Purification system and method based on photocatalytic degradation of landfill leachate

Abstract

The invention discloses a purification system and method based on photocatalytic degradation of landfill leachate, and belongs to the technical field of landfill leachate purification, the purification system comprises a reaction unit, a photocatalytic unit and a control system; the reaction unit comprises a reaction chamber as well as an electrolysis assembly and a delivery pump which are arranged in the reaction chamber; the reaction chamber is connected with a liquid inlet pipe and a liquid outlet pipe; the photocatalysis unit comprises a photocatalysis chamber and a photocatalysis assembly arranged in the photocatalysis chamber, the photocatalysis chamber is communicated with the reaction chamber through a communicating pipe, and the photocatalysis chamber is provided with a filter at the outlet end of the communicating pipe; a liquid return pipe communicated with the reaction chamber is arranged at the rear end of the photocatalysis assembly in the photocatalysis chamber; the control system comprises a power supply unit and a control panel, and the control panel can control starting or stopping of the electrolysis assembly, the conveying pump and the photocatalysis assembly. The electrolysis system is adopted to remove inorganic substances in sewage, scale deposition on the surface of the photocatalysis system is prevented, and the synergistic purification treatment effect with the photocatalysis system is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of landfill leachate purification, and in particular to a landfill leachate purification system and method based on photocatalytic degradation. Background Art

[0002] In recent years, the treatment of leachate from landfills has become a huge challenge in the process of environmental governance. This is mainly because leachate contains a large amount of organic matter, humic acid and fulvic acid, as well as foreign organic compounds (such as aromatic hydrocarbons, phenols, chlorinated aliphatic groups, pesticides and plasticizers), which leads to its low biodegradability and limits the application of many traditional water purification methods. At present, the main treatment technologies for leachate include coagulation and sedimentation, adsorption, membrane separation, etc. At present, various types of traditional leachate treatment methods have disadvantages such as high cost, secondary treatment, and complex processes. Therefore, there is an urgent need for a new and environmentally friendly water treatment technology with strong pertinence that can effectively treat a large amount of organic pollutants in leachate.

[0003] As an advanced oxidation technology, photocatalytic technology has the characteristics of low cost, environmental protection, pollution-free, flexible operation and strong oxidizing ability. It has broad application prospects in the treatment of difficult-to-degrade organic wastewater. Many researchers at home and abroad have developed and prepared a series of photocatalysts to solve environmental pollution problems, especially in the treatment of landfill leachate. Some good results have been achieved. Among them, single-type photocatalysts such as TiO2, ZnO, CuS, and CdS are the most common. These photocatalysts have the ability to degrade organic pollutants in landfill leachate to varying degrees. Current research shows that photocatalytic technology has potential in the field of landfill leachate degradation.

[0004] The local atomic structure of zinc tungstate is an asymmetric monoclinic wolframite structure, with a space group of P2 / c, and its ionic radius crystallization is a scheelite structure. Thanks to the tungsten cluster network, the covalent nature of the WO bond formed is more stable. When the electron-hole pairs are formed by light excitation, the WO6 cluster acts as an electron acceptor, and the Zn and W vacancies act as hole traps. This structure also helps the separation of charge carriers. The unique crystal structure of ZnWO4 gives it high thermal stability, excellent optical and electrical properties, and is widely used in photocatalysis, photoluminescence, and lithium battery negative electrode materials. However, zinc tungstate has defects such as low specific surface area and complex preparation methods when used as a photocatalyst for photocatalytic degradation. Summary of the invention

[0005] Technical problem to be solved: In view of the problems existing in the prior art in the purification process of landfill leachate, the present invention provides a purification system and method for landfill leachate based on photocatalytic degradation, wherein an electrolysis system is used to remove inorganic substances in sewage, in which water is oscillated and electrolyzed to remove scale deposits on the surface of the photocatalytic system, thereby achieving a coordinated purification effect with the photocatalytic system; a zinc tungstate catalyst with a nanofiber structure is synthesized based on electrospinning technology, and zinc tungstate at the nanometer size can obtain stronger redox ability due to the quantum size effect, and the fiber mesh structure can greatly increase its specific surface area, thereby obtaining a better ability to adsorb and degrade organic pollutants.

[0006] Technical solution: The present invention discloses a purification system based on photocatalytic degradation of landfill leachate, the purification system comprising a reaction unit, a photocatalytic unit and a control system; The reaction unit comprises a reaction chamber for storing leachate, an electrolytic component and a delivery pump placed in the reaction chamber, and the electrolytic component and the delivery pump are electrically connected to the control system; the reaction chamber is connected to a liquid inlet pipe and a liquid outlet pipe; The photocatalytic unit comprises a photocatalytic chamber and a photocatalytic component placed in the photocatalytic chamber, wherein the photocatalytic chamber is connected to the reaction chamber through a connecting pipe, and a filter is provided at the outlet end of the connecting pipe of the photocatalytic chamber; the photocatalytic chamber is provided with a liquid return pipe connected to the reaction chamber at the rear end of the photocatalytic component; The control system includes a power supply unit and a control panel, and the control panel can control the start or stop of the electrolytic component, the delivery pump and the photocatalytic component.

[0007] Preferably, the reaction unit comprises at least one electrolytic assembly, wherein the electrolytic assembly comprises an anode and a cathode arranged opposite to each other and an electrode box disposed outside the anode and the cathode.

[0008] Preferably, the anode and cathode are made of one of zinc, magnesium alloy, copper, iron, stainless steel, titanium alloy, aluminum alloy and platinum; the anode and cathode are plate, rod or cylindrical structures.

[0009] Preferably, the electrode box is a cylindrical structure with a grid surface, made of stainless steel, titanium or other rust-resistant metals; the contact parts between the electrode box and the cathode and the anode are coated with a synthetic resin coating to ensure insulation.

[0010] Preferably, the filter is made of porous oxide ceramics, alumina, synthetic resin fiber or activated carbon material; the synthetic resin fiber is a non-woven fabric processed from polypropylene fiber; the pore size of the filter is 60-200 meshes.

[0011] Preferably, the photocatalytic component comprises a plurality of ultraviolet lamp groups and photocatalyst carriers which are equally spaced and relatively alternately arranged; the photocatalyst carrier is made of porous titanium dioxide and is loaded with a zinc tungstate photocatalyst having a nanofiber structure.

[0012] Preferably, the ultraviolet lamp groups are electrically connected to the control system respectively, and emit a radiation light source with a spectrum range of 180~400nm, which can irradiate adjacent photocatalyst carriers; each ultraviolet lamp group is composed of a double silicon glass tube, and the outer tube is used as a sheath to protect the internal light-emitting element.

[0013] Preferably, the ultraviolet lamp group and the photocatalyst carrier are arranged parallel to the water flow, so that the leachate flows along the length of the ultraviolet lamp group and the photocatalyst carrier.

[0014] Preferably, the specific preparation method of the zinc tungstate photocatalyst is: Step 1: Take 10 mL of deionized water and add it to a 50 mL conical flask. Then weigh 0.2634 g of zinc acetate and 1.05 g of citric acid and add them to the conical flask. After magnetic stirring to dissolve, add 0.306 g of ammonium paratungstate. Immediately move the conical flask to a water bath and heat it at 75° for 8 min. Then take it out and add 10 ml of anhydrous ethanol and 3.0 g of PVP as a polymer skeleton. After magnetic stirring for 12 hours, prepare for spinning. Step 2: During the electrospinning process, the prepared spinning solution was transferred to a 20 mL syringe with a No. 21 stainless steel needle. A receiving roller covered with aluminum foil was used as a receiving device. The distance between the tip of the stainless steel needle and the receiving roller was 25 cm. A positive voltage of 28 kV was applied to the stainless steel needle and a negative voltage of 5 kV was applied to the receiving roller. The receiving roller rotated at 300 rpm and the syringe pushed liquid at a speed of 3.0 mL / h to perform electrospinning. Step 3: After the electrospinning is completed, the obtained fiber is placed in a muffle furnace and heated to 600°C at a heating rate of 1°C / min and kept warm for 3 h, and then naturally cooled to room temperature to obtain zinc tungstate nanofibers; Step 4: calcining the obtained zinc tungstate photo-nanofibers to remove the polymer PVP skeleton, and preparing the zinc tungstate photocatalyst.

[0015] The present invention also discloses a method for purifying landfill leachate based on photocatalytic degradation, the method comprising: Step 1: The collected and pre-treated landfill leachate is transported to the reaction chamber for storage through the liquid inlet pipe, and the inorganic compounds in the landfill leachate are stripped and removed by flocculation and precipitation under the electrolysis of the electrolytic components in the reaction chamber; Step 2: After the electrolysis treatment, the leachate flows into the photocatalytic chamber through the connecting pipe under the action of the delivery pump, and the filter filters the leachate entering the photocatalytic chamber to remove inorganic flocculants; Step 3: The leachate stored in the photocatalytic chamber is irradiated by an ultraviolet lamp group, and the organic pollutants are degraded and purified under the action of the zinc tungstate photocatalyst loaded on the photocatalyst carrier; Step 4: The purified liquid after the photocatalytic purification treatment flows back to the reaction chamber through the return pipe for storage, and after the electrolysis and photocatalytic treatment processes are circulated for multiple times, it is discharged through the drainage pipe of the reaction chamber.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The purification system of the present invention adopts an electrolysis system to remove inorganic substances from sewage. In the electrolysis system, water is oscillated and electrolyzed to remove inorganic substances, thereby preventing scale deposition on the surface of the photocatalytic system and achieving a coordinated purification and treatment effect with the photocatalytic system. 2. This purification method synthesizes a zinc tungstate catalyst with a nanofiber structure based on electrospinning technology. Zinc tungstate at the nanometer size can obtain stronger redox ability due to the quantum size effect, and the fiber mesh structure can greatly increase its specific surface area and obtain better ability to adsorb and degrade organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the purification system process structure of the present invention; Figure 2 is the XRD diagram of the zinc tungstate photocatalyst in the present invention; Figure 3 is a SEM image of the zinc tungstate photocatalyst of the present invention; Figure 4 This is a graph showing the degradation performance of the zinc tungstate photocatalyst of the present invention.

[0018] Figure numerals: 100, purification system; 1, reaction unit; 2, photocatalytic unit; 3, electrolytic assembly; 3A, cathode; 3B, anode; 3C, electrode box; 4, delivery pump; 5, filter; 6, ultraviolet lamp group; 7, photocatalyst carrier; 8, connecting pipe; 9, liquid return pipe; 10, control system; 11, reaction chamber; 12, liquid inlet pipe; 13, liquid discharge pipe; 14, leachate; 15, photocatalytic chamber; 151, water inlet end of photocatalytic chamber; 152, water outlet end of photocatalytic chamber. DETAILED DESCRIPTION

[0019] To make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the following will be combined with the attached Figures 1 to 4The technical solutions of the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0020] Example 1: Figure 1 As shown, a purification system for landfill leachate based on photocatalytic degradation of the present invention, the purification system 100 includes a reaction unit 1, a photocatalytic unit 2 and a control system 10.

[0021] The reaction unit 1 includes a reaction chamber 11 for storing leachate 14, and an electrolytic component 3 and a delivery pump 4 placed in the reaction chamber 11. The electrolytic component 3 and the delivery pump 4 are electrically connected to the control system 10. A liquid inlet pipe 12 is connected to the top of the reaction chamber 11, and a liquid discharge pipe 13 is arranged on one side of the bottom thereof. The liquid inlet pipe 12 meets the liquid inlet demand of the garbage leachate, and the liquid discharge pipe 13 meets the discharge demand of the garbage leachate after purification.

[0022] The reaction unit 1 includes at least one electrolytic component 3. The increase in the number of electrolytic components 3 can improve its purification efficiency for landfill leachate. The electrolytic component 3 includes an anode 3B and a cathode 3A arranged opposite to each other, and an electrode box 3C placed outside the anode 3B and the cathode 3A. The anode 3B and the cathode 3A can be made of one of zinc, magnesium alloy, copper, iron, stainless steel, titanium alloy, aluminum alloy, and platinum; any of the above metal materials can be used as electrode materials, which can provide degradation redox potential for the leachate, but when platinum-plated titanium alloy is used as the electrode material, the effect is particularly significant. The anode 3B and the cathode 3A electrodes can be made into plates, rods or cylindrical structures. The electrode box 3C is a cylindrical structure with a grid surface, made of stainless steel, titanium or other rust-resistant metals; the contact parts between it and the cathode 3A and the anode 3B are coated with a synthetic resin coating to ensure insulation. The electrode box 3C can be used to prevent scale from being deposited on the cathode 3A and the anode 3B, thereby collecting cathode scale, and can also reduce scale deposition on the downstream ultraviolet lamp group 6.

[0023] The photocatalytic unit 2 includes a photocatalytic chamber 15 and a photocatalytic component placed in the photocatalytic chamber 15. The water inlet end 151 of the photocatalytic chamber is connected to the reaction chamber 11 through a connecting pipe 8, and the water inlet end 151 of the photocatalytic chamber is located at the outlet end of the connecting pipe 8 and is provided with a filter 5; the water outlet end 152 of the photocatalytic chamber is located at the rear end of the photocatalytic component and is provided with a return liquid pipe 9 connected to the reaction chamber 11. The filter 5 is made of porous oxide ceramic, alumina, synthetic resin fiber or activated carbon material; the synthetic resin fiber is a non-woven fabric processed from polypropylene fiber; the pore size of the filter 5 is 60-200 meshes, and the inorganic flocculants generated in the electrolysis process in the reaction chamber 11 can be filtered and blocked to prevent the inorganic flocculants from entering the tube catalyst chamber and causing the photocatalytic component to be polluted and ineffective.

[0024] The photocatalytic component includes a plurality of ultraviolet lamp groups 6 and photocatalyst carriers 7 which are equally spaced and relatively alternately arranged. The ultraviolet lamp groups 6 are electrically connected to the control system 10 respectively, and emit a radiation light source with a spectrum range of 180 to 400 nm, which can irradiate the adjacent photocatalyst carriers 7; each ultraviolet lamp group 6 is composed of a double silicon glass tube, and the outer tube is used as a sheath to protect the internal light-emitting element from the influence of water. The photocatalyst carrier 7 is made of porous titanium dioxide, and a zinc tungstate photocatalyst with a nanofiber structure is loaded thereon. There is a synergistic effect between the titanium dioxide and the zinc tungstate photocatalyst, which can enhance the photocatalytic purification performance of the landfill leachate.

[0025] In a preferred embodiment, the ultraviolet lamp group 6 and the photocatalyst carrier 7 are arranged parallel to the water flow, so that the leachate flows along the length of the ultraviolet lamp group 6 and the photocatalyst carrier 7, extending the contact time between the leachate and the photocatalyst carrier 7, thereby improving the photocatalytic purification efficiency of the leachate.

[0026] The control system 10 includes a power supply unit and a control panel. The power supply system uses an external mains or battery pack to power various electrical appliances in the purification system. The control panel uses existing technology to integrate various control functions. The control panel can control the start or stop of the electrolytic component 3, the delivery pump 4 and the photocatalytic component.

[0027] Most conventional photocatalytic water treatment technologies face the same problem: during long-term sewage treatment, the photocatalytic system will deposit scale and oil on the silicon glass shell of the ultraviolet lamp group 6, reducing the ultraviolet transmittance, resulting in a decrease in the performance of the ultraviolet lamp group 6, which reduces the sewage purification capacity. The purification system of the present invention uses an electrolysis system to remove inorganic substances in sewage. In the electrolysis system, water is oscillated and electrolyzed to remove it, preventing scale deposition on the surface of the photocatalytic system, thereby achieving a coordinated purification and treatment effect with the photocatalytic system.

[0028] Example 2: The specific preparation method of the zinc tungstate photocatalyst with nanofiber structure in Example 1 is: Step 1: Take 10 mL of deionized water and add it to a 50 mL conical flask. Weigh 0.2634 g of zinc acetate and 1.05 g of citric acid in turn and add them to the conical flask. Stir magnetically until dissolved. Then add 0.306 g of ammonium paratungstate. Immediately move the conical flask to a water bath and heat it at 75° for 8 min. Then take it out and add 10 ml of anhydrous ethanol and 3.0 g of PVP as the polymer skeleton. Stir magnetically for 12 hours before spinning.

[0029] Step 2: During the electrospinning process, the prepared spinning solution was transferred to a 20 mL syringe with a No. 21 stainless steel needle. A receiving roller covered with aluminum foil was used as a receiving device. The distance between the tip of the stainless steel needle and the receiving roller was 25 cm. A positive voltage of 28 kV was applied to the stainless steel needle and a negative voltage of 5 kV was applied to the receiving roller. The receiving roller rotated at 300 rpm and the syringe pushed liquid at a speed of 3.0 mL / h to perform electrospinning.

[0030] Step 3: After the electrospinning is completed, the obtained fiber is placed in a muffle furnace and heated to 600°C at a heating rate of 1°C / min and kept warm for 3 h, and then naturally cooled to room temperature to obtain zinc tungstate nanofibers.

[0031] Step 4: calcining the obtained zinc tungstate photo-nanofibers to remove the polymer PVP skeleton, and preparing the zinc tungstate photocatalyst.

[0032] Figure 2 is the XRD structural characterization diagram of the prepared zinc tungstate photocatalyst, in which the diffraction peaks of the sample are 15.45°, 18.97°, 23.73°, 24.51°, 30.46°, 31.35°, 36.31°, 38.37°, 41.37°, 44.44°, 45.79°, 48.69°, 50.35°, 51.77°, 53.89°, 61.78°, 64.85°, and 68.26°, respectively. (010), (100), (011), (110), (111), (020), (021), (200), (121), (112), (211), (022), (220), (130), (-202), (113), (-311), and (041). All diffraction peaks can be labeled as monoclinic zinc tungstate structure with space group P2 / C, which is consistent with JCPDS No. 88-0251.

[0033] Figure 3 This is the microscopic morphology of zinc tungstate photocatalyst. Figure 3 (a) is a W / Zn / PVP composite nanofiber obtained by electrospinning. Its spatial distribution is uniform, the fiber surface is smooth without beads, the average diameter is about 500nm, and there are interconnected macropores. After calcination to remove the polymer PVP skeleton, the obtained Figure 3 (b) is the morphology of pure zinc tungstate nanofibers. Its average diameter is narrowed to about 200~300nm, and a large number of pore structures appear on the fiber surface, which provides a large number of reaction sites and adsorption capacity for the degradation of landfill leachate.

[0034] The degradation performance test of the zinc tungstate photocatalyst prepared in Example 2 was carried out. The specific test method was: 100 mL of diluted landfill leachate was measured and placed in a quartz reactor equipped with a cooling water circulation device, 0.1 g of zinc tungstate photocatalyst was added, and it was first stirred in the dark for 0.5 h to reach adsorption-desorption equilibrium, and then a 300 W xenon lamp was turned on for light irradiation reaction. Samples were taken every 40 minutes, and the samples were filtered through a 0.22 micron filter membrane and then subjected to a COD test. The COD test method was the dichromate method. Figure 3 This is the degradation performance diagram of zinc tungstate photocatalyst, C0 is the initial COD concentration, C is the COD concentration after the reaction. It can be seen that as the photocatalytic reaction proceeds, the COD concentration in the test sample decreases significantly, and the COD degradation rate reaches 78.2% when the photocatalytic reaction lasts for 160 minutes.

[0035] When zinc tungstate is used as a photocatalyst for photocatalytic degradation, it has the defects of low specific surface area and complex preparation method. In order to overcome and improve the defects of zinc tungstate and improve its practical application effect in photocatalytic degradation of landfill leachate, the present invention synthesizes a zinc tungstate catalyst with a nanofiber structure based on electrospinning technology. Zinc tungstate at the nanometer size can obtain stronger redox ability due to the quantum size effect, and the fiber mesh structure can greatly increase its specific surface area and obtain better ability to adsorb and degrade organic pollutants.

[0036] Example 3: The present invention also discloses a method for purifying landfill leachate based on photocatalytic degradation, the purification method is: Step 1: The collected and pre-treated landfill leachate is transported to the reaction chamber 11 through the liquid inlet pipe 12 for storage, and the inorganic compounds in the landfill leachate are stripped and removed by flocculation and precipitation under the electrolysis of the electrolytic component 3 in the reaction chamber 11; Step 2: After the electrolysis treatment, the leachate flows into the photocatalytic chamber 15 through the connecting pipe 8 under the action of the delivery pump 4, and the filter 5 filters the leachate entering the photocatalytic chamber 15 to remove inorganic flocculants; Step 3: The leachate stored in the photocatalytic chamber 15 is irradiated by the ultraviolet lamp group 6, and the organic pollutants are degraded and purified under the action of the zinc tungstate photocatalyst loaded on the photocatalyst carrier 7; Step 4: The purified liquid after the photocatalytic purification treatment flows back to the reaction chamber 11 through the return pipe 9 for storage, and after the electrolysis and photocatalytic treatment processes are circulated for multiple times, it is discharged through the drain pipe 13 of the reaction chamber 11.

[0037] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A purification system based on photocatalytic degradation of landfill leachate, characterized in that: The purification system (100) comprises a reaction unit (1), a photocatalytic unit (2) and a control system (10); The reaction unit (1) comprises a reaction chamber (11) for storing leachate, and an electrolytic component (3) and a delivery pump (4) disposed in the reaction chamber (11), wherein the electrolytic component (3) and the delivery pump (4) are electrically connected to a control system (10); the reaction chamber (11) is connected to a liquid inlet pipe (12) and a liquid outlet pipe (13); The photocatalytic unit (2) comprises a photocatalytic chamber (15) and a photocatalytic component disposed in the photocatalytic chamber (15); the photocatalytic chamber (15) is connected to the reaction chamber (11) via a connecting pipe (8), and a filter (5) is provided at the outlet end of the connecting pipe (8) in the photocatalytic chamber (15); and a liquid return pipe (9) is provided at the rear end of the photocatalytic component in the photocatalytic chamber (15) and is connected to the reaction chamber (11); The control system (10) comprises a power supply unit and a control panel, and the control panel can control the start or stop of the electrolysis component (3), the delivery pump (4) and the photocatalytic component.

2. The purification system based on photocatalytic degradation of landfill leachate according to claim 1 is characterized in that: The reaction unit (1) comprises at least one electrolytic component (3), wherein the electrolytic component (3) comprises an anode (3B) and a cathode (3A) arranged opposite to each other, and an electrode box (3C) disposed outside the anode (3B) and the cathode (3A).

3. The purification system based on photocatalytic degradation of landfill leachate according to claim 2 is characterized in that: The anode (3B) and cathode (3A) are made of one of zinc, magnesium alloy, copper, iron, stainless steel, titanium alloy, aluminum alloy and platinum; the anode (3B) and cathode (3A) are plate, rod or cylindrical structures.

4. The purification system based on photocatalytic degradation of landfill leachate according to claim 2 is characterized in that: The electrode box (3C) is a cylindrical structure with a grid surface and is made of stainless steel, titanium or other rust-resistant metals; the contact parts between the electrode box and the cathode (3A) and the anode (3B) are coated with a synthetic resin coating to ensure insulation.

5. The purification system based on photocatalytic degradation of landfill leachate according to claim 1 is characterized in that: The filter (5) is made of porous oxide ceramics, aluminum oxide, synthetic resin fibers or activated carbon materials; the synthetic resin fibers are non-woven fabrics processed from polypropylene fibers; and the pore size of the filter (5) is 60-200 meshes.

6. The purification system based on photocatalytic degradation of landfill leachate according to claim 1 is characterized in that: The photocatalytic component comprises a plurality of ultraviolet lamp groups (6) and a photocatalyst carrier (7) which are equally spaced and relatively alternately arranged; the photocatalyst carrier (7) is made of porous titanium dioxide and is loaded with a zinc tungstate photocatalyst having a nanofiber structure.

7. The purification system based on photocatalytic degradation of landfill leachate according to claim 6 is characterized in that: The ultraviolet lamp groups (6) are electrically connected to the control system (10) respectively, and emit a radiation light source with a spectrum range of 180-400 nm, and the radiation light source can irradiate the adjacent photocatalyst carrier (7); each ultraviolet lamp group (6) is composed of a double silicon glass tube, and the outer tube is used as a sheath to protect the internal light-emitting element.

8. The purification system based on photocatalytic degradation of landfill leachate according to claim 6 is characterized in that: The ultraviolet lamp group (6) and the photocatalyst carrier (7) are arranged parallel to the water flow, so that the leachate flows along the length of the ultraviolet lamp group (6) and the photocatalyst carrier (7).

9. The purification system based on photocatalytic degradation of landfill leachate according to claim 6 is characterized in that: The specific preparation method of the zinc tungstate photocatalyst is: Step 1: Take 10 mL of deionized water and add it to a 50 mL conical flask. Then weigh 0.2634 g of zinc acetate and 1.05 g of citric acid and add them to the conical flask. After magnetic stirring to dissolve, add 0.306 g of ammonium paratungstate. Immediately move the conical flask to a water bath and heat it at 75° for 8 min. Then take it out and add 10 ml of anhydrous ethanol and 3.0 g of PVP as a polymer skeleton. After magnetic stirring for 12 hours, prepare for spinning. Step 2: During the electrospinning process, the prepared spinning solution was transferred to a 20 mL syringe with a No. 21 stainless steel needle. A receiving roller covered with aluminum foil was used as a receiving device. The distance between the tip of the stainless steel needle and the receiving roller was 25 cm. A positive voltage of 28 kV was applied to the stainless steel needle and a negative voltage of 5 kV was applied to the receiving roller. The receiving roller rotated at 300 rpm and the syringe pushed liquid at a speed of 3.0 mL / h to perform electrospinning. Step 3: After the electrospinning is completed, the obtained fiber is placed in a muffle furnace and heated to 600°C at a heating rate of 1°C / min and kept warm for 3 h, and then naturally cooled to room temperature to obtain zinc tungstate nanofibers; Step 4: calcining the obtained zinc tungstate photo-nanofibers to remove the polymer PVP skeleton, and preparing the zinc tungstate photocatalyst.

10. A method for purifying landfill leachate based on photocatalytic degradation, characterized in that: Using any one of the purification systems 1 to 9, the purification method is: Step 1: The collected and pre-treated landfill leachate is transported to a reaction chamber (11) for storage through a liquid inlet pipe (12), and inorganic compounds in the landfill leachate are stripped and removed by flocculation and precipitation under the electrolysis of an electrolytic component (3) in the reaction chamber (11); Step 2: After the electrolytic treatment, the leachate flows into the photocatalytic chamber (15) through the connecting pipe (8) under the action of the delivery pump (4), and the filter (5) filters the leachate entering the photocatalytic chamber (15) to remove inorganic flocculants; Step 3: The leachate stored in the photocatalytic chamber (15) is irradiated by the ultraviolet lamp group (6), and the organic pollutants are degraded and purified under the action of the zinc tungstate photocatalyst loaded on the photocatalyst carrier (7); Step 4: The purified liquid that has undergone photocatalytic purification treatment flows back to the reaction chamber (11) through the return pipe (9) for storage, and after the electrolysis and photocatalytic treatment processes are circulated for multiple times, it is discharged through the discharge pipe (13) of the reaction chamber (11).

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