Sustainable membranes from industrial waste valorization for microbial electrochemical desalination systems.

Freshwater scarcity and the environmental burden of reverse osmosis (RO) reject streams demand sustainable desalination alternatives. Microbial desalination cells (MDCs), integrated with bioelectrochemical processes, have emerged as eco-friendly platforms for simultaneous wastewater treatment, ion removal, and energy recovery. However, their reliance on costly, ion-exchange membranes limits scalability. This review critically examines low-cost waste-valorized membranes fabricated from agricultural residues, polymeric wastes, ceramics, and industrial byproducts as green substitutes for conventional membranes in MDCs. This review critically discusses the past progress of low-cost waste additives to multifunctional, biofunctionalized membranes with superior ion transport, antifouling, and self-cleaning capabilities. The major focus of the paper is on strategies such as graphene oxide doping, enzyme immobilization, and magnetic biochar integration that can enhance performance, conductivity, and fouling resistance, alongside reducing cost and carbon dioxide footprint. Based on the in-depth analysis, a comprehensive roadmap is proposed encompassing feedstock standardization, green fabrication, novel manufacturing techniques including digital process optimization, techno-economic analysis, integrated MDC-RO systems, and end-of-life recycling, aimed at enabling scalable, decentralized, and cost-effective desalination solutions. Further, the integration of waste-derived membranes into MDC-RO hybrids is presented as a viable pathway to increase water recovery, reduce fouling, and lower energy demand. This work underscores the potential of waste-valorized membranes as next-generation sustainable solutions for water-energy nexus challenges.