PFAS removal from water via Foam Fractionation with Non-Thermal Plasma

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants detected in surface and drinking waters at ng/L concentrations. This study examines Foam Fractionation (FF) viability for PFAS removal under environmentally relevant conditions (500 ng/L), with attention to potential enhancement provided by Non-Thermal Plasma (NTP) air. Challenges included the in-house construction and validation of a laboratory-scale experimental setup (aeration, foam collection and off-gas treatment units), NTP integration and the evaluation of critical operational parameters (surfactant addition, airflow rate, bubbling time, matrix ionic strength, injected gas type). Analytical PFAS determination was performed by LC-MS. The system demonstrated effective separation and PFAS enrichment in the foamate: under optimized conditions, removal efficiency exceeded 70%, with peaks approaching 90-100% and foam enrichment exceeded 1000%. Significant variability was observed due to low influent concentrations, analytical uncertainty near detection limits and challenges in achieving stable and reproducible foam. Foam formation emerged as a critical factor: a cationic surfactant was necessary to ensure stable foam, enhancing the removal of long-chain PFAS and sulphonates. The absence of surfactant resulted in poor performance while short-chain PFAS showed a general greater persistence. Ionic strength of the water also influenced process efficiency, with higher conductivity promoting stable foam through electrostatic and salting-out effects. NTP-air did not provide clear quantitative improvement over untreated air, but trends suggested potential benefits, especially for long-chain and sulfonated compounds. Despite these limitations, the results confirm the feasibility of FF for PFAS removal at environmentally relevant concentrations, highlight the potential of NTP as a complementary strategy and underline the importance of matrix effects and operational stability for full-scale application.