Electrocatalytic Oxidation Of Dye Wastewater With Pulse Electrolysis

Electrocatalytic oxidation is an advanced electrochemical oxidation processes and the uesd of some metal oxides as electrode was benificical to the electrogeneration of hydroxyl radicals and other radicals which would destroy the pollutants to carbon dioxide and water. In the recent years, there has developed great interest in the development of environmentally firendly electrochemical methods to degrade recalcitrant organic pollutants in wasterwaters.The pulse electrolysis processes has a advantage in terms of that can reduce both the energy and electrode consumption. Up to now, little attention was paid to the treatment of dye wastewater using the combination of pulse electrolysis and electrocatalytic oxidation. Therefore, electrocatalytic oxidation of the dye indigo carmine (IC) with pulse electrolysis was systematically investigated in the present paper. The kinetics and mineralization of the processes was studied. The degradation pathway and reactive mechanism of IC in the electrocatalytic oxidation system with pulse electrolysis was explored. The treatment of15kinds of dyes was performed in the system. The effect of dye physico-chemical properties on the treatment efficiency was further studied. The primary results obtained are as follows:(1) During the processes, initial IC concentration, NaCl concentration, voltage and frequency were observed to have effect on the discoloration efficiency. The reaction kinetics followed a pseudo-first order in the process. The total reaction kinetics equation was established and the effect of the four parameters on the reaction rate followed the order:NaC1concentration> voltage> frequency> IC concentration.(2) Several factors have effect on the TOC removal efficiency, such as pH value, initial IC concentration, NaCl addition, voltage, frequency and duty ratio. Under the optimization condition of the process was performed at pH3,220mg/L IC,1.5g/L NaCl,15V,4kHz and duty ratio of0.4decreases in the TOC of31.2%was achieved after180min. Furthermore, the biodegradability of the water was improved significantly. The energy consumption was159kwh/kgTOC and the current efficiency was15.3%.(3) Decomposition of IC in the electrocatalytic oxidation reactor with pulse electrolysis was proposed to be firstly initiated by the cleavage of C=C, which resulted in decolorization of the solution. Afterwards, the C-N and C-S were further oxidaized to some benzene-type compounds and then to oxalic and oxamic acids resulted from the aromatic ring cleavage. Finally, these carboxylic acids were converted into CO2, H2O, NH4+and NO3to accomplish an entire mineralization process.(4) The TOC removal efficiency was47.1%after180min treatment with3.5g/L NaCl. The removal of organic compound in this system was the process combined the oxidation of hydroxyl radical (·OH) and active chlorine (Cl2, HClO, and ClO-), which respectively contrubute to13.8%and33.3%of TOC removal efficiency.(5) Degradation of15kinds of dyes was performed in the system and found out that some factors such as dye stucture type, number of sulfonate group, number of azo chromophore group and aromatic ring in the dye molecule had some effect on the treatment efficiency. The quantitative relationship between the TOC removal efficiency and molecular descriptors such as the ratio of the molecular weight to the number of sulfonate group, the ratio of the hydrophilicity to the lipophilicity and the number of azo chromophore group was studied. The results indicated that good linear correlations exist between the TOC removal efficiency and their molecular descriptors. In particular, the ratio of the molecular weight to the number of sulfonate group has most prominent contribution to the TOC removal rate.