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Sequential anaerobic reductive dechlorination of polychlorinated biphenyl (PCB) 2,2′,3,4,4′,5′ chlorobiphenyl (138-CB) was studied in landfill leachate from a Subtitle D designed landfill for type II, or municipal, wastes. The effect of biosurfactant on congener product profiles and rates was also examined. Rhamnolipid biosurfactant amendment had little effect, perhaps due to a lack of weathering of the spiked PCBs, or due to the presence of endogenous chemical surfactants in the leachate. The redox of the leachate averaged −405±19.6 mV with a pH of 7.8±0.07. The biologically active landfill samples averaged 68.6% degradation of 2,2′,3,4,4′,5′ chlorobiphenyl (138-CB) over the first 7 days. The majority of this was accounted for in the observed reductive dechlorination products; 2,2′,4′,5 tetrachlorobiphenyl (48-CB), 2,2′,3,5′ tetrachlorobiphenyl (44-C), and 2,2′,3,4 tetrachlorobiphenyl (42-CB). 2,2′,3,5′ tetrachlorobiphenyl (44-CB) was the major product accounting for 36.4% of the observed breakdown products with biosurfactant amended leachate, 66.1% of those observed in unamended leachate, and 65.2% of the breakdown products observed in the negative control. All observed breakdown products contain four chlorines and represent the terminal PCB congeners observed in these anaerobic studies. These results indicate that initial reductive dechlorination rates for highly chlorinated PCBs may be rapid in landfill environments, however, certain congener dechlorination products, such as those observed here, are expected to exhibit greater longevity in landfills. |
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