EFFECTS OF ELECTRON-DONORS AND INHIBITORS ON REDUCTIVE DECHLORINATIONOF 2,4,6-TRICHLOROPHENOL

Reductive dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) to 2,4-d ichlorophenol and to 4-chlorophenol is found in mixed methanogenic cul tures enriched from municipal sludge digesters. In this study, electro n donors, including hydrogen, acetate and fructose, were effectively c onverted to methane and supported this dehalogenation in periods of 2 to 4 weeks. When bromoethanesulfonic acid (BESA) and vancomycin were u sed, dechlorination and methanogenesis were strongly affected. With hy drogen, BESA nearly completely inhibited lithotrophic methanogenesis; acetate accumulated from lithotrophic acetogenesis and dehalogenation proceeded. Vancomycin, however, inhibited dehalogenation while methano genesis was not affected. With acetate, BESA completely inhibited meth anogenesis and substantially slowed dehalogenation; the acetate was no t used. Vancomycin, on the other hand, stopped dehalogenation, while m ethanogenesis proceeded. With fructose plus titanium citrate, BESA inh ibited methanogenesis; acetate and propionate accumulated, and dehalog enation proceeded; vancomycin inhibited dehalogenation. Autoclaved con trols had neither dehalogenation nor methanogenesis. These results poi nt to biological dehalogenation by eubacteria, rather than methanogens . In the case of acetate, where both inhibitors effectively stopped de halogenation, they also indicate a syntrophic relation between acetocl astic methanogens and the dehalogenating bacteria. In further studies with 2,4,6-TCP concentrations ranging up to 160 mg/l there was increas ing toxicity to methanogens and changes in accumulation of fatty acids , but dehalogenation persisted at the highest concentrations.