Organic matter treatment apparatus, organic matter treatment method, and method for producing fuel gas

Abstract

This organic matter treatment apparatus is for converting organic matter into a fuel gas and comprises: a hydrolysis treatment device for hydrolyzing the organic matter under a high-temperature high-pressure condition in which the organic matter and water are mixed; a first fermentation tank for generating the fuel gas by causing the organic matter to ferment under a first temperature condition; and a second fermentation tank for generating the fuel gas by causing the organic matter to ferment under a second temperature condition. The temperature in the first temperature condition is higher than the temperature in the second temperature condition.

Description

Organic matter treatment device, organic matter treatment method, and fuel gas production method

[0001] The present invention relates to an organic matter treatment device, an organic matter treatment method, and a fuel gas production method. This application claims priority to Japanese Patent Application No. 2024-083580, filed May 22, 2024, the contents of which are incorporated herein by reference.

[0002] BACKGROUND ART Conventionally, there is an organic waste treatment system that uses a subcritical water treatment device to reduce the molecular weight of organic waste and generate biogas from the reduced molecular weight organic waste (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2021-070005

[0004] However, with conventional technologies, it is difficult to set the temperature for subcritical water treatment, and in some cases, organic waste cannot be treated efficiently. For example, if the set temperature for subcritical water treatment is increased, the efficiency of the subcritical water treatment improves, but the carbonization of organic matter progresses, making it unusable for biogas production. Alternatively, if the set temperature for subcritical water treatment is decreased, the carbonization of organic matter can be suppressed, but the efficiency of the subcritical water treatment decreases. In this case, the organic waste is not sufficiently reduced in molecular weight, and the fermentation efficiency in the fermentation process after subcritical water treatment decreases, resulting in a decrease in the efficiency of biogas production. Furthermore, conventional technologies require a large amount of energy for subcritical water treatment, resulting in high costs for the entire system.

[0005] Aspects of the present invention provide an organic matter treatment apparatus, an organic matter treatment method, and a fuel gas production method that can more efficiently treat organic waste.

[0006] The organic matter treatment device, organic matter treatment method, and fuel gas production method according to the present invention employ the following configuration: (1): An organic matter treatment device according to one aspect of the present invention is an apparatus for converting organic matter into fuel gas, and includes a hydrolysis treatment device that hydrolyzes a mixture of the organic matter and water under high-temperature and high-pressure conditions, a first fermenter that produces the fuel gas by fermenting the organic matter under first temperature conditions, and a second fermenter that produces the fuel gas by fermenting the organic matter under second temperature conditions, wherein the temperature under the first temperature conditions is higher than the temperature under the second temperature conditions.

[0007] (2) In the above aspect (1), the temperature difference between the temperature under the first temperature condition and the temperature under the second temperature condition is 10° C. or more.

[0008] (3) In the above aspect (1), the temperature under the first temperature condition is 70° C. or higher.

[0009] (4) In the above aspect (1), the temperature under the second temperature condition is 65° C. or less.

[0010] (5): In the above aspect (1), the fuel gas contains methane.

[0011] (6) In the above aspect (5), a reaction to produce methane using hydrogen as a reactant is caused in the first fermenter.

[0012] (7) In the above aspect (5), a reaction for producing methane is caused to occur in the second fermenter using an organic acid as a reactant.

[0013] (8) In the above aspect (5), the fermentation is anaerobic fermentation.

[0014] (9) Another aspect of the present invention provides an organic matter treatment method, in which an organic matter treatment apparatus for converting organic matter into fuel gas uses a hydrolysis treatment apparatus to hydrolyze the organic matter under high-temperature and high-pressure conditions in which the organic matter is mixed with water, and produces the fuel gas by fermenting the organic matter under first temperature conditions in a first fermentation tank, and produces the fuel gas by fermenting the organic matter under second temperature conditions in a second fermentation tank, wherein the temperature under the first temperature conditions is higher than the temperature under the second temperature conditions.

[0015] (10): Another aspect of the present invention provides a method for producing fuel gas by converting organic matter into fuel gas, the method comprising the steps of: a hydrolysis treatment step in which the organic matter is mixed with water and hydrolyzed under high-temperature and high-pressure conditions; a step in which the organic matter treated in the hydrolysis treatment step is fermented under first temperature conditions to produce the fuel gas; and a step in which the organic matter treated in the hydrolysis treatment step is fermented under second temperature conditions to produce the fuel gas, wherein the temperature under the first temperature conditions is higher than the temperature under the second temperature conditions.

[0016] According to aspects (1) to (10), organic waste can be treated more efficiently. More specifically, in conventional technology, when the temperature of the fermenter is set to a high temperature, methane fermentation does not proceed properly, and when the temperature of the fermenter is set to a low temperature, the rate of hydrolysis is slow, resulting in a contradictory problem of reduced treatment efficiency when solids remain in the preceding subcritical water treatment process. In contrast, according to aspects (1) to (10), by providing two fermenters, a first fermenter and a second fermenter, it is possible to set fermentation conditions suitable for each treatment, even if solids and solubilized matter (in a low-molecular-weight state) are mixed in the organic waste after subcritical water treatment.

[0017] Furthermore, according to aspect (2), since the temperature difference between the temperature related to the temperature conditions of the first fermentation tank and the temperature related to the temperature conditions of the second fermentation tank is 10°C or more, the fermentation reaction can be suitably promoted in both the high-temperature tank and the low-temperature tank.

[0018] FIG. 1 is a diagram illustrating an outline of an organic waste treatment method according to a first embodiment. FIG. 2 is a diagram illustrating an example of the configuration of an organic waste treatment device according to the first embodiment. FIG. 3 is a diagram illustrating an effect obtained by the organic waste treatment device according to the first embodiment. FIG. 4 is a diagram illustrating an example of the configuration of a subcritical water treatment device according to the first embodiment. FIG. 5 is a diagram illustrating an example of the configuration of an organic waste treatment device according to the second embodiment. FIG. 6 is a diagram illustrating an example of the configuration of an organic waste treatment device according to the third embodiment. FIG. 7 is a diagram illustrating an example of the configuration in which a pressure accumulation device according to the third embodiment functions as a moving means and an agitation means (part 1). FIG. 8 is a diagram illustrating an example of the configuration in which a pressure accumulation device according to the third embodiment functions as a moving means and an agitation means (part 2). FIG. 9 is a diagram illustrating an example of the connection configuration between a mixing tank and a high-temperature fermenter according to the third embodiment. FIG. 10 is a diagram illustrating an example of the configuration of an organic waste treatment device according to a fourth embodiment. FIG. 11 is a diagram illustrating an example of the material changes until a fuel gas is produced in the organic waste treatment device according to the first embodiment.

[0019] Hereinafter, with reference to the drawings, embodiments of the organic matter treatment device, organic matter treatment method, and fuel gas production device of the present invention will be described. The organic matter treatment device, organic matter treatment method, and fuel gas production device of the embodiment enable the recovery of biogas (fuel gas) from organic waste, such as food waste, livestock manure, plastics, fibers, and wood chips, by decomposing the organic waste through processes such as fermentation and anaerobic digestion. In this embodiment, it is assumed that methane is primarily recovered as biogas, but gases other than methane may also be collected as biogas as long as they are obtained by decomposition. Furthermore, while this embodiment assumes the treatment of waste containing organic matter (organic waste), the treatment target does not necessarily have to be waste; it may also be organic matter, such as biomass generated as a biogas feedstock.

[0020] <First embodiment> Figure 1 is a diagram illustrating an outline of an organic waste treatment method according to an embodiment. The organic waste treatment method according to the embodiment includes a high-rate hydrolysis process using subcritical water treatment, a high-temperature fermentation process in which methane fermentation is promoted in a high-temperature environment for the organic waste solubilized in the high-rate hydrolysis process, and a low-temperature fermentation process in which methane fermentation is promoted in a low-temperature environment for the organic waste treated in the high-temperature fermentation process, and the methane gas generated in the high-temperature fermentation process and the low-temperature fermentation process is recovered as biogas.

[0021] The rapid hydrolysis process is a process in which organic waste is decomposed and reduced in molecular weight through a rapid hydrolysis reaction in a high-temperature, high-pressure region using subcritical water treatment. For example, in subcritical water treatment, hydrolysis is promoted in an environment where H+ ions and OH- ions, which contribute to hydrolysis, are present in greater amounts than in a steady-state, constant-pressure environment. This subcritical water treatment promotes the reduction in molecular weight and solubilization of organic waste, converting it into a state more suitable for methane fermentation. In other words, the rapid hydrolysis process is positioned as a pretreatment process for efficiently carrying out the subsequent high-temperature fermentation process and low-temperature fermentation process. Subcritical water treatment makes it possible to solubilize organic matter more effectively in a shorter time than conventional hydrolysis reactions. The rapid hydrolysis process is carried out under conditions, for example, at a temperature of approximately 160°C and in an aerobic environment with a pH of 3 to 4.

[0022] Subcritical water treatment has the advantage of being able to simultaneously treat many types of organic waste through rapid hydrolysis reactions in a high-temperature, high-pressure region. However, due to the ease of solubilization, some of the organic waste may be carbonized. Therefore, in the organic waste treatment method of this embodiment, the treatment conditions of the subcritical water treatment are adjusted to suit the organic waste to be treated that is easily solubilized. Organic waste that is not solubilized in the rapid hydrolysis step is also solubilized by hydrolysis by hydrolytic bacteria in the subsequent high-temperature fermentation step and consumed in the acid production reaction. This reduces the processing load of the subcritical water treatment, reduces the cost and energy consumption of the equipment, and also suppresses carbonization of the organic waste, allowing for more effective conversion of organic waste to biogas.

[0023] The high-temperature fermentation process is a process that promotes methane fermentation of organic waste in a high-temperature anaerobic environment. For this reason, in the high-temperature fermentation process, methane fermentation is promoted using methanogens classified as thermophilic bacteria. For example, hydrogen-utilizing methanogens (anaerobic microorganisms) are an example of methanogens classified as thermophilic bacteria. Hydrogen-utilizing methanogens promote hydrogen-utilizing methane fermentation. Generally, methane fermentation reactions of organic matter are broadly divided into hydrogen-utilizing fermentation reactions (4H ２ +CO ２ →CH ４ +2H ２ O) and acetate-utilizing fermentation reaction (CH ３ COOH→CH ４ +CO ２ The high-temperature fermentation process promotes the hydrogen-utilizing methane fermentation reaction among these fermentation reactions. As a result, a large amount of hydrogen and carbon dioxide is consumed in the high-temperature fermentation process, resulting in the production of large amounts of organic acids such as acetic acid, which are the raw materials for methane fermentation.

[0024] Furthermore, consuming hydrogen in the high-temperature fermentation process can prevent hydrogen from inhibiting the methane fermentation reaction in the subsequent mesophilic fermentation process. Consuming carbon dioxide in the high-temperature fermentation process can increase the methane concentration in the recovered biogas. In addition to the hydrogen-utilizing methane fermentation reaction described above, the high-temperature fermentation process also further promotes the hydrolysis of organic waste that remained as solids in the preceding rapid hydrolysis process due to the high temperature conditions. Therefore, subcritical water treatment can be performed in the rapid hydrolysis process under conditions that leave a certain amount of solids. This shortens the time required for the rapid hydrolysis process and also suppresses carbonization of organic matter, allowing for the utilization of more organic matter. The high-temperature fermentation process is carried out under conditions, for example, at a temperature of 70 to 90°C and in an anaerobic environment with a pH of approximately 6.5.

[0025] The low-temperature fermentation process is a process for converting excess organic acids (e.g., acetic acid) in the organic waste after the high-temperature fermentation process into methane. Specifically, in the low-temperature fermentation process, acetic acid is converted into methane gas by promoting an acetogenic methane fermentation reaction using acetogenic methanogens (anaerobic microorganisms) that are tolerant to low temperatures. The low-temperature fermentation process is carried out under conditions such as a temperature of around 38°C or 55°C and an anaerobic environment with a pH of around 7. Note that, although not as severe as in the high-temperature fermentation process, the hydrogen-assimilating methane fermentation reaction also proceeds to a certain extent in the low-temperature fermentation process.

[0026] It is known that the activity of hydrogen-utilizing methanogens and acetate-utilizing methanogens differs depending on the temperature (see, for example, the following literature: "Microbial Communities Involved in Methane Fermentation Processes," by Toru Shigematsu, Japan Society for Biotechnology, Journal of Biotechnology, Vol. 87, No. 12, pp. 570-596, 2009). More specifically, hydrogen-utilizing methanogens are active over a wide temperature range, including temperatures above 65°C, whereas acetate-utilizing methanogens are not active above 65°C. For this reason, conventional methods for simultaneously promoting hydrogen-utilizing methane fermentation and acetate-utilizing methane fermentation reactions require adjusting the temperature within a narrow range to match the activity of the acetate-utilizing methanogens. For this reason, conventional organic waste treatment methods are difficult to operate and expensive. Furthermore, the difficulty of adjusting the temperature can sometimes prevent efficient promotion of both the hydrogen-utilizing methane fermentation and acetate-utilizing methane fermentation reactions, resulting in low overall treatment efficiency.

[0027] For example, since acetogenic methanogens cannot tolerate high temperatures, if the treatment temperature is set high to activate hydrogen-utilizing methanogens, the acetogenic methanogens will be inactivated, making it impossible to promote acetogenic methane fermentation and preventing the acidogenic bacteria from consuming the acetic acid produced. On the other hand, if the treatment temperature is set low to activate acetogenic methanogens, the reaction rates of hydrolytic bacteria, acidogenic bacteria, and hydrogen-utilizing methanogens will decrease according to the Arrhenius law, so while the acetogenic methanogens will be active, the low temperature will prevent maximum promotion of the activities of hydrolytic bacteria, acidogenic bacteria, and hydrogen-utilizing methanogens.

[0028] The organic waste treatment method of the embodiment focuses on the difference in activity due to temperature, and aims to improve the overall treatment efficiency by separating the hydrogen-utilizing methane fermentation process and the acetate-utilizing methane fermentation process into separate processes and optimizing them individually.

[0029] As mentioned above, acetate-utilizing methanogens cannot tolerate high temperatures and therefore cannot be added to the organic waste in advance in the high-rate hydrolysis step or the high-temperature fermentation step. Therefore, it is recommended that the acetate-utilizing methanogens be added after the temperature of the organic waste after the high-temperature fermentation step has been cooled to a temperature below which the acetate-utilizing methanogens can tolerate. The cooling of the organic waste for the low-temperature fermentation step may be performed as a post-treatment in the high-temperature fermentation step, as a pre-treatment in the low-temperature fermentation step, or during the process of transferring the organic waste from the high-temperature fermentation step to the low-temperature fermentation step.

[0030] According to the organic waste treatment method of this embodiment, organic waste is treated in the above-mentioned order of high-rate hydrolysis, high-temperature fermentation, and low-temperature fermentation, thereby enabling more efficient treatment of organic waste. More specifically, by separating the hydrogen-assimilation methane fermentation reaction and the acetogenic methane fermentation reaction into a high-temperature fermentation step and a low-temperature fermentation step and performing them separately, it becomes possible to individually optimize each methane fermentation reaction, and as a result, it becomes possible to optimize the organic waste treatment as a whole.

[0031] Furthermore, by treating the organic waste in the above order, the temperature of the high-temperature fermentation process can be adjusted using the temperature of the organic waste that has undergone the high-rate hydrolysis process, and the temperature of the low-temperature fermentation process can be adjusted using the temperature of the organic waste that has undergone the high-temperature fermentation process. In other words, according to the organic waste treatment method of this embodiment, the temperature of the subsequent process can be adjusted (raised) using the temperature of the organic waste that has undergone the previous high-temperature process, making it possible to adjust the temperature without requiring a large energy input other than subcritical water treatment. For example, assuming that the treatment temperature in the high-temperature fermentation process is maintained at 70°C to 90°C, if the treatment temperature drops to 70°C, the organic waste treated in the previous process can be introduced into the high-temperature fermentation process, thereby raising the treatment temperature to 90°C. Here, the treatment temperature in the high-temperature fermentation process is an example of a "first temperature condition," and the temperature associated with the first temperature condition is 70°C or higher. Furthermore, the treatment temperature in the low-temperature fermentation process is an example of a "second temperature condition," and the temperature associated with the second temperature condition is 65°C or lower.

[0032] On the other hand, conventional organic waste treatments simultaneously promote both the hydrogen-assimilating methane fermentation reaction and the acetogenic methane fermentation reaction, which makes it difficult to set the treatment temperature and results in poor overall efficiency because the treatment temperature is not optimal for either fermentation reaction. In contrast, the organic waste treatment method of this embodiment can carry out the hydrogen-assimilating methane fermentation reaction (high-temperature fermentation process) and the acetogenic methane fermentation reaction (low-temperature fermentation process) at their optimal treatment temperatures, thereby improving the energy efficiency of each methane fermentation reaction.

[0033] Furthermore, in conventional organic waste treatment, each methane fermentation reaction is not carried out under optimal temperature conditions, which results in an insufficient reaction rate for each methane fermentation reaction, resulting in poor efficiency in terms of treatment speed. In contrast, the organic waste treatment method of this embodiment can carry out the hydrogen-assimilation methane fermentation reaction (high-temperature fermentation process) and the acetogenic methane fermentation reaction (low-temperature fermentation process) at their respective optimal treatment temperatures, thereby optimizing the reaction rate for the methane fermentation reaction.

[0034] In this way, according to the organic waste treatment method of the embodiment, it is possible to treat organic waste more efficiently not only in terms of energy efficiency but also in terms of treatment speed. Below, we will explain in detail the configuration of an organic waste treatment device that can treat organic waste according to the above organic waste treatment method.

[0035] 2 is a diagram showing an example of the configuration of an organic waste treatment apparatus 1 according to an embodiment. The organic waste treatment apparatus 1 includes a subcritical water treatment apparatus 10, a mixing tank 20, a high-temperature fermentation tank 30, a low-temperature fermentation tank 40, and a digested liquid tank 50. The subcritical water treatment apparatus 10 is an apparatus that realizes a high-rate hydrolysis process. The subcritical water treatment apparatus 10 includes a treatment tank for holding the organic waste to be treated, a thermometer for measuring the temperature in the treatment tank, and a pressure sensor for measuring the pressure in the treatment tank, and also includes means for adjusting the temperature and pressure in the treatment tank for subcritical water treatment based on these measurements. The subcritical water treatment apparatus 10 solubilizes the organic waste in the treatment tank by subcritical water treatment and sends the solubilized organic waste to the downstream mixing tank 20.

[0036] The mixing tank 20 is a device that mixes the organic waste sent from the subcritical water treatment device 10 with the treated organic waste (the fermentation residue that has undergone the high-temperature fermentation process and the low-temperature fermentation process, hereinafter referred to as the "digestion liquid") returned from the digestion liquid tank 50, and supplies the mixed organic waste to the high-temperature fermentation tank 30. The mixing tank 20 has a device such as a stirrer (not shown) as a means for mixing the sent organic waste with the digestion liquid. The mixing tank 20 may also be equipped with a thermometer for measuring the temperature of the organic waste in the tank and various sensors for measuring the moisture content and pH of the organic waste in the tank, and may also be equipped with a means for adjusting the state (temperature, moisture content, pH, etc.) of the organic waste to be supplied to the high-temperature fermentation tank 30 based on these measurements. The means for adjusting the state of the organic waste may be provided on the transport path from the mixing tank 20 to the high-temperature fermentation tank 30, or may be provided in the high-temperature fermentation tank 30.

[0037] The high-temperature fermenter 30 is an apparatus that realizes the high-temperature fermentation process. The high-temperature fermenter 30 is equipped with various sensors for measuring the temperature and pH within the tank, and is also equipped with means for adjusting the organic waste within the tank to conditions (temperature, pH, etc.) suitable for methane fermentation by hydrogen-assimilating methanogens based on these measurements. The high-temperature fermenter 30 also has means for injecting hydrogen-assimilating methanogens into the organic waste within the tank. The amount of hydrogen-assimilating methanogens injected may be determined according to the progress of methane fermentation while monitoring the state of the organic waste. The high-temperature fermenter 30 collects methane gas generated within the tank and sends the treated organic waste to the downstream low-temperature fermenter 40.

[0038] The low-temperature fermenter 40 is an apparatus that realizes the low-temperature fermentation process. The low-temperature fermenter 40 is equipped with various sensors for measuring the temperature and pH within the tank, and is also equipped with means for adjusting the organic waste within the tank to conditions (such as temperature and pH) suitable for methane fermentation by acetogenic methanogens based on these measurements. The low-temperature fermenter 40 also has means for injecting acetogenic methanogens into the organic waste within the tank. The amount of acetogenic methanogens injected may be determined according to the progress of methane fermentation while monitoring the state of the organic waste. The low-temperature fermenter 40 collects methane gas generated within the tank and sends the treated organic waste to the downstream digestion liquid tank 50.

[0039] The digester liquid tank 50 is a storage tank for the organic waste (digestion liquid) that has been treated in the low-temperature fermenter 40. The amount of digestion liquid stored in the digester liquid tank 50 is adjusted as needed by discarding a portion of the digestion liquid or sending it to a recycling process. As described above, a portion of the digestion liquid sent to the digester liquid tank 50 can be returned to the subcritical water treatment device 10 or the mixing tank 20 for the purposes of adjusting the water content, temperature, pH, and components of the organic waste, recycling the bacteria contained in the digestion liquid, and reprocessing the organic waste remaining in the digestion liquid.

[0040] As described above, the organic waste treatment device 1 sequentially performs the high-rate hydrolysis, high-temperature fermentation, and low-temperature fermentation processes by feeding the input organic waste through the subcritical water treatment device 10, the high-temperature fermentation tank 30, and the low-temperature fermentation tank 40 in this order, thereby decomposing the organic waste. In this case, completely treating the organic waste in each process before sending it to the subsequent process is not necessarily efficient in terms of the energy and time required for treatment. Therefore, the organic waste treatment device 1 is configured to simultaneously perform treatment in each process while sending the organic waste to the subsequent process at a predetermined rate (continuous system). The flow rate of the organic waste may be appropriately adjusted depending on the progress of treatment in each process. To adjust the flow rate, devices such as flow meters for measuring flow rate and pumps and valves for adjusting flow rate may be appropriately installed in the subcritical water treatment device 10, the mixing tank 20, the high-temperature fermentation tank 30, the low-temperature fermentation tank 40, the digested liquid tank 50, and the organic waste transport paths between these devices. In the organic waste treatment apparatus 1, the subcritical water treatment apparatus 10 may be configured as a batch type rather than a continuous type from the viewpoint of temperature adjustment and fermentation amount adjustment in the subsequent processes.

[0041] Each of the subcritical water treatment apparatus 10, the high-temperature fermentation tank 30, and the low-temperature fermentation tank 40 may be provided with a means (not shown) (e.g., a stirrer) for homogenizing the state of the organic waste so that the progress of treatment can be accurately monitored. The various adjusting means that the subcritical water treatment apparatus 10, the high-temperature fermentation tank 30, and the low-temperature fermentation tank 40 have for adjusting the environment within the treatment tank may be configured to be manually operated by an operator, or may be configured to automatically adjust based on measurements from various sensors, or may be a combination of these.

[0042] According to the organic waste treatment device 1 of this embodiment configured as described above, the methane fermentation process of organic waste is separated into a high-temperature fermentation process that promotes a hydrogen-utilizing methane fermentation reaction, and a low-temperature fermentation process that promotes an acetic acid-utilizing methane fermentation reaction, and by carrying out each of the high-temperature fermentation process and the low-temperature fermentation process under their respective optimum temperature conditions, it becomes possible to more efficiently recover biogas from organic waste.

[0043] FIG. 3 is a diagram illustrating the effects achieved by the organic waste treatment device 1 of this embodiment. As described above, the organic waste treatment device 1 of this embodiment performs decomposition treatment of organic waste in the following order: high-rate hydrolysis, high-temperature fermentation, and low-temperature fermentation. More specifically, as shown in FIG. 3 , in the high-rate hydrolysis, subcritical water treatment is used to decompose carbohydrates, proteins, and lipids contained in the organic waste into higher fatty acids, amino acids, and monosaccharides. Subsequently, in the high-temperature fermentation, acid-producing bacteria convert the higher fatty acids, amino acids, and monosaccharides into acetic acid, hydrogen, and carbon dioxide, while hydrogen-utilizing methanogens convert the hydrogen and carbon dioxide into methane gas. Furthermore, in the high-temperature fermentation, high temperatures activate hydrolytic bacteria, accelerating the decomposition treatment of organic waste through hydrolysis. Subsequently, in the low-temperature fermentation, acetic acid is converted into methane gas and carbon dioxide.

[0044] In the organic waste treatment device 1 of this embodiment, subcritical water treatment is performed on the organic waste as a pretreatment for the fermentation process, thereby enabling the organic waste to be rapidly depolymerized and solubilized, thereby improving the treatment efficiency of the organic waste treatment device 1. Furthermore, in the organic waste treatment device 1 of this embodiment, a high-temperature fermentation process is performed after the high-rate hydrolysis process. By connecting the subcritical water treatment device 10 and the high-temperature fermenter 30 with a heat exchanger such as a heat pump, the waste heat from the subcritical water treatment can be effectively utilized in the high-temperature fermentation process. Conventionally, after subcritical water treatment, hydrogen-assimilating methane fermentation and acetogenic methane fermentation are simultaneously performed in low-temperature fermentation. However, this requires a cooling process for the organic waste before the fermentation process, which prevents effective energy utilization. In contrast, the organic waste treatment device 1 of this embodiment can utilize the thermal energy generated in the high-rate hydrolysis process in the high-temperature fermentation process, thereby improving the energy efficiency of the organic waste treatment device 1.

[0045] Furthermore, subcritical water treatment generates gases such as ammonia and carbon dioxide, and these gases (especially ammonia) can inhibit the methane fermentation reaction in the subsequent stage. However, in the organic waste treatment device 1 of this embodiment, the high-temperature fermenter 30 is provided downstream of the subcritical water treatment device 10, so the solubility of these gases dissolved in water decreases, particularly in the high-temperature fermenter 30, and they are released into the gas phase, thereby reducing the impact of inhibitors on the fermentation process. In this way, the organic waste treatment device 1 of this embodiment makes it possible to remove inhibitors in the early stages of the fermentation process, thereby suppressing a decrease in the efficiency of the methane fermentation reaction and improving the treatment efficiency of the organic waste treatment device 1.

[0046] Furthermore, in the high-temperature fermentation step, by activating hydrogen-utilizing methanogens in a high-temperature environment, the hydrogen-utilizing methane fermentation reaction can be efficiently carried out, thereby improving the treatment efficiency of the organic waste treatment device 1. Furthermore, because the high-temperature fermentation step is carried out in a high-temperature environment, the hydrolysis reaction by hydrolytic bacteria and the acetic acid production reaction by acid-producing bacteria can be promoted in parallel with the hydrogen-utilizing methane fermentation reaction (Arrhenius law). Therefore, even if a certain amount of solid matter remains in the organic waste after subcritical water treatment, the high temperature of the subsequent high-temperature fermentation step can be advantageously used to efficiently decompose the remaining solid matter. In this way, in the organic waste treatment device 1 of this embodiment, the low-temperature fermentation step is carried out after the high-temperature fermentation step, and the acetic acid production reaction can be promoted in the high-temperature fermentation step, allowing the subsequent low-temperature fermentation step to be efficiently carried out, thereby improving the treatment efficiency of the organic waste treatment device 1.

[0047] Furthermore, by carrying out the high-temperature fermentation process and the low-temperature fermentation process as separate processes in this way, it is possible to optimize the high-temperature fermentation process and the low-temperature fermentation process separately, thereby reducing the amount of energy required for the high-temperature fermentation process and improving overall energy efficiency.

[0048] [Configuration of Subcritical Water Treatment Apparatus] Figure 4 is a diagram showing an example of the configuration of a subcritical water treatment apparatus 10 according to this embodiment. As described above, the subcritical water treatment apparatus 10 is an apparatus that performs subcritical water treatment on organic waste. As described above, subcritical water treatment is a high-speed hydrolysis treatment under a high-temperature, high-pressure environment. For this reason, as shown in Figure 4, the subcritical water treatment apparatus 10 of this embodiment includes, for example, a treatment tank 110 for holding the organic waste to be treated, a hydration means 120 for supplying water into the treatment tank, and a heating means 130 for creating a high temperature and high pressure inside the treatment tank.

[0049] For example, the treatment tank 110 is configured as a sealable cylindrical pressure-resistant container. The treatment tank 110 is configured to be rotatable about a rotation axis M. The treatment tank 110 may be configured integrally with the rotation axis M and configured to rotate together with the rotation axis M. Alternatively, the treatment tank 110 may be configured separately from the rotation axis M and configured to rotate relative to the rotation axis M by a drive mechanism (not shown). When the treatment tank 110 is rotated while being installed so that the rotation axis M is oriented horizontally, the materials (organic waste, water, etc.) in the treatment tank are agitated by the rotational motion and the falling motion due to gravity.

[0050] The treatment tank 110 may be provided with an agitator in order to improve the agitation performance by rotation. For example, the treatment tank 110 may be provided with an agitator 111 that rotates on the same rotation axis M as the treatment tank 110, as shown in Figure 4. The agitator 111 may be configured integrally with the central axis M and configured to rotate together with the central axis M, or may be configured integrally with the treatment tank 110 and configured to rotate together with the treatment tank 110.

[0051] The water supplying means 120 includes devices such as pumps and valves, and controls these devices to supply water from outside the treatment tank 110 to the treatment tank 110. More specifically, the water supplying means 120 is configured to supply the digestive fluid sent from the digestive fluid tank 50 as water to the treatment tank 110. The water supplying means 120 may be configured to supply water supplied from sources other than the digestive fluid tank 50 to the treatment tank 110, in addition to the digestive fluid returned from the digestive fluid tank 50. The water supplying means 120 is equipped with various sensors for acquiring information necessary to determine the amount of digestive fluid to be supplied, and is configured to adjust the amount of digestive fluid to be supplied based on measurements from the various sensors. The water supplying means 120 may also be configured to communicate with an overall control function of the organic waste treatment device 1 and adjust the amount of digestive fluid to be supplied under control of the overall control function.

[0052] The heating means 130 includes, for example, devices such as a heater and a heat exchanger, and heats the treatment tank 110 by controlling these devices. More specifically, the heating means 130 is configured to heat the treatment tank 110 from outside. For example, the heating means 130 may be configured as a housing that covers the treatment tank 110. Furthermore, for example, the heating means 130 may be attached along the cylindrical outer periphery of the treatment tank 110. The heating means 130 may be configured as a part of the subcritical water treatment system 10, or as a device separate from the subcritical water treatment system 10. The heating means 130 may include various sensors for acquiring information necessary to determine the amount of heat to be supplied to the treatment tank 110 (amount of supplied heat), and may be configured to adjust the amount of supplied heat based on measurements from the various sensors. The heating means 130 may also be configured to communicate with an overall control function of the organic waste treatment system 1 and adjust the amount of supplied heat under control of the overall control function.

[0053] The water adding means 120 and the heating means 130 work together to create a high-temperature, high-pressure subcritical water treatment environment inside the subcritical water treatment apparatus 10. As described above, the treatment tank 110 is a pressure-resistant container, and as the water inside the treatment tank 110 is heated, the temperature and pressure inside the treatment tank 110 increase. Furthermore, because the treatment tank 110 is a sealed container, as the water inside the treatment tank 110 is heated, the water does not boil at 100°C, and the temperature and pressure inside the treatment tank 110 continue to increase. In this way, the subcritical water treatment apparatus 10 can create a high-temperature, high-pressure subcritical water treatment environment inside itself by controlling the heating means 130.

[0054] As described above, the organic waste treatment device 1 of this embodiment can improve the energy efficiency and treatment efficiency in organic waste treatment from multiple perspectives, making it possible to treat organic waste more efficiently than conventional methods.

[0055] More specifically, conventional subcritical water treatment systems typically use a boiler to generate high-temperature, high-pressure steam and supply it to a treatment tank. Because water used in boilers generally meets certain water quality standards (e.g., JIS B8223:2015), supplying digested fluid to a subcritical water treatment system was not anticipated, and no organic waste treatment system equipped with such a supply mechanism was developed. Even if digested fluid were used to supply water to a boiler, water treatment was required to meet the boiler's water quality standards, resulting in high costs. Furthermore, conventional subcritical water treatment systems pump steam higher than the set temperature into the treatment tank, resulting in uneven organic waste treatment results, such as areas directly exposed to the steam becoming hotter and more susceptible to carbonization. In contrast, the organic waste treatment system 1 of this embodiment does not use a conventional boiler, but instead includes a water-addition and heating-type subcritical water treatment system 10 using a water-addition means 120 and a heating means 130. This allows for effective use of digested fluid while also resolving the above and other issues.

[0056] Furthermore, according to the organic waste treatment device 1 of this embodiment, by returning the digested liquid to the subcritical water treatment device 10, it is possible to adjust the moisture content, temperature, and pH of the organic waste depending on the conditions of the subsequent fermentation process. For example, if the moisture content of the organic waste is too low (the proportion of solids is high) during fermentation, methanogens are inactivated and only acid production is promoted (rancidity). Therefore, it is possible to adjust the moisture content of the organic waste so that the proportion of solids does not become too high (for example, about 10%). This makes it possible to carry out the high-temperature fermentation process and the low-temperature fermentation process under more suitable conditions, thereby improving the energy efficiency and treatment efficiency of the entire system.

[0057] <Second embodiment> Figure 5 is a diagram showing an example of the configuration of an organic waste treatment device 1 of a second embodiment. The organic waste treatment device 1 of the second embodiment differs from the organic waste treatment device 1 of the first embodiment in that it includes a digestion liquid tank 50A instead of the digestion liquid tank 50. As the other configuration is the same as that of the organic waste treatment device 1 of the first embodiment, in Figure 5 similar configurations are assigned the same reference numerals as in Figure 2 and description thereof will be omitted.

[0058] The digester fluid tank 50A differs from the digester fluid tank 50 of the first embodiment in that it further includes a digester fluid discharge unit 51 that discharges the digester fluid in the tank to the outside of the organic waste treatment system 1, and a concentration sensor 52 that measures the concentration of a predetermined component in the organic waste in the tank. The digester fluid discharge unit 51 includes devices such as a pump and a valve, and controls these devices to adjust the flow rate of the digester fluid discharged from the digester fluid tank 50A to the outside of the system. More specifically, the digester fluid discharge unit 51 discharges a portion of the digester fluid stored in the digester fluid tank 50A to the outside of the system when the concentrations of various components measured by the concentration sensor 52 satisfy predetermined conditions.

[0059] According to the organic waste treatment device 1 of the second embodiment, the concentration of the target component in the digestive fluid in the digester fluid tank 50A can be monitored while performing the organic waste decomposition process (high-speed hydrolysis process, high-temperature fermentation process, and low-temperature fermentation process), and when the target component meets a predetermined concentration condition, a portion of the digestive fluid can be discharged outside the system. In this way, for example, components contained in the digestive fluid that do not contribute to methane fermentation (or inhibit methane fermentation) can be concentrated and discharged outside the system, thereby making it possible to effectively utilize the digestive fluid outside the system.

[0060] For example, nitrogen (N), potassium (K), and phosphorus (P) are components contained in organic waste. Although they do not contribute to methane fermentation, they can be used as fertilizer, and these components can be used as target components. Meanwhile, the organic waste treatment device 1 of this embodiment is configured to return a portion of the digested fluid sent to the digested fluid tank 50A to the upstream stage of the fermentation process and circulate it. This allows the target components to gradually become concentrated as the organic waste decomposition process progresses. The organic waste treatment device 1 of the second embodiment monitors the concentrations of these target components and discharges them from the system when they are appropriately concentrated (i.e., when the concentration of the target components exceeds a predetermined concentration), thereby enabling the digested fluid to be effectively used as liquid fertilizer. Furthermore, the organic waste treatment device 1 of this embodiment can also produce other valuable materials, such as fulvic acid, in addition to the above-mentioned fertilizer-use components. Furthermore, the organic waste treatment device 1 of this embodiment has undergone subcritical water treatment of the target components, thereby sterilizing or killing harmful bacteria such as E. coli, eliminating the need for additional treatments, which is advantageous in terms of safety and cost.

[0061] <Third Embodiment> Figure 6 is a diagram showing an example of the configuration of an organic waste treatment device 1 of a third embodiment. The organic waste treatment device 1 of the third embodiment differs from the organic waste treatment device 1 of the first embodiment in that it further includes a pressure accumulation device 60. The organic waste treatment device 1 of the third embodiment also differs from the organic waste treatment device 1 of the first embodiment in that it does not include power equipment (e.g., pumps) for transporting organic waste between the subcritical water treatment device 10 and the mixing tank 20, and between the mixing tank 20 and the high-temperature fermenter 30. Since the other configuration is the same as that of the organic waste treatment device 1 of the first embodiment, in Figure 5 similar configurations are assigned the same reference numerals as in Figure 2, and description thereof will be omitted.

[0062] The pressure accumulation device 60 is a device configured to accumulate pressure generated in the subcritical water treatment device 10 and to optionally release the accumulated pressure. For example, the pressure accumulation device 60 may be a so-called pressure accumulator (also referred to as an accumulator). For example, the pressure accumulation device 60 is connected to the subcritical water treatment device 10 by a second transport path L12 separate from the first transport path L11 that transports organic waste between the subcritical water treatment device 10 and the mixing tank 20, and is connected to the first transport path L11 by a third transport path L13. Alternatively, for example, the pressure accumulation device 60 is connected to the mixing tank 20 by a fourth transport path L14 separate from the first transport path L11.

[0063] The pressure inside the subcritical water treatment apparatus 10 is supplied to the pressure accumulator 60 via the second transport path L12. Meanwhile, the pressure accumulator 60 can supply the accumulated pressure to the first transport path L11 via the third transport path L13. At this time, the supplied pressure pushes the organic waste in the first transport path L11 toward the mixing tank 20. In other words, the pressure accumulator 60 can function as a transfer means for transferring the organic waste from the subcritical water treatment apparatus 10 toward the mixing tank 20.

[0064] The pressure accumulator 60 can also supply pressure to the mixing tank 20 via the fourth transport path L14. At this time, the pressure in the mixing tank 20 increases, and pressure is applied to the liquid organic waste in the mixing tank 20, causing the organic waste to be transferred from the mixing tank 20 to the high-temperature fermenter 30 via the fifth transport path L15. This also causes a flow of organic waste in the high-temperature fermenter 30, and this flow agitates the organic waste in the tank. In other words, the pressure accumulator 60 can function as a transfer means for transferring the organic waste from the mixing tank 20 to the high-temperature fermenter 30, and as an agitation means for agitating the organic waste sent to the high-temperature fermenter 30.

[0065] The organic waste treatment apparatus 1 of the third embodiment has a configuration in which the pressure accumulation device 60 is connected to a mixing tank 20 arranged upstream of the fermenter tank. Therefore, by separating the organic waste (liquid) from the gas using the mixing tank 20, the organic waste treatment apparatus 1 of the third embodiment can prevent gas from flowing into the downstream fermenter tank and inhibiting the fermentation reaction, while also making it possible to utilize the pressure energy of the subcritical water treatment apparatus 10 as power for the organic waste transfer means and / or agitation means.

[0066] 7 shows an example of a configuration in which the pressure accumulation device 60 of the third embodiment functions as a moving means and an agitating means. Here, it is assumed that the first transport path L11, the second transport path L12, the third transport path L13, the fourth transport path L14, and the fifth transport path L15 are respectively equipped with a first valve V11, a second valve V12, a third valve V13, a fourth valve V14, and a fifth valve V15 to adjust the transport volume of organic waste. However, the number and arrangement of the valves may be designed arbitrarily as long as the same function can be realized. It is also assumed that the opening degree of each valve can be controlled by the control function of the organic waste treatment device 1.

[0067] In this case, while or after the subcritical water treatment apparatus 10 is performing subcritical water treatment, the first valve V11, the third valve V13, and the fourth valve V14 are closed and the second valve V12 is opened, so that the pressure inside the subcritical water treatment apparatus 10 flows into the pressure accumulation device 60. Thereafter, the second valve V12 is closed, so that pressure can be accumulated in the pressure accumulation device 60. Note that the pressure accumulation device 60 is assumed to include a valve (hereinafter referred to as an internal valve) inside the apparatus for retaining the organic waste that has flowed into it.

[0068] Meanwhile, with pressure accumulated in the pressure accumulating device 60, the first valve V11, the second valve V12, and the fourth valve V14 are closed and the third valve V13 is opened, whereby the pressure flows into the first transport path L11 via the third transport path L13. As a result, the organic waste that has been retained in the first transport path L11 is swept toward the mixing tank 20 and flows into the mixing tank 20. In this case, the pressure accumulating device 60 can serve as a transfer means for transferring the organic waste treated in the subcritical water treatment device 10 to the mixing tank 20.

[0069] On the other hand, with pressure accumulated in the pressure accumulation device 60, the first valve V11, the second valve V12, and the third valve V13 are closed and the fourth valve V14 is opened, causing high-temperature, high-pressure organic waste to flow into the mixing tank 20 via the fourth transport line L14. At this time, the fifth valve V15 is opened, causing the organic waste to flow into the high-temperature fermentation tank 30 via the fifth transport line L15. This causes a flow (agitation flow) in the organic waste in the high-temperature fermentation tank 30, and the organic waste is agitated by this flow. In this case, the pressure accumulation device 60 can serve as agitation means for agitating the organic waste in the high-temperature fermentation tank 30.

[0070] In this case, the organic waste treatment device 1 controls itself so that the organic waste contains a certain amount of liquid when sent to the mixing tank 20, as shown in Fig. 7. For example, the organic waste treatment device 1 can control the moisture content of the organic waste in the mixing tank 20 by adjusting the amount of digested liquid sent from the digested liquid tank 50 to the mixing tank 20. Furthermore, for example, the organic waste treatment device 1 may control the moisture content of the organic waste sent to the mixing tank 20 by adjusting the conditions for performing subcritical water treatment in the subcritical water treatment device 10 (temperature, pressure, treatment time, etc.).

[0071] Furthermore, in this case, the mixing tank 20 and the high-temperature fermentation tank 30 are connected at a position lower than the liquid level of the organic waste in the high-temperature fermentation tank 30. By doing so, it is possible to more effectively generate an agitation flow in the high-temperature fermentation tank 30. Furthermore, in order to more efficiently agitate the organic waste in the high-temperature fermentation tank 30, the fifth transport line L15 and the high-temperature fermentation tank 30 may be connected at a point (for example, the bottom) or at an angle that causes the agitation flow to become an upward flow.

[0072] 7, for simplicity, the first transport path L11 used as the organic waste transfer means and the fourth transport path L14 used as the agitation means for the mixing tank 20 are provided separately, but the first transport path L11 and the fourth transport path L14 may be configured as a single transport path. In this case, the organic waste treatment device 1 of the third embodiment may be connected to the transport path L21 connecting the subcritical water treatment device 10 and the mixing tank 20 so as to relay the organic waste midway, as shown in FIG.

[0073] In this case, during or after the subcritical water treatment by the subcritical water treatment apparatus 10, the second valve V22 is closed and the first valve V21 is opened, so that high-temperature, high-pressure organic waste flows into the pressure accumulation device 60. Thereafter, the first valve V21 is closed, so that pressure can be accumulated in the pressure accumulation device 60.

[0074] Meanwhile, with pressure accumulated in the pressure accumulating device 60, the first valve V21 and the second valve V22 are opened, and the pressure accumulating device 60 also opens the internal valve, thereby promoting the flow of organic waste in the first transport path L21 and causing the organic waste to flow into the mixing tank 20. With this configuration, the pressure accumulating device 60 can realize a means for transferring organic waste.

[0075] As described above, the organic waste treatment apparatus 1 of the third embodiment is equipped with a pressure accumulation device 60 that accumulates pressure from the subcritical water treatment apparatus 10, and uses the pressure energy accumulated in the pressure accumulation device 60 as power for the organic waste transfer means and agitation means. As long as such transfer means and / or agitation means can be realized, the connection configuration and valve arrangement of the pressure accumulation device 60 in the organic waste treatment apparatus 1 may be appropriately changed from the contents of Figures 7 and 8.

[0076] FIG. 9 is a diagram showing an example of a connection configuration between the mixing tank 20 and the high-temperature fermentation tank 30. FIG. 9 is a vertical bird's-eye view of the high-temperature fermentation tank 30. For example, the high-temperature fermentation tank 30 may be configured as a cylinder having a central axis M, as shown in FIG. 9. FIG. 9 shows an example in which the fifth transport path L15 is connected to such a cylindrical high-temperature fermentation tank 30 so that the organic waste flows in at a position radially offset by a predetermined distance H from the central axis M. Connecting the fifth transport path L15 to the high-temperature fermentation tank 30 in this manner can generate a swirling flow rotating around the central axis M in the organic waste in the high-temperature fermentation tank 30, thereby further improving the mixing effect. Furthermore, the fifth transport path L15 may be connected to the high-temperature fermentation tank 30 so that the organic waste flows in obliquely upward. This allows the pressure accumulation device 60 to generate an upward swirling flow inside the high-temperature fermentation tank 30, further improving the mixing effect.

[0077] According to the organic waste treatment apparatus 1 of the third embodiment configured as described above, by providing a pressure accumulation device 60 that accumulates pressure energy from the subcritical water treatment apparatus 10, the energy efficiency of the entire organic waste treatment apparatus 1 is improved, and organic waste can be treated more efficiently. More specifically, the organic waste treatment apparatus 1 can improve its energy efficiency by utilizing the pressure energy generated in the subcritical water treatment apparatus 10 as power for transferring the organic waste treated in the subcritical water treatment apparatus 10 to the mixing tank 20 and / or high-temperature fermentation tank 30. Furthermore, the organic waste treatment apparatus 1 can improve its energy efficiency by utilizing the pressure energy generated in the subcritical water treatment apparatus 10 as power for agitating the high-temperature fermentation tank 30.

[0078] In the organic waste treatment device 1 of the above embodiment, the high-rate hydrolysis step, high-temperature fermentation step, and low-temperature fermentation step may be performed either continuously or batchwise. However, using a batch system allows for even greater efficiency. More specifically, performing subcritical water treatment in a batch system (also called a batch system) allows thermal energy to be periodically supplied to the reaction tank, thereby reducing the amount of energy input to the organic waste treatment device 1. Furthermore, configuring the organic waste treatment device 1 to perform each step in a batch system simplifies the internal configuration, thereby reducing the device size and reducing the device cost. Furthermore, in a continuous system, a cooling time is required when sending subcritical water-treated organic waste to a subsequent process. However, in the organic waste treatment device 1 of the embodiment, the high-temperature organic waste treated in the subcritical water treatment device 10 is sent to the subsequent high-temperature fermentation tank 30 without cooling, thereby reducing waiting time and improving time efficiency. Furthermore, by quickly sending the organic waste treated in the subcritical water treatment device 10 to the high-temperature fermenter 30, acid production within the organic waste can be suppressed, allowing the fermentation process to proceed more effectively.

[0079] Fourth Embodiment FIG. 10 is a diagram showing an example of the configuration of an organic waste treatment apparatus 1 according to a fourth embodiment. The organic waste treatment apparatus 1 includes, for example, a subcritical water treatment apparatus 10, a high-temperature fermenter 30, a low-temperature fermenter 40, a solid-liquid separation apparatus 70, and a heat exchanger 80. In addition to these components, the organic waste treatment apparatus 1 may also include various meters, sensors, and control devices provided in each device. The organic waste treatment apparatus 1 may be configured to control the temperature and pressure in each treatment tank, the flow rate of organic waste between treatment tanks, and the injection amount of various bacteria based on the output of various meters and sensors provided in the organic waste treatment apparatus 1. The various control functions of the organic waste treatment apparatus 1 are realized by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). The subcritical water treatment apparatus 10, high-temperature fermenter 30, and low-temperature fermenter 40 in FIG. 10 are essentially the same as those in the first embodiment.

[0080] Subcritical water treatment apparatus 10 includes, for example, a thermometer 11, a pressure gauge 12, and a valve 13. Thermometer 11 measures the temperature inside subcritical water treatment apparatus 10. Pressure gauge 12 measures the pressure inside subcritical water treatment apparatus 10. The temperature and pressure of subcritical water treatment apparatus 10 may be adjusted based on the measured values ​​of thermometer 11 and pressure gauge 12. Valve 13 can adjust the amount of water transferred to solid-liquid separation apparatus 70 (described later) by opening and closing it.

[0081] The solid-liquid separator 70 is connected to the subcritical water treatment device 10 and receives hydrolyzed organic waste from the subcritical water treatment device 10. The solid-liquid separator 70 separates the hydrolyzed organic waste sent from the subcritical water treatment device 10 into a first treated product with a low liquid ratio and a second treated product with a high liquid ratio (solid-liquid separation process). Here, the first treated product is organic waste with a high liquid ratio, and the second treated product is organic waste with a low liquid ratio. The solid-liquid separator 70 separates the organic waste into the first treated product and the second treated product using, for example, filtration, gravity settling, or centrifugation. The solid-liquid separator 70 transfers the first treated product to the high-temperature fermenter 30 using a pump 41 and transfers the second treated product to the heat exchanger 80 using a pump 42.

[0082] The high-temperature fermenter 30 is connected to the solid-liquid separator 70 and receives the first treated material separated by the solid-liquid separation process from the solid-liquid separator 70. The high-temperature fermenter 30 ferments the first treated material sent from the solid-liquid separator 70 under high-temperature conditions to produce fuel gas (high-temperature fermentation process). As described above, the high-temperature fermenter 30 is a fermenter that provides an environment in which hydrogen-utilizing methanogens are easily activated. A portion of the organic waste (digested liquid) treated in the high-temperature fermenter 30 can be returned to the subcritical water treatment device 10. This return of the digested liquid allows adjustment of the operating conditions (e.g., water content, temperature, etc.) of the rapid hydrolysis process (subcritical water treatment). To return the digested liquid, a pump 21, a valve 22, a flow meter 23, etc. are installed in the digested liquid return path between the high-temperature fermenter 30 and the subcritical water treatment device 10.

[0083] The low-temperature fermenter 40 is connected to the heat exchanger 80 and receives the second processed product separated by the solid-liquid separation process from the heat exchanger 80. The low-temperature fermenter 40 ferments the second processed product sent from the heat exchanger 80 under low-temperature conditions to produce fuel gas (low-temperature fermentation process). As described above, the low-temperature fermenter 40 is a fermenter in which acetate-utilizing methanogens are easily activated.

[0084] A portion of the organic waste (digestion liquid) treated in the low-temperature fermenter 40 can be returned to the subcritical water treatment device 10 via the heat exchanger 80. This return of the digestion liquid makes it possible to adjust the conditions (e.g., water content, temperature, etc.) for the high-rate hydrolysis step (subcritical water treatment). To return the digestion liquid in this way, a pump 36, a flow meter 52, etc. are installed in the digestion liquid return path from the low-temperature fermenter 40 to the subcritical water treatment device 10. Furthermore, a portion of the digestion liquid in the low-temperature fermenter 40 can be supplied to the high-temperature fermenter 30. This return of the digestion liquid makes it possible to adjust the conditions (e.g., water content, temperature, etc.) for the high-temperature fermentation step. To return the digestion liquid in this way, a pump 36, a valve 37, etc. are installed in the digestion liquid return path between the low-temperature fermenter 40 and the high-temperature fermenter 30.

[0085] The low-temperature fermentation tank 40 is capable of fermenting the second treated material and then removing the concentrated digested liquid from the organic waste treatment device 1. The concentrated digested liquid is a concentrated residue (digested liquid) from the methane fermentation process, and can be used as fertilizer, etc. The low-temperature fermentation tank 40 includes, for example, a pump 31, a nitrogen sensor 32, a phosphorus sensor 33, a potassium sensor 34, a valve 35, and a pump 36. The pump 31 is connected to the outside of the organic waste treatment device 1 and transports the concentrated digested liquid. The nitrogen sensor 32, the phosphorus sensor 33, and the potassium sensor 34 measure the concentrations of nitrogen, phosphorus, and potassium, respectively. The valve 35 opens and closes the flow path of the concentrated digested liquid. The pump 36 will be described later.

[0086] The heat exchanger 80 is provided between the solid-liquid separator 70 and the low-temperature fermenter 40. Because the organic waste treated with subcritical water is at a high temperature, if the second treated product is directly supplied to the low-temperature fermenter 40, the acetate-utilizing methanogens in the low-temperature fermenter 40 will be inactivated. Therefore, in the organic waste treatment device 1 of this embodiment, the heat exchanger 80 performs heat exchange between the second treated product and the circulating digestion liquid (low-temperature digestion liquid) returned from the low-temperature fermenter 40 to the subcritical water treatment device 10, thereby lowering the temperature of the second treated product to a temperature suitable for the low-temperature fermentation step before supplying it to the low-temperature fermenter 40. A thermometer 51 is provided between the heat exchanger 80 and the low-temperature fermenter 40 to adjust this temperature.

[0087] Furthermore, the heat exchanger 80 can increase the temperature of the low-temperature digested fluid by the heat exchange when returning the low-temperature digested fluid from the low-temperature fermenter 40 to the subcritical water treatment device 10. In this way, the amount of energy input to the subcritical water treatment device 10 can be reduced by using the thermal energy of the second treatment product sent from the solid-liquid separator 70 to increase the temperature of the low-temperature digested fluid to be returned to the subcritical water treatment device 10.

[0088] 11 is a diagram showing an example of the changes in substances occurring before fuel gas is produced in the organic waste treatment device 1. Through subcritical water treatment in the subcritical water treatment device 10, the carbohydrates, proteins, and lipids contained in the organic waste are hydrolyzed to lower molecular weights, and are decomposed into monosaccharides, amino acids, and higher fatty acids. The decomposed organic waste containing acetic acid is separated into a first treated product (low liquid ratio) and a second treated product (high liquid ratio) by the solid-liquid separator 70, and the first treated product is transferred to the high-temperature fermenter 30, and the second treated product is transferred to the low-temperature fermenter 40, respectively.

[0089] Furthermore, in the high-temperature fermenter 30, monosaccharides and amino acids are decomposed by acid-producing bacteria into low-molecular-weight fatty acids, valeric acid, butyric acid, propionic acid, etc. These are then decomposed into acetic acid, hydrogen, and carbon dioxide by the action of volatile organic acid-degrading bacteria. In the high-temperature fermenter 30, hydrogen and carbon dioxide are converted into methane gas by the action of hydrogen-utilizing methanogens. Meanwhile, in the low-temperature fermenter 40, acetic acid is converted into methane gas by the action of acetogenic methanogens.

[0090] In addition to methane gas, carbon dioxide is also produced in the low-temperature fermentation tank 40. The carbon dioxide produced in the low-temperature fermentation tank 40 may be supplied to the high-temperature fermentation tank 30. In the high-temperature fermentation step, carbon dioxide is consumed in methane fermentation by hydrogen-utilizing methanogens, so by supplying the carbon dioxide produced in the low-temperature fermentation tank 40 to the high-temperature fermentation tank 30, the processing efficiency of the high-temperature fermentation step can be improved and methane gas can be recovered at a high concentration. This configuration can also be applied to the first to third embodiments described above.

[0091] The organic waste treatment device 1 of this embodiment separates the organic waste into a first treated product intended for the high-temperature fermenter 30 and a second treated product intended for the low-temperature fermenter 40 in the solid-liquid separator 70 and transfers the organic waste to each of these, thereby simultaneously promoting methane fermentation using a treatment method appropriate for each. As described above, conventionally, organic waste that has undergone subcritical water treatment has generally been fermented in bulk. However, with this conventional method, temperature control of the fermenter is cumbersome, and depending on the type of methanogen, the temperature conditions for methane fermentation may be limited, making it difficult to efficiently convert the organic waste into methane gas. In contrast, the organic waste treatment device 1 of this embodiment ferments the organic waste separately in the high-temperature fermenter 30 and the low-temperature fermenter 40, making it easier to control the temperature of each fermenter. Fermentation proceeds at appropriate temperatures in the separate fermenters, thereby shortening the time required to produce methane gas. In other words, organic waste can be treated more efficiently.

[0092] Furthermore, in the organic waste treatment device 1 of the embodiment, by separating the fermentation tanks, if there are insufficient bacteria for each fermentation, additional bacteria can be added. For example, in the organic waste treatment device 1 of the embodiment, by adding additional hydrogen-utilizing methanogens when starting fermentation in the high-temperature fermentation tank 30, fermentation can be promoted and the time until methane gas is produced can be shortened. In the low-temperature fermentation tank 40, by adding acetate-utilizing methanogens when starting fermentation, fermentation can be promoted and the time until methane gas is produced can be shortened.

[0093] Furthermore, in the high-temperature fermentation tank 30, fermentation is performed at a high temperature, so solubilization is rapid and methane gas can be produced in a short period of time, which allows the size of the high-temperature fermentation tank 30 to be reduced. In the low-temperature fermentation tank 40, the treated material is fermented, solubilized, and has a high liquid ratio (where acid production has progressed), so methane gas can be produced in a short period of time, which allows the low-temperature fermentation tank 40 to be reduced in size.

[0094] In addition to the subcritical water treatment device 10, mixing tank 20, high-temperature fermenter 30, low-temperature fermenter 40, and digested liquid tank 50, the organic waste treatment device 1 of this embodiment may also include a control device (not shown) that controls the overall organic waste treatment by these devices. The control device may be configured to control the temperature and pressure in each treatment tank, the flow rate of organic waste between each treatment tank, the amount of various bacteria injected, and the like, based on the outputs of various meters and sensors included in the organic waste treatment device 1. The control device is realized, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of the components of the control device may be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by a combination of software and hardware. The program may be stored in advance in a storage device (a storage device having a non-transitory storage medium) such as a hard disk drive (HDD) or flash memory, or may be stored in a removable storage medium (a non-transitory storage medium) such as a DVD or CD-ROM, and installed by inserting the storage medium into a drive device. Furthermore, some or all of the functions of the control device may be distributed among the subcritical water treatment device 10, the mixing tank 20, the high-temperature fermenter 30, the low-temperature fermenter 40, and the digested liquid tank 50.

[0095] According to the organic waste treatment device 1 of the first to fourth embodiments described above, it is possible to improve the energy efficiency and treatment efficiency in organic waste treatment from multiple perspectives, making it possible to treat organic waste more efficiently than with conventional methods.

[0096] The above-described embodiment can be expressed as follows: An organic matter treatment apparatus for converting organic matter into fuel gas, comprising: a hydrolysis treatment apparatus; a first fermenter; a second fermenter; a storage medium storing computer-readable instructions; and a processor connected to the storage medium, wherein the processor executes the computer-readable instructions to: control the hydrolysis treatment apparatus to hydrolyze the organic matter mixed with water under high-temperature and high-pressure conditions; control the first fermenter to produce the fuel gas by fermenting the organic matter under first temperature conditions; and control the second fermenter to produce the fuel gas by fermenting the organic matter under second temperature conditions, wherein the temperature under the first temperature conditions is higher than the temperature under the second temperature conditions.

[0097] The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made within the scope that does not deviate from the gist of the present invention.

[0098] REFERENCE SIGNS LIST 1 Organic waste treatment device 10 Subcritical water treatment device 110 Treatment tank 111 Agitator 120 Water adding means 130 Heating means 20 Mixing tank 30 High temperature fermentation tank 32 Nitrogen sensor 33 Phosphorus sensor 34 Potassium sensor 40 Low temperature fermentation tank 50, 50A Digested liquid tank 51 Digested liquid discharge section 51 Thermometer 52 Concentration sensor 60 Pressure accumulation device 70 Solid-liquid separation device 80 Heat exchanger

Claims

1. An apparatus for converting organic matter into fuel gas, comprising: a hydrolysis treatment apparatus that hydrolyzes a mixture of the organic matter and water under high-temperature and high-pressure conditions; a first fermenter that produces the fuel gas by fermenting the organic matter under first temperature conditions; and a second fermenter that produces the fuel gas by fermenting the organic matter under second temperature conditions, wherein the temperature under the first temperature conditions is higher than the temperature under the second temperature conditions.

2. The organic matter treatment device according to claim 1, wherein the temperature difference between the temperature according to the first temperature condition and the temperature according to the second temperature condition is 10°C or more.

3. The organic matter treatment device according to claim 1, wherein the temperature according to the first temperature condition is 70°C or higher.

4. The organic matter treatment device according to claim 1, wherein the temperature according to the second temperature condition is 65°C or less.

5. The organic matter treatment device according to claim 1, wherein the fuel gas contains methane.

6. The organic matter treatment device according to claim 5, wherein a reaction to produce methane using hydrogen as a reactant occurs in the first fermenter.

7. The organic matter treatment device according to claim 5, wherein a reaction to produce methane using an organic acid as a reactant occurs in the second fermenter.

8. The organic matter treatment device according to claim 1, wherein the fermentation is anaerobic fermentation.

9. An organic matter treatment method for converting organic matter into fuel gas, the method comprising: hydrolyzing the organic matter mixed with water under high temperature and high pressure conditions using a hydrolysis treatment device; fermenting the organic matter under first temperature conditions in a first fermentation tank to produce the fuel gas; and fermenting the organic matter under second temperature conditions in a second fermentation tank to produce the fuel gas, wherein the temperature under the first temperature conditions is higher than the temperature under the second temperature conditions.

10. A method for producing fuel gas by converting organic matter into fuel gas, comprising: a hydrolysis treatment step in which the organic matter is mixed with water and hydrolyzed under high-temperature and high-pressure conditions; a step in which the organic matter treated in the hydrolysis treatment step is fermented under first temperature conditions to produce the fuel gas; and a step in which the organic matter treated in the hydrolysis treatment step is fermented under second temperature conditions to produce the fuel gas, wherein the temperature under the first temperature conditions is higher than the temperature under the second temperature conditions.

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