Application of Anaerobic and Multiple-Electron-Acceptor Bioremediation to Chlorinated Aliphatic Subsurface Contamination

Principal Investigators
G.F. Parkin, University of Iowa

Abstract

Goal: The goal of this project is to advance understanding of anaerobic and mixed-electron acceptor bioremediation of chlorinated aliphatics to a level that full-scale evaluation of these processes is possible. If successful, field-scale evaluation of technologies developed in this research will be pursued.

Rationale: The U.S. EPA Hazardous Substance Research Centers and national agencies such as the Department of Defense and Department of Energy have identified research on remediation processes for chlorinated aliphatic-contaminated subsurfaces as a high priority. A promising technique is use of in situ bioremediation, and full-scale evaluations of this process are ongoing at trichloroethene-contaminated sites. All of these efforts have focused on use of aerobic bacteria, particularly methanotrophs. However, several of the chlorinated aliphatics of greatest concern are not degraded by aerobic bacteria. Unlike aerobic biological processes, anaerobic biotransformations of all chlorinated aliphatics occur. This lack of specificity, coupled with the fact that most contaminated aquifers are anaerobic, may make anaerobic bioremediation an alternative or supplement to aerobic processes.

Approach: This research will focus on three chlorinated aliphatics that are not degraded by aerobic bacteria: perchloroethene, 1,1,1-trichloroethane, and carbon tetrachloride. If successful, field-scale evaluation of technologies developed in this research will be pursued. In order to accurately assess potential for anaerobic or combined electron acceptor bioremediation technology, all experimental systems will be operated under conditions similar to those observed in contaminated aquifers. Additionally, soil cores will be obtained from contaminated sites as a source of organisms that are indigenous to contaminated areas. These cultures may be considerably different than those obtained from anaerobic digesters and may contain organisms particularly suited for chlorinated aliphatic degradation.

Status: The scope of this project may need to be scaled back because some expected funding was not secured. Operational equipment which is necessary to the project is being updated. A new GC column which will allow separation of all parent compounds and all expected, volatile chlorinated metabolites has been purchased. Methanogenic enrichment cultures are well established and methanotrophic enrichments have begun. Column reactors have been constructed and seeded except for methanotrophic columns. Kinetic experiments will commence as soon as the GC has been calibrated and a detailed quality assurance/quality control plan developed. The anaerobic columns to be used in the sequential studies have been developed; methanotrophic columns will be seeded as soon as the methanotrophic enrichment culture has reached quasi-steady-state. This project is in its first year.

Clients/Users: Results from this research will be of interest to other researchers, U.S. Environmental Protection Agency, U.S. Department of Defense, U.S. Department of Energy, and others.

Key words: anaerobic, bioremediation, chlorinated aliphatics, mixed-electron acceptor.

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