Innovative hybrid approach for enhanced PFAS degradation and removal: Integrating membrane distillation, cathodic electro-Fenton, and anodic oxidation

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants that pose significant toxicity risks to humans and ecosystems. Traditional advanced oxidation processes using boron-doped diamond (BDD) anodes degrade PFAS in wastewater effectively but suffer from slow kinetics and high energy costs, limiting commercial application. This study introduces a hybrid process combining cathodic electro-Fenton (EF), anodic oxidation via a BDD anode, and membrane distillation (MD) to improve perfluorooctanoate (PFOA) degradation efficiency and reduce energy use. Increasing the current density from 50 to 500 A/m2 significantly raised the concentration of produced H2O2 from 0.25 mM to 2.3 mM, accelerating PFOA degradation and mineralization. At 50 A/m2, no mineralization of PFOA occurred in the EF/BDD process, while the EF/BDD-MD process achieved 45% mineralization due to increased PFOA concentration in the electrolytic cell. At 500 A/m2, the EF/BDD-MD process achieved 95% PFOA mineralization. Findings reveal that while EF-generated •OH radicals assist degradation, the BDD(•OH) anode was the primary driver, driving 80% of the reaction. This degradation was initiated by direct electron transfer at the BDD surface, followed by homogeneous and heterogeneous •OH radicals enhancing the degradation and mineralization process. The hybrid process also lowered energy consumption, making the treatment feasible for large scales.