Independent power supply small methane fermentation treatment system

Abstract

To provide a methane fermentation treatment system that can be downsized, and can efficiently perform methane fermentation treatment, while saving energy during operation.SOLUTION: The methane fermentation treatment system according to one embodiment, which ferments organic waste in fermentation tanks 3 and 4, comprises a biogas hot-water supply device 9 that warms water using biogas generated by fermenting the organic waste, water flow stirring means that stirs fermentation liquid by water flow, a natural energy generator, and a power storage battery that stores electric power energy generated by the natural energy generator, and further comprises an independent power supply control unit that can supply all energy that is required in the methane fermentation treatment, from internal energy constituted of natural energy and the biogas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation treatment system, and more particularly to a compact methane fermentation treatment system that can be operated with an independent power source. [Background technology]

[0002] Traditionally, organic waste, including food waste from households, has been incinerated or disposed of in landfills. Incineration requires a lot of energy and produces carbon dioxide. From the perspective of environmental issues, there is a demand for effective utilization methods other than incineration.

[0003] Methane fermentation is one method for effectively utilizing organic waste. Methane fermentation involves decomposing organic matter using a variety of microorganisms, including methane bacteria, to produce biogas and methane fermentation digestate. Biogas contains high concentrations of methane gas and is attracting attention as a non-exhaustible renewable energy source. Furthermore, methane fermentation digestate is characterized by its high content of fertilizer components, making it promising for effective use as a fertilizer substitute.

[0004] The most commonly used methane fermentation treatment equipment is a large-scale methane fermentation treatment facility. Large-scale methane fermentation treatment facilities can process large amounts of organic waste, but because they collect waste from a wide area, the CO2 generated during collection is an issue. Another issue is finding a place to use the large amount of digestive fluid, and if the waste cannot be used for agricultural purposes, the wastewater must be treated. This is costly and places a heavy burden on the environment.

[0005] In recent years, there has been an increasing demand for locally processed organic waste and for the effective use of the energy and digestive fluids produced there, leading to the development and study of small-scale methane fermentation treatment facilities. Small-scale methane fermentation treatment facilities tend to have higher construction and operating costs per unit of treatment volume compared to large-scale facilities. Furthermore, methane fermentation treatment facilities require energy for operation, as they are equipped with crushers, pumps, agitators, heating devices, and other equipment. Therefore, in order to promote the widespread use of small-scale methane fermentation treatment facilities, there is a demand for even more energy-efficient methane fermentation treatment systems, and research and development is underway.

[0006] For example, Patent Document 1 describes a method of stirring the inside of a fermentation tank by blowing gas generated in the fermentation tank into the liquid using the siphon principle. Patent Document 2 describes a method of using the pressure of biogas to generate a liquid level difference between an upstream fermentation tank and a downstream fermentation tank, stirring and transferring the fermentation liquid through a connecting pipe. Patent Document 3 describes a system that improves the power generation efficiency of a solar power generation device, uses warm wastewater used to cool the solar power generation device as a heat source for a methane fermentation tank, and produces methane by anaerobic fermentation of biomass grown underground at the solar power generation device, thereby achieving combined use of renewable energy. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-276897 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-247100 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-65620 Summary of the Invention [Problem to be solved by the invention]

[0008] However, Patent Document 1 uses gas generated in the fermenter for agitation, but the fermentation liquid is equipped with multiple liquid suction tubes. To agitate the fermentation liquid, the fermentation liquid must be sucked up from the bottom of the fermentation liquid, which contains solids, without any power source. This requires the liquid suction tubes to be thin, resulting in poor agitation efficiency and making the system unsuitable for small-scale methane fermentation processes. Patent Document 2 also uses generated gas for agitation, but the fermenter requires a high height to create a water level difference, necessitating a larger device. Furthermore, the system requires a structure that can withstand the high pressure, resulting in high construction costs. Patent Document 3 describes a system that utilizes multiple renewable energies, but it is not a small-scale system due to limitations on installation location and the need for a large area of ​​land suitable for biomass cultivation. Thus, while there are methods for agitating the fermentation liquid without power source, such as using generated biogas, there are currently no systems suitable for small-scale methane fermentation processes.

[0009] Furthermore, if an external power source is not required and the energy consumed during operation, including agitation power, can be minimized, it can be installed in places where it is difficult to secure an external power source, and it is expected that small-scale methane fermentation treatment equipment will become more widespread.

[0010] Therefore, an object of the present invention is to provide a methane fermentation treatment system that can efficiently perform methane fermentation treatment while reducing energy consumption during operation and that can be made compact. Another object of the present invention is to provide a methane fermentation treatment system that can reduce energy consumption during operation and is equipped with a stirring means that is useful for making the system compact. [Means for solving the problem]

[0011] As a result of extensive research to achieve the above object, the inventors have found that a methane fermentation treatment facility equipped with a gas dissolution agitation system, a water jet agitation system, and a heater-free hot water supply system can reduce the energy required for operation and can perform methane fermentation treatment without external energy sources by utilizing methane gas generated during the methane fermentation treatment and natural energy. The present invention was completed based on these findings.

[0012] One embodiment of the present invention is a methane fermentation treatment system for fermenting organic waste in a fermenter, The biogas hot water supply system comprises a biogas hot water supply system that heats water using biogas generated by the fermentation of organic waste, a water flow agitation means that agitates the fermented liquid with a water flow, a natural energy power generation system, and a storage battery that stores the electric energy generated by the natural energy power generation system. The present invention provides a methane fermentation treatment system equipped with an independent power supply control unit that can supply all of the energy required for methane fermentation treatment from natural energy and internal energy from the biogas.

[0013] Hot water is used to heat the fermenter, etc. In one embodiment, the system includes a biogas water heater that heats water using biogas generated by fermentation of organic waste, and the hot water can be produced by the biogas water heater. The system also includes a natural energy power generation system and a storage battery that stores electrical energy generated by the natural energy power generation system. This allows the electrical energy generated by the natural energy power generation system or stored in the storage battery to be used to power a pump used for transporting the fermentation liquid, etc. In addition, by providing a water flow agitation means, the fermentation liquid can be agitated with no or minimal power. Furthermore, by providing an independent power supply control unit that can supply all of the energy required for methane fermentation treatment from internal energy generated by natural energy and the biogas, the methane fermentation treatment system can be operated without using external power. According to one embodiment of the present invention, a methane fermentation treatment system that can efficiently perform methane fermentation treatment while reducing operating energy and that can be miniaturized can be provided.

[0014] Another embodiment of the present invention is a methane fermentation treatment system for fermenting organic waste in a fermenter, The methane fermentation treatment system includes a gas dissolving and stirring means for increasing the internal pressure of the fermenter to dissolve biogas generated by the fermentation of organic waste in a fermentation liquid, releasing the pressure when the internal pressure reaches a predetermined level, vaporizing the biogas dissolved in the fermentation liquid, and causing the vaporized biogas to diffuse and / or float up in the fermentation liquid, thereby increasing the fluidity of the fermentation liquid.

[0015] The gas dissolving and agitating means dissolves biogas generated by fermentation of organic waste into the fermentation liquid by increasing the internal pressure of the fermenter, and releases the pressure when the internal pressure reaches a predetermined level. This vaporizes the biogas dissolved in the fermentation liquid, and the vaporized biogas diffuses and / or rises to the surface of the fermentation liquid, thereby agitating the fermentation liquid. This gas dissolving and agitating means allows the fermentation liquid to be agitated with no or minimal power, reducing energy consumption during operation and providing a methane fermentation treatment system equipped with an agitating means useful for miniaturization.

[0016] Yet another embodiment of the present invention is a methane fermentation treatment system in which organic waste is introduced from an introduction tank into a fermentation tank and the organic waste is fermented in the fermentation tank, The present invention provides a methane fermentation treatment system comprising a water flow agitation means for agitating a fermentation broth by a water flow, as described below in (i) and / or (ii). It is also preferable that the water flow agitation means be provided in embodiments other than this embodiment. (i) A means for returning the fermented liquid from the fermenter to the input tank and agitating the fermented liquid with a water jet (ii) A means for agitating the fermented liquid in at least one of the fermentation tanks by using a water level difference between the fermentation tanks, the means comprising a plurality of fermentation tanks connected by a communication pipe;

[0017] The water current agitation means can agitate the fermentation liquid by utilizing the water current generated by transferring the liquid between the input tank and the fermenter tank, or between multiple fermenters. This water current agitation means can agitate the fermentation liquid with no or minimal power, reducing energy consumption during operation and providing a methane fermentation treatment system equipped with an agitation means useful for downsizing.

[0018] The methane fermentation treatment system includes the water flow agitation means (i), and the input tank and the fermenter are connected by a input line and a return line via a return valve; It is preferable to generate the water flow and perform the water flow agitation by charging the organic waste into the charging tank and returning the fermentation liquid in the fermentation tank to the charging tank through the return line by opening the return valve.

[0019] The methane fermentation treatment system may be provided with the water flow agitation means (ii). In this case, the plurality of fermenters may include a first fermenter connected to the input tank by an input line, and a second fermenter located downstream of the first fermenter, The input tank and the second fermenter are connected by a return line via a return valve, It is preferable that the return valve is opened, the fermentation liquid in the second fermentation tank is returned to the input tank through the return line, and when the volume of the fermentation liquid in the input tank reaches a desired value as a result of the return, the organic waste is input from the input tank to the first fermentation tank through the input line, thereby generating the water level difference among the input tank, the first fermentation tank, and the second fermentation tank, thereby performing the water flow agitation.

[0020] It is preferable that the discharge port of the feeding line in the fermenter connected to the feeding tank via the feeding line is placed in the fermentation liquid in the fermenter.

[0021] The input line is provided with a siphon break function to prevent siphoning, and the siphon break function preferably uses biogas generated by fermentation of the organic waste.

[0022] The methane fermentation treatment system includes a gas holder for storing biogas generated by fermentation of the organic waste, and a gas line for transporting the biogas from the fermenter to the gas holder; It is preferable to provide an automatic on-off valve on the gas line.

[0023] The methane fermentation treatment system preferably includes an automatic control means that closes the automatic on-off valve when the pressure in the fermenter is less than 10 kPa and opens the automatic on-off valve when the pressure in the fermenter is 10 kPa or higher.

[0024] The methane fermentation treatment system preferably includes an internal pressure increasing period in which the biogas stored in the gas holder is transferred to the gas phase portion within the fermenter, thereby increasing the internal pressure of the fermenter.

[0025] The methane fermentation treatment system preferably includes a solar water heating system that heats water with solar heat to produce hot water, and supplies the hot water to a hot water pipe to heat the fermenter.

[0026] The methane fermentation treatment system preferably includes a foreign matter removal device that removes hard-to-decompose solid matter.

[0027] It is preferable that hot water heated by the biogas hot water supply device is supplied to a hot water pipe to heat the fermenter.

[0028] It is preferable that the methane fermentation treatment system includes a plurality of fermentation tanks connected by communication pipes, and the water flow agitation means agitates the fermentation liquid in at least one of the fermentation tanks by using a water level difference between the plurality of fermentation tanks.

[0029] The electric energy stored in the storage battery is preferably used as energy for one or more systems selected from the group consisting of a pump, a crusher, and an electronic control system of the methane fermentation treatment system. [Effects of the Invention]

[0030] The methane fermentation treatment system of the present invention can efficiently perform methane fermentation treatment while reducing energy consumption during operation, and can be made smaller. In addition, other methane fermentation treatment systems of the present invention also reduce energy consumption during operation, making them useful for miniaturization. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a flow diagram of a methane fermentation treatment system according to one embodiment of the present invention when a gas dissolving and stirring means is not implemented. [Figure 2] FIG. 1 is a flow diagram of a methane fermentation treatment system when a gas dissolving and stirring means is implemented according to one embodiment of the present invention. [Figure 3] FIG. 1 is a flow diagram showing an embodiment of a gas line during an organic waste input period. [Figure 4] FIG. 10 is an implementation flow diagram showing one embodiment of a gas dissolving and stirring means. [Figure 5] FIG. 1 is a flow diagram of the methane fermentation treatment system of Example 1. [Figure 6] FIG. 10 is a flow diagram of a methane fermentation treatment system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0032] [Methane fermentation treatment system] Fig. 1 is a diagram showing a schematic diagram of the basic configuration of a methane fermentation treatment system according to one embodiment of the present invention. As shown in Fig. 1, the methane fermentation treatment system according to one embodiment of the present invention includes a water tank 1, an input tank 2, a first fermenter 3, a second fermenter 4, a liquid fertilizer tank 5, a first gas holder 6, a second gas holder 7, a solar hot water heater 8, a biogas hot water heater 9, a hot water tank 10, and a pulverizer 11. In addition, the system may include a foreign matter removal device, a gas purification device, a natural energy power generation device, a biogas power generation device, and a storage battery.

[0033] Conventionally, a large amount of energy was required to perform methane fermentation treatment in a small device, but the methane fermentation treatment system of the present invention makes it possible to perform methane fermentation treatment with less energy by using hot water produced from biogas using a hot water supply device or hot water produced by a solar hot water device to heat the fermenter, eliminating the need for a heater, and by using gas dissolution and stirring by biogas and water flow stirring to eliminate the need for an agitator. Furthermore, the system is constructed so that other electricity is supplied from natural energy, and no external power source is required, which reduces running costs and minimizes restrictions on installation location. For this reason, it is preferable that the methane fermentation treatment system of the present invention is small. In this specification, a small-scale methane fermentation treatment system is defined as a system with a total fermenter volume of 5 m 3 It refers to the following:

[0034] First, organic waste 12 is fed into a crusher 11. Here, organic waste refers to waste that is easily decomposed by microorganisms, such as food waste from households, food residue from schools and businesses, food factory waste, human waste, sewage sludge, and biodegradable plastics. The fed organic waste passes through the crusher 11 and is then fed into the feeding tank 2. There are no particular restrictions on the size of the crushed organic waste, but a size of 10 mm or less is preferred. From the perspective of ease of decomposition in the fermentation tank, a size of 5 mm or less is more preferred. The crusher 11 is preferably a hammer type. A hammer type has the advantage of being less likely to clog and become caught in fibrous materials.

[0035] The crushed organic waste is mixed with water delivered from the water tank 1 by a pump (water supply pump) P1 and sent to the input tank 2 through the pipe 13, where it is stored. When crushed in the crusher 11, water from the water tank 1 is also added to the crusher 11 to improve transportability. The volume ratio of organic waste to water is not particularly limited, but a ratio of approximately 1:1 is preferable. Water can be added directly to the crushing chamber of the crusher 11 or can be supplied through an input port. Adding water simultaneously with crushing reduces the load on the crusher 11. The inner diameter of the pipe 13 used to send the crushed organic waste to the input tank 2 after crushing is not particularly limited, but is preferably 50 mm or greater. If it is less than 50 mm, it may become clogged with crushed organic waste. A shorter pipe length is preferable. If the pipe is longer, a larger amount of water is required to transport the organic waste. To absorb the vibrations of the crusher, the pipe should be made of a material that easily absorbs vibrations. To improve the transferability, it is preferable that the inside of the pipe 13 does not have any protrusions.

[0036] It is advisable to provide a liquid level sensor in the charging tank 2. The liquid level sensor may be of an ultrasonic type, an electrode type, a pressure type, or the like. The ultrasonic type is preferable because it is not affected by impurities.

[0037] The mixture of organic waste and water stored in the input tank 2 is input into the first fermenter 3 via the input line 14 by pump P2. Alternatively, the mixture may be input into the second fermenter 4, located downstream of the first fermenter 3, via the input line 14 by pump P2. For example, the mixture may be input from the input tank 2 to the first fermenter 3 by pump P2, and then periodically input into the second fermenter 4. By doing so, if scum has formed in the upper layer of the second fermenter 4, the impact of inputting the organic waste can destroy the scum. If scum forms in the upper layer of the second fermenter 4, the piping of the liquid fertilizer tank 5 may become clogged. For example, the route change valve 30 may be periodically switched using a time switch or the like to switch the destination of the mixture between the first fermenter and the second fermenter. The timing and frequency of inputting the mixture into the second fermenter 4 are not particularly limited and can be set appropriately depending on the situation.

[0038] Pump P2 is preferably a pump suitable for transporting liquids with a high solids concentration. If the suction port is in contact with the bottom, it is prone to clogging with settled organic waste, so it is preferable that the suction port be at least 5 cm higher than the bottom. When pump P2 feeds the organic waste in input tank 2 into the fermenter, the liquid level in input tank 2 can be set to any value that prevents pump P2 from drawing in air. Input tank 2 is designed to receive gas along with the organic waste via crusher 11, but by designing pump P2 to not draw in air, all fermenters and other equipment from input line 14 onward can be kept anaerobic, allowing for efficient methane fermentation. The organic waste transported via input line 14 is fed into first fermenter 3.

[0039] The discharge port of the input line 14 is installed in the fermentation liquid (in the fermentation liquid phase) in the fermenter (e.g., first fermenter 3) to be transferred. If the discharge port is located above the liquid level of the fermentation liquid, the organic waste transferred by pump P2 will be thrown against the liquid surface, weakening the flow rate and reducing the effect of agitating the fermentation liquid with the water flow. On the other hand, by installing the discharge port in the fermentation liquid phase, the effect of water flow agitation can be further enhanced. To further enhance the effect of water flow agitation, it is preferable that the discharge port be located near the center of the fermenter in order to agitate the fermentation liquid.

[0040] The input line 14 is equipped with a siphon break function (siphon break structure) to prevent siphoning. The siphon break structure is, for example, configured by connecting the input line 14 and the desulfurized gas header 20 via a check valve. The siphon break function can use the biogas generated by the fermentation of the organic waste. When pump P2 completes its liquid transfer, the siphon break function changes the pressure inside the piping from positive to negative, drawing in the biogas and causing a siphon break. Using biogas for the siphon break allows the anaerobic nature of the methane fermentation treatment system to be maintained.

[0041] The fermenter may be a single tank or multiple tanks (multi-tank fermenter). In FIG. 1, the fermenter is composed of a first fermenter 3 and a second fermenter 4. Preferably, the fermenter is a multi-tank type having a first tank (e.g., first fermenter 3) that decomposes coarse organic matter and a second or more tanks (e.g., second fermenter 4) that decompose the fine organic matter decomposed in the first tank. In the case of a multi-tank fermenter, the multiple fermenters may be arranged in series (e.g., an arrangement in which the mixture can be introduced from the introduction tank 2 into the first fermenter 3 and transferred from the first fermenter 3 to the second fermenter 4), or in parallel (e.g., an arrangement in which the mixture can be introduced from the introduction tank 2 into both the first fermenter 3 and the second fermenter 4), or a combination thereof.

[0042] In the case of a multi-tank fermenter, consecutive fermenters, for example, a first fermenter and a second fermenter, are connected by a communicating pipe. Specifically, for example, a first fermenter 3 and a second fermenter 4 are connected by communicating pipes 16 and 17. Organic waste introduced via an introduction line 14 is transferred from the first fermenter 3 to the second fermenter 4 via the communicating pipes 16 and 17. To maximize the water flow agitation effect due to the water level difference, it is preferable that there is one communicating pipe, but two or more communicating pipes may also be used, and there is no particular limitation.

[0043] In the first fermenter 3 and the second fermenter 4, organic waste is decomposed to produce biogas. The biogas produced in the fermenters such as the first fermenter 3 and the second fermenter 4 is sent to the gas header 20 via gas lines 18 and 19 and stored in the first gas holder 6 and the second gas holder 7. As the biogas passes between the gas lines 18 and 19 and the gas header 20, it may have water and sulfur components removed by passing through a condensation tower and a desulfurization agent. The system may have one or more gas holders, which can be set appropriately depending on the amount of biogas to be stored.

[0044] The input tank and the fermenter preferably have a return line for returning the fermentation liquid from the fermenter to the input tank. For example, when the pulverizer is operated, the return valve of the return line connecting the input tank and the fermenter opens, and the fermentation liquid in the fermenter is returned to the input tank. When the operation of the pulverizer is completed and the volume of the input tank reaches a desired value, the pump installed in the input tank is operated, and the organic waste is input from the input tank to the fermenter via the input line. In this example, the pulverizer 11 and the return valve 31 are linked to automatically open and close the return valve 31. However, this is not limited to this embodiment. For example, the weight of the input tank may be detected and linked to the return valve, the water level in the input tank may be detected and linked to the return valve, or other sensing may be linked to the return valve. In this way, water flow mixing is performed by returning the liquid from the fermenter to the input tank and inputting it from the input tank to the fermenter, eliminating the need for an agitator in the fermenter.

[0045] Furthermore, for example, when the volume of fermentation liquid is large or when the water flow agitation effect needs to be further enhanced, it is advisable to use a multi-tank system with two or more fermenters and connect the multiple fermenters with a communicating pipe. For example, in the case of two fermenters as shown in Figure 1, the input tank 2 and the second fermenter 4 are provided with a return line 15 that returns the fermentation liquid from the second fermenter 4 to the input tank 2. When the crusher 11 is operated during input of organic waste, the return valve 31 of the return line 15 connecting the input tank 2 and the second fermenter 4 opens, and the fermentation liquid in the second fermenter 4 is returned to the input tank 2. When the operation of the crusher 11 is completed, the return valve 31 closes, and the return ends. During the return, the fermentation liquid in the second fermenter 4 decreases, causing a difference in water level between the first fermenter 3 and the second fermenter 4. When the volume inside the input tank 2 reaches a desired value due to the return from the second fermenter 4, the pump P2 inside the input tank 2 is operated, and the organic waste is input from the input tank 2 to the first fermenter 3 via the input line 14. The input of the organic waste into the first fermenter 3 creates a further difference in water level between the first fermenter 3 and the second fermenter 4. The difference in water level causes the fermentation liquid in the first fermenter 3 to be forcefully transferred to the second fermenter 4 through the connecting pipes 16 and 17, stirring the fermentation liquid. The connection position of at least one connecting pipe (e.g., connecting pipe 16) is preferably at the lower part of the first fermenter 3 and the second fermenter 4. By connecting the connecting pipe to the lower part of the fermenter, the flow rate of the fermentation liquid transferred from the first fermenter 3 to the second fermenter 4 increases, enhancing the stirring effect. Again, this case is not limited to the example in which the crusher 11 and the return valve 31 are linked to automatically open and close the return valve 31; various types of sensors may be linked to the return valve.

[0046] In this way, by returning the fermentation liquid from the second fermentation tank 4 to the input tank 2 and inputting it from the input tank 2 to the first fermentation tank 3, the fermentation liquid is transferred from the first fermentation tank 3 to the second fermentation tank 4 through the connecting pipes 16, 17, and the fermentation liquid inside the fermentation tanks can be agitated by water flow in both the first fermentation tank 3 and the second fermentation tank 4. In addition, by performing water flow agitation using the water level difference described above, the agitation effect can be further improved, and the fermentation liquid can be agitated without installing an agitator inside the fermentation tank. This makes it possible to realize an energy-saving system that does not require an agitator.

[0047] A methane treatment fermentation system according to one embodiment of the present invention includes a water-flow agitation means for agitating the fermentation liquid by a water flow. Examples of the water-flow agitation means include, as described above, (i) a means for returning the fermentation liquid from the fermenter to the input tank and agitating the fermentation liquid by a water flow, and (ii) a means for agitating the fermentation liquid in at least one fermenter by using the difference in water levels in the fermenter tanks, which are provided with a plurality of fermenters connected by communicating pipes.

[0048] When the fermenter is a single tank, it is preferable to have the water flow agitation means (i) above. In (i) above, the input tank and the fermenter are preferably connected by a feed line and a return line via a return valve. With this structure, when the organic waste is returned to the input tank, the return valve opens and the fermentation liquid in the fermenter is returned to the input tank through the return line. Then, a water flow can be generated by the return of the fermentation liquid and the input of the organic waste, thereby performing water flow agitation.

[0049] When the fermenter is a multi-tank type having a plurality of fermenters, it is preferable to provide the water flow agitation means of (ii) above, and more preferably to provide both the water flow agitation means of (i) and (ii) above. Referring to FIG. 1 , in (ii) above, the plurality of fermenters include a feeder 2, a first fermenter 3 connected by a feed line 14, and a second fermenter 4, which is a fermenter located downstream of the first fermenter 3. The feeder 2 and the second fermenter 4 are connected by a return line 15 via a return valve 31. The return valve 31 is opened by sensing, such as by operating the crusher 11, to return the fermentation liquid in the second fermenter 4 to the feeder 2 through the return line 15. When the volume of the fermentation liquid in the feeder 2 reaches a desired value due to this return, the organic waste is fed from the feeder 2 to the first fermenter 3 through the feed line 14. This generates a water level difference among the feeder 2, the first fermenter 3, and the second fermenter 4, enabling water flow agitation.

[0050] The manner in which the fermenter and the gas holder are connected is not particularly limited, and may be the manner shown in Fig. 1 or the manner shown in Fig. 2. Fig. 1 is a flow diagram of a methane fermentation treatment system including a connection between the fermenter and the gas holder when a gas dissolving and stirring means is not implemented, and Fig. 2 is a flow diagram of a methane fermentation treatment system including a connection between the fermenter and the gas holder when a gas dissolving and stirring means is implemented.

[0051] In the embodiment shown in FIG. 2 , the first fermenter 3 and the second fermenter 4 are connected to the first gas holder 6 via a gas line G1. The gas line G1 is equipped with a pressure gauge and an automatic on-off valve 22. The first fermenter 3 and the second fermenter 4 are connected to the second gas holder 7 via a gas line G2. The gas line G2 is equipped with an automatic on-off valve 21. The first fermenter 3 and the second fermenter 4 are connected to the second gas holder 7 via a gas line G3 from a branch on the gas line G2 before the automatic on-off valve 21. The gas line G3 is equipped with an automatic on-off valve 24 and a pump P4. The gas line G1 and the gas line G2 are connected via a gas line G4. The gas line G4 connects a branch point located between the automatic on-off valve 22 and the gas header 20 on the gas line G1 to a branch point located between the automatic on-off valve 21 on the gas line G2 and the point where the gas line G2 branches to the gas line G3. The gas line G4 is equipped with a pressure regulator 23 and an automatic on-off valve 29.

[0052] Gas line G1 is a gas line used when filling the first gas holder 6 with gas from the first fermentation tank 3 and the second fermentation tank 4 (for example, during the organic waste introduction period described below). Gas line G3 is a gas line used when transferring gas from the second gas holder 7 to the gas phase sections of the first fermentation tank 3 and the second fermentation tank 4 (for example, by the gas dissolving and stirring means described below). Gas line G4 is a gas line that transfers surplus gas that was not transferred to the gas phase section when transferring gas from the second gas holder 7 to the gas phase sections of the first fermentation tank 3 and the second fermentation tank 4 to the first gas holder 6. Gas line G2 is a gas line used when filling the second gas holder 7 with gas in the gas phase sections of the first fermentation tank 3 and the second fermentation tank 4 or gas dissolved in the fermentation liquid.

[0053] Figure 3 shows a gas line flow diagram during the organic waste charging period. As shown in Figure 3, during the organic waste charging period, automatic on-off valves 21 and 24 are closed, and automatic on-off valves 22 and 28 are open. The organic waste charging period refers to the period when organic waste is crushed as needed and charged from charging tank 2 to the fermenter. The organic waste charging period can be selected appropriately depending on the management conditions of the methane fermentation treatment system, for example, from 9:00 to 18:00. During the organic waste charging period, the gas dissolving and stirring means is not operated. The biogas generated during this period is sent from first fermenter 3 and second fermenter 4 via gas line G1 and filled into first gas holder 6. Before being filled into first gas holder 6, the biogas passes through a desulfurization device and a condensation tower to be desulfurized and dehydrated, and then filled into first gas holder 6.

[0054] A methane treatment fermentation system according to one embodiment of the present invention is equipped with a gas dissolving and stirring means that increases the internal pressure within the fermenter to dissolve biogas generated by fermentation of organic waste in a fermentation liquid, releases the pressure when the internal pressure reaches a predetermined level, vaporizes the biogas dissolved in the fermentation liquid, and causes the vaporized biogas to diffuse and / or float up in the fermentation liquid, thereby increasing the fluidity of the fermentation liquid.

[0055] The gas dissolving and stirring means is preferably carried out during times other than when organic waste is being added, such as at night, but this can be selected appropriately depending on the management conditions under which the methane fermentation treatment system is installed. This is because the addition of organic waste increases the internal pressure of the fermentation tank, making it difficult to dissolve biogas in the fermentation liquid.

[0056] The gas dissolving and agitating means comprises an "internal pressure increase period" in which the biogas stored in the gas holder is transferred to the gas phase within the fermenter to increase the internal pressure of the fermenter; a "gas dissolution period" in which biogas is generated and dissolved in the fermentation liquid; and a "gas release and agitation period" in which the pressure in the fermenter is released, the dissolved biogas is rapidly gasified, and the fermentation liquid is agitated. The gas dissolving and agitating means can be implemented, for example, by a configuration including gas lines G2, G3, G4, a pressure gauge, automatic on-off valves 21, 24, and 29, a pressure control valve 23, a pump P4, and a second gas holder 7. The internal pressure increase period can be provided to increase the internal pressure within the fermenter to create a state in which gas is more easily dissolved, thereby dissolving the gas and achieving more efficient gas dissolution and agitation, but it does not necessarily have to be provided in the gas dissolving and agitating means.

[0057] FIG. 4 shows a flow diagram of the gas dissolving and agitating means. First, the "internal pressure rising period" will be described. During the organic waste loading period, the automatic on-off valves 21 and 24 are closed, and the automatic on-off valves 22 and 28 are open. However, when the gas dissolving and agitating means begins operation, as shown in FIG. 4, the automatic on-off valves 22 and 29 are closed, the automatic on-off valve 28 is closed, the path change valve 30 is closed, the automatic on-off valve 24 is opened, and the pump P4 is turned on. The biogas stored in the second gas holder 7 is then sent through the gas line G3 to the gas phases of the first fermenter 3 and the second fermenter 4. The pressure setting of the pressure regulating valve 23 connected to the gas line G4 is not particularly limited, but is preferably set to a value lower than the pressure at which the automatic on-off valve 21 opens. In this case, as the biogas is transferred to the first fermenter 3 and the second fermenter 4, the internal pressure of the first fermenter 3 and the second fermenter 4 increases. When the internal pressure exceeds the set pressure, the pressure regulating valve 23 opens, and excess gas is transferred to the first gas holder 6. When the gas transfer from the second gas holder 7 is complete, the pump P4 is stopped. The transfer time is estimated from the amount of gas in the second gas holder 7 and the flow rate of the pump P4, and the pump P4 is then stopped. It is preferable to provide an automatic control means that closes the pressure regulating valve 23 when the pressure inside the first fermenter 3 and the second fermenter 4 is below the set pressure, and opens the automatic on-off valve 23 when the pressure exceeds the set pressure. With this configuration, the internal pressure increase period can be completed automatically. The set pressure of the pressure regulating valve 23 can be appropriately set depending on the set pressure at which the automatic on-off valve 21 opens, the volume of the fermentation liquid and the fermenter, the number of times gas dissolution and stirring are performed, etc.

[0058] Next, the "gas dissolution period" will be explained. The internal pressure of the first fermentation tank 3 and the second fermentation tank 4 is increased, and after the gas transfer of the second gas holder 7 is completed, the automatic on-off valve 29 and the automatic on-off valve 24 are closed. As a result, all valves connected to the first fermentation tank 3 and the second fermentation tank 4 are closed, and the newly generated biogas from the fermentation liquid dissolves in the fermentation liquid as the internal pressure increases.

[0059] Next, the "gas release agitation period" will be described. During the gas dissolution period, biogas generation further increases the pressure in the fermenter. When the pressure gauge connected to gas line G1 reaches 10 kPa or higher, the automatic on-off valve 21 is opened. At the same time as the automatic on-off valve 21 opens, the gas in the fermenter is rapidly transferred to the second gas holder 7 via gas line G2, reducing the pressure in the first fermenter 3 and the second fermenter 4. The biogas dissolved in the fermentation liquid is gasified throughout the fermentation liquid. The impact of gasification and the rising of the gasified gas within the fermentation liquid increase the fluidity of the entire fermentation liquid, resulting in agitation. Furthermore, the biogas generated during the gas release agitation period adheres to the undecomposed organic matter that has settled at the bottom of the fermenter, reducing its specific gravity and causing it to rise within the fermentation liquid. After rising, the gas transitions to the gas phase, and the undecomposed organic matter that has separated from the gas settles back to the bottom of the fermenter. The release of the gas causes the dissolved gas to evaporate, resulting in vertical agitation of the sediment in the fermentation liquid, further enhancing the agitation effect.

[0060] The pressure when opening the automatic on-off valve 21 is set to 10 to 100 kPa. The pressure is preferably 20 to 100 kPa, and more preferably 30 to 60 kPa. If the pressure is 10 kPa or higher, the fermentation liquid can be stirred more thoroughly. If the pressure is 30 kPa or higher, the entire fermentation liquid can be stirred even more thoroughly. If the pressure is too high, such as above 100 kPa, the load on the fermentation tank increases, and there is also a risk that the gas and fermentation liquid will spray out together when the gas is released. Therefore, a pressure of 10 to 100 kPa is preferable. It is advisable to select a fermentation tank that can withstand this pressure.

[0061] During the gas release and agitation period, biogas is transferred to the second gas holder 7 through the gas line G2. However, biogas may also be transferred to the first gas holder 6 through the gas line G4 and the gas line G1. When using the gas line G4 and the gas line G1, the automatic on-off valve 29 may be opened. However, because a desulfurization device or other device is present on the gas line G1 connecting the first gas holder 6 and the fermenter, for example, when biogas is transferred using the gas line G1 during the gas release and agitation period, the resistance of the desulfurization device or other device prevents the gas from escaping all at once to the first gas holder 6, resulting in a decrease in agitation capacity due to the gas release. For this reason, when using the first gas holder 6 during the gas release and agitation period, it is preferable to use it together with the second gas holder 7. The pressure at which the automatic on-off valve 29 opens may be the same as or higher than the pressure at which the automatic on-off valve 21 opens. Using the first gas holder 6 together with the second gas holder 7 allows excess gas that does not enter the gas holder 7 to be stored in the first gas holder 6.

[0062] The automatic on-off valve 21 is opened, and once biogas gasification, floating, and diffusing and mixing are complete, the automatic on-off valve 21 is closed. Closing of the automatic on-off valve 21 upon completion of biogas gasification, floating, and diffusing and mixing should be performed by time control. The time required to complete biogas gasification, floating, and diffusing and mixing depends on the size of the fermentation tank, the amount of fermentation liquid, etc., so it is best to check this in advance and set it to an arbitrary value.

[0063] The automatic shutoff valve 21 is closed, the automatic shutoff valve 24 is opened, and the system transitions again to the "internal pressure increase period," repeating the series of steps of the "internal pressure increase period," "gas dissolution period," and "gas release and agitation period." As shown in Figure 2, the gas dissolving and agitation means includes gas lines connecting the first fermentation tank 3 and the second fermentation tank 4 with the second gas holder 7. These lines are gas line G2, used during the gas release period, and gas line G3, used during the internal pressure increase period. During the gas release period, it is important to quickly transfer the gas in the fermentation tank to the gas holder and reduce the pressure. This allows the dissolved gas in the fermentation liquid to evaporate rapidly, increasing the agitation force. If gas lines G2 and G3 were combined into a single gas line, the pump resistance in the gas line would weaken the gasification rate and reduce the agitation capacity. Therefore, it is recommended to install gas lines G2 and G3 separately.

[0064] When switching from the gas dissolving and agitating means operating period to the organic waste input period, the automatic on-off valve 21 is closed, the automatic on-off valve 24 is closed, the automatic on-off valve 22 is opened, the automatic on-off valve 28 is opened, and the route change valve 30 is opened after the gas release and agitation period. At this time, gas remains stored in the second gas holder 7, and this gas is used again to increase the internal pressure of the fermentation tank with the gas dissolving and agitating means. Furthermore, when operating the gas dissolving and agitating means, the automatic on-off valve 28 of the overflow pipe 25 connecting the fermentation tank and the liquid fertilizer tank 5 is closed. This is because if the gas dissolving and agitating means is operated with the on-off valve 28 of the overflow pipe 25 open, the fermentation liquid will flow out of the overflow pipe 25 as the pressure in the fermentation tank increases. Furthermore, when operating the gas dissolving and agitating means, the route change valve (four-way valve) 30 of the input line 14 is closed. This is because if the gas dissolving and stirring means is operated with the route change valve 30 of the input line 14 open, the fermentation liquid will flow back into the input tank 2 through the input line 14 as the pressure in the fermenter increases.

[0065] 1 and 2, the biogas filled in the first gas holder 6 can be passed from the gas header 20 through a gas line 26 and a gas purification device, and then used in a known or conventional manner in a biogas hot water supply system 9, a biogas power generation system, or the like, or can be sent through a gas line 27 to a siphon breaker in the input line 14. Furthermore, biogas filled in a gas holder other than the first gas holder 6, such as the second gas holder 7, or in multiple gas holders, can also be used as described above through a desulfurization device and a condensation tower.

[0066] When both the gas dissolving and stirring means and the water flow stirring means are provided, the fermentation liquid can be stirred more sufficiently without installing an agitator in the fermentation tank, thereby realizing power saving in the methane fermentation treatment system.

[0067] There are no particular limitations on the installation height of the crusher 11, input tank 2, first fermenter 3, and second fermenter 4, but to prevent leakage, it is preferable that the height of the input port of the crusher 11 and input tank 2 be equal to or higher than the liquid levels in the first fermenter 3 and second fermenter 4. Small methane fermentation treatment systems often do not have a designated manager on-site like a plant, so it is desirable for the system to have a structure that minimizes the risk of leakage.

[0068] The fermented liquid in the fermenter is desirably heated to optimize methane fermentation. For example, in mesophilic fermentation, a temperature of 32 to 37°C is desirable. Heating can be performed using circulating water (hot water) heated by a solar water heating system 8 or a biogas water heater 9. The solar water heating system 8 heats water using solar heat to produce hot water. The circulating water (hot water) heated by the solar water heating system 8 or the biogas water heater 9 is stored in a hot water tank 10 and undergoes heat exchange through hot water piping (shown by dotted lines in Figures 1 and 2) that runs from the hot water tank 10 through the fermenter. After heat exchange, the circulating water returns to the solar water heating system 8 or the biogas water heater 9 and is heated again. The biogas water heater 9 heats the circulating water by burning biogas generated by methane fermentation.

[0069] Biogas is generally composed of about 60% methane and about 40% carbon dioxide. Methane gas burns, but carbon dioxide does not. Because biogas has a methane concentration of about 60%, it is difficult to burn in the city gas stoves currently in use. Removing the carbon dioxide from biogas and increasing the methane concentration results in a gas with higher combustion efficiency. For example, if it is refined to a methane concentration of about 90%, it can be burned in a city gas stove.

[0070] Methods for removing carbon dioxide from biogas include known or conventional biogas purification methods. Examples of biogas purification methods include passing the biogas through an alkaline solution, dissolving the carbon dioxide in the alkaline solution, and recovering only the undissolved methane gas. The alkaline solution is not particularly limited, but limewater may be used from the viewpoint of ease of handling. Reaction of limewater with carbon dioxide produces calcium carbonate. This limewater containing calcium carbonate is preferably used for agricultural purposes in combination with liquid fertilizer. Other alkaline solutions include, for example, potassium hydroxide solution. Reaction of potassium hydroxide solution with carbon dioxide produces potassium carbonate, which is also preferably used for agricultural purposes as fertilizer. The methane concentration to which the biogas is purified can be appropriately selected depending on the intended use of the concentrated gas, such as combustion in a city gas stove or biogas power generation, and the equipment using the gas.

[0071] The second fermenter 4 and the liquid fertilizer tank 5 are connected by an overflow pipe 25. The fermented liquid after methane fermentation passes through the overflow pipe 25 and is stored in the liquid fertilizer tank 5. This liquid fertilizer contains useful components as a fertilizer, so it is preferably applied to agricultural land. In recent years, the rising prices of fertilizer components have become a problem, and using fertilizer derived from these organic wastes not only helps with environmental issues and resource recycling, but also has great economic benefits.

[0072] A foreign matter removal device may be provided in the return line 15 connecting the second fermenter 4 and the input tank 2. The foreign matter referred to here refers to non-biodegradable plastic pieces and stickers, as well as persistent solids such as seeds and fibrous materials that are not suitable for fermentation (require a long time for fermentation). In particular, fibrous materials, if contained in the fermentation liquid, can cause the formation of a scum layer, so it is recommended to remove them periodically.

[0073] The foreign matter removal device is not particularly limited, but may be a device in which the return line 15 is branched and a strainer is installed on one side. During normal operation, the fermentation liquid circulates through the return line 15, which is not equipped with a strainer, and during maintenance, the line is switched so that the fermentation liquid circulates through a pipe equipped with a strainer, thereby removing foreign matter in the fermentation liquid.

[0074] In addition, an antifoaming agent may be added to the fermentation liquid to prevent the formation of a scum layer. In this specification, scum refers to undecomposed organic matter that rises to the surface together with biogas and forms a thick film. Adding an antifoaming agent destroys the bubbles in the scum, preventing the undecomposed organic matter from floating up and promoting the fermentation of the undecomposed organic matter.

[0075] The methane fermentation treatment system may be equipped with a natural energy power generation device. Electric energy generated by the natural energy power generation device can be used to power various devices and means in the methane fermentation treatment system. Components that consume electric energy in the methane fermentation treatment system include a crusher 11 that crushes organic waste, a water supply pump P1 installed in the water tank 1, a pump P2 installed in the charging tank 2 that transfers the mixture from the charging tank 2 to the first fermentation tank 3, a pump P3 that transfers hot water from the solar hot water heater 8 or the biogas hot water heater 9 to the hot water piping, a pump P4 in the gas dissolving and stirring means as shown in Figure 2, and an electronic control system.

[0076] Examples of the natural energy power generation device include well-known or commonly used solar power generation devices, wind power generation devices, and geothermal power generation devices. Among these, solar power generation devices are preferred because they are small and can generate sufficient electrical energy. The solar power generation device can be installed, for example, on the top or wall of the methane fermentation treatment system. The size and capacity of the solar power generation device can be selected appropriately based on an estimate of the size and power consumption of the methane fermentation treatment system. A methane fermentation treatment system with high power consumption requires a solar power generation device that is too large to fit in the methane fermentation treatment system. However, the present methane fermentation treatment system consumes less power than conventional systems, allowing for a balance between supply and demand of electricity to be achieved using a solar power generation device that fits in a space that can be installed in a small methane fermentation treatment system. Furthermore, because the amount of power generated by solar power generation is affected by weather, it is preferable to provide a storage battery to ensure a stable supply of power to the methane fermentation treatment system. The electrical energy stored in the storage battery can be used to power one or more systems selected from the group consisting of a pump, a grinder, and an electronic control system of the methane fermentation treatment system.

[0077] As described above, in this methane fermentation treatment system, the supplied energy sources are thermal energy for hot water from the solar hot water heater 8, thermal energy for hot water from the biogas hot water heater 9, electric energy from the natural energy power generation system, electric energy from the biogas power generation system, and biogas produced during methane fermentation. These supplied energies can cover all of the energy required for the methane fermentation treatment. In this way, this methane fermentation treatment system is equipped with an independent power supply control unit that can supply all of the energy required for the methane fermentation treatment from internal energy from natural energy and the biogas. [Example]

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0079] Example 1 Figure 5 shows a flow diagram of the methane fermentation treatment system of Example 1. As shown in Figure 5, the methane fermentation treatment system of Example 1 includes a water tank 1, a grinder 11, a charging tank 2, a first fermentation tank 3, a second fermentation tank 4, a liquid fertilizer tank 5, a first gas holder 6, a biogas hot water supply device 9, a solar power generation device, and a storage battery. Example 1 describes a case where food waste discharged from a household is treated in a two-tank methane fermentation treatment system.

[0080] The capacity of the first fermentation tank 3 and the second fermentation tank 4 is 1 m 3 The daily input amount of food waste is 35 kg / day, and when 35 kg of food waste is input per day, the amount of biogas generated is 3 m 3 The capacity is 1000 kJ / day. The first fermentation tank 3, the second fermentation tank 4, and the food waste input tank were installed in series, with the first gas holder 6 installed above the fermentation tank and the biogas water heater 9 installed on the side of the fermentation tank. The methane fermentation treatment system in this configuration included the water tank 1, the grinder 11, the input tank 2, the first fermentation tank 3, the second fermentation tank 4, the first gas holder 6, the biogas water heater 9, the liquid fertilizer tank 5, a storage battery, and associated pumps, piping, and electronic control devices. Its dimensions were 4,500 mm wide, 2,400 mm high, and 2,000 mm deep, making it a fairly compact methane fermentation treatment system among commercially available small methane fermentation treatment systems. This small methane fermentation treatment system was installed in a vacant lot without a power source, and food waste was input and methane fermentation was carried out. No agitator was installed inside the fermentation tank; instead, the fermentation liquid was dispersed by water flow agitation due to the water level difference using the water flow agitation means (i) and (ii) described above. The generated biogas was burned to heat water, producing hot water, which was then used to heat the fermentation liquid. A solar power generation system was installed on the roof of the small-scale methane fermentation treatment system, and the obtained electrical energy was used to power the crusher 11, etc. The solar power generation system was designed to be large enough to be placed on the roof of the small-scale methane fermentation treatment system, with panels measuring 3m. 2The water flow agitation using the water level difference is a process that is carried out every time food waste is added, so the amount of food waste added at one time was set at about 500g, and it was carried out 70 times a day. The water flow agitation described above ensured that the fermented liquid was sufficiently dispersed, and there was no generation of scum or clogging of the pipes. Methane fermentation also proceeded without any problems, with a volume of 3m in 24 hours. 3 The amount of biogas produced was 1000 kJ / h. When the generated biogas was measured with a gas concentration meter, the methane concentration was found to be 59.5%. The hot water produced by burning the biogas was used to heat the fermentation liquid, and the temperature of the fermentation liquid was able to be maintained at 35-37°C throughout the day. The amount of electricity generated by solar power generation was 2 kWh, and was used to operate the crusher, pump, etc. of the methane fermentation treatment system. The daily electricity supply and consumption in Example 1 are shown in Table 1.

[0081] [Table 1]

[0082] In the methane fermentation treatment system of Example 1, the introduction of water flow agitation using water level difference eliminated the need for an agitator, and the introduction of the biogas hot water supply device 9 eliminated the need for a heater, achieving power savings for the system. The small-scale methane fermentation treatment system could be operated stably using only the biogas produced by methane fermentation and electricity generated by solar power generation (i.e., an independent power source). The system's power savings have the advantage of minimizing the amount of power demand, thereby enabling the size of the solar power generation panels, which are the power supply source, to be reduced. This reduces initial costs and allows the solar panels to be mounted on the roof area of ​​the small-scale methane fermentation treatment system and integrated, contributing to further miniaturization of the equipment.

[0083] Example 2 Figure 6 shows a flow diagram of the methane fermentation treatment system of Example 2. As shown in Figure 6, the methane fermentation treatment system of Example 1 includes a water tank 1, a grinder 11, a charging tank 2, a first fermenter 3, a liquid fertilizer tank 5, a first gas holder 6, a second gas holder 7, a biogas hot water supply device 9, a solar power generation device, and a storage battery. Example 2 describes the case where food waste discharged from a household is treated in a single-tank methane fermentation treatment system.

[0084] The capacity of the first fermenter 3 is 1m 3 The daily input amount of food waste is 17 kg / day, and when 17 kg of food waste is input per day, the amount of biogas generated is 1.5 m 3The system's capacity is 1000 sq m / day. The first fermenter 3 and the food waste feed tank were installed in series, with the first gas holder 6 installed above the fermenter and the biogas water heater 9 installed on the side of the fermenter. The methane fermentation treatment system, in addition to the liquid fertilizer tank, included the water tank 1, the grinder 11, the feed tank 2, the first fermenter 3, the first gas holder 6, the second gas holder 7, the biogas water heater 9, the liquid fertilizer tank 5, the storage battery, associated pumps and piping, and an electronic control device. It measured 3,500 mm wide, 2,400 mm high, and 1,700 mm deep, making it one of the smallest methane fermentation treatment systems available. This small methane fermentation treatment system was installed in a vacant lot without a power source, and food waste was fed and fermented. No agitator was installed inside the fermenter; instead, the fermented liquid was dispersed by water flow agitation (water flow agitation means (i) above) via the organic waste feed and return line from the first fermenter 3 to the feed tank 2, as well as by a gas dissolving agitation means. In addition, a solar water heating system 8 was installed on the roof of the methane fermentation treatment system, and the hot water produced was used to heat the fermentation tank. The generated biogas was also burned to heat water, producing hot water that was then used to heat the fermentation liquid. When heating was stopped, the heat radiation temperature of the fermentation liquid was 4°C, but by heating the fermentation liquid with hot water from the solar water heating system 8 and the biogas hot water heater 9, the temperature of the fermentation liquid could be maintained at 35-37°C. In cold regions and during the winter, the heat radiation temperature of the fermentation liquid increases, so if the temperature of the fermentation liquid cannot be maintained by heating alone through biogas combustion, adding a solar water heating system makes it possible to implement a methane fermentation treatment system that does not require electricity.

[0085] A solar power generation system was installed on the wall of the small-scale methane fermentation treatment system, and the obtained electric energy was used to power the crusher 11, etc. The solar power generation system was designed to be large enough to be installed on the wall of the small-scale methane fermentation treatment system, with a panel size of 1.5 m. 2 I selected something like that.

[0086] The gas dissolving and agitating means was operated during the nighttime (6:00 PM to 8:00 AM) when no food waste was being added. At 6:00 PM, automatic on-off valves 22 and 28 and path change valve 30 were closed, automatic on-off valves 24 and 29 were opened, and pump P4 was used to transfer the biogas from the second gas holder 7 to the first fermenter 3 via gas line G3 connecting the second gas holder 7 and the first fermenter 3. When the pressure gauge installed in the first fermenter 3 reached 25 kPa, the pump was stopped, automatic on-off valve 29 was closed, and automatic on-off valve 24 on gas line G3 connecting the second gas holder 7 and the first fermenter 3 was closed, stopping the transfer of biogas. Methane fermentation progressed in the first fermenter 3, producing biogas, but due to the high pressure inside the first fermenter 3, it could not be gasified and some of it remained dissolved in the fermentation liquid. When the pressure gauge reached 35 kPa, automatic on-off valve 21 was opened, and the pressure inside the first fermenter 3 was returned to normal pressure. At this time, the biogas dissolved in the fermentation liquid was gasified all at once, and the impact caused the fermentation liquid to disperse, with the gas moving from the bottom of the fermentation liquid to the top, into the gas phase, and diffusing throughout the fermentation liquid. The gasified biogas was stored in the second gas holder 7 through gas line G2. The gas was again transferred to the first fermentation tank 3 by a pump, the internal pressure inside the first fermentation tank 3 was increased, and the gas dissolving and stirring means, which stirs the liquid with the gas produced by methane fermentation, was repeatedly operated. Between 6:00 pm and 8:00 am, the gas dissolving and stirring means stirred the fermentation liquid, and there was no generation of scum or clogging of the pipes, and methane fermentation also proceeded without any problems, reaching 1.5 m in 24 hours. 3 The amount of biogas produced was 59.5%. When the generated biogas was measured with a gas concentration meter, the methane concentration was 59.5%. As in Example 2, by adding a gas dissolving and stirring means to the methane fermentation treatment system of Example 1, the stirring effect of the fermentation liquid could be further improved, promoting stable methane fermentation. The daily power supply and consumption in Example 2 are shown in Table 2.

[0087] [Table 2]

[0088] In the methane fermentation treatment system of Example 2, the introduction of a water flow agitation and gas dissolving agitation means via a return line eliminated the need for an agitator, and the introduction of a solar hot water heater 8 and a biogas hot water heater 9 eliminated the need for a heater, achieving power savings for the system. The small-scale methane fermentation treatment system could be operated stably using only the biogas produced by methane fermentation and electricity generated by solar power generation (i.e., an independent power source). The system's power savings have the advantage of minimizing power demand, thereby enabling the size of the solar power generation panels, which serve as the power supply source, to be reduced. This reduces initial costs and allows the solar panels to be mounted on the roof of the small-scale methane fermentation treatment system for integration, contributing to further miniaturization of the equipment. [Explanation of symbols]

[0089] 1 aquarium 2 Loading tank 3 First fermentation tank 4. Second fermenter 5 Liquid fertilizer tank 6. First Gas Holder 7 Second Gas Holder 8 Solar water heating system 9. Biogas water heater 10 Hot water tank 11 Crusher 12 Organic waste 13 Piping 14 Input line 15 Return Line 16,17 Communication pipe 18,19 Gas lines 20 Gas Header 21, 22, 24, 28, 29 Automatic shut-off valve 23 Pressure Regulating Valve 25 Overflow pipe 26,27 Gas lines 30. Route change valve 31 Return valve G1, G2, G3, G4 gas lines P1, P2, P3, P4 pumps

Claims

1. A methane fermentation treatment system in which organic waste is fed from a feeding tank to a fermentation tank and the organic waste is fermented in the fermentation tank, A methane fermentation treatment system comprising a water flow agitation means for agitating a fermentation liquid by a water flow, as described in (i) and / or (ii) below. (i) a means for returning the fermented liquid from the fermenter to the input tank and agitating the fermented liquid with a water jet; (ii) A means for providing a plurality of fermenters connected by communicating pipes and for agitating the fermented liquid in at least one of the fermenters by the difference in water levels in the plurality of fermenters;

2. The system further comprises a biogas hot water supply system that heats water using biogas generated by fermenting organic waste, a natural energy power generation system, and a storage battery that stores the electric energy generated by the natural energy power generation system, 2. The methane fermentation treatment system according to claim 1, further comprising an independent power supply control unit capable of supplying all of the energy required for the methane fermentation treatment from natural energy and internal energy produced by the biogas.

3. 2. The methane fermentation treatment system according to claim 1, further comprising a gas dissolving and stirring means that increases the internal pressure of the fermenter to dissolve biogas generated by fermentation of organic waste in the fermentation liquid, releases the pressure when the internal pressure reaches a predetermined level, vaporizes the biogas dissolved in the fermentation liquid, and causes the vaporized biogas to diffuse and / or float up in the fermentation liquid, thereby increasing the fluidity of the fermentation liquid.

4. This is a methane fermentation treatment system that ferments organic waste in a fermentation tank. The methane fermentation treatment system is equipped with a gas dissolving and stirring means that increases the internal pressure of the fermenter to dissolve biogas generated by fermentation of organic waste in a fermentation liquid, releases the pressure when the internal pressure reaches a predetermined level, vaporizes the biogas dissolved in the fermentation liquid, and causes the vaporized biogas to diffuse and / or float up in the fermentation liquid, thereby increasing the fluidity of the fermentation liquid.

5. The apparatus is provided with the water flow agitation means (i), and the feeding tank and the fermenter are connected by a feeding line and a return line via a return valve; 4. The methane fermentation treatment system according to claim 1, wherein the water flow is generated by charging the organic waste into the charging tank and returning the fermentation liquid in the fermentation tank to the charging tank through the return line by opening the return valve.

6. The system is equipped with the water flow agitation means (ii), and the plurality of fermenters include a first fermenter connected to the input tank by an input line and a second fermenter located downstream of the first fermenter, The input tank and the second fermenter are connected by a return line via a return valve, 3. The methane fermentation treatment system according to claim 1, wherein the return valve is opened to return the fermentation liquid in the second fermentation tank to the input tank through the return line, and when the volume of the fermentation liquid in the input tank reaches a desired value due to the return, the organic waste is input from the input tank to the first fermentation tank through the input line, thereby generating the water level difference among the input tank, the first fermentation tank, and the second fermentation tank, thereby performing the water flow agitation.

7. 6. The methane fermentation treatment system according to claim 5, wherein the discharge port of the charging line in the fermenter connected to the charging tank via the charging line is placed in the fermentation liquid in the fermenter.

8. 6. The methane fermentation treatment system according to claim 5, wherein the input line is provided with a siphon break function for preventing siphoning, and the siphon break function uses biogas generated by fermentation of the organic waste.

9. a gas holder for storing biogas generated by fermentation of the organic waste; and a gas line for transporting the biogas from the fermenter to the gas holder; 5. The methane fermentation treatment system according to claim 3, further comprising an automatic on-off valve on the gas line.

10. 10. The methane fermentation treatment system according to claim 9, further comprising an automatic control means for closing the automatic on-off valve when the pressure in the fermenter is less than 10 kPa and opening the automatic on-off valve when the pressure in the fermenter is 10 kPa or more.

11. 11. The methane fermentation treatment system according to claim 10, further comprising an internal pressure increasing period in which the biogas stored in the gas holder is transferred to a gas phase portion in the fermenter, thereby increasing the internal pressure of the fermenter.

12. 5. The methane fermentation treatment system according to claim 1, further comprising a solar water heating device that heats water using solar heat to produce hot water, and supplies the hot water to a hot water pipe to heat the fermenter.

13. The methane fermentation treatment system according to any one of claims 1 to 4, further comprising a foreign matter removal device that removes hard-to-decompose solid matter.

14. 3. The methane fermentation treatment system according to claim 2, wherein the hot water heated by the biogas hot water supply device is supplied to a hot water pipe to heat the fermenter.

15. The methane fermentation treatment system according to any one of claims 1 to 3, comprising a plurality of fermentation tanks connected by communicating pipes, and the water flow agitation means water-flow agitates the fermented liquid in at least one of the fermentation tanks by using a water level difference between the plurality of fermentation tanks.

16. 3. The methane fermentation treatment system according to claim 2, wherein the electric energy stored in the storage battery is used as energy for one or more systems selected from the group consisting of a pump, a grinder, and an electronic control system of the methane fermentation treatment system.

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