Method for preparing autotrophic simultaneous denitrification and phosphorus removal agent by mechanically and chemically activating iron sulfide and application method thereof

Abstract

The application discloses a method for preparing a self-sustaining simultaneous denitrification and phosphorus removal agent by mechanically and chemically activating iron sulfide and an application method thereof, and is characterized in that iron sulfide (including magnetite pyrite ore, low-sulfur fine powder and sulfur fine powder) is used as a main raw material, iron oxide and iron carbonate are used as accelerators, the two are compounded, mixed and ground, then a slurry is prepared by using water and is mechanically and chemically activated to obtain a slurry-shaped denitrification and phosphorus removal agent, or the activated product is vacuum dried and mixed with molten sulfur to obtain a granular denitrification and phosphorus removal agent. The method can greatly improve the biological reaction activity of the iron sulfide and greatly improve the efficiency of the simultaneous denitrification and phosphorus removal.

Description

Technical Field

[0001] This invention relates to the fields of mineral resource and environmental material utilization, and deep denitrification and phosphorus removal in wastewater treatment, and more specifically to a technical method for simultaneous sulfur autotrophic denitrification and phosphorus removal. Background Technology

[0002] Nitrogen and phosphorus are the main elements leading to eutrophication of water bodies. As eutrophication of water bodies becomes more and more serious, especially with the widespread occurrence of black and odorous rivers in cities, nitrate nitrogen, total nitrogen, and total phosphorus have all been included in the discharge and water pollution control indicators, and various regions have formulated increasingly strict nitrogen and phosphorus control standards.

[0003] Phosphorus removal from domestic sewage mainly relies on microbial treatment, but the total phosphorus concentration in the effluent from secondary treatment can only be stabilized at around 1 mg / L, making it difficult to meet higher requirements. Currently, advanced phosphorus removal from domestic sewage commonly employs methods such as adding iron and aluminum salts to form precipitates of iron phosphate and aluminum phosphate compounds, which are then removed through sand filtration, coagulation, and magnetic separation.

[0004] Nitrogen removal from wastewater commonly employs nitrification-heterotrophic denitrification technology, which converts organic nitrogen and ammonia nitrogen in the water into nitrate nitrogen through an aerobic process. The wastewater is then returned to an anoxic tank where organic matter in the wastewater serves as an electron donor, and heterotrophic denitrifying microorganisms convert nitrate nitrogen into nitrogen gas. The reflux denitrification technology faces several obstacles in meeting increasingly stringent total nitrogen standards for wastewater discharge: First, a high reflux ratio is required to achieve the discharge standards, leading to excessive energy consumption and uneconomical water treatment. Second, due to the long retention time of wastewater in septic tanks and drainage pipes, microbial degradation of organic matter consumes some carbon sources, resulting in insufficient carbon sources and a low carbon-to-nitrogen ratio in the wastewater entering the wastewater treatment plant, failing to meet the organic carbon requirements of heterotrophic denitrification. Third, in cases of insufficient carbon sources, the common practice is to add carbon sources to anoxic tanks or add anaerobic biological filters after secondary sedimentation tanks to achieve heterotrophic denitrification. However, the addition of agents such as sodium acetate leads to excessively high denitrification costs, and improper dosage control can result in excessively high COD in the effluent, causing secondary pollution.

[0005] To compensate for the shortcomings of heterotrophic denitrification and meet the demands of advanced nitrogen removal in water treatment, sulfur autotrophic denitrification technology has rapidly developed in recent years as a representative autotrophic denitrification technology. Sulfur autotrophic denitrification involves facultative anaerobic microorganisms such as denitrifying thiobacilli using inorganic carbon as a carbon source to complete anabolism, while simultaneously using sulfur and reducing sulfur compounds (thiosulfates, sulfites, and sulfides) as electron donors to reduce nitrates to nitrogen gas. Using sulfur as an electron donor for denitrification is the mainstream direction of development. Sulfur autotrophic denitrification technology has attracted widespread attention from scholars both domestically and internationally because it does not require an external carbon source. It has advantages such as abundant and inexpensive sulfur resources, low sludge production, and low treatment costs, making it a current research hotspot in the field of nitrogen removal. However, the process of using sulfur as an electron donor in autotrophic denitrification can lead to water acidification; therefore, limestone or other carbonates are typically used as pH-stabilizing media for the system. Existing sulfur-limestone autotrophic denitrification systems use a mixture of limestone and elemental sulfur particles in a specific ratio as packing material, which is then loaded into a reaction filter column for wastewater treatment. The limestone continuously dissolves during the treatment process, thus buffering the pH decrease. This necessitates the construction of new denitrification biological filters in existing wastewater treatment plants. However, existing wastewater treatment plants often lack the space for such facilities, posing a significant challenge to technological upgrades. Solving this problem is an urgent technical requirement for upgrading and retrofitting older wastewater treatment plants. Current advanced wastewater denitrification and phosphorus removal technologies suffer from the following prominent issues:

[0006] (1) The addition of carbon sources to heterotrophic denitrification increases greenhouse gas emissions, sludge production, and operating costs. Sodium acetate, as a carbon source for deep denitrification, has the advantages of safe use and storage, fast denitrification speed, and short hydraulic retention time. However, the conversion of organic carbon to inorganic carbon and the release of N2O increase greenhouse gas emissions. Heterotrophic denitrification microorganisms proliferate rapidly, generating a large amount of sludge during the denitrification process. The consumption of sodium acetate, frequent backwashing, and sludge treatment all contribute to the excessively high cost of heterotrophic denitrification, placing a heavy burden on enterprises. There is an urgent need to develop new technologies to reduce denitrification costs.

[0007] (2) The problem of low bioactivity of denitrification and phosphorus removal by iron sulfide denitrification. Sulfur autotrophy has been a research hotspot in recent years. For example, patent CN101973629A discloses the use of pyrite for simultaneous denitrification and phosphorus removal (Li Ruihua, Nanjing University); patent CN111362405A discloses a material prepared by granulation of 100-200 mesh sulfur powder or 60-150 mesh pyrite and biomass waste as raw materials; patent CN109052641A discloses the preparation of denitrification and phosphorus removal materials using pyrrhotite + sulfur + carbonate minerals; patent CN112390380A discloses the composite denitrification and phosphorus removal of iron manganese sulfide and sulfur, wherein the highly active iron manganese sulfide is natural colloidal pyrrhotite, natural pyrrhotite, pyrrhotite formed by thermally activated pyrrhotite, sulfide products of iron manganese oxide or iron manganese hydroxide, or iron manganese sulfide by-products of wastewater and waste gas desulfurization. These patented technologies all demonstrate simultaneous nitrogen and phosphorus removal. Their mechanism involves sulfur in sulfides and the combined sulfur acting as electron donors for nitrogen removal, while iron released from iron sulfides combines with phosphate to remove phosphate from the water. However, whether iron sulfides are used alone for simultaneous nitrogen and phosphorus removal or in combination with sulfur as electron donors, the biochemical reaction between iron sulfides and microorganisms is the rate-limiting step. The excessively low bioreactivity restricts the application of these materials and technologies in advanced wastewater nitrogen and phosphorus removal. This is because natural iron sulfide minerals have high crystallinity, especially pyrite, which has very strong para-sulfur bonds, resulting in very small solubility products and low chemical and biological reactivity, leading to a very slow reaction rate with anaerobic denitrifying thiobacteria. Activating iron sulfides to significantly improve their biochemical activity is the solution to these problems. Summary of the Invention

[0008] Based on extensive static and dynamic nitrogen and phosphorus removal experiments, this invention provides a method for preparing an autotrophic simultaneous nitrogen and phosphorus removal agent using the mechanochemical activation of iron sulfides, and its application method, in order to solve the problems existing in the prior art and provide technical support for the application of sulfur autotrophic denitrification in the field of wastewater treatment.

[0009] The technical solution adopted in this invention is as follows:

[0010] This invention first discloses a method for preparing an autotrophic simultaneous denitrification and phosphorus removal agent by mechanochemical activation of iron sulfide. The method is characterized by: mixing and grinding iron sulfide raw materials with an activation promoter, adding water to prepare a slurry, and then performing mechanochemical activation by grinding to obtain a slurry-like autotrophic simultaneous denitrification and phosphorus removal agent.

[0011] The slurry-like autotrophic simultaneous denitrification and phosphorus removal agent is mixed with molten sulfur and shaped into granules to obtain granular autotrophic simultaneous denitrification and phosphorus removal agent.

[0012] Alternatively, the slurry-like autotrophic simultaneous denitrification and phosphorus removal agent can be mixed with sulfur raw materials to obtain a sulfur-containing slurry-like autotrophic simultaneous denitrification and phosphorus removal agent.

[0013] Furthermore, the slurry-like self-trophic simultaneous denitrification and phosphorus removal agent is prepared according to the following steps:

[0014] Iron sulfide raw materials and activation promoters are mixed at a mass ratio of 3-20:1 and ground to obtain powder with a mesh size of 200 or higher. Then, water is added to prepare a slurry with a mass concentration of 10-40%. The slurry is mechanically and chemically activated in a high-efficiency grinding equipment for 2-48 hours to achieve the nano-sizing of iron sulfide crystals, the defective crystal structure, and the activation of surface reactivity, which greatly improves its reactivity with microorganisms, thus obtaining the slurry-like autotrophic synchronous denitrification and phosphorus removal agent.

[0015] Furthermore, the granular autotrophic simultaneous nitrogen and phosphorus removal agent is prepared according to the following steps:

[0016] Iron sulfide raw materials and activation accelerators are mixed and ground at a mass ratio of 3-20:1 to obtain powder with a mesh size of 200 or higher. Then, water is added to prepare a slurry with a mass concentration of 10-40%. The slurry is mechanically and chemically activated in a high-efficiency grinding equipment for 2-48 hours to obtain a slurry-like autotrophic synchronous denitrification and phosphorus removal agent.

[0017] The slurry-like synchronous denitrification and dephosphorization agent is vacuum dried, pulverized and passed through a 200-mesh sieve, and then added to the molten sulfur at a mass ratio of 5-15% and stirred evenly. The material temperature is maintained at 130-160℃ to maintain good flow and uniform mixing of the material, thus obtaining a mixed molten material.

[0018] The mixed molten material is sprayed into droplets and cooled to obtain near-spherical particles with a particle size of 3-8 mm, which is the granular autotrophic simultaneous denitrification and dephosphorization agent; or, the mixed molten material is spread into a thin layer of 3-8 mm thickness, cooled, crushed, and sieved to obtain material with a particle size of 3-8 mm, which is the granular autotrophic simultaneous denitrification and dephosphorization agent.

[0019] Furthermore, the sulfur-containing slurry-like autotrophic simultaneous denitrification and phosphorus removal agent is prepared according to the following steps:

[0020] Iron sulfide raw materials and activation accelerators are mixed and ground at a mass ratio of 3-20:1 to obtain powder with a mesh size of 200 or higher. Then, water is added to prepare a slurry with a mass concentration of 10-40%. The slurry is mechanically and chemically activated in a high-efficiency grinding equipment for 2-48 hours to obtain a slurry-like autotrophic synchronous denitrification and phosphorus removal agent.

[0021] The slurry-like autotrophic simultaneous denitrification and dephosphorization agent is mixed with sulfur raw material at a mass ratio of 1:5 to 20, and then ball-milled with water to prepare a slurry with a mass concentration of 10 to 30%, thereby obtaining a sulfur-containing slurry-like autotrophic simultaneous denitrification and dephosphorization agent.

[0022] Furthermore, in the above method: the iron sulfide raw material includes at least one of pyrrhotite ore, low-sulfur concentrate and sulfur concentrate, preferably low-sulfur concentrate, and the content of iron sulfide in the iron sulfide raw material is not less than 90%, and the total content of heavy metals Cu, Zn, Pb and As is not higher than 0.3%.

[0023] Furthermore, in the above method: the activation promoter includes at least one of limonite ore, thermally activated limonite, iron concentrate produced during the fluidized bed roasting process of sulfur concentrate, sulfuric acid slag, and siderite ore and their thermal decomposition products, and the iron and manganese content in the activation promoter is not less than 50%.

[0024] Furthermore, in the above method: the sulfur raw material includes, but is not limited to, at least one of industrial sulfur powder, industrial sulfur flakes, desulfurization by-product sulfur paste, and sulfur-rich waste; the content of non-biodegradable toxic and hazardous substances in the sulfur-rich waste does not exceed the limits specified in the National Hazardous Waste Catalogue.

[0025] This invention further provides a method for applying the autotrophic simultaneous nitrogen and phosphorus removal agent prepared according to the above method, characterized in that:

[0026] Granular autotrophic simultaneous denitrification and phosphorus removal agent was used as the packing material for the sulfur autotrophic denitrification biological filter, and the filter was operated with a hydraulic retention time of 30-60 minutes.

[0027] Alternatively, the slurry-like autotrophic simultaneous denitrification and phosphorus removal agent or the sulfur-containing slurry-like autotrophic simultaneous denitrification and phosphorus removal agent can be diluted with water to a mass concentration of 0.1-10%, and then pumped and added to the influent of the anoxic denitrification tank of the sewage treatment plant, the influent of the denitrification deep bed filter, or the influent of the denitrification and phosphorus removal fluidized bed reactor to replace part or all of the organic carbon source for denitrification.

[0028] The technical principles and beneficial effects of this invention are reflected in:

[0029] (1) Experimental studies of this invention have found that when iron sulfides (including pyrrhotite ore, low-sulfur concentrate, and sulfur concentrate) are mixed with an activation promoter and then subjected to ultrafine grinding and mechanochemical activation, the particle size of the iron sulfides is transformed from coarse particles of tens of micrometers to fine particles of several nanometers to several micrometers (e.g., ... Figure 1 , Figure 2 As shown), on the other hand, it distorts the lattice of iron sulfides, forms a large number of structural defects, and significantly reduces the crystallinity (as shown). Figure 3-5 As shown), both of these effects significantly improve the bioreactivity of iron sulfides, that is, the efficiency of simultaneous nitrogen and phosphorus removal is greatly improved (e.g., Figure 6 (As shown).

[0030] (2) Experimental studies of this invention have found that adding a certain proportion of activation promoters, such as nano-iron oxides, iron carbonate minerals and their decomposition products, during the mechanochemical activation process of iron sulfides, causes a mechanochemical reaction between the two under mechanical force. This promotes the mild oxidation of sulfur in the iron sulfide minerals to form elemental sulfur, polysulfides, and thiosulfates, which are highly bioactive species. The ferric iron in the iron oxides is reduced to highly bioactive and chemically active ferrous iron, thereby improving the reactivity of iron sulfides and their simultaneous denitrification and phosphorus removal with sulfur complexes (e.g., ...). Figure 7 (As shown).

[0031] (n+2)Fe 1-x S + 2FeOOH → (n - nx + 2)Fe 2+ +S n 2- +S2O3 2- +H2O(1)

[0032] (3) Electron microscopy studies of this invention revealed that goethite in limonite ore exhibits nanocrystalline characteristics and can be further thermally decomposed into porous hematite with even finer crystallographic particle size. Figure 8 (As shown); the iron concentrate produced during the fluidized bed roasting process of sulfur concentrate has a porous nanostructure (such as...). Figure 9 As shown), the thermal decomposition products of iron-manganese carbonates also possess a nanoporous structure (e.g., Figure 10 As shown in the figure, these nanoporous iron oxides can promote the activation of iron sulfides.

[0033] (4) Experimental studies of this invention have found that the addition of iron oxides not only promotes the mechanochemical activation of iron sulfides, but also enhances the abiotic effects of anaerobic microbial denitrification by generating active ferrous ions. Ferrous ions can react chemically with intermediate products of nitrate biological denitrification (Equation 2) to convert nitrite nitrogen into nitrogen gas and eliminate nitrite accumulation; the generated active ferric ions react directly with iron sulfides (Equations 3 and 4) to generate ferrous ions again, realizing the iron ion cycle and generating elemental sulfur and polysulfides; the active ferric ions react with phosphate ions in the water to generate iron phosphate (Equation 5), which can fix phosphorus in a wide pH range of 6-9, thereby removing phosphorus while denitrifying wastewater. The aforementioned multiple abiotic chemical reactions are basically in acid-base balance, which can stabilize the pH of the effluent.

[0034] Fe 2+ +2NO2 - +4H + -------Fe 3+ +N2+2H2O(2)

[0035] 2Fe 3+ +FeS2-------3Fe 2++2S(3)

[0036] 2Fe 3+ +Fe 1-x S-------(3-x)Fe 2+ +S(4)

[0037] Fe 3+ +HPO4 2- +OH - -------FePO4++H2O(5). Attached Figure Description

[0038] Figure 1 The particle size distribution curve of low-sulfur concentrate after mechanical and chemical activation by ball milling for 48 hours (limonite: low-sulfur concentrate = 1:4) shows that the product contains a small amount of nanoparticles, most of which are 1-8 micrometer particles, which is significantly reduced in size compared with the original 70-micrometer particles.

[0039] Figure 2 The SEM image shows that the low-sulfur concentrate (limonite: low-sulfur concentrate = 1:4) was mechanically and chemically activated by a drum ball mill for 48 hours. The particle morphology is irregular and the particle size is 0.1-8 micrometers.

[0040] Figure 3 The crystallinity changes of pyrrhotite before and after mechanical and chemical activation by ball milling (ball milling alone for 24 hours, or ball milling with limonite at a mass ratio of 4:1 for 24 hours) show that the characteristic diffraction peaks of pyrrhotite decrease and the crystallinity becomes lower after ball milling with the addition of limonite.

[0041] Figure 4 The crystallinity changes of low-sulfur concentrate before and after mechanical and chemical activation by drum ball milling (ball milling alone for 24 hours, or ball milling with limonite at a mass ratio of 4:1 for 24 hours) show that the characteristic diffraction peaks of pyrrhotite and pyrite decrease after ball milling with the addition of limonite, indicating a lower crystallinity.

[0042] Figure 5 The effect of mechanical and chemical activation time of low-sulfur concentrate-limonite (mass ratio 4:1) synergistic drum ball milling on the crystallinity of low-sulfur concentrate.

[0043] Figure 6To investigate the denitrification performance of different iron sulfides and limonite after mechanical and chemical activation (24 h) by ball milling, the following method was used: The ball-milled composite material was added to 500 mL reaction flasks in duplicate. 450 mL of simulated wastewater with an initial nitrate nitrogen concentration of 50 mg / L and 50 mL of denitrifying Thiobacillus bacterial solution were added. The flasks were sealed with rubber stoppers and aluminum foil caps. After deoxygenation by purging with argon gas for 5 min, the flasks were placed in a constant-temperature shaker at 150 r / min and 25 °C for denitrification experiments. Periodically, 5 mL of solution was taken from each reaction flask for NO3 analysis. - -N, NO2 - -N, SO4 2- pH and TOC were measured. Suspension samples were filtered, and some solid samples were immobilized for microbial observation using SEM and TEM; others were analyzed using XRD, XPS, Raman spectroscopy, and microbial community analysis. The denitrification performance of different iron sulfides and limonite through drum ball milling mechanochemical activation (24 h) was investigated. Results showed that the denitrification performance of the mixed-milling mineral system was generally better than that of the single system. This indicates that nanoporous iron oxides, as activators, effectively promoted the activation of iron sulfides, thereby enhancing the utilization of iron sulfides by microorganisms and resulting in better denitrification performance. Among these, the denitrification performance of the mixed-milling of low-sulfur concentrate and limonite was the best, completely removing 50 mg / L of nitrate nitrogen within 43 h.

[0044] Figure 7 To investigate the effect of the mechanical and chemical activation time of co-milling low-sulfur concentrate and limonite on the denitrification rate, the static experimental operation method was the same as above. Experimental results showed that when the mixed milling times were 12h, 24h, and 48h, the nitrate nitrogen removal rate reached 100% at 18h, 43h, and 73h, respectively, indicating that the denitrification effect was optimal at a milling time of 48h. This demonstrates that denitrification performance is directly proportional to milling time. The reason for this is that extending the milling time reduces the powder particle size, significantly decreases crystallinity, and creates numerous structural defects, which are more conducive to microbial utilization and greatly enhance the reactivity of iron sulfides.

[0045] Figure 8 SEM images of 5nm hematite crystals and nanopores formed by thermal activation (heating at 300℃ for 30 min) of 80nm diameter goethite.

[0046] Figure 9 The images show SEM images of nanostructured iron oxide formed by boiling and calcining sulfur powder with a particle size of micrometers. (a) is a scanning electron microscope image magnified 5000 times, showing the overall characteristics of the sulfur powder particles after boiling and calcining; (b) is a scanning electron microscope image magnified 20000 times, showing the characteristics of the newly formed nano-iron oxide particles after boiling and calcining sulfur powder.

[0047] Figure 10SEM image of nanostructured iron oxide formed by calcination of siderite. Detailed Implementation

[0048] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0049] Example 1

[0050] Low-sulfur concentrate from a certain mine was used as the iron sulfide raw material, and limonite ore was used as the activation promoter raw material. The low-sulfur concentrate and limonite were mixed and ground through a 200-mesh sieve at a mass ratio of 10:1. Water was added to prepare a slurry with a mass concentration of 25%. The slurry was mechanically and chemically activated in a drum for 12 hours to obtain a slurry-like denitrification and dephosphorization agent.

[0051] The slurry-like denitrification and phosphorus removal agent was diluted with water to a 5% concentration and pumped into a mature, autotrophic denitrification fluidized bed reactor. The influent contained nitrate nitrogen of 12-15 mg / L, COD of 25-30 mg / L, and TP of 1.1-1.5 mg / L, with a water temperature of 17-25℃. The reactor was operated with a hydraulic retention time of 0.5 h. The effluent nitrate nitrogen, nitrite nitrogen, TN, total phosphorus concentration, and pH were measured daily. All effluent indicators consistently met the Class IV surface water quality standard.

[0052] Example 2

[0053] Using lumpy pyrrhotite ore from a certain mine as raw material, and calcined siderite at 500℃ as raw material for activation promoter, the ore was crushed and pulverized through a 300-mesh sieve. The pyrrhotite powder and limonite powder were mixed at a mass ratio of 5:1, and water was added to prepare a slurry with a mass concentration of 30%. The slurry was mechanically and chemically activated in a drum for 24 hours to obtain a slurry-like denitrification and dephosphorization agent.

[0054] The slurry-like denitrifying and dephosphorizing agent is heated to 70-80℃ and vacuum dried. It is then pulverized and passed through a 200-mesh sieve. The powder is further mixed with sulfur at a mass ratio of 1:10 and heated to 140-160℃ to melt the sulfur. Under the condition of heat preservation, the mixture is stirred evenly and spread into a thin layer of 3-6mm. The thin layer of melt is cooled, crushed, and sieved to obtain a material with a particle size of 3-8mm, which is the granular denitrifying and dephosphorizing agent.

[0055] The denitrification and phosphorus removal agent is filled into the sulfur autotrophic denitrification biological filter column, which is then filled with enriched sulfur autotrophic denitrification bacterial solution. Sodium nitrate is added to make the nitrate nitrogen in the filter column reach 200 mg / L. Water is circulated according to the hydraulic retention time of 4 hours to promote the growth and biofilm formation of denitrification microorganisms on the surface of the filter media until the total nitrogen in the water reaches below 4 mg / L, thus completing the microbial biofilm formation.

[0056] The effluent from the secondary sedimentation tank is used as the feedwater for the denitrification reactor. The feedwater contains nitrate nitrogen of 12-15 mg / L, COD of 25-30 mg / L, TP of 0.8-1.5 mg / L, and water temperature of 15-25℃. The reactor is operated with a hydraulic retention time of 0.5 h. The concentrations of nitrate nitrogen, nitrite nitrogen, TN, total phosphorus, and pH in the effluent are measured daily. The effluent consistently meets the Class IV surface water quality standard.

[0057] Example 3

[0058] Lump pyrrhotite ore from a certain mine was used as the iron sulfide raw material, and limonite and siderite ores were used as activation promoter raw materials. Pyrrhotite, limonite, and siderite were mixed at a mass ratio of 10:1:1, coarsely crushed and mixed, and then ultra-finely ground to 300 mesh in a grinding mill. Water was added to prepare a slurry with a mass concentration of 25%, and mechanically and chemically activated for 8 hours to obtain a slurry-like denitrification and phosphorus removal agent. The water treatment experiment was the same as in Example 1.

[0059] Example 4

[0060] Low-sulfur concentrate from a certain mine was used as the iron sulfide raw material, and iron concentrate produced by calcining sulfur concentrate in a fluidized bed furnace was used as the activation promoter raw material. The low-sulfur concentrate and iron concentrate were mixed at a mass ratio of 5:1, and water was added to prepare a slurry with a mass concentration of 30%. After mechanical and chemical activation for 15 hours, a slurry-like denitrification and dephosphorization agent was obtained.

[0061] The slurry-like denitrifying and dephosphorizing agent was vacuum dried and pulverized to a 200-mesh sieve. The powder was then added to molten sulfur at a mass ratio of 2:10 and stirred until homogeneous. The material temperature was maintained above 140°C to ensure good flowability of the mixture. The molten mixture was extruded, cooled, and granulated to obtain rod-shaped or near-spherical particles with a diameter of 3–6 mm, which is the granular denitrifying and dephosphorizing agent. The water treatment experiment was the same as in Example 2.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing autotrophic simultaneous nitrogen and phosphorus removal agent by mechanical-chemical activation of iron sulfide, characterized in that: Fe-sulfide raw material is mixed with activation accelerator in a mass ratio of 3-20:1, ground into powder of more than 200 mesh, then water is added to prepare a slurry with a mass concentration of 10-40%, and the slurry is mechanically and chemically activated in a high-efficiency grinding device for 2-48 hours to obtain a slurry-like autotrophic simultaneous denitrification and phosphorus removal agent; The slurry-like autotrophic simultaneous denitrification and phosphorus removal agent is mixed with molten liquid sulfur and formed into granular particles to obtain a granular autotrophic simultaneous denitrification and phosphorus removal agent; Alternatively, the slurry-like autotrophic simultaneous denitrification and phosphorus removal agent is mixed with sulfur raw material to obtain a slurry-like autotrophic simultaneous denitrification and phosphorus removal agent containing sulfur. The Fe-sulfide raw material includes at least one of pyrrhotite ore, low-sulfur fine powder and sulfur fine powder, and the content of Fe-sulfide in the Fe-sulfide raw material is not less than 90%, and the total content of Cu, Zn, Pb and As heavy metals is not higher than 0.3%; the activation accelerator includes at least one of limonite ore, thermally activated limonite, iron fine powder produced in a sulfur fine powder boiling roasting process, sulfuric acid cinder and siderite ore and thermal decomposition products thereof, and the content of iron and manganese in the activation accelerator is not less than 50%.

2. The method of claim 1, wherein, The granular autotrophic simultaneous denitrification and phosphorus removal agent is prepared by the following steps: The slurry-like autotrophic simultaneous denitrification and phosphorus removal agent is vacuum dried, crushed and passed through a 200-mesh sieve, then added to molten liquid sulfur in a mass ratio of 5-15% and stirred uniformly, the material temperature is maintained at 130-160℃, and the material is kept in a good flow state and uniformly mixed to obtain a mixed molten material; The mixed molten material is sprayed into droplets and cooled to obtain near-spherical particles with a particle size of 3-8 mm, which are the granular autotrophic simultaneous denitrification and phosphorus removal agent; or the mixed molten material is spread into a thin layer with a thickness of 3-8 mm, cooled, broken and sieved to obtain material with a particle size of 3-8 mm, which are the granular autotrophic simultaneous denitrification and phosphorus removal agent.

3. The method of claim 1, wherein, The slurry-like autotrophic simultaneous denitrification and phosphorus removal agent containing sulfur is prepared by the following steps: The slurry-like autotrophic simultaneous denitrification and phosphorus removal agent is mixed with sulfur raw material in a mass ratio of 1:5-20, and water is added to ball mill to prepare a slurry with a mass concentration of 10-30%, thereby obtaining the slurry-like autotrophic simultaneous denitrification and phosphorus removal agent containing sulfur.

4. The method of claim 3, wherein: The sulfur raw material includes at least one of industrial sulfur powder, industrial sulfur sheet, desulfurization by-product sulfur paste and waste rich in sulfur.

5. An autotrophic simultaneous denitrification and phosphorus removal agent prepared by the method of any one of claims 1-4.

6. A method for using the autotrophic simultaneous denitrification and phosphorus removal agent of claim 5, characterized in that: The granular autotrophic simultaneous denitrification and phosphorus removal agent is used as the filler of a sulfur autotrophic denitrification biofilter, and the operation is carried out at a hydraulic retention time of 30-60 min; Alternatively, the slurry-like autotrophic simultaneous denitrification and phosphorus removal agent or the slurry-like autotrophic simultaneous denitrification and phosphorus removal agent containing sulfur is diluted with water to prepare a dilute slurry with a mass concentration of 0.1-10%, and the slurry is pumped and added to the influent of an anoxic denitrification tank, or added to the influent of a denitrification and phosphorus removal fluidized reactor, or added to the influent of a denitrification deep bed filter to replace part or all of the organic carbon source for denitrification.

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