Decolorization of Congo Red with three-dimensional flow-by packed-bed electrodes.

The electrochemical removal of the color of the dyestuff Congo Red was investigated experimentally by using packed graphite anodes as well as packed graphite or C-304 stainless steel cathodes in an undivided reactor. The effects of the applied apparent current density, the amount of chloride ion addition, the pH value of the solution, the cathode material, the operating temperature, the volumetric flow rate and the initial concentration of Congo Red on the removal efficiencies were investigated in this study. Experimental results showed that the main pathway of color removal was by the hypochlorite generated in-situ at the anodes. Compared with the indirect oxidation, the color removal due to direct oxidation was insignificant. Cathodic oxidation by using graphite cathodes had little influence on the removal rate in an undivided electrochemical cell.