Anaerobic reductive dechlorination of 1-chloro-1-fluoroethene to track the transformation of vinyl chloride.

1-Chloro-1-fluoroethene (1,1-CFE) was studied as a reactive tracer to quantify the anaerobic transformation of vinyl chloride (VC). Batch kinetic studies of 1,1-CFE and VC transformation were performed with an enrichment culture obtained from the Evanite site in Corvallis, OR. The culture is capable of completely transforming trichloroethene (TCE) through cis-dichloroethene (c-DCE) and VC to ethene. The culture also transforms fluorinated analogues, such as trichlorofluoroethene (TCFE), to fluoroethene (FE) as a final product. The transformation sequence of the fluorinated analogue was correlated with that achieved for the chlorinated ethene with the same degree of chloride substitution. For example, the production of 1,1-CFE, the major CFE isomer formed from TCFE transformation, was correlated with the production of VC from TCE transformation. Since the 1,1-CFE and its product, FE, have a distinct analytical signature, 1,1-CFE may be used as a reactive in situ tracer to evaluate the VC transformation potential. The half-saturated constants (K(S)) of VC and 1,1-CFE were 63 and 87 microM, respectively, while similar maximum utilization rates (kmaxX) of 334 and 350 microM/d were achieved. Acetylene inhibited both VC and 1,1-CFE transformation. A competitive inhibition model with the independently measured K(S) values used as the inhibition constants predicted rates of transformation of both VC and 1,1-CFE when both compounds were present. 1,1-CFE transformation was also tested with three different cultures. With all the cultures, 1,1-CFE transformation was associated with VC transformation to ethene, and the rates of transformation were comparable. The results demonstrated that 1,1-CFE was a good reactive surrogate for evaluating the rates of VC transformation.

Acetylene inhibition of trichloroethene and vinyl chloride reductive dechlorination.

Kinetic studies reported here have shown that acetylene is a potent reversible inhibitor of reductive dehalogenation of trichloroethene (TCE) and vinyl chloride (VC) by a mixed dehalogenating anaerobic culture. The mixed culture was enriched from a contaminated site in Corvallis, OR, and exhibited methanogenic, acetogenic, and reductive dehalogenation activities. The H2-fed culture transformed TCE to ethene via cis-dichloroethene (c-DCE) and VC as intermediates. Batch kinetic studies showed acetylene reversibly inhibited reduction of both TCE and VC, and the levels of inhibition were strongly dependent on acetylene concentrations in both cases. Acetylene concentrations of 192 and 12 microM, respectively, were required to achieve 90% inhibition in rates of TCE and VC transformation at an aqueous concentration of 400 microM. Acetylene also inhibited methane production (90% inhibition at 48 microM) but did not inhibit H2-dependent acetate production. Mass balances conducted during the studies of VC inhibition showed that acetogenesis, VC transformation to ethene, and methane production were responsible for 52%, 47%, and 1% of the H2 consumption, respectively. The results indicate that halorespiration is the dominant process responsible for VC and TCE transformation and that dehalorespiring organisms are the target of acetylene inhibition. Acetylene has potential use as a reversible inhibitor to probe the biological activities of reductive dechlorination and methanogenesis. It can be added to inhibit reactions and then removed to permit reactions to proceed. Thus, it can be a powerful tool for investigating intrinsic and enhanced anaerobic remediation of chloroethenes at contaminated sites. The results also suggest that acetylene produced abiotically by reactions of chlorinated ethenes with zero-valent iron could inhibit the biological transformation of VC to ethene.