Inhibition, kinetic and modeling studies of acetylene and 1-chloro-1-fluoroethene on reductive dechlorination of TCE and vinyl chloride Public Deposited

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  • Laboratory and modeling studies were performed with a mixed-anaerobic-culture obtained from the Evanite site in Corvallis, Oregon. The culture completely transforms trichloroethene (TCE) to cis-dichloroethene (c-DCE), vinyl chloride (VC), and finally to ethene. Acetylene inhibition studies were used to examine the culture's microbial activities. Kinetic studies determined the half-saturated constant (K[subscript s]), the maximum utilization rate (k[subscript max]X), and inhibition constants (K[subscript I]). The kinetic constants were used to model the results of inhibition studies using competitive and uncompetitive inhibition models. Acetylene was found to function as a reversible inhibitor and was used to probe the activities of reductive dechlorination. Various acetylene concentrations were used to differentiate microbial processes, including methanogenesis, acetogenesis, and halorespiration. Acetylene concentrations of 48, 192, and 12 μM, respectively, were required to achieve 90% inhibition in the rates of methanogenesis, TCE and VC transformation. H₂-dependent acetate production was not inhibited by acetylene. K[subscript s] values for TCE and VC were 12 μM and 63 μM, respectively. Model fitting of acetylene inhibition constants (K[subscript IC]) for TCE and VC transformations yielded the same value (0.4 μM) for a competitive inhibition model. However, for uncompetitive inhibition the estimated K[subscript IU] for TCE to c-DCE, TCE to 1,1-DCE and VC to ethene were 13.3, 14.1 and 2.2 μM, respectively. Competitive and uncompetitive inhibition models simulated experimental data equally well for results obtained at high TCE and VC concentrations. The models were further verified to fit transient data of acetylene inhibition at lower TCE and VC concentrations, and competitive inhibition resulted in a better fit to the experimental data. 1-chloro-1-fluoroethene (1,1-CFE) was found to track the rate of VC transformation well, since VC and 1,1-CFE had similar maximum transformation rates and K[subscript s] values. A competitive inhibition model with the measured K[subscript s] values, 63 and 87 μM. was used to predict the rates of VC and 1,1-CFE transformation, respectively. The similar rates and results of acetylene and compound inhibition studies indicated VC and 1,1-CFE were transformed by the same enzyme. 1,1-CFE transformation by three different cultures, clearly demonstrate that 1,1-CFE was an excellent surrogate to track rates of VC transformation.
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