Ultrasonic cleaning in the membrane process: From phenomenon to mechanism and mathematical model

An inhibition effect of cavitation bubbles on cake removal was observed for the first time in the ultrasonic cleaning process. Then, a mathematical model simultaneously considering inhibition effect, bubble dynamics, and actual nonuniform cake structure was established based on force analysis. The result showed that model could precisely predict the flux recovery rate (FRR) (R2 > 0.97). Furthermore, the model was used to determine the theoretical cleaning efficiencies (FRR*) under different conditions: FRR* increased with power whereas decreased with frequency, the highest value was 91.26%(1.0 W/cm2&20 kHz). Besides, a comparison between FRR* and FRR indicated that a duration of 120 s was enough in ultrasonic cleaning. Critical duration determined by the half-life period method successfully evaluated the significant jump in FRR. Additionally, different foulants and multi-cycle experiments were carried out to validate the application of the model and energy conservation (60–70%) of periodical ultrasonic cleaning. This study provided significant insights into industrial ultrasonic cleaning process.