Evaluation and optimization of textile synthetic effluent discoloration using anodic oxidation on BDD electrode: application of the experimental design methodology

In the present study, the anodic oxidation of an azoic dye Acid Orange 8 (AO8) was performed on boron-doped diamond electrode. Cyclic voltammetry of AO8 dye solution at pH 0 and 10 proved the existence of direct and indirect electrochemical reactions in the potential region between 1.0 and 2.3 V/saturated calomel electrode. A factorial design methodology was implemented to evaluate statistically the effects of operating parameters, including current intensity (0.1–0.6 A), initial pH (0–10), initial dye concentration (0.01–0.1 mmol L-1), and electrolysis time (10–90 min), on discoloration efficiency. The equation describing the behavior of the response function of the selected factors was developed and verified by different tests such as ANOVA. The optimized parameters determined in this study were set as follows: current intensity of 0.35 A, initial pH = 0, initial dye concentration of 0.055 mmol L-1, and electrolysis time of 45 min. Under these conditions, 98% of discoloration efficiency was obtained. The anodic oxidation of AO8 was found to follow pseudo-first-order reaction kinetics, and also an apparent rate constant (kapp) of 0.082 min-1 was found. The chemical oxygen demand was reduced by 70%.