Application Of Plasma In Degradation Of Simulated Printing And Dyeing Wastewater

The problem of industrial water pollution is a severe challenge to the contemporary society.Dye wastewater is a kind of industrial wastewater.The harm of dye wastewater includes large amount of water,high chroma and difficult degradation.Dye wastewater is harmful to human body and environment.In this paper,atmospheric pressure direct-current(DC)glow discharge plasma technology was used to establish a plasma solution cycle degradation system.The setup can degrade methylene blue(MB)in simulated organic printing and dyeing wastewater.The effects of gas electric parameters,initial solution conditions,additives,environment and working gas on MB degradation were studied.The degradation effect and mechanism of MB were studied by Chemical Oxygen Demand(COD)test and Liquid Chromatograph Mass Spectrometer(LC-MS)test.This paper provides a theoretical basis for the practical application of DC glow discharge plasma technology in the treatment of organic printing and dyeing wastewater.The results are as follows:(1)The gas electric characteristics of the setup,the initial conditions of the solution and the additives of the solution were studied:The current intensity can change the excitation power of the plasma to adjust the degradation effect of MB.When the current increased,the intensity of plasma was enhanced and the degradation rate was enhanced.The discharge electrode distance increased,the plasma volume became larger,and the degradation efficiency was improved.When the gas flow rate into the electrode was 30 sccm,the effect was better than other gas flow rates,because the appropriate gas flow rate is conducive to the formation of a more stable plasma to improve the degradation efficiency.It was found that the degradation efficiency of MB at 7mg/L was better than that at 1 mg/L,when the initial concentration of the solution was changed,and the degradation rates were all above 92%.This indicates that this technique has a good degradation effect for low concentrations of MB,and is more suitable for degrading high concentrations of MB.The degradation effect was improved by 23%when adjusting the initial p H of MB aqueous solution to 4.44 than that at 10.76.The electric field of MB aqueous solution is stable and stronger when the conductivity was low.Low conductivity is beneficial to degradation.After the addition of·OH radical scavenger ethanol,isopropanol and H₂O₂scavenger catalase(CAT),the degradation rate decreased a lot.The degradation rate decreased by 57%at most.After adding·OH radical promoter H₂O₂,the degradation rate increased by 30%.The dominant role of·OH radical for the degradation of organic dyeing wastewater was printed.As far as we know,this paper is the first to use CAT in the experiment of wastewater degradation by DC glow discharge plasma.The degradation effect was significantly enhanced by the addition of Fe²⁺.(2)The plasma is an ionized gaseous substance.In this paper,the main sources of plasma ionized gas are the gas flowing into the tungsten steel electrode(working gas)and the gas environment(ambient gas)where the discharge occurs.Working gas and ambient gas have great influence on the properties of plasma ionized gas.In order to achieve independent control of ambient gas and working gas,two kinds of innovation setups were built in this experiment.The setups can study these two factors systematically.The two kinds of setups were the acrylic protective cover which covers the whole reaction tank and the protective cover which covers the gas outlet of tungsten steel electrode.The results showed that changing ambient gas had more effect on the degradation effect of the setup than changing working gas.The degradation effect was quite good with both ambient gas and working gas being air.The degradation rate reached more than 80%after 12 min reaction using 20 m A discharge current.Experimental result is very favorable for the practical application of this technique to treat organic dyeing wastewater.A setup using tungsten steel electrodes wrapped in a protective cover.When both working gas and ambient gas were argon,the setup achieved extremely excellent degradation with a degradation rate of 82%.Several conjectures about the cause of the experimental results were put forward.These conjectures were partially confirmed by experiments.(3)COD and LC-MS were used to test the solution after the reaction:the COD of MB aqueous solution decreased by 60%after 15 min reaction.The results are better than most of the same type of plasma degradation experiments.The LC-MS test showed that the MB molecules of m/z 320 were effectively degraded into small molecular weight products after 15 min degradation.It is speculated that MB undergoes bond breaking oxidation and ring opening oxidation in the plasma reactor.Finally,organic acids with small molecular weight,CO₂and H₂O were produced.