The Electrochemical-adsorptive Treatment Technology For Dye Wastewater

In this paper, Alizarin Red S simulated dye wastewater was taken as an example to show the treatment results of electrochemical method. And the effects of several factors on the removal rate of COD and chromaticity were also discussed. Namely, the initial concentration of dye wastewater, electric current density, and initial pH value, the distance between electrodes, types of dyes, etc. By orthogonal experiments, the optimum conditions of electrochemical techniques both for the soluble anodes and dimensionally stable anodes (DSA) had been obtained. The results showed that when white iron was taken as anode, the electric current density was 25mA/cm2, the distance between electrodes was 2.0cm, the initial pH value was 3.5, and the reaction time was 40min, the removal rates of COD and chromaticity by electrochemical method were 93.05% and 93.14% respectively; and when using DSA, the reaction time was 30min, the applied quantity of NaCl was 3.0g/L, the electric current density was 25mA/cm2, the distance between electrodes was 3.0cm, the removal rate of chromaticity by indirect electro-catalytic oxidation method was above 95%, while the removal rate of COD was comparatively low because of the generation of some halide which was more difficult to degrade. The reaction mechanism of the electrochemical treatment process was also analyzed. The results showed that the electrochemical treatment method was a complex reaction process that consists of electrocoagulation, electro- flotation and electro-catalytic oxidation. Moreover, according to the results based on the above study of electrochemical treatment of simulated dye wastewater, the combined technology of electrochemical-adsorptive method was discussed. During the process, electrochemical method played an important role, and the adsorption came to the second place. The optimum conditions of the combined technology obtained by orthogonal experiments was obtained as follows, the initial pH value was 3.5, the applied quantity of PAC was 3.0g/L, the reaction temperature was 30℃,and the electric current density was 25mA/cm2, the distance between electrodes was 2.0cm。The combined technology showed its advantage when being applied to different types of dye wastewater. Comparing with the pure electrochemical method and adsorptive method, the treatment efficiency was improved greatly, and it could entirely meet up with the requirement of GB8978-1996, the national standard of dye wastewater's outflow. Finally, the mechanism of powdery activated carbon was analyzed.