Treatment Of Landfill Leachate Biochemical Tailwater Using Iron Compound Catalyzed Persulfate Oxidation

With leachate biotreated tailwater from Mai Yuan landfill as the object of the research, we constructed Fe2+/ persulfate system, ZVI / persulfate system, Fe3O4/ persulfate system to treat it. On the basis of optimizing impact parameters of different oxidation systems by single factor method, significance analysis was carried out on the different impact parameters by orthogonal experiments. Further, removal features of leachate biochemical tailwater pollutants by different oxidation systems were explored using Fourier infrared spectrum, ultraviolet spectrum, the three dimensional fluorescence spectrum. And the microstructure of(ZVI and Fe3O4) were analyzed by means of X ray diffraction(XRD), electron microscope scanning(SEM) and X ray photoelectron spectroscopy(XPS). The conclusions are as follows:(1)Treatment of biochemical tail water of landfill leachate by Fe2+/Na2S2O8 system:Appropriate process parameters: With the COD and color are removed 60% and 95%respectively, when the optimum process parameters are the Fe2+ dosage of 1 g/L, initial p H value of 4.0, dosage of 4.0 g/L, and reaction time of 12 h. Orthogonal experiments were designed to optimize the oxidation conditions based on the single affected factor. The results showed that the influences on COD of operating factors followed the order of Na2S2O8 dosage > p H > Fe2+dosage > reaction time.By means of three dimensional fluorescence and ultraviolet spectrum analysis of the water samples before and after the reaction: The degree of organic pollutants and a lot of humic acid were decreased by treated with Fe2+/Na2S2O8 system in water samples. The dissolved organic matter(DOM) was aslo decreased in wastewater.(2)Treatment of biochemical tail water of landfill leachate by ZVI/Na2S2O8 system:Appropriate process parameters: It was the best parameters that the p H of solution is 3,the dosage of zero-Valent iron is 0.5g/L and the dosage of sodium sulfate is 2.5g/L. Under these conditions, the removal rates of COD is up to 71%. Orthogonal experiments were designed to optimize the oxidation conditions based on the single affected factor. The results showed that the influences on comprehensive index of operating factors followed the order of ZVI dosage > Na2S2O8 dosage> p H > reaction time.Three dimensional fluorescence,UV and IR spectra of water samples were analyzed with before and after treatment: By the system of ZVI/ Na2S2O8(DOM) treated,the solubleorganic matter is reduced and humic substances being large removed water pollution degree.The molecular condensation degree of organic compounds is weakened as will as aromatic ring structure.the light energy mass and structure of organic matter have a certain change.The ZVI was characterized by electron microscopy(SEM), XRD- ray diffraction(X)and other modern characterization methods: ZVI not only contains Fe0 but also containing Fe2+, Fe3+in the catalytic surface which containing flocculent oxide covered on its surface after reaction.(3)Treatment of biochemical tail water of landfill leachate by Fe3O4/Na2S2O8 system:It was the p H of solution is 3, the dosage of Fe3O4 iron is 1.5g/L, and the the dosage of Na2S2O8 is 3.5 g/L,at the reaction time of 24 h. Under these conditions, the removal rates of COD and colour are up to 63% and 100% respectively. Orthogonal experiments were designed to optimize the oxidation conditions based on the single affected factor. The results showed that the influences on comprehensive index of operating factors followed the order of p H > Fe2+dosage > Na2S2O8 dosage > reaction time.By means of three-dimensional fluorescence spectrum, ultraviolet spectrum and Fourier infrared spectrum analysis: Most humic acids are oxidated to fulvic acid which is smaller molecular weight and more structured unstableby by the Fe3O4/ Na2S2O8 system treated.Sulfate free radical with oxidated fulvic acid being degradaten;The main structure and light energy group of the organic matter changed,and conjugate double bond in the water sample was decreased significantly, Aromaticity of dissolved organic matter(DOM)reduced,with whose substituted group classes had a decrease simultaneously.Scanning electron microscopy(SEM), X ray diffraction(XRD), X ray photoelectron spectroscopy(XPS), BET analyzer and other modern characterization method can be used to analysis the micro morphology Fe3O4 of before and after the reaction:It can be found that Fe3O4 has been oxidized into r-Fe2O3 and particle size was decreased with structure becomed empty after the reaction by Using XRD and SEM.The changes of iron content structure of nano Fe3O4 were found in the surface by using XPS. The Fe3+/Fe2+was decreased from 1.8 to 0.8 after the reaction. The BET characterization of the nano Fe3O4 was found to increase the surface area of the catalyst which was found to increase the surface area of the catalyst before and after the reaction.