Fate and removal of per- and polyfluoroalkyl substances throughout landfill leachate treatment processes: Uncovering precursor transformation and sludge-mediated reappearance.

Per- and polyfluoroalkyl substances (PFAS) in municipal solid waste (MSW) landfill leachate have emerged as a critical research focus because of their substantial environmental and health risks. However, the fate and transformation of PFAS across different treatment processes, particularly within specific techniques such as biotreatment, remains understudied in current research. This study systematically investigated the occurrence, fate, and removal of PFAS in a full-scale MSW landfill leachate treatment system in Shanghai, China. Thirty-two PFAS were analyzed in the raw leachate and the whole treatment process, including the equalization tank, the membrane bioreactor (MBR) system, and the nanofiltration (NF) process. Results showed that perfluorooctanoic acid (PFOA) and perfluorobutanesulfonic acid (PFBS) were the predominant compounds in both the raw leachate and effluents. The MBR process exhibited negative removal efficiencies for short-chain PFAS (-187.4 % to -103.5 %), indicating substantial precursor transformation, while NF achieved effective removal (42.1 % to 95.6 %). Solid phases of the sludge samples accumulated long-chain PFAS (log K_d up to 4.4), acting as significant secondary sources. Mass flow analysis revealed that denitrification processes increased the absolute daily load of PFOA (calculated as concentration × flow rate) by 4286 %, with the total oxidizable precursor (TOP) assays demonstrating thefluorotelomer-based precursors were the major contributors to perfluoroalkyl carboxylic acids (PFCAs) formation. The findings provide essential insights for developing more effective leachate treatment strategies and sludge management approaches to mitigate PFAS environmental release from MSW landfills.