Per- and polyfluoroalkyl substances (PFAS) in wastewater and sewage sludge: occurrence, concentrations, and regulatory challenges

Abstract

This review examines the role of wastewater treatment plants (WWTPs) as important pathways for the release of per- and polyfluoroalkyl substances (PFAS) into the environment. WWTPs receive municipal, industrial, and other wastewater, including landfill leachate, and subsequently discharge treated effluent and sewage sludge, which may act as secondary sources of PFAS. The literature indicates that, although conventional treatment and sludge management processes can partially remove some micropollutants, many persistent and potentially hazardous PFAS remain in treated wastewater and accumulate in sewage sludge. This review also highlights that the lack of comprehensive and harmonized data on PFAS occurrence, transformation, and fate in these matrices limits reliable risk assessment and effective environmental management. In addition, current European Union legislation regulating hazardous substances in WWTP effluent and sewage sludge does not establish specific concentration limits for PFAS. Existing regulations are often limited to individual PFAS classes or specific countries, or take the form of recommendations rather than legally binding standards. Based on the available literature, PFAS occurrence and concentrations are highly variable and do not consistently depend on wastewater origin, including municipal, industrial, or landfill leachate. Reported WWTP influent concentrations differ widely across regions, ranging from 22 to 346.2 ng L^–1, and attempts to relate these variations to plant capacity, population equivalent, or industrial activity remain inconclusive. The studies reviewed herein indicate that temporal variability is common, but consistent seasonal trends are rare. Moreover, PFAS concentrations in the WWTP effluent are not always lower than in the influent, often due to transformation of precursor compounds during treatment processes. Reported effluent concentrations ranged from 13.4 to 1357 ng L⁻¹, with the highest values observed in industrially impacted WWTPs. This review further highlights a significant geographical imbalance in available data: although numerous studies have been conducted worldwide, information from Central and Eastern Europe remains limited. In Poland, in particular, the few available studies have mainly focused on PFAS in surface water and drinking water, whereas systematic studies of PFAS in municipal or industrial wastewater and sewage sludge are still largely absent. Nevertheless, the PFAS concentrations reported in municipal sewage sludge in the manuscript range from 3.7 even to 1124 ng g⁻¹ dw, whereas in sewage sludge/biosolids after treatment of industrial wastewater they range from a few to several hundred ng g⁻¹ dw.