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

Abstract

This method for capturing fine particles in a liquid comprises: a concentration step in which a liquid is passed through a first filtration membrane (11) in a first direction and microparticles (61) are accumulated on the surface of the first filtration membrane (11); and a recovery step in which, after the concentration step, a release liquid is passed through the first filtration membrane (11) in a second direction that is opposite to the first direction, and the release liquid that has passed through the first filtration membrane (11) is passed through a second filtration membrane (21) that is different from the first filtration membrane (11), so that the microparticles (61) are separated from the first filtration membrane (11) and captured on the surface of the second filtration membrane (21).

Description

Method for capturing and detecting particles in a liquid, and device for capturing particles

[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.

[0002] Ultrapure water production systems that produce ultrapure water for use in the manufacture of semiconductor devices and pharmaceuticals typically include 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. The subsystem contains various devices, such as an ultraviolet oxidation device and an ion exchange device, arranged in series. 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 (POU), and a membrane filtration device, such as an ultrafiltration membrane device (UF) or a microfiltration membrane device (MF), is located immediately before the point of use in the ultrapure water supply pathway to remove particulates.

[0003] In recent years, demands for the quality of ultrapure water have become increasingly stringent. For example, particles contained in ultrapure water used in semiconductor device manufacturing directly affect the yield of semiconductor products. Therefore, strict control of both particle size and concentration of particles contained in ultrapure water is required. For example, it is sometimes necessary to control the particle concentration, i.e., the number of particles contained in a unit volume of ultrapure water, below a specified value. One known method for detecting particles in pure water or ultrapure water is the direct microscopic method specified in JIS (Japanese Industrial Standards) K0554-1995, "Method for Measuring Particles in Ultrapure Water." This method first filters pure water or ultrapure water through a filtration membrane to capture particles on the membrane. The filtration membrane is then observed using an observation device such as an optical microscope or a scanning electron microscope (SEM) to detect the particles trapped on the membrane. Small particles can be detected by using a filtration membrane with a pore size smaller than the particle size of the target particle. The filtration membrane used to capture particles has pores with a pore size equal to the lower limit of the particle size of the particles to be captured. Filtration membranes are required to have small variations in the pore size of their pores. For example, pores created by anodizing metals or pores created by irradiating polymer materials with heavy particle beams and then etching to enlarge the pore size are used as pores in filtration membranes.

[0004] In direct microscopy, to ensure reliable detection of particle counts, it is desirable to capture a number of particles on the filtration membrane equal to or greater than the number of particles initially present on the filtration membrane. To achieve this, a sufficient amount of ultrapure water or pure water must be passed through the filtration membrane. Furthermore, the smaller the particle size of the particles to be detected, the smaller the pore size of the filtration membrane must be, resulting in increased pressure loss across the filtration membrane. Since the pores in the filtration membrane used to capture particles are formed using the special method described above to reduce the pore size variation, the surface density of the pores in the filtration membrane cannot be increased, resulting in even greater pressure loss. For these reasons, detecting small particles requires filtering the pure or ultrapure water to be used for particle detection for a long period of time.

[0005] As an attempt to shorten the filtration time in direct microscopy, Patent Document 1 discloses the use of a centrifugal filter. In the technology described in Patent Document 1, a 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 a rotating part, centrifugal force acts on the liquid in the liquid chamber toward the filtration membrane, increasing the flow rate of the liquid permeating the filtration membrane and, as a result, shortening the time required for filtration.

[0006] JP 2016-55240 A

[0007] When detecting particles by direct microscopy, the smaller the particle size of the target particles and the smaller the lower limit of quantification for the number of particles, the longer the time required for filtration to capture the particles. Even when using a centrifugal filter as described in Patent Document 1, filtration requires a long time. The longer the filtration time, the longer the time required to detect particles by direct microscopy. Ultrapure water used in the manufacture of semiconductor devices is required to control particles with a particle size of 10 nm or more at a level of several particles per mL, for example. This control requires that particle detection results be obtained quickly. Therefore, when detecting particles by direct microscopy, the filtration time required to capture the particles needs to be shortened. To shorten the filtration time, it is necessary to process a large amount of liquid in a short period of time and capture the particles contained in the liquid.

[0008] The object of the present invention is to provide a capture method that can capture particles contained in a liquid in a short period of time, a detection method that detects particles using this capture method, and a capture device that captures particles.

[0009] According to one aspect of the present invention, a capture method for capturing fine particles in a liquid includes a concentration step of passing the liquid through a first filtration membrane in a first direction to accumulate the 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 in a second direction opposite to the first direction, and passing the stripping liquid that has permeated the first filtration membrane through a second filtration membrane different from the first filtration membrane to peel the fine particles from the first filtration membrane and capture them on the surface of the second filtration membrane. Note that with respect to the first direction and the second direction in the liquid flow direction through the first filtration membrane, the flow direction when the liquid passes through the first filtration membrane in a direction that filters and removes the fine particles in the liquid is defined as the first direction, and the flow direction opposite to the first direction is defined as the second 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.

[0010] According to one aspect of the present invention, the detection method is a detection method for detecting particles in a liquid, in which the capture method of the above-mentioned aspect is performed on the liquid, and then the particles captured on the surface of the second filtration membrane are observed with an observation device to detect the particles.

[0011] According to one aspect of the present invention, a capture device is a capture device for capturing fine particles in a liquid, and includes a first filtration membrane and a second filtration membrane. The capture device passes a liquid through the first filtration membrane in a first direction to accumulate 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, and passes the stripping liquid that has permeated the first filtration membrane through a 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.

[0012] According to the present invention, it is possible to capture particles contained in liquid such as ultrapure water in a short time, and therefore, according to the present invention, it is possible to detect particles by direct microscopy in a short time.

[0013] FIG. 1 is a diagram illustrating a method for detecting particles according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a process for concentrating particles using a first filtration membrane. FIG. 3 is a diagram illustrating a process for recovering particles using a second filtration membrane. FIG. 4 is a diagram illustrating a concentration process in each test example. FIG. 5 is a diagram illustrating a recovery process in test examples 1 and 3. FIG. 6 is a diagram illustrating a recovery process in test example 2. FIG. 7 is a diagram illustrating a recovery process in test example 4. FIG. 8 is a diagram illustrating a recovery process in test example 5.

[0014] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a method for detecting particles according to one embodiment of the present invention. In this embodiment, particles having a particle size of, for example, several nanometers to several micrometers contained in a liquid are detected by direct microscopy. The liquid in which particles are to be detected is not particularly limited, but examples include ultrapure water and pure water used in the manufacture of semiconductor devices and pharmaceuticals. In the following description, the liquid in which particles are to be detected is referred to as sample water. The sample water contains particles 61.

[0015] 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, as shown in Figure 1. The concentration step and the recovery step constitute the method of capturing particles according to the present invention.

[0016] (a) Concentration Process First, the concentration process will be described. In the concentration process, sample water is filtered by passing it through a first filtration device 10 equipped with a first filtration membrane 11 that does not allow the 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 example shown in FIG. 1 , the sample water flows from the inlet 12 to the outlet 13 of the first filtration device 10. Because the first filtration membrane 11 itself is not the object of observation by the observation device, the first filtration membrane 11 can be made to have a large surface area to increase the amount of sample water that passes through. From this perspective, membranes widely used as ultrafiltration membranes or microfiltration membranes can be used as the first filtration membrane 11. A filtration device is a device incorporating a filtration membrane into a module. Therefore, commercially available ultrafiltration membrane devices or microfiltration membrane devices can be used as the first filtration device 10. Ultrafiltration membranes and microfiltration membranes have a larger effective filtration area and a larger permeate volume than membranes used for detecting particle counts using conventional direct microscopy, making them advantageous for capturing particles. However, to increase the capture efficiency of particles 61 in the first filtration membrane, it is preferable to pass sample water through the first filtration membrane 11 using a dead-end filtration method. In the present invention, passing water through the first filtration membrane 11 using a dead-end filtration method, in other words, passing water through the first filtration membrane 11 in a dead-end permeation mode, includes not only passing the entire amount of sample water through the first filtration membrane 11, but also not passing a portion of the sample water through the first filtration membrane 11 to the extent that it does not affect particle detection accuracy. Because the first filtration membrane 11 is used to remove particles 61 from the sample water, it is also called a particle removal filtration membrane.

[0017] (b) Recovery Step Next, the recovery step will be described. In the recovery step, after the concentration step, the flow path is switched to pass the stripping solution through the first filtration membrane 11 in a flow direction opposite to that in the concentration step, thereby backwashing the first filtration membrane 11, and the stripping solution that has permeated the first filtration membrane 11 is passed 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 flows from the inlet 12 to the outlet 13 in the first filtration device 10 during the concentration step. Therefore, in the recovery step, the stripping solution flows from the outlet 13 to the inlet 12 in the first filtration device 10. The second filtration membrane 21 is a surface filtration membrane, also known as a particle-capturing filtration membrane, and captures 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 diameter of the pores on the surface of the second filtration membrane 21 corresponds to the smallest particle size of the particles 61 to be detected. The pores may be formed with the same pore diameter from the front to the back of the same second filtration membrane 21, or may be formed so that the pore diameter increases from the front to the back. Therefore, particles and molecules with a particle size smaller than the pore diameter of the pores can pass through the second filtration membrane 21, but particles 61 with a particle size equal to or larger than the pore diameter 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 conventionally used for detecting particles by direct microscopy can be used.

[0018] In the recovery process, the first filtration membrane 11 is backwashed with a stripping solution, causing the fine particles 61 that accumulated on the surface of the first filtration membrane 11 during the concentration process to peel off from the surface and migrate into the stripping solution. The fine particles 61 that have migrated into the stripping solution are then captured on the surface of the second filtration membrane 21 when the stripping solution is passed through the second filtration membrane 21. While ultrapure water can be used as the stripping solution, it is preferable to use functional water adjusted to an alkaline side as the stripping solution to enhance the peeling efficiency of the fine particles 61 that have accumulated on the surface of the first filtration membrane 11. It is more preferable that the stripping solution contain dissolved hydrogen. For example, the stripping solution preferably has a pH of 10 or higher and a dissolved hydrogen concentration of 1 mg / L or higher. Furthermore, it is preferable to vibrate the first filtration membrane 11 during the recovery process to promote the peeling of the fine particles 61 from the first filtration membrane 11 during backwashing. 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 step, it is preferable that the entire amount of the stripping solution that has permeated the first filtration membrane 11 passes through the second filtration membrane 21.

[0019] Here, we will explain the differences 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. The first filtration membrane 11 has a large effective filtration area and is capable of filtering large amounts of sample water. In contrast, the second filtration membrane 21 has a smaller effective filtration area than the first filtration membrane 11 and is capable of capturing fine particles in the stripping solution with a small amount of permeated water. Commercially available ultrafiltration membranes or microfiltration membranes 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 of approximately the same size as those that can be captured by the second filtration membrane 21. However, when the first filtration membrane 11 itself is used as a filtration membrane for capturing fine particles to detect fine particles by direct microscopy, there are disadvantages as described below. First, to ensure accurate particle detection, when observing the surface of a filtration membrane that has captured particles, the observation area must be at least a certain percentage of the effective filtration area of ​​the filtration membrane. If particles are captured using a first filtration membrane 11 with a large effective filtration area, observing the particles will take a long time. Furthermore, if an ultrafiltration membrane or microfiltration membrane is used as the first filtration membrane 11, it may be difficult to remove the filtration membrane from a filtration device equipped with such a filtration membrane without damaging the membrane. Techniques for increasing the effective filtration area of ​​a filtration membrane include the use of hollow fiber membranes, cylindrical membranes, and pleated membranes, but such membranes with uneven surfaces are not suitable for observation using an observation device. In contrast, the second filtration membrane 21, which has a small effective filtration area, can be a flat membrane, making it easier to observe the surface of the filtration membrane.

[0020] (c) Observation Step The observation step will now be described. After the microparticles are captured on the surface of the second filtration membrane 21 in the recovery step, the observation step is then carried out. In the observation step, 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. The surface of the second filtration membrane 21, i.e., the filtration surface, is observed with the observation device to detect the microparticles 61. If the pore diameter of the pores formed in the second filtration membrane 21 is d, microparticles 61 with a particle diameter of d or greater cannot pass through the second filtration membrane 21. Therefore, by counting the number of microparticles 61 captured in the observation image 60, the number of microparticles 61 with a particle diameter of d or greater contained in the stripping solution can be calculated. The number of microparticles may be counted visually in the observation image 60, or may be counted by software image processing of the observation image 60. In the concentration step, the volume of the sample water passed through the first filtration membrane 11 is defined as the filtrate volume Q, and the observation rate is defined as η. The number of particles N per unit volume is expressed by the following formula (1). The observation rate η is the effective filtration area S of the second filtration membrane 21. ｆ is the ratio of the area of ​​the part actually observed by the observation device to the area of ​​the

[0021]

[0022] 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 acquire a large number of observation images 60. In such a case, the number of captured observation images is defined as n, and the field area of ​​the observation device is defined as S. ｖ As an example, the effective filtration area S of the second filtration membrane 21 is expressed by the following equation (2): ｆ is several hundred square millimeters, and the field of view area S ｖ When is on the order of 0.0001 square millimeters, by acquiring several hundred observation images 60, it is possible to achieve an observation rate η of about 0.01%.

[0023]

[0024] In the detection method described above, a filtration membrane with a large surface area, such as an ultrafiltration membrane or a microfiltration membrane, can be selected compared to filtration membranes commonly used for capturing microparticles. A filtration membrane with 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, and the microparticles 61 are first accumulated on the first filtration membrane 11. Next, in the recovery step, the first filtration membrane 11 is backwashed with a small amount of stripping solution to strip the microparticles 61 from the surface of the first filtration membrane 11, and the stripping solution containing the stripped microparticles 61 is passed through the second filtration membrane 21. Because the first filtration membrane 11 can filter the sample water at a high liquid passage rate, a large amount of sample water can be processed in a short period of time, allowing the microparticles 61 in the sample water to accumulate on the first filtration membrane 11. The microparticles 61 accumulated on the first filtration membrane 11 are then transferred to the second filtration membrane 21 using a small amount of stripping solution. At this time, the concentration of the particles 61 in the stripping solution is much greater than the concentration of the particles 61 in the sample water during the concentration process. Because the amount of stripping solution passed through the second filtration membrane 21 is small, the filtration time through 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, thereby significantly shortening the filtration time required for particle detection by direct microscopy. By significantly shortening the filtration time required for particle detection, this embodiment makes it easier to track trends in water quality changes, facilitates the determination of abnormalities, and increases the frequency of sampling for particle count measurement, from once a month to once every few days.

[0025] 2A and 2B are diagrams illustrating the detection method of this embodiment when a commercially available ultrafiltration membrane device is used as the first filtration device 10, with FIG. 2A showing the concentration process and FIG. 2B showing the recovery process. The ultrafiltration membrane device is, for example, a module incorporating hollow fiber ultrafiltration membranes. The first filtration device 10 described here is a cylindrical container in which multiple ultrafiltration membranes (first filtration membranes 11), each of which is a hollow fiber membrane, are arranged parallel to one another. In typical usage, hollow fiber ultrafiltration membranes are configured to pass water to the outside of the hollow fiber membranes in a crossflow manner, and filtered water (i.e., permeate) is obtained from the inside of the hollow fiber membranes. Therefore, the cylindrical container is provided with an inlet 12 for water to be treated and an outlet 16 for concentrated water. Caps 15A and 15B are provided at both ends of the container, and the internal space of each ultrafiltration membrane is connected to the caps 15A and 15B. The cap portions 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. Pipes are provided to interconnect the outlets 13A and 13B, and valves 19 are connected to these pipes. Fixing portions 17A and 17B made of epoxy resin or the like are provided adjacent to the cap portions 15A and 15B, respectively, 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.

[0026] In the concentration step, as shown in FIG. 2A , valve 22 is closed, and sample water is supplied to inlet 12 via valve 14. The sample water permeates the ultrafiltration membrane, which is the first filtration membrane 11, and is discharged as wastewater from outlets 13A and 13B via valve 19. Fine particles 61 in the sample water accumulate on the surface of the ultrafiltration membrane. Subsequently, in the recovery step, as shown in FIG. 2B , valve 14 is closed, valve 22 is opened, and a stripping solution is injected into the ultrafiltration membrane device via outlets 13A and 13B via valve 19. The stripping solution is supplied to the internal space of the hollow fiber ultrafiltration membrane, which backwashes the ultrafiltration membrane. The stripping solution that permeates the ultrafiltration membrane flows into second filtration device 20 via valve 22. Fine particles 61 in the stripping solution are captured by second filtration membrane 21 in second filtration device 20. Although the ultrafiltration membrane serving as the first filtration membrane 11 is described herein as being a hollow fiber membrane, the shape of the ultrafiltration membrane used as the first filtration membrane 11 is not limited to this. Furthermore, a microfiltration membrane device having a microfiltration membrane in a shape such as a hollow fiber or pleated shape can also be used as the first filtration device 10.

[0027] The present invention will be explained in more detail by describing test examples carried out in connection with the present invention. The members used in each test example are described below.

[0028] Thermo Fisher polystyrene latex (PSL) with a particle size of 100 nm was used as the standard particle simulating the fine particles 61 contained in the sample water. Asahi Kasei's LaboModule UF, an ultrafiltration membrane device, was used as the first filtration device 10. This first filtration device 10 includes a hollow fiber 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. While a device with two permeate outlets was used here, the number of permeate outlets may also be one. A Nuclepore membrane with a pore size of 50 nm was used as the second filtration membrane 21, which is a filtration membrane for capturing fine particles. The functional water used as the stripping solution 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 higher, and the dissolved hydrogen concentration was 1 mg / L or higher.

[0029] [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 the inlet I of the first filtration device 10 via a pipe 31. The pipe 31 is provided with a valve 42 and a flow meter 43. A pipe 32 is provided connecting the concentrated water outlet C of the first filtration device 10 to the second filtration device 20, and a valve 44 is provided on the pipe 32. A pipe 33 is provided connecting the two permeate outlets P1 and P2 of the first filtration device 10 to each other, and a pipe 34 branches off from the pipe 33 and is provided with a valve 45 on the pipe 34. A container 46 containing a microparticle dispersion liquid in which standard particles are dispersed in ultrapure water is provided, and a pipe 35 is provided connecting the container 46 to 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 generated by the vortex mixer during operation are transmitted to the first filtration device 10. The apparatus configuration shown in FIG. 3 is common to all test examples when carrying out the concentration step.

[0030] First, a concentration step was performed. With valves 42 and 45 open and valve 44 closed, ultrapure water from the ultrapure water source 41 was supplied as sample water to the first filtration device 10 at 1,300 mL / min for 90 minutes. During this time, the pump 47 was operated, and a microparticle dispersion was added to the ultrapure water so that the concentration α 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) added to the ultrapure water were accumulated on the first filtration membrane 11, which is a microparticle removal filtration membrane.

[0031] After the concentration process was completed, the flow path was switched to perform the recovery process. In the recovery process, the valve 42 was closed, and the stripping solution stored in the storage tank 48 was supplied to the pipe 34 via the pump 49. This stripping solution passed through the valve 45 and the pipe 33 and flowed into the first filtration device 10 from the permeate outlets P1 and P2. The functional water having a pH of 10 or higher and a dissolved hydrogen concentration of 1 mg / L or higher was used as the stripping solution. The vibrator 15 was operated to vibrate the first filtration membrane 11, while the first filtration membrane 11 was backwashed with the stripping solution. The backwashed stripping solution was passed through the second filtration membrane 21. The flow rate of the stripping solution passed through the first filtration membrane 11 was 5 mL / min, which allowed for complete filtration by the second filtration membrane 21.

[0032] After the recovery step, the second filtration membrane 21 was removed from the second filtration device 20 and observed with an observation device at an observation rate η of 0.01% to count the number of microparticles 61 on the second filtration membrane 21. The recovery rate R, which indicates how many of the microparticles 61 injected in the concentration step were present on the second filtration membrane 21, was calculated and found to be 75%. The recovery rate R is given by equation (3). Here, α indicates the concentration of the standard particles added, and in the example described here, α = 100 particles / mL.

[0033]

[0034] [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 R was determined. The recovery rate R was 5%. Figure 5 shows the device configuration in the recovery process of Test Example 1.

[0035] Test Example 2 A 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 R was determined. The recovery rate R was 12%.

[0036] [Test Example 3] After the concentration process was performed in the same manner as in the basic test example, the flow path was switched and the recovery process was performed. In the recovery process of Test Example 3, the same functional water as in the basic test example was used as the stripping liquid. As shown in FIG. 6, 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 10 via the pipe 36 and the pump 49. The valves 42 and 45 were closed, and the valve 44 was opened. The vibrator 15 was operated to apply vibration to the first filtration membrane 11 while the stripping liquid was flowed from the inlet I of the first filtration device 10 toward the concentrated water outlet C, and the stripping liquid discharged from the concentrated water outlet C was passed through the second filtration membrane 21. In this case, the flow direction of the stripping liquid was the same as the flow direction of the concentrated water in the first filtration membrane 11. The flow rate of the stripping liquid at this time was 5 mL / min, which allows full filtration by the second filtration membrane 21. The recovery rate R was calculated in the same manner as in the basic test example, and was found to be 11%.

[0037] Test Example 4 In the basic test example, a bypass pipe 37 equipped with a valve 50 was connected to the concentrated water outlet C of the first filtration device 10 as shown in Fig. 7. The flow rate of the stripping solution in the recovery step was set to be sufficiently higher than 5 mL / min, so that the amount of stripping solution 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%.

[0038] The results obtained in the basic test example and test examples 1 to 4 are shown in Table 1.

[0039]

[0040] From the results shown in Table 1, the following (1) to (4) were found: (1) In the recovery process, it is preferable to vibrate the first filtration membrane 11, which is a filtration membrane for removing fine particles, while peeling off the fine particles 61; (2) It is preferable to use functional water rather than ultrapure water as the stripping liquid used in the recovery process, and it is particularly preferable to use functional water that is adjusted to be alkaline and contains dissolved hydrogen; (3) In the recovery process, it is preferable that the direction in which the stripping liquid passes through the first filtration membrane 11 is the backwash direction; (4) It is preferable that the flow rate of the stripping liquid in the recovery process be within a range that can be completely processed by the second filtration membrane 21, which is a filtration membrane for capturing fine particles.

[0041] In relation to the present invention, when it is said that the "range in which the entire amount can be processed by the second filtration membrane 21" or, in other words, when it is said that the entire amount is passed through the second filtration membrane, it includes not only the range in which the entire amount of eluent can be passed through the second filtration membrane 21, but also the case in which the range in which the entire amount of eluent can be passed through the second filtration membrane 21 exceeds the range in which the entire amount of eluent can be passed through the second filtration membrane 21, as long as it does not affect the accuracy of particle detection.

[0042] REFERENCE SIGNS LIST 10 First filtration device 11 First filtration membrane 15 Vibrator 20 Second filtration device 21 Second filtration membrane 60 Observed image 61 Fine particles

Claims

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

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. A capture method as described in claim 1 or 2, wherein vibration is applied to the first filtration membrane in the recovery step.

4. A capture 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 permeation form.

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

8. The detection method described in claim 7, wherein 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, and the second filtration membrane is a membrane having pores with a pore size equivalent to the particle size of the microparticles to be detected.

9. A capture device for capturing fine particles in a liquid, comprising: a first filtration membrane; and a second filtration membrane, wherein the 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 opposite to the first direction by switching the flow path, so that 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.

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

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