Method and system for regulating and controlling nitrogen products in process of electrochemically removing nitrate nitrogen

Abstract

The invention discloses a method and a system for regulating and controlling a nitrogen product in a process of electrochemically removing nitrate nitrogen, and belongs to the technical field of nitrogenous wastewater treatment.According to the method, the required ammonia nitrogen concentration and the concentration of the nitrogen product in an electrolytic tank are used as regulation and control bases, and the concentration of added chloride ions and the reaction time are intelligently regulated and controlled; nitrate nitrogen in water is efficiently removed, and nitrogen products are regulated and controlled at the same time, so that reutilization of resources is realized, and the resources are saved. The method has the advantages of moderate cost, no need of additional addition of chemical agents, simple operation conditions, environmental friendliness, high efficiency and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of nitrogen-containing wastewater treatment, and in particular relates to a method and system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen. Background Art

[0002] In recent years, with the rapid development of chemical, petroleum, pharmaceutical and food industries, the discharge of various nitrogen-containing wastewaters has increased, and the problem of excessive nitrate nitrogen has become increasingly serious. - -N pollution has developed into a global environmental problem. Excessive nitrogen content can cause eutrophication of water bodies, cause algae outbreaks, induce aquatic animal diseases, and seriously damage the ecological environment. Therefore, efficient nitrogen-containing wastewater treatment technology has also become a current research hotspot. China is the world's largest consumer of nitrogen fertilizer. In 2020, China's nitrogen fertilizer application reached 25.9Tg·N, accounting for about 23% of the world's total nitrogen fertilizer application. Nitrate nitrogen can be converted into ammonia nitrogen, and nitrogen fertilizer can be prepared using ammonia nitrogen water, which can increase the nitrogen fertilizer yield and effectively remove nitrate nitrogen.

[0003] Many physical, biological, and chemical techniques have been designed for nitrate reduction, including reverse osmosis, ion exchange, electrodialysis, and chemical catalysis, but most of these techniques are unable to obtain high yields of ammonia nitrogen, and their slow reaction kinetics and the significant drawbacks of generating by-products make them impractical on an industrial scale.

[0004] The physical methods mainly include adsorption, ion exchange, membrane separation and electrodialysis. The disadvantage of physical methods for removing nitrate nitrogen is that it cannot remove NO3 - -N is to separate nitrate from aqueous solution, which is only the transfer and concentration of pollutants. It cannot fundamentally remove nitrate nitrogen. Its ammonia nitrogen production is bound to be low and still requires secondary treatment. Improper treatment will also cause secondary pollution. The biological method is based on biological denitrification. In an oxygen-deficient environment, denitrifying bacteria are used to convert NO3 - -N is gradually reduced to N2, and this process does not produce ammonia nitrogen. Moreover, for low C / N ratio and / or high salt organic wastewater and NO3 in groundwater - -N removal, biological treatment process usually requires external supplementation of organic matter to produce dedicated microbial communities and provide protons or exogenous electron donors for nitrate reduction. In addition, biological denitrification often requires a long cycle, the removal process is time-consuming, and a large amount of biological sludge is generated during the denitrification process, which requires further treatment. Chemical reduction method is to use the oxidizing property of nitrate itself, and then add reducing agents or use reducing substances generated in situ to reduce NO3 --N is reduced by chemical reduction. Chemical reduction is based on inorganic electron donors and is easy to operate and highly efficient, which has attracted more and more attention. It mainly includes active metal reduction, heterogeneous catalytic reduction, photochemical reduction and electrochemical reduction. However, active metal reduction and heterogeneous catalytic reduction are greatly affected by water quality factors in practical applications, and complex process conditions also limit their large-scale application. Although photochemical reduction can achieve high treatment efficiency and N2 selectivity, it cannot directly produce ammonia nitrogen.

[0005] Therefore, in comparison, nitrate electroreduction (ERN) has become an alternative method due to its moderate cost, no need to add additional chemicals, simple operating conditions, environmental friendliness, and high efficiency. However, most electrodes currently use electrochemical reduction of nitrate to obtain a small amount of ammonia nitrogen and a low ammonia nitrogen yield. The purpose of some electrode electrocatalysis is to directly convert nitrate nitrogen into nitrogen gas to achieve nitrogen removal in water bodies. At this time, the nitrogen is difficult to collect, and ammonia nitrogen cannot be used as a raw material for the production of nitrogen fertilizers. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a method and system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen, which uses the required ammonia nitrogen concentration and the nitrogen product concentration in the electrolytic cell as the basis for regulation, intelligently regulates the concentration of added chloride ions and the reaction time, efficiently removes nitrate nitrogen in water and regulates nitrogen products, thereby achieving resource reuse and saving resources. The method of the present invention has the advantages of moderate cost, no need to add additional chemical agents, simple operating conditions, environmental friendliness and high efficiency.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention:

[0009] A system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen, the system comprising:

[0010] Lifting pump, grille, dosing tank, mixing tank, water inlet valve, water inlet pump, electrochemical reactor, first sensor, second sensor, water outlet valve, reflux valve and control device;

[0011] wherein the lift pump, the grille, the mixing tank, the water inlet valve, the water inlet pump, the first sensor, the electrochemical reactor and the water outlet valve are connected in series in sequence;

[0012] The electrochemical reactor is connected to a reflux pipe and refluxes through the reflux valve to the front of the water inlet pump; the lift pump delivers the nitrogen-containing wastewater to the mixing tank through the grid, and the agent is added through the dosing tank to control the pH of the inlet water;

[0013] The lifting pump, the grille, the dosing tank, the mixing tank, the water inlet valve, the water inlet pump, the electrochemical reactor, the first sensor, the second sensor, the water outlet valve and the reflux valve are all electrically connected to the control device.

[0014] The present invention uses Co3O4 / GF electrode to reduce nitrate nitrogen in water by applying voltage in an electrochemical workstation. When the chloride ion concentration is 0, nitrate nitrogen can be completely converted into ammonia nitrogen. At this time, it relies on the indirect reduction mediated by H* (atomic hydrogen) and the direct reduction by direct electron transfer. As the chloride ion concentration increases, Cl - Indirect oxidation of ammonia nitrogen results in a decrease in its ammonia nitrogen yield and an increase in nitrogen gas yield. Selective regulation of nitrogen products is achieved by controlling the concentration of added chloride ions and the reaction time. The specific regulation method is as follows: through the PLC control system, the first sensor detects the concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the influent, and a fuzzy neural network model (FNN) is used to predict the relationship between the amount of chlorination, reaction time and ammonia nitrogen production. When the amount of chlorination is large, the amount of ammonia nitrogen obtained in a short time is small, and most of the nitrate nitrogen is reduced to nitrogen gas. The amount of chlorination and the reaction time are determined according to the amount of ammonia nitrogen required for the initial nitrate nitrogen concentration, and are controlled by the PLC control system, wherein the amount of chlorination is controlled by the PLC to control the chlorination system, and the electrochemical reaction parameters (such as reaction time) are set by the PLC to control the electrochemical workstation.

[0015] Preferably, an electric stirrer is provided in the mixing tank.

[0016] Preferably, the electrochemical reactor comprises:

[0017] Electrochemical workstation, Co3O4 / GF electrode, Ag / AgCl reference electrode, platinum counter electrode, magnetic rotor, single-chamber electrolytic cell, magnetic stirrer, chlorination system, sensor and PLC control system;

[0018] The electrochemical workstation, the Co3O4 / GF electrode, the Ag / AgCl reference electrode, and the platinum counter electrode are connected to form a three-electrode circuit through electric wires, that is, the electrochemical workstation is connected to a three-electrode system, which are the Co3O4 / GF electrode (working electrode), the Ag / AgCl reference electrode, and the platinum counter electrode;

[0019] The chlorination system is connected to the single-chamber electrolytic cell via a first line pipeline; the sensor is externally connected to the single-chamber electrolytic cell via a second line; the electrochemical workstation, the chlorination system and the sensor are electrically connected to the PLC control system via a third line.

[0020] Preferably, the magnetic stirrer is started continuously and slowly stirred at a speed of 150 r / min to accelerate the electron transfer rate.

[0021] Preferably, the pH of the influent is controlled within a neutral range (pH=6-8) by adding sulfuric acid solution and sodium hydroxide solution of corresponding concentrations into the dosing tank to adjust the pH.

[0022] Preferably, the preparation method of the Co3O4 / GF electrode is:

[0023] The graphite felt substrate is pretreated, and then the pretreated graphite felt (GF) substrate is used as a working electrode, a platinum sheet is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, and boric acid, cobalt nitrate hexahydrate and sodium dodecyl sulfate are used as electrolytes to perform electrodeposition. After the electrodeposition, the surface of the working electrode is cleaned, dried, calcined, and cooled to obtain the Co3O4 / GF electrode.

[0024] The Co3O4 / GF electrode has a good ability to convert nitrate nitrogen into ammonia nitrogen. By adding chlorine and realizing anodic oxidation at the same time as cathode reduction, the ammonia nitrogen can be effectively oxidized into nitrogen gas to achieve denitrification.

[0025] Preferably, in the preparation method of Co3O4 / GF electrode, the calcination temperature is 500°C, the heating rate is 5°C / min, and the holding time is 2h.

[0026] More preferably, the preparation method of the Co3O4 / GF electrode is:

[0027] S1. Pre-treated graphite felt (GF) substrate: GF (3.0×4.0cm 2 ) were sonicated in acetone, hydrochloric acid (1 M) and distilled water, respectively;

[0028] S2. Prepare electrolyte for electrodeposition: 0.5 M boric acid, 0.1 M cobalt nitrate hexahydrate and 2.0 g / L sodium dodecyl sulfate were used as electrolyte, pretreated graphite felt (GF) electrode was used as working electrode, platinum sheet was used as counter electrode, Ag / AgCl electrode was used as reference electrode, and deposition was carried out at -2.0 V vs. AgCl / Ag voltage for 120 s;

[0029] S3. Calcination and annealing: Clean the surface of the working electrode after deposition with deionized water, dry it in an oven at 60°C, and then place it in a tubular furnace and heat it to 500°C at a rate of 5°C / min. Calcinate at a constant temperature for 2 hours and then cool it naturally.

[0030] Preferably, the sensor is used to monitor changes in various nitrogen products, pH and temperature in the single-chamber electrolytic cell;

[0031] The sensors include a nitrate nitrogen sensor, an ammonia nitrogen sensor, a nitrite nitrogen sensor, a total nitrogen sensor, a pH sensor and a temperature sensor.

[0032] The second technical solution of the present invention:

[0033] The present invention also provides a method for regulating nitrogen products in the process of electrochemical removal of nitrate nitrogen, using the above system to electrochemically remove nitrogen products in the process of nitrate nitrogen, that is, the present invention uses Co3O4 / GF electrodes and chloride ions to regulate nitrogen products in the process of electrochemical removal of nitrate nitrogen.

[0034] Preferably, the method for regulating nitrogen products in the electrochemical removal of nitrate nitrogen is divided into three stages, namely a first treatment stage, a second circulation stage and a third replenishment stage, and comprises the following steps:

[0035] When nitrate nitrogen-containing wastewater enters the system, nitrate nitrogen is electrochemically removed according to the required ammonia nitrogen generation amount. First, the first treatment stage is carried out: the water inlet valve is opened, the water outlet valve and the reflux valve are closed, and the nitrate nitrogen-containing wastewater is lifted by a lifting pump. The water delivered by the lifting pump passes through the grid, passes through the mixing tank, and is adjusted to a neutral pH by adding medicine in the dosing tank. After flowing through the water inlet valve, it is transported to the electrochemical reaction device by the water inlet pump for electrochemical reduction of nitrate nitrogen. The concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the inlet water are detected in the first sensor. The nitrate water reaching the electrochemical reaction device enters the single-chamber electrolytic cell. The reaction time and the amount of chlorination are determined according to the required amount of ammonia nitrogen by the prediction results of the FNN model, and the control is carried out by the PLC control system, wherein the amount of chlorination is controlled by the PLC control chlorination system, and the electrochemical reaction is set by the PLC control electrochemical workstation. After the reaction is completed, if the ammonia nitrogen content displayed by the second sensor is consistent with the required content, the water outlet valve is opened to obtain the outlet water with the corresponding ammonia nitrogen content;

[0036] If the nitrate water reaching the electrochemical reaction device enters the electrolytic cell, the reaction time and the amount of chlorine added are determined according to the required amount of ammonia nitrogen, and the control is performed through the PLC control system. When the ammonia nitrogen content displayed by the second sensor after the reaction is completed is less than the expected value, the second circulation stage is entered: at this time, the water inlet valve and the water outlet valve are both closed, and the reflux valve is opened. The water in the single-chamber electrolytic cell is transported to the front of the water inlet pump through the reflux pipe and the reflux valve, and re-enters the electrochemical reaction device. At this time, the first sensor detects the concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the re-entering water. The reaction time and the amount of chlorine added are determined by the required amount of ammonia nitrogen according to the prediction results of the FNN model, and the control is performed through the PLC control system, wherein the amount of chlorine added is controlled by the PLC control chlorination system, and the electrochemical reaction is set by the PLC control electrochemical workstation, and the cycle is continuously performed until the ammonia nitrogen value displayed by the second sensor reaches the expected requirement, the water outlet valve is opened, and the reflux valve is closed;

[0037] If the ammonia nitrogen content displayed by the second sensor is greater than the expected value, the third replenishment stage is entered: at this time, the water inlet valve is opened, the reflux valve is closed, and the lifting pump lifts the nitrate nitrogen-containing wastewater. The water delivered by the lifting pump passes through the grille through the mixing tank and is added through the dosing tank to adjust the pH to neutral. After flowing through the water inlet valve, it is transported to the electrochemical reaction device through the water inlet pump for electrochemical reduction of nitrate nitrogen. According to the concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the inlet water detected by the first sensor, the reaction time and the amount of chlorine added are determined by the remaining required amount of ammonia nitrogen, and controlled by the PLC control system, wherein the amount of chlorine added is controlled by the PLC controlling the chlorination system, and the electrochemical reaction is set by the PLC controlling the electrochemical workstation. After the expected reaction time is reached, until the ammonia nitrogen content displayed by the sensor meets the requirements, the water outlet valve is opened to obtain outlet water with the corresponding ammonia nitrogen content.

[0038] Preferably, in the method for regulating nitrogen products during electrochemical removal of nitrate nitrogen of the present invention, the solution pH (i.e., the pH of the wastewater containing nitrate nitrogen) is 3.0-7.0, and the voltage is 1.8-2.2V.

[0039] The Co3O4 / GF electrode of the present invention is a very economical and friendly electrode. - Selectively regulate the presence of ammonia nitrogen and N2, and establish the reaction time and Cl through FNN - The relationship between dosage and ammonia nitrogen generation: add as much chlorine as needed for ammonia nitrogen, and use long / short time reaction to regulate nitrogen products.

[0040] Mechanism of the present invention: When chloride ions exist in the solution, Cl - Adsorbed on the anode surface and oxidized to generate HOCl / OCl - , HOCl / OCl - Then with NH4 + The reaction generates N2. The process of electrochemical reduction of nitrates includes both nitrate reduction at the cathode and ammonia nitrogen oxidation at the anode. The final ideal product is N2. Electrode materials with superior electrochemical properties can achieve high nitrate removal rates and NH4 + Or N2 selectivity. The Co3O4 / GF electrode in the present invention is mainly caused by 50% direct reduction by direct electron transfer and 50% indirect reduction mediated by H*. For the Co3O4 / GF electrode, the indirect reduction mediated by atomic H* accounts for only 1% of NO3 - Therefore, on the Co3O4 / GF electrode, atomic H* in NO3 - The contribution to electrocatalytic reduction is limited, while direct electron transfer is the main - Another reason for electrocatalytic reduction. The present invention selectively generates ammonia nitrogen with specific requirements through nitrate nitrogen, using Cl- To achieve product regulation, an economical and friendly electrode (i.e., Co3O4 / GF electrode) has been developed to selectively regulate ammonia nitrogen and N2, saving resources while saving time and labor. Therefore, the present invention can selectively regulate the ammonia nitrogen production through efficient nitrate electroreduction and chloride ion oxidation.

[0041] Preferably, the electrochemical workstation performs a reduction reaction on the nitrate nitrogen in the single-chamber electrolytic cell at a voltage intensity of -1.61 V vs. Ag / AgCl.

[0042] Preferably, when selectively regulating the ammonia nitrogen product by controlling the concentration of the added chloride ions and the reaction time, the substance added in the chlorination system is potassium chloride, the chloride ion concentration addition range is 0-4000 mg / L, and the ammonia nitrogen yield is 0%-100%. The ammonia nitrogen source is nitrate nitrogen in water, and the chloride ion concentration is controlled according to the total amount of nitrate nitrogen substances to obtain the required amount of ammonia nitrogen.

[0043] Preferably, the water storage capacity during the first treatment phase is 60±5% of the reaction tank; and the water storage capacity during the third replenishment phase shall not exceed 30% of the total water storage capacity of the reaction tank.

[0044] Preferably, the PLC control system uses a fuzzy neural network model (FNN) for prediction, and uses a multi-input single-output FNN model for analysis. Based on the technical principle of electrochemical reduction of nitrate nitrogen, the factors affecting the concentration of nitrogen products after the reaction are analyzed to determine the input and output parameters of the FNN neural network modeling. Based on the measured data, the training and prediction sample sets required for modeling are determined, and the optimal number of trainings is selected after multiple trainings to obtain the prediction results.

[0045] Compared with the prior art, the present invention has the following advantages and technical effects:

[0046] The present invention provides a method and system for regulating nitrogen products by using a Co3O4 / GF cathode and chloride ions in the process of electrochemically removing nitrate nitrogen. The Co3O4 / GF electrode has excellent performance in completely electroreducing nitrate nitrogen to ammonia nitrogen. At the same time, the oxidation of chloride ions can synchronously oxidize ammonia nitrogen to nitrogen gas, thereby further removing ammonia nitrogen in water. The selection of nitrogen products is achieved by Co3O4 / GF cathode reduction and chloride ion anode oxidation, that is, the amount of chloride ions added is controlled according to the required amount of ammonia nitrogen, and a fuzzy neural network model (FNN) is used for prediction to obtain ammonia nitrogen of the required concentration. The remaining nitrate nitrogen is converted into nitrogen gas into the atmosphere, which can achieve a green, environmentally friendly and sustainable treatment effect. It is an environmentally friendly process, which is helpful for resource recovery and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0048] Figure 1 The overall structure schematic diagram of the system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen of the present invention, wherein 101-lifting pump, 102-grid, 103-mixing tank, 104-dosing tank, 105-water inlet valve, 106-water inlet pump, 107-electrochemical reactor, 108-first sensor, 109-second sensor, 110-water outlet valve, 111-reflux valve, 112-regulating device;

[0049] Figure 2 It is a schematic diagram of the main structure of the electrochemical reactor of the present invention, wherein 1-electrochemical workstation, 2-Co3O4 / GF electrode, 3-Ag / AgCl reference electrode, 4-platinum counter electrode, 5-magnetic rotor, 6-single-chamber electrolytic cell, 7-magnetic stirrer, 8-chlorination system, 9-sensor, 10-PLC control system;

[0050] Figure 3 Schematic diagram of the preparation process of Co3O4 / GF electrode in Example 1 of the present invention;

[0051] Figure 4 The SEM images of the Co3O4 / GF electrode in Example 1 of the present invention at different magnifications are shown in Figure 1, where (a) is 2500×, (b) is 10000×, (c) is 25000×, and (d) is 50000×;

[0052] Figure 5 The system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen by the present invention treats different Cl - Nitrogen product concentration at concentration;

[0053] Figure 6 The system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen by the present invention is different from the system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen by the present invention. - Nitrogen product profiles at concentrations;

[0054] Figure 7 The ammonia nitrogen prediction result of the system for regulating nitrogen products in the electrochemical removal of nitrate nitrogen in the present invention;

[0055] Figure 8 A regression line of system training samples for regulating nitrogen products in the electrochemical removal of nitrate nitrogen in the present invention;

[0056] Fig. 9 The expected and predicted output results of the system for regulating nitrogen products in the electrochemical removal of nitrate nitrogen in the present invention;

[0057] Fig.10 It is a three-dimensional simulation diagram of the chlorine addition amount versus ammonia nitrogen concentration at different times in the system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen in the present invention;

[0058] Fig.11 Figure 2 is the influencing factors of nitrate nitrogen removal by Co3O4 / GF electrode, where (a) is the effect of initial nitrate nitrogen concentration on nitrate nitrogen removal, (b) is the effect of initial nitrate nitrogen concentration on ammonia nitrogen generation, (c) is the effect of initial nitrate nitrogen concentration on nitrite nitrogen generation, (d) is the effect of pH on nitrate nitrogen removal, (e) is the effect of pH on ammonia nitrogen generation, (f) is the effect of pH on nitrite nitrogen generation, (g) is the effect of voltage intensity on nitrate nitrogen removal, (h) is the effect of voltage intensity on ammonia nitrogen removal, and (i) is the effect of voltage intensity on nitrite nitrogen generation. DETAILED DESCRIPTION

[0059] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0060] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0061] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0062] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0063] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0064] All raw materials used in the examples of the present invention are commercially available.

[0065] Unless otherwise specified, the room temperature in the present invention is 25±2°C.

[0066] Matters not described in detail in the present invention are conventional technical means in the art and are not the focus of the present invention, such as the FNN neural network modeling process.

[0067] The overall structural diagram of the system for regulating nitrogen products in the electrochemical removal of nitrate nitrogen in the present invention is shown in Figure 1 , wherein 101-lifting pump, 102-grid, 103-mixing tank, 104-dosing tank, 105-water inlet valve, 106-water inlet pump, 107-electrochemical reactor, 108-first sensor, 109-second sensor, 110-water outlet valve, 111-reflux valve, 112-regulating device.

[0068] The main structural schematic diagram of the electrochemical reactor of the present invention is shown in Figure 2 , including 1-electrochemical workstation, 2-Co3O4 / GF electrode, 3-Ag / AgCl reference electrode, 4-platinum counter electrode, 5-magnetic rotor, 6-single-chamber electrolytic cell, 7-magnetic stirrer, 8-chlorination system, 9-sensor, 10-PLC control system.

[0069] The technical solution of the present invention is further illustrated by the following embodiments.

[0070] Example 1

[0071] This embodiment provides a system for regulating nitrogen products in the process of electrochemically removing nitrate nitrogen, comprising:

[0072] Lifting pump 101, grid 102, dosing tank 104, mixing tank 103, water inlet valve 105, water inlet pump 106, electrochemical reactor 107, first sensor 108, second sensor 109, water outlet valve 110, reflux valve 111 and control device 112;

[0073] The lifting pump 101, the grid 102, the dosing tank 104, the mixing tank 103, the water inlet valve 105, the water inlet pump 106, the first sensor 108, the electrochemical reactor 107 and the water outlet valve 110 are connected in series in sequence;

[0074] The electrochemical reactor 107 is connected to a reflux pipe and refluxes to the front of the water inlet pump 106 through a reflux valve 111; the lifting pump 101 delivers the nitrogen-containing wastewater to the mixing tank 103 through the grid 102, and the reagent is added through the dosing tank 104 to control the pH of the inlet water. An electric stirrer is provided in the mixing tank 103;

[0075] The lifting pump 101 , the grid 102 , the dosing tank 104 , the mixing tank 103 , the water inlet valve 105 , the water inlet pump 106 , the electrochemical reactor 107 , the first sensor 108 , the second sensor 109 , the water outlet valve 110 and the reflux valve 111 are all electrically connected to the control device 112 .

[0076] The electrochemical reactor 107 comprises:

[0077] Electrochemical workstation 1, Co3O4 / GF electrode 2, Ag / AgCl reference electrode 3, platinum counter electrode 4, magnetic rotor 5, single-chamber electrolytic cell 6, magnetic stirrer 7, chlorination system 8, sensor 9 and PLC control system 10; wherein the electrochemical workstation 1, Co3O4 / GF electrode 2, Ag / AgCl reference electrode 3, platinum counter electrode 4 are connected to form a three-electrode circuit through electric wires; the chlorination system 8 is connected to the single-chamber electrolytic cell 6 through a first line pipeline; the sensor 9 is externally connected to the single-chamber electrolytic cell 6 through a second line; the electrochemical workstation 1, the chlorination system 8 and the sensor 9 are electrically connected to the PLC control system 10 through a third line;

[0078] The sensor 9 is used to monitor the changes of various nitrogen products, pH and temperature in the single-chamber electrolytic cell 6. The sensor 9 includes a nitrate nitrogen sensor, an ammonia nitrogen sensor, a nitrite nitrogen sensor, a total nitrogen sensor, a pH sensor and a temperature sensor.

[0079] The Co3O4 / GF electrode was prepared by electrodeposition-calcination method. The specific preparation method is as follows:

[0080] S1. Pre-treated GF substrate: GF (3.0×4.0cm 2 ) were ultrasonically treated in acetone, 1 M hydrochloric acid and distilled water, respectively;

[0081] S2. Prepare electrolyte for electrodeposition: 0.5 M boric acid, 0.1 M cobalt nitrate hexahydrate and 2.0 g / L sodium dodecyl sulfate were used as electrolyte, pretreated graphite felt GF electrode was used as working electrode, platinum sheet was used as counter electrode, Ag / AgCl electrode was used as reference electrode, and deposition was carried out at -2.0 V vs. AgCl / Ag voltage for 120 s;

[0082] S3. Calcination and annealing: Clean the surface of the working electrode after deposition with deionized water, dry it in an oven at 60°C, and then place it in a tube furnace and heat it to 500°C at a rate of 5°C / min. After calcining at a constant temperature for 2 hours, cool it naturally to room temperature, take it out, clean it and set it aside. See the schematic diagram of the preparation process of Co3O4 / GF electrode for details. Figure 3 , SEM images of Co3O4 / GF electrode at different magnifications are shown in Figure 4 , it can be seen that uniform cubic spinel structured Co3O4 is loaded on the GF fiber structure.

[0083] The method for regulating nitrogen products in the electrochemical removal of nitrate nitrogen is divided into three stages, namely the first treatment stage, the second circulation stage and the third replenishment stage, including the following steps:

[0084] When the wastewater containing nitrate nitrogen enters the system, the nitrate nitrogen is electrochemically removed according to the required ammonia nitrogen generation amount. First, the first treatment stage is carried out: the water inlet valve 105 is opened, the water outlet valve 110 and the reflux valve 111 are closed, and the wastewater containing nitrate nitrogen is lifted by the lifting pump 101. The water delivered by the lifting pump 101 passes through the grid 102, passes through the mixing tank 103, and is adjusted to a neutral pH by adding drugs in the dosing tank 108. After flowing through the water inlet valve 105, it is delivered to the electrochemical reaction device 107 by the water inlet pump 106 for electrochemical reduction. The original nitrate nitrogen, the first sensor 108 detects the concentration of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the influent, and the nitrate water reaching the electrochemical reaction device 107 enters the single-chamber electrolytic cell 6. The reaction time and the amount of chlorine are determined by the prediction result of the fuzzy neural network model according to the required amount of ammonia nitrogen, and are controlled by the PLC control system 10, wherein the amount of chlorine is controlled by the PLC control chlorination system 8. The added material is potassium chloride. The electrochemical workstation 1 is controlled by the PLC to set the electrochemical reaction at a voltage intensity of -1.61V vs.Ag / AgCl to reduce the nitrate nitrogen in the single-chamber electrolytic cell 6. After the reaction is completed, if the ammonia nitrogen content displayed by the second sensor 109 is consistent with the required content, the outlet valve 110 is opened to obtain the outlet water with the corresponding ammonia nitrogen content. When the water is inlet in the first treatment stage, the water storage volume is 60±5% of the reaction tank;

[0085] If the nitrate water reaching the electrochemical reaction device 107 enters the electrolytic cell, the reaction time and the amount of chlorine are determined according to the required amount of ammonia nitrogen, and the control is performed through the PLC control system 10. When the ammonia nitrogen content displayed by the second sensor 109 is less than the expected value after the reaction is completed, the second circulation stage is entered: at this time, the water inlet valve 105 and the water outlet valve 110 are both closed, and the reflux valve 111 is opened. The water in the single-chamber electrolytic cell 6 is transported to the front of the water inlet pump 106 through the reflux pipe and the reflux valve 111, and re-enters the electrochemical reaction device 107. At this time, the first sensor 108 detects the concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the re-entering water. The reaction time and the amount of chlorine are determined by the required amount of ammonia nitrogen according to the prediction results of the fuzzy neural network model, and the control is performed through the PLC control system 10, wherein the amount of chlorine is controlled by the PLC control chlorination system 8, and the electrochemical reaction is set by the PLC control electrochemical workstation 1, and the cycle is continuously performed until the second sensor 109 shows that the ammonia nitrogen value reaches the expected requirement, the water outlet valve 110 is opened, and the reflux valve 111 is closed;

[0086] If the ammonia nitrogen content displayed by the second sensor 109 is greater than the expected value, the third replenishment stage is entered: at this time, the water inlet valve 105 is opened, the reflux valve 111 is closed, and the lifting pump 101 lifts the nitrate nitrogen-containing wastewater. The water delivered by the lifting pump 101 passes through the grid 102, the mixing tank 103, and the pH is adjusted to neutral by adding medicine in the dosing tank 108. After flowing through the water inlet valve 105, it is transported to the electrochemical reaction device 107 through the water inlet pump 106 for electrochemical reduction of nitrate nitrogen. The concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen are determined by the remaining required amount of ammonia nitrogen to determine the reaction time and the amount of chlorine added, which are controlled by a PLC control system 10, wherein the amount of chlorine added is controlled by a PLC-controlled chlorination system 8, and an electrochemical reaction is set by a PLC-controlled electrochemical workstation 1. After the expected reaction time is reached, until the ammonia nitrogen content displayed by the first sensor 108 meets the requirements, the outlet valve 110 is opened to obtain outlet water with the corresponding ammonia nitrogen content. The water inlet in the third replenishment stage shall not exceed 30% of the total water storage in the reaction tank.

[0087] The electroreduction of nitrate nitrogen was carried out at a voltage of -1.61 V vs. Ag / AgCl for 2 h at chloride ion concentrations of 0, 100, 300, 500, 1000, 1500, 2000, 2500, 3000 and 3500 mg / L. The concentrations of nitrate nitrogen and byproducts were measured every 20 min. The results are shown in Table 1. Figure 5 As shown, when Cl - When the concentration increases, NO3 - -N removal rate is maintained at 100%, and the NO2 produced by the Co3O4 / GF electrode in the process of reducing nitrate nitrogen --N is less than 2%, and shows a trend of first increasing and then decreasing. When the system contains chloride ions, different Cl - The free residual chlorine and combined residual chlorine at different concentrations (Table 1) show that almost no hydrazine and disinfection by-products are generated. Basically, the adverse reaction of the ideal product N2 can be ignored. The system for regulating nitrogen products in the process of electrochemical removal of nitrate nitrogen using the present invention is different under different Cl - The nitrogen product distribution diagram under the concentration is shown in Figure 6 , where green represents nitrite nitrogen. The nitrite nitrogen generated during the electrochemical reduction of nitrate nitrogen is less than 1%. Figure 6 It is almost invisible. - With the addition of NH4 + The amount of Cl - The removal rate of total nitrogen was also gradually increasing. - Oxidation at the anode generates Cl2, which further combines with H2O to generate ClO - Strong oxidant, NH4 + and NO2 - Converted into N2 and NO3 respectively - . At 500mg / L, 1500mg / L and 2000mg / L Cl - Under these conditions, NH4 + The residual amounts of -N were 78.59 mg / L, 57.82 mg / L and 41.76 mg / L respectively. The removal rates of total nitrogen were 20.56%, 28.49% and 55.93% respectively. - When the concentration reaches 3000mg / L, NH4 is almost undetectable in the electrolyte. + The total nitrogen removal rate reached 98.63%, which can almost achieve complete removal of nitrogen.

[0088] Table 1. Different Cl - Free residual chlorine and combined residual chlorine at different concentrations

[0089]

[0090] Based on the principle of electrochemical reduction of nitrate nitrogen treatment process technology, the factors affecting the concentration of nitrogen products after the reaction were analyzed, and the multi-input single-output fuzzy neural network model was used for analysis, and the gradient descent algorithm was used for iterative analysis. A total of 60 groups of chlorine addition and ammonia nitrogen concentration data were selected as the data set for this study. The data set is divided into a training set and a test set, of which 42 groups of data are training sample sets and 18 groups of data are prediction sample sets. The data selected in this study came from the timed sampling test in a single-chamber reactor, including the production of ammonia nitrogen at different times (0-120min) and chlorine addition (KCl, 0-3500mg / L). Reaction time (T) and chloride ion concentration (C) are input parameters, and ammonia nitrogen concentration is the output parameter. The number of neurons in the input layer of the fuzzy neural network is n=2, and the number of fuzzy rules is m=15, so the number of membership function neurons is 2×15, and the number of output neurons is 1. In order to ensure the reliability of the model, the training set and the test set were randomly shuffled and re-divided 30 times. The performance of the BP neural network model (Back Propagation Neural Network), the BP neural network model optimized by genetic algorithm (GA) (GA-BP model) and the BP neural network model optimized by particle swarm algorithm (PSO-BP model) were compared with the fuzzy neural network model and the applicability was evaluated. The mean absolute error (MAE), mean square error (MSE), root mean square error (RMSE) and determination coefficient (R 2 ) Four statistical parameters are used to evaluate the prediction accuracy of the FNN model, and their definitions are shown in equations (1)-(4).

[0091]

[0092]

[0093] In the formula, y i is the actual observed value, is the model prediction value, is the average of the observed values.

[0094] Two models (BP and FNN) were tested to fit the obtained data to predict the ammonia nitrogen concentration. - Generate NH4 + A total of 60 sets of data were tested, and after 30 different random splits, these data were divided into training and test data sets. The parameter results learned through multiple training are shown in Table 2. It can be seen that compared with BP, BP-GA, and BP-PSO models, FNN performs best, with MAE, MSE, RMSE, and R 2They are 0.200, 0.083, 0.270 and 0.995 respectively, which have high prediction accuracy and stability.

[0095] Figure 7-Figure 9 The fitting effect of the FNN model on the training samples and test samples is shown. It can be seen that the predicted values ​​are highly consistent with the measured values. According to the regression line ( Figure 8 ) It can be seen that except for a few extreme points, all data points and fitting lines of the test set are closely aligned with the X=Y line, basically achieving the fitting of this function, further proving the high fitting accuracy and stability of the model.

[0096] Table 2. Model indicators of different models on the training set and test set

[0097]

[0098] All data are calculated using 30 sets of performance indicators of randomly shuffled and repartitioned training and test sets. MAE: mean absolute error; MSE: mean square error; RMSE: root mean square error; R 2 : Coefficient of determination.

[0099] In summary, compared with the traditional BP model, the fuzzy neural network FNN has stronger prediction performance and has the best prediction results. Therefore, the above values ​​are selected for each parameter in the electro-reduction nitrate nitrogen prediction model. After the sample training is completed, the corresponding weight set is saved. The three-dimensional graph obtained by prediction is shown in Fig.10 In this embodiment, a certain amount of chloride ions is introduced into the electrolyte, which can significantly improve the selectivity of nitrogen and reduce the production of ammonia nitrogen. When the chloride ion concentration reaches 3000 mg L -1 When NH4 was hardly detected after 120 min of electrolysis + The N2 selectivity of the reaction reached 98.63%. The fuzzy neural network model was used to make a simple prediction of ammonia nitrogen generation and chlorine addition. - When the concentration is high, less ammonia nitrogen is generated in a short period of time; while when the chloride ion concentration is low, more ammonia nitrogen products are generated.

[0100] According to the above embodiments, the present invention provides a method and system for regulating nitrogen products in the process of nitrate nitrogen removal by using Co3O4 / GF cathode and chloride ions. It can perform fine regulation according to the changes in nitrate nitrogen, ammonia nitrogen, nitrite nitrogen, total nitrogen, temperature and pH in the effluent of the electrochemical reactor, thereby achieving rapid, economical and effective treatment of nitrate nitrogen wastewater, and can effectively control the amount of ammonia nitrogen generated for recycling. The process has the characteristics of simple operation, mild reaction conditions and environmental friendliness.

[0101] Example 2

[0102] When there are no chloride ions in the solution, the Co3O4 / GF cathode reduces nitrate nitrogen. Electrochemical reduction is performed using a standard three-electrode in a typical single-chamber quartz electrolytic cell. The Co3O4 / GF electrode prepared in Example 1 is used as the working electrode, the platinum sheet is used as the counter electrode, and the Ag / AgCl is used as the reference electrode. The electrochemical reduction of nitrate nitrogen (NO3 - -N), reaction solution 100mL (100mg / L NO3 - -N and 0.1M Na2SO4), initial pH = 7.0, reaction time 2h, test every 20min. Under pH = 7.0, Co3O4 / GF cathode can convert NO3 into NH3 in 2h at -1.61V vs.Ag / AgCl voltage. - -N is completely reduced to ammonia nitrogen (NH4 + -N), at this time the ammonia nitrogen output is the largest, and it can be directly used as the raw material for the production of nitrogen fertilizer.

[0103] The main factors affecting the removal of nitrate nitrogen and the generation of ammonia nitrogen are as follows:

[0104] Effect of initial nitrate concentration: Fig.11 As shown in (a)-(c), after 120 minutes of reaction under the conditions of nitrate nitrogen initial concentration of 50mg / L, 150mg / L, 200mg / L and 250mg / L, the nitrate nitrogen concentrations were 0mg / L, 0mg / L, 65.62mg / L and 104.73mg / L, respectively, and the nitrate nitrogen removal rates were 100% (60min), 100%, 68.35%, 60.90%, respectively; the nitrite nitrogen concentrations were 0.05mg / L, 0.23mg / L, 0.31mg / L and 0.21mg / L, respectively; the ammonia nitrogen concentrations were 40.23mg / L, 128.60mg / L, 126.27mg / L and 145.91mg / L, respectively. It can be seen that the higher the initial nitrate nitrogen concentration, the lower the nitrate nitrogen removal rate. The ammonia nitrogen generation increased and the ammonia nitrogen selectivity was almost 100% within 120min. This is because within a certain concentration range, the nitrate nitrogen adsorbed on the cathode surface is affected by concentration diffusion, and the removal rate of nitrate nitrogen increases with the increase of concentration.

[0105] Effect of initial pH: Fig.11As shown in (d)-(f), after 120 minutes of reaction under the initial pH conditions of 3, 5, 7 and 9, the nitrate nitrogen concentrations were 0 mg / L, 0 mg / L, 1.35 mg / L and 28.73 mg / L, respectively, and the nitrate nitrogen removal rates were 100%, 100%, 98.60%, and 73.19%, respectively; the nitrite nitrogen concentrations were 0.12 mg / L, 0.01 mg / L, 0 mg / L and 0.54 mg / L, respectively; and the ammonia nitrogen concentrations were 97.02 mg / L, 98.23 mg / L, 96.31 mg / L and 64.01 mg / L, respectively. The nitrate nitrogen removal effect was the best under the condition of pH = 5.0, and nitrate nitrogen could be converted into ammonia nitrogen more quickly. In both acidic and neutral environments, the nitrate nitrogen reduction effect of Co3O4 / GF electrode can reach almost 100% after 120 minutes. However, under the condition of pH = 9.0, the removal rate of nitrate nitrogen decreased by 26.81%. This is because under acidic conditions, the reduction of nitrate nitrogen on the cathode surface can be promoted, as shown in equations (5)-(6). At the same time, under alkaline conditions, OH - It will be adsorbed on the surface of the cathode electrode, reducing the active sites on the electrode surface available for nitrate nitrogen and inhibiting the cathode reaction of nitrate nitrogen.

[0106] NO3 - +2e - +H2O→NO2 - +2OH - (5)

[0107] NO2 - +6e - +6H2O→NH4 + +8OH - (6)

[0108] The influence of voltage intensity: Fig.11As shown in (g)-(i), when the applied negative voltage is 1.2V, 1.4V, 1.61V, 1.8V, 2.0V and 2.2V (vs. Ag / AgCl), the concentration of nitrate nitrogen drops to 53.93mg / L, 31.85mg / L, 1.36mg / L, 0.7mg / L, 5.54mg / L and 0mg / L respectively after 120min of electrochemical reduction, and the nitrate nitrogen removal rate is 37.70%, 86.06%, 98.60%, 99.31%, 93.86% and 100% respectively. It can be seen that as the voltage intensity increases, the nitrate nitrogen removal rate also increases. This is because as the applied voltage increases, the current density increases, and the cathode generates more electrons, which is more conducive to the reduction of nitrate nitrogen on the cathode surface, which accelerates the reaction rate of nitrate nitrogen. Among them, the nitrate nitrogen reduction efficiency decreased at 2.0V, which can be attributed to the enhancement of hydrogen evolution reaction at this potential and the obstruction of electron transfer on the cathode surface by hydrogen bubbles. From 1.2V-1.8V (vs.Ag / AgCl), the generation of ammonia nitrogen gradually increased within 120min, and the generation concentrations of ammonia nitrogen were 54.28mg / L, 87.48mg / L, 95.73mg / L and 97.30mg / L, respectively. When the applied potential increased to 2.0V and 2.2V (vs.Ag / AgCl), the generation concentration of ammonia nitrogen decreased to 92.35mg / L and 90.51mg / L, respectively, and the removal of total nitrogen began to appear at a voltage of 1.8V (vs.Ag / AgCl), and the total nitrogen removal gradually increased with the increase of voltage intensity. Under the condition of a voltage of 2.2V, the total nitrogen removal reached 10.98%. The generation of nitrite nitrogen was still less than 1mg / L at any potential.

[0109] The above content can determine the optimal conditions for electro-reduction of nitrate nitrogen to ammonia nitrogen, control the PLC system to set the electrochemical workstation parameter value (voltage) and control the dosing tank to control the pH value. The solution pH is in the range of 3.0-7.0 for NO3 - The effect of electrocatalytic reduction is small, and the voltage in the range of 1.8-2.2V is favorable for NO3 - Electrocatalytic reduction.

[0110] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A system for regulating nitrogen products in the process of electrochemical removal of nitrate nitrogen, characterized in that: The system comprises: A lifting pump (101), a grille (102), a dosing tank (104), a mixing tank (103), a water inlet valve (105), a water inlet pump (106), an electrochemical reactor (107), a first sensor (108), a second sensor (109), a water outlet valve (110), a reflux valve (111) and a control device (112); The lift pump (101), the grille (102), the mixing tank (103), the water inlet valve (105), the water inlet pump (106), the first sensor (108), the electrochemical reactor (107) and the water outlet valve (110) are sequentially connected in series; The electrochemical reactor (107) is connected to a reflux pipe and refluxes to the front of the water inlet pump (106) through the reflux valve (111); the lift pump (101) delivers the nitrogen-containing wastewater to the mixing tank (103) through the grid (102), and the chemical is added through the chemical dosing tank (104) to control the pH of the inlet water; The lifting pump (101), the grille (102), the dosing tank (104), the mixing tank (103), the water inlet valve (105), the water inlet pump (106), the electrochemical reactor (107), the first sensor (108), the second sensor (109), the water outlet valve (110) and the return valve (111) are all electrically connected to the control device (112).

2. The system for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 1, characterized in that: The mixing tank (103) is provided with an electric stirrer.

3. The system for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 1, characterized in that: The electrochemical reactor (107) comprises: Electrochemical workstation (1), Co3O4 / GF electrode (2), Ag / AgCl reference electrode (3), platinum counter electrode (4), magnetic rotor (5), single-chamber electrolytic cell (6), magnetic stirrer (7), chlorination system (8), sensor (9) and PLC control system (10); The electrochemical workstation (1), the Co3O4 / GF electrode (2), the Ag / AgCl reference electrode (3), and the platinum counter electrode (4) are connected to form a three-electrode circuit via electric wires; The chlorination system (8) is connected to the single-chamber electrolytic cell (6) via a first line pipeline; the sensor (9) is externally connected to the single-chamber electrolytic cell (6) via a second line; and the electrochemical workstation (1), the chlorination system (8) and the sensor (9) are electrically connected to the PLC control system (10) via a third line.

4. The system for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 3, characterized in that: The preparation method of the Co3O4 / GF electrode (2) is as follows: The graphite felt substrate is pretreated, and then the pretreated graphite felt substrate is used as a working electrode, a platinum sheet is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, and boric acid, cobalt nitrate hexahydrate and sodium dodecyl sulfate are used as electrolytes to perform electrodeposition. After the electrodeposition, the surface of the working electrode is cleaned, dried, calcined, and cooled to obtain the Co3O4 / GF electrode (2).

5. The system for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 3, characterized in that: The sensor (9) is used to monitor the changes in various nitrogen products, pH and temperature in the single-chamber electrolytic cell (6); The sensor (9) comprises a nitrate nitrogen sensor, an ammonia nitrogen sensor, a nitrite nitrogen sensor, a total nitrogen sensor, a pH sensor and a temperature sensor.

6. A method for regulating nitrogen products in the process of electrochemical removal of nitrate nitrogen, characterized in that: The nitrogen products in the process of electrochemically removing nitrate nitrogen are obtained by using the system described in any one of claims 1 to 5.

7. The method for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 6, characterized in that: It is divided into three stages, namely the first processing stage, the second circulation stage and the third replenishment stage, including the following steps: When wastewater containing nitrate nitrogen enters the system, nitrate nitrogen is electrochemically removed according to the required ammonia nitrogen generation amount. First, the first treatment stage is performed: the water inlet valve (105) is opened, the water outlet valve (110) and the reflux valve (111) are closed, and the wastewater containing nitrate nitrogen is lifted by the lifting pump (101). The water delivered by the lifting pump (101) passes through the grid (102) and the mixing tank (103) and is adjusted to a neutral pH value by adding a medicine through the dosing tank (108). After flowing through the water inlet valve (105), it is delivered to the electrochemical reaction device (107) through the water inlet pump (106) for electrochemical reduction of nitrate nitrogen. The first sensor ( 108) detects the concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the influent, and the nitrate water reaching the electrochemical reaction device (107) enters the single-chamber electrolytic cell (6), and the reaction time and the amount of chlorine are determined according to the prediction results of the fuzzy neural network model based on the required amount of ammonia nitrogen, and are controlled by a PLC control system (10), wherein the amount of chlorine is controlled by a PLC-controlled chlorination system (8), and an electrochemical reaction is set by a PLC-controlled electrochemical workstation (1). After the reaction is completed, if the ammonia nitrogen content displayed by the second sensor (109) is consistent with the required content, the water outlet valve (110) is opened to obtain water outlet with the corresponding ammonia nitrogen content; If the nitrate solution reaching the electrochemical reaction device (107) enters the electrolytic cell, the reaction time and the amount of chlorine added are determined according to the required amount of ammonia nitrogen, and controlled by the PLC control system (10). When the ammonia nitrogen content displayed by the second sensor (109) is less than the expected value after the reaction is completed, the second circulation stage is entered: at this time, the water inlet valve (105) and the water outlet valve (110) are both closed, the reflux valve (111) is opened, and the water in the single-chamber electrolytic cell (6) is transported to the front of the water inlet pump (106) through the reflux pipe and the reflux valve (111), and re-enters the electrochemical reaction device (107), at this time, the first sensor (108) detects the concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the re-entering water, and the reaction time and the amount of chlorine are determined by the required amount of ammonia nitrogen according to the prediction result of the fuzzy neural network model, and controlled by the PLC control system (10), wherein the amount of chlorine is controlled by the PLC control chlorination system (8), and the electrochemical reaction is set by the PLC control electrochemical workstation (1), and the cycle is continuously repeated until the second sensor (109) shows that the ammonia nitrogen value meets the expected requirements, the water outlet valve (110) is opened, and the return valve (111) is closed; If the ammonia nitrogen content displayed by the second sensor (109) is greater than the expected value, the third replenishment stage is entered: at this time, the water inlet valve (105) is opened, the return valve (111) is closed, and the lifting pump (101) lifts the nitrate nitrogen-containing wastewater. The water delivered by the lifting pump (101) passes through the grid (102) and the mixing tank (103) and is adjusted to a neutral pH value by adding drugs through the dosing tank (108). After flowing through the water inlet valve (105), it is delivered to the electrochemical reaction device (107) through the water inlet pump (106) for electrochemical reduction of nitrate. According to the concentrations of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen in the influent detected by the first sensor (108), the reaction time and the amount of chlorine added are determined by the remaining required amount of ammonia nitrogen, and the control is performed by a PLC control system (10), wherein the amount of chlorine added is controlled by a PLC-controlled chlorination system (8), and an electrochemical reaction is set by a PLC-controlled electrochemical workstation (1). After the expected reaction time is reached, until the ammonia nitrogen content displayed by the first sensor (108) meets the requirements, the water outlet valve (110) is opened to obtain water outlet with a corresponding ammonia nitrogen content.

8. The method for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 7, characterized in that: The electrochemical workstation (1) performs a reduction reaction on the nitrate nitrogen in the single-chamber electrolytic cell (6) at a voltage intensity of -1.61 V vs. Ag / AgCl.

9. The method for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 7, characterized in that: When selective regulation of ammonia nitrogen products is achieved by controlling the concentration of added chloride ions and the reaction time, the substance added in the chlorination system (8) is potassium chloride, and the chloride ion concentration addition range is 0-4000 mg / L.

10. The method for regulating nitrogen products in the electrochemical removal of nitrate nitrogen according to claim 7, characterized in that: During the first treatment phase, the water storage volume is 60±5% of the reaction tank; during the third replenishment phase, the water intake shall not exceed 30% of the total water storage volume of the reaction tank.

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