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

Abstract

The invention discloses an electrochemical system and method for treating nitrogen-containing organic wastewater based on a double-sided cathode. The electrochemical system comprises a reactor, an aeration device, a power supply, an anode and the double-sided cathode, and the double-sided cathode is prepared by loading a functional catalyst through a double-sided rolling coating process. Under the condition of not adding exogenous iron ions and H2O2, the side, with the electro-catalytic degradation function, in the double-sided cathode generates. OH in situ through the oxygen reduction reaction of two electrons and the electro-Fenton process, so that efficient degradation of organic pollutants is realized; meanwhile, NO3 <-> can be converted into N2 to be discharged under the synergistic effect of the sides, with the denitrification function, of the DSA and the double-sided cathode, organic pollutants and total nitrogen are synchronously removed, the denitrification function and the electrocatalytic degradation function are integrated in the single cathode, the device is more compact and efficient, the current efficiency and the mass transfer efficiency are improved, and the device is suitable for large-scale popularization and application. The complexity and the occupied area of the system are reduced, and the energy consumption and the operation cost are reduced.

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 have become increasingly stringent, and more stringent requirements have been put forward for industrial wastewater treatment technology. However, industrial wastewater is extremely difficult to treat due to its complex and variable composition and large fluctuations in pollutant concentrations, which has become a major problem in the field of water treatment.

[0003] Compared with domestic sewage, industrial wastewater, especially wastewater from the chemical, pharmaceutical, printing and dyeing, and livestock and poultry farming industries, has a higher chemical oxygen demand (COD) value and contains high concentrations of nitrates. Among them, COD is mainly composed of organic matter that is difficult to biodegrade; and nitrates are due to the action of nitrifying bacteria in the water, which converts nitrogen-containing compounds and ammonia nitrogen into nitrate nitrogen and accumulates in the water body. These characteristics make industrial wastewater treatment particularly difficult. Traditional wastewater treatment methods often have limited effects when treating industrial wastewater and are difficult to meet emission standards. Therefore, how to effectively remove difficult-to-degrade organic matter and high-concentration nitrates in industrial wastewater has become a key issue that needs to be urgently addressed in the current field of water pollution control and remediation.

[0004] In the related technology, 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. A three-dimensional electrocatalytic treatment device and process for simultaneous pollution reduction, carbon reduction, denitrification and phosphorus removal is disclosed, which relates to the field of wastewater treatment technology, solves the problem that the existing three-dimensional electrocatalysis focuses on the removal of COD in wastewater and cannot simultaneously remove nitrogen and phosphorus, and 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 arranged 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 footprint, 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 to achieve 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 floor space of the system, and reduces energy consumption and operating costs.

[0006] The purpose of the present invention is achieved by 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 the reactor is provided with a liquid inlet and a liquid outlet respectively connected to 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 for supplying 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 substrate, the first side of the electrode substrate forms a first cathode with a denitrification function, and the second side of the electrode substrate 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 electrode is prepared from a first catalyst material with a denitrification function, a second catalyst material with an electrocatalytic degradation function, and an electrode substrate; wherein the first side of the electrode substrate is loaded with a catalyst material with a denitrification function to form a first cathode, and the first side of the electrode substrate is loaded with a catalyst material with 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 electrode adopts a roll-to-roll coating rolling system; and comprises the following steps:

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

[0017] Unwinding step: the unwinding shaft releases the electrode substrate and moves toward the winding shaft, and 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 closely attached to the electrode substrate, and the pre-prepared first catalyst ink and second catalyst ink are respectively and evenly coated on the opposite sides of the electrode substrate by using the surface texture of the anilox rollers, thereby forming an electrode structure with 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℃, the heating time is 0.5-3min, and the tension of the double-sided electrode in the heating and drying device is maintained at 6-15N;

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

[0021] Further, 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 of carbon paper, carbon cloth, carbon felt and graphite felt or a combination of at least two thereof, 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: 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 to dry 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, and then wash it with deionized water until it is neutral; finally, place the graphite felt in an oven at 60-80°C to dry 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: weigh 0.5g Pd powder, add it to a mixed solution containing 50mL deionized water, 50mL anhydrous ethanol and 5mL perfluorosulfonic acid type polymer (5wt%), ultrasonicate for 0.5-2h to make it completely dispersed, and stir 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 electrode.

[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 make it completely dispersed, 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 electrode with electrocatalytic degradation function.

[0029] An electrochemical treatment method for treating nitrogen-containing organic wastewater based on a double-sided cathode, using the above 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 input 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 - Converted to Cl· and diffused into the water phase; the first cathode of the double-sided cathode converts NO3 - Reduction 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.

[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 voltage of the electrode 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 can achieve efficient degradation of organic pollutants by in-situ generation of ·OH on one side of the double-sided cathode with electrocatalytic degradation function through two-electron oxygen reduction reaction and electro-Fenton process without the need for exogenous addition of iron ions and H2O2; at the same time, NO3 - Under the synergistic effect of DSA (anode) 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; in addition, the present invention integrates the two functions of denitrification and electrocatalytic degradation into a single cathode, which is more compact and efficient than the double cathode electrochemical system, improves the current efficiency and mass transfer efficiency, greatly shortens the sewage treatment process, reduces the complexity and floor space of the system, and reduces energy consumption and operating costs. The present invention provides a new wastewater purification solution for the treatment of industrial wastewater containing nitrates.

[0036] 2. The present invention applies the 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 thickness control. Through the double-sided rolling coating process, the catalyst with denitrification function and electrocatalytic degradation function is successfully loaded independently on both sides of the electrode substrate, solving the problem of catalyst mixing in the traditional method. 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 It is a comparison chart of the electrocatalytic removal of nitric acid and ions by Example 1 and Comparative Example 1.

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

[0042] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment. Unless otherwise specified, the materials and equipment used in this embodiment can be purchased from the market.

[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 the reactor is provided with a liquid inlet and a liquid outlet respectively connected to 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 for supplying 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 substrate, the first side of the electrode substrate forms a first cathode with a denitrification function, and the second side of the electrode substrate 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. On the side with denitrification function (first cathode) in the double-sided cathode, NO3- can be 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 on it 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 industrial wastewater; under the synergistic effect of the above-mentioned electrode system, denitrification and purification of wastewater is achieved.

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

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

[0052] Cl - -e - →Cl

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

[0054]

[0055] 2H2O+2e - →2H*+2OH -

[0056]

[0057] 3. The second cathode undergoes the following reaction:

[0058] O2+2H + +2e - →H2O2

[0059] Fe(II)+H2O2→Fe(III)+OH - + OH

[0060] Fe(III)+e - →Fe(II).

[0061] In summary, under the condition that no exogenous addition of iron ions and H2O2 is required, the side of the double-sided cathode with the 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- can be converted into N2 and discharged under the synergistic effect of DSA and the side of the double-sided cathode with the denitrification function, thereby achieving 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 floor space of the system, and reduces energy consumption and operating costs.

[0062] As a preferred embodiment, the distance between the anode and the double-sided cathode is maintained between 1-5 cm. Reasonable electrode spacing makes the electric field more evenly distributed in the reaction chamber, which is conducive to all parts of the wastewater being fully electrochemically acted upon. Accurate control of the electrode spacing helps to form a stable electrochemical reaction zone between the anode and the cathode, thereby enhancing the removal effect of organic pollutants and nitrates.

[0063] As a preferred embodiment, the double-sided electrode is prepared from a first catalyst material with a denitrification function, a second catalyst material with an electrocatalytic degradation function, and an electrode substrate; wherein the first side of the electrode substrate is loaded with a catalyst material with a denitrification function to form a first cathode, and the first side of the electrode substrate is loaded with a catalyst material with an electrocatalytic degradation function to form a second cathode; both the first catalyst material and the second catalyst material contain a conductive binder.

[0064] As a preferred embodiment, the method for preparing the double-sided electrode adopts a roll-to-roll coating rolling system; comprising the following steps:

[0065] Material preparation step: preparing the electrode substrate, the first catalyst ink and the second catalyst ink in advance and setting them aside;

[0066] 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. If the unwinding tension is too large, the electrode substrate is easily stretched and deformed. If the tension is too small, it may cause uneven coating or even missing coating, and affect the stability of the entire coating process. Therefore, strict control of the unwinding tension is very important.

[0067] Coating step: the electrode substrate passes through the anilox rollers on both sides, the anilox rollers are closely attached to the electrode substrate, and the pre-prepared first catalyst ink and second catalyst ink are respectively and evenly coated on the opposite sides of the electrode substrate by using the surface texture of the anilox rollers, thereby forming an electrode structure with double-sided coating;

[0068] 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 0.5-3min to ensure the effective curing of the ink. The tension of the double-sided electrode in the heating and drying device is maintained at 6-15N to further ensure the stability and quality of the curing process.

[0069] Winding step: The coated electrode is wound up by the winding shaft, and the winding tension is 4-12N. This is to avoid the increase of internal stress of the electrode caused by excessive tension, which in turn causes deformation problems.

[0070] 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 thickness control. Through the double-sided rolling coating process, the catalyst with denitrification function and electrocatalytic degradation function is successfully loaded independently on both sides of the electrode substrate, solving the problem of catalyst mixing in the traditional method. 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.

[0071] 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;

[0072] 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;

[0073] Alternatively, the electrode substrate is a carbon material or a metal material, the carbon material includes any one of carbon paper, carbon cloth, carbon felt and graphite felt or a combination of at least two thereof, and the metal material includes Pt, Ru, Rh, Fe, Co, Ni, Cu and Ti as well as alloy electrodes based on these elements;

[0074] 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.

[0075] 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.

[0076] As a preferred embodiment, the preparation method of the electrode substrate is: 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 to dry 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 to enhance its hydrophilicity, and then wash it with deionized water until it is neutral; finally, place the graphite felt in a 60-80°C oven to dry for 12-24 hours to obtain pretreated graphite felt as an electrode substrate.

[0077] As a preferred embodiment, the preparation method of the first catalyst ink is: weigh 0.5g Pd powder, add it to a mixed solution containing 50mL deionized water, 50mL anhydrous ethanol and 5mL perfluorosulfonic acid type polymer (5wt%), ultrasonicate for 0.5-2h to make it completely dispersed, and stir 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 electrode.

[0078] As a preferred embodiment, 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 type polymer (5wt%), and the dispersion ratio can optimize the electrocatalytic activity of the catalyst and maximize its adhesion firmness to achieve optimal performance; then, 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 electrode with electrocatalytic degradation function.

[0079] An electrochemical treatment method for treating nitrogen-containing organic wastewater based on a double-sided cathode, using the above electrochemical system, comprises the following steps:

[0080] Aeration step: start the aeration device to aerate the reaction chamber of the reactor;

[0081] Power-on steps: Start the power supply, and use constant voltage or pulse mode to control the electrodes on the double-sided cathode;

[0082] Reaction steps: After power is turned on, nitrogen-containing organic wastewater is input 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 - Converted to Cl· and diffused into the water phase; the first cathode of the double-sided cathode converts NO3 - Reduction 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.

[0083] 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 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.

[0084] As a preferred embodiment, the aeration flow rate is controlled between 0.2-2.0L / min. By controlling the aeration flow rate between 0.2-2.0L / min, sufficient supply of oxygen in the reaction chamber is ensured, which not only avoids the decrease in electrocatalytic degradation efficiency caused by insufficient oxygen, but also prevents waste of resources and energy loss caused by excessive oxygen. Reasonable aeration flow rate can enhance the turbulence of wastewater and promote effective contact between solutes in wastewater and electrode surfaces, thereby improving mass transfer efficiency. Stable aeration flow rate helps to maintain the relative stability of the environment in the reaction chamber and reduce reaction instability caused by airflow fluctuations.

[0085] As a preferred embodiment, during the reaction process, the double-sided cathode uses a constant voltage or pulse mode to control the electrode, and the electrode voltage is -5 to 2V relative to the standard hydrogen electrode potential, which inhibits excessive hydrogen evolution reaction and other competing processes to effectively improve the current efficiency.

[0086] Embodiment 1:

[0087] 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 oxide hydroxide (FeOOH) is close to the aeration port; the constant voltage mode is adopted, and the constant voltage is -1.05V (relative to the Ag / AgCl reference electrode, after conversion, -0.5V is 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.

[0088] The nitrogen-containing organic wastewater is simulated wastewater, and each 1L of simulated wastewater contains 50mmolNa2SO4, 50mgNaCl, 20mgNaNO3 and 20mg tetracycline;

[0089] The thickness of the graphite felt is between 1-5 mm. After the graphite felt is ultrasonically cleaned with deionized water, acetone, and anhydrous ethanol for 15-30 minutes, it 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 60-85°C water bath for 6-10 hours, and then washed with deionized water until neutral. Finally, the graphite felt is placed in a 60-80°C oven and dried for 12-24 hours, and marked as pretreated graphite felt. The pretreated graphite felt is loaded with functional catalysts by a double-sided rolling coating process with the aid of a roll-to-roll coating roller system, and then cut to a suitable size for standby use. The present invention simultaneously loads different functional catalysts on both sides of the substrate through a double-sided rolling coating process, and accelerates the curing of the catalyst ink by infrared heating and drying. 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 affect the use effect.

[0090] The roll-to-roll coating roller system was purchased from Hefei Kejing, model MSK-AFA-MC200, with an optional micro-gravure coating method, equipped with an MSK-155 feeding device and an infrared heating drying oven, and the roller diameter of the micro-gravure coating method is 30mm. The electrode substrate is placed in the roll-to-roll coating roller system, the thickness of the electrode substrate material is 0.1-5mm, the above catalyst ink is placed in the feeding device, and the coating speed is 0.1-0.4m / min.

[0091] The specific coating process on the coating machine includes unwinding, coating, infrared curing and winding. The specific steps are as follows:

[0092] Unwinding: The unwinding shaft releases the electrode substrate and moves toward the winding shaft. The unwinding tension of the unwinding shaft is 10-22N.

[0093] Coating: The electrode substrate passes through the anilox rollers on both sides. The anilox rollers are closely attached to the electrode substrate and use their surface texture to evenly coat the pre-prepared catalyst ink on the corresponding side of the electrode substrate, thereby forming an electrode structure with double-sided coating.

[0094] Infrared curing: The double-sided electrode enters the heating and drying device. The heating method is infrared heating. The heating temperature is between 50-80℃. The heating time is 0.5-3min. The tension of the double-sided electrode in the heating and drying device is maintained at 6-15N.

[0095] Winding: The coated electrode is wound up by the winding shaft, and the winding tension is 4-12N.

[0096] In this embodiment, Pd powder is a commercial catalyst with a particle size of 50 nm purchased; FeOOH is synthesized by hydrothermal method:

[0097] 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.

[0098] 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, the mass concentration of the NaOH precursor solution is between 60-100 g / L, the mixing and stirring speed of the precursor solution is not less than 300 rpm, the stirring time is between 1-3 hours, the water bath synthesis temperature is between 150-180°C, and the insulation time is 16-24 hours. The vacuum drying temperature of the product is between 60-85°C, and the drying time is 12-24 hours.

[0099] In this embodiment, the precursor solution is prepared by dissolving 4.0567gFeCl3·6H2O in 30mL deionized water and magnetically stirring at room temperature for 30min. Then, 2.8989gNaOH is dissolved in another 40mL deionized water to prepare a NaOH solution, and then the NaOH solution is slowly added to the above FeCl3 aqueous solution, and further stirred at a speed of 600rpm for 1h. Finally, the mixed solution is transferred to a Teflon-lined autoclave, heated to 160°C in a blast drying oven, and kept warm for 16h. After the reaction is completed, it is naturally cooled to room temperature, the product is collected, washed with deionized water 3-5 times, and then dried in a vacuum drying oven at 60°C for 12h.

[0100] 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.

[0101] In this embodiment, 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 Nafion (5wt%), ultrasonicate for 0.5-2h to make it completely dispersed, and stir at a speed of 400-1000rpm for 1-3h to prepare the first catalyst ink for coating the side with denitrification function in the double-sided electrode, and set it aside.

[0102] 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 for 0.5-2h to make it completely dispersed, and stir at a speed of 400-1000rpm for 1-3h to prepare a first catalyst ink for coating the side of the double-sided electrode with electrocatalytic degradation function, and set it aside.

[0103] 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 of 3 cm × 2 cm in size for use.

[0104] Embodiment 2:

[0105] 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.

[0106] Embodiment 3:

[0107] 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.

[0108] Comparative Example 1

[0109] 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.

[0110] Comparative Example 2

[0111] 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.

[0112] Comparative Example 3

[0113] 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.

[0114] 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 was as high as 86.84%, while the electrocatalytic system without double-sided cathode (Comparative Example 1) had a 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.

[0115] from Figure 4 It can be seen from the analysis that the double-sided cathode based electrocatalytic system of the present invention has excellent removal effects on a variety of organic pollutants, and the degradation rates of tetracycline, sulfamethoxazole and rhodamine B are as high as 95.46%, 98.69% and 100%, respectively, while the electrocatalytic system without a double-sided cathode has removal rates of tetracycline, sulfamethoxazole and rhodamine B of only 28.57%, 32.95% and 41.28, respectively. The comparison illustrates the excellent degradation ability of the electrocatalytic system based on the double-sided cathode for a variety of organic pollutants.

[0116] The above implementation modes 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 substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. An electrochemical system for treating nitrogen-containing organic wastewater based on double-sided cathode, characterized in that: include: A reactor, wherein a reaction chamber is defined in the reactor, and the reactor is provided with a liquid inlet and a liquid outlet respectively connected to 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 for supplying power; an anode connected to the positive electrode of the power supply; 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 substrate, the first side of the electrode substrate forms a first cathode with a denitrification function, and the second side of the electrode substrate 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.

2. The electrochemical system for treating nitrogen-containing organic wastewater based on 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 double-sided electrode is prepared from a first catalyst material with a denitrification function, a second catalyst material with an electrocatalytic degradation function, and an electrode substrate; wherein the first side of the electrode substrate is loaded with a catalyst material with a denitrification function to form a first cathode, and the first side of the electrode substrate is loaded with a catalyst material with an electrocatalytic degradation function to form a second cathode; both the first catalyst material and the second catalyst material contain a conductive binder.

4. The electrochemical system for treating nitrogen-containing organic wastewater based on double-sided cathode according to claim 3, characterized in that: The method for preparing the double-sided electrode adopts a roll-to-roll coating rolling system and comprises the following steps: Material preparation step: preparing the electrode substrate, the first catalyst ink and the second catalyst ink in advance and setting them aside; Unwinding step: the unwinding shaft releases the electrode substrate and moves toward the winding shaft, and 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 closely attached to the electrode substrate, and the pre-prepared first catalyst ink and second catalyst ink are respectively and evenly coated on the opposite sides of the electrode substrate by using the surface texture of the anilox rollers, thereby forming an electrode structure with 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℃, the heating time is 0.5-3min, and the tension of the double-sided electrode in the heating and drying device is maintained at 6-15N; Winding step: The coated electrode is wound up by a winding shaft, and the winding tension is 4-12N.

5. The electrochemical system for treating nitrogen-containing organic wastewater based on double-sided cathode according to claim 3, characterized in that: 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; 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; Alternatively, the electrode substrate is a carbon material or a metal material, the carbon material includes any one of carbon paper, carbon cloth, carbon felt and graphite felt or a combination of at least two thereof, and the metal material includes Pt, Ru, Rh, Fe, Co, Ni, Cu and Ti as well as alloy electrodes based on these elements; Alternatively, the conductive adhesive is any one of polyvinylidene fluoride, perfluorosulfonic acid polymer, polytetrafluoroethylene and polydimethylsiloxane, or a combination of at least two thereof.

6. 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.

7. The electrochemical system for treating nitrogen-containing organic wastewater based on double-sided cathode according to claim 4, characterized in that: The preparation method of the electrode substrate is as follows: selecting graphite felt with a thickness of 1-5 mm, using deionized water, acetone, and anhydrous ethanol to ultrasonically clean the graphite felt for 15-30 minutes each, and then placing it in a vacuum drying oven at 60-80° C. to dry 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. to dry it for 12-24 hours to obtain pretreated graphite felt as the electrode substrate.

8. The electrochemical system for treating nitrogen-containing organic wastewater based on double-sided cathode according to claim 4, characterized in that: 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 a perfluorosulfonic acid polymer with a weight content of 5wt%, ultrasonicate for 0.5-2h to make it completely dispersed, and stir 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 electrode.

9. The electrochemical system for treating nitrogen-containing organic wastewater based on double-sided cathode according to claim 4, characterized in that: 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 make it completely dispersed, 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 electrode with electrocatalytic degradation function.

10. 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 9 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. - Converted to Cl· and diffused into the water phase; the first cathode of the double-sided cathode converts NO3 - Reduction 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, 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 voltage of the electrode is -5~2V relative to the standard hydrogen electrode potential.

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