Degradability of chlorinated aliphatic compounds in methanogenic leachates sampled at eight landfills

The degradability of chlorinated aliphatic compounds (tetrachloromethane (TeCM); 1,1,1-trichloroethane (1,1,1-TCA); 1,1,2-trichloroethane (1,1,2-TCA); tetrachloroethene/perchloroethylene (PCE); and trichloroethene/trichloroethylene (TCE)) was studied under methanogenic conditions in batch reactors with leachate from eight landfills in Denmark. All landfill leachates showed fast abiotic degradation of TeCM and 1,1,1-TCA, while 1,1,2-TCA seemed unaffected during the methanogenic incubation. PCE and TCE were degraded biologically by reductive dehalogenation, but only in three of the eight leachates. The conversion rates of the chlorinated ethenes (PCE, TCE, dichloroethene (DCE)) and monochloroethene/vinyl chloride (VC) varied significantly between the three landfill leachates transforming chlorinated ethenes. In one leachate, complete conversion of all ethenes, including conversion of VC, was observed within 40 days, while another leachate during the same period showed only about 50% conversion of PCE. This indicates that transformation of these common solvents in the landfill environment may vary substantially between landfills.