Regeneration efficiency of strong‐base anion exchange resin for perfluoroalkyl and polyfluoroalkyl substances

Abstract

The objectives of this research were to evaluate the regeneration efficiency of strong-base anion exchange resin (AER) considering (i) total perfluoroalkyl and polyfluoroalkyl substances (PFAS) concentration, (ii) AER polymer composition, and (iii) regeneration solution composition. Laboratory column experiments were conducted over multiple treatment and regeneration cycles using groundwater spiked with six perfluoroalkyl acids (PFAAs): perfluorobutanoic acid, perfluorohexanoic acid perfluorooctanoic acid, perfluorobutane sulfonic acid, perfluorohexane sulfonic acid, and perfluorooctane sulfonic acid. Regeneration efficiency was calculated as the mass of PFAAs desorbed from the resin during regeneration divided by the mass of PFAAs adsorbed to the resin during treatment. Higher PFAS concentration in the influent resulted in higher PFAS loading on the resin and higher regeneration efficiency. This was especially true for polystyrene AER, which exhibited greater removals of perfluoroalkyl sulfonic acids than perfluoroalkyl carboxylic acids, and greater removal of long-chain PFAAs than short-chain analogs. The most important result was the higher regeneration efficiency for solution composed of salt + organic cosolvent than the aqueous-only solution.

Removal of PFAS from groundwater using weak‐base anion exchange resins

“…The more hydrophobic character of PFOS compared to remaining PFAAs is justified by physicochemical properties such as lower water solubility (570 vs. ≥3400 mg/L), higher octanol–water partition coefficient at pH 7 (log D OW = 3.05 vs. ≤1.58), and higher M W (500.13 vs. ≤414.07 g/mol) (Brooke et al, 2004; Park et al, 2020; Yu et al, 2009). For the same number of carbons, PFSAs have longer alkyl chains with one carbon not residing in the acid head group as opposed to PFCAs; hence the greater adsorption of PFOS than PFOA which was supported in previous studies showing similar results (Dietz et al, 2021; Laura del Moral et al, 2020). Therefore, the uptake of PFOS by the polyacrylic resin can be viewed as a migration to the surface of the resin by repelling water molecules followed by electrostatic binding to the resin.…”

Tools for Understanding and Predicting the Affinity of Per- and Polyfluoroalkyl Substances for Anion-Exchange Sorbents

“…The relative contributions of hydrophobic and electrostatic interactions in the retention of PFAS by anion-exchange sorbents also have implications for sorbent regeneration. Multiple studies have established the need for solvent in addition to salt to regenerate anion-exchange sorbents. ,, Zaggia et al (2016) compared the regeneration of three Purolite anion-exchange resins: A600E, A520E, and A532E. For one resin, A532E, salts alone were sufficient to recover nearly 100% of PFAS.…”

“…Multiple studies have established the need for solvent in addition to salt to regenerate anion-exchange sorbents. 12,39,40 Zaggia et al ( 2016) compared the regeneration of three Purolite anion-exchange resins: A600E, A520E, and A532E. For one resin, A532E, salts alone were sufficient to recover nearly 100% of PFAS.…”

Removal of perfluoroalkyl acids and common drinking water contaminants by weak-base anion exchange resins: Impacts of solution pH and resin properties

“…The high value of the pH-corrected octanol-water partition coefficient (log D ow ) for PFOS (Table S1) is indicative of its substantially more hydrophobic and less water soluble character than remaining PFAAs (i.e., two orders of magnitude) ( Park et al., 2020a ; Zeng et al., 2020 ). PFOS partitions even into relatively polar resin (e.g., polyacrylic) in response to a driving force while the polystyrene resin has inherent affinity for hydrophobic compounds ( Dietz et al., 2021 ). PFAAs become more hydrophobic (i.e., less polarizable) as the number of electron-withdrawing C-F n group increases given the highly nonpolarizable character of fluorine atoms (i.e., high electron binding energy) ( Liu and Sun, 2021 ; Moody and Field, 2000 ).…”