Effect of additional Fe2+ salt on electrocoagulation process for the degradation of methyl orange dye: An optimization and kinetic study

The wastewater generated from textile industries is highly colored and contains dyes including azo dyes, which are toxic to human and water-living organisms. The treatment of these azo dyes using conventional treatment techniques is challenging due to their recalcitrant properties. In the current study, the effect of additional Fe2+ on electrocoagulation (EC) using Fe electrodes has been studied for the removal of methyl orange (MO) azo dye. pH between 4-5 was found to be optimum for EC and treatment efficiency decreased with increasing dye concentrations. With the addition of Fe2+ salt, dye removal for a certain concentration was increased with the increase of current density and Fe2+ up to a certain limit and after that, the removal efficiency decreased. The COD, color and dye removals were 88.5%, 93.1% and 100%, respectively, for EC of 200 mg.L-1 dye solution using only 0.20 mmol.L-1 Fe2+ for 0.40 mA cm(-2) current density, whereas for EC, the respective removal efficiencies were 76.7%, 63.4% and 82.4% for 32 min. The respective operating cost for EC was $768 kg(-1) removed dye ($0.342 m(-3)), whereas, for EC with additional Fe2+ salt, it was $350 kg(-1) removed dye ($0.189 m(-3)). The kinetic results revealed that the first-order kinetic model was fitted best for EC, whereas the second-order kinetic model was best fitted for Fe2+ added EC. For real textile wastewater, 57.6% COD removal was obtained for 0.15 mmol.L-1 Fe2+ added EC compared to 27.8% COD removal for EC for 32 min. Based on the study we can conclude that Fe2+ assisted EC can be used for effective treatment of textile wastewater containing toxic compounds like azo dyes.