Thin film composite forward-osmosis membranes with enhanced internal osmotic pressure for internal concentration polarization reduction

Thin-film composite (TFC) forward-osmosis (FO) membranes with enhanced internal osmotic pressure (IOP) were used to reduce internal concentration polarization in this study. These TFC membranes contained a selective polyamide layer deposited by interfacial polymerization on a support substrate cast from a polymer blend of polysulfone (PSf) and sulfonated poly(phenylene oxide) (SPPO). The immobilized counter ions (Na⁺) in SPPO gave rise to an IOP which facilitated water transport in the AL-FS operating mode (i.e., the active layer is facing the feed solution, also referred to as the FO mode) but retarded water transport in the AL-DS operating mode (i.e., the active layer is facing the draw solution, also called as the pressure retarded osmosis (PRO) mode). An optimized TFC membrane could draw a water flux of 39 LMH (Lm^-2h^-1) in the AL-FS mode, which is among the highest in the current literature; and 57 LMH in the AL-DS mode, which is comparable to other published works using deionized water as the feed and 2M NaCl as the draw solution. The optimized SPPO/PSf TFC membrane also outperformed other published FO membranes in simulated seawater desalination. Extremely high water fluxes of 25 and 19 LMH could be obtained in the AL-DS and AL-FS modes respectively. The impressive high water flux in the AL-FS mode makes this membrane particularly suitable for FO operations where internal concentration polarization (ICP) and membrane fouling are major concerns.