The present study deals with disintegration of biological sludge by ozone oxidation and ultrasonic treatment. The effects of ozone and ultrasonic treatment were investigated on aerobic sludge bio-processing as comparatively. 9690 kJ/kg TS of specific energy and 0.1 g O(3)/kg TS were applied to sludge samples preceding aerobic sludge digestion. In terms of sludge stabilization, the highest volatile solids reduction and protein degradation were obtained with ultrasonic treatment. Moreover, digesters fed with disintegrated sludge had higher bacterial activities in terms of oxygen uptake rate (OUR) and volatile suspended solids (VSS)/ suspended solids (SS) ratio than control one during the operation period. In terms of dewatering characteristics of digested sludge, ultrasonic treatment led to increase the sludge's resistance to dewatering. This negative effect was not observed in ozone oxidation. In addition, disintegration processes used in this study did not contribute to an improvement in cake solids on a crown press application. (c) 2010 Elsevier Ltd. All rights reserved.