Magnetization activated sludge-short-cut denitrification coupled sewage treatment process

Abstract

The present application relates to sewage treatment and resource utilization technical field, especially a kind of magnetized activated sludge-short distance denitrification coupling sewage treatment process, steps are as follows: the pretreated wastewater is introduced into anaerobic tank, and Fe3O4@C composite magnetic medium with surface load denitrifying bacteria is added;Anaerobic tank effluent is introduced into aeration tank, and Fe3O4@TiO2 composite magnetic medium with surface load nitrifying bacteria is added, and segmented aeration mode is used;Aeration tank effluent is introduced into magnetic-membrane coupling separation unit containing magnetic hollow fiber membrane module;Concentrate is separated magnetic medium by ultrasonic-high speed shearing combined equipment;Composite magnetic medium is recycled by magnetic drum grading recovery system.By means of Fe3O4@C composite magnetic medium and Fe3O4@TiO2 composite magnetic medium to adapt anaerobic, aerobic section respectively, combined with segmented aeration to form smooth denitrification chain, realize efficient synergy of denitrification function, with the advantages of high sludge-water separation efficiency, magnetic medium can be recycled, stable operation.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource utilization technology in environmental protection, and in particular to a magnetized activated sludge-short-cut denitrification coupled wastewater treatment process. Background Technology

[0002] With the rapid development of industry and urbanization, the discharge of nitrogen pollutants in wastewater has surged, exacerbating the risk of eutrophication and placing higher demands on the denitrification efficiency of wastewater treatment systems. Current wastewater treatment processes generally face three core problems: first, low denitrification efficiency; second, high operating costs, with aeration energy consumption and carbon source addition accounting for over 60% of total operating costs; and third, a heavy burden of sludge treatment, with high moisture content and high disposal costs of residual sludge, easily causing secondary pollution. Specifically, the traditional activated sludge process, as the mainstream technology, relies on gravity sedimentation to separate sludge from water. Limited by the density of the sludge flocs, the sludge concentration within the system can only be maintained at 3000–4000 mg / L. This results in insufficient degradation capacity for high-concentration nitrogenous wastewater (total nitrogen > 50 mg / L), and filamentous sludge bulking easily occurs under low-temperature, high-load conditions, leading to excessive suspended solids in the secondary sedimentation tank effluent and severely impacting treatment efficiency. While short-cut denitrification processes can significantly reduce aeration and carbon source consumption by controlling the nitrification process to remain at the nitrite nitrogen stage, they are extremely sensitive to operating conditions. For example, fluctuations in dissolved oxygen and temperature changes can disrupt the nitrite nitrogen accumulation balance. Furthermore, the ecological niche differences between nitrifying bacteria (autotrophic) and denitrifying bacteria (heterotrophic) are significant, resulting in poor population stability. In practical engineering, the total nitrogen removal rate is extremely low, making stable operation difficult. To overcome the aforementioned technical bottlenecks, researchers have attempted to introduce magnetic media into wastewater treatment systems. Utilizing the high specific gravity of magnetic powders, they aim to accelerate sludge floc settling and enhance sludge-water separation efficiency. Furthermore, the porous structure or active groups on the surface of the magnetic media facilitate microbial immobilization. While magnetic powders are widely used in wastewater treatment due to their strong magnetism, resistance to acid and alkali corrosion, and excellent chemical stability, their application in denitrification processes has significant limitations. They can only increase the settling rate by increasing sludge floc density, failing to simultaneously enhance the activity and optimize the functional division of labor of corresponding functional microbial communities in the two core stages of nitrification and denitrification. Even though some current improvement schemes have explored the combined application of magnetic media and microorganisms, their approaches still have significant limitations: existing magnetic activated sludge processes lack dedicated magnetic media and synergistic mechanisms for anaerobic denitrification and aerobic nitrification functional stages, suffer from insufficient magnetic separation and process integration, high operating energy consumption, and microbial interference disrupting the continuity of the denitrification chain. These limitations make it difficult to synergistically optimize denitrification efficiency, process continuity, and operational economy.

[0003] Therefore, it is urgent for technical personnel to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a magnetized activated sludge-short-cut denitrification coupled wastewater treatment process, which aims to solve the problems of low denitrification efficiency, difficulty in achieving stable standards, high operating costs, heavy sludge treatment burden, easy to cause secondary pollution, and the single function of the magnetic medium, which cannot form a coherent denitrification chain with nitrifying / denitrifying bacteria in the existing design.

[0005] This invention relates to a magnetized activated sludge-short-cut denitrification coupled wastewater treatment process, specifically including the following steps: S1. After pretreatment by screen and grit removal, the wastewater is introduced into the anaerobic tank. Fe3O4@C composite magnetic media with surface-loaded denitrifying bacteria is added to the anaerobic tank. At the same time, the operating conditions of the anaerobic tank are controlled as follows: water temperature 25-35℃, pH value 7.0-8.0, dissolved oxygen concentration ≤0.5mg / L, and hydraulic retention time 1.5-2h. S2. The effluent from the anaerobic tank is introduced into the aeration tank, and Fe3O4@TiO2 composite magnetic media with nitrifying bacteria loaded on the surface is added to the aeration tank. The reaction conditions are controlled by a segmented aeration mode: the dissolved oxygen is controlled at 1.0-1.5 mg / L in the first 0-1.5 h and at 0.5-1.0 mg / L in the second 1.5-3.0 h. S3. Introduce the effluent from the aeration tank into the magnetic-membrane coupling separation unit; the magnetic-membrane coupling separation unit has a built-in magnetic hollow fiber membrane module, and an alternating magnetic field of 0.2 to 0.4T is applied to the membrane module through an external magnetic field generator; S4. The concentrated liquid generated by the magnetic-membrane coupling separation unit is introduced into the ultrasonic-high-speed shearing combined equipment. It is first pretreated by ultrasound and then subjected to high-speed shearing treatment. The Fe3O4@C composite magnetic media and Fe3O4@TiO2 composite magnetic media can be separated from sludge flocs and membrane pollutants. S5. The sheared mixture is introduced into the magnetic drum graded recovery system. By adjusting the magnetic field strength, the Fe3O4@C composite magnetic media and Fe3O4@TiO2 composite magnetic media are graded and recovered. The recovered Fe3O4@TiO2 composite magnetic media is returned to the aeration tank, and the recovered Fe3O4@C composite magnetic media is returned to the anaerobic tank for recycling. The remaining non-magnetic sludge and membrane pollutants enter the secondary sedimentation tank for sedimentation and reflux or discharge.

[0006] As a further improvement to the technical solution disclosed in this invention, in step S1, the preparation method of the Fe3O4@C composite magnetic medium is as follows: using FeCl3 Using 6H2O as the iron source and glucose as the carbon source, the reaction was carried out via a hydrothermal method at 180–200℃ for 8–12 hours. After the reaction, the product was cooled, washed, dried, and calcined to obtain Fe3O4@C composite magnetic media; the specific surface area of ​​the Fe3O4@C composite magnetic media was 150–200 m² / g. 2 / g, pore size 10-30μm, phosphate adsorption capacity 20-30mg / g, denitrifying bacteria loading 10 9 ~10 10 The dosage is 3-5% of the COD mass of the anaerobic tank influent.

[0007] As a further improvement to the technical solution disclosed in this invention, in step S2, the preparation method of Fe3O4@TiO2 composite magnetic medium is as follows: Fe3O4 magnetic powder is dispersed in tetrabutyl titanate ethanol solution, TiO2 layer is coated on the surface of Fe3O4 magnetic powder by sol-gel method, and then calcined at 500-600℃ for 2-4h to obtain Fe3O4@TiO2 composite magnetic medium; the TiO2 coating amount in Fe3O4@TiO2 composite magnetic medium is 10-15% of the total mass of magnetic powder, the nitrite nitrogen accumulation rate is 85-95%, and its addition amount is 8-12% of the mass of activated sludge in the aeration tank.

[0008] As a further improvement to the technical solution disclosed in this invention, in step S2, a slow-release carbon source filler is added to the aeration tank; the slow-release carbon source filler is polyhydroxy fatty acid ester particles with a particle size of 2-5 mm, and the addition amount is 5-8% of the effective volume of the aeration tank.

[0009] As a further improvement to the technical solution disclosed in this invention, in step S3, the membrane material of the magnetic hollow fiber membrane module is polyvinylidene fluoride, the membrane pore size is 0.1-0.2 μm, the inner diameter of the membrane fibers is 0.8-1.2 mm, and the outer diameter is 1.5-2.0 mm; the alternating frequency of the external magnetic field generator is 50-100 Hz, and the magnetic field strength increases linearly along the length of the membrane module from 0.2 T at the inlet end to 0.4 T at the outlet end; the membrane flux of the magnetic-membrane coupling separation unit is 80-120 L / (m²). h).

[0010] As a further improvement to the technical solution disclosed in this invention, in step S4, the operating parameters of the ultrasonic-high-speed shearing combined device are: ultrasonic frequency 20-40kHz, power 300-500W, and processing time 5-10min; the shearing rate of the high-speed shearing machine is 2000-4000r / min, the shearing gap is 0.1-0.3mm, and the processing time is 10-15min.

[0011] As a further improvement to the technical solution disclosed in this invention, in step S5, the magnetic drum graded recycling system includes a primary weak magnetic recycling unit and a secondary strong magnetic recycling unit; the magnetic field strength of the primary weak magnetic recycling unit is 0.1 to 0.2 T, used to recycle Fe3O4@C composite magnetic media; the magnetic field strength of the secondary strong magnetic recycling unit is 0.3 to 0.5 T, used to recycle Fe3O4@TiO2 composite magnetic media.

[0012] As a further improvement to the technical solution disclosed in this invention, both the recovered Fe3O4@C composite magnetic media and Fe3O4@TiO2 composite magnetic media were subjected to activity testing. When the microbial activity retention rate of the recovered Fe3O4@C composite magnetic media is ≥90%, it is directly returned to the anaerobic tank for reuse; when its activity retention rate is between 80% and 90%, it is supplemented with 5% to 10% of the total mass of the recovered Fe3O4@C composite magnetic media with fresh Fe3O4@C composite magnetic media before being returned to the anaerobic tank for reuse. When the microbial activity retention rate of the recovered Fe3O4@TiO2 composite magnetic media is ≥90%, it is directly returned to the aeration tank for reuse; when the activity retention rate is between 80% and 90%, it is supplemented with 5% to 10% of the total mass of the recovered Fe3O4@TiO2 composite magnetic media with fresh Fe3O4@TiO2 composite magnetic media before being returned to the aeration tank for reuse.

[0013] As a further improvement to the technical solution disclosed in this invention, in step S1, trisodium citrate is added to the anaerobic tank as an inducer for denitrifying bacteria, and the amount added is 1 to 2% of the total nitrogen mass of the anaerobic tank influent.

[0014] In practical applications, the magnetized activated sludge-short-cut denitrification coupled wastewater treatment process disclosed in this invention can achieve at least the following beneficial technical effects, specifically: 1) This invention addresses the functional requirements of the nitrogen removal stage in wastewater treatment by customizing two specialized composite magnetic media that are precisely adapted to different treatment stages: In the anaerobic stage, Fe3O4@C composite magnetic media with surface-loaded denitrifying bacteria is added. This porous structure precisely matches the survival and metabolic needs of denitrifying bacteria. Simultaneously, by controlling the anaerobic tank water temperature at 25–35℃ and the pH value at 7.0–8.0, the activity of denitrifying bacteria can be fully stimulated, accelerating the degradation reaction of nitrogen pollutants. In the aeration stage, Fe3O4@TiO2 composite magnetic media with surface-loaded nitrifying bacteria is added, combined with a segmented aeration mode. The oxygen content is adjusted according to the different dissolved oxygen requirements at different stages of the nitrification reaction to ensure the activity of nitrifying bacteria and nitrification efficiency. Fe3O4@C composite magnetic media with surface-loaded denitrifying bacteria and Fe3O4@TiO2 composite magnetic media with surface-loaded nitrifying bacteria are deeply matched with the reaction characteristics of the anaerobic and aerobic sections, respectively, to construct a smooth denitrification process, achieve efficient synergy of denitrification functions, and significantly improve the removal efficiency of total nitrogen and ammonia nitrogen. 2) Both the Fe3O4@C composite magnetic media with surface-loaded denitrifying bacteria and the Fe3O4@TiO2 composite magnetic media with surface-loaded nitrifying bacteria possess excellent microbial immobilization capabilities. They can stably immobilize the corresponding functional bacterial communities on the surface of the magnetic media, significantly improving the retention rate of denitrifying and nitrifying bacteria in the wastewater treatment system and reducing the ineffective consumption of carbon sources caused by the loss of bacteria with the effluent, thereby reducing the amount of carbon source added. Furthermore, the segmented aeration mode can precisely control the dissolved oxygen concentration in the aeration tank according to the progress of the nitrification reaction and the oxygen demand pattern, avoiding the energy redundancy of the constant aeration mode in traditional processes, further reducing the energy consumption of the aeration stage, reducing the process operating cost from both the "material consumption" and "energy consumption" dimensions, and significantly improving the overall economic efficiency of the treatment process. 3) The magnetic-membrane coupling separation unit incorporates a magnetic hollow fiber membrane module made of polyvinylidene fluoride. An alternating magnetic field of 0.2–0.4T is applied to the membrane module via an external magnetic field generator. The magnetic field and membrane separation function work synergistically to enhance sludge-water separation efficiency, rapidly separating activated sludge, magnetic media, and treated water, while effectively intercepting suspended solids and minute pollutants in the water, ensuring the stability of the effluent quality. The concentrated liquid generated by the magnetic-membrane coupling separation unit is introduced into an ultrasonic-high-speed shearing device, where it undergoes ultrasonic pretreatment followed by high-speed shearing treatment to achieve Fe3O4@C composite magnetic coating with denitrifying bacteria on the surface. The process achieves precise separation of the Fe3O4@TiO2 composite magnetic medium with nitrifying bacteria on its surface from sludge flocs and membrane pollutants. The resulting mixture is then introduced into a magnetic drum grading and recovery system. The Fe3O4@C composite magnetic medium with denitrifying bacteria on its surface is recovered through a primary weak magnetic recovery unit, while the Fe3O4@TiO2 composite magnetic medium with nitrifying bacteria on its surface is recovered through a secondary strong magnetic recovery unit. The recovered composite magnetic media are then returned to the anaerobic tank and aeration tank for recycling, forming a closed-loop circulation system for the magnetic media. This reduces the loss of magnetic media resources and further improves the continuity and stability of the process operation. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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 can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the magnetized activated sludge-short-cut denitrification coupled wastewater treatment process disclosed in this invention. Detailed Implementation

[0017] To deepen the understanding of this process, the following detailed description of the magnetized activated sludge-short-cut denitrification coupled wastewater treatment process is provided in conjunction with comparative examples and embodiments. The embodiments described are for illustrative purposes only and do not constitute a limitation on the scope of protection of this process; unless otherwise specified, the process methods are conventional wastewater treatment operating methods.

[0018] Comparative example: Conventional activated sludge denitrification process The specific steps are as follows: S1. Wastewater is directly introduced into the aeration tank after being treated by a screen and grit removal. S2. Add ordinary activated sludge to the aeration tank, adopt a constant aeration mode, control the dissolved oxygen at 2.0-3.0 mg / L, and the hydraulic retention time at 8-10 h; S3. The effluent from the aeration tank is introduced into the secondary sedimentation tank, where sludge-water separation is achieved by gravity settling, with sludge settling time of 2-4 hours. S4. The remaining sludge from the secondary sedimentation tank directly enters the sludge treatment system, without any magnetic media recovery process. S5. The concentrations of total nitrogen and ammonia nitrogen in the effluent are detected using a water quality analyzer; the content of suspended solids in the effluent is detected using a turbidity meter.

[0019] Example: Magnetized activated sludge-short-cut denitrification coupled wastewater treatment process like Figure 1 As shown, the specific steps are as follows: Anaerobic treatment (S1): Wastewater is pretreated by screen and grit removal and then introduced into the anaerobic tank. Fe3O4@C composite magnetic media with surface-loaded denitrifying bacteria is added to the anaerobic tank (preparation method: FeCl3). Using 6H₂O as the iron source and glucose as the carbon source, the mixture is prepared by hydrothermal reaction at 180–200 °C for 8–12 h, followed by washing, drying, and calcination; its specific surface area is 150–200 m² / g. 2 / g, pore size 10–30 μm, denitrifying bacteria loading 10 9 ~10 10 (CFU / g, dosage is 3-5% of the COD mass of the anaerobic tank influent). Simultaneously control the anaerobic tank water temperature at 25-35℃, pH at 7.0-8.0, dissolved oxygen concentration ≤0.5mg / L, and hydraulic retention time at 1.5-2h; additionally add trisodium citrate as a denitrifying bacteria inducer, dosage is 1-2% of the total nitrogen mass of the anaerobic tank influent. In the aeration stage (S2), effluent from the anaerobic tank is introduced into the aeration tank. Fe3O4@TiO2 composite magnetic media with nitrifying bacteria loaded on the surface is added to the aeration tank (preparation method: Fe3O4 magnetic powder is dispersed in tetrabutyl titanate ethanol solution, coated with TiO2 layer by sol-gel method, and then calcined at 500-600℃ for 2-4h; wherein the TiO2 coating amount is 10-15% of the total mass of magnetic powder, the nitrite nitrogen accumulation rate is 85-95%, and the addition amount is 8-12% of the mass of activated sludge in the aeration tank). Slow-release carbon source filler (polyhydroxyalkanoate particles, particle size 2-5mm, addition amount is 5-8% of the effective volume of the aeration tank) is also added. The reaction conditions were controlled using a segmented aeration mode: the dissolved oxygen was controlled at 1.0–1.5 mg / L for the first 0–1.5 h, and at 0.5–1.0 mg / L for the last 1.5–3.0 h. Magnetic-membrane coupling separation (S3) introduces effluent from the aeration tank into the magnetic-membrane coupling separation unit. This unit contains a magnetic hollow fiber membrane module made of polyvinylidene fluoride (0.1–0.2 μm pore size, 0.8–1.2 mm inner diameter, and 1.5–2.0 mm outer diameter). An alternating magnetic field of 0.2–0.4 T (alternating frequency 50–100 Hz, magnetic field strength linearly increasing from 0.2 T at the inlet to 0.4 T at the outlet) is applied to the membrane module via an external magnetic field generator. The membrane flux is controlled to be 80–120 L / (m²). h); Magnetic media separation (S4): The concentrated liquid generated by the magnetic-membrane coupling separation unit is introduced into an ultrasonic-high-speed shearing device. It is first pretreated by ultrasound (frequency 20-40kHz, power 300-500W, treatment time 5-10min), and then subjected to high-speed shearing treatment (shear rate 2000-4000r / min, shear gap 0.1-0.3mm, treatment time 10-15min) to separate the Fe3O4@C composite magnetic media and Fe3O4@TiO2 composite magnetic media from the sludge flocs and membrane pollutants. Magnetic media recovery and reuse (S5): The sheared mixture is introduced into a magnetic drum staged recovery system (including a primary weak magnetic recovery unit with a magnetic field strength of 0.1–0.2T, recovering Fe3O4@C composite magnetic media; and a secondary strong magnetic recovery unit with a magnetic field strength of 0.3–0.5T, recovering Fe3O4@TiO2 composite magnetic media). The recovered magnetic media undergoes activity testing: if the microbial activity retention rate of the Fe3O4@C composite magnetic media is ≥90%, it is directly returned to the anaerobic tank for reuse; if the activity retention rate is 80–90%, 5–10% fresh magnetic media is added before reuse. The same applies to the Fe3O4@TiO2 composite magnetic media. The remaining non-magnetic sludge and membrane pollutants enter a secondary sedimentation tank for sedimentation and recirculation or discharge.

[0020] Experimental data verification Compared to the comparative example, the wastewater treated in this embodiment achieved a total nitrogen removal rate of 92% (comparative example: 75%, with significant nitrogen pollutant residue), an ammonia nitrogen removal rate of 98% (comparative example: 85%, with effluent ammonia nitrogen easily exceeding the standard), a magnetic media recycling rate of over 95% (comparative example: no magnetic media recovery, carbon source addition leading to high operating costs), and a 30% reduction in aeration energy consumption (comparative example: aeration energy consumption accounted for a high proportion, resulting in poor economic efficiency).

[0021] This embodiment, through systematic optimization design of all process steps, constructs a complete processing system with tightly connected links and complementary functions, which is fundamentally different from the decentralized operation of the traditional process in the comparison example: The comparative example uses a conventional activated sludge treatment process, where the steps lack synergy. It simply adds ordinary activated sludge to the aeration tank, relying on natural microbial metabolism for denitrification without optimizing environmental conditions for different needs of nitrification and denitrification. This results in poor microbial stability and low denitrification efficiency. The sludge-water separation stage relies solely on gravity settling in the secondary sedimentation tank without additional enhancement measures, making it susceptible to sludge bulking and causing significant fluctuations in suspended solids and nitrogen pollutant levels in the effluent. Furthermore, the entire process lacks resource recovery design; sludge is directly disposed of without recycling, requiring continuous carbon source replenishment and resulting in high operating costs.

[0022] This embodiment, starting from the overall operational logic of the process, ensures deep adaptation and synergistic efficiency among each step: In the anaerobic stage, Fe3O4@C composite magnetic media with surface-loaded denitrifying bacteria is added, along with temperature, pH control, and inducer addition, creating an optimal reaction environment for the denitrifying bacteria. In the aeration stage, Fe3O4@TiO2 composite magnetic media with surface-loaded nitrifying bacteria is added, combined with segmented aeration for precise control of dissolved oxygen, adapting to the needs of different stages of nitrification. These two steps form a continuous denitrification reaction chain, solving the problem of discontinuous denitrification in traditional processes. In the subsequent magnetic-membrane coupling separation stage, a magnetic hollow fiber membrane combined with an alternating magnetic field replaces the traditional gravity sedimentation in the secondary settling tank, enhancing sludge-water separation efficiency and effluent stability. Then, ultrasonic-high-speed shearing breaks down sludge flocs, and magnetic drums stage and recover the magnetic media, allowing the two composite magnetic media to be reused in the anaerobic and aeration tanks respectively. This reduces magnetic media loss, and activity testing ensures the reuse effect of the Fe3O4@C and Fe3O4@TiO2 composite magnetic media.

[0023] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A magnetized activated sludge-short-cut denitrification coupled wastewater treatment process, characterized in that, Specifically, the following steps are included: S1. After pretreatment by screen and grit removal, the wastewater is introduced into the anaerobic tank. Fe3O4@C composite magnetic media with surface-loaded denitrifying bacteria is added to the anaerobic tank. At the same time, the operating conditions of the anaerobic tank are controlled as follows: water temperature 25-35℃, pH value 7.0-8.0, dissolved oxygen concentration ≤0.5mg / L, and hydraulic retention time 1.5-2h. S2. The effluent from the anaerobic tank is introduced into the aeration tank, and Fe3O4@TiO2 composite magnetic media with nitrifying bacteria loaded on the surface is added to the aeration tank. The reaction conditions are controlled by a segmented aeration mode: the dissolved oxygen is controlled at 1.0-1.5 mg / L in the first 0-1.5 h and at 0.5-1.0 mg / L in the second 1.5-3.0 h. S3. Introduce the effluent from the aeration tank into the magnetic-membrane coupling separation unit; the magnetic-membrane coupling separation unit has a built-in magnetic hollow fiber membrane module, and an alternating magnetic field of 0.2 to 0.4T is applied to the membrane module through an external magnetic field generator; S4. The concentrated liquid generated by the magnetic-membrane coupling separation unit is introduced into the ultrasonic-high-speed shearing combined equipment. It is first pretreated by ultrasound and then subjected to high-speed shearing treatment. The Fe3O4@C composite magnetic media and Fe3O4@TiO2 composite magnetic media can be separated from sludge flocs and membrane pollutants. S5. The sheared mixture is introduced into the magnetic drum graded recovery system. The graded recovery of Fe3O4@C composite magnetic media and Fe3O4@TiO2 composite magnetic media is achieved by adjusting the magnetic field strength. The recovered Fe3O4@TiO2 composite magnetic media is returned to the aeration tank, and the recovered Fe3O4@C composite magnetic media is returned to the anaerobic tank for recycling. The remaining non-magnetic sludge and membrane pollutants enter the secondary sedimentation sedimentation backflow or discharge. In step S1, the Fe3O4@C composite magnetic medium is prepared by using FeCl3·6H2O as the iron source and glucose as the carbon source, reacting at 180–200℃ for 8–12 h via a hydrothermal method. After the reaction, the product is cooled, washed, dried, and calcined to obtain the Fe3O4@C composite magnetic medium. The specific surface area of ​​the Fe3O4@C composite magnetic medium is 150–200 m² / g. 2 / g, pore size 10-30μm, phosphate adsorption capacity 20-30mg / g, denitrifying bacteria loading 10 9 ~10 10 The dosage of CFU / g is 3-5% of the COD mass of the influent to the anaerobic tank. In step S2, the preparation method of Fe3O4@TiO2 composite magnetic media is as follows: Fe3O4 magnetic powder is dispersed in tetrabutyl titanate ethanol solution, TiO2 layer is coated on the surface of Fe3O4 magnetic powder by sol-gel method, and then calcined at 500-600℃ for 2-4h to obtain Fe3O4@TiO2 composite magnetic media; the TiO2 coating amount in Fe3O4@TiO2 composite magnetic media is 10-15% of the total mass of magnetic powder, the nitrite nitrogen accumulation rate is 85-95%, and its addition amount is 8-12% of the mass of activated sludge in aeration tank.

2. The magnetized activated sludge-short-cut denitrification coupled wastewater treatment process according to claim 1, characterized in that, In step S2, a slow-release carbon source filler is also added to the aeration tank; the slow-release carbon source filler is polyhydroxy fatty acid ester particles with a particle size of 2-5 mm, and the addition amount is 5-8% of the effective volume of the aeration tank.

3. The magnetized activated sludge-short-cut denitrification coupled wastewater treatment process according to claim 1, characterized in that, In step S3, the membrane material of the magnetic hollow fiber membrane module is polyvinylidene fluoride, with a pore size of 0.1–0.2 μm, an inner diameter of 0.8–1.2 mm, and an outer diameter of 1.5–2.0 mm; the alternating frequency of the external magnetic field generator is 50–100 Hz, and the magnetic field strength increases linearly along the length of the membrane module from 0.2 T at the inlet to 0.4 T at the outlet; the membrane flux of the magnetic-membrane coupling separation unit is 80–120 L / (m²). 2 •h).

4. The magnetized activated sludge-short-cut denitrification coupled wastewater treatment process according to claim 1, characterized in that, In step S4, the operating parameters of the ultrasonic-high-speed shearing combined equipment are: ultrasonic frequency 20-40kHz, power 300-500W, and processing time 5-10min; the shearing rate of the high-speed shearing machine is 2000-4000r / min, the shearing gap is 0.1-0.3mm, and the processing time is 10-15min.

5. The magnetized activated sludge-short-cut denitrification coupled wastewater treatment process according to claim 1, characterized in that, In step S5, the magnetic drum grading and recycling system includes a primary weak magnetic recycling unit and a secondary strong magnetic recycling unit; the magnetic field strength of the primary weak magnetic recycling unit is 0.1 to 0.2 T, which is used to recycle Fe3O4@C composite magnetic media; the magnetic field strength of the secondary strong magnetic recycling unit is 0.3 to 0.5 T, which is used to recycle Fe3O4@TiO2 composite magnetic media.

6. The magnetized activated sludge-short-cut denitrification coupled wastewater treatment process according to claim 5, characterized in that, Both the recovered Fe3O4@C composite magnetic media and Fe3O4@TiO2 composite magnetic media underwent activity testing. When the microbial activity retention rate of the recovered Fe3O4@C composite magnetic media is ≥90%, it is directly returned to the anaerobic tank for reuse; when its activity retention rate is between 80% and 90%, it is supplemented with 5% to 10% of the total mass of the recovered Fe3O4@C composite magnetic media with fresh Fe3O4@C composite magnetic media before being returned to the anaerobic tank for reuse. When the microbial activity retention rate of the recovered Fe3O4@TiO2 composite magnetic media is ≥90%, it is directly returned to the aeration tank for reuse; when the activity retention rate is between 80% and 90%, it is supplemented with 5% to 10% of the total mass of the recovered Fe3O4@TiO2 composite magnetic media with fresh Fe3O4@TiO2 composite magnetic media before being returned to the aeration tank for reuse.

7. The magnetized activated sludge-short-cut denitrification coupled wastewater treatment process according to claim 1, characterized in that, In step S1, trisodium citrate is added to the anaerobic tank as an inducer for denitrifying bacteria, and the amount added is 1 to 2% of the total nitrogen mass of the anaerobic tank influent.

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