Anaerobic biodegradation of chlorophenols in fresh and acclimated sludge

Abstract

We investigated the anaerobic biodegradation of mono- and dichloroophenol isomers by fresh (unacclimated) sludge and by sludge acclimated to either 2-chlorophenol, 3-chlorophenol, or 4-chlorophenol. Biodegradation was evaluated by monitoring substrate disappearance and, in selected cases, production of 14CH4 from labeled substrates. In unacclimated sludge, each of the monochlorphenol isomers was degraded. The relative rates of disappearance were in this order: ortho > para. For the dichlorophenols in unacclimated sludge, reductive dechlorination of the C1 group ortho to phenolic OH was observed, and the monochlorphenol compounds released were subsequently degraded. 3,4-Dichlorophenol and 3,5-dichlorophenol were persistent. Sludge acclimated to 3-chlorophenol cross-acclimated to 4-chlorophenol but did not utilize 2-chlorophenol. This sludge also degraded 2,4-dichlorophenol. Sludge acclimated to 3-chlorophenol cross-acclimated to 4-chlorophenol but not to 2-chlorophenol. This sludge degraded 3,4- and 3,5-dichlorophenol but not to 2,3- or 2,5-dichlorophenol. The specific cross-acclimation patterns observed for monochlorophenol degradation demonstrated the existence of two unique microbial activities that were in turn different from fresh sludge. The sludge acclimated to 4-chlorophenol could degrade all three monochorophenol isomers and 2,4- and 3,4-dichlorophenol. The active microbial population in this sludge appeared to be a mixture of populations present in the 2-chlorophenol- and 3-chlorophenol-acclimated sludges, both of which could utilize 4-chlorophenol. Experiments with 14C-radiolabeled p-chlorophenol, o-chlorophenol, and 2,4-dichlorophenol demonstrated that these compounds were converted to 14CH4 and 14CO2.