Membrane distillation process: Fundamentals, applications, and challenges

Abstract

Traditional thermal-based processes such as multistage flash and multi-effect distillation have been used for thousands of years to obtain freshwater from saline water. Recently, with the development of membrane-based technology, membrane distillation (MD) as a thermally driven membrane process has received significant attention. The driving force in MD is the vapor pressure gradient induced by temperature difference through hydrophobic microporous membrane pores. The membrane used for MD should be hydrophobic and microporous. In MD, the mechanism of transport involves simultaneously heat and mass transfers, which moves from the hot feed side to the cold permeate side. The performance of MD is evaluated based on various performance metrics including permeate flux, recovery ratio, thermal efficiency, gained output ratio, and specific thermal energy consumption. It has good ability for various industrial uses due to its moderate applied temperature and pressure, high rejection rate, less membrane fouling tendency and its ability to treat high-saline water. The water production cost still remains high compared to conventional processes. Therefore, MD can be cost-effectively when integrated with solar energy, geothermal energy and waste heat. Nevertheless, MD process requires focused research to improve its efficiency to become more mature and economically competitive at large scale.