Toward sustainable membrane recycling via controlled oxidation: Smart strategies for effluent treatment in the pulping process

The pulping industry consumes billions of cubic meters of freshwater annually, and generates substantial volumes of highly contaminated wastewater creating a large pressure on freshwater resources and treatment infrastructure. Simultaneously, over two million end-of-life (EoL) reverse osmosis (RO) modules are expected to be discarded annually by 2025. This study investigated technical feasibility of recycling EoL RO membranes through controlled chemical degradation of the polyamide (PA) selective layer for treatment of alkaline filtrate effluent from pulp mill. Controlled oxidation using sodium hypochlorite (NaOCl) with calcium chloride (CaCl 2 ) catalysis reduced treatment time by ∼ 50% and markedly accelerated PA degradation compared to NaOCl alone. Characterization via Fourier transform infrared spectroscopy, scanning electron microscopy, and permeance analysis confirmed progressive PA removal and the functional transformation into nanofiltration (NF)- or ultrafiltration (UF)-like configurations. Recycled membranes exhibited pure water permeances from 4.3 to 223 L m − 2 h − 1 bar −1 and molecular weight cut-off (MWCO) values of 580–10,300 Da. Oxidized EoL membranes outperformed commercial UF membranes (1–10 kDa range), achieving higher permeance while maintaining comparable MWCO. Applied to alkaline pulp mill effluent, the most effective low-to-moderately oxidized membrane (permeance ∼ 20 LMHb, MWCO ∼ 640 Da) removed ∼ 4×more chemical oxygen demand, ∼ 1.4×more total dissolved carbon, and ∼ 8.3×more conductivity than the commercial UF membrane UH004 P. Superior performance resulted from higher flux due to increased surface hydrophilicity and wettability from oxidation. Results indicate that controlled oxidation successfully transforms waste membranes into high-performance (NF/UF-like) application-specific membranes. This innovative approach delivers significant environmental and economic advantages while providing a practical pathway for integrating circular economy principles into membrane technology and industrial wastewater treatment.