Enhancement of site specific anaerobic reductive dechlorination of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are widespread, priority pollutants which persist in the environment and tend to bioaccumulate. Toxicological data has shown that PCBs elicit a spectrum of toxic responses in both humans and laboratory animals. These characteristics have implicated PCBs in the decline of fish eating birds and mammals. Although they are considered recalcitrant microorganisms can degrade PCBs. The bioremediation of PCBs has been conceptualized as a sequential process involving the anaerobic reductive dechlorination of PCBs followed by aerobic mineralization. This has not been realized because the full potential of anaerobic reductive dechlorination of PCBs is rarely achieved. This dissertation describes investigations designed to identify and overcome site specific limitations to the maximum extent of anaerobic PCB dechlorination.; Because PCBs are of industrial origin they are usually associated with related environmental pollutants. Residual petroleum hydrocarbons and other non-polar contaminants were found to reduce both the rate and extent of PCB dechlorination. This response was identical to that which would be predicted based solely on the reduction of PCB solution concentrations due to an innocuous sorptive phase. This suggests that petroleum hydrocarbons reduce the bioavailability of PCBs to dechlorinating microorganisms.; Heavy metals are the most commonly observed co-contaminant associated with PCBs. Anaerobic reductive dechlorination of PCBs in laboratory assays were adversely affected by zinc solution concentrations less than or equal to those found at many PCB contaminated sites. We therefore tested two means of alleviating metal toxicity: precipitation (adding FeSO{dollar}sb4{dollar}) and chelation (adding citrate or EDTA). Metal toxicity was reversed by additions of EDTA or citrate; however, in slurries amended with FeSO{dollar}sb4{dollar} dechlorination was enhanced. Subsequent experiments designed to elucidate the mechanism of enhancement suggest that sulfate stimulates the growth of sulfate reducing organisms responsible for PCB dechlorination, while Fe{dollar}sp{lcub}2+{rcub}{dollar} reduces sulfide bioavailability and hence toxicity. Ferrous sulfate is an inexpensive, innocuous compound which could be utilized to overcome factors limiting both the extent of in-situ dechlorination in metal and non-metal contaminated sediments as well as the implementation of sequential anaerobic/aerobic biotreatment systems.