Removal of hazardous azo dye metanil yellow from industrial wastewater using electrochemical technique

The environmental challenge of synthetic azo dyes is of increasing concern due to the serious health effects on animals and human being. Metanil yellow (monosodium salt of 4-m-sulphophenylazodiphenylamine) was selected as the model compounds for this study because of its wide application in various textile industries either as such or in combinations with some other dyes as color additives. The azo dye degradation with electrochemical method in aqueous solution has been studied with platinum and steel electrode. A well–defined irreversible cathodic peak at 0.293 V was obtained and this may be attributed to the reduction of azo (–N=N-) group. Results indicate that the electrode process is diffusion controlled. Number of electron transferred was calculated and is found to be 4e and reduction mechanism proposed. During controlled potential electrolysis (CPE) peak current reduced substantially with a considerable decrease in color and absorbance. The reaction follows a first order dependence with k values 2.41 x 10 abs min and 2.30 x 10 abs min at platinum and steel foil respectively. The efficiency of different electrode materials for color removal is compared. Chemical oxygen demand (COD) decreases substantially from 2160 ppm to 180 ppm at platinum (91.7% COD removal) and 292 ppm at steel electrode (86.5% COD removal). No peak could be observed in the voltammograms after CPE, indicating the absence of any electroactive breakdown products.