Toxicity and fate of pentachlorophenol in anaerobic acidogenic systems

Toxic effects of organic pollutants and their fate in anaerobic acidogenic systems have not been studied extensively despite the potential of acidogenic treatment to be an efficient and economical pretreatment process. The objective of this paper was to study the toxicity and fate of pentachlorophenol (PCP) in an acidogenic, glucose-degrading anaerobic enrichment system. Chemostat cultures (1.5-day SRT) were acclimated to 21–59 μM (6–17 mg/l) PCP for 159–261 days. Up to 121 μM (35 mg/l) PCP allowed greater than 99.5% influent glucose removal in chemostats, but serum bottle experiments showed that these PCP concentrations partially inhibited glucose degradation. In contrast to the control, the test chemostats with PCP showed formation of lactate and ethanol with lower acetate concentrations. Hydrogen-utilizing methanogens were inhibited by 21–121 μM (6–35 mg/l) PCP. No biodegradation of PCP was observed even in acclimated cultures. Even with significant removal of PCP in both and serum bottles, chlorophenol intermediates were not found, and batch experiments showed that such chlorophenol intermediates, if formed, would have undergone little degradation. Extraction of PCP in serum bottles showed sorption to biomass was the dominant mechanism for PCP removal in acidogenic cultures. Hence, contrary to expectations, the usefulness of anaerobic acidogenic cultures for degradation of PCP could not be substantiated. Further research on factors stimulating PCP degradation by nonmethanogenic anaerobes is necessary.