Toward Circular and Sustainable Urban Wastewater Treatment: Integrating Adsorption and Advanced Oxidation Processes

Wastewater treatment is fundamental to sustainable urban development, and recent European legislation now requires quaternary treatment of final effluent at wastewater treatment plants. Among the technologies evaluated for this purpose, adsorption and Advanced Oxidation Processes (AOPs) have demonstrated the highest removal efficiencies, and the ongoing shift toward more circular and sustainable urban wastewater management, positioning them as two of the most strategically significant technologies in the field. Quaternary treatments with ozonation and activated carbon adsorption (PAC/GAC) achieve median micropollutant removal above 80%. GAC is generally associated with the highest costs, followed by PAC and ozonation, typically in the range of approximately 0.035 to 0.3 € per cubic meter in European settings. This review presents a systematic comparison of adsorption and AOPs for the removal of urban wastewater pollutants, with emphasis on removal efficiency, energy requirements, carbon footprint, and operational limitations. It delineates the conditions under which each technology demonstrates superior performance and highlights its complementary strengths across different contaminant groups and treatment objectives. Beyond conventional performance indicators, the review frames these technologies as key enablers of circular wastewater treatment through material regeneration, resource recovery, and process integration.