Method for capturing fine particles in liquid, method for detecting fine particles in liquid, and apparatus for capturing fine particles

Abstract

To shorten the time required for capturing when capturing fine particles for detection of the fine particles in liquid, or the like.SOLUTION: A method for capturing fine particles in liquid includes: a concentration step in which the liquid is passed through a first filtration membrane 11 in a first direction, and fine particles 61 are accumulated on the surface of the first filtration membrane 11; and a recovery step in which, after the concentration step, separation liquid is passed through the first filtration membrane 11 in a second direction being the reverse direction to the first direction, the separation liquid that has passed through the first filtration membrane 11 is then passed through a second filtration membrane 21 different from the first filtration membrane 11, the fine particles 61 are separated from the first filtration membrane 11 and captured on the surface of the second filtration membrane 21.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the measurement of particles in a liquid, and more particularly to a method for trapping particles in a liquid, a method for detecting the trapped particles, and a trapping device for trapping the particles. [Background technology]

[0002] An ultrapure water production system that produces ultrapure water for use in the manufacture of semiconductor devices and pharmaceuticals typically comprises a primary pure water production system that produces primary pure water from raw water, and a subsystem that produces ultrapure water from the primary pure water. In the subsystem, various devices such as an ultraviolet oxidation device and an ion exchange device are arranged in series, and the primary pure water is sequentially treated by these devices to produce ultrapure water. The produced ultrapure water is supplied to a point of use, and a membrane filtration device such as an ultrafiltration membrane device (UF) or a microfiltration membrane device (MF) is arranged just before the point of use in the supply path of the ultrapure water to remove fine particles.

[0003] In recent years, the requirements for the quality of ultrapure water have become stricter. For example, fine particles contained in ultrapure water used in the manufacture of semiconductor devices directly affect the yield of semiconductor products. Therefore, strict management is required for both the particle size and concentration of fine particles contained in ultrapure water. For example, it may be required to control the concentration of fine particles, that is, the number of fine particles contained in a unit volume of ultrapure water, to a specified value or less. As a method for detecting fine particles in pure water or ultrapure water, for example, a direct microscopic method specified in JIS (Japanese Industrial Standards) K0554-1995 "Method for measuring fine particles in ultrapure water" is known. In this method, first, the pure water or ultrapure water is filtered through a filtration membrane to capture fine particles on the filtration membrane, and then the filtration membrane is observed using an observation device such as an optical microscope or a scanning electron microscope (SEM) to detect the fine particles captured on the filtration membrane. Fine particles with small diameters can be detected by using a filtration membrane with a pore size smaller than the diameter of the fine particles to be detected. The filtration membrane used to capture fine particles has pores with a pore size equivalent to the lower limit of the diameter of the fine particles to be captured. Filtration membranes are required to have small variations in the pore size of their pores; for example, pores produced by anodizing metals, or pores produced by irradiating a polymer material with heavy particle beams or the like and then enlarging the pore size by etching, are used as pores in filtration membranes.

[0004] In the direct microscopy method, in order to ensure the reliability of the detection of the number of particles, it is desirable to capture on the filtration membrane a number of particles equal to or greater than the number of particles that are originally present on the filtration membrane, and for this purpose, a sufficient amount of ultrapure water or pure water must be passed through the filtration membrane. In addition, the smaller the particle size of the particles to be detected, the smaller the pore size of the filtration membrane must be used, and the pressure loss in the filtration membrane increases. In the filtration membrane used to capture particles, the pores are formed by the above-mentioned special method in order to reduce the variation in the pore size of the pores, so the surface density of the pores in the filtration membrane cannot be increased, and the pressure loss increases accordingly. For these reasons, in order to detect particles with small diameters, it is necessary to filter the pure water or ultrapure water that is the target of particle detection for a long period of time. As an attempt to shorten the filtration time in the direct microscopy method, Patent Document 1 discloses filtration using a centrifugal filter. In the technology described in Patent Document 1, the filtration membrane is held in a cartridge, and the cartridge and the filtration membrane form a liquid chamber in which the liquid is retained. By attaching such a cartridge to the rotating part, centrifugal force acts on the liquid in the liquid chamber toward the filtration membrane, increasing the flow rate of liquid passing through the filtration membrane, and as a result, the time required for filtration can be shortened. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-55240 A Summary of the Invention [Problem to be solved by the invention]

[0006] When detecting particles by direct microscopy, the smaller the particle diameter of the target particles and the smaller the lower limit of quantification of the number of particles, the longer the time required for filtration to capture the particles. Even if a centrifugal filter is used as described in Patent Document 1, filtration takes a long time. If the filtration time is long, the time required to detect particles by direct microscopy also becomes longer. In ultrapure water used in the manufacture of semiconductor devices, it is required to manage particles with a diameter of 10 nm or more at a level of several particles / mL, and in this management, it is required to quickly obtain the detection result of the particles. Therefore, when detecting particles by direct microscopy, it is required to shorten the filtration time for capturing the particles. In order to shorten the filtration time, it is necessary to process a large amount of liquid in a short time and capture the particles contained in the liquid.

[0007] An object of the present invention is to provide a capture method capable of capturing particles contained in a liquid in a short period of time, a detection method for detecting particles using this capture method, and a capture device for capturing the particles. [Means for solving the problem]

[0008] A capturing method according to one embodiment of the present invention is a capturing method for capturing fine particles in a liquid, which includes a concentration step of passing the liquid through a first filtration membrane in a first direction to accumulate fine particles on the surface of the first filtration membrane, and a recovery step of passing a stripping liquid through the first filtration membrane in a second direction opposite to the first direction after the concentration step, passing the stripping liquid through the first filtration membrane through a second filtration membrane different from the first filtration membrane, and stripping the fine particles from the first filtration membrane and capturing them on the surface of the second filtration membrane. Note that the first direction and the second direction in the liquid passing direction through the first filtration membrane refer to the first direction as the flow direction when the liquid passes through the first filtration membrane in the direction in which the fine particles in the liquid are filtered and removed, and the second direction as the flow direction opposite to the first direction. In other words, when a general filtration membrane is used as the first filtration membrane, the direction from the inlet side membrane surface of the filtration membrane, through the filtration membrane, toward the outlet side membrane surface is the first direction, and the direction from the outlet side membrane surface of the filtration membrane, through the filtration membrane, toward the inlet side membrane surface is the second direction.

[0009] One embodiment of the detection method of the present invention is a detection method for detecting fine particles in a liquid, which involves subjecting the liquid to the capture method of the above-mentioned embodiment, and then detecting the fine particles by observing the fine particles captured on the surface of the second filtration membrane with an observation device.

[0010] One embodiment of the present invention is a capture device that captures fine particles in a liquid, and includes a first filtration membrane and a second filtration membrane. A liquid is passed through the first filtration membrane in a first direction to accumulate the fine particles on the surface of the first filtration membrane, and then a stripping liquid is passed through the first filtration membrane in a second direction that is opposite to the first direction by switching the flow path, and the stripping liquid that has permeated the first filtration membrane is passed through the second filtration membrane, and the fine particles stripped from the first filtration membrane by the stripping liquid are captured on the surface of the second filtration membrane. Effect of the Invention

[0011] According to the present invention, it is possible to capture particles contained in liquid such as ultrapure water in a short time, and therefore it is possible to detect the particles by direct microscopy in a short time. [Brief description of the drawings]

[0012] [Figure 1] 1A to 1C are diagrams illustrating a method for detecting particles according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram illustrating a method for capturing fine particles when an ultrafiltration membrane is used as the first filtration membrane. [Diagram 3] FIG. 1 is a diagram illustrating the concentration process in each test example. [Figure 4] FIG. 1 is a diagram illustrating the recovery process in Test Examples 1 and 3. [Diagram 5] FIG. 1 is a diagram illustrating the recovery process in Test Example 2. [Figure 6] FIG. 13 is a diagram illustrating the recovery process in Test Example 4. [Figure 7] FIG. 13 is a diagram illustrating the recovery process in Test Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a method for detecting particles according to an embodiment of the present invention. In this embodiment, particles having a particle size of, for example, about several nm to several μm contained in a liquid are detected by a direct microscopic method. The liquid in which particles are detected is not particularly limited, but may be, for example, ultrapure water or pure water used in the manufacture of semiconductor devices and pharmaceuticals. In the following description, the liquid in which particles are detected is called sample water. The sample water contains particles 61.

[0014] The detection method of this embodiment is roughly divided into three steps: (a) a step of concentrating particles, (b) a step of recovering particles, and (c) a step of observing particles. The concentration step and the recovery step constitute the method of capturing particles according to the present invention.

[0015] First, the concentration process will be described. In the concentration process, the sample water is filtered by passing it through the first filtration device 10 equipped with the first filtration membrane 11 that does not allow the detection target particles 61 to pass through. Since the particles 61 cannot pass through the first filtration membrane 11, they accumulate on the surface of the first filtration membrane 11 and are concentrated. In the illustrated example, the sample water is flowed in a direction from the inlet 12 to the outlet 13 of the first filtration device 10. Since the first filtration membrane 11 itself is not an object of observation by the observation device, the first filtration membrane 11 can be a membrane with a large area in order to increase the amount of sample water passing through. From this perspective, a membrane that is widely used as an ultrafiltration membrane or a microfiltration membrane can be used as the first filtration membrane 11. A device in which a filtration membrane is incorporated into a module is a filtration device, and therefore a commercially available ultrafiltration membrane device or microfiltration membrane device can be used as the first filtration device 10. Ultrafiltration membranes and microfiltration membranes have a larger effective filtration area and a larger amount of permeated water than filtration membranes used in the detection of the number of particles by the conventional direct microscopic method, and are therefore advantageous for collecting particles. However, in order to increase the efficiency of collection of particles 61 in the first filtration membrane, it is preferable to pass sample water through the first filtration membrane 11 in a total amount filtration mode. In the present invention, passing water through the first filtration membrane 11 in a total amount filtration mode, in other words, passing water through the first filtration membrane 11 in a total amount permeation mode, includes not only the case where the entire amount of sample water is passed through the first filtration membrane 11, but also the case where a part of the sample water is not passed through the first filtration membrane 11 within a range that does not affect the accuracy of particle detection. The first filtration membrane 11 is a membrane used to remove particles 61 from the sample water, and is therefore also called a particle removal filtration membrane.

[0016] In the recovery process, after the concentration process, the flow path is switched to pass the stripping liquid through the first filtration membrane 11 in the opposite flow direction to that in the concentration process, thereby backwashing the first filtration membrane 11, and passing the stripping liquid that has permeated the first filtration membrane 11 through a second filtration membrane 21 different from the first filtration membrane 11. The second filtration membrane 21 is provided inside the second filtration device 20. The second filtration device 20 may be a centrifugal filtration device. In the example shown in FIG. 1, the sample water is passed through the first filtration device 11 in the direction from the inlet 12 to the outlet 13 in the concentration process, so that in the recovery process, the stripping liquid is made to flow in the direction from the outlet 13 to the inlet 12 in the first filtration device 11. The second filtration membrane 21 is a filtration membrane by surface filtration and is also called a filtration membrane for capturing fine particles, and captures fine particles on its surface for observation with an observation device such as an optical microscope or SEM. The surface of the second filtration membrane 21 has pores that communicate with the back side of the second filtration membrane 21. The pore size of the pore on the surface of the second filtration membrane 21 corresponds to the minimum particle size of the particles 61 to be detected. The pores may be formed with the same pore size from the surface to the back surface of the same second filtration membrane 21, or may be formed so that the pore size increases from the surface to the back surface. Therefore, particles and molecules having a particle size smaller than the pore size of the pore can pass through the second filtration membrane 21, but particles 61 having a particle size equal to or larger than the pore size of the pore cannot pass through the second filtration membrane 21 and are captured on the surface of the second filtration membrane 21. As the second filtration membrane 21, a filtration membrane that has been conventionally used for detecting particles by a direct microscopic method can be used.

[0017] In the recovery step, the first filtration membrane 11 is backwashed with the stripping liquid, so that the fine particles 61 accumulated on the surface of the first filtration membrane 11 in the concentration step are peeled off from the surface of the first filtration membrane 11 and transferred into the stripping liquid. The fine particles 61 transferred into the stripping liquid are then captured on the surface of the second filtration membrane 21 when the stripping liquid is passed through the second filtration membrane 21. For example, ultrapure water can be used as the stripping liquid, but in order to increase the peeling efficiency of the fine particles 61 accumulated on the surface of the first filtration membrane 11, it is preferable to use functional water adjusted to the alkaline side as the stripping liquid. It is more preferable that the stripping liquid contains dissolved hydrogen. As an example, it is preferable that the pH of the stripping liquid is 10 or more and the dissolved hydrogen concentration is 1 mg / L or more. Furthermore, in order to promote the peeling of the fine particles 61 from the first filtration membrane 11 during backwashing, it is preferable to apply vibration to the first filtration membrane 11 in the recovery step. 1, the vibrator 15 applies vibration to the entire first filtration device 10, thereby applying vibration to the first filtration membrane 11. In addition, in the recovery process, it is preferable that the entire amount of the stripping liquid that has permeated the first filtration membrane 11 is passed through the second filtration membrane 21.

[0018] Here, the difference in membrane properties between the first filtration membrane 11, which is a filtration membrane for removing fine particles, and the second filtration membrane 21, which is a filtration membrane for capturing fine particles, will be described. The first filtration membrane 11 is a filtration membrane that has a large effective filtration area and is capable of filtering a large amount of sample water, whereas the second filtration membrane 21 is a membrane that has an effective filtration area smaller than that of the first filtration membrane 11 and captures fine particles in a stripping solution with a small amount of permeated water. A commercially available ultrafiltration membrane or microfiltration membrane can be used for the first filtration membrane 11, and it is possible to use the first filtration membrane 11 as a filtration membrane for capturing fine particles to capture fine particles of the same size as those that the second filtration membrane 21 can capture. However, when the first filtration membrane 11 itself is used as a filtration membrane for capturing fine particles to detect fine particles by a direct microscopic method, there are disadvantages as described below. First, in order to ensure the accuracy of detecting fine particles, when observing the surface of the filtration membrane that has captured fine particles, the area to be observed needs to be a certain ratio or more to the effective filtration area of ​​the filtration membrane, and when the fine particles are captured by the first filtration membrane 11 with a large effective filtration area, it takes a long time to observe the fine particles. In addition, when an ultrafiltration membrane or a microfiltration membrane is used as the first filtration membrane 11, it may not be possible to remove the filtration membrane from a filtration device equipped with such a filtration membrane without damaging the filtration membrane. As a method for increasing the effective filtration area of ​​the filtration membrane, a hollow fiber membrane, a cylindrical membrane, or a pleated membrane may be used, but such membranes with an uneven surface are not suitable for observation with an observation device. In contrast, the second filtration membrane 21 with a small effective filtration area can be a flat membrane, and the surface of the filtration membrane can be easily observed.

[0019] After the particles are captured on the surface of the second filtration membrane 21 in the recovery process, the observation process is performed. In the observation process, the second filtration membrane 21 is removed from the second filtration device 20, and the second filtration membrane 21 is placed in an observation device such as an optical microscope or SEM, and the surface of the second filtration membrane 21, i.e., the filtration surface, is observed with the observation device to detect the particles 61. If the pore size of the pores formed in the second filtration membrane 21 is d, the particles 61 having a particle size of d or more cannot pass through the second filtration membrane 21. Therefore, by counting the number of the particles 61 captured in the observation image 60, the number of the particles 61 having a particle size of d or more contained in the stripping solution can be calculated. The number of particles may be counted by visually counting the observation image 60, or may be measured by image processing of the observation image 60 using software. Equation (1) represents the number of particles per unit volume, and the amount of filtered water is the volume of the sample water passed through the first filtration membrane 11 in the concentration process.

[0020]

number

[0021] In formula (1), the observation rate is the ratio of the area of ​​the portion actually observed by the observation device to the effective filtration area of ​​the second filtration membrane 21. When an SEM or a high-magnification optical microscope is used as the observation device, the field of view of the observation device is narrow, so it is necessary to obtain a large number of observation images 60. In such a case, the observation rate is expressed by formula (2). As an example, when the effective filtration area of ​​the second filtration membrane 21 is several hundred square millimeters and the field of view area of ​​one observation image 60 is on the order of 0.0001 square millimeters, it is possible to achieve an observation rate of about 0.01% by obtaining several hundred observation images 60.

[0022]

number

[0023] In the detection method described above, it is possible to select a filtration membrane having a large area, such as an ultrafiltration membrane or a microfiltration membrane, as compared with a filtration membrane generally used for capturing fine particles, and a filtration membrane having a small pressure loss when configured as a filtration membrane device is used as the first filtration membrane. Then, in the concentration step, filtration is performed using the first filtration membrane 11 to first accumulate the fine particles 61 on the first filtration membrane 11. Next, in the recovery step, the first filtration membrane 11 is backwashed using a small amount of stripping liquid to strip the fine particles 61 from the surface of the first filtration membrane 11, and the stripping liquid containing the stripped fine particles 61 is passed through the second filtration membrane 21. Since the first filtration membrane 11 can filter the sample water at a high liquid passing speed, a large amount of sample water can be processed in a short time to accumulate the fine particles 61 in the sample water on the first filtration membrane 11. The fine particles 61 accumulated on the first filtration membrane 11 are then transferred onto the second filtration membrane 21 using a small amount of stripping liquid. At this time, the concentration of the particles 61 in the stripping liquid is much higher than the concentration of the particles 61 in the sample water in the concentration step. Since the amount of the stripping liquid passed through the second filtration membrane 21 is small, the filtration time in the second filtration membrane 21, which is a filtration membrane for capturing particles, is short. In this embodiment, the particles 61 contained in a large amount of sample water can be captured on the surface of the second filtration membrane 21 in a short time, so that the filtration time for detecting the particles by the direct microscopy method can be significantly shortened. By significantly shortening the filtration time for detecting the particles, according to this embodiment, it becomes easier to follow the trend of water quality changes, and it becomes easier to determine the occurrence of abnormalities, and the frequency of sampling for measuring the number of particles can be increased, for example, from once a month to once every few days.

[0024] FIG. 2 is a diagram for explaining the detection method of this embodiment when a commercially available ultrafiltration membrane device is used as the first filtration device 10. Here, the concentration process shown in (a) and the recovery process shown in (b) are explained. The ultrafiltration membrane device is, for example, a hollow fiber ultrafiltration membrane incorporated in a module. The first filtration device 10 explained here is a cylindrical container in which a large number of ultrafiltration membranes (first filtration membrane 11), each of which is a hollow fiber membrane, are arranged parallel to each other. In a general method of using an ultrafiltration membrane made of a hollow fiber membrane, the water to be treated is made to flow outside the hollow fiber membrane in a crossflow method, and filtered water (i.e., permeated water) is obtained from the inside of the hollow fiber membrane. For this reason, the cylindrical container is provided with an inlet 12 for the water to be treated and an outlet 16 for concentrated water. Cap parts 15A and 15B are provided at both ends of the container, and the internal space of each ultrafiltration membrane is connected to the cap parts 15A and 15B. The cap parts 15A and 15B are provided with outlets 13A and 13B, respectively, through which liquid that has permeated the ultrafiltration membrane, i.e., the first filtration membrane 11, is discharged. A pipe is provided to connect the outlets 13A and 13B to each other, and a valve 19 is connected to this pipe. Fixing parts 17A and 17B made of epoxy resin or the like are provided adjacent to the cap parts 15A and 15B, respectively, in order to bundle the ultrafiltration membranes. When such an ultrafiltration membrane device is used as the first filtration device 10, a second filtration device 20 can be connected to the concentrated water outlet 16 via a valve 22.

[0025] In the concentration step (FIG. 2(a)), the valve 22 is closed, and the sample water is supplied to the inlet 12 via the valve 14. The sample water permeates the ultrafiltration membrane, which is the first filtration membrane 11, and is discharged as wastewater from the outlets 13A and 13B via the valve 19, and the fine particles 61 in the sample water are accumulated on the surface of the ultrafiltration membrane. Next, in the recovery step (FIG. 2(b)), the valve 14 is closed, the valve 22 is opened, and the stripping liquid is injected into the ultrafiltration membrane device from the outlets 13A and 13B via the valve 19. The stripping liquid is supplied to the internal space of the ultrafiltration membrane, which is a hollow fiber membrane, so that the ultrafiltration membrane is backwashed, and the stripping liquid that has permeated the ultrafiltration membrane flows into the second filtration device 20 via the valve 22. The fine particles 61 in the stripping liquid are captured by the second filtration membrane 21 in the second filtration device 20. In this embodiment, the ultrafiltration membrane serving as the first filtration membrane 11 is a hollow fiber membrane, but the shape of the ultrafiltration membrane used as the first filtration membrane 11 is not limited to this. Also, a microfiltration membrane device having a microfiltration membrane having a hollow fiber shape, pleated shape, or the like can also be used as the first filtration device 10. EXAMPLES

[0026] The present invention will be described in more detail by explaining test examples carried out in relation to the present invention. The members used in each test example are described below.

[0027] Polystyrene latex (PSL) manufactured by Thermo Fisher, particle size: 100 nm, was used as the standard particle simulating the fine particles 61 contained in the sample water. Asahi Kasei's Lab Module UF, which is an ultrafiltration membrane device, was used as the first filtration device 10. This first filtration device 10 is equipped with a hollow fiber-shaped ultrafiltration membrane used as the first filtration membrane 11 in each test example, and is equipped with an inlet I, a concentrated water outlet C, and two permeate outlets P1 and P2. Here, a filter having two permeate outlets was used, but the number of permeate outlets may be one. Nuclepore membrane: pore size 50 nm was used as the second filtration membrane 21, which is a filter membrane for capturing fine particles. The functional water used as the stripping liquid was produced by adding ammonia to hydrogen water obtained using Organo's Acid-Kan-Oh (registered trademark). The pH of the functional water was 10 or more, and the dissolved hydrogen concentration was 1 mg / L or more.

[0028] [Basic test example] The apparatus shown in FIG. 3 was assembled. In the apparatus shown in FIG. 3, ultrapure water from an ultrapure water source 41 is supplied to an inlet I of a first filtration device 10 through a pipe 31. A valve 42 and a flow meter 43 are provided on the pipe 31. A pipe 32 is provided to connect a concentrated water outlet C of the first filtration device 10 to a second filtration device 20, and a valve 44 is provided on the pipe 32. A pipe 33 is provided to connect two permeate outlets P1 and P2 of the first filtration device 10 to each other, a pipe 34 branches off from the pipe 33, and a valve 45 is provided on the pipe 34. A container 46 is provided to store a microparticle dispersion liquid in which standard particles are dispersed in ultrapure water, and a pipe 35 is provided to connect the container 46 and the pipe 31. A pump 47 is provided on the pipe 35. Furthermore, a vibrator 15 is attached to the first filtration device 10. A vortex mixer is used as the vibrator 15, and vibrations during operation of the vortex mixer are transmitted to the first filtration device 10. The apparatus configuration shown in FIG. 3 is common to the concentration step in each test example.

[0029] First, a concentration step was carried out. With the valves 42 and 45 open and the valve 44 closed, ultrapure water from the ultrapure water source 41 was supplied as sample water to the first filtration device 10 at 1300 mL / min for 90 minutes. At this time, the pump 47 was operated to add a microparticle dispersion to the ultrapure water so that the concentration of the standard particles in the ultrapure water was 100 particles / mL. The ultrapure water that permeated the first filtration membrane 11 was discharged as wastewater from the permeate outlets P1 and P2 via the pipes 33 and 34, and the microparticles 61 (standard particles) that had been added to the ultrapure water were accumulated on the first filtration membrane 11, which is a filtration membrane for removing microparticles.

[0030] After the concentration process was completed, the flow path was switched to carry out the recovery process. In the recovery process, the valve 42 was closed, and the stripping liquid stored in the storage tank 48 was supplied to the pipe 34 via the pump 49, and this stripping liquid was made to flow into the first filtration device 10 from the permeate outlets P1 and P2 via the valve 45 and the pipe 33. As the stripping liquid, the functional water having a pH of 10 or more and a dissolved hydrogen concentration of 1 mg / L or more was used. The vibrator 15 was operated to apply vibration to the first filtration membrane 11, while backwashing the first filtration membrane 11 with the stripping liquid, and the stripping liquid after backwashing was passed through the second filtration membrane 21. The flow rate of the stripping liquid passed through the first filtration membrane 11 at this time was set to 5 mL / min, which allows the second filtration membrane 21 to filter the entire amount.

[0031] After the recovery step was performed, the second filtration membrane 21 was removed from the second filtration device 20 and observed with an observation device at an observation rate of 0.01% to count the number of particles 61 on the second filtration membrane 21. The recovery rate, which indicates how many of the particles 61 injected in the concentration step were present on the second filtration membrane 21, was calculated to be 75%. The recovery rate is given by equation (3).

[0032]

number

[0033] [Test Example 1] A test was performed in the same manner as in the basic test example, except that the vibrator 15 was removed, and the recovery rate was calculated. The recovery rate was 5%. Figure 5 shows the device configuration in the recovery process of test example 1.

[0034] [Test Example 2] The test was carried out in the same manner as in the basic test example, except that ultrapure water was used as the stripping solution, and the recovery rate was calculated. The recovery rate was 12%.

[0035] [Test Example 3] After the concentration step was performed in the same manner as in the basic test example, the flow path was switched to perform the recovery step. In the recovery step in the test example 3, the same functional water as in the basic test example was used as the stripping liquid, and the stripping liquid stored in the storage tank 48 was supplied to the pipe 31 connected to the inlet I of the first filtration device 11 via the pipe 36 and the pump 49 as shown in FIG. 6. The valves 42 and 45 were closed, and the valve 44 was opened. The stripping liquid was caused to flow from the inlet I of the first filtration device 10 to the concentrated side outlet C while vibrating the first filtration membrane 11 by operating the vibrator 15, and the stripping liquid discharged from the concentrated side outlet C was allowed to pass through the second filtration membrane 21. In this case, the flow direction of the stripping liquid is the direction in which the concentrated water flows in the first filtration membrane 11. The flow rate of the stripping liquid at this time was set to 5 mL / min, which allows the second filtration membrane 21 to filter the entire amount. The recovery rate was calculated in the same manner as in the basic test example, and was 11%.

[0036] [Test Example 4] In the basic test example, a bypass pipe 37 equipped with a valve 50 was connected to the concentrated side outlet C of the first filtration device 10 as shown in Fig. 7. The flow rate of the stripping liquid in the recovery process was set to be sufficiently higher than 5 mL / min, so that the stripping liquid exceeding 5 mL / min flowed at a high flow rate through the bypass pipe 37. The recovery rate was determined in the same manner as in the basic test example, and was found to be 0%.

[0037] The results obtained in the basic test example and test examples 1 to 4 are shown in Table 1.

[0038] [Table 1]

[0039] From the results shown in Table 1, in the recovery process, (1) It is preferable to perform the peeling of the fine particles 61 while applying vibration to the first filtration membrane 11, which is a filtration membrane for removing fine particles. (2) As the stripping solution, it is preferable to use functional water rather than ultrapure water, and it is particularly preferable to use functional water adjusted to the alkaline side and containing dissolved hydrogen. (3) It is preferable that the direction in which the stripping solution is passed through the first filtration membrane 11 is the backwash direction. (4) The flow rate of the stripping solution is preferably within a range in which the entire amount can be treated by the second filtration membrane 21, which is a filtration membrane for capturing fine particles. It has been found that, in the present invention, the phrase "a range in which the entire amount can be processed by the second filtration membrane 21", in other words, "passing the entire amount through the second filtration membrane in a permeable form" refers not only to the range in which the entire amount of the eluent can pass through the second filtration membrane 21, but also to the case where the range exceeds the range in which the entire amount of the eluent can pass through the second filtration membrane 21 without affecting the particle detection accuracy. [Explanation of symbols]

[0040] 10 First filtration device 11 First filtration membrane 15. Vibrator 20 Second filtration device 21 Second filtration membrane 60 Observation image 61 Fine particles

Claims

1. A method for trapping fine particles in a liquid, comprising the steps of: a concentration step of passing the liquid through a first filtration membrane in a first direction to accumulate the fine particles on a surface of the first filtration membrane; a recovery step of passing a stripping liquid through the first filtration membrane in a second direction opposite to the first direction after the concentration step, passing the stripping liquid that has permeated the first filtration membrane through a second filtration membrane different from the first filtration membrane, and stripping the fine particles from the first filtration membrane and capturing them on a surface of the second filtration membrane; The capture method comprising:

2. The capture method according to claim 1 , wherein the first filtration membrane is an ultrafiltration membrane or a microfiltration membrane, and in the concentration step, the liquid is passed through the first filtration membrane in a total permeation form.

3. The capture method according to claim 1 or 2, wherein the first filtration membrane is subjected to vibration in the recovery step.

4. The capturing method according to claim 1 or 2, wherein the second filtration membrane is a filtration membrane for capturing fine particles, and in the recovery step, the stripping liquid is passed through the second filtration membrane in a total-amount permeation form.

5. 3. The capturing method according to claim 1, wherein the stripping solution is functional water adjusted to be alkaline.

6. The capture method according to claim 5 , wherein the pH of the stripping solution is 10 or higher.

7. A method for detecting particles in a liquid, comprising: A detection method comprising the steps of: subjecting the liquid to the capture method according to claim 1 or 2; and then observing the particles captured on the surface of the second filtration membrane with an observation device to detect the particles.

8. The first filtration membrane is an ultrafiltration membrane or a microfiltration membrane and has an effective membrane area larger than the effective membrane area of ​​the second filtration membrane; 8. The detection method according to claim 7, wherein the second filtration membrane is a membrane having pores with a pore size equivalent to the particle size of the particles to be detected.

9. A trapping device for trapping fine particles in a liquid, comprising: A first filtration membrane; A second filtration membrane; and Equipped with A capture device that passes the liquid through the first filtration membrane in a first direction to accumulate the fine particles on the surface of the first filtration membrane, and then switches the flow path to pass a stripping liquid through the first filtration membrane in a second direction that is opposite to the first direction, so that the stripping liquid that has permeated the first filtration membrane passes through the second filtration membrane, and captures the fine particles stripped from the first filtration membrane by the stripping liquid on the surface of the second filtration membrane.

10. The capture device of claim 9 , further comprising a vibrator for applying vibrations to the first filtration membrane.

Images