Electrochemical degradation of methylene blue dye using a graphite doped PbO2 anode: Optimization of operational parameters, degradation pathway and improving the biodegradability of textile wastewater

An anodic oxidation process with graphite anode coated with lead dioxide (G/β-PbO2) was optimized for the degradation of methylene blue (MB) and the treatment of real textile wastewater. The G/β-PbO2 anode was prepared by the electrochemical precipitation method. The scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses confirmed the successful coating of graphite substrate with the β-PbO2 film. The effect of four independent variables including pH, reaction time, current density, and electrolyte concentration of Na2SO4 on the performance of the electrochemical oxidation system was modeled by using a complete central composite design and was then optimized by genetic algorithm method. The accuracy of the proposed quadratic model by CCD was confirmed with p-value 0.9. The optimum conditions for solution pH, reaction time, current density, and Na2SO4 electrolyte concentration were obtained to be 5.75, 50 min, 10 mA/cm2, and 78.8 mg/L, respectively. In these conditions, the experimental removal efficiencies of MB using G/β-PbO2 and graphite anodes were 96.2% and 68.3%, respectively. The electrochemical removal of MB using both G/β-PbO2 and graphite anodes well followed the pseudo-first-order reaction (R2 > 0.9). Cyclohexane, cyclohexa-2,5-dien-1-ylium, and N-(sec-butyl) aniline were the most abundant intermediates identified by LC-MS analysis. However, the complete mineralization of MB was achieved in 60 min. The optimized anodic oxidation process successfully improved the biodegradability of real textile wastewater ( B O D / C O D > 0.4 ).