Study On Dye Wastewater Treatment By Dielectric Barrier Discharge Plasma

The dye wastewater is a kind of refractory wastewater,which has the characteristics of complex components,large chroma and high CODcr value.Non-thermal plasma technology,as a new advanced oxidation technology,can produce a series of physical and chemical effects without adding other chemical reagents,such as ultraviolet light,shock wave,electric field and oxygen-containing active species?·OH,·O,O₃,H₂O₂,etc.?.Among these,the oxygen-containing active species can effectively treat the refractory wastewater through the ring opening and bond breaking of the organic compounds.Dielectric barrier discharge plasma has attracted much research attention because of its advantages of simple operation and stable discharge.However,in the field of wastewater treatment,there are still some problems such as high energy consumption,low mineralization rate and unclear mechanism,which limit the further application of the technology.In order to improve the efficiency of the plasma active species,reduce the energy consumption and increase the mineralization rate,a dielectric barrier discharge plasma reactor combining a bead-packed bed and a microporous aeration plate was developed in this paper.Based on this plasma reactor,this paper first studied the discharge mechanism of the reactor.The treatment of dye wastewater using single plasma technique and coupled system of plasma and other wastewater treatment method was respectively investigated.The results can provide a theoretical basis and technical support for the application of dielectric barrier discharge plasma technology in dye wastewater treatment.The main contents and conclusions are listed as follows:?1?In order to explore the discharge mechanism of the plasma reactor and investigate the generation mechanism of the plasma during discharge process,a fluid model was established to analyze the discharge behavior in the bead-packed bed and the microporous aeration plate using the COMSOL Multiphysics software.The effects of input voltage and dielectric constant on the distribution of the electric field intensity,electron density and ion density were investigated.The results showed that the plasma species which reacted with wastewater was composed of long-life species produced in the packed bed area and short-life species generated in the gas film on the surface of the micro-porous aeration plate.The use of the dielectric barrier can enhance the local field strength and generate discharge plasma at lower input voltage.At lower voltage,the electrons were mainly distributed in the discharge cavity with large local field strength.The larger the discharge voltage was,the stronger the electric field strength was and the greater the average electron density was.When the dielectric constant?_rof the packed dielectric was less than 50,the field strength and electron density of the discharge space increased with increasing?_r.In addition,the result of the geometrical model of the microporous plate showed that the density of electrons existing in the gas film on the surface of plate reached 10¹⁶m^-3,indicating the in-situ generation of plasma active species in the reactor.?2?The degradation of dye wastewater in the plasma reactor was conducted using methylene blue solution as the model wastewater.The effects of discharge voltage,air flow rate,initial solution concentration,initial p H value and initial conductivity value on the degradation of methylene blue were examined.The possible mechanism of the degradation of methylene blue was analyzed using the techniques of FT-IR and LC-MS.Under the discharge voltage of 7 k V and air flow rate of 1.5 L/min,the degradation efficiency of methylene blue with and without packed beads were 97.5%and 65%,respectively,which indicated that more plasma active species can be generated in reactor with packed beads.Compared to ozone alone treatment,higher CODcr removal?48.3%?and TOC removal?38.5%?were acquired under plasma treatment,which can be attributed to the in-situ generation of hydroxyl radical.In addition,the energy yield reached 9.3 g/k Wh after 10 min plasma treatment.No obvious change in methylene blue degradation efficiency was obtained for solutions with various initial p H or initial conductivity.The mechanism of methylene blue degradation showed that high energy electron,ozone and hydroxyl radical were the main species in methylene blue degradation.?3?To further improve the degradation efficiency and mineralization rate of wastewater,a carbon-based material?AC/PUF?was introduced to investigate the synergetic effect of coupled system of plasma and AC/PUF on methylene blue degradation.The degradation efficiency and energy yield of methylene blue reached97.9%and 13.5 g/k Wh with 10 min treatment,respectively.After 30 min treatment,the CODcr removal was as high as 90.6%.In addition,the G₅₀ of the coupled system was up to 38.3 g/k Wh.The results showed that the coupled system can enhance the degradation efficiency of methylene blue and greatly increase the solution mineralization rate while reducing the energy consumption.?4?The degradation performance of the dielectric barrier discharge plasma technology on the actual dye wastewater was investigated using three azo dyes,i.e.,reactive red 241,reactive yellow EDA and reactive black 5,as the raw materials.The change in absorbance under the corresponding characteristic wavelength and CODcr removal were analyzed for the three dyes.The results showed that the plasma technology had the best degradation performance on reactive yellow EDA wastewater.After 30 min single plasma treatment,the degradation efficiency reached 100%and the CODcr removal rate reached 94.8%.For the coupled system of plasma and AC/PUF,the degradation efficiency and CODcr removal achieved 100%after 20 min and 30 min treatment,respectively.For the actual mixed wastewater,the degradation efficiency and the CODcr removal obtained for the coupled system were higher than those for the single plasma treatment,which showed the advantage of the coupled system.In addition,the value of BOD₅/CODcr increased from initial 0.21 to 0.67 after plasma treatment,indicating that the plasma treatment can greatly improve the biodegradability of the actual mixed wastewater.