| The high voltage discharge non-thermal plasma technology is one of brand-new advanced oxidized technologies and being applied gradually in the water treatment researches. The study on the influencing factors, treatment effects, reaction mechanisms and kinetics of the process was emphasized for the decolorization process of refractory organic dye with a novel discharge non-thermal plasma reactor in this paper.The research contents, results and conclusions are as follows:(1) A new discharge non-thermal plasma reactor was designed. It consists of the dielectric barrier discharge system and the corona discharge system. The advantages of this reactor are that as soon as the voltages reach the discharge voltage, the atomized water starts to discharge, and many filamentary streamer discharge channels are formed in the atomizing region, in witch the active species are produced and contact closely with the dye molecules to form a better mass transfer pattern. All of the non-thermal plasma is included in the atomizing region of treated water. Therefore the densest regions of both the non-thermal plasma active species and the water atomizing droplets situate in the same one, in order to achieve the better energy efficiency.(2) The reactor parameters were tested and optimized. The results shown when electrode spacing of the dielectric barrier discharge system and the corona discharge system is respectively 30 mm and 25 mm and the power voltage is 25 kV, the full atomization occur in both the two discharge systems and the sizes of most droplets are 100-500μm, even the sizes of some atomizing droplets reach below 100μm. The atomization droplets possess formidable surface energy because of the smaller size and the bigger specific surface area. The surface dye molecules can contact completely with the active species, in order to be oxidized and decomposed in the discharge process.(3) The reactor craft parameters and the influence of dye solution nature on the decolorization were determined. The decolorizing efficiency of the experiment dye solution was increased as the voltage was rising and the process time was extended, and the higher the voltage was, the more rapidly the decolorizing efficiency increased during a short time. But after the decolorizing efficiency achieved a high level the enhancement became slow. The decolorizing efficiency reduced as the dye concentration was increasing, and the absolutely decolorizing efficiency increased along with the dye concentration. Under the acidic condition, the decolorization rate of Erie Congo Dye solution is the lowest. Under the neutral condition, decolorization rate during the first 1 hour was higher than the alkalinity and the acidic condition, but the decolorization rate increased for the solution of a initial high pH value (≈12) after the first 1 hour.(4) The analysis has determined the influence of the reactor craft parameters on the energy efficiency. The energy efficiency of the low voltage was high, and along with the voltages increased the energy efficiency was dropping. When electrode spacing of the dielectric barrier discharge system was small, the reactor energy efficiency was high. However the reactor energy efficiency dropped rapidly along with electrode spacing enlarged and the differences of energy efficiency for different electrode spacing reduced as the voltages were rising. The differences of influences for corona discharge spacing on energy efficiency were smaller and reduced along with rising voltages. When the voltage was 20 kV or 25 kV, the energy efficiencies of different electrode spacing almost were the same.(5)The best working status of this reactor was fixed. According to the effect of electrode spacing and the voltage on decolorization rate of dye solution as well energy efficiency, The best working status areas follow: dielectric barrier discharge system of the electrode spacing is 30 mm, corona discharge system for electrode spacing is 25 mm, voltage is 20 kV, and the best working status of this reactor is defined.(6) The degrading process of Direct Scarlet Dye was determined and analyzed. Through taken the measurements of pH, TOC, UV-Vis spectra and high-performance liquid chromatograph in the degrading process of solution ,it was found that the COD of dye solution increased, pH continuing declined and TOC reduced gradually. The UV-Vis spectra and high-performance shown that though dye molecules had been destroyed, Strong Chromophore Azo Double Bond of dye was certainly under attack, the big conjugated system was vandalized and dye molecules were decolorized degradation, but they were not completely changed into carbon dioxide and other inorganic matter by mineralization, it appeared accumulation of aromatic ring and double benzene nucleus, so it is thus evident that complete destruction of aromatic ring is more difficult than the double benzene.(7)The degradation mechanism of dye was analyzed. After the high voltage applied on the discharge electrode in reactor, the electrons in the air produce gas discharge under the affection of electric force and yield a lot of active species. When the active species touch the surface of atomized droplets, they oxidize the dye molecules, dissolved into the droplets and react with dye molecules. At the same time, by the action of communication high voltage electric field, droplets ejected from the nozzle take distortion and produce the micro-discharges in the pointed ends of droplets, then produce a lot of active species and they react with the dye of inter and the surface of the droplets and dye is degraded. When charged droplets flow down to the points of the dielectric plate, the point corona discharges occur and again produce lots of active species, which are in touch with the droplets and continue to take surface oxidation. At the same time the H2O2 and O3 are dissolved in the droplets and the active species fall into storage water tank so that the oxidation reaction continues. (8) The kinetic equation has been set up and analyzed. The result shows that at the experimental conditions of the different initial concentrations, pH and the supplying voltages,the mass concentration of the direct red dye in solution decreases exponentially with the lengthening reaction time. The kinetic process of the plasma degradation of dyes is limited by the experimental conditions. At decolorizing efficient experimental conditions, the degradation process accords with the first order reaction kinetics. At this moment, the degradation rate constant decreases with the increase of initial dye concentration and increases with the rise of voltage and pH. |
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