Potential application of hybrid forward osmosis – Membrane distillation (FO-MD) system for various water treatment processes

Abstract

Different membrane processes have been used to address water scarcity issues. Among them, membrane distillation (MD) is a promising technology due to its capacity to treat hypersaline water. Forward osmosis (FO) is another innovative technology that has the advantage of low operational energy. A hybrid system of these two technologies has proven to be an effective technique for the water treatment industry particularly for water reclamation and resource recovery. Understanding the fundamentals of this amalgamation and the challenges that brings with it is an important topic for the scientific and research community. This work presents a detailed review of the FO-MD systems enriched with the recent advances in this system. The opportunities and challenges for the individual technologies and the system overall were critically addressed. Successful pilot designs for the hybrid system were illustrated. Mathematical modeling for the water transfer in the hybrid system was also elaborated to identify the key points and boundaries of the processes. It is apparent that the inherent low energy conversion in MD and the need for draw solution regeneration are the prominent challenges of this system. Another important aspect to be highlighted is that the water transfer balance between MD and FO is the key requirement for a stable and successful operation. The use of alternative energy is possible but it is only feasible in specific cases such as the existence of seawater and wastewater facilities in a proximity or the case of produced water that contains geothermal heat. Implementing heat recovery in the MD stage, using functionalized particles as a source of osmolarity in the draw solution, and developing membrane materials with unique characteristics such as omniphobic and Janus MD membranes are effective strategies that have just recently shown to improve the systems economics and such strategies should be explored further.