Disintegration of sewage sludge with bifrequency ultrasonic treatment.

A bifrequency ultrasonic generating trough was used to improve disintegration of sewage sludge from thickener tanks. Ultrasonic operating parameters such as frequency, power, and time were optimized. Ultrasonic treatment successfully disintegrated the floc structure of sewage sludge and promoted the release of organic matter and metal ions such as Ca2+ and Mg2+. After ultrasonic treatment, soluble chemical oxygen demand (SCOD) in the sludge solution increased 11.28-49.06%, while the concentrations of Ca2+ and Mg2+ rose 5.5-25.0% and 2.7-19.0%, respectively. The ultrasonic frequency of 25 kHz was most effective in disintegrating sludge, and high energy densities and longer treatment time increased SCOD and metal ion release. The optimal parameters that promoted the increase SCOD were 25 kHz, 75 W/L and 60 s. Under these conditions, double-frequency ultrasonication was more effective than single-frequency ultrasonication.