JP7643125B2 - Hollow fiber membrane, hollow fiber membrane module, wastewater treatment device, and wastewater treatment method - Google Patents

Description

The present invention relates to a hollow fiber membrane, a hollow fiber membrane module, a wastewater treatment device, and a wastewater treatment method.

Industrial wastewater and domestic wastewater are treated to remove organic matter contained in the wastewater, and then either reused as industrial water or discharged into rivers, etc. Typical methods for treating industrial wastewater include activated sludge treatment, in which the water to be treated is aerated and organic matter is decomposed by aerobic microorganisms. Such biological water treatment methods, such as activated sludge treatment, use aerobic microorganisms and denitrifying bacteria to remove nitrate nitrogen. In recent years, treatment has also been carried out using the membrane separation activated sludge (MBR) method, which combines activated sludge treatment with membrane filtration using a separation membrane module.

When using aerobic microorganisms to treat wastewater, it is necessary to aerate the water being treated with air or oxygen in order to maintain the activity of the microorganisms and improve the treatment capacity. Thus, a method using hollow fiber membranes is adopted as a method for efficiently aerating the water being treated. This hollow fiber membrane is used in various fields, such as wastewater treatment, drinking water production, water purification, etc.

Recently, a method has been proposed for treating wastewater using a hollow fiber membrane, in which a microbial layer (biofilm) derived from microorganisms in wastewater is formed on the outer surface of the hollow fiber membrane and wastewater treatment is performed in this state. In a bioreactor that forms a microbial layer on the outer surface of the hollow fiber membrane and supplies oxygen from the inner side of the hollow fiber membrane, a so-called membrane aeration biofilm reactor (MABR), an oxygen gradient is formed in the thickness direction of the microbial layer. As a result, aerobic treatment (BOD oxidation, nitrification of ammonia) progresses on the inner layer side of the microbial layer, while anaerobic treatment of nitrate (BOD oxidation, denitrification) progresses on the outer layer side of the microbial layer, making it possible to remove various pollutants in a single process. Therefore, compared to the conventional membrane separation activated sludge method, in which aerobic treatment and anaerobic treatment are performed in separate treatment tanks, equipment that requires less space can be realized.

In addition, the inclusion of a microbial layer in the MABR increases the oxygen dissolution efficiency compared to conventional systems, which reduces the operating load of the blower that supplies oxygen and reduces the generation of sludge, making it possible to reduce the running costs of the entire facility. Furthermore, the formation of a microbial layer ensures a large membrane surface area for the hollow fiber membrane, making it possible to perform stable treatment even with fluctuations in the inflow load of wastewater. Therefore, the introduction of the MABR is being considered in a wide range of wastewater treatment equipment.
For example, Patent Document 1 discloses a method for increasing the adhesion and retention of a microbial layer by covering the outer surface of a hollow fiber membrane with fibers.

International Publication No. 2014/130043

However, the method described in Patent Document 1 does not necessarily provide a satisfactory adhesion property for the microbial layer.
An object of the present invention is to provide a hollow fiber membrane, a hollow fiber membrane module, a wastewater treatment device, and a wastewater treatment method in which a microbial layer is easily formed.

The present invention has the following aspects.
[1] A hollow fiber membrane for wastewater treatment, in which a microbial layer derived from microorganisms or bacteria in the wastewater is formed on the outer surface during the wastewater treatment,
The hollow fiber membrane comprises a hollow membrane body and a covering fiber,
The covering yarn is wound around the outer surface of the membrane body,
The covering yarn comprises a spun yarn.
[2] The hollow fiber membrane according to [1], wherein the covering yarn is wound 100 times or more per 1 m of the membrane body.
[3] The hollow fiber membrane according to [1] or [2], wherein the covering yarn has a fineness of 0.01 to 30 tex.
[4] The hollow fiber membrane according to any one of [1] to [3], wherein the membrane body has a multilayer structure including one or more porous layers and one or more non-porous layers, and the porous layers are disposed as outermost layers.
[5] The hollow fiber membrane according to [4] above, wherein the porous layer is made of a material containing one or more selected from a polyolefin-based resin, a polyurethane-based resin, and a fluorine-based resin.
[6] The hollow fiber membrane according to [4] or [5], wherein the non-porous layer is made of a material containing one or more selected from a styrene-based resin and a polyolefin-based resin.
[7] A hollow fiber membrane module comprising the hollow fiber membrane according to any one of [1] to [6].
[8] A wastewater treatment device comprising the hollow fiber membrane module according to [7].
[9] A wastewater treatment method for treating wastewater using the hollow fiber membrane module of [7] or the wastewater treatment device of [8], comprising the steps of:
The wastewater treatment method comprises forming the microbial layer derived from microorganisms or bacteria in the wastewater on the outer surface of the hollow fiber membrane, and then supplying an oxygen-containing gas into the hollow portion of the hollow fiber membrane.

The present invention provides a hollow fiber membrane, a hollow fiber membrane module, a wastewater treatment device, and a wastewater treatment method that are easy to form a microbial layer.

FIG. 1 is a partial perspective view showing a multi-layer structure of a hollow fiber membrane for typically explaining one embodiment of the hollow fiber membrane according to the present invention. FIG. 1 is a partial perspective view showing a state in which a microbial layer has been formed on the outer surface of a membrane body and the surface of a covering fiber provided in a hollow fiber membrane, for illustrating one embodiment of the hollow fiber membrane according to the present invention. FIG. 1 is a schematic diagram showing an aerobic treatment region and an anaerobic treatment region in a microbial layer, for illustrating one embodiment of a hollow fiber membrane according to the present invention. FIG. 2 is a partial side view for illustrating a schematic diagram of another embodiment of the hollow fiber membrane according to the present invention. FIG. 2 is a partial side view for illustrating a schematic diagram of another embodiment of the hollow fiber membrane according to the present invention. FIG. 1 is a schematic diagram showing the overall configuration of an apparatus including a wastewater treatment tank, for typically explaining one embodiment of a hollow fiber membrane module, a wastewater treatment apparatus, and a wastewater treatment method according to the present invention. FIG. 2 is a schematic diagram for illustrating another embodiment of the hollow fiber membrane module according to the present invention. FIG. 2 is a diagram illustrating a method for measuring the adhesion amount of a microbial layer.

Hereinafter, an embodiment of the hollow fiber membrane, hollow fiber membrane module, wastewater treatment device, and wastewater treatment method according to the present invention will be described in detail with reference to Figs. 1 to 7 as appropriate.
In addition, in each drawing used in the following description, characteristic parts may be enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may differ from the actual ones. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately changed and implemented within the scope of the present invention.

As shown in Figures 1 to 7, the hollow fiber membrane 1 of this embodiment, the hollow fiber membrane module 10 including this hollow fiber membrane 1, the wastewater treatment device 100 including a plurality of these hollow fiber membrane modules 10, and the wastewater treatment method using the hollow fiber membrane module 10 or the wastewater treatment device 100 are used for treatment (wastewater treatment) to remove organic matter and the like contained in industrial wastewater, domestic wastewater, etc.

[Hollow fiber membrane]
Hereinafter, one embodiment of the hollow fiber membrane of the present invention will be described in detail.
As shown in Figs. 1 and 2, the hollow fiber membrane 1 of this embodiment has a microbial layer 6 derived from microorganisms or bacteria in the wastewater formed on its outer surface during wastewater treatment.
The hollow fiber membrane 1 in the illustrated example comprises a hollow membrane body 7 and a covering yarn 8 wound around the outer surface of the membrane body 7 .

<Membrane body>
The membrane body 7 in the illustrated example has a multi-layer structure including two porous layers 2 and 4 and one non-porous layer 3, with the porous layer 4 disposed as the outermost layer. In the illustrated example, it has a three-layer structure in which the non-porous layer 3 is disposed between the two porous layers 2 and 4. In the following specification, the porous layer 2 disposed as the innermost layer is also referred to as the "first porous layer 2," and the porous layer 4 disposed as the outermost layer is also referred to as the "second porous layer 4."

The membrane body 7 in the illustrated example has a hollow portion 5 on the inner surface 2b side (the surface opposite to the side in contact with the non-porous layer 3) of the first porous layer 2, which is the innermost layer. By supplying oxygen to this hollow portion 5, oxygen can be transmitted from the inner surface 2b side toward the surface 4a of the second porous layer 4 on the outer layer side.

(Porous Layer)
In the membrane body 7 of this embodiment, the two porous layers, the first porous layer 2 and the second porous layer 4, are concentrically arranged via the non-porous layer 3. Although not shown in the figure, the first porous layer 2 and the second porous layer 4 are each composed of a membrane having a plurality of pores, and the pores are formed over the entire circumference of these porous layers 2, 4.

In this embodiment, the pores formed in the first porous layer 2 and the second porous layer 4 refer to holes that communicate at least from the inner surface side to the outer surface. For example, as shown in Fig. 3, in the first porous layer 2, the pores refer to holes that communicate from the inner surface 2b side to the outer surface (the surface in contact with the non-porous layer 3) 2a side, and in the second porous layer 4, the pores refer to holes that communicate from the inner surface (the surface in contact with the non-porous layer 3) 4b side to the surface 4a side.
Furthermore, the "pores" described in this embodiment refer to the gaps in the membrane substrate that form a three-dimensional structure, and refer to the portions that serve as paths through which oxygen passes when it permeates from the inner surface side to the surface (outer surface) side.

The porous layers 2 and 4 are formed, for example, by the melt-drawing method. In the melt-drawing method, the resin that is to be the material for the porous layers is first heated to a fluid state above its melting point and then extruded into a cylindrical shape. The extruded resin in a fluid state is then cooled to make it non-fluid and fix the shape. The resin with the fixed shape is then stretched under optimal conditions to form the porous structure.

The porous layers 2, 4 are preferably made of a material containing one or more selected from polyolefin resins, polyurethane resins, and fluorine resins, for example, from the viewpoint of further increasing oxygen permeability. By making the porous layers from a material containing one or more of the above resins, it becomes possible to form the porous structure as described above while controlling it, and oxygen permeability is further increased, and oxidation resistance, chemical resistance, heat resistance, and mechanical durability can be imparted. In addition, solubility in a solvent when preparing the film-forming solution is also improved.
The first porous layer 2 and the second porous layer 4 may be made of the same material or different materials. In particular, the first porous layer 2 and the second porous layer 4 are preferably made of a material containing a polyolefin resin.

The thickness of each of the first porous layer 2 and the second porous layer 4 is preferably such that the total thickness of the entire porous layer, i.e., the average thickness Dp of the total of the first porous layer 2 and the second porous layer 4 in the illustrated example, is 10 to 100 μm. If the average thickness Dp of the total of the porous layers is 10 μm or more, this contributes to ensuring sufficient mechanical strength in the entire hollow fiber membrane 1. On the other hand, if the average thickness Dp of the total of the porous layers is 100 μm or less, the outer diameter of the membrane does not become larger than necessary, and therefore it is possible to prevent the membrane packing amount from becoming small when the hollow fiber membrane 1 is modularized.
From the above viewpoint, the average total thickness Dp of all the porous layers is more preferably 15 to 90 μm, and further preferably 20 to 80 μm.

The average thickness of the porous layers 2 and 4 was determined by observing the cross section of the hollow fiber membrane with a scanning electron microscope (SEM), analyzing the image, measuring the thickness of the porous layers 2 and 4 at multiple locations (5 locations), and calculating the average value.

In the membrane body 7 of this embodiment, a porous layer is disposed in the outermost layer. In this way, by disposing a porous layer in the outermost layer, sufficient oxygen permeability can be ensured.

The average pore diameter of the pores formed in the porous layers 2 and 4 is preferably 0.01 to 5 μm. If the average pore diameter of the pores in the porous layers 2 and 4 is 0.01 μm or more, they are unlikely to act as a resistance that affects oxygen permeation. Furthermore, if the average pore diameter of the pores in the porous layers 2 and 4 is 5 μm or less, sufficient membrane strength can be obtained.
From the above viewpoint, the average pore size of the pores in the porous layers 2 and 4 is more preferably 0.03 to 4 μm, and further preferably 0.05 to 3 μm.

The average pore diameter of the multiple pores formed in the porous layers 2 and 4 was determined by observing the outer surface of the porous layers using a SEM, randomly selecting 30 pores, measuring the longest diameter of each pore, and averaging the longest diameters of these 30 pores.

(Non-porous layer)
In the membrane body 7 of the present embodiment, the non-porous layer 3 is provided as a single layer between the first porous layer 2 and the second porous layer 4 .

The non-porous layer 3 is preferably made of a material containing one or more selected from, for example, a styrene-based resin and a polyolefin-based resin. By making the non-porous layer 3 out of a material containing one or more of the above resins, it is possible to further increase the mechanical strength of the entire hollow fiber membrane 1 while ensuring sufficient oxygen permeability. Among the above resins, it is more preferable that the non-porous layer 3 be made of a material containing a styrene-based resin from the viewpoint of further increasing oxygen permeability.

The styrene-based resin is a polymer obtained by polymerizing a styrene-based monomer, or a polymer obtained by polymerizing a styrene-based monomer and another monomer.
Examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 1,3-dimethylstyrene, vinylnaphthalene, and vinylanthracene.
Examples of other monomers include maleic anhydride, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, and acrylonitrile.

The styrene resin preferably contains 50 to 100% by mass of styrene monomer units relative to the total mass of the monomer units constituting the styrene resin, more preferably 70 to 100% by mass, and even more preferably 90 to 100% by mass. In particular, the styrene resin preferably contains 50 to 100% by mass of styrene units relative to the total mass of the monomer units constituting the styrene resin, more preferably 70 to 100% by mass, and even more preferably 90 to 100% by mass.

The average thickness of the non-porous layer 3 is preferably 0.3 to 10 μm. If the average thickness of the non-porous layer 3 is 0.3 μm or more, no defects are generated during manufacturing, and stable production becomes possible. Furthermore, if the average thickness of the non-porous layer 3 is 10 μm or less, a decrease in oxygen permeability that would affect practical use can be suppressed.
From the above viewpoints, the average thickness of the non-porous layer 3 is more preferably from 0.5 to 8 μm, and further preferably from 1 to 6 μm.

The average thickness of the non-porous layer 3 was determined by observing the cross section of the hollow fiber membrane with a scanning electron microscope (SEM), analyzing the image, measuring the thickness of the non-porous layer 3 at multiple locations (five or more), and calculating the average value.

As shown in FIG. 3, it is preferable that the total average thickness Dn of the non-porous layer 3, i.e., the average thickness Dn of the non-porous layer 3 formed as a single layer, and the total average thickness Dp of the porous layers 2 and 4, i.e., the total average thickness Dp of the first porous layer 2 and the second porous layer 4, satisfy the relationship expressed by the following equation: {0.005≦Dn/Dp≦1.0}.
When the relationship between the average thickness Dn of the non-porous layer 3 and the average thickness Dp of the porous layers 2 and 4 satisfies the relationship expressed by the above formula, the ratio of the thickness of the non-porous layer 3 to the total thickness of the porous layers 2 and 4 and the non-porous layer 3 becomes small. Therefore, the non-porous layer can be made thinner while ensuring sufficient mechanical strength suitable for practical use, thereby further improving oxygen permeability.
From the above viewpoint, the relationship between the total average film thickness Dn of the non-porous layer 3 and the total average film thickness Dp of the porous layers 2 and 4 is preferably expressed by the following formula: {0.007≦Dn/Dp≦0.9}, and more preferably expressed by the following formula: {0.01≦Dn/Dp≦0.8}.

(Outer shape and average outer diameter D of the membrane body)
The outer shape of the membrane body 7 is not particularly limited, but may be, for example, substantially cylindrical.
Here, the term "approximately cylindrical" as used in this embodiment refers to a three-dimensional shape in which the shape of any cross section perpendicular to the longitudinal direction is, for example, a perfect circle, egg, oval, ellipse, or other oval shape.

When a non-porous layer 3 is disposed between the first porous layer 2 and the second porous layer 4 as shown in Figures 1 to 3, the area consisting of the porous layers 2 and 4 and the area consisting of the non-porous layer 3 may slightly intersect at the interface between them.

The outer diameter of the membrane body 7 is not particularly limited, but the average outer diameter D is preferably 0.01 to 3.0 mm. By making the average outer diameter D of the membrane body 7 3.0 mm or less, it is possible to prevent the membrane packing amount from becoming small when forming a membrane module. Furthermore, by making the average outer diameter D of the membrane body 7 0.01 mm or more, it is possible to ensure a sufficient inner diameter of the hollow portion 5, thereby reducing the effect of a decrease in the flow rate of oxygen flowing through the hollow portion 5 due to pressure loss, etc.
Furthermore, it is more preferable that the average outer diameter D of the membrane body 7 is a dimension that ensures a surface area sufficient to prevent the microbial layer 6 formed on the surface 4a of the second porous layer 4 and the surface of the covering yarn 8 from peeling off.

The "average outer diameter D of the membrane body 7" described in this embodiment means the diameter of the smallest circle that inscribes the outer edge of the cut surface when the membrane body 7 before the covering thread 8 is wound is cut on any plane perpendicular to the longitudinal direction. The average outer diameter D of the membrane body 7 can be calculated by measuring any three or more and ten or less points on the cut surface and averaging the measurements.

<Covering yarn>
The covering yarn 8 includes a spun yarn, and is wound around the outer surface of the membrane body 7 (the surface 4a of the second porous layer 4 in this embodiment).
Since the covering yarn 8 including the spun yarn is wound around the outer surface of the membrane body 7, the microbial layer 6 adheres to the covering yarn 8 so as to be aligned therewith, and the microbial layer 6 is easily formed in a short period of time. In addition, the retention of the microbial layer 6 is also improved.
As the wastewater treatment progresses, the microbial layer 6 swells, and it is therefore necessary to periodically peel off the microbial layer 6. Since the covering yarn 8 including the spun yarn is wound around the outer surface of the membrane body 7, the microbial layer 6 that has been peeled off once reattaches to the covering yarn 8 in a short time.

Examples of spun yarns include natural fibers such as wool, silk, cotton, and hemp, regenerated fibers such as rayon, cupra, and refined cellulose fibers, semi-synthetic fibers such as acetate fibers and promix fibers, and synthetic fibers such as nylon fibers, polyethylene terephthalate (PET) fibers, acrylic fibers, aramid fibers, and polyolefin fibers (e.g., polyethylene fibers, polypropylene fibers, etc.). Among these, polyethylene terephthalate (PET) fibers and acrylic fibers are preferred from the viewpoint of cost.
These spun yarns may be used alone or in combination of two or more kinds, that is, in a blended form.

The ratio of the spun yarn to the total mass of the covering yarn 8 is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, and particularly preferably 100% by mass. If the ratio of the spun yarn is 20% by mass or more, the microbial layer 6 is formed in a shorter period of time.

The covering yarn 8 may contain yarns other than spun yarns (hereinafter also referred to as "other yarns") as long as the effects of the present invention are not impaired.
Other yarns include filament yarns.
The ratio of the other yarns to the total mass of the covering yarn 8 is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably does not substantially contain other yarns. Here, "substantially does not contain" means that other yarns are not intentionally blended, except for those that are unintentionally contained.

The fineness of the covering yarn 8 is preferably 0.01 to 30 tex, more preferably 0.05 to 25 tex, and even more preferably 0.05 to 20 tex. If the fineness of the covering yarn 8 is 0.01 tex or more, sufficient mechanical strength of the covering yarn can be ensured. Furthermore, if the fineness of the covering yarn 8 is 30 tex or less, it is possible to prevent the membrane filling amount from becoming small when the hollow fiber membrane 1 is modularized.

The covering thread 8 in the illustrated example is wound helically around the outer surface of the membrane body 7 .
The covering yarn 8 is preferably wound 50 times or more per meter of the membrane body 7, more preferably 100 times or more, even more preferably 200 times or more, and particularly preferably 300 times or more. If the number of windings of the covering yarn 8 per meter of the membrane body 7 is 50 times or more, the amount of the microbial layer 6 attached thereto is further increased.
The amount of the microbial layer 6 attached tends to increase as the number of windings increases, but if the number of windings increases too much, the effect will plateau. Therefore, the number of windings of the covering yarn 8 per meter of the membrane body 7 is preferably 800 times or less, more preferably 600 times or less, and even more preferably 500 times or less.

The covering yarn 8 is preferably evenly wound around the membrane body 7 from one end to the other. The winding interval (pitch) P is preferably 1 to 20 mm, more preferably 1 to 10 mm, even more preferably 2 to 8 mm, and particularly preferably 3 to 5 mm. If the winding interval (pitch) P is within the above range, an excellent balance between the amount of adhesion of the microbial layer 6 and the oxygen permeability of the membrane body 7 is achieved.

<Microbial layer>
For example, when the hollow fiber membrane 1 is used as a hollow fiber membrane module described later for wastewater treatment, activated sludge already used in another wastewater treatment plant or the like is used as a seed to grow microorganisms or bacteria, and the hollow fiber membrane module is immersed in the solution at a predetermined concentration, whereby the microbial layer 6 is formed on the outer surface of the hollow fiber membrane 1, originating from the microorganisms or bacteria. In the case of this embodiment, the microbial layer 6 is formed along the covering yarn 8. The microbial layer 6 formed along the covering yarn 8 swells as the wastewater treatment progresses, and appears as if it were formed on the outer surface of the hollow fiber membrane 1.

The activated sludge mentioned above has various component compositions and ratios depending on the type of wastewater, but it is possible to use activated sludge that has multiplied by feeding on the BOD (organic matter) components and nutrients (nitrogen, phosphorus, etc.) contained in the wastewater. Then, a microbial layer 6 is formed along the covering thread 8 as a layer derived from the microorganisms and bacteria contained in it.

Figure 3 is a schematic diagram showing the aerobic treatment area and the anaerobic treatment area in the microbial layer 6 (see also Figure 2). As shown in Figure 3, in the hollow fiber membrane 1 of this embodiment, by forming the above-mentioned microbial layer 6, oxygen that has permeated from the hollow part 5 of the hollow fiber membrane 1 through the first porous layer 2, the non-porous layer 3, and the second porous layer 4 in order is dissolved and diffused in the microbial layer 6, forming an oxygen gradient (concentration) in the thickness direction of the microbial layer 6, and the inner layer side is in an oxygen-rich aerobic state, while the outer layer side is in an oxygen-reduced anaerobic state. As a result, the microbial layer 6 is in a state in which an aerobic treatment area 6A is formed on the inner layer side and an anaerobic treatment area 6B is formed on the outer layer side.

In the aerobic treatment area 6A, the ammonia contained in the wastewater is oxidized to nitrate through aerobic treatment (BOD oxidation). Furthermore, in the anaerobic treatment area 6B, the nitrate produced in the aerobic treatment area 6A is converted to nitrogen by anaerobic bacteria through anaerobic treatment (BOD oxidation), and is denitrified. This allows both aerobic and anaerobic treatment to be carried out in a single process, which allows for space-saving equipment and improved treatment efficiency compared to the conventional system in which aerobic and anaerobic treatment were carried out in separate treatment tanks.

The thickness of the microbial layer 6 is not particularly limited, and when it reaches a certain thickness or a certain treatment time, operations such as air bubbling cleaning can be performed to adjust the thickness to a thickness that allows optimal aerobic and anaerobic treatment.

<Method of manufacturing hollow fiber membrane>
Hereinafter, one embodiment of a method for producing the hollow fiber membrane 1 will be described.
The method for producing the hollow fiber membrane 1 of this embodiment includes a spinning step, a stretching step, and a winding step. It is preferable to include an annealing step between the spinning step and the stretching step.

(Spinning process)
The spinning step is a step in which a molten resin is spun to obtain a hollow fiber membrane precursor.
As shown in the figure, when manufacturing a three-layered membrane body 7 in which one non-porous layer 3 is sandwiched between two porous layers 2 and 4, a composite nozzle die in which an innermost layer nozzle part, a middle layer nozzle part, and an outermost layer nozzle part are arranged concentrically is used to perform the spinning process. Specifically, the material for forming the first porous layer 2 is supplied in a molten state to the innermost layer nozzle part. The material for forming the non-porous layer 3 is supplied in a molten state to the middle layer nozzle part. The material for forming the second porous layer 4 is supplied in a molten state to the outermost layer nozzle part. Next, each material is extruded from each nozzle part and wound up.
The discharge temperature when each material is extruded may be any temperature at which each material is sufficiently melted and can be spun.
The extrusion speed and winding speed are appropriately adjusted, and the unstretched non-porous layer precursor is cooled and solidified to obtain a hollow fiber membrane precursor. The hollow fiber membrane precursor has a three-layer structure in which one unstretched non-porous layer precursor is sandwiched between two porous layer precursors in a non-porous state.

(Annealing process)
The annealing step is a step of annealing (fixed length heat treatment) the hollow fiber membrane precursor obtained in the spinning step.
The hollow fiber membrane precursor obtained in the spinning step is preferably subjected to a fixed length heat treatment (annealing treatment) at a temperature equal to or lower than the melting point of each material before the stretching step. When polyethylene is used as the material for forming the porous layers 2, 4, the fixed length heat treatment is preferably performed at 105 to 130°C for 8 to 16 hours. If the temperature of the fixed length heat treatment is 105°C or higher, a hollow fiber membrane 1 with good quality is likely to be obtained. If the temperature of the fixed length heat treatment is 130°C or lower, sufficient elongation is likely to be obtained, stability during stretching is improved, and stretching at a high ratio is facilitated. In addition, if the treatment time is 8 hours or more, a hollow fiber membrane 1 with good quality is likely to be obtained.

(Stretching process)
The stretching step is a step in which the hollow fiber membrane precursor obtained in the spinning step or the annealed hollow fiber membrane precursor is stretched to obtain the membrane body 7 .
In the stretching step, it is preferable to stretch the hollow fiber membrane precursor obtained in the spinning step or the annealed hollow fiber membrane precursor at a stretching temperature T that is equal to or lower than the Vicat softening point of the material forming the porous layers 2, 4. If the stretching temperature T is equal to or lower than the Vicat softening point of the material forming the porous layers 2, 4, the pore size of the membrane body 7 can be enlarged. If the stretching temperature T exceeds the Vicat softening point, the crystalline lamellar structure becomes easily broken, and conversely, the porous portion that was once opened may become blocked.

In the stretching step, it is preferable to carry out the above-mentioned annealing step as necessary and then cold stretching before stretching (hot stretching) at a stretching temperature T. Specifically, it is preferable to carry out two-stage stretching in which cold stretching is followed by hot stretching, or multi-stage stretching in which cold stretching is followed by hot stretching divided into two or more stages.
Cold stretching is a stretching method that causes destruction of the membrane structure and generates micro cracks at a relatively low temperature. The cold stretching temperature is preferably within a range from 0° C. to a temperature lower than the Vicat softening point −20° C.

The stretching ratio can be set appropriately depending on the material forming the non-porous layer 3 and the material forming the porous layers 2 and 4, but it is preferable to set the final ratio (total stretching ratio) for the unstretched hollow fiber membrane precursor to 2 to 5 times. If the total stretching ratio is 2 times or more, the porosity of the porous layers 2 and 4 is likely to be high, and excellent oxygen permeability is likely to be obtained. If the total stretching ratio is 5 times or less, the breaking elongation of the hollow fiber membrane 1 is likely to be high.

In order to improve the dimensional stability of the hollow fiber membrane, it is preferable to perform relaxation heat setting on the membrane body 7 after stretching while the membrane body 7 is in a fixed length state or in a state where it is slightly relaxed within a range of 70% or less of the fixed length. To perform the relaxation heat setting effectively, the relaxation heat setting temperature is preferably equal to or higher than the stretching temperature T. In addition, the relaxation heat setting temperature is preferably equal to or lower than the melting point of the lower of the material forming the non-porous layer 3 and the material forming the porous layers 2 and 4.

(Winding process)
The winding step is a step of winding the covering yarn 8 around the outer surface of the membrane body 7 to obtain the hollow fiber membrane 1 .
The method of winding the covering thread 8 on the outer surface of the membrane body 7 is not particularly limited, but it is preferable to, for example, fix the beginning of the winding of the covering thread 8 to the outer surface of the membrane body 7 using an adhesive, wind the covering thread 8 spirally on the outer surface of the membrane body 7 at a predetermined number of times or pitch, and then fix the end of the winding of the covering thread 8 to the outer surface of the membrane body 7 using an adhesive.
The adhesive may be, for example, a urethane resin or an epoxy resin.

<Action and effect>
As described above, in the hollow fiber membrane 1 of this embodiment, the covering yarn 8 is wound around the outer surface of the membrane body 7, so that the microbial layer 6 adheres along the covering yarn 8, and the microbial layer 6 is formed in a short period of time. In addition, the retention of the microbial layer 6 is also improved. Oxygen is effectively diffused and dissolved in the thickness direction of the microbial layer 6, and further, an aerobic treatment region 6A rich in oxygen and an anaerobic treatment region 6B little in oxygen are formed, so that aerobic treatment and anaerobic treatment can be performed in a single process.
Furthermore, even if the enlarged microbial layer 6 is peeled off, the microbial layer 6 reattaches along the covering thread 8 in a short period of time.
Furthermore, since the hollow fiber membrane 1 of this embodiment adopts a multilayer structure including the porous layers 2, 4 and the non-porous layer 3, it is possible to achieve both high oxygen permeability due to the porous layers 2, 4 and high membrane strength due to the non-porous layer 3, thereby obtaining excellent water treatment efficiency and mechanical properties.

<Other embodiments>
The hollow fiber membrane of the present invention is not limited to the above.
For example, the membrane body may include one porous layer, or may include three or more porous layers, although in either case, it is preferable that the porous layer is disposed as the outermost layer.
The membrane body may also include two or more non-porous layers.
Furthermore, the hollow fiber membrane may include layers other than the porous layer, the non-porous layer, and the microbial layer. When adopting a configuration including other layers, it is preferable that the other layers have high oxygen permeability from the viewpoint of further increasing the oxygen permeability of the entire hollow fiber membrane.

In addition, in the hollow fiber membrane described above, one covering thread is wound around the outer surface of one membrane body, but for example, as in the hollow fiber membrane 1A shown in Figure 4, a covering thread 8 may be wound around the outer surface of a membrane bundle 9 in which multiple membrane bodies 7 are bundled together.

Also, for example, as in the hollow fiber membrane 1B shown in Fig. 5, two or more covering yarns 8 may be wound around the outer surface of the membrane body 7. In the hollow fiber membrane 1B shown in Fig. 5, two covering yarns 8 are wound in a spiral shape around the outer surface of a membrane bundle 9 in which a plurality of membrane bodies 7 are bundled together, so as to cross each other. Note that, in the hollow fiber membrane 1B shown in Fig. 5, two or more covering yarns 8 may be wound around the outer surface of one membrane body 7.
When two or more covering yarns 8 are wound around the outer surface of the membrane body 7, the covering yarns 8 may be of the same type or different types. Also, a spun yarn may be used as at least one covering yarn 8, and other yarns may be used as the remaining covering yarns 8.

[Hollow fiber membrane module and wastewater treatment device]
The hollow fiber membrane module 10 of this embodiment shown in FIG. 6 includes the hollow fiber membrane 1 of this embodiment.
The wastewater treatment device 100 of this embodiment is configured to include a hollow fiber membrane module 10 .
The hollow fiber membrane module 10 and the wastewater treatment device 100 of this embodiment will be described in detail below.

<Hollow fiber membrane module>
As shown in FIG. 6, the hollow fiber membrane module 10 of this embodiment is generally composed of a housing 12 (an upper housing 12A and a lower housing 12B) and a hollow fiber membrane sheet 11 in which a plurality of hollow fiber membranes 1 are formed into a sheet shape.

The hollow fiber membrane sheet 11 is formed by bundling together a plurality of hollow fiber membranes 1 according to the present embodiment as described above. Both ends of the hollow fiber membrane sheet 11 are inserted into the housing 12, the details of which will be described later, and are open, and the hollow fiber membrane sheet 11 is configured as a flat sheet overall.

The housing 12 is a substantially hollow member into which both ends of the hollow fiber membrane sheet 11 are inserted and fixed, and in the illustrated example, is composed of an upper housing 12A and a lower housing 12B. That is, the hollow fiber membrane sheet 11 is held in a sheet-like form between the upper housing 12A and the lower housing 12B.
In the illustrated example, a gas supply line 120 is connected to the upper housing 12A so that oxygen or air is supplied to the inside of the upper housing 12A.

The hollow fiber membrane module 10 is configured such that oxygen or air supplied from a blower (not shown) is sent through the housing 12 into the hollow portions of the multiple hollow fiber membranes 1, and as shown in Figures 2 and 3, for example, the oxygen or air permeates the first porous layer 2, the non-porous layer 3, and the second porous layer 4, and is further dissolved and diffused in the microbial layer 6 in the membrane thickness direction.

Although not shown in FIG. 6, it is more preferable to provide a pair of supports made of rod-shaped members or the like between the upper housing 12A and the lower housing 12B so as to connect both ends of the upper housing 12A and the lower housing 12B. By providing such a pair of supports and maintaining a constant distance between the upper housing 12A and the lower housing 12B, the surface shape of the hollow fiber membrane sheet 11 can be maintained to form a flat hollow fiber membrane module 10.

In addition, in the illustrated example, the hollow fiber membrane module 10 is shown in the form of a flat sheet, but this is not limited to this, and for example, the hollow fiber membrane module can also be configured in a cylindrical or rectangular tube shape, etc.

Also, for example, as in the hollow fiber membrane module 10A shown in FIG. 7, both ends of the plurality of hollow fiber membranes 1A or the plurality of hollow fiber membranes 1B may be inserted into and fixed in the housing 12 (upper housing 12A and lower housing 12B).

<Wastewater treatment equipment>
The wastewater treatment device 100 of this embodiment is generally configured to include the hollow fiber membrane module 10 of this embodiment in the form of a single unit or a plurality of units. The wastewater treatment device 100 of the illustrated example is configured such that the hollow fiber membrane module 10 is accommodated inside a treatment tank 110.
An assembly of multiple hollow fiber membrane modules is also called a "hollow fiber membrane module unit."

The treatment tank 110 contains wastewater W, which is the water to be treated. As the treatment tank 110, any tank that has been conventionally used in this field, such as a large metal container-shaped treatment tank, can be used without any restrictions. In addition, although detailed illustration is omitted in FIG. 6, the treatment tank 110 is connected to a wastewater inlet pipe for containing the wastewater, which is the water to be treated, and a discharge pipe for discharging the treated water out of the tank after treatment is completed.

A hollow fiber membrane module 10 is accommodated in the treatment tank 110, and the hollow fiber membrane module 10 is arranged so as to be immersed in the wastewater W. The hollow fiber membrane module 10 is preferably accommodated in the treatment tank 110 so that the longitudinal direction of the hollow fiber membrane 1 is vertical. If the hollow fiber membrane module 10 is accommodated in the treatment tank 110 so that the longitudinal direction of the hollow fiber membrane 1 is vertical, condensed water (water condensed as water in the membrane from moisture contained in oxygen, air, etc., and moisture in the wastewater) is less likely to accumulate inside the hollow fiber membrane 1, and the wastewater treatment capacity can be maintained better.
As described above, the gas supply line 120 is connected to the upper housing 12A of the hollow fiber membrane module 10, and oxygen, air, or a gas whose component ratio has been changed by a process of separating or concentrating air is supplied.

With the above configuration, the wastewater treatment device 100 of this embodiment can simultaneously carry out aerobic and anaerobic treatments on the wastewater W in the treatment tank 110 using the hollow fiber membranes 1 that make up the hollow fiber membrane module 10, and can treat the wastewater in a single process. This allows the device to be made smaller and more space-saving than conventional devices in which aerobic and anaerobic treatments are carried out in separate treatment tanks.

In the treatment tank 110, the hollow fiber membrane module 10 may be housed from the opening 111 side of the treatment tank 110 by, for example, a frame member (not shown) or the like that is arranged so as not to interfere with the flow of the wastewater W. In this case, one end of the frame member may be fixed near the opening 111 of the treatment tank 110, and the upper housing 12A provided on the hollow fiber membrane module 10 may be fixed to the other end of the frame member.
Moreover, instead of the hollow fiber membrane module 10, a hollow fiber membrane module 10A shown in FIG.

<Action and effect>
The hollow fiber membrane module 10 of this embodiment includes the hollow fiber membrane 1 of the present invention described above, and thus, similarly to the above, the microbial layer 6 is easily formed. In addition, high oxygen permeability due to the porous layer and high membrane strength due to the non-porous layer can be achieved at the same time, and excellent water treatment efficiency and mechanical properties can be obtained, and aerobic treatment and anaerobic treatment can be performed in a single process. Moreover, it is possible to make the module even more compact and energy-efficient than conventional MABRs.

The wastewater treatment device 100 of this embodiment is equipped with the hollow fiber membrane module 10 of the present invention described above, and thus, as described above, the microbial layer 6 is easily formed. In addition, excellent water treatment efficiency and mechanical properties are obtained, and both aerobic treatment and anaerobic treatment, which were previously performed in separate devices, can be performed in the microbial layer alone, resulting in space saving. Furthermore, since the entire device can be made smaller according to the present invention, a wastewater treatment device 100 can be provided that is extremely suitable for applications requiring simple wastewater treatment or applications requiring wastewater treatment in a small space, for example.

[Wastewater treatment method]
The wastewater treatment method of the present embodiment is a method of treating wastewater using a hollow fiber membrane module 10 of the present embodiment or a wastewater treatment device 100 of the present embodiment as shown in FIG.

Specifically, in the wastewater treatment method of this embodiment, first, wastewater W, which is the water to be treated, is introduced into the treatment tank 110. At this time, the treatment tank 110 is filled with wastewater W so that the hollow fiber membrane module 10 arranged in the treatment tank 110 is immersed in the wastewater W.

Next, oxygen or air is supplied to the hollow fiber membrane module 10 from a blower (not shown) via a gas supply line 120, so that oxygen or air is transmitted from the hollow portion 5 of the hollow fiber membrane 1 to the first porous layer 2, the non-porous layer 3, and the second porous layer 4, as shown in Figs. 2 and 3, for example. In this embodiment, in such an initial stage of wastewater treatment, microorganisms, bacteria, etc. present in the wastewater W are attached along the covering yarn 8, and a microbial layer 6 derived from them is formed.

Thereafter, by continuing to supply oxygen or air to the hollow fiber membrane module 10, the dissolution and diffusion of oxygen in the thickness direction of the microbial layer 6 proceeds as described above, and an aerobic treatment area 6A and an anaerobic treatment area 6B are formed as shown in FIG. 3.

Then, in the aerobic treatment area 6A, ammonia contained in the wastewater is converted to nitrate through aerobic treatment. In addition, in the anaerobic treatment area 6B, the nitrate produced in the aerobic treatment area 6A is converted to nitrogen through anaerobic treatment, and is denitrified. In this way, by carrying out both aerobic treatment and anaerobic treatment in a single process, treatment efficiency is improved compared to when these are carried out in separate treatment tanks.

Next, after carrying out the above biological treatment for a predetermined period of time, the microbial layer 6 is detached from the hollow fiber membrane 1, for example, by a bubbling process using an air diffuser (not shown) arranged below the hollow fiber membrane module 10.
Thereafter, sludge containing the detached microbial layer is collected by using a solid-liquid separation method using a separation membrane (not shown) or the like, completing the wastewater treatment.

The pressure of the gas (oxygen or air) supplied from the inner surface 2b side of the first porous layer 2, i.e., the hollow portion 5, is not particularly limited, but is preferably 200 kPa or less. If the gas pressure is 200 kPa or less, it is possible to prevent oversupply of gas that does not contribute to the wastewater treatment effect, and to prevent damage to components due to this oversupply. The lower limit of the gas pressure may be, for example, 5 kPa or more, from the viewpoint of obtaining a wastewater treatment effect sufficient for practical use.

The oxygen-containing gas supplied to the hollow fiber membrane module 10 is preferably, for example, pure oxygen. In this way, by supplying highly pure oxygen to the hollow fiber membrane module 10, the concentration of oxygen dissolved and diffused in the microbial layer 6 becomes sufficient, allowing the above-mentioned aerobic and anaerobic treatments to proceed efficiently, enabling more effective wastewater treatment.

When supplying air containing oxygen to the hollow fiber membrane module 10, this air may be air from the atmosphere. In this way, using air from the atmosphere for wastewater treatment has the advantage of reducing running costs compared to using oxygen.

Furthermore, the oxygen-containing gas supplied to the hollow fiber membrane module 10 may be, for example, atmospheric air with a changed component ratio, which has been subjected to a process of separating or concentrating the air. In this way, when atmospheric air with a changed component ratio is used for wastewater treatment, as described above, the running costs are reduced compared to the case where oxygen is used, and treatment can be performed in accordance with the characteristics of the wastewater to be treated.

Also, an aeration device (not shown) may be disposed below the hollow fiber membrane module 10, and a gas containing a high concentration of nitrogen (high-nitrogen concentration gas) may be supplied from the aeration device to aerate the wastewater W. Bubbles of the high-nitrogen concentration gas come into contact with the microbial layer 6 formed on the outer surface of the hollow fiber membrane 1, further reducing the oxygen concentration in the anaerobic treatment area 6B. This makes the anaerobic treatment area 6B more anaerobic. In addition, the wastewater W is agitated by the bubbles generated from the aeration device, and the wastewater W becomes an anaerobic environment overall, so that anaerobic bacteria become predominant in the microbial flora of the flocs floating in the wastewater W.
Moreover, instead of the hollow fiber membrane module 10, a hollow fiber membrane module 10A shown in FIG. 7 may be used to treat wastewater.

<Action and effect>
According to the wastewater treatment method of this embodiment, a method is adopted in which the hollow fiber membrane module 10 or wastewater treatment device 100 of the present invention described above is used to form a microbial layer 6 on the outer surface of the hollow fiber membrane 1, and then an oxygen-containing gas is supplied from the hollow portion 5 on the inner surface 2b side of the hollow fiber membrane 1 to treat the wastewater W. As a result, as with the above, both aerobic treatment and anaerobic treatment, which have conventionally been performed in separate processes, can be performed in one process, resulting in excellent treatment efficiency and enabling the device to be made smaller.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
The various measurements are as follows:

[Measurement method]
<Measurement of Average Thickness of Porous Layer and Non-Porous Layer>
The cross section of the hollow fiber membrane was observed with a scanning electron microscope (SEM), and the image was analyzed to measure the thickness of the porous layer and the non-porous layer at five points, and the average values were calculated.

<Measurement of the average pore size of the pores in the porous layer>
The outer surface portion of the porous layer was observed using an SEM, 30 pores were randomly selected, the longest diameter of each pore was measured, and the average value was calculated.

<Measurement of the average outer diameter of hollow fiber membrane>
Before the formation of a microbial layer, the hollow fiber membrane was cut at five random planes perpendicular to the longitudinal direction, and the diameter of the smallest circle inscribed on the outer edge of each cut plane was measured using a projector, and the average value was calculated.

<Measurement of adhesion amount of microbial layer>
8, the hollow fiber membrane module 10 was housed in a water tank 210, and wastewater W was stored in a wastewater tank 220. The water tank 210 and the wastewater tank 220, the wastewater tank 220 and the pump 230, and the pump 230 and the water tank 210 were each connected with a tube 240, and the pump 230 was operated to circulate the wastewater W between the water tank 210 and the wastewater tank 220 under the conditions shown below, exposing the hollow fiber membrane module 10 to the wastewater and forming a microbial layer on the outer surface of the hollow fiber membrane 1.
Wastewater W: Activated sludge having MLSS (Mixed Liquor Suspended Solids) of 1000 mg / L.
・Circulation flow: Upward flow (from bottom to top).
Circulation time: 2 hours.
- Membrane area: 140cm ² .
- Effective length of membrane: 200 mm.
- Activated sludge volume: 2L.

The wastewater W was circulated for 2 hours, after which the MLSS was measured.
Separately, without containing the hollow fiber membrane module 10 in the water tank 210, the wastewater W was circulated between the water tank 210 and the wastewater tank 220 for 2 hours, and the MLSS before and after the circulation was measured, and the difference therebetween (MLSS before circulation - MLSS after circulation) was calculated and used as the MLSS change in the blank test.
The amount of sludge attached per unit membrane area of the hollow fiber membrane (mg/m ² ) was calculated from the following formula (1), and this was taken as the amount of attached microbial layer (mg/m ² ).
a={(c ₀ -c _t +c _b )×b}/d...(1)
In formula (1), "a" is the amount of sludge attached (amount of microbial layer attached) per unit membrane area of the hollow fiber membrane, " _c0 " is the MLSS before circulation (1000 mg/L), " _ct " is the MLSS after circulation for t hours (2 hours), " _cb " is the MLSS change in the blank test, "b" is the volume of activated sludge (2 L), and "d" is the membrane area (140 ^cm2 ).

[Example 1]
A composite nozzle die having an innermost layer nozzle part, a middle layer nozzle part, and an outermost layer nozzle part arranged concentrically was used to carry out the spinning process as described below.
The innermost layer nozzle portion and the outermost layer nozzle portion were supplied with high-density polyethylene (manufactured by Asahi Kasei Corporation, product name "Suntech (registered trademark) B161") produced by homopolymerization using a Ziegler-Natta catalyst as a resin for forming the porous layer.
On the other hand, polyethylene (manufactured by Japan Polyethylene Corporation, product name "Harmolex NF324A") was supplied to the intermediate layer nozzle portion as a resin for forming the non-porous layer.
Then, melt spinning was performed at a discharge port temperature of 190° C. and a take-up speed of 100 m/min, and the obtained hollow fiber membrane precursor was taken up on a bobbin (spinning step).
The hollow fiber membrane precursor obtained in the spinning step was wound around a bobbin and subjected to a fixed length heat treatment (annealing treatment) at 108° C. for 12 hours (annealing step).
After the annealing step, the film was continuously cold-stretched at room temperature (20° C.) to a total stretch ratio of 150%, and then hot-stretched in a heating furnace heated to 106° C. until a total stretch ratio of 620% was reached. Further, relaxation heat setting was performed in a heating furnace heated to 115° C. so that a total stretch ratio of 400% was reached (stretching step), and a film body was obtained.
The average outer diameter D of the obtained membrane body was 0.28 mm (280 μm). The average total thickness Dp of the porous layers was 279 μm, the average thickness Dn of the non-porous layers was 1 μm, and Dn/Dp=0.003. The average pore diameter of the pores of the first porous layer was 0.1 μm, and the average pore diameter of the pores of the second porous layer was 0.1 μm.

Sixteen of the obtained membrane bodies were bundled together to form a membrane bundle, and a covering yarn was spirally wound around the outer periphery of the membrane bundle to obtain a hollow fiber membrane. A spun yarn made of acrylic fiber (fineness 0.06 tex) was used as the covering yarn. The number of times the covering yarn was wound per 1 m of the membrane body was 50 times, and the winding interval (pitch) was 20 mm.
Eight hollow fiber membranes thus obtained were prepared and arranged in a circle, and both ends of the eight hollow fiber membranes were fixed to the water tank 210. The amount of attached microbial layer was measured using the obtained hollow fiber membrane module. The results are shown in Table 1.

[Example 2]
A hollow fiber membrane module was produced in the same manner as in Example 1, except that a spun yarn made of polyethylene terephthalate (PET) fiber (fineness 19.7 tex) was used as the covering yarn, the number of times the covering yarn was wound around 1 m of the membrane body was 400, and the winding interval (pitch) was 2.5 mm, and the amount of adhesion of the microbial layer was measured. The results are shown in Table 1.

[Example 3]
A hollow fiber membrane module was produced in the same manner as in Example 1, except that a spun yarn made of polyethylene terephthalate (PET) fiber (fineness 14.7 tex) was used as the covering yarn, the number of times the covering yarn was wound around 1 m of the membrane body was 400, and the winding interval (pitch) was 2.5 mm, and the amount of adhesion of the microbial layer was measured. The results are shown in Table 1.
It should be noted that Examples 1 to 3 are reference examples.

[Example 4]
A hollow fiber membrane module was produced in the same manner as in Example 1, except that the number of windings of the covering yarn per meter of the membrane body was 320 times and the winding interval (pitch) was 3.1 mm, and the amount of adhesion of the microbial layer was measured. The results are shown in Table 1.

[Comparative Example 1]
A hollow fiber membrane module was produced in the same manner as in Example 1, except that no covering yarn was wound around the outer surface of the membrane bundle, and the amount of the microbial layer attached was measured. The results are shown in Table 1.

[Comparative Example 2]
A hollow fiber membrane module was produced in the same manner as in Example 1, except that a filament yarn made of polyethylene fiber was used as the covering yarn, the number of times the covering yarn was wound around 1 m of the membrane body was 400, and the winding interval (pitch) was 2.5 mm, and the amount of adhesion of the microbial layer was measured. The results are shown in Table 1.

"PET" in Table 1 stands for polyethylene terephthalate.
As is clear from Table 1, the hollow fiber membranes obtained in Examples 1 to 4 were prone to the formation of a microbial layer on the surface.
On the other hand, the hollow fiber membrane of Comparative Example 1, in which no covering yarn was wrapped around the outer surface of the membrane bundle, and the hollow fiber membrane of Comparative Example 2, in which filament yarn was used as the covering yarn, were less likely to form a microbial layer on their surfaces than the hollow fiber membranes obtained in each Example.

The hollow fiber membrane, hollow fiber membrane module, wastewater treatment device, and wastewater treatment method of the present invention are suitable for treating, for example, domestic wastewater and industrial wastewater because they facilitate the formation of a microbial layer and enable miniaturization and energy saving.

1 Hollow fiber membrane 2 First porous layer (porous layer)
2a outer surface 2b inner surface 3 non-porous layer 4 second porous layer (porous layer)
Reference Signs List 4a Surface 4b Inner surface 5 Hollow portion 6 Microbial layer 6A Aerobic treatment area 6B Anaerobic treatment area 7 Membrane body 8 Covering fiber 9 Membrane bundle 10 Hollow fiber membrane module 11 Hollow fiber membrane sheet 12 Housing 12A Upper housing 12B Lower housing 100 Wastewater treatment device 110 Treatment tank 111 Opening 210 Water tank 220 Wastewater tank 230 Pump 240 Tube

Claims (10)

A hollow fiber membrane for wastewater treatment, in which a microbial layer derived from microorganisms or bacteria in the wastewater is formed on the outer surface during the wastewater treatment,
The hollow fiber membrane comprises a hollow membrane body and a covering fiber,
The membrane body has a multilayer structure having one or more porous layers and one or more non-porous layers, and the porous layer is disposed as an outermost layer;
The covering yarn is wound around the outer surface of the membrane body 100 times or more per 1 m of the membrane body ,
The covering yarn comprises an acrylic fiber . 2. The hollow fiber membrane according to claim 1, wherein the covering yarn is spirally wound around the outer surface of the membrane body. 3. The hollow fiber membrane according to claim 2, wherein the covering yarn is evenly wound around the membrane body from one end to the other end, and the winding interval P is 1 to 20 mm. The hollow fiber membrane according to any one of claims 1 to 3 , wherein the covering yarn has a fineness of 0.01 to 30 tex. The hollow fiber membrane according to any one of claims 1 to 4, wherein the porous layer is made of a material containing at least one selected from the group consisting of polyolefin-based resins, polyurethane-based resins, and fluorine-based resins. The hollow fiber membrane according to any one of claims 1 to 5, wherein the non-porous layer is made of a material containing at least one selected from a styrene-based resin and a polyolefin-based resin. A hollow fiber membrane module comprising the hollow fiber membrane according to any one of claims 1 to 6. A wastewater treatment device comprising the hollow fiber membrane module according to claim 7. A wastewater treatment method for treating wastewater using the hollow fiber membrane module according to claim 7 or the wastewater treatment device according to claim 8, comprising the steps of:
The wastewater treatment method comprises forming the microbial layer derived from microorganisms or bacteria in the wastewater on the outer surface of the hollow fiber membrane, and then supplying an oxygen-containing gas into the hollow portion of the hollow fiber membrane. A method for producing the hollow fiber membrane according to any one of claims 1 to 6,
A method for manufacturing a hollow fiber membrane, comprising a winding step of fixing a start portion of the covering yarn to the outer surface of the membrane body using an adhesive, winding the covering yarn spirally onto the outer surface of the membrane body at a predetermined number of times or pitch, and fixing an end portion of the covering yarn to the outer surface of the membrane body using the adhesive.

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