Response surface optimization of electro-oxidation process for the treatment of C.I. Reactive Yellow 186 dye: reaction pathways

In this study, central composite design at five levels (-beta, -1, 0, +1, +beta) combined with response surface methodology has been applied to optimize C.I. Reactive Yellow 186 using electro-oxidation process with graphite electrodes in a batch reactor. The variables considered were the pH (X-1), NaCl concentration (M) (X-2), and electrolysis time (min) (X-3) on C. I. Reactive Yellow 186 were studied. A second-order empirical relationship between the response and independent variables was derived. Analysis of variance showed a high coefficient of determination value (R-2 = 0.9556 and 0.9416 for color and COD, respectively). The optimized condition of the electro-oxidation of Reactive Yellow 186 is as follows: pH 3.9; NaCl concentration 0.11 M; and electrolysis time 18 min. Under this condition, the maximal decolorization efficiency of 99 % and COD removal 73 % was achieved. Detailed physico-chemical analysis of electrode and residues of the electro-oxidation process has also been carried out UV-Visible and Fourier transform infrared spectroscopy. The intermediate compounds formed during the oxidation were identified using a gas chromatography coupled with mass spectrometry. According to these results, response surface methodology could be useful for reducing the time to treat effluent wastewater.