Preparation method and application of hollow fiber purification membrane for refining edible oil

Abstract

The invention discloses a preparation method and application of a hollow fiber purification membrane for edible oil refining, and belongs to the technical field of membrane separation and edible oil processing, the purification membrane is formed by spinning a core solution and a membrane casting solution, a perfluoropolyether nonionic surfactant is introduced into the membrane casting solution, and an amphiphilic structure forms a protective layer on the surface of the membrane, so that the hollow fiber purification membrane is formed. Pollutants such as grease, phospholipid, nigre, wax and the like are difficult to wet and attach, and the anti-pollution capability is excellent; after long-time use, impurities can be easily stripped in the conventional back flushing and chemical cleaning processes; after being cleaned, the membrane can be recovered to a very high level, so that the stability of production capacity is ensured, the chemical cleaning period of the membrane is prolonged, and the downtime is reduced; high performance can be maintained even if the material works in high-temperature and strong-alkali environments for a long time; according to the purification membrane process, multistage pretreatment and grafting processes are avoided, and the preparation is simple.

Description

Technical Field

[0001] This application belongs to the fields of membrane separation technology and edible oil processing technology, and in particular relates to a method for preparing and applying a hollow fiber purification membrane for edible oil refining. Background Technology

[0002] Edible oil refining is a crucial process for removing undesirable components from vegetable oils, such as gums, free fatty acids, pigments, odor substances, and waxes. Traditional refining processes (such as alkali refining, hydration, adsorption decolorization, and physical / chemical deodorization) have many drawbacks: long process flow, high energy consumption, use of large amounts of chemical reagents (such as caustic soda and bleaching clay) leading to significant oil loss (neutral oil saponification and adsorption), and generation of large amounts of wastewater (washing wastewater) and solid waste (waste bleaching clay), which are environmentally unfriendly and may affect the natural nutritional components and flavor of the oil.

[0003] Membrane separation technology, as an emerging green and efficient separation method, has shown great potential in the field of oil purification. Its advantages include no need to add chemical reagents, mild operating conditions, low energy consumption, no phase change, and better retention of active substances in oils. Currently, some studies have tried to use polymer ultrafiltration or nanofiltration membranes for degumming, deacidification, and dehazing of edible oils.

[0004] Patent CN111732732A discloses a polyethersulfone-grafted polyethylene glycol methacrylate copolymer, a film, and a method for preparing the same. The method involves washing and soaking the polyethersulfone raw material, followed by drying. The dried polyethersulfone is then mixed with polyethylene glycol methacrylate monomer to form a homogeneous solution. In this homogeneous solution containing both polyethylene glycol methacrylate monomer and polyethersulfone, a co-radiative grafting reaction is performed on the polyethylene glycol methacrylate monomer and polyethersulfone. The resulting homogeneous solution is then post-treated. The homogeneous solution is reverse-phase precipitated in deionized water. The resulting solid is washed, soaked in deionized water, and then vacuum-dried to constant weight. This invention grafts PEGMA onto the PES material matrix, allowing for the preparation of graft copolymers with different grafting ratios as needed, providing greater application flexibility and improving the properties of the graft copolymer itself.

[0005] Polymer materials such as polyvinylidene fluoride and polypropylene are widely used in hollow fiber membrane materials, but their use in edible oil filtration still has the following drawbacks: High-temperature oxidation: The grease before the deodorization section is exposed to high temperature and trace oxygen. Long-term operation will cause the polymer polymer chain to undergo oxidative degradation, making the membrane brittle and reducing its performance. Strong alkaline cleaning: Although commonly used hot alkaline cleaning (such as 1-2% NaOH, 80 °C) can be tolerated in the short term, long-term and frequent strong alkaline impacts will slowly erode the membrane surface. In particular, if the membrane has a modified layer, it will accelerate the loss of the modifier, thereby causing membrane pore blockage and surface fouling, resulting in a sharp drop in membrane flux. Frequent cleaning will cause membrane aging or degradation, resulting in a short lifespan and affecting the stability and economy of long-term operation. Summary of the Invention

[0006] The purpose of this application is to provide a method for preparing and applying a hollow fiber purification membrane for edible oil refining, in order to solve the technical problems existing in the prior art where membrane materials are oxidized, the modified layer fails, and the overall performance of the purification membrane declines due to prolonged exposure to high temperature and strong alkaline environments.

[0007] To achieve the above objectives, the technical solution adopted in this application is: to provide a method for preparing a hollow fiber purification membrane for edible oil refining, specifically including the following steps: (a) Preparation of core solution: Core solution is prepared by mixing a polar solvent with water; (II) Preparation of casting solution: After adding a polar solvent to a closed container and heating, the polymer is slowly added and dissolved while stirring. After cooling, inorganic nanoparticles, polyvinylpyrrolidone, and perfluoropolyether nonionic surfactants are added respectively. After uniform dispersion and degassing, the casting solution is obtained. (III) Membrane Forming: The casting liquid and core liquid are injected into the spinneret, extruded into shape, and solidified in a coagulation bath after passing through a short air gap. The hollow fiber purification membrane is then obtained through post-treatment.

[0008] In one embodiment, In step (i), the volume percentage of water to polar solvent is 20-30% : 70-80%.

[0009] In one embodiment, The casting solution, by weight percentage, comprises 15-18% polymer, 2-5% inorganic nanoparticles, 70-75% polar solvent, 4-8% polyvinylpyrrolidone, and 0.5-2% perfluoropolyether nonionic surfactant.

[0010] In one embodiment, The polymer is one of polyvinylidene fluoride (PVDF), polypropylene (PP) or polyethylene (PE), preferably PVDF; the perfluoropolyether nonionic surfactant is perfluoroalkyl polyoxyethylene ether or perfluoroalkyl ethanol polyoxyethylene ether; the polar solvent is N-methylpyrrolidone, xylene or dimethylacetamide.

[0011] In one embodiment, The inorganic nanoparticles are TiO2 or SiO2, and the particle size of the inorganic nanoparticles is 10-30 nm.

[0012] In one embodiment, In step (ii), the heating temperature is 60-70 °C and the cooling temperature is 40-50 °C.

[0013] In one embodiment, The hollow fiber purification membrane has a pore size of 70-90 nm and a thickness of 200-205 µm; the outer skin layer has a pore size of 2-5 nm.

[0014] In one embodiment, Polyvinylidene fluoride (PVDF) needs to undergo fluorination treatment, specifically: after thoroughly drying the PVDF powder, it reacts with fluorine gas to obtain fluorinated PVDF; the fluorine gas is fluorine gas diluted with high-purity nitrogen, and the reaction temperature is 80 °C. Polypropylene or polyethylene needs to be pretreated, specifically by heating to 165 °C and dissolving the polypropylene or polyethylene in a polar solvent.

[0015] This application also provides an application of a hollow fiber purification membrane for edible oil refining. The application of the hollow fiber purification membrane in the edible oil refining filtration process specifically includes the following steps: Forward flushing, filtration, reverse suction, backwashing, air backwashing, and sewage discharge.

[0016] In one embodiment, The forward flow rate is 900 L / h. During the filtration process, the feed rate is 550 L / h, the filtration rate is 500 L / h, and the return flow rate is 0-50 L / h. The reverse suction rate is 500 L / h, the backwash rate is 500 L / h, and the gas backwash rate is 5 m³ / h. 3 / h, sewage discharge rate is 500 L / h; forward flushing time is 15 s, filtration time is 3600 s, back suction time is 50 s, backwashing time is 50 s, air backwashing time is 50 s, sewage discharge time is 50 s.

[0017] This application provides a method for preparing a hollow fiber purification membrane for edible oil refining and its application, which has the following advantages compared with the prior art: 1. The fluorocarbon chain of perfluoropolyether nonionic surfactants is a polyether structure, possessing extremely low surface tension and excellent chemical inertness. Its amphiphilic structure (the perfluoroalkyl chain is a strongly hydrophobic and oleophobic segment, while the polyoxyethylene ether chain is a hydrophilic segment) spontaneously migrates and accumulates on the membrane surface and pore walls during phase inversion, forming a protective layer on the membrane surface. This layer significantly reduces the free energy of the membrane surface, making it difficult for contaminants such as grease, phospholipids, soap residue, and waxes to wet and adhere, achieving a non-stick effect from the source and exhibiting excellent antifouling capabilities. Even after prolonged use, impurities can be easily removed during routine backwashing and chemical cleaning. After cleaning, the membrane can recover to a high level, ensuring stable production capacity, extending the chemical cleaning cycle of the membrane, and reducing downtime. Perfluoropolyether nonionic surfactants are inherently highly chemically inert. Their ether bond structure is more resistant to alkali hydrolysis than ester bonds, and they have a good affinity for polymers. They can easily withstand strong acids, strong alkalis, and oxidants. Perfluoropolyether nonionic surfactants can be permanently bonded to the film surface through chemical reactions, and will not be washed away. They are long-lasting and do not peel off even after prolonged use. This application innovatively introduces perfluoropolyether nonionic surfactants into the purification membrane. By using polymers with a high degree of fluorination, perfluoropolyether nonionic surfactants can be easily introduced through blending without the need for complex grafting processes, thus simplifying the preparation method and improving the compounding effect. In this process, perfluoropolyether nonionic surfactants are added as additives to the casting solution. By utilizing the property of perfluoropolyether nonionic surfactants migrating to the surface during phase transformation, surface modification is achieved, avoiding the aforementioned complex steps. 2. Integrated deep purification: a single filtration can replace or simplify the traditional multi-step refining process. The hollow fiber filtration membrane system replaces the plate and frame filter, solving the drawbacks of the plate and frame filter that require frequent cleaning and have poor filtration effect. This enables continuous and automated production, reducing labor costs and labor intensity. 3. Excellent physical and chemical stability: The selected membrane materials and inorganic nanoparticles endow the purification membrane with good resistance to organic solvents, high temperature resistance and mechanical strength, which are fully adapted to the working conditions of edible oil refining. 4. Green, environmentally friendly and economical: The refining process requires no or significantly reduces the use of chemical additives, reducing wastewater and waste residue emissions at the source, while improving refining yield and reducing overall production costs, meeting the requirements of clean production and sustainable development; the retained impurities are returned to the upstream raw material tank in the form of concentrated liquid, and the oil is fully recovered, which has significant economic benefits for large-scale production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 Characterization diagram of pore size of hollow fiber purification membrane; Figure 2 Images of raw oil and filtrate samples for C-type soap semi-finished product; Figure 3 Images of raw oil and filtrate samples of N-soap semi-finished oil; Figure 4 Images of crude C soap oil raw material and filtrate samples; Figure 5 Images of crude N-soap oil raw material and filtrate samples. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, this application will be further described in detail. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0021] Example 1 A method for preparing a hollow fiber purification membrane for edible oil refining specifically includes the following steps: (a) Preparation of core fluid: Under low-speed magnetic stirring, 700 mL of N-methylpyrrolidone and 300 mL of water are slowly mixed for 40 min to obtain the core fluid, which is then sealed and stored. This ratio is a "weakly solidifying" core fluid, which can slow down the phase separation rate of the inner surface, help to form a more open and permeable inner surface structure, reduce mass transfer resistance, and is suitable for oil purification. (II) PVDF Fluorination Treatment: Select a corrosion-resistant reactor, thoroughly dry the polyvinylidene fluoride powder and load it into the reactor, purge the reactor with nitrogen to ensure that the reactor is free of water and oxygen, purge with fluorine gas diluted with high-purity nitrogen (5% F2), maintain a slight positive pressure, raise the temperature to 80 °C and react for 10 h to obtain fluorinated PVDF; after the reaction is completed, the tail gas is recovered and purified. (III) Preparation of casting solution: 75 g of N-methylpyrrolidone was added to a sealed container and heated to 65 °C. 18 g of fluorinated PVDF was slowly added under vigorous stirring for 6 h to dissolve until the fluorinated PVDF was completely dissolved, forming a transparent, viscous homogeneous solution. The temperature was lowered to 45 °C, and 3 g of hydrophilic nano-SiO2 with a particle size of 10-30 nm was slowly added and stirred for 2 h. Then 5 g of polyvinylpyrrolidone was added and stirred until completely dissolved. 2 g of perfluoroalkyl polyoxyethylene ether was then slowly added dropwise to the system and stirred vigorously for 3 h to obtain the casting solution. After the reaction was completed, stirring was stopped, and the prepared casting solution was degassed under a vacuum of -0.095 MPa for 1 h to allow the bubbles to escape naturally. (iv) Film Forming S1. Spinning conditions: casting solution temperature 45 °C, core solution temperature room temperature, casting solution delivery rate 4 mL / min, core solution delivery rate 2 mL / min, air gap 6 cm. S2. Using a precision metering pump, the casting solution and core solution are respectively injected into the outer annulus and inner tube of the hollow fiber spinneret. At the spinneret outlet, the core solution is enveloped in the center of the casting solution, and together they are extruded to form the initial hollow fiber liquid flow. The extruded hollow fiber liquid flow passes through a pre-set air gap. At this stage, a small amount of solvent evaporates from the fiber surface, and preliminary phase separation begins, forming a dense outer skin layer. The fiber is then placed in a water bath for curing (water bath temperature 25 °C). Vigorous bidirectional diffusion occurs between the water and the solvent in the fiber, resulting in liquid-liquid phase separation and instantaneous curing, thus producing a hollow fiber purification membrane. Figure 1 As shown, the pore size is 80 nm and the thickness is 202 µm; the outer skin layer has a pore size of 5 nm. S3. Post-treatment: Rinse the hollow fiber purification membrane three times with deionized water for 20 minutes each time to remove residual solvent and most of the soluble polyvinylpyrrolidone. Then soak it in a 25% glycerol aqueous solution for 24 hours, take it out, air dry it, and roll it up for later use.

[0022] Example 2 The difference between this embodiment and Embodiment 1 is that in step (iv), the mass of fluorinated PVDF is 20 g, the mass of SiO2 is 2 g, the mass of polyvinylpyrrolidone is 4 g, the mass of N-methylpyrrolidone is 70 g, and the mass of perfluoroalkyl polyoxyethylene ether is 0.5 g. The remaining operations are the same, and a hollow fiber purification membrane is obtained.

[0023] Example 3 The difference between this embodiment and Embodiment 1 is that in step (iv), the mass of fluorinated PVDF is 18 g, the mass of SiO2 is 5 g, the mass of polyvinylpyrrolidone is 8 g, the mass of N-methylpyrrolidone is 75 g, and the mass of perfluoroalkyl polyoxyethylene ether is 2 g. The remaining operations are the same, and a hollow fiber purification membrane is obtained.

[0024] Example 4 The difference between this embodiment and Example 1 is that the polar solvent is dimethylacetamide, but the rest of the operations are the same.

[0025] Example 5 The difference between this embodiment and Embodiment 1 is that the perfluoropolyether nonionic surfactant is perfluoroalkyl ethanol polyoxyethylene ether, while the rest of the operation is the same.

[0026] Example 6 The difference between this embodiment and Embodiment 1 is that commercially available PVDF with a high degree of fluorination is used, eliminating the need for fluorination treatment and allowing for direct preparation of the base layer. The remaining operations are the same.

[0027] Example 7 A method for preparing a hollow fiber purification membrane for edible oil refining specifically includes the following steps: (a) Preparation of core solution: Under low-speed magnetic stirring, 700 mL of xylene and 300 mL of water were slowly mixed for 40 min to obtain the core solution, which was then sealed and stored. (II) Preparation of casting solution: Heat to 165 °C, dissolve PP in xylene, and slowly add 18 g of PP while stirring vigorously for 6 h until the PP is completely dissolved, forming a transparent, viscous homogeneous solution; cool to 45 °C, slowly add 3 g of hydrophilic nano-SiO2 with a particle size of 10-30 nm and stir for 2 h, then add 5 g of polyvinylpyrrolidone and continue stirring until completely dissolved, then slowly add 2 g of perfluoroalkyl polyoxyethylene ether to the system and stir vigorously for 3 h to obtain the casting solution; after the reaction is complete, stop stirring and degas the prepared casting solution under a vacuum of -0.095 MPa for 1 h to allow the bubbles to escape naturally; (iv) Film Forming S1. Spinning conditions: casting solution temperature 45 °C, core solution temperature room temperature, casting solution delivery rate 4 mL / min, core solution delivery rate 2 mL / min, air gap 6 cm. S2. Using a precision metering pump, the casting solution and core solution are respectively injected into the outer annulus and inner tube of the hollow fiber spinneret. At the spinneret outlet, the core solution is wrapped in the center of the casting solution and extruded together to form the initial hollow fiber liquid flow. The extruded hollow fiber liquid flow passes through an air gap of a set length. At this stage, a small amount of solvent evaporates from the fiber surface, and preliminary phase separation begins to occur, forming a dense outer skin layer. The fiber enters a water bath for curing (water bath temperature 25 °C). The water and the solvent in the fiber undergo intense bidirectional diffusion, resulting in liquid-liquid phase separation and instantaneous curing, thus obtaining a hollow fiber purification membrane. S3. Post-treatment: Rinse the hollow fiber purification membrane three times with deionized water for 20 minutes each time to remove residual solvent and most of the soluble polyvinylpyrrolidone. Then soak it in a 25% glycerol aqueous solution for 24 hours, take it out, air dry it, and roll it up for later use.

[0028] Example 8 The difference between this embodiment and embodiment 7 is that PP is replaced with PE, while the rest of the operations are the same, to obtain a hollow fiber purification membrane.

[0029] Experimental Example 1 Small-scale filtration test of edible oil: The membrane prepared in Example 1 was used, with a membrane area of ​​0.016 m². 2 The pressure is negative 0.08 MPa, 200-300 g of oil is filtered, and the flow rate is measured. Oil 1: C soap semi-finished oil (800ml), Oil 2: N soap semi-finished oil (900ml), Oil 3: C soap crude oil (900ml), Oil 4: N soap crude oil (900ml); Measurement throughput is shown in Table 1; Comparison of oil feedstock and filtered oil samples is shown in... Figure 2-5 ; Table 1 Flux Data

[0030] Experimental Example 2 The hollow fiber purification membranes prepared in Examples 1 and 7-8 were assembled into a membrane testing module, and a constant pressure filtration test was performed on crude soybean oil (initial phospholipid content 500 ppm, FFA content 2%, color red value 15) (operating pressure: 0.8 MPa, temperature: 50 ℃). result: Example 1: Phospholipid removal rate >99.5%, FFA removal rate >85%, and color red value reduced to below 4.0; the initial flux reached 35 L / m²·h, and after 4 hours of operation, the flux stabilized at 33 L / m²·h, showing good anti-fouling performance; Example 7: Phospholipid removal rate >99.5%, FFA removal rate >85%, and color red value reduced to below 4.0; the initial flux reached 32 L / m²·h, and after 4 hours of operation, the flux stabilized at 30 L / m²·h, showing good anti-fouling performance; Example 8: Phospholipid removal rate >99.5%, FFA removal rate >85%, and color red value reduced to below 4.0; the initial flux reached 31 L / m²·h, and after 4 hours of operation, the flux stabilized at 28 L / m²·h, showing good anti-fouling performance.

[0031] The results above show that all three base polymer materials have excellent anti-fouling properties.

[0032] Comparative Example The same batch of crude soybean oil was treated under the same conditions using a commercially available composite purification membrane (molecular weight cutoff of 10 kDa). Results: Phospholipid removal rate was about 95%, but the removal effect on FFA and pigments was very poor (FFA removal rate <10%, color red value hardly changed), and the flux decayed rapidly, with the flux dropping to 40% of the initial value after 2 hours.

[0033] Example 9 The difference between this embodiment and Example 1 is that the amount of N-methylpyrrolidone is 800 mL and the amount of water is 300 mL, while the rest of the operation is the same, and a hollow fiber purification membrane is obtained.

[0034] Example 10 An application of a hollow fiber purification membrane for edible oil refining involves using the hollow fiber purification membrane prepared in Example 1 in the refining and filtration process of peanut oil, specifically including the following steps: Forward flushing, filtration, reverse suction, backwashing, air backwashing, and sewage discharge; The forward flow rate is 900 L / h. During the filtration process, the feed rate is 550 L / h, the filtration rate is 500 L / h, and the return flow rate is 0-50 L / h. The reverse suction rate is 500 L / h, the backwash rate is 500 L / h, and the gas backwash rate is 5 m³ / h. 3 / h, sewage discharge rate is 500 L / h; forward flushing time is 15 s, filtration time is 3600 s, back suction time is 50 s, backwashing time is 50 s, air backwashing time is 50 s, sewage discharge time is 50 s.

[0035] According to the method of Example 10, the purification membrane prepared in Examples 7-8 can be replaced in Examples 1 to realize the refining filtration process of edible oil; edible oil includes peanut oil, sesame oil, rapeseed oil, etc., which are not limited here.

[0036] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a hollow fiber purification membrane for edible oil refining, characterized in that, Specifically, the following steps are included: (a) Preparation of core solution: Core solution is prepared by mixing a polar solvent with water; (II) Preparation of casting solution: After adding a polar solvent to a closed container and heating, the polymer is slowly added and dissolved while stirring. After cooling, inorganic nanoparticles, polyvinylpyrrolidone, and perfluoropolyether nonionic surfactants are added respectively. After uniform dispersion and degassing, the casting solution is obtained. (III) Film Forming: The casting liquid and core liquid are injected into the spinneret, extruded and formed, and solidified in a coagulation bath after passing through a short air gap. The hollow fiber purification membrane is then obtained through post-treatment.

2. The method for preparing a hollow fiber purification membrane for edible oil refining according to claim 1, characterized in that, In step (i), the volume percentage of water to polar solvent is 20-30% : 70-80%.

3. The method for preparing a hollow fiber purification membrane for edible oil refining according to claim 1, characterized in that, The casting solution, by weight percentage, comprises 15-18% polymer, 2-5% inorganic nanoparticles, 70-75% polar solvent, 4-8% polyvinylpyrrolidone, and 0.5-2% perfluoropolyether nonionic surfactant.

4. The method for preparing a hollow fiber purification membrane for edible oil refining according to claim 1, characterized in that, The polymer is one of polyvinylidene fluoride, polypropylene, or polyethylene; the perfluoropolyether nonionic surfactant is perfluoroalkyl polyoxyethylene ether or perfluoroalkyl ethanol polyoxyethylene ether; the polar solvent is N-methylpyrrolidone, xylene, or dimethylacetamide.

5. The method for preparing a hollow fiber purification membrane for edible oil refining according to claim 1, characterized in that, The inorganic nanoparticles are TiO2 or SiO2, and the particle size of the inorganic nanoparticles is 10-30 nm.

6. The method for preparing a hollow fiber purification membrane for edible oil refining according to claim 1, characterized in that, In step (ii), the heating temperature is 60-70 °C and the cooling temperature is 40-50 °C.

7. The method for preparing a hollow fiber purification membrane for edible oil refining according to claim 1, characterized in that, The hollow fiber purification membrane has a pore size of 70-90 nm and a thickness of 200-205 µm; the outer skin layer has a pore size of 2-5 nm.

8. The method for preparing a hollow fiber purification membrane for edible oil refining according to claim 4, characterized in that, The polyvinylidene fluoride is subjected to fluorination treatment, specifically by: thoroughly drying the polyvinylidene fluoride powder and reacting it with fluorine gas to obtain fluorinated polyvinylidene fluoride; the fluorine gas is fluorine gas diluted with high-purity nitrogen gas, and the reaction temperature is 80 °C. The polypropylene or polyethylene needs to be pretreated, specifically by heating to 165 °C and dissolving the polypropylene or polyethylene in a polar solvent.

9. An application of a hollow fiber purification membrane for edible oil refining, characterized in that, The application of hollow fiber purification membranes in the refining and filtration process of edible oils includes the following steps: Forward flushing, filtration, reverse suction, backwashing, air backwashing, and sewage discharge.

10. The application of the hollow fiber purification membrane for edible oil refining according to claim 9, characterized in that, The forward impulse is 900 L / h. In the filtration step, the feed rate is 550 L / h, the filtration rate is 500 L / h, and the return flow rate is 0-50 L / h; the back suction rate is 500 L / h, the backwash rate is 500 L / h, and the gas backwash rate is 5 m³. 3 / h, sewage discharge rate is 500 L / h; forward flushing time is 15 s, filtration time is 3600 s, back suction time is 50 s, backwashing time is 50 s, air backwashing time is 50 s, sewage discharge time is 50 s.

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