Dry-type methane fermentation system and dry-type methane fermentation method

Abstract

To provide a dry-type methane fermentation system and a dry-type methane fermentation method which can perform preprocessing of an organic resource that is subjected to methane fermentation, with a simple structure and efficiently perform methane fermentation.SOLUTION: The dry-type methane fermentation system is provided with a kneading blasting machine that kneads and blasts an organic resource to manufacture organic resource pulverized materials, and a dry-type methane fermentation tank that stores the organic resource pulverized materials to perform dry-type methane fermentation. The kneading blasting machine has an enclosure having a cylindrical space and an Archimedean screw arranged in the space. The enclosure has an input port into which the organic resource placed at one cylindrical end part side in the space is put and an extraction port through which the organic resource pulverized materials at the other cylindrical end part side in the space are extracted. Pitch of the Archimedean screw gradually decreases from the input port toward the extraction port.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a dry methane fermentation system and a dry methane fermentation method. [Background technology]

[0002] In order to make effective use of limited resources and create a prosperous society, solutions to many social issues, such as preventing global warming and ensuring a stable energy supply, are being considered. Among these social issues, waste disposal has become one of the most important themes to be resolved in recent years. Organic waste, including food waste, agricultural, forestry, and fishery products, and livestock waste, exceeds 200 million tons per year. Burying this waste requires a vast amount of land, and incineration is extremely costly.

[0003] Methane fermentation technology is a technology that uses methanogens to treat organic matter to produce biogas containing useful gases such as methane and hydrogen. Methane and hydrogen can be used as energy by burning them, and are also useful as raw materials for chemicals. By applying this type of methane fermentation technology to organic waste, it is possible to convert the waste into a useful resource, thereby reducing the burden associated with disposal and the carbon dioxide emissions associated with incineration. Furthermore, if methane fermentation is carried out near the site where the organic waste is generated, it becomes possible to produce and consume resources locally, eliminating the costs and burden associated with transporting the organic waste and the resources obtained.

[0004] This methane fermentation technology includes wet methane fermentation, which performs methane fermentation at a relatively low solid concentration, for example, 10% or less, and dry methane fermentation, which performs methane fermentation at a relatively high solid concentration, for example, 15% to 45%.

[0005] Wet methane fermentation has the advantage of simple equipment and low maintenance costs, but has disadvantages such as lower gas production compared to dry methane fermentation, a large amount of wastewater and high treatment costs.On the other hand, dry methane fermentation produces a large amount of biogas, but has disadvantages such as high power consumption and relatively complex equipment.

[0006] Patent Document 1 proposes a dry methane fermentation apparatus equipped with a pretreatment means for separating at least a portion of non-biodegradable organic matter from organic waste as a pretreatment residue. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-177008 Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, when performing dry methane fermentation, it is preferable to perform some pretreatment on the organic raw material (organic resource). For example, in order to promote methane fermentation of the organic resource, it is preferable to micronize the raw material and increase its surface area. In addition, by heating the organic resource, the organic resource can be denatured and made more susceptible to enzymatic action. Furthermore, in order to perform dry methane fermentation, it is essential to adjust the moisture content of the organic resource, and drying is usually performed as a pretreatment. To perform such micronization, heating, and moisture adjustment of the organic resource, a complex configuration combining several devices is required.

[0009] Furthermore, in dry methane fermentation, it is naturally preferable to obtain as much methane gas as possible from organic raw materials as efficiently as possible.

[0010] Therefore, an object of the present invention is to provide a dry methane fermentation system and a dry methane fermentation method that are capable of pretreating organic resources to be subjected to methane fermentation with a simple configuration and that enable efficient methane fermentation. [Means for solving the problem]

[0011] As a result of extensive research to achieve the above-mentioned object, the inventors have discovered that when organic resources to be subjected to dry methane fermentation are mixed and crushed using a mixer-exploder equipped with an Archimedes screw, it is possible to simultaneously pulverize the organic resources, heat them, and adjust the moisture content, despite the relatively simple configuration. Further research led to the present invention.

[0012] The gist of the present invention is as follows. [1] A kneading and explosion machine for kneading and explosion-crushing organic resources to produce pulverized organic resources; a dry methane fermentation tank for accommodating the pulverized organic resource and performing dry methane fermentation; The kneading and explosion crusher has a housing having a cylindrical space and an Archimedes screw disposed in the space, The housing has an inlet for introducing the organic resource at one cylindrical end side of the space, and an outlet for removing the pulverized organic resource at the other cylindrical end side of the space, A dry methane fermentation system, wherein the pitch of the Archimedes screw gradually decreases from the inlet to the outlet. [2] The dry methane fermentation system according to [1], wherein the pitch of the Archimedes screw closest to the outlet is 5.0% or more and 70% or less of the pitch of the inlet. [3] The kneading and crushing machine is configured to crush the organic material near the outlet by 2.5 x 10 5 Over 14.0 x 10 5 N / m 2 The dry methane fermentation system according to [1], wherein the pitch of the Archimedes screw is adjusted so that the following pressure is applied: [4] Further, an acetic acid assimilating fermenter is provided in which the gas and liquid generated from the organic resource in the kneading and crushing machine are fermented with symbiotic acetogenic bacteria to produce a fermented product containing acetic acid, The dry methane fermentation system according to [1], wherein the dry methane fermentation tank is a tank for accommodating the fermented material containing acetic acid together with the pulverized organic resource and performing dry methane fermentation. [5] The dry methane fermentation system according to [1], comprising a plurality of batch-type dry methane fermentation tanks. [6] A first step of kneading and blasting an organic resource using a kneading and blasting machine to obtain a pulverized organic resource; A second step of performing dry methane fermentation on the pulverized organic resource, The kneading and explosion crusher has a housing having a cylindrical space and an Archimedes screw disposed in the space, The housing has an inlet for introducing the organic resource at one cylindrical end side of the space, and an outlet for removing the pulverized organic resource at the other cylindrical end side of the space, The dry methane fermentation method, wherein the pitch of the Archimedes screw gradually decreases from the inlet to the outlet. [7] The dry methane fermentation method according to [6] further comprises a third step of producing a fermented product containing acetic acid from the gas and liquid produced from the organic resource in the kneading and explosion mill using a symbiotic acetogenic bacteria group, and in the second step, dry methane fermentation is carried out on the pulverized organic resource and the fermented product containing acetic acid. [8] Repeating the first step and the second step; In the second step, the methane fermentation is carried out in a batch dry methane fermenter, [6] The dry methane fermentation method according to [6], wherein in the second step or later, the pulverized organic resource is introduced into the batch-type dry methane fermenter different from the batch-type dry methane fermenter into which the pulverized organic resource was introduced in the previous second step. [Effects of the Invention]

[0013] As described above, according to the present invention, it is possible to provide a dry methane fermentation system and a dry methane fermentation method that are capable of pretreating organic resources to be subjected to methane fermentation with a simple configuration and that enable efficient methane fermentation. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram for explaining the process of decomposition of organic resources by methane fermentation. [Figure 2] FIG. 2 is a configuration diagram of a dry methane fermentation system according to one embodiment of the present invention. [Figure 3] FIG. 3 is a longitudinal cross-sectional view of a kneading and explosion machine provided in the dry methane fermentation system shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view in the width direction of the kneading and explosion crusher shown in FIG. [Figure 5] FIG. 5 is a perspective view showing the vicinity of the outlet of the kneading and explosion crusher shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the dry methane fermentation apparatus and the dry methane fermentation method according to the present invention will be described in detail below with reference to the drawings.

[0016] <1. Principle of dry methane fermentation> Prior to describing preferred embodiments of the present invention, an outline of general methane fermentation will be first described. Figure 1 is a schematic diagram for explaining the process of decomposition of organic resources in methane fermentation.

[0017] Methane fermentation is a method of fermenting organic resources derived from living organisms under anaerobic conditions, recovering the fermentation heat and methane gas, and using them as energy or chemical raw materials. Organic resources generally come from waste materials that have no other uses, such as livestock waste and food waste.

[0018] Organic resources are usually composed of polymeric organic matter, which can be broadly classified into proteins, lipids, carbohydrates, etc. As shown in Figure 1, these polymeric organic matter are broken down by hydrolytic microorganisms into their constituent units, amino acids, glycerin and fatty acids, and low-molecular-weight organic matter such as sugars (e.g., glucose) (catabolic reaction (1)).

[0019] Next, the hydrolyzed low-molecular-weight organic matter is decomposed into volatile fatty acids (VFAs) such as propionic acid, butyric acid, and isobutyric acid by the oxidative action of acid-producing bacteria (catabolic reaction (2)).The volatile fatty acids are then decomposed into hydrogen, carbon dioxide, acetic acid, and other substances by syntrophic acetogenic bacteria (catabolic reaction (3)).

[0020] Methanogenic archaea use this hydrogen, carbon dioxide, and acetic acid as energy sources to produce methane (catabolic reactions (4) and (5)). Specifically, acetic acid is broken down into methane (CH4) and carbon dioxide (CO2) by acetic acid-utilizing methanogenic bacteria in the reaction shown below (Equation 1) (catabolic reaction (4)). Hydrogen reacts with carbon dioxide (CO2) by hydrogen-utilizing methanogenic bacteria in the reaction shown below (Equation 2), producing methane (CH4) and water (H2O) (catabolic reaction (5)).

[0021] (Formula 1) CH3COOH→CH4+CO2 (Formula 2) 4H2+CO2→CH4+2H2O

[0022] Gas containing CH4 and CO2 produced by decomposition of organic matter is called "biogas." Biogas obtained from a generally managed methane fermentation tank is composed of, for example, approximately 55% to 60% by mass of methane, approximately 35% to 40% by mass of carbon dioxide, approximately 2% by mass of hydrogen sulfide, 2% by mass or less of nitrogen, 2% by mass or less of oxygen, and 1% by mass or less of hydrogen.

[0023] As mentioned above, the microbial community in a methane fermentation tank generally consists of a bacterial community that decomposes high molecular weight organic matter and a methanogenic archaea community that produces methane. Usually, methane fermentation is carried out using a single methane fermentation tank, so the above reactions occur simultaneously in the single methane fermentation tank.

[0024] There are two known types of methane fermentation: thermophilic methane fermentation, in which the decomposition rate accelerates at approximately 55°C, and mesophilic methane fermentation, in which the decomposition rate accelerates at approximately 35°C. Because thermophilic methane fermentation decomposes organic matter faster than mesophilic methane fermentation, it can recover approximately two to four times as much biogas as mesophilic methane fermentation. High temperatures are also expected to be effective in killing pathogenic bacteria. However, thermophilic methane fermentation requires a greater amount of heat energy to maintain the equipment compared to mesophilic methane fermentation.

[0025] High temperatures are expected to be effective in killing pathogenic bacteria, so up until now, most research aimed at killing pathogenic bacteria has used high-temperature treatment for methane fermentation. However, this has the disadvantage of requiring a large amount of heat energy to maintain the facility, so most methane fermentation facilities currently use mesophilic methane fermentation.

[0026] Furthermore, the fermentation residue discharged after methane fermentation contains fertilizer components such as inorganic and organic nitrogen (N), phosphorus (P), and potassium (K), making it possible to use the fermentation residue as fertilizer for crop cultivation.

[0027] <2. Dry methane fermentation equipment> Next, a dry methane fermentation apparatus according to a preferred embodiment of the present invention will be described. Fig. 2 is a configuration diagram of a dry methane fermentation system according to one embodiment of the present invention, Fig. 3 is a longitudinal cross-sectional view of a kneading and exploding machine provided in the dry methane fermentation system shown in Fig. 2, Fig. 4 is a width-wise cross-sectional view of the kneading and exploding machine shown in Fig. 3, and Fig. 5 is a perspective view showing the vicinity of the outlet of the kneading and exploding machine shown in Fig. 3. In the figures, the size of each component is appropriately exaggerated for ease of explanation, and the actual proportions and sizes of each component are not shown.

[0028] The dry methane fermentation system 1 shown in FIG. 2 is an apparatus for fermenting an organic resource 200 by dry methane fermentation to obtain biogas containing methane.

[0029] Examples of the organic resources 200 used in this embodiment include household garbage (e.g., food waste), household waste such as paper waste, animal-derived waste such as sewage sludge and livestock manure, wood waste (e.g., waste wood, sawdust, parks, packaging waste, board scraps, waste chips, felled wood (thinned wood, etc.), pruned branches, and stumps), crop residues (picked leaves, fruit, cut grass, etc.), and plant-derived waste such as waste mushroom beds. Only one of these may be used as the organic resource 200, or two or more may be combined and used as the organic resource 200.

[0030] The dry methane fermentation system 1 includes a crusher 11, a kneading and explosion machine 100, a kneader 13, an acid-producing fermenter 15, a hydrogen-utilizing fermenter 17, an acetic acid-utilizing fermenter 19, a dry methane fermenter 21, a desulfurization device 23, a gas storage tank 25, and a return culture tank 27.

[0031] The crusher 11 crushes the organic resource 200 into pieces of an appropriate size. Examples of the crusher 11 include a cutting chipper, a cutter knife chipper, a hammer crusher, a chain crusher, a single-shaft crusher, and a multi-shaft crusher (e.g., a biaxial crusher), and one of these can be used alone or two or more can be used in combination. The organic resource 200 crushed in the crusher 11 is transferred to the kneading / explosion crusher 100. Note that if only organic resources 200 that are already of an appropriate size are used, the crusher 11 can be omitted.

[0032] The kneading and explosion crusher 100 kneads and explodes an organic resource 200 to produce pulverized organic resource material. The kneading and explosion crusher 100 will be described below with reference to Figures 3 to 5. As shown in Figure 2, the kneading and explosion crusher 100 includes a housing 110, an archimedes screw 120, an outlet 130, side blades 140, an outlet-side blade 150, and a water pipe 160.

[0033] The housing 110 is a casing of the kneading and explosion-crushing machine 100, and includes a cylindrical housing body 111. The housing body 111 forms a cylindrical space 113 in which the Archimedes screw 120 and the like are housed. An opening serving as an inlet is provided above the base end of the housing body 111, and a hopper 115 for charging the organic resource 200 is connected to the opening.

[0034] As described above, the Archimedes screw 120 is disposed in the cylindrical space 113 formed by the housing body 111, with its longitudinal direction aligned with the axial direction of the space 113. The Archimedes screw 120 has its tip 121 inserted into a bearing 133 of the outlet 130 and rotatably fixed thereto. On the other hand, a drive source 170 for rotating the Archimedes screw 120 is connected to the base end 123.

[0035] The Archimedes screw 120 also has a spiral screw blade 125 that runs along its axial direction. As shown in Fig. 4, when viewed perpendicularly to its axis, the screw blade 125 has a circular periphery that corresponds to the inner surface formed by the housing body 111 of the housing 110, and the circle has a diameter that is close to the side blade 140, which will be described later. As the Archimedes screw 120 rotates, the organic resource 200 stored in the space 113 of the housing body 111 is transported toward the outlet 130 as the screw blade 125 rotates and pushes the organic resource 200.

[0036] 3, the helical pitch of the screw blade 125 gradually decreases from the inlet to the outlet 130. Therefore, when the organic resource 200 is transported by the Archimedes screw 120, a pressure corresponding to the pitch of the screw blade 125 is applied to the organic resource 200.

[0037] The pitch of the screw blades 125 of the Archimedes screw 120 is the smallest P MIN The one closest to the inlet has the largest P MAXHere, the pitch P on the outlet side MIN is the pitch P on the inlet side MAX The ratio can be 5.0% or more and 70% or less, and preferably 10% or more and 50% or less, of the total mass of the organic resource 200. This allows the organic resource 200 to be kneaded while being sufficiently compressed, and also allows the explosive action described below to be sufficiently achieved.

[0038] In addition, the pitch of the Archimedes screw 120 is 2.5 x 10 5 Over 14.0 x 10 5 N / m 2 It is preferable that the pitch of the Archimedes screw 120 is adjusted so that a pressure of 4.0 × 10 or less is applied to the organic resource near the outlet. This makes it possible to obtain a sufficient blasting effect, which will be described later, and to sufficiently compress the organic resource 200. More preferably, the pitch of the Archimedes screw 120 is adjusted so that a pressure of 4.0 × 10 or less is applied to the organic resource near the outlet. 5 Over 12.0 x 10 5 N / m 2 The following pressures are applied:

[0039] 3 and 5, outlet 130 is disk-shaped and is attached to the tip side of housing body 111 of housing 110 so as to seal the cylinder formed by housing body 111. As shown in Fig. 5, outlet 130 has a plurality of through-holes 131, and pulverized organic resource 200 is pushed out from housing 110 to the outside through these through-holes 131. Furthermore, outlet 130 has a bearing 133 at its center that receives the shaft of archimedes screw 120.

[0040] A plurality of side blades 140 are arranged on the inner surface of the casing body 111 along the axial direction so as to surround the periphery of the archimedes screw 120. As shown in FIG. 5, the side blades 140 are arranged so as to abut or be adjacent to the screw blades 125 of the archimedes screw 120. When the screw blades 125 rotate, the organic resource 200 introduced into the casing 110 rotates in the circumferential direction of the archimedes screw 120 and abuts against the side blades 140. The organic resource 200 is then further rotated by the archimedes screw 120, and is subjected to shearing force by the abutting side blades 140, thereby being sheared and ground. Furthermore, the side blades 140 act as baffles, stirring the organic resource 200.

[0041] The outlet-side blade 150 is attached to the tip side (the outlet side) of the archimedes screw 120. The outlet-side blade 150 is rotatable relative to the housing 110 together with the rotation of the archimedes screw 120. The outlet-side blade 150 cuts the organic resource 200 extruded from the outlet 130.

[0042] The water supply pipe 160 is a pipe that supplies water into the space 113 from the side of the housing 110. An on-off valve 161 is provided midway along the water supply pipe 160, and by operating this valve, it is possible to start and stop the supply of water into the space 113 and adjust the amount of water supplied. For example, excessive heat may be generated due to friction, compression, etc. of the organic resource 200 caused by the rotation of the Archimedes screw 120. In such cases, by supplying water through the water supply pipe 160, the water acts as a lubricant and can suppress excessive friction of the organic resource 200.

[0043] When the organic resource 200 is fed into the kneading and explosion crusher 100 described above and the Archimedes screw 120 rotates, the organic resource 200 is conveyed toward the discharge port 130 while rotating. In this case, the organic resource 200 is subjected to shearing force due to the relative movement of the side blades 140 and the screw blades 125, and is crushed, ground, and kneaded. In addition, as the pitch of the screw blades 125 gradually decreases toward the discharge port 130, the organic resource 200 is gradually compressed, generating heat. As a result, the organic resource 200 softens due to the action of heat, accelerating the crushing, grinding, and kneading described above.

[0044] Then, near the outlet 130, the pressure is suddenly released, causing the organic resource 200 to expand, burst, and be exploded and released from the kneading and explosion-crushing machine 100. Through the above-mentioned action, the organic resource 200 is pulverized into pulverized organic resource material.

[0045] The kneading and explosion action of the organic resource 200 by such a kneading and explosion machine 100 is particularly effective for fibrous organic resources 200, such as plant resources such as wood resources. Plant resources are mainly composed of fibers such as cellulose and hemicellulose. Fibers have high tensile strength and are difficult to defibrate by simple cutting. However, by pulverizing and grinding the organic resource 200 due to the rotation of the archimedes screw 120 and by blasting at the discharge port 130, the fiber is sufficiently defibrated and refined, making it easier for microbial groups to come into contact with the fiber during fermentation.

[0046] In particular, wood resources, among plant resources, have lignin, a hard polymer, attached to the periphery of sugars such as cellulose that make up the fiber, and lignin inhibits the decomposition of sugars by microorganisms. On the other hand, lignin softens when heated. In the kneading and explosion machine 100, the organic resource 200 is kneaded and exploded while being heated, so that the lignin attached to the fiber softens and fiber defibration easily progresses.

[0047] Furthermore, when the kneading and explosion-crushing machine 100 is used, the organic resource 200 is heated, and therefore some of the moisture is released from the organic resource 200 and becomes steam or a liquid separated from the solid matter of the organic resource 200. This makes it easier to adjust the moisture content in the subsequent kneader 13.

[0048] Furthermore, the organic resource 200 typically contains moisture. When pressurized and heated in the presence of moisture, some components of the organic resource 200 decompose and / or denature. For example, starch and protein are denatured by heating, making them susceptible to the action of enzymes released by the microorganisms during fermentation.

[0049] In particular, natural starch particles are generally not susceptible to enzymatic action in their original state. Specifically, starch particles are formed by regularly arranged molecules and are insoluble in water. Therefore, in this state, enzymes and starch molecules are less likely to bond, making them less susceptible to enzymatic action. Therefore, it is preferable to heat these starch particles together with water to gelatinize them and turn them into a gel. The gelatinized starch particles lose their regularity and water is absorbed into the starch molecules, making it easier for enzymes to penetrate into the starch molecules.

[0050] In addition, sugars such as modified starch, cellulose, and hemicellulose are partially hydrolyzed and converted into monosaccharides such as glucose and various oligosaccharides with relatively small molecular weights. Furthermore, proteins are also partially hydrolyzed and converted into smaller molecules. In this process, organic acids present in the organic resource 200 act as acid catalysts for the hydrolysis. These decomposition products, such as monosaccharides, oligosaccharides, and amino acids, are soluble in water and are eluted from the organic resource 200.

[0051] In this way, components that have been decomposed and / or denatured are generally susceptible to the action of enzymes released from the microorganisms during fermentation, and are in a state where they are easily decomposed. Furthermore, the solubilized matter in the organic resource 200 will dissolve in the heated water even if it has not been decomposed.

[0052] As described above, when the kneading and explosion treatment is carried out by the kneading and explosion crusher 100, the organic resource 200 is pulverized and defibrated by crushing, grinding, and explosion, and at the same time, the organic resource 200 is kneaded. At the same time, the components in the organic resource 200 are denatured and decomposed. In this way, when the kneading and explosion treatment is carried out by the kneading and explosion crusher 100, the organic resource 200 is simultaneously subjected to physical and chemical effects, and is brought into a state in which it is easy to ferment.

[0053] Furthermore, among the components of the organic resource 200, components with relatively small molecular weights are dissolved in the moisture and steam released from the organic resource 200. That is, when the kneading and explosion treatment is performed by the kneading and explosion-crushing machine 100, component separation is also performed at the same time.

[0054] The organic resource explosion product, which is mainly composed of solids, of the organic resource 200 that has been subjected to the kneading and explosion treatment is transported to the kneader 13. In addition, the released gas and liquid from the organic resource 200 are transported to the acetic acid assimilating fermenter 19.

[0055] The kneader 13 is a device that performs kneading to mix the pulverized organic resource material exploded in the kneading and explosion machine 100 with seed bacteria. Examples of the kneader 13 include a single-shaft mixer, a multi-shaft mixer (e.g., a two-shaft mixer), an open roll, a pressure kneader, an internal mixer, and a Banbury mixer, and one of these can be used alone or two or more can be used in combination. The pulverized organic resource material mixed with the seed bacteria in the kneader 13 is transferred to an acid-producing fermenter 15. Note that in this embodiment, reverting bacteria obtained as fermentation residue after dry methane fermentation is transferred and charged into the kneader 13 as seed bacteria.

[0056] The acid-producing fermenter 15 is a fermenter for performing primary fermentation on the pulverized organic resource mixed with the seed culture to produce a primary fermentation product and a gas containing hydrogen and carbon dioxide. In this embodiment, the primary fermentation in the acid-producing fermenter 15 decomposes the pulverized organic resource into volatile fatty acids (VFAs) such as propionic acid, butyric acid, and isobutyric acid.

[0057] The acid-producing fermenter 15 is configured to be sealable during primary fermentation, thereby ensuring an anaerobic environment during primary fermentation and preventing leakage of generated gaseous components such as hydrogen and carbon dioxide. The acid-producing fermenter 15 is also equipped with a pressure gauge, a thermometer, and a temperature control device, allowing for temperature control according to the conditions of primary fermentation. The acid-producing fermenter 15 may also be equipped with an appropriate stirring device to enable stirring of the pulverized organic resource material. The acid-producing fermenter 15 is also equipped with a pressure reducing valve, which allows the generated gaseous components to be transferred to the hydrogen-assimilating fermenter 17 when the pressure of the gaseous components reaches a predetermined level or higher.

[0058] The bacterial community contained in the acid-producing fermenter 15 during primary fermentation is essentially a complex community of microorganisms derived from the seed culture. Of the catabolic reactions shown in Figure 1, catabolic reactions (1) and (2) primarily occur in the acid-producing fermenter 15, where organic resources (high molecular weight organic matter) are decomposed into low molecular weight organic matter and then into a mixture containing volatile fatty acids. Gases containing hydrogen and carbon dioxide are also produced as a result of the decomposition of high molecular weight organic matter into volatile fatty acids during primary fermentation.

[0059] Therefore, the complex microbial consortium that can be accommodated in the acid-producing fermenter 15 can include activated hydrolytic bacteria and acidogenic bacteria. Furthermore, since the catabolic reactions shown in Fig. 1 occur in parallel, the complex microbial consortium that can be accommodated in the acid-producing fermenter 15 can also include symbiotic acetogenic bacteria involved in the catabolic reaction (3) (e.g., acetate-oxidizing bacteria belonging to the order Thermotogales, which are thermophilic bacteria, and decomposing bacteria of the order Clostridiales, which decompose proteins and carbohydrates), and methanogenic archaea involved in the catabolic reactions (4) and (5) (hydrogen-utilizing methanogens, such as Methanoculleus thermopyilus, Methanobacteriaceae, and Methanothermaceae, as well as acetate-utilizing methanogens, such as Metyanosarcina thermophia).

[0060] Furthermore, if the pressure exceeds a predetermined level, some of the gaseous components (hydrogen, carbon dioxide, steam, etc.) produced in the acid-producing fermenter 15 are transferred via a pressure reducing valve to the hydrogen-assimilation fermenter 17. The remainder of the primary fermentation product (a mixture of liquid and solid components) and gaseous components (hydrogen, carbon dioxide, steam, etc.) produced in the acid-producing fermenter 15 are transferred to the dry methane fermenter 21.

[0061] The hydrogen-assimilating fermenter 17 is a tank that stores the gas components (hydrogen, carbon dioxide, steam, etc.) generated in the acidogenic fermenter 15 and ferments them with hydrogen-assimilating bacteria. The hydrogen-assimilating bacteria in the hydrogen-assimilating fermenter 17 use hydrogen and carbon dioxide as substrates to produce methane. The microorganisms that may be present in the hydrogen-assimilating fermenter 17 include those that were present in the acidogenic fermenter 15, but the hydrogen-assimilating bacteria are particularly active. The stored gas components (hydrogen, carbon dioxide, steam, etc.) are then converted to methane by the catabolic reaction (4) shown in FIG. 1.

[0062] The hydrogen-assimilating fermenter 17 is configured to be sealable during fermentation, thereby ensuring an anaerobic environment during fermentation and preventing leakage of generated gases, such as methane. Furthermore, the hydrogen-assimilating fermenter 17 is equipped with a pressure gauge, a thermometer, and a temperature control device, allowing for temperature control according to the fermentation status. The hydrogen-assimilating fermenter 17 may also be equipped with an appropriate stirring device to allow stirring of the fermented product in the hydrogen-assimilating fermenter 17.

[0063] Furthermore, in this embodiment, the hydrogen-assimilating fermenter 17 includes a porous inorganic medium. By accommodating such a porous inorganic medium in the hydrogen-assimilating fermenter 17, a medium for the hydrogen-assimilating bacteria is ensured and a sufficient reaction field for the methane production reaction by the hydrogen-assimilating methanogens is provided. In particular, because the substrate in the hydrogen-assimilating fermenter 17 is a gas, the contact interface between the hydrogen-assimilating bacteria and the substrate is generally limited. However, because the porous inorganic medium is porous, a sufficient contact interface between the hydrogen-assimilating bacteria and the substrate is provided, and fermentation is sufficiently promoted.

[0064] The porous inorganic medium may be in any shape, such as granular, plate-like, block-like, ring-like, ball-like, pellet-like, etc. Furthermore, multiple porous inorganic media of different shapes may be combined. Among the above-mentioned types, the porous inorganic medium is preferably granular, and therefore preferably contains porous inorganic granules. Such porous inorganic granules themselves have a relatively large surface area, and pores resulting from the porosity are generated on the surface of the porous inorganic granules, making it possible to obtain a larger contact interface compared to other shapes. Furthermore, when the porous inorganic medium contains porous inorganic granules, stirring of the fermented material in the hydrogen-assimilating fermenter 17 is easy.

[0065] In addition, the porous inorganic culture medium may be made of any material, such as glass, ceramics, activated carbon, zeolite, humic substances, etc., and one of these may be used alone or two or more may be used in combination.

[0066] Thus, the porous inorganic particulates can be, for example, one or more selected from the group consisting of glass foam particulates, zeolite particulates, ceramic particulates, and activated carbon.

[0067] Among the above, glass foam granules have an appropriate pore size and water retention capacity, and are particularly suitable as a porous inorganic medium for the hydrogen-utilizing fermenter 17, which requires a reaction at the gas-liquid interface.

[0068] The particle size of the porous inorganic granules described above, based on JIS Z8815-1994, is not particularly limited, but is, for example, 0.30 mm to 8.0 mm, preferably 0.50 mm to 6.0 mm, and more preferably 1.0 mm to 3.0 mm. When the particle size of the porous inorganic granules is within the above range, stirring of the fermented product in the hydrogen-assimilating fermenter 17 can be facilitated, and fermentation can be further promoted.

[0069] The fermented product (a mixture of liquid and solid components) and gas components (methane, steam, etc.) produced in the hydrogen assimilative fermenter 17 are transported to a dry methane fermenter 21 .

[0070] The acetic acid-utilizing fermenter 19 is a tank that receives the gas and liquid released in the kneading and explosion-crushing machine 100 and produces a fermented product containing acetic acid by the acid-producing bacteria and symbiotic acetogenic bacteria. As described above, the gas and liquid released in the kneading and explosion-crushing machine 100 contain low-molecular-weight compounds such as relatively low-molecular-weight sugars (monosaccharides, oligosaccharides, etc.), low-molecular-weight peptides, and amino acids. Therefore, in the acetic acid-utilizing fermenter 19, the catabolic reactions (2) and (3) shown in FIG. 1 mainly proceed to decompose these compounds. The microbial communities that may be present in the acetic acid-utilizing fermenter 19 may include those that were present in the acid-producing fermenter 15, but the acid-producing bacteria and symbiotic acetogenic bacteria are particularly activated.

[0071] The acetic acid assimilating fermenter 19 is configured to be sealable during fermentation, thereby ensuring an anaerobic environment during fermentation and preventing leakage of generated gases, such as hydrogen and carbon dioxide. The acetic acid assimilating fermenter 19 is further equipped with a pressure gauge, a thermometer, and a temperature control device, allowing temperature control according to the fermentation status. The acetic acid assimilating fermenter 19 may also be equipped with an appropriate stirring device to allow stirring of the fermented product in the acetic acid assimilating fermenter 19. The acetic acid assimilating fermenter 19 may also be configured to allow external addition of microorganisms, such as symbiotic acetogenic bacteria.

[0072] The fermentation products (for example, acetic acid, etc.) and gas components (hydrogen, carbon dioxide, etc.) produced in the acetate-utilizing fermenter 19 are transported to a dry methane fermenter 21.

[0073] The dry methane fermentation tank 21 contains the primary fermentation product of the crushed organic resource obtained in the acid-producing fermentation tank 15, the methane-containing fermentation product obtained in the hydrogen-assimilating fermentation tank 17, and the acetic acid-containing fermentation product obtained in the acetic acid-assimilating fermentation tank 19, and performs dry methane fermentation.

[0074] Furthermore, in this embodiment, the dry methane fermenter 21 is provided with a plurality of batch-type dry methane fermenters 21A to 21C. In this way, by providing the dry methane fermenter 21 with a plurality of batch-type dry methane fermenters 21A to 21C, after the material is charged, fermentation can be carried out in one of the batch-type dry methane fermenters 21A to 21C until the fermentation reaches a target stage without opening or closing the dry methane fermenter 21A to 21C, and leakage of the produced biogas can be suppressed.

[0075] That is, for example, after materials are added to the dry methane fermenter 21A and fermentation is initiated, if new materials to be fermented are produced in the dry methane fermenter 21, the materials can be added to the dry methane fermenter 21B and fermentation can be initiated thereafter. In this way, by sequentially adding materials to different dry methane fermenters 21A-C and carrying out fermentation, it is possible to complete fermentation up to the target stage in each of the dry methane fermenters 21A-21C without opening or closing the fermenter. The biogas generated in the dry methane fermenter 21 is the target of the dry methane fermentation system 1, but conventionally, leakage of biogas during methane fermentation has been a problem. However, in this embodiment, this problem is prevented by providing multiple dry methane fermenters 21A-21C.

[0076] Furthermore, the fermented products stored in the dry methane fermenters 21A-21C contain relatively large amounts of hydrogen, carbon dioxide, and acetic acid. Therefore, the dry methane fermenters 21A-21C contain microorganisms derived from the acidogenic fermenter 15, the acetate-utilizing fermenter 19, and the hydrogen-utilizing fermenter 17. Among these, methanogenic archaea are primarily activated, particularly hydrogen-utilizing methanogens and acetate-utilizing methanogens. Hydrogen and carbon dioxide are then converted to methane primarily by the catabolic reaction (4) shown in FIG. 1. Furthermore, the fermented product containing a large amount of acetic acid is converted to methane primarily by the catabolic reaction (5) shown in FIG. 1. The other catabolic reactions (1)-(3) shown in FIG. 1 occur in parallel with the catabolic reactions (4) and (5) as appropriate, depending on the amount of substrate present. The methane-containing gas produced in the dry methane fermenter 21 is transferred as biogas to the gas storage tank 25 via the desulfurization device 23. Furthermore, a part of the fermentation residue after fermentation is transported to a bacteria returning tank 27, and the remainder is used as organic compost 210.

[0077] Each of the dry methane fermentation tanks 21A-21C is configured to be sealable during fermentation, thereby ensuring an anaerobic environment during fermentation and preventing leakage of generated gases, such as methane. Each of the dry methane fermentation tanks 21A-21C is also equipped with a pressure gauge, a thermometer, and a temperature control device, allowing temperature control according to the fermentation status. Each of the dry methane fermentation tanks 21A-21C may also be equipped with an appropriate stirring device to allow stirring of the fermented product in each of the dry methane fermentation tanks 21A-21C. Each of the dry methane fermentation tanks 21A-21C may also be configured to allow a target microorganism group to be added from outside.

[0078] In addition, in the illustrated embodiment, only three batch-type dry methane fermenters 21A to 21C are specifically described as the dry methane fermenter 21, but the dry methane fermenter 21 can be provided with, for example, 1 to 20, preferably 2 to 15, more preferably 3 to 10 dry methane fermenters, and this can be changed depending on the method of use.

[0079] The desulfurization device 23 is a device for removing sulfur oxides (SOx) from the biogas. The desulfurization device 23 may be any device that can remove sulfur compounds, and desulfurization devices that employ various methods, such as wet methods employing the lime-gypsum method, magnesium hydroxide method, soda method, etc., dry methods such as activated carbon adsorption method, electron beam method, lime ash method, furnace desulfurization method, and semi-dry methods such as spray drying method, can be appropriately used. The gas storage tank 25 is a pressure-resistant tank that stores the biogas desulfurized in the desulfurization device 23.

[0080] The return culture tank 27 is a tank for fermenting a part of the fermentation residue produced in the dry methane fermenter 21 to produce seed cultures for each fermenter including the acid-producing fermenter 15 .

[0081] The reconstitution tank 27 is configured to be airtight during fermentation, thereby ensuring an anaerobic environment during fermentation. Furthermore, the reconstitution tank 27 is equipped with a pressure gauge, a thermometer, and a temperature control device, and is configured to be able to control the temperature according to the fermentation status. Furthermore, the vinegar reconstitution tank 27 may be equipped with an appropriate stirring device so that the fermented product in the reconstitution tank 27 can be stirred. Furthermore, the reconstitution tank 27 may be configured so that a desired group of microorganisms can be added from outside.

[0082] <3. Dry methane fermentation method> Next, a dry methane fermentation method according to a preferred embodiment of the present invention will be described together with a method of using the above-described dry methane fermentation system 1.

[0083] The dry methane fermentation method of the present invention includes a first step of kneading and exploding an organic resource using a kneading and explosion machine to obtain a pulverized organic resource, and a second step of performing dry methane fermentation on the pulverized organic resource, The kneading and crushing machine has a housing with a cylindrical space and an Archimedes screw arranged within the space, the housing having an inlet at one cylindrical end of the space for feeding the organic resource and an outlet at the other cylindrical end of the space for removing the crushed organic resource, and the pitch of the Archimedes screw gradually decreases from the inlet to the outlet.

[0084] 3 to 5 is used as the kneading and explosion machine in this embodiment, but it goes without saying that a kneading and explosion machine other than the kneading and explosion machine 100 can be used in the present invention. Also, in this embodiment, an example using the dry methane fermentation system 1 described above will be described, but it goes without saying that a dry methane fermentation system other than the dry methane fermentation system 1 can be used in the dry methane fermentation method of the present invention.

[0085] (3.1.) Crushing process In this step, the organic resource 200 is crushed into pieces of an appropriate size using a crusher 11. The size of the crushed pieces is not particularly limited as long as it is compatible with the kneading and explosion crusher 100 used in the next step, but can be, for example, 50 mm or less. Note that if the organic resource 200 already has an appropriate size, this step is omitted.

[0086] (3.2.) Kneading and Explosion Process (First Process) Next, the crushed organic resource 200 is kneaded and exploded by the kneading and explosion crusher 100. Specifically, the crushed organic resource 200 is fed into the space 113 from the hopper 115 of the casing 110 while the Archimedes screw 120 is rotated.

[0087] As a result, the organic resource 200 is conveyed by the archimedes screw 120 toward the discharge port 130, while being kneaded and crushed by the relative motion between the side blades 140 and the screw blades 125 of the archimedes screw 120. Furthermore, as the organic resource 200 is conveyed by the archimedes screw 120, the pitch gradually decreases, causing it to be compressed and heated. This heating also promotes the above-mentioned crushing and heating.

[0088] Then, near the outlet 130, the pressure is suddenly released, causing the organic resource 200 to expand, burst, and be exploded and released from the kneading and explosion-crushing machine 100. Through the above-mentioned action, the organic resource 200 is pulverized into pulverized organic resource material.

[0089] Furthermore, since the organic resource 200 is heated, some of the moisture is released from the organic resource 200 and becomes steam or a liquid separated from the solid matter of the organic resource 200. This makes it easier to adjust the moisture content in the kneader 13 in the subsequent stage.

[0090] Furthermore, the organic resource 200 typically contains moisture. When pressurized and heated in the presence of moisture, some components of the organic resource 200 decompose and / or denature. For example, starch and protein are denatured by heating, making them susceptible to the action of enzymes released by the microorganisms during fermentation. Furthermore, the solubilized matter in the organic resource 200 will dissolve in the heated water even if it has not been decomposed.

[0091] As described above, when the kneading and explosion treatment is carried out by the kneading and explosion crusher 100, the organic resource 200 is pulverized and defibrated by crushing, grinding, and explosion, and at the same time, the organic resource 200 is kneaded. At the same time, the components in the organic resource 200 are denatured and decomposed. In this way, when the kneading and explosion treatment is carried out by the kneading and explosion crusher 100, the organic resource 200 is simultaneously subjected to physical and chemical effects, and is brought into a state in which it is easy to ferment.

[0092] Furthermore, among the components of the organic resource 200, components with relatively small molecular weights are dissolved in the moisture and steam released from the organic resource 200. In other words, when the kneading and explosion treatment is performed by the kneading and explosion crusher 100, component separation is also performed at the same time. Furthermore, the release of moisture from the organic resource 200 makes it possible to dehydrate and dry the resulting pulverized organic resource, facilitating moisture adjustment in the subsequent primary fermentation and dry methane fermentation.

[0093] Furthermore, it is preferable to carry out the kneading and explosion so that the moisture content of the organic resource 200 is, for example, 60% by mass or more and 80% by mass or less, and preferably 70% by mass or more and 75% by mass or less. Here, in this embodiment, the water content refers to the ratio of the mass of water to the mass of the entire composition.

[0094] The moisture content of the organic resource 200 can be adjusted, for example, by adjusting the kneading and explosion time by the kneading and explosion crusher 100. This is because the longer the kneading and explosion time, the more moisture is removed from the organic resource 200, and the more drying progresses. For example, when the moisture content of the organic resource 200 is 90% by mass or more, it is preferable to perform kneading and explosion for 30 minutes or more. On the other hand, when the moisture content of the organic resource 200 is less than 90% by mass, it is preferable to perform kneading and explosion for less than 30 minutes.

[0095] In addition, in order to ensure an anaerobic atmosphere in each fermentation process described below, it is preferable to cool the temperature of the pulverized organic resource material as quickly as possible after kneading and explosion, for example, within one hour, to 70°C or less, particularly 55°C to 65°C.

[0096] After kneading and explosion, the resulting pulverized organic material is subjected to a kneading process and the subsequent acidogenic fermentation process. The liquid and gas separated from the pulverized organic material are then subjected to an acetic acid assimilative fermentation process.

[0097] (3.3.) Mixing process In this process, the pulverized organic resource material and the seed culture are mixed by kneading them together. Specifically, the pulverized organic resource material and the seed culture are placed in a kneader 13 and kneaded. The kneading time is not particularly limited and can be, for example, from 10 minutes to 180 minutes, preferably from 30 minutes to 60 minutes. In addition, in this process, the ratio of the pulverized organic resource material to the seed culture can be, for example, within a range of 5:5 to 9:1, preferably 6:4 to 8:2, by mass.

[0098] The seed culture can be a revertant culture obtained after methane fermentation. Alternatively, a separate seed culture can be prepared and mixed. The seed culture can be obtained, for example, by mixing polyphenols produced by the metabolism of microorganisms, trace elements such as minerals, and any organic matter, and then subjecting the mixture to anaerobic fermentation.

[0099] The resulting inoculum may include microbial communities such as hydrolytic bacteria, acidogenic bacteria, symbiotic acetogenic bacteria (e.g., thermophilic acetate-oxidizing bacteria belonging to the order Thermotogales, and decomposing bacteria of the order Clostridiales that degrade proteins and carbohydrates), and methanogenic archaea (hydrogen-utilizing methanogens such as Methanoculleus thermopyilus, Methanobacteriaceae, and Methanothermaceae, as well as acetate-utilizing methanogens such as Metyanosarcina thermophia). Research has shown that in methane fermentation, approximately 80% of methane production is due to acetate-oxidizing bacteria and hydrogen-utilizing methanogens, while approximately 20% is due to acetate-utilizing methanogens. In methane fermentation, methane is produced through highly efficient acetic acid decomposition by the combined action of acetate-oxidizing bacteria and hydrogen-utilizing methanogens.

[0100] The moisture content of the pulverized organic resource material after mixing with the seed culture in this step is not particularly limited, but can be, for example, 50% to 80% by mass, and preferably 55% to 70% by mass. When the moisture content of the pulverized organic resource material is within this range, dry methane fermentation can be carried out effectively in the dry methane fermentation step described below.

[0101] (3.4.) Acidogenic fermentation process Next, the mixed pulverized organic resource material is subjected to primary fermentation to obtain a primary fermentation product of the pulverized organic resource material and a gas containing hydrogen and carbon dioxide. In this embodiment, the primary fermentation is carried out in an anaerobic atmosphere in an acid-producing fermenter 15.

[0102] In this embodiment, the pulverized organic material undergoes primary fermentation in the acid-producing fermenter 15, where it is decomposed into volatile fatty acids (VFAs) such as propionic acid, butyric acid, and isobutyric acid. Specifically, of the catabolic reactions shown in FIG. 1, catabolic reactions (1) and (2) primarily occur in the acid-producing fermenter 15, where the organic material, which is a high-molecular-weight organic material, is converted into low-molecular-weight organic material and then into volatile fatty acids. In this process, the hydrolytic bacteria and acid-producing bacteria are primarily activated. Furthermore, because the catabolic reactions shown in FIG. 1 occur in parallel, some of the catabolic reactions (3) to (5) naturally also occur in this process. Furthermore, in this process, hydrogen and carbon dioxide are produced as the high-molecular-weight organic material is decomposed into volatile fatty acids by primary fermentation.

[0103] The fermentation temperature in the primary fermentation is not particularly limited and is, for example, 28° C. to 60° C., preferably 30° C. to 55° C. This allows the hydrolytic bacteria and acid-producing bacteria to be sufficiently activated, allowing the desired catabolic reaction to proceed sufficiently.

[0104] The hydraulic retention time (HRT) in the primary fermentation is not particularly limited, but is, for example, 30 hours or more and 120 hours or less, preferably 60 hours or more and 80 hours or less.

[0105] The moisture content of the pulverized organic resource material during primary fermentation in this step is not particularly limited, but can be, for example, 50% to 80% by mass, preferably 55% to 70% by mass. When the moisture content of the pulverized organic resource material is within this range, primary fermentation proceeds efficiently and dry methane fermentation can be carried out effectively in the dry methane fermentation step described below.

[0106] Furthermore, the generated gas components (hydrogen and carbon dioxide) may be subjected to the hydrogen-assimilating methanogenic fermentation step described below even during primary fermentation. For example, a pressure reducing valve may be provided in the acid-producing fermenter 15 that opens when the pressure exceeds a predetermined level, so that when a certain amount of gas accumulates, it is transferred to the hydrogen-assimilating fermenter 17. This prevents a decrease in the reaction rates of the catabolic reactions (1) and (2) due to excessive hydrogen accumulation.

[0107] After primary fermentation in this process, if the pressure exceeds a predetermined level, some of the gaseous components (hydrogen, carbon dioxide, steam, etc.) are supplied to the hydrogen-utilizing methane production process via a pressure reducing valve. The primary fermentation product (a mixture of liquid and solid components) and the remainder of the gaseous components (hydrogen, carbon dioxide, steam, etc.) produced in this process are supplied to the dry methane fermentation process.

[0108] (3.5.) Hydrogen-utilizing methanogenic fermentation process In this step, the gas components (hydrogen, carbon dioxide, steam, etc.) generated in the acidogenic fermentation step are fermented by hydrogen-assimilating bacteria. In this embodiment, this step can be carried out in an anaerobic atmosphere in a hydrogen-assimilating fermenter 17.

[0109] In this embodiment, the hydrogen-assimilating bacteria produce methane using hydrogen and carbon dioxide as substrates in the hydrogen-assimilating fermenter 17. The microorganisms that may be present in the hydrogen-assimilating fermenter 17 may also be those that were present in the acid-producing fermenter 15, but the hydrogen-assimilating bacteria are particularly activated. The stored gas components (hydrogen, carbon dioxide, steam, etc.) are then converted to methane by the catabolic reaction (4) shown in FIG. 1.

[0110] The fermentation temperature in this step is not particularly limited and is, for example, from 40° C. to 70° C., preferably from 50° C. to 60° C. This allows the hydrogen-assimilating bacteria to be sufficiently activated, allowing the desired catabolic reaction to proceed sufficiently.

[0111] The hydraulic retention time (HRT) in this step is not particularly limited, but is, for example, 30 hours or more and 300 hours or less, preferably 50 hours or more and 200 hours or less.

[0112] In this step, the pH of the liquid component present is not particularly limited, but is, for example, 5.0 to 8.0, preferably 5.5 to 7.5. In addition, in this step, the pressure inside the hydrogen-assimilating fermenter 17 is not particularly limited, but is, for example, 0.10 MPa to 0.90 MPa, preferably 0.15 MPa to 0.25 MPa.

[0113] Furthermore, it is preferable to use a porous inorganic medium as the medium in this step. This ensures a medium for the hydrogen-utilizing bacteria and provides a sufficient reaction field for the methane production reaction by the hydrogen-utilizing methanogens. In particular, since the substrate in this step is a gas, the contact interface between the hydrogen-utilizing bacteria and the substrate is generally limited. However, the porosity of the porous inorganic medium provides a sufficient contact interface between the hydrogen-utilizing bacteria and the substrate, and fermentation is sufficiently promoted. Preferred porous inorganic media are as described above.

[0114] (3.6.) Acetic acid assimilative fermentation step (third step) In this step, the gas and liquid released in the kneading and explosion machine 100 are contained, and a fermentation product containing acetic acid is produced by the symbiotic acetogenic bacteria. In this embodiment, this step can be carried out in an acetic acid assimilating fermenter 19 under an anaerobic atmosphere.

[0115] As mentioned above, the gas and liquid produced in the kneading and explosion process contain low-molecular-weight compounds such as relatively low-molecular-weight sugars (monosaccharides, oligosaccharides, etc.), low-molecular-weight peptides, and amino acids. Therefore, in this process, the catabolic reactions (2) and (3) shown in Figure 1 mainly proceed to decompose these compounds. In this process, acid-producing bacteria and symbiotic acetogenic bacteria are particularly activated.

[0116] The fermentation temperature in this step is not particularly limited and is, for example, from 20° C. to 40° C., preferably from 25° C. to 35° C. This allows the acidogenic bacteria and symbiotic acetogenic bacteria to be sufficiently activated, allowing the desired catabolic reactions to proceed sufficiently.

[0117] The hydraulic retention time (HRT) in this step is not particularly limited, but is, for example, from 24 hours to 168 hours, preferably from 72 hours to 120 hours.

[0118] In this step, the pH of the liquid component present is not particularly limited, but is, for example, 3.5 to 7.0, preferably 4.0 to 6.5. By adjusting the pH of the liquid component within this range, activation of the symbiotic acetogenic bacteria can be further promoted.

[0119] After this step, the fermentation products (for example, acetic acid, etc.) and gas components (methane, water vapor, etc.) that are produced are subjected to a dry methane fermentation step.

[0120] (3.7.) Dry methane fermentation process (second process) In this step, the fermented products produced in the acidogenic fermentation step, the hydrogen-assimilating methanogenic fermentation step, and the acetate-assimilating fermentation step are further subjected to dry methane fermentation to obtain biogas containing methane.

[0121] Here, the hydrogen-assimilating methanogenic fermentation step is carried out after the acidogenic fermentation step, and the acetic acid-assimilating fermentation step is carried out in parallel with the hydrogen-assimilating methanogenic fermentation step and the acidogenic fermentation step. Therefore, fermented products from each step derived from the same organic resource 200 are usually not obtained at the same time. For this reason, dry methane fermentation may be carried out using fermented products from each step derived from different lots of organic resource 200.

[0122] Here, in this embodiment, dry methane fermentation is carried out in a dry methane fermenter 21. The dry methane fermenter 21 has a plurality of batch-type dry methane fermenters 21A to 21C. In this embodiment, each step is usually carried out repeatedly. In such a case, in the second or subsequent steps of this step, it is preferable to carry out dry methane fermentation using a batch-type dry methane fermenter different from the batch-type dry methane fermenter used in the previous step. This makes it possible to suppress the opening and closing of each dry methane fermenter during dry methane fermentation, and to prevent unintended leakage of biogas. More preferably, in the second or subsequent steps of this step, dry methane fermentation is carried out using an unused batch-type dry methane fermenter or a batch-type dry methane fermenter in which dry methane fermentation has been completed.

[0123] In this embodiment, this step is usually carried out under an anaerobic atmosphere. The fermented products resulting from each step of dry methane fermentation contain large amounts of acetic acid and volatile fatty acids. Therefore, in this step, the catabolic reactions (3) to (5) shown in Figure 1 mainly proceed. Therefore, in this step, the symbiotic acetogenic bacteria and methanogenic archaea (especially acetate-utilizing methanogenic fermentation bacteria and hydrogen-utilizing methanogens) are particularly activated.

[0124] The fermentation temperature in this step is not particularly limited, and is, for example, 20°C or higher and 70°C or lower, preferably 25°C or higher and 60°C or lower.

[0125] In particular, it is preferable to set the fermentation temperature to 50°C or higher and 65°C or lower. In methane fermentation tanks that use methane fermentation, the fermentation state may become unstable due to the accumulation of organic acids. An example of an organic acid that is likely to accumulate is propionic acid. However, under the above temperature environment, propionate-oxidizing bacteria and hydrogen-utilizing methanogenic archaea can grow sufficiently simultaneously, reducing the accumulation of propionic acid and activating acetate-utilizing methanogens.

[0126] The hydraulic retention time (HRT) in this step is not particularly limited, but is, for example, 168 hours to 720 hours, preferably 240 hours to 480 hours, and more preferably 288 hours to 432 hours. By setting the HRT in this range, the amount of methane obtained is maximized.

[0127] The moisture content of the fermented material in this step is not particularly limited, but can be, for example, 50% to 80% by mass, preferably 55% to 70% by mass. When the moisture content of the fermented material is within this range, dry methane fermentation can be carried out effectively.

[0128] In this manner, biogas is obtained. The obtained biogas is desulfurized by the desulfurization device 23 and stored in the gas storage tank 25.

[0129] Furthermore, with regard to the fermentation residue after the dry methane fermentation, a part of it is fermented in the reverting bacteria tank 27 and used as reverting bacteria, and the remainder can be used as organic compost 210, for example.

[0130] (3.7.) Reversion culture generation process In this step, the fermentation residue produced in the dry methane fermentation step is fermented in an anaerobic atmosphere to obtain return bacteria (seed bacteria).

[0131] The fermentation temperature in this step is not particularly limited, and is, for example, 20°C or higher and 50°C or lower, preferably 25°C or higher and 45°C or lower. The hydraulic retention time (HRT) in this step is not particularly limited, but is, for example, 24 hours or more and 120 hours or less, preferably 48 hours or more and 96 hours or less. In this step, the pH of the liquid component present is not particularly limited, but is, for example, 6.0 or more and 9.0 or less, preferably 7.0 or more and 8.0 or less.

[0132] <4. Effects> Next, the effects achieved by the dry methane fermentation system 1 and the dry methane fermentation method according to this embodiment will be described.

[0133] In this embodiment, the organic resource 200 is kneaded and exploded using a kneading and explosion crusher 100 equipped with an Archimedes screw 120. In this kneading and explosion crusher, the organic resource 200 is pulverized and defibrated by pulverization, grinding, and explosion, while the organic resource 200 is kneaded. At the same time, the components in the organic resource 200 are heated by the heat generated by compression and are denatured and decomposed. In this way, when the kneading and explosion treatment is performed using the kneading and explosion crusher 100, the organic resource 200 is simultaneously subjected to physical and chemical effects, and is brought into a state in which it is easy to ferment.

[0134] Furthermore, among the components of the organic resource 200, components with relatively small molecular weights are dissolved in the moisture and steam released from the organic resource 200. That is, when the kneading and explosion treatment is performed by the kneading and explosion-crushing machine 100, component separation is also performed at the same time.

[0135] In particular, during the kneading and explosion process using the kneading and explosion crusher 100, moisture is removed from the organic resource (pulverized organic resource) 200. In other words, the organic resource 200 can be dried. This makes it easier to adjust the moisture content during primary fermentation and dry methane fermentation.

[0136] In dry methane fermentation, the moisture content of the material to be fermented is lower than in wet methane fermentation, and for this reason, in the past, drying treatment was often required as a pretreatment. However, in this embodiment, the drying treatment can be essentially performed simultaneously with the above-mentioned kneading and explosion-crushing, and a separate drying treatment can be omitted. As a result, in this embodiment, the device configuration required for pretreatment of dry methane fermentation can be simplified.

[0137] As described above, according to this embodiment, the organic resource 200 can be pretreated using a simple device configuration, and the pretreatment converts the organic resource 200 into a pulverized organic resource suitable for dry methane fermentation. As a result, efficient methane fermentation becomes possible.

[0138] In particular, in this embodiment, the gas and liquid generated during the kneading and explosion process are contained, and a fermentation product containing acetic acid is produced by acid-producing bacteria and symbiotic acetogenic bacteria. The gas and liquid generated during the kneading and explosion process contain many relatively low-molecular-weight substances among the components derived from the organic resource 200. By separately fermenting these low-molecular-weight compartments in an acetic acid-utilizing fermenter 19 together with a microorganism group including symbiotic acetogenic bacteria, it is possible to efficiently produce acetic acid, hydrogen, and carbon dioxide, which serve as substrates for dry methane fermentation.

[0139] That is, in each of the catabolic reactions (1) to (3) shown in FIG. 1, hydrogen is generated as the substrate is broken down into smaller molecules. When these catabolic reactions (1) to (3) occur in parallel, the hydrogen generated by catabolic reactions (1) and (2), which convert high-molecular-weight organic matter into low-molecular-weight organic matter and produce volatile fatty acids, slows the rate of catabolic reaction (3), which produces acetic acid from volatile fatty acids. Similarly, the hydrogen generated by catabolic reaction (3) can also slow the rate of catabolic reactions (1) and (2). In this embodiment, the gas and liquid generated during the kneading and explosion process, which contain relatively low-molecular-weight components, are fermented separately from the fermentation of the pulverized organic resource, thereby preventing such a decrease in reaction rate and, as a result, improving the efficiency of dry methane fermentation.

[0140] Furthermore, in this embodiment, prior to the dry methane fermentation of the pulverized organic resource material, the pulverized organic resource material is subjected to primary fermentation in an acid-producing fermenter 15 to obtain a primary fermented product of the pulverized organic resource material and a gas containing hydrogen and carbon dioxide (acid-producing fermentation step).Then, the primary fermented product of the pulverized organic resource material is subjected to dry methane fermentation in a dry methane fermenter 21 (dry methane fermentation step).

[0141] Furthermore, when the acidogenic fermentation process and the dry methane fermentation process are combined, the primary fermentation in the acidogenic fermentation process is dominated by the above-mentioned catabolic reactions (1) and (2), while the dry methane fermentation in the dry methane fermentation process is dominated by catabolic reactions (3) to (5). Therefore, combining the acidogenic fermentation process and the dry methane fermentation process also prevents the hydrogen produced by catabolic reactions (1) and (2), which convert high molecular weight organic matter into low molecular weight organic matter and produce volatile fatty acids in the dry methane fermentation process, from slowing the rate of catabolic reaction (3), which produces acetic acid from volatile fatty acids, in the dry methane fermentation process. At the same time, the hydrogen produced by catabolic reaction (3) in the acidogenic fermentation process also prevents a slowdown in the rate of catabolic reactions (1) and (2). As a result, the overall efficiency of the dry methane fermentation process is improved.

[0142] As described above, the catabolic reactions (3) to (5) mainly occur in the dry methane fermentation process carried out in the dry methane fermenter 21. Here, the catabolic reaction (3) of volatile fatty acids to acetic acid by the symbiotic acetogenic bacteria is expressed as follows, taking propionic acid as an example. CH3CH2COO - +3H2O → CH3COO - +HCO3 - +H + +3H2 (formula 1)

[0143] Here, the standard free energy ΔG of the reaction expressed by Eq. 0 is +76.1 kJ / mol. Therefore, the reaction represented by Equation 1 is an endothermic reaction that requires heat to be supplied from an external source. Also, the reaction rate of Equation 1 slows down as hydrogen (H2) accumulates.

[0144] On the other hand, the catabolic reaction (4) of hydrogen and carbon dioxide to methane by hydrogen-utilizing methanogens can be expressed as follows: 4H2+HCO3 - +H + →CH4+3H2O (Formula 2)

[0145] Here, the standard free energy ΔG of the reaction expressed by Eq. 0is -135.6 kJ / mol. Therefore, the reaction represented by Equation 2 is an exothermic reaction that does not require an external heat supply. When the catabolic reactions (3) and (4) represented by Equations 1 and 2 are coupled, they are expressed as the following coupled reaction equation: 4CH3CH2COO - +3H2O → CH3COO - +HCO3 - +H + +3CH4 (formula 3)

[0146] Here, the standard free energy of the conjugation reaction, ΔG, is expressed as Eq. 0 is -102.4 kJ / mol. Therefore, the coupled reaction represented by formula 3 is an exothermic reaction that does not require the supply of heat from an external source. Therefore, when the catabolic reactions (3) and (4) represented by formulas 1 and 2 are coupled, the reaction proceeds naturally without the input of heat from an external source. Furthermore, when the catabolic reactions (3) and (4) represented by formulas 1 and 2 are coupled, the hydrogen produced in the catabolic reaction (3) is consumed in equal amounts in the catabolic reaction (4), so no hydrogen accumulates in the coupled reaction. For these reasons, in this embodiment, the dry methane fermentation performed after the primary fermentation in the acidogenic fermentation step has excellent fermentation efficiency.

[0147] In particular, in this embodiment, gaseous components (hydrogen, carbon dioxide, etc.) produced in the primary fermentation of the acidogenic fermentation step are fermented in the hydrogen-assimilating fermenter 17 to obtain a gas containing methane (hydrogen-assimilating methanogenic fermentation step). In this way, hydrogen, which may inhibit the catabolic reactions (1) to (3) in the acidogenic fermentation step and the dry methane fermentation step, is converted into methane in the hydrogen-assimilating methanogenic fermentation step, thereby improving the overall efficiency of the dry methane fermentation. Furthermore, in this embodiment, the use of a porous inorganic medium in the hydrogen-assimilating methanogenic fermentation step also improves the efficiency of the fermentation itself in the hydrogen-assimilating methanogenic fermentation step.

[0148] The present invention has been described in detail above based on a preferred embodiment, but the present invention is not limited to this, and each component can be replaced with any component that can perform a similar function, or any component can be added.

[0149] In the above-described embodiment, the gas and liquid released from the kneading-explosion machine are fermented in the acetic acid assimilating fermenter, but the present invention is not limited to this. For example, the dry methane fermentation system of the present invention does not need to include an acetic acid assimilating fermenter. In this case, the gas and liquid released from the kneading-explosion machine are subjected to primary fermentation together with the pulverized organic resource in the acid-producing fermenter.

[0150] In the above-described embodiment, the pulverized organic resource is subjected to primary fermentation in an acid-producing fermenter, but the present invention is not limited to this, and the dry methane fermentation system of the present invention does not necessarily have to include an acid-producing fermenter. In this case, the pulverized organic resource is directly subjected to dry methane fermentation in the dry methane fermenter.

[0151] Furthermore, in the above-described embodiment, the methane-containing gas obtained by fermentation in the hydrogen-assimilating fermenter 17 is transferred to the dry methane fermenter 21, but the present invention is not limited to this. For example, the methane-containing gas obtained by fermentation in the hydrogen-assimilating fermenter 17 may pass directly through the desulfurization device 23 without being transferred to the dry methane fermenter 21, and may be stored directly in the gas storage tank 25 as biogas.

[0152] In the above-described embodiment, the dry methane fermentation system has been described as including multiple batch-type dry methane fermenters, but the present invention is not limited to this. For example, the dry methane fermentation may be a continuous fermenter. Also, for example, the dry methane fermentation system may have only one dry methane fermenter. [Explanation of symbols]

[0153] 1. Dry methane fermentation system 11 Crusher 13 Kneader 15 Acid-producing fermenter 17 Hydrogen-utilizing fermenter 19 Acetic acid utilization fermenter 21, 21A, 21B, 21C Dry methane fermentation tank 23 Desulfurization equipment 25 Gas storage tank 27 Reconstitution tank 100 Kneading and Explosion Machine 110 Case 111 Housing body 113 Space 115 Hopper 120 Archimedes Screw 121 Tip 123 Proximal end 125 screw blade 130 Outlet 131 Through hole 133 Bearings 140 Side blade 150 Outlet side blade 160 Water pipe 170 Power Source

Claims

1. A kneading and explosion machine that kneads and explodes organic resources to produce pulverized organic resources; a dry methane fermentation tank for accommodating the pulverized organic resource and performing dry methane fermentation; The kneading and explosion crusher has a housing having a cylindrical space and an Archimedes screw disposed in the space, The housing has an inlet for introducing the organic resource at one cylindrical end side of the space, and an outlet for removing the pulverized organic resource at the other cylindrical end side of the space, The dry methane fermentation system, wherein the pitch of the Archimedes screw gradually decreases from the inlet to the outlet.

2. 2. The dry methane fermentation system according to claim 1, wherein the pitch of the Archimedes screw closest to the outlet side is 5.0% to 70% of the pitch of the inlet side.

3. The kneading and crushing machine is configured to apply 2.5×10 ５ Above 14.0 x 10 ５ N / m ２ 2. The dry methane fermentation system according to claim 1, wherein the pitch of the archimedes screw is adjusted so that the following pressure is applied:

4. The apparatus further includes an acetic acid assimilating fermenter in which a symbiotic acetogenic bacteria group produces a fermented product containing acetic acid from the gas and liquid produced from the organic resource in the kneading and explosion machine, The dry methane fermentation system according to claim 1 , wherein the dry methane fermentation tank is a tank for accommodating the fermented material containing acetic acid together with the pulverized organic resource and performing dry methane fermentation.

5. The dry methane fermentation system according to claim 1 , comprising a plurality of the dry methane fermentation tanks in a batchwise manner.

6. A first step of kneading and blasting an organic resource using a kneading and blasting machine to obtain a pulverized organic resource; A second step of performing dry methane fermentation on the pulverized organic resource, The kneading and explosion crusher has a housing having a cylindrical space and an Archimedes screw disposed in the space, The housing has an inlet for introducing the organic resource at one cylindrical end side of the space, and an outlet for removing the pulverized organic resource at the other cylindrical end side of the space, The dry methane fermentation method, wherein the pitch of the Archimedes screw gradually decreases from the inlet to the outlet.

7. 7. The dry methane fermentation method according to claim 6, further comprising a third step of producing a fermented product containing acetic acid from the gas and liquid produced from the organic resource in the kneading and explosion machine using a symbiotic acetogenic bacteria group, and in the second step, dry methane fermentation is performed on the pulverized organic resource and the fermented product containing acetic acid.

8. Repeating the first step and the second step, In the second step, the methane fermentation is carried out in a batch dry methane fermenter, 7. The dry methane fermentation method according to claim 6, wherein in the second step or later, the pulverized organic resource material is introduced into the batch-type dry methane fermenter different from the batch-type dry methane fermenter into which the pulverized organic resource material was introduced in the previous second step.

Images