Effect of Ultrasonic Treatment on Characteristics of Waste Activated Sludge

Ultrasonic treatment has been adopted as a strategy to accelerate the hydrolysis step of waste activated sludge. The chemical characteristics of WAS under various sonication time and energy intensities during ultrasonic treatment were investigated in this study. Results showed that SCOD and ammonium nitrogen concentration and temperature of sludge increase as a function of both sonication time and energy intensity. COD solubilization was from 9.4% in the raw WAS to 56.3% when WAS was sonicated for 30 min with an energy intensity of 1.5W/ml. Compared with strong SCOD increment, a weak increment of ammonium nitrogen concentration around 5.1% ~ 35.6% was detected. A slight pH decrease was found in ultrasonic treated sludge along with sufficient alkalinity. During ultrasonic treatment, TS and VS concentrations of sludge were maintained almost constant averaging 20272 and 15816 mg/L, respectively. However, the SS and VSS concentrations gradually decreased with an increase in sonication time, suggesting that ultrasonic treatment greatly facilitated mass transfer from the solid phase into the aqueous phase.