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.