Novel permeable catalytic anodic system for the energy efficient oxidation of micropollutants

Abstract

Micropollutants (MPs) have issued as increasing concerns due to its high impacts on human and ecological health. Among treatment technologies for MPs, electrochemical oxidation processes (EO) have been highlighted due to their compact reactor configurations and simple operational methods. However, low Faradaic efficiency (FE) during the oxidation of MPs induced the low energy efficiency inevitably. In the electrochemical oxidation cell, FE is mainly governed by the mass transfer rate of target chemicals to anodic electrodes and the overpotential of the system. In the previous research in the group, pristine carbon-nanotube-based hollow-fiber membrane electrode (CHF) was fabricated and applied to electrochemical oxidation cells to overcome the mass transfer limitation of electrochemical oxidation system. Although the previous study exhibited the enhanced energy efficiency with significantly higher removals of MPs compared to general electrodes, there are some problems unsolved such as high overpotential and low specific water flux. In this study, modification of CHF and optimization of operating conditions were performed to overcome the current mass transfer limitation of the electrochemical oxidation system.In chapter 2, CHF was fabricated, and electrochemical oxidation of three MPs (bisphenol A, diclofenac, sulfamethoxazole) was performed with the flux into CHF (flow-through operation) or without flux into CHF (flow-by operation). As the increase of flux in flow-through operation, Faradaic efficiency was improved by the increased mass transfer rate in the CHF system. However, the removal efficiency of MPs was decreased as the increase of flow rate in flow-by mode due to the mass transfer limitation. For all tested conditions, complete removals were achieved in flow-through operation, and theoretical minimum Faradaic efficiency was significantly enhanced up to 23.9% at 800 LMH of CHF flux. In chapter 3, the catalytic modification of CHF was performed using TiO2 nanoparticles for the increase of specific water flux, low overpotential, and the increased radical generation. The fabricated TiO2-CHF possessed the oxygen evolution reaction (OER) potential of 1.6 V, which is significantly lower than CHF (2.1V), and the hydrophilic surface with 17.9 times higher specific water flux compared to CHF. As a result, the TiO2-CHF electrode can remove 100% of target micropollutants even at 1,200 LMH. The TiO2-CHF electrode also showed an increase of Faradaic efficiency to 34.5 % at 1,600 LMH.In conclusion, by designing electrochemical cells and fabricating TiO2-CHF, water flux and faradaic efficiency were significantly improved compared to existing CHF. Thus, novel TiO2-CHF could be applied for the treatment of MPs during water or wastewater effluent treatment processes.