Development in forward Osmosis-Membrane distillation hybrid system for wastewater treatment

Water scarcity is one of the major issues that has put economic growth, societal stability, and ecosystem balance unstable. Wastewater reuse has been recognised as a viable method for securing potable water supply. Due to its inherent advantages over pressure-driven and energy-intensive reverse osmosis (RO), forward osmosis (FO) is one of the most researched technologies for wastewater reuse applications. However, the draw solution (DS) regeneration stage is one of the key bottlenecks of the process. Membrane distillation (MD), on the other hand, is an emerging technology that could provide a cost-effective thermally-driven purification process, especially when combined with waste heat or solar thermal. Nevertheless, the MD process also has several drawbacks, such as membrane pore wetting. The MD process can effectively regenerate the FO draw solution and produce high-quality water when integrated with the FO process. Within the hybrid process, the FO membrane removes the contaminants from the feed solution and the MD process is only used to regenerate the DS with no significant membrane wetting. It is, therefore, important to study the integrated FO-MD process to overcome the limitations of individual membrane processes. Integrated FO-MD economics, process design, and modelling of different applications are thoroughly reviewed in this contribution. Future research directions and prospects for scale-up are suggested.