Raw water spacer and method for operating water treatment device

Abstract

Provided are: a raw water spacer with which it is possible to constitute a separation membrane module in which adhesion of a cationic substance to the surface of a separation membrane is suppressed; and a method for operating a water treatment device which is provided with the separation membrane module. This raw water spacer has a plurality of first linear bodies and a plurality of second linear bodies which constitute a mesh-like planar body. The plurality of first linear bodies and the plurality of second linear bodies are composed of a composite material which is obtained by adding carbon nanotubes into a base resin, and 1 part by mass to 7 parts by mass of the carbon nanotubes are contained in 100 parts by mass of the composite material. The surface roughness of the plurality of first linear bodies and the surface roughness of the plurality of second linear bodies are configured so that respective arithmetic mean heights Sa set forth in ISO 25178 is 0.2 µm to 0.5 µm.

Description

Operating method of raw water spacer and water treatment device

[0001] This disclosure relates to a raw water spacer and a method for operating a water treatment device.

[0002] In water treatment systems that perform multi-stage filtration, there are known water treatment devices that use filtered water from the previous filtration stage as raw water and separate target components that could not be separated in the previous filtration stage using a reverse osmosis membrane (hereinafter referred to as RO membrane). Examples of target components include ions and TOC (Total Organic Carbon). In such water treatment devices, for example, a spiral-type separation membrane module in which multiple separation membranes are wound around a water passage pipe is used.

[0003] In this type of water treatment system, raw water containing the components to be separated and water is passed through a separation membrane module to separate it into permeate water that permeates through the separation membrane located inside the module and concentrated water that does not permeate the separation membrane. Inside the separation membrane module, a raw water spacer is placed between the two separation membranes to ensure a flow path for the raw water.

[0004] Patent Document 1 discloses a mesh-like raw water spacer made of a molded article containing polypropylene resin and carbon nanotubes, and which is configured separately from the separation membrane, as described above. In the technology described in Patent Document 1, the blending ratio of carbon nanotubes is specified as 5.3 to 18 parts by mass per 100 parts by mass of polypropylene resin.

[0005] Patent No. 7072175

[0006] When separating raw water into permeate and concentrated water using an RO membrane placed inside a separation membrane module, cationic substances contained in the raw water may adhere to and accumulate on the surface of the RO membrane. For example, when organic matter in sewage or contaminated water is decomposed and purified by biological treatment, even if a filtration treatment is performed after the biological treatment, the filtered water may contain cationic proteins derived from microorganisms that could not be separated in the previous filtration treatment. When such filtered water is used as raw water, cationic proteins may adhere to and accumulate on the surface of the separation membrane, leading to a decrease in the performance of the separation membrane.

[0007] Furthermore, when cleaning electronic materials, the cleaning water used in the cleaning process may contain cationic surfactants. If used cleaning water from such a cleaning process is used as the raw water, the cationic surfactants may adhere to and accumulate on the surface of the separation membrane, leading to a decrease in the performance of the separation membrane.

[0008] If cationic substances adhere to and accumulate on the surface of a separation membrane, adding a washing process to remove them from the membrane surface will reduce the operating rate of the water treatment system and increase costs due to the time required for the washing process. Therefore, from the perspective of improving the operating rate of the water treatment system, a separation membrane module that does not easily accumulate cationic substances on its surface is desired.

[0009] Against this backdrop, the inventors of this invention conducted extensive research on separation membranes that are less susceptible to the adhesion of cationic substances. As a result, they discovered that by using a raw water spacer that meets specific conditions as the raw water spacer placed inside the separation membrane module, cationic substances become less likely to adhere to the surface of the separation membrane, thus completing this technology.

[0010] In one aspect of this disclosure, it is desirable to provide a raw water spacer capable of constructing a separation membrane module in which the adhesion of cationic substances to the separation membrane surface is suppressed, and a method for operating a water treatment apparatus equipped with the separation membrane module.

[0011] One aspect of the present disclosure relates to a water treatment apparatus that separates raw water containing components to be separated and water into permeate water that permeates through a separation membrane arranged inside the separation membrane module and concentrated water that does not permeate the separation membrane, wherein the raw water spacer is arranged inside the separation membrane module to secure a flow path for raw water between two separation membranes, and comprises a plurality of first linear bodies and a plurality of second linear bodies. The first linear bodies are arranged in parallel with each other. The second linear bodies are arranged in parallel with each other. The plurality of first linear bodies and the plurality of second linear bodies are arranged in directions that intersect with each other to form a mesh-like planar body. When the raw water spacer is positioned between two separation membranes, multiple first linear bodies contact one of the separation membranes, and multiple second linear bodies are interposed between the multiple first linear bodies and the other separation membrane to secure a gap that serves as a flow path for the raw water. Furthermore, multiple second linear bodies contact the other separation membrane, and multiple first linear bodies are interposed between the multiple second linear bodies and the one separation membrane to secure a gap that serves as a flow path for the raw water. Moreover, the multiple first linear bodies and the multiple second linear bodies are made of a composite material in which carbon nanotubes are compounded with a base resin, and 1 to 7 parts by mass of carbon nanotubes are contained in 100 parts by mass of the composite material. The surface roughness of the multiple first linear bodies and the multiple second linear bodies is configured such that the arithmetic mean height Sa, as defined in ISO 25178, is between 0.2 μm and 0.5 μm.

[0012] In one aspect of this disclosure, a composite material is prepared by adding a base resin to the composite material to dilute the concentration of carbon nanotubes in the composite material by 100 times, molding the diluted material to a thickness of 0.3 mm, and when three 2 mm x 2 mm fields of view are randomly selected from an image of the surface of the molded product and each field of view is observed, the particle area observed in each field of view is 25 μm. ２ 100 μm or more ２ The number of carbon nanotube particles less than 50 was less than 50 on average across three locations, and the particle area observed in each field of view was 100 μm. ２ 20000 μm or more ２ The material may also have a carbon nanotube particle count of less than 10 on average across three locations.

[0013] In one aspect of this disclosure, the square mesh formed by the first and second linear bodies may have a diagonal pitch of 4.0 mm to 5.0 mm. One aspect of this disclosure is a method for operating a water treatment apparatus that separates raw water containing components to be separated and water into permeate water that permeates through a separation membrane arranged inside the separation membrane module and concentrated water that does not permeate the separation membrane, wherein a raw water spacer is arranged inside the separation membrane module to secure a flow path for raw water between two separation membranes. The raw water spacer has a plurality of first linear bodies and a plurality of second linear bodies. The first linear bodies are arranged in parallel with each other. The second linear bodies are arranged in parallel with each other. The plurality of first linear bodies and the plurality of second linear bodies are arranged in directions that intersect with each other to form a mesh-like planar body. When the raw water spacer is positioned between two separation membranes, multiple first linear bodies contact one of the separation membranes, and multiple second linear bodies are interposed between the multiple first linear bodies and the other separation membrane to secure a gap that serves as a flow path for the raw water. Furthermore, multiple second linear bodies contact the other separation membrane, and multiple first linear bodies are interposed between the multiple second linear bodies and the one separation membrane to secure a gap that serves as a flow path for the raw water. Moreover, the multiple first linear bodies and the multiple second linear bodies are made of a composite material in which carbon nanotubes are compounded with a base resin, and 1 to 7 parts by mass of carbon nanotubes are contained in 100 parts by mass of the composite material. The surface roughness of the multiple first linear bodies and the multiple second linear bodies is configured such that the arithmetic mean height Sa, as defined in ISO 25178, is between 0.2 μm and 0.5 μm.

[0014] In one aspect of this disclosure, instead of a composite material, a base resin that does not contain carbon nanotubes is used, and in comparison with a control raw water spacer that is otherwise configured the same as the raw water spacer, the mass transfer coefficient on the surface of each of the two separation membranes positioned on either side of the raw water spacer or the control raw water spacer is configured to be 1.3 to 2.4 times that of the control raw water spacer under conditions of a linear velocity of 0.02 m / s to 0.14 m / s when the solute of the raw water is NaCl.

[0015] In one aspect of this disclosure, the raw water may contain a cationic substance, which is at least one selected from cationic proteins and cationic surfactants, as the component to be separated.

[0016] Figure 1A is a plan view of the raw water spacer. Figure 1B is an enlarged view of section IB shown in Figure 1A. Figure 2A is an explanatory diagram showing the flow path of raw water in a plan view of a part of the raw water spacer. Figure 2B is an explanatory diagram showing the flow path of raw water in the cross section shown by the line IIB-IIB in Figure 2A. Figure 3 is a graph showing the measurement results of the arithmetic mean height of the surface of the raw water spacer for Examples 1-4 and Comparative Examples 1-2. Figures 4A, 4B, and 4C are photographs showing the dispersibility of the composite material of Example 1. Figures 4D, 4E, and 4F are photographs showing the dispersibility of the composite material of Comparative Example 1. Figure 5A is a graph showing the measurement results of the mass transfer coefficients for Examples 1-4 and Comparative Examples 1-2. Figure 5B is a graph showing the rate of change of the mass transfer coefficients of Examples 1-4 and Comparative Example 1 compared to Comparative Example 2. Figure 6A is a graph showing the measurement results of the mass transfer coefficients for Examples 1, 5, Comparative Example 2, and Comparative Example 3. Figure 6B is a graph showing the rate of change of the mass transfer coefficients of Examples 1, 5, and Comparative Example 3 compared to Comparative Example 2. Figure 7A is a graph showing the measurement results of the mass transfer coefficients for Example 6 and Comparative Example 4. Figure 7B is a graph showing the rate of change of the mass transfer coefficient for Example 6 compared to Comparative Example 4. Figure 8A is a graph showing the change in permeability coefficient over time for Examples 1-4 and Comparative Example 2. Figure 8B is a graph showing the change in permeability coefficient over time for Examples 1-4 and Comparative Example 2. Figure 9A is an explanatory diagram showing the simulation results of the lysozyme adhesion state to the CNT / PP model. Figure 9B is an explanatory diagram showing the simulation results of the lysozyme adhesion state to the PP model. Figure 10 is a graph showing the relationship between the water flow velocity near the surface of the raw water spacer and the distance from the surface of the raw water spacer.

[0017] Next, the operation method of the raw water spacer and water treatment device described above will be explained with reference to exemplary embodiments. (1) Configuration of the raw water spacer As shown in Figures 1A and 1B, the raw water spacer 1 has a plurality of first linear bodies 11A arranged in parallel and a plurality of second linear bodies 11B arranged in parallel. The plurality of first linear bodies 11A and the plurality of second linear bodies 11B are arranged in positions where they intersect each other and form a square mesh. When viewed from the direction shown in Figure 1B, the plurality of first linear bodies 11A are arranged in front of the plurality of second linear bodies 11B. The plurality of first linear bodies 11A and the plurality of second linear bodies 11B are welded to each other at their intersections.

[0018] A mesh structure of this kind can be manufactured by rotary extrusion molding. In rotary extrusion molding, the molten raw water spacer 1 is extruded vertically downward from a die lip comprising an annular outer die and an annular inner die fitted to the inner circumference of the outer die. Multiple grooves parallel to the axial direction are engraved at regular intervals in the circumferential direction on the inner circumference of the outer die on the leading end side in the extrusion direction and on the outer circumference of the inner die on the leading end side in the extrusion direction.

[0019] When the constituent material of the raw water spacer 1 is pushed out from multiple grooves engraved on the outer die and inner die while both the outer die and inner die are rotated in opposite directions, the constituent material is pushed out in a linear shape. At that time, the pushed-out linear body is pushed out in a spiral pattern as the outer die and inner die rotate. However, the rotation directions of the outer die and inner die are different.

[0020] Therefore, the spiral twist directions of the multiple linear bodies extruded from the grooves of the outer die and the multiple linear bodies extruded from the grooves of the inner die are opposite to each other. The linear bodies extruded from the grooves of either the outer die or the inner die will have a left-handed spiral shape, while the linear bodies extruded from the grooves of the other die will have a right-handed spiral shape.

[0021] Furthermore, the inner circumference of the outer die and the outer circumference of the inner die are in contact with each other. Therefore, multiple linear bodies extruded from the grooves of the outer die and multiple linear bodies extruded from the grooves of the inner die are extruded in a spiral pattern at the point where they are in contact with each other. As a result, linear bodies that trace a left-handed spiral and linear bodies that trace a right-handed spiral intersect to form a mesh-like structure. At this time, the linear bodies that trace a left-handed spiral and linear bodies that trace a right-handed spiral are welded together at the intersections, as they are still softened by the high temperature.

[0022] The tubular mesh formed in this way is pulled down vertically by a take-up machine. At this time, the tubular mesh is shaped to a predetermined size using a sizing machine and then cooled in a cooling layer. The tubular mesh cooled in the cooling layer is cut open axially at one point in the circumferential direction by a cutting machine, thereby processing it into a planar mesh. The planar mesh is then annealed in a relaxation tank and then wound up by a winding machine.

[0023] In this embodiment, the diameters of the first linear body 11A and the second linear body 11B are each approximately 0.4 mm. Furthermore, at the intersection of the first linear body 11A and the second linear body 11B, one side is welded to the other side with approximately 0.1 mm embedded in it. As a result, the thickness of the raw water spacer 1 is approximately 0.7 mm.

[0024] With a raw water spacer 1 having such a structure, as shown in Figures 2A and 2B, when the raw water spacer 1 is positioned between two separation membranes 21 and 22, a plurality of first linear bodies 11A contact one of the separation membranes 21. A plurality of second linear bodies 11B are interposed between the plurality of first linear bodies 11A and the other separation membrane 22, ensuring a gap 23. Furthermore, a plurality of second linear bodies 11B contact the other separation membrane 22. A plurality of first linear bodies 11A are interposed between the plurality of second linear bodies 11B and one of the separation membranes 21, ensuring a gap 24.

[0025] As described above, the thickness of the raw water spacer 1 is approximately 0.7 mm, and the diameters of the first linear body 11A and the second linear body 11B are approximately 0.4 mm, so the dimensions of the gaps 23 and 24 are approximately 0.3 mm. By ensuring these gaps 23 and 24, a flow path F is secured between the two separation membranes 21 and 22, as illustrated by the dashed arrows in Figures 2A and 2B.

[0026] The pitch of the square mesh formed by the first linear body 11A and the second linear body 11B is configured such that the pitch in one diagonal direction is 4 mm-5 mm and the pitch in the other diagonal direction is 4 mm-5 mm. If the pitch in both diagonal directions is 4 mm or more, the mesh area will not be too small, so a sufficient flow path for raw water passing through the mesh can be secured. If the pitch in both diagonal directions is 5 mm or less, the mesh area will not be too large, so contact between separation membranes through the mesh can be suppressed, and the blockage of the raw water flow path due to contact between separation membranes can be suppressed.

[0027] As the constituent material for forming the raw water spacer 1, a composite material is used in which carbon nanotubes (hereinafter abbreviated as CNTs) are compounded with a base resin. In this embodiment, polypropylene (hereinafter abbreviated as PP) is used as the base resin. The CNTs have a structure such that a graphene sheet is wound into a cylindrical shape, with a diameter of several nanometers to tens of nanometers and a length of tens to thousands of times or more the diameter. CNTs are classified into single-walled CNTs, in which the graphene sheet is substantially one layer, and multi-walled CNTs, in which there are two or more layers. As long as the purpose of this disclosure is not impaired, either single-walled CNTs or multi-walled CNTs may be used as the CNTs.

[0028] Each 100 parts by mass of the composite material contains 1 to 7 parts by mass of carbon nanotubes (CNTs). When the amount of CNTs in 100 parts by mass of the composite material is 1 part by mass or more, the mass transfer coefficient, described later, can be improved to 1.3 times or more compared to using a base resin without CNTs. Furthermore, when the amount of CNTs in 100 parts by mass of the composite material is 7 parts by mass or less, excessive viscosity of the composite material can be suppressed, thus preventing poor processability. Additionally, by limiting the amount of CNTs to 7 parts by mass or less, material costs can be reduced, thus lowering the product price of the raw water spacer 1.

[0029] Furthermore, the surface roughness of the first linear body 11A and the second linear body 11B is configured such that the arithmetic mean height Sa, as defined in ISO 25178, is 0.2 μm to 0.5 μm. By setting the arithmetic mean height Sa to 0.2 μm to 0.5 μm, the mass transfer coefficient, described later, can be increased by 1.3 to 2.4 times compared to using a base resin that does not contain CNTs.

[0030] Furthermore, it is preferable that the composite material described above is a material in which the dispersibility of CNTs is sufficiently high. That is, it is preferable that the CNTs are sufficiently broken down into fine particles and dispersed in the base resin. However, it is not easy to determine whether the CNTs are sufficiently dispersed by simply observing the composite material described above. Therefore, the inventors of this invention determined the dispersibility of CNTs using the following method.

[0031] First, a base resin is added to the composite material described above to dilute the concentration of CNTs in the composite material by 100 times, and the diluted material is molded to a thickness of 0.3 mm. Three 2 mm x 2 mm fields of view are randomly selected from the image of the surface of the molded product and each field of view is observed. In this embodiment, the surface of the molded product was photographed with a digital microscope (manufactured by Keyence Corporation, model number: VHX-7000).

[0032] By using such a method, the interparticle distance of CNTs is increased, and the overlap of multiple particles is eliminated. Therefore, the size of each particle can be observed, and it is possible to specify what sizes of particles are included in the composite material. Note that the coarse particles of CNTs that are not sufficiently crushed are aggregates of CNTs in which multiple CNTs are irregularly intertwined and form a yarn-like shape. Therefore, even if the dilution treatment as described above is carried out, the intertwined CNTs hardly unravel, and the yarn-like structure is maintained. Thus, since the particle size of CNTs does not change even if the dilution treatment as described above is performed, the size and number of particles contained in the composite material can be appropriately specified.

[0033] When observing as described above, the first condition is that the number of CNT particles with a particle area of 25 μm ２ or more and 100 μm ２ or less is 50 or less on average at three locations. Also, the second condition is that the number of CNT particles with a particle area of 100 μm ２ or more and 20000 μm ２ or less is 10 or less on average at three locations.

[0034] If a molded product that satisfies these first and second conditions can be obtained, the above composite material is considered to be a material in which CNTs are sufficiently crushed into fine particles and dispersed in the base resin. If the number of CNT particles with a particle area of 25 μm ２ or more and 100 μm ２ or less is 50 or less on average at three locations, the arithmetic mean height Sa defined in ISO 25178 can be made 0.5 μm or less. Also, although the CNT particles with a particle area of 100 μm ２ or more and 20000 μm ２ or less are coarse particles, if the number of such particles is 10 or less on average at the above three locations, the influence caused by the presence of the coarse particles can be suppressed to a negligible level.

[0035] (2) Performance Evaluation (2.01) Configuration of the Separation Membrane Module for Evaluation Prepare the raw water spacers as described in Examples 1 - 6 and Comparative Examples 1 - 4 below, and construct a separation membrane module incorporating the raw water spacers, and evaluate their respective performances.

[0036] [Example 1] Using a composite material with CNT blended with the base resin based on PP, the raw water spacer was manufactured by the above-described rotational extrusion molding method. In Example 1, a composite material in which 7 parts by mass of CNT was blended in 100 parts by mass of the composite material was used. As a pre-step, CNT and the base resin were vigorously stirred to sufficiently pulverize the CNT. After that pre-step, the base resin was melted and kneaded. The diameters of the first linear body and the second linear body were each about 0.4 mm, and the thickness of the raw water spacer was about 0.7 mm. The pitch of the square mesh formed by the first linear body and the second linear body was 4 mm in one diagonal direction and 4 mm in the other diagonal direction.

[0037] Using the raw water spacer as described above, a separation membrane module was constructed. As the RO membrane, an RO membrane taken out by disassembling a commercially available separation membrane module (manufactured by Nitto Denko Corporation, product number: ESPA2 - 4040) was used. The effective area of the separation membrane module was 1800 cm ２ , the diameter was 5 cm, and the axial length was 30 cm. The above-mentioned commercially available separation membrane module from which the RO membrane of Example 1 was taken out can be used at ultra-low pressure and is a product that can be used for various applications mainly in industrial wastewater recovery and sewage treatment.

[0038] [Comparative Example 1] Omit the above-described pre-step, and manufacture the raw water spacer and construct the separation membrane module with the other procedures and conditions being the same as those in Example 1.

[0039] [Example 2] Using a composite material in which 1 part by mass of CNT was blended in 100 parts by mass of the composite material, manufacture the raw water spacer and construct the separation membrane module with the other procedures and conditions being the same as those in Example 1.

[0040] [Example 3] A raw water spacer was manufactured and a separation membrane module was constructed using a composite material containing 3 parts by mass of CNTs in 100 parts by mass of composite material, with all other procedures and conditions being the same as in Example 1.

[0041] [Example 4] A raw water spacer was manufactured and a separation membrane module was constructed using a composite material containing 5 parts by mass of CNTs in 100 parts by mass of composite material, with all other procedures and conditions being the same as in Example 1.

[0042] [Comparative Example 2] Instead of the composite material, a base resin without CNTs was used to manufacture a raw water spacer, and the other procedures and conditions were the same as in Example 1, to constitute a separation membrane module. The raw water spacer in Comparative Example 2 corresponds to the control raw water spacer as referred to in this disclosure.

[0043] [Comparative Example 3] The pitch of the square mesh formed by the first and second linear bodies was set to 3 mm in one diagonal direction and 3 mm in the other diagonal direction, while the other procedures and conditions were the same as in Example 1 to manufacture a raw water spacer and construct a separation membrane module.

[0044] [Example 5] The pitch of the square mesh formed by the first and second linear bodies was set to 5 mm in one diagonal direction and 5 mm in the other diagonal direction, and the other procedures and conditions were the same as in Example 1 to manufacture a raw water spacer and construct a separation membrane module.

[0045] [Example 6] A raw water spacer equivalent to that of Example 1 was manufactured, and a separation membrane module was constructed using this raw water spacer. However, as the RO membrane, a different commercially available separation membrane module (DuPont, product name: FilmTec BW30-4040) was disassembled and the RO membrane extracted from it was used, which was different from that used in Example 1. The commercially available separation membrane module from which the RO membrane of Example 6 was extracted is a product mainly used for the production of pure water, etc.

[0046] [Comparative Example 4] A raw water spacer equivalent to that of Comparative Example 2 (i.e., a control raw water spacer as referred to in this disclosure) was manufactured, and a separation membrane module was constructed using this raw water spacer. However, the same RO membrane as in Example 6 was used as the RO membrane.

[0047] (2.02) Measurement of Surface Roughness The raw water spacers described in Examples 1-4 and Comparative Examples 1-2 were measured for their surface roughness, with the arithmetic mean height Sa defined in ISO 25178 being measured. A commercially available confocal laser microscope (product name: 3D measuring laser microscope LEXT OLS4000, manufactured by Olympus Corporation) was used to measure the arithmetic mean height Sa. The measurement results are shown in Figure 3.

[0048] The raw water spacers described in Examples 1-4 had an arithmetic mean height Sa within the range of 0.2 μm to 0.5 μm. On the other hand, the raw water spacers described in Comparative Examples 1-2 had an arithmetic mean height Sa exceeding 0.5 μm. In Examples 1-4, it is presumed that the CNTs are oriented in the extrusion direction within the extruded material, resulting in a smoother surface of the molded product. In Comparative Example 1, although the amount of CNTs is the same as in Example 1, it contains more coarse particles than Example 1. Therefore, it is presumed that the surface of the molded product becomes rougher in Comparative Example 1, resulting in an arithmetic mean height Sa exceeding 0.5 μm. In Comparative Example 2, unlike Examples 1-4, it does not contain CNT particles. Therefore, it is presumed that the CNTs are not oriented within the extruded material, resulting in a rougher surface of the molded product.

[0049] (2.03) Verification of Dispersibility The dispersibility of CNT particles contained in the constituent materials of each raw water spacer was confirmed using the method described above, with reference to the raw water spacers described in Example 1 and Comparative Example 1. Specifically, first, a base resin was added to the constituent material of each raw water spacer to dilute the concentration of CNTs in the composite material by 100 times, and the diluted material was molded to a thickness of 0.3 mm.

[0050] Images of the molded product surface were captured using a digital microscope, and three 2 mm x 2 mm fields of view were randomly selected and observed. For the material corresponding to Example 1, images of the three fields of view are shown in Figures 4A, 4B, and 4C. For the material corresponding to Comparative Example 1, images of the three fields of view are shown in Figures 4D, 4E, and 4F.

[0051] In each field of view, the dark areas correspond to CNT particles. Therefore, the area of ​​each dark area was calculated using computer analysis, and the particle area was 25 μm. ２ 100 μm or more ２ Number of CNT particles less than 100 μm² and particle area 100 μm² ２ 20000 μm or more ２ The number of CNT particles less than 5 was counted. The counting results are shown in Table 1.

[0052]

[0053] Comparing Example 1 and Comparative Example 1, although the amount of CNTs in 100 parts by mass of the composite material was the same at 7 parts by mass in both, it became clear that Comparative Example 1 contained more coarse CNT particles and the CNTs were not uniformly dispersed.

[0054] (2.04) Relationship between surface roughness and mass transfer coefficient The separation membrane modules described in Examples 1-4 and Comparative Examples 1-2 were set in a cross-flow apparatus, and the mass transfer coefficient on the surface of the separation membrane was measured according to the following procedure.

[0055] First, pure water was prepared as the raw water (supply water), and this raw water was passed through the separation membrane module. The supply water flow rate was set to 1000 mL / min, and the supply pressure to 0.35-0.50 MPa. Every 30 minutes, the water volume (permeate, concentrated water), water temperature (raw water, permeate, concentrated water), concentration (raw water, permeate, concentrated water), pH (raw water), and supply pressure were measured.

[0056] Next, a saline solution with a NaCl concentration of 0.1% (1000 ppm) was prepared as the raw water, and the solution pH was adjusted to 7 (adjusted with 0.1 mol / L of NaOH). The mass transfer coefficient was then measured. The feed water flow rate was set to 250-2000 mL / min, and the supply pressure to 0.35 MPa (variable as needed). Every 30 minutes, the water volume (permeate, concentrated water), water temperature (raw water, permeate, concentrated water), concentration (raw water, permeate, concentrated water), pH (raw water), and supply pressure were measured.

[0057] Based on these measurement results, the mass transfer coefficient was calculated using the following procedure. First, the permeation flux of pure water was measured to determine the permeation coefficient Lp [m / d / MPa]. Based on the permeation rate of pure water Jw [m / d] and the supply water pressure ΔP [Pa], the permeation coefficient Lp [m / d / MPa] is given by Lp = Jw / ΔP. Next, the permeation flux of saline solution was measured at varying flow rates to determine the osmotic pressure Δπ [Pa] for each flow rate. Based on the permeation rate of saline solution Jv [m / d], the osmotic pressure Δπ [Pa] is given by Δπ = ΔP - Jv / Lp.

[0058] Next, the membrane concentration Cm [mg / L] is determined from the osmotic pressure Δπ. The gradient coefficient f between the concentration of saline solution and osmotic pressure is set to "0.8479" from literature values, van't Hoff's equation, etc., so the membrane concentration Cm [mg / L] is Cm = Δπ / f. Next, the mass transfer coefficient k [m / d] is determined from the membrane concentration Cm using the concentration polarization equation. Based on the supply water concentration Cb [mg / L] of the saline solution, the mass transfer coefficient k is k = Jv / ln(Cm / Cb).

[0059] Figures 5A and 5B show the measurement results of the mass transfer coefficients using the separation membrane modules for Examples 1-4 and Comparative Examples 1-2. As is clear from Figure 5A, in Examples 1-4, where the arithmetic mean height Sa of the raw water spacer surface is in the range of 0.2 μm-0.5 μm, the measurement results of the mass transfer coefficients were higher than those of Comparative Examples 1-2, where the arithmetic mean height Sa exceeded 0.5 μm.

[0060] Figure 5B is a graph showing how many times the mass transfer coefficients of Examples 1-4 and Comparative Example 1 change compared to Comparative Example 2, which corresponds to the control raw water spacer (hereinafter referred to as the mass transfer coefficient change rate). In the case of Examples 1-4, the mass transfer coefficient change rate is 1.3 times or more at each linear velocity.

[0061] On the other hand, in Comparative Example 1, the rate of change in the mass transfer coefficient gradually approaches 1.0 times as the linear velocity increases. There is no difference in the amount of CNTs added between Example 1 and Comparative Example 1, but as mentioned above, there is a difference in the surface roughness of the raw water spacer. Therefore, it is considered that by adding CNTs and adjusting the surface roughness of the raw water spacer so that the arithmetic mean height Sa is within the range of 0.2 μm to 0.5 μm, the rate of change in the mass transfer coefficient compared to the control raw water spacer can be increased to 1.3 times or more.

[0062] (2.05) Relationship between mesh pitch and mass transfer coefficient The separation membrane modules described in Example 5 and Comparative Example 3 were set in a cross-flow apparatus, and the mass transfer coefficient on the surface of the separation membrane was measured in the same procedure as described in Section (2.04) above.

[0063] Figures 6A and 6B show the measurement results of the mass transfer coefficients using the separation membrane modules for Example 1, Example 5, Comparative Example 2, and Comparative Example 3. As is clear from Figure 6A, in Example 1, Example 5, and Comparative Example 3, the measurement results of the mass transfer coefficients were higher than those of Comparative Example 2, which did not contain CNTs.

[0064] Figure 6B is a graph showing how many times the mass transfer coefficient of Example 1, Example 5, and Comparative Example 3 changes compared to Comparative Example 2 (i.e., the rate of change in the mass transfer coefficient), with Comparative Example 2 as the baseline. In the case of Example 1 and Example 5, the rate of change in the mass transfer coefficient is approximately 1.3 times or more at each linear velocity. Therefore, it is considered that the rate of change in the mass transfer coefficient can be increased to 1.3 times or more by using raw water spacers with a vertical and horizontal pitch of 4 mm or more.

[0065] On the other hand, in Comparative Example 3, the rate of change in the mass transfer coefficient decreased to less than 1.3 times at linear velocities of 0.02 m / s and 0.07 m / s. Therefore, it was found that the mass transfer coefficient decreases when the mesh pitch is less than 4 mm. It is presumed that when the mesh pitch is less than 4 mm, the raw water spacer obstructs the flow of raw water, leading to pressure loss of the raw water, a decrease in the stirring capacity at the membrane surface, and as a result, a decrease in the mass transfer coefficient.

[0066] (2.06) Influence of differences in separation membranes The separation membrane modules described in Example 6 and Comparative Example 4 were set in a cross-flow apparatus, and the mass transfer coefficient on the surface of the separation membrane was measured in the same procedure as described in Section (2.04) above.

[0067] The measurement results of the mass transfer coefficients using the separation membrane modules for Example 6 and Comparative Example 4 are shown in Figures 7A and 7B. As is clear from Figure 7A, in Example 6, the measurement result of the mass transfer coefficient was higher than that of Comparative Example 4, which did not contain CNTs.

[0068] Figure 7B is a graph showing how many times the mass transfer coefficient of Example 6 changes compared to Comparative Example 4 (i.e., the rate of change in the mass transfer coefficient), with Comparative Example 4 as the baseline. In the case of Example 6, the rate of change in the mass transfer coefficient was 1.7 times or more at each linear velocity, and showed a maximum of 2.4 times. Therefore, even when the performance of the separation membrane differs, it is suggested that by constructing the raw water spacer with a composite material containing CNTs, the mass transfer coefficient is increased compared to the control raw water spacer.

[0069] (2.07) Relationship between mass transfer coefficient and salt permeation rate. As the mass transfer coefficient increases, the amount of salt that permeates through the separation membrane decreases. Table 2 below shows the relationship between the mass transfer coefficient and salt permeation rate.

[0070]

[0071] When the mass transfer coefficient increases from 1.0 [m / d] to 1.3 [m / d], the amount of salt permeated through the separation membrane decreases by 10%. When the mass transfer coefficient increases from 1.0 [m / d] to 2.4 [m / d], the amount of salt permeated through the separation membrane decreases by 23%. Therefore, increasing the mass transfer coefficient can improve the salt separation performance in the separation membrane module.

[0072] Generally, to increase the mass transfer coefficient (i.e., to thin the concentration polarization layer on the membrane surface), excess feedwater is transferred horizontally to the separation membrane surface, forcing the components concentrated on the membrane surface to be removed by back-diffusion. However, this method increases the energy required for water transport, necessitating larger pumps and other measures, which contributes to increased water production costs.

[0073] In contrast, using the raw water spacer described above improves the mass transfer coefficient compared to using a control raw water spacer, leading to a reduction in water production costs. Furthermore, a larger mass transfer coefficient and a thinner concentration polarization layer are effective in reducing solute precipitation and protein concentration in the separation membrane. Consequently, the lifespan of the separation membrane module is extended, allowing for longer continuous operation of the water treatment system.

[0074] (2.08) Fouling evaluation using lysozyme The separation membrane modules described in Examples 1-4 and Comparative Example 2 were set in a cross-flow apparatus, and the permeability coefficient in the separation membrane was measured according to the following procedure.

[0075] First, lysozyme, a cationic protein, was added to pure water as a foulant to prepare raw water with a foulant concentration of 1 mg / L. The solution pH was adjusted to 7 (adjusted with 0.1 mol / L NaOH), and fouling measurements were started. The water supply flow rate during measurement was 1000 mL / min, and the supply pressure was 0.5 MPa. At 0h, 3h, 21h, 24h, 27h, 45h, and 48h after the start of measurement, water volume (permeate, concentrated water), water temperature (raw water, permeate, concentrated water), pH (raw water), and supply pressure were measured once each. Immediately after measurement, the solution pH was adjusted to 7 (adjusted with 0.1 mol / L NaOH), and the pressure, water supply volume, and water temperature were adjusted.

[0076] After the fouling measurement was completed, the separation membrane module was subjected to alkaline washing using caustic soda pH 11-12 as the washing solution, under the conditions of washing time 60 minutes, flow rate 2000 mL / min, and water temperature 25°C. After alkaline washing, neutralization was performed with HCl 3 mol / min, and the amount of permeate after washing was confirmed at a feed water flow rate of 1000 mL / min and a feed pressure of 0.5 MPa.

[0077] The measurement results are shown in Figures 8A and 8B. As shown in Figure 8A, the permeability coefficient decreased over time in all of Examples 1-4 and Comparative Example 2. However, compared to Comparative Example 2, Examples 1-4 maintained a high permeability coefficient, suggesting that foulant substances were less likely to adhere to the separation membrane than in Comparative Example 2. Furthermore, Examples 1-4 also exhibited superior cleaning recovery after alkaline cleaning compared to Comparative Example 2.

[0078] (2.09) Analysis of Lysozyme Adhesion to Raw Water Spacer Surface The adhesion state of lysozyme to the raw water spacer surface was analyzed using molecular dynamics simulation. Molecular dynamics simulation was performed using LAMMPS (Large-scale Atomic / Molecular Massively Parallel Simulator). Two models were prepared: a PP model corresponding to Comparative Example 2 and a CNT / PP model corresponding to Example 1.

[0079] The PP model had 100 PP chains, and to avoid spherical aggregation, spring-like dots were added to arbitrarily selected PP atoms. The CNT / PP model had three layers of graphene placed beneath the PP model. The atomic charges of each model were determined using the charge equilibrium method. The molecular structure of lysozyme was obtained by downloading a file from the Protein Data Bank (PDB) and extracting a single chain from that file.

[0080] To evaluate the interaction between each model and lysozyme, lysozyme was placed on the surface of each model and the evaluation was carried out. The simulation results for the CNT / PP model are shown in Figure 9A. The simulation results for the PP model are shown in Figure 9B.

[0081] In the CNT / PP model, as shown in Figure 9A, lysozyme did not adhere to the raw water spacer surface and detached immediately. On the other hand, in the PP model, as shown in Figure 9B, lysozyme adhered to the PP surface. This difference in adhesion characteristics is presumed to be due to the influence of interactions with polar and nonpolar amino acid residues contained in lysozyme. It is thought that adding CNTs to PP material changes the polarity of the surface of the composite material, increasing its repulsive properties with lysozyme. A similar effect is thought to occur with cationic solutes other than lysozyme.

[0082] (2.10) Relationship between water flow velocity near the surface of the raw water spacer and distance from the surface of the raw water spacer The relationship between water flow velocity near the surface of the raw water spacer and distance from the surface of the raw water spacer was analyzed for the PP model (corresponding to Comparative Example 2; hereinafter referred to as the PP spacer) and the CNT / PP model (corresponding to Example 1; hereinafter referred to as the CNT / PP spacer) described in section (2.09) above. The results of the analysis are shown in Figure 10.

[0083] According to the analysis results shown in Figure 10, in the case of the CNT / PP spacer, the water flow velocity is approximately 0.1 m / s in the range where the distance from the raw water spacer surface is 5 angstroms or less. From this, it can be inferred that in the case of the CNT / PP spacer, a layer of interfacial water with a thickness of approximately 5 angstroms is formed near the raw water spacer surface.

[0084] On the other hand, in the case of PP spacers, even in the range where the distance from the raw water spacer surface is 5 angstroms or less, the water flow velocity is approximately 0.22 m / s or higher. From this, it can be inferred that in the case of PP spacers, a layer of interfacial water, as seen in the case of CNT / PP spacers, does not form.

[0085] If we let V40 be the water flow velocity at a distance of 40 angstroms from the surface of the raw water spacer, and V5 be the water flow velocity at a distance of 5 angstroms from the surface of the raw water spacer, then the velocity difference D is D = V40 - V5. In the case of a CNT / PP spacer, the water flow velocity V40 = 1.34 m / s and the water flow velocity V5 = 0.12 m / s, so the velocity difference D = 1.22 m / s. On the other hand, in the case of a CNT / PP spacer, the water flow velocity V40 = 1.35 m / s and the water flow velocity V5 = 0.27 m / s, so the velocity difference D = 1.08 m / s.

[0086] In other words, the velocity difference D described above is greater for the CNT / PP spacer than for the PP spacer. The larger this velocity difference D, the greater the stirring force that agitates the water flow, and the surface of the separation membrane is agitated by that water flow. Therefore, it is presumed that using a CNT / PP spacer will result in a higher mass transfer coefficient at the separation membrane surface than using a PP spacer.

[0087] (3) Effects of this embodiment As described above, with the raw water spacer, the arithmetic mean height Sa as defined in ISO 25178 is within the range of 0.2 μm to 0.5 μm, as described in Examples 1 to 4 above. Therefore, compared with Comparative Example 2, in which the arithmetic mean height Sa exceeds 0.5 μm, the mass transfer coefficient on the separation membrane surface can be increased by 1.3 times or more. Thus, mass transfer on the separation membrane surface can be promoted by the raw water spacer, and the adhesion of foulant substances to the separation membrane surface can be suppressed. In addition, cationic substances such as lysozyme are less likely to adhere to the surface of the raw water spacer, so the foulant substances attached to the raw water spacer can act as a starting point to suppress the growth of a cationic foulant membrane toward the separation membrane.

[0088] Furthermore, in this embodiment, as described in Example 1 above, when CNT particles are observed using the method described above, the particle area is 25 μm. ２ 100 μm or more ２ The number of CNT particles smaller than 50 is 50 or less on average at the three locations mentioned above. Also, the particle area is 100 μm. ２ 20000 μm or more ２ The number of CNT particles smaller than 10 is 10 or less on average at the three locations mentioned above. Therefore, the surface smoothness of the raw water spacer is higher compared to Comparative Example 1, which contains coarse CNT particles. If the surface of the raw water spacer is smooth, the raw water spacer will no longer obstruct the flow of raw water, and it is presumed that the raw water will be more easily agitated near the separation membrane surface. Therefore, it is thought that the mass transfer coefficient at the separation membrane surface will be higher due to these factors.

[0089] (4) Other Embodiments Above, exemplary embodiments have been described regarding the raw water spacer and the operation method of the water treatment device, but the embodiments described above are merely illustrative examples of one aspect of the present disclosure. That is, the present disclosure is not limited to the exemplary embodiments described above, and can be implemented in various forms without departing from the technical idea of ​​the present disclosure.

[0090] Furthermore, multiple functions realized by one component as exemplified in the above embodiment may be realized by multiple components. One function realized by one component as exemplified in the above embodiment may be realized by multiple components. Multiple functions realized by multiple components as exemplified in the above embodiment may be realized by one component. One function realized by multiple components as exemplified in the above embodiment may be realized by one component. Some of the configurations exemplified in the above embodiment may be omitted. At least a part of the configuration exemplified in one of the above embodiments may be added to or replaced with the configuration exemplified in the other embodiments.

[0091] (5) Technical concept disclosed herein [Item 1] A water treatment apparatus that separates raw water containing components to be separated and water into permeate water that permeates through a separation membrane arranged inside the separation membrane module and concentrated water that does not permeate the separation membrane, wherein a raw water spacer is arranged inside the separation membrane module to secure a flow path for the raw water between two separation membranes, and comprises: a plurality of first linear bodies arranged in parallel with each other, and a plurality of second linear bodies arranged in parallel with each other, wherein the plurality of first linear bodies and the plurality of second linear bodies are arranged in directions that intersect with each other to form a mesh-like planar body, When the raw water spacer is positioned between the two separation membranes, a plurality of the first linear bodies contact one of the separation membranes, and a plurality of the second linear bodies are interposed between the plurality of the first linear bodies and the other separation membrane to secure a gap that serves as a flow path for the raw water, and a plurality of the second linear bodies contact the other separation membrane, and a plurality of the first linear bodies are interposed between the plurality of the second linear bodies and one of the separation membranes to secure a gap that serves as a flow path for the raw water, and the plurality of the first linear bodies and the plurality of the second linear bodies are made of a composite material in which carbon nanotubes are compounded with a base resin, and 1 to 7 parts by mass of carbon nanotubes are contained in 100 parts by mass of the composite material, and the surface roughness of the plurality of the first linear bodies and the plurality of the second linear bodies is configured such that the arithmetic mean height Sa as defined in ISO 25178 is 0.2 μm to 0.5 μm, the raw water spacer.

[0092] [Item 2] The raw water spacer described in Item 1, wherein the composite material is diluted 100-fold by adding the base resin to the composite material, the concentration of carbon nanotubes in the composite material is diluted 100-fold, the diluted material is molded to a thickness of 0.3 mm, and when three 2 mm x 2 mm fields of view are randomly selected in an image of the surface of the molded product and each field of view is observed, the particle area observed in each field of view is 25 μm. ２ 100 μm or more ２The number of carbon nanotube particles less than 50 on average across the three locations, and the particle area observed in each field of view is 100 μm². ２ 20000 μm or more ２ A raw water spacer, wherein the number of carbon nanotube particles less than 10 on average at the three locations is 10 or less.

[0093] [Item 3] A raw water spacer according to Item 1 or Item 2, wherein the square mesh formed by the first linear body and the second linear body has a diagonal pitch of 4.0 mm to 5.0 mm.

[0094] [Item 4] A method for operating a water treatment apparatus that separates raw water containing components to be separated and water into permeate water that permeates through a separation membrane arranged inside the separation membrane module and concentrated water that does not permeate the separation membrane, wherein a raw water spacer is arranged inside the separation membrane module to secure a flow path for the raw water between two separation membranes, the raw water spacer has a plurality of first linear bodies arranged in parallel with each other, and a plurality of second linear bodies arranged in parallel with each other, the plurality of first linear bodies and the plurality of second linear bodies are arranged in directions that intersect with each other to form a mesh-like planar body, A method for operating a water treatment apparatus, wherein when the raw water spacer is positioned between the two separation membranes, a plurality of the first linear bodies contact one of the separation membranes, a plurality of the second linear bodies are interposed between the plurality of the first linear bodies and the other separation membrane to secure a gap that serves as a flow path for the raw water, and a plurality of the second linear bodies contact the other separation membrane, a plurality of the first linear bodies are interposed between the plurality of the second linear bodies and one of the separation membranes to secure a gap that serves as a flow path for the raw water, and furthermore, the plurality of the first linear bodies and the plurality of the second linear bodies are made of a composite material in which carbon nanotubes are compounded with a base resin, and 1 to 7 parts by mass of carbon nanotubes are contained in 100 parts by mass of the composite material, and the surface roughness of the plurality of the first linear bodies and the plurality of the second linear bodies is configured such that the arithmetic mean height Sa as defined in ISO 25178 is 0.2 μm to 0.5 μm.

[0095] [Item 5] A method for operating the water treatment apparatus described in Item 4, wherein, in comparison with a control raw water spacer which uses the base resin without carbon nanotubes instead of the composite material and is otherwise configured to be the same as the raw water spacer, when the solute of the raw water is NaCl, the mass transfer coefficient on the surface of each of the two separation membranes arranged on both sides of the raw water spacer or the control raw water spacer is configured to be 1.3 to 2.4 times that of the control raw water spacer under the condition of a linear velocity of 0.02 m / s to 0.14 m / s.

[0096] [Item 6] A method for operating a water treatment apparatus as described in Item 4 or Item 5, wherein the raw water contains at least one cationic substance selected from cationic proteins and cationic surfactants as the component to be separated.

[0097] 1... Raw water spacer, 11A... First linear body, 11B... Second linear body, 21, 22... Separation membrane, 23, 24... Gaps.

Claims

1. In a water treatment apparatus that separates raw water containing components to be separated and water into permeate water that permeates through a separation membrane arranged inside the separation membrane module and concentrated water that does not permeate the separation membrane, a raw water spacer is arranged inside the separation membrane module to secure a flow path for the raw water between two separation membranes, and comprises a plurality of first linear bodies arranged in parallel with each other, and a plurality of second linear bodies arranged in parallel with each other, wherein the plurality of first linear bodies and the plurality of second linear bodies are arranged in directions that intersect with each other to form a mesh-like planar body, When the raw water spacer is positioned between the two separation membranes, a plurality of the first linear bodies contact one of the separation membranes, and a plurality of the second linear bodies are interposed between the plurality of the first linear bodies and the other separation membrane to secure a gap that serves as a flow path for the raw water, and a plurality of the second linear bodies contact the other separation membrane, and a plurality of the first linear bodies are interposed between the plurality of the second linear bodies and one of the separation membranes to secure a gap that serves as a flow path for the raw water, and the plurality of the first linear bodies and the plurality of the second linear bodies are made of a composite material in which carbon nanotubes are compounded with a base resin, and 1 to 7 parts by mass of carbon nanotubes are contained in 100 parts by mass of the composite material, and the surface roughness of the plurality of the first linear bodies and the plurality of the second linear bodies is configured such that the arithmetic mean height Sa as defined in ISO 25178 is 0.2 μm to 0.5 μm, the raw water spacer.

2. The raw water spacer according to claim 1, wherein the composite material is obtained by adding the base resin to the composite material to dilute the concentration of carbon nanotubes in the composite material by 100 times, molding the diluted material to a thickness of 0.3 mm, and when three 2 mm x 2 mm fields of view are randomly selected in an image of the surface of the molded product and each field of view is observed, the particle area observed in each field of view is 25 μm. ２ 100 μm or more ２ The number of carbon nanotube particles less than 50 on average across the three locations, and the particle area observed in each field of view is 100 μm². ２ 20000 μm or more ２ A raw water spacer, wherein the number of carbon nanotube particles less than 10 on average at the three locations is 10 or less.

3. A raw water spacer according to claim 1 or claim 2, wherein the square mesh formed by the first linear body and the second linear body has a diagonal pitch of 4.0 mm to 5.0 mm.

4. A method for operating a water treatment apparatus that separates raw water containing components to be separated and water into permeate water that permeates through a separation membrane arranged inside the separation membrane module and concentrated water that does not permeate the separation membrane, wherein a raw water spacer is arranged inside the separation membrane module to secure a flow path for the raw water between two separation membranes, the raw water spacer has a plurality of first linear bodies arranged in parallel with each other, and a plurality of second linear bodies arranged in parallel with each other, the plurality of first linear bodies and the plurality of second linear bodies are arranged in directions that intersect with each other to form a mesh-like planar body, A method for operating a water treatment apparatus, wherein when the raw water spacer is positioned between the two separation membranes, a plurality of the first linear bodies contact one of the separation membranes, a plurality of the second linear bodies are interposed between the plurality of the first linear bodies and the other separation membrane to secure a gap that serves as a flow path for the raw water, and a plurality of the second linear bodies contact the other separation membrane, a plurality of the first linear bodies are interposed between the plurality of the second linear bodies and one of the separation membranes to secure a gap that serves as a flow path for the raw water, and furthermore, the plurality of the first linear bodies and the plurality of the second linear bodies are made of a composite material in which carbon nanotubes are compounded with a base resin, and 1 to 7 parts by mass of carbon nanotubes are contained in 100 parts by mass of the composite material, and the surface roughness of the plurality of the first linear bodies and the plurality of the second linear bodies is configured such that the arithmetic mean height Sa as defined in ISO 25178 is 0.2 μm to 0.5 μm.

5. A method for operating a water treatment apparatus according to claim 4, wherein, in comparison with a control raw water spacer which is otherwise configured the same as the raw water spacer, the mass transfer coefficient on the surface of each of the two separation membranes arranged on both sides of the raw water spacer or the control raw water spacer is 1.3 to 2.4 times that of the control raw water spacer under the condition of a linear velocity of 0.02 m / s to 0.14 m / s, when the solute of the raw water is NaCl.

6. A method for operating a water treatment apparatus according to claim 4 or claim 5, wherein the raw water contains a cationic substance, which is selected from cationic proteins and cationic surfactants as the component to be separated.

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