How clean is clean enough? Short-chain PFAS remain dominant in treated landfill leachate.

Per and polyfluoroalkyl substances (PFAS) have emerged as ubiquitous contaminants in municipal solid waste (MSW) landfill leachates due to their widespread industrial applications, environmental persistence, and the disposal of PFAS-containing waste in landfill. This study presents a multi-regional investigation of PFAS occurrence, influencing factors, and treatment performance in 17 landfill leachates and 9 corresponding effluents across China. Sum PFAS concentrations in raw leachates ranged from 634 to 46,400 ng/L, with short-chain perfluoroalkyl acids (PFAAs) dominating the compositional profile (65.4 to 97.2%). Landfill age exhibited a significant positive correlation with PFAS levels (p ≤ 0.05). Moreover, physicochemical parameters of leachate such as electrical conductivity and ammonia nitrogen exhibited strong positive correlations with PFAS concentrations (p ≤ 0.05), while meteorological variables showed compound-specific (perfluorobutanoic acid, PFBA and perfluorodecanesulfonic acid, PFDS) associations. PFAS concentrations in the treated effluents ranged from 6.29 to 7390 ng/L, with short-chain PFAAs dominating. Among the evaluated technologies, two-stage (TS) membrane bioreactor (MBR) combined with membrane separation systems achieved the lowest effluent concentrations (<10 ng/L) and the highest apparent removal efficiencies (up to ∼99.9%) in this dataset. However, removal effectiveness varied considerably across compounds, especially for short-chain PFAAs and PFAA-precursors. Overall, this study provides an assessment of PFAS occurrence and treatment performance in landfill leachate systems, highlights key environmental and operational factors, and provides insights for improving PFAS management in landfill leachate treatment.