Combined (alkaline + ultrasonic) technology could be applied as pretreatment to disintegrate sludge flocs and disrupt bacterial cells' walls. Influence factors were investigated, including ultrasonic density, ultrasonic intensity, sludge pH and sludge concentration. Based on the test data, kinetics model for sludge disintegration was established by applying multivariable linear regression method. It could be inferred from the kinetics model that sludge pH had the most significant effect on the sludge disintegration. (C) 2010 Elsevier Ltd. All rights reserved.