ESTIMATION OF ANAEROBIC BIODEGRADATION RATES FOR TOXIC ORGANIC-COMPOUNDS IN MUNICIPAL SLUDGE-DIGESTION

The removal of selected toxic compounds during anaerobic digestion of municipal sludge was investigated at pilot scale. In primary digestion, isoquinoline, p-cresol, 4-chlorophenol, 2,4,5-chlorophe nol, diethyl phthalate, di-n-butyl phthalate and butylbenzyl phthalate were removed at efficiencies greater than 90%. Bis-2-ethylhexyl phthalate, o-cresol and 2,5-dichlorophenol were removed at efficiencies of between 55 and 65%. Greater than 60% of the toxic compounds entering secondary digestion were degraded. The anaerobic biomass appeared to acclimate to biodegrade the chlorophenolic compounds during the experimental period. A dynamic model, developed to predict the fate of toxics during primary sludge digestion, was calibrated with data from the experiment. Biodegradation rate coefficients only could be estimated due to statistical redundancy of the sorption partitioning parameter during the non-linear regression. The sorption partition coefficients were estimated from literature octanol-water partitioning coefficients.