A method for nitrogen removal by PN-Anammox integrated method enhanced by iron-supported biochar

Abstract

This invention discloses a method for enhanced PN-Anammox integrated nitrogen removal using iron-loaded biochar. First, suitable biochar material is selected, dried, and then impregnated in an iron salt solution followed by post-treatment to obtain Fe / BC biochar particles loaded with micro- and nano-iron. Next, Fe / BC is inoculated with anaerobic ammonia oxidation sludge in an anaerobic reactor for cultivation, and process parameters are adjusted to form Fe / BC-Anammox composite anaerobic sludge particles. Subsequently, these particles are inoculated into a reactor containing well-acclimated short-cut nitrification sludge, and reaction conditions are adjusted to construct an integrated nitrogen removal system. The effect is monitored, and the nitrogen removal system is kept stable within a certain dissolved oxygen fluctuation range. This method has broad prospects in the field of ammonia nitrogen wastewater treatment and provides a new approach to solving the poor stability of related PN-Anammox integrated nitrogen removal systems.

Description

Technical Field

[0001] This invention relates to the fields of functional materials and environmental engineering, particularly to biological treatment technologies related to nitrogen removal, and specifically to an integrated denitrification method for PN-Anammox enhanced by iron-supported biochar. Background Technology

[0002] With the rapid development of industry and cities, rare earth elements are widely used due to their excellent optical, electrical, and magnetic properties. Currently, the main mining process for rare earth ore is in-situ leaching using ammonium sulfate as the leaching agent. This leaves a large amount of ammonium salts in the soil after leaching. Under rainwater irrigation conditions, these ammonium salts easily migrate downwards, settling into surface water or seeping into groundwater, leading to the enrichment of ammonia nitrogen in deep mine layers, acidification of surface water in mining areas, and excessive ammonia nitrogen levels, causing eutrophication of water bodies. This poses a serious threat to the surrounding environment, affecting people's living conditions and physical and mental health. Therefore, the removal of residual ammonium salts from rare earth tailings is an urgent task. Traditional nitrogen removal methods, such as nitrification and denitrification processes, typically require large amounts of energy consumption, especially dissolved oxygen (DO). However, the short-cut nitrification-anaerobic ammonia oxidation (PN-Anammox) integrated reaction system, due to its high efficiency and energy-saving characteristics, has gradually become a research hotspot in the field of ammonia nitrogen pollution control. The integrated PN-Anammox microbial particles mainly contain AnAOB bacteria, which require an anaerobic environment, while the outer layer contains AOB bacteria, which require an aerobic environment. Therefore, the difference in dissolved oxygen requirements of integrated microbial particles has become a technical bottleneck for integrated PN-Anammox denitrification.

[0003] However, the stable operation of the PN-Anammox integrated system faces several challenges. Start-up is difficult, and the slow growth rate of functional bacteria in the PN-Anammox sludge makes it difficult for the system to quickly achieve the desired nitrogen removal effect. Furthermore, the system's biochemical reaction conditions are quite demanding; factors such as temperature, pH, and ammonia nitrogen concentration have a significant impact on the reaction process, and even slight errors can lead to system instability. Dissolved oxygen is the key factor controlling the stable operation of the integrated denitrification system; excessive dissolved oxygen inhibits the Anammox reaction, thus affecting nitrogen removal efficiency. At the same time, the optimal environmental conditions required for AOB and AnAOB differ, especially in dissolved oxygen concentration control. Therefore, precise control of dissolved oxygen in the reactor is crucial to improving system operating efficiency and removal performance.

[0004] Biochar, as a material with high specific surface area and good adsorption performance, has been widely used in environmental pollution control. Iron, as an important metallic element, is a cofactor for many enzymes in microbial cells, a redox carrier, and an important component of the electron transport chain. Modifying biochar with iron can significantly improve its adsorption performance. This not only enhances the activity of anaerobic ammonia oxidizing bacteria but also utilizes its redox properties as a buffer coating material, enabling effective control of dissolved oxygen within the system. A stable environment is formed within the reactor, promoting the synergistic effect of AOB and AnAOB in the same reactor, thereby improving the nitrogen removal efficiency of the short-cut nitrification-anaerobic ammonia oxidation integrated system. The application of such composite materials provides new ideas and possibilities for optimizing ammonia nitrogen removal technology and improving system energy efficiency. Therefore, studying the application of iron-loaded biochar in the PN-Anammox integrated reactor, especially its role in dissolved oxygen control and system stability, has significant ecological and engineering implications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for regulating dissolved oxygen in an iron-supported biochar-based PN-Anammox integrated nitrogen removal system, solving the problems of unstable dissolved oxygen concentration and low anaerobic ammonia oxidation efficiency during PN-Anammox integrated cultivation, thereby improving nitrogen removal efficiency and system stability. This invention is simple to operate, environmentally friendly, and provides a technical approach to solving the dissolved oxygen control problem in PN-Anammox integrated systems.

[0006] To achieve the above objectives, the present invention provides an integrated denitrification method for PN-Anammox enhanced by iron-supported biochar, characterized by comprising the following steps:

[0007] S1) Select suitable biomass materials, dry them under certain temperature conditions to remove moisture, and then carbonize them to obtain unmodified biochar material BC. Put BC into an iron salt solution for impregnation, and then reduce it to obtain iron-loaded micro-nano biochar particles.

[0008] S2) Inoculate mature anaerobic ammonia oxidation sludge and iron-loaded micro-nano biochar particles into the anaerobic reactor. By adjusting the process parameters in the reactor, the system can achieve a stable denitrification effect and form Fe / BC-Anammox composite anaerobic sludge particles.

[0009] S3) The Fe / BC-Anammox composite anaerobic sludge particles from step S2) are inoculated into a reactor containing acclimatized and mature short-cut nitrification sludge. In the reactor, the reaction conditions are adjusted to promote the interaction between short-cut nitrification and anaerobic ammonia oxidation bacteria, thereby constructing an integrated denitrification system. The denitrification effect of the integrated short-cut nitrification-anaerobic ammonia oxidation system is monitored.

[0010] Furthermore, the biomass mentioned in step S1) includes, but is not limited to, common straw or sawdust biomass materials, whose main components include one or more of cellulose, hemicellulose, lignin and sugars.

[0011] Furthermore, the iron salt is one or both of FeCl3•6H2O and FeSO4•6H2O; the impregnation temperature is 20~30℃, and the impregnation time is 2~24h.

[0012] Furthermore, the iron in the iron-loaded biochar prepared in step S1) is Fe. 0 It is one or more of FeO or Fe3O4.

[0013] Furthermore, the process parameters are: temperature, pH, aeration rate, and n(NH4) within the reactor. + -N): n(NO2) - -N), stirring rate. By adjusting the temperature, pH, aeration rate, and n(NH4) in the reactor. + -N): n(NO2) - By adjusting process parameters such as -N and stirring rate, ideal nitrogen removal efficiency and nitrogen treatment load are obtained, and the system is continuously operated until a stable nitrogen removal effect is achieved, forming Fe / BC-Anammox composite anaerobic sludge particles.

[0014] Furthermore, the reaction conditions are characterized by temperature, pH value, dissolved oxygen concentration, and ammonia nitrogen concentration. The reaction conditions, such as temperature, pH value, dissolved oxygen concentration, and ammonia nitrogen concentration, are adjusted to cultivate the interaction between short-cut nitrification and anaerobic ammonia oxidation bacteria, constructing an integrated denitrification system and monitoring the integrated denitrification effect of short-cut nitrification-anaerobic ammonia oxidation.

[0015] Furthermore, the method is characterized in that, in step S2), the amount of iron-loaded biochar material inoculated into the anaerobic reactor relative to the ammonia nitrogen wastewater is 0.5~5.0 wt%; the volume percentage of anaerobic ammonia oxidation sludge relative to the ammonia nitrogen wastewater is 0.5~2.0 wt%; the ammonia nitrogen concentration is 50~400 mg / L; the temperature is 25~35℃; and the pH is 7~10.

[0016] Furthermore, the characteristic feature is that the ratio of nitrite concentration to ammonia nitrogen concentration in the effluent is 1 to 1.5.

[0017] Furthermore, the feature is that the temperature is adjusted to 20~40℃, the pH to 7~10, and the dissolved oxygen to 0~1.5mg / L by adopting an intermittent aeration method.

[0018] Furthermore, the reduction treatment method described in step S1) can be a reduction by adding a soluble organic / inorganic reducing agent or a pyrolysis reduction; the pyrolysis reduction temperature is 350~700℃, and the time is 1~4 h.

[0019] During the operation of the integrated system, the ideal control range of dissolved oxygen (DO) is set according to the requirements of the denitrification reaction. Dissolved oxygen sensors or probes are installed at key locations in the system (such as the inlet and outlet of the reaction tank) to achieve real-time monitoring of dissolved oxygen concentration. This allows for timely assessment of the denitrification efficiency and stability of the denitrification system under fluctuating aeration conditions.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1) Adjust the dissolved oxygen concentration within the PN / A integrated system to improve the system's denitrification stability.

[0022] The iron-modified biochar used in this invention is a composite material with a high specific surface area and good adsorption performance. The introduction of iron not only improves the adsorption capacity of the biochar but also enhances the redox environment of the system. Using iron-loaded biochar as a buffer material effectively regulates the dissolved oxygen concentration in the reactor. In traditional nitrogen removal systems, excessive dissolved oxygen inhibits anaerobic ammonium oxidation, leading to low nitrogen removal efficiency. This invention optimizes dissolved oxygen control through the redox properties of iron-loaded biochar, enabling short-cut nitrification and anaerobic ammonium oxidation to operate in coordination within an ideal dissolved oxygen range in the same reactor. This avoids the problem of nitrogen removal efficiency being affected by microbial competition or incompatibility in traditional systems, thereby improving the system's nitrogen removal efficiency and long-term stability.

[0023] 2) Green and environmentally friendly, easy to operate and implement

[0024] This invention is simple to operate and environmentally friendly. The preparation method of iron-supported biochar material uses common biomass materials and iron salt modification. The entire process does not involve complex chemicals or high-energy-consuming operations, meets environmental protection requirements, and the materials can be recycled during the preparation process, reducing waste generation. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without creative effort. In the drawings:

[0026] Figure 1 is a schematic diagram of the structure of the present invention.

[0027] Figure 2 shows the scanning electron microscope images of unloaded iron bagasse biochar and magnetic Fe3O4-loaded bagasse biochar.

[0028] Figure 3 shows the effect of adding magnetic Fe3O4 bagasse biochar on the denitrification of the integrated system compared to not adding any loading.

[0029] Figure 4 The effect of adding magnetic Fe3O4 bagasse biochar as a load on dissolved oxygen in an integrated system compared to not adding any load. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of a descriptive feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or sets.

[0032] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, only one of components with the same structure or function is shown schematically, or only one is labeled. In this document, "one" can mean not only "only one" but also "more than one".

[0033] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0034] In the embodiments shown in the accompanying drawings, the directional indications (such as up, down, left, right, front, and back) used to explain the structure and movement of the various components of the invention are relative rather than absolute. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, these directional indications also change accordingly.

[0035] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation of the present invention will be described below with reference to the accompanying drawings.

[0037] Example 1

[0038] A method for removing ammonia nitrogen from rare earth mine wastewater using iron-supported biochar-enhanced PN-Anammox integrated system includes the following steps:

[0039] 1) Preparation of unmodified biochar materials (BC)

[0040] Sugarcane bagasse biomass was selected as the raw material. After washing away the sugar content, it was dried in an oven at 80℃. The dried bagasse was then placed in a ceramic boat, wrapped in tin foil, and placed in a muffle furnace. The temperature was increased to 550℃ at a rate of 10℃ / min and held for 1 hour. After the pyrolysis process, the resulting biochar was naturally cooled to ambient temperature to obtain unmodified sugarcane bagasse biochar material for later use. (The method for preparing unmodified biochar in the following examples is the same and will not be repeated.)

[0041] 2) Preparation of magnetic Fe3O4 bagasse biochar material (Fe3O4 / BC)

[0042] This material was prepared by co-precipitation. 300 mL of deionized water was placed in a 500 mL three-necked flask, and nitrogen gas was purged for 30 min at room temperature to purge air. Then, 2.25 g of FeCl3·6H2O and 1.15 g of FeSO4·6H2O were added to the flask, and the mixture was mechanically stirred for 20 min at room temperature, resulting in an orange-red solution. 0.69 g of BC was weighed into the mixture, and the mixture was mechanically stirred for 3 h at room temperature. 35 mL of concentrated ammonia was added to the mixture, resulting in a black precipitate. Anhydrous ethanol was quickly added to the mixture to prevent precipitate aggregation, and the pH of the mixture was measured to reach 10. The mixture was heated in a 60 °C water bath with continued mechanical stirring for 4 h, then cooled to room temperature. The entire process was carried out under a nitrogen atmosphere. The product was separated using a magnet, washed three times with deionized water and three times with anhydrous ethanol, and then dried in a 70 °C oven for 20 h. The final product was an iron-carbon composite material with an iron-carbon ratio of 1:1, which was then ready for use.

[0043] 3) Prepare simulated ammonia nitrogen wastewater for culturing anaerobic ammonia-oxidizing bacteria, with the following specific components: 50~100 mg / L NH4 + -N, 65~132 mg / L NO2 --N, 1000 mg / L NaHCO3, 1000 mg / L KHCO3, 27 mg / L KH2PO4, 136 mg / L CaCl2, 20 mg / L MgSO4, 1.0 mL / L trace element solution I, and 1.2 mL / L trace element solution II. Trace element solution I consists of 5.0 g / L EDTA and 5.0 g / L FeSO4·7H2O. The composition of trace element solution II is: 5.0 g / L EDTA, 0.22 g / L NaMoO4·2H2O, 0.19 g / L NiCl2·6H2O, 0.25 g / L CuSO4·5H2O, 0.24 g / L CoCl2·6H2O, 0.43 g / L ZnSO4·7H2O, and 0.99 g / L MnCl2·4H2O. (The composition of the simulated ammonia nitrogen wastewater in the following examples is the same and will not be repeated). Anaerobic ammonia oxidation sludge was inoculated into the reactor, and Fe3O4 / BC material was added. The temperature was set at 30℃ and the hydraulic retention time was 22 h. The influent was changed regularly every day. After the influent was replaced, N2 was introduced into the reactor for 5 min to maintain an anaerobic environment. The NH4 content in the reactor was measured regularly every day. + -N, NO2 - -N, NO3 - The nitrogen concentration changes until the nitrogen removal performance of the anaerobic ammonia oxidation system stabilizes;

[0044] 4) Add the stable-performance anaerobic ammonia oxidation sludge loaded with Fe3O4 / BC material from step 3) to the stably operating short-cut nitrification reactor to construct an integrated short-cut nitrification-anaerobic ammonia oxidation denitrification system. The amount of anaerobic ammonia oxidation sludge used is 2% of the mass of ammonia nitrogen wastewater; the amount of short-cut nitrification sludge used is 2% of the volume of ammonia nitrogen wastewater. Intermittent aeration is adopted, with an aeration mode of 30 minutes of aeration followed by 30 minutes of aeration stoppage, and a glass rotor flowmeter is used to control the dissolved oxygen level to below 1.2 mg / L. The initial concentration of ammonia nitrogen in the influent was 150 mg / L. The pH of the ammonia nitrogen wastewater was adjusted to 8.0. After denitrification treatment for 10 days at a temperature of 30℃ and a rotation speed of 150 r / min, the average effluent ammonia nitrogen concentration was 7.24 mg / L, the average ammonia nitrogen removal rate was 95.17%, the average effluent nitrate nitrogen was 2.14 mg / L, the average nitrite nitrogen was 0.03 mg / L, and the oxygen concentration in the system solution was 0.3~0.5 mg / L.

[0045] Comparative Example 1

[0046] A method for constructing an integrated short-cut nitrification-anaerobic ammonium oxidation system using iron-supported biochar includes the following steps:

[0047] 1) Prepare simulated ammonia nitrogen wastewater for culturing anaerobic ammonia-oxidizing bacteria. Inoculate the reactor with anaerobic ammonia-oxidizing sludge without adding any additional materials. Set the temperature to 30℃ and the hydraulic retention time to 22 hours. Change the influent regularly each day. After the influent is completely replaced, introduce N2 into the reactor for 5 minutes to maintain an anaerobic environment. Take samples of the influent and effluent daily to measure the NH4 content in the reactor. + -N, NO2 - -N, NO3 - The nitrogen concentration changes until the nitrogen removal performance of the anaerobic ammonia oxidation system stabilizes;

[0048] 2) Add the stable anaerobic ammonia oxidation sludge from step 1) of this example to the stably operating short-cut nitrification reactor to construct an integrated short-cut nitrification-anaerobic ammonia oxidation denitrification system. The amount of anaerobic ammonia oxidation sludge used is 2% of the mass of the ammonia nitrogen wastewater; the amount of short-cut nitrification sludge used is 2% of the volume of the ammonia nitrogen wastewater. Intermittent aeration is adopted, with an aeration mode of 30 minutes of aeration followed by 30 minutes of aeration stoppage, and a glass rotor flowmeter is used to control the dissolved oxygen level to below 1.2 mg / L. The initial concentration of ammonia nitrogen in the influent was 150 mg / L. The pH of the ammonia nitrogen wastewater was adjusted to 8.0. After denitrification treatment for 10 days at 30℃ and 150 r / min, the average effluent ammonia nitrogen concentration was 47.4 mg / L, the average ammonia nitrogen removal rate was 68.4%, the average effluent nitrate nitrogen was 73.52 mg / L, the average nitrite nitrogen was 17.11 mg / L, and the oxygen concentration in the system solution was 1~1.2 mg / L.

[0049] Comparative Example 2

[0050] A method for constructing a short-cut nitrification-anaerobic ammonium oxidation integrated system with added unmodified biochar includes the following steps:

[0051] 1) Prepare simulated ammonia nitrogen wastewater for cultivating anaerobic ammonia-oxidizing bacteria. Inoculate the reactor with anaerobic ammonia-oxidizing sludge, add unmodified biochar material, set the temperature to 30℃ and the hydraulic retention time to 22h, and change the influent regularly every day. After the influent is completely replaced, introduce N2 into the reactor for 5 minutes to maintain an anaerobic environment. Take samples of the influent and effluent daily to measure the NH4 content in the reactor. + -N, NO2 - -N, NO3 - The nitrogen concentration changes until the nitrogen removal performance of the anaerobic ammonia oxidation system stabilizes;

[0052] 2) Add the stable anaerobic ammonia oxidation sludge from step 1) of this example to the stably operating short-cut nitrification reactor to construct an integrated short-cut nitrification-anaerobic ammonia oxidation denitrification system. The amount of anaerobic ammonia oxidation sludge used is 2% of the mass of the ammonia nitrogen wastewater; the amount of short-cut nitrification sludge used is 2% of the volume of the ammonia nitrogen wastewater. Intermittent aeration is adopted, with an aeration mode of 30 minutes of aeration followed by 30 minutes of aeration stoppage, and a glass rotor flowmeter is used to control the dissolved oxygen level to below 1.2 mg / L. The initial concentration of ammonia nitrogen in the influent was 150 mg / L. The pH of the ammonia nitrogen wastewater was adjusted to 8.0. After denitrification treatment for 10 days at 30℃ and 150 r / min, the average effluent ammonia nitrogen concentration was 35.69 mg / L, the average ammonia nitrogen removal rate was 76.21%, the average effluent nitrate nitrogen was 51.56 mg / L, the average nitrite nitrogen was 32.18 mg / L, and the oxygen concentration in the system was 0.7~0.9 mg / L.

[0053] Example 2

[0054] A method for removing ammonia nitrogen from rare earth mine wastewater using iron-supported biochar-enhanced PN-Anammox integrated system includes the following steps:

[0055] 1) Preparation of zero-valent iron-loaded sugarcane bagasse biochar material (Fe 0 / BC)

[0056] The solution was prepared using a liquid-phase reduction method. 2.78 g of FeSO4•6H2O was weighed and dissolved in anhydrous ethanol / water solution (V(anhydrous ethanol):(water) = 30:70). The solution was transferred to a three-necked flask, and a certain amount of unmodified biochar was added to achieve a BC to nano-zero-valent iron mass ratio of 2:1 in the composite material. Nitrogen gas was then introduced, and the mixture was mechanically stirred. After 20 min of aeration, 100 ml of a 0.04 mol / L sodium borohydride (NaBH4) solution (pH=8) was added dropwise to the three-necked flask from a constant-pressure funnel at a rate of 2 drops / s, and vigorous mechanical stirring continued for 50 min. After the reduction reaction was complete, nitrogen gas was continued to be introduced until no significant hydrogen gas was produced in the reactor. The mixture was poured out and transferred to a nitrogen-filled glove box for filtration. After filtration, the mixture was washed with anhydrous ethanol and centrifuged repeatedly three times. A portion of the supernatant was then poured out, and the remaining solid was dried in an oven under N2 protection and stored in a sealed container for later use.

[0057] 2) Prepare simulated ammonia nitrogen wastewater for culturing anaerobic ammonia-oxidizing bacteria. Inoculate the anaerobic ammonia-oxidizing sludge into the reactor and add the Fe prepared in step 1) of this example. 0 / BC reactor was set to a temperature of 30℃ and a hydraulic retention time of 22 hours. The influent was changed regularly each day. After the influent was replaced, N2 was introduced into the reactor for 5 minutes to maintain an anaerobic environment. NH4 levels in the influent and effluent were measured regularly each day.+ -N, NO2 - -N, NO3 - The nitrogen concentration changes until the nitrogen removal performance of the anaerobic ammonia oxidation system stabilizes;

[0058] 3) Add the stable denitrification performance of the anaerobic ammonia oxidation sludge loaded with FeO / BC material from step 2) to the stably operating short-cut nitrification reactor to construct an integrated short-cut nitrification-anaerobic ammonia oxidation denitrification system. The amount of anaerobic ammonia oxidation sludge used is 2% of the mass of ammonia nitrogen wastewater; the amount of short-cut nitrification sludge used is 2% of the volume of ammonia nitrogen wastewater. Intermittent aeration is adopted, with an aeration mode of 30 minutes of aeration followed by 30 minutes of aeration stoppage, and a glass rotor flowmeter is used to control the dissolved oxygen level to below 1.2 mg / L. The initial concentration of ammonia nitrogen in the influent was 150 mg / L. The pH of the ammonia nitrogen wastewater was adjusted to 8.0. After denitrification treatment for 10 days at a temperature of 30℃ and a rotation speed of 150 r / min, the average effluent ammonia nitrogen concentration was 5.64 mg / L, the average ammonia nitrogen removal rate was 96.24%, the average effluent nitrate nitrogen was 3.2 mg / L, the average nitrite nitrogen was 0 mg / L, and the oxygen concentration in the system solution was 0.2~0.4 mg / L.

[0059] Example 3

[0060] A method for removing ammonia nitrogen from rare earth mine wastewater using iron-supported biochar-enhanced PN-Anammox integrated system includes the following steps:

[0061] 1) Preparation of iron-loaded sugarcane bagasse biochar material (Fe 2+ / BC)

[0062] 2.5 g of unmodified biochar material was impregnated and stirred for 3 h with 50 mL of a mixture of FeCl3·6H2O and Na2S·9H2O of different concentrations (iron-sulfur molar ratio of 20:1). After solid-liquid separation and drying, the mixture was pyrolyzed under anaerobic conditions for 3 h. The thoroughly stirred mixture was then poured into centrifuge tubes for solid-liquid separation. The separated sludge was dried at 60 °C for 12 h. The dried precursor was placed in a tube furnace and pyrolyzed and carbonized under anaerobic conditions, heated to 500 °C and held for 2 h. After cooling to room temperature, it was removed, ground into powder, and collected through an 80-mesh sieve to prepare the resulting ferrous sulfide-biochar composite material (FeCl3·6H2O·Na2S·9H2O·FeCl3·6H2O·Na2S·9H2O·FeCl3·6H2O·Na2S·9H2O·Na2S ... 2+ / BC).

[0063] 2) Prepare simulated ammonia nitrogen wastewater for culturing anaerobic ammonia-oxidizing bacteria. Inoculate the anaerobic ammonia-oxidizing sludge into the reactor and add the Fe prepared in step 1) of this example. 2+ / BC reactor was set to a temperature of 30℃ and a hydraulic retention time of 22 hours. The influent was changed regularly each day. After the influent was replaced, N2 was introduced into the reactor for 5 minutes to maintain an anaerobic environment. NH4 levels in the influent and effluent were measured regularly each day. + -N, NO2 - -N, NO3 - The nitrogen concentration changes until the nitrogen removal performance of the anaerobic ammonia oxidation system stabilizes;

[0064] 3) Add the nitrogen removal performance stable and Fe-loaded process from step 2) to a stable short-path nitrification reactor. 2+ A short-cut nitrification-anammox integrated nitrogen removal system was constructed using anammox sludge made of BC material. The amount of anammox sludge used was 2% of the mass of ammonia nitrogen wastewater; the amount of short-cut nitrification sludge used was 2% of the volume of ammonia nitrogen wastewater. Intermittent aeration was used, with an aeration mode of 30 minutes of aeration followed by 30 minutes of aeration and then stopping. A glass rotor flowmeter was used to control the dissolved oxygen level to below 1.2 mg / L. The initial influent ammonia nitrogen concentration was 150 mg / L, and the pH of the ammonia nitrogen wastewater was adjusted to 8.0. After 10 days of denitrification treatment at 30℃ and a rotation speed of 150 r / min, the average effluent ammonia nitrogen concentration was 14.28 mg / L, the average ammonia nitrogen removal rate was 90.48%, the average effluent nitrate nitrogen was 4.55 mg / L, the average nitrite nitrogen was 2.02 mg / L, and the system solution oxygen level was 0.5–0.7 mg / L.

[0065] Figure 1 This is a schematic diagram of the structure of the present invention. The present invention prepares an iron-loaded biochar composite material by introducing iron-loaded material onto an unmodified biochar base. This composite material has an excellent porous structure, providing more attachment sites for anaerobic ammonia oxidizing bacteria. Simultaneously, its reducing properties help reduce the adverse effects of external environmental fluctuations, especially dissolved oxygen, on the activity of anaerobic ammonia oxidizing bacteria. Fe / BC-Anammox composite anaerobic sludge particles are formed through anaerobic cultivation and then inoculated into a short-cut nitrification-anaerobic ammonia oxidation integrated system. The inner layer of this structure provides a suitable anaerobic environment for anaerobic ammonia oxidizing bacteria, while aerobic ammonia oxidizing bacteria grow in the outer layer with sufficient contact with oxygen. This effectively solves the problems of low nitrogen removal efficiency and difficulty in starting up short-cut nitrification-anaerobic ammonia oxidation systems due to the difficulty in controlling dissolved oxygen.

[0066] Figure 2The image shows scanning electron microscope (SEM) images of unmodified biochar (BC) in the left image and magnetic Fe3O4 bagasse biochar (Fe3O4 / BC) in the right image of Example 1. As can be seen from the images, the unmodified biochar mainly has a sheet-like structure with a relatively smooth surface and few pores. In contrast, the magnetic Fe3O4 bagasse biochar exhibits a significantly different surface structure. Specifically, the Fe3O4 / BC surface shows more micropores, forming a more uniformly distributed pore structure, with a rougher surface and a significantly increased specific surface area. This is due to the successful loading of small-diameter, spherical nZVI microstructures onto the BC surface. The abundant specific surface area and uniform pore structure provide an ideal support platform for microbial attachment, reproduction, and growth. Its excellent pore structure can also regulate the dissolved oxygen (DO) concentration in the integrated system, reducing adverse factors in the denitrification process and thus improving denitrification efficiency.

[0067] Figure 3 and Figure 4 The changes in the concentration of nitrogen trioxides in the effluent of the system and the changes in the average dissolved oxygen concentration within the system are shown in Example 1 and Comparative Example 1, respectively. Figure 4 It can be observed that, under the same reaction conditions, the average dissolved oxygen concentration (0.3–0.5 mg / L) of the integrated system containing Fe3O4 / BC supported biochar is lower than that of the conventional integrated system without any materials (1–1.2 mg / L). Existing research indicates that a dissolved oxygen concentration of 0.3–0.5 mg / L is sufficient to ensure the smooth progress of short-cut nitrification, and this concentration range also helps to create a near-anaerobic environment in the inner layer of Fe3O4 / BC supported biochar, thereby effectively promoting the anaerobic ammonia oxidation denitrification process and improving the denitrification performance of the integrated system. This phenomenon is observed in… Figure 3 Further verification was conducted, showing that the concentration of nitrogen oxides in the effluent from the integrated system containing Fe3O4 / BC supported biochar was significantly lower than that of the conventional integrated system, and the ammonia nitrogen removal rate reached 95.17%, an improvement of 26.77% compared to the conventional integrated system. The main reason for this improvement is that, in the dynamic environment created by sufficient aeration within the system in a short period, the Fe3O4 / BC supported biochar has reducing properties and can react with excess oxygen in the system; its porous structure can also adsorb some oxygen, providing a buffer for the anaerobic ammonia-oxidizing bacteria in the inner layer, placing them in a near-anaerobic environment, thus ensuring the efficient denitrification reaction. In contrast, in the conventional integrated system without any materials, the anaerobic ammonia-oxidizing bacteria are directly exposed to oxygen. Although the ammonia oxidation process can effectively remove some ammonia nitrogen, nitrite-oxidizing bacteria (NOB) are not effectively inhibited under this environment, resulting in a high nitrate nitrogen concentration in the system. Furthermore, the high dissolved oxygen concentration also inhibits the activity of anaerobic ammonia-oxidizing bacteria, thus affecting the overall denitrification effect of the system.

[0068] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for integrated PN-Anammox nitrogen removal enhanced by iron-supported biochar, characterized in that, Includes the following steps: S1) Select suitable biomass materials, dry them under certain temperature conditions to remove moisture, and then carbonize them to obtain unmodified biochar material BC. Put BC into an iron salt solution for impregnation, and then reduce it to obtain iron-loaded micro-nano biochar particles. S2) Mature anaerobic ammonia oxidation sludge and iron-loaded micro / nano biochar particles are inoculated into an anaerobic reactor. By adjusting the process parameters within the reactor, a stable denitrification effect is achieved, forming Fe / BC-Anammox composite anaerobic sludge particles. The process parameters include the reactor temperature, pH, aeration rate, and n(NH4+) concentration. + -N): n (NO2) - -N), stirring rate; S3) The Fe / BC-Anammox composite anaerobic sludge granules from step S2) are inoculated into a reactor containing acclimated and mature short-cut nitrification sludge. In this reactor, the reaction conditions are controlled by intermittent aeration, adjusting the temperature to 20-40℃, pH to 7-10, and dissolved oxygen concentration to 0-1.5 mg / L, to promote the interaction between short-cut nitrification and anaerobic ammonia oxidation bacteria, constructing an integrated denitrification system, and monitoring the integrated denitrification effect of short-cut nitrification-anaerobic ammonia oxidation. In step S1, the iron in the prepared iron-supported biochar is Fe. 0 It is one or a combination of FeO or Fe3O4.

2. The iron-supported biochar-enhanced PN-Anammox integrated denitrification method according to claim 1, characterized in that, Step S1) The biomass includes, but is not limited to, common straw or sawdust biomass materials, whose main components include one or more of cellulose, hemicellulose, lignin and sugars.

3. The iron-supported biochar-enhanced PN-Anammox integrated denitrification method according to claim 1, characterized in that, The iron salt is one or both of FeCl3•6H2O and FeSO4•6H2O; the impregnation temperature is 20~30℃ and the impregnation time is 2~24h.

4. The iron-supported biochar-enhanced PN-Anammox integrated denitrification method according to claim 1, characterized in that, The reaction conditions are temperature, pH value, dissolved oxygen concentration, and ammonia nitrogen concentration.

5. The iron-supported biochar-enhanced PN-Anammox integrated denitrification method according to claim 1, characterized in that, In step S2), the amount of iron-loaded biochar material inoculated into the anaerobic reactor relative to ammonia nitrogen wastewater is 0.5~5.0 wt%; the volume percentage of anaerobic ammonia oxidation sludge relative to ammonia nitrogen wastewater is 0.5~2.0 wt%; the ammonia nitrogen concentration is 50~400 mg / L; the temperature is 25~35℃; and the pH is 7~10.

6. The iron-supported biochar-enhanced PN-Anammox integrated denitrification method according to claim 5, characterized in that, The ratio of nitrite concentration to ammonia nitrogen concentration in the effluent is 1~1.

5.

7. The iron-supported biochar-enhanced PN-Anammox integrated denitrification method according to claim 6, characterized in that, The reduction treatment in step S1) can be carried out by adding a soluble organic / inorganic reducing agent or by pyrolysis reduction; the pyrolysis reduction temperature is 350~700℃ and the time is 1~4 h.

Images