A Critical Review on Ultrasonic-Assisted Fouling Control and Cleaning of Fouled Membranes

Fouling is one of the most challenging problems impacting the performance of membrane-based separationtechnology. In recent years, ultrasound have been widely applied as an unconventional method to controlmembrane fouling, as well as to enhance membrane cleaning. The aim of the present work is to review thecurrentliteratureandtherecentdevelopmentsrelatedtotheuseofultrasoundasaninnovativeandalternativeapproachtoimprovethefoulingbehaviorofmembraneseparationprocesses.Thetheoryunderlyingultrasonic-assisted phenomena is reviewed, together with operational factors that influence the effectiveness of the ul-trasound treatment, such as frequency, power intensity, pressure, temperature, pH, and operation mode.Ultrasoundirradiationeffectivelyaidsthecleaningofcontaminatedsurfacesandenhancesthepermeateflux,owingtocavitationphenomenaandpowerfulconvectivecurrents,associatedwithsecondaryphenomena,suchas microstreamers, shock waves, and heating. However, the lifetime of the membranes should be carefullyevaluatedwhenapplyingultrasonicationasatechniqueofcleaningorcontrollingmembranefouling.Indeed,theintegrityofmembranesaftersonicationandthecontroloferosionproducedbyhighultrasonicintensitiesarekeyissueshinderingthescale-upofthisapproachinthemembraneindustry.Thisreviewshighlightsthetopicsrequiringmoreinvestigations,specificallytoevaluatetheeconomicaspectsofultrasonicassistedfoulingcontrolandcleaninginmembraneprocess