Investigation On Degradation Of Dye Pollutants By Gas Phase Surface Discharge Plasma

Aiming at the problems of large output,complex water quality,high organic concentration,poor biodegradability and strong pollution of dye wastewater,the plasma technology of gas phase surface discharge?GSD?was used for degradation treatment to achieve the purpose of reducing pollutant content.Firstly,according to the ozone?O₃?generation and energy utilization efficiency,the structure of discharge reactor was optimized,the effects of discharge parameters were investigated.Finally,dye was as the target,dye degradability by GSD was explored through the investigation of dye decoloration,biodegradability,degradation of organic and carbon-containing substances.The mechanism of dye degradability by GSD was studied through the investigation of the active substances and O₃ catalyst.The results of this study are as follows:1.When optimizing GSD reactor structure,it was found that O₃ generation and energy utilization efficiency enhanced with the increase of the spirals distance of high voltage electrode and the decrease of the spirals diameter of high voltage electrode.Energy utilization efficiency showed a trend of increasing first and then decreasing with the increase of wall thickness of dielectric discharge tube,tube inner diameter and the ratio of inner surface area to volume of discharge dielectric tube.The two-tube reactor was the optimal discharge structure.When investigating the effect of discharge parameters,it was found that pH,conductivity,and liquid temperature showed a trend of decrease,increase and increase in discharge process,respectively,the first two tends were because of the acidic ions which was produced by the oxidization of nitrogen,the last trend was due to the electron collisions and heat accumulation,discharge phenomenon was more intense under the condition of inert gas.O₃ dissolved concentration showed a trend of increase first and decrease at last with the increase of pH,it improved with the increase of liquid conductivity and the decrease of liquid temperature.O₃ generation achieved the best under the discharge voltage of 6.0 kV,frequency of 7.0 kHz and gas flow rate of 0.6 L·min^-1.2.When investigating the dye degradability by GSD,it was found that the decolorization rate of dye increased first and then decreased with the increase of initial pH,dye concentration and gas flow rate,it improved with the increase of conductivity,voltage,frequency and decrease of liquid temperature.After the treatment by optimized GSD system,component concentration of dye decreased,the contents of organics and carbonaceous materials reduced,biodegradability enhanced.The decolorization rate of single dye and the organic degradation rate of mixture dyes reached 99.05%and 73.21%within 20 min,respectively.The intermediate products of dyes were detected,including biphenyl,tetramethylbiphenyl,azobenzene,phthalic acid,benzene diacetic acid,benzoic acid and hexanoic acid.3.When investigating the mechanism of dye degradability by GSD system,it was found that hydroxyl radicals,ultraviolet rays,direct and indirect oxides of O₃ produced in discharge process had a contribution rate of more than 23.3%,10.3%and 73.5%for dye decolorization,the participation part of O₃ was more than half of its total production.The mechanism of dye degradation promoted by O₃ catalyst supported by manganese oxide was studied,the characterizations of SEM and BET showed that porous structure of Al₂O₃ carrier ball of Mn_xO_y-Al₂O₃ catalyst were covered by Mn_xO_y,the surface structure of catalyst became rougher after being loaded.Furthermore,the number of pores,average pore size and pore volume decreased after being loaded.The characterization of XRD found that Mn_xO_y was mainly MnO₂,a small amount of Mn₂O₃ contained.The characterization of TPR showed that the oxidation of Mn_xO_y-Al₂O₃ catalyst enhanced after O₃ catalytic activation.MB decolorization rate increased by 17.78%within 9 min under the condition of 1.5 g·L^-1 of Mn_xO_y-Al₂O₃ catalyst.