Concentration polarization controlin stand-alone and hybrid forward osmosis systems: Recent technological advancements and future directions

Forward osmosis (FO) has received significant attention recently. FO has high potentials for integration with other water treatment technologies. However, concentration polarization (CP) remains a significant challenge in FO membrane applications. In particular, internal CP (ICP) reduces the permeability of FO membranes by nearly 80%. The development of FO processes and their applications can greatly benefit from strategies that detect and control CP in standalone and integrated FO systems. This requires consideration of FO membrane structures, materials, configurations, operating conditions, and modification and cleaning strategies. This review provides a state-of-the-art analysis of recent literature on CP detection and control with a specific focus on ICP as a major issue in FO processes. This helps to understand current CP mitigation strategies and their challenges and prospects. The first section reviews the structures of different FO membranes and related CP mechanisms. Research on CP and the impacts of various parameters on its magnitude are then discussed, followed by a review of CP phenomena in hybrid FO processes and applied ICP control strategies. Finally, recommendations for future research in CP detection and control are made. This review serves as a valuable reference for future research on FO processes and may contribute to developing more ICP-resistant FO membranes.