Surface modification of membrane substrates for nanofiltration-based removal of essential and energy-critical metals from industrial wastewater

Heavy metal ions in water pose significant health and environmental risks due to their persistence, as they do not biodegrade and are prone to accumulating in aquatic organisms. Consequently, effective removal methods are critical, with membrane technology emerging as a promising approach for treating contaminated water. In this study, thin-film composite active layers were systematically synthesized on three different support substrates: polyethylene (PE), polyvinylidene fluoride (PVDF), and polyethersulfone (PES). The resulting membranes were characterized to evaluate their surface morphology, roughness, and porosity using various analytical techniques, including SEM, AFM, FT-IR, XPS, and contact angle measurements. Thin-film composite polyamide layers synthesized on different support substrates exhibited different surface properties and porosity. Dead-end filtration tests showed that the modified PVDF membrane (TFL-PVDF) has a higher pure water flux compared to its PE (TFL-PE) and PES (TFL-PES) counterparts. However, in single-metal ion solutions, TFL-PES demonstrated superior rejection of Ca²⁺, Mg²⁺, and Ni²⁺, attributed to steric exclusion mechanisms. Further investigation into operational parameters such as pressure, feed concentration, associated anions, and pH confirmed the robust performance of TFL-PES membranes. The removal efficiency of the TFL-PES membrane was also evaluated in simulated industrial wastewater and mixed metal solutions over 24 h. TFL-PES maintained high removal rates for Ca²⁺, Mg²⁺, Ni²⁺, and Fe, confirming its strong potential for application in industrial wastewater treatment.