Concomitant Removal of Perfluorooctanoic Acid (PFOA) and Humic Acid from Water Using a Cationic Cellulose Nanofiber

Per- and polyfluoroalkyl substances (PFAS), particularly perfluorooctanoic acid (PFOA), are persistent, mobile, and difficult-to-remove contaminants in water systems. This study investigates a hybrid adsorption system combining cationic cellulose nanofibers (Cat-CNF) with humic acid (HA) in solution to enhance the removal of PFOA from high-concentration contaminated water sources, such as AFFF-impacted groundwater, industrial effluents, and landfill leachates. Batch experiments spanning a wide concentration range (200-600,000 μg L^-1 PFOA), pH (4.0-11.0), and HA loading (20-100 mg L^-1) revealed that HA strongly binds to Cat-CNF, forming hydrophobic domains that promote PFOA uptake via combined electrostatic and hydrophobic interactions. PFOA adsorption remained high across the full pH range, especially at elevated HA concentrations, and was unaffected by competitive HA presence. Kinetic studies showed that over 90% of PFOA uptake occurred within the first 90 min, reaching equilibrium within 4 h. Isotherm studies showed a steep uptake curve and saturation at ∼250 mg g^-1, with strong fits to both Langmuir (R ² = 0.98) and Freundlich (R ² = 0.89) models. Regeneration experiments demonstrated stable HA retention and progressive improvement in PFOA desorption over multiple cycles, confirming the system's reusability. These findings highlight the Cat-CNF/HA hybrid as a robust and regenerable adsorbent with rapid equilibrium attainment (within 4 h) for PFOA remediation in high-contamination scenarios, with HA contributing both to contaminant binding and adsorbent performance.