A comprehensive review of standalone and hybrid forward osmosis for water treatment: Membranes and recovery strategies of draw solutions

Abstract

Forward osmosis (FO) is a membrane separation technique used to recover water from feed solution (FS) across a semi-permeable membrane, using a concentrated draw solution (DS). The feed solution could be sea/brackish water, wastewater, or other contaminated water. The DS and membrane play important roles in its overall performance. Permeate in FO is not pure water but a diluted DS. So, FO requires an additional step to regenerate DS and to recover freshwater as a product. This additional regeneration process might increase the total capital investment and energy requirement for the FO process. Selecting a proper DS and designing an energy-efficient DS regeneration system are the main challenges to make the FO process energetically viable. The FO process has significant advantages as it operates with very low hydrodynamic pressure, due to which it shows lower membrane fouling propensity. Hence, it helps for saving energy and reducing membrane replacement costs. It has some limitations, such as reverse solute flux, internal and external surface concentration polarization, that need to address before making it commercially more viable. This review focuses on the FO process's recent significant advancements in FO membranes, draw solutions, regeneration processes of draw solutions, overall energy efficiency, membrane fouling, overall performance during the long-term run, and future research directions.