Complete biological reductive transformation of tetrachloroethene to ethane

Abstract

Reductive dechlorination of tetrachloroethene (perchloroethylene; PCE) was observed at 20°C in a fixed-bed column, filled with a mixture (3:1) of anaerobic sediment from the Rhine river and anaerobic granular sludge. In the presence of lactate (1 mM) as an electron donor, 9 υM PCE was dechlorinated to ethene. Ethene was further reduced to ethane. Mass balances demonstrated an almost complete conversion (95 to 98%), with no chlorinated compounds remaining (<0.5 μg/liter). When the temperature was lowered to 10°C, an adaptation of 2 weeks was necessary to obtain the same performance as at 20°C. Dechlorination by column material to ethene, followed by a slow ethane production, could also be achieved in batch cultures. Ethane was not formed in the presence of bromoethanesulfonic acid, an inhibitor of methanogenesis. The high dechlorination rate (3.7 μmol · l-1 · h-1), even at low temperatures and considerable PCE concentrations, together with the absence of chlorinated end products, makes reductive dechlorination an attractive method for removal of PCE in bioremediation processes.