High‐rate continuous biodegradation of concentrated chlorinated aliphatics by a durable enrichment of methanogenic origin under carrier‐dependent conditions

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Abstract
The simultaneous biodegradation of toxic compounds in mixtures is a major current concern. To bioremediate a toxic mixture, we designed a strategy combining an ad‐sorbent carrier with an ecological and nutritional system which allowed work close to heavily polluted conditions in nature. Starting from a methanogenic community, we developed a microbial consortium acclimated to a mixture of about 30 chlorinated aliphatics in a fixed‐film stationary‐bed bioreactor. Prior to the establishment of a durable period of dechlorination, an interval of progressive dechlorination of the toxic mixture was observed during which the excess of the toxic compounds was stored on the carrier. The latter, consisting of activated carbon in a polyurethane foam, allowed us to work at concentrations far above the solubility of the toxic compounds (apparent concentrations of about 10 g/L). The complete disappearance of hexachloroethane as well as its lower homologues, penta‐, tetra‐, and trichloroethane, present in the toxic mixture, was observed. Additionally, octachlorocyclopentene, carbon tetrachloride, trichloro‐ethylene, tetrachloroethylene, and hexachloro‐1,3‐butadiene also completely disappeared. For the four latter compounds, from mass balances in the bioreactor, degradation rates around 10 μmol/L per day were determined with total dechlorination. The enrichment culture thus developed exhibited high degradation performances similar to those reported in the literature for pure or enriched anaerobic microbial cultures in contact with a single toxic compound. The results demonstrate the possibility of concurrent high‐rate degradation of several highly chlorinated toxic compounds, under conditions approximating field situations.© 1995 John Wiley & Sons, Inc