Electrokinetically Assisted Adsorption of Per- and Polyfluoroalkyl Substances in Granular Activated Carbon

Sammanfattning

Per- and polyfluoroalkyl substances comprise a large group of anthropogenic persistent contaminants associated with adverse health effects. They do not fully degrade in natural environment and can migrate through air, soil and water systems. Primarily sources for PFAS include Aqueous Film-Forming Foam (AFFF), landfill leachate, and contaminated biosolids. Activated carbon is one of the most widely used sorbents for PFAS removal and can be applied in-situ, for example, in permeable reactive barriers. However, sorbent saturation limits its long-term remediation performance. Therefore, the aim of this study was to investigate the effect of electrokinetic (EK) on prolonging the lifespan of granular activated carbon (GAC). In addition, the immobilization of PFAS by GAC in groundwater generated from contaminated soil was evaluated. The method involved pumping generated groundwater through five columns; one column with sand as a control, two duplicate GAC columns and two duplicate GAC columns with EK treatment. Nineteen PFAS compounds were analysed of which eleven were detected and reported. The results of batch adsorption tests and column experiments were consistent, showing that PFSAs exhibited stronger adsorption than PFCAs. Adsorption efficiency increased with compound hydrophobicity. For PFSAs, adsorption followed the order: PFNS > PFOS > PFHpS > PFHxS > PFPeS > PFBS, while for PFCAs the order was PFOA > PFHpA > PFHxA > PFPeA > PFBA. For all detected PFAS compounds, the effluent concentrations were consistently lower in the columns operated with EK treatment, indicating enhanced adsorption performance. However, PFAS breakthrough was not reached during the experimental period, suggesting that longer operational times are required to fully evaluate sorbent longevity. In addition to PFAS mobilization induced by the applied electric field, the lower pH values generated during EK treatment may have contributed to enhanced PFAS adsorption onto GAC.