Simultaneous removal of methyl orange and methyl red dyes by electrocoagulation process in aqueous medium using central composite design

The effects of various operating parameters for the simultaneous removal of methyl red and methyl orange azo dyes by electrocoagulation with iron electrodes were examined in this study using response surface methodology. The electrocoagulation process was optimized and the direct and interaction effects of the different factors were assessed using the central composite design. Current intensity (X 1 ), initial dye concentration (X 2 ), pH (X 3 ), and treatment time (X 4 ) were studied as factors to assess their effect on each dye removal efficiency. The main factors such as current intensity (X 1 ), initial concentration (X 2 ) and time (X 4 ) had no significant positive effects, whatever the nature of the dye. However, the effect of pH was predominant and significant compared to the others on the responses. It had a negative coefficient of 5.93, which is about 25 times greater than that of current intensity and about 4 times greater than that of initial concentration and time for methyl red. For methyl orange, the pH has a negative coefficient of 3.76, corresponding to an effect approximately 14 times greater than that of current intensity and 2 times greater than that of initial concentration and time. The effects due to the interactions of the main factors initial concentration and pH (X 2 × 3 ), pH and time (X 3 × 4 ) have a significant contribution a95 % confidence level. Similarly, the quadratic effects of all four factors show significant contributions at 95 % confidence level, with the exception of the methyl red elimination model, where the quadratic effect of the time shows no significant effect. The optimum conditions for maximum methyl red removal 96.303 % were: 155.1 mA for current intensity, 75 mg/L for initial methyl red concentration, pH value of 4.7, and 47 min for electrolysis time. Optimum conditions for the complete removal of methyl orange were; 155.1 mA for current intensity, 75 mg/L for initial methyl red concentration, pH value of 5.1, and a duration of 51 min. The most influential factor for the degradation of dyes by electrocoagulation is the pH of the medium. As a result, the electrocoagulation technique proved to be an effective, easy-to-implement, promising, and environmentally friendly technique for dye removal and could be applied for the treatment of wastewater. • Simultaneous degradation of two dyes leads to total elimination. • Optimization using the central composite plan methodology best corresponds to our work because it takes into account the interactions between the different parameters. • The pH of the solution has a significant effect on the degradation of our two dyes. • The interactions between pH and time have a significant contribution of 95 %. • The optimum parameters allowing optimal degradation have been obtained.