Indirect electrochemical treatment of saline dyestuff wastewater

Dyestuff wastewater is always found to contain highly-concentrated sodium c hloride. In many cases, biological processes are not available to dispose s aline dyestuff wastewater. In. this paper, both direct and indirect electro chemical oxidation of saline dyestuff wastewater were carried out and the a ccessibility of indirect electrochemical oxidation by electrochemically gen erated hypochlorite was investigated. It was found that the indirect electr ochemical process removed COD by 87% and color by 100% in 50 minutes while the direct electrochemical process removed COD by 47% and color by 50% in 5 hours. The rate-limiting step for hypochlorite evolution at the anode was found to be diffusion-controlled. For the two processes, COD removal kineti cs could be simplified as the pseudo first-order kinetics. The rate constan ts of COD removal were 0.038 min(-1) and 0.0018 min(-1) for the indirect an d direct oxidation respectively. Current efficiency of the indirect process was 1 while that of the direct process was 0.16; cost efficiency of the tw o processes was 8000 mg-COD (kWh)(-1) and 1000 mg-COD (kWh)(-1) respectivel y. It can be concluded that the indirect electrochemical process is a promi sing method for the disposal of saline dyestuff wastewater.