An efficient, green, and residual oxidant-free wastewater treatment technique enabled by coupling a dual-cathode heterogeneous electro-Fenton process and UV radiation in tandem

Abstract

Efficient implementation of a catalyst-integrated cathode-based heterogeneous electro-Fenton (HEF) process usually suffers from the conflict between the optimal potentials of the two targeted reduction reactions (O₂ to H₂O₂ and metal⁽ⁿ⁺¹⁾⁺ to metalⁿ⁺). In addition, the residual H₂O₂ in the HEF effluent poses a potential environmental risk to aquatic ecosystems and would further make the HEF technology impractical. Herein, a tandem system of dual-cathode HEF and UV radiation is proposed to bypass these issues. In the dual-cathode HEF unit, the air-diffusion cathode (ADC) without aeration and the FeOCl-functionalized graphite felt (FeOCl/GF) perform their respective functions at different operating current densities (100 mA cm⁻² for ADC and 5 mA cm⁻² for FeOCl/GF) to achieve efficient H₂O₂ production, ˙OH formation and Fe(III) electroreduction simultaneously. Subsequently, the underutilized H₂O₂ in the HEF effluent will be reactivated in the UV module to eliminate the risk of oxidant residues while further improving the decontamination efficiency. Importantly, interesting antagonistic and synergistic phenomena governed by the cathodic current density of the ADC in this tandem system were also highlighted by constructing different standalone/coupled processes. The HEF/UV tandem strategy proposed in the present work offers a promising scheme for distributed wastewater treatment due to the demonstrated preeminent process efficiency, as well as the reagent- and residual-oxidant-free green chemistry concept.