PFAS Remediation through an Ion-Exchange Resin: Role of PFAS Chain Length and Investigation of Adsorption Behavior in a Mixed-Solute System

Abstract

The widespread occurrence of per- and polyfluoroalkyl substances (PFAS) in aquatic environments has necessitated the development of effective treatment technologies capable of removing both short-chain and long-chain PFOA. In this study, the performance of an unreported commercial resin, Monoplus TP109, was evaluated for the removal of short- and long-chain PFOA. Batch adsorption experiments were conducted to assess adsorption capacity, kinetics, pH effects, and the influence of PFAS chain length, while regeneration studies investigated the effectiveness of various organic solvent and inorganic salt combinations. The resin exhibited substantial adsorption capacities toward all investigated PFAS. The maximum equilibrium uptake capacities predicted by the Langmuir isotherm model determined using the Langmuir model were 1732.16 μg/g for PFOA, 1582.67 μg/g for PFPeA, 1432.87 μg/g for PFBA, 1421.32 μg/g for PFBS, and 1248.729 μg/g for PFPrA for the isotherm fitting performed for the data in the concentration range of 1−100 μg/L each. In single-solute systems, PFAS uptake generally increased with the increasing carbon−fluorine chain length. However, in mixed-solute systems, enhanced partitioning of the short-chain PFPrA toward the resin phase was observed. The resin demonstrated excellent selectivity for PFAS under a realistic water matrix of domestic tap water. PFAS adsorption occurred through a synergistic combination of electrostatic attraction, ion exchange, hydrophobic partitioning, and pore-filling processes. Continuous-flow column experiments revealed distinct retention behaviors among PFAS species in a mixed-solute system. The breakthrough of PFOA and PFBS occurred at approximately 11,500 bed volumes, while no breakthrough of PFPrA, PFBA, and PFPeA was observed up to 17,000 bed volumes. Regeneration studies identified 50% ethanol and 0.1% NaCl aqueous solution as the most effective regenerant. Although complete desorption was not achieved, the resin maintained high PFAS removal efficiencies (approximately 90−97%) over five adsorption−desorption cycles, demonstrating promising reusability and operational stability.