The use of ultrasound to mitigate membrane fouling in desalination and water treatment

Fouling is recognized as a serious challenge in reverse osmosis desalination and in different membrane-based separation technologies. Membrane fouling not only reduces the permeate flux and the membrane productivity but also significantly decreases the membrane lifespan, increases the energy and feed pressure requirement, and increases membrane maintenance and replacement costs. As a result, the consequences of membrane fouling have always stimulated research investigations into different fouling mitigation strategies. In this context, application of ultrasound is an effective technique that can be used as an external aid for both membrane fouling control and membrane cleaning. The purpose of this review paper is to provide an updated and comprehensive review of ultrasound as an effective tool for membrane flux enhancement and membrane cleaning. In addition to briefly discussing the mechanisms of membrane fouling, theories related to ultrasonic waves, acoustic cavitation, cavitational collapse, and ultrasound-induced effects are addressed. The key challenges in industrial application of ultrasound for flux enhancement and membrane cleaning are also discussed.