Biological-friendly zeolite / nano zero-valent iron composite material as well as preparation method and application thereof

Abstract

The invention relates to a preparation method of a bio-friendly zeolite / nano zero-valent iron composite material, which comprises the following steps: dissolving bivalent iron salt into a solvent to obtain an iron salt solution; washing and drying zeolite, activating at high temperature, and grinding to obtain a zeolite material; mixing the obtained zeolite material with a bivalent iron salt solution, and obtaining a composite solution of zeolite and bivalent iron salt by adopting an ultrasonic impregnation method; the method comprises the following steps: dropwise adding a NaBH4 solution into a composite solution of zeolite and iron salt in a protective gas under a magnetic stirring condition, and obtaining a composite solution of zeolite and nano zero-valent iron by adopting a liquid phase reduction method; and carrying out vacuum suction filtration on the obtained composite solution of the zeolite and the nano zero-valent iron, and washing and drying the obtained precipitate to obtain the zeolite / nano zero-valent iron composite material. According to the zeolite / nano zero-valent iron composite material disclosed by the invention, the nitrate removal rate can be improved by 28.6%, the activity of an electron transfer system is improved by 66.51%, and the biological compatibility and environmental stability of nano zero-valent iron are enhanced while the denitrification efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a bio-friendly zeolite / nano-zero-valent iron composite material, a preparation method thereof, and application thereof in enhancing biological denitrification degradation of nitrate wastewater. Background Art

[0002] Nitrates entering natural water bodies not only degrade the water quality but also pose the risk of eutrophication. When ingested by the human body, they generate nitrites, which bind to proteins in the body to form highly carcinogenic nitroso compounds. Nitrates cannot be removed by simple physical or chemical methods. Biological treatment methods are environmentally friendly and cost-effective, but biological denitrification is plagued by low denitrification rates. Nanoscale zero-valent iron (NZVI) has attracted considerable attention due to its excellent reducing power and high reactivity. Furthermore, the addition of NZVI effectively promotes electron transfer, thereby increasing the efficiency of nitrate denitrification, offering a novel solution for biological aquatic treatment. However, the high surface energy of NZVI may cause it to come into contact with bacterial cell membranes, disrupting membrane structure and causing cell damage or death. Furthermore, the oxidation and reduction processes of NZVI may release iron ions (Fe²⁺ or Fe³⁺). These metal ions, at high concentrations, can inhibit microbial growth and metabolism. Furthermore, NZVI tends to aggregate and precipitate in water treatment systems, resulting in decreased reactivity. The above are the problems that need to be solved in the current application of nano zero-valent iron in water treatment processes.

[0003] In existing water treatment technologies, the choice of carrier material significantly impacts pollutant removal efficiency and microbial activity. Natural clinoptilolite, an abundant and low-cost natural aluminosilicate material, is widely used in environmental remediation due to its excellent molecular sieve properties, large specific surface area, unique pore structure, and easily modifiable surface functional groups. Natural clinoptilolite exhibits significant advantages in the construction of composite denitrification systems. Firstly, its near-neutral pH reduces the physiological activity of denitrifying microorganisms compared to acidic or alkaline mineral materials. During heterotrophic denitrification, pH fluctuations can reduce the activity of key enzyme systems (such as nitrate reductase and nitrite reductase), thereby affecting overall denitrification efficiency. The neutral mineral surface of clinoptilolite can, to a certain extent, buffer local pH fluctuations generated during microbial metabolism, providing a stable microenvironment and helping to maintain normal microbial metabolism and reduction activity. Secondly, when loaded with nano-zero-valent iron (ZVI), clinoptilolite improves the stability of the composite structure and slows the oxidation rate of the nano-ZVI, thereby inhibiting the release of large amounts of iron ions and reducing transient toxicity to microorganisms. Furthermore, its porous structure facilitates the loading and sustained release of nano-zero-valent iron, enabling a continuous supply of electrons and enhancing the stability of the electron transfer process in the system, which has a positive effect on improving nitrate removal efficiency. Therefore, choosing natural clinoptilolite as the loading matrix for nano-zero-valent iron not only combines structural support and active release regulation functions, but also, with its high adaptability to microorganisms and low toxic interference, provides reliable support for the application of composite materials in the field of biological denitrification, and has good ecological compatibility and practical promotion potential.

[0004] The present invention aims to develop a zeolite / nano-zero-valent iron composite material with good loading performance and biocompatibility, and explore its application in the denitrification process in order to improve the efficiency of denitrification and expand the application scope of nano-zero-valent iron materials in environmental governance. It has important research significance and practical application value. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the existing technology and provide a bio-friendly, anti-aggregation zeolite / nano-zero-valent iron composite material. Its application in the denitrification and denitrification process can improve the efficiency of denitrification and expand the application scope of nano-zero-valent iron materials in environmental governance.

[0006] The present invention solves the technical problem by the following technical solutions: A method for preparing a bio-friendly zeolite / nano-zero-valent iron composite material, the preparation method comprising the following steps: Step 1) dissolving a divalent iron salt in a solvent to obtain an iron salt solution; Step 2) washing and drying the zeolite, activating it at high temperature, and grinding it to obtain the zeolite material; Step 3) mixing the obtained zeolite material with a divalent iron salt solution, and using an ultrasonic impregnation method to obtain a composite solution of zeolite and divalent iron salt; Step 4) In a protective gas atmosphere, a NaBH4 solution is added dropwise to the composite solution of zeolite and iron salt under magnetic stirring conditions, and a liquid phase reduction method is used to obtain a composite solution of zeolite and nano-zero-valent iron; Step 5) The obtained composite solution of zeolite and nano-zero-valent iron is vacuum filtered, and the obtained precipitate is washed and dried to obtain a zeolite / nano-zero-valent iron composite material.

[0007] Moreover, the divalent iron salt in step 1) is ferrous sulfate, and in step 3) the zeolite material is mixed with the iron salt solution, wherein the mass ratio of the zeolite material to the divalent iron salt is 2.5-3.5:1.

[0008] Moreover, the solvent in step 1) is a mixed solution of water and anhydrous ethanol in a volume ratio of 2.5-3.5:1.

[0009] Moreover, the zeolite in step 2) is selected from natural clinoptilolite with a particle size of 180-220 mesh; and the high-temperature activation condition is high-temperature calcination in a muffle furnace at 350-450° C. for 3-4 hours.

[0010] Furthermore, in the step 3), the ultrasonic immersion method is carried out at a temperature of 35-45° C., an ultrasonic frequency of 50-56 kHz, and an ultrasonic duration of 10-14 hours.

[0011] Moreover, the protective gas in step 4) is inert gas nitrogen; the molar ratio of the iron salt to NaBH4 in step 4) is 1:3-5; the composite solution of zeolite and nano-zero-valent iron obtained in step 4) is fully reacted under a nitrogen atmosphere for 25-35 minutes.

[0012] Furthermore, the vacuum filtration in step 5) uses a 0.4-0.5 μm water filter membrane, and the drying condition is drying in a vacuum drying oven at 60-80° C. for 11-13 hours.

[0013] Moreover, the zeolite washing conditions in step 2) are washing with tap water three times and washing with distilled water three times; the precipitate washing conditions in step S5) are washing with ultrapure water three times and washing with anhydrous ethanol three times.

[0014] A bio-friendly zeolite / nano-zero-valent iron composite material is prepared by adopting the preparation method.

[0015] Application of a bio-friendly zeolite / nano-zero-valent iron composite material in enhanced biological denitrification degradation of nitrate wastewater.

[0016] The beneficial effects of the present invention are: 1. The biofriendly zeolite / nano-zero-valent iron composite material of the present invention and its preparation method use zeolite, a natural mineral material that is abundant in resources, low in cost, and environmentally friendly, and has good structural stability and molecular sieve properties. Compared with traditional acidic or alkaline inorganic carriers, natural clinoptilolite has a near-neutral pH characteristic, making it more bioadaptable in constructing denitrification systems involving microorganisms and providing a stable and mild growth environment for microorganisms.

[0017] 2. The bio-friendly zeolite / nano-zero-valent iron composite material of the present invention and its preparation method are characterized by the zeolite used in controlling the release rate and reactivity of nano-zero-valent iron, thereby reducing the damage that sudden and excessive reactions may cause to the microbial population. The zeolite can also effectively isolate the surface activity of nano-zero-valent iron, reducing its toxicity to microorganisms. In this way, the composite material can achieve optimal results in the water treatment process while maximally protecting the activity of microorganisms.

[0018] 3. The bio-friendly zeolite / nano-zero-valent iron composite material of the present invention and its preparation method use zeolite as a carrier. The negative charge on the zeolite surface can adsorb positively charged nano-zero-valent iron particles, reducing the aggregation tendency of the iron particles and maintaining their dispersion in water. This adsorption effect effectively slows the oxidation aggregation rate of the nano-zero-valent iron, extending the service life of the nano-zero-valent iron, ensuring its long-term activity during the process of water treatment to remove nitrate nitrogen, and significantly improving the efficiency of nitrate nitrogen removal.

[0019] 4. The bio-friendly zeolite / nano-zero-valent iron composite material of the present invention and its preparation method are as follows: by adding a certain amount of denitrification activated sludge solution to nitrate-nitrogen-containing wastewater using the prepared bio-friendly zeolite / nano-zero-valent iron composite material, the nitrate is reduced to nitrogen gas by utilizing the ability of microorganisms to use nitrate as an electron acceptor, completing the treatment process of the nitrogen-containing wastewater; the electron donor is mainly the electron generated by the oxidation reaction of the nano-zero-valent iron with the electrons produced by the metabolism of organic matter by microorganisms. At the same time, the nano-zero-valent iron can achieve a highly efficient electron transfer process by promoting the microbial electron transfer system; during the denitrification process of the nitrate-nitrogen-containing wastewater, a certain amount of the bio-friendly zeolite / nano-zero-valent iron composite material prepared by the present invention is added, and the nano-zero-valent iron is oxidized to generate electron donors, thereby improving the efficiency of microbial electron transfer, thereby removing nitrate nitrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 FITR diagram of the zeolite / nano-zero-valent iron composite material prepared in Example 1 of the present invention; Figure 2 TEM image of the zeolite / nano-zero-valent iron composite material prepared in Example 1 of the present invention; Figure 3This is a diagram showing the effect of the zeolite / nano-zero-valent iron composite material prepared in Example 1 of the present invention on removing nitrate nitrogen; Figure 4 This is a diagram showing the effect of adding ETSA to the zeolite / nano-zero-valent iron composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be described in more detail below through specific examples. These examples are intended to provide further understanding and explanation of the present invention, are merely illustrative, and do not constitute any limitation on the scope of protection of the present invention.

[0022] A method for preparing a bio-friendly zeolite / nano-zero-valent iron composite material, the preparation method comprising the following steps: Step 1) dissolving a divalent iron salt in a solvent to obtain an iron salt solution, wherein the divalent iron salt is ferrous sulfate, and the solvent is a mixed solution of water and anhydrous ethanol in a volume ratio of 2.5-3.5:1.

[0023] Step 2) The zeolite is washed, dried, activated at high temperature, and ground to obtain a zeolite material; the zeolite is selected from natural clinoptilolite with a particle size of 180-220 mesh; the zeolite is washed three times with tap water and three times with distilled water; the high temperature activation condition is calcined in a muffle furnace at 350-450°C for 3-4 hours.

[0024] Step 3) The obtained zeolite material is mixed with a divalent iron salt solution, and an ultrasonic impregnation method is used to obtain a composite solution of zeolite and divalent iron salt; the zeolite material and the iron salt solution are mixed wherein the mass ratio of the zeolite material to the divalent iron salt is 2.5-3.5:1; the ultrasonic impregnation method is carried out at a temperature of 35-45°C, an ultrasonic frequency of 50-56 kHz, and an ultrasonic time of 10-14 hours.

[0025] Step 4) In a protective gas atmosphere, a NaBH4 solution is added dropwise to the composite solution of zeolite and iron salt under magnetic stirring, and a liquid phase reduction method is used to obtain a composite solution of zeolite and nano-zero-valent iron; the protective gas is nitrogen, an inert gas; the molar ratio of iron salt to NaBH4 is 1:3-5; the obtained composite solution of zeolite and nano-zero-valent iron is fully reacted under a nitrogen atmosphere for 25-35 minutes.

[0026] Step 5) The resulting zeolite and nano-zero-valent iron composite solution is vacuum filtered, and the resulting precipitate is washed and dried to obtain a zeolite / nano-zero-valent iron composite material. The vacuum filtration is performed using a 0.4-0.5 μm aqueous filter membrane and drying is performed in a vacuum drying oven at 60-80°C for 11-13 hours. The precipitate is washed three times with ultrapure water and three times with anhydrous ethanol.

[0027] A biofriendly zeolite / nano-zero-valent iron composite material is prepared by the above-mentioned preparation method.

[0028] A bio-friendly zeolite / nano-zero-valent iron composite material is used to enhance biological denitrification of nitrate wastewater. The biological method is microbial heterotrophic denitrification. The nitrogen-containing wastewater is specifically simulated wastewater containing nitrate nitrogen.

[0029] Example 1 A bio-friendly zeolite / nano-zero-valent iron composite material is prepared by the following specific steps: (1) Dissolve 6.205 g of ferrous sulfate (heptahydrate) in 200 mL of a solvent, which is a mixed solution of 150 mL of ultrapure water and 50 mL of anhydrous ethanol, and fully dissolve under ultrasonic conditions to obtain an iron salt solution.

[0030] (2) A certain amount of 200-mesh zeolite was washed three times with tap water and three times with distilled water, dried at 105°C, and fully ground. It was then fired in a muffle furnace at 400°C for 3.5 hours to complete the activation of the zeolite.

[0031] (3) 3.75 g of activated zeolite was accurately weighed in a mass ratio of zeolite to iron salt of 3:1, and then added to the above iron salt solution. The mixture was then ultrasonicated at 53 kHz for 12 h to obtain a composite solution of zeolite and iron salt.

[0032] (4) 3.377 g of NaBH₄ was weighed and dissolved in 100 mL of ultrapure water at a molar ratio of 1:4 to obtain a NaBH₄ solution. The composite solution of zeolite and nano-zero-valent iron was maintained under a nitrogen atmosphere for 15 min under magnetic stirring. The NaBH₄ solution was then added dropwise and maintained under a nitrogen atmosphere for 30 min to allow the reaction to complete.

[0033] (5) After the reaction, the resulting zeolite / nano-zero-valent iron composite solution was vacuum filtered using a 0.45 μm aqueous filter membrane. The resulting precipitate was washed three times with ultrapure water and then three times with anhydrous ethanol. The precipitate was then vacuum dried at 70°C for 12 h. The resulting zeolite / nano-zero-valent iron composite was stored in anhydrous ethanol.

[0034] The prepared zeolite / nano-zero-valent iron composite material was subjected to FTIR analysis, and the obtained FTIR spectrum was as follows: Figure 1 The zeolite / nano-zero-valent iron composite still exhibits the characteristic absorption peaks of zeolite, though the intensity of the absorption peak at 1000-1200 cm⁻¹ has weakened somewhat, indicating that the zeolite's network structure remains intact after loading with nano-zero-valent iron, and the basic framework remains unchanged. The zeolite / nano-zero-valent iron composite also exhibits Fe-O stretching vibration peaks at 400-600 cm⁻¹, characteristic of nano-zero-valent iron, indicating successful binding of the nano-zero-valent iron to the zeolite.

[0035] The prepared zeolite / nano-zero-valent iron composite material was subjected to TEM analysis, and the obtained TEM spectrum was as follows: Figure 2 Compared with the single nano zero-valent iron material ( Figure 2 (a)) Compared with the zeolite / nano-zero-valent iron composite material ( Figure 2 (b) The dispersibility of nano-zero-valent iron particles is significantly improved, indicating that the loading effect of zeolite effectively inhibits the agglomeration of nanoparticles, thus benefiting their reactivity and stability.

[0036] The prepared zeolite / nano-zero-valent iron composite material was used in a comparative experiment on the removal of biological nitrate nitrogen. The results are as follows: Weigh 0.06g of zeolite, 0.02g of nano-zero-valent iron, and 0.08g of zeolite / nano-zero-valent iron composite into a 250mL anaerobic serum bottle. Transfer 200mL of a prepared 50mg / L nitrate solution to a predetermined volume of acclimated activated sludge mixture. Mix thoroughly and shake in a 28°C air bath on a constant-temperature oscillator for 12 hours. Every two hours, 1mL of the supernatant was collected and measured using UV spectrophotometry to determine the nitrate-nitrogen degradation effect of the different materials. ETSA analysis was performed on 5mL of the sludge-water mixture after the 12-hour reaction using the INT reduction method.

[0037] like Figure 3 As shown, after 12 hours of reaction with the zeolite / nano-zero-valent iron composite material in Example 1, the average nitrate concentration was 1.84 mg / L, with a removal rate of 96.4%. Meanwhile, after 12 hours of reaction with the nano-zero-valent iron, the average nitrate concentration was 8.84 mg / L, with a removal rate of 82.65%. After 12 hours of reaction with the zeolite, the average nitrate concentration was 11.01 mg / L, with a removal rate of 78.41%. After 12 hours of reaction without the material, the average nitrate concentration was 12.76 mg / L, with a removal rate of 74.97%. This indicates that the addition of the zeolite / nano-zero-valent iron composite material significantly improves nitrate removal efficiency, demonstrating that the composite material exhibits excellent performance in nano-zero-valent iron water treatment.

[0038] The ETSA concentration of the zeolite / nano-zero-valent iron composite material of Example 1 was measured after 12 hours of reaction. Figure 4 The results showed that the ETSA concentration in the nZVI / Z group was 4858.09 μg / min·gVSS, significantly higher than that in the nano-zero-valent iron group (4167.61 μg / min·gVSS), the zeolite group (4036.35 μg / min·gVSS), and the blank control group (2917.49 μg / min·gVSS). This result demonstrates that the zeolite / nano-zero-valent iron composite prepared in this invention significantly enhances the electron transfer capacity and metabolic activity of microorganisms, thereby accelerating the efficiency of nitrate nitrogen reduction and demonstrating excellent denitrification enhancement.

[0039] Example 2 A bio-friendly zeolite / nano-zero-valent iron composite material is prepared by the following specific steps: (1) Dissolve 7.084 g of ferrous sulfate (hexahydrate) in 200 mL of a solvent, which is a mixed solution of 150 mL of ultrapure water and 50 mL of anhydrous ethanol, and fully dissolve under ultrasonic conditions to obtain an iron salt solution.

[0040] (2) A certain amount of 180 mesh zeolite was washed three times with tap water and three times with distilled water, dried at 105°C, and fully ground. It was then fired in a muffle furnace at 350°C for 3 hours to complete the activation of the zeolite.

[0041] (3) 3.573 g of activated zeolite was accurately weighed in a mass ratio of zeolite to iron salt of 2.5:1, and then added to the above iron salt solution at a temperature of 35°C. The mixture was then ultrasonicated at 50 kHz for 10 h to obtain a composite solution of zeolite and iron salt.

[0042] (4) Weigh 2.892 g of NaBH₄ in a molar ratio of 1:3 and dissolve it in 100 mL of ultrapure water to obtain a NaBH₄ solution. The zeolite-nano-zero-valent iron composite solution was maintained under a nitrogen atmosphere for 15 minutes under magnetic stirring. The NaBH₄ solution was then added dropwise and maintained under a nitrogen atmosphere for 25 minutes to allow the reaction to complete.

[0043] (5) After the reaction, the resulting zeolite / nano-zero-valent iron composite solution was vacuum filtered using a 0.45 μm aqueous filter membrane. The resulting precipitate was washed three times with ultrapure water and then three times with anhydrous ethanol. The precipitate was then vacuum dried at 60°C for 11 h. The resulting zeolite / nano-zero-valent iron composite was stored in anhydrous ethanol.

[0044] Example 3 A bio-friendly zeolite / nano-zero-valent iron composite material is prepared by the following specific steps: (1) Dissolve 5.515 g of ferrous sulfate (hexahydrate) in 200 mL of a solvent, which is a mixed solution of 150 mL of ultrapure water and 50 mL of anhydrous ethanol, and fully dissolve under ultrasonic conditions to obtain an iron salt solution.

[0045] (2) A certain amount of 220 mesh zeolite was washed three times with tap water and three times with distilled water, dried at 105°C, and fully ground, and fired in a muffle furnace at 450°C for 4 hours to complete the activation of the zeolite.

[0046] (3) 3.889 g of activated zeolite was accurately weighed according to the mass ratio of zeolite to iron salt of 3.5:1, and then added to the above iron salt solution at 40°C. The mixture was then ultrasonicated at 56 kHz for 14 h to obtain a composite solution of zeolite and iron salt.

[0047] (4) 3.752 g of NaBH₄ was weighed and dissolved in 100 mL of ultrapure water at a molar ratio of 1:5 to obtain a NaBH₄ solution. The composite solution of zeolite and nano-zero-valent iron was maintained under a nitrogen atmosphere for 15 min under magnetic stirring. The NaBH₄ solution was then added dropwise and maintained under a nitrogen atmosphere for 35 min to allow for complete reaction.

[0048] (5) After the reaction, the resulting zeolite / nano-zero-valent iron composite solution was vacuum filtered using a 0.45 μm aqueous filter membrane. The resulting precipitate was washed three times with ultrapure water and then three times with anhydrous ethanol. The precipitate was then vacuum dried at 80°C for 13 h. The resulting zeolite / nano-zero-valent iron composite was stored in anhydrous ethanol.

[0049] The composite material of the present invention consists of neutral natural clinoptilolite and nano-zero-valent iron, with the nano-zero-valent iron loaded into the pores and surface of the clinoptilolite. The selected clinoptilolite has a neutral pH and excellent ion exchange properties, providing a stable and suitable living environment for microorganisms, preventing the inhibition of microbial metabolism caused by pH fluctuations and enhancing their activity and community stability. The nano-zero-valent iron acts as an electron donor, forming a stable electron-releasing platform when loaded onto the zeolite. It effectively participates in the electron transport chain during heterotrophic denitrification, significantly improving the efficiency of electron supply to the nitrate reduction pathway. This structure reduces the aggregation and oxidation rate of the nano-zero-valent iron, minimizes excessive iron ion release, and significantly reduces its toxic effects on microorganisms. Application results show that the zeolite / nano-zero-valent iron composite of the present invention increased nitrate removal efficiency by 28.6% and the electron transport system activity (ETSA) by 66.51% compared to the blank control group. While improving denitrification efficiency, it also enhances the biocompatibility and environmental stability of the nano-zero-valent iron, showing broad application prospects in biological water treatment.

[0050] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for preparing a biofriendly zeolite / nano-zero-valent iron composite material, characterized by: The steps of the preparation method are: Step 1) dissolving a divalent iron salt in a solvent to obtain an iron salt solution; Step 2) washing and drying the zeolite, activating it at high temperature, and grinding it to obtain the zeolite material; Step 3) mixing the obtained zeolite material with a divalent iron salt solution, and using an ultrasonic impregnation method to obtain a composite solution of zeolite and divalent iron salt; Step 4) In a protective gas atmosphere, a NaBH4 solution is added dropwise to the composite solution of zeolite and iron salt under magnetic stirring, and a liquid phase reduction method is used to obtain a composite solution of zeolite and nano-zero-valent iron; Step 5) The obtained composite solution of zeolite and nano-zero-valent iron is vacuum filtered, and the obtained precipitate is washed and dried to obtain a zeolite / nano-zero-valent iron composite material.

2. The method for preparing the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 1, wherein: In step 1), the divalent iron salt is ferrous sulfate, and in step 3), the zeolite material is mixed with the iron salt solution, wherein the mass ratio of the zeolite material to the divalent iron salt is 2.5-3.5:

1.

3. The method for preparing the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 1, wherein: The solvent in step 1) is a mixed solution of water and anhydrous ethanol in a volume ratio of 2.5-3.5:

1.

4. The method for preparing the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 1, wherein: In the step 2), the zeolite is selected from natural clinoptilolite with a particle size of 180-220 mesh; and the high-temperature activation condition is high-temperature firing in a muffle furnace at 350-450° C. for 3-4 hours.

5. The method for preparing the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 1, wherein: In the step 3), the ultrasonic immersion method is carried out at a temperature of 35-45° C. and an ultrasonic frequency of 50-56 kHz, and the ultrasonic duration is 10-14 hours.

6. The method for preparing the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 1, wherein: The protective gas in step 4) is nitrogen, an inert gas; the molar ratio of the iron salt to NaBH4 in step 4) is 1:3-5; the composite solution of zeolite and nano-zero-valent iron obtained in step 4) is fully reacted under a nitrogen atmosphere for 25-35 minutes.

7. The method for preparing the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 1, characterized in that: In the step 5), the filter membrane used for vacuum filtration is a 0.4-0.5 μm water filter membrane, and the drying condition is drying in a vacuum drying oven at 60-80° C. for 11-13 hours.

8. The method for preparing the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 1, characterized in that: The zeolite is washed three times with tap water and three times with distilled water in step 2); the precipitate is washed three times with ultrapure water and three times with anhydrous ethanol in step S5).

9. A bio-friendly zeolite / nano-zero-valent iron composite material, characterized by: The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the bio-friendly zeolite / nano-zero-valent iron composite material according to claim 9 in enhancing biological denitrification degradation of nitrate wastewater.

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