Sorption of Per-and Poly-Fluoroalkyl Substances on geotextile components of geosynthetic composite lining systems

We present here an experimental investigation on the sorption kinetics of two perfluoroalkyl acids (PFAAs): namely, perfluorooctane sulfonic acid (PFOS) and perfluorobutane sulfonic acid (PFBS) to polypropylene nonwoven cover and woven carrier geotextiles commonly used in geosynthetic clay liners, as well as polyester nonwoven geotextiles typically used in modern geosynthetic composite lining systems for protection function purposes. In this study, the time required for the adsorption of each PFAA compound on geotextiles to reach equilibrium was 1-72h. The fraction of analyte remaining in the liquid phase at equilibrium followed the order: nonwoven polyester > woven polypropylene > nonwoven polypropylene for both PFOS and PFBS, suggesting that the structural and polymeric composition of the geotextile fibres strongly dictates the sorption. The PFAAs exhibited varying sorption affinities following the order: PFOS > PFBS. Thus, it can be inferred that PFAAs with longer carbon chains prefer partitioning to the solid phase. Furthermore, the biexponential adsorption model, which postulates sorption as a two-step mechanism controlled by diffusion, provided a better fit for polypropylene (PP) geotextiles than the pseudo-first order (PFO) and pseudo-second order (PSO) models. For the polyester (PET) geotextile, PFO, PSO, and biexponential adsorption models provided a similar fit, suggesting that PFAAs adsorption onto PET geotextiles was mainly through physical interactions. Since the PFO and PSO models do not explain the diffusion of solute into an adsorbent, it is inferred that the diffusion of molecules through the PET geotextile was minimal due to the absence of available channels and pores.