Future Municipal Wastewater Reclamation: A Fit-for-Purpose Roadmap Toward Water Sustainability and Low-Carbon Resource Recovery

Municipal wastewater reclamation is becoming increasingly important for alleviating water scarcity, reducing dependence on freshwater resources and improving the sustainability of urban water systems. This review examines the current status and major challenges of municipal wastewater reclamation and discusses its future development from the perspectives of water quality, energy use, resource recovery and greenhouse-gas mitigation. Future reclamation systems are expected to place greater emphasis on end-use-oriented treatment, energy efficiency, resource retention and carbon-conscious process design. Several emerging process configurations are evaluated, including aerobic and anaerobic membrane bioreactor systems coupled with reverse osmosis, algal–bacterial membrane processes, nutrient-retaining treatment for agricultural reuse and non-RO advanced treatment based on oxidation and biological filtration. Their applicability varies with the intended reuse because of differences in water quality control, energy demand, resource recovery and residual-stream generation. Future technology selection should therefore integrate treatment intensity with deployment scale. RO-based and non-RO-based pathways can be selected according to the dominant water quality constraints, while centralized, decentralized and hybrid systems should be matched to local infrastructure, reuse distance, water demand and resource recovery opportunities. The system-level evaluation of water quality, energy consumption, greenhouse-gas emissions, economic performance and residual-stream management will be essential for guiding future deployment. Municipal wastewater reclamation is expected to evolve toward adaptable, fit-for-purpose treatment portfolios that support water sustainability, resource circularity and the transition toward low-carbon urban water systems.