Design of an ammonium chloride aqueous solution concentration process using osmotically assisted reverse osmosis (OARO)

This study evaluated the separation performance of an ammonium ion concentration process in aqueous solutions using osmotically assisted reverse osmosis (OARO) membrane separation. The investigation focused on the advanced separation of an aqueous ammonium chloride solution (flow rate: 1000 kg/day, concentration: 0.4 wt%) by analyzing discharge pressure, membrane area, and reflux ratio as the main parameters for both OARO and RO systems. The results indicated that OARO achieved higher separation performance and energy efficiency compared to RO under conditions where discharge pressure exceeded 4.0 MPa, the reflux ratio was above 7.2, and the membrane area was at least 45 m 2 . It was found that as the discharge pressure, membrane area and reflux ratio increased in OARO, the concentration ratio increased up to 50 times. Notably, it was suggested that reducing the membrane area towards the downstream side in OARO improves the concentration performance regardless of the total membrane area, identifying this as a key parameter in process design.