Wastewater treatment infrastructure in the European Union and micropollutant removal under the recast Urban Wastewater Treatment Directive

The recast Urban Wastewater Treatment Directive (Directive (EU) 2024/3019) introduces micropollutant-removal requirements alongside stricter nutrient standards. This study assesses EU wastewater infrastructure readiness, reviews regulatory obligations and options for quaternary treatment, and identifies technological and strategic gaps. Data for 22,024 urban wastewater treatment plants (UWWTPs) from the European Environment Agency Waterbase dataset were evaluated using descriptive statistics and hierarchical clustering at Member State level. Regulatory provisions and treatment options were reviewed in relation to infrastructure patterns. Small UWWTPs (<10,000 PE) represented 54.7% of facilities but treated less than 8% of wastewater flow, whereas large plants (≥150,000 PE) accounted for 4.9% of facilities yet processed 53.9% of the flow. Large UWWTPs therefore represent priority targets for reducing micropollutant emissions, while clustering revealed differences among national infrastructure and treatment profiles. The reviewed options include ozonation, activated carbon adsorption and membrane-based processes, whose applicability depends on plant configuration, effluent characteristics and economic conditions. In contrast, chlorination, conventional UV irradiation and sand filtration primarily provide disinfection or solids removal and should not be interpreted as broad-spectrum micropollutant-removal technologies. Persistent gaps in nitrogen and phosphorus removal indicate that robust secondary and tertiary treatment remains important for efficient implementation of quaternary treatment. Nearly tenfold differences in gross domestic product per UWWTP indicate uneven financial capacity for modernization. Monitoring requirements for microplastics and per- and polyfluoroalkyl substances also require harmonized analytical methods. Effective implementation will depend on prioritizing high-flow facilities, strengthening nutrient removal, selecting site-specific treatment configurations and establishing comparable monitoring frameworks.