Date of Award

5-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Engineering and Science

Advisor

Freedman, David L.

Committee Member

Kurtz , Harry D.

Committee Member

Lee , Cindy M.

Committee Member

Carraway , Elizabeth R.

Abstract

ABSTRACT
Bioremediation of high concentrations of halomethanes e.g., carbon tetrachloride (CT), trichlorofluoromethane (CFC-11) and chloroform (CF) has seldom been addressed before and remains highly challenging. A microcosm study was conducted to investigate bioremediation strategies for groundwater contaminated with CT (6 to 10 mg/L), CFC-11 (1 to 26 mg/L), CF (3-500 mg/L), and 1,1-dichloroethene (1,1-DCE; up to 9 mg/L) at a former industrial site in California. Biostimulation with corn syrup and catalytic amounts of vitamin B12 was demonstrated as a feasible remedial strategy and bioaugmentation with B12 represents the most promising bioremediation method of the ones studied. Halomethane transformation occurred sequentially, i.e., CT was transformed first, followed by CFC-11, then CF. 14C analyses revealed that the dominant end products of CT and CF transformation were CO, CO2 and organic acids. Bioaugmentation with enriched indigenous sulfate-reducing cultures grown on lactate or ethanol without prior acclimation to halomethanes was effective in enhancing transformation of CT and CFC-11, although limitations existed. In addition, a fermentative enrichment culture appeared to be a promising bioaugmentation culture for transforming high concentrations of CF.

Bioremediation of high concentrations of CF in groundwater is challenging because of its high toxicity and inhibitory effect on most anaerobic prokaryotes. Enrichment and field applications of cultures that can transform high concentrations of CF (>100 mg/L) are not currently available. DHM-1, a fermentative enrichment culture grown on corn syrup, was developed in this study by using soil samples from the California industrial site. DHM-1 was demonstrated to transform over 500 mg/L CF in the presence of catalytic amounts of vitamin B12 at a rate as high as 22 mg/L/d in a mineral salts medium. Production of non-toxic end products, i.e., CO, CO2, and organic acids indicates hydrolytic reactions as the dominating pathway. DHM-1 is facultative and can grow on corn syrup while transforming high concentrations of CF, which makes it a promising culture for bioaugmentation. The two strains isolated from DHM-1 are related to Pantoea spp., and both possess equal or even slightly better CF transforming capability than the DHM-1 enrichment. Development of DHM-1 and isolation of the two Pantoea spp. makes bioremediation of source zone CF contamination possible for the first time.

Following the development and characterization of DHM-1, the capacity of DHM-1 for biotransformation of high concentrations of halogenated methanes was explored. With the addition of catalytic amounts of vitamin B12, DHM-1 can readily transform at least 2000 mg/L CF, which is equal to one fourth of the CF solubility in water. In addition, DHM-1 is able to transform CT and CFC-11 as well. Complete transformation of a mixture of 11 mg/L CT, 24 mg/L CFC-11 and 500 mg/L CF was achieved in less than four months by DHM-1 in a mineral salts medium. This study also demonstrated the capability of SDC-9, a commercially available mixed culture, to transform high concentrations of halomethanes. DHM-1 has an advantage over SDC-9 in terms of the rate of CF transformation, while SDC-9 exhibited better kinetics with CFC-11. A second microcosm study with soil and water from the California industrial site further demonstrated the use of these two cultures for bioaugmentation to enhance in situ bioremediation of groundwater contaminated by high concentrations of halomethanes.

This study for the first time makes source zone bioremediation of halomethanes contamination possible. DHM-1 and the two isolates (patent pending) developed in this study are the first mixed and pure cultures, respectively, reported to biotransform high concentrations of CF and other halomethanes to non-toxic end products. DHM-1 is a promising bioaugmentation culture for in situ bioremediation of high concentrations of halomethanes owing to its distinctive characteristics.

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