A mixed-charged polyelectrolyte complex nanofiltration membrane for mitigating scaling during high-recovery wastewater effluent desalination

Abstract

The high salinity of wastewater effluent restricts its sustainable use for irrigation. Nanofiltration (NF) membranes can desalinate effluent. However, the applicability of polyamide NF membranes for effluent desalination is limited by high scaling, particularly calcium phosphate, and the permeate's high sodium adsorption ratio (SAR). This research presents a simple method to fabricate a mixed-charged polyelectrolyte complex NF (PECNF) membrane to overcome these challenges. The performance of the PECNF membranes was optimized by varying the polyanion-polycation ratio and total polyelectrolytes mass load and utilizing crosslinking. The resultant PECNF membrane exhibited 7.2 LMH/bar permeance and similar rejection of different types of ions. Scaling experiments using synthetic and real effluents mimicking 80 % recovery revealed that the PECNF membrane has lower scalant forming ions rejection and comparable TDS rejection (35 %) than commercial polyamide NF membrane (NF 270). Consequently, the scaling propensity of the PECNF membrane, evaluated by permeate flux reduction (∼33 %) after 50 h of filtration, was lower than that of the NF 270 membrane (∼70 % reduction). Additionally, the SAR value of the PECNF membrane's permeate was substantially lower. The PECNF membrane's stability, permeate quality, and anti-scaling properties make it a promising alternative to polyamide membranes for high-recovery effluent desalination.