Kinetic and isotherm insights on PFAS sorption to commercial colloidal and powdered activated carbons

The use of colloidal (CAC) and powdered (PAC) activated carbon is an effective groundwater remediation technology for perfluoroalkyl substances (PFAS). Laboratory-derived sorption kinetic and isotherm data for materials of contrasting characteristics are critical for evaluating sorption performance, particularly when accounting for site-specific groundwater chemistry. Batch sorption isotherms were conducted for eleven PFAS (including ultra-short PFAS such as TFA and TFMS as well as other short- and long-chain PFAS) in ultrapure water using two CAC product and one PAC materials to assess sorption differences depending on both PFAS and AC properties, while sorption kinetics were quantified for PFOA and a single representative AC. Sorption isotherms are generally non-linear and follow the Freundlich and Polanyi-Dubinin-Manes models, with less sorption for activated carbons containing organic stabilizers. Sorption kinetics reveal contributions of both film and intraparticle pore diffusion, with the latter dominating at late times. Solid-liquid distribution coefficients (log K d ) range from 1.3 to 10.8 depending on PFAS concentration, chain length and activated carbon characteristics, and indicate strong PFAS sorption affinity. Furthermore, log K d values correlate inversely with PFAS water solubility, providing a basis to interpolate sorption for untested PFAS. Finally, sorption experiments using impacted groundwater with high salinity and elevated dissolved organic carbon yielded log K d values ranging from 3.7 to 7.4 and showed good agreement with solubility-based predictions, confirming the high potential for AC to reduce PFAS mobility. Overall, these results provide a quantitative basis for AC selection and for predicting PFAS immobilization under field conditions, including estimates of equilibrium behavior.