Biol. activated sludge was disintegrated in ultrasound or/and microwave fields to study the sonolysis of microorganism cells by detn. of capillary suction time, sludge particle size and total solids. As a result of 3-step treatment, a decrease in disintegration time, increase in COD and a decrease in suction time were achieved. An advanced dewatering of the sludge was obsd.