ANAEROBIC DECHLORINATION OF TRICHLOROETHENE, TETRACHLOROETHENE AND 1,2-DICHLOROETHANE BY AN ACETOGENIC MIXED CULTURE IN A FIXED-BED REACTOR

An anaerobic enrichment culture with glucose as the sole source of carbon and energy plus trichloroethene (TCE) as a potential electron acceptor was inoculated with material from a full size anaerobic charcoal reactor that biologically eliminated dichloromethane from contaminated groundwater (Stromeyer et al. 1991). In subcultures of this enrichment complete sequential transformation of 10 mu M TCE via cis-dichloroethene and chloroethene to ethene was reproducibly observed. Maintenance of this activity on subcultivation required the presence of TCE in the medium. The enrichment culture was used to inoculate an anaerobic fixed-bed reactor containing sintered glass Raschig elements as support material. The reactor had a total volume of 1780 mi and was operated at 20 degrees C in an up-flow mode with a flow rate of 50 ml/h. It was fed continuously with 2 mM glucose and 55 mu M TCE. Glucose was converted to acetate as the major product and to a minor amount of methane; TCE was quantitatively dehalogenated to ethene. When, in addition to TCE, tetrachloroethene or 1,2-dichloroethane were added to the system, these compounds were also dehalogenated to ethene. In contrast, 1,1,1-trichloroethane was not dehalogenated, but at 40 mu M severely inhibited acetogenesis and methanogenesis. When the concentration of TCE in the feed was raised to 220 mu M, chloroethene transiently accumulated, but after an adaptation period ethene was again the only volatile product detected in the effluent. The volumetric degradation rate at this stage amounted to 6.2 mu mol/l/h. Since complete transformation of TCE occurred in the first sixth of the reactor volume, the degradation capacity of the system is estimated to exceed this value by factor of about ten.