ANAEROBIC TREATMENT OF PCP IN FLUIDIZED-BED GAC BIOREACTORS

A fluidized-bed granular activated carbon (GAC) bioreactor was evaluat ed for anaerobically treating wastewater containing pentachlorophenol (PCP). PCP removal efficiencies of greater than 99.9% were achieved at PCP loadings as high as 4 g/kg of GAC per day and influent PCP concen trations as high as 1333 mg/litre. In addition to PCP, ethanol was Fed to the bioreactors as the primary substrate. The chemical oxygen dema nd (COD) loading to the reactor was increased several times as high as 63 g/kg of GAC per day using reactor empty bed contact rimes as low a s 9.3 h in order to exhaust the adsorptive capacity of the GAC for PCP , thus allowing for the development of a PCP-degrading biofilm on the carbon. A major proportion of the influent COD, ranging from 70 to 90% , was converted to methane, which constituted more than 85% of the pro duct eas stream. Due to incomplete mineralization, nearly all PCP was stoichiometrically converted to 3- and 4-chlorophenols. Low levels of 2,4,6- and 3.4,5-trichlorophenols, 2,4- and 3,4-dichlorophenols rind p henol were observed in the reactor. The primary biotransformation prod uct of PCP, 4-chlorophenol. inhibited the methanogenic culture at conc entrations as low as 116 mg/litre. Toxicity was minimized by controlli ng the influent PCP concentration, the primary source of the inhibitor y products. (C) 1997 Elsevier Science Ltd.