Method for extracting micro-plastics in soil of refuse landfill

Abstract

The invention discloses a method for extracting micro-plastics in soil of a refuse landfill. The method comprises the following steps: pretreating a refuse landfill soil sample to obtain sample soil; the sample soil and an extracting agent are fully mixed and oscillated and then stand for layering, first supernate is obtained, the extracting agent is added at least twice, the types of the extracting agent added each time are different, and the extracting agent added each time is one of saturated sodium chloride, saturated sodium bromide and saturated sodium iodide; the first supernate is extracted and fully mixed with a digesting agent, the mixture is shaken and then stands for layering again, second supernate is obtained, and the digesting agent is at least one of 30% hydrogen peroxide, a Fenton reagent, pepsin and trypsin; and filtering the second supernatant to obtain the micro-plastic. Therefore, the extraction method provided by the embodiment of the invention has multiple technical effects of high efficiency, deep digestion, accurate filtration, wide applicability, environmental friendliness and the like.

Description

Technical Field

[0001] The present application relates to the field of chemical technology, and in particular to a method for extracting microplastics from soil in a landfill. Background Art

[0002] As the production and waste of plastics increase dramatically year by year, the problem of plastic pollution has become increasingly prominent and has become a major environmental issue of global concern. Landfill is a common waste disposal method worldwide, and one-third of the world's plastic waste is stored in landfills. At the same time, as the final destination of plastic waste in terrestrial ecosystems, even if efforts are made to control the production and consumption of plastics and the amount of plastic waste generated, the accumulated amount of plastic landfill continues to increase due to the continuous imbalance between economic levels and landfill processing capacity. As a relatively sealed container for biochemical and physical reactions, plastic waste in landfills changes in more severe environmental conditions, such as leachate pH, high salinity, temperature fluctuations, gas generation (such as carbon dioxide and methane), physical stress, and microbial degradation, which may cause plastic fragments to be converted into microplastics.

[0003] During long-term exposed stacking, microplastics formed in the landfill layer are easily migrated and diffused into the surrounding soil under the influence of leachate and natural rainfall. Microplastics are a kind of organic synthetic polymer material, which is light, cheap, stable, waterproof and insulating. It is easy to enter the human body through the food web and is difficult to degrade in the environment in a short period of time. Therefore, it has many adverse effects on the ecological environment and humans. At the same time, since landfill soil is a complex three-phase system and is easily affected by soil texture, organic matter and aggregate structure, the extraction of microplastics in landfill soil is more difficult than that in leachate, resulting in a gap in the spatiotemporal distribution, formation evolution, emission flux and ecological and environmental risks of microplastics in landfill soil.

[0004] The methods currently developed for extracting microplastics from ordinary soil, such as density separation, oil separation, electrostatic separation, magnetic separation, and solvent extraction, are unable to accurately and effectively extract microplastics from landfills. Among them, density separation is the most commonly used technology for extracting microplastics. Its principle is to separate microplastics from soil particles based on the density difference between microplastics and solutions, and then recover microplastics in the supernatant. However, the soil in the landfill has the characteristics of complex environmental medium composition and a wide range of plastic density. Some microplastics, such as polystyrene, have high density and are easily covalently bound to landfill soil particles. At this time, the extraction effect of using a single sodium chloride as an extractant is not ideal. In addition, since the landfill soil has the characteristics of complex environmental components and high organic matter content, the density of some components (such as soil organic matter) is similar to that of microplastics. These components can also be floated by high-salinity solutions, affecting the extraction of microplastics. Therefore, a method for extracting microplastics from landfill soil is needed to assess the ecological and environmental risks of microplastics in landfill soil. Summary of the invention

[0005] The embodiments of the present application provide a method for extracting microplastics from landfill soil, thereby solving the technical problem that the prior art methods for extracting microplastics from ordinary soil cannot accurately and effectively extract microplastics from landfill soil.

[0006] The present application embodiment provides a method for extracting microplastics from soil in a landfill, comprising:

[0007] Pre-treating landfill soil samples to obtain sample soil;

[0008] The sample soil and the extractant are fully mixed, shaken, and then allowed to stand for stratification to obtain a first supernatant, wherein the extractant is added at least twice, and the type of the extractant added each time is different, and the extractant added each time is one of saturated sodium chloride, saturated sodium bromide and saturated sodium iodide;

[0009] Extracting the first supernatant, mixing it thoroughly with a digestive agent, shaking it, and letting it stand again to separate layers to obtain a second supernatant, wherein the digestive agent is at least one of 30% hydrogen peroxide, Fenton's reagent, pepsin, and trypsin;

[0010] The second supernatant was filtered to obtain a sample of microplastics.

[0011] In one possible implementation, a first supernatant is extracted and mixed with a digestive agent, shaken and allowed to stand again for stratification to obtain a second supernatant, wherein the digestive agent is added twice, and the type of digestive agent added each time is different, and the digestive agent added each time is one of 30% hydrogen peroxide, Fenton's reagent, pepsin and trypsin.

[0012] In a possible implementation, the first supernatant extracted is 100 ml, and the amount of digestion agent added each time is 20 ml; the weight of the sample soil is 50 g, and the amount of extraction agent added each time is 100 ml.

[0013] In a possible implementation, the digestive agent added for the first time is trypsin, and the digestive agent added for the second time is 30% hydrogen peroxide.

[0014] In a possible implementation, the extractant added for the first time is saturated sodium bromide, and the extractant added for the second time is saturated sodium chloride.

[0015] In a possible implementation, the sample soil and the extractant are thoroughly mixed and the temperature is maintained at 25°C;

[0016] The first supernatant was extracted and mixed thoroughly with the digestion agent, and the temperature was maintained at 40°C.

[0017] In a possible implementation, after each addition of the extractant, the mixture is shaken by an oscillator, the rotation speed of the oscillator is 140-160 rpm, the shaking time is 25-45 min, and the standing stratification time is 11 h-13 h;

[0018] After each addition of the digestion agent, the mixture was oscillated by an oscillator with a rotation speed of 140-160 rpm, an oscillation time of 25-45 min, and a standing stratification time of 11 h-13 h.

[0019] In a possible implementation, the method for extracting microplastics from landfill soil further includes:

[0020] Fluorescent polystyrene was added to the sample soil as a tracer;

[0021] The sample soil with added tracer is divided into M groups, different extractants are added to each group, and the mixture is shaken and mixed evenly, and then allowed to stand for stratification to obtain a first supernatant;

[0022] The first supernatant of each group was extracted and the fluorescence intensity was tested to evaluate the extraction efficiency of different extractants on the extracted microplastics.

[0023] In a possible implementation, the method for extracting microplastics from landfill soil also includes:

[0024] The first supernatant was extracted and divided into N groups;

[0025] Different digestive agents were added to each group, and the mixture was shaken and mixed evenly, and then allowed to stand to separate layers, thereby obtaining a second supernatant;

[0026] The second supernatant of each group was extracted and measured by a total organic carbon analyzer, a laser particle size analyzer and a Fourier transform infrared spectrometer, respectively, to evaluate the mass change, size change and infrared carbonyl index change of polyethylene, polystyrene and polylactic acid after digestion with different digestants.

[0027] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects:

[0028] The method for extracting microplastics from landfill soil provided in the embodiment of the present application includes: pre-treating landfill soil samples to obtain sample soil; fully mixing the sample soil and the extractant, standing and stratifying after oscillation to obtain a first supernatant, wherein the extractant is added at least twice, and the type of extractant added each time is different, and the extractant added each time is one of saturated sodium chloride, saturated sodium bromide and saturated sodium iodide; extracting the first supernatant, and fully mixing it with the digestant, standing and stratifying again after oscillation to obtain a second supernatant, wherein the digestant is at least one of 30% hydrogen peroxide, Fenton's reagent, pepsin and trypsin; filtering the second supernatant to obtain microplastics. First, pre-treat the landfill soil sample to lay a solid foundation for subsequent steps. Then, different types of saturated salt solutions (including saturated sodium chloride, saturated sodium bromide and saturated sodium iodide) are added step by step as extractants. These salt solutions can efficiently separate microplastics from soil particles in the sample soil, thereby improving the extraction efficiency. Each time a different type of extractant is added, it is intended to carry out a more comprehensive and detailed extraction of microplastics of different properties, effectively avoiding the problem of incomplete extraction that may be caused by a single extractant. After successfully obtaining the first supernatant, it is further mixed with a digestive agent (such as 30% hydrogen peroxide, Fenton's reagent, pepsin and trypsin, etc.). These digestive agents can decompose organic matter attached to the surface of microplastics, significantly reduce their interference with the extraction of microplastics, and thus improve the purity of the extraction. Therefore, the method for extracting microplastics from landfill soil provided in the embodiment of the present application has multiple technical effects such as high efficiency, deep digestion, precise filtration, wide applicability and environmental friendliness, which provides relevant references and theoretical support for the control and research of microplastic pollution in landfill soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments of the present application. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 A process flow chart of a method for extracting microplastics from landfill soil provided in an embodiment of the present application;

[0031] Figure 2 This is a graph showing the recovery rate of fluorescent polystyrene by different extractants provided in the examples of the present application;

[0032] Figure 3 This is a diagram showing the removal rate of organic matter by different digestants provided in the embodiments of the present application;

[0033] Figure 4 A graph showing the changes in the mass of polyethylene, polystyrene and polylactic acid in microplastics after digestion with different digestive agents provided in the examples of the present application;

[0034] Figure 5 A diagram showing the changes in the sizes of polyethylene, polystyrene and polylactic acid in microplastics after digestion with different digestive agents provided in the examples of the present application;

[0035] Figure 6 Fourier transform infrared spectra of polyethylene, polystyrene and polylactic acid in microplastics after digestion with different digestive agents provided in the examples of the present application. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. The terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0038] The present application embodiment provides a method for extracting microplastics from landfill soil, such as Figures 1 to 6The method for extracting microplastics from landfill soil includes steps S1-S4:

[0039] S1: Pretreatment of landfill soil samples to obtain sample soil.

[0040] It should be noted that soil samples were collected from the Huangyan District domestic waste landfill in Taizhou City, Zhejiang Province, and the collected soil samples were sealed in sealed bags for preservation; the collected soil samples were dried in an oven at 60°C to constant weight, and sieved through a 2mm diameter stainless steel sieve to remove large impurities (gravel, branches, etc.); no obvious microplastic particles were found during the sieving process. The basic physical and chemical properties of the sample soil, such as organic matter (SOM), soil pH, total nitrogen content (TN) in the soil, and soil water content, were determined using standard methods. Table 1 shows the basic physical and chemical properties of the sample soil.

[0041] Table 1 Basic physical and chemical properties of sample soil

[0042] index SOM(g / kg) pH TN(g / kg) Moisture content (%) Soil Sample 15.17 6.74 1.38 21.3

[0043] S2: The sample soil and the extractant are fully mixed, shaken and then allowed to stand for stratification to obtain a first supernatant, wherein the extractant is added at least twice, and the type of the extractant added each time is different, and the extractant added each time is one of saturated sodium chloride, saturated sodium bromide and saturated sodium iodide.

[0044] Furthermore, density separation method was used to extract microplastics from sample soil.

[0045] S3: extracting the first supernatant, and fully mixing it with a digestive agent, shaking it, and letting it stand again to separate the layers, to obtain a second supernatant, wherein the digestive agent is at least one of 30% hydrogen peroxide, Fenton's reagent, pepsin and trypsin.

[0046] It should be noted that the present application can effectively decompose and remove organic matter, soil particles and other impurities attached to the surface of microplastics by adding digestive agents, such as 30% hydrogen peroxide, Fenton's reagent (usually containing hydrogen peroxide and iron ions), pepsin and trypsin.

[0047] S4: Filter the second supernatant to obtain a microplastic sample.

[0048] Specifically, the present application filters the second supernatant through a Buchner funnel, and finally causes the microplastics to adhere to a 0.22 μm mixed cellulose filter membrane.

[0049] It should be noted that, first, the landfill soil samples are pretreated to lay a solid foundation for subsequent steps. Then, different types of saturated salt solutions (including saturated sodium chloride, saturated sodium bromide and saturated sodium iodide) are added step by step as extractants. These salt solutions can efficiently separate microplastics from soil particles in the sample soil, thereby improving the extraction efficiency. Each time a different type of extractant is added, it is intended to extract microplastics of different properties more comprehensively and meticulously, effectively avoiding the problem of incomplete extraction that may be caused by a single extractant. After successfully obtaining the first supernatant, it is further mixed with a digestive agent (such as 30% hydrogen peroxide, Fenton's reagent, pepsin and trypsin, etc.). These digestive agents can decompose organic matter attached to the surface of microplastics, significantly reduce their interference with the extraction of microplastics, and thus improve the purity of the extraction. Therefore, the landfill soil microplastic extraction method provided in the embodiment of the present application has multiple technical effects such as high efficiency, deep digestion, precise filtration, wide applicability and environmental friendliness. This method provides a new and effective technical means for the monitoring and research of microplastics in landfill soil.

[0050] In an embodiment of the present application, a first supernatant is extracted and mixed with a digestive agent, and then allowed to stand and separate layers again after shaking to obtain a second supernatant, wherein the digestive agent is added twice, and the type of digestive agent added each time is different, and the digestive agent added each time is one of 30% hydrogen peroxide, Fenton's reagent, pepsin and trypsin.

[0051] It should be noted that, compared with the prior art, the embodiments of the present application have been significantly optimized in the use of digestive agents. In the prior art, in order to remove organic matter in the soil, a large amount of Fenton's reagent or hydrogen peroxide is often added to the sample soil before extraction. Although these strong oxidants can effectively oxidize and remove organic matter in the soil, they often cause great damage to the microplastics in the sample during the treatment process, thereby affecting the subsequent analysis and research of microplastics. In the embodiments of the present application, a strategy of adding different types of digestive agents in batches is adopted. This strategy not only avoids the damage of microplastics by a single strong oxidant, but also through the synergistic effect of different digestive agents, it can more comprehensively remove organic matter and other interfering substances in the soil. At the same time, the addition of digestive agents in batches can also be flexibly adjusted according to the actual situation of the soil sample and the type of microplastics, thereby further improving the extraction efficiency and purity.

[0052] In the present embodiment, the first supernatant extracted is 100 ml, the amount of digestion agent added each time is 20 ml, the weight of the sample soil is 50 g, and the amount of extraction agent added each time is 100 ml.

[0053] It should be noted that setting a reasonable amount of digestant can ensure that the digestant fully contacts and reacts with the organic matter in the supernatant, thereby improving the removal efficiency of the organic matter.

[0054] Mixing 50g of sample soil with 100ml of extractant can ensure that the extractant fully penetrates into the soil particles and effectively separates microplastics from the sample soil. At the same time, this ratio selection also helps to reduce the interference of impurities in the sample soil on the extraction results, thereby improving the purity of the extracted microplastics.

[0055] In the embodiment of the present application, the digestive agent added for the first time is trypsin, and the digestive agent added for the second time is 30% hydrogen peroxide.

[0056] In the examples of the present application, the extractant added for the first time is saturated sodium bromide, and the extractant added for the second time is saturated sodium chloride.

[0057] In the examples of the present application, the sample soil and the extractant were fully mixed and the temperature was maintained at 25°C.

[0058] The first supernatant was extracted and mixed thoroughly with the digestion agent, and the temperature was maintained at 40°C.

[0059] It should be noted that at a temperature of 40°C, trypsin can maintain a high activity and effectively decompose proteins and other polypeptide substances in the first supernatant, reducing damage to microplastics. 30% hydrogen peroxide is a strong oxidant that can oxidize and remove organic matter and other substances in the soil that are difficult to decompose with trypsin. After trypsin pretreatment, 30% hydrogen peroxide can further remove residual organic matter and improve the purity of the extraction.

[0060] In the examples of the present application, after each addition of the extractant, the extractant was shaken by an oscillator, the speed of the oscillator was 140-160 rpm, the oscillation time was 25-45 min, and the standing stratification time was 11 h-13 h.

[0061] After each addition of the digestion agent, the mixture was oscillated by an oscillator with a rotation speed of 140-160 rpm, an oscillation time of 25-45 min, and a standing stratification time of 11 h-13 h.

[0062] In an embodiment of the present application, the method for extracting microplastics from soil in a landfill further includes: dividing the sample soil to which the tracer is added into M groups, adding a different extractant to each group, oscillating and mixing the mixture evenly, and then standing the mixture to separate layers to obtain a first supernatant;

[0063] The first supernatant of each group was extracted and the fluorescence intensity was tested to evaluate the extraction efficiency of different extractants on the extracted microplastics.

[0064] It should be noted that M in this application is 12, and the sample soil is divided into 12 groups, 50 mL of sample soil is taken from each group, and it is placed in a thread-mouth bottle, and fluorescent polystyrene is added as a tracer, and 100 mL of extractant is added to each thread-mouth bottle each time, and after being fully mixed, it is oscillated by an oscillator, the speed of the oscillator is 150 rpm, and the oscillation time is 30 min to obtain a soil suspension system, and the soil suspension system is allowed to stand for stratification for 12 h to obtain a first supernatant. The type of extractant used for extraction is detailed in Table 2.

[0065] Table 2 shows the types of extractants used for extraction

[0066] Group Primary Extraction Agent Secondary Extraction Agent Tertiary Extraction Agent 1 NaCl 2 NaBr 3 NaI 4 NaCl NaCl 5 NaCl NaBr 6 NaCl NaI 7 NaBr NaCl 8 NaBr NaI 9 NaI NaCl 10 NaCl NaBr NaI 11 NaBr NaCl NaI 12 NaI NaCl NaBr

[0067] NaCl, NaBr and NaI represent saturated sodium chloride, saturated sodium bromide and saturated sodium iodide, respectively.

[0068] 50 ml of the first supernatant was extracted from each group and filtered through a 0.22 μm filter. The fluorescence intensity of the treated fluorescent polystyrene was measured using a fluorescence spectrophotometer.

[0069] The recovery rate of fluorescent polystyrene is calculated as R m =C m / C0;

[0070] In the formula, R m is the recovery rate of fluorescent polystyrene, C0 is the initial fluorescence intensity of fluorescent polystyrene, that is, the fluorescence intensity of fluorescent polystyrene before any treatment or change of experimental conditions, C m It is the fluorescence intensity of fluorescent polystyrene measured from the sample after specific treatment, specifically refers to the fluorescence intensity of 50 ml of the first supernatant extracted from each group after being filtered through a 0.22 μm filter head and measured using a fluorescence spectrophotometer.

[0071] The recovery rate of fluorescent polystyrene after multiple flotation is calculated as R n =C n / C0;

[0072] In the formula, R n is the recovery rate of fluorescent polystyrene after multiple flotation, C n is the total fluorescence intensity of fluorescent polystyrene obtained by multiple flotation.

[0073] like Figure 2As shown, the recovery rates of fluorescent polystyrene by different extraction agent combinations vary greatly, among which the two combinations with the highest recovery rates are the secondary extraction of saturated sodium bromide + saturated sodium chloride (with a recovery rate of 97.85%) and the tertiary extraction of saturated sodium bromide + saturated sodium chloride + saturated sodium iodide (with a recovery rate of 97.88%). Considering the practicality and safety, saturated sodium bromide + saturated sodium chloride is the best extraction agent combination for landfill soil.

[0074] It should be noted that the reason why fluorescent polystyrene is used in this application is that it has advantages in both weight and volume - it is heavy and small. This feature allows both heavy and light microplastics, both small and large microplastics, to be effectively extracted, thereby improving the accuracy and reliability of the test.

[0075] In the embodiment of the present application, the method for extracting microplastics from landfill soil also includes:

[0076] The first supernatant was extracted and divided into N groups;

[0077] Different digestive agents were added to each group, and the mixture was shaken and mixed evenly, and then allowed to stand to separate layers, thereby obtaining a second supernatant;

[0078] The second supernatant of each group was extracted and measured by a total organic carbon analyzer, a laser particle size analyzer and a Fourier transform infrared spectrometer, respectively, to evaluate the mass change, size change and infrared carbonyl index change of polyethylene, polystyrene and polylactic acid after digestion with different digestants.

[0079] It should be noted that the first supernatant extracted above is obtained by adding saturated sodium bromide and saturated sodium chloride as extractants twice. N in this application is 8.

[0080] The first supernatant was extracted and divided into 8 groups. 100 ml of the first supernatant was taken from each group and put into a thread-mouth bottle. 20 ml of digestion agent was added into the thread-mouth bottle each time. After being fully mixed, the mixture was shaken by an oscillator at a speed of 150 rpm for 30 min to obtain the second supernatant after digestion. The types of digestion agents used for digestion are detailed in Table 3.

[0081] Table 3 shows the types of digestive agents used for digestion

[0082] Group Primary Extraction Agent Secondary Extraction Agent Temperature(℃) 1 30% Hydrogen Peroxide 65 2 Fenton's reagent 25 3 Pepsin 40 4 Trypsin 40 5 Pepsin 30% Hydrogen Peroxide 40 6 Pepsin Fenton's reagent 40 7 Trypsin 30% Hydrogen Peroxide 40 8 Trypsin Fenton's reagent 40

[0083] For each group of digested samples, 50 mL of the second supernatant was taken for subsequent analysis and the dissolved organic carbon content was determined by a total organic carbon analyzer;

[0084] The calculation formula for organic matter removal rate is:

[0085] Where, T m Represents the organic matter removal rate, T0C m T0C0 represents the content of dissolved organic matter in the sample after treatment, that is, the DOC value in the second supernatant after digestion treatment, and T0C0 represents the content of dissolved organic carbon in the sample before treatment, that is, the DOC value in the first supernatant.

[0086] like Figure 3 As shown, the removal rates of soil organic matter by different digestant combinations vary greatly, among which the two combinations with the highest removal rates are trypsin + Fenton's reagent secondary digestion (91.3%) and trypsin + 30% hydrogen peroxide secondary digestion (90.5%).

[0087] This application uses the mass method to determine the mass changes of polyethylene, polystyrene, and polylactic acid in microplastics after digestion with different digestive agents, such as Figure 4 As shown, the digestion agent combination with the greatest impact on the mass change of polyethylene, polystyrene and polylactic acid is Fenton's reagent, and the largest change is polylactic acid (mass reduction of 33.40%). The digestion agent combination with the least impact on the mass change of polyethylene, polystyrene and polylactic acid is trypsin + 30% hydrogen peroxide, and the smallest change is polystyrene (mass reduction of 0.01%).

[0088] This application uses a laser particle size analyzer to measure the size changes of polyethylene, polystyrene, and polylactic acid after digestion with different digestants, such as Figure 5 As shown, polylactic acid changes the most, polystyrene changes the least, and the digestion agent combination with the least effect on the size changes of polyethylene, polystyrene and polylactic acid is trypsin + 30% hydrogen peroxide.

[0089] The present application uses Fourier transform infrared spectrometer to measure the changes in infrared carbonyl index of polyethylene, polystyrene and polylactic acid after digestion with different digestants.

[0090] The calculation formula of infrared carbonyl index is CI = A (1) / A (2) ;

[0091] In the formula, A (1) The wavelengths of polyethylene, polystyrene and polylactic acid are 1600-1768, 1573-1770 and 1573-1770cm respectively. -1 The comprehensive area of ​​the carbonyl peak at (2) is the integrated area of ​​the reference peak. Figure 6a, b and c in the figure represent the Fourier infrared spectra of polyethylene, polystyrene and polylactic acid after digestion with different digestants. Table 4 lists the changes in infrared carbonyl index of polyethylene, polystyrene and polylactic acid after treatment with different digestants. Among them, the group with the lowest change in infrared carbonyl index before and after treatment was the trypsin group; at the same time, the combination of trypsin + 30% hydrogen peroxide, which has the ability to efficiently remove organic matter, has little effect on the functional groups of polyethylene, polystyrene and polylactic acid.

[0092] Table 4 Changes in infrared carbonyl index of polyethylene, polystyrene and polylactic acid

[0093]

[0094] The following is the observation and analysis of the extracted microplastics:

[0095] The microplastics were observed through an optical stereo microscope (LEICAS8AP0), separated and collected using stainless steel tweezers and dissecting needles, and the composition of the microplastics was identified using a Fourier transform infrared spectrometer. The specific operations were as follows:

[0096] In a dry environment, take a sample visible to the naked eye (a small amount of sample is obtained, especially a smaller amount of black sample) and an appropriate amount of dry potassium bromide powder and add them to a mortar. Grind them several times and then put them into a tablet press (pressed into a transparent sheet). When testing, collect the background first, and then collect the infrared spectrum of the sample. Resolution: 4cm -1 , the scanning times are 32 times, and the test wave number range is 400 / 600-4000cm -1 .

[0097] In order to avoid data distortion caused by air precipitation, synthetic fibers in clothing, etc. during the experiment, the following protective measures were taken:

[0098] During sampling and experiment, avoid using any plastic products and use stainless steel or glass products;

[0099] Throughout the experiment, the subjects wore cotton rather than synthetic clothing;

[0100] The water used in the test was pre-filtered through a 0.45 μm microporous membrane to remove possible microplastics;

[0101] Rinse tools and containers with ultrapure water two to three times and seal them with tin foil when not in use to prevent possible microplastics from the air from entering the containers;

[0102] After each individual step, all materials and containers were covered with aluminum foil.

[0103] A blank sample was set up and the test was carried out under the same conditions. After filtering with ultrapure water using a 0.45μm mixed acetate filter membrane through a vacuum pump, the filter membrane was placed in a laboratory environment for 24 hours. No microplastic particles were detected.

[0104] During the filtration and density flotation process, the entire system was covered with plastic wrap to avoid potential microplastic contamination from the ambient air. Similarly, instrumental analysis of the samples was performed in a clean room to prevent contamination.

[0105] This study conducted an in-depth study on the separation of microplastics and organic matter removal in the soil of microplastic landfills through analytical experiments. The experiment considered the effects of extractant combinations, digestant combinations, and microplastic types on the extraction rate, and proposed an optimization scheme. The optimized scheme was used to extract microplastics, and the main results are as follows:

[0106] For fluorescent polystyrene, the extraction rate was only 85.42% when a single saturated sodium chloride solution was used for extraction. The extraction rate was increased to 97.85% by the secondary extraction method of saturated sodium bromide + saturated sodium chloride; the extraction rate was slightly increased (97.88%) by the tertiary extraction method of saturated sodium bromide + saturated sodium chloride + saturated sodium iodide. However, considering the extraction rate, cost and environmental friendliness, the secondary extraction method of saturated sodium bromide + saturated sodium chloride is recommended as a method for separating microplastics in landfill soil.

[0107] Compared with traditional single oxidants hydrogen peroxide and Fenton's reagent, the trypsin + 30% hydrogen peroxide combination can remove more than 90% of organic matter at a lower temperature, while causing less damage to plastics such as polyethylene, polystyrene, and polylactic acid. Therefore, this combination can be used as an efficient method to remove soil organic matter during the extraction of microplastics in landfill soil.

[0108] This application also analyzes the removal method of a large amount of organic matter in landfill soil. By purposefully selecting and optimizing factors such as the type of digestant and the order of digestant combination, the oxidant-based organic matter removal method can more efficiently extract and recover easily degradable microplastics such as polylactic acid. Experimental results show that compared with a single hydrogen peroxide or Fenton reagent, the secondary digestion method using trypsin + hydrogen peroxide is more conducive to removing organic matter from landfill microplastics at a lower temperature, and will not cause significant damage to the microplastics themselves. Therefore, this application successfully improved the extraction rate of microplastics and the removal efficiency of organic matter by optimizing the combination of extractants and digestants. It is recommended to use a secondary extraction method of saturated sodium bromide + saturated sodium chloride to separate microplastics from landfill soil, and a secondary digestion method of trypsin + 30% hydrogen peroxide to efficiently remove organic matter. This application explores a new method for extracting microplastics from landfill soil, which provides relevant references and theoretical support for the control and research of microplastic pollution in landfill soil.

[0109] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other. Each embodiment focuses on the differences from other embodiments.

[0110] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for extracting microplastics from landfill soil, characterized in that: include: Pre-treating landfill soil samples to obtain sample soil; The sample soil and the extractant are fully mixed, shaken, and then allowed to stand for stratification to obtain a first supernatant, wherein the extractant is added at least twice, and the type of the extractant added each time is different, and the extractant added each time is one of saturated sodium chloride, saturated sodium bromide and saturated sodium iodide; Extracting the first supernatant, mixing it thoroughly with a digestive agent, shaking it, and letting it stand again to separate layers to obtain a second supernatant, wherein the digestive agent is at least one of 30% hydrogen peroxide, Fenton's reagent, pepsin, and trypsin; The second supernatant was filtered to obtain microplastics.

2. The method for extracting microplastics from landfill soil according to claim 1, characterized in that: The first supernatant is extracted and mixed with a digestive agent, and then allowed to stand and separate again after shaking to obtain a second supernatant, wherein the digestive agent is added twice, and the type of digestive agent added each time is different, and the digestive agent added each time is one of 30% hydrogen peroxide, Fenton's reagent, pepsin and trypsin.

3. The method for extracting microplastics from landfill soil according to claim 2, characterized in that: The first supernatant extracted was 100 ml, and the amount of digestion agent added each time was 20 ml; the weight of the sample soil was 50 g, and the amount of extraction agent added each time was 100 ml.

4. The method for extracting microplastics from landfill soil according to claim 3, characterized in that: The first added digestion agent was trypsin, and the second added digestion agent was 30% hydrogen peroxide.

5. The method for extracting microplastics from landfill soil according to claim 3, characterized in that: The first added extractant is saturated sodium bromide, and the second added extractant is saturated sodium chloride.

6. The method for extracting microplastics from landfill soil according to claim 4, characterized in that: The sample soil and extractant were mixed thoroughly and the temperature was maintained at 25°C; The first supernatant was extracted and mixed thoroughly with the digestion agent, and the temperature was maintained at 40°C.

7. The method for extracting microplastics from landfill soil according to claim 2, characterized in that: After each addition of the extractant, the mixture was shaken by an oscillator at a speed of 140-160 rpm, for 25-45 min, and for 11-13 h of standing and stratification; After each addition of the digestion agent, the mixture was oscillated by an oscillator with a rotation speed of 140-160 rpm, an oscillation time of 25-45 min, and a standing stratification time of 11 h-13 h.

8. The method for extracting microplastics from landfill soil according to claim 1, characterized in that: Also includes: Fluorescent polystyrene was added to the sample soil as a tracer; The sample soil with added tracer is divided into M groups, different extractants are added to each group, and the mixture is shaken and mixed evenly, and then allowed to stand for stratification to obtain a first supernatant; The first supernatant of each group was extracted and the fluorescence intensity was tested to evaluate the extraction efficiency of different extractants on the extracted microplastics.

9. The method for extracting microplastics from landfill soil according to claim 2, characterized in that: Also includes: The first supernatant was extracted and divided into N groups; Different digestive agents were added to each group, and the mixture was shaken and mixed evenly, and then allowed to stand to separate layers, thereby obtaining a second supernatant; The second supernatant of each group was extracted and measured by a total organic carbon analyzer, a laser particle size analyzer and a Fourier transform infrared spectrometer, respectively, to evaluate the mass change, size change and infrared carbonyl index change of polyethylene, polystyrene and polylactic acid after digestion with different digestants.

Images