Method and apparatus for observing microplastics

Abstract

To provide a method for observing microplastics in water using infrared light, and a small-sized observation device therefor.SOLUTION: An observation method flows water so as to form a flux that flows at a constant speed along an axial line, then linearly irradiates a straight line perpendicular to the axial line with infrared rays from a light source, and guides transmitted light onto a uniaxial array detector in which photodetection elements are arranged in a row, to detect light. The observation device comprises: a flow cell that allows water to flow so as to form a flux flowing at a constant speed along an axial line; and an optical system that linearly irradiates a straight line perpendicular to the axial line with infrared rays from a light source, and guides transmitted light onto a uniaxial array detector in which photodetection elements are arranged in a row, to detect light.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for observing microplastics in water using infrared rays and an observation apparatus therefor.

Background Art

[0002] There have been reports that plastic waste is finely fragmented in the environment and becomes minute plastic pieces, such as "microplastics" having a size of 5 mm or less, which float in the ocean or rivers, and humans and animals take them into their bodies and suffer health damage. For the observation of such microplastics, after pre-treating a liquid collected from the ocean or the like (hereinafter simply referred to as "water") to separate the microplastics, observation is performed by a method as required (see, for example, Patent Document 1 and Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

[0005] The aforementioned literature describes the observation of microplastics captured on a filter after filtering water. For example, Non-Patent Document 1 uses an infrared lamp to illuminate the filter and performs spectroscopic measurements with a spectrometer. However, there was a need for a small device that could directly observe microplastics in collected water and that could be easily used even in places like ships at sea. Therefore, it was considered to use infrared light that can optically identify the resin type of microplastics. However, infrared light absorption in water is very high, making it difficult to observe tiny, moving fragments like microplastics.

[0006] The present invention has been made in view of the above circumstances, and its objective is to provide a method for observing microplastics in water using infrared light and a small observation device therefor. [Means for solving the problem]

[0007] The present invention provides an observation method for observing microplastics in water using infrared light, characterized in that the water is flowed in such a way that it forms a flux flowing at a constant speed along an axis, infrared light from a light source is irradiated linearly along a straight line perpendicular to the axis, and the transmitted light is guided onto a uniaxial array detector in which photodetectors are arranged in a row to perform photodetection.

[0008] Furthermore, the observation device of the present invention is an observation device for microplastics in water using infrared light, and is characterized by including a flow cell that flows water to form a flux that flows at a constant speed along an axis, and an optical system that linearly irradiates infrared light from a light source along a straight line perpendicular to the axis, and guides the transmitted light that passes through onto a uniaxial array detector in which photodetectors are arranged in a row, and performs photodetection.

[0009] These characteristics allow for a reduction in the irradiation area, thereby increasing the light intensity per unit area even with the same light source. This makes it possible to create a compact observation device without increasing the size of the light source, even for infrared light, which is heavily absorbed in water. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram (partially a perspective view) of an observation device as an embodiment of the present invention. [Figure 2] These are (a) a photograph of the inside of the pipeline and (b) a two-dimensional image obtained using an observation device during the demonstration test. [Figure 3] These are (a) a photograph of the inside of the pipeline and (b) a two-dimensional image obtained using an observation device during the demonstration test. [Modes for carrying out the invention]

[0011] Below, an observation apparatus and observation method for microplastics, which is one embodiment of the present invention, will be described with reference to Figure 1.

[0012] As shown in Figure 1, the observation device 1 is a device for observing microplastics floating in water, and comprises a flow cell 10 having a flow channel (pipe) 11 for flowing the water to be observed, an illumination-side optical system 20 for irradiating the flow cell 10 with infrared light, and a light-receiving-side optical system 30 for observing the transmitted light that has passed through the flow cell 10.

[0013] The flow cell 10 can flow water in such a way that it forms a flux that flows at a constant velocity along axis A. For example, such a flux can be formed by keeping the shape of the cross section perpendicular to axis A of the flow channel 11 constant. In this embodiment, the cross section perpendicular to axis A of the flow channel 11 is rectangular. Furthermore, while axis A is perpendicular to the direction of infrared transmission, the shorter side of this rectangle is arranged to be parallel to the direction of infrared transmission.

[0014] Furthermore, since infrared rays are easily absorbed by water, depending on the light source intensity, it is preferable to shorten the length of such short pieces and reduce the thickness of the water in the channel 11 so that infrared rays can pass through, from the viewpoint of suppressing the attenuation of infrared rays. In addition, by making the cross-sectional shape perpendicular to the axis A of the channel 11 rectangular, the distance that infrared rays pass through the channel 11 in the width direction of the channel 11 can be made constant, and transmitted light can be obtained under uniform conditions, which is preferable. Moreover, if water is flowed so as to fill the channel 11, it is also preferable to obtain transmitted light under uniform conditions in the width direction of the channel 11.

[0015] Regarding the flow path 11, there are no restrictions on the orientation of its axis A relative to gravity. However, considering the difference in specific gravity between water and floating microplastics, it is preferable to orient axis A horizontally. When axis A is horizontal, even if the difference in specific gravity causes a relative velocity between the microplastics and water, no velocity difference will occur in the direction of the flux flow in the flow path 11. Therefore, it is possible to avoid affecting the shape of the microplastics observed by the observation device 1.

[0016] Therefore, in this case, the flow cell 10 was positioned so that axis A was oriented horizontally. Furthermore, of the rectangular cross-section of the flow channel 11 described above, the shorter side was oriented vertically, so that infrared light was irradiated from above the flow cell 10 and transmitted downwards. The following will explain the case in this configuration.

[0017] On the other hand, the irradiation-side optical system 20 includes a light source 21 that emits infrared light while changing its wavelength, a beam expander 22 that expands the beam of the emitted infrared light, a mirror 23 that reflects it, and a cylindrical lens 24 that focuses the beam of light from the mirror 23 into a linear shape. The light source 21 is capable of emitting infrared light while changing its wavelength, and for example, a quantum cascade laser capable of rapidly changing the emitted wavelength can be used. As described above, the beam expander 22, mirror 23, and cylindrical lens 24 are arranged so that infrared light can be irradiated in a linear shape by passing through them, and this can be guided to the upper surface of the flow channel 11 of the flow cell 10. In other words, the irradiation-side optical system 20 functions as a so-called laser line generator. In particular, the infrared light irradiated into the flow channel 11 is focused into a straight line perpendicular to axis A and horizontal. As a result, the infrared light is irradiated so as to pass through the flow channel 11 from top to bottom along a plane perpendicular to axis A. Here, in particular, the mirror 23 and the cylindrical lens 24 can be replaced with optical elements known for that purpose.

[0018] Furthermore, in the range of 1 to 10 μm wavelengths of infrared radiation emitted by the light source 21, shorter wavelengths tend to be less absorbed by water. Therefore, from the viewpoint of suppressing infrared radiation attenuation, it is preferable to use near-infrared radiation with a wavelength of about 1 to 2 μm. On the other hand, from the viewpoint of identifying the resin type of microplastic, it is also important to use infrared radiation in a wavelength range suitable for this purpose. This is because many wavelengths absorbed by microplastics are within the infrared wavelength range, but the amount of information obtained differs depending on the wavelength. Here, the observation device 1 has an optical system that focuses infrared radiation assuming attenuation due to infrared radiation absorption. Therefore, it is preferable to select the infrared wavelength range used in the observation device 1 prioritizing suitability for identifying resin types over the viewpoint of suppressing infrared radiation attenuation.

[0019] The light-receiving side optical system 30 includes a uniaxial array detector 32 that receives the transmitted light that has passed through the flow path 11 by the infrared rays irradiated on the flow cell 10, and a light-receiving side lens 31 that guides such transmitted light onto the uniaxial array detector 32. The light-receiving side lens 31 is adjusted in arrangement so as to be focused so that an image in the flow path 11 by the transmitted light can be formed on the uniaxial array detector 32. The uniaxial array detector 32 is a light detector in which a plurality of light detection elements 33 are arranged in a row, and can receive the transmitted light from the flow path 11 and perform light detection. The uniaxial array detector 32 arranges a plurality of light detection elements 33 in a direction perpendicular to the axis A in the horizontal plane, and is arranged so that the linearly transmitted light can be widely received in the width direction of the flow path 11. Further, the uniaxial array detector 32 is connected to the analysis device 40, and can output information regarding the intensity of the received transmitted light as an electrical signal toward the analysis device 40.

[0020] Based on the output of the uniaxial array detector 32, the analysis device 40 can obtain a spectrum at each position of the light detection element 33. Further, by comparing the obtained spectrum with the spectrum of the transmitted light obtained by the same observation device using a plastic piece of a known resin type, the resin type constituting the microplastics floating in the water in the flow path 11 can be determined. That is, the analysis device 40 is used as the analysis unit of the observation device 1.

[0021] In such a spectrum comparison, for example, instead of measuring all at each wavelength condition within the spectrum range, it is preferable to extract and measure the wavelength portion having characteristics due to the difference in resin type among the spectra because the resin type can be determined in a shorter time. As a method for selecting this characteristic wavelength portion, for example, principal component analysis can be mentioned. Further, as a method for performing spectrum comparison, for example, a method using a correlation coefficient can be mentioned.

[0022] In addition, although the irradiated infrared rays have a certain wavelength range, the transmitted light received by the photodetector 33 may be spectrally analyzed in advance corresponding to such a wavelength range. Specifically, in the photodetector 33, the infrared rays are spectrally analyzed into wavelength portions that can be characterized by the resin type among the wavelength range of the infrared rays, and the spectral intensity is output corresponding to the wavelength range. That is, the intensity of each of the spectrally analyzed wavelength portions is output. Then, based on this, the resin type is determined in the analyzer 40. Thus, it is also preferable that the resin type can be determined in a short time.

[0023] The analyzer 40 can further form an image of the shape of the microplastics floating in water. That is, the determination of the resin type described above is continuously performed at a predetermined time interval, and a two-dimensional image is created based on the time and the position of the photodetector 33. For example, the product of the flow velocity of the water flowing in the flow path 11 and the above-described time interval corresponds to the distance in the direction along the axis A in the flow path 11, and the positions of the photodetectors 33 arranged in a row correspond to the distance in the width direction of the flow path 11. Then, when color separation and imaging are performed based on the determination of the resin type described above, an image of the shape of the microplastics in the flow path 11 passing above the photodetector 33 together with water can be formed. Note that the output from the photodetector 33 may be intermittently performed corresponding to the flow velocity, and an image may be formed in the same manner by performing the determination of the resin type each time the output is received. That is, the analyzer 40 also functions as an image processing unit of the observation device 1.

[0024] Note that known devices can be used as the one-axis array detector 32 and the analyzer 40. For example, as the analyzer 40, a personal computer equipped with spectral analysis software or the like can be used.

[0025] [Demonstration test] The results of observing plastic pieces of known resin types by the observation device 1 described above will be described. The prepared plastic pieces are of four resin types: polymethyl methacrylate resin (acrylic), polystyrene resin, polyethylene resin, and polypropylene resin.

[0026] First, plastic pieces of each resin type were molded to approximately 5 mm square and 1 mm thick, and then immersed in water. The width of cell 10 is approximately 10 mm, and its vertical dimension is 3 mm. The water was filled to fill the flow path 11, so the water thickness where the plastic pieces are located is 2 mm.

[0027] As shown in Figure 2(a), four types of plastic pieces were observed in appearance, and as shown in Figure 2(b), it was observed that the same shapes as the appearance were obtained in the 2D image obtained by the observation device 1. Note that the areas enclosed by the dotted lines correspond to each other in Figures 2(a) and 2(b).

[0028] Furthermore, this 2D image is color-coded based on the resin type determination by the analysis device 40. It was found that this color coding based on determination corresponds to the resin type symbols shown on the appearance in Figure (a) (PMMA: polymethyl methacrylate resin (acrylic), PS: polystyrene resin, PE, polyethylene resin, PP: polypropylene resin). Thus, the 2D image obtained by the observation device 1 was able to represent the resin type and shape of at least the four types of plastic pieces described above with almost accuracy.

[0029] Next, plastic pieces of each resin type were molded to approximately 1 mm square and 1 mm thick, and the vertical dimension of cell 10 was changed to 2 mm, meaning the water thickness at the location of the plastic piece was changed to 1 mm, and the same observations were performed.

[0030] As shown in Figure 3(a), four types of plastic fragments could be observed in appearance, and as shown in Figure 3(b), it was observed that the same shape as the appearance could be obtained in the 2D image obtained by the observation device 1.

[0031] Furthermore, it was found that the color coding based on the resin type corresponds to the resin type symbols shown on the appearance in Figure (a). Thus, it was found that the 2D images obtained by observation device 1 can similarly represent the resin type and shape with almost accuracy for plastic pieces of at least about 1 mm square in size.

[0032] As described above, the observation device 1 makes it possible to observe microplastics in water using infrared light. In particular, the irradiation optical system 20 focuses the infrared light in a straight line, reducing the irradiation area and increasing the light intensity per unit area even with the same light source. Therefore, even infrared light, which is absorbed greatly in water, can be observed without increasing the size of the light source, allowing for a compact observation device. With such an observation device 1, for example, it becomes easy to observe microplastics in seawater from a ship.

[0033] Although representative embodiments of the present invention have been described above, the present invention is not necessarily limited thereto, and those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the attached claims. [Explanation of symbols]

[0034] 1. Observation device 10 flow cells 11 channels 20 Irradiation side optical system 30 Receiving side optical system 40 Analyzer A axis

Claims

1. A method for observing the resin type of microplastics in sampled water collected from the ocean or rivers in a manner that allows for identification, A method for observing microplastics, characterized by filling a pipeline with the collected water and allowing it to flow at a constant speed along the axis, irradiating a linear infrared light with a wavelength width from a light source onto a straight line perpendicular to the axis, and guiding the transmitted infrared light that passes through the flux of the collected water flowing through the pipeline onto a uniaxial array detector in which photodetectors are arranged in a row, outputting spectral intensity corresponding to the wavelength width, and performing photodetection while identifying the resin type constituting the microplastics.

2. The method for observing microplastics according to claim 1, characterized in that the output from the uniaxial array detector is made to correspond to the velocity of the flux to form an image of the shape of the microplastics.

3. The method for observing microplastics according to claim 1 or 2, characterized in that the infrared radiation is in the range of 1 to 10 μm.

4. The method for observing microplastics according to claim 1, characterized in that the conduit has a rectangular cross-section perpendicular to the axis.

5. An apparatus for observing the resin type of microplastics in sampled water collected from the ocean or rivers, A flow cell that fills the pipeline with the collected water and allows it to flow through the pipeline so as to form a flux flowing at a constant speed along the axis, A microplastic observation device characterized by including an optical system that linearly irradiates infrared light having a wavelength width from a light source along a straight line perpendicular to the axis, guides the transmitted infrared light that passes through the flux of the sampled water flowing through the pipeline onto a uniaxial array detector in which photodetectors are arranged in a row, outputs a spectral intensity corresponding to the wavelength width, and performs photodetection while identifying the resin type constituting the microplastic.

6. The microplastic observation apparatus according to claim 5, characterized in that the optical system includes a cylindrical lens that focuses the infrared light in a linear manner.

7. The microplastic observation apparatus according to claim 5, further comprising an image processing unit that corresponds the output from the uniaxial array detector to the velocity of the flux to form an image of the shape of the microplastic.

8. The microplastic observation device according to one of claims 5 to 7, characterized in that the infrared light is in the range of 1 to 10 μm.

9. The microplastic observation device according to claim 5, characterized in that the conduit has a rectangular cross-section perpendicular to the axis.

Images