Multi-path synergistic nitrogen removal method based on iron ammonia oxidation driving

Abstract

The invention discloses a multi-path synergistic denitrification method based on iron ammonia oxidation driving. The method comprises the following steps: S1, adding magnetite as a filler into a reactor; s2, anaerobic ammonia oxidation sludge and sewage plant secondary sedimentation tank sludge are inoculated in a reactor, and sodium acetate is added; s3, carrying out nitrogen stripping treatment on the wastewater, and continuously introducing the wastewater into the reactor; s4, under the anaerobic condition, controlling the pH, temperature and hydraulic retention time (HRT) of the wastewater in the reactor; and S5, setting internal reflux in the reactor. According to the method disclosed by the invention, under the conditions of iron content and unbalanced carbon and nitrogen, microorganisms take Fe (III) as an electron acceptor to oxidize ammonia nitrogen to generate Fe (II), N2, NO3 <-> and NO2 <->, and meanwhile, the generated substrates Fe (II), NO3 <-> and NO2 <-> are metabolized through Anammox, NDFO and HD under the action of the microorganisms, so that the system forms multi-way synergistic denitrification under the driving of iron ammonia oxidation.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a multi-pathway synergistic denitrification method driven by iron-ammonia oxidation. Background Art

[0002] As water pollution becomes increasingly serious, nitrogen pollution has a significant impact on the ecological environment, and innovation in sewage treatment technology is particularly important. Although traditional denitrification processes such as nitrification-denitrification are mature, there are still many technical problems and disadvantages in practical applications: (1) High equipment and operating costs. Traditional nitrification-denitrification processes require complex reactors and control systems, including aeration facilities, mixing devices, etc. The investment and maintenance costs of these equipment are high, especially when applied on a large scale, the operating costs increase significantly; (2) Secondary pollution of nitrates. During the nitrification-denitrification process, nitrogen exists in the form of nitrates. If not properly treated, nitrates may re-enter the water body, causing eutrophication of the water body, which in turn leads to the proliferation of algae and deterioration of water quality; (3) During the nitrification process, microbial metabolism produces acidic substances, so alkaline substances are often needed to neutralize these acidities. This process not only increases operating costs, but may also introduce additional chemical management issues. In the denitrification stage, in order to provide the electron donors required for the reaction, an external organic carbon source is usually required, which further increases the operating cost of the entire treatment system. Therefore, there is an urgent need to find new technological solutions to improve the sustainability and efficiency of wastewater treatment.

[0003] In recent years, the new technology combining anaerobic ammonia oxidation (Anammox) and iron reduction (Feammox) has significantly reduced energy consumption and improved denitrification efficiency by using inorganic substances as electron donors. Especially in wastewater environments with carbon-nitrogen imbalance, Feammox has shown its unique advantages and can efficiently oxidize ammonia into N2 and NO3. - and NO2 - Therefore, the present invention hopes to use the magnetite-mediated Feammox system to drive multiple denitrification pathways to form a synergistic mechanism, further improve the technical efficiency while saving energy and reducing consumption, so as to promote the sustainable development of sewage treatment technology. Summary of the invention

[0004] In view of this, the present invention proposes a multi-pathway synergistic denitrification method based on iron-ammonia oxidation drive to solve the above technical problems.

[0005] The technical solution of the present invention is achieved in this way:

[0006] A multi-path synergistic denitrification method based on iron-ammonia oxidation drive comprises the following steps:

[0007] S1, adding magnetite as filler in the reactor;

[0008] S2. Inoculate the reactor with anaerobic ammonium oxidation sludge and sludge from the secondary sedimentation tank of the sewage treatment plant, the inoculation ratio of anaerobic ammonium oxidation sludge to sludge from the secondary sedimentation tank of the sewage treatment plant is 1:8-10; add soluble organic matter SCOD into the reactor, the SCOD concentration is 50-180 mg / L;

[0009] S3. Nitrogen stripping is performed on the wastewater to be treated to reduce the dissolved oxygen (DO) concentration to less than 0.2 mg·L -1 , the treated wastewater is continuously introduced into the reactor;

[0010] S4. Under anaerobic conditions, the pH of the wastewater in the reactor is controlled to be 7.5-8.0, the temperature to be 26°C-30°C and the hydraulic retention time (HRT) to be 10-12h, and the purified water is discharged from the outlet of the reactor;

[0011] S5. The reactor is provided with internal reflux to reflux part of the effluent and pass it into the reactor.

[0012] Preferably, the soluble organic matter SCOD is sodium acetate.

[0013] Preferably, the particle size of the magnetite is 6 to 10 mm, and the magnetite accounts for 30% of the reactor filling ratio.

[0014] Preferably, the magnetite is obtained from treated waste slag, and the preparation method of the magnetite is as follows: (1) crushing and screening the slag to remove impurities and large particles; (2) placing the screened slag in a muffle furnace, heating it to 800-1000°C, and keeping it for 3 hours; (3) slowly cooling the sample to room temperature; (4) placing the cooled sample in a magnetic separator to separate the magnetic particles; (5) using X-ray diffraction (XRD) technology to identify the mineral phase and confirm the presence of magnetite.

[0015] Preferably, in step S2, the inoculation ratio of anaerobic ammonium oxidation sludge to sewage treatment plant secondary sedimentation tank sludge is 1:9.

[0016] Preferably, the SCOD concentration in step S2 is 153.4±1.3 mg / L.

[0017] Preferably, the treated wastewater in step S3 is introduced into the reactor in an upward continuous mode.

[0018] Preferably, the reactor is provided with internal reflux, specifically by refluxing the outlet water of the reflux port through a reflux pump and passing it into the reactor.

[0019] Preferably, the internal reflux ratio of the internal reflux in step S5 is 1 to 2 times.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a multi-path synergistic denitrification method based on iron-ammonia oxidation drive, which is based on the magnetite-mediated electron transfer mechanism under the condition of iron and carbon-nitrogen imbalance, so that microorganisms use Fe(III) as an electron acceptor to oxidize ammonia nitrogen to generate Fe(II), N2, NO3 - and NO2 - , and the metabolic substrate NO2 - It is used as an electron acceptor by anaerobic ammonium oxidizing bacteria (AnAOB) to oxidize ammonia nitrogen. The coupling of Feammox (anaerobic iron ammonia oxidation) and Anammox (anaerobic ammonium oxidation) forms an effective symbiosis, revealing the reason why ammonia nitrogen is efficiently removed. At the same time, the generated Fe(II) is further used by iron-type denitrifying bacteria to oxidize NO x - -N generates Fe(III) and N2, and the cooperation of Feammox-NDFO (anaerobic iron ammonia oxidation coupled with iron-type denitrification) promotes the N-Fe cycle of the system. On the one hand, it reduces the dosage of the added iron source and saves energy and reduces consumption; on the other hand, the N-Fe cycle reduces the probability of sludge mineralization and improves the stability of the system. Mixing anaerobic ammonia oxidation sludge with sludge from the secondary sedimentation tank of the sewage treatment plant can accelerate the enrichment of iron ammonia oxidizing bacteria and shorten the start-up time of the reactor. Through the intervention of sodium acetate and organic carbon sources, the system is enriched with heterotrophic denitrifying bacteria, which in turn induces the synergistic denitrification of Feammox (anaerobic iron ammonia oxidation) coupled with Anammox (anaerobic ammonia oxidation), NDFO (iron-type denitrification) and HD (heterotrophic denitrification), improving the denitrification efficiency and resistance to environmental stress of the system. In addition, the setting of internal reflux can improve the distribution and mixing state of the water flow, ensure the uniformity of the hydraulic properties in the reactor and prevent sludge deposition. The contact between microorganisms and the substrate is enhanced, and the circulation of iron ions in the system is improved, thereby enhancing the conversion of N-Fe. The process of the present invention is simple, the operation and management cost is low, and the denitrification efficiency is high. The ammonia nitrogen removal rate can reach 95.9±0.8%, the total nitrogen removal rate can reach 87.7±3.5%, and the SCOD removal rate can reach 69.5±4.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a diagram of the operating device of the present invention. DETAILED DESCRIPTION

[0023] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0024] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0025] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0026] The operating device of the present invention (such as Figure 1 The invention discloses a method for preparing a three-phase separator for a water discharge device (shown in FIG. 1 ), comprising a water inlet bucket (1), a water inlet pump (2), magnetite (3), a reactor (4), a three-phase separator (5), an exhaust hole (6), an overflow port (7), a water outlet (8), a reflux port (9), a water outlet bucket (10), a mud outlet (11), and a reflux pump (12).

[0027] The magnetite used in the embodiment of the present invention is obtained by processing waste slag. The preparation method of magnetite is as follows: (1) crushing and screening the slag to remove impurities and large particles; (2) placing the screened slag in a muffle furnace, heating it to 800-1000°C, and keeping it for 3 hours to promote phase change; (3) slowly cooling the sample to room temperature to prevent brittle cracking; (4) placing the cooled sample in a magnetic separator to separate magnetic particles; (5) using X-ray diffraction (XRD) technology to identify the mineral phase and confirm the presence of magnetite.

[0028] Example 1

[0029] A multi-path synergistic denitrification method based on iron-ammonia oxidation drive comprises the following steps:

[0030] S1. Add magnetite as filler in the reactor, the particle size is 6-10 mm, and the magnetite accounts for 30% of the reactor filling ratio;

[0031] S2. The reactor was inoculated with sludge from the secondary sedimentation tank of the sewage plant (MLVSS 6800 mg·L -1 ), the inoculation volume is 1 L, and a reactor filled with secondary sedimentation tank sludge is obtained;

[0032] S3. The inlet bucket is filled with wastewater containing only ammonia nitrogen as an electron donor. The wastewater is stripped with nitrogen to reduce the dissolved oxygen (DO) concentration to less than 0.2 mg·L -1 , the treated wastewater is continuously introduced into the reactor;

[0033] S4. Under anaerobic conditions, the pH of the wastewater in the reactor is controlled to be 7.5-8.0, the temperature to be 26°C-30°C and the hydraulic retention time (HRT) to be 10h, and the purified water is discharged from the outlet of the reactor;

[0034] S5. The outlet water of the reflux port is refluxed by a reflux pump, and the internal reflux ratio is 0 (ie, no internal reflux is set).

[0035] The wastewater in the water inlet bucket in step S3 contains NH4Cl (70.1±1.1 mg·L -1 )、NaHCO3(800mg·L -1 )、MgSO4·7H2O(180mg·L -1 )、KH2PO4(36mg·L -1)、CaCl2(280mg·L -1 ); Trace element 1: EDTA (5000mg·L -1 )、FeSO4·7H2O(5000mg·L -1 ); Trace element 2: EDTA (15000mg·L -1 )、MnCl2·4H2O(990mg·L -1 )、CuSO4·5H2O(250mg·L -1 )、ZnSO4·7H2O(430mg·L -1 )、NiCl2·6H2O(190mg·L -1 )、Na2MoO4·2H2O(210mg·L -1 )、H3BO4(14mg·L -1 ).

[0036] In this example, after the reactor was operated for 48 days, the effluent ammonia nitrogen concentration was stabilized at 10.5±1.1 mg·L -1 , nitrite nitrogen concentration 4.6±0.6mg·L -1 , nitrate nitrogen concentration 18.2±2.3mg·L -1 , Fe(II) concentration 6.1±0.3mg·L -1 , the ammonia nitrogen removal rate was stable at 85.0±1.3%, and the total nitrogen removal rate was stable at 52.5±2.3%.

[0037] Example 2

[0038] A multi-path synergistic denitrification method based on iron-ammonia oxidation drive comprises the following steps:

[0039] S1. Add magnetite as filler in the reactor, the particle size is 6-10 mm, and the magnetite accounts for 30% of the reactor filling ratio;

[0040] S2. Inoculate the reactor with anaerobic ammonium oxidation sludge (MLVSS 8000mg·L -1 ) and sewage plant secondary sedimentation tank sludge (MLVSS 6000mg·L -1 ), the inoculation ratio was 1:9, the inoculation volume was 1 L, and a reactor filled with mixed sludge was obtained;

[0041] S3. The inlet bucket is filled with wastewater containing only ammonia nitrogen as an electron donor. The wastewater is stripped with nitrogen to reduce the dissolved oxygen (DO) concentration to less than 0.2 mg·L -1 , the treated wastewater is continuously introduced into the reactor;

[0042] S4. Under anaerobic conditions, the pH of the wastewater in the reactor is controlled to be 7.5-8.0, the temperature to be 26°C-30°C and the hydraulic retention time (HRT) to be 10h, and the purified water is discharged from the outlet of the reactor;

[0043] S5. The outlet water of the reflux port is refluxed by a reflux pump, and the internal reflux ratio is 0 (ie, no internal reflux is set).

[0044] The wastewater in the water inlet bucket in step S3 contains NH4Cl (70.5±1.4mg·L -1 )、NaHCO3(800mg·L -1 )、MgSO4·7H2O(180mg·L -1 )、KH2PO4(36mg·L -1 )、CaCl2(280mg·L -1 ); Trace element 1: EDTA (5000mg·L -1 )、FeSO4·7H2O(5000mg·L -1 ); Trace element 2: EDTA (15000mg·L -1 )、MnCl2·4H2O(990mg·L -1 )、CuSO4·5H2O(250mg·L -1 )、ZnSO4·7H2O(430mg·L -1 )、NiCl2·6H2O(190mg·L -1 )、Na2MoO4·2H2O(210mg·L -1 )、H3BO4(14mg·L -1 ).

[0045] In this example, after the reactor was operated for 32 days, the effluent ammonia nitrogen concentration was stabilized at 6.6±1.1 mg·L -1 , nitrite nitrogen concentration 3.2±0.6mg·L -1 , nitrate nitrogen concentration 28.6±1.8mg·L -1 , Fe(II) concentration 7.2±0.2mg·L -1 , the ammonia nitrogen removal rate was stabilized at 90.6±1.6%, and the total nitrogen removal rate was stabilized at 45.5±1.4%. Compared with Example 1, the reactor stabilization time was shortened by 16 days, and the ammonia nitrogen removal rate was increased by 5.6%, which means that AnAOB in anaerobic ammonia oxidation sludge promoted the domestication of the iron ammonia oxidation system as a functional denitrifying bacteria, and revealed that the removal efficiency of ammonia nitrogen can be enhanced through the synergistic effect of AnAOB and iron ammonia oxidation microorganisms.

[0046] Example 3

[0047] A multi-path synergistic denitrification method based on iron-ammonia oxidation drive comprises the following steps:

[0048] S1. Add magnetite as filler in the reactor, the particle size is 6-10 mm, and the magnetite accounts for 30% of the reactor filling ratio;

[0049] S2. The sludge inoculated in the reactor is the same as that in Example 2, i.e., anaerobic ammonium oxidation sludge (MLVSS 8000 mg·L -1 ) and sewage plant secondary sedimentation tank sludge (MLVSS 6000mg·L -1 ), the inoculation ratio was 1:9, the inoculation volume was 1 L, and a reactor filled with mixed sludge was obtained;

[0050] S3. The inlet bucket is filled with wastewater containing only ammonia nitrogen as an electron donor. The wastewater is stripped with nitrogen to reduce the dissolved oxygen (DO) concentration to less than 0.2 mg·L -1 , the treated wastewater is continuously introduced into the reactor;

[0051] S4. Under anaerobic conditions, the pH of the wastewater in the reactor is controlled to be 7.5-8.0, the temperature to be 26°C-30°C and the hydraulic retention time (HRT) to be 10h, and the purified water is discharged from the outlet of the reactor;

[0052] S5. The outflow water from the reflux port is refluxed through a reflux pump, and the internal reflux ratio is 1 (the ratio between the reflux volume and the inlet wastewater volume).

[0053] The wastewater in the water inlet bucket in step S3 contains NH4Cl (70.9±1.4mg·L -1 )、NaHCO3(800mg·L -1 )、MgSO4·7H2O(180mg·L -1 )、KH2PO4(36mg·L -1 )、CaCl2(280mg·L -1 ); Trace element 1: EDTA (5000mg·L -1 )、FeSO4·7H2O(5000mg·L -1 ); Trace element 2: EDTA (15000mg·L -1 )、MnCl2·4H2O(990mg·L -1 )、CuSO4·5H2O(250mg·L -1 )、ZnSO4·7H2O(430mg·L -1 )、NiCl2·6H2O(190mg·L -1 )、Na2MoO4·2H2O(210mg·L -1)、H3BO4(14mg·L -1 ).

[0054] In this example, after the reactor was operated for 7 days, the ammonia nitrogen concentration in the effluent was stabilized at 3.5±0.8 mg·L -1 , nitrite nitrogen concentration 2.1±0.8mg·L -1 , nitrate nitrogen concentration 30.2±3.6mg·L -1 , Fe(II) concentration 8.4±0.2mg·L -1 , the ammonia nitrogen removal rate was stabilized at 95.0±1.1%, and the total nitrogen removal rate was stabilized at 48.9±3.5%. Compared with Example 2, the adjustment of the internal reflux ratio enhanced the contact between microorganisms and the substrate, while improving the circulation of iron ions in the system, thereby enhancing the conversion of N-Fe.

[0055] Example 4

[0056] A multi-path synergistic denitrification method based on iron-ammonia oxidation drive comprises the following steps:

[0057] S1. Add magnetite as filler in the reactor, the particle size is 6-10 mm, and the magnetite accounts for 30% of the reactor filling ratio;

[0058] S2. The sludge inoculated in the reactor was the same as that in Example 3, i.e., anaerobic ammonium oxidation sludge (MLVSS 8000 mg·L -1 ) and sewage plant secondary sedimentation tank sludge (MLVSS 6000mg·L -1 ), the inoculation ratio was 1:9, the inoculation volume was 1 L, and a reactor filled with mixed sludge was obtained; sodium acetate (SCOD) 55.9 ± 1.2 mg·L was added into the reactor -1 ;

[0059] S3. The inlet bucket is filled with wastewater containing only ammonia nitrogen as an electron donor. The wastewater is stripped with nitrogen to reduce the dissolved oxygen (DO) concentration to less than 0.2 mg·L -1 , the treated wastewater is continuously introduced into the reactor;

[0060] S4. Under anaerobic conditions, the pH of the wastewater in the reactor is controlled to be 7.5-8.0, the temperature to be 26°C-30°C and the hydraulic retention time (HRT) to be 10h, and the purified water is discharged from the outlet of the reactor;

[0061] S5. The outflow water from the reflux port is refluxed through a reflux pump, and the internal reflux ratio is 1 (the ratio between the reflux volume and the inlet wastewater volume).

[0062] The wastewater in the water inlet bucket in step S3 contains NH4Cl (70.4±1.1mg·L -1)、NaHCO3(800mg·L -1 )、MgSO4·7H2O(180mg·L -1 )、KH2PO4(36mg·L -1 )、CaCl2(280mg·L -1 ); Trace element 1: EDTA (5000mg·L -1 )、FeSO4·7H2O(5000mg·L -1 ); Trace element 2: EDTA (15000mg·L -1 )、MnCl2·4H2O(990mg·L -1 )、CuSO4·5H2O(250mg·L -1 )、ZnSO4·7H2O(430mg·L -1 )、NiCl2·6H2O(190mg·L -1 )、Na2MoO4·2H2O(210mg·L -1 )、H3BO4(14mg·L -1 ).

[0063] In this example, after the reactor was operated for 24 days, the ammonia nitrogen concentration in the effluent was stabilized at 3.2±1.5 mg·L -1 , nitrite nitrogen concentration 0.4±0.1mg·L -1 , nitrate nitrogen concentration 17.5±1.4mg·L -1 , Fe(II) concentration 2.4±0.2mg·L -1 , SCOD concentration 24.7±1.0mg·L -1 , the ammonia nitrogen removal rate was stable at 95.4±0.7%, the total nitrogen removal rate was stable at 71.0±2.2%, and the SCOD removal rate was 55.9±1.7%. Compared with Example 3, the concentrations of nitrate nitrogen and nitrite nitrogen in the effluent decreased by 41.7% and 81.0%, respectively, indicating that the presence of biodegradable organic matter can promote heterotrophic denitrification with nitrate nitrogen and nitrite nitrogen as electron acceptors. More specifically, SCOD inevitably changes the cooperative pathway of nitrogen degradation, in which case facultative NDFO (iron-type denitrification) participants may oxidize iron (II), combine with nitrogen oxide-nitrogen reduction, minimize the liquid iron (II) concentration, and share the oxidized iron with Feammox.

[0064] Example 5

[0065] A multi-path synergistic denitrification method based on iron-ammonia oxidation drive comprises the following steps:

[0066] S1. Add magnetite as filler in the reactor, the particle size is 6-10 mm, and the magnetite accounts for 30% of the reactor filling ratio;

[0067] S2. The sludge inoculated in the reactor was the same as that in Example 3, i.e., anaerobic ammonium oxidation sludge (MLVSS 8000 mg·L -1 ) and sewage plant secondary sedimentation tank sludge (MLVSS 6000mg·L -1 ), the inoculation ratio was 1:9, the inoculation volume was 1 L, and a reactor filled with mixed sludge was obtained; sodium acetate (SCOD) 153.4 ± 1.3 mg·L was added into the reactor -1 ;

[0068] S3. The inlet bucket is filled with wastewater containing only ammonia nitrogen as an electron donor. The wastewater is stripped with nitrogen to reduce the dissolved oxygen (DO) concentration to less than 0.2 mg·L -1 , the treated wastewater is continuously introduced into the reactor;

[0069] S4. Under anaerobic conditions, the pH of the wastewater in the reactor is controlled to be 7.5-8.0, the temperature to be 26°C-30°C and the hydraulic retention time (HRT) to be 10h, and the purified water is discharged from the outlet of the reactor;

[0070] S5. The outflow water from the reflux port is refluxed through a reflux pump, and the internal reflux ratio is 1 (the ratio between the reflux volume and the inlet wastewater volume).

[0071] The wastewater in the water inlet bucket in step S3 contains NH4Cl (69.7±0.8mg·L -1 )、NaHCO3(800mg·L -1 )、MgSO4·7H2O(180mg·L -1 )、KH2PO4(36mg·L -1 )、CaCl2(280mg·L -1 ); Trace element 1: EDTA (5000mg·L -1 )、FeSO4·7H2O(5000mg·L -1 ); Trace element 2: EDTA (15000mg·L -1 )、MnCl2·4H2O(990mg·L -1 )、CuSO4·5H2O(250mg·L -1 )、ZnSO4·7H2O(430mg·L -1 )、NiCl2·6H2O(190mg·L -1 )、Na2MoO4·2H2O(210mg·L -1 )、H3BO4(14mg·L-1 ).

[0072] In this example, after the reactor was operated for 16 days, the ammonia nitrogen concentration in the effluent was stabilized at 2.8±0.5 mg·L -1 , nitrite concentration 1.1±0.4mg·L -1 , nitrate nitrogen concentration 4.6±2.5mg·L -1 , Fe(II) concentration 5.5±0.3mg·L -1 , SCOD concentration 46.9±2.1mg·L -1 , the ammonia nitrogen removal rate was stable at 95.9±0.8%, the total nitrogen removal rate was stable at 87.7±3.5%, and the SCOD removal rate was 69.5±4.5%. Compared with Example 4, the SCOD and total nitrogen removal rates increased to 69.5±4.5% and 87.7±3.5%, respectively. This means that the Feammox process is closely related to the improvement of SCOD removal rate, and it also shows that Feammox as the main nitrogen degradation reaction is compatible with heterotrophic environment.

[0073] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-path synergistic denitrification method based on iron-ammonia oxidation driven, characterized in that: The following steps are involved: S1, adding magnetite as filler in the reactor; S2. Inoculate the reactor with anaerobic ammonium oxidation sludge and sludge from the secondary sedimentation tank of the sewage treatment plant, the inoculation ratio of anaerobic ammonium oxidation sludge to sludge from the secondary sedimentation tank of the sewage treatment plant is 1:8-10; add soluble organic matter SCOD into the reactor, the SCOD concentration is 50-180 mg / L; S3. Nitrogen stripping is performed on the wastewater to be treated to reduce the dissolved oxygen concentration to less than 0.2 mg·L -1 , the treated wastewater is continuously introduced into the reactor; S4. Under anaerobic conditions, the pH of the wastewater in the reactor is controlled to be 7.5-8.0, the temperature is 26°C-30°C and the hydraulic retention time is 10-12h, and the purified water is discharged from the outlet of the reactor; S5. The reactor is provided with internal reflux to reflux part of the effluent and pass it into the reactor.

2. A multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 1, characterized in that: The soluble organic matter SCOD is sodium acetate.

3. The multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 1 is characterized in that: The particle size of the magnetite is 6-10 mm, and the magnetite accounts for 30% of the filling ratio of the reactor.

4. A multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 3, characterized in that: The magnetite is obtained by processing waste slag, and the preparation method of the magnetite is as follows: (1) crushing and screening the slag to remove impurities and large particles; (2) placing the screened slag in a muffle furnace, heating it to 800-1000° C., and maintaining it for 3 hours; (3) slowly cooling the sample to room temperature; (4) placing the cooled sample in a magnetic separator to separate the magnetic particles; and (5) using X-ray diffraction technology to identify the mineral phase and confirm the presence of magnetite.

5. The multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 1 is characterized in that: In step S2, the inoculation ratio of the anaerobic ammonium oxidation sludge to the sludge from the secondary sedimentation tank of the sewage treatment plant is 1:

9.

6. The multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 1 is characterized in that: The SCOD concentration in step S2 is 153.4±1.3 mg / L.

7. The multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 1 is characterized in that: The treated wastewater in step S3 is introduced into the reactor in an upward continuous mode.

8. The multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 1 is characterized in that: The reactor is provided with internal reflux, specifically, the effluent from the reflux port is refluxed by a reflux pump and passed into the reactor.

9. A multi-path synergistic denitrification method based on iron-ammonia oxidation drive according to claim 8, characterized in that: The internal reflux ratio of the internal reflux is 1 to 2 times.

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