Sorption and desorption of per-fluoroalkyl substances (PFAS) on waste containment liner components

This paper examines the sorption kinetics, isotherms and desorption behaviour of six per-fluoroalkyl substances (PFAS) from single- and multi-compound solutions with various landfill liner materials currently in use and those proposed for future lining systems. The compounds examined include perfluorooctanesulfonic acid, perfluorooctanoic acid, perfluorohexanoic acid, perfluorobutanesulfonic acid, pentafluoropropionic acid and trifluoromethanesulfonic acid. The impact of landfill leachate on the sorption properties of selected liner components, namely geotextiles, bentonite and a proposed bentonite modifier, was also investigated. No significant competitive effects on sorption were observed at typical environmental PFAS concentrations (1-80 nM). Biexponential and pseudo-second-order kinetics models sufficiently described the sorption process. Furthermore, the Freundlich isotherm model generally provided a better fit to the experimental data than the Langmuir model. The maximum PFAS sorption capacity for each material followed the order: ion exchange resin > activated carbon amended bentonite > clays > nonwoven polypropylene geotextile > woven polypropylene geotextile > bentonite > polyester nonwoven geotextile. Sorption generally increased with longer carbon-chain lengths, with sulfonate species exhibiting a stronger affinity than carboxylic acids. The desorption of PFAS from the liner constituents aligned with their sorption behaviour. The presence of matrix co-constituents in leachate reduced the sorptive affinity of most PFAS. The results suggest that incorporating activated carbon into geosynthetic clay liners may reduce the migration of long-chain PFAS but may be less effective for shorter-chain compounds. Adding additional sorptive materials to lining systems, such as ion exchange resins, may be necessary to effectively attenuate short and ultrashort PFAS compounds.