System and method for efficient electrocatalytic degradation of urea wastewater

Abstract

The invention provides a system and a method for efficient electrocatalytic degradation of urea wastewater, and belongs to the technical field of wastewater treatment. The system comprises a multi-electrode-plate electro-catalysis reaction tank, a plurality of anode plates and cathode plates which are alternately arranged are arranged in the reaction tank, anodes and cathodes are mesh electrodes, the anode plates are made of titanium-based ruthenium electrodes, and the cathode electrodes are made of one or more of pure titanium meshes or copper-based electrodes. The urea wastewater treatment efficiency is improved, the energy consumption is reduced and the service life of the electrode is prolonged by optimizing the electrode material, the multi-electrode plate design and the reaction condition, the water treatment device has the function of removing urea and total nitrogen at the same time, the removal rate of urea can reach 97% or above, and the removal efficiency of total nitrogen can reach 90% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a method and a device for efficiently degrading urea wastewater by electrocatalysis technology, which is widely applicable to the removal of urea pollutants in chemical wastewater, agricultural wastewater and domestic sewage. Background Art

[0002] As an important chemical raw material, urea is widely used in the chemical, pesticide, pharmaceutical and other industries, but it often produces a large amount of high-concentration urea wastewater. Since it cannot be directly treated in the enterprise sewage treatment system, otherwise the ammonia nitrogen and total nitrogen in the sewage treatment system effluent will not meet the discharge requirements, so necessary pretreatment is required. At present, some studies have used a large amount of water dilution and then biochemical treatment, but this method requires the addition of a large amount of external carbon source, which greatly increases the cost of wastewater treatment. At the same time, it will also greatly increase the amount of wastewater discharged, occupying the total amount of wastewater pollutant emissions, which is difficult for enterprises to bear. Although evaporation technology can greatly remove urea from wastewater, the high operating cost and the cost of hazardous waste disposal of evaporated salt residue are unacceptable to enterprises, resulting in some enterprises directly disposing of high-concentration urea wastewater as hazardous waste. Therefore, enterprises are in urgent need of economical and efficient treatment technology for urea-containing wastewater.

[0003] In recent years, electrocatalytic oxidation technology has gradually become a research hotspot for urea wastewater treatment due to its advantages such as high efficiency, environmental protection and strong controllability. This technology uses active species (hydroxyl radicals OH and active chlorine species) generated on the electrode surface to oxidize urea into harmless small molecule products (nitrogen, carbon dioxide and water), thereby achieving the removal of urea from wastewater. Compared with traditional methods, electrocatalytic oxidation has significant advantages: no additional chemical reagents are required, the oxidation efficiency is high, urea can be completely degraded in a short time, and only electricity is consumed, which is a green and environmentally friendly technology.

[0004] At present, the research on electrocatalytic oxidation degradation of urea mainly focuses on the research of anode materials, mainly including precious metal electrodes, transition metal electrodes and metal oxide electrodes. Precious metal electrodes such as Pt have the advantages of good stability, high oxygen evolution potential and strong catalytic activity, but they are expensive and difficult to achieve industrial application. Although transition metal catalysts have the advantages of low cost and high reserves, their degradation efficiency is not high when treating high-concentration urea wastewater. 3 S 2 / Co 3 O 4 -NF anode material, after continuous electrolysis of 0.5mol / L alkaline urea solution for 35 hours, the urea degradation efficiency reached 71%. Yang Lijun [2] The prepared bifunctional multi-level 2D / 3D hybrid structure of Co 2 P-CeO x Integrated electrode (Co2 P-CeO x / NF), in an alkaline solution containing 0.33 mol / L urea, the current density reached 30 mA / cm 2 When the electrocatalytic urea degradation efficiency reaches 76.4% after 10 hours. Another commonly used anode material is RuO 2 Composite metal oxide coating material electrode (DSA electrode). Simka et al. used Ti / (RuO 2 -TiO 2 )40:60 electrode treated 10g / L urea solution, and after 3h of electrocatalysis, the urea removal efficiency was 70%. Wang Yuqin used ruthenium-based electrode as anode to electrocatalyze 10mg / L simulated urea wastewater for 30min. Under the conditions of electrolyte dosage of 400mg / L and voltage of 20V, the urea removal efficiency was 77.62%.

[0005] The research on electrocatalytic oxidation degradation of urea is still in the experimental stage, and it still faces the following technical bottlenecks in practical engineering applications. First, the oxidation efficiency is limited. At low current density or when using ordinary electrode materials, the generation rate of oxidizing species is low, resulting in a degradation rate of urea that is insufficient to meet industrial needs. Secondly, the energy consumption is high, the activity of the electrode material is insufficient, and the internal resistance of the reaction system is large, so that the system usually requires a higher current density to achieve the ideal degradation efficiency, which significantly increases the energy consumption. In addition, the poor stability of the electrode is also an important problem. Some electrode materials are prone to corrosion or deactivation during long-term operation, resulting in a decrease in system performance and increased maintenance costs. Finally, at high current density, the oxygen evolution reaction may become the main side reaction, which not only wastes electrical energy, but also reduces the selectivity of urea oxidation. These technical bottlenecks urgently need further research and resolution to promote the practical application and development of electrocatalytic technology. Summary of the invention

[0006] In view of the above-mentioned problems, the present invention provides an electrocatalytic degradation system and method that can efficiently remove urea and reduce the total nitrogen concentration. By optimizing electrode materials, multi-electrode plate design and reaction conditions, the urea wastewater treatment efficiency is significantly improved, energy consumption is reduced, and the electrode life is extended, thereby providing a practical solution for the treatment of urea pollution.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A system for efficiently electrocatalytically degrading urea wastewater, the system comprising a multi-electrode electrocatalytic reaction tank, a wastewater storage tank connected to the bottom of the multi-electrode electrocatalytic reaction tank via a water inlet peristaltic pump, and an upper portion of the multi-electrode electrocatalytic reaction tank connected to the wastewater storage tank via a water outlet peristaltic pump;

[0009] A plurality of alternately arranged anode plates and cathode plates are arranged in the multi-polar plate electrocatalytic reaction tank. The anode and cathode are both mesh electrodes. The anode plate material is a titanium-based ruthenium electrode, and the cathode electrode is one or more of pure titanium mesh or copper-based electrodes.

[0010] In the technical solution of the present invention, the titanium-based ruthenium-based electrode is selected from one or more of a ruthenium-iridium-titanium electrode, a tin-ruthenium-titanium electrode or a pure ruthenium dioxide-based titanium electrode.

[0011] In the technical solution of the present invention, the titanium-based ruthenium-based electrode is prepared by thermal decomposition oxidation method, and the specific steps are:

[0012] Substrate pretreatment: The titanium mesh is pretreated by mechanical grinding, degreasing, ultrasonic cleaning, oxalic acid solution soaking and water cleaning in sequence to obtain a pretreated titanium mesh;

[0013] Preparation of active coating: Weigh tin tetrachloride and ruthenium trichloride in a molar ratio of 1 to 5:1, dissolve in a mixture of isopropanol and hydrochloric acid to obtain a solution with a total metal concentration of 0.5 to 1.5 M, and fully stir and dissolve to obtain a coating solution;

[0014] The coating liquid is applied to the surface of the pretreated titanium mesh, first placed in a blast drying oven at 85-95°C for 10-30 minutes, then transferred to a muffle furnace at 500-600°C for calcination for 10-20 minutes, taken out and cooled to room temperature before the next brushing; the above brushing-drying-calcining process is repeated 10-15 times, and finally calcined at 500-600°C for 0.5-1.5h to sinter into a titanium-based ruthenium electrode.

[0015] In the technical solution of the present invention, the distance between the anode plate and the cathode plate is 5-15 mm.

[0016] In the technical solution of the present invention, the anode plates and cathode plates are arranged in parallel or in a porous mesh format.

[0017] A method for realizing efficient electrocatalytic degradation of urea wastewater using the above system, wherein high-concentration urea wastewater is input into a reaction tank by a peristaltic pump for electrocatalytic degradation reaction, and the effluent solution is returned to a raw water storage tank by the effluent peristaltic pump for circulation treatment or discharged after meeting the requirements.

[0018] In the above preparation method, the current density is 10-40 mA / cm 2 , preferably: current density is 20~35mA / cm 2 .

[0019] In the above preparation method, the electrolysis time of the circulation treatment is 1 to 15 hours.

[0020] In the above preparation method, the flow rate of wastewater entering the reaction tank is 250 to 1500 mL / h.

[0021] In the above preparation method, an electrolyte is added to high-concentration urea wastewater, and the electrolyte is sodium sulfate and / or sodium chloride. Preferably, the sodium sulfate concentration in the wastewater is 0-0.1 mol / L; the sodium chloride concentration is 0-5000 mg / L.

[0022] Beneficial effects of the present invention:

[0023] The present invention improves the urea wastewater treatment efficiency, reduces energy consumption, and prolongs the electrode life by optimizing electrode materials, multi-electrode plate design, and reaction conditions. The water treatment device has the function of removing urea and total nitrogen at the same time. The process of the present invention can make the urea removal rate reach more than 97%, and the total nitrogen removal efficiency reach more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram of the reaction device of the present invention.

[0025] Figure 2 Urea and total nitrogen removal rates in Example 2.

[0026] Figure 3 Urea and total nitrogen removal rates in Example 3.

[0027] Figure 4 Urea and total nitrogen removal rates in Example 4.

[0028] Figure 5 Urea and total nitrogen removal rates in Example 5.

[0029] Among them: 1. Wastewater storage tank, 2. Multi-electrode electrocatalytic reaction tank, 3. Anode plate, 4. Cathode plate, 5. DC power supply, 6. Inlet peristaltic pump, 7. Outlet peristaltic pump. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with embodiments, but the protection scope of the present invention is not limited thereto:

[0031] like Figure 1 As shown, a system for electrocatalytic oxidation of urea wastewater includes a multi-electrode electrocatalytic reaction tank 2, a wastewater storage tank 1 connected to the bottom of the multi-electrode electrocatalytic reaction tank 2 through an inlet peristaltic pump 6, and an upper part of the multi-electrode electrocatalytic reaction tank 2 connected to the wastewater storage tank 1 through an outlet peristaltic pump; the system includes a multi-electrode electrocatalytic reaction tank 2, in which a plurality of alternating anode plates 3 and cathode plates 4 are arranged, and the spacing between the anode plates 3 and cathode plates 4 is 10 mm. The anode plates 3 and cathode plates 4 are arranged in parallel or in a porous mesh format.

[0032] The multi-electrode electrocatalytic reaction tank described in this embodiment is a 1000ml rectangular reaction tank made of organic glass.

[0033] The anode and cathode are both mesh electrodes, the anode plate material is a titanium-based ruthenium electrode, and the cathode electrode is a pure titanium mesh electrode. The titanium-based ruthenium electrode is prepared by thermal decomposition oxidation method, and the specific steps are:

[0034] Substrate pretreatment: The titanium mesh was pretreated by mechanical grinding, degreasing, ultrasonic cleaning, immersion in oxalic acid solution and water cleaning in sequence. The concentration of the oxalic acid solution was 12%, the immersion temperature was 90°C, and the immersion time was 1 h to obtain the pretreated titanium mesh.

[0035] Preparation of active coating: Weigh tin tetrachloride and ruthenium trichloride in a molar ratio of 3:1, dissolve in isopropanol and hydrochloric acid in a volume ratio of 15:1 to prepare a solution with a total metal concentration of 1M, and stir thoroughly to dissolve to obtain a coating solution.

[0036] The coating liquid was applied to the surface of the pretreated titanium mesh, placed in a 90°C forced air drying oven for 20 minutes, then transferred to a 550°C muffle furnace for calcination for 15 minutes, and then taken out and cooled to room temperature before the next brush coating. The above brush coating-drying-calcination process was repeated 13 times, and finally calcined at 550°C for 1 hour to sinter and form, thus obtaining a titanium-based ruthenium electrode.

[0037] The positive electrode of the DC power supply 5 is connected to the anode plate 3, and the negative electrode of the DC power supply 5 is connected to the cathode plate 4. The constant current density of the DC power supply involved is 5-30 mA / cm 2 .

[0038] In the circulation system, the water inlet peristaltic pump 6 is between the outlet of the wastewater storage tank 1 and the inlet of the electrocatalytic reaction tank 2, and the water outlet peristaltic pump 7 is between the outlet of the electrocatalytic reaction tank 2 and the inlet of the wastewater storage tank 1. The flow rate of the water inlet peristaltic pump device 6 is set to 250-1500mL / h. The sodium sulfate concentration in the wastewater is 0-0.1mol / L; the sodium chloride concentration is 0-5000mg / L.

[0039] The parameters involved in the above method, such as the electrolytic cell size, electrode size, current density, water inlet flow rate, voltage, etc., can be optimized according to the actual flow rate of the treated water sample.

[0040] Example 2

[0041] Water quality parameters are: urea concentration is 20000mg / L, total nitrogen concentration is 10000mg / L, electrolyte concentration is 0.01mol / L, sodium chloride concentration is 1000mg / L

[0042] Electrocatalytic reactor configuration: the anode material is titanium-based ruthenium electrode, the cathode is titanium electrode, the number of plates is 3 pairs, and the distance between the plates is 10 mm

[0043] Current density: 25mA / cm 2

[0044] Electrolysis time: 12h

[0045] Wastewater pH: 8.0

[0046] Circulation system flow rate: 1L / h

[0047] Experimental steps: High-concentration urea wastewater is input into the reaction tank 2 through the inlet peristaltic pump 6 for electrocatalytic degradation reaction. When the simulated wastewater fills the outlet, the DC power supply 5 is turned on. The DC power supply 5 operates in a constant current mode and returns the solution to the raw water storage tank through the outlet peristaltic pump 7. The current density is set to 25 mA / cm 2 , start the reaction and keep the system running stably, and continue electrolysis for 12 hours. Regularly check the urea concentration, total nitrogen concentration and system energy consumption during the reaction, and monitor the electrode surface condition.

[0048] Experimental results: Figure 2 As shown in the figure, when the reaction was carried out for 12 hours, the urea concentration dropped from 20000 mg / L to 57 mg / L, and the total nitrogen concentration dropped from 10000 mg / L to 896 mg / L. The urea removal rate reached 99%, and the total nitrogen removal rate was 91%. There was no obvious fouling or corrosion on the electrode surface, and the electrode performance was stable without failure. Because under the condition of less electrode plates, the electrocatalytic reaction efficiency is low and the reaction time is long.

[0049] Example 3

[0050] Water quality parameters are: urea concentration is 20000mg / L, total nitrogen concentration is 10000mg / L, sodium sulfate concentration is 0.01mol / L, sodium chloride concentration is 1000mg / L

[0051] Electrocatalytic reactor configuration: the anode material is titanium-based ruthenium electrode, the cathode is titanium electrode, the number of plates is 6 pairs, and the distance between the plates is 5 mm

[0052] Current density: 20mA / cm 2

[0053] Electrolysis time: 6h

[0054] Wastewater pH: 8.0

[0055] Circulation system flow rate: 0.5L / h

[0056] Experimental steps: High-concentration urea wastewater is input into the reaction tank 2 through the inlet peristaltic pump 6 for electrocatalytic degradation reaction. When the simulated wastewater fills the outlet, the DC power supply 5 is turned on. The DC power supply 5 operates in a constant current mode and returns the solution to the raw water storage tank 1 through the outlet peristaltic pump 7. The current density is set to 20 mA / cm 2 , start the reaction and keep the system running stably, and continue electrolysis for 6 hours. Regularly check the urea concentration, total nitrogen concentration and system energy consumption during the reaction, and monitor the electrode surface condition.

[0057] Experimental results: Figure 3 As shown in the figure, after 6 hours of electrocatalytic degradation, the urea concentration dropped from 20,000 mg / L to 32 mg / L, and the total nitrogen concentration dropped from 10,000 mg / L to 561 mg / L. The urea removal rate reached 99%, and the total nitrogen removal rate was 94%. This is because the number of plates increased, the electrode area involved in the reaction increased, and the amount of reactants that can be processed per unit time also increased, which promoted the improvement of pollutant removal efficiency. The reduction in the distance between the plates will also make the electric field strength between the plates higher, the mass transfer rate faster, and the generated active substances can reach the surface of the plates faster, promoting the oxidation of urea and other nitrogen compounds.

[0058] Example 4

[0059] Water quality parameters are: urea concentration 50000mg / L, total nitrogen concentration 23000mg / L, sodium sulfate concentration 0.1mol / L, sodium chloride concentration 5000mg / L

[0060] Electrocatalytic reactor configuration: the anode material is titanium-based ruthenium electrode, the cathode is titanium electrode, the number of plates is 8 pairs, and the distance between the plates is 5 mm

[0061] Current density: 35mA / cm 2

[0062] Electrolysis time: 8h

[0063] Wastewater pH: 8.0

[0064] Circulation system flow rate: 0.5L / h

[0065] Experimental steps: High-concentration urea wastewater is input into the reaction tank 2 through the inlet peristaltic pump 6 for electrocatalytic degradation reaction. When the simulated wastewater fills the outlet, the DC power supply 5 is turned on. The DC power supply 5 operates in a constant current mode and returns the solution to the raw water storage tank 1 through the outlet peristaltic pump 7. The current density is set to 35 mA / cm 2 , start the reaction and keep the system running stably, and continue electrolysis for 8 hours. Regularly check the urea concentration, total nitrogen concentration and system energy consumption during the reaction, and monitor the electrode surface condition.

[0066] Experimental results: Figure 4 As shown in the figure, after 8 hours of electrocatalytic degradation, the urea removal rate reached 97% and the total nitrogen removal rate reached 90%. When the urea concentration increases, the number of plates and the current density are increased, the driving force of the electrons is increased, the migration rate of the electrons between the plates is accelerated, and more active substances and active free radicals are prompted to participate in the reaction, so as to achieve the purpose of removing urea and total nitrogen. At the same time, increasing the concentration of electrolyte and sodium chloride will produce more active chlorine to increase the electrocatalytic indirect oxidation rate, so as to achieve the purpose of removing pollutants and reducing energy consumption.

[0067] Example 5

[0068] Water quality parameters are: urea concentration 30000mg / L, total nitrogen concentration 14000mg / L, sodium sulfate concentration 0.01mol / L, sodium chloride concentration 1000mg / L

[0069] Electrocatalytic reactor configuration: the anode material is a titanium-based ruthenium electrode, the cathode is a copper-based electrode, the number of plates is 12 pairs, and the plate spacing is 5 mm

[0070] Current density: 20mA / cm 2

[0071] Electrolysis time: 4h

[0072] Wastewater pH: 8.0

[0073] Circulation system flow rate: 1L / h

[0074] Experimental steps: High-concentration urea wastewater is input into the reaction tank 2 through the inlet peristaltic pump 6 for electrocatalytic degradation reaction. When the simulated wastewater fills the outlet, the DC power supply 5 is turned on. The DC power supply 5 operates in a constant current mode and returns the solution to the raw water storage tank 1 through the outlet peristaltic pump 7. The current density is set to 20 mA / cm 2 , start the reaction and keep the system running stably, and continue electrolysis for 4 hours. Regularly check the urea concentration, total nitrogen concentration and system energy consumption during the reaction, and monitor the electrode surface condition.

[0075] Experimental results: Figure 5 As shown in the figure, after 4 hours of electrocatalytic degradation, the urea removal rate reached 99% and the total nitrogen removal rate reached 97%. When the urea concentration increases, the number of plates is increased, and the area where the electrode reaction occurs increases. After increasing the surface area, the amount of urea that can be removed per unit time also increases. At the same time, the copper-based electrode of the cathode improves the removal efficiency of by-products, thereby achieving the purpose of improving the removal efficiency of total nitrogen under the high removal efficiency of urea.

Claims

1. A system for high-efficiency electrocatalytic degradation of urea wastewater, characterized in that: The system comprises a multi-electrode electrocatalytic reaction tank (2), a wastewater storage tank (1) connected to the bottom of the multi-electrode electrocatalytic reaction tank (2) via a water inlet peristaltic pump (6), and an upper part of the multi-electrode electrocatalytic reaction tank (2) connected to the wastewater storage tank (1) via a water outlet peristaltic pump; A plurality of alternately arranged anode plates (3) and cathode plates (4) are provided in the multi-polar plate electrocatalytic reaction tank (2); the anode and cathode are both mesh electrodes; the anode plate material is a titanium-based ruthenium electrode; the cathode electrode is one or more of a pure titanium mesh or a copper-based electrode.

2. The system for high-efficiency electrocatalytic degradation of urea wastewater according to claim 1 is characterized in that: The titanium-based ruthenium-based electrode is selected from one or more of a ruthenium-iridium-titanium electrode, a tin-ruthenium-titanium electrode or a pure ruthenium dioxide-based titanium electrode.

3. The system for high-efficiency electrocatalytic degradation of urea wastewater according to claim 2 is characterized in that: The titanium-based ruthenium electrode is prepared by thermal decomposition oxidation method, and the specific steps are as follows: Substrate pretreatment: The titanium mesh is pretreated by mechanical grinding, degreasing, ultrasonic cleaning, oxalic acid solution soaking and water cleaning in sequence to obtain a pretreated titanium mesh; Preparation of active coating: Weigh tin tetrachloride and ruthenium trichloride in a molar ratio of 1 to 5:1, dissolve in a mixture of isopropanol and hydrochloric acid to obtain a solution with a total metal concentration of 0.5 to 1.5 M, and fully stir and dissolve to obtain a coating solution; The coating liquid is applied to the surface of the pretreated titanium mesh, first placed in a blast drying oven at 85-95°C for 10-30 minutes, then transferred to a muffle furnace at 500-600°C for calcination for 10-20 minutes, taken out and cooled to room temperature before the next brushing; the above brushing-drying-calcining process is repeated 10-15 times, and finally calcined at 500-600°C for 0.5-1.5h to sinter into a titanium-based ruthenium electrode.

4. The system for high-efficiency electrocatalytic degradation of urea wastewater according to claim 1 is characterized in that: The distance between the anode plate (3) and the cathode plate (4) is 5-15 mm.

5. The system for high-efficiency electrocatalytic degradation of urea wastewater according to claim 1 is characterized in that: The anode plate (3) and the cathode plate (4) are arranged in parallel or in a porous mesh format.

6. A method for realizing efficient electrocatalytic degradation of urea wastewater using the system of claim 1, characterized in that: The method uses a peristaltic pump (6) to input high-concentration urea wastewater into a reaction tank (2) for electrocatalytic degradation reaction, and the effluent solution is returned to a raw water storage tank (1) through an effluent peristaltic pump (7) for circulation treatment or is discharged after meeting requirements.

7. The method according to claim 5, characterized in that Current density is 10~40mA / cm 2 , preferably: current density is 20~35mA / cm 2 .

8. The method according to claim 5, characterized in that The electrolysis time of the circulation treatment is 1 to 15 hours.

9. The method according to claim 5, characterized in that The flow rate of wastewater entering the reaction tank is 250-1500 mL / h.

10. The method according to claim 5, characterized in that An electrolyte is added to the high-concentration urea wastewater, and the electrolyte is sodium sulfate and / or sodium chloride. Preferably, the sodium sulfate concentration in the wastewater is 0-0.1 mol / L; the sodium chloride concentration is 0-5000 mg / L.

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