Two-Step Bioremediation of PCBs in Soils

Complex mixtures of polychlorinatedbiphenyls (PCBs) are common soil contaminants. Several hundred congeners, together with physical weathering and microbial dechlorination and oxication, add to the complexity of PCB mixtures found inthe environment. PCBs are hydrophobic and associate with soil, whether wet or dry. Excavation is disruptive and often leads to dispersion of fine particles carrying contaminants. Physical separation can concentrate but not destroy PCBs; further, separation is not a viable in-situ process. Purely anaerobic biodegradation is improbable; aerobic dechlorination, followed by mineralization, is possible but undemontrated. Destruction via fungal metabolism has been proposed but has not been demonstrated at full -scale.TWO-STEP MICROBIAL DEGRADATION, ANAEROBIC DECHLORINATION FOLLOWED BY OXIDATION, IS PROPOSED FOR IN-SITU REMEDIATION. Highly chlorinated congeners, i.e., three or more chlorine atoms on Biphenyl, are dechlorinated in place under anaerobic conditions. This process is site specific and requires injection of deaerated water amended with electron acceptor (nitrate), nutrients (if not present in adequate concentration) and a supplementary carbon source. Biodegradation is based on microbial communities present at the site. Dichlor-, monochlor- and base Biphenyl are mineralized microbially via oxidation in a subsequent aerobic process. Humidified air is injected into the soil system that has had anaerobic pretreatment.