Numerical simulation and experimental optimization of ultrasonic cracking in excess sludge

Ultrasonic treatment of municipal sludge can effectively reduce the moisture content, improve sludge stability, and create optimal conditions for subsequent sludge disposal. Methods to optimize the ultrasonic treatment of excess sludge have great practical significance. This study determined the influence of ultrasonic frequency, the axial distance between the thermal and ultrasonic probes, ultrasonic power, and other factors involved in cavitation experiments, The MATLAB and FLUENT software were used to simulate the ultrasonic sludge treatment effects under varying conditions; these simulations were verified by microscopic and biochemical analyses. The results showed that lower frequency and higher power yielded stronger temporal and spatial effects; the optimal conditions were 20 kHz and 1,000 W. After 30 min of treatment, the sludge particle size was significantly reduced, with d50 decreasing from 34.82 & mu;m in the original sludge to 2.99 & mu;m, and a small number of nanoscale particles formed. Therefore, ultrasonic treatment yields an excellent cracking effect on excess sludge. The results of simulation analysis and experiments can provide a reference to achieve effective stabilization, resource utilization, safety, and excess sludge reduction.