Depollution of indigo dye by anodic oxidation and electro-Fenton using B-doped diamond anode

Hazardous wastes are generated in the synthesis of dyes and pigments applied in industries. Efficient methods are thus needed to clean wastewaters. Here, we use anodic oxidation and electro-Fenton with B-doped diamond anode to degrade the synthetic dye indigo in aqueous sodium dithionite. Results show the near-complete mineralization of the dye within 80 min at 500 mA. Mineralization was faster by electro-Fenton than anodic oxidation. The second-order rate constant (k) for the reaction of indigo with (OH)-O-center dot was measured as 4.03 x 10(9) M-1 s(-1) at pH 3.0 and was compared with the rate constants of reactions between dyes and (OH)-O-center dot. The results clearly demonstrate that both electro-Fenton and anodic oxidation can be used to depollute dyes in textile effluent with high efficiency and low cost. The main oxidant, (OH)-O-center dot, being a non-selective reagent, the method could be applied to degrade other organic pollutants.