could be effective for treating high-Fe and moderate-Zn concentrations, whereas chemical oxidation without pH adjustment may be effective for treating high-Fe and moderate-Al concentrations.

Photoreduction fuels biogeochemical cycling of iron in Spain's acid rivers

USGS Publications Warehouse

Gammons, C.H.; Nimick, D.A.; Parker, S.R.; Snyder, D.M.; McCleskey, R. Blaine; Amils, R.; Poulson, S.R.

2008-01-01

A number of investigations have shown that photoreduction of Fe(III) causes midday accumulations of dissolved Fe(II) in rivers and lakes, leading to large diel (24-h) fluctuations in the concentration and speciation of total dissolved iron. Less well appreciated is the importance of photoreduction in providing chemical energy for bacteria to thrive in low pH waters. Diel variations in water chemistry from the highly acidic (pH 2.3 to 3.1) Ri??o Tinto, Ri??o Odiel, and Ri??o Agrio of southwestern Spain (Iberian Pyrite Belt) resulted in daytime increases in Fe(II) concentration of 15 to 66????M at four diel sampling locations. Dissolved Fe(II) concentrations increased with solar radiation, and one of the stream sites showed an antithetic relationship between dissolved Fe(II) and Fe(III) concentrations; both results are consistent with photoreduction. The diel data were used to estimate rates of microbially catalyzed Fe(II) oxidation (1 to 3??nmol L- 1 s- 1) and maximum rates of Fe(III) photoreduction (1.7 to 4.3??nmol L- 1 s- 1). Bioenergetic calculations indicate that the latter rates are sufficient to build up a population of Fe-oxidizing bacteria to the levels observed in the Ri??o Tinto in about 30??days. We conclude that photoreduction plays an important role in the bioenergetics of the bacterial communities of these acidic rivers, which have previously been shown to be dominated by autotrophic Fe(II)-oxidizers such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans. Given the possibility of the previous existence of acidic, Fe(III)-rich water on Mars, photoreduction may be an important process on other planets, a fact that could have implications to astrobiological research. ?? 2008 Elsevier B.V. All rights reserved.

Simulated nitrogen deposition reduces CH4 uptake and increases N2O emission from a subtropical plantation forest soil in southern China.

PubMed

Wang, Yongsheng; Cheng, Shulan; Fang, Huajun; Yu, Guirui; Xu, Minjie; Dang, Xusheng; Li, Linsen; Wang, Lei

2014-01-01

To date, few studies are conducted to quantify the effects of reduced ammonium (NH4+) and oxidized nitrate (NO3-) on soil CH4 uptake and N2O emission in the subtropical forests. In this study, NH4Cl and NaNO3 fertilizers were applied at three rates: 0, 40 and 120 kg N ha(-1) yr(-1). Soil CH4 and N2O fluxes were determined twice a week using the static chamber technique and gas chromatography. Soil temperature and moisture were simultaneously measured. Soil dissolved N concentration in 0-20 cm depth was measured weekly to examine the regulation to soil CH4 and N2O fluxes. Our results showed that one year of N addition did not affect soil temperature, soil moisture, soil total dissolved N (TDN) and NH4+-N concentrations, but high levels of applied NH4Cl and NaNO3 fertilizers significantly increased soil NO3(-)-N concentration by 124% and 157%, respectively. Nitrogen addition tended to inhibit soil CH4 uptake, but significantly promoted soil N2O emission by 403% to 762%. Furthermore, NH4+-N fertilizer application had a stronger inhibition to soil CH4 uptake and a stronger promotion to soil N2O emission than NO3(-)-N application. Also, both soil CH4 and N2O fluxes were driven by soil temperature and moisture, but soil inorganic N availability was a key integrator of soil CH4 uptake and N2O emission. These results suggest that the subtropical plantation soil sensitively responses to atmospheric N deposition, and inorganic N rather than organic N is the regulator to soil CH4 uptake and N2O emission.

Microanalysis of dissolved iron and phosphate in pore waters of hypersaline sediment

NASA Technical Reports Server (NTRS)

Haddad, R.; Shaw, T.

1985-01-01

Diurnal fluctuations of reduced iron concentrations, expected to occur in reduced sediments in the photic zone, were studied. Iron concentration was compared to O2-H2S, a microcanalysis of sulfate reduction was performed, as well as an examination of diurnal concentration of dissolved phosphate and changes in interstitial CO2. The iron profiles suggest a strong correlation between iron remobilization and processes occurring in the light. Phosphate profiles suggest the removal of phosphate is strongly correlated with precipitation of oxidized iron in the upper 2 mm to 5 mm of the sediments. Pore water CO2 concentrations and carbon isotope ratios are presented. These data are from the analyses of minisediment cores collected from the 42 per mil salt pond and incubated in the laboratory under light and dark conditions.

Dissolution behavior of MgO based inert matrix fuel for the transmutation of minor actinides

NASA Astrophysics Data System (ADS)

Mühr-Ebert, E. L.; Lichte, E.; Bukaemskiy, A.; Finkeldei, S.; Klinkenberg, M.; Brandt, F.; Bosbach, D.; Modolo, G.

2018-07-01

This study explores the dissolution properties of magnesia-based inert matrix nuclear fuel (IMF) containing transuranium elements (TRU). Pure MgO pellets as well as MgO pellets containing CeO2, as surrogate for TRU oxides, and are considered as model systems for genuine magnesia based inert matrix fuel were fabricated. The aim of this study is to identify conditions at which the matrix material can be selectively dissolved during the head-end reprocessing step, allowing a separation of MgO from the actinides, whereas the actinides remain undissolved. The dissolution behavior was studied in macroscopic batch experiments as a function of nitric acid concentration, dissolution medium volume, temperature, stirring velocity, and pellet density (85, 90, 96, and 99%TD). To mimic pellets with various burn-ups the density of the here fabricated pellets was varied. MgO is soluble even under mild conditions (RT, 2.5 mol/L HNO3). The dissolution rates of MgO at different acid concentrations are rather similar, whereas the dissolution rate is strongly dependent on the temperature. Via a microscopic approach, a model was developed to describe the evolution of the pellet surface area during dissolution and determine a surface normalized dissolution rate. Moreover, dissolution rates of the inert matrix fuel containing CeO2 were determined as a function of the acid concentration and temperature. During the dissolution of MgO/CeO2 pellets the MgO dissolves completely, while CeO2 (>99%) remains undissolved. This study intends to provide a profound understanding of the chemical performance of magnesia based IMF containing fissile material. The feasibility of the dissolution of magnesia based IMF with nitric acid is discussed.

Effects of volcanic deposit disaggregation on exposed water composition

NASA Astrophysics Data System (ADS)

Back, W. E.; Genareau, K. D.

2016-12-01

Explosive volcanic eruptions produce a variety of hazards. Pyroclastic material can be introduced to water through ash fallout, pyroclastic flows entering water bodies, and/or lahars. Remobilization of tephras can occur soon after eruption or centuries later, introducing additional pyroclastic material into the environment. Introduction of pyroclastic material may alter the dissolved element concentration and pH of exposed waters, potentially impacting drinking water supplies, agriculture, and ecology. This study focuses on the long-term impacts of volcanic deposits on water composition due to the mechanical breakup of volcanic deposits over time. Preliminary work has shown that mechanical milling of volcanic deposits will cause significant increases in dissolved element concentrations, conductivity, and pH of aqueous solutions. Pyroclastic material from seven eruptions sites was collected, mechanically milled to produce grain sizes <32 microns, and a standard ash leachate protocol was performed. Milled tephras were analyzed using X-Ray Fluorescence (XRF) and water leachates were analyzed with Inductively Coupled Plasma Optical-Emission Spectroscopy (ICP-OES). Mechanical disaggregation increases the surface area of the material as well as the amount of active surface sites for leaching. The samples tested consist of felsic (Taupo and Valles Caldera), intermediate (Kelud, Soufriere Hills, Ruapehu), mafic (Lathrop Wells) and ultramafic (mantle xenoliths) volcanic deposits. Lathrop Wells has an average bulk concentration of 49.15 wt.% SiO2, 6.11 wt. % MgO, and 8.39 wt. % CaO and produces leachate concentrations of 85.69 mg/kg for Ca and 37.22 mg/kg for Mg. Taupo and Valles Caldera samples have a bulk concentration of 72.9 wt.% SiO2, 0.59 wt. % MgO, and 1.48 wt. % CaO, and produces leachate concentrations of 4.08 mg/kg for Ca and 1.56 mg/kg for Mg. Similar testing will be conducted on the intermediate and ultramafic samples to test the hypothesis that bulk magma composition and mineralogy will directly relate to the increased dissolved element concentration of exposed waters. The measured effects on aqueous solutions will aid in evaluation of impacts to marine and freshwater systems exposed to volcanic deposits.

Cyanobacterial and microcystins dynamics following the application of hydrogen peroxide to waste stabilisation ponds

NASA Astrophysics Data System (ADS)

Barrington, D. J.; Ghadouani, A.; Ivey, G. N.

2013-02-01

Cyanobacteria and cyanotoxins are a risk to human and ecological health, and a hindrance to biological wastewater treatment. This study investigated the use of hydrogen peroxide (H2O2) for the removal of cyanobacteria and cyanotoxins from within waste stabilization ponds (WSPs). The daily dynamics of cyanobacteria and microcystins (a commonly occurring cyanotoxin) were examined following the addition of H2O2 to wastewater within both the laboratory and at the full-scale within a WSP. Hydrogen peroxide treatment at concentrations ≥ 10-4 g H2O2 μg-1 of total phytoplankton chlorophyll a led to the death of cyanobacteria, in turn releasing intracellular microcystins to the dissolved state. In the full-scale trial, dissolved microcystins were then degraded to negligible concentrations by H2O2 and environmental processes within five days. A shift in the phytoplankton assemblage towards beneficial chlorophyta species was also observed within days of H2O2 addition. However, within weeks, the chlorophyta population was significantly reduced by the re-establishment of toxic cyanobacterial species. This re-establishment was likely due to the inflow of cyanobacteria from ponds earlier in the treatment train, suggesting that whilst H2O2 may be a suitable short-term management technique, it must be coupled with control over inflows if it is to improve WSP performance in the longer term.

Flume experiments elucidate relationships between stream morphology, hyporheic residence time, and nitrous oxide production

NASA Astrophysics Data System (ADS)

Quick, Annika; Farrell, Tiffany B.; Reeder, William Jeffrey; Feris, Kevin P.; Tonina, Daniele; Benner, Shawn G.

2015-04-01

The hyporheic zone is a potentially important producer of nitrous oxide, a powerful greenhouse gas. The location and magnitude of nitrous oxide generation within the hyporheic zone involves complex interactions between multiple nitrogen species, redox conditions, microbial communities, and hydraulics. To better understand nitrous oxide generation and emissions from streams, we conducted large-scale flume experiments in which we monitored pore waters along hyporheic flow paths within stream dune structures. Measurements of dissolved oxygen, ammonia, nitrate, nitrite, and dissolved nitrous oxide showed distinct spatial relationships reflecting redox changes along flow paths. Using residence times along a flow path, clear trends in oxygen conditions and nitrogen species were observed. Three dune sizes were modeled, resulting in a range of residence times, carbon reactivity levels and respiration rates. We found that the magnitude and location of nitrous oxide production in the hyporheic zone is related to nitrate loading, dune morphology, and residence time. Specifically, increasing exogenous nitrate levels in surface water to approximately 3 mg/L resulted in an increase in dissolved N2O concentrations greater than 500% (up to 10 µg/L N-N2O) in distinct zones of specific residence times. We also found, however, that dissolved N2O concentrations decreased to background levels further along the flow path due to either reduction of nitrous oxide to dinitrogen gas or degassing. The decrease in measurable N2O along a flow path strongly suggests an important relationship between dune morphology, residence time, and nitrous oxide emissions from within stream sediments. Relating streambed morphology and loading of nitrogen species allows for prediction of nitrous oxide production in the hyporheic zone of natural systems.

Analysis of maximum allowable fragment heights during dissolution of high flux isotope reactor fuel in an h-canyon dissolver

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daniel, G.; Rudisill, T.

2017-07-17

As part of the Spent Nuclear Fuel (SNF) processing campaign, H-Canyon is planning to begin dissolving High Flux Isotope Reactor (HFIR) fuel in late FY17 or early FY18. Each HFIR fuel core contains inner and outer fuel elements which were fabricated from uranium oxide (U 3O 8) dispersed in a continuous Al phase using traditional powder metallurgy techniques. Fuels fabricated in this manner, like other SNF’s processed in H-Canyon, dissolve by the same general mechanisms with similar gas generation rates and the production of H 2. The HFIR fuel cores will be dissolved using a flowsheet developed by the Savannahmore » River National Laboratory (SRNL) in either the 6.4D or 6.1D dissolver using a unique insert. Multiple cores will be charged to the same dissolver solution maximizing the concentration of dissolved Al. The recovered U will be down-blended into low-enriched U for subsequent use as commercial reactor fuel. During the development of the HFIR fuel dissolution flowsheet, the cycle time for the initial core was estimated at 28 to 40 h. Once the cycle is complete, H-Canyon personnel will open the dissolver and probe the HFIR insert wells to determine the height of any fuel fragments which did not dissolve. Before the next core can be charged to the dissolver, an analysis of the potential for H 2 gas generation must show that the combined surface area of the fuel fragments and the subsequent core will not generate H 2 concentrations in the dissolver offgas which exceeds 60% of the lower flammability limit (LFL) of H 2 at 200 °C. The objective of this study is to identify the maximum fuel fragment height as a function of the Al concentration in the dissolving solution which will provide criteria for charging successive HFIR cores to an H-Canyon dissolver.« less

Dissolution flowsheet for high flux isotope reactor fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foster, T.

2016-09-27

As part of the Spent Nuclear Fuel (SNF) processing campaign, H-Canyon is planning to begin dissolving High Flux Isotope Reactor (HFIR) fuel in late FY17 or early FY18. Each HFIR fuel core contains inner and outer fuel elements which were fabricated from uranium oxide (U 3O 8) dispersed in a continuous Al phase using traditional powder metallurgy techniques. Fuels fabricated in this manner, like other SNF’s processed in H-Canyon, dissolve by the same general mechanisms with similar gas generation rates and the production of H 2. The HFIR fuel cores will be dissolved and the recovered U will be down-blendedmore » into low-enriched U. HFIR fuel was previously processed in H-Canyon using a unique insert in both the 6.1D and 6.4D dissolvers. Multiple cores will be charged to the same dissolver solution maximizing the concentration of dissolved Al. The objective of this study was to identify flowsheet conditions through literature review and laboratory experimentation to safely and efficiently dissolve the HFIR fuel in H-Canyon. Laboratory-scale experiments were performed to evaluate the dissolution of HFIR fuel using both Al 1100 and Al 6061 T6 alloy coupons. The Al 1100 alloy was considered a representative surrogate which provided an upper bound on the generation of flammable (i.e., H 2) gas during the dissolution process. The dissolution of the Al 6061 T6 alloy proceeded at a slower rate than the Al 1100 alloy and was used to verify that the target Al concentration in solution could be achieved for the selected Hg concentration. Mass spectrometry and Raman spectroscopy were used to provide continuous monitoring of the concentration of H 2 and other permanent gases in the dissolution offgas allowing the development of H 2 generation rate profiles. The H 2 generation rates were subsequently used to evaluate if a full HFIR core could be dissolved in an H-Canyon dissolver without exceeding 60% of the calculated lower flammability limit (LFL) for H 2 at a given Hg concentration.« less

Shifting nitrous oxide source/sink behaviour in a subtropical estuary revealed by automated time series observations

NASA Astrophysics Data System (ADS)

Reading, Michael J.; Santos, Isaac R.; Maher, Damien T.; Jeffrey, Luke C.; Tait, Douglas R.

2017-07-01

The oceans are a major source of the potent greenhouse gas nitrous oxide (N2O) to the atmosphere. However, little information is available on how estuaries and the coastal ocean may contribute to N2O budgets, and on the drivers of N2O in aquatic environments. This study utilised five time series stations along the freshwater to marine continuum in a sub-tropical estuary in Australia (Coffs Creek, Australia). Each time series station captured N2O, radon (222Rn, a natural submarine groundwater discharge tracer), dissolved nitrogen, and dissolved organic carbon (DOC) concentrations for a minimum of 25 h. The use of automated time series observations enabled spatial and tidal-scale variability of N2O to be captured. Groundwater was highly enriched in N2O (up to 306 nM) compared to the receiving surface water. Dissolved N2O supersaturation as high as 386% (27.4 nM) was observed in the upstream freshwater and brackish water areas which represented only a small (∼13%) proportion of the total estuary area. A large area of N2O undersaturation (as low as 53% or 3.9 nM) was observed in the mangrove-dominated lower estuary. This undersaturated area likely resulted from N2O consumption due to nitrate/nitrite (NOx) limitation in mangrove sediments subject to shallow porewater exchange. Overall, the estuary was a minor source of N2O to the atmosphere as the lower mangrove-dominated estuary sink of N2O counteracted groundwater-dominated source of N2O in the upper estuary. Average area-weighted N2O fluxes at the water-air interface approached zero (0.2-0.7 μmol m-2 d-1, depending on piston velocity model used), and were much lower than nitrogen-rich Northern Hemisphere estuaries that are considered large sources of N2O to the atmosphere. This study revealed a temporally and spatially diverse estuary, with areas of N2O production and consumption related to oxygen and total dissolved nitrogen availability, submarine groundwater discharge, and uptake within mangroves.

Comparative evaluation of human pulp tissue dissolution by different concentrations of chlorine dioxide, calcium hypochlorite and sodium hypochlorite: An in vitro study

PubMed Central

Taneja, Sonali; Mishra, Neha; Malik, Shubhra

2014-01-01

Introduction: Irrigation plays an indispensable role in removal of tissue remnants and debris from the complicated root canal system. This study compared the human pulp tissue dissolution by different concentrations of chlorine dioxide, calcium hypochlorite and sodium hypochlorite. Materials and Methods: Pulp tissue was standardized to a weight of 9 mg for each sample. In all,60 samples obtained were divided into 6 groups according to the irrigating solution used- 2.5% sodium hypochlorite (NaOCl), 5.25% NaOCl, 5% calcium hypochlorite (Ca(OCl)2), 10% Ca(OCl)2, 5%chlorine dioxide (ClO2) and 13% ClO2. Pulp tissue was placed in each test tube carrying irrigants of measured volume (5ml) according to their specified subgroup time interval: 30 minutes (Subgroup A) and 60 minutes (Subgroup B). The solution from each sample test tube was filtered and was left for drying overnight. The residual weight was calculated by filtration method. Results: Mean tissue dissolution increases with increase in time period. Results showed 5.25% NaOCl to be most effective at both time intervals followed by 2.5% NaOCl at 60 minutes, 10%Ca(OCl)2 and 13% ClO2 at 60 minutes. Least amount of tissue dissolving ability was demonstrated by 5% Ca(OCl)2 and 5% ClO2 at 30 minutes. Distilled water showed no pulp tissue dissolution. Conclusion: Withinthe limitations of the study, NaOCl most efficiently dissolved the pulp tissue at both concentrations and at both time intervals. Mean tissue dissolution by Ca(OCl)2 and ClO2 gradually increased with time and with their increase in concentration. PMID:25506141

Effect of temperature and dissolved oxygen on biological nitrification at high ammonia concentrations.

PubMed

Weon, S Y; Lee, S I; Koopman, B

2004-11-01

Effect of temperature and dissolved oxygen concentration on nitrification rate were investigated with enrichment cultures of nitrifying bacteria. Values of specific nitrite oxidation rate in the absence of ammonia were 2.9-12 times higher than maximum specific ammonia oxidation rates at the same temperatures. The presence of high ammonia levels reversed this relationship, causing maximum specific nitrite oxidation rates to fall to 19 to 45% as high as maximum specific ammonia oxidation rates. This result suggests that nitrification at high ammonia levels will invariably result in nitrite accumulation. The K(O2) for nitrite oxidation in the presence of high ammonia levels was higher than the K(O2) for ammonia oxidation when temperature exceeded 18 degrees C, whereas the opposite was true at lower temperatures. These results indicate that low oxygen tensions will exacerbate nitrite accumulation when water temperature is high.

N2 Fluxes From Amazon Cropland Are a Significant Component of Watershed N Budgets.

NASA Astrophysics Data System (ADS)

Fox, R. J.; Neill, C.; Macedo, M.; Davidson, E. A.; Lefebvre, P.; Jankowski, K.; Maracahipes-Santos, L.

2017-12-01

Amazon tropical rainforests have experienced significant deforestation and conversion to cropland. Recently, cropping has intensified to include higher application rates of N fertilizer, typically in a soybean-corn rotation. Our previous work in Mato Grosso, Brazil, suggests that the addition of N fertilizer (80 Kg N ha-1 yr-1) has not increased N2O fluxes from soils or elevated dissolved N concentrations in streams or groundwater. Here, we investigate whether N fertilizer is converted to N2 in groundwater. We collected samples during January and October 2016 from streams and well transects across riparian forest buffers bordering cropland or within intact riparian forests. Samples were collected using a positive pressure pump and analyzed using Membrane Inlet Mass Spectrometry (MIMS) for N2, Ar, and O2 and gas chromatography for N2O and CH4. N2 concentrations in excess of solubility (based on Ar) were measured at nearly all locations in January and ranged from -15 to 220 in cropland and -2 to 93 µmol N2-N L-1 in intact forest. N2 concentrations were generally lower in October and ranged from -0.9 to 95 in cropland and -0.6 to 52 µmol N2-N L-1 in intact forest. Higher N2 concentrations accumulated at lower dissolved oxygen concentrations and at the borders between cropland and riparian forest. N2O concentrations were significantly lower than N2 concentrations on both dates and ranged between 0.01 and 0.33 µmol N2O-N L-1. Preliminary estimates suggest that N2 losses from cropland ranged from 10 to 20 kg N ha-1 y-1 and losses from forests ranged from 2 to 12 kg N ha-1 y-1. High concentrations of N2 in groundwater have been found in and around agricultural fields in temperate regions, but direct N2 measurements in tropical agricultural regions have not been previously documented. These results suggest that N2 fluxes from tropical cropland receiving modest amounts of N fertilizer could be substantial.

Combined Effects of Dissolved Nutrients and Oxygen on Plant Litter Decomposition and Associated Fungal Communities.

PubMed

Gomes, Patrícia Pereira; Ferreira, Verónica; Tonin, Alan M; Medeiros, Adriana Oliveira; Júnior, José Francisco Gonçalves

2018-05-01

Aquatic ecosystems worldwide have been substantially altered by human activities, which often induce changes in multiple factors that can interact to produce complex effects. Here, we evaluated the combined effects of dissolved nutrients (nitrogen [N] and phosphorus [P]; three levels: concentration found in oligotrophic streams in the Cerrado biome, 10× and 100× enriched) and oxygen (O 2 ; three levels: hypoxic [4% O 2 ], depleted [55% O 2 ], and saturated [96% O 2 ]) on plant litter decomposition and associated fungal decomposers in laboratory microcosms simulating stream conditions under distinct scenarios of water quality deterioration. Senescent leaves of Maprounea guianensis were incubated for 10 days in an oligotrophic Cerrado stream to allow microbial colonization and subsequently incubated in microcosms for 21 days. Leaves lost 1.1-3.0% of their initial mass after 21 days, and this was not affected either by nutrients or oxygen levels. When considering simultaneous changes in nutrients and oxygen concentrations, simulating increased human pressure, fungal biomass accumulation, and sporulation rates were generally inhibited. Aquatic hyphomycete community structure was also affected by changes in nutrients and oxygen availability, with stronger effects found in hypoxic treatments than in depleted or saturated oxygen treatments. This study showed that the effects of simultaneous changes in the availability of dissolved nutrients and oxygen in aquatic environments can influence the activity and composition of fungal communities, although these effects were not translated into changes in litter decomposition rates.

Glacial alteration of volcanic terrains: A chemical investigation of the Three Sisters, Oregon, USA.

NASA Astrophysics Data System (ADS)

Rutledge, Alicia; Horgan, Briony; Havig, Jeff

2017-04-01

Glacial silica cycling is more efficient than previously reported, and in some settings, particularly glaciated mafic volcanics, can be the dominant weathering process. Based on field work at glaciated volcanic sites, we hypothesize that this is due to a combination of high rates of silica dissolution from mafic bedrock and reprecipitation of silica in the form of opaline silica coatings and other poorly crystalline silicate alteration phases. The high rate of bedrock comminution in subglacial environments results in high rates of both chemical and physical weathering, due to the increased reactive mineral surface area formed through glacial grinding. In most bedrock types, carbonate weathering is enhanced and silica fluxes are depressed in glacial outwash compared with global average riverine catchment runoff due to low temperatures and short residence times. However, in mafic systems, higher dissolved SiO2 concentrations have been observed. The major difference between observed glacial alteration of volcanic bedrock and more typical continental terrains is the absence of significant dissolved carbonate in the former. In the absence of carbonate minerals which normally dominate dissolution processes at glacier beds, carbonation of feldspar can become the dominant weathering process, which can result in a high proportion of dissolved silica fluxes in glacial outwash waters compared to the total cation flux. Mafic volcanic rocks are particularly susceptible to silica mobility, due to the high concentration of soluble minerals (i.e. plagioclase) as compared to the high concentration of insoluble quartz found in felsic rocks. To investigate melt-driven chemical weathering of mafic volcanics, water and rock samples were collected during July 2016 from glaciated volcanic bedrock in the Three Sisters Wilderness, Oregon, U.S.A. (44°9'N, 121°46'W): Collier Glacier (basaltic andesite, andesite), Hayden Glacier (andesite, dacite), and Diller Glacier (basalt). Here we report major anion and cation concentrations in meltwaters for the summer 2016 melt season, with emphasis on SiO2. Dissolved silica concentration (range: below detectable levels to 240 μM) tends to increase with pH (range: 4.3 to 8.5), consistent with silica solubility increasing with pH. Proglacial streams, springs, and lakes exhibit dissolved silica concentrations that are greater than observed in glacial snow/ice. The highest silica concentrations were measured in moraine-sourced springs. More mafic glaciovolcanic sites exhibit higher concentrations of dissolved silica in outwash waters compared to more felsic glaciovolcanic sites. Though basalts have lower SiO2 content than more felsic volcanic rocks, they are more susceptible to silica mobility due to their higher content of minerals such as olivine, pyroxene, and plagioclase, which are more soluble than quartz. These mineral breakdown reactions are potentially enhanced by microbial populations at the glacier bed. The measured high silica concentrations in springs are potentially due to moraines acting as sediment traps. Moraines are poorly sorted sediments with a high proportion of subglacially ground fine particles, and glacial flour further accumulates by aeolian deposition. The increased fine-grained component - and thus increased surface area - and longer residence times due to associated decreased permeability could contribute to the observed high dissolved silica concentrations.

Microfluidic dissolved oxygen gradient generator biochip as a useful tool in bacterial biofilm studies.

PubMed

Skolimowski, Maciej; Nielsen, Martin Weiss; Emnéus, Jenny; Molin, Søren; Taboryski, Rafael; Sternberg, Claus; Dufva, Martin; Geschke, Oliver

2010-08-21

A microfluidic chip for generation of gradients of dissolved oxygen was designed, fabricated and tested. The novel way of active oxygen depletion through a gas permeable membrane was applied. Numerical simulations for generation of O(2) gradients were correlated with measured oxygen concentrations. The developed microsystem was used to study growth patterns of the bacterium Pseudomonas aeruginosa in medium with different oxygen concentrations. The results showed that attachment of Pseudomonas aeruginosa to the substrate changed with oxygen concentration. This demonstrates that the device can be used for studies requiring controlled oxygen levels and for future studies of microaerobic and anaerobic conditions.

Geochemical modeling of iron, sulfur, oxygen and carbon in a coastal plain aquifer

NASA Astrophysics Data System (ADS)

Brown, C. J.; Schoonen, M. A. A.; Candela, J. L.

2000-11-01

Fe(III) reduction in the Magothy aquifer of Long Island, NY, results in high dissolved-iron concentrations that degrade water quality. Geochemical modeling was used to constrain iron-related geochemical processes and redox zonation along a flow path. The observed increase in dissolved inorganic carbon is consistent with the oxidation of sedimentary organic matter coupled to the reduction of O 2 and SO 42- in the aerobic zone, and to the reduction of SO 42- in the anaerobic zone; estimated rates of CO 2 production through reduction of Fe(III) were relatively minor by comparison. The rates of CO 2 production calculated from dissolved inorganic carbon mass transfer (2.55×10 -4 to 48.6×10 -4 mmol l -1 yr-1) generally were comparable to the calculated rates of CO 2 production by the combined reduction of O 2, Fe(III) and SO 42- (1.31×10 -4 to 15×10 -4 mmol l -1 yr-1). The overall increase in SO 42- concentrations along the flow path, together with the results of mass-balance calculations, and variations in δ34S values along the flow path indicate that SO 42- loss through microbial reduction is exceeded by SO 42- gain through diffusion from sediments and through the oxidation of FeS 2. Geochemical and microbial data on cores indicate that Fe(III) oxyhydroxide coatings on sediment grains in local, organic carbon- and SO 42--rich zones have been depleted by microbial reduction and resulted in localized SO 42--reducing zones in which the formation of iron disulfides decreases dissolved iron concentrations. These localized zones of SO 42- reduction, which are important for assessing zones of low dissolved iron for water-supply development, could be overlooked by aquifer studies that rely only on groundwater data from well-water samples for geochemical modeling.

The combined effects of oxygen availability and salinity on physiological responses and scope for growth in the green-lipped mussel Perna viridis.

PubMed

Wang, Youji; Hu, Menghong; Wong, Wai Hing; Shin, Paul K S; Cheung, Siu Gin

2011-01-01

Mussels were maintained for 4 weeks under different combinations of dissolved oxygen concentration (1.5, 3.0 and 6.0 mg O2 l(-1)) and salinity (15, 20, 25 and 30) in a 3×4 factorial design experiment. Clearance rate (CR), absorption efficiency (AE), respiration rate (RR) and scope for growth (SFG) decreased with decreasing salinity and dissolved oxygen concentration (DO), while excretion rate (ER) increased with decreasing salinity and increasing DO. The O:N ratio was <10 at salinities of 15 and 20, irrespective of DO levels. SFG was negative in most of the treatments, except for those under 6.0 mg O2 l(-1) or at a salinity of 30 when DO was lower. The results may help explain the distribution pattern of Perna viridis in Hong Kong waters and provide guidelines for mussel culture site selection. Copyright © 2011 Elsevier Ltd. All rights reserved.

The effect of probe choice and solution conditions on the apparent photoreactivity of dissolved organic matter.

PubMed

Maizel, Andrew C; Remucal, Christina K

2017-08-16

Excited triplet states of dissolved organic matter ( 3 DOM) are quantified directly with the species-specific probes trans,trans-hexadienoic acid (HDA) and 2,4,6-trimethylphenol (TMP), and indirectly with the singlet oxygen ( 1 O 2 ) probe furfuryl alcohol (FFA). Although previous work suggests that these probe compounds may be sensitive to solution conditions, including dissolved organic carbon concentration ([DOC]) and pH, and may quantify different 3 DOM subpopulations, the probes have not been systematically compared. Therefore, we quantify the apparent photoreactivity of diverse environmental waters using HDA, TMP, and FFA. By conducting experiments under ambient [DOC] and pH, with standardized [DOC] and pH, and with solid phase extraction isolates, we demonstrate that much of the apparent dissimilarity in photochemical measurements is attributable to solution conditions, rather than intrinsic differences in 3 DOM production. In general, apparent quantum yields (Φ 1 O 2 ≥ Φ 3 DOM,TMP ≫ Φ 3 DOM,HDA ) and pseudo-steady state concentrations ([ 1 O 2 ] ss > [ 3 DOM] ss,TMP > [ 3 DOM] ss,HDA ) show consistent relationships in all waters under standardized conditions. However, intrinsic differences in 3 DOM photoreactivity are apparent between DOM from diverse sources, as seen in the higher Φ 1 O 2 and lower Φ 3 DOM,TMP of wastewater effluents compared with oligotrophic lakes. Additionally, while conflicting trends in photoreactivity are observed under ambient conditions, all probes observe quantum yields increasing from surface wetlands to terrestrially influenced waters to oligotrophic lakes under standardized conditions. This work elucidates how probe selection and solution conditions influence the apparent photoreactivity of environmental waters and confirms that 3 DOM or 1 O 2 probes cannot be used interchangeably in waters that vary in [DOC], pH, or DOM source.

Inside Story of Gas Processes within Stormwater Biofilters: Does Greenhouse Gas Production Tarnish the Benefits of Nitrogen Removal?

PubMed

Payne, Emily G I; Pham, Tracey; Cook, Perran L M; Deletic, Ana; Hatt, Belinda E; Fletcher, Tim D

2017-04-04

Stormwater biofilters are dynamic environments, supporting diverse processes that act to capture and transform incoming pollutants. However, beneficial water treatment processes can be accompanied by undesirable greenhouse gas production. This study investigated the potential for nitrous oxide (N 2 O) and methane (CH 4 ) generation in dissolved form at the base of laboratory-scale stormwater biofilter columns. The influence of plant presence, species, inflow frequency, and inclusion of a saturated zone and carbon source were studied. Free-draining biofilters remained aerobic with negligible greenhouse gas production during storm events. Designs with a saturated zone were oxygenated at their base by incoming stormwater before anaerobic conditions rapidly re-established, although extended dry periods allowed the reintroduction of oxygen by evapotranspiration. Production of CH 4 and N 2 O in the saturated zone varied significantly in response to plant presence, species, and wetting and drying. Concentrations of N 2 O typically peaked rapidly following stormwater inundation, associated with limited plant root systems and poorer nitrogen removal from biofilter effluent. Production of CH 4 also commenced quickly but continued throughout the anaerobic interevent period and lacked clear relationships with plant characteristics or nitrogen removal performance. Dissolved greenhouse gas concentrations were highly variable, but peak concentrations of N 2 O accounted for <1.5% of the incoming total nitrogen load. While further work is required to measure surface emissions, the potential for substantial release of N 2 O or CH 4 in biofilter effluent appears relatively low.

Singlet oxygen in the coupled photochemical and biochemical oxidation of dissolved organic matter.

PubMed

Cory, Rose M; McNeill, Kristopher; Cotner, James P; Amado, Andre; Purcell, Jeremiah M; Marshall, Alan G

2010-05-15

Dissolved organic matter (DOM) is a significant (>700 Pg) global C pool. Transport of terrestrial DOM to the inland waters and coastal zones represents the largest flux of reduced C from land to water (215 Tg yr(-1)) (Meybeck, M. Am. J. Sci. 1983, 282, 401-450). Oxidation of DOM by interdependent photochemical and biochemical processes largely controls the fate of DOM entering surface waters. Reactive oxygen species (ROS) have been hypothesized to play a significant role in the photooxidation of DOM, because they may oxidize the fraction of DOM that is inaccessible to direct photochemical degradation by sunlight. We followed the effects of photochemically produced singlet oxygen ((1)O(2)) on DOM by mass spectrometry with (18)O-labeled oxygen, to understand how (1)O(2)-mediated transformations of DOM may lead to altered DOM bioavailability. The photochemical oxygen uptake by DOM attributed to (1)O(2) increased with DOM concentration, yet it remained a minority contributor to photochemical oxygen uptake even at very high DOM concentrations. When DOM samples were exposed to (1)O(2)-generating conditions (Rose Bengal and visible light), increases were observed in DOM constituents with higher oxygen content and release of H(2)O(2) was detected. Differential effects of H(2)O(2) and (1)O(2)-treated DOM showed that (1)O(2)-treated DOM led to slower bacterial growth rates relative to unmodified DOM. Results of this study suggested that the net effect of the reactions between singlet oxygen and DOM may be production of partially oxidized substrates with correspondingly lower potential biological energy yield.

Nitrate loading and CH4 and N2O Flux from headwater streams

NASA Astrophysics Data System (ADS)

Sousa, C. H. R. D.; Hilker, T.; Hall, F. G.; Moura, Y. M.; McAdam, E.

2014-12-01

Freshwater ecosystems transport and process significant amounts of terrestrial carbon and can be considerable sources of CO2, CH4, and N2O. A great deal of uncertainty, however, remains in both global estimates and our understanding of drivers of freshwater greenhouse gas emissions. Furthermore, small headwater streams have received insufficient attention to date and may contribute disproportionately to global GHG flux. Our objective was to quantify GHG flux and assess the impact of changes in DOC and NO3 concentrations in surface and subsurface water on flux rates in three streams in the Lamprey River watershed in New Hampshire, USA, that contrast in surface water DOC:NO3. We measured DOC, NO3 and dissolved gas concentrations in surface waters of each stream monthly from May 2011 to April 2012. Empirical measurements of reaeration coefficients were used to convert dissolved gas concentrations to fluxes. We found higher GHG concentrations and fluxes in the two streams with high DOC concentrations, particularly gases produced by anaerobic metabolism (CH4, N2O from methanogenesis and denitrification, respectively). The stream with high DOC and high NO3 showed high N2O and low CH4 flux, while the high DOC, low NO3 stream showed high CH4 and low N2O flux. Our results are consistent with a model in which C inputs drive total GHG production, while NO3 input regulates the relative importance of CH4 and N2O by suppressing methanogenesis and stimulating denitrification. The magnitude of GHG fluxes suggests that streams in this region are likely to be small sources of CO2, but potentially important sources of CH4 and N2O. Since CH4 and N2O are many times more powerful than CO2 at trapping heat in the atmosphere, freshwater emissions of these gases have the potential to offset a significant proportion of the climate benefits of the terrestrial carbon sink, a possibility that has not been sufficiently incorporated into climate models.

Nitrate loading and CH4 and N2O Flux from headwater streams

NASA Astrophysics Data System (ADS)

Schade, J. D.; Bailio, J.; McDowell, W. H.

2015-12-01

Freshwater ecosystems transport and process significant amounts of terrestrial carbon and can be considerable sources of CO2, CH4, and N2O. A great deal of uncertainty, however, remains in both global estimates and our understanding of drivers of freshwater greenhouse gas emissions. Furthermore, small headwater streams have received insufficient attention to date and may contribute disproportionately to global GHG flux. Our objective was to quantify GHG flux and assess the impact of changes in DOC and NO3 concentrations in surface and subsurface water on flux rates in three streams in the Lamprey River watershed in New Hampshire, USA, that contrast in surface water DOC:NO3. We measured DOC, NO3 and dissolved gas concentrations in surface waters of each stream monthly from May 2011 to April 2012. Empirical measurements of reaeration coefficients were used to convert dissolved gas concentrations to fluxes. We found higher GHG concentrations and fluxes in the two streams with high DOC concentrations, particularly gases produced by anaerobic metabolism (CH4, N2O from methanogenesis and denitrification, respectively). The stream with high DOC and high NO3 showed high N2O and low CH4 flux, while the high DOC, low NO3 stream showed high CH4 and low N2O flux. Our results are consistent with a model in which C inputs drive total GHG production, while NO3 input regulates the relative importance of CH4 and N2O by suppressing methanogenesis and stimulating denitrification. The magnitude of GHG fluxes suggests that streams in this region are likely to be small sources of CO2, but potentially important sources of CH4 and N2O. Since CH4 and N2O are many times more powerful than CO2 at trapping heat in the atmosphere, freshwater emissions of these gases have the potential to offset a significant proportion of the climate benefits of the terrestrial carbon sink, a possibility that has not been sufficiently incorporated into climate models.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehta, Vrajesh; Maillot, Fabien; Wang, Zheming

Uranyl phosphate solids are often found with uranium ores, and their low solubility makes them promising target phases for in situ remediation of uranium-contaminated subsurface environments. The products and solubility of uranium(VI) precipitated with phosphate can be affected by the pH, dissolved inorganic carbon (DIC) concentration, and co-solute composition (e.g. Na+/Ca2+) of the groundwater. Batch experiments were performed to study the effect of these parameters on the products and extent of uranium precipitation induced by phosphate addition. In the absence of co-solute cations, chernikovite [H3O(UO2)(PO4)•3H2O] precipitated despite uranyl orthophosphate [(UO2)3(PO4)2•4H2O] being thermodynamically more favorable under certain conditions. As determined usingmore » X-ray diffraction, electron microscopy, and laser induced fluorescence spectroscopy, the presence of Na+ or Ca2+ as a co-solute led to the precipitation of sodium autunite ([Na2(UO2)2(PO4)2] and autunite [Ca(UO2)2(PO4)2]), which are structurally similar to chernikovite. In the presence of sodium, the dissolved U(VI) concentrations were generally in agreement with equilibrium predictions of sodium autunite solubility. However, in the calcium-containing systems, the observed concentrations were below the predicted solubility of autunite, suggesting the possibility of uranium adsorption to or incorporation in a calcium phosphate precipitate in addition to the precipitation of autunite.« less

Experimental constraints on hydrothermal activities in Enceladus

NASA Astrophysics Data System (ADS)

Sekine, Y.; Shibuya, T.; Suzuki, K.; Kuwatani, T.

2012-12-01

One of the most remarkable findings by the Cassini-Huygens mission is perhaps water-rich plumes erupting from the south-pole region of Enceladus [1]. Given such geological activity and the detection of sodium salts in the plume, the interior of Enceladus is highly likely to contain an interior ocean interacting with the rock core [2]. A primary question regarding astrobiology and planetary science is whether Enceladus has (or had) hydrothermal activities in the interior ocean. Because N2 might be formed by thermal dissociation of primordial NH3 [3], the presence of N2 in the plume may be a possible indicator for the presence of hydrothermal activities in Enceladus. However, the Cassini UVIS revealed that the plumes do not contain large amounts of N2 [4]. Although these observations may not support the presence of hydrothermal activities, whether NH3 dissociation proceeds strongly depends on the kinetics of hydrothermal reactions and interactions with the rock components, which remain largely unknown. Furthermore, the Cassini CDA recently showed that small amounts of SiO2 might have been included in the plume dusts [5]. Formation of amorphous SiO2 usually occurs when high-temperature and/or high-pH solution with high concentrations of dissolved SiO2 cools and/or is neutralized. Thus, the presence of SiO2 in the plume dusts may suggest the presence of a temperature and/or pH gradient in the ocean. However, no laboratory experiments have investigated what processes control pH and SiO2 concentrations in hydrothermal fluids possibly existing in Enceladus. Here, we show the results of laboratory experiments simulating hydrothermal systems on Enceladus. As the initial conditions, we used both aqueous solution of high concentrations (0.01-2%) of NH3 and NaHCO3 and powdered olivine as an analog for the rock components. Our experimental results show that formation of N2 from NH3 is kinetically and thermodynamically inhibited even under high temperature conditions (< 400°C). This is because NH3 decomposition proceeds inefficiently due to efficient H2 production via serpentinization. Our experimental results also suggest that SiO2 concentration dissolved in hydrothermal fluids simulating Enceladus' condition would be buffered by the serpentine-brucite system. The presence of NH3 in the hydrothermal conditions keeps pH of the solution high (pH 9-11). We suggest that under such conditions, SiO2 concentrations in the fluids would be 0.1 mmol/L or less for temperature < 350°C. Given the SiO2 solubility of 1-10 mmol/L at 0°C and pH 9-11, direct formation of amorphous SiO2 would not occur in Enceladus' hydrothermal systems. To produce amorphous SiO2, large-scale hydrothermal activities and subsequent concentration of dissolved SiO2 in the ocean (due to freezing and/or evaporation of liquid water) would be required, which is consistent with high concentrations of radiogenic Ar and sodium salts in the plume [2, 6]. [1] Porco et al., Science 311, 1393 (2006). [2] Postberg et al., Nature 459, 1098 (2009). [3] Matson et al., Icarus 187, 569 (2007). [4] Hansen t al., Geophs. Res. Lett. 38, L11202 (2011). [5] Hsu et al., EOS Trans. AGU, (2010). [6] Waite et al., Nature 460, 487 (2009).

Synthesis of ITO Powder by Dry Process and Lifetime Characteristics of the ITO Target Fabricated with its Powder

NASA Astrophysics Data System (ADS)

Takahashi, Seiichiro; Itoh, Hironori; Komatsu, Ryuichi

Lifetime of an indium tin oxide (ITO) target is an important characteristic in the production of liquid crystal displays (LCDs). Increasing the sintering density of the ITO target is assumed to lead to an increased lifetime. So far, it has been clarified that the carbon concentration in In2O3 powder, the raw material of ITO targets, influences remarkably the target lifetime. In this study, with the aim of reducing the concentration of carbon in In2O3 powder, the synthesis of In2O3 powder containing dissolved Sn by a dry process was performed.

Experimental Determination of the H2O-undersaturated Peridotite Solidus

NASA Astrophysics Data System (ADS)

Sarafian, E. K.; Gaetani, G. A.; Hauri, E.; Sarafian, A.

2015-12-01

Knowledge of the H2O-undersaturated lherzolite solidus places important constraints on the process of melt generation beneath oceanic spreading centers. While it is generally accepted that the small concentration of H2O (~50-200 ug/g) dissolved in the oceanic upper mantle has a strong influence on the peridotite solidus, but this effect has not been directly determined through experiments. This is because (1) precisely controlling low concentrations of H2O in high-pressure melting experiments is thought to be difficult, (2) small amounts of melt are difficult to identify, and (3) the size of mineral grains that grow in near-solidus experiments is too small to be analyzed for H2O by either Fourier transform infrared (FTIR) spectroscopy or secondary ion mass spectrometry (SIMS). We have developed an experimental approach for determining the peridotite solidus as a function of H2O content that overcomes these difficulties. Our approach utilizes large (~300 um diameter) spheres of San Carlos olivine to monitor the concentration and behavior of H2O in our experiments.. The spheres are mixed in 5:95 proportions with a synthetic peridotite that has the composition of the depleted MORB mantle of Workman and Hart (2005). Partial melting experiments are conducted in is a piston cylinder device using pre-conditioned Au80Pd20 capsules. During an experiment, the H2O content of the San Carlos olivine spheres diffusively equilibrates with the peridotite matrix. After each experiment, the concentration of H2O dissolved in the olivine spheres is determined by secondary ion mass spectrometry. By analyzing the H2O content of the San Carlos olivine spheres and performing a simple mass balance, we can then calculate the amount of H2O in the capsule. The spheres also provides a means to determine the solidus temperature due to the strong partitioning of H2O into silicate melt compared to olivine, pyroxene, and spinel. When a small amount of melt is present the H2O partitions into the melt and the H2O content of the spheres drops in a predictable fashion. The H2O-undersaturated solidus indicated by our experimental results is in agreement with previous experimental determinations of the nominally anhydrous solidus. This suggests that the potential temperature of the oceanic upper mantle is higher than existing petrologic estimates.

Cyanobacterial and microcystins dynamics following the application of hydrogen peroxide to waste stabilisation ponds

NASA Astrophysics Data System (ADS)

Barrington, D. J.; Ghadouani, A.; Ivey, G. N.

2013-06-01

Cyanobacteria and cyanotoxins are a risk to human and ecological health, and a hindrance to biological wastewater treatment. This study investigated the use of hydrogen peroxide (H2O2) for the removal of cyanobacteria and cyanotoxins from within waste stabilization ponds (WSPs). The daily dynamics of cyanobacteria and microcystins (commonly occurring cyanotoxins) were examined following the addition of H2O2 to wastewater within both the laboratory and at the full scale within a maturation WSP, the final pond in a wastewater treatment plant. Hydrogen peroxide treatment at concentrations ≥ 0.1 mg H2O2 μg-1 total phytoplankton chlorophyll a led to the lysis of cyanobacteria, in turn releasing intracellular microcystins to the dissolved state. In the full-scale trial, dissolved microcystins were then degraded to negligible concentrations by H2O2 and environmental processes within five days. A shift in the phytoplankton assemblage towards beneficial Chlorophyta species was also observed within days of H2O2 addition. However, within weeks, the Chlorophyta population was significantly reduced by the re-establishment of toxic cyanobacterial species. This re-establishment was likely due to the inflow of cyanobacteria from ponds earlier in the treatment train, suggesting that whilst H2O2 may be a suitable short-term management technique, it must be coupled with control over inflows if it is to improve WSP performance in the longer term.

A new method for collection of nitrate from fresh water and the analysis of nitrogen and oxygen isotope ratios

USGS Publications Warehouse

Silva, S.R.; Kendall, C.; Wilkison, D.H.; Ziegler, A.C.; Chang, Cecily C.Y.; Avanzino, R.J.

2000-01-01

A new method for concentrating nitrate from fresh waters for ??15N and ??18O analysis has been developed and field-tested for four years. The benefits of the method are: (1) elimination of the need to transport large volumes of water to the laboratory for processing; (2) elimination of the need for hazardous preservatives; and (3) the ability to concentrate nitrate from fresh waters. Nitrate is collected by, passing the water-sample through pre-filled, disposable, anion exchanging resin columns in the field. The columns are subsequently transported to the laboratory where the nitrate is extracted, converted to AgNO3 and analyzed for its isotope composition. Nitrate is eluted from the anion exchange columns with 15 ml of 3 M HCl. The nitrate-bearing acid eluant is neutralized with Ag2O, filtered to remove the AgCl precipitate, then freeze-dried to obtain solid AgNO3, which is then combusted to N2 in sealed quartz tubes for ?? 15N analysis. For ?? 18O analysis, aliquots of the neutralized eluant are processed further to remove non-nitrate oxygen-bearing anions and dissolved organic matter. Barium chloride is added to precipitate sulfate and phosphate; the solution is then filtered, passed through a cation exchange column to remove excess Ba2+, re-neutralized with Ag2O, filtered, agitated with activated carbon to remove dissolved organic matter and freeze-dried. The resulting AgNO3 is combusted with graphite in a closed tube to produce CO2, which is cryogenically purified and analyzed for its oxygen isotope composition. The 1?? analytical precisions for ??15N and ??18O are ?? 0.05%o and ??0.5???, respectively, for solutions of KNO3 standard processed through the entire column procedure. High concentrations of anions in solution can interfere with nitrate adsorption on the anion exchange resins, which may result in isotope fractionation of nitrogen and oxygen (fractionation experiments were conducted for nitrogen only; however, fractionation for oxygen is expected). Chloride, sulfate, and potassium biphthalate, an organic acid proxy for dissolved organic material, added to KNO3 standard solutions caused no significant nitrogen fractionation for chloride concentrations below about 200 mg/l (5.6 meq/l) for 1000 ml samples, sulfate concentrations up to 2000 mg/1 (41.7 meq/l) in 100 ml samples, and Potassium biphthalate for concentrations up to 200 mg/l carbon in 100 ml samples. Samples archived on the columns for up to two years show minimal nitrogen isotope fractionation.

Sustainable oil and grease removal from synthetic stormwater runoff using bench-scale bioretention studies.

PubMed

Hong, Eunyoung; Seagren, Eric A; Davis, Allen P

2006-02-01

One of the principal components of the contaminant load in urban stormwater runoff is oil and grease (O&G) pollution, resulting from vehicle emissions. A mulch layer was used as a contaminant trap to remove O&G (dissolved and particulate-associated naphthalene, dissolved toluene, and dissolved motor oil hydrocarbons) from a synthetic runoff during a bench-scale infiltration study. Approximately 80 to 95% removal of all contaminants from synthetic runoff was found via sorption and filtration. Subsequently, approximately 90% of the sorbed naphthalene, toluene, oil, and particulate-associated naphthalene was biodegraded within approximately 3, 4, 8, and 2 days after the event, respectively, based on decreases in contaminant concentrations coupled with increases of microbial populations. These results indicate the effectiveness and sustainability of placing a thin layer of mulch on the surface of a bioretention facility for reducing O&G pollution from urban stormwater runoff.

Nitrous oxide emissions and dissolved oxygen profiling in a full-scale nitrifying activated sludge treatment plant.

PubMed

Aboobakar, Amina; Cartmell, Elise; Stephenson, Tom; Jones, Mark; Vale, Peter; Dotro, Gabriela

2013-02-01

This paper reports findings from online, continuous monitoring of dissolved and gaseous nitrous oxide (N₂O), combined with dissolved oxygen (DO) and ammonia loading, in a full-scale nitrifying activated sludge plant. The study was conducted over eight weeks, at a 210,000 population equivalent sewage treatment works in the UK. Results showed diurnal variability in the gaseous and dissolved N₂O emissions, with hourly averages ranging from 0 to 0.00009 kgN₂O-N/h for dissolved and 0.00077-0.0027 kgN₂O-N/h for gaseous nitrous oxide emissions respectively, per ammonia loading, depending on the time of day. Similarly, the spatial variability was high, with the highest emissions recorded immediately after the anoxic zone and in the final pass of the aeration lane, where ammonia concentrations were typically below 0.5 mg/L. Emissions were shown to be negatively correlated to dissolved oxygen, which fluctuated between 0.5 and 2.5 mgO₂/L, at the control set point of 1.5 mgO₂/L. The resulting dynamic DO conditions are known to favour N₂O production, both by autotrophic and heterotrophic processes in mixed cultures. Average mass emissions from the lane were greater in the gaseous (0.036% of the influent total nitrogen) than in the dissolved (0.01% of the influent total nitrogen) phase, and followed the same diurnal and spatial patterns. Nitrous oxide emissions corresponded to over 34,000 carbon dioxide equivalents/year, adding 13% to the carbon footprint associated with the energy requirements of the monitored lane. A clearer understanding of emissions obtained from real-time data can help towards finding the right balance between improving operational efficiency and saving energy, without increasing N₂O emissions. Copyright © 2012 Elsevier Ltd. All rights reserved.

Evaluation of headspace equilibration methods for quantifying greenhouse gases in groundwater.

PubMed

Jahangir, M M R; Johnston, P; Khalil, M I; Grant, J; Somers, C; Richards, K G

2012-11-30

The objective of the study was to evaluate the different headspace equilibration methods for the quantification of dissolved greenhouse gases in groundwater. Groundwater samples were collected from wells with contrasting hydrogeochemical properties and degassed using the headspace equilibration method. One hundred samples from each well were randomly selected, treatments were applied and headspace gases analysed by gas chromatography. Headspace equilibration treatments varied helium (He):water ratio, shaking time and standing time. Mean groundwater N(2)O, CO(2) and CH(4) concentrations were 0.024 mg N L(-1), 13.71 mg C L(-1) and 1.63 μg C L(-1), respectively. All treatments were found to significantly influence dissolved gas concentrations. Considerable differences in the optimal He:water ratio and standing time were observed between the three gases. For N(2)O, CO(2) and CH(4) the optimum operating points for He:water ratio was 4.4:1, 3:1 and 3.4:1; shaking time was 13, 12 and 13 min; and standing time was 63, 17 and 108 min, respectively. The headspace equilibration method needs to be harmonised to ensure comparability between studies. The experiment reveals that He:water ratio 3:1 and shaking time 13 min give better estimation of dissolved gases than any lower or higher ratios and shaking times. The standing time 63, 17 and 108 min should be applied for N(2)O, CO(2) and CH(4), respectively. Copyright © 2012. Published by Elsevier Ltd.

Reconciling "Whiffs" of O2 with the Archean MIF S Record: Insights from Sulfide Oxidation Experiments

NASA Astrophysics Data System (ADS)

Johnson, A.; Reinhard, C. T.; Romaniello, S. J.; Greaney, A. T.; Garcia-Robledo, E.; Revsbech, N. P.; Canfield, D. E.; Lyons, T. W.; Anbar, A. D.

2016-12-01

The Archean-Proterozoic transition is marked by the first appreciable accumulation of O2 in Earth's oceans and atmosphere at 2.4 billion years ago (Ga). However, this Great Oxidation Event (GOE) is not the first evidence for O2 in Earth's surface environment. Paleoredox proxies preserved in ancient marine shales (Mo, Cr, Re, U) suggest transient episodes of oxidative weathering before the GOE, perhaps as early as 3.0 Ga. One marine shale in particular, the 2.5 Ga Mount McRae Shale of Western Australia, contains a euxinic interval with Mo enrichments up to 50 ppm. This enrichment is classically interpreted as the result of oxidative weathering of sulfides on the continental surface. However, prior weathering models based on experiments suggested that sulfides require large amounts of O2 [>10-4 present atmospheric level (PAL) pO2] to produce this weathering signature, in conflict with estimates of Archean pO2 from non-mass-dependent (NMD) sulfur isotope anomalies (<10-5 PAL pO2). To reconcile these datasets, we conducted aqueous oxidation experiments of pyrite and molybdenite from 3 - 700 nM O2 (equivalent at equilibrium to 10-5 - 10-3 PAL) to measure oxidation kinetics as a function of the concentration of dissolved O2. We measured rates by injecting oxygenated water at a steady flow rate and monitoring dissolved O2 concentrations with LUMOS sensors. Our data extend the O2 range explored in pyrite oxidation experiments by three orders of magnitude and provide the first rates for molybdenite oxidation at O2 concentrations potentially analogous to those characteristic of the Archean atmosphere. Our results show that pyrite and molybdenite oxidize significantly more rapidly at lower O2 levels than previously thought. As a result, our revised weathering model demonstrates that the Mo enrichments observed in late Archean marine shales are potentially attainable at extremely low atmospheric pO2 values (e.g., <10-5 PAL), reconciling large sedimentary Mo enrichments with co-occurring NMD sulfur isotope anomalies.

Obtaining accurate amounts of mercury from mercury compounds via electrolytic methods

DOEpatents

Grossman, Mark W.; George, William A.

1987-01-01

A process for obtaining pre-determined, accurate rate amounts of mercury. In one embodiment, predetermined, precise amounts of Hg are separated from HgO and plated onto a cathode wire. The method for doing this involves dissolving a precise amount of HgO which corresponds to a pre-determined amount of Hg desired in an electrolyte solution comprised of glacial acetic acid and H.sub.2 O. The mercuric ions are then electrolytically reduced and plated onto a cathode producing the required pre-determined quantity of Hg. In another embodiment, pre-determined, precise amounts of Hg are obtained from Hg.sub.2 Cl.sub.2. The method for doing this involves dissolving a precise amount of Hg.sub.2 Cl.sub.2 in an electrolyte solution comprised of concentrated HCl and H.sub.2 O. The mercurous ions in solution are then electrolytically reduced and plated onto a cathode wire producing the required, pre-determined quantity of Hg.

Obtaining accurate amounts of mercury from mercury compounds via electrolytic methods

DOEpatents

Grossman, M.W.; George, W.A.

1987-07-07

A process is described for obtaining pre-determined, accurate rate amounts of mercury. In one embodiment, predetermined, precise amounts of Hg are separated from HgO and plated onto a cathode wire. The method for doing this involves dissolving a precise amount of HgO which corresponds to a pre-determined amount of Hg desired in an electrolyte solution comprised of glacial acetic acid and H[sub 2]O. The mercuric ions are then electrolytically reduced and plated onto a cathode producing the required pre-determined quantity of Hg. In another embodiment, pre-determined, precise amounts of Hg are obtained from Hg[sub 2]Cl[sub 2]. The method for doing this involves dissolving a precise amount of Hg[sub 2]Cl[sub 2] in an electrolyte solution comprised of concentrated HCl and H[sub 2]O. The mercurous ions in solution are then electrolytically reduced and plated onto a cathode wire producing the required, pre-determined quantity of Hg. 1 fig.

Availability of O(2) and H(2)O(2) on pre-photosynthetic Earth.

PubMed

Haqq-Misra, Jacob; Kasting, James F; Lee, Sukyoung

2011-05-01

Old arguments that free O(2) must have been available at Earth's surface prior to the origin of photosynthesis have been revived by a new study that shows that aerobic respiration can occur at dissolved oxygen concentrations much lower than had previously been thought, perhaps as low as 0.05 nM, which corresponds to a partial pressure for O(2) of about 4 × 10(-8) bar. We used numerical models to study whether such O(2) concentrations might have been provided by atmospheric photochemistry. Results show that disproportionation of H(2)O(2) near the surface might have yielded enough O(2) to satisfy this constraint. Alternatively, poleward transport of O(2) from the equatorial stratosphere into the polar night region, followed by downward transport in the polar vortex, may have brought O(2) directly to the surface. Thus, our calculations indicate that this "early respiration" hypothesis might be physically reasonable.

Seasonal and Latitudinal Variations in Dissolved Methane from 42 Lakes along a North-South Transect in Alaska

NASA Astrophysics Data System (ADS)

Sepulveda-Jauregui, A.; Walter Anthony, K. M.; Martinez-Cruz, K. C.; Anthony, P.; Thalasso, F.

2013-12-01

Armando Sepulveda-Jauregui,* Katey M. Walter Anthony,* Karla Martinez-Cruz,* ** Peter Anthony,* and Frederic Thalasso**. * Water and Environmental Research Center, Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, Alaska. ** Biotechnology and Bioengineering Department, Cinvestav, Mexico city, D. F., Mexico. Northern lakes are important reservoirs and sources to the atmosphere of methane (CH4), a potent greenhouse gas. It is estimated that northern lakes (> 55 °N) contribute about 20% of the total global lake methane emissions, and that emissions from these lakes will increase with climate warming. Temperature rise enhances methane production directly by providing the kinetic energy to methanogenesis, and indirectly by supplying organic matter from thawing permafrost. Warmer lakes also store less methane since methane's solubility is inversely related to temperature. Alaskan lakes are located in three well-differentiated permafrost classes: yedoma permafrost with high labile carbon stocks, non-yedoma permafrost with lower carbon stocks, and areas without permafrost, also with generally lower carbon stocks. We sampled dissolved methane from 42 Alaskan lakes located in these permafrost cover classes along a north-south Alaska transect from Prudhoe Bay to the Kenai Peninsula during open-water conditions in summer 2011. We sampled 26 of these lakes in April, toward the end of the winter ice-covered period. Our results indicated that the largest dissolved methane concentrations occurred in interior Alaska thermokarst lakes formed in yedoma-type permafrost during winter and summer, with maximal concentrations of 17.19 and 12.76 mg L-1 respectively. In these lakes, emission of dissolved gases as diffusion during summer and storage release in spring were 18.4% and 17.4% of the annual emission budget, while ebullition (64.2 %) comprised the rest. Dissolved oxygen was inversely correlated with dissolved methane concentrations in both seasons; the absence of O2 enhances methane production, while high concentration of O2 could favor methane oxidation. These relationships suggest that permafrost type, and specifically the availability of permafrost organic matter, influences methane cycling in Alaskan lakes.

Photochemical Production of Singlet Oxygen from Dissolved Organic Matter in Ice.

PubMed

Fede, Alexis; Grannas, Amanda M

2015-11-03

Dissolved natural organic matter (DOM) is a ubiquitous component of natural waters and an important photosensitizer. A variety of reactive oxygen species (ROS) are known to be produced from DOM photochemistry, including singlet oxygen, 1O2. Recently, it has been determined that humic-like substances and unknown organic chromophores are significant contributors to sunlight absorption in snowpack; however, DOM photochemistry in snow/ice has received little attention in the literature. We recently showed that DOM plays an important role in indirect photolysis processes in ice, producing ROS and leading to the efficient photodegradation of a probe hydrophobic organic pollutant, aldrin.1 ROS scavenger experiments indicated that 1O2 played a significant role in the indirect photodegradation of aldrin. Here we quantitatively examine 1O2 photochemically produced from DOM in frozen and liquid aqueous solutions. Steady-state 1O2 production is enhanced up to nearly 1000 times in frozen DOM samples compared to liquid samples. 1O2 production is dependent on the concentration of DOM, but the nature of the DOM source (terrestrial vs microbial) does not have a significant effect on 1O2 production in liquid or frozen samples, with different source types producing similar steady-state concentrations of 1O2. The temperature of frozen samples also has a significant effect on steady-state 1O2 production in the range of 228-262 K, with colder samples producing more steady-state 1O2. The large enhancement in 1O2 in frozen samples suggests that it may play a significant role in the photochemical processes that occur in snow and ice, and DOM could be a significant, but to date poorly understood, oxidant source in snow and ice.

A record of deep-ocean dissolved O2 from the oxidation state of iron in submarine basalts.

PubMed

Stolper, Daniel A; Keller, C Brenhin

2018-01-18

The oxygenation of the deep ocean in the geological past has been associated with a rise in the partial pressure of atmospheric molecular oxygen (O 2 ) to near-present levels and the emergence of modern marine biogeochemical cycles. It has also been linked to the origination and diversification of early animals. It is generally thought that the deep ocean was largely anoxic from about 2,500 to 800 million years ago, with estimates of the occurrence of deep-ocean oxygenation and the linked increase in the partial pressure of atmospheric oxygen to levels sufficient for this oxygenation ranging from about 800 to 400 million years ago. Deep-ocean dissolved oxygen concentrations over this interval are typically estimated using geochemical signatures preserved in ancient continental shelf or slope sediments, which only indirectly reflect the geochemical state of the deep ocean. Here we present a record that more directly reflects deep-ocean oxygen concentrations, based on the ratio of Fe 3+ to total Fe in hydrothermally altered basalts formed in ocean basins. Our data allow for quantitative estimates of deep-ocean dissolved oxygen concentrations from 3.5 billion years ago to 14 million years ago and suggest that deep-ocean oxygenation occurred in the Phanerozoic (541 million years ago to the present) and potentially not until the late Palaeozoic (less than 420 million years ago).

A record of deep-ocean dissolved O2 from the oxidation state of iron in submarine basalts

NASA Astrophysics Data System (ADS)

Stolper, Daniel A.; Keller, C. Brenhin

2018-01-01

The oxygenation of the deep ocean in the geological past has been associated with a rise in the partial pressure of atmospheric molecular oxygen (O2) to near-present levels and the emergence of modern marine biogeochemical cycles. It has also been linked to the origination and diversification of early animals. It is generally thought that the deep ocean was largely anoxic from about 2,500 to 800 million years ago, with estimates of the occurrence of deep-ocean oxygenation and the linked increase in the partial pressure of atmospheric oxygen to levels sufficient for this oxygenation ranging from about 800 to 400 million years ago. Deep-ocean dissolved oxygen concentrations over this interval are typically estimated using geochemical signatures preserved in ancient continental shelf or slope sediments, which only indirectly reflect the geochemical state of the deep ocean. Here we present a record that more directly reflects deep-ocean oxygen concentrations, based on the ratio of Fe3+ to total Fe in hydrothermally altered basalts formed in ocean basins. Our data allow for quantitative estimates of deep-ocean dissolved oxygen concentrations from 3.5 billion years ago to 14 million years ago and suggest that deep-ocean oxygenation occurred in the Phanerozoic (541 million years ago to the present) and potentially not until the late Palaeozoic (less than 420 million years ago).

Assessing the Influence of Copper-Nickel-Bearing Bedrock on Baseline Water Quality in Filson Creek Watershed, Northeast Minnesota

NASA Astrophysics Data System (ADS)

Runkel, R. L.; Jones, P. M.; Elliott, S. M.; Woodruff, L. G.

2017-12-01

Mining sulfide-bearing copper (Cu), nickel (Ni), and platinum-group-elements (PGE) deposits in the Duluth Complex of northeast Minnesota could have detrimental effects on surrounding water resources and associated ecosystems. A study was conducted to 1) assess copper, nickel, and other metal concentrations in surface water, bedrock, streambed sediments, and soils in watersheds where the basal part of the Duluth Complex is exposed or near the land surface; and 2) determine if these concentrations, and metal-bearing deposits, are currently influencing regional water quality in areas of potential base-metal mining. One of the watersheds that was assessed was the Filson Creek watershed, where shallow Cu-Ni-PGE deposits are present. Field water-quality, streambed sediments, soils, bedrock, and streamflow data set were collected in Filson Creek and it's watershed in 2014 and 2015. Surface-water samples were analyzed for 12 trace metals (dissolved and total concentrations), 14 inorganic constituents (dissolved concentrations), alkalinity, 18 O /16O and 2H/1H isotopes, and total and dissolved organic carbon. Background total Cu and Ni concentrations in the creek in 2014 and 2015 ranged from 1.2 to 10.8 micrograms per liter (µg/L), and 1.7 to 8.4 µg/L, respectively. The concentrations of copper, nickel, and other trace metals in surface waters and streambed sediments reflects the geochemistry of underlying rock types and glacially transported unconsolidated material, establishing baseline conditions prior to any mining. Dissolved and total organic carbon (DOC and TOC) concentrations in surface waters are very high compared to most surface waters in Minnesota, ranging from 21.3 to 43.2 milligrams per liter (mg/L), and 22.4 and 53.5 mg/L. Synoptic water-quality and flow data from a tracer test conducted over a stream segment of Filson Creek above a shallow Cu-Ni-PGE deposit (Spruce Road Deposit) was used with the 2014-15 water-quality and synthetic flow data to calibrate the reactive transport model. Results from transport modeling suggest that the high DOC content exert control on copper and other trace metal transport.

Composition of steam in the system NaCl-KCl-H2O-quartz at 600°C

USGS Publications Warehouse

Fournier, Robert O.; Thompson, J. Michael

1993-01-01

In the system NaCl-KCl-H2O, with and without ??-quartz present, steam was equilibrated in a large-volume reaction vessel with brine and/or precipitated salt at 600??C and pressures ranging from about 100 to 0.4 MPa. Episodically, steam was extracted for chemical analysis, accompanied by a decrease in pressure within the reaction vessel. In the absence of precipitated salt, within the analytical uncertainty stoichiometric quantities of Cl and total alkali, metals (Na + K) dissolve in steam coexisting with chloriderich brine. In contrast, in the presence of precipitated salt (in our experiments halite with some KCl in solid solution), significant excess chloride as associated hydrogen chloride (HCl0??) dissolves in steam. The HCl0 is generated by the reaction of steam with solid NaCl(s), producing solid NaOH(s) that diffuses into halite, forming a solid solution. In our quasistatic experiments, compared to dynamic flow-through experiments of others, higher initial ratios of H2O/NaCl have apparently resulted in higher model fractions of NaOH(s) in solid solution in halite. This, in turn, resulted in incrementally higher concentrations of associated NaOHo dissolved in steam. Addition of quartz to the system NaCl + KC1 + H2O resulted in an order of magnitude increase in the concentration of HCl0 dissolved in steam, apparently as a consequence of the formation of sodium disilicate by reaction of silica with NaOH(s). The measured dissolved silica in steam saturated with alkali halides at 600??C in the pressure range 7-70 MPa agrees nicely with calculated values of the solubility of ??-quartz obtained using the equation of Fournier and Potter (1982), corrected for dissolved salt by the method of fournier (1983). Na K ratios in steam at 600??C tend to be slightly greater than in coexisting brine. When precipitated halite is present, larger mole fractions of NaOH(s) in solid solution in that halite apparently result in even larger Na K ratios in coexisting steam. Precipitation of more halite as a consequence of repeated depressurization episodes results in decreased Na K ratios in both the brine and coexisting steam phases, indicating that the lower pressures begin to favor K over Na in the vapor. When steam is in contact with precipitated salts in the absence of brine, the Na K ratio in the steam is less than that of the bulk composition of the salt-H2O system. ?? 1993.

Photocatalytic degradation of E. coliform in water.

PubMed

Sun, Darren Delai; Tay, Joo Hwa; Tan, Koh Min

2003-08-01

This study aims to further investigate the total mineralization of the bacteria to the extent of death and cell-mass inactivation using a TiO2-Fe2O3 membrane photocatalytic oxidation reactor. Experimental results clearly indicated that dissolved oxygen (DO), hydraulic retention time (HRT) and concentration of the model bacteria (Escherichia coliform) affected the removal efficiency. It was found that the ultimate removal efficiency was 99% at DO level of 21.34 mg/l, HRT at 60s and high concentration of E. coli at 10(9)CFU/ml. The morphologic studies also showed that E. coliform could be further mineralized into CO2 and H2O. Dissolved organic carbon, pH and gas chromatograph analysis had justified most importantly the evolution of CO2. Experimental results revealed that the photomineralization rate of E. coliform followed pseudo-first-order kinetics by the role of DO. The derived empirical models were found consistent with the proposed reaction pathways of a combined UV breakdown on mass cell and a dual-site Langmuir-Hinshelwood mechanism where the rate-controlling step is the surface interaction between the adsorbed cleavage bacterial cells and hydroxyl radicals.

Effect of nitrate concentration on filamentous bulking under low level of dissolved oxygen in an airlift inner circular anoxic-aerobic incorporate reactor.

PubMed

Su, Yiming; Zhang, Yalei; Zhou, Xuefei; Jiang, Ming

2013-09-01

This laboratory research investigated a possible cause of filamentous bulking under low level of dissolved oxygen conditions (dissolved oxygen value in aerobic zone maintained between 0.6-0.8 mg O2/L) in an airlift inner-circular anoxic-aerobic reactor. During the operating period, it was observed that low nitrate concentrations affected sludge volume index significantly. Unlike the existing hypothesis, the batch tests indicated that filamentous bacteria (mainly Thiothrix sp.) could store nitrate temporarily under carbon restricted conditions. When nitrate concentration was below 4 mg/L, low levels of carbon substrates and dissolved oxygen in the aerobic zone stimulated the nitrate-storing capacity of filaments. When filamentous bacteria riched in nitrate reached the anoxic zone, where they were exposed to high levels of carbon but limited nitrate, they underwent denitrification. However, when nonfilamentous bacteria were exposed to similar conditions, denitrification was restrained due to their intrinsic nitrate limitation. Hence, in order to avoid filamentous bulking, the nitrate concentration in the return sludge (from aerobic zone to the anoxic zone) should be above 4 mg/L, or alternatively, the nitrate load in the anoxic zone should be kept at levels above 2.7 mg NO(3-)-N/g SS.

Geochemical processes controlling selenium in ground water after mining, Powder River Basin, Wyoming, U.S.A.

USGS Publications Warehouse

Naftz, D.L.; Rice, J.A.

1989-01-01

Geochemical data for samples of overburden from three mines in the Powder River Basin indicate a statistically significant (0.01 confidence level) positive correlation (r = 0.74) between Se and organic C. Results of factor analysis with varimax rotation on the major and trace element data from the rock samples indicate large (>50) varimax loadings for Se in two of the three factors. In Factor 1, the association of Se with constituents common to detrital grains indicates that water transporting the detrital particles into the Powder River Basin also carried dissolved Se. The large (>50) varimax loadings of Se and organic C in Factor 2 probably are due to the organic affinities characteristic of Se. Dissolved Se concentrations in water samples collected at one coal mine are directly related to the dissolved organic C concentrations. Hydrophilic acid concentrations in the water samples from the mine ranged from 35 to 43% of the total dissolved organic C, and hydrophobic acid concentrations ranged from 40 to 49% of the total dissolved organic C. The largest dissolved organic C concentrations in water from the same mine (34-302 mg/l), coupled with the large proportion of acidic components, may saturate adsorption sites on geothite and similar minerals that comprise the aquifer material, thus decreasing the extent of selenite (SeO32-) adsorption as a sink for Se as the redox state of ground water decreases. ?? 1989.

Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water

NASA Astrophysics Data System (ADS)

Zhang, Y.; Xie, H.

2015-08-01

Rates and apparent quantum yields of photomineralization (AQYDOC) and photomethanification (AQYCH4) of chromophoric dissolved organic matter (CDOM) in Saguenay River surface water were determined at three widely differing dissolved oxygen concentrations ([O2]) (suboxic, air-saturation, and oxygenated) using simulated-solar radiation. Photomineralization increased linearly with CDOM absorbance photobleaching for all three O2 treatments. Whereas the rate of photochemical dissolved organic carbon (DOC) loss increased with increasing [O2], the ratio of fractional DOC loss to fractional absorbance loss showed an inverse trend. CDOM photodegradation led to a nearly complete mineralization under suboxic conditions but to only a partial mineralization under oxic conditions. AQYDOC determined under oxygenated, suboxic, and air-saturated conditions increased, decreased, and remained largely constant with photobleaching, respectively; AQYDOC obtained under air-saturation with short-term irradiations could thus be applied to longer exposures. AQYDOC decreased successively from ultraviolet B (UVB) to ultraviolet A (UVA) to visible (VIS), which, alongside the solar irradiance spectrum, points to VIS and UVA being the primary drivers for photomineralization in the water column. The photomineralization rate in the Saguenay River was estimated to be 2.31 × 108 mol C yr-1, accounting for only 1 % of the annual DOC input into this system. Photoproduction of CH4 occurred under both suboxic and oxic conditions and increased with decreasing [O2], with the rate under suboxic conditions ~ 7-8 times that under oxic conditions. Photoproduction of CH4 under oxic conditions increased linearly with photomineralization and photobleaching. Under air-saturation, 0.00057 % of the photochemical DOC loss was diverted to CH4, giving a photochemical CH4 production rate of 4.36 × 10-6 mol m-2 yr-1 in the Saguenay River and, by extrapolation, of (1.9-8.1) × 108 mol yr-1 in the global ocean. AQYCH4 changed little with photobleaching under air-saturation but increased exponentially under suboxic conditions. Spectrally, AQYCH4 decreased sequentially from UVB to UVA to VIS, with UVB being more efficient under suboxic conditions than under oxic conditions. On a depth-integrated basis, VIS prevailed over UVB in controlling CH4 photoproduction under air-saturation while the opposite held true under O2-deficiency. An addition of micromolar levels of dissolved dimethyl sulfide (DMS) substantially increased CH4 photoproduction, particularly under O2-deficiency; DMS at nanomolar ambient concentrations in surface oceans is, however, unlikely a significant CH4 precursor. Results from this study suggest that CDOM-based CH4 photoproduction only marginally contributes to the CH4 supersaturation in modern surface oceans and to both the modern and Archean atmospheric CH4 budgets, but that the photochemical term can be comparable to microbial CH4 oxidation in modern oxic oceans. Our results also suggest that anoxic microniches in particulate organic matter and phytoplankton cells containing elevated concentrations of precursors of the methyl radical such as DMS may provide potential hotspots for CH4 photoproduction.

Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water

NASA Astrophysics Data System (ADS)

Zhang, Y.; Xie, H.

2015-11-01

Rates and apparent quantum yields of photomineralization (AQYDOC) and photomethanification (AQYCH4) of chromophoric dissolved organic matter (CDOM) in Saguenay River surface water were determined at three widely differing dissolved oxygen concentrations ([O2]) (suboxic, air saturation, and oxygenated) using simulated-solar radiation. Photomineralization increased linearly with CDOM absorbance photobleaching for all three O2 treatments. Whereas the rate of photochemical dissolved organic carbon (DOC) loss increased with increasing [O2], the ratio of fractional DOC loss to fractional absorbance loss showed an inverse trend. CDOM photodegradation led to a higher degree of mineralization under suboxic conditions than under oxic conditions. AQYDOC determined under oxygenated, suboxic, and air-saturated conditions increased, decreased, and remained largely constant with photobleaching, respectively; AQYDOC obtained under air saturation with short-term irradiations could thus be applied to longer exposures. AQYDOC decreased successively from ultraviolet B (UVB) to ultraviolet A (UVA) to visible (VIS), which, alongside the solar irradiance spectrum, points to VIS and UVA being the primary drivers for photomineralization in the water column. The photomineralization rate in the Saguenay River was estimated to be 2.31 × 108 mol C yr-1, accounting for only 1 % of the annual DOC input into this system. Photoproduction of CH4 occurred under both suboxic and oxic conditions and increased with decreasing [O2], with the rate under suboxic conditions ~ 7-8 times that under oxic conditions. Photoproduction of CH4 under oxic conditions increased linearly with photomineralization and photobleaching. Under air saturation, 0.00057 % of the photochemical DOC loss was diverted to CH4, giving a photochemical CH4 production rate of 4.36 × 10-6 mol m-2 yr-1 in the Saguenay River and, by extrapolation, of (1.9-8.1) × 108 mol yr-1 in the global ocean. AQYCH4 changed little with photobleaching under air saturation but increased exponentially under suboxic conditions. Spectrally, AQYCH4 decreased sequentially from UVB to UVA to VIS, with UVB being more efficient under suboxic conditions than under oxic conditions. On a depth-integrated basis, VIS prevailed over UVB in controlling CH4 photoproduction under air saturation while the opposite held true under O2-deficiency. An addition of micromolar levels of dissolved dimethyl sulfide (DMS) substantially increased CH4 photoproduction, particularly under O2-deficiency; DMS at nanomolar ambient concentrations in surface oceans is, however, unlikely a significant CH4 precursor. Results from this study suggest that CDOM-based CH4 photoproduction only marginally contributes to the CH4 supersaturation in modern surface oceans and to both the modern and Archean atmospheric CH4 budgets, but that the photochemical term can be comparable to microbial CH4 oxidation in modern oxic oceans. Our results also suggest that anoxic microniches in particulate organic matter and phytoplankton cells containing elevated concentrations of precursors of the methyl radical such as DMS may provide potential hotspots for CH4 photoproduction.

Estimating gas exchange of CO2 and CH4 between headwater systems and the atmosphere in Southwest Sweden

NASA Astrophysics Data System (ADS)

Somlai, Celia; Natchimuthu, Sivakiruthika; Bastviken, David; Lorke, Andreas

2015-04-01

Quantifying the role of inland water systems in terms of carbon sinks and sources and their connection to the terrestrial ecosystems and landscapes is fundamental for improving the balance approach of regional and global carbon budgets. Recent research showed that freshwater bodies emit significant amounts of CO2 and CH4 into the atmosphere. The extent of the emissions from small streams and headwaters, however, remains uncertain due to a limited availability of data. Studies have shown that headwater systems receive most of the terrestrial organic carbon, have the highest dissolved CO2 concentration and the highest gas exchange velocities and cover the largest fractional surface area within fluvial networks. The gas exchange between inland waters and the atmosphere is controlled by two factors: the difference between the dissolved gas concentration and its atmospheric equilibrium concentration, and the gas exchange velocity. The direct measurement of the dissolved gas concentration of greenhouse gases can be measured straightforwardly, for example, by gas chromatography from headspace extraction of water sample. In contrast, direct measurement of gas exchange velocity is more complex and time consuming, as simultaneous measurements with a volatile and nonvolatile inert tracer gas are needed. Here we analyze measurements of gas exchange velocities, concentrations and fluxes of dissolved CO2 and CH4, as well as loads of total organic and inorganic carbon in 10 reaches in headwater streams in Southwest Sweden. We compare the gas exchange velocities measured directly through tracer injections with those estimated through various empirical approaches, which are based on modelled and measured current velocity, stream depth and slope. Furthermore, we estimate the resulting uncertainties of the flux estimates. We also present different time series of dissolved CO2, CH4 and O2 concentration, water temperature, barometric pressure, electro conductivity, and pH values measured during the period of tracer injection.

Dissolved Greenhouse Gas Concentration Patterns and Relationships with Stream Chemistry in Tropical Headwater Streams

NASA Astrophysics Data System (ADS)

López-Lloreda, C.; McDowell, W. H.; Potter, J.

2017-12-01

Recent studies have shown that freshwater ecosystems, mainly lakes and large rivers, can be an important source of greenhouse gas (GHG) emissions. Headwater streams have received less attention but have been identified as being a potentially important contributor to these emissions. The complex biogeochemical interactions between dissolved GHG, stream chemistry and other physicochemical parameters in streams are not well understood, particularly in small, tropical headwater streams. Surface water samples were taken at weekly intervals at 8 sites in the Luquillo Experimental Forest in Puerto Rico. Samples were analyzed for carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) as well as dissolved organic carbon (DOC), nitrate (NO3) and other major cations and anions. Additionally, physicochemical parameters and discharge (at a subset of sites) were recorded for each sample. Initial analyses of stream greenhouse gas concentrations showed very little seasonality across all sites as well as no change in concentrations during a drought in 2015. One of our hypothesized drivers, discharge, did not show any significant relationship with any of the greenhouse gases at our two gaged sites. Relationships between GHG and stream chemistry, mainly DOC and NO3, varied across sites. A significant negative relationship was found between NO3 and N2O when data were pooled across all sites, but no significant relationship was found at any individual site. CH4 was positively correlated with NO3, but only at one of our sites. N2O showed a significant positive relationship with DOC at two of our sites but interestingly, CO2 and CH4 did not show any significant relationship with DOC. Our initial results suggest that NO3 can be an important driver for N2O and CH4 concentrations, while DOC can be an important driver for N2O. Our results differ from those found in lowland tropical rivers, suggesting that river order and floodplain connections may be important drivers of GHG biogeochemistry. We have also observed a decoupling between DOC and CO2, similar to that which has been observed in previous long-term research in other biomes. The role of tropical montane streams in GHG evasion thus needs to be assessed directly, and cannot be inferred from work on larger tropical rivers.

Single particle ICP-MS method development for the determination of plant uptake and accumulation of CeO2 nanoparticles.

PubMed

Dan, Yongbo; Ma, Xingmao; Zhang, Weilan; Liu, Kun; Stephan, Chady; Shi, Honglan

2016-07-01

Cerium dioxide nanoparticles (CeO2NPs) are among the most broadly used engineered nanoparticles that will be increasingly released into the environment. Thus, understanding their uptake, transportation, and transformation in plants, especially food crops, is critical because it represents a potential pathway for human consumption. One of the primary challenges for the endeavor is the inadequacy of current analytical methodologies to characterize and quantify the nanomaterial in complex biological samples at environmentally relevant concentrations. Herein, a method was developed using single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) technology to simultaneously detect the size and size distribution of particulate Ce, particle concentration, and dissolved cerium in the shoots of four plant species including cucumber, tomato, soybean, and pumpkin. An enzymatic digestion method with Macerozyme R-10 enzyme previously used for gold nanoparticle extraction from the tomato plant was adapted successfully for CeO2NP extraction from all four plant species. This study is the first to report and demonstrate the presence of dissolved cerium in plant seedling shoots exposed to CeO2NPs hydroponically. The extent of plant uptake and accumulation appears to be dependent on the plant species, requiring further systematic investigation of the mechanisms.

Measures of net oxidant concentration in seawater

NASA Astrophysics Data System (ADS)

Jackson, George A.; Williams, Peter M.

1988-02-01

Dissolved oxygen deficits in the ocean have been used as a measure of the organic matter oxidized in a volume of water. Such organic matter is usually assumed to be predominantly settled particles. Using dissolved oxygen concentration in this way has two problems: first, it does not differentiate between oxidant consumed by the pool of dissolved organic matter present near the ocean surface and oxidant consumed by organic matter contained by falling particles; second, it does not account for other oxidant sources, such as nitrate, which can be as important to organic matter decay as oxygen in low-oxygen water, such as off Peru or in the Southern California submarine basins. New parameters provide better measures of the net oxidant concentration in a water parcel. One such, NetOx, is changed only by gaseous exchange with the atmosphere, exchange with the benthos, or the production or consumption of sinking particles. A simplified version of NetOx, NetOx = [O2] + 1.25[NO3-] - [TOC], where TOC (total organic carbon), the dissolved organic carbon (DOC) plus the suspended particulate organic carbon (POC), provides an index based on the usually dominant variables. Calculation of NetOx and a second property, NetOC ([O2] - [TOC]), for data from GEOSECS and ourselves in the Atlantic and Pacific oceans using property-property graphs show differences from those from oxygen deficits alone. Comparison of NetOx and NetOC concentrations at high and low latitudes of the Pacific Ocean shows the difference in surface water oxidant concentrations is even larger than the difference in oxygen concentration. Vertical particle fluxes off Peru calculated from NetOx gradients are much greater than those calculated from oxygen gradients. The potential value of NetOx and NetOC as parameters to understand particle fluxes implies that determination of TOC should be a routine part of hydrographic measurements.

Nonlinear partitioning of OH between Ca-rich plagioclase and arc basaltic melt

NASA Astrophysics Data System (ADS)

Hamada, M.; Ushioda, M.; Takahashi, E.

2011-12-01

The hydrogen in nominally anhydrous minerals (NAMs) is becoming a new proxy for dissolved H2O in silicate melts. Plagioclase is one of the NAMs which accommodates hydrogen as OH. Here, we report experimental results on the partitioning of OH between Ca-rich plagioclase and arc basaltic melt. We carried out hydrous melting experiments of arc basaltic magma at 350 MPa using an internally-heated pressure vessel. Starting material was hydrous glass (0.8 wt.%≦H2O≦4.5 wt.%) of an undifferentiated rock from Miyakejima volcano, a frontal-arc volcano in Izu-arc (MTL rock: 50.5% SiO2, 18.1% Al2O3, 4.9% MgO). A grain of Ca-rich plagioclase (≈ 1 mg, about An95, FeOt ≈ 0.5 wt.%) and ≈ 10 mg of powdered glasses were sealed in Au80Pd20 alloy capsule and kept at around the liquidus temperature. Liquidus phase of MTL rock at 350 MPa is always plagioclase with 0 to 4.5 wt.% H2O in melt, and therefore, a grain of plagioclase and hydrous melt are nearly in equilibrium. Oxygen fugacity during the melting experiments was not controlled; the estimated oxygen fugacity was 3 log unit above Ni-NiO buffer. Experiments were quenched after 24-48 hours. Concentrations of H2O in melt and concentration of OH in plagioclase were analyzed by infrared spectroscopy. Obtained correlation between H2O concentration in melt and OH concentration in plagioclase is nonlinear; partition coefficient in molar basis is ≈ 0.01 with low H2O in melt (≤ 1 wt.%), while it decreases down to ≈ 0.005 with increasing H2O in melt (Fig.1). The OH concentration of Ca-rich plagioclase (about An90) from the 1986 summit eruption of Izu-Oshima volcano, also a frontal-arc volcano in Izu arc, shows variation ranging from <50 ppm H2O through 300 ppm H2O as a result of polybaric degassing (Hamada et al. 2011, EPSL 308, 259-266). Melting experiments of hydrous basalts constrained that An90 plagioclase crystallizes form H2O-rich melt (up to 6 wt.% H2O). In consistent with previous studies, our experiments demonstrate that plagioclase with 300 ppm of OH can be in equilibrium with H2O-rich melt dissolving 5-6 wt.% H2O (Fig.1). Plagioclase from the 1986 summit eruption of Izu-Oshima volcano records polybaric degassing history of magma from 5-6 wt.% H2O in melt (300 ppm of OH in plagioclase) to almost dry melt (50 ppm of OH in plagioclase).

Method 366.0 Determination of Dissolved Silicate in Estuarine and Coastal Watersby Gas Segmented Continuous Flow Colorimetric Analysis

EPA Science Inventory

This method provides a procedure for the determination of dissolved silicate concentration in estuarine and coastal waters. The dissolved silicate is mainly in the form of silicic acid, H SiO , in estuarine and 4 4 coastal waters. All soluble silicate, including colloidal silici...

A 17-year record of environmental tracers in spring discharge, Shenandoah National Park, Virginia, USA: use of climatic data and environmental conditions to interpret discharge, dissolved solutes, and tracer concentrations

USGS Publications Warehouse

Busenberg, Eurybiades; Plummer, Niel

2014-01-01

A 17-year record (1995–2012) of a suite of environmental tracer concentrations in discharge from 34 springs located along the crest of the Blue Ridge Mountains in Shenandoah National Park (SNP), Virginia, USA, reveals patterns and trends that can be related to climatic and environmental conditions. These data include a 12-year time series of monthly sampling at five springs, with measurements of temperature, specific conductance, pH, and discharge recorded at 30-min intervals. The monthly measurements include age tracers (CFC-11, CFC-12, CFC-113, CFC-13, SF6, and SF5CF3), dissolved gases (N2, O2, Ar, CO2, and CH4), stable isotopes of water, and major and trace inorganic constituents. The chlorofluorocarbon (CFC) and sulfur hexafluoride (SF6) concentrations (in pptv) in spring discharge closely follow the concurrent monthly measurements of their atmospheric mixing ratios measured at the Air Monitoring Station at Big Meadows, SNP, indicating waters 0–3 years in age. A 2-year (2001–2003) record of unsaturated zone air displayed seasonal deviations from North American Air of ±10 % for CFC-11 and CFC-113, with excess CFC-11 and CFC-113 in peak summer and depletion in peak winter. The pattern in unsaturated zone soil CFCs is a function of gas solubility in soil water and seasonal unsaturated zone temperatures. Using the increase in the SF6 atmospheric mixing ratio, the apparent (piston flow) SF6 age of the water varied seasonally between about 0 (modern) in January and up to 3 years in July–August. The SF6 concentration and concentrations of dissolved solutes (SiO2, Ca2+, Mg2+, Na+, Cl−, and HCO3−) in spring discharge demonstrate a fraction of recent recharge following large precipitation events. The output of solutes in the discharge of springs minus the input from atmospheric deposition per hectare of watershed area (mol ha−1 a−1) were approximately twofold greater in watersheds draining the regolith of Catoctin metabasalts than that of granitic gneisses and granitoid crystalline rocks. The stable isotopic composition of water in spring discharge broadly correlates with the Oceanic Niño Index. Below normal precipitation and enriched stable isotopic composition were observed during El Niño years.

Lattice Parameter Behavior with Different Nd and O Concentrations in (U 1-yNd y)O 2±x Solid Solution

DOE PAGES

Lee, Seung Min; Knight, Travis W.; Voit, Stwart L.; ...

2016-02-02

The solid solution of (U1-yFPy)O- 2±x, has the same fluorite structure as UO 2±x lambda, and the lattice parameter is affected by dissolved fission product and oxygen concentrations. We investigated the relation between the lattice parameter and the concentrations of neodymium and oxygen in the fluorite structure of (U 1-yNd y)O 2±x using X-ray diffraction. Moreover, the lattice parameter behavior in the (U 1-yNd y)O 2±x, solid solution shows a linear change as a function of the oxygen-to-metal ratio and solubility of neodymium. The lattice parameter depends on the radii of ions forming the fluorite structure and also can bemore » expressed by a particular rule (modified Vegard's law). Furthermore, the numerical analyses of the lattice parameters for the stoichiometric and nonstoichionietric solid solutions were conducted, and the lattice parameter model for the (U1-yNdy)O 2±x, solid solution was assessed. There is a very linear relationship between the lattice parameter and the Nd and O concentration for the stoichiometry and nonstoichiometry of the (U 1-yNd y)O 2±x solid solution was verified.« less

Quantification of conservative and reactive transport using a single groundwater tracer test in a fractured media

NASA Astrophysics Data System (ADS)

Chatton, Eliot; Labasque, Thierry; Guillou, Aurélie; Béthencourt, Lorine; de La Bernardie, Jérôme; Boisson, Alexandre; Koch, Florian; Aquilina, Luc

2017-04-01

Identification of biogeochemical reactions in aquifers and determining kinetics is important for the prediction of contaminant transport in aquifers and groundwater management. Therefore, experiments accounting for both conservative and reactive transport are essential to understand the biogeochemical reactivity at field scale. This study presents the results of a groundwater tracer test using the combined injection of dissolved conservative and reactive tracers (He, Xe, Ar, Br-, O2 and NO3-) in order to evaluate the transport properties of a fractured media in Brittany, France. Dissolved gas concentrations were continuously monitored in situ with a CF-MIMS (Chatton et al, 2016) allowing a high frequency (1 gas every 2 seconds) multi-tracer analysis (N2, O2, CO2, CH4, N2O, H2, He, Ne, Ar, Kr, Xe) over a large resolution (6 orders of magnitude). Along with dissolved gases, groundwater biogeochemistry was monitored through the sampling of major anions and cations, trace elements and microbiological diversity. The results show breakthrough curves allowing the combined quantification of conservative and reactive transport properties. This ongoing work is an original approach investigating the link between heterogeneity of porous media and biogeochemical reactions at field scale. Eliot Chatton, Thierry Labasque, Jérôme de La Bernardie, Nicolas Guihéneuf, Olivier Bour and Luc Aquilina; Field Continuous Measurement of Dissolved Gases with a CF-MIMS: Applications to the Physics and Biogeochemistry of Groundwater Flow; Environmental Science & Technology, in press, 2016.

[Characteristics of Dissolved CH₄ and N₂O Concentrations of Weihe River in Xinxiang Section in Spring].

PubMed

Hou, Cui-cui; Zhang, Fang; Li, Ying-chen; Wang, Qi-bo; Liu, Sai

2016-05-15

Distributions of CH₄ and N₂O concentrations in Weihe River in Xinxiang City were monitored in spring of 2015, and their influencing factors were discussed. The result showed that CH₄ and N₂O were super-saturated in surface water of Weihe River. The variation ranges of two gases' saturations in the surface water of Weihe River were 147.59-2667.85 (CH₄) and 4.06-188.25 (N₂O). In the urban area, significant correlation existed between N₂O and NH₄⁺-N concentrations (P < 0.01), but in the new district, dissolved N₂O concentration showed sharp increase because of the water input from the urban sewage plants, illustrating that the controlling mechanism on N₂O production varied as pollutant characteristics changed. Stepwise regression analysis showed that CH₄ concentrations could be explained by NH₄⁺-N concentrations and water temperature, and CH₄ concentrations in the surface water of Weihe River was significantly correlated with NH₄⁺-N concentrations (R² = 0.70, P < 0.01), suggesting that NH₄⁺-N was the key factor in regulating the production and assumption of CH₄oxidation in Weihe River in spring. Besides, this study showed that when there was less NO₃⁻-N but more NH₄⁺-N in river water, CH₄and N₂O concentrations would be positively correlated, indicating that different nitrogen sources would impact the coupling mechanism of CH₄and N₂O productions.

Transient changes in shallow groundwater chemistry during the MSU ZERT CO2 injection experiment

USGS Publications Warehouse

Apps, J.A.; Zheng, Lingyun; Spycher, N.; Birkholzer, J.T.; Kharaka, Y.; Thordsen, J.; Kakouros, E.; Trautz, R.

2011-01-01

Food-grade CO2 was injected into a shallow aquifer through a perforated pipe placed horizontally 1-2 m below the water table at the Montana State University Zero Emission Research and Technology (MSU-ZERT) field site at Bozeman, Montana. The possible impact of elevated CO2 levels on groundwater quality was investigated by analyzing 80 water samples taken before, during, and following CO2 injection. Field determinations and laboratory analyses showed rapid and systematic changes in pH, alkalinity, and conductance, as well as increases in the aqueous concentrations of trace element species. The geochemical data were first evaluated using principal component analysis (PCA) in order to identify correlations between aqueous species. The PCA findings were then used in formulating a geochemical model to simulate the processes likely to be responsible for the observed increases in the concentrations of dissolved constituents. Modeling was conducted taking into account aqueous and surface complexation, cation exchange, and mineral precipitation and dissolution. Reasonable matches between measured data and model results suggest that: (1) CO2 dissolution in the groundwater causes calcite to dissolve. (2) Observed increases in the concentration of dissolved trace metals result likely from Ca+2-driven ion exchange with clays (smectites) and sorption/desorption reactions likely involving Fe (hydr)oxides. (3) Bicarbonate from CO2 dissolution appears to compete for sorption with anionic species such as HAsO4-2, potentially increasing dissolved As levels in groundwater. ?? 2011 Published by Elsevier Ltd.

Analysis of engineered nanomaterials in the environment

NASA Astrophysics Data System (ADS)

Reed, Robert Bruce

With increasing incorporation of engineered nanoparticles (NPs) into consumer products, there is concern that these materials will be released to the environment with unknown ecological effects. Methods for detection and characterization of these materials at environmentally relevant concentrations are crucial to understanding this potential risk. A relatively new method, single particle inductively coupled plasma mass spectrometry (spICPMS), was applied to analysis of metal oxide NPs such as ZnO, CeO2, and TiO2, as well as silver nanowires and carbon nanotubes. A lack of nanoparticulate "pulses" in spICPMS analysis of nano-ZnO led to a study on ZnO NP solubility in a variety of matrices. Dissolution of nano-ZnO was observed in nanopure water (7.18 - 7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (~5 mg/L), but much more dissolution was observed in Dulbecco's Modified Eagle's Medium (DMEM), where the dissolved Zn concentration exceeded 34 mg/L. These results suggest that solution chemistry exerts a strong influence on ZnO NP dissolution and can result in limits on zinc solubility due to precipitation of less soluble solid phases. Detection and sizing of metal-containing NPs was achieved at concentrations predicted for environmental samples (part-per trillion levels) using spICPMS. Sizing of silver nanowires, titanium dioxide and cerium oxide NPs was done by correlating ICP-MS response (pulses) from NPs entering the plasma to mass of metal in dissolved standards. The ratio of NP pulse detections to the total number of readings during analysis was optimized at 2.5% or less to minimize coincident pulses while still allowing definition of a size distribution. Detection of single walled carbon nanotubes (CNTs) was performed using spICPMS. This study focuses on using trace catalytic metal nanoparticles intercalated in the CNT structure as proxies for the nanotubes. The small, variable, amount of trace metal in each CNT makes separation from instrumental background challenging, and multiple approaches to this problem were attempted. To highlight the potential of spICPMS in environmental studies the release of CNTs from polymer nanocomposites into solution was monitored, showcasing the technique's ability to detect changes in released CNT concentrations as a function of CNT loading.

Lake Metabolism: Comparison of Lake Metabolic Rates Estimated from a Diel CO2- and the Common Diel O2-Technique.

PubMed

Peeters, Frank; Atamanchuk, Dariia; Tengberg, Anders; Encinas-Fernández, Jorge; Hofmann, Hilmar

2016-01-01

Lake metabolism is a key factor for the understanding of turnover of energy and of organic and inorganic matter in lake ecosystems. Long-term time series on metabolic rates are commonly estimated from diel changes in dissolved oxygen. Here we present long-term data on metabolic rates based on diel changes in total dissolved inorganic carbon (DIC) utilizing an open-water diel CO2-technique. Metabolic rates estimated with this technique and the traditional diel O2-technique agree well in alkaline Lake Illmensee (pH of ~8.5), although the diel changes in molar CO2 concentrations are much smaller than those of the molar O2 concentrations. The open-water diel CO2- and diel O2-techniques provide independent measures of lake metabolic rates that differ in their sensitivity to transport processes. Hence, the combination of both techniques can help to constrain uncertainties arising from assumptions on vertical fluxes due to gas exchange and turbulent diffusion. This is particularly important for estimates of lake respiration rates because these are much more sensitive to assumptions on gradients in vertical fluxes of O2 or DIC than estimates of lake gross primary production. Our data suggest that it can be advantageous to estimate respiration rates assuming negligible gradients in vertical fluxes rather than including gas exchange with the atmosphere but neglecting vertical mixing in the water column. During two months in summer the average lake net production was close to zero suggesting at most slightly autotrophic conditions. However, the lake emitted O2 and CO2 during the entire time period suggesting that O2 and CO2 emissions from lakes can be decoupled from the metabolism in the near surface layer.

Lake Metabolism: Comparison of Lake Metabolic Rates Estimated from a Diel CO2- and the Common Diel O2-Technique

PubMed Central

Peeters, Frank; Atamanchuk, Dariia; Tengberg, Anders; Encinas-Fernández, Jorge; Hofmann, Hilmar

2016-01-01

Lake metabolism is a key factor for the understanding of turnover of energy and of organic and inorganic matter in lake ecosystems. Long-term time series on metabolic rates are commonly estimated from diel changes in dissolved oxygen. Here we present long-term data on metabolic rates based on diel changes in total dissolved inorganic carbon (DIC) utilizing an open-water diel CO2-technique. Metabolic rates estimated with this technique and the traditional diel O2-technique agree well in alkaline Lake Illmensee (pH of ~8.5), although the diel changes in molar CO2 concentrations are much smaller than those of the molar O2 concentrations. The open-water diel CO2- and diel O2-techniques provide independent measures of lake metabolic rates that differ in their sensitivity to transport processes. Hence, the combination of both techniques can help to constrain uncertainties arising from assumptions on vertical fluxes due to gas exchange and turbulent diffusion. This is particularly important for estimates of lake respiration rates because these are much more sensitive to assumptions on gradients in vertical fluxes of O2 or DIC than estimates of lake gross primary production. Our data suggest that it can be advantageous to estimate respiration rates assuming negligible gradients in vertical fluxes rather than including gas exchange with the atmosphere but neglecting vertical mixing in the water column. During two months in summer the average lake net production was close to zero suggesting at most slightly autotrophic conditions. However, the lake emitted O2 and CO2 during the entire time period suggesting that O2 and CO2 emissions from lakes can be decoupled from the metabolism in the near surface layer. PMID:28002477

Study of the Solvent Extraction of V(V) from Nitrate Medium by Tri- n-Octylamine Dissolved in Kerosene

NASA Astrophysics Data System (ADS)

Biswas, Ranjit Kumar; Karmakar, Aneek Krishna; Mottakin, Mohammad

2017-10-01

The liquid-liquid extraction of V(V) from a nitrate medium by tri- n-Octylamine [( n-C8H17)3N; abbreviated as TOA] dissolved in distilled colorless kerosene has been investigated as a function of various experimental parameters. The equilibration time is less than 10 min. It is observed that the extraction ratio increases with increasing [V(V)] in the aqueous phase, which is possibly a result of the formation of V10O26(OH) 2 4- (via reaction: 10 VO2 + + 8 H2O → V10O26(OH) 2 4- + 14 H+) with increasing concentration in the aqueous phase. The nature of the species extracted into the organic phase depends on the existing aqueous species prevailing at a certain pH. At lower pH values, the extraction of VO2 + occurs via cation (H+) exchange of (C8H17)3NHNO3. On the other hand, at higher pH values, anionic V(V) species such as V10O26(OH) 2 4- , V10O27(OH)5-, V10O28 6- etc. are extracted by solvated ion-pair formation mechanism. The TOA concentration dependence varies from 2 at a lower pH region ( 2.3) to 1 at a higher pH region ( 5.7). The extraction is also found to be favored by a rise of nitrate concentration in the aqueous phase. Temperature has a pronounced effect with Δ H < -58 kJ/mol. Kerosene is demonstrated as the best diluent for this system. Increased organic to aqueous phase volume ratio (O/A) enhances extraction ratio. The extracted species can be stripped by 0.75 mol/L NH4OH solution to the extent of 72% in a single stage. But stage-wise stripping is not so effective. It is observed a very high loading, of the order of 2.3 mol V(V) per mol TOA.

Continuous high-frequency dissolved O2/Ar measurements by equilibrator inlet mass spectrometry.

PubMed

Cassar, Nicolas; Barnett, Bruce A; Bender, Michael L; Kaiser, Jan; Hamme, Roberta C; Tilbrook, Bronte

2009-03-01

The oxygen (O(2)) concentration in the surface ocean is influenced by biological and physical processes. With concurrent measurements of argon (Ar), which has similar solubility properties as oxygen, we can remove the physical contribution to O(2) supersaturation and determine the biological oxygen supersaturation. Biological O(2) supersaturation in the surface ocean reflects the net metabolic balance between photosynthesis and respiration, i.e., the net community productivity (NCP). We present a new method for continuous shipboard measurements of O(2)/Ar by equilibrator inlet mass spectrometry (EIMS). From these measurements and an appropriate gas exchange parametrization, NCP can be estimated at high spatial and temporal resolution. In the EIMS configuration, seawater from the ship's continuous intake flows through a cartridge enclosing a gas-permeable microporous membrane contactor. Gases in the headspace of the cartridge equilibrate with dissolved gases in the flowing seawater. A fused-silica capillary continuously samples headspace gases, and the O(2)/Ar ratio is measured by mass spectrometry. The ion current measurements on the mass spectrometer reflect the partial pressures of dissolved gases in the water flowing through the equilibrator. Calibration of the O(2)/Ar ion current ratio (32/40) is performed automatically every 2 h by sampling ambient air through a second capillary. A conceptual model demonstrates that the ratio of gases reaching the mass spectrometer is dependent on several parameters, such as the differences in molecular diffusivities and solubilities of the gases. Laboratory experiments and field observations performed by EIMS are discussed. We also present preliminary evidence that other gas measurements, such as N(2)/Ar and pCO(2) measurements, may potentially be performed with EIMS. Finally, we compare the characteristics of the EIMS with the previously described membrane inlet mass spectrometry (MIMS) approach.

Effects of pH2O, pH2 and fO2 on the Diffusion of H-Bearing Species in Lunar Basalt and an Iron-Free Basaltic Analog at 1 atm

NASA Astrophysics Data System (ADS)

Newcombe, M. E.; Beckett, J. R.; Baker, M. B.; Newman, S.; Guan, Y.; Eiler, J. M.; Stolper, E. M.

2016-12-01

We have conducted water diffusion experiments in synthetic Apollo 15 "yellow glass" (LG) and an iron-free basaltic analog melt (AD) at 1 atm and 1350 °C over a range of fO2 conditions from IW-2.2 to IW+6.7 and over a range of pH2/pH2O from nominally zero to 10. The water concentrations measured in our quenched experimental glasses by SIMS and FTIR vary from a few ppm to 430 ppm. Many studies of water diffusion at higher water concentrations indicate that the apparent diffusivity of total water (D*water; see [1]) in silicate melts is highly concentration dependent at water contents >0.1 wt% (e.g., [1]). However, water concentration gradients in each of our AD and LG experiments are well described by models in which D*water is assumed to be constant. Best-fit values of D*water obtained for our AD and LG experiments are consistent with a modified speciation model [2] in which both molecular water and hydroxyl are allowed to diffuse, and in which hydroxyl is the dominant diffusing species at the low total water concentrations of our experiments. Water concentration gradients generated during hydration and dehydration experiments conducted simultaneously propagate approximately equal distances into the melt and have the same concentration of water dissolved in the melt at the melt-vapor interface, suggesting that hydration and dehydration are symmetric under the conditions of our experiments. Best-fit values of D*water for our LG experiments vary within a factor of 2 over a range of pH2/pH2O from 0.007 to 9.7 (a range of ƒO2 from IW-2.2 to IW+4.9) and a water concentration range from 80 ppm to 280 ppm. The relative insensitivity of D*water to variations in pH2 suggests that loss of H during the degassing of the lunar melts described by [3] was not primarily by loss of dissolved H2. The value of D*water chosen by [3] for modeling diffusive degassing of lunar volcanic glasses is within a factor of three of our measured value in LG melt at 1350 °C. [1] Zhang et al. (1991) GCA 55, 441-456; [2] Ni et al. (2013) GCA 103, 36-48; [3] Saal et al. (2008) Nature 454, 192-195.

Statistical Modeling to Predict N2O Production Within the Hyporheic Zone by Coupling Denitrifying Microbial Community Abundance to Geochemical and Hydrological Parameters

NASA Astrophysics Data System (ADS)

Farrell, T. B.; Quick, A. M.; Reeder, W. J.; Benner, S. G.; Tonina, D.; Feris, K. P.

2015-12-01

The hyporheic zone (HZ) of streams may be a significant source of nitrous oxide (N2O). However, the biogeochemical processes controlling N2O emissions remain poorly constrained due to difficulties in obtaining high-resolution chemical, physical, and biological data from streams. Our research elucidates specific controls on N2O production within the HZ by coupling the distribution of denitrifying microbial communities to flow dynamics (i.e. hydraulics and streambed morphology) and biogeochemical processes. We conducted a large-scale flume experiment that allowed us to constrain streambed morphology, flow rate, organic carbon loading, grain size distribution, and exogenous nitrate loading while enabling regular monitoring of dissolved oxygen, pH, alkalinity, nitrogen species, and elemental concentrations in the HZ. We also employed real-time PCR (qPCR) to quantify the distribution of denitrifying functional genes (nirS and nosZ, nitrite reductase and nitrous oxide reductase genes, respectively) in HZ sediment cores as a measure of denitrifying microorganism abundance. A steady increase in N2O was observed after 8 hours of residence time with a peak in concentration (9.5 μg-N/L) recorded at hour 18. Abundance of nosZ increased an order of magnitude between hours 8 and 18 (2.6x106 to 2.1x107 gene copy #/g dry sediment). nirS abundance remained within the same order of magnitude between hours 8 and 18 (1.7x107 to 3.8x107). Linear and nonlinear mixed-effects models were used to investigate N2O production in the HZ as a function of total nitrogen, nirS, nosZ, residence time, and dissolved oxygen. N2O production was localized at redox-controlled hotspots within the subsurface and concentrations were strongly correlated with the availability of nitrogen when an interaction with nosZ abundance was considered. On-going analysis will provide predictions of N2O production and support for conditions under which the HZ could be a significant contributor of N2O emissions. These results are also being used to parameterize a reactive transport model for predicting N2O production from stream sediments with different bedform morphologies, flow rates, and reactant concentrations.

A Laughing Gas Greenhouse for the Proterozoic?

NASA Astrophysics Data System (ADS)

Roberson, A. L.; Roadt, J.; Halevy, I.; Kasting, J. F.

2010-12-01

An anoxic, sulfidic ‘Canfield ocean’ during the Proterozoic (0.75-2.3 Ga) would have had limited trace metal abundances because of the low solubility of metal sulfides. The limitation on copper, specifically, would have had a significant impact on marine denitrification. Copper is needed for the enzyme that controls the final step of denitrification, from N2O to N2. Today, only about 5-6 percent of denitrification results in release of N2O. If all denitrification stopped at N2O during the Proterozoic, the N2O flux could have been 15-20 times higher than today. Other parts of the nitrogen cycle should have been able to operate at rates comparable to today, as catalysts for these reactions should have existed. The high N2O flux should have created higher atmospheric N2O concentrations; although this effect may have been offset by faster rates of N2O photolysis if O2 concentrations were lower than today. N2O concentrations of 0.3 to 30 ppmv, along with methane levels of 30-100 ppm, could have kept the surface warm during the Proterozoic without necessitating high CO2 levels. The high methane concentrations were a consequence of lack of dissolved O2 and sulfate in the deep ocean, which should have led to a high CH4 flux from marine sediments. A second oxygenation event at the end of the Proterozoic would have resulted in a shift to a more modern ocean and, consequently, more modern concentrations of atmospheric N2O and CH4.

Nanoparticles with Embedded Porphyrin Photosensitizers for Photooxidation Reactions and Continuous Oxygen Sensing.

PubMed

Kubát, Pavel; Henke, Petr; Berzediová, Veronika; Štěpánek, Miroslav; Lang, Kamil; Mosinger, Jiří

2017-10-18

We report the synthesis and characterization of sulfonated polystyrene nanoparticles (average diameter 30 ± 14 nm) with encapsulated 5,10,15,20-tetraphenylporphyrin or ionically entangled tetracationic 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin, their photooxidation properties, and the application of singlet oxygen-sensitized delayed fluorescence (SODF) in oxygen sensing. Both types of nanoparticles effectively photogenerated singlet oxygen, O 2 ( 1 Δ g ). The O 2 ( 1 Δ g ) phosphorescence, transient absorption of the porphyrin triplet states, and SODF signals were monitored using time-resolved spectroscopic techniques. The SODF intensity depended on the concentration of the porphyrin photosensitizer and dissolved oxygen and on the temperature. After an initial period (a few microseconds), the kinetics of the SODF process can be approximated as a monoexponential function, and the apparent SODF lifetimes can be correlated with the oxygen concentration. The oxygen sensing based on SODF allowed measurement of the dissolved oxygen in aqueous media in the broad range of oxygen concentrations (0.2-38 mg L -1 ). The ability of both types of nanoparticles to photooxidize external substrates was predicted by the SODF measurements and proven by chemical tests. The relative photooxidation efficacy was highest at a low porphyrin concentration, as indicated by the highest fluorescence quantum yield (Φ F ), and it corresponds with negligible inner filter and self-quenching effects. The photooxidation abilities were sensitive to the influence of temperature on the diffusion and solubility of oxygen in both polystyrene and water media and to the rate constant of the O 2 ( 1 Δ g ) reaction with a substrate. Due to their efficient photogeneration of cytotoxic O 2 ( 1 Δ g ) at physiological temperatures and their oxygen sensing via SODF, both types of nanoparticles are promising candidates for biomedical applications.

Oxidation and reduction rates for organic carbon in the Amazon mainstream tributary and floodplain, inferred from distributions of dissolved gases

NASA Technical Reports Server (NTRS)

Richey, Jeffrey E.; Devol, Allan H.; Wofsy, Steven C.; Victoria, Reynaldo; Riberio, Maria N. G.

1986-01-01

Concentrations of CO2, O2, CH4, and N2O in the Amazon River system reflect an oxidation-reduction sequence in combination with physical mixing between the floodplain and the mainstem. Concentrations of CO2 ranged from 150 microM in the Amazon mainstem to 200 to 300 microM in aerobic waters of the floodplain, and up to 1000 microM in oxygen-depleted environments. Apparent oxygen utilization (AOU) ranged from 80 to 250 microM. Methane was highly supersaturated, with concentrations ranging from 0.06 microM in the mainstem to 100 microM on the floodplain. Concentrations of N2O were slightly supersaturated in the mainstem, but were undersaturated on the floodplain. Fluxes calculated from these concentrations indicated decomposition of 1600 g C sq m y(-1) of organic carbon in Amazon floodplain waters. Analysis of relationships between CH4, O2, and CO2 concentrations indicated that approximately 50 percent of carbon mineralization on the floodplain is anaerobic, with 20 percent lost to the atmoshphere as CH4. The predominance of anaerobic metabolism leads to consumption of N2O on the flood plane. Elevated concentrations of CH4 in the mainstem probably reflect imput from the floodplain, while high levels of CO2 in the mainstem are derived from a combination of varzea drainage and in situ respiration.

Separation of rare earths from transition metals by liquid-liquid extraction from a molten salt hydrate to an ionic liquid phase.

PubMed

Rout, Alok; Binnemans, Koen

2014-02-28

The solvent extraction of trivalent rare-earth ions and their separation from divalent transition metal ions using molten salt hydrates as the feed phase and an undiluted fluorine-free ionic liquid as the extracting phase were investigated in detail. The extractant was tricaprylmethylammonium nitrate, [A336][NO3], and the hydrated melt was calcium nitrate tetrahydrate, Ca(NO3)2·4H2O. The extraction behavior of rare-earth ions was studied for solutions of individual elements, as well as for mixtures of rare earths in the hydrated melt. The influence of different extraction parameters was investigated: the initial metal loading in the feed phase, percentage of water in the feed solution, equilibration time, and the type of hydrated melt. The extraction of rare earths from Ca(NO3)2·4H2O was compared with extraction from CaCl2·4H2O by [A336][Cl] (Aliquat 336). The nitrate system was found to be the better one. The extraction and separation of rare earths from the transition metals nickel, cobalt and zinc were also investigated. Remarkably high separation factors of rare-earth ions over transition metal ions were observed for extraction from Ca(NO3)2·4H2O by the [A336][NO3] extracting phase. Furthermore, rare-earth ions could be separated efficiently from transition metal ions, even in melts with very high concentrations of transition metal ions. Rare-earth oxides could be directly dissolved in the Ca(NO3)2·4H2O phase in the presence of small amounts of Al(NO3)3·9H2O or concentrated nitric acid. The efficiency of extraction after dissolving the rare-earth oxides in the hydrated nitrate melt was identical to extraction from solutions with rare-earth nitrates dissolved in the molten phase. The stripping of the rare-earth ions from the loaded ionic liquid phase and the reuse of the recycled ionic liquid were also investigated in detail.

Carbon dioxide induced bubble formation in a CH4-CO2-H2O ternary system: a molecular dynamics simulation study.

PubMed

Sujith, K S; Ramachandran, C N

2016-02-07

The extraction of methane from its hydrates using carbon dioxide involves the decomposition of the hydrate resulting in a CH4-CO2-H2O ternary solution. Using classical molecular dynamics simulations, we investigate the evolution of dissolved gas molecules in the ternary system at different concentrations of CO2. Various compositions considered in the present study resemble the solution formed during the decomposition of methane hydrates at the initial stages of the extraction process. We find that the presence of CO2 aids the formation of CH4 bubbles by causing its early nucleation. Elucidation of the composition of the bubble revealed that in ternary solutions with high concentration of CO2, mixed gas bubbles composed of CO2 and CH4 are formed. To understand the role of CO2 in the nucleation of CH4 bubbles, the structure of the bubble formed was analyzed, which revealed that there is an accumulation of CO2 at the interface of the bubble and the surrounding water. The aggregation of CO2 at the bubble-water interface occurs predominantly when the concentration of CO2 is high. Radial distribution function for the CH4-CO2 pair indicates that there is an increasingly favorable direct contact between dissolved CH4 and CO2 molecules in the bubble-water interface. It is also observed that the presence of CO2 at the interface results in the decrease in surface tension. Thus, CO2 leads to greater stability of the bubble-water interface thereby bringing down the critical size of the bubble nuclei. The results suggest that a rise in concentration of CO2 helps in the removal of dissolved CH4 thereby preventing the accumulation of methane in the liquid phase. Thus, the presence of CO2 is predicted to assist the decomposition of methane hydrates in the initial stages of the replacement process.

Light absorption and the photoformation of hydroxyl radical and singlet oxygen in fog waters

NASA Astrophysics Data System (ADS)

Kaur, R.; Anastasio, C.

2017-09-01

The atmospheric aqueous-phase is a rich medium for chemical transformations of organic compounds, in part via photooxidants generated within the drops. Here we measure light absorption, photoformation rates and steady-state concentrations of two photooxidants - hydroxyl radical (•OH) and singlet molecular oxygen (1O2*) - in 8 illuminated fog waters from Davis, California and Baton Rouge, Louisiana. Mass absorption coefficients for dissolved organic compounds (MACDOC) in the samples are large, with typical values of 10,000-15,000 cm2 g-C-1 at 300 nm, and absorption extends to wavelengths as long as 450-600 nm. While nitrite and nitrate together account for an average of only 1% of light absorption, they account for an average of 70% of •OH photoproduction. Mean •OH photoproduction rates in fogs at the two locations are very similar, with an overall mean of 1.2 (±0.7) μM h-1 under Davis winter sunlight. The mean (±1σ) lifetime of •OH is 1.6 (±0.6) μs, likely controlled by dissolved organic compounds. Including calculated gas-to-drop partitioning of •OH, the average aqueous concentration of •OH is approximately 2 × 10-15 M (midday during Davis winter), with aqueous reactions providing approximately one-third of the hydroxyl radical source. At this concentration, calculated lifetimes of aqueous organics are on the order of 10 h for compounds with •OH rate constants of 1 × 1010 M-1 s-1 or higher (e.g., substituted phenols such as syringol (6.4 h) and guaiacol (8.4 h)), and on the order of 100 h for compounds with rate constants near 1 × 109 M-1 s-1 (e.g., isoprene oxidation products such as glyoxal (152 h), glyoxylic acid (58 h), and pyruvic acid (239 h)). Steady-state concentrations of 1O2* are approximately 100 times higher than those of •OH, in the range of (0.1-3.0) × 10-13 M. Since 1O2* is a more selective oxidant than •OH, it will only react appreciably with electron-rich species such as dimethyl furan (lifetime of 2.0 h) and substituted polycyclic aromatic hydrocarbons (e.g., 9,10-dimethylbenz[a]anthracene with a lifetime of 0.7 h). Comparing our current Davis samples with Davis fogs collected in the late 1990s shows a decrease in dissolved organic carbon content, similar mass absorption coefficients, lower •OH concentrations, but very similar 1O2* concentrations.

Greenhouse gases emissions in rivers of the Tibetan Plateau.

PubMed

Qu, Bin; Aho, Kelly Sue; Li, Chaoliu; Kang, Shichang; Sillanpää, Mika; Yan, Fangping; Raymond, Peter A

2017-11-29

Greenhouse gases (GHGs) emissions from streams are important to regional biogeochemical budgets. This study is one of the first to incorporate stream GHGs (CO 2 , CH 4 and N 2 O) concentrations and emissions in rivers of the Tibetan Plateau. With one-time sampling from 32 sites in rivers of the plateau, we found that most of the rivers were supersaturated with CO 2 , CH 4 and N 2 O during the study period. Medians of partial pressures of CO 2 (pCO 2 ), pCH 4 and pN 2 O were presented 864 μatm, 6.3 μatm, and 0.25 μatm respectively. Based on a scaling model of the flux of gas, the calculated fluxes of CO 2 , CH 4 and N 2 O (3,452 mg-C m 2 d -1 , 26.7 mg-C m 2 d -1 and 0.18 mg-N m 2 d -1 , respectively) in rivers of the Tibetan Plateau were found comparable with most other rivers in the world; and it was revealed that the evasion rates of CO 2 and CH 4 in tributaries of the rivers of the plateau were higher than those in the mainstream despite its high altitude. Furthermore, concentrations of GHGs in the studied rivers were related to dissolved carbon and nitrogen, indicating that riverine dissolved components could be used to scale GHGs envision in rivers of the Tibetan Plateau.

Sonochemical reduction of carbon dioxide.

PubMed

Harada, H

1998-06-01

Sonolysis of carbon dioxide dissolved in water was performed from a standpoint of reducing this material in atmosphere. During one hour of sonication, the amount of CO2 decreased to about half at 5 degrees C under CO2-Ar atmosphere. The decreasing rate for CO2 followed the order Ar > He > H2 > N2 and it was down with increasing temperature in the range of 5-45 degrees C. The most favorable concentration for reducing CO2 was 0.03 (mole fraction of CO2 in gas phase). This concentration in gas phase means an equal mixture of CO2 and Ar in water, because CO2 is more soluble than Ar. Since carbon dioxide dissolved in water would be partly ionized, the roles of ions on the sonolysis were also examined. Gaseous reaction products were CO, H2 and a small amount of O2. Carbon monoxide and hydrogen might be obtained from CO2 and H2O by sonolysis, respectively. Both gases are fuel and react each other to C1 compounds such as methanol, and so on. Therefore, irradiation of ultrasonic waves should be an important technique for reducing CO2.

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

NASA Astrophysics Data System (ADS)

Reinoso-Maset, Estela; Steefel, Carl I.; Um, Wooyong; Chorover, Jon; O'Day, Peggy A.

2017-06-01

Uranyl oxyhydroxide minerals are important weathering products in uranium-contaminated surface and subsurface environments that regulate dissolved uranium (U) concentrations. However, dissolution rates for this class of minerals and associated dissolution mechanisms have not been previously reported for circumneutral pH conditions, particularly for the case of flow through porous media. In this work, the dissolution rates of K- and Na-compreignacite (K2(UO2)6O4(OH)6·8H2O and Na2(UO2)6O4(OH)6·8H2O, respectively) were measured using flow-through columns reacted with two simulated background porewater (BPW) solutions of low and high dissolved carbonate concentration (ca. 0.2 and 2.8 mmol L-1). Column materials were characterized before and after reaction with electron microscopy, bulk chemistry, and EXAFS to identify structural and chemical changes during dissolution and to obtain insight into molecular-scale processes. The reactive transport code CrunchFlow was used to calculate overall dissolution rates while accounting for fluid transport and changes in mineral volume and reactive surface area, and results were compared to steady-state dissolution rate calculations. In low carbonate BPW systems, interlayer K and Na were initially leached from both minerals, and in Na-compreignacite, K and minor divalent cations from the input solution were incorporated into the mineral structure. Results of characterization analyses suggested that after reaction both K- and Na-compreignacite resembled a disordered K-compreignacite with altered surfaces. A 10-fold increase in dissolved carbonate concentration and corresponding increase in pH (from 6.65 to 8.40) resulted in a net removal of 58-87% of total U mass from the columns, compared to <1% net loss in low carbonate BPW systems. Steady-state release of dissolved U was not observed with high carbonate solutions and post-reaction characterizations indicated a lack of development of leached or altered surfaces. Dissolution rates (normalized to specific surface area) were 2.5-3 orders-of-magnitude faster in high versus low carbonate BPW systems, with Na-compreignacite dissolving more rapidly than K-compreignacite under both BPW conditions, possibly due to greater ion exchange (1.57 · 10-10 vs. 1.28 · 10-13 mol m-2 s-1 [log R = -9.81 and -12.89] and 5.79 · 10-10 vs. 3.71 · 10-13 mol m-2 s-1 [log R = -9.24 and -12.43] for K- and Na-compreignacite, respectively). Experimental and spectroscopic results suggest that the dissolution rate is controlled by bond breaking of a uranyl group and detachment from polyhedral layers of the mineral structure. With higher dissolved carbonate concentrations, this rate-determining step is accelerated by the formation of Ca-uranyl carbonate complexes (dominant species under these conditions), which resulted in an increase of the dissolution rates. Optimization of both dissolution rate and mineral volume fraction in the reactive transport model to account for U mass removal during dissolution more accurately reproduced effluent data in high carbonate systems, and resulted in faster overall rates compared with a steady-state dissolution assumption. This study highlights the importance of coupling reaction and transport processes during the quantification of mineral dissolution rates to accurately predict the fate of contaminants such as U in porous geomedia.

Monitoring, field experiments, and geochemical modeling of Fe(II) oxidation kinetics in a stream dominated by net-alkaline coal-mine drainage, Pennsylvania, USA

USGS Publications Warehouse

Cravotta, Charles A.

2015-01-01

Watershed-scale monitoring, field aeration experiments, and geochemical equilibrium and kinetic modeling were conducted to evaluate interdependent changes in pH, dissolved CO2, O2, and Fe(II) concentrations that typically take place downstream of net-alkaline, circumneutral coal-mine drainage (CMD) outfalls and during aerobic treatment of such CMD. The kinetic modeling approach, using PHREEQC, accurately simulates observed variations in pH, Fe(II) oxidation, alkalinity consumption, and associated dissolved gas concentrations during transport downstream of the CMD outfalls (natural attenuation) and during 6-h batch aeration tests on the CMD using bubble diffusers (enhanced attenuation). The batch aeration experiments demonstrated that aeration promoted CO2 outgassing, thereby increasing pH and the rate of Fe(II) oxidation. The rate of Fe(II) oxidation was accurately estimated by the abiotic homogeneous oxidation rate law −d[Fe(II)]/dt = k1·[O2]·[H+]−2·[Fe(II)] that indicates an increase in pH by 1 unit at pH 5–8 and at constant dissolved O2 (DO) concentration results in a 100-fold increase in the rate of Fe(II) oxidation. Adjusting for sample temperature, a narrow range of values for the apparent homogeneous Fe(II) oxidation rate constant (k1′) of 0.5–1.7 times the reference value of k1 = 3 × 10−12 mol/L/min (for pH 5–8 and 20 °C), reported by Stumm and Morgan (1996), was indicated by the calibrated models for the 5-km stream reach below the CMD outfalls and the aerated CMD. The rates of CO2 outgassing and O2ingassing in the model were estimated with first-order asymptotic functions, whereby the driving force is the gradient of the dissolved gas concentration relative to equilibrium with the ambient atmosphere. Although the progressive increase in DO concentration to saturation could be accurately modeled as a kinetic function for the conditions evaluated, the simulation of DO as an instantaneous equilibrium process did not affect the model results for Fe(II) or pH. In contrast, the model results for pH and Fe(II) were sensitive to the CO2 mass transfer rate constant (kL,CO2a). The value of kL,CO2a estimated for the stream (0.010 min−1) was within the range for the batch aeration experiments (0–0.033 min−1). These results indicate that the abiotic homogeneous Fe(II) oxidation rate law, with adjustments for variations in temperature and CO2 outgassing rate, may be applied to predict changes in aqueous iron and pH for net-alkaline, ferruginous waters within a stream (natural conditions) or a CMD treatment system (engineered conditions).

Differences in soil solution chemistry between soils amended with nanosized CuO or Cu reference materials: implications for nanotoxicity tests.

PubMed

McShane, Heather V A; Sunahara, Geoffrey I; Whalen, Joann K; Hendershot, William H

2014-07-15

Soil toxicity tests for metal oxide nanoparticles often include micrometer-sized oxide and metal salt treatments to distinguish between toxicity from nanometer-sized particles, non-nanometer-sized particles, and dissolved ions. Test result will be confounded if each chemical form has different effects on soil solution chemistry. We report on changes in soil solution chemistry over 56 days-the duration of some standard soil toxicity tests-in three soils amended with 500 mg/kg Cu as nanometer-sized CuO (nano), micrometer-sized CuO (micrometer), or Cu(NO3)2 (salt). In the CuO-amended soils, the log Cu2+ activity was initially low (minimum -9.48) and increased with time (maximum -5.20), whereas in the salt-amended soils it was initially high (maximum -4.80) and decreased with time (minimum -6.10). The Cu2+ activity in the nano-amended soils was higher than in the micrometer-amended soils for at least the first 11 days, and lower than in the salt-amended soils for at least 28 d. The pH, and dissolved Ca and Mg concentrations in the CuO-amended soils were similar, but the salt-amended soils had lower pH for at least 14 d, and higher Ca and Mg concentrations throughout the test. Soil pretreatments such as leaching and aging prior to toxicity tests are suggested.

Ecosystem Metabolism and Air-Water Fluxes of Greenhouse Gases in High Arctic Wetland Ponds

NASA Astrophysics Data System (ADS)

Lehnherr, I.; Venkiteswaran, J.; St. Louis, V. L.; Emmerton, C.; Schiff, S. L.

2012-12-01

Freshwater lakes and wetlands can be very productive systems on the Arctic landscape compared to terrestrial tundra ecosystems and provide valuable resources to many organisms, including waterfowl, fish and humans. Rates of ecosystem productivity dictate how much energy flows through food webs, impacting the abundance of higher-level organisms (e.g., fish), as well as the net carbon balance, which determines whether a particular ecosystem is a source or sink of carbon. Climate change is predicted to result in warmer temperatures, increased precipitation and permafrost melting in the Arctic and is already altering northern ecosystems at unprecedented rates; however, it is not known how freshwater systems are responding to these changes. To predict how freshwater systems will respond to complex environmental changes, it is necessary to understand the key processes, such as primary production and ecosystem respiration, that are driving these systems. We sampled wetland ponds (n=8) and lakes (n=2) on northern Ellesmere Island (81° N, Nunavut, Canada) during the open water season for a suite of biogeochemical parameters, including concentrations of dissolved gases (O2, CO2, CH4, N2O) as well as stable-isotope ratios of dissolved inorganic carbon (δ13C-DIC), dissolved oxygen (δ18O-DO), and water (δ18O-H2O). We will present rates of primary production and ecosystem respiration, modeled from the concentration and stable isotope ratios of DIC and DO, as well as air-water gas exchange of greenhouse gases in these high Arctic ponds and lakes. Preliminary results demonstrate that ecosystem metabolism in these ponds was high enough to result in significant deviations in the isotope ratios of DIC and DO from atmospheric equilibrium conditions. In other words ecosystem rates of primary production and respiration were faster than gas exchange even in these small, shallow, well-mixed ponds. Furthermore, primary production was elevated enough at all sites except Lake Hazen, a large cold ultra-oligotrophic lake, to result in a shift in the δ18O of DO towards more depleted values. Two of the ponds also exhibited enriched δ13C-DIC indicative of high rates of DIC uptake and primary production. However most sites appear to be net heterotrophic systems, with the exception of a few net autotrophic ponds. Interestingly, due to the high DIC concentrations in pond waters, δ13C-DIC values are reflective of ecosystem metabolism on a somewhat longer time scale than δ18O-DO values, which might be useful for examining temporal changes in production and respiration. Finally, most ponds were sources of both CO2 and CH4 to the atmosphere, but were surprisingly under-saturated with respect to N2O, demonstrating that they are sinks for atmospheric N2O. Rates of N2O consumption (denitrification) were modeled from concentration-time data and ranged from <0.1 to 1.1 nmol L-1 h-1.

AFS-2 FLOWSHEET MODIFICATIONS TO ADDRESS THE INGROWTH OF PU(VI) DURING METAL DISSOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crapse, K.; Rudisill, T.; O'Rourke, P.

2014-07-02

In support of the Alternate Feed Stock Two (AFS-2) PuO{sub 2} production campaign, Savannah River National Laboratory (SRNL) conducted a series of experiments concluding that dissolving Pu metal at 95°C using a 6–10 M HNO{sub 3} solution containing 0.05–0.2 M KF and 0–2 g/L B could reduce the oxidation of Pu(IV) to Pu(VI) as compared to dissolving Pu metal under the same conditions but at or near the boiling temperature. This flowsheet was demonstrated by conducting Pu metal dissolutions at 95°C to ensure that PuO{sub 2} solids were not formed during the dissolution. These dissolution parameters can be used formore » dissolving both Aqueous Polishing (AP) and MOX Process (MP) specification materials. Preceding the studies reported herein, two batches of Pu metal were dissolved in the H-Canyon 6.1D dissolver to prepare feed solution for the AFS-2 PuO{sub 2} production campaign. While in storage, UV-visible spectra obtained from an at-line spectrophotometer indicated the presence of Pu(VI). Analysis of the solutions also showed the presence of Fe, Ni, and Cr. Oxidation of Pu(IV) produced during metal dissolution to Pu(VI) is a concern for anion exchange purification. Anion exchange requires Pu in the +4 oxidation state for formation of the anionic plutonium(IV) hexanitrato complex which absorbs onto the resin. The presence of Pu(VI) in the anion feed solution would require a valence adjustment step to prevent losses. In addition, the presence of Cr(VI) would result in absorption of chromate ion onto the resin and could limit the purification of Pu from Cr which may challenge the purity specification of the final PuO{sub 2} product. Initial experiments were performed to quantify the rate of oxidation of Pu(IV) to Pu(VI) (presumed to be facilitated by Cr(VI)) as functions of the HNO{sub 3} concentration and temperature in simulated dissolution solutions containing Cr, Fe, and Ni. In these simulated Pu dissolutions studies, lowering the temperature from near boiling to 95 °C reduced the oxidation rate of Pu(IV) to Pu(VI). For 8.1 M HNO{sub 3} simulated dissolution solutions, at near boiling conditions >35% Pu(VI) was present in 50 h while at 95 °C <10% Pu(VI) was present at 50 h. At near boiling temperatures, eliminating the presence of Cr and varying the HNO{sub 3} concentration in the range of 7–8.5 M had little effect on the rate of conversion of Pu(IV) to Pu(VI). HNO{sub 3} oxidation of Pu(IV) to Pu(VI) in a pure solution has been reported previously. Based on simulated dissolution experiments, this study concluded that dissolving Pu metal at 95°C using a 6 to 10 M HNO{sub 3} solution 0.05–0.2 M KF and 0–2 g/L B could reduce the rate of oxidation of Pu(IV) to Pu(VI) as compared to near boiling conditions. To demonstrate this flowsheet, two small-scale experiments were performed dissolving Pu metal up to 6.75 g/L. No Pu-containing residues were observed in the solutions after cooling. Using Pu metal dissolution rates measured during the experiments and a correlation developed by Holcomb, the time required to completely dissolve a batch of Pu metal in an H-Canyon dissolver using this flowsheet was estimated to require nearly 5 days (120 h). This value is reasonably consistent with an estimate based on the Batch 2 and 3 dissolution times in the 6.1D dissolver and Pu metal dissolution rates measured in this study and by Rudisill et al. Data from the present and previous studies show that the Pu metal dissolution rate decreases by a factor of approximately two when the temperature decreased from boiling (112 to 116°C) to 95°C. Therefore, the time required to dissolve a batch of Pu metal in an H-Canyon dissolver at 95°C would likely double (from 36 to 54 h) and require 72 to 108 h depending on the surface area of the Pu metal. Based on the experimental studies, a Pu metal dissolution flowsheet utilizing 6–10 M HNO{sub 3} containing 0.05–0.2 M KF (with 0–2 g/L B) at 95°C is recommended to reduce the oxidation of Pu(IV) to Pu(VI) as compared to near boiling conditions. The time required to completely dissolve a batch of Pu metal will increase, however, by approximately a factor of two as compared to initial dissolutions at near boiling (assuming the KF concentration is maintained at nominally 0.1 M). By lowering the temperature to 95°C under otherwise the same operating parameters as previous dissolutions, the Pu(VI) concentration should not exceed 15% after a 120 h heating cycle. Increasing the HNO{sub 3} concentration and lowering Pu concentration are expected to further limit the amount of Pu(VI) formed.« less

Developmental phytotoxicity of metal oxide nanoparticles to Arabidopsis thaliana.

PubMed

Lee, Chang Woo; Mahendra, Shaily; Zodrow, Katherine; Li, Dong; Tsai, Yu-Chang; Braam, Janet; Alvarez, Pedro J J

2010-03-01

Phytotoxicity is an important consideration to understand the potential environmental impacts of manufactured nanomaterials. Here, we report on the effects of four metal oxide nanoparticles, aluminum oxide (nAl(2)O(3)), silicon dioxide (nSiO(2)), magnetite (nFe(3)O(4)), and zinc oxide (nZnO), on the development of Arabidopsis thaliana (Mouse-ear cress). Three toxicity indicators (seed germination, root elongation, and number of leaves) were quantified following exposure to each nanoparticle at three concentrations: 400, 2,000, and 4,000 mg/L. Among these particles, nZnO was most phytotoxic, followed by nFe(3)O(4), nSiO(2), and nAl(2)O(3), which was not toxic. Consequently, nZnO was further studied to discern the importance of particle size and zinc dissolution as toxicity determinants. Soluble zinc concentrations in nanoparticle suspensions were 33-fold lower than the minimum inhibitory concentration of dissolved zinc salt (ZnCl(2)), indicating that zinc dissolution could not solely account for the observed toxicity. Inhibition of seed germination by ZnO depended on particle size, with nanoparticles exerting higher toxicity than larger (micron-sized) particles at equivalent concentrations. Overall, this study shows that direct exposure to nanoparticles significantly contributed to phytotoxicity and underscores the need for eco-responsible disposal of wastes and sludge containing metal oxide nanoparticles.

Composition characteristics and regularities of dissolving of hydroxyapatite materials obtained in water solutions with varied content of silicate ions

NASA Astrophysics Data System (ADS)

Solonenko, A. P.

2018-01-01

Research aimed at developing new bioactive materials for the repair of defects in bone tissues, do not lose relevance due to the strengthening of the regenerative approach in medicine. From this point of view, materials based on calcium phosphates, including silicate ions, consider as one of the most promising group of substances. Methods of synthesis and properties of hydroxyapatite doped with various amounts of SiO4 4- ions are described in literature. In the present work synthesis of a solid phase in the systems Ca(NO3)2 - (NH4)2HPO4 - Na2SiO3 - NH4OH - H2O (Cca/CP = 1.70) performed with a wide range of sodium silicate additive concentration (y = CSi/CP = 0 ÷ 5). It is established that under the studied conditions at y ≥ 0.3 highly dispersed poorly crystallized apatite containing isomorphic impurities of CO3 2- and SiO4 4- precipitates in a mixture with calcium hydrosilicate and SiO2. It is shown that the resulting composites can gradually dissolve in physiological solution and initiate passive formation of the mineral component of hard tissues.

Measuring Concentrations of Dissolved Methane and Ethane and the 13 C of Methane in Shale and Till.

PubMed

Hendry, M Jim; Barbour, S Lee; Schmeling, Erin E; Mundle, Scott O C

2017-01-01

Baseline characterization of concentrations and isotopic values of dissolved natural gases is needed to identify contamination caused by the leakage of fugitive gases from oil and gas activities. Methods to collect and analyze baseline concentration-depth profiles of dissolved CH 4 and C 2 H 6 and δ 13 C-CH 4 in shales and Quaternary clayey tills were assessed at two sites in the Williston Basin, Canada. Core and cuttings samples were stored in Isojars ® in a low O 2 headspace prior to analysis. Measurements and multiphase diffusion modeling show that the gas concentrations in core samples yield well-defined and reproducible depth profiles after 31-d equilibration. No measurable oxidative loss or production during core sample storage was observed. Concentrations from cuttings and mud gas logging (including IsoTubes ® ) were much lower than from cores, but correlated well. Simulations suggest the lower concentrations from cuttings can be attributed to drilling time, and therefore their use to define gas concentration profiles may have inherent limitations. Calculations based on mud gas logging show the method can provide estimates of core concentrations if operational parameters for the mud gas capture cylinder are quantified. The δ 13 C-CH 4 measured from mud gas, IsoTubes ® , cuttings, and core samples are consistent, exhibiting slight variations that should not alter the implications of the results in identifying the sources of the gases. This study shows core and mud gas techniques and, to a lesser extent, cuttings, can generate high-resolution depth profiles of dissolved hydrocarbon gas concentrations and their isotopes. © 2016, National Ground Water Association.

In-situ arsenic remediation by aquifer iron coating: Field trial in the Datong basin, China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Xianjun; Pi, Kunfu; Liu, Yaqing

2016-01-01

In situ As removal from groundwater used for water supply has been performed in Daying village of Shanyin County where mild alkaline groundwater contains high dissolved As concentration. The objective of this study was to evaluate in situ As treatment by aquifer Fe coating technology. The groundwater in the studied aquifer contains As dominated by aqueous As(III) and low dissolved Fe(II) concentration, which are unfavorable conditions for forming Fe-oxides/hydroxides for As removal. In addition, high As(III) concentration limits As adsorption onto Fe-oxides/hydroxides. Accordingly, dissolved Fe(II) (5mM) and NaClO (5mM) were injected into the studied aquifer to form Fe-oxides/hydroxides and oxidizemore » As(III) to As(V), creating favorable conditions for As removal via adsorption and/or co-precipitation. During alternatively cycled injection of Fe(II) and NaClO, the As concentration in groundwater from the pumping well significantly decreased to below drinking water standard. The developed approach can be applied similarly in many parts of the world containing high As concentrations.« less

Pyrite oxidation in the presence of hematite and alumina: I. Batch leaching experiments and kinetic modeling calculations.

PubMed

Tabelin, Carlito Baltazar; Veerawattananun, Suchol; Ito, Mayumi; Hiroyoshi, Naoki; Igarashi, Toshifumi

2017-02-15

Pyrite is one of the most common and geochemically important sulfide minerals in nature because of its role in the redox recycling of iron (Fe). It is also the primary cause of acid mine drainage (AMD) that is considered as a serious and widespread problem facing the mining and mineral processing industries. In the environment, pyrite oxidation occurs in the presence of ubiquitous metal oxides, but the roles that they play in this process remain largely unknown. This study evaluates the effects of hematite (α-Fe 2 O 3 ) and alumina (α-Al 2 O 3 ) on pyrite oxidation by batch-reactor type experiments, surface-sensitive characterization of the oxidation layer and thermodynamic/kinetic modeling calculations. In the presence of hematite, dissolved sulfur (S) concentration dramatically decreased independent of the pH, and the formation of intermediate sulfoxy anionic species on the surface of pyrite was retarded. These results indicate that hematite minimized the overall extent of pyrite oxidation, but the kinetic model could not explain how this suppression occurred. In contrast, pyrite oxidation was enhanced in the alumina suspension as suggested by the higher dissolved S concentration and stronger infrared (IR) absorption bands of surface-bound oxidation products. Based on the kinetic model, alumina enhanced the oxidative dissolution of pyrite because of its strong acid buffering capacity, which increased the suspension pH. The higher pH values increased the oxidation of Fe 2+ to Fe 3+ by dissolved O 2 (DO) that enhanced the overall oxidative dissolution kinetics of pyrite. Copyright © 2016 Elsevier B.V. All rights reserved.

THE EFFECT OF DNOM PROPERTIES ON THE KINETICS OF OZONE DECOMPOSITION AND HYDROXYL RADICAL SCAVENGING

EPA Science Inventory

The influence of temperature, pH, alkalinity, and type and concentration of the dissolved organic matter (DOM) on the rate of ozone (O3) decomposition, O3-exposure, *OH-exposure and the ratio R ct of the concentrations of *OH and O3 has been studied. For a standardized single oz...

HYDROXYL RADICAL/OZONE RATIOS DURING OZONATION PROCESSES. II. THE EFFECT OF TEMPERATURE, PH, ALKALINITY, AND DOM PROPERTIES

EPA Science Inventory

The influence of temperature, pH, alkalinity, and type and concentration of the dissolved organic matter (DOM) on the rate of ozone (O3) decomposition, O3-exposure, .OH-exposure and the ratio Rct of the concentrations of .OH and O3 has been studied. For a standardized single ozon...

Quantitative evaluation of the effect of H2O degassing on the oxidation state of magmas

NASA Astrophysics Data System (ADS)

Lange, R. A.; Waters, L.

2014-12-01

The extent to which degassing of the H2O component affects the oxidation state of hydrous magmas is widely debated. Several researchers have examined how degassing of mixed H-C-O-S-Cl fluids may change the Fe3+/FeT ratio of various magmas, whereas our focus is on the H2O component. There are two ways that degassing of H2O by itself may cause oxidation: (1) the reaction: H2O (melt) + 2FeO (melt) = H2 (fluid) + Fe2O3 (melt), and/or (2) if dissolved water preferentially enhances the activity of ferrous vs. ferric iron in magmatic liquids. In this study, a comparison is made between the pre-eruptive oxidation states of 14 crystal-poor, jet-black obsidian samples (obtained from two Fe-Ti oxides) and their post-eruptive values (analyzed with the Wilson 1960 titration method tested against USGS standards). The obsidians are from Medicine Lake (CA), Long Valley (CA), and the western Mexican arc; all have low FeOT (1.1-2.1 wt%), rendering their Fe2+/Fe3+ ratios highly sensitive to the possible effects of substantial H2O degassing. The Fe-Ti oxide thermometer/oxybarometer of Ghiorso and Evans, (2008) gave temperatures for the 14 samples that range for 720 to 940°C and ΔNNO values of -0.9 to +1.4. With temperature known, the plagioclase-liquid hygrometer was applied and show that ≤ 6.5 wt% H2O was dissolved in the melts prior to eruption. In addition, pre-eruptive Cl and S concentrations were constrained on the basis of apatite analyses (Webster et al., 2009) and sulfur concentrations needed for saturation with pyrrhotite (Clemente et al., 2004), respectively. Maximum pre-eruptive chlorine and sulfur contents are 6000 and 200 ppm, respectively. After eruption, the rhyolites lost nearly all of their volatiles. Our results indicate no detectable change between pre- and post-eruptive Fe2+ concentrations, with an average deviation of ± 0.1 wt % FeO. Although degassing of large concentrations of S and/or Cl may affect the oxidation state of magmas, at the pre-eruptive levels in these 14 rhyolitic magmas, no effect is detected. Therefore, it can be robustly concluded that degassing of substantial amounts of the H2O component (≤ 6.5 wt%), by itself, does not induce oxidation in erupted magmas, particularly those more iron-rich than rhyolites (e.g., arc basalts).

Postperovskite phase equilibria in the MgSiO3-Al2O3 system.

PubMed

Tsuchiya, Jun; Tsuchiya, Taku

2008-12-09

We investigate high-P,T phase equilibria of the MgSiO(3)-Al(2)O(3) system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh(2)O(3)(II) phase, present calculations demonstrate that (i) dissolving Al(2)O(3) tends to decrease the postperovskite transition pressure of MgSiO(3) but the effect is not significant ( approximately -0.2 GPa/mol% Al(2)O(3)); (ii) Al(2)O(3) produces the narrow perovskite+postperovskite coexisting P,T area (approximately 1 GPa) for the pyrolitic concentration (x(Al2O3) approximately 6 mol%), which is sufficiently responsible to the deep-mantle D'' seismic discontinuity; (iii) the transition would be smeared (approximately 4 GPa) for the basaltic Al-rich composition (x(Al2O3) approximately 20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh(2)O(3)(II) with increasing the Al concentration involving small displacements of the Mg-site cations.

Postperovskite phase equilibria in the MgSiO3–Al2O3 system

PubMed Central

Tsuchiya, Jun; Tsuchiya, Taku

2008-01-01

We investigate high-P,T phase equilibria of the MgSiO3–Al2O3 system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh2O3(II) phase, present calculations demonstrate that (i) dissolving Al2O3 tends to decrease the postperovskite transition pressure of MgSiO3 but the effect is not significant (≈-0.2 GPa/mol% Al2O3); (ii) Al2O3 produces the narrow perovskite+postperovskite coexisting P,T area (≈1 GPa) for the pyrolitic concentration (xAl2O3 ≈6 mol%), which is sufficiently responsible to the deep-mantle D″ seismic discontinuity; (iii) the transition would be smeared (≈4 GPa) for the basaltic Al-rich composition (xAl2O3 ≈20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh2O3(II) with increasing the Al concentration involving small displacements of the Mg-site cations. PMID:19036928

In vitro immunotoxicology of quantum dots and comparison with dissolved cadmium and tellurium.

PubMed

Bruneau, Audrey; Fortier, Marlene; Gagne, Francois; Gagnon, Christian; Turcotte, Patrice; Tayabali, Azam; Davis, Thomas A; Auffret, Michel; Fournier, Michel

2015-01-01

The increasing use of products derived from nanotechnology has raised concerns about their potential toxicity, especially at the immunocompetence level in organisms. This study compared the immunotoxicity of cadmium sulfate/cadmium telluride (CdS/Cd-Te) mixture quantum dots (QDs) and their dissolved components, cadmium chloride (CdCl2 )/sodium telluride (NaTeO3 ) salts, and a CdCl2 /NaTeO3 mixture on four animal models commonly used in risk assessment studies: one bivalve (Mytilus edulis), one fish (Oncorhynchus mykiss), and two mammals (mice and humans). Our results of viability and phagocytosis biomarkers revealed that QDs were more toxic than dissolved metals for blue mussels. For other species, dissolved metals (Cd, Te, and Cd-Te mixture) were more toxic than the nanoparticles (NPs). The most sensitive species toward QDs, according to innate immune cells, was humans (inhibitory concentration [IC50 ] = 217 μg/mL). However, for adaptative immunity, lymphoblastic transformation in mice was decreased for small QD concentrations (EC50 = 4 μg/mL), and was more sensitive than other model species tested. Discriminant function analysis revealed that blue mussel hemocytes were able to discriminate the toxicity of QDs, Cd, Te, and Cd-Te mixture (Partial Wilk's λ = 0.021 and p < 0.0001). For rainbow trout and human cells, the immunotoxic effects of QDs were similar to those obtained with the dissolved fraction of Cd and Te mixture. For mice, the toxicity of QDs markedly differed from those observed with Cd, Te, and dissolved Cd-Te mixture. The results also suggest that aquatic species responded more differently than vertebrates to these compounds. The results lead to the recommendation that mussels and mice were most able to discriminate the effects of Cd-based NPs from the effects of dissolved Cd and Te at the immunocompetence level. © 2013 Wiley Periodicals, Inc.

Evolution of melt-vapor surface tension in silicic volcanic systems: Experiments with hydrous melts

USGS Publications Warehouse

Mangan, M.; Sisson, T.

2005-01-01

We evaluate the melt-vapor surface tension (??) of natural, water-saturated dacite melt at 200 MPa, 950-1055??C, and 4.8-5.7 wt % H2O. We experimentally determine the critical supersaturation pressure for bubble nucleation as a function of dissolved water and then solve for ?? at those conditions using classical nucleation theory. The solutions obtained give dacite melt-vapor surface tensions that vary inversely with dissolved water from 0.042 (??0.003) J m-2 at 5.7 wt% H2O to 0.060 (??0.007) J m-2 at 5.2 wt% H2O to 0.073 (??0.003) J m-2 at 4.8 wt% H2O. Combining our dacite results with data from published hydrous haplogranite and high-silica rhyolite experiments reveals that melt-vapor surface tension also varies inversely with the concentration of mafic melt components (e.g., CaO, FeOtotal, MgO). We develop a thermodynamic context for these observations in which melt-vapor surface tension is represented by a balance of work terms controlled by melt structure. Overall, our results suggest that cooling, crystallization, and vapor exsolution cause systematic changes in ?? that should be considered in dynamic modeling of magmatic processes.

Nitrogen removal from wastewater and bacterial diversity in activated sludge at different COD/N ratios and dissolved oxygen concentrations.

PubMed

Zielińska, Magdalena; Bernat, Katarzyna; Cydzik-Kwiatkowska, Agnieszka; Sobolewska, Joanna; Wojnowska-Baryła, Irena

2012-01-01

The impact of the organic carbon to nitrogen ratio (chemical oxygen demand (COD)/N) in wastewater and dissolved oxygen (DO) concentration on carbon and nitrogen removal efficiency, and total bacteria and ammonia-oxidizing bacteria (AOB) communities in activated sludge in constantly aerated sequencing batch reactors (SBRs) was determined. At DO of 0.5 and 1.5 mg O2/L during the aeration phase, the efficiency of ammonia oxidation exceeded 90%, with nitrates as the main product. Nitrification and denitrification achieved under the same operating conditions suggested the simultaneous course of these processes. The most effective nitrogen elimination (above 50%) was obtained at the COD/N ratio of 6.8 and DO of 0.5 mg O2/L. Total bacterial diversity was similar in all experimental series, however, for both COD/N ratios of 6.8 and 0.7, higher values were observed at DO of 0.5 mg O2/L. The diversity and abundance of AOB were higher in the reactors with the COD/N ratio of 0.7 in comparison with the reactors with the COD/N of 6.8. For both COD/N ratios applied, the AOB population was not affected by oxygen concentration. Amplicons with sequences indicating membership of the genus Nitrosospira were the determinants of variable technological conditions.

Effect of dissolved ozone or ferric ions on photodegradation of thiacloprid in presence of different TiO2 catalysts.

PubMed

Cernigoj, Urh; Stangar, Urska Lavrencic; Jirkovský, Jaromír

2010-05-15

Combining TiO(2) photocatalysis with inorganic oxidants (such as O(3) and H(2)O(2)) or transition metal ions (Fe(3+), Cu(2+) and Ag(+)) often leads to a synergic effect. Electron transfer between TiO(2) and the oxidant is usually involved. Accordingly, the degree of synergy could be influenced by TiO(2) surface area. With this in mind, the disappearance of thiacloprid, a neonicotinoid insecticide, was studied applying various photochemical AOPs and different TiO(2) photocatalysts. In photocatalytic ozonation experiments, synergic effect of three different TiO(2) photocatalysts was quantified. Higher surface area resulted in a more pronounced synergic effect but an increasing amount of TiO(2) did not influence the degree of the synergy. This supports the theory that the synergy is a consequence of adsorption of ozone on the TiO(2) surface. No synergy was observed in photocatalytic degradation of thiacloprid in the presence of dissolved iron(III) species performed under varied experimental conditions (concentration, age of iron(III) solution, different TiO(2) films, usage of TiO(2) slurries). This goes against the literature for different organic compounds (i.e., monuron). It indicates different roles of iron(III) in the photodegradation of different organic molecules. Moreover, TiO(2) surface area did not affect photodegradation efficiency in iron(III)-based experiments which could confirm absence of electron transfer between TiO(2) photocatalyst and iron(III). Copyright (c) 2009 Elsevier B.V. All rights reserved.

Silicate Carbonation in Supercritical CO2 Containing Dissolved H2O: An in situ High Pressure X-Ray Diffraction Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaef, Herbert T.; Miller, Quin RS; Thompson, Christopher J.

2013-06-30

Technological advances have been significant in recent years for managing environmentally harmful emissions (mostly CO2) resulting from combustion of fossil fuels. Deep underground geologic formations are emerging as reasonable options for long term storage of CO2 but mechanisms controlling rock and mineral stability in contact with injected supercritical fluids containing water are relatively unknown. In this paper, we discuss mineral transformation reactions occurring between supercritical CO2 containing water and the silicate minerals forsterite (Mg2SiO4), wollastonite (CaSiO3), and enstatite (MgSiO3). This study utilizes newly developed in situ high pressure x-ray diffraction (HXRD) and in situ infra red (IR) to examine mineralmore » transformation reactions. Forsterite and enstatite were selected as they are important minerals present in igneous and mafic rocks and have been the subject of a large number of aqueous dissolution studies that can be compared with non-aqueous fluid tests in this study. Wollastonite, classified as a pyroxenoid (similar to a pyroxene), was chosen as a suitably fast reacting proxy for examining silicate carbonation processes associated with a wet scCO2 fluid as related to geologic carbon sequestration. The experiments were conducted under modest pressures (90 to 160 bar), temperatures between 35° to 70° C, and varying concentrations of dissolved water. Under these conditions scCO2 contains up to 3,500 ppm dissolved water.« less

Characteristics of N2O production and hydroxylamine variation in short-cut nitrification SBR process.

PubMed

Hu, Bo; Ye, Junhong; Zhao, Jianqiang; Ding, Xiaoqian; Yang, Liwei; Tian, Xiaolei

2018-01-01

In order to study the characteristics of nitrous oxide (N 2 O) production and hydroxylamine (NH 2 OH) variation under oxic conditions, concentrations of NH 2 OH and N 2 O were simultaneously monitored in a short-cut nitrification sequencing batch reactor (SBR) operated with different influent ammonia concentrations. In the short-cut nitrification process, N 2 O production was increased with the increasing of ammonia concentration in influent. The maximum concentrations of dissolved N 2 O-N in the reactor were 0.11 mg/L and 0.52 mg/L when ammonia concentrations in the influent were 50 mg/L and 70 mg/L respectively. Under the low and medium ammonia load phases, the concentrations of NH 2 OH-N in the reactor were remained at a low level which fluctuated around 0.06 mg/L in a small range, and did not change with the variation of influent NH 4 + -N concentration. Based on the determination results, the half-saturation of NH 2 OH in the biochemical conversion process of NH 2 OH to NO 2 - -N was very small, and the value of 0.05 mg NH 2 OH-N/L proposed in the published literature was accurate. NH 2 OH is an important intermediate in the nitrification process, and the direct determination of NH 2 OH in the nitrification process was beneficial for revealing the kinetic process of NH 2 OH production and consumption as well as the effects of NH 2 OH on N 2 O production in the nitrification process.

Nitrous oxide production from temperate and tropical oyster species in response to nutrient loading

NASA Astrophysics Data System (ADS)

Chan, H.; Garate, M.; Moseman-Valtierra, S.

2016-02-01

Anthropogenic pollution, such as nitrogen (N), has the potential to increase greenhouse gas (GHG) emissions in marine ecosystems. Some organisms can be used as important biological indicators for GHG emissions to their environment based on their feeding habits. With large inputs of these anthropogenic pollutants, emissions of nitrous oxide (N2O), a potent GHG, can be potentially increased from temperate invertebrates, though not much is known about tropical invertebrates. Thus, we compared N2O emissions in response to N additions from the temperate oyster species Crassostrea virginica and compared it to a tropical species, Isognomon alatus, found in Puerto Rico. Oysters were exposed to two seawater treatments: (1) no nutrient addition (control) and (2) 100µM ammonium nitrate. Each treatment had 4-5 replicates. Measurements for dissolved N2O and nutrients were taken at the start of the incubation and then at two, four, and five hours by collecting water samples of each tank. Dissolved N2O concentrations were analyzed using gas chromatography. We hypothesized that the N addition treatment would produce more N2O for both Rhode Island and Puerto Rico. We found that there was no significant difference between the control and N enriched treatments for C. virginica over the short timespan, although the N enriched treatment did have a steady trend in increasing in N2O concentration over time. Further analysis is needed for the I. alatus, though we expect an increase in N2O emissions due to warmer water temperatures, which might enhance microbial metabolism and production of N2O. This differs from work previously done in a long-term experiment on C. virginica, which showed that N2O significantly in the N enriched treatment over 28-days. Our study shows that short-term pulses of N may not potentially increase N2O emissions, though further analysis is needed for longer-term exposures.

A Multi-Pumping Flow System for In Situ Measurements of Dissolved Manganese in Aquatic Systems

PubMed Central

Meyer, David; Prien, Ralf D.; Dellwig, Olaf; Waniek, Joanna J.; Schuffenhauer, Ingo; Donath, Jan; Krüger, Siegfried; Pallentin, Malte; Schulz-Bull, Detlef E.

2016-01-01

A METals In Situ analyzer (METIS) has been used to determine dissolved manganese (II) concentrations in the subhalocline waters of the Gotland Deep (central Baltic Sea). High-resolution in situ measurements of total dissolved Mn were obtained in near real-time by spectrophotometry using 1-(2-pyridylazo)-2-naphthol (PAN). PAN is a complexing agent of dissolved Mn and forms a wine-red complex with a maximum absorbance at a wavelength of 562 nm. Results are presented together with ancillary temperature, salinity, and dissolved O2 data. Lab calibration of the analyzer was performed in a pressure testing tank. A detection limit of 77 nM was obtained. For validation purposes, discrete water samples were taken by using a pump-CTD system. Dissolved Mn in these samples was determined by an independent laboratory based method (inductively coupled plasma–optical emission spectrometry, ICP-OES). Mn measurements from both METIS and ICP-OES analysis were in good agreement. The results showed that the in situ analysis of dissolved Mn is a powerful technique reducing dependencies on heavy and expensive equipment (pump-CTD system, ICP-OES) and is also cost and time effective. PMID:27916898

Overview of groundwater quality in the Piceance Basin, western Colorado, 1946--2009

USGS Publications Warehouse

Thomas, J.C.; McMahon, P.B.

2013-01-01

Groundwater-quality data from public and private sources for the period 1946 to 2009 were compiled and put into a common data repository for the Piceance Basin. The data repository is available on the web at http://rmgsc.cr.usgs.gov/cwqdr/Piceance/index.shtml. A subset of groundwater-quality data from the repository was compiled, reviewed, and checked for quality assurance for this report. The resulting dataset consists of the most recently collected sample from 1,545 wells, 1,007 (65 percent) of which were domestic wells. From those samples, the following constituents were selected for presentation in this report: dissolved oxygen, dissolved solids, pH, major ions (chloride, sulfate, fluoride), trace elements (arsenic, barium, iron, manganese, selenium), nitrate, benzene, toluene, ethylbenzene, xylene, methane, and the stable isotopic compositions of water and methane. Some portion of recharge to most of the wells for which data were available was derived from precipitation (most likely snowmelt), as indicated by δ2H [H2O] and δ18O[H2O] values that plot along the Global Meteoric Water Line and near the values for snow samples collected in the study area. Ninety-three percent of the samples were oxic, on the basis of concentrations of dissolved oxygen that were greater than or equal to 0.5 milligrams per liter. Concentration data were compared with primary and secondary drinking-water standards established by the U.S. Environmental Protection Agency. Constituents that exceeded the primary standards were arsenic (13 percent), selenium (9.2 percent), fluoride (8.4 percent), barium (4.1 percent), nitrate (1.6 percent), and benzene (0.6 percent). Concentrations of toluene, xylenes, and ethylbenzene did not exceed standards in any samples. Constituents that exceeded the secondary standard were dissolved solids (72 percent), sulfate (37 percent), manganese (21 percent), iron (16 percent), and chloride (10 percent). Drinking-water standards have not been established for methane, which was detected in 24 percent of samples. Methane concentrations were greater than or equal to 1 milligram per liter in 8.5 percent of samples. Methane isotopic data for samples collected primarily from domestic wells in Garfield County indicate that methane in samples with relative high methane concentrations were derived from both biogenic and thermogenic sources. Many of the constituents that exceeded standards, such as arsenic, fluoride, iron, and manganese, were derived from rock and sediment in aquifers. Elevated nitrate concentrations were most likely derived from human sources such as fertilizer and human or animal waste. Information about the geologic unit or aquifer in which a well was completed generally was not provided by data sources. However, limited data indicate that Quaternary deposits in Garfield and Mesa Counties, the Wasatch Formation in Garfield County, and the Green River Formation in Rio Blanco County had some of the highest median concentrations of selected constituents. Variations in concentration with depth could not be evaluated because of the general lack of well-depth and water-level data. Concentrations of several important constituents, such as arsenic, manganese, methane, and nitrate, were related to concentrations of dissolved oxygen. Concentrations of arsenic, manganese, and methane were significantly higher in groundwater with low dissolved-oxygen concentrations than in groundwater with high dissolved-oxygen concentrations. In contrast, concentrations of nitrate were significantly higher in groundwater with high dissolved-oxygen concentrations than in groundwater with low dissolved-oxygen concentrations. These results indicate that measurements of dissolved oxygen may be a useful indicator of groundwater vulnerability to some human-derived contaminants and enrichment from some natural constituents. Assessing such a large and diverse dataset as the one available through the repository poses unique challenges for reporting on groundwater quality in the study area. The repository contains data from several studies that differed widely in purpose and scope. In addition to this variability in available data, gaps exist spatially, temporally, and analytically in the repository. For example, groundwater-quality data in the repository were not evenly distributed throughout the study area. Several key water-quality constituents or indicators, such as dissolved oxygen, were underrepresented in the repository. Ancillary information, such as well depth, depth to water, and the geologic unit or aquifer in which a well was completed, was missing for more than 50 percent of samples. Future monitoring could avoid several limitations of the repository by making relatively minor changes to sample- collection and data-reporting protocols. Field measurements for dissolved oxygen could be added to sampling protocols, for example. Information on well construction and the geologic unit or aquifer in which a well was completed should be part of the water-quality dataset. Such changes would increase the comparability of data from different monitoring programs and also add value to each program individually and to that of the regional dataset as a whole. Other changes to monitoring programs could require greater resources, such as sampling for a basic set of constituents that is relevant to major water-quality issues in the regional study area. Creation of such a dataset for the regional study area would help to provide the kinds of information needed to characterize background conditions and the spatial and temporal variability in constituent concentrations associated with those conditions. Without such information, it is difficult to identify departures from background that might be associated with human activities.

The Effect of CaO on Gas/Slag/Matte/Tridymite Equilibria in Fayalite-Based Copper Smelting Slags at 1473 K (1200 °C) and P(SO2) = 0.25 Atm

NASA Astrophysics Data System (ADS)

Fallah-Mehrjardi, Ata; Hayes, Peter C.; Jak, Evgueni

2018-04-01

Fundamental experimental studies have been undertaken to determine the effect of CaO on the equilibria between the gas phase (CO/CO2/SO2/Ar) and slag/matte/tridymite phases in the Cu-Fe-O-S-Si-Ca system at 1473 K (1200 °C) and P(SO2) = 0.25 atm. The experimental methodology developed in the Pyrometallurgy Innovation Centre was used. New experimental data have been obtained for the four-phase equilibria system for fixed concentrations of CaO (up to 4 wt pct) in the slag phase as a function of copper concentration in matte, including the concentrations of dissolved sulfur and copper in slag, and Fe/SiO2 ratios in slag at tridymite saturation. The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input to optimize the thermodynamic database for the copper-containing multi-component multi-phase system.

Removal of H 2S via an iron catalytic cycle and iron sulfide precipitation in the water column of dead end tributaries

NASA Astrophysics Data System (ADS)

Ma, Shufen; Noble, Abigail; Butcher, Derek; Trouwborst, Robert E.; Luther, George W., III

2006-11-01

The oxidation and precipitation of H 2S were investigated in Torquay Canal and Bald Eagle Creek, two tributaries of northern Rehoboth Bay, one of the Delaware Inland Bays. These man-made dead end canals develop seasonal anoxia and have been the site of past fish kills and harmful algal blooms. The canals have multiple holes over 5.5 m deep compared to an average low tide depth of 2 m. In situ determination for dissolved O 2, H 2S and other Fe and S redox species were conducted with a solid-state Au/Hg microelectrode in 2003 and 2004. Laboratory analyses of discrete samples were also performed to measure dissolved and particulate Fe, Mn, and S 8 to follow the seasonal dynamics of O, S, Fe and Mn redox species. Our results indicate that the water in the holes becomes stratified with O 2 decreasing with depth and H 2S increasing with depth. Dissolved Fe was as high as 30 μM whereas dissolved Mn was only 0.2 μM in the water column, indicating that Fe is the dominant metal involved in S redox cycling and precipitation. In surface oxic waters, the dominant form of Fe was particulate Fe(III) (oxy)hydroxides. When seasonal anoxia developed, Fe(III) (oxy)hydroxides were reduced by H 2S to Fe(II) at the oxic-anoxic interface. The Fe(II) reduced from particulate Fe can be re-oxidized to Fe(III) by O 2 above and at the interface to form a catalytic cycle to oxidize H 2S. Elemental S is the predominant oxidation product and was as high as 30 μM level (as S 0) at the interface. When the system was stable, the Fe catalytic cycle prevented H 2S from being released into surface waters during seasonal anoxia. However, when storms came, the water column was overturned and H 2S was released to the surface water. The reaction rates for the Fe catalytic cycle are not fast enough and the concentration of Fe was not high enough to regulate the high concentration of H 2S in surface waters during storm and mixing events.

Modeling of Nitrous Oxide Production from Nitritation Reactors Treating Real Anaerobic Digestion Liquor.

PubMed

Wang, Qilin; Ni, Bing-Jie; Lemaire, Romain; Hao, Xiaodi; Yuan, Zhiguo

2016-04-29

In this work, a mathematical model including both ammonium oxidizing bacteria (AOB) and heterotrophic bacteria (HB) is constructed to predict N2O production from the nitritation systems receiving the real anaerobic digestion liquor. This is for the first time that N2O production from such systems was modeled considering both AOB and HB. The model was calibrated and validated using experimental data from both lab- and pilot-scale nitritation reactors. The model predictions matched the dynamic N2O, ammonium, nitrite and chemical oxygen demand data well, supporting the capability of the model. Modeling results indicated that HB are the dominant contributor to N2O production in the above systems with the dissolved oxygen (DO) concentration of 0.5-1.0 mg O2/L, accounting for approximately 75% of N2O production. The modeling results also suggested that the contribution of HB to N2O production decreased with the increasing DO concentrations, from 75% at DO = 0.5 mg O2/L to 25% at DO = 7.0 mg O2/L, with a corresponding increase of the AOB contribution (from 25% to 75%). Similar to HB, the total N2O production rate also decreased dramatically from 0.65 to 0.25 mg N/L/h when DO concentration increased from 0.5 to 7.0 mg O2/L.

Rates of arsenopyrite oxidation by oxygen and Fe(III) at pH 1.8-12.6 and 15-45 degrees C.

PubMed

Yu, Yunmei; Zhu, Yongxuan; Gao, Zhenmin; Gammons, Christopher H; Li, Denxian

2007-09-15

The oxidation rate of arsenopyrite by dissolved oxygen was measured using a mixed flow reactor at dissolved O2 concentrations of 0.007-0.77 mM, pH 1.8-12.6, and temperatures of 15-45 degrees C. As(III) was the dominant redox species (>75%) in the experimental system, and the As(III)/As(V) ratio of effluent waters did not change with pH. The results were used to derive the following rate law expression (valid between pH 1.8 and 6.4): r = 10((-2211 +/- 57)T) (mO2)(0.45 +/- 0.05), where r is the rate of release of dissolved As in mol m(-2) s(-1) and T is in Kelvin. Activation energies (Ea) for oxidation of arsenopyrite by 02 at pH 1.8 and 5.9 are 43 and 57 kJ/mol, respectively, and they compare to an Ea value of 16 kJ/mol for oxidation by Fe(III) at pH 1.8. Apparent As release rates passed through a minimum in the pH range 7-8, which may have been due to oxidation of Fe2+ to hydrous ferric oxide (HFO) with attenuation of dissolved As onto the freshly precipitated HFO.

Hydrologic control on redox and nitrogen dynamics in a peatland soil.

PubMed

Rubol, Simonetta; Silver, Whendee L; Bellin, Alberto

2012-08-15

Soils are a dominant source of nitrous oxide (N(2)O), a potent greenhouse gas. However, the complexity of the drivers of N(2)O production and emissions has hindered our ability to predict the magnitude and spatial dynamics of N(2)O fluxes. Soil moisture can be considered a key driver because it influences oxygen (O(2)) supply, which feeds back on N(2)O sources (nitrification versus denitrification) and sinks (reduction to dinitrogen). Soil water content is directly linked to O(2) and redox potential, which regulate microbial metabolism and chemical transformations in the environment. Despite its importance, only a few laboratory studies have addressed the effects of hydrological transient dynamics on nitrogen (N) cycling in the vadose zone. To further investigate these aspects, we performed a long term experiment in a 1.5 m depth soil column supplemented by chamber experiments. With this experiment, we aimed to investigate how soil moisture dynamics influence redox sensitive N cycling in a peatland soil. As expected, increased soil moisture lowered O(2) concentrations and redox potential in the soil. The decline was more severe for prolonged saturated conditions than for short events and at deep than at the soil surface. Gaseous and dissolved N(2)O, dissolved nitrate (NO(3)(-)) and ammonium (NH(4)(+)) changed considerably along the soil column profile following trends in soil O(2) and redox potential. Hot spots of N(2)O concentrations corresponded to high variability in soil O(2) in the upper and lower parts of the column. Results from chamber experiments confirmed high NO(3)(-) reduction potential in soils, particularly from the bottom of the column. Under our experimental conditions, we identified a close coupling of soil O(2) and N(2)O dynamics, both of which lagged behind soil moisture changes. These results highlight the relationship among soil hydrologic properties, redox potential and N cycling, and suggest that models working at a daily scale need to consider soil O(2) dynamics in addition to soil moisture dynamics to accurately predict patterns in N(2)O fluxes. Copyright © 2012 Elsevier B.V. All rights reserved.

Groundwater nitrate reduction versus dissolved gas production: A tale of two catchments.

PubMed

McAleer, E B; Coxon, C E; Richards, K G; Jahangir, M M R; Grant, J; Mellander, Per E

2017-05-15

At the catchment scale, a complex mosaic of environmental, hydrogeological and physicochemical characteristics combine to regulate the distribution of groundwater and stream nitrate (NO 3 - ). The efficiency of NO 3 - removal (via denitrification) versus the ratio of accumulated reaction products, dinitrogen (excess N 2 ) & nitrous oxide (N 2 O), remains poorly understood. Groundwater was investigated in two well drained agricultural catchments (10km 2 ) in Ireland with contrasting subsurface lithologies (sandstone vs. slate) and landuse. Denitrification capacity was assessed by measuring concentration and distribution patterns of nitrogen (N) species, aquifer hydrogeochemistry, stable isotope signatures and aquifer hydraulic properties. A hierarchy of scale whereby physical factors including agronomy, water table elevation and permeability determined the hydrogeochemical signature of the aquifers was observed. This hydrogeochemical signature acted as the dominant control on denitrification reaction progress. High permeability, aerobic conditions and a lack of bacterial energy sources in the slate catchment resulted in low denitrification reaction progress (0-32%), high NO 3 - and comparatively low N 2 O emission factors (EF 5g 1). In the sandstone catchment denitrification progress ranged from 4 to 94% and was highly dependent on permeability, water table elevation, dissolved oxygen concentration solid phase bacterial energy sources. Denitrification of NO 3 - to N 2 occurred in anaerobic conditions, while at intermediate dissolved oxygen; N 2 O was the dominant reaction product. EF 5g 1 (mean: 0.0018) in the denitrifying sandstone catchment was 32% less than the IPCC default. The denitrification observations across catchments were supported by stable isotope signatures. Stream NO 3 - occurrence was 32% lower in the sandstone catchment even though N loading was substantially higher than the slate catchment. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Sustaining 1,2-Dichloroethane Degradation in Nanoscale Zero-Valent Iron induced Fenton system by using Sequential H2O2 Addition at Natural pH

NASA Astrophysics Data System (ADS)

Phenrat, T.; Le, T. S. T.

2017-12-01

1,2-Dichloroethane (1,2-DCA) is a prevalent subsurface contaminant found in groundwater and soil around the world. Nanoscale zero-valent iron (NZVI) is a promising in situ remediation agent for chlorinated organics. Nevertheless, 1,2-DCA is recalcitrant to reductive dechlorination using NZVI. Chemical oxidation using Fenton's reaction with conventional Fe2+ is a valid option for 1,2-DCA remediation with a major technical challenge, i.e. aquifer acidification is needed to maintain Fe2+ for catalytic reaction. In this work, NZVI Fenton's process at neutral pH was applied to degrade 1,2-DCA at high concentration (2,000 mg/L) representing dissolved 1,2-DCA concentration close to non-aqueous phase liquid source zone. Instead of using acidification to maintain dissolved Fe2+ concentration, NZVI Fenton's process is self-catalytic based on oxidative dissolution of NZVI in the present of H2O2. Interfacial H+ is produced at NZVI surface to provide appropriate local pH which continuously releases Fe2+ for Fenton's reaction. Approximately, 87% of 1,2-DCA was degraded at neutral pH with the pseudo first-order rate constant of 0.98 hour-1 using 10 g/L of NZVI and 200 mM of H2O2. However, the reaction was prohibited quickly within 3 hours presumably due to the rapid depletion of H2O2. The application of sequential H2O2 addition provided a better approach to prevent rapid inhibition via controlling the H2O2 concentration in the system to be sufficient but not excess, thus resulting in the higher degradation efficiency (the pseudo first-order rate constant of 0.49 hour-1 and 99 % degradation in 8 hours). Using NZVI with sequential H2O2 addition was also successful in degrading 1,2-DCA sorbed on to soil, yielding 99% removal of 1,2-DCA within 16 hours at the rate constant of 0.23 hour-1, around two times slower than in the system without soil presumably due to rate-limited 1,2-DCA desorption from soil. Mechanistic understanding of how sequential addition of H2O2, in comparison to the simultaneous H2O2 addition, can sustain oxidative degradation of 1,2-DCA was also proposed in addition to the investigation of NZVI reusability in three consecutive 1, 2-DCA degradation cycles.

Dissolution Flowsheet for High Flux Isotope Reactor Fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daniel, W. E.; Rudisill, T. S.; O'Rourke, P. E.

2016-09-27

As part of the Spent Nuclear Fuel (SNF) processing campaign, H-Canyon is planning to begin dissolving High Flux Isotope Reactor (HFIR) fuel in late FY17 or early FY18. Each HFIR fuel core contains inner and outer fuel elements which were fabricated from uranium oxide (U 3O 8) dispersed in a continuous Al phase using traditional powder metallurgy techniques. Fuels fabricated in this manner, like other SNF’s processed in H-Canyon, dissolve by the same general mechanisms with similar gas generation rates and the production of H 2. The HFIR fuel cores will be dissolved and the recovered U will be down-blendedmore » into low-enriched U. HFIR fuel was previously processed in H-Canyon using a unique insert in both the 6.1D and 6.4D dissolvers. Multiple cores will be charged to the same dissolver solution maximizing the concentration of dissolved Al. The objective of this study was to identify flowsheet conditions through literature review and laboratory experimentation to safely and efficiently dissolve the HFIR fuel in H-Canyon. Laboratory-scale experiments were performed to evaluate the dissolution of HFIR fuel using both Al 1100 and Al 6061 T6 alloy coupons. The Al 1100 alloy was considered a representative surrogate which provided an upper bound on the generation of flammable (i.e., H 2) gas during the dissolution process. The dissolution of the Al 6061 T6 alloy proceeded at a slower rate than the Al 1100 alloy, and was used to verify that the target Al concentration in solution could be achieved for the selected Hg concentration. Mass spectrometry and Raman spectroscopy were used to provide continuous monitoring of the concentration of H 2 and other permanent gases in the dissolution offgas, allowing the development of H 2 generation rate profiles. The H 2 generation rates were subsequently used to evaluate if a full HFIR core could be dissolved in an H-Canyon dissolver without exceeding 60% of the calculated lower flammability limit (LFL) for H 2 at a given Hg concentration. Complete dissolution of the Al 1100 and Al 6061 T6 alloys up to a final Al concentration of 2 M was obtained using a 7 M HNO 3 solution containing a 0.002 M Hg catalyst. However, following the dissolutions, solids were observed in the solution. The solids were amorphous, but likely originated from the Si present in the alloys. No crystalline materials, such as Al(NO 3) 3 were observed. During the course of the dissolution experiments, it was determined that delaying the addition of Hg once the HNO 3 solution reached the boiling point can reduce the total offgas and H 2 generation rates. The delay in starting the Hg addition is not necessary for HFIR fuel dissolution, but could be useful in other research reactor dissolution campaigns. The potential to generate flammable concentrations of H 2 in the offgas during a HFIR fuel dissolution was evaluated using the experimental data. The predicted H 2 concentration in the dissolver offgas stream was compared with 60% of the calculated H 2 LFL at 200 °C using several prototypical experiments. The calculations showed that a full HFIR core can be dissolved using nominally 0.002 M Hg to catalyze the dissolution. The margin between the predicted H 2 concentration and the calculated LFL was greater when the solution was allowed to boil for 45 min prior to initiating the Hg addition. When the Hg was increased to 0.004 M, the predicted H 2 concentration exceeded the calculated LFL early in the dissolution. The dissolution experiments also demonstrated that additional Hg (beyond the initial 0.002 M) could be added as the Al concentration increases. The ability to add more Hg during a HFIR fuel dissolution could be beneficial if slow dissolution rates are observed at high Al concentrations. Experimental data were used to demonstrate that the predicted H 2 concentration in a dissolver was below 60% of the calculated LFL at 200 °C when 0.004 M Hg was used to catalyze the dissolution if the Al concentration is conservatively greater than 0.5 M. Data also show that the Hg concentration during a HFIR fuel dissolution can be increased from 0.002 to 0.008 M at an Al concentration of 1.3 M.« less

Gene transcription patterns and energy reserves in Daphnia magna show no nanoparticle specific toxicity when exposed to ZnO and CuO nanoparticles.

PubMed

Adam, Nathalie; Vergauwen, Lucia; Blust, Ronny; Knapen, Dries

2015-04-01

There is still a lot of contradiction on whether metal ions are solely responsible for the observed toxicity of ZnO and CuO nanoparticles to aquatic species. While most experiments have studied nanoparticle effects at organismal levels (e.g. mortality, reproduction), effects at lower levels of biological organization may clarify the role of metal ions, nanoparticles and nanoparticle aggregates. In this study, the effect of ZnO and CuO nanoparticles was tested at two lower levels: energy reserves and gene transcription and compared with zinc and copper salts. Daphnia magna was exposed during 96h to 10% immobilization concentrations of all chemicals, after which daphnids were sampled for determination of glycogen, lipid and protein concentration and for a differential gene transcription analysis using microarray. The dissolved, nanoparticle and aggregated fraction in the medium was characterized. The results showed that ZnO nanoparticles had largely dissolved directly after addition to the test medium. The CuO nanoparticles mostly formed aggregates, while only a small fraction dissolved. The exposure to zinc (both nano and metal salt) had no effect on the available energy reserves. However, in the copper exposure, the glycogen, lipid and protein concentration in the exposed daphnids was lower than in the unexposed ones. When comparing the nanoparticle (ZnO or CuO) exposed daphnids to the metal salt (zinc or copper salt) exposed daphnids, the microarray results showed no significantly differentially transcribed gene fragments. The results indicate that under the current exposure conditions the toxicity of ZnO and CuO nanoparticles to D. magna is solely caused by toxic metal ions. Copyright © 2015 Elsevier Inc. All rights reserved.

Hydrogen peroxide measurements in recreational marine bathing waters in Southern California, USA.

PubMed

Clark, Catherine D; De Bruyn, Warren J; Hirsch, Charlotte M; Jakubowski, Scott D

2010-04-01

Hydrogen peroxide (H(2)O(2)) was measured in the surf zone at 13 bathing beaches in Southern California, USA. Summer dry season concentrations averaged 122 +/- 38 nM with beaches with tide pools having lower levels (50-90 nM). No significant differences were observed for ebb waters at a salt marsh outlet vs. a beach (179 +/- 20 vs. 163 +/- 26 nM), and between ebb and flood tides at one site (171 +/- 24 vs. 146 +/- 42 nM). H(2)O(2) levels showed little annual variation. Diel cycling was followed over short (30 min; 24 h study) and long (d) time scales, with maximum afternoon concentration = 370 nM and estimated photochemical production rate of 44 nM h(-1). There was no correlation between the absorbance coefficient at 300 nm (used as a measure of chromophoric dissolved organic matter (CDOM) levels) and H(2)O(2). H(2)O(2) concentrations measured in this study are likely sufficient to inhibit fecal indicator bacteria in marine recreational waters through indirect photoinactivation. Copyright (c) 2009 Elsevier Ltd. All rights reserved.

Assessment of the toxic potential of engineered metal oxide nanomaterials using an acellular model: citrated rat blood plasma.

PubMed

Gormley, Patrick Thomas; Callaghan, Neal Ingraham; MacCormack, Tyson James; Dieni, Christopher Anthony

2016-10-01

Citrated Sprague-Dawley rat blood plasma was used as a biologically relevant exposure medium to assess the acellular toxic potential of two metal oxide engineered nanomaterials (ENMs), zinc oxide (nZnO), and cerium oxide (nCeO 2 ). Plasma was incubated at 37 °C for up to 48 h with ENM concentrations ranging between 0 and 200 mg/L. The degree of ENM-induced oxidation was assessed by assaying for reactive oxygen species (ROS) levels using dichlorofluorescein (DCF), pH, ferric reducing ability of plasma (FRAP), lipase activity, malondialdehyde (MDA), and protein carbonyls (PC). Whereas previous in vitro studies showed linear-positive correlations between ENM concentration and oxidative damage, our results suggested that low concentrations were generally pro-oxidant and higher concentrations appeared antioxidant or protective, as indicated by DCF fluorescence trends. nZnO and nCeO 2 also affected pH in a manner dependent on concentration and elemental composition; higher nZnO concentrations maintained a more alkaline pH, while nCeO 2 tended to decrease pH. No other biomarkers of oxidative damage (FRAP, MDA, PC, lipase activity) showed changes at any ENM concentration or time-point tested. Differential dissolution of the two ENMs was also observed, where as much as ∼31.3% of nZnO was instantaneously dissolved to Zn 2+  and only negligible nCeO 2 was degraded. The results suggest that the direct oxidative potential of nZnO and nCeO 2 in citrated rat blood plasma is low, and that a physiological or immune response is needed to generate appreciable damage biomarkers. The data also highlight the need for careful consideration when selecting a model for assessing ENM toxicity.

Survival, development, and growth of fall Chinook salmon embryos, alevin, and fry exposed to variable thermal and dissolved oxygen regimes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geist, David R.; Abernethy, Cary S.; Hand, Kristine D.

2006-11-15

Some fall Chinook salmon (Oncorhynchus tshawytscha) initiate spawning in the Snake River downstream of Hells Canyon Dam at temperatures that exceed 13?C and at intergravel dissolved oxygen concentrations that are less than 8 mg O2/L. Although water temperature declines and dissolved oxygen increases soon after spawning, these temperature and dissolved oxygen levels do not meet the water quality standards established by the states of Oregon and Idaho for salmonid spawning. Our objective was to determine if temperatures from 13 to 17 C and dissolved oxygen levels from 4 to greater than 8 mg O2/L during the first 40 days ofmore » incubation followed by declining temperature and rising dissolved oxygen affected survival, development, and growth of Snake River fall Chinook salmon embryos, alevins, and fry. During the first 40 days of incubation, temperatures were adjusted downward approximately 0.2 C/day and oxygen was increased in increments of 2 mg O2/L to mimic the thermal and oxygen regime of the Snake River where these fish spawn. At 40 days post-fertilization, embryos were moved to a common exposure regime that followed the thermal and dissolved oxygen profile of the Snake River through emergence. Mortality of fall Chinook salmon embryos increased markedly at initial incubation temperatures equal to or greater than 17?C, and a rapid decline in survival occurred between 16.5 C and 17 C, with no significant difference in survival at temperatures less than or equal to 16.5 C. Initial dissolved oxygen levels as low as 4 mg O2/L over a range of initial temperatures from 15 to 16.5 C did not affect embryo survival to emergence. There were no significant differences across the range of initial temperature exposures for alevin and fry size at hatch and emergence. The number of days from fertilization to eyed egg, hatch, and emergence was highly related to temperature and dissolved oxygen; it took from 6 to 10 days longer to reach hatch at 4 mg O2/L than at saturation and up to 24 days longer to reach emergence. In contrast, within each dissolved oxygen treatment, it took about 20 days longer to reach hatch at 13 C than at 16.5 C (no data for 17 C) and up to 41 days longer to reach emergence. Overall, this study indicates that exposure to water temperatures up to 16.5 C will not have deleterious impacts on survival or growth from egg to emergence if temperatures decline at a rate of greater than or equal to 0.2 C/day following spawning. Although fall Chinook salmon survived low initial dissolved oxygen levels, the delay in emergence could have significant long-term effects on their survival. Thus, an exemption to the state water quality standards for temperature but not oxygen may be warranted in the Snake River where fall Chinook salmon spawn.« less

Hydrogen concentration in plagioclaes as a hygrometer of magmas: Approaches from melt inclusion analyses and hydrous melting experiments

NASA Astrophysics Data System (ADS)

Hamada, M.; Ushioda, M.; Fujii, T.; Takahashi, E.

2012-12-01

Plagioclase is one of the nominally anhydrous minerals (NAMs) which accommodates hundreds wt. ppm of hydrogen. Hydrogen in igneous plagioclase (OH) can act as a proxy of dissolved H2O in silicate melt. In order to use it as a practical hygrometer of magmas, we studied partitioning of hydrogen between plagioclase and basaltic melt dis-solving H2O (0.3˜5.5 wt.%) by two approaches: analyses of plagioclase-hosted melt inclusions (H2O≈0.3 wt.%) from mid-ocean ridge basalt (MORB) and hydrogen partitioning experiments between An96 plagioclase and hydrous basaltic melt (0.8 wt.%≦H2O≦5.5 wt.%) at 0.35 GPa. Concentration hydrogen in plagioclase and concentration of H2O in basaltic glasses were analyzed by infrared spectroscopy. As a first series of this study, plagioclase-hosted melt inclusions in MORB (50.5% SiO2, 15.1% Al2O3, 7.4% MgO) from the Rodriguez triple junction in the Indian Ocean were analyzed. The hydrogen concentration of plagioclase is less than 50 wt. ppm water, and no correlation between hydrogen concentration and anorthite content is recognized. Average H2O concentrations in melt inclusions is 0.3 wt.%. Therefore, apparent partition coefficient of hydrogen between plagioclase and melt is ≈ 0.01 in molar basis. As a second series of this study, hydrous melting experiments of arc basaltic magma were performed at 350 MPa using internally-heated pressure vessel. Starting material was hydrous glass (0.8 wt.%≦H2O≦5.5 wt.%) of an undifferentiated rock from Miyakejima volcano, a frontal-arc volcano in Izu-arc (MTL rock: 50.5% SiO2, 18.1% Al2O3, 4.9% MgO). A grain of Ca-rich plagioclase (≈1 mg, about An96) and 10 mg of powdered glasses were sealed in Au80Pd20 alloy capsule, and then kept at temperature at around the liquidus. Liquidus phase of MTL rock at 350 MPa is always plagioclase with 0 to 5.5 wt.% H2O in melt, and therefore, a grain of plagioclase and hydrous melt were nearly in equilibrium. Oxygen fugacity (fO2) during the melting experiments was not controlled, which was estimated to be 3 log unit above Ni-NiO buffer. Experiments were quenched after 24 hours, long enough to attain equi-librium partitioning of hydrogen between plagioclase and melt. Combining two series of study, we formulated empirical equation to correlate hydrogen concentration in plagioclase and H2O concentration in melt as: Hydrogen in plagioclase (wt. ppm water) ≈ 94.3×√(H2O in melt, wt.%). We also determined partition coefficient of hydrogen between plagioclase and basaltic melt to be 0.01±0.005 under H2O-poor conditions (≤150 wt. ppm water in plagioclase, ≤2 wt.% H2O in melt) and to be 0.008±0.002 under H2O-rich conditions (≥150 wt. ppm water in plagioclase, ≥2 wt.% H2O in melt). Slight decrease in hydrogen partitioning with increasing H2O can be related to change in hydrogen site in crystal structure of plagioclase (possibly tetrahedral sites). Peak position of infrared absorbance spectra lies at 3200-3400 cm-1 under H2O-poor condition and at 3600 cm-1 under H2O-rich condition, suggesting expansion of O-H…O bond length with increasing H2O.

N-nitrosodimethylamine and trihalomethane formation and minimisation in Southeast Queensland drinking water.

PubMed

Knight, Nicole; Watson, Kalinda; Farré, Maria José; Shaw, Glen

2012-07-01

This study assesses the prevalence of disinfection by-product (DBP) precursors in some Southeast Queensland drinking water sources by conducting formation potential experiments for the four regulated trihalomethanes (THMs), and the potent carcinogen, N-nitrosodimethylamine (NDMA). NDMA formation potentials were consistently low (<5-21 ng/L), and total THM (tTHM) formation potentials were consistently below the Australian Drinking Water Guideline (250 μg/L). NDMA concentration of finished drinking waters was also monitored and found to be <5 ng/L in all cases. The effect of coagulation and advanced oxidation on the formation of NDMA and THMs is also reported. UV/H(2)O(2) pre-treatment was effective in producing water with very low THMs concentrations, and UV irradiation was an effective method for NDMA degradation. H(2)O(2) was not required for the observed NDMA degradation to occur. Coagulation using alum, ferric chloride or poly(diallyldimethylammonium chloride) (polyDADMAC) was ineffective in removing DBPs precursors from the source water studied, irrespective of the low dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) attained. Rather, coagulation with polyDADMAC caused an increase in NDMA formation potential upon chloramination, and all coagulants led to an increased tTHM formation potential upon chlorination due to the high bromide concentration of the source water studied.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Seung Min; Knight, Travis W.; Voit, Stwart L.

The solid solution of (U1-yFPy)O- 2±x, has the same fluorite structure as UO 2±x lambda, and the lattice parameter is affected by dissolved fission product and oxygen concentrations. We investigated the relation between the lattice parameter and the concentrations of neodymium and oxygen in the fluorite structure of (U 1-yNd y)O 2±x using X-ray diffraction. Moreover, the lattice parameter behavior in the (U 1-yNd y)O 2±x, solid solution shows a linear change as a function of the oxygen-to-metal ratio and solubility of neodymium. The lattice parameter depends on the radii of ions forming the fluorite structure and also can bemore » expressed by a particular rule (modified Vegard's law). Furthermore, the numerical analyses of the lattice parameters for the stoichiometric and nonstoichionietric solid solutions were conducted, and the lattice parameter model for the (U1-yNdy)O 2±x, solid solution was assessed. There is a very linear relationship between the lattice parameter and the Nd and O concentration for the stoichiometry and nonstoichiometry of the (U 1-yNd y)O 2±x solid solution was verified.« less

Nitrous oxide fluxes from tree stems of temperate forests

NASA Astrophysics Data System (ADS)

Wen, Yuan; Corre, Marife D.; Rachow, Christine; Veldkamp, Edzo

2017-04-01

Although trees are recognized as conduits of soil-generated N2O, little is known about N2O fluxes from mature trees under field conditions and thier contributions to total forest N2O fluxes. Here, we quantified in situ stem N2O fluxes from mature alder trees on poorly-drained soil and mature beech and spruce trees on well-drained soils in Solling, Germany from March to October 2015. Soil N2O fluxes, soil N2O concentrations at 40-cm depth, and soil and climatic variables known to influence N2O fluxes were also measured concurrently with the stem N2O fluxes. Alder, beech and spruce consistently emitted N2O via stems and all displayed higher emission rates in summer than in spring and in autumn. Stem N2O fluxes from alder stand were higher than those from beech and spruce stands (P < 0.01), which was attributed to the presence of aerenchyma and lenticels as well as higher soil water content and soil C and N availability in the alder stand (P < 0.01-0.05). The correlations of stem N2O fluxes from alder with soil N2O fluxes, soil N2O concentrations, soil and air temperature and vapor pressure deficit (R = 0.60 - 0.90, P < 0.01-0.05) suggest that N2O transport in alder was facilitated by a combination of passive gas diffusion through aerenchyma and active transport of dissolved N2O through sap flow. In the beech and spruce stands, correlations of stem N2O fluxes with soil and air temperature and vapor pressure deficit (R = 0.57 - 0.78, P < 0.01-0.07) suggest that active transport of dissolved N2O via xylem sap was the major mechanism for stem N2O emissions in upland trees. Stem N2O fluxes represented 8-11% of the total (soil + stem) N2O fluxes in the spruce and beech stands whereas in the alder stand, with its large soil N2O emission, stem emission contributed only 1% of the total flux. Our results suggest that the relative contribution of tree-mediated N2O fluxes is more important in upland trees than in wetland trees.

A review of the contrasting behavior of two magmatic volatiles: Chlorine and carbon dioxide

USGS Publications Warehouse

Lowenstern, J. B.

2000-01-01

Chlorine (Cl) and carbon dioxide (CO2) are common magmatic volatiles with contrasting behaviors. CO2 solubility increases with pressure whereas Cl solubility shows relatively little pressure or temperature effect. CO2 speciation changes with silicate melt composition, dissolving as carbonate in basaltic magmas and molecular CO2 in more silicic compositions. In H2O-bearing systems, the strongly non-ideal behavior of alkali chlorides causes unmixing of the volatile phase to form a H2O-rich vapor and a hydrosaline phase with important implications for the maximum concentration of Cl in magmas. Addition of CO2 to magma hastens immiscibility at crustal pressures (<500 MPa), inducing the formation of CO2-rich vapors and Cl-rich hydrosaline melts. (C) 2000 Elsevier Science B.V. All rights reserved.Chlorine (Cl) and carbon dioxide (CO2) are common magmatic volatiles with contrasting behaviors. CO2 solubility increases with pressure whereas Cl solubility shows relatively little pressure or temperature effect. CO2 speciation changes with silicate melt composition, dissolving as carbonate in basaltic magmas and molecular CO2 in more silicic compositions. In H2O-bearing systems, the strongly non-ideal behavior of alkali chlorides causes unmixing of the volatile phase to form a H2O-rich vapor and a hydrosaline phase with important implications for the maximum concentration of Cl in magmas. Addition of CO2 to magma hastens immiscibility at crustal pressures (<500 MPa), inducing the formation of CO2-rich vapors and Cl-rich hydrosaline melts.

Simultaneous and continuous measurements of dissolved CO2, CH4, N2O and CO in rivers using Fourier-Transform-InfraRed (FTIR) spectrometry

NASA Astrophysics Data System (ADS)

Warneke, Thorsten; Müller, Denise; Caldow, Christopher; Rixen, Tim; Notholt, Justus

2015-04-01

We have coupled a Fourier-Transform InfraRed (FTIR) trace gas analyser to an equilibrator, which allows the simultaneous and continuous measurement of dissolved CO2, CH4, N2O and CO in water. The FTIR-technique has a high precision over a wide range of concentrations, making it very suitable for the measurement of these gases in freshwater systems. We have employed this measurement system on a commercial river barge on the Elbe river (Czech Republic, Germany) and on a fisher boat in the coastal area of Sarawak (Malaysia). In addition we have performed stationary continuous measurements at a small river in Northern Germany over the duration of 3 months. The presentation will outline the advantages and disadvantages of the FTIR-technique for freshwater measurements and will present results from the measurement campaigns.

Carbon Fluxes in Dissolved and Gaseous Forms for a Restored Peatland in British Columbia, Canada

NASA Astrophysics Data System (ADS)

D'Acunha, B.; Johnson, M. S.; Lee, S. C.; Christen, A.

2016-12-01

Peatlands are wetlands where gross primary production exceeds organic matter decomposition causing an accumulation of partially decomposed matter, also called peat. These ecosystems can accumulate more carbon than tropical rainforests. However, dissolved and gaseous fluxes of carbon (as dissolved organic carbon (DOC), CO2 and methane (CH4)) must also be considered to determine if these ecosystems are net sinks or sources of greenhouse gases (GHGs) to the atmosphere, which depends in part on the environmental conditions and the state of the ecosystem. We conducted research in Burns Bog, Delta, BC, Canada, a raised domed peat bog located in the Fraser River Delta and one of the largest raised peat bogs on the west coast of the Americas, but which has been heavily impacted by a range of human activities. Currently, ecological restoration efforts are underway by a large-scale ditch blocking program, with the aim to re-establish a high water table. This is approached in partnership with research on the ecosystem services that the bog provides, including its role in a regional GHG inventory. Here we present data on ecosystem-scale fluxes of CO2 and CH4 determined by eddy covariance (EC) on a floating tower platform, and complementary data on (i) evasion fluxes of CO2, CH4 and nitrous oxide (N2O) from the water surface to the atmosphere, and (ii) the flux and composition of dissolved organic carbon in water draining Burns Bog. Concentrations of dissolved CO2, CH4 and N2O were determined by headspace equilibration, and evasion rates from the water surface were quantified and are used to estimate the role of the hydrosphere in the ecosystem-scale measurements. Water samples collected from five saturated areas in the flux tower footprint were analyzed for DOC concentrations and composition. Results indicated that, even though the whole system is a net C sink, the water surface behaved as a source of CO2 and CH4, and a sink for N2O throughout the study period. Drainage waters were high in DOC (> 30 mg L-1). DOC export was found to offset about 20% of the apparent net C uptake determined by EC, indicating that the EC system overestimates carbon accumulation by not accounting for DOC drainage.

Oxic limestone drains for treatment of dilute, acidic mine drainage

USGS Publications Warehouse

Cravotta, Charles A.

1998-01-01

Limestone treatment systems can be effective for remediation of acidic mine drainage (AMD) that contains moderate concentrations of dissolved O2 , Fe3+ , or A13+ (1‐5 mg‐L‐1 ). Samples of water and limestone were collected periodically for 1 year at inflow, outflow, and intermediate points within underground, oxic limestone drains (OLDs) in Pennsylvania to evaluate the transport of dissolved metals and the effect of pH and Fe‐ and Al‐hydrolysis products on the rate of limestone dissolution. The influent was acidic and relatively dilute (pH <4; acidity < 90 mg‐L‐1 ) but contained 1‐4 mg‐L‐1 Of O2 , Fe3+ , A13+ , and Mn2+ . The total retention time in the OLDs ranged from 1.0 to 3.1 hours. Effluent remained oxic (02 >1 mg‐L‐1 ) but was near neutral (pH = 6.2‐7.0); Fe and Al decreased to less than 5% of influent concentrations. As pH increased near the inflow, hydrous Fe and Al oxides precipitated in the OLDs. The hydrous oxides, nominally Fe(OH)3 and AI(OH)3, were visible as loosely bound, orange‐yellow coatings on limestone near the inflow. As time elapsed, Fe(OH)3 and AI(OH)3 particles were transported downflow. During the first 6 months of the experiment, Mn 2+ was transported conservatively through the OLDs; however, during the second 6 months, concentrations of Mn in effluent decreased by about 50% relative to influent. The accumulation of hydrous oxides and elevated pH (>5) in the downflow part of the OLDs promoted sorption and coprecipitation of Mn as indicated by its enrichment relative to Fe in hydrous‐oxide particles and coatings on limestone. Despite thick (~1 mm) hydrous‐oxide coatings on limestone near the inflow, CaCO3 dissolution was more rapid near the inflow than at downflow points within the OLD where the limestone was not coated. The rate of limestone dissolution decreased with increased residence time, pH, and concentrations of Ca2+ and HCO3‐ and decreased PCO2. The following overall reaction shows alkalinity as an ultimate product of the iron hydrolysis reaction in an OLD:Fe2+ + 0.25 O2 +CaCO3 + 2.5 H2O --> Fe(OH)3 + 2 Ca2+ + 2 HCO3-where 2 moles of CaCO3 dissolve for each mole of Fe(OH)3 produced. Hence, in an OLD, rapidly dissolving limestone surfaces are not stable substrates for Fe(OH)3 attachment and armoring. Because overall efficiency is increased by combining neutralization and hydrolysis reactions, an OLD followed by a settling pond requires less land area than needed for a two‐stage treatment system consisting of an anoxic limestone drain an oxidation‐settling pond or wetland. To facilitate removal of hydrous‐oxide sludge, a perforated‐pipe subdrain can be installed within an OLD.

The self-setting properties and in vitro bioactivity of tricalcium silicate.

PubMed

Zhao, Wenyuan; Wang, Junying; Zhai, Wanyin; Wang, Zheng; Chang, Jiang

2005-11-01

In this study, tricalcium silicate (Ca(3)SiO(5)), as a new promising injectable bioactive material, was employed to investigate its physical and chemical properties for an injectable bioactive cement filler. The workable Ca(3)SiO(5) pastes with a liquid to powder (L/P) ratio of 0.8--.2 mlg(-1)could be injected for 15--60 min (nozzle diameter 2.0mm). The setting process yielded cellular structures with compressive strength of 6.4--20.2 MPa after 2--28 days. The in vitro bioactivity of Ca(3)SiO(5) paste was investigated by soaking in simulated body fluid (SBF) for various periods. The result showed that the Ca(3)SiO(5) paste could induce hydroxyapatite (HA) formation and dissolve slowly in SBF. The result of indirect cytotoxicity evaluation indicated that Ca(3)SiO(5) paste had a stimulatory effect on cell growth in a certain concentration range. The exothermic process showed that Ca(3)SiO(5) had lower heat evolution rate during the hydration as compared to calcium phosphate cement (CPC). Our results indicated that Ca(3)SiO(5) paste was bioactive and dissolvable, and it is a progressive candidate for further investigation as injectable tissue repairing substitute.

The isotopic imprint of fixed nitrogen elimination in the redox transition zone of Lake Lugano, Switzerland

NASA Astrophysics Data System (ADS)

Wenk, Christine; Blees, Jan; Niemann, Helge; Zopfi, Jakob; Schubert, Carsten J.; Veronesi, Mauro; Simona, Marco; Koba, Keisuke; Lehmann, Moritz F.

2010-05-01

Nitrogen (N) loading in lakes from natural and anthropogenic sources is partially mitigated by microbially mediated processes that take place in redox transition zones (RTZ) in the water column and in sediments. However, the role of lakes as a terrestrial sink of fixed N is still poorly constrained. Furthermore, modes of suboxic N2 (and N2O) production other than canonical denitrification (e.g. anaerobic ammonium oxidation, or anammox) have barely been investigated in lakes, and the microbial communities involved in N transformations in lacustrine RTZ are mostly unknown. The isotopic composition of dissolved nitrogen species can serve as a reliable indicator of N-transformations in aquatic environments. However, the successful application of N (and O) isotope measurements in natural systems requires a solid understanding of the various N-transformation-specific isotope effects. The deep, south-alpine Lake Lugano, with a permanent chemocline in its North Basin, is an excellent model system for a biogeochemically dynamic lake, in which to study N isotope ratio variations associated with fixed N elimination and regeneration processes. We present the first comprehensive dataset of hydrochemical parameters (including N2/Ar and dissolved N2O concentrations), natural abundance stable isotope ratios of dissolved inorganic nitrogen (DIN) compounds (nitrate, nitrite, ammonium, dinitrogen, nitrous oxide), and the isotopomeric composition of water column N2O for the North Basin of Lake Lugano. Isotopic data will be integrated with molecular microbiological phylogenetic analyses and results from incubation experiments with 15N-labeled N-substrates. Strong gradients in DIN concentrations, as well as in the N and O isotope (and isotopomeric) compositions of nitrate and N2O towards the redox-transition zone indicate nitrate reduction, occurring with a high community N-fractionation. The site preference of N2O isotopomers above the chemocline indicates that the N2O is not only produced by denitrification. Furthermore, the ratio of nitrate N versus O isotope enrichment is 0.6, significantly lower than the ratio expected for sole water column denitrification. Ammonium concentrations in the hypolimnion constantly decrease to 0µM at about 20m below the oxycline, suggesting that anammox, the anaerobic oxidation of ammonium, takes place below the RTZ. First results from 16S rDNA analysis confirmed the presence of anammox bacteria (Candidatus ‘Kuenenia') in the water column. Further phylogenetic and isotope-labeling experiments will provide more information on the spatial and seasonal distribution of anammox bacteria in the water column, on the quantitative partitioning between the candidate N elimination processes, and thus likely on the N isotope fractionation of single N transformation pathways.

Rapid nitrous oxide cycling in the suboxic ocean

NASA Astrophysics Data System (ADS)

Babbin, Andrew R.; Bianchi, Daniele; Jayakumar, Amal; Ward, Bess B.

2015-06-01

Nitrous oxide (N2O) is a powerful greenhouse gas and a major cause of stratospheric ozone depletion, yet its sources and sinks remain poorly quantified in the oceans. We used isotope tracers to directly measure N2O reduction rates in the eastern tropical North Pacific. Because of incomplete denitrification, N2O cycling rates are an order of magnitude higher than predicted by current models in suboxic regions, and the spatial distribution suggests strong dependence on both organic carbon and dissolved oxygen concentrations. Furthermore, N2O turnover is 20 times higher than the net atmospheric efflux. The rapid rate of this cycling coupled to an expected expansion of suboxic ocean waters implies future increases in N2O emissions.

Photooxidation and its effects on the carboxyl content of dissolved organic matter in two coastal rivers in the southeastern United States.

PubMed

Xie, Huixiang; Zafiriou, Oliver C; Cai, Wei-Jun; Zepp, Richard G; Wang, Yongchen

2004-08-01

Photodecarboxylation (often stoichiometrically expressed as RCOOH + (1/2)O2 --> ROH + CO2) has long been postulated to be principally responsible for generating CO2 from photooxidation of dissolved organic matter (DOM). In this study, the quantitative relationships were investigated among O2 consumption, CO2 production, and variation of carboxyl content resulting from photooxidation of DOM in natural water samples obtained from the freshwater reaches of the Satilla River and Altamaha River in the southeastern United States. In terms of loss of dissolved organic carbon (DOC), loss of optical absorbance, and production of CO2, the rate of photooxidation of DOM was increased in the presence of Fe redox chemistry and with increasing O2 content. The ratio of photochemical O2 consumption to CO2 photoproduction ranged from approximately 0.8 to 2.5, depending on the O2 content, the extent of involvement of Fe, and probably the initial oxidation state of DOM as well. The absolute concentration of carboxyl groups ([-COOH]) on DOM only slightly decreased or increased over the course of irradiation, possibly depending on the stages of photooxidation, while the DOC-normalized carboxyl content substantially increased in the presence of Fe redox chemistry and sufficient O2. Both the initial [-COOH] and the apparent loss of this quantity over the course of irradiation was too small to account for the much larger production of CO2, suggesting that carboxyl groups were photochemically regenerated or that the major production pathway for CO2 did not involve photodecarboxylation. The results from this study can be chemically rationalized by a reaction scheme of (a) photodecarboxylation/ regeneration of carboxyl: CxHyOz(COOH)m + aO2 + (metals, hv) --> bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m-b(COOH)b or of (b) nondecarboxylation photooxidation: CxHyOz(COOH)m + aO2 + (metals, hv) --> bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m.

Mixed solvent electrolytes for ambient temperature secondary lithium cells

NASA Technical Reports Server (NTRS)

Shen, David H. (Inventor); Surampudi, Subbarao (Inventor); Deligiannis, Fotios (Inventor); Halpert, Gerald (Inventor)

1991-01-01

The present invention comprises an improved electrolyte for secondary lithium-based cells as well as batteries fabricated using this electrolyte. The electrolyte is a lithium containing salt dissolved in a non-aqueous solvent, which is made from a mixture of ethylene carbonate, ethylene propylene diene terpolymer, 2-methylfuran, and 2-methyltetrahydrofuran. This improved, mixed solvent electrolyte is more conductive than prior electrolytes and much less corrosive to lithium anodes. Batteries constructed with this improved electrolyte utilize lithium or lithium alloy anodes and cathodes made of metal chalcogenides or oxides, such as TiS.sub.2, NbSe.sub.3, V.sub.6 O.sub.13, V.sub.2 O.sub.5, MoS.sub.2, MoS.sub.3, CoO.sub.2, or CrO.sub.2, dissolved in a supporting polymer matrix, like EPDM. The preferred non-aqueous solvent mixture comprises approximately 5 to 30 volume percent ethylene carbonate, approximately 0.01 to 0.1 weight percent ethylene propylene diene terpolymer, and approximately 0.2 to 2 percent 2-methylfuran, with the balance being 2-methyltetrahydrofuran. The most preferred solvent comprises approximately 10 to 20 volume percent ethylene carbonate, about 0.05 weight percent ethylene propylene diene terpolymer, and about 1.0 percent 2-methylfuran, with the balance being 2-methyltetrahydrofuran. The concentration of lithium arsenic hexafluoride can range from about 1.0 to 1.8 M; a concentration 1.5 M is most preferred. Secondary batteries made with the improved electrolyte of this invention have lower internal impedance, longer cycle life, higher energy density, low self-discharge, and longer shelf life.

Novel ammonia sensor based on polyaniline/polylactic acid composite films

NASA Astrophysics Data System (ADS)

Sotirov, S.; Bodurov, I.; Marudova, M.

2017-01-01

We propose a new type of ammonia sensor based on composite film between polyaniline (emeraldine base) dissolved in dimethylformamide, and poly(DL-lactic) acid dissolved in chloroform. The two solutions were mixed in weight ratio of the components 1:1 and cast on Al2O3 substrate, on which silver electrodes were deposited previously. The active layer structure and morphology were examined by atomic force microscopy. The sensor resistance at constant humidity and different ammonia concentrations was measured. It was found that an increase in the ammonia concentration leads to resistance increase. This result is explained in the terms of ionic interactions between the polyaniline and the ammonia, which change the permittivity of the sensor active media. A response between 2% and 590% was shown depending on the ammonia concentration. The sensor is reversible and possesses response time of typically 100 s. Based on the changes of the sensor resistance, ammonia concentration from 10 ppm to 1000 ppm could be detected.

Technical insight on the requirements for CO2-saturated growth of microalgae in photobioreactors.

PubMed

Yuvraj; Padmanabhan, Padmini

2017-06-01

Microalgal cultures are usually sparged with CO 2 -enriched air to preclude CO 2 limitation during photoautotrophic growth. However, the CO 2 vol% specifically required at operating conditions to meet the carbon requirement of algal cells in photobioreactor is never determined and 1-10% v/v CO 2 -enriched air is arbitrarily used. A scheme is proposed and experimentally validated for Chlorella vulgaris that allows computing CO 2 -saturated growth feasible at given CO 2 vol% and volumetric O 2 mass-transfer coefficient (k L a) O . CO 2 sufficiency in an experiment can be theoretically established to adjust conditions for CO 2 -saturated growth. The methodology completely eliminates the requirement of CO 2 electrode for online estimation of dissolved CO 2 to determine critical CO 2 concentration (C crit ), specific CO 2 uptake rate (SCUR), and volumetric CO 2 mass-transfer coefficient (k L a) C required for the governing CO 2 mass-transfer equation. C crit was estimated from specific O 2 production rate (SOPR) measurements at different dissolved CO 2 concentrations. SCUR was calculated from SOPR and photosynthetic quotient (PQ) determined from the balanced stoichiometric equation of growth. Effect of light attenuation and nutrient depletion on biomass estimate is also discussed. Furthermore, a simple design of photosynthetic activity measurement system was used, which minimizes light attenuation by hanging a low depth (ca. 10 mm) culture over the light source.

Watershed Influences on Residence Time and Oxygen Reduction Rates in an Agricultural Landscape

NASA Astrophysics Data System (ADS)

Shope, C. L.; Tesoriero, A. J.

2015-12-01

Agricultural use of synthetic fertilizers and animal manure has led to increased crop production, but also elevated nitrogen concentrations in groundwater, resulting in impaired water quality. Groundwater oxygen concentrations are a key indicator of potential biogeochemical processes, which control water/aquifer interactions and contaminant transport. The U.S. Geological Survey's National Water-Quality Assessment Program has a long-history of studying nutrient transport and processing across the United States and the Glacial Aquifer system in particular. A series of groundwater well networks in Eastern Wisconsin is being used to evaluate the distribution of redox reaction rates over a range of scales with a focus on dissolved O2 reduction rates. An analysis of these multi-scale networks elucidates the influence of explanatory variables (i.e.: soil type, land use classification) on reduction rates and redox reactions throughout the Fox-Wolf-Peshtigo watersheds. Multiple tracers including dissolved gasses, tritium, helium, chlorofluorocarbons, sulfur hexafluoride, and carbon-14 were used to estimate groundwater ages (0.8 to 61.2 yr) at over 300 locations. Our results indicate O2 reduction rates along a flowpath study area (1.2 km2) of 0.15 mg O2 L-1 yr-1 (0.12 to 0.18 mg O2 L-1 yr-1) up to 0.41 mg O2 L-1 yr-1 (0.23 to 0.89 mg O2 L-1 yr-1) for a larger scale land use study area (3,300 km2). Preliminary explanatory variables that can be used to describe the variability in reduction rates include soil type (hydrologic group, bulk density) and chemical concentrations (nitrite plus nitrate, silica). The median residence time expected to reach suboxic conditions (≤ 0.4 mg O2 L-1) for the flowpath and the land use study areas was 66 and 25 yr, respectively. These results can be used to elucidate and differentiate the impact of residence time on groundwater quality vulnerability and sustainability in agricultural regions without complex flow models.

Ferrate(VI) enhanced photocatalytic oxidation of pollutants in aqueous TiO2 suspensions.

PubMed

Sharma, Virender K; Graham, Nigel J D; Li, Xiang-Zhong; Yuan, Bao-Ling

2010-02-01

Photocatalytic oxidation using UV irradiation of TiO(2) has been studied extensively and has many potential industrial applications, including the degradation of recalcitrant contaminants in water and wastewater treatment. A limiting factor in the oxidation process is the recombination of conduction band electrons (e(-)(cb)) with electron holes (h(vb)(+)) on the irradiated TiO(2) surface; thus, in aqueous conditions, the presence of an effective electron scavenger will be beneficial to the efficiency of the oxidation process. Ferrate (FeO(4)(2-)) has received much recent attention as a water treatment chemical since it behaves simultaneously as an oxidant and coagulant. The combination of ferrate [Fe(VI)] with UV/TiO(2) photocatalysis offers an oxidation synergism arising from the Fe(VI) scavenging of e(-)(cb) and the corresponding beneficial formation of Fe(V) from the Fe(VI) reduction. This paper reviews recent studies concerning the photocatalytic oxidation of problematic pollutants with and without ferrate. The paper reviews the published results of laboratory experiments designed to follow the photocatalytic degradation of selected contaminants of environmental significance and the influence of the experimental conditions (e.g. pH, reactant concentrations and dissolved oxygen). The specific compounds are as follows: ammonia, cyanate, formic acid, bisphenol-A, dibutyl- and dimethyl-phthalate and microcystin-LR. The principal focus in these studies has been on the rates of reaction rather than on reaction pathways and products. The presence of UV/TiO(2) accelerates the chemical reduction of ferrate, and the reduction rate decreases with pH owing to deprotonation of ferrate ion. For all the selected contaminant substances, the photocatalytic oxidation rate was greater in the presence of ferrate, and this was believed to be synergistic rather than additive. The presence of dissolved oxygen in solution reduced the degradation rate of dimethyl phthalate in the ferrate/photocatalysis system. In the study of microcystin-LR, it was evident that an optimal ferrate concentration exists, whereby higher Fe(VI) concentrations above the optimum leads to a reduction in microcystin-LR degradation. In addition, the rate of microcystin-LR degradation was found to be strongly dependent on pH and was greatest at pH 6. The initial rate of photocatalytic reduction under different conditions was analysed using a Langmuirian form. Decrease in rates in the presence of dissolved oxygen may be due to competition between oxygen and ferrate as electron scavengers and to non-productive radical species interactions. The reaction between ferrate(VI) and microcystins-LR in the pH range of 6.0-10.0 is most likely controlled by the protonated Fe(VI) species, HFeO(4)(-). The photocatalytic oxidation of selected, recalcitrant contaminants was found to be significantly greater in the presence of ferrate, arising from the role of ferrate in inhibiting the h(vb)(+)-e(-)(cb) pair recombination on TiO(2) surfaces and the corresponding generation of highly oxidative Fe(V) species. The performance of the ferrate/photocatalysis system is strongly influenced by the reaction conditions, particularly the pH and dissolved oxygen concentration, arising from the complex nature of the interactions between the catalyst and the solution. Overall, the treatment performance of the Fe(VI)-TiO(2)-UV system is generally superior to alternative chemical oxidation methods. The formation of intermediate Fe(V) species in the photocatalytic reduction of ferrate(VI) requires confirmation, and a method involving electron paramagnetic resonance spectroscopy could be applied for this. The reactivity of Fe(V) with the selected contaminants is required in order to better understand the role of ferrate in the Fe(VI)-TiO(2)-UV oxidation system. To increase the practical utility of the system, it is recommended that future studies involving the photocatalytic oxidation of pollutants in the presence of ferrate(VI) should focus on developing modified TiO(2) surfaces that are photocatalytic under visible light conditions.

Morphology-controlled preparation of lead powders by electrodeposition from different PbO-containing choline chloride-urea deep eutectic solvent

NASA Astrophysics Data System (ADS)

Ru, Juanjian; Hua, Yixin; Xu, Cunying; Li, Jian; Li, Yan; Wang, Ding; Qi, Cancan; Jie, Yafei

2015-04-01

Lead powders with different morphologies, including corals, rods, wires, needles, ferns and dendritic forms, are prepared by electrodeposition onto a stainless steel substrate from different PbO-containing (10-60 mM) choline chloride-urea deep eutectic solvent at cell voltage 2.5 V and 343 K for 2 h. The electrochemical behavior of the PbO dissolved in this solvent is investigated with cyclic voltammetry. It is demonstrated that the increasing of PbO concentration makes the reduction potential EPb(II)/Pb shift positively and facilitates the electrodeposition of lead from PbO in the deep eutectic solvent. According to the analysis of the morphological and crystallographic characteristics of lead powders, the predominant origin of the growth layers is turned away from centre type towards the edge and corner types with the increase in PbO concentration. Due to the large number of growth centres at higher PbO concentration, fine and irregular grains are observed on the surface of formed particles which results in the development of primary and secondary branches in dendrites.

Expression of denitrification enzymes in response to the dissolved oxygen level and respiratory substrate in continuous culture of Pseudomonas stutzeri.

PubMed Central

Körner, H; Zumft, W G

1989-01-01

The onset and cessation of the synthesis of denitrification enzymes of Pseudomonas stutzeri were investigated by using continuous culture and defined dissolved oxygen levels covering the full range of transition from air saturation to complete anaerobiosis. Expression of nitrate reductase, nitrite reductase (cytochrome cd1), and N2O reductase was controlled by discrete oxygen levels and by the nature of the nitrogenous oxide available for respiration. N2O reductase was synthesized constitutively at a low level; for enhanced expression, oxygen concentrations were required to decrease below 5 mg of O2 per liter. The threshold values for synthesis of nitrate reductase and cytochrome cd1 in the presence of nitrate were ca. 5 and ca. 2.5 mg of O2 per liter, respectively. With nitrous oxide as the respiratory substrate, nitrite reductase was again the most sensitive to oxygen concentration; however, thresholds for all denitrification enzymes shifted to lower oxygen levels. Whereas the presence of nitrate resulted in maximum expression and nearly uniform induction of all reductases, nitrite and nitrous oxide stimulated preferably the respective enzyme catalyzing reduction. In the absence of a nitrogenous oxide, anaerobiosis did not induce enzyme synthesis to any significant degree. The accumulation of nitrite seen during both the aerobic-anaerobic and anaerobic-aerobic transition phases was caused by the differences in onset or cessation of synthesis of nitrate and nitrite reductases and an inhibitory effect of nitrate on nitrite reduction. Images PMID:2764573

Dissolved oxygen concentration profiles in the hyporheic zone through the use of a high density fiber optic measurement network

NASA Astrophysics Data System (ADS)

Reeder, W. J.; Quick, A. M.; Farrell, T. B.; Benner, S. G.; Feris, K. P.; Tonina, D.

2013-12-01

The hyporheic zone (HZ) is a potentially important source of the potent greenhouse gas, nitrous oxide (N2O); stream processes may account for up to 10% of global anthropogenic N2O emissions. However, mechanistic understanding and predictive quantification of this gas flux is hampered by complex temporally and spatially variable interactions between flow dynamics and biogeochemical processes. Reactive inorganic nitrogen (Nr) is typically present at low concentrations in natural stream waters, but many rural and urban streams suffer from an excess of Nr, typically in the form of ammonium (NH4+) and nitrate (NO3-). These reactive species are either assimilated by living biomass or transformed by microbial processes. The two primary microbial transformations of Nr are nitrification (NH4+ to NO3-) and denitrification (NO3- to N2). Denitrification, which occurs almost exclusively in the anoxic zone of the HZ, permanently removes between 30-70% of all Nr entering streams, other mechanisms may retain nitrogen. The mass transport of reactive species (i.e. O2, NO3- and N2O) by hyporheic flow strongly influences reaction rates, residence times, and subsequent N2O flux. By extension, stream flow and channel morphology presumably control, and may be effective predictors of, N2O generation rates. By recreating the stream processes in the University of Idaho flume, we are able to control the bed morphology, fluxes and residence times through the HZ and concentrations of Nr from exogenous (stream water) and endogenous (organic material in the streambed) sources. For the present experiment, the flume was divided into three streams, each with different morphologies (3, 6 and 9cm dunes) and all using the same source water. Stream water for this first experimental phase had no significant loading of Nr. As such, all reaction products were the result of endogenous sources of Nr. To measure dissolved oxygen (DO) concentrations we deployed 120 channels of a novel, fiber-optic optode system which was coupled with an advanced optical multiplexer that allowed us to cycle continuously through all 120 channels. Using this approach, we were able to accurately map the evolution and extent of the anoxic regions within the HZ and demonstrate that bed morphology exhibits significant control over residence times and the spatial temporal evolution of the anoxic region. In addition to the DO measurements, we deployed 240 Rhizon water samplers to extract pore water, which we used to measure Nr and N2O concentrations, and an ion Clark-type electrode sensor to measure N2O concentrations at the streambed surface (results discussed separately). Integrating these various results will allow us to refine the existing models for N2O emissions from urban and rural streams.

The influence of tides on biogeochemical dynamics at the mouth of the Amazon River

NASA Astrophysics Data System (ADS)

Ward, N. D.; Sawakuchi, H. O.; Neu, V.; de Matos Valerio, A.; Less, D.; Guedes, V.; Wood, J.; Brito, D. C.; Cunha, A. C.; Kampel, M.; Richey, J. E.

2017-12-01

A major barrier to computing the flux of constituents from the world's largest rivers to the ocean is understanding the dynamic processes that occur along tidally-influenced river reaches. Here, we examine the response of a suite of biogeochemical parameters to tide-induced flow reversals at the mouth of the Amazon River. Continuous measurements of pCO2, pCH4, dissolved O2, pH, turbidity, and fluorescent dissolved organic matter (FDOM) were made throughout tidal cycles while held stationary in the center of the river and during hourly transects for ADCP discharge measurements. Samples were collected hourly from the surface and 50% depth during stationary samplings and from the surface during ADCP transects for analysis of suspended sediment concentrations along with other parameters such as nutrient and mercury concentrations. Suspended sediment and specific components of the suspended phase, such as particulate mercury, concentrations were positively correlated to mean river velocity during both high and low water periods with a more pronounced response at 50% depth than the surface. Tidal variations also influenced the concentration of O2 and CO2 by altering the dynamic balance between photosynthesis, respiration, and gas transfer. CO2 was positively correlated and O2 and pH were negatively correlated with river velocity. The concentration of methane generally increased during low tide (i.e. when river water level was lowest) both in the mainstem and in small side channels. In side channels concentrations increased by several orders of magnitude during low tide with visible bubbling from the sediment, presumably due to a release of hydrostatic pressure. These results suggest that biogeochemical processes are highly dynamic in tidal rivers, and these dynamic variations need to be quantified to better constrain global and regional scale budgets. Understanding these rapid processes may also provide insight into the long-term response of aquatic systems to change.

Nitrous oxide production in the eastern tropical South Pacific oxygen minimum zone

NASA Astrophysics Data System (ADS)

Ji, Qixing; Altabet, Mark; Arevalo-Martinez, Damian; Bange, Hermann; Ma, Xiao; Marandino, Christa; Sun, Mingshuang; Grundle, Damian

2017-04-01

Nitrous oxide (N2O) is an important climate active trace gas that contributes to both atmospheric warming and ozone destruction, and the ocean is an important source of N2O to the atmosphere. Dissolved oxygen concentrations play an important role in regulating N2O production in the ocean, such that under low oxygen conditions major shifts in the predominant production pathways (i.e. nitrification vs. denitrification) can occur and the magnitude of production may increase substantially. To this end, major oceanic oxygen minimum zones (OMZs) are responsible for a disproportionately high amount of marine N2O production. During the October 2015 ASTRA-OMZ cruise to the eastern tropical South Pacific (ETSP), one of the three major oceanic OMZs, we measured a suite of N2O parameters which included N2O concentrations, N2O production, and natural abundance N2O isotope (i.e. del 15N and del 18O) and isotopomer (i.e. 15N site-preference) signatures. Based on the results from these measurements, our presentation will demonstrate how N2O production and the different production pathways change along the oxygen concentration gradients from the oxygenated surface waters through the oxygen minimum layer. Our data could better constrain the importance of the ETSP-OMZ as source of marine N2O. Results from this work will provide insights into how N2O cycling responds to ocean deoxygenation as a result of climate change.

Dissolved major elements exported by the Congo and the Ubangi rivers during the period 1987 1989

NASA Astrophysics Data System (ADS)

Probst, Jean-Luc; NKounkou, Renard-Roger; Krempp, Gérard; Bricquet, Jean-Pierre; Thiébaux, Jean-Pierre; Olivry, Jean-Claude

1992-07-01

On the basis of monthly sampling during the period 1987-1989, the geochemistry of the Congo and the Ubangi (second largest tributary of the Congo) rivers was studied in order (1) to understand the seasonal variations of the physico-chemical parameters of the waters and (2) to estimate the annual dissolved fluxes exported by the two rivers. The results presented here correspond to the first three years of measurements carried out for a scientific programme (Interdisciplinary Research Programme on Geodynamics of Peri-Atlantic Intertropical Environments, Operation 'Large River Basins' (PIRAT-GBF) undertaken jointly by Institut National des Sciences de l'Univers (INSU) and Institut Français de Recherche Scientifique pour le Développement en Coopération (ORSTOM) planned to run for at least ten years. The Congo River is more diluted than the Ubangi (34 mgl -1 vs. 42 mgl -1). For both rivers, the inorganic dissolved load is composed mainly of HCO 3- and SiO 2. The chemical composition of the water does not change with time. In the Ubangi River, because of the presence of Precambrian carbonate rocks in its catchment, the proportions of HCO 3- and Ca 2+ are higher. On a seasonal scale, the concentration of dissolved cations and anions varies inversely with discharge, except silica. The comparison of the discharge-concentration relationship with a theoretical 'zero dilution' shows that the evolution of the concentration of dissolved substances is a simple dilution by the surface waters, with, in the case of the Ubangi, a small supply of dissolved substances by the surface waters. Using three different methods of calculation, the estimated annual inorganic dissolved flux of the Congo ranges from 39 × 10 6 to 44 × 10 6 tons (according to the year), with about 10% of this coming from the Ubangi drainage basin.

Temperature and Salinity Effects on Quantitative Raman Spectroscopic Analysis of Dissolved Volatiles Concentration in Geofluids

NASA Astrophysics Data System (ADS)

Wu, X.; Lu, W.

2017-12-01

The concentration detection of the volatiles such as CH4 and CO2 in the hydrothermal systems and fluid inclusions is critical for understanding the fluxes of volatiles from mantle to crust and atmosphere. In-situ Raman spectroscopy has been developed successfully in laboratory, fluid inclusions and submarine environment because of its non-destructive and non-contact advantages. For improving the ability of detecting different species quantitatively by in-situ Raman spectroscopy in the extreme environment, such as the hydrothermal system and fluid inclusion, we studied the temperature- and salinity-dependence of Raman scattering cross section (RSCS) of the water OH stretching band at temperatures from 20 to 300 oC under 30 MPa. This is important because the water is often used as internal standard in the Raman quantitative application. Based on our previous study of NaCl-H2O system, we made further investigation on the CaCl2-H2O system. Our results revealed that the cation shows negligible effect on the RSCS of water OH stretching band, while the cations seems to have more obvious different effect on the structure of water within high temperatures. Besides the NaCl-CH4-H2O system, we also take the CO2-H2O system into account. Further conclusion can be made that the variation of the Raman quantitative factor (QF) (both PAR/mCH4 and PAR/mCO2) with the temperature and salinity is mainly caused by the temperature- and Cl- concentration-dependence of the relative RSCS of the water OH stretching band. If the Raman quantitative factor at ambient condition still being used, the RSCS of the water OH stretching band would induce about 47%, 34% and 29% error for the determined concentration of dissolved CH4 or CO2 (in mol/kg·H2O) by in-situ Raman spectroscopy for 0 m Cl-, 3 m Cl- and 5 m Cl- aqueous system when the temperature increases from 20 to 300 oC, respectively. Considering the wide range of the temperature and salinity in hydrothermal systems and fluid inclusions, the following equation can be used to calculate the relative QF at different temperatures and salinity referencing to the 0 m Cl- aqueous solution at 20 oC: QF(T, salinity)/QF(20 oC, 0 m Cl-)=k(T-20 oC)+b, where a=-0.0035× mCl-1/2+0.00168, b=-0.03× mCl-+1;

Optimized alumina coagulants for water treatment

DOEpatents

Nyman, May D [Albuquerque, NM; Stewart, Thomas A [Albuquerque, NM

2012-02-21

Substitution of a single Ga-atom or single Ge-atom (GaAl.sub.12 and GeAl.sub.12 respectively) into the center of an aluminum Keggin polycation (Al.sub.13) produces an optimal water-treatment product for neutralization and coagulation of anionic contaminants in water. GaAl.sub.12 consistently shows .about.1 order of magnitude increase in pathogen reduction, compared to Al.sub.13. At a concentration of 2 ppm, GaAl.sub.12 performs equivalently to 40 ppm alum, removing .about.90% of the dissolved organic material. The substituted GaAl.sub.12 product also offers extended shelf-life and consistent performance. We also synthesized a related polyaluminum chloride compound made of pre-hydrolyzed dissolved alumina clusters of [GaO.sub.4Al.sub.12(OH).sub.24(H.sub.2O).sub.12].sup.7+.

Solubility of reduced C-O-H volatiles in basalt as a function of fCO: Implications for the early Earth, the moon, and Mars

NASA Astrophysics Data System (ADS)

Armstrong, L. S.; Hirschmann, M. M.

2013-12-01

Magmatic C-O-H volatiles influence the evolution of planetary atmospheres and, when precipitated and stored in solidified mantles, the dynamical evolution of planetary interiors. In the case of the Earth, the fO2 of the mantle near the end of core formation should have been ~IW-2, and subsequently increased to present-day values [1]. In experiments with fO2 ≤ IW, a variety of reduced volatile species have been found dissolved in magmas, including H2, CH4, CO, Fe(CO)5 and possibly Fe(CO)62+. However, there remains significant disagreement regarding the identity and concentrations of these volatiles in natural magmas, as well as their dependencies on intensive variables (T, P, fO2, fCO, fH2)[2-6]. Previous experiments document the importance of CO-related species [2,6], but were conducted over a limited range of fCO and had potentially interfering effects from poorly controlled variations in H2O. We aim to experimentally determine the solubility of C-O-H volatiles in basaltic magmas under reduced, C-saturated conditions while minimizing water content. The relationship between volatile speciation, fO2, and fCO at 1.2 GPa and 1400°C are constrained, laying the groundwork for a more extensive study at a range of conditions relevant to the interiors of the terrestrial planets and the moon. Both MORB and a martian basalt were studied, contained in Pt-C capsules with Fe × Pt × Si metal added to generate reducing conditions and to monitor fO2. A nominal amount of H2O is unavoidable in experimental charges, but was minimized by drying capsules prior to welding. Phase compositions were determined by electron microprobe and volatile concentrations were measured by FTIR spectroscopy. In preliminary experiments with fO2 of IW-0.70 to +1.75 (corresponding to log fCO of 3.3-4.5), H2O and CO2 concentrations as determined by FTIR are 113-13283 and 12-721 ppm, respectively. Most experiments also display a small FTIR peak at 2205 cm-1, whereas the most reduced experiments lack this peak but have peaks at 3370 and/or 1615 cm-1. The 2205 cm-1 peak was previously observed in similar experiments [6], and attributed to a C=O bond, possibly in the Fe-carbonyl Fe(CO)62+ [7]. The normalized intensity of the 2205 cm-1 peak is zero at IW -0.70 and increases with greater fO2 and fCO. This suggests that over a small fO2 and fCO range with the CCO buffer as an upper limit, CO-bearing species account for a portion of the dissolved C in reduced, graphite-saturated magmas. These volatiles could play an important role in martian magmatism, in the early Earth's mantle post-core formation, and in more oxidized regions of the lunar mantle. However, the fO2 during terrestrial core formation would have been too low for CO2 or the CO-bearing species to dissolve in a magma ocean. Ongoing work will extend the study to more reducing conditions and determine total C and H2O concentrations by SIMS. References: [1] Frost et al. (2008) Phil. Trans. R. Soc. A 366, 4315-4337. [2] Wetzel D. et al. (2013) PNAS, doi:10.1073/pnas.1219266110. [3] Dasgupta et al. (2013) GCA 102, 191-212. [4] Hirschmann et al. (2012) EPSL 345, 38-48. [5] Ardia et al. (2013) GCA 114, 52-71. [6] Stanley et al. (in review), GCA. [7] Bley et al. (1997) Inorg. Chem. 36, 158-160.

Localized zones of denitrification in a floodplain aquifer in southern Wisconsin, USA

NASA Astrophysics Data System (ADS)

Craig, Laura; Bahr, Jean M.; Roden, Eric E.

2010-12-01

A floodplain aquifer within an agricultural watershed near Madison, Wisconsin (USA), was studied to determine whether denitrification was occurring below the surface organic layer. Groundwater levels and concentrations of O2, Cl-, NO{3/-}, SO{4/2-}, dissolved organic carbon (DOC), and major cations were monitored over a 1-year period along a 230-m transect between an agricultural field and a stream discharge point. Seventeen groundwater samples were analyzed for δ15NNO3 and δ18ONO3 composition. Samples in which NO{3/-} was too low for stable isotope analysis were analyzed for excess dissolved N2. Groundwater NO{3/-} concentrations declined between the agricultural field and the discharge point. Chloride and δ15NNO3/δ18ONO3 data indicated that the drop in NO{3/-} was caused primarily by dilution of shallow NO{3/-}-rich water with deeper, NO{3/-}-depleted groundwater. Two localized zones of denitrification were identified in the upland-wetland transition by their δ15NNO3 and δ18ONO3 signatures, and two in the stream hyporheic zone by the presence of excess dissolved N2. The combined stratigraphic, hydrologic, and geochemical data in these locations correspond to groundwater mixing zones where NO{3/-} is delivered to subsurface layers that support denitrification fueled by dissolved (e.g. DOC or dissolved Fe(II)) and/or solid-phase (e.g. particulate organic carbon, solid-associated Fe(II), or pyrite) electron donors.

RESEARCH AT THE GULF ECOLOGY DIVISION ON THE EFFECTS OF LOW DISSOLVED OXYGEN ON ESTUARINE ANIMALS

EPA Science Inventory

Concerns about hypoxia and its effects on saltwater organisms are increasing as environmental conditions in the inshore and nearshore marine environments are better understood. Along the Gulf of Mexico coast, periods of very low dissolved oxygen (D.O.) concentrations have been re...

Analysis of dissolved gas and fluid chemistry in mountainous region of Goaping river watershed in southern Taiwan

NASA Astrophysics Data System (ADS)

Tang, Kai-Wen; Chen, Cheng-Hong; Liu, Tsung-Kwei

2016-04-01

Annual rainfall in Taiwan is up to 2500 mm, about 2.5 times the average value of the world. However due to high topographic relief of the Central Mountain Range in Taiwan, groundwater storage is critical for water supply. Mountain region of the Goaping river watershed in southern Taiwan is one of the potential areas to develop groundwater recharge model. Therefore the target of this study is to understand sources of groundwater and surface water using dissolved gas and fluid chemistry. Four groundwater and 6 surface water samples were collected from watershed, 5 groundwater and 13 surface water samples were collected from downstream. All samples were analyzed for stable isotopes (hydrogen and oxygen), dissolved gases (including nitrogen, oxygen, argon, methane and carbon dioxide), noble gases (helium and radon) and major ions. Hydrogen and oxygen isotopic ratios of surface water and groundwater samples aligned along meteoric water line. For surface water, dissolved gases are abundant in N2 (>80%) and O2 (>10%); helium isotopic ratio is approximately equal to 1 RA (RA is 3He/4He ratio of air); radon-222 concentration is below the detection limit (<200 Bq/m3); and concentrations of major anions and cations are low (Na+ <20 ppm, Ca2+ < 60 ppm, Cl- <2 ppm). All these features indicate that surface waters are predominately recharged by precipitation. For groundwater, helium isotopic ratios (0.9˜0.23 RA) are lower and radon-222 concentrations (300˜6000 Bq/m3) are much higher than the surface water. Some samples have high amounts of dissolved gases, such as CH4 (>20%) or CO2 (>10%), most likely contributed by biogenic or geogenic sources. On the other hand, few samples that have temperature 5° higher than the average of other samples, show significantly high Na+ (>1000 ppm), Ca2+ (>150 ppm) and Cl- (>80 ppm) concentrations. An interaction between such groundwater and local hot springs is inferred. Watershed and downstream samples differ in dissolved gas species and fluid chemistry for groundwater and surface water. The higher hydrogen and oxygen isotopic ratios for surface water from downstream are most probably caused by evaporation. Low radon-222 concentrations of some groundwater from downstream may represent sources from different aquifers. Therefore, we conclude that surface water from downstream are recharged directly from its watershed, but groundwater are influenced by the local geological environment. Keywords: groundwater, dissolved gas, noble gas, radon in water, 3He/4He

Ketoprofen-β-cyclodextrin inclusion complexes formation by supercritical process technology

NASA Astrophysics Data System (ADS)

Sumarno, Rahim, Rizki; Trisanti, Prida Novarita

2017-05-01

Ketoprofen was a poorly soluble which anti-inflammatory, analgesic and antipyretic drug, solubility of which can be enchanced by form complexation with β-cyclodextrin. Besides that, the inclusion complex reduces the incidence of gastrointestinal side effect of drug. The aims of this research are to study the effect of H2O concentration in the supercritical carbondioxide and operation condition in the formation of ketoprofen-β-Cyclodextrin inclusion complex. This research was began by dissolved H2O in supercritical CO2 at 40°C and various saturation pressures. Then, dissolved H2O contacted with (1:5 w/w) ketoprofen-β-Cyclodextrin mixture at 50°C and various operation pressures. It called saturation process. Saturation was done for ±2 hours with agitation process and continued by decompression process. The products were characterized by drug Release, Differential Scanning Calorimetry (DCS) dan Scanning Electron Microscopy (SEM) analyses. The percentage from this work were 76,82%-89,99% for inclusion complexes. The percentage drug release of ketoprofen were 82,83%-88,36% on various inclusion pressure and various inclusion period.

Isotopic Monitoring of N2O Emissions from Wastewater Treatment: Evidence for N2O Production Associated with Anammox Metabolism?

NASA Astrophysics Data System (ADS)

Harris, E. J.; Wunderlin, P.; Joss, A.; Emmenegger, L.; Kipf, M.; Wolf, B.; Mohn, J.

2015-12-01

Microbial production is the major source of N2O, the strongest greenhouse gas produced within the nitrogen cycle, and the most important stratospheric ozone destructant released in the 21st century. Wastewater treatment is an important and growing source of N2O, with best estimates predicting N2O emissions from this sector will have increased by >25% by 2020. Novel treatment employing partial nitritation-anammox, rather than traditional nitrification-denitrification, has the potential to achieve a neutral carbon footprint due to increased biogas production - if N2O production accounts for <0.5-1% of total nitrogen turnover. As a further motivation for this research, microbial pathways identified from wastewater treatment can be applied to our understanding of N cycling in the natural environment. This study presents the first online isotopic measurements of offgas N2O from a partial-nitritation anammox reactor 1. The measured N2O isotopic composition - in particular the N2O isotopic site preference (SP = δ15Nα - δ15Nβ) - was used to understand N2O production pathways in the reactor. When N2O emissions peaked due to high dissolved oxygen concentrations, low SP showed that N2O was produced primarily via nitrifier denitrification by ammonia oxidizing bacteria (AOBs). N2O production by AOBs via NH2OH oxidation, in contrast, did not appear to be important under any conditions. Over the majority of the one-month measurement period, the measured SP was much higher than expected following our current understanding of N2O production pathways 2. SP reached 41‰ during normal operating conditions and achieved a maximum of 45‰ when nitrite was added under anoxic conditions. These results could be explained by unexpectedly strong heterotrophic N2O reduction despite low dissolved organic matter concentrations, or by an incomplete understanding of isotopic fractionation during N2O production from NH2OH oxidation by AOBs - however the explanation most consistent with all results is a previously unknown N2O production pathway associated with anammox metabolism. Harris et al. (2015) Water Res., 83: 258-270. Wunderlin et al. (2013) Env. Sci. Tech., 47: 1339-1348.

Water-quality effects and characterization of indicators of onsite wastewater disposal systems in the east-central Black Hills area, South Dakota, 2006-08

USGS Publications Warehouse

Putnam, Larry D.; Hoogestraat, Galen K.; Sawyer, J. Foster

2008-01-01

Onsite wastewater disposal systems (OWDS) are used extensively in the Black Hills of South Dakota where many of the watersheds and aquifers are characterized by fractured or solution-enhanced bedrock with thin soil cover. A study was conducted during 2006-08 to characterize water-quality effects and indicators of OWDS. Water samples were collected and analyzed for potential indicators of OWDS, including chloride, bromide, boron, nitrite plus nitrate (NO2+NO3), ammonia, major ions, nutrients, selected trace elements, isotopes of nitrate, microbiological indicators, and organic wastewater compounds (OWCs). The microbiological indicators were fecal coliforms, Escherichia coli (E. coli), enterococci, Clostridium perfringens (C. perfringens), and coliphages. Sixty ground-water sampling sites were located either downgradient from areas of dense OWDS or in background areas and included 25 monitoring wells, 34 private wells, and 1 spring. Nine surface-water sampling sites were located on selected streams and tributaries either downstream or upstream from residential development within the Precambrian setting. Sampling results were grouped by their hydrogeologic setting: alluvial, Spearfish, Minnekahta, and Precambrian. Mean downgradient dissolved NO2+NO3 concentrations in ground water for the alluvial, Spearfish, Minnekahta, and Precambrian settings were 0.734, 7.90, 8.62, and 2.25 milligrams per liter (mg/L), respectively. Mean downgradient dissolved chloride concentrations in ground water for these settings were 324, 89.6, 498, and 33.2 mg/L, respectively. Mean downgradient dissolved boron concentrations in ground water for these settings were 736, 53, 64, and 43 micrograms per liter (ug/L), respectively. Mean dissolved surface-water concentrations for NO2+NO3, chloride, and boron for downstream sites were 0.222 mg/L, 32.1 mg/L, and 28 ug/L, respectively. Mean values of delta-15N and delta-18O (isotope ratios of 14N to 15N and 18O to 16O relative to standard ratios) for nitrate in ground-water samples were 10.4 and -2.0 per mil (0/100), respectively, indicating a relatively small contribution from synthetic fertilizer and probably a substantial contribution from OWDS. The surface-water sample with the highest dissolved NO2+NO3 concentration of 1.6 mg/L had a delta-15N value of 12.36 0/100, which indicates warm-blooded animals (including humans) as the nitrate source. Fecal coliforms were detected in downgradient ground water most frequently in the Spearfish (19 percent) and Minnekahta (9.7 percent) settings. E. coli was detected most frequently in the Minnekahta (29 percent) and Spearfish (13 percent) settings. Enterococci were detected more frequently than other microbiological indicators in all four settings. Fecal coliforms and E. coli were detected in 73 percent and 95 percent of all surface-water samples, respectively. Enterococci, coliphages (somatic), and C. perfringens were detected in 50, 70, and 50 percent of surface-water samples, respectively. Of the 62 OWC analytes, 12 were detected only in environmental samples, 10 were detected in at least one environmental and one blank sample (not necessarily companion pairs), 2 were detected only in blank samples, and 38 were not detected in any blank, environmental, or replicate sample from either ground or surface water. Eleven different organic compounds were detected in ground-water samples at eight different sites. The most frequently occurring compound was DEET, which was found in 32 percent of the environmental samples, followed by tetrachloroethene, which was detected in 20 percent of the samples. For surface-water samples, 16 organic compounds were detected in 9 of the 10 total samples. The compound with the highest occurrence in surface-water samples was camphor, which was detected in 50 percent of samples. The alluvial setting was characterized by relatively low dissolved NO2+NO3 concentrations, detection of ammonia nitrogen, and relatively high concentr

Modeling of Nitrous Oxide Production from Nitritation Reactors Treating Real Anaerobic Digestion Liquor

PubMed Central

Wang, Qilin; Ni, Bing-Jie; Lemaire, Romain; Hao, Xiaodi; Yuan, Zhiguo

2016-01-01

In this work, a mathematical model including both ammonium oxidizing bacteria (AOB) and heterotrophic bacteria (HB) is constructed to predict N2O production from the nitritation systems receiving the real anaerobic digestion liquor. This is for the first time that N2O production from such systems was modeled considering both AOB and HB. The model was calibrated and validated using experimental data from both lab- and pilot-scale nitritation reactors. The model predictions matched the dynamic N2O, ammonium, nitrite and chemical oxygen demand data well, supporting the capability of the model. Modeling results indicated that HB are the dominant contributor to N2O production in the above systems with the dissolved oxygen (DO) concentration of 0.5–1.0 mg O2/L, accounting for approximately 75% of N2O production. The modeling results also suggested that the contribution of HB to N2O production decreased with the increasing DO concentrations, from 75% at DO = 0.5 mg O2/L to 25% at DO = 7.0 mg O2/L, with a corresponding increase of the AOB contribution (from 25% to 75%). Similar to HB, the total N2O production rate also decreased dramatically from 0.65 to 0.25 mg N/L/h when DO concentration increased from 0.5 to 7.0 mg O2/L. PMID:27125491

Food-grade submicrometer particles from salts prepared using ethanol-in-oil mixtures.

PubMed

Paques, Jerome P; van der Linden, Erik; Sagis, Leonard M C; van Rijn, Cees J M

2012-08-29

A simple method for preparing food-grade particles in the submicrometer range of ethanol soluble salts using ethanol-in-oil (E/O) mixtures is described. Salts CaCl2·2H2O and MgCl2·6H2O were dissolved in ethanol that subsequently was mixed with a medium-chain triglyceride oil phase. It was found that type and concentration of salt have a significant influence on the miscibility of ethanol and oil phase and on the stability of E/O mixtures. The ethanol phase was evaporated from the mixture at elevated temperatures, and salt particles with dimensions in the submicrometer range (6-400 nm) remained suspended in the oil phase. It was found that the concentration of salt and volume fraction of ethanol in MCT oil have a significant influence on the size distribution of salt particles. The size of CaCl2 and MgCl2 submicrometer particles was ascertained by scanning electron microscopy and dynamic light scattering.

Productions of Volatile Organic Compounds (VOCs) in Surface Waters from Reactions with Atmospheric Ozone

NASA Astrophysics Data System (ADS)

Hopkins, Frances; Bell, Thomas; Yang, Mingxi

2017-04-01

Ozone (O3) is a key atmospheric oxidant, greenhouse gas and air pollutant. In marine environments, some atmospheric ozone is lost by reactions with aqueous compounds (e.g. dissolved organic material, DOM, dimethyl sulfide, DMS, and iodide) near the sea surface. These reactions also lead to formations of volatile organic compounds (VOCs). Removal of O3 by the ocean remains a large uncertainty in global and regional chemical transport models, hampering coastal air quality forecasts. To better understand the role of the ocean in controlling O3 concentrations in the coastal marine atmosphere, we designed and implemented a series of laboratory experiments whereby ambient surface seawater was bubbled with O3-enriched, VOC-free air in a custom-made glass bubble equilibration system. Gas phase concentrations of a range of VOCs were monitored continuously over the mass range m/z 33 - 137 at the outflow of the bubble equilibrator by a proton transfer reaction - mass spectrometer (PTR-MS). Gas phase O3 was also measured at the input and output of the equilibrator to monitor the uptake due to reactions with dissolved compounds in seawater. We observed consistent productions of a variety of VOCs upon reaction with O3, notably isoprene, aldehydes, and ketones. Aqueous DMS is rapidly removed from the reactions with O3. To test the importance of dissolved organic matter precursors, we added increasing (milliliter) volumes of Emiliania huxleyi culture to the equilibrator filled with aged seawater, and observed significant linear increases in gas phase concentrations of a number of VOCs. Reactions between DOM and O3 at the sea-air interface represent a potentially significant source of VOCs in marine air and a sink of atmospheric O3.

Rates of 1O 2 ( 1Δ g) production upon direct excitation of molecular oxygen by 1270 nm laser radiation in air-saturated alcohols and micellar aqueous dispersions

NASA Astrophysics Data System (ADS)

Krasnovsky, A. A.; Rоumbal, Ya. V.; Strizhakov, A. A.

2008-06-01

The oxygenation rates of the 1O2 trap, 1,3-diphenylisobenzofuran were measured in air-saturated H2O-sodium dodecyl sulfate dispersions, ethanol, methanol and benzene upon direct excitation of dissolved oxygen by infrared (1269 ± 1 nm) laser radiation. In aqueous dispersions, variation of the detergent concentration from 0.1 to 1 M resulted in the 2.5-time increase of the photooxygenation rate. The absorbance and molar absorption coefficients of oxygen were estimated in all tested systems, water and the micellar phase of detergent dispersions and compared with the rate constants of 1O2 radiative deactivation obtained from the measurement of the quantum yields of photosensitized 1O2 phosphorescence.

Reduction of nitrate in aquifer microcosms by carbon additions

USGS Publications Warehouse

Obenhuber, Donald C.; Lowrance , Richard

1991-01-01

Aquifer microcosms were used to examine the effects of NO−3 and C amendments on groundwater from the Claiborne aquifer. Nitrate concentrations of 12.17 mg L−1 in aquifer microcosms were reduced 0.92%/d to 5.84 mg L−1 by the addition of 10 mg C L−1 for 35 d. Nitrate disappearance correlated with increases in number of denitrifiers and dissolved N2O concentration and decreases in dissolved oxygen, suggesting biological denitrification. Nitrate/chloride ratios decreased in microcosms with 10 mg C L−1 added and then increased when the C addition was removed. Carbon additions of 0.4 mg C L−1 had no effect on the microbial or chemical properties of the microcosms. Nitrous oxide levels in wells sampling the Claiborne aquifer showed an increase with depth, indicating N2O production within the aquifer. Microcosms are useful tools to examine biological transformations of chemical contaminants in unconsolidated aquifer material. The remediation of NO−3 contaminated aquifers by organic infusion is possible and appears to be a function of microbial denitrification.

Using multiple chemical indicators to characterize and determine the age of groundwater from selected vents of the silver springs group, Central Florida, USA

USGS Publications Warehouse

Knowles, L.; Katz, B.G.; Toth, D.J.

2010-01-01

The Silver Springs Group, Florida (USA), forms the headwaters of the Silver River and supports a diverse ecosystem. The 30 headwater springs divide into five subgroups based on chemistry. Five selected spring vents were sampled in 2007 to better understand the contaminant sources and groundwater flow system. Elevated nitrate-N concentrations (>0.8mg/L) in the five spring vents likely originate from inorganic (fertilizers) and organic sources, based on nitrogen and oxygen isotope ratios of nitrate. Evidence for denitrification in the Lost River Boil spring includes enriched ??15N and ??18O, excess N2 gas, and low dissolved O2 concentrations (<0.5mg/L). Multiple age-tracer data (SF6, 3H, tritiogenic 3He) for the two uppermost springs (Mammoth East and Mammoth West) indicate a binary mixture dominated by recent recharge water (mean age 6-7 years, and 87-97% young water). Tracer data for the three downstream spring vents (Lost River Boil, Catfish Hotel-1, and Catfish Conventional Hall-1) indicate exponential mixtures with mean ages of 26-35 years. Contamination from non-atmospheric sources of CFCs and SF5CF3 precluded their use as age tracers here. Variations in chemistry were consistent with mean groundwater age, as nitrate-N and dissolved O2 concentrations were higher in younger waters, and the Ca/Mg ratio decreased with increasing mean age. ?? 2010 Springer-Verlag (outside the USA).

Using multiple chemical indicators to characterize and determine the age of groundwater from selected vents of the Silver Springs Group, central Florida, USA

NASA Astrophysics Data System (ADS)

Knowles, Leel; Katz, Brian G.; Toth, David J.

2010-12-01

The Silver Springs Group, Florida (USA), forms the headwaters of the Silver River and supports a diverse ecosystem. The 30 headwater springs divide into five subgroups based on chemistry. Five selected spring vents were sampled in 2007 to better understand the contaminant sources and groundwater flow system. Elevated nitrate-N concentrations (>0.8 mg/L) in the five spring vents likely originate from inorganic (fertilizers) and organic sources, based on nitrogen and oxygen isotope ratios of nitrate. Evidence for denitrification in the Lost River Boil spring includes enriched δ15N and δ18O, excess N2 gas, and low dissolved O2 concentrations (<0.5 mg/L). Multiple age-tracer data (SF6, 3H, tritiogenic 3He) for the two uppermost springs (Mammoth East and Mammoth West) indicate a binary mixture dominated by recent recharge water (mean age 6-7 years, and 87-97% young water). Tracer data for the three downstream spring vents (Lost River Boil, Catfish Hotel-1, and Catfish Conventional Hall-1) indicate exponential mixtures with mean ages of 26-35 years. Contamination from non-atmospheric sources of CFCs and SF5CF3 precluded their use as age tracers here. Variations in chemistry were consistent with mean groundwater age, as nitrate-N and dissolved O2 concentrations were higher in younger waters, and the Ca/Mg ratio decreased with increasing mean age.

Transport of oxidized multi-walled carbon nanotubes through silica based porous media: influences of aquatic chemistry, surface chemistry, and natural organic matter.

PubMed

Yang, Jin; Bitter, Julie L; Smith, Billy A; Fairbrother, D Howard; Ball, William P

2013-12-17

This paper provides results from studies of the transport of oxidized multi-walled carbon nanotubes (O-MWCNTs) of varying surface oxygen concentrations under a range of aquatic conditions and through uniform silica glass bead media. In the presence of Na(+), the required ionic strength (IS) for maximum particle attachment efficiency (i.e., the critical deposition concentration, or CDC) increased as the surface oxygen concentration of the O-MWCNTs or pH increased, following qualitative tenets of theories based on electrostatic interactions. In the presence of Ca(2+), CDC values were lower than those with Na(+) present, but were no longer sensitive to surface oxygen content, suggesting that Ca(2+) impacts the interactions between O-MWCNTs and glass beads by mechanisms other than electrostatic alone. The presence of Suwannee River natural organic matter (SRNOM) decreased the attachment efficiency of O-MWCNTs in the presence of either Na(+) or Ca(2+), but with more pronounced effects when Na(+) was present. Nevertheless, low concentrations of SRNOM (<4 mg/L of dissolved organic carbon) were sufficient to mobilize all O-MWCNTs studied at CaCl2 concentrations as high as 10 mM. Overall, this study reveals that NOM content, pH, and cation type show more importance than surface chemistry in affecting O-MWCNTs deposition during transport through silica-based porous media.

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reinoso-Maset, Estela; Steefel, Carl I.; Um, Wooyong

Uranyl oxyhydroxide minerals are important weathering products in uranium-contaminated surface and subsurface environments that regulate dissolved uranium concentrations. However, dissolution rates for this class of minerals and associated dissolution mechanisms have not been previously reported for circumneutral pH conditions, particularly for the case of flow through porous media. In this paper, the dissolution rates of K- and Na-compreignacite (K 2(UO 2) 6O 4(OH) 6·8H 2O and Na 2(UO 2) 6O 4(OH) 6·8H 2O respectively) were measured using flow-through columns reacted with two simulated background porewater (BPW) solutions of low and high dissolved total carbonate content (ca. 0.2 and 2.8 mmolmore » L -1). Column materials were characterized before and after reaction with electron microscopy, bulk chemistry, and EXAFS to identify structural and chemical changes during dissolution and to obtain insight into molecular-scale processes. The reactive transport code CrunchFlow was used to calculate overall dissolution rates while accounting for fluid transport and changes in mineral volume and reactive surface area and results were compared to steady-state dissolution rate calculations. In low carbonate BPW systems, interlayer K and Na were initially leached from both minerals, and in Na-compreignacite, K and minor divalent cations from the input solution were incorporated into the mineral structure. Results of characterization analyses suggested that after reaction both K- and Na-compreignacite resembled a disordered K-compreignacite with altered surfaces. A 10-fold increase in dissolved carbonate concentration and corresponding increase in pH (from 6.65 to 8.40) resulted in a net removal of 58-87% of total uranium mass from the columns, compared to <1% net loss in low carbonate BPW systems. Steady-state release of dissolved uranium was not observed with high carbonate solutions and post-reaction characterizations indicated a lack of development of leached or altered surfaces. Dissolution rates (normalized to specific surface area) were about 2.5-3 orders-of-magnitude faster in high versus low carbonate BPW systems, with Na-compreignacite dissolving more rapidly than K-compreignacite under both BPW conditions, possibly due to greater ion exchange (1.57·10 -10 vs. 1.28·10 -13 mol m -2 s -1 [log R = -9.81 and -12.89] and 5.79·10 -10 vs. 3.71·10 -13 mol m -2 s -1 [log R = -9.24 and -12.43] for K- and Na-compreignacite respectively). Experimental and spectroscopic results suggest that the dissolution rate is controlled by bond breaking of a uranyl group and detachment from polyhedral layers of the mineral structure. With higher dissolved carbonate concentrations, this rate-determining step is accelerated by the formation of Ca-uranyl carbonate complexes (dominant species under these conditions), which resulted in an increase of the dissolution rates. Optimization of both dissolution rate and mineral volume fraction in the reactive transport model to account for uranium mass removal during dissolution more accurately reproduced effluent data in high carbonate systems, and resulted in faster overall rates compared with a steady-state dissolution assumption. Finally, this study highlights the importance of coupling reaction and transport processes during the quantification of mineral dissolution rates to accurately predict the fate of contaminants such as uranium in porous geomedia.« less

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

DOE PAGES

Reinoso-Maset, Estela; Steefel, Carl I.; Um, Wooyong; ...

2017-06-01

Uranyl oxyhydroxide minerals are important weathering products in uranium-contaminated surface and subsurface environments that regulate dissolved uranium concentrations. However, dissolution rates for this class of minerals and associated dissolution mechanisms have not been previously reported for circumneutral pH conditions, particularly for the case of flow through porous media. In this paper, the dissolution rates of K- and Na-compreignacite (K 2(UO 2) 6O 4(OH) 6·8H 2O and Na 2(UO 2) 6O 4(OH) 6·8H 2O respectively) were measured using flow-through columns reacted with two simulated background porewater (BPW) solutions of low and high dissolved total carbonate content (ca. 0.2 and 2.8 mmolmore » L -1). Column materials were characterized before and after reaction with electron microscopy, bulk chemistry, and EXAFS to identify structural and chemical changes during dissolution and to obtain insight into molecular-scale processes. The reactive transport code CrunchFlow was used to calculate overall dissolution rates while accounting for fluid transport and changes in mineral volume and reactive surface area and results were compared to steady-state dissolution rate calculations. In low carbonate BPW systems, interlayer K and Na were initially leached from both minerals, and in Na-compreignacite, K and minor divalent cations from the input solution were incorporated into the mineral structure. Results of characterization analyses suggested that after reaction both K- and Na-compreignacite resembled a disordered K-compreignacite with altered surfaces. A 10-fold increase in dissolved carbonate concentration and corresponding increase in pH (from 6.65 to 8.40) resulted in a net removal of 58-87% of total uranium mass from the columns, compared to <1% net loss in low carbonate BPW systems. Steady-state release of dissolved uranium was not observed with high carbonate solutions and post-reaction characterizations indicated a lack of development of leached or altered surfaces. Dissolution rates (normalized to specific surface area) were about 2.5-3 orders-of-magnitude faster in high versus low carbonate BPW systems, with Na-compreignacite dissolving more rapidly than K-compreignacite under both BPW conditions, possibly due to greater ion exchange (1.57·10 -10 vs. 1.28·10 -13 mol m -2 s -1 [log R = -9.81 and -12.89] and 5.79·10 -10 vs. 3.71·10 -13 mol m -2 s -1 [log R = -9.24 and -12.43] for K- and Na-compreignacite respectively). Experimental and spectroscopic results suggest that the dissolution rate is controlled by bond breaking of a uranyl group and detachment from polyhedral layers of the mineral structure. With higher dissolved carbonate concentrations, this rate-determining step is accelerated by the formation of Ca-uranyl carbonate complexes (dominant species under these conditions), which resulted in an increase of the dissolution rates. Optimization of both dissolution rate and mineral volume fraction in the reactive transport model to account for uranium mass removal during dissolution more accurately reproduced effluent data in high carbonate systems, and resulted in faster overall rates compared with a steady-state dissolution assumption. Finally, this study highlights the importance of coupling reaction and transport processes during the quantification of mineral dissolution rates to accurately predict the fate of contaminants such as uranium in porous geomedia.« less

The effect of dissolved oxygen on the relaxation rates of blood plasma: Implications for hyperoxia calibrated BOLD.

PubMed

Ma, Yuhan; Berman, Avery J L; Pike, G Bruce

2016-12-01

To determine the contribution of paramagnetic dissolved oxygen in blood plasma to blood-oxygenation-level-dependent (BOLD) signal changes in hyperoxic calibrated BOLD studies. Bovine blood plasma samples were prepared with partial pressures of oxygen (pO 2 ) ranging from 110 to 600 mmHg. R 1 , R 2 , and R 2 * of the plasma with dissolved oxygen were measured using quantitative MRI sequences at 3 Tesla. Simulations were performed to predict the relative effects of dissolved oxygen and deoxyhemoglobin changes in hyperoxia calibrated BOLD. The relaxivities of dissolved oxygen in plasma were found to be r 1, O2 =1.97 ± 0.09 ×10 -4 s -1 mmHg -1 , r 2, O2 =2.3 ± 0.7 ×10 -4 s -1 mmHg -1 , and r 2, O2 * = 2.3 ± 0.7 ×10 -4 s -1 mmHg -1 . Simulations predict that neither the transverse nor longitudinal relaxation rates of dissolved oxygen contribute significantly to the BOLD signal during hyperoxia. During hyperoxia, the increases in R 2 and R 2 * of blood from dissolved oxygen in plasma are considerably less than the decreases in R 2 and R 2 * from venous deoxyhemoglobin. R 1 effects due to dissolved oxygen are also predicted to be negligible. As a result, dissolved oxygen in arteries should not contribute significantly to the hyperoxic calibrated BOLD signal. Magn Reson Med 76:1905-1911, 2016. © 2015 International Society for Magnetic Resonance in Medicine. © 2015 International Society for Magnetic Resonance in Medicine.

Continuous monitoring of dissolved gases with membrane inlet mass spectrometry to fingerprint river biochemical activity

NASA Astrophysics Data System (ADS)

Vautier, Camille; Chatton, Eliot; Abbott, Benjamin; Harjung, Astrid; Labasque, Thierry; Guillou, Aurélie; Pannard, Alexandrine; Piscart, Christophe; Laverman, Anniet; Kolbe, Tamara; Massé, Stéphanie; de Dreuzy, Jean-Raynald; Thomas, Zahra; Aquilina, Luc; Pinay, Gilles

2017-04-01

Water quality in rivers results from biogeochemical processes in contributing hydrological compartments (soils, aquifers, hyporheic and riparian zones) and biochemical activity in the river network itself. Consequently, chemical fluxes fluctuate on multiple spatial and temporal scales, leading eventually to complex concentration signals in rivers. We characterized these fluctuations with innovative continuous monitoring of dissolved gases, to quantify transport and reaction processes occurring in different hydrological compartments. We performed stream-scale experiments in two headwater streams in Brittany, France. Factorial injections of inorganic nitrogen (NH4NO3), inorganic phosphate (P2O5) and multiple sources of labile carbon (acetate, tryptophan) were implemented in the two streams. We used a new field application of membrane inlet mass spectrometry to continuously monitor dissolved gases for multiple day-night periods (Chatton et al., 2016). Quantified gases included He, O2, N2, CO2, CH4, N2O, and 15N of dissolved N2 and N2O. We calibrated and assessed the methodology with well-established complementary techniques including gas chromatography and high-frequency water quality sensors. Wet chemistry and radon analysis complemented the study. The analyses provided several methodological and ecological insights and demonstrated that high frequency variations linked to background noise can be efficiently determined and filtered to derive effective fluxes. From a more fundamental point of view, the tested stream segments were fully characterized with extensive sampling of riverbeds and laboratory experiments, allowing scaling of point-level microbial and invertebrate diversity and activity on in-stream processing. This innovative technology allows fully-controlled in-situ experiments providing rich information with a high signal to noise ratio. We present the integrated nutrient demand and uptake and discuss limiting processes and elements at the reach and catchment scales. Eliot Chatton, Thierry Labasque, Jérôme de La Bernardie, Nicolas Guihéneuf, Olivier Bour, Luc Aquilina. 2016. Field Continuous Measurement of Dissolved Gases with a CF-MIMS: Applications to the Physics and Biogeochemistry of Groundwater Flow. Environ. Sci. Technol.

Improved Electrolytic Hydrogen Peroxide Generator

NASA Technical Reports Server (NTRS)

James, Patrick I.

2005-01-01

An improved apparatus for the electrolytic generation of hydrogen peroxide dissolved in water has been developed. The apparatus is a prototype of H2O2 generators for the safe and effective sterilization of water, sterilization of equipment in contact with water, and other applications in which there is need for hydrogen peroxide at low concentration as an oxidant. Potential applications for electrolytic H2O2 generators include purification of water for drinking and for use in industrial processes, sanitation for hospitals and biotechnological industries, inhibition and removal of biofouling in heat exchangers, cooling towers, filtration units, and the treatment of wastewater by use of advanced oxidation processes that are promoted by H2O2.

Exploration of H2O-CO2 Solubility in Alkali Basalt at low-H2O

NASA Astrophysics Data System (ADS)

Roggensack, K.; Allison, C. M.; Clarke, A. B.

2017-12-01

A number of recent experimental studies have found conflicting evidence for and against the influence of H2O on CO2 solubility in basalt and alkali-rich mafic magma (e.g. Behrens et al., 2009; Shishkina et al., 2010;2014; Iacono-Marziano et al., 2012). Some of the uncertainty is due to the error with spectroscopic determination (FTIR) of carbon and the challenge of controlling H2O abundance in experiments. It's been widely observed that even experimental capsules without added H2O may produce hydrous glasses containing several wt.% H2O. We conducted fluid-saturated, mixed-fluid (H2O-CO2) experiments to determine the solubility in alkali basalt with particular emphasis on conditions at low-H2O. To limit possible H2O contamination, materials were dried prior to loading and experimental capsules were sealed under vacuum. Experiments were run using a piston-cylinder, in Pt (pre-soaked in Fe) or AuPd capsules and operating at pressures from 400 to 600 MPa. Post-run the capsules were punctured under vacuum and fluids were condensed, separated, and measured by mercury manometry. A comparison between two experiments run at the same temperature and pressure conditions but with different fluid compositions illustrates the correlation between carbonate and H2O solubility. Uncertainties associated with using concentrations calculated from FTIR data can be reduced by directly comparing analyses on wafers of similar thickness. We observe that the experiment with greater H2O absorbance also has a higher carbonate absorbance than the experiment with lower H2O absorbance. Since the experiments were run at the same pressure, the experiment with more water-rich fluid, and higher dissolved H2O, has lower CO2 fugacity, but surprisingly has higher dissolved CO2 content. Overall, the results show two distinct trends. Experiments conducted at low-H2O (0.5 to 0.8 wt.%) show lower dissolved CO2 than those conducted at moderate-H2O (2 to 3 wt.%) at similar CO2 fugacity. These data show that the presence of H2O enhances CO2 solubility at low to moderate H2O abundance. One implication of these results is that volatile-saturated magmas will behave differently depending on H2O abundance. Magmas with low H2O abundance could undergo isobaric degassing through addition of a CO2-rich fluid.

Factors influencing the stability and type of hydroxyapatite stabilized Pickering emulsion.

PubMed

Zhang, Ming; Wang, Ai-Juan; Li, Jun-Ming; Song, Na; Song, Yang; He, Rui

2017-01-01

Hydroxyapatite (HAp) nanoparticle stabilized Pickering emulsion was fabricated with poly(l-lactic acid) dissolved in dichloromethane (CH 2 Cl 2 ) solution as oil phase and HAp aqueous dispersion as aqueous phase. Pickering emulsion was cured via in situ solvent evaporation method. Effect of PLLA concentrations, pH value, HAp concentrations, oil-water ratio, emulsification rates and times were studied on emulsion stability and emulsion type, etc. The results indicated emulsion stability increased with the increase of HAp concentration, emulsification rate and time; it is very stable when pH value of aqueous phase was adjusted to 10. Stable W/O and O/W emulsions were fabricated successfully using as-received HAp particles as stabilizer by adjusting the fabricating parameters. The interaction between HAp and PLLA played an important role to stabilize Pickering emulsions. SEM results indicated that both microsphere and porous materials were fabricated using emulsion stabilized by unmodified HAp nanoparticles, implying that both W/O and O/W emulsion type were obtained. Copyright © 2016 Elsevier B.V. All rights reserved.

The effect of oxygen fugacity on the solubility of carbon-oxygen fluids in basaltic melt

NASA Technical Reports Server (NTRS)

Pawley, Alison R.; Holloway, John R.; Mcmillan, Paul F.

1992-01-01

The solubility of CO2-CO fluids in a midocean ridge basalt have been measured at 1200 C, 500-1500 bar, and oxygen fugacities between NNO and NNO-4. In agreement with results of previous studies, the results reported here imply that, at least at low pressures, CO2 dissolves in basaltic melt only in the form of carbonate groups. The dissolution reaction is heterogeneous, with CO2 molecules in the fluid reacting directly with reactive oxygens in the melt to produce CO3(2-). CO, on the other hand, is insoluble, dissolving neither as carbon, molecular CO, nor CO3(2-). It is shown that, for a given pressure and temperature, the concentration of dissolved carbon-bearing species in basaltic melt in equilibrium with a carbon-oxygen fluid is proportional to the mole fraction of CO2 in the fluid, which is a function of fO2. At low pressures CO2 solubility is a linear function of CO2 fugacity at constant temperatures.

Biological groundwater denitrification systems: Lab-scale trials aimed at nitrous oxide production and emission assessment.

PubMed

Capodici, Marco; Avona, Alessia; Laudicina, Vito Armando; Viviani, Gaspare

2018-07-15

Bio-trenches are a sustainable option for treating nitrate contamination in groundwater. However, a possible side effect of this technology is the production of nitrous oxide, a greenhouse gas that can be found both dissolved in the liquid effluent as well as emitted as off gas. The aim of this study was to analyze NO 3 - removal and N 2 O production in lab-scale column trials. The column contained olive nut as organic carbon media. The experimental study was divided into three phases (I, II and III) each characterized by different inlet NO 3 - concentrations (30, 50, 75mgNO 3 -NL -1 respectively). Sampling ports deployed along the length of the column allowed to observe the denitrification process as well as the formation and consumption of intermediate products, such as nitrite (NO 2 - ) and nitrous oxide (N 2 O). In particular, it was observed that N 2 O production represent only a small fraction of removed NO 3 - during Phase I and II, both for dissolved (0.007%) and emitted (0.003%) phase, and it was recorded a high denitrification efficiency, over 99%. Nevertheless, significantly higher values were recorded for Phase 3 concerning emitted phase (0.018%). This fact is due to increased inlet concentration which resulted in a carbon limitation and in a consequent decrease in denitrification efficiency (76%). Copyright © 2018 Elsevier B.V. All rights reserved.

Sulfur geochemistry of hydrothermal waters in Yellowstone National Park, Wyoming, USA. II. Formation and decomposition of thiosulfate and polythionate in Cinder Pool

NASA Astrophysics Data System (ADS)

Xu, Y.; Schoonen, M. A. A.; Nordstrom, D. K.; Cunningham, K. M.; Ball, J. W.

2000-04-01

Cinder Pool is an acid-sulfate-chloride boiling spring in Norris Geyser Basin, Yellowstone National Park. The pool is unique in that its surface is partially covered with mm-size, black, hollow sulfur spherules, while a layer of molten sulfur resides at the bottom of the pool (18 m depth). The sulfur speciation in the pool was determined on four different days over a period of two years. Samples were taken to evaluate changes with depth and to evaluate the importance of the sulfur spherules on sulfur redox chemistry. All analyses were conducted on site using a combination of ion chromatography and colorimetric techniques. Dissolved sulfide (H2S), thiosulfate (S2O32-), polythionates (SxO62-), and sulfate were detected. The polythionate concentration was highly variable in time and space. The highest concentrations were found in surficial samples taken from among the sulfur spherules. With depth, the polythionate concentrations dropped off. The maximum observed polythionate concentration was 8 μM. Thiosulfate was rather uniformly distributed throughout the pool and concentrations ranged from 35 to 45 μM. Total dissolved sulfide concentrations varied with time, concentrations ranged from 16 to 48 μM. Sulfate was relatively constant, with concentrations ranging from 1150 to 1300 μM. The sulfur speciation of Cinder Pool is unique in that the thiosulfate and polythionate concentrations are significantly higher than for any other acid-sulfate spring yet sampled in Yellowstone National Park. Complementary laboratory experiments show that thiosulfate is the intermediate sulfoxyanion formed from sulfur hydrolysis under conditions similar to those found in Cinder Pool and that polythionates are formed via the oxidation of thiosulfate by dissolved oxygen. This last reaction is catalyzed by pyrite that occurs as a minor constituent in the sulfur spherules floating on the pool's surface. Polythionate decomposition proceeds via two pathways: (1) a reaction with H2S, yielding thiosulfate and elemental sulfur; and (2) by disproportionation to sulfate and thiosulfate. This study demonstrates that the presence of a subaqueous molten sulfur pool and sulfur spherules in Cinder Pool is of importance in controlling the pathways of aqueous sulfur redox reactions. Some of the insights gained at Cinder Pool may be relevant to acid crater lakes where sulfur spherules are observed and variations in polythionate concentrations are used to monitor and predict volcanic activity.

Assessing the Risk of Engineered Nanomaterials in the Environment: Development and Application of the nanoFate Model.

PubMed

Garner, Kendra L; Suh, Sangwon; Keller, Arturo A

2017-05-16

We developed a dynamic multimedia fate and transport model (nanoFate) to predict the time-dependent accumulation of metallic engineered nanomaterials (ENMs) across environmental media. nanoFate considers a wider range of processes and environmental subcompartments than most previous models and considers ENM releases to compartments (e.g., urban, agriculture) in a manner that reflects their different patterns of use and disposal. As an example, we simulated ten years of release of nano CeO 2 , CuO, TiO 2 , and ZnO in the San Francisco Bay area. Results show that even soluble metal oxide ENMs may accumulate as nanoparticles in the environment in sufficient concentrations to exceed the minimum toxic threshold in freshwater and some soils, though this is more likely with high-production ENMs such as TiO 2 and ZnO. Fluctuations in weather and release scenario may lead to circumstances where predicted ENM concentrations approach acute toxic concentrations. The fate of these ENMs is to mostly remain either aggregated or dissolved in agricultural lands receiving biosolids and in freshwater or marine sediments. Comparison to previous studies indicates the importance of some key model aspects including climatic and temporal variations, how ENMs may be released into the environment, and the effect of compartment composition on predicted concentrations.

Groundwater denitrification in two agricultural river catchments: influence of hydro-geological setting and aquifer geochemistry

NASA Astrophysics Data System (ADS)

McAleer, Eoin; Mellander, Per-Erik; Coxon, Catherine; Richards, Karl G.; Jahangir, Mohammad M. R.

2015-04-01

Identifying subsurface environments with a natural capacity for denitrification is important for improving agricultural management. At the catchment scale, a complex hierarchy of landscape, hydro-geological and physico-chemical characteristics combine to affect the distribution of groundwater nitrate (NO3-). This study was conducted along four instrumented hillslopes in two ca. 10km2 agricultural river catchments in Ireland, one dominated by arable and one by grassland agriculture. Both catchments are characterised by well drained soils, but have differing aquifer characteristics. The arable catchment is underlain by weathered Ordovician slate bedrock which is extensively fractured with depth. The grassland catchment is characterised by Devonian sandstone bedrock, exhibiting both lateral (from upslope to near stream) and vertical variations in permeability along each hillslope. The capacity for groundwater denitrification was assessed by examining the concentration and distribution patterns of N species (total nitrogen, nitrate, nitrite, ammonium), dissolved organic carbon (DOC), dissolved oxygen (DO) and redox potential (Eh) in monthly samples from shallow and deep groundwater piezometers (n=37). Additionally, the gaseous products of denitrification: nitrous oxide (N2O) and excess dinitrogen (excess N2) were measured seasonally using gas chromatography and membrane inlet mass spectroscopy, respectively. The slate catchment was characterised by uniformity, both laterally and vertically, in aquifer geochemistry and gaseous denitrification products. The four year spatial mean groundwater NO3--N concentration was 6.89 mg/l and exhibited low spatial and temporal variability (temporal SD: 1.19 mg/l, spatial SD: 1.185 mg/l). Elevated DO concentrations (mean: 9.75 mg/l) and positive Eh (mean: +176.5mV) at all sample horizons indicated a setting with little denitrification potential. This non-reducing environment was reflected in a low accumulation of denitrification products (excess N2 mean: 1.57 mg/l, N2O mean: 1.61µg/l). Groundwater in the sandstone catchment had a comparable mean NO3--N concentration to that of the slate site (6.24mg/l) and while temporal variation was low (SD: 0.9 mg/l), spatial variation was substantially greater (SD: 3.63 mg/l). The accumulation of denitrification products in the sandstone catchment showed a large contrast to that of the slate with excess N2 ranging from 0.16-8.77 mg/l and N2O from 0.07-66.42 µg/l. Mean dissolved oxygen concentration and redox potential were 5.6mg/l and 67.5mV respectively. The near stream zones in particular were marked by favourable denitrifying conditions: hydraulic conductivity (<2m/day), Eh (<50mV) and DO (<5mg/l). Winter recharge had a diluting effect, increasing the concentration of DO and Eh with a concurrent decrease in excess N2 and N2O. The evolution of groundwater geochemistry along a subsurface flow path is a function of residence time. While both catchments are characterised as permeable, the slate catchment exhibits greater hydraulic conductivity values, particularly at depth, with groundwater geochemistry in all horizons reflective of recently recharged water. The deeper groundwater pathways and near stream zones in the sandstone catchment have a lower hydraulic conductivity. As such, dissolved oxygen and redox gradients occur with depth, causing the development of NO3- reducing zones.

Comparative evolution of oxygen, carbon dioxide, nitrogen, and sulfites during storage of a rosé wine bottled in PET and glass.

PubMed

Toussaint, Marie; Vidal, Jean-Claude; Salmon, Jean-Michel

2014-04-02

The management of dissolved and headspace gases during bottling and the choice of packaging are both key factors for the shelf life of wine. Two kinds of 75 cL polyethylene terephthalate (PET) bottles (with or without recycled PET) were compared to glass bottles filled with a rosé wine, closed with the same screwcaps and stored upright at 20 °C in light or in the dark. Analytical monitoring (aphrometric pressure, headspace volume, O2, N2, CO2, and SO2) was carried out for 372 days. After the consumption of O2 trapped during bottling, the total O2 content in glass bottles remained stable. A substantial decrease of CO2 and SO2 concentration and an increase of O2 concentration were observed in the PET bottles after 6 months because of the considerable gas permeability of monolayer PET. Light accelerated O2 consumption during the early months. Finally, the kinetic monitoring of partial pressures in gas and liquid phases in bottles showed contrasting behavior of O2 and N2 in comparison with CO2.

Agriculture-related trends in groundwater quality of the glacial deposits aquifer, central Wisconsin

USGS Publications Warehouse

Saad, D.A.

2008-01-01

Measuring and understanding trends in groundwater quality is necessary for determining whether changes in land-management practices have an effect on groundwater quality. This paper describes an approach that was used to measure and understand trends using data from two groundwater studies conducted in central Wisconsin as part of the USGS NAWQA program. One of the key components of this approach, determining the age of sampled groundwater, gave a temporal component to the snapshots of water quality that were obtained through synoptic-sampling efforts. This approach can be used at other locations where groundwater quality data are collected, groundwater age can be determined, and associated temporal data are available. Results of these studies indicate measured concentrations of nitrate and atrazine plus deethylatrazine were correlated to historical patterns of fertilizer and atrazine use. Concentrations of nitrate in groundwater have increased over time; concentrations of atrazine plus deethylatrazine increased and then decreased. Concentrations of nitrate also were correlated to screen depth below the water level and concentrations of dissolved O2; concentrations of atrazine plus deethylatrazine were correlated to dissolved O2 and annual precipitation. To measure trends in concentrations of atrazine plus deethylatrazine, the data, collected over a near-decadal period, were adjusted to account for changes in laboratory-reporting levels and analytical recoveries. Only after accounting for these changes was it apparent that the median concentrations of atrazine plus deethylatrazine decreased over the near-decadal interval between sampling efforts. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Greenhouse gases concentrations and fluxes from subtropical small reservoirs in relation with watershed urbanization

NASA Astrophysics Data System (ADS)

Wang, Xiaofeng; He, Yixin; Yuan, Xingzhong; Chen, Huai; Peng, Changhui; Yue, Junsheng; Zhang, Qiaoyong; Diao, Yuanbin; Liu, Shuangshuang

2017-04-01

Greenhouse gas (GHG) emissions from reservoirs and global urbanization have gained widespread attention, yet the response of GHG emissions to the watershed urbanization is poorly understood. Meanwhile, there are millions of small reservoirs worldwide that receive and accumulate high loads of anthropogenic carbon and nitrogen due to watershed urbanization and can therefore be hotspots of GHG emissions. In this study, we assessed the GHG concentrations and fluxes in sixteen small reservoirs draining urban, agricultural and forested watersheds over a period of one year. The concentrations of pCO2, CH4 and N2O in sampled urban reservoirs that received more sewage input were higher than those in agricultural reservoirs, and were 3, 7 and 10 times higher than those in reservoirs draining in forested areas, respectively. Accordingly, urban reservoirs had the highest estimated GHG flux rate. Regression analysis indicated that dissolved total phosphorus, dissolved organic carbon (DOC) and chlorophyll-a (Chl-a) had great effect on CO2 production, while the nitrogen (N) and phosphorus (P) content of surface water were closely related to CH4 and N2O production. Therefore, these parameters can act as good predictors of GHG emissions in urban watersheds. Given the rapid progress of global urbanization, small urban reservoirs play a crucial role in accounting for regional GHG emissions and cannot be ignored.

The effects of a whole-watershed calcium addition on the chemistry of stream storm events at the Hubbard Brook Experimental Forest in NH, USA.

PubMed

Cho, Youngil; Driscoll, Charles T; Blum, Joel D

2009-10-01

Patterns of storm runoff chemistry from a wollastonite (calcium-silicate mineral, CaSiO(3)) treated watershed (W1) were compared with a reference watershed (W6) at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire (NH), USA to investigate the role of Ca(2+) supply in the acid-base status of stream chemistry. In the summer of 2003, six storm events were studied in W1 and W6 to evaluate the effects of the wollastonite treatment on the episodic acidification of stream waters. Although mean values of Ca(2+) concentrations decreased slightly from 33.8 to 31.7 mumol/L with increasing stream discharge in W1 during the events, the mean value of acid neutralizing capacity (ANC) was positive (1.2 mueq/L) during storm events, compared to negative values (-0.2 mueq/L) in W6. This pattern is presumably due to enhanced Ca(2+) supply in W1 (20.7 to 29.0% of dissolved Ca(2+) derived from the added wollastonite) to stream water as a result of interflow along shallow flowpaths. In addition, the application of wollastonite increased pH and dissolved silica (H(4)SiO(4)) concentrations, and decreased the concentration of inorganic monomeric Al (Al(i)) in W1 in comparison with W6 during storm events. Despite an increase in SO(4)(2-) concentration, likely due to desorption of sulfate from soil after the treatment, the watershed showed an increase in ANC compared to the reference watershed, serving to mitigate episodic acidification.

Relating N2O emissions during biological nitrogen removal with operating conditions using multivariate statistical techniques.

PubMed

Vasilaki, V; Volcke, E I P; Nandi, A K; van Loosdrecht, M C M; Katsou, E

2018-04-26

Multivariate statistical analysis was applied to investigate the dependencies and underlying patterns between N 2 O emissions and online operational variables (dissolved oxygen and nitrogen component concentrations, temperature and influent flow-rate) during biological nitrogen removal from wastewater. The system under study was a full-scale reactor, for which hourly sensor data were available. The 15-month long monitoring campaign was divided into 10 sub-periods based on the profile of N 2 O emissions, using Binary Segmentation. The dependencies between operating variables and N 2 O emissions fluctuated according to Spearman's rank correlation. The correlation between N 2 O emissions and nitrite concentrations ranged between 0.51 and 0.78. Correlation >0.7 between N 2 O emissions and nitrate concentrations was observed at sub-periods with average temperature lower than 12 °C. Hierarchical k-means clustering and principal component analysis linked N 2 O emission peaks with precipitation events and ammonium concentrations higher than 2 mg/L, especially in sub-periods characterized by low N 2 O fluxes. Additionally, the highest ranges of measured N 2 O fluxes belonged to clusters corresponding with NO 3 -N concentration less than 1 mg/L in the upstream plug-flow reactor (middle of oxic zone), indicating slow nitrification rates. The results showed that the range of N 2 O emissions partially depends on the prior behavior of the system. The principal component analysis validated the findings from the clustering analysis and showed that ammonium, nitrate, nitrite and temperature explained a considerable percentage of the variance in the system for the majority of the sub-periods. The applied statistical methods, linked the different ranges of emissions with the system variables, provided insights on the effect of operating conditions on N 2 O emissions in each sub-period and can be integrated into N 2 O emissions data processing at wastewater treatment plants. Copyright © 2018. Published by Elsevier Ltd.

Nitrous oxide as an indicator of nitrogen transformation in a septic system plume

NASA Astrophysics Data System (ADS)

Li, L.; Spoelstra, J.; Robertson, W. D.; Schiff, S. L.; Elgood, R. J.

2014-11-01

This study evaluates the use of ground water N2O concentration and stable isotope composition for providing insights into nitrogen cycling processes in a large septic system plume in southern Ontario, Canada. An extremely large range of dissolved N2O concentrations were measured (0.4-1071 μg N/L) that were higher than atmospheric equilibrium values of ∼0.3 μg N/L, demonstrating substantial N2O production in the subsurface. The highest N2O concentrations occurred around the periphery of a mid-depth zone where NO3- attenuation, elevated DOC concentration, and NO3- stable isotope ratios provided evidence that denitrification was occurring. Broad ranges in δ15N-N2O (-45.8‰ to +30.6‰) and δ18O-N2O (+20.4‰ to +96.0‰) were evident. Using literature isotopic enrichment factors, which differ for N2O produced during nitrification and denitrification, and measured ranges of plume NH4+ and NO3- isotopic ratios, zones of both nitrifier-derived N2O (shallow zone) and denitrifier-N2O (mid-depth and deeper zones) could be identified. Time series sampling showed that nitrifier N2O was present early in the summer season (June) but then denitrifier N2O was more dominant later in the season. In a mid-depth NO3- depleted zone, the production of denitrifier-N2O was evident early in the season when 15N and 18O enrichment of NO3- was not sufficiently advanced to be indicative of denitrification, although δ15N and δ18O values of NO3- increased later in the season. The analysis of N2O concentrations and stable isotopic composition, in conjunction with conventional chemical analyses, provides insights into N-cycling processes in the Long Point ground water septic plume. However, large ranges in the isotopic composition of N2O produced by nitrifiers and denitrifiers meant that δ15N and δ18O analysis of ground water N2O provided qualitative, rather than quantitative, information on denitrifier versus nitrifier production of N2O at this site.

Water-chemistry data for selected springs, geysers, and streams in Yellowstone National Park, Wyoming, 1999-2000

USGS Publications Warehouse

Ball, James W.; McCleskey, R. Blaine; Nordstrom, D. Kirk; Holloway, JoAnn M.; Verplanck, Philip L.; Sturtevant, Sabin A.

2002-01-01

Sixty-seven water analyses are reported for samples collected from 44 hot springs and their overflow drainages and two ambient-temperature acid streams in Yellowstone National Park (YNP) during 1990-2000. Thirty-seven analyses are reported for 1999, 18 for June of 2000, and 12 for September of 2000. These water samples were collected and analyzed as part of research investigations in YNP on microbially mediated sulfur oxidation in stream water, arsenic and sulfur redox speciation in hot springs, and chemical changes in overflow drainages that affect major ions, redox species, and trace elements. Most samples were collected from sources in the Norris Geyser Basin. Two ambient-temperature acidic stream systems, Alluvium and Columbine Creeks and their tributaries in Brimstone Basin, were studied in detail. Analyses were performed at or near the sampling site, in an on-site mobile laboratory truck, or later in a USGS laboratory, depending on stability of the constituent and whether or not it could be preserved effectively. Water temperature, specific conductance, pH, Eh, dissolved oxygen (D.O.), and dissolved H2S were determined on-site at the time of sampling. Alkalinity, acidity, and F were determined within a few days of sample collection by titration with acid, titration with base, and ion-selective electrode or ion chromatography (IC), respectively. Concentrations of S2O3 and SxO6 were determined as soon as possible (minutes to hours later) by IC. Concentrations of Br, Cl, NH4, NO2, NO3, SO4, Fe(II), and Fe(total) were determined within a few days of sample collection. Densities were determined later in the USGS laboratory. Concentrations of Li and K were determined by flame atomic absorption spectrometry. Concentrations of Al, As(total), B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe(total), K, Li, Mg, Mn, Na, Ni, Pb, Se, Si, Sr, V, and Zn were determined by inductively-coupled plasma-optical emission spectrometry. Trace concentrations of Cd, Cr, Cu, Pb, and Sb were determined by Zeeman-corrected graphitefurnace atomic-absorption spectrometry. Trace concentrations of As(total) and As(III) were determined by hydride generation atomic-absorption spectrometry using a flow-injection analysis system. Concentrations of Cl, NO3, Br, and SO4 were determined by IC. Concentrations of Fe(II) and Fe(total) were determined by the ferrozine colorimetric method. Concentrations of NO2 were determined by colorimetry using matrix-matched standards. Concentrations of NH4 were determined by IC, with reanalysis by colorimetry where separation of Na and NH4 peaks was poor. Dissolved organic carbon (DOC) concentrations were determined by the wet persulfate oxidation method.

Hydrographic and Ecological Effects of Enlargement of the Chesapeake and Delaware Canal. Appendix IV. Benthos of Delaware Waters in and Near C and D Canal.

DTIC Science & Technology

1973-09-01

stations in the last three sampling periods of this project to supplement the regular I infaunal sampling schedule. Salinity , dissolved oxygen, water...summer. Salinity was quite variable but tended to be * highest in late summer (range 0.1 — 10 O/~~~~~~ )~~~ Dissolved oxygen, being an inverse...function of both salinity and temperature, dropped in summer. Concentrations in the 2—3 mg/l range were not unusual. The physical data collected in

Effects of Bubble-Mediated Processes on Nitrous Oxide Dynamics in Denitrifying Bioreactors

NASA Astrophysics Data System (ADS)

McGuire, P. M.; Falk, L. M.; Reid, M. C.

2017-12-01

To mitigate groundwater and surface water impacts of reactive nitrogen (N), agricultural and stormwater management practices can employ denitrifying bioreactors (DNBs) as low-cost solutions for enhancing N removal. Due to the variable nature of hydrologic events, DNBs experience dynamic flows which can impact physical and biological processes within the reactors and affect performance. A particular concern is incomplete denitrification, which can release the potent greenhouse gas nitrous oxide (N2O) to the atmosphere. This study aims to provide insight into the effects of varying hydrologic conditions upon the operation of DNBs by disentangling abiotic and biotic controls on denitrification and N2O dynamics within a laboratory-scale bioreactor. We hypothesize that under transient hydrologic flows, rising water levels lead to air entrapment and bubble formation within the DNB porous media. Mass transfer of oxygen (O2) between trapped gas and liquid phases creates aerobic microenvironments that can inhibit N2O reductase (NosZ) enzymes and lead to N2O accumulation. These bubbles also retard N2O transport and make N2O unavailable for biological reduction, further enhancing atmospheric fluxes when water levels fall. The laboratory-scale DNB permits measurements of longitudinal and vertical profiles of dissolved constituents as well as trace gas concentrations in the reactor headspace. We describe a set of experiments quantifying denitrification pathway biokinetics under steady-state and transient hydrologic conditions and evaluate the role of bubble-mediated processes in enhancing N2O accumulation and fluxes. We use sulfur hexafluoride and helium as dissolved gas tracers to examine the impact of bubble entrapment upon retarded gas transport and enhanced trace gas fluxes. A planar optode sensor within the bioreactor provides near-continuous 2-D profiles of dissolved O2 within the bioreactor and allows for identification of aerobic microenvironments. We use qPCR to examine the relative abundance of the denitrifying genes nitrate reductase and NosZ within the bioreactor and explore gradients in denitrification biomarkers coinciding with denitrification intermediate profiles. Insights gained from this study will advance understanding of gas dynamics within environmental porous media.

Characterization and mitigation of nitrous oxide (N2 O) emissions from partial and full-nitrification BNR processes based on post-anoxic aeration control.

PubMed

Brotto, Ariane Coelho; Li, Huosheng; Dumit, Muriel; Gabarró, Jordi; Colprim, Jesús; Murthy, Sudhir; Chandran, Kartik

2015-11-01

It has been reported that a directional change from anoxic to aerobic conditions is a common trigger for nitrous oxide (N2 O) production by ammonia oxidizing bacteria (AOB). By extension, during anoxic-aerobic cycling, post-anoxic dissolved oxygen (DO) concentrations might likely play a role in the magnitude of N2 O emissions observed. The overall goal of this study was to determine the impact of three select post-anoxic DO concentrations (0.8, 2.0, and 3.0 mg O2 /L) on N2 O emissions from partial-nitrification (PN) and full-nitrification (FN) reactors subjected to anoxic-aerobic cycling and, ultimately, to explore the development of strategies to minimize N2 O emissions from PN and FN based biological nitrogen removal (BNR) processes. Statistically similar N2 O emissions were observed during anoxia for both PN (0.62 ± 0.21% N load) and FN (0.61 ± 0.070% N load) processes. In contrast, N2 O emissions were statistically lower for PN (0.86 ± 0.25% N load) than for FN (4.6 ± 2.8% N load), during the post-anoxic aerobic phase, when compared together for all three post-anoxic DO concentrations. Further, for PN, the highest N2 O emissions were observed at the highest post-anoxic DO concentration of 3.0 mg O2 /L (1.2% N load), likely due to the highest corresponding AOB specific growth rate. In contrast, for FN, the highest N2 O emissions were at the lowest post-anoxic DO concentration of 0.8 mg O2 /L (8.5% N load). The higher emissions from FN process at low DO concentrations were associated with a lag in nitrite oxidizing bacteria activity upon recovery to aerobic conditions. This lag phase contributed to transient nitrite accumulation, and in turn correlated positively to the observed N2 O emissions. Based on our findings, a gradual ramp up in post-anoxic DO concentrations can minimize N2 O emissions during PN-based BNR, whereas a completely different strategy, entailing a rapid increase in post-anoxic DO concentrations can minimize emissions during FN-based BNR operations. © 2015 Wiley Periodicals, Inc.

Concentrations of dissolved oxygen in the lower Puyallup and White rivers, Washington, August and September 2000 and 2001

USGS Publications Warehouse

Ebbert, J.C.

2002-01-01

The U.S. Geological Survey, Washington State Department of Ecology, and Puyallup Tribe of Indians conducted a study in August and September 2001 to assess factors affecting concentrations of dissolved oxygen in the lower Puyallup and White Rivers, Washington. The study was initiated because observed concentrations of dissolved oxygen in the lower Puyallup River fell to levels ranging from less than 1 milligram per liter (mg/L) to about 6 mg/L on several occasions in September 2000. The water quality standard for the concentration of dissolved oxygen in the Puyallup River is 8 mg/L.This study concluded that inundation of the sensors with sediment was the most likely cause of the low concentrations of dissolved oxygen observed in September 2000. The conclusion was based on (1) knowledge gained when a dissolved-oxygen sensor became covered with sediment in August 2001, (2) the fact that, with few exceptions, concentrations of dissolved oxygen in the lower Puyallup and White Rivers did not fall below 8 mg/L in August and September 2001, and (3) an analysis of other mechanisms affecting concentrations of dissolved oxygen.The analysis of other mechanisms indicated that they are unlikely to cause steep declines in concentrations of dissolved oxygen like those observed in September 2000. Five-day biochemical oxygen demand ranged from 0.22 to 1.78 mg/L (mean of 0.55 mg/L), and river water takes only about 24 hours to flow through the study reach. Photosynthesis and respiration cause concentrations of dissolved oxygen in the lower Puyallup River to fluctuate as much as about 1 mg/L over a 24-hour period in August and September. Release of water from Lake Tapps for the purpose of hydropower generation often lowered concentrations of dissolved oxygen downstream in the White River by about 1 mg/L. The effect was smaller farther downstream in the Puyallup River at river mile 5.8, but was still observable as a slight decrease in concentrations of dissolved oxygen caused by photosynthesis and respiration. The upper limit on oxygen demand caused by the scour of anoxic bed sediment and subsequent oxidation of reduced iron and manganese is less than 1 mg/L. The actual demand, if any, is probably negligible.In August and September 2001, concentrations of dissolved oxygen in the lower Puyallup River did not fall below the water-quality standard of 8 mg/L, except at high tide when the saline water from Commencement Bay reached the monitor at river mile 2.9. The minimum concentration of dissolved oxygen (7.6 mg/L) observed at river mile 2.9 coincided with the maximum value of specific conductance. Because the dissolved-oxygen standard for marine water is 6.0 mg/L, the standard was not violated at river mile 2.9. The concentration of dissolved oxygen at river mile 1.8 in the White River dropped below the water-quality standard on two occasions in August 2001. The minimum concentration of 7.8 mg/L occurred on August 23, and a concentration of 7.9 mg/L was recorded on August 13. Because there was some uncertainty in the monitoring record for those days, it cannot be stated with certainty that the actual concentration of dissolved oxygen in the river dropped below 8 mg/L. However, at other times when the quality of the monitoring record was good, concentrations as low as 8.2 mg/L were observed at river mile 1.8 in the White River.

Vanadium Flow Battery Electrolyte Synthesis via Chemical Reduction of V2O5 in Aqueous HCl and H2SO4.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Small, Leo J.; Pratt, Harry; Staiger, Chad

We report a simple method to synthesize V 4+ (VO 2+ ) electrolytes as feedstock for all- vanadium redox flow batteries (RFB). By dissolving V 2 O 5 in aqueous HCl and H 2 SO 4 , subsequently adding glycerol as a reducing agent, we have demonstrated an inexpensive route for electrolyte synthesis to concentrations >2.5 M V 4+ (VO 2+ ). Electrochemical analysis and testing of laboratory scale RFB demonstrate improved thermal stability across a wider temperature range (-10-65 degC) for V 4+ (VO 2+ ) electrolytes in HCl compared to in H 2 SO 4 electrolytes.

Supersaturation of Dissolved Hydrogen and Methane in Rumen of Tibetan Sheep

PubMed Central

Wang, Min; Ungerfeld, Emilio M.; Wang, Rong; Zhou, Chuan She; Basang, Zhu Zha; Ao, Si Man; Tan, Zhi Liang

2016-01-01

Hydrogen (H2) is an essential substrate for methanogens to produce methane (CH4), and also influences pathways of volatile fatty acids (VFA) production in the rumen. Dissolved H2 (H2 (aq)) is the form of H2 available to microbes, and dissolved CH4 (CH4 (aq)) is important for indicating methanogens activity. Rumen H2 (aq) concentration has been estimated by assuming equilibrium with headspace gaseous H2 (H2 (g)) concentration using Henry's law, and has also been directly measured in the liquid phase in some in vitro and in vivo experiments. In this in vivo study, H2 (aq) and CH4 (aq) concentration measured directly in rumen fluid and their corresponding concentrations estimated from their gaseous phase concentrations, were compared to investigate the existence of equilibrium between the gas and liquid phases. Twenty-four Tibetan sheep were randomly assigned to two mixed diets containing the same concentrate mixed with oat grass (OG diet) or barley straw (BS diet). Rumen gaseous phase and contents were sampled using rumenocentesis and oral stomach tubing, respectively. Rumen H2 (aq) and CH4 (aq) concentration and VFA profile differed between sheep fed OG and BS diets. Measured H2 (aq) and CH4 (aq) concentration were greater than H2 (aq) and CH4 (aq) concentrations estimated using gas concentrations, indicating lack of equilibrium between gas and liquid phase and supersaturation of H2 and CH4 in rumen fluid. As a consequence, Gibbs energy changes (ΔG) estimated for various metabolic pathways were different when calculated using dissolved gases concentrations directly measured and when using dissolved gases concentrations assuming equilibrium with the gaseous phase. Dissolved CH4, but not CH4 (g), was positively correlated with H2 (aq). Both H2 (aq) and H2 (g) concentrations were positively correlated with the molar percentage of butyrate and negatively correlated with the molar percentage of acetate. In summary, rumen fluid was supersaturated with both H2 and CH4, and H2 (aq) was closely associated with the VFA profile and CH4 (aq) concentration. The assumption of equilibrium between dissolved gases and gaseous phase affected ΔG estimation. PMID:27379028

Estimates of atmospheric O2 in the Paleoproterozoic from paleosols

NASA Astrophysics Data System (ADS)

Kanzaki, Yoshiki; Murakami, Takashi

2016-02-01

A weathering model was developed to constrain the partial pressure of atmospheric O2 (PO2) in the Paleoproterozoic from the Fe records in paleosols. The model describes the Fe behavior in a weathering profile by dissolution/precipitation of Fe-bearing minerals, oxidation of dissolved Fe(II) to Fe(III) by oxygen and transport of dissolved Fe by water flow, in steady state. The model calculates the ratio of the precipitated Fe(III)-(oxyhydr)oxides from the dissolved Fe(II) to the dissolved Fe(II) during weathering (ϕ), as a function of PO2 . An advanced kinetic expression for Fe(II) oxidation by O2 was introduced into the model from the literature to calculate accurate ϕ-PO2 relationships. The model's validity is supported by the consistency of the calculated ϕ-PO2 relationships with those in the literature. The model can calculate PO2 for a given paleosol, once a ϕ value and values of the other parameters relevant to weathering, namely, pH of porewater, partial pressure of carbon dioxide (PCO2), water flow, temperature and O2 diffusion into soil, are obtained for the paleosol. The above weathering-relevant parameters were scrutinized for individual Paleoproterozoic paleosols. The values of ϕ, temperature, pH and PCO2 were obtained from the literature on the Paleoproterozoic paleosols. The parameter value of water flow was constrained for each paleosol from the mass balance of Si between water and rock phases and the relationships between water saturation ratio and hydraulic conductivity. The parameter value of O2 diffusion into soil was calculated for each paleosol based on the equation for soil O2 concentration with the O2 transport parameters in the literature. Then, we conducted comprehensive PO2 calculations for individual Paleoproterozoic paleosols which reflect all uncertainties in the weathering-relevant parameters. Consequently, robust estimates of PO2 in the Paleoproterozoic were obtained: 10-7.1-10-5.4 atm at ∼2.46 Ga, 10-5.0-10-2.5 atm at ∼2.15 Ga, 10-5.2-10-1.7 atm at ∼2.08 Ga and more than 10-4.6-10-2.0 atm at ∼1.85 Ga. Comparison of the present PO2 estimates to those in the literature suggests that a drastic rise of oxygen would not have occurred at ∼2.4 Ga, supporting a slightly rapid rise of oxygen at ∼2.4 Ga and a gradual rise of oxygen in the Paleoproterozoic in long term.

Minimizing nitrous oxide in biological nutrient removal from municipal wastewater by controlling copper ion concentrations.

PubMed

Zhu, Xiaoyu; Chen, Yinguang; Chen, Hong; Li, Xiang; Peng, Yongzhen; Wang, Shuying

2013-02-01

In this study, nitrous oxide (N(2)O) production during biological nutrient removal (BNR) from municipal wastewater was reported to be remarkably reduced by controlling copper ion (Cu(2+)) concentration. Firstly, it was observed that the addition of Cu(2+) (10-100 μg/L) reduced N(2)O generation by 54.5-73.2 % and improved total nitrogen removal when synthetic wastewater was treated in an anaerobic-aerobic (with low dissolved oxygen) BNR process. Then, the roles of Cu(2+) were investigated. The activities of nitrite and nitrous oxide reductases were increased by Cu(2+) addition, which accelerated the bio-reductions of both nitrite to nitric oxide (NO (2) (-)  → NO) and nitrous oxide to nitrogen gas (N(2)O → N(2)). The quantitative real-time polymerase chain reaction assay indicated that Cu(2+) addition increased the number of N(2)O reducing denitrifiers. Further investigation showed that more polyhydoxyalkanoates were utilized in the Cu(2+)-added system for denitrification. Finally, the feasibility of reducing N(2)O generation by controlling Cu(2+) was examined in two other BNR processes treating real municipal wastewater. As the Cu(2+) in municipal wastewater is usually below 10 μg/L, according to this study, the supplement of influent Cu(2+) to a concentration of 10-100 μg/L is beneficial to reduce N(2)O emission and improve nitrogen removal when sludge concentration in the BNR system is around 3,200 mg/L.

Diel variations in stream chemistry and isotopic composition of dissolved inorganic carbon, upper Clark Fork River, Montana, USA

USGS Publications Warehouse

Parker, Stephen R.; Gammons, Christopher H.; Poulson, Simon R.; DeGrandpre, Michael D.

2007-01-01

Many rivers undergo diel (24-h) concentration fluctuations of pH, dissolved gases, trace metals, nutrients, and other chemical species. A study conducted in 1994 documented such behavior in the upper Clark Fork River, Montana, a stream whose headwaters have been severely impacted by historic metal mining, milling, and smelting. The purpose of the present investigation was to expand on these earlier findings by conducting simultaneous diel samplings at two sites on the upper Clark Fork River separated by 2.5 h of stream travel time. By monitoring two stations, it was possible to more closely examine the processes that control temporal and spatial gradients in stream chemistry. Another objective was to examine diel changes in the δ13C composition of dissolved inorganic C (DIC) and their relationship to biological activity in the stream. The most important findings of this study include: (1) concentrations of dissolved and particulate heavy metals increased during the night and decreased during the day, in agreement with previous work; (2) these changes were positively correlated to diel changes in pH, dissolved O2, and water temperature; (3) dissolved concentrations increased during the night at the lower site, but showed the opposite behavior at the upper site; and (4) diel changes in δ13C-DIC were noted at both sites, although the timing and magnitudes of the cycles differed. Hypotheses to explain the first two observations include: cyclic co-precipitation of divalent metals with carbonate minerals; pH- and temperature-dependent sorption of metal cations onto the streambed and suspended particles; or photosynthetically enhanced oxidation and removal of Fe and Mn oxides at biofilm surfaces during the daytime. The latter model explains the majority of the field observations, including night-time increases in particulate forms of Fe and other elements.

Major and minor oxide and trace element determination in silicate rocks by direct current plasma optical emission echelle spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bankston, D.C.; Humphris, S.E.; Thompson, G.

1979-07-01

A technique for the determination of major concentrations of SiO/sub 2/, Al/sub 2/O/sub 3/, Fe/sub 2/O/sub 3/, MgO, CaO, Na/sub 2/O, and K/sub 2/O, minor levels of TiO/sub 2/, P/sub 2/O/sub 5/, and MnO, and trace concentrations of Ba, Cr, Cu, Ni, Sr, V, and Zn, in semi-microsamples 200 mg) of powdered whole rock, is described. Chemically diverse standard reference rocks are used both for calibration and assessment of accuracy. A lithium metaborate fusion melt of each standard or sample is dissolved in dilute HNO/sub 3/ containing Cs/sup +/ at a level of 0.2% (w/v). The resulting solution is usedmore » to perform all analyses except those for Na/sub 2/O and K/sub 2/O, which are determined in a portion of the original sample solution wherein the Cs/sup +/ concentration has been raised to 0.32% (w/v). Analyses of both portions of each sample solution are performed using an optical emission spectrometer/spectrograph equipped with an echelle monochromator and a dc argon plasma excitation source. Trace element detection limits ranged from 2 ppM for Cu to 15 ppM for Zn. A study of precision based on replicate determinations in three splits of the proposed USGS reference basalt BHVO-1 yielded the following results: (1) For analyses of the major and minor oxide constituents, values of the percent relative standard deviation (RSD) ranged from 1 for CaO, to 21 for P/sub 2/O/sub 5/. 2) For trace element determinations, values of the RSD ranged from 2 for Cu, to 19 for Zn. 2 figures, 11 tables.« less

Seasonal variability of total dissolved fluxes and origin of major dissolved elements within a large tropical river: The Orinoco, Venezuela

NASA Astrophysics Data System (ADS)

Laraque, Alain; Moquet, Jean-Sébastien; Alkattan, Rana; Steiger, Johannes; Mora, Abrahan; Adèle, Georges; Castellanos, Bartolo; Lagane, Christèle; Lopez, José Luis; Perez, Jesus; Rodriguez, Militza; Rosales, Judith

2013-07-01

Seasonal variations of total dissolved fluxes of the lower Orinoco River were calculated taking into account four complete hydrological cycles during a five-year period (2005-2010). The modern concentrations of total dissolved solids (TDS) of the Orinoco surface waters were compared with data collected during the second half of the last century published in the literature. This comparison leads to the conclusion that chemical composition did not evolve significantly at least over the last thirty to forty years. Surface waters of the Orinoco at Ciudad Bolivar are between bicarbonated calcic and bicarbonated mixed. In comparison to mean values of concentrations of total dissolved solids (TDS) of world river surface waters (89.2 mg l-1), the Orinoco River at Ciudad Bolivar presents mainly low mineralized surface waters (2005-10: TDS 30 mg l-1). The TDS fluxes passing at this station in direction to the Atlantic Ocean between 2005 and 2010 were estimated at 30 × 106 t yr-1, i.e. 36 t km-2 yr-1. It was observed that the seasonal variations (dry season vs wet season) of total dissolved fluxes (TDS and dissolved organic carbon (DOC)) are mainly controlled by discharge variations. Two groups of elements have been defined from dilution curves and molar ratio diagrams. Ca2+, Mg2+, HCO3-, Cl- and Na+ mainly come from the same geographic and lithologic area, the Andes. K+ and SiO2 essentially come from the Llanos and the Guayana Shield. These findings are important for understanding fundamental geochemical processes within the Orinoco River basin, but also as a baseline study in the perspective of the development of numerous mining activities related with aluminum and steel industries; and the plans of the Venezuelan government to construct new fluvial ports on the lower Orinoco for the transport of hydrocarbons.

Accelerated effects of nano-ZnO on phosphorus removal by Chlorella vulgaris: Formation of zinc phosphate crystallites.

PubMed

Xiao, Huaixian; Liu, Na; Tian, Ke; Liu, Shixiang; Ge, Fei

2018-09-01

Nanoparticles have been reported to induce toxicity to aquatic organisms, however, their potential impacts on phosphorus removal from wastewater by algae are unclear. In this study, the effects of nanoparticle ZnO (nano-ZnO) on phosphate (PO 4 3- ) removal by a green alga Chlorella vulgaris were investigated. We found that PO 4 3- removal efficiency was accelerated with high concentrations of nano-ZnO (0.04-0.15mM) but reduced with low concentrations of nano-ZnO (0.005-0.04mM) compared to the control (without nano-ZnO), suggesting that PO 4 3- removal efficiency by C. vulgaris was related to nano-ZnO concentrations. Moreover, we observed changes of nano-ZnO morphology and detected element P on the surface of nano-ZnO by using transmission electronic microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDX), indicating that PO 4 3- was interacted with nano-ZnO or the dissolved Zn 2+ from nano-ZnO. Furthermore, we confirmed this interaction induced the formation of Zn 3 (PO 4 ) 2 crystallites sedimentation by employing X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS), which finally accelerates the removal of PO 4 3- . Copyright © 2018 Elsevier B.V. All rights reserved.

Methane oxidation in a crude oil contaminated aquifer: Delineation of aerobic reactions at the plume fringes

USGS Publications Warehouse

Amos, R.T.; Bekins, B.A.; Delin, G.N.; Cozzarelli, I.M.; Blowes, D.W.; Kirshtein, J.D.

2011-01-01

High resolution direct-push profiling over short vertical distances was used to investigate CH4 attenuation in a petroleum contaminated aquifer near Bemidji, Minnesota. The contaminant plume was delineated using dissolved gases, redox sensitive components, major ions, carbon isotope ratios in CH4 and CO2, and the presence of methanotrophic bacteria. Sharp redox gradients were observed near the water table. Shifts in ??13CCH4 from an average of - 57.6??? (?? 1.7???) in the methanogenic zone to - 39.6??? (?? 8.7???) at 105 m downgradient, strongly suggest CH4 attenuation through microbially mediated degradation. In the downgradient zone the aerobic/anaerobic transition is up to 0.5 m below the water table suggesting that transport of O2 across the water table is leading to aerobic degradation of CH4 at this interface. Dissolved N2 concentrations that exceeded those expected for water in equilibrium with the atmosphere indicated bubble entrapment followed by preferential stripping of O2 through aerobic degradation of CH4 or other hydrocarbons. Multivariate and cluster analysis were used to distinguish between areas of significant bubble entrapment and areas where other processes such as the infiltration of O 2 rich recharge water were important O2 transport mechanisms. ?? 2011 Elsevier B.V. All rights reserved.

Transport and cycling of iron and hydrogen peroxide in a freshwater stream: Influence of organic acids

USGS Publications Warehouse

Scott, Durelle T.; Runkel, Robert L.; McKnight, Diane M.; Voelker, Bettina M.; Kimball, Briant A.; Carraway, Elizabeth R.

2003-01-01

An in-stream injection of two dissolved organic acids (phthalic and aspartic acids) was performed in an acidic mountain stream to assess the effects of organic acids on Fe photoreduction and H2O2 cycling. Results indicate that the fate of Fe is dependent on a net balance of oxidative and reductive processes, which can vary over a distance of several meters due to changes in incident light and other factors. Solution phase photoreduction rates were high in sunlit reaches and were enhanced by the organic acid addition but were also limited by the amount of ferric iron present in the water column. Fe oxide photoreduction from the streambed and colloids within the water column resulted in an increase in the diurnal load of total filterable Fe within the experimental reach, which also responded to increases in light and organic acids. Our results also suggest that Fe(II) oxidation increased in response to the organic acids, with the result of offsetting the increase in Fe(II) from photoreductive processes. Fe(II) was rapidly oxidized to Fe(III) after sunset and during the day within a well-shaded reach, presumably through microbial oxidation. H2O 2, a product of dissolved organic matter photolysis, increased downstream to maximum concentrations of 0.25 ??M midday. Kinetic calculations show that the buildup of H2O2 is controlled by reaction with Fe(III), but this has only a small effect on Fe(II) because of the small formation rates of H2O2 compared to those of Fe(II). The results demonstrate the importance of incorporating the effects of light and dissolved organic carbon into Fe reactive transport models to further our understanding of the fate of Fe in streams and lakes.

Distributions and Relationships of CO2, O2, and Dimethylsulfide in the Changjiang (Yangtze) Estuary and Its Adjacent Waters in Summer

NASA Astrophysics Data System (ADS)

Wu, Xi; Tan, Tingting; Liu, Chunying; Li, Tie; Liu, Xiaoshou; Yang, Guipeng

2018-04-01

The distributions and relationships of O2, CO2, and dimethylsulfide (DMS) in the Changjiang (Yangtze) Estuary and its adjacent waters were investigated in June 2014. In surface water, mean O2 saturation level, partial pressure of CO2 (pCO2), and DMS concentrations (and ranges) were 110% (89%-167%), 374 μatm (91-640 μatm), and 8.53 nmol L-1 (1.10-27.50 nmol L-1), respectively. The sea-to-air fluxes (and ranges) of DMS and CO2 were 8.24 μmol m-2 d-1 (0.26-62.77 μmol m-2 d-1), and -4.7 mmol m-2 d-1 (-110.8-31.7 mmol m-2 d-1), respectively. Dissolved O2 was oversaturated, DMS concentrations were relatively high, and this region served as a sink of atmospheric CO2. The pCO2 was significantly and negatively correlated with the O2 saturation level, while the DMS concentration showed different positive relationships with the O2 saturation level in different water masses. In vertical profiles, a hypoxic zone existed below 20 m at a longitude of 123°E. The stratification of temperature and salinity caused by the Taiwan Warm Current suppressed seawater exchange between upper and lower layers, resulting in the formation of a hypoxic zone. Oxidative decomposition of organic detritus carried by the Changjiang River Diluted Water (CRDW) consumed abundant O2 and produced additional CO2. The DMS concentrations decreased because of low phytoplankton biomass in the hypoxic zone. Strong correlations appeared between the O2 saturation level, pCO2 and DMS concentrations in vertical profiles. Our results strongly suggested that CRDW played an important role in the distributions and relationships of O2, CO2, and DMS.

Passive aerobic treatment of net-alkaline, iron-laden drainage from a flooded underground anthracite mine, Pennsylvania, USA

USGS Publications Warehouse

Cravotta, C.A.

2007-01-01

This report evaluates the results of a continuous 4.5-day laboratory aeration experiment and the first year of passive, aerobic treatment of abandoned mine drainage (AMD) from a typical flooded underground anthracite mine in eastern Pennsylvania, USA. During 1991-2006, the AMD source, locally known as the Otto Discharge, had flows from 20 to 270 L/s (median 92 L/s) and water quality that was consistently suboxic (median 0.9 mg/L O2) and circumneutral (pH ??? 6.0; net alkalinity >10) with moderate concentrations of dissolved iron and manganese and low concentrations of dissolved aluminum (medians of 11, 2.2, and <0.2 mg/L, respectively). In 2001, the laboratory aeration experiment demonstrated rapid oxidation of ferrous iron (Fe 2+) without supplemental alkalinity; the initial Fe2+ concentration of 16.4 mg/L decreased to less than 0.5 mg/L within 24 h; pH values increased rapidly from 5.8 to 7.2, ultimately attaining a steady-state value of 7.5. The increased pH coincided with a rapid decrease in the partial pressure of carbon dioxide (PCO2) from an initial value of 10 -1.1atm to a steady-state value of 10-3.1atm. From these results, a staged aerobic treatment system was conceptualized consisting of a 2 m deep pond with innovative aeration and recirculation to promote rapid oxidation of Fe2+, two 0.3 m deep wetlands to facilitate iron solids removal, and a supplemental oxic limestone drain for dissolved manganese and trace-metal removal. The system was constructed, but without the aeration mechanism, and began operation in June 2005. During the first 12 months of operation, estimated detention times in the treatment system ranged from 9 to 38 h. However, in contrast with 80-100% removal of Fe2+ over similar elapsed times during the laboratory aeration experiment, the treatment system typically removed less than 35% of the influent Fe2+. Although concentrations of dissolved CO2 decreased progressively within the treatment system, the PCO2 values for treated effluent remained elevated (10-2.4 to 10-1.7atm). The elevated PCO 2 maintained the pH within the system at values less than 7 and hence slowed the rate of Fe2+ oxidation compared to the aeration experiment. Kinetic models of Fe2+ oxidation that consider effects of pH and dissolved O2 were incorporated in the geochemical computer program PHREEQC to evaluate the effects of detention time, pH, and other variables on Fe2+ oxidation and removal rates. These models and the laboratory aeration experiment indicate that performance of this and other aerobic wetlands for treatment of net-alkaline AMD could be improved by aggressive, continuous aeration in the initial stage to decrease PCO 2, increase pH, and accelerate Fe2+ oxidation. ?? 2007 Springer-Verlag.

Arsenic in ground-water under oxidizing conditions, south-west United States

USGS Publications Warehouse

Robertson, F.N.

1989-01-01

Concentrations of dissolved arsenic in ground-water in alluvial basins of Arizona commonly exceed 50 ??g L-1 and reach values as large as 1,300 ??g L-1. Arsenic speciation analyses show that arsenic occurs in the fully oxidized state of plus 5 (As+5), most likely in the form of HAsO4???2, under existing oxidizing and pH conditions. Arsenic in source areas presumably is oxidized to soluble As before transport into the basin or, if after transport, before burial. Probable sources of arsenic are the sulphide and arsenide deposits in the mineralized areas of the mountains surrounding the basins. Arsenic content of alluvial material ranged from 2 to 88 ppm. Occurrence and removal of arsenic in ground-water are related to the pH and the redox condition of the ground-water, the oxidation state of arsenic, and sorption or exchange. Within basins, dissolved arsenic correlates (P<0.01) with dissolved molybdenum, selenium, vanadium, and fluoride and with pH, suggesting sorption of negative ions. The sorption hypothesis is further supported by enrichment of teachable arsenic in the basin-fill sediments by about tenfold relative to the crustal abundance and by as much as a thousandfold relative to concentrations found in ground-water. Silicate hydrolysis reactions, as defined within the alluvial basins, under closed conditions cause increases in pH basinward and would promote desorption. Within the region, large concentrations of arsenic are commonly associated with the central parts of basins whose chemistries evolve under closed conditions. Arsenic does not correlate with dissolved iron (r = 0.09) but may be partly controlled by iron in the solid phase. High solid-phase arsenic contents were found in red clay beds. Large concentrations of arsenic also were found in water associated with red clay beds. Basins that contain the larger concentrations are bounded primarily by basalt and andesite, suggesting that the iron content as well as the arsenic content of the basin fill may play a role in the occurrence of arsenic in ground-water. Under oxidizing conditions in Arizona, arsenic in ground-water appears to be controlled in part by sorption or desorption of HAsO4???2 on active ferric oxyhydroxide surfaces. ?? 1989 Sciences and Technology Letters.

Near-infrared spectroscopic investigation of water in supercritical CO2 and the effect of CaCl2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zheming; Felmy, Andrew R.; Thompson, Christopher J.

2013-01-01

Near-infrared (NIR) spectroscopy was applied to investigate the dissolution and chemical interaction of water dissolved into supercritical carbon dioxide (scCO2) and the influence of CaCl2 in the co-existing aqueous phase at fo empe e : 40 50 75 nd 100 C at 90 atm. Consistent with the trend of the vapor pressure of water, the solubility of pure water in scCO2 inc e ed f om 40 °C (0.32 mole%) o 100 °C (1.61 mole%). The presence of CaCl2 negatively affects the solubility of water in scCO2: at a given temperature and pressure the solubility of water decreased as themore » concentration of CaCl2 in the aqueous phase increased, following the trend of the activity of water. A 40 °C, the water concentration in scCO2 in contact with saturated CaCl2 aqueous solution was only 0.16 mole%, a drop of more than 50% as compared to pure water while that a 100 °C was 1.12 mole%, a drop of over 30% as compared to pure water, under otherwise the same conditions. Analysis of the spectral profiles suggested that water dissolved into scCO2 exists in the monomeric form under the evaluated temperature and pressure conditions, for both neat water and CaCl2 solutions. However, its rotational degrees of freedom decrease at lower temperatures due to higher fluid densities, leading to formation of weak H2O:CO2 Lewis acid-base complexes. Similarly, the nearly invariant spectral profiles of dissolved water in the presence and absence of saturated CaCl2 under the same experimental conditions was taken as evidence that CaCl2 dissolution in scCO2 was limited as the dissolved Ca2+/CaCl2 would likely be highly hydrated and would alter the overall spectra of waters in the scCO2 phase.« less

The effect of fuel chemistry on UO2 dissolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casella, Amanda; Hanson, Brady; Miller, William

2016-08-01

The dissolution rate of both unirradiated UO2 and used nuclear fuel has been studied by numerous countries as part of the performance assessment of proposed geologic repositories. In the scenario of waste package failure and groundwater infiltration into the fuel, the effects of variables such as temperature, dissolved oxygen, and water and fuel chemistry on the dissolution rates of the fuel are necessary to provide a quantitative estimate of the potential release over geologic time frames. The primary objective of this research was to determine the influence these parameters have on the dissolution rate of unirradiated UO2 under repository conditionsmore » and compare them to the rates predicted by current dissolution models. Both unirradiated UO2 and UO2 doped with varying concentrations of Gd2O3, to simulate used fuel composition after long time periods where radiolysis has minor contributions to dissolution, were examined. In general, a rise in temperature increased the dissolution rate of UO2 and had a larger effect on pure UO2 than on those doped with Gd2O3. Oxygen dependence was observed in the UO2 samples with no dopant and increased as the temperature rose; in the doped fuels less dependence was observed. The addition of gadolinia into the UO2 matrix showed a significant decrease in the dissolution rate. The matrix stabilization effect resulting from the dopant proved even more beneficial in lowering the dissolution rate at higher temperatures and dissolved O2 concentrations in the leachate where the rates would typically be elevated.« less

Dissolved metals and associated constituents in abandoned coal-mine discharges, Pennsylvania, USA. Part 2: Geochemical controls on constituent concentrations

USGS Publications Warehouse

Cravotta, C.A.

2008-01-01

Water-quality data for discharges from 140 abandoned mines in the Anthracite and Bituminous Coalfields of Pennsylvania reveal complex relations among the pH and dissolved solute concentrations that can be explained with geochemical equilibrium models. Observed values of pH ranged from 2.7 to 7.3 in the coal-mine discharges (CMD). Generally, flow rates were smaller and solute concentrations were greater for low-pH CMD samples; pH typically increased with flow rate. Although the frequency distribution of pH was similar for the anthracite and bituminous discharges, the bituminous discharges had smaller median flow rates; greater concentrations of SO4, Fe, Al, As, Cd, Cu, Ni and Sr; comparable concentrations of Mn, Cd, Zn and Se; and smaller concentrations of Ba and Pb than anthracite discharges with the same pH values. The observed relations between the pH and constituent concentrations can be attributed to (1) dilution of acidic water by near-neutral or alkaline ground water; (2) solubility control of Al, Fe, Mn, Ba and Sr by hydroxide, sulfate, and/or carbonate minerals; and (3) aqueous SO4-complexation and surface-complexation (adsorption) reactions. The formation of AlSO4+ and AlHSO42 + complexes adds to the total dissolved Al concentration at equilibrium with Al(OH)3 and/or Al hydroxysulfate phases and can account for 10-20 times greater concentrations of dissolved Al in SO4-laden bituminous discharges compared to anthracite discharges at pH of 5. Sulfate complexation can also account for 10-30 times greater concentrations of dissolved FeIII concentrations at equilibrium with Fe(OH)3 and/or schwertmannite (Fe8O8(OH)4.5(SO4)1.75) at pH of 3-5. In contrast, lower Ba concentrations in bituminous discharges indicate that elevated SO4 concentrations in these CMD sources could limit Ba concentrations by the precipitation of barite (BaSO4). Coprecipitation of Sr with barite could limit concentrations of this element. However, concentrations of dissolved Pb, Cu, Cd, Zn, and most other trace cations in CMD samples were orders of magnitude less than equilibrium with sulfate, carbonate, and/or hydroxide minerals. Surface complexation (adsorption) by hydrous ferric oxides (HFO) could account for the decreased concentrations of these divalent cations with increased pH. In contrast, increased concentrations of As and, to a lesser extent, Se with increased pH could result from the adsorption of these oxyanions by HFO at low pH and desorption at near-neutral pH. Hence, the solute concentrations in CMD and the purity of associated "ochres" formed in CMD settings are expected to vary with pH and aqueous SO4 concentration, with potential for elevated SO4, As and Se in ochres formed at low pH and elevated Cu, Cd, Pb and Zn in ochres formed at near-neutral pH. Elevated SO4 content of ochres could enhance the adsorption of cations at low pH, but decrease the adsorption of anions such as As. Such information on environmental processes that control element concentrations in aqueous samples and associated precipitates could be useful in the design of systems to reduce dissolved contaminant concentrations and/or to recover potentially valuable constituents in mine effluents.

The influence of headspace and dissolved oxygen level on growth and haemolytic BL enterotoxin production of a psychrotolerant Bacillus weihenstephanensis isolate on potato based ready-to-eat food products.

PubMed

Samapundo, S; Everaert, H; Wandutu, J N; Rajkovic, A; Uyttendaele, M; Devlieghere, F

2011-04-01

The major objective of this study was to determine the influence of the initial headspace and dissolved O(2) level and vacuum packaging on growth and diarrhoeal enterotoxin production by Bacillus weihenstephanensis on potato based ready-to-eat food products. In general, the lower the initial headspace or dissolved O(2) level the slower the maximum growth rate (μ(max), log(10) CFU g(-1) d(-1)), the longer the lag phase duration (λ, d) and the smaller the maximum population density (N(max), log(10) CFU g(-1)) became. The slowest μ(max), the longest λ and the smallest N(max) were generally found for growth under vacuum packaging. This implies shorter shelf-lives will occur at higher initial headspace or dissolved O(2) levels as the growth of B. weihenstephanensis to the infective dose of 10(5) CFU g(-1) in such atmospheres takes a shorter time. Significant consumption of dissolved O(2) only occurred when growth shifted from the lag to the exponential phase and growth generally transitioned from the exponential to the stationary phase when the dissolved O(2) levels fell below ca. 75 ppb. Diarrhoeal enterotoxin production (determined via detection of the L2 component of haemolytic BL) was similar for growth under initial headspace O(2) levels of 1-20.9%, and was only reduced when growth took place under vacuum packaging. The reduction in L2 production when growth took place under vacuum was most probably related to the low final cell densities observed under this condition. Both growth and L2 production were inhibited over a 32-day incubation period at 7 °C by 40% CO(2) irrespective of the headspace or dissolved O(2) levels. The results illustrate the importance of residual O(2) and CO(2) on the shelf-stability and safety of modified atmosphere packaged potato based ready-to-eat food products with regards to B. weihenstephanensis. Copyright © 2010 Elsevier Ltd. All rights reserved.

Geochemistry of shallow ground water in coastal plain environments in the southeastern United States: Implications for aquifer susceptibility

USGS Publications Warehouse

Tesoriero, A.J.; Spruill, T.B.; Eimers, J.L.

2004-01-01

Ground-water chemistry data from coastal plain environments have been examined to determine the geochemical conditions and processes that occur in these areas and assess their implications for aquifer susceptibility. Two distinct geochemical environments were studied to represent a range of conditions: an inner coastal plain setting having more well-drained soils and lower organic carbon (C) content and an outer coastal plain environment that has more poorly drained soils and high organic C content. Higher concentrations of most major ions and dissolved inorganic and organic C in the outer coastal plain setting indicate a greater degree of mineral dissolution and organic matter oxidation. Accordingly, outer coastal plain waters are more reducing than inner coastal plain waters. Low dissolved oxygen (O2) and nitrate (NO 3-) concentrations and high iron (Fe) concentrations indicate that ferric iron (Fe (III)) is an important electron acceptor in this setting, while dissolved O2 is the most common terminal electron acceptor in the inner coastal plain setting. The presence of a wide range of redox conditions in the shallow aquifer system examined here underscores the importance of providing a detailed geochemical characterization of ground water when assessing the intrinsic susceptibility of coastal plain settings. The greater prevalence of aerobic conditions in the inner coastal plain setting makes this region more susceptible to contamination by constituents that are more stable under these conditions and is consistent with the significantly (p<0.05) higher concentrations of NO3- found in this setting. Herbicides and their transformation products were frequently detected (36% of wells sampled), however concentrations were typically low (<0.1 ??g/L). Shallow water table depths often found in coastal plain settings may result in an increased risk of the detection of pesticides (e.g., alachlor) that degrade rapidly in the unsaturated zone.

In situ arsenic removal in an alkaline clastic aquifer

USGS Publications Warehouse

Welch, A.H.; Stollenwerk, K.G.; Paul, A.P.; Maurer, D.K.; Halford, K.J.

2008-01-01

In situ removal of As from ground water used for water supply has been accomplished elsewhere in circum-neutral ground water containing high dissolved Fe(II) concentrations. The objective of this study was to evaluate in situ As ground-water treatment approaches in alkaline ground-water (pH > 8) that contains low dissolved Fe (

Oxygen and superoxide-mediated redox kinetics of iron complexed by humic substances in coastal seawater.

PubMed

Fujii, Manabu; Rose, Andrew L; Waite, T David; Omura, Tatsuo

2010-12-15

Complexes with terrestrially derived humic substances represent one of the most reactive pools of dissolved Fe in natural waters. In this work, redox kinetics of Fe-humic substance complexes (FeL) in simulated coastal seawater were investigated using chemiluminescence techniques with particular attention given to interactions with dioxygen (O2) and superoxide (O2•-). Although rate constants of FeIIL oxidation by O2 (5.6-52 M-1 · s-1) were 4-5 orders of magnitude less than those for O2•- (6.9-23 × 105 M-1 · s-1),O2 is likely to outcompete O2•- for FeIIL oxidation in coastal seawaters where steady-state O2•- concentrations are generally subnanomolar. Rate constants for FeIIIL reduction by O2•- of 1.8-5.6 × 104 M-1 · s-1 were also determined. From the balance of FeIIL oxidation rates and O2•- -mediated FeIIIL reduction rates, steady-state FeIIL concentrations were estimated to be in the subpicomolar to picomolar range, which is generally lower than measured in situ Fe(II) concentrations under relevant conditions. This suggests that (i) processes other than O2•- -mediated reduction (such as photochemical ligand-to-metal charge transfer) may be responsible for Fe(II) formation, (ii) the in situ ligands differ significantly from the humic substances used in this work, and/ or (iii) the influence of other environmental factors such as pH and temperature on Fe redox kinetics may have to be considered.

Impact of dissolved oxygen concentration on some key parameters and production of rhG-CSF in batch fermentation.

PubMed

Krishna Rao, Dasari V; Ramu, Chatadi T; Rao, Joginapally V; Narasu, Mangamoori L; Bhujanga Rao, Adibhatla Kali S

2008-09-01

The impact of different levels of agitation speed, carbondioxide and dissolved oxygen concentration on the key parameters and production of rhG-CSF in Escherichia coli BL21(DE3)PLysS were studied. Lower carbondioxide concentrations as well as higher agitation speeds and dissolved oxygen concentrations led to reduction in the acetate concentrations, and enhanced the cell growth, but inhibited plasmid stability and rhG-CSF expression. Similarly, higher carbondioxide concentrations and lower agitation speeds as well as dissolved oxygen concentrations led to enhanced acetate concentrations, but inhibited the cell growth and protein expression. To address the bottlenecks, a two-stage agitation control strategy (strategy-1) and two-stage dissolved oxygen control strategy (strategy-2) were employed to establish the physiological and metabolic conditions, so as to improve the expression of rhG-CSF. By adopting strategy-1 the yields were improved 1.4-fold over constant speed of 550 rpm, 1.1-fold over constant dissolved oxygen of 45%, respectively. Similarly, using strategy-2 the yields were improved 1.6-fold over constant speed of 550 rpm, 1.3-fold over constant dissolved oxygen of 45%, respectively.

Emission, fate and effects of soluble silicates (waterglass) in the aquatic environment.

PubMed

van Dokkum, Henno P; Hulskotte, Ian H J; Kramer, Kees J M; Wilmot, Joël

2004-01-15

Soluble silicates, commercially known as waterglass, are among the largest volume synthetic chemicals in the world. Silicon from waterglass is rapidly transformed to the biologically active orthosilicic acid (referred to as dissolved silicate). This paper aims to assess the impact of waterglass on the aquatic environment in Western Europe. The emission to surface waters from the four most relevant application areas, household detergents, pulp and paper production, water and wastewater treatment, and soil stabilization, is estimated to be ca. 88-121 kton of SiO2 per year. This is a small fraction (<2%) of the estimated total amount of dissolved silicate transported by rivers to the oceans. Locally, increases in dissolved silicate concentration will decrease the ratios of N:Si and P:Si, which could influence phytoplankton species composition and favor the growth of diatoms over other groups of algae. Significant adverse effects in aquatic ecosystems are not expected.

Silica removal from steamflood-produced water: South Texas tar sands pilot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, S.A.; Yost, M.E.; Cathey, S.R.

1987-05-01

Steamflood-produced waters commonly contain suspended solids, oil, hardness-causing minerals, sulfide, and silica. Removal of these contaminants would make many of these waters suitable for recycling as steamer feedwater. Reuse of steamflood-produced waters increases steamer feedwater supplies and reduces water disposal requirements. This paper describes a field pilot study of silica removal from steamflood-produced water in the south Texas tar sands region. A hot-lime precipitation process was used to reduce dissolved silica (SiO/sub 2/) concentrations from 400 to less than 50 mg/L SiO/sub 2/ in Mary R. Saner Ranch produced water. Most water systems using hot-lime precipitation for silica removal requiremore » the addition of magnesium salt, as well as lime, to enhance silica removal. In this field study, however, addition of magnesium salt did not improve silica removal efficiency. Hydrated lime, CA(OH)/sub 2/, alone was sufficient to attain desired silica residual, 50 mg/L SiO/sub 2/. The dissolved silica adsorbed onto the CaCO/sub 3/ crystals formed by lime reacting with the alkalinity present in the produced water. Required lime dosage was approximately 900 mg/L Ca(OH)/sub 2/.« less

Evaluating nanoparticle breakthrough during drinking water treatment.

PubMed

Abbott Chalew, Talia E; Ajmani, Gaurav S; Huang, Haiou; Schwab, Kellogg J

2013-10-01

Use of engineered nanoparticles (NPs) in consumer products is resulting in NPs in drinking water sources. Subsequent NP breakthrough into treated drinking water is a potential exposure route and human health threat. In this study we investigated the breakthrough of common NPs--silver (Ag), titanium dioxide (TiO2), and zinc oxide (ZnO)--into finished drinking water following conventional and advanced treatment. NPs were spiked into five experimental waters: groundwater, surface water, synthetic freshwater, synthetic freshwater containing natural organic matter, and tertiary wastewater effluent. Bench-scale coagulation/flocculation/sedimentation simulated conventional treatment, and microfiltration (MF) and ultrafiltration (UF) simulated advanced treatment. We monitored breakthrough of NPs into treated water by turbidity removal and inductively coupled plasma-mass spectrometry (ICP-MS). Conventional treatment resulted in 2-20%, 3-8%, and 48-99% of Ag, TiO2, and ZnO NPs, respectively, or their dissolved ions remaining in finished water. Breakthrough following MF was 1-45% for Ag, 0-44% for TiO2, and 36-83% for ZnO. With UF, NP breakthrough was 0-2%, 0-4%, and 2-96% for Ag, TiO2, and ZnO, respectively. Variability was dependent on NP stability, with less breakthrough of aggregated NPs compared with stable NPs and dissolved NP ions. Although a majority of aggregated or stable NPs were removed by simulated conventional and advanced treatment, NP metals were detectable in finished water. As environmental NP concentrations increase, we need to consider NPs as emerging drinking water contaminants and determine appropriate drinking water treatment processes to fully remove NPs in order to reduce their potential harmful health outcomes.

Enhancing dissolved oxygen control using an on-line hybrid fuzzy-neural soft-sensing model-based control system in an anaerobic/anoxic/oxic process.

PubMed

Huang, Mingzhi; Wan, Jinquan; Hu, Kang; Ma, Yongwen; Wang, Yan

2013-12-01

An on-line hybrid fuzzy-neural soft-sensing model-based control system was developed to optimize dissolved oxygen concentration in a bench-scale anaerobic/anoxic/oxic (A(2)/O) process. In order to improve the performance of the control system, a self-adapted fuzzy c-means clustering algorithm and adaptive network-based fuzzy inference system (ANFIS) models were employed. The proposed control system permits the on-line implementation of every operating strategy of the experimental system. A set of experiments involving variable hydraulic retention time (HRT), influent pH (pH), dissolved oxygen in the aerobic reactor (DO), and mixed-liquid return ratio (r) was carried out. Using the proposed system, the amount of COD in the effluent stabilized at the set-point and below. The improvement was achieved with optimum dissolved oxygen concentration because the performance of the treatment process was optimized using operating rules implemented in real time. The system allows various expert operational approaches to be deployed with the goal of minimizing organic substances in the outlet while using the minimum amount of energy.

Magnesium transport extraction of transuranium elements from LWR fuel

DOEpatents

Ackerman, John P.; Battles, James E.; Johnson, Terry R.; Miller, William E.; Pierce, R. Dean

1992-01-01

A process of separating transuranium actinide values from uranium values present in spent nuclear oxide fuels which contain rare earth and noble metal fission products. The oxide fuel is reduced with Ca metal in the presence of CaCl.sub.2 and a U-Fe alloy containing not less than about 84% by weight uranium at a temperature in the range of from about 800.degree. C. to about 850.degree. C. to produce additional uranium metal which dissolves in the U-Fe alloy raising the uranium concentration and having transuranium actinide metals and rare earth fission product metals and the noble metal fission products dissolved therein. The CaCl.sub.2 having CaO and fission products of alkali metals and the alkali earth metals and iodine dissolved therein is separated and electrolytically treated with a carbon electrode to reduce the CaO to Ca metal while converting the carbon electrode to CO and CO.sub.2. The Ca metal and CaCl.sub.2 is recycled to reduce additional oxide fuel. The U-Fe alloy having transuranium actinide metals and rare earth fission product metals and the noble metal fission products dissolved therein is contacted with Mg metal which takes up the actinide and rare earth fission product metals. The U-Fe alloy retains the noble metal fission products and is stored while the Mg is distilled and recycled leaving the transuranium actinide and rare earth fission products isolated.

A robust and reliable optical trace oxygen sensor

NASA Astrophysics Data System (ADS)

McDowell, G. R.; Holmes-Smith, A. S.; Uttamlal, M.; Mitchell, C.; Shannon, P. H.

2017-05-01

In applications of nitrogen (N2) generation, industrial gas manufacturing and food packaging there is a need to ensure oxygen (O2) is absent from the environment, even at the lowest concentration levels. Therefore, there has been an increased growth in the development of trace O2 parts per million (ppm) sensors over the past decade to detect and quantify the concentration of molecular O2 in the environment whether it be dissolved or gaseous O2. The majority of commercially available trace O2 sensors are based on electrochemical, zirconia and paramagnetic technologies. Here, the development of a luminescence-based optical trace O2 sensor is presented. Luminescence-based sensing is now regarded as one of the best techniques for the detection and quantification of O2. This is due to the high detection sensitivity, no O2 is consumed and there are a vast array of luminescent indicators and sensing platforms (polymers) that can be selected to suit the desired application. The sensor will be shown to operate from -30 °C to +60 °C in the 0-1000 ppm and/or 0-1200 μbar partial pressure of oxygen (ppO2) range and is equipped with temperature and pressure compensation. The luminescence non-depleting principle, sensor specifications and miniaturized nature offers an attractive alternative to other sensing technologies and advantages over other luminescence-based O2 ppm sensors.

Bioaugmentation for Aerobic Bioremediation of RDX Contaminated Groundwater

DTIC Science & Technology

2016-01-06

Subsequent higher concentration (15 to 24 mM) fructose additions during high carbon biostimulation in DW-1 and MW-28 resulted in a slight decrease in pH ...that has suitable transport properties and high RDX degradation rates for a given site may not be able to be developed; (2) the selected...phase; attached cells were not measured. Minimal secondary groundwater quality degradation pH , dissolved oxygen (O2), oxidation

Constraints on the utility of MnO2 cartridge method for the extraction of radionuclides: A case study using 234Th

USGS Publications Warehouse

Baskaran, M.; Swarzenski, P.W.; Biddanda, B.A.

2009-01-01

[1] Large volume (102-103 L) seawater samples are routinely processed to investigate the partitioning of particle reactive radionuclides and Ra between solution and size-fractionated suspended particulate matter. One of the most frequently used methods to preconcentrate these nuclides from such large volumes involves extraction onto three filter cartridges (a prefilter for particulate species and two MnO2-coated filters for dissolved species) connected in series. This method assumes that the extraction efficiency is uniform for both MnO2-coated cartridges, that no dissolved species are removed by the prefilter, and that any adsorbed radionuclides are not desorbed from the MnO2-coated cartridges during filtration. In this study, we utilized 234Th-spiked coastal seawater and deionized water to address the removal of dissolved Th onto prefilters and MnO2-coated filter cartridges. Experimental results provide the first data that indicate (1) a small fraction of dissolved Th (<6%) can be removed by the prefilter cartridge; (2) a small fraction of dissolved Th (<5%) retained by the MnO2 surface can also be desorbed, which undermines the assumption of uniform extraction efficiency for Th; and (3) the absolute and relative extraction efficiencies can vary widely. These experiments provide insight on the variability of the extraction efficiency of MnO 2-coated filter cartridges by comparing the relative and absolute efficiencies and recommend the use of a constant efficiency on the combined activity from two filter cartridges connected in series for future studies of dissolved 234Th and other radionuclides in natural waters using sequential filtration/extraction methods. ?? 2009 by the American Geophysical Union.

An experimental study of basaltic glass-H2O-CO2 interaction at 22 and 50 ° C: Implications for subsurface storage of CO2

NASA Astrophysics Data System (ADS)

Galeczka, Iwona; Wolff-Boenisch, Domenik; Oelkers, Eric H.; Gislason, Sigurdur R.

2014-05-01

A novel high pressure column flow reactor (HPCFR) was used to investigate the evolution of fluid chemistry along a 2.3 meter flow path during 37-104 days of pure water- and CO2-charged water- (0.3 M CO2(aq)) basaltic glass interaction experiments at 22 and 50 ° C. The scale of the HPCFR, the ability to sample a reactive fluid at discrete spatial intervals under pressure and the possibility to measure the dissolved inorganic carbon and pH in situ all render the HPCFR unique in comparison with other reactors constructed for studies of CO2-charged water-rock interaction. During the pure water-basaltic glass interaction experiment, the pH of the injected water evolved rapidly from 6.7 to 9-9.5 and most of the dissolved iron was consumed by secondary mineral formation, similar to natural basaltic groundwater systems. In contrast to natural systems, however, the dissolved aluminium concentration remained relatively high along the entire flow path. The reactive fluid was undersaturated with respect to basaltic glass and carbonate minerals, but supersaturated with respect to zeolites, clays, and Fe hydroxides. Basaltic glass dissolution in the CO2-charged water was closer to stoichiometry than in pure water. The mobility of metals increased significantly in the reactive fluid and the concentration of some metals, including Mn, Fe, Cr, Al, and As exceeded the WHO (World Health Organisation) allowable drinking water limits. Iron was mobile and the aqueous Fe2+/Fe3+ ratio increased along the flow path. Basaltic glass dissolution in the CO2-charged water did not overcome the pH buffer capacity of the fluid. The pH rose only from an initial pH of 3.4 to 4.5 along the first 18.5 cm of the column, then remained constant during the remaining 2.1 meters of the flow path. Increasing the temperature of the CO2-charged fluid from 22 to 50 ° C increased the relative amount of dissolved divalent iron along the flow path. After a significant initial increase along the first metre of the column, the dissolved aluminium concentration decreased consistent with its incorporation into secondary minerals. The dissolved chromium concentration evolution mimicked that of Al at 50 ° C, suggesting substitution of trivalent Cr for Al in secondary phases. According to PHREEQC calculations, the CO2-charged fluid was always undersaturated with respect to carbonate minerals within the column, but supersaturated with respect to clays and Fe hydroxides at 22 ° C and with respect to clays and Al hydroxides at 50 ° C. Substantial differences were found between modelled and measured dissolved element concentrations in the fluids during the experiments. These differences underscore the need to improve computational models before they can be used to predict with confidence the fate and consequences of carbon dioxide injected into the subsurface.

Oxygen isotope systematics in the aragonite-CO2-H2O-NaCl system up to 0.7 mol/kg ionic strength at 25 °C

USGS Publications Warehouse

Kim, Sang-Tae; Gebbinck, Christa Klein; Mucci, Alfonso; Coplen, Tyler B.

2014-01-01

To investigate the oxygen isotope systematics in the aragonite-CO2-H2O-NaCl system, witherite (BaCO3) was precipitated quasi-instantaneously and quantitatively from Na-Cl-Ba-CO2 solutions of seawater-like ionic strength (I = 0.7 mol/kg) at two pH values (~7.9 and ~10.6) at 25 °C. The oxygen isotope composition of the witherite and the dissolved inorganic carbon speciation in the starting solution were used to estimate the oxygen isotope fractionations between HCO3¯ and H2O as well as between CO3 2 and H2O. Given the analytical error on the oxygen isotope composition of the witherite and uncertainties of the parent solution pH and speciation, oxygen isotope fractionation between NaHCO3° and HCO3¯, as well as between NaCO3¯ and CO3 2, is negligible under the experimental conditions investigated. The influence of dissolved NaCl concentration on the oxygen isotope fractionation in the aragonite-CO2-H2O-NaCl system also was investigated at 25 °C. Aragonite was precipitated from Na-Cl-Ca-Mg-(B)-CO2 solutions of seawater-like ionic strength using passive CO2 degassing or constant addition methods. Based upon our new experimental observations and published experimental data from lower ionic strength solutions by Kim et al. (2007b), the equilibrium aragonite-water oxygen isotope fractionation factor is independent of the ionic strength of the parent solution up to 0.7 mol/kg. Hence, our study also suggests that the aragonite precipitation mechanism is not affected by the presence of sodium and chloride ions in the parent solution over the range of concentrations investigated.

Spatial distribution of dissolved constituents in Icelandic river waters

NASA Astrophysics Data System (ADS)

Oskarsdottir, Sigrídur Magnea; Gislason, Sigurdur Reynir; Snorrason, Arni; Halldorsdottir, Stefanía Gudrún; Gisladottir, Gudrún

2011-02-01

SummaryIn this study we map the spatial distribution of selected dissolved constituents in Icelandic river waters using GIS methods to study and interpret the connection between river chemistry, bedrock, hydrology, vegetation and aquatic ecology. Five parameters were selected: alkalinity, SiO 2, Mo, F and the dissolved inorganic nitrogen and dissolved inorganic phosphorus mole ratio (DIN/DIP). The highest concentrations were found in rivers draining young rocks within the volcanic rift zone and especially those draining active central volcanoes. However, several catchments on the margins of the rift zone also had high values for these parameters, due to geothermal influence or wetlands within their catchment area. The DIN/DIP mole ratio was higher than 16 in rivers draining old rocks, but lowest in rivers within the volcanic rift zone. Thus primary production in the rivers is limited by fixed dissolved nitrogen within the rift zone, but dissolved phosphorus in the old Tertiary catchments. Nitrogen fixation within the rift zone can be enhanced by high dissolved molybdenum concentrations in the vicinity of volcanoes. The river catchments in this study were subdivided into several hydrological categories. Importantly, the variation in the hydrology of the catchments cannot alone explain the variation in dissolved constituents. The presence or absence of central volcanoes, young reactive rocks, geothermal systems and wetlands is important for the chemistry of the river waters. We used too many categories within several of the river catchments to be able to determine a statistically significant connection between the chemistry of the river waters and the hydrological categories. More data are needed from rivers draining one single hydrological category. The spatial dissolved constituent distribution clearly revealed the difference between the two extremes, the young rocks of the volcanic rift zone and the old Tertiary terrain.

Bulk Dissolution Rates of Cadmium and Bismuth Tellurides As a Function of pH, Temperature and Dissolved Oxygen.

PubMed

Biver, Marc; Filella, Montserrat

2016-05-03

The toxicity of Cd being well established and that of Te suspected, the bulk, surface-normalized steady-state dissolution rates of two industrially important binary tellurides-polycrystalline cadmium and bismuth tellurides- were studied over the pH range 3-11, at various temperatures (25-70 °C) and dissolved oxygen concentrations (0-100% O2 in the gas phase). The behavior of both tellurides is strikingly different. The dissolution rates of CdTe monotonically decreased with increasing pH, the trend becoming more pronounced with increasing temperature. Activation energies were of the order of magnitude associated with surface controlled processes; they decreased with decreasing acidity. At pH 7, the CdTe dissolution rate increased linearly with dissolved oxygen. In anoxic solution, CdTe dissolved at a finite rate. In contrast, the dissolution rate of Bi2Te3 passed through a minimum at pH 5.3. The activation energy had a maximum in the rate minimum at pH 5.3 and fell below the threshold for diffusion control at pH 11. No oxygen dependence was detected. Bi2Te3 dissolves much more slowly than CdTe; from one to more than 3.5 orders of magnitude in the Bi2Te3 rate minimum. Both will readily dissolve under long-term landfill deposition conditions but comparatively slowly.

Isotopomer analysis of production and consumption mechanisms of N2O and CH4 in an advanced wastewater treatment system.

PubMed

Toyoda, Sakae; Suzuki, Yuuri; Hattori, Shohei; Yamada, Keita; Fujii, Ayako; Yoshida, Naohiro; Kouno, Rina; Murayama, Kouki; Shiomi, Hiroshi

2011-02-01

Wastewater treatment processes are believed to be anthropogenic sources of nitrous oxide (N(2)O) and methane (CH(4)). However, few studies have examined the mechanisms and controlling factors in production of these greenhouse gases in complex bacterial systems. To elucidate production and consumption mechanisms of N(2)O and CH(4) in microbial consortia during wastewater treatment and to characterize human waste sources, we measured their concentrations and isotopomer ratios (elemental isotope ratios and site-specific N isotope ratios in asymmetric molecules of NNO) in water and gas samples collected by an advanced treatment system in Tokyo. Although the estimated emissions of N(2)O and CH(4) from the system were found to be lower than those from the typical treatment systems reported before, water in biological reaction tanks was supersaturated with both gases. The concentration of N(2)O, produced mainly by nitrifier-denitrification as indicated by isotopomer ratios, was highest in the oxic tank (ca. 4000% saturation). The dissolved CH(4) concentration was highest in in-flow water (ca. 3000% saturation). It decreased gradually during treatment. Its carbon isotope ratio indicated that the decrease resulted from bacterial CH(4) oxidation and that microbial CH(4) production can occur in anaerobic and settling tanks.

Hydrology and water quality of Elkhead Creek and Elkhead Reservoir near Craig, Colorado, July 1995-September 2001

USGS Publications Warehouse

Kuhn, Gerhard; Stevens, Michael R.; Elliott, John G.

2003-01-01

The U.S. Geological Survey, in cooperation with the Colorado River Water Conservation District, collected and analyzed baseline streamflow and water-quality information for Elkhead Creek and water-quality and trophic-state information for Elkhead Reservoir from July 1995 through September 2001. In the study area, Elkhead Creek is a meandering, alluvial stream dominated by snowmelt in mountainous headwaters that produces most of the annual discharge volume and discharge peaks during late spring and early summer. During most of water year 1996 (a typical year), daily mean discharge at station 09246400 (downstream from the reservoir) was similar to daily mean discharge at station 09246200 (upstream from the reservoir). Flow-duration curves for stations 09246200 and 09246400 were nearly identical, except for discharges less than about 10 cubic feet per second. Specific conductance generally had an inverse relation to discharge in Elkhead Creek. During late fall and winter when discharge was small and derived mostly from ground water, specific conductance was high, whereas during spring and early summer, when discharge was large and derived mostly from snowmelt, specific conductance was low. Water temperatures in Elkhead Creek were smallest during winter, about 0.0 degrees Celsius (oC), and largest during summer, about 20?25oC. Concentrations of major ions, nutrients, trace elements, organic carbon, and suspended sediment in Elkhead Creek indicated no substantial within-year variability and no substantial differences in variability from one year to the next. A seasonal pattern in the concentration data was evident for most constituents. The seasonal concentration pattern for most of the dissolved constituents followed the seasonal pattern of specific conductance, whereas some nutrients, some trace elements, and suspended sediment followed the seasonal pattern of discharge. Statistical differences between station 09246200 (upstream from the reservoir) and station 09246400 (downstream from the reservoir) were indicated for specific conductance, dissolved calcium, magnesium, sodium, and sulfate, acid-neutralizing capacity, and dissolved solids. Trend analysis indicated upward temporal trends for pH, dissolved ammonia plus organic nitrogen, total nitrogen, and total phosphorus at station 09246200; upward temporal trends for dissolved and total ammonia plus organic nitrogen, total nitrogen, and total phosphorus were indicated at station 09246400. No downward trends were indicated for any constituents. Annual loads for dissolved constituents during water years 1996?2001 were consistently larger at station 09246400 than at station 09246200, except for silica and sulfate. Mean monthly loads for dissolved constituents followed the seasonal pattern of discharge, indicating that most of the annual loads were transported during March?June. Annual dissolved nutrient loads at stations 09246400 and 09246200 were not substantially different, except for total phosphorus and total nitrogen loads, which were smaller at the downstream station than at the upstream station, most likely due to biological uptake and settling in the reservoir. Mean annual suspended-sediment load during water years 1996?2001 was about 87-percent smaller at the downstream station than at the upstream station. Temperature in Elkhead Reservoir varied seasonally, from about 0oC during winter when ice develops on the reservoir to about 20oC during summer. Specific conductance varied from minimums of 138 to 169 microsiemens per centimeter at 25oC (?S/cm) during snowmelt inflow to maximums of 424 to 610 ?S/cm during early spring low flow (April). Median pH in the reservoir ranged from 7.2 to 8.0 at all sites near the surface. Median dissolved oxygen ranged from 7.1 to 7.2 milligrams per liter (mg/L) in near-surface samples and from 4.8 to 5.6 mg/L in near-bottom samples. During reservoir stratification, specific conductance generally was largest in the e

Effect of Oxygen Gas on the Decomposition of Dye by Pulsed Discharge in Water Droplet Spray

NASA Astrophysics Data System (ADS)

Nose, Taisuke; Yokoyama, Yuzo; Nakamura, Akira; Minamitani, Yasushi

Effect of O2 on the decolorization of indigo carmine and on the production of dissolved species such as NO2-, NO3-, O3 and H2O2 in the treatment water by pulsed discharge in water droplet spray was investigated by controlling the O2/N2 ratios as carrier gases in the reactor. The decolorization rate gradually increased with rise in O2 ratio, which reached a constant value in the range of 50% to 90% O2 ratio and decreased in pure O2. The maximum value was about 2 times as high as that of 20% O2 ratio. The decolorization efficiency was not affected by gas flow rate in the range of 4 L/min to 50 L/min. NO2- in the treatment water was only detected in pure N2, but NO3- was produced in O2/N2. NO2- added to the treatment water was not oxidized in pure N2, but was perfectly converted to NO3- in O2/N2. These results implied that hydroxyl radical produced in gas phase does not directly contribute to the oxidation of substances in water. O3 concentration gradually increased with rise in O2 ratio, whereas H2O2 concentration decreased. In the range of 50 to 80% O2 ratio, O3 and H2O2 concentrations were approximately constant value, similar to the trend of decolorization rate. Moreover rate constants on various gas mixing ratio of O2/N2 were determined from the kinetics study. These results suggested that hydroxyl radical produced in the treatment water by the chain reactions of O3 and hydroperoxy radical (HO2·) plays an important role of the decomposition of molecules in water.

Kinetics of microbial reduction of Solid phase U(VI).

PubMed

Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M; Wang, Zheming; Dohnalkova, Alice; Fredrickson, James K

2006-10-15

Sodium boltwoodite (NaUO2SiO3OH x 1.5 H2O) was used to assess the kinetics of microbial reduction of solid-phase U(VI) by a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1. The bioreduction kinetics was studied with Na-boltwoodite in suspension or within alginate beads in a nongrowth medium with lactate as electron donor at pH 6.8 buffered with PIPES. Concentrations of U(VI)tot and cell number were varied to evaluate the coupling of U(VI) dissolution, diffusion, and microbial activity. Microscopic and spectroscopic analyses with transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and laser-induced fluorescence spectroscopy (LIFS) collectively indicated that solid-phase U(VI) was first dissolved and diffused out of grain interiors before it was reduced on bacterial surfaces and/or within the periplasm. The kinetics of solid-phase U(VI) bioreduction was well described by a coupled model of bicarbonate-promoted dissolution of Na-boltwoodite, intragrain uranyl diffusion, and Monod type bioreduction kinetics with respect to dissolved U(VI) concentration. The results demonstrated that microbial reduction of solid-phase U(VI) is controlled by coupled biological, chemical, and physical processes.

The interaction of molecular hydrogen with α-radiolytic oxidants on a (U,Pu)O2 surface

NASA Astrophysics Data System (ADS)

Bauhn, Lovisa; Hansson, Niklas; Ekberg, Christian; Fors, Patrik; Delville, Rémi; Spahiu, Kastriot

2018-07-01

In order to assess the impact of α-radiolysis of water on the oxidative dissolution of spent fuel, an un-irradiated, annealed MOX fuel pellet with high content of Pu (∼24 wt%), and a specific α-activity of 4.96 GBq/gMOX, was leached in carbonate-containing solutions of low ionic strength. The high Pu content in the pellet stabilizes the (U,Pu)O2(s) matrix towards oxidative dissolution, whereas the α-decays emitted from the surface are expected to produce ∼3.6 × 10-7 mol H2O2/day, contributing to the oxidative dissolution of the pellet. Two sets of leaching tests were conducted under different redox conditions: Ar gas atmosphere and deuterium gas atmosphere. A relatively slow increase of the U and Pu concentrations was observed in the Ar case, with U concentrations increasing from 1·10-6 M after 1 h to ∼7 × 10-5 M after 58 days. Leaching under an atmosphere starting at 1 MPa deuterium gas was undertaken in order to evaluate any effect of dissolved hydrogen on the radiolytic dissolution of the pellet, as well as to investigate any potential recombination of the α-radiolytic products with dissolved deuterium. For the latter purpose, isotopic analysis of the D/H content was carried out on solution samples taken during the leaching. Despite the continuous production of radiolytic oxidants, the concentrations of U and Pu remained quite constant at the level of ∼3 × 10-8 M during the first 30 days, i.e. as long as the deuterium pressure remained higher than 0.8 MPa. These data rule out any oxidative dissolution of the pellet during the first month. The un-irradiated MOX fuel does not contain metallic ε-particles, hence it is mainly the interaction of radiolytic oxidants and dissolved deuterium with the surface of the mixed actinide oxide that causes the neutralization of the oxidants. This conclusion is supported by the steadily increasing levels of HDO measured in the leachate samples.

Silica removal from steamflood produced water: South Texas Tar Sands Pilot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, S.A.; Cathey, S.R.; Yost, M.E.

1984-09-01

Steamflood produced waters commonly contain suspended solids, oil, hardness, sulfide, and silica. Removal of these contaminants would make many of these waters suitable candidates for recycling as steam feedwater. Reuse of steamflood produced waters will increase steamer feedwater supplies, as well as reduce water disposal requirements. This paper describes a field pilot study of silica removal from steamflood produced water in the South Texas Tar Sands region. A hot-lime precipitation process was used to reduce dissolved silica concentrations from 400 mg/l to less than 50 mg/l SiO/sub 2/ in Mary R. Saner Ranch produced water. Most water systems using hot-limemore » precipitation for silica removal call for the addition of magnesium salts, as well as lime, to enhance silica removal. In this field study, however, magnesium salt addition did not improve silica removal efficiency. Hydrated lime ((Ca(OH)/sub 2/), alone, was sufficient to attain the desired silica residual, 50 mg/l SiO/sub 2/. The dissolved silica adsorbed onto the CaCO/sub 3/ crystals formed by lime reacting with the alkalinity present in the produced water. Required lime dosage was approximately 900 mg/lCa(OH)/sub 2/. Residual silica concentrations were found to be strongly related to both precipitator pH and calcium ion concentration. Therefore, on-line pH and hardness monitoring may be used to estimate and control residual silica concentration. A 50,000-BPD (7,900 m/sup 3//d) produced water treating plant has been designed using results from this pilot study.« less

Expression of seasonal and ENSO forcing in climatic variability at lower than ENSO frequencies: evidence from Pleistocene marine varves off California

USGS Publications Warehouse

Anderson, R.Y.; Linsley, B.K.; Gardner, J.V.

1990-01-01

Upper Pleistocene marine sediments along the upper continental slope off northern and central California contain alternations of varved and bioturbated sediments and associated changes in biota and sediment composition. These alternations can be related to conditions that accompany El Nin??o and anti-El Nin??o (ENSO) circulation. Anti-El Nin??o conditions are characterized by increased upwelling and productivity and by low concentrations of dissolved oxygen in the oxygen minimum zone that resulted in varve preservation. El Nin??o conditions are characterized by little or no upwelling, low productivity, and higher concentrations of dissolved oxygen that resulted in zones of bioturbation. Alternations of varves and zones of bioturbation, that range from decades to millennia, occur through the upper Pleistocene section. The inferred long-term alternations in El Nin??o and anti-El Nin??o conditions appear to be a re-expression of ENSO's primary 3-7 year cycle. Decadal to millennial cycles of productivity associated with El Nin??o and anti-El Nin??o conditions may have served as a "carbon pump" and transferred atmospheric CO2 to the marine reservoir. Changes in sediment composition and organisms associated with El Nin??o or anti-El Nin??o conditions can be related to both seasonal and ENSO phenomena. Expression of these changes at lower-than-ENSO frequencies may be partly explained by adding the effects of seasonal variability to effects produced by a self-oscillating ENSO system. However, deterministic mechanisms, including solar modulation of ENSO, may also contribute to long-term alternations of El Nin??o and anti-El Nin??o conditions. ?? 1990.

Occurrence of greenhouse gases (CO2, N2O and CH4) in groundwater of the Walloon Region (Belgium).

NASA Astrophysics Data System (ADS)

Jurado, Anna; Borges, Alberto V.; Pujades, Estanislao; Hakoun, Vivien; Knöller, Kay; Brouyère, Serge

2017-04-01

Greenhouse gases (GHGs) are an environmental problem because their concentrations in the atmosphere have continuously risen since the industrial revolution. They can be indirectly transferred to the atmosphere through groundwater discharge into surface water bodies such as rivers. However, their occurrence is poorly evaluated in groundwater. The aim of this work is to identify the hydrogeological contexts (e.g., chalk and limestone aquifers) and the most conductive conditions for the generation of GHGs in groundwater at a regional scale. To this end, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) concentrations, major and minor elements and environmental isotopes were monitored in several groundwater bodies of the Walloon Region (Belgium) from September 2014 to June 2016. The concentrations of GHGs in groundwater ranged from 1769 to 100519 ppm for the partial pressure of CO2 and from 0 to 1064 nmol/L and 1 to 37062 nmol/L for CH4 and N2O respectively. Overall, groundwater was supersaturated in GHGs with respect to atmospheric equilibrium, suggesting that groundwater contribute to the atmospheric GHGs budget. Prior inspection of the data suggested that N2O in groundwater can be produced by denitrification and nitrification. The most suitable conditions for the accumulation of N2O are promoted by intermediate dissolved oxygen concentrations (2.5-3 mg L-1) and the availability of nitrate (NO3-). These observations will be compared with the isotopes of NO3-. CH4 was less detected and at lower concentration than N2O, suggesting that groundwater redox conditions are not reducing enough to promoted the production of CH4. The results will be presented and discussed in detail in the presentation.

A thermodynamic model for the prediction of phase equilibria and speciation in the H 2O-CO 2-NaCl-CaCO 3-CaSO 4 system from 0 to 250 °C, 1 to 1000 bar with NaCl concentrations up to halite saturation

NASA Astrophysics Data System (ADS)

Li, Jun; Duan, Zhenhao

2011-08-01

A thermodynamic model is developed for the calculation of both phase and speciation equilibrium in the H 2O-CO 2-NaCl-CaCO 3-CaSO 4 system from 0 to 250 °C, and from 1 to 1000 bar with NaCl concentrations up to the saturation of halite. The vapor-liquid-solid (calcite, gypsum, anhydrite and halite) equilibrium together with the chemical equilibrium of H+,Na+,Ca, CaHCO3+,Ca(OH)+,OH-,Cl-, HCO3-,HSO4-,SO42-, CO32-,CO,CaCO and CaSO 4(aq) in the aqueous liquid phase as a function of temperature, pressure and salt concentrations can be calculated with accuracy close to the experimental results. Based on this model validated from experimental data, it can be seen that temperature, pressure and salinity all have significant effects on pH, alkalinity and speciations of aqueous solutions and on the solubility of calcite, halite, anhydrite and gypsum. The solubility of anhydrite and gypsum will decrease as temperature increases (e.g. the solubility will decrease by 90% from 360 K to 460 K). The increase of pressure may increase the solubility of sulphate minerals (e.g. gypsum solubility increases by about 20-40% from vapor pressure to 600 bar). Addition of NaCl to the solution may increase mineral solubility up to about 3 molality of NaCl, adding more NaCl beyond that may slightly decrease its solubility. Dissolved CO 2 in solution may decrease the solubility of minerals. The influence of dissolved calcite on the solubility of gypsum and anhydrite can be ignored, but dissolved gypsum or anhydrite has a big influence on the calcite solubility. Online calculation is made available on www.geochem-model.org/model.

Solar photocatalitycal treatment of carbofuran at lab and pilot scale: effect of classical parameters, evaluation of the toxicity and analysis of organic by-products.

PubMed

Lopez-Alvarez, Blady; Torres-Palma, Ricardo A; Peñuela, Gustavo

2011-07-15

In this work the TiO(2) solar-photocatalytical degradation of the pesticide carbofuran (CBF) in water, at lab and pilot scale, was studied. At lab scale the evaluation of CBF concentration (14-282 μmol L(-1)) showed that the system followed a Langmuir-Hinshelwood kinetics type. TiO(2) concentration (0.05-2 g L(-1)) and initial pH (3-9) were also evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, initial pH 7.60 and 1.43 g L(-1) of TiO(2) favoured the efficiency of the process. Under optimal conditions the evolution of substrate, chemical oxygen demand, dissolved organic carbon, toxicity and organics by-products were evaluated. In the pilot scale tests, using direct sunlight, 55 mg L(-1) of CBF in a commercial formulation was eliminated after 420 min; while after 900 min of treatment 80% of toxicity (1/E(50) on Vibrium Fischeri), 80% of chemical oxygen demand and 60% of dissolved organic carbon were removed. The analysis and evolution of five CBF by-products, as well the evaluation of the treatment in the presence of isopropanol or using acetonitrile as a solvent suggest that the degradation is mainly carried out by OH radical attack. Finally, a schema depicting the main degradation pathway is proposed. Copyright © 2011 Elsevier B.V. All rights reserved.

Efficacy of controlled-release KMnO4 (CRP) for controlling dissolved TCE plume in groundwater: a large flow-tank study.

PubMed

Lee, Byung Sun; Kim, Jeong Hee; Lee, Ki Churl; Kim, Yang Bin; Schwartz, Franklin W; Lee, Eung Seok; Woo, Nam Chil; Lee, Myoung Ki

2009-02-01

A well-based, reactive barrier system using controlled-release potassium permanganate (CRP system) was recently developed as a long-term treatment option for dilute plumes of chlorinated solvents in groundwater. In this study, we performed large-scale (L x W x D = 8 m x 4 m x 2 m) flow-tank experiments to examine remedial efficacy of the CRP system. A total of 110 CRP rods (OD x L=5 cm x 150 cm) were used to construct a well-based CRP system (L x W x D = 3 m x 4 m x 1.5 m) comprising three discrete barriers installed at 1-m interval downstream. Natural sands having oxidant demand of 3.7 g MnO(4)(-)kg(-1) for 500 mg L(-1)MnO(4)(-) were used as porous media. After MnO(4)(-) concentrations were somewhat stabilized (0.5-6.0 mg L(-1)), trichloroethylene (TCE) plume was flowed through the flow-tank for 53 d by supplying 1.19 m(3)d(-1) of TCE solution. Mean initial TCE concentrations were 87 microg L(-1) for first 20 d and 172 microg L(-1) for the next 33 d. During TCE treatment, flow velocity (0.60md(-1)), pH (7.0-8.2), and concentrations of dissolved metals ([Al]=0.7 mg L(-1), [Fe]=0.01 mg L(-1)) showed little variations. The MnO(2)(s) contents in the sandy media measured after the TCE treatment ranged from 21 to 26 mg kg(-1), slightly increased from mean baseline value of 17 mg kg(-1). Strengths of the TCE plume considerably diminished by the CRP system. For the 87 microg L(-1) plume, TCE concentrations decreased by 38% (53), 67% (29), and 74% (23 microg L(-1)) after 1st, 2nd, and 3rd barriers, respectively. For the 172 microg L(-1) plume, TCE concentrations decreased by 27% (125), 46% (93), and 65% (61 microg L(-1)) after 1st, 2nd, and 3rd barriers, respectively. Incomplete destruction of TCE plume was attributed to the lack of lateral dispersion in the unpumped well-based barrier system. Development of delivery systems that can facilitate lateral spreading and mixing of permanganate with contaminant plume is warranted.

The effect of hydrogen peroxide on uranium oxide films on 316L stainless steel

NASA Astrophysics Data System (ADS)

Wilbraham, Richard J.; Boxall, Colin; Goddard, David T.; Taylor, Robin J.; Woodbury, Simon E.

2015-09-01

For the first time the effect of hydrogen peroxide on the dissolution of electrodeposited uranium oxide films on 316L stainless steel planchets (acting as simulant uranium-contaminated metal surfaces) has been studied. Analysis of the H2O2-mediated film dissolution processes via open circuit potentiometry, alpha counting and SEM/EDX imaging has shown that in near-neutral solutions of pH 6.1 and at [H2O2] ⩽ 100 μmol dm-3 the electrodeposited uranium oxide layer is freely dissolving, the associated rate of film dissolution being significantly increased over leaching of similar films in pH 6.1 peroxide-free water. At H2O2 concentrations between 1 mmol dm-3 and 0.1 mol dm-3, formation of an insoluble studtite product layer occurs at the surface of the uranium oxide film. In analogy to corrosion processes on common metal substrates such as steel, the studtite layer effectively passivates the underlying uranium oxide layer against subsequent dissolution. Finally, at [H2O2] > 0.1 mol dm-3 the uranium oxide film, again in analogy to common corrosion processes, behaves as if in a transpassive state and begins to dissolve. This transition from passive to transpassive behaviour in the effect of peroxide concentration on UO2 films has not hitherto been observed or explored, either in terms of corrosion processes or otherwise. Through consideration of thermodynamic solubility product and complex formation constant data, we attribute the transition to the formation of soluble uranyl-peroxide complexes under mildly alkaline, high [H2O2] conditions - a conclusion that has implications for the design of both acid minimal, metal ion oxidant-free decontamination strategies with low secondary waste arisings, and single step processes for spent nuclear fuel dissolution such as the Carbonate-based Oxidative Leaching (COL) process.

Determination of exchangeable protons in natural organic matter using a home-made hydrogen/carbon analyser.

PubMed

Haiber, S; Barth, U

2001-01-01

A home made hydrogen/carbon analyser was used to determine the portion of exchangeable protons in aquatic humic substances. For this purpose, equal sample amounts were dissolved in H2O and D2O, respectively, dried and combusted in a stream of oxygen. The amount of water resulting from combustion was measured by an infrared detector which recorded the OH bending vibration of H2O. The bands stemming from HOD or D2O were not registered by the detection unit. Thus, combustion of organic samples containing exchangeable protons dissolved in D2O resulted in a significantly smaller signal compared to the signal observed for the same sample dissolved in H2O. The relative intensity loss of the H2O signal observed after combustion was used to derive the portion of exchangeable protons in a standard reference material, a humic substance isolated by the International Humic Substances Society (Suwannee River fulvic acid). According to this method about 20% of the sample protons could be identified as exchangeable protons. With regard to titration data the portion of protons bound to non acidic hydroxy functions could be estimated. The validity of this procedure was proved by combustion experiments using commercially available deuterated substances as well as organic model compounds dissolved in D2O and H2O, respectively.

Critical zone structure controls concentration-discharge relationships and solute generation in forested tropical montane watersheds

NASA Astrophysics Data System (ADS)

Wymore, Adam S.; Brereton, Richard L.; Ibarra, Daniel E.; Maher, Kate; McDowell, William H.

2017-07-01

Concentration-discharge (C-Q) relationships are poorly known for tropical watersheds, even though the tropics contribute a disproportionate amount of solutes to the global ocean. The Luquillo Mountains in Puerto Rico offer an ideal environment to examine C-Q relationships across a heterogeneous tropical landscape. We use 10-30 years of weekly stream chemistry data across 10 watersheds to examine C-Q relationships for weathering products (SiO2(aq), Ca2+, Mg2+, and Na+) and biologically controlled solutes (dissolved organic carbon [DOC], dissolved organic nitrogen [DON], NH4+, NO3-, PO43-, K+, and SO42-). We analyze C-Q relationships using power law equations and a solute production model and use principal component analysis to test hypotheses regarding how the structure of the critical zone controls solute generation. Volcaniclastic watersheds had higher concentrations of weathering solutes and smaller tributaries were approximately threefold more efficient at generating these solutes than larger rivers. Lithology and vegetation explained a significant amount of variation in the theoretical maximum concentrations of weathering solutes (r2 = 0.43-0.48) and in the C-Q relationships of PO43- (r2 = 0.63) and SiO2(aq) (r2 = 0.47). However, the direction and magnitude of these relationships varied. Across watersheds, various forms of N and P displayed variable C-Q relationships, while DOC was consistently enriched with increasing discharge. Results suggest that PO43- may be a useful indicator of watershed function. Relationships between C-Q and landscape characteristics indicate the extent to which the structure and function of the Critical zone controls watershed solute fluxes.

In situ mid-infrared spectroscopic titration of forsterite with water in supercritical CO2: Dependence of mineral carbonation on quantitative water speciation

NASA Astrophysics Data System (ADS)

Loring, J. S.; Thompson, C. J.; Wang, Z.; Schaef, H. T.; Martin, P.; Qafoku, O.; Felmy, A. R.; Rosso, K. M.

2011-12-01

Geologic sequestration of carbon dioxide holds promise for helping mitigate CO2 emissions generated from the burning of fossil fuels. Supercritical CO2 (scCO2) plumes containing variable water concentrations (wet scCO2) will displace aqueous solution and dominate the pore space adjacent to caprocks. It is important to understand possible mineral reactions with wet scCO2 to better predict long-term caprock integrity. We introduce novel in situ instrumentation that enables quantitative titrations of reactant minerals with water in scCO2 at temperatures and pressures relevant to target geologic reservoirs. The system includes both transmission and attenuated total reflection mid-infrared optics. Transmission infrared spectroscopy is used to measure concentrations of water dissolved in the scCO2, adsorbed on mineral surfaces, and incorporated into precipitated carbonates. Single-reflection attenuated total reflection infrared spectroscopy is used to monitor water adsorption, mineral dissolution, and carbonate precipitation reactions. Results are presented for the infrared spectroscopic titration of forsterite (Mg2SiO4), a model divalent metal silicate, with water in scCO2 at 100 bar and at both 50 and 75°C. The spectral data demonstrate that the quantitative speciation of water as either dissolved or adsorbed is important for understanding the types, growth rates, and amounts of carbonate precipitates formed. Relationships between dissolved/adsorbed water, water concentrations, and the role of liquid-like adsorbed water are discussed. Our results unify previous in situ studies from our laboratory based on infrared spectroscopy, nuclear magnetic resonance spectroscopy and X-ray diffraction.

Remediation of a winery wastewater combining aerobic biological oxidation and electrochemical advanced oxidation processes.

PubMed

Moreira, Francisca C; Boaventura, Rui A R; Brillas, Enric; Vilar, Vítor J P

2015-05-15

Apart from a high biodegradable fraction consisting of organic acids, sugars and alcohols, winery wastewaters exhibit a recalcitrant fraction containing high-molecular-weight compounds as polyphenols, tannins and lignins. In this context, a winery wastewater was firstly subjected to a biological oxidation to mineralize the biodegradable fraction and afterwards an electrochemical advanced oxidation process (EAOP) was applied in order to mineralize the refractory molecules or transform them into simpler ones that can be further biodegraded. The biological oxidation led to above 97% removals of dissolved organic carbon (DOC), chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5), but was inefficient on the degradation of a bioresistant fraction corresponding to 130 mg L(-1) of DOC, 380 mg O2 L(-1) of COD and 8.2 mg caffeic acid equivalent L(-1) of total dissolved polyphenols. Various EAOPs such as anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), UVA photoelectro-Fenton (PEF) and solar PEF (SPEF) were then applied to the recalcitrant effluent fraction using a 2.2 L lab-scale flow plant containing an electrochemical cell equipped with a boron-doped diamond (BDD) anode and a carbon-PTFE air-diffusion cathode and coupled to a photoreactor with compound parabolic collectors (CPCs). The influence of initial Fe(2+) concentration and current density on the PEF process was evaluated. The relative oxidative ability of EAOPs increased in the order AO-H2O2 < EF < PEF ≤ SPEF. The SPEF process using an initial Fe(2+) concentration of 35 mg L(-1), current density of 25 mA cm(-2), pH of 2.8 and 25 °C reached removals of 86% on DOC and 68% on COD after 240 min, regarding the biologically treated effluent, along with energy consumptions of 45 kWh (kg DOC)(-1) and 5.1 kWh m(-3). After this coupled treatment, color, odor, COD, BOD5, NH4(+), NO3(-) and SO4(2-) parameters complied with the legislation targets and, in addition, a total dissolved polyphenols content of 0.35 mg caffeic acid equivalent L(-1) was found. Respirometry tests revealed low biodegradability enhancement along the SPEF process. Copyright © 2015 Elsevier Ltd. All rights reserved.

Distribution of polycyclic aromatic hydrocarbons in southern Chesapeake Bay surface water: Evaluation of three methods for determining freely dissolved water concentrations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gustafson, K.E.; Dickhut, R.M.

1997-03-01

Gas sparging, semipermeable-membrane devices (SPMDs), and filtration with sorption of dissolved polycyclic aromatic hydrocarbons (PAHs) to XAD-2 resin were evaluated for determining the concentrations of freely dissolved PAHs in estuarine waters of southern Chesapeake Bay at sites ranging from rural to urban and highly industrialized. Gas sparging had significant sampling artifacts due to particle scavenging by rising bubbles, and SPMDs were kinetically limited for four-ring and larger PAHs relative to short-term temporal changes in water concentrations. Filtration with sorption of the dissolved contaminant fraction to XAD-2 resin was found to be the most accurate and feasible method for determining concentrationsmore » of freely dissolved PAHs in estuarine water. Concentrations and distribution coefficients of dissolved and particulate PAHs were measured using the filtration/XAD-2 method. Concentrations of PAHs in surface waters of southern Chesapeake Bay were higher than those reported for the northern bay; concentrations in the Elizabeth River were elevated relative to all other sites. A gradient for particulate PAHs was observed from urban to remote sites. No seasonal trends were observed in dissolved or particle-bound PAH fractions at any site. Distributions of dissolved and particulate PAHs in surface waters of the Chesapeake Bay are near equilibrium at all locations and during all seasons.« less

Evaluation of Fe(II) oxidation at an acid mine drainage site using laboratory-scale reactors

NASA Astrophysics Data System (ADS)

Brown, Juliana; Burgos, William

2010-05-01

Acid mine drainage (AMD) is a severe environmental threat to the Appalachian region of the Eastern United States. The Susquehanna and Potomac River basins of Pennsylvania drain to the Chesapeake Bay, which is heavily polluted by acidity and metals from AMD. This study attempted to unravel the complex relationships between AMD geochemistry, microbial communities, hydrodynamic conditions, and the mineral precipitates for low-pH Fe mounds formed downstream of deep mine discharges, such as Lower Red Eyes in Somerset County, PA, USA. This site is contaminated with high concentrations of Fe (550 mg/L), Mn (115 mg/L), and other trace metals. At the site 95% of dissolved Fe(II) and 56% of total dissolved Fe is removed without treatment, across the mound, but there is no change in the concentration of trace metals. Fe(III) oxides were collected across the Red Eyes Fe mound and precipitates were analyzed by X-ray diffraction, electron microscopy and elemental analysis. Schwertmannite was the dominant mineral phase with traces of goethite. The precipitates also contained minor amounts of Al2O3, MgO,and P2O5. Laboratory flow-through reactors were constructed to quantify Fe(II) oxidation and Fe removal over time at terrace and pool depositional facies. Conditions such as residence time, number of reactors in sequence and water column height were varied to determine optimal conditions for Fe removal. Reactors with sediments collected from an upstream terrace oxidized more than 50% of dissolved Fe(II) at a ten hour residence time, while upstream pool sediments only oxidized 40% of dissolved Fe(II). Downstream terrace and pool sediments were only capable of oxidizing 25% and 20% of Fe(II), respectively. Fe(II) oxidation rates measured in the reactors were determined to be between 3.99 x 10-8and 1.94 x 10-7mol L-1s-1. The sediments were not as efficient for total dissolved Fe removal and only 25% was removed under optimal conditions. The removal efficiency for all sediments decreased as residence time decreased and as water column depth increased. Control reactors with Co-60 irradiated sediments showed an increase in Fe concentration as a result of dissolution of the sediments; thus, it was concluded that Fe(II) oxidation in the reactors was a result of biological processes and not abiotic oxidation. It was also concluded that Fe(II) oxidation and removal rates were dependent upon geochemical gradients (pH, Fe(II) concentration) rather than depositional facies. Fluorescent in situ hybridization was also performed on field and reactor samples to determine which microbial communities were responsible for the highest Fe(II) oxidation rates.

Circulation and oxygen cycling in the Mediterranean Sea: Sensitivity to future climate change

NASA Astrophysics Data System (ADS)

Powley, Helen R.; Krom, Michael D.; Van Cappellen, Philippe

2016-11-01

Climate change is expected to increase temperatures and decrease precipitation in the Mediterranean Sea (MS) basin, causing substantial changes in the thermohaline circulation (THC) of both the Western Mediterranean Sea (WMS) and Eastern Mediterranean Sea (EMS). The exact nature of future circulation changes remains highly uncertain, however, with forecasts varying from a weakening to a strengthening of the THC. Here we assess the sensitivity of dissolved oxygen (O2) distributions in the WMS and EMS to THC changes using a mass balance model, which represents the exchanges of O2 between surface, intermediate, and deep water reservoirs, and through the Straits of Sicily and Gibraltar. Perturbations spanning the ranges in O2 solubility, aerobic respiration kinetics, and THC changes projected for the year 2100 are imposed to the O2 model. In all scenarios tested, the entire MS remains fully oxygenated after 100 years; depending on the THC regime, average deep water O2 concentrations fall in the ranges 151-205 and 160-219 µM in the WMS and EMS, respectively. On longer timescales (>1000 years), the scenario with the largest (>74%) decline in deep water formation rate leads to deep water hypoxia in the EMS but, even then, the WMS deep water remains oxygenated. In addition, a weakening of THC may result in a negative feedback on O2 consumption as supply of labile dissolved organic carbon to deep water decreases. Thus, it appears unlikely that climate-driven changes in THC will cause severe O2 depletion of the deep water masses of the MS in the foreseeable future.

Removal of elevated level of chromium in groundwater by the fabricated PANI/Fe3O4 nanocomposites.

PubMed

Ramachandran, Aruna; Prasankumar, T; Sivaprakash, S; Wiston, Biny R; Biradar, Santhosh; Jose, Sujin

2017-03-01

In this work, we report the reduction of chromium concentration in the polluted groundwater samples from Madurai Kamaraj University area, India, where the dissolved salts in groundwater are reported as serious health hazards for its inhabitants. The water samples have intolerable amounts of total dissolved solids (TDS) and chromium is a prominent pollutant among them. Chromium reduction was achieved by treating the polluted groundwater with PANI/Fe 3 O 4 nanocomposites synthesized by in situ polymerization method. Further experimentation showed that the nanocomposites exhibit better chromium removal characteristics upon increasing the aniline concentration during the synthesis. We were able to reduce chromium concentration in the samples from 0.295 mg L -1 to a tolerable amount of 0.144 mg L -1 . This work is expected to open doors for chromium-free groundwater in various regions of India, when improved to an industrial scale.

CO2 Solubility in Natural Rhyolitic Melts at High Pressures - Implications for Carbon Flux in Subduction Zones by Sediment Partial Melts

NASA Astrophysics Data System (ADS)

Duncan, M. S.; Dasgupta, R.

2011-12-01

Partial melts of subducting sediments is thought to be a critical agent in carrying trace elements and water to arc basalt source regions. For subduction zones that contain significant amount of carbonates in ocean-floor sediments, sediment melts likely also act as a carrier of CO2. However, the CO2 carrying capacity of natural rhyolitic melts at sub-arc depths remains unconstrained. We conducted experiments on a synthetic composition, similar to average, low-degree experimental partial melt of pelitic sediments. The composition was constructed with reagent grade oxides and carbonates, the source of excess CO2. Experiments were conducted between 1 and 3 GPa at 1200 °C in Au80Pd20 capsules using a piston cylinder apparatus with a half-inch BaCO3 assembly at Rice University. Quench products showed glasses with bubbles, the latter suggesting saturation of the melt with a CO2-rich vapor phase. Oxygen fugacity during the experiments was not strictly controlled but the presence of CO2 bubbles and absence of graphite indicates fO2 above the CCO buffer. Major element concentrations of glasses were measured using EPMA. The CO2 and H2O contents of experimental doubly polished (50-110 μm), bubble-free portions of the glass chips were determined using a Thermo Nicolet Fourier Transform Infrared Spectrometer. Spectra were recorded with a resolution of 4 cm-1, 512 scans, from 650 to 4000 cm-1, under a nitrogen purge to eliminate atmospheric gases. Dissolved volatile concentrations were quantified using the Beer-Lambert law and linear molar absorption coefficients from previous studies [1, 2]. Total dissolved carbon dioxide of experimental glasses was determined from the intensity of the ν3 antisymmetric stretch bands of CO32- at 1430 cm-1 and CO2mol at 2348 cm-1. Dissolved water content of experimental glasses was determined from the intensity of O-H stretching at 3520 cm-1. Estimated total CO2 concentrations at 3 GPa are in the range of 1-2 wt%, for melts with H2O contents between 1.5 and 2.5 wt%. Compared to previous work on CO2 solubility in complex rhyolitic melts at lower pressures [3-5], there is a general trend of increasing CO2 solubility with pressure. Dissolved CO2 is present both as molecular CO2 and as CO32-, consistent with previous, simple system studies at high pressures [e.g. 2, 6]. The CO2mol/CO2Tot values are within the range of previous high pressure studies [e.g. 7] and range from 0.35 to 0.55. Experiments at variable P, T, and melt water content are underway. [1] Fine and Stolper (1985), CMP, 91, 105-121; [2] Stolper et al. (1987), AM, 72, 1071-1085; [3] Blank et al. (1993), EPSL, 119, 27-36; [4] Fogel and Rutherford (1990), AM, 75, 1331-1326; [5] Tamic et al. (2001), CG, 174, 333-347; [6] Mysen and Virgo (1980), AM, 65, 855-899; [7] Mysen (1976), AJS, 276, 969-996.

Agglomeration behaviour of titanium dioxide nanoparticles in river waters: A multi-method approach combining light scattering and field-flow fractionation techniques.

PubMed

Chekli, L; Roy, M; Tijing, L D; Donner, E; Lombi, E; Shon, H K

2015-08-15

Titanium dioxide nanoparticles (TiO2 NPs) are currently one of the most prolifically used nanomaterials, resulting in an increasing likelihood of release to the environment. This is of concern as the potential toxicity of TiO2 NPs has been investigated in several recent studies. Research into their fate and behaviour once entering the environment is urgently needed to support risk assessment and policy development. In this study, we used a multi-method approach combining light scattering and field-flow fractionation techniques to assess both the aggregation behaviour and aggregate structure of TiO2 NPs in different river waters. Results showed that both the aggregate size and surface-adsorbed dissolved organic matter (DOM) were strongly related to the initial DOM concentration of the tested waters (i.e. R(2) > 0.90) suggesting that aggregation of TiO2 NPs is controlled by the presence and concentration of DOM. The conformation of the formed aggregates was also found to be strongly related to the surface-adsorbed DOM (i.e. R(2) > 0.95) with increasing surface-adsorbed DOM leading to more compact structures. Finally, the concentration of TiO2 NPs remaining in the supernatant after sedimentation of the larger aggregates was found to decrease proportionally with both increasing IS and decreasing DOM concentration, resulting in more than 95% sedimentation in the highest IS sample. Copyright © 2015 Elsevier Ltd. All rights reserved.

Hydroxylamine diffusion can enhance N₂O emissions in nitrifying biofilms: a modeling study.

PubMed

Sabba, Fabrizio; Picioreanu, Cristian; Pérez, Julio; Nerenberg, Robert

2015-02-03

Wastewater treatment plants can be significant sources of nitrous oxide (N2O), a potent greenhouse gas. However, little is known about N2O emissions from biofilm processes. We adapted an existing suspended-growth mathematical model to explore N2O emissions from nitrifying biofilms. The model included N2O formation by ammonia-oxidizing bacteria (AOB) via the hydroxylamine and the nitrifier denitrification pathways. Our model suggested that N2O emissions from nitrifying biofilms could be significantly greater than from suspended growth systems under similar conditions. The main cause was the formation and diffusion of hydroxylamine, an AOB nitrification intermediate, from the aerobic to the anoxic regions of the biofilm. In the anoxic regions, hydroxylamine oxidation by AOB provided reducing equivalents used solely for nitrite reduction to N2O, since there was no competition with oxygen. For a continuous system, very high and very low dissolved oxygen (DO) concentrations resulted in lower emissions, while intermediate values led to higher emissions. Higher bulk ammonia concentrations and greater biofilm thicknesses increased emissions. The model effectively predicted N2O emissions from an actual pilot-scale granular sludge reactor for sidestream nitritation, but significantly underestimated the emissions when the NH2OH diffusion coefficient was assumed to be minimal. This numerical study suggests an unexpected and important role of hydroxylamine in N2O emission in biofilms.

Sensing Characteristics of Flame-Spray-Made Pt/ZnO Thick Films as H2 Gas Sensor

PubMed Central

Tamaekong, Nittaya; Liewhiran, Chaikarn; Wisitsoraat, Anurat; Phanichphant, Sukon

2009-01-01

Hydrogen sensing of thick films of nanoparticles of pristine, 0.2, 1.0 and 2.0 atomic percentage of Pt concentration doped ZnO were investigated. ZnO nanoparticles doped with 0.2–2.0 at.% Pt were successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate as precursors dissolved in xylene. The particle properties were analyzed by XRD, BET, SEM and TEM. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spheroidal and hexagonal particles were found to be ranging from 5 to 20 nm while ZnO nanorods were seen to be 5–20 nm wide and 20–40 nm long. ZnO nanoparticles paste composed of ethyl cellulose and terpineol as binder and solvent respectively was coated on Al2O3 substrate interdigitated with gold electrodes to form thin films by spin coating technique. The thin film morphology was analyzed by SEM technique. The gas sensing properties toward hydrogen (H2) was found that the 0.2 at.% Pt/ZnO sensing film showed an optimum H2 sensitivity of ∼164 at hydrogen concentration in air of 1 volume% at 300 °C and a low hydrogen detection limit of 50 ppm at 300 °C operating temperature. PMID:22399971

DISSOLUTION OF PLUTONIUM METAL IN 8-10 M NITRIC ACID

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudisill, T. S.; Pierce, R. A.

2012-07-02

The H-Canyon facility will be used to dissolve Pu metal for subsequent purification and conversion to plutonium dioxide (PuO{sub 2}) using Phase II of HB-Line. To support the new mission, the development of a Pu metal dissolution flowsheet which utilizes concentrated (8-10 M) nitric acid (HNO{sub 3}) solutions containing potassium fluoride (KF) is required. Dissolution of Pu metal in concentrated HNO{sub 3} is desired to eliminate the need to adjust the solution acidity prior to purification by anion exchange. The preferred flowsheet would use 8-10 M HNO{sub 3}, 0.015-0.07 M KF, and 0.5-1.0 g/L Gd to dissolve the Pu upmore » to 6.75 g/L. An alternate flowsheet would use 8-10 M HNO{sub 3}, 0.05-0.2 M KF, and 1-2 g/L B to dissolve the Pu. The targeted average Pu metal dissolution rate is 20 mg/min-cm{sup 2}, which is sufficient to dissolve a “standard” 2250-g Pu metal button in 24 h. Plutonium metal dissolution rate measurements showed that if Gd is used as the nuclear poison, the optimum dissolution conditions occur in 10 M HNO{sub 3}, 0.04-0.05 M KF, and 0.5-1.0 g/L Gd at 112 to 116 °C (boiling). These conditions will result in an estimated Pu metal dissolution rate of ~11-15 mg/min-cm{sup 2} and will result in dissolution times of 36-48 h for standard buttons. The recommended minimum and maximum KF concentrations are 0.03 M and 0.07 M, respectively. The data also indicate that lower KF concentrations would yield dissolution rates for B comparable to those observed with Gd at the same HNO{sub 3} concentration and dissolution temperature. To confirm that the optimal conditions identified by the dissolution rate measurements can be used to dissolve Pu metal up to 6.75 g/L in the presence of representative concentrations of Fe and Gd or B, a series of experiments was performed to demonstrate the flowsheets. In three of the five experiments, the offgas generation rate during the dissolution was measured and samples were analyzed for hydrogen gas (H{sub 2}). The use of 10 M HNO{sub 3} containing 0.03-0.05 M KF, 0.5-1.0 g/L Gd, and 1.9 g/L Fe resulted in complete dissolution of the metal in 2.0-3.5 h. When B was used as the neutron poison, 10 M HNO{sub 3} solutions containing 0.05-0.1 M KF, 1.9 g/L Fe, and 1 g/L B resulted in complete dissolution of the metal in 0.75-2.0 h. Dissolution rates estimated using data from the flowsheet demonstrations agreed reasonably well with the measured rates; although, a discrepancy was observed in the Gd system. The presence of 1 g/L Gd or B in the dissolving solution had about the same effect on the dissolution rate. The predominant Pu valence in the dissolving solution was Pu(IV). The concentration of Pu(VI) was evaluated by UV-visible spectroscopy and was estimated to be significantly less than 1 wt %. The offgas generation rates and H{sub 2} concentrations measured in the offgas from experiments performed using 10 M HNO{sub 3} containing 0.05 M KF, 1.9 g/L Fe and either 1 g/L Gd or B were approximately the same. These data support the conclusion that the presence of either 1 g/L Gd or B had the same general effect on the dissolution rate. The calculated offgas generation during the dissolutions was 0.6 mol offgas/mol of Pu. The H{sub 2} concentration measured in the offgas from the dissolution using Gd as the neutron poison was approximately 0.5 vol %. In the B system, the H{sub 2} ranged from nominally 0.8 to 1 vol % which is about the same as measured in the Gd system within the uncertainty of the analysis. The offgas generation rate for the dissolution performed using 10 M HNO{sub 3} containing 0.03 M KF, 0.5 g/L Gd, and 1.9 g/L Fe was approximately a factor of two less than produced in the other dissolutions; however, the concentration of H{sub 2} measured in the offgas was higher. The adjusted concentration ranged from 2.7 to 8.8 vol % as the dissolution proceeded. Higher concentrations of H{sub 2} occur when the Pu dissolution proceeds by a metal/acid reaction rather than nitrate oxidation. The higher H{sub 2} concentration could be attributed to the reduced activity of the fluoride due to complexation with Pu as the dissolution progressed. Dissolution of Pu metal at 20 °C in 10 M HNO{sub 3} containing 0.05 M KF showed that the Pu metal dissolves slowly without any visible gas generation. As the Pu metal dissolves, it forms a more-dense Pu-bearing solution which sank to the bottom of the dissolution vessel. The dissolved Pu did not form a boundary layer around the sample and failed to distribute homogeneously due to minimal (thermally-induced) mixing. This indicates that in the H-Canyon dissolver insert, the Pu will diffuse out of the insert into the bulk dissolver solution where it will disperse. At 35 °C, the Pu metal dissolved without visible gas generation. However, due to thermal currents caused by maintaining the solution at 35 °C, the dissolved Pu distributed evenly throughout the dissolver solution. It did not form a boundary layer around the sample.« less

Capture and release of cancer cells using electrospun etchable MnO2 nanofibers integrated in microchannels

NASA Astrophysics Data System (ADS)

Liu, Hui-qin; Yu, Xiao-lei; Cai, Bo; You, Su-jian; He, Zhao-bo; Huang, Qin-qin; Rao, Lang; Li, Sha-sha; Liu, Chang; Sun, Wei-wei; Liu, Wei; Guo, Shi-shang; Zhao, Xing-zhong

2015-03-01

This paper introduces a cancer cell capture/release microchip based on the self-sacrificed MnO2 nanofibers. Through electrospinning, lift-off and soft-lithography procedures, MnO2 nanofibers are tactfully fabricated in microchannels to implement enrichment and release of cancer cells in liquid samples. The MnO2 nanofiber net which mimics the extra cellular matrix can lead to high capture ability with the help of a cancer cell-specific antibody bio-conjugation. Subsequently, an effective and friendly release method is carried out by using low concentration of oxalic acid to dissolve the MnO2 nanofiber substrate while keeping high viability of those released cancer cells at the same time. It is conceivable that our microchip may have potentials in realizing biomedical analysis of circulating tumor cells for biological and clinical researches in oncology.

The role of iron and reactive oxygen species in the production of CO2 in arctic soil waters

NASA Astrophysics Data System (ADS)

Trusiak, Adrianna; Treibergs, Lija A.; Kling, George W.; Cory, Rose M.

2018-03-01

Hydroxyl radical (radOH) is a highly reactive oxidant of dissolved organic carbon (DOC) in the environment. radOH production in the dark was observed through iron and DOC mediated Fenton reactions in natural environments. Specifically, when dissolved oxygen (O2) was added to low oxygen and anoxic soil waters in arctic Alaska, radOH was produced in proportion to the concentrations of reduced iron (Fe(II)) and DOC. Here we demonstrate that Fe(II) was the main electron donor to O2 to produce radOH. In addition to quantifying radOH production, hydrogen peroxide (H2O2) was detected in soil waters as a likely intermediate in radOH production from oxidation of Fe(II). For the first time in natural systems we detected carbon dioxide (CO2) production from radOH oxidation of DOC. More than half of the arctic soil waters tested showed production of CO2 under conditions conducive for production of radOH. Findings from this study strongly suggest that DOC is the main sink for radOH, and that radOH can oxidize DOC to yield CO2. Thus, this iron-mediated, dark chemical oxidation of DOC may be an important component of the arctic carbon cycle.

Mechanisms of N2O production in biological wastewater treatment under nitrifying and denitrifying conditions.

PubMed

Wunderlin, Pascal; Mohn, Joachim; Joss, Adriano; Emmenegger, Lukas; Siegrist, Hansruedi

2012-03-15

Nitrous oxide (N2O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N2O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions. Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N2O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N2O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N2O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N2O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N2O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO2/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment. Under anoxic conditions, nitrate reducing experiments confirmed that N2O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N2O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations. Copyright © 2011 Elsevier Ltd. All rights reserved.

Sulfur geochemistry of hydrothermal waters in Yellowstone National Park, Wyoming, USA. II. Formation and decomposition of thiosulfate and polythionate in Cinder Pool

USGS Publications Warehouse

Xu, Y.; Schoonen, M.A.A.; Nordstrom, D. Kirk; Cunningham, K.M.; Ball, J.W.

2000-01-01

Cinder Pool is an acid-sulfate-chloride boiling spring in Norris Geyser Basin, Yellowstone National Park. The pool is unique in that its surface is partially covered with mm-size, black, hollow sulfur spherules, while a layer of molten sulfur resides at the bottom of the pool (18 m depth). The sulfur speciation in the pool was determined on four different days over a period of two years. Samples were taken to evaluate changes with depth and to evaluate the importance of the sulfur spherules on sulfur redox chemistry. All analyses were conducted on site using a combination of ion chromatography and colorimetric techniques. Dissolved sulfide (H2S), thiosulfate (S2O32−), polythionates (SxO62−), and sulfate were detected. The polythionate concentration was highly variable in time and space. The highest concentrations were found in surficial samples taken from among the sulfur spherules. With depth, the polythionate concentrations dropped off. The maximum observed polythionate concentration was 8 μM. Thiosulfate was rather uniformly distributed throughout the pool and concentrations ranged from 35 to 45 μM. Total dissolved sulfide concentrations varied with time, concentrations ranged from 16 to 48 μM. Sulfate was relatively constant, with concentrations ranging from 1150 to 1300 μM. The sulfur speciation of Cinder Pool is unique in that the thiosulfate and polythionate concentrations are significantly higher than for any other acid-sulfate spring yet sampled in Yellowstone National Park. Complementary laboratory experiments show that thiosulfate is the intermediate sulfoxyanion formed from sulfur hydrolysis under conditions similar to those found in Cinder Pool and that polythionates are formed via the oxidation of thiosulfate by dissolved oxygen. This last reaction is catalyzed by pyrite that occurs as a minor constituent in the sulfur spherules floating on the pool's surface. Polythionate decomposition proceeds via two pathways: (1) a reaction with H2S, yielding thiosulfate and elemental sulfur; and (2) by disproportionation to sulfate and thiosulfate. This study demonstrates that the presence of a subaqueous molten sulfur pool and sulfur spherules in Cinder Pool is of importance in controlling the pathways of aqueous sulfur redox reactions. Some of the insights gained at Cinder Pool may be relevant to acid crater lakes where sulfur spherules are observed and variations in polythionate concentrations are used to monitor and predict volcanic activity.

Testing and Validation Studies of the NSMII-Benthic Sediment Diagenesis Module

DTIC Science & Technology

2016-07-01

NSMII analytical vs. numerical solutions of sediment methane ............................ 27 3.2.4 Comparisons of the diagenesis rates of three sediment...26 Figure 12. Comparisons of NSMII analytical vs. numerical solutions of sediment methane : (a) layer 2’s CH4, (b...oxygen demand mg-O2 L-1 0-10 CH4 Methane mg-O2 L-1 On/Off HxS Total dissolved sulfides mg-O2 L-1 On/Off DO Dissolved oxygen mg-O2 L-1 On BSi

Structurally integrated organic light emitting device-based sensors for gas phase and dissolved oxygen.

PubMed

Shinar, Ruth; Zhou, Zhaoqun; Choudhury, Bhaskar; Shinar, Joseph

2006-05-24

A compact photoluminescence (PL)-based O2 sensor utilizing an organic light emitting device (OLED) as the light source is described. The sensor device is structurally integrated. That is, the sensing element and the light source, both typically thin films that are fabricated on separate glass substrates, are attached back-to-back. The sensing elements are based on the oxygen-sensitive dyes Pt- or Pd-octaethylporphyrin (PtOEP or PdOEP, respectively), which are embedded in a polystyrene (PS) matrix, or dissolved in solution. Their performance is compared to that of a sensing element based on tris(4,7-diphenyl-l,10-phenanthroline) Ru II (Ru(dpp)) embedded in a sol-gel film. A green OLED light source, based on tris(8-hydroxy quinoline Al (Alq3), was used to excite the porphyrin dyes; a blue OLED, based on 4,4'-bis(2,2'-diphenylviny1)-1,1'-biphenyl, was used to excite the Ru(dpp)-based sensing element. The O2 level was monitored in the gas phase and in water, ethanol, and toluene solutions by measuring changes in the PL lifetime tau of the O2-sensitive dyes. The sensor performance was evaluated in terms of the detection sensitivity, dynamic range, gas flow rate, and temperature effect, including the temperature dependence of tau in pure Ar and O2 atmospheres. The dependence of the sensitivity on the preparation procedure of the sensing film and on the PS and dye concentrations in the sensing element, whether a solid matrix or solution, were also evaluated. Typical values of the detection sensitivity in the gas phase, S(g) identical with tau(0% O2)/tau(100% O2), at 23 degrees C, were approximately 35 to approximately 50 for the [Alq3 OLED[/[PtOEP dye] pair; S(g) exceeded 200 for the Alq3/PdOEP sensor. For dissolved oxygen (DO) in water and ethanol, S(DO) (defined as the ratio of tau in de-oxygenated and oxygen-saturated solutions) was approximately 9.5 and approximately 11, respectively, using the PtOEP-based film sensor. The oxygen level in toluene was measured with PtOEP dissolved directly in the solution. That sensor exhibited a high sensitivity, but a limited dynamic range. Effects of aggregation of dye molecules, sensing film porosity, and the use of the OLED-based sensor arrays for O2 and multianalyte detection are also discussed.

Nitritating-anammox biomass tolerant to high dissolved oxygen concentration and C/N ratio in treatment of yeast factory wastewater.

PubMed

Zekker, Ivar; Rikmann, Ergo; Tenno, Toomas; Seiman, Andrus; Loorits, Liis; Kroon, Kristel; Tomingas, Martin; Vabamäe, Priit; Tenno, Taavo

2014-01-01

Maintaining stability of low concentration (< 1 g L(-1)) floccular biomass in the nitritation-anaerobic ammonium oxidation (anammox) process in the sequencing batch reactor (SBR) system for the treatment of high COD (> 15,000 mg O2 L(-1)) to N (1680 mg N L(-1)) ratio real wastewater streams coming from the food industry is challenging. The anammox process was suitable for the treatment of yeast factory wastewater containing relatively high and abruptly increased organic C/N ratio and dissolved oxygen (DO) concentrations. Maximum specific total inorganic nitrogen (TIN) loading and removal rates applied were 600 and 280 mg N g(-1) VSS d(-1), respectively. Average TIN removal efficiency over the operation period of 270 days was 70%. Prior to simultaneous reduction of high organics (total organic carbon > 600mg L(-1)) and N concentrations > 400 mg L(-1), hydraulic retention time of 15 h and DO concentrations of 3.18 (+/- 1.73) mg O2 L(-1) were applied. Surprisingly, higher DO concentrations did not inhibit the anammox process efficiency demonstrating a wider application of cultivated anammox biomass. The SBR was fed rapidly over 5% of the cycle time at 50% volumetric exchange ratio. It maintained high free ammonia concentration, suppressing growth of nitrite-oxidizing bacteria. Partial least squares and response surface modelling revealed two periods of SBR operation and the SBR performances change at different periods with different total nitrogen (TN) loadings. Anammox activity tests showed yeast factory-specific organic N compound-betaine and inorganic N simultaneous biodegradation. Among other microorganisms determined by pyrosequencing, anammox microorganism (uncultured Planctomycetales bacterium clone P4) was determined by polymerase chain reaction also after applying high TN loading rates.

Spatial and temporal distribution of singlet oxygen in Lake Superior.

PubMed

Peterson, Britt M; McNally, Ann M; Cory, Rose M; Thoemke, John D; Cotner, James B; McNeill, Kristopher

2012-07-03

A multiyear field study was undertaken on Lake Superior to investigate singlet oxygen ((1)O(2)) photoproduction. Specifically, trends within the lake were examined, along with an assessment of whether correlations existed between chromophoric dissolved organic matter (CDOM) characteristics and (1)O(2) production rates and quantum yields. Quantum yield values were determined and used to estimate noontime surface (1)O(2) steady-state concentrations ([(1)O(2)](ss)). Samples were subdivided into three categories based on their absorbance properties (a300): riverine, river-impacted, or open lake sites. Using calculated surface [(1)O(2)](ss), photochemical half-lives under continuous summer sunlight were calculated for cimetidine, a pharmaceutical whose reaction with (1)O(2) has been established, to be on the order of hours, days, and a week for the riverine, river-impacted, and open lake waters, respectively. Of the CDOM properties investigated, it was found that dissolved organic carbon (DOC) and a300 were the best parameters for predicting production rates of [(1)O(2)](ss). For example, given the correlations found, one could predict [(1)O(2)](ss) within a factor of 4 using a300 alone. Changes in the quantum efficiency of (1)O(2) production upon dilution of river water samples with lake water samples demonstrated that the CDOM found in the open lake is not simply diluted riverine organic matter. The open lake pool was characterized by low absorption coefficient, low fluorescence, and low DOC, but more highly efficient (1)O(2) production and predominates the Lake Superior system spatially. This study establishes that parameters that reflect the quantity of CDOM (e.g., a300 and DOC) correlate with (1)O(2) production rates, while parameters that characterize the absorbance spectrum (e.g., spectral slope coefficient and E2:E3) correlate with (1)O(2) production quantum yields.

Coupled oxygen-carbon dioxide modelling to partition potential external contribution to stream carbon dioxide concentrations.

NASA Astrophysics Data System (ADS)

Butman, D. E.; Holtgrieve, G. W.

2017-12-01

Recent modelling studies in large catchments have estimated that in excess of 74% of the dissolved carbon dioxide found in first and second order streams originate from allochthonous sources. Stable isotopes of carbon-13 in carbon dioxide have been used to identify ground water seeps in stream systems, where decreases in δ13CO2 occur along gaining stream reaches, suggesting that carbon dioxide in ground water is more depleted than what is found in surface water due to fractionation of CO2 during emissions across the air water interface. Although isotopes represent a chemical tracer in stream systems for potential groundwater contribution, the temporal resolution of discrete samples make partitioning allochthonous versus autochthonous sources of CO2 difficult on hydrologically relevant time scales. Here we show results of field deployments of high frequent dissolved CO2, O2, PAR, Temperature and pH from the Thornton Creek Watershed, the largest urban watershed in Seattle, WA. We present an exploration into using high resolution time series of dissolved oxygen and carbon dioxide in a dual gas approach to separate the contribution of in stream respiration from external sources. We extend upon previous efforts to model stream metabolism across diel cycles by incorporating simultaneous direct measurements of dissolved oxygen, PCO2, and pH within an inverse modeling framework and Bayesian parameter estimation. With an initial assumption of a stoichiometric ratio of 1:1 for O2 and CO2 for autochthonous driven metabolism, we investigate positive or negative departures from this ratio as an indicator of external CO2 to the stream (terrestrial or atmospheric) and factors contributing to this flux.

Exceptional selectivity for dissolved silicas in industrial waters using mixed oxides

DOE PAGES

Sasan, Koroush; Brady, Patrick V.; Krumhansl, James L.; ...

2017-11-07

The removal of silica, ubiquitous in produced and industrial waters, by novel mixed oxides is investigated in this present study. We have combined the advantage of high selectivity hydrotalcite (HTC, (Mg 6Al 2(OH) 16(CO 3)·4H 2O)), with large surface area of active alumina (AA, (Al 2O 3)) for effective removing of the dissolved silica from cooling tower water. The batch test results indicated the combined HTC/AA is a more effective method for removing silica from CTW than using each of HTC or AA separately. The silica uptake was confirmed by Fourier transform infrared (FTIR), and Energy dispersive spectroscopy (EDS). Ourmore » results indicate HTC/AA effectively removes silica from cooling tower water (CTW), even in the presence of large concentrations of competing anions, such as Cl -, NO 3 - HCO 3 -, CO 3 2- and SO 4 2-. The Single Path Flow Through (SPFT) tests confirmed to rapid uptake of silica by combined HTC/AA during column filtration. The experimental data of silica adsorption fit best to Freundlich isotherm model.« less

Exceptional selectivity for dissolved silicas in industrial waters using mixed oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sasan, Koroush; Brady, Patrick V.; Krumhansl, James L.

The removal of silica, ubiquitous in produced and industrial waters, by novel mixed oxides is investigated in this present study. We have combined the advantage of high selectivity hydrotalcite (HTC, (Mg 6Al 2(OH) 16(CO 3)·4H 2O)), with large surface area of active alumina (AA, (Al 2O 3)) for effective removing of the dissolved silica from cooling tower water. The batch test results indicated the combined HTC/AA is a more effective method for removing silica from CTW than using each of HTC or AA separately. The silica uptake was confirmed by Fourier transform infrared (FTIR), and Energy dispersive spectroscopy (EDS). Ourmore » results indicate HTC/AA effectively removes silica from cooling tower water (CTW), even in the presence of large concentrations of competing anions, such as Cl -, NO 3 - HCO 3 -, CO 3 2- and SO 4 2-. The Single Path Flow Through (SPFT) tests confirmed to rapid uptake of silica by combined HTC/AA during column filtration. The experimental data of silica adsorption fit best to Freundlich isotherm model.« less

Aqueous Mesocosm Techniques Enabling the Real-Time Measurement of the Chemical and Isotopic Kinetics of Dissolved Methane and Carbon Dioxide.

PubMed

Chan, Eric W; Kessler, John D; Shiller, Alan M; Joung, DongJoo; Colombo, Frank

2016-03-15

Previous studies of microbially mediated methane oxidation in oceanic environments have examined the many different factors that control the rates of oxidation. However, there is debate on what factor(s) are limiting in these types of environments. These factors include the availability of methane, O2, trace metals, nutrients, the density of cell population, and the influence that CO2 production may have on pH. To look at this process in its entirety, we developed an automated mesocosm incubation system with a Dissolved Gas Analysis System (DGAS) coupled to a myriad of analytical tools to monitor chemical changes during methane oxidation. Here, we present new high temporal resolution techniques for investigating dissolved methane and carbon dioxide concentrations and stable isotopic dynamics during aqueous mesocosm and pure culture incubations. These techniques enable us to analyze the gases dissolved in solution and are nondestructive to both the liquid media and the analyzed gases enabling the investigation of a mesocosm or pure culture experiment in a completely closed system, if so desired.

Impacts of Nitrate Input on Nitrous Oxide Production in Lake Sediments

NASA Astrophysics Data System (ADS)

Ruder, C. K.; Schade, J. D.

2016-12-01

Denitrification in lake sediments removes nitrogen from the ecosystem and produces the greenhouse gas nitrous oxide (N2O) as a byproduct. However, little is understood about the rates and controls of N2O production in lake sediments. Agricultural activity in lake catchments often results in the runoff of nitrogen fertilizers, leading to increased N inputs in the form of nitrate (NO3-). This study evaluates the influence of nitrate input on N2O concentrations in a series of lakes across a range of agricultural land use intensities. We measured N2O concentrations in lakes across seasons, and also used lake sediment samples to perform anaerobic incubations with NO3- additions, with and without the addition of acetylene (blocking conversion of N2O to N2), to assess denitrification potentials and the rate of N2O production in sediments. Our results suggest that N2O concentrations are strongly impacted by the availability of NO3- across all agricultural land use intensities, with incubation NO3- additions leading to a marked increase in N2O production. However, sediments reacted differently by site in incubations without experimental additions of NO3- or acetylene, with half of the study lakes experiencing net N2O production and half exhibiting net N2O consumption over the course of the 24-hour incubation period. These results suggest the potential influence of sediment organic matter as a control on N2O concentrations. The positive influence of NO3- on N2O production is supported by observational data at each of the study sites, though water column total nitrogen (TN) appears to be a better indicator of dissolved N2O concentrations than aqueous NO3-, perhaps due to variations in internal N recycling. This study concludes that agricultural runoff of NO3- has the potential to enhance sediment N2O production; however, further investigation into the effects of sediment organic matter on N2O production, analysis of N2O vertical diffusion efficiency to link production rates in the sediment to actual surface emissions, and microbial community comparisons between study sites are necessary to adequately model the impact of agricultural land use on emissions of N2O from lakes.

Comparing the behaviour of two ocean surface models in simulating dissolved O 2 concentration at O.W.S.P.

NASA Astrophysics Data System (ADS)

Thomas, F.; Minster, J. F.; Gaspar, P.; Gregoris, Y.

1993-02-01

We compare the simulation of the O 2 concentration in the mixed layer at Sta. P using two different mixed layer models with the same biological production-consumption function. One is the integral mixed layer model already used by THOMASet al. (Deep-Sea Research, 37, 463-491, 1990). The other is the eddy kinetic energy (EKE) model of GASPARet al. (Journal of Geophysical Research, 95, 16179-16194, 1990). The latter simulates better both the seasonal and the short time evolution of the oxygen concentration. The submixed layer summer supersaturation is also closer to observations, by about 25%, though a factor of 2 too high: this could be improved by adjustment of the production function. The net annual gas exchange flux with the atmosphere is always a degassing of the order of 10% of the total biological production. In general, the model values are smaller (within a factor of 3 for the EKE model) than the data. However, the latter may not be robust as 96 measurements per year are necessary to estimate this flux within a factor of 10.

UV-vis spectroscopy study of plasma-activated water: Dependence of the chemical composition on plasma exposure time and treatment distance

NASA Astrophysics Data System (ADS)

Oh, Jun-Seok; Szili, Endre J.; Ogawa, Kotaro; Short, Robert D.; Ito, Masafumi; Furuta, Hiroshi; Hatta, Akimitsu

2018-01-01

Plasma-activated water (PAW) is receiving much attention in biomedical applications because of its reported potent bactericidal properties. Reactive oxygen and nitrogen species (RONS) that are generated in water upon plasma exposure are thought to be the key components in PAW that destroy bacterial and cancer cells. In addition to developing applications for PAW, it is also necessary to better understand the RONS chemistry in PAW in order to tailor PAW to achieve a specific biological response. With this in mind, we previously developed a UV-vis spectroscopy method using an automated curve fitting routine to quantify the changes in H2O2, NO2 -, NO3 - (the major long-lived RONS in PAW), and O2 concentrations. A major advantage of UV-vis is that it can take multiple measurements during plasma activation. We used the UV-vis procedure to accurately quantify the changes in the concentrations of these RONS and O2 in PAW. However, we have not yet provided an in-depth commentary of how we perform the curve fitting procedure or its implications. Therefore, in this study, we provide greater detail of how we use the curve fitting routine to derive the RONS and O2 concentrations in PAW. PAW was generated by treatment with a helium plasma jet. In addition, we employ UV-vis to study how the plasma jet exposure time and treatment distance affect the RONS chemistry and amount of O2 dissolved in PAW. We show that the plasma jet exposure time principally affects the total RONS concentration, but not the relative ratios of RONS, whereas the treatment distance affects both the total RONS concentration and the relative RONS concentrations.

Investigating the Geochemical Model for Molybdenum Mineralization in the JEB Tailings Management Facility at McClean Lake, Saskatchewan: An X-ray Absorption Spectroscopy Study.

PubMed

Blanchard, Peter E R; Hayes, John R; Grosvenor, Andrew P; Rowson, John; Hughes, Kebbi; Brown, Caitlin

2015-06-02

The geochemical model for Mo mineralization in the JEB Tailings Management Facility (JEB TMF), operated by AREVA Resources Canada at McClean Lake, Saskatchewan, was investigated using X-ray Absorption Near-Edge Spectroscopy (XANES), an elemental-specific technique that is sensitive to low elemental concentrations. Twenty five samples collected during the 2013 sampling campaign from various locations and depths in the TMF were analyzed by XANES. Mo K-edge XANES analysis indicated that the tailings consisted primarily of Mo(6+) species: powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3·8H2O), and molybdate adsorbed on ferrihydrite (Fe(OH)3 - MoO4). A minor concentration of a Mo(4+) species in the form of molybdenite (MoS2) was also present. Changes in the Mo mineralization over time were inferred by comparing the relative amounts of the Mo species in the tailings to the independently measured aqueous Mo pore water concentration. It was found that ferrimolybdite and molybdate adsorbed on ferrihydrite initially dissolves in the TMF and precipitates as powellite.

Naphthenic acids removal from high TDS produced water by persulfate mediated iron oxide functionalized catalytic membrane, and by nanofiltration.

PubMed

Aher, Ashish; Papp, Joseph; Colburn, Andrew; Wan, Hongyi; Hatakeyama, Evan; Prakash, Prakhar; Weaver, Ben; Bhattacharyya, Dibakar

2017-11-01

Oil industries generate large amounts of produced water containing organic contaminants, such as naphthenic acids (NA) and very high concentrations of inorganic salts. Recovery of potable water from produced water can be highly energy intensive is some cases due to its high salt concentration, and safe discharge is more suitable. Here, we explored catalytic properties of iron oxide (Fe x O y nanoparticles) functionalized membranes in oxidizing NA from water containing high concentrations of total dissolved solids (TDS) using persulfate as an oxidizing agent. Catalytic decomposition of persulfate by Fe x O y functionalized membranes followed pseudo-first order kinetics with an apparent activation energy of 18 Kcal/mol. Fe x O y functionalized membranes were capable of lowering the NA concentrations to less than discharge limits of 10 ppm at 40 °C. Oxidation state of iron during reaction was quantified. Membrane performance was investigated for extended period of time. A coupled process of advanced oxidation catalyzed by membrane and nanofiltration was also evaluated. Commercially available nanofiltration membranes were found capable of retaining NA from water containing high concentrations of dissolved salts. Commercial NF membranes, Dow NF270 (Dow), and NF8 (Nanostone) had NA rejection of 79% and 82%, respectively. Retentate for the nanofiltration was further treated with advanced oxidation catalyzed by Fe x O y functionalized membrane for removal of NA.

Titania/CnTAB Nanoskeleton as adsorbent and photocatalyst for removal of alkylphenols dissolved in water.

PubMed

Sakai, Toshio; Da Loves, Albar; Okada, Tomohiko; Mishima, Shozi

2013-03-15

We report here on the removal of alkylphenols (phenol, 4-n-propylphenol, 4-n-heptylphenol and 4-nonylphenol) dissolved in water using the composite particles of nanocrystalline titania and alkyltrimethylammonium bromide (CnH2n+1N(CH3)3Br, CnTAB; n=12, 14, 16 and 18) (named as TiO2/CnTAB Nanoskeleton) as adsorbents and photocatalysts. In particular, the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton in water was investigated in terms of hydrophobic interaction between alkylphenols and CnTAB, surface area, pore structure and crystal size of TiO2/CnTAB Nanoskeleton. We revealed that CnTAB incorporated in the TiO2/CnTAB Nanoskeleton promotes the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton due to the hydrophobic interaction between alkylphenols and CnTAB. On the other hand, the surface area, pore structure and crystal size of TiO2/CnTAB Nanoskeleton did not affect the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton. We also found that the alkylphenols dissolved in water were completely removed by the combination of adsorption and photocatalytic degradation by the TiO2/CnTAB Nanoskeleton under UV irradiation. These results prove that the TiO2/CnTAB Nanoskeleton acts as in tandem an adsorbent and a photocatalyst for removal of alkylphenols dissolved in water. Copyright © 2013 Elsevier B.V. All rights reserved.

Long Term Stability in Thin Film Ferroelectric Memories

DTIC Science & Technology

1992-09-29

concentration is adjusted to IM. IM PT stock solution is prepared from Pb acetate and Ti isopropoxide dissolved in 2-MOE, and is added to the PMN stock...is necessary to understand that defect chemistry in detail. While PbTi0 3, PbZrO3 , and their solid- solutions , PZT, have not been thoroughly studied...methoxyethanol (2-MOE) is added. The ethanol and excess 2-MOE are removed by distillation. Pb precursor solution (Pb acetate in 2-MOE) is added and the 13

Mobility of nutrients and trace metals during weathering in the late Archean

NASA Astrophysics Data System (ADS)

Hao, Jihua; Sverjensky, Dimitri A.; Hazen, Robert M.

2017-08-01

The evolution of the geosphere and biosphere depends on the availability of bio-essential nutrients and trace metals. Consequently, the chemical and isotopic variability of trace elements in the sedimentary record have been widely used to infer the existence of early life and fluctuations in the near-surface environment on the early Earth, particularly fluctuations in the redox state of the atmosphere. In this study, we applied late Archean weathering models (Hao et al., 2017), developed to estimate the behavior of major elements and the composition of late Archean world average river water, to explore the behavior of nutrient and trace metals and their potential for riverine transport. We focused on P, Mn, Cr, and Cu during the weathering of olivine basalt. In our standard late Archean weathering model (pCO2,g = 10-1.5 bars, pH2,g = 10-5.0 bars), crustal apatite was totally dissolved by the acidic rainwater during weathering. Our model quantitatively links the pCO2,g of the atmosphere to phosphate levels transported by rivers. The development of late Archean river water (pH = 6.4) resulted in riverine phosphate of at least 1.7 μmolar, much higher than at the present-day. At the end of the early Proterozoic snowball Earth event when pCO2,g could be 0.01-0.10 bars, river water may have transported up to 70 μmolar phosphate, depending on the availability of apatite, thereby stimulating high levels of oxygenic photosynthesis in the marine environment. Crustal levels of Mn in olivine dissolved completely during weathering, except at large extents of weathering where Mn was stored as a component of a secondary carbonate mineral. The corresponding Mn content of river water, about 1.2 μmolar, is higher than in modern river water. Whiffs of 10-5 mole O2 gas or HNO3 kg-1 H2O resulted in the formation of pyrolusite (MnO2) and abundant hematite and simultaneous dramatic decreases in the concentration of Mn(II) in the river water. Chromite dissolution resulted in negligible dissolved Cr in Archean river water. However, amorphous Cr(OH)3 representing easily-weatherable Cr-bearing minerals dissolved totally during the weathering simulations, resulting in concentrations of Cr(III) in the river water of up to 0.14 μmolar, higher than at the present-day. Late Archean weathering of accessory chalcopyrite produced chalcocite and bornite, and extremely low concentrations of Cu (<10-15 molar) because of the low solubilities of the copper sulfides. However, pulses of either O2,g or HNO3 produced native copper, chalcocite, and bornite, much more hematite, and river water containing levels of dissolved Cu comparable to the present-day. Copper mineralogy predicted by weathering models might provide a new correlation with evidence from studies of copper mineral evolution. Overall, our results implied that the redox state of the atmosphere, the pH of surface waters, and the availability of easily-weatherable minerals are all important factors controlling the dissolution of trace elements in river water. Interpretation of the sedimentary signatures of trace elements should consider not only the redox state but also the pH and availability of accessory minerals.

Temporal variability and annual budget of inorganic dissolved matter in Andean Pacific Rivers located along a climate gradient from northern Ecuador to southern Peru

NASA Astrophysics Data System (ADS)

Moquet, Jean-Sébastien; Guyot, Jean-Loup; Morera, Sergio; Crave, Alain; Rau, Pedro; Vauchel, Philippe; Lagane, Christelle; Sondag, Francis; Lavado, Casimiro Waldo; Pombosa, Rodrigo; Martinez, Jean-Michel

2018-01-01

In Ecuador and Peru, geochemical information from Pacific coastal rivers is limited and scarce. Here, we present an unedited database of major element concentrations from five HYBAM observatory stations monitored monthly between 4 and 10 years, and the discrete sampling of 23 Andean rivers distributed along the climate gradient of the Ecuadorian and Peruvian Pacific coasts. Concentration (C) vs. discharge (Q) relationships of the five monitored basins exhibit a clear dilution behavior for evaporites and/or pyrite solutes, while the solute concentrations delivered by other endmembers are less variable. Spatially, the annual specific fluxes for total dissolved solids (TDS), Ca2+, HCO3-, K+, Mg2+, and SiO2 are controlled on the first order by runoff variability, while Cl-, Na+ and SO42- are controlled by the occurrence of evaporites and/or pyrite. The entire Pacific basin in Ecuador and Peru exported 30 Mt TDS·yr-1, according to a specific flux of ∼70 t·km-2·yr-1. This show that, even under low rainfall conditions, this orogenic context is more active, in terms of solute production, than the global average.

Evaluating the influence of fire history on dissolved pyrogenic C exported from coniferous and deciduous forest soils in northern Great Lakes Region

NASA Astrophysics Data System (ADS)

Santos, F.; Wagner, S.; Rothstein, D.; Miesel, J. R.; Jaffe, R.

2015-12-01

Pyrogenic carbon (PyC) is formed from the thermal decomposition of plant biomass and fossil fuels, and accounts for a significant portion of the dissolved organic matter pool in rivers worldwide. While PyC mobilization and leaching from fire-impacted terrestrial ecosystems are thought to be the primary source of dissolved PyC (DPC) in riverine environments, the influence of recent biomass burning on the fluxes of DPC leached from soils remains poorly quantified. Here we examined differences in DPC leaching fluxes between (1) red pine sites that experienced post-logging slash burning in the late 19th century, and (2) sugar maple sites that show no evidence of burning in the past 200 years. We collected spring snowmelt leachates from zero-tension lysimeters installed underneath O and E soil horizons of Spodosols in both red pine and sugar maple ecosystems. We quantified DPC in leachates by measuring Benzene Polycarboxylic Acids. We also determined DPC in leachates collected from lysimeters installed beneath B horizons in the red pine ecosystem. Average concentrations of DPC leached from O and E horizons in red pine and sugar maple sites were 1.22 ± 0.33 mg L-1 and 0.96 ±0.58 mg L-1, respectively. Although DPC concentrations in either the O or E horizon leachates did not differ between the two ecosystem types, the proportion of DPC in the dissolved organic C pool was 62% higher in red pine than in sugar maple in E horizon leachates. In red pine sites, DPC concentrations were significantly lower in the B horizon leachates than in the upper soil horizons leachates, likely due to DPC immobilization in the mineral subsoil. Our preliminary results showed that a single production of PyC was not the main source of DPC exported from soils, suggesting that DPC mobilized and released from the ecosystems studied here likely integrates PyC produced at a millennial time-scale in the Great Lakes Region.

Annual methane and nitrous oxide emissions from rice paddies and inland fish aquaculture wetlands in southeast China

NASA Astrophysics Data System (ADS)

Wu, Shuang; Hu, Zhiqiang; Hu, Tao; Chen, Jie; Yu, Kai; Zou, Jianwen; Liu, Shuwei

2018-02-01

Inland aquaculture ponds have been documented as important sources of atmospheric methane (CH4) and nitrous oxide (N2O), while their regional or global source strength remains unclear due to lack of direct flux measurements by covering more typical habitat-specific aquaculture environments. In this study, we compared the CH4 and N2O fluxes from rice paddies and nearby inland fish aquaculture wetlands that were converted from rice paddies in southeast China. Both CH4 and N2O fluxes were positively related to water temperature and sediment dissolved organic carbon, but negatively related to water dissolved oxygen concentration. More robust response of N2O fluxes to water mineral N was observed than to sediment mineral N. Annual CH4 and N2O fluxes from inland fish aquaculture averaged 0.51 mg m-2 h-1 and 54.78 μg m-2 h-1, amounting to 42.31 kg CH4 ha-1 and 2.99 kg N2O-N ha-1, respectively. The conversion of rice paddies to conventional fish aquaculture significantly reduced CH4 and N2O emissions by 23% and 66%, respectively. The emission factor for N2O was estimated to be 0.46% of total N input in the feed or 1.23 g N2O-N kg-1 aquaculture production. The estimate of sustained-flux global warming potential of annual CH4 and N2O emissions and the net economic profit suggested that such conversion of rice paddies to inland fish aquaculture would help to reconcile the dilemma for simultaneously achieving both low climatic impacts and high economic benefits in China. More solid direct field measurements from inland aquaculture are in urgent need to direct the overall budget of national or global CH4 and N2O fluxes.

Methane and Nitrous Oxide Emissions Reduced Following Conversion of Rice Paddies to Inland Crab-Fish Aquaculture in Southeast China.

PubMed

Liu, Shuwei; Hu, Zhiqiang; Wu, Shuang; Li, Shuqing; Li, Zhaofu; Zou, Jianwen

2016-01-19

Aquaculture is an important source of atmospheric methane (CH4) and nitrous oxide (N2O), while few direct flux measurements are available for their regional and global source strength estimates. A parallel field experiment was performed to measure annual CH4 and N2O fluxes from rice paddies and rice paddy-converted inland crab-fish aquaculture wetlands in southeast China. Besides N2O fluxes dependent on water/sediment mineral N and CH4 fluxes related to water chemical oxygen demand, both CH4 and N2O fluxes from aquaculture were related to water/sediment temperature, sediment dissolved organic carbon, and water dissolved oxygen concentration. Annual CH4 and N2O fluxes from inland aquaculture averaged 0.37 mg m(-2) h(-1) and 48.1 μg m(-2) h(-1), yielding 32.57 kg ha(-1) and 2.69 kg N2O-N ha(-1), respectively. The conversion of rice paddies to aquaculture significantly reduced CH4 and N2O emissions by 48% and 56%, respectively. The emission factor for N2O was estimated to be 0.66% of total N input in the feed or 1.64 g N2O-N kg(-1) aquaculture production in aquaculture. The conversion of rice paddies to inland aquaculture would benefit for reconciling greenhouse gas mitigation and agricultural income increase as far as global warming potentials and net ecosystem economic profits are of concomitant concern. Some agricultural practices such as better aeration and feeding, and fallow season dredging would help to lower CH4 and N2O emissions from inland aquaculture. More field measurements from inland aquaculture are highly needed to gain an insight into national and global accounting of CH4 and N2O emissions.

Synthesis of ultrafine powders by microwave heating

DOEpatents

Meek, T.T.; Sheinberg, H.; Blake, R.D.

1987-04-24

A method of synthesizing ultrafine powders using microwaves is described. A water soluble material is dissolved in water and the resulting aqueous solution is exposed to microwaves until the water has dissolved. The resulting material is an ultrafine powder. This method can be used to make Al/sub 2/O/sub 3/, NiO /plus/ Al/sub 2/O/sub 3/ and NiO as well as a number of other materials including GaBa/sub 2/Cu/sub 3/O/sub x/. 1 tab.

Engineered in situ bioremediation of a petroleum hydrocarbon-contaminated aquifer: assessment of mineralization based on alkalinity, inorganic carbon and stable carbon isotope balances

NASA Astrophysics Data System (ADS)

Hunkeler, Daniel; Höhener, Patrick; Bernasconi, Stefano; Zeyer, Josef

1999-04-01

A concept is proposed to assess in situ petroleum hydrocarbon mineralization by combining data on oxidant consumption, production of reduced species, CH 4, alkalinity and dissolved inorganic carbon (DIC) with measurements of stable isotope ratios. The concept was applied to a diesel fuel contaminated aquifer in Menziken, Switzerland, which was treated by engineered in situ bioremediation. In the contaminated aquifer, added oxidants (O 2 and NO 3-) were consumed, elevated concentrations of Fe(II), Mn(II), CH 4, alkalinity and DIC were detected and the DIC was generally depleted in 13C compared to the background. The DIC production was larger than expected based on the consumption of dissolved oxidants and the production of reduced species. Stable carbon isotope balances revealed that the DIC production in the aquifer originated mainly from microbial petroleum hydrocarbon mineralization, and that geochemical reactions such as carbonate dissolution produced little DIC. This suggests that petroleum hydrocarbon mineralization can be underestimated if it is determined based on concentrations of dissolved oxidants and reduced species.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Li-Fang; Ou, Chin-Ching; Striebel, Kathryn A.

The goal of this research was to measure Mn dissolution from a thin porous spinel LiMn{sub 2}O{sub 4} electrode by rotating ring-disk collection experiments. The amount of Mn dissolution from the spinel LiMn{sub 2}O{sub 4} electrode under various conditions was detected by potential step chronoamperometry. The concentration of dissolved Mn was found to increase with increasing cycle numbers and elevated temperature. The dissolved Mn was not dependent on disk rotation speed, which indicated that the Mn dissolution from the disk was under reaction control. The in situ monitoring of Mn dissolution from the spinel was carried out under various conditions.more » The ring currents exhibited maxima corresponding to the end-of-charge (EOC) and end-of-discharge (EOD), with the largest peak at EOC. The results suggest that the dissolution of Mn from spinel LiMn{sub 2}O{sub 4} occurs during charge/discharge cycling, especially in a charged state (at >4.1 V) and in a discharged state (at <3.1 V). The largest peak at EOC demonstrated that Mn dissolution took place mainly at the top of charge. At elevated temperatures, the ring cathodic currents were larger due to the increase of Mn dissolution rate.« less

Characterization of Raw and Decopperized Anode Slimes from a Chilean Refinery

NASA Astrophysics Data System (ADS)

Melo Aguilera, Evelyn; Hernández Vera, María Cecilia; Viñals, Joan; Graber Seguel, Teófilo

2016-04-01

This work characterizes raw and decopperized slimes, with the objective of identifying the phases in these two sub-products. The main phases in copper anodes are metallic copper, including CuO, which are present in free form or associated with the presence of copper selenide or tellurides (Cu2(Se,Te)) and several Cu-Pb-Sb-As-Bi oxides. During electrorefining, the impurities in the anode release and are not deposited in the cathode, part of them dissolving and concentrated in the electrolyte, and others form a raw anode slime that contains Au, Ag, Cu, As, Se, Te and PGM, depending on the composition of the anode. There are several recovery processes, most of which involve acid leaching in the first step to dissolve copper, whose product is decopperized anode slime. SEM analysis revealed that the mineralogical species present in the raw anode slime under study were mainly eucarite (CuAgSe), naumannite (Ag2Se), antimony arsenate (SbAsO4), and lead sulfate (PbSO4). In the case of decopperized slime, the particles were mainly composed of SbAsO4 (crystalline appearance), non-stoichiometric silver selenide (Ag(2- x)Se), and chlorargyrite (AgCl).

Performance of Hybrid Photocatalytic-Ceramic Membrane System for the Treatment of Secondary Effluent

PubMed Central

Song, Lili; Zhu, Bo; Gray, Stephen; Duke, Mikel; Muthukumaran, Shobha

2017-01-01

Evaluation of an advanced wastewater treatment system that combines photocatalysis with ceramic membrane filtration for the treatment of secondary effluent was undertaken. The results showed that, after photocatalysis and ceramic membrane filtration, the removal of dissolved organic carbon and UV254 was 60% and 54%, respectively, at a concentration of 4 g/L of TiO2. Dissolved organic matter (DOM) present in the secondary effluent was characterised with a liquid chromatography-organic carbon detector (LC-OCD) technique. The results showed low removal of humics, building blocks, the other oxidation by-products and no removal of biopolymers after TiO2/UV photocatalytic treatment. This suggested that the radical non-selective oxidation mechanisms of TiO2/UV process resulted in secondary effluent in which all of the DOM fractions were present. However, the hybrid system was effective for removing biopolymers with the exception of low molecular weight (LMW) compounds acids, which accumulated from the beginning of the reaction. In addition, monitoring of the DOM fractions with LC-OCD analysis demonstrated that the reduction of the effluent aromaticity was not firmly correlated with the removal of humic substances for the combined processes. PMID:28350320

H2O-CO2-S-Cl partitioning and mixing in rhyolitic melts and fluid - Implications on closed-system degassing in rhyolite

NASA Astrophysics Data System (ADS)

Ding, S.; Webster, J. D.

2017-12-01

Magmatic degassing involving multiple volatile components (C, O, H, S, Cl, etc.) is one of the key factors influencing the timing and nature of volcanic eruptions, and the chemistry of volcanic gases released to the surface. In particular, exsolution of these volatiles from silicic magma during ascent could trigger explosive volcanic eruptions, which can exert strong impacts on surface temperature, ecology and human health. However, quantitative evaluation of this process in silicic magma remains ambiguous due to the lack of experiments in such chemically complex systems. Rhyolite-fluid(s) equilibria experiments were conducted in an IHPVat 100-300 MPa and 800 ° C to determine the solubilities, fluid-melt partitioning, and mixing properties of H2O, CO2, S, and Cl in the oxygen fugacity (fO2) range of FMQ to FMQ+3. The integrated bulk fluids contain up to 94 mol% H2O, 32 mol% CO2, 1 mol% S and 1mol% Cl. Rhyolite melt dissolved 20- 770 ppm CO2 and 4-7 wt.% H2O, varying with pressure, fluid composition, and fO2. Concentrations of H2O and CO2 in melt from C-O-H-S-Cl- bearing experiments at 100 and 200 MPa, and from C-O-H only experiments are generally consistent with the predictions of existing CO2-H2O solubility models based on the C-O-H only system [1-4], while the solubilities of H2O and CO2 in melt with addition of S±Cl at 300 MPa are less than those of the C-O-H- only system. This reduction in H2O and CO2 solubilities exceeds the effects of simple dilution of the coexisting fluid owing to addition of other volatiles, and rather, reflects complex mixing relations. Rhyolite melt also dissolved 20-150 ppm S and 850-2000 ppm Cl, varying with pressure. At 300 MPa, S concentrations in the melt change with fO2. The partitioning of CO2 and S between fluid and melt varies as a function of fluid composition and fO2. Solubilities and complex mixing relationships of CO2, H2O, S and Cl revealed in our experiments can be applied to massive rhyolitic eruptions like those of the Bishop tuff, Toba tuff and Pinatubo to better understand the degassing process, to estimate fluid compositions, and thus, to evaluate the potential environmental impacts of these super eruptions. [1] Ghiorso amd Gualda, 2015, CMP; [2] Liu et al., 2005, J. Volcanol. Geotherm. Res.; [3] Newman and Lowenstern, 2002, Comput. Geosci.; [3] Tamic et al., 2001, Chem. Geol..

Influence of soil pH on the toxicity of zinc oxide nanoparticles to the terrestrial isopod Porcellionides pruinosus.

PubMed

Tourinho, Paula S; van Gestel, Cornelis A M; Lofts, Stephen; Soares, Amadeu M V M; Loureiro, Susana

2013-12-01

The effects of soil pH on the toxicity of ZnO nanoparticles (NPs) to the terrestrial isopod Porcellionides pruinosus were evaluated. Isopods were exposed to a natural soil amended with CaCO3 to reach 3 different pH(CaCl2) levels (4.5, 6.2, and 7.3) and to standard LUFA 2.2 soil (pH 5.5) spiked with ZnO NPs (30 nm), non-nano ZnO (200 nm), and ionic Zn as ZnCl₂. Toxicity was expressed based on total Zn concentration in soil, as well as total Zn and free Zn²⁺ ion concentrations in porewater. Compared with ZnO-spiked soils, the ZnCl₂-spiked soils had lower pH and higher porewater Ca²⁺ and Zn levels. Isopod survival did not differ between Zn forms and soils, but survival was higher for isopods exposed to ZnO NPs at pH 4.5. Median effect concentrations (EC50s) for biomass change showed similar trends for all Zn forms in all soils, with higher values at intermediate pH. Median lethal concentration (LC50) and EC50 values based on porewater Zn or free Zn ion concentrations were much lower for ZnO than for ionic zinc. Zn body concentrations increased in a dose-related manner, but no effect of soil pH was found. It is suggested not only that dissolved or free Zn in porewater contributed to uptake and toxicity, but also that oral uptake (i.e., ingestion of soil particles) could be an important additional route of exposure. © 2013 SETAC.

[Studies on six heavy metal elements dissolution characteristics of Andrographis herb by ICP-OES].

PubMed

Tang, Rui; Li, Tian-Peng; Gu, Xue-Shi; Li, Yong-Jian; Yang, Yi

2010-02-01

A simple and accurate method for the simultaneous determination of As, Ba, Cd, Cr, Cu and Pb in andrographis herb by inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. The samples were digested by HNO3-HClO4. The digestion-determination method was evaluated with the relative standard deviations for all these elements between 2.1% and 4.6%, and the recoveries were between 92.0% and 103.2%. The measuring method was proved to be simple, reliable and highly sensitive. The dissolution characteristics of the 6 heavy metal elements in different solvents and with different extraction methods such as refluxing, soaking, and ultrasonic assisted extraction were studied. The experimental results showed that Ba was in the highest concentration followed by Cu and Cr, and the concentration of As, Pb and Cd was relatively lower in the herb. With the increase in ethanol concentration, the dissolution amount of Ba decreased but that of Cu and Cr increased, and the highest concentration of Cd was dissolved in acidic solution. Overall, Cd and Pb were difficult to dissolve out with 85% ethanol refluxing, but As dissolved comparatively more under the same condition. Comparing the extraction methods, the higher concentration of these 6 metals was obtained by refluxing water or alkaline water than that by 85% ethanol maceration. These differences might be related to the existent forms of these six elements in the herb. The determination and study on dissolution characteristics of these elements by using ICP-OES was important for rational using medicinal resources and ensuring the safety of drugs.

Atmospheric hydrogen peroxide and Eoarchean iron formations.

PubMed

Pecoits, E; Smith, M L; Catling, D C; Philippot, P; Kappler, A; Konhauser, K O

2015-01-01

It is widely accepted that photosynthetic bacteria played a crucial role in Fe(II) oxidation and the precipitation of iron formations (IF) during the Late Archean-Early Paleoproterozoic (2.7-2.4 Ga). It is less clear whether microbes similarly caused the deposition of the oldest IF at ca. 3.8 Ga, which would imply photosynthesis having already evolved by that time. Abiological alternatives, such as the direct oxidation of dissolved Fe(II) by ultraviolet radiation may have occurred, but its importance has been discounted in environments where the injection of high concentrations of dissolved iron directly into the photic zone led to chemical precipitation reactions that overwhelmed photooxidation rates. However, an outstanding possibility remains with respect to photochemical reactions occurring in the atmosphere that might generate hydrogen peroxide (H2 O2 ), a recognized strong oxidant for ferrous iron. Here, we modeled the amount of H2 O2 that could be produced in an Eoarchean atmosphere using updated solar fluxes and plausible CO2 , O2 , and CH4 mixing ratios. Irrespective of the atmospheric simulations, the upper limit of H2 O2 rainout was calculated to be <10(6) molecules cm(-2) s(-1) . Using conservative Fe(III) sedimentation rates predicted for submarine hydrothermal settings in the Eoarchean, we demonstrate that the flux of H2 O2 was insufficient by several orders of magnitude to account for IF deposition (requiring ~10(11) H2 O2 molecules cm(-2) s(-1) ). This finding further constrains the plausible Fe(II) oxidation mechanisms in Eoarchean seawater, leaving, in our opinion, anoxygenic phototrophic Fe(II)-oxidizing micro-organisms the most likely mechanism responsible for Earth's oldest IF. © 2014 John Wiley & Sons Ltd.

Pilot plant demonstration of stable and efficient high rate biological nutrient removal with low dissolved oxygen conditions.

PubMed

Keene, Natalie A; Reusser, Steve R; Scarborough, Matthew J; Grooms, Alan L; Seib, Matt; Santo Domingo, Jorge; Noguera, Daniel R

2017-09-15

Aeration in biological nutrient removal (BNR) processes accounts for nearly half of the total electricity costs at many wastewater treatment plants. Even though conventional BNR processes are usually operated to have aerated zones with high dissolved oxygen (DO) concentrations, recent research has shown that nitrification can be maintained using very low-DO concentrations (e.g., below 0.2 mg O 2 /L), and therefore, it may be possible to reduce energy use and costs in BNR facilities by decreasing aeration. However, the effect of reduced aeration on enhanced biological phosphorus removal (EBPR) is not understood. In this study, we investigated, at the pilot-scale level, the effect of using minimal aeration on the performance of an EBPR process. Over a 16-month operational period, we performed stepwise decreases in aeration, reaching an average DO concentration of 0.33 mg O 2 /L with stable operation and nearly 90% phosphorus removal. Under these low-DO conditions, nitrification efficiency was maintained, and nearly 70% of the nitrogen was denitrified, without the need for internal recycling of high nitrate aeration basin effluent to the anoxic zone. At the lowest DO conditions used, we estimate a 25% reduction in energy use for aeration compared to conventional BNR operation. Our improved understanding of the efficiency of low-DO BNR contributes to the global goal of reducing energy consumption during wastewater treatment operations. Copyright © 2017 Elsevier Ltd. All rights reserved.

The Benthic Exchange of O2, N2 and Dissolved Nutrients Using Small Core Incubations.

PubMed

Owens, Michael S; Cornwell, Jeffrey C

2016-08-03

The measurement of sediment-water exchange of gases and solutes in aquatic sediments provides data valuable for understanding the role of sediments in nutrient and gas cycles. After cores with intact sediment-water interfaces are collected, they are submerged in incubation tanks and kept under aerobic conditions at in situ temperatures. To initiate a time course of overlying water chemistry, cores are sealed without bubbles using a top cap with a suspended stirrer. Time courses of 4-7 sample points are used to determine the rate of sediment water exchange. Artificial illumination simulates day-time conditions for shallow photosynthetic sediments, and in conjunction with dark incubations can provide net exchanges on a daily basis. The net measurement of N2 is made possible by sampling a time course of dissolved gas concentrations, with high precision mass spectrometric analysis of N2:Ar ratios providing a means to measure N2 concentrations. We have successfully applied this approach to lakes, reservoirs, estuaries, wetlands and storm water ponds, and with care, this approach provides valuable information on biogeochemical balances in aquatic ecosystems.

Reversal of Increasing Tropical Ocean Hypoxia Trends With Sustained Climate Warming

NASA Astrophysics Data System (ADS)

Fu, Weiwei; Primeau, Francois; Keith Moore, J.; Lindsay, Keith; Randerson, James T.

2018-04-01

Dissolved oxygen (O2) is essential for the survival of marine animals. Climate change impacts on future oxygen distributions could modify species biogeography, trophic interactions, biodiversity, and biogeochemistry. The Coupled Model Intercomparison Project Phase 5 models predict a decreasing trend in marine O2 over the 21st century. Here we show that this increasing hypoxia trend reverses in the tropics after 2100 in the Community Earth System Model forced by atmospheric CO2 from the Representative Concentration Pathway 8.5 and Extended Concentration Pathway 8.5. In tropical intermediate waters between 200 and 1,000 m, the model predicts a steady decline of O2 and an expansion of oxygen minimum zones (OMZs) during the 21st century. By 2150, however, the trend reverses with oxygen concentration increasing and OMZ volume shrinking through 2300. A novel five-box model approach in conjunction with output from the full Earth system model is used to separate the contributions of biological and physical processes to the trends in tropical oxygen. The tropical O2 recovery is caused mainly by reductions in tropical biological export, coupled with a modest increase in ventilation after 2200. The time-evolving oxygen distribution impacts marine nitrogen cycling, with potentially important climate feedbacks.

234U— 238U— 230Th— 232Th systematics in saline groundwaters from central Missouri

NASA Astrophysics Data System (ADS)

Banner, Jay L.; Wasserburg, G. J.; Chen, James H.; Moore, Clyde H.

1990-12-01

Saline groundwaters with 4.7 to 26‰ total dissolved solids were sampled from springs and artesian wells in Mississippian and Ordovician carbonates and sandstones in central Missouri. U—Th isotopic variations provide a means of evaluating processes of water-rock interaction and fluid mixing and estimating the time scales of element transport. Recently developed mass spectrometric techniques are used to make isotopic measurements on small-volume groundwater samples (0.1-4 l) with high precision (e.g., < ±5% for 234U/ 238U activity ratios). The groundwaters have a wide range of 238U concentrations, 50 × 10 -12 to 200 × 10 -12 g/g; 234U/ 234U activity ratios, 2.15-16.0; 232Th concentrations, 0.10 × 10 -12 to 33 × 10 -12 g/g; and 230Th concentrations, 0.91 × 10 -17 to 26 × 10 -17 g/g. Unfiltered and filtered (0.4 μm, 0.1 μm) aliquots of a saline sample have the same isotopic composition and concentration of U, indicating that 234U and 238U occur almost entirely as dissolved species. The concentration of 232Th is up to seven times lower in filtered vs. unfiltered aliquots, indicating that 232Th is predominantly associated with particulates in the groundwaters. In contrast, most of the 230Th is in solution. Previous geochemical studies indicate that: (1) the saline waters originated as meteoric recharge and evolved through halite dissolution, reactions with silicates and saline-dilute mixing processes during a long-distance flow history; and (2) interaction with limestone and dolomite aquifer rocks in central Missouri has been limited. A consistent relationship between U/Ca and 234U/ 238U activity ratio is observed in the groundwaters and provides constraints on the U/Ca ratios and 234U/ 238U activity ratios of end-member reservoirs and on the processes of isotopic exchange in this water-rock system. Model calculations that simulate (1) saline-dilute groundwater mixing and (2) limited extents of dissolution of carbonate aquifer minerals by the groundwaters can account for the variations in U/Ca, 234U/ 238U and 18O/ 16O in the suite of water samples. The model calculations demonstrate that dissolved U isotopic compositions can be a sensitive indicator of water-rock interaction, which in turn limits the usefulness of 234U— 238U disequilibria for groundwater age determinations. The concentration of dissolved 230Th in the groundwaters is (1) two to three orders of magnitude below 230Th— 234U equilibrium activity levels, and (2) significantly in excess of concentrations estimated for the supply of Th to solution via desorption and dissolution. A model involving the derivation of the excess 230Th from the in situ decay of dissolved 234U in the groundwaters indicates the operation of an adsorption mechanism on the time scale of 10-10 3 years. The results reported here may have broader application to the assessment and management of hazardous chemical species in natural environments.

Distributions and seasonal variations of dissolved carbohydrates in the Jiaozhou Bay, China

NASA Astrophysics Data System (ADS)

Yang, Gui-Peng; Zhang, Yan-Ping; Lu, Xiao-Lan; Ding, Hai-Bing

2010-06-01

Surface seawater samples were collected in the Jiaozhou Bay, a typical semi-closed basin located at the western part of the Shandong Peninsula, China, during four cruises. Concentrations of monosaccharides (MCHO), polysaccharides (PCHO) and total dissolved carbohydrates (TCHO) were measured with the 2,4,6-tripyridyl- s-triazine spectroscopic method. Concentrations of TCHO varied from 10.8 to 276.1 μM C for all samples and the ratios of TCHO to dissolved organic carbon (DOC) ranged from 1.1 to 67.9% with an average of 10.1%. This result indicated that dissolved carbohydrates were an important constituent of DOC in the surface seawater of the Jiaozhou Bay. In all samples, the concentrations of MCHO ranged from 2.9 to 65.9 μM C, comprising 46.1 ± 16.6% of TCHO on average, while PCHO ranged from 0.3 to 210.2 μM C, comprising 53.9 ± 16.6% of TCHO on average. As a major part of dissolved carbohydrates, the concentrations of PCHO were higher than those of MCHO. MCHO and PCHO accumulated in January and July, with minimum average concentration in April. The seasonal variation in the ratios of TCHO to DOC was related to water temperature, with high values in January and low values in July and October. The concentrations of dissolved carbohydrates displayed a decreasing trend from the coastal to the central areas. Negative correlations between concentrations of TCHO and salinity in July suggested that riverine input around the Jiaozhou Bay had an important effect on the concentrations of dissolved carbohydrates in surface seawater. The pattern of distributions of MCHO and PCHO reported in this study added to the global picture of dissolved carbohydrates distribution.

Evaluation of calcium-bearing material for treatment of CO2 leakage-induced pollution

NASA Astrophysics Data System (ADS)

Park, J.; Park, M.; Jeong, H. Y.

2017-12-01

Several Ca2+-bearing materials were evaluated for their capability to treat CO2 leakage-induced pollution for the application of permeable reactive barriers (PRBs). In this regard, a series of batch experiments were carried out with Portland cement, quick lime (CaO), and gypsum (CaSO4). Each of these materials was added to 50 mL of CO2-saturated solutions ( 7.5-8.5 mM) in serum vials sealed with Teflon-coated grey butyl stopper. Subsequently, the resultant batches were agitated at room temperature for 24 h. At predetermined intervals, each vial was sacrificed to monitor changes in pH, EC, and dissolved CO2 concentration. Despite the pH-neutralizing capacity, 0.15 g of Portland cement did not lower any dissolved CO2. When amended with 0.05 g of Ca(OH)2 or Mg(OH)2, the cement at this loading could sequester dissolved CO2, with the former being more effective. Even without such amendments, the cement at or greater than 0.2 g was shown to completely sequester dissolved CO2. In case of quick lime, its loading as low as 0.05 g instantaneously removed all dissolved CO2, which was also noted for Portland cement at 0.5 g. For gypsum, its loading at 0.12 g was not effective for immobilizing dissolved CO2. By both X-ray diffraction (XRD) and thermogravimetry (TG) analyses, the CO2 sequestration by Ca2+-bearing materials was found to be mainly due to the formation of calcite (CaCO3). Funding source: The "R&D Project on Environmental Management of Geologic CO2 Storage" from the KEITI (Project Number: 2014001810003).

Strategies of Nitrosomonas europaea 19718 to counter low dissolved oxygen and high nitrite concentrations.

PubMed

Yu, Ran; Chandran, Kartik

2010-03-04

Nitrosomonas europaea is a widely studied chemolithoautotrophic ammonia oxidizing bacterium. While significant work exists on the ammonia oxidation pathway of N. europaea, its responses to factors such as dissolved oxygen limitation or sufficiency or exposure to high nitrite concentrations, particularly at the functional gene transcription level are relatively sparse. The principal goal of this study was to investigate responses at the whole-cell activity and gene transcript levels in N. europaea 19718 batch cultures, which were cultivated at different dissolved oxygen and nitrite concentrations. Transcription of genes coding for principal metabolic pathways including ammonia oxidation (amoA), hydroxylamine oxidation (hao), nitrite reduction (nirK) and nitric oxide reduction (norB) were quantitatively measured during batch growth, at a range of DO concentrations (0.5, 1.5 and 3.0 mg O2/L). Measurements were also conducted during growth at 1.5 mg O2/L in the presence of 280 mg-N/L of externally added nitrite. Several wide ranging responses to DO limitation and nitrite toxicity were observed in N. europaea batch cultures. In contrast to our initial hypothesis, exponential phase mRNA concentrations of both amoA and hao increased with decreasing DO concentrations, suggesting a mechanism to metabolize ammonia and hydroxylamine more effectively under DO limitation. Batch growth in the presence of 280 mg nitrite-N/L resulted in elevated exponential phase nirK and norB mRNA concentrations, potentially to promote utilization of nitrite as an electron acceptor and to detoxify nitrite. This response was in keeping with our initial hypothesis and congruent with similar responses in heterotrophic denitrifying bacteria. Stationary phase responses were distinct from exponential phase responses in most cases, suggesting a strong impact of ammonia availability and metabolism on responses to DO limitation and nitrite toxicity. In general, whole-cell responses to DO limitation or nitrite toxicity, such as sOUR or nitrite reduction to nitric oxide (NO) did not parallel the corresponding mRNA (nirK) profiles, suggesting differences between the gene transcription and enzyme translation or activity levels. The results of this study show that N. europaea possesses specific mechanisms to cope with growth under low DO concentrations and high nitrite concentrations. These mechanisms are additionally influenced by the physiological growth state of N. europaea cultures and are possibly geared to enable more efficient substrate utilization or nitrite detoxification.

Abatement of the antibiotic levofloxacin in a solar photoelectro-Fenton flow plant: Modeling the dissolved organic carbon concentration-time relationship.

PubMed

Coria, Gabriela; Pérez, Tzayam; Sirés, Ignasi; Brillas, Enric; Nava, José L

2018-05-01

The degradation of solutions of the antibiotic levofloxacin (LVN) in sulfate medium at pH 3.0 has been investigated at pre-pilot scale by solar photoelectro-Fenton (SPEF) process. The flow plant included an FM01-LC filter-press cell equipped with a Ti|Pt anode and a three-dimensional-like air-diffusion cathode, connected to a compound parabolic collector as photoreactor and a continuous stirred tank under recirculation batch mode. The effect of volumetric flow rate on H 2 O 2 electrogeneration from O 2 reduction was assessed. Then, the influence of initial LVN concentration and Fe 2+ concentration as catalyst on dissolved organic carbon (DOC) removal was thoroughly investigated. LVN was gradually mineralized by SPEF process, with faster DOC abatement at 0.50 mM Fe 2+ , yielding 100% after 360 min at applied cathodic potential of -0.30 V|SHE. The high mineralization current efficiency (MCE) and low specific energy consumption (EC DOC ) revealed the extraordinary role of homogeneous hydroxyl radicals and natural UV light, which allowed the degradation of the antibiotic and its by-products with MCE values greater than 100%. Five cyclic by-products, N,N-diethylformamide and three short-chain linear carboxylic acids were detected by GC-MS and HPLC analyses. A parametric model to simulate the DOC decay versus electrolysis time was implemented for the SPEF pre-pilot flow plant, showing good agreement with experimental data. Copyright © 2018 Elsevier Ltd. All rights reserved.

Electrochemical detection of copper ions leached from CuO nanoparticles in saline buffers and biological media using a gold wire working electrode

NASA Astrophysics Data System (ADS)

Baldisserri, Carlo; Costa, Anna Luisa

2016-04-01

We performed explorative cyclic voltammetry in phosphate-buffered saline buffers, Dulbecco's modified Eagle's medium (DMEM), and fetal bovine serum-added DMEM using Au wire as working electrode, both in the absence and in the presence of known nominal concentrations of Cu2+ ions or 15 nm CuO nanoparticles. Addition of either Cu2+ ions or aqueous suspension of CuO nanoparticles caused a single anodic peak to appear in the double-layer region of all three pristine media. The height of the anodic peak was found to increase in a monotonic fashion vs. Cu2+ concentration in Cu2+-added media, and versus time since CuO addition in CuO-added media. Stepwise addition of glycine to Cu2+-added phosphate-buffered saline buffer caused an increasing cathodic shift of the anodic peak accompanied by decreasing peak currents. Results indicate that preparing Cu2+-free suspensions of CuO nanoparticles in such media is difficult, owing to the presence of leached copper ions. The implications on results of experiments in which CuO nanoparticle-added biological media are used as cell culture substrates are discussed. Literature data on the interactions between Cu2+ ions, dissolved carbon dioxide in aqueous CuO suspensions, and amino acids present in such media are compared to our results.

Distribution of dissolved green-house gases (CO2, CH4, N2O) in Lakes Edward and George: Results from the first field cruise of the HIPE project

NASA Astrophysics Data System (ADS)

Borges, Alberto V.; Morana, Cédric D. T.; Lambert, Thibault; Okello, William; Bouillon, Steven

2017-04-01

Inland waters (streams, rivers, lakes, reservoirs) are quantitatively important components of the global budgets of atmospheric emissions of long-lived greenhouse gases (GHGs) (CO2, CH4, N2O). Available data indicate that a very large fraction of CO2 and CH4 emissions from rivers and reservoirs occurs at tropical latitudes. Data on GHGs at tropical latitudes from lakes however are much more scarse, and the relative importance of emissions, in particular in Africa, remains to be determined. Large tropical lakes are net autotrophic (hence potentially sinks for atmospheric CO2) due generally low dissolved organic carbon concentrations, seasonally near constant light and temperature conditions, and generally deep water columns favourable for export of organic matter to depth. This sharply contrasts with their much better documented temperate and boreal counterparts, usually considered as CO2 sources to the atmosphere sustained by net heterotrophy. Here, we report a data-set of dissolved CO2, CH4, N2O obtained in October 2016 in Lakes Edward and George and adjacent streams and crater lakes in the frame of Belgian Science Policy (BELSPO) HIPE (Human impacts on ecosystem health and resources of Lake Edward, http://www.co2.ulg.ac.be/hipe/) project. Lake George and part of Lake Edward were sinks for atmospheric CO2 and N2O due to high primary production and denitrification in sediments, respectively, and modest sources of CH4 to the atmosphere. Sampled rivers and streams were oversaturated in CO2 and CH4 and close to atmospheric equilibrium with regards to N2O. Spatial variations within rivers and streams were related to elevation and vegetation characteristics on the catchments (savannah versus forest). Levels of CO2, CH4, and N2O were within the range of those we reported in other African rivers. Crater lakes acted as sinks for atmospheric CO2 and N2O but were extremely over-saturated in CH4, due to intense primary production sustained by cyanobacteria. These CH4 levels were much higher than what we have reported in other lakes and reservoirs elsewhere in Sub-Saharan Africa.

Substantial nitrous oxide emissions from intertidal sediments and groundwater in anthropogenically-impacted West Falmouth Harbor, Massachusetts.

PubMed

Moseman-Valtierra, Serena; Kroeger, Kevin D; Crusius, John; Baldwin, Sandra; Green, Adrian; Brooks, T Wallace; Pugh, Emily

2015-01-01

Large N2O emissions were observed from intertidal sediments in a coastal estuary, West Falmouth Harbor, MA, USA. Average N2O emission rates from 41 chambers during summer 2008 were 10.7 mol N2O m(-2) h(-1)±4.43 μmol N2O m(-2) h(-1) (standard error). Emissions were highest from sediments within a known wastewater plume, where a maximum N2O emission rate was 155 μmol N2O m(-2) h(-1). Intertidal N2O fluxes were positively related to porewater ammonium concentrations at 10 and 25 cm depths. In groundwater from 7 shoreline wells, dissolved N2O ranged from 488% of saturation (56 nM N2O) to more than 13000% of saturation (1529 nM N2O) and was positively related to nitrate concentrations. Fresh and brackish porewater underlying 14 chambers was also supersaturated in N2O, ranging from 2980% to 13175% of saturation. These observations support a relationship between anthropogenic nutrient loading and N2O emissions in West Falmouth Harbor, with both groundwater sources and also local N2O production within nutrient-rich, intertidal sediments in the groundwater seepage face. N2O emissions from intertidal "hotspot" in this harbor, together with estimated surface water emissions, constituted 2.4% of the average overall rate of nitrogen export from the watershed to the estuary. This suggests that N2O emissions factors from coastal ecosystems may be underestimated. Since anthropogenic nutrient loading affects estuaries worldwide, quantification of N2O dynamics is warranted in other anthropogenically-impacted coastal ecosystems. Copyright © 2014 Elsevier Ltd. All rights reserved.

Substantial nitrous oxide emissions from intertidal sediments and groundwater in anthropogenically-impacted West Falmouth Harbor, Massachusetts

USGS Publications Warehouse

Moseman-Valtierra, Serena; Kroeger, Kevin D.; Crusius, John; Baldwin, Sandy; Green, Adrian; Brooks, Thomas W.; Pugh, E.

2015-01-01

Large N2O emissions were observed from intertidal sediments in a coastal estuary, West Falmouth Harbor, MA, USA. Average N2O emission rates from 41 chambers during summer 2008 were 10.7 mol N2O m(-2) h(-1)±4.43 μmol N2O m(-2) h(-1) (standard error). Emissions were highest from sediments within a known wastewater plume, where a maximum N2O emission rate was 155 μmol N2O m(-2) h(-1). Intertidal N2O fluxes were positively related to porewater ammonium concentrations at 10 and 25 cm depths. In groundwater from 7 shoreline wells, dissolved N2O ranged from 488% of saturation (56 nM N2O) to more than 13000% of saturation (1529 nM N2O) and was positively related to nitrate concentrations. Fresh and brackish porewater underlying 14 chambers was also supersaturated in N2O, ranging from 2980% to 13175% of saturation. These observations support a relationship between anthropogenic nutrient loading and N2O emissions in West Falmouth Harbor, with both groundwater sources and also local N2O production within nutrient-rich, intertidal sediments in the groundwater seepage face. N2O emissions from intertidal "hotspot" in this harbor, together with estimated surface water emissions, constituted 2.4% of the average overall rate of nitrogen export from the watershed to the estuary. This suggests that N2O emissions factors from coastal ecosystems may be underestimated. Since anthropogenic nutrient loading affects estuaries worldwide, quantification of N2O dynamics is warranted in other anthropogenically-impacted coastal ecosystems.

Spatial variability of total dissolved copper and copper speciation in the inshore waters of Bermuda.

PubMed

Oldham, V E; Swenson, M M; Buck, K N

2014-02-15

Total dissolved copper (Cu) and Cu speciation were examined from inshore waters of Bermuda, in October 2009 and July-August 2010, to determine the relationship between total dissolved Cu, Cu-binding ligands and bioavailable, free, hydrated Cu(2+) concentrations. Speciation was performed using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV). Mean total dissolved Cu concentrations ranged from 1.4 nM to 19.2 nM, with lowest concentrations at sites further from shore, consistent with previous measurements in the Sargasso Sea, and localized Cu enrichment inshore in enclosed harbors. Ligand concentrations exceeded dissolved [Cu] at most sites, and [Cu(2+)] were correspondingly low at those sites, typically <10(-13) M. One site, Hamilton Harbour, was found to have [Cu] in excess of ligands, resulting in [Cu(2+)] of 10(-10.7) M, and indicating that Cu may be toxic to phytoplankton here. Copyright © 2013 Elsevier Ltd. All rights reserved.

Hopewell Beneficial CO2 Capture for Production of Fuels, Fertilizer and Energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

UOP; Honeywell Resins & Chemicals; Honeywell Process Solutions

2010-09-30

For Phase 1 of this project, the Hopewell team developed a detailed design for the Small Scale Pilot-Scale Algal CO2 Sequestration System. This pilot consisted of six (6) x 135 gallon cultivation tanks including systems for CO2 delivery and control, algal cultivation, and algal harvesting. A feed tank supplied Hopewell wastewater to the tanks and a receiver tank collected the effluent from the algal cultivation system. The effect of environmental parameters and nutrient loading on CO2 uptake and sequestration into biomass were determined. Additionally the cost of capturing CO2 from an industrial stack emission at both pilot and full-scale wasmore » determined. The engineering estimate evaluated Amine Guard technology for capture of pure CO2 and direct stack gas capture and compression. The study concluded that Amine Guard technology has lower lifecycle cost at commercial scale, although the cost of direct stack gas capture is lower at the pilot scale. Experiments conducted under high concentrations of dissolved CO2 did not demonstrate enhanced algae growth rate. This result suggests that the dissolved CO2 concentration at neutral pH was already above the limiting value. Even though dissolved CO2 did not show a positive effect on biomass growth, controlling its value at a constant set-point during daylight hours can be beneficial in an algae cultivation stage with high algae biomass concentration to maximize the rate of CO2 uptake. The limited enhancement of algal growth by CO2 addition to Hopewell wastewater was due at least in part to the high endogenous CO2 evolution from bacterial degradation of dissolved organic carbon present at high levels in the wastewater. It was found that the high level of bacterial activity was somewhat inhibitory to algal growth in the Hopewell wastewater. The project demonstrated that the Honeywell automation and control system, in combination with the accuracy of the online pH, dissolved O2, dissolved CO2, turbidity, Chlorophyll A and conductivity sensors is suitable for process control of algae cultivation in an open pond systems. This project concluded that the Hopewell wastewater is very suitable for algal cultivation but the potential for significant CO2 sequestration from the plant stack gas emissions was minimal due to the high endogenous CO2 generation in the wastewater from the organic wastewater content. Algae cultivation was found to be promising, however, for nitrogen remediation in the Hopewell wastewater.« less

Influence of infrastructure on water quality and greenhouse gas dynamics in urban streams

NASA Astrophysics Data System (ADS)

Smith, Rose M.; Kaushal, Sujay S.; Beaulieu, Jake J.; Pennino, Michael J.; Welty, Claire

2017-06-01

Streams and rivers are significant sources of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) globally, and watershed management can alter greenhouse gas (GHG) emissions from streams. We hypothesized that urban infrastructure significantly alters downstream water quality and contributes to variability in GHG saturation and emissions. We measured gas saturation and estimated emission rates in headwaters of two urban stream networks (Red Run and Dead Run) of the Baltimore Ecosystem Study Long-Term Ecological Research project. We identified four combinations of stormwater and sanitary infrastructure present in these watersheds, including: (1) stream burial, (2) inline stormwater wetlands, (3) riparian/floodplain preservation, and (4) septic systems. We selected two first-order catchments in each of these categories and measured GHG concentrations, emissions, and dissolved inorganic and organic carbon (DIC and DOC) and nutrient concentrations biweekly for 1 year. From a water quality perspective, the DOC : NO3- ratio of streamwater was significantly different across infrastructure categories. Multiple linear regressions including DOC : NO3- and other variables (dissolved oxygen, DO; total dissolved nitrogen, TDN; and temperature) explained much of the statistical variation in nitrous oxide (N2O, r2 = 0.78), carbon dioxide (CO2, r2 = 0.78), and methane (CH4, r2 = 0.50) saturation in stream water. We measured N2O saturation ratios, which were among the highest reported in the literature for streams, ranging from 1.1 to 47 across all sites and dates. N2O saturation ratios were highest in streams draining watersheds with septic systems and strongly correlated with TDN. The CO2 saturation ratio was highly correlated with the N2O saturation ratio across all sites and dates, and the CO2 saturation ratio ranged from 1.1 to 73. CH4 was always supersaturated, with saturation ratios ranging from 3.0 to 2157. Longitudinal surveys extending form headwaters to third-order outlets of Red Run and Dead Run took place in spring and fall. Linear regressions of these data yielded significant negative relationships between each gas with increasing watershed size as well as consistent relationships between solutes (TDN or DOC, and DOC : TDN ratio) and gas saturation. Despite a decline in gas saturation between the headwaters and stream outlet, streams remained saturated with GHGs throughout the drainage network, suggesting that urban streams are continuous sources of CO2, CH4, and N2O. Our results suggest that infrastructure decisions can have significant effects on downstream water quality and greenhouse gases, and watershed management strategies may need to consider coupled impacts on urban water and air quality.

Superiority of solar Fenton oxidation over TiO2 photocatalysis for the degradation of trimethoprim in secondary treated effluents.

PubMed

Michael, I; Hapeshi, E; Michael, C; Fatta-Kassinos, D

2013-01-01

The overall aim of this work was to examine the degradation of trimethoprim (TMP), which is an antibacterial agent, during the application of two advanced oxidation process (AOP) systems in secondary treated domestic effluents. The homogeneous solar Fenton process (hv/Fe(2+)/H2O2) and heterogeneous photocatalysis with titanium dioxide (TiO2) suspensions were tested. It was found that the degradation of TMP depends on several parameters such as the amount of iron salt and H2O2, concentration of TiO2, pH of solution, solar irradiation, temperature and initial substrate concentration. The optimum dosages of Fe(2+) and H2O2 for homogeneous ([Fe(2+)] = 5 mg L(-1), [H2O2] = 3.062 mmol L(-1)) and TiO2 ([TiO2] = 3 g L(-1)) for heterogeneous photocatalysis were established. The study indicated that the degradation of TMP during the solar Fenton process is described by a pseudo-first-order reaction and the substrate degradation during the heterogeneous photocatalysis by the Langmuir-Hinshelwood kinetics. The toxicity of the treated samples was evaluated using a Daphnia magna bioassay and was finally decreased by both processes. The results indicated that solar Fenton is more effective than the solar TiO2 process, yielding complete degradation of the examined substrate within 30 min of illumination and dissolved organic carbon (DOC) reduction of about 44% whereas the respective values for the TiO2 process were ∼70% degradation of TMP within 120 min of treatment and 13% DOC removal.

Annual dynamics of N2O, CH4 and CO2 fluxes from the agricultural irrigation watersheds in southeast China

NASA Astrophysics Data System (ADS)

Wu, S.; Zou, J.; Liu, S.; Chen, J.; Kong, D.; Geng, Y.

2017-12-01

Agricultural irrigation watershed covers a large area in southeast of China and is a potentially important source of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). However, the flux magnitudes contribution to the overall catchment greenhouse gas (GHGs) fluxes and their drivers of seasonal variability are limited in agricultural irrigation watersheds. An in-situ observation was performed to measure annual CO2, CH4 and N2O fluxes from an agricultural irrigation watershed in southeast of China from September 2014 to September 2016. GHGs fluxes were measured using floating chambers and a gas exchange model was also used to predict CH4 and N2O fluxes. All GHGs showed varied seasonally with highest fluxes in early summer (July) and lowest in winter. Estimated seasonal CH4-C fluxes (11.5-97.6 mg m-2 hr-1) and N2O-N fluxes (2.8-80.8μg m-2 hr-1) were in relative agreement with measured CH4-C fluxes (0.05-74.9mg m-2 hr-1) and N2O-N fluxes (3.9-68.7μg m-2 hr-1) fluxes using floating chambers. Both CH4 and N2O fluxes were positively related to water temperature. The CH4 fluxes were negatively related to water dissolved oxygen (DO) concentration but positively related to sediment dissolved organic carbon (DOC). The N2O fluxes were positively related to water NH4+ and NO3-. The calculated EF5-r value in this study (mean = 0.0016; range = 0.0013-0.0018) was below the current IPCC (2006) default value of 0.0025. This implied that IPCC methodology may over estimates of N2O emissions associated with nitrogen leaching and runoff from agriculture.

Characterization of SnO2 Film with Al-Zn Doping Using Sol-Gel Dip Coating Techniques

NASA Astrophysics Data System (ADS)

Doyan, A.; Susilawati; Ikraman, N.; Taufik, M.

2018-04-01

Sn1-2x AlxZnxO2 film has been developed using sol-gel dip coating technique. The materials SnCl2.2H2O, AlCl3 and ZnCl2 dissolved in water and ethanol with 5:95 volume ratio. Variations dopant concentration x = 0.000, 0.005, 0.0025, and 0.050. The film was grown with sol concentration 0.4 M, the withdrawal speed of 12 cm/min and sintering at 600 °C for 30 minutes. The characteristics Sn1-2x AlxZnxO2 films with various doping concentration phase were characterized by XRD. The morphological characteristics and the composition of the constituent elements of the film were characterized by SEM-EDX. The characteristics of the shape, structure, and size of the particles were characterized by TEM. The XRD results show that all films have a tetragonal SnO2 rutile phase without any secondary phase with an average particle size in the range 5.14 – 2.09 nm. The SEM results show that the film grown has a smooth morphology with a striped texture (x = 0.00), and there is a crack (x = 0.050). The EDX results show that the composition and distribution of the constituent elements of the film are uniformly distributed. TEM results show that the particle films has tetragonal rutile structure, orthorhombic and amorphous with a spherical shape.

Solubility, Partitioning, and Speciation of Carbon in Shallow Magma Oceans of Terrestrial Planets Constrained by High P-T Experiments

NASA Astrophysics Data System (ADS)

Chi, H.; Dasgupta, R.; Shimizu, N.

2011-12-01

Deep planetary volatile cycles have a critical influence on planetary geodynamics, atmospheres, climate, and habitability. However, the initial conditions that prevailed in the early, largely molten Earth and other terrestrial planets, in terms of distribution of volatiles between various reservoirs - metals, silicates, and atmosphere - remains poorly constrained. Here we investigate the solubility, partitioning, and speciation of carbon-rich volatile species in a shallow magma ocean environment, i.e., in equilibrium with metallic and silicate melts. A series of high pressure-temperature experiments using a piston cylinder apparatus were performed at 1-3 GPa, 1500-1800 °C on synthetic basaltic mixtures + Fe-Ni metal powders contained in graphite capsules. All the experiments produced glassy silicate melt pool in equilibrium with quenched metal melt composed of dendrites of cohenite and kamacite. Major element compositions of the resulting phases and the carbon content of metallic melts were analyzed by EPMA at NASA-JSC. Carbon and hydrogen concentrations of basaltic glasses were determined using Cameca IMS 1280 SIMS at WHOI and speciation of dissolved volatiles was constrained using FTIR and Raman spectroscopy at Rice University. Based on the equilibria - FeO (silicate melt) = Fe (metal alloy melt) + 1/2O2, we estimate the oxygen fugacity of our experiments in the range of ΔIW of -1 to -2. FTIR analysis on doubly polished basaltic glass chips suggests that the concentrations of dissolved CO32- or molecular CO2 are negligible in graphite and metal saturated reduced conditions, whereas the presence of dissolved OH- is evident from the asymmetric peak at 3500 cm-1. Collected Raman spectra of basaltic glasses in the frequency range of 200-4200 cm-1 suggest that hydrogen is present both as dissolved OH- species (band at 3600 cm-1) and as molecular H2 (band near 4150 cm-1) for all of our experiments. Faint peaks near 2915 cm-1 and consistent peaks near 740 cm-1 suggest that possible carbon species in our reduced glasses are likely minor CH4 and Si-C, respectively and are consistent with the recent solubility studies at reduced conditions [1,2]. Carbon solubility (calibrated using 12C/30Si) at graphite saturation in our reduced basaltic glasses is only in the range 20-100 ppm C, with H2O contents in the range of 0.2-0.7 wt.%. In contrast to the low dissolved carbon concentration in the basaltic silicate melts, carbon solubility in quenched metallic melts vary in the range of 5-7 wt.%. Our preliminary work indicates that the solubility of carbon in reduced basaltic melts relevant for early magma conditions may be several orders of magnitude lower compared to the solubility of carbon in modern terrestrial basalts. This coupled with significant solubility of carbon in Fe-Ni metallic melt suggests that most of magma ocean carbon was likely partitioned into deep metallic melts. Further metal-silicate experiments with more depolymerized basaltic melts of variable compositions are underway and will be presented. [1] Kadik et al. JPetrol 45, 1297-1310, 2004; [2] Kadik et al. Geochem Int 44, 33-47, 2006.

Are dual isotope and isotopomer ratios of N2O useful indicators for N2O turnover during denitrification in nitrate-contaminated aquifers?

NASA Astrophysics Data System (ADS)

Well, Reinhard; Eschenbach, Wolfram; Flessa, Heinz; von der Heide, Carolin; Weymann, Daniel

2012-08-01

Denitrifying aquifers are sources of the greenhouse gas N2O. Isotopic signatures reflect processes of production and reduction of N2O, but it is not clear to which extent these can be used to quantify those processes. We investigated the spatial distribution of isotopologue values of N2O (δ18O, average δ15N, and 15N site preference, SP) in two denitrifying sandy aquifers to study N2O production and reduction and associated isotope effects in groundwater. For the first time, we combined this approach with direct estimation of N2O reduction from excess-N2 analysis. Groundwater samples were collected from 15 monitoring wells and four multilevel sampling wells and analysed for NO3-, dissolved N2O, dissolved O2, excess N2 from denitrification and isotopic signatures of NO3- and N2O. Both aquifers exhibited high NO3- concentrations with average concentrations of 22 and 15 mg N L-1, respectively. Evidence of intense denitrification with associated N2O formation was obtained from mean excess-N2 of 3.5 and 4.3 mg N L-1, respectively. Isotopic signatures of N2O were highly variable with ranges of 17.6-113.2‰ (δ18O), -55.4 to 89.4‰ (δ15Nbulk) and 1.8-97.9‰ (SP). δ15N and δ18O of NO3- ranged from -2.1‰ to 65.5‰ and from -5‰ to 33.5‰, respectively. The relationships between δ15N of NO3-, δ15Nbulk and SP were not in good agreement with the distribution predicted by a Rayleigh-model of isotope fractionation. The large ranges of δ18O and SP of N2O as well as the close correlation between these values could be explained by the fact that N2O reduction to N2 was strongly progressed but variable. We confirm and explain that a large range in SP and δ18O is typical for N2O from denitrifying aquifers, showing that this source signature can be distinguished from the isotopic fingerprint of N2O emitted from soils without water-logging. We conclude that isotopologue values of N2O in our sites were not suitable to quantify production or reduction of N2O or the contribution of different processes to the total N2O flux, apparently because these values were not only governed by individual pathways but eventually also by the spatial distribution of substrates and activity within the aquifers. These observations could be explained by the dynamics of N2O production, reduction and transport in water-saturated systems with heterogenic distribution of microbial activity and by a combination of diffusive and enzymatic isotope effects.

Thermodynamic and hydrochemical controls on CH4 in a coal seam gas and overlying alluvial aquifer: new insights into CH4 origins

PubMed Central

Owen, D. Des. R.; Shouakar-Stash, O.; Morgenstern, U.; Aravena, R.

2016-01-01

Using a comprehensive data set (dissolved CH4, δ13C-CH4, δ2H-CH4, δ13C-DIC, δ37Cl, δ2H-H2O, δ18O-H2O, Na, K, Ca, Mg, HCO3, Cl, Br, SO4, NO3 and DO), in combination with a novel application of isometric log ratios, this study describes hydrochemical and thermodynamic controls on dissolved CH4 from a coal seam gas reservoir and an alluvial aquifer in the Condamine catchment, eastern Surat/north-western Clarence-Moreton basins, Australia. δ13C-CH4 data in the gas reservoir (−58‰ to −49‰) and shallow coal measures underlying the alluvium (−80‰ to −65‰) are distinct. CO2 reduction is the dominant methanogenic pathway in all aquifers, and it is controlled by SO4 concentrations and competition for reactants such as H2. At isolated, brackish sites in the shallow coal measures and alluvium, highly depleted δ2H-CH4 (<310‰) indicate acetoclastic methanogenesis where SO4 concentrations inhibit CO2 reduction. Evidence of CH4 migration from the deep gas reservoir (200–500 m) to the shallow coal measures (<200 m) or the alluvium was not observed. The study demonstrates the importance of understanding CH4 at different depth profiles within and between aquifers. Further research, including culturing studies of microbial consortia, will improve our understanding of the occurrence of CH4 within and between aquifers in these basins. PMID:27578542

Dissolved organic matter reduces CuO nanoparticle toxicity to duckweed in simulated natural systems.

PubMed

Rippner, Devin A; Green, Peter G; Young, Thomas M; Parikh, Sanjai J

2018-03-01

With increasing demand for recycled wastewater for irrigation purposes, there is a need to evaluate the potential for manufactured nanomaterials in waste water to impact crop production and agroecosystems. Copper oxide nanoparticles (CuO NPs) have previously been shown to negatively impact the growth of duckweed (Landoltia punctata) a model aquatic plant consumed by water fowl and widely found in agricultural runoff ditches in temperate climates. However, prior studies involving CuO NP toxicity to duckweed have focused on systems without the presence of dissolved organic matter (DOM). In the current study, duckweed growth inhibition was shown to be a function of aqueous Cu 2+ concentration. Growth inhibition was greatest from aqueous CuCl 2 and, for particles, increased with decreasing CuO particle size. The dissolution of CuO NPs in ½ Hoagland's solution was measured to increase with decreasing particle size and in the presence of Suwannee river humic and fulvic acids (HA; FA). However, the current results suggest that HA, and to a lesser extent, FA, decrease the toxicity of both CuO NPs and free ionized Cu to duckweed, likely by inhibiting Cu availability through Cu-DOM complex formation. Such results are consistent with changes to Cu speciation as predicted by speciation modeling software and suggest that DOM changes Cu speciation and therefore toxicity in natural systems. Copyright © 2017 Elsevier Ltd. All rights reserved.

High-Resolution Experimental Investigation of mass transfer enhancement by chemical oxidation from DNAPL entrapped in variable-aperture fractures

NASA Astrophysics Data System (ADS)

Arshadi, M.; Rajaram, H.; Detwiler, R. L.; Jones, T.

2012-12-01

Permanganate oxidation of DNAPL- contaminated fractured rock is an effective remediation technology. Permanganate ion reacts with dissolved DNAPL in a bi-molecular oxidation-reduction reaction. The consumption of dissolved DNAPL in this reaction results in increased concentration gradients away from the free-phase DNAPL, resulting in reaction-enhanced mass transfer, which accelerates contaminant removal. The specific objective of our research was to perform high-resolution non-intrusive experimental studies of permanganate oxidation in a 15.24 × 15.24 cm, transparent, analog, variable-aperture fracture with complex initial TCE entrapped phase geometry. Our experimental system uses light-transmission techniques to accurately measure both fracture aperture and the evolution of individual entrapped DNAPL blobs during the remediation experiments at high resolution (pixel size : 6.2×10-3 cm). Three experiments were performed with different flow rates and permanganate inflow concentrations to observe DNAPL-permanganate interactions across a broader range of conditions. Prior to initiating each experiment, the aperture field within the fracture was measured. The oxidation experiment was initiated by TCE injection into the water saturated fracture till the TCE reached the outflow end, followed by water re-injection through the fracture. The flowing water mobilized some TCE. We continued injection of water till TCE mobilization ceased, leaving behind the residual TCE entrapped within the variable-aperture fracture. Subsequently, permanganate injection through the fracture resulted in propagation of a fingered reaction front into the fracture. We developed image processing algorithms to analyze the evolution of DNAPL phase geometry over the duration of the experiment. The permanganate consumption rate varied significantly within the fracture due to the complex flow and DNAPL concentration fields. Precipitated MnO2 was clearly evident on the downstream side of DNAPL blobs near the inflow boundary indicating high reaction rates in these regions. This behavior is explained by the diversion of permanganate around entrapped DNAPL blobs and downstream advection of dissolved DNAPL. Our results indicate that the total rate of mass transfer from the DNAPL blobs is higher at early times, when not much MnO2 has formed and precipitated. With time, MnO2 precipitation in the fracture leads to changes the aperture field and flow field. Precipitated MnO2 around TCE blobs also decreases the DNAPL accessible surface area. By comparing the results of three experiments, we conclude that low permanganate concentrations and high flow rates lead to more efficient DNAPL remediation, resulting from the fact that under these conditions there would be slower MnO2 formation and less precipitation within the fracture. We also present results on the time-evolution of fracture-scale permanganate consumption and DNAPL removal rates. The experimental observations are being used to develop improved high-resolution numerical models of reactive transport in variable-aperture fractures. The overall goal is to relate the coupled processes of DNAPL removal, permanganate consumption, MnO2 formation and associated changes in aperture and interface area; to derive fracture-scale effective representations of these processes.

Photochemical-biological treatment of a real industrial biorecalcitrant wastewater containing 5-amino-6-methyl-2-benzimidazolone.

PubMed

Sarria, V; Parra, S; Invernizzi, M; Peringer, P; Pulgarin, C

2001-01-01

5-amino-6-methyl-2-benzimidazolone (AMBI), used in the manufacture of dyes, was characterised as a biorecalcitrant compound by means of different biodegradability tests. In order to enhance the biodegradability of this important pollutant, the application of Advanced Oxidation Process (AOPs) as a pretreatment was explored. Some experiments were addressed to find the most efficient AOP. The systems H2O2/hv, TiO2/H2O2/hv, Fe3+/hv, Fe3+/H2O2 and Fe3+/H2O2/hv were compared. The photo-Fenton system was the most efficient and the optimal conditions (AMBI, Fe3+, H2O2 concentrations) for the degradation of AMBI were found. During the photo-Fenton degradation, experiments were also made to obtain information concerning the evolution of: (a) organic carbon and initial compound concentration; (b) the oxidation state; (c) the toxicity; (d) the biodegradability; and (e) the chemical nature of the intermediates. These analyses show that the solution resulting from the treatment of AMBI is biologically compatible and complete mineralisation can be performed by biological means. A combined photochemical (Fenton) and biological flow reactor for the degradation of AMBI was successfully operated in continuous mode at laboratory scale. 100% of the initial concentration of AMBI and 80.3% of Dissolved Organic Carbon (DOC) were removed in 3.5 hours of total residence time. Finally, some field experiments under direct sunlight carried out at the Plataforma Solar de Almeria, Spain, demonstrated that this solar catalytic system is an effective treatment for this kind of industrial wastewater.

Analysis of dissolved organic carbon concentration and 13C isotopic signature by TOC-IRMS - assessment of analytical performance

NASA Astrophysics Data System (ADS)

Kirkels, Frédérique; Cerli, Chiara; Federherr, Eugen; Kalbitz, Karsten

2013-04-01

Stable carbon isotopes provide a powerful tool to assess carbon pools and their dynamics. Dissolved organic carbon (DOC) has been recognized to play an important role in ecosystem functioning and carbon cycling and has therefore gained increased research interest. However, direct measurement of 13C isotopic signature of carbon in the dissolved phase is technically challenging particularly using high temperature combustion. Until recently, mainly custom-made systems existed which were modified for coupling of TOC instruments with IRMS for simultaneous assessment of C content and isotopic signature. The variety of coupled systems showed differences in their analytical performances. For analysis of DOC high temperature combustion is recognized as best performing method, owing to its high efficiency of conversion to CO2 also for highly refractory components (e.g. humic, fulvic acids) present in DOC and soil extracts. Therefore, we tested high temperature combustion TOC coupled to IRMS (developed by Elementar Group) for bulk measurements of DOC concentration and 13C signature. The instruments are coupled via an Interface to exchange the carrier gas from O2 to He and to concentrate the derived CO2 for the isotope measurement. Analytical performance of the system was assessed for a variety of organic compounds characterized by different stability and complexity, including humic acid and DOM. We tested injection volumes between 0.2-3 ml, thereby enabling measurement of broad concentration ranges. With an injection volume of 0.5 ml (n=3, preceded by 1 discarded injection), DOC and 13C signatures for concentrations between 5-150 mg C/L were analyzed with high precision (standard deviation (SD) predominantly <0.1‰), good accuracy and linearity (overall SD <0.9‰). For the same settings, slightly higher variation in precision was observed among the lower concentration range and depending upon specific system conditions. Differences in 13C signatures of about 50‰ among samples did not affect the precision of the analysis of natural abundance and labeled samples. Natural DOM, derived from different soils and assessed at various concentrations, was measured with similar good analytical performance, and also tested for the effect of freezing and re-dissolving. We found good performance of TOC-IRMS in comparison with other systems capable of determining C concentration and isotopic signatures. We recognize the advantages of this system providing: - High sample throughput, short measurement time (15 minutes), flexible sample volume - Easy maintenance, handling, rapid sample preparation (no pretreatment) This preliminary assessment highlights wide-ranging opportunities for further research on concentrations and isotopic signatures by TOC-IRMS to elucidate the role of dissolved carbon in terrestrial and aquatic systems.

Zn0-CNTs-Fe3O4 catalytic in situ generation of H2O2 for heterogeneous Fenton degradation of 4-chlorophenol.

PubMed

Yang, Zhao; Gong, Xiao-Bo; Peng, Lin; Yang, Dan; Liu, Yong

2018-06-04

A novel Zn 0 -CNTs-Fe 3 O 4 composite was synthesized by the chemical co-precipitation combined with high sintering process at nitrogen atmosphere. The as-prepared composite was characterized by SEM, EDS, XRD, XPS, VSM and N 2 adsorption/desorption experiments. A novel heterogeneous Fenton-like system, composed of Zn 0 -CNTs-Fe 3 O 4 composite and dissolved oxygen (O 2 ) in solution, which can in situ generate H 2 O 2 and OH, was used for the degradation of 4-chlorophenol (4-CP). The influences of various operational parameters, including the initial pH, dosage of Zn 0 -CNTs-Fe 3 O 4 and initial concentration of 4-CP on the removal of 4-CP were investigated. The removal efficiencies of 4-CP and total organic carbon (TOC) were 99% and 57%, respectively, at the initial pH of 1.5, Zn 0 -CNTs-Fe 3 O 4 dosage of 2 g/L, 4-CP initial concentration of 50 mg/L and oxygen flow rate of 400 mL/min. Based on the results of the radical scavenger effect study, the hydroxyl radical was considered as the main reactive oxidants in Zn 0 -CNTs-Fe 3 O 4 /O 2 system and a possible degradation pathway of 4-CP was proposed. Copyright © 2018. Published by Elsevier Ltd.

Assessment of water quality and factors affecting dissolved oxygen in the Sangamon River, Decatur to Riverton, Illinois, summer 1982

USGS Publications Warehouse

Schmidt, A.R.; Stamer, J.K.

1987-01-01

Water quality and processes that affect the dissolved-oxygen concentration in a 45.9 mile reach of the Sangamon River from Decatur to Riverton, Illinois, were determined from data collected during low-flow periods in the summer of 1982. Relations among dissolved oxygen, water discharge, biochemical oxygen demand, ammonia and nitrite plus nitrate concentrations, and photosynthetic-oxygen production were simulated using a one-dimensional, steady-state computer model. Average dissolved oxygen concentrations ranged from 8.0 milligrams per liter at the upstream end of the study reach at Decatur to 5.2 milligrams per liter 12.2 miles downstream. Ammonia concentrations ranged from 45 milligrams per liter at the mouth of Stevens Creek (2.6 miles downstream from Decatur) to 0.03 milligram per liter at the downstream end of the study reach. Un-ionized ammonia concentrations exceeded the maximum concentration specified in the State water quality standard (0.04 milligram per liter) throughout most of the study reach. Model simulations indicated that oxidation of ammonia to form nitrite plus nitrate was the most significant process leading to low dissolved oxygen concentrations in the river. (USGS)

Tidal and spatial variability of nitrous oxide (N2O) in Sado estuary (Portugal)

NASA Astrophysics Data System (ADS)

Gonçalves, Célia; Brogueira, Maria José; Nogueira, Marta

2015-12-01

The estimate of the nitrous oxide (N2O) fluxes is fundamental to assess its impact on global warming. The tidal and spatial variability of N2O and the air-sea fluxes in the Sado estuary in July/August 2007 are examined. Measurements of N2O and other relevant environmental parameters (temperature, salinity, dissolved oxygen and dissolved inorganic nitrogen - nitrate plus nitrite and ammonium) were recorded during two diurnal tidal cycles performed in the Bay and Marateca region and along the estuary during ebb, at spring tide. N2O presented tidal and spatial variability and varied spatially from 5.0 nmol L-1 in Marateca region to 12.5 nmol L-1 in Sado river input. Although the Sado river may constitute a considerable N2O source to the estuary, the respective chemical signal discharge was rapidly lost in the main body of the estuary due to the low river flow during the sampling period. N2O varied with tide similarly between 5.2 nmol L-1 (Marateca) and 10.0 nmol L-1 (Sado Bay), with the maximum value reached two hours after flooding period. The influence of N2O enriched upwelled seawater (˜10.0 nmol L-1) was well visible in the estuary mouth and apparently represented an important contribution of N2O in the main body of Sado estuary. Despite the high water column oxygen saturation in most of Sado estuary, nitrification did not seem a relevant process for N2O production, probably as the concentration of the substrate, NH4+, was not adequate for this process to occur. Most of the estuary functioned as a N2O source, and only Marateca zone has acted as N2O sink. The N2O emission from Sado estuary was estimated to be 3.7 Mg N-N2O yr-1 (FC96) (4.4 Mg N-N2O yr-1, FRC01). These results have implications for future sampling and scaling strategies for estimating greenhouse gases (GHGs) fluxes in tidal ecosystems.

Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments

DOE PAGES

Perdrial, Nicolas; Vázquez-Ortega, Angélica; Wang, Guohui; ...

2017-12-05

Uranium speciation and lability are strongly coupled to mineral transformations in silicate sediments, particularly for sediments subjected to weathering in acidic, high-level radioactive waste, as occurred at the Department of Energy's Hanford (WA) site. Here, uncontaminated Hanford sediments were reacted for 365 days with acidic (pH 3), uranium-bearing waste solutions, with and without phosphate in batch experiments, prior to detailed characterizations using electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. In PO 4-reactant free systems, uranium speciation was controlled initially by precipitation of compreignacite [K 2(UO 2) 6O 4(OH) 6·8H 2O]- and becquerelite [Ca(UO 2) 6O 4(OH) 6·8H 2O]-like species.more » Subsequent further removal of uranium coincided with that of Si and accumulation of boltwoodite, [(K, Na)(UO 2) 2O 4(HSiO 4) 2•0.5(H 2O)]-like species of uranium at 180 and 365 days. When present, PO 4 exerted a direct and strong control over U speciation. Furthermore, the detection of meta-ankoleite, [K 2(UO 2) 2O 4(PO 4) 2·6H 2O] at all reaction times when U was present emphasizes the importance of dissolved phosphate as a control on U speciation. Here, meta-ankoleite appears well crystallized and when it occurs as the principal product of sediment weathering, its low solubility is expected to limit dissolved U(VI) concentrations in groundwater. Although boltwoodite solubility is also low, it is formed more slowly (and only when PO 4 is absent), after initial precipitation of more soluble, less crystalline uranyl hydroxides. In the context of Hanford crib waste our results suggest that with PO 4 present, nearly all uranium would have precipitated in the upper soil.« less

Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perdrial, Nicolas; Vázquez-Ortega, Angélica; Wang, Guohui

Uranium speciation and lability are strongly coupled to mineral transformations in silicate sediments, particularly for sediments subjected to weathering in acidic, high-level radioactive waste, as occurred at the Department of Energy's Hanford (WA) site. In this study, uncontaminated Hanford sediments were reacted for 365 days with acidic (pH 3), uranium-bearing waste solutions, with and without phosphate in batch experiments, prior to detailed characterizations using electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. In PO(4)(-)reactant free systems, uranium speciation was controlled initially by precipitation of compreignacite [K-2(UO2)(6)O-4(OH)(6)center dot 8H(2)O]-and becquerelite [Ca(UO2)(6)O-4(OH)(6)center dot 8H(2)O]-like species. Subsequent further removal of uranium coincided withmore » that of Si and accumulation of boltwoodite, [(K, Na)(UO2)(2)O-4(HSiO4)(2)center dot 0.5(H2O)]-like species of uranium at 180 and 365 days. When present, PO4 exerted a direct and strong control over U speciation. The detection of meta-ankoleite, [K-2(UO2)(2)O-4(PO4)(2)center dot 6H(2)O] at all reaction times when U was present emphasizes the importance of dissolved phosphate as a control on U speciation. Here, meta-ankoleite appears well crystallized and when it occurs as the principal product of sediment weathering, its low solubility is expected to limit dissolved U(VI) concentrations in groundwater. Although boltwoodite solubility is also low, it is formed more slowly (and only when PO4 is absent), after initial precipitation of more soluble, less crystalline uranyl hydroxides. In the context of Hanford crib waste our results suggest that with PO4 present, nearly all uranium would have precipitated in the upper soil.« less

Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perdrial, Nicolas; Vázquez-Ortega, Angélica; Wang, Guohui

Uranium speciation and lability are strongly coupled to mineral transformations in silicate sediments, particularly for sediments subjected to weathering in acidic, high-level radioactive waste, as occurred at the Department of Energy's Hanford (WA) site. Here, uncontaminated Hanford sediments were reacted for 365 days with acidic (pH 3), uranium-bearing waste solutions, with and without phosphate in batch experiments, prior to detailed characterizations using electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. In PO 4-reactant free systems, uranium speciation was controlled initially by precipitation of compreignacite [K 2(UO 2) 6O 4(OH) 6·8H 2O]- and becquerelite [Ca(UO 2) 6O 4(OH) 6·8H 2O]-like species.more » Subsequent further removal of uranium coincided with that of Si and accumulation of boltwoodite, [(K, Na)(UO 2) 2O 4(HSiO 4) 2•0.5(H 2O)]-like species of uranium at 180 and 365 days. When present, PO 4 exerted a direct and strong control over U speciation. Furthermore, the detection of meta-ankoleite, [K 2(UO 2) 2O 4(PO 4) 2·6H 2O] at all reaction times when U was present emphasizes the importance of dissolved phosphate as a control on U speciation. Here, meta-ankoleite appears well crystallized and when it occurs as the principal product of sediment weathering, its low solubility is expected to limit dissolved U(VI) concentrations in groundwater. Although boltwoodite solubility is also low, it is formed more slowly (and only when PO 4 is absent), after initial precipitation of more soluble, less crystalline uranyl hydroxides. In the context of Hanford crib waste our results suggest that with PO 4 present, nearly all uranium would have precipitated in the upper soil.« less

Performance evaluation of different solar advanced oxidation processes applied to the treatment of a real textile dyeing wastewater.

PubMed

Manenti, Diego R; Soares, Petrick A; Silva, Tânia F C V; Módenes, Aparecido N; Espinoza-Quiñones, Fernando R; Bergamasco, Rosângela; Boaventura, Rui A R; Vilar, Vítor J P

2015-01-01

The performance of different solar-driven advanced oxidation processes (AOPs), such as TiO2/UV, TiO2/H2O2/UV, and Fe(2+)/H2O2/UV-visible in the treatment of a real textile effluent using a pilot plant with compound parabolic collectors (CPCs), was investigated. The influence of the main photo-Fenton reaction variables such as iron concentration (20-100 mg Fe(2+) L(-1)), pH (2.4-4.5), temperature (10-50 °C), and irradiance (22-68 WUV m(-2)) was evaluated in a lab-scale prototype using artificial solar radiation. The real textile wastewater presented a beige color, with a maximum absorbance peak at 641 nm, alkaline pH (8.1), moderate organic content (dissolved organic carbon (DOC) = 129 mg C L(-1) and chemical oxygen demand (COD) = 496 mg O2 L(-1)), and high conductivity mainly associated to the high concentration of chloride (1.1 g Cl(-) L(-1)), sulfate (0.4 g SO 4 (2 -) L(- 1)), and sodium (1.2 g Na(+) L(-1)) ions. Although all the processes tested contributed to complete decolorization and effective mineralization, the most efficient process was the solar photo-Fenton with an optimum catalyst concentration of 60 mg Fe(2+) L(-1), leading to 70 % mineralization (DOCfinal = 41 mg C L(-1); CODfinal < 150 mg O2 L(-1)) at pH 3.6, requiring a UV energy dose of 3.5 kJUV L(-1) (t 30 W = 22.4 min; [Formula: see text]; [Formula: see text]) and consuming 18.5 mM of H2O2.

Sediment-water fluxes of dissolved inorganic carbon, O2,nutrients, and N2 from the hypoxic region of the Louisianacontinental shelf

EPA Science Inventory

Sediment fluxes of dissolved inorganic carbon (DIC), O2, nutrients, and N2 (denitrification) were measured on the Louisiana Continental Shelf during six cruises from 2005 to 2007. On each cruise, three to seven stations were occupied in regions of the shelf that experience summer...

Effect of iron on inhibition of acid demineralisation of bovine dental enamel in vitro.

PubMed

Buzalaf, Marília Afonso Rabelo; de Moraes Italiani, Flávia; Kato, Melissa Thiemi; Martinhon, Cleide Cristina Rodrigues; Magalhães, Ana Carolina

2006-10-01

Iron ions (Fe(2+)) have been shown to be cariostatic in many studies particularly by their ability to reduce bacterial metabolism. Nevertheless, the role of iron ions on dissolution of enamel is unexplored. The aim of the present study was therefore to investigate the protective effect of increasing concentrations (0-120mmol/L) of Fe(2+) on the dissolution of enamel. Enamel powder was subjected to acetic acid made with increasing concentrations with respect to FeSO(4)x7H(2)O. In order to determine the amount of enamel dissolved, the phosphate released in the medium was analysed spectrophotometrically using the Fiske-Subarrow method. Data were tested using Kruskall-Wall and Dunn's tests (p<0.05). The degree of protection was found to approach maximum at about 15mmol/L Fe(2+). Higher concentrations of Fe(2+) did not have an extra effect on inhibition of dissolution of enamel powder. In the next step, the protective effect of 15mmol/L Fe(2+) against mineral dissolution of the bovine enamel was evaluated using a simple abiotic model system. Enamel blocks were exposed to a sequence of seven plastic vials, each containing 1mL of 10mmol/L acetic acid. The acid in vial 4 was made 15mmol/L with respect to FeSO(4)x7H(2)O. The mineral dissolved during each challenge was thus determined by phosphate released as described above. Data were tested using two-way ANOVA (p<0.05). Lower demineralisation (around 45%) was found in vial 4 (with Fe) that continued stable until vial 7. Thus, our data suggest that Fe(2+) can be effective on inhibition of dissolution of enamel and that this effect may be durable.

Kinetics of Microbial Reduction of Solid Phase U(VI)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chongxuan; Jeon, Byong Hun; Zachara, John M.

2006-10-01

Sodium boltwoodite (NaUO2SiO3OH ?1.5H2O) was used to assess the kinetics of microbial reduction of solid phase U(VI) by a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1. The bioreduction kinetics was studied with Na-boltwoodite in suspension or within alginate beads. Concentrations of U(VI)tot and cell number were varied to evaluate the coupling of U(VI) dissolution, diffusion, and microbial activity. Batch experiments were performed in a non-growth medium with lactate as electron donor at pH 6.8 buffered with PIPES. Microscopic and spectroscopic analyses with transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and laser-induced fluorescence spectroscopy (LIFS) collectively indicated that solidmore » phase U(VI) was first dissolved and diffused out of grain interiors before it was reduced on bacterial surfaces and/or within the periplasm. The kinetics of solid phase U(VI) bioreduction was well described by a coupled model of bicarbonate-promoted dissolution of Na-boltwoodite, intraparticle uranyl diffusion, and Monod type bioreduction kinetics with respect to dissolved U(VI) concentration. The results demonstrated the intimate coupling of biological, chemical, and physical processes in microbial reduction of solid phase U(VI).« less

Effect of soil organic matter content and pH on the toxicity of ZnO nanoparticles to Folsomia candida.

PubMed

Waalewijn-Kool, Pauline L; Rupp, Svenja; Lofts, Stephen; Svendsen, Claus; van Gestel, Cornelis A M

2014-10-01

Organic matter (OM) and pH may influence nanoparticle fate and effects in soil. This study investigated the influence of soil organic matter content and pH on the toxicity of ZnO-NP and ZnCl2 to Folsomia candida in four natural soils, having between 2.37% and 14.7% OM and [Formula: see text] levels between 5.0 and 6.8. Porewater Zn concentrations were much lower in ZnO-NP than in ZnCl2 spiked soils, resulting in higher Freundlich sorption constants for ZnO-NP. For ZnCl2 the porewater Zn concentrations were significantly higher in less organic soils, while for ZnO-NP the highest soluble Zn level (23mgZn/l) was measured in the most organic soil, which had the lowest pH. Free Zn(2+) ion concentrations were higher for ZnCl2 than for ZnO-NP and were greatly dependent on pH (pHpw) and dissolved organic carbon content of the pore water. The 28-d EC50 values for the effect of ZnCl2 on the reproduction of F. candida increased with increasing OM content from 356 to 1592mgZn/kg d.w. For ZnO-NP no correlation between EC50 values and OM content was found and EC50 values ranged from 1695 in the most organic soil to 4446mgZn/kg d.w. in the higher pH soil. When based on porewater and free Zn(2+) concentrations, EC50 values were higher for ZnCl2 than for ZnO-NP, and consistently decreased with increasing pHpw. This study shows that ZnO-NP toxicity is dependent on soil properties, but is mainly driven by soil pH. Copyright © 2014 Elsevier Inc. All rights reserved.

Process for the removal of acid forming gases from exhaust gases and production of phosphoric acid

DOEpatents

Chang, Shih-Ger; Liu, David K.

1992-01-01

Exhaust gases are treated to remove NO or NO.sub.x and SO.sub.2 by contacting the gases with an aqueous emulsion or suspension of yellow phosphorous preferably in a wet scrubber. The addition of yellow phosphorous in the system induces the production of O.sub.3 which subsequently oxidizes NO to NO.sub.2. The resulting NO.sub.2 dissolves readily and can be reduced to form ammonium ions by dissolved SO.sub.2 under appropriate conditions. In a 20 acfm system, yellow phosphorous is oxidized to yield P.sub.2 O.sub.5 which picks up water to form H.sub.3 PO.sub.4 mists and can be collected as a valuable product. The pressure is not critical, and ambient pressures are used. Hot water temperatures are best, but economics suggest about 50.degree. C. The amount of yellow phosphorus used will vary with the composition of the exhaust gas, less than 3% for small concentrations of NO, and 10% or higher for concentrations above say 1000 ppm. Similarly, the pH will vary with the composition being treated, and it is adjusted with a suitable alkali. For mixtures of NO.sub.x and SO.sub.2, alkalis that are used for flue gas desulfurization are preferred. With this process, better than 90% of SO.sub.2 and NO in simulated flue gas can be removed. Stoichiometric ratios (P/NO) ranging between 0.6 and 1.5 were obtained.

Biogeochemistry of the sulfur oxidizer Thiomicrospira thermophila

NASA Astrophysics Data System (ADS)

Houghton, J.; Fike, D. A.; Wills, E.; Foustoukos, D.

2013-12-01

Near-seafloor hydrothermal environments such as diffuse flow venting or subsurface mixing are characterized by rapidly changing conditions and steep chemical and thermal gradients. Microorganisms living in these environments can take advantage of these changes by switching among metabolic pathways rather than specializing. We present reaction stoichiometry and rates for T. thermophila grown in a closed system both at ambient and elevated pressure (50 bars) that demonstrate substantial metabolic flexibility, shifting between up to 5 different sulfur cycling reactions over a 24 hour period. Based on the stoichiometry between S2O3 consumed and SO4 produced, three reactions are sulfur oxidation and two are disproportionation, which has not previously been demonstrated for Thiomicrospira strains. Reactants include S2O3, elemental S (both polymeric S chains and S8 rings), HS-, and O2, while products include polymeric elemental S, SO4, HS-, and polysulfides. The presence of μmolal concentrations of HS- has been confirmed during the time series only when stoichiometry predicts disproportionation. Production of HS- in the presence of elemental S results in abiotic conversion to polysulfides, keeping the sulfide concentrations low in solution. The transition from oxidation to disproportionation appears to be triggered by a depletion in dissolved oxygen and the rate of reaction is a second order function of S2O3 and O2 concentrations. Growth was tested at conditions spanning their pH tolerance (5.0 - 8.0) using a citrate buffer (pH 5.0), unbuffered media (initial pH 7.0), and Tris buffer (pH 8.0). The highest rates are observed at pH 8.0 with rates decreasing as a function of pH. The lowest rate occurs at pH 5.0 and exhibits pseudo-first order behavior over a 24 hour period, likely due to a long lag and very slow growth. Repeat injections after the culture is acclimated to the experimental conditions result in very high pseudo-first order rates due to rapid consumption of all available thiosulfate prior to oxygen depletion. Results from high-pressure closed system experiments (at 50 bars, buffered at pH 5.0) exhibit comparable rates to the corresponding ambient pressure condition. Future work will address the effect of dissolved O2 on sulfur disproportionation using continuous culturing of T. thermophila at deep-sea pressure conditions (>200 bar).

Evaluating the spatial variation of total mercury in young-of-year yellow perch (Perca flavescens), surface water and upland soil for watershed-lake systems within the southern Boreal Shield.

PubMed

Gabriel, Mark C; Kolka, Randy; Wickman, Trent; Nater, Ed; Woodruff, Laurel

2009-06-15

The primary objective of this research is to investigate relationships between mercury in upland soil, lake water and fish tissue and explore the cause for the observed spatial variation of THg in age one yellow perch (Perca flavescens) for ten lakes within the Superior National Forest. Spatial relationships between yellow perch THg tissue concentration and a total of 45 watershed and water chemistry parameters were evaluated for two separate years: 2005 and 2006. Results show agreement with other studies where watershed area, lake water pH, nutrient levels (specifically dissolved NO(3)(-)-N) and dissolved iron are important factors controlling and/or predicting fish THg level. Exceeding all was the strong dependence of yellow perch THg level on soil A-horizon THg and, in particular, soil O-horizon THg concentrations (Spearman rho=0.81). Soil B-horizon THg concentration was significantly correlated (Pearson r=0.75) with lake water THg concentration. Lakes surrounded by a greater percentage of shrub wetlands (peatlands) had higher fish tissue THg levels, thus it is highly possible that these wetlands are main locations for mercury methylation. Stepwise regression was used to develop empirical models for the purpose of predicting the spatial variation in yellow perch THg over the studied region. The 2005 regression model demonstrates it is possible to obtain good prediction (up to 60% variance description) of resident yellow perch THg level using upland soil O-horizon THg as the only independent variable. The 2006 model shows even greater prediction (r(2)=0.73, with an overall 10 ng/g [tissue, wet weight] margin of error), using lake water dissolved iron and watershed area as the only model independent variables. The developed regression models in this study can help with interpreting THg concentrations in low trophic level fish species for untested lakes of the greater Superior National Forest and surrounding Boreal ecosystem.

Development of copper recovery process from flotation tailings by a combined method of high‒pressure leaching‒solvent extraction.

PubMed

Han, Baisui; Altansukh, Batnasan; Haga, Kazutoshi; Stevanović, Zoran; Jonović, Radojka; Avramović, Ljiljana; Urosević, Daniela; Takasaki, Yasushi; Masuda, Nobuyuki; Ishiyama, Daizo; Shibayama, Atsushi

2018-06-15

Sulfide copper mineral, typically Chalcopyrite (CuFeS 2 ), is one of the most common minerals for producing metallic copper via the pyrometallurgical process. Generally, flotation tailings are produced as a byproduct of flotation and still consist of un‒recovered copper. In addition, it is expected that more tailings will be produced in the coming years due to the increased exploration of low‒grade copper ores. Therefore, this research aims to develop a copper recovery process from flotation tailings using high‒pressure leaching (HPL) followed by solvent extraction. Over 94.4% copper was dissolved from the sample (CuFeS 2 as main copper mineral) by HPL in a H 2 O media in the presence of pyrite, whereas the iron was co‒dissolved with copper according to an equation given as C Cu  = 38.40 × C Fe . To avoid co‒dissolved iron giving a negative effect on the subsequent process of electrowinning, solvent extraction was conducted on the pregnant leach solution for improving copper concentration. The result showed that 91.3% copper was recovered in a stripped solution and 98.6% iron was removed under the optimal extraction conditions. As a result, 86.2% of copper was recovered from the concentrate of flotation tailings by a proposed HPL‒solvent extraction process. Copyright © 2018 Elsevier B.V. All rights reserved.

Geo- and biogeochemical processes in a heliothermal hypersaline lake

NASA Astrophysics Data System (ADS)

Zachara, John M.; Moran, James J.; Resch, Charles T.; Lindemann, Stephen R.; Felmy, Andrew R.; Bowden, Mark E.; Cory, Alexandra B.; Fredrickson, James K.

2016-05-01

Water chemical variations were investigated over three annual hydrologic cycles in hypersaline, heliothermal, meromictic Hot Lake in north-central Washington State, USA. The lake contains diverse biota with dramatic zonation related to salinity and redox state. Water samples were collected at 10-cm depth intervals through the shallow lake (2.4 m) during 2012-2014, with comprehensive monitoring performed in 2013. Inorganic salt species, dissolved carbon forms (DOC, DIC), oxygen, sulfide, and methane were analyzed in lake water samples. Depth sonde measurements of pH and temperature were also performed to track their seasonal variations. A bathymetric survey of the lake was conducted to enable lake water volume and solute inventory calculations. Sediment cores were collected at low water and analyzed by X-ray diffraction to investigate sediment mineralogy. The primary dissolved salt in Hot Lake water was Mg2+-SO42- whereas sediments were dominated by gypsum (CaSO4·2H2O). Lake water concentrations increased with depth, reaching saturation with epsomite (MgSO4·7H2O) that was exposed at lake bottom. At maximum volume in spring, Hot Lake exhibited a relatively dilute mixolimnion; a lower saline metalimnion with stratified oxygenic and anoxygenic photosynthetic microbiological communities; and a stable, hypersaline monimolimnion, separated from above layers by a chemocline, containing high levels of sulfide and methane. The thickness of the mixolimnion regulates a heliothermal effect that creates temperatures in excess of 60 °C in the underlying metalimnion and monimolimnion. The mixolimnion was dynamic in volume and actively mixed. It displayed large pH variations, in-situ calcium carbonate precipitation, and large evaporative volume losses. The depletion of this layer by fall allowed deeper mixing into the metalimnion, more rapid heat exchange, and lower winter lake temperatures. Solubility calculations indicate seasonal biogenic and thermogenic aragonite precipitation in the mixolimnion and metalimnion, but the absence of calcareous sediments at depth suggests dissolution and recycling during winter months. Dissolved carbon concentrations [dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC)] increased with depth, reaching ∼0.04 mol/L at the metalimnion-monimolimnion boundary. DIC concentrations were seasonally variable in the mixolimnion and metalimnion, and were influenced by calcium carbonate precipitation. DOC concentrations mimicked those of conservative salts (e.g., Na+-Cl-) in the mixolimnion and metalimnion, but decreased in the monimolimnion where mass loss by anaerobic microbial processes is implied. Biogenic reduced solutes originating in monimolimnion (H2S and CH4) were biologically oxidized in the metalimnion as they were not observed in more shallow lake waters. Multi-year solute inventory calculations indicated that Hot Lake is a stable, albeit seasonally and annually dynamic feature, with inorganic solutes cycled between lake waters and sediments depending on annual recharge, temperature, and lake water dilution state. With its extreme geochemical and thermal regime, Hot Lake functions as analog of early earth and extraterrestrial life environments.

Water-quality conditions and streamflow gain and loss of the South Prong of Spavinaw Creek basin, Benton County, Arkansas

USGS Publications Warehouse

Joseph, Robert L.; Green, W. Reed

1994-01-01

A study of the South Prong of Spavinaw Creek Basin conducted baween July 14 and July 23. 1993. described the surface- and ground-water quality of the basin and the streamflow gain and loss. Water samples were collected from 10 sites on the mainstem of the South Prong of Spavinaw Creek and from 4 sites on tributaries during periods of low to moderate streamflow (less than 11 cubic feet per second). Water samples were collected from 4 wells and 10 springs located in the basin. In 14 surface-water samples, nitrite plus nitrate concentrations ranged from 0.75 to 4.2 milligrams per liter as nitrogen (mg/L). Orthophosphorus concentrations ranged from 0 03 to O. 15 mg/L as phosphorus. Fecal coliform bacteria counts ranged from 61 to 1,400 colonies per 100 milliliters (col/lOO mL), with a median of 120 col/100 mL. Fecal streptococci bacteria counts ranged from 70 to greater than 2,000 col/100 mL with a median of 185 col/lOO mL. Analysis for selected metals collected at one surface-water sites indicates that concentrations were usually below the reporting limit. Diel dissolved oxygen concentrations and temperatures were measured at an upstream and downstream site on the mainstem of the stream. At the upstream site, dissolved oxygen concentrations ranged from 7.2 to 83 mg/L and temperatures ranged from 15.5 to 17.0 C. Dissolved oxygen concentrations were higher and temperature values were lower at lhe upstream site, which is located close to two springs that produce all of the flow at that site. Dissolved nitrite plus nitrate was present in all four wells sampled in the basin with concentrations ranging from 0.04 to 3.5 mg/L as nitrogen. Orthophosphorus was present in concentrations ranging from less than 0.01 to 0.07 mg/L as phosphorus. Volatile organic compound analyses in two wells indicate that toluene was present in both wells and chloroform was present in one well. All other volatile organic compounds were found to be below the reporting limits. Analysis for common constituents and selected metals indicated that fluoride concentrations in one well exceeded the U.S. Environmental Protection Agency's primary maximum contamination levels for drinking water. Analyses of water samples collected from springs indicate that nitrite plus nitrate concen- trations ranged from 0.43 to 3.9 mg/L as nitrogen. Dissolved ammonia plus organic nitrogen concentrations ranged from less than 0.20 to 0.64 mg/L as nitrogen. Dissolved ammonia plus organic nitrogen concentrations ranged from less than 0.20 to 0.64 mg/L at nitrogen. Orthophosphorus concentrations ranged from 0.02 to 0.09 mg/L as phosphorus. Fecal coliform bacteria counts ranged from less than 3 to more than 2,000 col/100 mL, with a median of 370 col/100 mL. Fecal streptococci bacteria counts ranged from less than 4 to greater than 2,000 col/100 mL with a median of 435 col/100 mL. Streamflow in nine reaches of the mainstream increased an average of 20 percent. Six losing reaches were identified during the study, one located on the mainstem and the other five located on tributaries to the mainstem.

Direct oxygen removal technique for recycling titanium using molten MgCl2 salt.

PubMed

Okabe, Toru H; Hamanaka, Yuki; Taninouchi, Yu-Ki

2016-08-15

Deoxidation of Ti, or direct removal of O dissolved in metallic Ti, is known to be extremely difficult when Mg is used as the deoxidizing agent. This difficulty arises because the chemical potential of O2, pO2, under Mg/MgO equilibrium is high (approximately 10(-41) atm at 1200 K) and is equivalent to that of Ti containing ∼2 mass% O at 1200 K. Therefore, when deoxidizing Ti to the commercial level of high-grade pure Ti (below 0.05 mass% O) using an Mg reductant at 1200 K, the activity of the reaction product MgO (aMgO) must be decreased to below ∼0.025, which is difficult in practice. In this study, the removal of O in Ti in molten MgCl2 salt using an electrochemical technique was examined at ∼1173 K with the objective of obtaining Ti containing less than 0.05 mass% O. Ti samples and graphite electrodes immersed in molten MgCl2 served as the cathode and anode, respectively. A constant voltage was applied between the electrodes using an external DC source. Molten MgCl2 was employed to produce the deoxidizing agent Mg and to facilitate deoxidation of Ti by decreasing the activity of the reaction product MgO. By applying a voltage of approximately 3.1 V between the electrodes, the chemical potential of Mg in the molten MgCl2 was increased at the surface of the Ti cathode, and the Ti samples were deoxidized. The resulting O species, mainly formed O(2-) dissolved in the molten MgCl2, was removed from the molten salt by reacting with the C anode to form CO (or CO2) gas. Ti wires containing 0.12 mass% O were deoxidized to less than 0.02 mass% O. In some cases, the O concentration in the Ti samples was reduced to the level of 0.01 mass%, which cannot be accomplished using the conventional Kroll process. The possible application of this deoxidation technique to practical industrial recycling processes is discussed.

Electrolysis of Titanium Oxide to Titanium in Molten Cryolite Salt

NASA Astrophysics Data System (ADS)

Yan, Bennett Chek Kin

Cost-effective production of titanium is becoming a challenge being tackled in the metallurgical and sustainability sector and technological advancements are required to effectively separate the metal from its oxide. The existing methods of Ti production are extremely energy intensive and slow. This proof-of-concept study investigated the feasibility of separating and capturing Ti from TiO2 through electrolysis after it has been dissolved in a cryolite bath at 1050°C. XRD and SEM/EDS results verified that TiO 2 is only partially reduced. However, addition of Al assisted in the precipitation of Ti in the form of TiAl and TiAl3. Parameters such as electrolysis time, concentration of TiO2, and electrolysis potential were explored. The experiments that were run for 4h, with TiO2 <15wt% of the total bath gave promising results as there was intermetallic formation without the excessive evaporation of cryolite.

Detection of gain enhancement in laser-induced fluorescence of rhodamine B lasing dye by silicon dioxide nanostructures-coated cavity

NASA Astrophysics Data System (ADS)

Al-Tameemi, Mohammed N. A.

2018-03-01

In this work, nanostructured silicon dioxide films are deposited by closed-field unbalanced direct-current (DC) reactive magnetron sputtering technique on two sides of quartz cells containing rhodamine B dye dissolved in ethanol with 10‒5 M concentration as a random gain medium. The preparation conditions are optimized to prepare highly pure SiO2 nanostructures with a minimum particle size of about 20 nm. The effect of SiO2 films as external cavity for the random gain medium is determined by the laser-induced fluorescence of this medium, and an increase of about 200% in intensity is observed after the deposition of nanostructured SiO2 thin films on two sides of the dye cell.

Zinc oxide nanoparticle toxicity in embryonic zebrafish: Mitigation with different natural organic matter.

PubMed

Kteeba, Shimaa M; El-Adawi, Hala I; El-Rayis, Osman A; El-Ghobashy, Ahmed E; Schuld, Jessica L; Svoboda, Kurt R; Guo, Laodong

2017-11-01

Exposure experiments were conducted to evaluate the influence of dissolved organic matter (DOM) on the toxicity of ZnO-NPs (10-30 nm) and dissolved Zn at sub-lethal doses (50 and 5 ppm, respectively) to zebrafish (Danio rerio). Humic acid, alginic acid, bovine serum albumin and various natural DOM isolated from rivers as the Milwaukee River-WI (NOMW), Yukon River-AK (NOMA) and Suwannee River-GA DOM (NOMS) were used to represent humic substances (HA), carbohydrates (CHO), proteins (PTN), and natural organic matter (NOM), respectively. Initial experiments were carried out to confirm the toxic effect of ZnO-NPs at 50 ppm, followed by mitigation experiments with different types and concentrations of DOM (0.4-40 mg-C/L). Compared to 0% hatch of 50 ppm ZnO-NPs exposed embryos at 72 h post fertilization (hpf), NOMS, NOMW and HA had the best mitigative effects on hatching (53-65%), followed by NOMA, CHO and PTN (19-35%); demonstrating that the mitigation effects on ZnO-NPs toxicity were related to DOM's quantity and composition. At 96 hpf, 20% of embryos exposed to 50 ppm ZnO-NPs hatched, 100% of embryos reared in embryo medium hatched, and close to 100% of the embryos hatched upon mitigation, except for those mitigated with PTN which had less effect. Dissolved Zn (5 ppm) also exhibited the same toxicity on embryos as ZnO-NPs (50 ppm). However, in the presence of HA, NOM and CHO, the hatching rates at 72 and 96 hpf increased significantly compared to 5% hatch without DOM. The overall mitigation effects produced by DOM followed the order of HA ≥ NOMS > NOM (A&W) > CHO > PTN, although specific mitigation effects varied with DOM concentration and functionalities. Our results also indicate that the toxicity of ZnO-NPs to embryos was mostly derived from NPs although dissolved Zn released from ZnO-NPs also interacted with embryos, affecting hatching, but to a less extent. Copyright © 2017 Elsevier Ltd. All rights reserved.

Seasonal and flow-driven dynamics of particulate and dissolved mercury and methylmercury in a stream impacted by an industrial mercury source

DOE PAGES

Riscassi, Ami; Miller, Carrie; Brooks, Scott

2015-11-17

Sediments and floodplain soils in the East Fork Poplar Creek watershed (Oak Ridge, TN, USA) are contaminated with high levels of mercury (Hg) from an industrial source at the headwaters. Although baseflow conditions have been monitored, concentrations of Hg and methylmercury (MeHg) during high-flow storm events, when the stream is more hydrologically connected to the floodplain, have yet to be assessed. This paper evaluated baseflow and event-driven Hg and MeHg dynamics in East Fork Poplar Creek, 5 km upstream of the confluence with Poplar Creek, to determine the importance of hydrology to in-stream concentrations and downstream loads and to ascertainmore » whether the dynamics are comparable to those of systems without an industrial Hg source. Particulate Hg and MeHg were positively correlated with discharge (r 2 = 0.64 and 0.58, respectively) and total suspended sediment (r 2 = 0.97 and 0.89, respectively), and dissolved Hg also increased with increasing flow (r 2 = 0.18) and was associated with increases in dissolved organic carbon (r 2 = 0.65), similar to the dynamics observed in uncontaminated systems. Dissolved MeHg decreased with increases in discharge (r 2 = 0.23) and was not related to dissolved organic carbon concentrations (p = 0.56), dynamics comparable to relatively uncontaminated watersheds with a small percentage of wetlands (<10%). Finally, although stormflows exert a dominant control on particulate Hg, particulate MeHg, and dissolved Hg concentrations and loads, baseflows were associated with the highest dissolved MeHg concentration (0.38 ng/L) and represented the majority of the annual dissolved MeHg load.« less

Effect of salinity on the precipitation of dissolved metals in the wastewater that produced during fly ash disposal

NASA Astrophysics Data System (ADS)

Lv, Lina; Yang, Yanling; Tian, Junguo; Li, Yaojian; Li, Jun; Yan, Shengjun

2018-02-01

In this study, a salinity wastewater was produced during the fly ash treatment in the waste incineration plant. Chemical precipitation method was applied for heavy metals removal in the salinity wastewater. The effect of salinity on the removal of dissolved heavy metal ions (Zn2+, Cu2+, Pb2+, Ni2+ and Cd2+) was studied, especially on the removal of Pb2+ and Cd2+. Because of the formation of [PbCl3]- and [PbCl4]2- complexes, the residual concentration of dissolved Pb2+ increased from 0.02 mg/L to 4.08 mg/L, as the NaCl concentration increased from 0 % to 10 %. And the residual concentration of dissolved Cd2+ increased from 0.02 mg/L to 1.39 mg/L, due to the formation of [CdCl3]-, [CdCl4]2- and [CdCl6]4- complexes.

Catchment tracers reveal discharge, recharge and sources of groundwater-borne pollutants in a novel lake modelling approach

NASA Astrophysics Data System (ADS)

Kristensen, Emil; Madsen-Østerbye, Mikkel; Massicotte, Philippe; Pedersen, Ole; Markager, Stiig; Kragh, Theis

2018-02-01

Groundwater-borne contaminants such as nutrients, dissolved organic carbon (DOC), coloured dissolved organic matter (CDOM) and pesticides can have an impact the biological quality of lakes. The sources of pollutants can, however, be difficult to identify due to high heterogeneity in groundwater flow patterns. This study presents a novel approach for fast hydrological surveys of small groundwater-fed lakes using multiple groundwater-borne tracers. Water samples were collected from the lake and temporary groundwater wells, installed every 50 m within a distance of 5-45 m to the shore, were analysed for tracer concentrations of CDOM, DOC, total dissolved nitrogen (TDN, groundwater only), total nitrogen (TN, lake only), total dissolved phosphorus (TDP, groundwater only), total phosphorus (TP, lake only), δ18O / δ16O isotope ratios and fluorescent dissolved organic matter (FDOM) components derived from parallel factor analysis (PARAFAC). The isolation of groundwater recharge areas was based on δ18O measurements and areas with a high groundwater recharge rate were identified using a microbially influenced FDOM component. Groundwater discharge sites and the fractions of water delivered from the individual sites were isolated with the Community Assembly via Trait Selection model (CATS). The CATS model utilized tracer measurements of TDP, TDN, DOC and CDOM from the groundwater samples and related these to the tracer measurements of TN, TP, DOC and CDOM in the lake. A direct comparison between the lake and the inflowing groundwater was possible as degradation rates of the tracers in the lake were taken into account and related to a range of water retention times (WRTs) of the lake (0.25-3.5 years in 0.25-year increments). These estimations showed that WRTs above 2 years required a higher tracer concentration of inflowing water than found in any of the groundwater wells around the lake. From the estimations of inflowing tracer concentration, the CATS model isolated groundwater discharge sites located mainly in the eastern part of the lake with a single site in the southern part. Observations from the eastern part of the lake revealed an impermeable clay layer that promotes discharge during heavy precipitation events, which would otherwise be difficult to identify using traditional hydrological methods. In comparison to the lake concentrations, high tracer concentrations in the southern part showed that only a smaller fraction of water could originate from this area, thereby confirming the model results. A Euclidean cluster analysis of δ18O isotopes identified recharge sites corresponding to areas adjacent to drainage channels, and a cluster analysis of the microbially influenced FDOM component C4 further identified five sites that showed a tendency towards high groundwater recharge rate. In conclusion, it was found that this methodology can be applied to smaller lakes within a short time frame, providing useful information regarding the WRT of the lake and more importantly the groundwater recharge and discharge sites around the lake. Thus, it is a tool for specific management of the catchment.

Characterization, Cytotoxicity, and Genotoxicity of TiO2 and Folate-Coupled Chitosan Nanoparticles Loading Polyprenol-Based Nanoemulsion.

PubMed

Tao, Ran; Wang, Chengzhang; Zhang, Changwei; Li, WenJun; Zhou, Hao; Chen, Hongxia; Ye, Jianzhong

2018-07-01

The structure and bioactivity of Ginkgo biloba leaves polyprenol (GBP) are similar to that of dolichol which widely exists in human and mammalian organs. GBP possesses potential pharmacological activities against cancer. This study involved oil-in-water type nanoemulsion (NE) loading GBP was prepared by dissolving polyprenol in nanoemulsion of sodium tripolyphosphate (TPP)/TiO 2 solution, Triton X-100, and 1-octanol by inversed-phase emulsification (EIP) and ultrasonic emulsification (UE) method. Folic acid (FA)-coupled chitosan (CS) nanoparticles (NPs), GBP-FA-CS-NPs and GBP-TiO 2 -FA-CS-NPs, were fabricated by ionic cross-linking of positively charged FA-CS conjugates and negatively charged nanoemulsion with TPP/TiO 2 . And characterizations of them were investigated by TEM, SEM, FTIR, particle size, and zeta potential. The cytotoxic and genotoxic effects of GBP-TiO 2 -FA-CS-NP treatment were higher than GBP-NE, GBP-FA-CS-NPs, TiO 2 -NE, GBP-TiO 2 -NE, TiO 2 -FA-CS-NPs, and GBP-TiO 2 -FA-CS-NP treatment at the same tested concentrations in HepG2 cells. GBP-TiO 2 -FA-CS-NPs at low TiO 2 concentration (from 1 to 2.5 μg/ml) showed good inhibition capacity on HepG2 cells and low cytotoxic and genotoxic effects on HL-7702 cells. The possible mechanism of cytotoxicity on GBP-TiO 2 -FA-CS-NPs against HepG2 cells is by preventing excessive intracellular Ca 2+ into extracellular spaces via inhibiting Ca 2+ -ATPase and Ca 2+ /Mg 2+ -ATPase.

A dissolved cobalt plume in the oxygen minimum zone of the eastern tropical South Pacific

NASA Astrophysics Data System (ADS)

Hawco, Nicholas J.; Ohnemus, Daniel C.; Resing, Joseph A.; Twining, Benjamin S.; Saito, Mak A.

2016-10-01

Cobalt is a nutrient to phytoplankton, but knowledge about its biogeochemical cycling is limited, especially in the Pacific Ocean. Here, we report sections of dissolved cobalt and labile dissolved cobalt from the US GEOTRACES GP16 transect in the South Pacific. The cobalt distribution is closely tied to the extent and intensity of the oxygen minimum zone in the eastern South Pacific with highest concentrations measured at the oxycline near the Peru margin. Below 200 m, remineralization and circulation produce an inverse relationship between cobalt and dissolved oxygen that extends throughout the basin. Within the oxygen minimum zone, elevated concentrations of labile cobalt are generated by input from coastal sources and reduced scavenging at low O2. As these high cobalt waters are upwelled and advected offshore, phytoplankton export returns cobalt to low-oxygen water masses underneath. West of the Peru upwelling region, dissolved cobalt is less than 10 pM in the euphotic zone and strongly bound by organic ligands. Because the cobalt nutricline within the South Pacific gyre is deeper than in oligotrophic regions in the North and South Atlantic, cobalt involved in sustaining phytoplankton productivity in the gyre is heavily recycled and ultimately arrives from lateral transport of upwelled waters from the eastern margin. In contrast to large coastal inputs, atmospheric deposition and hydrothermal vents along the East Pacific Rise appear to be minor sources of cobalt. Overall, these results demonstrate that oxygen biogeochemistry exerts a strong influence on cobalt cycling.

Transport of nitrate in the Mississippi river in July-August 1999

USGS Publications Warehouse

Kendall, Carol; Böhlke, John Karl; McMahon, Peter B.; Coupe, Richard H.; Battaglin, William A.

2013-01-01

Lagrangian sampling was conducted on the Mississippi River in late July through early August 1999 to test the hypothesis that nitrate (NO3-) is transported conservatively in the Mississippi River. Three different approaches were pursued to test the hypothesis: (1) a mass balance for NO3 was evaluated for evidence of net gains and losses, (2) stable isotopes of NO3 were measured (δ15N and δ18O) to determine if fractionation occurred, and (3) the concentrations of dissolved gases (N2O, N2 and Ar) in river water were measured and compared to theoretical equilibrium concentrations. Integrated water samples and flow measurements were obtained at 10 sites on the Mississippi River and 7 sites near the mouths of major tributaries from northern Iowa to southern Louisiana, a distance of about 2,250 river kilometers. Mass balance calculations indicate that more than 80 percent of the NO3 mass discharged from the Mississippi River (1,930 metric tons/day) during the study period originated in the first 500 river kilometers of the study reach. The mass balance calculations alsoindicate that NO3- was not lost from the water column upstream of Vicksburg, MS, but that there might have been some loss of NO3- in the lower 700 kilometers ofthe study reach. The stable isotope ratios of N and O (δ15N and δ18O) of NO3- were consistent with mixing and transport in the absence of fractionating gains or losses. The concentrations of nitrogen (N2) and argon (Ar) dissolved in river water decreased in the downstream direction, approximately in equilibrium with air at increasing temperatures, giving no evidence of gains or losses of N2 by nitrogen fixation or denitrification. Nitrous oxide (N2O) concentrations in the Mississippi River were approximately 26 to 200 percent of air saturation, indicating relatively low net production by combination of nitrification and denitrification. Results from this study indicate that most (>90%) of theNO3- that entered the Mississippi River during July-August 1999 was transported to the Gulf of Mexico.

Evaluation of Titanium Dioxide as a Binding Phase for the Passive Sampling of Glyphosate and Aminomethyl Phosphonic Acid in an Aquatic Environment.

PubMed

Fauvelle, Vincent; Nhu-Trang, Tran-Thi; Feret, Thibaut; Madarassou, Karine; Randon, Jérôme; Mazzella, Nicolas

2015-06-16

Glyphosate is the most widely used herbicide on a world scale for the last 40 years, for both urban and agricultural uses. Here we describe the first passive sampling method for estimating the concentration of glyphosate and AMPA (aminomethyl phosphonic acid, one of its major degradation products) in surface water. The sampling method is based on a newly developed configuration of the diffusive gradient in thin-film (DGT) technique, which includes a TiO2 binding phase, already in use for a wide range of anions. Glyphosate and AMPA were retained well on a TiO2 binding phase, and elution in a 1 mL of 1 M NaOH led to recoveries greater than 65%. We found no influence of pH or flow velocity on the diffusion coefficients through 0.8 mm polyacrylamide gels, although they did increase with temperature. TiO2 binding gels were able to accumulate up to 1167 ng of P for both glyphosate and AMPA, and linear accumulation was expected over several weeks, depending on environmental conditions. DGT sampling rates were close to 10 mL day(-1) in ultrapure water, while they were less than 1 mL day(-1) in the presence of naturally occurring ions (e.g., copper, iron, calcium, magnesium). These last results highlighted (i) the ability of DGT to measure only the freely dissolved fraction of glyphosate and AMPA in water and (ii) the needs to determine which fraction (total, particulate, dissolved, freely dissolved) is indeed bioactive.

Contemporary reliance on bicarbonate acquisition predicts increased growth of seagrass Amphibolis antarctica in a high-CO2 world

PubMed Central

Burnell, Owen W.; Connell, Sean D.; Irving, Andrew D.; Watling, Jennifer R.; Russell, Bayden D.

2014-01-01

Rising atmospheric CO2 is increasing the availability of dissolved CO2 in the ocean relative to HCO3−. Currently, many marine primary producers use HCO3− for photosynthesis, but this is energetically costly. Increasing passive CO2 uptake relative to HCO3− pathways could provide energy savings, leading to increased productivity and growth of marine plants. Inorganic carbon-uptake mechanisms in the seagrass Amphibolis antarctica were determined using the carbonic anhydrase inhibitor acetazolamide (AZ) and the buffer tris(hydroxymethyl)aminomethane (TRIS). Amphibolis antarctica seedlings were also maintained in current and forecasted CO2 concentrations to measure their physiology and growth. Photosynthesis of A. antarctica was significantly reduced by AZ and TRIS, indicating utilization of HCO3−-uptake mechanisms. When acclimated plants were switched between CO2 treatments, the photosynthetic rate was dependent on measurement conditions but not growth conditions, indicating a dynamic response to changes in dissolved CO2 concentration, rather than lasting effects of acclimation. At forecast CO2 concentrations, seedlings had a greater maximum electron transport rate (1.4-fold), photosynthesis (2.1-fold), below-ground biomass (1.7-fold) and increase in leaf number (2-fold) relative to plants in the current CO2 concentration. The greater increase in photosynthesis (measured as O2 production) compared with the electron transport rate at forecasted CO2 concentration suggests that photosynthetic efficiency increased, possibly due to a decrease in photorespiration. Thus, it appears that the photosynthesis and growth of seagrasses reliant on energetically costly HCO3− acquisition, such as A. antarctica, might increase at forecasted CO2 concentrations. Greater growth might enhance the future prosperity and rehabilitation of these important habitat-forming plants, which have experienced declines of global significance. PMID:27293673

Contemporary reliance on bicarbonate acquisition predicts increased growth of seagrass Amphibolis antarctica in a high-CO2 world.

PubMed

Burnell, Owen W; Connell, Sean D; Irving, Andrew D; Watling, Jennifer R; Russell, Bayden D

2014-01-01

Rising atmospheric CO2 is increasing the availability of dissolved CO2 in the ocean relative to HCO3 (-). Currently, many marine primary producers use HCO3 (-) for photosynthesis, but this is energetically costly. Increasing passive CO2 uptake relative to HCO3 (-) pathways could provide energy savings, leading to increased productivity and growth of marine plants. Inorganic carbon-uptake mechanisms in the seagrass Amphibolis antarctica were determined using the carbonic anhydrase inhibitor acetazolamide (AZ) and the buffer tris(hydroxymethyl)aminomethane (TRIS). Amphibolis antarctica seedlings were also maintained in current and forecasted CO2 concentrations to measure their physiology and growth. Photosynthesis of A. antarctica was significantly reduced by AZ and TRIS, indicating utilization of HCO3 (-)-uptake mechanisms. When acclimated plants were switched between CO2 treatments, the photosynthetic rate was dependent on measurement conditions but not growth conditions, indicating a dynamic response to changes in dissolved CO2 concentration, rather than lasting effects of acclimation. At forecast CO2 concentrations, seedlings had a greater maximum electron transport rate (1.4-fold), photosynthesis (2.1-fold), below-ground biomass (1.7-fold) and increase in leaf number (2-fold) relative to plants in the current CO2 concentration. The greater increase in photosynthesis (measured as O2 production) compared with the electron transport rate at forecasted CO2 concentration suggests that photosynthetic efficiency increased, possibly due to a decrease in photorespiration. Thus, it appears that the photosynthesis and growth of seagrasses reliant on energetically costly HCO3 (-) acquisition, such as A. antarctica, might increase at forecasted CO2 concentrations. Greater growth might enhance the future prosperity and rehabilitation of these important habitat-forming plants, which have experienced declines of global significance.

Effects of natural organic matter properties on the dissolution kinetics of zinc oxide nanoparticles

USGS Publications Warehouse

Jiang, Chuanjia; Aiken, George R.; Hsu-Kim, Heileen

2015-01-01

The dissolution of zinc oxide (ZnO) nanoparticles (NPs) is a key step of controlling their environmental fate, bioavailability, and toxicity. Rates of dissolution often depend upon factors such as interactions of NPs with natural organic matter (NOM). We examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution using anodic stripping voltammetry to directly measure dissolved zinc concentrations. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg C L–1) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. The findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NOM interactions with metal-based nanoparticles.

The Activity of Trace Metals in Aqueous Systems and the Effect of Corrosion Control Inhibitors

DTIC Science & Technology

1975-10-01

corrosion product on metallic zinc 49 Uncombined slilica as quartz or cristobalite forms by the hydrothermal alteration of solid zilicates or by direct... hydrothermally . The com- position of the solids are dependent on temperature and pressure as well as on the relative concentrations of the dissolved...of the few anhydrous simple silicates formed hydrotherm - ally. The sodium silicates, Na2SiO 3 and BNa 2Si205, are somewhat soluble in high temperature

More on the losses of dissolved CO(2) during champagne serving: toward a multiparameter modeling.

PubMed

Liger-Belair, Gérard; Parmentier, Maryline; Cilindre, Clara

2012-11-28

Pouring champagne into a glass is far from being inconsequential with regard to the dissolved CO(2) concentration found in champagne. Three distinct bottle types, namely, a magnum bottle, a standard bottle, and a half bottle, were examined with regard to their loss of dissolved CO(2) during the service of successively poured flutes. Whatever the bottle size, a decreasing trend is clearly observed with regard to the concentration of dissolved CO(2) found within a flute (from the first to the last one of a whole service). Moreover, when it comes to champagne serving, the bottle size definitely does matter. The higher the bottle volume, the better its buffering capacity with regard to dissolved CO(2) found within champagne during the pouring process. Actually, for a given flute number in a pouring data series, the concentration of dissolved CO(2) found within the flute was found to decrease as the bottle size decreases. The impact of champagne temperature (at 4, 12, and 20 °C) on the losses of dissolved CO(2) found in successively poured flutes for a given standard 75 cL bottle was also examined. Cold temperatures were found to limit the decreasing trend of dissolved CO(2) found within the successively poured flutes (from the first to the last one of a whole service). Our experimental results were discussed on the basis of a multiparameter model that accounts for the major physical parameters that influence the loss of dissolved CO(2) during the service of a whole bottle type.

Biological and chemical characteristics of the coral gastric cavity

NASA Astrophysics Data System (ADS)

Agostini, S.; Suzuki, Y.; Higuchi, T.; Casareto, B. E.; Yoshinaga, K.; Nakano, Y.; Fujimura, H.

2012-03-01

All corals have a common structure: two tissue layers enclose a lumen, which forms the gastric cavity. Few studies have described the processes occurring inside the gastric cavity and its chemical and biological characteristics. Here, we show that the coral gastric cavity has distinct chemical characteristics with respect to dissolved O2, pH, alkalinity, and nutrients (vitamin B12, nitrate, nitrite, ammonium, and phosphate) and also harbors a distinct bacterial community. From these results, the gastric cavity can be described as a semi-closed sub-environment within the coral. Dissolved O2 shows very low constant concentrations in the deepest parts of the cavity, creating a compartmentalized, anoxic environment. The pH is lower in the cavity than in the surrounding water and, like alkalinity, shows day/night variations different from those of the surrounding water. Nutrient concentrations in the cavity are greater than the concentrations found in reef waters, especially for phosphate and vitamin B12. The source of these nutrients may be internal production by symbiotic bacteria and/or the remineralization of organic matter ingested or produced by the corals. The importance of the bacteria inhabiting the gastric cavity is supported by the finding of a high bacterial abundance and a specific bacterial community with affiliation to bacteria found in other corals and in the guts of other organisms. The findings presented here open a new area of research that may help us to understand the processes that maintain coral health.

Shallow groundwater denitrification capacity at three contrasting hydrogeological environments in Ireland

NASA Astrophysics Data System (ADS)

Mofizur Rahman Jahangir, Mohammad; Johnston, Paul; Khalil, Mohammad Ibrahim; Richards, Karl

2010-05-01

Denitrification may be regarded as the dominant nitrate removal or attenuation process in shallow groundwater. A major concern arising from the denitrification process is that it not only serves as a natural pathway for excess NO3- removal but its intermediate product, N2O, is a potent greenhouse gas. A groundwater monitoring network was established on grazed grassland at research farms at Johnstown Castle (JC) and Solohead (SH) on tillage at Oak Park (OP) in Ireland, to investigate the denitrification capacity and N2O:(N2O+N2) ratio within the shallow groundwater zone. The geology of this zone at the 3 sites was i) JC: sand and gravel intermixed with clay, ii) SH: silt and gravel intermixed with dense clay and iii) OP: dense gravel with interbedded clays. Average groundwater table was respectively 3.2, 2.4 and 4.0 m below ground level. Ten piezometers of 50 mm ID with 2 m screen sections were installed at 3.5-6.0 m below ground level using a rotary air drilling method at the three sites. Groundwater sampling was carried out monthly for 6 months (February to July, 2009) using a bladder pump following the USEPA low flow sampling procedures. Dissolved groundwater N2O was separated by degassing groundwater in a sealed serum bottle (160ml) using high purity He (water:He = 3:1) and the collected headspace equilibrium gas was analyzed on a Varian gas chromatograph. The N2/Ar ratio, measured using a Membrane Inlet Mass Spectrometer, was used to estimate the denitrified N2 concentrations. The mean NO3-N concentrations were 7.0, 2.5 and 11.0 mg L-1 in JC, SH and OP, respectively. Ground water dissolved N2O concentrations ranged from 0.01 to 0.05, 0.01 to 0.06 and 0.002 to 0.06 mg L-1, with corresponding mean values of 0.03, 0.02, 0.02 mg N.L-1 in JC, SH and OP, respectively. The mean values for total denitrification (N2O+N2) were 1.94, 1.03 and 0.38 mg N.L-1, which accounted for 22, 29 and 3% losses of total NO3- -N in JC, SH and OP, respectively. The higher denitrification measured on the grassland compared to tillage is most likely related to the hydrogeological conditions e.g. DOC, DO and redox-potential rather than land-use. More importantly, the mean N2O:N2O+N2 ratios, being 0.01, 0.02 and 0.05, respectively in JC, SH and OP indicated that 95-99% of total denitrification was molecular N2 (98-99% in grassland and 95% in tillage farm). With respect to temporal changes, denitrification losses were higher in May in grassland systems and in April in tillage farming systems. Shallow groundwater denitrification appeared to be an important process in reducing NO3- , with low N2O concentrations indicating low losses of this greenhouse gas to the atmosphere upon discharging to surface water.

Phase relations among K-feldspar, muscovite and H2O at 1.0 GPa and 800°C: Implications for metasediment dissolution and melting at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Fineman, D.; Manning, C. E.

2016-12-01

Melting and solubility of K-feldspar (ksp) and muscovite (mus) were investigated in the system KSi3O6.5 -Al2O3 - H2O at 1.0 GPa and 800 °C with rapid-quench piston-cylinder techniques. Equilibrium assemblages of ksp, mus, silicate liquid (L) and aqueous fluid (V) were deduced from optical and scanning electron microscopy. Quenched silicate liquids and aqueous fluids were distinguished using the methodology of Burnham and Jahns (1962, Am J Sci, 260, 721) and Makhluf et al. (2016, CMP, in press). Experiments on a range of bulk compositions constrain the locations of the V, ksp+V, ms+V, and ksp+L+V fields. This allowed geometrical constraints to be placed on additional phase boundaries in the ternary system. The results show that ksp dissolves incongruently in H2O, with residual liquid or ms depending on the fluid-rock ratio. In contrast, ms dissolves congruently in H2O and KSi3O6.5 -H2O solutions with up to 25 wt% KSi3O6.5. Results indicate that stable hydrous liquid at these conditions has an Al content intermediate between ksp and ms. There is no stable liquid along the ksp-H2O join, consistent with results of Goldsmith and Peterson (1990, Am Min, 75, 1362). All data are consistent with the stability of a supercritical fluid on the KAlSi3O8 -H2O join, with 5-10 wt% dissolved Al2O3. Compositional constraints imply that the liquid phase contains 25 wt% H2O and coexists with a V phase containing 25 wt% dissolved solutes. This in turn implies critical mixing of the fluid phases at higher temperature, which is similar to the systems NaAlSi3O8-H2O and simple granite-H2O. Our results help constrain the conditions of production of supercritical granitic-H2O fluids systems in deep crustal and subduction zone settings.

Effects of dissolved organic matter from a eutrophic lake on the freely dissolved concentrations of emerging organic contaminants.

PubMed

Xiao, Yi-Hua; Huang, Qing-Hui; Vähätalo, Anssi V; Li, Fei-Peng; Chen, Ling

2014-08-01

The authors studied the effects of dissolved organic matter (DOM) on the bioavailability of bisphenol A (BPA) and chloramphenicol by measuring the freely dissolved concentrations of the contaminants in solutions containing DOM that had been isolated from a mesocosm in a eutrophic lake. The abundance and aromaticity of the chromophoric DOM increased over the 25-d mesocosm experiment. The BPA freely dissolved concentration was 72.3% lower and the chloramphenicol freely dissolved concentration was 56.2% lower using DOM collected on day 25 than using DOM collected on day 1 of the mesocosm experiment. The freely dissolved concentrations negatively correlated with the ultraviolent absorption coefficient at 254 nm and positively correlated with the spectral slope of chromophoric DOM, suggesting that the bioavailability of these emerging organic contaminants depends on the characteristics of the DOM present. The DOM-water partition coefficients (log KOC ) for the emerging organic contaminants positively correlated with the aromaticity of the DOM, measured as humic acid-like fluorescent components C1 (excitation/emission=250[313]/412 nm) and C2 (excitation/emission=268[379]/456 nm). The authors conclude that the bioavailability of emerging organic contaminants in eutrophic lakes can be affected by changes in the DOM. © 2014 SETAC.

The Paradox of a Wet (High H2O) and Dry (Low H2O/Ce) Mantle: High Water Concentrations in Mantle Garnet Pyroxenites from Hawaii

NASA Technical Reports Server (NTRS)

Peslier, Anne H.; Bizimis, Michael

2013-01-01

Water dissolved as trace amounts in anhydrous minerals has a large influence on the melting behavior and physical properties of the mantle. The water concentration of the oceanic mantle is inferred from the analyses of Mid-Ocean Ridge Basalt (MORB) and Oceanic Island Basalt (OIB). but there is little data from actual mantle samples. Moreover, enriched mineralogies (pyroxenites, eclogites) are thought as important sources of heterogeneity in the mantle, but their water concentrations and their effect on the water budget and cycling in the mantle are virtually unknown. Here, we analyzed by FTIR water in garnet clinopyroxenite xenoliths from Salt Lake Crater, Oahu, Hawaii. These pyroxenites are high-pressure (>20kb) crystal fractionates from alkalic melts. The clinopyroxenes (cpx) have 260 to 576 ppm wt H2O, with the least differentiated samples (Mg#>0.8) in the 400-500 ppm range. Orthopyroxene (opx) contain 117-265 ppm H2O, about half of that of cpx, consistent with other natural sample studies, but lower than cpx/opx equilibrium from experimental data. The pyroxenite cpx and opx H2O concentrations are at the high-end of on-and off-craton peridotite xenolith concentrations and those of Hawaiian spinel peridotites. In contrast, garnet has extremely low water contents (<5ppm H2O). There is no correlation between H2O in cpx and lithophile element concentrations. Phlogopite is present in some samples, and its modal abundance shows a positive correlation in Mg# with cpx, implying equilibrium. However, there is no correlation between H2O concentrations and or the presence of phlogopite. These data imply that cpx and opx may be at water saturation, far lower than experimental data suggest. Reconstructed bulk rock pyroxenite H2O ranges from 200-460 ppm (average 331 +/- 75 ppm), 2 to 8 times higher than H2O estimates for the MORB source (50-200 ppm), but in the range of E-MORB, OIB and the source of rejuvenated Hawaiian magmas. The average bulk rock pyroxenite H2O/Ce is 69 +/-35, lower than estimates of the MORB source (approx 150) or FOZO, C (200-250) mantle component, but consistent with "dry" EM sources (<100). These data suggest that a metasomatized, refertilized oceanic lithosphere that contains pyroxenitic veins (e.g. the lower part of an oceanic plate, where ascending melts can become trapped and crystallize), will have both higher water concentrations and low H2O/Ce, and may contribute to EM-type OIB sources, like that of Samoa basalts. Therefore, a low H2O/Ce mantle source may not necessarily be "dry".

Experimental determination of magnesia and silica solubilities in graphite-saturated and redox-buffered high-pressure COH fluids in equilibrium with forsterite + enstatite and magnesite + enstatite

NASA Astrophysics Data System (ADS)

Tiraboschi, Carla; Tumiati, Simone; Sverjensky, Dimitri; Pettke, Thomas; Ulmer, Peter; Poli, Stefano

2018-01-01

We experimentally investigated the dissolution of forsterite, enstatite and magnesite in graphite-saturated COH fluids, synthesized using a rocking piston cylinder apparatus at pressures from 1.0 to 2.1 GPa and temperatures from 700 to 1200 °C. Synthetic forsterite, enstatite, and nearly pure natural magnesite were used as starting materials. Redox conditions were buffered by Ni-NiO-H2O (ΔFMQ = - 0.21 to - 1.01), employing a double-capsule setting. Fluids, binary H2O-CO2 mixtures at the P, T, and fO2 conditions investigated, were generated from graphite, oxalic acid anhydrous (H2C2O4) and water. Their dissolved solute loads were analyzed through an improved version of the cryogenic technique, which takes into account the complexities associated with the presence of CO2-bearing fluids. The experimental data show that forsterite + enstatite solubility in H2O-CO2 fluids is higher compared to pure water, both in terms of dissolved silica ( mSiO2 = 1.24 mol/kgH2O versus mSiO2 = 0.22 mol/kgH2O at P = 1 GPa, T = 800 °C) and magnesia ( mMgO = 1.08 mol/kgH2O versus mMgO = 0.28 mol/kgH2O) probably due to the formation of organic C-Mg-Si complexes. Our experimental results show that at low temperature conditions, a graphite-saturated H2O-CO2 fluid interacting with a simplified model mantle composition, characterized by low MgO/SiO2 ratios, would lead to the formation of significant amounts of enstatite if solute concentrations are equal, while at higher temperatures these fluid, characterized by MgO/SiO2 ratios comparable with that of olivine, would be less effective in metasomatizing the surrounding rocks. However, the molality of COH fluids increases with pressure and temperature, and quintuplicates with respect to the carbon-free aqueous fluids. Therefore, the amount of fluid required to metasomatize the mantle decreases in the presence of carbon at high P- T conditions. COH fluids are thus effective carriers of C, Mg and Si in the mantle wedge up to the shallowest level of the upper mantle.

A method of calculating quartz solubilities in aqueous sodium chloride solutions

USGS Publications Warehouse

Fournier, R.O.

1983-01-01

The aqueous silica species that form when quartz dissolves in water or saline solutions are hydrated. Therefore, the amount of quartz that will dissolve at a given temperature is influenced by the prevailing activity of water. Using a standard state in which there are 1,000 g of water (55.51 moles) per 1,000 cm3 of solution allows activity of water in a NaCl solution at high temperature to be closely approximated by the effective density of water, pe, in that solution, i.e. the product of the density of the NaCl solution times the weight fraction of water in the solution, corrected for the amount of water strongly bound to aqueous silica and Na+ as water of hydration. Generally, the hydration of water correction is negligible. The solubility of quartz in pure water is well known over a large temperature-pressure range. An empirical formula expresses that solubility in terms of temperature and density of water and thus takes care of activity coefficient and pressure-effect terms. Solubilities of quartz in NaCl solutions can be calculated by using that equation and substituting pe, for the density of pure water. Calculated and experimentally determined quartz solubilities in NaCl solutions show excellent agreement when the experiments were carried out in non-reactive platinum, gold, or gold plus titanium containers. Reactive metal containers generally yield dissolved silica concentrations higher than calculated, probably because of the formation of metal chlorides plus NaOH and H2. In the absence of NaOH there appears to be no detectable silica complexing in NaCl solutions, and the variation in quartz solubility with NaCl concentration at constant temperature can be accounted for entirely by variations in the activity of water. The average hydration number per molecule of dissolved SiO2 in liquid water and NaCl solutions decreases from about 2.4 at 200??C to about 2.1 at 350??C. This suggests that H4SiO4 may be the dominant aqueous silica species at 350??C, but other polymeric forms become important at lower temperatures. ?? 1983.

Factors Related with CH4 and N2O Emissions from a Paddy Field: Clues for Management implications

PubMed Central

Wang, Chun; Lai, Derrick Y. F.; Sardans, Jordi; Wang, Weiqi; Zeng, Congsheng; Peñuelas, Josep

2017-01-01

Paddy fields are major sources of global atmospheric greenhouse gases, including methane (CH4) and nitrous oxide (N2O). The different phases previous to emission (production, transport, diffusion, dissolution in pore water and ebullition) despite well-established have rarely been measured in field conditions. We examined them and their relationships with temperature, soil traits and plant biomass in a paddy field in Fujian, southeastern China. CH4 emission was positively correlated with CH4 production, plant-mediated transport, ebullition, diffusion, and concentration of dissolved CH4 in porewater and negatively correlated with sulfate concentration, suggesting the potential use of sulfate fertilizers to mitigate CH4 release. Air temperature and humidity, plant stem biomass, and concentrations of soil sulfate, available N, and DOC together accounted for 92% of the variance in CH4 emission, and Eh, pH, and the concentrations of available N and Fe3+, leaf biomass, and air temperature 95% of the N2O emission. Given the positive correlations between CH4 emission and DOC content and plant biomass, reduce the addition of a carbon substrate such as straw and the development of smaller but higher yielding rice genotypes could be viable options for reducing the release of greenhouse gases from paddy fields to the atmosphere. PMID:28081161

Surface micro-dissolve method of imparting self-cleaning property to cotton fabrics in NaOH/urea aqueous solution

NASA Astrophysics Data System (ADS)

Fan, Tao; Hu, Ruimin; Zhao, Zhenyun; Liu, Yiping; Lu, Ming

2017-04-01

A simple and economical micro-dissolved process of embedding titanium dioxide (TiO2) nanoparticles into surface zone of cotton fabrics was developed. TiO2 was coated on cotton fabrics in 7% wt NaOH/12% wt urea aqueous solution at low temperature. Photocatalytic efficiency of cotton fabrics treated with TiO2 nanoparticles was studied upon measuring the photocatalytic decoloration of Rhodamine B (RhB) under ultraviolet irradiation. Self-cleaning property of cotton fabric coated with TiO2 was evaluated with color depth of samples (K/S value). The treated fabrics were characterized using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FITR), tensile strength, stiffness and whiteness. The results indicated, TiO2 nanoparticles could be embedded on the surface layer of cotton fabrics throuth surface micro-dissolve method. Treated cotton fabrics possessed distinct photocatalytic efficiency and self-cleaning properties. Tensile strength and whiteness of modified cotton fabrics appeared moderately increasement.

Aspects of the history of 66095 based on trace elements in clasts and whole rock

NASA Technical Reports Server (NTRS)

Jovanovic, S.; Reed, G. W., Jr.

1982-01-01

Halogens, P, U and Na are reported in anorthositic and basaltic clasts and matrix from rusty rock 66095. Large fractions of Cl and Br associated with the separated phases from 66095 are soluble in H2O. Up to two orders of magnitude variation in concentrations of these elements in the breccia components and varying H2O-soluble Cl/Br ratios indicate different sources of volatiles. An approximately constant ratio of the H2O- to 0.1 M HNO3-soluble Br in the various components suggests no appreciable alteration in the original distributions of this element in the breccia forming processes. Up to 50% or more of the phosphorus and of the non-H2O-soluble Cl was dissolved from most of the breccia components by 0.1 M HNO3. Clast and matrix residues from the leaching steps contain, in most cases, the Cl/P2O5 ratio found in 66095 whole rock and in a number of other Apollo 16 samples. Evidence that phosphates are the major P-phases in the breccia is based on the 0.1 M acid solubility of Cl and P in the matrix sample and on elemental concentrations which are consistent with those of KREEP.

Attenuation of Microbial Stress Due to Nano-Ag and Nano-TiO2 Interactions under Dark Conditions.

PubMed

Wilke, Carolyn M; Tong, Tiezheng; Gaillard, Jean-François; Gray, Kimberly A

2016-10-04

Engineered nanomaterials (ENMs) are incorporated into thousands of commercial products, and their release into environmental systems creates complex mixtures with unknown toxicological outcomes. To explore this scenario, we probe the chemical and toxicological interactions of nanosilver (n-Ag) and nanotitania (n-TiO 2 ) in Lake Michigan water, a natural aqueous medium, under dark conditions. We find that the presence of n-Ag induces a stress response in Escherichia coli, as indicated by a decrease in ATP production observed at low concentrations (in the μg L -1 range), with levels that are environmentally relevant. However, when n-Ag and n-TiO 2 are present together in a mixture, n-TiO 2 attenuates the toxicity of n-Ag at and below 20 μg L -1 by adsorbing Ag + (aq) . We observe, however, that toxic stress cannot be explained by dissolved silver concentrations alone and, therefore, must also depend on silver associated with the nanoscale fraction. Although the attenuating effect of n-TiO 2 on n-Ag's toxicity is limited, this study emphasizes the importance of probing the toxicity of ENM mixtures under environmental conditions to assess how chemical interactions between nanoparticles change the toxicological effects of single ENMs in unexpected ways.

The effects of iron(II) on the kinetics of arsenic oxidation and sorption on manganese oxides.

PubMed

Wu, Yun; Li, Wei; Sparks, Donald L

2015-11-01

In this study, As(III) oxidation kinetics by a poorly-crystalline phyllomanganate (δ-MnO2) in the presence and absence of dissolved Fe(II) was investigated using stirred-flow and batch experiments. Chemically synthetic δ-MnO2 was reacted with four influent solutions, containing the same As(III) concentration but different Fe(II) concentrations, at pH 6. The results show an initial rapid As(III) oxidation by δ-MnO2, which is followed by an appreciably slow reaction after 8h. In the presence of Fe(II), As(III) oxidation is inhibited due to the competitive oxidation of Fe(II) as well as the formation of Fe(III)-(hydr)oxides on the δ-MnO2 surface. However, the sorption of As(III), As(V) and Mn(II) are increased, for the newly formed Fe(III)-(hydr)oxides provide additional sorption sites. This study suggests that the competitive oxidation of Fe(II) and consequently the precipitation of Fe(III) compounds on the δ-MnO2 surface play an important role in As(III) oxidation and As sequestration. Understanding these processes would be helpful in developing in situ strategies for remediation of As-contaminated waters and soils. Copyright © 2015 Elsevier Inc. All rights reserved.

Retail lighting and packaging influence consumer acceptance of fluid milk.

PubMed

Potts, H L; Amin, K N; Duncan, S E

2017-01-01

Little is known about the effect of retail light-emitting diode (LED) exposure on consumer acceptance of milk. The study objective was to determine effects of fluorescent and LED lighting under retail storage conditions on consumer acceptance of milk. Consumer acceptance of milk stored under retail conditions was determined through sensory evaluation (2 studies; n=150+ each) and analytical measures (dissolved oxygen, secondary oxidation products, riboflavin retention). Study 1 evaluated milk stored in high-density polyethylene (HDPE) packages for 4h under LED light (960 lx). Commercially available HDPE package treatments included translucent HDPE (most commonly used), white HDPE [low concentration (1.3%) TiO 2 ], and yellow HDPE; in addition, HDPE with a higher TiO 2 concentration (high white; 4.9% TiO 2 ) and a foil-wrapped translucent HDPE (control) were tested. Translucent and control packages also were tested under fluorescent light. Study 2 evaluated polyethylene terephthalate (PET) packages for 4h under fluorescent and LED light (1,460 lx). The PET packaging included 2 treatments (medium, 4.0% TiO 2 ; high, 6.6% TiO 2 ) as well as translucent HDPE (exposed to fluorescent), clear PET (fluorescent and LED), and light-protected control. Overall mean acceptability of milk ranged from "like slightly" to "like moderately" with significantly lower acceptability for milk exposed to fluorescent light. Milk in HDPE and PET packages had comparable overall acceptability scores when exposed to LED light. Only the fluorescent light condition (both PET and HDPE) diminished overall acceptability. Fluorescent light exposure negatively influenced flavor with significant penalty (2.0-2.5 integers) to overall acceptability of milk in translucent HDPE and clear PET. The LED also diminished aftertaste of milk packaged in translucent HDPE. Changes in dissolved oxygen content, as an indication of oxidation, supported the observed differences in consumer acceptance of milk stored under fluorescent and LED light. Consumers like the flavor of fresh milk, which can be protected by selecting appropriate packaging that blocks detrimental light wavelengths. Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Physical and chemical properties of San Francisco Bay, California, 1980

USGS Publications Warehouse

Ota, Allan Y.; Schemel, L.E.; Hager, S.W.

1989-01-01

The U.S. Geological Survey conducted hydrologic investigations in both the deep water channels and the shallow-water regions of the San Francisco Bay estuarine system during 1980. Cruises were conducted regularly, usually at two-week intervals. Physical and chemical properties presented in this report include temperature , salinity, suspended particulate matter, turbidity, extinction coefficient, partial pressure of CO2, partial pressure of oxygen , dissolved organic carbon, particulate organic carbon, discrete chlorophyll a, fluorescence of photosynthetic pigments, dissolved silica, dissolved phosphate, nitrate plus nitrite, nitrite, ammonium, dissolved inorganic nitrogen, dissolved nitrogen, dissolved phosphorus, total nitrogen, and total phosphorus. Analytical methods are described. The body of data contained in this report characterizes hydrologic conditions in San Francisco Bay during a year with an average rate of freshwater inflow to the estuary. Concentrations of dissolved silica (discrete-sample) ranged from 3.8 to 310 micro-M in the northern reach of the bay, whereas the range in the southern reach was limited to 63 to 150 micro-M. Concentrations of phosphate (discrete-sample) ranged from 1.3 to 4.4 micro-M in the northern reach, which was narrow in comparison with that of 2.2 to 19.0 micro-M in the southern reach. Concentrations of nitrate plus nitrite (discrete-sample) ranged from near zero to 53 micro-M in the northern reach, and from 2.3 to 64 micro-M in the southern reach. Concentrations of nitrite (discrete-sample) were low in both reaches, exhibiting a range from nearly zero to approximately 2.3 micro-M. Concentrations of ammonium (discrete-sample) ranged from near zero to 14.2 micro-M in the northern reach, and from near zero to 8.3 micro-M in the southern reach. (USGS)

Electrochemically assisted localized etching of ZnO single crystals in water using a catalytically active Pt-coated atomic force microscopy probe

NASA Astrophysics Data System (ADS)

Shibata, Takayuki; Yamamoto, Kota; Sasano, Junji; Nagai, Moeto

2017-09-01

This paper presents a nanofabrication technique based on the electrochemically assisted chemical dissolution of zinc oxide (ZnO) single crystals in water at room temperature using a catalytically active Pt-coated atomic force microscopy (AFM) probe. Fabricated grooves featured depths and widths of several tens and several hundreds of nanometers, respectively. The material removal rate of ZnO was dramatically improved by controlling the formation of hydrogen ions (H+) on the surface of the catalytic Pt-coated probe via oxidation of H2O molecules; this reaction can be enhanced by applying a cathodic potential to an additional Pt-wire working electrode in a three-electrode configuration. Consequently, ZnO can be dissolved chemically in water as a soluble Zn2+ species via a reaction with H+ species present in high concentrations in the immediate vicinity of the AFM tip apex.

Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming, Water Years 1999-2008

USGS Publications Warehouse

Clark, Melanie L.; Davidson, Seth L.

2009-01-01

Southwestern Wyoming is an area of diverse scenery, wildlife, and natural resources that is actively undergoing energy development. The U.S. Department of the Interior's Wyoming Landscape Conservation Initiative is a long-term science-based effort to assess and enhance aquatic and terrestrial habitats at a landscape scale, while facilitating responsible energy development through local collaboration and partnerships. Water-quality monitoring has been conducted by the U.S. Geological Survey on the Green River near Green River, Wyoming, and Muddy Creek near Baggs, Wyoming. This monitoring, which is being conducted in cooperation with State and other Federal agencies and as part of the Wyoming Landscape Conservation Initiative, is in response to concerns about potentially increased dissolved solids in the Colorado River Basin as a result of energy development. Because of the need to provide real-time dissolved-solids concentrations for the Green River and Muddy Creek on the World Wide Web, the U.S. Geological Survey developed regression equations to estimate dissolved-solids concentrations on the basis of continuous specific conductance using relations between measured specific conductance and dissolved-solids concentrations. Specific conductance and dissolved-solids concentrations were less varied and generally lower for the Green River than for Muddy Creek. The median dissolved-solids concentration for the site on the Green River was 318 milligrams per liter, and the median concentration for the site on Muddy Creek was 943 milligrams per liter. Dissolved-solids concentrations ranged from 187 to 594 milligrams per liter in samples collected from the Green River during water years 1999-2008. Dissolved-solids concentrations ranged from 293 to 2,485 milligrams per liter in samples collected from Muddy Creek during water years 2006-08. The differences in dissolved-solids concentrations in samples collected from the Green River compared to samples collected from Muddy Creek reflect the different basin characteristics. Relations between specific conductance and dissolved-solids concentrations were statistically significant for the Green River (p-value less than 0.001) and Muddy Creek (p-value less than 0.001); therefore, specific conductance can be used to estimate dissolved-solids concentrations. Using continuous specific conductance values to estimate dissolved solids in real-time on the World Wide Web increases the amount and improves the timeliness of data available to water managers for assessing dissolved-solids concentrations in the Colorado River Basin.

Removal of dissolved actinides from alkaline solutions by the method of appearing reagents

DOEpatents

Krot, Nikolai N.; Charushnikova, Iraida A.

1997-01-01

A method of reducing the concentration of neptunium and plutonium from alkaline radwastes containing plutonium and neptunium values along with other transuranic values produced during the course of plutonium production. The OH.sup.- concentration of the alkaline radwaste is adjusted to between about 0.1M and about 4M. [UO.sub.2 (O.sub.2).sub.3 ].sup.4- ion is added to the radwastes in the presence of catalytic amounts of Cu.sup.+2, Co.sup.+2 or Fe.sup.+2 with heating to a temperature in excess of about 60.degree. C. or 85.degree. C., depending on the catalyst, to coprecipitate plutonium and neptunium from the radwaste. Thereafter, the coprecipitate is separated from the alkaline radwaste.

Oxidation of naturally reduced uranium in aquifer sediments by dissolved oxygen and its potential significance to uranium plume persistence

NASA Astrophysics Data System (ADS)

Davis, J. A.; Smith, R. L.; Bohlke, J. K.; Jemison, N.; Xiang, H.; Repert, D. A.; Yuan, X.; Williams, K. H.

2015-12-01

The occurrence of naturally reduced zones is common in alluvial aquifers in the western U.S.A. due to the burial of woody debris in flood plains. Such reduced zones are usually heterogeneously dispersed in these aquifers and characterized by high concentrations of organic carbon, reduced mineral phases, and reduced forms of metals, including uranium(IV). The persistence of high concentrations of dissolved uranium(VI) at uranium-contaminated aquifers on the Colorado Plateau has been attributed to slow oxidation of insoluble uranium(IV) mineral phases found in association with these reducing zones, although there is little understanding of the relative importance of various potential oxidants. Four field experiments were conducted within an alluvial aquifer adjacent to the Colorado River near Rifle, CO, wherein groundwater associated with the naturally reduced zones was pumped into a gas-impermeable tank, mixed with a conservative tracer (Br-), bubbled with a gas phase composed of 97% O2 and 3% CO2, and then returned to the subsurface in the same well from which it was withdrawn. Within minutes of re-injection of the oxygenated groundwater, dissolved uranium(VI) concentrations increased from less than 1 μM to greater than 2.5 μM, demonstrating that oxygen can be an important oxidant for uranium in such field systems if supplied to the naturally reduced zones. Dissolved Fe(II) concentrations decreased to the detection limit, but increases in sulfate could not be detected due to high background concentrations. Changes in nitrogen species concentrations were variable. The results contrast with other laboratory and field results in which oxygen was introduced to systems containing high concentrations of mackinawite (FeS), rather than the more crystalline iron sulfides found in aged, naturally reduced zones. The flux of oxygen to the naturally reduced zones in the alluvial aquifers occurs mainly through interactions between groundwater and gas phases at the water table. Seasonal variations of the water table at the Rifle, CO site may play an important role in introducing oxygen into the system. Although oxygen was introduced directly to the naturally reduced zones in these experiments, delivery of oxidants to the system may also be controlled by other oxidative pathways in which oxygen plays an indirect role.

Effects of three years of simulated nitrogen deposition on soil nitrogen dynamics and greenhouse gas emissions in a Korean pine plantation of northeast China.

PubMed

Song, Lei; Tian, Peng; Zhang, Jinbo; Jin, Guangze

2017-12-31

Continuously enhanced nitrogen (N) deposition alters the pattern of N and carbon (C) transformations, and thus influences greenhouse gas emissions. It is necessary to clarify the effect of N deposition on greenhouse gas emissions and soil N dynamics for an accurate assessment of C and N budgets under increasing N deposition. In this study, four simulated N deposition treatments (control [CK: no N addition], low-N [L: 20kgNha -1 yr -1 ], medium-N [M: 40kgNha -1 yr -1 ], and high-N [H: 80kgNha -1 yr -1 ]) were operated from 2014. Carbon dioxide, methane and nitrous oxide fluxes were monitored semimonthly, as were soil variables such as temperature, moisture and the concentrations of total dissolved N (TDN), NO 3 - , NO 2 - , NH 4 + , and dissolved organic N (DON) in soil solutions. The simulated N deposition resulted in a significant increase in TDN, NO 3 - and DON concentrations in soil solutions. The average CO 2 emission rate ranged from 222.6mgCO 2 m -2 h -1 in CK to 233.7mgCO 2 m -2 h -1 in the high-N treatment. Three years of simulated N deposition had no effect on soil CO 2 emission, which was mainly controlled by soil temperature. The mean N 2 O emission rate during the whole 3years was 0.02mgN 2 Om -2 h -1 for CK, which increased significantly to 0.05mgN 2 Om -2 h -1 in the high-N treatment. The N 2 O emission rate positively correlated with NH 4 + concentrations, and negatively correlated with soil moisture. The average CH 4 flux during the whole 3years was -0.74μgCH 4 m -2 h -1 in CK, which increased to 1.41μgCH 4 m -2 h -1 in the low-N treatment. CH 4 flux positively correlated with NO 3 - concentrations. These results indicate that short-term N deposition did not affect soil CO 2 emissions, while CH 4 and N 2 O emissions were sensitive to N deposition. Copyright © 2017 Elsevier B.V. All rights reserved.

Dissolved oxygen control and monitoring implementation in the liquid lead bismuth eutectic loop: HELIOS

NASA Astrophysics Data System (ADS)

Nam, Hyo On; Lim, Jun; Han, Dong Yoon; Hwang, Il Soon

2008-06-01

A 12 m tall LBE coolant loop, named as HELIOS, has been developed by thermal-hydraulic scaling of the PEACER-300MWe. Thermo-hydraulic experiment and materials test are the principal purposes of HELIOS operation. In this study, an yttria stabilized zirconia (YSZ) based oxygen sensor that was hermetically sealed for long-term applications using the electromagnetically swaged metal-ceramic joining method, have been developed for high temperature oxygen control application over a long period of time. The rugged electrode design has been calibrated to absolute metal-oxide equilibrium by using a first principle of detecting pure metal-oxide transition using electrochemical impedance spectroscopy (EIS). During the materials tests in HELIOS, dissolved oxygen concentration was administered at the intended condition of 10 -6 wt% by direct gas bubbling with Ar + 4%H 2, Ar + 5%O 2 and/or pure Ar while corrosion tests were conducted for up to 1000 h with inspection after each 333 h. During the total 1000 h corrosion test, oxygen concentration was measured by oxygen sensor. The result confirmed that the direct gas bubbling method is a viable and practical option for controlling oxygen concentration in large loops including HELIOS.

Solubility of platinum-arsenide melt and sperrylite in synthetic basalt at 0.1 MPa and 1200 °C with implications for arsenic speciation and platinum sequestration in mafic igneous systems

NASA Astrophysics Data System (ADS)

Canali, A. C.; Brenan, J. M.; Sullivan, N. A.

2017-11-01

To better understand the Pt-As association in natural magmas, experiments were done at 1200 °C and 0.1 MPa to measure the solubility of Pt and Pt-arsenide phases (melt and sperrylite, PtAs2), as well as to determine the oxidation state, and identify evidence for Pt-As complexing, in molten silicate. Samples consisting of synthetic basalt contained in chromite crucibles were subject to three experimental procedures. In the first, platinum solubility in the synthetic basalt was determined without added arsenic by equilibrating the sample with a platinum source (embedded wire or bead) in a gas-mixing furnace. In the second, the sample plus a Pt-arsenide source was equilibrated in a vacuum-sealed fused quartz tube containing a solid-oxide oxygen buffer. The third approach involved two steps: first equilibrating the sample in a gas-mixing furnace, then with added arsenide melt in a sealed quartz tube. Oxygen fugacity was estimated in the latter step using chromite/melt partitioning of vanadium. Method two experiments done at high initial arsenic activity (PtAs melt + PtAs2), showed significant loss of arsenic from the sample, the result of vapour transfer to newly-formed arsenide phases in the buffer. Method three experiments showed no loss of arsenic, yielding a uniform final distribution in the sample. Analyses of run-product glasses from experiments which did not show arsenic loss reveal significant increase in arsenic concentrations with fO2, varying from ∼10 ppm (FMQ-3.25) to >10,000 ppm (FMQ + 5.5). Despite very high arsenic loadings (>1000 ppm), the solubility of Pt is similar in arsenic-bearing and arsenic-free glasses. The variation in arsenic solubility with fO2 shows a linear relationship, that when corrected for the change in the activity of dissolved arsenic with the melt ferric/ferrous ratio, yields a solubility-fO2 relationship consistent with As3+ as the dissolved species. This result is confirmed by X-ray absorption near edge structure (XANES) determination on run-product glasses. Levels of arsenic required for Pt-arsenide saturation are 50-500 ppm over the fO2 range of most terrestrial basalts (FMQ to FMQ-2), >100× higher than the arsenic concentrations typical of such magmas, indicating significant enrichment of arsenic is required if Pt-arsenide saturation is to occur. In contrast, the level of dissolved Pt required to saturate in sperrylite is >8× lower than for pure Pt, suggesting that arsenic enrichment could lead to Pt removal at concentrations much less than required for pure metal saturation.

Oxidative Weathering of Archean Sulfides: Implications for the Great Oxidation Event

NASA Astrophysics Data System (ADS)

Johnson, A.; Romaniello, S. J.; Reinhard, C.; Garcia-Robledo, E.; Revsbech, N. P.; Canfield, D. E.; Lyons, T. W.; Anbar, A. D.

2015-12-01

The first widely accepted evidence for oxidation of Earth's atmosphere and oceans occurs ~2.45 Ga immediately prior to the Great Oxidation Event (GOE). A major line of evidence for this transition includes the abundances and isotopic variations of redox-sensitive transition metals in marine sediments (e.g., Fe, Mo, Re, Cr, and U). It is often assumed that oxidative weathering is required to liberate these redox-sensitive elements from sulfide minerals in the crust, and hence that their presence in early Archean marine sediments signifies that oxidative weathering was stimulated by small and/or transient "whiffs" of O2 in the environment.1 However, studies of crustal sulfide reactivity have not been conducted at O2 concentrations as low as those that would have prevailed when O2 began its rise during the late Archean (estimated at <10-5 present atmospheric O2).2 As a result, it is difficult to quantify O2 concentrations implied by observed trace metal variations. As a first step toward providing more quantitative constraints on late Archean pO2, we conducted laboratory studies of pyrite and molybdenite oxidation kinetics at the nanomolar O2 concentrations that are relevant to late Archean environments. These measurements were made using recently developed, highly sensitive optical O2 sensors to monitor the rates at which the powdered minerals consumed dissolved O2 in a range of pH-buffered solutions.3Our data extend the range of experimental pyrite oxidation rates in the literature by three orders of magnitude from ~10-3 present atmospheric O2 to ~10-6. We find that molybdenite and pyrite oxidation continues to <1 nM O2 (4 x 10-6 present atmospheric O2). This implies that oxidative weathering of sulfides could occur under conditions which preserve MIF S fractionation. Furthermore, our results indicate that the rate law and reaction order of pyrite oxidation kinetics change significantly at nanomolar concentrations of O2 when compared to previous compilations.2 Our results provide new empirical data that should allow for more precise quantitative constraints on atmospheric pO2 based on the sedimentary rock record. 1Anbar, A.D. et al., 2007. Science, 317, i. 5846: 1903-1906. 2Williamson & Rimstidt, 1994. Geochim. et Cosmochim. Acta, 58, n. 24: 5443-5454. 3Lehner et al., 2015. PLoS ONE, 10, n. 6: 1-15.

Effect of pulsed corona discharge voltage and feed gas flow rate on dissolved ozone concentration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasetyaningrum, A., E-mail: ajiprasetyaningrum@gmail.com; Ratnawati,; Jos, B.

Ozonization is one of the methods extensively used for water purification and degradation of organic materials. Ozone (O{sub 3}) is recognized as a powerful oxidizing agent. Due to its strong oxidability and better environmental friendless, ozone increasing being used in domestic and industrial applications. Current technology in ozone production utilizes several techniques (corona discharge, ultra violet radiation and electrolysis). This experiment aimed to evaluating effect of voltage and gas flow rate on ozone production with corona discharge. The system consists of two net-type stainless steel electrode placed in a dielectric barrier. Three pulsed voltage (20, 30, 40 KV) and flowmore » rate (5, 10, 15 L/min) were prepare for operation variable at high frequency (3.7 kHz) with AC pulsed power supply. The dissolved ozone concentration depends on the applied high-voltage level, gas flow rate and the discharge exposure duration. The ozone concentration increases with decreasing gas flow rate. Dissolved ozone concentrations greater than 200 ppm can be obtained with a minimum voltage 40 kV.« less

Effect of pulsed corona discharge voltage and feed gas flow rate on dissolved ozone concentration

NASA Astrophysics Data System (ADS)

Prasetyaningrum, A.; Ratnawati, Jos, B.

2015-12-01

Ozonization is one of the methods extensively used for water purification and degradation of organic materials. Ozone (O3) is recognized as a powerful oxidizing agent. Due to its strong oxidability and better environmental friendless, ozone increasing being used in domestic and industrial applications. Current technology in ozone production utilizes several techniques (corona discharge, ultra violet radiation and electrolysis). This experiment aimed to evaluating effect of voltage and gas flow rate on ozone production with corona discharge. The system consists of two net-type stainless steel electrode placed in a dielectric barrier. Three pulsed voltage (20, 30, 40 KV) and flow rate (5, 10, 15 L/min) were prepare for operation variable at high frequency (3.7 kHz) with AC pulsed power supply. The dissolved ozone concentration depends on the applied high-voltage level, gas flow rate and the discharge exposure duration. The ozone concentration increases with decreasing gas flow rate. Dissolved ozone concentrations greater than 200 ppm can be obtained with a minimum voltage 40 kV.

[Preparation and photoluminescence study of Er3+ : Y2O3 transparent ceramics].

PubMed

Luo, Jun-ming; Li, Yong-xiu; Deng, Li-ping

2008-10-01

Y2O3 acted as the matrix material, which was doped with different concentrations of Er3+, Er3+ : Y2O3 nanocrystalline powder was prepared by co-precipitation method, and Er3+ : Y2O3 transparent ceramics was fabricated by vacuum sintering at 1700 degrees C, 1 x 10(-3) Pa for 8 h. By using the X-ray diffraction (D/MAX-RB), transmission electron microscopy(Philips EM420), automatic logging spectrophotometer(DMR-22), fluorescence analyzer (F-4500) and 980 nm diode laser, the structural, morphological and luminescence properties of the sample were investigated. The results show that Er3+ dissolved completely in the Y2O3 cubic phase, the precursor was amorphous, weak diffraction peaks appeared after calcination at 400 degrees C, and if calcined at 700 degrees C, the precursor turned to pure cubic phase. With increasing the calcining temperature, the diffraction peaks became sharp quickly, and when the calcining temperature reached 1100 degrees C, the diffraction peaks became very sharp, indicating that the grains were very large. The particles of Er+ : Y2O3 is homogeneous and nearly spherical, the average diameter of the particles is in the range of 40-60 nm after being calcined at 1000 degrees C for 2 h. The relative density of Er3+ : Y2O3 transparent ceramics is 99.8%, the transmittance of the Er2+ : Y2O3 transparent ceramics is markedly lower than the single crystal at the short wavelength, but the transmittance is improved noticeably with increasing the wavelength, and the transmittance exceeds 60% at the wavelength of 1200 nm. Excited under the 980 nm diode laser, there are two main up-conversion emission bands, green emission centers at 562 nm and red emission centers at 660 nm, which correspond to (4)S(3/2) / (2)H(11/2) - (4)I(15/2) and (4)F(9/2) - (4)I(15/2) radiative transitions respectively. By changing the doping concentrations of Er3+, the color of up-conversion luminescence can be tuned from green to red gradually. The luminescence intensity is not reinforce with the increase in the concentration, so the doping concentration of Er3+ should not exceed 2%. If the doping concentration of Er3+ exceeds the range, the concentration has very small effect on the improvement of luminescence intensity.

Real-solution stability diagrams: A thermodynamic tool for modeling corrosion in wide temperature and concentration ranges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderko, A.; Sanders, S.J.; Young, R.D.

1997-01-01

A method was developed for construction of stability diagrams for metals in the presence of realistically modeled aqueous solutions. The method was based on a comprehensive thermodynamic model that combines the Helgeson-Kirkham-Flowers (HKF) equation of state for standard-state properties with a solution nonideality model based on the activity coefficient expressions developed by Bromley and Pitzer. Composition-dependent nonideality effects were incorporated into the calculation of predominance areas for dissolved and solid species. Using the combined thermodynamic model, stability diagrams can be computed for systems involving concentrated solutions (i.e., with molalities up to 30 mol/kg) at temperatures up to 573 K andmore » pressures up to 100 MPa. Since the diagrams are based on a realistic thermodynamic model for the aqueous phase, they are referred to as real-solution stability diagrams. In addition to customary potential (E) and pH variables, concentrations of various active species (e.g., complexing agents) can be used as independent variables, making it possible to analyze effects of various compounds that promote or inhibit corrosion. Usefulness of the methodology was demonstrated by generating real-solution stability diagrams for five representative systems (i.e., sulfur-water [S-H{sub 2}O], copper-ammonia-water [Cu-NH{sub 3}-H{sub 2}O], titanium-chlorine-calcium-water [Ti-Cl-Ca-H{sub 2}O], iron-sulfur-water [Fe-S-H{sub 2}O], and zinc-water [Zn-H{sub 2}O]).« less

Hydrological and Geochemical Influences on the Dissolved Silica Concentrations in Natural Water in a Steep Headwater Catchment

NASA Astrophysics Data System (ADS)

Asano, Y.; Uchida, T.; Ohte, N.

2002-12-01

Dissolved silica has been used as a useful indicator of a chemical weathering in many geochemical studies in natural environment. Previous hydrological studies indicated that various hydrological processes affect the dissolution and precipitation of silica in hillslope and transport of this silica to stream; however, information is still limited to link this knowledge to understand geochemical processes. The observations of dissolved silica concentration in groundwater, spring and stream water was conducted at the unchannelled hillslope in the Tanakami Mountains of central Japan; (1) to clarify the effects of preferential flowpaths including lateral and vertical flow in soil layer and flow through bedrock fracture in the variation of dissolved silica concentration in runoff and groundwater, and (2) to isolate the effects of mixing of water from geochemically diverse water sources on the dissolved silica concentration. The mean dissolved silica concentrations in soil water at 40 cm depth and transient groundwater formed in upslope area were relatively constant independent of the variation in the new water ratio. The mean dissolved silica concentrations were similar regardless of the sampling depth in soil although the mean residence times of water increase with depth. These results indicated that dissolved silica concentrations in soil water and transient groundwater were defined almost independent of contact time of water with minerals. While the mean dissolved silica concentration in perennial groundwater, which was recharged by infiltrating water through soil and water emerging from bedrock in a area near to spring, was more than twice that of transient groundwater and the variation was relatively large. The mean dissolved silica concentration increased significantly at downslope from perennial groundwater, spring to the stream and the spring and stream concentrations also showed large variation. The dissolved silica concentrations of those perennial groundwater, the spring and the stream was controlled by the mixing of water from soil and bedrock. Our results demonstrated that in most areas of this headwater catchment, the preferential flowpaths give only small effect on dissolved silica concentrations. While in a small area (less than 10% of the longitudinal axis of the hollow near the spring), the dissolved silica concentration were controlled by the mixing of water from geochemically diverse water sources.

Solar Fenton and solar TiO2 catalytic treatment of ofloxacin in secondary treated effluents: evaluation of operational and kinetic parameters.

PubMed

Michael, I; Hapeshi, E; Michael, C; Fatta-Kassinos, D

2010-10-01

Two different technical approaches based on advanced oxidation processes (AOPs), solar Fenton homogeneous photocatalysis (hv/Fe(2+)/H(2)O(2)) and heterogeneous photocatalysis with titanium dioxide (TiO(2)) suspensions were studied for the chemical degradation of the fluoroquinolone ofloxacin in secondary treated effluents. A bench-scale solar simulator in combination with an appropriate photochemical batch reactor was used to evaluate and select the optimal oxidation conditions of ofloxacin spiked in secondary treated domestic effluents. The concentration profile of the examined substrate during degradation was determined by UV/Vis spectrophotometry. Mineralization was monitored by measuring the dissolved organic carbon (DOC). The concentrations of Fe(2+) and H(2)O(2) were the key factors for the solar Fenton process, while the most important parameter of the heterogeneous photocatalysis was proved to be the catalyst loading. Kinetic analyses indicated that the photodegradation of ofloxacin can be described by a pseudo-first-order reaction. The rate constant (k) for the solar Fenton process was determined at different Fe(2+) and H(2)O(2) concentrations whereas the Langmuir-Hinshelwood (LH) kinetic expression was used to assess the kinetics of the heterogeneous photocatalytic process. The conversion of ofloxacin depends on several parameters based on the various experimental conditions, which were investigated. A Daphnia magna bioassay was used to evaluate the potential toxicity of the parent compound and its photo-oxidation by-products in different stages of oxidation. In the present study solar Fenton has been demonstrated to be more effective than the solar TiO(2) process, yielding complete degradation of the examined substrate and DOC reduction of about 50% in 30 min of the photocatalytic treatment. Copyright © 2010 Elsevier Ltd. All rights reserved.

Significance of CO2 donor on the production of succinic acid by Actinobacillus succinogenes ATCC 55618

PubMed Central

2011-01-01

Background Succinic acid is a building-block chemical which could be used as the precursor of many industrial products. The dissolved CO2 concentration in the fermentation broth could strongly regulate the metabolic flux of carbon and the activity of phosphoenolpyruvate (PEP) carboxykinase, which are the important committed steps for the biosynthesis of succinic acid by Actinobacillus succinogenes. Previous reports showed that succinic acid production could be promoted by regulating the supply of CO2 donor in the fermentation broth. Therefore, the effects of dissolved CO2 concentration and MgCO3 on the fermentation process should be investigated. In this article, we studied the impacts of gaseous CO2 partial pressure, dissolved CO2 concentration, and the addition amount of MgCO3 on succinic acid production by Actinobacillus succinogenes ATCC 55618. We also demonstrated that gaseous CO2 could be removed when MgCO3 was fully supplied. Results An effective CO2 quantitative mathematical model was developed to calculate the dissolved CO2 concentration in the fermentation broth. The highest succinic acid production of 61.92 g/L was obtained at 159.22 mM dissolved CO2 concentration, which was supplied by 40 g/L MgCO3 at the CO2 partial pressure of 101.33 kPa. When MgCO3 was used as the only CO2 donor, a maximal succinic acid production of 56.1 g/L was obtained, which was just decreased by 7.03% compared with that obtained under the supply of gaseous CO2 and MgCO3. Conclusions Besides the high dissolved CO2 concentration, the excessive addition of MgCO3 was beneficial to promote the succinic acid synthesis. This was the first report investigating the replaceable of gaseous CO2 in the fermentation of succinic acid. The results obtained in this study may be useful for reducing the cost of succinic acid fermentation process. PMID:22040346

Nitrogen distribution in a tropical urbanized estuarine system in northeastern Brazil.

PubMed

Dos Santos, Celimarcos Bezerra; Silva, Maria Aparecida Macêdo; de Souza, Marcelo F Landim; da Silva, Daniela Mariano Lopes

2018-01-08

Nitrogen enters estuaries mostly through fluvial discharge and tide, although anthropogenic sources are known to influence the amount of this element in these aquatic ecosystems. Thus, the objective of this work was to verify which river (Cachoeira, Fundão, and/or Santana) exerts greater influence on the distribution of dissolved N forms (Dissolved Organic Nitrogen and Dissolved Inorganic Nitrogen = NH 3 /NH 4 + , NO 2 - , and NO 3 - ) along a tropical urbanized estuarine system in northeastern Brazil. The studies estuarine system lies with in urban municipality, and the upper portion of the Cachoeira river estuary receives the treated effluent from this municipality through a sewage treatment station and untreated effluents from nearby villages. The selected sampling stations were located near the outfall of the rivers in the estuaries to the treatment plant and the villages. Of all the nitrogen forms, dissolved organic nitrogen (DON) prevailed in the estuarine system, followed by nitrate (NO 3 - ) as the main inorganic form. The highest concentrations were recorded in the fluvial portion and upper estuary of Cachoeira river in the dry season. Based on the N concentrations found in the estuarine system, Cachoeira river has the greatest anthropogenic influence due to the amount of untreated effluents from the villages and treated effluents from the sewage treatment plant (STP) in the upper portion of the estuary.

Increasing Regulatory Acceptance of Passive Samplers

DTIC Science & Technology

2010-12-01

microextraction ( SPME ) • Accumulate freely-dissolved organic contaminants from surrounding water into a solid phase • Contaminant concentrations of the...based on SPME (pg/L) D i s s o l v e d C o n c e n t r a t i o n b a s e d o n M u s s e l s ( p g / L ) 4,4’-DDE 4,4’-DDD 4,4’-DDT 1:1 line

Groundwater arsenic and fluoride in Rajnandgaon District, Chhattisgarh, northeastern India

NASA Astrophysics Data System (ADS)

Patel, Khageshwar Singh; Sahu, Bharat Lal; Dahariya, Nohar Singh; Bhatia, Amarpreet; Patel, Raj Kishore; Matini, Laurent; Sracek, Ondra; Bhattacharya, Prosun

2017-07-01

The groundwater of Ambagarh Chouki, Rajnandgaon, India, shows elevated levels of As and F-, frequently above the WHO guidelines. In this work, the concentrations of As, F-, Na+, Mg2+, Ca2+, Cl-, SO4 2-, HCO3 -, Fe, dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in the groundwater of Ambagarh Chouki are described. The sources of dissolved components in the groundwater are investigated using the cluster and factor analysis. Five factors have been identified and linked to processes responsible for the formation of groundwater chemistry. High concentrations of dissolved As seems to be linked to high concentrations of DOC, suggesting reductive dissolution of ferric oxyhydroxides as arsenic mobilization process. Fluoride is found in shallow depth water, presumably as a consequence of evaporation of water and removal of Ca2+ by precipitation of carbonates.

Environmentally friendly system for the degradation of multipesticide residues in aqueous media by the Fenton's reaction.

PubMed

Guimarães, Bruno de S; Kleemann, Natiele; Caldas, Sergiane S; Costa, Fabiane P; Silveira, Maria A K; Duarte, Fabio A; Primel, Ednei G

2014-01-01

A Fenton oxidation system employing zero-valent iron (whose source was swarf, a residue of metallurgical industries, in powder form) and hydrogen peroxide for the treatment of an aqueous solution with six pesticides was developed, and the effect of the iron metal content, pH, and hydrogen peroxide concentration was evaluated. The characterization of the aqueous solution resulted in: pH 5.6, 105 mg L(-1) of dissolved organic carbon, and 44.6 NTU turbidity. In addition, the characterization of the swarf by FAAS and ICP-MS showed 98.43 ± 7.40 % of zero-valent iron. The removal was strongly affected by the content of iron metal, pH, and hydrogen peroxide concentration. The best degradation conditions were 2.0 g swarf, pH 2.0, and 5 mmol L(-1) H2O2. At the end of the treatment, the pesticide degradation ranged from 60 to 100%, leading to 55% mineralization. Besides, all hydrogen peroxide was consumed and the determination of total dissolved iron resulted in 2 mg L(-1). Thus, the advantages of this system are rapid degradation (up to 20 min), high-degradation rates, simple handling, and low cost.

Assessment of diel chemical and isotopic techniques to investigate biogeochemical cycles in the upper Klamath River, Oregon, USA

USGS Publications Warehouse

Poulson, S.R.; Sullivan, A.B.

2009-01-01

The upper Klamath River experiences a cyanobacterial algal bloom and poor water quality during the summer. Diel chemical and isotopic techniques have been employed in order to investigate the rates of biogeochemical processes. Four diel measurements of field parameters (temperature, pH, dissolved oxygen concentrations, and alkalinity) and stable isotope compositions (dissolved oxygen-??18O and dissolved inorganic carbon-??13C) have been performed between June 2007 and August 2008. Significant diel variations of pH, dissolved oxygen (DO) concentration, and DO-??18O were observed, due to varying rates of primary productivity vs. respiration vs. gas exchange with air. Diel cycles are generally similar to those previously observed in river systems, although there are also differences compared to previous studies. In large part, these different diel signatures are the result of the low turbulence of the upper Klamath River. Observed changes in the diel signatures vs. sampling date reflect the evolution of the status of the algal bloom over the course of the summer. Results indicate the potential utility of applying diel chemical and stable isotope techniques to investigate the rates of biogeochemical cycles in slow-moving rivers, lakes, and reservoirs, but also illustrate the increased complexity of stable isotope dynamics in these low-turbulence systems compared to well-mixed aquatic systems. ?? 2009 Elsevier B.V.

O2 reduction and denitrification rates in shallow aquifers

NASA Astrophysics Data System (ADS)

Tesoriero, Anthony J.; Puckett, Larry J.

2011-12-01

O2 reduction and denitrification rates were determined in shallow aquifers of 12 study areas representing a wide range in sedimentary environments and climatic conditions. Zero- and first-order rates were determined by relating reactant or product concentrations to apparent groundwater age. O2 reduction rates varied widely within and between sites, with zero-order rates ranging from <3 μmol L-1 yr-1 to more than 140 μmol L-1 yr-1 and first-order rates ranging from 0.02 to 0.27 yr-1. Moderate denitrification rates (10-100 μmol N L-1 yr-1; 0.06-0.30 yr-1) were observed in most areas with O2 concentrations below 60 μmol L-1, while higher rates (>100 μmol N L-1 yr-1; >0.36 yr-1) occur when changes in lithology result in a sharp increase in the supply of electron donors. Denitrification lag times (i.e., groundwater travel times prior to the onset of denitrification) ranged from <20 yr to >80 yr. The availability of electron donors is indicated as the primary factor affecting O2 reduction rates. Concentrations of dissolved organic carbon (DOC) and/or sulfate (an indicator of sulfide oxidation) were positively correlated with groundwater age at sites with high O2 reduction rates and negatively correlated at sites with lower rates. Furthermore, electron donors from recharging DOC are not sufficient to account for appreciable O2 and nitrate reduction. These relations suggest that lithologic sources of DOC and sulfides are important sources of electrons at these sites but surface-derived sources of DOC are not. A review of published rates suggests that denitrification tends to occur more quickly when linked with sulfide oxidation than with carbon oxidation.

O 2 reduction and denitrification rates in shallow aquifers

USGS Publications Warehouse

Tesoriero, A.J.; Puckett, L.J.

2011-01-01

O 2 reduction and denitrification rates were determined in shallow aquifers of 12 study areas representing a wide range in sedimentary environments and climatic conditions. Zero-and first-order rates were determined by relating reactant or product concentrations to apparent groundwater age. O 2 reduction rates varied widely within and between sites, with zero-order rates ranging from <3 ??mol L -1 yr -1 to more than 140 ??mol L -1 yr -1 and first-order rates ranging from 0.02 to 0.27 yr -1. Moderate denitrification rates (10-100 ??mol N L -1 yr -1; 0.06-0.30 yr -1) were observed in most areas with O 2 concentrations below 60 mol L -1, while higher rates (>100 mol N L -1 yr -1; >0.36 yr -1) occur when changes in lithology result in a sharp increase in the supply of electron donors. Denitrification lag times (i.e., groundwater travel times prior to the onset of denitrification) ranged from <20 yr to >80 yr. The availability of electron donors is indicated as the primary factor affecting O 2 reduction rates. Concentrations of dissolved organic carbon (DOC) and/or sulfate (an indicator of sulfide oxidation) were positively correlated with groundwater age at sites with high O 2 reduction rates and negatively correlated at sites with lower rates. Furthermore, electron donors from recharging DOC are not sufficient to account for appreciable O 2 and nitrate reduction. These relations suggest that lithologic sources of DOC and sulfides are important sources of electrons at these sites but surface-derived sources of DOC are not. A review of published rates suggests that denitrification tends to occur more quickly when linked with sulfide oxidation than with carbon oxidation. copyright 2011 by the American Geophysical Union.

Simulation of hydrodynamics, temperature, and dissolved oxygen in Beaver Lake, Arkansas, 1994-1995

USGS Publications Warehouse

Haggard, Brian; Green, W. Reed

2002-01-01

The tailwaters of Beaver Lake and other White River reservoirs support a cold-water trout fishery of significant economic yield in northwestern Arkansas. The Arkansas Game and Fish Commission has requested an increase in existing minimum flows through the Beaver Lake dam to increase the amount of fishable waters downstream. Information is needed to assess the impact of additional minimum flows on temperature and dissolved-oxygen qualities of reservoir water above the dam and the release water. A two-dimensional, laterally averaged hydrodynamic, thermal and dissolved-oxygen model was developed and calibrated for Beaver Lake, Arkansas. The model simulates surface-water elevation, currents, heat transport and dissolved-oxygen dynamics. The model was developed to assess the impacts of proposed increases in minimum flows from 1.76 cubic meters per second (the existing minimum flow) to 3.85 cubic meters per second (the additional minimum flow). Simulations included assessing (1) the impact of additional minimum flows on tailwater temperature and dissolved-oxygen quality and (2) increasing initial water-surface elevation 0.5 meter and assessing the impact of additional minimum flow on tailwater temperatures and dissolved-oxygen concentrations. The additional minimum flow simulation (without increasing initial pool elevation) appeared to increase the water temperature (<0.9 degrees Celsius) and decrease dissolved oxygen concentration (<2.2 milligrams per liter) in the outflow discharge. Conversely, the additional minimum flow plus initial increase in pool elevation (0.5 meter) simulation appeared to decrease outflow water temperature (0.5 degrees Celsius) and increase dissolved oxygen concentration (<1.2 milligrams per liter) through time. However, results from both minimum flow scenarios for both water temperature and dissolved oxygen concentration were within the boundaries or similar to the error between measured and simulated water column profile values.

Meta-omic signatures of microbial metal and nitrogen cycling in marine oxygen minimum zones

PubMed Central

Glass, Jennifer B.; Kretz, Cecilia B.; Ganesh, Sangita; Ranjan, Piyush; Seston, Sherry L.; Buck, Kristen N.; Landing, William M.; Morton, Peter L.; Moffett, James W.; Giovannoni, Stephen J.; Vergin, Kevin L.; Stewart, Frank J.

2015-01-01

Iron (Fe) and copper (Cu) are essential cofactors for microbial metalloenzymes, but little is known about the metalloenyzme inventory of anaerobic marine microbial communities despite their importance to the nitrogen cycle. We compared dissolved O2, NO3−, NO2−, Fe and Cu concentrations with nucleic acid sequences encoding Fe and Cu-binding proteins in 21 metagenomes and 9 metatranscriptomes from Eastern Tropical North and South Pacific oxygen minimum zones and 7 metagenomes from the Bermuda Atlantic Time-series Station. Dissolved Fe concentrations increased sharply at upper oxic-anoxic transition zones, with the highest Fe:Cu molar ratio (1.8) occurring at the anoxic core of the Eastern Tropical North Pacific oxygen minimum zone and matching the predicted maximum ratio based on data from diverse ocean sites. The relative abundance of genes encoding Fe-binding proteins was negatively correlated with O2, driven by significant increases in genes encoding Fe-proteins involved in dissimilatory nitrogen metabolisms under anoxia. Transcripts encoding cytochrome c oxidase, the Fe- and Cu-containing terminal reductase in aerobic respiration, were positively correlated with O2 content. A comparison of the taxonomy of genes encoding Fe- and Cu-binding vs. bulk proteins in OMZs revealed that Planctomycetes represented a higher percentage of Fe genes while Thaumarchaeota represented a higher percentage of Cu genes, particularly at oxyclines. These results are broadly consistent with higher relative abundance of genes encoding Fe-proteins in the genome of a marine planctomycete vs. higher relative abundance of genes encoding Cu-proteins in the genome of a marine thaumarchaeote. These findings highlight the importance of metalloenzymes for microbial processes in oxygen minimum zones and suggest preferential Cu use in oxic habitats with Cu > Fe vs. preferential Fe use in anoxic niches with Fe > Cu. PMID:26441925

Photoproduction of hydrogen peroxide in aqueous solution from model compounds for chromophoric dissolved organic matter (CDOM).

PubMed

Clark, Catherine D; de Bruyn, Warren; Jones, Joshua G

2014-02-15

To explore whether quinone moieties are important in chromophoric dissolved organic matter (CDOM) photochemistry in natural waters, hydrogen peroxide (H2O2) production and associated optical property changes were measured in aqueous solutions irradiated with a Xenon lamp for CDOM model compounds (dihydroquinone, benzoquinone, anthraquinone, napthoquinone, ubiquinone, humic acid HA, fulvic acid FA). All compounds produced H2O2 with concentrations ranging from 15 to 500 μM. Production rates were higher for HA vs. FA (1.32 vs. 0.176 mM h(-1)); values ranged from 6.99 to 0.137 mM h(-1) for quinones. Apparent quantum yields (Θ app; measure of photochemical production efficiency) were higher for HA vs. FA (0.113 vs. 0.016) and ranged from 0.0018 to 0.083 for quinones. Dihydroquinone, the reduced form of benzoquinone, had a higher production rate and efficiency than its oxidized form. Post-irradiation, quinone compounds had absorption spectra similar to HA and FA and 3D-excitation-emission matrix fluorescence spectra (EEMs) with fluorescent peaks in regions associated with CDOM. Copyright © 2014 Elsevier Ltd. All rights reserved.

Interannual Variations in Global Net Carbon Production in the Absence of Fixed Nitrogen: Implication of New Production Supported by Dinitrogen Fixing Microorganisms

NASA Astrophysics Data System (ADS)

Lee, K.; Ko, Y. H.

2016-12-01

In the ocean without the measurable levels of nitrate, new production, i.e. the amount of carbon transported from the sunlit upper water to deep water, was estimated by summing the seasonal reduction in the total dissolved inorganic carbon (NCT = CT x 35/S) concentration in the surface mixed layer. Total reduction in the mixed layer NCT inventory in each 4o latitude by 5o longitude was calculated using an annual cycle of NCT, which was deduced from global monthly records of partial pressure of CO2 (based on more than 6.5 million data) and total alkalinity fields using thermodynamic models. The estimation of total NCT reduction for each pixel was then corrected for small changes caused by atmospheric nitrogen deposition and net air-sea CO2 exchange. This novel method yields 0.8 ± 0.3 petagrams of global new production per year (Pg C yr, Pg = 1015 grams), which is likely to be mediated exclusively by dinitrogen (N2) fixing microorganisms. These organisms utilize the inexhaustible pool of dissolved N2 and thereby circumvent nitrate limitation, particularly in the oligotrophic tropical and subtropical ocean.

Triple oxygen isotope composition of photosynthetic oxygen

NASA Astrophysics Data System (ADS)

van der Meer, Anne; Kaiser, Jan

2013-04-01

The measurement of biological production rates is essential for our understanding how marine ecosystems are sustained and how much CO2 is taken up through aquatic photosynthesis. Traditional techniques to measure marine production are laborious and subject to systematic errors. A biogeochemical approach based on triple oxygen isotope measurements in dissolved oxygen (O2) has been developed over the last few years, which allows the derivation of gross productivity integrated over the depth of the mixed layer and the time-scale of O2 gas exchange (Luz and Barkan, 2000). This approach exploits the relative 17O/16O and 18O/16O isotope ratio differences of dissolved O2 compared to atmospheric O2 to work out the rate of biological production. Two parameters are key for this calculation: the isotopic composition of dissolved O2 in equilibrium with air and the isotopic composition of photosynthetic oxygen. Recently, a controversy has emerged in the literature over these parameters (Kaiser, 2011) and one of the goals of this research is to provide additional data to resolve this controversy. In order to obtain more information on the isotopic signature of biological oxygen, laboratory experiments have been conducted to determine the isotopic composition of oxygen produced by different phytoplankton cultures.

An experimental study of ^{{{{Fe}}^{2 + } {-}{{Mg}}}} K_{{D}} between orthopyroxene and rhyolite: a strong dependence on H2O in the melt

NASA Astrophysics Data System (ADS)

Waters, Laura E.; Lange, Rebecca A.

2017-06-01

The effect of temperature, pressure, and dissolved H2O in the melt on the Fe2+-Mg exchange coefficient between orthopyroxene and rhyolite melt was investigated with a series of H2O fluid-saturated phase-equilibrium experiments. Experiments were conducted in a rapid-quench cold-seal pressure vessel over a temperature and pressure range of 785-850 °C and 80-185 MPa, respectively. Oxygen fugacity was buffered with the solid Ni-NiO assemblage in a double-capsule assembly. These experiments, when combined with H2O-undersaturated experiments in the literature, show that ^{{{{Fe}}^{2 + } {-}{{Mg}}}} K_{{D}} between orthopyroxene and rhyolite liquid increases strongly (from 0.23 to 0.54) as a function of dissolved water in the melt (from 2.7 to 5.6 wt%). There is no detectable effect of temperature or pressure over an interval of 65 °C and 100 MPa, respectively, on the Fe2+-Mg exchange coefficient values. The data show that Fe-rich orthopyroxene is favored at high water contents, whereas Mg-rich orthopyroxene crystallizes at low water contents. It is proposed that the effect of dissolved water in the melt on the composition of orthopyroxene is analogous to its effect on the composition of plagioclase. In the latter case, dissolved hydroxyl groups preferentially complex with Na+ relative to Ca2+, which reduces the activity of the albite component, leading to a more anorthite-rich (calcic) plagioclase. Similarly, it is proposed that dissolved hydroxyl groups preferentially complex with Mg2+ relative to Fe2+, thus lowering the activity of the enstatite component, leading to a more Fe-rich orthopyroxene at high water contents in the melt. The experimental results presented in this study show that reversely zoned pyroxene (i.e., Mg-rich rims) in silicic magmas may be a result of H2O degassing and not necessarily the result of mixing with a more mafic magma.

Preparation of Zinc Oxide (ZnO) Thin Film as Transparent Conductive Oxide (TCO) from Zinc Complex Compound on Thin Film Solar Cells: A Study of O2 Effect on Annealing Process

NASA Astrophysics Data System (ADS)

Muslih, E. Y.; Kim, K. H.

2017-07-01

Zinc oxide (ZnO) thin film as a transparent conductive oxide (TCO) for thin film solar cell application was successfully prepared through two step preparations which consisted of deposition by spin coating at 2000 rpm for 10 second and followed by annealing at 500 °C for 2 hours under O2 and ambient atmosphere. Zinc acetate dehydrate was used as a precursor which dissolved in ethanol and acetone (1:1 mol) mixture in order to make a zinc complex compound. In this work, we reported the O2 effect, reaction mechanism, structure, morphology, optical and electrical properties. ZnO thin film in this work shows a single phase of wurtzite, with n-type semiconductor and has band gap, carrier concentration, mobility, and resistivity as 3.18 eV, 1.21 × 10-19cm3, 11 cm2/Vs, 2.35 × 10-3 Ωcm respectively which is suitable for TCO at thin film solar cell.

Reevaluation of the global warming impacts of algae-derived biofuels to account for possible contributions of nitrous oxide.

PubMed

Bauer, Sarah K; Grotz, Lara S; Connelly, Elizabeth B; Colosi, Lisa M

2016-10-01

The environmental impacts of algae biofuels have been evaluated by life-cycle assessment (LCA); however, these analyses have overlooked nitrous oxide (N2O), a potent greenhouse gas. A literature analysis was performed to estimate algal N2O emissions and assess the impacts of growth conditions on flux magnitudes. Nitrogen source and dissolved oxygen concentration were identified as possible key contributors; therefore, their individual and combined impacts were evaluated using bench-scale experiments. It was observed that maximum N2O emissions (77.5μg/galgae/day) occur under anoxic conditions with nitrite. Conversely, minimum emissions (6.25μg/galgae/day) occur under oxic conditions with nitrate. Aggregated N2O flux estimates were then incorporated into a LCA framework for algae biodiesel. Accounting for "low" N2O emissions mediated no significant increase (<1%) compared to existing GWP estimates; however, "high" N2O emissions mediate an increase of roughly 25%, potentially jeopardizing the anticipated economic and environmental performances of algae biofuels. Copyright © 2016 Elsevier Ltd. All rights reserved.

The use of catalyst to enhance the wet oxidation process.

PubMed

Maugans, C; Kumfer, B

2007-01-01

Wet oxidation tests were performed on two pure compound streams: acetic acid and ammonia; and on two wastewater streams: acrylic acid wastewater and sulphide laden spent caustic. Test results showed that Mn/Ce and Pt/TiO2 were effective catalysts that greatly enhanced acetic acid, ammonia and acrylic acid wastewater destruction. However, the Mn/Ce catalyst performance appears to be inhibited by concentrated salts dissolved in solution. This could limit the applicability of this catalyst for the treatment of brackish wastewaters. Zr, Ce and Ce nanoparticles were also shown to exhibit some catalytic activity, however not to the extent of the Mn/Ce and the Pt/TiO2.

Use of dissolved H2 concentrations to determine distribution of microbially catalyzed redox reactions in anoxic groundwater

USGS Publications Warehouse

Lovley, D.R.; Chapelle, F.H.; Woodward, J.C.

1994-01-01

The potential for using concentrations of dissolved H2 to determine the distribution of redox processes in anoxic groundwaters was evaluated. In pristine aquifers in which standard geochemical measurements indicated that Fe-(III) reduction, sulfate reduction, or methanogenesis was the terminal electron accepting process (TEAP), the H2 concentrations were similar to the H2 concentrations that have previously been reported for aquatic sediments with the same TEAPs. In two aquifers contaminated with petroleum products, it was impossible with standard geochemical analyses to determine which TEAPs predominated in specific locations. However, the TEAPs predicted from measurements of dissolved H2 were the same as those determined directly through measurements of microbial processes in incubated aquifer material. These results suggest that H2 concentrations may be a useful tool for analyzing the redox chemistry of nonequilibrium groundwaters.

[Effects of nitrogen addition and elevated CO2 concentration on soil dissolved organic carbon and nitrogen in rhizosphere and non-rhizosphere of Bothriochloa ischaemum].

PubMed

Xiao, Lie; Liu, Guo Bin; Li, Peng; Xue, Sha

2017-01-01

A pot experiment was conducted to study soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the rhizosphere and non-rhizosphere of Bothriochloa ischaemum in loess hilly-gully region under the different treatments of CO 2 concentrations (400 and 800 μmol·mol -1 ) and nitrogen addition (0, 2.5, 5.0 g N·m -2 ·a -1 ). The results showed that eleva-ted CO 2 treatments had no significant effect on the contents of DOC, dissolved total nitrogen (DTN), DON, dissolved ammonium nitrogen (NH 4 + -N) and dissolved nitrate nitrogen (NO 3 - -N) in the soil of rhizosphere and non-rhizosphere of B. ischaemum. The contents of DTN, DON, and NO 3 - -N in the rhizosphere soil were significantly increased with the nitrogen application and the similar results of DTN and NO 3 - -N also were observed in the non-rhizosphere of B. ischaemum. Nitrogen application significantly decreased DOC/DON in the rhizosphere of B. ischaemum. The contents of DTN, NO 3 - -N and DON in the soil of rhizosphere were significantly lower than that in the non-rhizosphere soil, and DOC/DON was significantly higher in the rhizosphere soil than that in the non-rhizosphere soil. It indicated that short-term elevated CO 2 concentration had no significant influence on the contents of soil dissolved organic carbon and nitrogen. Simulated nitrogen deposition, to some extent, increased the content of soil dissolved nitrogen, but it was still insufficient to meet the demand of dissolved nitrogen for plant growing.

Crustacean zooplankton release copious amounts of dissolved organic matter as taurine in the ocean.

PubMed

Clifford, Elisabeth L; Hansell, Dennis A; Varela, Marta M; Nieto-Cid, Mar; Herndl, Gerhard J; Sintes, Eva

2017-11-01

Taurine (Tau), an amino acid-like compound, is present in almost all marine metazoans including crustacean zooplankton. It plays an important physiological role in these organisms and is released into the ambient water throughout their life cycle. However, limited information is available on the release rates by marine organisms, the concentrations and turnover of Tau in the ocean. We determined dissolved free Tau concentrations throughout the water column and its release by abundant crustacean mesozooplankton at two open ocean sites (Gulf of Alaska and North Atlantic). At both locations, the concentrations of dissolved free Tau were in the low nM range (up to 15.7 nM) in epipelagic waters, declining sharply in the mesopelagic to about 0.2 nM and remaining fairly stable throughout the bathypelagic waters. Pacific amphipod-copepod assemblages exhibited lower dissolved free Tau release rates per unit biomass (0.8 ± 0.4 μmol g -1 C-biomass h -1 ) than Atlantic copepods (ranging between 1.3 ± 0.4 μmol g -1 C-biomass h -1 and 9.5 ± 2.1 μmol g -1 C-biomass h -1 ), in agreement with the well-documented inverse relationship between biomass-normalized excretion rates and body size. Our results indicate that crustacean zooplankton might contribute significantly to the dissolved organic matter flux in marine ecosystems via dissolved free Tau release. Based on the release rates and assuming steady state dissolved free Tau concentrations, turnover times of dissolved free Tau range from 0.05 d to 2.3 d in the upper water column and are therefore similar to those of dissolved free amino acids. This rapid turnover indicates that dissolved free Tau is efficiently consumed in oceanic waters, most likely by heterotrophic bacteria.

Photoluminescence, chemiluminescence and anodic electrochemiluminescence of hydrazide-modified graphene quantum dots

NASA Astrophysics Data System (ADS)

Dong, Yongqiang; Dai, Ruiping; Dong, Tongqing; Chi, Yuwu; Chen, Guonan

2014-09-01

Single-layer graphene quantum dots (SGQDs) were refluxed with hydrazine (N2H4) to prepare hydrazide-modified SGQDs (HM-SGQDs). Compared with SGQDs, partial oxygen-containing groups have been removed from HM-SGQDs. At the same time, a lot of hydrazide groups have been introduced into HM-SGQDs. The introduced hydrazide groups provide HM-SGQDs with a new kind of surface state, and give HM-SGQDs unique photoluminescence (PL) properties such as blue-shifted PL emission and a relatively high PL quantum yield. More importantly, the hydrazide-modification made HM-SGQDs have abundant luminol-like units. Accordingly, HM-SGQDs exhibit unique and excellent chemiluminescence (CL) and anodic electrochemiluminescence (ECL). The hydrazide groups of HM-SGQDs can be chemically oxidized by the dissolved oxygen (O2) in alkaline solutions, producing a strong CL signal. The CL intensity is mainly dependent on the pH value and the concentration of O2, implying the potential applications of HM-SGQDs in pH and O2 sensors. The hydrazide groups of HM-SGQDs can also be electrochemically oxidized in alkaline solutions, producing a strong anodic ECL signal. The ECL intensity can be enhanced sensitively by hydrogen peroxide (H2O2). The enhanced ECL intensity is proportional to the concentration of H2O2 in a wide range of 3 μM to 500 μM. The detection limit of H2O2 was calculated to be about 0.7 μM. The results suggest the great potential applications of HM-SGQDs in the sensors of H2O2 and bio-molecules that are able to produce H2O2 in the presence of enzymes.Single-layer graphene quantum dots (SGQDs) were refluxed with hydrazine (N2H4) to prepare hydrazide-modified SGQDs (HM-SGQDs). Compared with SGQDs, partial oxygen-containing groups have been removed from HM-SGQDs. At the same time, a lot of hydrazide groups have been introduced into HM-SGQDs. The introduced hydrazide groups provide HM-SGQDs with a new kind of surface state, and give HM-SGQDs unique photoluminescence (PL) properties such as blue-shifted PL emission and a relatively high PL quantum yield. More importantly, the hydrazide-modification made HM-SGQDs have abundant luminol-like units. Accordingly, HM-SGQDs exhibit unique and excellent chemiluminescence (CL) and anodic electrochemiluminescence (ECL). The hydrazide groups of HM-SGQDs can be chemically oxidized by the dissolved oxygen (O2) in alkaline solutions, producing a strong CL signal. The CL intensity is mainly dependent on the pH value and the concentration of O2, implying the potential applications of HM-SGQDs in pH and O2 sensors. The hydrazide groups of HM-SGQDs can also be electrochemically oxidized in alkaline solutions, producing a strong anodic ECL signal. The ECL intensity can be enhanced sensitively by hydrogen peroxide (H2O2). The enhanced ECL intensity is proportional to the concentration of H2O2 in a wide range of 3 μM to 500 μM. The detection limit of H2O2 was calculated to be about 0.7 μM. The results suggest the great potential applications of HM-SGQDs in the sensors of H2O2 and bio-molecules that are able to produce H2O2 in the presence of enzymes. Electronic supplementary information (ESI) available: AFM images of SGQDs and HM-SGQDs (Fig. S1), FT-IR spectra of SGQDs and HM-SGQDs (Fig. S2), UV-vis and PL emission spectra of R-SGQDs (Fig. S3), cathodic ECL responses of SGQD, R-SGQDs and HM-SGQDs (Fig. S4), and the pH effect on the anodic ECL responses of HM-SGQDs (Fig. S5). See DOI: 10.1039/c4nr02539c

Greenhouse gases emission from the sewage draining rivers.

PubMed

Hu, Beibei; Wang, Dongqi; Zhou, Jun; Meng, Weiqing; Li, Chongwei; Sun, Zongbin; Guo, Xin; Wang, Zhongliang

2018-01-15

Carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) concentration, saturation and fluxes in rivers (Beitang drainage river, Dagu drainage rive, Duliujianhe river, Yongdingxinhe river and Nanyunhe river) of Tianjin city (Haihe watershed) were investigated during July and October in 2014, and January and April in 2015 by static headspace gas chromatography method and the two-layer model of diffusive gas exchange. The influence of environmental variables on greenhouse gases (GHGs) concentration under the disturbance of anthropogenic activities was discussed by Spearman correlative analysis and multiple stepwise regression analysis. The results showed that the concentration and fluxes of CO 2 , CH 4 and N 2 O were seasonally variable with >winter>fall>summer, spring>summer>winter>fall and summer>spring>winter>fall for concentrations and spring>summer>fall>winter, spring>summer>winter>fall and summer>spring>fall>winter for fluxes respectively. The GHGs concentration and saturation were higher in comprehensively polluted river sites and lower in lightly polluted river sites. The three GHGs emission fluxes in two sewage draining rivers of Tianjin were clearly higher than those of other rivers (natural rivers) and the spatial variation of CH 4 was more obvious than the others. CO 2 and N 2 O air-water interface emission fluxes of the sewage draining rivers in four seasons were about 1.20-2.41 times and 1.13-3.12 times of those in the natural rivers. The CH 4 emission fluxes of the sewage draining rivers were 3.09 times in fall to 10.87 times in spring of those in the natural rivers in different season. The wind speed, water temperature and air temperature were related to GHGs concentrations. Nitrate and nitrite (NO 3 - +NO 2 - -N) and ammonia (NH 4 + -N) were positively correlated with CO 2 concentration and CH 4 concentration; and dissolved oxygen (DO) concentration was negatively correlated with CH 4 concentration and N 2 O concentration. The effect of human activities on carbon and nitrogen cycling in river is great. Copyright © 2017 Elsevier B.V. All rights reserved.

Biological Productivity from an Oxygen Mass Balance in the subarctic North Pacific

NASA Astrophysics Data System (ADS)

Giesbrecht, K. E.; Hamme, R. C.

2008-12-01

Biological productivity is an important process controlling the export of carbon into the deep ocean and thus influencing the earth's climate. An O2 mass balance of the upper ocean can estimate this export of organic carbon if the physical processes affecting the O2 concentrations are accounted for. This can be accomplished by measuring the dissolved O2/Ar ratio, because their similar physical properties allow us to consider Ar an 'abiotic' O2 analogue. Here we present a two-year data set of O2/N2/Ar ratio measurements collected at Station Papa and along Line P in 2007/08. Line P, situated in the subarctic North Pacific, is a series of oceanographic stations running from the southwest tip of Vancouver Island to Station Papa (50°N, 145°W), one of the oldest deep-ocean time series in existence which is located in the High-Nutrient/Low-Chlorophyll (HNLC) region of the subarctic gyre. Current cruises along Line P run three times per year, typically in February, June and August. The dissolved gas ratios are measured using a stable isotope mass spectrometer and oxygen concentrations by titration. In a simple steady state, we equate biological O2 production to diffusive gas exchange, using the O2/Ar ratio to normalize the physical component of the oxygen signal and calculate the net biological oxygen production. Diffusive gas exchange is calculated using a wind speed parameterization. Preliminary estimates of the net biological production in the mixed layer at Station Papa for 2007 are calculated at 30.9 and 14.0 mmol C m-2 d- 1 for June and August respectively, both exhibiting mixed layer O2/Ar supersaturations. The O2/Ar undersaturation in the mixed layer for February 2007 suggests net respiration at that time. The wind speed parameterization of diffusive gas exchange is the major source of error for this method. We plan to refine our productivity calculation to account for vertical mixing and also by measuring rates of production using a number of different methods, so that we may determine if the values obtained converge on a result. Future investigations to obtain a better-constrained estimate of the biological carbon export in this region by measuring Nitrogen and Carbon uptake rates in the euphotic zone using dual, stable isotope tracer 15N/13C incubations in addition to the oxygen mass balance will be discussed.

DEVELOPMENT AND DEPLOYMENT OF VACUUM SALT DISTILLATION AT THE SAVANNAH RIVER SITE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pierce, R.; Pak, D.; Edwards, T.

2010-10-28

The Savannah River Site has a mission to dissolve fissile materials and disposition them. The primary fissile material is plutonium dioxide (PuO{sub 2}). To support dissolution of these materials, the Savannah River National Laboratory (SRNL) designed and demonstrated a vacuum salt distillation (VSD) apparatus using both representative radioactive samples and non-radioactive simulant materials. Vacuum salt distillation, through the removal of chloride salts, increases the quantity of materials suitable for processing in the site's HB-Line Facility. Small-scale non-radioactive experiments at 900-950 C show that >99.8 wt % of the initial charge of chloride salt distilled from the sample boat with recoverymore » of >99.8 wt % of the ceric oxide (CeO{sub 2}) - the surrogate for PuO{sub 2} - as a non-chloride bearing 'product'. Small-scale radioactive testing in a glovebox demonstrated the removal of sodium chloride (NaCl) and potassium chloride (KCl) from 13 PuO{sub 2} samples. Chloride concentrations were distilled from a starting concentration of 1.8-10.8 wt % to a final concentration <500 mg/kg chloride. Initial testing of a non-radioactive, full-scale production prototype is complete. A designed experiment evaluated the impact of distillation temperature, time at temperature, vacuum, product depth, and presence of a boat cover. Significant effort has been devoted to mechanical considerations to facilitate simplified operation in a glovebox.« less

Dissolved and particulate 230Th-232Th in the Central Equatorial Pacific Ocean: Evidence for far-field transport of the East Pacific Rise hydrothermal plume

NASA Astrophysics Data System (ADS)

Lopez, Grecia I.; Marcantonio, Franco; Lyle, Mitch; Lynch-Stieglitz, Jean

2015-12-01

We assess the distribution of 230Th and 232Th along a latitudinal gradient in the Central Equatorial Pacific Ocean (∼155°W-159°W) at two sites: 8°N and the equator. The dissolved 230Th concentration profile at 8°N increases nearly linearly from the surface to 2000 m, exhibiting behavior consistent with thermodynamic reversible scavenging. However, from 2000 m to 3000 m, the dissolved 230Th concentrations exhibit little change, before increasing slightly from 3000 m to the bottom. At this site dissolved 230Th concentrations range from 1.1 fg/kg at 100 m to 55.2 fg/kg at 4600 m. At the equator, dissolved 230Th concentrations are slightly lower, and range from undetectable at 25 m to 19.1 fg/kg at 3038 m. The pattern in the dissolved 230Th concentration profile at the equator is indistinguishable from that at 8°N. The mid-depth-water deviation from equilibrium reversible scavenging between 2 and 3 km in the 230Th profiles (lower concentrations than expected) at both sites occurs in the interval of the water column that is consistent with an interval that has high concentrations of 3He and dissolved Fe at other nearby sites. This 3He- and Fe-rich signal has been traced to hydrothermal plumes from the East Pacific Rise, thousands of kilometers away. We hypothesize that the lower concentrations of 230Th in mid-depth waters of the Central Equatorial Pacific are a result of a 5000-km transit of waters that have had their 230Th scavenged by Fe-Mn particulates close to the EPR. Oceanic residence times of thorium combined with dissolved 232Th concentrations suggest dust fluxes of about ∼ 0.5- 0.6 gm-2yr-1 to the sea surface. These fluxes are in agreement with other empirical studies in the Pacific, but are higher than those suggested by global atmospheric circulation models.

Measured Fluid Flow in an Active H2O-CO2 Geothermal Well as an Analog to Fluid Flow in Fractures on Mars: Preliminary Report

NASA Technical Reports Server (NTRS)

Kieffer, Susan W.; Brown, K. L.; Simmons, Stuart F.; Watson, Arnold

2004-01-01

Water in the Earth's crust generally contains dissolved gases such as CO2. Models for both 'Blue Mars' (H2O-driven processes) and 'White Mars' (CO2-driven processes) predict liquid H2O with dissolved CO2 at depth. The fate of dissolved CO2 as this mixture rises toward the surface has not been quantitatively explored. Our approach is a variation on NASA's 'Follow the Water' as we 'Follow the Fluid' from depth to the surface in hydrothermal areas on Earth and extrapolate our results to Mars. This is a preliminary report on a field study of fluid flow in a producing geothermal well. For proprietary reasons, the name and location of this well cannot be revealed, so we have named it 'Earth1' for this study.

Denitrification in the karstic Floridan Aquifer

NASA Astrophysics Data System (ADS)

Fork, M.; Albertin, A. R.; Heffernan, J. B.; Katz, B. G.; Cohen, M. J.

2010-12-01

Nitrate concentrations in the karstic Floridan Aquifer have increased dramatically over the past 50 years, owing to agricultural intensification and urbanization. Due to low concentrations of organic matter and moderately oxic conditions in the Floridan Aquifer, groundwater denitrification has been assumed to be negligible. In this study, we evaluate that assumption using both existing and new data describing dissolved gases (Ne, N2, O2, Ar) and NO3- concentration and isotopic composition (δ18O- and δ15N-NO3) in the aquifer’s artesian springs. For new data, we collected samples from 33 spring vents representing a gradient of both DO and NO3- concentrations in northern Florida and used Membrane Inlet Mass Spectrometry (MIMS) to directly measure dissolved N2 and Ar. We modeled the physical processes (recharge temperature, dissolution of excess air) driving super-saturation of N2 gas using Ne and Ar where data describing Ne were available. Ar concentrations were correlated closely with recharge temperature, which ranged from 15.7 - 22.2°C, while Ne was closely correlated with excess air, which ranged from 1.05 to 2.66 mg L-1 and averaged 1.83 mg L-1. Estimates of physical mechanisms allowed calculation of expected N2 concentrations that were compared to observed N2 concentrations. Where Ne data were unavailable, we assumed excess air equal to the empirical average. Overall, observed N2 exceeded expectations based on physical processes in 33 of 47 cases; average excess N2 was 0.48 mg L-1 across all sites. In addition, excess N2 was negatively correlated with DO (r2 = 0.46); springs with low DO (<2.5 mg L-1) had an average of 0.84 mg L-1 excess N2 while springs with higher DO contain little to no excess N2 (0.04 mg L-1). In addition, excess N2 was positively correlated with δ15N-NO3-. These observations are consistent with the widespread occurrence of denitrification in the Floridan Aquifer. Low DOC concentrations indicate that alternative electron donors may fuel nitrate reduction. Scaling to regional estimates of N2 production based on springs discharge and DO concentrations indicates that subsurface denitrification may account for some of the imbalance in springshed nutrient budgets. In addition, we conclude that use of δ15N-NO3- to diagnose isotope sourcing may be conflated by fractionation of aquifer nitrate pools by denitrification.

Optimization of chemical structure of Schottky-type selection diode for crossbar resistive memory.

PubMed

Kim, Gun Hwan; Lee, Jong Ho; Jeon, Woojin; Song, Seul Ji; Seok, Jun Yeong; Yoon, Jung Ho; Yoon, Kyung Jean; Park, Tae Joo; Hwang, Cheol Seong

2012-10-24

The electrical performances of Pt/TiO(2)/Ti/Pt stacked Schottky-type diode (SD) was systematically examined, and this performance is dependent on the chemical structures of the each layer and their interfaces. The Ti layers containing a tolerable amount of oxygen showed metallic electrical conduction characteristics, which was confirmed by sheet resistance measurement with elevating the temperature, transmission line measurement (TLM), and Auger electron spectroscopy (AES) analysis. However, the chemical structure of SD stack and resulting electrical properties were crucially affected by the dissolved oxygen concentration in the Ti layers. The lower oxidation potential of the Ti layer with initially higher oxygen concentration suppressed the oxygen deficiency of the overlying TiO(2) layer induced by consumption of the oxygen from TiO(2) layer. This structure results in the lower reverse current of SDs without significant degradation of forward-state current. Conductive atomic force microscopy (CAFM) analysis showed the current conduction through the local conduction paths in the presented SDs, which guarantees a sufficient forward-current density as a selection device for highly integrated crossbar array resistive memory.

Glass fiber dissolution in simulated lung fluid and measures needed to improve consistency and correspondence to in vivo dissolution.

PubMed Central

Mattson, S M

1994-01-01

The dissolution of a range of glass fibers including commercial glass and mineral wools has been studied using a modification of Gamble's solution in a flow system at pH 7.4 and 37 degrees C. Dissolution has been followed by weight loss, effluent analysis, and morphology change of fibers and bulk glass. Flow per glass surface area can strongly affect both dissolution rate and morphology due to the effect of the dissolution process on the fluid. Effluent pH is shown to be a guide for choice of optimum flow/area conditions. These conditions provide measurable concentrations of dissolved glass in the effluent while maintaining their concentrations below the point at which they significantly affect the dissolution process. SiO2 and Al2O3 vary widely in the extent to which they are involved in the leaching process, which removes alkalis, alkaline earths, and B2O3. This makes analysis of a single component in the effluent unsuitable as a means of comparing the dissolution rates of a wide range of compositions. PMID:7882963

Crystallization of primitive basaltic magmas at crustal pressures and genesis of the calc-alkaline igneous suite: experimental evidence from St Vincent, Lesser Antilles arc

NASA Astrophysics Data System (ADS)

Pichavant, M.; MacDonald, R.

2007-11-01

Near-liquidus crystallization experiments have been carried out on two basalts (12.5 and 7.8 wt% MgO) from Soufriere, St Vincent (Lesser Antilles arc) to document the early stages of differentiation in calc-alkaline magmas. The water-undersaturated experiments were performed mostly at 4 kbar, with 1.6 to 7.7 wt% H2O in the melt, and under oxidizing conditions (ΔNNO = -0.8 to +2.4). A few 10 kbar experiments were also performed. Early differentiation of primitive, hydrous, high-magnesia basalts (HMB) is controlled by ol + cpx + sp fractionation. Residual melts of typical high-alumina basalt (HAB) composition are obtained after 30-40% crystallization. The role of H2O in depressing plagioclase crystallization leads to a direct relation between the Al2O3 content of the residual melt and its H2O concentration, calibrated as a geohygrometer. The most primitive phenocryst assemblage in the Soufriere suite (Fo89.6 olivine, Mg-, Al- and Ti-rich clinopyroxene, Cr-Al spinel) crystallized from near-primary (Mg# = 73.5), hydrous (˜5 wt% H2O) and very oxidized (ΔNNO = +1.5-2.0) HMB liquids at middle crustal pressures and temperatures from ˜1,160 to ˜1,060°C. Hornblende played no role in the early petrogenetic evolution. Derivative HAB melts may contain up to 7-8 wt% dissolved H2O. Primitive basaltic liquids at Soufriere, St Vincent, have a wide range of H2O concentrations (2-5 wt%).

Water quality study of the Riley Creek (Blanchard River, Ottawa, Ohio)

NASA Astrophysics Data System (ADS)

Spiese, C. E.; Berry, J. M.

2012-12-01

Riley Creek in northwest central Ohio is one of the most heavily impacted tributaries in the Blanchard River watershed. Anthropogenic inputs of phosphorus and nitrogen from agriculture have led to heavy eutrophication over the past decades. Because the Blanchard River is part of the Lake Erie basin, controls on phosphorus and nitrogen, among other inputs, are critical for restoration of ecosystem health in Lake Erie. A previous study in the Riley Creek watershed has shown high historical loadings of both nitrogen and phosphorus. Additionally, bacterial impairment has been noted in the watershed, from both municipal sources and failing septic tanks. This study is the most recent data detailing water quality parameters both chemical and microbiological in Riley Creek. This is also the first data set in Riley Creek examining the spectral characteristics of dissolved organic matter (DOM). From May to August, 2012, dissolved oxygen concentrations at six sites in the watershed declined from a maximum of 13.2 mg/L (154% O2 saturation) to 1.1 mg/L (12.9%). Median dissolved oxygen during the same period was 5.96 mg/L. Water pH was relatively steady, ranging from 8.6 to 7.9, with values generally declining with time. All six sites were found to have nitrate concentrations above the enforcement target (1 mg/L NO3--N) at various times, with four out of 73 samples falling below this value. Dissolved reactive phosphorus was generally low, with concentrations ranging from 0.074 mg P/L to below detection limits (<0.005 mg P/L). Dissolved organic matter concentrations (measured as mg C/L, potassium hydrogen phthalate equivalent) ranged from 24.1 to 3.5 mg C/L (mean = 9.8 ± 3.8 mg C/L), with no apparent temporal trends. Spectral slope ratios, a proxy for molecular mass, were relatively constant at 0.9 ± 0.2, with only intermittent excursions. No correlation to either flow or time was observed. Tests for fecal coliform bacteria were almost universally positive at all sites, with 10 of 69 samples showing a presumptive positive with presence-absence broth. Overall, the health of the Riley Creek watershed appears to be either stable or declining. Phosphorus and nitrogen loadings have not shown any appreciable change over approximately the past decade. Declines in dissolved oxygen were not noted in previous studies, and may signal an emerging problem in the watershed.

Evaluating Nanoparticle Breakthrough during Drinking Water Treatment

PubMed Central

Chalew, Talia E. Abbott; Ajmani, Gaurav S.; Huang, Haiou

2013-01-01

Background: Use of engineered nanoparticles (NPs) in consumer products is resulting in NPs in drinking water sources. Subsequent NP breakthrough into treated drinking water is a potential exposure route and human health threat. Objectives: In this study we investigated the breakthrough of common NPs—silver (Ag), titanium dioxide (TiO2), and zinc oxide (ZnO)—into finished drinking water following conventional and advanced treatment. Methods: NPs were spiked into five experimental waters: groundwater, surface water, synthetic freshwater, synthetic freshwater containing natural organic matter, and tertiary wastewater effluent. Bench-scale coagulation/flocculation/sedimentation simulated conventional treatment, and microfiltration (MF) and ultrafiltration (UF) simulated advanced treatment. We monitored breakthrough of NPs into treated water by turbidity removal and inductively coupled plasma–mass spectrometry (ICP-MS). Results: Conventional treatment resulted in 2–20%, 3–8%, and 48–99% of Ag, TiO2, and ZnO NPs, respectively, or their dissolved ions remaining in finished water. Breakthrough following MF was 1–45% for Ag, 0–44% for TiO2, and 36–83% for ZnO. With UF, NP breakthrough was 0–2%, 0–4%, and 2–96% for Ag, TiO2, and ZnO, respectively. Variability was dependent on NP stability, with less breakthrough of aggregated NPs compared with stable NPs and dissolved NP ions. Conclusions: Although a majority of aggregated or stable NPs were removed by simulated conventional and advanced treatment, NP metals were detectable in finished water. As environmental NP concentrations increase, we need to consider NPs as emerging drinking water contaminants and determine appropriate drinking water treatment processes to fully remove NPs in order to reduce their potential harmful health outcomes. Citation: Abbott Chalew TE, Ajmani GS, Huang H, Schwab KJ. 2013. Evaluating nanoparticle breakthrough during drinking water treatment. Environ Health Perspect 121:1161–1166; http://dx.doi.org/10.1289/ehp.1306574 PMID:23933526

The role of copper and oxalate in the redox cycling of iron in atmospheric waters

NASA Astrophysics Data System (ADS)

Sedlak, David L.; Hoigné, Jürg

During daytime, the redox cycling of dissolved iron compounds in atmospheric waters, and the related in-cloud transformations of photooxidants, are affected by reactions of Fe and Cu with hydroperoxy (HO 2) and superoxide (O 2-) radicals and the photoreduction of Fe(III)-oxalato complexes. We have investigated several of the important chemical reactions in this redox cycle, through laboratory simulation of the system, using γ-radiation to produce HO 2/O 2-. At concentrations comparable to those measured in atmospheric waters, the redox cycling of Fe was dramatically affected by the presence of oxalate and trace concentrations of Cu. At concentrations more than a hundred times lower than Fe, Cu consumed most of the HO 2/O 2-, and cycled between the Cu(II) and Cu(I) forms. Cu + reacted with FeOH 2+ to produce Fe(II) and Cu(II), with a second order rate constant of approximately 3 × 10 7 M -1s -1. The presence of oxalate resulted in the formation of Fe(III)-oxalato complexes that were essentially unreactive with HO 2/O 2-. Only at high oxalate concentrations was the Fe(II)C 2O 4 complex also formed, and it reacted relatively rapidly with hydrogen peroxide ( k = (3.1 ± 0.6) × 10 4 M -1s -1). Simulations incorporating measurements for other redox mechanisms, including oxidation by ozone, indicate that, during daytime, Fe should be found mostly in the ferrous oxidation state, and that reactions of FeOH 2+ with Cu(I) and HO 2/O 2-, and to a lesser degree, the photolysis of Fe(III)-oxalato complexes, are important mechanisms of Fe reduction in atmospheric waters. The catalytic effect of Cu(II)/Cu(I) and Fe(III)/Fe(II) should also significantly increase the sink function of the atmospheric liquid phase for HO 2 present in a cloud. A simple kinetic model for the reactions of Fe, Cu and HO 2/O 2-, accurately predicted the changes in Fe oxidation states that occurred when authentic fogwater samples were exposed to HO 2/O 2-.

Hydrogen self-diffusion in single crystal olivine and electrical conductivity of the Earth's mantle.

PubMed

Novella, Davide; Jacobsen, Benjamin; Weber, Peter K; Tyburczy, James A; Ryerson, Frederick J; Du Frane, Wyatt L

2017-07-13

Nominally anhydrous minerals formed deep in the mantle and transported to the Earth's surface contain tens to hundreds of ppm wt H 2 O, providing evidence for the presence of dissolved water in the Earth's interior. Even at these low concentrations, H 2 O greatly affects the physico-chemical properties of mantle materials, governing planetary dynamics and evolution. The diffusion of hydrogen (H) controls the transport of H 2 O in the Earth's upper mantle, but is not fully understood for olivine ((Mg, Fe) 2 SiO 4 ) the most abundant mineral in this region. Here we present new hydrogen self-diffusion coefficients in natural olivine single crystals that were determined at upper mantle conditions (2 GPa and 750-900 °C). Hydrogen self-diffusion is highly anisotropic, with values at 900 °C of 10 -10.9 , 10 -12.8 and 10 -11.9 m 2 /s along [100], [010] and [001] directions, respectively. Combined with the Nernst-Einstein relation, these diffusion results constrain the contribution of H to the electrical conductivity of olivine to be σ H  = 10 2.12 S/m·C H2O ·exp -187kJ/mol/(RT) . Comparisons between the model presented in this study and magnetotelluric measurements suggest that plausible H 2 O concentrations in the upper mantle (≤250 ppm wt) can account for high electrical conductivity values (10 -2 -10 -1  S/m) observed in the asthenosphere.

Cr(III) solubility in aqueous fluids at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Watenphul, Anke; Schmidt, Christian; Jahn, Sandro

2014-02-01

Trivalent chromium is generally considered relatively insoluble in aqueous fluids and melts. However, numerous counterexamples in nature indicate Cr(III) mobilization by aqueous fluids during metamorphism or hydrothermal alteration of chromite-bearing rocks, or by pegmatite melts. So far, very little is known about the chromium concentrations and speciation in such fluids. In this study, the solubility of eskolaite (Cr2O3) in 1.6-4.2 m aqueous HCl solutions was determined in situ at elevated pressures up to 1 GPa and temperatures ranging between 400 and 700 °C using synchrotron micro-X-ray fluorescence spectroscopy (μ-XRF). Determined concentrations of dissolved Cr ranged between about 900-18,000 ppm, with the highest concentrations found at 500 °C and 861 MPa. The Cr(III) solubility in aqueous HCl fluids is retrograde in the studied temperature range and increases with pressure. In addition, Cr(III) complexation in these fluids was explored by Raman spectroscopy on a 12.3 mass% HCl fluid in equilibrium with eskolaite at 400 and 600 °C, 0.3-1.6 GPa. All spectra show two prominent Cr-Cl stretching bands at about 275 and 325 cm-1, which display some fine structure, and in some spectra weak bands in the region between 380 and 500 cm-1. The sum of the integrated intensities of the two dominant bands reveals qualitatively the same changes with temperature along an isochore, with pressure at constant temperature, and with the time required for equilibration as the Cr(III) concentrations in the fluid determined by μ-XRF. Complementary ab initio molecular dynamics simulations of a 4 m HCl solution at two different densities (0.8 and 0.97 g/cm3) and temperatures (427 and 727 °C) were performed to investigate the vibrational properties of various(O)y3-x and (O)y(OH)z3-x-z complexes with 3⩽x+z⩽4 and 0⩽y⩽2. Quasi-normal mode analysis reveals that both the tetrahedral symmetric and antisymmetric Cr-Cl stretching vibrations of CrCl4(H2O)0-2- have characteristic frequencies in the range of the two strongest experimentally observed Raman bands, whereas Cr-O stretching vibrations of hydroxy-chloride complexes occur at wavenumbers above 400 cm-1. Solubility and complexation of Cr(III) depend strongly on the activities of Cl- and H+. At high H+ and Cl- activity, the results are consistent with CrCl(H2O)0-2-1-0 complexes as major Cr(III) species, the Cr coordination number of which increases with pressure by becoming more aquated. At low Cl- activity, i.e. in our study at high-temperature low-pressure conditions, the data indicate mixed CrClx((OH)z3-x-z complexes with Cl-Cr ratios less than three. In situ μ-XRF solubility experiments conducted with eskolaite + (H2O + 29 mass% Na2CO3) and kosmochlor + (H2O + 44 mass% Na2Si3O7) resulted in dissolved Cr concentrations at or below the detection limit of 500 ppm. Thus, acidic chloridic fluids seem to be more efficient agents for Cr(III) mobilization and transport at crustal conditions than aqueous alkali carbonate or silicate solutions.

No evidence of the genotoxic potential of gold, silver, zinc oxide and titanium dioxide nanoparticles in the SOS chromotest.

PubMed

Nam, Sun-Hwa; Kim, Shin Woong; An, Youn-Joo

2013-10-01

Gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO2 NPs) are widely used in cosmetic products such as preservatives, colorants and sunscreens. This study investigated the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO2 NPs using the SOS chromotest with Escherichia coli PQ37. The maximum exposure concentrations for each nanoparticle were 3.23 mg l(-1) for Au NPs, 32.3 mg l(-1) for Ag NPs and 100 mg l(-1) for ZnO NPs and TiO2 NPs. Additionally, in order to compare the genotoxicity of nanoparticles and corresponding dissolved ions, the ions were assessed in the same way as nanoparticles. The genotoxicity of the titanium ion was not assessed because of the extremely low solubility of TiO2 NPs. Au NPs, Ag NPs, ZnO NPs, TiO2 NPs and ions of Au, Ag and Zn, in a range of tested concentrations, exerted no effects in the SOS chromotest, evidenced by maximum IF (IFmax) values of below 1.5 for all chemicals. Owing to the results, nanosized Au NPs, Ag NPs, ZnO NPs, TiO2 NPs and ions of Au, Ag and Zn are classified as non-genotoxic on the basis of the SOS chromotest used in this study. To the best of our knowledge, this is the first study to evaluate the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO2 NPs using the SOS chromotest. Copyright © 2012 John Wiley & Sons, Ltd.

Metal assisted photochemical etching of 4H silicon carbide

NASA Astrophysics Data System (ADS)

Leitgeb, Markus; Zellner, Christopher; Schneider, Michael; Schwab, Stefan; Hutter, Herbert; Schmid, Ulrich

2017-11-01

Metal assisted photochemical etching (MAPCE) of 4H-silicon carbide (SiC) in Na2S2O8/HF and H2O2/HF aqueous solutions is investigated with platinum as metallic cathode. The formation process of the resulting porous layer is studied with respect to etching time, concentration and type of oxidizing agent. From the experiments it is concluded that the porous layer formation is due to electron hole pairs generated in the semiconductor, which stem from UV light irradiation. The generated holes are consumed during the oxidation of 4H-SiC and the formed oxide is dissolved by HF. To maintain charge balance, the oxidizing agent has to take up electrons at the Pt/etching solution interface. Total dissolution of the porous layers is achieved when the oxidizing agent concentration decreases during MAPCE. In combination with standard photolithography, the definition of porous regions is possible. Furthermore chemical micromachining of 4 H-SiC at room temperature is possible.

Simultaneous determination of dissolved gases and moisture in mineral insulating oils by static headspace gas chromatography with helium photoionization pulsed discharge detection.

PubMed

Jalbert, J; Gilbert, R; Tétreault, P

2001-07-15

This paper presents the development of a static headspace capillary gas chromatographic method (HS-GC) for simultaneously determining dissolved gases (H2, O2, N2, CO, CO2, CH4, C2H6, C2H4, C2H2, C3H8) and moisture from a unique 15-mL mineral oil sample. A headspace sampler device is used to equilibrate the sample species in a two-phase system under controlled temperature and agitation conditions. A portion of the equilibrated species is then automatically split-injected into two chromatographic channels mounted on the same GC for their separation. The hydrocarbons and the lighter gases are separated on the first channel by a GS-Q column coupled with a MolSieve 5-A column via a bypass valve, while the moisture is separated on the second channel using a Stabilwax column. The analytes are detected by using two universal pulsed-discharge helium ionization detectors (PDHID). The performance of the method was established using equilibrated vials containing known amounts of gas mixture, water, and blank oil. The signal is linear over the concentration ranges normally found for samples collected from open-breathing power transformers. Determination sensitivity varies with the nature of the species considered with values as high as 21 500 A x 10(-9) s (microg/ g)(-1) for H2O, 46-216 A x 10(-9) s (microL/L)(-1) for the hydrocarbons and carbon oxides, and as low as 8-21 A x 10(-9) s (microL/L)(-1) for the O2 and N2 permanent gases. The detection limit of the method is between 0.08 and 6 microL/L for the dissolved gases, except for O2, N2, and CO2, where higher values are observed due to air intrusion during sampler operations, and 0.1 microg/g for the dissolved water. Ten consecutive measurements in the low and high levels of the calibration curves have shown a precision better than 12% and 6%, respectively, in all cases. A comparison study between the HS-GC method and the ASTM standard procedures on 31 field samples showed a very good agreement of the results. The advantages of configuring the arrangement with two PDHID over the conventional flame ionization and thermal conductivity detectors were clearly demonstrated.

METHOD OF PREPARING PROTACTINIUM VALUES

DOEpatents

Katzin, L.I.; Larson, R.G.; Thompson, R.C.; Van Winkle, Q.

1959-05-19

Separation and purification from initial acid leaches of pitchblende of Pa is described. This supernatant acid solution is treated with alkali metal carbonates to precipitate Pa. Silica is removed from the precipitate by hydroxide treatment. The Pa residue is dissolved in HNO/sub 3/ and Pa is concentrated by cyclic precipitations with MnO/sub 2/. The last solution is hydrolyzed to precipitate Pa. The Pa precipitate contains Ti and Zr which are removed by ion exchange. (T.R.H.)

Precipitation Coating of Monazite on Woven Ceramic Fibers: 1. Feasibility (Postprint)

DTIC Science & Technology

2007-02-01

08 Aug 2006. Paper contains color . 14. ABSTRACT Monazite coatings were deposited on woven cloths and tows of NextelTM 610 fibers by heterogeneous...by dissolving concentrated phosphoric acid ( Fish - er Scientific Co., Pittsburgh, PA) or a combination of lantha- num nitrate (Aldrich Chemical Co...Boccaccini, P. Karapappas, J. M. Marijuan, and C. Kaya, ‘‘ TiO2 Coat- ings on Silicon Carbide Fiber Substrates by Electrophoretic Deposition,’’ J.Mater. Sci

Sulfur dioxide-hydrogen peroxide relationships in clean air, clouds, and precipitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwartz, S.E.; Daum, P.H.

1988-01-01

In-cloud oxidation by H/sub 2/O/sub 2/ is a major route for conversion of atmospheric SO/sub 2/ to sulfate, as indicated by kinetic calculations for representative H/sub 2/O/sub 2/ concentrations and supported by the observation of mutual exclusivity of gaseous SO/sub 2/ and aqueous H/sub 2/O/sub 2/ in non-precipitating liquid-water stratiform clouds, which generally persist sufficiently for reaction to proceed to completion. Measurements reported here indicate the aqueous S(IV) and H/sub 2/O/sub 2/ are also mutually exclusive in surface precipitation samples, but that SO/sub 2/ and aqueous H/sub 2/O/sub 2/ often coexist in precipitating clouds. Gaseous SO/sub 2/ and H/sub 2/O/submore » 2/ are also commonly simultaneously present in clear air; in the mixed layer either species maybe in excess, but H/sub 2/O/sub 2/ present with SO/sub 2/ in precipitating clouds is attributed to material dissolved in falling hydrometeors which has not had time to react with SO/sub 2/. This supported by model calculations evaluating the characteristic time and distance for reaction of aqueous H/sub 2/O/sub 2/ in droplets falling through an SO/sub 2/-containing layer. 29 refs., 6 figs.« less

Environmental Monitoring of Microbe Metabolic Transformation

NASA Technical Reports Server (NTRS)

Bebout, Brad (Inventor); Fleming, Erich (Inventor); Piccini, Matthew (Inventor); Beasley, Christopher (Inventor); Bebout, Leslie (Inventor)

2013-01-01

Mobile system and method for monitoring environmental parameters involved in growth or metabolic transformation of algae in a liquid. Each of one or more mobile apparati, suspended or partly or wholly submerged in the liquid, includes at least first and second environmental sensors that sense and transmit distinct first and second environmental, growth or transformation parameter values, such as liquid temperature, temperature of gas adjacent to and above the exposed surface, liquid pH, liquid salinity, liquid turbidity, O.sub.2 dissolved in the liquid, CO.sub.2 contained in the liquid, oxidization and reduction potential of the liquid, nutrient concentrations in the liquid, nitrate concentration in the liquid, ammonium concentration in the liquid, bicarbonate concentration in the liquid, phosphate concentration in the liquid, light intensity at the liquid surface, electrical conductivity of the liquid, and a parameter.alpha.(alga) associated with growth stage of the alga, using PAM fluorometry or other suitable parameter measurements.

Water resources and effects of potential surface coal mining on dissolved solids in Hanging Woman Creek basin, southeastern Montana

USGS Publications Warehouse

Cannon, M.R.

1989-01-01

Groundwater resources of the Hanging Woman Creek basin, Montana include Holocene and Pleistocene alluvial aquifers and sandstone , coal, and clinker aquifers in the Paleocene Fort Union Formation. Surface water resources are composed of Hanging Woman Creek, its tributaries, and small stock ponds. Dissolved-solids concentrations in groundwater ranged from 200 to 11,00 mg/L. Generally, concentrations were largest in alluvial aquifers and smallest in clinker aquifers. Near its mouth, Hanging Woman Creek had a median concentration of about 1,800 mg/L. Mining of the 20-foot to 35-foot-thick Anderson coal bed and 3-foot to 16-foot thick Dietz coal bed could increase dissolved-solids concentrations in shallow aquifers and in Hanging Woman Creek because of leaching of soluble minerals from mine spoils. Analysis of saturated-paste extracts from 158 overburden samples indicated that water moving through mine spoils would have a median increase in dissolved-solids concentration of about 3,700 mg/L, resulting in an additional dissolved-solids load to Hanging Woman Creek of about 3.0 tons/day. Hanging Woman Creek near Birney could have an annual post-mining dissolved-solids load of 3,415 tons at median discharge, a 47% increase from pre-mining conditions load. Post-mining concentrations of dissolved solids, at median discharge, could range from 2,380 mg/L in March to 3,940 mg/L in August, compared to mean pre-mining concentrations that ranged from 1,700 mg/L in July, November, and December to 2,060 mg/L in May. Post-mining concentrations and loads in Hanging Woman Creek would be smaller if a smaller area were mined. (USGS)

Effects of titanium dioxide (TiO2) nanoparticles on the photodissolution of particulate organic matter: Insights from fluorescence spectroscopy and environmental implications.

PubMed

Hu, Bin; Wang, Peifang; Hou, Jun; Wang, Chao; Qian, Jin; Zhang, Nannan; Yuan, Qiusheng

2017-10-01

Widely used titanium dioxide (TiO 2 ) nanoparticles are likely to accumulate ultimately in sediments and potentially pose a risk to water ecosystems. This study evaluated the effect of TiO 2 nanoparticles on the photodissolution of particulate organic matter (POM) through fluorescence spectroscopy. Excitation-emission matrices and parallel factor analyses revealed that the fluorescent characteristics of produced dissolved organic matter (DOM) during photodissolution of suspended sediment and synthetic particulate organic matter (SPOM) were primarily humic-like. SPOM particles appeared to simulate well the photodissolution of suspended sediment. Quasi-complete increases in fluorescence intensity and chromophoric DOM (CDOM) abundance were reached after 90, 60, and 50 min irradiation for TiO 2 concentrations of 0, 2, and 5 mg L -1 , respectively. The faster increment of fluorescence intensity and CDOM abundance indicated the photocatalytic dissolution of SPOM, as opposite charges between TiO 2 and SPOM at pH = 4 favored the adsorption of TiO 2 onto SPOM. For sediments, the CDOM abundance and fluorescence intensity decreased with increasing TiO 2 concentration, resulting from the photocatalytic degradation of photoproduced DOM from sediments. These results demonstrated that pH plays an important role in the photocatalytic dissolution of POM by TiO 2 . Therefore, appropriate pH controls should be implemented when TiO 2 are used to treat sediments contaminated with organic pollutants. Finally, with increasing use of TiO 2 , its accumulation in sediments may affect the fate of carbon, nutrients, and heavy metals in shallow-water ecosystems. Copyright © 2017 Elsevier Ltd. All rights reserved.

Hydrogen peroxide produced by glucose oxidase affects the performance of laccase cathodes in glucose/oxygen fuel cells: FAD-dependent glucose dehydrogenase as a replacement.

PubMed

Milton, Ross D; Giroud, Fabien; Thumser, Alfred E; Minteer, Shelley D; Slade, Robert C T

2013-11-28

Hydrogen peroxide production by glucose oxidase (GOx) and its negative effect on laccase performance have been studied. Simultaneously, FAD-dependent glucose dehydrogenase (FAD-GDH), an O2-insensitive enzyme, has been evaluated as a substitute. Experiments focused on determining the effect of the side reaction of GOx between its natural electron acceptor O2 (consumed) and hydrogen peroxide (produced) in the electrolyte. Firstly, oxygen consumption was investigated by both GOx and FAD-GDH in the presence of substrate. Relatively high electrocatalytic currents were obtained with both enzymes. O2 consumption was observed with immobilized GOx only, whilst O2 concentration remained stable for the FAD-GDH. Dissolved oxygen depletion effects on laccase electrode performances were investigated with both an oxidizing and a reducing electrode immersed in a single compartment. In the presence of glucose, dramatic decreases in cathodic currents were recorded when laccase electrodes were combined with a GOx-based electrode only. Furthermore, it appeared that the major loss of performance of the cathode was due to the increase of H2O2 concentration in the bulk solution induced laccase inhibition. 24 h stability experiments suggest that the use of O2-insensitive FAD-GDH as to obviate in situ peroxide production by GOx is effective. Open-circuit potentials of 0.66 ± 0.03 V and power densities of 122.2 ± 5.8 μW cm(-2) were observed for FAD-GDH/laccase biofuel cells.

Hydrogen peroxide photocycling in the Gulf of Aqaba, Red Sea.

PubMed

Shaked, Yeala; Harris, Raviv; Klein-Kedem, Nir

2010-05-01

The dynamics of hydrogen peroxide (H(2)O(2)) was investigated from December 2007 to October 2008 in the Gulf of Aqaba, which in the absence of H(2)O(2) contribution from biological production, rain and runoff, turned out to be a unique natural photochemical laboratory. A distinct seasonal pattern emerged, with highest midday surface H(2)O(2) concentrations in spring-summer (30-90 nM) as compared to winter (10-30 nM). Similarly, irradiation normalized net H(2)O(2) formation rates obtained in concurrent ship-board experiments were faster in spring-summer than in winter. These seasonal patterns were attributed to changes in water characteristics, namely elevated spring-summer chromophoric dissolved organic matter (CDOM). The role of trace elements in H(2)O(2) photoformation was studied by simultaneously measuring superoxide (O(2)(-)), Fe(II), and H(2)O(2) formation and loss in ambient seawater and in the presence of superoxide dismutase, iron and copper. O(2)(-) was found to decay fast in the Gulf water, with a half-life of 15-28 s, primarily due to catalytic reactions with trace metals (predominantly copper). Hence, H(2)O(2) formation in the Gulf involves metal-catalyzed O(2)(-) disproptionation. Added iron moderately lowered net H(2)O(2) photoformation, probably due to its participation in Fe(II) oxidation, a process that may also modify H(2)O(2) formation in situ.

Reactivity of uranium(iii) with H2E (E = S, Se, Te): synthesis of a series of mononuclear and dinuclear uranium(iv) hydrochalcogenido complexes.

PubMed

Franke, Sebastian M; Rosenzweig, Michael W; Heinemann, Frank W; Meyer, Karsten

2015-01-01

We report the syntheses, electronic properties, and molecular structures of a series of mono- and dinuclear uranium(iv) hydrochalcogenido complexes supported by the sterically demanding but very flexible, single N-anchored tris(aryloxide) ligand ( Ad ArO) 3 N) 3- . The mononuclear complexes [(( Ad ArO) 3 N)U(DME)(EH)] (E = S, Se, Te) can be obtained from the reaction of the uranium(iii) starting material [(( Ad ArO) 3 N)U III (DME)] in DME via reduction of H 2 E and the elimination of 0.5 equivalents of H 2 . The dinuclear complexes [{(( Ad ArO) 3 N)U} 2 (μ-EH) 2 ] can be obtained by dissolving their mononuclear counterparts in non-coordinating solvents such as benzene. In order to facilitate the work with the highly toxic gases, we created concentrated THF solutions that can be handled using simple glovebox techniques and can be stored at -35 °C for several weeks.

Effective removal of trace thallium from surface water by nanosized manganese dioxide enhanced quartz sand filtration.

PubMed

Huangfu, Xiaoliu; Ma, Chengxue; Ma, Jun; He, Qiang; Yang, Chun; Zhou, Jian; Jiang, Jin; Wang, Yaan

2017-12-01

Thallium (Tl) has drawn wide concern due to its high toxicity even at extremely low concentrations, as well as its tendency for significant accumulation in the human body and other organisms. The need to develop effective strategies for trace Tl removal from drinking water is urgent. In this study, the removal of trace Tl (0.5 μg L -1 ) by conventional quartz sand filtration enhanced by nanosized manganese dioxide (nMnO 2 ) has been investigated using typical surface water obtained from northeast China. The results indicate that nMnO 2 enhanced quartz sand filtration could remove trace Tl(I) and Tl(III) efficiently through the adsorption of Tl onto nMnO 2 added to a water matrix and onto nMnO 2 attached on quartz sand surfaces. Tl(III)-HA complexes might be responsible for higher residual Tl(III) in the effluent compared to residual Tl(I). Competitive Ca 2+ cations inhibit Tl removal to a certain extent because the Ca 2+ ions will occupy the Tl adsorption site on nMnO 2 . Moreover, high concentrations of HA (10 mgTOC L -1 ), which notably complexes with and dissolves nMnO 2 (more than 78%), resulted in higher residual Tl(I) and Tl(III). Tl(III)-HA complexes might also enhance Tl(III) penetration to a certain extent. Additionally, a higher pH level could enhance the removal of trace Tl from surface water. Finally, a slight increase of residual Tl was observed after backwash, followed by the reduction of the Tl concentration in the effluent to a "steady" state again. The knowledge obtained here may provide a potential strategy for drinking water treatment plants threatened by trace Tl. Copyright © 2017. Published by Elsevier Ltd.

Ability of rabbit alveolar macrophages to dissolve metals.

PubMed

Lundborg, M; Lind, B; Camner, P

1984-01-01

Manganese dioxide particles, 0.1-0.5 micron, were added to samples of 2-3 X 10(6) rabbit alveolar macrophages. The amount of manganese added and dissolved from the particles, over periods of 0, 1, 3, and 5 days, was determined by flame atomic absorption spectrophotometry. Macrophages from six rabbits received about 10 micrograms of Mn, macrophages from two rabbits about 30 micrograms, and macrophages from another two rabbits about 100 micrograms. Over periods of 1, 3, and 5 days the macrophages in all three dose groups dissolved two to three times more Mn than was dissolved in control experiments. In control experiments solubility was studied in the medium without macrophages. Macrophages cultivated 3 days before the addition of MnO2 dissolved the particles within another 2 days to an extent similar to that in the control experiments. The ability of the macrophages to dissolve MnO2 particles might be related to the low pH values in the phagosomes. Studies of the ability of macrophages from various species to dissolve metal particles as well as of pH values in their phagosomes might lead to a better understanding of alveolar clearance of metal particles.

Effect of residual H2O2 from advanced oxidation processes on subsequent biological water treatment: A laboratory batch study.

PubMed

Wang, Feifei; van Halem, Doris; Liu, Gang; Lekkerkerker-Teunissen, Karin; van der Hoek, Jan Peter

2017-10-01

H 2 O 2 residuals from advanced oxidation processes (AOPs) may have critical impacts on the microbial ecology and performance of subsequent biological treatment processes, but little is known. The objective of this study was to evaluate how H 2 O 2 residuals influence sand systems with an emphasis on dissolved organic carbon (DOC) removal, microbial activity change and bacterial community evolution. The results from laboratory batch studies showed that 0.25 mg/L H 2 O 2 lowered DOC removal by 10% while higher H 2 O 2 concentrations at 3 and 5 mg/L promoted DOC removal by 8% and 28%. A H 2 O 2 dosage of 0.25 mg/L did not impact microbial activity (as measured by ATP) while high H 2 O 2 dosages, 1, 3 and 5 mg/L, resulted in reduced microbial activity of 23%, 37% and 37% respectively. Therefore, DOC removal was promoted by the increase of H 2 O 2 dosage while microbial activity was reduced. The pyrosequencing results illustrated that bacterial communities were dominated by Proteobacteria. The presence of H 2 O 2 showed clear influence on the diversity and composition of bacterial communities, which became more diverse under 0.25 mg/L H 2 O 2 but conversely less diverse when the dosage increased to 5 mg/L H 2 O 2 . Anaerobic bacteria were found to be most sensitive to H 2 O 2 as their growth in batch reactors was limited by both 0.25 and 5 mg/L H 2 O 2 (17-88% reduction). In conclusion, special attention should be given to effects of AOPs residuals on microbial ecology before introducing AOPs as a pre-treatment to biological (sand) processes. Additionally, the guideline on the maximum allowable H 2 O 2 concentration should be properly evaluated. Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.

Ammonium in thermal waters of Yellowstone National Park: processes affecting speciation and isotope fractionation

USGS Publications Warehouse

Holloway, J.M.; Nordstrom, D. Kirk; Böhlke, J.K.; McCleskey, R. Blaine; Ball, J.W.

2011-01-01

Dissolved inorganic nitrogen, largely in reduced form (NH4(T)≈NH4(aq)++NH3(aq)o), has been documented in thermal waters throughout Yellowstone National Park, with concentrations ranging from a few micromolar along the Firehole River to millimolar concentrations at Washburn Hot Springs. Indirect evidence from rock nitrogen analyses and previous work on organic compounds associated with Washburn Hot Springs and the Mirror Plateau indicate multiple sources for thermal water NH4(T), including Mesozoic marine sedimentary rocks, Eocene lacustrine deposits, and glacial deposits. A positive correlation between NH4(T) concentration and δ18O of thermal water indicates that boiling is an important mechanism for increasing concentrations of NH4(T) and other solutes in some areas. The isotopic composition of dissolved NH4(T) is highly variable (δ15N = −6‰ to +30‰) and is positively correlated with pH values. In comparison to likely δ15N values of nitrogen source materials (+1‰ to +7‰), high δ15N values in hot springs with pH >5 are attributed to isotope fractionation associated with NH3(aq)o loss by volatilization. NH4(T) in springs with low pH typically is relatively unfractionated, except for some acid springs with negative δ15N values that are attributed to NH3(g)o condensation. NH4(T) concentration and isotopic variations were evident spatially (between springs) and temporally (in individual springs). These variations are likely to be reflected in biomass and sediments associated with the hot springs and outflows. Elevated NH4(T) concentrations can persist for 10s to 1000s of meters in surface waters draining hot spring areas before being completely assimilated or oxidized.

Carbonate component reduces o,oEDDHA/Fe sorption on two-line ferrihydrite

NASA Astrophysics Data System (ADS)

Yunta, F.; Lucena, J. J.; Smolders, E.

2012-04-01

The o,oEDDHA/Fe is the most common and effective iron chelate used as fertilizer in calcareous soils. Several authors have reported that the anionic o,oEDDHA/Fe complex is adsorbed to soil components such as ferrihydrite. The bicarbonate anion may be a competing ion for this sorption, however no studies have yet identified the extent and mechanism of this interaction. The aim of this work was to study the carbonate (bicarbonate + carbonate) effect on EDDHA/Fe adsorption on two-line ferrihydrite. Two-line ferrihydrite was synthetized adding NaOH on a nitrate iron (III) solution up to a final pH to be 8.0 and allowing to age for 22 hours at 20°C. Dialyzed ferrihydrite was characterized by determining specific parameters such as Fe/OH ratio, BET surface, point zero of charge and x-ray diffraction. The sorption was performed at three pH levels (5, 7.5 and 9.5) and three initial carbonate concentrations (from 0 to 2 mM). Initial EDDHA/Fe, ferrihydrite and ionic strength concentrations were adjusted to 0.18 mM, 10 g L-1 and 5 mM respectively. Total dissolved FeEDDHA concentrations were quantified at 480 nm. The o,oEDDHA/Fe isomers (rac-o,oEDDHA/Fe and meso-o,oEDDHA/Fe) were separated and quantified by High Performance Liquid Chromatography (HPLC) fitting a photodiode array detector (PDA). Distribution factor (KD) and sorbed o,oEDDHA/Fe concentration were determined. Actual carbonate concentration was determined using a multi N/C analyzer. Ferrihydrite samples showed a typical XRD pattern of two-line ferrihydrite, two broad peaks at about 35 and 62° respectively. The BET surfaces (two replicates) were 259.2 ± 3.1 m2/g and 256.0 ± 2.5 m2/g. The Point Zero of Salt Effect (PZSE) was 7.9 ± 0.2 as bibliographically supported for all fresh and thus not rigorously de-carbonated ferrihydrite samples. The KD of the o,oEDDHA/Fe increased from 27.4 ± 0.6 to 304 ± 6 l/kg by decreasing pH from 9.5 and 5.0 when no carbonate was added. Increasing equilibrium carbonate concentrations between 8.6 10-2 and 76 10-2 mM decreased the KD about two-fold at pH 7.5. The KD values from meso-o,oEDDHA/Fe were up to 1000 fold larger than those of rac-o,oEDDHA/Fe at highest carbonate concentration at pH 7.5 and pH dependency suggests that former binds as inner sphere whereas latter binds as outer sphere. Despite the carbonate competition is unlikely to largely affect the net sorption of the chelate in soil, clear differences between meso-o,oEDDHA/Fe and rac-o,oEDDHA/Fe sorption rate on ferrihydrite in presence of carbonate were found.

A coupled geochemical and biogeochemical approach to characterize the bioreactivity of dissolved organic matter from a headwater stream

NASA Astrophysics Data System (ADS)

Sleighter, Rachel L.; Cory, Rose M.; Kaplan, Louis A.; Abdulla, Hussain A. N.; Hatcher, Patrick G.

2014-08-01

The bioreactivity or susceptibility of dissolved organic matter (DOM) to microbial degradation in streams and rivers is of critical importance to global change studies, but a comprehensive understanding of DOM bioreactivity has been elusive due, in part, to the stunningly diverse assemblages of organic molecules within DOM. We approach this problem by employing a range of techniques to characterize DOM as it flows through biofilm reactors: dissolved organic carbon (DOC) concentrations, excitation emission matrix spectroscopy (EEMs), and ultrahigh resolution mass spectrometry. The EEMs and mass spectral data were analyzed using a combination of multivariate statistical approaches. We found that 45% of stream water DOC was biodegraded by microorganisms, including 31-45% of the humic DOC. This bioreactive DOM separated into two different groups: (1) H/C centered at 1.5 with O/C 0.1-0.5 or (2) low H/C of 0.5-1.0 spanning O/C 0.2-0.7 that were positively correlated (Spearman ranking) with chromophoric and fluorescent DOM (CDOM and FDOM, respectively). DOM that was more recalcitrant and resistant to microbial degradation aligned tightly in the center of the van Krevelen space (H/C 1.0-1.5, O/C 0.25-0.6) and negatively correlated (Spearman ranking) with CDOM and FDOM. These findings were supported further by principal component analysis and 2-D correlation analysis of the relative magnitudes of the mass spectral peaks assigned to molecular formulas. This study demonstrates that our approach of processing stream water through bioreactors followed by EEMs and FTICR-MS analyses, in combination with multivariate statistical analysis, allows for precise, robust characterization of compound bioreactivity and associated molecular level composition.

Theoretical technique for predicting the cumulative impact of iron and manganese oxidation in streams receiving discharge from coal mines

USGS Publications Warehouse

Bobay, Keith E.

1986-01-01

Two U.S. Geological Survey computer programs are modified and linked to predict the cumulative impact of iron and manganese oxidation in coal-mine discharge water on the dissolved chemical quality of a receiving stream. The coupled programs calculate the changes in dissolved iron, dissolved manganese, and dissolved oxygen concentrations; alkalinity; and, pH of surface water downstream from the point of discharge. First, the one-dimensional, stead-state stream, water quality program uses a dissolved oxygen model to calculate the changes in concentration of elements as a function of the chemical reaction rates and time-of-travel. Second, a program (PHREEQE) combining pH, reduction-oxidation potential, and equilibrium equations uses an aqueous-ion association model to determine the saturation indices and to calculate pH; it then mixes the discharge with a receiving stream. The kinetic processes of the first program dominate the system, whereas the equilibrium thermodynamics of the second define the limits of the reactions. A comprehensive test of the technique was not possible because a complete set of data was unavailable. However, the cumulative impact of representative discharges from several coal mines on stream quality in a small watershed in southwestern Indiana was simulated to illustrate the operation of the technique and to determine its sensitivity to changes in physical, chemical, and kinetic parameters. Mine discharges averaged 2 cu ft/sec, with a pH of 6.0, and concentrations of 7.0 mg/L dissolved iron, 4.0 mg/L dissolved manganese, and 8.08 mg/L dissolved oxygen. The receiving stream discharge was 2 cu ft/sec, with a pH of 7.0, and concentrations of 0.1 mg/L dissolved iron, 0.1 mg/L dissolved manganese, and 8.70 mg/L dissolved oxygen. Results of the simulations indicated the following cumulative impact on the receiving stream from five discharges as compared with the effect from one discharge: 0.30 unit decrease in pH, 1.82 mg/L increase in dissolved iron, 1.50 mg/L increase in dissolved manganese, and 0.24 mg/L decrease in dissolved oxygen concentration.

The Role of Alpine Wetlands as Hot Spots of Dissolved Organic Carbon Fluxes in the East River, Colorado

NASA Astrophysics Data System (ADS)

Winnick, M.; Rainaldi, G. R.; Lawrence, C. R.; McCormick, M. E.; Hsu, H. T.; Druhan, J. L.; Williams, K. H.; Maher, K.

2016-12-01

Dissolved organic carbon (DOC) is a critical chemical attribute of freshwater systems, affecting nutrient availability, toxicity and solubility of metals, and biological activity via the absorption of light and microbial consumption of O2 during DOC mineralization. Although DOC contributions to streams are distributed across the landscape in the shallow subsurface, many studies have demonstrated area-outsized contributions from riparian zones with high biological productivity and low subsurface O2 concentrations. In the East River, CO, a high-elevation watershed located in the central Rocky Mountains, initial observations show that DOC concentrations of two tributaries, Rock Creek and Gothic Creek, are elevated by 3-10 times compared to concentrations in the main East River and its other tributaries. These elevated concentrations are qualitatively linked to the unique presence of large wetlands in the headwaters of Rock and Gothic creeks, which due to potential anoxic conditions, experience reduced rates of organic matter decomposition and serve as an elevated source of DOC. In this study we quantify the cycling of organic matter in these alpine wetlands and their area-outsized contributions to East River DOC fluxes. We present concentration profiles of DOC along stream reaches and along subsurface flowpaths that span the transition from hillslope to wetland coupled with high-resolution mapping of chronically-saturated zones and calculate area-weighted fluxes of DOC from wetlands to Rock and Gothic creeks at multiple times through the 2016 growing season. Additionally, soil and groundwater DOC fluxes are compared with depth-resolved organic carbon content from soil cores, substrate quality (C:N), and soil surface CO2 fluxes to evaluate organic carbon budgets in the hillslope and wetland areas feeding Rock Creek. The characterization of these hotspots of DOC generation and transport in the East River is vital to the ability to predict nutrient cycling changes into the future.

Effect of exposure to sunlight and phosphorus-limitation on bacterial degradation of coloured dissolved organic matter (CDOM) in freshwater.

PubMed

Kragh, Theis; Søndergaard, Morten; Tranvik, Lars

2008-05-01

This study reports on the interacting effect of photochemical conditioning of dissolved organic matter and inorganic phosphorus on the metabolic activity of bacteria in freshwater. Batch cultures with lake-water bacteria and dissolved organic carbon (DOC) extracted from a humic boreal river were arranged in an experimental matrix of three levels of exposure to simulated sunlight and three levels of phosphorus concentration. We measured an increase in bacterial biomass, a decrease in DOC and bacterial respiration as CO(2) production and O(2) consumption over 450 h. These measurements were used to calculate bacterial growth efficiency (BGE). Bacterial degradation of DOC increased with increasing exposure to simulated sunlight and availability of phosphorus and no detectable growth occurred on DOC that was not pre-exposed to simulated sunlight. The outcome of photochemical degradation of DOC changed with increasing availability of phosphorus, resulting in an increase in BGE from about 5% to 30%. Thus, the availability of phosphorus has major implications for the quantitative transfer of carbon in microbial food webs.

Comparative in vitro genotoxicity study of ZnO nanoparticles, ZnO macroparticles and ZnCl2 to MDCK kidney cells: Size matters.

PubMed

Kononenko, Veno; Repar, Neža; Marušič, Nika; Drašler, Barbara; Romih, Tea; Hočevar, Samo; Drobne, Damjana

2017-04-01

In the present study, we evaluated the roles that ZnO particle size and Zn ion release have on cyto- and genotoxicity in vitro. The Madin-Darby canine kidney (MDCK) cells were treated with ZnO nanoparticles (NPs), ZnO macroparticles (MPs), and ZnCl 2 as a source of free Zn ions. We first tested cytotoxicity to define sub-cytotoxic exposure concentrations and afterwards we performed alkaline comet and cytokinesis-block micronucleus assays. Additionally, the activities of both catalase (CAT) and glutathione S-transferase (GST) were evaluated in order to examine the potential impairment of cellular stress-defence capacity. The amount of dissolved Zn ions from ZnO NPs in the cell culture medium was evaluated by an optimized voltammetric method. The results showed that all the tested zinc compounds induced similar concentration-dependent cytotoxicity, but only ZnO NPs significantly elevated DNA and chromosomal damage, which was accompanied by a reduction of GST and CAT activity. Although Zn ion release from ZnO NPs in cell culture medium was significant, our results show that this reason alone cannot explain the ZnO genotoxicity seen in this experiment. We discuss that genotoxicity of ZnO NPs depends on the particle size, which determines the physical principles of their dissolution and cellular internalisation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Downstream composition changes of acidic volcanic waters discharged into the Banyupahit stream, Ijen caldera, Indonesia

NASA Astrophysics Data System (ADS)

Delmelle, P.; Bernard, A.

2000-04-01

The crater lake of Kawah Ijen volcano contains extremely low pH (<0.4) waters with high SO4 (∼70000 mg/kg), Cl (∼21000 mg/kg), F (∼1500 mg/kg), Al (∼5000 mg/kg), Fe (∼2000 mg/kg) and trace metal (Cu ∼0.5, Zn ∼4, Pb ∼3 mg/kg) contents. These brines seep outward through the western crater rim and reappear on the other side as streamlets, which form the headwaters of the Banyupahit stream. The Banyupahit first mixes with fresh rivers and thermal springs in the Ijen caldera and then irrigates a coastal agricultural plain which is 30 km from the summit crater. We discuss the downstream composition changes affecting the Banyupahit waters by using stable isotope, chemical and mineralogical data collected from sites along the stream length. The saturation of the stream waters with respect to minerals was evaluated with SOLVEQ and WATEQ4F and compared with the geochemical observations. An aluminous mineralogy (alunogen, pickeringite, tamarugite and kalinite) develops in the upper part of the Banyupahit due to concentration of the headwaters by evaporation. Downstream attenuation of dissolved element concentrations results principally from dilution and from mineral precipitation. The stream pH changes from ∼0 at the source to >4 close to the mouth. The δD and δ18O values and the relative SO4-Cl-F contents of the Banyupahit waters indicate that the tributaries are mostly meteoric. Dissolved SO4 in the acidic stream come only from the crater lake seepages and are not involved later in microbially mediated reactions, as shown by their δ34S and δ18O values. Re-equilibration of the stream SO4 oxygen-isotope composition with H2O from tributaries does not occur. Calcium, SiO2, Al, Fe, K and SO4 behave non-conservatively in the stream waters. Gypsum, silica (amorphous or poorly ordered), a basic aluminum hydroxysulfate (basaluminite?), K-jarosite and amorphous ferric hydroxide may exert a solubility control on these elements along the entire stream length, or in certain stream sections, consistent with the thermochemical model results. Downstream concentration trends and mineral saturation levels suggest that precipitation of Sr-, Pb-rich barite and celestite consume Ba, Sr and Pb, whereas dissolved Cu, Pb and Zn may adsorb onto solid particles, especially after the junctions of the acidic stream with non-acidic rivers. We calculated that significant fluxes of SO4, F, Cl, Al, SiO2, Ti, Mn and Cu may reach the irrigation system, possibly causing serious environmental impacts such as soil acidification and induration.

Effects of Low-Molecular-Weight Organic Acids on the Dissolution of Hydroxyapatite Nanoparticles in Batch and Column Experiments: A Perspective from Phosphate Oxygen Isotope Fractionation

NASA Astrophysics Data System (ADS)

Wang, D.; Jaisi, D. P.; Jin, Y.

2015-12-01

Hydroxyapatite nanoparticles (HANPs) are increasingly being advocated as an efficient and environment-friendly "green" phosphorus nanofertilizer attributed to their nanoscale dimension, large reactive surface area, and low leaching potential. However, knowledge of how naturally occurring low-molecular-weight organic acids (LMWOAs) that are secreted by plant roots mediate the dissolution of HANPs (releasing PO43- ion for plant growth) is nonexistent. Here three most commonly encountered LMWOAs (acetic acid, oxalic acid, and citric acid) at environmentally relevant concentration (1 mM) were evaluated for their effects on HANPs' dissolution in static batch and dynamic column systems. Particularly, phosphate oxygen isotope fractionation of HANPs during dissolution was examined to disentangle mechanisms controlling the evolution of O-isotopic composition of dissolved PO43- ion. Our results reveal that in batch experiments the dissolution of HANPs was fast but the overall dissolution efficiency of HANPs was limited (≤30%). In contrast, ~100% HANPs were dissolved in columns where LMWOAs were continuously injected. The limited dissolution of HANPs in static batch systems was due primarily to pH buffer effect (pH increased sharply when LMWOA was added in HANPs suspension), whereas in dynamic column systems the HANPs were continuously dissolved by low pH LMWOAs and leached away. Regardless of LMWOA type and experimental system, the isotopically light phosphate (P16O4) was preferentially released during dissolution and the O-isotopic composition of dissolved PO43- ion increased gradually with increasing dissolution due to equilibrium isotope effect between dissolved PO43- ion and HANPs. However, the overall magnitude of O-isotopic fractionation of dissolved PO43- ion was less in batch than in column systems, due to less mass transfer between dissolved PO43- ions and HANPs in batch relative to column experiments. Our findings provide new insights into bioavailability, transformation, and evolution of O-isotopic signatures of phosphate-based nanoparticles in agricultural soils particularly in the rhizosphere where such LMWOAs are ubiquitous.

Solubility of nano-zinc oxide in environmentally and biologically important matrices

PubMed Central

Reed, Robert B.; Ladner, David A.; Higgins, Christopher P.; Westerhoff, Paul; Ranville, James F.

2011-01-01

Increasing manufacture and use of engineered nanoparticles (NPs) is leading to a greater probability for release of ENPs into the environment and exposure to organisms. In particular, zinc oxide (ZnO) is toxic, although it is unclear whether this toxicity is due to the zinc oxide nanoparticles (ZnO), dissolution to Zn2+, or some combination thereof. The goal of this study was to determine the relative solubilites of both commercially available and in-house synthesized ZnO in matrices used for environmental fate and transport or biological toxicity studies. Dissolution of ZnO was observed in nanopure water (7.18– 7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (~5 mg/L), but much more dissolution was observed in Dulbecco’s Modified Eagle’s Medium (DMEM), where the dissolved Zn concentration exceeded 34 mg/L. Moderately hard water exhibited low zinc solubility, likely due to precipitation of a zinc carbonate solid phase. Precipitation of a zinc-containing solid phase in RPMI also appeared to limit zinc solubility. Equilibrium conditions with respect to ZnO solubility were not apparent in these matrices, even after more than 1,000 h of dissolution. These results suggest that solution chemistry exerts a strong influence on ZnO dissolution and can result in limits on zinc solubility due to precipitation of less soluble solid phases. PMID:21994124