Date of Award

12-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Advisor

Freedman, David L

Committee Member

Finneran , Kevin T

Committee Member

Lee , Cindy

Abstract

Halogenated aliphatic hydrocarbons are among the most common contaminants in soil and groundwater found at hazardous waste sites throughout the United States. Among them are tetrachloroethene (PCE), 1,2-dichloroethane (1,2-DCA) and ethylene dibromide (EDB). Organohalide respiration of each compound has been reported. However, considerably less information is known about EDB than PCE and 1,2-DCA, including the yield that occurs during growth with EDB as the sole TEA. The main objective of this project was to determine which types of chlororespiring microbes predominate during growth of enrichment cultures when PCE, 1,2-DCA and EDB served as the TEA, and what their yield is. Based on previous studies, the genera of interest were Dehalococcoides, Dehalobacter, and Desulfitobacterium.
The yield of Dehalococcoides during growth with EDB was 7.13±0.63 _ 106 gene copies per µmol Br-, based on qPCR quantification of the 16S rRNA gene. This is similar to the yield reported by Eaddy (10), using a similar enrichment culture. No other reports of yields during respiration of EDB were found in the literature. Dehalobacter was also present in the EDB-grown enrichment culture, but at a concentration several orders of magnitude lower than Dehalococcoides. Desulfitobacterium was not detected, based on a lack of amplification of its 16S rRNA gene.
The yield of Dehalococcoides during growth with 1,2-DCA was 4.59±0.036 _ 107 gene copies per µmol Cl-. A similar yield was measured when the enrichment culture grown with EDB was switched to 1,2-DCA as the TEA, supporting the observation that Dehalococcoides were responsible for dehalogenation of both compounds in both enrichment cultures. Dehalobacter and Desulfitobacterium, the two other genera known to respire 1,2-DCA, were present either at much lower concentrations than Dehalococcoides, or were not detected at all.
The yield for Dehalococcoides in the 1,2-DCA enrichment culture was similar in magnitude to the yield for PCE in this study (2.11±0.082 _ 108) and other pure and mixed cultures containing Dehalococcoides grown with chlorinated ethenes. It is not yet known why the yield for Dehalococcoides was significantly lower when grown with EDB. This is especially notable considering that, when EDB and 1,2-DCA are added to either enrichment culture at the same time, EDB is always used preferentially to 1,2-DCA (38). Overall, the results of this study contribute to a general understanding of organohalide respiration with chlorinated and brominated compounds.

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