Metabolism and kinetics of pentachlorophenol transformation in anaerobic granular sludge

Dechlorination of pentachlorophenol (PCP) was investigated in experiments using a granular sludge obtained from an upflow anaerobic sludge blanket reactor that was operated with a mineral medium containing PCP, phenol and glucose for 18 months. Amendment of sludge with hydrogen, formate, butyrate, ethanol and acetone before incubation did not stimulate dechlorination but addition of glucose increased the dechlorination rate by 150-200 per cent. Addition of sulphate had little effect on PCP transformation in the absence of glucose and was slightly inhibitory in glucose-amended sludge, while nitrate was strongly inhibitory. Kinetics experiments indicated that the initial dechlorination of PCP and removal of the intermediate 3,5-dichlorophenol were rate-limiting, and the dechlorinating consortium showed a high affinity for PCP, with an apparent half-saturation constant value of 580 ug PCP per litre. Dechlorination rates generally were reduced by various specific inhibitors indicating that dechlorination was a biological process. A most probable number technique enumerated only 10-100 dechlorinating organisms per ml in a sample of disintegrated granular sludge, compared to 100,000-1,000,000 glucose degraders and 1000-100,000 methanogens; no activity was observed in a sample of boiled sludge tested for spore formers.