Advances in Wastewater Treatment: Energy Efficiency, Micropollutants, and Circular Resource Recovery

The field of wastewater treatment is evolving from conventional organic load removal towards integrated, multi-barrier systems that address nutrients, pathogens and emerging micropollutants. This review evaluates current treatment strategies, from activated sludge and biological nutrient removal to advanced oxidation processes, membrane technologies, and hybrid systems, focusing on performance, operational complexity, and energy demand. Tertiary or quaternary interventions are required for persistent contaminants, including pharmaceuticals, endocrine-disrupting compounds, and PFAS. Emerging approaches such as hydrodynamic cavitation, photocatalysis, microbial fuel cells, forward osmosis, cold plasma, and controlledrelease oxidants are assessed for their feasibility, scalability, and potential for integration. Regulatory frameworks in the European Union and the United States are increasingly driving the adoption of advanced treatment processes and circular resource recovery strategies. The analysis emphasises the importance of coordinated system integration, digital process optimisation and energy recovery in order to achieve sustainable, energy-efficient and highquality effluents. The next generation of wastewater treatment plants is envisioned as a hub for resource recovery and water reuse, combining biological, physicochemical and digital solutions to meet increasingly stringent effluent standards while minimising environmental and economic costs. This synthesis provides a roadmap for implementing innovative, regulatory-compliant, circular wastewater treatment strategies in a rapidly changing environmental and technological landscape.