The production of excess sludge is one of the most serious challenges in biological wastewater treatment. In the present work, disintegration is added as a new additional unit operation in a wastewater treatment plant, and the main objective is to reduce the amount of excess sludge. The use of high power ultrasound can effectively disintegrate the bacterial cells, and thereby, enhance the subsequent biodegradation during digestion. In the study, attempts are made to determine the disintegration capacity of waste activated sludge that has different total solids (TS) concentrations with low ultrasound frequency (20 kHz) and a fixed amplitude value (50%). The results show that in terms of soluble chemical oxygen demand (SCOD) release, sludge disintegration was primarily governed by ultrasonic density (W mL(-1)), whereas specific energy input appears to be more critical for protein release. A SCOD release of about 329 mg SCOD gTS(-1) was obtained at a TS content of 2% and specific energy input of 5 kWs gTS(-1). The SCOD release decreased to 248.5 and 124.2 mgSCOD gTS(-1) at TS contents of 4 and 6%, respectively. The highest protein release of 80.7 mg gTS(-1) was obtained at a TS content of 2% and a specific energy input of 10 kWs g(-1). The sludge disintegration efficiency declined significantly at higher TS content.