Lorah, MM; Majcher, E; Jones, E; Voytek, M; Dworatzek, S; Graves, D
A wetland sediment-derived microbial consortium, WBC-2, developed to anaerobically dechlorinate a suite of chlorinated alkanes and alkenes, including 1,1,2,2- tetrachloroethene, trichloroethene, 1,1,2-trichloroethane, 1,2-dichoroethene, 1,2- dichloroethane, and vinyl chloride, also has the capacity to completely degrade the chlorinated methanes carbon tetrachloride and chloroform. Chlorinated methanes tend to inhibit activity of a wide range of microorganisms, including the Dehalococcoides species known to degrade chlorinated alkenes. Dehalococcoides, however, is not dominant in WBC-2, comprising only about 1 percent of the microbial population. The broad substrate range of WBC-2 increases the potential for bioremediation of sites contaminated with chlorinated methanes and with mixtures of chlorinated solvents. To test the capacity of WBC-2 to degrade chlorinated methanes, a series of batch experiments in medium and in bioaugmented wetland sediment and composts were conducted, followed by flow-through column experiments where concentrations could be increased and contaminant mixtures could be evaluated. Although toxicity effects from carbon tetrachloride addition were observed with WBC-2 in initial tests with the culture in media alone (without sediment), WBC-2 in the bioaugmented batch and column experiments degraded carbon tetrachioride and chloroform simultaneously with complete degradation of the chlorinated ethanes and ethenes. Carbon tetrachloride and chloroform were degraded rapidly in all bioaugmented treatments to non-chlorinated end-products and with little transient accumulation of dichioromethane. In the bioaugmented columns, average half-lives of 0.25 and 0.30 days, respectively, were determined for carbon tetrachloride and chloroform (initial concentrations of 15 mg/L for each). Degradation half- life for 1,1,2,2-tetrachloroethane remained about 0.30 days with or without addition of carbon tetrachloride and chloroform. Although tetrachloroethene and trichloroethene degradation rates decreased in the bioaugmented columns after addition of the chlorinated methanes, degradation rates were still rapid (half-lives of about 0.90 days) and allowed complete degradation of all parent and daughter products over the length of the column. In a field pilot test, a flow-through barrier composed of a peat-compost mixture and bioaugmented with WBC-2 consistently removed greater than 95 percent of the mass of mixed chlorinated methanes, ethanes, ethenes from the groundwater. Additional tests are being conducted to re-evaluate the ability of WBC-2 to degrade chioromethanes in sediment-free culture medium.