Long-term tetrachlorethene degradation sustained by endogenous cell decay

The role of endogenous decay in the reductive dechlorination of tetrachlorethene (PCE) was studied in a sand column containing an anaerobic microbial consortium that included Dehalococcoides ethenogenes. The column consortium had continuously transformed PCE to vinyl chloride (<5%) and ethene (>95%) with the addition of ethanol and yeast extract for a 3 year period. The column was operated for a further period of 1 year with the addition of 60 µM PCE only. In the absence of external electron donors, PCE dechlorination in the column initially slowed but continued at a relatively constant rate for 1 year. The conversion to vinyl chloride (VC) and ethene (ETH) was significantly reduced with cis-dichloroethylene (cis-DCE) becoming the major (90%) end product of dechlorination. Microcosm studies, with no external electron donor added, indicated that reductive dechlorination was sustained by reducing equivalents derived from endogenous decay products. Measures of cellular adenosine triphosphate (ATP) along the length of the column indicated that even after 1 year of only PCE addition, an active biological community was sustained. Key words: tetrachloroethene (PCE), ethanol, anaerobic biodegradation, endogenous decay, column study.