Catalytic Ozonation And Reduction Of Dye Wastewater Using Zero-Valent Iron As A Catalyst

Zero-Valent iron has been widely used in water treatment industry because it costs less and the production process is simpler and it will not cause secondary pollution to the environment.The electrode reaction products-new eco-hydrogen [H]-together with Fe²⁺ can react with many components in wastewater which will destroy the chromophoric group of dyes leading the dyes' decolorization.Ozone oxidation can produce strong oxidizing and low selectivity hydroxyl radical which is widely used as well.However,so far ozone oxidation is inefficient and selective.So catalytic ozonation technology was developed to improve the ozone utilization and oxidation capacity.In this study,zero valent iron was chosen as the catalyst to combine the reduction of zero valent iron with the oxidation of ozone,so as to degrade dye wastewater more completely and efficiently.In the catalytic ozonation system,The gas source of ozone generator was the air.so the gas it produced was the mixture of ozone and other gases.The most suitable ozone flow rate was 320ml/min in 500 m L dye wastewater system.And two surge flasks were connected to make the mixture stable and uniform.In this paper,the feasibility of catalyzed ozonation system using zero valent iron as a catalyst and the influence of various factors on catalytic efficiency had been discussed.Specific conclusions are as follows:?1?The degradation rate constants of catalyzed ozonation system was 0.853 satisfying the first-order kinetic when the initial conditions were controlled as follows: The pH was 5.5,zero valent irion dosage was 0.1g/L,temperature was 24±0.5?,the ozone flow rate was 320ml/min,and the reaction time was 4min.Zero valent iron alone can hardly degrade Indigotindisulfonate Sodium,and the degradation rate constant of ozone alone was 0.588.Apparently,the degradation rate constants of catalyzed ozonation system was higher than that of zero valent iron alone and ozone alone,indicating that zero valent iron can accelerate the degradation of organic by ozone.?2?The degradation rate constants of catalyzed ozonation system using micro scale zero valent iron and nanoscale zero valent iron were 0.853 and 0.667.So it's more suitable to use nZVI as the catalyst.?3?In the catalytic ozonation using nZVI as a catalyst system,pH is the most significant factor.The most suitable pH was 8.The degradation rate constants increased with the increase of pH from 5 to 8.When pH decreased to 3,the degradation rate constants increased because the large amount of H+ in the solution was benefit for nZVI to produce [H].Other conditions including the nZVI dosage and the temperature was 0.5g/L and 50?.Besides,Cl-and SO₄^2- will promote the reaction,while NO₃^- will inhibit the reaction.In result,the method should be used carefully when it contains large amounts of NO₃^-.?4?It can be seen from the UV-Vis Spectrum and mass spectrum analysis that the intermediate products produced in the ozone alone system is the same as that of the zero valent iron catalyzed ozonation system.[H] produced by the interaction of zero valent iron with water molecules plays a role in reducing the catalytic ozonation system.And it was possible that nZVI can accelerate the producing of free radical.Combined with free radical inhibition experiments and electron spin resonance spectra,it can be proved that the main oxidation active substances in the catalytic ozonation system are ozone molecules and superoxide radical.In the catalytic ozonation using mixed metal oxides as catalysts system,The gas source of ozone generator was the high purity oxygen.The catalyst was prepared by impregnation method,and the ultrasonic pretreatment did not help to improve the activity of the catalyst.The suitable concentration of the MnCl₂ solution was 0.05mol/L,and the suitable dosage of 0.1mol/L NaOH was 5 drops.The degradation rate of Reactive Brilliant Red X-3B using mixed metal oxides as catalysts was improved by 126% compared with that of ozone alone,but the degradation rate was improved with the increase of 56% compared with that of steel wire ball as catalysts.