Foam fractionation of PFAS from landfill leachate using a membrane electrochemical reactor

The effective removal of PFAS from chemically complex landfill leachate remains a significant challenge for the solid waste industry. To address this, a membrane electrochemical reactor (MER) was investigated for PFAS removal from landfill leachate at low pH (∼2.0) in the anode chamber. The MER achieved 95.6 % PFAS removal from landfill leachate within seven hours of operation, with 98.3 % of perfluorosulfonic acids (PFSA) and 85.5 % of perfluorocarboxylic acids (PFCA) removed from the leachate. Short-chain PFSAs (C ≤ 6, 92.5-99.1 %) were removed more efficiently than PFCAs (C ≤ 6, 80.8-90 %), possibly due to their stronger affinity for the air-water interface, which enhanced foam-based separation. Long-chain PFAS (C > 6) showed near-complete removal (96.1-100 %). Importantly, PFAS precursors such as fluorotelomer carboxylic acids and perfluoroalkane sulfonyl fluorides were not detected in defoamed leachate, suggesting their removal through both oxidative transformation and foam-phase partitioning in the MER. Simple pH adjustment to 2.0 using concentrated H₂SO₄, conducted for comparison with the MER, resulted in 83.1 % of PFAS separation into foam and 11.3 % into settled solids. Additionally, short-chain PFAS were separated into foam (59.2-84.7 %) and settled solids (5.7-13 %), while long-chain PFAS showed similar trends with 78.3-86 % in foam and 5.3-18.2 % in settled solids. The addition of 0.1 M NaHCO₃ before pH adjustment enhanced foam formation, increasing PFAS separation in foam to 92.5 %. This study highlights MER's effective PFAS removal performance without any solid precipitate generation. Further research should explore the effect of MER operational conditions and leachate-PFAS chemistry on the treatment performance.