Evaluation of the adsorption behavior of mixed perfluoroalkyl and polyfluoroalkyl substances onto granular activated carbon and Styrene-divinylbenzene resins

Because of the remarkable chemical structure of perfluoroalkyl and polyfluoroalkyl substances (PFAS), as well as the complex conditions of water, selecting an appropriate adsorbent for treating PFAS is critical. Adsorption needs to be environmentally friendly, low cost, and consider the types of adsorbents that work well in mixed PFAS solutions. In the present study, we used mixed PFAS to estimate the PFAS activity. This research aimed to evaluate and compare the efficacy of the adsorption of PFAS from water using different adsorbents: granular activated carbon (GAC), IRA 910 (strong anion resin), and DOWEX MB-50 (mixed exchange resin). Batch adsorption isotherms and kinetic studies were performed for perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and perfluorohexane sulfonic acid (PFHxS). Freundlich models consistently described the kinetic behavior with a high correlation coefficient (R-2 > 0.98). PFAS adsorption capacities on GAC and IRA910 were dependent on the chain length (PFOS > PFOA > PFHxS). The adsorption capacity of DOWEX MB-50 decreased because of the sulfonate effects (PFOS > PFHxS > PFOA). The rate constants (k(2)) that represented the adsorption of PFAS on different adsorbents observed within 96 h were accurately determined by the pseudo-second-order (PSO) model. GAC achieved followed the relationship k(2)(PFOS) > k(2)(PFOA) > k(2)(PFHxS). Furthermore, k(2) of IRA910 decreased in the order of k(2)(PFOA) > k(2)(PFOS) > k(2)(PFHxS), implying that IRA910 promoted hydrophobicity more significantly on the adsorption of PFCAs than perfluoroalkane (-alkyl) sulfonic acids. The kinetics of DOWEX MB-50 revealed k(2)(PFHxS) > k(2)(PFOS) > k(2)(PFOA) because gel-type resins like DOWEX MB-50 are more suitable for shorter-chain PFAS. Further investigation is needed to determine the effect of organic matter under natural conditions and evaluate adsorptive selection caused by operational complexities.

Automated summary

Selecting an appropriate adsorbent for treating perfluoroalkyl and polyfluoroalkyl substances (PFAS) is critical due to their remarkable chemical structure and the complex conditions of water. In this study, different adsorbents including granular activated carbon (GAC), IRA 910 (strong anion resin), and DOWEX MB-50 (mixed exchange resin) were evaluated and compared for their efficacy in adsorbing PFAS from water. The kinetic behavior of PFAS adsorption on the adsorbents was described by Freundlich models with high correlation coefficients. The adsorption capacity of GAC and IRA910 depended on the chain length of PFAS, while DOWEX MB-50 showed decreased adsorption capacity due to sulfonate effects. The rate constants for PFAS adsorption were accurately determined using the pseudo-second-order model, with GAC being the most effective for PFOS, IRA910 being the most effective for PFOA, and DOWEX MB-50 being the most effective for PFHxS.