| During last few years, large number of papers published on direct current glow discharge plasma (GDP) in and in contact with liquids due to the increasing interest in its application for wastewater treatment. Glow discharge in and in contact with liquids can dissociate water molecule into hydroxyl radical (-OH), hydrogen radical (·H) and hydrogen peroxide (H2O2), etc. These reactive species can diffuse into the surrounding liquid and react with the substrate. Among them,-OH and H2O2are oxidizing species, especially·OH with higher oxidant potential, which can oxidize any organic molecule into "harmless" carbon dioxide in a non selective way. This makes GDP particularly suitable for decontamination and sterilization proposes. This is the mean reason why GDP has been studied extensively as effective method for the removal of hazardous chemicals in aqueous solution. So far, much attention has been paid to the application of contact glow discharge electrolysis (CGDE), but less research on diaphragm glow discharge (DGD). There are so many investigation about the utilization of oxidizing species produced, while the utilization of·H is scarce. In addition, energy efficiency with different reactors has not systematically investigated. Therefore, this dissertation is to systematically investigate the onset of DGD and its application for the oxidative degradation of acid orange7(AO) and the reduciton of chromium. Furthermore, the combined process (DGD+Fe or DGD+PS) is also employed to improve the decolorization efficiency of AO.First of all, this work investigated the onset of DGD and recorded the phenomenon around the hole on the diaphragm. Glow discharge occurred around the hole on quartz tube between two submersed graphite electrodes. The sequence of events leading to full DGD involved normal electrolysis, shock wave, solvent vaporization near the hole by Joule heating, the formation of vapor sheath, ring flash and glow discharge around the hole. The characteristic voltage for the formation of shock wave, ring flash, breakdown voltage (VB) and critical voltage (VD) decreased with the increasing the conductivity, and then maintained at a certain value. I-V curve with multi-hole was similar to one hole in DGD. And the concentration of H2O2in anolyte increased with increasing applied voltage, initial conductivity and hole number. The energy efficiency of DGD (0.19g/kWh) was comparable to other electrical discharge such as pulsed arc discharge (0.18g/kWh) and dielectric barrier discharge (0.14g/kWh), but it was lower than CGDE (0.81g/kWh) and pulsed streamer discharge (1.56g/kWh)。In addition, this work also investigated the AO decolorization in aqueous solution with DGD. It was found that750V was optimal voltage for the decolorization of AO. The decolorization efficiency was in proportional to the initial conductivity, hole number and hole diameter. With stainless steel stick as the anode, the decolorization efficiency was greatly enhanced due to the anode corrosion. When the hole diameter was1.0and2.0mm, the decolorization efficiency was57.20%and91.12%with stainless steel stick as the anode, which higher those (20.63%and41.90%) with carbon rod as the anode. The trace amount of iron ion from stainless steel anodes played an important role as catalyst in Fenton-like reaction. Similarly, the addition of iron salts significantly enhanced the decolorization efficiency of AO due to the Fenton reaction. And Fe2+showed better catalytic effects than Fe3+. When the hole diameter was1.0mm, the decolorization efficiency of AO was93.65%and81.90%with0.2mM Fe2+or Fe3+, which was higher than that (20.63%) without iron salts. The addiiton of iron salts or with the stainless steel stcik as the anode, improve the decolorization effiicency of AO, TOC reduction and energy efficiency in DGD treatment. The energy efficiency (0.150,0.683g/kWh) of combined process (DGD+Fenton) was in the similar magnitude with CGDE (0.218g/kWh), pulsed corona discharge (0.370g/kWh) and and gliding arc discharge (0.295g/kWh).On the other hand, this work investigated Cr(VI) reduction with DGD. The experimental results showed that the reduction efficiency of Cr(VI) increased with the increase of applied voltage, initial conductivity, hole number and hole diameter. The effect of initial pH value on the reduction of Cr(VI) was not significant. The presence of phenol enhanced the reduction of Cr(VI) due to its scavenge ability to-OH. The energy efficiency for Cr(VI) with DGD (0.181g/kWh) was higher than UV/TiO2(0.036g/kWh), and comparable to pulsed corona discharge (0.200g/kWh), but lower than that with CGDE (2.915g/kWh)。 In addition, this work investigated the Cr(VI) reduction and AO decolorization in cathodic and anodic compartment with DGD. The experimental results showed that the reduction efficiency of Cr(VI) and AO decolorization efficiency (91.58%,49.00%) in cathodic compartment was higher than those (70.34%,28.61%) in anodic compartment. Furthermore, DGD was utilized for the simultaneous reduction of Cr(VI) and AO decolorization. The decolorization efficiency of AO (55.06%,82.03%) in presence of Cr(VI) was higher than those (40.24%,25.65%). The presence of Cr(VI) in both compartments enhanced the AO decolorization. However, AO showed less effect on Cr(VI) reduction, since it was not hydroxyl radical scanvenger. The reduction efficiency (91.58%,70.34%) of Cr(VI) in presence of AO was close to those (89.60%,72.96%) without AO.Finally, this work investigated the degradation of AO with the combined process (DGD+PS). The experimental results demonstrated that the addition of PS showed less effect on AO decolorization at room temperature with cooling water. Instead, the addition of PS significantly improved the AO decolorization without circulating cooling water. When the concentration of PS was2.0g/L, the decolorization efficiency increased up to97.20%without circulating cooling water, which was much higher than that (20.43%) at30±2℃with circulating cooling water. The heat produced in DGD activated PS into SO4-·, which enhanced the degrdation of AO. The change of PS concentration demonstrated that PS underwent decompose in the combined process without circulating cooling water. Furthermore, the main intermediate products identified by GC-MS/IC were phthalic anhydride,1,2-benzenedicarboxylic acid, toluene, o-xylene, ethylbenzene and benzoquinone, formic acid, acetic acid and oxalic acid. |
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