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Yubin Dong - One of the best experts on this subject based on the ideXlab platform.

Philippe Van Cappellen - One of the best experts on this subject based on the ideXlab platform.

  • Arsenic binding to organic and inorganic sulfur species during microbial sulfate reduction: a sediment Flow-through Reactor experiment
    Environmental Chemistry, 2013
    Co-Authors: Raoul-marie Couture, Dirk Wallschläger, Jérôme Rose, Philippe Van Cappellen
    Abstract:

    Environmental context The use of water contaminated with arsenic for drinking and irrigation is linked to water and food borne diseases throughout the world. Although reducing conditions in soils and sediments are generally viewed as enhancing arsenic mobility in subsurface environments, we show they can actually promote As sequestration in the presence of reduced sulfur species and labile organic matter. We propose that sulfurisation of organic matter and subsequent binding of As to thiol groups may offer an innovative pathway for As remediation. Abstract Flow-through Reactors (FTRs) were used to assess the mobility of arsenic under sulfate reducing conditions in natural, undisturbed lake sediments. The sediment slices in the FTRs were supplied continuously with inflow solutions containing sulfate and soluble AsIII or AsV and, after 3 weeks, also lactate. The experiment ran for a total of 8 weeks. The dissolved iron concentration, pH, redox potential (Eh), as well as aqueous As and sulfur speciation were monitored in the outflow solutions. In FTRs containing surface sediment enriched in labile organic matter (OM), microbial sulfate reduction led to an accumulation of organically bound S, as evidenced by X-ray absorption spectroscopy. For these FTRs, the inflowing dissolved As concentration of 20μM was lowered by two orders of magnitude, producing outflow concentrations of 0.2μM monothioarsenate and 0.1μM arsenite. In FTRs containing sediment collected at greater depth, sulfide and zero-valent S precipitated as pyrite and elemental S, while steady-state outflow arsenite concentrations remained near 5μM. The observations thus suggest that As sequestration is enhanced when sediment OM buffers the free sulfide and zero-valent S concentrations. An updated conceptual model for the fate of As in the anoxic As–C–S–Fe system is presented based on the results of this study.

  • kinetics of microbial sulfate reduction in estuarine sediments
    Geochimica et Cosmochimica Acta, 2006
    Co-Authors: Celine Pallud, Philippe Van Cappellen
    Abstract:

    Abstract Kinetic parameters of microbial sulfate reduction in intertidal sediments from a freshwater, brackish and marine site of the Scheldt estuary (Belgium, the Netherlands) were determined. Sulfate reduction rates (SRR) were measured at 10, 21, and 30 °C, using both Flow-through Reactors containing intact sediment slices and conventional sediment slurries. At the three sites, and for all depth intervals studied (0–2, 2–4, 4–6 and 6–8 cm), the dependence of potential SRR on the sulfate concentration followed the Michaelis–Menten rate equation. Apparent sulfate half-saturation concentrations, K m , measured in the Flow-through Reactor experiments were comparable at the freshwater and marine sites (0.1–0.3 mM), but somewhat higher at the brackish site (0.4–0.9 mM). Maximum potential SRR, R max , in the 0–4 cm depth interval of the freshwater sediments were similar to those in the 0–6 cm interval of the marine sediments (10–46 nmol cm −3  h −1 at 21 °C), despite much lower in situ sulfate availability and order-of-magnitude lower densities of sulfate-reducing bacteria (SRB), at the freshwater site. Values of R max in the brackish sediments were lower (3.7–7.6 nmol cm −3  h −1 at 21 °C), probably due to less labile organic matter, as inferred from higher C org /N ratios. Inflow solutions supplemented with lactate enhanced potential SRR at all three sites. Slurry incubations systematically yielded higher R max values than Flow-through Reactor experiments for the freshwater and brackish sediments, but similar values for the marine sediments. Transport limitation of potential SRR at the freshwater and brackish sites may be related to the lower sediment porosities and SRB densities compared to the marine site. Multiple rate controls, including sulfate availability, organic matter quality, temperature, and SRB abundance, modulate in situ sulfate-reducing activity along the estuarine salinity gradient.

Jiancheng Wang - One of the best experts on this subject based on the ideXlab platform.

A. Martin-garin - One of the best experts on this subject based on the ideXlab platform.

  • Identifiability of sorption parameters in stirred Flow-through Reactor experiments and their identification with a Bayesian approach
    Journal of Environmental Radioactivity, 2016
    Co-Authors: V. Nicoulaud-gouin, A. Martin-garin, L. Garcia-sanchez, M. Giacalone, J.c. Attard, Frédéric Y. Bois
    Abstract:

    This paper addresses the methodological conditions –particularly experimental design and statistical inference– ensuring the identifiability of sorption parameters from breakthrough curves measured during stirred Flow-through Reactor experiments also known as continuous flow stirred-tank Reactor (CSTR) experiments. The equilibrium-kinetic (EK) sorption model was selected as nonequilibrium parameterization embedding the Kd approach. Parameter identifiability was studied formally on the equations governing outlet concentrations. It was also studied numerically on 6 simulated CSTR experiments on a soil with known equilibrium-kinetic sorption parameters. EK sorption parameters can not be identified from a single breakthrough curve of a CSTR experiment, because Kd,1 and k− were diagnosed collinear. For pairs of CSTR experiments, Bayesian inference allowed to select the correct models of sorption and error among sorption alternatives. Bayesian inference was conducted with SAMCAT software (Sensitivity Analysis and Markov Chain simulations Applied to Transfer models) which launched the simulations through the embedded simulation engine GNU-MCSim, and automated their configuration and post-processing. Experimental designs consisting in varying flow rates between experiments reaching equilibrium at contamination stage were found optimal, because they simultaneously gave accurate sorption parameters and predictions. Bayesian results were comparable to maximum likehood method but they avoided convergence problems, the marginal likelihood allowed to compare all models, and credible interval gave directly the uncertainty of sorption parameters θ. Although these findings are limited to the specific conditions studied here, in particular the considered sorption model, the chosen parameter values and error structure, they help in the conception and analysis of future CSTR experiments with radionuclides whose kinetic behaviour is suspected.

  • Kinetics of selenate sorption in soil as influenced by biotic and abiotic conditions: a stirred Flow-through Reactor study.
    Journal of environmental radioactivity, 2014
    Co-Authors: L. Garcia-sanchez, A. Martin-garin, N. Loffredo, Stéphane Mounier, F. Coppin
    Abstract:

    Abstract This study (i) quantified the kinetics of selenate sorption and (ii) measured the influence of biotic processes in soil selenate stabilisation. Stirred Flow-through Reactor experiments were conducted on samples of a silty clay soil (pH = 8, Eh = 240–300 mV) from Bure (France) in both non-sterile and sterile conditions. Parameters of the proposed two-site sorption model (EK), adapted from van Genuchten and Wagenet (1989) , were estimated by nonlinear regression. Fast selenate sorption on type-1 sites was moderate, with an equilibrium constant of 25.5 and 39.1 L/kg for non-sterile and sterile conditions. Rate-limited sorption on type-2 sites increased with time, and was predominant for longer periods of time in non-sterile conditions. At equilibrium, it would represent over 96% of the sorbed inventory, with mean sorption times of 17 h and 191 h for non-sterile and sterile conditions. Our results showed for Bure soil that (i) selenate sorption in flowing and mildly-oxidising conditions was strongly kinetically controlled, especially in non-sterile conditions, (ii) selenate desorption was much slower than sorption, which suggests its pseudo-irreversible stabilisation, and (iii) microbial activity increased the contribution of rate-limited sorption on type-2 sites, for which it increased sorption rate by a factor 7 but also facilitated its reversibility. This work stresses the limits of the K d approach to represent selenate sorption in flowing conditions and supports an alternative formulation like the EK model, but also points out that biotic conditions are significant sources of variability for sorption parameters.

  • Kinetics of selenate sorption in soil as influenced by biotic and abiotic conditions: A stirred Flow-through Reactor study
    Journal of Environmental Radioactivity, 2014
    Co-Authors: L. Garcia-sanchez, A. Martin-garin, N. Loffredo, Stéphane Mounier, F. Coppin
    Abstract:

    This study (i) quantified the kinetics of selenate sorption and (ii) measured the influence of biotic processes in soil selenate stabilisation. Stirred Flow-through Reactor experiments were conducted on samples of a silty clay soil (pH=8, Eh=240-300mV) from Bure (France) in both non-sterile and sterile conditions. Parameters of the proposed two-site sorption model (EK), adapted from van Genuchten and Wagenet (1989), were estimated by nonlinear regression. Fast selenate sorption on type-1 sites was moderate, with an equilibrium constant of 25.5 and 39.1L/kg for non-sterile and sterile conditions. Rate-limited sorption on type-2 sites increased with time, and was predominant for longer periods of time in non-sterile conditions. At equilibrium, it would represent over 96% of the sorbed inventory, with mean sorption times of 17h and 191h for non-sterile and sterile conditions. Our results showed for Bure soil that (i) selenate sorption in flowing and mildly-oxidising conditions was strongly kinetically controlled, especially in non-sterile conditions, (ii) selenate desorption was much slower than sorption, which suggests its pseudo-irreversible stabilisation, and (iii) microbial activity increased the contribution of rate-limited sorption on type-2 sites, for which it increased sorption rate by a factor 7 but also facilitated its reversibility. This work stresses the limits of the K d approach to represent selenate sorption in flowing conditions and supports an alternative formulation like the EK model, but also points out that biotic conditions are significant sources of variability for sorption parameters. ?? 2014 Elsevier Ltd.

  • Aqueous cadmium uptake by calcite: a stirred Flow-through Reactor study ☆
    Geochimica et Cosmochimica Acta, 2003
    Co-Authors: A. Martin-garin, P. Van Cappellen, Laurent Charlet
    Abstract:

    Abstract Uptake of cadmium ions from solution by a natural Mg-containing calcite was investigated in stirred Flow-through Reactor experiments. Input NaCl solutions were pre-equilibrated with calcite (pH 8.0) or not (pH 6.0), prior to being spiked with CdCl2. For water residence times in the Reactor less than 0.5 h, irreversible uptake of Cd by diffusion into the bulk crystal had a minor effect on the measured cadmium breakthrough curves, hence allowing us to quantify “fast” Cd2+ adsorption. At equal aqueous activities of Cd2+, adsorption was systematically lower for the pre-equilibrated input solutions. The effect of variable solution composition on Cd2+ adsorption was reproduced by a Ca2+-Cd2+ cation exchange model and by a surface complexation model for the calcite-aqueous solution interface. For the range of experimental conditions tested, the latter model predicted binding of aqueous Ca2+ and Cd2+ to the same population of carbonate surface sites. Under these circumstances, both adsorption models were equivalent. Desorption released 80 to 100% of sorbed cadmium, confirming that fast uptake of Cd2+ was mainly due to binding at surface sites. Slow, irreversible cadmium uptake by the solid phase was measured in Flow-through Reactor experiments with water residence times exceeding 0.7 h. The process exhibited first-order kinetics with respect to the concentration of adsorbed Cd2+, with a linear rate constant at 25°C of 0.03 h−1. Assuming that diffusion into the calcite lattice was the mechanism of slow uptake, a Cd2+ solid-state diffusion coefficient of 8.5×10−21 cm2 s−1 was calculated. Adsorbed Cd2+ had a pronounced effect on the dissolution kinetics of calcite. At maximum Cd2+ surface coverage (∼10−5 mol m−2), the calcite dissolution rate was 75% slower than measured under initially cadmium-free conditions. Upon desorption of cadmium, the dissolution rate increased again but remained below its initial value. Thus, the calcite surface structure and reactivity retained a memory of the adsorbed Cd2+ cations after their removal.

L. Garcia-sanchez - One of the best experts on this subject based on the ideXlab platform.

  • Identifiability of sorption parameters in stirred Flow-through Reactor experiments and their identification with a Bayesian approach
    Journal of Environmental Radioactivity, 2016
    Co-Authors: V. Nicoulaud-gouin, A. Martin-garin, L. Garcia-sanchez, M. Giacalone, J.c. Attard, Frédéric Y. Bois
    Abstract:

    This paper addresses the methodological conditions –particularly experimental design and statistical inference– ensuring the identifiability of sorption parameters from breakthrough curves measured during stirred Flow-through Reactor experiments also known as continuous flow stirred-tank Reactor (CSTR) experiments. The equilibrium-kinetic (EK) sorption model was selected as nonequilibrium parameterization embedding the Kd approach. Parameter identifiability was studied formally on the equations governing outlet concentrations. It was also studied numerically on 6 simulated CSTR experiments on a soil with known equilibrium-kinetic sorption parameters. EK sorption parameters can not be identified from a single breakthrough curve of a CSTR experiment, because Kd,1 and k− were diagnosed collinear. For pairs of CSTR experiments, Bayesian inference allowed to select the correct models of sorption and error among sorption alternatives. Bayesian inference was conducted with SAMCAT software (Sensitivity Analysis and Markov Chain simulations Applied to Transfer models) which launched the simulations through the embedded simulation engine GNU-MCSim, and automated their configuration and post-processing. Experimental designs consisting in varying flow rates between experiments reaching equilibrium at contamination stage were found optimal, because they simultaneously gave accurate sorption parameters and predictions. Bayesian results were comparable to maximum likehood method but they avoided convergence problems, the marginal likelihood allowed to compare all models, and credible interval gave directly the uncertainty of sorption parameters θ. Although these findings are limited to the specific conditions studied here, in particular the considered sorption model, the chosen parameter values and error structure, they help in the conception and analysis of future CSTR experiments with radionuclides whose kinetic behaviour is suspected.

  • Kinetics of selenate sorption in soil as influenced by biotic and abiotic conditions: a stirred Flow-through Reactor study.
    Journal of environmental radioactivity, 2014
    Co-Authors: L. Garcia-sanchez, A. Martin-garin, N. Loffredo, Stéphane Mounier, F. Coppin
    Abstract:

    Abstract This study (i) quantified the kinetics of selenate sorption and (ii) measured the influence of biotic processes in soil selenate stabilisation. Stirred Flow-through Reactor experiments were conducted on samples of a silty clay soil (pH = 8, Eh = 240–300 mV) from Bure (France) in both non-sterile and sterile conditions. Parameters of the proposed two-site sorption model (EK), adapted from van Genuchten and Wagenet (1989) , were estimated by nonlinear regression. Fast selenate sorption on type-1 sites was moderate, with an equilibrium constant of 25.5 and 39.1 L/kg for non-sterile and sterile conditions. Rate-limited sorption on type-2 sites increased with time, and was predominant for longer periods of time in non-sterile conditions. At equilibrium, it would represent over 96% of the sorbed inventory, with mean sorption times of 17 h and 191 h for non-sterile and sterile conditions. Our results showed for Bure soil that (i) selenate sorption in flowing and mildly-oxidising conditions was strongly kinetically controlled, especially in non-sterile conditions, (ii) selenate desorption was much slower than sorption, which suggests its pseudo-irreversible stabilisation, and (iii) microbial activity increased the contribution of rate-limited sorption on type-2 sites, for which it increased sorption rate by a factor 7 but also facilitated its reversibility. This work stresses the limits of the K d approach to represent selenate sorption in flowing conditions and supports an alternative formulation like the EK model, but also points out that biotic conditions are significant sources of variability for sorption parameters.

  • Kinetics of selenate sorption in soil as influenced by biotic and abiotic conditions: A stirred Flow-through Reactor study
    Journal of Environmental Radioactivity, 2014
    Co-Authors: L. Garcia-sanchez, A. Martin-garin, N. Loffredo, Stéphane Mounier, F. Coppin
    Abstract:

    This study (i) quantified the kinetics of selenate sorption and (ii) measured the influence of biotic processes in soil selenate stabilisation. Stirred Flow-through Reactor experiments were conducted on samples of a silty clay soil (pH=8, Eh=240-300mV) from Bure (France) in both non-sterile and sterile conditions. Parameters of the proposed two-site sorption model (EK), adapted from van Genuchten and Wagenet (1989), were estimated by nonlinear regression. Fast selenate sorption on type-1 sites was moderate, with an equilibrium constant of 25.5 and 39.1L/kg for non-sterile and sterile conditions. Rate-limited sorption on type-2 sites increased with time, and was predominant for longer periods of time in non-sterile conditions. At equilibrium, it would represent over 96% of the sorbed inventory, with mean sorption times of 17h and 191h for non-sterile and sterile conditions. Our results showed for Bure soil that (i) selenate sorption in flowing and mildly-oxidising conditions was strongly kinetically controlled, especially in non-sterile conditions, (ii) selenate desorption was much slower than sorption, which suggests its pseudo-irreversible stabilisation, and (iii) microbial activity increased the contribution of rate-limited sorption on type-2 sites, for which it increased sorption rate by a factor 7 but also facilitated its reversibility. This work stresses the limits of the K d approach to represent selenate sorption in flowing conditions and supports an alternative formulation like the EK model, but also points out that biotic conditions are significant sources of variability for sorption parameters. ?? 2014 Elsevier Ltd.