Abstract
Purchase PDF (222 K)
E-mail Article
Add to my Quick Links
Cited By in Scopus (14)
50 μg L−1) where reduction of FeOOH is complete and its entire load of sorbed As is released to solution, at which point the aquifer sediments become grey in colour as FeOOH vanishes. Where reduction is incomplete, the sediments are brown in colour and resorption of As to residual FeOOH keeps As concentrations below 10 μg L−1 in the presence of dissolved Fe. Sorbed As released by reduction of Mn oxides does not increase As in ground water because the As resorbs to FeOOH. High concentrations of As are common in alluvial aquifers of the Bengal Basin arise because Himalayan erosion supplies immature sediments, with low surface-loadings of FeOOH on mineral grains, to a depositional environment that is rich in organic mater so that complete reduction of FeOOH is common.
Purchase PDF (1405 K)
50% of Mn, Cu, Zn, Cd and Pb. These elements were predominantly adsorbed on the hydrous oxide precipitate, or to some extent (Mn and Pb) coprecipitated, as indicated from a sequential leaching procedure and powder X-ray diffractometry. All the elements, particularly Cu, were to a significant degree associated with organic matter.
doi:10.1016/S0098-3004(03)00008-6 
Published by Elsevier Science Ltd.
Comparison of approaches for simulating reactive solute transport involving organic degradation reactions by multiple terminal electron acceptors
Received 7 March 2002;
References and further reading may be available for this article. To view references and further reading you must purchase this article.
Abstract
Reactive solute transport models are useful tools for analyzing complex geochemical behavior resulting from biodegradation of organic compounds by multiple terminal electron acceptors (TEAPs). The usual approach of simulating the reactions of multiple TEAPs by an irreversible Monod rate law was compared with simulations that assumed a partial local equilibrium or kinetically controlled reactions subject to the requirement that the Gibbs free energy of reaction (ΔG) was either less than zero or less than a threshold value. Simulations were performed using a single organic substrate and O2, FeOOH, SO4−2 and CO2 as the terminal electron acceptors. It was assumed that the organic substrate was slowly and completely fermented to CO2 and H2 and the H2 was oxidized by the TEAPs. Simulations using the Monod approach showed that this irreversible rate law forced the reduction of both FeOOH and CO2 to proceed even when ΔG was positive. This resulted in an over prediction in amount of FeOOH reduced to Fe(II) in parts of the domain and it resulted in large errors in pH. Simulations using mass action kinetics agreed with equilibrium simulations for the case of large rate constants. The extent of reductive dissolution of FeOOH was strongly dependent on the thermodynamic stability of the FeOOH phase. Transport simulations performed assuming that the reactions of the TEAPs stopped when ΔG exceeded a threshold value showed that only simulated H2 concentrations were affected if the threshold value was the same for each TEAP. Simulated H2 concentrations were controlled by the fastest reaction of the TEAP, but it was common for reactions to occur concomitantly rather than sequentially.
Author Keywords: Biogeochemistry; Monod kinetics; Thermodynamics; Groundwater; Hydrogen
Article Outline
- 1. Introduction
- 2. Affect of geochemical conditions on reaction thermodynamics
- 3. TEAP modeling approaches
- 4. Example simulations
- 4.1. Effect of modeling approach
- 4.2. Influence of FeOOH thermodynamic properties
- 4.3. Effects of ΔGTHR
- 4.4. H2 as a TEAP indicator
- 5. Discussion and conclusions
- Acknowledgements
- References
