An apparatus and method for electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal.

Abstract

This invention discloses an apparatus and method for the electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal. The apparatus includes an equalization tank, an electrolytic cell, and a water storage tank connected sequentially via a liquid delivery pipeline. The electrolytic cell contains an anode and a cathode, which are respectively connected to an external power source via wires. The anode comprises a conductive substrate and a bimetallic single-atom catalyst supported on the conductive substrate. The cathode is selected from one of the following: Pt electrode, Cu electrode, stainless steel electrode, graphite electrode, and nickel electrode. This invention utilizes the bimetallic single-atom catalyst supported on the anode to directly remove ammonia nitrogen from wastewater through electrochemical oxidation. This method effectively achieves complete nitrogen removal without the need for other auxiliary devices, converting ammonia nitrogen in wastewater into environmentally friendly nitrogen gas, thus achieving resource recovery and harmlessness.

Description

Technical Field

[0001] This invention relates to the field of electrochemical reaction device technology, and in particular to a device and method for the electrochemical oxidation of ammonia nitrogen wastewater for complete denitrification. Background Technology

[0002] Ammonia nitrogen in water bodies mainly exists as free ammonia (NH3) or ammonium salts (NH4). + Ammonia nitrogen exists in the form of nitrogen oxides and is one of the main pollutants causing water pollution in my country, becoming a global environmental problem that threatens human health. Excessive ammonia nitrogen concentration leads to eutrophication in slow-moving water bodies, causing algae to proliferate, continuously consuming dissolved oxygen, and potentially releasing harmful toxins, severely disrupting the balance of aquatic ecosystems. Based on differences in ammonia nitrogen concentration, ammonia nitrogen wastewater can be divided into: low-concentration ammonia nitrogen wastewater (<50 mg / L), medium-concentration ammonia nitrogen wastewater (50 mg / L~500 mg / L), and high-concentration ammonia nitrogen wastewater (>500 mg / L). According to data from the "Second National Pollution Source Census Bulletin," the annual discharge of ammonia nitrogen in China's water pollutant discharge reaches 963,400 tons. This ammonia nitrogen wastewater mainly comes from the decomposition of nitrogen-containing organic matter in domestic wastewater, various industrial wastewaters, and livestock and agricultural tailwater. For example, the ammonia nitrogen content in landfill leachate can reach as high as 2000 mg / L, while the ammonia nitrogen content in coking wastewater is 700 mg / L, and the content in black film biogas digesters can reach as high as 4800 mg / L. However, according to my country's current environmental protection standards for ammonia nitrogen wastewater discharge, the standard limit range for ammonia nitrogen is 0.02 mg / L to 150 mg / L. Therefore, the above-mentioned wastewater far exceeds the limit range and requires further treatment to meet the discharge standards.

[0003] Traditional ammonia nitrogen removal methods include air stripping, breakpoint chlorination, and biological methods. Air stripping is commonly used to treat wastewater with high concentrations of ammonia nitrogen, offering stable performance and relatively low investment costs. However, the ammonia nitrogen concentration in the treated effluent can still be as high as 100 mg / L, requiring further advanced treatment to meet discharge standards. Furthermore, the equipment is prone to scaling during air stripping, affecting subsequent operation, thus necessitating regular equipment inspections. Breakpoint chlorination is only suitable for treating low-concentration ammonia nitrogen wastewater. This method consumes large amounts of liquid chlorine, and the storage and utilization of liquid chlorine have high safety requirements. When the organic matter content in the wastewater is high, the generated byproducts, such as chloramine and chlorinated organic compounds, can cause secondary pollution. For ammonia nitrogen wastewater with high biodegradability (BOD / COD > 0.3) (ammonia nitrogen concentration higher than 300 mg / L), biological methods can be used. However, this method requires a large land area, has stringent requirements for the microenvironment of biological organisms, and necessitates the addition of organic carbon sources at low concentrations, placing high demands on operation and management. Therefore, while researching how to improve traditional ammonia nitrogen treatment technologies, people are also seeking a new ammonia nitrogen treatment process that is more cost-effective, consumes less energy, and produces cleaner products. Summary of the Invention

[0004] This invention aims to overcome the aforementioned problems in existing ammonia nitrogen treatment processes and provides an apparatus and method for electrochemical oxidation of ammonia nitrogen wastewater for complete denitrification. The electrocatalytic device uses an electrode with a single atom catalyst supported on a bimetallic site as the anode and a Pt or Cu electrode as the cathode, which can effectively remove ammonia nitrogen from the wastewater. No other auxiliary devices are required, and the product is green, environmentally friendly, and free of secondary pollution, achieving complete denitrification.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An electrochemical oxidation device for complete nitrogen removal from ammonia nitrogen wastewater includes an equalization tank, an electrolytic cell, and a water storage tank connected sequentially via a liquid delivery pipeline; the electrolytic cell is equipped with an anode and a cathode, which are respectively connected to an external power source via wires; the anode includes a conductive substrate and a bimetallic site single-atom catalyst supported on the conductive substrate; the cathode is selected from one of Pt electrode, Cu electrode, stainless steel electrode, graphite electrode, and nickel electrode.

[0007] Electrocatalytic ammonia oxidation technology is a highly efficient, low-energy-consumption, and environmentally friendly treatment solution for removing ammonia nitrogen from wastewater. The device in this invention, through a bimetallic single-atom catalyst supported on the anode, can directly and efficiently convert ammonia nitrogen in wastewater into environmentally friendly nitrogen gas directly within the electrolytic cell, achieving complete denitrification. The main reaction formulas in the ammonia nitrogen removal process within the electrolytic cell of this invention are as follows:

[0008] Near the anode:

[0009] Anode: 2NH3(aq) + 6OH - →N2↑+6H2O+6e - (1)

[0010] Near the cathode:

[0011]

[0012] Overall reaction in the electrolyzer:

[0013]

[0014] The device in this invention has high ammonia nitrogen removal efficiency, achieving an ammonia nitrogen removal rate of over 98% in wastewater, realizing complete denitrification of wastewater and converting all ammonia nitrogen pollutants in the wastewater into environmentally harmless nitrogen gas. The treated effluent meets discharge standards and requires no further secondary treatment, further reducing treatment costs. Furthermore, no additional organic carbon source is needed during the reaction process, and the device has a simple structure, which can further reduce water treatment costs.

[0015] Preferably, the electrolytic cell is equipped with an ion exchange membrane to separate the anode and cathode. The electrolytic cell in this invention can be a single-cell form without an ion exchange membrane, or a multi-cell form with the anode and cathode separated by an ion exchange membrane; the appropriate form can be chosen flexibly according to the actual processing requirements.

[0016] Preferably, the bottom of the electrolyzer's outlet side and the top of the electrolyzer's inlet side are connected by an internal circulation pipeline, and a primary booster pump is installed on the side of the internal circulation pipeline located at the electrolyzer's outlet side. This invention, by setting up an internal circulation pipeline on the electrolyzer, can enhance the effective contact time and mass transfer efficiency between the electrode / electrolyte interface through the internal circulation of wastewater within the electrolyzer, thereby improving the ammonia nitrogen degradation efficiency.

[0017] Preferably, an inlet pump is installed on the liquid delivery pipeline between the equalization tank and the electrolytic cell; and a secondary booster pump is installed on the liquid delivery pipeline between the electrolytic cell and the water storage tank.

[0018] Preferably, the electrolytic cell is a columnar electrolytic cell or a square electrolytic cell.

[0019] Preferably, the external power supply is a DC voltage regulator with an effective voltage of 0-200V and an effective current of 0-20A.

[0020] Preferably, the anode and cathode can be circular, rectangular, or columnar; the surface area ratio of the anode to the cathode is 0.1–100; and the loading of the bimetallic single-atom catalyst in the anode is 0.001–10 mg / cm³. 2 .

[0021] Preferably, the conductive substrate in the anode is selected from one of the following: carbon paper, carbon fiber paper, carbon cloth, carbon fiber cloth, graphite felt, nickel foam, copper foam, titanium plate, boron-doped diamond film, ruthenium-iridium electrode plate, DSA electrode, and conductive glass.

[0022] Preferably, the preparation method of the bimetallic site single-atom catalyst includes the following steps:

[0023] (A) Citrate was pyrolyzed under an inert atmosphere, washed sequentially with acid solution and water, and dried to obtain an ordered porous carbon support;

[0024] (B) The ordered porous carbon support, metal salt M1, metal salt M2 and glucose are mixed and ground to obtain a mixture; then the mixture is mixed with a nitrogen source and ground again to obtain a precursor.

[0025] (C) The precursor obtained in step (B) is pyrolyzed under an inert atmosphere, cooled, and then ground to obtain the bimetallic site single-atom catalyst.

[0026] Generally, the ammonia oxidation reaction (AOR) has two mechanisms. One is the OS mechanism: *NH3 gradually dehydrogenates to form N species, which then dimerizes to N2. During this process, *N is highly susceptible to peroxidation, forming toxic byproducts such as NO2. - and NO3 - Secondly, the GM mechanism: *NH3 dehydrogenates to *NH2, *NH x and *NH y Dimerization forms *N2H x+y Then, in a single step, hydrogen is dehydrogenated to form N2. Current electrochemical ammonia oxidation processes generally employ nanoscale metal catalysts. However, nanoscale metal catalysts consist of nanoparticles and sub-nanoclusters of various sizes, possessing multiple active sites such as different crystal faces and vertices. The diverse expression of these sites makes it difficult to guarantee the effective generation of *N2H. x+y The formation of this hydrazine analogue means that the AOR reaction generally proceeds according to the OS mechanism, inducing excessive side reactions. Therefore, existing nanoscale metal catalysts exhibit low nitrogen selectivity and Faraday efficiency when used for electrocatalytic ammonia oxidation, resulting in high NO2 content. - NO3 - If too many toxic byproducts are generated, complete denitrification cannot be achieved.

[0027] This invention utilizes a bimetallic site single-atom catalyst as the anode catalyst, which exhibits a highly dispersed atomic distribution. This uniform site distribution allows the catalyst to achieve extremely high nitrogen selectivity, facilitating the ammonia oxidation reaction to proceed according to the GM mechanism: the electronic interactions between the bimetals effectively optimize the internal electronic structure to improve its adsorption capacity for intermediates. This promotes the adsorption of one ammonia molecule on the surface of each adjacent bimetallic site, followed by deprotonation to generate *N₂H with stable N / N bonds.x+y It further dehydrogenates to form N2, effectively suppressing NO2. - NO3 - The generation of toxic byproducts allows the device to achieve complete denitrification when treating ammonia nitrogen wastewater.

[0028] Preferably, the citrate in step (A) is selected from one or more of trisodium citrate, potassium citrate, potassium dihydrogen citrate, and sodium dihydrogen citrate; the acid solution is selected from sulfuric acid, hydrochloric acid, and nitric acid; the concentration of the acid solution is 1.0–8.0 mol / L; the pyrolysis temperature in step (A) is 700–900℃, and the pyrolysis time is 0.5–3 h.

[0029] In step (B), the metal salt M1 is selected from one of nickel sulfate, nickel chloride, nickel bromide, nickel nitrate, nickel acetate, and their hydrates; the metal salt M2 is selected from one of the sulfates, chlorides, nitrates, acetates, and their hydrates of copper, iron, cobalt, manganese, and zinc; the nitrogen source is selected from one or more of dicyandiamide, melamine, urea, and thiourea; in the mixture in step (B), the molar ratio of metal ions in metal salt M1 and metal salt M2 is 1:0.5–5; the ratio of the amount of ordered porous carbon support, metal ions in metal salt M1, and glucose added is 0.06 g:0.3–0.5 mmol:1.2–1.5 g; the mass ratio of the mixture to the nitrogen source in the precursor is 1:5–10;

[0030] The pyrolysis temperature in step (C) is 600–1000℃, and the pyrolysis time is 1–3 hours.

[0031] The present invention also provides a method for complete denitrification of ammonia nitrogen wastewater by electrochemical oxidation using the above-mentioned device, comprising the following steps:

[0032] Step 1: Ammonia nitrogen wastewater enters the equalization tank to balance water quality and quantity; preferably, the hydraulic retention time of the equalization tank is 10-40 minutes.

[0033] Step 2: Wastewater enters the electrolytic cell through the infusion pipeline. Power is supplied to the anode and cathode by an external power source to carry out an electrochemical reaction to remove ammonia nitrogen from the wastewater.

[0034] Step 3: After the wastewater is treated to meet the standards in the electrolytic cell, it enters the storage tank through the liquid delivery pipeline and is discharged periodically.

[0035] Preferably, the hydraulic retention time in the electrolytic cell in step 2 is 5 to 24 hours; the wastewater is circulated internally through the internal circulation pipeline during the reaction process in the electrolytic cell.

[0036] Therefore, the present invention has the following beneficial effects:

[0037] (1) The device is simple in structure and easy to operate; and all reaction processes are completed in a single reaction device without the need for other auxiliary equipment, resulting in low operating and operating costs.

[0038] (2) The anode used in the device is loaded with a bimetallic site single-atom catalytic catalyst, which can efficiently convert ammonia nitrogen in wastewater into nitrogen gas, achieving complete denitrification while promoting product resource utilization and harmlessness.

[0039] (3) The device has high efficiency in removing ammonia nitrogen, with an ammonia nitrogen removal rate of over 98% in wastewater, achieving complete denitrification of wastewater and converting all ammonia nitrogen pollutants in wastewater into nitrogen gas that is harmless to the environment.

[0040] (4) The effluent quality after treatment by the present invention meets the discharge standards and does not require any further secondary treatment, which further reduces the treatment cost. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the electrocatalytic device (single tank) used in Embodiment 1 of the present invention;

[0042] Figure 2 This is a schematic diagram of the electrocatalytic device (multi-tank) used in Embodiment 1 of the present invention;

[0043] In the diagram: 1. Equalization tank; 2. Electrolytic cell; 3. External power supply; 4. Anode; 5. Cathode; 6. Inlet pump; 7. Primary booster pump; 8. Secondary booster pump; 9. Infusion pipeline; 10. Wire; 11. Water storage tank; 12. Ion exchange membrane; 13. Internal circulation pipeline.

[0044] Figure 3 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the NiCu3-NC bimetallic site single-atom catalyst used in the anode of Example 1 of this invention.

[0045] Figure 4 These are linear sweep voltammetry (LSV) spectra of the catalysts used in the anodes of Examples 1, 1, and 2 of this invention.

[0046] Figure 5 This is a comparison of the ammonia nitrogen degradation curves and nitrogen selectivity of the NiCu3-NC bimetallic site single-atom catalyst used in the anode of Example 1 of this invention for simulated wastewater with different initial ammonia nitrogen concentrations.

[0047] Figure 6 The diagram shows the denitrification efficiency, nitrogen selectivity, Faraday efficiency, and energy consumption of the NiCu3-NC bimetallic site single-atom catalyst used in the anode of Example 1 of this invention, and the nanoscale catalysts in Comparative Examples 3 and 4. Detailed Implementation

[0048] The present invention will be further described in detail below through specific embodiments: The following embodiments are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0049] Example 1:

[0050] like Figure 1 As shown, a single-tank electrochemical oxidation device for complete denitrification of ammonia nitrogen wastewater includes an equalization tank 1, an electrolytic cell 2, and a water storage tank 11 connected sequentially by a liquid delivery pipeline 9; an inlet pump 6 is installed on the liquid delivery pipeline between the equalization tank and the electrolytic cell; a secondary booster pump 8 is installed on the liquid delivery pipeline between the electrolytic cell and the water storage tank; the bottom of the electrolytic cell outlet side and the top of the electrolytic cell inlet side are connected by an internal circulation pipeline 13, and a primary booster pump 7 is installed on the side of the internal circulation pipeline located at the electrolytic cell outlet.

[0051] Electrolytic cell 2 is a columnar electrolytic cell containing an anode 4 and a cathode 5. The anode and cathode are connected to an external power supply 3 via wires 10. The external power supply is a DC voltage regulator with an effective voltage of 0–200V and an effective current of 0–20A. The cathode is a Pt wire. The anode comprises a conductive substrate of carbon paper (CP) and a nickel-copper bimetallic site single-atom catalyst (NiCu3-NC DSAC) supported on the carbon paper. The surface area of ​​both the cathode and anode is 1 cm². 2 .

[0052] The method for preparing the anode is as follows:

[0053] (A) Weigh 10g of trisodium citrate and place it in a muffle furnace under a nitrogen (N2) atmosphere. Pyrolyze it at a constant temperature of 800℃ for 1 hour to obtain a black solid product. Wash it with 5mol / L dilute sulfuric acid solution to remove inorganic impurities. Then wash it with water and dry it to obtain an ordered porous carbon support (PC).

[0054] (B) Mix 0.06g of PC, 0.085g of nickel sulfate, 0.225g of copper sulfate and 1.328g of glucose, grind and weigh, and mix with melamine at a mass ratio of 1:5, grind again to obtain the precursor;

[0055] (C) The precursor was placed in a muffle furnace under N2 atmosphere and calcined at 800℃ for 2 hours. After cooling, the obtained product was taken out and ground to obtain a nickel-copper bimetallic site single-atom catalyst (NiCu3-NC DSAC).

[0056] (D) Weigh 0.01 g of NiCu3-NC DSAC sample and add it to a dispersion consisting of 1000 μL of anhydrous ethanol, 1000 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat the sample onto a carbon paper substrate (coating amount 1.5 mg / cm²). 2 After drying, the anode is obtained and denoted as NiCu3-NC / CP.

[0057] The above-mentioned apparatus is used for the electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal. The method is as follows:

[0058] Step 1: Select 25 mL of simulated ammonia nitrogen wastewater (pH value 13, initial ammonia nitrogen concentration 700 mg / L) with similar composition to the actual wastewater and let it stay in the equalization tank for 10 minutes to balance the water quality and quantity;

[0059] Step 2: Wastewater enters the electrolytic cell through the inlet pump and delivery pipeline. A voltage of 2.1V is applied to the anode and cathode by an external power supply to carry out an electrochemical reaction to remove ammonia nitrogen from the wastewater. During the reaction, the wastewater is circulated internally through the internal circulation pipeline by the primary booster pump. The hydraulic retention time in the electrolytic cell is 5 hours, and the ammonia nitrogen removal rate is 98.74%.

[0060] Step 3: After treatment, the wastewater that meets the standards is pumped into the storage tank through the infusion pipeline by the secondary booster pump and discharged periodically.

[0061] Example 2:

[0062] like Figure 2 As shown, a multi-tank electrochemical oxidation device for complete denitrification of ammonia nitrogen wastewater includes an equalization tank 1, an electrolytic cell 2, and a water storage tank 11 connected in sequence by a liquid delivery pipeline 9; an inlet pump 6 is installed on the liquid delivery pipeline between the equalization tank and the electrolytic cell; a secondary booster pump 8 is installed on the liquid delivery pipeline between the electrolytic cell and the water storage tank; the outlet and inlet of the electrolytic cell are connected by an internal circulation pipeline 13, and a primary booster pump 7 is installed on one side of the internal circulation pipeline located at the outlet of the electrolytic cell.

[0063] Electrolytic cell 2 is a columnar electrolytic cell, containing an anode 4, a cathode 5, and an ion exchange membrane 12 separating the anode and cathode. The anode and cathode are connected to an external power supply 3 via wires 10. The external power supply is a DC voltage regulator with an effective voltage of 0–200V and an effective current of 0–20A. The cathode is a Pt wire. The anode comprises a conductive carbon cloth substrate (CF) and a nickel-iron bimetallic site single-atom catalyst (NiFe-NC DSAC) supported on the carbon cloth. The surface area of ​​both the cathode and anode is 1 cm². 2 .

[0064] The method for preparing the anode is as follows:

[0065] (A) Weigh 10g of trisodium citrate and place it in a muffle furnace under a nitrogen (N2) atmosphere. Pyrolyze it at a constant temperature of 800℃ for 1 hour to obtain a black solid product. Wash it with 3mol / L dilute hydrochloric acid solution to remove inorganic impurities. Then wash it with water and dry it to obtain an ordered porous carbon support (PC).

[0066] (B) Mix 0.06g of PC, 0.085g of nickel sulfate, 0.065g of ferric sulfate and 1.328g of glucose, grind and weigh, and mix with melamine at a mass ratio of 1:8, grind again to obtain the precursor;

[0067] (C) The precursor was placed in a muffle furnace under N2 atmosphere and calcined at 900℃ for 2 hours. After cooling, the obtained product was taken out and ground to obtain a nickel-iron bimetallic site single-atom catalyst (NiFe-NC DSAC).

[0068] (D) Weigh 0.01 g of NiFe-NC DSAC sample and add it to a dispersion consisting of 1200 μL of anhydrous ethanol, 800 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat the sample onto a carbon cloth (CF) substrate (coating amount 2.0 mg / cm²). 2 After drying, the anode is obtained and is denoted as NiFe-NC / CF.

[0069] The above-mentioned apparatus is used for the electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal. The method is as follows:

[0070] Step 1: Select 25 mL of simulated ammonia nitrogen wastewater (pH value 12, initial ammonia nitrogen concentration 350 mg / L) with similar composition to the actual wastewater and let it stay in the equalization tank for 10 minutes to balance the water quality and quantity;

[0071] Step 2: Wastewater enters the electrolytic cell through the inlet pump and delivery pipeline. An external power supply applies a voltage of 1.8V to the anode and cathode to carry out an electrochemical reaction to remove ammonia nitrogen from the wastewater. During the reaction, the wastewater is circulated internally through the internal circulation pipeline by the primary booster pump. The hydraulic retention time in the electrolytic cell is 5 hours, and the ammonia nitrogen removal rate is 99.16%.

[0072] Step 3: After treatment, the wastewater that meets the standards is pumped into the storage tank through the infusion pipeline by the secondary booster pump and discharged periodically.

[0073] Example 3:

[0074] The device structure in Example 3 is the same as that in Example 1; wherein the cathode is 1cm 2A rectangular Cu sheet; the anode consists of a conductive substrate (ITO) and a nickel-cobalt bimetallic site single-atom catalyst (NiCo-N-CDSAC) supported on the conductive glass, with an anode area of ​​4 cm². 2 ;

[0075] The method for preparing the anode is as follows:

[0076] (A) Weigh 8g of sodium citrate and place it in a muffle furnace under an argon (Ar) atmosphere. Pyrolyze it at a constant temperature of 800℃ for 1 hour to obtain a black solid product. Wash it with 6mol / L dilute nitric acid solution to remove inorganic impurities. Then wash it with water and dry it to obtain an ordered porous carbon support (PC).

[0077] (B) Mix 0.06g of PC, 0.088g of nickel nitrate, 0.088g of cobalt nitrate and 1.328g of glucose, grind and weigh, and mix with urea at a mass ratio of 1:5, grind again to obtain the precursor;

[0078] (C) The precursor was placed in a muffle furnace under an Ar atmosphere and calcined at 950°C for 2 hours. After cooling, the obtained product was taken out and ground to obtain a nickel-cobalt bimetallic site single-atom catalyst (NiCo-NC DSAC).

[0079] (D) Weigh 0.01 g of NiCo-NC DSAC sample and add it to a dispersion consisting of 800 μL of anhydrous ethanol, 1200 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat the sample onto a conductive glass (ITO) substrate (coating amount 1.0 mg / cm²). 2 After drying, the anode is obtained and denoted as NiCo-NC / ITO.

[0080] The above-mentioned apparatus is used for the electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal. The method is as follows:

[0081] Step 1: Select 100 mL of simulated ammonia nitrogen wastewater (pH value 12, initial ammonia nitrogen concentration 1400 mg / L) with similar composition to the actual wastewater and let it stay in the equalization tank for 10 minutes to balance the water quality and quantity;

[0082] Step 2: Wastewater enters the electrolytic cell through the inlet pump and delivery pipeline. A voltage of 2.0V is applied to the anode and cathode by an external power supply to carry out an electrochemical reaction to remove ammonia nitrogen from the wastewater. During the reaction, the wastewater is circulated internally through the internal circulation pipeline by the primary booster pump. The hydraulic retention time in the electrolytic cell is 12 hours, and the ammonia nitrogen removal rate is 99.05%.

[0083] Step 3: After treatment, the wastewater that meets the standards is pumped into the storage tank through the infusion pipeline by the secondary booster pump and discharged periodically.

[0084] Example 4:

[0085] The device structure in Example 4 is the same as that in Example 1; wherein the cathode is 2cm. 2 The anode consists of a rectangular Cu sheet; the anode comprises a conductive titanium substrate (TB) and a nickel-zinc bimetallic site single-atom catalyst (NiZn-NC DSAC) supported on the titanium substrate, with an anode area of ​​10 cm². 2 ;

[0086] The method for preparing the anode is as follows:

[0087] (A) Weigh 10g of sodium dihydrogen citrate and place it in a muffle furnace under a nitrogen (N2) atmosphere. Pyrolyze it at a constant temperature of 800℃ for 1 hour to obtain a black solid product. Wash it with 4mol / L dilute sulfuric acid solution to remove inorganic impurities. Then wash it with water and dry it to obtain an ordered porous carbon support (PC).

[0088] (B) Mix 0.06g of PC, 0.088g of nickel nitrate, 0.070g of zinc nitrate and 1.328g of glucose, grind and weigh, and mix with dicyandiamide at a mass ratio of 1:10, and grind again to obtain the precursor;

[0089] (C) The precursor was placed in a muffle furnace under N2 atmosphere and calcined at 950°C for 2 hours. After cooling, the obtained product was taken out and ground to obtain a nickel-zinc bimetallic site single-atom catalyst (NiZn-NC DSAC).

[0090] (D) Weigh 0.01 g of NiZn-NC DSAC sample and add it to a dispersion consisting of 1000 μL of anhydrous ethanol, 1000 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat the sample onto a titanium (TB) substrate (coating amount 1.5 mg / cm²). 2 After drying, the anode is obtained and denoted as NiZn-NC / TB.

[0091] The above-mentioned apparatus is used for the electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal. The method is as follows:

[0092] Step 1: Select 200 mL of simulated ammonia nitrogen wastewater (pH value 13, initial ammonia nitrogen concentration 720 mg / L) with similar composition to the actual wastewater and let it stay in the equalization tank for 10 minutes to balance the water quality and quantity;

[0093] Step 2: Wastewater enters the electrolytic cell through the inlet pump and delivery pipeline. A voltage of 2.2V is applied to the anode and cathode by an external power supply to carry out an electrochemical reaction to remove ammonia nitrogen from the wastewater. During the reaction, the wastewater is circulated internally through the internal circulation pipeline by the primary booster pump. The hydraulic retention time in the electrolytic cell is 14 hours, and the ammonia nitrogen removal rate is 99.17%.

[0094] Step 3: After treatment, the wastewater that meets the standards is pumped into the storage tank through the infusion pipeline by the secondary booster pump and discharged periodically.

[0095] Example 5:

[0096] The device structure in Example 5 is the same as that in Example 1; wherein the cathode is 2cm. 2 A rectangular Cu sheet; the anode consists of a conductive substrate (ITO) and a nickel-manganese bimetallic site single-atom catalyst (NiMn-N-CDSAC) supported on the conductive glass, with an anode area of ​​10 cm². 2 ;

[0097] The method for preparing the anode is as follows:

[0098] (A) Weigh 10g of sodium citrate and place it in a muffle furnace under a nitrogen (N2) atmosphere. Pyrolyze it at a constant temperature of 800℃ for 1 hour to obtain a black solid product. Wash it with 5mol / L dilute sulfuric acid solution to remove inorganic impurities. Then wash it with water and dry it to obtain an ordered porous carbon support (PC).

[0099] (B) Mix 0.06g of PC, 0.069g of nickel acetate, 0.068g of manganese acetate and 1.328g of glucose, grind and weigh, and mix with thiourea at a mass ratio of 1:5, and grind again to obtain the precursor;

[0100] (C) The precursor was placed in a muffle furnace under N2 atmosphere and calcined at 700℃ for 2 hours. After cooling, the obtained product was taken out and ground to obtain a nickel-manganese bimetallic site single-atom catalyst (NiMn-NC DSAC).

[0101] (D) Weigh 0.01 g of NiMn-NC DSAC sample and add it to a dispersion consisting of 800 μL of anhydrous ethanol, 1200 μL of water, and 40 μL of 5 wt.% Nafion membrane solution. After ultrasonic homogenization, coat the sample onto a conductive glass (ITO) substrate (coating amount 1.8 mg / cm²). 2 After drying, the anode is obtained and denoted as NiMn-NC / ITO.

[0102] The above-mentioned apparatus is used for the electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal. The method is as follows:

[0103] Step 1: Select 150 mL of simulated ammonia nitrogen wastewater (pH value 11, initial ammonia nitrogen concentration 608 mg / L) with similar composition to the actual wastewater and let it stay in the equalization tank for 10 minutes to balance the water quality and quantity;

[0104] Step 2: Wastewater enters the electrolytic cell through the inlet pump and delivery pipeline. A voltage of 2.0V is applied to the anode and cathode by an external power supply to carry out an electrochemical reaction to remove ammonia nitrogen from the wastewater. During the reaction, the wastewater is circulated internally through the internal circulation pipeline by the primary booster pump. The hydraulic retention time in the electrolytic cell is 10 hours, and the ammonia nitrogen removal rate is 98.84%.

[0105] Step 3: After treatment, the wastewater that meets the standards is pumped into the storage tank through the infusion pipeline by the secondary booster pump and discharged periodically.

[0106] Comparative Example 1:

[0107] In the apparatus of Comparative Example 1, the catalyst supported on the anode was a nickel single-atom catalyst (Ni-NC SAC). In the anode preparation process, copper sulfate was not added in step (B), and the rest was the same as in Example 1.

[0108] Comparative Example 2:

[0109] In the apparatus of Comparative Example 2, the catalyst supported on the anode was a copper single-atom catalyst (Cu-NC SAC). In the anode preparation process, step (B) did not add nickel sulfate, and the rest was the same as in Example 1.

[0110] Comparative Example 3:

[0111] In the apparatus of Comparative Example 3, the anode was a Ni1Cu3-ST / CP catalytic electrode prepared by the method in Example 1 of patent CN202111073952.2, and the rest were the same as in Example 1.

[0112] Comparative Example 4:

[0113] In the apparatus of Comparative Example 4, the anode was a nanoscale nickel-copper bimetallic catalytic electrode (Ni1Cu1Co). 0.5 -ST / CP), the preparation method is as follows: pretreated carbon paper (CP, 1×1cm) is prepared by... 2 The platinum wire was fixed in an electrode holder as the working electrode of a three-electrode system, while the platinum wire and Hg / HgO served as the counter and reference electrodes, respectively. CP was electrodeposited at a deposition voltage of -1.3V for 120s, followed by alkaline electrochemical tuning in 1M NaOH solution using cyclic voltammetry (30 cycles) to obtain Ni1Cu1Co. 0.5-ST / CP catalytic electrode. The deposition electrolyte composition includes NiNO3·6H2O (0.40 mmol), CuNO3·3H2O (0.4 mmol), CoNO3·6H2O (0.20 mmol), urea (5.00 mmol), and thiourea (4.00 mmol);

[0114] Everything else is the same as in Example 1.

[0115] The anodic catalyst NiCu3-NC DSAC prepared in Example 1 was tested by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), as follows: Figure 3 As shown in the image, the support is a nitrogen-doped ordered porous carbon framework with numerous bright spots associated with Ni and Cu atoms on its surface, confirming the highly dispersed atomic structure. This is attributed to the metal-nitrogen coordination bonding, which creates an isolated state for the metal atoms. Furthermore, the surrounding bright spots of adjacent atoms also confirm the presence of bimetallic atomic sites.

[0116] The performance of the anodes prepared in the above examples and comparative examples in the electrocatalytic ammonia oxidation denitrification reaction was investigated. The method was as follows: Using a CHI 604E electrochemical workstation, with NiCu3-NC / CP as the working electrode, platinum wire as the counter electrode, and a mercury / mercury oxide electrode as the reference electrode, the electrochemical activity of the catalyst was tested using linear sweep voltammetry in a 1M NaOH + 0.2M NH4Cl solution. Then, given an operating potential of 0.6V vs. Hg / HgO, electrocatalytic ammonia oxidation treatment was carried out for 5 hours in simulated wastewater with ammonia nitrogen concentrations of 350, 700, and 1400 mg / L, respectively, to explore the catalyst's treatment capacity per unit time. The results are as follows: Figures 4-6 As shown in the image.

[0117] Figure 4 The LSV test results showed that, compared with the Ni-NC (Comparative Example 1) and Cu-NC (Comparative Example 2) single-atom catalysts, the NiCu3-NC DSAC prepared by the method of the present invention in Example 1 showed significantly improved electrochemical activity, achieving 90 mA / cm². 2 Maximum AOR current density, lowest onset potential (1.210V vs. RHE@5mA / cm) 2 Maximum switching frequency (TOF: 3.64s) -1 ).

[0118] like Figure 5As shown in Figure a, from a cost-effectiveness perspective over a 5-hour timeframe, the electrocatalytic ammonia oxidation is most efficient when the initial concentration is 700 mg / L. Further increasing the initial concentration leads to a decrease in efficiency, as the atomic sites become saturated within a given time. At this point, the catalyst achieves a 98.74% ammonia nitrogen removal rate and a 85.27% Faradaic efficiency, realizing highly efficient electrocatalytic ammonia oxidation. Simultaneously, its nitrogen selectivity reaches a high 97.87%, almost achieving complete nitrogen removal. Figure 5 b).

[0119] Finally, given an operating potential of 0.6 V vs. Hg / HgO, electrocatalytic ammonia oxidation was performed for 6 hours in actual ammonia nitrogen wastewater with a concentration of approximately 616 mg / L. Figure 6 As can be seen from this, compared to Ni1Cu3-ST / CP (Comparative Example 3) and Ni1Cu1Co 0.5 Two nanoscale catalysts, ST and CP (Comparative Example 4), showed that the atomic-scale NiCu3-NC DSAC exhibited excellent electrocatalytic ammonia oxidation performance. The ammonia nitrogen removal rate in the electrocatalytic ammonia oxidation system using this catalyst reached 99.72%, achieving a Faraday efficiency of 86.60% and a yield of 0.05 kW·h kg⁻¹. -1 Energy consumption for nitrogen (N). It is noteworthy that, compared to nanoscale catalysts, the NiCu3-NC DSAC significantly reduces nitrate content in the electrolysis system while simultaneously producing nitrogen through electrocatalytic ammonia oxidation. This is attributed to two factors: firstly, the cathode electrochemically reduces nitrate, while the highly selective ammonia oxidation at the anode greatly inhibits or even eliminates nitrate formation. In short, the NiCu3-NC DSAC and the electrolysis device constructed using it hold promise for achieving complete nitrogen removal from ammonia wastewater.

Claims

1. A method for the electrochemical oxidation of ammonia nitrogen wastewater for complete denitrification using an ammonia nitrogen wastewater electrochemical oxidation denitrification device, characterized in that, The process includes the following steps: Ammonia nitrogen wastewater enters an electrochemical oxidation denitrification device to remove ammonia nitrogen from the wastewater through an electrochemical reaction. After the wastewater treatment meets the standards, it is transferred to a storage tank through a pipeline and discharged periodically. The device for electrochemical oxidation of ammonia nitrogen wastewater for complete nitrogen removal includes an equalization tank (1), an electrolytic cell (2), and a water storage tank (11) connected in sequence via a liquid delivery pipeline (9); the electrolytic cell (2) is equipped with an anode (4) and a cathode (5), and the anode and cathode are respectively connected to an external power source (3) via wires (10); the anode includes a conductive substrate and a bimetallic site single-atom catalyst supported on the conductive substrate; the cathode is selected from one of Pt electrode, Cu electrode, stainless steel electrode, graphite electrode, and nickel electrode; The bimetallic site single-atom catalyst was prepared by the following steps: (A) Citrate was pyrolyzed under an inert atmosphere, washed sequentially with acid solution and water, and dried to obtain an ordered porous carbon support; (B) The ordered porous carbon support, metal salt M1, metal salt M2 and glucose are mixed and ground to obtain a mixture; the mixture is then mixed with a nitrogen source and ground to obtain a precursor; metal salt M1 is selected from one of nickel sulfate, nickel chloride, nickel bromide, nickel nitrate and nickel acetate; metal salt M2 is selected from one of the sulfate, chloride, nitrate and acetate of copper, iron, cobalt, manganese and zinc. (C) The precursor is pyrolyzed under an inert atmosphere, cooled and then ground to prepare a bimetallic site single-atom catalyst.

2. The method according to claim 1, characterized in that, The electrolytic cell (2) is provided with an ion exchange membrane (12) for separating the anode (4) and the cathode (5).

3. The method according to claim 1 or 2, characterized in that, The bottom of the electrolytic cell outlet side and the top of the electrolytic cell inlet side are connected by an internal circulation pipeline (13). A first-stage booster pump (7) is provided on the side of the internal circulation pipeline located at the electrolytic cell outlet side. An inlet pump (6) is provided on the liquid delivery pipeline (9) between the regulating tank (1) and the electrolytic cell (2). A second-stage booster pump (8) is provided on the liquid delivery pipeline (9) between the electrolytic cell (2) and the water storage tank (11).

4. The method according to claim 1, characterized in that, The external power supply (3) is a DC voltage regulator with an effective voltage of 0~200 V and an effective current of 0~20 A.

5. The method according to claim 1, characterized in that, The surface area ratio of the anode (4) to the cathode (5) is 0.1~100; the loading of the bimetallic site single-atom catalyst in the anode is 0.001~10 mg / cm³. 2 .

6. The method according to claim 1 or 5, characterized in that, The conductive substrate in the anode is selected from one of the following: carbon fiber paper, carbon fiber cloth, graphite felt, nickel foam, copper foam, titanium plate, boron-doped diamond film, ruthenium-iridium electrode plate, DSA electrode, and conductive glass.

7. The method according to claim 1, characterized in that, The citrate in step (A) is selected from one or more of trisodium citrate, potassium citrate, potassium dihydrogen citrate, and sodium dihydrogen citrate; the acid solution is selected from one of sulfuric acid, hydrochloric acid, and nitric acid; the concentration of the acid solution is 1.0~8.0 mol / L; the pyrolysis temperature in step (A) is 700~900℃, and the pyrolysis time is 0.5~3h; In step (B), the nitrogen source is selected from one or more of dicyandiamide, melamine, urea, and thiourea; in the mixture in step (B), the molar ratio of metal ions in metal salt M1 and metal salt M2 is 1:0.5~5; the ratio of the amount of ordered porous carbon support, metal ions in metal salt M1, and glucose added is 0.06g:0.3~0.5mmol:1.2~1.5g; the mass ratio of the mixture to the nitrogen source in the precursor is 1:5~10; The pyrolysis temperature in step (C) is 600~1000℃, and the pyrolysis time is 1~3h.

8. The method according to claim 1, characterized in that, The hydraulic retention time in the electrolytic cell is 5~24 h; the wastewater is circulated internally through the internal circulation pipeline during the reaction process in the electrolytic cell.

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