Comprehensive treatment process of landfill leachate

Abstract

The invention discloses a comprehensive treatment process of landfill leachate, and belongs to the field of sewage treatment. The treatment process comprises preparation of a catalyst PCN 224 / Fe3O4-loaded mesoporous silica and a landfill leachate treatment method. Fe3O4 is loaded through a PCN-224 (H) metal organic framework, mesoporous silica wraps the outer layer, on one hand, the PCN-224 (H) metal organic framework can generate singlet oxygen through photodynamic force, on the other hand, Zr and Fe construct a double-active center to generate a synergistic effect, the mesoporous silica protects an MOF core with catalytic activity and the Fe and Zr double-active center, and meanwhile, the photocatalytic activity of the metal organic framework is improved. And the catalytic activity of the catalyst cannot be reduced due to the permeability. The comprehensive treatment process disclosed by the invention is high in COD (Chemical Oxygen Demand) and total nitrogen removal amount, improves the utilization rate of Fenton reaction raw materials in the advanced oxidation treatment landfill leachate, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the field of sewage treatment, and in particular relates to a comprehensive treatment process for garbage leachate. Background Art

[0002] If the landfill leachate is discharged directly without treatment, it will cause serious pollution and harm to the surrounding groundwater, surface water, soil and other ecological environments and the surrounding people. However, the water quality of landfill leachate is complex and the concentration of pollutants is high. It changes greatly with the extension of landfill time, which increases the difficulty of selecting a suitable treatment process for landfill leachate.

[0003] At present, biochemical method and combined process are widely used in treating landfill leachate. However, the simple biochemical process is often difficult to adapt to the characteristics of the increasingly deteriorating water quality of the leachate, and the treatment efficiency is decreasing. The reverse osmosis process combined with it has high operating costs and generates concentrated liquid. The patent application with publication number CN114229984A discloses a two-stage Fenton-like treatment method for landfill leachate, which is adjusted to acidic by biochemically treating the landfill leachate, and enters a first-level Fenton-like reaction tower in a bottom-in and top-out manner, and hydrogen peroxide is added at the same time to obtain a first-level Fenton treatment process effluent; the first-level Fenton treatment process effluent is adjusted to acidic, and then enters a second-level Fenton-like reaction tower in a bottom-in and top-out manner, and hydrogen peroxide is added at the same time to obtain a second-level Fenton treatment process effluent; chemical and biological methods are used to degrade pollutants, and no concentrated water is generated; the COD content of the treated landfill leachate can be reduced to less than 50 mg / L. However, the existing Fenton advanced oxidation process uses a large amount of raw materials per ton of water for treatment, and the utilization rate is low; therefore, how to improve the utilization rate of raw materials is a problem that needs to be solved urgently. Summary of the invention

[0004] The object of the present invention is to provide a comprehensive treatment process for landfill leachate to solve the problem of low utilization rate of raw materials for Fenton reaction in advanced oxidation treatment of landfill leachate.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A comprehensive treatment process for landfill leachate comprises the following steps:

[0007] The catalyst PCN 224 / Fe3O4@mesoporous silica was added to the landfill leachate, and H2O2 was added, and the mixture was fully reacted under near-infrared light.

[0008] Furthermore, the dosage of the catalyst PCN 224 / Fe3O4@mesoporous silica is 0.1-1 g / L; the COD value of the landfill leachate is 1650-1800 mg / L, and the total nitrogen content is 1100-1200 mg / L; the dosage of H2O2 is 400-600 mg / L, and the reaction time is 1-4 h.

[0009] Furthermore, the preparation method of the catalyst PCN 224 / Fe3O4@mesoporous silica is as follows:

[0010] 1) Dispersing the PCN-224(H) metal organic framework and Fe3O4 in N,N-dimethylformamide, dissolving by ultrasonication, stirring and heating at 120-130°C for 10-12h, centrifuging and washing to obtain PCN 224 / Fe3O4;

[0011] 2) Dispersing PCN 224 / Fe3O4 in deionized water / ethanol solvent, adding hexadecyltrimethylammonium bromide, heating to 50-60°C and stirring for 1-1.5h; then adding NH3·H2O, and then dropping tetraethoxysilane / ethanol solution in portions, continuing to stir at 50-60°C for 6-8h, centrifugally washing, extracting, and drying to obtain a precipitate;

[0012] 3) The precipitate is dispersed in deionized water to obtain a suspension, which is heated to 100-105° C. and stirred for 22-24 h. The PCN 224 / Fe 3 O 4 @mesoporous silica is obtained after washing and drying.

[0013] Furthermore, the usage ratio of the PCN-224(H) metal organic framework, Fe3O4 and N,N-dimethylformamide is 100-110 mg: 50-55 mg: 100-120 mL.

[0014] Furthermore, the usage ratio of PCN 224 / Fe3O4, deionized water / ethanol solvent, hexadecyltrimethylammonium bromide, NH3·H2O, tetraethoxysilane / ethanol solution and NH4·NO3 solution is 100-105 mg: 120-130 mL: 1.3-1.5 g: 0.5-1 mL: 10-12 mL: 120-150 mL.

[0015] Furthermore, the dripping is performed in 5 times with an interval of 1 hour between each times.

[0016] Furthermore, the volume ratio of deionized water and ethanol in the deionized water / ethanol solvent is 5:1, the dosage ratio of tetraethoxysilane and ethanol in the tetraethoxysilane / ethanol solution is 0.6-0.7 g:12-14 mL; and the dosage ratio of the precipitate and deionized water is 20-25 g:10-15 mL.

[0017] Furthermore, the extraction is performed using NH4·NO3 at 75-80°C for 6-7h.

[0018] Beneficial effects of the present invention:

[0019] (1) The PCN-224(H) metal organic framework used in the present invention is a MOF formed by a hydrothermal method from Zr clusters and meso-tetrakis(4-carboxyphenyl)porphine, which has high chemical stability. Meso-tetrakis(4-carboxyphenyl)porphine undergoes a type II photodynamic reaction under near-infrared light, consumes oxygen, produces singlet oxygen, and oxidizes organic matter in the leachate. The oxygen produced by the decomposition of hydrogen peroxide can provide oxygen for it, thereby improving the utilization efficiency of hydrogen peroxide. At the same time, Zr can form a dual active center with Fe.

[0020] (2) The Fe3O4 used in the present invention not only acts as a catalyst for the Fenton reaction, but also establishes a dual active center between Fe and Zr. The electrons on the surface of Fe(II) are directed to Zr, making it easier for Fe(II) to lose electrons, which is beneficial to the reduction of H2O2. However, in addition to the generation of hydroxyl radicals (·OH), the Fenton reaction is also accompanied by the generation of superoxide anions (O2 ·- ), when superoxide anion (O2 ·- ) When the Zr center loses electrons, it forms 1 O2 participates in the redox reaction, and these electrons can be transferred to Fe(III), accelerating the reduction of Fe(III) to Fe(II), improving the catalytic efficiency of the catalyst and increasing the service life of the catalyst.

[0021] (3) The mesoporous silica used in the present invention as the outer shell of the material protects the catalytically active MOF core and the dual active centers of Fe and Zr, and slows down the decomposition of the overall material during the catalytic reaction. On the other hand, since it is a permeable mesoporous SiO2 shell, it avoids the problem of the outer shell structure completely blocking the active sites. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1

[0024] This embodiment provides a comprehensive treatment process for landfill leachate, and the specific implementation method is as follows:

[0025] In the first step, 100 mg PCN 224 and 50 mg Fe3O4 were dispersed in 100 mL N, N-dimethylformamide, dissolved by ultrasonication, heated with stirring at 120-130°C for 10-12 h, and washed by centrifugation to obtain PCN 224 / Fe3O4;

[0026] In the second step, 100 mg PCN 224 / Fe3O4 was dispersed in 120 mL deionized water / ethanol solvent, and 1.5 g hexadecyltrimethylammonium bromide was added, heated to 50-60 ° C and stirred for 1-1.5 h; then 0.5 mL NH3·H2O was added, and then 10 mL tetraethoxysilane / ethanol solution was added dropwise 5 times with an interval of 1 h each time, and the mixture was stirred at 50-60 ° C for 6-8 h, centrifuged and washed, and then extracted with 120 mL NH4·NO3 at 75-80 ° C for 6-7 h, and the precipitate was obtained after drying;

[0027] 20 g of the precipitate was dispersed in 10 mL of deionized water to obtain a suspension, which was heated to 100-105° C. and stirred for 22-24 h. After washing and drying, PCN 224 / Fe 3 O 4 @mesoporous silica was obtained.

[0028] In the third step, 0.5 g of catalyst PCN 224 / Fe3O4@mesoporous silica was added to 1 L of landfill leachate (COD value was 1650 mg / L, total nitrogen content was 1100 mg / L), and 400 mg of H2O2 was added, and the mixture was fully reacted for 3 h under near-infrared light irradiation.

[0029] Example 2

[0030] The present embodiment is different from the embodiment 1 in that “0.5 g catalyst PCN 224 / Fe3O4@mesoporous silica” is changed to “0.1 g catalyst PCN 224 / Fe3O4@mesoporous silica”.

[0031] The remaining raw materials and preparation process remain the same as in Example 1.

[0032] Example 3

[0033] The present embodiment is different from the embodiment 1 in that “0.5 g of catalyst PCN 224 / Fe3O4@mesoporous silica” is changed to “1 g of catalyst PCN 224 / Fe3O4@mesoporous silica”.

[0034] The remaining raw materials and preparation process remain the same as in Example 1.

[0035] Example 4

[0036] The difference between this embodiment and embodiment 1 is that "400 mg H2O2" is changed to "600 mg H2O2".

[0037] The remaining raw materials and preparation process remain the same as in Example 1.

[0038] Comparative Example 1

[0039] Compared with Example 1, this comparative example is different in that the second step is removed, and the specific implementation steps are as follows:

[0040] In the first step, 100 mg PCN 224 and 50 mg Fe3O4 were dispersed in 100 mL N, N-dimethylformamide, dissolved by ultrasonication, heated with stirring at 120-130°C for 10-12 h, and washed by centrifugation to obtain PCN 224 / Fe3O4;

[0041] In the second step, 0.5 g of catalyst PCN 224 / Fe3O4 was added to 1 L of landfill leachate, and 400 mg of H2O2 was added, and the mixture was fully reacted for 3 h under near-infrared light irradiation.

[0042] The remaining raw materials and preparation process remain the same as in Example 1.

[0043] Comparative Example 2

[0044] Compared with Example 1, this comparative example differs in that the first and second steps are removed, and the specific implementation steps are as follows:

[0045] 0.5 g of catalyst PCN 224 was added to 1 L of landfill leachate, and 400 mg of H2O2 was added, and the mixture was fully reacted for 3 h under near-infrared light irradiation.

[0046] The remaining raw materials and preparation process remain the same as in Example 1.

[0047] Comparative Example 3

[0048] Compared with Example 1, this comparative example is different in that the first and second steps are removed and the catalyst is changed to Fe3O4. The specific implementation steps are as follows:

[0049] 0.5 g of catalyst Fe3O4 was added to 1 L of landfill leachate, and 400 mg of H2O2 was added, and the mixture was fully reacted for 3 h under near-infrared light irradiation.

[0050] The remaining raw materials and preparation process remain the same as in Example 1.

[0051] Comparative Example 4

[0052] Compared with Example 1, this comparative example is different in that in the third step, no near-infrared light irradiation is performed, and the reaction is placed in the dark. The specific implementation steps are:

[0053] In the fourth step, 0.5 g of catalyst PCN 224 / Fe3O4@mesoporous silica was added to 1 L of landfill leachate (COD value was 1650 mg / L, total nitrogen content was 1100 mg / L), and 400 mg of H2O2 was added, and the reaction was carried out in the dark for 3 h.

[0054] The remaining raw materials and preparation process remain the same as in Example 1.

[0055] The performance tests were performed on Examples 1 to 4 and Comparative Examples 1 to 4.

[0056] According to GB / T 34500.2-2017 "Chemical Analysis Methods for Rare Earth Waste Residues and Wastewater Part 2: Determination of Chemical Oxygen Demand (COD)", the chemical oxygen demand test was performed on each embodiment and comparative example of the present application;

[0057] According to GB / T 11894-1989 "Determination of total nitrogen in water - Alkaline potassium persulfate digestion ultraviolet spectrophotometry", the total nitrogen content of each embodiment and comparative example of the present application was tested;

[0058] The results are shown in Table 1:

[0059] Table 1

[0060]

[0061] It can be seen from Table 1 that compared with Example 1, when the catalyst addition amount is 0.5 g / L and the hydrogen peroxide content addition amount is 400 mg / L, the COD removal rate and total nitrogen removal rate of Examples 2 to 4 are 95.8% and 88.7% respectively, and the comprehensive effect is the best. Compared with Example 1, in Comparative Example 1, without synthesizing the mesoporous silica shell, the weak combination of Fe3O4 and PCN224 leads to the decrease of the activity of the dual active centers of Fe and Zr, resulting in the decrease of COD and total nitrogen removal; in Comparative Example 2, compared with Example 1, the COD and total nitrogen removal rates are very low, because the PCN224 material alone can only produce singlet oxygen, and cannot produce more active hydroxyl radicals; in Comparative Example 3, compared with Example 1, Fe3O4 alone can only produce Fenton reaction, and Fe(II) is difficult to be reduced to Fe(II) again after being oxidized to Fe(III), and the oxygen generated by the decomposition of hydrogen peroxide cannot be utilized, the utilization rate of hydrogen peroxide decreases, and the catalytic effect is reduced; in Comparative Example 4, compared with Example 1, in the absence of near-infrared light, the oxygen generated by the decomposition of hydrogen peroxide cannot be converted into singlet oxygen, resulting in a decrease in the removal effect.

[0062] In summary, the comprehensive treatment process for landfill leachate provided by the present invention has high COD and total nitrogen removal rates, improves the utilization rate of Fenton reaction raw materials in advanced oxidation treatment of landfill leachate, and has good application prospects.

[0063] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0064] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A comprehensive treatment process for landfill leachate, characterized in that: The steps include: The catalyst PCN 224 / Fe3O4@mesoporous silica was added to the landfill leachate, and H2O2 was added to fully react under near-infrared light irradiation; The dosage of the catalyst PCN 224 / Fe3O4@mesoporous silica is 0.1-1 g / L; the COD value of the landfill leachate is 1650-1800 mg / L, and the total nitrogen content is 1100-1200 mg / L; the dosage of H2O2 is 400-600 mg / L, and the reaction time is 1-4 hours.

2. A comprehensive treatment process for landfill leachate according to claim 1, characterized in that: The preparation method of the catalyst PCN 224 / Fe3O4@mesoporous silica is as follows: 1) Dispersing the PCN-224(H) metal organic framework and Fe3O4 in N,N-dimethylformamide, dissolving by ultrasonication, stirring and heating at 120-130°C for 10-12h, centrifuging and washing to obtain PCN 224 / Fe3O4; 2) Dispersing PCN 224 / Fe3O4 in deionized water / ethanol solvent, adding hexadecyltrimethylammonium bromide, heating to 50-60°C and stirring for 1-1.5h; then adding NH3·H2O, and then dropping tetraethoxysilane / ethanol solution in portions, continuing to stir at 50-60°C for 6-8h, centrifugally washing, extracting, and drying to obtain a precipitate; 3) The precipitate is dispersed in deionized water to obtain a suspension, which is heated to 100-105° C. and stirred for 22-24 h. The PCN 224 / Fe 3 O 4 @mesoporous silica is obtained after washing and drying.

3. A comprehensive treatment process for landfill leachate according to claim 2, characterized in that: The usage ratio of the PCN-224(H) metal organic framework, Fe3O4 and N,N-dimethylformamide is 100-110 mg: 50-55 mg: 100-120 mL.

4. The comprehensive treatment process for landfill leachate according to claim 2, characterized in that: The usage ratio of the PCN 224 / Fe3O4, deionized water / ethanol solvent, hexadecyltrimethylammonium bromide, NH3·H2O, tetraethoxysilane / ethanol solution and NH4·NO3 solution is 100-105 mg: 120-130 mL: 1.3-1.5 g: 0.5-1 mL: 10-12 mL: 120-150 mL.

5. The comprehensive treatment process for landfill leachate according to claim 2, characterized in that: The stepwise addition is performed in 5 times with an interval of 1 hour between each times.

6. The comprehensive treatment process for landfill leachate according to claim 2, characterized in that: The volume ratio of deionized water to ethanol in the deionized water / ethanol solvent is 5:1, the dosage ratio of tetraethoxysilane to ethanol in the tetraethoxysilane / ethanol solution is 0.6-0.7 g:12-14 mL; the dosage ratio of the precipitate to deionized water is 20-25 g:10-15 mL.

7. The comprehensive treatment process for landfill leachate according to claim 2, characterized in that: The extraction is carried out at 75-80°C with NH4·NO3 for 6-7h.

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