An electrochemical system and method for treating nitrogen-containing organic wastewater based on double-sided cathode

Abstract

The present invention discloses an electrochemical system and method for treating nitrogen-containing organic wastewater based on a double-sided cathode, comprising a reactor, an aeration device, a power supply, an anode, and a double-sided cathode. The double-sided cathode is prepared by a double-sided rolling coating process to load a functional catalyst. Without the need for exogenous addition of iron ions and H2O2, the present invention achieves efficient degradation of organic pollutants by in-situ generation of ·OH on the side of the double-sided cathode with electrocatalytic degradation function through a two-electron oxygen reduction reaction and an electro-Fenton process. At the same time, NO3 ‑ Under the synergistic effect of DSA and the side with denitrification function in the double-sided cathode, it can be converted into N2 for discharge, realizing the simultaneous removal of organic pollutants and total nitrogen. The present invention integrates the two functions of denitrification and electrocatalytic degradation into a single cathode, which is more compact and efficient, improves the current efficiency and mass transfer efficiency, reduces the complexity and footprint of the system, and reduces energy consumption and operating costs.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical systems, and in particular to an electrochemical system and method for treating nitrogen-containing organic wastewater based on a double-sided cathode. Background Art

[0002] With the rapid advancement of my country's industrial modernization, the country's industrial wastewater discharge standards are becoming increasingly stringent, placing even more stringent demands on industrial wastewater treatment technologies. However, due to its complex and variable composition and large fluctuations in pollutant concentrations, industrial wastewater is extremely difficult to treat, becoming a major challenge in the water treatment field.

[0003] Compared to domestic sewage, industrial wastewater, particularly wastewater from the chemical, pharmaceutical, printing and dyeing, and livestock and poultry industries, has higher chemical oxygen demand (COD) values and contains high concentrations of nitrates. COD is primarily composed of recalcitrant organic matter, while nitrates accumulate in the water due to the action of nitrifying bacteria, which convert nitrogenous compounds and ammonia nitrogen into nitrate nitrogen. These characteristics make industrial wastewater treatment particularly challenging. Traditional wastewater treatment methods often have limited effectiveness in treating industrial wastewater, making it difficult to meet discharge standards. Therefore, effectively removing recalcitrant organic matter and high nitrate concentrations from industrial wastewater has become a critical issue in the field of water pollution control and remediation.

[0004] In the related art, the application number is CN202310392806.9, and the name is a three-dimensional electrocatalytic treatment device and process for simultaneous pollution reduction, carbon reduction, denitrification and phosphorus removal. Disclosed is a three-dimensional electrocatalytic treatment device and process for simultaneous pollution reduction, carbon reduction, denitrification and phosphorus removal, which relates to the field of wastewater treatment technology and solves the problem that existing three-dimensional electrocatalysis focuses on the removal of COD in wastewater and cannot simultaneously remove nitrogen and phosphorus. It includes an electrocatalytic reaction tank, a sedimentation tank, a first power supply, a second power supply, and an aeration pipe. One end of the electrocatalytic reaction tank is provided with a water inlet pipe, and the other end is provided with an overflow pipe connected to the sedimentation tank. Carbon felt electrodes, iron electrodes, foam copper electrodes, and titanium-based coating electrodes are arranged in sequence at intervals in the electrocatalytic reaction tank. The cathode of the first power supply is connected to the carbon felt electrode, and the anode is connected to the iron electrode. The cathode of the second power supply is connected to the foam copper electrode, and the anode is connected to the titanium-based coating electrode. A three-dimensional particle electrode and an aeration disk are provided between the foam copper electrode and the titanium-based coating electrode, and the aeration disk is connected to the aeration pipe. However, the above structure adopts two independent cathode structures, which has the disadvantages of complex system, large floor space, high energy consumption and high operating cost. Summary of the Invention

[0005] In order to overcome the defects of the prior art, the purpose of the present invention is to provide an electrochemical system and method for treating nitrogen-containing organic wastewater based on a double-sided cathode. Under the condition that no exogenous iron ions and H2O2 are added, the side of the double-sided cathode with electrocatalytic degradation function can generate OH in situ through a two-electron oxygen reduction reaction and an electro-Fenton process, thereby achieving efficient degradation of organic pollutants. At the same time, NO3 - Under the synergistic effect of DSA and the side with denitrification function in the double-sided cathode, it can be converted into N2 and discharged, realizing the simultaneous removal of organic pollutants and total nitrogen; the present invention integrates the two functions of denitrification and electrocatalytic degradation into a single cathode, which is more compact and efficient than the dual-cathode electrochemical system, improves the current efficiency and mass transfer efficiency, reduces the complexity and footprint of the system, and reduces energy consumption and operating costs.

[0006] The purpose of the present invention is achieved by adopting the following technical solutions:

[0007] An electrochemical system for treating nitrogen-containing organic wastewater based on a double-sided cathode, comprising:

[0008] A reactor, wherein a reaction chamber is defined in the reactor and a liquid inlet and a liquid outlet are provided on the reactor, respectively communicating with the reaction chamber;

[0009] an aeration device, wherein the aeration port of the aeration device is connected to the reaction chamber, and the aeration device is used to aerate the reaction chamber;

[0010] a power supply, the power supply being used to supply power;

[0011] an anode connected to the positive electrode of the power supply;

[0012] A double-sided cathode, the double-sided cathode is connected to the negative electrode of the power supply, the double-sided cathode includes an electrode base, the first side of the electrode base forms a first cathode with a denitrification function, and the second side of the electrode base opposite to the first cathode forms a second cathode with electrocatalytic degradation; the first cathode faces the anode, and the second cathode is adjacent to the aeration port of the air pump.

[0013] Furthermore, the distance between the anode and the double-sided cathode is maintained between 1-5 cm.

[0014] Furthermore, the double-sided cathode is prepared from a first catalyst material having a denitrification function, a second catalyst material having an electrocatalytic degradation function, and an electrode substrate; wherein the first side of the electrode substrate is loaded with a catalyst material having a denitrification function to form a first cathode, and the first side of the electrode substrate is loaded with a catalyst material having an electrocatalytic degradation function to form a second cathode; both the first catalyst material and the second catalyst material contain a conductive binder.

[0015] Furthermore, the method for preparing the double-sided cathode adopts a roll-to-roll coating system and comprises the following steps:

[0016] Material preparation step: prepare the electrode substrate, the first catalyst ink and the second catalyst ink in advance and set them aside;

[0017] Unwinding step: The unwinding shaft releases the electrode substrate and moves toward the winding shaft. The unwinding tension of the unwinding shaft is 10-22N.

[0018] Coating step: The electrode substrate passes through the anilox rollers on both sides. The anilox rollers are tightly attached to the electrode substrate and use their surface texture to evenly coat the pre-mixed first catalyst ink and second catalyst ink on opposite sides of the electrode substrate, thereby forming an electrode structure with a double-sided coating.

[0019] Infrared curing step: The electrode structure with double-sided coating enters the heating and drying device. The heating method is infrared heating. The heating temperature is between 50-80℃ and the heating time is 0.5-3 minutes. The tension of the double-sided cathode in the heating and drying device is maintained at 6-15N.

[0020] Winding step: The coated electrode is wound up by a winding shaft with a winding tension of 4-12N.

[0021] Furthermore, the catalyst material having a denitrification function includes any one or a combination of at least two of Pd, Pt, Ru, Ag, Au, Fe, Co, Ni and Cu;

[0022] Alternatively, the catalyst material having the electrocatalytic degradation function includes any one or a combination of at least two of Fe2O3, Fe3O4, FeOOH, Fe-MOF and Fe-MOF derivatives;

[0023] Alternatively, the electrode substrate is a carbon material or a metal material, the carbon material includes any one or a combination of at least two of carbon paper, carbon cloth, carbon felt and graphite felt, and the metal material includes Pt, Ru, Rh, Fe, Co, Ni, Cu and Ti, as well as alloy electrodes based on these elements;

[0024] Alternatively, the conductive adhesive is any one of polyvinylidene fluoride (PVDF), perfluorosulfonic acid polymer (Nafion), polytetrafluoroethylene (PTFE) and polydimethylsiloxane (PDMS), or a combination of at least two thereof.

[0025] Furthermore, the anode is a coated titanium plate / mesh anode, and the coating includes any one or a combination of at least two of Pt, IrO2, RuO2, Ti4O7, Ta2O5, PbO2, SnO2 and Sb2O5.

[0026] Furthermore, the preparation method of the electrode substrate is as follows: selecting graphite felt with a thickness of 1-5 mm, ultrasonically cleaning the graphite felt with deionized water, acetone, and anhydrous ethanol for 15-30 minutes each, and then placing it in a vacuum drying oven at 60-80°C and drying it for 6-12 hours; soaking the dried graphite felt in concentrated nitric acid, activating it in a water bath at 60-85°C for 6-10 hours, and then washing it with deionized water until it is neutral; finally, placing the graphite felt in an oven at 60-80°C and drying it for 12-24 hours to obtain pretreated graphite felt as the electrode substrate.

[0027] Furthermore, the preparation method of the first catalyst ink is as follows: weigh 0.5g of Pd powder, add it to a mixed solution containing 50mL of deionized water, 50mL of anhydrous ethanol and 5mL of perfluorosulfonic acid polymer (5wt%), ultrasonicate it for 0.5-2h to make it completely dispersed, and stir it at a speed of 400-1000rpm for 1-3h to prepare a first catalyst ink for coating the side with denitrification function in the double-sided cathode.

[0028] Furthermore, the preparation method of the second catalyst ink is: weigh 1g of FeOOH, add it to a mixed solution containing 40mL of deionized water, 60mL of anhydrous ethanol and 10mL of perfluorosulfonic acid polymer (5wt%), ultrasonicate for 0.5-2h to completely disperse it, and stir at a speed of 400-1000rpm for 1-3h to prepare a second catalyst ink for coating the side of the double-sided cathode with electrocatalytic degradation function.

[0029] An electrochemical treatment method for treating nitrogen-containing organic wastewater based on a double-sided cathode, using the above-mentioned electrochemical system, comprises the following steps:

[0030] Aeration step: start the aeration device to aerate the reaction chamber of the reactor;

[0031] Power-on steps: Start the power supply and use constant voltage or pulse mode to control the electrodes on the double-sided cathode;

[0032] Reaction steps: After power is turned on, nitrogen-containing organic wastewater is fed into the reaction chamber through the water inlet, and an anodic oxidation reaction occurs on the anode surface to oxidize and degrade organic pollutants. At the same time, Cl in the wastewater is - Converted to Cl·Diffused into the water phase; the first cathode of the double-sided cathode converts NO3 - Reduced to N2 or NH4 + , NH4 +It will further react with Cl· to generate N2 and be discharged; the Fe(Ⅲ) in the iron-based catalyst loaded on the second cathode of the double-sided cathode is reduced to Fe(Ⅱ), and at the same time, O2 undergoes a two-electron reduction reaction on the electrode surface to generate H2O2 and is activated by Fe(Ⅱ) to ·OH with strong oxidizing properties, thereby simultaneously removing organic pollutants in nitrogen-containing organic wastewater.

[0033] Furthermore, during the reaction process, the aeration flow rate is controlled between 0.2-2.0 L / min, the double-sided cathode adopts a constant voltage or pulse mode to control the electrode, and the electrode voltage is -5 to 2 V relative to the standard hydrogen electrode potential.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention adopts a double-sided cathode with dual functions of denitrification and electrocatalytic degradation. Compared with the traditional Fenton technology, the present invention does not require the addition of exogenous iron ions and H2O2. The side of the double-sided cathode with electrocatalytic degradation function can generate OH in situ through the two-electron oxygen reduction reaction and the electro-Fenton process, thereby achieving efficient degradation of organic pollutants. At the same time, NO3 - The synergistic effect of the DSA (anode) and the denitrification side of the double-sided cathode converts nitrogen into nitrogen for discharge, achieving the simultaneous removal of organic pollutants and total nitrogen. Furthermore, this invention integrates both denitrification and electrocatalytic degradation into a single cathode, making it more compact and efficient than dual-cathode electrochemical systems. This improves current and mass transfer efficiencies, significantly shortens the wastewater treatment process, reduces system complexity and footprint, and lowers energy consumption and operating costs. This invention provides a novel wastewater purification solution for the treatment of nitrate-containing industrial wastewater.

[0036] 2. The present invention applies a double-sided rolling coating process to the loading of the catalyst, achieving uniform distribution of the catalyst on both sides of the electrode substrate and precise control of the thickness. Through the double-sided rolling coating process, the catalyst with denitrification and electrocatalytic degradation functions is successfully loaded independently on both sides of the electrode substrate, solving the problem of catalyst mixing in traditional methods. Combined with infrared heating and drying technology, the curing process of the catalyst ink is accelerated, and the production efficiency and electrode performance are improved. Compared with the traditional drip coating method, it effectively solves the problems of uneven catalyst loading, difficult to control the thickness of the catalyst layer, and the penetration of the catalyst ink during drip coating, which causes the catalyst to mix and affects the use effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the electrochemical system based on double-sided cathode.

[0038] Among them, 1. Reactor; 2. Power supply; 3. Aeration device; 4. Anode; 5. Double-sided cathode; 5-1. First cathode; 5-2. Second cathode.

[0039] Figure 2 This is a scanning electron microscope (SEM) image of FeOOH synthesized in Example 1.

[0040] Figure 3 This is a comparison chart of the electrocatalytic removal of nitric acid and ions between Example 1 and Comparative Example 1.

[0041] Figure 4 This is a performance comparison chart of the electrocatalytic degradation of organic pollutants in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3. DETAILED DESCRIPTION

[0042] The present invention is further described below with reference to the accompanying drawings and specific embodiments. It should be noted that, provided no conflicts exist, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. Unless otherwise specified, the materials and equipment used in this embodiment are commercially available.

[0043] An electrochemical system for treating nitrogen-containing organic wastewater based on a double-sided cathode, comprising:

[0044] A reactor, wherein a reaction chamber is defined in the reactor and a liquid inlet and a liquid outlet are provided on the reactor, respectively communicating with the reaction chamber;

[0045] an aeration device, wherein the aeration port of the aeration device is connected to the reaction chamber, and the aeration device is used to aerate the reaction chamber;

[0046] a power supply, the power supply being used to supply power;

[0047] an anode connected to the positive electrode of the power supply;

[0048] A double-sided cathode, the double-sided cathode is connected to the negative electrode of the power supply, the double-sided cathode includes an electrode base, the first side of the electrode base forms a first cathode with a denitrification function, and the second side of the electrode base opposite to the first cathode forms a second cathode with electrocatalytic degradation; the first cathode faces the anode, and the second cathode is adjacent to the aeration port of the air pump.

[0049] The mechanism of the present invention is described as follows: an anodic oxidation reaction occurs on the surface of the anode (DSA) to oxidize and degrade organic pollutants, while the Cl - Converted into Cl·Diffused into the water phase. In the double-sided cathode with denitrification function (first cathode), NO3 - Reduced to N2 or NH4 + , NH4 +It will further react with Cl· to generate N2 and be discharged; on the side of the double-sided cathode with electrocatalytic degradation function (the second cathode), the Fe(III) in the iron-based catalyst loaded thereon is reduced to Fe(II), and at the same time, O2 undergoes a two-electron reduction reaction on the electrode surface to generate H2O2 and is activated by Fe(II) to form ·OH with strong oxidizing properties, thereby simultaneously removing organic pollutants in industrial wastewater; under the synergistic effect of the above-mentioned electrode system, denitrification and purification of wastewater are achieved.

[0050] The main reaction formula involved in the present invention is as follows:

[0051] 1. The following reaction occurs at the anode:

[0052]

[0053] 2. The following reaction occurs at the first cathode:

[0054]

[0055]

[0056]

[0057]

[0058]

[0059] .

[0060] 3. The following reaction occurs at the second cathode:

[0061]

[0062]

[0063] .

[0064] In summary, the present invention can achieve efficient degradation of organic pollutants by in situ generation of ·OH through a two-electron oxygen reduction reaction and an electro-Fenton process on the side of the double-sided cathode with electrocatalytic degradation function without the need for exogenous addition of iron ions and H2O2; at the same time, NO3 - Under the synergistic effect of DSA and the side with denitrification function in the double-sided cathode, it can be converted into N2 and discharged, realizing the simultaneous removal of organic pollutants and total nitrogen; at the same time, the present invention integrates the two functions of denitrification and electrocatalytic degradation into a single cathode, which is more compact and efficient than the dual-cathode electrochemical system, improves the current efficiency and mass transfer efficiency, reduces the complexity and footprint of the system, and reduces energy consumption and operating costs.

[0065] As a preferred embodiment, the distance between the anode and the double-sided cathode is maintained between 1 and 5 cm. A reasonable electrode spacing ensures a more uniform distribution of the electric field within the reaction chamber, ensuring that all parts of the wastewater are fully exposed to the electrochemical action. Precise control of the electrode spacing helps form a stable electrochemical reaction zone between the anode and cathode, thereby enhancing the removal of organic pollutants and nitrates.

[0066] As a preferred embodiment, the double-sided cathode is prepared by a first catalyst material having a denitrification function, a second catalyst material having an electrocatalytic degradation function, and an electrode substrate; wherein the first side of the electrode substrate is loaded with a catalyst material having a denitrification function to form a first cathode, and the first side of the electrode substrate is loaded with a catalyst material having an electrocatalytic degradation function to form a second cathode; both the first catalyst material and the second catalyst material contain a conductive binder.

[0067] As a preferred embodiment, the method for preparing the double-sided cathode adopts a roll-to-roll coating system and comprises the following steps:

[0068] Material preparation step: prepare the electrode substrate, the first catalyst ink and the second catalyst ink in advance and set them aside;

[0069] Unwinding step: The unwinding shaft releases the electrode substrate and moves it toward the reeling shaft. The unwinding tension of the unwinding shaft is 10-22N. If the unwinding tension is too high, the electrode substrate is easily stretched and deformed. If the tension is too low, it may cause uneven coating or even coating leakage, and affect the stability of the entire coating process. Therefore, strict control of the unwinding tension is crucial.

[0070] Coating step: The electrode substrate passes through the anilox rollers on both sides. The anilox rollers are tightly attached to the electrode substrate and use their surface texture to evenly coat the pre-mixed first catalyst ink and second catalyst ink on opposite sides of the electrode substrate, thereby forming an electrode structure with a double-sided coating.

[0071] Infrared curing step: The electrode structure with double-sided coating enters the heating and drying device. The heating method is infrared heating. The heating temperature is between 50-80℃ and the heating time is 0.5-3 minutes to ensure effective curing of the ink. The tension of the double-sided cathode in the heating and drying device is maintained at 6-15N to further ensure the stability and quality of the curing process.

[0072] Winding step: The coated electrode is wound up by the winding shaft with a winding tension of 4-12 N. This is to avoid the increase of internal stress in the electrode caused by excessive tension, which may lead to deformation problems.

[0073] The present invention applies a double-sided rolling coating process to the loading of the catalyst, achieving uniform distribution of the catalyst on both sides of the electrode substrate and precise control of the thickness. Through the double-sided rolling coating process, a catalyst with denitrification and electrocatalytic degradation functions is successfully loaded independently on both sides of the electrode substrate, solving the problem of catalyst mixing in traditional methods. Combined with infrared heating and drying technology, the curing process of the catalyst ink is accelerated, and the production efficiency and electrode performance are improved. Compared with the traditional drip coating method, it effectively solves the problems of uneven catalyst loading, difficult to control the thickness of the catalyst layer, and the penetration of the catalyst ink during drip coating, which causes the catalyst to mix and affects the use effect.

[0074] As a preferred embodiment, the catalyst material having a denitrification function includes any one or a combination of at least two of Pd, Pt, Ru, Ag, Au, Fe, Co, Ni and Cu;

[0075] Alternatively, the catalyst material having the electrocatalytic degradation function includes any one or a combination of at least two of Fe2O3, Fe3O4, FeOOH, Fe-MOF and Fe-MOF derivatives;

[0076] Alternatively, the electrode substrate is a carbon material or a metal material, the carbon material includes any one or a combination of at least two of carbon paper, carbon cloth, carbon felt and graphite felt, and the metal material includes Pt, Ru, Rh, Fe, Co, Ni, Cu and Ti, as well as alloy electrodes based on these elements;

[0077] Alternatively, the conductive adhesive is any one of polyvinylidene fluoride (PVDF), perfluorosulfonic acid polymer (Nafion), polytetrafluoroethylene (PTFE) and polydimethylsiloxane (PDMS), or a combination of at least two thereof.

[0078] As a preferred embodiment, the anode is a coated titanium plate / mesh anode, and the coating includes any one or a combination of at least two of Pt, IrO2, RuO2, Ti4O7, Ta2O5, PbO2, SnO2 and Sb2O5.

[0079] As a preferred embodiment, the preparation method of the electrode substrate is as follows: select graphite felt with a thickness of 1-5 mm, use deionized water, acetone, and anhydrous ethanol to ultrasonically clean the graphite felt for 15-30 minutes each, and then place it in a vacuum drying oven at 60-80°C and dry it for 6-12 hours; soak the dried graphite felt in concentrated nitric acid, activate it in a water bath at 60-85°C for 6-10 hours, so that the surface of the graphite felt is rich in -COOH groups and its hydrophilicity is enhanced, and then, it is washed with deionized water until it is neutral; finally, place the graphite felt in an oven at 60-80°C and dry it for 12-24 hours to obtain pretreated graphite felt as the electrode substrate.

[0080] As a preferred embodiment, the preparation method of the first catalyst ink is: weighing 0.5g of Pd powder, adding it to a mixed solution containing 50mL of deionized water, 50mL of anhydrous ethanol and 5mL of perfluorosulfonic acid polymer (5wt%), ultrasonicating it for 0.5-2h to completely disperse it, and stirring it at a speed of 400-1000rpm for 1-3h to prepare a first catalyst ink for coating the side with denitrification function in the double-sided cathode.

[0081] As a preferred embodiment, the preparation method of the second catalyst ink is: weighing 1g of FeOOH, adding it to a mixed solution containing 40mL of deionized water, 60mL of anhydrous ethanol and 10mL of perfluorosulfonic acid polymer (5wt%), the dispersion ratio can optimize the electrocatalytic activity of the catalyst and maximize its adhesion firmness to achieve optimal performance; then, ultrasonicating for 0.5-2h to completely disperse it, and stirring at a speed of 400-1000rpm for 1-3h to prepare a second catalyst ink for coating the side of the double-sided cathode with electrocatalytic degradation function.

[0082] An electrochemical treatment method for treating nitrogen-containing organic wastewater based on a double-sided cathode, using the above-mentioned electrochemical system, comprises the following steps:

[0083] Aeration step: start the aeration device to aerate the reaction chamber of the reactor;

[0084] Power-on steps: Start the power supply and use constant voltage or pulse mode to control the electrodes on the double-sided cathode;

[0085] Reaction steps: After power is turned on, nitrogen-containing organic wastewater is fed into the reaction chamber through the water inlet, and an anodic oxidation reaction occurs on the anode surface to oxidize and degrade organic pollutants. At the same time, Cl in the wastewater is - Converted to Cl·Diffused into the water phase; the first cathode of the double-sided cathode converts NO3 - Reduced to N2 or NH4 + , NH4 + It will further react with Cl· to generate N2 and be discharged; the Fe(Ⅲ) in the iron-based catalyst loaded on the second cathode of the double-sided cathode is reduced to Fe(Ⅱ), and at the same time, O2 undergoes a two-electron reduction reaction on the electrode surface to generate H2O2 and is activated by Fe(Ⅱ) to ·OH with strong oxidizing properties, thereby simultaneously removing organic pollutants in nitrogen-containing organic wastewater.

[0086] In the present invention, without the need for external addition of iron ions and H2O2, the side of the double-sided cathode with electrocatalytic degradation function can generate OH in situ through the two-electron oxygen reduction reaction and the electro-Fenton process, thereby achieving efficient degradation of organic pollutants; at the same time, NO3 -Under the synergistic effect of DSA and the side with denitrification function in the double-sided cathode, it can be converted into N2 and discharged, realizing the simultaneous removal of organic pollutants and total nitrogen.

[0087] As a preferred embodiment, the aeration flow rate is controlled between 0.2-2.0 L / min. By controlling the aeration flow rate between 0.2-2.0 L / min, an adequate supply of oxygen is ensured in the reaction chamber, which not only avoids the decrease in electrocatalytic degradation efficiency caused by insufficient oxygen, but also prevents the waste of resources and energy loss caused by excessive oxygen. A reasonable aeration flow rate can enhance the turbulence of the wastewater and promote effective contact between the solutes in the wastewater and the electrode surface, thereby improving the mass transfer efficiency. A stable aeration flow rate helps to maintain the relative stability of the environment in the reaction chamber and reduce the reaction instability caused by airflow fluctuations.

[0088] As a preferred embodiment, during the reaction process, the double-sided cathode adopts constant voltage or pulse mode to control the electrode, and the voltage of the electrode is -5 to 2V relative to the standard hydrogen electrode potential, which suppresses excessive hydrogen evolution reaction and other competing processes to effectively improve the current efficiency.

[0089] Example 1:

[0090] In this embodiment, the anode (DSA) uses a commercial ruthenium-iridium-titanium mesh electrode with a size of 20*30*1mm, and the double-sided cathode uses a graphite felt cathode loaded with a catalyst; the DSA is connected to the counter electrode of the electrochemical workstation, and the double-sided cathode is connected to the working electrode of the electrochemical workstation. The distance between the DSA and the double-sided cathode is 2cm, and the side of the double-sided cathode coated with the Pd powder catalyst faces the DSA, and the side coated with iron oxyhydroxide (FeOOH) is close to the aeration port; a constant voltage mode is used, and the constant voltage is -1.05V (relative to the Ag / AgCl reference electrode, after conversion, -0.5V relative to the reversible hydrogen electrode potential); the aeration volume of the air pump is 0.8L / min; the treatment volume of nitrogen-containing organic wastewater is 100mL, and the reactor is a cylindrical quartz electrolytic cell with a volume of 150mL; sampling is taken every 15 minutes, and the concentrations of tetracycline and nitrate nitrogen are determined by ultraviolet spectrophotometry, and the degradation experiment is completed after 2 hours. The denitrification and organic pollutant degradation effects are respectively as follows: Figure 3 and Figure 4 shown.

[0091] Nitrogen-containing organic wastewater is simulated wastewater, and each 1L of simulated wastewater contains 50mmolNa2SO4, 50mgNaCl, 20mgNaNO3 and 20mgtetracycline;

[0092] The thickness of the graphite felt is between 1-5mm. After ultrasonically cleaning the carbon felt with deionized water, acetone, and anhydrous ethanol for 15-30 minutes each, the graphite felt is placed in a vacuum drying oven at 60-80°C and dried for 6-12 hours. The dried graphite felt is soaked in concentrated nitric acid, activated in a water bath at 60-85°C for 6-10 hours, and then washed with deionized water until neutral. Finally, the graphite felt is placed in an oven at 60-80°C and dried for 12-24 hours, and marked as pretreated graphite felt. The pretreated graphite felt is loaded with functional catalysts through a double-sided rolling coating process with the help of a roll-to-roll coating roller system, and then cut to a suitable size for use. The present invention simultaneously loads different functional catalysts on both sides of the substrate through a double-sided rolling coating process, and uses infrared heating and drying to accelerate the curing of the catalyst ink. Compared with the traditional drop coating method, it effectively solves the problems of uneven catalyst loading, difficult to control the thickness of the catalyst layer, and the penetration of the catalyst ink during drop coating, which causes the catalyst to mix and affects the use effect.

[0093] The roll-to-roll coating system, model MSK-AFA-MC200, was purchased from Hefei Kejing. It features a micro-gravure coating method, equipped with an MSK-155 feeder and an infrared heating drying oven. The roll diameter for the micro-gravure coating method is 30 mm. The electrode substrate, with a thickness of 0.1-5 mm, was placed in the roll-to-roll coating system. The catalyst ink was placed in the feeder at a coating speed of 0.1-0.4 m / min.

[0094] The specific coating process on the coating machine includes unwinding, coating, infrared curing and winding. The specific steps are as follows:

[0095] Unwinding: The unwinding shaft releases the electrode substrate and moves toward the reeling shaft. The unwinding tension of the unwinding shaft is 10-22 N.

[0096] Coating: The electrode substrate passes through the anilox rollers on both sides. The anilox rollers are tightly attached to the electrode substrate and use their surface texture to evenly coat the pre-mixed catalyst ink on the corresponding side of the electrode substrate, thus forming an electrode structure with double-sided coating.

[0097] Infrared curing: The double-sided cathode enters the heating and drying device. The heating method is infrared heating. The heating temperature is between 50-80℃ and the heating time is 0.5-3 minutes. The tension of the double-sided cathode in the heating and drying device is maintained at 6-15 N.

[0098] Winding: The coated electrode is wound up by the winding shaft with a winding tension of 4-12 N.

[0099] In this embodiment, Pd powder is a commercial catalyst with a particle size of 50 nm; FeOOH is synthesized by hydrothermal method:

[0100] The iron salt is at least one selected from ferric chloride hexahydrate (FeCl3.6H2O), ferric chloride, ferric sulfate hydrate, ferric sulfate, ferric nitrate nonahydrate and ferric nitrate.

[0101] The mass ratio of iron salt to sodium hydroxide is 0.8:1 to 2:1. The mass concentration of the iron salt precursor solution is between 50-200 g / L, and the mass concentration of the NaOH precursor solution is between 60-100 g / L. The precursor solutions are stirred at a speed of no less than 300 rpm for 1-3 hours. The water bath synthesis temperature is 150-180°C, and the holding time is 16-24 hours. The product is vacuum dried at a temperature of 60-85°C for 12-24 hours.

[0102] In this embodiment, the precursor solution was prepared by dissolving 4.0567g of FeCl3·6H2O in 30mL of deionized water and magnetically stirring at room temperature for 30 minutes. Then, 2.8989g of NaOH was dissolved in another 40mL of deionized water to prepare a NaOH solution, which was then slowly added to the above-mentioned FeCl3 aqueous solution and further stirred at 600rpm for 1 hour. Finally, the mixed solution was transferred to a Teflon-lined autoclave, heated to 160°C in a forced air drying oven, and kept warm for 16 hours. After the reaction was completed, it was naturally cooled to room temperature, and the product was collected, washed with deionized water 3-5 times, and then dried in a vacuum drying oven at 60°C for 12 hours.

[0103] The volume ratio of anhydrous ethanol to deionized water is 1:1 to 10:1, the volume ratio of anhydrous ethanol to conductive binder is 5:1 to 15:1, and the catalyst loading on one side of the double-sided cathode is 0.2-2 mg / cm 2 between.

[0104] In this embodiment, the preparation method of the first catalyst ink is as follows: weigh 0.5 g of Pd powder, add it to a mixed solution containing 50 mL of deionized water, 50 mL of anhydrous ethanol and 5 mL of Nafion (5 wt %), ultrasonicate it for 0.5-2 hours to completely disperse it, and stir it at a speed of 400-1000 rpm for 1-3 hours to prepare the first catalyst ink for coating the side with denitrification function in the double-sided cathode, and set it aside.

[0105] In this embodiment, the preparation method of the second catalyst ink is as follows: weigh 1g of FeOOH, add it to a mixed solution containing 40mL of deionized water, 60mL of anhydrous ethanol and 10mL of Nafion (5wt%), ultrasonicate it for 0.5-2h to completely disperse it, and stir it at a speed of 400-1000rpm for 1-3h to prepare a first catalyst ink for coating the side of the double-sided cathode with electrocatalytic degradation function, and set it aside.

[0106] In this embodiment, a graphite felt with a thickness of 5 mm is used, and then a roll-to-roll coating roller system is used to load the functional catalyst onto the pretreated graphite felt through a double-sided rolling coating process. The coating speed is 0.2 m / min, and infrared heating and drying are used to accelerate the curing of the catalyst ink. Finally, the graphite felt loaded with the catalyst is cut into a rectangular shape with a size of 3 cm × 2 cm for use.

[0107] Example 2:

[0108] This example uses the same experimental conditions as Example 1, except that sulfamethoxazole is used instead of tetracycline in the simulated sewage. The degradation effect of organic pollutants is as follows: Figure 4 shown.

[0109] Example 3:

[0110] This example uses the same experimental conditions as Example 1, except that rhodamine B is used instead of tetracycline in the simulated sewage. The degradation effect of organic pollutants is as follows: Figure 4 shown.

[0111] Comparative Example 1

[0112] This example uses the same experimental conditions as Example 1, except that pretreated graphite felt is used instead of the double-sided cathode. The denitrification and organic pollutant degradation effects are as follows: Figure 3 and Figure 4 shown.

[0113] Comparative Example 2

[0114] This example uses the same experimental conditions as Comparative Example 1, except that sulfamethoxazole is used instead of tetracycline in the simulated sewage. The degradation effect of organic pollutants is as follows: Figure 4 shown.

[0115] Comparative Example 3

[0116] This example uses the same experimental conditions as comparative example 1, except that rhodamine B is used instead of tetracycline in the simulated sewage. The degradation effect of organic pollutants is as follows: Figure 4 shown.

[0117] The results of Example 1 and Comparative Example 1 ( Figure 3 ) It can be seen that after the nitrogen-containing organic wastewater is treated by the double-sided cathode electrocatalytic system in Example 1, NO3 - The removal rate of NO3 - The content only decreased by 17.27%, thus proving that the double-sided cathode-based electrocatalytic system of the present invention can achieve efficient denitrification of organic wastewater.

[0118] from Figure 4 From the analysis, it can be seen that the double-sided cathode electrocatalytic system of the present invention has excellent removal effects on a variety of organic pollutants. The degradation rates of tetracycline, sulfamethoxazole and rhodamine B are as high as 95.46%, 98.69% and 100%, respectively. The electrocatalytic system without double-sided cathode has a removal rate of only 28.57%, 32.95% and 41.28 for tetracycline, sulfamethoxazole and rhodamine B. The comparison illustrates the excellent degradation ability of the electrocatalytic system based on double-sided cathode for a variety of organic pollutants.

[0119] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by those skilled in the art on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. An electrochemical system for treating nitrogen-containing organic wastewater based on a double-sided cathode, characterized in that: include: A reactor, wherein a reaction chamber is defined in the reactor and a liquid inlet and a liquid outlet are provided on the reactor, respectively communicating with the reaction chamber; an aeration device, wherein the aeration port of the aeration device is connected to the reaction chamber, and the aeration device is used to aerate the reaction chamber; a power supply, the power supply being used to supply power; an anode connected to the positive electrode of the power supply; A double-sided cathode connected to the negative electrode of the power supply, comprising an electrode base, a first side of the electrode base forming a first cathode having a denitrification function, and a second side of the electrode base opposite to the first cathode forming a second cathode having an electrocatalytic degradation function; the first cathode faces the anode, and the second cathode is adjacent to the aeration port of the air pump; The double-sided cathode is prepared from a first catalyst material having a denitrification function, a second catalyst material having an electrocatalytic degradation function, and an electrode substrate; wherein the first side of the electrode substrate is loaded with the catalyst material having a denitrification function to form a first cathode, and the first side of the electrode substrate is loaded with the catalyst material having an electrocatalytic degradation function to form a second cathode; both the first catalyst material and the second catalyst material contain a conductive binder; The method for preparing the double-sided cathode adopts a roll-to-roll coating system and comprises the following steps: Material preparation step: prepare the electrode substrate, the first catalyst ink and the second catalyst ink in advance and set them aside; Unwinding step: The unwinding shaft releases the electrode substrate and moves toward the winding shaft. The unwinding tension of the unwinding shaft is 10-22N. Coating step: The electrode substrate passes through the anilox rollers on both sides. The anilox rollers are tightly attached to the electrode substrate and use their surface texture to evenly coat the pre-mixed first catalyst ink and second catalyst ink on opposite sides of the electrode substrate, thereby forming an electrode structure with a double-sided coating. Infrared curing step: The electrode structure with double-sided coating enters the heating and drying device. The heating method is infrared heating. The heating temperature is between 50-80℃ and the heating time is 0.5-3 minutes. The tension of the double-sided cathode in the heating and drying device is maintained at 6-15N. Winding step: The coated electrode is wound up by a winding shaft with a winding tension of 4-12N; The first catalyst ink is prepared by weighing 0.5 g of Pd powder, adding it to a mixed solution containing 50 mL of deionized water, 50 mL of anhydrous ethanol, and 5 mL of a 5 wt% perfluorosulfonic acid polymer, sonicating for 0.5-2 hours to completely disperse it, and stirring at 400-1000 rpm for 1-3 hours to prepare a first catalyst ink for coating the side of a double-sided cathode having a denitrification function; The preparation method of the second catalyst ink is as follows: weigh 1g of FeOOH, add it to a mixed solution containing 40mL of deionized water, 60mL of anhydrous ethanol and 10mL of a perfluorosulfonic acid polymer with a weight content of 5wt%, then ultrasonicate it for 0.5-2h to completely disperse it, and stir it at a speed of 400-1000rpm for 1-3h to prepare a second catalyst ink for coating the side of the double-sided cathode with electrocatalytic degradation function.

2. The electrochemical system for treating nitrogen-containing organic wastewater based on a double-sided cathode according to claim 1, characterized in that: The distance between the anode and the double-sided cathode is maintained between 1-5 cm.

3. The electrochemical system for treating nitrogen-containing organic wastewater based on double-sided cathode according to claim 1, characterized in that: The anode is a coated titanium plate / mesh anode, and the coating includes any one or a combination of at least two of Pt, IrO2, RuO2, Ti4O7, Ta2O5, PbO2, SnO2 and Sb2O5.

4. The electrochemical system for treating nitrogen-containing organic wastewater based on a double-sided cathode according to claim 1, characterized in that: The preparation method of the electrode substrate comprises the following steps: selecting graphite felt with a thickness of 1-5 mm, ultrasonically cleaning the graphite felt with deionized water, acetone, and anhydrous ethanol for 15-30 minutes each, and then drying the graphite felt in a vacuum drying oven at 60-80° C. for 6-12 hours; immersing the dried graphite felt in concentrated nitric acid, activating it in a water bath at 60-85° C. for 6-10 hours, and then washing it with deionized water until it becomes neutral; and finally, drying the graphite felt in an oven at 60-80° C. for 12-24 hours to obtain pretreated graphite felt as the electrode substrate.

5. An electrochemical treatment method for treating nitrogen-containing organic wastewater based on double-sided cathode, characterized in that: The electrochemical system according to any one of claims 1 to 4 comprises the following steps: Aeration step: start the aeration device to aerate the reaction chamber of the reactor; Power-on steps: Start the power supply and use constant voltage or pulse mode to control the electrodes on the double-sided cathode; Reaction steps: After power is turned on, nitrogen-containing organic wastewater is fed into the reaction chamber through the water inlet, and an anodic oxidation reaction occurs on the anode surface to oxidize and degrade organic pollutants, while the Cl in the wastewater is - Converted to Cl·Diffused into the water phase; the first cathode of the double-sided cathode converts NO3 - Reduced to N2 or NH4 + , NH4 + It will further react with Cl· to generate N2 and be discharged; the Fe(Ⅲ) in the iron-based catalyst loaded on the second cathode of the double-sided cathode is reduced to Fe(Ⅱ), and at the same time, O2 undergoes a two-electron reduction reaction on the electrode surface to generate H2O2 and is activated by Fe(Ⅱ) to become ·OH with strong oxidizing properties, thereby simultaneously removing organic pollutants in nitrogen-containing organic wastewater; during the reaction process, the aeration flow rate is controlled between 0.2-2.0L / min, and the double-sided cathode adopts constant voltage or pulse mode to control the electrode, and the electrode voltage is -5~2V relative to the standard hydrogen electrode potential.

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