Methane fermentation device and methane fermentation method

Abstract

To simply perform a maintenance work such as exchange of conductive substances without opening a methane fermentation tank while preventing deterioration in an effective volume in a methane fermentation tank.SOLUTION: A device includes a methane fermentation tank 2 for methane fermentation treatment of an organic waste A, a contact part 3 provided outside of the methane fermentation tank 2 and provided with a conductive substance D, and a methane fermentation liquid feed section 4 for feeding a methane fermentation liquid B in the methane fermentation tank 2 to the contact part 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation apparatus and a methane fermentation method for treating organic waste by methane fermentation. [Background technology]

[0002] Methane fermentation (anaerobic fermentation) is widely used to reduce the volume of organic waste generated in wastewater treatment, such as sludge and biomass, and to convert it into energy. Methane fermentation is a technology in which organic matter is stored under anaerobic conditions for a certain period of time, and the organic waste is decomposed by anaerobic microorganisms to produce biogas such as methane gas and carbon dioxide. This technology is widely used in waste treatment facilities and wastewater treatment facilities in Japan.

[0003] The proportion of methane gas contained in biogas obtained by methane fermentation is affected by the type of organic waste used in the methane fermentation process, but is approximately 60%, with carbon dioxide making up the majority of the remainder. To further improve the efficiency of methane production, for example, Patent Document 1 discloses a method of contacting the methane fermentation liquid with a conductive material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-98265 Summary of the Invention [Problem to be solved by the invention]

[0005] In the method of Patent Document 1, a fixing part for fixing the conductive material inside the methane fermentation tank is provided, which may reduce the effective capacity of the methane fermentation tank. Furthermore, when replacing the conductive material, the methane fermentation tank must be opened, which is costly and time-consuming, and may have a negative impact on the environment, such as the release of malodorous components.

[0006] In view of this situation, the main object of the present invention is to provide a methane fermentation apparatus and a methane fermentation method that can prevent the effective volume in the methane fermentation tank from decreasing while easily performing maintenance work such as replacing conductive materials without opening the methane fermentation tank. [Means for solving the problem]

[0007] A first characteristic configuration of the present invention is a methane fermentation tank for treating organic waste by methane fermentation, a contact portion disposed outside the methane fermentation tank and having a conductive material disposed therein; and a methane fermentation liquid supply unit that supplies the methane fermentation liquid in the methane fermentation tank to the contact unit.

[0008] According to this configuration, since the contact part is disposed outside the methane fermentation tank, there is no need to provide a structure for fixing the conductive material inside the methane fermentation tank, and it is possible to prevent a decrease in the effective volume of the methane fermentation tank. Moreover, maintenance work such as replacing the conductive material can be easily performed without opening the methane fermentation tank.

[0009] A second characteristic configuration of the present invention is that a first discharge section is provided that discharges the biogas obtained in the contact section to the outside without returning the methane fermentation liquid supplied to the contact section to the methane fermentation tank.

[0010] According to this configuration, the unreacted organic components in the methane fermentation liquid supplied to the contact section by the methane fermentation liquid supply section can be gasified in the contact section, and the gasified biogas can be discharged to the outside by the first discharge section, so the amount of unreacted organic components in the methane fermentation liquid is reduced, thereby reducing the burden on various downstream facilities such as wastewater treatment and sludge treatment facilities. Moreover, because the methane fermentation liquid supplied to the contact section is not returned to the methane fermentation tank, there is no need to provide a configuration for returning the methane fermentation liquid to the methane fermentation tank, which simplifies the configuration.

[0011] A third characteristic configuration of the present invention is that it is provided with a methane fermentation liquid return section that returns the methane fermentation liquid supplied to the contact section to the methane fermentation tank, and a second discharge section that discharges the biogas obtained in the methane fermentation tank to the outside.

[0012] According to this configuration, the methane fermentation liquid is returned from the contact section to the methane fermentation tank in the methane fermentation liquid returning section, so that the methane fermentation liquid in the methane fermentation tank can be circulated through the methane fermentation liquid supply section and the methane fermentation liquid returning section. This increases the number of times the methane fermentation liquid comes into contact with the conductive material, and enables efficient conversion of organic matter in the methane fermentation liquid to methane gas. Biogas containing the converted methane gas can be discharged outside the methane fermentation tank in the second discharge section and supplied to another biogas utilization device, etc.

[0013] A fourth characteristic configuration of the present invention is that at least a portion of the organic waste is mixed with at least a portion of the methane fermentation liquid returned by the methane fermentation liquid returning section to generate organic waste for input, and the generated organic waste for input is input into the methane fermentation tank.

[0014] According to this configuration, the organic waste is mixed with the methane fermentation liquid returned by the return section before being charged into the methane fermentation tank, so that the decomposition reaction of the organic waste begins before being charged into the methane fermentation tank due to the action of microorganisms in the methane fermentation liquid that contribute to the methane fermentation process, and biogas can be efficiently produced. Also, for example, if the organic waste has a low moisture content, the organic waste can be diluted by mixing it with the methane fermentation liquid without having to supply water separately.

[0015] A fifth characteristic feature of the present invention is that the conductive material is in the form of powder, granules, porous material, fibers, or metal pieces.

[0016] According to this configuration, the conductive material is in the form of powder, granules, porous material, fibers, or metal pieces, so that the surface area can be increased and contact with the methane fermentation liquid can be made more effective.

[0017] A sixth characteristic configuration of the present invention is a first discharge unit that discharges the biogas obtained in the contact unit to the outside without returning the methane fermentation liquid supplied to the contact unit to the methane fermentation tank; a methane fermentation liquid returning section that returns the methane fermentation liquid supplied to the contact section to the methane fermentation tank; a second discharge section that discharges the biogas obtained in the methane fermentation tank to the outside; The present invention is characterized in that it is provided with an operating state switching unit that can freely switch between a first operating state in which the methane fermentation liquid supplied to the contact section is discharged to the outside by the first discharge section without being returned to the methane fermentation tank, and a second operating state in which the methane fermentation liquid supplied to the contact section is returned to the methane fermentation tank by the methane fermentation liquid returning unit, and the biogas is discharged to the outside by the second discharge section, based on the total amount of biogas obtained from at least one or both of the first discharge section and the second discharge section.

[0018] In the first operating state, the methane fermentation liquid supplied to the contact section is not returned to the methane fermentation tank, and biogas is discharged to the outside at the first discharge section. Therefore, by gasifying the unreacted organic matter in the methane fermentation liquid at the contact section, the amount of unreacted organic matter in the methane fermentation liquid is reduced, thereby reducing the burden on various downstream facilities such as wastewater treatment and sludge treatment facilities.

[0019] In the second operating state, the methane fermentation liquid in the methane fermentation tank is circulated through the methane fermentation liquid supply section and the methane fermentation liquid return section, thereby increasing the number of contacts between the methane fermentation liquid and the conductive material in the contact section and improving the efficiency of methane gas production.

[0020] Therefore, with this configuration, the operating state switching unit switches between the first operating state and the second operating state based on the total amount of biogas obtained from at least one or both of the first discharge unit and the second discharge unit. This makes it possible to switch to an appropriate operating state depending on the total amount of biogas obtained, thereby achieving a reduction in running costs while obtaining a desired amount of biogas.

[0021] A seventh characteristic configuration of the present invention is a methane fermentation method for treating organic waste by methane fermentation in a methane fermentation tank, The methane fermentation liquid supply step is performed in which the methane fermentation liquid in the methane fermentation tank is supplied from a methane fermentation liquid supply unit to a contact unit disposed outside the methane fermentation tank and having a conductive material disposed therein.

[0022] According to this configuration, since the contact part is disposed outside the methane fermentation tank, there is no need to provide a structure for fixing the conductive material inside the methane fermentation tank, and it is possible to prevent a decrease in the effective volume of the methane fermentation tank. Moreover, maintenance work such as replacing the conductive material can be easily performed without opening the methane fermentation tank.

[0023] An eighth characteristic configuration of the present invention is a methane fermentation liquid returning step in which the methane fermentation liquid supplied to the contact section is returned to the methane fermentation tank by a methane fermentation liquid returning section; a biogas discharge step in which the biogas obtained in the methane fermentation tank is discharged to the outside in a second discharge section; The methane fermentation liquid in the methane fermenter is circulated through the methane fermentation liquid supply section and the methane fermentation liquid return section a number of times set within a range of 1 to 10 times per day.

[0024] By circulating the methane fermentation liquid in the methane fermentation tank through the methane fermentation liquid supply section and the methane fermentation liquid return section, the number of times the methane fermentation liquid comes into contact with the conductive material in the contact section can be increased, which is expected to improve the efficiency of methane gas production. However, if the number of times the methane fermentation liquid is circulated too many times, the energy consumption of the circulation pump and other components increases, resulting in increased running costs.

[0025] Therefore, according to this configuration, the number of times the methane fermentation liquid is circulated is set within a range of 1 to 10 times per day. This prevents the number of circulations from becoming too high, which would increase running costs, and allows the methane fermentation liquid to come into contact with the conductive material in the contact section, thereby improving the efficiency of methane gas production. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a methane fermentation apparatus according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing a schematic configuration of a methane fermentation apparatus according to a second embodiment. [Figure 3] FIG. 10 is a diagram showing a schematic configuration of a methane fermentation apparatus according to a third embodiment. [Figure 4] FIG. 10 is a diagram showing a schematic configuration of a methane fermentation apparatus according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] A methane fermentation apparatus and a methane fermentation method according to the present invention will be described with reference to the drawings. [First embodiment] As shown in FIG. 1, this methane fermentation apparatus 1 is equipped with a methane fermentation tank 2 that subjects organic waste A to methane fermentation to produce biogas C, a contact section 3 in which a conductive material D is placed, a methane fermentation liquid supply section 4 that supplies a methane fermentation liquid B containing organic waste A in the methane fermentation tank 2 to the contact section 3, and a methane fermentation liquid return section 5 that returns the methane fermentation liquid B supplied to the contact section 3 to the methane fermentation tank 2.

[0028] The methane fermentation tank 2 is used to carry out a methane fermentation treatment process in which organic waste A, such as sewage sludge or food waste, is subjected to methane fermentation (anaerobic fermentation). In the methane fermentation tank 2, a methane fermentation liquid B containing organic waste A is stored, and biogas C is produced by carrying out methane fermentation treatment while maintaining the temperature of the methane fermentation liquid B within a predetermined range.

[0029] The organic matter volume load of the methane fermentation tank 2 is not particularly limited and may be set appropriately, but is preferably 0.5 to 30 kg / (m 3 ·day), more preferably 1 to 6 kg / (m 3The organic matter volume load is the value obtained by dividing the amount of organic matter (VS) in the methane fermentation raw material supplied to the methane fermentation tank 2 by the volume of the methane fermentation liquid B in the methane fermentation tank 2.

[0030] Regarding the predetermined range of optimum temperatures in methane fermentation treatment, when methane fermentation treatment is performed at a medium temperature, the predetermined range of optimum temperatures can be set to, for example, a temperature range of 30°C to 45°C, and when methane fermentation treatment is performed at a high temperature, the predetermined range of optimum temperatures can be set to, for example, a temperature range of 50°C to 60°C.

[0031] The methane fermentation tank 2 is equipped with an organic waste supply section 21 that supplies organic waste A into the methane fermentation tank 2, an agitator (not shown) that agitates the methane fermentation liquid B in the methane fermentation tank 2, a heating device (not shown) that heats the methane fermentation liquid B in the methane fermentation tank 2, and a discharge device (not shown) that discharges sediments and the like that accumulate in the methane fermentation tank 2.

[0032] The methane fermentation tank 2 receives and stores the methane fermentation liquid B containing the organic waste A. For this reason, more than half of the methane fermentation tank 2 in its height direction (vertical direction) is a liquid phase section 22 in which the methane fermentation liquid B is stored, and the remaining upper part is a gas phase section 23 in which the methane fermentation liquid B is not stored.

[0033] A second discharge section 24 is disposed above the methane fermentation tank 2, and discharges the biogas C obtained from the methane fermentation tank 2. The second discharge section 24 is preferably disposed, for example, so as to discharge the biogas C from the gas phase section 23 of the methane fermentation tank 2, and the biogas C obtained from the methane fermentation tank 2 can be appropriately discharged to the outside. The biogas C discharged in the second discharge section 24 can be supplied to various types of biogas utilization facilities.

[0034] The contact section 3 is disposed outside the methane fermentation tank 2, and can be configured, for example, as a filled tank that can be freely filled with the conductive material D. This eliminates the need to provide a structure for fixing the conductive material D inside the methane fermentation tank 2, and can prevent a decrease in the effective volume inside the methane fermentation tank 2. Moreover, maintenance work such as replacing the conductive material D can be easily performed without opening the methane fermentation tank 2. Furthermore, since the conductive material D is not supplied into the methane fermentation tank 2, the conductive material D is prevented from accumulating as sediment in the methane fermentation tank 2, and the generation of sediment in the methane fermentation tank 2 can be prevented.

[0035] The conductive substance D may be in the form of powder, granules, porous material, fibers, or metal pieces. This increases the surface area of ​​the conductive substance D, enabling it to come into effective contact with the methane fermentation liquid B. The conductive substance D may be, for example, steel wool, activated carbon, or metal powder. Examples of metals that can be used include copper and iron.

[0036] When using a relatively small conductive material D, such as activated carbon, it is preferable to use a retaining material such as a membrane or net to prevent the conductive material D from leaking out of the contact portion 3.

[0037] Although not shown in the figure, the contact section 3 may be equipped with an agitator or a flow direction control section that controls the flow direction of the methane fermentation liquid B, thereby improving the contact efficiency between the conductive material D and the methane fermentation liquid B.

[0038] The temperature of the methane fermentation liquid B in the contact section 3 can be set within a predetermined suitable temperature range, as in the methane fermentation tank 2. When methane fermentation treatment is performed at a medium temperature, the predetermined suitable temperature range can be set, for example, to a temperature range of 30°C to 45°C, and when methane fermentation treatment is performed at a high temperature, the predetermined suitable temperature range can be set, for example, to a temperature range of 50°C to 60°C. Incidentally, although not shown, in order to keep the temperature of the methane fermentation liquid B in the contact section 3 within the predetermined suitable temperature range, a heating device (heat exchanger for heating) or the like can be provided at an intermediate position on the methane fermentation liquid supply path 41. When a heating device is provided at an intermediate position on the methane fermentation liquid supply path 41 or the like in this way, it can also be used as a heating device for adjusting the temperature of the methane fermentation liquid B in the methane fermentation tank 2.

[0039] The methane fermentation liquid supply unit 4 is equipped with a methane fermentation liquid supply path 41 that extracts the methane fermentation liquid B from the methane fermenter 2 and supplies it to the contact unit 3, and a methane fermentation liquid supply pump 42. The upstream end of the methane fermentation liquid supply path 41 is connected to a lower portion of the methane fermenter 2 (a portion corresponding to the liquid phase portion 22), and the downstream end is connected to the contact unit 3. The methane fermentation liquid supply pump 42 is disposed midway along the methane fermentation liquid supply path 41.

[0040] The methane fermentation liquid supply unit 4 supplies the methane fermentation liquid B in the methane fermenter 2 to the contact unit 3 through a methane fermentation liquid supply path 41, and a methane fermentation liquid discharge unit 43 branches off from a midpoint of the methane fermentation liquid supply path 41. This allows a portion of the methane fermentation liquid B in the methane fermenter 2 to be supplied to the contact unit 3 through the methane fermentation liquid supply path 41, while the remaining portion is discharged through the methane fermentation liquid discharge unit 43. The methane fermentation liquid discharge unit 43 is not limited to being branched off from a midpoint of the methane fermentation liquid supply path 41, and for example, the upstream end of the methane fermentation liquid discharge unit 43 can be connected to the methane fermenter 2, and the methane fermentation liquid supply path 41 and the methane fermentation liquid discharge unit 43 can be provided separately.

[0041] The methane fermentation liquid returning section 5 is provided with a methane fermentation liquid returning path 51 that returns the methane fermentation liquid B from the contact section 3 to the methane fermentation tank 2. The upstream end of the methane fermentation liquid returning path 51 is connected to the contact section 3, and the downstream end is connected to an upper part (a part corresponding to the gas phase section 23) of the methane fermentation tank 2. The upper part is not limited to a part corresponding to the gas phase section 23, and may be a part corresponding to the liquid phase section 22 as long as it is above the upstream end of the methane fermentation liquid supply path 41.

[0042] When returning the methane fermentation liquid B to the methane fermentation tank 2, the methane fermentation liquid return section 5 can not only return the methane fermentation liquid B directly to the methane fermentation tank 2, but also indirectly return the methane fermentation liquid B to the methane fermentation tank 2 via the organic waste supply section 21 by supplying the methane fermentation liquid B to the organic waste supply section 21, as shown by the dotted line in Figure 1.

[0043] 1, the downstream end of the methane fermentation liquid return path 51 is connected to the organic waste supply unit 21. As a result, at least a portion of the organic waste A is mixed with at least a portion of the methane fermentation liquid B returned by the methane fermentation liquid return unit 5 to generate organic waste A1 for input, and the generated organic waste A1 for input can be input into the methane fermentation tank 2.

[0044] By operating the methane fermentation liquid supply pump 42 in the methane fermentation liquid supply unit 4, the methane fermentation liquid B in the methane fermentation tank 2 can be circulated by passing it through the methane fermentation liquid supply path 41, the contact unit 3, and the methane fermentation liquid return path 51 in this order. This increases the number of times the methane fermentation liquid B comes into contact with the conductive material D in the contact unit 3, and enables the organic components in the methane fermentation liquid B to be efficiently converted into methane gas.

[0045] In this embodiment, by operating the methane fermentation liquid supply pump 42, a methane fermentation liquid supply process is carried out in which the methane fermentation liquid B in the methane fermentation tank 2 is supplied to the contact section 3 by the methane fermentation liquid supply section 4, and further, a methane fermentation liquid return process is carried out in which the methane fermentation liquid B supplied to the contact section 3 is returned from the contact section 3 to the methane fermentation tank 2 by the methane fermentation liquid return section 5, and a biogas discharge process is carried out in which the biogas C obtained in the methane fermentation tank 2 is discharged to the outside by the second discharge section 24.

[0046] The number of times that the methane fermentation liquid supply pump 42 is operated to circulate the methane fermentation liquid B in the methane fermentation tank 2 through the methane fermentation liquid supply section 4 and the methane fermentation liquid return section 5 is set within a set range, for example, from once to ten times per day. Thus, a circulation state control section 6 is provided that controls the operating state of the methane fermentation liquid supply pump 42 so that the circulation number falls within the set range. Incidentally, the circulation number is a value obtained by dividing the pump flow rate by the effective volume of the methane fermentation tank 2, and for example, when the pump flow rate is 20 m 3 / hr, the effective volume of methane fermentation tank 2 is 1000m 3 In this case, the number of cycles is 1000 ÷ (20 × 24) ≒ 2 times per day.

[0047] At this time, the circulation state control unit 6 can perform continuous operation by continuously operating the methane fermentation liquid supply pump 42 so that the circulation number is within a set range, but can also perform intermittent operation by, for example, operating the methane fermentation liquid supply pump 42 for a set operation time and then stopping the methane fermentation liquid supply pump 42 for a set stop time, thereby repeatedly operating and stopping the methane fermentation liquid supply pump 42.

[0048] Furthermore, the circulation state control unit 6 can simply operate the methane fermentation liquid supply pump 42 at all times, rather than setting the circulation number within a set range. Furthermore, the circulation state control unit 6 can control the circulation state of the methane fermentation liquid B by controlling the operating state of the methane fermentation liquid supply pump 42 based on the discharge amount of biogas C discharged from the second discharge unit 24 and the methane gas concentration of biogas C, etc. Possible circulation states of the methane fermentation liquid B include, for example, whether or not to circulate the methane fermentation liquid B, the timing at which to circulate it, and the duration of circulation.

[0049] 1 illustrates an example of a filled tank filled with a conductive substance D as the contact unit 3, but the contact unit 3 may also be provided as a filler filled with a conductive substance D on the methane fermentation liquid supply path 41 and the methane fermentation liquid return path 51. The location of the contact unit 3 can be changed as appropriate, and is not limited to being installed at a location separate from the methane fermentation tank 2. For example, the contact unit 3 may be provided as an integral part of the methane fermentation tank 2 by being freely attachable and detachable to the outer wall of the methane fermentation tank 2. Furthermore, the outside of the methane fermentation tank 2 may be any location that is outward from the internal space of the methane fermentation tank 2. For example, the filled tank itself may be manufactured from a material containing the conductive substance D, and the tank itself, which is disposed outward from the internal space of the methane fermentation tank 2, may serve as the contact unit 3, and the methane fermentation liquid B in the methane fermentation tank 2 may be brought into contact with the contact unit 3 (the tank itself).

[0050] The contact unit 3 is not limited to a fixed type that is fixed to a desired installation location, but may be a portable type that can be transported to a location corresponding to an existing methane fermentation tank 2 and installed there.

[0051] When an existing methane fermentation tank 2 is used, it may already be equipped with a circulation path for circulating the methane fermentation liquid B. In this case, the existing circulation path can be used as the methane fermentation liquid supply path 41 and the methane fermentation liquid return path 51, and there is no need to newly provide the methane fermentation liquid supply path 41 and the methane fermentation liquid return path 51.

[0052] Second Embodiment This second embodiment is an embodiment different from the first embodiment in that it is different from the first embodiment in that it is different in the flow state of the methane fermentation liquid B from the contact section 3. The other configurations are the same as those of the first embodiment, so the description will be centered on the flow state of the methane fermentation liquid B from the contact section 3, with reference to Fig. 2, and the other configurations will be denoted by the same reference numerals, and description thereof will be omitted.

[0053] In the first embodiment, as shown in FIG. 1 , a methane fermentation liquid return section 5 is provided, so that the methane fermentation liquid B from the contact section 3 is returned to the methane fermentation tank 2, and the methane fermentation liquid B in the methane fermentation tank 2 is circulated through the methane fermentation liquid supply section 4 and the methane fermentation liquid return section 5.

[0054] In contrast, in the second embodiment, as shown in FIG. 2, a first discharge section 31 is provided that discharges the biogas C obtained in the contact section 3 to the outside without returning the methane fermentation liquid B supplied to the contact section 3 to the methane fermentation tank 2, and a methane fermentation liquid discharge section 32 is provided that discharges a portion of the methane fermentation liquid B supplied to the contact section 3 to the outside.

[0055] As a result, unreacted organic components in the methane fermentation liquid B supplied to the contact section 3 by the methane fermentation liquid supply section 4 can be gasified in the contact section 3, and the gasified biogas C can be discharged to the outside by the first discharge section 31. A portion of the methane fermentation liquid B supplied to the contact section 3 can be discharged to the outside of the contact section 3 by the methane fermentation liquid discharge section 32. Although not shown, a pump for supplying the methane fermentation liquid B from the methane fermentation tank 2 to the contact section 3 can be disposed at a midpoint of the methane fermentation liquid supply path 41 of the methane fermentation liquid supply section 4. Incidentally, by providing a difference in elevation between the installation location of the methane fermentation tank 2 and the installation location of the contact section 3 so that the contact section 3 is lower, the difference in elevation can be used to supply the methane fermentation liquid B from the methane fermentation tank 2 to the contact section 3, and in this case the pump can be omitted.

[0056] In FIG. 2, the first discharge section 31 and the methane fermentation liquid discharge section 32 are arranged separately, but by providing one fluid flow path, it is possible to discharge the biogas C obtained in the contact section 3 and a portion of the methane fermentation liquid B supplied to the contact section 3 together to the outside.

[0057] In the second embodiment shown in FIG. 2, the methane fermentation liquid return section 5 can be omitted compared to the first embodiment shown in FIG. 1. Therefore, even if an existing methane fermentation tank 2 does not have a circulation path for circulating the methane fermentation liquid B, the second embodiment can be applied to the existing methane fermentation tank 2 by simply providing the methane fermentation liquid supply section 4.

[0058] Third Embodiment This third embodiment is a variation of the contact portion 3 in the second embodiment. Other configurations are the same as those in the first and second embodiments, so the following description will focus on the configuration of the contact portion 3 with reference to Fig. 3, and the other configurations will be denoted by the same reference numerals and will not be described again.

[0059] As shown in Fig. 3, the contact section 3 is configured using a seal pot that forms a liquid phase section 33 with the supplied methane fermentation liquid B. The contact section 3 is provided with a storage section 34 that stores the supplied methane fermentation liquid B, and an overflow section 35 to which the methane fermentation liquid B is supplied as the methane fermentation liquid B overflows from the storage section 34, as shown by the outline arrow in Fig. 3.

[0060] The downstream end of the methane fermentation liquid supply path 41 of the methane fermentation liquid supply unit 4 is extended to the inside of the storage unit 34 of the contact unit 3, and the methane fermentation liquid B is supplied to the inside of the liquid phase unit 33 formed by the methane fermentation liquid B stored in the storage unit 34. The storage unit 34 is filled with a conductive material D (the portion shown in gray in FIG. 3 ), and is configured so that the methane fermentation liquid B stored in the storage unit 34 comes into contact with the conductive material D.

[0061] In the contact section 3, a methane fermentation liquid discharge section 32 is provided at the lower end of the overflow section 35. The methane fermentation liquid B that overflows from the storage section 34 and is supplied to the overflow section 35 can be discharged to the outside of the contact section 3 through the methane fermentation liquid discharge section 32. In the contact section 3, a first discharge section 31 is provided at the upper end of the overflow section 35. The biogas C obtained in the contact section 3 can be discharged to the outside of the contact section 3 through the first discharge section 31.

[0062] When a contact section 3 using a seal pot is provided, the methane fermentation liquid B is supplied from the methane fermentation tank 2 to the contact section 3 by the pressure of the organic waste A supplied to the methane fermentation tank 2 and the biogas C obtained in the methane fermentation tank 2, and the methane fermentation liquid B overflows from the storage section 34 to the overflow section 35 and can be discharged from the methane fermentation liquid discharge section 32 to the outside of the contact section 3. In this way, in view of the principle of supplying the methane fermentation liquid B using a seal pot, a pump is not necessary for supplying the methane fermentation liquid B from the methane fermentation tank 2 to the contact section 3, but the provision of a pump does not impair the effects of the invention and may therefore be provided as appropriate.

[0063] [Fourth embodiment] This fourth embodiment has a configuration that combines the configuration shown in the first embodiment and the configuration shown in the second embodiment with respect to the flow state of the methane fermentation liquid B from the contact section 3. Since the other configurations are the same as those of the first and second embodiments, the configuration that combines the configuration shown in the first embodiment with the configuration shown in the second embodiment with respect to the flow state of the methane fermentation liquid B from the contact section 3 will be mainly described with reference to Fig. 4, and the other configurations will be denoted by the same reference numerals, and description thereof will be omitted.

[0064] As shown in Fig. 4, similarly to the first embodiment shown in Fig. 1, in addition to the methane fermentation liquid supply unit 4, a methane fermentation liquid return unit 5 that returns the methane fermentation liquid B supplied to the contact unit 3 to the methane fermentation tank 2 is provided. The methane fermentation liquid return unit 5 is provided with a methane fermentation liquid return path 51 that connects the contact unit 3 and the methane fermentation tank 2, and a return pump 52 arranged midway along the methane fermentation liquid return path 51.

[0065] As shown in Fig. 4, similarly to the second embodiment shown in Fig. 2, a first discharge section 31 is provided that discharges the biogas C obtained in the contact section 3 to the outside. As a result, the biogas C obtained in the contact section 3 can be discharged to the outside of the contact section 3 at the first discharge section 31, and the biogas C obtained in the methane fermentation tank 2 can be discharged to the outside of the methane fermentation tank 2 at the second discharge section 24. The first discharge section 31 and the second discharge section 24 are joined at a confluence discharge section 61, and the biogas C from the first discharge section 31 and the biogas C from the second discharge section 24 are joined and configured to flow through the confluence discharge section 61.

[0066] The confluence discharge section 61 is provided with a biogas total amount acquisition section 62 that detects the flow rate and the like of the biogas C. Whether the biogas C is discharged from only one of the first discharge section 31 and the second discharge section 24 or whether the biogas C is discharged from both the first discharge section 31 and the second discharge section 24, the biogas total amount acquisition section 62 detects the flow rate and the like of the biogas C at the confluence discharge section 61 to acquire the total amount of biogas C obtained from at least one of the first discharge section 31 and the second discharge section 24.

[0067] In this fourth embodiment, by combining the first and second embodiments, the flow state of the methane fermentation liquid B can be freely switched between a first operating state indicated by the solid black arrow in Figure 4 and a second operating state indicated by the hollow arrow in Figure 4.

[0068] In the first operating state, as shown by the filled arrows in Fig. 4, the methane fermentation liquid B supplied to the contact section 3 is not returned to the methane fermentation tank 2 but is discharged to the outside of the contact section 3 by the methane fermentation liquid discharge section 32. In contrast, in the second operating state, as shown by the hollow arrows in Fig. 4, the methane fermentation liquid B supplied to the contact section 3 is returned to the methane fermentation tank 2 by the methane fermentation liquid return section 5, thereby circulating the methane fermentation liquid B.

[0069] The methane fermentation apparatus 1 is provided with an operating state switching unit 7 that switches between a first operating state and a second operating state. The operating state switching unit 7 switches to the first operating state by stopping the operation of the return pump 52, and switches to the second operating state by operating the return pump 52. In this way, the operating state switching unit 7 is configured to be able to freely switch between the first operating state and the second operating state by controlling the operating state of the return pump 52.

[0070] 4, a return pump 52 is shown as an example of a return interruption unit that interrupts the return of the methane fermentation liquid B from the contact unit 3 to the methane fermentation tank 2 by the methane fermentation liquid return unit 5, but it is also possible to combine it with, for example, an on-off valve that opens and closes the methane fermentation liquid return path 51. The return interruption unit that interrupts the return of the methane fermentation liquid B from the contact unit 3 to the methane fermentation tank 2 by the methane fermentation liquid return unit 5 is not limited to the return pump 52, and various return interruption units can be used.

[0071] The operating state switching unit 7 switches between the first operating state and the second operating state based on the total amount of biogas acquired by the total biogas amount acquiring unit 62. In the first operating state, biogas C is obtained from both the contact unit 3 and the methane fermentation tank 2, so the total amount of biogas C discharged from the first discharge unit 31 and the second discharge unit 24 can be acquired by the total biogas amount acquiring unit 62. In the second operating state, the methane fermentation liquid B and the conductive material D are in contact with each other in the contact unit 3, so it is considered that biogas C is basically obtained from both the contact unit 3 and the methane fermentation tank 2. Therefore, the total amount of biogas C discharged from the first discharge unit 31 and the second discharge unit 24 can be acquired by the total biogas amount acquiring unit 62. However, depending on various conditions such as the flow state of the methane fermentation liquid B in the contact unit 3 and the circulation conditions of the methane fermentation liquid B, it is also possible that biogas C is obtained only from the methane fermentation tank 2. At this time, only the biogas C discharged from the second discharge unit 24 is acquired by the total biogas amount acquisition unit 62 as the total amount of biogas.

[0072] For example, the state switched to the first operating state is set as the basic operating state, and in the basic operating state, if the total amount of biogas acquired by the total biogas amount acquisition unit 62 is equal to or greater than the first set amount, the operating state switching unit 7 maintains the basic operating state, and when the total amount of biogas acquired by the total biogas amount acquisition unit 62 becomes less than the first set amount, the operating state switching unit 7 can switch from the basic operating state to the second operating state.

[0073] Conversely, the state switched to the second operating state can also be set as the basic operating state, and the switching conditions for switching between the first operating state and the second operating state based on the total amount of biogas acquired by the total biogas amount acquisition unit 62 can be changed as appropriate, and various conditions can be set.

[0074] The switching conditions for switching between the first operating state and the second operating state are not limited to conditions based on the total amount of biogas acquired by the total biogas amount acquisition unit 62, but various conditions can be applied, such as the methane gas concentration of biogas C in the confluence discharge unit 61, the operating time between the first operating state and the second operating state, and predetermined priorities. [Explanation of symbols]

[0075] 1. Methane fermentation equipment 2. Methane fermentation tank 3 Contact area 4. Methane fermentation liquid supply section 5. Methane fermentation liquid return section 7 Operation state switching section 24 2nd discharge section 31 1st discharge section A. Organic waste A1 Organic waste for input B. Methane fermentation liquid C. Biogas D conductive material

Claims

1. a methane fermentation tank for treating organic waste through methane fermentation; a contact portion disposed outside the methane fermentation tank and having a conductive material disposed therein; a methane fermentation liquid supply section that supplies the methane fermentation liquid in the methane fermentation tank to the contact section.

2. 2. The methane fermentation apparatus according to claim 1, further comprising a first discharge section that discharges the biogas obtained in the contact section to the outside without returning the methane fermentation liquid supplied to the contact section to the methane fermentation tank.

3. 2. The methane fermentation apparatus according to claim 1, further comprising: a methane fermentation liquid return section that returns the methane fermentation liquid supplied to the contact section to the methane fermentation tank; and a second discharge section that discharges the biogas obtained in the methane fermentation tank to the outside.

4. 4. The methane fermentation apparatus according to claim 3, wherein at least a portion of the organic waste is mixed with at least a portion of the methane fermentation liquid returned by the methane fermentation liquid returning section to generate organic waste for input, and the generated organic waste for input is input into the methane fermentation tank.

5. 4. The methane fermentation apparatus according to claim 1, wherein the conductive material is in the form of a powder, granules, porous material, fiber, or metal piece.

6. a first discharge section that discharges the biogas obtained in the contact section to the outside without returning the methane fermentation liquid supplied to the contact section to the methane fermentation tank; a methane fermentation liquid returning section that returns the methane fermentation liquid supplied to the contact section to the methane fermentation tank; a second discharge section that discharges the biogas obtained in the methane fermentation tank to the outside; 4. The methane fermentation apparatus according to claim 1, further comprising an operating state switching unit that can switch between a first operating state in which the methane fermentation liquid supplied to the contact section is discharged to the outside by the first discharge section without being returned to the methane fermentation tank, and a second operating state in which the methane fermentation liquid supplied to the contact section is returned to the methane fermentation tank by the methane fermentation liquid returning unit, and the biogas is discharged to the outside by the second discharge section, based on the total amount of biogas obtained from at least one or both of the first discharge section and the second discharge section.

7. A methane fermentation method for subjecting organic waste to methane fermentation in a methane fermentation tank, A methane fermentation method comprising a methane fermentation liquid supply step in which the methane fermentation liquid in the methane fermentation tank is supplied from a methane fermentation liquid supply section to a contact section disposed outside the methane fermentation tank and having a conductive material disposed therein.

8. a methane fermentation liquid returning step in which the methane fermentation liquid supplied to the contact section is returned to the methane fermentation tank by a methane fermentation liquid returning section; a biogas discharge step of discharging the biogas obtained in the methane fermentation tank to the outside in a second discharge section; The methane fermentation method according to claim 7, wherein the number of times the methane fermentation liquid in the methane fermentation tank is circulated through the methane fermentation liquid supply section and the methane fermentation liquid return section is set in the range of 1 to 10 times per day.

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