A STUDY OF THE BIODEGRADABLE FRACTION OF SLUDGES IN AEROBIC AND ANAEROBIC SYSTEMS

A combination of experimental testing and modeling was employed to assess the biodegradable fraction of primary and waste activated sludges generated by municipal wastewater treatment. Batch anaerobic digestion tests of primary sludge and waste activated sludge were conducted for a duration of 123 days to determine the ultimate degradability of the sludges under anaerobic conditions. The results indicate that for primary sludges the inert fraction of the particulate COD that was predicted by the wastewater models could be employed to predict their biodegradability under anaerobic conditions. The degradation of waste activated sludge was adequately characterized for the first 60 days of digestion using a model that assumed equivalent biodegradability of particulate COD components under aerobic and anaerobic conditions. However after 60 days of anaerobic digestion it appeared that decay of the endogenous products was occurring. This could be described mathematically using a first order decay function with a decay coefficient of 0.0075 d−1. The results suggest that the extent of digestibility can be improved by enhancing the degradability of endogenous decay products.