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) < dimethylethanolamines (M600) < tributylamines (PSR2Plus). Adsorption on PSR2Plus was much less inhibited by the presence of inorganic anions compared to the other resins. Depending on the water matrix and AER used, the relative residual concentration of perfluorocarboxylates as a function of the number of alkyl carbons in the molecule decreased logarithmically, with adjusted r 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. • Adsorption of ultra-short chain; short chain PFAAs onto anion exchange resins. • PFAA adsorption and inorganic anion concentrations correlate double-logarithmically. • PFAA adsorption inhibited by SO 4 2– /Cl – in the order of A111 > M600 > PSR2Plus. • A tool for resin selection for PFAA removal at specific SO 4 2– /Cl – concentrations. • Predicting stoichiometric PFAA breakthroughs at specific SO 4 2– /Cl – concentrations.