Membrane properties overview in integrated forward osmosis/osmotically assisted reverse osmosis systems

Abstract

Integration of forward osmosis (FO) and osmotically assisted reverse osmosis (OARO) provides low energy consumption and controlled fouling for brine treatment. This study explains the membrane properties required for cost–optimal OARO-based systems. A detailed model accounting for the relationship between burst pressure, permeate spacer gap, and structural parameters of OARO membranes was implemented with woven and non-woven spacers. Results indicate that the tradeoff between internal concentration polarization (ICP) and permeate–side pressure drop in OARO stages is a crucial consideration for optimal membrane element design. Due to the lower ICP of no-woven spacers, a system using non-woven spacers yielded lower levelized cost of water (LCOW) and specific energy consumption (5.83 $/m3 and 11.65 kWh/m3, respectively) as compared to the system with woven spacers (7.31 $/m3 and 9.90 kWh/m3, respectively) for dewatering a stream of 75 g/L salinity with 70 % water recovery. Sensitivity analysis shows that increasing the maximum pressure in OARO membranes requires a higher membrane structural parameter, aggravating ICP; however, the elevated driving force mitigates adverse effects of ICP. Moreover, a 15 % reduction in LCOW can be achieved if the membrane replacement factor of RO and OARO is reduced from 15 % to 5 %, which accounts for mitigated fouling.