Microcosm study of enhanced biotransformation of vinyl chloride to ethylene with TCE additions under anaerobic conditions from Point Mugu, California

Graduation date: 2001This microcosm study demonstrated the enhanced anaerobic transformation\ud of vinyl chloride (VC) to ethylene. A previous microcosm study from Point Mugu\ud site showed the accumulation of VC due to the slow transformation step of VC to\ud ethylene. To overcome the rate-limiting step, two laboratory experiments tested the\ud effect of trichloroethylene (TCE) additions on the rate enhancement, repeated low\ud TCE additions and high TCE concentration additions.\ud TCE (2 μmol) was repeatedly added over a two week interval. In a parallel\ud study, an equal amount of VC was added to another set of microcosms. TCE\ud addition increased VC transformation to ethylene, with nearly 19% VC conversion\ud to ethylene compared to 4% VC conversion in the VC added controls. However,\ud the increased VC transformation rates were not sufficient enough to avoid VC\ud accumulation. Rate of VC transformation decreased once TCE addition was stopped. This indicated the mixed culture required the transformation of TCE to\ud maintain VC transformation rates.\ud With TCE added at high concentrations (100 mg/L and 200 mg/L), nearly\ud complete transformation of TCE to ethylene was observed. After the addition of\ud high TCE concentrations, low concentration TCE (3 μmol) was added and near\ud 95% transformed to ethylene in 45 days. Two different low hydrogen yielding\ud substrates, butyrate and propionate, were tested. Both were equally effective in\ud promoting TCE dechlorination. Methanogenesis was inhibited at high TCE\ud concentration with both substrates. Kinetic analysis of VC transformation data\ud showed VC transformation followed the first order kinetics with respect to\ud concentrations using a modified Monod equation. First-order kinetic constants\ud increased after the addition of high ICE concentrations. After 200 mg/L of TCE\ud addition, the first-order kinetic constant increased by factor of six compared to the\ud rate obtained from the earlier low TCE concentration addition. However,\ud reintroduction of TCE at low concentration maintained similar enhanced kinetic\ud constants, as achieved at high concentration. This indicated the enhancement of\ud VC transformation to ethylene was likely due to the growth of microorganisms\ud using TCE as a terminal electron acceptor. These microorganisms were likely\ud responsible for the transformation of VC to ethylene