Method for comprehensively recovering nitrogen, phosphorus and carbon pollutants in wastewater and waste gas through electrolytic process

Abstract

The invention relates to a method for comprehensively recovering carbon, nitrogen and phosphorus pollutants in waste water and waste gas through an electrolytic process, which comprises the following steps: preparing cerium oxide supported NH2-MIL-88B through a one-step hydrothermal method, and deriving cerium oxide dispersed atomic-scale iron rich in vacancy through high-temperature carbonization; the material prepared in the first step is used as a cathode, titanium dioxide is used as an anode, and the cathode and the anode are separated by a proton exchange membrane; ultra-low voltage is provided through direct current, nitrate, nitrite and carbon dioxide are reduced into urea in the cathode region under current driving, and magnesium ions are separated out from natural magnesite in the electrolytic process of the anode region; when the concentration of the magnesium ions reaches 100 ppm, the solution in the anode region is introduced into the cathode region through a peristaltic pump, and the local environment is adjusted to enable ammonia nitrogen, phosphate radicals and the magnesium ions to generate struvite precipitates under the appropriate alkaline condition. The method provides a new thought, can efficiently recover nutrient substances such as carbon, nitrogen and phosphorus in the industrial wastewater, and provides technical support for recycling of the industrial wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of waste gas and sewage treatment, and in particular to a method for comprehensively recovering nitrogen, phosphorus and carbon pollutants in waste water and waste gas by electrolysis. Background Art

[0002] At present, the global population is constantly increasing, the world's economy is also constantly developing, and human demand for food is growing. In the field of agriculture, in the past century, food grown with nitrogen fertilizers has fed about 27% of the world's population. Among them, urea is considered to be one of the important nitrogen fertilizers due to its high nitrogen content (nitrogen content of 46%), so sustainable urea production is of great significance to meet the growing population demand. At present, the industrial synthesis of urea mainly includes two steps: first, ammonia (NH3) is synthesized from nitrogen (N2) and hydrogen (H2), and then urea is synthesized from ammonia and carbon dioxide (CO2).

[0003] In the process of implementing the technical method of the embodiment of the present invention, the inventor of this patent found at least the following technical problems in the prior art: 1. High energy consumption: The traditional ammonia synthesis process (Haber-Bosch reaction) needs to be carried out at high temperature (generally 400-500°C) and high pressure (150-300 atm), which leads to huge energy consumption. It is estimated that this reaction consumes about 2% of the world's energy each year, increasing production costs and exacerbating the environmental burden.

[0004] 2. High carbon emissions: Since the Haber-Bosch reaction requires a large amount of fossil fuels (mainly natural gas) to provide hydrogen, the entire process is accompanied by significant carbon dioxide emissions. This is contrary to the current sustainable development goals, and it is necessary to find more environmentally friendly synthesis routes to reduce carbon footprints.

[0005] 3. Complex production process: The synthesis process of urea involves multiple reaction steps and complex equipment, and usually needs to go through multiple stages such as ammonia synthesis and reaction of ammonia with carbon dioxide, which increases the complexity of the production process and maintenance costs.

[0006] 4. Low conversion efficiency: Although the traditional process can improve the conversion rate by optimizing the reaction conditions, there are still many reaction steps and losses, which makes the efficiency of resource and raw material utilization fail to reach the best.

[0007] 5. Environmental impact: In addition to greenhouse gas emissions, traditional urea production may still cause environmental problems such as nitrogen oxide emissions, which will burden the atmosphere and water bodies and affect the health of the ecosystem.

[0008] 6. Dependence on raw materials: The existing process is highly dependent on the sources of raw materials such as nitrogen and hydrogen, which may affect the production stability and cost of urea in the event of resource shortages or price fluctuations.

[0009] 7. By-product and waste disposal issues: Various by-products or wastes may be generated during the production process, which increases the difficulty and cost of disposal and also imposes a burden on the environment.

[0010] 8. High equipment investment and maintenance costs: Due to the complex process, the required equipment investment and daily maintenance costs are high, which affects the economic feasibility of urea production, especially for small-scale producers.

[0011] In summary, the existing urea synthesis process has significant defects in energy consumption, environmental impact, production process complexity and economy, which poses a challenge to the sustainable development of nitrogen fertilizer production. Therefore, it is urgent to develop more efficient and green alternative technologies to improve the urea synthesis process to meet the growing food demand and environmental protection requirements. Summary of the invention

[0012] The present invention relates to a method for comprehensive recovery of nitrogen, phosphorus and carbon pollutants in wastewater and waste gas by electrolysis, and in particular to an efficient and green treatment technology, which aims to simultaneously recover nitrogen, phosphorus and other resources by electrochemical means and achieve purification of wastewater and waste gas.

[0013] A method for comprehensive recovery of nitrogen, phosphorus and carbon pollutants in waste water and waste gas by electrolysis, comprising the following steps: Step 1: Prepare cathode: Prepare NH2-MIL-88B supported by ceria by one-step hydrothermal method, and derive vacancy-rich ceria-dispersed atomic-level iron by high-temperature carbonization; Step 2: Build an H-type electrolysis device: Use the material prepared in the first step as the cathode, titanium dioxide as the anode, separate the cathode and anode regions with a proton exchange membrane, and introduce the gas, electrolyte, nitrogen and phosphorus waste liquid and natural magnesite used in the experiment into the cathode and anode regions; The third step is electrochemical experiment: ultra-low voltage is provided by direct current. Under the drive of current, nitrate, nitrite and carbon dioxide are reduced to urea in the cathode area. The special environment generated during the electrolysis process in the anode area will promote the precipitation of magnesium ions from natural magnesite. When the magnesium ion concentration reaches 100 ppm, the anode area solution is introduced into the cathode area through a peristaltic pump to adjust the local environment so that ammonia nitrogen, phosphate and magnesium ions form struvite precipitation under a suitable alkalinity environment.

[0014] Optionally, in the first step, the raw materials include ferric chloride hexahydrate, cerium oxide, 2-aminoterephthalic acid, and N,N-dimethylformamide. Ferric chloride hexahydrate, cerium oxide, and 2-aminoterephthalic acid are added to an N,N-dimethylformamide solution in a molar ratio of 1:1:1, ultrasonically stirred until uniformly mixed, and then placed in a reactor and heated at 160 degrees Celsius for 12 hours; after cooling to room temperature, centrifugal drying, grinding and sieving are obtained to obtain NH2-MIL-88B@CeO2; NH2-MIL-88B@CeO2 is further carbonized to derive atomic-level iron dispersed in vacancy-rich cerium oxide, and the temperature, gas atmosphere and time need to be controlled; the prepared material is coated on a 5*5 cm foam copper substrate as a cathode for standby use.

[0015] Optionally, in the second step, 5*5 cm titanium dioxide is selected as the anode, the wastewater is prepared according to the actual ratio of nitrate, nitrite and ammonia nitrogen in the water body, the carbon dioxide waste gas discharged by the enterprise is used as the source of carbon dioxide, and natural dolomite is selected as the granular electrode and placed into the anode area.

[0016] Optionally, in the third step, the electrochemical test improves the conversion rate of urea and reduces the production of by-product ammonia nitrogen by means of constant potential and pulse potential, wherein the multi-stage potential is -0.3--0.9 V vs. RHE, and the cathode and anode electrolysis process is used to generate an acidic and alkaline environment, and the anode acidic environment dissolves natural magnesite to precipitate magnesium ions, providing a magnesium source for the subsequent preparation of struvite; after the natural magnesite releases the magnesium source in the anode area, it is introduced into the cathode area through a peristaltic pump, thereby providing general conditions for the formation of struvite; in addition to the magnesium source, ammonia nitrogen and phosphate, the formation of struvite also requires a pH value of 8-10, and a pulse potential, that is, a positive and negative voltage cycle, is used to generate hydroxyl radicals on the electrode surface of the cathode area during the negative voltage period, thereby promoting the magnesium ions, ammonia nitrogen and phosphate on the electrode surface to form struvite.

[0017] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: Efficient removal of harmful pollutants: The present invention can effectively remove nitrogen, phosphorus and carbon pollutants in wastewater and waste gas, especially in the cathode area, it can efficiently convert nitrate, nitrite and carbon dioxide into urea, significantly reducing environmental pollution. Resource recovery and reuse: Urea and struvite (slow-release fertilizer) are produced by this method, and waste is converted into reusable resources, which embodies the concept of "waste utilization" and promotes the recycling of resources. Green and environmentally friendly treatment process: This method uses ultra-low voltage direct current drive, does not require the use of a large amount of chemicals, reduces secondary pollution and energy consumption, and has good environmental performance. Simple process and convenient operation: The entire electrolysis process is relatively simple, easy to operate in practical applications, and suitable for large-scale production and application. Innovation of magnesium ion precipitation mechanism: The special environment generated in the anode area promotes the precipitation of magnesium ions from natural magnesite, creating ideal conditions for subsequent struvite precipitation and improving the overall treatment efficiency. Wide adaptability and customizability: This method is suitable for various nitrogen and phosphorus wastewaters, and the environmental conditions can be adjusted according to actual needs, which enhances the flexibility and adaptability of the process. Improve economic benefits: Through efficient pollutant treatment and resource conversion, the treatment cost is reduced, and new economic value may be created for related industries. Promote sustainable development: This technology meets the needs of sustainable development, can effectively combine wastewater and waste gas treatment with resource recovery, and provides new ideas for environmental protection and resource utilization. Through the above effects, the method of the present invention has important application value and potential market prospects in promoting the advancement of pollutant treatment technology and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The performance diagram of electrochemical urea synthesis in one embodiment of the present invention is compared with other research performance diagrams; Figure 2 This is a graph showing the concentration of magnesium ions deposited at the anode in one embodiment of the present invention; Figure 3 This is the XRD spectrum of struvite generated in one embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention relates to a method for comprehensive recovery of nitrogen, phosphorus and carbon pollutants in wastewater and waste gas by electrolysis, and in particular to an efficient and green treatment technology, which aims to simultaneously recover nitrogen, phosphorus and other resources by electrochemical means and achieve purification of wastewater and waste gas.

[0020] 1. Overview of steps Preparation of cathode: Ceria-supported NH2-MIL-88B was prepared by a one-step hydrothermal method, and vacancy-rich ceria-dispersed atomic-scale iron was subsequently derived by high-temperature carbonization to enhance the electrocatalytic performance of the cathode and the efficiency of the nitridation reaction.

[0021] Build an H-type electrolysis device: The device uses the material prepared in the first step as the cathode and titanium dioxide as the anode. The cathode and anode regions are separated by a proton exchange membrane to ensure effective operation under different reaction environments. The gases, electrolytes, nitrogen and phosphorus waste liquids, and natural magnesite required for the experiment are introduced into the corresponding cathode and anode regions.

[0022] Electrochemical experiments: Driven by direct current, a low-voltage electrochemical reaction is implemented, and the cathode area reduces nitrate, nitrite and carbon dioxide to urea. The anode area creates a specific environment to promote the precipitation of magnesium ions in natural magnesite. When the magnesium ion concentration reaches 100 ppm, a peristaltic pump is used to introduce the anode area solution into the cathode area to adjust the local environment so that ammonia nitrogen, phosphate and magnesium ions are precipitated into struvite under suitable alkalinity conditions, achieving efficient resource recovery.

[0023] 2. Step details 1. Cathode Preparation Details The raw materials used include ferric chloride hexahydrate, cerium oxide, 2-aminoterephthalic acid and N,N-dimethylformamide. After mixing in a molar ratio of 1:1:1, ultrasonic stirring is performed, followed by hydrothermal reaction at 160°C for 12 hours. After the reaction is completed, it is cooled, centrifuged, dried, and then ground and sieved to obtain the amino monitor NH2-MIL-88B@CeO2. Atomic-level iron dispersed with vacancy-rich cerium oxide is prepared through a subsequent carbonization step, and finally coated on a 5*5 cm foam copper substrate as a cathode.

[0024] 2. Construction details of H-type electrolysis device The titanium dioxide anode is selected with a specification of 5*5 cm. The ratio of nitrate, nitrite and ammonia nitrogen in the prepared wastewater conforms to the actual water condition. At the same time, the carbon dioxide waste gas discharged by the enterprise is selected as the CO2 source, and natural dolomite particles are added as auxiliary electrodes.

[0025] 3. Electrochemical testing method Constant potential and pulse potential were used in the experiment to improve the urea conversion rate and reduce the generation of byproduct ammonia nitrogen. The multi-stage potential was cycled in the range of -0.3 to -0.9 V vs. RHE. The acidic environment of the anode can promote the release of magnesium ions from natural magnesite, thereby providing the necessary magnesium source for the formation of struvite. After the magnesium ions released from the anode area were introduced, the pH value was adjusted to 8-10, and the pulse potential was used to generate hydroxyl radicals in the cathode area, which promoted the reaction of magnesium ions, ammonia nitrogen and phosphate, and finally formed struvite.

[0026] Based on the redox reaction of direct current on nitrogen and phosphorus in wastewater and carbon dioxide in waste gas, the present invention adopts H-type electrolysis, with FeNC dispersed with oxygen-rich CeO2 as cathode, titanium dioxide plate as anode, and the cathode and anode areas separated by a proton exchange membrane; pollutants (carbon dioxide, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen and phosphate) are placed in the cathode area, and an appropriate amount of natural minerals (natural magnesite) are added to the anode area. Nitrate nitrogen, nitrite nitrogen and carbon dioxide are coupled into urea through the cathode, and the acidic environment generated in the anode area causes natural magnesite to dissolve magnesium ions. After the cathode and cathode are mixed and the pH of the solution is adjusted, the unused ammonia nitrogen, phosphate and magnesium ions are co-precipitated into struvite. Then process evaluation and economic evaluation are carried out.

[0027] The present invention is further described below in conjunction with embodiments Example 1: Electrochemical treatment of groundwater and factory exhaust gas in a northern city Step 1: Prepare the cathode Ceria-supported NH2-MIL-88B was synthesized by a one-step hydrothermal method, and vacancy-rich ceria-dispersed atomic-level iron was obtained by a high-temperature carbonization process to enhance its catalytic activity and electrochemical performance.

[0028] Step 2: Build an H-type electrolysis device An H-type electrolysis device was constructed, with the cathode material prepared in the first step as the cathode and titanium dioxide as the anode. The cathode and anode regions were separated by a proton exchange membrane. Carbon dioxide from industrial waste gas and pollutants such as nitrates, nitrites and phosphates were introduced into the cathode region; an appropriate amount of electrolyte and natural magnesite were introduced into the anode region to optimize the reaction conditions.

[0029] Step 3: Electrochemical Experiment Ultra-low current is provided by a DC power supply to drive the electrochemical reaction. Under the action of the current, the cathode area reduces nitrate, nitrite and carbon dioxide to urea. Figure 1 The urea yield obtained by this process is compared with the yield of the existing process, showing a significant efficiency improvement. The special environment formed during the electrolysis process in the anode area will promote the precipitation of magnesium ions in natural magnesite. Figure 2 The magnesium ion release concentration corresponding to different dosages of natural dolomite is shown. When the magnesium ion concentration reaches 100 ppm, the magnesium ions will be introduced into the cathode area, thereby adjusting the local environment, so that ammonia nitrogen, phosphate and magnesium ions form struvite precipitation under suitable alkalinity conditions. Figure 3 The struvite produced by this process is shown, and its crystal structure is completely consistent with the standard comparison card.

[0030] Step 4: Result evaluation The feasibility of the experiment was verified, and economic accounting and environmental impact assessment were carried out, ultimately confirming the feasibility of the process in engineering applications.

[0031] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for comprehensive recovery of nitrogen, phosphorus and carbon pollutants from waste water and waste gas by electrolysis, characterized in that: The steps include: Step 1: Prepare cathode: Prepare NH2-MIL-88B supported by ceria by one-step hydrothermal method, and derive vacancy-rich ceria-dispersed atomic-level iron by high-temperature carbonization; Step 2: Build an H-type electrolysis device: Use the material prepared in the first step as the cathode, titanium dioxide as the anode, separate the cathode and anode regions with a proton exchange membrane, and introduce the gas, electrolyte, nitrogen and phosphorus waste liquid and natural magnesite used in the experiment into the cathode and anode regions; The third step is electrochemical experiment: ultra-low voltage is provided by direct current. Under the drive of current, nitrate, nitrite and carbon dioxide are reduced to urea in the cathode area. The special environment generated during the electrolysis process in the anode area will promote the precipitation of magnesium ions from natural magnesite. When the magnesium ion concentration reaches 100 ppm, the anode area solution is introduced into the cathode area through a peristaltic pump to adjust the local environment so that ammonia nitrogen, phosphate and magnesium ions form struvite precipitation under a suitable alkalinity environment.

2. The method according to claim 1, characterized in that In the first step, the raw materials include ferric chloride hexahydrate, cerium oxide, 2-aminoterephthalic acid, and N,N-dimethylformamide. Ferric chloride hexahydrate, cerium oxide, and 2-aminoterephthalic acid are added to an N,N-dimethylformamide solution in a molar ratio of 1:1:1, ultrasonically stirred until uniformly mixed, and then placed in a reactor and heated at 160 degrees Celsius for 12 hours; after cooling to room temperature, centrifugal drying, grinding, and sieving are performed to obtain NH2-MIL-88B@CeO2; NH2-MIL-88B@CeO2 is further carbonized to derive atomic-level iron dispersed in cerium oxide rich in vacancies, and the temperature, gas atmosphere, and time need to be controlled; the prepared material is coated on a 5*5 cm foam copper substrate as a cathode for standby use.

3. The method according to claim 2, characterized in that In the second step, 5*5 cm titanium dioxide is selected as the anode, the wastewater is prepared according to the actual proportion of nitrate, nitrite and ammonia nitrogen in the water body, the carbon dioxide waste gas discharged by the enterprise is used as the source of carbon dioxide, and natural dolomite is selected as the granular electrode and placed in the anode area.

4. The method according to claim 3, characterized in that In the third step, the electrochemical test improves the conversion rate of urea and reduces the production of by-product ammonia nitrogen by means of constant potential and pulse potential, wherein the multi-stage potential is -0.3--0.9 V vs. RHE, and the cathode and anode electrolysis process is used to generate an acidic and alkaline environment, and the anode acidic environment dissolves the natural dolomite to precipitate magnesium ions, providing a magnesium source for the subsequent preparation of struvite; after the natural dolomite releases the magnesium source in the anode area, it is introduced into the cathode area through a peristaltic pump, thereby providing the general conditions for the formation of struvite; in addition to the magnesium source, ammonia nitrogen and phosphate, the formation of struvite also requires a pH value of 8-10, and a pulse potential, that is, a positive and negative voltage cycle, is used to generate hydroxyl radicals on the electrode surface of the cathode area during the negative voltage period, which promotes the magnesium ions, ammonia nitrogen and phosphate on the electrode surface to form struvite.

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