China is one of the largest countries with output industrial wastewater in the world, in which 35% are printing and dyeing wastewater. With the characteristics of large chroma, high content of organic pollutants and complex water quality, they have wide range impact and serious hazard. In this thesis , a DC pulse power supply was used to generate cathodic arc plasma discharge on the cathode surface, and methyl violet dye wastewater was decolorized. By changing the applied voltage, electrode shape, electrolyte type and other conditions, factors that affecting decolorization rate of methyl violet dye wastewater were analyzed. The evolution of methyl violet intermediates were analyzed by means of high performance liquid chromatograph (HPLC), UV-visible spectrophotometer (UV-vis) and High Performance Liquid Chromatography-Mass Spectrometry (LC-MS), moreover, the decolorization mechanism was evaluated.

      When using titanium bar as the cathode, platinum plate as the anode, the decolorization rate of methyl violet dye wastewater increased with the increasing of voltage in a range of 360 V - 400 V. The shape of the electrode affected the uniformity and stability of plasma discharge. The tip discharge on the strip electrode is prone to leading over-burning of the electrode, while the bar electrode discharged more uniform and stable. Under the same voltage and experimental conditions, the effect of support electrolyte was compared. It was found that when using SO42- as electrolyte anion, the decolorization of the methyl violet dye would be hindered. When the anion was Cl-, it could interact with the cathodic plasma and significantly accelerate the decolorization

of the dye wastewater. In the process of cathodic plasma discharge, methyl violet dye was firstly broken into of methyl violet 6B and methyl violet 10B from the crosslinked macromolecules, and then broken into the molecular fragments of methyl violet 6B and methyl violet 2B, then finally decomposed.

     When the solution contained SO42-, the decolorization rate of methyl violet dye wastewater will temporarily increase. However, under the action of electric field, the broken methyl violetmolecules will recombine, resulting in the abnormal phenomenon that the solution partial recovery after decolorization. When a small amount of Cl- was added to methyl violet solution, the decolorization rate was significantly improved. Cl- in the aqueous solution would preferentially attack the functional groups on the benzene ring and hydrolyze them. On the other hand, under the action of cathodic plasma discharge, active chlorine and other active particles were generated to decolorize methyl violet dye molecule. It was found that the excellent decolorization performance of Cl- was only produced during the cathodic plasma discharge in liquid phase and independent of the solution temperature, there was not secondary pollution in this process.

    The cathode plasma discharge technology and the intervention of Cl- can accelerate the decolorization of dye wastewater, significantly improve the decolorization rate. The titanium electrode material has good stability and low price. This technology shows a good application prospect in the field of printing and dyeing wastewater treatment.