Ozonation of sewage sludge prior to anaerobic digestion

Anaerobic digestion has traditionally been employed to reduce the mass and volume of waste sludge and to enhance the sludge dewaterability. In practice, anaerobic digestion of biosolids has a number of shortcomings, i.e. the low biodegradability of the microbial cells and the high retention times due to the rate limiting hydrolysis step. An oxidative sludge pre-treatment with ozone was therefore used to solubilize the organic compounds and increase their biodegradability. It is shown that the pre-treatment could significantly enhance anaerobic sludge digestion. Moreover, a novel approach in which the sludge was separated in a thickened sediment fraction and a supernatant was investigated. The sediment was digested anaerobically and the supernatant was treated aerobically. The overall COD-removal efficiency of the biosolids was 72%.