A mobile bed bio-membrane denitrification strengthening method based on low-intensity rare earth waste weak magnetic carrier fluidization and construction of endogenous weak magnetic micro-environment and application

Abstract

The application discloses a mobile bed biofilm denitrification strengthening method based on a low-intensity rare earth waste weak magnetic carrier fluidization and construction of an endogenous weak magnetic microenvironment and application. Rare earth waste weak magnetic biological carriers are added to a mobile bed biofilm reactor and inoculated with activated sludge, and the carriers are suspended, fluidized, circulated and migrated through continuous aeration; the magnetic induction intensity of the carrier surface is 0.05-0.20 mT, and the filling rate is 20%-30%. No coil, electromagnet or external permanent magnet is arranged in and outside the reactor, and a dynamic coupling endogenous weak magnetic microenvironment with spatial multi-point distribution is formed in the process of approaching, collision, separation and position migration of multiple carriers, and is used for biological denitrification treatment of sewage.

Description

Technical Field

[0001] This invention relates to the field of wastewater biological treatment technology, and in particular to a method and its application for constructing a dynamic distributed endogenous weak magnetic microenvironment without an external magnetic field during the fluidized bed operation of a moving bed biofilm reactor using low-intensity rare earth waste as a weak magnetic carrier, and for the biological denitrification treatment of wastewater. Background Technology

[0002] Traditional biofilm systems generally suffer from problems in practical engineering applications, such as long biofilm formation and start-up cycles, slow biomass accumulation, loose biofilm structure that is easy to detach, and slow nitrification start-up, which makes it difficult to further improve the removal efficiency of ammonia nitrogen and total nitrogen as well as the long-term stability of the system.

[0003] Existing enhancement methods mainly focus on carrier surface modification, specific surface area increase, and optimization of aeration and hydraulic conditions. Some studies have also used magnetic materials as biofilm carriers or applied magnetic field stimulation outside the reactor to improve microbial attachment, EPS secretion, and nitrogen conversion capabilities. However, most of these technologies remain at the level of "magnetic materials as attachment substrates" or "external magnetic fields as fixed stimulation sources," and it is difficult to achieve synergistic regulation of the entire biofilm system from the perspectives of carrier fluidization spatial distribution, construction of endogenous weak magnetic microenvironment, EPS matrix, electron transfer, and functional enzyme activity.

[0004] In recent years, weak magnetic fields have been found to influence microbial attachment behavior, extracellular polymer secretion, respiratory metabolism, and electron transport processes, and to promote nitrification. Existing research typically relies on external coils, electromagnets, or external permanent magnets to apply magnetic stimulation to the reactor, or simply uses ordinary magnetic packing as a carrier. However, these methods generally suffer from problems such as complex equipment structures, increased energy consumption or maintenance costs, uneven spatial distribution of the magnetic field, significant differences in enhancement effects between the near-magnet side and the far-magnet side, and insufficient stability for engineering scale-up.

[0005] Therefore, there is an urgent need to propose a wastewater biological denitrification enhancement method that differs from external magnetic field stimulation, ordinary Fe3O4 magnetic packing, and simple carrier material modification. This method would utilize low-strength rare earth waste weak magnetic carriers as migratory endogenous weak magnetic units within a moving bed biofilm reactor under the aeration and hydraulic fluidization effects. Through dynamic approach, collision, separation, and spatial position changes among the carriers, a dynamic coupled endogenous weak magnetic microenvironment would be formed, which is non-fixed, non-unidirectional, and spatially multi-point distributed. This microenvironment would continuously act on the biofilm initiation, growth, EPS matrix formation, electron transfer, and nitrification metabolism processes, thereby achieving wastewater denitrification enhancement without increasing the external magnetic field generating device or additional energy consumption. Summary of the Invention

[0006] The purpose of this invention is to provide a method for enhancing nitrogen removal from a moving bed biofilm based on the fluidization of low-intensity rare earth waste weak magnetic carriers to construct an endogenous weak magnetic microenvironment. This method utilizes the suspended fluidization, dynamic contact, collision, and continuous spatial position changes of the low-intensity rare earth waste weak magnetic biological carriers within a moving bed biofilm reactor. This allows multiple carriers to form a dynamically coupled endogenous weak magnetic microenvironment within the reactor, characterized by non-fixed points, non-unidirectional orientation, and multi-point spatial distribution.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for enhancing nitrogen removal from a moving bed biofilm based on fluidized bed construction of an endogenous weak magnetic microenvironment using low-intensity rare earth waste weak magnetic carriers. The method includes adding the rare earth waste weak magnetic biological carriers to a moving bed biofilm reactor and maintaining the carrier suspension fluidization, dynamic circulation, dynamic contact, and continuous spatial position changes through continuous aeration.

[0008] Furthermore, the rare earth waste weak magnetic biological carriers undergo dynamic approach, collision, separation, and spatial migration within the reactor, resulting in the formation of a dynamic coupled endogenous weak magnetic microenvironment between adjacent carriers that is not fixed, not unidirectional, and spatially distributed at multiple points. Moreover, the formation of the endogenous weak magnetic microenvironment does not depend on external coils, electromagnets, or external permanent magnets.

[0009] Furthermore, the surface magnetic induction intensity of the rare earth waste weak magnetic biological carrier is 0.05-0.20 mT.

[0010] Furthermore, the filling rate of the rare earth waste weak magnetic biological carrier in the moving bed biofilm reactor is 20%-30%.

[0011] Furthermore, the operating conditions of the moving bed biofilm reactor are as follows: dissolved oxygen 2.0-6.0 mg / L, hydraulic retention time 3-12 h, pH 6.5-8.5, and temperature 15-35℃.

[0012] Furthermore, the moving bed biofilm reactor includes a reaction vessel, a continuous aeration system, an influent control system, an effluent control system, and a hydraulic circulation unit for maintaining the suspension and dynamic distribution of the carrier. The continuous aeration system supplies air through an aeration component located at the bottom of the reaction vessel, and no coils, electromagnets, or external permanent magnets for generating an external magnetic field are installed inside or outside the reactor.

[0013] Furthermore, the rare earth waste weak magnetic biological carrier is a composite porous carrier containing rare earth waste magnetic powder and a polymer matrix. The rare earth waste magnetic powder contains Nd, Fe, and B components. The mass of the rare earth waste magnetic powder accounts for 3%-10% of the total mass of the composite porous carrier, and the particle size is 70-100 mesh. The polymer matrix is ​​an acrylonitrile-butadiene-styrene copolymer. The composite porous carrier is a three-dimensional printed porous carrier with an equivalent diameter of 20-30 mm, a porosity of 80%-90%, and a pore size of 0.8-2.5 mm. The density of the rare earth waste weak magnetic biological carrier is 0.95-1.10 g / cm3.

[0014] The present invention also provides an application of the above method in wastewater denitrification treatment.

[0015] Compared with the prior art, the present invention has at least the following advantages and technical effects: (1) This invention does not rely on external coils, electromagnets or external permanent magnets. Instead, it forms an endogenous weak magnetic microenvironment through the suspension fluidization and dynamic spatial distribution of low-intensity rare earth waste weak magnetic biological carriers in a moving bed biofilm reactor. This avoids the problems of complex structure, high energy consumption, uneven magnetic field distribution and difficulty in engineering scale-up of external magnetic field devices.

[0016] (2) In this invention, the weak magnetic carrier of rare earth waste is transformed from a simple biofilm attachment material into a migratory microenvironment control unit inside the reactor. Through the dynamic approach, collision, separation and spatial position change between carriers, a weak magnetic action area is formed that is not fixed, not unidirectional and distributed in multiple spatial points, so that the weak magnetic action can continuously act on the entire process of biofilm initiation, growth and stable operation.

[0017] (3) The present invention can promote the preferential attachment and enrichment of microorganisms on the weak magnetic carrier surface of rare earth waste, increase the attached biomass, volatile attached biomass and extracellular polymer content, especially promote the accumulation of protein extracellular polymers, thereby improving the biofilm density, structural stability and water erosion resistance.

[0018] (4) The present invention can enhance the activity of the electron transport system, dehydrogenase activity and ammonia monooxygenase activity of the biomembrane, and transform the biomembrane from a common attached structure to a functional structure with high electron transport, high energy metabolism and high nitrification activity.

[0019] (5) This invention achieves stable removal of ammonia nitrogen and total nitrogen in wastewater through a synergistic pathway of “fluidization of low-intensity rare earth waste weak magnetic carrier - dynamic distributed endogenous weak magnetic microenvironment - EPS matrix reinforcement - electron transfer enhancement - nitrification function improvement - denitrification performance improvement”. Under the same or similar surface magnetic induction intensity conditions, its operating results are better than those of ordinary Fe3O4 magnetic powder carrier system and external permanent magnet reinforcement system. It has the advantages of simple operation, low energy consumption, more uniform spatial effect and high potential for engineering scale-up. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in 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 can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic diagram of the fluidized bed operation structure of the MBBR reactor and the low-strength rare earth waste weak magnetic carrier. Figure 2 A three-dimensional structural model of a weak magnetic biological carrier made from low-intensity rare earth waste. Figure 3 The graph shows the change in total biofilm (SS) attached to different carrier systems in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 over time. Figure 4 The graph shows the change of volatile attached biomass (VSS) over time for different carrier systems in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4. Figure 5 The graph shows the change in total EPS amount over time for different carrier systems in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. Figure 6 The graph shows the change in the content of extracellular polymeric protein (PN) in different carrier systems of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 as a function of running time. Figure 7 Comparative graphs of ammonia monooxygenase (AMO) activity in different carrier systems of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4; Figure 8 This is a comparison diagram of the dehydrogenase (DHA) activities of different carrier systems in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. Figure 9 This is a comparison chart of the electron transport system activity (ETSA) of different carrier systems in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While specific methods and materials are described herein, similar or equivalent methods and materials may be used in the implementation or testing of this invention. In case of conflict with other documents, the contents of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] This invention provides a method for enhancing nitrogen removal from a moving bed biofilm based on the fluidization of low-intensity rare earth waste as a weak magnetic carrier to construct an endogenous weak magnetic microenvironment. This method utilizes the suspension, fluidization, dynamic circulation, collision contact, and spatial migration of the rare earth waste weak magnetic biological carrier within a moving bed biofilm reactor to form a dynamically distributed endogenous weak magnetic microenvironment, which is then used for biological nitrogen removal from wastewater.

[0028] In some embodiments of the present invention, the surface magnetic induction intensity of the rare earth waste weak magnetic biological carrier is 0.05-0.20 mT.

[0029] When the carrier is in a fluidized state, a multi-point, weak-intensity, dynamically coupled endogenous weak magnetic microenvironment can be formed between adjacent carriers, rather than an external magnetic field stimulus with a fixed position and direction.

[0030] In some embodiments of the present invention, the rare earth waste weak magnetic biological carrier is filled at a rate of 20%-30% in the reactor, and the carrier is kept suspended, circulated, contacted, separated and dispersed by continuous aeration.

[0031] In some embodiments of the present invention, the moving bed biofilm reactor includes a reaction vessel, a low-strength rare earth waste weak magnetic biological carrier, inoculated activated sludge, a continuous aeration system, an influent / effluent control system, and a hydraulic circulation unit for maintaining the fluidization and dynamic distribution of the carrier; the continuous aeration system supplies air through an aeration component located at the bottom of the reaction vessel.

[0032] In some embodiments of the present invention, the low-strength rare earth waste weak magnetic biological carrier is a composite porous carrier containing rare earth waste magnetic powder and a polymer matrix. The rare earth waste magnetic powder contains Nd, Fe, and B components, and the mass of the rare earth waste magnetic powder accounts for 3%-10% of the total mass of the composite porous carrier, with a particle size of 70-100 mesh. The polymer matrix is ​​an acrylonitrile-butadiene-styrene copolymer. The composite porous carrier is a three-dimensional printed porous carrier with an equivalent diameter of 20-30 mm, a porosity of 80%-90%, and a pore size of 0.8-2.5 mm. The density of the rare earth waste weak magnetic biological carrier is 0.95-1.10 g / cm3.

[0033] In some embodiments of the present invention, the operating conditions of the moving bed biofilm reactor are: HRT of 3-12h, DO of 2.0-6.0 mg / L, pH of 6.5-8.5, and temperature of 15-35℃.

[0034] Example 1 A method for enhancing nitrogen removal from a moving bed biofilm based on a fluidized bed of low-strength rare-earth waste magnetic carrier to construct an endogenous weak magnetic microenvironment includes the following steps: ABS is selected as the matrix material, and 5% by mass of crushed and sieved rare-earth waste magnetic powder containing Nd, Fe, and B components is added; the ABS and rare-earth waste magnetic powder are thoroughly mixed and melt-blended, followed by the preparation of a composite printing filament using an extruder; based on the carrier structure model, a low-strength rare-earth waste weak magnetic biocarrier R3 is prepared using fused deposition modeling (FDM) 3D printing technology. The R3 has an equivalent diameter of 25 mm, a porosity of 86%, a pore size of 1.5 mm, and a density of 1.01 g / cm³. 3 .

[0035] The surface magnetic induction intensity of R3 was measured to be 0.10 mT. A moving bed biofilm reactor was constructed, and R3 was added to the reactor along with activated sludge, with an R3 filling rate of 20%. Continuous aeration was achieved through aeration heads located at the bottom of the reactor to maintain the R3 in a suspended fluidized state; the hydraulic retention time (HRT) was controlled at 6 h, dissolved oxygen (DO) at 3.8 mg / L, pH at 7.5, and temperature at 20℃. No coils, electromagnets, or external permanent magnets for generating an external magnetic field were installed inside or outside the reactor.

[0036] Example 2 A moving bed biofilm denitrification enhancement method based on fluidized bed construction of endogenous weak magnetic microenvironment using low-strength rare earth waste weak magnetic carriers differs from Example 1 in that the mass fraction of rare earth waste magnetic powder incorporated is 3%, and the surface magnetic induction intensity of the resulting low-strength rare earth waste weak magnetic biocarrier is 0.05 mT.

[0037] Example 3 A moving bed biofilm denitrification enhancement method based on fluidized bed construction of endogenous weak magnetic microenvironment using low-strength rare earth waste weak magnetic carriers differs from Example 1 in that the mass fraction of rare earth waste magnetic powder incorporated is 10%, and the surface magnetic induction intensity of the resulting low-strength rare earth waste weak magnetic biocarrier is 0.20 mT.

[0038] Comparative Example 1 A biomembrane reaction system, differing from Example 1 only in that a commercial non-magnetic carrier (R1) is added as a conventional carrier control.

[0039] Comparative Example 2 A biofilm reaction system differs from Example 1 in that: rare earth waste magnetic powder is not added, and a three-dimensionally printed ordinary non-magnetic carrier R2 with the same structure and size as in Example 1 is used.

[0040] Comparative Example 3 A biofilm reaction system differs from Example 1 in that rare earth waste magnetic powder is replaced with ordinary Fe3O4 magnetic powder, and the amount added is adjusted so that the surface magnetic induction intensity of the resulting carrier R4 is 0.10 mT.

[0041] Comparative Example 4 A biofilm reaction system differs from Example 1 in that: a three-dimensional printed ordinary non-magnetic carrier with the same structure and size as in Example 1 is added, and a permanent magnet is placed outside the reactor so that the local magnetic induction intensity near the magnet is 0.10 mT, forming an external permanent magnet reinforcement system R5.

[0042] The total amount of attached biofilm (SS), volatile attached biomass (VSS), total EPS, extracellular protein polymers (PN), AMO activity, DHA activity, ETSA, and the removal efficiency of NH4+-N and TN were measured periodically in Examples 1 and Comparative Examples 1-4 to evaluate the effect of the endogenous weak magnetic microenvironment formed by the fluidization of low-intensity rare earth waste weak magnetic carriers on biofilm structure and denitrification function.

[0043] like Figure 3 As shown, the total amount of biofilm (SS) attached to the surface of different carriers generally showed a gradual increasing trend with the running time. After 36 days of operation, the SS of R1, R2, R3, R4 and R5 were 49.0, 54.4, 61.8, 58.5 and 56.4 mg SS / g carrier, respectively. Example 1 (R3) had the highest SS, indicating that the dynamic distributed endogenous weak magnetic microenvironment formed by fluidization of low-strength rare earth waste weak magnetic carriers is more conducive to biofilm accumulation than ordinary structural carriers, ordinary Fe3O4 magnetic powder carriers and external permanent magnet reinforcement systems.

[0044] like Figure 4 As shown, the variation pattern of VSS is basically consistent with that of SS. After 36 days of operation, the VSS of R1, R2, R3, R4 and R5 were 34.4, 38.0, 43.3, 41.1 and 39.8 mg VSS / g carrier, respectively, indicating that Example 1 not only increased the total amount of attached material, but also promoted the enrichment of active biomass.

[0045] like Figure 5 As shown, the total EPS increased rapidly during the initial stage and then gradually stabilized. After 60 days of operation, the total EPS of R1, R2, R3, R4 and R5 were 64, 86, 121, 105 and 97, respectively, with Example 1 showing the highest value, indicating that the endogenous weak magnetic microenvironment can promote extracellular polymer synthesis and biomembrane matrix construction.

[0046] like Figure 6 As shown, the PN content increases with operating time and tends to stabilize. After 60 days of operation, the PN contents of R1, R2, R3, R4 and R5 are 42, 51, 73, 63 and 58 mg / g, respectively. The protein extracellular polymers in Example 1 are significantly enriched, indicating that this system is more likely to form protein-rich, highly functional biomembrane matrices.

[0047] like Figure 7 As shown, the AMO activity of each system increased with operation. At the end of operation, the AMO activities of R1, R2, R3, R4 and R5 were 4.45, 4.85, 6.10, 5.45 and 5.15 U / g, respectively, with Example 1 showing the highest activity, indicating that the endogenous weak magnetic microenvironment can enhance the key rate-limiting step of ammonia oxidation.

[0048] like Figure 8As shown, at the end of the run, the DHA activities of R1, R2, R3, R4, and R5 were 5.00, 6.80, 8.45, 7.55, and 7.15 μg·h⁻¹, respectively. -1 ·g -1 Example 1 showed significantly higher levels than the comparative examples, indicating that its overall biomembrane respiratory and metabolic capacity and electron donor conversion capacity were stronger.

[0049] like Figure 9 As shown, the ETSA values ​​of R1, R2, R3, R4, and R5 are 7.3±0.6, 8.5±0.6, 10.1±0.6, 9.3±0.5, and 8.9±0.6 (10⁻² μg O₂·g⁻¹), respectively. -1 ·min -1 The electron transport system in Example 1 exhibits the highest activity, indicating that its electron transport chain process and energy conversion process are further enhanced.

[0050] The results of nitrogen removal during the stationary phase showed that NH4+ from R1, R2, R5, R4, and R3 was significantly reduced. + -N removal rates were 70%-72%, 73%-75%, 78%-80%, 82%-84%, and 87%-90%, respectively, while TN removal rates were 44%-46%, 48%-50%, 53%-55%, 57%-59%, and 62%-65%, respectively. The corresponding NH4 levels in the effluent during the stabilization period were... + The nitrogen (N) concentrations were 8.4-9.0, 7.5-8.1, 6.0-6.6, 4.8-5.4, and 3.0-3.9 mg / L, respectively, while the effluent TN concentrations were 21.6-22.4, 20.0-20.8, 18.0-18.8, 16.4-17.2, and 14.0-15.2 mg / L, respectively. These results indicate that, under the same or similar magnetic induction intensity conditions, Example 1 exhibits superior denitrification performance compared to the conventional Fe3O4 magnetic powder carrier and external permanent magnet reinforcement system.

[0051] Spatial uniformity results showed that, at 36 days, the SS (surface density) of the R5 external permanent magnet enhanced system in the near-magnet / upper, middle, and far-magnet / lower parts were 59.5, 56.0, and 53.5 mg SS / g carrier, respectively, with an average of 56.3; while the corresponding values ​​for Example 1 (R3) were 62.3, 61.8, and 61.2 mg SS / g carrier, with an average of 61.8. After 60 days of operation, the EPS spatial distribution of R5 was 106, 97, and 88, with an average of 97; the EPS spatial distribution of R3 was 122, 121, and 120, with an average of 121. This indicates that although the external permanent magnet enhanced system can generate some magnetic stimulation, it exhibits significant spatial non-uniformity. Example 1, relying on the fluidized circulation of the magnetic carrier to form a dynamic distributed endogenous weak magnetic microenvironment, can achieve a more uniform and stable biofilm-enhanced denitrification effect.

[0052] In summary, under the condition of surface magnetic induction intensity of 0.10 mT, although ordinary Fe3O4 magnetic powder carriers show a certain strengthening effect compared with non-magnetic carriers, their removal effects of SS, VSS, EPS, PN, AMO, DHA, ETSA and nitrogen are all lower than those of low-intensity rare earth waste weak magnetic biological carriers. Although the external permanent magnet strengthening system can generate magnetic stimulation, its spatial effect is uneven, and the overall strengthening effect is not as good as the rare earth waste weak magnetic carrier fluidization system of the present invention.

[0053] Therefore, it can be seen that the core of this invention is not simply to provide a magnetic carrier, but to construct a dynamic distributed endogenous weak magnetic microenvironment without an external magnetic field device by fluidizing and dynamically distributing low-strength rare earth waste weak magnetic biological carriers inside a moving bed biofilm reactor, and to achieve enhanced wastewater denitrification through a synergistic pathway of "EPS matrix enhancement - electron transfer enhancement - energy metabolism enhancement - nitrification function enhancement".

[0054] The embodiments described above are merely illustrative of specific implementations of the present invention and are not intended to limit the scope of the invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for enhancing nitrogen removal from a moving bed biofilm based on fluidized bed construction of an endogenous weak magnetic microenvironment using low-strength rare earth waste as a weak magnetic carrier, characterized in that... Includes the following steps: S1. Add the rare earth waste weak magnetic biological carrier to the moving bed biofilm reactor, and inoculate the moving bed biofilm reactor with activated sludge; S2. Through continuous aeration, the rare earth waste weak magnetic biological carrier is kept in a suspended fluidized state, dynamically circulating, colliding and contacting, and with continuously changing spatial positions within the reactor. S3. During the fluidization process of the rare earth waste weak magnetic biological carrier, the spatial distribution, mutual approach, collision, separation, and positional migration of multiple rare earth waste weak magnetic biological carriers are utilized to form a dynamic coupled endogenous weak magnetic microenvironment with non-fixed points, non-unidirectional directions, and multi-point spatial distribution within the reactor. S4. Without setting up coils, electromagnets, or external permanent magnets to generate an external magnetic field inside or outside the reactor, the moving bed biofilm reactor is continuously operated to perform biological denitrification treatment on wastewater.

2. The method according to claim 1, characterized in that, The surface magnetic induction intensity of the rare earth waste weak magnetic biological carrier is 0.05-0.20 mT.

3. The method according to claim 1, characterized in that, The filling rate of the rare earth waste weak magnetic biological carrier in the moving bed biofilm reactor is 20%-30%.

4. The method according to claim 1, characterized in that, The moving bed biofilm reactor includes a reaction vessel, a continuous aeration system, an influent control system, an effluent control system, and a hydraulic circulation unit. The continuous aeration system supplies air through an aeration component located at the bottom of the reaction vessel. The hydraulic circulation unit is used to maintain the suspension, fluidization, and dynamic distribution of the rare earth waste weak magnetic biological carrier within the reactor.

5. The method according to claim 1, characterized in that, The operating conditions of the moving bed biofilm reactor are as follows: dissolved oxygen 2.0-6.0 mg / L, hydraulic retention time 3-12 h, pH 6.5-8.5, and temperature 15-35℃.

6. The method according to claim 1, characterized in that, The rare earth waste weak magnetic biological carrier is a composite porous carrier containing rare earth waste magnetic powder and a polymer matrix, wherein the rare earth waste magnetic powder contains Nd, Fe and B components.

7. The method according to claim 6, characterized in that, The rare earth waste magnetic powder accounts for 3%-10% of the total mass of the composite porous carrier, and the particle size of the rare earth waste magnetic powder is 70-100 mesh.

8. The method according to claim 6, characterized in that, The polymer matrix is ​​an acrylonitrile-butadiene-styrene copolymer, and the composite porous carrier is a three-dimensional printed porous carrier with an equivalent diameter of 20-30 mm, a porosity of 80%-90%, and a pore size of 0.8-2.5 mm.

9. The method according to claim 1, characterized in that, The density of the rare earth waste weak magnetic biological carrier is 0.95-1.10 g / cm³. 3 .

10. The application of the method according to any one of claims 1-9 in wastewater denitrification treatment.

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