FATE OF POLYNUCLEAR AROMATIC-HYDROCARBONS DURING ANAEROBIC-DIGESTION OF MUNICIPAL WASTE-WATER SLUDGES

The fate of six polynuclear aromatic hydrocarbons during anaerobic digestion of municipal sludges was investigated in a two-stage pilot-scale digester system. Primary digester removal efficiencies ranged from 23% for acenaphthene to 62% for acenaphthylene; secondary digester removal efficiencies ranged from 22% for acenaphthylene to 42% for phenanthrene. Most of the remaining mass of candidate compounds was present in the secondary digester waste sludge stream. Less than 2.5% of the candidate compounds entering the digestion system was present in the secondary digester supernatant. A dynamic model of the primary digester incorporating mixed first-order biodegradation kinetics was calibrated for each of the candidate compounds. The biodegradation rate coefficients that were estimated for the primary digester ranged from 0.004 L/g . d for acenaphthene to 0.16 L/g . d for acenaphthylene. The biodegradation rate coefficient for acenaphthene did not significantly differ from zero.