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Use of Vegetable Oil in Reductive Dechlorination of Tetrachloroethene

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Master's thesis

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Reductive dechlorination is an effective bioremediation method for treating tetrachloroethene and its daughter compounds. Common techniques of stimulating reductive dechlorination involve the injection of costly, soluble electron donors into the contaminated plume. Vegetable oil is a cheaper alternative to such donors on a cost-per-mass basis, and may even be more economically implemented. This study applied microcosm studies to investigate the effectiveness of vegetable oil as an electron donor. Cultures fed with vegetable oil were observed to completely dechlorinate tetrachloroethene to ethene. Dechlorination by vegoil was also sustainable over a period of 140 days without the addition of nutrient amendments. Nevertheless, vegetable oil was found to ferment relatively quickly, leading to low donor efficiency. Biomass and acetate were the most significant products of vegoil-fed microcosms. Volatile fatty acids longer than 2 carbons rarely persisted. Since these acids can act as good secondary donors in the aqueous phase, their absence implies that the dechlorination zone does not extend very far from the vegoil phase. Inference from biomass measurements and dechlorination behavior hints that endogenous decay of large quantities of biomass could provide a stable source of electron donor. Perhaps a similar method of growing up a large pool of biomass for electron-donating purposes could be investigated in the future. Since acetate rarely ferments further to produce more hydrogen, and methanogenic biomass is fairly immobile, one good area of application for vegoil would be in bio-barriers. Interception of a contaminated plume by constructing biobarriers downstream reduces the need to maintain a large zone of treatment, although treatment times could be longer. For example, vegetable-oil-coated sand particles could be used to back-fill a trench to intercept and treat a plume consisting of dissolved chlorinated ethenes.

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  • Biochemistry
  • Physical Chemistry

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