Adsorption dynamics of four per-and polyfluoroalkyl substances (PFAS) onto activated sludge (AS) and aerobic granular sludge (AGS)

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants of emerging concern, known for resisting removal in conventional biological wastewater treatment, like activated sludge (AS). In biological systems, adsorption is the primary mechanism for removing PFAS, creating a need to explore the adsorption extend of alternative treatments which can more effectively sorb PFAS. The primary goal of this study was to identify which sludge type achieves the highest adsorption capacity and, thus, the most effective PFAS removal. The experimental design encompassed on the adsorption dynamics of four representative PFAS compounds, a mix of two perfluorosulfonic acids (PFSAs) and two perfluoroalkyl carboxylic acids (PFCAs), using activated sludge and aerobic granular sludge (AGS) as sorbents. Results demonstrate that AGS exhibits a tenfold greater adsorption capacity for PFAS than AS, as evidenced by significantly higher K d values. While AS presented maximum K d values of −40, 32, 57 for PFPeA, PFOA and PFDS, the K d values using AGS were 254, 205 and 207, respectively. PFDS was the compound with the highest adsorption affinity in both sorbents, achieving K d values of approx. 11000 for AS and 71000 for AGS. This discrepancy in adsorption capacity could be attributed to AGS’ granular structure, which may trap PFAS more effectively and the high surface hydrophobicity, which allows for stronger hydrophobic interactions with PFAS molecules. These findings underscore the prospective of aerobic granular sludge as an enhanced treatment technology for PFAS separation in WWTPs. • PFDS had the highest adsorption, indicating strong retention of long-chain PFAS by sludge. • AGS adsorbed up to 10 × more PFAS than AS, highlighting its potential for improved removal. • AGS followed a multilayer isotherm, suggesting its structure enhances PFAS adsorption. • Negative Kd values showed significant PFAS desorption from AS, posing a risk of re-release. • The impact of synthetic wastewater vs. Milli-Q varied depending on the order of testing.