Dichloromethane utilized by an anaerobic mixed culture: acetogenesis and methanogenesis

Key words: anaerobic dehalogenation f dichloromethane; dichloromethane, anaerobic degradation; anaerobic fixed-bed reactor, dichloromethane; C-1 metabolism Dichloromethane (8.9 mg/1) was eliminated from industrially polluted, anaerobic groundwater in a fixed-bed reactor (43 m 3) which was packed with activated charcoal and operated continuously for over three years. The elimination f dichloromethane over this period was some ten-fold in excess of the sorptive capacity of the charcoal, and the elimination (3.7 mg/h. [kg of charcoal]: residence time, 49 h) was tentatively attributed to deha]ogenative microorganisms immobilized on the charcoal. Anaerobic enrichment cultures, with dichloromethane as the sole added source of carbon and energy, were inoculated with material from the reactor. Reproducibly complete substrate disappearance in subcultures was observed when traces of ground-water (1%) or yeast extract (0.01%) were supplied. Fed-batch experiments under an atmosphere of CO2 plus N2 led to the conversion i 11 days of 11 mM dichloromethane to 3 mM acetate and 2 mM methane, with a growth yield of 0.4 g of protein/mol f dichloromethane; insignificant amounts (< 1/zM) of chloromethane accumulated. Methanogenesis could be inhibited by 50 mM 2-bromoethane sulfonate without any effect on the dehalogenation rate. The maximum dehalogenation rate was 0.13 mmol dichloromethane/h-1 (2.6 mkat/ kg of protein). Abbreviation: DCM- dichloromethan