A novel flow-through dual-system electro-Fenton for boosting PAEs removal efficiency in natural waters

In a conventional electro-Fenton system with a single cathode, it is difficult to attain both high H₂O₂ generation by oxygen reduction reaction (ORR) and efficient iron reduction reaction (FRR). For this study, a flow-through dual-system electro-Fenton (FT-DEF) reactor was designed to overcome this shortcoming and promote mass transfer to effectively remove dimethyl phthalate (DMP) from water. By comparing the ORR and FRR performances of four different commercial carbon electrodes, the graphite felt with the highest amount of H₂O₂ generation was selected as the cathode of the ORR system, and the activated carbon fiber with the best Fe (III) reduction effect was selected as another cathode of the FRR system. The ORR system and FRR system operate simultaneously to form the DEF system. The FT-DEF system displayed many advantages compared with the conventional electro-Fenton (CI-ORR), presenting an improved efficiency and low energy consumption in phthalates removal. Under optimal reaction conditions, the FT-DEF system is capable to degrade 100% DMP in 20 min, which is 25% higher than the CI-ORR, while the reaction rate constant (0.271 min^-1) is 16 times that of CI-ORR system (0.017min^-1). In addition, the TOC removal of FT-DEF achieving 72.3% within 2 h with energy consumption of 2.35 kW h·m^-3 is much better than CI-ORR that only achieves 18.3% TOC removal within 2 h with energy consumption of 8.13 kW h·m^-3. Furthermore, control parameters and mechanism of FT-DEF were investigated in detail. The main intermediate products of DMP were analyzed by UPLC-ESI-HRMS, and the possible degradation path of DMP was speculated. In addition, application of FT-DEF in three types of natural water demonstrated its universal applicability of the system.