Composite membrane and membrane bioreactor

Abstract

The present invention provides a composite membrane, which includes a filler with photocatalytic properties; the present invention also provides a membrane bioreactor, which uses the above-mentioned composite membrane; compared with the prior art, the present invention realizes a photocatalytic self-cleaning function by introducing a filler with photocatalytic properties into the membrane material, which can effectively slow down the accumulation of membrane pollutants and reduce membrane clogging, and does not rely on external mechanical or chemical cleaning measures.

Description

Technical Field

[0001] The present application relates to the field of sewage treatment, and in particular to a composite membrane and a membrane bioreactor. Background Art

[0002] Membrane bioreactor (MBR) technology has been widely used in recent years due to its excellent sewage treatment capacity and small footprint. However, membrane fouling has always been a key bottleneck restricting the further promotion and application of MBR technology. Membrane fouling will lead to decreased membrane flux, reduced effluent quality, increased cleaning frequency and shortened membrane service life, thereby increasing the operating cost of the system. Common membrane fouling mainly includes organic pollution, inorganic pollution and biological pollution. These pollutants will gradually accumulate on the membrane surface, hindering the flow of water through the membrane pores, resulting in decreased membrane performance.

[0003] Existing solutions mainly rely on physical cleaning and chemical cleaning, but frequent cleaning will not only damage the membrane material, but also increase the system downtime and maintenance costs. Summary of the invention

[0004] The invention provides a composite film, which comprises a filler with photocatalytic performance.

[0005] Optionally, the filler with photocatalytic properties is an inorganic nanofiller with photocatalytic properties.

[0006] Optionally, the filler with photocatalytic properties includes one or more of titanium oxide, zinc oxide, cadmium sulfide, tungsten trioxide, and ferric oxide.

[0007] Optionally, the filler with photocatalytic properties is titanium oxide or zinc oxide.

[0008] Optionally, the addition amount of the filler with photocatalytic performance is 5-15%.

[0009] Optionally, the composite film comprises:

[0010] A substrate layer, the substrate layer comprising a polymer film; the filler having photocatalytic properties is dispersed in the substrate layer, and,

[0011] The surface layer covers the outer surface of the substrate layer; the surface layer has hydrophilic groups, and the surface layer is used to improve the hydrophilicity of the composite membrane surface.

[0012] Optionally, the polymer membrane is a polyvinylidene fluoride membrane or a polyethersulfone membrane.

[0013] Optionally, the polymer membrane is a composite of one or more of polyvinylidene fluoride membrane, polyethersulfone membrane, polyethylene membrane and polypropylene membrane.

[0014] Optionally, the surface layer includes a hydrophilic polymer.

[0015] The invention also provides a membrane bioreactor, comprising the composite membrane.

[0016] Compared with the prior art, the present invention realizes the photocatalytic self-cleaning function by introducing fillers with photocatalytic properties into the membrane material, which can effectively slow down the accumulation of membrane pollutants and reduce membrane clogging, and does not rely on external mechanical or chemical cleaning measures. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0019] In the field of sewage treatment and water resource reuse, MBR, also known as membrane bioreactor (Membrane Bio-Reactor), is a new water treatment technology that combines a membrane separation unit with a biological treatment unit.

[0020] Membrane bioreactor is a new type of wastewater treatment system that organically combines membrane separation technology with biological treatment technology. The membrane components replace the terminal secondary sedimentation tank of traditional biological treatment technology, maintain a high concentration of activated sludge in the bioreactor, increase the organic load of biological treatment, thereby reducing the area occupied by sewage treatment facilities and reducing the amount of residual sludge by maintaining a low sludge load.

[0021] The principle of membrane bioreactor is to use membrane separation equipment to intercept activated sludge and macromolecular organic matter in water. Due to its effective interception effect, membrane bioreactor can retain microorganisms with a long generation cycle and achieve deep purification of sewage; in addition, nitrifying bacteria can fully reproduce in the system, and the nitrification effect of nitrifying bacteria can be used to make membrane bioreactor have the function of deep phosphorus removal and nitrogen removal.

[0022] In the prior art, a membrane bioreactor generally comprises:

[0023] A water inlet well, wherein the water inlet well is provided with an overflow port and a water inlet gate;

[0024] Screens: Sewage often contains a lot of debris. In order to ensure the normal operation of the MBR system, various fibers, slag, waste paper and other large-sized debris must be intercepted outside the system, so a screen needs to be set in front of the system. The screen residue needs to be cleaned to avoid being blocked by debris.

[0025] Adjustment tank: The amount and quality of sewage collected by the system change over time. In order to ensure the normal operation of the subsequent treatment system and reduce the system operation load, the amount and quality of sewage need to be adjusted. Therefore, an adjustment tank is designed before entering the biological treatment system. The sediment in the adjustment tank needs to be cleaned regularly. In the prior art, the adjustment tank is generally equipped with an overflow to ensure the normal operation of the system when the load is too large.

[0026] MBR reaction tank: Organic pollutants are degraded and mud and water are separated in the MBR reaction tank. As the core part of the treatment system, the reaction tank includes microbial colonies, membrane components, water collection system, water outlet system, and aeration system.

[0027] Disinfection device: According to the requirements of water output, the system is also designed with a disinfection device, which can automatically add medicine and control the amount of medicine added; the medicine is a chemical substance with bactericidal effect.

[0028] Metering device: In order to ensure the smooth operation of the system, a certain metering device is required to monitor the system parameters. The metering control instrument includes flow meter and water meter.

[0029] Electric control device: including electric control box, which is installed in the equipment room; its main function is to control the water inlet pump, fan and suction pump. The control mode generally includes manual control and automatic control. The water inlet pump runs automatically according to the water level of each reaction tank under the control of PLC. The operation of the suction pump is intermittently controlled according to the preset time period. For example, when the water level of the MBR reaction tank is low, the suction pump stops automatically to protect the membrane module.

[0030] In the above-mentioned device, the MBR reaction tank is the core component of the membrane bioreactor, and the key component in the MBR reaction tank is the membrane assembly for filtration; the membrane assembly generally includes a filter membrane, which achieves the filtering effect by blocking the solid matter and other harmful substances in the sewage; in the process of equipment operation, the membrane pollution problem has always been the key bottleneck restricting the further promotion and application of MBR technology. The reason is that the filter membrane is very susceptible to pollution. Membrane pollution will lead to a decrease in membrane flux, a decrease in effluent quality, an increase in cleaning frequency and a shortened membrane service life, thereby greatly increasing the operating cost of the system. Common membrane pollution mainly includes organic pollution, inorganic pollution and biological pollution. These pollutants will gradually accumulate on the membrane surface, hindering the flow of water through the membrane pores, resulting in a decrease in membrane performance.

[0031] In order to solve or partially solve the above technical problems, the present invention provides a composite film, wherein the composite film includes a filler having photocatalytic properties.

[0032] In an optional embodiment, the filler with photocatalytic properties is an inorganic nanofiller with photocatalytic properties. Further, the filler with photocatalytic properties includes one or more of titanium oxide, zinc oxide, cadmium sulfide, tungsten trioxide, and ferric oxide. It can be understood that the filler with photocatalytic properties can also include other types of inorganic nanofillers with photocatalytic properties in the prior art, which are not exhaustive here; further, the filler with photocatalytic properties can be selected from titanium oxide; the filler with photocatalytic properties can also be selected from zinc oxide. In the above embodiment, the titanium dioxide or zinc oxide has good photocatalytic activity. Under the irradiation of ultraviolet light and sunlight, active oxygen species such as hydroxyl radicals can be generated. These active substances can effectively degrade organic pollutants attached to the surface of the film. The addition of nanoparticles also enhances the mechanical strength and wear resistance of the film. Further, the addition amount of the filler with photocatalytic properties is 5 to 15%.

[0033] In an optional embodiment, the composite membrane includes: a substrate layer, the substrate layer includes a polymer membrane; the filler with photocatalytic properties is dispersed in the substrate layer, and a surface layer, the surface layer covers the outer surface of the substrate layer; the surface layer has hydrophilic groups, and the surface layer is used to improve the hydrophilicity of the surface of the composite membrane. Further, the filler with photocatalytic properties is dispersed in the polymer membrane; further, the filler with photocatalytic properties can be mixed in the preparation process of the polymer membrane to form an island structure, and the filler is dispersed in the polymer membrane as a dispersed phase; further, the preparation of the membrane material: the preparation of the composite membrane material adopts advanced membrane manufacturing processes such as phase inversion method, sol-gel method or electrospinning technology. During the preparation process, the filler with photocatalytic properties (also known as photocatalyst) is uniformly dispersed in the polymer substrate by physical or chemical means, thereby ensuring its uniform distribution on the membrane surface.

[0034] In a preferred embodiment, the polymer membrane is a polyvinylidene fluoride membrane or a polyethersulfone membrane; the polymer membrane may also be a composite of one or more of polyvinylidene fluoride membrane, polyethersulfone membrane, polyethylene membrane and polypropylene membrane.

[0035] In a preferred embodiment, the surface layer may be a hydrophilic group introduced into the surface of the substrate layer through chemical modification.

[0036] In a preferred embodiment, the surface layer includes a hydrophilic polymer; further, the hydrophilic polymer is coated on one or both sides of the substrate layer to form the surface layer. Preferably, the hydrophilic polymer can be polyethylene glycol (PEG) or other water-soluble polymers, which can significantly reduce the adsorption of pollutants on the membrane surface, thereby reducing the accumulation of organic matter and microorganisms on the membrane surface and improving the membrane's anti-pollution ability.

[0037] In a preferred embodiment, the surface layer is a substrate layer whose surface is treated with oxygen plasma or chemically modified so that the surface exhibits higher hydrophilicity, significantly reducing the adsorption of organic matter and microorganisms in sewage on the membrane surface.

[0038] The present invention also provides a membrane bioreactor, comprising the composite membrane mentioned above.

[0039] In order to further demonstrate the technical efficacy of the present invention, the present invention provides a number of specific embodiments:

[0040] Embodiment 1:

[0041] A composite membrane containing 10% titanium dioxide (TiO2) nanoparticles was prepared using polyvinylidene fluoride (PVDF) as a substrate. The membrane surface was treated with oxygen plasma to further enhance the hydrophilicity of the membrane.

[0042] Embodiment 2:

[0043] A polyethersulfone (PES) substrate was used, 7% zinc oxide (ZnO) nanoparticles were added, the photocatalyst was uniformly attached to the membrane surface using the sol-gel method, and further hydrophilic surface modification treatment was performed.

[0044] Comparative Example:

[0045] The composite membrane uses polyvinylidene fluoride (PVDF) as the substrate. The membrane surface is treated with oxygen plasma to further enhance the hydrophilicity of the membrane.

[0046] Performance Testing:

[0047] Membrane fouling performance test:

[0048] Experimental setup: Flat membrane flux test system.

[0049] step:

[0050] 1. Install the composite membrane samples prepared according to the above-mentioned Example 1, Example 2 and Comparative Example in a filtration device and continuously run simulated sewage.

[0051] 2. The water flux and transmembrane pressure (TMP) of the membrane were recorded every 5 hours, and the experimental period was 30 days.

[0052] 3. Regularly take photos of membrane surface contamination and collect membrane contaminants for analysis.

[0053] The simulated sewage is a mixed solution containing protein (simulated organic pollutants), calcium ions (simulated inorganic pollutants) and activated sludge (simulated microbial pollutants).

[0054] The operating parameters of the filtration device are as follows: the water flux is controlled to be 30L / (m 2 ·h), transmembrane pressure 0.2 bar.

[0055] Photocatalytic performance test:

[0056] step:

[0057] 1. Irradiate the contaminated composite membrane surface with ultraviolet light in a dark room and measure the membrane flux recovery rate every 10 minutes.

[0058] 2. The concentration of organic matter after photocatalytic degradation was detected by liquid chromatography-mass spectrometry (LC-MS).

[0059] The light source conditions in this test experiment are: ultraviolet light (365nm, light intensity 10mW / cm 2 ) or simulated sunlight (light intensity 50mW / cm 2 ).

[0060] Membrane cleaning frequency test:

[0061] step:

[0062] 1. The number of physical cleaning and chemical cleaning of the composite membranes prepared according to the methods of the above-mentioned Example 1, Example 2 and the comparative example during the experimental period was counted respectively.

[0063] 2. Compare the flux recovery rates of each membrane after cleaning.

[0064] Stability of membrane anti-fouling performance:

[0065] step:

[0066] 1. The composite membrane samples prepared according to the methods of the above-mentioned Example 1, Example 2 and Comparative Example were recycled for 5 times under the same pollution conditions, and were cleaned after each operation for 7 days.

[0067] 2. Statistical analysis of the flux recovery rate and TMP changes after 5 cycles.

[0068] The flux of the membrane refers to the amount of fluid passing through a unit membrane area per unit time, generally expressed in m 3 / (m 2 *s) or L / (m 2 *h) (or m / s).

[0069] The calculation formula of membrane flux J is: J = V / (T×A)

[0070] Where: J is the flux of the membrane (L / m2·h); V is the sampling volume (L); T is the sampling time (h); A is the effective area of ​​the membrane (m 2 );

[0071] The membrane flux recovery rate is calculated as follows:

[0072] Recovery rate = (membrane flux after cleaning / new membrane flux) × 100%

[0073] The experimental results are shown in Table 1 and Table 2:

[0074] Table 1:

[0075]

[0076] Table 2:

[0077]

[0078] The experimental results show:

[0079] The membrane flux of the composite membrane in the comparative example decreased by 70% within 30 days, and the transmembrane pressure difference increased by 150%, indicating serious membrane fouling.

[0080] The composite membranes with added photocatalysts (Examples 1 and 2) showed significantly reduced pollution, with Example 1 showing the best effect, with a flux drop of only 20% and a TMP increase of only 30%.

[0081] The organic matter degradation rate of the composite membrane of the comparative example is only 10%, which mainly relies on the bioreactor for degradation. The organic matter degradation rates of the composite membranes of Example 1 and Example 2 are 85% and 80% respectively, indicating that the photocatalyst significantly decomposes organic pollutants under UV light.

[0082] The composite membrane of the comparative example requires frequent physical cleaning (10 times) and chemical cleaning (5 times), while the composite membranes of Examples 1 and 2 require significantly fewer cleanings, thereby reducing operating costs.

[0083] In the cyclic operation experiment, the composite membranes of Examples 1 and 2 maintained flux recovery rates of up to 95% and 90%, which are much better than the composite membrane of the comparative example (75%). The membrane life is expected to be extended to more than twice that of the traditional membrane.

[0084] The experimental results show that the composite membrane with photocatalytic fillers (such as TiO2 or ZnO) significantly enhances the anti-pollution performance and self-cleaning ability of the membrane: the flux retention capacity is significantly improved. The cleaning cycle and frequency are significantly reduced, saving operating costs. The service life of the membrane is significantly extended, and the economic benefits are outstanding. This experimental data further verifies the actual effect of the present invention and provides reliable technical support for the research and development of membrane materials and industrial applications.

[0085] The principle may be that when the film is exposed to ultraviolet or visible light, the photocatalyst is excited and generates electron-hole pairs, which further react with water and oxygen molecules in the air to form hydroxyl radicals (·OH) and superoxide anion radicals (O2 - ). These highly active free radicals can degrade organic pollutants attached to the membrane surface and destroy the cell walls of microorganisms, thereby inhibiting the formation of biofilms and maintaining the cleanliness of the membrane surface. Therefore, compared with traditional physical and chemical cleaning methods, photocatalytic self-cleaning can extend the service life of the membrane, reduce system downtime, and reduce the use of chemical reagents, with better environmental friendliness and economic benefits.

[0086] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A composite film, characterized in that The composite film includes a filler having photocatalytic properties.

2. The composite membrane according to claim 1, characterized in that The filler with photocatalytic performance is an inorganic nano filler with photocatalytic performance.

3. The composite membrane according to claim 1, characterized in that The filler with photocatalytic performance includes one or more of titanium oxide, zinc oxide, cadmium sulfide, tungsten trioxide, and ferric oxide.

4. The composite membrane according to claim 1, characterized in that The filler with photocatalytic performance is titanium oxide or zinc oxide.

5. The composite film according to any one of claims 1 to 4, characterized in that: The addition amount of the filler with photocatalytic performance is 5-15%.

6. The composite membrane according to claim 5, characterized in that The composite film comprises: A substrate layer, the substrate layer comprising a polymer film; the filler having photocatalytic properties is dispersed in the substrate layer, and, The surface layer covers the outer surface of the substrate layer; the surface layer has hydrophilic groups, and the surface layer is used to improve the hydrophilicity of the composite membrane surface.

7. The composite membrane according to claim 6, characterized in that The polymer membrane is a polyvinylidene fluoride membrane or a polyethersulfone membrane.

8. The composite membrane according to claim 6, characterized in that The polymer membrane is a composite of one or more of polyvinylidene fluoride membrane, polyethersulfone membrane, polyethylene membrane and polypropylene membrane.

9. The composite membrane according to claim 6, characterized in that The surface layer includes a hydrophilic polymer.

10. A membrane bioreactor, characterized in that: The composite film comprises the composite film according to any one of claims 1 to 9.

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