Filtration device, filtration system, and filtration method

Abstract

A filtration device, a filtration system, and a filtration method are provided that can improve filtration efficiency. [Solution] The container comprises an inner tube extending in the vertical direction and capable of holding a liquid, at least one ascending flow generating section that generates an ascending flow containing air bubbles in an outer flow space formed outside the inner tube or an inner flow space formed inside the inner tube, and a filtration membrane section arranged inside the inner tube, wherein the inner flow space and the outer flow space are connected at the upper and lower sides of the inner tube and are configured to be able to form a circulation flow path that circulates air bubbles, and the filtration membrane section has an outlet at its lower end that discharges permeated liquid that has passed through the filtration membrane section.

Description

[Technical Field]

[0001] The present invention relates to a filtration device, a filtration system, and a filtration method. [Background technology]

[0002] Conventionally, there is a hollow fiber membrane module that includes a housing having openings on both ends, a hollow fiber membrane bundle that is composed of a plurality of hollow fiber membranes that filter the liquid to be filtered and is accommodated in the housing, a first nozzle that is provided on the side surface of one end of the housing and that can discharge the filtrate filtered by the hollow fiber membranes, and a second nozzle that is provided on the side surface of the other end of the housing and that can also discharge the filtrate (for example, Patent Document 1). Moreover, the hollow fiber membrane bundle described in Patent Document 1 has one end fixed to one opening side and the other end fixed to the other opening side.

[0003] The hollow fiber membrane module described in Patent Document 1 is arranged so that the openings at both ends extend vertically, and a liquid to be filtered containing suspended matter is introduced through the opening on the lower side. The liquid to be filtered introduced into the hollow fiber membrane module moves upward through the flow path of the hollow fiber membrane, and suspended matter is filtered out through holes formed in the tube wall of the hollow fiber membrane. Then, a clean filtrate flows out of the hollow fiber membrane. The outflowing filtrate is taken out from the first nozzle and the second nozzle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2024-72125 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional hollow fiber membrane modules, such as the hollow fiber membrane module described in Patent Document 1, require a suction pump to suck up the liquid to be filtered from the bottom to the top of the flow path of the hollow fiber membrane. However, hollow fiber membranes have a set pressure resistance, and if the hollow fiber membranes are sucked up at a pressure above a certain pressure resistance (e.g., 0.2 to 0.6 MPa), the hollow fiber membranes become clogged and become unusable. Therefore, conventional hollow fiber membrane modules have the problem of limited suction pressure for the liquid to be filtered, and therefore limited suction speed and filtration speed of the liquid to be filtered.

[0006] In particular, when a hollow fiber membrane module is used for water treatment in a tank several meters deep, the liquid to be filtered in the flow path of the hollow fiber membrane is subjected to a large water pressure (hydraulic head pressure), and it is necessary to apply pressure sufficient to offset the water pressure while sucking the liquid to be filtered within a specified pressure resistance range, which results in a significant loss of filtration efficiency.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a filtration device, a filtration system, and a filtration method that can improve filtration efficiency. [Means for solving the problem]

[0008] The filtration device of the present invention comprises an inner cylinder extending in the vertical direction, a storage container capable of holding a liquid, at least one ascending flow generating unit that generates an ascending flow containing air bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder, and a filtration membrane unit arranged within the inner cylinder, wherein the inner flow space and the outer flow space are connected at the upper and lower sides of the inner cylinder and are configured to be able to form a circulation flow path for circulating air bubbles, and the filtration membrane unit has an outlet at its lower end for discharging the permeated liquid that has passed through the filtration membrane unit.

[0009] In the filtration device according to the present invention, the filtration membrane portion may include a hollow fiber membrane having a cylindrical filtration surface, a hollow portion defined by the filtration surface, and the outlet for discharging the permeated liquid from the hollow portion.

[0010] In the filtration device of the present invention, the upward flow generating section may have at least one gas release section that releases gas into the outer flow space or the inner flow space below the middle part of the storage container in the vertical direction.

[0011] The filtration device according to the present invention may have at least one of an inner swirling flow generating section that converts the flow in the inner flow space into a swirling flow along the circumferential direction of the inner tube of the storage container, and an outer swirling flow generating section that converts the flow in the outer flow space into a swirling flow along the circumferential direction of the inner tube of the storage container.

[0012] In the filtration device according to the present invention, the inner swirl flow generating section and the outer swirl flow generating section may each have a blade section.

[0013] The filtration system of the present invention is a filtration system comprising a filtration device that filters a liquid, a liquid supply device that supplies the liquid to the filtration device, and a permeate supply device that is supplied with permeate filtered by the filtration device, wherein the filtration device has an inner cylinder that extends in the vertical direction and comprises a storage container that can store the liquid, at least one ascending flow generating unit that generates an ascending flow containing air bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder, and a filtration membrane unit arranged in the inner cylinder, wherein the inner flow space and the outer flow space are connected at the upper and lower sides of the inner cylinder and are configured to be able to form a circulation flow path that circulates air bubbles, and the filtration membrane unit has an outlet at its lower end that discharges the permeate that has permeated through the filtration membrane unit.

[0014] In the filtration system of the present invention, the storage container has a bottom that closes the lower end and a top that closes the upper end, the permeate liquid supply device is configured in a bottomed cylindrical shape and has a top surface that closes the open end of the permeate liquid supply device, the filtration device and the permeate liquid supply device are configured to be able to change the pressure in their internal spaces and are connected via a permeate liquid supply path, and the filtration device may be configured to be able to filter the liquid by the filtration membrane section by creating a negative pressure in the internal space of the permeate liquid supply device.

[0015] The filtration method of the present invention is a filtration method for filtering a liquid using a filtration device comprising: a storage container having an inner cylinder extending in the vertical direction and capable of containing a liquid; at least one ascending flow generating unit that generates an ascending flow containing air bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder; and a filtration membrane unit arranged within the inner cylinder, wherein the inner flow space and the outer flow space are connected to each other on the upper and lower sides of the inner cylinder and are configured to be able to form a circulation flow path for circulating air bubbles; and the permeated liquid that has permeated the filtration membrane unit is discharged from the lower end of the filtration membrane unit. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a filtration device, a filtration system, and a filtration method that can improve filtration efficiency. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram illustrating a filtration system according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view showing a filtering device and a permeated liquid supplying device according to the present embodiment. [Figure 3] FIG. 1 is a diagram showing a hollow fiber membrane according to an embodiment of the present invention. [Figure 4] FIG. 2 is an enlarged view showing a part of the separation device according to the present embodiment. [Figure 5] FIG. 2 is an enlarged view showing a part of the separation device according to the present embodiment. [Figure 6]FIG. 2 is a schematic diagram showing the flow in the filtering device according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] The best mode for carrying out the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. Furthermore, the drawings are schematic diagrams in which emphasis, omission, and proportion adjustments have been made as appropriate to illustrate the present invention, and may differ from the actual shapes, positional relationships, and proportions.

[0019] [Configuration of the filtration system according to this embodiment] First, an overview of a filtration system 1 according to an embodiment of the present invention will be provided. As shown in Fig. 1, the filtration system 1 according to this embodiment generally comprises a filtration device 30 that filters a liquid, a liquid supply device 10 that supplies a liquid to the filtration device 30, and a permeated liquid supplied device 70 that is supplied with permeated liquid filtered by the filtration device 30. The filtration system 1 also comprises a liquid supply path 3 that connects the liquid supply device 10 and the filtration device 30 and supplies the liquid in the liquid supply device 10 to the filtration device 30, and a permeated liquid supply path 5 that connects the filtration device 30 and the permeated liquid supplied device 70 and supplies the permeated liquid filtered by the filtration device 30 to the permeated liquid supplied device 70.

[0020] In this embodiment, the liquid supply device 10 is, for example, a biological treatment tank for water treatment, an aquarium, a fermenter used in producing fermented foods and beverages, a biomass reaction tank, or other biological tank. However, the liquid in the liquid supply device 10 contains various impurities. The liquid supply device 10 also has a pump (not shown) for supplying the liquid to the filtration device 30.

[0021] [Configuration of filtration device] The filtration device 30 includes a storage container 32 capable of storing a liquid, and a filtration membrane unit 50 disposed within the storage container 32. As shown in FIG. 2, the filtration device 30 further includes a separation device (not shown). As shown in FIG. 2, the storage container 32 includes an outer cylinder 35 extending in the up-down direction (vertical direction in this embodiment), and an inner cylinder 36 disposed inside the outer cylinder 35. In this embodiment, "vertical" includes both completely vertical and approximately vertical. "Approximately vertical" means being slightly inclined relative to the vertical, specifically, being inclined to an extent that does not impede the action and effect of the filtration device 30.

[0022] The outer cylinder 35 and the inner cylinder 36 are each formed in a cylindrical shape with an open upper end and lower end. The outer diameter of the inner cylinder 36 is formed to be smaller than the inner diameter of the outer cylinder 35. The vertical length of the inner cylinder 36 is also formed to be shorter than the vertical length of the outer cylinder 35. The shapes of the outer cylinder 35 and the inner cylinder 36 are not limited to cylindrical shapes, and may be, for example, rectangular, conical, or pyramidal.

[0023] The storage vessel 32 has a bottom 33 that closes the lower end of the outer cylinder 35, and a top 34 that closes the upper end of the outer cylinder 35. The bottom 33 is formed in a bottomed cylindrical shape with an open upper end. The bottom 33 is configured to close the lower end of the outer cylinder 35 by fitting the lower end of the outer cylinder 35 into it. The top 34 is formed in a topped cylindrical shape with an open lower end. The top 34 is configured to close the upper end of the outer cylinder 35 by fitting the upper end of the outer cylinder 35 into it. The pressure in the internal space of the storage vessel 32 is configured to be changeable. In this embodiment, the pressure in the internal space of the storage vessel 32 is changed by changing the pressure in the internal space 70a of the permeate liquid supply device 70, which will be described later, using a negative pressure generating device, which will be described later. However, the present invention is not limited to this.

[0024] The storage container 32 also has an outer flow space 37 formed between the outer cylinder 35 and the inner cylinder 36, and an inner flow space 38 formed inside the inner cylinder 36. The outer flow space 37 and the inner flow space 38 are connected to each other above and below the inner cylinder 36, and are configured to be able to form a circulation flow path CP that circulates the objects to be separated and bubbles B (see FIG. 6). Specifically, a liquid containing the objects to be separated and bubbles B circulates inside the circulation flow path CP. The storage container 32 also has an inlet (not shown) that allows liquid to flow into the storage container 32 from the liquid supply device 10 via the liquid supply path 3.

[0025] The filtration membrane section 50 includes hollow fiber membranes 52. In this embodiment, the filtration membrane section 50 includes a plurality of hollow fiber membranes 52, which are supported in a bundle by an upper bundling section 66 and a lower bundling section 68. In this embodiment, the plurality of hollow fiber membranes 52 supported in a bundle form a cylindrical membrane module. The filtration membrane section 50 includes a permeate supply channel 5 extending in the extension direction of the hollow fiber membranes 52 in the center of the cylindrical membrane module.

[0026] 3, the hollow fiber membrane 52 has a cylindrical filtration circumferential surface 54, a hollow portion 55 defined by the filtration circumferential surface 54, and an outlet 58 for discharging permeated liquid from the hollow portion 55. The outlet 58 is provided at one end of the hollow fiber membrane 52. Furthermore, when the filtration membrane section 50 does not have an upper bundling section 66, or when the upper bundling section 66 is configured in a cylindrical shape rather than a bottomed cylindrical shape as described below, the hollow fiber membrane 52 may have an inlet 56 at the other end of the hollow fiber membrane 52 for allowing liquid to flow into the hollow portion 55.

[0027] In this embodiment, the hollow fiber membrane 52 is a micro-filtration (MF) membrane. However, the present invention is not limited to this. The hollow fiber membrane 52 can have any of a variety of configurations depending on the size of the impurities (substances to be separated) contained in the liquid. For example, the hollow fiber membrane 52 may be an ultra-filtration (UF) membrane, a nano-filtration (NF) membrane, or a reverse osmosis (RO) membrane.

[0028] Furthermore, in this embodiment, the hollow fiber membranes 52 are arranged in the storage container 32 so that the longitudinal direction of the hollow fiber membranes 52 is aligned with the up-down direction (vertical direction in this embodiment) of the storage container 32. Furthermore, the discharge ports 58 of the hollow fiber membranes 52 communicate with a lower bundling part 68, which will be described later, as shown in Fig. 2. Specifically, the ends of the plurality of hollow fiber membranes 52 on the discharge port 58 side communicate with an internal space 68a of the lower bundling part 68, which will be described later.

[0029] The upper bundling part 66 is configured in the shape of a closed-topped cylinder with an open lower end, and is attached to an upper swirl flow generating part 150 of the separation device, which will be described later. The upper bundling part 66 is configured to close the upper ends of the plurality of hollow fiber membranes 52. The lower bundling part 68 is configured in the shape of a closed-topped cylinder with an open upper end. The lower bundling part 68 is also communicated with the end of the hollow fiber membranes 52 on the discharge port 58 side, and is configured so that the permeate discharged from the discharge port 58 accumulates in an internal space 68a.

[0030] One end 5a of the permeate liquid supply channel 5 extends to the internal space 68a of the lower bundling part 68. The permeate liquid supply channel 5 having such a configuration is configured to be able to supply the permeate liquid accumulated in the internal space 68a of the lower bundling part 68 from the lower bundling part 68 to the permeate liquid supplied device 70. The other end 5b of the permeate liquid supply channel 5 is inserted through a ceiling part 72 (described later) of the permeate liquid supplied device 70 and extends to the internal space 70a (described later) of the permeate liquid supplied device 70. As will be described later, the other end 5b of the permeate liquid supply channel 5 is preferably located below the liquid level in the storage vessel 32 of the filtration device 30 in order to filter the liquid by the filtration device 30 by applying negative pressure to the permeate liquid supplied device 70. However, the present invention is not limited to this.

[0031] [Configuration of separation device] The separation device according to this embodiment is configured to separate a separation target within the filtration device 30. In this embodiment, the separation target is impurities contained in the liquid within the filtration device 30, specifically, impurities adhering to the filtration peripheral surface 54 of the filtration membrane unit 50 or floating around the filtration peripheral surface 54. As shown in FIG. 2 , the separation device includes an ascending flow generating unit 120 that generates an ascending flow containing bubbles B within the storage container 32, a lower swirling flow generating unit 140 provided below the inner cylinder 36, which will be described later, and an upper swirling flow generating unit 150 provided above the inner cylinder 36, which will be described later.

[0032] 2, the upward flow generating section 120 has a gas generating section 121 that generates gas, a gas releasing section 122 that releases the gas generated in the gas generating section 121 into the outer flow space 37 or the inner flow space 38, a gas supplying section 123 that supplies the gas generated in the gas generating section 121 to the gas releasing section 122, and a connecting section 124 that connects the gas releasing section 122 and the gas supplying section 123. In this embodiment, only one upward flow generating section 120 is provided, but this is not limited thereto, and two or more may be provided.

[0033] Gas generation unit 121 is, for example, a fan or the like, and has a switch 121a that starts or stops the generation of gas. One end of gas supply unit 123 is connected to gas generation unit 121, and the other end of gas supply unit 123 is connected to connection unit 124. One end of gas release unit 122 is connected to gas supply unit 123 via connection unit 124, and the other end is connected to mounting portion 143c of support unit 143, which will be described later.

[0034] Therefore, the gas release section 122 according to this embodiment is configured to release gas into the inner flow space 38 via the support section 143. Note that, from the viewpoint of generating an upward flow, the other end of the gas release section 122 only needs to be located below the middle section in the vertical direction of the storage container 32, and may be connected to, for example, the outer cylinder 35 or the inner cylinder 36. When the other end of the gas release section 122 is connected to the outer cylinder 35, the gas release section 122 is configured to release gas into the outer flow space 37.

[0035] The upward flow generating unit 120 having the above configuration is configured to generate an upward flow containing bubbles B in the inner flow space 38 by the gas release unit 122 releasing gas into the inner flow space 38. When the gas release unit 122 releases gas into the outer flow space 37, the upward flow generating unit 120 generates an upward flow containing bubbles B in the outer flow space 37. The upward flow generating unit 120 is also configured to be able to stop the circulation of the separation target and bubbles B by operating the switch 121a. However, the present invention is not limited to this, and the upward flow generating unit 120 does not have to be able to stop the circulation of the separation target and bubbles B.

[0036] Next, the lower swirl flow generating section 140 will be described with reference to Figures 2 and 4. The lower swirl flow generating section 140 has a plurality of (seven in this embodiment) blade sections 142 (lower blade sections) provided at predetermined intervals in the circumferential direction of the inner cylinder 36, and a support section 143 capable of supporting the inner cylinder 36.

[0037] The blades 142 are provided on the bottom surface of the bottom 33 of the container 32 and are non-rotatable. Each blade 142 extends radially around the inner tube 36 and has a curved shape in the circumferential direction of the inner tube 36. That is, the blades 142 are provided radially around the axis of the inner tube 36. In plan view, the inner end of each blade 142 in the extension direction is located within the area of ​​the inner tube 36, and the outer end of each blade 142 in the extension direction is located within the area between the outer tube 35 and the inner tube 36. Furthermore, each blade 142 is formed so that its height increases from the outer side in the extension direction to the inner side in the extension direction. This has the advantage of allowing efficient swirling without obstructing the flow from the outer flow space 37 or the flow from the inner flow space 38.

[0038] The support part 143 is formed in a cylindrical shape with open upper and lower ends, and has a shape that tapers from the lower end to the upper end. The support part 143 has an insertion groove 143a at its upper end into which the lower end of the inner tube 36 can be inserted, and is configured to support the inner tube 36 by inserting the lower end of the inner tube 36 into the insertion groove 143a. The support part 143 also has an annular tube part 143b at its lower end that surrounds the periphery of the blade part 142. The support part 143 also has an attachment part 143c to which the gas release part 122 is attached.

[0039] The pipe section 143b is formed in a tubular shape having an internal space that allows the gas supplied from the gas release section 122 to flow. Outlet holes 143d are formed in the inner circumferential section (the end on the blade section 142 side) of the pipe section 143b, through which the gas supplied from the gas release section 122 flows out. In this embodiment, the outlet holes 143d are one or more openings formed at predetermined intervals in the circumferential direction of the pipe section 143b. The outlet holes 143d may be an annular opening extending along the circumferential direction of the pipe section 143b. The attachment section 143c is formed to extend upward from a portion of the circumferential direction of the pipe section 143b, and the gas supplied from the gas release section 122 is supplied to the pipe section 143b via the attachment section 143c.

[0040] The support part 143 having the above-described configuration is configured to communicate the outer flow space 37 and the inner flow space 38 between the lower end of the support part 143 and the bottom surface of the bottom part 33 of the storage container 32. Note that, in the present embodiment, the configuration in which the support part 143 includes the pipe part 143b and the attached part 143c has been described, but the present invention is not limited to this, and the support part 143 may be configured not to include these parts.

[0041] Next, the upper swirl flow generating section 150 will be described with reference to Figures 2 and 5. For ease of explanation, Figure 5 omits part of the permeate supply channel 5 and the upper bundling section 66. The upper swirl flow generating section 150 has a top plate section 151 provided opposite the upper opening 36a of the inner cylinder 36, a plurality of (six in this embodiment) blade sections 152 (upper blade sections) provided at predetermined intervals in the circumferential direction of the inner cylinder 36, and an attachment section 153 that can be attached to the inner cylinder 36. The top plate section 151 has a shape in which the center in the planar direction is recessed downward, and is formed into a generally conical shape overall.

[0042] The blades 152 extend downward from the lower surface of the top plate 151 and are configured to be non-rotatable. Each blade 152 extends radially of the inner tube 36 and has a shape that is curved in the circumferential direction of the inner tube 36. In other words, the blades 152 are provided radially around the axis of the inner tube 36. From the viewpoint of efficiently swirling the objects to be separated and the bubbles B, the direction of curvature of the blades 152 is preferably the same as the direction of curvature of the blades 142, but is not limited to this.

[0043] In bottom view, the inner end of each blade 152 in the extension direction is located within the area of ​​the inner cylinder 36, and the outer end of each blade 152 in the extension direction is located within the area between the outer cylinder 35 and the inner cylinder 36. Each blade 152 is formed so that its height decreases from the outer side in the extension direction to the inner side in the extension direction. This has the advantage of allowing efficient swirling without impeding the flow from the outer flow space 37 or the flow from the inner flow space 38.

[0044] The attachment portion 153 is formed in a ring shape that surrounds the periphery of the lower end of the blade portion 152. That is, the upper swirl flow generating portion 150 according to this embodiment is configured to communicate the outer flow space 37 and the inner flow space 38 between the lower surface of the top plate portion 151, the surface of the blade portion 152, and the inner peripheral portion of the attachment portion 153 (the end portion on the blade portion 152 side).

[0045] In this embodiment, either the lower swirl flow generating section 140 or the upper swirl flow generating section 150 functions as an inner swirl flow generating section 160 that causes the flow in the inner flow space 38 to swirl. The other either the lower swirl flow generating section 140 or the upper swirl flow generating section 150 functions as an outer swirl flow generating section 170 that causes the flow in the outer flow space 37 to swirl.

[0046] Whether the lower swirl flow generating section 140 and the upper swirl flow generating section 150 function as the inner swirl flow generating section 160 or the outer swirl flow generating section 170 depends on the position at which the upflow generating section 120 generates an upflow. Specifically, when the upflow generating section 120 generates an upflow in the inner flow space 38, the lower swirl flow generating section 140 functions as the inner swirl flow generating section 160, and the upper swirl flow generating section 150 functions as the outer swirl flow generating section 170. On the other hand, when the upflow generating section 120 generates an upflow in the outer flow space 37, the lower swirl flow generating section 140 functions as the outer swirl flow generating section 170, and the upper swirl flow generating section 150 functions as the inner swirl flow generating section 160.

[0047] The separation device having the above configuration is configured to be able to clean the filtration peripheral surface 54 of the hollow fiber membrane 52 of the filtration membrane section 50 and remove impurities adhering to the filtration peripheral surface 54 by generating a swirling flow (a spiral swirling flow in this embodiment) containing bubbles B in the inner flow space 38 while the filtration of the liquid by the filtration device 30 is completed and the filtration process is stopped. Note that the separation device may generate a swirling flow during the filtration process by the filtration device 30.

[0048] The permeate liquid supplied device 70 is, for example, a vacuum tank. The permeate liquid supplied device 70 is configured in a cylindrical shape with a bottom, and has a top surface portion 72 that closes the open end of the permeate liquid supplied device 70. The other end 5b of the permeate liquid supply path 5 is inserted into the top surface portion 72, and the permeate liquid filtered by the filtration device 30 is stored in the permeate liquid supplied device 70. In this embodiment, the filtration system 1 further includes a negative pressure generator (not shown) that generates negative pressure in the internal space 70a of the permeate liquid supplied device 70. The permeate liquid supplied device 70 is configured so that the pressure in the internal space 70a can be changed by the negative pressure generator.

[0049] The permeate liquid supplied device 70 also has an outlet 74 through which the permeate liquid stored in the bottom portion flows out. The outlet 74 is connected to a supply path for the next process (not shown), and the permeate liquid flowing out from the outlet 74 is supplied to the device for the next process through the supply path for the next process. In this embodiment, the permeate liquid supplied device 70 is configured to allow the permeate liquid to flow out from the outlet 74 by creating a negative pressure in the internal space 70a with a negative pressure generator. However, this is not limiting. The permeate liquid supplied device 70 may also be configured so that the permeate liquid flows out from the outlet 74 due to the weight of the stored permeate liquid (head pressure) when the negative pressure state created by the negative pressure generator is released (the internal space 70a is opened to the atmosphere).

[0050] Furthermore, in this embodiment, the permeate liquid supplied device 70 is disposed to the side of the filtration device 30. However, this is not a limitation. The permeate liquid supplied device 70 can be disposed in various arbitrary positions, such as below the filtration device 30. When the permeate liquid supplied device 70 is disposed below the filtration device 30, the permeate supply channel 5 may extend from the internal space 68a of the lower bundling part 68 toward the bottom 33 of the storage container 32. With this configuration, when the outlet part 74 is opened, the filtration system 1 can allow the permeate discharged from the outlet 58 of the hollow fiber membrane 52 to flow out of the internal space 68a of the lower bundling part 68 by gravity and supply it to the permeate liquid supplied device 70 without using a negative pressure generator.

[0051] The filtration system 1 having the above configuration is configured so that the filtration device 30 can filter the liquid using the filtration membrane unit 50 by creating a negative pressure in the internal space 70a of the permeated liquid supplied device 70. Specifically, the filtration system 1 creates a negative pressure in the internal space 70a of the permeated liquid supplied device 70 using a negative pressure generator while liquid is supplied to the storage container 32 of the filtration device 30, thereby creating a negative pressure in the permeated liquid supply channel 5, and ultimately in the lower bundling portion 68 of the filtration membrane unit 50 and the hollow portion 55 of the hollow fiber membrane 52. The liquid in the storage container 32 is then drawn from the filtration circumferential surface 54 of the hollow fiber membrane 52 into the hollow portion 55, and is filtered by the filtration circumferential surface 54.

[0052] The permeate filtered by the hollow fiber membranes 52 is discharged from the outlet 58 of the hollow fiber membranes 52 and accumulates in the internal space 68a of the lower bundling part 68. Thereafter, the permeate accumulated in the internal space 68a of the lower bundling part 68 is drawn into the permeate supply channel 5 from one end 5a of the permeate supply channel 5 and supplied to the permeate supplied device 70. Furthermore, by supplying liquid from the liquid supply device 10 to the filtration device 30 so that the liquid level in the storage container 32 is maintained higher than the other end 5b of the permeate supply channel 5, as filtration by the filtration membrane part 50 progresses, the permeate supply channel 5 and the hollow part 55 of the hollow fiber membranes 52 are constantly filled with permeate.

[0053] Even if the negative pressure generator is stopped in this state, the permeated liquid stored in the internal space 70a of the permeated liquid supplied device 70 is discharged from the outlet 74, thereby performing filtration by the filtration membrane unit 50. Furthermore, when the hollow fiber membrane 52 is filled with the permeated liquid, the circular cross section of the hollow section 55 is maintained without being crushed, and therefore it is possible to prevent the cross section of the hollow section 55 from being blocked and filtration from stopping.

[0054] [Filtration method according to this embodiment] Next, a filtration method using the filtration system 1 according to this embodiment will be described. The filtration method according to this embodiment generally comprises a storage container 32 having an inner cylinder 36 extending in the vertical direction and capable of storing a liquid, at least one ascending flow generating unit 120 that generates an ascending flow containing bubbles B in an outer flow space 37 formed outside the inner cylinder 36 or an inner flow space 38 formed inside the inner cylinder 36, and a filtration membrane unit 50 arranged within the inner cylinder 36, the inner flow space 38 and the outer flow space 37 communicating with each other at the upper and lower sides of the inner cylinder 36, and a circulation flow path CP that circulates the objects to be separated and the bubbles B. The permeated liquid that has permeated the filtration membrane unit 50 is discharged from the lower end of the filtration membrane unit 50.

[0055] Specifically, in the filtration system 1 according to this embodiment, first, liquid is supplied from the liquid supply device 10 to the filtration device 30 through the liquid supply path 3. The liquid flows into the storage container 32 of the filtration device 30 from an inlet provided above the storage container 32. The liquid in the storage container 32 then permeates the filtration circumferential surfaces 54 of the plurality of hollow fiber membranes 52 of the filtration membrane section 50 (see arrow FF1 in FIG. 6).

[0056] The liquid is filtered as it passes through the filtration peripheral surface 54, and the permeated liquid that has passed through the filtration peripheral surface 54 moves downward within the hollow portion 55 (see arrow FF2 in FIG. 6). The permeated liquid within the hollow portion 55 is then discharged from the outlet 58 and accumulates in the internal space 68a of the lower bundling portion 68. The permeated liquid accumulated in the internal space 68a is supplied to the permeated liquid supply destination device 70 through the permeated liquid supply path 5.

[0057] After or during the filtration process by the filtration device 30, in the separation device, the gas generating section 121 of the ascending flow generating section 120 generates gas, and the lower swirling flow generating section 140 or the upper swirling flow generating section 150 makes the flow in the inner flow space 38 a swirling flow, thereby generating a swirling flow in the inner flow space 38 formed inside the inner cylinder 36 of the storage vessel 32. Then, the swirling flow generated in the inner flow space 38 removes impurities attached to the filtration peripheral surface 54 of the hollow fiber membrane 52 of the filtration membrane section 50 attached inside the inner cylinder 36 from the filtration peripheral surface 54.

[0058] Specifically, first, gas generation is started by the switch 121a of the gas generation unit 121, and the generated gas is supplied to the gas release unit 122 via the gas supply unit 123 and the connection unit 124 of the upward flow generation unit 120. Next, the gas release unit 122 releases the gas into the inner flow space 38 of the inner cylinder 36 via the support unit 143 of the lower swirl flow generation unit 140. This generates an upward flow containing bubbles B in the inner flow space 38 (see arrow SF1 in FIG. 6). The gas released into the inner flow space 38 flows and swirls between the blades 142 of the lower swirl flow generation unit 140, generating a swirling upward flow in the inner flow space 38. That is, the liquid and bubbles B in the inner flow space 38 rise in the inner flow space 38 while swirling.

[0059] When the liquid in the inner flow space 38 rises in the inner flow space 38, the liquid in the outer flow space 37 is drawn into the inner flow space 38 (see arrow SF2 in FIG. 6), and a downward flow is generated in the outer flow space 37 (see arrow SF3 in FIG. 6). The liquid drawn from the outer flow space 37 to the inner flow space 38 flows between the blade portions 142, and therefore, coupled with the swirling force of the gas released from the gas release portion 122, the liquid rises in the inner flow space 38 while swirling.

[0060] Meanwhile, the liquid and bubbles B rising in the inner flow space 38 rise to the top plate 151 of the upper swirl flow generating section 150. The filtration circumferential surfaces 54 of the hollow fiber membranes 52 of the filtration membrane section 50 of the filtration device 30 located in the inner flow space 38 are exposed to the flow in the inner flow space 38. Therefore, impurities adhering to the filtration circumferential surfaces 54 are removed as the liquid and bubbles B in the inner flow space 38 rise to the top plate 151. The liquid and bubbles B containing impurities that have risen to the top plate 151 then flow along the inclined surface 151a of the top plate 151 into the outer flow space 37 and descend through the outer flow space 37 (see arrow SF4 in FIG. 6 ). The liquid and bubbles B flowing into the outer flow space 37 swirl between the blades 152 of the upper swirl flow generating section 150, generating a swirling downward flow in the outer flow space 37. That is, the liquid and bubbles B in the outer flow space 37 descend within the outer flow space 37 while swirling.

[0061] The liquid and bubbles B circulate through the circulation flow path CP as described above. During this circulation process, when the liquid and bubbles B are drawn from the outer flow space 37 to the inner flow space 38, the flow velocity increases (pressure decreases), and the bubbles B become finer. Furthermore, the bubbles B circulating through the circulation flow path CP become finer as they swirl through the inner flow space 38 and the outer flow space 37 and are sheared by the blades 142 of the lower swirl flow generating section 140 and the blades 152 of the upper swirl flow generating section 150. In other words, the more the bubbles B circulate through the circulation flow path CP, the finer they become.

[0062] In this way, the separation device according to this embodiment is configured to be capable of generating fine bubbles. By generating fine bubbles, the total surface area of ​​the bubbles B generated within the separation device increases, thereby improving separation performance. Note that fine bubbles include microbubbles (bubbles with a diameter of 1 μm or more and less than 100 μm) and ultrafine bubbles (bubbles with a diameter of less than 1 μm).

[0063] The generation of gas is stopped at any or predetermined timing by the switch 121a of the gas generation unit 121. This stops the release of gas by the gas release unit 122, and the circulation of the liquid and bubbles B in the circulation flow path CP stops. When the circulation stops, the bubbles B rise in the inner flow space 38 and the outer flow space 37 while adsorbing suspended matter in the liquid (impurities adhering to the filtration peripheral surface 54 of the hollow fiber membrane 52). This makes it possible to separate the liquid from the impurities contained in it. The filtration method using the filtration system 1 according to this embodiment is carried out by the above series of steps.

[0064] [Advantages of the filtration device, filtration system, and filtration method according to the present embodiment] As described above, the filtration device 30 of this embodiment has an inner tube 36 extending in the vertical direction, a storage container 32 capable of containing a liquid, at least one ascending flow generating section 120 that generates an ascending flow containing bubbles B in the outer flow space 37 formed outside the inner tube 36 or the inner flow space 38 formed inside the inner tube 36, and a filtration membrane section 50 arranged inside the inner tube 36, the inner flow space 38 and the outer flow space 37 being connected to each other on the upper and lower sides of the inner tube 36 and configured to be able to form a circulation flow path CP that circulates the bubbles B, and the filtration membrane section 50 has an outlet 58 at its lower end that discharges the permeate that has passed through the filtration membrane section 50.

[0065] The filtration device 30 according to the present embodiment, with such a configuration, unlike conventional hollow fiber membrane modules in which permeate is discharged from above the filtration membrane unit 50, discharges permeate from below the filtration membrane unit 50 in the same direction as the hydraulic head pressure. This allows for greater pressure to be applied to the liquid to be filtered, thereby improving the filtration rate and, ultimately, the filtration efficiency. Furthermore, because the hydraulic head pressure of the liquid in the storage vessel 32 can be used to pressurize the liquid, filtration can be performed faster than conventional methods without the need to suction the liquid using a suction pump. Furthermore, conventional hollow fiber membrane modules require, for example, frequent interruptions in the filtration process to clean the hollow fiber membranes 52 with backwash liquid to prevent the filtration membrane unit 50 from clogging due to impurities contained in the liquid and reducing filtration efficiency. However, the filtration device 30 according to the present embodiment can remove impurities adhering to the filtration membrane unit 50 even during the filtration process by using the upward flow generated in the inner flow space 38 of the inner cylinder 36 by the upward flow generating unit 120. This has the advantage of improving filtration efficiency compared to conventional methods.

[0066] Furthermore, in the filtration device 30 according to this embodiment, the filtration membrane unit 50 includes a hollow fiber membrane 52 having a cylindrical filtration circumferential surface 54, a hollow portion 55 defined by the filtration circumferential surface 54, and an outlet 58 for discharging permeate from the hollow portion 55. Unlike conventional hollow fiber membrane modules in which the liquid to be filtered moves from the bottom to the top of the flow path of the hollow fiber membrane 52 and the permeate is discharged from the upper end of the hollow fiber membrane 52, the filtration device 30 according to this embodiment has such a configuration. This discharging the permeate from the outlet 58 provided at the lower end of the hollow fiber membrane 52 makes it possible to apply a greater pressure to the liquid to be filtered than conventionally, thereby improving the filtration rate and, ultimately, the filtration efficiency. Furthermore, the filtration device 30 according to this embodiment has the advantage of being able to remove impurities adhering to the filtration circumferential surface 54 during the filtration process by the upward flow generated by the upward flow generating unit 120, thereby improving the filtration efficiency compared to conventionally.

[0067] Furthermore, in the filtration device 30 according to this embodiment, the upward flow generating section 120 has at least one gas release section 122 that releases gas into the outer flow space 37 or the inner flow space 38, below the middle section in the vertical direction of the storage container 32. With this configuration, an upward flow containing bubbles B can be generated simply by releasing gas from the gas release section 122, and the separation target (impurities contained in the filtered liquid in this embodiment) and bubbles B can be circulated, which has the advantages of allowing the separation target to be separated at low cost and also providing high reliability and durability.

[0068] Furthermore, the filtration device 30 according to this embodiment includes at least one of an inner swirling flow generating section 160 that generates a swirling flow in the inner flow space 38 along the circumferential direction of the inner tube 36 of the storage vessel 32 and an outer swirling flow generating section 170 that generates a swirling flow in the outer flow space 37 along the circumferential direction of the inner tube 36 of the storage vessel 32. This configuration advantageously generates a swirling flow, thereby facilitating the removal of impurities adhering to the hollow fiber membranes 52. Furthermore, the swirling flow facilitates the circulation of the separation target (impurities contained in the filtered liquid in this embodiment) and the air bubbles B, thereby preventing the separated impurities from adhering again to the filtration surface 54 of the hollow fiber membranes 52. Another advantage is that the swirling of the air bubbles B can reduce the size of the air bubbles B. Furthermore, reducing the size of the air bubbles B increases the total surface area of ​​the air bubbles B, thereby improving separation performance.

[0069] Furthermore, in the filtration device 30 according to this embodiment, the inner swirl flow generating section 160 and the outer swirl flow generating section 170 include blade sections 142 (or blade sections 152). This configuration has the advantage of generating a swirl flow simply by moving the object to be separated (the impurities contained in the liquid filtered in this embodiment) between the blade sections 142 (or blade sections 152). Another advantage is that the bubbles B are sheared by the blade sections 142 (or blade sections 152), which allows the bubbles B to be refined. Another advantage is that the impurities are refined and floated up easily because not only the bubbles B but also solid impurities are sheared by the blade sections 142 (or blade sections 152). Furthermore, since a spiral swirl flow can be generated, impurities adhering to the upper part of the hollow fiber membranes 52 can be more reliably removed, which has the advantage of preventing the hollow fiber membranes 52 from becoming clogged and blocked.

[0070] [Variations] Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above-described embodiments. Various modifications and improvements can be made to the above-described embodiments.

[0071] For example, in the above-described embodiment, the filtration membrane unit 50 has been described as including hollow fiber membranes 52 each having a cylindrical filtration circumferential surface 54, a hollow portion 55 defined by the filtration circumferential surface 54, and an outlet 58 for discharging permeate from the hollow portion 55. However, the filtration membrane unit 50 is not limited to this. The filtration membrane unit 50 may not include the hollow fiber membranes 52, but may instead include a flat membrane module, a spiral membrane module or pleated membrane module using a flat membrane, a tubular membrane module using a tubular membrane, or the like.

[0072] In the above-described embodiment, the upward flow generating section 120 has been described as having at least one gas release section 122 that releases gas into the outer flow space 37 or the inner flow space 38 below the middle section in the vertical direction of the storage container 32, but is not limited to this. The upward flow generating section 120 does not necessarily have to have the gas release section 122.

[0073] In the above-described embodiment, the filtration device 30 has been described as having at least one of the inner swirling flow generating section 160 that generates a swirling flow in the inner flow space 38 along the circumferential direction of the inner cylinder 36 of the storage vessel 32 and the outer swirling flow generating section 170 that generates a swirling flow in the outer flow space 37 along the circumferential direction of the inner cylinder 36 of the storage vessel 32, but this is not limited thereto. The filtration device 30 does not necessarily have to have the inner swirling flow generating section 160 or the outer swirling flow generating section 170. Furthermore, the filtration device 30 has been described as having the lower swirling flow generating section 140 and the upper swirling flow generating section 150, but this is not limited thereto and the filtration device 30 may have only one of these or neither.

[0074] In the above-described embodiment, the inner swirl flow generating section 160 and the outer swirl flow generating section 170 have been described as having the blade portion 142 (or the blade portion 152), but this is not limited thereto. The inner swirl flow generating section 160 and the outer swirl flow generating section 170 do not have to have the blade portion 142 (or the blade portion 152). Furthermore, in the above-described embodiment, the blade portion 142 (or the blade portion 152) has been described as having a shape curved in the circumferential direction of the inner cylinder 36, but this is not limited thereto. The blade portion 142 (or the blade portion 152) may not have a shape curved in the circumferential direction of the inner cylinder 36, but may have a shape that extends radially in the radial direction of the inner cylinder 36, for example.

[0075] In the above-described embodiment, the storage vessel 32 has a bottom 33 closing the lower end and a top 34 closing the upper end, the permeated liquid supplied device 70 is configured as a bottomed cylinder and has a top 72 closing the open end of the permeated liquid supplied device 70, the filtration device 30 and the permeated liquid supplied device 70 are configured to change the pressure in the internal space 70a and are connected via the permeated liquid supply path 5, and the filtration device 30 is configured to filter the liquid using the filtration membrane unit 50 by creating a negative pressure in the internal space 70a of the permeated liquid supplied device 70. However, this is not limited to this. The storage vessel 32 may not have a top 34, and the upper end may be open to the atmosphere. Similarly, the permeated liquid supplied device 70 may not have a top 72. Furthermore, the filtration device 30 and the permeated liquid supplied device 70 do not have to be configured to change the pressure in the internal space 70a. Furthermore, the filtration device 30 does not necessarily have to be configured to be able to filter the liquid with the filtration membrane unit 50 by creating a negative pressure in the internal space 70a of the permeated liquid supply device 70. For example, the filtration device 30 may be configured to be able to filter the liquid with the filtration membrane unit 50 by utilizing the hydraulic head pressure of the liquid in the storage vessel 32, or may be configured to be able to filter the liquid with the filtration membrane unit 50 by pressurizing the inside of the storage vessel 32.

[0076] In the above-described embodiment, the plurality of hollow fiber membranes 52 are described as constituting a cylindrical membrane module, but this is not limiting, and the plurality of hollow fiber membranes 52 may also constitute a sheet-type membrane module. Furthermore, in the above-described embodiment, the filtration membrane unit 50 is described as having the upper bundling portion 66 and the lower bundling portion 68, but this is not limiting, and the filtration membrane unit 50 may not have the upper bundling portion 66 and the lower bundling portion 68.

[0077] In the above-described embodiment, the filtration device 30 has been described as including a separation device configured to separate the objects to be separated within the filtration device 30, but is not limited to this. The filtration device 30 is only required to be able to remove impurities adhering to the filtration membrane unit 50 by the upward flow generated in the inner flow space 38 of the inner cylinder 36 by the upward flow generating unit 120, and does not necessarily have to be able to separate the impurities from the liquid containing the removed impurities. [Explanation of symbols]

[0078] 1. Filtration system 3 Liquid supply path 5 Permeate supply path 10 Liquid supply device 30 Filtration device 32 Containment vessel 33 Bottom 34 Top 35 outer cylinder 36 Inner cylinder 36a Upper opening 37 Outer flow space 38 Inner flow space 50 Filtration membrane section 52 Hollow fiber membrane 54 Filter peripheral surface 55 Hollow part 56 Inlet 58 Outlet 60 Housing 66 Upper binding part 68 Lower binding part 68a Interior space 70 Permeate supply device 70 Interior Space 72 Top section 74 Outflow section 120 Upward flow generation section 121 Gas generation unit 121a switch 122 Gas release section 123 Gas supply section 124 Connection 140 Lower swirl flow generation section 142 Wing 143 Support part 143a Insertion groove 143b Pipe section 143c Mounted part 143d Outflow hole 150 Upper swirl flow generation section 151 Top plate 151a Slope 152 Wing 153 Mounting part 160 Inner swirl flow generating section 170 Outer swirl flow generation section B. Air bubbles CP circulation flow path

Claims

1. a container having an inner cylinder extending in a vertical direction and capable of containing a liquid; at least one upward flow generating unit that generates an upward flow containing bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder; a filtration membrane portion disposed in the inner cylinder; Equipped with the inner flow space and the outer flow space are connected to each other at the upper and lower sides of the inner cylinder, and are configured to be able to form a circulation flow path for circulating bubbles, The filtration membrane unit has a discharge port at a lower end for discharging permeated liquid that has permeated the filtration membrane unit, The storage vessel includes an upper swirl flow generating unit provided above the inner cylinder, The upper swirl flow generating unit is configured to generate a swirl flow from a downward flow. Filtration device.

2. The filtration membrane unit includes a hollow fiber membrane having a cylindrical filtration peripheral surface, a hollow portion defined by the filtration peripheral surface, and the outlet for discharging the permeated liquid from the hollow portion. The filtration device of claim 1 .

3. The upward flow generating section has at least one gas release section that releases gas into the outer flow space or the inner flow space below a middle section of the container in the vertical direction.

3. The filtration device according to claim 1 or 2.

4. an inner swirl flow generating section that generates a swirling flow in the inner flow space along the circumferential direction of the inner cylinder of the storage vessel, and / or an outer swirl flow generating section that generates a swirling flow in the outer flow space along the circumferential direction of the inner cylinder of the storage vessel, The upper swirl flow generating section functions as the inner swirl flow generating section or the outer swirl flow generating section.

3. The filtration device according to claim 1 or 2.

5. The inner swirl flow generating portion and the outer swirl flow generating portion have blade portions.

5. The filtration device of claim 4.

6. A storage container having an inner tube extending in the vertical direction and capable of storing a liquid; at least one upward flow generating unit that generates an upward flow containing bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder; a filtration membrane portion disposed in the inner cylinder; Equipped with the inner flow space and the outer flow space are connected to each other at the upper and lower sides of the inner cylinder, and are configured to be able to form a circulation flow path for circulating bubbles; the filtration membrane unit has a discharge port at a lower end for discharging permeated liquid that has permeated the filtration membrane unit, and is provided with a permeated liquid supply path that communicates with a permeated liquid supply device; The internal space of the permeated liquid supply device is made negative pressure, thereby enabling filtration of the liquid by the filtration membrane unit. Filtration device.

7. a filtration device for filtering the liquid; a liquid supply device that supplies the liquid to the filtering device; a permeated liquid supply device to which the permeated liquid filtered by the filtration device is supplied; A filtration system comprising: The filtration device is a container having an inner cylinder extending in a vertical direction and capable of containing the liquid; at least one upward flow generating unit that generates an upward flow containing bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder; a filtration membrane portion disposed in the inner cylinder; Equipped with the inner flow space and the outer flow space are connected to each other at the upper and lower sides of the inner cylinder, and are configured to be able to form a circulation flow path for circulating bubbles, the filtration membrane unit has a discharge port at a lower end for discharging the permeated liquid that has permeated the filtration membrane unit, The storage vessel includes an upper swirl flow generating unit provided above the inner cylinder, The upper swirl flow generating unit is configured to generate a swirl flow from a downward flow. Filtration system.

8. A filtration device for filtering a liquid; a liquid supply device that supplies the liquid to the filtering device; a permeated liquid supply device to which the permeated liquid filtered by the filtration device is supplied; A filtration system comprising: The filtration device is a container having an inner cylinder extending in a vertical direction and capable of containing the liquid; at least one upward flow generating unit that generates an upward flow containing bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder; a filtration membrane portion disposed in the inner cylinder; Equipped with the inner flow space and the outer flow space are connected to each other at the upper and lower sides of the inner cylinder, and are configured to be able to form a circulation flow path for circulating bubbles; the filtration membrane unit has a discharge port at a lower end for discharging the permeated liquid that has permeated the filtration membrane unit, the container has a bottom portion that closes the lower end and a top portion that closes the upper end, the permeated liquid supply device is configured in a cylindrical shape with a bottom and has a top surface portion that closes an open end of the permeated liquid supply device, the filtering device and the permeated liquid supply device are configured to be able to change the pressure of their internal spaces, and are in communication with each other via a permeated liquid supply path; The filtering device is configured to be able to filter the liquid by the filtering membrane portion by creating a negative pressure in the internal space of the permeated liquid supply device. Filtration system.

9. A filtration method for filtering a liquid using a filtration device comprising: a container having an inner cylinder extending in a vertical direction and capable of containing a liquid; at least one ascending flow generating unit that generates an ascending flow containing air bubbles in an outer flow space formed outside the inner cylinder or an inner flow space formed inside the inner cylinder; and a filtration membrane unit arranged within the inner cylinder, wherein the inner flow space and the outer flow space are connected to each other at an upper side and a lower side of the inner cylinder, and a circulation flow path that circulates air bubbles is formed, the storage vessel includes an upper swirl flow generating unit provided above the inner cylinder, the upper swirl flow generating unit being configured to turn the downward flow into a swirl flow, The permeated liquid that has permeated the filtration membrane portion is discharged from the lower end of the filtration membrane portion. Filtration method.

10. A filtration method for filtering a liquid using a filtration device comprising: a container having an inner tube extending in a vertical direction and capable of containing a liquid; at least one rising flow generating section for generating an rising flow containing bubbles in an outer flow space formed outside the inner tube or an inner flow space formed inside the inner tube; and a filtration membrane section arranged within the inner tube, wherein the inner flow space and the outer flow space are connected on the upper and lower sides of the inner tube and are configured to be able to form a circulation flow path for circulating the bubbles, The filtration membrane unit includes a permeate supply passage communicating with a permeate supply device, and the liquid is filtered by creating a negative pressure in the internal space of the permeate supply device, and the permeate that has permeated the filtration membrane unit is discharged from the lower end of the filtration membrane unit. Filtration method.

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