A method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients

Abstract

The present invention belongs to the field of environmental protection technology, and relates to a method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients. The method comprises: applying straw and / or biochar to soil containing plastic and mixing. Applying straw to soil containing plastic is beneficial to reducing greenhouse gas emissions, improving the plastic degradation efficiency in the soil and improving soil nutrients, and applying biochar is beneficial to improving the plastic degradation efficiency in the soil and improving soil nutrients.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, and relates to a method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients. Background Art

[0002] In recent years, global warming caused by the increase of greenhouse gas emissions has become a global research hotspot. Soil nitrous oxide (N2O) is one of the most important greenhouse gases in the atmosphere and plays an important role in the global carbon and nitrogen cycle. Farmland ecosystems are the main component of terrestrial ecosystems and contribute about 20% to global greenhouse gas emissions. The IPCC Fourth Assessment Report pointed out that agriculture is one of the most important sources of greenhouse gas emissions.

[0003] The term "plastic" refers to any material containing polymers as basic components discovered since the beginning of the 20th century. We live in the "plastic age". According to research data, more than 240 million tons of plastic are produced and used worldwide each year. The World Economic Forum reports that the global carbon dioxide emissions from the production and use of plastic products (excluding incineration and landfill) reach 390 million tons. The large-scale use of plastic products has caused serious pollution to the global marine and terrestrial ecological environment. Plastic pollution has become one of the most urgent global hot environmental issues in the 21st century.

[0004] Plastics themselves contain toxic and harmful ingredients such as plasticizers or additives, and they can directly harm the ecological environment as carriers of pathogens, hazardous chemicals and toxins. Plastics have now been identified as global environmental pollutants. Plastics are ubiquitous in the global environment, and soils in terrestrial farmland and urban ecosystems have become the main environmental reservoirs for plastics. However, due to the complexity of the soil environment and the limitations of plastic analysis methods, research on plastics in terrestrial ecosystems is very lacking, and there is also insufficient knowledge of the ecological impacts of plastic pollution in terrestrial soil environments. Studies have shown that plastic pollution can change the physical and chemical properties of the soil and reduce soil fertility; at the same time, plastics are difficult to degrade, and how to improve the degradation efficiency of plastics has become a global problem. At present, research on plastic degradation mainly focuses on microbial degradation in aquatic environments, and there is very little research on methods and technologies for plastic degradation in soil environments.

[0005] Therefore, finding effective methods to reduce greenhouse gas emissions from agricultural plastic-contaminated soil and improve the degradation efficiency of plastics in the soil environment and soil nutrients are key issues that need to be urgently addressed in agricultural soil environmental management. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies in the prior art and provide a method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients, the method comprising: applying straw and / or biochar to soil containing plastic and mixing.

[0009] There is no limit to the amount of straw and / or biochar applied to the soil containing plastic. Applying any amount of straw is beneficial to reducing greenhouse gas emissions, improving the efficiency of plastic degradation in the soil, and improving soil nutrients. Applying any amount of biochar is beneficial to improving the efficiency of plastic degradation in the soil and improving soil nutrients.

[0010] Straw refers to the stem and leaf part of mature crops, including but not limited to corn straw, wheat straw, rice straw, rape straw, cotton straw, sorghum straw, soybean straw, etc.

[0011] Preferably, the length of the straw is ≤20 cm. The shorter the straw length, the better it is for improving the degradation rate of plastic.

[0012] Preferably, the biochar is prepared using straw as raw material.

[0013] Preferably, the method for preparing biochar comprises the following steps: washing the straw with water, drying to constant weight, then crushing and grinding to less than 2 mm, wrapping with aluminum foil, placing in a muffle furnace for oxygen-free burning, and sieving to obtain biochar.

[0014] Preferably, after the straw is placed in the muffle furnace, the temperature of the muffle furnace is increased to 450-600° C. at a rate of 7-13° C. / min, and the temperature is maintained for 30-90 minutes.

[0015] Preferably, the biochar is sieved through a 16-mesh sieve.

[0016] Preferably, the method comprises: applying a mixture of straw and biochar to soil containing plastic and mixing.

[0017] Preferably, the mass ratio of the straw to the biochar is 1:(1-3). Adding straw is beneficial to greenhouse gas emission reduction and can also improve the degradation efficiency of plastics, but the degradation efficiency of plastics in the soil by adding straw alone is not as good as the degradation efficiency of plastics by adding biochar. When straw and biochar are added to the soil at the same time in a suitable ratio, greenhouse gas emission reduction and plastic degradation efficiency are greatly improved.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention adds straw to the soil containing plastic, which is beneficial to reducing greenhouse gas emissions, improving the degradation efficiency of plastic in the soil and improving soil nutrients;

[0020] 2. The present invention adds biochar to the soil containing plastic, which is beneficial to improving the degradation efficiency of plastic in the soil and improving soil nutrients;

[0021] 3. The present invention adds a mixture of straw and biochar to the soil containing plastic. The interaction between straw and biochar greatly reduces greenhouse gas emissions and improves the plastic degradation efficiency and nutrients in the soil;

[0022] 4. The method developed by the present invention for reducing greenhouse gas emissions from agricultural plastic-contaminated soil and improving the degradation efficiency of plastics in the soil environment is very simple and is of great significance for achieving sustainable and healthy development of agricultural soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an appearance diagram of corn stalks added in an embodiment of the present invention;

[0024] Figure 2 It is a comparison chart of the annual emission rate of N2O of Example 1 and Comparative Example 1;

[0025] Figure 3 It is a comparison chart of the annual cumulative flux change of N2O in Example 1 and Comparative Example 1;

[0026] Figure 4 It is a comparison chart of annual degradation efficiency of granular plastics of Example 1 and Comparative Example 1;

[0027] Figure 5 The scanning electron microscope images of the granular plastics of Example 1 and Comparative Example 1 after 365 days of cultivation;

[0028] Figure 6 It is a comparison chart of the changes of total carbon and total nitrogen in soil of Example 1 and Comparative Example 1;

[0029] Figure 7 It is a comparison chart of the annual emission rate of N2O of Example 2 and Comparative Example 2;

[0030] Figure 8 It is a comparison chart of the annual cumulative flux change of N2O in Example 2 and Comparative Example 2;

[0031] Fig. 9 It is a comparison chart of the annual degradation efficiency of the film plastic of Example 2 and Comparative Example 2;

[0032] Fig.10 The scanning electron microscope images of the film plastics of Example 2 and Comparative Example 2 after 365 days of cultivation;

[0033] Fig.11 It is a comparison chart of the changes in soil total carbon and total nitrogen in Example 2 and Comparative Example 2;

[0034] Fig.12This is an appearance diagram of the biochar added in the embodiment of the present invention;

[0035] Fig.13 It is a comparison chart of annual degradation efficiency of granular plastics of Example 3 and Comparative Example 3;

[0036] Fig.14 The scanning electron microscope images of the granular plastics of Example 3 and Comparative Example 3 after 365 days of cultivation;

[0037] Fig.15 It is a comparison chart of the changes of total carbon and total nitrogen in soil of Example 3 and Comparative Example 3;

[0038] Fig.16 It is a comparison chart of annual degradation efficiency of granular plastics of Example 4 and Comparative Example 4;

[0039] Fig.17 The scanning electron microscope images of the film plastics of Example 4 and Comparative Example 4 after 365 days of cultivation;

[0040] Fig.18 It is a comparison chart of the changes in total carbon and total nitrogen in the soil of Example 4 and Comparative Example 4. DETAILED DESCRIPTION

[0041] The technical scheme of the present invention is further described below by specific examples and accompanying drawings. It should be understood that the specific examples described herein are only used to help understand the present invention and are not intended for specific limitations of the present invention. The accompanying drawings used herein are only for better illustrating the disclosure of the present invention and do not have a limiting effect on the scope of protection. If not otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0042] The present invention studies the influence of straw and / or biochar on soil containing plastic through experiments. The specific experiments are as follows:

[0043] Example 1

[0044] The non-plastic-contaminated garden soil in Hailu Village, Beilun District, Ningbo City, Zhejiang Province was used as the test soil. The topsoil of 0-20 cm was taken, air-dried, and roots, litter, earthworms, etc. were removed and passed through a 2 mm sieve. Then 3 kg was taken and placed in a culture bucket. The diameter of the culture bucket is 20 cm and the height is 33 cm. A top cover with a rubber seal, thread and gas sampling device is set on the top of the culture bucket to ensure the sealing of the space during gas sample collection. A drainage device is set at the bottom of the culture bucket to prevent water accumulation. At the same time, a filter is set to prevent soil animals in the sample site from migrating into the culture bucket. A thin aluminum sheet is set on the wall of the culture bucket to isolate the barrel wall from the culture soil. Polyethylene particles and corn stalks are added to the culture soil (polyethylene particles and corn stalks are 2% of the mass of the culture soil, respectively). The polyethylene particles are crushed to 4-5 mm, and the corn stalks are cut into straw segments with a hay cutter. Figure 1 shown.

[0045] Greenhouse gases produced by the test plots were collected using a static box method and brought back to the laboratory for determination of N2O gas concentration using an Agilent 7890A gas chromatograph. Samples were collected and measured once on day 0 before adding plastic particles and straw, and greenhouse gas samples were taken on days 1, 3, 7, 14, 21, 30, 45, 60, 75, 90, 105, 120, 150, 180, 210, 240, 270, 300, 330, and 365 after adding. The N2O emission rate of the cultivated soil was determined. The results are as follows: Figure 2 As shown, the greenhouse gas release flux is calculated, and the result is as follows Figure 3 Soil samples were collected 30, 90, 180, 270 and 365 days after adding plastic pellets and straw to determine the total carbon and total nitrogen content. The results are shown in Figure 6 After adding plastic particles and straw, the plastic particles were collected 365 days later, cleaned, dried, and weighed to calculate the annual degradation rate of plastic. The results are as follows Figure 4 The results were shown in the scanning electron microscope. Figure 5 shown.

[0046] Comparative Example 1

[0047] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, only polyethylene particles are added to the culture soil, and no corn stalks are added. The rest is the same as Example 1.

[0048] Greenhouse gases produced by the test plots were collected using a static box method and brought back to the laboratory for determination of N2O gas concentration using an Agilent 7890A gas chromatograph. The samples were collected and measured once on day 0 before adding plastic particles, and greenhouse gas samples were collected and sampled on days 1, 3, 7, 14, 21, 30, 45, 60, 75, 90, 105, 120, 150, 180, 210, 240, 270, 300, 330, and 365 after adding plastic particles. The N2O emission rate of the culture soil was determined. The results are as follows: Figure 2As shown, the greenhouse gas release flux is calculated, and the result is as follows Figure 3 Soil samples were collected 30, 90, 180, 270 and 365 days after adding plastic particles to determine the total carbon and total nitrogen content. The results are shown in Figure 6 365 days after adding plastic particles, the plastic particles were collected, cleaned, dried and weighed to calculate the annual degradation rate of plastic. The results are as follows Figure 4 The results were shown in the scanning electron microscope. Figure 5 shown.

[0049] Figure 2 This is a comparison chart of the annual N2O emission rate changes of Example 1 and Comparative Example 1. It can be seen from the figure that after straw treatment, the N2O emission rate of the granular plastic contaminated soil is reduced; Figure 3 The comparison chart of the annual cumulative flux of N2O in Example 1 and Comparative Example 1 shows that the addition of straw reduces the annual cumulative emission flux of N2O in the soil contaminated by granular plastic by 41.15%; Figure 4 The figure is a comparison chart of the annual degradation efficiency of the granular plastics of Example 1 and Comparative Example 1. After being treated with straw, the annual degradation efficiency of the granular plastics is increased by 23.58% compared with that of the granular plastics not treated with straw. Figure 5 The scanning electron microscope images of the granular plastics of Example 1 and Comparative Example 1 after 365 days of cultivation show that after being treated with straw, the cracks and pores on the surface of the granular plastics increase and deepen; Figure 6 This is a comparison chart of the changes in total carbon and total nitrogen in the soil of Example 1 and Comparative Example 1. It can be seen that after the straw treatment, the total carbon and total nitrogen in the soil increased significantly.

[0050] Example 2

[0051] The difference between Example 2 and Example 1 is that 4-5 mm polyethylene film and corn stalks are added to the culture soil (the polyethylene film and corn stalks are 2% of the mass of the culture soil respectively), and the rest is the same as Example 1.

[0052] Comparative Example 2

[0053] The difference between Comparative Example 2 and Example 2 is that in Comparative Example 2, only polyethylene film is added to the culture soil, and no corn stalks are added. The rest is the same as Example 1.

[0054] Greenhouse gases generated by the test plots of Example 2 and Comparative Example 2 were collected by a static box method and brought back to the laboratory for determination of N2O gas concentration by a gas chromatograph of Agilent 7890A in the United States. The samples were collected and measured once on day 0 before adding plastic film and straw, and greenhouse gas samples were taken on days 1, 3, 7, 14, 21, 30, 45, 60, 75, 90, 105, 120, 150, 180, 210, 240, 270, 300, 330, and 365 after adding. The N2O emission rate of the culture soil was determined. The results are shown in the figure. Figure 7 As shown, the greenhouse gas release flux is calculated, and the result is as follows Figure 8 Soil samples were collected 30, 90, 180, 270 and 365 days after adding plastic film to determine the total carbon and total nitrogen content. The results are shown in Fig.11 After adding the plastic film, the plastic film was collected 365 days later, cleaned, dried, and weighed to calculate the annual degradation rate of the plastic. The results are as follows Fig. 9 The results were shown in the scanning electron microscope. Fig.10 shown.

[0055] Figure 7 The figure is a comparison chart of the annual N2O emission rate changes of Example 2 and Comparative Example 2. It can be seen from the figure that after straw treatment, the N2O emission rate of the film plastic contaminated soil is reduced; Figure 8 The comparison chart of the annual cumulative flux of N2O in Example 2 and Comparative Example 2 shows that the addition of straw reduces the annual cumulative emission flux of N2O in the soil contaminated by film plastic by 20.94%; Fig. 9 This is a comparison chart of the annual degradation efficiency of the film plastic of Example 2 and Comparative Example 2. After being treated with straw, the annual degradation efficiency of the film plastic is increased by 36.75% compared with that of the film plastic not treated with straw. Fig.10 The scanning electron microscope images of the film plastics of Example 2 and Comparative Example 2 after 365 days of cultivation show that after being treated with straw, the cracks and pores on the surface of the film plastics are significantly increased and deepened; Fig.11 This is a comparison chart of the changes in total carbon and total nitrogen in the soil of Example 2 and Comparative Example 2. It can be seen that after the straw treatment, the total carbon and total nitrogen in the soil increased significantly.

[0056] Example 3

[0057] The non-plastic-contaminated garden soil in Hailu Village, Beilun District, Ningbo City, Zhejiang Province was used as the test soil. 0-20 cm of topsoil was taken, air-dried, and roots, litter, and earthworms were removed and sieved through a 2 mm sieve. Then 3 kg was taken and placed in a culture bucket. The diameter of the culture bucket is 20 cm and the height is 33 cm. A drainage device is set at the bottom of the culture bucket to prevent water accumulation. At the same time, a filter is set to prevent soil animals in the sample plot from migrating into the culture bucket. A thin aluminum sheet is set on the wall of the culture bucket to isolate the wall from the culture soil. Polyethylene particles and biochar are added to the culture soil (polyethylene particles and biochar are 2% of the mass of the culture soil, respectively), and the polyethylene particles are crushed to 4-5 mm. Biochar was prepared by the following method: corn stalks collected from a corn field were washed three times with tap water and deionized water, then dried at 75°C to a constant mass, the dried corn stalks were crushed and ground to <2 mm, then placed in a muffle furnace, heated to 500°C at a rate of 10°C / min, and kept at 500°C for 1 hour without oxygen, and passed through a 16-mesh sieve to obtain biochar particles. The obtained biochar was as follows: Fig.12 shown.

[0058] Soil samples were collected 30, 90, 180, 270 and 365 days after adding plastic pellets and biochar to determine the total carbon and total nitrogen content. Fig.15 After adding plastic particles and biochar, the plastic particles were collected 365 days later, cleaned, dried, and weighed to calculate the annual degradation rate of the plastic. The results are as follows Fig.13 The results were shown in the scanning electron microscope. Fig.14 shown.

[0059] Comparative Example 3

[0060] The difference between Comparative Example 3 and Example 3 is that in Comparative Example 3, only polyethylene particles are added to the culture soil, and no biochar is added. The rest is the same as Example 3.

[0061] Soil samples were collected 30, 90, 180, 270 and 365 days after adding plastic pellets to determine the total carbon and total nitrogen content. Fig.15 365 days after adding plastic particles, the plastic particles were collected, cleaned, dried and weighed to calculate the annual degradation rate of plastic. The results are as follows Fig.13 The results were shown in the scanning electron microscope. Fig.14 shown.

[0062] Fig.13 This is a comparison chart of the annual degradation efficiency of granular plastics of Example 3 and Comparative Example 3. After biochar treatment, the annual degradation efficiency of granular plastics is increased by 44.40% compared with that without biochar treatment. Fig.14 The scanning electron microscope images of the granular plastics of Example 3 and Comparative Example 3 after 365 days of cultivation show that after being treated with biochar, the cracks and pores on the surface of the granular plastics increase and deepen; Fig.15 This is a comparison chart of the changes in total carbon and total nitrogen in the soil of Example 3 and Comparative Example 3. It can be seen that after biochar treatment, the total carbon and total nitrogen in the soil increased significantly.

[0063] Example 4

[0064] The difference between Example 4 and Example 3 is that 4-5 mm polyethylene film and biochar are added to the culture soil (the polyethylene film and biochar are 2% of the mass of the culture soil respectively), and the rest is the same as Example 3.

[0065] Comparative Example 4

[0066] The difference between Comparative Example 4 and Example 3 is that in Comparative Example 4, only polyethylene film is added to the culture soil, and no biochar is added. The rest is the same as Example 3.

[0067] Soil samples were collected 30, 90, 180, 270 and 365 days after adding plastic film and biochar to determine the total carbon and total nitrogen contents. Fig.18After adding the plastic film, the plastic film was collected 365 days later, cleaned, dried, and weighed to calculate the annual degradation rate of the plastic. The results are as follows Fig.16 The results were shown in the scanning electron microscope. Fig.17 shown.

[0068] Fig.16 This is a comparison chart of the annual degradation efficiency of the film plastic of Example 4 and Comparative Example 4. After biochar treatment, the annual degradation efficiency of the film plastic is increased by 73.32% compared with that without biochar treatment. Fig.17 The scanning electron microscope images of the film plastics of Example 4 and Comparative Example 4 after 365 days of cultivation show that after the biochar treatment, the cracks and pores on the surface of the film plastics significantly increase and deepen; Fig.18 This is a comparison chart of the changes in total carbon and total nitrogen in the soil of Example 4 and Comparative Example 4. It can be seen that after biochar treatment, the total carbon and total nitrogen in the soil increased significantly.

[0069] Example 5

[0070] The difference between Example 5 and Example 1 is that:

[0071] In Example 5, polyethylene particles, corn straw and biochar were added to the culture soil (the polyethylene particles accounted for 2% of the mass of the culture soil, the total amount of corn straw and biochar was 2% of the mass of the culture soil, and the mass ratio of corn straw to biochar was 1:1), and the rest was the same as in Example 1.

[0072] Greenhouse gases generated by the test plot were collected by the static box method, and the N2O gas concentration was measured by the gas chromatograph of Agilent7890A in the United States in the laboratory. The samples were collected and measured once for 0d before adding plastic particles, and greenhouse gas sampling was performed at 1, 3, 7, 14, 21, 30, 45, 60, 75, 90, 105, 120, 150, 180, 210, 240, 270, 300, 330, and 365d after adding. The N2O emission rate of the culture soil was measured, and the greenhouse gas release flux was calculated. Compared with Comparative Example 1, Example 5 added corn stalks and biochar to reduce the annual cumulative emission flux of N2O in the soil contaminated by granular plastic by 44.2%. After adding plastic particles, the plastic particles were collected 365 days later, washed, dried, and weighed to calculate the annual degradation rate of the plastic. After corn stalks and biochar treatment, Example 5 increased the annual degradation efficiency of granular plastic by 74.3% compared with Comparative Example 1 which was not treated with stalks and biochar.

[0073] Example 6

[0074] The difference between Example 6 and Example 2 is that:

[0075] In Example 6, polyethylene film, corn straw and biochar are added to the culture soil (the polyethylene film is 2% of the mass of the culture soil, the total amount of corn straw and biochar is 2% of the mass of the culture soil, and the mass ratio of corn straw to biochar is 1:3), and the rest is the same as in Example 2.

[0076] Greenhouse gases generated by the test plot were collected by static box method, and the N2O gas concentration was measured by Agilent7890A gas chromatograph in the United States. Before adding plastic film, the samples were collected and measured once for 0d, and greenhouse gas samples were taken 1, 3, 7, 14, 21, 30, 45, 60, 75, 90, 105, 120, 150, 180, 210, 240, 270, 300, 330, and 365d after adding. The N2O emission rate of the culture soil was measured, and the greenhouse gas release flux was calculated. Compared with Comparative Example 2, Example 6 added corn stalks and biochar to reduce the annual cumulative emission flux of N2O in the soil contaminated by film plastic by 40.5%. After adding plastic particles, the plastic film was collected 365 days later, cleaned, dried, and weighed to calculate the annual degradation rate of the plastic. After corn stalks and biochar treatment, Example 6 increased the annual degradation efficiency of film plastic by 82.5% compared with Comparative Example 2, which was not treated with stalks and biochar.

[0077] The various aspects, embodiments, and features of the present invention should be considered to be illustrative in all aspects and not limiting of the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

[0078] Finally, it should be noted that the specific embodiments described herein are merely examples of the present invention, and are not intended to limit the implementation methods of the present invention. A person skilled in the art of the present invention may make various modifications or supplements to the specific embodiments described, or replace them in a similar manner. It is not necessary and impossible to provide all examples of all implementation methods here. However, these obvious changes or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention, and interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients, characterized in that: The method comprises: applying straw and biochar to soil containing polyethylene, mixing, the polyethylene being 2% of the mass of the soil, and the total amount of straw and biochar being 2% of the mass of the soil; The mass ratio of the straw to the biochar is 1:(1-3); The preparation method of biochar comprises the following steps: washing the straw with water, drying to constant weight, then crushing and grinding to less than 2 mm, wrapping with aluminum foil, placing in a muffle furnace for oxygen-free burning, and sieving to obtain biochar.

2. The method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients according to claim 1, characterized in that: The length of the straw is ≤20 cm.

3. The method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients according to claim 1, characterized in that: After being placed in the muffle furnace, the temperature of the muffle furnace is raised to 450~600℃ at a rate of 7~13℃ / min, and the temperature is maintained for 30~90min.

4. The method for reducing greenhouse gas emissions from plastic-contaminated soil and simultaneously improving plastic degradation efficiency and soil nutrients according to claim 1, characterized in that: The biochar was obtained by passing through a 16-mesh sieve.

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