Filtration device and filtration method

Abstract

This filtration device comprises a spiral-type membrane module, wherein the membrane module comprises an element around which a leaf comprising a filtration membrane is wound, and the inlet pressure of a stock solution flowing into the membrane module is less than 0.2 MPa.

Description

Filtration device and filtration method

[0001] The present invention relates to a filtering device and a filtering method.

[0002] Patent Document 1 discloses a spiral seawater desalination system comprising: a spiral pressure vessel containing a plurality of reverse osmosis membrane elements connected by permeate pipes, each element having a spiral reverse osmosis membrane that removes salt from raw water to obtain permeate; a raw water supply line that supplies raw water into the pressure vessel; a concentrated water discharge line that discharges concentrated water concentrated in the pressure vessel to the outside; and a permeate line that discharges the permeate from the permeate pipe to the outside.

[0003] Patent No. 5535491

[0004] In the above Patent Document 1, an example is given in which a pressure of 70 kg / cm ２ The paper describes an experiment in which raw water was supplied to the pressure vessel at a pressure of 1000 kJ / s. Such high-pressure operation consumes a lot of power.

[0005] The present invention was made by the inventors of the present application by focusing on the above-mentioned problem, and an object of the present invention is to provide a filtration device and a filtration method that can reduce power consumption.

[0006] A filtration device according to one aspect of the present invention includes a spiral membrane module, the membrane module including an element wound with a leaf having a filtration membrane, and the inlet pressure of the raw liquid flowing into the membrane module is less than 0.2 MPa.

[0007] A filtration device according to another aspect of the present invention includes a spiral membrane module, the membrane module including an element having a leaf wound therearound, and further including a pump for supplying a raw liquid to the membrane module, wherein an upper limit of the discharge pressure of the pump is less than 0.45 MPa.

[0008] A filtration method according to one aspect of the present invention is a filtration method in a filtration apparatus including a spiral membrane module, wherein the membrane module includes an element around which a leaf having a filtration membrane is wound, and in the filtration method, a raw liquid is introduced into the membrane module at an inlet pressure of less than 0.2 MPa.

[0009] According to the filtering device and the like of the present invention, power consumption can be reduced.

[0010] FIG. 1 is a schematic diagram showing the overall configuration of a filtration device according to an embodiment. FIG. 2 is a perspective view showing the configuration of a membrane module according to an embodiment. FIG. 3 is a front view, a bottom view, and a top view showing the configuration of a membrane module according to an embodiment. FIG. 4 is a perspective view showing the configuration of a first element according to an embodiment. FIG. 5 is a plan view and a cross-sectional view showing the configuration of a leaf according to an embodiment. FIG. 6 is a flowchart showing each step of a filtration method in a filtration device according to an embodiment. FIG. 7 is a front view, a bottom view, and a top view showing the configuration of a membrane module that forms a part of a membrane module according to an embodiment. FIG. 8 is a front view showing a process for manufacturing a membrane module according to an embodiment. FIG. 9 is a front view showing the configuration of a membrane module according to a first modification of the embodiment. FIG. 10 is a schematic diagram showing the overall configuration of a filtration device according to a second modification of the embodiment.

[0011] (1) A filtration device according to one embodiment of the present invention includes a spiral membrane module, the membrane module including an element wound with a leaf having a filtration membrane, and the inlet pressure of the raw liquid flowing into the membrane module is less than 0.2 MPa.

[0012] In the filtration device according to one embodiment of the present invention, the inlet pressure of the raw liquid flowing into the spiral membrane module is less than 0.2 MPa. By performing low-pressure operation by setting the inlet pressure of the raw liquid flowing into the membrane module to less than 0.2 MPa, the power required to pressurize the raw liquid can be reduced, thereby reducing power consumption.

[0013] (2) In the filtration device described in (1) above, the filtration membrane may be a microfiltration membrane.

[0014] According to the filtration device described in (2) above, the filtration membrane of the element provided in the spiral membrane module is a microfiltration membrane. Conventional spiral membrane modules used RO (reverse osmosis) or UF (ultrafiltration) membranes with relatively small pore sizes, so sufficient filtrate volume could not be obtained unless they were operated under high pressure, with the raw liquid inlet pressure being a high pressure of 0.2 MPa or higher. Spiral membrane modules using microfiltration (MF) membranes were also operated under high pressure, similar to those using RO or UF membranes. In the process of considering the application of spiral membrane modules to the filtration and concentration of biological systems such as microalgae, the inventors discovered a problem that high-pressure operation could destroy cells and kill the organisms. After extensive research, they discovered that operation under a sufficiently low raw liquid inlet pressure (low-pressure operation) would not destroy cells and could filter and concentrate microalgae alive. Further investigation revealed that when a membrane module using a microfiltration membrane is operated at low pressure, it can be used practically with low power consumption for purposes other than filtration and concentration of biological systems.

[0015] (3) In the filtration device described in (2) above, the pore size of the microfiltration membrane may be 0.1 μm or more and 0.4 μm or less.

[0016] According to the filtration device described in (3) above, the pore size of the microfiltration membrane provided in the spiral membrane module is 0.1 μm or more and 0.4 μm or less. Here, the microfiltration membrane is used to filter substances with an average particle size of approximately 0.05 μm to 10 μm, particularly substances with an average particle size exceeding 0.4 μm. When the inlet pressure of the raw liquid is high, i.e., during high-pressure operation, substances with particle sizes slightly larger than the pore size of the microfiltration membrane may be deformed by the applied pressure and pushed into the pores of the microfiltration membrane, resulting in clogging of the pores. In contrast, during low-pressure operation, the inlet pressure of the raw liquid is low, so the problem of clogging of the pores by substances with particle sizes slightly larger than the pore size of the micropores is less likely to occur. On the other hand, when the pore size of the micropores is less than 0.1 μm, it is difficult to obtain the required amount of filtrate during low-pressure operation. For these reasons, when a spiral-type membrane module using a microfiltration membrane is operated at low pressure, it is preferable to set the pore size of the microfiltration membrane to 0.1 μm or more and 0.4 μm or less, which makes it possible to prevent clogging of the micropores and to obtain a sufficient amount of filtrate.

[0017] (4) In the filtration device according to any one of (1) to (3) above, the inlet pressure may be 0.1 MPa or less.

[0018] According to the filtration device described in (4) above, the inlet pressure of the raw liquid flowing into the spiral membrane module is 0.1 MPa or less. Thus, by performing low-pressure operation with the inlet pressure of the raw liquid flowing into the membrane module set to 0.1 MPa or less, the power required to pressurize the raw liquid can be further reduced, thereby further reducing power consumption. Furthermore, by performing even lower-pressure operation, clogging of the micropores by filtered matter can be made less likely. In the process of considering the application of spiral membrane modules to the filtration and concentration of biological systems such as microalgae, the inventors discovered a problem that high-pressure operation could destroy cells and kill the organisms. By performing low-pressure operation with the inlet pressure of the raw liquid flowing into the membrane module set to 0.1 MPa or less, cells are not destroyed, and microalgae and other organisms can be filtered and concentrated alive. It is preferable to use a microfiltration membrane in the membrane module because, under low-pressure operation where the raw liquid inlet pressure is 0.1 MPa or less, a sufficient amount of filtrate can be obtained and filtration efficiency can be improved compared to when an RO membrane or UF membrane is used in the membrane module.This makes it possible to filter and concentrate with high filtration efficiency while suppressing cell destruction of microalgae and the like.

[0019] (5) In the filtration device according to any one of (1) to (4) above, the element may include a collection tube for collecting filtrate.

[0020] According to the filtration device described in (5) above, the element of the spiral membrane module is provided with a filtrate collection pipe. Since the filtration device is operated at a low pressure, that is, the inlet pressure of the raw liquid flowing into the membrane module is set to less than 0.2 MPa, a configuration that can reduce the resistance of the filtrate when it flows is preferable. Therefore, by configuring the filtrate to be collected in the collection pipe and then flowing, the resistance of the filtrate when it flows can be reduced.

[0021] (6) In the filtration device described in any one of (1) to (5) above, the leaf may include a filtrate net that forms a flow path for the filtrate, the length of the filtration membrane in the winding direction may be 800 mm or less, and the thickness of the filtrate net may be 0.2 mm or more.

[0022] According to the filtration device described in (6) above, in the element provided in the spiral-type membrane module, the length of the filtration membrane in the winding direction is 800 mm or less, and the thickness of the filtrate net is 0.2 mm or more. Conventional spiral-type membrane modules are often used for general crossflow filtration, such as "cakeless filtration," which does not form membrane surface deposits (cake layers). In this case, high-pressure operation is performed. During high-pressure operation, resistance due to pressure loss in the winding direction of the filtration membrane can be ignored, so there is almost no benefit to shortening the length of the filtration membrane in the winding direction. Therefore, the length of the filtration membrane in the winding direction is relatively long. In contrast, the filtration device performs low-pressure operation in which the inlet pressure of the raw liquid flowing into the membrane module is lowered to less than 0.2 MPa. Therefore, increasing the length of the filtration membrane in the winding direction reduces the amount of filtrate. Therefore, in the filtration device described in (6) above, the length of the filtration membrane in the winding direction is shortened to 800 mm or less, thereby reducing resistance due to pressure loss in the winding direction of the filtration membrane. Furthermore, the thickness of the filtrate net is set to 0.2 mm or more to ensure space for the filtrate to flow. By adopting these configurations, it is possible to reduce the overall pressure loss and increase the amount of filtrate. As such, the use of this configuration to increase the amount of filtrate under the specific condition of low-pressure operation would not have been predictable based on prior art that assumes high-pressure operation.

[0023] (7) In the filtration device described in (6) above, the effective filtration area per leaf of the element is 1.3 m ２ It may be the following:

[0024] According to the filtration device described in (7) above, the effective filtration area per leaf of the element provided in the spiral membrane module is 1.3 m ２ In this way, in a filtration device using a filtration membrane with a short length in the winding direction, the effective filtration area per leaf is 1.3 m or less. ２By setting the following, it is possible to reduce not only the pressure loss in the filtrate flow path but also the circulation pressure loss. Here, "pressure loss in the filtrate flow path" means the pressure loss in the path through which the filtrate that has permeated the filtration membrane flows. Furthermore, "circulation pressure loss" means the pressure loss in the path through which the raw liquid flows. The pressure loss in the filtrate flow path and the circulation pressure loss do not pose a problem during high-pressure operation (generally high-circulation operation), but have a significant impact during low-pressure operation (which inevitably results in low-circulation operation). Therefore, when the effective filtration area per leaf is set to 1.3 m during low-pressure operation, ２ By setting the value to a small value of not more than 1 / 2, the pressure loss in the filtrate flow path and the circulation pressure loss in one leaf can be reduced.

[0025] (8) In the filtration device described in (7) above, the number of leaves of the element may be 16 or more.

[0026] According to the filtration device described in (8) above, the number of leaves of the element provided in the spiral membrane module is 16 or more. Here, by shortening the length of the filtration membrane in the winding direction and reducing the effective filtration area per leaf, it is possible to reduce the pressure loss in the filtrate flow path and the circulation pressure loss in the case of low-pressure operation. However, if the effective filtration area of ​​the entire element is reduced, a sufficient amount of filtrate cannot be obtained. Therefore, the length of the filtration membrane in the winding direction is set to 800 mm or less, and the effective filtration area per leaf is set to 1.3 m. ２ When the number of leaves is set to 16 or more in the case of low-pressure operation, it is possible to secure a larger amount of filtrate while maintaining low pressure loss in the filtrate flow path and circulation pressure loss.

[0027] (9) Another embodiment of the present invention provides a filtration device comprising a spiral membrane module, the membrane module comprising an element wound with a leaf having a filtration membrane, and further comprising a pump for supplying a raw liquid to the membrane module, wherein the upper limit of the discharge pressure of the pump is less than 0.45 MPa.

[0028] According to another embodiment of the filtration apparatus of the present invention, in a spiral membrane module, the upper limit of the discharge pressure of the pump supplying the raw liquid to the membrane module is less than 0.45 MPa. By reducing the upper limit of the pump discharge pressure to less than 0.45 MPa, the power required to pressurize the raw liquid can be reduced, thereby reducing power consumption. Conventional filtration apparatuses equipped with spiral membrane modules had to operate under high pressure conditions, with the inlet pressure of the raw liquid flowing into the membrane module at 0.45 MPa or higher, in order to obtain a sufficient amount of filtrate even when RO or UF membranes were used in the membrane module. Therefore, conventional apparatuses employed pumps with sufficiently high discharge pressure performance for supplying the raw liquid. For example, pumps with an upper limit of the discharge pressure of 0.45 MPa or higher were used. In conventional apparatuses, there was no need to reduce the upper limit of the pump discharge pressure to less than 0.45 MPa, and no such attempt was made. In response to this issue, as explained above, the inventors discovered a phenomenon in which high-pressure operation could destroy cells and kill organisms while studying the application of spiral membrane modules to the filtration and concentration of biological systems such as microalgae. This led them to focus on operating the raw liquid entering the membrane module at a low inlet pressure (low-pressure operation). As a result of studying practical applications of a filtration device suitable for such low-pressure operation, they discovered that a pump with an upper discharge pressure of less than 0.45 MPa could be used to supply raw liquid to the spiral membrane module. They also discovered that using such a pump could reduce power consumption during operation. This filtration device is suitable for filtration operation at an inlet pressure of less than 0.2 MPa for the raw liquid supplied to the spiral membrane module.

[0029] (10) A filtration method according to one embodiment of the present invention is a filtration method in a filtration apparatus including a spiral membrane module, the membrane module including an element around which a leaf having a filtration membrane is wound, and in the filtration method, a raw liquid is introduced into the membrane module at an inlet pressure of less than 0.2 MPa.

[0030] According to the filtration method of one embodiment of the present invention, the raw liquid is introduced into the spiral membrane module at an inlet pressure of less than 0.2 MPa. By operating the membrane module at a low pressure by setting the inlet pressure of the raw liquid flowing into the membrane module at less than 0.2 MPa, the power required to pressurize the raw liquid can be reduced, thereby reducing power consumption.

[0031] Hereinafter, a filtration device and a filtration method according to embodiments of the present invention (including variations thereof) will be described with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection forms, processes, process sequences, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. In each drawing, dimensions, etc. are not strictly illustrated. In each drawing, the same or similar components are designated by the same reference numerals.

[0032] In the following description and drawings, the height direction (vertical direction) of the membrane module in the filtration device, the longitudinal direction of the membrane module, the longitudinal direction of the element of the membrane module, the direction in which the winding axis of the element extends (predetermined direction), or the arrangement direction of the first membrane module and the second membrane module is defined as the X-axis direction. The front-to-rear direction of the membrane module in the filtration device is defined as the Y-axis direction. The left-to-right direction of the membrane module in the filtration device is defined as the Z-axis direction. These X-axis, Y-axis, and Z-axis directions intersect each other (orthogonal in this embodiment). Depending on the usage mode, the X-axis direction may not be the height direction (vertical direction); however, for convenience of explanation, the following description will be made assuming that the X-axis direction is the height direction (vertical direction).

[0033] In the following description, the positive X-axis direction refers to the direction of the X-axis arrow, and the negative X-axis direction refers to the direction opposite to the positive X-axis direction. When simply referring to the X-axis direction, it refers to both or either of the positive X-axis direction and the negative X-axis direction. The same applies to the Y-axis direction and the Z-axis direction. Expressions indicating relative directions or attitudes, such as parallel and orthogonal, also include cases where the directions or attitudes are not strictly those. Two directions being parallel (or orthogonal) does not only mean that the two directions are completely parallel (or orthogonal), but also means that the directions are substantially parallel (or orthogonal), that is, there is a difference of, for example, about a few percent.

[0034] (Embodiment) [1. Description of Filtration Device 1] First, a general configuration of a filtration device 1 according to this embodiment will be described. Fig. 1 is a schematic diagram showing the general configuration of a filtration device 1 according to this embodiment.

[0035] As shown in FIG. 1 , the filtration device 1 includes a membrane module 10 , a raw liquid tank 20 , and a pump 30 .

[0036] The membrane module 10 is a crossflow filtration filter that filters solids in a raw liquid by flowing the raw liquid parallel to a filtration membrane. The membrane module 10 is a spiral-type membrane module with a wound filtration membrane. In the membrane module 10, the raw liquid is supplied through a first opening 114a of the first membrane module 100, and the raw liquid (concentrated liquid) is extracted through a second opening 214a of the second membrane module 200. In this case, in the membrane module 10, the filtrate (permeated liquid) is extracted through a first outlet 114b of the first membrane module 100 and a second outlet 214b of the second membrane module 200. In this embodiment, the filtration device 1 includes two membrane modules 10 connected in parallel. A detailed description of the configuration of the membrane modules 10 will be given later.

[0037] The stock solution tank 20 is a container (storage tank) that stores the stock solution 21. That is, the stock solution tank 20 stores the stock solution 21 to be filtered by the membrane module 10. In this embodiment, the stock solution tank 20 stores the stock solution 21 that circulates through the membrane module 10 (the stock solution 21 before being filtered by the membrane module 10 and the stock solution 21 after being filtered by the membrane module 10).

[0038] The pump 30 is a pump that supplies the raw liquid to the membrane modules 10. The pump 30 sends the raw liquid 21 stored in the raw liquid tank 20 and supplies it to the membrane modules 10. Specifically, the pump 30 extracts the raw liquid 21 from the raw liquid tank 20, discharges the extracted raw liquid 21 at a discharge pressure P1, and sends it to the two membrane modules 10 via the pipe 41.

[0039] The stock solution 21 discharged from the pump 30 is supplied to the two membrane modules 10 from the first opening 114a of the first membrane module 100 provided in each of the two membrane modules 10. Specifically, the stock solution 21 flows into one of the two membrane modules 10 (positive direction of the Z axis) at an inlet pressure P2, and the stock solution 21 flows into the other membrane module 10 (negative direction of the Z axis) at an inlet pressure P3. The inlet pressure P3 is slightly different from the inlet pressure P2 due to pressure loss when the stock solution 21 passes through the pipe 41, but it may be set to the same pressure as the inlet pressure P2 without considering the pressure loss.

[0040] The inlet pressures P2 and P3 of the raw liquid 21 flowing into the membrane module 10 are less than 0.2 MPa. The inlet pressures P2 and P3 are preferably 0.1 MPa or less, more preferably 0.07 MPa or less (or less than 0.07 MPa), and even more preferably 0.05 MPa or less (or less than 0.05 MPa). The inlet pressures P2 and P3 are preferably 0.001 MPa or more, more preferably 0.01 MPa or more, and even more preferably 0.05 MPa or more.

[0041] Since the inlet pressures P2 and P3 of the feedstock 21 flowing into the membrane module 10 are lower than 0.2 MPa, the discharge pressure P1 of the pump 30 may be low. In this embodiment, the upper limit of the discharge pressure P1 of the pump 30 is lower than 0.45 MPa. The upper limit of the discharge pressure P1 of the pump 30 is preferably 0.3 MPa or less, more preferably 0.2 MPa or less, and even more preferably 0.1 MPa or less. The lower limit of the discharge pressure P1 of the pump 30 is preferably 0.0014 MPa or more, more preferably 0.014 MPa or more, and even more preferably 0.07 MPa or more. The discharge pressure P1 of the pump 30 is adjusted by inverter control so as to match the set values ​​of the inlet pressures P2 and P3 of the feedstock 21 flowing into the membrane module 10. The discharge pressure P1 of the pump 30 may be adjusted by a flow rate adjustment valve (not shown).

[0042] The stock solution 21 is filtered (the filtrate is removed) and concentrated by the two membrane modules 10, then discharged from the second opening 214a of the second membrane module 200 provided in each of the two membrane modules 10, and returned to the stock solution tank 20 through the pipe 42. Specifically, the stock solution 21 is discharged from one of the two membrane modules 10 (in the positive direction of the Z axis) at an outlet pressure P4, and the stock solution 21 is discharged from the other membrane module 10 (in the negative direction of the Z axis) at an outlet pressure P5. The outlet pressure P4 is lower than the inlet pressure P2, and the outlet pressure P5 is lower than the inlet pressure P3. In other words, the outlet pressures P4 and P5 are lower than 0.2 MPa. The outlet pressures P4 and P5 are preferably 0.1 MPa or less, more preferably 0.07 MPa or less (or less than 0.07 MPa), and even more preferably 0.05 MPa or less (or less than 0.05 MPa). The outlet pressures P4 and P5 may be the same or different. The stock solution 21 may be taken out of the filtration device 1 via piping or the like, rather than being returned to the stock solution tank 20.

[0043] The filtrate (permeated liquid) obtained by filtering the raw liquid 21 through the two membrane modules 10 and removing solids is discharged from the first outlet 114b of the first membrane module 100 and the second outlet 214b of the second membrane module 200, which are provided in each of the two membrane modules 10. The filtrate discharged from the first outlet 114b of the first membrane module 100 is taken out of the membrane module 10 through pipes 43 and 45. The filtrate discharged from the second outlet 214b of the second membrane module 200 is taken out of the membrane module 10 through pipes 44 and 45.

[0044] [2 Description of Membrane Module 10] Next, the configuration of the membrane module 10 will be described in detail. Since the two membrane modules 10 included in the filtration device 1 have the same configuration, the configuration of one membrane module 10 will be described in detail below. FIG. 2 is a perspective view showing the configuration of the membrane module 10 according to the present embodiment. FIG. 2 is an enlarged perspective view of one membrane module 10 shown in FIG. 1 removed from the filtration device 1. FIG. 3 is a front view, a bottom view, and a top view showing the configuration of the membrane module 10 according to the present embodiment. Specifically, FIG. 3(a) is a front view showing the configuration of the membrane module 10 shown in FIGS. 1 and 2 when viewed from the negative Y-axis direction. FIG. 3(b) is a bottom view showing the configuration of the membrane module 10 shown in FIGS. 1 and 2 when viewed from the negative X-axis direction. FIG. 3(c) is a top view showing the configuration of the membrane module 10 shown in FIGS. 1 and 2 when viewed from the positive X-axis direction.

[0045] As shown in Figures 2 and 3, the membrane module 10 includes a first membrane module 100 and a second membrane module 200. The first membrane module 100 and the second membrane module 200 are spiral membrane modules of a cross-flow filtration type. The first membrane module 100 and the second membrane module 200 are arranged side by side in a predetermined direction (in this embodiment, the X-axis direction). Specifically, the second membrane module 200 is arranged on one side of the first membrane module 100 in the predetermined direction (in this embodiment, the positive direction of the X-axis).

[0046] The first membrane module 100 includes a first container 110 and a first element 120 housed in the first container 110. The second membrane module 200 includes a second container 210 and a second element 220 housed in the second container 210. Here, the first container 110 and the second container 210 are referred to as containers 11, and the first element 120 and the second element 220 are referred to as elements 12. In other words, the membrane module 10 includes an element 12 formed by winding a filtration membrane around a winding axis A (see FIG. 4 ) extending in a predetermined direction (X-axis direction), and a container 11 that houses the element 12. The container 11 includes the first container 110 and a second container 210 disposed on one side of the first container 110 in the predetermined direction (the positive direction of the X-axis). The element 12 includes a first element 120 housed in the first container 110 and a second element 220 housed in the second container 210. Each of these components will be described in detail below.

[0047] [2.1 Description of the First Container 110 of the First Membrane Module 100] First, the configuration of the first container 110 included in the first membrane module 100 will be described in detail. As shown in Figures 2 and 3 , the first container 110 is a cylindrical (tubular) container extending in the X-axis direction and having a space (cavity) formed therein that extends in the X-axis direction. The material of the first container 110 is not particularly limited, and examples of the first container 110 include a container made of resin such as polyvinyl chloride or engineering plastic, or a metal container. The first container 110 includes a first container body 111 and flange portions 112, 113, and 114.

[0048] The first container body 111 is a cylindrical (circular tubular) part that forms the main body of the first container 110 and extends in the X-axis direction, and houses the first element 120 therein. The shape of the first container body 111 is not particularly limited as long as it can house the first element 120 therein, and may be a polygonal cylinder such as an elliptical cylinder, an elongated cylinder, or a square cylinder.

[0049] The flange portion 112 is an annular, plate-shaped portion located at the end of the first container 110 in the positive direction of the X axis, and connected to the end of the first container body 111 in the positive direction of the X axis. The flange portion 112 has a portion that protrudes outward from the first container body 111, and this portion is provided with a plurality of connection portions 112a, which are circular through-holes that penetrate the flange portion 112 in the X axis direction. The shape of the flange portion 112 is not particularly limited as long as it has a portion that protrudes outward from the first container body 111, and the outer shape when viewed in the X axis direction may be an ellipse, an oval, a polygon such as a square, or the like.

[0050] The connecting portion 112a is disposed at a position opposite to a connecting portion 212a provided on a flange portion 212 of the second membrane module 200 (described later) and is connected to the connecting portion 212a. Specifically, connecting members (not shown) such as bolts are inserted between the connecting portion 112a and the connecting portion 212a and coupled with connecting members (not shown) such as nuts, thereby connecting the connecting portion 112a and the connecting portion 212a. As a result, the flange portion 112 and the flange portion 212 are connected (fixed) in a contacting state. The shape of the connecting portion 112a is not particularly limited as long as it can be connected to the connecting portion 212a. It may be a through-hole having an elliptical shape, an oval shape, a polygonal shape such as a square shape, or the like, or it may not be a through-hole. The connecting portion 112a may be a portion connected by connecting members other than bolts and nuts.

[0051] The flange portion 113 is an annular, plate-shaped portion located at the end of the first container 110 in the negative X-axis direction, and connected to the end of the first container body 111 in the negative X-axis direction. The flange portion 113 has a portion that protrudes outward from the first container body 111, and this portion is provided with a plurality of connection portions 113a, which are circular through-holes that penetrate the flange portion 113 in the X-axis direction. The shape of the flange portion 113 is not particularly limited as long as it has a portion that protrudes outward from the first container body 111, and the outer shape when viewed in the X-axis direction may be an ellipse, an oval, a polygon such as a square, or the like.

[0052] The connecting portion 113a is disposed opposite a connecting portion 114c provided on the flange portion 114, which will be described later, and is connected to the connecting portion 114c. Specifically, connecting members (not shown) such as bolts are inserted between the connecting portion 113a and the connecting portion 114c and coupled with connecting members (not shown) such as nuts, thereby connecting the connecting portion 113a and the connecting portion 114c. This allows the flange portion 113 and the flange portion 114 to be connected (fixed) in a contacting state. The shape of the connecting portion 113a is not particularly limited as long as it can be connected to the connecting portion 114c. The connecting portion 113a may be a through-hole having an elliptical, oval, or polygonal shape such as a square, or may not be a through-hole. The connecting portion 113a may be a portion that is connected by connecting members other than a bolt and a nut.

[0053] The flange portion 114 is a disk-shaped member that is disposed in the negative X-axis direction of the flange portion 113 and is connected to the flange portion 113. The flange portion 114 has the same outer shape as the flange portion 113 when viewed from the X-axis direction. The outer shape of the flange portion 114 when viewed from the X-axis direction may be an ellipse, an oval, a polygon such as a square, or the like, or may have an outer shape different from that of the flange portion 113. The flange portion 114 is provided with a first opening 114a, a first outlet 114b, and a plurality of connection portions 114c.

[0054] The first opening 114a is a circular through-hole that penetrates the flange portion 114 in the X-axis direction and is positioned in the positive Z-axis direction relative to the center position (first outlet 114b) of the flange portion 114. The first opening 114a serves as an inlet or outlet for the concentrate. In this embodiment, the first opening 114a serves as an inlet for the concentrate and is larger than the first outlet 114b. The shape of the first opening 114a is not particularly limited as long as it serves as an inlet or outlet for the concentrate, and it may be a through-hole with an elliptical, oval, or polygonal shape such as a square. The position and size of the first opening 114a are also not particularly limited. The first opening 114a may be positioned anywhere on the flange portion 114, such as in the negative Z-axis direction relative to the center position of the flange portion 114, or in the positive or negative Y-axis direction relative to the center position.

[0055] The first outlet 114b is a circular through-hole that penetrates the flange portion 114 in the X-axis direction and is disposed at the center of the flange portion 114. The first outlet 114b is an opening that serves as an outlet for the filtrate and is directly connected to a liquid collection tube 130 of the first element 120, which will be described later. The shape of the first outlet 114b is not particularly limited as long as it is an opening that serves as an outlet for the filtrate, and may be a through-hole that is elliptical, oval, or polygonal such as rectangular. The position and size of the first outlet 114b are also not particularly limited.

[0056] The connecting portion 114c is a circular through-hole that penetrates the flange portion 114 in the X-axis direction and is disposed at a position facing the connecting portion 113a of the flange portion 113. As described above, the connecting portion 114c is connected to the connecting portion 113a, thereby connecting (fixing) the flange portion 114 to the flange portion 113. The shape of the connecting portion 114c is not particularly limited as long as it can be connected to the connecting portion 113a, and it may be a through-hole that is elliptical, oval, polygonal (e.g., rectangular), or the like, or may not be a through-hole. The connecting portion 114c may be a portion that is connected by a connecting member other than a bolt and a nut.

[0057] [2.2 Description of First Element 120 of First Membrane Module 100] Next, the configuration of the first element 120 included in the first membrane module 100 will be described in detail with reference to Figs. 4 and 5. Fig. 4 is a perspective view showing the configuration of the first element 120 according to this embodiment. Fig. 5 is a plan view and a cross-sectional view showing the configuration of a leaf 121 according to this embodiment. Fig. 5(a) is a plan view showing the configuration when one leaf 121 is unfolded and spread out flat, and Fig. 5(b) is a cross-sectional view showing a cross section of the leaf 121 when cut in the thickness direction. In Fig. 5, components other than the one leaf 121 and the liquid collection pipe 130 are omitted from the illustration.

[0058] The first element 120 is a cylindrical portion extending in the X-axis direction, and is housed in the first container 110 to filter the stock solution flowing into the first container 110. As shown in Figures 3 and 4 , the first element 120 includes a leaf 121, a liquid collection tube 130, and a blocking member 140.

[0059] Each leaf 121 includes a filtration membrane 122, and a plurality of leaves 121 are wound around a liquid collection pipe 130 about a winding axis A (see FIG. 4 ) to form a spiral-type first element 120. In this embodiment, the number of leaves 121 in the first element 120 is 16 or more. That is, the spiral-type first element 120 is formed by winding 16 or more leaves 121 around the liquid collection pipe 130. The number of leaves 121 is preferably 18 or more, more preferably 20 to 40, and even more preferably 20 to 26 from the viewpoint of ease of manufacture.

[0060] 4 and 5, the leaf 121 includes filtration membranes 122a and 122b as the filtration membrane 122, a filtrate net 123, and an undiluted liquid net 124. In the present embodiment, the filtration membrane 122a, the filtrate net 123, the filtration membrane 122b, and the undiluted liquid net 124 are stacked in this order in the leaf 121.

[0061] The filtration membrane 122 (122a and 122b) is a microfiltration membrane (MF membrane). Specifically, the filtration membrane 122 has a large number of micropores, and the pore diameter of the micropores is 0.1 μm or more and 0.4 μm or less. The pore diameter is measured by measuring the mean flow pore diameter using a pore size distribution measuring device capable of measuring pore diameter by the bubble point method (a method for evaluating the maximum pore diameter of filters specified in JIS K 3832). The filtration membrane 122 preferably has a pore diameter of 0.15 μm or more and 0.35 μm or less, more preferably 0.2 μm or more and 0.3 μm or less, and even more preferably 0.23 μm or more and 0.27 μm or less. The filtration membrane 122 can be, for example, a polymer membrane having a large number of micropores formed on the surface of a substrate that is a nonwoven fabric made of synthetic resin.

[0062] The filtration membranes 122 (122a and 122b) are sheet-like members wound around a winding axis A (see FIG. 4) extending in a predetermined direction (X-axis direction) and have a rectangular (rectangular or square) shape when unrolled and spread out flat. In FIG. 5A, the length of the filtration membrane 122 (leaf 121) in the winding direction is length L1, and the length of the filtration membrane 122 (leaf 121) in the winding axis direction is length L2. The winding direction of the filtration membrane 122 is the direction in which the filtration membrane 122 is wound, and is illustrated as the Y-axis direction in FIG. 5A. The winding axis direction of the filtration membrane 122 is the direction in which the winding axis A extends when the filtration membrane 122 is wound, and in this embodiment, is the X-axis direction.

[0063] The length L1 of the filtration membrane 122 (122a and 122b) in the winding direction is 800 mm or less. The length L1 of the filtration membrane 122 in the winding direction is preferably 700 mm or less, more preferably 600 mm or less, and even more preferably 500 mm or less. The length L1 of the filtration membrane 122 in the winding direction is preferably 300 mm or more, more preferably 400 mm or more, and even more preferably 420 mm or more. The length L2 of the filtration membrane 122 (122a and 122b) in the winding axis direction (X-axis direction) is 800 mm or less. The length L2 of the filtration membrane 122 in the winding axis direction is preferably 700 mm or less, more preferably 600 mm or less, and even more preferably 500 mm or less. The length L2 of the filtration membrane 122 in the direction of the winding axis is preferably 300 mm or more, more preferably 400 mm or more, and even more preferably 420 mm or more.

[0064] The length L2 is also the length of the first element 120 (excluding the liquid collection tube 130) in the direction of the winding axis. That is, the length L2 of the first element 120 in the predetermined direction, i.e., the winding axis direction (X-axis direction), is 800 mm or less. The length L2 of the first element 120 in the direction of the winding axis is preferably 700 mm or less, more preferably 600 mm or less, and even more preferably 500 mm or less. The length L2 of the first element 120 in the direction of the winding axis is preferably 300 mm or more, more preferably 400 mm or more, and even more preferably 420 mm or more.

[0065] With such a size of the filtration membrane 122, the effective filtration area per leaf 121 of the first element 120 is 1.3 m ２ The effective filtration area per leaf 121 is the total area of ​​the filtration membranes 122 in one leaf 121, that is, the total area of ​​the filtration membranes 122a and 122b. The effective filtration area per leaf 121 is 1.0 m ２ Preferably it is 0.8 m or less. ２ More preferably, it is 0.4 m or less. ２ More preferably, it is:

[0066] The filtration membranes 122a and 122b sandwich the filtrate net 123, and three sides of the filtration membranes 122a and 122b are closed to form a bag, with the remaining side communicating with the liquid collection pipe 130. The method for manufacturing the bag using the filtration membranes 122a and 122b can be various methods similar to those used for conventional spiral-type membrane modules. The bag may be manufactured by welding or adhering three sides of a sheet of filtration membrane 122, or by folding a strip of filtration membrane 122 zigzag and welding or adhering two sides of the filtration membrane 122.

[0067] The filtrate net 123 is a member that forms a flow path for the filtrate (filtrate flow path forming member). The filtrate net 123 is disposed between the filtration membranes 122a and 122b, and maintains the distance between the filtration membranes 122a and 122b to ensure the flow of the filtrate. The filtrate net 123 is in communication with the liquid collection pipe 130, and the filtrate filtered by the filtration membranes 122a and 122b is sent to the liquid collection pipe 130 through the filtrate net 123.

[0068] The filtrate net 123 can be made of various materials and shapes as long as it can maintain the gap between the filtration membranes 122a and 122b and ensure a flow path for the filtrate. The filtrate net 123 can be made of a net made of synthetic resin fibers such as polyolefin, polyester, or polyamide. The filtrate net 123 can be made of a net with a structure in which filaments forming the mesh cross three-dimensionally.

[0069] The mesh size of the net used for the filtrate net 123 is such that the density of parallel filaments (number of filaments per unit length) is preferably 30 or more per inch, more preferably 35 or more per inch, and even more preferably 40 or more per inch. If the filament density is low, the filtration membrane 122 may cut into the filtrate net 123. However, by setting the filament density within the above range, it is possible to prevent the filtration membrane 122 from cutting into the filtrate net 123.

[0070] The thickness of the filtrate net 123 is 0.2 mm or more. In other words, the distance between the filtration membranes 122a and 122b is 0.2 mm or more. The thickness of the filtrate net 123 is preferably 0.21 mm or more, more preferably 0.22 mm or more, and even more preferably 0.23 mm or more. The thickness of the filtrate net 123 is preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.4 mm or less. If the thickness of the filtrate net 123 is too small, the filtrate flow path becomes narrow, making it difficult to ensure the flow of the filtrate, while if the thickness of the filtrate net 123 is too large, the first element 120 becomes too large.

[0071] The stock solution net 124 is a member that forms a flow path for the stock solution (stock solution flow path forming member). The stock solution net 124 is arranged so as to sandwich the filtration membrane 122a or the filtration membrane 122b between the stock solution net 123. As a result, the stock solution net 124 is arranged between the filtration membranes 122a and 122b, maintaining the distance between the filtration membranes 122a and 122b and ensuring the flow of the stock solution.

[0072] The stock solution net 124 can be made of various materials and shapes as long as it can maintain the gap between the filtration membranes 122a and 122b and ensure a flow path for the stock solution. The stock solution net 124 can be made of the same material and structure as the filtrate net 123. In this embodiment, the density of the filaments of the stock solution net 124 is the same as or smaller than the density of the filaments of the filtrate net 123. The thickness of the stock solution net 124 is the same as or larger than the thickness of the filtrate net 123.

[0073] The collection pipe 130 is a tubular member that collects filtrate. The collection pipe 130 is disposed at the center of the first element 120 when viewed from the X-axis direction, and is a cylindrical member extending in the X-axis direction. The collection pipe 130 has a plurality of holes 131 aligned in the X-axis direction. The plurality of holes 131 are through-holes through which the filtrate passes. The collection pipe 130 is connected to the filtrate flow path formed by the filtrate net 123, and collects the filtrate filtered by the filtration membrane 122 through the plurality of holes 131 into the collection pipe 130. The collection pipe 130 flows the collected filtrate in the X-axis direction along the flow path inside the collection pipe 130. The shape of the collection pipe 130 is not particularly limited as long as it is capable of collecting filtrate, and may be a polygonal cylinder such as an elliptical cylinder, an oblong cylinder, or a square cylinder. The liquid collection pipe 130 is made of resin or the like, but the material is not particularly limited, and any material that can be used for liquid collection pipes in conventional spiral-type membrane modules may be used. The number, size, shape, etc. of the holes 131 provided in the liquid collection pipe 130 are not particularly limited.

[0074] The blocking member 140 is a member (insert plug) that blocks the opening of the liquid collection tube 130. The blocking member 140 is formed of resin or the like, but the material is not particularly limited and may be the same material as the liquid collection tube 130 or a different material from the liquid collection tube 130. In this embodiment, the blocking member 140 is disposed at the end of the liquid collection tube 130 in the positive direction of the X axis and inserted into the opening (filtrate outlet) at the end of the liquid collection tube 130 in the positive direction of the X axis to block the opening (filtrate outlet). As a result, the liquid collection tube 130 causes the collected filtrate to flow in the negative direction of the X axis and to be discharged from the opening 132 at the end of the liquid collection tube 130 in the negative direction of the X axis.

[0075] [2.3 Description of the Second Membrane Module 200] The second membrane module 200 has the same configuration as the first membrane module 100 flipped in the X-axis direction and flipped in the Z-axis direction. In other words, the second membrane module 200 has the same configuration as the first membrane module 100 rotated 180° about the Y-axis. Therefore, the second container 210 of the second membrane module 200 has the same configuration as the first container 110 of the first membrane module 100, and the second element 220 of the second membrane module 200 has the same configuration as the first element 120 of the first membrane module 100. Therefore, the description of each component of the second membrane module 200 will be simplified or omitted.

[0076] The second container 210 includes a second container body 211 having the same configuration as the first container body 111, and flange portions 212, 213, and 214 having the same configuration as the flange portions 112, 113, and 114. The flange portion 212 is provided with a plurality of connection portions 212a having the same configuration as the plurality of connection portions 112a of the flange portion 112. The flange portion 213 is provided with a plurality of connection portions 213a having the same configuration as the plurality of connection portions 113a of the flange portion 113. The flange portion 214 is provided with a second opening 214a having the same configuration as the first opening 114a of the flange portion 114, a second outlet 214b having the same configuration as the first outlet 114b, and a plurality of connection portions 214c having the same configuration as the plurality of connection portions 114c. The second opening 214a is an opening that serves as an outlet for the concentrate, and is positioned in the negative Z-axis direction from the center position (second outlet 214b) of the flange portion 214. The second opening 214a may be positioned at any position on the flange portion 214, such as in the positive direction of the Z axis from the center position of the flange portion 214, or in the positive or negative direction of the Y axis from the center position.

[0077] The second element 220 includes a leaf 221 having the same configuration as the leaf 121, a liquid collection pipe 230 having the same configuration as the liquid collection pipe 130, and a blocking member 240 having the same configuration as the blocking member 140. The blocking member 240 is disposed at the end of the liquid collection pipe 230 in the negative X-axis direction, and is inserted into an opening (filtrate outlet) at the end of the liquid collection pipe 230 in the negative X-axis direction to block the opening (filtrate outlet). As a result, the liquid collection pipe 230 causes the collected filtrate to flow in the positive X-axis direction and to be discharged from the opening at the end of the liquid collection pipe 230 in the positive X-axis direction.

[0078] [2.4 Overall Description of Membrane Module 10] As described above, the first container 110 of the first membrane module 100 is provided with a first outlet 114b for the filtrate, and the second container 210 of the second membrane module 200 is provided with a second outlet 214b for the filtrate. That is, the container 11 is provided with a filtrate outlet in each of the first container 110 and the second container 210. In this embodiment, the first outlet 114b is provided in the flange portion 114 of the first container 110, and the second outlet 214b is provided in the flange portion 214 of the second container 210. Therefore, the first outlet 114b is located at the end of the first container 110 on the other side in the predetermined direction (the negative X-axis direction). This end of the first container 110 is the portion between the end face of the leaf 121 of the first element 120 in the negative X-axis direction and the end face of the flange portion 114 in the negative X-axis direction. The second outlet 214b is disposed at an end of the second container 210 on one side in the predetermined direction (positive X-axis direction). This end of the second container 210 is the portion between the end face of the leaf 221 of the second element 220 in the positive X-axis direction and the end face of the flange portion 214 in the positive X-axis direction. In other words, the container 11 has filtrate outlets at both ends in the predetermined direction (X-axis direction). Specifically, the first outlet 114b is formed in the end face of the first container 110 on the other side in the predetermined direction (negative X-axis direction). The second outlet 214b is formed in the end face of the second container 210 on one side in the predetermined direction (positive X-axis direction). In other words, the container 11 has filtrate outlets at both end faces in the predetermined direction (X-axis direction).

[0079] A closing member 140 is disposed at the opening (filtrate outlet) at the end of the collection tube 130 disposed in the first container 110 in the positive X-axis direction, and a closing member 240 is disposed at the opening (filtrate outlet) at the end of the collection tube 230 disposed in the negative X-axis direction. As a result, the end of the filtrate flow path at one end of the first container 110 in the predetermined direction (positive X-axis direction) is blocked. The end of the filtrate flow path at the other end of the second container 210 in the predetermined direction (negative X-axis direction) is blocked. The flange portion 112 of the first container 110 and the flange portion 212 of the second container 210 are connected in a contacting state. Therefore, the container 11 is formed by connecting the end face of the first container 110 on one side in the predetermined direction (positive X-axis direction) and the end face of the second container 210 on the other side in the predetermined direction (negative X-axis direction). As a result, the flow path of the concentrate in the first container 110 and the flow path of the concentrate in the second container 210 are connected.

[0080] The first container 110 of the first membrane module 100 further includes a first opening 114a serving as an inlet or outlet (inlet in this embodiment) for the raw liquid. The second container 210 of the second membrane module 200 further includes a second opening 214a serving as an outlet or inlet (outlet in this embodiment) for the raw liquid. That is, the container 11 includes an inlet for the raw liquid in one of the first container 110 and the second container 210, and an outlet for the raw liquid in the other. When the first opening 114a is the inlet for the raw liquid, the second opening 214a is the outlet for the raw liquid. When the first opening 114a is the outlet for the raw liquid, the second opening 214a is the inlet for the raw liquid. In this embodiment, the first opening 114a is provided in the flange portion 114 of the first container 110, and the second opening 214a is provided in the flange portion 214 of the second container 210. For this reason, the first container 110 has a first opening 114a at its end on the other side in the predetermined direction (the negative X-axis direction). The second container 210 has a second opening 214a at its end on one side in the predetermined direction (the positive X-axis direction). In other words, the container 11 has an inlet for the concentrate at one end in the predetermined direction (the negative X-axis direction) and an outlet for the concentrate at the other end. Specifically, the first opening 114a is formed on the end face of the first container 110 on the other side in the predetermined direction (the negative X-axis direction). The second opening 214a is formed on the end face of the second container 210 on one side in the predetermined direction (the positive X-axis direction). In other words, the container 11 has an inlet for the concentrate at one end face in the predetermined direction (the negative X-axis direction) and an outlet for the concentrate at the other end face.

[0081] [3. Description of Filtration Method in Filtration Device 1] Next, a description will be given of a filtration method in the filtration device 1 using the membrane module 10 having the above configuration. Fig. 6 is a flowchart showing each step of the filtration method in the filtration device 1 according to this embodiment.

[0082] As shown in FIG. 6, first, the raw liquid is introduced into the membrane module 10 at an inlet pressure of less than 0.2 MPa (S102: raw liquid introduction step).

[0083] Specifically, the raw liquid 21 is extracted from the raw liquid tank 20 by the pump 30, and the extracted raw liquid 21 is supplied to the membrane module 10 from the first opening 114a of the first container 110 provided in the first membrane module 100 of the membrane module 10 at an inlet pressure of less than 0.2 MPa (inlet pressure P2 or P3 in Figure 1).

[0084] Next, the raw liquid that has flowed into the membrane module 10 is filtered by the filtration membrane, and a cake layer is formed on the filtration membrane (S104: filtration and cake layer formation step).

[0085] Specifically, the stock solution flowing in through the first opening 114a flows through the stock solution nets 124 of each leaf 121 of the first element 120. As a result, a portion of the stock solution is filtered by the filtration membrane 122, flows through the filtrate net 123, and flows into the liquid collection pipe 130. At this time, a portion of the solids contained in the stock solution are captured and deposited on the surface of the filtration membrane 122, and a cake layer (deposits on the filtration membrane surface) is formed on the surface of the filtration membrane 122. The stock solution that has passed through the first element 120 flows through the stock solution nets of each leaf 221 of the second element 220. As a result, a portion of the stock solution is filtered by the filtration membrane, flows through the filtrate net, and flows into the liquid collection pipe 230. As with the first element 120, a cake layer is also formed on the surface of the filtration membrane in the second element 220. These cake layers may be removed by flushing or the like on a regular or irregular basis. In this way, the first membrane module 100 and the second membrane module 200 are filters of a crossflow filtration type that perform crossflow operation in which the supplied raw liquid is made to flow parallel to the filtration membrane 122, etc., to filter out solids in the raw liquid.

[0086] Next, the stock solution (concentrate) and filtrate (permeate) are discharged from the membrane module 10 (S106: stock solution and filtrate discharge step). Specifically, the stock solution (concentrate) that has passed through the second element 220 is discharged from the second opening 214a of the second container 210 of the second membrane module 200. The filtrate (permeate) that has flowed into the liquid collection pipe 130 is discharged from the first outlet 114b of the first container 110 of the first membrane module 100. The filtrate (permeate) that has flowed into the liquid collection pipe 230 is discharged from the second outlet 214b of the second container 210 of the second membrane module 200. The stock solution (concentrate) discharged from the membrane module 10 is returned to the stock solution tank 20. The filtrate (permeate) discharged from the membrane module 10 is supplied to a filtrate tank (not shown) or the like.

[0087] [4 Description of Manufacturing Process of Membrane Module 10] Next, the manufacturing process of the membrane module 10 will be described. FIG. 7 is a front view, a bottom view, and a top view showing the configuration of a membrane module 50 that forms a part of the membrane module 10 according to this embodiment. FIG. 7(a) is a front view of the membrane module 50 as seen from the negative Y-axis direction, FIG. 7(b) is a bottom view of the membrane module 50 as seen from the negative X-axis direction, and FIG. 7(c) is a top view of the membrane module 50 as seen from the positive X-axis direction. FIGS. 7(a) to 7(c) correspond to FIGS. 3(a) to 3(c). FIG. 8 is a front view showing a manufacturing process of the membrane module 10 according to this embodiment. FIG. 8(a) shows the membrane module 50 and the membrane module 60 that form a part of the membrane module 10. FIG. 8(b) shows a state in which the first membrane module 100 has been separated from the membrane module 50 and the second membrane module 200 has been separated from the membrane module 60. FIG. 8(c) shows the membrane module 10 in which the first membrane module 100 and the second membrane module 200 are connected.

[0088] As shown in Fig. 7, the membrane module 50 is a spiral-type membrane module of a cross-flow filtration type including one vessel (first vessel 110) and one element (first element 120). The membrane module 50 has a configuration in which a flange portion 115 is connected to the end of the first membrane module 100 in the positive direction of the X axis. The flange portion 115 has a configuration similar to that of the flange portion 214 of the second membrane module 200, but does not have an outlet for the filtrate.

[0089] Specifically, the flange portion 115 is a disk-shaped member disposed in the positive direction of the X-axis of the flange portion 112 and connected to the flange portion 112. The flange portion 115 is provided with a third opening 115a and a plurality of connection portions 115c. The third opening 115a is an opening that serves as an inlet or outlet for the raw liquid. The third opening 115a may be disposed at any position on the flange portion 115. In the membrane module 50, the third opening 115a serves as an inlet for the raw liquid and the first opening 114a serves as an outlet for the raw liquid. Alternatively, the first opening 114a may serve as an inlet for the raw liquid and the third opening 115a as an outlet for the raw liquid. The connection portion 115c is disposed at a position opposite the connection portion 112a of the flange portion 112, and is connected to the connection portion 112a, thereby connecting (fixing) the flange portion 115 to the flange portion 112.

[0090] When manufacturing the membrane module 10, a membrane module 50 and a membrane module 60 are prepared as shown in FIG. 8( a). The membrane module 60 has the same configuration as the membrane module 50 inverted in the X-axis direction and inverted in the Z-axis direction. In other words, the membrane module 60 has the same configuration as the membrane module 50 rotated 180° about the Y-axis. That is, in FIG. 8( a), two membrane modules 50 are prepared. In the membrane module 60, the portion of the membrane module 50 corresponding to the first membrane module 100 is the second membrane module 200, and the portion corresponding to the flange portion 115 is the flange portion 215. That is, the membrane module 60 has a configuration in which the flange portion 215 is connected to the end of the second membrane module 200 in the negative X-axis direction.

[0091] 8(b), the flange portion 115 is removed from the membrane module 50 to separate the first membrane module 100 from the membrane module 50. Similarly, the flange portion 215 is removed from the membrane module 60 to separate the second membrane module 200 from the membrane module 60.

[0092] 8(c), the flange portion 112 of the first membrane module 100 is connected to the flange portion 212 of the second membrane module 200, thereby connecting the first membrane module 100 and the second membrane module 200. In this way, the membrane module 10 is manufactured.

[0093] [5. Description of Effects] As described above, according to the filtration device 1 of this embodiment, in the spiral membrane module 10, the inlet pressure of the raw liquid flowing into the membrane module 10 is lower than 0.2 MPa. In this way, by performing low-pressure operation by setting the inlet pressure of the raw liquid flowing into the membrane module 10 to be lower than 0.2 MPa, it is possible to reduce the power required to pressurize the raw liquid, and therefore power consumption.

[0094] The filtration membranes of the elements 12 (the filtration membrane 122 of the first element 120 and the filtration membrane of the second element 220) included in the spiral membrane module 10 are microfiltration membranes. Conventional spiral membrane modules used RO (reverse osmosis) or UF (ultrafiltration) membranes with relatively small pore sizes, and therefore required high-pressure operation, in which the raw liquid inlet pressure was 0.2 MPa or higher, to obtain a sufficient amount of filtrate. Spiral membrane modules using microfiltration (MF) membranes were also operated at high pressures, similar to those using RO or UF membranes. While considering the application of spiral membrane modules to the filtration and concentration of biological systems such as microalgae, the inventors discovered a problem: high-pressure operation could destroy cells and kill the organisms. After extensive research, they discovered that operation at a sufficiently low raw liquid inlet pressure (low-pressure operation) would not destroy cells and allow microalgae and other organisms to be filtered and concentrated alive. Further investigation revealed that when the membrane module 10 using a microfiltration membrane is operated at low pressure, it can be used practically with low power consumption for purposes other than filtration and concentration of biological systems.

[0095] The pore size of the microfiltration membrane provided in the spiral membrane module 10 is 0.1 μm or more and 0.4 μm or less. Here, the microfiltration membrane is used to filter substances with an average particle size of approximately 0.05 μm to 10 μm, particularly substances with an average particle size exceeding 0.4 μm. When the inlet pressure of the raw liquid is high, i.e., during high-pressure operation, substances with particle sizes slightly larger than the pore size of the microfiltration membrane may be deformed by the applied pressure and pushed into the pores of the microfiltration membrane, resulting in clogging of the pores. In contrast, during low-pressure operation, the inlet pressure of the raw liquid is low, so the problem of clogging of the pores by substances with particle sizes slightly larger than the pore size of the microfiltration membrane is less likely to occur. On the other hand, when the pore size of the microfiltration membrane is less than 0.1 μm, it is difficult to obtain the required amount of filtrate during low-pressure operation. For the above reasons, when a spiral-type membrane module 10 using a microfiltration membrane is operated at low pressure, it is preferable to set the pore size of the microfiltration membrane to 0.1 μm or more and 0.4 μm or less, which makes it possible to prevent clogging of the micropores and to obtain a sufficient amount of filtrate.

[0096] The inlet pressure of the raw liquid flowing into the spiral membrane module 10 is 0.1 MPa or less. Thus, by performing low-pressure operation with the inlet pressure of the raw liquid flowing into the membrane module 10 set to 0.1 MPa or less, the power required to pressurize the raw liquid can be further reduced, thereby further reducing power consumption. Furthermore, by performing even lower-pressure operation, clogging of the micropores by filtered matter can be made less likely. In the process of considering the application of spiral membrane modules to the filtration and concentration of biological systems such as microalgae, the inventors discovered a problem in that high-pressure operation could destroy cells and kill the organisms. By performing low-pressure operation with the inlet pressure of the raw liquid flowing into the membrane module 10 set to 0.1 MPa or less, cells are not destroyed and microalgae and other organisms can be filtered and concentrated alive. It is preferable to use a microfiltration membrane for the membrane module 10 because, under low-pressure operation where the raw liquid inlet pressure is 0.1 MPa or less, a sufficient amount of filtrate can be obtained and filtration efficiency can be improved compared to when an RO membrane or UF membrane is used for the membrane module 10.This makes it possible to filter and concentrate with high filtration efficiency while suppressing cell destruction of microalgae and the like.

[0097] The elements 12 included in the spiral-type membrane module 10 are equipped with filtrate collection pipes (collection pipe 130 of the first element 120, collection pipe 230 of the second element 220). The filtration device 1 is operated at a low pressure, that is, the inlet pressure of the raw liquid flowing into the membrane module 10 is set to less than 0.2 MPa, and therefore a configuration that can reduce the resistance to the flow of the filtrate is preferable. For this reason, by configuring the filtrate to be collected in the collection pipes and then flowing, the resistance to the flow of the filtrate can be reduced.

[0098] In the elements 12 included in the spiral-wound membrane module 10, the length of the filtration membranes (the filtration membrane 122 of the first element 120 and the filtration membrane of the second element 220) in the winding direction is 800 mm or less. The thickness of the filtrate nets (the filtrate net 123 of the first element 120 and the filtrate net of the second element 220) is 0.2 mm or more. Conventional spiral-wound membrane modules are often used for general crossflow filtration, specifically for the purpose of "cakeless filtration," which does not form membrane surface deposits (cake layers). In this case, high-pressure operation is performed. During high-pressure operation, resistance due to pressure loss in the winding direction of the filtration membrane can be ignored, so there is almost no benefit to shortening the winding direction length of the filtration membrane. Therefore, the winding direction length of the filtration membrane is relatively long. In contrast, the filtration device 1 performs low-pressure operation, in which the inlet pressure of the raw liquid flowing into the membrane module 10 is set to less than 0.2 MPa. Therefore, increasing the winding direction length of the filtration membrane (such as the filtration membrane 122) reduces the amount of filtrate. For this reason, the length of the filtration membrane (e.g., filtration membrane 122) in the winding direction is shortened to 800 mm or less to reduce resistance due to pressure loss in the winding direction of the filtration membrane (e.g., filtration membrane 122). Furthermore, the thickness of the filtrate net (e.g., filtrate net 123) is set to 0.2 mm or more to ensure space for the filtrate to flow. By adopting these configurations, it is possible to reduce overall pressure loss and increase the amount of filtrate. In this way, the use of this configuration to increase the amount of filtrate under the specific condition of low-pressure operation would not have been predictable from conventional technology that assumes high-pressure operation.

[0099] The effective filtration area per leaf of the element 12 (leaf 121 of the first element 120, leaf 221 of the second element 220) included in the spiral membrane module 10 is 1.3 m ２ In this way, in the filtration device 1 using a filtration membrane (such as the filtration membrane 122) having a short length in the winding direction, the effective filtration area per leaf (such as the leaf 121) is set to 1.3 m or less. ２ By setting the following, it is possible to reduce not only the pressure loss in the filtrate flow path but also the circulation pressure loss. Here, "pressure loss in the filtrate flow path" means the pressure loss in the path through which the filtrate that has permeated the filtration membrane flows. Furthermore, "circulation pressure loss" means the pressure loss in the path through which the raw liquid flows. The pressure loss in the filtrate flow path and the circulation pressure loss do not pose a problem during high-pressure operation (generally high-circulation operation), but have a significant impact during low-pressure operation (which inevitably results in low-circulation operation). Therefore, when the effective filtration area per leaf (e.g., leaf 121) is set to 1.3 m during low-pressure operation, ２ By setting the value to a small value of 0.1 or less, the pressure loss in the filtrate flow path and the circulation pressure loss in one leaf (leaf 121, etc.) can be reduced.

[0100] The number of leaves (the leaves 121 of the first element 120 or the leaves 221 of the second element 220) of the element 12 included in the spiral membrane module 10 is 16 or more. Here, by shortening the length of the filtration membrane (the filtration membrane 122, etc.) in the winding direction and reducing the effective filtration area per leaf (the leaf 121, etc.), it is possible to reduce the pressure loss in the filtrate flow path and the circulation pressure loss in the case of low-pressure operation. However, if the effective filtration area of ​​the entire element becomes small, a sufficient amount of filtrate cannot be obtained. Therefore, the length of the filtration membrane (the filtration membrane 122, etc.) in the winding direction is set to 800 mm or less, and the effective filtration area per leaf (the leaf 121, etc.) is set to 1.3 m ２ In the case where the number of leaves (such as leaf 121) is set to 16 or more, it is possible to secure a larger amount of filtrate while maintaining low pressure loss in the filtrate flow path and circulation pressure loss during low-pressure operation.

[0101] In the spiral-wound membrane module 10, the upper limit of the discharge pressure of the pump 30 that supplies the raw liquid to the membrane module 10 is less than 0.45 MPa. By reducing the upper limit of the discharge pressure of the pump 30 to less than 0.45 MPa, the power required to pressurize the raw liquid can be reduced, thereby reducing power consumption. Conventional filtration systems equipped with spiral-wound membrane modules had to operate under high pressure conditions, with the inlet pressure of the raw liquid flowing into the membrane module at 0.45 MPa or higher, in order to obtain a sufficient amount of filtrate even when RO or UF membranes were used in the membrane module. Therefore, conventional systems employed pumps with sufficiently high discharge pressure performance for supplying the raw liquid. For example, pumps with an upper limit of the discharge pressure of 0.45 MPa or higher were used. In conventional systems, there was no need to reduce the upper limit of the discharge pressure of the pump below 0.45 MPa, and no such attempt was made. In response to this, as explained above, the inventors discovered a phenomenon in which high-pressure operation could destroy cells and kill the organisms while studying the application of spiral membrane modules to the filtration and concentration of biological systems such as microalgae. This led them to focus on operating the raw liquid flowing into the membrane module at a low inlet pressure (low-pressure operation). As a result of studying the practical application of a filtration device suitable for such low-pressure operation, they discovered that a pump 30 with an upper limit discharge pressure of less than 0.45 MPa could be used to supply raw liquid to the spiral membrane module 10. They also discovered that using such a pump 30 could reduce power consumption during operation. This filtration device 1 is suitable for filtration operation under conditions in which the inlet pressure of the raw liquid supplied to the spiral membrane module 10 is less than 0.2 MPa. It is preferable to use an upper limit value for the discharge pressure of the pump 30 of this device of 0.3 MPa or less or 0.14 MPa, as this further reduces power consumption. These upper limit values ​​are suitable for filtration operation under conditions where the raw liquid inlet pressure is 0.15 MPa or less and 0.1 MPa, respectively.

[0102] According to the filtration method of the present embodiment, the raw liquid is introduced into the spiral membrane module 10 at an inlet pressure of less than 0.2 MPa. By performing low-pressure operation by making the inlet pressure of the raw liquid flowing into the membrane module 10 less than 0.2 MPa in this way, the power required to pressurize the raw liquid can be reduced, and therefore power consumption can be reduced.

[0103] The vessel 11 of the spiral membrane module 10 includes a first vessel 110 and a second vessel 210. The first vessel 110 includes a first filtrate outlet 114b, and the second vessel 210 includes a second filtrate outlet 214b. In this configuration, the vessel 11 includes the first vessel 110 and the second vessel 210. Since the first vessel 110 and the second vessel 210 each have a filtrate outlet, the filtrate can be extracted from two outlets (the first outlet 114b and the second outlet 214b). This shortens the flow distance of the filtrate, reducing resistance to the filtrate flow and allowing for an increase in the amount of filtrate. Furthermore, since the area of ​​the filtrate outlet is large, resistance to the filtrate flow can be reduced, allowing for an increase in the amount of filtrate.

[0104] In particular, in wastewater treatment devices and the like, while a small installation area is required, requirements regarding the height direction (the above-mentioned predetermined direction, the X-axis direction) are often not strict. From this perspective, in the membrane module 10, it is sometimes required to arrange the first membrane module 100 and the second membrane module 200 in series (the first container 110 and the second container 210 are aligned in a predetermined direction) rather than in parallel. Even in such cases, this configuration is preferable in order to reduce the resistance to the flow of filtrate and increase the amount of filtrate.

[0105] The first outlet 114b is disposed at the end of the first container 110 on the other side in the predetermined direction (the negative X-axis direction), and the second outlet 214b is disposed at the end of the second container 210 on one side in the predetermined direction (the positive X-axis direction). This allows two filtrate outlets (the first outlet 114b and the second outlet 214b) to be disposed at both ends of the container 11 in the predetermined direction. Therefore, the filtrate is taken out from both ends of the container 11 in the predetermined direction (the X-axis direction), so the filtrate outlets can be provided without a complex structure. Furthermore, when the filtrate outlets are provided at the ends of the container 11 excluding the end faces, it becomes easy to connect three or more containers, such as a third container that houses a third element, in addition to the first container 110 and the second container 210.

[0106] The first outlet 114b is formed on the end face of the first container 110 on the other side in the predetermined direction (negative X-axis direction), and the second outlet 214b is formed on the end face of the second container 210 on one side in the predetermined direction (positive X-axis direction). This allows two filtrate outlets (first outlet 114b and second outlet 214b) to be formed on both end faces of the container 11 in the predetermined direction (X-axis direction). Therefore, the filtrate outlet and the filtrate path can be directly connected, simplifying the structure of the container 11. By connecting the end face of the first container 110 or the second container 210 to another member (not shown), the first outlet 114b or the second outlet 214b can be easily connected to the other member.

[0107] The container 11 can be formed with a simple configuration in which the raw liquid flow path in the first container 110 and the raw liquid flow path in the second container 210 are connected by connecting an end face on one side in a predetermined direction (positive direction of the X axis) of the first container 110 to an end face on the other side in a predetermined direction (negative direction of the X axis) of the second container 210. This makes it easy to realize a configuration in which the raw liquid passes between the first container 110 and the second container 210. The inventors have newly discovered a problem in that when multiple containers (hereinafter also referred to as individual containers) such as the first container 110 and the second container 210 containing elements (hereinafter also referred to as individual elements) such as a first element 120 and a second element 220 are integrally connected in series so that their end faces are connected, rather than via piping, and the filtrate flow paths of the individual elements are connected at the connecting faces of the individual containers and filtrate is extracted only from the downstream individual container, the filtrate does not come out of the downstream membrane module, and in some cases the filtrate flows back to the raw liquid side. When multiple individual containers are connected in series by piping rather than by connecting the end faces of each individual container, the filtrate from each individual element inevitably joins through piping that passes outside the individual containers, and the above phenomenon is unlikely to be a major problem, so such issues are not a concern. When multiple individual containers containing individual elements are connected in series integrally so that their end faces are connected rather than through piping, such issues can be resolved by extracting filtrate from these individual containers individually. Furthermore, the above issues can be resolved more effectively if the filtrate flow paths of the individual elements contained in the multiple individual containers are not connected by blocking the filtrate flow paths at the connecting faces of the multiple individual containers.

[0108] By blocking the filtrate outlet at one end of the first vessel 110 in a predetermined direction (positive direction of the X-axis) and the filtrate outlet at the other end of the second vessel 210 in a predetermined direction (negative direction of the X-axis), it is possible to prevent one filtrate from affecting the other filtrate. For example, it is possible to prevent the filtrate on the high-pressure side from obstructing the flow of the filtrate on the low-pressure side. This configuration is particularly effective when the membrane module 10 is operated at low pressure, because the filtrate on the high-pressure side is likely to obstruct the flow of the filtrate on the low-pressure side. Since the filtrate in the first vessel 110 and the filtrate in the second vessel 210 can flow through separate paths, resistance to filtrate flow can be reduced. When connecting the first membrane module 100 and the second membrane module 200, there is no need to remove the insert plug and attach a connector connecting the liquid collection pipe 130 and the liquid collection pipe 230, and the first membrane module 100 and the second membrane module 200 can be easily connected.

[0109] Specifically, by blocking the filtrate outlet at one end of the first container 110 in the predetermined direction and blocking the filtrate outlet at the other end of the second container 210 in the predetermined direction, the filtrate flow paths of each individual element can be made independent of each other. The filtrate pressure depends on the average of the inlet and outlet pressures of each individual element. Therefore, when multiple individual elements are connected in series and the filtrate flow paths are also connected at the connection points of the individual elements, the inlet pressure of the raw liquid of the downstream individual element may become equal to or lower than the filtrate pressure of the individual element. In this case, problems may occur such as the filtrate not coming out of the individual element or, in some cases, the filtrate flowing back into the raw liquid side. By blocking the filtrate outlet at one end of the first container 110 in the predetermined direction and blocking the filtrate outlet at the other end of the second container 210 in the predetermined direction, the filtrate pressure in the downstream individual element is prevented from being affected by the filtrate pressure in the upstream individual element, making it less likely that the difference between the raw liquid pressure and the filtrate pressure in the downstream individual element will become small, thereby reducing the risk of a decrease in filtration performance.

[0110] The first container 110 has a first opening 114a at its end on the other side in the predetermined direction (the negative X-axis direction), and the second container 210 has a second opening 214a at its end on one side in the predetermined direction (the positive X-axis direction). This allows two openings (the first opening 114a and the second opening 214a) that serve as the inlet and outlet for the concentrate to be located at both ends in the predetermined direction (the X-axis direction) of the container 11. Therefore, the concentrate can flow from one end to the other end in the predetermined direction (the X-axis direction) of the container 11, making it possible to efficiently secure a flow path for the concentrate in a limited space.

[0111] The first opening 114a is formed on the end face of the first container 110 on the other side in the predetermined direction (negative X-axis direction), and the second opening 214a is formed on the end face of the second container 210 on one side in the predetermined direction (positive X-axis direction). This allows two openings (first opening 114a and second opening 214a) serving as the inlet and outlet for the concentrate to be formed on both end faces of the container 11 in the predetermined direction (X-axis direction). Therefore, the concentrate can flow from one end face of the container 11 to the other end face in the predetermined direction (X-axis direction), further shortening the length of the container 11 in the predetermined direction (X-axis direction) while ensuring the length of the concentrate path. Furthermore, because the inlet and outlet for the concentrate are located on the end faces of the container 11, it is easy to connect three or more containers at their respective end faces. In other words, by connecting the end face of the first container 110 or the second container 210 to another container or other component (not shown), the first opening 114a or the second opening 214a can be easily connected to the other container or other component.

[0112] At least one of the first element 120 and the second element 220 has a length in a predetermined direction, i.e., in the winding axis direction, of 800 mm or less. This reduces the effect of pressure loss in the element's winding axis direction and reduces differences in filtration efficiency depending on the location in the winding axis direction. Therefore, for example, when the first container 110 containing the first element 120 and the second container 210 containing the second element 220 are connected in series, and the second container 210 is disposed on one side of the first container 110 in the predetermined direction, the problem of differences in filtration efficiency between the first element 120 and the second element 220 is unlikely to occur. Furthermore, elements with a short length in the winding axis direction can be used alone, in series connections, or in parallel connections, facilitating equipment design tailored to the installation environment, the properties of the material to be removed, and the like.

[0113] When the vessel 11 is formed by connecting an end face on one side in a predetermined direction of the first vessel 110 to an end face on the other side in the predetermined direction of the second vessel 210, thereby connecting the raw liquid flow path in the first vessel 110 and the raw liquid flow path in the second vessel 210, it is more preferable that the inlet pressure of the raw liquid flowing into the membrane module 10 is lower than 0.2 MPa. In the above embodiment (one end face of the first vessel 110 is connected to the other end face of the second vessel 210 + the raw liquid flow paths are connected in series), when the inlet pressure of the raw liquid flowing into the membrane module 10 is low, the possibility that the inlet pressure of the raw liquid in the downstream individual element will be equal to or lower than the pressure of the filtrate increases compared to the case of high-pressure operation. To address this problem, the filtrate flow paths of the multiple individual elements are made independent of each other, and the first container 110 containing the first element 120 and the second container 210 containing the second element 220 are arranged along a predetermined direction, with the first container 110 having a first filtrate outlet 114b and the second container 210 having a second filtrate outlet 214b. This configuration prevents the filtrate from becoming difficult to discharge in the downstream individual elements, i.e., prevents a decrease in filtration efficiency.

[0114] The inlet pressure of the raw liquid flowing into the membrane module 10 is less than 0.2 MPa. Here, the filtration device 1 is configured so that by extracting filtrate from two outlets (the first outlet 114b and the second outlet 214b), the distance through which the filtrate flows can be shortened and the resistance to the flow of the filtrate can be reduced. Therefore, even if the length of the container 11 is increased by connecting the first container 110 and the second container 210, the resistance to the flow of the filtrate can be reduced, and operation can be performed at a low inlet pressure through which the raw liquid flows. Therefore, low-pressure operation can be performed so that the inlet pressure of the raw liquid flowing into the membrane module 10 is less than 0.2 MPa, thereby reducing the power required for pressurization and, as a result, reducing power consumption.

[0115] [6. Description of Modifications] The filtering device 1 according to the present embodiment has been described above, but the present invention is not limited to the above embodiment. The embodiment disclosed herein is illustrative in all respects and is not restrictive, and the scope of the present invention includes all modifications within the meaning and scope of the claims.

[0116] (Variation 1) In the above embodiment, the membrane module 10 is provided with filtrate outlets (first outlet 114b and second outlet 214b) at both ends (both end faces) of the vessel 11, but this is not limited thereto. The membrane module 10 may be provided with filtrate outlets in both the first vessel 110 and the second vessel 210. Fig. 9 is a front view showing the configuration of a membrane module 10a according to Variation 1 of this embodiment. Fig. 9 is a view corresponding to Fig. 3(a).

[0117] As shown in FIG. 9, the membrane module 10a in this modified example includes a first membrane module 101 and a second membrane module 201 instead of the first membrane module 100 and the second membrane module 200 included in the membrane module 10 in the above embodiment.

[0118] The first membrane module 101 is provided with a first filtrate outlet 133 connected to the liquid collection pipe 130, on the side surface of the end of the first container 110 (first container body 111) in the negative X-axis direction. As described above, this end of the first container 110 is the portion between the end face of the leaf 121 of the first element 120 in the negative X-axis direction and the end face of the flange portion 114 in the negative X-axis direction. Therefore, the first outlet 133 is disposed in the X-axis direction between the end face of the leaf 121 of the first element 120 in the negative X-axis direction and the end face of the flange portion 114 in the negative X-axis direction (the end face of the flange portion 113 in the positive X-axis direction in this modified example). The flange portion 114 is not provided with a filtrate outlet (first outlet 114b in the above embodiment).

[0119] The second membrane module 201 is provided with a second filtrate outlet 233 connected to the liquid collection pipe 230, on the side surface of the end portion of the second container 210 (second container body 211) in the positive direction of the X axis. As described above, this end portion of the second container 210 is the portion between the end surface of the leaf 221 of the second element 220 in the positive direction of the X axis and the end surface of the flange portion 214 in the positive direction of the X axis. Therefore, the second outlet 233 is disposed in the X axis direction between the end surface of the leaf 221 of the second element 220 in the positive direction of the X axis and the end surface of the flange portion 214 in the positive direction of the X axis (the end surface of the flange portion 213 in the negative direction of the X axis in this modified example). The flange portion 214 is not provided with a filtrate outlet (second outlet 214b in the above embodiment).

[0120] The membrane module 10a according to this modification can also achieve the same effects as the above embodiment. In particular, in this modification, there is no need to provide filtrate outlets on both end faces of the vessel 11, which improves the degree of freedom in arranging the filtrate outlets. Because the filtrate outlets are provided at positions other than the end faces of the vessel 11, it becomes easy to connect three or more vessels, such as a third vessel that houses a third element, in addition to the first vessel 110 and the second vessel 210.

[0121] In this modified example, a first outlet for filtrate may be provided on a side surface of the end of the first container 110 in the positive X-axis direction. A second outlet for filtrate may be provided on a side surface of the end of the second container 210 in the negative X-axis direction. The first outlet for filtrate may be provided in the center of the first container 110 in the X-axis direction. The second outlet for filtrate may be provided in the center of the second container 210 in the X-axis direction. In other words, at least one of the first outlet and the second outlet may be located in the center of at least one of the first container 110 and the second container 210 in a predetermined direction (X-axis direction).

[0122] (Variation 2) In the above embodiment, the filtration device 1 is described as including two membrane modules 10 connected in parallel, but this is not limited thereto. The filtration device 1 may include three or more membrane modules 10 connected in parallel, or may include only one membrane module 10. The filtration device 1 may also include a plurality of membrane modules 10 connected in series. Fig. 10 is a schematic diagram showing the general configuration of a filtration device 2 according to Variation 2 of this embodiment. Fig. 10 is a diagram corresponding to Fig. 1.

[0123] 10 , the filtration device 2 in this modification has two membrane modules 10 connected in series. Of the two membrane modules 10, the membrane module 10 in the negative Z-axis direction has the first membrane module 100 arranged in the negative X-axis direction and the second membrane module 200 arranged in the positive X-axis direction. Of the membrane module 10 in the positive Z-axis direction, the first membrane module 100 arranged in the positive X-axis direction and the second membrane module 200 arranged in the negative X-axis direction.

[0124] In this configuration, the stock solution 21 discharged from the pump 30 passes through the pipe 41 and is supplied to the membrane module 10 from the first opening 114a of the membrane module 10 in the negative Z-axis direction at an inlet pressure P6. The inlet pressure P6 has a pressure range similar to the inlet pressures P2 or P3 in the above-described embodiment, such as less than 0.2 MPa. The stock solution 21 is filtered through the membrane module 10 in the negative Z-axis direction, discharged from the second opening 214a of the membrane module 10 at an outlet pressure P7, and passed through the pipe 46 and supplied to the membrane module 10 from the first opening 114a of the membrane module 10 in the positive Z-axis direction at an inlet pressure P8. The outlet pressure P7 and the inlet pressure P8 have pressure ranges similar to the outlet pressures P4 or P5 in the above-described embodiment, such as less than 0.2 MPa. The stock solution 21 is filtered by the membrane module 10 in the positive direction of the Z axis, discharged from the second opening 214a of the membrane module 10 at outlet pressure P9, and returned to the stock solution tank 20 through piping 47. The filtrate (permeated liquid) obtained by filtering the stock solution 21 through the two membrane modules 10 and removing solids is discharged through piping 43, 44, and 45 from the first outlet 114b and second outlet 214b provided on each of the two membrane modules 10.

[0125] The filtration device 2 according to this modification can also achieve the same effects as those of the above embodiment. As in this modification, multiple membrane modules 10 can be connected in series, so that the multiple membrane modules 10 can be connected in various configurations.

[0126] (Other Modifications) In the above embodiment, the membrane module 10 is provided with an inlet and an outlet (first opening 114a and second opening 214a) for the raw liquid on both end surfaces of the container 11, but this is not limited to this. The opening serving as the inlet or outlet for the raw liquid may be provided on a side surface, such as the end or center in the X-axis direction, of the first container 110 or the second container 210, and may be provided at any position in the container 11 of the membrane module 10.

[0127] In the above embodiment, the flange portion 112 has the connecting portion 112a at a portion that protrudes outward from the first container body 111, and the flange portion 212 has the connecting portion 212a at a portion that protrudes outward from the second container body 211, and the connecting portion 112a and the connecting portion 212a are connected to each other. However, the flange portion 112 does not necessarily have a portion that protrudes outward from the first container body 111, and the flange portion 212 does not necessarily have a portion that protrudes outward from the second container body 211. In this case, the flange portion 112 and the flange portion 212 may be connected to each other by a joint. The same applies to the connection between the flange portion 113 and the flange portion 114, the connection between the flange portion 213 and the flange portion 214, and the other connections between flange portions.

[0128] In the above embodiment, the filtration membrane provided in the membrane module 10 is a microfiltration membrane (MF membrane) having a pore size of 0.1 μm or more and 0.4 μm or less, but a microfiltration membrane with a pore size other than that may be used, or a filtration membrane other than a microfiltration membrane may be used.

[0129] In the above embodiment, the upper limit of the discharge pressure of the pump 30 is set to be lower than 0.45 MPa, but it may be set to be equal to or higher than 0.45 MPa.

[0130] In the above embodiment, the length of the filtration membrane in the winding direction included in the membrane module 10 is 800 mm or less, and the thickness of the filtrate net is 0.2 mm or more, but this is not limiting. The length of the filtration membrane in the winding direction may be greater than 800 mm, and the thickness of the filtrate net may be less than 0.2 mm.

[0131] In the above embodiment, the length in the predetermined direction (winding axis direction) of both the first element 120 (excluding the liquid collection tube 130) and the second element 220 (excluding the liquid collection tube) is set to 800 mm or less, but this is not limited to this. The length in the predetermined direction (winding axis direction) of the first element 120 or the second element 220 may be greater than 800 mm. In other words, it is sufficient that at least one of the first element 120 and the second element 220 has a length in the predetermined direction (winding axis direction) of 800 mm or less. Alternatively, the length in the predetermined direction (winding axis direction) of both the first element 120 and the second element 220 may be greater than 800 mm.

[0132] In the above embodiment, the effective filtration area per leaf of the element provided in the membrane module 10 is 1.3 m ２ Although it was decided that it should be less than 1.3m ２ It may be larger than

[0133] In the above embodiment, the number of leaves of the element provided in the membrane module 10 is 16 or more, but it may be less than 16.

[0134] In the above embodiment, the first container 110 of the first membrane module 100 has an end of the filtrate flow path blocked at one end in the predetermined direction, and the second container 210 of the second membrane module 200 has an end of the filtrate flow path blocked at the other end in the predetermined direction. However, this is not limited to this. The end of the filtrate flow path is not limited to this combination; the end of the filtrate flow path may be blocked at the other end in the predetermined direction of the first container 110, or the end of the filtrate flow path may be blocked at one end in the predetermined direction of the second container 210. In other words, a configuration may be possible in which the ends in the predetermined direction of both the first container 110 and the second container 210 are not blocked, and the filtrate is taken out from outlets at both ends of the first container 110 and the second container 210. A configuration in which the end of the filtrate flow path of at least one of the first container 110 and the second container 210 is not blocked may also be used.

[0135] In the above embodiment, the first container 110 of the first membrane module 100 and the second container 210 of the second membrane module 200 are directly connected at their end faces, but this is not limited to this and they may be connected via other components such as piping.

[0136] In the above embodiment, the first membrane module 100 and the second membrane module 200 have the same configuration, but they may have different configurations.

[0137] In the above embodiment, a cake layer is formed on the filtration membrane included in the membrane module 10, but a cake layer does not necessarily have to be formed.

[0138] In the above embodiment, the filtration apparatus 1 includes a membrane module 10 composed of multiple membrane modules. However, the filtration apparatus 1 may include a membrane module 50 composed of a single membrane module. In this case, the number of membrane modules 50 included in the filtration apparatus 1 may be one or more. When the filtration apparatus 1 includes multiple membrane modules 50, the multiple membrane modules 50 may be connected in series or in parallel. In this case, the inlet pressure of the raw liquid flowing into the membrane module 50 is in the same range as the inlet pressure P2 or P3 in the above embodiment, such as less than 0.2 MPa. Connecting multiple membrane modules 50 in parallel can equalize the pressure applied to each membrane module 50, thereby improving filtration efficiency and enabling operation with lower power consumption compared to a series connection. In this way, since each membrane module 50 contains an element in its container, the membrane module 50 can be used alone (neither in parallel nor in series), in a parallel connection, in a series connection, or in a combination of parallel and series connections. The configuration can be changed depending on the usage environment or situation. Furthermore, since the length of the element in the winding axis direction (the above-mentioned length L2) is not too long, ie, 800 mm or less, the membrane module 50 can be easily modified into various forms.

[0139] In the above embodiment, all of the membrane modules 10 have the above configuration, but any of the membrane modules 10 may not have the above configuration.

[0140] Any combination of the above-described embodiments and their modifications is also included within the scope of the present invention.

[0141] 1, 2 Filtration device 10, 10a, 50, 60 Membrane module 11 Container 12 Element 20 Stock solution tank 21 Stock solution 30 Pump 41, 42, 43, 44, 45, 46, 47 Piping 100, 101 First membrane module 110 First container 111 First container body 112, 113, 114, 115, 212, 213, 214, 215 Flange portion 112a, 113a, 114c, 115c, 212a, 213a, 214c Connection portion 114a First opening 114b, 133 First outlet 115a Third opening 120 First element 121, 221 Leaf 122, 122a, 122b Filtration membrane 123 Filtrate net 124 Stock solution net 130, 230 Liquid collection tube 131 Hole 132 Opening 140, 240 Closing member 200, 201 Second membrane module 210 Second container 211 Second container body 214a Second opening 214b, 233 Second outlet 220 Second element

Claims

1. A filtration device comprising a spiral-type membrane module, the membrane module comprising an element having a wound leaf with a filtration membrane, and an inlet pressure of a raw liquid flowing into the membrane module is less than 0.2 MPa.

2. The filtration device according to claim 1, wherein the filtration membrane is a microfiltration membrane.

3. The filtration device according to claim 2, wherein the pore size of the microfiltration membrane is 0.1 μm or more and 0.4 μm or less.

4. A filtration device according to any one of claims 1 to 3, wherein the inlet pressure is 0.1 MPa or less.

5. The filtration device according to any one of claims 1 to 3, wherein the element is provided with a collection tube for collecting filtrate.

6. A filtration device according to any one of claims 1 to 3, wherein the leaf is provided with a filtrate net that forms a flow path for the filtrate, the length of the filtration membrane in the winding direction is 800 mm or less, and the thickness of the filtrate net is 0.2 mm or more.

7. The effective filtration area of ​​each leaf of the element is 1.3 m ２ The filtration device according to claim 6, wherein:

8. The filtration device according to claim 7, wherein the number of leaves of the element is 16 or more.

9. A filtration device comprising a spiral-type membrane module, the membrane module comprising an element having a leaf wound thereon with a filtration membrane, and further comprising a pump for supplying a raw liquid to the membrane module, the upper limit of the discharge pressure of the pump being less than 0.45 MPa.

10. A filtration method in a filtration apparatus equipped with a spiral-type membrane module, the membrane module having an element in which a leaf having a filtration membrane is wound, the filtration method comprising the steps of: flowing a raw liquid into the membrane module at an inlet pressure of less than 0.2 MPa.