Reductive Dechlorination of Tetrachloroethene in Polluted Aquifer Microcosms and Isolation of Anaerobic Bacteria from a Tetrachloroethene-Dechlorinating Enrichment
Thesis - University Access Only
Master of Science (MS)
Department / School
Biology and Microbiology
Reductive dehalogenation is the only known means of biodegradation of certain highly chlorinated pollutants. Some of these include polychlorinated biphenyls, hexachlorobenzene, pentachlorophenol, and tetrachloroethene. Reductive dehalogenation is an anaerobic process that occurs more readily in complex mutualistic environments. Tetrachloroethene has received much attention due to its frequent occurrence in groundwater and its potential health threat to those exposed to higher levels of it. The objective of this research was to determine whether dechlorination of tetrachloroethene could be stimulated in contaminated aquifer microcosms, and to determine the metabolic types of organisms in a tetrachloroethenedechlorinating enrichment obtained from another contaminated site. The use of surfactants to enhance the solubility of dense nonaqueous phase liquids, such as tetrachloroethene, may aid in the remediation of contaminated aquifers. Several polyoxyethylene ether surfactants were chosen based on their potential for anaerobic biodegradability. In abiotic solubility studies the surfactants enhanced the solubility of tetrachloroethene in artificial groundwater. The ability of the surfactants to be degraded in aquifer microcosms was monitored by pressure increases occurring in the microcosms. No change in pressure was observed in any of the surfactant microcosms. One replicate of a Brij 98 plus butyrate treatment showed an increase in pressure. In microcosms containing only butyrate there was a slight increase in pressure, indicating that there were viable organisms present. Straight-chain fatty acids, such as butyrate, are commonly examined as electron donors in dechlorination experiments. Fatty acids ranging in number of carbons from 2 to 18 were examined for both ability to support dehalogenation of tetrachloroethene and also ability to increase tetrachloroethene solubility. The influence these fatty acids would have on the solubility of tetrachloroethene was examined abiotically in artificial groundwater. They were found to have little impact on the solubility of tetrachloroethene in groundwater. The ability to stimulate dechlorination by the addition of straightchain fatty acids and surfactants to aquifer microcosms spiked with 10-15 parts per million tetrachloroethene was examined in two trials. The surfactants and fatty acids were the same as those used in the solubility trials. The first trial was performed with soil taken from the capillary fringe zone of the aquifer. The second trial was performed on soil taken from the saturated zone of the aquifer. No dechlorination of tetrachloroethene was observed in microcosms from Wurtsmith Air Force Base after 110-166 days of incubation for wdl microcosms and 80 days of incubation for wd2 microcosms. The presence of fermentable organic carbon may have influenced the results. Dechlorination has been shown to be inhibited by higher levels of organic carbon. Once the organic carbon has been fermented, dechlorination can then proceed. The threshold amount of tetrachloroethene that becomes toxic to organisms is not known. Saturating levels of tetrachloroethene were added to microcosms with various carbon sources. These microcosms were monitored for dechlorination and viable organisms. No dechlorination was observed in any of the microcosms. Phase microscopic observations indicated that there were viable organisms present in the microcosms. The metabolic types of organisms present in dechlorinating enrichments is generally not known. If the types of organisms present could be determined, there would be a better understanding of how the community functions. A butyrate/tetrachloroethene-utilizing enrichment culture was examined. To identify the types of organisms present, the enrichment culture was used to inoculate minimal media amended with butyrate, crotonate, acetate, and H2/C02 as substrates. Once isolated colonies were obtained the isolates were further characterized by the antibiotic susceptibility, 02 tolerance, selective inhibitors, and doubling time determination. Isolates were obtained from the crotonate, acetate, and H2/C02 amendments. The crotonate isolate was obtained in pure culture. The acetate and H2/C02 isolates were not obtained in pure culture. Further tests and genetic analyses of the isolates would help in the characterization of these organisms.
Library of Congress Subject Headings
Water -- Purification -- Chlorination
Number of Pages
South Dakota State University
Carlson, Christopher D., "Reductive Dechlorination of Tetrachloroethene in Polluted Aquifer Microcosms and Isolation of Anaerobic Bacteria from a Tetrachloroethene-Dechlorinating Enrichment" (1997). Electronic Theses and Dissertations. 307.