A comprehensive treatment process for landfill leachate

Abstract

The application discloses a kind of comprehensive treatment process of landfill leachate, belong to sewage treatment field.The treatment process includes preparation of catalyst PCN 224 / Fe3O4 mesoporous silica and landfill leachate treatment method.The application is by PCN-224 (H) metal organic framework load Fe3O4, mesoporous silica is wrapped in outer layer, PCN-224 (H) metal organic framework one side can generate singlet oxygen by photodynamic, the other side Zr and Fe construct double active center and produce synergistic effect, mesoporous silica protects the MOF core with catalytic activity and Fe and Zr double active center, simultaneously, because its permeability will not reduce the catalytic activity of catalyst.The comprehensive treatment process of the application has high COD and total nitrogen removal amount, improves the utilization rate of fenton reaction raw materials in high-level oxidation treatment landfill leachate, and has good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of sewage treatment, and particularly relates to a comprehensive treatment process of landfill leachate. BACKGROUND

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

[0003] At present, biochemical method and combined process are widely used in the treatment of landfill leachate. However, the simple biochemical method process is often difficult to adapt to the characteristics of the deteriorating water quality of the leachate, and the treatment efficiency is declining. The reverse osmosis process combined with it has high operating cost and generates concentrated liquid. The patent application with the publication number CN114229984A discloses a two-stage Fenton-like treatment method for landfill leachate. The landfill leachate after biochemical treatment is adjusted to be acidic, enters a first Fenton-like reaction tower by the way of down-in and up-out, and hydrogen peroxide is added at the same time to obtain the effluent of the first Fenton treatment process. The effluent of the first Fenton treatment process is adjusted to be acidic, and then enters a second Fenton-like reaction tower by the way of down-in and up-out, and hydrogen peroxide is added at the same time to obtain the effluent of the second Fenton treatment process. The pollutants are degraded by chemical and biological methods, and no concentrated water is generated. The COD content of the treated landfill leachate can be reduced to below 50 mg / L. However, the existing Fenton advanced oxidation process has a large amount of raw materials per ton of water 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 at present. SUMMARY

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

[0005] The purpose of the present application can be achieved by the following technical solutions:

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

[0007] The catalyst PCN 224 / Fe3O4@mesoporous silica is added to the landfill leachate, and H2O2 is added, and the reaction is carried out under near-infrared light irradiation.

[0008] Further, the amount 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 amount of H2O2 is 400-600 mg / L, and the reaction time is 1-4 h.

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

[0010] 1) PCN-224(H) metal organic framework and Fe3O4 are dispersed in N,N-dimethylformamide, ultrasonic dissolution, stirring and heating at 120-130 °C for 10-12 h, centrifugal washing to obtain PCN 224 / Fe3O4;

[0011] 2) PCN 224 / Fe3O4 is dispersed in deionized water / ethanol solvent, and cetyltrimethylammonium bromide is added, heated to 50-60 °C and stirred for 1-1.5 h; then NH3·H2O is added, and then tetraethoxysilane / ethanol solution is added dropwise in several times, and stirring is continued at 50-60 °C for 6-8 h, centrifugal washing, extraction, drying to obtain a precipitate;

[0012] 3) The precipitate is dispersed in deionized water to obtain a suspension, heated to 100-105 °C and stirred for 22-24 h, washed and dried to obtain PCN 224 / Fe3O4@mesoporous silica.

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

[0014] Further, the amount ratio of PCN 224 / Fe3O4, deionized water / ethanol solvent, cetyltrimethylammonium 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] Further, the dropwise addition is in 5 times with 1 h interval each time.

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

[0017] Further, the extraction is carried out at 75-80℃ for 6-7h with NH4·NO3.

[0018] The beneficial effects of the present application are:

[0019] (1) The PCN-224(H) metal organic framework used in the present application is a MOF formed by Zr clusters and meso-tetra(4-carboxyphenyl) porphyrin through hydrothermal method, which has high chemical stability. The meso-tetra(4-carboxyphenyl) porphyrin undergoes 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 supply oxygen to it, improving the utilization efficiency of hydrogen peroxide. At the same time, Zr can form a double active center with Fe.

[0020] (2) The Fe3O4 used in the present application not only acts as a catalyst for Fenton reaction, but also establishes a double 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 conducive to the reduction of H2O2. However, in addition to producing hydroxyl radicals (·OH) in Fenton reaction, superoxide anion (O2 ·- ) is also generated. When the superoxide anion (O2 ·- ) loses electrons at the Zr center, it forms 1 O2, which participates in the redox reaction. 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 extending the service life of the catalyst.

[0021] (3) The mesoporous silica used in the present application serves as a shell for the material, protecting the MOF core with catalytic activity and the Fe and Zr double active center, and slowing down the decomposition of the overall material during the catalytic reaction. On the other hand, since it is a permeable mesoporous SiO2 shell, it also avoids the problem of the shell structure completely blocking the active sites. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0023] Embodiment 1

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

[0025] First step, 100 mg PCN 224 and 50 mg Fe3O4 were dispersed into 100 mL N, N- dimethylformamide, ultrasonic dissolution, stirring and heating at 120-130℃ for 10-12h, centrifugal washing, PCN 224 / Fe3O4 was obtained;

[0026] Second step, 100 mg PCN 224 / Fe3O4 was dispersed in 120 mL deionized water / ethanol solvent, and 1.5 g cetyl trimethyl ammonium bromide was added, heated to 50-60℃ and stirred for 1-1.5h; then 0.5 mL NH3·H2O was added, and then 10 mL tetraethoxysilane / ethanol solution was added dropwise for 5 times with 1h interval, and continued to stir at 50-60℃ for 6-8h, centrifugal washing, and then extracted with 120 mL NH4·NO3 at 75-80℃ for 6-7h, dried to obtain the precipitate;

[0027] 20 g of the precipitate was dispersed in 10 mL deionized water to obtain a suspension, heated to 100-105℃ and stirred for 22-24h, washed and dried to obtain PCN 224 / Fe3O4@mesoporous silica.

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

[0029] Example 2

[0030] The difference between this example and Example 1 is that “0.5 g of catalyst PCN 224 / Fe3O4@mesoporous silica” is changed to “0.1 g of catalyst PCN 224 / Fe3O4@mesoporous silica”.

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

[0032] Example 3

[0033] The difference between this example and Example 1 is 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 are the same as Example 1.

[0035] Example 4

[0036] The difference between this example and Example 1 is that “400 mg of H2O2” is changed to “600 mg of H2O2”.

[0037] The remaining raw materials and preparation process are the same as those of Example 1.

[0038] Comparative Example 1

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

[0040] In the first step, 100 mg of PCN 224 and 50 mg of Fe3O4 are dispersed into 100 mL of N, N-dimethylformamide, ultrasonically dissolved, and stirred and heated at 120-130°C for 10-12 h, and then centrifuged and washed to obtain PCN 224 / Fe3O4.

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

[0042] The remaining raw materials and preparation process are the same as those of Example 1.

[0043] Comparative Example 2

[0044] This comparative example is different from Example 1 in that the first to second steps are removed, and the specific implementation steps are as follows:

[0045] In the second step, 0.5 g of the catalyst PCN 224 is added to 1 L of landfill leachate, and 400 mg of H2O2 is added, and the reaction is carried out under near-infrared light irradiation for 3 h.

[0046] The remaining raw materials and preparation process are the same as those of Example 1.

[0047] Comparative Example 3

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

[0049] In the second step, 0.5 g of the catalyst Fe3O4 is added to 1 L of landfill leachate, and 400 mg of H2O2 is added, and the reaction is carried out under near-infrared light irradiation for 3 h.

[0050] The remaining raw materials and preparation process are the same as those of Example 1.

[0051] Comparative Example 4

[0052] This comparative example is different from Example 1 in that, in the third step, no near-infrared light irradiation is performed, and the reaction is carried out in the dark, and the specific implementation steps are as follows:

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

[0054] The remaining raw materials and preparation process were the same as those of Example 1.

[0055] Performance tests were conducted on Examples 1-4 and Comparative Examples 1-4,

[0056] According to GB / T 34500.2-2017 "Chemical Analysis Method for Rare Earth Waste Residue and Waste Water Part 2: Determination of Chemical Oxygen Demand (COD)", the chemical oxygen demand of each example and comparative example of the present application was tested;

[0057] According to GB / T 11894-1989 "Determination of Total Nitrogen in Water by Alkaline Persulfate Digestion UV Spectrophotometry", the total nitrogen content of each example and comparative example of the present application was tested;

[0058] The results are shown in Table 1:

[0059] Table 1

[0060]

[0061] As can be seen from Table 1, compared with Example 1, Examples 2-4 have the best comprehensive effect with COD removal rate and total nitrogen removal rate of 95.8% and 88.7% respectively when the catalyst dosage is 0.5 g / L and the hydrogen peroxide content dosage is 400 mg / L. Compared with Example 1, Comparative Example 1 has a decrease in COD and total nitrogen removal due to the decrease in activity of Fe and Zr double active centers caused by the combination of Fe3O4 and PCN224 without the synthesis of mesoporous silica shell. Comparative Example 2 has very low COD and total nitrogen removal rate compared with Example 1 because PCN224 alone can only produce singlet oxygen and cannot produce hydroxyl radicals with higher activity. Comparative Example 3 has a decrease in catalytic effect due to the decrease in utilization rate of hydrogen peroxide because Fe3O4 alone can only produce Fenton reaction, Fe(II) is difficult to be reduced to Fe(II) again after oxidation to Fe(III), and the oxygen produced by the decomposition of hydrogen peroxide cannot be utilized. Comparative Example 4 has a decrease in removal effect because the oxygen produced by the decomposition of hydrogen peroxide cannot be converted to singlet oxygen without near-infrared light irradiation.

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

[0063] It has to be noted that, in the present document, the terms "first", "second", etc. merely serve to identify different entities or actions from each other, without necessarily requiring or implying any actual relationship or order between these entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0064] While embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, changes, and variations can be made in the embodiments without departing from the spirit and scope of the present application, which is defined by the appended claims and their equivalents.

Claims

1. A process for the integrated treatment of landfill leachate, characterized in that, It comprises the following steps: The catalyst PCN 224 / Fe3O4@mesoporous silica is added into the landfill leachate, and H2O2 is added, and under near-infrared light irradiation, it is fully reacted. The amount 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 amount of H2O2 is 400-600 mg / L, and the reaction time is 1-4 h. The preparation method of the catalyst PCN 224 / Fe3O4@mesoporous silica is as follows: 1) PCN-224(H) metal organic framework and Fe3O4 are dispersed in N,N-dimethylformamide, ultrasonic dissolution, stirring and heating at 120-130°C for 10-12 h, centrifugal washing, and PCN 224 / Fe3O4 is obtained; 2) PCN 224 / Fe3O4 is dispersed in deionized water / ethanol solvent, and cetyltrimethylammonium bromide is added, heated to 50-60°C and stirred for 1-1.5 h; then NH3·H2O is added, and then tetraethoxysilane / ethanol solution is added dropwise in several times, and stirring is continued at 50-60°C for 6-8 h, centrifugal washing, extraction, drying, and then the precipitate is obtained; 3) The precipitate is dispersed in deionized water to obtain a suspension, heated to 100-105°C and stirred for 22-24 h, washed and dried to obtain PCN 224 / Fe3O4@mesoporous silica.

2. The integrated treatment process of landfill leachate according to claim 1, characterized in that, The amount ratio of PCN-224(H) metal organic framework, Fe3O4 and N,N-dimethylformamide is 100-110 mg: 50-55 mg: 100-120 mL.

3. The integrated treatment process of landfill leachate according to claim 1, characterized in that, The dropwise addition is 5 times, each time interval is 1 h.

4. The integrated treatment process of landfill leachate according to claim 1, characterized in that, The extraction is carried out at 75-80°C with NH4·NO3 for 6-7 h.

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