A method for synchronously removing nitrogen and phosphorus and recovering struvite by electrochemical cathode and anode

Abstract

The present application relates to the field of sewage treatment, and specifically discloses a method for electrochemical anode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite. The specific method is to use a double electrode system, the anode is a magnesium anode, and an oxidation reaction occurs at the anode to produce Mg 2+ ; Reduction reaction occurs at the cathode, specifically NO3 ‑ Reduced to NH4 + Mg 2+ NH4 + The phosphate in the system generates struvite under alkaline conditions. The present invention develops a new wastewater treatment resource technology, which can simultaneously achieve the effective removal and resource recovery of nitrate nitrogen and phosphate in wastewater. The present invention organically combines the cathode and anode of the electrochemical system to achieve the simultaneous removal and recovery of nitrogen and phosphorus in wastewater, providing a new idea for achieving carbon neutrality technology in wastewater treatment.

Description

Technical Field

[0001] The present application relates to the field of sewage treatment, and more specifically, to a method for electrochemical anode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite. Background Art

[0002] At present, the raw water of urban sewage treatment plants has insufficient carbon sources and low carbon-nitrogen ratio, which makes it difficult for traditional denitrification processes to achieve the expected treatment effect, and the problem of total nitrogen in the effluent is difficult to meet the standard. Nitrate nitrogen is the main form of total nitrogen in domestic sewage. Urban sewage treatment plants usually need to add a large amount of external carbon source, which can effectively reduce the nitrate concentration in the water and achieve the standard discharge of total nitrogen in the secondary effluent, but it greatly increases the cost of sewage treatment. At the same time, the phosphorus removal effect of conventional biological treatment methods is limited, and chemical phosphorus removal or the combination of biological methods and chemical phosphorus removal is often required. Chemical phosphorus removal mainly involves adding flocculants containing iron and aluminum effective ingredients to domestic sewage to remove them in the form of phosphate precipitation. From this point of view, in order to achieve the standard discharge of domestic sewage, the addition of carbon sources and flocculants is an indispensable link in sewage treatment, which ultimately greatly increases the operating cost of sewage treatment plants. Therefore, it is of great practical significance to find a new process for efficient and low-cost denitrification and phosphorus removal in the secondary effluent of urban sewage treatment plants.

[0003] Compared with biological treatment and chemical methods, electrochemical technology does not require the addition of carbon sources and reagents, and is easy to operate, and has attracted the attention and research of more and more scholars. At present, most of the research on electrochemical denitrification and phosphorus removal focuses on denitrification as a single purpose or phosphorus removal as a single purpose. However, there are not many reaction processes that combine electrochemical denitrification and phosphorus removal processes. For this reason, it is necessary to provide a method for the synergistic effect of electrochemical anodes and cathodes to achieve the simultaneous removal of nitrogen and phosphorus in sewage and recover them as struvite, so as to achieve the simultaneous removal of nitrogen and phosphorus in water and resource utilization. Summary of the invention

[0004] In order to achieve the purpose of simultaneously removing nitrogen and phosphorus from sewage and recovering struvite, the present application provides a method for simultaneously removing nitrogen and phosphorus and recovering struvite using electrochemical cathodes and anodes.

[0005] The present application provides a method for electrochemical anode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite using the following technical solution:

[0006] A method for electrochemical cathode and anode synchronously removing nitrogen and phosphorus and recovering struvite, using a dual-electrode system,

[0007] The anode is a magnesium anode, where an oxidation reaction occurs to produce Mg 2+ ;

[0008] A reduction reaction occurs at the cathode, specifically NO3 - Reduced to NH4+ ;

[0009] Mg 2+ NH4 + It reacts with phosphate in the system to form struvite under alkaline conditions.

[0010] By adopting the above technical scheme, magnesium ions are provided to the reaction system using a magnesium anode, thereby reducing the dosage of chemical magnesium salts, which not only saves resources but also reduces the adverse effects of chloride ions or sulfate ions contained in magnesium salts in subsequent sewage treatment. The cathode catalyzes the reduction of nitrate ions to ammonium ions, which can improve the efficiency of nitrate production of ammonia on the one hand, and on the other hand, the pH at the cathode continues to increase, which can provide the alkaline environment required for the reaction and reduce the dosage of alkaline regulators, thereby achieving the simultaneous removal of nitrogen and phosphorus while maximizing resource utilization.

[0011] Preferably, the anode has a length of 1-5 cm, a width of 1-2 cm, and a thickness of 0.5-200 mm.

[0012] Preferably, the anode is made of magnesium alloy, specifically AZ31B magnesium alloy plate, with a length of 2 cm, a width of 2 cm and a thickness of 200 mm.

[0013] Preferably, the cathode is an iridium electrode, a ruthenium electrode, an iron electrode, a copper-iron alloy electrode, a copper-nickel alloy electrode, a titanium dioxide electrode, a Fe3O4 electrode, a Co3O4 electrode, a Co3O4@NiO electrode or a LaCoO3 / CC composite electrode.

[0014] Preferably, the cathode is a LaCoO3 / CC composite electrode, which is prepared by loading the perovskite oxide on a hydrophilic conductive carbon cloth substrate in a dropwise manner.

[0015] Preferably, the hydrophilic conductive carbon cloth substrate is prepared by soaking the carbon cloth in an acidic solution for 23-25 ​​hours, washing, and drying; the acidic solution is prepared by mixing concentrated sulfuric acid, concentrated nitric acid, and deionized water in a mass ratio of 1:1:(0.8-1.2).

[0016] Preferably, the perovskite oxide is prepared by mixing La(NO3)3·6H2O, Co(NO3)2·6H2O, citric acid, ethylene glycol and water, drying to obtain a dry gel, and calcining the dry gel to obtain the perovskite oxide.

[0017] Preferably, when preparing perovskite oxide, La(NO3)3·6H2O, Co(NO3)2·6H2O, citric acid, ethylene glycol and water are mixed, and then attapulgite treated with oxidized polyethylene wax is added, followed by drying and calcining; at the same time, a coupling agent solution is sprayed on the hydrophilic conductive carbon cloth substrate and then dried.

[0018] By adopting the above technical scheme, the perovskite oxide has a better catalytic effect and can effectively catalyze the reduction of nitrate ions in the system to ammonium ions. By introducing a coupling agent on the hydrophilic conductive carbon cloth substrate, when the perovskite oxide is loaded on the hydrophilic conductive carbon cloth substrate, the coupling agent can form a connection with the attapulgite in the perovskite oxide, thereby enhancing the stability and firmness of the perovskite oxide loaded on the hydrophilic conductive carbon cloth substrate.

[0019] Preferably, the specific operating parameters are that the current density is 14-16 mA / cm 2 , the electrolysis time is 50-70min.

[0020] Preferably, stirring is continued during the reaction, and the stirring speed is 100-300 rpm.

[0021] By adopting the above technical solution, it is beneficial to the anode and cathode products NH4 + Mg 2+ and H2PO4 - Mutual collision can effectively promote the reaction and help the formation of struvite.

[0022] Preferably, the specific reaction is:

[0023] Cathode: NO3 - +10H + +8e - →NH4 + +3H2O;

[0024] Anode: Mg-2e - →Mg 2+ ;

[0025] Overall reaction: Mg 2+ +NH4 + +H2PO4 - +6H2O→MgNH4PO4·6H2O↓+2H + .

[0026] In summary, this application has the following beneficial effects:

[0027] 1. The present application selects a magnesium anode to continuously provide magnesium ions to the reaction system, and utilizes a cathode to promote the generation of ammonium ions, so that in the reaction system, magnesium ions, ammonium ions and phosphates in the system can generate struvite, thereby achieving the purpose of simultaneously removing nitrogen and phosphorus.

[0028] 2. This application uses perovskite oxide and carbon cloth to make the cathode. Perovskite oxide has high catalytic efficiency and can effectively catalyze the reduction of nitrate ions to ammonium ions. By hydrophilizing the carbon cloth, the perovskite oxide can be stably loaded on the carbon cloth, ensuring that the reaction can proceed stably without being affected.

[0029] 3. The present application continuously stirs during the reaction process, which is beneficial for the collision between the anode product magnesium ions, the cathode product ammonium ions and the dihydrogen phosphate ions in the system, thereby promoting the reaction and the production of struvite. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of an electrochemical reaction device provided by the present application;

[0031] Figure 2 is a schematic diagram of the concentration changes of nitrate nitrogen and phosphate in the reaction system in Example 2;

[0032] Figure 3 This is a graph showing the removal rate of phosphate in the reaction system in Example 2.

[0033] Figure 4 This is the XRD detection diagram of the precipitate generated in Example 2. DETAILED DESCRIPTION

[0034] In order to achieve the simultaneous removal and resource recovery of nitrogen and phosphorus in sewage, the present invention provides a method for electrochemical anode and cathode synchronously removing nitrogen and phosphorus and recovering struvite, and an electrochemical reaction device is used to treat simulated water samples containing nitrogen and phosphorus by electrochemical oxidation-reduction method.

[0035] The catalyst loaded on the working electrode of the electrochemical reaction device is the perovskite oxide LaCoO3; it should be noted that the perovskite oxide material is used for NO3 - Electroreduction to produce NH4 + , can make full use of the rich active sites of electrode materials to achieve NO3 - →NH4 + efficient conversion.

[0036] Reference Figure 1 As an explanation of the electrochemical reaction device, the cathode reaction is mainly the electroreduction of nitrate to ammonium ions and the release of hydroxide ions, while the anode reaction is the loss of electrons by metallic magnesium and the conversion to magnesium ions. The increase in pH brought about by the electrochemical reaction is combined with the hydrogen phosphate ions in the solution to eventually form struvite precipitates.

[0037] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0038] Preparation Example 1

[0039] A carbon cloth with a size of 2cm*2cm is immersed in an acidic solution for 23 hours. The acidic solution is a mixture of concentrated sulfuric acid, concentrated nitric acid and deionized water in a mass ratio of 1:1:0.8. After immersion, it is washed with deionized water and dried to obtain a hydrophilic conductive carbon cloth substrate.

[0040] 4mmol La(NO3)3·6H2O, 4mmol Co(NO3)2·6H2O, 2mmol ethylene glycol, 1mmol citric acid and 35ml deionized water were mixed, stirred evenly at room temperature, and then dried at 80°C for 12h, and then dried at 120°C for 12h to obtain a dry gel; the dry gel was then placed in a muffle furnace, calcined at 300°C for 3h, and then heated to 700°C at 5°C / min, and continued to calcine for 2h to obtain a perovskite oxide;

[0041] 20 mg of perovskite oxide and 100 uL of Nafion solution (dupont, 5%) were dispersed in 2 mL of a mixed solution of ethanol and water (ethanol and water were mixed in a mass ratio of 3:1), and ultrasonicated for 30 min to obtain ink; the ink was dropwise coated on a 2*2 cm 2 The LaCoO3 / CC composite electrode was obtained after drying on a hydrophilic conductive carbon cloth substrate of 5 mg / cm 2 .

[0042] Preparation Example 2

[0043] A carbon cloth with a size of 2 cm*2 cm is immersed in an acidic solution for 24 hours. The acidic solution is a mixture of concentrated sulfuric acid, concentrated nitric acid and deionized water in a mass ratio of 1:1:1. After immersion, the carbon cloth is washed with deionized water and dried to obtain a hydrophilic conductive carbon cloth substrate.

[0044] 4mmol La(NO3)3·6H2O, 4mmol Co(NO3)2·6H2O, 2mmol ethylene glycol, 1mmol citric acid and 35ml deionized water were mixed, stirred evenly at room temperature, and then dried at 80°C for 12h, and then dried at 120°C for 12h to obtain a dry gel; the dry gel was then placed in a muffle furnace, calcined at 300°C for 3h, and then heated to 700°C at 5°C / min, and continued to calcine for 2h to obtain a perovskite oxide;

[0045] 20 mg of perovskite oxide and 100 uL of Nafion solution (dupont, 5%) were dispersed in 2 mL of a mixed solution of ethanol and water (ethanol and water were mixed in a mass ratio of 3:1), and ultrasonicated for 30 min to obtain ink; the ink was dropwise coated on a 2*2 cm 2The LaCoO3 / CC composite electrode was obtained after drying on a hydrophilic conductive carbon cloth substrate of 5 mg / cm 2 .

[0046] Preparation Example 3

[0047] A carbon cloth with a size of 2 cm*2 cm is immersed in an acidic solution for 25 hours, wherein the acidic solution is a mixture of concentrated sulfuric acid, concentrated nitric acid and deionized water in a mass ratio of 1:1:1.2, and then washed with deionized water and dried to obtain a hydrophilic conductive carbon cloth substrate;

[0048] 4mmol La(NO3)3·6H2O, 4mmol Co(NO3)2·6H2O, 2mmol ethylene glycol, 1mmol citric acid and 35ml deionized water were mixed, stirred evenly at room temperature, and then dried at 80°C for 12h, and then dried at 120°C for 12h to obtain a dry gel; the dry gel was then placed in a muffle furnace, calcined at 300°C for 3h, and then heated to 700°C at 5°C / min, and continued to calcine for 2h to obtain a perovskite oxide;

[0049] 20 mg of perovskite oxide and 100 uL of Nafion solution (dupont, 5%) were dispersed in 2 mL of a mixed solution of ethanol and water (ethanol and water were mixed in a mass ratio of 3:1), and ultrasonicated for 30 min to obtain ink; the ink was dropwise coated on a 2*2 cm 2 The LaCoO3 / CC composite electrode was obtained after drying on a hydrophilic conductive carbon cloth substrate of 5 mg / cm 2 .

[0050] Preparation Example 4

[0051] A carbon cloth with a size of 2cm*2cm is soaked in an acidic solution for 23 hours. The acidic solution is a mixture of concentrated sulfuric acid, concentrated nitric acid and deionized water in a mass ratio of 1:1:0.8. After soaking, it is washed with deionized water and dried to obtain a hydrophilic conductive carbon cloth substrate. Then, a KH-550 aqueous solution with a concentration of 3wt% is sprayed on the hydrophilic conductive carbon cloth substrate, and dried for use.

[0052] 4mmol La(NO3)3·6H2O, 4mmol Co(NO3)2·6H2O, 2mmol ethylene glycol, 1mmol citric acid and 35ml deionized water were mixed and stirred evenly at room temperature; then attapulgite was added, and the attapulgite was pretreated: oxidized polyethylene wax (purchased from Nantong Xitai Chemical, model HA-soft80), KH-550 and water were mixed in a mass ratio of 10:3:100, heated to 60°C, and attapulgite was added to react for 30min, then filtered and dried; after adding attapulgite, it was dried at 80°C for 12h, and then dried at 120°C for 12h to obtain a dry gel; then the dry gel was placed in a muffle furnace, calcined at 300°C for 3h, and then heated to 700°C at 5°C / min, and continued to calcine for 2h to obtain a perovskite oxide;

[0053] 20 mg of perovskite oxide and 100 uL of Nafion solution (dupont, 5%) were dispersed in 2 mL of a mixed solution of ethanol and water (ethanol and water were mixed in a mass ratio of 3:1), and ultrasonicated for 30 min to obtain ink; the ink was dropwise coated on a 2*2 cm 2 The LaCoO3 / CC composite electrode was obtained after drying on a hydrophilic conductive carbon cloth substrate of 5 mg / cm 2 .

[0054] Example 1

[0055] A method for electrochemically removing nitrogen and phosphorus and recovering struvite by simultaneously using anode and cathode, adopting a double electrode system, wherein the anode is an AZ31B magnesium alloy plate with a length of 2 cm, a width of 2 cm, and a thickness of 200 mm, and the cathode is the LaCoO3 / CC composite electrode prepared in Preparation Example 1, and the distance between the anode and the cathode is 1.5 cm.

[0056] 100 mL of simulated water sample was prepared with sodium nitrate, sodium dihydrogen phosphate and sodium sulfate. The concentration of sodium nitrate in the water sample was 50 mg / L, the concentration of sodium dihydrogen phosphate was 20 mg / L, and the concentration of sodium sulfate was 50 mg / L. The reaction was carried out at room temperature and pressure, and the current density was 14 mA / cm 2 , electrolysis time 50min, pH of the reaction system controlled at 7, stirring continuously at 100rpm during the reaction, the precipitate generated by the reaction is struvite.

[0057] In this embodiment, through detection, the nitrogen removal rate reached 89.9%, the phosphorus removal rate reached 99.1%, and the precipitate generated by the reaction was determined to be struvite through XRD characterization analysis.

[0058] Example 2

[0059] A method for electrochemically removing nitrogen and phosphorus and recovering struvite by simultaneously using anode and cathode, adopting a double electrode system, wherein the anode is an AZ31B magnesium alloy plate with a length of 2 cm, a width of 2 cm, and a thickness of 200 mm, and the cathode is the LaCoO3 / CC composite electrode prepared in Preparation Example 2, and the distance between the anode and the cathode is 1.5 cm.

[0060] 100 mL of simulated water sample was prepared with sodium nitrate, sodium dihydrogen phosphate and sodium sulfate. The concentration of sodium nitrate in the water sample was 50 mg / L, the concentration of sodium dihydrogen phosphate was 20 mg / L, and the concentration of sodium sulfate was 50 mg / L. The reaction was carried out at room temperature and pressure, and the current density was 15 mA / cm 2 , electrolysis time 60min, pH of the reaction system controlled at 7, stirring continuously at 200rpm during the reaction, the precipitate generated by the reaction is struvite.

[0061] In this embodiment, refer to Figure 2 The concentration changes of nitrate nitrogen and phosphate are shown. Figure 3 The removal rate of phosphates shown shows that the removal rate of nitrogen and phosphorus by the method in this application reaches 99.1% for nitrogen and 99.2% for phosphorus. Moreover, through testing, after 60 minutes of reaction, the residual concentration of phosphates in the system is lower than the 0.5 mg / L specified by the emission standard. In addition, the precipitation generated at the bottom of the electrolytic cell is tested and dried at 40°C. Figure 4 It can be seen that the precipitate was determined to be struvite through XRD characterization analysis.

[0062] Example 3

[0063] A method for electrochemically removing nitrogen and phosphorus and recovering struvite by simultaneously using anode and cathode, adopting a double electrode system, wherein the anode is an AZ31B magnesium alloy plate with a length of 2 cm, a width of 2 cm, and a thickness of 200 mm, and the cathode is the LaCoO3 / CC composite electrode prepared in Preparation Example 1, and the distance between the anode and the cathode is 1.5 cm.

[0064] 100 mL of simulated water sample was prepared with sodium nitrate, sodium dihydrogen phosphate and sodium sulfate. The concentration of sodium nitrate in the water sample was 50 mg / L, the concentration of sodium dihydrogen phosphate was 20 mg / L, and the concentration of sodium sulfate was 50 mg / L. The reaction was carried out at room temperature and pressure, and the current density was 16 mA / cm 2 , electrolysis time 70min, pH of the reaction system controlled at 7, stirring continuously at 300rpm during the reaction, the precipitate generated by the reaction is struvite.

[0065] In this embodiment, through detection, the nitrogen removal rate reached 99.2%, the phosphorus removal rate reached 99.4%, and the precipitate generated by the reaction was determined to be struvite through XRD characterization analysis.

[0066] Example 4

[0067] A method for electrochemically removing nitrogen and phosphorus and recovering struvite by simultaneously using anode and cathode, adopting a double electrode system, wherein the anode is an AZ31B magnesium alloy plate with a length of 2 cm, a width of 2 cm, and a thickness of 200 mm, and the cathode is the LaCoO3 / CC composite electrode prepared in Preparation Example 2, and the distance between the anode and the cathode is 1.5 cm.

[0068] 100 mL of simulated water sample was prepared with sodium nitrate, sodium dihydrogen phosphate and sodium sulfate. The concentration of sodium nitrate in the water sample was 50 mg / L, the concentration of sodium dihydrogen phosphate was 20 mg / L, and the concentration of sodium sulfate was 50 mg / L. The reaction was carried out at room temperature and pressure, and the current density was 14 mA / cm 2 , electrolysis time 50min, pH of the reaction system controlled at 7, stirring continuously at 100rpm during the reaction, the precipitate generated by the reaction is struvite.

[0069] In this embodiment, through testing, the nitrogen removal rate reached 99.0%, the phosphorus removal rate reached 99.2%, and the precipitate generated by the reaction was determined to be struvite through XRD characterization analysis.

[0070] Example 5

[0071] A method for electrochemically removing nitrogen and phosphorus and recovering struvite by simultaneously using anode and cathode, adopting a double electrode system, wherein the anode is an AZ31B magnesium alloy plate with a length of 2 cm, a width of 2 cm, and a thickness of 200 mm, and the cathode is the LaCoO3 / CC composite electrode prepared in Preparation Example 3, and the distance between the anode and the cathode is 1.5 cm.

[0072] 100 mL of simulated water sample was prepared with sodium nitrate, sodium dihydrogen phosphate and sodium sulfate. The concentration of sodium nitrate in the water sample was 50 mg / L, the concentration of sodium dihydrogen phosphate was 20 mg / L, and the concentration of sodium sulfate was 50 mg / L. The reaction was carried out at room temperature and pressure, and the current density was 14 mA / cm 2 , electrolysis time 50min, pH of the reaction system controlled at 7, stirring continuously at 100rpm during the reaction, the precipitate generated by the reaction is struvite.

[0073] In this embodiment, through detection, the nitrogen removal rate reached 99.2%, the phosphorus removal rate reached 99.3%, and the precipitate generated by the reaction was determined to be struvite through XRD characterization analysis.

[0074] Example 6

[0075] A method for electrochemically removing nitrogen and phosphorus and recovering struvite by simultaneously using anode and cathode, adopting a double electrode system, wherein the anode is an AZ31B magnesium alloy plate with a length of 2 cm, a width of 2 cm, and a thickness of 200 mm, and the cathode is the LaCoO3 / CC composite electrode prepared in Preparation Example 4, and the distance between the anode and the cathode is 1.5 cm.

[0076] 100 mL of simulated water sample was prepared with sodium nitrate, sodium dihydrogen phosphate and sodium sulfate. The concentration of sodium nitrate in the water sample was 50 mg / L, the concentration of sodium dihydrogen phosphate was 20 mg / L, and the concentration of sodium sulfate was 50 mg / L. The reaction was carried out at room temperature and pressure, and the current density was 14 mA / cm 2 , electrolysis time 50min, pH of the reaction system controlled at 7, stirring continuously at 100rpm during the reaction, the precipitate generated by the reaction is struvite.

[0077] In this embodiment, through testing, the nitrogen removal rate reached 99.5%, the phosphorus removal rate reached 99.6%, and the precipitate generated by the reaction was determined to be struvite through XRD characterization analysis.

[0078] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for electrochemical cathode and anode synchronously removing nitrogen and phosphorus and recovering struvite, characterized in that: A dual-electrode system is used, with the anode being a magnesium anode, where an oxidation reaction occurs to produce Mg 2+ ; A reduction reaction occurs at the cathode, specifically NO3 - Reduced to NH4 + Mg 2+ NH4 + With the phosphate in the system, it forms struvite under alkaline conditions; The cathode is a LaCoO3 / CC composite electrode, which is prepared by loading the perovskite oxide on a hydrophilic conductive carbon cloth substrate in a dropwise manner; The preparation of the hydrophilic conductive carbon cloth substrate is as follows: the carbon cloth is immersed in an acidic solution for 23-25 ​​hours, washed, and dried; the acidic solution is prepared by mixing concentrated sulfuric acid, concentrated nitric acid, and deionized water in a mass ratio of 1:1:(0.8-1.2).

2. The method for electrochemical cathode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite according to claim 1, characterized in that: The anode has a length of 1-5 cm, a width of 1-2 cm, and a thickness of 0.5-200 mm.

3. The method for electrochemical cathode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite according to claim 1, characterized in that: The anode is made of magnesium alloy, specifically AZ31B magnesium alloy plate, with a length of 2 cm, a width of 2 cm, and a thickness of 200 mm.

4. The method for electrochemical cathode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite according to claim 1, characterized in that: The perovskite oxide is prepared by mixing La(NO3)3·6H2O, Co(NO3)2·6H2O, citric acid, ethylene glycol and water, drying to obtain a dry gel, and calcining the dry gel to obtain the perovskite oxide.

5. The method for electrochemical cathode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite according to claim 1, characterized in that: The specific operating parameters are: current density of 14-16 mA / cm 2 , the electrolysis time is 50-70min.

6. The method for electrochemical cathode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite according to claim 1, characterized in that: The reaction was continued with stirring at a speed of 100-300 rpm.

7. The method for electrochemical cathode-cathode synchronous removal of nitrogen and phosphorus and recovery of struvite according to claim 1, characterized in that: The specific reactions are: Cathode: NO3 - +10H + +8e - →NH4 + +3H2O; Anode: Mg-2e - →Mg 2+ ; Overall reaction: Mg 2+ +NH4 + +H2PO4 - +6H2O→MgNH4PO4·6H2O↓+2H + .

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