In this study, chlorine dioxide (ClO(2)) instead of chlorine (Cl(2)) was proposed to minimize the formation of chlorine-based by-products and was incorporated into a sequencing batch reactor (SBR) for excess sludge reduction. The results showed that the sludge disintegrability of ClO(2) was excellent. The waste activated sludge at an initial concentration of 15 g MLSS/L was rapidly reduced by 36% using ClO(2) doses of 10 mg ClO(2)/g dry sludge which was much lower than that obtained using Cl(2) based on similar sludge reduction efficiency. Maximum sludge disintegration was achieved at 10 mg ClO(2)/g dry sludge for 40 min. ClO(2) oxidation can be successfully incorporated into a SBR for excess sludge reduction without significantly harming the bioreactor performance. The incorporation of ClO(2) oxidation resulted in a 58% reduction in excess sludge production, and the quality of the effluent was not significantly affected. (C) 2011 Elsevier B.V. All rights reserved.