Enhancement and optimization of membrane distillation processes: A systematic review of influential mechanisms, optimization and applications

To face the challenges of global water scarcity and water pollution, membrane distillation (MD), represented by hydrophobic microporous membranes, has recently received considerable attention and has shown great potential in processes such as seawater desalination, production of potable water from poor quality water, and wastewater treatment. MD technology has only been implemented in a few pilot plants around the world, a gap that needs to be filled through research and development. The focus of this review is to provide an overview of the effects of operating conditions and the current state of research on the MD process. To further improve the performance of the MD process, three statistical optimization techniques including response surface methodology, evolutionary algorithms, and artificial neural networks for optimizing MD operating parameters are analyzed. Five externally assisted techniques for enhancing the MD process are then reviewed, including electric field, ultrasonic, electromagnetic field, micro bubble aeration, and two-phase flow techniques. Finally, important applications of MD in recent years are discussed, mainly including MD-coupled process applications and thermally positioned solar distillation systems, with the aim of providing new R&D ideas to advance MD technology from emerging to mature.