Transport mechanisms behind enhanced solute rejection in forward osmosis compared to reverse osmosis mode

Forward osmosis (FO) as emerging technology for water treatment was reported to exhibit higher solute rejections compared reverse (RO). In this work, the rejection of two uncharged organic compounds (nicotinamide, caffeine) were investigated first time in low-pressure (LPRO) mode and FO under similar process conditions utilizing same hollow fiber forward membrane modules. consistently showed than LPRO both nicotinamide (FO: 94.8%, LPRO: 85.5%) caffeine 99.9%, 99.2%). To elucidate influence draw on rejection, different salts (NaCl, MgCl2, MgSO4), concentrations, flow rates investigated. A rise concentration increased all (RNaCl:94.1?97.2%,RMgCl2:94.5?97.5%,RMgSO4:90.0?94.7%) indicating an enhancement due presence salt permeate side membrane. Two theories are proposed: While resistance feed transport could be counter-directed flux support layer, driving force diffusion might lowered ionic compound