PFAS Removal in Drinking Water Treatment Evaluating Granular Activated Carbon Performance Across Filter Conditions and Compound Chain Lengths

Abstract

Safe drinking water requires the effective removal of persistent chemical contami nants, of which per- and polyfluoroalkyl substances (PFAS) represent a particularly concerning group due to their environmental persistence, resistance to degradation, and documented toxicity at low concentrations. This study investigated the occur rence of PFAS in drinking water systems, evaluated the limitations of conventional and advanced treatment methods, and examined how the condition of granular ac tivated carbon (GAC) filter media affects PFAS removal efficiency. Batch adsorption experiments were conducted using fresh (F-GAC), thermally re generated (R-GAC), and aged (A-GAC) filter media across a range of PFAS com pounds varying in carbon chain length, including the ultra-short-chain TFA (C2) through to the long-chain PFOA (C8). Removal efficiency, adsorption kinetics, and isotherm behaviour were analysed and compared across filter conditions. The results demonstrated that GAC filter condition has a substantial impact on removal performance. Fresh GAC achieved >99% removal for all analysed PFAS compounds, with kinetics well described by the pseudo-first-order model, consistent with rapid adsorption onto abundant accessible surface sites. Regenerated GAC retained considerable removal capacity, though with greater dependence on chain length and kinetics better described by the pseudo-second-order model, reflecting increased surface heterogeneity and more complex adsorption interactions following thermal regeneration. The aged GAC filter showed severely limited capacity, achiev ing meaningful removal only for PFOA, while short-chain and ultra-short-chain com pounds exhibited desorption behaviour, with effluent concentrations exceeding influ ent concentrations. Across all conditions, adsorption affinity and capacity increased with carbon chain length, consistent with the role of hydrophobic interactions as the dominant adsorption mechanism. These findings highlight the critical importance of filter condition in drinking water treatment and suggest that aged GAC may pose an active risk of PFAS release. Timely regeneration or replacement of GAC filter media is essential for maintaining effective PFAS removal, particularly for shorter-chain compounds.