Hollow fiber membrane, hollow fiber membrane module, water treatment device, and water treatment method

Abstract

This hollow fiber membrane having oxygen permeability comprises: a body part formed in a cylindrical shape extending in a longitudinal direction; and a plurality of first protruding parts protruding in a radial direction from an outer surface of the body part, extending in the longitudinal direction, and separated in a circumferential direction. The membrane thickness of the body part is less than 30 μm, and the height of the plurality of first protruding parts from the outer surface in the radial direction is 0.5-7 times the membrane thickness of the body part.

Description

Hollow fiber membrane, hollow fiber membrane module, water treatment device and water treatment method

[0001] This application claims priority to Japanese Patent Application No. 2024-017995 filed in Japan on February 8, 2024, and Japanese Patent Application No. 2024-018182 filed in Japan on February 8, 2024, the contents of which are incorporated herein by reference.

[0002] Industrial wastewater and domestic wastewater are treated to remove organic matter and the like from the water before being reused as industrial water or discharged into rivers, etc. Typical methods for treating industrial wastewater and the like include activated sludge treatment, in which the water to be treated is aerated and aerobic microorganisms are used to decompose the organic matter and the like. Such biological water treatment methods, typified by activated sludge treatment, utilize aerobic microorganisms and denitrifying bacteria for removing nitrate nitrogen. Recently, treatment using a membrane bioreactor (MBR) method, which combines activated sludge treatment with membrane filtration using a separation membrane module, has become common.

[0003] When treating water using aerobic microorganisms, it is necessary to aerate the water to be treated with air or oxygen to maintain the activity of the microorganisms and improve the treatment capacity. As such, a method using hollow fiber membranes has been adopted as a method for efficiently aerating the water to be treated. These hollow fiber membranes are used in various fields, such as wastewater treatment, drinking water production, and water purification.

[0004] Furthermore, recently, a method has been proposed for water treatment using hollow fiber membranes, in which a microbial layer (biofilm) derived from microorganisms in water is formed on the outer surface of the hollow fiber membrane and water treatment is performed in this state. In a bioreactor, known as a membrane aeration biofilm reactor (MABR), in which a microbial layer is formed on the outer surface of the hollow fiber membrane and oxygen is supplied from the inner side of the hollow fiber membrane, an oxygen gradient is formed in the thickness direction of the microbial layer. This allows aerobic treatment (BOD oxidation, nitrification of ammonia) to proceed on the inner side of the microbial layer, while anaerobic treatment of nitrate (BOD oxidation, denitrification) to proceed on the outer side of the microbial layer, making it possible to remove various pollutants in a single process. Therefore, compared to conventional methods such as membrane separation activated sludge processes, in which aerobic treatment and anaerobic treatment are performed in separate treatment tanks, equipment requiring less space can be realized.

[0005] Furthermore, the inclusion of a microbial layer in MABR increases the oxygen dissolution efficiency compared to conventional systems, thereby reducing the operating load on the blower that supplies oxygen and reducing sludge generation, thereby enabling a reduction in the running costs of the entire facility. Furthermore, the formation of a microbial layer ensures a large membrane surface area for the hollow fiber membrane, enabling stable treatment even with fluctuations in the water inflow load. Therefore, MABR is being widely considered for use in various water treatment devices. For example, a hollow fiber membrane such as that described in Patent Document 1 is known.

[0006] Japanese Patent Application Laid-Open No. 2022-147165

[0007] Improving the oxygen permeability of the membrane is important for improving the treatment capacity of water treatment using MABR as in Patent Document 1. Although the oxygen permeability can be improved by reducing the thickness of the hollow fiber membrane, there is a risk that sufficient mechanical strength cannot be ensured throughout the hollow fiber membrane.

[0008] An object of the present invention is to provide a hollow fiber membrane, a hollow fiber membrane module, a water treatment device, and a water treatment method that can improve the oxygen permeability of the membrane while ensuring mechanical strength.

[0009] In view of the above problems, the inventors of the present invention discovered that a membrane that combines mechanical strength and oxygen permeability can be obtained by designing a plurality of convex ridge portions on the outer surface and / or inner surface of a hollow fiber membrane, and completed the present invention. That is, the present invention has the following configurations: [1] An oxygen-permeable hollow fiber membrane comprising: a main body portion formed into a tubular shape extending in the longitudinal direction; and a plurality of first convex ridge portions protruding radially from the outer surface of the main body portion and extending in the longitudinal direction, wherein the membrane thickness of the main body portion is less than 30 μm, the plurality of first convex ridge portions are spaced apart circumferentially from each other, and the height of the plurality of first convex ridge portions from the outer surface in the radial direction is 0.5 to 7 times the membrane thickness of the main body portion. [2] An oxygen-permeable hollow fiber membrane comprising: a main body portion formed into a tubular shape extending in the longitudinal direction; and a reinforcing structure extending from the inner surface of the main body portion. [3] The hollow fiber membrane according to [2], wherein the reinforcing structure has a plurality of second convex ridge portions protruding radially from the inner surface and extending in the longitudinal direction, and wherein each of the plurality of second convex ridge portions is spaced apart in the circumferential direction of the main body portion. [4] The hollow fiber membrane according to [2], wherein the reinforcing structure is connected to the inner surface at two or more locations, has a plate shape extending in the longitudinal direction, and has an average thickness of 30 μm or less. [5] The hollow fiber membrane according to [4], wherein the average thickness of the reinforcing structure is greater than the membrane thickness of the main body portion. [6] The hollow fiber membrane according to [4], wherein, in a cross-section of the hollow fiber membrane perpendicular to the longitudinal direction, the cross-sectional area of ​​the reinforcing structure is 50% or less of the cross-sectional area of ​​the inner region of the hollow fiber membrane. [7] The hollow fiber membrane according to any one of [2] to [6], further comprising a plurality of first convex ridge portions protruding radially from the outer surface of the main body portion and extending in the longitudinal direction, and wherein each of the plurality of first convex ridge portions is spaced apart in the circumferential direction of the main body portion.[8] The hollow fiber membrane according to any one of [4] to [6], wherein the reinforcing structure has a plurality of second convex ridge portions protruding radially from the inner surface and extending in the longitudinal direction, each of the plurality of second convex ridge portions being spaced apart in the circumferential direction of the main body portion; a plurality of first convex ridge portions protruding radially from the outer surface of the main body portion and extending in the longitudinal direction, each of the plurality of first convex ridge portions being spaced apart in the circumferential direction of the main body portion; and at least one pair of the first convex ridge portions and the second convex ridge portions protruding in the same radial direction. [9] The hollow fiber membrane according to [1], wherein the number of the first convex ridge portions is a multiple of 3.

[10] The hollow fiber membrane according to [1] or [2], wherein the hollow fiber membrane is a single-layer membrane having a non-porous structure.

[11] The hollow fiber membrane according to [1], wherein the total length of all portions of the outer surface in the circumferential direction where the first convex ridge portions are formed is equal to or less than half the circumferential length of the outer surface.

[12] The hollow fiber membrane according to [1] or [2], wherein the outer diameter of the main body is 1 mm or less.

[13] The hollow fiber membrane according to [1] or [2], formed containing polyolefin.

[14] A hollow fiber membrane module comprising the hollow fiber membrane according to [1] or [2].

[15] A water treatment device comprising the hollow fiber membrane module according to

[14] .

[16] A water treatment method for treating water to be treated using the water treatment device according to

[15] , wherein, when the water to be treated is treated, microorganisms derived from microorganisms or bacteria in the water to be treated can be formed on the outer surface of the main body.

[0010] According to the present invention, it is possible to provide a hollow fiber membrane, a hollow fiber membrane module, a water treatment device, and a water treatment method that can improve the oxygen permeability of the membrane while ensuring mechanical strength.

[0011] 1 is a cross-sectional view showing a hollow fiber membrane according to the first embodiment. FIG. 2 is a perspective view showing the hollow fiber membrane. FIG. 3 is a cross-sectional view showing a hollow fiber membrane according to Modification 1. FIG. 4 is a cross-sectional view showing a hollow fiber membrane according to Modification 2. FIG. 5 is a cross-sectional view showing a hollow fiber membrane according to Modification 3. FIG. 6 is a cross-sectional view showing a hollow fiber membrane according to the second embodiment. FIG. 7 is a cross-sectional view showing a hollow fiber membrane according to Modification 4. FIG. 8 is a cross-sectional view showing a hollow fiber membrane according to Modification 5. FIG. 9 is a cross-sectional view showing a hollow fiber membrane according to Modification 6. FIG. 10 is a cross-sectional view showing a hollow fiber membrane according to Modification 7. FIG. 11 is a perspective view showing the hollow fiber membrane. FIG. 12 is a cross-sectional view showing a hollow fiber membrane according to Modification 13. FIG. 14 is a cross-sectional view showing a hollow fiber membrane according to Modification 14. FIG. 15 is a schematic diagram showing the overall configuration of an apparatus including a water treatment tank, for schematically explaining one embodiment of a hollow fiber membrane module and a water treatment apparatus. FIG. 16 is a cross-sectional view of a hollow fiber membrane according to a conventional prior art. 1 is a cross-sectional view showing a state in which a microbial layer is formed on the outer surface of a hollow fiber membrane according to a conventional prior art. FIG. 2 is a diagram showing measurement results of Comparative Examples 1 and 2 and Examples 1 to 7.

[0012] Hereinafter, hollow fiber membranes, hollow fiber membrane modules, water treatment devices, and water treatment methods according to embodiments will be described with reference to the drawings. In the following description, components having the same or similar functions will be assigned the same reference numerals. Duplicate descriptions of those components may be omitted.

[0013] [Hollow fiber membrane] Figure 21 is a cross-sectional view of a hollow fiber membrane 1Z according to a conventional prior art. Figure 22 is a cross-sectional view showing the state in which a microbial layer B is formed on the outer surface of a hollow fiber membrane 1Z according to a conventional prior art. As shown in Figure 21, the hollow fiber membrane 1Z according to the conventional prior art has a substantially circular cross-section. As shown in Figure 22, in the hollow fiber membrane 1Z according to the conventional prior art, a microbial layer B derived from microorganisms or bacteria in the water to be treated is formed on the outer surface 3a during water treatment.

[0014] (First embodiment) A hollow fiber membrane 1 of a first embodiment will be described with reference to Figures 1 to 5. First, the overall configuration of the hollow fiber membrane 1 will be described. However, the hollow fiber membrane 1 does not need to have all of the components described below, and some components may be omitted as appropriate.

[0015] The hollow fiber membrane 1 is cylindrical. In this embodiment, the "longitudinal direction A" means the longitudinal direction of the side surface of the hollow fiber membrane 1. In this embodiment, the "circumferential direction C" means the circumferential direction of the cross section of the hollow fiber membrane 1. In this embodiment, the "radial direction R" means the radial direction of the hollow fiber membrane 1. In this embodiment, the "cross section" means the cut surface when the hollow fiber membrane 1 is cut in a direction perpendicular to the longitudinal direction A. In this embodiment, the "height of the convex portion" means the height from the surface of the hollow fiber membrane 1 in the radial direction R.

[0016] As shown in Figures 1 to 20, the hollow fiber membrane 1 of this embodiment, the hollow fiber membrane module 10 including the hollow fiber membrane 1, and the water treatment device 100 including a plurality of hollow fiber membrane modules 10 are used for treatment (water treatment) of removing organic matter and the like contained in industrial wastewater, domestic wastewater, etc.

[0017] The hollow fiber membrane 1 of this embodiment is an oxygen-permeable hollow fiber membrane, i.e., a microbial layer B derived from microorganisms in the water to be treated or microorganisms is formed on the outer surface 3a during water treatment, and the membrane is capable of transmitting oxygen. The presence or absence of oxygen permeability can be determined by the speed at which oxygen moves per unit area (O ２ The permeation flux is calculated using the following conversion formula: O ２ Flux = (O ２ The O measured by the water displacement method was ２ The flux value is usually 0.001 m ３ / m ２ If the tensile strength is 1 / h / MPa or more, it is considered to have oxygen permeability.

[0018] Fig. 1 is a cross-sectional view showing a hollow fiber membrane 1. Fig. 2 is a perspective view showing the hollow fiber membrane 1. The hollow fiber membrane 1 of this embodiment is characterized in that a plurality of first convex portions 4 are formed on the surface to ensure mechanical strength despite being a thin film. As shown in Fig. 1, the hollow fiber membrane 1 includes a main body portion 3 and first convex portions 4.

[0019] The main body 3 is cylindrical and extends in the longitudinal direction A. Because the main body 3 is cylindrical, it has a hollow interior and has an outer surface 3a and an inner surface 3b. The main body 3 is capable of transmitting oxygen from the inner surface 3b to the outer surface 3a. The main body 3 has an oxygen passageway that connects the inner surface 3b to the outer surface 3a.

[0020] In the main body 3, the film thickness L1 is preferably less than 30 μm and the outer diameter L2 is preferably 1 mm or less. The film thickness L1 is preferably 2 μm or more and 27 μm or less, more preferably 5 μm or more and 20 μm or less, and even more preferably 10 μm or more and 15 μm or less. If the film thickness L1 exceeds the upper limit, the oxygen permeability is insufficient, and if it is less than the lower limit, the mechanical strength is insufficient.

[0021] The hollow fiber membrane 1 of this embodiment is formed containing polyolefin, polyurethane, fluorine-based resin, and silicone-based resin. The hollow fiber membrane 1 is a single-layer membrane having a non-porous structure. Examples of polyolefin include polyethylene, polypropylene, and polymethylpentene. From the viewpoint of cost, it is preferable that the hollow fiber membrane 1 is formed containing polyethylene. From the viewpoint of oxygen permeability, it is preferable that the hollow fiber membrane 1 is formed containing low-density polyethylene. As the silicone-based resin, polydimethylsiloxane (PMDS) is preferable from the viewpoint of oxygen permeability. The hollow fiber membrane 1 may be made of one type of material or two or more types of materials.

[0022] The first convex ridge portions 4 protrude from the outer surface 3a in the radial direction R and extend in the longitudinal direction A. A plurality of first convex ridge portions 4 are formed on the outer surface 3a, and are spaced apart in the circumferential direction C. In the hollow fiber membrane 1 of this embodiment, 12 first convex ridge portions 4 are formed, and are formed at equal intervals in the circumferential direction C. However, the number of first convex ridge portions 4 is not limited to the above. For example, it is preferable that 12 or fewer first convex ridge portions 4 are formed, more preferably 9 or fewer first convex ridge portions 4, and even more preferably 6 or fewer first convex ridge portions 4. It is also preferable that three or more first convex ridge portions 4 are formed. When the number of first convex ridge portions 4 is 12 or fewer and 3 or more, it is believed that sufficient mechanical strength can be ensured.

[0023] When multiple first convex ridge portions 4 are formed at approximately equal intervals in the circumferential direction C, the number of first convex ridge portions 4 formed on the hollow fiber membrane 1 is not particularly limited, but is more preferably a multiple of 3. The hollow fiber membrane 1 shown in Figure 1 has 12 first convex ridge portions 4 formed. When the number of multiple first convex ridge portions 4 is a multiple of 3, it becomes possible for the first convex ridge portions 4 to form one or more triangular reinforcing structures, and as a result, it is thought that the mechanical strength of the hollow fiber membrane 1 is further improved.

[0024] In order to maintain uniform mechanical strength, the first convex portions 4 are preferably formed at equal intervals. The first convex portions 4 are made of the same material as the main body portion 3, and the main body portion 3 and the first convex portions 4 are manufactured integrally. The first convex portions 4 may extend in a direction angled from the longitudinal direction A.

[0025] In the hollow fiber membrane 1 of this embodiment, the height L3 of the first convex ridge portions 4 from the outer surface 3a in the radial direction R is preferably 0.5 to 7 times the thickness L1 of the hollow fiber membrane 1, more preferably 1 to 5 times, and even more preferably 1.5 to 4 times the thickness L1 of the hollow fiber membrane 1. The total length L4 of the portions of the outer surface 3a in the circumferential direction C where the first convex ridge portions 4 are formed is preferably half or less of the circumferential length of the outer surface 3a. If it is half or less, it is thought that both mechanical strength and oxygen permeability can be achieved.

[0026] According to the hollow fiber membrane 1 of this embodiment, the first convex ridge portions 4 increase the mechanical strength, so the membrane thickness L1 can be made thinner than that of conventional hollow fiber membranes. By reducing the membrane thickness L1, the oxygen permeability of the membrane can be improved. The improved oxygen permeability allows the nitrification reaction to proceed even when the gas pressure is reduced, thereby achieving energy savings.

[0027] (Variation 1) Next, a variation of the hollow fiber membrane 1 will be described. Fig. 3 is a cross-sectional view showing a hollow fiber membrane 1B, which is a variation of the hollow fiber membrane 1. Four first convex ridge portions 4B are formed in the hollow fiber membrane 1B. The length L4B of the portion of the outer surface 3a of the hollow fiber membrane 1B in the circumferential direction C where the first convex ridge portions 4B are formed is longer than the length L4 of the portion of the outer surface 3a of the hollow fiber membrane 1 in the circumferential direction C where the first convex ridge portions 4 are formed.

[0028] (Variation 2) Figure 4 is a cross-sectional view showing a hollow fiber membrane 1C, which is a variation of the hollow fiber membrane 1. Four first convex ridge portions 4C are formed in the hollow fiber membrane 1C. The height L3C of the first convex ridge portions 4C of the hollow fiber membrane 1C is greater than the height L3 of the first convex ridge portions 4 of the hollow fiber membrane 1. The length L4C of the portion of the outer surface 3a of the hollow fiber membrane 1C in the circumferential direction C where the first convex ridge portions 4C are formed is greater than the length L4 of the portion of the outer surface 3a of the hollow fiber membrane 1 in the circumferential direction C where the first convex ridge portions 4 are formed.

[0029] (Variation 3) Figure 5 is a cross-sectional view showing a hollow fiber membrane 1D, which is a variation of the hollow fiber membrane 1. Four first convex ridge portions 4D are formed in the hollow fiber membrane 1D. The width of the first convex ridge portions 4D of the hollow fiber membrane 1D in the circumferential direction C decreases with increasing distance from the outer surface 3a, and the cross-sectional shape is a substantially isosceles trapezoid. The length L4D of the portion of the outer surface 3a of the hollow fiber membrane 1D in the circumferential direction C where the first convex ridge portions 4D are formed is longer than the length L4 of the portion of the outer surface 3a of the hollow fiber membrane 1 in the circumferential direction C where the first convex ridge portions 4D are formed.

[0030] (Second embodiment) Next, a hollow fiber membrane 1F of a second embodiment will be described with reference to Figs. 6 to 10. The second embodiment differs from the first embodiment in that it has a reinforcing portion 5 on the inner surface 3b. In the following description, components that are common to those already described will be assigned the same reference numerals, and redundant description will be omitted. First, the overall configuration of the hollow fiber membrane 1F will be described. However, the hollow fiber membrane 1F does not need to have all of the components described below, and some components may be omitted as appropriate.

[0031] During water treatment, the hollow fiber membrane 1F of this embodiment has a microbial layer B formed on the outer surface by microorganisms in the water to be treated or derived from microorganisms, and allows oxygen to permeate.

[0032] Fig. 6 is a cross-sectional view showing a hollow fiber membrane 1F having a reinforcing portion 5 on the inner surface 3b. The hollow fiber membrane 1F of this embodiment is characterized by having multiple reinforcing structures formed on the surface to ensure mechanical strength despite being a thin film. As shown in Fig. 6, the hollow fiber membrane 1F includes a main body portion 3 and reinforcing portions (reinforcing structures) 5.

[0033] The reinforcing portion 5 has a plurality of second convex portions 6. The second convex portions 6 protrude from the inner surface 3b in the radial direction R and extend in the longitudinal direction A. In the hollow fiber membrane 1F of this embodiment, four second convex portions 6 are formed, and are formed at equal intervals in the circumferential direction C. However, the number of second convex portions 6 is not limited to the above, and for example, two or more are preferably formed, and four or more are more preferably formed. Preferably, 12 or fewer second convex portions 6 are formed, and more preferably 10 or fewer are formed. It is believed that within the above range, both mechanical strength and oxygen permeability can be achieved. In order to maintain uniform mechanical strength, the second convex portions 6 are preferably formed at equal intervals.

[0034] In the hollow fiber membrane 1F of this embodiment, the height L5 from the surface of the hollow fiber membrane 1F in the radial direction R of the second convex portion 6 is preferably greater than the membrane thickness L1 of the hollow fiber membrane 1F in order to ensure sufficient mechanical strength.

[0035] (Variation 4) Next, a variation of the hollow fiber membrane 1F will be described. FIG. 7 is a cross-sectional view showing a hollow fiber membrane 1G, which is a variation of the hollow fiber membrane 1F. The hollow fiber membrane 1G further includes first convex portions 4 that protrude from the outer surface 3a in the radial direction R and extend in the longitudinal direction A. Multiple first convex portions 4 are formed and are equally spaced apart in the circumferential direction C. In the hollow fiber membrane 1G, four second convex portions 6 are formed on the inner surface 3b, and twelve first convex portions 4 are formed on the outer surface 3a. However, the number of first convex portions 4 is not limited to the above. For example, a single first convex portion 4 may be formed on the outer surface 3a, or twelve or more first convex portions 4 may be formed on the outer surface 3a. Furthermore, as shown in FIG. 7, in order to ensure sufficient oxygen permeability, it is preferable that at least one pair of the first convex portion 4 formed on the outer surface 3a and the second convex portion 6 formed on the inner surface 3b protrude in the same radial direction R.

[0036] 8 is a cross-sectional view showing a hollow fiber membrane 1H, which is a modification of the hollow fiber membrane 1G. In the hollow fiber membrane 1H, of the four second convex ridge portions 6H formed on the inner surface 3b, a pair of opposing second convex ridge portions 6H has a height L5H that is greater than the height L5 of the second convex ridge portions 6 of the hollow fiber membrane 1G.

[0037] 9 is a cross-sectional view showing a hollow fiber membrane 11 which is a modification of the hollow fiber membrane 1G. The height L5I of the second convex ridge portions 6I formed on the inner surface 3b of the hollow fiber membrane 11 is greater than the height L5 of the second convex ridge portions 6 formed on the inner surface 3b of the hollow fiber membrane 1G.

[0038] 10 is a cross-sectional view showing a hollow fiber membrane 1J, which is a modification of the hollow fiber membrane 1G. In the hollow fiber membrane 1J, the tip of a second convex portion 6J formed on the inner surface 3b has a convex portion 6Ja. The convex portion 6Ja has, for example, a circular cross-sectional shape.

[0039] (Third embodiment) Next, a hollow fiber membrane 1K of a third embodiment will be described with reference to Figs. 11 to 19. The third embodiment differs from the first embodiment in that it has a reinforcing portion 5 on the inner surface 3b. In the following description, components that are common to those already described will be assigned the same reference numerals, and redundant description will be omitted. First, the overall configuration of the hollow fiber membrane 1K will be described. However, the hollow fiber membrane 1K does not need to have all of the components described below, and some components may be omitted as appropriate.

[0040] During water treatment, the hollow fiber membrane 1K of this embodiment has a microbial layer B formed on the outer surface by microorganisms in the water to be treated or derived from microorganisms, and allows oxygen to permeate.

[0041] Fig. 11 is a cross-sectional view showing a hollow fiber membrane 1K. Fig. 12 is a perspective view showing the hollow fiber membrane 1K. The hollow fiber membrane 1K of this embodiment is characterized in that a reinforcing structure is formed on the inner surface 3b to ensure mechanical strength despite being a thin film. As shown in Fig. 11, the hollow fiber membrane 1K includes a main body portion 3 and a reinforcing portion (reinforcing structure) 5K.

[0042] The reinforcing portion 5K extends from the inner surface 3b in the radial direction R and has a plate shape extending in the longitudinal direction A. Both ends of the reinforcing portion 5K in the radial direction R are connected to the inner surface 3b. The reinforcing portion 5K divides the internal space of the hollow fiber membrane 1K into two or more portions. In this embodiment, the reinforcing portion 5K is formed from the same material as the main body portion 3.

[0043] However, the reinforcing portion 5K is not limited to the above, and does not have to extend in the radial direction R, does not have to extend in the longitudinal direction A, and does not have to be plate-shaped. The reinforcing portion 5K does not have to divide the internal space of the hollow fiber membrane 1K into two or more portions.

[0044] In this embodiment, the reinforcing portion 5K is connected to the inner surface 3b at two or more locations. However, the reinforcing portion 5K may be connected to the inner surface 3b at only one location.

[0045] In this embodiment, the average thickness L6 of the reinforcing portion 5K is preferably 30 μm or less and is preferably greater than the membrane thickness L1 of the main body portion 3. In the shape of a cut surface perpendicular to the longitudinal direction A of the hollow fiber membrane 1K, the cross-sectional area of ​​the reinforcing portion 5K is preferably 50% or less of the cross-sectional area of ​​the inner region of the hollow fiber membrane 1K.

[0046] According to the hollow fiber membrane 1K of this embodiment, the reinforcing portion 5K increases the mechanical strength, so the membrane thickness L1 can be made thinner than that of conventional hollow fiber membranes. By reducing the membrane thickness L1, the oxygen permeability of the membrane can be improved. The improved oxygen permeability allows the nitrification reaction to proceed even when the gas pressure is reduced, resulting in energy savings.

[0047] (Variation 8) Next, a variation of the hollow fiber membrane 1K will be described. Fig. 13 is a cross-sectional view showing a hollow fiber membrane 1L, which is a variation of the hollow fiber membrane 1K. The hollow fiber membrane 1L differs from the hollow fiber membrane 1K in the shape of the reinforcing portion 5L.

[0048] The reinforcing portion 5L has three plate-like members extending in the longitudinal direction A, and when viewed in cross section, the three plate-like members each extend from the inner surface 3b and are connected at one intersection 7. For example, as shown in Fig. 13, the reinforcing portion 5L may have a shape in which the three plate-like members each extend from the inner surface 3b to the center in the radial direction R and are connected at the center.

[0049] (Modification 9) Fig. 14 is a cross-sectional view showing a hollow fiber membrane 1M which is a modification of the hollow fiber membrane 1K. The hollow fiber membrane 1M differs from the hollow fiber membrane 1K in the shape of the reinforcing portion 5M.

[0050] The reinforcing portion 5M has four plate-like members extending in the longitudinal direction A, and when viewed in cross section, the four plate-like members each extend from the inner surface 3b and are connected at one intersection 7. For example, as shown in Fig. 14, the reinforcing portion 5M may have a shape in which the four plate-like members each extend from the inner surface 3b to the center in the radial direction R and are connected at the center. The four plate-like members are connected to the inner surface 3b at equal intervals in the circumferential direction C.

[0051] (Modification 10) Fig. 15 is a cross-sectional view showing a hollow fiber membrane 1N, which is a modification of the hollow fiber membrane 1K. The hollow fiber membrane 1N differs from the hollow fiber membrane 1K in the shape of the reinforcing portion 5N.

[0052] The reinforcing portion 5N has four plate-like members extending in the longitudinal direction A, and when viewed in cross section, the four plate-like members each extend from the inner surface 3b and are connected at one intersection 7. For example, as shown in Fig. 15, the reinforcing portion 5N may have a shape in which the four plate-like members each extend from the inner surface 3b to the center in the radial direction R and are connected at the center. The four plate-like members are not connected to the inner surface 3b at equal intervals in the circumferential direction C.

[0053] (Modification 11) Fig. 16 is a cross-sectional view showing a hollow fiber membrane 1P which is a modification of the hollow fiber membrane 1K. The hollow fiber membrane 1P differs from the hollow fiber membrane 1K in the shape of the reinforcing portion 5P.

[0054] The reinforcing portion 5P has six plate-like members extending in the longitudinal direction A, and when viewed in cross section, the six plate-like members each extend from the inner surface 3b and are connected at one intersection 7. For example, as shown in Fig. 16 , the reinforcing portion 5P may have a shape in which the six plate-like members each extend from the inner surface 3b to the center in the radial direction R and are connected at the center.

[0055] (Modification 12) Fig. 17 is a cross-sectional view showing a hollow fiber membrane 1Q which is a modification of the hollow fiber membrane 1K. The hollow fiber membrane 1Q differs from the hollow fiber membrane 1K in the shape of the reinforcing portion 5Q.

[0056] The reinforcing portion 5Q has a plate portion 5Qa extending in the longitudinal direction A and a plate portion 5Qb extending in the longitudinal direction A. The plate portion 5Qa passes through the center of the cross section of the hollow fiber membrane 1Q, has one end connected to the inner surface 3b, extends in the radial direction R, and has the other end connected to the inner surface 3b. The plate portion 5Qb has one end connected to the inner surface 3b, extends in the same direction as the extension of the plate portion 5Qa, and has the other end connected to the inner surface 3b. Two plate portions 5Qb are provided.

[0057] (Modification 13) Fig. 18 is a cross-sectional view showing a hollow fiber membrane 1R, which is a modification of the hollow fiber membrane 1K. The hollow fiber membrane 1R differs from the hollow fiber membrane 1K in the shape of the reinforcing portion 5R.

[0058] The reinforcing portion 5R has a plate portion 5Ra extending in the longitudinal direction A and a plate portion 5Rb extending in the longitudinal direction A. One end of the plate portion 5Ra is connected to the inner surface 3b, extends in a direction intersecting the longitudinal direction A, and has the other end connected to the inner surface 3b. The plate portion 5Rb has one end connected to the inner surface 3b, extends in the same direction as the extending direction of the plate portion 5Ra, and has the other end connected to the inner surface 3b.

[0059] (Modification 14) Fig. 19 is a cross-sectional view showing a hollow fiber membrane 1S, which is a modification of the hollow fiber membrane 1M. The hollow fiber membrane 1S further has a first convex portion 4S in the hollow fiber membrane 1M.

[0060] The first convex portions 4S protrude from the outer surface 3a in the radial direction R and extend in the longitudinal direction A. A plurality of first convex portions 4S are formed on the outer surface 3a, and are spaced apart in the circumferential direction C. Twelve first convex portions 4S are formed, and are formed at equal intervals in the circumferential direction C. However, the number of first convex portions 4S is not limited to the above, and, for example, two or more are preferably formed, and four or more are more preferably formed. Preferably, 12 or fewer first convex portions 4S are formed, and more preferably 10 or fewer are formed. Within the above range, oxygen permeability can be improved while maintaining mechanical strength. To ensure uniform mechanical strength, the first convex portions 4S are preferably formed at equal intervals.

[0061] [Hollow Fiber Membrane Module 10 and Water Treatment Device 100] FIG. 20 is a schematic diagram showing the overall configuration of the device, including a water W treatment tank 110, for schematically illustrating one embodiment of the hollow fiber membrane module 10 and water treatment device 100. The hollow fiber membrane module 10 of this embodiment includes the hollow fiber membrane 1, hollow fiber membrane 1B, hollow fiber membrane 1C, hollow fiber membrane 1D, hollow fiber membrane 1F, hollow fiber membrane 1G, hollow fiber membrane 1H, hollow fiber membrane 1I, hollow fiber membrane 1J, hollow fiber membrane 1K, hollow fiber membrane 1L, hollow fiber membrane 1M, hollow fiber membrane 1N, hollow fiber membrane 1P, hollow fiber membrane 1Q, hollow fiber membrane 1R, or hollow fiber membrane 1S (hereinafter referred to as "hollow fiber membrane 1, etc."). The water treatment device 100 of this embodiment is configured to include a hollow fiber membrane module 10. The hollow fiber membrane module 10 and water treatment device 100 of this embodiment will be described below.

[0062] <Hollow Fiber Membrane Module 10> As shown in FIG. 20, the hollow fiber membrane module 10 of this embodiment has a hollow fiber membrane sheet 11 and a housing 12.

[0063] The hollow fiber membrane sheet 11 is formed by bundling a plurality of hollow fiber membranes 1, etc. Both ends of the hollow fiber membrane sheet 11 are inserted into the housing 12 and are open, and the hollow fiber membrane sheet 11 is configured as a flat sheet overall.

[0064] The housing 12 is a substantially hollow member into which both ends of the hollow fiber membrane sheet 11 are inserted and fixed, and is composed of an upper housing 12a and a lower housing 12b as shown in Fig. 20. That is, the hollow fiber membrane sheet 11 is held in a sheet form between the upper housing 12a and the lower housing 12b. As shown in Fig. 20, a gas supply line 120 may be connected to the upper housing 12a so that oxygen or air can be supplied into the upper housing 12a.

[0065] The hollow fiber membrane module 10 is configured such that oxygen or air supplied from a blower (not shown) is sent through the housing 12 into the hollow portions of the plurality of hollow fiber membranes 1, etc., and passes through the hollow fiber membranes 1, etc. from the inner surface 3b to the outer surface 3a, and then dissolves and diffuses in the membrane thickness direction within the microbial layer B.

[0066] Although the hollow fiber membrane module 10 of this embodiment is formed in a flat sheet shape, the present invention is not limited to this, and the hollow fiber membrane module 10 may be formed in, for example, a cylindrical or rectangular tubular shape.

[0067] <Water Treatment Device 100> As shown in FIG. 20, the water treatment device 100 includes a treatment tank 110 and a hollow fiber membrane module 10.

[0068] The treatment tank 110 is, for example, a large metal container that contains the water W to be treated. A water inlet pipe (not shown) for containing the water W to be treated therein and a discharge pipe (not shown) for discharging the treated water out of the tank after treatment are connected to the treatment tank 110.

[0069] A hollow fiber membrane module 10 is housed in the treatment tank 110, and this hollow fiber membrane module 10 is arranged so as to be immersed in water W. The hollow fiber membrane module 10 is preferably housed in the treatment tank 110 so that the longitudinal direction A of the hollow fiber membranes 1, etc. is vertical. If the hollow fiber membrane module 10 is housed in the treatment tank 110 so that the longitudinal direction A of the hollow fiber membranes 1, etc. is vertical, condensed water (water condensed as water within the membrane from oxygen, air, etc., or water in water) is less likely to accumulate inside the hollow fiber membranes 1, etc., and the treatment capacity for water W can be better maintained. In this embodiment, a gas supply line 120 is connected to the upper housing 12a of the hollow fiber membrane module 10, and oxygen, air, or a gas whose component ratio has been changed by a process of separating or concentrating air is supplied.

[0070] With the above-described configuration, the water treatment device 100 of this embodiment can perform water treatment in a single process by simultaneously performing aerobic treatment and anaerobic treatment on the water W in the treatment tank 110 using the hollow fiber membranes 1 and the like that make up the hollow fiber membrane module 10. This allows the device to be made smaller and more space-saving than conventional devices in which aerobic treatment and anaerobic treatment are performed in separate treatment tanks.

[0071] In the treatment tank 110, the hollow fiber membrane module 10 may be housed from the opening 111 side of the treatment tank 110 by, for example, a frame member or the like (not shown) that is arranged so as not to interfere with the flow of water W. In this case, one end of the frame member may be fixed near the opening 111 of the treatment tank 110, and the upper housing 12a provided on the hollow fiber membrane module 10 may be fixed to the other end of this frame member.

[0072] The hollow fiber membrane module 10 according to the present embodiment includes the hollow fiber membrane 1 of the present invention, and therefore can achieve both high oxygen permeability and high mechanical strength, thereby achieving excellent water treatment efficiency and mechanical properties. Furthermore, it can be made even more compact and energy-efficient than conventional MABRs.

[0073] The water treatment device 100 according to this embodiment is equipped with the hollow fiber membrane module 10 of the present invention, and therefore can achieve both high oxygen permeability and high mechanical strength, thereby achieving excellent water treatment efficiency and mechanical properties. Furthermore, it can be made even more compact and energy-efficient than conventional MABRs.

[0074] A hollow fiber membrane was produced by melt spinning using a nozzle die having the cross-sectional shape of the designed membrane. Low-density polyethylene was used as the resin material. The outlet temperature was 180°C, and the winding speed was 75 m / min. The hollow fiber membranes were bundled into a sheet to form a hollow fiber membrane sheet, and both ends of the sheet were inserted into an upper housing and a lower housing, respectively, and fixed with a potting resin (manufactured by Tosoh Corporation, trade name "Coronate") to form a hollow fiber membrane module. The effective length of the hollow fiber membrane was 15 cm. The oxygen permeability was measured by changing the number of first convex portions, the number of second convex portions (reinforcement structures), and the membrane thickness L1 formed on the hollow fiber membrane. The oxygen permeability was measured using the oxygen transmission rate (O ２ The flux (flux) was measured. The measurement results for Comparative Examples 1 and 2 and Examples 1 to 7 are shown in Figure 23. In Figure 23, "unable to form a membrane" in the membrane formation category means that the mechanical strength was insufficient and the hollow fiber membrane was crushed, making it impossible to form a membrane.

[0075] As is clear from the above Comparative Example 2, when the membrane thickness L1 in the membrane-forming nozzle was adjusted to less than 30 μm, membrane production was impossible. The reason for this is that the hollow fiber membrane had a thin membrane thickness, and therefore its mechanical strength (particularly, its mechanical strength when a force is applied from the outer surface) was insufficient, and the hollow fiber membrane was crushed when spun from the nozzle, resulting in membrane production failure. Furthermore, as is clear from the above Examples, even when the membrane thickness L1 was set to less than 30 μm, the provision of the first convex portion or the reinforcing structure improved the mechanical strength, and membrane production was successful. Furthermore, assuming that the membrane material is the same, as the membrane thickness L1 of the hollow fiber membrane becomes thinner, the oxygen transmission rate (O ２ A tendency for the flux to increase was confirmed.

[0076] As described above, by having a first convex portion on the outer surface of a hollow fiber membrane and / or a second convex portion (reinforcing structure) on the inner surface, a membrane that combines mechanical strength and oxygen permeability can be obtained.When treating water using this membrane, microorganisms derived from microorganisms or bacteria in the water can be formed on the outer surface of the main body, allowing for efficient water treatment.

[0077] DESCRIPTION OF SYMBOLS 1 hollow fiber membrane 3 main body 3a outer surface 3b inner surface 4 first convex portion 5 reinforcing portion (reinforcing structure) 6 second convex portion 7 intersection 10 hollow fiber membrane module 11 hollow fiber membrane sheet 12 housing 100 water treatment device 110 treatment tank B microbial layer W water A longitudinal direction C circumferential direction R radial direction

Claims

1. An oxygen-permeable hollow fiber membrane comprising: a main body portion formed in a tubular shape extending in the longitudinal direction; and a plurality of first convex portions protruding radially from the outer surface of the main body portion and extending in the longitudinal direction, wherein the thickness of the main body portion is less than 30 μm, each of the plurality of first convex portions is spaced apart circumferentially from the main body portion, and the height of each of the plurality of first convex portions from the outer surface in the radial direction is between 0.5 and 7 times the thickness of the main body portion.

2. An oxygen-permeable hollow fiber membrane comprising: a main body formed in a tubular shape extending in the longitudinal direction; and a reinforcing structure extending from the inner surface of the main body.

3. The hollow fiber membrane according to claim 2, wherein the reinforcing structure has a plurality of second convex portions that protrude radially from the inner surface and extend in the longitudinal direction, and each of the plurality of second convex portions is spaced apart in the circumferential direction of the main body portion.

4. The hollow fiber membrane according to claim 2, wherein the reinforcing structure is connected to the inner surface at two or more locations, is a plate extending in the longitudinal direction, and has an average thickness of 30 μm or less.

5. The hollow fiber membrane according to claim 4, wherein the average thickness of the reinforcing structure is greater than the membrane thickness of the main body portion.

6. The hollow fiber membrane according to claim 4, wherein, in a cross-section perpendicular to the longitudinal direction of the hollow fiber membrane, the cross-sectional area of the reinforcing structure is 50% or less of the cross-sectional area of the inner region of the hollow fiber membrane.

7. The hollow fiber membrane according to any one of claims 2 to 6, further comprising a plurality of first convex portions protruding radially from the outer surface of the main body portion and extending in the longitudinal direction, each of the plurality of first convex portions being spaced apart in the circumferential direction of the main body portion.

8. A hollow fiber membrane according to any one of claims 4 to 6, wherein the reinforcing structure has a plurality of second convex portions protruding radially from the inner surface and extending in the longitudinal direction, each of the plurality of second convex portions being spaced apart in the circumferential direction of the main body portion; a plurality of first convex portions protruding radially from the outer surface of the main body portion and extending in the longitudinal direction, each of the plurality of first convex portions being spaced apart in the circumferential direction of the main body portion; and at least one pair of the first convex portions and the second convex portions protruding in the same radial direction.

9. The hollow fiber membrane according to claim 1, wherein the number of first convex portions provided is a multiple of three.

10. The hollow fiber membrane according to claim 1 or 2, which is a single-layer membrane having a non-porous structure.

11. The hollow fiber membrane according to claim 1, wherein the total length of all the portions of the outer surface in the circumferential direction where the first convex portions are formed is equal to or less than half the circumferential length of the outer surface.

12. The hollow fiber membrane according to claim 1 or 2, wherein the outer diameter of the main body is 1 mm or less.

13. The hollow fiber membrane according to claim 1 or 2, which is formed by containing a polyolefin.

14. A hollow fiber membrane module comprising the hollow fiber membrane according to claim 1 or 2.

15. A water treatment device comprising the hollow fiber membrane module according to claim 14.

16. A water treatment method for treating water to be treated using the water treatment device according to claim 15, wherein, when the water to be treated is treated, microorganisms derived from microorganisms or bacteria in the water to be treated can be formed on the outer surface of the main body.

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