Degradation Of Organic Pollutants In Water By Discharge Plasma With Persulfate

As a new kind of advanced oxidation technology,plasma discharge treatment is markedby the generation of active substances like hydroxyl radicals,hydrogen peroxide and ozone,besides of physicochemical effects like UV and Joule heat.Discharge plasma has advantages like fast,high efficiency and no secondary pollution,but has shortcomings like high energy consumption at the same time in the treatment of organic pollutants.In this paper the method of activation of persulfate(PS)by discharge plasma was carried out,i.e.ultraviolet,heat and other physicochemical effects which can not be directly involved in the degradation of pollutants were used to active PS.Thereby sulfate radicals with higher oxidation-reduction potential were produced to promote the mineralization of organic pollutants.Azo dyes and phenol were chosen as objects.Reaction parameters like applied voltage,discharge gas gap,dosage of PS and so on were analysed.The mechanisms of the activation of PS and function of active substances were analysed through emission spectrum and varies of discharge atmosphere.The results are as follows.1.The treatment of acid orange 7(AO7)(1)The increase of voltage and decrease of discharge gap can both enhance the intensity of Dielectric barrier discharge(DBD)plasma and promote the activation of PS.With the applied voltage increased from 15 to 19 k V,the AO7 decolorization rate and the corresponding increase of AO7 decolorization rate caused by the addition of PS both increased.The decolorization rate and corresponding increase of AO7 both decreased with the discharge gap increasing from 2 to 8 mm.(2)The effects of initial concentration of AO7,PS dosage and initial p H value of the solution: with the increase of initial AO7 concentration,AO7 decolorization percentage and the corresponding increase caused by PS both decreased.But the absolute amount of AO7 that was decolorized was improved and the corresponding energy efficiency increased from0.16 g/k Wh to 0.75 g/k Wh.With the increase of PS dosage,the decolorization rate and the corresponding increase were both remained unchanged after first increase.With conditions:voltage of 17 k V,discharge gas gap of 4 mm,molar ratio of PS and AO7 of 60:1,the addition of PS increased AO7 decolorization rate and corresponding energy efficiency by 44% and0.16 g/k Wh.Besides,the corresponding removal rate of TOC of AO7 solution was increased from 14.2% to 53.8%.2.The treatment of P-nitrophenol(PNP)(1)With applied voltage increasing from 15 to 19 k V,the PNP degradation percentage and corresponding increase of PNP degradation percentage caused by PS both increased.With the increase of PS dosage,the degradation rate and the corresponding increase were both remained unchanged after the first increase.With conditions: voltage of 17 k V,discharge gas gap of 4 mm,molar ratio of PS and PNP of 70:1,PNP degradation rate and corresponding energy efficiency were 63.6% and 0.18 g/k Wh with an increase of 28.8% and 0.08 g/k Wh caused by PS respecticely.(2)The effects of Cl-and Fe2+ on PNP degradation were analyzed.The results showed that the degradation rate of PNP kept unchanged after the first decrease with the increase of Cl-dosage,and unchanged after the first increase with the increase of Fe2+ dosage.But there was no synergistic effect between Fe2+ and PS in the process.3.Activation mechanism of PS and action mechanism of active substances(1)The emission spectrum of discharge process was measured and fitted.The results showed that different intensity of UV emission spectrum marked by emission spectrum of N2(C3?u-B3?g,? = 280-450 nm)was measured.In addition,the temperature of discharge gas was obtained by fitting emission spectrum(370-382 nm)and was approximately 340 K.The results indicated that the activation of ultraviolet and heat to PS during the treatment process existed actually.(2)The action mechanism of active substances was analysed by changing discharge atmosphere.The results showed that air and argon discharge plasma can both effectively activate PS and AO7 decolorization rate was increased by 44.8% and 51.9% respectively.And O3 played a key role in the decolorization process of AO7.