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In anaerobic metabolism, nitrate, sulfate, carbon dioxide, oxidized metals, or organic compounds may replace oxygen as the electron acceptor. Depending on the contaminant of concern, a subset of these activities may be cultivated. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated SitesĪnaerobic: Direct anaerobic metabolism involves microbial reactions occurring in the absence of oxygen and encompasses many processes, including fermentation, methanogenesis, reductive dechlorination, sulfate-reducing activities, and denitrification. These conditions may be present naturally but often in the presence of a source area oxygen and a substrate such as methane or propane will need to be introduced. For aerobic cometabolism to occur there must be sufficient oxygen and a suitable substrate which allows the microbe to produce the appropriate enzyme.

At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal. Cometabolic dechlorination does not appear to produce energy for the organism. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. This can sometimes be reversed by adding oxygen in the form of air (air sparging, bioventing), ozone, or slow oxygen release compound (e.g., ORC(r)).Īerobic dechlorination may also occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. Degradation of contaminants that are susceptible to aerobic degradation but not anaerobic often ceases in the vicinity of the source zone because of oxygen depletion. The bacteria uses a carbon substrate as the electron donor and oxygen as the electron acceptor. Technical and Technology Support ServicesĪerobic: Direct aerobic metabolism involves microbial reactions that require oxygen to go forward.Measurement and Monitoring Technologies for the 21st Century (21M 2).