Influence of Process Parameters on Electrochemical Removal of Indole: Response Surface Methodology, Mechanism and Energy Consumption

In this study, the degradation of indole wastewater by a tin-antimony anode (Ti/SnO2-Sb) modified by carbon nanotubes (CNTs) was evaluated in an electrochemical oxidation system. The Box-Behnken design with response surface methodology was proposed to evaluate the effects of current density, Na2SO4 concentration, and initial pH on the total organic carbon (TOC) removal rate. Subsequently, the process of indole degradation was optimized. Under optimal conditions (current density of 23.43 mA/cm2, Na2SO4 concentration of 45.44 mmol/L, and initial pH of 9.49), the TOC removal rate reached 95.36%. Further, the electrochemical oxidation of indole at the Ti/SnO2-Sb-CNTs anode was determined to be caused by hydroxyl and sulfate radicals using radical scavenger experiments and a mechanism analysis. The energy consumption of the electrochemical oxidation of indole was 392.74 kWh/kgTOC, and the mineralization current efficiency at 10 min was 40.40%. It would provide a reference for the engineering application of advanced treatment of industrial wastewater.