Biodegradation facility for biodegradable plastics and plant cultivation facility using the same

Abstract

To provide an effective utilization method for CO2 generating in biodegradation of biodegradable plastics.SOLUTION: Disclosed is a plastic biodegradation facility provided in a plant cultivation facility for degrading biodegradable plastics. The biodegradation facility biodegrades the biodegradable plastics by utilizing microbes in soils, in which the activation temperature of biodegradable microbes by the ambient temperature of the plant cultivation facility is secured, and carbon dioxide generating by biodegradation is supplied to plants.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This research relates to technology for reducing the environmental impact caused by carbon dioxide generation, particularly technology for treating carbon dioxide generated from biodegradable plastics. [Background technology]

[0002] The Act on Promotion of Resource Recycling Related to Plastics was enacted in June 2021. This law aims to take measures to promote plastic resource circulation (3R + Renewable) among all parties involved, from product design to plastic waste disposal. It sets goals such as reducing single-use plastics, designing plastics to be reusable and recyclable, promoting the reuse and recycling of used plastics, and switching raw materials to recycled materials and renewable resources. The effective utilization rate of waste plastic has been increasing year by year, reaching 86% in 2019 (material recycling: 22%, chemical recycling: 3%, thermal recycling: 61%), with 8% being simply incinerated and 6% being landfilled. However, the percentage of waste plastic that can be materially recycled is not high due to factors such as the type of resin being unknown or mixed, contamination or foreign matter attached, and the quantity not being organized (approximately half is unused production and processing loss (21.5%) and PET bottles (27.4%)), and thermal recycling and incineration account for 70%. In Europe and the United States, thermal recycling, which reuses the heat generated by burning waste plastic, is not included in recycling, but is treated as heat recovery or energy recovery. Based on this thinking, the recycling rate in 2019 was 25%, which is not high. Global warming caused by the depletion of fossil fuel resources and greenhouse gases such as CO2 generated as a result of their use has become a serious problem. In 2015, the Paris Agreement was adopted at the Conference of the Parties to the United Nations Framework Convention on Climate Change (COP21), establishing a new international framework for reducing greenhouse gas emissions from 2020 onwards. In Japan, a Cabinet decision was made on a global warming countermeasure plan in 2016. As mentioned above, from the perspective of promoting resource circulation related to plastics and reducing greenhouse gas emissions, there is a need to promote the reduction and recycling of waste plastics, switch to recycled materials and renewable resources, and reduce CO2 emissions. The use of biodegradable plastics is one way to reduce waste plastics, and the use of biomass plastics is one way to switch to renewable resources, but it cannot be said that the effect of these measures in reducing CO2 emissions is sufficient. The present invention relates to the reduction of CO2 emissions throughout the life cycle of biodegradable plastics, regardless of whether they are derived from biomass or petroleum, by effectively utilizing the CO2 generated during the biodegradation of such plastics.

[0003] Biodegradable plastics are divided into biomass-derived, biomass-derived + petroleum-derived, and petroleum-derived. Biomass plastics are divided into biomass-derived and biomass-derived + petroleum-derived, and are either biodegradable or non-biodegradable. Some plastics are used in the natural environment, construction sites, food-related applications, and packaging and wrapping applications, where soil, foreign matter, and dirt can adhere to them, making them difficult to recycle and resulting in a relatively short service life. Because these applications generate an increasing amount of waste that cannot be recycled, there are hopes for the use of biodegradable plastics, which can be broken down by microorganisms into CO2 and water. While biodegradable plastics have limited physical properties, it is difficult to replace all general-purpose plastics, but it is possible to replace some. However, whether the waste is disposed of by biodegradation or incineration, a considerable amount of CO2 is emitted. If petroleum-derived plastics are converted into biomass-derived plastics (biomass plastics), CO2 emissions over the life cycle will be reduced by the amount of CO2 taken in from the air during the plant growth process. However, when we look at waste generated after use, if the raw materials used for general-purpose plastics are simply converted and the plastics are not biodegradable, waste will not be reduced, since they are the same plastics whether the raw materials are petroleum-based or biomass-based.On the other hand, if the plastics are biodegradable, waste will be reduced, but a considerable amount of CO2 will be emitted whether they are biodegraded or incinerated. As mentioned above, while biodegradable plastics are effective in reducing waste, they also emit a considerable amount of CO2 during biodegradation, just like incineration, and this is not discussed much. The reason for this is thought to be that in the case of biodegradable plastics derived from biomass, the CO2 emitted during biodegradation is offset by the CO2 absorbed by plants during the growth process. However, CO2 is emitted in each process, from raw material procurement to resin manufacturing and product processing, so this is not sufficient to reduce CO2 emissions over the life cycle. In order to reduce CO2 emissions over the life cycle, it is necessary to recycle the CO2 emitted during biodegradation. Plants grow by absorbing fertilizer and water through their roots, taking in CO2 through their leaves, and using the energy of sunlight to synthesize carbohydrates. The current CO2 concentration in the atmosphere is around 400 ppm, but the concentration changes significantly in a closed environment such as a greenhouse. At night, the greenhouse is sealed and CO2 is released through the respiration of plants and microorganisms, resulting in a higher concentration than the outside air. During the day, the amount absorbed by plants through photosynthesis exceeds the CO2 concentration, resulting in a lower concentration than the outside air. Plants can photosynthesize efficiently up to CO2 concentrations similar to those found in the outside air, and many plants can do so even more efficiently at higher concentrations. For this reason, CO2 application is used as a technique to increase CO2 concentrations in greenhouses, and it has been shown to increase yields. CO2 application can be done at relatively high concentrations, mainly in the early morning, or at low concentrations for extended periods of time. Carbon dioxide can be supplied in liquefied form by installing a cylinder, or by burning kerosene or other fuels. Cogeneration (combined heat and power) systems are becoming popular as an energy-saving technology, and agricultural trigeneration systems, which actively separate CO2 from exhaust gases and use it in agriculture, are also beginning to attract attention. However, the liquefied carbon dioxide used in CO2 application and the carbon dioxide generated by combustion generate CO2 to increase agricultural productivity, and are not reused. Also, agricultural trigeneration systems reuse CO2 generated from heat sources, but they involve many processes such as CO2 separation, capture, and transportation, and new CO2 is generated in the process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 59-179022 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-134104 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-045036 [Non-patent literature]

[0005] [Non-Patent Document 1] Yoshiro Okino: Characteristics and latest information of polybutylene succinate (PBS)-based Green Plastic, Environmental Technology, Vol. 34, No. 6, pp. 406-410, 2005 [Non-patent document 2] Kochi Prefecture Agriculture Promotion Department, Environmental Agriculture Promotion Division: Survey Report on Energy Conservation in Horticultural Agriculture (III), p. 39, February 2012 Summary of the Invention [Problem to be solved by the invention]

[0006] Biodegradable plastics are effective in reducing waste, but like incineration, they emit a considerable amount of CO2 during biodegradation. In the case of biomass-derived biodegradable plastics, the CO2 generated during biodegradation is offset by the CO2 absorbed by the plants during their growth process, but CO2 is generated in each process from raw material procurement to resin manufacturing and product processing, so this is not sufficient to reduce CO2 emissions over the life cycle. In the case of petroleum-derived biodegradable plastics, CO2 is not absorbed, so CO2 emissions increase accordingly. In other words, if the CO2 generated during biodegradation can be effectively utilized, it will lead to a corresponding reduction in CO2 emissions over the life cycle. Therefore, an object of the present invention is to provide a method for effectively utilizing CO2 generated during the biodegradation of biodegradable plastics. [Means for solving the problem]

[0007] The present invention reduces the environmental impact of carbon dioxide associated with plastic disposal by installing a facility for biodegrading biodegradable plastics within a plant cultivation facility, utilizing the temperature of the plant cultivation facility as the temperature at which microorganisms are active, and directly supplying and fixing the CO2 generated by biodegradation to plants. Hereinafter, in this specification, a "biodegradable plastic biodegradation facility" may be referred to as a "biodegradation house," and a "plant cultivation facility" may be referred to as a "greenhouse." The main configuration of the present invention is as follows. 1. A biodegradable plastic biodegradation facility installed within a plant cultivation facility for decomposing biodegradable plastics, The biodegradable plastic biodegradation facility is a facility that uses microorganisms in the soil to biodegrade biodegradable plastics. It is characterized by ensuring that the temperature at which biodegrading microorganisms are active is maintained by the room temperature of the plant cultivation facility, and supplying the plants with carbon dioxide generated by biodegradation. 2. The biodegradable plastic biodegradation facility described in 1. is characterized in that it forms an enclosed space, has an entrance and exit that allows direct entry and exit from outside the greenhouse, and has openable and closable openings for air intake and exhaust on the walls or roof of the enclosed space. 3. A biodegradable plastic biodegradation facility as described in 2., characterized in that the intake and exhaust openings are located at different heights, and temperature difference ventilation is performed by utilizing the difference in height. 4. A biodegradable plastic biodegradation facility according to any one of 1. to 3., wherein at least a portion of the roof of the biodegradable plastic biodegradation facility is made of a material that transmits sunlight. 5. A biodegradable plastic biodegradation facility described in any one of 1. to 4., characterized in that the opening of the biodegradable plastic biodegradation facility is closed at night to retain the carbon dioxide generated by biodegradation within the biodegradable plastic biodegradation facility, and the opening is opened during the day to supply the carbon dioxide generated by biodegradation into the plant cultivation facility. 6. A plant cultivation facility characterized by installing a biodegradable plastic biodegradation facility according to any one of 1. to 5. within a plant cultivation facility, and supplying carbon dioxide generated by the biodegradation of biodegradable plastic to plants. [Effects of the Invention]

[0008] 1. According to the present invention, a facility for biodegrading biodegradable plastics is installed within a plant cultivation facility, so the temperature of the plant cultivation facility can be used as the activity temperature for biodegrading bacteria, ensuring the decomposition rate of biodegradable plastics, and supplying CO2 generated by biodegradation to plants, thereby suppressing CO2 emissions into the environment. 2. According to the present invention, CO2 generated during the biodegradation process of biodegradable plastics can be used for plant photosynthesis. In this invention, the plant cultivation area and the biodegradable plastic decomposition area are separated within the greenhouse, making it possible to manage plant growth and biodegradable plastic decomposition independently. 3. By installing a biodegradable plastic decomposition facility within the plant cultivation facility, the present invention provides the following benefits: first, CO2 generated by the decomposition of biodegradable plastics is provided to promote plant growth, and oxygen generated by plant photosynthesis is provided to the microorganisms that decompose biodegradable plastics, resulting in a gas exchange effect; second, the plant cultivation facility's inherent function of maintaining an optimal temperature for plant cultivation and the heat generated by the decomposition activity of the microorganisms that demonstrate their biodegradability of biodegradable plastics work together to provide a heating effect that promotes plant growth and stimulates the decomposition activity of the microorganisms, thereby accelerating the decomposition of biodegradable plastics; in particular, the heating effect contributes to mitigating temperature drops within the greenhouse during winter and other periods. 4. The biodegradable plastic decomposition facility is equipped with openable openings for ventilation at two or more locations at different heights, so that air can be drawn in through the lower opening by utilizing temperature difference ventilation, and air containing CO2 generated during biodegradation can be supplied to the plants through the higher opening. By opening and closing the opening, air containing CO2 generated during biodegradation can be supplied at a time that suits the condition of the plants. 5. At least part of the roof of the biodegradable plastic decomposition facility is made of a material that transmits sunlight, which increases the temperature inside the facility and increases the temperature difference with the plant cultivation facility. This increases the temperature difference ventilation and promotes the supply of CO2 generated by biodegradation to the plants. 6. At night, the openings of the biodegradable plastic decomposition facility are closed to keep the CO2 generated by biodegradation within the facility, and during the day the openings are opened to supply the CO2 generated by biodegradation into the greenhouse. This means that CO2 is supplied only during the day when photosynthesis is occurring, allowing the CO2 generated by biodegradation to be used effectively. 7. When the plant cultivation facility is not ventilated, the opening of the biodegradable plastic decomposition facility is opened to supply CO2 generated by biodegradation into the greenhouse, and when the greenhouse is ventilated, the opening of the biodegradable plastic decomposition facility is closed to prevent the CO2 generated by biodegradation from diffusing outdoors. Also, in general plant cultivation greenhouses, the CO2 concentration drops during the day in winter when ventilation is reduced, but by supplying CO2 generated by biodegradation, this drop in CO2 concentration can be prevented. By supplying CO2 generated by biodegradation early in the morning, photosynthesis during the day can be promoted. [Brief explanation of the drawings]

[0009] [Figure 1] A diagram showing the basic structure of a plant cultivation facility with a biodegradable plastic decomposition facility inside. [Figure 2] A diagram showing an example of the basic structure of a biodegradable plastic decomposition facility (biodegradation house) [Figure 3] A diagram showing an example of a biodegradable house equipped with an exhaust tower [Figure 4] A diagram showing an example of the layout inside a biodegradable greenhouse [Figure 5] FIG. 1 shows an example of the arrangement of biodegradation houses in a greenhouse in Example 1. [Figure 6] A diagram showing an example of a heating system installed inside a biodegradation house. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Implementation) FIG. 1 shows an outline of the basic configuration of a plant cultivation facility equipped with a biodegradable plastic decomposition facility of the present invention. The figure shows a plant cultivation facility A in which a biodegradable plastic facility 3 is installed inside a plant cultivation facility 2. The plant cultivation facility 2 is a greenhouse for cultivating plants, with a framework made of steel or pipes and covered with a transparent vinyl sheet. Hereinafter, it may be simply referred to as a greenhouse. This greenhouse has an entrance 22 on the gable side. Plants 21 are cultivated inside. The example shown in the figure is a steel-framed greenhouse with a triangular roof. It can also be applied to a round-roofed pipe greenhouse. A biodegradable plastic decomposition facility 3 is installed inside this plant cultivation facility 2. Hereinafter, it may be simply referred to as a biodegradation house. The biodegradable plastic decomposition facility 3 is an independent space that can be shielded. An entrance / exit 32 is provided, and a connecting path 24 is provided that leads from outside the greenhouse 2. Biodegradable plastic 1 is brought in through this connecting path 24 and entrance / exit 32. Multiple ventilation openings 33 are provided on the walls and top surface of the biodegradable plastic decomposition facility. In this invention, biodegradable plastic 1 to be discarded is biodegraded in a biodegradable plastic decomposition facility (biodegradation house) 3 installed in a plant cultivation facility (greenhouse) 2, and the CO2 generated is supplied to plants 21 in the greenhouse 2 and used for plant growth. Because the greenhouse 2 is a closed environment, the diffusion of CO2 generated by biodegradation into the atmosphere is minimized, making it possible to use it for the growth of the plants 21.

[0011] <Biodegradable plastic decomposition facility (biodegradation house)> An outline example of the basic structure of a biodegradable plastic decomposition facility (biodegradation house) is shown in Figure 2. Figure 2(a) shows a biodegradation house with a flat ceiling, and Figure 2(b) shows a biodegradation house with a triangular sloped ceiling. The biodegradable house 3 of the present invention is covered with soil 31 and is provided with an entrance / exit 32 and two or more openable / closable openings 33 for ventilation. The biodegradation house 3 is different from a composting device in that the biodegradable plastic 1 is buried in the soil 31 and decomposed into CO2 and water by microorganisms. A composting system is a device that agitates and heats food waste together with chips and other materials in a sealed container to decompose it, and the resulting product (compost) is periodically removed and used as fertilizer either directly or after a maturation process. Composting systems have problems such as odor and energy consumption. In contrast, the biodegradation house 3 does not decompose food waste but biodegradable plastic 1, so it is less likely to produce odors, and does not require the high temperatures of a composting machine, so energy consumption is reduced. Also, because the biodegradation house 3 is installed inside the greenhouse 2, a warm environment is maintained regardless of the season or day or night, compared to outdoors. Generally, the higher the temperature, the faster the biodegradation rate, but the heat retention effect inside the greenhouse 2 can be utilized without inputting energy for heating.

[0012] <Soil inside the biodegradation greenhouse> The soil 31 of the biodegradation house 3 is preferably soil that is abundant in microorganisms, such as farmland or cultivated land. It is more preferable to evaluate the number of decomposing bacteria and the activity of esterase enzymes in the soil in advance and select soil with a large number of bacteria or high esterase activity. It is also effective to supply a nitrogen source such as ammonium sulfate to promote the growth of decomposing bacteria. If the biodegradation capacity decreases, the soil can be replaced.

[0013] <Entrance to the biodegradable house> The entrance / exit 32 of the biodegradation house is used as an entrance / exit for bringing in and out soil 31, biodegradable plastic for disposal 1, necessary equipment, etc. An entrance / exit 32 for the biodegradation house is provided separately from the entrance / exit 22 of the greenhouse, and an enclosed connecting path 24 is provided that approaches the entrance / exit 32 of the biodegradation house from the wall of the greenhouse. This connecting path 24 makes it possible to reduce dust and the influence of the environment outside the greenhouse when bringing in and out of the biodegradation house.

[0014] <Ventilation opening> The biodegradation house 3 is provided with two or more openable and closable openings 33 for ventilation. By opening and closing these openings 33, air containing CO2 generated by biodegradation can be supplied to the plants 21 at the appropriate time. Furthermore, since plants absorb CO2 through photosynthesis and release oxygen, air containing this oxygen can also be supplied to the biodegradation house through the openings 33. When the openings are closed, they are sealed to minimize air leakage. In the illustrated example, an air intake opening 33a is provided at a low position, and an exhaust opening 33b is provided at a high position. Ventilation is based on natural temperature difference ventilation to reduce energy consumption. Air inside the greenhouse enters through the intake opening 33a at the bottom of the biodegradation house, and warmer air inside the house is exhausted through the exhaust opening 33b at the top. Since the ventilation volume for temperature difference ventilation is proportional to the opening area, the square root of the difference in height between the intake and exhaust openings, and the square root of the temperature difference between inside and outside, the difference in height between the intake opening 33a and exhaust opening 33b should be made as large as possible.

[0015] For example, by providing an exhaust tower 34 with multiple exhaust openings 33b, such as four-way openings, at the top of the roof of the biodegradation house, and providing multiple air intake openings 33a on the side of the biodegradation house, it is possible to supply air from multiple directions and exhaust air in multiple directions, while at the same time increasing the difference in height between the air intake and exhaust openings (see Figures 3(a) and (b)). In addition, because the exhaust is from a high place in multiple directions, it is possible to supply air containing the CO2 generated by biodegradation over a wider area. Furthermore, increasing the amount of ventilation can promote the supply of CO2 generated by biodegradation to plants and the supply of oxygen generated by photosynthesis to the biodegradation greenhouse. Exhaust tower and non-exhaust tower types can be used appropriately, and both types can be installed in the same greenhouse. Mechanical ventilation can also be introduced in environments with small temperature differences, situations where increased ventilation volume is required, or when air needs to be supplied to the soil. Closing the opening 33 makes it possible to prevent the diffusion of dust into the greenhouse, which is generated when materials are carried in and out of the biodegradation house or when the soil 31 is manipulated, such as by plowing it in. The opening 33 can be opened or closed manually or automatically. In the case where the opening 33 of the biodegradation house is set to open only when the greenhouse is not being ventilated, it may be linked to the opening. When it is set to open automatically, renewable energy such as solar panels is used as the power source.

[0016] <Means for supplying water and solutions inside the biodegradation house> Solutions containing necessary components such as water, liquid fertilizer, and nitrogen source can be manually supplied to the soil, but supply means can also be provided inside the biodegradation house. For example, a sprinkler device such as the sprinkler device 35 may be used, or a device may be buried in the soil and used for supplying water.

[0017] <Biodegradable greenhouse shape and materials> The biodegradation greenhouse 3 uses materials such as glass and plastic. These materials allow sunlight to pass through and are susceptible to the radiation of heat absorbed by the ground. Furthermore, because the biodegradable greenhouse is not exposed to the outside air, the temperature inside the greenhouse is higher than that inside a greenhouse. Biodegradation reactions generally tend to be accelerated as temperatures rise, which is advantageous. In particular, in cold conditions such as winter, when decomposition efficiency in outdoor environments is reduced, the temperature inside the biodegradation greenhouse tends to rise in addition to the temperature of the greenhouse, leading to improved decomposition rates.

[0018] Figure 6 shows an example of a heating system. Highly thermally conductive heat transfer plates 37 made of metal or the like are provided around the inside of the inner wall 36 of the biodegradation house (placed so that the upper part is above ground and the lower part is in the soil), and the solar heat from sunlight received by the upper part of the plates is transferred inside the house and into the soil 31, thereby raising the temperature inside the biodegradation house and promoting temperature difference ventilation, as well as raising the temperature in the soil and improving the biodegradation reaction. Heat transfer plate 37a is provided inside the inner wall 36, and soil 31 is spread in contact with it. Heat transfer plate 37b is provided between the inner wall 36 and heat transfer plate 37a in contact with it, and its position can be moved up and down, changing the area that receives solar heat and preventing excessive temperature increases. In high temperature conditions such as summer, the position of the heat transfer plate 37b can be lowered as shown in Figure 6(b) to prevent it from receiving solar heat, and in low temperature seasons such as winter, the position of the plate can be raised as shown in Figure 6(c) to increase the area that receives solar heat.

[0019] The heat from the heat transfer plate 37b that receives solar heat is radiated into the biodegradation house and is also transferred to the soil 31 via the heat transfer plate 37a. This allows for temperature difference ventilation to be promoted using only solar energy, and biodegradation reactions to be accelerated even in winter conditions. The heat transfer plate 37 can be divided into multiple pieces and placed along the inner wall 36, and each heat transfer plate 37b can also be moved independently. This allows for adjustment of the position of sunlight irradiation and the area exposed to solar heat. When the temperature of the soil 31 is raised by the heat transfer plate 37, biodegradation is promoted, but when the soil becomes dry, biodegradation decreases, so water, liquid fertilizer, solutions containing necessary ingredients such as nitrogen sources, etc. are replenished manually or with a sprinkler system 35.

[0020] The biodegradable house 3 may have any shape. It can be flat (Fig. 2(a), Fig. 3(a)), or if the roof or the roof and walls are made of glass, glass fiberboard, or plastic (polyvinyl chloride, polyolefin, fluorine film, polycarbonate, acrylic, or plastics improved for transparency and heat retention, biomass plastics can also be used), the following shapes can be selected appropriately taking into account the construction area and location conditions: a double-roof type like those seen in greenhouses (a north-south building averages the amount of light received and provides good ventilation) (Fig. 2(b), Fig. 3(b)), a single-roof type (high light reception in winter and good heat retention), a scalene-shaped roof (high light reception in winter and good heat retention, but prone to high temperatures in summer), a round-roof type (averages the amount of light received and provides good ventilation), or a rhombus-shaped roof (structurally stable, but not suitable for large structures).

[0021] <Location and number of biodegradation houses> The number and location of the biodegradation houses 3 to be placed within the greenhouse 2 are optional. The relationship between the amount of CO2 absorbed by the plants and the amount of decomposition of the biodegradable plastic is one of the criteria for determining the size and number of the biodegradation houses 3. Figure 4 shows an example of the layout of a biodegradation house 3 inside a greenhouse 2. (a) shows an example of the layout of a non-exhaust tower type biodegradation house 3, and (b) shows an example of the layout of a biodegradation house 3 with an exhaust tower type. Space necessary for greenhouse management, such as aisles and shelves, must also be secured. The solid arrows represent exhaust air (air containing CO2 generated by biodegradation), and the dashed arrows represent intake air (air with a low CO2 concentration due to photosynthesis).

[0022] <Other> Compared to recycling facilities and incineration facilities commonly used to dispose of waste plastic, the facility of the present invention offers greater flexibility in terms of timing and location of installation and removal, and also allows for shorter transportation distances.

[0023] <Types of biodegradable plastics to be treated> The object of treatment in the biodegradation house is biodegradable plastic waste. Biodegradable plastics are divided into those derived from biomass, biomass and petroleum, and petroleum. Examples of biodegradable plastics derived from biomass include polyhydroxyalkanoates such as 3-hydroxybutyrate-3-hydroxyhexanoate copolymer polyesters, and polylactic acid. Biomass-derived and petroleum-derived biodegradable plastics include biopolybutylene succinate, polybutylene adipate terephthalate-polylactic acid compound, and starch polyester resin.

[0024] Examples of petroleum-derived biodegradable plastics include polyvinyl alcohol, polyglycolic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, and polyethylene terephthalate succinate. It is predicted that some biomass-derived and petroleum-derived, and petroleum-derived biodegradable plastics will be biomass-derived in the future. Compounds of biodegradable plastics are also included. Any other plastics that have biodegradability are also included. However, for materials that biodegrade after hydrolysis, such as polylactic acid, they must be hydrolyzed before being transported to the biodegradation house.

[0025] Next-generation enzyme-encapsulated biodegradable plastics, which respond to various stimuli and turn on their biodegradation switch, are also included in the treatment targets of biodegradation houses. For example, research and development is underway on mechanisms that activate the biodegradation switch through potential differences or friction, but mechanisms have already been developed that can be used as everyday items and, when placed in 40°C water after use, decompose down to the molecular level in a few days. During the manufacturing stage of biodegradable plastics, polyester-degrading enzymes encapsulated in polymers are mixed in, and when placed in 40°C water, the polymer dissolves and decomposition begins.

[0026] <Uses of biodegradable plastics to be treated> The use of the waste to be treated in the biodegradation house can be any use that uses biodegradable plastics. For example, major uses include agricultural materials (mulch film, vegetation netting, transplant seedling pots, etc.), civil engineering and construction materials (water-retaining sheets for construction, civil engineering and construction sheets, sandbags, vegetation netting, etc.), outdoor leisure products (disposable products for golf, fishing, marine sports, etc.), everyday items in office supply stores (pen cases, lead cases, toothbrushes, cups, cushioning materials, etc.), food containers and packaging, detergent packaging, textiles, etc. Other potential targets include food containers, food residue (garbage) collection bags, cutlery, and compost bags, but items that contain a lot of food residue and generate odors should be avoided as much as possible.

[0027] Biodegradable plastics are expected to be one solution to the problem of disposing of large amounts of plastic waste. Because they are decomposed into CO2 and water by microorganisms, they are incorporated into the natural carbon cycle without accumulating in the environment. Therefore, applications that take advantage of their properties, such as their use in the natural environment and their usefulness in composting organic waste, have been explored. In general, biodegradable plastics are more decomposable under composting conditions than in the natural environment, and polylactic acid is also decomposed. However, in recent years, the issue of global warming has made it urgent to reduce atmospheric CO2, and simply returning the CO2 generated during biodegradation to nature is no longer sufficient. In this invention, the CO2 generated during biodegradation is actively utilized, which will lead to an expansion of the use of biodegradable plastics, such as one-way applications that are difficult to recycle and can be recovered. Such applications are also included in the treatment targets in the biodegradation house.

[0028] Plant cultivation facilities (greenhouses) <Greenhouse equipment, structure, and materials> The greenhouse 2 may have the characteristics and facilities of a general greenhouse. The structure is a cultivation facility with a frame exterior covered with glass, polyvinyl chloride, polyolefin, fluorine film, etc. This includes both so-called glasshouses and vinyl greenhouses (plastic greenhouses). They can also be covered with polycarbonate, acrylic, plastics improved for transparency and heat retention, glass fiber boards, etc. Biomass plastics can also be used. Roof types include double-roof (north-south buildings average the amount of sunlight received and provide good ventilation) (Figure 2(b), Figure 3(b)), single-roof (receives a lot of sunlight in winter and has good heat retention), scalene-shaped roof (receives a lot of sunlight in winter and has good heat retention, but tends to get hot in summer), round-roof (averages the amount of sunlight received and provides good ventilation), and chess-shaped roof (structurally stable, but not suitable for large buildings).These types can be selected appropriately taking into account the construction area and location conditions.

[0029] <Plant> Plant 21 is any plant that can be cultivated in a greenhouse. Plants that are not generally cultivated in greenhouses are also included as long as they can be cultivated in a greenhouse.

[0030] <CO2 fluctuations in the greenhouse> Soil respiration is the production of CO2 through cellular respiration in the underground parts of plants and by microorganisms in the soil, and is responsible for the carbon cycle between the soil and the atmosphere. In agricultural land, atmospheric CO2 is taken up by crops through photosynthesis, then converted into glucose and stored as starch, providing a source of energy and body composition. Respiration occurs in the roots of crops, absorbing oxygen and breaking down starch and other substances, obtaining the energy necessary for growth while simultaneously releasing CO2. Microorganisms in the soil decompose and absorb organic matter, such as secretions from the roots and root hairs released from the roots, and convert them into cellular components, some of which are then broken down into CO2 and water to extract energy. The same is true in greenhouses, but at night, CO2 increases due to soil respiration, and because it is a closed space, the concentration is higher than the outside air. During the day, CO2 is taken in and oxygen is released due to photosynthesis, which exceeds respiration, and because it is a closed space, the CO2 concentration is lower than the outside air. In this way, the rate of increase and decrease in CO2 concentration is large in greenhouses, and while the current CO2 concentration in the atmosphere is around 400 ppm, observations have shown that in winter it is 800 ppm at night and around 200 ppm during the day.

[0031] <Biodegradable greenhouse installed inside the greenhouse> For example, in applications where plants and biodegradable plastics coexist in the soil, such as the use of biodegradable plastic pots for flowerbed seedling production, various behaviors, including the respiration of soil microorganisms, may be affected. Furthermore, if the addition of biodegradable plastics increases the C / N ratio in the soil, plants may suffer from a nitrogen source deficiency, making it difficult to manage nitrogen source supply. In contrast, in the present invention, the biodegradable plastics are isolated from the plants in the greenhouse, eliminating the above-mentioned effects. Therefore, plant growth and biodegradable plastic decomposition can be managed independently. Therefore, conventional greenhouse cultivation can be carried out during periods when there is no biodegradable plastic to dispose of. [Example]

[0032] The following shows an example of the size, arrangement and planting of the biodegradation greenhouse in the greenhouse. <Amount of CO2 generated by biodegradation> In a biodegradation test in field soil of a film (20 μm thick) made from polybutylene succinate (PBS), a biodegradable plastic, it was reported that 60% of the film had decomposed in 10 weeks and 95% in 18 weeks (Non-Patent Document 1). From these results, it can be estimated that the time required for complete decomposition is 19 weeks.

[0033] The density of PBS is 1.26g / cm 3 is. When 1 kg of PBS is completely decomposed, it is estimated that 2.05 kg of CO2 will be generated based on the chemical formula. The biodegradation house is 4.5m x 13m, of which the soil area is 4m x 12m. Three layers of PBS film are laid over the soil area (with a 5cm soil layer between each film). The amount of CO2 generated by biodegradation in a year is 400cm x 1200cm x 0.002cm x 3 pieces x 1.26g / cm 3 ×365 days / 133 days×2.05=20.4 kg (It is estimated that this is even faster in a greenhouse under warm conditions.)

[0034] <CO2 absorption by plants> It has been reported that the annual CO2 absorption by vegetables is 500-1800 kg / 10a for fruit vegetables and 200-800 kg / 10a for leafy vegetables (Non-Patent Document 2). Calculating the average of the median values ​​from these results gives a figure of 0.825 kg / m 2 This becomes:

[0035] <Planting area> The area required to absorb 20.4 kg of CO2 generated by biodegradation in one year is 24.7 m 2 This becomes: Assuming that 20% of the CO2 absorbed by plants is supplied from biodegradation-derived CO2, the figure is 123.5m 2 This becomes:

[0036] <Example of biodegradation greenhouse layout> Figure 5 shows an example of the layout of biodegradation greenhouses in a greenhouse that reflects the above results. [Example]

[0037] An example of operating a biodegradable greenhouse is shown below. <Inside the biodegradable house> In the biodegradation house, waste biodegradable plastics buried in the soil are gradually decomposed, producing CO2 and water throughout the day. Because the biodegradation house is located inside a greenhouse, the temperature is higher than in the outdoor environment, which is a condition that promotes the biodegradation reaction.

[0038] <Inside the greenhouse> In greenhouses, CO2 increases at night due to soil respiration, and because it is a closed space, the concentration becomes higher than the outside air, and during the day, CO2 is taken in and oxygen is released due to photosynthesis, which exceeds respiration, and because it is a closed space, the CO2 concentration becomes lower than the outside air.In this way, the rate of increase and decrease in CO2 concentration is large in greenhouses, and while the current CO2 concentration in the atmosphere is around 400 ppm, there are reported observations that in winter it can reach 800 ppm at night and around 200 ppm during the day.

[0039] <Opening and closing the biodegradable house> The ventilation openings in the biodegradation greenhouse are basically closed at night when photosynthesis does not occur, to keep the CO2 produced by biodegradation inside the greenhouse, and open during the day when photosynthesis occurs to supply CO2 to the plants, so that as much of the CO2 produced by biodegradation as possible can be used for plant photosynthesis. Table 1 shows the recommended operation methods for each season. "Open" indicates ventilation, and "Closed" indicates no ventilation.

[0040] Basically, (a) When ventilating the greenhouse, close the openings of the biodegradation house. (b) Close the opening of the biodegradation house at night. (c) In the early morning, regardless of the season, the ventilation of the greenhouse is stopped and the opening of the biodegradation house is opened. (d) If necessary for greenhouse management apart from the biodegradation house, openings will be opened and closed depending on whether or not the greenhouse is ventilated.

[0041] The opening and closing of the greenhouse in spring and autumn is determined by the temperature a°C and the CO2 concentration in ppm. However, the above (d) also applies in this season. Temperature a is set to a temperature suitable for the plant once the plant to be cultivated has been decided. The CO2 concentration b differs between C4 plants and C3 plants. The CO2 concentration b value for C4 plants is preferably 150 ppm or higher, more preferably 200 ppm or higher. The CO2 concentration b value for C3 plants is preferably 250 ppm or higher, more preferably 300 ppm or higher. The compensation point for C4 plants is considered to be 0-5 ppm or 0-10 ppm, while that for C3 plants is 30-70 ppm or 50-100 ppm. Below these concentrations, respiration loss exceeds photosynthetic fixation, making photosynthetic growth impossible. C4 plants are said to reach saturation in CO2 fixation at around 300 ppm, and increasing CO2 fixation from 350 ppm to 700 ppm is thought to result in little increase in CO2 fixation. Furthermore, C3 plants' photosynthetic rate increases even when CO2 concentrations exceed the current atmospheric concentration of 400 ppm. However, when CO2 concentrations fall to around 200 ppm, the level commonly observed during the daytime in greenhouses during winter, photosynthetic rates decline, affecting plant growth.

[0042] This allows the CO2 produced by biodegradation to be used only during the day when photosynthesis occurs. During certain periods in winter and spring and autumn, ventilation of the greenhouse during the day is restricted, allowing the plants to receive CO2 generated by biodecomposition for a long period of time. These periods are when CO2 is likely to be insufficient in ordinary greenhouses, so the supply of CO2 generated by biodecomposition can help to compensate for this. During certain periods in summer and spring and autumn, the greenhouse is ventilated during the day, so the supply of CO2 generated by biodegradation occurs from early morning until ventilation begins. However, because ventilation lasts for a long period during this period, the introduction of outside air results in small fluctuations in the CO2 concentration inside the greenhouse, and the impact on plant growth is also small.

[0043] [Table 1] [Explanation of symbols]

[0044] 1. Biodegradable plastics 2 Plant cultivation facilities (greenhouses) 21 Plants 3. Biodegradable plastic decomposition facility (biodegradation house) 31 Soil 32 Entrance / Exit 33 Aperture 33a Air supply opening 33b Exhaust opening 34 Exhaust tower 35 Sprinkler system 36 Inner wall 37, 37a, 37b Heat transfer plate

Claims

1. A biodegradable plastic biodegradation facility for decomposing biodegradable plastics installed in a plant cultivation facility, comprising: The biodegradable plastic biodegradation facility is a closed space, equipped with an entrance that allows direct entry and exit from the outside of the greenhouse, and has an openable opening on the wall or roof of the closed space for ventilation and exhaust. A biodegradable plastic biodegradation facility is a facility that uses microorganisms in the soil to biodegrade biodegradable plastics, and is characterized by ensuring that the temperature at which the biodegrading microorganisms are active is maintained by the room temperature of the plant cultivation facility, and supplying carbon dioxide generated by biodegradation to the plants.

2. 2. The biodegradable plastic biodegradation facility according to claim 1, characterized in that the openings for intake and exhaust are provided at different heights, and temperature difference ventilation is performed by utilizing the difference in height.

3. 3. The biodegradable plastic biodegradation facility according to claim 1, wherein at least a portion of the roof of the biodegradable plastic biodegradation facility is made of a material that transmits sunlight.

4. A biodegradable plastic biodegradation facility as described in any one of claims 1 to 3, characterized in that the opening of the biodegradable plastic biodegradation facility is closed at night to retain carbon dioxide generated by biodegradation within the biodegradable plastic biodegradation facility, and the opening is opened during the day to supply carbon dioxide generated by biodegradation to the plant cultivation facility.

5. A plant cultivation facility comprising the biodegradable plastic biodegradation facility according to any one of claims 1 to 4 installed within a plant cultivation facility, and carbon dioxide generated by the biodegradation of biodegradable plastics is supplied to plants.

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