Effective PFAS degradation in aquatic systems: Performance evaluation and mechanistic drivers of peroxydisulfate activation by thermal energy

Per- and polyfluoroalkyl substances (PFAS) are highly persistent contaminants due to strong C–F bonds, making conventional water treatment ineffective for PFAS destruction. In this study, heat-activated peroxydisulfate (PDS, S 2 O 8 2- ) was evaluated for PFAS degradation in aquatic systems. Degradation efficiency of 99% for perfluorooctanoic acid (PFOA, C 0 = 0.3 mg L⁻ 1 ) was achieved within 24 hours using a heat-activated peroxydisulfate (PDS, 30 mM) system at 80 °C (T:80 °C/PDS) and pH 5.0 (unadjusted). The degradation of PFOA remained consistently high (97–99%) across a broad pH range of 3 to 11, indicating the robustness of the T:80 °C/PDS system. Reactive oxygen species (ROS) formation was confirmed by scavenger tests and electron spin resonance (ESR) spectroscopy analysis, revealing hydroxyl radicals ( • OH) and sulfate radicals (SO 4 • ⁻), with non-radical singlet oxygen ( 1 O 2 ) contributing to a multi-pathway transformation mechanism. Degradation was significantly inhibited by chloride (Cl⁻), bicarbonate (HCO 3 ⁻), phosphate (HPO 4 2 ⁻), and humic acid (HA), indicating radical scavenging and competitive interactions. Tentative degradation pathways were proposed based on the identified byproducts. In spiked surface water from Lake Tuscaloosa, PFOA degradation remained high (>97%), validating performance in real-world matrices. The T:80 °C/PDS system also effectively degraded PFBA (98%) and GenX (96%), moderately degraded PFOS (60%), and exhibited minimal degradation of PFBS and PFHxS (15% and 16%, respectively). These differences were likely attributed to stronger C–S bonds and higher electron density, reducing susceptibility to radical attack. The T:80 °C/PDS system effectively removed long-chain PFAS, remained robust across pH variations, and worked in real water, demonstrating potential for sustainable remediation.