Enhanced retention of PFAS by air-sparging

Per- and polyfluoroalkyl substances (PFAS) are a group of over 10,000 synthetic chemicals known for their persistence, mobility, and adverse health effects, including bioaccumulation and carcinogenicity. Their widespread industrial use and environmental persistence have led to global contamination, particularly threatening groundwater resources. Despite regulatory restrictions, remediation remains a major challenge due to PFAS resistance to conventional degradation processes. This study, inspired by Newell et al. (2021), investigates the potential application of in situ air-sparging – a technique historically used for volatile organic compounds – for the remediation of PFAS-contaminated groundwater. PFAS behave as surfactants and exhibit strong partitioning to air-water interface, that induces their adsorption into rising gas bubbles generated during air-sparging. This facilitates vertical transport through the porous medium, as PFAS are carried upward by the buoyant flow of the sparging gas. The process results in their progressive accumulation from the saturated zone toward the water table. The goal is to assess whether air-sparging can promote vertical transport and retention at the air-water interface in the capillary fringe. The potential advantages of using this technique include a reduction in the extent of the PFAS-contaminated plume and an enhancement in PFAS removal from the subsurface. Laboratory-scale column experiments were conducted where air-sparging was applied over a six-day period to evaluate PFAS migration and retention behaviors. A mixture of short- and long-chained PFAS and precursors was tested in coarse and fine sand solid matrix. Water samples were collected periodically from lateral ports along the column. Results show that after six days of air-sparging, PFAS concentration decreased at the bottom of the column and increased at intermediate depths, indicating that vertical mobilization occurred in both coarse and fine solid matrices. Within 48 hours of air-sparging, long-chained PFAS and precursors migrate vertically, accumulating at the air-water interface in the capillary fringe. Short-chained PFAS exhibited a similar migration behavior, though over a longer timescale and at lower concentrations, due to their lower tendency to adsorption at the air-water interface. These results demonstrate that air-sparging can effectively induce vertical PFAS transport and enhance their redistribution in the subsurface, supporting its potential application for in situ remediation strategies. While the results are promising, further studies under field conditions are needed to assess the long-term effectiveness and scalability of air-sparging for PFAS remediation.