Acclimation of anaerobic systems to biodegrade tetrachloroethene in the presence of carbon tetrachloride and chloroform

Two concerns in remediating tetrachloroethene (PCE)-contaminated sites are the stimulation of PCE degradation and the effect of other contaminants on PCE degradation. In ethanol-fed microcosms receiving 8.3 μM PCE, increasing the yeast extract concentration from 2 to 100 mg L−1 decreased the time required to produce cis-1,2-dichloroethene (DCE) from 36 to 9 days. The addition of 19 μM carbon tetrachloride to microcosms completely inhibited PCE degradation, as did 4 μM chloroform although 0.7 μM chloroform was not inhibitory. PCE-degrading capability had not developed in a column receiving carbon tetrachloride after 161 days although carbon tetrachloride was transformed to chloroform and dichloromethane. Once carbon tetrachloride was removed and the yeast extract concentration increased, PCE degradation to cis-1,2-DCE was observed within 45 days, although measurable degradation of cis-1,2-DCE to vinyl chloride and ethene required another 130 days. These results suggest that multiple-zone remediation strategies may be required for sites contaminated with mixtures of PCE, carbon tetrachloride and/or chloroform.