Polyelectrolyte fabricated nanofiltration membrane with heterogeneously charged channels for high efficient cephalexin wastewater treatment

Nanofiltration (NF) for treatments of pharmaceutical wastewater is a promising direction for water protection and resources recovery. Herein, a novel membrane with heterogeneously charged channels was constructed by modified layer-by-layer assembly methods. Within the well-designed pores, the polyanion structure excludes the cephalexin and the cationic structure slows down its diffusion, thereby rejections for cephalexin are improved. The hydrophilic property of polyelectrolytes simultaneously guarantees the water transport. Fabricated heterogeneously charged channels are shown to strengthen the electrostatic barrier and prevent monovalent cephalexin anions penetration. Optimized nanofiltration membrane exhibits rejections of 98.9 % for 3650 ppm cephalexin, maintaining steady rejection during 69 h of continuous operations. The flux recovers to 99.3 % of the original flux after water washing. Benefiting from the separation performance of fabricated membranes, multi-stage NF processes effectively enrich the cephalexin wastewater. This work offers significant prospects for achieving high-efficiency pharmaceutical wastewater treatment and amphoteric drug recovery.