Date of Award

8-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Advisor

Freedman, David L

Committee Member

Lee , Cindy

Committee Member

Finneran , Kevin

Abstract

Bioremediation is an attractive remediation strategy for groundwater contaminated with tetrachloroethene (PCE) since it can result in complete reductive dechlorination to non-hazardous ethene, often at a lower cost than other treatment methods. The optimum pH for microbes that chlororespire chlorinated ethenes is in the range of 6.5-7.5. However, the groundwater at many locations is outside this range, and typically on the low side. Addition of a base to increase the pH is problematic due to the difficulty of achieving homogenous distribution and the potential for clogging caused by precipitation. The objectives of this thesis were 1) to develop anaerobic enrichment cultures that are capable of chlororespiring chlorinated ethenes at a pH of 5.5; 2) to compare the use of phosphate versus 2-(N-morpholino) ethanesulfonic acid (MES) as buffering agents for the enrichment cultures, with the intent of maintaining a stable pH in the vicinity of 5.5; and 3) to compare the use of lactate, hydrogen and emulsified vegetable oil as electron donors for the low pH enrichment cultures to support PCE dechlorination to ethene
Development of enrichment cultures began with construction of microcosms using soil and groundwater samples from two locations in which there was field evidence for dechlorination activity at a pH below 6. In addition, enrichment cultures that were started in a previous project, using inoculum from a third hazardous waste site, were continued for this research. Combinations of enrichment cultures from two of the sites were also evaluated.
Several enrichment cultures were successfully developed with the capacity to dechlorinate PCE to ethene and/or ethane at a pH of 5.5. The most effective enrichment culture was created by combining enrichments from two of the hazardous waste sites. Phosphate buffered medium was effective for maintaining enrichment cultures at a pH close to 5.5; MES did not provide any better control of the pH. Lactate and hydrogen were effective electron donors for the low pH enrichment cultures, although lactate is more acceptable for practical application. Use of emulsified vegetable was discontinued after it failed to show any advantages in microcosms from one of the sites. Further development of the enrichment cultures will be necessary prior to evaluating their potential for bioaugmentation of chloroethene-contaminated groundwater with a pH below 6.

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