Ultrasound-assisted membrane technologies for fouling control and performance improvement: A review

Membrane separation is widely used in wastewater treatment and desalination due to its high performance and ability to handle feed solutions of different qualities. Despite vast history of success, membrane fouling remains a major system deficiency that imposes substantial process limitations by reducing permeate production and increasing energy demand. Besides, chemical cleaning-in-place (CIP) adversely affects membrane integrity and generates an extra waste stream. Ultrasound (US) is a relatively new cleaning technique that improves process performance by mitigating fouling accumulation at a membrane surface and improving permeate flux by promoting mass and heat transfer. US-assisted membrane processes is an efficient method for fouling reduction and significant flux improvement. This study comprehensively reviews US applications in pressure-, thermally- and osmotic-driven membrane technologies and their impact on process performance. It also explores the impact of US operating conditions on membrane separation properties and how these parameters can be tuned to achieve the desirable outcome. To date, the application of US in membrane technologies is limited to laboratory tests. In the authors' opinion, there is a niche market for US-assisted membrane technology in heavily contaminated water such as wastewater and brine. After critical analysis of the literature, we found that there are still several aspects of the process need to be scrutinized carefully to make an adequate evaluation of its feasibility on an industrial scale. The most urgent one is the techno-economic evaluation of the technology based on large-scale and long-term tests. The study proposed a set of recommendations for future research directions of US applications in membrane technologies.