Disintegration of biological sludge. A comparison between ozone oxidation and ultrasonic pretreatment

The effects of ozone oxidation and ultrasonic pretreatment on anaerobic sludge bio-processing have been studied. Ultrasound (9690 kJ/kg total solids (TS) of specific energy) and ozone (0.1 g O₃/kg TS) were applied to sludge samples preceding anaerobic sludge digestion for disintegration purpose. Organic matter reduction and methane production were measured, as well as physicochemical characteristics (pH, alkalinity, and particles size) and dewatering characteristics of sludge during semi-batch anaerobic digestion. For each treatment, 5 days of sludge retention time were applied on mesophilic conditions for 30 days operation period. The highest volatile solids reduction was obtained with ozone oxidation. Moreover, disintegrated sludge with ozone oxidation and ultrasonic pretreatment provided 55% and 49% higher methane production comparing to the raw sludge, respectively. In terms of dewatering characteristics of digested sludge, ultrasonic treatment led to an increase in the sludge’s resistance to dewatering. This negative effect was not observed in ozone oxidation.