- 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
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.