Study On Degradation Of Organic Contaminants By Hydro-Plasma

The technology of high-voltage discharge plasma is a newly developed advanced oxidation technology of removing hazardous organic compounds from waste water. It relates to a wide range of disciplines such as plasma physics, plasma chemistry, hydro-mechanics, thermodynamics, kinetics, high-voltage technology, and environ- mental engineering. The plasma degradation processes the synergistic effects of many water treatment technologies such as high temperature pyrolysis, photochemical oxidation, liquid electric cavitation degradation, superciritical water oxidation, and ozonization. Nonthermal plasma is produced during the discharge processes where a large amount of high energy electrons, active species (such as active radicals and molecules etc) are generated. Those active species directly react with organic molecules dissolved in water and oxidize them or even get them completely mineralized. It does not cause secondary pollution in treatment. It is one of the potentially applicable wastewater treatment technologies for treating refractory organic pollutants wastewaters such as papermaking wastewater, pharmaceutical wastewater and dyeing wastewater, the pollute water resource severely.The experiments of producing of H₂O₂ and O₃ by pulsed high voltage discharge in water were carried out by meants of a lab-made apparatus with two electrodes of needle and pipe shape. The effect of some conditions, such as the distance of electrodes, the voltage, the discharge time, the styles of water treatments and the exposed treatments on the producing of H₂O₂ and O₃ were studied. The results showed out that the distance of electrodes and the discharge time have a marked influence on the H₂O₂ and O₃ concentrations in water, but little effect of the discharge voltage and the discharge time. When the air was blowed into the water in the process of high voltage, the anions , NO₂^- and NO₃^-were produced and the pH valuce of water decreased, while the conductivity increased.Degradation rate of 95.2% for methyl red was obtained after discharge of 120 min at 30 kV of peak voltage, 150 Hz of fiequency and 2 mm of distance in needle-pipe continuous reactor with bubbling gas. Wastewater of methyl red was treated by discharge plasma and the pH valuce of water decreased therewith the conductivity increased. The study is indicative that the aeration, pH and conductivity affect the degradation. Higher aeration, lower original pH valuce and lower conductivity can improve degradation rate. FT-IR and Gas Chromatogram-Mass Spectrum were used to monitor the degradation process and to identify the major oxidation intermediates. The mechanisms of the degradation are proposed on the basis of detected intermediates. The methyl red degradation in the system is due to radical reaction and one of the structure destruction was induced by the break of the azo bond.The discharge degradation of phenol wastewater by was also studied in this article. Degradation rate of 91.2% for paranitrophenol was obtained after 120 min discharge at 30 kV of peak voltage, 150 Hz of fiequency and 2 mm of distance in needle- pipe continuous reactor with bubbling gas. The study shows original concentration, pH value, conductivity affect the degradation. Lower original concentration, original pH value and conductivity can improve degradation rate. FT-IR, High Performance Liquid Chromatography and LC/MS were also used to monitor the degradation process and to identify the major oxidation intermediates. The mechcanism of degradation of them are proposed on the basis of detection of intermediates. The activity of paranitrophenol is attacked and permuted by hydroxyl radical and the quinine was detected then.