Removal of Congo red dye by electrochemical advanced oxidation process: optimization, degradation pathways, and mineralization

Abstract The degradation of Congo red dye has been studied by electrochemical advanced oxidation process based on the generation of powerful oxidizing agents especially hydroxyl radicals ·OH. In this study, the effect of several experimental parameters, such as pH, ferrous ion concentration, electrolyte support concentration and current intensity, on the process was investigated. The experimental design of Doehlert was applied to determine the optimum conditions of three factors, namely current intensity, initial Fe 2+ concentration and electrolysis time for the Congo red removal. The relationship of response to experimental variables was represented graphically by the construction of the two-dimensional iso-response contour plots and those indicated that 360 mA, 19 mM Fe 2+ and 30 min reaction time were optimal under 50 mM Na 2 SO 4 at pH 3, leading to a total Congo red degradation. A quadratic polynomial model was determined and its statistical significance was verified through the variance analysis, which indicated that the proposed model was statistically meaningful and convenient for the results prediction. The mineralization of Congo red under the obtained optimum conditions was examined and the results showed a high TOC removal rate (81.1%) after 300 min of reaction time. Finally, a plausible degradation pathway was suggested.