Hollow fiber membrane module

Abstract

To provide a hollow fiber membrane module in which hollow fiber membranes are hardly detached from a fixed part of the hollow fiber membranes.SOLUTION: A hollow fiber membrane module comprises: a plurality of hollow fiber membranes with polytetrafluoroethylene as its main component; and a fixed part in which ends of the plurality of hollow fiber membranes are embedded. The fixed part is constituted of a resin composition with silicone resin as its main component. In the hollow fiber membranes, at least a portion of an outer surface side of a region embedded in the fixed part is impregnated with the resin composition.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a hollow fiber membrane module.

Background Art

[0002] As a type of filtration membrane for filtering treated water to remove solids for various purposes such as wastewater treatment, a hollow fiber membrane in which a porous body is formed into a relatively small-diameter cylindrical shape may be used.

[0003] For example, as a hollow fiber membrane module including such a hollow fiber membrane, a hollow fiber membrane made of a fluororesin and an end sealing portion having a silicone-based resin obtained by curing a liquid silicone rubber are provided. An ozone-resistant membrane module has been proposed that is less likely to deteriorate even when exposed to the strong oxidizing power of ozone and enables stable water treatment for a long period of time (see Japanese Patent Application Laid-Open No. 6-296836).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above hollow fiber membrane module, when an external force is applied, the hollow fiber membrane may come off from the end sealing portion. In particular, when the hollow fiber membrane is formed of polytetrafluoroethylene, polytetrafluoroethylene has low adhesion to other materials compared to other resins, so the hollow fiber membrane is likely to come off from a fixing portion that fixes the hollow fiber membrane such as the end sealing portion. When the hollow fiber membrane comes off from the fixing portion, it leads to a decrease in filtration performance.

[0006] Therefore, an object is to provide a hollow fiber membrane module in which the hollow fiber membrane is difficult to come off from the fixing portion.

Means for Solving the Problems

[0007] A hollow fiber membrane module according to one aspect of the present disclosure made to solve the above problems includes a plurality of hollow fiber membranes mainly composed of polytetrafluoroethylene, and a fixing part in which the ends of the plurality of hollow fiber membranes are embedded. The fixing part is composed of a resin composition mainly composed of a silicone resin, and at least a part of the outer surface side of the region embedded in the fixing part in the hollow fiber membrane is impregnated with the resin composition.

Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a hollow fiber membrane module in which the hollow fiber membrane is difficult to come off from the fixing part of the hollow fiber membrane.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Best Mode for Carrying Out the Invention

[0010] [Description of Embodiments of the Present Disclosure] A hollow fiber membrane module according to one aspect of the present disclosure includes a plurality of hollow fiber membranes mainly composed of polytetrafluoroethylene, and a fixing portion in which the ends of the plurality of hollow fiber membranes are embedded. The fixing portion is composed of a resin composition mainly composed of a silicone resin, and at least a part of the outer surface side of the region embedded in the fixing portion in the hollow fiber membrane is impregnated with the resin composition.

[0011] As described above, since PTFE has relatively low adhesion to other materials, the adhesion of the hollow fiber membrane mainly composed of PTFE to other members is also relatively low. However, since the resin composition constituting the fixing portion is impregnated on the outer surface side of the hollow fiber membrane mainly composed of such PTFE, the adhesion between the hollow fiber membrane and the fixing portion is enhanced. Therefore, in the hollow fiber membrane module, it is difficult for the hollow fiber membrane to come off from the fixing portion.

[0012] The hollow fiber membrane preferably includes a porous structure having a plurality of fibers mainly composed of polytetrafluoroethylene and a plurality of nodules connected to each other by these fibers, and the fibers in the region embedded in the fixing portion in the hollow fiber membrane are partially cut. By the fibers in the region embedded in the fixing portion being partially cut, the voids into which the resin composition constituting the fixing portion is impregnated (filled) become larger in the region embedded in the fixing portion, so that the adhesion between the hollow fiber membrane and the fixing portion is more reliably enhanced.

[0013] The average depth of impregnation of the resin composition into the region embedded in the fixing portion is preferably 0.3% or more of the average thickness of the hollow fiber membrane. By the depth of impregnation satisfying the above range, the adhesion between the hollow fiber membrane and the fixing portion can be further improved.

[0014] It is preferable that the ratio of the isopropyl alcohol bubble point of the region embedded in the fixing portion to the region not embedded in the fixing portion in the hollow fiber membrane is 0.4 or more and 0.8 or less. By having the ratio of the isopropyl alcohol bubble point within the above range, the adhesion between the hollow fiber membrane and the fixing portion can be further improved.

[0015] Here, the "main component" is the component with the largest content, for example, it means a component with a content of 50% by mass or more. "The resin composition constituting the fixing portion is impregnated" means that the resin composition constituting the fixing portion is impregnated in the region facing the outer peripheral surface of the hollow fiber membrane in the fixing portion. "Isopropyl alcohol bubble point (hereinafter also referred to as 'IPA-BP')" means a value measured in accordance with JIS-K3832 (1990) using isopropyl alcohol, and it is an index corresponding to the maximum pore diameter of the porous structure (for example, the porous structure described later) of the hollow fiber membrane.

[0016] [Details of Embodiments of the Present Disclosure] Hereinafter, embodiments of the hollow fiber membrane module according to the present disclosure will be described in detail with reference to the drawings, taking the case where the hollow fiber membrane module is provided in a wastewater treatment apparatus as an example.

[0017] [Wastewater Treatment Apparatus] As shown in FIG. 1, a wastewater treatment apparatus including a hollow fiber membrane module according to an embodiment of the present disclosure includes a treatment water tank T for storing treated water containing activated sludge, and one or more hollow fiber membrane modules 1 disposed in the treatment water tank T. The hollow fiber membrane module 1 functions as a filtration module. The wastewater treatment apparatus further includes a pump 2 for sucking out the treated water in the treatment water tank T through the hollow fiber membrane module 1.

[0018] In addition, although not shown in the drawings, the wastewater treatment apparatus may include an aeration device for supplying air (oxygen) to the activated sludge, a carrier to which the activated sludge adheres at a high concentration, a bubbling device for supplying bubbles for cleaning the hollow fiber membrane module 1, a sludge extraction device for discharging excess activated sludge, a frame for supporting other components in the treatment water tank T, a control device, and the like.

[0019] The above wastewater treatment apparatus decomposes organic substances in wastewater to be treated, such as domestic wastewater, sewage, and industrial wastewater, using activated sludge, which is an aerobic microorganism, and separates and discharges impurities using the hollow fiber membrane module 1. That is, in the present embodiment, the above wastewater treatment apparatus is an apparatus for treating wastewater by the membrane separation activated sludge method.

[0020] 〔Treatment water tank〕 The treatment water tank T stores the wastewater to be treated so that the hollow fiber membrane module 1 can be immersed. As the material of the treatment water tank T, for example, resin, metal, concrete, etc. can be used.

[0021] 〔Hollow fiber membrane module〕 The hollow fiber membrane module 1 includes a plurality of hollow fiber membranes 3 mainly composed of PTFE, and a pair of fixing parts 7 in which both ends of the plurality of hollow fiber membranes 3 are embedded to fix both ends of the hollow fiber membranes 3. The fixing part 7 is composed of a resin composition mainly composed of silicone resin. At least a part of the outer surface side of the region of the above hollow fiber membrane embedded in the fixing part 7 contains the resin composition constituting the fixing part 7. In the present embodiment, as shown in FIG. 2, the hollow fiber membrane module 1 includes a plurality of hollow fiber membranes 3 held in a state aligned in one direction (vertical direction), a pair of fixing parts 7 that respectively fix both ends of the plurality of hollow fiber membranes 3, and a pair of holding parts (first holding part 4 and second holding part 5) that hold the hollow fiber membranes 3 fixed by each fixing part 7.

[0022] <Hollow fiber membrane> The hollow fiber membrane 3 is formed of a resin composition mainly composed of PTFE. The lower limit of the PTFE content in the hollow fiber membrane 3 is 50% by mass, preferably 90% by mass, more preferably 95% by mass, and even more preferably 99% by mass. The upper limit of the PTFE content in the hollow fiber membrane 3 may be 100% by mass. Further, the resin composition for forming the hollow fiber membrane 3 may contain resins other than polytetrafluoroethylene and additives such as lubricants.

[0023] As the lower limit of the average outer diameter of the hollow fiber membrane 3, 1 mm is preferable, 1.5 mm is more preferable, and 2 mm is even more preferable. On the other hand, as the upper limit of the average outer diameter of the hollow fiber membrane 3, 6 mm is preferable, 5 mm is more preferable, and 4 mm is even more preferable. If the average outer diameter of the hollow fiber membrane 3 is less than the above lower limit, the mechanical strength of the hollow fiber membrane 3 may be insufficient. On the other hand, if the average outer diameter of the hollow fiber membrane 3 exceeds the above upper limit, the ratio of the surface area to the cross-sectional area of the hollow fiber membrane 3 may become small, and the filtration efficiency may decrease.

[0024] As the lower limit of the average inner diameter of the hollow fiber membrane 3, 0.3 mm is preferable, 0.5 mm is more preferable, and 0.9 mm is even more preferable. On the other hand, as the upper limit of the average inner diameter of the hollow fiber membrane 3, 4 mm is preferable, and 3 mm is more preferable. If the average inner diameter of the hollow fiber membrane 3 is less than the above lower limit, the pressure loss when discharging the treated water in the hollow fiber membrane 3 may become too large. On the other hand, if the average inner diameter of the hollow fiber membrane 3 exceeds the above upper limit, the thickness of the hollow fiber membrane 3 may become too small, and the mechanical strength and the effect of preventing the permeation of impurities may be insufficient.

[0025] As the lower limit of the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3, 3 / 10 is preferable, and 2 / 5 is more preferable. On the other hand, as the upper limit of the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3, 4 / 5 is preferable, and 3 / 5 is more preferable. When the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3 is less than the above lower limit, the thickness of the hollow fiber membrane 3 may become too large and the water permeability of the hollow fiber membrane 3 may decrease. On the other hand, when the ratio of the average inner diameter to the average outer diameter of the hollow fiber membrane 3 exceeds the above upper limit, the thickness of the hollow fiber membrane 3 may become too small and the mechanical strength and the effect of preventing the permeation of impurities may become insufficient.

[0026] In the hollow fiber membrane module 1, as the lower limit of the average effective length along the central axis of the hollow fiber membrane 3, 1 m is preferable, and 2 m is more preferable. On the other hand, as the upper limit of the average effective length of the hollow fiber membrane 3, 8 m is preferable, and 7 m is more preferable. When the average effective length of the hollow fiber membrane 3 is less than the above lower limit, the volume efficiency of the hollow fiber membrane module 1 may become too small. On the other hand, when the average effective length of the hollow fiber membrane 3 exceeds the above upper limit, the deflection of the hollow fiber membrane 3 may become too large due to its own weight, or the handleability during installation of the hollow fiber membrane module 1 may decrease.

[0027] As the lower limit of the average thickness (wall thickness) of the hollow fiber membrane 3, 100 μm is preferable, 200 μm is more preferable, and 300 μm is even more preferable. On the other hand, as the upper limit of the above average thickness, 600 μm is preferable, 500 μm is more preferable, and 400 μm is even more preferable. When the above average thickness is less than the above lower limit, the strength of the hollow fiber membrane 3 may be insufficient. On the other hand, when the above average thickness exceeds the above upper limit, the filtration efficiency may decrease too much.

[0028] The hollow fiber membrane 3 preferably includes a porous structure having a plurality of fibers (fibrils) mainly composed of PTFE and a plurality of nodules (nodes) connected to each other by these fibers. The hollow fiber membrane 3 having such a porous structure is formed by an extrusion molding method. By adjusting the stretching temperature, stretching ratio, etc. in the extrusion molding, the size of the pores can be adjusted.

[0029] The hollow fiber membrane 3 may be a single-layer tubular hollow fiber membrane or a tubular hollow fiber membrane having a plurality of layers in the radial direction.

[0030] FIG. 3 shows an example of the hollow fiber membrane 3 having a plurality of layers. The hollow fiber membrane 3 shown in FIG. 3 has a porous support layer 3a formed in a tubular shape and a porous filtration layer 3b laminated on the outer surface of the support layer 3a. As shown in FIG. 4, the support layer 3a has a first porous structure 31 having a plurality of first fibers 32 mainly composed of PTFE and a plurality of first nodules 33 connected to each other by these first fibers 32, and the filtration layer 3b has a second porous structure 34 having a plurality of second fibers 35 mainly composed of PTFE and second nodules 36 connected to each other by these second fibers 35.

[0031] As the lower limit of the average thickness of the support layer 3a, 0.3 mm is preferable, and 0.5 mm is more preferable. On the other hand, as the upper limit of the average thickness of the support layer 3a, 1.0 mm is preferable, and 0.8 mm is more preferable. If the average thickness of the support layer 3a is less than the lower limit, the strength of the support layer 3a and thus the hollow fiber membrane 3 may be insufficient. On the other hand, if the average thickness of the support layer 3a exceeds the upper limit, the inner cavity diameter of the hollow fiber membrane 3 may become too small and the pressure loss when discharging the treated water may become too large.

[0032] As the lower limit of the average pore diameter of the support layer 3a, 1 μm is preferable, and 1.5 μm is more preferable. On the other hand, as the upper limit of the average pore diameter of the support layer 3a, 3 μm is preferable, and 2.5 μm is more preferable. If the average pore diameter of the support layer 3a is less than the lower limit, the water permeability of the hollow fiber membrane 3 may be insufficient. On the other hand, if the average pore diameter of the support layer 3a exceeds the upper limit, there is a possibility that the permeation of impurities cannot be sufficiently blocked. The average pore diameter of the support layer 3a is measured by a pore diameter distribution measuring device (for example, the palm porometer "CFP-1200A" of PMI).

[0033] As the lower limit of the porosity of the support layer 3a, 40% is preferable, and 50% is more preferable. On the other hand, as the upper limit of the porosity of the support layer 3a, 90% is preferable, and 85% is more preferable. When the porosity of the support layer 3a is less than the lower limit, the water permeability of the hollow fiber membrane 3 may be insufficient. On the other hand, when the porosity of the support layer 3a exceeds the upper limit, the strength of the hollow fiber membrane 3 may be insufficient. Note that the "porosity" means the ratio of the total volume of the pore portion to the volume of the hollow fiber membrane. The measured volume (apparent volume) of the hollow fiber membrane is measured, the true volume of the hollow fiber membrane (calculated from the dry mass and the true density of the hollow fiber membrane) is calculated, and the percentage of the difference between the measured volume and the true volume with respect to the measured volume is calculated.

[0034] As the lower limit of the average thickness of the filtration layer 3b, 10 μm is preferable, and 12 μm is more preferable. On the other hand, as the upper limit of the average thickness of the filtration layer 3b, 100 μm is preferable, and 80 μm is more preferable. When the average thickness of the filtration layer 3b is less than the lower limit, there is a risk that the permeation of impurities cannot be sufficiently blocked. On the other hand, when the average thickness of the filtration layer 3b exceeds the upper limit, the water permeability of the hollow fiber membrane 3 may be insufficient.

[0035] As the lower limit of the average pore diameter of the filtration layer 3b, 0.01 μm is preferable, and 0.05 μm is more preferable. On the other hand, as the upper limit of the average pore diameter of the filtration layer 3b, 0.45 μm is preferable, and 0.3 μm is more preferable. When the average pore diameter of the filtration layer 3b is less than the lower limit, the water permeability of the hollow fiber membrane 3 may be insufficient. On the other hand, when the average pore diameter of the filtration layer 3b exceeds the upper limit, there is a risk that the permeation of impurities cannot be sufficiently blocked. Note that the length L in FIG. 4 indicates the maximum length of the second porous structure 34 of the filtration tank 3b. The maximum length of this second porous structure 34 indicates the length that becomes the maximum when the length of the pore structure is measured at an arbitrary position. The smaller this maximum length is, the smaller the average pore diameter of the filtration tank 3b becomes. The average pore diameter of the filtration layer 3b is measured by a pore diameter distribution measuring device (for example, the palm porometer "CFP-1200A" of PMI).

[0036] As the lower limit of the porosity of the filtration layer 3b, 40% is preferable, and 50% is more preferable. On the other hand, as the upper limit of the porosity of the filtration layer 3b, 80% is preferable, and 70% is more preferable. When the porosity of the filtration layer 3b is less than the lower limit, the water permeability of the hollow fiber membrane 3 may be insufficient. On the other hand, when the porosity of the filtration layer 3b exceeds the upper limit, the pore diameter of the hollow fiber membrane 3 may become non-uniform.

[0037] (Roughened part of the hollow fiber membrane) The hollow fiber membrane 3 has a roughened part 8 on the outer surface side of the region embedded in the fixing part 7, where a roughening treatment (a treatment to roughen the surface) is performed. The roughened part 8 of the hollow fiber membrane 3 has a large pore diameter due to the roughening treatment. And at least a part of the roughened part 8 is impregnated (more specifically, impregnated and solidified) with the resin composition constituting the fixing part 7. In the embodiment shown in FIG. 3, the roughened part 8 and the region impregnated with the resin composition coincide.

[0038] Examples of the method for roughening the surface of the hollow fiber membrane 3 to form the roughened part 8 include conventionally known methods, such as a method of heating the outer surface of the hollow fiber membrane 3 with a burner, a method of blasting the hollow fiber membrane 3, a method of plasma-treating the hollow fiber membrane 3, and a method of treating the hollow fiber membrane 3 with a treatment liquid. Examples of the treatment liquid used in the method of treating with a treatment liquid include a sodium metal-naphthalene complex solution. Examples of the sodium metal-naphthalene complex solution include Tetraetch (registered trademark), which is a commercially available product. The operating conditions in these methods may be appropriately set so that the hollow fiber membrane 3 is less likely to come off from the solidified part 7. For example, in the method of treating with a treatment liquid, by adjusting the immersion time of the hollow fiber membrane in the treatment liquid, the pore diameter of the roughened part 8 can be made larger than that of the region (non-roughened part) of the hollow fiber membrane 3 that is not embedded in the fixing part 7. Among these methods, the method of treating with a treatment liquid is preferable because it is easy to adjust the pore diameter of the roughened part 8.

[0039] When the resin composition constituting the fixing portion 7 is impregnated in the roughened portion 8, the PTFE in the roughened portion 8 and the siloxane group of the silicone resin in the fixing portion 7 are chemically bonded by a chemical reaction, and the resin compositions constituting the roughened portion 8 and the fixing portion 7 are physically bonded by an anchor effect due to meshing. Here, depending on the type of water to be treated processed by the hollow fiber membrane module 1, the above chemical bond may be broken. For example, when the water to be treated is an oxidizing (oxidizing ability) water to be treated such as an aqueous solution containing sodium hypochlorite (NaClO), hydrogen peroxide (H2O2), etc., the above chemical bond tends to be easily broken due to contact with this water to be treated. However, since the roughened portion 8 and the fixing portion 7 are bonded not only by a chemical bond but also by a physical bond, even when the chemical bond is weakened, the bond between the roughened portion 8 and the fixing portion 7 is maintained by the physical bond. Therefore, by impregnating the resin composition constituting the fixing portion 7 in the roughened portion 8, the adhesion between the hollow fiber membrane 3 and the fixing portion 7 is enhanced.

[0040] Also, the roughened portion 8 of the hollow fiber membrane 3 has higher wettability with respect to the silicone resin than the non-roughened portion. Therefore, since the hollow fiber membrane 3 has the roughened portion 8, it becomes easier to impregnate the resin composition constituting the fixing portion 7 in the roughened portion 8, and thus the manufacturability of the hollow fiber membrane module 1 is improved.

[0041] When the hollow fiber membrane 3 has the porous structure described above, it is preferable that the fibers in the porous structure in the roughened portion 8 are partially cut. By the fibers in the roughened portion 8 being partially cut, in the roughened portion 8 compared to the non-roughened portion, the voids into which the resin composition constituting the fixing portion 7 is impregnated become larger, so that the adhesion between the hollow fiber membrane 3 and the fixing portion 7 is more reliably enhanced.

[0042] As described above, when the hollow fiber membrane 3 has the support layer 3a and the filtration layer 3b, the average pore diameter and porosity of the support layer 3a in the roughened portion 8 may be the same as those in the non-roughened portion. As the lower limit of the average pore diameter of the filtration layer 3b in the roughened portion 8, 0.05 μm is preferable, and 0.08 μm is more preferable. On the other hand, as the upper limit of the average pore diameter of the filtration layer 3b in the roughened portion 8, 0.5 μm is preferable, and 0.4 μm is more preferable. As the lower limit of the porosity of the filtration layer 3b in the roughened portion 8, 45% is preferable, and 55% is more preferable. On the other hand, as the upper limit of the porosity of the filtration layer 3b in the roughened portion 8, 95% is preferable, and 85% is more preferable.

[0043] As the lower limit of the IPA-BP of the roughened portion 8, 60 kPa is preferable, and 80 kPa is more preferable. On the other hand, as the upper limit of the IPA-BP of the roughened portion 8, 200 kPa is preferable, and 180 kPa is more preferable. When the IPA-BP is less than the lower limit, there is a risk that a part of the solidified portion 7 is excessively impregnated with the resin composition up to the hollow portion of the hollow fiber membrane 3 (that is, the hollow portion inside the support layer 3a). On the other hand, when the IPA-BP exceeds the upper limit, there is a risk that the resin composition is difficult to be impregnated.

[0044] On the other hand, as the lower limit of the IPA-BP of the region not embedded in the fixed portion 7 in the hollow fiber membrane 3, 60 kPa is preferable, and 80 kPa is more preferable. On the other hand, as the upper limit of the IPA-BP, 200 kPa is preferable, and 180 kPa is more preferable. When the IPA-BP is less than the lower limit, there is a risk that impurities cannot be sufficiently separated. On the other hand, when the IPA-BP exceeds the upper limit, there is a risk that the water permeability of the hollow fiber membrane 3 becomes insufficient.

[0045] As the lower limit of the ratio of the region embedded in the fixing portion to the region not embedded in the fixing portion in the hollow fiber membrane 3, 0.4 is preferable, and 0.5 is more preferable. On the other hand, as the upper limit of the ratio of the isopropyl alcohol bubble point, 0.8 is preferable, and 0.6 is more preferable. When the ratio of the isopropyl alcohol bubble point is less than the lower limit, there is a risk that a part of the solidified portion 7 is excessively impregnated with the resin composition up to the hollow portion of the hollow fiber membrane 3 (that is, the hollow portion inside the support layer 3a). On the other hand, when the ratio of the isopropyl alcohol bubble point exceeds the upper limit, there is a risk that the resin composition becomes difficult to be impregnated.

[0046] (Fixing portion) The fixing portion 7 fixes the outer peripheral portion of the roughened portion 8 at both ends in the central axis direction of the hollow fiber membrane 3, and fills the gap between the first holding portion 4 and the second holding portion 5 and the hollow fiber membrane 3. In the present embodiment, both ends of the hollow fiber membrane 3 are fixed by the fixing portions 7, respectively, but only one of the ends may be fixed by the fixing portion 7. In the present embodiment, both ends are fixed by the respective fixing portions 7 so that both ends of the hollow fiber membrane 3 are open, but at least one opening of the hollow fiber membrane 3 may be sealed by at least one fixing portion 7.

[0047] The fixing portion 7 is formed of a resin composition mainly composed of a silicone resin. The silicone resin may be a fluorinated silicone resin. The lower limit of the content of the silicone resin in the fixing portion 7 is 50% by mass, preferably 90% by mass, more preferably 95% by mass, and even more preferably 99% by mass. The upper limit of the content of the silicone resin in the fixing portion 7 may be 100% by mass. Further, the resin composition forming the fixing portion 7 may contain resins other than the silicone resin and additives such as lubricants.

[0048] The resin composition constituting the fixing portion 7 is impregnated into at least a part of the roughened portion 8 of the hollow fiber membrane 3. As the lower limit of the average depth of impregnation of the resin composition in the roughened portion 8, 0.3% of the average thickness of the hollow fiber membrane 3 is preferable, 0.5% is more preferable, and 1.0% is even more preferable. On the other hand, as the upper limit of the average depth of impregnation, 3% of the average thickness of the hollow fiber membrane 3 is preferable, 2% is more preferable, and 1.4% is even more preferable. When the average depth of impregnation is less than the lower limit, the adhesion between the hollow fiber membrane 3 and the fixing portion 7 may be insufficient. On the other hand, when the average depth of impregnation exceeds the upper limit, the strength of the hollow fiber membrane 3 may decrease. The "average depth of impregnation" is the average value of the measured values obtained by cutting the impregnated portion of the hollow fiber membrane 3 with a laser in cross-section, observing the cut surface with a scanning electron microscope (SEM), and measuring the impregnation depth at 5 locations.

[0049] As the lower limit of the pulling-out strength of the hollow fiber membrane 3 from the fixing portion 7, for example, 0.2 MPa is preferable, and 0.3 MPa is more preferable. When the pulling-out strength is equal to or higher than the lower limit, it becomes more certain that the hollow fiber membrane 3 is difficult to come off from the fixing portion 7. On the other hand, the greater the pulling-out strength, the better, and it is not particularly limited. For example, it may be 2 MPa, 1 MPa, or 0.5 MPa. The "pulling-out strength" means the tensile strength when the fixing portion and the hollow fiber membrane are pulled with a tensile testing machine and the hollow fiber membrane is pulled out from the fixing portion. The "pulling-out strength" is measured by a tensile testing machine with a chuck interval of 100 mm so that the length (effective length) from the fixing portion 7 in the hollow fiber membrane 3 becomes 100 mm. The fixing portion 7 and the hollow fiber membrane 3 are respectively chucked, pulled in the longitudinal direction at a speed of 100 mm / min, and the tensile strength when the hollow fiber membrane 3 is pulled out from the fixing portion 3 is measured 3 times (3 cases), and it is the average value of the obtained measured values.

[0050] When the hollow fiber membrane 3 has the support layer 3a and the filtration layer 3b as described above, the upper limit of the depth of the impregnation is preferably not more than the maximum thickness of the filtration layer 3b, and more preferably the same as the maximum thickness of the filtration layer 3b. Here, as described above, since the average pore diameter of the support layer 3a is larger than the average pore diameter of the filtration layer 3b, the resin composition constituting the fixing portion 7 is less likely to be impregnated into the filtration layer 3b compared to the support layer 3a. Therefore, when the depth of the impregnation is not more than the average thickness of the filtration layer 3b, it becomes possible to impregnate the resin composition constituting the fixing portion 7 into the filtration portion 3a which is relatively difficult to impregnate, and thus the superiority of the hollow fiber membrane module 1 is enhanced.

[0051] The fixing portion 7 is formed by using a conventionally known method, embedding both end portions of a plurality of hollow fiber membranes 3 in an uncured resin composition mainly composed of a silicone resin, and then curing it.

[0052] <Upper holding member> The first holding portion 4 holds the upper ends of a plurality of hollow fiber membranes 3 fixed by the upper fixing portion 7 in FIG. 2. The first holding portion 4 forms an internal space communicating with the inner cavity of the hollow fiber membrane 3 to be held, and has a drain nozzle 10 for discharging the treated water filtered by the hollow fiber membrane 3 from this internal space. That is, the pump 2 is connected to the drain nozzle 10 of the first holding portion 4.

[0053] <Lower holding member> The second holding portion 5 holds the lower ends of a plurality of hollow fiber membranes 3 fixed by the lower fixing portion 7 in FIG. 2. The second holding portion 5 may form an internal space in the same manner as the first holding portion 4 described above, or may hold the lower ends of the hollow fiber membranes 3 in such a way as to block the openings of the hollow fiber membranes 3. The second holding portion 5 may be a member configured to fold back the hollow fiber membrane 3. That is, in the hollow fiber membrane module 1, the adjacent hollow fiber membranes 3 may have their lower ends folded back.

[0054] 〔Advantages〕 Since at least a part of the outer surface side of the region embedded in the fixing part of the hollow fiber membrane mainly composed of PTFE is impregnated with the resin composition constituting the fixing part, the adhesion between the hollow fiber membrane and the fixing part is enhanced, so it is difficult for the hollow fiber membrane to come off from the fixing part.

[0055] [Other Embodiments] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configuration of the above embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0056] The hollow fiber membrane module is not limited to an immersion type in which the water to be treated permeates to the inner peripheral surface side by negative pressure on the inner peripheral surface side. For example, an external pressure type in which the outer peripheral surface side of the hollow fiber membrane is made high pressure and the water to be treated permeates to the inner peripheral surface side of the hollow fiber membrane, an internal pressure type in which the inner peripheral surface side of the hollow fiber membrane is made high pressure and the water to be treated permeates to the outer peripheral surface side of the hollow fiber membrane, etc. can be of any type.

[0057] The hollow fiber membrane module may be used to filter water to be treated other than water containing activated sludge.

[0058] The wastewater treatment apparatus equipped with the hollow fiber membrane module may further include a water tank for precipitating suspended substances in the water to be treated, a water tank for decomposing organic substances solely by activated sludge, etc., in addition to the treatment water tank in which the hollow fiber membrane module is disposed.

[0059] In the above embodiment, the mode in which the hollow fiber membrane module does not include an outer cylinder and is directly disposed in the treatment water tank of the wastewater treatment apparatus for wastewater treatment has been described. However, for example, the hollow fiber membrane module may include an outer cylinder and may be employed for purified water treatment. As this mode, for example, the hollow fiber membrane module includes an outer cylinder that houses the hollow fiber membrane in a state where one end of the hollow fiber membrane is fixed by the fixing portion and the other end is sealed with a known sealing material, a first cap portion attached to the end of the outer cylinder on the fixing portion side, and a second cap portion attached to the end of the outer cylinder on the side opposite to the fixing portion (sealing side). The second cap portion has an opening for introducing the water to be treated into the inside of the outer cylinder, and the first cap portion is configured to have an opening for leading the treated water to the outside of the outer cylinder. In this configuration, for example, the hollow fiber membrane module is arranged such that the second cap portion is located below and the first cap portion is located above, an introduction pipe for introducing the water to be treated is connected to the opening of the second cap portion, and a lead-out pipe for leading out the treated water is connected to the opening of the first cap portion. Then, the water to be treated is introduced into the inside of the outer cylinder through the second cap from the introduction pipe, the water to be treated introduced into the outer cylinder is treated by passing through the hollow fiber membrane from the outside to the inside, and the treated water is led out from the inside of the hollow fiber membrane through the first cap portion to the lead-out pipe, whereby purified water treatment can be performed. A circulation pipe for circulating the water to be treated that has not passed through the hollow fiber membrane may be connected to the outer cylinder.

Example

[0060] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples.

[0061] [Example 1] As the hollow fiber membrane, a tubular support layer (average outer diameter: 2.3 mm, average inner diameter: 1.1 mm, average pore diameter 2 μm) formed of polytetrafluoroethylene and a tubular filtration layer (average pore diameter: 0.1 μm, average thickness: 15 μm) laminated on the outer peripheral surface of this support layer were prepared. The IPA-BP of the hollow fiber membrane was 140 kPa and the porosity was 80%.

[0062] Both ends of the above hollow fiber membrane were surface-treated (roughening treatment) by immersing them in a metal sodium-naphthalene complex solution (Tetraetch (registered trademark)) for 5 seconds under atmospheric pressure, and then the complex solution was dried to form a roughened portion.

[0063] After embedding the outer peripheral surface of the roughened portion treated as described above in an uncured resin composition mainly composed of a silicone resin, the resin composition was impregnated into the porous interior of the roughened portion while being cured to form a fixing portion.

[0064] Regarding the resin composition mainly composed of the silicone resin impregnated into the formed roughened portion, when the average depth of the impregnated portion was measured by the above-described measurement method, it was 15 μm, and the ratio of the average depth of the impregnated portion to the average thickness of the hollow fiber membrane was 2.5%. The results are shown in Table 1. Further, the results of photographing the outer peripheral surface (before forming the fixing portion) of the end portion treated with the above complex solution in Example 1 with an electron microscope are shown in FIGS. 5 (1000 times) and 6 (5000 times).

[0065] [Comparative Example 1] As shown in Table 1, a hollow fiber membrane module of Comparative Example 1 was produced in the same manner as in Example 1 except that the hollow fiber membrane was not treated with the above complex solution. When the average depth of impregnation was measured in the same manner as in Example 1, it was 0 μm. Further, the results of photographing the outer peripheral surface (before forming the fixing portion) of the end portion not treated with the above complex solution with an electron microscope are shown in FIGS. 7 (1000 times) and 8 (5000 times).

[0066] [Comparative Example 2] As shown in Table 1, a hollow fiber membrane module of Comparative Example 2 was produced in the same manner as in Comparative Example 1 except that polyvinylidene fluoride (PVDF) was used as the main component instead of the hollow fiber membrane mainly composed of PTFE (without immersing it in the above complex solution). When the average depth of impregnation was measured in the same manner as in Example 1, it was 0 μm.

[0067] [Evaluation] [Isopropyl Alcohol Bubble Point] Regarding the hollow fiber membrane obtained in Example 1, the isopropyl alcohol bubble point of the region (non-roughened part) not embedded in the fixing part in the hollow fiber membrane and the isopropyl alcohol bubble point of the region (roughened part) embedded in the fixing part were measured, and the ratio of the isopropyl alcohol bubble point of the roughened part to the non-roughened part was determined.

[0068] [Pull-out test] Regarding the hollow fiber membranes of Example 1, Comparative Example 1, and Comparative Example 2 fixed at the fixing part, the pull-out strength (initial pull-out strength) of the hollow fiber membrane from the fixing part was measured as follows. That is, the hollow fiber membrane and the fixing part were respectively chucked at a chuck interval of 100 mm by an autograph as a tensile testing machine so that the length (effective length) from the fixing part in the hollow fiber membrane was 30 mm, and pulled in the longitudinal direction at a speed of 100 mm / min. The tensile strength when the hollow fiber membrane was pulled out from the fixing part was measured 3 times (3 cases). The average value of the obtained measured values was calculated as the pull-out strength. The results are shown in Table 1.

[0069] Referring to Patent Document 1 as an example of the oxidizing water to be treated, ozone water containing 3 ppm of ozone was used, and the hollow fiber membrane fixed at the fixing part of Example 1 was immersed in the ozone water for 4 weeks, and then the pull-out strength of the hollow fiber membrane from the fixing part was measured in the same manner as above. The results are shown in Table 1.

[0070]

Table 1

[0071] From the comparison between FIGS. 5 and 6 showing the outer peripheral surface of the end portion treated with the complex solution in Example 1 and FIGS. 7 and 8 showing the outer peripheral surface of the end portion not treated with the complex solution in Comparative Example 1, in the roughened part of Example 1, the fibers of the porous structure of the hollow fiber membrane were cut, and it was shown that the voids (pores) were larger compared to the surface of Comparative Example 1. It is clear that the surface of the portion (non-roughened part) not treated with the complex solution in the hollow fiber membrane of Example 1 is the same as the surface shown in FIGS. 7 and 8 of Comparative Example 1.

[0072] As shown in Table 1, Example 1, which was treated with the complex solution and had a roughened portion, was found to have a much greater draw strength of the hollow fiber membrane than Comparative Example 1, which was not treated with the complex solution and had no roughened portion, and Comparative Example 2, which had PVDF as the main component. Also, in Example 1, even after immersion in ozone water for 4 weeks, no significant decrease in the draw degree was observed. Therefore, the oxidation resistance of the hollow fiber membrane module of Example 1 was demonstrated. Although the draw strength after immersion in ozone water for 4 weeks was not confirmed in Comparative Example 1 and Comparative Example 2, since the initial draw strength of Comparative Example 1 and Comparative Example 2 was much smaller than that of Example 1, it is presumed that the draw strength after immersion of Comparative Example 1 and Comparative Example 2 in ozone water for 4 weeks is much smaller than that of Example 1. Note that in the hollow fiber membrane having PVDF as the main component, no roughened portion is formed even when immersed in the complex solution, and it is presumed that the effect of increasing the draw strength by surface treatment of the hollow fiber membrane is specific to the hollow fiber membrane having PTFE as the main component.

[0073] As a result of the above, it was shown that the hollow fiber membrane is difficult to come off from the fixed portion of the hollow fiber membrane module.

Industrial Applicability

[0074] The present invention can be suitably used for wastewater treatment devices, water purification facilities, and the like.

Explanation of Signs

[0075] 1 Hollow fiber membrane module 2 Pump 3 Hollow fiber membrane 3a Support layer 3b Filtration layer 31 First porous structure 32 First fiber 33 First node 34 Second porous structure 35 Second fiber 36 Second node 4 First holding portion 5 Second holding portion 7 Fixed portion 8 Roughening section 10 Drain nozzle T treatment water tank

Claims

1. A plurality of hollow fiber membranes mainly composed of polytetrafluoroethylene, a fixing part in which the ends of the plurality of hollow fiber membranes are embedded, and comprising: the fixing part is composed of a resin composition mainly composed of a silicone resin, the ends of the hollow fiber membranes are roughened, the ratio of the isopropyl alcohol bubble point of the ends to the regions other than the ends in the hollow fiber membranes is 0.4 or more and 0.8 or less, a hollow fiber membrane module in which at least a part of the outer surface side of the region embedded in the fixing part in the hollow fiber membrane is impregnated with the resin composition.

2. the hollow fiber membranes include a porous structure having a plurality of fibers mainly composed of polytetrafluoroethylene and a plurality of nodules connected to each other by these fibers, the hollow fiber membrane module according to claim 1, wherein the fibers in the region embedded in the fixing part are partially cut.

3. The hollow fiber membrane module according to claim 1 or claim 2, wherein an average depth of the portion impregnated with the resin composition in the region embedded in the fixing part is 0.3% or more of an average thickness of the hollow fiber membrane.

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