The Study On The Degradation Of Thiamethoxam By Dielectric Barrier Discharge Non-thermal Plasma In Aqueous Water

With the rapid development of agriculture and the increased demand for food, the pesticides are used extensively, which caused serious environmental pollution problems. Thiamethoxam is a kind of highly efficient, lasting new neonicotinoid broad spectrum insecticide, which makes an outstanding contribution to environmental pollution because of its widely used. In current, the pesticide is developing toward the trend of photolysis, hydrolysis and oxidation resistance, which brings great challenge to wastewater treatment, therefore, in recent years, the advanced oxidative technology caused high attention in water treatment field.According to the development trend of advanced oxidation technology and the pesticide wastewater characteristics (high CODcr concentration, complex pollution compositions, high toxicity and difficult to be biodegraded), this topic used dielectric barrier discharge technology to treat new neonicotinoid pesticide thiamethoxam in water. The reactor has a structure of radial flow sedimentation basin, which is improved through the introduction of loaded TiO2ceramic honeycomb into the reactor.This experiment adopted the gol-gel method to make TiO2thin film, whose property was determined by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The effects of dielectric barrier discharge voltage, initial concentration, initial conductivity, solution pH and n-butyl alcohol on degradation efficiency were discussed. To improve the degradation efficiency, Fe2+and Cu2+were added into the thiamethoxam solution, and their change regular was explored. By comparing the loaded TiO2and TiO2powder ultraviolet catalytic efficiency to confirm TiO2film advantages, and also the relative degradation efficiency of O3, TiO2film and ultraviolet were studied. The results showed that when the discharge voltage was75V, the initial concentration was l00mg/L and degradation of160min, the removal rate of thiamethoxam reached85.88%. When increased initial electrical conductivity and initial pH or adding n-butyl alcohol, the degradation process would be inhibited, while adding Fe2+, Cu2+and TiO2(in proper) would promote the degradation of thiamethoxam pesticides. The catalytic efficiency of TiO2film was a little higher than TiO2powder. The removal rate of thiamethoxam was poor with UV only. When UV existed, TiO2film has a good degradation efficiency of thiamethoxam compared with ozone. The optimum discharge voltage, solution concentration, pH and solution conductivity were determined through orthogonal experiment.This study avoided a series of chemical reactions during the dielectric barrier discharge degradation of thiamethoxam process to study the apparent kinetics and establish the reaction dynamic equation. The reaction law of dielectric barrier discharge plasma technology degradation of thiamethoxam was explored from the macro perspective, which employed the theoretical basis for optimizing the reaction conditions and improving the effect of the degradation. With different discharge voltage, initial concentration and different solution conductivity, initial solution pH as the research object to study the degradation kinetics.During the degradation reaction process, pH gradually reduced, the solution conductivity increased gradually, the TOC remained relatively stable, and the CODcr rendered the trend of down-up-down. The introduction of titanium dioxide thin film increased the concentration of ozone and hydroxyl free radical in the solution.The degradation products were analyzed by HPLC-MS, the experimental results showed that low temperature dielectric barrier discharge plasma could effectively degrade the thiamethoxam in aqueous and turn it into a variety of intermediate products.The experiment results showed that the dielectric barrier discharge plasma had a good degradation effect on the thiamethoxam in water, which laid a solid foundation in the field of pesticide wastewater treatment.