Evaluating the influence of air sparging technique on PFAS desorption and mobilization in soil using short-term column experiments

Air sparging is a promising in situ technique for mobilizing per - and polyfluoroalkyl substances (PFAS) via air–water interfacial processes and advective mixing. The short-term effects of air sparging on PFAS desorption were investigated using field-contaminated soil collected from the Sundsvall Timrå Airport site (Sweden). Experiments were conducted under a fixed influent flow of 50 mL/min. Trial 1 employed a single soil column operated sequentially under water-only conditions, followed by air sparging. Trial 2 used two parallel columns: one operated under water-only flow, and the other under combined water flow and air sparging. In Trial 1, sparging increased aqueous perfluorooctane sulfonate (PFOS) concentrations by ~30-fold, while 6:2 fluorotelomer betaine (6:2 FTAB) and 6:2 fluorotelomer sulfonate (6:2 FTSA) increased ~8-fold and ~ 1.5-fold, respectively. In Trial 2, the water-only column resulted in declining aqueous PFAS masses (0.01–0.30-fold of initial values), indicating redistribution without effective mobilization. In contrast, the water-air column exhibited substantial increases in aqueous-phase mass, indicating enhanced soil-to-water mass transfer. Long-chain sulfonates such as perfluoroheptane sulfonate (PFHpS), perfluorohexane sulfonate (PFHxS), and PFOS showed pronounced mobilization and foam enrichment under sparging conditions. Foam generated during sparging acted as an additional removal pathway, capturing up to 38% of perfluorooctanoate (PFOA), 21% of PFHpS, and 16% of 6:2 FTAB. Most PFAS decreased in the soil phase under sparging, with evidence of compound-specific redistribution (e.g., PFHxS). Overall, air sparging enhanced PFAS transfer from soil to mobile phases and promoted interfacial enrichment, supporting its application for targeted in situ management of saturated PFAS source zones.