Membrane-method ammonia nitrogen removal process flow

Abstract

The invention relates to a membrane-method ammonia nitrogen removal process flow, and belongs to the technical field of wastewater treatment. The process comprises the following steps: injecting an acid solution into the circulating acid storage tank, absorbing ammonia nitrogen in the ammonia nitrogen wastewater through the modified hollow fiber membrane, returning the ammonia nitrogen wastewater to the circulating acid storage tank, and carrying out secondary absorption, so as to complete the treatment of the ammonia nitrogen wastewater and generate an inorganic ammonium salt solution. Wherein the modified hollow fiber membrane is prepared from polyvinylidene fluoride, sodium silicate and nano silicon dioxide through specific steps, and has excellent ammonia nitrogen absorption performance. In the technological process, the ammonia-nitrogen wastewater is subjected to aeration treatment after the pH value is adjusted by alkali liquor, and ammonia nitrogen is absorbed by the modified hollow fiber membrane, so that efficient denitrification is realized. In addition, the types and concentrations of the acid solution and the alkali solution, aeration treatment parameters and the like are specified in detail, so that the treatment effect is ensured. Finally, the inorganic ammonium salt solution is discharged out of the system through a sewage pump for subsequent treatment. The method is simple in process flow, convenient to operate, high in denitrification efficiency and suitable for treatment of various wastewater containing ammonia nitrogen, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment and relates to a membrane method for ammonia nitrogen removal process flow. Background Technique

[0002] The treatment of ammonia nitrogen wastewater is an important topic in the environmental protection field. With the acceleration of the industrialization process, the discharge of ammonia nitrogen wastewater increases year by year, causing serious pollution to the water environment. Traditional ammonia nitrogen wastewater treatment methods have problems such as low treatment efficiency, high cost, and secondary pollution. Therefore, it is particularly important to develop efficient, economical, and environmentally friendly ammonia nitrogen wastewater treatment technologies.

[0003] As a new treatment method, the membrane method for ammonia nitrogen removal technology has the advantages of high treatment efficiency, small floor area, and simple operation, and has gradually become a research hotspot in the field of ammonia nitrogen wastewater treatment. However, there are still some problems in the actual application of the existing membrane method for ammonia nitrogen removal technology, such as the selection of membrane materials, the modification of membranes, and the optimization of treatment processes, which limit the wide application of the membrane method for ammonia nitrogen removal technology.

[0004] The present invention provides an improved membrane method for ammonia nitrogen removal process flow. By adopting a specific modified hollow fiber membrane and the method of recycling the absorbent liquid, the absorption efficiency of ammonia nitrogen and the production rate of inorganic ammonium salts are improved, while the treatment cost and environmental impact are reduced. The purpose of the present invention is to solve the problems existing in the existing membrane method for ammonia nitrogen removal technology and provide an efficient, economical, and environmentally friendly ammonia nitrogen wastewater treatment method to meet the increasingly strict environmental protection requirements and the needs of industrial production. Summary of the Invention

[0005] The purpose of the present invention is to provide a membrane method for ammonia nitrogen removal process flow, which has the characteristic of high ammonia nitrogen removal efficiency.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A membrane method for ammonia nitrogen removal process flow, the specific steps of the process flow are as follows

[0008] S1: Inject an acid solution with a mass fraction of 10-30% into the circulating acid storage tank, start the circulation, and pass the dilute acid solution into the modified hollow fiber membrane in the ammonia nitrogen wastewater tank;

[0009] S2: Pass the wastewater containing ammonia nitrogen into the ammonia nitrogen wastewater tank, adjust the pH value with an alkali solution, detect the pH value of the ammonia nitrogen wastewater, and after meeting the standard, perform aeration treatment on the wastewater;

[0010] S3: Use the modified hollow fiber membrane to absorb ammonia nitrogen from the aerated ammonia nitrogen wastewater and generate an inorganic ammonium salt solution, and return the generated inorganic ammonium salt solution to the circulating acid storage tank through the action of a circulation pump for secondary absorption to complete the treatment of the ammonia nitrogen wastewater;

[0011] S4: Drain the inorganic ammonium salt solution from the system through a sewage pump for subsequent product separation and purification.

[0012] Furthermore, the preparation method of the modified hollow fiber membrane in S1 is as follows.

[0013] S1.1: Heat polyvinylidene fluoride to 165 - 180 °C to make it in a molten state, add N,N-dimethylacetamide DMAC at a mass ratio of 1:1, and stir at a speed of 200 r / min for 1 h to obtain a uniformly mixed mixed solution A.

[0014] S1.2: Dissolve sodium silicate in deionized water to obtain a sodium silicate aqueous solution with a mass fraction of 20 - 30%, disperse nano-silica in the sodium silicate aqueous solution with a solid-liquid mass ratio of 1:2, then add 2 wt% of silane coupling agent KH550 to the solid-liquid mixture, and stir at a speed of 300 r / min for 1 - 2 h to obtain a solid-liquid mixture B.

[0015] S1.3: Mix the solid-liquid mixture B and the mixed solution A at a volume ratio of 1:(2 - 4), increase the speed to 800 r / min, add a 5 wt% trifluoroacetic acid solution and 7 wt% of p-toluenesulfonyl fluoride after stirring for 2 h, and continue to stir for 0.5 h to obtain a casting solution.

[0016] S1.4: Use a hollow fiber membrane spinning machine with a spinning machine temperature of 30 - 40 °C, extrude the casting solution through a hollow spinneret, inject nitrogen while extruding, and immerse the extruded membrane in deionized water at 20 - 30 °C for solidification to form the structure of the hollow fiber membrane.

[0017] S1.5: Rinse the obtained hollow fiber membrane to remove residual solvents and additives, dry it at 80 °C in a nitrogen atmosphere, coat a 10 wt% polydimethylsiloxane solution on the surface after drying, and let it stand and dry at room temperature to obtain the modified hollow fiber membrane.

[0018] Furthermore, the acid solution in S1 is one or more of sulfuric acid, phosphoric acid, hydrochloric acid, and nitric acid.

[0019] Furthermore, the pH value in the circulating acid storage tank in S1 is 1 - 2.

[0020] Furthermore, the mass fraction of trifluoroacetic acid in the trifluoroacetic acid solution in S1.3 is 3 - 5%.

[0021] Furthermore, the inlet flow rate of nitrogen in S1.4 is 5 m / s, and the pressure is 0.2 - 0.3 MPa.

[0022] Further, the lye in S2 is one or more of calcium hydroxide, sodium hydroxide, and sodium carbonate.

[0023] Further, the mass fraction of the lye in S2 is 30-50%.

[0024] Further, the pH value of the ammonia-nitrogen wastewater in S2 > 10.

[0025] Further, the parameters of the aeration treatment in S2 are an aeration duty cycle of 100%, an aeration flow rate of 2.5 m 3 / L, and an air flow temperature of 50 °C.

[0026] In the present invention, the acidic circulating solution in the circulating acid storage tank enters the modified hollow fiber membrane under the action of a circulating pump, and absorbs NH3 generated by the ammonia-nitrogen wastewater in the ammonia-nitrogen wastewater pool in the modified hollow fiber membrane, reducing the ammonia-nitrogen concentration, and continuously reducing the ammonia-nitrogen concentration through circulation; the circulating acid storage tank replenishes the acid solution to maintain the pH value of the acidic circulating solution between 1-2; the ammonia-nitrogen wastewater pool replenishes the lye to make the pH of the ammonia-nitrogen wastewater > 10, improving the ammonia-nitrogen removal effect.

[0027] The present invention realizes the efficient removal of ammonia-nitrogen by injecting an acid solution into the circulating acid storage tank and effectively absorbing the ammonia-nitrogen wastewater by using the modified hollow fiber membrane to generate an inorganic ammonium salt solution. The present invention uses a modified hollow fiber membrane for ammonia-nitrogen absorption, improving the absorption efficiency and selectivity, while forming a closed-loop circulation system, reducing wastewater discharge, and improving resource utilization. In addition, the process flow of the present invention further optimizes the treatment effect by precisely adjusting the pH value of the wastewater and the aeration treatment.

[0028] The ammonia-nitrogen wastewater is aerated by an aeration device to ensure that the suspended solids in the influent are evenly separated, reducing the accumulation of suspended solids on the membrane surface. At the same time, the pollutants on the membrane surface can be removed, improving the ammonia-nitrogen removal effect, and the ammonia-nitrogen wastewater with high-concentration suspended solids can be treated.

[0029] The modified hollow fiber membrane prepared by the present invention shows significant advantages in the membrane method for ammonia-nitrogen removal process. This membrane not only has a high ammonia-nitrogen absorption capacity and can effectively reduce the ammonia-nitrogen content in the wastewater, but also shows good chemical stability and mechanical strength, ensuring long-term stable operation effect.

[0030] In the preparation process, various additives play a crucial role. Polyvinylidene fluoride, as the basis of the membrane material, provides excellent mechanical support and chemical inertness and is the main component of the membrane structure. N,N-dimethylacetamide DMAC, as a solvent, helps polyvinylidene fluoride form a uniform solution, laying the foundation for the subsequent spinning process.

[0031] The introduction of aqueous sodium silicate and nano-silica significantly enhances the mechanical strength and pore structure of the membrane. As an inorganic framework, sodium silicate interacts with nano-silica to form a more robust membrane structure. Meanwhile, the dispersion of nano-silica increases the surface area and porosity of the membrane, facilitating the adsorption and transport of ammonia nitrogen molecules. The addition of silane coupling agent KH550 further improves the compatibility between inorganic fillers and organic polymers, ensuring the stability and uniformity of the membrane structure.

[0032] Trifluoroacetic acid solution and p-toluenesulfonyl fluoride are used as surfactants to finely regulate the surface properties of the membrane. They can adjust the pore size and distribution of the membrane, optimizing the selective absorption ability of the membrane for ammonia nitrogen molecules. The addition of trifluoroacetic acid solution and p-toluenesulfonyl fluoride not only acts as a surfactant to regulate the surface properties of the membrane but also plays a more important role.

[0033] Trifluoroacetic acid solution has extremely strong hydrophobicity. It can form a dense hydrophobic layer on the membrane surface, effectively preventing the penetration of water molecules, thereby improving the anti-fouling performance and selectivity of the membrane. At the same time, its special molecular structure can also interact with the molecular chains of polyvinylidene fluoride, enhancing the stability and mechanical strength of the membrane structure; p-toluenesulfonyl fluoride mainly acts as a pore regulator, and by affecting the phase separation process of the casting solution, it finely regulates the pore structure and distribution inside the membrane. This regulatory effect not only optimizes the adsorption and transport paths of ammonia nitrogen molecules by the membrane but also further improves the separation efficiency and selectivity of the membrane; the synergistic mechanism between the two lies in that the hydrophobic effect of trifluoroacetic acid solution and the pore regulation effect of p-toluenesulfonyl fluoride complement and promote each other. The formation of the hydrophobic layer reduces the interference of water molecules, providing more favorable conditions for the optimization of the pore structure; while the optimization of the pore structure further enhances the effect of the hydrophobic layer, making the modified hollow fiber membrane exhibit more excellent performance in the treatment of ammonia nitrogen wastewater.

[0034] The present invention also uses polydimethylsiloxane solution to form a hydrophobic layer on the membrane surface, which effectively prevents the penetration of moisture and other impurities, maintaining the stability and high efficiency of the internal structure of the membrane. This hydrophobic layer not only improves the durability of the membrane but also ensures the continuous high-efficiency performance of the membrane during the treatment of ammonia nitrogen wastewater.

[0035] In the present invention, polyvinylidene fluoride is purchased from Wuhan Lanaibai Pharmaceutical Chemical Co., Ltd., with a purity of 98%; trifluoroacetic acid in the present invention is purchased from Jinan Zhonglan Chemical Co., Ltd., with a purity of 99.9%; p-toluenesulfonyl fluoride in the present invention is purchased from Anhui Zesheng Technology Co., Ltd., with a purity of 98%; polydimethylsiloxane in the present invention is purchased from Jinan Longcheng Organosilicon Co., Ltd., with a purity of 99.99%.

[0036] Advantages of the present invention:

[0037] The present invention realizes the efficient removal of ammonia nitrogen by adopting the modified hollow fiber membrane technology to treat ammonia nitrogen wastewater. By injecting an acid solution into the circulating acid storage tank and using the modified hollow fiber membrane to absorb the ammonia nitrogen wastewater to generate an inorganic ammonium salt solution, the ammonia nitrogen concentration in the wastewater is significantly reduced. At the same time, the present invention reduces wastewater discharge and improves resource utilization rate through a secondary circulation system;

[0038] The modified hollow fiber membrane prepared by the present invention not only has high ammonia nitrogen absorption capacity, but also exhibits good chemical stability and mechanical strength, ensuring long-term stable operation effect. In the preparation process, additives such as polyvinylidene fluoride, N,N-dimethylacetamide, sodium silicate aqueous solution, nano-silica, silane coupling agent KH550, trifluoroacetic acid solution and p-toluenesulfonyl fluoride play a key role and jointly construct the excellent performance of the membrane. Brief Description of the Drawings

[0039] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with the drawings.

[0040] Figure 1 Schematic diagram of the membrane method for ammonia nitrogen removal. Detailed Embodiments

[0041] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following will, in conjunction with the drawings and preferred embodiments, describe in detail the specific embodiments, structures, features and effects according to the present invention.

[0042] Example 1

[0043] S1: Inject a sulfuric acid solution with a mass fraction of 20% into the circulating acid storage tank, the pH value in the circulating acid storage tank is 2, start the circulation, and introduce the dilute acid solution into the modified hollow fiber membrane in the ammonia nitrogen wastewater tank;

[0044] The preparation method of the modified hollow fiber membrane is as follows,

[0045] S1.1: Heat polyvinylidene fluoride to 175°C to make it in a molten state, add N,N-dimethylacetamide DMAC in a mass ratio of 1:1, and stir at a speed of 200 r / min for 1 h to obtain a uniformly mixed mixed solution A;

[0046] S1.2: Dissolve sodium silicate in deionized water to obtain a sodium silicate aqueous solution with a mass fraction of 30%, disperse nano-silica in the sodium silicate aqueous solution, the solid-liquid mass ratio is 1:2, and then add 2 wt% of the silane coupling agent KH550 to the solid-liquid mixture, and stir at a speed of 300 r / min for 2 h to obtain a solid-liquid mixture B;

[0047] S1.3: Mix the solid-liquid mixture B and the mixed solution A at a volume ratio of 1:3, increase the rotation speed to 800 r / min, stir for 2 h, then add a 5 wt% trifluoroacetic acid solution and 7 wt% p-toluenesulfonyl fluoride. The mass fraction of the trifluoroacetic acid solution is 5%, and continue to stir for 0.5 h to obtain a casting solution;

[0048] S1.4: Use a hollow fiber membrane spinning machine with a temperature of 35 °C. Extrude the casting solution through a hollow spinneret, and inject nitrogen while extruding. The flow rate of the nitrogen is 5 m / s and the pressure is 0.3 MPa. Immerse the extruded membrane in deionized water at 25 °C for solidification to form the structure of the hollow fiber membrane;

[0049] S1.5: Rinse the obtained hollow fiber membrane to remove residual solvents and additives. Dry it at 80 °C in a nitrogen atmosphere, and then coat a 10 wt% polydimethylsiloxane solution on the surface and let it dry at room temperature to obtain the modified hollow fiber membrane.

[0050] S2: Pass the ammonia-nitrogen-containing wastewater into the ammonia-nitrogen wastewater tank, and use a calcium hydroxide solution with a mass fraction of 30 - 50% to adjust the pH value. Detect the pH value of the ammonia-nitrogen wastewater. When the pH value of the ammonia-nitrogen wastewater > 10 and meets the standard, conduct aeration treatment on the wastewater. The parameters of the aeration treatment are an aeration duty cycle of 100%, an aeration flow rate of 2.5 m 3 / L, and an air flow temperature of 50 °C;

[0051] S3: Use the modified hollow fiber membrane to absorb ammonia-nitrogen from the aerated ammonia-nitrogen wastewater and generate an inorganic ammonium salt solution. Return the generated inorganic ammonium salt solution to the circulating acid storage tank through the action of a circulating pump for secondary absorption to complete the treatment of the ammonia-nitrogen wastewater;

[0052] S4: Drain the inorganic ammonium salt solution from the system through a sewage pump for subsequent product separation and purification treatment.

[0053] Example 2

[0054] S1: Inject a 10 wt% phosphoric acid solution into the circulating acid storage tank. The pH value in the circulating acid storage tank is 1.5. Start the circulation and pass the dilute acid solution into the modified hollow fiber membrane in the ammonia-nitrogen wastewater tank;

[0055] The preparation method of the modified hollow fiber membrane is as follows,

[0056] S1.1: Heat polyvinylidene fluoride to 165 °C to make it in a molten state. Add N,N-dimethylacetamide DMAC at a mass ratio of 1:1 and stir at a rotation speed of 200 r / min for 1 h to obtain a uniformly mixed mixed solution A;

[0057] S1.2: Dissolve sodium silicate in deionized water to obtain an aqueous sodium silicate solution with a mass fraction of 20%. Disperse nano-silica in the aqueous sodium silicate solution with a solid-liquid mass ratio of 1:2. Then add 2 wt% of silane coupling agent KH550 to the solid-liquid mixture and stir for 1 h at a rotation speed of 300 r / min to obtain a solid-liquid mixture B.

[0058] S1.3: Mix the solid-liquid mixture B and the mixed solution A at a volume ratio of 1:4. Increase the rotation speed to 800 r / min. After stirring for 2 h, add a 5 wt% trifluoroacetic acid solution and 7 wt% p-toluenesulfonyl fluoride, where the mass fraction of the trifluoroacetic acid solution is 3%. Continue to stir for 0.5 h to obtain a casting solution.

[0059] S1.4: Use a hollow fiber membrane spinning machine with a temperature of 30 °C. Extrude the casting solution through a hollow spinneret, and inject nitrogen while extruding. The inlet flow rate of nitrogen is 5 m / s and the pressure is 0.3 MPa. Immerse the extruded membrane in deionized water at 30 °C for coagulation to form the structure of the hollow fiber membrane.

[0060] S1.5: Rinse the obtained hollow fiber membrane to remove residual solvents and additives. Dry it at 80 °C in a nitrogen atmosphere. After drying, coat a 10 wt% polydimethylsiloxane solution on the surface and let it stand and dry at room temperature to obtain the modified hollow fiber membrane.

[0061] S2: Pass the ammonia-nitrogen-containing wastewater into an ammonia-nitrogen wastewater tank, and use a 30 wt% sodium hydroxide solution to adjust the pH value. Detect the pH value of the ammonia-nitrogen wastewater. When the pH value of the ammonia-nitrogen wastewater > 10 and meets the standard, conduct aeration treatment on the wastewater. The parameters of the aeration treatment are an aeration duty cycle of 100% and an aeration flow rate of 2.5 m 3 / L, and the air flow temperature is 50 °C;

[0062] S3: Use the modified hollow fiber membrane to absorb ammonia-nitrogen from the aerated ammonia-nitrogen wastewater and generate an inorganic ammonium salt solution. Return the generated inorganic ammonium salt solution to the circulating acid storage tank through the action of a circulating pump for secondary absorption to complete the treatment of the ammonia-nitrogen wastewater.

[0063] S4: Drain the inorganic ammonium salt solution from the system through a sewage pump for subsequent product separation and purification treatment.

[0064] Example 3

[0065] S1: Inject a 30 wt% nitric acid solution into the circulating acid storage tank. The pH value in the circulating acid storage tank is 1.5. Start the circulation and pass the dilute acid solution into the modified hollow fiber membrane in the ammonia-nitrogen wastewater tank.

[0066] The preparation method of the modified hollow fiber membrane is as follows,

[0067] S1.1: Heat polyvinylidene fluoride to 180 °C to make it in a molten state, add N,N-dimethylacetamide (DMAC) in a mass ratio of 1:1, and stir for 1 h at a rotation speed of 200 r / min to obtain a uniformly mixed mixed solution A;

[0068] S1.2: Dissolve sodium silicate in deionized water to obtain a sodium silicate aqueous solution with a mass fraction of 30%. Disperse nano-silica in the sodium silicate aqueous solution with a solid-liquid mass ratio of 1:2, and then add 2 wt% of silane coupling agent KH550 to the solid-liquid mixture, and stir at a rotation speed of 300 r / min for 1 - 2 h to obtain a solid-liquid mixture B;

[0069] S1.3: Mix the solid-liquid mixture B and the mixed solution A in a volume ratio of 1:2, increase the rotation speed to 800 r / min, stir for 2 h, then add a 5 wt% trifluoroacetic acid solution and 7 wt% p-toluenesulfonyl fluoride, where the mass fraction of the trifluoroacetic acid solution is 5%, and continue to stir for 0.5 h to obtain a casting solution;

[0070] S1.4: Use a hollow fiber membrane spinning machine with the spinning machine temperature at 30 °C. Extrude the casting solution through a hollow spinneret, and inject nitrogen while extruding. The inlet flow rate of nitrogen is 5 m / s and the pressure is 0.2 MPa. Immerse the extruded membrane in deionized water at 20 °C for coagulation to form the structure of the hollow fiber membrane;

[0071] S1.5: Rinse the obtained hollow fiber membrane to remove residual solvents and additives, dry it in a nitrogen atmosphere at 80 °C, and then coat a 10 wt% polydimethylsiloxane solution on the surface and let it stand and dry at room temperature to obtain the modified hollow fiber membrane.

[0072] S2: Pass the ammonia-nitrogen-containing wastewater into an ammonia-nitrogen wastewater pool, and use a 50 wt% sodium carbonate solution to adjust the pH value. Detect the pH value of the ammonia-nitrogen wastewater. When the pH value of the ammonia-nitrogen wastewater > 10 and meets the standard, perform aeration treatment on the wastewater. The parameters of the aeration treatment are an aeration duty cycle of 100%, an aeration flow rate of 2.5 m 3 / L, and the air flow temperature is 50 °C;

[0073] S3: Use the modified hollow fiber membrane to absorb ammonia-nitrogen from the aerated ammonia-nitrogen wastewater and generate an inorganic ammonium salt solution. Return the generated inorganic ammonium salt solution to the circulating acid storage tank through the action of a circulating pump for secondary absorption to complete the treatment of the ammonia-nitrogen wastewater;

[0074] S4: Discharge the inorganic ammonium salt solution from the system through a sewage pump for subsequent product separation and purification treatment.

[0075] Comparative Example 1

[0076] In this comparative example, sodium silicate is not added during the preparation of the modified hollow fiber membrane, and the remaining steps are the same as those in Example 1.

[0077] Comparative Example 2

[0078] In this comparative example, nano-silica is not added during the preparation of the modified hollow fiber membrane, and the remaining steps are the same as those in Example 1.

[0079] Comparative Example 3

[0080] In this comparative example, trifluoroacetic acid solution is not added during the preparation of the modified hollow fiber membrane, and the remaining steps are the same as those in Example 1.

[0081] Comparative Example 4

[0082] In this comparative example, p-toluenesulfonyl fluoride is not added during the preparation of the modified hollow fiber membrane, and the remaining steps are the same as those in Example 1.

[0083] Comparative Example 5

[0084] In this comparative example, polydimethylsiloxane solution is not coated on the surface during the preparation of the modified hollow fiber membrane, and the remaining steps are the same as those in Example 1.

[0085] The results obtained from the examples and comparative examples were tested, and the ammonia nitrogen removal rate in the ammonia nitrogen wastewater was tested. The experimental results are summarized in the following table.

[0086]

[0087]

[0088] From the experimental data, it can be seen that the prepared modified hollow fiber membrane in the present invention has a better ammonia nitrogen removal rate.

[0089] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed as above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes, but as long as the technical content of the present invention is not departed from, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A membrane method for removing ammonia nitrogen, characterized in that: The specific steps of the process are as follows: S1: injecting an acid solution with a mass fraction of 10-30% into the circulating acid storage tank, starting the circulation, and passing the dilute acid solution into the modified hollow fiber membrane in the ammonia nitrogen wastewater pool; S2: passing the wastewater containing ammonia nitrogen into the ammonia nitrogen wastewater pool, and adjusting the pH value with alkaline solution, testing the pH value of the ammonia nitrogen wastewater, and aerating the wastewater after it meets the standard; S3: The ammonia nitrogen wastewater after aeration treatment is subjected to a modified hollow fiber membrane to absorb ammonia nitrogen and generate an inorganic ammonium salt solution, and the generated inorganic ammonium salt solution is returned to the circulating acid storage tank through the action of a circulating pump for secondary absorption to complete the treatment of the ammonia nitrogen wastewater; S4: The inorganic ammonium salt solution is discharged from the system through a sewage pump for subsequent product separation and purification.

2. A membrane method for removing ammonia nitrogen according to claim 1, characterized in that: The preparation method of the modified hollow fiber membrane in S1 is as follows: S1.1: Heat polyvinylidene fluoride to 165-180°C to make the polyvinylidene fluoride molten, add N,N-dimethylacetamide DMAC at a mass ratio of 1:1, and stir at a speed of 200 r / min for 1 hour to obtain a uniformly mixed mixed solution A; S1.2: Sodium silicate is dissolved in deionized water to obtain a sodium silicate aqueous solution with a mass fraction of 20-30%, nano-silicon dioxide is dispersed in the sodium silicate aqueous solution with a solid-liquid mass ratio of 1:2, and then 2wt% of silane coupling agent KH550 is added to the solid-liquid mixture, and stirred at a speed of 300r / min for 1-2h to obtain a solid-liquid mixture B; S1.3: The solid-liquid mixture B and the mixed solution A are mixed in a volume ratio of 1:(2-4), the rotation speed is increased to 800 r / min, and after stirring for 2 h, 5 wt % trifluoroacetic acid solution and 7 wt % p-toluenesulfonyl fluoride are added, and stirring is continued for 0.5 h to obtain a casting solution; S1.4: Using a hollow fiber membrane spinning machine, the spinning machine temperature is 30-40°C, the casting solution is extruded through a hollow spinneret, nitrogen is injected while extruding, and the extruded membrane is immersed in deionized water at 20-30°C for coagulation to form a hollow fiber membrane structure; S1.5: Rinse the prepared hollow fiber membrane to remove residual solvent and additives, dry it at 80°C in a nitrogen atmosphere, coat a layer of 10% by mass polydimethylsiloxane solution on the surface, and let it stand and dry at room temperature to obtain the modified hollow fiber membrane.

3. A membrane method for removing ammonia nitrogen according to claim 1, characterized in that: The acid solution in S1 is one or more of sulfuric acid, phosphoric acid, hydrochloric acid and nitric acid.

4. A membrane method for removing ammonia nitrogen according to claim 1, characterized in that: The pH value in the circulating acid storage tank in S1 is 1-2.

5. The membrane method for removing ammonia nitrogen according to claim 1, characterized in that: The mass fraction of trifluoroacetic acid in the trifluoroacetic acid solution in S1.3 is 3-5%.

6. A membrane method for removing ammonia nitrogen according to claim 1, characterized in that: The nitrogen in said S1.4 has an inlet flow rate of 5 m / s and a pressure of 0.2-0.3 MPa.

7. The membrane method for removing ammonia nitrogen according to claim 1 is characterized in that: The alkali solution in S2 is one or more of calcium hydroxide, sodium hydroxide and sodium carbonate.

8. The membrane method for removing ammonia nitrogen according to claim 1 is characterized in that: The mass fraction of the alkali solution in S2 is 30-50%.

9. A membrane method for removing ammonia nitrogen according to claim 1, characterized in that: The pH value of the ammonia nitrogen wastewater in the S2 is greater than 10.

10. The membrane method for removing ammonia nitrogen according to claim 1, characterized in that: The parameters of the aeration treatment in S2 are an aeration duty cycle of 100% and an aeration flow rate of 2.5 m 3 / L, air flow temperature 50℃.

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