Microplastic sampling column, microplastic collection device and in-situ digestion method

Abstract

The present invention discloses a microplastic sampling column, comprising a main column, a filter sheet, an upper end cover and a lower end cover, wherein the upper end cover and the lower end cover are detachably connected to the top and the bottom of the main column to form a cylindrical inner cavity, and the filter sheet is arranged at the bottom of the inner cavity. A microplastic collection device comprises the microplastic sampling column, a surface water sampler and a water pump, a flow meter, a conversion valve and an electrical control system. Microplastics can be collected at a large flow rate by the microplastic collection device. An in-situ digestion method for collecting microplastics comprises placing the main column after sampling into a sleeve, adding an oxidant solution, covering it with a sleeve cover and sealing it, standing it for cleaning and drying, and then identifying the microplastics. Compared with the prior art, the present invention can effectively enrich microplastics in water bodies, and the detection accuracy of microplastics is improved by 1-2 orders of magnitude compared with traditional methods; the in-situ digestion method does not need to transfer the enriched sample first, thereby reducing errors and saving pre-processing time.

Description

Technical Field

[0001] The present application belongs to the field of water body detection, and in particular relates to a microplastic sampling column, a microplastic collection device and an in-situ digestion method for collecting and in-situ digesting microplastics in water bodies. Background Art

[0002] Microplastics refer to a general term for various plastic pellets, microfibers, plastic particles, foam plastics and films with a size less than 5.0 mm. The sources of microplastics in the marine environment are very complex, including land-based inputs such as rivers, sewage, garbage dumps, and marine inputs during offshore operations and ship transportation. At the same time, some industrial products such as detergents, daily skin care products and industrial raw materials also contain a large amount of microplastic components. Microplastics entering the environment can migrate under external forces such as wind, rivers and ocean currents due to their small particle size and low density. Microplastics are relatively stable and can exist in the environment for a long time, but their surface physical and chemical properties will change under the influence of sunlight, wind, waves, etc. Microplastics are small in size, large in specific surface area, and highly hydrophobic, making them ideal carriers of many hydrophobic organic pollutants and heavy metals. Microplastics are easily ingested by plankton and fish, can remain in organisms for a long time, and are transferred and enriched in the food web, posing a threat to ecological and environmental safety.

[0003] At present, the equipment and methods for collecting microplastics in water bodies have not been standardized. The trawl method is currently the most commonly used method for collecting microplastics. The trawl method collects microplastics by usually using a plankton net with a pore size range of 333μm-335μm to drag a certain distance in the water. The amount of enriched water is quantitatively calculated based on the size of the net mouth and the towing distance, and the collected substances are then transferred to glass bottles for subsequent analysis.

[0004] There are limitations to the trawl method for collecting microplastic samples. The concentration of larger microplastic particles (300 μm-5 mm) in seawater is relatively low. According to existing reports, the concentration of microplastics in China's coastal waters is 0.167±0.138 n / m 3 (Zhao et al., 2014, Marine Pollution Bulletin, 86, 562-568), microplastics were collected by trawl netting. Microplastics are easily adsorbed on the nylon mesh wall and are not enriched on the plankton net. Because the total amount of microplastics in seawater is relatively small, even individual errors may cause large fluctuations in the total amount of microplastics. Summary of the invention

[0005] In view of the shortcomings or deficiencies of the above-mentioned prior art, the technical problem to be solved by the present invention is to provide a microplastic sampling column, a microplastic collection device and an in-situ digestion method that are suitable for the collection and analysis of microplastics in surface waters and have extremely high collection efficiency.

[0006] In order to solve the above technical problems, the present invention has the following structure:

[0007] A microplastic sampling column comprises a main column, a filter sheet, an upper end cover and a lower end cover, wherein the upper end cover and the lower end cover are detachably connected to the top and the bottom of the main column to form a cylindrical inner cavity, and the upper end cover and the lower end cover are respectively provided with a sampling inlet and a sampling outlet for connecting the inner cavity with the outside of the microplastic sampling column, and the filter sheet is arranged at the bottom of the inner cavity, close to the sampling outlet.

[0008] Furthermore, the inner diameter of the main column is 20-80 mm.

[0009] Furthermore, the length of the main column is 20-120 mm.

[0010] Furthermore, in the microplastic sampling column, the pore size of the filter is 10-300 μm.

[0011] Furthermore, the inner cavity wall of the three-dimensional column is provided with a groove for installing the filter mesh, and the filter mesh is movably installed on the groove through a pressure ring.

[0012] A microplastic collection device includes a microplastic sampling column, a surface water sampler and a water pump.

[0013] Furthermore, the water inlet of the water pump is connected to a surface water sampler, which is placed on the surface of the water body to collect microplastics in the surface water body. The water outlet of the water pump is connected to the sampling inlet of the microplastic sampling column, and the water sample collected by the surface water sampler is transported to the microplastic sampling column through the water pump.

[0014] Furthermore, the surface water sampler includes a sampling container, a buoyancy device and a regulator. A sampling tube is arranged in the sampling container, a sampling port is arranged on the sampling tube, one end of the sampling tube is connected to the water inlet of the water pump through a water pipe, the sampling container is connected to the buoyancy device through the regulator, and the sampling depth of the sampling container is adjusted by the regulator.

[0015] Furthermore, the microplastic collection device also includes a flow meter, a conversion valve and an electrical control system. The flow meter is connected to the sampling outlet of the microplastic sampling column, the conversion valve is arranged between the sampling inlet of the microplastic sampling column and the water outlet of the water pump, and the electrical control system is connected to the water pump to provide power to the water pump and control the start and stop of the water pump.

[0016] The in-situ digestion method based on the microplastic sampling column adopts an in-situ digestion device including a sleeve and a cover, wherein the diameter and height of the sleeve are slightly larger than the diameter and height of the main column, and the cover is used to seal the sleeve after the main column is placed in the stainless steel sleeve, and comprises the following steps:

[0017] Putting the main column after sampling into the casing of the in-situ digestion device;

[0018] Adding an oxidant solution into the inner cavity of the main column so that the oxidant solution at least covers the filter mesh in the inner cavity of the main column, and sealing with a cover;

[0019] Let it sit for a preset time;

[0020] Wash the main column multiple times with ultrapure water;

[0021] The main column is dried.

[0022] Furthermore, in the in-situ digestion method based on the microplastic sampling column, the oxidant solution is a 35% hydrogen peroxide solution.

[0023] The present invention can effectively enrich and analyze microplastics in water bodies; a microplastic collection device is used to collect microplastics in surface water bodies (including seawater bodies and surface water bodies), and the sampling column is in a closed state during the sampling process and the digestion process, which greatly improves the enrichment efficiency and ensures the reliability and accuracy of the data; the in-situ digestion treatment does not require the enriched sample to be transferred out before digestion, which reduces errors and saves pre-processing time, with excellent results. The patent of the present invention improves the detection accuracy by 1-2 orders of magnitude compared with traditional methods such as trawling. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0025] Figure 1 : The present invention is used to collect microplastics in water body sampling column structure diagram;

[0026] Figure 2 :like Figure 1 A longitudinal cross-sectional view of the sampling column for microplastics shown;

[0027] Figure 3 :based on Figure 1 A schematic diagram of a microplastic collection device of a microplastic sampling column is shown;

[0028] Figure 4 : Schematic diagram of the surface water sampler; DETAILED DESCRIPTION

[0029] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention.

[0030] like Figure 1 , Figure 2 As shown, a sampling column 1 for collecting microplastics in water provided in one embodiment of the present invention includes a main column 11, a filter mesh 15, an upper end cover 12 and a lower end cover 13, wherein the upper end cover 12 and the lower end cover 13 are detachably connected to the top and the bottom of the main column 11 to form a cylindrical inner cavity, and a sampling inlet 17 and a sampling outlet 18 are respectively provided on the upper end cover 12 and the lower end cover 13 for connecting the inner cavity with the outside of the microplastic sampling column, and the filter mesh 15 is arranged at the bottom of the inner cavity, close to the sampling outlet 18.

[0031] There are a variety of connection methods to choose from for the detachable connection between the upper end cover 12, the lower end cover 13 and the main column 11. In principle, as long as the sealing effect of the sampling column can be satisfied, it can be used. Threaded connection method: an external thread structure is provided on the outer walls at the upper and lower ends of the main column 11, and the upper end cover 12 is provided with an internal thread structure. The internal thread structure at the lower end of the upper end cover 12 is matched and connected with the external thread structure at the upper end of the main column 11, and the internal thread structure at the upper end of the lower end cover 13 is matched and connected with the external thread structure at the lower end of the main column 11. Snap connection method: a snap structure is provided on the outer walls at the upper and lower ends of the main column 11, and a snap groove matching the snap structure of the main column 11 is provided on the lower end of the upper end cover 12 and the upper end of the lower end cover 13. The snap groove at the lower end of the upper end cover 12 can be matched and connected with the snap structure at the upper end of the main column 11, and the snap groove at the upper end of the lower end cover 13 can be matched and connected with the snap structure at the lower end of the main column 11.

[0032] The inner diameter of the main column 11 is 20-80 mm. The length of the main column 11 is 20-120 mm. Liquid can freely pass through the three-dimensional column 11. The three-dimensional column 11 will be soaked in an oxidant in the subsequent digestion process. The inner diameter of the three-dimensional column 11 is not the larger the better. The larger the inner diameter, the more oxidant is required. In one embodiment of the present application, the inner diameter of the main column 11 is 66 mm and the length is 100 mm as a better setting.

[0033] A groove 14 is provided on the inner cavity wall at 80 mm from top to bottom of the main column 11 for installing a filter mesh 15. The filter mesh 15 is movably installed on the groove 14 by a pressure ring 16. The pressure ring 16 fixes the filter mesh 15 to prevent the filter mesh 15 from shifting during sampling or digestion. The pore size of the filter mesh 15 is 10-300 μm. Generally, the pore size of microplastics is larger than the pore size (10-300 μm) of the filter mesh 15 in this application. Water samples containing microplastics are filtered through the filter mesh 15, and the microplastics can remain on the filter mesh 15. Preferably, the diameter of the filter mesh 15 is 66 mm.

[0034] like Figure 3 , Figure 4 As shown, an embodiment of the present application provides a collection device for collecting microplastics in water bodies, including a microplastic sampling column 1, a surface water sampler 3 and a water pump 4. The water inlet of the water pump 4 is connected to the surface water sampler 3, and the water outlet of the water pump 4 is connected to the sampling inlet 17 of the microplastic sampling column 1. Since microplastics float on the surface of the water body, if the sampling layer is too deep, the microplastics cannot be collected. The surface water sampler 3 is placed on the surface of the water body, and the position of the water sampling layer must be properly controlled to facilitate the collection of microplastics in the surface water body. The water sample collected by the surface water sampler 3 can be transported to the microplastic sampling column 1 by the water pump 4.

[0035] The surface water sampler 3 includes a sampling container 31, a buoyancy device 34 and a regulator 32. A sampling tube 33 is provided in the sampling container 3. A sampling port is provided on the sampling tube 33. One end of the sampling tube 33 is connected to the water inlet of the water pump 4 through a water pipe. The sampling container 31 is connected to the buoyancy device 34 through the regulator 32, and the sampling depth of the sampling container 3 is adjusted by the regulator 32. There are multiple sampling ports, which are distributed around the tube wall of the sampling tube 33. The sampling port is placed under the surface water body, and the water sample can enter the sampling container 3 through the sampling port. After the water sample enters the sampling container 3, it is pumped away through the sampling tube 33 under the action of the water pump 4. In one embodiment of the present invention, a regulator 32 is connected to the upper end of the sampling tube 33, and the buoyancy devices 34-buoyancy balls are symmetrically arranged at both ends of the regulator 32. In order to ensure the collection quantity and quality of microplastics, it is necessary to ensure the depth of the water collection layer. The regulator 32 adjusts the position of the buoyancy device 34 by moving up and down the sampling tube 33 to ensure that the water sampling layer is 0-5 cm below the surface of the water body. The shape of the buoyancy device 34 is not limited as long as it can generate buoyancy for the surface water sampler 3.

[0036] The microplastic collection device also includes an electrical control system 2, a conversion valve 5 and a flow meter 6. The electrical control system 2 is connected to the water pump 4 to provide power to the water pump 4 and control the start and stop of the water pump 4. The electrical control system 2 is connected to an external power supply and placed on land. Turn on the power switch and the operation switch of the electrical control system 2, the indicator light comes on, and the microplastic collection device starts to work. The conversion valve 5 is arranged between the sampling inlet 17 of the microplastic sampling column 1 and the water outlet of the water pump 4, and the conversion valve 5 plays the role of exhausting air and adding drinking water. When the water pump 4 starts to work, if there is air in the water pump 4, it may cause the water to fail to come on. The conversion valve 5 fills the water pump 4 with water before the water pump 4 works, and the air in the water pump 4 is discharged cleanly, so that the water pump 4 can work normally. The inner wall of the connection between the lower end cover 13 of the microplastic sampling column 1 and the flow meter 6 is provided with an internal thread structure, which is also the sampling outlet 18 of the microplastic sampling column 1. The microplastic sampling column 1 and the flow meter 6 are matched and connected by the thread structure to make the device sealed. The flow meter 6 can control the sampling flow rate of the microplastic sampling column 1. Preferably, the water pumping flow rate of the water pump 4 is 2.4m 3 / h. The water sample continuously enters the inner cavity of the microplastic sampling column 1, and the microplastics are enriched on the filter sheet 15 at the lower end of the main column 11.

[0037] Using the above-mentioned microplastic collection device, microplastic samples in water bodies are collected through multiple groups of embodiments, and the collected microplastic particles are subjected to technical and characteristic recording and other analytical work.

[0038] Embodiment 1

[0039] The specific parameters for collecting water samples are: seawater from a certain sea area; sampling time: 100 min; water volume: 1.630 m 3 The sample collected this time is recorded as ES01.

[0040] Separating the microplastics from other impurities in the collected ES01 sample is a crucial step in the analysis and identification of microplastics. Therefore, the microplastic sampling column 1 enriched with seawater microplastic samples needs to be digested in situ. Seawater contains organic matter such as algae, which needs to be removed before microplastic identification. In the in-situ digestion method based on the microplastic sampling column in the embodiment of the present invention, a stainless steel sleeve (with a matching stainless steel sleeve cover) is used as a digestion device, and the diameter and height of the selected stainless steel sleeve are slightly larger than the diameter and height of the main column 11.

[0041] The in situ digestion method is as follows:

[0042] Remove the upper end cap 12 and the lower end cap 13 of the microplastic sampling column 1 after sampling, leaving only the main column 11 and placing it in the stainless steel casing;

[0043] Add 50 ml of 35% hydrogen peroxide solution into the inner cavity of the main column 11 and cover it with a stainless steel cover to seal it; hydrogen peroxide is a strong oxidant that can digest organic matter such as algae on the filter screen 15;

[0044] Let it stand for 24 hours to allow the digestion process to proceed fully;

[0045] Take out the main column 11, and use ultrapure water to wash the main column 11 multiple times to remove the hydrogen peroxide remaining on the filter sheet 15;

[0046] The cleaned main column 11 is placed in a 45° constant temperature box to dry the main column 11. Hydrogen peroxide can fully decompose organic matter in the sample, while relatively inert microplastics can be retained.

[0047] In order to conduct qualitative and quantitative analysis of the microplastics in the collected samples, it is necessary to identify the microplastics. The identification of microplastics is divided into two steps: visual identification and instrumental identification. Visual identification is the use of a stereo microscope to count and record the characteristics of suspected microplastic particles. This step can often only identify suspected microplastic particles, and it is necessary to calibrate through subsequent instrumental identification steps. Instrumental identification uses a microscopic infrared spectrometer (Nicolet iN 10) to accurately identify the chemical structure of suspected microplastic particles, determine whether they are made of plastic material and determine their specific polymer type. The following table shows a comparative analysis of the chemical structure of suspected microplastic particles and microplastic components (polyethylene terephthalate (PET), polyethylene (PE), etc.) of the collected microplastic sample ES01 using a microscopic infrared spectrometer:

[0048] Table 1: Analysis data of microplastic samples by ES01 infrared spectrometer (Nicolet iN 10)

[0049]

[0050]

[0051] From the data in the table, we can see that among the microplastic samples ES01 collected by the microplastic collection device, 12 samples were visually identified to have shapes similar to those of microplastics. Through microscopic infrared spectrometer identification, it was found that the chemical structure of the suspected microplastic particles in these samples was more than 50% similar to the polymer structure of microplastics, and some even reached more than 90% similarity. It can be concluded that the collected samples do contain microplastics.

[0052] Among them, the detection concentration of microplastics in microplastic sample ES01 in this example is: 7.35 pieces / m 3 The current literature reports that the concentration of microplastics in China's coastal waters is 0.167±0.138n / m3 (Zhao et al., 2014, Marine Pollution Bulletin, 86, 562-568). The concentration of microplastics detected by the present invention is 44 times higher than that reported in the literature, indicating that the present invention can effectively enrich microplastics in water bodies; a microplastic sampling device is used to collect microplastics in surface water bodies (including seawater and surface water bodies), and the sampling column is in a closed state during the sampling process and the digestion process, which greatly improves the enrichment efficiency and ensures the reliability and accuracy of the data; the in-situ digestion treatment is directly carried out in the sampling column, and there is no need to transfer the enriched sample first and then digest it, which reduces errors and saves pre-processing time, with excellent results. The patent of the present invention improves the detection accuracy of microplastics by 1-2 orders of magnitude compared with traditional methods such as trawling.

[0053] Embodiment 2

[0054] The specific parameters of the water sample collection are: tap water from a laboratory, the water volume collected is 50L, and the sample collected this time is recorded as ES02.

[0055] Tap water is injected into the experimental pool, and a small amount of polypropylene (PP) particles with a diameter of about 100 μm are added. The microplastic particles in the experimental pool are collected using a microplastic collection device, and the pore size of the filter 15 is selected to be 20 μm. Because tap water basically does not contain organic matter such as algae, digestion treatment is not required. In this embodiment, the digestion step can be omitted.

[0056] After the sampling is completed, the filter sheet 15 in the main column 11 is removed, placed in a 45° C. oven for drying, and then directly analyzed and identified.

[0057] Instrument identification uses a Raman spectrometer (LabRAMXploRA PLUS), with excitation wavelengths of 532nm and 785nm, and an objective lens of 50×LWD. Raman spectroscopy, as a fingerprint spectrum, can identify different types of polymers. By performing Raman imaging on the filter membrane, the distribution and size information of the particles can be obtained.

[0058] The figure below shows the Raman spectrum of the ES02 experimental sample and the corresponding graph of the standard PP spectrum in the database.

[0059]

[0060] Raman spectra of experimental samples and database comparison results

[0061] Particle Statistical Analysis:

[0062] First, the image is converted into black and white by the system software, and then the particle analysis is performed, and the location of the particle is marked with a red dot; after the particle is located, the size information of the particle size (diameter of equal specific surface area) can be given. In this analysis, a total of 53 particles were found, most of which had a diameter of less than 100μm, and the larger particles were about 400μm.

[0063]

[0064] Statistical results of particle analysis on Raman images

[0065] This embodiment can illustrate that the use of a microplastic collection device can simulate the collection of microplastics under laboratory conditions, and the microplastic collection device effectively enriches microplastics in tap water samples.

[0066] The above embodiments are only used to illustrate the technical solution of the present invention but not to limit it. The present invention is described in detail with reference to the preferred embodiments. It should be understood by those skilled in the art that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, and all should be included in the scope of the claims of the present invention.

Claims

1. A microplastic collection device, characterized in that: It includes a sampling column, a surface water sampler and a water pump; the sampling column includes a main column, a filter sheet, an upper end cover and a lower end cover, the upper end cover and the lower end cover are detachably connected to the top and bottom of the main column to form a cylindrical inner cavity, the upper end cover and the lower end cover are respectively provided with a sampling inlet and a sampling outlet, which are used to connect the inner cavity and the outside of the microplastic sampling column, and the filter sheet is arranged in the inner cavity, close to the sampling outlet; The water inlet of the water pump is connected to a surface water sampler, which is placed on the surface of the water body to collect microplastics in the surface water body. The water outlet of the water pump is connected to the sampling inlet of the microplastic sampling column, and the water sample collected by the surface water sampler is transported to the microplastic sampling column through the water pump. The surface water sampler includes a sampling container, a buoyancy device and a regulator. A sampling tube is arranged in the sampling container, a sampling port is arranged on the sampling tube, one end of the sampling tube is connected to the water inlet of a water pump through a water pipe, the sampling container is connected to the buoyancy device through the regulator, and the regulator adjusts the position of the buoyancy device by moving up and down on the sampling tube, thereby adjusting the sampling depth of the sampling container.

2. The microplastic collection device according to claim 1, characterized in that: The inner diameter of the main column is 20-80 mm.

3. The microplastic collection device according to claim 1, characterized in that: The length of the main column is 20-120 mm.

4. The microplastic collection device according to claim 1, characterized in that: The pore size of the filter screen is 10-300 μm.

5. The microplastic collection device according to claim 1, characterized in that: The inner cavity wall of the main body column is provided with a groove for installing the filter mesh, and the filter mesh is movably installed on the groove through a pressure ring.

6. The microplastic collection device according to any one of claims 1 to 5, characterized in that: The microplastic collection device also includes a flow meter, a conversion valve and an electrical control system. The flow meter is connected to the sampling outlet of the microplastic sampling column. The conversion valve is arranged between the sampling inlet of the microplastic sampling column and the water outlet of the water pump. The electrical control system is connected to the water pump to provide power to the water pump and control the start and stop of the water pump.

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