Evaluation of Commercial Sorbents for Separation of Ultrashort-, Short-, and Long-chain Per- and Polyfluoroalkyl Substances (PFAS) from Municipal Wastewater Effluent

Abstract

PFAS are a diverse class of synthetic compounds that, are persistent, mobile, and have been detected ubiquitously in the environment in all parts of the world. In addition to the continued detection of "legacy PFAS" such as, PFOA and PFOS, there is increasing awareness and concern over ultrashort-chain and short-chain perfluoroalkyl acids (PFAAs) in treated wastewater effluent. Traditional adsorptive media such as granular activated carbon (GAC) and ion exchange (IX) resins have demonstrated inhibited PFAS removal due to the presence of organic matter (OM), co-occurring ionic constituents, and relatively poor uptake of short- and ultrashort-chain PFAAs. This study evaluated commercially available sorbent media for the removal of ultrashort-, short-, and long-chain per- and polyfluoroalkyl substances (PFAS) from a variety of aquatic matrices including ultrapure water, synthetic wastewater effluent and treated municipal wastewater effluent – with a focus on addressing the influence of matrix interferences in the form of wastewater effluent-derived organic matter and co-occurring constituents on PFAS removal. The adsorptive media we evaluated included GACs, non-selective and "PFAS-selective" ion exchange resins (IX), and two alternative adsorbent materials that are commercially marketed as PFAS treatment technologies: an anonymized surface-modified clay (SMC), and a β-cyclodextrin-based polymeric adsorbent (DEXSORB®, Cyclopure®). Batch adsorption capacity and kinetics tests were conducted in both ultrapure (UP) and synthetic wastewater (SW) matrices to characterize PFAS removal prior to continuous-flow rapid small-scale column tests (RSSCTs) using artificially spiked tertiary treated municipal wastewater effluent from an ultrafiltration (UF) membrane pilot system. In UP water, long-chain PFAS outcompeted and displaced (ultra)short-chain PFAS across all sorbents, suppressing (ultra)short-chain uptake and driving strong preferential adsorption of long-chain PFSAs and PFCAs. While GAC and DEXSORB® exhibit pronounced chain-length–dependent sorption dominated by hydrophobic interactions, the IX resins show more balanced uptake across PFAS chain-lengths, reflecting the greater role of electrostatic interactions in their removal. Despite strong adsorption in ultrapure water, IRA910 IX performed similarly to GAC in the SW matrix, demonstrating inhibited adsorption kinetics and capacities across all PFAS chain-lengths, especially for PFCAs and short- and ultrashort-chain PFAS, while PFA694 IX and DEXSORB® were least affected by the SW matrix. In the RSSCTs, the PFA694 IX resin treated the suite of 18 PFAS to the lowest effluent concentrations for the longest operational times compared to DEXSORB, F400 GAC, and non-selective IRA910 IX resin. Although, PFA694 IX only exhibited incremental improvement over GAC for treating short- and ultrashort-chain PFCAs. Agreement between SW batch tests and column results underscores the need to evaluate PFAS treatment media under realistic wastewater conditions. Fundamentally, further characterization and elucidation of the physical and chemical characteristics of the adsorbent media, particularly the proprietary PFAS-selective IX resins, in addition to evaluations of single-PFAS solute systems in ultrapure and complex aqueous matrices, will help improve the mechanistic understanding of the removal of ultrashort-, short-, and long-chain PFAAs and other PFAS widespread in the environment and municipal wastewater effluents. The results of this study suggest that in an ideally designed treatment train scenario installation of a PFAS-selective IX resin employed as a polishing step following tertiary treatment of secondary wastewater effluent could be a feasible method to target PFAS for removal from municipal wastewater.