Preparation method of biological carrier suitable for growth of nitrite bacteria and anaerobic ammonium oxidizing bacteria

Abstract

This invention discloses a method for preparing a biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria, by preparing and combining a mixture rich in amino groups and Fe... 3+ Polyurethane carrier and rich in hydroxyl, amino and Mg 2+ A polyurethane carrier was used, and the biofilm formation effect of microorganisms was enhanced by adjusting the internal pore structure of the carrier. Since nitrifying bacteria are aerobic bacteria and anaerobic ammonia-oxidizing bacteria are anaerobic bacteria, when this biofilm carrier was placed in the PN / A integrated reactor, nitrifying bacteria biofilm grew on the outer surface of the carrier, while anaerobic ammonia-oxidizing bacteria biofilm grew on the inner surface, thereby improving the biofilm formation capacity of microorganisms in the reactor.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a method for preparing a biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria. Background Technology

[0002] The partial nitrification-anammox (PNA) nitrogen removal process offers energy-saving advantages. Nitrifying bacteria (AOB) oxidize ammonia nitrogen to nitrite nitrogen, requiring an aerobic environment, while anammox bacteria (AnAOB) react ammonia nitrogen with the generated nitrite nitrogen to produce nitrogen gas, achieving wastewater denitrification, but requiring a strictly anaerobic environment. Since AOB is aerobic and AnAOB is strictly anaerobic, controlling dissolved oxygen levels is crucial for their growth when they coexist in the same reactor. Therefore, controlling the local dissolved oxygen distribution is key to the synergistic growth of both types of bacteria, i.e., ensuring the simultaneous presence of aerobic and anaerobic zones. Furthermore, both AOB and AnAOB are autotrophic bacteria with slow growth. Adding carriers can increase the concentration of AOB and AnAOB cells in the reactor; however, current carriers generally suffer from slow biofilm growth rates for autotrophic bacteria. Constructing carrier surfaces suitable for the growth and attachment of AOB and AnAOB respectively can overcome the shortcomings of current synergistic growth methods and carrier limitations.

[0003] The growth of microbial biofilms on carrier surfaces is related to the functional groups, potential, and porosity of the carrier surface. Introducing hydrophilic groups (such as carboxyl, amino, hydroxyl, and sulfonic acid groups) into the carrier surface can enhance its hydrophilicity. Furthermore, the polar groups on the carrier surface have stronger hydrogen bonding interactions with proteins, polysaccharides, and DNA on the microbial surface, which is beneficial for enhancing the attachment speed and strength of microorganisms. Since most carrier surfaces are negatively charged, and the surfaces of aquatic microorganisms also have negative charges, electrostatic repulsion occurs between the microorganisms and the carrier surface, resulting in low microbial adhesion, easy biofilm detachment, and long system start-up time. Studies have found that biofilms on carrier surfaces with smaller pore sizes have higher stability but lower oxygen penetration efficiency during biofilm formation; while biofilms on carrier surfaces with larger pore sizes have higher biofilm diversity but lower stability and better oxygen penetration. Summary of the Invention

[0004] To address the above problems, this invention provides a method for preparing a biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria. This invention synthesizes carriers with different pore sizes by controlling pressure and controlling the distribution of dissolved oxygen in different regions of the carrier within the reactor. By constructing a carrier surface suitable for the growth of AOB and AnAOB, the invention promotes the synergistic growth of AOB and AnAOB biofilms in different regions of the carrier.

[0005] The present invention discloses a method for preparing a biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria, comprising the following steps:

[0006] Step 1: Preparation of amino-rich cationic gel

[0007] Magnesium oxide particles were ground in a mortar, and the particle size after grinding was determined to be approximately 100 μm through a 150-mesh sieve. Powdered chitosan was dissolved in a 10% acetic acid solution at 80°C to prepare a chitosan solution. Magnesium oxide powder was added to the chitosan solution and stirred evenly. Then, a 2% (w / w) glutaraldehyde solution was added for cross-linking modification to obtain an amino-rich cationic gel.

[0008] In step 1, the chitosan solution contains 2% to 4% by mass. The mass ratio of the chitosan solution to the glutaraldehyde solution is 250:1.

[0009] In step 1, the magnesium oxide content in the amino-rich cationic gel is 3%.

[0010] Step 2: Preparation of large-pore support for gas exchange

[0011] A foaming agent, stabilizer, polyether polyol, triethanolamine, and dimethylolbutyric acid are added to a reactor in a certain proportion. Isocyanate is slowly added to the reactor and the mixture is stirred at 600-900 rpm for 2-4 hours under a vacuum of 0.10-0.12 MPa and a temperature of 25±2℃ to obtain polyurethane flexible foam. The obtained polyurethane flexible foam is placed in a sealed meshing device, filled with nitrogen, and N,N-dimethylformamide solution is used to dissolve the polyurethane membrane in the pores to ensure that a pore size of 2 mm-4 mm is formed on the surface of the carrier.

[0012] In step 2, the components are composed of the following parts by mass: 4-8 parts of foaming agent, 2-3 parts of stabilizer, 100 parts of polyether polyol, 6 parts of triethanolamine, 3 parts of dimethylolbutyric acid, and 1.14 parts of isocyanate.

[0013] The foaming agent is a mixture of triethylamine and dichloromethane in a mass ratio of 1:1; the stabilizer is silicone oil; the polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, and polyether 220. The isocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate. When the foam is uniformly cured under low-temperature conditions, the temperature is controlled between 25±2℃.

[0014] In step 2, the nitrogen charging pressure is 0.10 MPa to 0.11 MPa.

[0015] Step 3: Preparation of nitrosation support with positive surface potential and hydrophilic groups

[0016] Introduce oxygen into the amino-rich cationic gel prepared in step 1 to generate bubbles inside the gel. When uniform and fine bubbles are formed inside the gel, immerse the large-pore carrier prepared in step 2 into the gel for 5 minutes. Remove the carrier and place it in a 60°C drying oven to dry for 1 hour. Repeat steps 2 to 3 times to ensure that the gel is fully and uniformly coated on the surface of the carrier.

[0017] Step 4: Preparation of amino-rich iron-containing gel

[0018] Iron oxide was ground in a mortar, and the particles were then passed through a 150-mesh sieve to determine that the particle size was approximately 100 μm. Powdered chitosan was dissolved in a 10% acetic acid solution at 80°C to prepare a chitosan solution. Iron oxide powder was added to the chitosan solution, followed by a 2% (w / w) glutaraldehyde solution for cross-linking modification, resulting in an amino-rich cationic gel.

[0019] In step 4, the chitosan solution contains 2% to 4% by mass. The mass ratio of the chitosan solution to the glutaraldehyde solution is 250:1.

[0020] The mass fraction of iron oxide in the amino-rich cationic gel prepared in step 4 is 5%.

[0021] Step 5: Preparation of small-pore carriers for controlling dissolved oxygen permeation

[0022] Aromatic diisocyanate is gradually added to the carrier mold along with foaming agent, polyether polyol and catalyst during stirring. At this time, uniform and fine bubbles will gradually form inside the system. The obtained polyurethane flexible foam is placed in a sealed meshing device, filled with nitrogen, and N,N-dimethylformamide solution is used to dissolve the polyurethane membrane in the pores to ensure that the carrier surface forms a pore size of 0.3mm~0.4mm.

[0023] In step 5, the components are composed of the following parts by mass: 4-8 parts of foaming agent, 70-80 parts of polyether polyol, 0.5-1.5 parts of catalyst, and 7-8 parts of aromatic diisocyanate.

[0024] The foaming agent is a mixture of triethylamine and dichloromethane in a mass ratio of 1:1. The polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, and polyether 220. The catalyst is dibutyltin dilaurate. The aromatic diisocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate. When the foam is uniformly cured under low-temperature conditions, the temperature is controlled between 30℃ and 40℃.

[0025] In step 5, after nitrogen is introduced, the pressure is controlled at 0.05 MPa to 0.08 MPa to control the foam size.

[0026] Step 6: Preparation of anaerobic ammonium oxidation support with iron ions and hydrophilic groups on its surface

[0027] Hydrogen gas is introduced into the gel prepared in step 4 to generate bubbles inside the gel. When uniform and fine bubbles are formed inside the gel, the small-pore carrier prepared in step 5 is immersed in the gel for 5 minutes. The carrier is then removed and placed in a 60°C drying oven to dry for 1 hour. Repeat the above steps 2 to 3 times to ensure that the hydrogel is fully and uniformly coated on the surface of the carrier.

[0028] Step 7: Combination of nitrification carrier and anaerobic ammonia-oxidizing bacteria carrier

[0029] Using polyurethane adhesive as a binder (diluted with acetone at one-third to one-half its volume), the nitrosation carrier prepared in step 3 and the anaerobic ammonia oxidation carrier prepared in step 6 are combined, with the nitrosation carrier prepared in step 3 serving as the top and bottom layers (AOB adsorption carrier), and the anaerobic ammonia oxidation carrier prepared in step 6 serving as the middle layer (AnAOB adsorption carrier), forming a sandwich structure.

[0030] In the specific operation, evenly coat one side of the AOB adsorption carrier with diluted polyurethane adhesive, then lay it flat on the mesh frame and let it stand for 5 minutes to ensure that the polyurethane adhesive no longer drips. After the polyurethane adhesive becomes slightly tacky, firmly adhere the AOB adsorption carrier to the surface of the AnAOB adsorption carrier, ensuring that the AnAOB carrier is completely encapsulated. Place the entire carrier in a 60℃ oven for drying. After drying, remove the carrier and place it in ultrapure water, then use an ultrasonic cleaner for 30 minutes to remove surface impurities and uncured adhesive.

[0031] In step 7, the polyurethane adhesive is obtained in-house. Specifically, 1 part toluene diisocyanate is dissolved in 50 parts N,N-dimethylformamide (DMF) and prepolymerized for 5 minutes. Then, 1 part polyethylene glycol is added to the solution. Next, the mixture is thoroughly stirred at room temperature for 2 hours.

[0032] The biomimetic carrier prepared by this invention can be used in the PN / A integrated process to promote the rapid enrichment of microorganisms.

[0033] This invention has the following advantages and positive effects:

[0034] (1) This invention utilizes pressure differences to construct polyurethane carriers with different pore sizes, and controls the distribution of dissolved oxygen in the reactor by adjusting the pore size of the polyurethane carriers, thereby creating conditions for the co-enrichment of nitrifying bacteria and anaerobic ammonia oxidation.

[0035] (2) This invention uses polyurethane material as the supporting matrix for biofilms and utilizes chitosan adsorption gel as a hydrophilic modification material. Since the surface of chitosan contains abundant amino and hydroxyl groups, the introduction of chitosan enhances the hydrophilicity of the carrier surface, which is beneficial to accelerating the adhesion of biofilms. Furthermore, chitosan gel is simple to prepare and is conducive to industrial production.

[0036] (3) When the chitosan gel is loaded onto the surface of the carrier, the present invention generates uniform bubbles by using an aeration method, which helps to increase the surface area of ​​the carrier. Furthermore, when oxygen is used for aeration, it helps to maintain the oxidized groups on the surface of the chitosan and promotes the attachment of the carrier to microorganisms.

[0037] (4) In this invention, magnesium oxide and iron oxide are used to enhance the positive potential of the carrier surface. Magnesium oxide has a high isoelectric point and carries a lot of positive charge on its surface. The hydrogel loaded with magnesium oxide is positively charged. When the gel is added to the carrier surface, it can effectively increase the positive potential of the carrier surface. Iron oxide powder can accelerate the aggregation of anaerobic ammonia oxidizing bacteria due to the iron affinity of anaerobic ammonia oxidizing bacteria and the positive potential of its surface.

[0038] (5) The present invention uses an adhesive method to splice the two carriers, which is simple to operate and easy to produce.

[0039] (6) The carrier prepared by the present invention has the characteristics of high porosity, low relative density, high mechanical strength, corrosion resistance and aging resistance, and can be applied to various reactors such as UASB and CSTR. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the production process of the biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria according to the present invention.

[0041] Figure 2 This is a schematic diagram of the structure and working principle of the biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia oxidizing bacteria according to the present invention.

[0042] Figure 3 This is a schematic diagram of the structure of the biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria according to the present invention.

[0043] Figure 4 This refers to the water contact angle of the surface of amino gels with different contents in this invention.

[0044] Figure 5 This invention describes the adsorption effect of a nitrifying carrier with a positive potential and hydrophilic groups on activated sludge.

[0045] Figure 6 This invention describes the adsorption effect of an anaerobic ammonia oxidation carrier with iron ions and hydrophilic groups on activated sludge.

[0046] Figure 7 This invention describes the adsorption effect of a biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria on activated sludge. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0048] The present invention provides a method for preparing a biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria, as detailed below:

[0049] (1) Preparation of amino-rich cationic gel. Magnesium oxide particles were ground in a mortar and then passed through a 150-mesh sieve to determine that the particle size of both was approximately 100 μm. Powdered chitosan was placed in a 10% acetic acid solution and dissolved completely at 80°C to prepare a chitosan solution with a mass fraction of 2%–4%. 3% magnesium oxide powder was added to the gel and stirred evenly. A 2% glutaraldehyde solution was added to the chitosan gel for cross-linking modification to obtain an amino-rich cationic gel. The mass ratio of chitosan solution to glutaraldehyde solution was 250:1, and the mixture was stirred for 1–2 h.

[0050] (2) Preparation of a large-pore carrier that facilitates gas exchange. A foaming agent, stabilizer, polyol, triethanolamine, and dimethylolbutyric acid are added to a reactor in a certain proportion. Isocyanate is slowly added, and the mixture is stirred at 600–900 rpm for 2–4 hours under a vacuum of 0.10–0.12 MPa and a temperature of 25 ± 2℃ to obtain polyurethane flexible foam. The foaming agent comprises 4–8 parts, stabilizer 2–3 parts, polyether polyol 100 parts, triethanolamine 6 parts, dimethylolbutyric acid 3 parts, and isocyanate 1.14 parts. The polyurethane flexible foam is placed in a sealed mesh filling device and filled with nitrogen at a pressure of 0.10 MPa–0.11 MPa. The filled polyurethane carrier is then dissolved in N,N-dimethylformamide solution to ensure that the carrier surface forms a pore size of approximately 2 mm–4 mm. The foaming agent is a mixture of triethylamine and dichloromethane in a mass ratio of 1:1. The stabilizer is silicone oil. The polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, and polyether 220. The catalyst is dibutyltin dilaurate. The isocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate.

[0051] (3) Preparation of a nitrosation support with positive potential and hydrophilic groups on its surface. Oxygen was introduced into the gel prepared in (1) to generate bubbles inside the gel. When uniform and fine bubbles formed inside the gel, the large-pore support prepared in step 2 was immersed in the gel for 5 minutes. The support was then removed and dried in a 60°C drying oven for 1 hour. Steps 2-3 were repeated to ensure the hydrogel was fully and uniformly coated on the support surface.

[0052] (4) Preparation of amino-rich iron-containing gel. Iron oxide was ground in a mortar and passed through a 150-mesh sieve to determine that the particle size was approximately 100 μm. Powdered chitosan was dissolved in a 10% acetic acid solution at 80°C to prepare a chitosan solution with a chitosan mass fraction of 2%–4%. Iron oxide powder was added to the gel, followed by a 2% glutaraldehyde solution for cross-linking modification to obtain an amino-rich cationic gel. The mass ratio of chitosan solution to glutaraldehyde solution was 250:1, and the mixture was magnetically stirred for 1–2 hours. The mass fraction of iron oxide powder was 5%.

[0053] (5) Preparation of a small-pore carrier for controlling dissolved oxygen permeation. Add a foaming agent, polyether polyol, and catalyst to the carrier mold according to mass. The mass fractions of each component are: 4-8 parts foaming agent, 70-80 parts polyether polyol, and 0.5-1.5 parts catalyst. During stirring, gradually add aromatic diisocyanate, of which 7-8 parts isocyanate. At this time, uniform and fine bubbles will gradually form inside the system. Place the polyurethane flexible foam in a sealed mesh filling device and fill it with nitrogen gas, while controlling the pressure at 0.05 MPa-0.08 MPa to control the foam size. Dissolve the polyurethane membrane in the pores of the filled polyurethane carrier using N,N-dimethylformamide solution to ensure that the carrier surface forms a pore size of about 0.3 mm-0.4 mm. The foaming agent is a mixture of triethylamine and dichloromethane in a mass ratio of 1:1. The polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, and polyether 220. The catalyst is dibutyltin dilaurate. The isocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate. To ensure uniform curing of the foam under low-temperature conditions, the temperature is controlled between 30℃ and 40℃.

[0054] (6) Preparation of a small-pore anaerobic ammonium oxidation carrier rich in amino and iron ions. Hydrogen gas was introduced into the gel prepared in (4) to generate bubbles inside the gel. When uniform and fine bubbles were formed inside the gel, the large-pore carrier prepared in step 2 was immersed in the gel for 5 minutes. The carrier was then removed and placed in a drying oven at 60°C for 1 hour. Steps 2-3 were repeated to ensure that the hydrogel was fully and uniformly coated on the surface of the carrier.

[0055] (7) Combination of nitrifying carrier and anaerobic ammonia-oxidizing bacteria carrier. The carriers prepared in (3) and (6) were combined by adhesive bonding, with the large-pore carrier as the outer layer and the small-pore carrier as the inner layer. The adhesive used was polyurethane glue, which was prepared as follows: 1 part toluene diisocyanate was dissolved in 50 parts N,N-dimethylformamide (DMF) and prepolymerized for 5 minutes. Then, 1 part polyethylene glycol was added to the solution. Next, the mixture was thoroughly stirred at room temperature for 2 hours. One-third of the volume of acetone was added to the polyurethane glue for dilution. One side of the AOB adsorption carrier was evenly coated with the diluted polyurethane glue, and then it was laid flat on the mesh frame and left to stand for 5 minutes to ensure that the polyurethane glue no longer dripped. After the polyurethane glue became slightly sticky, the AOB adsorption carrier was tightly attached to the surface of the AnAOB adsorption carrier to ensure that the AnAOB carrier was completely wrapped. The entire carrier was placed in an oven at 60°C for drying. After drying, the carrier is removed and placed in ultrapure water, and cleaned with an ultrasonic device for 30 minutes to remove surface impurities and uncured adhesive.

[0056] Example 1: Study on the optimal amount of chitosan added to amino-rich gels

[0057] Chitosan solutions containing 1%, 2%, 3%, and 4% chitosan were dissolved in a 10% acetic acid solution at 80°C to prepare chitosan solutions. A 2% glutaraldehyde solution was added to the chitosan gel for cross-linking modification, with a chitosan solution to glutaraldehyde solution mass ratio of 250:1, and the mixture was stirred for 1-2 hours. The gel was then poured onto a plate to form a film, and the water contact angle of its surface was measured. It was found that the water contact angle increased with increasing chitosan content, reaching 76.8°, 63.1°, 56°, and 42.7° respectively. Theoretically, higher chitosan content results in better hydrophilicity; however, higher hydrophilicity can also inhibit microbial attachment and growth. Therefore, the chitosan content was set at 3%.

[0058] Example 2: Preparation of nitrosation carriers with positive surface potential and hydrophilic groups and their adsorption to microorganisms.

[0059] 1. Grind magnesium oxide particles in a mortar until the particle size is approximately 100 μm, then pass them through a 150-mesh sieve. Dissolve powdered chitosan in a 10% acetic acid solution at 80°C to prepare a chitosan solution with a chitosan mass fraction of 3%. Add 3% magnesium oxide powder to the gel and stir until homogeneous. Add a 2% glutaraldehyde solution to the chitosan gel for cross-linking modification to obtain an amino-rich cationic gel. The mass ratio of chitosan solution to glutaraldehyde solution is 250:1. Stir for 1-2 hours.

[0060] 2. Add the foaming agent, stabilizer, polyol, triethanolamine, and dimethylolbutyric acid (DMSA) to a reactor in a certain proportion. Add isocyanate and stir at 600–900 rpm for 2–4 hours under vacuum conditions of 0.10–0.12 MPa and a temperature of 25 ± 2℃ to obtain polyurethane flexible foam. The mixture contains 6 parts foaming agent, 3 parts stabilizer, 100 parts polyether polyol, 6 parts triethanolamine, 3 parts DMSA, and 1.14 parts isocyanate. Place the polyurethane flexible foam in a sealed mesh filling device and fill it with nitrogen gas at a pressure of 0.10 MPa–0.11 MPa. Dissolve the polyurethane membrane in the pores of the filled polyurethane carrier using N,N-dimethylformamide solution to ensure that the carrier surface forms pores with a diameter of approximately 2 mm–4 mm.

[0061] 3. Infuse the prepared gel with oxygen to generate bubbles inside. Once uniform and fine bubbles have formed inside the gel, immerse the prepared carrier in the gel for 5 minutes. Remove the carrier and place it in a 60°C drying oven for 1 hour. Repeat the above steps 2-3 times to ensure that the hydrogel is fully and uniformly coated on the carrier surface.

[0062] (1) Preparation of a gel without adding a cationic carrier

[0063] A foaming agent, stabilizer, polyol, triethanolamine, and dimethylolbutyric acid (DMSA) are added to a reactor in a certain proportion. Isocyanate is added, and the mixture is stirred at 600–900 rpm for 2–4 hours under a vacuum of 0.10–0.12 MPa and a temperature of 25 ± 2 °C to obtain polyurethane flexible foam. The foaming agent consists of 6 parts, stabilizer 3 parts, polyether polyol 100 parts, triethanolamine 6 parts, DMSA 3 parts, and isocyanate 1.14 parts. The polyurethane flexible foam is placed in a sealed mesh filling device and filled with nitrogen at a pressure of 0.10 MPa–0.11 MPa. The filled polyurethane carrier is then dissolved in N,N-dimethylformamide solution to ensure a pore size of approximately 2 mm–4 mm on the carrier surface. Powdered chitosan is dissolved in a 10% acetic acid solution at 80 °C to prepare a chitosan solution with a chitosan mass fraction of 3%. A 2% (w / w) glutaraldehyde solution was added to the chitosan gel for cross-linking modification, resulting in an amino-rich cationic gel. The mass ratio of chitosan solution to glutaraldehyde solution was 250:1, and the mixture was stirred for 1-2 hours. Oxygen was introduced into the prepared gel to generate bubbles inside. Once uniform and fine bubbles formed inside the gel, the prepared large-pore carrier was immersed in the gel for 5 minutes. The carrier was then removed and dried in a 60°C oven for 1 hour. This process was repeated 2-3 times to ensure that the hydrogel was fully and uniformly coated on the carrier surface.

[0064] (2) Preparation of the control group

[0065] A foaming agent, stabilizer, polyol, triethanolamine, and dimethylolbutyric acid (DMSA) are added to a reactor in a certain proportion. Isocyanate is then added, and the mixture is stirred at 600–900 rpm for 2–4 hours under a vacuum of 0.10–0.12 MPa and a temperature of 25 ± 2 °C to obtain polyurethane flexible foam. The mixture contains 6 parts foaming agent, 3 parts stabilizer, 100 parts polyether polyol, 6 parts triethanolamine, 3 parts DMSA, and 1.14 parts isocyanate. The polyurethane flexible foam is placed in a sealed mesh filling device and filled with nitrogen gas at a pressure of 0.10 MPa–0.11 MPa. The filled polyurethane carrier is then dissolved in N,N-dimethylformamide solution to dissolve the polyurethane membrane in the pores, ensuring that the carrier surface forms pores of approximately 2 mm–4 mm.

[0066] Prepare three 250mL Erlenmeyer flasks, adding 10 samples of activated sludge of the same concentration and 10 samples of each of the three different carriers. The carrier without gel served as the control group, the carrier with gel only served as experimental group 1, and the carrier with amino-rich cationic gel served as experimental group 2. At 25±2℃, the flasks were stirred on a shaker at approximately 300rpm. Every 3 minutes, the carriers were removed from the flasks, drained of surface moisture, and weighed to detect the change in the mass of activated sludge adsorbed on the carriers over time.

[0067] As shown in the figure, the carrier with added amino-rich cationic gel exhibited the best adsorption effect on activated sludge. Furthermore, it was found that the adsorption effect of the carrier with added amino-rich gel was significantly improved compared to the carrier without any added substances. Specifically, the adsorption capacity of activated sludge on the surface of the carrier without any added substances reached 0.8 g / (g carrier), while the adsorption capacity of the carrier with added amino-rich gel reached 2.2 g / (g carrier), and the adsorption capacity of the carrier with added amino-rich cationic gel reached 2.35 g / (g carrier). This represents an increase of 1.55 g / (g carrier) compared to the large-pore carrier without added cationic gel.

[0068] Example 3: Preparation of a small-pore anaerobic ammonium oxidation support rich in amino and iron ions

[0069] 1. Grind iron oxide in a mortar until the particle size is approximately 100 μm, then pass it through a 150-mesh sieve. Dissolve powdered chitosan in a 10% acetic acid solution at 80°C to prepare a chitosan solution with a chitosan mass fraction of 3%. Add iron oxide powder to the gel, then add a 2% glutaraldehyde solution to the chitosan gel for cross-linking modification to obtain an amino-rich cationic gel. The mass ratio of chitosan solution to glutaraldehyde solution is 250:1. Stir magnetically for 1-2 hours. The mass fraction of iron oxide powder is 5%.

[0070] 2. Add the foaming agent, polyether polyol, and catalyst to the mold according to the mass ratio. The mass fractions of each component are: 6 parts foaming agent, 70 parts polyether polyol, and 1.5 parts catalyst. During stirring, gradually add aromatic diisocyanate, of which 7 parts are isocyanate. At this time, uniform and fine bubbles will gradually form inside the system. Place the polyurethane flexible foam in a sealed mesh filling device and fill it with nitrogen gas, while controlling the pressure at 0.05 MPa~0.08 MPa to control the foam size. Dissolve the polyurethane film in the pores of the filled polyurethane carrier with N,N-dimethylformamide solution to ensure that the carrier surface forms a pore size of about 0.3 mm~0.4 mm. The foaming agent is a mixture of triethylamine and dichloromethane in a mass ratio of 1:1. The polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, and polyether 220. The catalyst is dibutyltin dilaurate. The isocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate. To ensure uniform curing of the foam under low-temperature conditions, the temperature is controlled between 30℃ and 40℃.

[0071] 3. Inflate the prepared gel with hydrogen gas to generate bubbles inside the gel. Once uniform and fine bubbles have formed inside the gel, immerse the large-pore carrier in the gel for 5 minutes. Remove the carrier and place it in a 60°C drying oven for 1 hour. Repeat the above steps 2-3 times to ensure that the hydrogel is fully and uniformly coated on the carrier surface.

[0072] (1) Preparation of gel carrier without adding Fe ions

[0073] Powdered chitosan was dissolved in a 10% acetic acid solution at 80°C to prepare a chitosan solution with a chitosan mass fraction of 3%. A 2% glutaraldehyde solution was added to the chitosan gel for cross-linking modification, resulting in an amino-rich cationic gel. The mass ratio of chitosan solution to glutaraldehyde solution was 250:1, and the mixture was stirred for 1-2 hours. A foaming agent, polyether polyol, and catalyst were added to a mold according to their mass fractions: 6 parts foaming agent, 70 parts polyether polyol, and 1.5 parts catalyst. During stirring, aromatic diisocyanate (7 parts isocyanate) was gradually added. Uniform, fine bubbles gradually formed within the system. Nitrogen gas was introduced into a sealed mesh filling device for polyurethane flexible foam, with the pressure controlled at 0.05 MPa to 0.08 MPa to regulate foam size. The inflated polyurethane carrier was then dissolved in N,N-dimethylformamide solution to ensure a pore size of approximately 0.3 mm to 0.4 mm on the carrier surface. The foaming agent is a mixture of triethylamine and dichloromethane in a mass ratio of 1:1. The polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, and polyether 220. The catalyst is dibutyltin dilaurate. The isocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate. When the foam is uniformly cured at low temperatures, the temperature is controlled between 30℃ and 40℃. Oxygen is introduced into the prepared gel to generate bubbles inside. When uniform and fine bubbles form inside the gel, the prepared large-pore carrier is immersed in the gel for 5 minutes. The carrier is then removed and dried in a 60℃ drying oven for 1 hour. The above steps are repeated 2-3 times to ensure that the hydrogel is fully and uniformly coated on the carrier surface.

[0074] (2) Preparation of the control group

[0075] Add a foaming agent, polyether polyol, and catalyst to the mold according to mass. The mass fractions of each component are: 6 parts foaming agent, 70 parts polyether polyol, and 1.5 parts catalyst. During stirring, add aromatic diisocyanate, of which 7 parts are isocyanate. At this time, uniform and fine bubbles will gradually form inside the system. Place the polyurethane flexible foam in a sealed mesh filling device and fill it with nitrogen gas, while controlling the pressure at 0.05 MPa~0.08 MPa to control the foam size. Dissolve the polyurethane film in the pores of the filled polyurethane carrier with N,N-dimethylformamide solution to ensure that the carrier surface forms a pore size of about 0.3 mm~0.4 mm. The foaming agent is a mixture of triethylamine and dichloromethane in a mass ratio of 1:1. The polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, and polyether 220. The catalyst is dibutyltin dilaurate. The isocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate. To ensure uniform curing of the foam under low-temperature conditions, the temperature is controlled between 30℃ and 40℃.

[0076] Three 250mL Erlenmeyer flasks were prepared, each containing 10 samples of activated sludge of the same concentration and 10 samples of each of the three different carriers. The carrier without gel served as the control group, the carrier with gel only served as experimental group 1, and the carrier with amino-rich Fe ion gel served as experimental group 2. The flasks were stirred on a shaker at approximately 300rpm at 25±2℃. Every 3 minutes, the carrier was removed from the flask, drained of surface moisture, and weighed to detect the change in the mass of activated sludge adsorbed on the carrier over time. The results showed that the adsorption capacity of activated sludge on the surface of the carrier without gel was 1.03 g / (g carrier), while the adsorption capacity of the carrier with gel only reached 2.43 g / (g carrier), and the adsorption capacity of the carrier with hydroxyl-rich iron-containing gel reached 2.52 g / (g carrier). Compared to the carrier without gel, the adsorption efficiency was improved by 1.49 g / (g carrier).

[0077] Example 4: Combination of nitrification carrier and anaerobic ammonia-oxidizing bacteria carrier

[0078] The nitrosation carrier and the anaerobic ammonia oxidation carrier are combined using an adhesive method, with a large-pore carrier as the outer layer and a small-pore carrier as the inner layer. The adhesive is a polyurethane adhesive, prepared as follows: 1 part toluene diisocyanate is dissolved in 50 parts N,N-dimethylformamide (DMF) and prepolymerized for 5 minutes. Then, 1 part polyethylene glycol is added to the solution. Next, the mixture is thoroughly stirred at room temperature for 2 hours. One-third of the volume of acetone is added to the polyurethane adhesive for dilution. One side of the AOB adsorption carrier is evenly coated with the diluted polyurethane adhesive, then laid flat on a mesh frame and allowed to stand for 5 minutes to ensure the polyurethane adhesive no longer drips. After the polyurethane adhesive becomes slightly tacky, the AOB adsorption carrier is pressed tightly against the surface of the AnAOB adsorption carrier, ensuring the AnAOB carrier is completely coated. The entire carrier is then placed in a 60°C oven for drying. After drying, the carrier is removed and placed in ultrapure water, and cleaned with an ultrasonic device for 30 minutes to remove surface impurities and uncured adhesive.

[0079] (1) Preparation of gel carrier without the addition of cationic and Fe ions

[0080] One-third of the volume of acetone was added to the polyurethane adhesive for dilution. The diluted polyurethane adhesive was evenly applied to one side of the AOB adsorption carrier, which was then laid flat on a mesh frame and allowed to stand for 5 minutes to ensure the adhesive no longer dripped. Once the adhesive became slightly tacky, the AOB adsorption carrier was pressed firmly against the surface of the AnAOB adsorption carrier, ensuring the AnAOB carrier was completely encapsulated. The entire carrier was then placed in a 60°C oven for drying. After drying, the carrier was removed and placed in ultrapure water, where it was ultrasonically cleaned for 30 minutes to remove surface impurities and uncured adhesive.

[0081] (2) Preparation of the control group

[0082] One-third of the volume of acetone was added to the polyurethane adhesive for dilution. One side of the AOB adsorption carrier was evenly coated with the diluted polyurethane adhesive, then laid flat on a mesh frame and allowed to stand for 5 minutes to ensure the adhesive no longer dripped. Once the adhesive became slightly tacky, the large-pore carrier (without gel coating) was pressed tightly against the surface of the small-pore carrier (without gel coating), ensuring the small-pore carrier was completely encapsulated. The entire carrier was then placed in a 60°C oven for drying. After drying, the carrier was removed and placed in ultrapure water, then ultrasonically cleaned for 30 minutes to remove surface impurities and uncured adhesive.

[0083] Three 250mL Erlenmeyer flasks were prepared, each containing the same concentration of activated sludge and three different carriers. The carrier without gel served as the control group, the carrier with gel only as experimental group 1, and the carrier with amino-rich cationic and Fe ion gel as experimental group 2. At 25±2℃, the flasks were stirred on a shaker at approximately 300rpm. Every 3 minutes, the carriers were removed, drained, and weighed to measure the change in the mass of activated sludge adsorbed on the carriers over time. The results showed that the adsorption capacity of activated sludge on the surface of the carrier without gel was 1.46 g / (g carrier), the adsorption capacity of the carrier with gel only reached 3.05 g / (g carrier), and the adsorption capacity of the carrier with hydroxyl-rich iron-containing gel reached 3.36 g / (g carrier). This indicates that the adsorption capacity of activated sludge was significantly increased when two carriers were combined.

Claims

1. A method for preparing a biological carrier suitable for the growth of nitrifying bacteria and anaerobic ammonia-oxidizing bacteria, characterized in that... Includes the following steps: Step 1: Preparation of amino-rich cationic gel Magnesium oxide particles were ground and passed through a 150-mesh sieve; powdered chitosan was placed in a 10% acetic acid solution and fully dissolved at 80°C to prepare a chitosan solution; magnesium oxide powder was added to the chitosan solution and stirred evenly, and then a 2% glutaraldehyde solution was added for cross-linking modification to obtain an amino-rich cationic gel. Step 2: Preparation of large-pore support for gas exchange A foaming agent, stabilizer, polyether polyol, triethanolamine, and dimethylolbutyric acid are added to a reactor in a certain proportion. Isocyanate is slowly added to the reactor and the mixture is stirred at 600-900 rpm for 2-4 hours under a vacuum of 0.10-0.12 MPa and a temperature of 25±2℃ to obtain polyurethane flexible foam. The obtained polyurethane flexible foam is placed in a sealed meshing device, filled with nitrogen, and N,N-dimethylformamide solution is used to dissolve the polyurethane membrane in the pores to ensure that a pore size of 2 mm-4 mm is formed on the surface of the carrier. Step 3: Preparation of nitrosation support with positive surface potential and hydrophilic groups Introduce oxygen into the amino-rich cationic gel prepared in step 1 to generate bubbles inside the gel. When uniform and fine bubbles are formed inside the gel, immerse the large-pore carrier prepared in step 2 into the gel for 5 minutes. Remove the carrier and dry it. Repeat steps 2 to 3 times to ensure that the gel is fully and uniformly coated on the surface of the carrier. Step 4: Preparation of amino-rich iron-containing gel Iron oxide was ground and passed through a 150-mesh sieve; powdered chitosan was placed in a 10% acetic acid solution and fully dissolved at 80°C to prepare a chitosan solution; iron oxide powder was added to the chitosan solution, and then a 2% glutaraldehyde solution was added for cross-linking modification to obtain an amino-rich cationic gel. Step 5: Preparation of small-pore carriers for controlling dissolved oxygen permeation Aromatic diisocyanate is gradually added to the carrier mold along with foaming agent, polyether polyol and catalyst during stirring. At this time, uniform and fine bubbles will gradually form inside the system. The obtained polyurethane soft foam is placed in a sealed meshing device, filled with nitrogen, and N,N-dimethylformamide solution is used to dissolve the polyurethane membrane in the pores to ensure that a pore size of 0.3 mm to 0.4 mm is formed on the carrier surface. Step 6: Preparation of anaerobic ammonium oxidation support with iron ions and hydrophilic groups on its surface Hydrogen gas is introduced into the gel prepared in step 4 to generate bubbles inside the gel. When uniform and fine bubbles are formed inside the gel, the small-pore carrier prepared in step 5 is immersed in the gel for 5 minutes. After removing the carrier, it is dried. Repeat the above steps 2 to 3 times to ensure that the hydrogel is fully and uniformly coated on the surface of the carrier. Step 7: Combination of nitrification carrier and anaerobic ammonia-oxidizing bacteria carrier Using polyurethane adhesive as a binder, the nitrosation carrier prepared in step 3 and the anaerobic ammonia oxidation carrier prepared in step 6 are combined, with the nitrosation carrier prepared in step 3 serving as the top and bottom layers and the anaerobic ammonia oxidation carrier prepared in step 6 serving as the middle layer, forming a sandwich structure.

2. The preparation method according to claim 1, characterized in that: In step 1, the chitosan solution contains 2% to 4% by mass; the chitosan solution and glutaraldehyde solution have a mass ratio of 250:

1.

3. The preparation method according to claim 1, characterized in that: In step 1, the magnesium oxide content in the amino-rich cationic gel is 3%.

4. The preparation method according to claim 1, characterized in that: In step 2, the components are composed of the following parts by mass: 4-8 parts of foaming agent, 2-3 parts of stabilizer, 100 parts of polyether polyol, 6 parts of triethanolamine, 3 parts of dimethylolbutyric acid, and 1.14 parts of isocyanate.

5. The preparation method according to claim 1, characterized in that: In step 2, the nitrogen charging pressure is 0.10 MPa to 0.11 MPa.

6. The preparation method according to claim 1, characterized in that: In step 4, the chitosan solution contains 2% to 4% by mass; the mass ratio of the chitosan solution to the glutaraldehyde solution is 250:

1.

7. The preparation method according to claim 1, characterized in that: The mass fraction of iron oxide in the amino-rich cationic gel prepared in step 4 is 5%.

8. The preparation method according to claim 1, characterized in that: In step 5, the components are composed of the following parts by mass: 4-8 parts of foaming agent, 70-80 parts of polyether polyol, 0.5-1.5 parts of catalyst, and 7-8 parts of aromatic diisocyanate.

9. The preparation method according to claim 1, characterized in that: In step 5, after nitrogen is introduced, the pressure is controlled at 0.05 MPa to 0.08 MPa to control the foam size.

Images