In this paper the effect of ultrasonic energy density on sludge dewatering performance was investigated and the related mechanism was discussed.Experimental results showed that time of ultrasonic action had little influence on sludge dewatering performance at the lower energy density.Sludge dewatering performance was improved when energy density increased from 0.25 kW·L-1 to 0.5 kW·L-1.At the ultrasonic energy density of 0.5 kW·L-1

sludge dewatering performance reached the highest at the time of 10 s with mud cake water content 83.8%

specific resistance filtration (SRF) 0.8×109 s2·g-1

viscosity 16.8 mPa·s and capillary suction time (CST) 10.7 s.At the higher energy density

sludge floc was destroyed and dispersed which resulted in the increase of filtration resistance and the deterioration of sludge dewatering performance.At the energy density of 4 kW·L-1

and time of ultrasonic action 120 s

mud cake water content

SRF

viscosity and CST were up to 89.4%

3.1×109 s2·g-1

43.2 mPa·s and 56.2 s

respectively.