The development of electrochemical advanced oxidation processes for wastewater treatment: From two-dimensional to three-dimensional
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Electrochemical oxidation has been used as a wastewater treatment method to remove organic contaminants for decades. During electrolysis, electron-rich organics are directly oxidized on anode surface and/or indirectly oxidized by oxidants that generated from the anode. Electrochemical oxidation is considered highly efficient for chemical oxygen demands (COD) reduction, especially for the destruction of emerging contaminants that are refractory to conventional methods. However, its large-scale applications are hampered by high electrode cost, high energy consumption, and low oxidation efficiency. Electrochemical advanced oxidation process (EAOP) is a new type of electrochemical oxidation. As an indirect electrochemical oxidation method, EAOP can generate hydroxyl radicals (HO·) from water on the anode. Hydroxyl radicals is a highly reactive oxidant that can react with nearly all organic contaminants and eventually mineralize them to CO2 and H2O non-selectively in ambient pressure and atmospheric temperature. This study focuses on advancing the understanding of the electrochemical oxidation systems and developing EAOP a more commercially applicable technology. The efforts include: first, develop novel anode materials that can generate more hydroxyl radicals; second, investigate and improve in-reactor mass transfer process to increase the overall oxidation efficiency; and third, develop a novel electrochemical system that can significantly lower the energy consumption. To be specific, novel inactive semiconductor-based anode materials are fabricated. These anodes include TiO2-based SnO2-Sb/polytetrafluoroethylene resin (FR)-PbO2, blue TiO2-based SnO2-Sb etc., are promising to generate hydroxyl radicals with lower energy input and better stability. The mass transfer impact is quantitatively investigated regarding the hydrodynamic parameters. A mathematical model associated with electrochemical oxidation kinetics and mass transfer impact is established and validated with experimental data. A novel three-dimensional electrochemical system is developed with the integration of meshed electrodes and proton exchange membranes. In contrast with the conventional two-dimensional system, the oxidations in the three-dimensional system do not require additional electrolytes. Moreover, the three-dimensional configuration can significantly lower the overall energy consumption of using electrochemical method for wastewater treatment.