Mixed, acetate-fed methanogenic cultures were used to assess the effect of increasing tetrachloroethylene (PCE), trichloroethylene (TCE) and cis-1,2-dichloroethylene (cDCE) concentrations on the reductive dechlorination and primary metabolism (methane production) processes. In addition, the effect of TCE on the rate and extent of the reductive dechlorination of PCE was investigated. All cultures were developed in serum bottles and incubation was carried out at 35°C in the dark. Soil samples from two sites contaminated with chlorinated solvents served as the inoculum for this study. All chlorinated alkenes used were supplied as saturated solutions in the culture media. The rate of PCE dechlorination increased with increasing PCE concentrations. Both TCE and cDCE showed an increase in the dechlorination rate up to a solvent threshold concentration followed by a decrease. In all cases, the methane production rate decreased as the chlorinated alkene concentrations increased. However, the effect of chlorinated alkenes was more pronounced on methane production rather than on the extent of dechlorination. The relative toxicity of the chlorinated alkenes tested in this study formed the following ascending series: PCE < TCE < < cDCE.

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