Fate of pentachlorophenol (PCP) in an anaerobic digester.

To investigate the potential use of an anaerobic digester for treating pentachlorophenol (PCP) wastes in wastewater treatment plants (WWTPs), the fate of PCP in a digester was examined. In this study, two laboratory-scale anaerobic digesters were operated in parallel. One was dosed with PCP; the other was not and served as a control. Before any PCP addition, the digesters were seeded and fed with digested and raw sludges, respectively, from a local WWTP, then went through a lengthy startup period. When the digesters became stable, their overall performances were similar to the full-scale digesters located at the WWTP. The fate study of PCP was conducted under steady-state conditions using two methods: (a) using radioactively labeled 14 C PCP and (b) studying mass conservation of added PCP. Steady state was assumed as the similarity of pH, daily digester gas production, and solids data between the PCP-acclimated and control digesters. The 14 C radioactivity, PCP, and chlorophenols were measured in the aqueous, solid, and gaseous phases. From the radioactively labeled PCP study, results showed that approximately 19.5% of 14 C PCP was recovered from the aqueous phase, 78% from the solid phase, and 2.5% from gaseous phase. From the mass-balance study, results indicated that chlorophenols present in the digester effluent contained 95% (molar basis) of 3-monochlorophenol (16.8% in the aqueous phase), 4.5% of 3,4-dichlorophenol (0.3%), and 0.5% of 3,5-dichlorophenol (0.1%). No chlorophenols were detected in the gaseous phase.