The environmental fate of PFAS in wastewater treatment plants: current insights and future directions

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals defined by strong C-F bonds and polar functional groups, giving them chemical–physical properties such as hydrophobicity, volatility, and bioaccumulation. These properties make PFAS persistent and mobile in wastewater systems. Main contributors to PFAS loads entering wastewater treatment plants include industrial effluents discharged into sewer systems, landfill leachates co-treated in municipal WWTPs, and urban runoff conveyed through combined sewer systems. In wastewater treatment plants, PFAS behaviour is influenced by sludge characteristics, metal oxides, pH, temperature, ionic strength, hydraulic retention time, and the presence of precursors, which can transform into stable PFAS during biological treatment. Moreover, PFAS partition between water and sludge is based on chain length: short-chain compounds remain in water, while long-chain ones accumulate in sludge. Discharging water into surface basins can lead to significant pollution, while improper sludge disposal can accelerate soil contamination and degradation. Additionally, PFAS can accumulate in plants and animals over time. Conventional WWTP processes are ineffective, especially for short-chain PFAS, prompting exploration of advanced treatments. Regulatory frameworks have evolved throughout the years, but emerging variants of PFAS remain a concern. Greater regulatory efforts should focus on controlling PFAS at their sources, particularly wastewater discharges, which are now recognized as key pathways for PFAS release into surface waters. To ensure the realization of this outcome, effective PFAS management in WWTPs emerges as both technical and regulatory priority.