The effect of inorganic anions on the adsorption of perfluoroalkyl acids to various polymeric anion exchange resins

Anion exchange resins (AERs) are promising adsorbents for removing perfluoroalkyl acids (PFAAs). However, little is known about competitive effects of specific co-solutes at typical drinking water concentrations. Therefore, this study investigated the adsorption of eight PFAAs (1–7 perfluorinated carbons) on three commercial AERs (A111, M600, PSR2Plus) with different functional groups, and examined competitive effects of chloride and sulphate at varying concentrations. Using regression modelling and the stoichiometric breakthrough model, PFAA breakthroughs in fixed-bed filters were simulated, dependent on the concentration of inorganic anions. Generally, the adsorption of PFAAs increased with increasing number and length of alkyl moieties in the functional resin group in the order of dimethylamines (A111) 2 ≥ 0.93 and slopes between −0.25 and −0.65 log units per additional carbon. When sulphate and chloride were present simultaneously, sulphate had a stronger inhibitory effect on the adsorption of PFAAs on all resins. Furthermore, a double logarithmic correlation was found between the adsorption of PFAAs and the concentrations of inorganic anions. The results and procedures presented here can be used by water utilities, scientific consultants, and researchers to facilitate the informed selection of AERs for PFAA adsorption and their practical application in fixed-bed filters. © 2024 The Authors