Advancing drinking water safety: Facile fabrication of nanofiltration membrane for enhanced antibiotics removal and efficient water softening

Long-term water consumption with contaminated antibiotics and high levels of hardness threatens the health of humans and animals. In this study, a novel positively charged nanofiltration membrane was designed for the dual purpose of efficiently removing antibiotics and softening hard water. The membrane was fabricated by casting P84 polymer solution onto non-woven fabrics, followed by immersion in the polyethyleneimine (PEI) solution for phase inversion and cross-linking, and finalized interfacial polymerization with trimesoyl chloride. Notably, the rapid immersion of the P84 substrate into PEI drastically reduces preparation time by 95 % compared to the regular method while maximizing PEI storage, resulting in uniform pore sizes and a positively charged surface. The optimal membrane showed a high water permeance of 11.3 L m−2 h−1 bar−1 and exceptional antibiotic rejection, i.e., 99.6 % for enrofloxacin, 99.2 % for ciprofloxacin, and 96.3 % for sulfamethoxazole, as well as a highly effective removal in water hardness (over 96 % of Ca2+ and Mg2+) at 4 bar. Simulated water separation tests showed that the optimal membrane effectively controls hard water salinity within optimum drinking water ranges (Ca2+ ≤ 80 mg/L; Mg2+ ≤ 30 mg/L), providing efficient water softening and antibiotic capture ability. Additionally, the optimal membrane demonstrated a superior anti-bacterial and long-term stability performance. This study has significant potential for improving drinking water supply safety and addressing pressing public health and environmental concerns.