Hollow fiber membrane, hollow fiber membrane module, wastewater treatment device, and wastewater treatment method

Abstract

To provide a hollow fiber membrane that can improve wastewater treatment capacity of MABR, and to provide a hollow fiber membrane module, a wastewater treatment device and a wastewater treatment method.SOLUTION: A wastewater treatment device 100 for treatment of wastewater W uses a hollow fiber membrane used for wastewater treatment, having a surface at which a microorganism layer derived from microorganisms or bacterium in the wastewater W is formed during wastewater treatment and of which arithmetic average roughness (SRa) is 25 nm or more, and having an initial tensile resistivity of 0.5-20 cN / dtex which is obtained on the basis of JIS L 1013:2010, as a hollow fiber membrane 1 included in a hollow fiber membrane module 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hollow fiber membrane, a hollow fiber membrane module, a wastewater treatment device, and a wastewater treatment method. [Background technology]

[0002] Industrial and domestic wastewater are treated to remove organic matter and other substances before being reused as industrial water or discharged into rivers, etc. Common treatment methods for industrial wastewater include activated sludge treatment, which involves aerating the treated water and allowing aerobic microorganisms to decompose organic matter. These biological water treatment methods, such as activated sludge treatment, utilize aerobic microorganisms and denitrifying bacteria to remove nitrate nitrogen.

[0003] Conventional activated sludge treatment methods involve setting up a nitrification tank that utilizes aerobic microorganisms and a denitrification tank that utilizes anaerobic microorganisms such as denitrifying bacteria, and supplying oxygen to the nitrification tank by aeration. However, this treatment method has the problem of requiring large equipment because the nitrification tank and denitrification tank are installed separately. Furthermore, even if oxygen is supplied by aeration, there are limits to the oxygen utilization efficiency, even if the bubble size is reduced and the surface area of ​​the bubbles is increased to improve contact efficiency, or the residence time in the treated water is extended, resulting in high running costs.

[0004] Therefore, a method of wastewater treatment using a so-called membrane aeration type biofilm reactor (MABR) has been proposed, in which a microbial layer (biofilm) derived from microorganisms in wastewater is formed on the surface of a hollow fiber membrane, and oxygen is supplied from the inner side of the hollow fiber membrane (Patent Document 1). In wastewater treatment using MABR, an oxygen gradient is formed in the direction of the thickness of the microbial layer, and aerobic treatment (BOD oxidation, nitration of ammonia) proceeds on the inner side of the microbial layer, while anaerobic treatment of nitrate (BOD oxidation, denitrification) proceeds on the outer side of the microbial layer. In this way, aerobic and anaerobic treatment can be performed in the same treatment tank, so the equipment can be made more compact compared to conventional treatment methods. In addition, because oxygen is supplied from the inner side of the hollow fiber membrane, the oxygen utilization efficiency is higher than aeration, and running costs can be reduced. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-62331 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In wastewater treatment methods using MABR, such as those described in Patent Document 1, it is important to more stably form a microbial layer on the surface of the hollow fiber membrane to enhance the wastewater treatment capacity. The present invention aims to provide a hollow fiber membrane, a hollow fiber membrane module, a wastewater treatment device, and a wastewater treatment method that can improve the wastewater treatment capacity of MABR. [Means for solving the problem]

[0007] The inventors conducted diligent research and discovered that the adhesion of the microbial layer to the surface of the hollow fiber membrane is greatly influenced by the physical surface structure of the hollow fiber membrane and the flexibility that allows the hollow fiber membrane to move flexibly in wastewater. Based on these findings, the inventors completed the present invention. In other words, the present invention includes the following embodiments. [1] A hollow fiber membrane for wastewater treatment, wherein a microbial layer derived from microorganisms or bacteria in the wastewater is formed on its surface during wastewater treatment, the arithmetic mean roughness (SRa) of the surface measured by the arithmetic mean roughness measurement method described below is 25 nm or more, and the initial tensile resistance determined according to JIS L 1013:2010 is 0.5 to 20 cN / dtex. (Arithmetic mean roughness measurement method) The surface topography of the hollow fiber membrane was measured using a scanning probe microscope (SPM), and its cross-sectional curved surface was determined. Height in f(x,y) Expressed as Then, the absolute mean of f(x,y) is calculated from equation (1) below and defined as the arithmetic mean roughness (SRa).

[0008]

number

[0009] (However, in equation (1) above, L is the length in the x-direction within the curved cross-section, and M is the length in the y-direction within the curved cross-section.) [2] The hollow fiber membrane according to [1], comprising a material containing a polyolefin resin. [3] The hollow fiber membrane according to [2], wherein the polyolefin resin is polyethylene resin. [4] The hollow fiber membrane according to [3], wherein the polyethylene resin is low-density polyethylene. [5] A hollow fiber membrane according to any one of [1] to [4], which is a single layer membrane consisting of a nonporous layer. [6] A hollow fiber membrane according to any of [1] to [5], having an outer diameter of 1 mm or less. A hollow fiber membrane module comprising a hollow fiber membrane as described in any of [7][1] to [6]. A wastewater treatment apparatus comprising the hollow fiber membrane module described in [8][7]. A wastewater treatment method for treating wastewater using the hollow fiber membrane module described in [9] and [7], or the wastewater treatment apparatus described in [8], wherein the microbial layer derived from microorganisms or bacteria in the wastewater is formed on the surface of the hollow fiber membrane, and then an oxygen-containing gas is supplied to the hollow portion of the hollow fiber membrane. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a hollow fiber membrane, a hollow fiber membrane module, a wastewater treatment apparatus, and a wastewater treatment method that can improve the wastewater treatment ability by MABR.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram showing the configuration of the entire apparatus including a wastewater treatment tank for schematically explaining an embodiment of a hollow fiber membrane module, a wastewater treatment apparatus, and a wastewater treatment method according to the present invention.

Embodiments for Carrying Out the Invention

[0012] In this specification, when "~" is used to indicate a numerical range, the numerical values described before and after "~" are included as the lower limit value and the upper limit value.

[0013] [Hollow Fiber Membrane] The hollow fiber membrane of the present invention is a hollow fiber membrane for wastewater treatment in which a microbial layer derived from microorganisms or bacteria in wastewater is formed on the surface during wastewater treatment. That is, the hollow fiber membrane of the present invention is a hollow fiber membrane used for wastewater treatment by MABR, and is configured to be able to permeate oxygen from the inner surface side toward the surface by supplying oxygen to the hollow portion. Hereinafter, an embodiment of the hollow fiber membrane of the present invention will be described in detail.

[0014] The hollow fiber membrane of the present invention has an arithmetic mean roughness (SRa) of the surface measured by the arithmetic mean roughness measurement method described below of 25 nm or more, and an initial tensile resistance of 0.5 to 20 cN / dtex determined based on JIS L 1013:2010. A hollow fiber membrane satisfying such physical properties is excellent in the adhesion of a microbial layer (biofilm) to the surface, and thus can improve the wastewater treatment ability of MABR.

[0015] (Arithmetic Mean Roughness Measurement Method) The arithmetic mean roughness (SRa) of the surface of the hollow fiber membrane is determined by the following method. The surface (outer surface) of the hollow fiber membrane was measured using a scanning probe microscope (SPM), and its cross-sectional curved surface was determined. Height in f(x,y) Expressed as Then, the absolute mean of f(x,y) is calculated from equation (1) below and defined as the arithmetic mean roughness (SRa).

[0016]

number

[0017] However, in equation (1) above, L is the length in the x-direction within the curved cross-section, and M is the length in the y-direction within the curved cross-section.

[0018] The arithmetic mean roughness (SRa) of the hollow fiber membrane surface is 25 nm or more, preferably 30 nm or more. If the SRa of the hollow fiber membrane surface is above the lower limit, the adhesion of the microbial layer to the hollow fiber membrane surface is excellent, improving the wastewater treatment capacity of the MABR. The SRa of the hollow fiber membrane surface is preferably 1000 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and particularly preferably 100 nm or less. If the SRa of the hollow fiber membrane surface is below the upper limit, a uniform microbial layer is more easily formed on the surface of the hollow fiber membrane, making it easier to obtain high wastewater treatment capacity. The lower and upper limits of the SRa of the hollow fiber membrane surface can be arbitrarily combined, for example, 25 to 1000 nm is preferred. The arithmetic mean roughness (SRa) of the hollow fiber membrane surface can be adjusted by the stretching ratio of the hollow fiber membrane, the materials constituting the hollow fiber membrane, and other factors. Furthermore, "arithmetic mean roughness (SRa) of the hollow fiber membrane surface" refers to the average value of arithmetic mean roughness (SRa) measured randomly at at least three locations on a single hollow fiber membrane surface.

[0019] In this invention, the initial tensile resistance is used as an indicator of the flexibility of the hollow fiber membrane. The initial tensile resistance (cN / dtex) of the hollow fiber membrane is determined based on "8.10 Initial Tensile Resistance" of JIS L 1013:2010. The tensile test conditions for measuring tensile strength (cN) are a gripping distance of 100 mm and a tensile speed of 50 mm / min. For measuring the positive fineness (tex), Method B of "8.3.1 Positive Fineness" is used, where an initial load is applied, 20 samples of 50 cm in length are taken, their oven-dry mass is measured, and the positive fineness is calculated.

[0020] The initial tensile resistance of the hollow fiber membrane is 0.5 cN / dtex or higher, preferably 0.8 cN / dtex or higher, and more preferably 1.5 cN / dtex or higher. If the initial tensile resistance of the hollow fiber membrane is above the lower limit, the surface shape of the hollow fiber membrane is suppressed to change significantly due to swelling and elongation, resulting in excellent adhesion of the microbial layer to the surface of the hollow fiber membrane. The initial tensile resistance of the hollow fiber membrane is 20 cN / dtex or lower, preferably 15 cN / dtex or lower, and more preferably 10 cN / dtex or lower. If the initial tensile resistance of the hollow fiber membrane is below the upper limit, the hollow fiber membrane has sufficient flexibility and moves flexibly in wastewater, making it easier for microorganisms to adhere to the surface of the hollow fiber membrane. The lower and upper limits of the initial tensile resistance of the surface of the hollow fiber membrane can be arbitrarily combined, for example, 0.5 to 20 cN / dtex is preferred. The initial tensile resistance of a hollow fiber membrane can be adjusted by the layer structure of the hollow fiber membrane, the materials that make up the hollow fiber membrane, and so on.

[0021] The materials constituting the hollow fiber membrane are not particularly limited, and examples include polyolefin resin, polystyrene resin, polyurethane resin, and fluororesin. Among these, polyolefin resin is preferred from the viewpoint of oxygen permeability, polyethylene resin is more preferred, and low-density polyethylene is even more preferred. The materials constituting the hollow fiber membrane may be one type or two or more types.

[0022] The shape of the hollow fiber membrane is not particularly limited, and a roughly cylindrical shape can be given as an example. However, "roughly cylindrical" means a three-dimensional shape in which the shape of any cross-section perpendicular to the longitudinal direction is, for example, a perfect circle, egg, oblong, ellipse, or other oval shape.

[0023] The outer diameter of the hollow fiber membrane is preferably 1 mm or less, and more preferably 0.8 mm or less. If the outer diameter of the hollow fiber membrane is below the above upper limit, it is possible to suppress the reduction in the amount of hollow fiber membrane used for filling when forming a membrane module. The outer diameter of the hollow fiber membrane is preferably 0.05 mm or more, more preferably 0.1 mm or more, and even more preferably 0.2 mm or more. If the outer diameter of the hollow fiber membrane is above the above lower limit, the inner diameter of the hollow section can be sufficiently secured, thereby reducing the effect of the oxygen flow rate through the hollow section decreasing due to pressure loss, etc. The lower and upper limits of the outer diameter of the hollow fiber membrane can be arbitrarily combined, for example, 0.8 to 1 mm is preferred. The outer diameter of the hollow fiber membrane is defined as the diameter of the smallest circle inscribed within the outer edge of the cross-section when the hollow fiber membrane is cut by any plane perpendicular to its longitudinal direction. This is determined as the average value measured at any three to ten locations.

[0024] Because of its excellent flexibility and improved adhesion of the microbial layer to the membrane surface, the hollow fiber membrane is preferably a single-layer membrane consisting of a non-porous layer. The material constituting the non-porous layer is preferably polystyrene resin or polyolefin resin, more preferably polyolefin resin, even more preferably polyethylene resin, and particularly preferably low-density polyethylene. By making the non-porous layer a material containing one or more of the above resins, it is possible to increase the overall mechanical strength of the hollow fiber membrane while ensuring sufficient oxygen permeability. The material constituting the non-porous layer may be one type or two or more types.

[0025] [Hollow fiber membrane modules and wastewater treatment equipment] The following describes an example of the hollow fiber membrane module and wastewater treatment device of the present invention. The wastewater treatment device 100 of this embodiment, shown in Figure 1, is generally configured to include hollow fiber membrane modules 10 either individually or in multiple units. In the illustrated example of the wastewater treatment device 100, the hollow fiber membrane modules 10 are housed inside the treatment tank 110.

[0026] The treatment tank 110 contains the wastewater W to be treated. The treatment tank 110 can be any type of treatment tank that has been conventionally used in this field, such as a large metal container. Although not shown in detail in Figure 1, the treatment tank 110 is connected to a wastewater inlet pipe for receiving the wastewater and a discharge pipe for discharging the treated water outside the tank.

[0027] The hollow fiber membrane module 10 is generally composed of a housing 12 (upper housing 12A and lower housing 12B) and a hollow fiber membrane sheet 11 in which a plurality of hollow fiber membranes 1 are bundled together in a sheet shape. The hollow fiber membrane 1 used is the hollow fiber membrane of the present invention as described above. In this example, the hollow fiber membrane module 10 is positioned in the treatment tank 110 such that the longitudinal direction of the hollow fiber membrane 1 is vertical and that it is immersed in the wastewater W. This makes it difficult for condensed water (water that has condensed inside the membrane from oxygen, air, etc., and water in the wastewater) to accumulate inside the hollow fiber membrane 1, thereby maintaining better wastewater treatment capacity.

[0028] The upper housing 12A is a substantially hollow member positioned above the hollow fiber membrane sheet 11. The upper end of the hollow fiber membrane sheet 11 is inserted into the upper housing 12A, and this upper end is fixed to the upper housing 12A with the end faces of each hollow fiber membrane 1 open. The lower housing 12B is a substantially hollow member positioned below the hollow fiber membrane sheet 11. The lower end of the hollow fiber membrane sheet 11 is inserted into the lower housing 12B, and this lower end is fixed to the lower housing 12B with the end faces of each hollow fiber membrane 1 open. As a result, the hollow fiber membrane sheet 11 between the upper housing 12A and the lower housing 12B is held in a sheet-like shape.

[0029] In the hollow fiber membrane module 10, it is preferable to provide a pair of support columns that connect the ends of the upper housing 12A and the lower housing 12B, respectively. By providing a pair of support columns 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, and a flat hollow fiber membrane module 10 can be constructed. The hollow fiber membrane module 10 is not limited to a flat shape; for example, it can also be configured in a cylindrical or rectangular shape.

[0030] A gas supply line 120 is connected to the upper housing 12A, and oxygen, air, etc., is supplied to the interior of the upper housing 12A from a blower (not shown). The oxygen, air, etc., that is sent into the hollow portion of each hollow fiber membrane 1 via the upper housing 12A permeates from the inner surface to the outer surface of each hollow fiber membrane 1. An aeration device (not shown) may be placed below the hollow fiber membrane module 10.

[0031] [Wastewater treatment methods] The wastewater treatment method of this embodiment is a method of treating wastewater using the hollow fiber membrane module 10 of this embodiment or the wastewater treatment device 100 of this embodiment, as shown in Figure 1.

[0032] Specifically, the wastewater treatment method of this embodiment first introduces the wastewater W to be treated 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 placed inside the treatment tank 110 is immersed in the wastewater W. Next, oxygen or air is supplied to the hollow fiber membrane module 10 via a gas supply line 120 from a blower (not shown), thereby allowing oxygen or air to permeate from the hollow portion of the hollow fiber membrane 1 to the surface. In this embodiment, in the initial stage of wastewater treatment, microorganisms and bacteria present in the wastewater W adhere to the surface of each hollow fiber membrane 1, forming a microbial layer derived from microorganisms or bacteria.

[0033] Microorganisms or bacteria may be grown using activated sludge already in use at another wastewater treatment plant, etc., and then the hollow fiber membrane module may be immersed in the treated sludge at a predetermined concentration to pre-form a microbial layer derived from microorganisms or bacteria on the surface of the hollow fiber membrane 1. Activated sludge has various component compositions and proportions depending on the type of wastewater, but it can be used that has been grown by feeding on BOD (organic matter) components and nutrients (nitrogen, phosphorus, etc.) contained in the wastewater.

[0034] By continuously supplying oxygen or air to the hollow fiber membrane module 10, the oxygen that permeates from the hollow portion of each hollow fiber membrane 1 to the surface dissolves and diffuses within the microbial layer, forming an oxygen gradient (concentration) in the direction of the microbial layer's film thickness. As a result, the inner layer of the microbial layer becomes an oxygen-rich aerobic state, while the outer layer becomes an anaerobic state with reduced oxygen. Consequently, the microbial layer develops an aerobic treatment area on the inner side and an anaerobic treatment area on the outer side. In the aerobic treatment area, ammonia contained in the wastewater is oxidized through aerobic treatment (BOD oxidation) and converted to nitrate. In the anaerobic treatment area, the nitrate produced in the aerobic treatment area is treated as nitrogen through anaerobic treatment (BOD oxidation) and denitrified. In this way, both aerobic and anaerobic treatment are carried out in a single process within the treatment tank 110.

[0035] Each hollow fiber membrane 1 of the hollow fiber membrane module 10 may be supplied with air from the atmosphere, but it is preferable to supply pure oxygen. By supplying highly purified oxygen, the oxygen concentration that dissolves and diffuses into the microbial layer is more likely to be sufficient, improving the wastewater treatment capacity. Using air is preferable in that it can reduce running costs. The hollow fiber membrane module 10 may also be supplied with a gas whose component composition ratio has been changed by separation or concentration, for example, according to the characteristics of the wastewater to be treated. The pressure of the gas (oxygen or air) supplied to each hollow fiber membrane 1 is not particularly limited, but it is preferably 200 kPa or less, as this helps to suppress damage to the components due to oversupply. To obtain a wastewater treatment effect sufficient for practical use, the pressure of the gas supplied to each hollow fiber membrane 1 may be, for example, 5 kPa or more.

[0036] The thickness of the microbial layer is not particularly limited; for example, once a certain thickness or a predetermined processing time has been reached, operations such as bubbling with air can be performed to adjust the thickness to a level that allows for optimal aerobic and anaerobic treatment.

[0037] The wastewater W may be aerated by supplying a gas containing a high concentration of nitrogen (high nitrogen concentration gas) from an aeration device positioned below the hollow fiber membrane module 10. When bubbles of the high nitrogen concentration gas come into contact with the microbial layer, the oxygen concentration in the anaerobic treatment area decreases further, making it more anaerobic. In addition, the bubbles generated from the aeration device stir the wastewater W, making the wastewater W an anaerobic environment overall, so that anaerobic bacteria become dominant in the microbial flora of flocs suspended in the wastewater W.

[0038] After biological treatment, the microbial layer is detached from the hollow fiber membrane 1 by bubbling, for example, using an aeration device (not shown) located below the hollow fiber membrane module 10. Subsequently, the sludge containing the detached microbial layer is recovered using a solid-liquid separation method with a separation membrane (not shown), completing the wastewater treatment.

[0039] As described above, in this invention, a microbial layer is formed on the surface of a hollow fiber membrane, and oxygen is supplied to the microbial layer by permeating from the inner side to the outer side of the hollow fiber membrane. This allows both aerobic and anaerobic treatment to be performed in the microbial layer in a single process. Therefore, the oxygen utilization efficiency is higher compared to oxygen supply by aeration, and the equipment can be made more compact. Furthermore, in this invention, by using a hollow fiber membrane whose surface arithmetic mean roughness (SRa) and initial tensile resistance satisfy specific conditions, the adhesion of the microbial layer to the surface of the hollow fiber membrane is excellent, allowing for effective utilization of the entire membrane and achieving high wastewater treatment capacity. In addition, the rapid adhesion of the microbial layer to the surface of the hollow fiber membrane enables early start-up of operation, and also enables quick recovery of operation in the event of problems such as detachment of the microbial layer.

[0040] It should be noted that the present invention is not limited to the embodiments described above. Within the scope of the present invention, the components in the embodiments may be replaced with well-known components as appropriate, and the modifications described above may be combined as appropriate. [Examples]

[0041] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[0042] [Arithmetic mean roughness (SRa)] The surface topography of the hollow fiber membrane was measured using a scanning probe microscope (SPM), and its cross-sectional curved surface was determined. Height in f(x,y) Expressed as From equation (1), the absolute mean of f(x,y) was calculated and defined as the arithmetic mean roughness (SRa). SPM measurements were performed under the following conditions. Equipment: SFT-3500 (manufactured by SHIMAZU) Measurement mode: Dynamic mode Scanning area: 10 μm × 10 μm (256 × 256 pixels) Scanning speed: 1Hz Scanning mode: Constant force

[0043] [Initial tensile resistance] The initial tensile resistance (cN / dtex) of the hollow fiber membrane was determined based on "8.10 Initial Tensile Resistance" of JIS L 1013:2010. The tensile test conditions for measuring tensile strength (cN) were a gripping distance of 100 mm and a tensile speed of 50 mm / min. For measuring the positive fineness (tex), Method B of "8.3.1 Positive Fineness" was used, and 20 samples of 50 cm in length were taken with an initial load, their oven-dry mass was measured, and the positive fineness was calculated.

[0044] [Maximum nitrification rate] The wastewater W was treated using the wastewater treatment device 100 illustrated in Figure 1. Raw water from a public sewer system was used as the wastewater W, and the wastewater treatment was carried out for 60 days by supplying air to the hollow fiber membrane module 10 at a pressure of 30 kPa. As an indicator of wastewater treatment capacity, the maximum nitrification rate per unit membrane surface area was calculated using the following formula (2). NR={(NH4-N) i -(NH4-N) e} / A ···(2) However, the abbreviations in formula (2) above have the following meanings. NR: Maximum nitrification rate [g / m 2 ·d] (NH4-N) i : Ammonia nitrogen load of raw water [g / d] (NH4-N) e : Ammonia nitrogen load in treated water [g / d] A: Effective membrane area of ​​hollow fiber membrane [m²] 2 ]

[0045] [Example 1] Hollow fiber membranes were manufactured by melt spinning using a nozzle. Low-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd., product name "Harmolex N324A") was used as the resin material. The discharge temperature was 170°C and the winding speed was 120 m / min. The stretch ratio was 0. The outer diameter of the obtained hollow fiber membrane was 200 μm, the arithmetic mean surface roughness (SRa) was 55.5 nm, and the initial tensile resistance was 2.5 cN / dtex. Hollow fiber membranes were bundled into a sheet to form a hollow fiber membrane sheet, and both ends were inserted into an upper housing and a lower housing, respectively, and fixed with potting resin (manufactured by Tosoh Corporation, product name "Coronate") to form a hollow fiber membrane module. The effective length of the hollow fiber membrane is 350 mm, and the effective membrane area is 3200 cm². 2 That was the case. Table 1 shows the results of measuring the maximum nitrification rate when wastewater was treated using the obtained hollow fiber membrane modules.

[0046] [Comparative Example 1] Melt spinning was carried out using a nozzle die to produce a hollow fiber membrane. As the resin material, high-density polyethylene (manufactured by Asahi Kasei Corporation, trade name "Suntech B161") was used. The discharge temperature was 185 °C and the winding speed was 100 m / min. The draw ratio was 4 times. The outer diameter of the obtained hollow fiber membrane was 280 μm, the arithmetic mean roughness (SRa) of the surface was 18.0 nm, and the initial tensile strength was 38 cN / dtex. The hollow fiber membranes were bundled into a sheet-like shape to form a hollow fiber membrane sheet-like material, and both ends thereof were inserted into an upper housing and a lower housing, respectively, and fixed with a potting resin (manufactured by Toray Industries, Inc., trade name "Coronate") to obtain a hollow fiber membrane module. The effective length of the hollow fiber membrane was 350 mm, and the effective membrane area was 3200 cm 2 It was.

[0047] [Comparative Example 2] Melt spinning was carried out using a nozzle die to produce a hollow fiber membrane. As the resin material, high-density polyethylene (manufactured by Asahi Kasei Corporation, trade name "Suntech B161") was used. The discharge temperature was 185 °C and the winding speed was 146 m / min. The draw ratio was 3 times. The outer diameter of the obtained hollow fiber membrane was 280 μm, the arithmetic mean roughness (SRa) of the surface was 21.5 nm, and the initial tensile strength was 31.9 cN / dtex. The hollow fiber membranes were bundled into a sheet-like shape to form a hollow fiber membrane sheet-like material, and both ends thereof were inserted into an upper housing and a lower housing, respectively, and fixed with a potting resin (manufactured by Toray Industries, Inc., trade name "Coronate") to obtain a hollow fiber membrane module. The effective length of the hollow fiber membrane was 350 mm, and the effective membrane area was 3200 cm 2 [[ID=第十四条]]It was.

[0048] [Comparative Example 3] A commercially available hollow fiber membrane was used. The outer diameter of the hollow fiber membrane was 510 μm, the arithmetic mean roughness (SRa) of the surface was 57.5 nm, and the initial tensile strength was 0.1 cN / dtex. The hollow fiber membranes were bundled into a sheet-like shape to form a hollow fiber membrane sheet-like material, and both ends thereof were inserted into an upper housing and a lower housing, respectively, and fixed with a potting resin (manufactured by Toray Industries, Inc., trade name "Coronate") to obtain a hollow fiber membrane module. The effective length of the hollow fiber membrane was 350 mm, and the effective membrane area was 3200 cm2 That was the case.

[0049] Table 1 shows the arithmetic mean surface roughness (SRa) and initial tensile resistance for each example. Furthermore, wastewater treatment was performed using the obtained hollow fiber membrane modules, and the results of measuring the maximum nitrification rate are shown in Table 1.

[0050] [Table 1]

[0051] As shown in Table 1, Example 1, which used a hollow fiber membrane with appropriate surface arithmetic mean roughness (SRa) and initial tensile resistance, showed a faster maximum nitrification rate and higher wastewater treatment capacity compared to Comparative Examples 1-3, which used hollow fibers in which at least one of the surface arithmetic mean roughness (SRa) and initial tensile resistance was unsuitable. [Explanation of Symbols]

[0052] 1...Hollow fiber membrane, 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, 120...Gas supply line, W...Wastewater.

Claims

1. A hollow fiber membrane for water treatment, The hollow fiber membrane is a hollow fiber membrane for wastewater treatment using a membrane aeration type biofilm reactor. A hollow fiber membrane having an arithmetic mean roughness (SRa) of 25 nm or more on the surface of the hollow fiber membrane, as measured by the arithmetic mean roughness measurement method described below, and an initial tensile resistance of 0.5 to 20 cN / dtex as determined according to JIS L 1013:2010. (Arithmetic mean roughness measurement method) The surface topography of the hollow fiber membrane is measured using a scanning probe microscope (SPM) under the following conditions, and the height of the cross-sectional curved surface is expressed as f(x,y). The absolute mean of f(x,y) is calculated from equation (1) below and defined as the arithmetic mean roughness (SRa). <Measurement conditions> Equipment: SFT-3500 (manufactured by Shimazu) Measurement mode: Dynamic mode Scanning area: 10 μm × 10 μm (256 × 256 pixels) Scanning speed: 1 Hz Scanning mode: Constant force [Math 1] (However, in equation (1) above, L is the length in the x-direction within the curved cross-section, and M is the length in the y-direction within the curved cross-section.)

2. A hollow fiber membrane according to claim 1, comprising a material containing a polyolefin resin.

3. The hollow fiber membrane according to claim 2, wherein the polyolefin resin is polyethylene resin.

4. The hollow fiber membrane according to claim 3, wherein the polyethylene resin is low-density polyethylene.

5. A hollow fiber membrane according to any one of claims 1 to 4, wherein the single layer is made up of a non-porous layer.

6. A hollow fiber membrane according to any one of claims 1 to 5, wherein the outer diameter is 1 mm or less.

7. The hollow fiber film according to any one of claims 1 to 6, wherein the arithmetic mean roughness (SRa) of the surface is 30 nm or more and 1000 nm or less.

8. The hollow fiber membrane according to any one of claims 1 to 7, wherein the initial tensile resistance is 1.5 to 10 cN / dtex.

9. The hollow fiber membrane according to any one of claims 1 to 8, wherein the stretching ratio of the hollow fiber membrane is 0.

10. The hollow fiber membrane according to any one of claims 1 to 9, wherein a microbial layer derived from microorganisms or bacteria in the wastewater is formed on the surface of the hollow fiber membrane during wastewater treatment.

11. A hollow fiber membrane module comprising a hollow fiber membrane according to any one of claims 1 to 10.

12. A wastewater treatment apparatus comprising the hollow fiber membrane module described in claim 11.

13. A wastewater treatment method using a membrane aeration type biofilm reactor that treats wastewater using the hollow fiber membrane module described in claim 11 or the wastewater treatment apparatus described in claim 12, wherein A wastewater treatment method comprising forming a microbial layer on the surface of the hollow fiber membrane, derived from microorganisms or bacteria in the wastewater, and then supplying oxygen-containing gas to the hollow portion of the hollow fiber membrane.

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