Modified biological filler, its preparation method and application in the field of denitrification removal of nitrate

Abstract

The application discloses modified biological filler and a preparation method and application thereof in the field of denitrification removal of nitrate, and relates to the technical field of denitrification. The preparation method comprises the following steps: immersing polyurethane foam in an amination modification solution containing N-(2-aminoethyl)-3-aminopropyl trimethoxysilane to obtain amin-modified polyurethane foam; and then immersing the amin-modified polyurethane foam in a bacterial solution containing denitrification bacteria to obtain a biological-loaded polyurethane foam. The polyurethane foam with developed pores is used as a carrier, and the surface of the polyurethane foam is modified by N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, so that the adsorption amount and the binding strength of the denitrification bacteria can be improved. The modified biological filler loaded with the denitrification bacteria can shorten the acclimation period in the denitrification equipment, improve the denitrification rate in the initial stage, and improve the removal efficiency of the nitrate in wastewater.

Description

Technical Field

[0001] This invention relates to the field of denitrification technology, and in particular to a modified biological packing material, its preparation method, and its application in the field of denitrification for nitrate removal. Background Technology

[0002] Denitrification filters, as a biochemical treatment technology for removing nitrates from water, rely on the metabolic activities of denitrifying bacteria in the biofilm attached to the filter media. In a biochemical reaction system where carbon source acts as an electron donor and nitrate acts as an electron acceptor, denitrifying bacteria can gradually reduce nitrates to nitrogen gas through dissimilatory denitrification, ultimately achieving the harmless removal of nitrogen.

[0003] Currently, in conventional denitrification filter processes, traditional materials such as quartz sand and bio-ceramic granules are often used as carriers. The biofilm formation process of microorganisms on the surface of these materials is slow, which can lead to a long system acclimatization period and limit the efficiency of denitrification reaction in the initial stage of start-up. Summary of the Invention

[0004] This invention provides a modified biological packing material, its preparation method, and its application in the field of denitrification for nitrate removal. By amylating hydrophobic and porous polyurethane foam, a large number of hydrophilic amino groups can be introduced on the surface, which can improve the adsorption of denitrifying bacteria and form a biofilm on the surface. This can shorten the acclimatization period and improve the nitrate removal efficiency in the initial stage of start-up.

[0005] To address the aforementioned technical problems, one objective of this invention is to provide a method for preparing modified biological fillers, comprising the following steps: (1) The polyurethane foam is immersed in an aminated modification solution, wherein the aminated modification solution includes N-(2-aminoethyl)-3-aminopropyltrimethoxysilane with a mass fraction of 0.3%-0.8%, and after static reaction, it is sterilized to obtain aminated polyurethane foam. (2) The amino-modified polyurethane foam was soaked in a bacterial solution containing denitrifying bacteria, shaken, and then allowed to stand. After washing and drying, the bioloaded polyurethane foam was prepared.

[0006] The polyurethane foam used in this application has a well-developed pore network, and its high specific surface area can increase the loading of denitrifying bacteria in the packing material per unit volume. By using a low concentration of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to modify the surface of the polyurethane foam, a large number of amino functional groups can be introduced to improve hydrophilicity and adsorption to bacteria. The amino groups form ionic bonds or hydrogen bonds with carboxyl and hydroxyl groups on the bacterial surface, thereby increasing the adsorption capacity and binding strength of denitrifying bacteria. While ensuring the adsorption effect, the concentration of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is controlled to reduce the concentration, thereby improving the activity and survival rate of the loaded denitrifying bacteria. This modified biological packing material loaded with denitrifying bacteria can shorten the acclimatization period in denitrification equipment and improve the nitrate removal rate in the initial stage of start-up.

[0007] As a preferred embodiment, the bioloaded polyurethane foam prepared in step (2) is immersed in a first salt-containing denitrification medium and anaerobically cultured for 10-15 h, and then immersed in a second salt-containing denitrification medium and anaerobically cultured for 10-15 h, and dried at room temperature to obtain activated polyurethane foam; the activated polyurethane foam and saturated ammonium bicarbonate solution are placed alternately in a closed reaction device, inert gas is introduced, the ambient humidity is 80%-90%, and the reaction is carried out at a constant temperature of 33-36 ℃ for 10-15 h to prepare modified biological filler; The first salt-containing denitrification medium comprises NaCl at a concentration of 10-20 g / L; the second salt-containing denitrification medium comprises NaCl at a concentration of 25-35 g / L.

[0008] This application employs a gradient concentration of saline denitrification culture medium to acclimate denitrifying bacteria loaded with polyurethane foam to high salinity. Within this salinity range, the denitrifying bacteria maintain high denitrification activity and survival rate, and can adapt to the treatment of wastewater with high salinity, thereby improving denitrification efficiency. Simultaneously, basic amino functional groups are introduced onto the surface of the polyurethane foam. These groups can undergo a protonation reaction in water to acquire a positive charge, utilizing electrostatic adsorption of chloride ions from NaCl. After drying, NaCl particles are formed on the surface of the polyurethane foam. In the subsequent closed reaction equipment, the ammonia and carbon dioxide produced by the decomposition of ammonium bicarbonate form a water film on the surface of the polyurethane foam due to the high humidity environment. The surface NaCl particles, as well as the ammonia and carbon dioxide in the gas phase, dissolve in this water film, reacting and depositing on the surface of the polyurethane foam to form sodium bicarbonate particles with low solubility. The sodium bicarbonate granules can be slowly released during the subsequent denitrification process to provide a pH buffer. They can slowly release the pH of acidic or alkaline wastewater to provide a buffer period for denitrifying bacteria to adapt to pH fluctuations. They can also buffer the pH drop caused by acid production during denitrification, maintain pH stability, and improve the denitrification activity of bacteria.

[0009] As a preferred embodiment, the first and second salt-containing denitrification media are each independent and further include sodium acetate (0.5-2.5 g / L), KNO3 (0.1-0.3 g / L), KH2PO4 (0.05-0.15 g / L), MgSO4 (0.03-0.06 g / L), NaHCO3 (0.05-0.15 g / L), and the balance being water.

[0010] This application involves immersing polyurethane loaded with denitrifying bacteria in a culture medium with a low nutrient concentration. This provides the bacteria with the necessary carbon, nitrogen, and inorganic salts to promote rapid bacterial reproduction, activate the denitrifying enzyme system within the bacteria, and restore the bacteria's denitrification function. During the culture period, the extracellular polymers secreted by the bacteria can also strengthen the adhesion between the bacteria and the carrier, thereby ensuring high activity and survival rate of the bacteria after subsequent sodium bicarbonate deposition.

[0011] As a preferred embodiment, the inert gas comprises CO2 with a volume fraction of 3%-7%.

[0012] As a preferred embodiment, the inert gas is at least one of nitrogen, argon, and neon.

[0013] As a preferred embodiment, in step (2), the concentration of denitrifying bacteria in the bacterial solution is 5 × 10⁻⁶. 8 ~9×10 8 CFU / mL.

[0014] As a preferred embodiment, in step (2), the mass ratio of the amino-modified polyurethane foam to the bacterial solution is 1:(1-3).

[0015] This application, by controlling the mass ratio of amino-modified polyurethane foam and bacterial solution, as well as the bacterial species concentration in the bacterial solution, within the aforementioned range, can ensure the formation of a uniform biofilm on the polyurethane foam surface, and avoid excessive bacterial density leading to bacterial clusters clogging the pores. This ensures the flow of wastewater and the replacement of metabolic products and nutrients, thereby improving the denitrification rate of nitrates in wastewater.

[0016] As a preferred embodiment, in step (2), the denitrifying bacteria is Zobelella.

[0017] As a preferred embodiment, in step (1), the average pore size of the polyurethane foam is 4-10 μm.

[0018] As a preferred option, in step (1), the static reaction temperature is 35-45 ℃ and the time is 2-4 h.

[0019] As a preferred option, in step (1), the sterilization temperature is 121 °C, the pressure is 0.1 MPa, and the time is 20-30 min.

[0020] This application uses a low concentration of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to modify the surface of polyurethane foam with amino groups. High-temperature sterilization can destroy the microbial structure, avoid contamination by other microorganisms, and remove unreacted silane monomers and hydrolysis byproducts from the surface, thereby reducing the toxicity to bacteria and improving the survival rate and denitrification activity of denitrifying bacteria.

[0021] As a preferred option, in step (2), the oscillation treatment time is 20-26 h and the settling time is 10-14 h.

[0022] To address the aforementioned technical problems, a second objective of this invention is to provide a modified biological packing material.

[0023] To address the aforementioned technical problems, a third objective of this invention is to provide an application of a modified biological packing material in the field of denitrification for nitrate removal.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. This application utilizes N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to amino-modify polyurethane foam, thereby improving its hydrophilicity and adsorption to denitrifying bacteria, increasing the loading rate of denitrifying bacteria, shortening the acclimatization period in denitrification equipment, increasing the denitrification rate of modified biological packing material in the initial stage of start-up, and improving the removal rate of nitrates.

[0025] 2. This application uses a gradient concentration of salt-containing denitrification culture medium to acclimate denitrifying bacteria loaded on polyurethane foam to high salinity. After drying, NaCl particles are formed on the surface of the polyurethane foam. In a high-humidity closed reaction device, they can react with ammonia and carbon dioxide produced by the decomposition of ammonium bicarbonate and deposit sodium bicarbonate particles with low solubility on the surface of polyurethane foam. These particles can be slowly precipitated in the subsequent denitrification process to provide a pH buffer, maintain pH stability, and improve the denitrification activity of the bacteria.

[0026] 3. In this application, polyurethane loaded with denitrifying bacteria is immersed in a culture medium with a low nutrient concentration, which can promote the rapid reproduction of bacteria and restore the denitrification function of bacteria. During the culture period, the extracellular polymer secreted by bacterial proliferation can also strengthen the adhesion between bacteria and carrier, thereby ensuring that the bacteria have high activity and survival rate after subsequent sodium bicarbonate deposition. Attached Figure Description

[0027] Figure 1 The modified biological packing material prepared in Example 1 of this invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 A method for preparing a modified biological filler includes the following steps: (1) The polyurethane foam was completely immersed in the aminated modification solution. The average pore size of the polyurethane foam was 6 μm. The aminated modification solution included 0.5% N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and the remainder water. The foam was allowed to stand for 3 h at 40 °C. Then it was rinsed with deionized water and phosphate buffer. After high-temperature sterilization at 121 °C and 0.1 MPa for 20 min and cooling, the aminated polyurethane foam was obtained. (2) Denitrifying bacteria were inoculated into HB9198 denitrification medium. The denitrifying bacteria was Zobelella, with the accession number 1A00165 from the China Marine Microbiological Culture Collection Center (MCCC). The bacteria were cultured at 30 °C under anaerobic conditions with shaking until the logarithmic growth phase. After centrifugation, the bacterial cells were resuspended in PBS to obtain a bacterial concentration of 7 × 10⁻⁶. 8 Amino-modified polyurethane foam was soaked in a bacterial solution with a CFU / mL concentration. The mass ratio of amino-modified polyurethane foam to bacterial solution was 1:2. The foam was adsorbed under anaerobic conditions at 28 °C for 24 h with low-temperature shaking. After standing for 12 h, the foam was washed and dried at room temperature to obtain bioloaded polyurethane foam. (3) The bioloaded polyurethane foam was soaked in a first salt-containing denitrification medium, which included 1 g / L sodium acetate, 0.2 g / L KNO3, 0.1 g / L KH2PO4, 0.05 g / L MgSO4, 15 g / L NaCl, 0.1 g / L NaHCO3 and water, and anaerobic culture was carried out at 30 ℃ for 12 h. Then it was soaked in a second salt-containing denitrification medium, which included 2 g / L sodium acetate, 0.2 g / L KNO3, 0.1 g / L KH2PO4, 0.05 g / L MgSO4, 30 g / L NaCl, 0.1 g / L NaHCO3 and water, and anaerobic culture was carried out at 30 ℃ for 12 h. The activated polyurethane foam was then dried at room temperature. (4) The activated polyurethane foam was placed in a closed reaction apparatus, with saturated ammonium bicarbonate solution placed at intervals inside. A mixed gas containing CO2 and nitrogen was introduced, with the volume fraction of CO2 in the mixed gas being 5%. The ambient humidity was maintained at 85%, and the reaction was carried out at a constant temperature of 35 °C for 12 h to prepare the product as shown. Figure 1 The modified biological packing material shown.

[0030] Example 2 A method for preparing a modified biological filler includes the following steps: (1) The polyurethane foam was completely immersed in the aminated modification solution. The average pore size of the polyurethane foam was 4 μm. The aminated modification solution included 0.3% N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and the remainder water. The foam was allowed to stand for 4 h at 35 °C. Then it was rinsed with deionized water and phosphate buffer. After high-temperature sterilization at 121 °C and 0.1 MPa for 20 min and cooling, the aminated polyurethane foam was obtained. (2) Denitrifying bacteria were inoculated into HB9198 denitrification medium. The denitrifying bacteria was Zobelella, with the accession number 1A00165 from the China Marine Microbiological Culture Collection Center (MCCC). The bacteria were cultured at 30 °C under anaerobic conditions with shaking until the logarithmic growth phase. After centrifugation, the bacterial cells were resuspended in PBS to obtain a bacterial concentration of 5 × 10⁻⁶. 8 Amino-modified polyurethane foam was soaked in a bacterial solution with a CFU / mL concentration. The mass ratio of amino-modified polyurethane foam to bacterial solution was 1:3. The foam was adsorbed under anaerobic conditions at 28 °C for 20 h with low-temperature shaking. After standing for 10 h, the foam was washed and dried at room temperature to obtain bioloaded polyurethane foam. (3) The bioloaded polyurethane foam was soaked in a first salt-containing denitrification medium, which included 0.5 g / L sodium acetate, 0.1 g / L KNO3, 0.05 g / L KH2PO4, 0.03 g / L MgSO4, 10 g / L NaCl, 0.05 g / L NaHCO3 and water, and anaerobic culture was carried out at 30 ℃ for 12 h. Then it was soaked in a second salt-containing denitrification medium, which included 1.5 g / L sodium acetate, 0.1 g / L KNO3, 0.05 g / L KH2PO4, 0.03 g / L MgSO4, 25 g / L NaCl, 0.05 g / L NaHCO3 and water, and anaerobic culture was carried out at 30 ℃ for 12 h. The activated polyurethane foam was then dried at room temperature. (4) The activated polyurethane foam was placed in a closed reaction device, and saturated ammonium bicarbonate solution was placed in the closed reaction device at intervals. A mixed gas containing CO2 and nitrogen was introduced, with the volume fraction of CO2 in the mixed gas being 3%. The ambient humidity was kept at 90%, and the reaction was carried out at a constant temperature of 35 °C for 10 h to prepare the modified biological filler.

[0031] Example 3 A method for preparing a modified biological filler includes the following steps: (1) The polyurethane foam was completely immersed in the aminated modification solution. The average pore size of the polyurethane foam was 10 μm. The aminated modification solution included 0.8% N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and the remainder water. The foam was allowed to stand for 2 h at 45 °C. Then it was rinsed with deionized water and phosphate buffer. After high-temperature sterilization at 121 °C and 0.1 MPa for 20 min and cooling, the aminated polyurethane foam was obtained. (2) Denitrifying bacteria were inoculated into HB9198 denitrification medium. The denitrifying bacteria was Zobelella, with the accession number 1A00165 from the China Marine Microbiological Culture Collection Center (MCCC). The bacteria were cultured at 30 °C under anaerobic conditions with shaking until the logarithmic growth phase. After centrifugation, the bacterial cells were resuspended in PBS to obtain a bacterial concentration of 9 × 10⁻⁶. 8 Amino-modified polyurethane foam was soaked in a bacterial solution with a CFU / mL concentration. The mass ratio of amino-modified polyurethane foam to bacterial solution was 1:1. The foam was adsorbed under anaerobic conditions at 28 °C for 26 h with low-temperature shaking. After standing for 14 h, the foam was washed and dried at room temperature to obtain bioloaded polyurethane foam. (3) The bioloaded polyurethane foam was soaked in a first salt-containing denitrification medium, which included 1.5 g / L sodium acetate, 0.3 g / L KNO3, 0.15 g / L KH2PO4, 0.08 g / L MgSO4, 20 g / L NaCl, 0.15 g / L NaHCO3 and water, and anaerobic culture was carried out at 30 ℃ for 12 h. Then it was soaked in a second salt-containing denitrification medium, which included 2.5 g / L sodium acetate, 0.3 g / L KNO3, 0.15 g / L KH2PO4, 0.06 g / L MgSO4, 35 g / L NaCl, 0.15 g / L NaHCO3 and water, and anaerobic culture was carried out at 30 ℃ for 12 h. The activated polyurethane foam was then dried at room temperature. (4) The activated polyurethane foam was placed in a closed reaction device, and saturated ammonium bicarbonate solution was placed in the closed reaction device at intervals. A mixed gas containing CO2 and nitrogen was introduced, with the volume fraction of CO2 in the mixed gas being 7%. The ambient humidity was kept at 80%, and the reaction was carried out at a constant temperature of 35 °C for 15 h to prepare the modified biological filler.

[0032] Example 4 A method for preparing a modified biological filler differs from Example 1 in that, in step (1), the aminated modification solution includes 0.3% by mass of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and the remainder water.

[0033] Example 5 A method for preparing a modified biological filler differs from Example 1 in that, in step (1), the aminated modification solution includes 0.8% by mass of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and the remainder water.

[0034] Example 6 A method for preparing a modified biological packing material differs from Example 1 in that, in step (3), the first salt-containing denitrification medium comprises sodium acetate at a concentration of 1 g / L, KNO3 at a concentration of 0.2 g / L, KH2PO4 at a concentration of 0.1 g / L, MgSO4 at a concentration of 0.05 g / L, NaCl at a concentration of 10 g / L, NaHCO3 at a concentration of 0.1 g / L, and water; the second salt-containing denitrification medium comprises sodium acetate at a concentration of 2 g / L, KNO3 at a concentration of 0.2 g / L, KNO3 at a concentration of 0.1 g / L, KH2PO4 at a concentration of 0.05 g / L, MgSO4 at a concentration of 25 g / L, NaCl at a concentration of 0.1 g / L, NaHCO3 at a concentration of 0.1 g / L, and water.

[0035] Example 7 A method for preparing a modified biological packing material differs from Example 1 in that, in step (3), the first salt-containing denitrification medium comprises sodium acetate at a concentration of 1 g / L, KNO3 at a concentration of 0.2 g / L, KH2PO4 at a concentration of 0.1 g / L, MgSO4 at a concentration of 0.05 g / L, NaCl at a concentration of 20 g / L, NaHCO3 at a concentration of 0.1 g / L, and water.

[0036] Example 8 A method for preparing a modified biological filler differs from Example 1 in that, in step (4), the isothermal reaction temperature is 34 °C.

[0037] Example 9 A method for preparing a modified biological filler differs from Example 1 in that, in step (3), the isothermal reaction temperature is 36 °C.

[0038] Example 10 A method for preparing a modified biological filler differs from Example 1 in that, in step (4), activated polyurethane foam is placed in a closed reaction device, a saturated ammonium bicarbonate solution is placed in the closed reaction device, nitrogen gas is introduced, the ambient humidity is maintained at 85%, and the reaction is carried out at a constant temperature of 35 °C for 12 h to prepare the modified biological filler.

[0039] Example 11 A method for preparing a modified biological filler includes the following steps: (1) The polyurethane foam was completely immersed in the aminated modification solution. The average pore size of the polyurethane foam was 6 μm. The aminated modification solution included 0.5% N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and the remainder water. The foam was allowed to stand for 3 h at 40 °C. Then it was rinsed with deionized water and phosphate buffer. After high-temperature sterilization at 121 °C and 0.1 MPa for 20 min and cooling, the aminated polyurethane foam was obtained. (2) Denitrifying bacteria were inoculated into HB9198 denitrification medium. The denitrifying bacteria was Zobelella, with the accession number 1A00165 from the China Marine Microbiological Culture Collection Center (MCCC). The bacteria were cultured at 30 °C under anaerobic conditions with shaking until the logarithmic growth phase. After centrifugation, the bacterial cells were resuspended in PBS to obtain a bacterial concentration of 7 × 10⁻⁶. 8 Amino-modified polyurethane foam was soaked in a bacterial solution with a CFU / mL concentration. The mass ratio of amino-modified polyurethane foam to bacterial solution was 1:2. The solution was subjected to low-temperature shaking adsorption at 28 °C for 24 h under anaerobic conditions. After standing for 12 h, the solution was washed and dried at room temperature to prepare the modified biological packing material.

[0040] Comparative Example 1 A method for preparing a modified biological filler includes the following steps: Denitrifying bacteria, specifically *Zobelia zoysia* (accession number 1A00165), were inoculated into HB9198 denitrification medium. The bacteria were cultured at 30 °C under anaerobic conditions with shaking until the logarithmic growth phase. After centrifugation and resuspending the cells in PBS, a bacterial concentration of 7 × 10⁻⁶ was obtained. 8The modified biological packing material was prepared by soaking polyurethane foam in a bacterial solution with an average pore size of 6 μm and a mass ratio of 1:2 between the polyurethane foam and the bacterial solution. The mixture was then subjected to low-temperature shaking adsorption at 28 °C for 24 h under anaerobic conditions, followed by standing for 12 h, washing, and drying at room temperature.

[0041] Comparative Example 2 A method for preparing a modified biological filler differs from Example 1 in that, in step (3), the biologically loaded polyurethane foam is immersed in a first saline aqueous solution, which includes NaCl and water at a concentration of 15 g / L, and anaerobically cultured at 30 °C for 12 h. Subsequently, it is immersed in a second saline aqueous solution, which includes NaCl and water at a concentration of 30 g / L, and anaerobically cultured at 30 °C for 12 h. The activated polyurethane foam is then dried at room temperature.

[0042] Comparative Example 3 A method for preparing a modified biological filler differs from Example 1 in that, in step (4), the isothermal reaction temperature is 40 °C.

[0043] Comparative Example 4 A method for preparing a modified biological filler differs from Example 1 in that, in step (1), the aminated modification solution includes 2% by mass of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and the remainder water.

[0044] Comparative Example 5 A method for preparing a modified biological filler differs from Example 1 in that, in step (3), the biologically loaded polyurethane foam is immersed in a first salt-containing denitrification medium, which includes sodium acetate at a concentration of 1 g / L, KNO3 at a concentration of 0.2 g / L, KH2PO4 at a concentration of 0.1 g / L, MgSO4 at a concentration of 0.05 g / L, NaCl at a concentration of 40 g / L, NaHCO3 at a concentration of 0.1 g / L, and water. The foam is then anaerobically cultured at 30 °C for 24 h and dried at room temperature to obtain activated polyurethane foam.

[0045] Comparative Example 6 A method for preparing a modified biological filler differs from Example 1 in that, in step (3), the biologically loaded polyurethane foam is immersed in a first salt-containing denitrification medium, which includes sodium acetate at a concentration of 1 g / L, KNO3 at a concentration of 0.2 g / L, KH2PO4 at a concentration of 0.1 g / L, MgSO4 at a concentration of 0.05 g / L, NaCl at a concentration of 5 g / L, NaHCO3 at a concentration of 0.1 g / L, and water. The mixture is then anaerobic cultured at 30 °C for 24 h and dried at room temperature to obtain activated polyurethane foam.

[0046] Performance testing Weakly acidic wastewater, neutral wastewater, and weakly alkaline wastewater with nitrate concentrations of 70 mg / L were prepared, respectively. The pH of the weakly acidic wastewater was 6, and the pH of the weakly alkaline wastewater was 8. The biological packing materials prepared in the examples and comparative examples were placed in immobilized denitrification filters with a filling rate of 40%. The wastewater flow rate was controlled at 50 mL / min, the carbon-nitrogen ratio (C / N) was 10:1, and the dissolved oxygen was controlled to be less than 0.5 mg / L. The total nitrogen concentration in the effluent was monitored on the 4th day of filter startup. The experimental results are shown in Table 1 below.

[0047] Table 1 - Performance test results of biological packing materials prepared in the embodiments and comparative examples of this application As shown in Table 1, in Example 11 of this application, a low concentration of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was used to modify the surface of polyurethane foam with amino groups to improve its hydrophilicity and adsorption to denitrifying bacteria. This resulted in a high loading rate of denitrifying bacteria on the surface and in the pores of the polyurethane foam, which shortened the acclimatization period in the denitrification equipment and increased the denitrification rate of the modified biological packing material in the initial start-up phase. The total nitrogen concentration in the effluent was low on the 4th day, thus improving the nitrate removal rate. In contrast, the polyurethane foam in Comparative Example 1 did not undergo surface amino modification. When co-cultured with bacterial solution, the polyurethane foam carrier had a weaker binding with the denitrifying bacteria, leading to a significant decrease in the loading rate and a reduced denitrification rate of the biological packing material. Therefore, the total nitrogen concentration in its effluent was significantly higher than that in Example 11.

[0048] As shown in Table 1, in Example 1 of this application, the bioloaded polyurethane foam was acclimated to high salinity using a gradient concentration of salt-containing denitrification medium. After drying, NaCl particles formed on the surface. In a high-humidity, closed reaction device, these particles reacted with ammonia and carbon dioxide produced by the decomposition of ammonium bicarbonate, depositing sodium bicarbonate particles with low solubility on the polyurethane foam surface. These particles could slowly precipitate during subsequent denitrification to provide a pH buffer, reducing the impact of acidic or alkaline wastewater on the activity of denitrifying bacteria. Simultaneously, they balanced the pH of the acid produced during denitrification, increasing the denitrification rate in acidic and alkaline wastewater. However, in Example 11, no sodium bicarbonate particles were deposited on the polyurethane foam surface. In acidic and alkaline wastewater, pH fluctuations reduced the denitrification activity, resulting in a higher total nitrogen concentration in the effluent and a lower denitrification rate than in Example 1.

[0049] Compared to Example 1, in Comparative Example 2, the bioloaded polyurethane foam was subjected to high salinity acclimation using a gradient concentration of saline aqueous solution in step (3). The denitrifying bacteria loaded with the polyurethane foam could not obtain the carbon source, nitrogen source and other nutrients required for growth to promote reproduction and enzyme activation. As a result, the survival rate and denitrification activity of the denitrifying bacteria after the subsequent deposition of sodium bicarbonate particles were greatly reduced. Therefore, the denitrification rate of the wastewater was low, and the total nitrogen concentration of the effluent on the 4th day was above 20 mg / L.

[0050] In Examples 1 and 8-9 of this application, the isothermal reaction temperature during sodium bicarbonate particle deposition in step (4) is 34-36 ℃. Compared with Example 1, the isothermal reaction temperature of Comparative Example 3 is 40 ℃. At this time, the ambient temperature is too high. The denitrifying bacteria loaded with polyurethane foam stay in this high temperature environment for a long time, which will cause most of the bacteria to die and their activity to decrease. Ultimately, the denitrification rate of the modified biological packing for wastewater is greatly reduced, resulting in a significantly higher total nitrogen concentration in the effluent on the 4th day.

[0051] In Examples 1 and 4-5 of this application, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane with a concentration of 0.3%-0.8% was used to modify the surface amino group of polyurethane foam. Compared with Example 1, the concentration of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane in Comparative Example 4 was 2%. The excessively high concentration would result in too much silane monomer residue on the surface of the polyurethane foam, thereby affecting the subsequent loading of denitrifying bacteria and possibly having a slight toxic effect on denitrifying bacteria, thus affecting their denitrification activity and ultimately reducing the denitrification rate of wastewater. The total nitrogen concentration of the effluent on the 4th day was above 20 mg / L.

[0052] Compared to Example 1, in Comparative Example 5, the bioloaded polyurethane foam was directly immersed in a high-salt denitrification medium without undergoing low-salt acclimation, which affected the activity of denitrifying bacteria and ultimately led to a decrease in the denitrification rate. In Comparative Example 6, the bioloaded polyurethane foam was directly immersed in a low-salt denitrification medium. After drying, the salt content on the surface of the polyurethane foam was extremely low, resulting in very few sodium bicarbonate particles deposited in the subsequent reaction. Consequently, it could not provide an effective pH buffering effect, and the denitrification rate in acidic and alkaline wastewater was significantly reduced.

[0053] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for preparing a modified biological filler, characterized in that, Includes the following steps: (1) The polyurethane foam is immersed in an aminated modification solution, wherein the aminated modification solution includes N-(2-aminoethyl)-3-aminopropyltrimethoxysilane with a mass fraction of 0.3%-0.8%, and after static reaction, it is sterilized to obtain aminated polyurethane foam. (2) The amino-modified polyurethane foam was soaked in a bacterial solution containing denitrifying bacteria, shaken, and then allowed to stand. After washing and drying, the bioloaded polyurethane foam was prepared.

2. The method for preparing the modified biological filler as described in claim 1, characterized in that, The bioloaded polyurethane foam prepared in step (2) was immersed in a first salt-containing denitrification medium and anaerobically cultured for 10-15 h, and then immersed in a second salt-containing denitrification medium and anaerobically cultured for 10-15 h. After drying at room temperature, activated polyurethane foam was obtained. The activated polyurethane foam and saturated ammonium bicarbonate solution were placed alternately in a closed reaction device, inert gas was introduced, the ambient humidity was 80%-90%, and the reaction was carried out at a constant temperature of 33-36 ℃ for 10-15 h to prepare modified biological filler. The first salt-containing denitrification medium comprises NaCl at a concentration of 10-20 g / L; the second salt-containing denitrification medium comprises NaCl at a concentration of 25-35 g / L.

3. The method for preparing the modified biological filler as described in claim 2, characterized in that, The first and second salt-containing denitrification media are independent and also include sodium acetate (0.5-2.5 g / L), KNO3 (0.1-0.3 g / L), KH2PO4 (0.05-0.15 g / L), MgSO4 (0.03-0.06 g / L), NaHCO3 (0.05-0.15 g / L), and the balance water.

4. The method for preparing the modified biological filler as described in claim 2, characterized in that, The inert gas includes CO2 with a volume fraction of 3%-7%; And / or, the inert gas is at least one of nitrogen, argon, and neon.

5. The method for preparing the modified biological filler as described in claim 1, characterized in that, In step (2), the concentration of denitrifying bacteria in the bacterial solution is 5 × 10⁻⁶. 8 ~9×10 8 CFU / mL; And / or, in step (2), the mass ratio of the amino-modified polyurethane foam to the bacterial solution is 1:(1-3). And / or, in step (2), the denitrifying bacteria are Zobelella.

6. The method for preparing the modified biological filler as described in claim 1, characterized in that, In step (1), the average pore size of the polyurethane foam is 4-10 μm.

7. The method for preparing the modified biological filler as described in claim 1, characterized in that, In step (1), the static reaction temperature is 35-45 ℃ and the time is 2-4 h; And / or, in step (1), the sterilization process is performed at a temperature of 121 °C, a pressure of 0.1 MPa, and a time of 20-30 min.

8. The method for preparing the modified biological filler as described in claim 1, characterized in that, In step (2), the oscillation treatment time is 20-26 h and the settling time is 10-14 h.

9. A modified biological packing material prepared by the method described in any one of claims 1-8.

10. The application of the modified biological packing material as described in claim 9 in the field of denitrification for nitrate removal.

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