Abstract: The influences of ultrasonic time， ultrasonic frequency， ultrasonic power， ultrasonic pulse ratio， along with the interaction between ultrasonic time and frequency， time and power， power and frequency factors on the ultrasonic disintegration effect of excess sludge were studied by orthogonal test of mixedlevel interaction.The results show that the optimal combination parameters of the ultrasonic disintegration sludge list as the ultrasonic time of 7 minutes， the ultrasonic frequency of 20 kHz， the ultrasonic power of 600 W， the ultrasonic pulse ratio of 3∶1， and the interaction effects among the three factors of the four are not obvious. It is found that appropriately improving the sludge concentration would gain a better disintegration effect after studying the seven different solid concentration liquor suspended sludge disintegrated by ultrasonic. The time curves of ultrasonic disintegration sludge indicate that the disintegrating rate of each index increases slowly when the sludge is disintegrated after 40 minutes， and the highest energy utilization of ultrasonic disintegration sludge appears during 15 to 20 minutes.

Key words: excess sludge, sludge disintegration, ultrasonic, orthogonal experiment, mixed liquor suspended solids(MLSS)