Pilot scale treatment of PFAS-contaminated groundwater in a subsurface flow constructed wetland–evaluating multiple plant species

Groundwater contamination by per- and polyfluoroalkyl substances (PFAS) is an emerging threat to drinking water quality, highlighting the need for effective treatment solutions. This study investigated subsurface flow constructed wetlands for treating groundwater contaminated with PFAS. The wetlands used a peat, biochar, and lightweight expanded clay aggregate (LECA) filter substrate, planted with either tufted sedge (Carex elata), fiber hemp (Cannabis sativa Futura 75), or an intercropping of the two Salix clones S. Wilhelm and S. Loden. The experiment was conducted under field conditions in Sweden, during one growing season, using PFAS-contaminated groundwater impacted by landfill leachate. The study showed accumulation of PFAS in all plant species and the peat and biochar part of the filter substrate, with short-chain PFAS and perfluoroalkyl carboxylates (PFCAs) dominating when considering the whole plants (57 % and 77 % of ƩPFAS, respectively) and long-chain PFAS and perfluoroalkyl sulfonates (PFSAs) dominating in the peat and biochar filter substrate (77 % and 54 % of ƩPFAS, respectively). Sorption to the filter substrate was shown to be the primary mechanism for PFAS removal. The highest plant PFAS concentrations were found in leaves, followed by roots, for all species. There was a difference in the PFAS composition profile when comparing different plant tissues, with PFCAs dominating in leaves (84 % of ƩPFAS) and PFSAs dominating in roots (66 % of ƩPFAS). All plant species were determined to have an above-ground tissue/water phase concentrations >10/1 for C₃-PFCA (PFBA). This was also observed for C. sativa with C₄- and C₇-PFCAs (PFPeA, PFOA), and C₄- and C₅-PFSAs (PFBS, PFPeS), for C. elata with C₈-PFSA (L-PFOS), and for S. Loden with PFPeA. ∑PFAS phytoextraction potential from landfill leachate-impacted groundwater (mg/ha yr) was estimated to be 940 ± 670 for C. sativa, 390 ± 310 for S. Loden, 330 ± 160 for S. Wilhelm, and 160 ± 56 for C. elata.