JP7708586B2 - Hollow fiber membrane module - Google Patents

Description

The present invention relates to a hollow fiber membrane module equipped with multiple hollow fiber membranes.

Conventionally, hollow fiber membrane modules with multiple bundled hollow fiber membranes have been used in water treatment to remove impurities from water. In the filtration process of water treatment, raw water (water before filtration) is supplied into the hollow fiber membrane module through a raw water inlet provided in the module, and the filtered water that has passed through the membrane is discharged outside the module through a filtered water outlet provided in the module.

In hollow fiber membrane modules, when the filtration process of water treatment is performed, substances removed from the water (suspended solids (SS)) accumulate on the membrane surface. Thus, one of the important challenges is to efficiently remove the suspended solids that have accumulated on the membrane surface.

Generally, suspended pollutants are removed by a process known as backwashing (back pressure washing). In the backwashing process, a fluid flow in the opposite direction to the filtration process is created inside the module in order to lift suspended pollutants adhering to the membrane surface from the membrane. That is, fluids such as gas and liquid are supplied into the module through the filtrate outlet, and the fluid that passes through the membrane from the inside to the outside is discharged outside the module through the raw water inlet.

In this way, the suspended pollutants that have become partially suspended from the membrane surface as a result of the backwash process are then peeled off from the membrane surface by the bubbling process. In this bubbling process, cleaning gas is supplied to the module while it is filled with water, and the membrane is shaken by the bubbles of the supplied cleaning gas, causing the suspended pollutants on the membrane surface to peel off.

In the bubbling process, in order to more effectively remove suspended pollutants that have accumulated on the membrane surface, it is necessary to strongly rock the hollow fiber membrane. However, excessive rocking can cause abrasion due to contact between the hollow fiber membranes, breakage near the fixed parts of the hollow fiber membrane, and tangling of the hollow fiber membranes, making stable operation difficult. The following Patent Document 1 discloses a hollow fiber membrane module equipped with a configuration for appropriately rocking the hollow fiber membranes in the bubbling process.

In the hollow fiber membrane module described in Patent Document 1 below, a net-like object is provided to cover the entire hollow fiber membrane bundle in which multiple hollow fiber membranes are fixed in a bundle shape at the upper end.

Japanese Patent Application Publication No. 9-262441

In the above-mentioned Patent Document 1, all of the hollow fiber membranes constituting the hollow fiber membrane module are bundled into one hollow fiber membrane bundle, and this one hollow fiber membrane bundle is entirely covered with a net-like material. In this case, the oscillation of all of the hollow fiber membranes during the bubbling process is restricted by the same net-like material, so suspended pollutants attached to the membrane surface cannot be effectively removed. Furthermore, in a structure in which the entire hollow fiber membrane bundle is covered with a net-like material, there is a risk that the lower end of the hollow fiber membrane will get into the mesh of the net-like material due to the oscillation during the bubbling process. In this case, the hollow fiber membranes will become entangled with the net-like material, causing problems such as damage to the hollow fiber membranes.

The present invention was made in consideration of the above problems, and its purpose is to provide a hollow fiber membrane module that can effectively remove suspended pollutants that adhere to the membrane surface of the hollow fiber membrane during the bubbling process while suppressing tangling and damage to the hollow fiber membrane.

A hollow fiber membrane module according to one aspect of the present invention includes a housing having a fixing member fixed therein and forming an internal space, a plurality of hollow fiber membrane bundles each having a plurality of hollow fiber membranes and arranged in the internal space with upper ends of the plurality of hollow fiber membranes fixed to the fixing member, a gas supply unit supplying gas for cleaning the plurality of hollow fiber membrane bundles to the internal space, and a suppression member individually provided for each of the plurality of hollow fiber membrane bundles. Each of the suppression members is fixed to a side surface of the housing with its upper end spaced apart from the fixing member, and is configured to suppress the lower ends of the plurality of hollow fiber membranes from flying up in the corresponding hollow fiber membrane bundle while allowing the plurality of hollow fiber membranes to oscillate due to the gas supplied from the gas supply unit into the internal space.

According to this hollow fiber membrane module, the hollow fiber membranes constituting the hollow fiber membrane module are divided into a plurality of hollow fiber membrane bundles with their upper ends fixed to a fixing member, and each of the plurality of hollow fiber membrane bundles is provided with an individual suppression member. As a result, each hollow fiber membrane bundle is independent of the others due to the suppression member. Therefore, in the bubbling process in response to the supply of cleaning gas by the gas supply unit, the plurality of hollow fiber membranes oscillate within the hollow fiber membrane bundles in an independent state. As a result, the floating contaminants attached to the membrane surface are peeled off, but at this time, since each hollow fiber membrane bundle is independent of the others due to the suppression member, the floating contaminants peeled off from the membrane surface of the plurality of hollow fiber membranes within each hollow fiber membrane bundle can be discharged through the hollow fiber membrane bundles. As a result, the floating contaminants attached to the membrane surface of the hollow fiber membrane within each hollow fiber membrane bundle can be effectively removed. Moreover, the suppression member keeps each hollow fiber membrane bundle independent of the others, suppressing interference between hollow fiber membranes belonging to different hollow fiber membrane bundles. This makes it possible to suppress entanglement of hollow fiber membranes between hollow fiber membrane bundles and to suppress damage to the hollow fiber membranes that would otherwise occur.

The suppression member that keeps each hollow fiber membrane bundle independent is configured to suppress the bottom ends of the hollow fiber membranes from flying up while allowing the hollow fiber membranes to oscillate within the hollow fiber membrane bundle. In this way, the suppression member suppresses the bottom ends of the hollow fiber membranes from flying up within the hollow fiber membrane bundle, thereby restricting excessive movement of the hollow fiber membranes within the hollow fiber membrane bundle. This makes it possible to suppress excessive interference between the hollow fiber membranes, such as entanglement between hollow fiber membranes belonging to the same hollow fiber membrane bundle, and to suppress associated damage to the hollow fiber membranes.

In the hollow fiber membrane module described above, each of the suppression members may be configured as a mesh-like body having multiple meshes and extending in the vertical direction so as to cover the side surface of the corresponding hollow fiber membrane bundle. In this case, the lower ends of the suppression members are each located at a position capable of suppressing the lower ends of the multiple hollow fiber membranes oscillating within the corresponding hollow fiber membrane bundle from flying up, and capable of suppressing the lower ends of the multiple hollow fiber membranes from entering the meshes.

In this embodiment, the lower end of the suppression member, which is formed of a mesh-like body covering the side surface of the hollow fiber membrane bundle, is located at a position that can suppress the lower ends of the multiple hollow fiber membranes oscillating within the hollow fiber membrane bundle from flying up and can suppress the lower ends of the multiple hollow fiber membranes from entering the mesh. The suppression member suppresses the lower ends of the multiple hollow fiber membranes in the hollow fiber membrane bundle from flying up, thereby suppressing the hollow fiber membranes from becoming entangled with each other within the hollow fiber membrane bundle. Furthermore, by setting the position of the lower end of the suppression member so that it is possible to suppress the lower ends of the hollow fiber membranes from entering the mesh of the suppression member, it is possible to regulate the hollow fiber membranes from becoming entangled with the suppression member. This makes it possible to suppress damage to the hollow fiber membranes.

In the above hollow fiber membrane module, the upper ends of the suppression members may be fixed to the fixing members, and the lengths of the suppression members in the up-down direction may be set so as to satisfy the following formula (1):
0.7≦L1/L2≦1.0 (1)

In the above formula (1), "L1" indicates the vertical length of the suppression member, and "L2" indicates the effective length of the hollow fiber membrane.

In this embodiment, the vertical length of the suppression member, which is made of a mesh that covers the side surface of the hollow fiber membrane bundle, is set to satisfy the above formula (1). By setting the length of the suppression member to satisfy the left side of the above formula (1), "0.7≦L1/L2", the lower end of the suppression member can be positioned at a position that can suppress the lower ends of the multiple hollow fiber membranes from flying up. On the other hand, by setting the length of the suppression member to satisfy the right side of the above formula (1), "L1/L2≦1.0", the lower end of the suppression member can be positioned at a position that can suppress the lower ends of the multiple hollow fiber membranes from entering the mesh of the suppression member.

In the hollow fiber membrane module described above, each of the suppression members may be configured to have a function of separating the hollow fiber membrane bundles so that gaps are formed between the hollow fiber membrane bundles.

In this embodiment, the suppression member forms gaps between the hollow fiber membrane bundles, so that suspended pollutants that are peeled off in response to the oscillation of the hollow fiber membranes in each hollow fiber membrane bundle during the bubbling process can be discharged through the gaps between the hollow fiber membrane bundles. This can further enhance the effect of removing suspended pollutants that have adhered to the membrane surface of the hollow fiber membranes.

In the above hollow fiber membrane module, the gas supply unit may be configured to include an air diffusion member that is disposed below the hollow fiber membrane bundle, has a shape that spreads in the radial direction of the hollow fiber membrane bundle, and has a plurality of air diffusion holes formed at intervals in the radial direction. In this case, the air diffusion member includes a plate-shaped main body portion that spreads in the radial direction of the hollow fiber membrane bundle and has a plurality of air diffusion holes formed at intervals in the radial direction, and a gas receiving portion that has a cylindrical shape with one end connected to the lower surface of the main body portion and a gas receiving port formed on the other end side, and has a diffusion hole formed for guiding the gas contained in the cylinder to the air diffusion holes.

In addition, in the hollow fiber membrane module described above, the gas receiving portion may be configured to have an inner diameter that increases from the one end toward the other end.

In addition, in the hollow fiber membrane module described above, the aeration vents may be arranged on multiple circumferences spaced apart in the radial direction in the main body, and the number of the aeration vents on each circumference may be a multiple of the number of the hollow fiber membrane bundles.

As described above, the present invention can provide a hollow fiber membrane module that can effectively remove suspended pollutants adhering to the membrane surface of the hollow fiber membrane during the bubbling process while suppressing tangling and damage to the hollow fiber membrane.

1 is a schematic diagram showing a configuration of a filtration device according to an embodiment of the present invention. FIG. 1 is a diagram showing a configuration of a hollow fiber membrane module according to a first embodiment of the present invention. FIG. 2 is a diagram showing a planar structure of an air diffusing member provided in the hollow fiber membrane module. 4 is a diagram showing a cross-sectional structure of the air diffusing member taken along line IV-IV in FIG. 3. 3 is a diagram showing a cross-sectional structure of the water pipe taken along line V-V in FIG. 2. FIG. 3 is an enlarged view of a water pipe in region VI in FIG. 2 . FIG. 1 is a perspective view showing a state in which a suppression member is provided for each hollow fiber membrane bundle in a hollow fiber membrane module. FIG. 2 is a top view showing a state in which a suppression member is provided for each hollow fiber membrane bundle in a hollow fiber membrane module. FIG. 2 is a diagram showing a basic operating program of the filtration device. FIG. 11 is a perspective view showing a state in which a suppression member is provided for each hollow fiber membrane bundle in a hollow fiber membrane module according to a second embodiment of the present invention. FIG. 11 is a perspective view showing a state in which a suppression member is provided for each hollow fiber membrane bundle in a hollow fiber membrane module according to a third embodiment of the present invention. FIG. 13 is a perspective view showing a state in which a suppression member is provided for each hollow fiber membrane bundle in a hollow fiber membrane module according to a fourth embodiment of the present invention. FIG. 13 is a perspective view showing a state in which a suppression member is provided for each hollow fiber membrane bundle in a hollow fiber membrane module according to a fifth embodiment of the present invention.

The following describes in detail the embodiment of the present invention with reference to the drawings.

First Embodiment
[Filtration equipment, hollow fiber membrane module]
First, the configuration of a filtration device 1 including a hollow fiber membrane module 10 according to a first embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic diagram showing the configuration of the filtration device 1. Fig. 2 is a schematic diagram showing the configuration of the hollow fiber membrane module 10.

The filtration device 1 has an external pressure filtration type hollow fiber membrane module 10, a liquid delivery pump 20, an air compressor 30, piping connecting these, an on-off valve provided on the piping, and a control device 40. The hollow fiber membrane module 10 is an external pressure filtration type module that supplies raw liquid to the outer surface side of the hollow fiber membrane and extracts filtrate from the inner surface side.

As shown in FIG. 2, the hollow fiber membrane module 10 includes a housing 13 to which a fixing member 3 is fixed and which forms an internal space S1, a plurality of hollow fiber membrane bundles 15 arranged in the internal space S1, a water guide pipe (pipe member) 5 for introducing raw water into the internal space S1, a gas supply unit 2 for supplying gas (cleaning gas) for cleaning the plurality of hollow fiber membrane bundles 15 to the internal space S1, and a suppression member 100 provided individually for each of the plurality of hollow fiber membrane bundles 15.

Each of the hollow fiber membrane bundles 15 has a plurality of hollow fiber membranes 14, and the upper ends 14B of the hollow fiber membranes 14 are fixed to the fixing member 3 in an open state, and the lower ends 14A of the hollow fiber membranes 14 are sealed in an unfixed state. The fixing member 3 converges and fixes the upper ends 14B of the hollow fiber membranes 14 for each hollow fiber membrane bundle 15. The fixing member 3 liquid-tightly divides the space within the housing 13 into an internal space S1 on the raw water side and a space S2 on the filtrate side to allow the hollow fiber membranes 14 to function as a filtration membrane. Thermosetting resins such as epoxy resins, unsaturated polyester resins, and polyurethane resins are used for the fixing member 3. Methods for bonding each hollow fiber membrane bundle 15 to the fixing member 3 include centrifugal bonding and static bonding.

Various materials can be used as the material of the hollow fiber membrane 14, and there is no particular limitation. For example, it is preferable to include at least one selected from the group consisting of polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polysulfone, cellulose acetate, polyvinyl alcohol, and polyethersulfone, and polyvinylidene fluoride (PVDF) is more preferable in terms of membrane strength and chemical resistance.

The hollow fiber membrane module 10 is of the external pressure filtration type, and may be of the external pressure total flow filtration type or the external pressure circulation filtration type depending on the conditions of the membrane separation process and the required performance. From the viewpoint of membrane life, the external pressure circulation filtration type is preferred because it allows simultaneous surface cleaning of the filtration membrane, while the external pressure total flow filtration type is preferred from the viewpoints of simplicity of the equipment, installation costs, and operating costs.

The hollow fiber membrane module 10 can be operated at a higher filtration flow rate because the membrane area per module increases as the total number of hollow fiber membranes 14 constituting each hollow fiber membrane bundle 15 increases, but the efficiency of discharging suspended pollutants during cleaning decreases. Therefore, the membrane packing rate 100πndi2/4S(%) calculated from the outer diameter di(m) of the hollow fiber membrane 14, the total number n (pieces) of hollow fiber membranes 14, and the cross-sectional area ^S ( ^m2 ) of the housing 13 is preferably 10 to 60%, and more preferably 20 to 50%.

The housing 13 has a cylindrical shape with an upper surface 13A, a lower surface 13C, and a side surface 13B connecting them. The housing 13 has an internal space S1 in which multiple hollow fiber membrane bundles 15 are housed, and the internal space S1 is divided into an upper space S11 in which the upper portion of the hollow fiber membranes 14 is located above the center in the longitudinal direction (vertical direction), and a lower space S12 in which the lower portion of the hollow fiber membranes 14 is located below the center in the longitudinal direction.

A filtrate pipe 51 for extracting the filtrate is connected to the upper surface 13A of the housing 13, and the filtrate pipe 51 is provided with a filtrate outlet 52 and a filtrate-side gas inlet 53. A gas vent port 11 for discharging the gas in the internal space S1 to the outside of the system is provided directly below the fixing member 3 on the side surface 13B. The gas vent port 11 is an opening of the upper space S11. A drain outlet 12 for discharging the liquid in the internal space S1 to the outside of the system is provided directly above the lower surface 13C on the side surface 13B. A gas diffuser inlet 7 for supplying gas to the internal space S1 is provided near the center of the lower surface 13C.

As shown in FIG. 1, a gas vent pipe 61 is connected to the gas vent port 11, and gas within the housing 13 is discharged to the outside of the system through this. A gas discharge port valve 62 is provided on the gas vent pipe 61, and gas is discharged from within the housing 13 by opening this valve. A drain pipe 41 is connected to the drain vent port 12, and liquid within the housing 13 is discharged to the outside of the system through this valve. A raw liquid discharge port valve 42 is provided on the drain pipe 41, and liquid is discharged from the housing 13 by opening this valve.

Materials used for the housing 13 include SUS, modified PPE, polyvinyl chloride, polysulfone, polycarbonate, polyolefin, ABS resin, etc. The fixing member 3 may be adhesively fixed to the inner surface of the housing 13 to form a so-called integrated module. An O-ring or packing may also be attached to the outer periphery of the fixing member 3, so that the fixing member 3 is detachably and liquid-tightly attached to the housing 13. In this case, the fixing member 3 can be removed and each hollow fiber membrane bundle 15 replaced, allowing the housing 13 to be used repeatedly.

2, the water conduit 5 is disposed in a position in which it penetrates the center of the lower surface 13C of the housing 13 and extends toward the upper surface 13A, and its upper end is connected to the fixed member 3. The water conduit 5 has a raw liquid inlet 9 at its lower end and a gas inlet 8 for the water conduit on its side. With the water conduit 5, only the raw water before filtration introduced from the raw liquid inlet 9 can be supplied into the housing 13, and only the gas introduced from the gas inlet 8 for the water conduit can be supplied into the housing 13, and both raw water and gas can be supplied into the housing 13. The water conduit 5 constitutes part of the gas supply unit 2.

The gas supply unit 2 has the above-mentioned water guide pipe 5 and the air diffusion member 4. The air diffusion member 4 is a member for dispersing the gas supplied into the housing 13 from the air diffusion gas inlet 7 provided on the underside 13C of the housing 13 so that the gas spreads in the radial direction of each hollow fiber membrane bundle 15. The air diffusion member 4 is disposed below the multiple hollow fiber membrane bundles 15, and the water guide pipe 5 penetrates through the center of the air diffusion member 4. The detailed structures of the water guide pipe 5 and the air diffusion member 4 will be described later.

The suppression member 100 is provided individually for each of the multiple hollow fiber membrane bundles 15. Each suppression member 100 is a member that controls the movement of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 when gas is being supplied to the internal space S1 of the housing 13 by the gas supply unit 2. The detailed structure of the suppression member 100 will be described later.

As shown in FIG. 1, the liquid delivery pump 20 is connected to the raw liquid inlet 9 of the water conduit 5 via the raw liquid introduction pipe 21. The raw liquid introduction pipe 21 is provided with a raw liquid introduction valve 22 that switches between flow and blocking of raw water in the pipe. The liquid delivery pump 20 supplies raw water into the water conduit 5 via the raw liquid introduction pipe 21.

The air compressor 30 is connected to the filtrate-side gas inlet 53 via the first gas introduction pipe 31, to the gas inlet 7 for diffusion via the second gas introduction pipe 32, and to the gas inlet 8 for the water guide pipe via the third gas introduction pipe 33. The first gas introduction pipe 31 is provided with a first gas introduction valve 34 for switching between flow and blocking of gas in the pipe, and the second and third gas introduction pipes 32, 33 are similarly provided with second and third gas introduction valves 35, 36. Thus, in this embodiment, the third gas introduction pipe 33 and the third gas introduction valve 36 as gas supply means for the water guide pipe 5, and the second gas introduction pipe 32 and the second gas introduction valve 35 as gas supply means for the diffusion member 4 are provided separately.

The control device 40 controls the operation of the liquid delivery pump 20 and the air compressor 30, and also controls the opening and closing of each valve. The control device 40 is configured, for example, by a personal computer. The control device 40 has a memory unit that stores sequence information for each process (filling with water, filtration, backwashing, bubbling, drainage, etc.) that is executed sequentially in the filtration process, and a control unit that controls the operation of each device and the opening and closing of the valves according to the sequence information.

[Aeration components, water pipes]
Next, the detailed structures of the air diffusing member 4 and the water guide pipe 5 will be described with reference to Figures 2 to 5. Figure 3 shows the planar structure of the air diffusing member 4. Figure 4 shows the cross-sectional structure of the air diffusing member 4 taken along line segment IV-IV in Figure 3. Figure 5 shows the cross-sectional structure of the water guide pipe 5 taken along line segment V-V in Figure 2. In the hollow fiber membrane module 10, the gas supply unit 2 which supplies a gas (e.g., air) for cleaning the hollow fiber membranes 14 while dispersing it into the internal space S1 of the housing 13 has the air diffusing member 4 and the water guide pipe 5.

The air diffusion member 4 is disposed below the lower end 14A of the hollow fiber membranes 14 that constitute each hollow fiber membrane bundle 15. The air diffusion member 4 has a shape that spreads in the radial direction of each hollow fiber membrane bundle 15. The air diffusion member 4 has a plurality of air diffusion vents 43 formed at intervals in the radial direction for dispersing gas within the housing 13.

The air diffusion member 4 has a disk-shaped main body 44 with multiple air diffusion holes 43 formed therein, a peripheral wall 47 connected to the periphery of the main body 44, and a cylindrical gas receiving portion 45 connected to the underside of the main body 44, which are integrally formed.

The air diffusion holes 43 are formed so as to penetrate the main body 44 in the thickness direction. The air diffusion holes 43 are formed at intervals from each other in the radial and circumferential directions of the main body 44, and some of them are located radially outward from each hollow fiber membrane bundle 15. This allows the gas to be dispersed over a wide range in the radial direction for each hollow fiber membrane bundle 15. As shown in FIG. 3, the air diffusion holes 43 are arranged on multiple circumferences spaced apart in the radial direction in the main body 44. In this case, the number of air diffusion holes 43 on each circumference is set to be a multiple of the number of hollow fiber membrane bundles 15. Specifically, the number of air diffusion holes 43 on each circumference is set to be a multiple of the number of hollow fiber membrane bundles 15 so that the number of air diffusion holes 43 corresponding to each hollow fiber membrane bundle 15 is the same. In addition, a through hole 44A through which the water guide pipe 5 passes is formed in the center of the main body 44. The main body 44 is not limited to a disk shape as shown in FIG. 3, but may have various shapes.

The gas receiving portion 45 is a portion for temporarily storing the gas supplied from the gas inlet 7 into the housing 13. The gas receiving portion 45 has a cylindrical shape, with its upper end (one end) connected to the lower surface of the main body portion 44 and a gas receiving port 45A formed on its lower end (the other end). In this embodiment, the gas receiving portion 45 is configured so that the inner diameter is approximately constant from the upper end to the lower end. The gas receiving portion 45 may be configured so that the inner diameter increases from the upper end to the lower end. The gas receiving portion 45 has an inner diameter larger than the outer diameter of the water conduit 5 and stores gas in the gap between the gas receiving portion 45 and the outer peripheral surface of the water conduit 5.

The gas receiving portion 45 is located radially outward of the gas inlet 7 for diffusion, so that the gas supplied from the gas inlet 7 for diffusion into the housing 13 can be contained within the cylinder. As shown in FIG. 2, a gap is formed between the lower end of the gas receiving portion 45 and the lower wall of the housing 13, so that the liquid within the housing 13 can flow through the gap. This makes it possible to prevent liquid from accumulating at the bottom of the housing 13.

A plurality of dispersion holes 46 are formed at intervals in the circumferential direction at the upper end portion of the gas receiving portion 45. The dispersion holes 46 are formed so as to penetrate the gas receiving portion 45. The dispersion holes 46 allow the gas contained in the gas receiving portion 45 to escape radially outward from the gas receiving portion 45 and be guided to the air diffusion vent 43. The dispersion holes 46 may be formed at equal intervals in the circumferential direction, or may be formed at different intervals.

The peripheral wall portion 47 has a cylindrical shape that extends downward from the peripheral edge of the main body portion 44. The peripheral wall portion 47 can prevent the gas released from the dispersion hole 46 to the outside of the gas receiving portion 45 from spreading outward beyond the main body portion 44. This allows the gas to be retained on the underside of the main body portion 44 before it is dispersed from the air diffusion vent 43.

In the bubbling process, the gas supplied from the gas inlet 7 to the housing 13 is temporarily stored in the gas receiving portion 45, and then released to the outside through the diffusion hole 46, and then dispersed from the diffusion vent 43 to the lower space S12. In other words, in this embodiment, the diffusion vent 43 functions as a lower gas supply portion that diffuses gas into the housing 13 at a position lower than the lower space S12.

The water conduit 5 is arranged to extend vertically through the center of the housing 13. The water conduit 5 has a cylindrical shape, but is not limited to this. As shown in FIG. 2, the water conduit 5 passes through the aeration member 4 (main body 44), and the lower end is fixed to the raw liquid introduction pipe 21 (FIG. 1) via an optional sealing member (not shown). The method of fixing the water conduit 5 is not limited to this, and a separate pipe that protrudes above the upper surface of the main body 44 may be provided, and the water conduit 5 may be placed on the upper surface of the main body 44 so that the protruding portion is located inside the water conduit 5.

In the water conduit 5, a plurality of pipe vents 54 are formed at intervals along the entire longitudinal direction (vertical direction) in the portion protruding above the upper surface of the main body 44. More specifically, a plurality of pipe vents 54 are formed at intervals in the portion of the water conduit 5 located in the upper space S11, and a plurality of pipe vents 54 are also formed at intervals in the portion of the water conduit 5 located in the lower space S12. These pipe vents 54 can supply bubbling gas (cleaning gas) into the housing 13, and can also supply raw water filtered by the hollow fiber membrane 14 into the housing 13. The pipe vents 54 may be formed at equal intervals along the longitudinal direction, or may be formed at different intervals. The pipe vents 54 are circular, but are not limited to this.

The multiple pipe vents 54 are formed to be the same size in the longitudinal direction of the water conduit 5. The inner diameter of the pipe vents 54 is preferably designed to be 30 mm or less to enhance the bubbling effect. In addition, the inner diameter of the pipe vents 54 is preferably designed so that the total discharge flow rate of the raw water from each hole is 4 m/s or less, and more preferably 3 m/s or less, to reduce pressure loss during water flow.

As shown in FIG. 2, the pipe vent 54A formed at the top of the water pipe 5 is located above the bottom surface 11A of the gas vent port 11, and the second pipe vent 54B from the top is located below the bottom surface 11A. In other words, the water pipe 5 has pipe vents 54A and 54B formed at positions that sandwich the bottom surface 11A of the gas vent port 11 in the vertical direction.

As shown in FIG. 5, four pipe vents 54 are formed at equal intervals in the circumferential direction of the water conduit 5. In this embodiment, four pipe vents 54 are formed at 90° intervals in both the portion located in the upper space S11 and the portion located in the lower space S12, but the number and circumferential spacing are not particularly limited. In addition, the number and circumferential spacing of the pipe vents 54 may differ between the portion located in the upper space S11 and the portion located in the lower space S12.

Figure 6 is an enlarged view of the water conduit 5 in region VI in Figure 2. The aperture ratio of the pipe vents 54 in the water conduit 5 can be defined as follows. As shown in the shaded area in Figure 6, the area of the outer surface of the water conduit 5 in the range from the mid-height position of the uppermost pipe vent 54A to the mid-height position of the pipe vent 54B below it is S1, and the total aperture area of all the pipe vents 54A and 54B formed on the outer surface in that range is S2. The aperture ratio of the pipe vents can be defined as S2/S1 x 100. In this embodiment, it is preferable to design the aperture ratio to be 1% or more and 20% or less.

The water conduit 5 allows raw water to be supplied into the housing 13 from the pipe vent 54, and allows the gas introduced from the water conduit gas inlet 8 to rise by buoyancy and be dispersed into the housing 13 from the pipe vents 54A and 54B located in the upper space S11. In other words, in this embodiment, the pipe vents 54A and 54B function as upper gas supply units that disperse gas into the housing 13 at the position of the upper space S11.

The length of the water pipe 5 inserted into the housing 13 is preferably 1 to 2 times, and more preferably 1 to 1.5 times, the length of the hollow fiber membrane 14 so as to prevent the hollow fiber membrane module 10 from becoming bulky.

The inner diameter of the water conduit 5 is preferably designed so that the flow rate of water is 4 m/s or less, and more preferably 3 m/s or less, in order to reduce pressure loss during water flow.

[Suppression member]
Next, the detailed structure of the suppression member 100 will be described with reference to Fig. 2 as well as Fig. 7 and Fig. 8. In the hollow fiber membrane module 10 according to this embodiment, the hollow fiber membranes 14 constituting the hollow fiber membrane module 10 are divided into a plurality of hollow fiber membrane bundles 15 with the upper ends 14B fixed to the fixing member 3. The plurality of hollow fiber membrane bundles 15 are arranged in the internal space S1 of the housing 13 at equal intervals in the circumferential direction so as to surround the water guide pipe 5. In the example shown in Fig. 8, six hollow fiber membrane bundles 15 are arranged so as to surround the water guide pipe 5, but the number of hollow fiber membrane bundles 15 arranged is not particularly limited as long as it is two or more.

The suppression member 100 is provided individually for each of the multiple hollow fiber membrane bundles 15. As a result, each hollow fiber membrane bundle 15 is independent of each other due to the suppression member 100. Therefore, during the bubbling process in which cleaning gas is supplied to the internal space S1 of the housing 13 by the gas supply unit 2, the multiple hollow fiber membranes 14 oscillate within the hollow fiber membrane bundles 15 that are independent of each other.

The multiple hollow fiber membranes 14 in each hollow fiber membrane bundle 15 oscillate to cause floating pollutants attached to the membrane surface to peel off, but since the hollow fiber membrane bundles 15 are independent of each other due to the suppression member 100, the floating pollutants peeled off from the membrane surface of the multiple hollow fiber membranes 14 in each hollow fiber membrane bundle 15 can be discharged through the hollow fiber membrane bundles 15. This allows the floating pollutants attached to the membrane surface of the hollow fiber membranes 14 in each hollow fiber membrane bundle 15 to be effectively removed. Moreover, since the hollow fiber membrane bundles 15 are independent of each other due to the suppression member 100, interference between the hollow fiber membranes 14 belonging to different hollow fiber membrane bundles 15 is suppressed. This makes it possible to suppress entanglement of the hollow fiber membranes 14 between the hollow fiber membrane bundles 15, and to suppress damage to the hollow fiber membranes 14 that occurs as a result.

The suppression member 100, which keeps each hollow fiber membrane bundle 15 independent, is configured to suppress the lower ends 14A of the hollow fiber membranes 14 from flying up while allowing the hollow fiber membranes 14 to oscillate within the hollow fiber membrane bundle 15. In other words, the hollow fiber membranes 14 are suppressed from bending to such an extent that the lower ends 14A of the hollow fiber membranes 14 are positioned above the lower end 100A of the suppression member 100. The suppression member 100 suppresses the lower ends 14A of the hollow fiber membranes 14 from flying up within the hollow fiber membrane bundle 15, thereby restricting excessive movement of the hollow fiber membranes 14 within the hollow fiber membrane bundle 15. This makes it possible to suppress excessive interference between the hollow fiber membranes 14, such as entanglement between the hollow fiber membranes 14 belonging to the same hollow fiber membrane bundle 15, and to suppress damage to the hollow fiber membranes 14 that occurs as a result of this.

In addition, each suppression member 100 has the function of separating the hollow fiber membrane bundles 15 so that gaps are formed between the hollow fiber membrane bundles 15. By forming gaps between the hollow fiber membrane bundles 15 in this way by the suppression members 100, suspended pollutants that are peeled off in response to the oscillation of the hollow fiber membranes 14 within each hollow fiber membrane bundle 15 during the bubbling process can be discharged through the gaps between the hollow fiber membrane bundles 15. This can further enhance the effect of removing suspended pollutants that have adhered to the membrane surfaces of the hollow fiber membranes 14.

As shown in FIG. 7, each of the suppression members 100 has a plurality of meshes 101 and is configured as a mesh-like body extending in the vertical direction so as to cover the side surface of the corresponding hollow fiber membrane bundle 15. In this case, various materials can be used as the material for the suppression member 100, and are not particularly limited. Examples include polyethylene and polypropylene. The suppression member 100 configured as a mesh-like body has elasticity according to the deformation of the shape of the meshes 101. When the plurality of hollow fiber membranes 14 oscillate within the hollow fiber membrane bundle 15 during the bubbling process, the shape of the meshes 101 deforms and expands and contracts, thereby causing the suppression member 100 to oscillate the plurality of hollow fiber membranes 14 appropriately.

The lower end 100A of the suppression member 100, which is formed of a mesh-like body, is located within a lower end appropriate range that can suppress the lower ends 14A of the multiple hollow fiber membranes 14 oscillating within the corresponding hollow fiber membrane bundle 15 from flying up and can suppress the lower ends 14A of the multiple hollow fiber membranes 14 from entering the mesh 101. The lower end appropriate range is a range in which the lower end 100A of the suppression member 100 is spaced downward from the upper end 14B of the hollow fiber membrane 14 by a distance of 0.7 to 1.0 times the effective length L2 of the hollow fiber membrane 14. The effective length L2 of the hollow fiber membrane 14 is the vertical length of the portion of the hollow fiber membrane 14 that is exposed to the internal space S1 of the housing 13.

By suppressing the rising of the lower ends 14A of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 by the suppression member 100, it is possible to suppress the hollow fiber membranes 14 from becoming entangled with each other in the hollow fiber membrane bundle 15. Furthermore, by setting the position of the lower end 100A of the suppression member 100 so as to suppress the lower ends 14A of the hollow fiber membranes 14 from entering the mesh 101 of the suppression member 100, it is possible to restrict the hollow fiber membranes 14 from becoming entangled with the suppression member 100. This makes it possible to suppress damage to the hollow fiber membranes 14.

In this embodiment, the upper ends 100B of the suppression members 100, which are formed of a mesh-like body, are fixed to the upper ends 14B of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundles 15 and are also fixed to the fixing member 3. Specifically, the upper ends 100B of the suppression members 100 and the upper ends 14B of the multiple hollow fiber membranes 14 are fixed to the fixing member 3 so that their vertical height positions match. By fixing the upper ends 100B of the suppression members 100 to the fixing member 3, the sides of the hollow fiber membrane bundles 15 can be stably covered.

The vertical length L1 of the suppression member 100 formed of a mesh body is preferably set to satisfy the following formula (1): In the following formula (1), "L1" represents the vertical length of the suppression member 100, and "L2" represents the effective length of the hollow fiber membrane 14.
0.7≦L1/L2≦1.0 (1)

By setting the vertical length L1 of the suppression member 100 to satisfy the left side of the above formula (1) "0.7 ≦ L1/L2", the lower end 100A of the suppression member 100 can be positioned within the lower end appropriate range that can prevent the lower ends 14A of the multiple hollow fiber membranes 14 from flying up. On the other hand, by setting the vertical length L1 of the suppression member 100 to satisfy the right side of the above formula (1) "L1/L2 ≦ 1.0", the lower end 100A of the suppression member 100 can be positioned within the lower end appropriate range that can prevent the lower ends 14A of the multiple hollow fiber membranes 14 from entering the mesh 101 of the suppression member 100.

[Method for cleaning hollow fiber membrane module]
Next, the filtration operation by the filtration device 1 and the method of cleaning the hollow fiber membrane module 10 performed during the operation will be described with reference to Fig. 9. Fig. 9 shows the relationship between each step and the open/closed state of the valves in the basic operation method of the filtration device 1 shown in Fig. 1. A circle in Fig. 9 means that the corresponding valve is open.

First, the water filling process (before filtration) is carried out. In this process, all valves of the filtration device 1 are closed, and then the control device 40 opens the raw liquid inlet valve 22 and the gas outlet valve 62, and the liquid delivery pump 20 is operated. As a result, raw water is introduced from the liquid delivery pump 20 into the water conduit 5 via the raw liquid inlet piping 21, and raw water is supplied into the housing 13 through the pipe vent 54. As a result, the internal space S1 of the housing 13 is filled with water.

Next, the filtration process is carried out. In this process, after the raw water overflows from the gas vent port 11, the control device 40 opens the filtrate outlet valve 71 and closes the gas exhaust port valve 62. Then, the raw water filling the internal space S1 permeates from the outer surface side of the hollow fiber membrane 14 through the wall surface to the inner surface side, and is extracted as filtrate from the filtrate side space S2.

As the filtration time passes, suspended pollutants in the raw water adhere to the outer surface of the hollow fiber membrane 14, which reduces the filtration capacity. Therefore, after filtration has been performed for a certain period of time, the membrane surface of the hollow fiber membrane 14 is cleaned by carrying out the cleaning method for the hollow fiber membrane module 10 described below.

First, the backwash process is carried out. In this process, the control device 40 opens the raw liquid outlet valve 42 and the first gas introduction valve 34, and operates the air compressor 30. This introduces gas (e.g., air) from the filtrate-side gas inlet 53 into the filtrate-side space S2 of the housing 13, and the filtrate is pressurized by the gas. The filtrate is pushed from the inner surface side to the outer surface side of the hollow fiber membrane 14, and as a result, a portion of the liquid in the internal space S1 is discharged from the drain outlet 12 to the outside of the system. In this way, the hollow fiber membrane 14 is backwashed. After that, the filtrate-side pressure relief valve 81 is opened to reduce the pressure in the filtrate-side space S2.

Next, the water filling process (before lower bubbling) is carried out. In this process, in order to raise the liquid level in the internal space S1 that was lowered in the backwash process, the control device 40 opens the gas outlet valve 62 and the raw liquid introduction valve 22 and operates the liquid delivery pump 20. This introduces liquid into the internal space S1, causing the liquid level to rise. Thereafter, the liquid delivery pump 20 is stopped, the raw liquid introduction valve 22 is closed, and the supply of liquid is stopped.

Next, the lower bubbling process is carried out. In this process, with the internal space S1 filled with water, the second gas introduction valve 35 is opened by the control device 40, and the air compressor 30 is operated. As a result, gas is supplied from the diffusion gas inlet 7 into the housing 13 via the second gas introduction pipe 32. The gas is then accommodated in the gas receiving section 45, and is then dispersed from the diffusion vent 43 into the lower space S12. The gas rising from the lower space S12 to the upper space S11 causes the multiple hollow fiber membranes 14 in each hollow fiber membrane bundle 15, which are independent of each other due to the suppression member 100, to oscillate, and the suspended pollutants attached to the membrane surface are peeled off by this action. In this way, in the lower bubbling process, gas is dispersed in the housing 13 at a position below the multiple hollow fiber membrane bundles 15, and the gas is caused to rise to the upper space S11, thereby cleaning the hollow fiber membranes 14 located in the lower part of the lower space S12 and the upper space S11.

Floating pollutants peeled off from the membrane surfaces of the hollow fiber membranes 14 in each hollow fiber membrane bundle 15 are discharged through the gaps between the hollow fiber membrane bundles 15. This allows the floating pollutants attached to the membrane surfaces of the hollow fiber membranes 14 in each hollow fiber membrane bundle 15 to be effectively removed. Furthermore, the suppression member 100 makes each hollow fiber membrane bundle 15 independent of each other, suppressing interference between the hollow fiber membranes 14 belonging to different hollow fiber membrane bundles 15. This prevents the hollow fiber membranes 14 from becoming entangled between the hollow fiber membrane bundles 15, and also suppresses the associated damage to the hollow fiber membranes 14.

In addition, the suppression member 100 suppresses the lower ends 14A of the multiple hollow fiber membranes 14 from flying up in the hollow fiber membrane bundle 15, thereby restricting excessive movement of the multiple hollow fiber membranes 14 in the hollow fiber membrane bundle 15. This makes it possible to suppress excessive interference between the hollow fiber membranes 14, such as entanglement between the hollow fiber membranes 14 belonging to the same hollow fiber membrane bundle 15, and to suppress damage to the hollow fiber membranes 14 that occurs as a result. Furthermore, by setting the position of the lower end 100A of the suppression member 100 so as to suppress the lower end 14A of the hollow fiber membrane 14 from entering the mesh 101 of the suppression member 100, it is possible to restrict the hollow fiber membranes 14 from entangling with the suppression member 100. This makes it possible to suppress damage to the hollow fiber membranes 14.

Next, the drainage process is carried out. In this process, the control device 40 closes the second gas introduction valve 35 and opens the raw liquid outlet valve 42. This causes the liquid containing the suspended contaminants that have peeled off from the membrane surface in the lower bubbling process to be discharged outside the system via the drain outlet 12.

Next, the water filling process (before upper bubbling) is carried out. In this process, the gas outlet valve 62 and the stock solution introduction valve 22 are opened, and the liquid delivery pump 20 is operated to fill the internal space S1 with liquid again.

Next, the upper bubbling process is carried out. This process is carried out for the purpose of more reliably removing suspended contaminants adhering to the membrane surface at the upper end 14B of the hollow fiber membrane 14 that was not sufficiently cleaned in the lower bubbling process.

First, the control device 40 closes the raw liquid introduction valve 22 and opens the third gas introduction valve 36. This introduces gas into the water pipe 5 from the water pipe gas inlet 8 via the third gas introduction pipe 33. The gas then rises due to buoyancy in the pipe and is dispersed into the housing 13 from the pipe vents 54A and 54B located in the upper space S11. This allows the hollow fiber membrane 14 to be bubbling cleaned, mainly near the upper end 14B, and allows suspended contaminants attached to the membrane surface around the upper end 14B that could not be sufficiently removed in the lower bubbling process to be more reliably removed. In this way, in the upper bubbling process, the hollow fiber membrane 14 is cleaned by dispersing gas in the housing 13 at the position of the upper space S11.

In the upper bubbling process, the entire internal space S1 is filled with water immediately after the start of bubbling, so that it can be bubble-cleaned by the gas discharged from the uppermost pipe vent 54A and the pipe vent 54B below it. Then, after a certain time has passed since the start of bubbling, the liquid containing the gas is discharged from the gas vent 11, and the liquid level in the internal space S1 drops to the lower surface 11A. Even in this state, the buoyancy of the gas supplied to the water conduit 5 causes the water in the water conduit 5 to be ejected together with the gas from the pipe vent 54A above the lower surface 11A of the gas vent 11, and the water in the housing 13 to flow into the water conduit 5 from the pipe vent 54B below the lower surface 11A of the gas vent 11. This allows the liquid and gas mixture to be continuously ejected and bubbled from the pipe vent 54A above the lower surface 11A of the gas vent 11, effectively cleaning the hollow fiber membrane 14 up to the upper end 14B.

Next, the drainage process is carried out. In this process, the third gas introduction valve 36 is closed and the raw liquid outlet valve 42 is opened. This causes the liquid containing the suspended contaminants that have peeled off from the membrane surface in the upper bubbling process to be discharged from the system through the drain outlet 12. After the hollow fiber membrane module 10 has been cleaned in this manner, the filtration operation is resumed.

In both the upper and lower bubbling steps, the gas supply flow rate is preferably 12,000 NL/h or less, and is preferably in the range of 1,500 to 12,000 NL/h. In the lower bubbling step, if the gas supply flow rate is excessive, the hollow fiber membranes 14 may become entangled and the membrane surface may be damaged. In contrast, in this embodiment, in the lower bubbling step, the suppression member 100 suppresses excessive oscillation of the hollow fiber membranes 14 for each hollow fiber membrane bundle 15, so the upper limit gas supply flow rate in the lower bubbling step can be increased. In general, such problems are less likely to occur in the upper bubbling step, so the gas supply flow rate in the upper bubbling step may be set higher than in the lower bubbling step, but due to the effect of the suppression member 100, it is possible to supply gas in the lower bubbling step at a flow rate similar to that in the upper bubbling step.

Second Embodiment
Next, the structure of a hollow fiber membrane module 10 according to a second embodiment of the present invention will be described with reference to Fig. 10. The hollow fiber membrane module 10 according to the second embodiment basically has the same configuration as the first embodiment and achieves the same effects, but the structure of the suppression members 100 individually provided on each of the multiple hollow fiber membrane bundles 15 is different from that of the first embodiment.

In the hollow fiber membrane module 10 according to the second embodiment, each of the suppression members 100 has a plurality of meshes 101, as in the first embodiment, and is configured as a mesh-like body extending in the vertical direction so as to cover the side surface of the corresponding hollow fiber membrane bundle 15. In the first embodiment, the upper end 100B of the suppression member 100 is fixed to the fixing member 3, but in the second embodiment, the upper end 100B of the suppression member 100 is located below the upper end 14B of the hollow fiber membrane 14. In other words, the upper end 100B of the suppression member 100 is spaced apart from the fixing member 3. In this case, the suppression member 100 is adhesively fixed to the side surface 13B of the housing 13, for example.

As in the first embodiment, the lower end 100A of the suppression member 100 is located within the appropriate lower end range, which can suppress the lower ends 14A of the multiple hollow fiber membranes 14 oscillating within the corresponding hollow fiber membrane bundle 15 from flying up and can also suppress the lower ends 14A of the multiple hollow fiber membranes 14 from entering the mesh 101.

By suppressing the rising of the lower ends 14A of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 by the suppression member 100, it is possible to suppress the hollow fiber membranes 14 from becoming entangled with each other in the hollow fiber membrane bundle 15. Furthermore, by setting the position of the lower end 100A of the suppression member 100 so as to suppress the lower ends 14A of the hollow fiber membranes 14 from entering the mesh 101 of the suppression member 100, it is possible to restrict the hollow fiber membranes 14 from becoming entangled with the suppression member 100. This makes it possible to suppress damage to the hollow fiber membranes 14.

Third Embodiment
Next, the structure of a hollow fiber membrane module 10 according to a third embodiment of the present invention will be described with reference to Fig. 11. The hollow fiber membrane module 10 according to the third embodiment basically has the same configuration as the first embodiment and achieves the same effects, but the structure of the suppression members 100 individually provided on each of the multiple hollow fiber membrane bundles 15 is different from that of the first embodiment.

As shown in FIG. 11, each of the suppression members 100 of the third embodiment is formed with a plurality of through holes 103 and is configured with a cylindrical body 102 extending in the vertical direction so as to cover the side surface of the corresponding hollow fiber membrane bundle 15. The suppression member 100 of the first embodiment is configured with a mesh body and has elasticity according to the deformation of the shape of the mesh 101, but the suppression member 100 of the third embodiment has a rigidity that does not cause the shape of the through holes 103 to deform. This allows each of the suppression members 100 to more reliably keep each hollow fiber membrane bundle 15 independent from each other. Therefore, during the bubbling process, interference between hollow fiber membranes 14 belonging to different hollow fiber membrane bundles 15 is more reliably suppressed.

The upper end 100B of the suppression member 100 of the third embodiment is fixed to the upper ends 14B of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 and is also fixed to the fixing member 3. Similarly to the first embodiment, the lower end 100A of the suppression member 100 is located within the lower end appropriate range that can suppress the lower ends 14A of the multiple hollow fiber membranes 14 swaying in the corresponding hollow fiber membrane bundle 15 from flying up and can suppress the lower ends 14A of the multiple hollow fiber membranes 14 from entering the through holes 103.

By suppressing the lower ends 14A of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 from flying up, it is possible to suppress the hollow fiber membranes 14 from becoming entangled with each other in the hollow fiber membrane bundle 15. Furthermore, by setting the position of the lower end 100A of the suppression member 100 so as to suppress the lower end 14A of the hollow fiber membrane 14 from entering the through hole 103 of the suppression member 100, it is possible to restrict the hollow fiber membranes 14 from becoming entangled with the suppression member 100. This makes it possible to suppress damage to the hollow fiber membranes 14.

Fourth Embodiment
Next, the structure of a hollow fiber membrane module 10 according to a fourth embodiment of the present invention will be described with reference to Fig. 12. The hollow fiber membrane module 10 according to the fourth embodiment basically has the same configuration as the first embodiment and achieves the same effects, but the structure of the suppression members 100 individually provided on each of the multiple hollow fiber membrane bundles 15 is different from that of the first embodiment.

As shown in FIG. 12, each suppression member 100 of the fourth embodiment is composed of a spiral string-like body wound around the side of the corresponding hollow fiber membrane bundle 15. The suppression member 100 composed of a spiral string-like body makes each hollow fiber membrane bundle 15 independent from each other when wound around the side of the hollow fiber membrane bundle 15. This suppresses interference between hollow fiber membranes 14 belonging to different hollow fiber membrane bundles 15 during the bubbling process.

The upper end 100B of the suppression member 100 of the fourth embodiment is fixed to the upper ends 14B of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 and is also fixed to the fixing member 3. Similarly to the first embodiment, the lower end 100A of the suppression member 100 is located within the lower end appropriate range that can suppress the lower ends 14A of the multiple hollow fiber membranes 14 swaying in the corresponding hollow fiber membrane bundle 15 from flying up and can suppress the lower ends 14A of the multiple hollow fiber membranes 14 from getting caught on the suppression member 100.

The suppression member 100 suppresses the lower ends 14A of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 from flying up, thereby suppressing the hollow fiber membranes 14 from becoming entangled with each other in the hollow fiber membrane bundle 15. Furthermore, by setting the position of the lower end 100A of the suppression member 100 so as to suppress the lower end 14A of the hollow fiber membrane 14 from getting caught on the suppression member 100, it is possible to prevent the hollow fiber membranes 14 from becoming entangled with the suppression member 100. This makes it possible to suppress damage to the hollow fiber membranes 14.

Fifth Embodiment
Next, the structure of a hollow fiber membrane module 10 according to a fifth embodiment of the present invention will be described with reference to Fig. 13. The hollow fiber membrane module 10 according to the fifth embodiment basically has the same configuration as the first embodiment and achieves the same effects, but the structure of the suppression members 100 individually provided on each of the multiple hollow fiber membrane bundles 15 is different from that of the first embodiment.

As shown in FIG. 13, each suppression member 100 of the fifth embodiment is composed of a plurality of strips 104 wound around the side of the corresponding hollow fiber membrane bundle 15. The strips 104 are arranged at predetermined intervals in the vertical direction of the hollow fiber membrane bundle 15, and are adhesively fixed, for example, to the side surface 13B of the housing 13. The suppression member 100 composed of a plurality of strips 104 makes each hollow fiber membrane bundle 15 independent from each other with each strip 104 wound around the side surface of the hollow fiber membrane bundle 15. This suppresses interference between hollow fiber membranes 14 belonging to different hollow fiber membrane bundles 15 during the bubbling process.

The lowermost band 104 among the multiple bands 104 is located within the appropriate lower end range that can prevent the lower ends 14A of the multiple hollow fiber membranes 14 oscillating within the corresponding hollow fiber membrane bundle 15 from flying up. The suppression member 100 suppresses the lower ends 14A of the multiple hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 from flying up, thereby suppressing the hollow fiber membranes 14 from becoming entangled with each other within the hollow fiber membrane bundle 15.

[Examples of the present invention]
Next, examples illustrating the present invention more specifically will be described.

Example 1
The hollow fiber membrane bundle 15 used was a one-end free type with a membrane area of 40 ^m2 . The hollow fiber membrane 14 used was made of polyvinylidene fluoride resin hydrophilized with polyvinyl alcohol, had an average pore size of 0.02 microns, and had a vertical length (effective length) L2 of 1035 mm.

A polypropylene mesh was used as the suppression member 100. The upper end of the mesh was fixed to the upper ends 14B of the hollow fiber membranes 14 in the corresponding hollow fiber membrane bundle 15 and to the fixing member 3, and the vertical length L1 of the mesh was 725 mm. In this case, the lower end of the mesh was located within an appropriate lower end range that can suppress the lower ends 14A of the hollow fiber membranes 14 from flying up and can suppress the lower ends 14A of the hollow fiber membranes 14 from entering the mesh. In addition, the ratio (L1/L2) of the length L1 of the mesh to the effective length L2 of the hollow fiber membranes 14 was "0.7".

The water conduit 5 used was a cylinder with a length of 1090.5 mm and an inner diameter of 48.6 mm. The water conduit 5 was placed at the center of the housing 13 and fixed together with the hollow fiber membrane bundle 15 by the fixing member 3. In this case, multiple hollow fiber membrane bundles 15 were arranged to surround the water conduit 5. Multiple pipe vents 54 (36 in total) were formed in the water conduit 5 at intervals of 100 mm from a position 70 mm downward from the fixing member 3. The pipe vents 54 were formed at intervals of 90° in the circumferential direction and had a hole diameter of 10 mm.

The air diffusion member 4 was attached at a position 1060.5 mm below the fixed member 3. The air diffusion member 4 is composed of a disk-shaped main body 44 with multiple air diffusion holes 43, a gas receiving portion 45, and a peripheral wall portion 47. A water pipe gas inlet 8 was provided as a gas supply port to the water pipe 5, and a gas diffusion inlet 7 was provided as a gas supply port to the gas receiving portion 45 of the air diffusion member 4.

Using the hollow fiber membrane module 10 configured as above, clean water was used as the raw water and constant flow rate filtration was performed for 30 seconds at a flow rate of 4000 L/h using the external pressure total filtration method. After the filtration operation, back pressure cleaning was performed from the filtrate side of the hollow fiber membrane module 10 using 0.2 MPa compressed air, and then bubbling cleaning was performed. This operation was repeated 300 times. The flow rate of the bubbling air (cleaning gas) on the aeration member 4 side was changed in the range of 1500 to 12000 NL/h. The flow rate of the bubbling air (cleaning gas) on the water conduit 5 side was kept constant at 10000 NL/h.

Example 2
The same procedure as in Example 1 was used except that a mesh body having a vertical length L1 of 932 mm was used. In this case, the lower end of the mesh body was located within the appropriate lower end range. In addition, the ratio of the length L1 of the mesh body to the effective length L2 of the hollow fiber membrane 14 (L1/L2) was "0.9".

Example 3
The same procedure as in Example 1 was used except that a mesh body having a vertical length L1 of 1035 mm was used. In this case, the lower end of the mesh body was located within the appropriate lower end range. In addition, the ratio of the length L1 of the mesh body to the effective length L2 of the hollow fiber membrane 14 (L1/L2) was "1.0".

(Comparative Example 1)
The procedure was the same as in Example 1, except that the provision of the mesh body on the hollow fiber membrane bundle 15 was omitted.

(Comparative Example 2)
The same procedure was followed as in Example 1, except that a mesh body having a vertical length L1 of 518 mm was used. In this case, the lower end of the mesh body was located above the appropriate lower end range. In addition, the ratio of the length L1 of the mesh body to the effective length L2 of the hollow fiber membrane 14 (L1/L2) was 0.5.

(Comparative Example 3)
The same procedure was followed as in Example 1, except that a mesh body having a vertical length L1 of 1242 mm was used. In this case, the lower end of the mesh body was located below the appropriate lower end range. In addition, the ratio (L1/L2) of the length L1 of the mesh body to the effective length L2 of the hollow fiber membrane 14 was "1.2."

For the above Examples 1 to 3 and Comparative Examples 1 to 3, the occurrence of tangling or damage between the hollow fiber membranes 14 within the hollow fiber membrane bundle 15 was visually evaluated. The evaluation results are shown in Table 1. "◯" in Table 1 indicates that there was almost no occurrence of tangling or damage between the hollow fiber membranes 14 within the hollow fiber membrane bundle 15, and stable operation was possible. On the other hand, "×" in Table 1 indicates that there was noticeable occurrence of tangling or damage between the hollow fiber membranes 14 within the hollow fiber membrane bundle 15, and it became difficult to continue stable operation.

As is clear from the results in Table 1, in Examples 1 to 3, when the flow rate of the cleaning gas on the aeration member 4 side was in the range of 1,500 to 12,000 NL/h, entanglement and damage of the hollow fiber membranes 14 in the hollow fiber membrane bundle 15 was suppressed. This is because the mesh body suppressed the rising of the lower ends 14A of the multiple hollow fiber membranes 14 in the hollow fiber membrane bundle 15, thereby limiting excessive movement of the hollow fiber membranes 14.

In addition, in Examples 1 to 3, the lower end of the mesh body is located within an appropriate lower end range that can prevent the lower end 14A of the hollow fiber membrane 14 from flying up and can prevent the lower end 14A of the hollow fiber membrane 14 from entering the mesh. This is thought to have restricted entanglement of the hollow fiber membrane 14 with the mesh body and prevented damage to the hollow fiber membrane 14.

On the other hand, in Comparative Example 1, under conditions where the flow rate of the cleaning gas on the aeration member 4 side was 7000 NL/h or more, entanglement and damage of the hollow fiber membranes 14 within the hollow fiber membrane bundle 15 was significantly confirmed. This is because in Comparative Example 1, the installation of a mesh body was omitted, so the excessive movement of the multiple hollow fiber membranes 14 within the hollow fiber membrane bundle 15 was not restricted, and the lower ends 14A of the multiple hollow fiber membranes 14 were lifted up.

In Comparative Example 2, when the flow rate of the cleaning gas on the aeration member 4 side was 10,000 NL/h or more, the hollow fiber membranes 14 in the hollow fiber membrane bundle 15 were noticeably entangled and damaged. This is because, in Comparative Example 2, the lower end of the net-like body is located above the lower end appropriate range that can prevent the lower ends 14A of the multiple hollow fiber membranes 14 in the hollow fiber membrane bundle 15 from flying up. For this reason, in Comparative Example 2, when the flow rate of the cleaning gas on the aeration member 4 side was 10,000 NL/h or more, the lower ends 14A of the multiple hollow fiber membranes 14 in the hollow fiber membrane bundle 15 flew up, which is thought to have caused the hollow fiber membranes 14 to become entangled and damaged.

In addition, in Comparative Example 3, when the flow rate of the cleaning gas on the aeration member 4 side was in the range of 1500 to 12000 NL/h, entanglement and damage of the hollow fiber membranes 14 in the hollow fiber membrane bundle 15 was significantly confirmed. This is because in Comparative Example 3, the lower end of the mesh body was located below the appropriate lower end range that can prevent the lower end 14A of the hollow fiber membrane 14 from entering the mesh 101 and was in contact with the aeration member 4. For this reason, in Comparative Example 3, the hollow fiber membranes 14 became entangled with the suppression member 100, causing damage to the hollow fiber membranes 14.

The above results show that, compared to Comparative Examples 1 to 3, Examples 1 to 3 limit the excessive movement of the hollow fiber membrane 14 during the bubbling process, and are able to suppress entanglement and damage between the hollow fiber membranes 14 while ensuring the effect of removing suspended pollutants adhering to the membrane surface of the hollow fiber membrane 14.

The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as limiting. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

Reference Signs List 2 Gas supply section 4 Diffusion member 43 Diffusion vent 44 Main body 45 Gas receiver 45A Receiver 46 Diffusion hole 10 Hollow fiber membrane module 13 Housing 14 Hollow fiber membrane 15 Hollow fiber membrane bundle 100 Suppression member S1 Internal space

Claims (6)

a housing in which the fixing member is fixed and which defines an internal space;
a plurality of hollow fiber membrane bundles each having a plurality of hollow fiber membranes, the bundles being disposed in the internal space with upper ends of the plurality of hollow fiber membranes fixed to the fixing member;
a gas supply unit that supplies a gas for cleaning the plurality of hollow fiber membrane bundles to the internal space;
a suppression member provided individually for each of the plurality of hollow fiber membrane bundles,
the suppression members are each fixed to a side surface of the housing with their upper ends spaced apart from the fixing member, and are configured to suppress the lower ends of the plurality of hollow fiber membranes from flying up while allowing the plurality of hollow fiber membranes to oscillate in the corresponding hollow fiber membrane bundle due to the gas supplied from the gas supply section into the internal space. Each of the suppression members has a plurality of meshes and is configured as a mesh-like body extending in the vertical direction so as to cover the side surface of the corresponding hollow fiber membrane bundle,
2. The hollow fiber membrane module according to claim 1, wherein the lower ends of the suppression members are each positioned at a position capable of suppressing the lower ends of the plurality of hollow fiber membranes swaying within the corresponding hollow fiber membrane bundle from flying up and suppressing the lower ends of the plurality of hollow fiber membranes from entering the meshes. 3. The hollow fiber membrane module according to claim 1 or 2 , wherein each of the suppression members has a function of partitioning the hollow fiber membrane bundles so that gaps are formed between the plurality of hollow fiber membrane bundles. the gas supply unit includes an air diffusion member disposed below the hollow fiber membrane bundle, having a shape expanding in a radial direction of the hollow fiber membrane bundle, and having a plurality of air diffusion holes formed at intervals in the radial direction;
The air diffusing member is
a plate-like main body portion having a shape expanding in a radial direction of the hollow fiber membrane bundle and having a plurality of the air diffusion holes formed at intervals in the radial direction;
a gas receiving portion having a cylindrical shape with one end connected to the lower surface of the main body and the other end formed with a gas receiving port, and having a dispersion hole for guiding the gas contained in the cylinder to the gas diffusion vent. The hollow fiber membrane module according to claim 4 , wherein the gas receiving portion has an inner diameter that increases from the one end toward the other end. The air diffusion holes are arranged on a plurality of circumferences spaced apart in the radial direction in the main body,
6. The hollow fiber membrane module according to claim 4 , wherein the number of the air diffusion holes on each circumference is a multiple of the number of the hollow fiber membrane bundles.