A method for denitrification of landfill leachate

Abstract

The application discloses a denitrification method for landfill leachate, and relates to the field of water treatment. In the treatment of landfill leachate, zeolite is first reacted with 3-aminopropyltrimethoxysilane, then with p-phenylenediamine, 1,3,5-benzene triformaldehyde and 3-fluoro-4-formylphenyl boronic acid pinacol ester, and is finally complexed with iron ions, and is finally reacted with 4'-bromo-2,2':6',2''-terpyridine to prepare a functionalized zeolite; the landfill leachate is mixed with the functionalized zeolite, is irradiated, then a denitrification agent is added, and is aerated and stirred, filtered, transported to an ammonia nitrogen stripping unit, and the gas generated in the aeration and stirring process and the ammonia nitrogen stripping process is transported to an ammonia recovery unit to perform a denitrification cycle. The application is suitable for landfill leachate with ammonia nitrogen of various concentrations, can remove ammonia complexes, ammonia complexes, organic amines which are difficult to strip in the landfill leachate, and can remove heavy metal ions and decompose microplastics and other organic pollutants which are difficult to remove in the landfill leachate.

Description

Technical Field

[0001] This invention relates to the field of water treatment, specifically to a method for denitrification of landfill leachate. Background Technology

[0002] Landfill leachate, or ammonia nitrogen wastewater, is a highly concentrated organic wastewater with complex composition and severe pollution. Its water quality characteristics include high ammonia nitrogen content, high organic matter concentration, poor biodegradability, and complex composition. Ammonia nitrogen is an important factor causing eutrophication of water bodies and causes great environmental pollution.

[0003] Currently, the denitrification technologies used in ammonia nitrogen wastewater treatment both domestically and internationally mainly include biochemical methods, stripping, steam stripping, ion exchange, and breakpoint chlorination. However, biochemical methods are only suitable for low-concentration ammonia nitrogen wastewater because the concentration of ammonia nitrogen that the bacteria can tolerate is relatively low. Similarly, ion exchange is also only suitable for low-concentration ammonia nitrogen wastewater. Breakpoint chlorination involves large chlorination volumes, high costs, poor operational safety, severe equipment corrosion, and is prone to hazards. Landfill leachate contains not only inorganic ammonia nitrogen but also many organic amines. Stripping is very ineffective at removing organic amines that exist as complexes or coupling compounds. Therefore, this application introduces a denitrification method that is suitable for inorganic ammonia nitrogen wastewater but even more suitable for organic ammonia nitrogen wastewater. Summary of the Invention

[0004] The purpose of this invention is to provide a method for denitrification of landfill leachate to solve the problems existing in the prior art.

[0005] A method for denitrification of landfill leachate, wherein the method involves mixing the landfill leachate with functionalized zeolite, irradiating it with light, adding a denitrifying agent, aerating and stirring, filtering, and conveying it to an ammonia stripping unit. The gas generated during the aeration and stirring process and the ammonia stripping process is then conveyed to an ammonia recovery unit for denitrification cycle.

[0006] The functionalized zeolite is prepared by reacting zeolite with 3-aminopropyltrimethoxysilane, then with p-phenylenediamine, 1,3,5-pyromellitic acid, and 3-fluoro-4-carboxymethylbenzeneboronic acid pinacol ester, and complexing with iron ions, and finally reacting with 4'-bromo-2,2':6',2''-terpyridine.

[0007] As an optimization, the denitrification method for landfill leachate mainly includes the following steps:

[0008] (1) Modified zeolite, 4'-bromo-2,2':6',2''-terpyridine, bis(triphenylphosphine)palladium dichloride, potassium acetate and 1,4-dioxane were mixed in a mass ratio of 1:0.1~0.2:0.02~0.03:0.3~0.4:18~22 and stirred for 11.5~12.5 h at 78~82℃, 200~300 r / min under nitrogen protection. The mixture was filtered, washed with ethanol 3~5 times, and vacuum dried at -10~0℃ for 22~26 h to obtain functionalized zeolite.

[0009] (2) Mix landfill leachate with functionalized zeolite at a mass ratio of 1:0.1~0.2, irradiate under visible light for 24~26h, filter to obtain landfill leachate pretreatment liquid; add denitrifying agent to landfill leachate pretreatment liquid, adjust pH to 10~12, aerate and stir, let stand for 0.5~1.5h, filter to obtain treatment liquid, send to ammonia nitrogen stripping unit, and send the gas generated during aeration and stirring and ammonia nitrogen stripping to ammonia recovery unit. Repeat the above operation 2~4 times for denitrification.

[0010] As an optimization, the modified zeolite in step (1) is prepared by mixing p-phenylenediamine and 1,4-dioxane at a mass ratio of 1:9~11, sonicating for 5~7 min, then adding an equal mass of 1,3,5-pyromellitic methyl ether and 0.1~0.2 times the mass of p-phenylenediamine in pinacol ester of 3-fluoro-4-carboxyphenylboronic acid, and sonicating for 8~12 min to obtain a precursor solution; the pre-modified zeolite is immersed in the precursor solution, and acetic acid with a volume of 0.02~0.03 times that of 1,4-dioxane is added uniformly over 6~8 min at 200~300 r / min. Stir for 70-80 minutes, filter, and obtain the modified zeolite precursor; mix octadecylamine, deionized water, and acetic acid at a mass ratio of 1:230-250:0.24-0.26 to obtain a modification solution; immerse the modified zeolite precursor in the modification solution, let it stand at 48-52℃ for 9-11 hours, filter, wash with deionized water 3-5 times, soak in a 10% (w / w) ferric nitrate nonahydrate aqueous solution for 24-26 hours, filter, wash again with deionized water 3-5 times, and vacuum dry at -10-0℃ for 22-26 hours to obtain the modified zeolite precursor.

[0011] As an optimization, the pre-modified zeolite is prepared by mixing 10-mesh zeolite, 3-aminopropyltrimethoxysilane, and isopropanol in a mass ratio of 1:0.2~0.3:20~23, sonicating for 8~10 min, stirring at 200~300 r / min and 105~115℃ for 5~7 h, filtering, washing with ethanol 4~6 times, and vacuum drying at -10~0℃ for 23~25 h.

[0012] As an optimization, the concentration of the denitrifying agent in step (2) is 0.1-0.5 g / L, containing hydroxide ions to adjust the pH of the landfill leachate pretreatment liquid; and also containing cations to displace ammonium ions in the coupling material in the landfill leachate pretreatment liquid.

[0013] As an optimization, the aeration and stirring in step (2) refers to using an air compressor or blower for aeration and stirring or stripping. The gas used for aeration and stirring or stripping is oxygen or air, and the gas flow rate is 1~10L / min; the gas-liquid volume ratio is 1000~5000:1.

[0014] As an optimization, the ammonia nitrogen stripping unit in step (2) includes a stripping tower, the ammonia nitrogen stripping time is 0.5~3h, and the stripping temperature is 30~60℃.

[0015] As an optimization, the ammonia recovery unit in step (2) includes an ammonia absorption tower and a cooling crystallizer. The ammonia absorption liquid in the absorption tower is an aqueous solution of organic acid and / or inorganic acid with a pH less than 3, and the absorption temperature is 40~50℃. When the mother liquor after ammonia absorption in the ammonia absorption tower is close to saturation, the mother liquor is transported to the cooling crystallizer.

[0016] As an optimization, the cooling crystallizer filters and refines the precipitated crystals at a cooling temperature of 20~30℃, and then the filtrate is sent to the ammonia absorption tower.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0018] In treating landfill leachate, this invention involves reacting zeolite with 3-aminopropyltrimethoxysilane, then with p-phenylenediamine, 1,3,5-pyromellitic acid, and pinacol ester of 3-fluoro-4-carboxymethylbenzeneboronic acid, and complexing with iron ions. Finally, it reacts with 4'-bromo-2,2':6',2''-terpyridine to prepare functionalized zeolite. The landfill leachate is then mixed with the functionalized zeolite, irradiated with light, and a denitrifying agent is added. The mixture is aerated, stirred, filtered, and then transported to an ammonia stripping unit. The gas generated during the aeration and stirring process and the ammonia stripping process is also transported to an ammonia recovery unit for denitrification cycle.

[0019] First, zeolite is reacted with 3-aminopropyltrimethoxysilane, then with p-phenylenediamine, 1,3,5-pyromellitic acid, and pinacol ester of 3-fluoro-4-carboxyphenylboronic acid, and complexed with iron ions. Finally, it is reacted with 4'-bromo-2,2':6',2''-terpyridine to prepare functionalized zeolite. Then, zeolite is reacted with 3-aminopropyltrimethoxysilane, then with p-phenylenediamine, 1,3,5-pyromellitic acid, and pinacol ester of 3-fluoro-4-carboxyphenylboronic acid, and complexed with iron ions to grow MOF structures on the zeolite surface. Further complexation with iron ions allows the iron-based MOF to activate oxygen molecule generation through photogenerated electron transfer. Reactive oxygen species (such as hydroxyl radicals) can break polymer chains, enabling microplastic degradation and better removal of organic pollutants from landfill leachate. Finally, it reacts with 4'-bromo-2,2':6',2''-terpyridine, introducing terpyridine groups through the reaction of the bromine group with the borate pinacol ester group. The three pyridine rings in the terpyridine group provide lone pairs of electrons through nitrogen atoms, forming coordinate bonds with the empty orbitals of heavy metal ions. This chelation effect significantly enhances the material's affinity for metal ions, enabling it to rapidly adsorb and fix heavy metal ions, thereby removing heavy metal ion pollutants from landfill leachate.

[0020] Secondly, the landfill leachate is mixed with functionalized zeolite, exposed to sunlight, and then a denitrifying agent is added. The mixture is aerated, stirred, filtered, and then transported to the ammonia nitrogen stripping unit. The gas generated during aeration and ammonia nitrogen stripping is transported to the ammonia recovery unit for denitrification recycling. This denitrification method combines chemical and existing physical methods. The denitrifying agent continuously reacts chemically with ammonia complexes, ammonia compounds, or organic amines in the wastewater. It is suitable not only for low, medium, and high concentrations of ammonia nitrogen wastewater existing in the form of ammonium ions, but also for removing difficult-to-strip ammonia complexes, ammonia compounds, or organic amines from landfill leachate, achieving a higher ammonia nitrogen removal rate. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] In the following examples and comparative examples, the leachate concentrations were as follows: ammonia nitrogen concentration of 5000 mg / L, Kjeldahl nitrogen concentration of 5500 mg / L, chromium ion concentration of 40 mg / L, and polyethylene terephthalate microplastic concentration of 20 mg / L. The denitrifying agent was a 0.3 g / L sodium hydroxide aqueous solution, and the pH of the pretreated leachate was adjusted to 12. Air was used for aeration and mixing at a flow rate of 6 L / min and a gas-liquid volume ratio of 3000:1. The stripping tower was used for ammonia nitrogen stripping for 2 hours at a temperature of 45°C. The ammonia absorption liquid was a sulfuric acid aqueous solution with a pH of 2.8. Example 1

[0023] A method for denitrification of landfill leachate mainly includes the following steps:

[0024] (1) Mix 10-mesh zeolite, 3-aminopropyltrimethoxysilane, and isopropanol in a mass ratio of 1:0.2:20, sonicate for 8 min, stir at 200 r / min and 105 °C for 5 h, filter, wash 4 times with ethanol, and vacuum dry at -10 °C for 23 h to obtain pre-modified zeolite; mix p-phenylenediamine and 1,4-dioxane in a mass ratio of 1:9, sonicate for 5 min, then add an equal mass of 1,3,5-pyromellitic acid tricarboxaldehyde and 0.1 times the mass of p-phenylenediamine, and sonicate for 8 min to obtain a precursor solution; immerse the pre-modified zeolite in the precursor solution, add 0.02 times the volume of acetic acid of 1,4-dioxane at a uniform rate within 6 min, stir at 200 r / min for 70 min, filter, and obtain modified zeolite precursor; Octadecylamine, deionized water, and acetic acid were mixed evenly at a mass ratio of 1:230:0.24 to prepare a modification solution. The modified zeolite precursor was immersed in the modification solution and allowed to stand at 48℃ for 9 hours. After filtration, the mixture was washed three times with deionized water and then soaked in a 10% (w / w) aqueous solution of ferric nitrate nonahydrate for 24 hours. After filtration, the mixture was washed three times again with deionized water and then vacuum dried at -10℃ for 22 hours to obtain the modified zeolite. The modified zeolite, 4'-bromo-2,2':6',2''-terpyridine, bis(triphenylphosphine)palladium dichloride, potassium acetate, and 1,4-dioxane were mixed at a mass ratio of 1:0.1:0.02:0.3:18 and stirred at 78℃, 200 r / min, and nitrogen protection for 11.5 hours. After filtration, the mixture was washed three times with ethanol and then vacuum dried at -10℃ for 22 hours to obtain the functionalized zeolite.

[0025] (2) Mix the landfill leachate with functionalized zeolite at a mass ratio of 1:0.1, irradiate under visible light for 24 hours, filter, and obtain landfill leachate pretreatment liquid; add denitrifying agent to landfill leachate pretreatment liquid, adjust pH to 10, aerate and stir, let stand for 0.5 hours, filter to obtain treatment liquid, and send it to ammonia nitrogen stripping unit. The gas generated during aeration and stirring and ammonia nitrogen stripping is sent to ammonia recovery unit. The denitrification cycle is repeated twice, and the above operation is repeated. Example 2

[0026] A method for denitrification of landfill leachate mainly includes the following steps:

[0027] (1) Mix 10-mesh zeolite, 3-aminopropyltrimethoxysilane and isopropanol in a mass ratio of 1:0.25:21.5, sonicate for 9 min, stir at 250 r / min and 110 °C for 6 h, filter, wash with ethanol 5 times, and vacuum dry at -5 °C for 24 h to obtain pre-modified zeolite.

[0028] A precursor solution was prepared by mixing p-phenylenediamine and 1,4-dioxane at a mass ratio of 1:10 and sonicating for 6 min. Then, an equal mass of 1,3,5-pyromellitic methyl ether and 0.15 times the mass of p-phenylenediamine (pinacol ester of 3-fluoro-4-carboxyphenylboronic acid) were added and sonicated for 10 min to obtain the precursor solution. Pre-modified zeolite was immersed in the precursor solution, and 0.025 times the volume of 1,4-dioxane (acetic acid) was added uniformly over 7 min. The mixture was stirred at 250 r / min for 7 minutes. After 5 minutes, the mixture was filtered to obtain the modified zeolite precursor. Octadecylamine, deionized water, and acetic acid were mixed evenly at a mass ratio of 1:240:0.25 to prepare a modification solution. The modified zeolite precursor was immersed in the modification solution and allowed to stand at 50°C for 10 hours. After filtration, the mixture was washed 4 times with deionized water and soaked in a 10% (w / w) aqueous solution of ferric nitrate nonahydrate for 25 hours. After filtration, the mixture was washed 4 times again with deionized water and dried under vacuum at -5°C for 24 hours to obtain the modified zeolite.

[0029] Modified zeolite, 4'-bromo-2,2':6',2''-terpyridine, bis(triphenylphosphine)palladium dichloride, potassium acetate, and 1,4-dioxane were mixed in a mass ratio of 1:0.15:0.025:0.35:20 and stirred for 12 h at 80 °C and 250 r / min under nitrogen protection. The mixture was then filtered, washed four times with ethanol, and dried under vacuum at -5 °C for 24 h to obtain functionalized zeolite.

[0030] (2) Mix the landfill leachate with functionalized zeolite at a mass ratio of 1:0.15, irradiate under visible light for 25 hours, filter, and obtain landfill leachate pretreatment liquid; add denitrifying agent to landfill leachate pretreatment liquid, adjust pH to 11, aerate and stir, let stand for 1 hour, filter to obtain treatment liquid, and send to ammonia nitrogen stripping unit, and send the gas generated during aeration and stirring and ammonia nitrogen stripping to ammonia recovery unit, denitrify cycle 3 times, and repeat the above operation. Example 3

[0031] A method for denitrification of landfill leachate mainly includes the following steps:

[0032] (1) Mix 10-mesh zeolite, 3-aminopropyltrimethoxysilane and isopropanol in a mass ratio of 1:0.3:23, sonicate for 10 min, stir at 300 r / min and 115 °C for 7 h, filter, wash with ethanol 6 times, and vacuum dry at 0 °C for 25 h to obtain pre-modified zeolite.

[0033] A precursor solution was prepared by mixing p-phenylenediamine and 1,4-dioxane at a mass ratio of 1:11 and sonicating for 7 min. Then, an equal mass of 1,3,5-trimethylbenzaldehyde and 0.2 times the mass of p-phenylenediamine (3-fluoro-4-carboxyphenylboronic acid pinacol ester) were added and sonicated for 12 min to obtain the precursor solution. The pre-modified zeolite was immersed in the precursor solution, and 0.03 times the volume of 1,4-dioxane (acetic acid) was added uniformly over 8 min. The mixture was stirred at 300 r / min for 80 min, filtered, and the modified zeolite precursor was obtained. A modified solution was prepared by mixing octadecylamine, deionized water, and acetic acid at a mass ratio of 1:250:0.26. The modified zeolite precursor was then immersed in the modified solution. The modified zeolite was prepared by standing in a solution at 52℃ for 11 hours, filtering, washing 5 times with deionized water, soaking in a 10% (w / w) ferric nitrate nonahydrate aqueous solution for 26 hours, filtering, washing 5 times again with deionized water, and vacuum drying at 0℃ for 26 hours. The modified zeolite, 4'-bromo-2,2':6',2''-terpyridine, bis(triphenylphosphine)palladium dichloride, potassium acetate, and 1,4-dioxane were mixed in a mass ratio of 1:0.2:0.03:0.4:22, stirred at 82℃, 300 r / min under nitrogen protection for 12.5 hours, filtered, washed 5 times with ethanol, and vacuum drying at 0℃ for 26 hours.

[0034] (2) Mix the landfill leachate with functionalized zeolite at a mass ratio of 1:0.2, irradiate under visible light for 26 hours, filter, and obtain landfill leachate pretreatment liquid; add denitrifying agent to landfill leachate pretreatment liquid, adjust pH to 12, aerate and stir, let stand for 1.5 hours, filter to obtain treatment liquid, and send it to ammonia nitrogen stripping unit. The gas generated during aeration and stirring and ammonia nitrogen stripping is sent to ammonia recovery unit. The denitrification cycle is repeated 4 times, and the above operation is repeated.

[0035] Comparative Example 1:

[0036] The difference between the denitrification method for landfill leachate in Comparative Example 1 and Example 2 lies in the difference in step (1). Step (1) is modified as follows: (1) 10-mesh zeolite, 3-aminopropyltrimethoxysilane, and isopropanol are mixed in a mass ratio of 1:0.25:21.5, sonicated for 9 min, stirred for 6 h at 250 r / min and 110 °C, filtered, washed 5 times with ethanol, and vacuum dried at -5 °C for 24 h to obtain pre-modified zeolite; p-phenylenediamine and 1,4-dioxane are mixed in a mass ratio of 1:10, sonicated for 6 min, and then 1,3,5-pyromellitic tricarboxaldehyde of equal mass and 0.15 times the mass of p-phenylenediamine, 3-fluoro-4-carboxyphenylboronic acid pinacol ester are added. The precursor solution was prepared by sonication for 10 min. The pre-modified zeolite was immersed in the precursor solution, and acetic acid with a volume of 0.025 times that of 1,4-dioxane was added uniformly over 7 min. The mixture was stirred at 250 r / min for 75 min, filtered, and the modified zeolite precursor was obtained. Octadecylamine, deionized water, and acetic acid were mixed evenly at a mass ratio of 1:240:0.25 to prepare a modification solution. The modified zeolite precursor was immersed in the modification solution and allowed to stand at 50°C for 10 h. The mixture was filtered, washed four times with deionized water, soaked in a 10% (w / w) aqueous solution of ferric nitrate nonahydrate for 25 h, filtered, washed four more times with deionized water, and vacuum dried at -5°C for 24 h to obtain the functionalized zeolite. The remaining steps were the same as in Example 2.

[0037] Comparative Example 2:

[0038] The difference between Comparative Example 2 and Example 2 in the denitrification method for landfill leachate is that the zeolite is not modified. The remaining steps are the same as in Example 2.

[0039] Test Example 1:

[0040] Ammonia nitrogen removal test 1:

[0041] Test methods: The ammonia nitrogen concentration and Kjeldahl nitrogen concentration of the treated leachate were determined by Nessler's reagent spectrophotometry and Kjeldahl nitrogen determination method, and the ammonia nitrogen removal rate and Kjeldahl nitrogen removal rate were calculated. The ammonia nitrogen removal rate was calculated as follows: (ammonia nitrogen concentration in leachate before treatment - ammonia nitrogen concentration in leachate after treatment) / ammonia nitrogen concentration in leachate before treatment × 100%; the Kjeldahl nitrogen removal rate was calculated as follows: (Kjeldahl nitrogen concentration in leachate before treatment - Kjeldahl nitrogen concentration in leachate after treatment) / Kjeldahl nitrogen concentration in leachate before treatment × 100%. The results are shown in Table 1.

[0042] Table 1

[0043] ammonia nitrogen removal rate Kjeldahl nitrogen removal rate Example 1 99.87% 99.81% Example 2 99.91% 99.85% Example 3 99.88% 99.84% Comparative Example 1 99.90% 99.82% Comparative Example 2 99.88% 99.83%

[0044] A comparison of the experimental data in Table 1 shows that the denitrification method for landfill leachate prepared in this invention has a high ammonia nitrogen removal rate and Kjeldahl nitrogen removal rate, and can effectively remove impurities from landfill leachate.

[0045] Test Example 2:

[0046] Ammonia nitrogen removal test 2:

[0047] Test Method: The landfill leachate was treated using the process described in Example 2. The ammonia nitrogen and Kjeldahl nitrogen concentrations in the leachate were adjusted. The ammonia nitrogen concentration in leachate 1 was 1000 mg / L and the Kjeldahl nitrogen concentration was 1200 mg / L; the ammonia nitrogen concentration in leachate 2 was 10000 mg / L and the Kjeldahl nitrogen concentration was 13000 mg / L. The ammonia nitrogen and Kjeldahl nitrogen concentrations of the treated leachate were tested again using Nessler's reagent spectrophotometry and the Kjeldahl nitrogen determination method, and the ammonia nitrogen removal rate and Kjeldahl nitrogen removal rate were calculated. The ammonia nitrogen removal rate was calculated as follows: (ammonia nitrogen concentration in leachate before treatment - ammonia nitrogen concentration in leachate after treatment) / ammonia nitrogen concentration in leachate before treatment × 100%; the Kjeldahl nitrogen removal rate was calculated as follows: (Kjeldahl nitrogen concentration in leachate before treatment - Kjeldahl nitrogen concentration in leachate after treatment) / Kjeldahl nitrogen concentration in leachate before treatment × 100%. The results are shown in Table 2.

[0048] Table 2

[0049] Landfill leachate 1 Landfill leachate 2 ammonia nitrogen removal rate 99.79% 99.97% Kjeldahl nitrogen removal rate 99.82% 99.95%

[0050] A comparison of the experimental data in Table 2 shows that the denitrification method for landfill leachate prepared in this invention has high ammonia nitrogen removal rate and Kjeldahl nitrogen removal rate for different concentrations of ammonia nitrogen, and can effectively remove impurities in landfill leachate.

[0051] Test Example 3:

[0052] Heavy metal ion and microplastic removal tests:

[0053] Heavy metal ion removal rate test method: Test the chromium ion concentration in the treated landfill leachate, and calculate the chromium ion removal rate in the landfill leachate, where the chromium ion removal rate = (chromium ion concentration in the landfill leachate before treatment - chromium ion concentration in the landfill leachate after treatment) / chromium ion concentration in the landfill leachate before treatment × 100%;

[0054] Microplastic removal rate test method: The concentration of polyethylene terephthalate (PET) microplastics in the treated landfill leachate was tested, and the PET microplastic removal rate in the landfill leachate was calculated. The PET microplastic removal rate = (PET microplastic concentration in the landfill leachate before treatment - PET microplastic concentration in the landfill leachate after treatment) / PET microplastic concentration in the landfill leachate before treatment × 100%. The results are shown in Table 3.

[0055] Table 3

[0056] Chromium ion removal rate Polyethylene terephthalate microplastic removal rate Example 1 98.7% 94.8% Example 2 98.9% 95.1% Example 3 98.6% 95.0% Comparative Example 1 59.8% 94.7% Comparative Example 2 59.6% 12.1%

[0057] A comparison of the experimental data in Table 3 shows that the denitrification method for landfill leachate prepared in this invention has good removal capabilities for heavy metal ions and microplastics.

[0058] A comparison of the experimental data from Examples 1, 2, and 3 and Comparative Example 1 in Table 3 reveals that Examples 1, 2, and 3 exhibit high chromium ion removal rates. The difference between Comparative Example 1 and the Examples lies in the absence of the introduction of a terpyridine group through the reaction of the bromine group with the borate pinacol ester group. This indicates that the three pyridine rings in the terpyridine group provide lone pairs of electrons through nitrogen atoms, forming coordinate bonds with the empty orbitals of heavy metal ions. This chelation effect significantly enhances the material's affinity for metal ions, enabling it to rapidly adsorb and fix heavy metal ions, thereby removing heavy metal ion pollutants from landfill leachate.

[0059] A comparison of the experimental data from Examples 1, 2, 3 and Comparative Example 2 reveals that the polyethylene terephthalate microplastics removed in Examples 1, 2, and 3 exhibit high removal rates. The difference between Comparative Example 2 and the Examples lies in the modification of zeolite, demonstrating the growth of MOF structures on the zeolite surface. These MOFs then complex with iron ions, and the iron-based MOFs can activate oxygen molecules through photogenerated electron transfer to generate reactive oxygen species (such as hydroxyl radicals). These reactive species can break polymer chains, achieving microplastic degradation and better removing organic pollutants from landfill leachate. Finally, the reaction with 4'-bromo-2,2':6',2''-terpyridine introduces terpyridine groups through the reaction of the bromine group with the borate pinacol ester group. The three pyridine rings in the terpyridine group provide lone pairs of electrons through nitrogen atoms, forming coordinate bonds with the empty orbitals of heavy metal ions. This chelation significantly enhances the material's affinity for metal ions, enabling it to rapidly adsorb and fix heavy metal ions, thereby removing heavy metal ion pollutants from landfill leachate.

[0060] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for denitrification of landfill leachate, characterized in that, The denitrification method for landfill leachate mainly comprises the following steps: (1) 10 parts of zeolite, 3-aminopropyltrimethoxysilane, isopropyl alcohol are mixed in a mass ratio of 1:0.2-0.3:20-23, ultrasonic for 8-10 min, stirred at 200-300 r / min, 105-115 DEG C for 5-7 h, filtered, washed with ethanol for 4-6 times, vacuum dried at-10-0 DEG C for 23-25 h, to obtain a pre-modified zeolite; 1,4-dioxane is mixed with p-phenylenediamine in a mass ratio of 1:9-11, ultrasonic for 5-7 min, then 1,3,5-triformylphloroglucinol is added in an amount of 1,3,5-triformylphloroglucinol and p-phenylenediamine, and 3-fluoro-4-formylphenylboronic acid pinacol ester is added in an amount of 0.1-0.2 times of p-phenylenediamine, ultrasonic for 8-12 min, to obtain a precursor solution; the pre-modified zeolite is immersed in the precursor solution, 0.02-0.03 times of acetic acid of 1,4-dioxane volume is added at a uniform speed within 6-8 min, stirred at 200-300 r / min for 70-80 min, filtered, to obtain a modified zeolite precursor; octadecylamine, deionized water and acetic acid are mixed in a mass ratio of 1:230-250:0.24-0.26, to obtain a modified solution, the modified zeolite precursor is immersed in the modified solution, and is placed at 48-52 DEG C for 9-11 h, filtered, washed with deionized water for 3-5 times, soaked in a 10% mass fraction of iron nitrate nonahydrate aqueous solution for 24-26 h, filtered, washed with deionized water for 3-5 times, vacuum dried at-10-0 DEG C for 22-26 h, to obtain a modified zeolite; the modified zeolite, 4'-bromo-2,2':6',2''-terpyridine, bis(triphenylphosphine)palladium dichloride, potassium acetate and 1,4-dioxane are mixed in a mass ratio of 1:0.1-0.2:0.02-0.03:0.3-0.4:18-22, stirred at 78-82 DEG C, 200-300 r / min under nitrogen protection for 11.5-12.5 h, filtered, washed with ethanol for 3-5 times, vacuum dried at-10-0 DEG C for 22-26 h, to obtain a functionalized zeolite; (2) landfill leachate and the functionalized zeolite are mixed in a mass ratio of 1:0.1-0.2, irradiated under visible light for 24-26 h, filtered, to obtain a landfill leachate pretreatment solution; a denitrification agent is added into the landfill leachate pretreatment solution, the pH is adjusted to 10-12, and after aeration and stirring, the solution is placed for 0.5-1.5 h, filtered to obtain a treatment solution, which is transported to an ammonia nitrogen stripping unit, and the gas generated in the aeration and stirring process and the ammonia nitrogen stripping process is transported to an ammonia recovery unit, the denitrification cycle is repeated for 2-4 times, and the above operation is repeated.

2. The method for denitrification of landfill leachate according to claim 1, characterized in that, The concentration of the denitrification agent in step (2) is 0.1-0.5 g / L, contains hydroxyl ions, and is used for adjusting the pH of the landfill leachate pretreatment solution; meanwhile, the denitrification agent contains cations, which are used for replacing ammonium ions in the coupled compounds in the landfill leachate pretreatment solution.

3. The method for denitrification of landfill leachate according to claim 1, characterized in that, The aeration stirring in step (2) is performed by using an air compressor or a blower, and the gas used for aeration stirring or stripping is oxygen or air, and the gas flow rate is 1-10 L / min, and the gas-liquid volume ratio is 1000-5000:

1.

4. The method for denitrification of landfill leachate according to claim 1, characterized in that, The ammonia nitrogen stripping unit in step (2) comprises a stripping tower, the ammonia nitrogen stripping time is 0.5-3 h, and the stripping temperature is 30-60 DEG C.

5. The method for denitrification of landfill leachate according to claim 1, characterized in that, The ammonia recovery unit in step (2) comprises an ammonia absorption tower and a cooling crystallizer, the ammonia absorption liquid in the absorption tower is an aqueous solution of an organic acid and / or an inorganic acid with a pH less than 3, and the absorption temperature is 40-50 DEG C; when the mother liquor after absorbing ammonia in the ammonia absorption tower approaches saturation, the mother liquor is transported to the cooling crystallizer.

6. The method for denitrification of landfill leachate according to claim 5, characterized in that, The cooling crystallizer filters, refines the precipitated crystals at a cooling temperature of 20-30 DEG C, and then transports the filtrate to the ammonia absorption tower.