The ability of a high-rate, tetrachloroethene (PCE)-dechlorinating culture with apparent dehalorespiring activity to function in the presence of fortuitously transformed cocontaminants carbon tetrachloride (CT) and 1,1,1trichloroethane (1,1,1-TCA) was examined. A PCE-acclimated, lactate-enrichment culture that demonstrated the ability to rapidly transform PCE to ethene in conjunction with methanogenesis was able to degrade both CT and 1,1,1TCA despite no previous exposure to these compounds. While the presence of <20 μM of 1,1,1-TCA had little effect on PCE removal, the addition of 10-15 μM of CT negatively impacted both the PCE and vinyl chloride (VC) transformation steps. CT and 1,1,1-TCA primarily inhibited methanogenesis before each compound was completely biotransformed. They served to further inhibit methanogenesis as well as utilization of acetate and propionate in PCE-containing treatments via increased persistence of metabolites such as VC. The inclusion of CT with PCE increased peak hydrogen concentrations from 2 to 20 μM, suggesting that CT disrupted the ability of dechlorinating and other hydrogenotrophic organisms to maintain low hydrogen thresholds. Despite the negative impacts on multiple populations as a result of the addition of CT and 1,1,1-TCA, transformation proceeded in treatments containing all three target compounds. This indicates that the specific dechlorinating organisms within the culture were capable of either transforming these cocontaminants or remaining functional, while nonspecific organisms mediated their removal.
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