Degradation Of Methyl Orange By Falling Water Film Dielectric Barrier Discharge Plasma

With the rapid development of dye and textile industries,large quantities of dye wastewater were generated.Dye wastewater is characterized by complicated components,high organic concentration,high toxic and poor biodegradability,which is difficult to decompose through some traditional sewage treatment methods.Dielectric barrier discharge?DBD?plasma technology combines the advantages of free radical oxidation,ultraviolet degradation,ozonation and other advanced oxidation process.In addition,DBD plasma technology owns the charictarstic of discharge stablility,high electron density,ease of operation and high efficiency.Therefore,this technology can effectively degrade dyestuff in wastewater,and provide a new approach for dye wastewater treatment.In this paper,methyl orange?MO?was selected as a simulative dye wastewater,and it was degraded by self-designed falling water film DBD reactor.The effects of technological parameters,atmospheres and catalysts on the degradation of methyl orange solution were investigated.The results showed that MO can be effectively decomposed by falling water film reactor with Ar bubbling.After 30 min discharge treatment,93.7%degradation rate and46.5%COD remove rate of MO were achieved and the corresponding energy yield was0.5813 g·?kW·h?^-1 with gas velocity of 300 m L·min^-1 and the input power of 72.5 W.MO was easier to decompose under acid and lower conductivity condition.There are different degradation effects on methyl orange with work gas Ar,O₂,air respectively.The worst degradation of methyl orange can be achieved when air was employed as the working gas of the DBD process.This phenomenon was due to that more energy was needed during air discharge.Moreover it can produce less reactive oxygen species and more nitrogen active particles with low activity which can increase conductivity of solution.A large amount of ozone with great oxidation ability can be generated when O₂ was employed as the working gas of the DBD process.The best degradation of MO can be attained,and 98%degradation rate and 54.93%COD removal rate of MO can be achived with 10 min treatment.The addition of Fe²⁺and persulfate?PS?into DBD system both improved the degradation of methyl orange.The former is because the oxidizing power of H₂O₂generated in DBD reactor was strengthened;the latter is due to PS can produce active particles by taking full advantage of heating effects and UV in the plasma process.DBD/Fe²⁺/PS system was confirmed to improve the degradation and COD removal rate of methyl orange remarkably.Because it can trigger multiple oxidation-reduction reactions.After 30 min discharge treatment,the highest degradation rate?100%?and COD removal rate?72.4%?accqured in this system with Ar bubbling.Tert-butyl alcohol as a·OH radical scavenger can siginificantly weaken methyl orange degradation,in the same time CCl₄ as a·H radical scavenger can strengthen methyl orange degradation,so·OH played a main role in the argon plasma reaction.According to bond dissociation energies?BDEs?theory and the intermediate products identified by LC-MS,the degradation mechanism of MO was proposed.The degradation pathway of methyl orange involved bond-breaking reaction,benzene ring-opening process and deep oxidation.