This microcosm study demonstrated the enhanced anaerobic transformation
of vinyl chloride (VC) to ethylene. A previous microcosm study from Point Mugu
site showed the accumulation of VC due to the slow transformation step of VC to
ethylene. To overcome the rate-limiting step, two laboratory experiments tested the
effect of trichloroethylene (TCE) additions on the rate enhancement, repeated low
TCE additions and high TCE concentration additions.
TCE (2 ��mol) was repeatedly added over a two week interval. In a parallel
study, an equal amount of VC was added to another set of microcosms. TCE
addition increased VC transformation to ethylene, with nearly 19% VC conversion
to ethylene compared to 4% VC conversion in the VC added controls. However,
the increased VC transformation rates were not sufficient enough to avoid VC
accumulation. Rate of VC transformation decreased once TCE addition was stopped. This indicated the mixed culture required the transformation of TCE to
maintain VC transformation rates.
With TCE added at high concentrations (100 mg/L and 200 mg/L), nearly
complete transformation of TCE to ethylene was observed. After the addition of
high TCE concentrations, low concentration TCE (3 ��mol) was added and near
95% transformed to ethylene in 45 days. Two different low hydrogen yielding
substrates, butyrate and propionate, were tested. Both were equally effective in
promoting TCE dechlorination. Methanogenesis was inhibited at high TCE
concentration with both substrates. Kinetic analysis of VC transformation data
showed VC transformation followed the first order kinetics with respect to
concentrations using a modified Monod equation. First-order kinetic constants
increased after the addition of high ICE concentrations. After 200 mg/L of TCE
addition, the first-order kinetic constant increased by factor of six compared to the
rate obtained from the earlier low TCE concentration addition. However,
reintroduction of TCE at low concentration maintained similar enhanced kinetic
constants, as achieved at high concentration. This indicated the enhancement of
VC transformation to ethylene was likely due to the growth of microorganisms
using TCE as a terminal electron acceptor. These microorganisms were likely
responsible for the transformation of VC to ethylene. / Graduation date: 2001
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33263 |
| Date | 25 September 2000 |
| Creators | Pang, Incheol Jonathan |
| Contributors | Semprini, Lewis |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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