Scalable Remediation of Short-Chain Poly- and Perfluoroalkyl Substances Using Montmorillonite–Polycation Composites: From Batch Adsorption to Continuous-Flow Treatment

Short-chain per- and polyfluoroalkyl substances (PFAS) remain challenging to remove due to their high mobility and low affinity for conventional adsorbents. Herein, we tested and optimized polycation–clay composites for effective and scalable PFAS remediation, focusing on perfluorobutanoic acid (PFBA) as a representative of short-chain species. Among various clay–polycation combinations, montmorillonite (MMT) modified with poly(diallyldimethylammonium chloride) (PDADMAC) achieved the highest PFBA removal. The adsorption mechanism was found to be primarily electrostatic; however, at high PDADMAC loading, steric repulsion blocked PFBA adsorption. Isotherm studies revealed a higher affinity and capacity for long-chain PFAS (PFOA and PFOS); however, effective PFBA removal was achieved in both single- and multi-solute batch experiments. In addition, adsorption of PFBA was unaffected by natural organic matter, demonstrating a clear advantage over carbon-based adsorbents. The composite was granulated for implementation in continuous column tests using real PFBA-contaminated groundwater. Results showed that PFBA concentration in the effluent remained below the current regulatory limit (0.1 μg/L) throughout the experiment (>105 pore volumes), when high hydraulic retention times were applied. Overall, MMT–PDADMAC granules offer a scalable and cost-effective solution for short-chain PFAS remediation.