The biodegradability of three of the most frequently halogenated aliphatics (trichloroethene, chloroform and 1.1.1.-trichloroethane) found in drinking water aquifers by a nitrifying enriched mixed biomass was investigated during batch tests. Within this mixed biomass, ammonia oxidisers were the effective degraders. The presence of ammonia stimulated chlorocarbon biodegradation, and the presence of chlorocarbon inhibited ammonia oxidation. This contrasted phenomenon was explained by a balance between electron supply from ammonia necessary to sustain the chlorocarbon oxidation and competitive inhibition for the ammonia monooxygenase active site between both substrates. About 0.03 to 0.2% of the electrons generated by ammonia oxidation were used for chlorocarbon degradation. Trichloroethene and chloroform oxidation induced a biomass inactivation (around 30 to 40 mg of proteins inactivated per μmol of chlorocarbn oxidised). Biomass re-activation due to exergonic ammonia catabolism was estimated to 24±6 mg of proteins reactivated per mmol of ammonia oxidised in both cases. No inactivation of re-activation was observed in the case of 1.1.1-trichloroethane.

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