A self-cleaning membrane bioreactor and its use method

Abstract

The present invention relates to the field of membrane bioreactors and discloses a self-cleaning membrane bioreactor and a method for using the same. The self-cleaning membrane bioreactor comprises a membrane assembly unit and an external focusing frame unit for focusing visible light onto the membrane assembly unit; the membrane assembly unit comprises one or more membrane sheets; the membrane sheets contain a modified TiO2-based visible light catalyst; the modified TiO2-based visible light catalyst is an acutospore-type TiO2 modified by doping with Mn, N, and Cu. The self-cleaning membrane bioreactor of the present invention adds a special modified TiO2-based visible light catalyst to the membrane sheet and is equipped with an external focusing frame unit. It does not require ultraviolet light irradiation and can achieve a good self-cleaning effect under sunlight, thereby reducing the energy consumption and cost of operating and maintaining the membrane bioreactor.

Description

Technical Field

[0001] The present invention relates to the field of membrane bioreactors, and in particular to a self-cleaning membrane bioreactor and a use method thereof. Background Art

[0002] The use of activated sludge for biochemical treatment is an important method for treating organic wastewater. Traditional activated sludge methods include sequential batch activated sludge process (SBR), anaerobic aerobic process (AO), anaerobic-anoxic-aerobic process (AAO), oxidation ditch process, membrane separation activated sludge process (MBR), etc. The first four methods all have the problem of sludge bulking, and in order to ensure the effluent quality, sedimentation tanks and filter tanks need to be set up, and the process occupies a large area. In comparison, the MBR method eliminates the sedimentation tanks and filter tanks, significantly reducing the floor space of the process equipment. It has the advantages of stable effluent water quality, high activated sludge concentration, and low residual sludge production, and has good development prospects.

[0003] The primary technical challenge facing MBR treatment technology currently is membrane fouling. Prolonged exposure of the MBR's filter membrane to high concentrations of activated sludge easily forms a fouling layer on the membrane surface, which affects the membrane's permeability, reduces the overall MBR equipment's water treatment efficiency, and increases process energy consumption. Membrane fouling caused by organic pollutants and microorganisms is the most problematic, as conventional membrane cleaning methods cannot effectively restore it. This can easily lead to irreversible membrane fouling, and in severe cases, the filter membrane loses its function and requires replacement. Therefore, MBR membrane fouling, which results in frequent and high maintenance costs for membrane materials, presents a technical challenge that urgently needs to be addressed.

[0004] Patent CN202221109657.8 discloses an MBR membrane assembly that uses photocatalytic advanced oxidation for self-cleaning. This involves adding LED ultraviolet light strips of appropriate wavelengths evenly distributed between the MBR membranes and adding a titanium dioxide layer to the exposed portion of the MBR membrane support frame. This, along with basic control logic, enables online automatic physical cleaning based on photocatalytic advanced oxidation. This patent uses titanium dioxide as a photocatalyst, but its photocatalytic activity under visible light is very low. Therefore, the MBR membrane cannot be self-cleaned under sunlight, requiring the use of ultraviolet light. This results in high energy consumption and high costs for operating and maintaining the MBR membrane assembly. Summary of the Invention

[0005] To address the technical issue of existing self-cleaning membrane bioreactors requiring ultraviolet light for self-cleaning, the present invention provides a self-cleaning membrane bioreactor and its use method. This self-cleaning membrane bioreactor incorporates a special modified TiO2-based visible light catalyst within the membrane and is equipped with an external focusing frame unit. This eliminates the need for ultraviolet light irradiation and enables effective self-cleaning under sunlight, reducing the energy consumption and cost of operating and maintaining the membrane bioreactor.

[0006] The specific technical solutions of the present invention are:

[0007] In the first aspect, the present invention provides a self-cleaning membrane bioreactor, comprising a membrane component unit and an external focusing frame unit for converging visible light onto the membrane component unit; the membrane component unit comprises one or more membrane sheets; the membrane sheets contain a modified TiO2-based visible light catalyst; the modified TiO2-based visible light catalyst is a sharp mineral-type TiO2 modified by doping with Mn, N and Cu.

[0008] In the modified TiO2-based visible light photocatalyst adopted in the present invention, Mn, N and Cu are co-doped with the sharp mineral type TiO2. Mn, N and Cu cooperate with each other to play a synergistic role, and the following effects can be obtained: the doping of Mn, N and Cu is conducive to making the crystal plane orientation of TiO2 disordered and the lattice arrangement disordered. When external light enters the interior of the catalyst, it is scattered and the light is absorbed and cannot be reflected out. Therefore, the doping of Mn, N and Cu helps to obtain a photocatalyst with an appearance close to black or black, so that it can absorb more visible light, thereby improving the utilization rate of visible light; and, compared with TiO2 doped with a single element or two of Mn, N and Cu, the sharp mineral type TiO2 co-doped with Mn, N and Cu has a smaller band gap energy, which can reach below 2.0 eV, and can absorb a wider range of light waves, thereby achieving photocatalytic effect under visible light.

[0009] In summary, by co-doping with Mn, N and Cu, the modified TiO2-based visible light catalyst can have a higher catalytic activity under visible light (sunlight). When the diaphragm containing the modified TiO2-based visible light catalyst is applied to the self-cleaning membrane bioreactor of the present invention, there is no need to use ultraviolet lamp irradiation. The external focusing frame unit is used to focus the visible light (sunlight) onto the membrane component unit, so that the modified TiO2-based visible light catalyst in the diaphragm can play a photocatalytic role, degrade the organic pollutants on the diaphragm, and achieve self-cleaning; and the modified TiO2-based visible light catalyst used in the present invention has a strong catalytic activity under visible light, and is equipped with an external focusing frame unit, which is conducive to improving the self-cleaning effect. In addition, in addition to good visible light catalytic performance, the modified TiO2-based visible light catalyst used in the present invention has certain antibacterial properties, which can reduce the attachment and growth of microorganisms on the surface of the diaphragm and reduce the occurrence of microbial contamination.

[0010] Therefore, when the self-cleaning membrane bioreactor of the present invention is in use, when the membrane is contaminated, it only needs to use sunlight and physical cleaning, without the need for external agents for chemical cleaning, to remove pollutants, so that the permeability of the membrane can be better restored. Therefore, it can simplify the membrane cleaning process and reduce the flushing frequency, thereby reducing the energy consumption and cost of membrane bioreactor operation and maintenance.

[0011] Preferably, the external focusing frame unit includes a plurality of one-way side mirrors connected end to end to form a cavity with the mirror surface facing the cavity; the membrane component unit is arranged in the cavity; and a flip-up focusing concave mirror is provided on the top of the cavity.

[0012] The external focusing frame unit composed of the one-way side mirror and the flip-cover focusing concave mirror can effectively collect and utilize sunlight, forming a "no dead angle" light reaction zone, and promoting the catalytic degradation process of organic pollution on the membrane by the modified TiO2-based visible light catalyst.

[0013] Preferably, the membrane assembly unit includes one or more membrane groups; the membrane group includes a fixed inner frame; membrane sheets, mesh outer partitions and fixed outer frames are symmetrically arranged on both sides of the fixed inner frame; and a water outlet is provided on the fixed inner frame.

[0014] In the above membrane assembly unit structure, the mesh outer partition can intercept a portion of particles to prevent them from adhering to the membrane, which helps to reduce the contamination of the membrane.

[0015] Furthermore, a mesh inner partition is provided between the diaphragm and the fixed inner frame.

[0016] The triple filtration of mesh outer layer, membrane and mesh inner layer can make the water cleaner.

[0017] Furthermore, in each membrane group, the fixed inner frame, the mesh inner partition, the membrane, the mesh outer partition and the fixed outer frame are fixedly connected by one or more fixing nuts and fixing screws adapted to the fixing nuts.

[0018] Preferably, the self-cleaning membrane bioreactor further includes a water outlet and cleaning unit; the water outlet and cleaning unit includes a clear water tank and a water outlet pipeline; the water outlet pipeline includes a water outlet pipe and a backwash pipe, both ends of which are connected to the water outlet and the clear water tank respectively.

[0019] During the operation of the self-cleaning membrane bioreactor, after the wastewater is filtered through the membrane group, the obtained clean water enters the clean water tank through the outlet and the outlet pipe; when the membrane is contaminated and the permeability is too poor, the clean water in the clean water tank flows into the module through the backwash pipe and the outlet to flush the module, and cooperates with the action of the modified TiO2-based visible light catalyst to complete self-cleaning.

[0020] Furthermore, the water outlet pipe is provided with a water outlet filter pump and a water outlet automatic valve.

[0021] During the operation of the self-cleaning membrane bioreactor, the effluent suction pump can be briefly turned on to provide power to form gravity flow and then turned off to utilize gravity operation. The effluent suction pump can also be continuously turned on to continuously provide power, depending on the actual water demand.

[0022] Furthermore, the backwash pipe is provided with a backwash pump and an automatic backwash valve.

[0023] Furthermore, a clear water tank outlet is provided on the clear water tank.

[0024] Preferably, the membrane assembly unit further comprises one or more membrane group fixing grooves; the bottom of the membrane group is installed in the membrane group fixing groove.

[0025] Preferably, the outer side of the one-way side mirror and the outer side of the flip cover light-focusing concave mirror are both covered with light-shielding material.

[0026] By covering the outside of the one-way side mirror and the flip-cover concave mirror with shading material, during the operation of the self-cleaning membrane bioreactor, by closing the flip-cover concave mirror, the inside of the reactor can be shielded from light, thereby preventing sunlight from affecting the degradation of organic matter in the wastewater by microorganisms; when self-cleaning is required, the flip-cover concave mirror is opened to focus sunlight on the membrane component unit to achieve self-cleaning.

[0027] Preferably, the preparation method of the modified TiO2-based visible light photocatalyst comprises the following steps:

[0028] S1.1: Dissolve a manganese source, a copper source, and a titanium dioxide precursor in solvent I and mix them uniformly to form solution A; the molar ratio of the copper source to the titanium dioxide precursor is 1:20 to 25, calculated as Cu and Ti, respectively;

[0029] S1.2: Dissolve a nitrogen source in solvent I, mix well, and adjust the pH to 1.7-2.5 to form solution B; the molar ratio of the manganese source, nitrogen source, and copper source is 1.0-1.5:87-95:1, calculated as Mn, N, and Cu, respectively;

[0030] S1.3: Add solution B dropwise to solution A under stirring, mix evenly, and then perform an ultrasonic-low-temperature solvothermal reaction to separate the product to obtain a modified TiO2-based visible light photocatalyst.

[0031] In the preparation process of modified TiO2-based visible light photocatalysts, the order and amount of raw material addition, as well as the reaction conditions, will affect the catalytic activity of the final product under visible light. Specifically:

[0032] (1) The present invention controls the pH, and the timing for adding acid to adjust the pH is when preparing solution B (step S1.2), rather than adjusting the pH after mixing solution A and solution B in step S1.3. This can avoid the premature precipitation of TiO2, and is therefore conducive to obtaining a black visible light catalyst.

[0033] (2) The present invention adopts an ultrasonic-low-temperature solvent thermal reaction method. The doping of Mn, N, and Cu combined with the ultrasonic action can make the crystal plane orientation of TiO2 disordered and the lattice arrangement disordered, thereby making the obtained modified TiO2-based visible light catalyst appear black or close to black.

[0034] (3) The dosage of manganese source, nitrogen source and copper source and their ratio will affect the color and band gap of the modified TiO2-based visible light photocatalyst, and thus affect its catalytic performance under visible light.

[0035] Based on this, the present invention uses Mn, N, and Cu doping to improve the catalytic activity of the photocatalyst under visible light. During the preparation of the photocatalyst, an ultrasonic-low-temperature solvent thermal method is used for reaction, and the timing of adding acid to adjust the pH is set when preparing solution B. At the same time, the molar ratio of the copper source and the titanium dioxide precursor is controlled to be 1:20-25, and the molar ratio of the manganese source, the nitrogen source, and the copper source is controlled to be 1.0-1.5:87-95:1. This can further improve the catalytic activity of the modified TiO2-based visible light catalyst under visible light, thereby improving the self-cleaning effect of the membrane bioreactor.

[0036] Furthermore, in step S1.3, the temperature of the ultrasound-low-temperature solvent thermal reaction is 150-300°C, the reaction time is 5-8 hours, the ultrasound is applied for 2.5-4 hours, and the ultrasound frequency is 10000-15000 Hz.

[0037] The present invention controls the temperature at 150-300°C and the reaction time at 5-8h, which is conducive to making the obtained modified TiO2-based visible light catalyst appear black in appearance, thereby further improving its photocatalytic effect under visible light and giving the membrane bioreactor a better self-cleaning effect.

[0038] Furthermore, in step S1.1, the manganese source is a manganese salt, and the copper source is a copper salt; in step S1.2, the nitrogen source is urea.

[0039] Furthermore, in step S1.1, the titanium dioxide precursor is tetrabutyl titanate.

[0040] Furthermore, in step S1.2, after the nitrogen source is dissolved in solvent I, ultrasonic treatment is performed for 4 to 8 hours, and then the pH is adjusted to 1.7 to 2.5.

[0041] Furthermore, in step S1.3, the process of separating the product includes the following steps: solid-liquid separation, washing, freezing for 10 to 24 hours, and freeze-drying for 36 to 48 hours.

[0042] Furthermore, in steps S1.1 and S1.2, the solvent I is an organic alcohol.

[0043] Preferably, the content of the modified TiO2-based visible light photocatalyst in the film is 3-8 wt%.

[0044] Preferably, the method for preparing the membrane comprises the following steps:

[0045] S2.1: Add the film substrate, porogen, and modified TiO2-based visible light photocatalyst to solvent II, fully dissolve them, and then degas and mature them to obtain a film casting solution;

[0046] S2.2: Transfer the casting solution to the non-woven fabric and scrape out a layer of liquid film;

[0047] S2.3: Transfer the non-woven fabric and the liquid film to a liquid bath for phase inversion reaction. After the film is completely solidified, transfer it to water to remove excess solvent II to obtain a membrane sheet.

[0048] Furthermore, in step S2.1, the porogen is polyethylene glycol with a weight average molecular weight of 5000 to 20000 Da.

[0049] Furthermore, in step S2.1, the mass ratio of the membrane substrate, the porogen and the solvent II is 1:0.10-0.15:4.5-5.0.

[0050] Furthermore, in step S2.1, the solvent II is N,N-dimethylacetamide (DMAc).

[0051] In the second aspect, the present invention provides a method for using the self-cleaning membrane bioreactor, comprising the following steps: under shading, introducing wastewater into the self-cleaning membrane bioreactor to treat the wastewater; after the membrane is contaminated, stopping the introduction of wastewater and irradiating the membrane component unit with sunlight to degrade the organic pollutants on the membrane.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] (1) The modified TiO2-based visible light catalyst used in the present invention has high catalytic activity under visible light and has certain antibacterial properties. In combination with an external focusing frame unit, the self-cleaning membrane bioreactor can achieve a good self-cleaning effect under sunlight without the need for ultraviolet lamps. The membrane cleaning process is simplified, thereby reducing the energy consumption and cost of membrane bioreactor operation and maintenance.

[0054] (2) The present invention adopts an external focusing frame unit composed of a one-way side mirror and a flip-cover focusing concave mirror, which can form a "no dead angle" light reaction zone and promote the self-cleaning of the membrane under the action of a modified TiO2-based visible light catalyst;

[0055] (3) In the process of preparing the modified TiO2-based visible light photocatalyst, the present invention can further improve the catalytic activity of the modified TiO2-based visible light photocatalyst under visible light by controlling the addition sequence and dosage of the raw materials, as well as the reaction conditions, thereby giving the membrane bioreactor a better self-cleaning effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a structural schematic diagram of the self-cleaning membrane bioreactor in the present invention.

[0057] Figure 2 Schematic diagram of a structure of the membrane group in the present invention.

[0058] Figure 3 This is the SEM image of the modified TiO2-based visible light photocatalyst prepared in Example 1.

[0059] Figure 4 This is the change in the permeation flux of the membrane group during the operation of the application example 1 system.

[0060] Figure 5 Surface SEM images of the diaphragm of Example 1 (right) and the ordinary diaphragm (left) after the system of Application Example 1 has been running for 72 hours.

[0061] The accompanying drawings are marked as: 1. External focusing frame unit, 11. One-way side mirror, 12. Flip-up focusing concave mirror, 13. Membrane group fixing groove, 2. Membrane assembly unit, 21. Membrane group, 221. Fixing nut, 222. Fixed outer frame, 223. Mesh outer partition, 224. Diaphragm, 225. Mesh inner partition, 226. Water outlet, 227. Fixed inner frame, 228. Fixing screw, 3. Water outlet and cleaning unit, 31. Water outlet pipe, 32. Water outlet filter pump, 33. Water outlet automatic valve, 34. Clear water tank, 35. Backwash automatic valve, 36. Clear water tank outlet, 37. Backwash pump. DETAILED DESCRIPTION

[0062] The present invention will be further described below with reference to the embodiments.

[0063] Overall embodiment

[0064] A self-cleaning membrane bioreactor comprises a membrane assembly unit 2 and an external focusing frame unit 1 for converging visible light onto the membrane assembly unit 2; the membrane assembly unit 2 comprises one or more membrane sheets 224; the membrane sheets 224 contain a modified TiO2-based visible light catalyst; the modified TiO2-based visible light catalyst is an acutospore-type TiO2 modified by doping with Mn, N and Cu.

[0065] In a specific embodiment, the external focusing frame unit 1 includes a plurality of one-way side mirrors 11 connected end to end to form a cavity, with the mirror surface facing the cavity; the membrane assembly unit 2 is disposed within the cavity; and the top of the cavity is provided with a flip-up focusing concave mirror 12. The outer sides of the one-way side mirrors 11 and the outer sides of the flip-up focusing concave mirror 12 are both coated with a light-shielding material.

[0066] As a specific embodiment, the membrane assembly unit 2 includes one or more membrane groups 21 and one or more membrane group fixing grooves 13 ; the bottom of the membrane group 21 is installed in the membrane group fixing groove 13 .

[0067] In one embodiment, the membrane module 21 includes a fixed inner frame 227; a mesh inner barrier 225, a membrane sheet 224, a mesh outer barrier 223, and a fixed outer frame 222 are symmetrically arranged on either side of the fixed inner frame 227; and a water outlet 226 is provided on the fixed inner frame 227. In each membrane module 21, the fixed inner frame 227, the mesh inner barrier 225, the membrane sheet 224, the mesh outer barrier 223, and the fixed outer frame 222 are fixedly connected by one or more fixing nuts 221 and fixing screws 228 adapted to the fixing nuts 221.

[0068] As a specific embodiment, the self-cleaning membrane bioreactor further includes a water outlet and cleaning unit 3; the water outlet and cleaning unit 3 includes a clear water tank 34 and a water outlet pipeline 31; the water outlet pipeline 31 includes a water outlet pipe and a backwash pipe, both ends of which are connected to the water outlet 226 and the clear water tank 34, respectively. The water outlet pipe is equipped with a water outlet filter pump 32 and a water outlet automatic valve 33; the backwash pipe is equipped with a backwash pump 37 and an automatic backwash valve 35. The clear water tank 34 is provided with a clear water tank outlet 36.

[0069] As a specific implementation, the content of the modified TiO2-based visible light photocatalyst in the membrane 224 is 3-8 wt%.

[0070] As a specific embodiment, the preparation method of the modified TiO2-based visible light photocatalyst comprises the following steps:

[0071] S1.1: Dissolve a manganese source, a copper source, and a titanium dioxide precursor in solvent I and mix them uniformly to form solution A; the molar ratio of the copper source to the titanium dioxide precursor is 1:20 to 25, calculated as Cu and Ti, respectively;

[0072] S1.2: Dissolve a nitrogen source in solvent I, sonicate for 4-8 hours, and adjust the pH to 1.7-2.5 to form solution B. The molar ratio of the manganese source, nitrogen source, and copper source is 1.0-1.5:87-95:1, calculated as Mn, N, and Cu, respectively.

[0073] S1.3: Add solution B dropwise to solution A under stirring conditions, mix evenly, and conduct ultrasonic-low-temperature solvent thermal reaction at a temperature of 150-300°C for 5-8 hours, during which ultrasonication is performed for 2.5-4 hours at an ultrasonic frequency of 10,000-15,000 Hz. Then, after solid-liquid separation, wash, freeze for 10-24 hours, and freeze-dry for 36-48 hours to obtain a modified TiO2-based visible light catalyst.

[0074] In the above specific embodiment, in step S1.1, the manganese source can be a manganese salt, the copper source can be a copper salt, and the titanium dioxide precursor can be tetrabutyl titanate; in step S1.2, the nitrogen source can be urea; in steps S1.1 and S1.2, the solvent I can be an organic alcohol.

[0075] As a specific embodiment, the method for preparing the diaphragm 224 includes the following steps:

[0076] S2.1: adding a film substrate, a porogen, and a modified TiO2-based visible light photocatalyst to solvent II in a mass ratio of 1:0.10-0.15:4.5-5.0; after sufficient dissolution, degassing and aging are performed to obtain a casting solution; S2.2: transferring the casting solution to a non-woven fabric and scraping out a layer of liquid film;

[0077] S2.3: Transfer the non-woven fabric and the liquid film to a liquid bath for phase inversion reaction. After the film is completely solidified, transfer it to water to remove excess solvent II to obtain a membrane sheet.

[0078] In the above specific embodiment, in step S2.1, the porogen can be polyethylene glycol with a weight average molecular weight of 5000 to 20000 Da, and the solvent II can be N,N-dimethylacetamide (DMAc).

[0079] A method for using the self-cleaning membrane bioreactor comprises the following steps: introducing wastewater into the self-cleaning membrane bioreactor under shading to treat the wastewater; when the membrane is contaminated, stopping the introduction of wastewater and irradiating the membrane assembly unit with sunlight to degrade organic pollutants on the membrane.

[0080] Example 1

[0081] A self-cleaning membrane bioreactor, such as Figure 1 As shown, it consists of an external focusing frame unit 1, a membrane assembly unit 2, and a water outlet and cleaning unit 3. The specific structures of the three units are as follows:

[0082] The external focusing frame unit 1 consists of four one-way side mirrors 11 and a flip-up focusing concave mirror 12. The four one-way side mirrors 11 are connected end-to-end to form a rectangular cavity, with all mirrors facing into the cavity. The flip-up focusing concave mirror 12 is located at the top of the rectangular cavity. Both the one-way side mirrors 11 and the flip-up focusing concave mirror 12 are covered with blackout cloth.

[0083] The membrane assembly unit 2 includes six parallel membrane group fixing grooves 13, each of which is equipped with two membrane groups 21 (the bottom of the membrane group 21 is installed in the membrane group fixing groove 13). The membrane group fixing groove 13 and the membrane group 21 are both located in a rectangular cavity surrounded by the one-way side mirror 11. The structure of the membrane group 21 is as follows: Figure 2 As shown, it includes a fixed inner frame 227, with a mesh inner interlayer 225, a membrane 224, a mesh outer interlayer 223, and a fixed outer frame 222 symmetrically arranged on either side. A set of fixing nuts 221 and corresponding fixing screws 228 are respectively provided at the four corners of the membrane assembly 21. The fixing screws 228 pass through the fixed inner frame 227, the mesh inner interlayer 225, the membrane 224, the mesh outer interlayer 223, and the fixed outer frame 222, and then connect to the fixing nuts 221. A water outlet 226 is provided at the top of the fixed inner frame 227. The membrane 224 contains a modified TiO2-based visible light catalyst.

[0084] The outlet and cleaning unit 3 consists of a clean water tank 34 and an outlet pipeline 31. The outlet pipeline 31 includes an outlet pipe and a backwash pipe, both ends of which are connected to the clean water tank 34 and the water outlet 226 in the membrane module 21, respectively. The outlet pipe is equipped with an outlet filter pump 32 and an automatic outlet valve 33; the backwash pipe is equipped with a backwash pump 37 and an automatic backwash valve 35. A clean water tank outlet 36 is provided in the clean water tank 34.

[0085] The preparation process of the diaphragm 224 used in this embodiment is as follows:

[0086] S2.1: Preparation of modified TiO2-based visible light photocatalyst:

[0087] S1.1: Dissolve 1.16 mmol of manganese chloride, 1 mmol of copper chloride, and 22 mmol of tetrabutyl titanate in 30 mL of anhydrous ethanol to form solution A.

[0088] S1.2: Dissolve 45 mmol of urea in 30 mL of anhydrous ethanol, sonicate for 6 hours, and adjust the pH to 2 by adding hydrochloric acid to form solution B.

[0089] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed in a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 6 hours. During the reaction, the temperature was controlled at 200°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 3 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst. The electron microscope image is shown as follows Figure 3 shown.

[0090] S2: Preparation of membrane:

[0091] S2.1: In a water bath (temperature controlled within the range of 60-90°C), 50,000 Da of PVC, 10,000 Da of PEG, and a modified TiO2-based visible light photocatalyst were added to DMAc (PVC - 17 wt%, PEG - 2 wt%, modified TiO2-based visible light photocatalyst - 0.6 wt%, DMAc - 80.4 wt%) and stirred for 6 hours. After the PVC and PEG were completely dissolved, the mixture was deaerated using a compression pump and allowed to stand in a water bath for 12 hours to form a casting solution.

[0092] S2.2: After the casting solution has cooled to room temperature, it is transferred to a 75-gram polyethylene terephthalate (PET) nonwoven fabric and a 200-μm-thick film is formed using a scraping machine.

[0093] S2.3: Transfer the non-woven fabric and the liquid membrane to a liquid bath at room temperature for phase inversion reaction. After the membrane is completely solidified, transfer it to deionized water to remove excess solvent. Finally, store the membrane in 20% glycerol water for preservation.

[0094] The self-cleaning membrane bioreactor of this embodiment is used as follows:

[0095] During operation (wastewater treatment), the flip-up concave mirror 12 is closed, the automatic outlet valve 33 is open, and the automatic backwash valve 35 is closed. Water first enters from the bottom of the external focusing frame unit, passes through the membrane 224 in the membrane assembly unit 2, and enters the outlet pipe. It then flows through the outlet filter pump 32 into the clean water tank before being discharged. If the membrane becomes contaminated and its permeability becomes poor, the flip-up concave mirror 12 is opened, and sunlight is used to catalyze the degradation of organic pollutants in the membrane module 21. The automatic outlet valve 33 is closed, and the automatic backwash valve 35 is opened, allowing water from the clean water tank to enter the membrane module 21 via the backwash pump 37 and backwash pipe, physically flushing the membrane module 21.

[0096] Example 2

[0097] The only difference between this embodiment and embodiment 1 is that the preparation process of the membrane 224 used in this embodiment is as follows:

[0098] S2.1: Preparation of modified TiO2-based visible light photocatalyst:

[0099] S1.1: Dissolve 1.48 mmol of manganese chloride, 1.1 mmol of copper chloride, and 22 mmol of tetrabutyl titanate in 30 mL of anhydrous ethanol to form solution A.

[0100] S1.2: Dissolve 52.2 mmol of urea in 30 mL of anhydrous ethanol, sonicate for 6 hours, and adjust the pH to 2 by adding hydrochloric acid to form solution B.

[0101] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed into a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 8 hours. During the reaction, the temperature was controlled at 150°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 4 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst.

[0102] S2: Preparation of membrane:

[0103] S2.1: In a water bath (temperature controlled within the range of 60-90°C), 50,000 Da of PVC, 10,000 Da of PEG, and a modified TiO2-based visible light photocatalyst were added to DMAc (PVC - 17 wt%, PEG - 2 wt%, modified TiO2-based visible light photocatalyst - 0.8 wt%, DMAc - 80.2 wt%) and stirred to dissolve for 6 hours. After the PVC and PEG were completely dissolved, the mixture was deaerated using a compression pump and allowed to stand in a water bath for 12 hours to form a casting solution.

[0104] S2.2: After the casting solution has cooled to room temperature, it is transferred to a 75-gram PET nonwoven fabric and a 200-μm-thick film is formed using a scraping machine.

[0105] S2.3: Transfer the non-woven fabric and the liquid membrane to a liquid bath at room temperature for phase inversion reaction. After the membrane is completely solidified, transfer it to deionized water to remove excess solvent. Finally, store the membrane in 20% glycerol water for preservation.

[0106] Example 3

[0107] The only difference between this embodiment and embodiment 1 is that the preparation process of the membrane 224 used in this embodiment is as follows:

[0108] S2.1: Preparation of modified TiO2-based visible light photocatalyst:

[0109] S1.1: Dissolve 1.32 mmol of manganese chloride, 0.88 mmol of copper chloride, and 22 mmol of tetrabutyl titanate in 30 mL of anhydrous ethanol to form solution A.

[0110] S1.2: Dissolve 38.3 mmol of urea in 30 mL of anhydrous ethanol, sonicate for 4 hours, and adjust the pH to 2 by adding hydrochloric acid to form solution B.

[0111] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed into a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 5 hours. During the reaction, the temperature was controlled at 300°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 2.5 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst.

[0112] S2: Preparation of membrane:

[0113] S2.1: In a water bath (temperature controlled within the range of 60-90°C), 50,000 Da of PVC, 10,000 Da of PEG, and a modified TiO2-based visible light photocatalyst were added to DMAc (PVC - 17 wt%, PEG - 2 wt%, modified TiO2-based visible light photocatalyst - 1.3 wt%, DMAc - 79.7 wt%) and stirred for 6 hours. After the PVC and PEG were completely dissolved, the mixture was deaerated using a compression pump and allowed to stand in a water bath for 12 hours to form a casting solution.

[0114] S2.2: After the casting solution has cooled to room temperature, it is transferred to a 75-gram PET nonwoven fabric and a 200-μm-thick film is formed using a scraping machine.

[0115] S2.3: Transfer the non-woven fabric and the liquid membrane to a liquid bath at room temperature for phase inversion reaction. After the membrane is completely solidified, transfer it to deionized water to remove excess solvent. Finally, store the membrane in 20% glycerol water for preservation.

[0116] Example 4

[0117] The only difference between this embodiment and embodiment 1 is that in this embodiment, the steps for preparing the modified TiO2-based visible light photocatalyst are as follows: S1.1: 3.0 mmol manganese chloride, 2.98 mmol copper chloride, and 22 mmol tetrabutyl titanate are dissolved in 30 mL anhydrous ethanol to form solution A;

[0118] S1.2: Dissolve 42.09 mmol of urea in 30 mL of anhydrous ethanol, sonicate for 8 hours, and adjust the pH to 2 by adding hydrochloric acid to form solution B.

[0119] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed into a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 6 hours. During the reaction, the temperature was controlled at 200°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 3 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst.

[0120] Example 5

[0121] The only difference between this embodiment and embodiment 1 is that in this embodiment, the steps for preparing the modified TiO2-based visible light photocatalyst are as follows: S1.1: 0.9 mmol manganese chloride, 2.0 mmol copper chloride, and 22 mmol tetrabutyl titanate are dissolved in 30 mL anhydrous ethanol to form solution A;

[0122] S1.2: Dissolve 44.13 mmol of urea in 30 mL of anhydrous ethanol, sonicate for 8 hours, and adjust the pH to 2 by adding hydrochloric acid to form solution B.

[0123] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed into a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 6 hours. During the reaction, the temperature was controlled at 200°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 3 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst.

[0124] Comparative Example 1

[0125] The only difference between this comparative example and Example 1 is that in this comparative example, the steps for preparing the modified TiO2-based visible light photocatalyst are as follows: S1.1: 1.0 mmol of copper chloride and 22 mmol of tetrabutyl titanate are dissolved in 30 mL of anhydrous ethanol to form solution A;

[0126] S1.2: Dissolve 45.0 mmol of urea in 30 mL of anhydrous ethanol, sonicate for 8 hours, and adjust the pH to 2 by adding hydrochloric acid to form solution B.

[0127] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed into a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 6 hours. During the reaction, the temperature was controlled at 200°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 3 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst.

[0128] Comparative Example 2

[0129] The only difference between this comparative example and Example 1 is that in this comparative example, the steps for preparing the modified TiO2-based visible light photocatalyst are as follows: S1.1: 1.16 mmol of manganese chloride, 1.0 mmol of copper chloride, and 22 mmol of tetrabutyl titanate are dissolved in 30 mL of anhydrous ethanol to form solution A;

[0130] S1.2: Ultrasonicate 30 mL of anhydrous ethanol for 8 hours, then add hydrochloric acid to adjust the pH to 2 to form Solution B.

[0131] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed into a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 6 hours. During the reaction, the temperature was controlled at 200°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 3 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst.

[0132] Comparative Example 3

[0133] The only difference between this comparative example and Example 1 is that in this comparative example, the steps for preparing the modified TiO2-based visible light photocatalyst are as follows: S1.1: 1.16 mmol of manganese chloride and 22 mmol of tetrabutyl titanate are dissolved in 30 mL of anhydrous ethanol to form solution A;

[0134] S1.2: Dissolve 45.0 mmol of urea in 30 mL of anhydrous ethanol, sonicate for 8 hours, and adjust the pH to 2 by adding hydrochloric acid to form solution B.

[0135] S1.3: Solution B was slowly added dropwise to solution A under stirring to mix. After the mixed solution was stirred until transparent, it was transferred into a polytetrafluoroethylene liner. The liner was then placed into a reactor, sealed, and transferred to an oven for ultrasonic-low-temperature solvent thermal reaction for 6 hours. During the reaction, the temperature was controlled at 200°C, and ultrasonication was performed every 30 seconds for 30 seconds each time. The total ultrasonication time was 3 hours, and the ultrasonic frequency was controlled at 12500Hz. After the reaction, it was cooled to room temperature, centrifuged, and washed with anhydrous ethanol. After washing 3 times, the precipitate was frozen for 12 hours, and then the precipitate was freeze-dried for 48 hours to obtain a modified TiO2-based visible light catalyst.

[0136] Application Example 1

[0137] 10m in a city 3 / h landfill leachate adopts air flotation + A 2 O+MBR process is used for treatment, in which flotation and A 2O all use conventional equipment, and MBR uses the self-cleaning membrane bioreactor in Example 1. After running for 15 days, the effluent enters the urban sewage network. In the self-cleaning membrane bioreactor, the effluent of the biochemical aerobic tank first enters from the bottom of the external focusing frame unit, passes through the diaphragm in the membrane assembly unit, enters the outlet pipe, and then enters the clear water tank through the outlet filter pump, and finally the water is discharged. There is a 5m drop (0.05MPa) between the membrane group and the outlet of the clear water tank, and the head pressure can be directly used for operation during the process. In the actual operation process, the self-cleaning membrane bioreactor adopts one use and one standby (that is, two reactors are connected in series, one of which is in operation and the other is on standby). When running, the flip-up focusing concave mirror is closed and the system is operated in a dark environment. Physical backwashing is performed during the operation, and the frequency is once every 12 hours; when on standby, the flip-up focusing concave mirror is opened, and sunlight is used to catalyze the degradation of organic pollutants in the membrane group, and the action time is controlled at 12h; the standby replacement frequency is once every 3 days.

[0138] Air flotation + A 2 During the operation of the O+MBR system, the permeation flux of the membrane group changes as follows: Figure 4 As shown. Figure 4 It can be seen that after the system is put into operation, the membrane flux of the membrane group shows an overall downward trend when the spare is not replaced. During this period, part of the flux can be restored through physical backwashing, and the overall decline rate of the flux is 17-20%; after the membrane group undergoes spare replacement and 12 hours of visible light catalytic treatment, the membrane flux recovery rate reaches more than 95%.

[0139] In air flotation + A 2 After the O+MBR system was operated for 72 hours (without sunlight irradiation treatment), the adhesion of E. coli on the membrane was observed; the membrane in Example 1 was replaced with a common membrane (the only difference from the membrane preparation method in Example 1 was that no modified TiO2-based visible light catalyst was added), and the system was operated for another 72 hours, and the adhesion of E. coli on the membrane was observed. Figure 5 As shown, compared with the ordinary film, the attachment rate of E. coli on the film of Example 1 is reduced by 90%, indicating that the modified TiO2-based visible light catalyst can effectively inhibit the growth and attachment of bacteria on the film.

[0140] Test Case

[0141] The performance tests of the modified TiO2-based visible light photocatalysts and films in Examples 1 to 5 and Comparative Examples 1 to 3 were conducted as follows: (1) 0.1 g of the modified TiO2-based visible light photocatalyst was used to catalyze the degradation of 100 mL of 20 mg / L methyl orange under simulated sunlight (35 W xenon lamp). The concentration of methyl orange was detected every 20 min, and the time until complete degradation was recorded.

[0142] (2) The bovine serum albumin (BSA) aqueous solution was filtered using a membrane to detect the pure water flux and BSA retention rate.

[0143] (3) After filtering the humic acid aqueous solution with the membrane, the membrane was physically cleaned (i.e., backwashed with filtered water), and the pure water flux recovery rate of the membrane was tested. Then, the membrane was exposed to simulated sunlight (using a 35W xenon lamp as a stable light source for 3 hours), and the pure water flux recovery rate was tested again.

[0144] The performance test results are shown in Table 1.

[0145] Table 1

[0146]

[0147] According to Table 1, we can see that:

[0148] (1) The photocatalysts of Examples 1 to 3 are all black and have a high catalytic degradation efficiency for methyl orange under simulated sunlight. When used in membranes, they can better restore the flux of contaminated membranes after exposure to sunlight. In addition, the membranes of Examples 1 to 3 have good permeability and filtration performance.

[0149] (2) Compared with Example 1, the photocatalytic degradation effect of Examples 4 and 5 on methyl orange under simulated sunlight was significantly weakened, and the recovery rate of pure water flux after the membrane was irradiated with simulated sunlight was less than that after physical cleaning. This indicates that the amount of manganese source, nitrogen source, and copper source used will affect the photocatalytic performance of the modified TiO2-based visible light catalyst under visible light (sunlight), thereby affecting the self-cleaning effect of the membrane.

[0150] (3) The modified TiO2-based visible light photocatalysts of Examples 1 to 5 are all black. Comparative Examples 1 to 3, based on Example 1, lack one of Mn, N, and Cu, respectively. The resulting photocatalysts are brown in color and have a significantly lower catalytic degradation efficiency for methyl orange under simulated sunlight than that of Example 1. Moreover, the flux recovery rate of the contaminated membrane after sunlight irradiation is significantly lower than that after physical cleaning than that of Example 1. This indicates that the co-doping of TiO2 with Mn, N, and Cu in the present invention can enhance the catalytic effect of the photocatalyst under visible light, thereby enhancing the self-cleaning effect of the membrane.

[0151] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0152] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a self-cleaning membrane bioreactor, characterized in that: include: S1: Dissolve a manganese source, a copper source, and a TiO2 precursor in solvent I and mix them to obtain solution A; the molar ratio of the copper source to the TiO2 precursor is 1:20-25, calculated as Cu and Ti respectively; dissolve a nitrogen source in solvent I, mix them, and adjust the pH to 1.7-2.5 to obtain solution B; the molar ratio of the manganese source, the nitrogen source, and the copper source is 1.0-1.5:87-95:1, calculated as Mn, N, and Cu respectively; dropwise add solution B into solution A under stirring, mix them, and then perform an ultrasonic-low-temperature solvothermal reaction to separate the product to obtain a modified TiO2-based visible light photocatalyst; S2: A self-cleaning membrane bioreactor having the following structure is made using a modified TiO2-based visible light catalyst: comprising a membrane component unit and an external focusing frame unit for converging visible light onto the membrane component unit; the membrane component unit comprises one or more membrane sheets; the membrane sheet contains a modified TiO2-based visible light catalyst.

2. The preparation method according to claim 1, wherein The external focusing frame unit includes a plurality of one-way side mirrors connected end to end to form a cavity and with the mirror surface facing the cavity; the membrane component unit is arranged in the cavity; and a flip-cover focusing concave mirror is provided on the top of the cavity.

3. The preparation method according to claim 1, wherein The membrane assembly unit includes one or more membrane groups; the membrane group includes a fixed inner frame; membrane sheets, mesh outer partitions and fixed outer frames are symmetrically arranged on both sides of the fixed inner frame; and a water outlet is provided on the fixed inner frame.

4. The preparation method according to claim 3, wherein A mesh inner partition is provided between the diaphragm and the fixed inner frame.

5. The preparation method according to claim 3, wherein It also includes a water outlet and cleaning unit; the water outlet and cleaning unit includes a clean water tank and a water outlet pipeline; the water outlet pipeline includes a water outlet pipe and a backwash pipe, both ends of which are connected to the water outlet and the clean water tank respectively.

6. The preparation method according to claim 3, wherein The membrane assembly unit further includes one or more membrane group fixing grooves; the bottom of the membrane group is installed in the membrane group fixing groove.

7. The preparation method according to claim 2, wherein The outer side of the one-way side mirror surface and the outer side of the flip cover light-focusing concave mirror surface are both covered with light-shielding materials.

8. The preparation method according to claim 1, wherein The content of the modified TiO2-based visible light photocatalyst in the membrane is 3-8 wt%.

9. A self-cleaning membrane bioreactor prepared by the preparation method according to any one of claims 1 to 8.

10. A method for using the self-cleaning membrane bioreactor according to claim 9, characterized in that: The method comprises the following steps: introducing wastewater into a self-cleaning membrane bioreactor under light shielding to treat the wastewater; When the membrane is contaminated, stop the flow of wastewater and irradiate the membrane assembly unit with sunlight to degrade the organic pollutants on the membrane.

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