State Water Resources Research Institute Program


Project ID: 2007WI164B
Title: Enhanced Reductive Dechlorination of Chlorinated Aliphatic Hydrocarbons: Molecular and Biochemical Analyses
Project Type: Research
Start Date: 3/01/2007
End Date: 2/29/2008
Congressional District: 2nd
Focus Categories: Toxic Substances, Geochemical Processes
Keywords: microbial processes, dechlorination, contaminants
Principal Investigator: Hickey, Bill
Federal Funds: $ 42,918
Non-Federal Matching Funds: $ 35,277
Abstract: Groundwater problem addressed. Chlorinated aliphatic hydrocarbons are pervasive groundwater contaminants for which enhanced reductive dechlorination (ERD) via electron donor augmentation is a major bioremedial technology. A primary goal of ERD is to stimulate late stage reactions (primarily dechlorination of cis-dichloroethylene (c-DCE) and vinyl chloride (VC) to ethene), which field data indicate proceed most effectively under methanogenic conditions. However, the microbial communities effecting late stage reactions are unknown, and the biodegradative pathways operative under methanogenic conditions are not fully understood. Because of its ability to mediate VC reduction to ethene, the chloridogenic (dehalorespiring) bacterium Dehalococcoides ethenogenes initially attracted much attention. But, VC reduction by D. ethenogenes is slow, and microcosm and field screening studies have indicated that this transformation can occur in the absence of D. ethenogenes. Recently, VC-respiring strains of Dehalococcoides sp. that are highly efficient in VC reduction have been isolated, but their role in effecting this process in methanogenic environments has not yet been ascertained. There is also growing recognition that varying composition and activities of fermentative organisms may also have significant effects on the activities of dechlorinators, but the nature and activities of fermentors active in methanogenic ERD are poorly understood. Furthermore, while microcosm studies with model amendments (organic acids and alcohols) have shown that the nature of the electron donor affects the structure and activity of the microbial community stimulated, little is known about the microbial communities established in response to amendments actually used in the field. Finally, to date, information on microbial community dynamics during ERD treatment have been largely restricted to microcosm tests; information from field studies is needed, but lacking in the literature.

Expected project contributions. This project will further our understanding of the microbes and microbial communities mediating biodegradative transformations that are key to effective ERD as it is applied in the field. By using a combination of phylogenetic and functional markers for microbial community analysis, we will gain information on the diversity and types of potentially important fermentative organisms as well as the dechlorinators. Integrating data from controlled microcosm tests and field tests may allow us to triangulate on particular organisms that carry out key functions in situ. We will learn how dynamics in microbial community composition, genetic markers and biochemical markers (e.g., fermentation products) correlate with changes in dechlorination activity, and thereby identify markers potentially useful as diagnostic tools for process assessment in the field.

Objectives. 1.) Delineate the microbial community dynamics induced by carbon source augmentation in microcosm and field samples, 2.) Elucidate the composition of methanogenic communities that effect complete dechlorination of CAH in microcosm and field samples, 3.) Delineate the dynamics of CAH degradation and fermentative reactions in microcosm samples and during the progress of a field-scale application of ERD, 4.) Apply numerical methods to microcosm and field data to develop correlations between microbial community composition, biochemical markers and dechlorination activity.

Approach. The field site will be a CAH-contaminated aquifer located in southeastern Wisconsin, which is scheduled to begin ERD treatment (carbon source amendment) in April of 2006. Sediment and water samples will be collected prior to initiation of ERD treatment, and used to establish baseline microbiological and biogeochemical parameters. Microcosms will be established with aquifer sediments, and amended for ERD treatment as applied to the field site. Periodically, field and microcosm samples will be analyzed for CAH, CAH degradation products, biochemical markers and microbial community composition. The latter will include automated ribosomal intergenic space analysis and polymerase chain reaction analysis of reductive dehalogenase genetic markers.

Users of project findings. Information gained will fill a major knowledge gap in the science of ERD, and may identify biomarkers useful for monitoring the progress of ERD in field applications. Findings will thus be of direct benefit to practitioners, regulatory agencies and basic science researchers.

Progress/Completion Report, PDF

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