Preparation of magnetic nitrogen-doped core-shell biochar and wastewater treatment technology and equipment

Abstract

The application discloses a kind of preparation of magnetic nitrogen-doped core-shell biochar and wastewater treatment technology and equipment, belong to wastewater treatment technical field.The application is rich in iron industrial solid waste as magnetic precursor, obtains interface stable magnetic core after surface activation coating, is mixed with high protein nitrogen-containing agroforestry biomass, by confined pyrolysis synchronous NH3 in-situ gas phase nitrogen supplementation, and the chemical bonding magnetic inner core-nitrogen-doped carbon shell structure biochar is prepared;It is added to activated sludge system to construct low-oxygen short-range nitrification system, through DO / ORP / MLSS / conductivity multi-parameter sensor cluster and PLC central control unit linkage, based on the biochar aging index model established independently, realize the self-adapting closed-loop control of magnetic recovery frequency, carbon supplement amount and aeration amount.The application material stability is strong, biological reinforcement effect is remarkable, equipment automation degree is high, can efficiently handle medicine, landfill leachate, chemical and other high ammonia nitrogen refractory wastewater, realize the synergy of solid waste resource and wastewater advanced treatment.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to the bio-enhanced treatment technology for high ammonia nitrogen and recalcitrant organic wastewater. More specifically, it relates to a magnetic nitrogen-doped core-shell biochar material, its preparation method, a process method for enhancing the biological treatment of wastewater, and a matching integrated intelligent treatment equipment. Background Technology

[0002] With the rapid advancement of my country's industrialization and urbanization, the discharge of industrial wastewater and municipal sewage continues to grow. Among them, the high ammonia nitrogen and difficult-to-degrade organic wastewater generated by industries such as pharmaceuticals, chemicals, landfill leachate, and coking is characterized by high pollutant concentration, carbon-nitrogen imbalance, strong biological toxicity, and poor biodegradability, making it a key and challenging area in the field of water treatment.

[0003] Traditional activated sludge processes and their improved versions (such as A / O and A² / O) remain the mainstream technologies for wastewater treatment. However, when treating wastewater with high ammonia nitrogen content and poor degradation resistance, the following core bottlenecks are commonly encountered: ① Strong dependence on carbon sources, resulting in extremely low denitrification efficiency under low carbon-to-nitrogen ratio conditions; ② High concentrations of pollutants and toxic substances easily inhibit microbial activity, leading to poor system resistance to shock loads; ③ Poor sludge settling performance, prone to sludge bulking, and large excess sludge production; ④ Long hydraulic retention time, large footprint, and high operating costs.

[0004] In recent years, biochar, due to its well-developed porous structure, abundant surface functional groups, good biocompatibility, and conductivity, has been introduced into wastewater biological treatment systems as a functional enhancement material. It can effectively improve microbial adhesion, promote biofilm formation, enhance pollutant adsorption and electron transfer, and improve biochemical treatment efficiency. However, ordinary biochar has significant drawbacks in practical applications: powdered biochar is difficult to settle and recover after dispersion in water, easily lost with the effluent, and long-term operation not only increases treatment costs but may also cause secondary pollution; biochar itself has no catalytic activity and its ability to degrade recalcitrant organic matter is limited; in complex wastewater environments, the surface of biochar is easily clogged by biofilms and pollutants, its activity rapidly declines, and in-situ regeneration is impossible.

[0005] To address the aforementioned issues, magnetically modified biochar has become a research hotspot. By loading magnetic components onto biochar, the material is endowed with magnetic response properties, enabling rapid separation and recovery via a magnetic field. However, existing magnetic biochar technology and supporting processing equipment still suffer from insurmountable technical shortcomings, specifically as follows: 1. Poor material structural stability and easy loss of magnetic components: Existing technologies mostly use impregnation or co-precipitation methods to load magnetic particles onto the surface or pores of biochar. The magnetic components and the carbon matrix only have physical adsorption and no chemical bonding. Under long-term hydraulic shear and complex water quality conditions, the magnetic particles are very easy to detach and leach out, which not only leads to a rapid decline in the magnetic responsiveness of the material, but also causes secondary pollution of heavy metals. For example, the invention patent with publication number CN113634232A directly mixes the iron source with sludge for carbonization. The magnetic components are not coated and protected, and the binding force with the carbon matrix is ​​weak, resulting in a continuous decline in recovery rate over long-term operation. The invention patent with publication number CN101597105A only performs surface acid modification on the magnetic powder, without carbon shell coating, and lacks the porous adsorption and bio-affinity characteristics of biochar, resulting in extremely weak treatment capacity for recalcitrant pollutants.

[0006] 2. Uncontrollable Nitrogen Doping and Limited Functional Enhancement: Nitrogen doping is a core method for improving the conductivity, catalytic activity, and microbial affinity of biochar. However, existing technologies mostly employ liquid-phase doping and in-situ biomass doping, which suffer from low nitrogen doping efficiency and uncontrollable nitrogen chemical states. This makes it impossible to directionally generate highly active pyridine nitrogen and graphitic nitrogen sites, resulting in limited improvement in the material's electron transport capacity and catalytic performance. For example, the invention patent with publication number CN120794188A only achieves nitrogen doping through co-fermentation of sludge and agricultural and forestry waste, without subsequent gas-phase nitrogen replenishment control. Nitrogen elements mostly exist in ineffective forms, and no core-shell structure is constructed, leading to insufficient material stability.

[0007] 3. Lack of precise activity monitoring and intelligent control system: The current application of magnetic biochar triggers recycling and regeneration based on single parameters such as effluent water quality, turbidity, and ORP. It is impossible to predict the activity decay and aging degree of biochar in real time, which often leads to problems of "over-regeneration" or "untimely regeneration". This increases operating energy consumption and cannot guarantee the long-term stability of effluent water quality. At the same time, operating parameters such as aeration rate, magnetic recovery frequency, and carbon replenishment rate rely on manual adjustment, which cannot achieve adaptive closed-loop control with multi-parameter linkage. The degree of automation is low and it is difficult to adapt to large-scale engineering applications.

[0008] 4. The recycling system is poorly designed and difficult to engineer: Existing technologies mostly use external magnetic separation drums, magnetic separators and other equipment to achieve magnetic biochar recovery. This requires pumping all the mud-water mixture in the reactor into the external separation equipment, which not only increases equipment investment and floor space, but also significantly increases the energy consumption of the booster pump. In addition, biochar is easily lost during the separation process, making the system complex and difficult to maintain.

[0009] In summary, existing technologies cannot simultaneously achieve the core objectives of "stable and controllable material structure, significant bio-enhancing effect, convenient and efficient recycling, and intelligent adaptive operation," which severely restricts the large-scale engineering application of magnetic biochar in wastewater treatment. Therefore, developing a magnetic biochar technology with stable structure, excellent performance, and a matching intelligent treatment system has significant practical significance and application value. Summary of the Invention

[0010] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a magnetic nitrogen-doped core-shell biochar material, its preparation method, a process method for enhancing the biological treatment of wastewater, and an integrated intelligent device. From four dimensions, namely material structure design, preparation process optimization, treatment process innovation, and intelligent device matching, this invention systematically solves the core bottlenecks of the prior art and achieves synergy between solid waste resource utilization and efficient treatment of high ammonia nitrogen recalcitrant wastewater.

[0011] To achieve the above objectives, the present invention proposes the following core technical solutions: (I) Design of magnetic nitrogen-doped core-shell biochar materials This invention innovatively designs a three-layer core-shell structure consisting of a magnetic core, a mesoporous induced layer, and a nitrogen-doped carbon shell. The core design logic is as follows: 1. The inner magnetic core is made of crystalline iron oxide / iron-nickel composite oxide, which gives the material excellent magnetic response performance and ensures rapid separation and recycling under magnetic field. 2. The intermediate mesoporous induction layer is a silica transition layer, formed by the hydrolysis of silicate coupling agent. On the one hand, it introduces a large number of active hydroxyl groups on the surface of the magnetic core, providing binding sites for the subsequent carbon shell coating, realizing Fe-OC covalent chemical bonding between the magnetic core and the carbon shell, and fundamentally solving the problem of magnetic component detachment. On the other hand, the mesoporous structure can effectively block the external environment from corroding the magnetic core, greatly reducing the risk of metal ion leaching and improving the long-term stability of the material. 3. The outer nitrogen-doped carbon shell adopts hierarchical porous graphitized carbon. Precise nitrogen doping is achieved through confined pyrolysis and in-situ gas-phase nitrogen supplementation, which directionally generates highly active pyridine nitrogen and graphitic nitrogen sites. Among them, pyridine nitrogen can provide abundant catalytic active sites, improve the Fenton-like catalytic performance of the material, and enhance the degradation of recalcitrant organic matter; graphitic nitrogen can significantly improve the conductivity of carbon materials, promote the extracellular electron transfer of microorganisms, and enhance the metabolic activity of denitrifying bacteria; pyrrole nitrogen can improve the surface polarity and biocompatibility of the material, and promote the adhesion and film formation of microorganisms on the material surface.

[0012] (II) Material preparation method The preparation method of this invention uses industrial solid waste and agricultural and forestry waste as the main raw materials to achieve "waste treatment". The core process consists of three major steps, and the process principle and parameter control of each step are as follows: 1. Pretreatment of iron-containing inorganic precursors: Differentiated pretreatment processes are adopted for different types of iron-rich industrial solid waste to ensure that the magnetic properties and iron content of the raw materials meet the standards, providing a stable raw material basis for subsequent magnetic core preparation; 2. Magnetic core surface activation and coating modification: By regulating the hydrolysis rate of iron ions through complexing ligands and utilizing the in-situ hydrolysis of silicate coupling agents, a uniform mesoporous silica transition layer is formed on the magnetic core surface, solving the core problem of weak interfacial bonding between the magnetic core and the carbon shell. 3. Confined pyrolysis and in-situ nitrogen doping: Programmed temperature confined pyrolysis is adopted to avoid the collapse of the carbon shell structure. Simultaneous introduction of NH3 / N2 mixed gas achieves in-situ gas-phase nitrogen replenishment. Compared with traditional liquid-phase doping, gas-phase nitrogen replenishment can achieve uniform doping of nitrogen in the carbon shell. Moreover, the chemical state of nitrogen can be precisely controlled by pyrolysis temperature and mixed gas concentration to ensure the proportion of highly active nitrogen sites.

[0013] (III) Enhance wastewater biological treatment processes and methods Based on the properties of the aforementioned materials, this invention constructs a complete treatment process of "low-oxygen short-range nitrification - intelligent prediction of biochar activity - in-situ magnetic recovery and regeneration," with the following core innovations: 1. Low-oxygen operation mode: By precisely controlling the dissolved oxygen concentration and combining the conductivity of the materials to enhance electron transfer, ammonia-oxidizing bacteria (AOB) are selectively enriched and nitrite-oxidizing bacteria (NOB) are inhibited to achieve stable short-cut nitrification and denitrification, significantly reducing carbon source consumption and aeration energy consumption, and solving the problem of denitrification of wastewater with high ammonia nitrogen and low carbon-to-nitrogen ratio. 2. Biochar Aging Index Model: We have independently developed an aging index calculation formula based on cumulative operating time and cumulative pollutant load, which can predict the active state of biochar in real time and solve the industry problem that traditional technologies cannot monitor biochar activity online. 3. In-situ magnetic elution and regeneration: Through the built-in magnetic recovery device in the reactor, in-situ adsorption and fixation of biochar, strong shear demembranes, and recycling are achieved, eliminating the need for external separation equipment, greatly simplifying the process, and reducing energy consumption and material loss rate.

[0014] (iv) Integrated intelligent processing equipment This invention includes a complementary integrated intelligent reactor that integrates reaction, monitoring, recovery, and control functions into one unit. The core design is as follows: 1. Zoned reactor structure: The reactor is divided into three functional zones by porous magnetically coated baffles to achieve gradient treatment of wastewater. At the same time, the magnetic coating on the surface of the baffles extends the residence time of biochar in the reaction zone and prevents the material from being lost with the effluent. 2. Multi-parameter sensor cluster: integrates full-dimensional monitoring of water quality, environment, and operating status, providing comprehensive data support for intelligent control; 3. In-situ magnetic recovery device: It adopts a surrounding electromagnetic coil array, which can quickly adjust the magnetic field strength to realize the in-situ adsorption and release of biochar without the need for external separation equipment; 4. PLC Central Control Unit: Built-in adaptive control strategy, which can realize unattended operation of the whole process. Based on the real-time water quality and biochar activity status, it automatically adjusts aeration, recovery, biochar replenishment and other operations to ensure that the effluent water quality meets the standards in a long-term stable manner.

[0015] Compared with the prior art, the present invention provides the following beneficial effects: 1. The magnetic nitrogen-doped core-shell biochar prepared by this invention completely solves the problems of easy detachment and leaching of magnetic components in traditional magnetic biochar through chemical bonding core-shell structure design. The metal ion leaching rate is ≤0.05mg / L, which is far below the national standard limit. Through precise in-situ nitrogen doping, the total proportion of highly active pyridine nitrogen and graphitic nitrogen is ≥65%, which greatly improves the conductivity and catalytic activity of the material. The specific surface area can reach up to 400m² / g, providing sufficient sites for microbial attachment and pollutant adsorption. The saturation magnetization can reach up to 80emu / g, and magnetic separation can be achieved within 1-2 minutes with a recovery rate of ≥95%.

[0016] 2. This invention uses industrial solid waste such as red mud from the steel industry, iron-rich sludge from water treatment, and fly ash as magnetic raw materials, and agricultural and forestry waste such as soybean straw and castor bean cake as carbon and nitrogen sources. The raw materials are inexpensive, readily available, and widely sourced, realizing the high-value resource utilization of solid waste, significantly reducing the cost of material preparation, and reducing the environmental risks caused by solid waste landfill, which meets the requirements of the "dual carbon" target.

[0017] 3. The materials and processes of this invention, for wastewater with high ammonia nitrogen and difficult degradation, can achieve a COD removal rate of ≥65%, an ammonia nitrogen removal rate of ≥90%, and a total nitrogen removal rate of ≥80%. Compared with the traditional activated sludge process, the hydraulic retention time is shortened by 30%-50%, the aeration energy consumption is reduced by 20%-30%, the excess sludge production is reduced by more than 40%, and the system's resistance to shock loads is significantly improved, making it adaptable to working conditions with large fluctuations in water quality.

[0018] 4. This invention achieves online prediction and adaptive control of biochar activity through an independently developed aging index model, solving the problems of lagging manual adjustment and unstable operation in traditional processes; the integrated equipment has a high degree of integration, a small footprint, and can achieve unattended operation throughout the entire process, greatly reducing operation and maintenance costs and labor intensity, making it suitable for large-scale engineering promotion.

[0019] 5. This invention adopts an in-situ magnetic recovery design, eliminating the need for external separation equipment and avoiding material loss during transportation. The material's cycle life can reach more than 2 years. Compared with traditional external magnetic separation systems, equipment investment is reduced by more than 30%, and operating energy consumption is reduced by more than 40%. Attached Figure Description

[0020] Figure 1 Scanning electron microscope (SEM) images of pure magnetic core (a) and magnetic nitrogen-doped core-shell biochar (b) prepared in Example 1 of this invention; Figure 2 The images are transmission electron microscope (TEM) images of the magnetic nitrogen-doped core-shell biochar prepared in Example 1 of the present invention, where (a) is a structural diagram of the interface between the carbon shell and the magnetic core at a scale of 5 nm, and (b) is a structural diagram of the core-shell bilayer structure at a scale of 100 nm. Figure 3 This is a comparison diagram of the hysteresis loops of the materials prepared in Example 1 and Comparative Examples 1-2 of the present invention; Figure 4 This is a comparison chart showing the changes in COD removal rates of the three systems R0, R1, and R2 of this invention over operating time. Figure 5 This is a comparison chart showing the change in total nitrogen removal rate of the three systems R0, R1, and R2 of this invention over operating time; Figure 6 This is a schematic diagram of the integrated intelligent processing device described in this invention.

[0021] Explanation of reference numerals in the attached diagram: 1. Reactor body; 2. Porous baffle; 3. Biochar addition zone; 4. Short-cut nitrification zone; 5. Magnetic recovery zone; 6. Sensor module; 7. Magnetic recovery device; 8. Central control unit. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments, comparative examples, and accompanying drawings, so that those skilled in the art can more clearly understand the technical solution of the present invention. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, the raw materials, reagents, instruments and equipment used in the embodiments of the present invention are all conventional commercially available products in the art; the testing methods used are all national standards or industry-standard methods in the art.

[0023] Example 1: Preparation of magnetic nitrogen-doped core-shell biochar 1. Raw material pretreatment: Iron-rich sludge from the Fenton process of a wastewater treatment plant was collected and dried in a 105℃ oven for 24 hours until constant weight. It was then pulverized in a planetary ball mill at 400 rpm for 3 hours and passed through a 150-mesh standard sieve. The pulverized sludge was placed in a tube furnace and pyrolyzed at 600℃ under a nitrogen atmosphere for 2 hours. After cooling, it was magnetically separated using a 0.8T magnetic field to obtain an iron-containing inorganic precursor. The total iron content (TFe) was determined to be 32.6% and the magnetic iron ratio (mFe / TFe) was 45.2% by potassium dichromate titration. Soybean straw was collected, dried at 105℃ for 24 hours, pulverized, and passed through an 80-mesh sieve. It was washed three times with deionized water to remove soluble impurities and then vacuum-dried at 80℃ for 12 hours. The crude protein content was determined to be 18.7% by the Kjeldahl nitrogen determination method.

[0024] 2. Magnetic core surface activation and coating modification: Take 100g of the above-mentioned iron-containing inorganic precursor and disperse it in 1.5L of 1.0mol / L ferric chloride solution. Add 5g of sodium citrate as a complexing ligand and stir at 250rpm and 25℃ for 30min. Slowly add 20% ammonia water to the mixture to adjust the pH of the system to 9.5. Continue stirring for 15min and then add 30mL of tetraethyl orthosilicate (TEOS). Continue stirring for 90min to allow TEOS to be hydrolyzed and deposited in situ on the particle surface. After the reaction is complete, wash the precipitate with deionized water until neutral, filter under vacuum and dry at 80℃ for 12h to obtain the coated and modified magnetic core.

[0025] 3. Confined pyrolysis and in-situ nitrogen doping: The above-mentioned coated magnetic core and pretreated soybean straw were mixed uniformly at a mass ratio of 1:1.2 and placed in a tube furnace. High-purity nitrogen was introduced as a protective gas at a flow rate of 150 mL / min. The temperature was programmed to rise to 500℃ at a heating rate of 5℃ / min and pyrolyzed at a constant temperature for 2 hours. During the pyrolysis, an 8% (v / v) NH3 / N2 mixed gas was introduced simultaneously for in-situ gas-phase nitrogen supplementation. The duration of the mixed gas introduction was consistent with the duration of the pyrolysis isothermal treatment. After the pyrolysis was completed, the mixture was naturally cooled to room temperature under nitrogen protection, removed, and ground through a 150-mesh sieve to obtain magnetic nitrogen-doped core-shell biochar, labeled as MBC-1.

[0026] Example 2: Preparation of magnetic nitrogen-doped core-shell biochar 1. Raw material pretreatment: Red mud from a steel plant was collected, dried at 105℃ for 24 hours to constant weight, pulverized in a ball mill at 500 rpm for 2 hours, passed through a 200-mesh standard sieve, and magnetically separated using a 1.0T magnetic field to obtain an iron-containing inorganic precursor with a total iron content (TFe) of 28.4% and a magnetic iron ratio (mFe / TFe) of 38.7%. Castor bean cake was collected, dried at 105℃ for 24 hours, pulverized and passed through an 80-mesh sieve, washed three times with deionized water, and vacuum dried at 80℃ for 12 hours for later use. Its crude protein content was 32.5%.

[0027] 2. Magnetic core surface activation and coating modification: Take 100g of the above iron-containing inorganic precursor and disperse it in 2L of 0.8mol / L iron-nickel mixed salt solution (Fe / Ni molar ratio 3:1). Add 6g of sodium citrate and stir at 300rpm for 30min. Add 20% ammonia water to adjust the pH to 10.5 and stir for 15min. Then add 40mL of KH-550 silane coupling agent and continue stirring for 120min. After the reaction is completed, wash until neutral, filter and dry to obtain coated magnetic cores.

[0028] 3. Confined pyrolysis and in-situ nitrogen-doped coated magnetic cores and castor bean cake were mixed at a mass ratio of 1:0.8 and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 550℃ at 6℃ / min and pyrolyzed at a constant temperature for 2.5h. During the pyrolysis process, a 10% volume fraction of NH3 / N2 mixed gas was simultaneously introduced. After cooling, the mixture was ground and sieved to obtain magnetic nitrogen-doped core-shell biochar, labeled as MBC-2.

[0029] Example 3: Preparation of magnetic nitrogen-doped core-shell biochar 1. Raw material pretreatment: Fly ash from a coal-fired power plant was collected, dried at 105℃ for 24 hours, pulverized in a ball mill at 300 rpm for 4 hours, passed through a 100-mesh standard sieve, pyrolyzed at 500℃ under a nitrogen atmosphere for 3 hours, and then magnetically separated under a 0.5T magnetic field to obtain an iron-containing inorganic precursor with a total iron content (TFe) of 26.1% and a magnetic iron ratio (mFe / TFe) of 31.5%. Rapeseed meal was collected, dried at 105℃ for 24 hours, pulverized and passed through an 80-mesh sieve, washed three times with deionized water, and vacuum dried at 80℃ for 12 hours for later use. Its crude protein content was 25.8%.

[0030] 2. Magnetic core surface activation and coating modification: Take 100g of the above iron-containing inorganic precursor, disperse it in 1L of 1.2mol / L ferric sulfate solution, add 4g of sodium citrate, and stir at 200rpm for 30min; add 20% ammonia water to adjust the pH to 8.5, stir for 15min, add 20mL of tetramethyl silicate, and continue stirring for 60min; after the reaction is completed, wash until neutral, filter and dry to obtain coated magnetic cores.

[0031] 3. Confined pyrolysis and in-situ nitrogen-doped coated magnetic cores and rapeseed meal were mixed at a mass ratio of 1:1.5 and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 450℃ at 3℃ / min and pyrolyzed at a constant temperature for 3h. During the pyrolysis process, a 5% (v / v) NH3 / N2 mixed gas was introduced simultaneously. After cooling, the mixture was ground and sieved to obtain magnetic nitrogen-doped core-shell biochar, labeled as MBC-3.

[0032] Comparative Example 1 Similar to Example 1, except that only step 2, the magnetic preparation, was performed. 1.5 mol / L of metal salt and treated soybean straw were mixed in an Erlenmeyer flask at a mass ratio of 1:1.2. 0.5 wt% sodium citrate was added as a ligand, and 20% ammonia water was slowly added dropwise to the Erlenmeyer flask until the pH reached 9-10. Finally, ethyl silicate was added to the mixed solution, and the mixture was stirred continuously for 30-60 min to promote particle growth. After cooling, the precipitate was rinsed to neutrality, and the precipitate was directly pyrolyzed. During the process, 10% NH3 / N2 mixed gas was simultaneously introduced. The mixture was pyrolyzed at 500℃ for 2 h and then kept in a nitrogen environment until natural cooling to obtain magnetic nitrogen-doped core-shell biochar MBC-2.

[0033] Comparative Example 2 Similar to Example 1, except that only the sludge magnetic separation in step 1 is performed, and the iron-containing inorganic precursor after magnetic separation is directly mixed with soybean straw at a mass ratio of 1:1.2. During the pyrolysis process, a 10% volume fraction of NH3 / N2 mixed gas is simultaneously introduced. After isothermal pyrolysis at 500℃ for 2 hours, the nitrogen environment is maintained until natural cooling to obtain magnetic nitrogen-doped core-shell biochar MBC-3.

[0034] Material performance testing and comparative analysis Specific surface area, SEM, TEM, and VSM were measured for Examples 1 and 1-2. The results are shown in Table 1. Figure 1-3 As shown.

[0035] Table 1. Test results of specific surface area, porosity, and average pore size. Table 1 shows the specific surface area, which strongly demonstrates the significant advantages of Example MBC-1. The high specific surface area indicates that the magnetic nitrogen-doped core-shell biochar has a greater number of micropores or mesopores. MBC-1 has the largest total pore volume and the smallest average pore size, indicating that it has a richer number of functionalized active sites. In contrast, the comparative examples lacked pretreatment or interface modification, resulting in a failure to form an effective core-shell synergy between the magnetic components and the biochar, leading to pore blockage or structural collapse.

[0036] Based on the SEM image, from Figure 1 (a) It can be seen that the prepared pure magnetic core structure exhibits obvious micro-nano particle clusters. The fine particle structure is conducive to the subsequent full mixing and in-situ coating with biomass precursors. Figure 1 (b) Clearly demonstrates the typical honeycomb porous carbon skeleton formed after biomass pyrolysis, which allows magnetic particles to be uniformly embedded and covered on the inner and outer surfaces of the biochar pores, and also provides a large amount of physical space for the attachment of microorganisms and the adsorption of pollutants.

[0037] Figure 2The TEM results show that the prepared magnetic nitrogen-doped core-shell biochar exhibits a distinct core-shell structure. At low magnification (100 nm scale bar), a high-electron-density magnetic core is observed to be uniformly coated with a continuous carbon layer, without obvious delamination or peeling. At high magnification (5 nm scale bar), clear lattice fringes are visible in the magnetic core region, with an interplanar spacing of approximately 0.25-0.30 nm, indicating that the magnetic core is a crystalline iron oxide structure. The outer carbon shell exhibits a graphite-like layered structure with a certain degree of graphitization. These results demonstrate that the material of this invention forms a stable magnetic core-conductive carbon shell composite structure.

[0038] The VSM display materials all exhibit excellent superparamagnetism, and the saturation magnetization of the example (MBC-1) reaches 65.6 emu / g, demonstrating excellent magnetic response. This means that when the central control unit outputs a small current to the electromagnetic coil, it can generate sufficient magnetic force to capture aged biochar, effectively improving the dispersibility and reusability of biochar in the wastewater treatment system.

[0039] Example 4: Enhancing the Application of Biological Treatment of Pharmaceutical Wastewater This embodiment uses the process method and integrated intelligent equipment of the present invention to treat high ammonia nitrogen pharmaceutical wastewater discharged by a pharmaceutical manufacturing enterprise. The wastewater quality parameters are as follows: COD=3800±150mg / L, ammonia nitrogen=520±35mg / L, TN=680±40mg / L, pH=7.6±0.3, C / N=5.7±0.3.

[0040] 1. Experimental apparatus: using the present invention Figure 6 The integrated intelligent device shown has an effective reactor volume of 100L, with two built-in porous baffles dividing it into three functional areas. The magnetic recovery device uses a surround-type Helmholtz electromagnetic coil, and the central control unit uses a Siemens S7-200SMART PLC, along with a complete sensor cluster.

[0041] 2. Test methods: (1) The inoculated sludge was taken from the aerobic section of the A² / O process of a certain urban sewage treatment plant. After inoculation, the MLSS in the reactor was 4500±200mg / L and the SVI was 92±5mL / g. (2) The MBC-1 prepared in Example 1 was added to the reactor at a volume fraction of 10% of the effective reactor volume and continuously aerated for 5 days to form a stable biochar-activated sludge composite system. (3) After the system is started, control the DO in the reactor to be 0.3-0.5 mg / L, HRT to be 8h, adjust the carbon-nitrogen ratio of the influent to 8:1 through feedback from the ORP sensor, and control the water temperature at 25±2℃; (4) Set the hydraulic abrasion coefficient α=0.0025, the biofilm clogging coefficient β=0.0085, and the central control unit calculates the biochar aging index D in real time. When D≥0.9, the magnetic washing and regeneration program is automatically triggered. (5) The system runs continuously for 60 days, and the influent and effluent water quality is tested every 5 days. At the same time, indicators such as sludge settling performance and biochar recovery rate are monitored.

[0042] Three control groups with different parameters were set up simultaneously. R0 was a blank control, without the addition of magnetic nitrogen-doped core-shell biochar; R1 was treated with magnetic nitrogen-doped core-shell biochar MBC-2; and R2 was treated with magnetic nitrogen-doped core-shell biochar MBC-1. After 60 days, the activated sludge was fully adapted, and the wastewater treatment performance gradually stabilized. Monitoring of COD and total nitrogen removal rates in the three systems (R0, R1, and R2) during the operating cycle yielded the following results: Figure 4 , 5 As shown, the pollutant removal rates of all three systems increased with operating time. This indicates that as operating time lengthens, a stable biofilm gradually forms on the biochar surface, establishing and enhancing the system's biochemical treatment capacity. In terms of COD and total nitrogen removal, group R2 significantly outperformed R1 and R0, demonstrating the inventiveness and practicality of the magnetic nitrogen-doped core-shell biochar described in this invention for enhancing the biological treatment of medical wastewater. Through nitrogen doping modification and core-shell structure design, not only was the physical adsorption capacity of pollutants increased, but the bottleneck of traditional biological treatment efficiency was also overcome through electrochemical enhancement, achieving superior effluent quality.

[0043] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 magnetic nitrogen-doped core-shell biochar material for enhancing biological wastewater treatment, characterized in that, The material comprises, from the inside out, a magnetic core and a nitrogen-doped carbon shell covering the outer surface of the magnetic core. The two are bonded together by Fe-OC covalent chemical bonding to form a stable core-shell structure. The magnetic core is at least one of crystalline iron oxide or iron-nickel composite oxide, and the core particle size is 50-120 μm. The nitrogen-doped carbon shell is a graphitized carbon layer with a hierarchical porous structure, and the shell thickness is 5-30 μm. The mass percentage of nitrogen in the carbon shell is 2.5-8.0%, and the nitrogen exists in three chemical states: pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen. Among them, the total proportion of pyridine nitrogen and graphitic nitrogen is ≥65%. The material has a specific surface area of ​​200-400 m² / g, a total pore volume of 0.15-0.35 cm³ / g, an average pore size of 2.5-5.0 nm, a saturation magnetization of 20-80 emu / g, a particle size D50 of 80-150 μm, and a metal ion leaching rate ≤0.05 mg / L.

2. A method for preparing the magnetic nitrogen-doped core-shell biochar material according to claim 1, characterized in that, Includes the following steps: Step 1, Pretreatment of iron-containing inorganic precursors: Collect iron-rich industrial waste, dry it at 105℃ for 24 hours to constant weight, then pulverize it using a planetary ball mill at 300-600 rpm for 2-4 hours, and pass it through a 100-200 mesh standard sieve; for non-magnetic iron-rich sludge, pyrolyze it in a tube furnace at 400-800℃ under an inert atmosphere for 1-3 hours, and then perform magnetic separation with a magnetic field strength of 0.5-1.0T; for magnetic iron ore raw materials, directly perform magnetic separation for later use; the final iron-containing inorganic precursor has a total iron content (TFe) ≥ 25% and a magnetic iron ratio (mFe / TFe) ≥ 30%; Step 2, Magnetic core surface activation and coating modification: The iron-containing inorganic precursor obtained in step (1) is dispersed in a 0.5-1.5 mol / L iron salt or iron-nickel mixed salt solution with a solid-liquid ratio of 1:10-1:20 (g / mL). 0.3-0.8 wt% sodium citrate is added as a complexing ligand, and the mixture is stirred at 200-300 rpm for 30 min. 20% ammonia water is slowly added dropwise to the mixture to adjust the pH of the system to 8.0-11.

0. After stirring for 15 min, a silicate coupling agent is added. The volume of the coupling agent added is 1.0-3.0% of the total volume of the mixture. Stirring is continued for 60-120 min to allow the coupling agent to be hydrolyzed and deposited in situ on the particle surface, forming a silica mesoporous induction layer with a thickness of 20-100 nm. After the reaction is completed, the precipitate is washed with deionized water until neutral, vacuum filtered, and dried at 80℃ for 12 h to obtain the coated and modified magnetic core. Step 3: Confined pyrolysis and in-situ nitrogen doping. The coated magnetic core obtained in Step 2 and the pretreated nitrogen-containing organic biomass are uniformly mixed at a mass ratio of 1:(0.1-2) and placed in a tube furnace. High-purity nitrogen is introduced as a protective gas at a flow rate of 100-200 mL / min. The temperature is programmed to rise to 400-600℃ at a rate of 3-8℃ / min and pyrolyzed at a constant temperature for 1-3 hours. During the pyrolysis process, a 5-10% (v / v) NH3 / N2 mixed gas is introduced simultaneously for in-situ gas-phase nitrogen replenishment. The duration of the mixed gas introduction is consistent with the duration of the pyrolysis isothermal treatment. After the pyrolysis is completed, the mixture is naturally cooled to room temperature under nitrogen protection, removed, and ground through a 150-mesh sieve to obtain the magnetic nitrogen-doped core-shell biochar product.

3. The preparation method according to claim 2, characterized in that, The iron-rich industrial waste mentioned in step one is at least one of the following: red mud from the iron and steel industry, fly ash from coal-fired power plants, iron-rich sludge from the Fenton process in water treatment, and hematite tailings from ore dressing plants; the iron salt mentioned in step two is at least one of ferric chloride, ferric sulfate, and ferric nitrate, and the Fe / Ni molar ratio in the iron-nickel mixed salt solution is 2:1-5:1; the silicate ester coupling agent is at least one of tetraethyl silicate, tetramethyl silicate, and γ-aminopropyltriethoxysilane (KH-550).

4. The preparation method according to claim 2, characterized in that, The nitrogen-containing organic biomass mentioned in step (3) is at least one of soybean straw, peanut straw, castor oil cake, and rapeseed cake, with a crude protein content ≥15%; the pretreatment method of the nitrogen-containing organic biomass is as follows: it is dried at 105℃ for 24h, crushed and passed through an 80-mesh sieve, washed three times with deionized water to remove soluble impurities, and then vacuum dried at 80℃ for 12h for later use.

5. A method for enhancing wastewater biological treatment using magnetic nitrogen-doped core-shell biochar as described in claim 1, characterized in that, Includes the following steps: The first step is to construct the composite system: The magnetic nitrogen-doped core-shell biochar is added to the activated sludge reactor at a volume fraction of 5-20% of the effective reactor volume. Activated sludge from the aerobic section of a wastewater treatment plant is inoculated, and the sludge concentration (MLSS) in the reactor is controlled at 3500-5500 mg / L, the sludge settling ratio (SV30) is 20-30%, and the reactor is continuously aerated and cultured for 3-7 days to form a biochar-activated sludge composite system. The second step is low-oxygen short-cut nitrification operation: After the composite system stabilizes, the wastewater to be treated is introduced. The dissolved oxygen (DO) concentration in the reactor is controlled to be stable at a low-oxygen environment of 0.2-1.5 mg / L through the microporous aeration system linked with the DO sensor. The hydraulic retention time (HRT) is 6-12 h. The influent carbon-nitrogen ratio is adjusted to 6:1-12:1 through feedback from the online ORP sensor to achieve simultaneous short-cut nitrification and denitrification. The third step involves the intelligent monitoring and circulation control system for biochar activity. During operation, a sensor cluster collects real-time data on influent COD, ammonia nitrogen concentration, influent flow rate, and cumulative operating time in 10-minute cycles. The central control unit's built-in algorithm then calculates the biochar aging index D in real-time. The calculation formula is as follows: In the formula: t is the cumulative operating time in days; ΣLoad is the total pollutant load per unit volume borne by the biochar in kg / m³; V is the effective volume of the reactor in m³; α is the preset hydraulic abrasion coefficient, ranging from 0.001 to 0.005; β is the preset biofilm clogging coefficient, ranging from 0.005 to 0.

015. When D < 0.6, the biochar is determined to be in a high-activity period, the system maintains a low-oxygen aeration mode, and the magnetic recovery device is on standby. When 0.6 ≤ D < 0.9, the biochar is determined to be in a stable period, the system maintains low-oxygen operation, and the frequency of effluent water quality monitoring is increased to once every 2 hours. When D ≥ 0.9, the biochar is determined to be in an aging period, and the magnetic elution regeneration program is immediately triggered. Step 4, Magnetic Elution Regeneration and Recycling: The magnetic elution regeneration procedure is performed as follows: ① Cut off the reactor inlet water and shut down the aeration system; ② Turn on the magnetic recovery device and increase the magnetic field strength to 1.5-2.0T to adsorb and fix the magnetic biochar suspended in the reactor for 3-5 minutes. ③ Turn on the aeration system and perform high-intensity aeration for 5-10 minutes at an air-to-water ratio of ≥20:1 to peel off the aged biofilm and blockages on the surface of the biochar through hydraulic shear force; ④ Turn off the aeration system, let it stand and settle for 10 minutes, then turn on the sludge pump to discharge the dead sludge and sediment that has peeled off from the bottom; ⑤ Turn off the magnetic field of the magnetic recovery device, and automatically calculate and add fresh magnetic biochar based on the aging index D before elution and the preset material loss rate of 5-20% to maintain a stable amount of biochar added in the reactor. ⑥ After the addition is completed, the cumulative pollutant load ΣLoad is reset to 0, and the cumulative running time t is weighted and corrected using the following formula: In the formula: λ is the ratio of the mass of fresh biochar added to the total mass of biochar in the reactor, usually taken as 5%-20%; ⑦ Start the inlet pump, and the system enters the next operating cycle.

6. An integrated intelligent device for enhanced biological treatment of wastewater, characterized in that, The device, loaded with the magnetic nitrogen-doped core-shell biochar of claim 1, comprises: The reactor body (1) is a closed tank. Inside the tank, 2-3 porous baffles (2) are vertically arranged along the water flow direction, dividing the inner cavity of the tank into a biochar addition zone (3), a short-cut nitrification zone (4), and a magnetic recovery zone (5) from left to right. The porous baffles (2) have a pore size of 2-5 mm and an opening rate of 30-40%. The surface of the baffles (2) is uniformly coated with a nano Fe3O4 coating with a thickness of 50-100 μm. The water inlet system includes a water inlet pump, a water inlet pipe and a water distributor. The water distributor is located in the biochar addition zone (3) at the bottom of the reactor body (1). The aeration system includes a blower, a main pipe, branch pipes and microporous aeration discs, with the microporous aeration discs located at the bottom of the short-cut nitrification zone (4); The sensor module (6) includes a DO sensor, an ORP probe, a conductivity sensor, an MLSS meter, an online COD monitor for influent, and an online ammonia nitrogen monitor. The DO sensor, ORP probe, conductivity sensor, and MLSS meter are all installed in the short-range nitrification zone (4), while the online COD monitor for influent and the online ammonia nitrogen monitor for influent are installed in the influent pipe. The magnetic recovery device (7) includes a Helmholtz electromagnetic coil array and a DC power controller. The electromagnetic coil array is installed around the outer wall of the reactor body (1) located in the magnetic recovery zone (5). The magnetic field strength is adjustable from 0.1 to 2.0 T, and the magnetic recovery frequency is 1 to 3 cycles / time. The central control unit (8) is an industrial-grade PLC controller. Its analog input terminal is electrically connected to all monitoring devices of the sensor module (6), and its digital output terminal is electrically connected to the DC power controller of the magnetic recovery device (7), the solenoid valve of the aeration system, the water inlet pump, the sludge discharge pump, and the dosing pump, respectively. The central control unit (8) has a built-in biochar activity evolution model and adaptive control strategy module, which can automatically output control commands to each execution component based on the real-time data collected by the sensor module.

7. The integrated intelligent device according to claim 6, characterized in that, The magnetic recycling device (7) is also equipped with an ultrasonic regeneration tank. The ultrasonic regeneration tank has an ultrasonic frequency of 400-600kHz and a power density of 0.3-0.5W / cm², which is used for offline deep regeneration of deactivated magnetic biochar. The top of the reactor body (1) is equipped with an outlet weir and an outlet pipe. An outlet solenoid valve and an online water quality monitor are installed on the outlet pipe. The online water quality monitor is electrically connected to the central control unit (8).

8. The application of the magnetic nitrogen-doped core-shell biochar material according to claim 1, the treatment method according to claim 5, and the integrated intelligent device according to claim 6 in wastewater treatment, characterized in that, The applications are for treating high-ammonia-nitrogen, difficult-to-degrade organic wastewater such as pharmaceutical wastewater, landfill leachate, chemical wastewater, dyeing and printing wastewater, and coking wastewater, as well as for the remediation of black and odorous rivers and eutrophic lakes.

Images