Enhancing PFASs Destruction in an Electro-Oxidation System by Homogeneous Hydroxyl Radical Production

An electro-oxidation (EO) system using boron-doped diamond (BDD) anodes shows promising removal performance of per- and polyfluoroalkyl substances (PFASs). To further enhance PFAS destruction, an electro-Fenton (EF) cathode was introduced and combined with the BDD anode to augment hydroxyl radicals (HO•) production and improve the degradation efficiency of PFASs. The integrated system achieved 99% and 93% removal efficiency of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) within 5 h at a potential of 3.5 V, with corresponding defluorination efficiencies of 65% and 51%, exhibiting better energy efficiency compared with other systems. Compared to the direct electron transfer on BDD anode surface, the HO• attack of bound PFASs on BDD can significantly decrease the free energy barrier for the deconstruction of tail groups of PFASs. The initial step was effectively complemented by homogeneously distributed HO• generated via the EF process in the bulk solution, which subsequently promoted the decomposition and defluorination of intermediate products. A stepwise chain-shortening pathway through repeated decarboxylation and β -fluorine elimination results in the formation of short carbon-chain PFASs with lower ecotoxicity. The system performance remained stable over multiple cycles (excessing 87% PFASs removal), demonstrating practical reliability. This synergistic approach provides an efficient and sustainable technology for destructively treating refractory PFAS contaminants in wastewater