Reductive Dechlorination of Aroclor 1254 by Marine Sediment Cultures

Reductive dechlorination of polychlorinated biphenyls (PCBs) was studied by methanogenic and sulfate-amended laboratory cultures enriched from marine sediments (Puget Sound, WA) in sea-salts media. One sulfate-amended and one methanogenic culture were incubated at a hydraulic retention time of 50 days and fed chitin, sodium benzoate, sodium acetate, and a mixture of four PCB congeners (2,3,3′,5-tetrachlorobiphenyl, 2,2′,4,5,6′-pentachlorobiphenyl, 2,3′,4,5′,6-pentachlorobiphenyl, and 2,2′,4,4′,5,5′- hexachlorobiphenyl), slowly increasing the concentrations to 6-9 mg/L over 17 months. In these cultures, no dehalogenation of the four congeners was observed. Two other cultures were batch fed Aroclor 1254 at a concentration of 100 mg/L; chitin was used as the PCB carrier and the sole carbon and electron source. Chitin was readily mineralized both under methanogenic and sulfidogenic conditions. Aroclor 1254 was dechlorinated both in the presence and absence of sulfate. The dechlorinations started in both cultures after 4 months of incubation. Under both culturing conditions, 14-15 % meta and 9-10 % of para chlorines were removed over a period of 1 year with the accumulation of mainly tetrachlorobiphenyls; the extent of dechlorination was 7-8%.