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Abstract.A stable methanogenic mixed culture was enriched from an industrial environment to utilize chloroacetate as sole carbon and energy source for growth. It immobilized spontaneously on activated charcoal and grew reproducibly on this carrier in a fluidized bed reactor when supplied with an anaerobic mineral salts medium. Substrate disappearance was complete. Methane, CO2 and chloride ions were conclusively identified as the metabolic products and quantified. The growth yield from chloroacetate was about I g of protein/mol of carbon. The calculated degradation rate in the fluidized bed reactor was 0.2 to 0.8 mmol/1-h. The first metabolic intermediate from [2-13C]monochloroacetat e in portions of biofilm-coated carrier was shown by 13C_NM R to be glycolate, from which 13C02 and 13CH4 were formed. Glycolate was formed in an oxygen-insensitive hydrolysis, but its conversion to C02 and CH4 was strictly anaerobic and sensitive to inhibition by bromoethanesulfonate. Degradation of [1-14C]-and [2-14C]_chloroacetat e each yielded the same amount of [14C]-methane. We thus presume glycolate to be cleaved to CO2 and Ha, which were the substrates for methanogenesis. Dehalogenation was limited to chloro-, bromo-, iodo-and dichloroacetate. These four compounds and glycolate were utilized as the sole carbon and energy sources by the methanogenic mixed culture.

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The removal of 5 mg l-1 1,2-dichloroethane [(CH2Cl)2] was studied in two granular activated carbon (GAC) reactors run with hydraulic retention times of below 1 h. One reactor was operated abiotically. The other one was inoculated with microorganisms able to degrade (CH2Cl)2. While the (CH2Cl)2-adsorption capacity of the non-inoculated GAC reactor was exhausted after 20 days, it apparently did not exhaust for at least 170 experimental days in the biologically activated system because (CH2Cl)2 was removed to over 95% as a result of the microbial degradation. The biodegradation was quantified: during the passage through the biologically activated GAC reactor, (CH2Cl)2 (5 +/- 1 mg l-1) disappeared, chloride ions (3.3 +/- 0.2 mg l-1) were produced, and oxygen (4 to 6 mg l-1) was consumed. Removal of 30% of GAC at the entrance of the reactor, which visibly carried most of the biomass, and its replacement by virgin GAC at the end of the column did not change the apparent (CH2Cl)2 removal capacity of the GAC column, indicating that still enough biomass was available to degrade most of the chemical fed. After the addition of the virgin carbon, the effluent concentration fell for a short period of time from about 200 micrograms l-1 to below 100 micrograms l-1, indicating partial adsorption of the non-degraded (CH2Cl)2 at the end of the reactor by the virgin carbon. Thus, the modification of the adsorption process by inoculation and maintenance of bacteria with special degradation capabilities resulted in a lower consumption of GAC and thus led to an extended service life of the GAC columns.