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. There-
fore, 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 func-
tional 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 per-
fluorocarboxylates as a function of the number of alkyl carbons in the molecule decreased logarithmically, with
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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.