REDUCTIVE DEHALOGENATION OF CHLORINATED ETHENES AND HALOGENATED ETHANES BY A HIGH-RATE ANAEROBIC ENRICHMENT CULTURE

An anaerobic enrichment culture, using CH3OH as an electron donor, dec hlorinated tetrachloroethene (PCE, 55 mumol added/100 mL of culture) n early stoichiometrically to vinyl chloride (VC) in 20 h with negligibl e buildup of other intermediates and at a maximum rate of 4.6 +/- 0.4 mumol of PCE transformed/mg of volatile suspended solids per day. Appr eciable conversion of VC to ETH occurred only after the PCE was nearly depleted, suggesting the inhibition of VC dechlorination by PCE. PCE, trichloroethene, cis-1,2-dichloroethene (DCE), and 1,1-DCE were all r apidly metabolized to VC with near zero-order kinetics and apparently inhibited subsequent VC dechlorination. trans-1,2-DCE was converted to VC with first-order kinetics and did not inhibit VC dechlorination. V C, when added alone, was dechlorinated to ETH with no lag and with fir st-order kinetics (half-life = 17.3 h). A computer simulation of the e xperimental data for PCE conversion to ETH was obtained using kinetic parameters estimated for the individual chlorinated ethenes and assumi ng competitive inhibition of VC dechlorination by the other chlorinate d ethenes. The rates of PCE dechlorination by this culture were signif icantly higher than those found for cometabolic PCE transformation by anaerobes, and the kinetics are considerably different from those obta ined for reductive dechlorination in vitro by transition metal cofacto rs. The culture rapidly dehalogenated 1,2-dichloroethane or 1,2-dibrom oethane to ETH, but did not use trichloroethanes, tetrachloromethane, trichloromethane, or dichloromethane.