A critical review on the recent progress in application of electro-Fenton process for decontamination of wastewater at near-neutral pH

One of the greatest engineering challenges of this century is development of new technologies for removing emerging hazardous contaminants from water sources. Electro-Fenton (EF) as one of the most promising approaches of advanced oxidation processes (AOPs) has received widespread attention for its excellent performance in the removal of recalcitrant pollutants due to generation of strong oxidizing species like hydroxyl radicals (center dot OH). However, the practical application of classical homogeneous EF process is hampered by a narrow pH range (2-4) and production of sludge at higher pH values. The information obtained so far highlights the need to enhance the removal efficiency and reduce the reaction time of EF process under neutral pH conditions. Herein, this review summarizes efficient approaches in recent years (2017-2023) applied in EF system with the aim of overcoming the low pH implementation barrier, such as application of heterogeneous catalysts in EF process (HEF), cathode modifications, using chelating agents, and hybridizing the EF with other treatment methods, including adsorption, membrane, and photo/catalysis. These strategies can accelerate the iron cycle and Fe3+ reduction; therefore, more H2O2 and center dot OH can be generated. Promoting the H2O2 utilization efficiency can provide more oxidative species, which leads to higher degradation and mineralization of contaminant. On the other hand, some strategies by preventing the Fe3+ precipitation at higher pH values help the system work in a wider pH range. In the final section, the challenges of these plans are discussed and perspectives for future research are proposed to improve the practicability and feasibility of the EF for wastewater treatment.