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

Abstract

To provide a hollow fiber membrane, a hollow fiber membrane module, a water treatment apparatus, and a water treatment method that can improve the oxygen transport rate of the membrane while ensuring mechanical strength. [Solution] A hollow fiber membrane that is permeable to oxygen and on which a microbial layer derived from microorganisms or bacteria in the water can be formed on the outer surface during water treatment, comprising a main body formed in a tubular shape extending in the longitudinal direction and forming the outer surface, and a plurality of reinforcing members that protrude radially from the outer surface, extend in the longitudinal direction and are spaced apart in the circumferential direction, wherein the reinforcing members are embedded from the surface and have recessed portions formed extending in the longitudinal direction.

Description

Technical Field

[0001] The present invention relates to a hollow fiber membrane (gear membrane) for MABR, a hollow fiber membrane module for MABR, a water treatment apparatus, and a water treatment method.

Background Art

[0002] River water, industrial wastewater, and domestic wastewater are reused as drinking water, domestic water, or industrial water after being treated to remove organic substances and the like contained in the water, or discharged into rivers or the like. For example, as a treatment method for industrial wastewater and the like, generally, an activated sludge treatment method in which the water to be treated is aerated to decompose organic substances and the like by aerobic microorganisms can be mentioned. In such a biological water treatment method represented by the activated sludge treatment method and the like, aerobic microorganisms, denitrifying bacteria for removing nitrate nitrogen, and the like are used. In recent years, treatment by a membrane separation activated sludge (MBR) method that combines treatment by the activated sludge treatment method and membrane filtration by a separation membrane module has been carried out.

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

[0004] Furthermore, in recent years, a method has been proposed for water treatment using hollow fiber membranes in which a microbial layer (biofilm) derived from microorganisms in the water is formed on the outer surface of the hollow fiber membrane, and water treatment is performed in this state. In a bioreactor that forms a microbial layer on the outer surface of a hollow fiber membrane and supplies oxygen from the inner side of the hollow fiber membrane, a so-called membrane aeration type biofilm reactor (MABR) is formed in the direction of the thickness of the microbial layer. As a result, aerobic treatment (BOD oxidation, ammonia nitration) proceeds on the inner side of the microbial layer, while anaerobic treatment of nitrate (BOD oxidation, denitrification) proceeds on the outer side of the microbial layer, making it possible to remove various pollutants in a single process. Therefore, compared to conventional membrane separation activated sludge methods, which perform aerobic and anaerobic treatment in separate treatment tanks, it is possible to realize equipment that saves space.

[0005] Furthermore, because MABR incorporates a microbial layer, it can improve oxygen dissolution efficiency compared to conventional systems, thereby reducing the operating load on the oxygen-supplying blower and decreasing sludge generation, thus lowering the overall running costs of the equipment. In addition, the formation of a microbial layer allows for a larger surface area of ​​the hollow fiber membrane, enabling stable treatment in response to fluctuations in water inflow load. For these reasons, MABR is being widely considered for introduction in various water treatment systems. For example, hollow fiber membranes like the one described in Patent Document 1 are known. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-147165 [Overview of the project] [Problems that the invention aims to solve]

[0007] To improve the treatment capacity of water treatment using MABR as described in Patent Document 1, it is important to improve the oxygen transfer rate (OTR) of the membrane. While the oxygen transfer rate can be improved by reducing the thickness of the hollow fiber membrane, there is a risk that sufficient mechanical strength cannot be ensured for the entire hollow fiber membrane.

[0008] The present invention aims to provide a hollow fiber membrane, a hollow fiber membrane module, and a water treatment device that can improve the oxygen transport rate of the membrane while ensuring mechanical strength. [Means for solving the problem]

[0009] In view of the above problems, the inventors of the present invention have found that by designing multiple reinforcing members on the outer surface of a hollow fiber membrane, it is possible to obtain a membrane that achieves both mechanical strength and oxygen transport speed, and have completed the present invention. In other words, the present invention has the following configuration. [1] An oxygen-permeable hollow fiber membrane on which a microbial layer derived from microorganisms or bacteria in the water may form on its outer surface during water treatment, A main body portion formed in a cylindrical shape extending in the longitudinal direction, on which the outer surface is formed, The system comprises a plurality of reinforcing members that protrude radially from the outer surface, extend in the longitudinal direction, and are spaced apart in the circumferential direction, The reinforcing structure is a hollow fiber membrane having a recessed portion that is embedded in the surface of the reinforcing member and extends in the longitudinal direction. [2] At the portion where the main body and the reinforcing member are in contact, a stress distribution portion is formed that connects the main body and the reinforcing member and extends in the longitudinal direction, The hollow fiber membrane according to [1], wherein the height of the stress distribution portion from the outer surface in the radial direction is one-third or more compared to the height of the reinforcing member from the outer surface in the radial direction. [3] The hollow fiber membrane according to [1] or [2], wherein the recessed portion is formed on the outer peripheral surface of the surface of the reinforcing member in the radial direction and is embedded in the radial direction from the surface of the reinforcing member. [4] The hollow fiber membrane according to any one of [1] to [3], wherein the depth of the recessed portion from the surface of the reinforcing member is one-tenth or more and one-half of the height of the reinforcing member from the outer surface in the radial direction. [5] The hollow fiber membrane according to any one of [1] to [4], wherein, when viewed from the longitudinal direction, the length of the portion of the surface of the reinforcing member in which the recess is formed is one-quarter or more and one-half or less compared to the circumferential length of the reinforcing member. [6] The hollow fiber membrane according to any one of [1] to [5], wherein three or more reinforcing members are formed. [7] The hollow fiber membrane according to any one of [1] to [6], wherein the circumferential length of the reinforcing member is 20 μm or more and 70 μm or less. [8] A hollow fiber membrane according to any of [1] to [7], wherein the film thickness is less than 30 μm. A hollow fiber membrane module comprising a hollow fiber membrane as described in any of [9][1] to [8]. A water treatment apparatus comprising the hollow fiber membrane module described in

[10] [9]. A water treatment method for treating water to be treated using the water treatment apparatus described in

[11] and

[10] .

[12] The hollow fiber membrane according to any one of [1] to [8], further comprising an internal reinforcing portion extending radially from the inner surface of the main body.

[13] The hollow fiber membrane according to

[12] , wherein the internal reinforcing portion is connected to the inner surface at two or more locations.

[14] The hollow fiber membrane according to claim

[12] or

[13] , wherein the internal reinforcing portion has a plurality of plate members, each of which extends radially from the inner surface and is connected at an intersection inside the main body.

[15] The hollow fiber membrane according to claim 14, wherein three plate members are provided, and the intersection is located in the center of the main body when viewed from the longitudinal direction.

[16] The hollow fiber membrane according to any one of

[12] to

[15] , wherein the internal reinforcing portion is formed along the direction in which the reinforcing member protrudes in the radial direction.

[17] The internal reinforcing part has an intersection reinforcing part at the intersection, and the intersection reinforcing part connects the plate members adjacent to each other in the circumferential direction, the hollow fiber membrane according to any one of

[12] to

[16] .

[18] The thickness of the internal reinforcing part in the direction perpendicular to the radial direction as viewed from the longitudinal direction is equal to the film thickness of the main body part, the hollow fiber membrane according to any one of

[12] to

[17] .

[19] A hollow fiber membrane module including the hollow fiber membrane according to any one of

[12] to

[18] .

[20] A water treatment device including the hollow fiber membrane module according to

[19] .

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

[20] . [Effect of the Invention]

[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 transfer rate of the membrane while ensuring mechanical strength. [Brief Description of the Drawings]

[0011] [Figure 1] It is a cross-sectional view showing the hollow fiber membrane according to the embodiment, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 2] It is a perspective view showing the same hollow fiber membrane. [Figure 3] It is a detailed view of the region surrounded by the broken line D3 of the same hollow fiber membrane shown in FIG. 1. [Figure 4] It is a cross-sectional view showing a cross-section of a hollow fiber membrane in which three reinforcing members are formed, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 5] It is a cross-sectional view showing a state in which a microbial layer is formed on the outer surface of the same hollow fiber membrane, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 6] It is a schematic view showing the overall configuration of an apparatus including a treatment tank for the water to be treated for schematically explaining an embodiment of a hollow fiber membrane module and a water treatment device. [Figure 7]A cross-sectional view of the hollow fiber membrane according to Comparative Example 1, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 8] A cross-sectional view of the hollow fiber membrane according to Example 1, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 9] A diagram showing the analysis results by simulation of Comparative Example 1, Example 1, and Example 2. [Figure 10] A diagram showing the range where the largest force is applied among the forces applied to Comparative Example 1, Example 1, and Example 2. [Figure 11] A cross-sectional view of the hollow fiber membrane according to the second embodiment, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 12] A cross-sectional view of the hollow fiber membrane according to Modification 1, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 13] A cross-sectional view of the hollow fiber membrane according to Modification 2, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 14] A cross-sectional view of the hollow fiber membrane according to Modification 2, showing a cross-section cut along a plane perpendicular to the longitudinal direction. [Figure 15] A diagram showing the analysis results by simulation of Experiment 2. [Figure 16] A diagram showing the range where the largest force is applied among the forces applied to Comparative Example 2 and Example 3. [Figure 17] A diagram showing the analysis results by simulation of Experiment 3. [Figure 18] A diagram showing the range where the largest force is applied among the forces applied to Comparative Example 3 and Example 4. [Figure 19] A diagram showing the analysis results by simulation of Experiment 4. [Figure 20] A diagram showing the range where the largest force is applied among the forces applied to Example 5.

Modes for Carrying Out the Invention

[0012] Hereinafter, a hollow fiber membrane, a hollow fiber membrane module water treatment apparatus, and a water treatment method according to the embodiment will be described with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals. Duplication of these components may be omitted.

[0013] (First Embodiment) [Hollow fiber membrane 1] The hollow fiber membrane 1 according to the first embodiment will be described with reference to Figures 1 to 5. First, the overall structure of the hollow fiber membrane 1 will be described. However, the hollow fiber membrane 1 does not need to have all of the structures described below, and some structures may be omitted as appropriate.

[0014] Figure 1 is a cross-sectional view of the hollow fiber membrane 1 according to this embodiment, showing a cross-section cut by a plane perpendicular to the longitudinal direction A. Figure 2 is a perspective view of the hollow fiber membrane 1.

[0015] The hollow fiber membrane 1 is a membrane used in water treatment, for example, to remove organic matter contained in industrial wastewater or domestic wastewater. The hollow fiber membrane 1 is a membrane that allows oxygen to permeate. During water treatment, the hollow fiber membrane 1 is a membrane in which a microbial layer 5 derived from microorganisms or bacteria in the water is formed on its outer surface 2a. The hollow fiber membrane 1 is a tubular membrane that extends in the longitudinal direction A.

[0016] In this embodiment, "longitudinal direction A" refers to the longitudinal direction of the hollow fiber membrane 1 formed in a cylindrical shape. In this embodiment, "circumferential direction C" refers to the circumferential direction of the hollow fiber membrane 1 formed in a cylindrical shape. In this embodiment, "radial direction R" refers to the radial direction of the hollow fiber membrane 1 formed in a cylindrical shape.

[0017] As shown in Figures 1 and 2, the hollow fiber membrane 1 comprises a cylindrical main body portion 2, a reinforcing member 3 protruding radially R from the outer surface 2a of the main body portion 2, and a stress distribution portion 4 formed at the point where the main body portion 2 and the reinforcing member 3 are in contact.

[0018] The main body portion 2 is a component that forms the main body of the hollow fiber membrane 1. The main body portion 2 has a cylindrical shape extending in the longitudinal direction A. Because the main body portion 2 has a cylindrical shape, its interior is hollow. In this embodiment, the main body portion 2 is formed in a substantially circular shape when viewed from the longitudinal direction A. That is, in this embodiment, the main body portion 2 is formed in a substantially cylindrical shape. However, the shape of the main body portion 2 is not limited.

[0019] In this embodiment, the film thickness L1 of the main body 2 is approximately 10 μm. Preferably, the film thickness L1 of the main body 2 is less than 30 μm. More preferably, the film thickness L1 of the main body 2 is 20 μm or less and 5 μm or more. Even more preferably, the film thickness L1 of the main body 2 is 15 μm or less and 7 μm or more. The smaller the film thickness L1 of the main body 2, the greater the oxygen transport rate of the main body 2, and the easier it is for oxygen to permeate. The larger the film thickness L1 of the main body 2, the stronger the mechanical strength of the main body 2.

[0020] The film thickness L1 of the main body 2 may be 30 μm or more. However, if the film thickness L1 of the main body 2 is 30 μm or more, the oxygen transport rate of the main body 2 will be low, and oxygen will not permeate sufficiently. Also, the film thickness L1 of the main body 2 may be less than 5 μm. However, if the film thickness L1 of the main body 2 is less than 5 μm, even if the reinforcing member 3 is formed, the mechanical strength of the main body 2 will be insufficient, and the processability of the film will also be poor.

[0021] In this embodiment, the outer diameter L2 of the main body 2 is approximately 295 μm. Preferably, the outer diameter L2 of the main body 2 is 1 mm or less. However, the outer diameter L2 of the main body 2 may be 100 μm or more. If the outer diameter L2 of the main body 2 is within this range, the mechanical strength of the hollow fiber membrane is sufficiently ensured while also having excellent processability.

[0022] The main body 2 is formed with a material that allows oxygen to permeate from the inner surface 2b to the outer surface 2a. The main body 2 does not have a porous structure from the inner surface 2b to the outer surface 2a, but oxygen dissolves and diffuses from the inner surface 2b to the outer surface 2a.

[0023] In this embodiment, the main body 2 is formed from a polyolefin resin, a polyurethane resin, a fluororesin, and a silicone resin. However, the materials used to form the main body 2 are not limited. The main body 2 may be made from one type of material or from two or more types of materials.

[0024] Examples of polyolefin resins used include polyethylene, polypropylene, and polymethylpentene. From a cost viewpoint, it is preferable that the main body 2 be formed containing polyethylene as the polyolefin resin. From the viewpoint of oxygen transport rate, it is more preferable that the main body 2 be formed containing low-density polyethylene (LDPE) as the polyolefin resin.

[0025] From the viewpoint of oxygen transport rate, the main body 2 is preferably formed containing polydimethylsiloxane (PMDS) as a silicone resin.

[0026] Figure 3 is a detailed view of the region enclosed by the dashed line D3 of the hollow fiber membrane 1 shown in Figure 1. The reinforcing member 3 is a member that protrudes radially R from the outer surface 2a of the main body 2. The formation of the reinforcing member 3 improves the mechanical strength of the hollow fiber membrane 1. As shown in Figure 3, the reinforcing member 3 has a reinforcing member body 31 that forms the main body of the reinforcing member 3, and a recessed portion 32 formed on the surface 31a of the reinforcing member body 31.

[0027] The reinforcing member body 31 is a member that protrudes radially R from the outer surface 2a of the main body 2. The reinforcing member body 31 is a member that extends in the longitudinal direction A along the outer surface 2a of the main body 2. The reinforcing member body 31 is a member that has a columnar shape extending in the longitudinal direction A. When the reinforcing member body 31 is cut with a plane perpendicular to the longitudinal direction A, it is preferable that it is formed in substantially the same shape regardless of the cross-section. By forming the reinforcing member body 31 in substantially the same shape regardless of the cross-section, the uniform mechanical strength of the hollow fiber membrane 1 is maintained. The shape of the reinforcing member body 31 is not limited.

[0028] In this embodiment, the height H1 of the reinforcing member body 31 from the outer surface 2a in the radial direction R is approximately 25 μm. As shown in Figure 3, the height H1 of the reinforcing member body 31 is the length from the vertex S1 of the extension line of the surface 31a of the reinforcing member body 31 to the center point S2 of the extension line of the outer surface 2a of the main body 2 in the radial direction R. From the viewpoint of the mechanical strength of the hollow fiber membrane 1, the height H1 of the reinforcing member body 31 is preferably 1 to 7 times the film thickness L1 of the main body 2, and more preferably 1.5 to 5 times. It is even more preferable that the height H1 of the reinforcing member body 31 is 2 to 4 times the film thickness L1 of the main body 2. Note that the height H1 of the reinforcing member body 31 is not limited.

[0029] In this embodiment, the length (width) L3 of the circumferential direction C of the reinforcing member body 31 is approximately 40 μm. The length (width) L3 of the reinforcing member body 31 is the length of the widest part in the circumferential direction C of the reinforcing member body 31. The length L3 of the reinforcing member body 31 is preferably 20 μm or more and 70 μm or less, and more preferably 30 μm or more and 50 μm or less. The length (width) L3 of the reinforcing member body 31 may be less than 20 μm. However, if the length (width) L3 of the reinforcing member body 31 is less than 20 μm, the hollow fiber membrane 1 will not maintain sufficient mechanical strength. The length (width) L3 of the reinforcing member body 31 may also exceed 70 μm. If the length (width) L3 of the reinforcing member body 31 exceeds 70 μm, the oxygen transport rate of the hollow fiber membrane 1 is low, and oxygen does not permeate sufficiently.

[0030] The reinforcing member body 31 is integrally formed with the main body portion 2 by machining. The reinforcing member body 31 has the same material as the main body portion 2. That is, in this embodiment, the reinforcing member body 31 is formed from a polyolefin resin, a polyurethane resin, a fluororesin, or a silicone resin. However, the reinforcing member body 31 does not necessarily have to be integrally formed with the main body portion 2, and the material of the reinforcing member body 31 is not limited.

[0031] The recessed portion 32 is embedded in the surface of the reinforcing member body 31. The recessed portion 32 is formed on the surface of the reinforcing member body 31 along the longitudinal direction A. The formation of the recessed portion 32 improves the mechanical strength of the hollow fiber membrane 1.

[0032] In this embodiment, the recessed portion 32 is formed on the outer peripheral surface 31a of the reinforcing member body 31, viewed from the longitudinal direction A in the radial direction R. The recessed portion 32 is embedded radially R from the surface 31a of the reinforcing member body 31. The position in which the recessed portion 32 is formed is not limited.

[0033] The recessed portion 32 is rounded when viewed from the longitudinal direction A. The recessed portion 32 is formed with a substantially semicircular diameter when viewed from the longitudinal direction A. When the recessed portion 32 is cut with a plane perpendicular to the longitudinal direction A, it is preferable that it is formed with substantially the same shape regardless of the cross-section. By forming the recessed portion 32 with substantially the same shape regardless of the cross-section, the uniform mechanical strength of the hollow fiber membrane 1 is maintained. The shape of the recessed portion 32 is not limited.

[0034] In this embodiment, the depth H2 of the recessed portion 32 from the surface 31a of the reinforcing member body 31 in the radial direction R is preferably 1 / 10 to 1 / 2 of the height H1 of the reinforcing member body 31, from the viewpoint of the mechanical strength of the hollow fiber membrane 1. As shown in Figure 3, the depth H2 of the recessed portion 32 is the length from the vertex S1 of the extension line of the surface 31a of the reinforcing member body 31 to the deepest center point S3 of the recessed portion 32 in the radial direction R. Note that the depth H2 of the recessed portion 32 is not limited.

[0035] Because a recess 32 is formed in the reinforcing member 3 of the hollow fiber membrane 1, the stress applied to the hollow fiber membrane 1 is absorbed by the recess 32. Since the strength of the reinforcing member 3 is greater than the strength of other parts of the hollow fiber membrane 1, the overall mechanical strength of the hollow fiber membrane 1 can be improved. Furthermore, when an external force is applied to the hollow fiber membrane 1, the displacement of the main body 2 can be suppressed compared to conventional hollow fiber membranes. In addition, even if the reinforcing member 3 is damaged due to a large force applied to it, water treatment can still be performed using the hollow fiber membrane 1 as long as the main body 2 does not break.

[0036] Viewed from the longitudinal direction A, the length (width) L4 of the portion of the surface 31a of the reinforcing member body 31 in which the recessed portion 32 is formed is preferably one-quarter to one-half of the length L3 of the circumferential direction C of the reinforcing member body 31, from the viewpoint of the mechanical strength of the hollow fiber membrane 1. The length (width) L4 in which the recessed portion 32 is formed is the length of the widest part of the recessed portion 32 in the circumferential direction C. Note that the length L4 of the recessed portion 32 is not limited.

[0037] As shown in Figures 1 and 2, multiple reinforcing members 3 are formed on the outer surface 2a of the main body 2. The multiple reinforcing members 3 are each formed apart in the circumferential direction C. In this embodiment, four reinforcing members 3 are formed.

[0038] It is preferable that 40 or fewer reinforcing members 3 are formed. It is more preferable that 30 or fewer reinforcing members 3 are formed. It is even more preferable that 20 or fewer reinforcing members 3 are formed. The fewer the number of reinforcing members 3 formed on the hollow fiber membrane 1, the larger the area exposed on the outer surface 2a of the main body 2, so that the oxygen transport rate of the hollow fiber membrane 1 increases and oxygen permeates more easily. It is also preferable that 3 or more reinforcing members 3 are formed. The more reinforcing members 3 are formed, the higher the mechanical strength of the hollow fiber membrane 1. From the viewpoint of the mechanical strength of the hollow fiber membrane 1, it is more preferable that 4 or more reinforcing members 3 are formed, and even more preferable that 6 or more are formed. When the number of reinforcing members 3 formed on the hollow fiber membrane 1 is 3 or less, it is considered that the mechanical strength of the hollow fiber membrane 1 is sufficiently ensured. Note that the number of reinforcing members 3 formed on the hollow fiber membrane 1 is not limited.

[0039] In this embodiment, the multiple reinforcing members 3 are formed at approximately equal intervals in the circumferential direction C. The formation of the multiple reinforcing members 3 at approximately equal intervals maintains the uniform mechanical strength of the hollow fiber membrane 1. The positions in which the multiple reinforcing members 3 are formed are not limited.

[0040] Figure 4 is a cross-sectional view showing a cross-section of a hollow fiber membrane 1C on which three reinforcing members 3 are formed, and the cross-section is shown as being cut by a plane perpendicular to the longitudinal direction A. When multiple reinforcing members 3 are formed at approximately equal intervals in the circumferential direction C, the number of reinforcing members 3 formed on the hollow fiber membrane is not particularly limited, but it is preferable to have three or more, and more preferably a multiple of three. The hollow fiber membrane 1C shown in Figure 4 is a hollow fiber membrane on which three reinforcing members 3 are formed. When the number of multiple reinforcing members 3 is a multiple of three, it becomes possible to form one or more triangular reinforcing structures with the reinforcing members 3, and as a result, the mechanical strength of the hollow fiber membrane 1 is thought to be further improved. Furthermore, it is preferable that the multiple reinforcing members 3 are arranged at approximately equal intervals in the circumferential direction C. This ensures that the hollow fiber membrane 1 has axial symmetry with respect to a cross-section cut by a plane perpendicular to the longitudinal direction A, and maintains uniform mechanical strength.

[0041] The sum of the lengths L3 in the circumferential direction C of the reinforcing member 3 is less than or equal to half the circumferential length of the outer surface 2a of the main body 2. If it is less than or equal to half, it is considered that both mechanical strength and oxygen transport velocity can be achieved. Note that the sum of the lengths L3 in the circumferential direction C of the reinforcing member 3 is not limited.

[0042] The reinforcing member 3 may be formed to protrude radially R from the inner surface 2b of the main body 2 and extend longitudinally A. In the reinforcing member 3 formed on the inner surface 2b of the main body 2, both ends in the radial direction R may be connected to the inner surface 2b of the main body 2. The reinforcing member 3 formed on the inner surface 2b of the main body 2 may divide the internal space of the hollow fiber membrane 1 into two or more parts. The position where the reinforcing member 3 is formed and the shape of the reinforcing member 3 are not limited.

[0043] The stress distribution section 4 is formed at the point where the main body 2 and the reinforcing member 3 are in contact. The stress distribution section 4 connects the main body 2 and the reinforcing member 3. The stress distribution section 4 is formed along the main body 2 and the reinforcing member 3, which extend in the longitudinal direction A, and extends in the longitudinal direction A. In this embodiment, the stress distribution section 4 has a slope when viewed from the longitudinal direction A. The shape of the stress distribution section 4 is not limited. The stress distribution section 4 may have a rounded shape when viewed from the longitudinal direction A.

[0044] In this embodiment, the height H3 of the stress distribution section 4 from the outer surface 2a in the radial direction R is at least one-third of the height H1 of the reinforcing member 3 from the outer surface 2a in the radial direction R. The height H3 of the stress distribution section 4 may also be at least half of the height H1 of the reinforcing member 3. The height H3 of the stress distribution section 4 is not limited, but may be equal to or less than the height H1 of the reinforcing member 3.

[0045] The stress distribution section 4 is a member formed between the tangent line T1 at the point of contact between the main body section 2 and the reinforcing member 3, the extension line T2 of the reinforcing member 3, and an auxiliary line T3 drawn such that the angle between the tangent line T1 and the extension line T2 is 120 degrees or more, as viewed from the longitudinal direction A.

[0046] Because a stress distribution section 4 is formed in the hollow fiber membrane 1, the stress applied to the hollow fiber membrane 1 can be distributed throughout the entire hollow fiber membrane 1. Since stress tends to concentrate in the area where the main body 2 and the reinforcing member 3 are in contact, the formation of the stress distribution section 4 improves the overall strength of the hollow fiber membrane 1.

[0047] [Microbial layer 5] Next, with reference to Figure 5, the microbial layer 5 formed on the outer surface 2a of the hollow fiber membrane 1 will be described.

[0048] Figure 5 is a cross-sectional view showing the formation of a microbial layer 5 on the outer surface 2a of the hollow fiber membrane 1, and shows a cross-section cut by a plane perpendicular to the longitudinal direction A.

[0049] The microbial layer 5 is formed on the outer surface 2a of the hollow fiber membrane 1 by microorganisms or bacteria when the hollow fiber membrane 1 is used as a hollow fiber membrane module 10, which will be described later, for water treatment. This is achieved by growing microorganisms or bacteria in activated sludge already used in another wastewater treatment plant, etc., and then immersing the hollow fiber membrane module 10 in a solution of this solution at a predetermined concentration.

[0050] Activated sludge can have various component compositions and proportions depending on the water conditions, but it is possible to use sludge that has been grown by feeding on BOD (organic matter) components and nutrients (nitrogen, phosphorus, etc.) contained in the water. Then, a microbial layer 5 is formed on the outer surface 2a of the hollow fiber membrane 1 as a layer derived from the microorganisms or bacteria contained in the grown activated sludge.

[0051] Since the hollow fiber membrane 1 has reinforcing members 3 formed on its outer surface 2a, as shown in Figure 5, the microbial layer 5 is formed on the part of the outer surface 2a where the reinforcing members 3 are not formed. Because the hollow fiber membrane 1 has a large area of ​​the outer surface 2a where the reinforcing members 3 are not formed, the area over which the microbial layer 5 is formed is wide.

[0052] As the microbial layer 5 forms on the hollow fiber membrane 1, oxygen that has passed from the inner surface 2b to the outer surface 2a of the hollow fiber membrane 1 dissolves and diffuses within the microbial layer 5, creating an oxygen gradient (concentration) in the radial direction R of the microbial layer 5. This results in an oxygen-rich aerobic state on the inner layer and an anaerobic state with reduced oxygen on the outer layer. Consequently, the microbial layer 5 forms an aerobic treatment region on the inner layer side and an anaerobic treatment region on the outer layer side.

[0053] The aerobic treatment area of ​​microbial layer 5 is formed by oxygen-loving bacteria. For example, the aerobic treatment area is formed by ammonia-oxidizing bacteria. The anaerobic treatment area of ​​microbial layer 5 is formed by oxygen-loving bacteria, second only to the bacteria that form the aerobic treatment area. For example, the anaerobic treatment area is formed by nitrite-oxidizing bacteria.

[0054] In the aerobic treatment area, ammonia contained in the water is oxidized through aerobic treatment (BOD oxidation) and converted to nitrate. Furthermore, in the anaerobic treatment area, the nitrate produced in the aerobic treatment area is treated as nitrogen by anaerobic bacteria through anaerobic treatment (BOD oxidation), resulting in denitrification. This allows for space-saving equipment and improved treatment efficiency compared to when aerobic and anaerobic treatments are performed in separate treatment tanks.

[0055] The thickness of the microbial layer 5 is not limited; once it reaches a predetermined thickness or a predetermined processing time, operations such as bubbling with air can be performed to adjust the thickness to a level that allows for optimal aerobic and anaerobic treatment.

[0056] According to the hollow fiber membrane 1 of this embodiment, because it has a reinforcing member 3, the mechanical strength of the hollow fiber membrane 1 is maintained even if the film thickness L1 of the hollow fiber membrane 1 is reduced. Therefore, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0057] According to the hollow fiber membrane 1 of this embodiment, because it has a recessed portion 32, the mechanical strength of the hollow fiber membrane 1 is maintained even if the film thickness L1 of the hollow fiber membrane 1 is reduced. Therefore, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0058] According to the hollow fiber membrane 1 of this embodiment, since it has a stress distribution section 4, the mechanical strength of the hollow fiber membrane 1 is maintained even if the film thickness L1 of the hollow fiber membrane 1 is reduced. Therefore, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0059] According to the hollow fiber membrane 1 of this embodiment, the depth H2 of the recess 32 is one-tenth to one-half of the height H1 of the reinforcing member 3. Therefore, even if the film thickness L1 of the hollow fiber membrane 1 is reduced, the mechanical strength of the hollow fiber membrane 1 is maintained. As a result, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0060] According to the hollow fiber membrane 1 of this embodiment, the length L4 of the circumferential C of the recessed portion 32 is one-quarter to one-half of the length L3 of the circumferential C of the reinforcing member 3. Therefore, even if the film thickness L1 of the hollow fiber membrane 1 is reduced, the mechanical strength of the hollow fiber membrane 1 is maintained. As a result, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0061] According to the hollow fiber membrane 1 of this embodiment, since the number of reinforcing members 3 formed is three or more, the mechanical strength of the hollow fiber membrane 1 is maintained even if the film thickness L1 of the hollow fiber membrane 1 is reduced. Therefore, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0062] According to the hollow fiber membrane 1 of this embodiment, since the length L3 of the circumferential C of the reinforcing member 3 is 40 μm or more and 70 μm or less, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0063] According to the hollow fiber membrane 1 of this embodiment, since the film thickness L1 is less than 30 μm, the hollow fiber membrane 1 can improve the oxygen transport rate of the membrane while ensuring mechanical strength.

[0064] [Hollow fiber membrane module 10] Next, the hollow fiber membrane module 10 according to the embodiment will be described with reference to Figure 6. However, the hollow fiber membrane module 10 does not need to have all of the configurations described below, and some configurations may be omitted as appropriate.

[0065] Figure 6 is a schematic diagram showing the overall configuration of the apparatus, including the treatment tank 110 for the water to be treated, for schematic explanation of one embodiment of the hollow fiber membrane module 10 and the water treatment apparatus 100.

[0066] The hollow fiber membrane module 10 according to this embodiment includes a hollow fiber membrane element (not shown) composed of a hollow fiber membrane 1. As shown in Figure 6, the hollow fiber membrane module 10 of this embodiment has a hollow fiber membrane sheet-like material 11 and a housing 12.

[0067] The hollow fiber membrane sheet 11 is formed by bundling together multiple hollow fiber membranes 1. Both ends of the hollow fiber membrane sheet 11 are inserted into the housing 12 and are open, and the whole structure is a flat sheet.

[0068] The housing 12 is a substantially hollow member into which both ends of the hollow fiber membrane sheet 11 are inserted and fixed, and as shown in Figure 6, it consists of an upper housing 12a and a lower housing 12b. That is, the hollow fiber membrane sheet 11 is held in a sheet-like manner between the upper housing 12a and the lower housing 12b.

[0069] As shown in Figure 6, a gas supply line 120 may be connected to the upper housing 12a, and oxygen or air may be supplied to the inside of the upper housing 12a.

[0070] The hollow fiber membrane module 10 is configured such that oxygen or air supplied from a blower (not shown) is introduced into the hollow parts of multiple hollow fiber membranes 1, etc., via the housing 12, permeates the hollow fiber membranes 1, etc., from the inner surface 2b to the outer surface 2a, and further dissolves and diffuses within the microbial layer 5 in the direction of film thickness.

[0071] In this embodiment, the hollow fiber membrane module 10 is formed in the shape of a flat sheet, but it is not limited to this, and for example, the hollow fiber membrane module 10 may be formed in the shape of a cylinder or a rectangular tube.

[0072] According to the hollow fiber membrane module 10 of this embodiment, because it includes a hollow fiber membrane 1, it is possible to achieve both high oxygen permeability and high mechanical strength, resulting in excellent water treatment efficiency and mechanical properties. Furthermore, it is possible to further reduce the size and energy consumption compared to conventional MABRs.

[0073] [Water treatment device 100] Next, the water treatment apparatus 100 according to the embodiment will be described with reference to Figure 6. However, the water treatment apparatus 100 does not need to have all of the configurations described below, and some configurations may be omitted as appropriate.

[0074] As shown in Figure 6, the water treatment device 100 includes a treatment tank 110 and a hollow fiber membrane module 10.

[0075] The treatment tank 110 contains the water to be treated W and is, for example, a large metal container. The treatment tank 110 is connected to a water inlet pipe (not shown) for containing the water to be treated W and a discharge pipe (not shown) for discharging the treated water outside the tank after treatment is complete.

[0076] A hollow fiber membrane module 10 is housed in the treatment tank 110, and the hollow fiber membrane module 10 is positioned so as to be immersed in the water to be treated W. Preferably, the hollow fiber membrane module 10 is housed in the treatment tank 110 such that the longitudinal direction A of the hollow fiber membrane 1 is vertical. If the hollow fiber membrane module 10 is housed in the treatment tank 110 such that the longitudinal direction A of the hollow fiber membrane 1 is vertical, condensed water (water that has condensed into the membrane from oxygen, air, etc., or water) is less likely to accumulate inside the hollow fiber membrane 1, and the water treatment capacity can be maintained more effectively.

[0077] 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 composition ratio has been altered by a process that separates or concentrates air is supplied.

[0078] With the above configuration, the water treatment apparatus 100 of this embodiment can simultaneously perform aerobic and anaerobic treatment on the water to be treated W in the treatment tank 110 using the hollow fiber membrane 1 and other components constituting the hollow fiber membrane module 10, thereby performing water treatment in a single process. As a result, the apparatus can be made smaller and more space-saving compared to conventional methods where aerobic and anaerobic treatment are performed in separate treatment tanks.

[0079] Within the treatment tank 110, the hollow fiber membrane module 10 can be housed from the opening 111 side of the treatment tank 110 by, for example, a frame member (not shown) that is positioned so as not to obstruct the flow of the water to be treated W. In this case, one end of the frame member can be fixed near the opening 111 of the treatment tank 110, and the upper housing 12a provided on the hollow fiber membrane module 10 can be fixed to the other end of this frame member.

[0080] According to the water treatment apparatus 100 of this embodiment, because it is equipped with a hollow fiber membrane module 10, it is possible to achieve both high oxygen permeability and high mechanical strength, resulting in excellent water treatment efficiency and mechanical properties. Furthermore, it is possible to make it even smaller and more energy-efficient than conventional MABRs.

[0081] Although embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments, and design modifications and the like are also included within the scope of the gist of the present invention. Furthermore, the components shown in the above embodiments can be combined as appropriate.

[0082] [Water treatment methods] A water treatment method using a water treatment device 100 to treat water (e.g., wastewater) will be described. Specifically, a microbial layer 5 (biofilm) derived from microorganisms in the water is formed on the outer surface 2a of the hollow fiber membrane 1, and water treatment is performed in this state. In a bioreactor, a so-called membrane aeration type biofilm reactor (MABR), where a microbial layer 5 is formed on the outer surface 2a of the hollow fiber membrane 1 and oxygen is supplied from the inner surface 2b of the hollow fiber membrane 1, an oxygen gradient is formed in the direction of the film thickness (radial direction R) of the microbial layer 5. As a result, aerobic treatment (BOD oxidation, ammonia nitration) proceeds on the inner layer side of the microbial layer 5, while anaerobic treatment of nitrate (BOD oxidation, denitrification) proceeds on the outer layer side of the microbial layer 5. Therefore, it becomes possible to remove various pollutants in a single process. Consequently, a space-saving facility can be realized compared to conventional membrane separation activated sludge methods, which perform aerobic and anaerobic treatment in separate treatment tanks.

[0083] (Second Embodiment) [Hollow fiber membrane 1D] Next, the hollow fiber membrane 1D according to the second embodiment will be described with reference to Figures 11 to 14. In the following description, components that are common to those already described will be denoted by the same reference numerals, and redundant explanations will be omitted. First, the overall configuration of the hollow fiber membrane 1D will be described. However, the hollow fiber membrane 1D does not need to have all of the components described below, and some components may be omitted as appropriate.

[0084] Figure 11 is a cross-sectional view of the hollow fiber membrane 1D according to the second embodiment, showing a cross-section cut by a plane perpendicular to the longitudinal direction A. The hollow fiber membrane 1D is a membrane used for water treatment, for example, to remove organic matter contained in industrial wastewater or domestic wastewater. The hollow fiber membrane 1 is a membrane that allows oxygen to permeate. During water treatment, the hollow fiber membrane 1 is a membrane in which a microbial layer 5 derived from microorganisms or bacteria in the water is formed on its outer surface 2a.

[0085] The hollow fiber membrane 1D has a similar structure to the hollow fiber membrane 1. The identical structure to that of the hollow fiber membrane 1 will not be explained here.

[0086] As shown in Figure 11, the hollow fiber membrane 1D comprises a main body 2, a reinforcing member 3, a stress distribution section 4, and an internal reinforcing section 6. The hollow fiber membrane 1D differs from the hollow fiber membrane 1 in that it includes the internal reinforcing section 6. The configurations of the main body 2, reinforcing member 3, stress distribution section 4, and internal reinforcing section 6 are described in the description of the hollow fiber membrane 1, so their explanation is omitted here.

[0087] The internal reinforcing portion 6 is a member that extends radially R from the inner surface 2b. The internal reinforcing portion 6 is connected to the inner surface 2b at two or more locations. For example, the internal reinforcing portion 6 is connected to the inner surface 2b at three locations. The internal reinforcing portion 6 divides the internal space of the hollow fiber membrane 1D into two or more sections. For example, the internal reinforcing portion 6 divides the internal space of the hollow fiber membrane 1D into three sections. The internal reinforcing portion 6 has a plurality of plate members 61.

[0088] The internal reinforcement section 6 has, for example, three plate members 61. These three plate members 61 are designated as the first plate member 61a, the second plate member 61b, and the third plate member 61c. The number of plate members 61 in the internal reinforcement section 6 is not limited.

[0089] The plate member 61 extends radially from the inner surface 2b toward R and is a plate-shaped member formed along the longitudinal direction A. The internal reinforcement section 6, when viewed from the longitudinal direction A, has a shape in which three plate members 61 each extend radially from the inner surface 2b toward R and connect at an intersection 7. The intersection 7 is located in the center of the main body section 2 when viewed from the longitudinal direction A. The internal reinforcement section 6 is formed in a Y shape.

[0090] In other words, of the ends of the first plate member 61a in the radial direction R, one end is connected to the inner surface 2b, and the other end is connected to the second plate member 61b and the third plate member 61c at the intersection 7. Similarly, of the ends of the second plate member 61b in the radial direction R, one end is connected to the inner surface 2b, and the other end is connected to the third plate member 61c and the first plate member 61a at the intersection 7. Similarly, of the ends of the third plate member 61c in the radial direction R, one end is connected to the inner surface 2b, and the other end is connected to the first plate member 61a and the second plate member 61b at the intersection 7.

[0091] The average thickness L5 of the internal reinforcement portion 6 is approximately equal to the film thickness L1 of the main body portion 2. Thickness L5 is the thickness of the internal reinforcement portion 6 in the direction perpendicular to the radial direction R when viewed from the longitudinal direction A. Note that the average thickness L5 of the internal reinforcement portion 6 may be greater than or less than the film thickness L1 of the main body portion 2.

[0092] In the shape of the cross-section perpendicular to the longitudinal direction A of the hollow fiber membrane 1D, the cross-sectional area of ​​the internal reinforcement portion 6 is 50% or less of the cross-sectional area of ​​the inner region of the hollow fiber membrane 1D. However, the cross-sectional area of ​​the internal reinforcement portion 6 may be 50% or more of the cross-sectional area of ​​the inner region of the hollow fiber membrane 1D.

[0093] The internal reinforcement portion 6 is formed integrally with the main body portion 2. The internal reinforcement portion 6 is made of polyolefin, polyurethane, fluororesin, or silicone resin. Examples of polyolefin include polyethylene, polypropylene, and polymethylpentene. From a cost viewpoint, it is preferable that the internal reinforcement portion 6 is made of polyethylene. From the viewpoint of using the same material as the main body portion 2, it is preferable that the internal reinforcement portion 6 is made of low-density polyethylene. From the viewpoint of oxygen permeability, polydimethylsiloxane (PMDS) is preferred as the silicone resin.

[0094] The material of the internal reinforcement section 6 may be one type or two or more types. The material of the internal reinforcement section 6 may be the same as the material of the main body section 2 or it may be different.

[0095] According to the hollow fiber membrane 1D of this embodiment, the internal reinforcement portion 6 increases the mechanical strength, allowing for a thinner film thickness than conventional hollow fiber membranes. By reducing the film thickness, the oxygen permeability of the membrane can be improved. Improved oxygen permeability allows the nitrification reaction to proceed even at lower gas pressures, resulting in energy savings.

[0096] (Variation 1) [Hollow fiber membrane 1E] Next, with reference to Figure 12, the hollow fiber membrane 1E according to Modification 1 will be described.

[0097] Figure 12 is a cross-sectional view showing a hollow fiber membrane 1E according to Modification 1, and shows a cross-section cut by a plane perpendicular to the longitudinal direction A. Hollow fiber membrane 1E is a modified example of hollow fiber membrane 1D. As shown in Figure 12, hollow fiber membrane 1D differs from hollow fiber membrane 1E in the arrangement of the internal reinforcing portion 6.

[0098] In the hollow fiber membrane 1E, the internal reinforcing portion 6 is formed along the direction in which the reinforcing member 3 protrudes within the radial direction R. When multiple reinforcing members 3 and plate members 61 are provided, each of the multiple plate members 61 is formed along the direction in which a different reinforcing member 3 protrudes.

[0099] The configuration of the internal reinforcement portion 6 in the hollow fiber membrane 1E will be explained in more detail. The hollow fiber membrane 1E is provided with six reinforcing members 3 spaced approximately equally apart in the circumferential direction C. The six reinforcing members 3 are designated as the first reinforcing member 3a, the second reinforcing member 3b, the third reinforcing member 3c, the fourth reinforcing member 3d, the fifth reinforcing member 3e, and the sixth reinforcing member 3f, in the order they are arranged in the circumferential direction C. The first plate member 61a is formed along the direction in which the first reinforcing member 3a protrudes in the radial direction R. The second plate member 61b is formed along the direction in which the third reinforcing member 3c protrudes in the radial direction R. The third plate member 61c is formed along the direction in which the fifth reinforcing member 3e protrudes in the radial direction R.

[0100] The configuration of the reinforcing member 3 and the internal reinforcing part 6 is not limited. The number of reinforcing members 3 is not limited, and the reinforcing members 3 do not have to be arranged with equal gaps between them. The plate member 61 may be formed along the direction in which the second reinforcing member 3b protrudes, or along the direction in which the fourth reinforcing member 3d protrudes, or along the direction in which the sixth reinforcing member 3f protrudes.

[0101] According to the hollow fiber membrane 1E of modified example 1, the internal reinforcement portion 6 increases the mechanical strength, making it possible to make the film thickness thinner than that of a conventional hollow fiber membrane.

[0102] (Modification 2) [Hollow fiber membrane 1F] Next, with reference to Figure 13, the hollow fiber membrane 1F according to modified example 2 will be described.

[0103] Figure 13 is a cross-sectional view showing the hollow fiber membrane 1F according to the modified example 2, and shows a cross-section cut by a plane perpendicular to the longitudinal direction A. The hollow fiber membrane 1F is a modified example of the hollow fiber membrane 1E. As shown in Figure 13, the hollow fiber membrane 1F differs from the hollow fiber membrane 1E in that it has an intersection reinforcement portion 8 in the internal reinforcement portion 6.

[0104] The intersection reinforcement section 8 is formed at the intersection 7 of the internal reinforcement section 6. The intersection reinforcement section 8 connects adjacent plate members 61 in the circumferential direction C. For example, the intersection reinforcement section 8 connects the first plate member 61a and the second plate member 61b, the second plate member 61b and the third plate member 61c, and the third plate member 61c and the first plate member 61a.

[0105] The intersection reinforcement section 8 is formed in a circular shape when viewed from the longitudinal direction A. In other words, the intersection reinforcement section 8 is curved and bulges outward in the radial direction R. However, the shape of the intersection reinforcement section 8 is not limited. For example, the intersection reinforcement section 8 may be formed in a polygonal shape when viewed from the radial direction R. The intersection reinforcement section 8 may also be formed in a triangular shape when viewed from the longitudinal direction A, as shown in Figure 14.

[0106] According to the hollow fiber membrane 1F of modified example 2, the mechanical strength is increased by the intersection reinforcement portion 8, so the film thickness can be made thinner than that of a conventional hollow fiber membrane.

[0107] Although a second embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope of the gist of the present invention. Furthermore, the components shown in the above-described embodiments and modifications can be combined as appropriate.

[0108] In the hollow fiber membrane 1D according to the second embodiment, the internal reinforcement portion 6 is connected to the inner surface 2b at two or more locations, but the configuration of the internal reinforcement portion 6 is not limited. The internal reinforcement portion 6 may be configured to be connected to the inner surface 2b at only one location.

[0109] In the hollow fiber membrane 1D according to the second embodiment, the internal reinforcement portion 6 divides the internal space of the hollow fiber membrane 1D into two or more parts, but the configuration of the internal reinforcement portion 6 is not limited. The internal reinforcement portion 6 does not need to divide the internal space of the hollow fiber membrane 1D into two or more parts.

[0110] In the hollow fiber membrane 1D according to the second embodiment, the internal reinforcing portion 6 has a plate member 61, but the configuration of the internal reinforcing portion 6 is not limited. For example, instead of the plate member 61, the internal reinforcing portion 6 may have a projection that protrudes radially R from the inner surface 2b.

[0111] In the hollow fiber membrane 1D according to the second embodiment, the plate member 61 extends in the radial direction R, but the configuration of the plate member 61 is not limited. The plate member 61 may extend in a direction shifted from the radial direction R to the circumferential direction C.

[0112] In the hollow fiber membrane 1D according to the second embodiment, the plate member 61 is formed along the longitudinal direction A, but the configuration of the plate member 61 is not limited. The plate member 61 may be formed along a direction shifted from the longitudinal direction A to the circumferential direction C.

[0113] In the hollow fiber membrane 1D according to the second embodiment, there are multiple plate members 61, but there are no multiple plate members 61. In this case, both ends of the plate member 61 may be connected to the inner surface 2b.

[0114] In the hollow fiber membrane 1D according to the second embodiment, multiple plate members 61 are connected at intersections 7, but the configuration of the plate members 61 is not limited. Multiple plate members 61 do not need to be connected to each other.

[0115] In the hollow fiber membrane 1D according to the second embodiment, the intersection 7 is located at the center of the main body 2 when viewed from the longitudinal direction A, but the position of the intersection 7 is not limited. The intersection 7 may be offset radially R from the center of the main body 2 when viewed from the longitudinal direction A.

[0116] The hollow fiber membrane module 10 may include a hollow fiber membrane 1D, a hollow fiber membrane 1E, or a hollow fiber membrane 1F. The water treatment device 100 may include a hollow fiber membrane 1D, a hollow fiber membrane 1E, or a hollow fiber membrane 1F. [Examples]

[0117] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0118] (Experiment 1) We performed a simulation analysis of the displacement of hollow fiber membranes when an external force is applied to them. Simultaneously with the simulation analysis of the displacement of the hollow fiber membranes, we also performed a simulation analysis of the stress acting on the hollow fiber membranes when an external force is applied. A force was applied to multiple hollow fiber membranes from the radial direction R. Approximately equal forces were applied to multiple hollow fiber membranes. The simulation analysis was performed using the 3D CAD software "Autodesk Inventor 2025". The calculation conditions specified "low-density polyethylene" as the material.

[0119] Figure 7 is a cross-sectional view of the hollow fiber membrane 1Z according to Comparative Example 1, showing a cross-section cut by a plane perpendicular to the longitudinal direction A. Figure 8 is a cross-sectional view of the hollow fiber membrane 1B according to Example 1, showing a cross-section cut by a plane perpendicular to the longitudinal direction.

[0120] Simulations were performed for Comparative Example 1, Example 1, and Example 2. In the hollow fiber membranes of Comparative Example 1, Example 1, and Example 2, the film thickness L1 was approximately the same. In the hollow fiber membranes of Comparative Example 1, Example 1, and Example 2, the outer diameter L2 was approximately the same.

[0121] As shown in Figure 7, the hollow fiber membrane 1Z according to Comparative Example 1 has a reinforcing member. The reinforcing member provided in the hollow fiber membrane 1Z according to Comparative Example 1 does not have a recessed portion 32. Furthermore, the hollow fiber membrane 1Z according to Comparative Example 1 does not have a stress distribution portion 4.

[0122] As shown in Figure 8, the hollow fiber membrane 1B according to Example 1 has a reinforcing member 3. The reinforcing member 3 provided in the hollow fiber membrane 1B according to Example 1 has a recessed portion 32. Note that the hollow fiber membrane 1B according to Example 1 does not have a stress distribution portion 4.

[0123] The hollow fiber membrane 1 according to Example 2 has a reinforcing member 3, as shown in Figure 1. The reinforcing member 3 provided in the hollow fiber membrane 1 according to Example 2 has a recessed portion 32. The hollow fiber membrane 1 according to Example 2 has a stress distribution portion 4.

[0124] In the reinforcing members provided on the hollow fiber membrane according to Comparative Example 1, Example 1, and Example 2, the length L3 of the reinforcing member in the circumferential direction C is approximately equal. The length L3 of the reinforcing member is the length of the widest part of the reinforcing member in the circumferential direction C.

[0125] In the reinforcing members provided on the hollow fiber membrane according to Comparative Example 1, Example 1, and Example 2, the height H1 of the reinforcing members is approximately equal. The height H1 of the reinforcing member is the length of the reinforcing member in the radial direction R.

[0126] Figure 9 shows the simulation results for Comparative Example 1, Example 1, and Example 2. Figure 10 shows the range in which the largest force is applied among the forces applied to Comparative Example 1, Example 1, and Example 2.

[0127] As shown in Figure 9, the retention rate of the maximum displacement of the hollow fiber membrane 1B in Example 1 is greater than the retention rate of the maximum displacement of the hollow fiber membrane 1Z in Comparative Example 1. As shown in Figure 9, the retention rate of the maximum displacement of the hollow fiber membrane 1 in Example 2 is greater than the retention rate of the maximum displacement of the hollow fiber membrane 1B in Example 1. The retention rate of the maximum displacement is the value obtained by subtracting the absolute value of the maximum displacement of the hollow fiber membrane from the value of the outer diameter of the hollow fiber membrane and dividing the result by the value of the outer diameter of the hollow fiber membrane. The closer the retention rate of the maximum displacement is to 1, the smaller the maximum displacement when force is applied, and the easier it is for the shape of the hollow fiber membrane to be maintained. The formula for calculating the maintenance rate of the maximum displacement is as follows: (Maintenance of maximum displacement) = (Outer diameter of membrane - Maximum displacement) / (Outer diameter of membrane) ... (Equation 1)

[0128] As shown in Figure 9, the hollow fiber membrane 1B according to Example 1 exhibits a smaller maximum displacement when force is applied and maintains its shape more easily compared to the hollow fiber membrane 1Z according to Comparative Example 1. In other words, the hollow fiber membrane 1B according to Example 1 has greater mechanical strength than the hollow fiber membrane 1Z according to Comparative Example 1. As shown in Figure 9, the hollow fiber membrane 1 according to Example 2 exhibits a smaller maximum displacement when force is applied and maintains its shape more easily compared to the hollow fiber membrane 1B according to Example 1. In other words, the hollow fiber membrane 1 according to Example 2 has greater mechanical strength than the hollow fiber membrane 1B according to Example 1.

[0129] As shown in Figure 9, the dispersion ratio of the maximum stress of the hollow fiber membrane 1B in Example 1 is greater than the dispersion ratio of the maximum stress of the hollow fiber membrane 1Z in Comparative Example 1. As shown in Figure 9, the dispersion ratio of the maximum stress of the hollow fiber membrane 1 in Example 2 is greater than the dispersion ratio of the maximum stress of the hollow fiber membrane 1B in Example 1. The dispersion ratio of the maximum stress is calculated as the inverse ratio of the force applied to the main body of the hollow fiber membrane to the value in Comparative Example 1. The greater the dispersion ratio of the maximum stress is, the smaller the maximum stress when a force is applied, and the more easily the force applied to the main body is dispersed in the hollow fiber membrane. The formula for calculating the rate of change (variance) of maximum stress is as follows: (Percentage change in maximum stress) = (Maximum stress in the example) / (Maximum stress in the comparative example) ... (Equation 2)

[0130] As shown in Figure 9, the hollow fiber membrane 1B according to Example 1 exhibits a smaller maximum stress when force is applied compared to the hollow fiber membrane 1Z according to Comparative Example 1, and the force applied to the main body is more easily dispersed. In other words, the hollow fiber membrane 1B according to Example 1 has greater mechanical strength compared to the hollow fiber membrane 1Z according to Comparative Example 1. As shown in Figure 9, the hollow fiber membrane 1 according to Example 2 exhibits a smaller maximum stress when force is applied compared to the hollow fiber membrane 1B according to Example 1, and the force applied to the main body is more easily dispersed. In other words, the hollow fiber membrane 1 according to Example 2 has greater mechanical strength compared to the hollow fiber membrane 1B according to Example 1.

[0131] As shown in Figure 10, the area where the greatest force is applied to the hollow fiber membrane 1 according to Example 2 is larger than the area where the hollow fiber membrane 1Z according to Comparative Example 1 and the hollow fiber membrane 1B according to Example 1 are applied. According to the results shown in Figure 9, the force is more easily dispersed in the hollow fiber membrane 1 according to Example 2 compared to the hollow fiber membrane 1Z according to Comparative Example 1 and the hollow fiber membrane 1B according to Example 1. In other words, the hollow fiber membrane 1 according to Example 2 has greater mechanical strength compared to the hollow fiber membrane 1Z according to Comparative Example 1 and the hollow fiber membrane 1B according to Example 1.

[0132] As shown in Figure 9, the hollow fiber membrane 1B with the recessed portion 32 has greater mechanical strength compared to the hollow fiber membrane 1Z without the recessed portion 32. Also, as shown in Figures 9 and 10, the hollow fiber membrane 1 with the stress-distributing portion 4 has greater mechanical strength compared to the hollow fiber membrane 1B without the stress-distributing portion 4. In other words, the hollow fiber membrane 1 has improved mechanical strength due to the formation of the recessed portion 32. Furthermore, the hollow fiber membrane 1 has improved mechanical strength due to the formation of the stress-distributing portion 4.

[0133] (Experiment 2) A simulation analysis was conducted to determine the displacement of hollow fiber membranes when external forces are applied to them. Forces were applied to multiple hollow fiber membranes from the radial direction R. Forces of approximately equal magnitude were applied to multiple hollow fiber membranes.

[0134] Comparative Example 2 and Example 3 were analyzed by simulation. Comparative Example 2 is a hollow fiber membrane in which the recessed portion 32 is not formed. Comparative Example 2 is a hollow fiber membrane that has the same configuration as hollow fiber membrane 1D except for the absence of the recessed portion 32. Example 3 is hollow fiber membrane 1D.

[0135] In Experiment 2, simulations were performed to analyze the displacement of the hollow fiber membrane when a force was applied to the reinforcing member 3 (CASE 1) and when a force was applied to the part of the main body 2 where the reinforcing member 3 was not formed (CASE 2).

[0136] Figure 15 shows the results of the simulation analysis for Experiment 2. Figure 16 shows the range where the greatest force is applied among the forces applied to Comparative Example 2 and Example 3. As shown in Figure 15, in CASE 1 and CASE 2, the retention rate of the maximum displacement of the hollow fiber membrane 1D according to Example 3 is greater than the retention rate of the maximum displacement of the hollow fiber membrane according to Comparative Example 2. Also, the rate of change of the maximum stress of the hollow fiber membrane 1D according to Example 3 is greater than the rate of change of the maximum stress of the hollow fiber membrane according to Comparative Example 2. Therefore, the hollow fiber membrane 1D according to Example 3 has a smaller maximum displacement when force is applied and maintains its shape more easily compared to the hollow fiber membrane according to Comparative Example 2. The hollow fiber membrane 1D according to Example 3 has greater mechanical strength compared to the hollow fiber membrane according to Comparative Example 2.

[0137] As shown in Figure 16, in CASE 1 and CASE 2, the area where the greatest force is applied to the hollow fiber membrane 1D according to Example 3 is wider than the area where the greatest force is applied to the hollow fiber membrane according to Comparative Example 2. The applied external force is more evenly distributed in the hollow fiber membrane 1D according to Example 3 compared to the hollow fiber membrane according to Comparative Example 2. In other words, the hollow fiber membrane 1D according to Example 3 has greater mechanical strength than the hollow fiber membrane according to Comparative Example 2.

[0138] The hollow fiber membrane 1D having the recessed portion 32 formed therein has greater mechanical strength compared to the hollow fiber membrane without the recessed portion 32. In other words, the hollow fiber membrane 1D has improved mechanical strength due to the formation of the recessed portion 32.

[0139] (Experiment 3) A simulation analysis was conducted to determine the displacement of hollow fiber membranes when external forces are applied to them. Forces were applied to multiple hollow fiber membranes from the radial direction R. Forces of approximately equal magnitude were applied to multiple hollow fiber membranes.

[0140] Comparative Example 3 and Example 4 were analyzed by simulation. Comparative Example 3 is a hollow fiber membrane in which the recessed portion 32 is not formed. Comparative Example 3 is a hollow fiber membrane that has the same configuration as hollow fiber membrane 1E except for the absence of the recessed portion 32. Example 4 is hollow fiber membrane 1E.

[0141] In Experiment 3, simulations were performed to analyze the displacement of the hollow fiber membrane when a force was applied to the reinforcing member 3 (CASE 1) and when a force was applied to the part of the main body 2 where the reinforcing member 3 was not formed (CASE 2).

[0142] Figure 17 shows the results of the simulation analysis for Experiment 3. Figure 18 shows the range where the greatest force is applied among the forces applied to Comparative Example 3 and Example 4. As shown in Figure 17, in CASE 1 and CASE 2, the retention rate of the maximum displacement value of the hollow fiber membrane 1E according to Example 4 is greater than the retention rate of the maximum displacement value of the hollow fiber membrane according to Comparative Example 3. The rate of change of the maximum stress of the hollow fiber membrane 1E according to Example 4 is greater than the rate of change of the maximum stress of the hollow fiber membrane according to Comparative Example 3. Therefore, the hollow fiber membrane 1E according to Example 4 has a smaller maximum displacement when force is applied and maintains its shape more easily compared to the hollow fiber membrane according to Comparative Example 3. The hollow fiber membrane 1E according to Example 4 has greater mechanical strength compared to the hollow fiber membrane according to Comparative Example 3.

[0143] As shown in Figure 18, in CASE 1 and CASE 2, the range over which the greatest force is applied to the hollow fiber membrane 1E according to Example 4 is wider than the range over which the greatest force is applied to the hollow fiber membrane according to Comparative Example 3. The applied external force is more evenly distributed in the hollow fiber membrane 1E according to Example 4 compared to the hollow fiber membrane according to Comparative Example 3. In other words, the hollow fiber membrane 1E according to Example 4 has greater mechanical strength than the hollow fiber membrane according to Comparative Example 3.

[0144] The hollow fiber membrane 1E in which the recessed portion 32 is formed has greater mechanical strength compared to the hollow fiber membrane in which the recessed portion 32 is not formed. In other words, the mechanical strength of the hollow fiber membrane 1E is improved by the formation of the recessed portion 32.

[0145] (Experiment 4) A simulation analysis was conducted to determine the displacement of hollow fiber membranes when external forces are applied to them. Forces were applied to multiple hollow fiber membranes from the radial direction R. Forces of approximately equal magnitude were applied to multiple hollow fiber membranes.

[0146] Comparative Example 4 and Example 5 were analyzed by simulation. Comparative Example 4 is a hollow fiber membrane in which the recessed portion 32 is not formed. Comparative Example 4 is a hollow fiber membrane that has the same configuration as hollow fiber membrane 1F except for the absence of the recessed portion 32. Example 5 is hollow fiber membrane 1F.

[0147] In Experiment 4, simulations were performed to analyze the displacement of the hollow fiber membrane when a force was applied to the reinforcing member 3 (CASE 1) and when a force was applied to the part of the main body 2 where the reinforcing member 3 was not formed (CASE 2).

[0148] Figure 19 shows the results of the simulation analysis for Experiment 4. Figure 20 shows the area where the greatest force is applied to Example 5. As shown in Figure 20, in CASE 1 and CASE 2, the retention rate of the maximum displacement of the hollow fiber membrane 1F according to Example 5 is greater than the retention rate of the maximum displacement of the hollow fiber membrane according to Comparative Example 4. The rate of change of the maximum stress of the hollow fiber membrane 1F according to Example 5 is greater than the rate of change of the maximum stress of the hollow fiber membrane according to Comparative Example 4. Therefore, the hollow fiber membrane 1F according to Example 5 has a smaller maximum displacement when force is applied and maintains its shape more easily compared to the hollow fiber membrane according to Comparative Example 4. The hollow fiber membrane 1F according to Example 5 has greater mechanical strength compared to the hollow fiber membrane according to Comparative Example 4.

[0149] As shown in Figure 20, in CASE 1 and CASE 2, the area over which the greatest force is applied to the hollow fiber membrane 1E according to Example 5 is wide. In the hollow fiber membrane 1F according to Example 5, the applied external force is distributed. In other words, the hollow fiber membrane 1F according to Example 5 has high mechanical strength.

[0150] The hollow fiber membrane 1F in which the recessed portion 32 is formed has greater mechanical strength compared to the hollow fiber membrane in which the recessed portion 32 is not formed. In other words, the mechanical strength of the hollow fiber membrane 1F is improved by the formation of the recessed portion 32. [Explanation of Symbols]

[0151] 1, 1B, 1C, 1D, 1E, 1F... Hollow fiber membrane, 2... Main body, 2a... Outer surface, 2b... Inner surface, 3... Reinforcement member, 3a... First reinforcement member, 3b... Second reinforcement member, 3c... Third reinforcement member, 3d... Fourth reinforcement member, 3e... Fifth reinforcement member, 3f... Sixth reinforcement member, 31... Reinforcement member body, 31a... Surface, 32... Recessed part, 4... Stress distribution part, 6... Internal reinforcement part, 61... Plate member, 61a... First plate member, 61b... Second plate member, 61c... Third plate member, 7... Intersection, 8... Intersection reinforcement part, 5... Microbial layer, 10... Hollow fiber membrane module Tube, 11...Hollow fiber membrane sheet, 12...Housing, 12a...Upper housing, 12b...Lower housing, 120...Gas supply line, 100...Water treatment device, 110...Treatment tank, 111...Opening, W...Water to be treated (wastewater), L1...Film thickness, L2...Outer diameter, L3...Length (width) of reinforcing member body 31, L4...Length (width) of recessed portion 32, L5...Average thickness of internal reinforcing portion 6, H1...Height of reinforcing member body 31, H2...Depth of recessed portion 32, H3...Height of stress distribution portion 4, A...Longitudinal direction, C...Circumferential direction, R...Radial direction

Claims

1. A hollow fiber membrane that is permeable to oxygen and on which a microbial layer derived from microorganisms or bacteria in the water may form on its outer surface during water treatment, The main body is formed in a cylindrical shape extending in the longitudinal direction and forms the outer surface, The system comprises a plurality of reinforcing members that protrude radially from the outer surface, extend in the longitudinal direction, and are spaced apart in the circumferential direction, The reinforcing member has a recessed portion that is embedded in the surface of the reinforcing member and extends in the longitudinal direction. Hollow fiber membrane.

2. At the portion where the main body and the reinforcing member are in contact, a stress distribution portion is formed that connects the main body and the reinforcing member and extends in the longitudinal direction. The height of the stress distribution portion from the outer surface in the radial direction is one-third or more of the height of the reinforcing member from the outer surface in the radial direction. The hollow fiber membrane according to claim 1.

3. The recessed portion is formed on the outer peripheral surface of the reinforcing member in the radial direction, and is embedded radially from the surface of the reinforcing member. A hollow fiber membrane according to claim 1 or claim 2.

4. The depth of the recessed portion from the surface of the reinforcing member is between one-tenth and one-half of the height of the reinforcing member from the outer surface in the radial direction. A hollow fiber membrane according to claim 1 or claim 2.

5. When viewed from the longitudinal direction, the length of the portion of the surface of the reinforcing member in which the recess is formed is between one-quarter and one-half of the circumferential length of the reinforcing member. A hollow fiber membrane according to claim 1 or claim 2.

6. Three or more of the aforementioned reinforcing members are formed. A hollow fiber membrane according to claim 1 or claim 2.

7. The circumferential length of the reinforcing member is 20 μm or more and 70 μm or less. A hollow fiber membrane according to claim 1 or claim 2.

8. The film thickness is less than 30 μm. A hollow fiber membrane according to claim 1 or claim 2.

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

10. A water treatment apparatus comprising the hollow fiber membrane module described in claim 9.

11. A water treatment method for treating water to be treated using the water treatment apparatus described in claim 10.

12. The main body portion further comprises an internal reinforcing portion extending radially from the inner surface of the main body portion. The hollow fiber membrane according to claim 1.

13. The aforementioned internal reinforcing portion is connected to the inner surface at two or more locations. The hollow fiber membrane according to claim 12.

14. The aforementioned internal reinforcing section has a plurality of plate members, Each of the plate members extends radially from its inner surface and is connected at an intersection within the main body. The hollow fiber membrane according to claim 12 or claim 13.

15. Three of the aforementioned plate members are provided. The aforementioned intersection is located in the center of the main body when viewed from the longitudinal direction. The hollow fiber membrane according to claim 14.

16. The internal reinforcing portion is formed along the radial direction in which the reinforcing member protrudes. The hollow fiber membrane according to claim 12 or claim 13.

17. The aforementioned internal reinforcement portion has an intersection reinforcement portion at the intersection, The aforementioned intersection reinforcement section connects the plate members that are adjacent to each other in the circumferential direction. The hollow fiber membrane according to claim 14.

18. The thickness of the internal reinforcing portion in the direction perpendicular to the radial direction when viewed from the longitudinal direction is equal to the thickness of the main body portion. The hollow fiber membrane according to claim 12 or claim 13.

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