PFAS-contaminated groundwater treatment by forward osmosis using pressure-stimuli-responsive nanofiltration membrane: Effects of chain length and operating conditions

Significant health concerns have been raised resulting from the increasing detection of per- and polyfluoroalkyl substances (PFAS) in various water bodies. Attention has shifted beyond long-chain compounds, carbon-chain length ≥ C7, to include the more mobile and persistent short, carbon-chain length C4-C6, and ultra-short-chain PFAS, carbon-chain length C1-C3. This study systematically investigated the rejection of PFAS-contaminated groundwater using a pressure-stimuli-responsive nanofiltration (PSRNF) membrane with varying pressures and pH of the feed solution. The rejection efficiency of long- and short-chain PFAS by the PSRNF membrane increased with both increasing pressure and pH, achieving 99.1 % to 100 % for long chains and 96.9 % to 98 % for short chains. In contrast, the ultra-short-chain PFAS rejection efficiency by the PSRNF membrane decreased at acidic pH with increasing pressure, but increased at alkaline pH, achieving up to 91.4 %. There was a higher tendency for membrane adsorption of long-chain PFAS due to strong hydrophobic interactions at low pressure, resulting from a longer contact time with the membrane. Ultra-short-chain PFAS exhibited no adsorption across all conditions due to their low hydrophobicity and minimal affinity for the membrane surface. This performance was closely linked to both the physicochemical properties of the PFAS species and the operational environment, such as pH and applied pressure. These findings highlight both the practical benefits of the PSRNF membrane and the importance of optimising operating conditions for effective removal of PFAS and heavy metals from contaminated water.