State-of-the-art methods for overcoming temperature polarization in membrane distillation process: A review

Membrane distillation (MD) technology has been mainly used as a treatment method for saline or contaminated wastewater. Despite the rapid progress in material engineering and design of novel MD systems, principal challenges as temperature polarization (TP) and high-energy consumption per unit of produced water still restrict its commercialization. Recently, TP mitigation has been addressed by modification and configuration of MD systems or by using advanced materials for membrane fabrication. These include coating thermally conductive or photonic nanomaterials on the membrane's surface or using thermally conductive metallic based membranes that impact heat dispersion along the membrane. In addition, frame-like turbulence promoters and modified feed channels were shown to lower TP by enhancing the characteristics of the feed flow. Finally, systems able to directly heat the membrane's surface without preheating the feed solution, including solar, Joule, and induction heating, were shown effective in eliminating TP due to the higher temperature at the membrane-water interface in comparison to the temperature of the bulk feed solution. The review aims to summarize recent advances made in TP mitigation for MD systems and assess their influence on distillation efficiency. We include a brief description of the TP phenomenon and its observed effects on MD and describe advanced MD processes from the aspects of low or negligible TP, high distillate flux, and improved energy efficiency.