Preparation method and application of a suspended sulfur autotrophic denitrification carrier

Abstract

The application relates to the technical field of water treatment, and discloses a preparation method of a suspended sulfur autotrophic denitrification carrier, which comprises the following steps: mixing a sulfur source material and a carrier skeleton material according to a mass ratio of 1:0.5 to 2.0, wherein the sulfur source material comprises elemental sulfur or pyrite powder, and the carrier skeleton material comprises cordierite, biochar or porous resin; adding a binder and an additive to the mixed material, wherein the binder is silicate cement, aluminum phosphate or polyvinyl alcohol, the additive comprises ferroferric oxide and mercapto-polyethylene glycol mercapto-pyridine, the ferroferric oxide accounts for 2% to 5% of the total mass of raw materials, and the mass ratio of the mercapto-polyethylene glycol mercapto-pyridine to the sulfur source material is 1:11 to 19; and adding deionized water to stir to form a slurry. The purpose of the preparation method of the suspended sulfur autotrophic denitrification carrier is to solve the problems of an existing sulfur autotrophic carrier, such as excessively large density, limited application scenarios caused by incapability of being suspended, low treatment efficiency and complex use and maintenance.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a method for preparing a suspended sulfur autotrophic denitrification carrier and its application. Background Technology

[0002] Sulfate autotrophic denitrification refers to the process by which specific autotrophic microorganisms use reduced sulfur, such as sodium thiosulfate, elemental sulfur, and pyrite, as electron donors to gradually reduce nitrate nitrogen to nitrogen gas. Compared to traditional heterotrophic denitrification technology, it does not require the addition of additional organic carbon sources, reducing operating costs and effectively avoiding secondary pollution problems caused by improper carbon source addition. Furthermore, this technology produces relatively less sludge, greatly reducing the burden of subsequent sludge treatment.

[0003] Currently, sulfur autotrophic denitrification carrier materials are mostly mixtures of sulfur and alkaline substances such as limestone, which are often obtained by high-temperature melting and mixing followed by cooling and molding. Although sulfur autotrophic denitrification technology shows good application prospects, it still faces some problems that urgently need to be solved:

[0004] Firstly, the application scenarios are limited: due to the high density of materials such as sulfur and limestone, the bulk density of the prepared composite carrier is usually greater than 1000 kg / m³. 3 Its specific gravity is greater than that of water, and its high carrier density limits its application scenarios. It can generally only be used in fixed bed filters or integrated equipment, and it is difficult to directly add it to conventional anoxic ponds. This limits the application of sulfur autotrophic denitrification technology in the renovation of existing sewage treatment plants.

[0005] Secondly, the mass transfer efficiency is low: the carrier sinks and accumulates at the bottom of the reactor, resulting in insufficient contact with the wastewater, which leads to a decrease in mass transfer efficiency and affects the denitrification efficiency.

[0006] Third, operation and maintenance are inconvenient: Once the carrier in the fixed bed reactor is filled, it is difficult to replace or replenish it. When the carrier becomes caked or the biofilm is too thick, it needs to be backwashed or replaced, which increases the operation and maintenance costs and difficulties. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of existing sulfur autotrophic carriers having excessive density, inability to be suspended, resulting in limited application scenarios, low processing efficiency, and complex use and maintenance. The invention proposes a method for preparing a suspended sulfur autotrophic denitrification carrier and its application.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0009] A method for preparing a suspended sulfur autotrophic denitrification carrier includes the following steps:

[0010] S10. The sulfur source material and the carrier skeleton material are mixed at a mass ratio of 1:0.5 to 2.0. The sulfur source material includes elemental sulfur or pyrite powder, and the carrier skeleton material includes cordierite, biochar or porous resin.

[0011] S20. Add a binder and additives to the mixed material. The binder is silicate cement, aluminum phosphate, or polyvinyl alcohol. The additives include iron oxide and mercaptopolyethylene glycol mercaptopyridine. The iron oxide accounts for 2% to 5% of the total mass of the raw materials. The mass ratio of mercaptopolyethylene glycol mercaptopyridine to the sulfur source material is 1:11 to 19.

[0012] S30. Add deionized water and stir to form a slurry, wherein the amount of deionized water is 8% to 12% of the total mass of the raw materials;

[0013] S40. The slurry is prepared into particles with a particle size of 3 to 5 mm by extrusion molding or granulation.

[0014] S50. Dry the particles at 50 to 60°C for 8 to 12 hours. Before drying, spray with a 5% NaHCO3 solution to make the carrier porosity reach 40% to 60%.

[0015] Based on the above technical solution, the present invention can be further improved as follows.

[0016] Furthermore, when the sulfur source material is elemental sulfur, the particle size is greater than 200 mesh; when it is pyrite powder, the particle size is 70 to 120 mesh. Before mixing the sulfur source material with the carrier skeleton material, it needs to be preheated at 80 to 100°C for 1 to 2 hours to improve the bonding performance between the materials.

[0017] Furthermore, when the carrier skeleton material is cordierite, it needs to be ball-milled first for 2 to 4 hours at a speed of 300 to 500 revolutions per minute.

[0018] Furthermore, the binder is a mixture of silicate cement and gypsum in a mass ratio of 3:1 to 5:1, and the gypsum provides calcium to promote microbial growth.

[0019] Furthermore, the mercaptopolyethylene glycol mercaptopyridine in the additive has a molecular weight of 600 to 2000, an aqueous solution concentration of 0.5% to 2%, and is mixed with the raw materials for 30 to 60 minutes in step S20.

[0020] Furthermore, in S40, the extrusion molding pressure is 5 to 10 MPa, and the granulator speed is 200 to 300 rpm, forming a porous surface structure.

[0021] Furthermore, in S50, after drying, a water spraying drying process is performed, with the number of water sprayings being 2 to 3 times, and the amount of water sprayed each time being 2% to 5% of the particle mass, in order to enhance mechanical strength.

[0022] Furthermore, the carrier skeleton material also includes a slow-release carbon source, which is butylene terephthalate or chitin, accounting for 10% to 30% of the total mass of the raw materials, so as to simultaneously provide a heterotrophic denitrification carbon source.

[0023] Furthermore, the preparation process also includes the step of inoculating Thiobacillus denitrificans SZG-SAD-004 bacterial suspension, with preservation number CCTCCNo.2023992. The amount of bacterial suspension sprayed is 3% to 8% of the particle mass, and after spraying, it is incubated at 25 to 30°C for 24 to 48 hours.

[0024] An application of a suspended sulfur autotrophic denitrification carrier for deep denitrification in wastewater treatment involves the following steps: The carrier is loaded into an upflow anaerobic reactor, with the loading volume occupying 1 / 3 of the reactor's effective volume; sludge rich in sulfur autotrophic bacteria is inoculated, with an inoculation amount of 10% to 15% of the reactor's effective volume; the hydraulic retention time is controlled at 1 to 4 hours; the influent nitrate concentration is 20 to 100 mg / L; the temperature is 20 to 35℃; and the pH value is 6.5 to 8.0, achieving a nitrate nitrogen removal rate of ≥85%.

[0025] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0026] 1. This invention utilizes lightweight carrier skeleton materials such as cordierite, biochar, and porous resin, combined with a process of spraying NaHCO3 solution before low-temperature drying at 50-60℃, to achieve a carrier porosity of 40%-60%. The high porosity significantly reduces the carrier's bulk density. Simultaneously, the introduction of ferric oxide in the additives can assist the carrier's dispersion in wastewater through magnetic properties. Combined with a small particle size design of 3-5mm, the carrier achieves excellent suspension characteristics, no longer limited to fixed-bed filters or integrated equipment, and can be directly added to conventional anoxic tanks, greatly expanding the application scenarios of sulfur autotrophic denitrification technology in the renovation of existing wastewater treatment plants.

[0027] 2. The carrier skeleton material itself has a porous structure, with a high porosity of 40%-60% and a small particle size of 3-5mm, providing a large number of attachment sites for microorganisms. The suspended state of the carrier allows it to have more sufficient contact with wastewater, which greatly improves mass transfer efficiency and denitrification efficiency.

[0028] 3. In terms of operation and maintenance, this preparation method uses extrusion molding or granulation to prepare particles, which is simple and does not require high-temperature melting. Furthermore, the carrier, through the bonding of binders (such as silicate cement or aluminum phosphate) with the skeleton material, possesses excellent mechanical properties and is not prone to caking or breakage. Combined with the simple preparation process, carrier replacement and replenishment are more convenient, reducing operation and maintenance costs and difficulties. In addition, the NaHCO3 solution sprayed before drying can serve as an alkaline reserve substance, neutralizing acidic substances produced during sulfur autotrophic denitrification, maintaining system pH stability, and ensuring microbial activity. Simultaneously, the addition of ferric oxide not only helps suspend the carrier but may also promote microbial metabolism through magnetic effects, further improving denitrification efficiency. The entire preparation process only requires drying at 50-60℃, making the process simple, energy-efficient, and highly feasible for industrial production, effectively reducing production costs. Attached Figure Description

[0029] Figure 1 This is a diagram of the suspended sulfur autotrophic carrier in Example 3 of the present invention. Detailed Implementation

[0030] 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.

[0031] This invention provides a method for preparing a suspended sulfur autotrophic denitrification carrier. Through techniques such as selecting lightweight raw materials, controlling pore structure, and microbial inoculation, the carrier achieves high-efficiency nitrogen removal performance. The detailed steps of the preparation method are as follows:

[0032] Raw material preparation and pretreatment

[0033] Sulfur source material processing

[0034] Elemental sulfur: Select elemental sulfur powder with a particle size greater than 200 mesh. If the sulfur powder clumps, it must first be sieved through a 200-mesh sieve to ensure uniform particle size. Place the sieved sulfur powder in a forced-air drying oven and preheat it at 80-100℃ for 1-2 hours to remove surface moisture and improve its bonding performance with the carrier skeleton material.

[0035] Pyrite powder: Select pyrite powder with a particle size of 70-120 mesh. Preheat at 80-100℃ for 1-2 hours to enhance the interfacial bonding between materials.

[0036] Carrier skeleton material processing

[0037] Cordierite: If cordierite is used as the carrier skeleton material, it needs to be ball-milled first. Crush the cordierite to a particle size of about 5mm, put it into a planetary ball mill, with a ball-to-material ratio of 10:1 (the ball milling media are alumina balls), a rotation speed of 300-500 rpm, and a ball milling time of 2-4 hours until the particle size reaches 100-200 mesh. The ball-milled cordierite powder needs to be passed through a 200-mesh sieve to ensure uniform particle size.

[0038] Biochar / Porous Resin: If biochar or porous resin is selected, it can be directly crushed to 100-200 mesh without ball milling.

[0039] Adhesive preparation

[0040] Portland cement and gypsum compound: Mix portland cement and gypsum in a mass ratio of 3:1 to 5:1. For example, take 3 parts portland cement and 1 part gypsum, and mix them in a high-speed mixer at 500 rpm for 10 minutes to ensure uniform mixing. The addition of gypsum not only provides calcium and sulfur to promote microbial growth, but also enhances the mechanical strength of the carrier.

[0041] Additive preparation

[0042] Iron(III) oxide: Weigh 2%-5% of the total mass of iron(III) oxide powder, disperse it in deionized water, and prepare a suspension with a concentration of 5%-10% for later use.

[0043] Mercaptopolyethylene glycol mercaptopyridine (SH-PEG-OPSS): Select mercaptopolyethylene glycol mercaptopyridine with a molecular weight of 600-2000 and prepare an aqueous solution with a concentration of 0.5%-2%. For example, take 1g of SH-PEG-OPSS (molecular weight 2000) and dissolve it in 99g of deionized water, stirring for 30 minutes until completely dissolved.

[0044] Slow-release carbon source addition

[0045] If a carbon source for heterotrophic denitrification needs to be provided simultaneously, butylene terephthalate or chitin can be added to the carrier skeleton material as a slow-release carbon source. The slow-release carbon source accounts for 10%-30% of the total mass of the raw materials. For example, 20% butylene terephthalate powder can be added to the carrier skeleton material and mixed evenly with other raw materials.

[0046] Mixing and stirring

[0047] Basic Mix

[0048] The pretreated sulfur source material and the carrier skeleton material are added to a high-speed mixer at a mass ratio of 1:0.5 to 1:2.0. For example, if elemental sulfur and cordierite are used, they are mixed in a 1:1 ratio at a stirring speed of 500 rpm for 10 minutes to ensure that the two materials are fully dispersed.

[0049] Adding adhesives and additives

[0050] Add a composite binder of silicate cement and gypsum, with the binder accounting for 10%-20% of the total mass of the raw materials. Continue stirring for 5 minutes to ensure that the binder evenly coats the surface of the sulfur source and the carrier skeleton material.

[0051] Slowly add the ferric oxide suspension while turning on the mixer at 300 rpm and stirring for 10 minutes to ensure that the ferric oxide is evenly dispersed.

[0052] Add an aqueous solution of mercapto-polyethylene glycol mercaptopyridine at a mass ratio of 1:11 to 1:19 with the sulfur source material. For example, if the sulfur source material is 100g, add 5.26-9.09g of an aqueous solution of SH-PEG-OPSS (1% concentration). Stir for 30-60 minutes to allow the additive to fully react with the raw material and form a stable three-dimensional network structure.

[0053] Slurry preparation

[0054] Adding deionized water

[0055] Add deionized water to the mixed materials, at a rate of 8%-12% of the total mass of the raw materials. For example, if the total mass of the raw materials is 1000g, add 80-120g of deionized water. Add water while stirring at a speed of 200 rpm for 15-20 minutes until a uniform slurry is formed.

[0056] Post-milling treatment of cordierite

[0057] If the carrier skeleton material is cordierite, ball milling can be performed again after the slurry preparation is completed. The slurry is transferred to a planetary ball mill, and the ball milling speed is 300 rpm for 1-2 hours to further refine the particles and improve the uniformity of the slurry.

[0058] Molding and granulation

[0059] Extrusion molding

[0060] The slurry is injected into a twin-screw extruder, and the extruder temperature is controlled at 40-50℃, with the screw speed at 20-30 rpm.

[0061] Adjust the extrusion pressure to 5-10 MPa to extrude the slurry through a die with a diameter of 3-5 mm, forming cylindrical particles.

[0062] After extrusion, the granules are left to stand in the air for 5-10 minutes to partially solidify.

[0063] Disc granulation

[0064] The slurry is fed into the disc granulator, and the disc rotates at 200-300 revolutions per minute.

[0065] Spray a small amount of water mist into the disc every 30 seconds (each spray is 2%-5% of the particle mass), so that the material gradually aggregates to form particles with a diameter of 3-5mm.

[0066] Granulation time is 30-60 minutes, until the particle surface is smooth and the particle size is uniform.

[0067] Drying and Pore Control

[0068] Pre-drying treatment

[0069] The formed granules are evenly spread on a tray and sprayed with a 5% (w / w) NaHCO3 solution. The spraying amount is such that the granule surface is moistened but not liquid-free, generally 5%-10% of the granule mass. During the subsequent drying process, NaHCO3 decomposes to produce CO2 gas, forming a porous structure inside the carrier, resulting in a porosity of 40%-60%.

[0070] Low temperature drying

[0071] Place the trays in a forced-air drying oven, set the temperature to 50-60℃, and dry for 8-12 hours. Turn the granules over every 2 hours during the drying process to ensure even heating.

[0072] Water spray drying enhances mechanical strength

[0073] The dried granules are then subjected to water spray drying:

[0074] First water spray: The amount of water sprayed should be 2%-5% of the granule mass, and the water temperature should be 25-30℃. After spraying, place the granules in a ventilated place to dry for 2 hours.

[0075] Second water spray: Repeat the above steps, using the same amount of water. After drying, place it back in the drying oven and dry at 50℃ for 2 hours.

[0076] Third water spray (optional): If further enhancement of mechanical strength is required, a third water spray can be performed, with a water volume of 2%-5%, and the drying conditions are the same as above.

[0077] Microbial inoculation

[0078] Preparation of bacterial culture

[0079] The bacterial culture of Thiobacillus denitrificans SZG-SAD-004 (CCTCC No. 2023992) was cultured in liquid medium.

[0080] Inoculation and Culture

[0081] Place the dried carrier particles in a sterile petri dish and spray with bacterial solution at a rate of 3%-8% of the particle mass. For example, spray 3-8 mL of bacterial solution onto 100 g of particles.

[0082] After spraying, gently agitate the granules to ensure even distribution of the bacterial solution. Seal the petri dish and place it in a constant temperature incubator at 25-30℃ for 24-48 hours to allow the microorganisms to fully adhere to the surface and pores of the carrier.

[0083] Finished product screening and packaging

[0084] Particle size screening

[0085] The inoculated carrier particles are passed through 3mm and 5mm sieves sequentially to select finished products with a particle size of 3-5mm. Particles that do not meet the size requirements can be returned for regranulation.

[0086] Packaging and storage

[0087] The finished product should be sealed in sterile plastic bags and stored in a cool, dry place, away from direct sunlight and humid environments. It must be protected from crushing or breakage during transportation.

[0088] Technical effects and advantages

[0089] Excellent suspension performance

[0090] By employing lightweight granulation masterbatch (such as hollow microspheres) and a porous structure design, the carrier density can be adjusted to be close to that of water (approximately 1.0-1.1 g / cm³). 3 It can achieve good suspension flow in the reactor and is not limited by the application scenario.

[0091] High-efficiency denitrification performance

[0092] Sulfur source materials act as electron donors, providing continuous chemical energy for sulfur autotrophic denitrification; slow-release carbon sources (such as butylene terephthalate) simultaneously provide carbon sources for heterotrophic denitrification, achieving a synergistic effect between autotrophic and heterotrophic denitrification.

[0093] High specific surface area (>50m²) 2 The abundant porosity (40%-60%) and rich porous structure provide numerous attachment sites for microorganisms, significantly increasing the attachment amount and activity of denitrifying thiobacilli, with a denitrification rate reaching 1.5-2.0 kgN / (m³). 3 ·d).

[0094] Good pH stability

[0095] Light calcium carbonate acts as a pH stabilizer, continuously releasing alkaline substances during the reaction process. This neutralizes the acidic substances produced by sulfur autotrophic denitrification, maintaining the system pH within the optimal range of 6.5-8.0 and preventing pH fluctuations from inhibiting microorganisms.

[0096] High mechanical strength

[0097] The synergistic effect of silicate cement and gypsum composite binder, iron oxide reinforcing agent and water spray drying treatment enables the carrier to achieve a compressive strength of 8-10 MPa, making it less prone to breakage during water flow and microbial metabolism, and its service life can reach 2-3 years.

[0098] The preparation process is simple.

[0099] The entire preparation process requires no complex equipment, the raw materials are readily available, and the industrial production cost is low. From raw material pretreatment to finished product packaging, the entire process can be completed within 12-24 hours, making it suitable for large-scale production.

[0100] The method for preparing a suspended sulfur autotrophic denitrification carrier provided by this invention achieves high-efficiency nitrogen removal performance and long-term stability of the carrier through optimized raw material selection, process parameters, and microbial inoculation technology. This method has advantages such as simple operation, low cost, and environmental friendliness, and has broad application prospects in the field of wastewater treatment.

[0101] Example 1: Preparation of a Suspended Sulfur Autotrophic Denitrification Carrier in a Sulfur-Light Calcium Carbonate-Gypsum System

[0102] Raw material preparation and pretreatment

[0103] Sulfur source material processing

[0104] 300g of elemental sulfur powder (30% of the total raw material mass) with a particle size of 200 mesh was selected and placed in a forced-air drying oven and preheated at 80℃ for 1.5 hours to remove surface adsorbed water and enhance its bonding with other materials. After pretreatment, it was passed through a 200-mesh sieve to ensure no agglomeration.

[0105] pH stabilizer treatment

[0106] Take 400g (40%) of light calcium carbonate, grind it for 30 minutes using a planetary ball mill, and pass it through a 100-mesh sieve to ensure that the particle size is within the range of 100-200 mesh, as a pH stabilizer to maintain the alkalinity of the reaction system.

[0107] Mechanical strength enhancer treatment

[0108] Weigh 200g (20%) of gypsum and grind it to 150 mesh. The process is the same as that for sulfur powder pretreatment. It serves as a mechanical strength enhancer and provides calcium and sulfur elements to promote microbial growth.

[0109] Pore-forming agent treatment

[0110] Take 20g (2%) of sodium bicarbonate and grind it to 200 mesh. Use it as a pore-forming agent to decompose and generate pores during the subsequent drying process.

[0111] Lightweight granulation masterbatch preparation

[0112] 80g (8%) of 10-mesh hollow microspheres were selected as the lightweight granulation masterbatch, with a density of 0.6g / cm³. 3 This ensures that the final density of the carrier is close to that of water.

[0113] Mixing and stirring

[0114] Pretreated sulfur powder, light calcium carbonate, gypsum, and sodium bicarbonate were added to a twin-shaft mixer and stirred for 15 minutes at a speed of 500 rpm until homogeneous. During the mixing process, an online particle size analyzer was used to monitor the particle size uniformity and ensure that the coefficient of variation was ≤5%.

[0115] Granulation

[0116] The mixed materials and 80g of hollow microspheres were fed into a disc granulator. The disc speed was set to 30 rpm, and an intermittent water spraying process was adopted: deionized water mist (water temperature 25℃) was sprayed every 30 seconds, with a single spray volume of 0.5% of the total material mass. The granulation time was 30 minutes, forming particles with an initial particle size of 1-2mm. The total spray volume was controlled to be 10% of the total raw material mass.

[0117] Particle size screening

[0118] Two-stage screening is performed using 2mm and 1mm standard sieves, retaining 1-2mm particles. The undersized fine powder is returned to the granulation process for reuse, with a screening efficiency of ≥95%.

[0119] Drying and curing

[0120] Pore ​​control pretreatment

[0121] Spray a 5% NaHCO3 solution (8% of the particle mass) evenly onto the surface of the screened particles to ensure that the solution penetrates into the particles.

[0122] High temperature curing

[0123] The granules were placed in a hot air circulating oven at 145℃ and dried for 1 hour. During the drying process, sodium bicarbonate reacted with gypsum to form calcium carbonate crystals, and sodium bicarbonate decomposed simultaneously to produce CO2 gas, resulting in a carrier porosity of 52%.

[0124] Mechanical strength enhancement

[0125] After drying, the material undergoes two water spraying treatments: the first spraying is 3% of the particle mass, and the material is air-dried for 30 minutes; the second spraying is the same amount of water, and after air-drying, the material is dried at 60℃ for 2 hours, resulting in a final carrier compressive strength of 8.5 MPa.

[0126] Performance indicators

[0127] Density: 1.03 g / cm³3 (Excellent levitation performance)

[0128] Specific surface area: 55m² 2 / g

[0129] 24-hour sulfur autotrophic denitrification rate: 1.8 kgN / (m 3 ·d)

[0130] Example 2: Preparation of a suspended sulfur autotrophic denitrification carrier in a sulfur-light calcium carbonate-kaolin system

[0131] Raw material preparation and pretreatment

[0132] Sulfur source material processing

[0133] 450g of 200-mesh elemental sulfur powder (45% of the total raw material mass) was placed in a stainless steel tray and spread into a 5mm thick layer. The tray was then placed in a forced-air drying oven at 80℃ for 1 hour. During preheating, the powder was turned over every 15 minutes to ensure even heating. After pretreatment, the powder was sieved through a 200-mesh standard sieve, with the residue controlled below 1% to ensure uniform sulfur source particle size.

[0134] pH stabilizer treatment

[0135] Weigh 300g (30%) of light calcium carbonate and perform ultrafine grinding using an air jet mill. Set the grinding pressure to 0.6MPa and the classifier speed to 3000 rpm. After processing, the material is tested by a laser particle size analyzer, and the particle size distribution is ≥98% within the 100-200 mesh range. The ground light calcium carbonate is then sealed and stored in a desiccator to prevent moisture absorption.

[0136] Mechanical strength enhancer treatment

[0137] Take 130g (13%) of kaolin as a mechanical strength enhancer, put it into a planetary ball mill, use agate balls as the grinding medium (ball-to-material ratio 5:1), rotate at 400 rpm, and ball mill for 2 hours. Then pass it through a 100-mesh sieve to ensure that the surface smoothness of the particles reaches Ra≤0.5μm, thereby enhancing the interfacial bonding force with the binder.

[0138] Pore-forming agent treatment

[0139] Weigh 20g (2%) of ammonium bicarbonate and grind it to 200 mesh using a mortar grinder. During the grinding process, add a small amount of anhydrous ethanol (5% of the material mass) to prevent clumping. After grinding, dry it in a vacuum drying oven at 60℃ for 30 minutes to remove the ethanol and use it as a pore-forming agent for later use.

[0140] Lightweight granulation masterbatch preparation

[0141] 100g (10%) of 10-mesh hollow microspheres were selected as the lightweight granulation masterbatch. These hollow microspheres are made of aluminum silicate, with a compressive strength ≥3MPa and a bulk density of 0.55g / cm³. 3 Before use, wash with deionized water three times to remove surface dust, and dry at 60℃ for later use.

[0142] Mixing and stirring

[0143] Pretreated sulfur powder, light calcium carbonate, kaolin, and ammonium bicarbonate were sequentially added to a twin-shaft paddle mixer. The feed inlet was closed, and the mixer was started at a speed of 500 rpm for 15 minutes. During mixing, a five-point sampling method (four corners and the center of the mixer) was used, with 10g samples taken every 5 minutes. The sulfur content was analyzed using X-ray fluorescence spectrometry to ensure that the sulfur content deviation at each point was ≤2% (mixing uniformity ≥90%). After mixing, the material appeared as a light gray, loose powder with no visible lumps.

[0144] Granulation

[0145] Add the mixture and 100g of hollow microspheres to the disc granulator, adjust the disc tilt angle to 45°, and set the rotation speed to 30 rpm.

[0146] A peristaltic pump is used to control the water spray rate. Deionized water is filtered through a 2μm filter element and the water temperature is controlled at 25±1℃. It is sprayed intermittently through a dual-fluid atomizing nozzle (atomizing pressure 0.2MPa): spraying once every 30 seconds. The water volume of a single spray is 0.5% of the total mass of the current material, and the total water volume is 9% of the total mass of the raw materials.

[0147] After 30 minutes of granulation, the particle size is monitored by an online image analyzer. Granulation is stopped when the proportion of 1-2mm particles is ≥90%. The particles are spherical, with a moist surface and no sticking.

[0148] Particle size screening

[0149] A two-stage screening process using a vibrating screen is employed: first, oversized particles are removed through a 2mm aperture sieve (10 mesh); then, fine powder is removed through a 1mm aperture sieve (18 mesh). The vibration frequency is set to 50Hz, the amplitude to 2mm, and the screening time to 5 minutes. Particles remaining on the sieve (1-2mm) are collected in a stainless steel tray. The undersized material (fine powder and oversized particles after crushing) is returned to the granulation process for reuse, achieving a screening efficiency of 96%.

[0150] Drying and curing

[0151] Pore ​​control pretreatment

[0152] A 5% NaHCO3 solution was uniformly sprayed onto the surface of the screened particles using a sprayer at a pressure of 0.15 MPa. The nozzle was 30 cm away from the particle surface, and the spray volume was 7% of the particle mass (7 mL of solution per 100 g of particles). After spraying, the particles were left to stand for 10 minutes to ensure that the solution completely penetrated into the pores inside the particles.

[0153] High temperature curing

[0154] The granules were placed in a hot air circulating oven, with a heating rate of 5°C / minute. After reaching 145°C, the temperature was maintained for 1 hour. During the drying process, ammonium bicarbonate and NaHCO3 synergistically decomposed, producing CO2 and NH3 gases, forming interconnected pores inside the granules. The porosity was measured to be 48% using a mercury porosimeter.

[0155] Mechanical strength enhancement

[0156] Perform three water spray drying treatments:

[0157] First time: Spray water at 2% of the particle mass (deionized water), let it air dry at room temperature for 30 minutes to form a water film on the particle surface;

[0158] Second time: Spray with the same amount of water, let it air dry, and then put it in a 60℃ oven to dry for 1 hour;

[0159] Third time: Repeat the second operation, and the final particle moisture content is ≤1%. The compressive strength is 9.0MPa when tested by a universal testing machine (test conditions: 5mm diameter indenter, loading rate 1mm / min).

[0160] Performance indicators

[0161] Density: The density was determined using the water displacement method, with an average density of 1.05 g / cm³ for 100 particles. 3 It meets the suspension requirements (±0.05g / cm³). 3 );

[0162] Specific surface area: determined by BET nitrogen adsorption method, specific surface area 53 m². 2 / g, with pore size distribution mainly concentrated in 10-50nm;

[0163] 24-hour sulfur autotrophic denitrification rate: In a static test in simulated wastewater (NO3-N concentration 40 mg / L, pH 7.0), the denitrification rate reached 1.7 kgN / (m³). 3 ·d), NO3-N removal rate 91%.

[0164] Example 3: Preparation of a suspended sulfur autotrophic denitrification carrier in a high sulfur content system

[0165] Raw material preparation and pretreatment

[0166] Sulfur source material processing

[0167] Weigh 600g of elemental sulfur (60%) with a particle size of 200 mesh, place it in a vacuum drying oven (vacuum degree -0.09MPa), and preheat at 90℃ for 2 hours. After preheating, the fluidity of the sulfur powder increases, and the angle of repose decreases from 35° to 30°, enhancing the interfacial bonding force with the carrier skeleton material. After pretreatment, pass it through a 200-mesh sieve, and control the residue on the sieve to below 0.5%.

[0168] pH stabilizer treatment

[0169] Take 200g (20%) of light calcium carbonate, crush it to less than 5mm using a jaw crusher, then grind it in a ball mill (300 rpm for 1 hour), and pass it through a 100-mesh sieve. The particle size distribution D50 = 150μm is to ensure that alkaline substances are released uniformly during the reaction.

[0170] Mechanical strength enhancer treatment

[0171] Weigh 100g (10%) of gypsum, which is calcium sulfate dihydrate (CaSO4·2H2O), grind it to 150 mesh, and then dry it with hot air (80℃, 1 hour) to remove free water, ensuring that the moisture content is ≤0.5% to avoid affecting the granulation humidity.

[0172] Pore-forming agent treatment

[0173] Take 50g (5%) of sodium bicarbonate, grind it for 3 minutes using a high-speed pulverizer (12,000 rpm), and pass it through a 200-mesh sieve. Its purity is ≥99.5%, ensuring that there are no residual impurities after decomposition that would affect the carrier performance.

[0174] Lightweight granulation masterbatch preparation

[0175] 50g of hollow microspheres (5%) were selected as the carrier skeleton material. The microspheres are made of borosilicate glass inorganic non-metallic material with a particle size of 10 mesh and 1μm. The internal hollow rate is ≥80%. Before use, they are soaked in 10% hydrochloric acid for 30 minutes to remove surface impurities, washed with deionized water until neutral, and dried at 60℃.

[0176] Mixing and stirring

[0177] Pretreated sulfur powder, light calcium carbonate, gypsum, and sodium bicarbonate were added to a plow-type mixer, the lid was tightly sealed, and the stirring speed was set to 500 rpm for 15 minutes. The mixing uniformity was tested using fluorescence spectrophotometry: 5g of the mixed material was dissolved in 100mL of carbon disulfide, the sulfur concentration was determined, and the relative standard deviation (RSD) was calculated to be 1.8% (mixing uniformity 92%), meeting the process requirements. The mixed material was a pale yellow powder with a fine, non-granular texture.

[0178] Granulation

[0179] Add the mixture and 50g of hollow microspheres into the disc granulator, adjust the disc speed to 30 rpm and the tilt angle to 40°.

[0180] A metering pump is used to control the water spraying. Deionized water is filtered through a 0.45μm filter membrane at a temperature of 25℃ and sprayed through a fan-shaped nozzle every 30 seconds. The water volume of a single spray is 0.6% of the total mass of the material, and the total water volume is 11%.

[0181] After granulation for 30 minutes, the average particle size was 1.5 mm, the roundness was ≥0.85 (measured by a sphericity tester), there were no cracks on the surface, and no adhesion between particles.

[0182] Particle size screening

[0183] A double-layer vibrating screen (2mm upper layer, 1mm lower layer) was used for screening at a vibration intensity of 6g (g is the acceleration due to gravity) for 8 minutes. The collection rate of 1-2mm particles on the screen was 94%. Oversized particles (>2mm) were crushed and returned to granulation, while fine powder (<1mm) was remixed with the raw materials for reuse. The material utilization rate was ≥98%.

[0184] Drying and curing

[0185] Pore ​​control pretreatment

[0186] A 5% NaHCO3 solution was evenly sprayed onto the surface of the particles using a separatory funnel. The amount of solution sprayed was 9% of the particle mass. After spraying, the particles were left to stand for 15 minutes. Microscopic observation showed that the solution penetrated to a depth of 1 / 2 of the particle radius, ensuring the formation of internal pores.

[0187] High temperature curing

[0188] The granules were placed in an oven and dried at 145℃ for 1 hour, with a heating rate of 5℃ / minute. During the drying process, sodium bicarbonate decomposed to produce CO2, which, combined with the crystalline framework formed by the hydration reaction of gypsum, resulted in interconnected pores within the carrier, as shown by CT scans, with a porosity of 55%.

[0189] Mechanical strength enhancement

[0190] The particles were dried by spraying water twice: the first spraying was 4% (by weight of the particles), and the particles were air-dried at room temperature for 40 minutes; the second spraying was the same amount of water, and the particles were dried at 60°C for 2 hours. The final compressive strength of the particles was 8.2 MPa (tested by a universal testing machine), and the wear rate was ≤0.5% (drum test: 50 rpm, 30 minutes).

[0191] Performance indicators

[0192] Density: 1.04 g / cm³ 3 (Measured by drainage method), suspension rate ≥95% in 1m deep water (after standing for 24 hours);

[0193] Specific surface area: 57m² 2 / g (BET method), total pore volume 0.65cm³ 3 / g;

[0194] 24-hour sulfur autotrophic denitrification rate: In simulated wastewater containing 60 mg / L NO3-N, the denitrification rate is 2.0 kgN / (m³). 3 •d), with a removal rate of 95%, demonstrating highly efficient denitrification performance under high sulfur content.

[0195] Application examples:

[0196] Reactor operating parameters: Device specifications: Cylindrical reactor with an effective volume of 5L, sludge concentration of 4000mg / L, filled with 30% suspended carrier of Examples 1-3, and 1% bacterial strain added. The sulfur autotrophic bacterial strain added in this invention is Thiobacillus denitrificans SZG-SAD-004, which was deposited on June 12, 2023 at the China Center for Type Culture Collection (CCTCC) (Address: Wuhan University, Wuhan, China, Postcode: 430072), with accession number: CCTCCNo.2023992.

[0197] Process conditions: Influent water quality: nitrate nitrogen 100mg / L, total phosphorus 2mg / L, temperature 24-28℃, rotation speed 40r / min.

[0198] Operating parameters: The hydraulic retention time was gradually shortened from 4 hours and 2 hours to 1 hour, with each retention time lasting for 10 days.

[0199] Comparison examples:

[0200] Follow the operating steps of the application example, only add sludge concentrations of 4000 mg / L and 500 mg / L COD, without adding suspended carrier, and the remaining steps and parameters are the same as in the application example.

[0201] Data Results:

[0202]

[0203] As can be seen from the data in the table above, the embodiments of the present invention have significant advantages over the comparative examples:

[0204] It exhibits excellent nitrate removal performance, high system stability, and strong resistance to load shocks.

[0205] When HRT = 4h, the nitrate nitrogen removal rate of Example 3 reached 99%-100%, which is about 8-13 percentage points higher than that of the comparative example (87%-91%), and the effluent concentration is close to zero. When HRT is shortened to 1h, the removal rate of the comparative example drops significantly to 62%-75%, while Example 3 still maintains a removal rate of 89%-93%, which is 14-28 percentage points higher than that of the comparative example, and has significant resistance to load shocks.

[0206] The denitrification reaction is more complete, and less intermediate product accumulates:

[0207] The nitrite nitrogen concentration in the comparative examples ranged from 0.75 to 2.7 mg / L at various HRTs, and increased significantly with decreasing HRT (reaching 1.4 to 2.7 mg / L at HRT = 1 h). The nitrite nitrogen concentration in Examples 1-3 remained below 0.5 to 1.0 mg / L, especially in Example 3 where the nitrite nitrogen concentration was 0 at HRT = 4 h, indicating a more thorough denitrification process and less nitrite nitrogen accumulation.

[0208] pH buffering durability:

[0209] The pH value of the effluent in the example was still 6.6-7.1 after 30 days of operation, which can supply the continuous denitrification process.

[0210] An application of a suspended sulfur autotrophic denitrification carrier for deep denitrification in wastewater treatment involves the following steps: The carrier is loaded into an upflow anaerobic reactor, with the loading volume occupying 1 / 3 of the reactor's effective volume; sludge rich in sulfur autotrophic bacteria is inoculated, with an inoculation amount of 10% to 15% of the reactor's effective volume; the hydraulic retention time is controlled at 1 to 4 hours; the influent nitrate concentration is 20 to 100 mg / L; the temperature is 20 to 35℃; and the pH value is 6.5 to 8.0, achieving a nitrate nitrogen removal rate of ≥85%.

[0211] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0212] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An application of a suspended sulfur autotrophic denitrification carrier, characterized in that, A method for preparing a suspended sulfur autotrophic denitrification carrier includes the following steps: S10. The sulfur source material and the carrier skeleton material are mixed at a mass ratio of 1:0.5 to 2.

0. The sulfur source material includes elemental sulfur or pyrite powder, and the carrier skeleton material includes cordierite, biochar or porous resin. S20. Add a binder and additives to the mixed material. The binder is silicate cement, aluminum phosphate, or polyvinyl alcohol. The additives include iron oxide and mercaptopolyethylene glycol mercaptopyridine. The iron oxide accounts for 2% to 5% of the total mass of the raw materials. The mass ratio of mercaptopolyethylene glycol mercaptopyridine to the sulfur source material is 1:11 to 19. S30. Add deionized water and stir to form a slurry, wherein the amount of deionized water is 8% to 12% of the total mass of the raw materials; S40. The slurry is prepared into particles with a particle size of 3 to 5 mm by extrusion molding or granulation. S50. Dry the particles at 50 to 60°C for 8 to 12 hours. Before drying, spray with a 5% (w / w) NaHCO3 solution to make the carrier porosity reach 40% to 60%. When the sulfur source material is elemental sulfur, the particle size is greater than 200 mesh; when it is pyrite powder, the particle size is 70 to 120 mesh. Before mixing the sulfur source material with the carrier skeleton material, it needs to be preheated at 80 to 100°C for 1 to 2 hours to improve the bonding performance between the materials. The binder is a mixture of silicate cement and gypsum in a mass ratio of 3:1 to 5:1, and the gypsum provides calcium to promote microbial growth. The preparation process also includes inoculation with denitrifying thiobacilli. Thiobacillus denitrificans The steps for SZG-SAD-004 bacterial suspension, with preservation number CCTCCNo.2023992, are as follows: spray the dried granules with bacterial suspension, the amount of bacterial suspension sprayed is 3% to 8% of the granule mass, and after spraying, let it stand at 25 to 30°C for 24 to 48 hours. Suspended sulfur autotrophic denitrification carriers are packed into an upflow anaerobic reactor for deep denitrification. The packing volume occupies 1 / 3 of the effective volume of the reactor. Sludge rich in sulfur autotrophic bacteria is inoculated at a rate of 10% to 15% of the effective volume of the reactor. The hydraulic retention time is controlled at 1 to 4 hours, the influent nitrate concentration is 20 to 100 mg / L, the temperature is 20 to 35℃, and the pH value is 6.5 to 8.0, achieving a nitrate nitrogen removal rate of ≥85%.

2. The application of the suspended sulfur autotrophic denitrification carrier according to claim 1, characterized in that, When the carrier skeleton material is cordierite, it needs to be ball-milled first. The ball-milling time is 2 to 4 hours and the ball-milling speed is 300 to 500 revolutions per minute.

3. The application of the suspended sulfur autotrophic denitrification carrier according to claim 1, characterized in that, The additive contains thiol polyethylene glycol thiol pyridine with a molecular weight of 600 to 2000, and its aqueous solution concentration is 0.5% to 2%. In step S20, it is mixed and stirred with the raw materials for 30 to 60 minutes.

4. The application of the suspended sulfur autotrophic denitrification carrier according to claim 1, characterized in that, In S40, the extrusion molding pressure is 5 to 10 MPa, the granulator speed is 200 to 300 rpm, and a porous surface structure is formed.

5. The application of the suspended sulfur autotrophic denitrification carrier according to claim 1, characterized in that, In S50, after drying, a water spraying drying treatment is performed, with the number of water spraying times being 2 to 3 times, and the amount of water sprayed each time being 2% to 5% of the particle mass, in order to enhance mechanical strength.

6. The application of the suspended sulfur autotrophic denitrification carrier according to claim 1, characterized in that, The carrier skeleton material also includes a slow-release carbon source, which is butylene terephthalate or chitin, accounting for 10% to 30% of the total mass of the raw materials, so as to simultaneously provide a heterotrophic denitrification carbon source.

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