A suspended sulfur preparation for wastewater denitrification and a preparation method thereof

Abstract

The present application relates to a kind of suspended sulfur preparation for sewage denitrification and its preparation method, the suspended sulfur preparation can be enriched sulfur autotrophic and iron autotrophic denitrification microorganism, by adding chitosan derivative and xanthan gum, synergistic stability biofilm, reduce the risk of iron hydroxide sludge expansion, can solve the problems such as poor stability of two kinds of microorganisms coexistence, low substrate utilization rate, high sludge production, and can inhibit the generation of FeS precipitation, thereby reducing the risk of sulfide residue and sulfate accumulation.Therefore, it is mainly used for low carbon-nitrogen ratio wastewater (C / N≤5) denitrification denitrification treatment, after inoculating anaerobic sludge, nitrate nitrogen removal rate is ≥95%, process controllable, cost controllable.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment materials, and in particular to a suspended sulfur preparation for wastewater denitrification and its preparation method. Background Technology

[0002] Thiodenitrification is a process that utilizes sulfides (such as H₂S, elemental sulfur (S), or sulfites) as electron donors to convert nitrates (NO₃⁻) into nitrogenous substances through autotrophic denitrifying bacteria (such as Thiobacillus denitrificans). - The process of reducing sulfur (S-N) to nitrogen (N2). Compared with traditional heterotrophic denitrification (which relies on organic carbon sources), its advantage lies in the fact that it does not require an external carbon source and is suitable for wastewater with a low carbon-to-nitrogen ratio (C / N). However, due to limitations in the reaction mechanism and environmental sensitivity, the traditional fixed-bed sulfur autotrophic denitrification process prepares sulfur and other auxiliary materials into granules, which slowly release electrons in the form of filter media for denitrification. This process has the following core drawbacks: 1. Risk of excessive sulfide residue and sulfate accumulation: When sulfur acts as an electron donor, if the S / N ratio is too high, H2S is generated. H2S is toxic, corrosive, and has an odor (threshold is only 0.03 ppm), which will lead to the deterioration of effluent quality and corrosion of equipment (such as pipes and reactors), increasing maintenance costs. When sulfur is insufficient or the reaction conditions (such as DO and pH) are suitable, sulfur is completely oxidized to SO4. 2- If sulfate (SO4) 2- Excessive accumulation will increase the osmotic pressure of wastewater and inhibit microbial activity.

[0003] 2. Poor microbial community stability and susceptibility to competitive inhibition: Autotrophic denitrifying bacteria have poor tolerance to environmental changes (such as sudden pH changes, increased dissolved oxygen (DO), and toxic substances), and are prone to population decline or even death due to environmental fluctuations (such as sudden changes in influent water quality). Heterotrophic bacteria (such as denitrifying polyphosphate-accumulating bacteria) may take advantage of this to occupy ecological niches, competing with autotrophic bacteria for substrates (such as sulfides) or space, further inhibiting the activity of autotrophic bacteria and resulting in weak resistance to interference in obligate microbial communities. Competition with other sulfur-oxidizing / reducing bacteria: Other sulfur-metabolizing microorganisms (such as sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) may exist in the system, whose metabolic pathways overlap with those of autotrophic denitrifying bacteria (such as both utilizing sulfides), which may lead to the diversion of electron donors (sulfides) and reduce denitrification efficiency.

[0004] 3. Challenges in Sulfur Source Addition and Management: Solid elemental sulfur requires stirring or aeration to promote dissolution and contact, resulting in low mass transfer efficiency and potentially uneven local sulfur concentrations (such as sulfur accumulation at the bottom of the reactor). Sulfur sources need to be added precisely according to the S / N ratio, but this is affected by fluctuations in the influent TN concentration (such as dilution during the rainy season leading to a decrease in TN), requiring real-time monitoring and dynamic adjustment of the dosage. However, in granular sulfur autotrophic denitrification filters, S is always in excess, wasting resources and exacerbating byproduct problems.

[0005] 4. Sludge Production and Settling Performance Issues: Although sulfur autotrophic denitrification does not require an organic carbon source, microbial proliferation still consumes inorganic carbon (such as CO2) and synthesizes its own cellular material, producing a certain amount of excess sludge (approximately 1 / 3 to 1 / 2 of that produced by traditional denitrification). Poor sludge settling performance (e.g., due to filamentous bulking or inorganic particle encapsulation) may lead to increased suspended solids (SS) in the effluent, necessitating the installation of additional sedimentation or filtration units. SO4 produced during the reaction... 2- Possibly related to Ca 2+ Mg 2+ Combined to form sulfate scale (such as gypsum) These inorganic byproducts exacerbate sludge hardening, adhere to packing materials or reactor walls, reduce mass transfer efficiency, and may even cause equipment blockage. Summary of the Invention

[0006] The purpose of this invention is to provide a suspended sulfur preparation for wastewater denitrification and its preparation method. This suspended sulfur preparation can enrich sulfur-autotrophic denitrifying microorganisms. By optimizing the components and ratios, it solves the problems of water acidification, management difficulties, and low microbial activity in the prior art. At the same time, it provides a preparation method to ensure that the process is controllable and the cost is controllable.

[0007] To achieve the objectives of this invention, the technical solution is as follows:

[0008] A suspended sulfur preparation for wastewater denitrification comprises, by total mass percentage, the following components: 30-35 parts powdered sulfur, 1-3 parts reduced iron powder, 3-5 parts powdered activated carbon, 1-3 parts chitosan derivative, 1-2 parts xanthan gum, 12-16 parts glycerol, 35-40 parts deionized water, and 0.3-0.7 parts ascorbic acid.

[0009] Preferably, 35 parts of powdered sulfur serve as an electron donor for sulfur-autotrophic bacteria; 2 parts of reduced iron powder serve as an electron donor for iron-autotrophic bacteria and a biofilm stabilizer; 4 parts of powdered activated carbon serve as a microbial carrier and adsorbent; 2 parts of chitosan derivative serve as a biofilm stabilizer; 1.5 parts of xanthan gum serve as a thixotropic agent and sludge settling agent, achieving thixotropy through dynamic helical conformational switching and promoting sludge settling through long-chain bridging and network capture; 15 parts of glycerol serve as an osmotic pressure regulator; 40 parts of deionized water serve as a dispersion medium; and 0.5 parts of ascorbic acid serve as an antioxidant.

[0010] Furthermore, the chitosan derivative is selected from one or two of carboxymethyl chitosan, chitosan hydrochloride, chitosan quaternary ammonium salt, chitosan lactate, chitosan glutamate, and chitosan sulfate, with chitosan hydrochloride being particularly preferred. More preferably, the chitosan hydrochloride is water-soluble and has a degree of deacetylation ≥85%.

[0011] Furthermore, the particle size of the powdered sulfur is 100 mesh to 200 mesh, and more preferably, the particle size D of the powdered sulfur is... 90 ≤50μm. The particle size of the reduced iron powder is 200 mesh to 300 mesh, and more preferably, the particle size D of the reduced iron powder is... 90 ≤30μm.

[0012] The preparation method of the suspended sulfur agent for wastewater denitrification includes the following steps:

[0013] S1. Raw material pretreatment: Sulfur powder and reduced iron powder are premixed; Powdered activated carbon is soaked in nitric acid solution, rinsed until neutral, and then dispersed in a mixture of glycerol and half of the deionized water. The mixture is ultrasonically mixed to form an activated carbon dispersion; Chitosan derivative is dissolved in acetic acid solution and the pH is adjusted to 4.0-5.0. The mixture is magnetically stirred until completely dissolved to form a chitosan derivative solution.

[0014] S2. Construction of dispersion system: The obtained chitosan derivative solution and the remaining deionized water were stirred evenly in a warm water bath, and the pH was adjusted to 6.5-7.0. Stirring was continued, and then xanthan gum was added and stirred until homogeneous to form a dispersion system.

[0015] S3, Activated carbon adsorption and sulfur-iron composite: The activated carbon dispersion is added to the dispersion system obtained in S2, and ultrasonic treatment is performed to form an activated carbon-dispersant composite; after stepwise addition of sulfur-iron powder premix, wet ball milling is performed to obtain sulfur-iron-activated carbon composite slurry.

[0016] S4. Antioxidant treatment and post-treatment: Add ascorbic acid to the sulfur-iron-activated carbon composite slurry, stir, and filter to obtain the final product.

[0017] Furthermore, in the preparation method, the powdered activated carbon is soaked in a nitric acid solution, wherein the mass percentage of the nitric acid solution is 4-6%, preferably 5%, the soaking time is 1.5-2.5 hours, preferably 2 hours, the ultrasonic power is 145-155 W, preferably 150 W, and the treatment time is 8-12 minutes, preferably 10 minutes.

[0018] Further, the obtained chitosan derivative solution is mixed with the remaining deionized water and stirred evenly in a warm water bath at a temperature of 55–65°C, preferably 60°C, and a stirring speed of 280–320 rpm, preferably 300 rpm. After adding xanthan gum, the stirring speed is increased to 480–520 rpm, preferably 500 rpm, and stirred until homogeneous for 30 minutes.

[0019] Furthermore, in step S3, the ultrasonic processing power is 145-155 W, preferably 150 W.

[0020] Furthermore, before adding the sulfur-iron powder premix in steps S3, stir at 450-550 rpm for 15-25 minutes to avoid excessively high local concentrations. Preferably, stir at 500 rpm for 20 minutes.

[0021] Furthermore, in step S3, the wet ball milling can be carried out using a planetary ball mill, wherein the diameter of the zirconia balls is 3-5 mm, the ball-to-material ratio is 5:1, and the rotation speed is 200 rpm. Even further, during wet ball milling, grinding is performed under an ice bath at 20-25℃ for 0.5-1.5 hours, preferably at 25℃, for a grinding time of 1 hour.

[0022] Furthermore, in step S4, ascorbic acid is added to the slurry, and the mixture is stirred at 280–320 rpm for 8–12 minutes to chelate free Fe. 2+ Preferably, the stirring speed is 300 rpm for 10 minutes.

[0023] Furthermore, in step S4, vacuum filtration is performed using a 0.22 μm filter membrane to remove undispersed particles and activated carbon agglomerates.

[0024] Furthermore, after step S4, the suspended sulfur preparation is sealed and dispensed into polyethylene drums for storage in a cool, dark place. As a specific embodiment, nitrogen gas sealing can be used.

[0025] Accordingly, the suspended sulfur preparation for wastewater denitrification provided by this invention is mainly used for denitrification treatment of wastewater with a low carbon-to-nitrogen ratio (C / N≤5). After inoculation with anaerobic sludge, it is operated under the conditions of pH 6.5~7.0, ORP (oxidation-reduction potential) of -200 to -150 mV, and temperature of 20~35℃, with a nitrate nitrogen removal rate of ≥95%.

[0026] The principle of this invention is that it alters the surface properties of sulfur powder, giving it hydrophilic properties and enabling it to adsorb microorganisms.

[0027] The chitosan hydrochloride-xanthan gum synergistic system constructs a robust three-dimensional framework through electrostatic complexation: positively charged chitosan hydrochloride and negatively charged xanthan gum form a polyelectrolyte complex (PEC) through electrostatic interaction. The rigid helical structure of xanthan gum resists hydraulic shear, while the flexible chains of chitosan fill and cross-link, significantly increasing gel density and reducing porosity, providing a stable physical space for microbial colonization. Simultaneously, this system induces microbial colonization and community building through dual biological signals: N-acetylglucosamine (GlcNAc) released by chitosan hydrochloride under the action of lysozyme serves as a carbon source and signaling molecule, inducing microorganisms to secrete extracellular polymeric proteins (EPS) to enhance adhesion; the mannose units of xanthan gum's side chains are recognized by specific bacterial groups, inducing the secretion of polysaccharide EPS to improve water retention. This synergistic effect effectively neutralizes the surface charge of microorganisms, promotes bacterial aggregation and biofilm formation, thereby significantly enhancing the stability and anti-competitive inhibition ability of the microbial community, improving settling performance, and controlling sludge production.

[0028] Compared with the prior art, the significant advantage of this invention is that this suspended sulfur preparation can be combined with existing anaerobic sludge to treat wastewater, and can:

[0029] (1) Strong byproduct inhibition ability: By synergistically stabilizing the biofilm with chitosan derivatives and xanthan gum, the risk of filamentous bacterial bulking in flocculent sludge is reduced. This avoids the problem of poor microbial community stability and susceptibility to competitive inhibition in existing fixed-bed sulfur autotrophic denitrification processes; compared with flocculent sludge systems, it reduces sludge production and lowers the settling ratio (SV). 30 By adding ascorbic acid to chelate free Fe. 2+ This can inhibit the formation of FeS precipitates, thereby reducing the risk of sulfide residues and sulfate accumulation.

[0030] (2) High efficiency of targeted enrichment: Through the synergistic effect of sulfur (electron donor) and reduced iron powder (auxiliary electron donor), the metabolic needs of sulfur autotrophic bacteria (such as Thiobacillus denitrificans) and iron autotrophic bacteria (such as Geobacter metallireducens) are met at the same time, so that the two microorganisms can coexist stably and the denitrification efficiency is 10-15% higher than that of a single microbial system.

[0031] (3) Cost and environmental friendliness: Using inexpensive sulfur and iron powder as the main raw materials, and glycerol as an osmotic pressure regulator to replace traditional high-priced reagents, the total cost is reduced by more than 30% compared with commercially available microbial agents; when treating urban sewage for deep denitrification, the sulfate accumulation is ≤100 mg / L and there is no hydrogen sulfide accumulation (complies with the "Discharge Standard of Pollutants for Urban Sewage Treatment Plants" GB 18918-2002), and the risk of secondary pollution is low.

[0032] (4) Compared with traditional sulfur autotrophic denitrification, this invention adds sulfur-iron powder premix to activated carbon-dispersant complex to form a homogeneous system, which changes the surface characteristics of sulfur particles, making them hydrophilic and able to adsorb microorganisms. This solves the problem of sulfur source addition and management. Traditional sulfur autotrophic denitrification either uses granular sulfur preparations as filter media, where sulfur is always in excess relative to nitrogen, easily generating hydrogen sulfide and causing a significant drop in water pH; or it directly adds powdered sulfur to the anoxic tank. Due to the hydrophobic properties of sulfur particles, they do not easily adsorb water and microorganisms, and the powder floats on the surface and takes a long time to sink into the water and be consumed. Due to its high specific gravity, it affects mass transfer, or it sinks to the bottom of the tank and accumulates, generating sulfides and inhibiting the activity of biochemical microorganisms.

[0033] (5) The present invention is less restricted by the S / N ratio and microbial activity, and can be directly added to the anoxic section of the wastewater treatment biochemical reactor, or added in series after the secondary sedimentation tank to achieve deep denitrification. The system sludge concentration is 2000 mg / L to 4500 mg / L, which is consistent with the activated sludge concentration of the wastewater treatment biochemical system. Compared with existing denitrification biological filters, the system is more stable and consumes less energy. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] In the following examples, NO3 is detected. - The method for determining -N is ion chromatography (IC), standard: EPA 300.0 / GB 8538-2022. The method for total nitrogen determination is alkaline potassium persulfate digestion-ultraviolet spectrophotometry (national standard HJ 636-2012).

[0036] Example 1

[0037] A suspended sulfur preparation for wastewater denitrification, based on a total mass of 100 g, comprises the following components: powdered sulfur (D... 90 ≤50 μm, meaning that when 90% of the particles pass through the sieve, the corresponding sieve aperture is 50 μm) 34g, reduced iron powder (D 90≤30μm, that is, when 90% of the particles pass through the sieve, the corresponding sieve aperture is 30 μm) 3g, powdered coconut shell activated carbon (iodine value ≥1000mg / g) 4g, chitosan hydrochloride 2g (water-soluble chitosan hydrochloride was purchased from Qingdao Bozhi Huili Biotechnology Co., Ltd., degree of deacetylation 85%), xanthan gum 1.5g, glycerol 15g, deionized water 40g, ascorbic acid 0.5g.

[0038] The preparation method of the suspended sulfur agent includes the following steps:

[0039] S1. Raw material pretreatment: Sulfur powder (34 g) was passed through a 200-mesh sieve, and reduced iron powder (3 g) was passed through a 300-mesh sieve. After premixing, the mixture was sealed. Powdered coconut shell activated carbon (4 g) was soaked in 5% nitric acid for 2 hours. The volume ratio of activated carbon to 5% nitric acid was 1:5 to remove surface oxides. The carbon was rinsed with deionized water until neutral. Then, it was dispersed in a mixture of glycerol and water (15 g glycerol + 21.5 g deionized water) and ultrasonically treated for 10 minutes at a power of 150 W to form an activated carbon dispersion. Chitosan hydrochloride (2 g) was dissolved in 1% acetic acid solution. The pH of the acetic acid solution of the chitosan derivative was adjusted to 4.5 and magnetically stirred for 30 minutes until completely dissolved.

[0040] S2. Construction of dispersion system: The remaining 21.5 g of deionized water was mixed with the chitosan derivative solution obtained in step S3, stirred in a water bath at 60°C for 10 minutes (300 rpm), and the pH was adjusted to 6.5-7.0 with 1 M phosphate buffer. Stirring was continued for 20 minutes, xanthan gum (1.5 g) was added, and the stirring speed was increased to 500 rpm. Stirring was carried out for 30 minutes until homogeneous to form a dispersion system.

[0041] S3, Activated Carbon Adsorption and Sulfur-Iron Composite: The activated carbon dispersion was added to the dispersion system obtained in S2, and ultrasonically treated for 10 minutes at 150W to form an activated carbon-dispersant composite. The sulfur-iron powder premix obtained in S1 was added in steps, and stirred at 500 rpm for 20 minutes to avoid excessively high local concentrations. Then, wet ball milling was performed using a planetary ball mill (QM-3SP4) with zirconia balls of 3-5 mm diameter, a ball-to-material ratio of 5:1, a rotation speed of 200 rpm, and grinding under ice bath (25℃) conditions for 1 hour to obtain a sulfur-iron-activated carbon composite slurry.

[0042] S4. Antioxidant treatment and post-treatment: Add 0.5g of ascorbic acid to the slurry obtained in step S6 and stir for 10 minutes (300 rpm) to chelate free Fe. 2+ Vacuum filtration using a 0.22 μm filter membrane removes undispersed particles and activated carbon agglomerates. The mixture is then sealed with nitrogen gas and dispensed into polyethylene drums (20 L each), stored in a cool, dark place (≤25℃).

[0043] Application testing:

[0044] Take 1000L of leachate from the aerobic treatment process of the wastewater treatment unit of an old landfill (operating for 30 years). COD=1200mg / L, NO3 - -N=200 mg / L, BOD5 / COD=approximately 0.1, which means the biodegradable COD is only 120 mg / L, i.e., B / N=0.6≤5, inoculated with anaerobic sludge (10 7 (CFU / mL, selected from the anaerobic tank of the wastewater treatment process at this landfill), add 1.5 kg of the suspended sulfur preparation prepared in this embodiment, control pH 7.0, ORP -200 mV, temperature 22℃, and slowly stir (to prevent sludge settling) for 36 hours. Then, use a metering pump to continuously supply water at a flow rate of 100 L / h, and dilute the suspended sulfur preparation prepared in this embodiment to a concentration of 5% (i.e., mix 5 g of suspended sulfur preparation with 95 g of deionized water). Use a metering pump (flow rate adjustable) at a flow rate of 2.8 L / h (the influent can be adjusted according to NO3). - NO3 (adjusted concentration) is added to the reactor inlet. The sludge return ratio is controlled at 100% (i.e., 200 L / h), the hydraulic retention time is 10 h, and NO3 is measured after 30 days of operation. - -N removal rate was 96%, and total nitrogen removal rate was 90%. Sludge concentration (MLSS) was 4500 mg / L, and settling ratio (SV) was [missing information]. 30 The percentage was 30%. No sulfides were detected in the effluent.

[0045] Example 2

[0046] A suspended sulfur preparation for wastewater denitrification, based on a total mass of 100 g, comprises the following components: 35 g of powdered sulfur, 3 g of reduced iron powder, 5 g of powdered activated carbon, 3 g of chitosan hydrochloride, 2 g of xanthan gum, 16 g of glycerol, 35.3 g of deionized water, and 0.7 g of ascorbic acid.

[0047] The preparation method and steps of the suspended sulfur preparation are the same as in Example 1, except that in S6, the ball milling time is adjusted to 1.5 hours (200 rpm, ice bath).

[0048] Application testing

[0049] Aquaculture wastewater (COD=15000 mg / L, total nitrogen=1200 mg / L, C / TN=12.5) has the following parameters before entering the anoxic tank after previous treatment: COD=850 mg / L, NO3=12.5. - -N concentration is 250 mg / L, C / N = 3.4, take 1200 L, and inoculate with anaerobic sludge (10 7(CFU / mL, selected from the anaerobic tank of the wastewater treatment process for this aquaculture wastewater), add 9.0 kg of the suspended sulfur preparation prepared in this embodiment, control pH 6.8, ORP -180 mV, temperature 25℃, and slowly stir (to prevent sludge settling) for 36 hours. Then, use a metering pump to continuously supply water at a flow rate of 100 L / h, and dilute the suspended sulfur preparation prepared in this embodiment to a concentration of 5% (i.e., mix 5 g of suspended sulfur preparation with 95 g of deionized water). Use a metering pump (flow rate adjustable) at a flow rate of 16.8 L / h (the influent can be adjusted according to NO3). - NO3 (NO3 concentration adjustment) is added to the reactor inlet. The sludge return ratio is controlled at 100% (i.e., 200 L / h), and the hydraulic retention time is 12 h. After 30 days of operation, NO3 is measured. - -N removal rate was 97%, total nitrogen removal rate was 90%, sludge concentration (MLSS) was 4500 mg / L, and settling ratio (SV) was [missing information]. 30 The percentage was 32%. No sulfides were detected in the effluent.

[0050] Example 3

[0051] Application testing:

[0052] A wastewater sample from a municipal wastewater treatment plant (COD = 200 mg / L, total nitrogen = 25 mg / L, C / TN = 8) underwent biochemical reactions. The resulting wastewater parameters were: COD = 40 mg / L, TN concentration = 15 mg / L, and NO3... - -N concentration is 12 mg / L, C / N = 2.67, take 100 L, and inoculate with anaerobic sludge (10 7 (CFU / mL, selected from the anaerobic tank of the wastewater treatment process in this wastewater treatment plant), add 1200L of the suspended sulfur preparation prepared in Example 2, control pH 7.0, ORP -150 mV, temperature 20℃, and slowly stir (to prevent sludge settling) for 24 hours. Then, use a metering pump to continuously supply water at a flow rate of 1600L / h, and dilute the suspended sulfur preparation prepared in this example to a concentration of 1% (i.e., 1g of suspended sulfur preparation mixed with 99g of deionized water). Use a metering pump (flow rate adjustable) at a flow rate of 4L / h (the influent can be adjusted according to NO3). - (NO3 concentration adjustment) is added to the reactor inlet. After 30 days of operation, NO3 is measured. - -N removal rate was 95%, total nitrogen removal rate was 90%, sludge concentration (MLSS) was 4000 mg / L, and settling ratio (SV) was [missing information]. 30 The concentration of sulfate was 30%, the cumulative sulfate concentration was 57 mg / L, and no sulfides were detected.

[0053] Examples 1-3 show that when using the suspended sulfur agent of the present invention to treat nitrate-containing wastewater, the sludge settling ratio in the denitrification biological treatment system is around 30%, and the sludge concentration (MLSS) is 4000-4500 mg / L. This is highly compatible with activated sludge wastewater treatment systems, and the dosage of the suspended sulfur agent can be adjusted according to the influent NO3. - -N concentration adjustment: Suspended sulfur agent dosage and the amount of NO3 to be removed - The ratio of -N to M is generally 3 to 6 times, with the specific value determined through on-site testing based on the wastewater characteristics of different industries. Once the dosage ratio is determined, concentration feedback can be used to achieve precise dosing of the reagent. Compared with existing sulfur autotrophic denitrification filters, this method avoids water acidification, thus eliminating the need for alkali adjustment of pH and saving reagent consumption; it also eliminates the need for backwashing, avoiding the loss of sulfur particles caused by backwashing and saving energy.

Claims

1. A suspended sulfur preparation for wastewater denitrification, characterized in that: Based on total mass percentages, it includes the following components: 30-35 parts powdered sulfur, 1-3 parts reduced iron powder, 3-5 parts powdered activated carbon, 1-3 parts chitosan derivative, 1-2 parts xanthan gum, 12-16 parts glycerol, 35-40 parts deionized water, and 0.3-0.7 parts ascorbic acid. The chitosan derivative is a water-soluble chitosan hydrochloride with a degree of deacetylation ≥85%. The preparation method of the suspended sulfur agent includes the following steps: S1. Raw material pretreatment: Sulfur powder and reduced iron powder are premixed; Powdered activated carbon is soaked in nitric acid solution, rinsed until neutral, and then dispersed in a mixture of glycerol and half of deionized water. It is ultrasonically mixed to form an activated carbon dispersion; Chitosan derivative is dissolved in acetic acid solution and the pH is adjusted to 4.0-5.

0. It is magnetically stirred until completely dissolved to form a chitosan derivative solution. S2. Construction of dispersion system: The obtained chitosan derivative solution and the remaining deionized water were stirred evenly in a warm water bath, and the pH was adjusted to 6.5-7.

0. Stirring was continued, and then xanthan gum was added and stirred until homogeneous to form a dispersion system. S3, Activated carbon adsorption and sulfur-iron composite: The activated carbon dispersion is added to the dispersion system obtained in S2, and ultrasonic treatment is performed to form an activated carbon-dispersant composite; after stepwise addition of sulfur-iron powder premix, wet ball milling is performed to obtain sulfur-iron-activated carbon composite slurry. S4. Antioxidant treatment and post-treatment: Add ascorbic acid to the sulfur-iron-activated carbon composite slurry, stir, and filter to obtain the final product.

2. The suspended sulfur preparation for wastewater denitrification according to claim 1, characterized in that: The suspended sulfur preparation comprises, by total mass percentage, the following components: 35 parts powdered sulfur, 2 parts reduced iron powder, 4 parts powdered activated carbon, 2 parts chitosan derivative, 1.5 parts xanthan gum, 15 parts glycerol, 40 parts deionized water, and 0.5 parts ascorbic acid.

3. The suspended sulfur preparation for wastewater denitrification according to claim 1, characterized in that: The powdered sulfur has a particle size of 100-200 mesh; the reduced iron powder has a particle size of 200-300 mesh.

4. The suspended sulfur preparation for wastewater denitrification according to any one of claims 1-3, characterized in that: The suspended sulfur preparation is used for denitrification treatment of wastewater with C / N ≤ 5. After inoculation with anaerobic sludge, it is operated under the conditions of pH 6.5 to 7.0, oxidation-reduction potential of -200 to -150 mV, and temperature of 20 to 35°C.

5. A method for preparing a suspended sulfur agent for wastewater denitrification, characterized in that: in, The suspended sulfur preparation is selected from the suspended sulfur preparations according to any one of claims 1-3, and the preparation method includes the following steps: S1. Raw material pretreatment: Sulfur powder and reduced iron powder are premixed; Powdered activated carbon is soaked in nitric acid solution, rinsed until neutral, and then dispersed in a mixture of glycerol and half of deionized water. It is ultrasonically mixed to form an activated carbon dispersion; Chitosan derivative is dissolved in acetic acid solution and the pH is adjusted to 4.0-5.

0. It is magnetically stirred until completely dissolved to form a chitosan derivative solution. S2. Construction of dispersion system: The obtained chitosan derivative solution and the remaining deionized water were stirred evenly in a warm water bath, and the pH was adjusted to 6.5-7.

0. Stirring was continued, and then xanthan gum was added and stirred until homogeneous to form a dispersion system. S3, Activated carbon adsorption and sulfur-iron composite: The activated carbon dispersion is added to the dispersion system obtained in S2, and ultrasonic treatment is performed to form an activated carbon-dispersant composite; after stepwise addition of sulfur-iron powder premix, wet ball milling is performed to obtain sulfur-iron-activated carbon composite slurry. S4. Antioxidant treatment and post-treatment: Add ascorbic acid to the sulfur-iron-activated carbon composite slurry, stir, and filter to obtain the final product.

6. The method for preparing suspended sulfur preparations for wastewater denitrification according to claim 5, characterized in that: In the preparation method, powdered activated carbon is soaked in nitric acid solution, the mass percentage of nitric acid solution is 4-6%, the soaking time is 1.5-2.5 hours, the ultrasonic power is 145-155 W, and the treatment time is 8-12 minutes.

7. The method for preparing suspended sulfur preparations for wastewater denitrification according to claim 5, characterized in that: In the preparation method, the obtained chitosan derivative solution and the remaining deionized water are stirred evenly in a warm water bath at a temperature of 55-65°C and a stirring speed of 280-320 rpm. After adding xanthan gum, the stirring speed is increased to 480-520 rpm.

8. The method for preparing suspended sulfur preparations for wastewater denitrification according to claim 5, characterized in that: In step S3 of the preparation method, the ultrasonic treatment power is 145-155W; before adding the sulfur-iron powder premix in step S3, it is stirred at 450-550 rpm; wet ball milling is performed using a planetary ball mill with a diameter of 3-5 mm for the zirconia balls, a ball-to-material ratio of 5:1, and a rotation speed of 200 rpm.