| Summary: | 碩士 === 國立中興大學 === 環境工程學系 === 91 === The objective of this study is trying to find out the probable reasons why the overall tetrachloroethylene (PCE) dechlorination increases with a decrease in biomass in anaerobic mixed cultures in the batch reactors. And then, We try to discuss the dechlorination of PCE in different environmental conditions, such as the addition of inhibitors. When biomass is diluted to 5% (v/v) by micronutritions, the effect of addition of 2-bromoethanesulfonate(BES),an methanogen inhibitor, and sulfite on the reductive dechlorination of PCE and the activity of methanogens in the batch experiments are investigated. The dechlorination and methanogenesis effects in the different redox potential by varying the dose of reductant Na2S are alse studied. Finally, we investigate the dechlorination of trichloroethylene (TCE), cis- dichloroethene (cis-DCE), and vinyl chloride(VC) , the intermediates of PCE reductive dechlorination, in the conditions that could be used to effectively dechlorinate PCE in our study.
The results indicated that methanogens were not the major dechlorinator in our culture, but they could rapidly utilite acetate to form mehtane. Because the excellent competition of acetate for methanogens, the lack of substrate decreased the dechlorination of PCE in high biomass conditions. Additions of BES and sulfite block the formation of methane, but the reductive dechlorination of PCE was not affected. A decrease in the trace metal significantly affect the dechlorination. There is almost no dechlorination, when the concerntration of CoCl2 decreased to 0.5 mg/L. In the experiment of various initial redox potentials under anaerobie condition, PCE could nearly be completely dechlorinated when the redox potential was below —350 mV. In addition, we found that lower chlorinated ethenes, cis-DCE and VC, could not be dechlorinated in our system in the conditions we adopt to dechlorinate PCE and TCE.
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