Hollow fiber membrane module, filtration operation method, and filtration device

Abstract

The purpose of the present invention is to provide a hollow fiber membrane module having high stability in removal rate in order to solve the problem that when a high-turbidity solution is filtered, the surface of a hollow fiber membrane is rubbed and the removal performance of the hollow fiber membrane is reduced due to the contact between a filtered stock solution and the hollow fiber membrane. Provided is a hollow fiber membrane module, a plurality of hollow fiber membranes accommodated between the first end and the second end in the cylindrical housing; and a stock solution inlet through which a stock solution to be filtered flows into the cylindrical housing, and a permeate outlet through which a permeate having permeated through the hollow fiber membranes flows out of the cylindrical case, the stock solution inlet being in communication with the outer surfaces of the plurality of hollow fiber membranes, and the stock solution inlet being in communication with the outer surfaces of the plurality of hollow fiber membranes at the ends of the plurality of hollow fiber membranes located on the first end side of the cylindrical case. The hollow fiber membrane module is provided with a first potting part which adheres the plurality of hollow fiber membrane bundles in a state where a plurality of hollow parts are opened, and in a cross section perpendicular to the height direction of the cylindrical case, when the cross-sectional area in the cylindrical case is set to 100%, the first potting part is provided with a second potting part which adheres the plurality of hollow fiber membrane bundles. The ratio of the area occupied by the plurality of hollow fiber membranes and the hollow parts thereof (hereinafter, the filling rate) is 40-80%, and the surface elastic modulus on the outside of the plurality of hollow fiber membranes is 200-500 MPa.

Description

Technical Field

[0001] The present invention relates to a hollow fiber membrane module, a filtration operation method using the hollow fiber membrane module, and a filtration device equipped with the hollow fiber membrane module. Background Art

[0002] In recent years, separation membranes such as microfiltration membranes and ultrafiltration membranes have been used in various fields such as water treatment fields such as water purification or drainage treatment, medical fields such as blood purification, and food industry fields. Compared with the treatment methods such as sedimentation and sand filtration that have been carried out in the past, the treatment using separation membranes has the great advantage of high and stable water quality. Therefore, the treatment using separation membranes has become popular on a large scale, especially in the field of water treatment. Recently, with the increase in population, in order to ensure water resources, it is required to have a membrane assembly that can stably obtain high-quality treated water quality for a long time even for a filtration stock solution containing a large amount of suspended matter (hereinafter sometimes referred to as "turbidity") that is considered difficult to filter. Hollow fiber separation membranes can fill a large amount of membrane area relative to the installation area of ​​the membrane assembly and are often used.

[0003] However, when filtering a raw liquid containing a large amount of turbidity (hereinafter sometimes referred to as "high-turbidity liquid"), the membrane surface may be damaged by friction caused by the turbidity and organic matter contained in the high-turbidity liquid, which are substances that do not pass through the membrane. If this friction-induced damage occurs, the components that the separation membrane is intended to remove may leak into the permeate side, forcing filtration to be interrupted. For example, if the desired removal performance cannot be maintained in a water treatment plant, there is a risk of bacteria and viruses being contaminated in the drinking water, necessitating replacement of the membrane module with a new one, which is very costly.

[0004] Until now, little research has been conducted on suppressing damage to separation membranes caused by friction, that is, performance degradation caused by rubbing. Patent Document 1 discloses a technique for suppressing a decrease in water permeability by increasing the aperture ratio of the separation membrane surface.

[0005] Furthermore, when filtering highly turbid liquids, turbid matter and organic matter contained in the liquid can sometimes accumulate within the membrane assembly, clogging the pores of the separation membrane and the spaces between the membranes within the assembly. Clogging can reduce the membrane assembly's processing speed, forcing filtration to be interrupted. In such cases, the membrane assembly is cleaned with chemicals. If chemical cleaning fails to restore the filtration efficiency, or if the removal rate decreases due to membrane degradation caused by the chemicals, the membrane assembly must be replaced with a new one, which is very costly.

[0006] Furthermore, to suppress performance degradation caused by clogging of the membrane module, there are methods for physically washing the membrane module before clogging completely develops. Specifically, back-pressure washing is disclosed, in which permeate, water, etc., is passed from the permeate side of the separation membrane to the feed liquid side to expel substances adhering to the membrane pores and membrane surface; air washing is disclosed, in which gas is supplied from the bottom of the hollow fiber membrane module to shake the hollow fiber membrane for physical washing (for example, see Patent Document 2); and a flushing method is disclosed, in which a feed liquid or chemical solution is passed through the membrane surface at a high linear velocity on the feed liquid side of the hollow fiber membrane (for example, see Patent Document 3).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: International Publication No. 2015 / 104871

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 11-342320

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2010-005615

[0012] Patent Document 4: International Publication No. 2002 / 070115 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, while the technology described in Patent Document 1 increases the surface aperture ratio of the separation membrane to suppress water permeability degradation caused by clogging and membrane surface abrasion, it only aims to improve water permeability before abrasion occurs and, even after abrasion has already occurred, to suppress the decline in water permeability. In other words, the technology in Patent Document 1 cannot suppress membrane surface abrasion itself. Furthermore, it does not address the need to maintain sufficient removal efficiency and achieve safe and secure water quality when treating highly turbid liquids.

[0015] Furthermore, when air washing (as disclosed in Patent Document 2) or flushing (as disclosed in Patent Document 3) is performed to prevent clogging, the high velocity of turbid matter near the hollow fiber membranes makes it easy for the turbid matter to collide with the hollow fiber membranes, particularly causing rubbing of the hollow fiber membranes. In other words, while the techniques of Patent Documents 2 and 3 remove attached matter and prevent clogging, they can also accelerate rubbing and damage the membrane surface.

[0016] Therefore, the present invention aims to provide a hollow fiber membrane module that achieves high and stable removal rates by suppressing rubbing during filtration of highly turbid liquids. By suppressing rubbing, physical cleaning of the hollow fiber membranes is effectively prevented from clogging, further enabling long-term, stable filtration. This provides a filtration method that can stably produce permeate of safe and secure quality over long periods of time, even for difficult-to-treat highly turbid liquids.

[0017] Means for solving problems

[0018] In order to solve the above-mentioned problems, the present invention provides a hollow fiber membrane module having the following configuration.

[0019] 1. A hollow fiber membrane module comprising: a cylindrical shell having a first end and a second end in a height direction of the cylindrical member; a plurality of hollow fiber membranes accommodated in the cylindrical shell between the first and second ends; a raw liquid inlet for allowing a raw liquid to be filtered to flow into the cylindrical shell; and a permeate outlet for allowing a permeate that has permeated the hollow fiber membranes to flow out of the cylindrical shell; the raw liquid inlet being connected to outer surfaces of the plurality of hollow fiber membranes; a first potting portion for bonding a bundle of the plurality of hollow fiber membranes with the plurality of hollow portions open at ends of the plurality of hollow fiber membranes located on the first end side of the cylindrical shell; in a cross section perpendicular to the height direction of the cylindrical shell, when the cross-sectional area within the cylindrical shell is set to 100%, a ratio of the area occupied by the plurality of hollow fiber membranes including the hollow portions (hereinafter referred to as a filling rate) is 40% to 80%, and a surface elastic modulus of the outer surfaces of the plurality of hollow fiber membranes is 200 MPa to 500 MPa.

[0020] 2. The hollow fiber membrane module according to item 1 above, wherein the number of pores observed on the outer surface of the hollow fiber membrane (hereinafter referred to as surface pores) per unit area is 200 pores / μm 2 ~2000 / μm 2 .

[0021] 3. The hollow fiber membrane module according to 1 or 2 above, wherein the opening ratio of the outer surface of the hollow fiber membrane is 1% to 10%.

[0022] 4. The hollow fiber membrane module according to any one of 1 to 3 above, wherein an average pore diameter of the outer surface of the hollow fiber membrane (hereinafter referred to as surface pore diameter) is 5 nm to 20 nm.

[0023] 5. The hollow fiber membrane module according to any one of 2 to 4 above, wherein the number of the surface pores per unit area [pores / μm 2 ] divided by the above surface pore diameter [nm]: α is 30 / μm 2 / nm~150 / μm2 / nm.

[0024] 6. The hollow fiber membrane module according to any one of 1 to 5 above, wherein in a circular cross section of the hollow fiber membrane, a cross-sectional porosity in a region from the outer surface of the hollow fiber membrane to 5 μm from the outer surface (hereinafter referred to as the outer surface portion) is 20% to 50%.

[0025] 7. The hollow fiber membrane module according to any one of 1 to 6 above, wherein the hollow fiber membrane structures between the pores in the outer surface of the hollow fiber membrane are pillars, and the average thickness of the pillars is 20 nm to 60 nm.

[0026] 8. The hollow fiber membrane module according to any one of 1 to 7 above, wherein the density of the pillars is 10 to 50 pillars / μm.

[0027] 9. The hollow fiber membrane assembly according to any one of 1 to 8 above, which comprises a second potting portion for bonding the bundle of the plurality of hollow fiber membranes located on the second end side of the cylindrical shell, and when the average length of the plurality of hollow fiber membranes between the second end side of the first potting portion and the first end side of the second potting portion is set to X, and the length in the height direction between the second end side of the first potting portion and the first end side of the second potting portion in the cylindrical shell is set to Y, the relationship is 2≤(XY) / X×100≤20(%).

[0028] 10. The hollow fiber membrane module according to any one of 1 to 9 above, wherein a raw liquid to be filtered having a turbidity of 3 to 50 NTU is filtered, and when a permeate is separated from the filtrate, the virus removal rate of the permeate is 4 log or greater.

[0029] 11. The hollow fiber membrane module according to any one of 1 to 10 above, wherein a raw liquid to be filtered having a turbidity of 3 to 50 NTU is filtered, and when a permeate is separated from the raw liquid to be filtered, the permeate has an SDI of 3 or less.

[0030] 12. A filtration operation method of a hollow fiber membrane module, comprising supplying a raw liquid to be filtered having a turbidity of 3 to 50 NTU to the hollow fiber membrane module according to any one of 1 to 11 above, and separating a permeate from the raw liquid to be filtered.

[0031] 13. A filtration operation method of a hollow fiber membrane module, comprising supplying a filtered stock solution having a total organic carbon (hereinafter, TOC) of 4 to 30 mg / L to the hollow fiber membrane module according to any one of 1 to 12 above, and separating a permeate from the filtered stock solution.

[0032] 14. A method for filtration operation of a hollow fiber membrane module, which is the method for filtration operation of a hollow fiber membrane module according to any one of 1 to 11 above, comprising the following steps (1) and (2):

[0033] The step (1) is a membrane separation step of supplying a raw liquid to the hollow fiber membrane module to separate the suspended matter from the liquid.

[0034] The step (2) is a washing step of stopping the step (1) and washing the suspended matter accumulated on the outer surface of the hollow fiber membrane and between the hollow fiber membranes.

[0035] The above-mentioned washing step (2) performs the following air washing operation: the above-mentioned raw liquid or a mixed flow of liquid and gas having a turbidity or TOC at least lower than that of the above-mentioned raw liquid flows toward the outer surface side of the above-mentioned hollow fiber membrane at a flow rate of a membrane surface linear velocity of greater than 0.3 m / s and less than 5.0 m / s.

[0036] 15. A hollow fiber membrane having an opening ratio of 1% to 10% relative to the area of ​​the outer surface of the hollow fiber membrane, and a surface elastic modulus of the outer surface of the hollow fiber membrane of 200 MPa to 500 MPa. Furthermore, to achieve a surface elastic modulus of 200 MPa to 500 MPa on the outer surface of the hollow fiber membrane, the cross-sectional porosity of the region from the outer surface to 5 μm from the outer surface (hereinafter referred to as the outer surface portion) in a circular cross section of the hollow fiber membrane is preferably 20% to 50%. Furthermore, the hollow fiber membrane structures between the pores in the outer surface portion of the hollow fiber membrane are formed as columns, the average thickness of the columns is preferably 20 nm to 60 nm, and the density of the columns is preferably 10 to 50 columns / μm.

[0037] 16. A filtration device comprising the hollow fiber membrane module according to any one of 1 to 11 above or the hollow fiber membrane according to 15 above.

[0038] Effects of the Invention

[0039] According to the present invention, by ensuring that the surface elastic modulus of the outer surface of the hollow fiber membrane, which contacts a turbidity-rich filtrate, is 200 MPa or greater, it is possible to suppress rubbing of the hollow fiber membrane and reduce the reduction in removal efficiency. This provides a filtration method that allows physical cleaning of hollow fiber membrane modules without reducing the removal efficiency caused by rubbing, enabling long-term filtration of highly turbid filtrate, and obtaining safe and reliable permeate water. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is an example of the hollow fiber membrane module of the present invention.

[0041] Figure 2This figure illustrates the wear test on the outer surface of a hollow fiber membrane.

[0042] Figure 3 This is an example of a TEM image of a cross section of the hollow fiber membrane of the present invention.

[0043] Figure 4 for Figure 3 An enlarged view of the outer surface of the .

[0044] Figure 5 Schematic diagram showing the process of forming a porous membrane on the outer surface of a hollow fiber membrane.

[0045] Figure 6 The results of the wear test on the outer surface of the hollow fiber membrane. DETAILED DESCRIPTION

[0046] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto. In addition, in this specification, "mass" and "weight" have the same meaning. In addition, the so-called "filter stock liquid" is the liquid to be filtered before passing through the separation membrane, and the "permeate" refers to the liquid after passing through the separation membrane. "Filter stock liquid" has the same meaning as "filtered stock liquid" or "filtrate", and both refer to the liquid to be filtered before passing through the separation membrane. In addition, the so-called high turbidity stock liquid refers to a liquid containing a large amount of turbidity and organic matter in the filter stock liquid. For example, a liquid with a turbidity of 3NTU or more, or a liquid with a total organic carbon (hereinafter, TOC) of 4mg / L or more. When turbidity and organic matter come into contact with the membrane surface, the membrane surface is irreversibly damaged, which is called scratching. The following describes the hollow fiber membrane assembly for suppressing scratching of the present invention.

[0047] Hollow fiber membrane modules

[0048] The hollow fiber membrane module of the present invention comprises at least a cylindrical shell having a first end and a second end in the height direction of the cylindrical member, a plurality of hollow fiber membranes housed in the first and second ends of the cylindrical shell, a raw liquid inlet for allowing a filtered raw liquid to flow into the cylindrical shell, and a permeate outlet for allowing a permeate that has passed through the hollow fiber membranes and been separated to flow out.

[0049] exist Figure 1 In the hollow fiber membrane module 100 , a plurality of hollow fiber membranes 2 are accommodated in a bundle in a cylindrical casing 1 having a first end and a second end arranged vertically. Figure 1 The lower cover 6 is connected to the cylindrical housing 1 and is provided with a raw liquid inlet 7. The upper cover 5 is connected to the cylindrical housing 1 and is provided with a permeate outlet 8. In addition, a raw liquid outlet 9 is provided in the cylindrical housing 1 at a position away from the raw liquid inlet 7.

[0050] Furthermore, a raw liquid inlet 7 is connected to the outer surface of the hollow fiber membranes 2. A first potting portion 3 is bonded to the ends of the plurality of hollow fiber membranes 2 located on the first end side of the cylindrical casing 1, with their hollow portions open. This connects the hollow end openings of the hollow fiber membranes 2 to the permeate outlet 8. As a result, the filtered raw liquid flowing in through the raw liquid inlet 7 is separated from the outer surfaces of the hollow fiber membranes 2 toward the interior, allowing the liquid permeating through the hollow fiber membranes to be withdrawn from the permeate outlet 8. The filling factor of the hollow fiber membranes 2 within the cylindrical casing 1 is required to be 40% to 80%, and the surface elastic modulus of the outer surfaces of the plurality of hollow fiber membranes is required to be 200 MPa to 500 MPa. The filling factor is the ratio of the combined area of ​​the plurality of hollow fiber membranes and their hollow portions, with the cross-sectional area of ​​the cylindrical casing inner side being 100%, in a cross section perpendicular to the height direction of the cylindrical casing 1.

[0051] The raw liquid inlet 7 is connected to the outer surfaces of the multiple hollow fiber membranes 2, allowing for so-called external pressure filtration, in which turbidity and organic matter contained in the raw liquid contact the outer surfaces of the hollow fiber membranes. Since the outer surface of the hollow fiber membranes has a larger surface area than the inner surface, the amount of turbidity and organic matter per unit area in contact with the hollow fiber membranes can be reduced, thus suppressing rubbing. Furthermore, by setting the proportion of hollow fiber membranes in a cross-section perpendicular to the height of the cylindrical shell, i.e., the filling factor, to 40% to 80%, the membrane area within the cylindrical shell can be increased without excessively increasing the turbidity concentration within the cylindrical shell. To increase the membrane area, the filling factor is preferably 45% or greater, more preferably 50% or greater, and particularly preferably 55% or greater. Furthermore, to reduce the turbidity concentration within the cylindrical shell, the filling factor is preferably 75% or less, more preferably 70% or less, and particularly preferably 65% ​​or less.

[0052] Using a microfiltration membrane or an ultrafiltration membrane as the hollow fiber membrane allows for efficient removal of turbidity, organic matter, and the like from the raw liquid while also producing a permeate. Using an ultrafiltration membrane is preferred because it facilitates increasing the surface elastic modulus of the outer surface of the hollow fiber membrane. The surface outside the hollow fiber membrane is sometimes referred to as the hollow fiber membrane outer surface, or simply as the outer surface.

[0053] The inventors and others have repeatedly conducted in-depth research and found that in order to suppress membrane abrasion, it is important to increase the surface elastic modulus of the outer side of the hollow fiber membrane in contact with turbidity. In the past, the so-called hollow fiber membrane with excellent durability was aimed at the stability of water permeability, and the stability of the removal rate to maintain high removal performance was not studied. The technology of Patent Document 1 did not study whether the removal rate, pore size, and pore shape changed, and the suppression of abrasion itself was not verified. Furthermore, it did not focus on the surface elastic modulus of the surface of the hollow fiber membrane. That is, as mentioned above, Patent Document 1 only improves the water permeability before abrasion, and is not a technology for suppressing abrasion itself. Therefore, the removal rate is reduced due to abrasion on the surface of the hollow fiber membrane. The stability of the removal rate is a particularly effective and indispensable function when performing high-precision filtration on high-turbidity liquids. Objects that should be removed in the raw liquid are, for example, turbidity, fungi, viruses, polysaccharides, proteins, organic compounds and their complexes. The inventors have found that when the removal rate: T of dextran having a weight-average molecular weight of 40,000 Da is 60% or more, it is easy to sufficiently remove components to be removed in water treatment.

[0054] The hollow fiber membrane assembly of the present invention can suppress the rubbing of the hollow fiber membrane and reduce the reduction in removal rate by making the surface elastic modulus of the outer side of the hollow fiber membrane in contact with the raw liquid containing a large amount of turbidity be 200 MPa or more. As a result, the reduction in removal rate caused by rubbing can be avoided and a high removal rate can be stably maintained. The surface elastic modulus of the outer surface of the hollow fiber membrane of the present invention is an indicator of the restoring force of the membrane to pressure. The greater the restoring force, the less likely it is to undergo irreversible deformation. If irreversible deformation, i.e., plastic deformation, occurs, the shape of the pores of the hollow fiber membrane changes, and the components to be removed by the hollow fiber membrane are likely to leak into the permeate. For example, although the compressive elastic modulus of the hollow fiber membrane is recorded in Patent Document 4, it is not taken seriously. In addition, the range is as low as 1.5 MPa to 10 MPa, which cannot suppress the rubbing of the surface of the hollow fiber membrane.

[0055] The present invention has discovered that by using a hollow fiber membrane with a high surface elastic modulus, even when turbid matter contacts and rubs the hollow fiber membrane, causing abrasion, the strong restoring force can suppress abrasion. In order to exert sufficient restoring force when turbid matter is pressed, the surface elastic modulus is preferably 230 MPa or more, more preferably 250 MPa or more, and particularly preferably 300 MPa or more. In addition, to provide the hollow fiber membrane with toughness and suppress cracking when turbid matter collides with it, the surface elastic modulus is preferably 450 MPa or less, more preferably 400 MPa or less, and particularly preferably 350 MPa. Examples of embodiments of hollow fiber membranes having a surface elastic modulus of 200 MPa or more are described in detail below in the sections "Structure of Hollow Fiber Membrane," "Raw Materials of Hollow Fiber Membrane," and "Method for Manufacturing Hollow Fiber Membrane."

[0056] The inventors observed the outer surface of the hollow fiber membrane with a scanning electron microscope in which the performance change caused by rubbing was confirmed in the physical washing (air washing) test described later. The results confirmed that the membrane was scraped and deformed in the area from the surface to hundreds of nm away from the surface. Therefore, the surface elastic modulus is preferably measured in the area from the surface to hundreds of nm away from the surface. It is expected that the activated carbon used in the physical washing test and the turbidity contained in the actual filtered stock solution have particles of different shapes, and their sizes are also distributed. It is speculated that when turbidity with a sharp shape or turbidity with a large surface roughness contacts the membrane surface, it is important to have a high surface elastic modulus on the surface in a range deeper than the convex part of the turbidity.

[0057] The surface elastic modulus can be tested and calculated using a commercially available nanoindenter according to ISO 14577. When measuring hollow fiber membranes, a dried hollow fiber membrane is fixed to a metal or glass plate, with a maximum load of 0.1 mN applied for 15 seconds and the maximum load maintained for 30 seconds. Measurements are conducted at room temperature (20°C to 25°C). The Poisson's ratio of the main component constituting the outer surface of the hollow fiber membrane is used to calculate the surface elastic modulus within an indentation depth range of 0.4 μm to 0.8 μm. For polyvinylidene fluoride resins, a Poisson's ratio of 0.35, for polysulfones, 0.37, for polyethersulfones, 0.40, and for cellulose acetate, a value of 0.30 can be used. Here, the main component is defined as the component with a weight fraction of 50% or more of the components constituting the hollow fiber membrane. The main component can be determined using conventional composition analysis equipment using known techniques, such as IR, NMR, and ICP. The surface elastic modulus was determined by measuring the surface elastic modulus five times using the same hollow fiber membrane with different measurement positions, further measuring the surface elastic modulus using three different hollow fiber membranes, and calculating the average of all the measured values.

[0058] In addition, the deviation of the surface elastic modulus of the outer surface of the hollow fiber membrane is preferably small. By the range of the value of the surface elastic modulus, that is, the distribution is small, it is easy to make it less likely that rubbing will occur from a position with a low surface elastic modulus. The distribution of the surface elastic modulus is determined by measuring the surface elastic modulus 5 times with the same hollow fiber membrane by changing the measurement position, further measuring 3 different hollow fiber membranes, and calculating the coefficient of variation from all these measured values. The coefficient of variation is preferably less than 0.3, more preferably less than 0.25, more preferably less than 0.2, and most preferably less than 0.1.

[0059] Next, the shape of the hollow fiber membrane module is described in detail. An example of the hollow fiber membrane module of the present invention is shown in FIG. Figure 1A plurality of hollow fiber membranes 2 are accommodated in a bundle in a cylindrical casing 1 in which a first end 110 and a second end 120 are arranged vertically. Figure 1 The lower cover 6 is connected to the cylindrical housing 1 and is provided with a raw liquid inlet 7. The upper cover 5 is connected to the cylindrical housing 1 and is provided with a permeate outlet 8. Furthermore, a raw liquid outlet 9 is provided in the cylindrical housing 1 at a position away from the raw liquid inlet 7. Furthermore, it is preferred to include a first potting portion 3 to which the ends of the plurality of hollow fiber membranes located on the first end side of the cylindrical housing 1 are bonded in an open state, and a second potting portion 4 to which the ends of the plurality of hollow fiber membranes located on the second end side of the cylindrical housing are bonded in a sealed state. The raw liquid inlet 7 is provided so that the raw liquid flows into the second potting portion 4, and the permeate outlet 8 is provided so that the permeate flows out from the first potting portion 3. Here, the second potting portion 4 can be bonded so that the ends of the plurality of hollow fiber membranes are bonded in an open state and sealed with a second potting housing 12 or the like that covers the ends of the second potting portion 4.

[0060] The filling rate in the cylindrical shell is Figure 1 The ratio of the hollow fiber membranes in the cylindrical housing in the AA section is shown in FIG. The filtered raw liquid, which is the liquid to be treated, is supplied into the hollow fiber membrane module from the raw liquid inlet 7, contacts the outer sides of the hollow fiber membranes 2, and is filtered toward the hollow portion of the hollow fiber membranes. The treated liquid is then withdrawn from the permeate outlet 8 provided in the upper cover 5.

[0061] By ensuring that the average length X of the hollow fiber membranes between the second end of the first potting section 3 and the first end of the second potting section 4 (i.e., the average length of the plurality of hollow fiber membranes between the first potting section 3 and the second potting section 4) and the height length Y between the second end of the first potting section and the first end of the second potting section in the cylindrical housing (i.e., the distance between the first potting section 3 and the second potting section 4) are in the relationship of 2(%) ≤ (XY) / Y×100 ≤ 20(%), the hollow fiber membranes can be effectively shaken by physical washing, making it easier to discharge turbidity accumulated between the hollow fiber membranes. This makes clogging between the hollow fiber membranes and within the membrane pores due to turbidity less likely to occur, which is preferable. The aforementioned relationship between X and Y indicates that the hollow fiber membranes within the hollow fiber membrane module have a predetermined amount of slack. Generally, when hollow fiber membranes have slack, blockage can be effectively eliminated by physical washing. On the other hand, there is a concern about scratching of the hollow fiber membranes. However, in a membrane module in which the outer surface of the hollow fiber membrane has a high surface elastic modulus, scratching can be suppressed, making it easier to filter high-turbidity liquids stably for a long time, which is preferred. From the perspective of improving the effectiveness of physical washing, (XY) / Y×100(%), which represents the amount of slack of the hollow fiber membrane, is more preferably 4% or more, further preferably 8% or more, and particularly preferably 12% or more. In addition, from the perspective of uniformly controlling the filling rate of the hollow fiber membrane in the cylindrical shell to an appropriate range, the amount of slack of the hollow fiber membrane is more preferably 18% or less, further preferably 16% or less, and particularly preferably 16% or less.

[0062] Hereinafter, the hollow fiber membrane, which is one of the components of the hollow fiber membrane module, will be described.

[0063] <Structure of Hollow Fiber Membrane>

[0064] The hollow fiber membrane module of the present invention has a surface elastic modulus of 200 MPa to 500 MPa on the outer side of the hollow fiber membrane in contact with a stock solution containing a large amount of turbidity. This can suppress damage to the hollow fiber membrane, such as scratching, and reduce the reduction in removal rate. Furthermore, the hollow fiber membrane of the present invention has a surface elastic modulus of 200 MPa to 500 MPa on the outer side of the hollow fiber membrane in contact with a stock solution containing a large amount of turbidity. This can suppress damage to the hollow fiber membrane, such as scratching, and reduce the reduction in removal rate. This prevents a reduction in removal rate caused by scratching and other damage, and stably maintains a high removal rate. Therefore, it is preferred to have a relatively small opening ratio of 1 to 10% on the outer surface of the hollow fiber membrane, thereby increasing the density of the outer side of the hollow fiber membrane and facilitating a high surface elastic modulus. Furthermore, a relatively small opening ratio on the outer surface makes it difficult for turbidity to enter the pores. Therefore, it is preferred to prevent turbidity from colliding near the pore entrance, deforming the pore shape, and thus reduce the occurrence of scratching. To achieve a high surface elastic modulus, the aperture ratio is preferably 10% or less, more preferably 8% or less, even more preferably 6% or less, and particularly preferably 4% or less. Furthermore, when the permeation resistance of the permeated liquid is low, turbid matter is less likely to be strongly pressed against the outer surface of the hollow fiber membrane, causing it to be rubbed. To achieve low permeation resistance, the surface aperture ratio is preferably 1% or more, more preferably 2% or more, and even more preferably 3% or more. Surface pores are the pores present in the surface when observing the outer surface of the hollow fiber membrane, and the aperture ratio is the ratio of the area of ​​the pores in the surface to that of the membrane.

[0065] In order to determine the opening ratio of the hollow fiber membrane surface, an image obtained by observing the surface of the hollow fiber membrane using a scanning electron microscope (hereinafter, "SEM") is binarized using the free software "ImageJ". When binarizing, set the Subtract Background to 1 pixel and Create Background (create background), and then select the condition "RenyiEntropy" in Threshold (binarization threshold). In the resulting binary image, the area of ​​each pore is determined by selecting "Area" in Analyze Particles. An area where more than a thousand pores can be counted is observed, the total area of ​​the pores is determined, and the opening ratio is determined by dividing it by the observed membrane area.

[0066] The surface average pore size on the outside of the hollow fiber membrane is in a relatively small range of 5nm to 20nm, thereby increasing the density on the outside of the hollow fiber membrane and making it easier to make the surface elastic modulus higher, which is preferred. The surface average pore size is further preferably 5nm to 10nm. The so-called surface average pore size is the average value of the surface pore size described later. In addition, the surface average pore size is smaller, so that turbidity is not easy to invade the pores. Therefore, it is preferred that turbidity is not easy to collide with the pores near the entrance and deform the shape of the pores. The so-called surface pore size is the diameter of the pores in the surface when the surface of the hollow fiber membrane is observed. When calculating the surface pore size of the hollow fiber membrane, the area of ​​each pore is calculated in the same way as when calculating the surface opening rate, each pore is assumed to be a circle, and the calculated diameter is set as the surface pore size. When calculating the average value of the surface pore size, the pore size of more than a thousand pores is averaged and calculated.

[0067] In the circular cross section of the hollow fiber membrane, the cross-sectional porosity in the area from the outside of the hollow fiber membrane to 5 μm away from it (hereinafter referred to as the outer surface portion) is smaller than the cross-sectional porosity in the area from the inside of the hollow fiber membrane to 5 μm away from it (hereinafter referred to as the inner surface portion), thereby increasing the density of the outer side of the hollow fiber membrane and making it easier to make the surface elastic modulus higher, which is preferred. In addition, the cross-sectional porosity of the inner surface portion is large, thereby reducing the permeation resistance of the filtered stock solution when passing through the hollow fiber membrane, and easily reducing the pressure when the turbidity is pressed against the outer surface portion. If the pressure on which the turbidity is pressed is low, the outer surface portion is not easily rubbed, which is preferred. The so-called circular cross section refers to a cross section perpendicular to the fiber length direction of the hollow fiber membrane. The cross-sectional porosity is calculated by obtaining an image of the circular cross section of the hollow fiber membrane (the thickness of the slice used as the observation sample is 100 nm) observed with a transmission electron microscope (hereinafter referred to as "TEM"), and calculating the ratio of the area of ​​the pore portion to the observed area as a percentage.

[0068] The circular cross-section sample for observation is obtained as follows: a hollow fiber membrane embedded with a commercially available frozen tissue section embedding agent is sliced ​​at a thickness of 100 nm using a freezing microtome at low temperature, and vacuum dried at room temperature for 12 hours. When observed with a TEM, information about the thickness direction of the slice being observed is reflected. Therefore, when a slice is cut out to form an observation sample with a microtome, it is important to simply make the thickness consistent and evaluate it. In the present invention, the slice thickness of the microtome is set to 100 nm as a thickness that is easy to reproducibly observe. The cross-section sample for observation is observed with a TEM and an image is obtained, which is binarized using the free software "ImageJ". When binarizing, the condition "Triangle" is selected in the Threshold (binarization threshold). In the resulting binarized image, the area of ​​each pore is obtained by selecting "Area" in "AnalyzeParticles". An area where more than 100 pores can be counted is observed, the total area of ​​the pores is obtained, and the cross-sectional porosity is obtained by dividing it by the area of ​​the observed membrane.

[0069] The surface elastic modulus is generally easily affected by the structure of a depth 5 to 10 times the depth of the pressed-in depth. That is, in the physical washing (air washing) test described later, it was confirmed that the surface elastic modulus at a depth of several hundred nm of rubbing is easily affected by the cross-sectional structure of the outer surface portion, which is the area from the outer surface to a depth of 5 μm from the outer surface. It is preferred that the cross-sectional porosity in the outer surface portion of the hollow fiber membrane is 20% to 50%, which makes it easy to make the density of the outer surface portion higher and to control the surface elastic modulus to an appropriate range. In order to easily increase the surface elastic modulus, the cross-sectional porosity is more preferably 45% or less, further preferably 40% or less, and particularly preferably 36% or less. In addition, in order to reduce the resistance of the permeated liquid, the cross-sectional porosity is more preferably 25% or more, further preferably 30% or more, and particularly preferably 35% or more.

[0070] On the outer surface, the hollow fiber membrane structures between the pores of the hollow fiber membrane are formed as pillars, with an average pillar thickness of 20 nm to 60 nm. This facilitates controlling the surface elastic modulus within an appropriate range, making it preferable. This is also preferable because it facilitates reducing the permeation resistance of the permeated liquid. Here, the pillars constituting the hollow fiber membrane refer to the structural elements of the hollow fiber membrane that exist between the pores of the hollow fiber membrane. When turbid matter, etc., presses against the outer surface, the average pillar thickness is preferably 25 nm or greater, more preferably 30 nm or greater, and particularly preferably 32 nm or greater, so that the pillars can more easily resist the force and exert a restoring force, that is, to increase the surface elastic modulus. Furthermore, to prevent excessive resistance to the permeated liquid due to the pillars, the average pillar thickness is more preferably 55 nm or less, more preferably 50 nm or less, and particularly preferably 45 nm or less. Regarding the thickness of the pillars, in the image obtained by observing the outer surface portion 102 of the circular cross section to a region 5 μm away therefrom using TEM, when depicting the thickness of the pillars relative to the surface 101 ( Figure 3 The line 103) is perpendicular to the line ( Figure 3 、 4 When the line 104 in the figure is used, the length of the overlap between the line 104 and the area between the holes (black part) is calculated as the column thickness. The column thickness 105 of 500 or more columns is used to calculate the average value. Figure 3 The image observed by TEM is shown in Figure 4 The thickness of the column 105 corresponds to the line segment of the resin portion shown in black within the line 104. Figure 4 In (b), there are two columns, and the length of each line segment is equal to the column thickness 105.

[0071] The density of the columns in the outer surface portion is defined as the number of columns per unit length on line 104, and is preferably 10 / μm to 50 / μm, since it is easy to control the surface elastic modulus to an appropriate range. It is speculated that this is because when turbidity or the like is pressed against the outer surface portion, the columns exist at a high density, making it easy to disperse the pressing force caused by the turbidity. In order to fully disperse the compression force caused by the turbidity and to easily increase the surface elastic modulus, the density of the columns is more preferably 15 / μm or more, further preferably 20 / μm or more, and particularly preferably 25 / μm or more. In addition, in order not to excessively impart resistance to the permeating liquid through the columns, the density of the columns is more preferably 45 / μm or less, further preferably 40 / μm or less, and particularly preferably 35 / μm or less. Regarding the density of the columns, in the image obtained by observing the outer surface portion of the circular cross section as a region from the outer surface to 5 μm away from the outer surface using TEM, when depicting the density of the columns relative to the surface ( Figure 3 The line 103) and the vertical line ( Figure 3 、 4 When the line 104 in the figure is obtained, the number of columns on the line 104 is obtained. Then, the number of columns counted is divided by the length of the line to obtain the column density. The column density is calculated as an average value using the number of columns of 500 or more. In the outer surface portion, it is preferable that the distribution of the density of the columns is small because it is easy to increase the surface elastic modulus. If the distribution of the density of the columns in the direction parallel to the surface is small, it is easy to make the coefficient of variation of the surface elastic modulus small, which is preferable. In addition, if the distribution of the density of the columns from the surface to the depth direction is small, it is easy to increase the surface elastic modulus on an average basis, which is preferable.

[0072] In order to obtain safe / reassuring water, it is preferred that the distribution of structure and pore size from the surface to the depth direction is small, which makes it easy to show excellent removability. In addition, as mentioned above, since it is easy to increase the surface elastic modulus, it is suppressed to avoid scratching and it is easy to show high removability for a long time, so it is preferred. In order to reduce the distribution of structure from the surface to the depth direction, it is preferred that there are substantially no macropores in the membrane cross section. The so-called macropores are pores with a major diameter of 5μm or more when the cross section of the hollow fiber membrane is photographed at 3000 times using a scanning electron microscope. In the case where it is difficult to judge the major diameter, the circle (equivalent circle) with an area equal to the area of ​​the hole is obtained by the above-mentioned binarization process, and the equivalent circle diameter is set as the major diameter of the hole. In the cross section of the hollow fiber membrane, 30 different places are observed. When there are no macropores or only macropores with a major diameter of less than 5μm are present, it is determined that there are no macropores with a major diameter of 5μm or more. Even if a macropore with a major diameter of 5μm or more is observed, it is judged that there are macropores with a major diameter of 5μm or more.

[0073] The pure water permeability of the hollow fiber membrane is 0.1 to 0.6 m 3 / m 2 / h / 50kPa, which is a lower range, so that the surface elastic modulus of the outer surface of the hollow fiber membrane can be easily controlled to a higher range. In order to increase the surface elastic modulus, the pure water permeability is preferably 0.6m 3 / m 2 / h / 50kPa or less, more preferably 0.5m 3 / m 2 / h / 50kPa or less, more preferably 0.4m 3 / m 2 / h / 50kPa or less. In addition, in order to prevent turbidity and the like from being strongly pressed against the hollow fiber membrane, the pure water permeability is preferably 0.1m 3 / m 2 / h / 50kPa or more, more preferably 0.2m 3 / m 2 / h / 50kPa or more, more preferably 0.3m3 / m 2 / h / 50kPa or more.

[0074] The hollow fiber membrane can be composed of a single layer or multiple layers. Even if it is composed of a single layer, it is possible to produce a structure with different cross-sectional porosity between the outer surface portion and the inner surface portion by changing the environment of the outer and inner sides during membrane formation. For example, the composition of the injection liquid discharged as the hollow portion of the hollow fiber during membrane formation and the coagulation bath for coagulating the discharged hollow fiber can be changed. In addition, in the case of a composite hollow fiber membrane composed of multiple layers, it is preferable to suppress friction of the outer surface portion by making the cross-sectional porosity of the outer surface portion lower than the cross-sectional porosity of the inner surface portion, thereby reducing the filtration resistance of the hollow fiber membrane.

[0075] The number of surface pores observed on the surface of the hollow fiber membrane was 200 / μm. 2 ~2000 / μm 2 , so that the pollutants in the filtration liquid can be dispersed in the hollow fiber membrane, and it is easy to implement the filtration of highly turbid water stably for a long time, which is preferred. The number of surface pores of the so-called hollow fiber membrane is the number of pores in the surface when the surface of the hollow fiber membrane is observed. Even if the pollutants in the filtration liquid partially block the surface pores as the filtration proceeds, if the number of surface pores is large, it is easy to fully ensure the number of flow paths for the filtration liquid to pass through the hollow fiber membrane, which is preferred. If the number of surface pores is 200 / μm 2 The above-mentioned number of pores on the surface of the hollow fiber membrane is more preferably 290 / μm. 2 ~1500 / μm 2 , particularly preferably 350 / μm 2 ~1000 / μm 2 .

[0076] By setting the number of pores observed in the outer surface of the hollow fiber membrane (hereinafter referred to as surface pores) per unit area [pores / μm 2 ] divided by the average value of the surface pore diameter [nm]: α is 30 / μm 2 / nm~150 / μm 2 / nm, thereby preventing the pollutants in the filtration stock solution and the removal objects from invading the hollow fiber membrane. At the same time, the number of flow paths through which the filtration stock solution passes through the hollow fiber membrane is sufficiently ensured, so it is easy to suppress clogging, which is preferred. As a result, it is easy to perform long-term filtration of high-turbidity stock solutions and easy to obtain permeated water with safe / reliable water quality. A large α means more small pores. Generally, when the pore size is small, in order to fill the pores of the hollow fiber membrane, the proportion of the polymer constituting the hollow fiber membrane tends to increase, and therefore the number of pores tends to decrease. As a result, there is a relationship that if the surface pore size becomes smaller, the surface pore number also becomes smaller, and the surface pore size and the surface pore number have a trade-off relationship.

[0077] The hollow fiber membrane of the present invention has small pores, thereby preventing coarse pollutants and removal objects in the filtration stock solution from invading the hollow fiber membrane. At the same time, the pores are large, thereby fully ensuring the number of flow paths for the filtration stock solution to pass through the hollow fiber membrane. In addition, the pollutants can be dispersed, thus easily suppressing clogging. Furthermore, the surface pores are small, thereby easily improving the surface elastic modulus, and the surface pores are large, thereby easily reducing the pressure of turbidity in contact with the membrane surface. That is, it is preferable to have both the small surface pore size and the large number of surface pores from the perspective of pollution resistance and scratch resistance. Since the number of surface pores and the surface pore size both satisfy a good positive correlation and contribute to pollution resistance, it is preferable to use the α value that takes both into account as an indicator of pollution resistance. In addition, since the number of surface pores has a negative correlation with the surface pore size, it is preferable to use the α value obtained by dividing by the surface pore size as an indicator compared to using only the number of surface pores as an indicator. Such a porous membrane with a large number of surface pores and a small surface pore size is not available in the prior art.

[0078] As described later, the porous membrane of the present invention suppresses excessive phase separation and coarsening by reducing the self-diffusion coefficient of the polymer during the formation process of the porous membrane, i.e., making it difficult for the polymer to move. Furthermore, the membrane solidifies in a state where the pores are fine and numerous, thereby easily breaking the trade-off between pore size and pore number. By setting α to 30 to 150 pores / μm, which is higher than the normal trade-off, the membrane is formed. 2 / nm, thereby showing excellent anti-fouling properties, and therefore is preferred, and more preferably 30 to 100 pieces / μm 2 / nm, more preferably 32 to 80 / μm 2 / nm, particularly preferably 50 to 70 / μm 2 / nm.

[0079] Hollow fiber membrane materials

[0080] In order to efficiently remove turbid matter and the like from the hollow fiber membrane module through physical washing, the hollow fiber membrane is preferably made of a flexible material, preferably containing a polymer as its main component. The type of polymer is not particularly limited, but specific examples include polysulfone resins, polyethersulfone resins, polyvinylidene fluoride resins, nylon, cellulose esters such as cellulose acetate and cellulose acetate propionate, fatty acid vinyl esters, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, polymers of acrylic acid esters or methacrylic acid esters such as ethylene oxide, propylene oxide, and polymethyl methacrylate, and copolymers thereof.

[0081] In particular, in order to use the hollow fiber membrane for long-term filtration, it is preferred that the accumulated pollutants be regularly washed with chemical reagents, and it is particularly preferred to include a polyvinylidene fluoride resin with excellent chemical resistance. The so-called polyvinylidene fluoride resin refers to a homopolymer of 1,1-difluoride or a copolymer of 1,1-difluoride. The so-called copolymer of 1,1-difluoride here refers to a polymer having a 1,1-difluoride residue structure. The polymer having a 1,1-difluoride residue structure is typically a copolymer of a 1,1-difluoride monomer and a fluorine-based monomer other than it. As such a fluorine-based monomer, for example, vinyl fluoride, tetrafluoroethylene, hexafluoropropylene or chlorotrifluoroethylene can be mentioned. In the above-mentioned copolymer of 1,1-difluoride, ethylene other than the above-mentioned fluorine-based monomer can be copolymerized to the extent that the effect of the present invention is not impaired.

[0082] When the weight of the hollow fiber membrane is taken as 100%, the polyvinylidene fluoride resin preferably comprises 50% by weight or more, and particularly preferably 60% by weight or more. A polymer weight-average molecular weight of 500,000 to 1,000,000 Da is preferred because it facilitates controlling the surface elastic modulus within a suitable range.

[0083] The thickness of the hollow fiber membrane is preferably 150 μm or more, which makes it easy to increase the surface elastic modulus and to reduce the deviation of the surface elastic modulus. The thickness of the hollow fiber membrane is more preferably 170 μm or more, and more preferably 200 μm or more. The thickness of the hollow fiber membrane is preferably 350 μm or less, which makes it easy to increase the surface area of ​​the outer surface of the hollow fiber membrane in the cylindrical component, that is, it is easy to reduce the amount of filtered raw liquid per unit membrane area. By reducing the amount of filtered raw liquid per unit membrane area, it is easy to suppress friction. The thickness of the hollow fiber membrane is more preferably 300 μm or less, and more preferably 250 μm or less. The thickness of the hollow fiber membrane is equivalent to half of the value obtained by subtracting the inner diameter from the outer diameter of the hollow fiber membrane.

[0084] <Method for producing hollow fiber membrane>

[0085] The hollow fiber membrane used in the hollow fiber membrane module of the present invention preferably comprises the following steps (A) and (B), wherein the step (A) is a step of dissolving a polymer in a solvent to obtain a polymer solution, and then the step (B) is a step of forming an outer surface portion of the hollow fiber membrane by solidifying the polymer solution in a non-solvent, wherein the self-diffusion coefficient [m] calculated by all-atom molecular dynamics calculation of the dissolved polymer in the polymer solution obtained in the step (A) is 2 / sec] is 0.8×10 -11 m 2 / sec~1.6×10 -11 m 2 / sec, the non-solvent used in step (B) contains 90 to 100 wt % of water, and the temperature of the non-solvent is 6°C to 45°C.

[0086] The type of polymer used in step (A) is not particularly limited. As a specific example, the resins listed in the above-mentioned <Raw materials for hollow fiber membranes> are preferably used. The weight average molecular weight of the polymer is preferably 5 to 1,000,000 Da, which makes it easy to control the self-diffusion coefficient described later to a slower and suitable range. In addition, multiple polymers can be used in combination. The solvent preferably contains a good solvent. The so-called "good solvent" here refers to a solvent that can dissolve more than 5% by weight of the polymer even in a low temperature range of less than 60°C. As good solvents, for example, N-methyl-2-pyrrolidone (hereinafter, "NMP"), 2-pyrrolidone (hereinafter, "2P"), ε-caprolactam (hereinafter, "ε-CL"), dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea or trimethyl phosphate or a mixed solvent thereof. The good solvent is further preferably contained in the solvent in an amount of 40% by weight or more, and particularly preferably contains 60% by weight or more. By including a large amount of a good solvent, the polymer chains in the polymer solution are extended, and it is preferable to easily control the self-diffusion coefficient described later to a slow and appropriate range.

[0087] Here, the so-called "non-solvent" of step (B) refers to a solvent that does not dissolve and swell the polymer even if the non-solvent is heated to a high temperature until the boiling point. As a non-solvent, for example, aliphatic hydrocarbons such as water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, pentanediol, hexylene glycol or low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyols, aromatic polyols, chlorinated hydrocarbons or other chlorinated organic liquids or their mixed solvents can be cited. In order to control the self-diffusion coefficient to a suitable range, the concentration (weight %) of the polymer in the polymer solution is preferably above the entanglement concentration, more specifically, preferably 10 to 40 weight %, more preferably 12 to 30 weight %, and particularly preferably 15 to 25 weight %. It was found that a concentration of 10 weight % or more of the polymer can make the self-diffusion coefficient slower, and can solidify in a state where the pores on the outer surface of the hollow fiber membrane are fine and present in large quantities. The polymer concentration is more preferably 12% by weight or greater, and particularly preferably 15% by weight or greater. Furthermore, by setting the polymer concentration to 40% by weight or less, the proportion of polymers in the outer surface can be reduced, thereby ensuring a sufficient number of pores. The polymer concentration is more preferably 30% by weight or less, and particularly preferably 25% by weight or less.

[0088] The step (B) of forming the outer surface portion of the porous membrane by solidifying the polymer solution in a nonsolvent is a step of forming a porous membrane using so-called nonsolvent-induced phase separation. When the polymer solution contacts the nonsolvent, the polymer becomes insoluble in the solvent, and phase separation occurs into a phase containing a large amount of the polymer and a phase containing a large amount of the solvent. Each phase coarsens while coalescing with surrounding similar phases.

[0089] Figure 5 The process of forming the porous membrane in step (B) is shown schematically. Figure 5 Phase separation proceeds in the polymer solution in the order of (a) to (f), and locations with high polymer concentrations (phase 301 containing a large amount of polymer) coarsen. During this phase separation and / or coarsening process, the solvent and nonsolvent exchange occurs. When the nonsolvent concentration rises above a certain level, the polymer solidifies, and the structure of the porous membrane is fixed. At this point, phase 302 containing a large amount of solvent becomes the pores of the porous membrane.

[0090] In the production of the hollow fiber membrane used in the hollow fiber membrane module of the present invention, the self-diffusion coefficient of the polymer is set to a relatively low range of 0.8×10 -11 m 2 / sec~1.6×10 -11 m 2 / sec, thereby suppressing excessive phase separation and coarsening, the phase 301 containing a large amount of polymer and the phase 302 containing a large amount of solvent are easily solidified in a fine and large amount state, and a large number of fine pores can be formed. -11 m 2 / sec or more, thus having a sufficient diffusion coefficient for phase separation between the polymer and the solvent, and pores are easily formed. The less phase separation is possible and the slower the diffusion of the polymer, the more difficult it is to form pores. -11 m 2 / sec or less, thereby suppressing excessive phase separation and coarsening, inhibiting the coalescence of pores, and facilitating the formation of a large number of micropores. In other words, by appropriately controlling the self-diffusion coefficient of the polymer within a low range, a porous membrane with a large number of micropores can be formed. The self-diffusion coefficient is more preferably 0.8×10 -11 m 2 / sec~1.4×10 -11 m 2 / sec, more preferably 0.8×10 -11 m 2 / sec~1.1×10 -11 m 2 / sec.

[0091] The self-diffusion coefficient can be determined by all-atom molecular dynamics calculations. All-atom molecular dynamics calculations are a method of solving the motion equations of a molecular group system for all constituent atoms one by one, thereby obtaining the trajectory of each atom. First, a polymer solution system is prepared in a manner that achieves the actual polymer concentration (weight %). At this time, a model polymer chain is modeled in a manner that has a molecular weight of 800 to 6000 and is 1 / 200 to 1 / 5 of the weight average molecular weight of the polymer actually used. Among the potential parameters used in molecular dynamics calculations, known parameters such as DREIDING [SL Mayo, BD Olafson, WA Goddard III, J. Phys. Chem. 94, 8897 (1990)], GAFF [J. Wang, RM Wolf, JW Caldwell, PA Kollman, DACase, J. Comput. Chem. 25, 1157 (2004)], OPLS-AA [WL Jorgensen, DS Maxwell, Julian Tirado-Rives, J. Am. Chem. Soc. 118, 11225 (1996)], and CHARMM [BR Brooks, RE Bruccoleri, BD Olafson, DJ States, S. Swaminathan, M. Karplus, J. Comput. Chem. 4, 187 (1983)] can be used, but it is preferred to use parameters that reproduce the density and cohesive energy, which are physical quantities representing the aggregation state of a solution system.

[0092] The inventors studied the reproducibility of the aggregation state and found that GAFF or OPLS-AA is particularly preferred. In addition, the temperature was controlled to 25°C by the Nose-Hoover method [Hoover, WG Phys. Rev. A, 31, 1695 (1985).] and the pressure was controlled to 1 bar by the Andersen method [HC Andersen, J. Chem. Phys. 72, 2384 (1980)], thereby forming a pressure / temperature constant ensemble. At this time, the close-range Lennard-Johns interaction was operated by applying a switching function from 1.0 nm and cutting off at 1.2 nm, and the long-range electrostatic interaction was calculated by the Particle Mesh Ewald method. In the pressure / temperature constant ensemble, after performing molecular dynamics calculations until the density becomes constant, the unit cell length is adjusted in a manner to achieve an average density, and an additional calculation of 11 ns is performed in the temperature constant ensemble. The mean square displacement (MSD) of each polymer atom was determined using a 10 ns trajectory, and the polymer self-diffusion coefficient was calculated using the following formula (1). Regarding the range of MSD and t used in the calculation of D, the value obtained by dividing log(MSD) by log(t) was confirmed to be within the range of 0.9 to 1.1. When a polymer solution is prepared by mixing multiple polymers, the self-diffusion coefficient of each polymer was weighted averaged based on the weight percentage of the polymer, which was used as the self-diffusion coefficient of the polymer in the polymer solution.

[0093] D=MSD / 6t·····Formula (1) D: self-diffusion coefficient t: time

[0094] In the manufacture of the hollow fiber membrane used in the hollow fiber membrane assembly of the present invention, the non-solvent used for coagulation contains 90 to 100% by weight of water, so that coagulation is fast, and the self-diffusion coefficient in the polymer solution tends to affect the speed of phase separation and coarsening. That is, it is easy to obtain the effect of controlling the self-diffusion coefficient in the polymer solution to a lower range. In addition, the temperature of the non-solvent is 6°C to 45°C, so that coagulation is fast, and the self-diffusion coefficient in the polymer solution tends to affect the speed of phase separation and coarsening. The temperature of the non-solvent is more preferably 10°C to 35°C, and more preferably 15°C to 30°C.

[0095] Regarding the manufacture of the hollow fiber membrane used in the hollow fiber membrane assembly of the present invention, in the above-mentioned step (A), the above-mentioned solvent contains a hydrogen bonding solvent with a molecular weight of 500Da or less having hydrogen bond donor properties and hydrogen bond acceptor properties, which is easy to control the self-diffusion coefficient of the polymer to an appropriate range, which is preferred. The so-called hydrogen bond donor property refers to a positively polarized hydrogen atom, specifically, a hydroxyl group (OH group), a carboxyl group (COOH group), an amino group (NH group), etc. The so-called hydrogen bond acceptor property refers to a lone electron pair, specifically, a carbonyl group, an alkoxy group, a cyano group, etc. The solvent is a hydrogen bond donor and a hydrogen bond acceptor, so that the interaction caused by the hydrogen bond between the solvent and the solvent is strong, which suppresses the movement of the solvated polymer and makes it easy to control the self-diffusion coefficient of the polymer to a slower and suitable range. The hydrogen bond donor and hydrogen bond acceptor solvents are not particularly limited, and specific examples include 2P, ε-CL, 1,3-dimethylurea, N-methylacetamide, hydantoin, 2-imidazolidinone, and DL-pyroglutamic acid.

[0096] In the above-mentioned step (A), it is preferred that the dissolved polymer contains a polymer having hydrogen bond donor properties and / or hydrogen bond acceptor properties, thereby making it easy to control the self-diffusion coefficient of the polymer to an appropriate range. The reason is that the polymer has hydrogen bond donor properties and / or hydrogen bond acceptor properties, thereby interacting with the solvent having hydrogen bond donor properties and hydrogen bond acceptor properties through hydrogen bonds, making it easy to control the self-diffusion coefficient of the polymer to a slower and suitable range. It is more preferred that the polymer having hydrogen bond donor properties and / or hydrogen bond acceptor properties is contained in the porous membrane in an amount of 10% to 50% by weight from the viewpoint of controlling the self-diffusion coefficient of the polymer to an appropriate range.

[0097] <Filtration Operation Method>

[0098] The hollow fiber membrane module of the present invention is preferably used in a filtration operation method in which a liquid with a turbidity of 3 to 50 NTU is supplied to the hollow fiber membrane module. This is because even highly turbid liquids that are prone to smearing can be treated stably and efficiently using the hollow fiber membrane module, which is less susceptible to smearing. When treating highly turbid liquids using a membrane module, pretreatment is often performed upstream of the membrane module to reduce turbidity. By supplying a liquid with a relatively high turbidity of 3 to 50 NTU as the filtration stock solution to the membrane module, the pretreatment load can be reduced, thereby improving the efficiency of the liquid treatment process. Pretreatment herein refers to processes such as coagulation and sedimentation, pressurized flotation, and centrifugal separation. To improve the overall efficiency of the liquid treatment process, the turbidity of the liquid supplied to the hollow fiber membrane module is more preferably 5 or higher, more preferably 10 or higher, and particularly preferably 20 or higher. Furthermore, to avoid excessively increasing the flow resistance of the liquid within the hollow fiber membrane module, the turbidity of the liquid supplied to the hollow fiber membrane module is more preferably 45 or lower, more preferably 40 or lower, and particularly preferably 30 or lower. The turbidity of the filtered raw liquid supplied to the hollow fiber membrane module can be controlled by the amount of pretreatment work, the amount of coagulant added, and the like.

[0099] The removal rate can be easily improved by adding an adsorbent such as activated carbon to the filtered stock solution supplied to the hollow fiber membrane module. On the other hand, activated carbon has a higher hardness than common turbid materials such as kaolin, and is prone to causing scratching of the hollow fiber membrane. Therefore, it was previously necessary to adjust the addition amount within a range where scratching does not occur. It is preferred to filter the filtered stock solution by supplying activated carbon to a hollow fiber membrane module using a hollow fiber membrane having a high surface elastic modulus of the present application, thereby easily and stably achieving a high removal rate.

[0100] The filtration operation method of the present invention is to supply a liquid with a TOC of 4 to 30 mg / L to the hollow fiber membrane module, so that a high turbidity liquid that is prone to scratching can be easily treated stably and efficiently by passing it through the hollow fiber membrane module that is not prone to scratching. When a high turbidity liquid is treated with a membrane module, pretreatment is often performed in the upstream section of the membrane module to reduce the TOC. By supplying a liquid with a high TOC of 4 to 30 mg / L as the filtration raw liquid to the membrane module, the load of the pretreatment is easily reduced and the efficiency of the liquid treatment process is easily improved. In order to improve the overall efficiency of the liquid treatment process, the TOC of the liquid supplied to the hollow fiber membrane module is more preferably 6 or more, more preferably 8 or more, and particularly preferably 10 or more. In addition, in order not to excessively increase the flow resistance of the liquid in the hollow fiber membrane module, the TOC of the liquid supplied to the hollow fiber membrane module is more preferably 25 or less, more preferably 20 or less, and particularly preferably 15 or less. The TOC of the filtered raw liquid supplied to the hollow fiber membrane module can be controlled by the amount of pretreatment work, the amount of coagulant added, and the like.

[0101] The filtered stock liquid supplied to the hollow fiber membrane module is concentrated in the hollow fiber membrane module as the filtration proceeds. When the turbidity in the hollow fiber membrane module becomes high to a certain extent, the turbidity in the hollow fiber membrane module is discharged during physical washing, and the filtered stock liquid is supplied to the hollow fiber membrane module again. Repeating such filtration and physical washing operations is preferred because the filtration continues for a long time. In order to improve the efficiency of the liquid treatment process, it is preferably controlled so that the maximum turbidity in the hollow fiber membrane module is 10 to 100 NTU. By controlling the maximum turbidity to be 10 NTU or more, the filtration duration until the physical washing can be prolonged, which makes it easier to improve the efficiency of the filtration. The maximum turbidity is preferably 10 or more, more preferably 15 or more, and particularly preferably 20 or more. In addition, from the perspective of suppressing scratching and clogging of the hollow fiber membrane module, the maximum turbidity is preferably 90 or less, more preferably 80 or less, and particularly preferably 70 or less. The maximum turbidity can be controlled by the frequency of physical washing.

[0102] When the TOC in the hollow fiber membrane module increases to a certain extent as the filtration proceeds, the TOC in the hollow fiber membrane module is discharged during physical washing, and the filtered stock solution is supplied to the hollow fiber membrane module again. Such repeated filtration and physical washing operations are preferred because the filtration continues for a long time. In order to improve the efficiency of the liquid treatment process, it is preferably controlled in such a way that the maximum TOC in the hollow fiber membrane module becomes 15 to 50 mg / L. By controlling in such a way that the maximum TOC becomes 15 mg / L or more, the filtration duration until the physical washing can be prolonged, and the efficiency of the filtration can be easily improved. The maximum TOC is preferably 15 or more, more preferably 20 or more, and particularly preferably 25 or more. In addition, from the viewpoint of suppressing the rubbing and clogging of the hollow fiber membrane module, the maximum TOC is preferably 50 or less, more preferably 45 or less, and particularly preferably 40 or less. The maximum TOC can be controlled by the frequency of physical washing.

[0103] In order to avoid excessive turbidity and TOC in the hollow fiber membrane module, it is preferred to stop filtering regularly and perform physical washing. It is particularly preferred to have the following steps: (1) a membrane separation step of supplying a raw liquid to the hollow fiber membrane module to separate suspended matter from the liquid; and (2) a washing step of stopping the membrane separation step and washing the suspended matter accumulated on the outer surface of the hollow fiber membrane and between the hollow fiber membranes. Regarding the washing method, it is preferred to perform the following air washing operation to effectively wash the inside of the hollow fiber membrane module. The above-mentioned air washing operation is to make the raw liquid or a mixed flow of liquid and gas with a turbidity or TOC at least lower than that of the raw liquid flow toward the outer surface side of the hollow fiber membrane at a membrane surface linear velocity of 0.3 m / s or more and 5.0 m / s or less. Here, the linear velocity is the value obtained by dividing the flow rate in the direction perpendicular to the filtration direction of the filtered raw liquid (i.e., the direction from the outer surface to the inner surface of the hollow fiber membrane) by the cross-sectional area of ​​the flow path of the fluid. Furthermore, regarding the washing method, it is preferable to perform backwashing operation of passing liquid from the inner surface side of the hollow fiber membrane to the outer surface side of the hollow fiber membrane simultaneously with air washing operation in order to further improve the washing efficiency.

[0104] By using the hollow fiber membrane module of the present invention, membrane rubbing can be suppressed, enabling filtration operations to achieve a virus removal rate of 4 log (99.99%) or higher, thereby facilitating the production of safe and secure permeate. To improve the virus removal rate, for example, it is preferable to increase the turbidity of the liquid in the hollow fiber membrane module to a high value of 3-50 NTU, thereby facilitating virus adsorption to the turbidity and improving the removal rate. Specifically, the hollow fiber membrane module of the present invention filters a raw material to be filtered with a turbidity of 3-50 NTU, and the permeate separated from the raw material to be filtered achieves a virus removal rate of 4 log or higher, achieving a high removal rate even with high turbidity. Furthermore, it is preferable to increase the TOC of the liquid in the hollow fiber membrane module to a high value of 4-30 mg / L, thereby facilitating virus adsorption to organic matter and improving the removal rate. Setting the maximum turbidity within the hollow fiber membrane module to 10-100 NTU also facilitates virus adsorption to the turbidity and improves the removal rate. It is preferable to adjust the maximum TOC in the hollow fiber membrane module to 15 to 50 mg / L, because viruses are adsorbed on organic matter and the removal rate is easily improved.

[0105] Unlike conventional hollow fiber membrane modules, the use of hollow fiber membranes with a high surface elastic modulus makes it easy to operate for a long time in the range of turbidity and high TOC, the virus removal rate is easy to improve, and the safety of the permeate water quality is easy to improve. In addition, by increasing the amount of coagulant added in the pre-treatment of the liquid treatment process including pre-treatment steps such as coagulation and precipitation in the front section of the membrane module, it is also easy to improve the virus removal rate. In addition, as a means of improving the virus removal rate in the membrane module without adding a coagulant, it is also possible to increase the filtration specific resistance of the microfiltration membrane or ultrafiltration membrane. This is a method of improving the virus removal rate by deliberately clogging the microfiltration membrane or ultrafiltration membrane. The filtration specific resistance is expressed by formula (2).

[0106] R m =(TMP-TMP0) / (μ×J) ······Equation (2)

[0107] Here, R m: filtration specific resistance [1 / m], TMP: transmembrane pressure difference during operation [Pa], TMPO: initial transmembrane pressure difference [Pa], μ: water viscosity coefficient [Pa·s], J: membrane filtration flux [m / s]. Methods for increasing the filtration specific resistance by clogging the microfiltration membrane or ultrafiltration membrane include increasing the membrane filtration flux, extending the filtration time (reducing the frequency of physical washing), reducing the flow rate and time of each physical washing, reducing the frequency of chemical solution countercurrent washing, and reducing the flow rate and time of each chemical solution countercurrent washing. By using such methods to improve the virus removal rate, the addition of a coagulant is no longer necessary, thus easily reducing the cost of chemical agents. The virus removal rate is preferably 4 log or higher, more preferably 5 log or higher, and particularly preferably 6 log or higher.

[0108] The use of the hollow fiber membrane module of the present invention can suppress membrane rubbing. By controlling the SDI (Silt Density Index) of the permeate of the hollow fiber membrane module to 3 or less, it is preferable to easily obtain a permeate of safe and secure water quality. Specifically, the hollow fiber membrane module of the present invention is preferably capable of filtering a raw liquid to be filtered with a turbidity of 3 to 50 NTU, and the separated permeate has an SDI of 3 or less. This allows for a high SDI reduction rate even for liquids with high turbidity, and is therefore preferable. To reduce the SDI of the permeate, for example, it is preferable to increase the turbidity of the liquid within the hollow fiber membrane module to 3 to 50 NTU. This allows silt to be adsorbed onto the turbidity, thereby increasing the removal rate and, in other words, reducing the SDI of the permeate. Furthermore, it is preferable to increase the TOC of the liquid within the hollow fiber membrane module to 15 to 50 mg / L. This allows silt to be adsorbed onto organic matter, thereby increasing the removal rate and, in other words, reducing the SDI of the permeate. A maximum turbidity within the hollow fiber membrane module of 10-100 NTU is preferred, as it allows sediment to be adsorbed on the turbidity, facilitating increased removal rates and, in other words, reducing the SDI of the permeate. A maximum TOC within the hollow fiber membrane module of 15-50 mg / L is also preferred, as it allows sediment to be adsorbed on organic matter, facilitating increased removal rates and, in other words, reducing the SDI of the permeate. Unlike conventional hollow fiber membrane modules, the use of hollow fiber membranes with a high surface elastic modulus facilitates long-term operation in high turbidity and TOC ranges, facilitating increased sediment removal rates and improving permeate quality.

[0109] Furthermore, in liquid treatment processes involving pretreatment steps such as coagulation and precipitation in the front end of a membrane assembly, the SDI of the membrane assembly permeate can be easily reduced even by increasing the amount of coagulant added during the pretreatment. Alternatively, as a means of reducing the SDI in a membrane assembly without adding a coagulant, increasing the specific resistance of the microfiltration or ultrafiltration membrane can be used. This is a method of intentionally clogging the microfiltration or ultrafiltration membrane to increase the sediment removal rate. Examples of methods for increasing the specific resistance by clogging the microfiltration or ultrafiltration membrane include increasing membrane filtration flux, extending the filtration time (reducing the frequency of physical washing), reducing the flow rate and time of each physical washing, reducing the frequency of chemical solution countercurrent washing, and reducing the flow rate and time of each chemical solution countercurrent washing. Reducing the SDI of the permeate through such methods eliminates the need for the addition of a coagulant, thereby easily reducing chemical costs. The SDI of the permeate is preferably 3 or less, more preferably 2 or less, and particularly preferably 1 or less.

[0110] SDI can be measured using the method described in ASTM D4189-95 (2002): Standard Test Method for Silt Density Index (SDI) of Water. The SDI value, also known as the FI value, indicates the concentration of fine turbidity in the water. It is calculated by filtering the water through a 0.45 μm filter at 0.2 MPa, calculating the time required to obtain 500 ml of filtered water after the start of filtration (T0), and the time required to obtain 500 ml of filtered water after 15 minutes of continued filtration under the same conditions (T15). The value is expressed as (1-T0 / T15) x 100 / 15. The SDI value is 0 for a completely turbid water-free state, and 6.67 for the most heavily contaminated water.

[0111] <Filtration device>

[0112] A filtration device that can perform filtration operations using the hollow fiber membrane module is preferred. Specifically, assuming that turbidity and TOC are within the above-mentioned appropriate ranges, other options include selecting a pump to increase the filtration resistance, selecting piping specifications, and selecting a membrane module pretreatment step.

[0113] Example

[0114] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto. First, the measurement method and the evaluation method are shown below.

[0115] (i) Determination of surface elastic modulus

[0116] A diamond-made Berkovich indenter was installed on Nano Indenter SA2 manufactured by KLM, and a test of applying and removing a compressive load was carried out in an atmosphere at room temperature according to the method of ISO14577. The dried hollow fiber membrane was cut into pieces of about 1 cm in length and fixed to a 1 cm square metal plate with double-sided tape for measurement. The maximum load was set to 0.1 mN, the application time was set to 15 seconds, and the maximum load holding time was set to 30 seconds. The measurement was carried out in the atmosphere at room temperature. When the hollow fiber membrane with polyvinylidene fluoride resin as the main component was measured, the Poisson's ratio was set to 0.35 and the surface elastic modulus was calculated. The surface elastic modulus was calculated in the range of 0.4 μm to 0.8 μm of the indentation depth by pressing in other positions with N=5. The same measurement was carried out using three different hollow fiber membranes, and the average value of all the measured values ​​was set as the measurement result of the surface elastic modulus.

[0117] (ii) Cross-sectional structure of the surface (cross-sectional porosity, average value of column thickness, density)

[0118] The hollow fiber membrane embedded with a commercially available embedding agent for frozen tissue sectioning (manufactured by Tissue Tech; OCT complex) was sliced ​​with a thickness of 100 nm at -40°C in a direction perpendicular to the surface using a cryo-ultramicrotome (manufactured by Leica; FC7), and vacuum dried at room temperature for 12 hours. The cross section of the outermost surface of the hollow fiber membrane was observed using a TEM (manufactured by JEOL Ltd.; JEM-1400Plus), and an image was obtained, which was binarized using the free software "ImageJ". When binarizing, the condition "Triangle" was selected in Threshold (binarization threshold). In the resulting binarized image, Area was selected in Analyze Particles to determine the area of ​​each cross-sectional pore. The area where more than 100 pores could be counted was observed, the total area of ​​the pores was determined, and the cross-sectional porosity was determined by dividing it by the area of ​​the observed membrane.

[0119] The column thickness was determined by drawing a line perpendicular to the surface in a TEM image of the circular cross section and calculating the length of the overlap between the line and the region between the pores. The column thicknesses of at least 100 columns were averaged. The column density was calculated by drawing a line perpendicular to the surface in a TEM image of the circular cross section and dividing the number of overlaps between the line and the region between the pores by the length of the line.

[0120] (iii) Surface structure (pore diameter, number of pores)

[0121] After the hollow fiber membrane was vacuum-dried at 25°C for 12 hours, it was observed using a SEM (manufactured by Hitachi High-Technologies Co., Ltd.; S-5500) at a magnification of 30,000 to 100,000 times. The image obtained by observing the surface of the hollow fiber membrane by SEM was binarized using the free software "ImageJ". When binarizing, after setting 1 pixel in Subtract Background and Creating Background (creating background), the condition: RenyiEntropy was selected in Threshold (binarization threshold). In the resulting binary image, by selecting Area in AnalyzeParticles, the number of surface pores and the area of ​​each surface pore were calculated, each surface pore was assumed to be a circle, and the calculated diameter was set to the surface pore diameter. When calculating the average value of the surface pore diameter, the surface pore diameters of more than a thousand pores were averaged and calculated.

[0122] (iv) Turbidity

[0123] The turbidity of the filtered raw liquid was measured using a portable turbidimeter 2100Q manufactured by HACH Co., Ltd. with N=5 values, and the average value was used.

[0124] (v)TOC

[0125] The TOC of the filtered raw liquid was measured using TOC-V CSH / ASI-V / TNM-1 manufactured by Shimadzu Corporation.

[0126] (vi) Wear test

[0127] The dried hollow fiber membrane was cut into pieces of about 1 cm in length and fixed to a 1 cm square metal plate with double-sided tape. During the measurement, a Berkovich indenter TI950 manufactured by Hysitron was installed and the measurement was carried out in an atmosphere at room temperature. Figure 2 A 5μm square area was scanned at a scanning speed of 20μm / s under a specified contact load to cause wear. A 20μm square area, encompassing both the unworn and worn areas, was then scanned at a scanning speed of 40μm / s under a contact load of 2μN to obtain a surface roughness profile. The difference between the lowest height of the unworn area and the lowest height of the worn area was taken as the maximum wear depth. A low maximum wear depth relative to the contact load during wear indicates that scuffing is suppressed.

[0128] (vii) Physical washing (air washing) test

[0129] 10,000 hollow fiber membranes with an outer diameter of 1.4 mm were loaded into a cylindrical shell with an inner diameter of 200 mm, and both ends were potted with epoxy resin to produce a hollow fiber membrane module with a filling rate of 49%. In addition, the hollow fiber membranes were filled into the shell in such a way that the distance Y between the potting at both ends and the average length X of the hollow fiber membrane were (XY) / X×100=10. The hollow fiber membrane module was filled with a 4000 mg / L suspension of Osaka Gas Chemicals' activated carbon for water treatment, trade name "White Eagle C". The hollow fiber membrane module was arranged in a vertical direction of the length of the cylindrical shell. With the side nozzle on the side of the cylindrical shell near the upper end open, air was introduced from the bottom of the hollow fiber membrane module at 100 NL / min to perform air washing. After 24 hours, the hollow fiber membrane was cut out and the removal rate of the weight-average molecular weight of 40,000 Da was evaluated. Using hard, turbid activated carbon as a model, the accelerated evaluation of the rubbing caused by air washing was performed. The performance fluctuation was small, and it was determined that the rubbing could be suppressed.

[0130] (viii) Removal efficiency of 40,000 Da dextran

[0131] Dextran (manufactured by Aldrich; weight average molecular weight 40,000 Da) was mixed with 1000 ppm of distilled water to prepare a dextran aqueous solution. The prepared dextran aqueous solution was supplied to the outside of the hollow fiber membrane at 25°C so that the transmembrane pressure difference became 10 kPa, and cross-flow filtration was performed at a cross-flow velocity of 1.0 m / sec. 1.3 g / m2 of dextran was added to the membrane area. 2 After the permeate was discarded, a sample of 2.0 g / m 2 The dextran aqueous solution (stock solution) supplied to the hollow fiber membrane was sampled at the time of sampling the permeate. The refractive indices of the permeate and stock solution were measured, and the removal rate: T (%) was calculated based on formula (3).

[0132] T = {(refractive index of original solution) - (refractive index of transmitted solution)} / (refractive index of original solution) × 100 ······Formula (3)

[0133] (ix) Pure water permeability of hollow fiber membranes

[0134] A small module with an effective length of 200 mm was produced, consisting of four hollow fiber membranes. Distilled water was fed to the outside of the hollow fiber membranes at a temperature of 25°C and a filtration differential pressure of 10 kPa for 1 hour, and the permeate volume (m 3 ), converted to per unit time (h) and per unit membrane area (m 2 ) is calculated by further converting the value into pressure (50 kPa).

[0135] (x) Virus removal rate

[0136] Bacteriophage MS-2ATCC 15597-B1 (MS-2 bacteriophage, particle size of about 25 nm) as the test virus was added to the filtered stock solution to prepare a 1.0×10 7 The test stock solution contained MS-2 bacteriophage at a concentration of PFU / mL. The filtered stock solution used was a liquid (TOC: 20 mg / L, turbidity: 17 NTU) to which Osaka Gas Chemicals' activated carbon for water treatment, "White Eagle C", was added to the wastewater of a chemical plant in such a manner that the concentration became 5 mg / L. The test stock solution was filtered through the hollow fiber membrane module used in (xi) at a temperature of 25°C and a filtration differential pressure of 100 kPa, and 200 mL / m2 of the sample was sampled per unit membrane area. 2 The permeate after filtration. Based on the overlay agar assay, Standard Method 9211-D (APHA, 1998, Standard methods for the examination of water and wastewater, 18th ed.), 1 mL of the diluted stock solution and 1 mL of the permeate were inoculated into test culture dishes and plaques were counted to determine the MS-2 phage concentrations before and after the filtration test. Using these concentrations, the virus removal rate (log) was calculated according to the following formula (4): TV. A safe and satisfactory removal rate of 3.0 or higher was considered acceptable.

[0137] Virus removal rate (log) = -log 10 {(MS-2 phage concentration in the filtrate) / (MS-2 phage concentration in the original solution)·······Formula (4)

[0138] (xi) Filtration test

[0139] 10,000 hollow fiber membranes with an outer diameter of 1.4 mm were loaded into a cylindrical shell with an inner diameter of 200 mm, and both ends were potted with epoxy resin to produce a hollow fiber membrane module with a filling rate of 49%. In addition, the hollow fiber membranes were filled in the shell in such a way that the distance Y between the potting at both ends and the average length X of the hollow fiber membrane became (XY) / X×100=10. The following test was carried out using the obtained hollow fiber membrane module. Lake water (fresh water from Lake Biwa, Japan) (TOC; 5 mg / L, turbidity; 5 NTU) or chemical plant wastewater with 5 mg / L of Osaka Gas Chemicals' activated carbon "White Eagle C" for water treatment added (TOC; 20 mg / L, turbidity; 17 NTU) was used as the filtered stock solution and supplied to the hollow fiber membrane module at 25°C. The entire amount was filtered by supplying it in such a way that the differential pressure between the membranes became 100 kPa, and the permeate volume was measured. The permeate volume becomes 28 L / m per unit membrane area. 2 Back filtration was performed at a pressure difference of 150 kPa between membranes until the back filtration permeation rate reached 3 L / m 2 At the same time as the reverse filtration, an air washing operation is performed to allow the mixed flow of the filtered raw liquid and air to flow to the outside of the hollow fiber membrane at a membrane surface linear velocity of 0.3m / s, thereby discharging the filtered raw liquid in the hollow fiber membrane module. Filtration, reverse filtration and air washing are repeated, and the filtration flux (F1) and the amount of permeate per unit membrane area immediately after the filtration begins become 600L / m 2 From the filtration flux (F2) immediately after the start of filtration, the filtration flux ratio (F2 / F1) was calculated and defined as the initial filtration flux ratio. The closer the initial filtration flux ratio is to 1, the more the initial properties are maintained, and the hollow fiber membrane is less likely to clog even after long-term use. A value of 0.50 or higher is sufficient to maintain good filtration.

[0140] (Example 1)

[0141] The hollow fiber membrane used was a composite hollow fiber membrane comprising a support membrane obtained by the following method. 38% by mass of PVDF (manufactured by Kureha Co., Ltd.; KF1300, weight-average molecular weight 350,000 Da) was mixed with 62% by mass of γ-butyrolactone and dissolved at 160°C to prepare a support membrane stock solution. An 85% by mass γ-butyrolactone aqueous solution was used as the hollow portion-forming liquid, and the hollow portion was discharged from a double-orifice die together with the support membrane stock solution. The discharged support membrane stock solution was solidified in a cooling bath at a temperature of 20°C, set 30 mm below the orifice, to which an 85% by mass γ-butyrolactone aqueous solution was added, to produce a hollow fiber-shaped support membrane with a spherical structure. The support membrane had an outer diameter of 1300 μm and an inner diameter of 800 μm.

[0142] 12% by mass of linear PVDF1 (Arkema; ​​"Kynar" (registered trademark) 710, weight average molecular weight 180,000 Da), 4.8% by mass of cellulose diacetate (Eastman; CA-398-3), 2.4% by mass of cellulose triacetate (Eastman; CA-436-80S), 68.8% by mass of N-methyl-2-pyrrolidone (hereinafter, "NMP"), and 12% by mass of 2-pyrrolidone (hereinafter, "2P") were mixed and stirred at 120°C for 4 hours to prepare a polymer solution. The self-diffusion coefficient of the polymer in the polymer solution is as small as 1.0×10 -11 m 2 / s.

[0143] Next, a polymer solution at 50°C was uniformly applied to the outer surface of the above-mentioned hollow fiber-shaped support membrane at 10 m / min (thickness 60 μm). The support membrane coated with the polymer solution was pulled at 10 m / min, and 1 second after coating, it was solidified by being immersed in a coagulation bath of distilled water at 25°C for 10 seconds, thereby forming a composite hollow fiber membrane with an outer diameter of 1.4 mm and a three-dimensional network structure on the outside. The surface elastic modulus of the outer side of the hollow fiber membrane is as high as 310 MPa. The cross-sectional porosity of the hollow fiber membrane from the outer surface to the outer surface portion with a thickness of 5 μm is as low as 36%. In addition, the hollow fiber membrane does not contain large pores. An image of a cross section of the outer surface portion of the hollow fiber membrane observed by TEM is shown in FIG. Figure 3 The pure water permeability of the hollow fiber membrane is 0.4m 3 / m 2 The value α, obtained by dividing the number of pores on the outer surface by the average pore diameter on the outer surface, is as high as 62.

[0144] A hollow fiber membrane module was fabricated using the resulting hollow fiber membranes, and a filtration test (xi) was performed. The results of the evaluation using lake water as the filtration stock solution are shown in Table 1. The filtration volume ratio (F2 / F1) was 0.7, which is satisfactory. Furthermore, the removal rate after the filtration test was equivalent to that before the filtration test.

[0145] (Example 2)

[0146] (xi) Filtration test was carried out using the same hollow fiber membrane assembly as in Example 1. The results of the evaluation using the filtration stock solution in which activated carbon was added to the factory wastewater are shown in Table 1. The ratio of the filtration amount (F2 / F1) was 0.6, which was good. In addition, the removal rate after the filtration test was improved compared to that before the filtration test. The filtration stock solution having high turbidity and TOC and added with activated carbon was supplied to a hollow fiber membrane assembly using a membrane with a high surface elastic modulus, and the results showed a high removal rate.

[0147] (Comparative Example 1)

[0148] In Example 1, the composition of the polymer solution was changed to 12% by mass of PVDF1 ("Kynar" (registered trademark) 710 manufactured by Arkema, with a weight-average molecular weight of 180,000 Da), 4.0% by mass of cellulose diacetate (CA-398-3 manufactured by Eastman Co., Ltd.), 4.0% by mass of cellulose triacetate (CA-436-80S manufactured by Eastman Co., Ltd.), and 80.0% by mass of NMP, and the coagulation bath temperature was set at 40°C. A composite hollow fiber membrane was obtained by the same membrane preparation method. The self-diffusion coefficient of the polymer in the polymer solution was as high as 1.8×10 -11 m 2 / s. The resulting outer surface elastic modulus of the hollow fiber membrane was as low as 150 MPa. The cross-sectional porosity of the hollow fiber membrane, from the outer surface to the 5 μm thickness, was as high as 57%. Furthermore, the hollow fiber membrane contained no macropores. The α value, obtained by dividing the number of pores on the outer surface by the average pore diameter on the outer surface, was as low as 13.

[0149] A hollow fiber membrane module was produced using the obtained hollow fiber membrane, and a filtration test (xi) was performed. The results of the evaluation using a filtration stock solution in which activated carbon was added to factory wastewater are shown in Table 1. The ratio of the filtration amount (F2 / F1) was as low as 0.4. The removal rate before the filtration test was as low as 55%, and the removal rate after the filtration test was further reduced compared to before the filtration test. The filtration stock solution with high turbidity and TOC and added with activated carbon was supplied to a hollow fiber membrane module using a membrane with a low surface elastic modulus, and the removal rate was reduced.

[0150] (Comparative Example 2)

[0151] In Example 1, the composition of the polymer solution was set to 12% by mass of branched PVDF2 (manufactured by Solvay Specialty Chemicals; Solef9009), 7% by mass of cellulose triacetate (manufactured by Daicel Co., Ltd.; LT-35), and 81% by mass of NMP, and the temperature of the coagulation bath was set to 15°C. A composite hollow fiber membrane was obtained by similar membrane preparation. The surface elastic modulus of the outer side of the hollow fiber membrane was as low as 98 MPa. The cross-sectional porosity of the hollow fiber membrane from the outer surface to the outer surface portion with a thickness of 5 μm was as high as 59%. In addition, a large number of large pores are present in the area including the outer surface portion of the hollow fiber membrane. The α value obtained by dividing the number of pores on the outer surface by the average pore size of the outer surface is as low as 6.

[0152] A hollow fiber membrane module was produced using the obtained hollow fiber membrane, and a filtration test (xi) was performed. The results of the evaluation using a filtration stock solution in which activated carbon was added to factory wastewater are shown in Table 1. The ratio of the filtration amount (F2 / F1) was as low as 0.4. The removal rate before the filtration test was as high as 71%, but the removal rate after the filtration test was lower than that before the filtration test. The filtration stock solution with high turbidity and TOC and added with activated carbon was supplied to a hollow fiber membrane module using a membrane with a low surface elastic modulus and many large pores, and as a result, the removal rate was reduced.

[0153] (Example 3)

[0154] A hollow fiber membrane module was produced using the hollow fiber membrane obtained in Example 1, and a physical washing (air washing) test (vii) was performed. The evaluation results are shown in Table 2. The membrane showed little change in the removal rate of 40,000 Da dextran:T after physical washing, indicating that high removal efficiency was maintained even after physical washing.

[0155] (Example 4)

[0156] In Example 1, the composition of the polymer solution was set to 12% by mass of PVDF1 (manufactured by Arkema; ​​"Kynar" (registered trademark) 710, weight-average molecular weight 180,000 Da), 4.8% by mass of cellulose diacetate (manufactured by Eastman; CA-398-3), 2.4% by mass of cellulose triacetate (manufactured by Eastman; CA-436-80S), 60.6% by mass of NMP, and 20.2% by mass of ε-caprolactam (hereinafter referred to as "CL"), and the temperature of the coagulation bath was set to 40°C. A composite hollow fiber membrane was formed by the same operation. The surface elastic modulus of the outer side of the hollow fiber membrane was as high as 253 MPa. The cross-sectional porosity of the hollow fiber membrane from the outer surface to the outer surface portion with a thickness of 5 μm was as low as 38%. In addition, the hollow fiber membrane does not contain macropores. The pure water permeability of the hollow fiber membrane is 0.3 m 3 / m 2 / h / 50kPa.

[0157] A hollow fiber membrane module was fabricated using the obtained hollow fiber membrane, and a physical washing (air washing) test (vii) was performed. The evaluation results are shown in Table 2. The membrane showed little change in the removal rate of 40,000 Da dextran:T after physical washing, indicating that high removal efficiency was maintained even after physical washing.

[0158] (Example 5)

[0159] In Example 4, the composition of the polymer solution was made into 12% by mass of PVDF1 (produced by Arkema; ​​"Kynar" (registered trademark) 710, weight-average molecular weight 180,000 Da), 4.8% by mass of cellulose diacetate (produced by Eastman; CA-398-3), 2.4% by mass of cellulose triacetate (produced by Eastman; CA-436-80S), 52.5% by mass of NMP, and 28.3% by mass of CL. A composite hollow fiber membrane was formed in the same manner. The surface elastic modulus of the outer side of the hollow fiber membrane was as high as 294 MPa. The cross-sectional porosity of the hollow fiber membrane from the outer surface to the outer surface portion with a thickness of 5 μm was as low as 35%. In addition, the hollow fiber membrane does not contain macropores. The pure water permeability of the hollow fiber membrane is 0.2 m 3 / m 2 / h / 50kPa.

[0160] A hollow fiber membrane module was fabricated using the obtained hollow fiber membrane, and a physical washing (air washing) test (vii) was performed. The evaluation results are shown in Table 2. The membrane showed little change in the removal rate of 40,000 Da dextran:T after physical washing, indicating that high removal efficiency was maintained even after physical washing.

[0161] (Example 6)

[0162] In Actual Example 4, a composite hollow fiber membrane was formed by the same operation except that the composition of the polymer solution was 12% by mass of PVDF1 (produced by Arkema; ​​"Kynar" (registered trademark) 710, weight-average molecular weight 180,000 Da), 4.8% by mass of cellulose diacetate (produced by Eastman; CA-398-3), 2.4% by mass of cellulose triacetate (produced by Eastman; CA-436-80S), 44.4% by mass of NMP, and 36.4% by mass of CL. The surface elastic modulus of the outer side of the hollow fiber membrane was as high as 352 MPa. The cross-sectional porosity of the hollow fiber membrane from the outer surface to the outer surface portion with a thickness of 5 μm was as low as 32%. In addition, the hollow fiber membrane does not contain macropores. The pure water permeability of the hollow fiber membrane is 0.2 m 3 / m 2 / h / 50kPa.

[0163] A hollow fiber membrane module was fabricated using the obtained hollow fiber membrane, and a physical washing (air washing) test (vii) was performed. The evaluation results are shown in Table 2. The membrane showed little change in the removal rate of 40,000 Da dextran:T after physical washing, indicating that high removal efficiency was maintained even after physical washing.

[0164] (Comparative Example 3)

[0165] A hollow fiber membrane module was produced using the hollow fiber membrane obtained in Comparative Example 1, and a physical washing (air washing) test (vii) was conducted. The evaluation results are shown in Table 3. The removal rate before the physical washing test was as low as 55%, and the removal rate after the physical washing test was further reduced compared to before the physical washing test.

[0166] (Comparative Example 4)

[0167] A hollow fiber membrane module was produced using the hollow fiber membrane obtained in Comparative Example 2, and a physical washing (air washing) test (vii) was performed. The evaluation results are shown in Table 3. While the removal rate before the physical washing test was as high as 70%, the removal rate after the physical washing test decreased compared to before the physical washing test.

[0168] (Comparative Example 5)

[0169] While the hollow fiber support membrane of Example 1 was used, the outer surface of the hollow fiber membrane module of the present invention was not formed on the outer surface of the support membrane. The surface elastic modulus of the outer surface of the hollow fiber membrane was as low as 130 MPa. The cross-sectional porosity of the hollow fiber membrane, extending from the outer surface to the 5 μm thickness of the outer surface, was as high as 62%.

[0170] A hollow fiber membrane module was prepared using the obtained hollow fiber membrane, and a physical washing (air washing) test (vii) was performed. The evaluation results are shown in Table 3. The removal rate before the physical washing test was as low as 20%, and the removal rate after the physical washing test was further reduced compared to before the physical washing test.

[0171] (Example 7)

[0172] The results of the abrasion test (vi) performed using the hollow fiber membrane obtained in Example 1 are shown in FIG. Figure 6 It can be seen that the maximum wear depth at a contact load of 30 μN is as small as 150 nm, and the scratching of the outer surface of the hollow fiber membrane is suppressed.

[0173] (Comparative Example 6)

[0174] The results of the abrasion test (vi) performed using the hollow fiber membrane obtained in Comparative Example 1 are shown in FIG. Figure 6 It is found that, compared with Example 7, the wear depth is large when wear is performed at any contact load, and the wear is easily abraded.

[0175] (Example 8)

[0176] Using the hollow fiber membrane module obtained in Example 1, (x) virus removal efficiency (TV) was evaluated before and after (xi) a filtration test using a filter stock solution containing activated carbon added to factory wastewater. The results showed a high virus removal efficiency for a long period of time, even after treating a filter stock solution with high turbidity and TOC and the addition of activated carbon.

[0177] (Comparative Example 7)

[0178] Using the hollow fiber membrane module obtained in Comparative Example 1, the virus removal rate (TV) described in (x) was evaluated before and after a filtration test (xi) using a filter stock solution containing activated carbon added to factory wastewater. The results showed a high removal rate of 3.6 before the filtration test, but decreased to 2.8 after the filtration test. After treating the filter stock solution with high turbidity and TOC and the addition of activated carbon, the high removal rate could not be maintained for a long period of time even with a high concentration of viruses in the filter stock solution. This is presumably because the hollow fiber membranes in the hollow fiber membrane module have a low surface elastic modulus, resulting in scratching of the outer surface.

[0179] (Example 9)

[0180] In Comparative Example 1, except that the temperature of the coagulation bath was set at 6°C, a composite hollow fiber membrane was obtained by the same membrane preparation method. The self-diffusion coefficient of the polymer in the polymer solution was as large as 1.8×10 -11 m 2 / s. The surface elastic modulus of the outer surface of the hollow fiber membrane is as high as 458MPa. The cross-sectional porosity of the hollow fiber membrane from the outer surface to the outer surface portion with a thickness of 5μm is as low as 3%. In addition, the hollow fiber membrane does not contain large pores. The number of pores on the outer surface is as few as 78 / μm. 2 The outer surface opening ratio is as low as 0.5%. The average pore size on the outer surface is as small as 8.0nm. The α value, obtained by dividing the number of pores on the outer surface by the average pore size on the outer surface, is as low as 10.

[0181] The resulting hollow fiber membranes were used to create hollow fiber membrane modules, and filtration tests (xi) were conducted. Evaluations were conducted using a filtration stock solution containing activated carbon added to factory wastewater. The filtration rate ratio (F2 / F1) was as low as 0.4. The removal rate before the filtration test was as high as 70%, and the removal rate after the filtration test remained unchanged compared to before the test, maintaining a high removal rate.

[0182] Table 1

[0183] Example 1 Example 2 Example 9 Comparative Example 1 Comparative Example 2 Surface elastic modulus MPa 310 310 458 150 98 Fill rate ％ 48 48 48 48 48 Opening ratio of the outer surface ％ 2.4 2.4 0.5 11 0.1 Average pore size on the outer surface nm 7.2 7.2 8.0 15 8.2 Cross-sectional porosity of the outer surface ％ 36 36 3 57 59 Cross-sectional porosity of the inner surface ％ 62 62 62 62 62 Average value of column thickness nm 32 32 10 66 50 Column density root / μm 20 20 40 6 8 (XY) / X×100 ％ 10 10 10 10 10 Number of holes on the outer surface <![CDATA[per μm 2 > 444 444 78 55 49 (Number of pores) / (average pore diameter) on the outer surface: α <![CDATA[per μm 2 / nm]]> 62 62 10 13 6 Filter the stock solution - lake water wastewater wastewater wastewater wastewater Turbidity NTU 5 17 17 17 17 TOC mg / L 5 20 20 20 20 Amount of activated carbon added mg / L 0 5 5 5 5 Filtration volume ratio before and after filtration test - 0.7 0.6 0.4 0.4 0.4 Dextran removal rate before filtration test: T ％ 72 72 70 55 71 Dextran removal rate after filtration test: T′ ％ 70 75 70 45 41

[0184] Table 2

[0185] Example 3 Example 4 Example 5 Example 6 Surface elastic modulus MPa 310 253 294 352 Fill rate ％ 48 48 48 48 Opening ratio of the outer surface ％ 2.4 4.1 6.5 5.8 Average pore size on the outer surface nm 7.2 7.6 7.9 8.4 Cross-sectional porosity of the outer surface ％ 36 38 35 32 Cross-sectional porosity of the inner surface ％ 62 62 62 62 Average value of column thickness nm 32 31 33 32 Column density root / μm 20 15 21 28 (XY) / X×100 ％ 10 10 10 10 Number of holes on the outer surface <![CDATA[per μm 2 > 444 681 999 788 (Number of pores) / (average pore diameter) on the outer surface: α <![CDATA[per μm 2 / nm]]> 62 90 126 94 Dextran removal rate before physical washing test: T ％ 72 69 71 74 Dextran removal rate after physical washing test: T′ ％ 70 64 70 72

[0186] Table 3

[0187] Comparative Example 3 Comparative Example 4 Comparative Example 5 Surface elastic modulus MPa 150 98 130 Fill rate ％ 48 48 48 Opening ratio of the outer surface ％ 11 0.1 40 Average pore size on the outer surface nm 15 7.3 316 Cross-sectional porosity of the outer surface ％ 57 59 62 Cross-sectional porosity of the inner surface ％ 62 62 62 Average value of column thickness nm 66 50 350 Column density root / μm 6 8 1 (XY) / X×100 ％ 10 10 10 Number of holes on the outer surface <![CDATA[pieces / μm 2 > 196 49 4 (Number of pores) / (average pore diameter) on the outer surface: α <![CDATA[pieces / μm 2 / nm]]> 13 6 0.01 Dextran removal rate before physical washing test: T ％ 55 70 20 Dextran removal rate after physical washing test: T′ ％ 41 45 15

[0188] Explanation of symbols

[0189] 100 Hollow fiber membrane modules

[0190] 110 End 1

[0191] 120 Second End

[0192] 1 Cylindrical shell

[0193] 2 Hollow fiber membrane

[0194] 3. 1st potting section

[0195] 4. Second potting section

[0196] 4A through hole

[0197] 4B gap

[0198] 5 Upper cover

[0199] 6 Lower cover

[0200] 7. Raw liquid inlet

[0201] 8. Permeate outlet

[0202] 9. Raw liquid outlet

[0203] 10 rectifier tube

[0204] 11 Rectifier hole

[0205] 12 Second potting part shell

[0206] 13 Non-wear area in the wear test on the outer surface of the hollow fiber membrane

[0207] 14 Wear area in the wear test on the outer surface of the hollow fiber membrane

[0208] 101 outer surface

[0209] 102 Appearance and face

[0210] 103 Lines on the outer surface of the hollow fiber membrane

[0211] 104 Line perpendicular to the outer surface

[0212] 105 column thickness

[0213] 300 polymer solution

[0214] 301 Phase containing a large number of polymers

[0215] 302 Phase containing a large amount of solvent.

Claims

1. A hollow fiber membrane module comprising at least a cylindrical housing having a first end and a second end in a height direction of the cylindrical member, a plurality of hollow fiber membranes housed within the cylindrical housing between the first end and the second end, a raw liquid inlet for allowing a raw liquid to be filtered to flow into the cylindrical housing, and a permeate outlet for allowing a permeate that has permeated the hollow fiber membranes to flow out of the cylindrical housing. The raw liquid inlet is connected to the outer surface of the plurality of hollow fiber membranes. The hollow fiber membrane module includes a first potting portion for bonding the bundle of the plurality of hollow fiber membranes to the ends of the plurality of hollow fiber membranes located on the first end side of the cylindrical housing with the plurality of hollow portions opened. In a cross section perpendicular to the height direction of the cylindrical shell, when the cross-sectional area inside the cylindrical shell is set to 100%, the proportion of the area occupied by the multiple hollow fiber membranes including the hollow part, that is, the filling rate, is 40% to 80%, and the surface elastic modulus of the outer surface of the multiple hollow fiber membranes is 200MPa to 500MPa.

2. The hollow fiber membrane module according to claim 1, wherein the number of pores observed in the outer surface of the hollow fiber membrane, i.e., surface pores, per unit area is 200 / μm 2 ~2000 / μm 2 . 3 . The hollow fiber membrane module according to claim 1 , wherein an opening ratio is 1% to 10% relative to the area of ​​the outer surface of the hollow fiber membrane. 4 . The hollow fiber membrane module according to claim 1 , wherein the average pore diameter of the outer surface of the hollow fiber membrane, ie, the surface pore diameter, is 5 nm to 20 nm. 5 . The hollow fiber membrane module according to claim 2 , wherein a value α obtained by dividing the number of surface pores per unit area by the surface pore diameter is 30 pores / μm. 2 / nm~150 / μm 2 / nm, the unit of the number of surface pores per unit area is / μm 2 , the unit of the surface pore size is nm. The hollow fiber membrane module according to any one of claims 1 to 5, wherein in a circular cross section of the hollow fiber membrane, a cross-sectional porosity in an outer surface portion (ie, an area from the outer surface to 5 μm from the outer surface) of the hollow fiber membrane is 20% to 50%. 7 . The hollow fiber membrane module according to claim 1 , wherein the hollow fiber membrane structures between the pores in the outer surface portion of the hollow fiber membrane are pillars, and the average thickness of the pillars is 20 nm to 60 nm. 8 . The hollow fiber membrane module according to claim 1 , wherein the density of the pillars is 10 to 50 pillars / μm.

9. The hollow fiber membrane assembly according to any one of claims 1 to 8, comprising a second potting portion for bonding the bundle of the plurality of hollow fiber membranes located on the second end side of the cylindrical shell, and having a relationship of 2≤(XY) / X×100≤20(%) when the average length of the plurality of hollow fiber membranes between the second end side of the first potting portion and the first end side of the second potting portion is set to X, and the length in the height direction between the second end side of the first potting portion and the first end side of the second potting portion in the cylindrical shell is set to Y. 10 . The hollow fiber membrane module according to claim 1 , wherein a raw liquid to be filtered having a turbidity of 3 to 50 NTU is filtered, and a permeate is separated from the raw liquid to be filtered, and the virus removal rate of the permeate is 4 log or more. The hollow fiber membrane module according to any one of claims 1 to 10, wherein a raw liquid to be filtered having a turbidity of 3 to 50 NTU is filtered, and when a permeate is separated from the raw liquid to be filtered, the permeate has an SDI of 3 or less.

12. A filtration operation method for a hollow fiber membrane module, wherein: A raw liquid to be filtered having a turbidity of 3 to 50 NTU is supplied to the hollow fiber membrane module according to any one of claims 1 to 11, and a permeate is separated from the raw liquid to be filtered.

13. A filtration operation method for a hollow fiber membrane module, wherein: A raw liquid to be filtered having a total organic carbon (TOC) content of 4 to 30 mg / L is supplied to the hollow fiber membrane module according to any one of claims 1 to 12, and a permeate is separated from the raw liquid to be filtered.

14. A method for filtration operation of a hollow fiber membrane module, the method for filtration operation of a hollow fiber membrane module according to any one of claims 1 to 11, comprising the following steps (1) and (2): The step (1) is a membrane separation step of supplying a raw liquid to the hollow fiber membrane module to separate suspended matter from the liquid. The step (2) is a washing step of stopping the step (1) and washing the suspended matter accumulated on the outer surface of the hollow fiber membrane and between the hollow fiber membranes. The washing step (2) performs the following air washing operation: the raw liquid or a mixed flow of liquid and gas having a turbidity or TOC at least lower than that of the raw liquid flows toward the outer surface side of the hollow fiber membrane at a flow rate of a membrane surface linear velocity of 0.3 m / s or more and 5.0 m / s or less.

15. A hollow fiber membrane, wherein an opening ratio is 1% to 10% relative to the area of ​​an outer surface of the hollow fiber membrane, and a surface elastic modulus of the outer surface of the hollow fiber membrane is 200 MPa to 500 MPa. 16 . A filtration device comprising the hollow fiber membrane module according to claim 1 or the hollow fiber membrane according to claim 15 .

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