Attapulgite-sulfur autotrophic denitrification composite filler, preparation method and application thereof

Abstract

This invention relates to the field of new water treatment materials and engineering ecological environmental protection technology, and discloses an attapulgite-sulfur autotrophic denitrification composite packing, its preparation method, and its application. The preparation method includes: Step S1: mixing elemental sulfur powder, carbonate mineral powder, attapulgite clay, and a composite pore-forming agent to obtain a homogeneous matrix powder; Step S2: hot-melting and mixing the homogeneous matrix powder to obtain a composite melt; Step S3: sequentially cooling, solidifying, and granulating the composite melt to obtain porous composite particles; Step S4: subjecting the porous composite particles to a short-time heat treatment at 120-128℃ for 10-20 minutes, and obtaining the attapulgite-sulfur autotrophic denitrification composite packing after cooling. The composite packing provided by this invention has a low water contact angle, a biofilm start-up time of 11-18 days, a stable total nitrogen removal rate of over 90%, a backwashing cycle of over 30 days, and maintains intact particle shape after 180 days of operation.

Description

Technical Field

[0001] This invention relates to the field of new water treatment materials and engineering ecological environmental protection technology, specifically to an attapulgite-sulfur autotrophic denitrification composite filler, its preparation method, and its application. Background Technology

[0002] With the continuous tightening of water pollutant discharge standards in my country and the full implementation of ultra-low emission limits for wastewater treatment plants across the country, the deep removal of nitrate nitrogen from municipal sewage effluent and industrial wastewater has become a critical issue that urgently needs to be addressed in the water treatment industry. The removal of nitrate nitrogen from wastewater mainly relies on microbial denitrification. Traditional heterotrophic denitrification technologies require the addition of organic carbon sources such as sodium acetate, methanol, or glucose as electron donors. This approach not only involves continuous reagent procurement and dosage costs, but also generates a large amount of greenhouse gases during the metabolism of the added carbon source.

[0003] Sulfur autotrophic denitrification technology, with its unique metabolic mechanism, uses solid elemental sulfur as an electron donor and nitrate nitrogen as an electron acceptor to reduce nitrates without the need for an external organic carbon source. It is considered an alternative denitrification technology with low carbon emissions and low operating costs, and has received widespread attention in recent years.

[0004] Currently, the packing materials used in sulfur autotrophic denitrification reactors mainly take the following forms: pure sulfur granules or block sulfur; sulfur granules physically mixed with carbonate minerals such as limestone and dolomite in a certain proportion; and composite packing materials made by pressing or extrusion molding with sulfur as the matrix and adding a small amount of binder or skeleton material. The above technical solutions have the following technical challenges in practical engineering applications.

[0005] The strong hydrophobic properties of elemental sulfur make it difficult for autotrophic denitrifying bacteria to attach effectively, resulting in a reactor biofilm formation start-up period of several weeks. During the reaction, the hydrogen ions continuously released by sulfur oxidation and the neutralization reaction with carbonate alkalinity cannot achieve kinetic matching in the micro-regions due to the large-scale spatial separation of sulfur and carbonate particles in the bed. This leads to severe local acidification, inhibits denitrifying enzyme activity, and causes the accumulation of nitrite nitrogen. At the same time, sulfur and carbonate, as consumable components, gradually dissolve during long-term operation, deteriorating the mechanical strength of the packing. Under the shear of water flow, the packing is crushed and muddied, and the debris fills the bed pores, causing a sharp increase in head loss and frequent caking and blockage. The existing preparation process has low porosity due to compression molding, sulfur loss due to high-temperature calcination, insufficient packing strength due to wet granulation, and lack of systematic optimization of particle size design. It is difficult to balance high specific surface area and low head loss, and the above problems cannot be solved simultaneously at the intrinsic material level.

[0006] Therefore, developing a novel sulfur autotrophic denitrification composite packing material and its preparation method that can simultaneously solve the above-mentioned multiple technical bottlenecks is of great significance for promoting the engineering application of sulfur autotrophic denitrification technology. Summary of the Invention

[0007] This invention aims to overcome multiple problems existing in the current sulfur autotrophic denitrification packing technology, such as slow hydrophobic biofilm formation, micro-region acid-base imbalance, structural collapse and blockage after consumption, and imperfect preparation process.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing attapulgite-sulfur autotrophic denitrification composite packing, comprising the following steps: Step S1: Mix elemental sulfur powder, carbonate mineral powder, attapulgite clay, and composite pore-forming agent to obtain a homogeneous matrix powder. Step S2: The homogeneous matrix powder is hot-melted and mixed to obtain a composite melt; Step S3: The composite melt is sequentially cooled, solidified, and granulated to obtain porous composite particles; Step S4: Perform a short-time heat treatment on the porous composite particles at 120-128℃ for 10-20 min, and after cooling, the attapulgite-sulfur autotrophic denitrification composite filler is obtained. The attapulgite-sulfur autotrophic denitrification composite filler has a particle size of 5-25 mm and a porosity of not less than 40%. In step S1, based on the total weight of the attapulgite-sulfur autotrophic denitrification composite filler being 100wt%, the percentage of elemental sulfur powder is 20-35wt%, the percentage of carbonate mineral powder is 40-65wt%, the percentage of attapulgite clay is 10-30wt%, and the percentage of composite pore-forming agent is 0.5-5wt%.

[0009] The second aspect of the present invention provides a method for preparing an attapulgite-sulfur autotrophic denitrification composite packing obtained by the preparation method described in the first aspect. The attapulgite-sulfur autotrophic denitrification composite packing is a porous granular material with a particle size of 5-25 mm and a porosity of not less than 40%.

[0010] The third aspect of the present invention provides the application of the attapulgite-sulfur autotrophic denitrification composite packing described in the second aspect in wastewater treatment, wherein the composite packing is filled in a fixed bed or expanded bed sulfur autotrophic denitrification reactor for removing nitrate nitrogen from municipal sewage effluent, industrial wastewater or surface water.

[0011] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention utilizes the intrinsic hydrophilicity of the high-density silanol groups on the surface of attapulgite clay crystals to significantly reduce the water contact angle of the composite filler surface from over 70° in traditional sulfur fillers to below 45°, shortening the biofilm initiation time to 11-18 days. This solves the engineering problem of the strong hydrophobicity of elemental sulfur making it difficult for bacteria to attach and colonize.

[0012] 2. This invention establishes a precise calculation formula for carbonate dosage. Based on reaction stoichiometry and introducing a self-buffering margin coefficient of 0.8-2.0, it enables the acid release and alkalinity neutralization to achieve kinetic matching at the microscale, effectively avoiding local acidification (pH can be maintained near neutral), and the total nitrogen removal rate can be stably maintained at over 90%.

[0013] 3. This invention uses attapulgite as a non-consumable inorganic rigid skeleton, which can maintain the integrity of the packing space geometry even after the active components are gradually consumed, fundamentally preventing particle crushing, mud formation and bed caking and blockage. The backwashing cycle is significantly extended from 3-5 days for traditional packing to more than 30 days, solving the core problem of the engineering application of sulfur autotrophic denitrification technology.

[0014] 4. This invention employs a low-temperature hot-melt extrusion process to achieve integrated composite of sulfur-carbonate-attapulgite three-phase microscale. Combined with a synergistic design of 5-25 mm particle size and a porosity of not less than 40%, it balances high biomass attachment, efficient mass transfer, and low head loss. Furthermore, it eliminates the need for external organic carbon sources, avoiding reagent costs and greenhouse gas emissions, making it a low-carbon and green deep denitrification technology. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] As mentioned above, the first aspect of the present invention provides a method for preparing attapulgite-sulfur autotrophic denitrification composite packing, comprising the following steps: Step S1: Mix elemental sulfur powder, carbonate mineral powder, attapulgite clay, and composite pore-forming agent to obtain a homogeneous matrix powder. Step S2: The homogeneous matrix powder is hot-melted and mixed to obtain a composite melt; Step S3: The composite melt is sequentially cooled, solidified, and granulated to obtain porous composite particles; Step S4: Perform a short-time heat treatment on the porous composite particles at 120-128℃ for 10-20 min, and after cooling, the attapulgite-sulfur autotrophic denitrification composite filler is obtained. The attapulgite-sulfur autotrophic denitrification composite filler has a particle size of 5-25 mm and a porosity of not less than 40%. In step S1, based on the total weight of the attapulgite-sulfur autotrophic denitrification composite filler being 100wt%, the percentage of elemental sulfur powder is 20-35wt%, the percentage of carbonate mineral powder is 40-65wt%, the percentage of attapulgite clay is 10-30wt%, and the percentage of composite pore-forming agent is 0.5-5wt%.

[0017] Preferably, in step S1, the mixing time is 20-40 min.

[0018] In a preferred embodiment, the amount of carbonate mineral powder used in step S1 is determined according to formula (I): M 碳酸盐 =M 硫粉 ×1.82×f / ω Equation (I); In equation (I), M 碳酸盐 M represents the mass of the carbonate mineral powder used. 硫粉 1.82 is the mass of the elemental sulfur powder used, 1.82 is the theoretical acid-base neutralization mass ratio derived from the sulfur autotrophic denitrification reaction equation, f is the self-buffering margin coefficient with a value range of 0.8-2.0, and ω is the mass percentage of effective carbonate components in the carbonate mineral powder.

[0019] It should be noted that in this invention, when the value of the self-buffering margin coefficient f is above 1.0, it indicates an excessive addition of carbonate mineral powder; when it is below 1.0, it indicates a theoretically insufficient amount of carbonate mineral powder, in order to verify the reliability of the boundary of the proportion range.

[0020] According to a preferred embodiment, in step S1, the carbonate mineral powder is at least one of dolomite powder, limestone powder, and oyster shell powder, and the particle size is 150-15 μm.

[0021] In a preferred embodiment, in step S1, the attapulgite clay is natural magnesium-rich palygorskite mineral powder with a particle size of 150-38 μm.

[0022] According to a preferred embodiment, in step S1, the composite pore-forming agent is at least one of sodium bicarbonate, stearic acid, anhydrous ethanol, and polyethylene glycol.

[0023] In a preferred embodiment, in step S1, the purity of the elemental sulfur powder is >99%, and the particle size is 150-48 μm.

[0024] It should be noted that in this invention, the term "particle size" refers to the average value of the equivalent sphere diameter distribution based on volume (D[4,3]) measured by laser diffraction.

[0025] Preferably, in step S2, the temperature of the hot melt mixing is 115-130°C.

[0026] Preferably, in step S3, the cooling and curing is carried out by air cooling, and the cooling rate is 5-15℃ / min.

[0027] The second aspect of the present invention provides a method for preparing an attapulgite-sulfur autotrophic denitrification composite packing obtained by the preparation method described in the first aspect. The attapulgite-sulfur autotrophic denitrification composite packing is a porous granular material with a particle size of 5-25 mm and a porosity of not less than 40%.

[0028] In a preferred embodiment, the water contact angle on the surface of the attapulgite-sulfur autotrophic denitrification composite packing is ≤45°.

[0029] The third aspect of the present invention provides the application of the attapulgite-sulfur autotrophic denitrification composite packing described in the second aspect in wastewater treatment, wherein the composite packing is filled in a fixed bed or expanded bed sulfur autotrophic denitrification reactor for removing nitrate nitrogen from municipal sewage effluent, industrial wastewater or surface water.

[0030] In preferred embodiment, after the attapulgite-sulfur autotrophic denitrification composite packing is filled in the reactor, no external organic carbon source is required. It utilizes elemental sulfur as an electron donor for autotrophic denitrification. The reactor start-up biofilm formation time is 11-18 days, and the total nitrogen removal rate is stably maintained at over 90%. During long-term operation, the packing particles maintain their spatial geometry intact, and the reactor backwashing cycle is ≥30 days.

[0031] The present invention will be described in detail below through examples. Unless otherwise specified, the raw materials used are all commercially available products.

[0032] In the following examples, unless otherwise specified, "room temperature" means a temperature of 20-28℃.

[0033] In the following examples, unless otherwise specified, each “parts by weight” means 10g.

[0034] In the following examples, unless otherwise specified, the particle size refers to the average value of the equivalent sphere diameter distribution based on volume (D[4,3]) measured by laser diffraction.

[0035] Elemental sulfur powder: purity >99%, particle size 75 μm; Carbonate mineral powder: Dolomite powder, with an effective carbonate component mass percentage of 76% and a particle size of 38 μm; Attapulgite clay: It is a natural magnesium-rich palygorskite mineral powder with a purity of 76% and a particle size of 75μm; Composite pore-forming agent: sodium bicarbonate.

[0036] Porosity determination: Referring to GB / T 21650.1-2026 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Porosimetry and Gas Adsorption Methods - Part 1: Mercury Porosimetry", the porosity of the filler was determined using the mercury porosimetry method. The specific procedure was as follows: After drying the filler sample in an oven at 105℃ to constant weight, an AutoPore IV 9500 mercury porosimeter (Micromeritics, USA) was used for measurement. The test pressure range was 0.01-200 MPa, and the percentage of the internal void volume to the total apparent volume of the filler was recorded. Three parallel samples were taken from each group of samples, and the average value of the results was used.

[0037] Water contact angle determination: Referring to GB / T 30447-2013 "Method for Measuring Contact Angle of Nanofilms", the water contact angle of the filler surface was determined using the seated drop method. The specific procedure was as follows: The filler sample was cut into a flat surface and placed on the sample stage of a JC2000D contact angle measuring instrument (Shanghai Zhongchen Digital Technology Equipment Co., Ltd.). Approximately 4 μL of deionized water was dropped onto the sample surface using a micro-syringe. During the droplet spreading, continuous photography was taken at a speed of not less than 2 frames / s. Five photographs were taken within the contact time range of 55-65 s. The liquid-solid interface contact angle was calculated using the spherical calculation method, and the arithmetic mean was taken. Measurements were taken at 5 different locations for each sample group, and the arithmetic mean was taken as the final water contact angle.

[0038] Example 1

[0039] This embodiment illustrates the method for preparing attapulgite-sulfur autotrophic denitrification composite packing provided by the present invention. Referring to the dosages and parameters in Table 1, the method comprises the following steps: Step S1: At room temperature, weigh out elemental sulfur powder, carbonate mineral powder, attapulgite clay and composite pore-forming agent according to the ratio, and mix them in a mixer for 30 minutes to obtain a homogeneous matrix powder. Step S2: The homogeneous matrix powder is fed into an extruder for hot melt mixing. The temperature is controlled at 125°C, so that elemental sulfur melts and microscopically coats and impregnates the fibrous pores of attapulgite and the surface of carbonate minerals to obtain a composite melt. Step S3: The composite melt is subjected to cooling solidification and granulation in sequence: First, the composite melt is extruded into a continuous strip through an extruder die, and then cooled and solidified by air cooling. Subsequently, it is granulated by a granulator to obtain porous composite particles with a particle size of 10 mm and a porosity of not less than 40%. Step S4: Place the porous composite particles in an oven and perform a short-time heat treatment at 120°C for 15 minutes. Cool to room temperature to obtain the attapulgite-sulfur autotrophic denitrification composite filler, named P1. The amount of carbonate mineral powder used is determined according to formula (I): M 碳酸盐 =M 硫粉 Equation (I) is given by: ×1.82×f / ω, where the self-buffering margin coefficient f is 0.8 and ω is 0.76.

[0040] Examples 2 and 3

[0041] The method is similar to that in Example 1, except that the amount of elemental sulfur powder used in step S1 is different, as detailed in Table 1. Finally, the attapulgite-sulfur autotrophic denitrification composite packings obtained in Examples 2 and 3 were named P2 and P3, respectively.

[0042] Examples 4-7

[0043] The same method as in Example 1 was used, except that in step S3, by changing the extrusion die with different apertures and adjusting the particle size of the granulation, the particle size of the final attapulgite-sulfur autotrophic denitrification composite filler was different, as detailed in Table 1. Finally, the attapulgite-sulfur autotrophic denitrification composite packings obtained in Examples 4-7 were named P4, P5, P6, and P7, respectively.

[0044] Example 8

[0045] The same method as in Example 1 was used, except that the amount of each substance was different in step S1, and the particle size of the granulation was adjusted by changing the extrusion die with different pore sizes, so that the particle size of the final attapulgite-sulfur autotrophic denitrification composite filler was 15 mm. See Table 1 for details. Finally, the attapulgite-sulfur autotrophic denitrification composite packing was obtained and named P8.

[0046] The water contact angle of P8 was measured to be 42.7°.

[0047] Examples 9 and 10

[0048] The method is similar to that in Example 8, except that the amount of attapulgite clay used in step S1 is different, as detailed in Table 1. Finally, the attapulgite-sulfur autotrophic denitrification composite packings obtained in Examples 9 and 10 were named P9 and P10, respectively.

[0049] The water contact angles of P9 and P10 were measured to be 32.1° and 25.6°, respectively.

[0050] Comparative Example 1 The method is similar to that in Example 1, except that the amount of elemental sulfur powder used in step S1 is different, as detailed in Table 1. Finally, the attapulgite-sulfur autotrophic denitrification composite packing was obtained and named DP1.

[0051] Comparative Examples 2-4 The same method as in Example 1 was used, except that in step S3, by changing the extrusion die with different apertures and adjusting the particle size of the granulation, the particle size of the final attapulgite-sulfur autotrophic denitrification composite filler was different, as detailed in Table 1. Finally, the attapulgite-sulfur autotrophic denitrification composite packings obtained in Comparative Examples 2-4 were named DP2, DP3, and DP4, respectively.

[0052] Comparative Examples 5 and 6 The method is similar to that in Example 1, except that the amount of attapulgite clay used in step S1 is different, as detailed in Table 1. Finally, the attapulgite-sulfur autotrophic denitrification composite packings obtained in Comparative Examples 5 and 6 were named DP5 and DP6, respectively.

[0053] The water contact angles of DP5 and DP6 were measured to be 70.6° and 18.9°, respectively.

[0054] Comparative Example 7 The method is similar to that in Example 1, except that the amount of elemental sulfur powder used in step S1 is different, as detailed in Table 1. Finally, the obtained attapulgite-sulfur autotrophic denitrification composite packing was named DP7.

[0055] Table 1

[0056] Note: In the table, "particle size" and "porosity" refer to the particle size and porosity of the attapulgite-sulfur autotrophic denitrification composite packing, respectively.

[0057] Table 1 (continued)

[0058] Note: In the table, "particle size" and "porosity" refer to the particle size and porosity of the attapulgite-sulfur autotrophic denitrification composite packing, respectively.

[0059] Test Example 1 This application example tests the denitrification performance of the attapulgite-sulfur autotrophic denitrification composite packing prepared in the above examples for use in a fixed-bed sulfur autotrophic denitrification reactor, including: The test packing material was loaded into a fixed-bed sulfur autotrophic denitrification reactor (effective volume 2 L, packing height 60 cm) to simulate nitrate wastewater (NO3). - NO3- concentration approximately 50 mg / L, pH 7.0-7.5) Continuous influent, hydraulic retention time (HRT) controlled at 4 h. NO3- in the effluent is measured every 24 h. - -N concentration, as measured by NO3 in effluent for 3 consecutive days - A stable NO removal rate of 80% or higher is considered a successful biofilm formation. The number of days required to achieve successful biofilm formation is recorded as the start-up biofilm formation time. After the reactor is running stably, the NO3 content in the influent and effluent is measured. - -N, NO2 - -N concentration was used to calculate the total nitrogen (TN) removal rate. The pH value of the effluent was monitored daily, and the change in head loss of the packing layer was recorded. The backwashing trigger condition was set when the head loss increased to twice the initial value. The number of days between two consecutive backwashes was recorded as the backwashing cycle, which is the clogging cycle.

[0060] Record the start-up biofilm formation time, the biomass attached to the packing surface when biofilm formation is successful, and the stability of the packing particle structure after 180 days of long-term operation. Some results are shown in Table 2.

[0061] The biomass adhering to the packing material surface was determined using a protein method. The specific procedure was as follows: After the reactor was running stably, approximately 5 g of packing material samples were taken from both the top and bottom of the packing layer, placed in 50 mL centrifuge tubes, and 25 mL of extraction solution was added. The samples were then processed in a cell disruptor for 3 min, filtered, and the protein content was determined using a Lowry reagent kit. Biomass was expressed as the amount of protein per gram of dry packing material (mg / g). Three parallel samples were taken from each group, and the average value of the results was used.

[0062] Table 2

[0063] Note: "-" indicates that it has not been tested.

[0064] Table 2 (continued)

[0065] Note: "-" indicates that it has not been tested.

[0066] The results showed that when the amount of elemental sulfur powder was in the range of 20-35 wt%, the porosity of the packing material remained stable above 40%, and the reactor could successfully complete biofilm formation and start-up within 14-18 days. During stable operation, the total nitrogen removal rate remained stable above 90%. When the amount of elemental sulfur powder was as low as 10 wt%, the system lacked sufficient electron donors, resulting in lower nitrogen removal performance, a start-up time extended to 22 days, and lower biomass. When the amount of elemental sulfur powder was as high as 50 wt%, the surface of the composite material was again covered by excessive sulfur, exhibiting the strong hydrophobic properties of elemental sulfur again. The start-up biofilm formation time deteriorated to 34 days, and due to severe dilution of carbonates and the porous framework, the system experienced localized acidification and physical fragmentation and collapse of the packing material during operation.

[0067] When the particle size of the attapulgite-sulfur autotrophic denitrification composite packing is within the range of 5-25 mm, and the porosity of the packing product can reach >40%, the abundant internal pores and suitable particle spacing work together to generate nitrogen microbubbles that can quickly desorb and disperse. The aged biofilm can also naturally detach, significantly extending the backwashing cycle from the traditional 3-5 days for fine-particle-size (1 mm) filters to over 30 days (74-113 days for 20 mm particles and over 90 days for 25 mm particles), completely solving the chronic problem of easy caking in pure sulfur filters. When the particle size is too large (30, 35 mm), although there is no risk of clogging, the small specific surface area leads to hindered mass transfer, significantly reduced biomass, and a substantial decrease in denitrification efficiency.

[0068] When the dosage of attapulgite clay is controlled within the range of 10-30 wt%, the high-density silanol groups on its crystal surface rapidly reduce the water contact angle of the packing surface from a hydrophobic state (70.6°) to a strongly hydrophilic region below 45°. The biofilm formation start-up time of the reactor is controlled within the optimal engineering window of 12-18 days, which is more than 50% shorter than the 37 days when the dosage is 0 wt%. When the dosage of attapulgite reaches 40 wt%, although the hydrophilicity and start-up time are further optimized (the water contact angle drops to 18.9° and the start-up time is shortened to 11 days), excessive addition will severely dilute the proportion of effective reactants such as elemental sulfur and carbonates, resulting in a significant decrease in the denitrification load per unit volume, which cannot meet the engineering design requirements for high-load deep denitrification. Insufficient addition (<10 wt%) cannot effectively improve the hydrophobic properties, and the packing is prone to crushing and collapse.

[0069] In summary, the composite packing provided by this invention can significantly reduce the water contact angle on the packing surface within a specific formulation range, greatly shortening the biofilm formation start-up time compared to traditional pure sulfur packing, and maintaining a stable total nitrogen removal rate of over 90%. At the same time, thanks to the inorganic skeleton support of attapulgite, the packing maintains its shape intact during 180 days of long-term operation, and the backwashing cycle is significantly extended to over 30 days compared to traditional packing, completely solving the engineering pain points of slow biofilm formation, easy acidification, and easy caking of sulfur autotrophic denitrification packing.

[0070] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing an attapulgite-sulfur autotrophic denitrification composite packing, characterized in that, Includes the following steps: Step S1: Mix elemental sulfur powder, carbonate mineral powder, attapulgite clay, and composite pore-forming agent to obtain a homogeneous matrix powder. Step S2: The homogeneous matrix powder is hot-melted and mixed to obtain a composite melt; Step S3: The composite melt is sequentially cooled, solidified, and granulated to obtain porous composite particles; Step S4: Perform a short-time heat treatment on the porous composite particles at 120-128℃ for 10-20 min, and after cooling, the attapulgite-sulfur autotrophic denitrification composite filler is obtained. The attapulgite-sulfur autotrophic denitrification composite filler has a particle size of 5-25 mm and a porosity of not less than 40%. In step S1, based on the total weight of the attapulgite-sulfur autotrophic denitrification composite filler being 100wt%, the percentage of elemental sulfur powder is 20-35wt%, the percentage of carbonate mineral powder is 40-65wt%, the percentage of attapulgite clay is 10-30wt%, and the percentage of composite pore-forming agent is 0.5-5wt%.

2. The preparation method according to claim 1, characterized in that, In step S1, the amount of carbonate mineral powder is determined according to formula (I): M 碳酸盐 =M 硫粉 ×1.82×f / ω Formula (I); In equation (I), M 碳酸盐 M represents the mass of the carbonate mineral powder used. 硫粉 1.82 is the mass of the elemental sulfur powder used, 1.82 is the theoretical acid-base neutralization mass ratio derived from the sulfur autotrophic denitrification reaction equation, f is the self-buffering margin coefficient with a value range of 0.8-2.0, and ω is the mass percentage of effective carbonate components in the carbonate mineral powder.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, the purity of the elemental sulfur powder is >99%, and the particle size is 150-48 μm.

4. The preparation method according to claim 1 or 2, characterized in that, In step S1, the carbonate mineral powder is at least one of dolomite powder, limestone powder, and oyster shell powder, and the particle size is 150-15 μm.

5. The preparation method according to claim 1 or 2, characterized in that, In step S1, the attapulgite clay is natural magnesium-rich palygorskite mineral powder with a particle size of 150-38 μm.

6. The preparation method according to claim 1 or 2, characterized in that, In step S1, the composite pore-forming agent is at least one of sodium bicarbonate, stearic acid, anhydrous ethanol, and polyethylene glycol.

7. An attapulgite-sulfur autotrophic denitrification composite packing, characterized in that, The attapulgite-sulfur autotrophic denitrification composite filler, prepared by any one of claims 1 to 6, is a porous granular material with a particle size of 5-25 mm and a porosity of not less than 40%.

8. The attapulgite-sulfur autotrophic denitrification composite packing according to claim 7, characterized in that, The water contact angle on the surface of the attapulgite-sulfur autotrophic denitrification composite packing is ≤45°.

9. The application of the attapulgite-sulfur autotrophic denitrification composite packing as described in claim 7 or 8 in wastewater treatment, characterized in that, The composite packing material is packed into a fixed-bed or expanded-bed sulfur autotrophic denitrification reactor to remove nitrate nitrogen from municipal sewage effluent, industrial wastewater or surface water.

10. The application according to claim 9, characterized in that, After the attapulgite-sulfur autotrophic denitrification composite packing is filled in the reactor, no external organic carbon source is required. It uses elemental sulfur as an electron donor for autotrophic denitrification. The reactor start-up biofilm formation time is 11-18 days, and the total nitrogen removal rate is stably maintained at over 90%. During long-term operation, the packing particles maintain their spatial geometry intact, and the reactor backwashing cycle is ≥30 days.

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