Graduate Thesis Or Dissertation
 

Effect of electron donors on the reductive dechlorination of trichlorofluoroethylene in anaerobic microcosms and in situ push-pull tests

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/jq085p623

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  • This research focuses on the anaerobic transformation of trichloroethylene (TCE) that is occurring in the subsurface of the Evanite site in Corvallis, OR. Two anaerobic studies were conducted to investigate the effects of microbial communities in the presence of different electron donors during the anaerobic degradation of trichlorofluoroethylene (TCFE), and TCE. The first study was conducted in the groundwater microcosm bottles, filled with groundwater collected from the monitoring well 15 at the site. Because TCE was present in low concentrations in this well, TCFE was added to the microcosms as a surrogate compound that might be dehalogenated like TCE. Lactate, formate and hydrogen were evaluated as substrates for driving the anaerobic transformations. These substrates and products are potential electron donors to enhance the dechlorination of TCE and possibly TCFE. When injecting TCFE with one of the substrates in the microcosm bottles, a quick reduction of TCFE was observed to cis-dichlorofluoroethylene (cis-DCFE), and the transformation of the substrates to acetate. When TCFE and TCE were present as mixtures, a faster reduction of TCE to cis-DCE was observed compared to TCFE to cis-DCFE. The second study was an in-situ push-pull test at well15. Formate and TCFE were added to groundwater extracted from well 15. The amended groundwater was injected and extracted after a reaction time ranging from 3 to 5 hours. This study was conducted to determine the in-situ response to the addition of an electron donor to enhance the biotransformation of TCFE and TCE. During the push-pull test no transformation of formate to acetate was observed. Some TCFE was transformed to cis-DCFE. It is possible that another electron donor was present in the aquifer that lead TCE to transform to cis-DCE and furthermore to VC, and TCFE to cis-DCFE under reductive dechlorination conditions. These anaerobic systems involve the interaction of several reactions within the microbial population. Different transformations throughout the experimentation were an indication that the microbial population was active during the different stages of the study.
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