Mechanisms and factors influencing the ultrasonic cleaning of particle-fouled ceramic membranes

This paper investigates factors affecting ultrasonic cleaning of particle-fouled ceramic membranes and possible mechanisms responsible for cleaning. Homogeneous ceramic membranes were fouled by sulfate polystyrene latex particles in a dead-end filtration cell and subsequently subjected to ultrasound at different frequencies, power intensities and durations of treatment. Flux measurements indicate that increased power intensity and lower frequency increase particle removal from a fouled membrane. These data along with SEM images suggest that cavitational mechanisms (i.e., microstreaming and microstreamers) are important in detaching particles from the membrane surface while turbulence associated with ultrasound (i.e., acoustic streaming) plays a role in the transport of particles away from the surface following detachment. Micro-jets did not appear to cause significant removal compared to microstreamers, although evidence of micro-jet pitting was visible in SEM images of the fouled surface. In addition, SEM images did not show any visible damage to the membrane surface, even for prolonged periods of ultrasound at high power intensity and low frequency (20 W cm−2, 20 kHz).