A method for preparing a polyurethane biomimetic carrier modified by extracellular polymers

Abstract

The present invention discloses a preparation method for a polyurethane biomimetic carrier modified with extracellular polymers. After pre-treatment of activated sludge, a portion is prepared into EPS freeze-dried powder, and the other portion is dried and crushed into fine particles as a bioparticle foam stabilizer. The bioparticle foam stabilizer is dissolved in polyurethane foaming raw materials and mixed for foaming. After the rapid foaming period of the polyurethane, an activated sludge EPS powder dispersion is added. The small bubbles in the dispersion are utilized and the pressure is regulated to uniformly distribute the EPS on the surface of the polyurethane foam. The particle size of the bioparticle foam stabilizer is optimized to effectively reduce the phenomenon of bubble collapse and combined bubbles. The polyurethane foam is uniformly matured by microwave low-temperature curing, and the EPS on the carrier surface is stabilized by formaldehyde fumigation. The present invention utilizes the EPS of activated sludge to introduce a large number of microbial functional groups on the surface of the carrier material, constructing a carrier surface that is a microbial environment and promoting the enrichment and biofilm formation of microorganisms on the carrier.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and particularly relates to a method for preparing a polyurethane biomimetic carrier modified by using extracellular polymers. Background Art

[0002] Polyurethane foam is considered an ideal medium for microbial growth due to its high porosity, low relative density, high mechanical strength, corrosion resistance and aging resistance. It is often used as a carrier for microbial biofilm formation in sewage treatment processes. However, the adsorption and bioaffinity of polyurethane materials themselves are poor, which is not conducive to the adhesion of microorganisms. In order to further enhance the adsorption of polyurethane materials, some powdered substances with large specific surface area are usually added to cross-link the surface of the carrier or mixed foaming. For example, patent CN1105649A adds powdered activated carbon, diatomaceous earth or kaolin during the processing of water treatment foam materials to achieve weight gain adsorption; in addition, patent CN113444360A adds active biological enzyme preparations and iron or manganese oxides during the polyurethane foaming process, so that after adding the modified polyurethane foam carrier, the biomass in the MBBR reactor increases by 7kg / m 3 about.

[0003] Studies have shown that similar functional groups can reduce intermolecular forces, while identical functional groups attract each other. To improve the microbial affinity of carrier materials and promote rapid microbial enrichment, creating a microbial environment on the carrier surface is an effective approach. Many studies have opted for biological pre-coating, initially forming heterotrophic / autotrophic biofilms on the carrier surface, believing this method may be more effective than chemical / physical modification of the material surface or the material itself. However, this method is costly, complex, and time-consuming. Summary of the Invention

[0004] The present invention addresses the shortcomings of the aforementioned prior art by providing a method for preparing a polyurethane biomimetic carrier modified with extracellular polymers. This method enhances the biocompatibility of the polyurethane foam surface and skeleton, promoting the accumulation of microorganisms on the carrier. Furthermore, microwave curing improves the pore structure of the polyurethane foam, making the carrier more conducive to microbial accumulation and biofilm formation.

[0005] The present invention provides a method for preparing a polyurethane biomimetic carrier modified with an extracellular polymer, comprising the following steps:

[0006] Step 1: Pretreatment of activated sludge

[0007] The activated sludge from the aeration tank of the sewage treatment plant was repeatedly sieved with a 30-mesh screen until no insoluble particulate impurities were present. The activated sludge was allowed to stand for 30 to 60 minutes, and the supernatant was removed. The sludge was washed with PBS buffer to remove soluble impurities, and then concentrated to a moisture content of 85% to 95%.

[0008] Step 2: Preparation of activated sludge EPS freeze-dried powder

[0009] 2a. Place the activated sludge pretreated in step 1 in an ice bath and place it in a 200w-400w ultrasonic machine. Ultrasonicate for 5 seconds and then rest for 10 seconds for a treatment time of 20-60 minutes to dissociate the EPS attached to the cell wall.

[0010] 2b. Then, add 30% to 60% by mass of a fixative (the fixative is purchased directly from the market) to the activated sludge after ultrasonic treatment for 1 to 6 hours to fix the microbial cells and reduce the outflow of intracellular substances.

[0011] 2c. Add alkali solution to the sludge under stirring and treat for 50 to 100 minutes to extract EPS;

[0012] 2d, centrifuging the sludge at a speed of 10,000 r / min to 20,000 r / min for 15 to 40 minutes, taking the supernatant to obtain an activated sludge EPS gel liquid; freeze-drying the obtained activated sludge EPS gel liquid and grinding it into fine particles to obtain activated sludge EPS freeze-dried powder;

[0013] Step 3: Preparation of biogranule foam stabilizer

[0014] The activated sludge pretreated in step 1 is placed in a vacuum drying oven at 50°C to 75°C, stirred continuously to ensure uniform heating, and then dried to complete dryness. The sludge is then crushed and sieved using a grinder to control the powder particle size to be between 100μm and 150μm.

[0015] Step 4: Preparation of biomimetic carrier

[0016] 4a. Add activated sludge EPS freeze-dried powder to sodium bicarbonate solution (concentration of 5% to 10%) and stir evenly to form EPS dispersion;

[0017] 4b. Add the blowing agent and bioparticle foam stabilizer to the mixing tank and disperse them evenly. Then add the polyether polyol and catalyst. Add the aromatic diisocyanate under stirring. Even small bubbles will gradually form in the system. After the addition is complete, stir at a speed of 600-1000 rpm until the raw materials turn white and a large amount of even foam is produced.

[0018] 4c. Wait for 20s to 30s. When the growth rate of the polyurethane foam in 4b slows down significantly, slowly add citric acid to the EPS dispersion in 4a while stirring. Small bubbles appear in the dispersion. Slowly add citric acid to the polyurethane foam while stirring. Control the pressure at 0.15MPa to 0.7MPa to prevent gas in the dispersion from escaping.

[0019] 4d. After the system in 4c is evenly mixed, the pressure is slowly reduced to 0.05MPa-0.1MPa. The small bubbles in the dispersion drive the EPS to float on the outer surface of the foam. The mixed material is then transferred to a mold, and the mold is placed in a vacuum microwave oven to allow the foam to mature evenly under low temperature conditions.

[0020] 4e. Cut the solidified polyurethane foam into cubes with a side length of 1 cm, and then spread them flat on the grid. Place a mixed solution of potassium permanganate, formaldehyde and warm water at the bottom of the grid. Use the heat released by the reaction of formaldehyde and potassium permanganate to perform formaldehyde fumigation treatment under closed conditions for 2 hours to 12 hours to stabilize the EPS on the carrier surface.

[0021] In step 2c, the alkali solution is a 1 mol / L sodium hydroxide or potassium hydroxide solution, which is added until the pH of the system is 8-10.

[0022] In step 2d, the particle size of the activated sludge EPS freeze-dried powder is ≤500 μm.

[0023] In step 4:

[0024] The foaming agent is triethylamine and dichloromethane, with a mass ratio of 1:1.

[0025] The polyether polyol is selected from one or more of polyether 330, polyether 330N, polyether 320, polyether 230, polyether 220, and the like.

[0026] The catalyst is dibutyltin dilaurate.

[0027] The aromatic diisocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate.

[0028] The mass ratio of sodium bicarbonate to citric acid added to the EPS dispersion was 1:1.

[0029] When the foam is uniformly matured under low temperature conditions, the temperature is controlled between 30℃ and 40℃.

[0030] The mass ratio of formaldehyde, potassium permanganate and warm water in the mixed solution of potassium permanganate, formaldehyde and warm water is 2:1:1, and the temperature of the warm water is between 35°C and 50°C.

[0031] In step 4, the raw materials are composed of the following components by mass:

[0032] 0.5-2 parts of sodium bicarbonate solution, 1-5 parts of activated sludge EPS freeze-dried powder, 4-8 parts of foaming agent, 2-3 parts of biological granule foam stabilizer, 70-80 parts of polyether polyol, 0.5-1.5 parts of catalyst, and 7-8 parts of aromatic diisocyanate.

[0033] Microorganisms secrete extracellular polymeric substances (EPS) when exposed to the environment. EPS coats the microorganism's surface, providing adhesion, protection, and protection from environmental shocks. It also provides energy and a carbon source for the microorganisms during periods of starvation. Therefore, EPS is essential for the stable adhesion of microorganisms to carriers.

[0034] Activated sludge is a plentiful source, rich in microbial communities and their secretions. However, activated sludge easily disperses in water and cannot be directly fixed to the surface of polyurethane foam. Therefore, the present invention utilizes activated sludge EPS powder for mixing and foaming, and through technical means, floats the EPS on the surface of the polyurethane foam, thereby introducing functional groups of the microbial community onto the surface of the polyurethane material. By utilizing the carrier surface, which simulates the microbial environment created by the activated sludge EPS, the enrichment of microorganisms on the carrier can be promoted. Curing polyurethane foam in a conventional drying oven causes the foam surface to cure faster than the interior, but microwave curing can achieve uniform curing at all points in the foam. Microwave curing also generates steam from the polyurethane interior, resulting in better pore conditions for the polyurethane foam. A foam stabilizer is essential to prevent foam collapse and merging. Activated sludge powder can be used as a granular foam stabilizer in the polyurethane foaming process and enhances the biocompatibility of the polyurethane foam skeleton. Therefore, the following modification method is developed: After pre-treating the activated sludge, a portion is converted into EPS freeze-dried powder, and the remaining portion is dried and crushed into fine particles to serve as a biogranular foam stabilizer. A bioparticle foam stabilizer is dissolved in the polyurethane foaming raw material and mixed to form foam. After the rapid foaming period of the polyurethane, an activated sludge EPS powder dispersion is added. The small bubbles in the dispersion are utilized and the pressure is controlled to uniformly distribute the EPS on the surface of the polyurethane foam. The particle size of the bioparticle foam stabilizer is optimized to effectively reduce the phenomenon of bubble collapse and bubble merging. The polyurethane foam is uniformly matured through microwave low-temperature curing, and the EPS on the carrier surface is stabilized through formaldehyde fumigation. This method strengthens the biocompatibility of the polyurethane foam surface and skeleton, promotes the enrichment of microorganisms on the carrier, and uses microwave curing to improve the pore structure of the polyurethane foam, making the carrier of the present invention more conducive to the enrichment and biofilm formation of microorganisms.

[0035] The bionic carrier prepared by the present invention can be used in various reactors such as UASB and CSTR, and can achieve rapid enrichment of microorganisms. Its dense small pore structure is particularly effective in improving the biofilm formation of autotrophic bacteria such as anaerobic ammonia oxidizing bacteria.

[0036] The present invention has the following advantages and positive effects:

[0037] 1. The present invention utilizes EPS extracted from activated sludge to construct a carrier surface rich in microbial community functional groups, simulates the microbial growth environment, significantly improves the bioaffinity of the traditional polyurethane carrier surface, and increases the enrichment rate of microorganisms on the polyurethane foam carrier surface.

[0038] 2. The present invention has high efficiency in preparing activated sludge EPS freeze-dried powder, better activity retention, and can be stored in batches.

[0039] 3. When preparing the carrier, the present invention controls the pressure so that the small bubbles in the dispersion drive the EPS to be evenly distributed on the surface of the polyurethane foam, thereby efficiently utilizing the EPS.

[0040] 4. The present invention utilizes formaldehyde fumigation to fix and stabilize the EPS floating on the surface of the polyurethane foam.

[0041] 5. The bio-granule foam stabilizer prepared by the present invention will not sink to the bottom due to gravity nor float up due to foaming when the foam is left to mature, but will be evenly dispersed in the carrier, effectively reducing the phenomenon of foam collapse and merging.

[0042] 6. The biological particle foam stabilizer used in the foaming process of the present invention simultaneously improves the pore conditions of the carrier and improves the biological affinity of the carrier.

[0043] 7. The present invention utilizes a microwave heating method to make the degree of maturation of each point inside the polyurethane foam relatively uniform, while generating a large amount of steam to drill out, thereby achieving a good cell-opening effect.

[0044] 8. The modified polyurethane carrier prepared by the present invention has fine and dense pores, and has a significant effect on improving the enrichment and biofilm formation of autotrophic bacteria such as anaerobic ammonia-oxidizing bacteria.

[0045] 9. In the present invention, the mixing and stirring speed of the raw materials during the carrier foaming stage does not need to be too high. The fastest stirring speed during the foaming stage is only 600 r / min to 1000 r / min, lasting for 20 to 30 seconds, and the aging temperature is low, and the energy consumption is low.

[0046] 10. The bionic 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 (a) is a flow chart of the preparation method of the activated sludge EPS freeze-dried powder and the biological granule foam stabilizer of the present invention; (b) is a general flow chart of the preparation method of the bionic carrier of the present invention.

[0048] Figure 2(a) is a physical picture and surface detail picture of the modified polyurethane bionic carrier prepared by the present invention; (b) is a physical picture and surface detail picture of the control polyurethane carrier No. 1 prepared by a conventional foaming method on the basis of the method of the present invention without adding activated sludge EPS dispersion and biological foam stabilizer; (c) is a physical picture and surface detail picture of the control polyurethane carrier No. 2 prepared by the method of the present invention without adding activated sludge EPS dispersion; (d) is a physical picture and surface detail picture of the control polyurethane carrier No. 3 prepared by the method of the present invention without adding biological particle foam stabilizer.

[0049] Figure 3 This is a photo of a modified polyurethane biomimetic carrier prepared using bioparticles with different particle sizes as foam stabilizers. Figure 3 The particle sizes of the bio-granular foam stabilizers in (a), (b) and (c) are 150 μm to 300 μm, 100 μm to 150 μm and 75 μm to 100 μm, respectively.

[0050] Figure 4 The adsorption performance curves of activated sludge for the modified polyurethane biomimetic carrier prepared by the present invention, control polyurethane carrier No. 1 prepared by a conventional foaming method based on the method of the present invention without adding activated sludge EPS dispersion and biological foam stabilizer, control polyurethane carrier No. 2 prepared by the method of the present invention without adding activated sludge EPS dispersion, and control polyurethane carrier No. 3 prepared by the method of the present invention without adding biological granule foam stabilizer.

[0051] Figure 5 (a) is the SEM electron microscope image of the carrier prepared by the present invention on the 3rd day after adsorbing activated sludge; (b) is the SEM electron microscope image of the No. 1 control polyurethane carrier prepared on the basis of the method of the present invention without adding activated sludge EPS dispersion and biological foam stabilizer, on the 3rd day after adsorbing activated sludge; (c) is the SEM electron microscope image of the No. 2 control polyurethane carrier prepared on the basis of the method of the present invention without adding activated sludge EPS dispersion, on the 3rd day after adsorbing activated sludge; (d) is the SEM electron microscope image of the No. 3 control polyurethane carrier prepared on the basis of the method of the present invention without adding biological granule foam stabilizer, on the 3rd day after adsorbing activated sludge.

[0052] Figure 6 Changes over time in the amount of microorganisms adsorbed in an anaerobic ammonia oxidation reactor by the modified polyurethane biomimetic carrier prepared in the present invention, control polyurethane carrier No. 1 prepared by a conventional foaming method based on the method of the present invention without adding activated sludge EPS dispersion and biological foam stabilizer, control polyurethane carrier No. 2 prepared based on the method of the present invention without adding activated sludge EPS dispersion, and control polyurethane carrier No. 3 prepared based on the method of the present invention without adding biological granule foam stabilizer. DETAILED DESCRIPTION

[0053] like Figure 1 As shown, the present invention utilizes the method for preparing a biomimetic carrier of extracellular polymer-modified polyurethane, which is specifically as follows:

[0054] 1. Activated sludge pretreatment: Take the activated sludge from the aeration tank of the sewage treatment plant and sieve it repeatedly with a 30-mesh screen until there are no insoluble particulate impurities. Let it stand for 30 to 60 minutes, remove the supernatant, and then wash the sludge two to three times with PBS buffer. Finally, concentrate the sludge to a moisture content of between 85% and 95%.

[0055] 2. Prepare activated sludge EPS freeze-dried powder. Place the pretreated sludge in an ice bath and place it in a 200W-400W ultrasonic machine to dissociate EPS attached to microbial cell walls. Ultrasonicate for 5 seconds with a 10-second pause, and continue sonicating for 20-60 minutes. Add a 30%-60% fixative solution by mass to the ultrasonically treated activated sludge for 1-6 hours. Then, slowly add a 1 mol / L sodium hydroxide or potassium hydroxide solution while stirring the sludge. Control the extraction pH to 8-10 for 50-100 minutes. The resulting sludge is then centrifuged at 10,000-20,000 rpm for 15-40 minutes. The supernatant is freeze-dried and ground to a particle size of less than 500 μm to obtain activated sludge EPS freeze-dried powder.

[0056] 3. Prepare the bio-granular foam stabilizer. Place the pretreated activated sludge in a vacuum drying oven at 50℃-75℃ and dry it while stirring. Use a grinder to crush the sludge while extracting the powder that passes through a 100-mesh sieve. Remove the powder that passes through a 150-mesh sieve and control the powder particle size to be between 100μm and 150μm.

[0057] 4. Prepare the biomimetic carrier. First, prepare 0.5-2 parts of a 5%-10% sodium bicarbonate solution. Add 1-5 parts of freeze-dried activated sludge EPS powder and gently stir to form an EPS dispersion. Then, place 4-8 parts of a foaming agent and 2-3 parts of a bioparticle foam stabilizer in a mixing tank. Stir thoroughly under ultrasonic conditions. After stopping the ultrasound, add 70-80 parts of a polyether polyol and 0.5-1.5 parts of dibutyltin dilaurate and stir again. Next, slowly add 7-8 parts by weight of toluene diisocyanate while stirring. After stirring, stir at a speed of 600-1000 rpm until the material turns white and a uniform foam forms. After 20-30 seconds, the foam growth rate slows significantly. At this point, slowly add citric acid to the EPS dispersion while stirring. Maintain a pressure of 0.15-0.7 MPa and slowly stir the dispersion into the polyurethane foam. After stirring evenly, reduce the pressure to 0.05MPa-0.1MPa, pour into a mold, and place in a vacuum microwave oven at 20℃-40℃ for curing. After curing, cut the polyurethane foam into cubes with a side length of 1cm and lay them flat on a grid. Fill a container with warm water under the grid, add potassium permanganate to the container, stir evenly, and then add formaldehyde for fumigation.

[0058] Example 1: Preparation of polyurethane biomimetic carrier modified with extracellular polymer and its control group

[0059] 1. Activated sludge pretreatment steps

[0060] Activated sludge was collected from the aeration tank of the Zhuzhuanjing Wastewater Treatment Plant in Hefei City and placed in a sludge bucket. The bucket was gently agitated and allowed to settle for 5 seconds to allow heavier minerals and other materials in the sludge to settle. The upper portion of the sludge was then poured out. The sludge was then repeatedly sieved through a 30-mesh sieve to remove impurities such as particles and straw. The sludge was allowed to stand for 40 minutes, and the supernatant was removed. The sludge was then washed three times with PBS buffer to prevent the high concentration of soluble chemicals such as ammonia nitrogen in the wastewater from affecting the experimental results. The sludge was finally concentrated to a moisture content of 92%.

[0061] 2. Preparation steps of activated sludge EPS freeze-dried powder

[0062] The pretreated activated sludge was placed in a 400W ultrasonic machine filled with an ice-water mixture to disrupt the microbial cell walls. Ultrasonication was repeated for 5 seconds, with a 10-second pause, and the process ended after 40 minutes. A 30% to 60% mass fraction of a fixative was then added to the activated sludge for 4 hours. A 1 mol / L sodium hydroxide solution was then slowly added while stirring the sludge, maintaining the extraction pH at 9 for 90 minutes. The resulting sludge was then centrifuged at 18,000 rpm for 20 minutes. The supernatant was freeze-dried and ground to fine particles less than 500 μm to produce activated sludge EPS freeze-dried powder.

[0063] 3. Preparation steps of biogranule foam stabilizer

[0064] The pre-treated activated sludge is placed in a 60°C vacuum drying oven for drying, while being slowly stirred by an agitator to evenly dry the water. After drying, it is repeatedly crushed using a crusher, while the powder passing through a 100-mesh sieve is extracted and the powder passing through a 150-mesh sieve is removed, controlling the powder particle size to between 100μm and 150μm.

[0065] 4. Preparation steps of modified polyurethane biomimetic carrier

[0066] Prepare an 8% sodium bicarbonate solution, take 0.3mL and add 0.6g of activated sludge EPS freeze-dried powder, gently stir to form an EPS dispersion. Place the mixing tank in an ultrasonic machine, add 1mL of triethylamine, 1mL of dichloromethane and 0.6g of bio-granule foam stabilizer to the mixing tank and stir to mix evenly. Stop the ultrasonication, add 20mL of polyether 330 and 0.35mL of dibutyltin dilaurate, stir again and slowly add 2mL of toluene diisocyanate while stirring. After the addition is complete, stir at 900r / min until it turns white and produces uniform foam. The foam growth rate slows down after about 20s. Slowly add 0.024g of citric acid to the EPS dispersion while stirring. Then control the pressure at 0.15MPa~0.7MPa, slowly add the activated sludge EPS dispersion into the polyurethane foam while stirring, and reduce the pressure to 0.05MPa~0.1MPa after stirring evenly. Pour the foam into the mold after 10 minutes and put it into a vacuum microwave oven at 30℃ for maturation. Cut the solidified polyurethane foam into cubes with a side length of 1cm and lay them flat on the grid. Fill 5mL of warm water in a crucible under the grid, add 5g of potassium permanganate and 10mL of formaldehyde to the warm water and fumigate for 8 hours. Figure 2 As shown in a.

[0067] 5. Preparation steps of control polyurethane carrier No. 1 (without adding activated sludge EPS dispersion and biogranule foam stabilizer)

[0068] Add 1mL triethylamine and 1mL dichloromethane to the mixing tank and stir to mix evenly, then add 20mL polyether 330 and 0.35mL dibutyltin dilaurate, stir evenly again, and slowly add 2mL toluene diisocyanate while stirring. After the addition is complete, stir at a speed of 900r / min until it turns white and produces uniform foam. The foam growth rate slows down after about 20s. At this time, pour the foam into the mold and put it into a vacuum microwave oven at 30℃ for maturation. Finally, cut the cured polyurethane foam into cubes with a side length of 1cm. Figure 2 As shown in b.

[0069] 6. Preparation steps of control polyurethane carrier No. 2 (without adding activated sludge EPS dispersion)

[0070] Place the mixing tank in an ultrasonic machine, add 1mL triethylamine, 1mL dichloromethane and 0.6g bio-particle foam stabilizer to the mixing tank and stir to mix evenly. Stop the ultrasound, add 20mL polyether 330 and 0.35mL dibutyltin dilaurate, stir evenly again, and slowly add 2mL toluene diisocyanate while stirring. After the addition is complete, stir at a speed of 900r / min until it turns white and produces uniform foam. After about 20s, the foam growth rate slows down. At this time, pour the foam into a mold and put it into a 30℃ vacuum microwave oven for maturation. Finally, cut the cured polyurethane foam into cubic blocks with a side length of 1cm. Figure 2 As shown in c.

[0071] 7. Preparation steps of control polyurethane carrier No. 3 (without adding bioparticle foam stabilizer)

[0072] Prepare an 8% sodium bicarbonate solution, take 0.3 mL, add 0.6 g of freeze-dried activated sludge EPS powder, and gently stir to form an EPS dispersion. Add 1 mL of triethylamine and 1 mL of dichloromethane to a mixing tank and stir to mix thoroughly. Then add 20 mL of Polyether 330 and 0.35 mL of dibutyltin dilaurate. Stir again to mix thoroughly. Slowly add 2 mL of toluene diisocyanate while stirring. After addition, stir at 900 rpm until a white, uniform foam forms. After about 20 seconds, the foam growth rate slows. Slowly add 0.024 g of citric acid to the EPS dispersion while stirring. Then, control the pressure between 0.15 MPa and 0.7 MPa and slowly add the activated sludge EPS dispersion to the polyurethane foam while stirring. After stirring thoroughly, reduce the pressure to 0.05 MPa to 0.1 MPa. After 10 minutes, pour the foam into a mold and cure in a vacuum microwave at 30°C. Cut the solidified polyurethane foam into cubes with a side length of 1 cm and lay them flat on the grid. Fill a crucible with 5 mL of warm water under the grid. Add 5 g of potassium permanganate and 10 mL of formaldehyde to the warm water and fumigate for 8 hours. Figure 2 As shown in d.

[0073] Example 2: Study on the Optimal Particle Size of Bioparticle Foam Stabilizers in the Preparation of Extracellular Polymer-Modified Polyurethane Biomimetic Carriers

[0074] The activated sludge EPS freeze-dried powder prepared in steps 1 and 2 of Example 1 was used to prepare a series of polyurethane biomimetic carriers modified with extracellular polymers. The main steps are as follows:

[0075] First, prepare the biogranular foam stabilizer. Place the pretreated activated sludge in a 60°C vacuum drying oven for drying, while slowly stirring with an agitator to evenly dry the water. Once completely dried, repeatedly crush the sludge using a crusher. While crushing, extract the powder that passes through a 50-mesh sieve and remove the powder that passes through a 100-mesh sieve, resulting in a biogranular foam stabilizer with a particle size of 150μm to 300μm. Continue crushing and extracting the powder that passes through a 100-mesh sieve, removing the powder that passes through a 150-mesh sieve, resulting in a biogranular foam stabilizer with a particle size of 100μm to 150μm. Continue crushing and extracting the powder that passes through a 150-mesh sieve, removing the powder that passes through a 200-mesh sieve, resulting in a biogranular foam stabilizer with a particle size of 75μm to 100μm.

[0076] Then, prepare three mixing tanks and add 0.3 mL of 8% sodium bicarbonate solution and 0.6 g of activated sludge EPS freeze-dried powder to each tank. Gently stir to form an EPS dispersion. Place the mixing tanks in an ultrasonic machine and add 1 mL of triethylamine, 1 mL of dichloromethane, and 0.6 g of a bio-granule foam stabilizer. The bio-granule foam stabilizers added to the three mixing tanks should have the three particle sizes mentioned above. Stop ultrasonication and add 20 mL of polyether 330 and 0.35 mL of dibutyltin dilaurate. Stir again to mix thoroughly. Slowly add 2 mL of toluene diisocyanate while stirring. After addition, stir at 900 rpm until the mixture turns white and a uniform foam forms. After about 20 seconds, the foam growth rate slows. Slowly add 0.024 g of citric acid to the EPS dispersion while stirring. Then control the pressure at 0.15MPa~0.7MPa, slowly add the activated sludge EPS dispersion into the polyurethane foam while stirring, and after stirring evenly, reduce the pressure to 0.05MPa~0.1MPa. After 10 minutes, pour the foam into the mold and put it into a 30℃ vacuum microwave oven for maturation.

[0077] like Figure 3 As shown in a, when the particle size of the bio-granule foam stabilizer is between 150 μm and 300 μm, the bio-granule foam stabilizer will sink to the bottom during the maturation process after the stirring is stopped; Figure 3 As shown in b, when the particle size is between 100 μm and 150 μm, the bioparticle foam stabilizer is evenly distributed in the carrier, and a relatively uniform pore is obtained; Figure 3 As shown in Figure c, when the particle size is between 75 μm and 100 μm, the biogranule foam stabilizer will float during the maturation process after stirring is stopped. Therefore, the optimal particle size range of the biogranule foam stabilizer is between 100 μm and 150 μm.

[0078] Example 3: Study on the adsorption performance of activated sludge using extracellular polymer-modified polyurethane biomimetic carriers

[0079] The adsorption performance of extracellular polymer modified polyurethane biomimetic carriers on sludge is expressed by the change in the mass of sludge adsorbed by 20 carriers after being immersed in sludge over time. Prepare four 250mL conical flasks, add the same bucket of stirred activated sludge solution and 20 carriers from each of the four groups. One of the four groups of carriers is the experimental group, which is the modified polyurethane biomimetic carrier prepared in Example 1, as shown in Figure 2. Figure 2 The other three groups are control groups, which are control polyurethane carrier No. 1, control polyurethane carrier No. 2 and control polyurethane carrier No. 3 prepared in Example 1, as shown in FIG. Figure 2 As shown in Figures 2b, 2c, and 2d. At 25 ± 2°C, the beaker was stirred at approximately 200 rpm using a magnetic stirrer. The carrier was removed from the beaker after 5, 10, 15, 20, 25, and 30 minutes, drained of surface moisture, and weighed to measure the change in the mass of activated sludge adsorbed on the carrier over time. The experiment was repeated three times.

[0080] like Figure 4 As shown in Figure 2, the adsorption rate of the experimental group carrier was the fastest, and the adsorption amount achieved within 30 minutes was also the largest, indicating that the carrier prepared by the method for preparing extracellular polymer-modified polyurethane biomimetic carriers of the present invention has improved the adsorption performance of activated sludge. The SEM electron microscope images of the experimental group carrier and the No. 1, No. 2 and No. 3 control group carriers after 30 minutes of sludge adsorption are shown in Figure 2. Figure 5 a. Figure 5 b. Figure 5 c and Figure 5 As shown in Figure d, it can be seen intuitively that the pore opening effect of the experimental group carrier is better than that of the three control group carriers, the pores are larger and more uniform, and the sludge adsorption capacity is also significantly greater.

[0081] Example 4: Anaerobic ammonia oxidation biofilm formation using extracellular polymer-modified polyurethane biomimetic carriers

[0082] The anaerobic ammonium oxidation reactor has an effective working volume of 40 L. The sludge SS in the reactor is 20.2 g / L, VSS is 8.7 g / L, and the pH is 7.3. The influent ammonia nitrogen is 300 mgN / L, and nitrite nitrogen is 396 mgN / L. The HRT is controlled at 24 h, and the temperature is maintained at 28-33°C.

[0083] The same four groups of carriers used in Example 3 were added to the reactor for comparative study. The experimental group carriers were placed in polyethylene ball No. 1; the other three control groups were placed in polyethylene balls No. 2, No. 3 and No. 4, respectively. The polyethylene balls were exactly the same except for the labeling. The reactor was controlled to operate normally, and the mass change of the carriers adsorbing anaerobic ammonia oxidation sludge was recorded for 35 days. At the same time, 20 carriers were taken out of each group, and the sludge discharged from the anaerobic ammonia oxidation reactor was placed in them, and pressed to fully adsorb the sludge, and the amount of sludge that can be adsorbed by the carrier per unit mass was calculated. The adsorption amount of anaerobic ammonia oxidation sludge was used as a comparison to reflect the film formation situation of the carrier in the reactor. The experiment showed that the mass of anaerobic ammonia oxidation sludge absorbed by the experimental group, control No. 1, control No. 2 and control No. 3 were 3.42g, 1.82g, 3.28g and 2.93g per gram of carrier, respectively. It can be seen that the amount of sludge that can be absorbed by the carrier per unit mass of the experimental group is more than that of the control group, indicating that the carrier in the experimental group is more conducive to the adsorption of anaerobic ammonia oxidation sludge; such as Figure 6 As shown, in the anaerobic ammonium oxidation reactor, the carrier in polyethylene ball No. 1 reached the maximum adsorption capacity the earliest, which was about 7 days, while the carriers in polyethylene balls No. 2, No. 3 and No. 4 needed about 18 days, 12 days and 15 days respectively, indicating that the carriers in the experimental group adsorbed anaerobic ammonium oxidation sludge faster than those in the control group; after reaching the maximum adsorption capacity, the carrier in polyethylene ball No. 1 increased its mass significantly more than the carriers in polyethylene balls No. 2, 3 and No. 4, indicating that the carriers in the experimental group had more biofilm.

Claims

1. A method for preparing a polyurethane biomimetic carrier modified with extracellular polymers, characterized in that The steps include: Step 1: Pretreatment of activated sludge The activated sludge from the aeration tank of the sewage treatment plant was repeatedly sieved until no insoluble particulate impurities were present. The activated sludge was allowed to stand for 30 to 60 minutes and the supernatant was removed. The sludge was washed with PBS buffer to remove soluble impurities and then concentrated to a moisture content of 85% to 95%. Step 2: Preparation of activated sludge EPS freeze-dried powder 2a. Place the activated sludge pretreated in step 1 in an ice bath and place it in a 200w-400w ultrasonic machine. Ultrasonicate for 5 seconds and then rest for 10 seconds for a treatment time of 20-60 minutes to dissociate the EPS attached to the cell wall. 2b. Then, a fixative solution is added to the activated sludge after ultrasonic treatment for 1 to 6 hours to fix the microbial cells and reduce the outflow of intracellular substances; 2c. Add alkali solution to the sludge under stirring and treat for 50 to 100 minutes to extract EPS; 2d, centrifuging the sludge at a speed of 10000 r / min to 20000 r / min for 15 min to 40 min, and taking the supernatant to obtain the activated sludge EPS gel liquid; The activated sludge EPS gel solution is freeze-dried and ground into fine particles to obtain activated sludge EPS freeze-dried powder; Step 3: Preparation of biogranule foam stabilizer The activated sludge pretreated in step 1 is placed in a vacuum drying oven at 50°C to 75°C, stirred continuously to ensure uniform heating, and then dried to complete dryness. The sludge is then crushed using a grinder and sieved. Step 4: Preparation of biomimetic carrier 4a. Add activated sludge EPS freeze-dried powder to the sodium bicarbonate solution and stir evenly to form EPS dispersion; 4b. Add the blowing agent and bioparticle foam stabilizer to the mixing tank and disperse them evenly. Then add the polyether polyol and catalyst. Add the aromatic diisocyanate under stirring. Even small bubbles will gradually form in the system. After the addition is complete, stir at a speed of 600-1000 rpm until the raw materials turn white and a large amount of even foam is produced. 4c. Wait for 20s to 30s. When the growth rate of the polyurethane foam in 4b slows down significantly, slowly add citric acid to the EPS dispersion in 4a while stirring. Small bubbles appear in the dispersion. Slowly add citric acid to the polyurethane foam while stirring. Control the pressure at 0.15MPa to 0.7MPa to prevent gas in the dispersion from escaping. 4d. After the system in 4c is evenly mixed, the pressure is slowly reduced to 0.05MPa-0.1MPa. The small bubbles in the dispersion drive the EPS to float on the outer surface of the foam. The mixed material is then transferred to a mold, and the mold is placed in a vacuum microwave oven to allow the foam to mature evenly under low temperature conditions. 4e. Cut the solidified polyurethane foam into cubes with a side length of 1 cm, and then spread them flat on the grid. Place a mixed solution of potassium permanganate, formaldehyde and warm water at the bottom of the grid. Use the heat released by the reaction of formaldehyde and potassium permanganate to perform formaldehyde fumigation treatment under closed conditions for 2 hours to 12 hours to stabilize the EPS on the carrier surface.

2. The preparation method according to claim 1, wherein: In step 2c, the alkali solution is a 1 mol / L sodium hydroxide or potassium hydroxide solution, which is added until the pH of the system is 8-10.

3. The preparation method according to claim 1, wherein: In step 2d, the particle size of the activated sludge EPS freeze-dried powder is ≤500 μm.

4. The preparation method according to claim 1, wherein: In step 3, the powder particle size of the biological particle foam stabilizer is between 100 μm and 150 μm.

5. The preparation method according to claim 1, wherein: In step 4: the foaming agent is 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; and the aromatic diisocyanate is selected from one or more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and naphthalene-1,5-diisocyanate.

6. The preparation method according to claim 5, characterized in that: In step 4, the raw materials are composed of the following components by mass: 0.5-2 parts of sodium bicarbonate solution, 1-5 parts of activated sludge EPS freeze-dried powder, 4-8 parts of foaming agent, 2-3 parts of biological granule foam stabilizer, 70-80 parts of polyether polyol, 0.5-1.5 parts of catalyst, and 7-8 parts of aromatic diisocyanate.

7. The preparation method according to claim 6, characterized in that: The mass ratio of sodium bicarbonate to citric acid added to the EPS dispersion was 1:

1.

8. The preparation method according to claim 1, wherein: When the foam is uniformly matured under low temperature conditions, the temperature is controlled between 30℃ and 40℃.

9. The preparation method according to claim 1, wherein: The mass ratio of formaldehyde, potassium permanganate and warm water in the mixed solution of potassium permanganate, formaldehyde and warm water is 2:1:

1.

10. The preparation method according to claim 9, characterized in that: The temperature of warm water is 35℃~50℃.

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