JP2009247965A - Hollow fiber membrane element and hollow fiber membrane module using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow fiber membrane element capable of aerating a biological treatment tank and cleaning a membrane surface. <P>SOLUTION: A hollow fiber membrane 20 is disposed around a support pipe 11 having an aeration pipe 12 and a water collecting pipe 13. The aeration pipe 12 has an air introducing pipe 18, a first pore group 14 and a second pore group 16. The pore diameter of the first pore group is smaller than the pore diameter of the second pore group 16, and a ventilation suppression member 17 which enables ventilation and generates ventilation resistance is disposed between the pore groups 14 and 16. By the action of the ventilation suppression member 17, fine bubbles are discharged from the first pore group 14 and large bubbles are discharged from the second pore group 16. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hollow fiber membrane element used by being immersed in a biological treatment tank or the like and a hollow fiber membrane module using the same.

  The hollow fiber membrane module is often used in an immersed state when used in a water treatment field having a relatively high turbidity such as a biological treatment liquid. In the case of such an immersion filtration type hollow fiber membrane module, there is a problem that, when filtration is continued, dirt due to suspended matter (SS) or the like adheres to the membrane surface and the filtration performance deteriorates. .

  Conventionally, dirt attached to the film surface is removed by air bubbling from below the film. However, dirt on the surface of the hollow fiber membrane positioned outside the hollow fiber membrane bundle is easy to remove, but dirt on the surface of the hollow fiber membrane inside the hollow fiber membrane bundle is difficult to remove, so air bubbling alone is sufficient. Recovery of filtration performance was difficult.

Patent Document 1 discloses an immersion filtration type hollow fiber membrane cartridge. In this hollow fiber membrane cartridge, a plurality of through holes 3c are formed in the adhesive fixing layer 3b on the lower side of the hollow fiber membrane bundle, and the hollow fiber membranes are washed by vibration caused by bubbles released from the through holes 3c. It is like that.
JP 2005-342690 A JP 2006-239642 A JP 2003-326140 A

  In the hollow fiber membrane modules of Patent Documents 1 and 2, the air supply unit and the hollow fiber membrane are mixed in the lower fixing part, but it is difficult to generate fine bubbles and the cleaning effect is not sufficient.

  Furthermore, in the module of Patent Document 2, an air supply pipe and an ejection hole are provided in the lower fixing part. In such a module, an air supply pipe and an ejection hole are processed in the adhesive layer of the fixing part. More man-hours and higher processing costs.

  The present invention has a simple structure, can wash the entire hollow fiber membrane bundle constituting the hollow fiber membrane bundle, can easily recover the filtration performance, and when applied to a biological treatment tank, aeration It is an object of the present invention to provide a hollow fiber membrane element and a hollow fiber membrane module using the same, in which both cleaning by aeration and aeration can be performed in parallel.

The present invention provides the following inventions as means for solving the problems.
1. A hollow fiber membrane element in which a number of hollow fiber membranes are arranged around a support tube,
The support pipe is of a double pipe structure having an outer diffuser pipe and a water collecting pipe disposed inside the diffuser pipe;
The air diffusion pipe is connected to one end side from an external air introduction pipe, the first pore group formed at a position closer to the other end side than the air introduction pipe, and the first pore group And the second pore group separated and formed at a position close to the other end side, the average pore diameter of the first pore group is smaller than the average pore diameter of the second pore group,
Furthermore, the hollow fiber membrane element in which the said air diffusing tube has an air flow suppressing portion that generates air flow resistance formed in the air flow path between the first pore group and the second pore group.
2. The hollow fiber membrane element according to claim 1, wherein the air flow suppressing portion is a portion where a gas flow suppressing member made of a porous material is disposed in the air flow path.
3. The hollow fiber membrane element according to claim 2, wherein the air flow suppressing member made of the porous material has a bulk density of 0.50 to 0.90 g / cm ³ .
4). The hollow fiber membrane element according to claim 2, wherein the air flow suppressing member made of the porous material has a porosity of 20 to 50%.
5. The hollow fiber membrane element according to claim 1, wherein the ventilation suppression site is a site where a cross-sectional area in the width direction of the ventilation channel is reduced.
6). The site of the cross-sectional area in the width direction is reduced in the ventilation path, the ratio of the cross-sectional area S ₁ of the vent path extending to the site and the sectional area S ₂ of the portion (S 2 _{/ S 1)} is 0. The hollow fiber membrane element according to claim 5, which is in the range of 001 to 0.5.
7). The first pore group is a micropore having a stretchable porous member that covers the surface of the pore group formed in the diffuser tube, and the second pore group is a pore group formed in the diffuser tube. The hollow fiber membrane element according to any one of claims 1 to 6, wherein
8). Both ends of the support tube and both ends of a large number of hollow fiber membranes are fixed to an upper water collecting cap and a lower water collecting cap, respectively, and collected from both ends. The hollow fiber membrane element as described.
9. An immersion filtration type hollow fiber membrane module comprising a plurality of hollow fiber membrane elements according to any one of claims 1 to 8,
The water collecting pipes of the plurality of hollow fiber membrane elements are connected to one or more water collecting main pipes,
An immersion filtration type hollow fiber membrane module in which the diffuser pipes of the plurality of hollow fiber membrane elements are connected to an air supply pipe via an air introduction pipe.
10. 9. The immersion filtration type hollow fiber membrane module according to claim 8, wherein the plurality of hollow fiber membrane elements are supported by a frame.
11. The plurality of hollow fiber membrane elements are detachably connected to the water collecting main pipe at least at the upper end side, and the water collecting pipes of the plurality of hollow fiber membrane elements communicate with the water collecting main pipe, respectively. The hollow filtration membrane module of the immersion filtration system according to claim 9 or 10.
When the hollow fiber membrane element of the present invention is used by being immersed in a biological treatment tank, the aeration in the biological treatment tank is caused by the action of an aeration suppressing part that is disposed in the diffuser tube and that allows ventilation and generates ventilation resistance. At the same time, the hollow fiber membrane surface to which dirt is attached by the filtration operation can be washed.

  When there is no ventilation suppression part arranged in the air diffuser pipe with the same structure as the hollow fiber membrane element of the present invention, air was introduced from one end side of the air diffuser pipe by an air inlet pipe connected to an external air source. In some cases, air is preferentially released in the form of bubbles from the second pore group having a larger average pore diameter, and the amount of bubbles released from the first pore group is very small. With this, the hollow fiber membrane surface can be sufficiently cleaned, but aeration in the biological treatment tank becomes insufficient, and it is necessary to use other aeration means substantially.

  However, in the hollow fiber membrane element of the present invention, when air is introduced from one end side of the air diffusing tube by the air introducing tube connected to an external air source, the action of the ventilation suppression portion arranged in the air diffusing tube Therefore, it becomes difficult for the air to pass through the ventilation suppression portion. For this reason, the pressure of the vicinity of the first pore group is increased by the action of the air sent from the air introduction pipe and the ventilation suppression portion, and a sufficiently small amount of bubbles are released from the first pore group. Then, by increasing the pressure in the vicinity of the first pore group, air passes through the aeration suppressing portion, and a sufficient amount of larger bubbles are released from the second pore group.

  There is no particular limitation on the method of forming the ventilation suppression portion that generates the ventilation resistance formed in the ventilation path of the air diffuser. For example, a method of arranging a ventilation suppression member that itself has ventilation resistance, a gap that generates the ventilation resistance, and the like. It is possible to apply a method of disposing an airflow suppressing member that can form an air gap and a method of forming a gap that generates airflow resistance by modifying the air diffuser tube itself.

  In the hollow fiber membrane element of the present invention, when all the pore diameters of the first pore group are uniform, the average pore diameter becomes the pore diameter of one pore, and similarly the pore diameter of the second pore group. When the pore diameters are all uniform, the average pore diameter is the pore diameter of one pore. When there is a variation in the pore diameter of the first pore group and the pore diameter of the second pore group, the maximum diameter in the pores of the first pore group is the second pore group. It is preferable that it is smaller than the minimum diameter in the pores.

  In the hollow fiber membrane element of the present invention, the stretchable porous member has a property of expanding by receiving the air pressure applied to the pore group of the diffuser tube, and the stretchable porous member is provided by the expansion. When the micropores are slightly enlarged, fine bubbles are released therefrom, so that aeration efficiency is increased (for example, the amount of dissolved oxygen per unit time or unit energy is increased). As the stretchable porous member, a sheet made of rubber, elastomer, plastic, or the like that is deformed under pressure but can maintain the state before deformation when there is no pressure is used.

  Since the hollow fiber membrane module of the present invention uses a plurality of the above-described hollow fiber membrane elements, for example, when immersed in a biological treatment tank and subjected to filtration operation, the hollow fiber membrane module is removed from the support tube of the hollow fiber membrane element. Since the inside of the tank can be aerated by aeration and the hollow fiber membrane bundle can be cleaned in parallel, the filtration efficiency is very high.

  The hollow fiber membrane element of the present invention can be used for both aeration and cleaning of the membrane surface with a single hollow fiber membrane element when used by being immersed in a biological treatment tank. For this reason, the hollow fiber membrane module using the hollow fiber membrane element of the present invention can perform a stable filtration operation for a long period of time.

<Hollow fiber membrane element>
(1) Hollow fiber membrane element of FIG. 1 FIG. 1 is a longitudinal sectional view of a hollow fiber membrane element 10A according to an embodiment of the present invention.

  The hollow fiber membrane element 10 </ b> A has a large number of hollow fiber membranes (hollow fiber membrane bundles) 20 arranged around the support tube 11.

  The support tube 11 has a double tube structure having an outer diffuser tube 12 and a water collecting tube 13 disposed inside the diffuser tube 12. The air diffuser 12 and the water collecting tube 13 are made of metal, plastic, or a combination thereof.

  The upper ends of the hollow fiber membrane bundle 20, the diffuser tube 12 and the water collecting tube 13 are fixed and integrated with a resin 33 such as urethane resin or epoxy resin in the upper ring 32. An upper water collecting cap 31 is screwed around the upper ring 32 so as to be integrated. The hollow fiber membrane bundle 20 facing the inside of the upper water collecting cap 31 and the ends of the water collecting pipe 13 are opened, and the air diffuser 12 is sealed with a resin 33 and is not opened.

  The lower ends of the hollow fiber membrane bundle 20, the diffuser pipe 12 and the water collection pipe 13 are fixed and integrated with a resin 43 such as urethane resin or epoxy resin in the lower ring 42. A lower water collecting cap 41 is screwed around the lower ring 42 so as to be integrated. The hollow fiber membrane bundle 20 facing the inside of the lower water collecting cap 41 and the ends of the water collecting pipe 13 are opened, and the air diffuser 12 is sealed with the resin 43 and is not opened.

  Such a fixing method using the resins 33 and 43 applies a known hollow fiber membrane bundle resin sealing method, and seals both ends of the hollow fiber membrane bundle 20, the diffuser main pipe 14 and the water collecting pipe 13 with resin. After stopping, a method of cutting and opening both ends of the hollow fiber membrane bundle 20 and the water collecting pipe 13 can be applied.

  The inside of the upper cap 31 is an upper water collecting chamber 35 and is connected to the water collecting main through a communication pipe 36 when used. The lower cap 41 is a lower water collecting chamber 45.

  The hollow fiber membranes constituting the hollow fiber membrane bundle 20 are publicly known, one having an outer diameter of about 1 to 3 mm, an inner diameter of about 0.5 to 2 mm, and a length of 30 to 300 cm per one hollow fiber membrane element. Several hundreds can be used.

  The air diffusion pipe 12 has an air introduction pipe 18 connected to one end side (upper water collecting cap 31 side), and air is introduced into the air diffusion pipe 12 from the external air source via the air introduction pipe 18.

  The air diffusion pipe 12 has a first pore group 14 formed at a position closer to the other end side (lower water collecting cap 41 side) than the air introduction pipe 18. The first pore group 14 is formed of holes (or slits) 14a formed in the air diffuser 12 and fine holes of the cylindrical rubber membrane 14b. The cylindrical rubber membrane 14b is obtained by winding a rubber membrane having a slit (about 1 mm in length) or a hole (about 1 mm in diameter) around the air diffuser 12. The average pore diameter of the first pore group is the average pore diameter when the rubber membrane 14b is closed without being expanded.

  The cylindrical rubber membrane 14b is put in close contact with the surface of the hole (or slit) 14a, and both ends are fixed by the upper fixing member 15a and the lower fixing member 15b.

The rubber membrane does not have a visible hole in a normal state (a state in which no pressure is applied). However, when the pressure is applied, the rubber membrane itself expands to generate fine holes. As such a rubber membrane, a fine hole is formed in a stretchable rubber sheet as disclosed in JP-A-2006-75771, JP-A-2007-14898, JP-A-2004-33889, and the like. Can be used. For example, in Japanese Patent Laid-Open No. 2006-75771, the thickness is 0.1 to 3.0 mm (preferably 0.1 to 3.0 mm), and 10,000 to 1 million pieces / m ² (preferably 10 mm). Those having fine ventilation holes of 10,000 to 1,000,000 pieces / m ² ) are described.

A second pore group 16 separated from the first pore group 14 is formed at a position closer to the other end side (lower water collecting cap 41 side) than the first pore group 14. . The pore diameter of the second pore group 16 can be in the range of 0.01 to 1 mm, and the pore density can be in the range of 100 to 10,000 holes / cm ² .

  The ventilation path between the first pore group 14 and the second pore group 16 in the air diffuser 12 is fitted with a ventilation suppression member 17 that is capable of ventilation and generates ventilation resistance. The site where the is fitted becomes the ventilation suppression site. The inside of the air diffusing tube 12 is separated into a first space 21 and a second space 22 by a ventilation suppressing member 17.

  The airflow suppression member 17 is a cylindrical shaped body having a through hole in the center (the portion where the water collecting pipe 13 is inserted) and having a donut-shaped cross section in the radial direction. The air flow suppression member 17 is made of plastic (ABS resin, olefin resin, etc.) or ceramics, but the shape and shape are not particularly limited, and for example, a shape that can be fitted into the support tube ( Cylindrical material with a cylindrical shape and a donut-shaped cross section in the radial direction, and a spherical material made of fiber such as cotton, plastic, or rubber in a breathable container (a container that can be easily vented) of the same shape as described above A material filled with a large number of materials can be used.

The air flow suppressing member 17 preferably has a bulk density of 0.50 to 0.90 g / cm ³ , more preferably 0.50 to 0.80 g / cm ³ , and still more preferably 0.60 to 0.75 g / cm ³ . There is. Moreover, it is preferable that the porosity of the ventilation | gas_flow suppression member 17 is 20 to 50% of range, and it is more preferable that it is the range of 35 to 45%. In addition, the measuring method of a bulk density and a porosity is as follows.

  The bulk density is determined from the mass per unit volume by measuring the volume and mass of the air flow suppressing member. As for the porosity, the ratio of the voids in the whole was calculated from an enlarged photograph (several hundred times to 1,000 times) of the cross section of the ventilation control member.

  When the bulk density of the air flow suppressing member 17 is within the above range, and further, when the porosity of the air flow suppressing member 17 is within the above range, fine bubbles are released from the first pore group, and from the second pore group. It is preferable for releasing larger bubbles.

  Since the inner surface of the air flow suppression member 17 is in close contact with the outer surface of the water collecting pipe 13 and the outer surface is in close contact with the inner surface of the air diffusion pipe 12, the first space 21 in the air diffusion pipe 12 from the air introduction pipe 18. The air introduced to the air always moves to the second space 22 through the air flow suppressing member 17.

  The opening direction of the fine pore group 14a and the second fine pore group 16 is not particularly limited, and may be any of a direction facing the hollow fiber membrane bundle 20, an obliquely upward direction, an obliquely downward direction, and a direction in which these directions are mixed.

The water collecting pipe 13 is disposed such that the central axis in the length direction thereof coincides with the central axis of the diffuser main pipe 14. The ratio of the outer diameter (d ₁ ) of the water collecting pipe 13 and the inner diameter (d ₂ ) of the diffuser pipe 14 is not particularly limited, and d ₁ / d ₂ is in the range of 0.2 to 0.8. Can be. The outer diameter of the air diffuser 14 can be about 10 to 30 mm.

(2) Hollow fiber membrane element of FIG. 2 FIG. 2 is a longitudinal sectional view of a hollow fiber membrane element 10B according to another embodiment of the present invention. The hollow fiber membrane element 10A in FIG. 1 has the same structure except for a part. Only different parts will be described below.

  One end side of the air introduction pipe 18 penetrates the resin 33 and communicates with the diffuser pipe 12, and the other end side penetrates the curved surface portion of the upper water collecting cap 31. In the case of this embodiment, the width of the hollow fiber membrane element 10B including the air introduction tube 18 is made narrower than the configuration in which the air introduction tube 18 is extended in the lateral direction as in the hollow fiber membrane element 10A of FIG. be able to.

  The upper end side of the diffusing tube 12 is connected to the upper adapter 19a, and the lower end side of the diffusing tube 12 is connected to the lower adapter 19b. Each connecting portion is detachably connected by a screwing method or a fitting method. The upper end side of the upper adapter 17 a is fixed and integrated with the resin 33 together with the upper end side of the hollow fiber membrane bundle 20 and the water collecting pipe 13. The lower end side of the lower adapter 17 b is fixed and integrated with the resin 43 together with the hollow fiber membrane bundle 20 and the lower end side of the water collecting pipe 13.

(3) Hollow fiber membrane element of Fig. 3 Fig. 3 (a) is a longitudinal sectional view of a hollow fiber membrane element 10C which is another embodiment of the present invention, and Fig. 3 (b) is a diagram of (a). It is a fragmentary sectional view of the width direction in a ventilation control part. FIG. 3C is a partial cross-sectional view in the width direction of the part, although only the ventilation suppression part is different from FIG. The hollow fiber membrane element 10C in FIGS. 3A and 3B has the same structure as the hollow fiber membrane element 10A in FIG. Only different parts will be described below.

  A ventilation suppressing member 27 is fitted in the ventilation path between the first pore group 14 and the second pore group 16 in the diffuser tube 12. The air flow suppression member 27 is a combination of an outer side suppression member 27a and an inner side suppression member 27b, both of which are cylindrical, and the cylindrical gap 28 between the outer side suppression member 27a and the inner side suppression member 27b suppresses air flow. It becomes a part. The cylindrical gap 28 may be in the form of an annular gap having a shorter length. The outer side suppression member 27a and the inner side suppression member 27b itself do not have air permeability.

The ratio (S ₂ / S ₁ ) between the cross-sectional area (S ₂ ) in the width direction of the cylindrical gap 28 and the cross-sectional area (S ₁ ) in the width direction of the first space 21 is preferably 0.001 to 0.5. More preferably, it is 0.001-0.4, More preferably, it is 0.005-0.3. When S ₁ and S ₂ satisfy the above relationship, it is preferable for releasing fine bubbles from the first pore group and releasing larger bubbles from the second pore group.

FIG. 3C shows a form in which the cylindrical gap 38 is formed by only one air flow suppressing member 37, and satisfies the same S ₂ / S ₁ relationship as described above. In the form of FIG. 3 (c), instead of the airflow suppression member 37, the corresponding portion of the air diffuser 12 is recessed or thickened so that a similar cylindrical gap (or annular gap) 38 is formed. Then, a constricted portion corresponding to the cylindrical gap (or annular gap) 38 may be formed.

<Hollow fiber membrane module>
FIG. 4 is a front view of the hollow fiber membrane module 100. Although the hollow fiber membrane element 10A is used in FIG. 4, the hollow fiber membrane element 10B may be used.

  A total of 12 hollow fiber membrane elements 10A (6 are not visible from the front side on the opposite side) are attached to the frame 101. The shape and structure of the frame body 101 are not particularly limited as long as the hollow fiber membrane element 10A can be fixed and held.

  The air introduction pipes 18 communicated with the air diffusion pipes 12 of the hollow fiber membrane element 10A are connected to two air supply pipes 105 (one is not visible from the front on the opposite side). Are connected to two water collecting main pipes 106 (one is not visible from the front on the opposite side) via the upper water collecting cap 31 and the communication pipe 36.

  Although the shape and structure of the communication pipe 36 are not particularly limited, a structure including a socket part 71 and a stud part 72 as shown in FIG. 4 of JP-A-2007-296432 can be used. As such a socket part 71 and the stud part 72, a brand name one-touch socket (made by Wamoto Co., Ltd.) etc. can be used, for example. This is a so-called one-touch type, and can be easily attached or removed with one hand, so the membrane element can be easily replaced.

  Next, the operation when the hollow fiber membrane element 10A shown in FIG. 1 is used in the hollow fiber membrane module 100 of FIG. 4 will be described.

  The hollow fiber membrane module 100 is used by being immersed in a biological treatment tank. The pump connected to the permeated water line is operated, and suction filtration is performed from the upper cap 31 side of the hollow fiber membrane element 10A.

  The permeated water filtered by the hollow fiber membrane bundle 20 flows into the upper water collecting chamber 35 and the lower water collecting chamber 45 located at both ends of the hollow fiber membrane bundle 20. The permeated water that has flowed into the upper water collecting chamber 35 passes through the communication pipe 36 and moves into the water collecting main pipe 106 and is sent to the permeated water line. The permeated water that has flowed into the lower water collecting chamber 45 flows into the upper water collecting chamber 35 through the water collecting pipe 13, and then moves into the water collecting main pipe 106 through the communication pipe 36. Sent to the line.

  In such a filtration operation, the hollow fiber membrane element 10A performs aeration in the biological treatment tank and aeration for cleaning the membrane surface (that is, for suppressing the amount of filtration cake formed on the membrane surface). Do. Aeration and aeration may be performed continuously from the start of operation or may be performed at appropriate intervals. Moreover, aeration and aeration may be performed in parallel or separately.

  Air is supplied in a pressurized state from the two air supply pipes 105 and is continuously fed into the diffuser pipe 12 through the air introduction pipe 18 of each hollow fiber membrane element 10A. The air sent into the air diffusing tube 12 is operated by the airflow suppressing member 17 (in FIGS. 3A and 3B, the cylindrical gap 28 formed by the airflow suppressing member 27 performs the same operation. In (c), the smooth movement from the first space 21 to the second space 22 is suppressed by the cylindrical gap 38 formed by the airflow suppression member 37 having the same action. For this reason, the pressure in the first space 21 is increased, and the cylindrical rubber membrane 14b expands to form fine holes, from which fine bubbles suitable for aeration are ejected. Since the amount of dissolved oxygen per unit time can be increased as the bubble diameter is finer, the biological treatment speed is also improved.

  As the pressure in the first space 21 rises, the air passes through the ventilation suppression member 17 and moves into the second space 22. Then, large bubbles suitable for cleaning the membrane surface are ejected from the second pore group 16. The ejected bubbles move from the inner side to the outer side and from the lower side to the upper side of the hollow fiber membrane bundle 20, so that the entire hollow fiber membrane bundle 20 is vibrated and the hollow fibers constituting the hollow fiber membrane bundle 20. When the bubbles come into contact with the film, the dirt on the film surface is removed.

  The hollow fiber membrane module 100 collects water from both ends, but collecting water from both ends increases the water collection efficiency (filtering amount per unit time), but stains the entire length of the hollow fiber membrane bundle 20 in the length direction. Will adhere. However, in the present invention, the support tube 11 has a double structure of the air diffusion tube 12 and the water collecting tube 13 and can diffuse air from the inside to the outside of the hollow fiber membrane bundle 20, so that the entire hollow fiber membrane bundle 20 can be easily cleaned. It is easy to recover the filtration performance.

The longitudinal end view of the hollow fiber membrane element of this invention. The longitudinal end view of the hollow fiber membrane element of the present invention which is another embodiment. (A) is a longitudinal end view of the hollow fiber membrane element of the present invention which is another embodiment, (b) is a partial sectional view of (a), and (c) is a partial sectional view of another embodiment different from (a). The front view of the hollow fiber membrane module of this invention.

Explanation of symbols

10A, 10B Hollow fiber membrane element 11 Support tube 12 Aeration tube 13 Water collecting tube 15a Upper fixing member 15b Lower fixing member 16 Ventilation holes 17, 27, 37 Ventilation suppression members 19a, 19b Adapter 18 Air introduction tube 20 Hollow fiber membrane bundle 31 Upper portion Catch cap 35 Upper catchment chamber 41 Lower catchment cap 45 Lower catchment chamber

Claims (11)

A hollow fiber membrane element in which a number of hollow fiber membranes are arranged around a support tube,
The support pipe is of a double pipe structure having an outer diffuser pipe and a water collecting pipe disposed inside the diffuser pipe;
The air diffusion pipe is connected to one end side from an external air introduction pipe, the first pore group formed at a position closer to the other end side than the air introduction pipe, and the first pore group And the second pore group separated and formed at a position close to the other end side, the average pore diameter of the first pore group is smaller than the average pore diameter of the second pore group,
Furthermore, the hollow fiber membrane element in which the said air diffusing tube has an air flow suppressing portion that generates air flow resistance formed in the air flow path between the first pore group and the second pore group.   The hollow fiber membrane element according to claim 1, wherein the air flow suppressing portion is a portion where a gas flow suppressing member made of a porous material is disposed in the air flow path. The porous consist material ventilation suppressing member, the bulk density is of 0.50~0.90g / cm ^3, the hollow fiber membrane element according to claim 2, wherein.   The hollow fiber membrane element according to claim 2, wherein the air flow suppressing member made of the porous material has a porosity of 20 to 50%.   The hollow fiber membrane element according to claim 1, wherein the ventilation suppression site is a site where a cross-sectional area in the width direction of the ventilation channel is reduced. The site of the cross-sectional area in the width direction is reduced in the ventilation path, the ratio of the cross-sectional area S ₁ of the vent path extending to the site and the sectional area S ₂ of the portion (S 2 _{/ S 1)} is 0. The hollow fiber membrane element according to claim 5, which is in the range of 001 to 0.5.   The first pore group is a micropore having a stretchable porous member that covers the surface of the pore group formed in the diffuser tube, and the second pore group is a pore group formed in the diffuser tube. The hollow fiber membrane element according to any one of claims 1 to 6, wherein   Both ends of the support tube and both ends of a large number of hollow fiber membranes are fixed to an upper water collecting cap and a lower water collecting cap, respectively, and collected from both ends. The hollow fiber membrane element as described. An immersion filtration type hollow fiber membrane module comprising a plurality of hollow fiber membrane elements according to any one of claims 1 to 8,
The water collecting pipes of the plurality of hollow fiber membrane elements are connected to one or more water collecting main pipes,
An immersion filtration type hollow fiber membrane module in which the diffuser pipes of the plurality of hollow fiber membrane elements are connected to an air supply pipe via an air introduction pipe.   9. The immersion filtration type hollow fiber membrane module according to claim 8, wherein the plurality of hollow fiber membrane elements are supported by a frame.   The plurality of hollow fiber membrane elements are detachably connected to the water collecting main pipe at least at the upper end side, and the water collecting pipes of the plurality of hollow fiber membrane elements communicate with the water collecting main pipe, respectively. The hollow filtration membrane module of the immersion filtration system according to claim 9 or 10.

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