Treatment method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation

Abstract

The present invention relates to a treatment method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonia oxidation, comprising the following steps: S1: preparing a carbon base material for an enzyme-like catalyst; S2: dispersing and loading copper and iron bimetallics on the carbon base material to obtain an enzyme-like catalyst; S3: loading the enzyme-like catalyst on a carbon carrier to obtain a working electrode loaded with the enzyme-like catalyst; S4: placing the working electrode, counter electrode and reference electrode obtained in step S3 into sewage containing nitrate, turning on a power supply, connecting the working electrode to the cathode of the power supply and the counter electrode to the anode of the power supply to perform sewage treatment; and S5: adding anaerobic ammonia oxidizing bacteria to the system in step S4 to perform sewage treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage nitrate treatment, and particularly relates to a treatment method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonia oxidation. Background Art

[0002] Excessive inorganic nitrogen in sewage can cause eutrophication of water bodies. my country's discharge standards for sewage treatment are also constantly improving, and higher requirements are placed on traditional biological denitrification processes, requiring the removal of high-concentration nitrates from sewage. The anaerobic ammonia oxidation process has the advantages of low energy consumption, low sludge production, and no need for external organic carbon sources. In the process of using anaerobic ammonia oxidation technology to remove high-concentration nitrates in wastewater, nitrate nitrogen is required to be converted into ammonia nitrogen and nitrite nitrogen in a specific concentration ratio. The closer to this specific ratio, the better the effect of anaerobic ammonia oxidation. At present, there is no suitable method to efficiently convert nitrate nitrogen in wastewater into ammonia nitrogen and nitrite nitrogen in a specific concentration ratio. This ratio is difficult to control, which reduces the denitrification performance of the anaerobic ammonia oxidation process and causes the anaerobic ammonia oxidation treatment results to be unstable. Summary of the Invention

[0003] In response to the above problems, the present invention provides a method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonia oxidation, comprising the following steps:

[0004] S1: Preparation of carbon-based materials for enzyme-like catalysts;

[0005] S2: Dispersing copper and iron bimetallic materials on a carbon substrate to produce an enzyme-like catalyst;

[0006] S3: loading the enzyme-like catalyst on a carbon support to obtain a working electrode loaded with the enzyme-like catalyst;

[0007] S4: placing the working electrode, counter electrode, and reference electrode obtained in step S3 into the wastewater containing nitrate, connecting the power supply, connecting the working electrode to the cathode of the power supply, and connecting the counter electrode to the anode of the power supply, to perform wastewater treatment;

[0008] S5: Add anaerobic ammonia-oxidizing bacteria to the system of step S4 to treat the sewage.

[0009] Optionally, in step S1, the method for preparing the carbon base material is specifically as follows:

[0010] (1) preparing a zinc chloride solution with a zinc chloride concentration of 0.05-0.1 g / ml; then preparing a dimethylimidazole solution with a dimethylimidazole concentration of 0.04-0.06 g / ml;

[0011] (2) mixing the zinc chloride solution and the dimethylimidazole solution, centrifuging and washing with ultrapure water to obtain a white solid;

[0012] (3) The white solid was dried and ground, and then heat-treated in a mixed atmosphere of ammonia and argon to obtain an activated carbon base material.

[0013] Further optionally, in step (1), the zinc chloride solution and the dimethylimidazole solution are both prepared using ultrapure water; in step (3), the white solid is dried at 60°C.

[0014] Further optionally, in step (3), the dried white solid powder is first heat-treated at 1000° C. for 30-40 min in a mixed atmosphere, wherein the volume ratio of ammonia to argon in the mixed atmosphere is 1:4;

[0015] The activated carbon substrate is then heat treated at 1000° C. for 180-200 minutes in a pure argon atmosphere and then cooled in the furnace to obtain the activated carbon substrate.

[0016] Optionally, step S2 is specifically as follows: first, the activated carbon base material, ferric nitrate and copper nitrate are dispersed in ultrapure water, ultrasonically treated for 2-3 hours, and then centrifuged to obtain a solid precursor; the solid precursor is vacuum dried at 60-80°C, and then heat treated at 180-200°C in a hydrogen atmosphere for 2-3 hours to obtain a Cu-Fe-NC single atom catalyst, which is an enzyme-like catalyst.

[0017] Optionally, the carbon support is a three-dimensional carbon felt. In step S3, the enzyme-like catalyst is dispersed in ultrapure water, and the three-dimensional carbon felt is also placed in ultrapure water for adsorption. The carbon felt is then taken out and dried to obtain a working electrode.

[0018] Optionally, in step S4, when the power supply voltage is in the range of -0.8V to -0.9V vs. SCE voltage, the treated product is nitrite nitrogen; when the power supply voltage is in the range of -1.0V to -1.2V vs. SCE voltage, the treated product is nitrite nitrogen and ammonia nitrogen coexisting; when the power supply voltage is greater than -1.2V vs. SCE, the treated product is ammonia nitrogen.

[0019] Further optionally, in step S4, the power supply voltage is within the range of -1.0V to -1.2V vs. SCE voltage, and by controlling the electrolysis time, the molar ratio of nitrite nitrogen and ammonia nitrogen in the treated products can be precisely controlled;

[0020] When the electrolysis time is 2.5 h, the molar ratio of nitrite nitrogen to ammonia nitrogen is 1:1.3; when the electrolysis time is less than 2.5 h, the product after treatment is mainly nitrite nitrogen with a small amount of ammonia nitrogen; when the electrolysis time is greater than 2.5 h, the product after treatment gradually becomes mainly ammonia nitrogen, and the nitrite nitrogen gradually decreases.

[0021] The treatment method provided by the present invention can process inorganic nitrogen in sewage into nitrite nitrogen and ammonia nitrogen coexisting, and the molar ratio of nitrite nitrogen to ammonia nitrogen is 1:1.3, which meets the molar stoichiometric ratio in the anaerobic ammonium oxidation process, thereby achieving efficient removal of nitrate in sewage, avoiding the cumulative poisoning of nitrate nitrogen in the anaerobic ammonium oxidation process, and stably achieving more than 90% removal of total nitrogen; there is no need to add an organic carbon source as an electron donor for microorganisms, reducing carbon emissions; and it can achieve automated and miniaturized production.

[0022] In order to improve the total nitrogen removal rate and enhance the treatment effect, the present invention also provides a composite working electrode, the preparation method of which is as follows:

[0023] (4) cutting two pieces of three-dimensional carbon felt of the same size, wherein the three-dimensional carbon felt is rectangular; crushing the roots, stems, and leaves of the herb to obtain plant debris;

[0024] (5) Under ultrasonic conditions, the enzyme-like catalyst obtained in step S2 is first uniformly dispersed in ultrapure water, and then plant debris is added. After the plant debris is also uniformly dispersed, the three-dimensional carbon felt is added;

[0025] (6) first subjecting the system of step (5) to ultrasonic treatment and then to stirring treatment, so that the enzyme-like catalyst is loaded onto the three-dimensional carbon felt and plant debris;

[0026] (7) taking out the three-dimensional carbon felt and drying it; then centrifuging the remaining solid and drying the obtained solid;

[0027] (8) evenly spreading the solid obtained in step (7) to the same area and shape as the three-dimensional carbon felt, and then hot pressing the upper and lower surfaces to obtain a core;

[0028] (9) The core is placed between two sheets of three-dimensional carbon felt, and then double-sided hot pressing is performed to obtain a complete working electrode.

[0029] Optionally, in step (4), the roots, stems and leaves of the herb are crushed into pieces of 0.1-1 cm. The smaller size of the plant debris is conducive to increasing the specific surface area and the loading amount of the enzyme-like catalyst.

[0030] Optionally, in steps (5) and (6), the enzyme-like catalyst is first added to ultrapure water and ultrasonically treated until uniformly dispersed; then the plant debris is added and ultrasonic treatment is continued until the enzyme-like catalyst and the plant debris are uniformly dispersed; then the three-dimensional carbon felt is added and ultrasonic treatment is continued; the power of the above ultrasonic treatment is 60-80 kW;

[0031] Then, the ultrasound is stopped and stirring is performed with a stirring intensity such that all the plant debris does not sink to the bottom and the three-dimensional carbon felt is always in a moving state.

[0032] In step (7), the three-dimensional carbon felt is loaded with the enzyme-like catalyst and then taken out, and the remaining solids are plant debris loaded with the enzyme-like catalyst and the suspended enzyme-like catalyst. These remaining solids are all centrifuged out and used to prepare the core, thereby making full use of the enzyme-like catalyst.

[0033] Optionally, in step (8), the dried plant debris loaded with enzyme-like catalysts and the unloaded enzyme-like catalysts are evenly spread together, the temperature of double-sided hot pressing is 150-180°C, and the time of double-sided hot pressing is 20-60 seconds. During the hot pressing process, the plant debris adheres to each other to form a whole, and the unloaded enzyme-like catalyst is also wrapped in the whole, eventually forming a core. Hot pressing shapes the plant debris, and the unloaded enzyme-like catalyst is also integrated into the core, realizing the full utilization of the enzyme-like catalyst. Moreover, during hot pressing, some plant debris undergoes varying degrees of carbonization, which improves the conductivity of the core. Combined with the evenly distributed enzyme-like catalyst, the conductivity of the core is guaranteed. Since the cells of the plant debris contain a small amount of water, combined with the appropriate hot pressing time, the plant debris will not catch fire during hot pressing.

[0034] Optionally, in step (9), the double-sided hot pressing temperature is 150-180°C and the double-sided hot pressing time is 2-5 minutes, so that the core and the three-dimensional carbon felt on both sides form a whole. Considering the liquid use environment of the working electrode, the core and the three-dimensional carbon felt can be tied and fixed with fine iron wire after hot pressing to prevent the core and the three-dimensional carbon felt from being misaligned after long-term use. The enzyme-like catalyst is a carbon-based material and is not affected by the hot pressing temperature.

[0035] The working electrode containing a core provided by the present invention expands the volume and surface area of ​​the carrier, and cleverly selects the debris of the roots, stems and leaves of herbaceous plants as the carrier. The fiber structure inside the core has good toughness, large porosity and long service life. In step (6), ultrasonic dispersion is first performed, and then ultrasonic loading is performed to improve the uniformity of the load. Then, the loading is continued under stirring conditions to avoid the ultrasonic time being too long so that the catalyst on the load falls off. In step (7), all catalysts can be recovered and used to prepare the working electrode, thereby increasing the utilization rate of the catalyst. In steps (8) and (9), the core and the working electrode are fixed by a double-sided hot pressing method, which is strong and firm. The present invention unexpectedly found that after the double-sided hot pressing in step (9), the catalytic effect of the entire working electrode is improved, which may be because the high temperature of the hot pressing has a reactivation effect on the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Transmission electron micrographs of enzyme-like catalysts (a is a transmission electron micrograph of the activated carbon substrate, b is an X-ray energy spectrum of the Fe element in the activated carbon substrate, c is an X-ray energy spectrum of the Cu element in the activated carbon substrate, and d is an overlay of the X-ray energy spectrum of the Cu and Fe elements in the activated carbon substrate);

[0037] Figure 2 The electrocatalytic product curve is a graph of a power supply voltage of -0.8 V vs. SCE;

[0038] Figure 3 The electrocatalytic product curve is a graph of the power supply voltage of -1.3V vs. SCE;

[0039] Figure 4 This is the electrocatalytic product curve when the power supply voltage is -1.2V vs. SCE. DETAILED DESCRIPTION

[0040] Example 1

[0041] This embodiment provides a method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation, comprising the following steps:

[0042] S1: Preparation of carbon-based materials for enzyme-like catalysts;

[0043] S2: Dispersing copper and iron bimetallic materials on a carbon substrate to produce an enzyme-like catalyst;

[0044] S3: loading the enzyme-like catalyst on a carbon support to obtain a working electrode loaded with the enzyme-like catalyst;

[0045] S4: placing the working electrode, counter electrode, and reference electrode obtained in step S3 into the wastewater containing nitrate, connecting the power supply, connecting the working electrode to the cathode of the power supply, and connecting the counter electrode to the anode of the power supply, to perform wastewater treatment;

[0046] S5: Adding anaerobic ammonium oxidizing bacteria to the system of step S4 to treat the wastewater;

[0047] Nitrate electroreduction is performed in an electrolytic cell, with a cation exchange membrane (Nafion 117) separating the cathode and anode compartments. During constant-potential electrochemical nitrate reduction experiments, the working electrode is connected to the cathode, the counter electrode is connected to the anode, and the reference electrode (saturated calomel electrode (SCE)) is also connected to the anode. The counter electrode is a metal rod, such as a carbon rod or stainless steel rod.

[0048] In step S1, the method for preparing the carbon base material is specifically as follows:

[0049] (1) preparing a zinc chloride solution with a zinc chloride concentration of 0.05 g / ml; then preparing a dimethylimidazole solution with a dimethylimidazole concentration of 0.04 g / ml;

[0050] (2) mixing the zinc chloride solution and the dimethylimidazole solution, centrifuging and washing with ultrapure water to obtain a white solid;

[0051] (3) The white solid was dried and ground, and then heat-treated in a mixed atmosphere of ammonia and argon to obtain an activated carbon base material.

[0052] Specifically, 5g of ZnCl2 was weighed and dissolved in 100ml of ultrapure water solution, ultrasonically stirred for 30 minutes to obtain a uniformly mixed zinc chloride solution; then 4g of dimethylimidazole was weighed and dissolved in 100ml of ultrapure water, ultrasonically stirred for 15 minutes to obtain a uniformly mixed dimethylimidazole solution; the fully dissolved zinc chloride solution and dimethylimidazole solution were then mixed and stirred for 24 hours to obtain a milky white liquid, which was centrifuged and washed with ultrapure water 3 times, and dried in a vacuum oven at 60°C overnight to obtain a white solid; after fully grinding the white solid, it was heat treated at 1000°C in a 20vol% NH3 and 80vol% Ar atmosphere for 30 minutes, and heat treated in a pure argon atmosphere for 200 minutes, and finally cooled with the furnace to obtain an activated carbon base material.

[0053] Step S2 is specifically as follows: 100 mg of activated carbon substrate material, 5 mg of ferric nitrate, and 5 mg of copper nitrate are weighed and dispersed in 20 ml of ultrapure water for 2 hours. After the metal salts are fully dissolved, centrifugation is performed and vacuum drying is performed at 80°C to obtain a Cu-Fe bimetallic single atom catalyst precursor. Subsequently, heat treatment is performed at 200°C in a hydrogen atmosphere for 2 hours to obtain a Cu-Fe-NC single atom catalyst, such as Figure 1 As shown in Figures b and c, the activated carbon substrate material successfully loaded two metals, Fe and Cu. Figure d shows that the Cu and Fe elements are evenly distributed on the activated carbon substrate.

[0054] The carbon support is a three-dimensional carbon felt with a size of 5cm╳5cm╳2cm. In step S3, the enzyme-like catalyst is dispersed in ultrapure water, and the three-dimensional carbon felt is also placed in ultrapure water for ultrasonic adsorption (60kw, 30 minutes). Then, the carbon felt is taken out and dried to obtain a working electrode.

[0055] like Figure 2-Figure 3 As shown, in step S4, when the power supply voltage is in the range of -0.8V to -0.9V vs. SCE voltage, the product after treatment is nitrite nitrogen; when the power supply voltage is in the range of -1.0V to -1.2V vs. SCE voltage, the product after treatment is nitrite nitrogen and ammonia nitrogen coexisting; when the power supply voltage is greater than -1.2V vs. SCE, the product after treatment is ammonia nitrogen.

[0056] like Figure 4 As shown, in step S4, the power supply voltage is within the range of -1.0V to -1.2V vs. SCE voltage. By controlling the electrolysis time, the molar ratio of the treated products, nitrite nitrogen and ammonia nitrogen, can be precisely controlled;

[0057] When the electrolysis time is 2.5 h, the molar ratio of nitrite nitrogen to ammonia nitrogen is 1:1.3; when the electrolysis time is less than 2.5 h, the product after treatment is mainly nitrite nitrogen with a small amount of ammonia nitrogen; when the electrolysis time is greater than 2.5 h, the product after treatment gradually becomes mainly ammonia nitrogen, and the nitrite nitrogen gradually decreases.

[0058] Table 1 Sewage treatment effect at power supply voltage of -1.2V vs. SCE

[0059]

[0060]

[0061] Table 2 Sewage treatment effect with power supply time of 2.5 hours

[0062] Supply voltage (V vs. SCE) Total nitrogen removal rate (%) -1.2 90 -0.8 78 -1.3 79

[0063] It can be seen from the above table that when the power supply voltage is -1.2V vs. SCE and the electrolysis time is 2.5h, the molar ratio of nitrite nitrogen to ammonia nitrogen is 1:1.3. After anaerobic ammonia oxidation treatment, the total nitrogen removal rate of sewage is relatively high.

[0064] Comparative Example 1

[0065] This comparative example provides an enzyme-like electrocatalytic coupled anaerobic ammonia oxidation treatment method for removing nitrate, which is the same as Example 1, except that the working electrode is a graphite carbon brush (carbon plate) electrode. Regardless of how the power supply voltage and electrolysis time change, the molar ratio change relationship of the product nitrite nitrogen and ammonia nitrogen in Example 1 cannot be presented.

[0066] When the power supply voltage was -1.2 V vs. SCE and the electrolysis time was 2.5 h, the total nitrogen removal rate of the sewage was 60% after anaerobic ammonium oxidation treatment.

[0067] Example 2

[0068] This embodiment provides a method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonia oxidation, which is the same as that of Example 1 except that the working electrode is different. Step S3 is specifically as follows:

[0069] (4) cutting two pieces of three-dimensional carbon felt of the same size into a rectangular shape; crushing the roots, stems, and leaves of the herb into pieces of 0.4-0.7 cm to obtain plant debris;

[0070] (5) Under ultrasonic conditions, the enzyme-like catalyst obtained in step S2 is first uniformly dispersed in ultrapure water, and then plant debris is added. After the plant debris is also uniformly dispersed, the three-dimensional carbon felt is added;

[0071] (6) first subjecting the system of step (5) to ultrasonic treatment and then to stirring treatment, so that the enzyme-like catalyst is loaded onto the three-dimensional carbon felt and plant debris;

[0072] (7) taking out the three-dimensional carbon felt and drying it; then centrifuging the remaining solid and drying the obtained solid;

[0073] (8) evenly spreading the solid obtained in step (7) to the same area and shape as the three-dimensional carbon felt, and then hot pressing the upper and lower surfaces to obtain a core;

[0074] (9) The core is placed between two sheets of three-dimensional carbon felt, and then double-sided hot pressing is performed to obtain a complete working electrode.

[0075] In steps (5) and (6), the enzyme-like catalyst is first added to ultrapure water and ultrasonically treated until uniformly dispersed; then the plant debris is added and ultrasonic treatment is continued until the enzyme-like catalyst and the plant debris are uniformly dispersed; then the three-dimensional carbon felt is added and ultrasonic treatment is continued; the power of the above ultrasonic treatment is 60 kW;

[0076] Then, the ultrasound is stopped and stirring is performed with a stirring intensity such that all the plant debris does not sink to the bottom and the three-dimensional carbon felt is always in a moving state.

[0077] In step (7), the three-dimensional carbon felt is taken out after being loaded with the enzyme-like catalyst, and the remaining solids are plant debris loaded with the enzyme-like catalyst and the suspended enzyme-like catalyst, and all of these remaining solids are centrifuged out.

[0078] In step (8), the dried plant debris loaded with the enzyme-like catalyst and the unloaded enzyme-like catalyst are evenly spread together, and the temperature of double-sided hot pressing is 150°C, and the time of double-sided hot pressing is 30 seconds. During the hot pressing process, the plant debris adheres to each other to form a whole, and the unloaded enzyme-like catalyst is also wrapped in the whole, finally forming a core.

[0079] In step (9), the temperature of double-sided hot pressing is 180° C., and the time of double-sided hot pressing is 5 minutes, so that the core body and the three-dimensional carbon felt on both sides form an integral whole.

[0080] Example 3

[0081] This embodiment provides a treatment method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonia oxidation, which is the same as that of Example 2, except that in step (9), the core and the two pieces of three-dimensional carbon felt are only bound with thin iron wires without double-sided hot pressing.

[0082] The total nitrogen removal rates in Examples 2 and 3 were 96% and 93%, respectively. The treatment method provided by the present invention, through control of voltage and electrolysis time, can convert inorganic nitrogen in wastewater into a coexistence of nitrite nitrogen and ammonia nitrogen. The molar ratio of nitrite nitrogen to ammonia nitrogen is 1:1.3, meeting the stoichiometric ratio required in the anaerobic ammonium oxidation process, thereby achieving efficient nitrate removal from wastewater. Furthermore, the provision of a composite working electrode further enhances the total nitrogen removal rate.

Claims

1. A method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation, characterized in that: The following steps are involved: S1: Preparation of carbon-based materials for enzyme-like catalysts; S2: Dispersing copper and iron bimetallic materials on a carbon substrate to produce an enzyme-like catalyst; S3: loading the enzyme-like catalyst on a carbon support to obtain a working electrode loaded with the enzyme-like catalyst; S4: placing the working electrode, counter electrode, and reference electrode obtained in step S3 into the wastewater containing nitrate, connecting the power supply, connecting the working electrode to the cathode of the power supply, and connecting the counter electrode to the anode of the power supply, to perform wastewater treatment; S5: Adding anaerobic ammonium oxidizing bacteria to the system of step S4 to treat the wastewater; Step S3 is specifically as follows: (4) Cutting two pieces of three-dimensional carbon felt of the same size, wherein the three-dimensional carbon felt is rectangular; crushing the roots, stems, and leaves of the herb to obtain plant debris; (5) Under ultrasonic conditions, the enzyme-like catalyst obtained in step S2 is first uniformly dispersed in ultrapure water, and then plant debris is added. After the plant debris is also uniformly dispersed, the three-dimensional carbon felt is added; (6) The system of step (5) is first subjected to ultrasonic treatment and then to stirring treatment, so that the enzyme-like catalyst is loaded onto the three-dimensional carbon felt and plant debris; (7) taking out the three-dimensional carbon felt and drying it; then centrifuging the remaining solid and drying the obtained solid; (8) The solid obtained in step (7) is evenly spread in an area and shape identical to that of the three-dimensional carbon felt, and then hot-pressed on both sides to obtain a core; (9) The core is placed between two pieces of three-dimensional carbon felt, and then double-sided hot pressing is performed to obtain a complete working electrode.

2. The method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation according to claim 1, characterized in that: In step S1, the method for preparing the carbon base material is specifically as follows: (1) Prepare a zinc chloride solution with a zinc chloride concentration of 0.05-0.1 g / ml; then prepare a dimethylimidazole solution with a dimethylimidazole concentration of 0.04-0.06 g / ml; (2) Mix the zinc chloride solution and the dimethylimidazole solution, centrifuge, and wash with ultrapure water to obtain a white solid; (3) The white solid is dried and ground, and then heat-treated in a mixed atmosphere of ammonia and argon to obtain an activated carbon base material.

3. The method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation according to claim 2, characterized in that: In step (3), the dried white solid powder is first heat-treated at 1000°C for 30-40 min in a mixed atmosphere, wherein the volume ratio of ammonia to argon in the mixed atmosphere is 1:4; Then, the activated carbon base material was obtained by heat treatment at 1000°C for 180-200 min in a pure argon atmosphere and then cooling with the furnace.

4. The method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation according to claim 3, characterized in that: Step S2 is specifically as follows: first, the activated carbon base material, ferric nitrate and copper nitrate are dispersed in ultrapure water, ultrasonically treated for 2-3 hours, and then centrifuged to obtain a solid precursor; the solid precursor is vacuum dried at 60-80°C, and then heat treated at 180-200°C in a hydrogen atmosphere for 2-3 hours to obtain a Cu-Fe-NC single atom catalyst, which is an enzyme-like catalyst.

5. The method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation according to claim 1, characterized in that: In step S4, when the power supply voltage is in the range of -0.8 V to -0.9 V vs. SCE, the treated product is nitrite nitrogen; when the power supply voltage is in the range of -1.0 V to -1.2 V vs. SCE, the treated product is a coexistence of nitrite nitrogen and ammonia nitrogen; when the power supply voltage is greater than -1.2 V vs. SCE, the treated product is ammonia nitrogen.

6. The method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation according to claim 5, characterized in that: In step S4, the power supply voltage is in the range of -1.0 V to -1.2 V vs. SCE voltage, the electrolysis time is 2.5 h, and the molar ratio of nitrite nitrogen to ammonia nitrogen is 1:1.

3. If the electrolysis time is less than 2.5 h, the treated product is mainly nitrite nitrogen with a small amount of ammonia nitrogen. If the electrolysis time is greater than 2.5 h, the treated product gradually becomes mainly ammonia nitrogen with a gradually decreasing amount of nitrite nitrogen.

7. The method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation according to claim 1, characterized in that: In steps (5) and (6), the enzyme-like catalyst is first added to ultrapure water and ultrasonically treated until uniformly dispersed; then the plant debris is added and ultrasonic treatment is continued until the enzyme-like catalyst and the plant debris are uniformly dispersed; then the three-dimensional carbon felt is added and ultrasonic treatment is continued; the power of the above ultrasonic treatment is 60-80 kW; Then, the ultrasound is stopped and stirring is performed with a stirring intensity that ensures that all the plant debris does not sink to the bottom and that the three-dimensional carbon felt is always in a moving state.

8. The method for removing nitrate by enzyme-like electrocatalysis coupled with anaerobic ammonium oxidation according to claim 1, characterized in that: In step (8), the dried plant debris loaded with the enzyme-like catalyst and the unloaded enzyme-like catalyst are evenly spread together, and the double-sided hot pressing temperature is 150-180° C., and the double-sided hot pressing time is 20-60 seconds; In step (9), the temperature of double-sided hot pressing is 150-180° C., and the time of double-sided hot pressing is 2-5 minutes, so that the core body and the three-dimensional carbon felt on both sides form a whole.

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