Microplastic-containing water concentrating apparatus and method for concentrating microplastic-containing water, microplastic concentration measuring apparatus and method for measuring microplastic concentration

Abstract

To provide a microplastic-containing water concentrating apparatus and a method for concentrating microplastic-containing water capable of obtaining a microplastics (MPs) concentrate in which the MPs amount having a particle size to be measured in water containing MPs is sufficiently reflected.SOLUTION: A microplastic concentration measuring apparatus 1 includes: a first filter 12 having a first mesh size for capturing microplastics by passing microplastic-containing water 21 from a first side 12a to a second side 12b; a water sampling device 11 for supplying the microplastic-containing water 21 to the first filter 12; a backwashing device 13 for obtaining a recovery liquid 23 by passing a washing liquid 22 from the second side to the first side of the first filter 12; a second filter 14 having a second mesh size smaller than the first mesh size; and a concentrating device 15 for passing the recovery liquid 23 through the second filter 14 to concentrate the recovery liquid 23 and obtain a concentrate 24 of a second volume. The apparatus also includes a measuring device 16 for measuring a microplastic content of the concentrate 24.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for concentrating microplastic-containing water, an apparatus and method for measuring the concentration of microplastics. [Background technology]

[0002] Marine pollution caused by marine plastic waste has been confirmed all over the world. Currently, there is a need to fully understand the extent of marine pollution caused by marine plastic waste, given its impact on marine ecosystems.

[0003] The impact of marine plastic waste on the marine ecosystem varies depending on the particle size of the waste. Marine plastic waste in seawater with a particle size of 5 mm or less is called microplastics. Conventionally, methods described in Patent Documents 1 to 3 have been proposed as methods for recovering microplastics contained in seawater.

[0004] Patent Document 1 discloses a microplastic recovery system that includes a water intake line, a water treatment filter that filters the water taken in through the water intake line, a microplastic-containing water recovery device that recovers the microplastics captured in the water treatment filter, and a microplastic recovery device that treats the water containing the microplastics recovered by the microplastic-containing water recovery device and concentrates or separates the microplastics for recovery.

[0005] Patent Document 2 describes a sampling system for sampling target substances contained in environmental water acquired by a ship. The sampling system described in Patent Document 2 includes a water intake line for taking environmental water into the ship, a water intake pump, a filtration device having a filter for filtering the environmental water flowing through the water intake line, a treated water storage tank for storing the filtered treated water, a treated water line connecting the filtration device and the treated water storage tank, a backwash line for supplying treated water to the filtration device in a direction opposite to the filtration direction of the filter, a backwash drain line for discharging the treated water supplied to the filtration device from the backwash line, and a sampling device for sampling a portion of the backwash drain water flowing through the backwash drain line.

[0006] Patent Document 3 discloses a method for treating ballast water for ships, which includes a water delivery process for taking in raw water and delivering it, and a treatment process for performing ballast water treatment on the delivered raw water and capturing microplastics. The treatment processes in the method for treating ballast water for ships described in Patent Document 3 include a primary treatment process for filtering the raw water, and a secondary treatment process for sterilizing the raw water filtered in the primary treatment process. Patent Document 3 also describes a method for treating ballast water for ships, which includes a backwashing process for cleaning filter elements that filter the raw water used in the primary treatment process, and a recovery process for recovering microplastics contained in the raw water cleaned in the backwashing process. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-108255 [Patent Document 2] Japanese Patent Publication No. 2022-66029 [Patent Document 3] Japanese Patent Publication No. 2022-161261 Summary of the Invention [Problem to be solved by the invention]

[0008] Conventionally, when quantifying the concentration of microplastics (hereinafter sometimes referred to as "MPs") in water containing MPs, such as seawater, a method has been used in which the water containing MPs is concentrated to produce an MPs concentrate, the number of MPs in the MPs concentrate is counted, and the results are used for calculations. Furthermore, fine MPs with a particle size of less than 300 μm cannot be visually confirmed. For this reason, conventionally, when quantifying the concentration of MPs in water containing fine MPs with a particle size of less than 300 μm, a method has been used in which the number of MPs in the concentrated MPs concentrate is counted using a photometer, and the results are used for calculations.

[0009] However, in conventional techniques, the MP concentrate obtained by concentrating water containing MPs may not adequately reflect the amount of MPs of the particle size to be measured contained in the MP-containing water, which may make it difficult to accurately quantify the MP concentration in MP-containing water, such as seawater.

[0010] Therefore, in order to investigate the effects of MPs contained in water containing MPs, such as seawater, there is a need for a microplastics-containing water concentrating device and method for concentrating microplastics-containing water that can produce an MPs concentrate that fully reflects the amount of MPs of the particle size you want to measure in water containing MPs, as well as a microplastics concentration measuring device and method that can accurately measure the MPs concentration in water containing MPs.

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide a microplastics-containing water concentrating device and a microplastics-containing water concentrating method that can obtain an MPs concentrated solution that fully reflects the amount of MPs of the particle size to be measured in water containing MPs. Another object of the present invention is to provide a microplastic concentration measuring device and a microplastic concentration measuring method that can measure the concentration of MPs contained in water containing MPs, such as seawater, with high accuracy. [Means for solving the problem]

[0012] In order to solve the above problems, the following means are provided. One embodiment of the present invention provides a microplastic-containing water concentrating device that includes a first filter with a first mesh size that captures microplastics by passing the microplastic-containing water from a first side to a second side; a water sampling device that supplies the microplastic-containing water to the first filter; a backwashing device that passes a cleaning solution from the second side to the first side of the first filter through which a first volume of the microplastic-containing water has passed to obtain a recovered liquid; a second filter with a second mesh size smaller than the first mesh size; and a concentrating device that passes the recovered liquid through the second filter to concentrate the recovered liquid and obtain a second volume of a concentrated liquid. [Effects of the Invention]

[0013] The microplastics-containing water concentrating device and method of the present invention make it possible to obtain an MPs concentrate that adequately reflects the amount of MPs with the particle size to be measured in water containing MPs. Furthermore, the microplastic concentration measuring device and microplastic concentration measuring method of the present invention can measure the concentration of MPs contained in water containing MPs, such as seawater, with high accuracy. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of the microplastic concentration measuring device of the present invention. [Figure 2] FIG. 2 is a perspective view illustrating an example of a flow cell included in the measuring device of the microplastic concentration measuring device shown in FIG. [Figure 3] FIG. 3 is a schematic diagram illustrating the configuration of the test device used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to solve the above problems and measure the concentration of MPs contained in water containing MPs, such as seawater, with high accuracy, the inventors focused on MPs concentrate obtained by concentrating water containing MPs and conducted extensive research. As a result, we discovered that a second volume of concentrated liquid can be produced by concentrating water containing MPs to obtain a concentrated MPs liquid, and then passing a cleaning solution through a first filter through which a first volume of water containing MPs has been passed from the opposite side of the water containing MPs to obtain a recovered liquid, and then passing the recovered liquid through a second filter with a mesh size smaller than that of the first filter to concentrate the recovered liquid, thereby producing a second volume of concentrated liquid, which led to the invention.

[0016] The second volume of concentrate thus obtained adequately reflects the amount of MPs having a particle size equal to or larger than the mesh size of the first filter contained in the first volume of water containing MPs. More specifically, MPs captured by passing the first volume of water containing MPs through the first filter are recovered at a high recovery rate in the recovery liquid by backwashing the first filter with a cleaning solution in the opposite direction to the MPs-containing water. Therefore, the MPs captured by the first filter are present at a high recovery rate in the second volume of concentrate obtained by passing the recovery liquid through a second filter with mesh sizes smaller than those of the first filter to separate and remove the cleaning solution from the recovery liquid. Therefore, the amount of MPs in the second volume of concentrate having a particle size equal to or larger than the mesh size of the first filter closely approximates the amount of MPs in the first volume of water containing MPs having a particle size equal to or larger than the mesh size of the first filter. Therefore, by calculating the concentration of MPs contained in the water containing MPs from the results obtained by measuring the MPs content in the second volume of concentrated liquid, the second volume, and the first volume, the MPs concentration in the water containing MPs can be measured with high accuracy.

[0017] The present invention includes the following aspects.

[0018] [1] A first filter having a first mesh size that captures microplastics by passing microplastic-containing water from the first side to the second side; A water sampling device that supplies the microplastics-containing water to the first filter; a backwashing device that passes a cleaning liquid from the second side to the first side of the first filter through which a first volume of the microplastic-containing water has passed, to obtain a recovered liquid; a second filter having a second opening smaller than the first opening; and a concentrator that passes the recovered liquid through the second filter to concentrate the recovered liquid and obtain a second volume of concentrated liquid.

[0019] [2] The apparatus for concentrating microplastic-containing water described in [1], wherein the first filter is a wedge filter. [3] The apparatus for concentrating microplastics-containing water described in [1], wherein the first mesh size is 1 μm to 350 μm.

[0020] [4] The apparatus for concentrating microplastic-containing water described in [1], wherein the concentrating device includes a suction means for sucking the recovered liquid that is passed through the second filter.

[0021] [5] A device for concentrating microplastic-containing water according to any one of [1] to [4], A microplastic concentration measuring device having a measuring device for measuring the microplastic content of the concentrated liquid.

[0022] [6] The microplastic concentration measuring device described in [5], wherein the measuring device includes a microscopic Raman spectrometer. [7] The measurement device includes a flow cell made of transparent glass, The microplastic concentration measuring device described in [6], wherein the measurement point of the microscopic Raman spectrometer of the flow cell has an internal space that contains the concentrated liquid, and the thickness dimension of the internal space is longer than the dimension of the first opening.

[0023] [8] The microplastic concentration measuring device described in [7], wherein the measurement points are 5,000 points of 50 rows and 100 columns arranged in a grid pattern with a pitch of 100 μm on the flow cell. [9] The microplastic concentration measuring device described in [7], wherein the measuring device is equipped with a pump that transports the concentrated liquid to the flow cell.

[0024]

[10] A capture step of passing a first volume of microplastic-containing water through a first filter having a first mesh size from a first side to a second side to capture microplastics in the first filter; a backwashing step of passing a cleaning liquid from the second side to the first side of the first filter to obtain a recovered liquid; and a concentration step of concentrating the recovered liquid by passing it through a second filter having a second mesh size smaller than the first mesh size to obtain a second volume of concentrated liquid.

[0025]

[11] A method for measuring microplastic concentration, comprising a measurement step of measuring the microplastic content of the concentrated liquid obtained by the method for concentrating microplastic-containing water described in

[10] .

[0026] The microplastics-containing water concentrating device and method, and the microplastics-containing water concentrating device and method, and the microplastics concentration measuring device and method of the present invention are described in detail below with reference to the drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity. Therefore, the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them. Appropriate modifications can be made within the scope of the present invention.

[0027] [Microplastic concentration measuring device] Figure 1 is a schematic diagram illustrating an example of a microplastics concentration measurement device of the present invention. As shown in Figure 1, the microplastics concentration measurement device 1 of this embodiment comprises a microplastics-containing water concentrating device of this embodiment, which comprises a water sampling device 11, a first filter 12, a backwashing device 13, a second filter 14, and a concentrating device 15, and a measuring device 16.

[0028] The microplastic concentration measuring device 1 of this embodiment has a sealable chamber 12c, as shown in Figure 1. A first filter 12 is placed approximately horizontally within the chamber 12c. The water sampling device 11 supplies MPs-containing water 21 to the first filter 12. In this embodiment, as shown in Fig. 1, it is preferable to use a device that has piping connected to the side of the chamber 12c below the first filter 12, and a pump 42 and a valve 32 attached to the piping, and that can supply MPs-containing water 21 to the first filter 12 at a predetermined flow rate. Also, as shown in Fig. 1, the piping between the valve 32 and the chamber 12c is equipped with a flow meter 5 that measures the volume of MPs-containing water 21 supplied to the chamber 12c.

[0029] As the pump 42, for example, a known pump such as a water sampling pump installed on a ship can be used. A known valve can be used as the valve 32. The valve 32 is opened when the first filter 12 traps MPs, and is closed when the backwash device 13 recovers the MPs trapped in the first filter 12. The flow meter 5 may be any known type that can measure the flow rate of the MPs-containing water 21 passing through the pipe.

[0030] The water sampling device 11 may supply MPs-containing water 21 collected from a water sampling location such as the ocean directly to the first filter 12, or it may supply MPs-containing water 21 collected at a water sampling location and stored in a storage tank or the like to the first filter 12.

[0031] The MPs-containing water 21 supplied to the first filter 12 may be any water containing MPa, including environmental water such as seawater, lake water, river water, tap water, drinking water, etc. The MPs-containing water 21 in this embodiment may be water from which impurities with particle sizes exceeding 5 mm have been removed in advance using a known method.

[0032] As shown in FIG. 1, the first filter 12 captures MPs by passing the MPs-containing water 21 from the first side 12a to the second side 12b. The first filter 12 can be a known filter that can capture MPs of a predetermined particle size by passing MPs-containing water 21 through it, and can be appropriately selected depending on the particle size of the MPs whose concentration in the MPs-containing water 21 is to be measured.

[0033] The first filter 12 is preferably made of metal because, when the first filter 12 is made of metal, even if foreign matter originating from the first filter 12 gets mixed into the concentrated liquid 24 described below, the measurement result of the MPs content in the concentrated liquid 24 is unlikely to be affected.

[0034] For example, a wedge filter, a membrane filter, or the like can be used as the first filter 12. Among these, it is preferable to use a wedge filter as the first filter 12. This is because a wedge filter is less likely to clog than filters such as a membrane filter, and by passing the cleaning liquid 22 from the second side 12b to the first side 12a of the first filter 12 using the backwash device 13, the MPs captured by the first filter 12 can be easily recovered with a high recovery rate.

[0035] The mesh size (first mesh size) of the first filter 12 is preferably 1 μm to 350 μm. If the first mesh size is 1 μm or larger, the MPs captured by the first filter 12 are less likely to contain fine MPs that are difficult to accurately detect using the measuring device 16. As a result, the content of MPs with particle sizes larger than the first mesh size in the MPs-containing water 21 can be measured with high accuracy using the measurement results of the MPs content in the second volume of concentrated liquid 24, which will be described later. Furthermore, if the first mesh size is 10 μm or larger, the first filter 12 is less likely to clog, allowing the MPs-containing water 21 to pass through efficiently in a short time. For this reason, the first mesh size of the first filter 12 is more preferably 10 μm or larger. Furthermore, if the first mesh size is 350 μm or smaller, the content of fine MPs that have a significant impact on living organisms in the MPs-containing water 21 can be measured with high accuracy using the measurement results of the MPs content in the second volume of concentrated liquid 24, which will be described later. The first mesh size of the first filter 12 may be 100 μm or smaller.

[0036] The first filter 12 may have any shape as long as it allows the MPs-containing water 21 to pass from the first side 12a to the second side 12b and the cleaning liquid 22 to pass from the second side 12b to the first side 12a. For example, the first filter 12 may be in the form of a sheet or plate arranged substantially horizontally, as shown in Fig. 1, or may be in the form of a cylinder or cup.

[0037] The first filter 12 is placed approximately horizontally in the chamber 12c. In this embodiment, the lower surface of the first filter 12 is the first side 12a, and the upper surface of the first filter 12 is the second side 12b. This is preferable because gravity allows the cleaning liquid 22 to efficiently pass from the second side 12b to the first side 12a, and the generated recovery liquid 23 can be discharged from the chamber 12c by gravity.

[0038] In this embodiment, an example will be described in which the lower surface of the first filter 12 is the first side 12a and the upper surface is the second side 12b, but the lower surface of the first filter 12 may be the second side and the upper surface may be the first side. In this case, gravity can be used to pass the MPs-containing water 21 from the first side to the second side of the first filter 12. Furthermore, for example, when the first filter 12 is cylindrical or cup-shaped, the first side may be on the inside and the second side on the outside, or the second side may be on the inside and the first side on the outside.

[0039] The first volume is the volume of MPs-containing water 21 passed through the first filter 12 from the first side 12a to the second side 12b to obtain a second volume of concentrated liquid 24. In this embodiment, the first volume is the volume of MPs-containing water 21 passed through the first filter 12 before passing the cleaning liquid 22 through the first filter 12 from the second side 12b to the first side 12a. The first volume is the volume of MPs-containing water 21 supplied to the chamber 12c and is measured by the flow meter 5.

[0040] The first volume is preferably determined in advance so that the first filter 12 does not become clogged and the MPs content in the second volume of concentrated liquid 24 does not become a concentration below the detection limit of the measuring device 16 described below. The first volume can be determined according to the size and concentration of the MPs contained in the MPs-containing water 21, the type of the first filter 12, and the first mesh size, and is not particularly limited.

[0041] For example, when the MPs-containing water 21 is seawater and the first filter 12 is a wedge filter with a first mesh size of 10 μm, the first volume is preferably in the range of 10,000 to 100,000 times the second volume, which is the volume of the concentrated liquid 24. This is because the first filter 12 is less likely to clog, the MPs content in the MPs-containing water 21 is less likely to become a concentration below the detection limit of the measuring device 16, and the MPs content can be measured with high accuracy.

[0042] In this embodiment, as shown in Fig. 1, a pipe for discharging MP-containing water from which MPs have been removed is installed on the side surface of chamber 12c above first filter 12. A known valve 33 is installed on this pipe. Valve 33 is opened when MPs are trapped in first filter 12. Valve 33 is preferably closed when MPs trapped in first filter 12 are recovered by backwash device 13.

[0043] The backwashing device 13 passes the cleaning liquid 22 from the second side 12b to the first side 12a of the first filter 12, through which a first volume of MPs-containing water 21 has been passed, to obtain a recovered liquid 23. The backwashing device 13 may be any device capable of supplying the cleaning liquid 22 to the first filter 12 from the second side 12b. For example, as shown in FIG. 1, it is preferable to use a device that has a piping connected to the upper surface of the chamber 12c above the first filter 12, a pump 41, and a valve 31 attached to the piping, and that can supply the cleaning liquid 22 to the first filter 12 at a predetermined flow rate and supply amount. Known pumps 41 and valves 31 can be used. The valve 31 is closed when MPs are trapped in the first filter 12 and is opened when the MPs trapped in the first filter 12 are recovered by the backwashing device 13.

[0044] The cleaning liquid 22 used in the backwash device 13 can be water or the like, and a gas such as air may be supplied to the first filter 12 from the second side 12b by a known method together with the cleaning liquid 22 or before the cleaning liquid 22 is supplied to the first filter 12.

[0045] A pipe is installed on the bottom surface of the chamber 12c for discharging the recovered liquid 23 obtained by passing the cleaning liquid 22 from the second side 12b to the first side 12a of the first filter 12. A known valve 34 can be used as the valve installed on this pipe. The valve 34 is closed when MPs are trapped in the first filter 12. The valve 34 is opened when the MPs trapped in the first filter 12 are recovered by the backwash device 13. This allows the recovered liquid 23 to be supplied to the hopper 15a of the concentration device 15. The valve 34 may be opened after the MPs trapped in the first filter 12 have been recovered.

[0046] The concentrator 15 passes the recovered liquid 23, obtained by passing the cleaning liquid 22 from the second side 12b to the first side 12a of the first filter 12, through the second filter 14 to concentrate the recovered liquid 23, thereby obtaining a second volume of concentrated liquid 24. The concentrator 15 preferably passes a portion of the recovered liquid 23 through the second filter 14 to obtain a second volume of concentrated liquid 24 consisting of the recovered liquid 23 that has not passed through the second filter 14. The reason for this is that, as in the case where the concentrator 15 passes the entire recovered liquid 23 through the second filter 14, a step of recovering the MPs separated from the recovered liquid 23 and dispersing them in water or the like to obtain a concentrated liquid is not required, and the second volume of concentrated liquid 24 can be produced with fewer steps.

[0047] In this embodiment, the concentrating device 15 includes a hopper 15a and a suction means. The suction means sucks the recovered liquid 23 that is passed through the second filter 14, thereby promoting the concentration of the recovered liquid 23. As the suction means, for example, as shown in FIG. 1, a device including a known airtight reduced-pressure container 15b and a known vacuum pump 15c can be used.

[0048] As shown in FIG. 1, the hopper 15a stores the recovered liquid 23 that is produced in the chamber 12c and sent via a pipe, and supplies the recovered liquid 23 to the second filter 14. 1, the reduced pressure container 15b is connected to a vacuum pump 15c via a pipe having a valve 35. The vacuum pump 15c creates a reduced pressure atmosphere inside the reduced pressure container 15b via the pipe, and sucks the recovery liquid 23 to be passed through the second filter 14. Furthermore, the reduced pressure container 15b stores the cleaning liquid 22 separated from the recovery liquid 23. As shown in FIG. 1, a pipe having a valve 36 is connected to the vicinity of the bottom surface of the reduced pressure container 15b, so that the cleaning liquid 22 stored in the reduced pressure container 15b can be discharged as needed.

[0049] The second filter 14 may be any known filter as long as it has a second mesh size smaller than the mesh size (first mesh size) of the first filter 12. The second filter 14 can be appropriately selected depending on the particle size of the MPs contained in the MPs-containing water 21 whose concentration is to be measured.

[0050] For example, a wedge filter, a membrane filter, or the like can be used as the second filter 14. Among these, it is preferable to use a membrane filter as the second filter 14. A membrane filter can completely capture the MPs in the recovered liquid 23 captured by the first filter 12. This is because the amount of MPs in the concentrated liquid 24 obtained by concentrating the recovered liquid 23 adequately reflects the amount of MPs having a particle size of the first mesh size or larger contained in the water containing the first volume of MPs that has passed through the first filter 12.

[0051] The mesh size (second mesh size) of the second filter 14 is preferably smaller than the first mesh size and is preferably 1 μm to 350 μm. If the second mesh size is 1 μm or larger, the MPs in the concentrated solution 24 are less likely to contain fine MPs that are difficult to accurately detect using the measuring device 16. As a result, the content of MPs with particle sizes larger than the first mesh size in the MPs-containing water 21 can be measured with high accuracy using the measurement results of the MPs content in the second volume of concentrated solution 24. Furthermore, if the second mesh size is 1 μm or larger, the second filter 14 is less likely to clog, allowing the recovered liquid 23 to be concentrated efficiently in a short time. For these reasons, the second mesh size of the second filter 14 is more preferably 10 μm or larger. Furthermore, if the second mesh size is 350 μm or smaller, the content of fine MPs in the MPs-containing water 21 that have a significant impact on living organisms can be measured with high accuracy using the measurement results of the MPs content in the second volume of concentrated solution 24. The second filter 14 may have a second mesh size of 100 μm or less.

[0052] The recovered liquid 23 is concentrated in the hopper 15a of the concentrator 15 to produce a concentrated liquid 24, which is sent to a measuring device 16 via piping as shown in Fig. 1. The measuring device 16 measures the MPs content of the concentrated liquid 24. The measuring device 16 may be any device capable of measuring the MPs content of the concentrated liquid 24, and may be one or more types selected from known measuring instruments such as a microscopic Raman spectrometer, a microscope, a Fourier transform infrared spectrophotometer (FTIR), a spectral camera, etc., and may be appropriately selected depending on the particle size of the MPs contained in the MPs-containing water 21 whose concentration is to be measured.

[0053] The measuring device 16 preferably includes a micro-Raman spectrometer. The micro-Raman spectrometer can measure MPs in the concentrate 24 directly without pretreatment. Therefore, compared to using a measuring device that requires pretreatment, the MP content in the concentrate 24 can be measured easily and efficiently with fewer steps. Furthermore, because the MPs in the concentrate 24 can be measured directly without pretreatment, the MPs are not damaged by the pretreatment, and the pretreatment for measuring MPs does not affect the quantitative results of the MPa in the concentrate 24. Therefore, the measurement results of the MP content in the concentrate 24 more accurately reflect the amount of MPs of the desired particle size in the MPs-containing water 21. Furthermore, the micro-Raman spectrometer can measure MPa with a particle size of 1 μm or more with high accuracy and can detect MPs with a particle size of 350 μm or less, which are of concern due to their significant biological impact, as well as even finer MPs with a particle size of 100 μm or less, with high accuracy.

[0054] When the measuring device 16 includes a micro-Raman spectrometer, the conditions such as laser intensity, wavelength, depth, and measurement frequency when measuring the concentration of MPs in the concentrated liquid 24 using the micro-Raman spectrometer can be appropriately determined depending on the particle diameter and concentration of the MPs contained in the MPs-containing water 21 whose concentration is to be measured.

[0055] When the measurement device 16 includes a Raman microscope, it is preferable to use a flow cell made of transparent glass that contains the concentrated liquid 24. The shape of the flow cell is not particularly limited, but it is preferable to use one in which the thickness dimension of the internal space that contains the concentrated liquid 24 at the measurement point of the Raman microscope is longer than the dimension of the first opening and is equal to or shorter than the maximum length of the particles to be detected. The reason for this is that the concentration of MPs in the concentrated liquid 24 can be detected with high accuracy.

[0056] When measuring the concentration of MPs in the concentrated solution 24 using a micro-Raman spectrometer, for example, a flow cell such as that shown in Fig. 2 can be used. Fig. 2 is a perspective view illustrating an example of a flow cell 16a included in the measuring device 16 of the microplastics concentration measuring device 1 shown in Fig. 1. The flow cell 16a shown in Fig. 2 is made of transparent glass and comprises a storage section 16b having a generally rectangular outer shape in plan view, and cylindrical inlet and outlet sections 16c connected to opposing short sides of the storage section 16b in plan view.

[0057] 2, the flow cell 16a may have an internal space of the storage section 16b with a width L1 of 10 mm, a length L2 of 40 mm, and a thickness L3 of 0.5 mm. In this embodiment, the measurement point of the Raman microscope is a substantially rectangular region with a width L1 of 10 mm and a length L2 of 40 mm that corresponds to the planar shape of the internal space of the storage section 16b and a thickness of 0.5 mm.

[0058] In this embodiment, it is preferable that the measurement points of the microscopic Raman spectrometer are arranged in a grid pattern of 50 rows and 100 columns at a pitch of 100 μm on the flow cell 16a, for a total of 5,000 points. This is because the MPs content in the concentrate 24 can be measured with high accuracy. Furthermore, 5,000 measurement points allows the MPs content in the flow cell 16a to be measured efficiently in a short measurement time of about one hour. Note that the number of measurement points of the microscopic Raman spectrometer arranged on the flow cell 16a is not limited to 5,000 points, and the pitch, number of rows, and number of columns of the measurement points can be determined appropriately depending on the size of the first mesh, the desired accuracy of the MPs content, etc.

[0059] One of the two inlet / outlet ports 16c of the flow cell 16a is connected to a pipe connected to the hopper 15a, and the concentrated solution 24, whose MPs concentration is to be measured, flows into the pipe. As shown in FIG. 1, the pipe connecting the hopper 15a and the flow cell 16a is provided with a pump 46 that transports the concentrated solution 24 to the flow cell 16a. By providing the pump 46, the concentrated solution 24 can be transported easily and efficiently from the hopper 15a to the flow cell 16a. Any pump that can transport the concentrated solution 24 to the flow cell 16a can be used as the pump 46, and any known pump can be used.

[0060] The pipe connecting the hopper 15a and the flow cell 16a may be connected to the flow cell 16a at all times, or may be connected only when the concentrated liquid 24 is flowed into the flow cell 16a. Of the two inflow / outflow sections 16c of the flow cell 16a, the other is preferably used as a discharge path for discharging the concentrated solution 24 after the measurement of the MPs concentration has been completed. When the piping connecting the hopper 15a and the flow cell 16a is connected only when the concentrated solution 24 is to flow into the flow cell 16a, either of the two inflow / outflow sections 16c may be used as a discharge path.

[0061] [Method for measuring microplastic concentration] Next, as an example of the microplastics concentration measurement method of the present invention, a case where the MPa concentration of MPs-containing water 21 is measured using the microplastics concentration measurement device 1 shown in FIG. 1 will be described. The microplastic concentration measurement method of this embodiment includes the microplastic-containing water concentration method of this embodiment, which has a capture process, a backwashing process, and a concentration process, and also includes a measurement process for measuring the MPs content of the concentrated liquid obtained thereby.

[0062] In this embodiment, first, valve 31 installed in the piping that supplies cleaning liquid 22 to the first filter 12 and valve 34 installed in the piping for discharging recovery liquid 23 are closed, and valve 33 installed in the piping that discharges MPs-containing water from which MPs have been removed is opened.

[0063] Then, the water sampling device 11 supplies the MPs-containing water 21 to the first filter 12 with a first mesh size. Specifically, the pump 42 is driven and the valve 32 is opened, and a first volume of the MPs-containing water 21 measured by the flow meter 5 is supplied to the chamber 12c at a predetermined flow rate. This causes the first volume of the MPs-containing water 21 to pass through the first filter 12 from the first side 12a (the lower side in FIG. 1) to the second side 12b (the upper side in FIG. 1), causing the first filter 12 to capture the MPs (capturing step).

[0064] Next, in this embodiment, the valve 32 installed in the pipe through which the MPs-containing water 21 passes and the valve 33 installed in the pipe for discharging the MPs-containing water from which the MPs have been removed are closed.

[0065] Then, pump 41 is driven, and valves 31 and 34 are opened to supply cleaning liquid 22 to chamber 12c at a predetermined flow rate. This causes cleaning liquid 22 to pass from second side 12b to first side 12a of first filter 12, thereby obtaining recovered liquid 23 (backwashing process). At this time, recovered liquid 23 produced in chamber 12c is sent to hopper 15a via piping and stored therein, as shown in FIG. 1. Thereafter, in this embodiment, the valve 31 installed in the pipe for supplying the cleaning liquid 22 to the first filter 12 is closed.

[0066] The volume of the cleaning liquid 22 used in the backwashing device 13 should be such that the MPs captured by the first filter 12 can be recovered in the recovery liquid 23 with a sufficiently high recovery rate, and can be determined appropriately depending on the first mesh size of the first filter 12, the amount of MPs captured by the first filter 12, etc. It is preferable that the volume of the cleaning liquid 22 used in the backwashing device 13 is not too large, as this shortens the time required to pass the recovery liquid 23 through the second filter 14.

[0067] The backwashing step may be performed only once or multiple times. The number of backwashing steps in this embodiment refers to the number of times the steps of opening the valves 31 and 34 to supply the cleaning liquid 22 to the chamber 12c, passing the cleaning liquid 22 from the second side 12b to the first side 12a of the first filter 12 through the chamber 12c, and discharging the recovery liquid 23 from the chamber 12c, and closing the valves 31 and 34 are performed after the capture step and before supplying new MPs-containing water 21 to the first filter 12.

[0068] Next, the vacuum pump 15c is driven and the valve 35 is opened to create a reduced pressure atmosphere inside the reduced pressure container 15b. This promotes the concentration of the recovered liquid 23 by sucking the recovered liquid 23 contained in the hopper 15a from below the second filter 14 and passing it through the second filter 14, which has a second mesh size smaller than the first mesh size, to obtain a second volume of concentrated liquid 24 consisting of the recovered liquid in the hopper 15a that has not passed through the second filter 14 (concentration step). Thereafter, in this embodiment, the vacuum pump 15c is stopped from being driven, and the valve 35 is closed.

[0069] Next, in this embodiment, a pump 46, such as a vacuum pump, is driven to transport and store a predetermined amount of concentrated liquid 24 via piping connected to hopper 15a into a flow cell 16a shown in FIG. 2, whose internal space in storage section 16b has a width L1 of 10 mm, a length L2 of 40 mm, and a thickness L3 of 0.5 mm. Then, a micro-Raman spectrometer is used to measure 5,000 locations on flow cell 16a, arranged in a 50-row, 100-column grid with a pitch of 100 μm. This allows the MPs content of concentrated liquid 24 to be measured (measurement step).

[0070] The MPs content of the concentrate 24 may be measured on only a portion of the second volume of the concentrate 24 or on the entire volume. Then, the concentration of MPs contained in the water containing MPs is calculated from the measurement results of the MPs content of the concentrated liquid 24, the second volume, and the volume (first volume) of the MPs-containing water 21 supplied to the chamber 12c measured by the flow meter 5.

[0071] The microplastic concentration measuring device 1 of this embodiment has a measuring device 16 that measures the MPs content of the second volume of concentrated liquid 24, and the second volume of concentrated liquid 24 adequately reflects the amount of MPs with particle sizes equal to or larger than the mesh size of the first filter 12 contained in the first volume of MPs-containing water 21. Therefore, the microplastic concentration measuring device 1 of this embodiment can measure the MPs concentration in the MPs-containing water 21 with high accuracy.

[0072] The above describes the embodiments of the present invention in detail, but each configuration and combination thereof in each embodiment is an example, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope that does not deviate from the spirit of the present invention.

[0073] For example, in the above-described embodiment, as shown in FIG. 1, the microplastic concentration measuring device 1 is described as having a measuring device 16 that measures the MPs content in the concentrate 24. However, if the first mesh size of the first filter 12 is 300 μm or larger, the measuring device 16 need not be provided. This is because the number of MPs with a particle size of 300 μm or larger can be measured visually. A method for visually measuring the number of MPs with a particle size of 300 μm or larger can be, for example, by placing the concentrate 24 in a flow cell 16a shown in FIG. 2, visually observing the entire area of ​​the internal space above the flow cell 16a, which has a thickness of 0.5 mm, and counting the number of MPs. [Example]

[0074] [Examples 1-1 to 1-5] The MPs concentration in the MPs-containing water was measured using the test equipment shown below and the method shown below, and the recovery rate (Rc) was calculated using the results.

[0075] (Test equipment) Figure 3 is a schematic diagram illustrating the configuration of the test device used in the examples. In the test device 1a shown in Figure 3, components that have the same functions as those in the microplastic concentration measuring device 1 shown in Figure 1 are given the same reference numerals.

[0076] The testing device 1a shown in Fig. 3 has a substantially cylindrical chamber 18 with a capacity of 1 L, and a water sampling device 11. The water sampling device 11 samples MPs-containing water 21 and supplies it to the first filter 12 via piping connected to the side of the chamber 18. As shown in Fig. 3, the water sampling device 11 has a pump (not shown) and a valve 32.

[0077] In the test apparatus 1a shown in Figure 3, a wedge filter (product name: Fine Wedge Strainer, manufactured by Toyo Screen Co., Ltd.) made of metal SUS316L and having a mesh size (first mesh size) of 10 µm was installed as the first filter 12. As shown in Figure 3, the first filter 12 was cup-shaped with a side surface arranged along the inner wall surface of a substantially cylindrical chamber and a bottom surface that was substantially circular in plan view. In the test apparatus 1a shown in Figure 3, MPs are captured by passing MPs-containing water 21 supplied from the water sampling device 11 to the first filter 12 from the outside (first side 12a) to the inside (second side 12b).

[0078] In the testing apparatus 1a shown in Fig. 3, an opening is provided on the top surface of a substantially cylindrical chamber 18, and piping is connected to a lid 18a placed on the opening. As shown in Fig. 3, a valve 33 is installed in the piping connected to the lid 18a. The valve 33 is opened when MPs are captured by the first filter 12. By opening the valve 33, the MPs-containing water that has passed through the first filter 12 and from which MPs have been removed is discharged by overflow.

[0079] In the testing apparatus 1a shown in Fig. 3, the bottom surface 18b of the substantially cylindrical chamber 18 has a conical shape that is deeper toward the center. A pipe is connected to the center of the bottom surface 18b of the chamber 18. As shown in Fig. 3, a valve 34 is installed in the pipe connected to the bottom surface 18b. The valve 34 is closed when supplying MPs-containing water 21 to the first filter 12 and allowing the first filter 12 to capture MPs.

[0080] After the first volume of MPs-containing water 21 has passed through the first filter 12, the valve 34 is opened together with the valve 33. This causes the MPs-containing water, from which the MPs contained inside (second side 12b) of the first filter 12 have been removed, to pass from the inside (second side 12b) to the outside (first side 12a), backwashing the first filter 12 and discharging the recovered liquid 23 containing the MPs captured in the first filter 12 from the bottom surface 18b of the chamber 18.

[0081] 3 is configured so that, with valve 33 open and valve 34 closed, tap water containing detergent can be supplied to first filter 12 by water sampling device 11 instead of MPs-containing water 21. This allows tap water containing detergent to be supplied to the inside of first filter 12 (second side 12b) through first filter 12.

[0082] By supplying tap water containing detergent to the inside (second side 12b) of first filter 12 and opening valves 33 and 34, backwashing can be performed, passing the tap water containing detergent contained inside first filter 12 from the inside (second side 12b) to the outside (first side 12a). Therefore, the water sampling device 11 in the testing device 1a shown in Figure 3 also functions as the backwashing device 13 in the microplastic concentration measuring device 1 shown in Figure 1.

[0083] (Test Method) In Examples 1-1 to 1-5, as MPs-containing water 21 to be collected by water sampling device 11, a sample containing polyethylene (PE) particles, which are a representative MP found in large quantities over a wide area of ​​the ocean, was prepared by the method described below.

[0084] 347 red-colored particles (6.5 mg (estimated value)) made of polyethylene (PE) with particle diameters of 250 μm to 300 μm (product name: UVPMS-BR-0.995, manufactured by Cospheric) were dispersed in 5 mL of tap water, and 1 mL of detergent (product name: Family Fresh, manufactured by Kao Corporation) was added to suspend and float the polyethylene particles in the MPs-containing water 21, thereby preparing the MPa solutions of Examples 1-1 to 1-5. The obtained MPa solutions of Examples 1-1 to 1-5 were mixed with tap water to obtain 100 L (first volume) of MPs-containing water 21.

[0085] (Capturing process) Next, valve 34 was closed and valve 33 was opened. Then, the pump (not shown) of the water sampling device 11 was driven and valve 32 was opened to supply the MPs-containing water 21 to the first filter 12. As a result, 100 L (first volume) of the MPs-containing water 21 was passed through the first filter 12 from the first side 12a (outside in FIG. 3) to the second side 12b (inside in FIG. 3).

[0086] Thereafter, simulating the case of measuring the MPs concentration on board a ship, the chamber 18 after the capture step was vibrated and stirred so that particles adhering to the inside of the chamber 18 were removed.

[0087] (Backwash process (1st time)) Next, valve 32 was closed, and valve 34 was opened while valve 33 was left open. This allowed the tap water containing detergent (MPs-containing water from which MPs had been removed) contained inside (second side 12b) of first filter 12 to pass from the inside (second side 12b) to the outside (first side 12a), and recovered liquid 23 containing MPs captured by first filter 12 was discharged from bottom surface 18b of chamber 18. The recovered liquid 23 discharged from chamber 18 was stored in a container.

[0088] (Backwashing process (2nd to 4th time)) Next, valve 34 was closed. Then, with valve 33 open, the pump (not shown) of water sampling device 11 was driven and valve 32 was opened, and 1 L of tap water containing detergent was supplied to first filter 12 in place of MPs-containing water 21. As the tap water containing detergent, a mixture of detergent (trade name: Family Fresh, manufactured by Kao Corporation) and tap water was used in a ratio of 1 mL of detergent to 250 mL of tap water.

[0089] Thereafter, valve 32 was closed, and valve 34 was opened while valve 33 was left open. As a result, tap water containing detergent stored inside (second side 12b) of first filter 12 was passed from the inside (second side 12b) to the outside (first side 12a), and recovered liquid 23 containing MPs captured by first filter 12 was discharged from bottom surface 18b of chamber 18. The recovered liquid 23 discharged from chamber 18 was stored in a container in the same manner as in the first backwashing step. Thereafter, third and fourth backwashing steps were carried out in the same manner as in the second backwashing step.

[0090] (concentration process) Next, the recovered liquid 23 obtained in the first to fourth backwashing steps was passed through a second filter 14 while being sucked using a pressure-reducing container and a vacuum pump. A membrane filter (manufactured by Merck Millipore Co., Ltd.) made of polytetrafluoroethylene (PTFE) with a diameter of 12.5 mm and a mesh size of 10 μm was used as the second filter 14. Thereafter, the polyethylene (PE) particles were recovered by washing the second filter with tap water containing the same detergent as above, and 30 mL (second volume) of a concentrated solution containing polyethylene (PE) particles was obtained.

[0091] (Measurement process) Next, a flow cell 16a shown in Fig. 2 was prepared, in which the internal space of the storage section 16b had a width L1 of 10 mm, a length L2 of 40 mm, and a thickness L3 of 0.5 mm. Then, 0.2 mL of the concentrated liquid stirred by rotating the stirrer at a rotation speed of 100 rpm was sampled and stored in the flow cell 16a.

[0092] Thereafter, the entire area of ​​the internal space above the flow cell 16a, which had a thickness of 0.5 mm, was visually observed, and the number of red-colored polyethylene (PE) particles present in the flow cell 16a was counted (first time). Subsequently, the second to ninth measurement steps were repeated in the same manner as the first measurement step, and the average value was taken as the number of polyethylene (PE) particles.

[0093] (Calculation of recovery rate) The concentration (C) of polyethylene (PE) particles contained in the MPs-containing water 21 was calculated from the number of polyethylene (PE) particles, the second volume, and the first volume of Examples 1-1 to 1-5 measured in this manner. The concentration (Ct) of polyethylene (PE) particles contained in the MPs-containing water 21 used in Examples 1-1 to 1-5 was also calculated from the amount of polyethylene (PE) particles used to prepare the MPs-containing water 21. Using these values, the recovery rate (Rc) was calculated according to the following formula (1). The results are shown in Table 1. Rc(%)=(C / Ct)×100 (1)

[0094] [Examples 2-1 to 2-3] 6.5 mg (estimated 14,298 particles) of uncolored polyethylene (PE) particles with particle diameters of 90 μm to 106 μm (product name: CPMS-0.96, manufactured by Cospheric LLC) were dispersed in 5 mL of tap water, and 1 mL of detergent (product name: Family Fresh, manufactured by Kao Corporation) was added to suspend the polyethylene particles in the MPs-containing water 21, thereby preparing the MPa solutions of Examples 2-1 to 2-3. The obtained MPa solutions of Examples 2-1 to 2-3 were mixed with tap water to obtain 100 L (first volume) of MPs-containing water 21.

[0095] Except for using 100 L (first volume) of MPs-containing water 21 obtained in this manner, the capture process, backwash process (first to fourth) and concentration process were carried out in the same manner as in Examples 1-1 to 1-5, and 30 mL (second volume) of concentrated solution containing polyethylene (PE) particles was obtained in Examples 2-1 to 2-3.

[0096] (Measurement process) 0.2 mL of each of the 30 mL (second volume) concentrates containing polyethylene (PE) particles in Examples 2-1 to 2-3 was placed in the flow cell 16a shown in FIG. 2 in the same manner as in Examples 1-1 to 1-5.

[0097] Thereafter, in Examples 2-1 to 2-3, unlike Examples 1-1 to 1-5, the number of polyethylene (PE) particles was counted (first time) at 5,000 locations on the flow cell 16a, arranged in a grid pattern of 50 rows and 100 columns with a pitch of 100 μm, using a micro-Raman spectrometer (product name: NRS-4500, manufactured by JASCO Corporation). The conditions for counting the number of polyethylene (PE) particles in the concentrated solution using the micro-Raman spectrometer were as follows. Thereafter, the second to sixth measurement steps were repeated in the same manner as the first measurement step, and the average value was taken as the number of polyethylene (PE) particles.

[0098] [Measurement conditions for the Raman microscope] Laser intensity: 41.4 W, wavelength: 532 nm Exposure time: 0.1 seconds Wavelength: 400~4000cm -1

[0099] (Calculation of recovery rate) The concentration (C) of polyethylene (PE) particles contained in the MPs-containing water 21 was calculated from the number of polyethylene (PE) particles, the second volume, and the first volume measured in Examples 2-1 to 2-3. The recovery rate (Rc) was calculated in the same manner as in Examples 1-1 to 1-5. The results are shown in Table 1.

[0100] [Examples 3-1 to 3-3] 351 particles (6.5 mg (estimated value)) of uncolored polyethylene (PE) particles with particle diameters of 300 μm to 355 μm (product name: CPMS-0.96, 300 μm to 355 μm, manufactured by Cospheric LLC) were dispersed in 5 mL of tap water, and 1 mL of detergent (product name: Family Fresh, manufactured by Kao Corporation) was added to suspend the polyethylene particles in the MPs-containing water 21, thereby preparing the MPa solutions of Examples 3-1 to 3-3. The obtained MPa solutions of Examples 3-1 to 3-3 were mixed with tap water to obtain 100 L (first volume) of MPs-containing water 21.

[0101] The capture step, backwashing step (first to fourth steps), concentration step, and measurement step (first step) were carried out in the same manner as in Examples 2-1 to 2-3, except that 100 L (first volume) of the MPs-containing water 21 thus obtained was used. Thereafter, the second to ninth measurement steps were repeated in the same manner as in the first measurement step, and the average value was taken as the number of polyethylene (PE) particles.

[0102] (Calculation of recovery rate) The concentration (C) of polyethylene (PE) particles contained in the MPs-containing water 21 was calculated from the number of polyethylene (PE) particles, the second volume, and the first volume measured in Examples 3-1 to 3-3. The recovery rate (Rc) was calculated in the same manner as in Examples 1-1 to 1-5. The results are shown in Table 1.

[0103] [Table 1]

[0104] As shown in Table 1, in all of Examples 1-1 to 1-5, Examples 2-1 to 2-3, and Examples 3-1 to 3-3, the recovery rates were within the range of 70% to 120%, which was within a fully acceptable range. From this, it was confirmed that the second volume of concentrates produced in Examples 1-1 to 1-5, Examples 2-1 to 2-3, and Examples 3-1 to 3-3 adequately reflected the amount of polyethylene (PE) particles contained in the MPs-containing water whose concentration was to be measured. Therefore, it was confirmed that the concentration of polyethylene (PE) particles in the MPs-containing water whose concentration was to be measured could be measured with high accuracy by calculating the concentration of polyethylene (PE) particles contained in the MPs-containing water whose concentration was to be measured from the number of polyethylene (PE) particles in the second volume of concentrates produced in the above examples, the second volume, and the first volume. [Explanation of symbols]

[0105] 1...microplastic concentration measuring device, 1a...testing device, 5...flow meter, 11...water sampling device, 12...first filter, 12a...first side, 12b...second side, 12c, 18...chamber, 13...backwashing device, 14...second filter, 15...concentrating device, 15a...hopper, 15b...pressure reducing vessel, 15c...vacuum pump, 16...measuring device, 16a...flow cell, 16b...storage section, 16c...inlet / outlet section, 21...MPs-containing water, 22...washing liquid, 23...recovery liquid, 24...concentrated liquid, 31, 32, 33, 34, 35, 36...valves, 41, 42, 46...pumps.

Claims

1. A first filter having a first mesh size that captures microplastics by passing microplastic-containing water from the first side to the second side; a water sampling device that supplies the microplastics-containing water to the first filter; a backwashing device that passes a cleaning liquid from the second side to the first side of the first filter through which a first volume of the microplastics-containing water has passed to obtain a recovered liquid; a second filter having a second mesh size smaller than the first mesh size; and a concentrating device that passes the recovered liquid through the second filter to concentrate the recovered liquid and obtain a second volume of concentrated liquid.

2. The device for concentrating microplastic-containing water according to claim 1 , wherein the first filter is a wedge filter.

3. The device for concentrating microplastics-containing water according to claim 1, wherein the first mesh size is 1 μm to 350 μm.

4. The apparatus for concentrating microplastic-containing water according to claim 1, wherein the concentrating device includes a suction means for suctioning the recovered liquid that is passed through the second filter.

5. The device for concentrating microplastic-containing water according to any one of claims 1 to 4, A microplastic concentration measuring device having a measuring device for measuring the microplastic content of the concentrated liquid.

6. The microplastic concentration measuring device according to claim 5 , wherein the measuring device includes a micro-Raman spectrometer.

7. The measurement device includes a flow cell made of transparent glass, The microplastic concentration measuring device described in claim 6, wherein the measurement point of the flow cell by the microscopic Raman spectrometer has an internal space that contains the concentrated liquid, and the thickness dimension of the internal space is longer than the dimension of the first opening.

8. The microplastic concentration measuring device described in claim 7, wherein the measurement points are 5,000 points arranged in a grid pattern of 50 rows and 100 columns with a pitch of 100 μm on the flow cell.

9. The microplastic concentration measurement device described in claim 7, wherein the measurement device is equipped with a pump that transports the concentrated liquid to the flow cell.

10. A capturing step of capturing microplastics in a first filter by passing a first volume of microplastic-containing water through the first filter having a first mesh size from a first side to a second side; a backwashing step of passing a cleaning liquid from the second side to the first side of the first filter to obtain a recovered liquid; and a concentration step of concentrating the recovered liquid by passing it through a second filter having a second mesh size smaller than the first mesh size to obtain a second volume of concentrated liquid.

11. A method for measuring microplastic concentration, comprising a measuring step of measuring the microplastic content of the concentrate obtained by the method for concentrating microplastic-containing water described in claim 10.

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