PILOT AND MODEL STUDIES OF TOXIC ORGANIC-COMPOUNDS IN MUNICIPAL SLUDGE-DIGESTION

The removal of selected toxic compounds during anaerobic and aerobic d igestion of municipal sludge was investigated at pilot scale. The cand idate compounds included a mixture of cresols, chlorophenols, heterocy clic nitrogenous compounds, phthalates, and polyaromatic hydrocarbons. A wide range of responses of the candidate compounds was observed in anaerobic digestion with seven compounds removed at efficiencies great er than 90% in primary digestion, four compounds demonstrating removal s of greater than 80% after secondary digestion, and five compounds de monstrating overall removals of less than 70%. The secondary digester demonstrated a substantial capacity to attenuate toxics. In aerobic di gestion, all of the compounds except the cresols, 2,4,5-trichloropheno l, and bis-2-ethylhexylphthalate were essentially eliminated. A dynami c model, developed to predict the fate of toxics during primary sludge digestion, was calibrated with data from the experiments. Biodegradat ion rate coefficients only could be estimated because of statistical r edundancy of the sorption partitioning parameter during the nonlinear regression. The sorption partition coefficients were estimated using o ctanol-water partitioning coefficients from literature.