A biochar suspension carrier with synchronous short-range nitrification and denitrification functions and its preparation method

Abstract

The present invention discloses a biochar suspension carrier with synchronous short-range nitrification and denitrification functions and a preparation method thereof, wherein the biochar suspension carrier includes a polymer resin, modified biochar, and calcium carbonate in a mass ratio of 100-150:5-15:10-30, wherein the polymer resin, the modified biochar, and the calcium carbonate are mixed evenly, extruded, and then immersed in a weak acid solution of a carbon source nitrite and dried to obtain the result. The suspension carrier provided by the present invention first utilizes the adsorption of the modified biochar to promote the growth of denitrifying functional bacteria on the surface of the suspended filler; secondly, the chitosan-nitrite composite film loaded by the suspension carrier is utilized to promote the growth of nitrifying bacteria and denitrifying bacteria, thereby improving the denitrification effect of the suspension carrier in the sewage treatment system when the carbon source is insufficient. The present invention provides a carrier that mainly solves the problems of low influent C / N, poor denitrification efficiency, and difficulty in increasing activated sludge concentration in the treatment process of traditional municipal sewage and village sewage.

Description

Technical Field

[0001] The invention relates to a biochar suspension carrier for biological treatment of environmental pollutants. Background Art

[0002] Since its successful development in the late 1980s, moving bed biofilm reactor technology has seen increasing application in wastewater treatment. Initially focused on degrading organic matter in wastewater, it has gradually evolved into carbon removal, denitrification, and deep denitrification. The research and development of suspended carriers—the habitat for microorganisms—is a key technology in the development of moving bed biofilm reactors, and their quality and performance are closely linked to their treatment effectiveness. However, the mainstream suspended carriers currently produced domestically are directly processed and molded from polymer materials such as polyethylene or polypropylene, without specific design and modification tailored to the characteristics and growth requirements of denitrifying bacteria. Modified suspended carriers produced on the market have specific requirements for the growth environment of wastewater treatment reactors. The wide variety of carriers, including anoxic and aerobic suspended carriers, increases the investment and operating costs of moving bed biofilm reactors and their combined processes, limiting their application.

[0003] Chinese patent publication number CN114804351A discloses an anoxic suspension carrier with mixotrophic denitrification capabilities and its preparation method. The anoxic suspension carrier comprises a polymer resin, modified biochar, polyquaternium salt, and sulfur powder in a mass ratio of 100-500:20-50:8-25:12-30. The polymer resin, modified biochar, polyquaternium salt, and sulfur powder are uniformly mixed and then extruded to form the product. The polymer resin is polyethylene or polypropylene. The anoxic suspension carrier in this invention selectively screens and enriches sulfur-autotrophic denitrifying bacteria under anoxic conditions. During biofilm formation, the time and efficiency of biofilm formation on the anoxic suspension carrier are shortened, and the biofilm formation effect of the carrier is enhanced, increasing the abundance of denitrifying bacteria on the biofilm surface from 10-20% to 40-70%. This patent is primarily suitable for enriching anaerobic denitrifying bacteria in anoxic environments and is not suitable for enriching nitrifying bacteria. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a biochar suspension carrier with synchronous short-term nitrification and denitrification functions and a preparation method thereof in view of the shortcomings of the existing technology, so as to realize the functions of synchronous short-term nitrification and denitrification in the aerobic zone, thereby reducing the operating cost and investment cost of sewage treatment.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a biochar suspension carrier with synchronous short-range nitrification and denitrification functions, comprising a polymer resin, modified biochar, and calcium carbonate in a mass ratio of 100-200:5-15:10-30, wherein the polymer resin, the modified biochar, and the calcium carbonate are uniformly mixed, extruded, immersed in a weak acid solution of a carbon source nitrite, and then dried to obtain the suspension carrier;

[0006] The weak acid solution of carbon source nitrite comprises a carbon source, nitrite and a weak acid in a mass ratio of 2-4:1-2:1.

[0007] Among them, the synchronous nitrification and denitrification function means that after the biochar suspension carrier is loaded with microorganisms, it can perform nitrification and denitrification functions at the same time.

[0008] The present invention adds modified biochar and calcium carbonate in polymer resin, works together, improves the affinity to denitrification functional bacteria, and promotes the growth of ammonia oxidizing bacteria and heterotrophic denitrifying bacteria. The suspended carrier provided by the present invention first utilizes the carbon source in the carrier film to promote the biofilm and enrichment of ammonia oxidizing bacteria, and realizes the short-range nitrification function; Secondly, the nitrite slowly released by the carrier film and the nitrite produced by short-range nitrification are provided as electron donors for heterotrophic denitrifying bacteria, and at the same time, the carbon source slowly released by the carrier surface film and the carbon source in the sewage are utilized to provide a carbon source for heterotrophic denitrifying bacteria, thereby realizing the short-range denitrification function. In the case of insufficient carbon source, ammonia oxidizing bacteria and heterotrophic denitrifying bacteria carry out synchronous short-range nitrification and denitrification, which not only saves the land occupied by sewage treatment plants, but also realizes the efficient denitrification of low C / N ratio (C / N is 3-5) municipal sewage, which mainly solves the problems such as poor denitrification effect caused by imbalance of influent C / N ratio in traditional municipal sewage and village sewage treatment processes.

[0009] This mass ratio of raw materials has two main effects: (1) ensuring good tensile and compressive strength of the biochar carrier, which helps it maintain its original shape and structure during the reaction in the aerobic zone of the biochemical pool, making it less likely to deform, and allowing good coupling between the various raw materials, making it easier to prepare and shape; (2) ensuring that the carrier has good bioaffinity, promoting rapid biofilm formation and startup. If the mass ratio is outside this range, it will result in defects such as too low or too high density, and the carrier will be difficult to shape and have insufficient structural strength.

[0010] In a preferred embodiment of the present invention, the carbon source is a carbon source that is viscous after dissolving in water. Preferably, the carbon source is one or both of chitosan and chitin. Preferably, the chitosan is chitosan with a degree of deacetylation greater than 80%.

[0011] The carbon source becomes sticky when dissolved in water, making it easy to load onto the carrier surface. The amino groups in chitosan promote the formation and accumulation of ammonia-oxidizing bacteria, achieving short-range nitrification.

[0012] In a preferred embodiment of the present invention, the nitrite is one or both of sodium nitrite and potassium nitrite.

[0013] Acceptable nitrites include sodium nitrite and potassium nitrite. These two salts are non-toxic to the growth of short-range denitrifying bacteria and ammonia-oxidizing bacteria, but they inhibit the growth of nitrite-oxidizing bacteria. Other types of nitrite cannot be used, in addition to their high price, because they can interfere with the normal growth of microorganisms.

[0014] In a preferred embodiment of the present invention, the weak acid is one or both of dilute hydrochloric acid and acetic acid solution, and the molar concentration of the weak acid solution is 0.05-0.2 mol / L.

[0015] If the molar concentration of the weak acid is less than 0.05 mol / L, the dissolution effect of chitosan is poor, which is not conducive to coating; if the weak acid concentration is greater than 0.2 mol / L, it will lead to a high nitrite concentration, which is not conducive to the enrichment of ammonia oxidizing bacteria.

[0016] In a preferred embodiment of the present invention, the modified biochar has a particle size of less than 0.18 mm, a porosity of 68-73%, and a pore size of 8-42 nm.

[0017] The modified biochar with the particle size, porosity and pore size improves the affinity to the denitrifying functional bacteria, is beneficial to the adsorption of refractory organic pollutants, and enhances the biofilm formation effect of the carrier on denitrifying bacteria.

[0018] The present invention also discloses a method for preparing a biochar suspension carrier with simultaneous nitrification and denitrification functions, comprising the following steps:

[0019] Step 1: Prepare a polymer resin: modified biochar: calcium carbonate mixture in a mass ratio of 100-200: 5-15: 10-30;

[0020] Step 2: Mix the raw materials weighed in step 1 thoroughly;

[0021] Step 3: Granulate the raw materials in step 2 and process them into cylindrical particles;

[0022] Step 4: Extrude the cylindrical particles prepared in step 3 at high temperature;

[0023] Step 5: The material extruded in step 4 is sucked by a vacuum system under negative pressure to form a cylindrical tube;

[0024] Step 6: Cooling the pipe obtained in step 5 in a cooling tank, and then mechanically cutting it to obtain a biochar suspension carrier;

[0025] Step 7: Soak the biochar suspension carrier prepared in step 6 in a weak acid solution of carbon source nitrite for coating, promote the carrier surface to load a composite film with a thickness of 0.3-0.5 mm, and dry.

[0026] This method for preparing a suspended carrier not only ensures thorough mixing of the biochar and polymer resin but also increases the carrier's surface roughness and specific surface area, facilitating the loading and coating of chitosan and a weak nitrite solution. A ratio of polymer resin:modified biochar:calcium carbonate below this mass fraction results in a low density biochar carrier, hindering effective fluidization. A ratio of polymer resin:modified biochar:calcium carbonate above this mass fraction results in a high density biochar carrier, hindering effective fluidization.

[0027] In a preferred embodiment of the present invention, the coating time in step 7 is 5-10 minutes.

[0028] Controlling the biochar carrier coating time within 5-10 minutes can ensure that the coating thickness is controlled within the range of 0.3-0.5mm. Coating time less than 5 minutes is not conducive to the compactness of the biochar carrier coating, and the coating thickness is less than 0.3mm. Coating time greater than 10 minutes will not only lead to a coating thickness greater than 0.5mm, reducing the carrier's flow area, which is not conducive to the enrichment of microorganisms and the removal of pollutants, but also increase the preparation cost.

[0029] In a preferred embodiment of the present invention, the temperature of the high-temperature extrusion molding in step 4 is 160-240°C;

[0030] The vacuum negative pressure condition in step 5 is -0.02~-0.25MPa.

[0031] The processing temperature of high-temperature shaping extrusion is lower than 160°C, which is not conducive to the dissolution and extrusion of the raw material particles, and the preparation condition higher than 240°C is not conducive to the molding of the carrier.

[0032] In a preferred embodiment of the present invention, the diameter of the cylindrical particles in step 3 is 3-5 mm;

[0033] In step 7, the product is dried at 60-80°C or air-dried under natural conditions.

[0034] In a preferred embodiment of the present invention, the method for preparing the modified biochar comprises the following steps:

[0035] (1) The biomass powder is sieved through a 100-mesh sieve and then dried at 60-80°C for 2-12 hours;

[0036] (2) Pyrolyzing the dried biomass powder at 500-700°C for 60-120 minutes to prepare powdered biochar;

[0037] (3) Soak the powdered biochar in a 0.05-0.3 mol / L sodium hypochlorite solution for 2-4 hours, stirring during the soaking process to maintain a uniform state of the biochar mixture;

[0038] (4) Soak the powdered biochar in a 0.1-0.35 mol / L potassium hydroxide solution for 2-4 hours, stirring during the soaking process to maintain a uniform state of the biochar mixture;

[0039] (5) After biochar modification, wash with distilled water 1-3 times until the pH value of the biochar solution is 6.0-8.0;

[0040] (6) After the pH of the biochar solution returns to neutral, it is filtered through an 80-200 mesh sieve and the filter residue is dried at 60-80°C.

[0041] The above biochar preparation process not only increases the specific surface area and porosity of biochar, but also increases the pore size range of biochar through the modification effect of sodium hypochlorite and potassium hydroxide solution, thereby promoting the enrichment and growth of bacteria. In addition, the above preparation process cleverly utilizes the principle of acid-base neutralization to reduce the distilled water required for the cleaning step, even if the biochar is weakly alkaline, it will promote the growth of ammonia oxidizing bacteria. The use of sodium hypochlorite and potassium hydroxide solutions below this concentration range is not conducive to the modification effect of biochar, resulting in a small pore size and an unobvious porosity improvement effect; sodium hypochlorite and potassium hydroxide solutions above this concentration range will lead to an increase in preparation costs, while the effect of increasing the pore size and porosity of biochar is very limited. The biochar prepared by this patent has the advantages of large porosity, a wide pore size range, and no need for cleaning.

[0042] The biomass powder is biomass powder made from biomass raw materials such as oil tea shells and branches.

[0043] The present invention also discloses the use of a biochar suspension carrier with simultaneous nitrification and denitrification functions in the biological treatment of municipal sewage and village sewage with a C / N ratio of 3-5.

[0044] Compared with the Chinese patent with publication number CN114804351A, the carrier of this patent invention can not only enrich short-range denitrifying bacteria, but also enrich ammonia oxidizing bacteria, realize the function of synchronous short-range nitrification and denitrification in the aerobic zone, reduce the operating cost and investment cost of sewage treatment, and solve the problem of high cost and large investment caused by the need to add aerobic suspended carriers and anoxic suspended carriers to the aerobic zone and the anoxic zone respectively in the moving bed biofilm reactor.

[0045] The present invention provides a biochar carrier that has good carbon removal effect, high denitrification efficiency, and economical production cost, and can quickly achieve simultaneous nitrification and denitrification functions. The present invention adds modified biochar and calcium carbonate to a polymer resin, which work together to improve the affinity for denitrification functional bacteria, promote the growth of ammonia oxidizing bacteria and heterotrophic denitrifying bacteria, and improve the denitrification effect of the suspended carrier in the sewage treatment system when the carbon source is insufficient. The thin film on the carrier surface promotes the rapid growth of ammonia oxidizing bacteria and short-range denitrifying bacteria in the early stage of biofilm formation, improves the biofilm formation efficiency of the suspended carrier, and quickly achieves the effect of simultaneous short-range nitrification and denitrification.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The biochar suspended carrier in this application has the effect of directional screening and enrichment cultivation of ammonia oxidizing bacteria and short-range denitrifying bacteria under low oxygen conditions, shortens the time and efficiency of suspended carrier biofilm formation during biofilm formation startup, strengthens the biofilm formation effect of the carrier on denitrifying bacteria, and increases the abundance of denitrifying functional bacteria on the surface of the carrier biofilm from 5-10% to 40-50%.

[0048] (2) Suspended carriers doped with modified biochar can not only adsorb refractory organic pollutants, but also adsorb and retain refractory organic matter and generate small molecular organic matter through hydrolysis, providing a carbon source for denitrifying bacteria and promoting the removal of refractory organic pollutants.

[0049] (3) Suspended carriers can significantly increase the biomass of biofilms, and the shock load resistance of sewage treatment systems with suspended carriers can be increased by 50-100%.

[0050] (4) The chitosan mixed in the surface film of the suspended carrier is not only conducive to the attachment of extracellular polymers produced by bacteria and other microorganisms, but also conducive to the renewal and regeneration of the film, and continuously promotes the growth of microorganisms such as short-range denitrifying bacteria on the surface of the carrier. In addition, the amino functional groups in chitosan are conducive to the growth and enrichment of ammonia oxidizing bacteria.

[0051] (5) The nitrite mixed in the surface film of the suspended carrier can not only serve as an electron donor for short-range denitrifying bacteria, but also as an inhibitor of nitrite-oxidizing bacteria, thereby promoting the realization of synchronous short-range nitrification and denitrification.

[0052] (6) The anoxic suspension carrier of the present invention is easy to process, has a simple process flow and reasonable production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a physical picture of the biochar suspension carrier in Example 1 of the present invention.

[0054] Figure 2 This is a photo of the biochar suspension carrier after biofilm formation in Example 2 of the present invention.

[0055] Figure 3 The sludge population structure before and after inoculation of the biochar suspension carrier in Example 3 of the present invention (S0 is inoculated sludge; S2 is anoxic biofilm formed for 25 days).

[0056] Figure 4 1 is a comparison of the differences in microbial population structure of the five carrier biofilms in Example 4 of the present invention. DETAILED DESCRIPTION

[0057] Example 1

[0058] Take 1 kg of polyethylene, 0.1 kg of modified biochar with a fineness of 100 mesh, and 0.1 kg of calcium carbonate particles with a particle diameter of 3-5 mm. The modified biochar is granulated with a polymer resin in proportion and placed in a granulator at a temperature of 170°C to prepare biochar resin particles. The biochar resin particles and calcium carbonate particles are fully mixed and added to the feed bin of the screw extruder. The temperatures of the feeding section, hot melt section, and mold section are 50°C, 170°C, and 160°C, respectively. After being extruded from the extruder, the raw materials enter the vacuum box and are sucked into a 25 mm diameter pipe by a vacuum pump. The negative pressure condition of the vacuum box is controlled in the range of -0.02~-0.25MPa. After the pipe is cooled in a cooling tank, it is cut into 10 mm long suspension carriers with a density of 0.98g / cm 3 The prepared biochar suspension carrier was soaked in 1 mol / L chitosan nitrite solution for 5-10 minutes and dried in a 60°C oven to obtain the biochar suspension carrier. The suspension carrier prepared in this embodiment was subjected to a solid surface contact angle test experiment. The test results showed that the surface contact angle of the suspension carrier was 77°, indicating that the surface of the suspension carrier was hydrophilic. The suspension carrier picture is as follows Figure 1 shown.

[0059] Example 2

[0060] 1.5 kg of polypropylene, 0.1 kg of modified biochar with a fineness of 100 mesh, and 0.3 kg of calcium carbonate particles with a particle diameter of 3-5 mm were added to a mixer and mixed evenly; the mixture was placed in a granulator and processed into granules at a temperature of 160°C; the granules were added to a screw extruder, and the temperatures of the feeding section, hot melt section, and mold section were 50°C, 160°C, and 150°C, respectively. After being extruded from the extruder, the raw materials entered a vacuum box and were sucked into a 25 mm diameter pipe by a vacuum pump under negative pressure. The pipe was cooled in a cooling tank and then cut into 10 mm long suspension carriers with a density of 0.96 g / cm 3. The prepared biochar suspension carrier was soaked in 0.5 mol / L chitosan nitrite solution for 5-10 minutes, and dried in an oven at 60°C to obtain the biochar suspension carrier. The suspension carrier prepared in this embodiment was subjected to a contact angle test, and the test results showed that the contact angle of the surface of the biochar carrier was 74°, indicating that the surface of the suspension carrier had strong hydrophilicity. The biochar suspension carrier prepared in this embodiment and the polypropylene suspension carrier (model K3, Jiangsu, Kunshan) were respectively added to the domestic sewage SBR aerobic reactor, and an intermittent water inlet treatment operation mode was adopted to conduct a comparative test of biofilm formation. The results showed that the time required for the biochar suspension carrier in this embodiment to form a biofilm was 5-10 days shorter than that of the polyethylene suspension carrier, indicating that the biochar suspension carrier prepared by the present invention has excellent biofilm formation performance, such as Figure 2 shown.

[0061] Example 3

[0062] 2 kg of polyethylene, 0.1 kg of modified biochar with a particle diameter of 3-5 mm, and 0.2 kg of calcium carbonate particles with a particle diameter of 3-5 mm were added to a mixer and mixed evenly; the mixture was placed in a granulator and processed into granules at a temperature of 170°C; the granules were added to a screw extruder, and the temperatures of the feeding section, hot melt section, and mold section were 60°C, 170°C, and 160°C, respectively. After being extruded from the extruder, the raw materials entered a vacuum box and were sucked into a 25 mm diameter pipe by a vacuum pump under negative pressure. The pipe was cooled in a cooling tank and then cut into 10 mm long suspension carriers with a density of 0.97 g / cm 3 The prepared biochar suspension carrier was soaked in a 0.6 mol / L chitosan nitrite solution for 5-10 minutes and dried in an oven at 60° C. to obtain the biochar suspension carrier.

[0063] The contact angle test was conducted on the biochar carrier prepared in this embodiment. The test results showed that the contact angle of the biological carrier surface was 75°, indicating that the surface of the suspended carrier had strong hydrophilicity. The prepared biochar carriers and polyethylene suspended carriers of the same shape and quantity were respectively added to the domestic sewage SBR aerobic reactor. The carbon-nitrogen ratio of the domestic sewage was 4.0. The reactor was operated in an intermittent water inlet treatment mode and a comparative biofilm formation test was conducted. The results showed that after 15-25 days of biofilm formation and enrichment culture, the content of ammonia oxidizing bacteria and short-range mixotrophic denitrifying bacteria in the biofilm of the biochar suspended carrier increased from about 1.5% and 10.5% in the inoculated sludge to 27% and 35%. The high-throughput sequencing results are as follows: Figure 3 The results show that the biochar suspension carrier prepared by the present invention has good synchronous short-range nitrification and denitrification effects.

[0064] Example 4

[0065] In the biofilm formation test of suspended carriers with different formulations, five formulation carriers: (1) biochar suspended carrier A (the carrier prepared in Example 3); (2) suspended carrier B (polyethylene + modified biochar + calcium carbonate); (3) suspended carrier C (polyethylene + modified biochar); (4) suspended carrier D (polyethylene + calcium carbonate); (5) suspended carrier E (polyethylene) were added to a 6L SBR aerobic reactor for a 30-day biofilm formation test. The sewage used in the biofilm formation test was domestic sewage with a low C / N ratio, a COD concentration of 100-140 mg / L, an ammonia nitrogen concentration of 25-30 mg / L, and a C / N ratio of 3.0-5.0. The biofilm formation effect of the comparative test is shown in Table 1 below. It can be seen that the biofilm formation speed, short-term facultative anaerobic denitrifying bacteria abundance, ammonia oxidizing bacteria abundance, TN removal rate, and synchronous short-term nitrification and denitrification effect of the carrier of the present invention are significantly better than those of other carriers. Comparison of differences in microbial population structure Figure 4 The carrier of the present invention has good synchronous short-range nitrification and denitrification performance.

[0066] Table 1 Comparison of biofilm formation effects of different formulations of suspension carriers

[0067]

[0068] Example 5

[0069] To compare the effects of different mass ratios on biochar carrier performance, three biochar carriers with different mass ratios were prepared: Biochar Carrier A (polymer resin: modified biochar: calcium carbonate mass ratio = 100:10:10), Biochar Carrier B (polymer resin: modified biochar: calcium carbonate mass ratio = 100:5:20), and Biochar Carrier C (polymer resin: modified biochar: calcium carbonate mass ratio = 100:15:30). These three biochar suspension carriers were tested for physical properties such as density, compressive strength, tensile strength, and surface contact angle. The results are shown in Table 2. As shown in Table 2, the mass ratios used in the present invention achieve the most balanced carrier physical parameters, making them most suitable for practical applications as suspension carriers.

[0070] Table 2 Comparison of physical properties of anoxic suspension carriers with different mass ratios

[0071]

[0072] The biochar carrier in the present invention has the effect of directional screening and enrichment cultivation on ammonia oxidizing bacteria and short-range facultative oxic denitrifying bacteria under low oxygen conditions (0.3-0.5 mg / L), shortens the time and efficiency of biofilm formation on the biochar suspension carrier during biofilm formation startup, strengthens the biofilm formation effect of the carrier on synchronous short-range nitrification and denitrification functional bacteria, and increases the abundance of ammonia oxidizing bacteria and short-range facultative oxic denitrifying bacteria on the surface of the carrier biofilm from 1-5% and 5-11% to 20-30% and 20-45%, respectively, which is conducive to the rapid startup of the synchronous short-range nitrification and denitrification function.

Claims

1. A biochar suspension carrier with synchronous short-range nitrification and denitrification functions, characterized by: The method comprises a polymer resin, modified biochar, and calcium carbonate in a mass ratio of 100-200:5-15:10-30, wherein the polymer resin, the modified biochar, and the calcium carbonate are uniformly mixed, extruded, immersed in a weak acid solution of a carbon source nitrite, and then dried to obtain a biochar suspension carrier; The weak acid solution of carbon source nitrite comprises a carbon source, nitrite and a weak acid in a mass ratio of 2-4:1-2:

1.

2. The biochar suspension carrier with synchronous short-range nitrification and denitrification function according to claim 1, characterized in that: The carbon source is a viscous carbon source after being dissolved in water.

3. The biochar suspension carrier with synchronous short-range nitrification and denitrification function according to claim 1, characterized in that: The carbon source is one or both of chitosan and chitin.

4. The biochar suspension carrier with synchronous short-range nitrification and denitrification function according to claim 3, characterized in that: Chitosan is chitosan with a deacetylation degree greater than 80%.

5. The biochar suspension carrier with synchronous short-range nitrification and denitrification function according to claim 1, characterized in that: The nitrite is one or both of sodium nitrite and potassium nitrite.

6. The biochar suspension carrier with synchronous short-range nitrification and denitrification functions according to claim 1, characterized in that: The weak acid is an acetic acid solution, and the molar concentration of the weak acid solution is 0.05-0.2 mol / L.

7. The biochar suspension carrier with synchronous short-range nitrification and denitrification functions according to claim 1, characterized in that: The modified biochar has a particle size of less than 0.18 mm, a porosity of 68-73%, and a pore size of 8-42 nm.

8. A method for preparing a biochar suspension carrier with synchronous short-range nitrification and denitrification functions, characterized in that: The following steps are involved: Step 1: Prepare a polymer resin: modified biochar: calcium carbonate mixture in a mass ratio of 100-200: 5-15: 10-30; Step 2: Mix the raw materials weighed in step 1 thoroughly; Step 3: Granulate the raw materials in step 2 and process them into cylindrical particles; Step 4: Extruding the cylindrical particles in step 3 at high temperature; Step 5: The material extruded in step 4 is sucked by a vacuum system under negative pressure to form a cylindrical tube; Step 6: Cooling the pipe obtained in step 5 in a cooling tank, and then mechanically cutting it to obtain a biochar suspension carrier; Step 7: Soak the biochar suspension carrier prepared in step 6 in a weak acid solution of carbon source nitrite for coating, promoting the loading of a composite film with a thickness of 0.3-0.5 mm on the carrier surface, and then drying; The weak acid solution of carbon source nitrite comprises a carbon source, nitrite and a weak acid in a mass ratio of 2-4:1-2:

1.

9. The method for preparing a biochar suspension carrier with synchronous short-range nitrification and denitrification functions according to claim 8, characterized in that: The coating time in step 7 is 5-10 minutes.

10. The method for preparing a biochar suspension carrier with synchronous short-range nitrification and denitrification functions according to claim 8, characterized in that: The temperature of high temperature extrusion molding in step 4 is 160-240°C; The vacuum negative pressure condition in step 5 is -0.02~-0.25MPa.

11. The method for preparing a biochar suspension carrier with synchronous short-range nitrification and denitrification functions according to claim 8, characterized in that: The diameter of the cylindrical particles in step 3 is 3-5 mm; In step 7, the product is dried at 60-80°C or air-dried under natural conditions.

12. The method for preparing a biochar suspension carrier with synchronous short-range nitrification and denitrification functions according to claim 8, characterized in that: The preparation method of the modified biochar comprises the following steps: (1) The biomass powder is sieved through a 100-mesh sieve and then dried at 60-80°C for 2-12 hours; (2) Pyrolyzing the dried biomass powder at 500-700°C for 60-120 minutes to prepare powdered biochar; (3) Soak the powdered biochar in a 0.05-0.3 mol / L sodium hypochlorite solution for 2-4 hours, stirring during the soaking process to maintain a uniform state of the biochar mixture; (4) Soak the powdered biochar in a 0.1-0.35 mol / L potassium hydroxide solution for 2-4 hours, stirring during the soaking process to maintain a uniform state of the biochar mixture; (5) After biochar modification, wash with distilled water 1-3 times until the pH value of the biochar solution is 6.0-8.0; (6) After the pH of the biochar solution returns to neutral, it is filtered through an 80-200 mesh sieve and the filter residue is dried at 60-80°C.

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