As one of the new techniques in the field of sludge treatment, ultrasonic wave irradiation could be employed to release nutrients from the solids to the soluble phase, which can subsequently be degraded by microorganisms in biological treatment. In this paper the Tehran Pegah Dairy Complex was selected to evaluate the effect of ultrasonic wave irradiation on soluble chemical oxygen demand (SCOD), nitrogen content, phosphors content, and also the causes of rising temperature of waste-activated sludge. Experimental investigation was carried out at 60, 120, 240, and 480 s contact times, and at output powers of 100, 300, and 500 W with 20 kHz operational frequency. Results revealed that the highest temperature was found around 12ºC at 500W output power and 480s contact time. Hydrolysis of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) also showed increasing trends at all different contact times. At 480 s contact time, the maximum of TP and TKN release was about 116% and 170%, which was observed at 500W and 100W. The maximum release of COD was found around 640%, which was observed at 300W output power.