Microbial dechlorination of polychlorinated biphenyls in anaerobic sewage sludge

The potential of a chlorophenol (CP)-adapted consortium to dechlorinate pol ychlorinated biphenyls (PCBs) in sewage sludge was investigated. Results sh ow that dechlorination rates differed significantly depending on sludge sou rce and PCB congener. Higher total solid concentrations in sewage sludge an d higher concentrations of chlorine in PCB resulted in slower dechlorinatio n rates. No significant difference was found for 2,3,4,5-CB dechlorination from pH 6.0 to pH 8.0; however, dechlorination did not occur at pH 9.0 duri ng a 41-day incubation period. Results show that at concentrations of 1 to 10 mg/L, the higher the PCB concentration, the faster the dechlorination ra te. In addition, dechlorination rates were in the following order: methanog enic conditions > sulfate-reducing conditions > denitrifying conditions. Th e addition of acetate, lactate, pyruvate, and ferric chloride decreased lag times and enhanced dechlorination; however, the addition of manganese diox ide had an inhibitory effect. Dechlorination rates were also enhanced by th e addition of PCB congeners, including 2,3,4-CB, 2,3,4.5-CB and 2,3,4,5,6-C B in mixture. Overall results show that the CP-adapted consortium has the p otential to enhance PCB dechlorination. The optimal dechlorination conditio ns presented in this paper may be used as a reference for feasibility studi es of PCB removal from sludge. (C) 1999 Elsevier Science Ltd. All rights re served.