Study On Degradation And Mechanism Of Congo Red By Pulse Electrolysis

As dye wastewater has features of high chroma, high toxicity, great damage, low degradability and so on, it has made serious impacts on the environment. How to degrade dye wastewater quickly and efficiently is always a hot topic for environmentalists. The pulse electrolysis is one of the process which has advantages in terms of saving energy, easy operation and low secondary pollution,so it is widely used in the field of treatments of organic wastewater that is hardly degraded. This article utilized electro-catalytic oxidation with pulse electrolysis to treat wastewater containing Congo red dye, with focus on affecting factors?the intermediate compounds and the mechanism of the degradation.Firstly, those factors which affect decolorization were studied by single factor experiment, and the results showed that, with increase of initial concentration of wastewater and initial p H, the decolorization of Congo red decreases, while with the increase of concentration of Na Cl, pulse voltage, frequency and ratio, the decolorization of CR increases. According to the result of single factor experiment, the conclusion on the basis of response surface methodology(RSM) was that peak of pulse voltage had the most powerful influence on the decolorization, and initial p H value and concentration of Na Cl had the strongest interaction. Then, in the experiment of verifying the relationship between the TOC removal rate and decolorization rate, with the change of voltage or initial concentration of Congo red, the change tendency of the TOC removal rate and decolorization rate was always consistent, while the former was much lower. By comparing the energy consumption of the system with voltage variation, we found that, when the peak of pulse voltage was 15 V, the consumption could reach the best one.Ion Chromatography(IC) and LC-MS were used to identifiy the intermediate compounds formed during the degradation and the proposed pathway of electrochemical degradation of Congo red, which was that CR was transformed into naphthol, followed by naphthoquinone and ketone, which later oxidizes into carboxylic acid, and finally at last stage completely mineralized into CO2 and H2 O. But most of CR was not completely mineralized, resulting in TOC removal rate being very low. Lastly, with hydroxyl radicals detected in electrolytic process by HPLC, the decolorization effect was compared between hydroxyl radicals and active chlorine respectively, leading to the result that active chlorine was the main cause in the degradation of Congo red.