A comprehensive review of membrane fouling and cleaning methods with emphasis on ultrasound-assisted fouling control processes

One of the most critical issues encountered in membrane-based separation processes is permeate flux decline in a system operating for a long period. The particles in the feed solution tend to foul the membrane surface or membrane pores, which results in pore blocking and/or cake formation on the surface. In this regard, the use of membrane cleaning techniques for the membrane flux restoration has gained more attention. Ultrasonic (US) irradiation is an alternative technique applied to the feed solution passing across the membrane surface to either prevent the fouling formation (fouling control) or dislodge the foulants (surface cleaning). Ultrasonic cleaning mechanisms are based on sound waves travelling through the liquid, which leads to physical and chemical effects. This cleaning technique is an environmentally friendly process in which no chemical or biological agents are used. This article briefly reviews different types of fouling and classes of foulants, fouling evolution mechanisms, mathematical modelling of fouling, surface cleaning and fouling control strategies, with the emphasis on ultrasound-assisted fouling control process as an innovative cleaning method. The effect of the operational parameters on the performance of the US-assisted filtration processes, highlights, challenges, and future outlook of US cleaning will be discussed.