| Pulse discharge plasma water treatment technology utilizes the physicochemical effectgenerated by high-voltage pulse discharge,can efficiently degrade hard organic compounds in water,and therefore has a good prospect.However,how to improve the energy efficiency is one of the keys to its practical application of this technology.This article proposes the method of adding persulfate to wastewater and activating persulfate through discharge plasma to increase the degradation efficiency.A multi-needle-plate over water surface structure reactor excited by high-voltage nanosecond pulsed power was designed,the spatial distribution of electrostatic field and the space-time distribution of equivalent electric field,electrons,etc.were analyzed through Comsol simulation,and optimize the electrode structure.The influence of electrical parameters on the discharge characteristics was studied through experiment to efficiently generate discharge plasma over water surface.Taking p-nitrophenol as the object,the effect of persulfate on the degradation of organics by discharge plasma over water surface was studied,and the activation and mechanism of persulfate were preliminary analyzed.The main results are as follows:(1)Electrostatic field and plasma simulation analysis was performed on over water surface discharge system.The spatial distribution of the electric field on the path from the needle tip to the ground electrode was investigated,and the needle-to-needle spacing of the electrode was optimized to 10 mm.The conductivity of liquid-phase has no effect on the electric field strength,and with the pulsed voltage increase and the gas gap spacing decreasing,the electric field strength is significantly enhanced.Electron density and electron energy increase gradually during plasma propagation,the mean electron energy reaches the maximum at the head of the plasma channel,about 7~9 e V.When the peak pulse voltage was increased from 14 k V to 18 k V,the maximum electron density was increased from 1.65×1018m-3 to 8.74×1020 m-3,and the area with high electron density also increased.(2)The physicochemical effects such as the discharge mode,light radiation,heat and active substance generation of the pulse discharge at atmospheric pressure were studied.The discharge device is equivalent to a static capacitance of 9.87 p F,with the increase of discharge intensity,the discharge process has three stages: corona mode,diffuse mode and spark discharge,then analyze the voltage and current waveform of different modes.Thespectral intensity of the nitrogen molecules was analyzed and the gas temperature during discharge was calculated to be about 340~394 K,when reach spark discharges,the light and heat in the spark mode are significantly higher than the diffuse and corona discharge mode.The discharge process produces high concentrations of ozone and hydrogen peroxide,and the concentration gradually increases as the discharge intensity and discharge time increase.(3)Taking p-nitrophenol wastewater as the target pollutant,the effects of persulfate addition,discharge intensity,and liquid properties on the activation of persulfate were studied.The degradation efficiency of p-nitrophenol first increases with the increase of the amount of persulfate and then tends to be gentle,the molar mass ratio of 80:1 was the optimal value.With the increase the pulsed voltage and the decrease the gas gap spacing can increase the effect of persulfate activation,and the effect is more pronounced when the spark mode,when the gas gap of 6 mm,pulse peak voltage of 22 k V,the degradation efficiency and the energy efficiency increase 19.6% and 7 mg/k Wh,respectively.The acidic environment is more conducive to wastewater treatment and persulfate activation,while the alkaline environment is not obvious.By analyzing the factors of discharge plasma activation persulfate,high energy electron and thermal effect may be the main factors of persulfate activation,hydrogen peroxide and ozone have no significant effect. |
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