Synchronous removal of antibiotics in sewage effluents by surface-anchored photocatalytic nanofiltration membrane in a continuous dynamic process

Abstract

Bifunctional photocatalytic nanofiltration (PNF) membranes have gradually become one of the research hotspots in the field of micropolluted water purification. However, their usability still needs to be greatly improved. To this end, a novel surface-anchored PNF membrane was developed for synchronously degrading and separating target antibiotics in actual sewage effluent under continuous flow-through. As expected, experimental results demonstrated that the optimized PNF-2 membrane was composed of an inner dense sub-nanoporous separating layer and an outer mesoporous, thinner, and hydrophilic degrading layer. Consequently, the activated PNF-2 membrane module was capable of simultaneously removing more than 99% of trimethoprim and sulfamethoxazole, almost without sacrificing water permeability (21.1 L m⁻² h⁻¹ bar⁻¹), indicating that the hydrophilic mesoporous degradation layer brings little additional hydraulic resistance. The removal rates of both selected antibiotics in practical water environment were slightly higher than those in the simulated water environment, mostly because of the increased steric hindrance of contaminants in the former case. Besides, after long-term operation up to 76 h, the minimum total and reversible fouling ratios (7.97% and 2.43%) together with only sporadic foulants remaining on the physically rinsed membrane surface were obtained. This is bound to greatly improve its cleaning threshold and maintain superior service performance. Moreover, the acute and chronic toxicities of its permeate were dramatically cut down to 4.14% and 1.56%, respectively. All these strongly prove that the dual functions of the PNF-2 membrane are synergetic in an uninterrupted permeating process and will boost the efficient removal of trace organic contaminants in real applications.