Quantifying Impacts of Microcosm Mass Loss on Kinetic Constant Estimation

Microcosm experiments to assess microbial reductive dechlorination of chlorinated aliphatic hydrocarbons typically experience 5–50% mass loss due to frequent sampling events and diffusion through septa. A literature review, however, reveals that models fit to such experiments for kinetic constant estimation have generally failed to account for experimental mass loss. To investigate possible resultant bias in best-fit parameters, a series of numerical experiments was conducted in which Monod kinetic models with and without mass loss were fit to more than 1300 synthetic data sets, generated using published microcosm data. Models that failed to account for mass loss resulted in significant fitted parameter bias. Bias ranged from 5 to 45% of the parameter magnitude for Monte Carlo simulations with low (approximately 10%) mass loss to 20–120% for simulations with high (approximately 40%) mass loss. In addition, for high mass loss simulations, best-fit values consistently fell along the bounds of the optimization range. These results suggest that failure to properly account for mass loss in microcosms may lead to inaccurate estimation of kinetic constants and may explain some of the literature-reported variability in these parameters. A model is presented that provides a method for including sampling and diffusional mass losses to improve kinetic constant estimation accuracy

Degradation Product Partitioning in Source Zones Containing Chlorinated Ethene Dense Non-Aqueous-Phase Liquid

Abiotic and biotic reductive dechlorination with chlorinated ethene dense non-aqueous-phase liquid (DNAPL) source zones can lead to significant fluxes of complete and incomplete transformation products. Accurate assessment of in situ rates of transformation and the potential for product sequestration requires knowledge of the distribution of these products among the solid, aqueous, and organic liquid phases present within the source zone. Here we consider the fluid−fluid partitioning of two of the most common incomplete transformation products, <i>cis</i>-1,2-dichloroethene (<i>cis</i>-DCE) and vinyl chloride (VC). The distributions of <i>cis</i>-DCE and VC between the aqueous phase and tetrachloroethene (PCE) and trichloroethene (TCE) DNAPLs, respectively, were quantified at 22 °C for the environmentally relevant, dilute range. The results suggest that partition coefficients (concentration basis) for VC and <i>cis</i>-DCE are 70 ± 1 L_aq/L_TCE DNAPL and 105 ± 1 L_aq/L_PCE DNAPL, respectively. VC partitioning data (in the dilute region) were reasonably approximated using the Raoult's law analogy for liquid−liquid equilibrium. In contrast, data for the partitioning of <i>cis</i>-DCE were well described only when well-parametrized models for the excess Gibbs free energy were employed. In addition, available vapor−liquid and liquid−liquid data were employed with our measurements to assess the temperature dependence of the <i>cis</i>-DCE and VC partition coefficients. Overall, the results suggest that there is a strong thermodynamic driving force for the reversible sequestration of <i>cis</i>-DC and VC within DNAPL source zones. Implications of this partitioning include retardation during transport and underestimation of the transformation rates observed through analysis of aqueous-phase samples

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment-3

<p><b>Copyright information:</b></p><p>Taken from "Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment"</p><p>Environmental Health Perspectives 2004;113(4):465-477.</p><p>Published online 8 Dec 2004</p><p>PMCID:PMC1278488.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment-2

<p><b>Copyright information:</b></p><p>Taken from "Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment"</p><p>Environmental Health Perspectives 2004;113(4):465-477.</p><p>Published online 8 Dec 2004</p><p>PMCID:PMC1278488.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Experimental Evaluation and Mathematical Modeling of Microbially Enhanced Tetrachloroethene (PCE) Dissolution

Experiments to assess metabolic reductive dechlorination (chlororespiration) at high concentration levels consistent with the presence of free-phase tetrachloroethene (PCE) were performed using three PCE-to-cis-1,2-dichloroethene (cis-DCE) dechlorinating pure cultures (Sulfurospirillum multivorans, Desulfuromonas michiganensis strain BB1, and Geobacter lovleyi strain SZ) and Desulfitobacterium sp. strain Viet1, a PCE-to-trichloroethene (TCE) dechlorinating isolate. Despite recent evidence suggesting bacterial PCE-to-cis-DCE dechlorination occurs at or near PCE saturation (0.9−1.2 mM), all cultures tested ceased dechlorinating at ∼0.54 mM PCE. In the presence of PCE dense nonaqueous phase liquid (DNAPL), strains BB1 and SZ initially dechlorinated, but TCE and cis-DCE production ceased when aqueous PCE concentrations reached inhibitory levels. For S. multivorans, dechlorination proceeded at a rate sufficient to maintain PCE concentrations below inhibitory levels, resulting in continuous cis-DCE production and complete dissolution of the PCE DNAPL. A novel mathematical model, which accounts for loss of dechlorinating activity at inhibitory PCE concentrations, was developed to simultaneously describe PCE-DNAPL dissolution and reductive dechlorination kinetics. The model predicted that conditions corresponding to a bioavailability number (Bn) less than 1.25 × 10-2 will lead to dissolution enhancement with the tested cultures, while conditions corresponding to a Bn greater than this threshold value can result in accumulation of PCE to inhibitory dissolved-phase levels, limiting PCE transformation and dissolution enhancement. These results suggest that microorganisms incapable of dechlorinating at high PCE concentrations can enhance the dissolution and transformation of PCE from free-phase DNAPL

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment-1

<p><b>Copyright information:</b></p><p>Taken from "Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment"</p><p>Environmental Health Perspectives 2004;113(4):465-477.</p><p>Published online 8 Dec 2004</p><p>PMCID:PMC1278488.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment-4

<p><b>Copyright information:</b></p><p>Taken from "Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment"</p><p>Environmental Health Perspectives 2004;113(4):465-477.</p><p>Published online 8 Dec 2004</p><p>PMCID:PMC1278488.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment-5

<p><b>Copyright information:</b></p><p>Taken from "Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment"</p><p>Environmental Health Perspectives 2004;113(4):465-477.</p><p>Published online 8 Dec 2004</p><p>PMCID:PMC1278488.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment-0

<p><b>Copyright information:</b></p><p>Taken from "Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment"</p><p>Environmental Health Perspectives 2004;113(4):465-477.</p><p>Published online 8 Dec 2004</p><p>PMCID:PMC1278488.</p><p>This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.</p