Energy-efficient Treatment of Refractory Industrial Effluent Using Flow-through Electrochemical Processes: Oxidation Mechanisms and Reduction of Chlorinated Byproducts

Abstract

While flow-through anodic oxidation (FTAO) technique has demonstrated high efficiency to treat various refractory waste streams, there is an increasing concern on the secondary hazard generation thereby. In this study, we developed an integrated system that couples FTAO and cathodic reduction processes (termed FTAO-CR) for sustainable treatment of chlorine-laden industrial wastewater. Among four common electrode materials (i.e., Ti4O7, β-PbO2, RuO2, and SnO2-Sb), RuO2 flow-through anode exhibited the best pollutant removal performance and relatively low ClO3 and ClO4 yields. Because of the significant scavenging effect of Cl− in real wastewater treatment, the direct electron transfer process played a dominant role in contaminant degradation for both active and nonactive anodes though active species (i.e., active chlorine) were involved in the subsequent transformation of the organic matter. A continuous FTAO-CR system was then constructed for simultaneous COD removal and organic and inorganic chlorinated byproduct control. The quality of the treated effluent could meet the national discharge permit limit at low energy cost (~4.52 kWh m3 or ~0.035 kWh g1-COD). Results from our study pave the way for developing novel electrochemical platforms for the purification of refractory waste streams whilst minimizing the secondary pollution. Environmental ImplicationsIndustrial wastewater usually features high organic matter content and complex composition, posing a significant environmental risk. While anodic oxidation has demonstrated high efficiency, there is increasing concern on the secondary hazard generation thereby. An energy-efficient system coupling flow-through anodic oxidation and cathodic reduction processes is therefore proposed, achieving simultaneous organic contaminant removal and chlorinated byproduct control. The direct electron transfer process imparts an advantage in treating chlorine-laden wastewater compared to the •OH-based advanced oxidation counterparts. The results of this study pave the way for developing novel electrochemical platforms for the purification of refractory waste streams whilst minimizing the secondary pollution.