Bio-methanation device and bio-methanation method

Abstract

To make a production amount of methane gas be larger to efficiently produce the methane gas.SOLUTION: There are provided: a methane fermentation tank 2 in which an organic waste A is subjected to a methane fermentation treatment; a bio-methanation tank 3 in which a bio-methanation treatment is conducted, that is arranged at a rear stage of the methane fermentation tank 2; a feed part 4 for feeding methane fermentation liquid C in the methane fermentation tank 2 and biogas D obtained by the methane fermentation treatment into the bio-methanation tank 3; and an anode 51 and a cathode 52. Also provided is a voltage application part 5 for applying a voltage to the methane fermentation liquid C inside the bio-methanation tank 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biomethanation device and a biomethanation method for converting carbon dioxide into methane gas using microorganisms. [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 through 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.

[0004] In order to obtain more methane gas, for example, Non-Patent Document 1 describes a process in which organic waste such as sludge generated in wastewater treatment is subjected to methane fermentation, and a voltage is applied to the methane fermentation liquid obtained by the methane fermentation process using electrodes to obtain methane gas and hydrogen.

[0005] Non-Patent Document 2 describes a method for producing methane gas by supplying hydrogen, carbon dioxide, and a nutrient medium to a reactor filled with activated carbon molded into pellets.

[0006] Patent Document 1 also describes a process for increasing the concentration of methane gas by supplying biogas obtained by methane fermentation to a carrier packed bed to which a methane fermentation liquid is sprayed and to which a voltage is applied by electrodes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-211976 [Non-patent literature]

[0008] [Non-Patent Document 1] Bo Wang,Wenzong Liu,Bin Liang,Jiandong Jiang,Aijie Wang,“Microbial fingerprints of methanation in a hybrid electro-biological anaerobic digestion”,Water Research,Volume 226,1 November 2022,119270 [Non-patent document 2] Alexandros Chatzis, Esteban Orellana, Maria Gaspari, Konstantinos Kontogiannopoulos, Laura Treu, Anastasios Zouboulis, Panagiotis G. Kougias, “Comparative study on packing materials for improved biological methanation in trickle Bed reactors”, Bioresource Technology, Volume 385, October 2023, 129456 Summary of the Invention [Problem to be solved by the invention]

[0009] In Non-Patent Document 1, simply applying a voltage to a methane fermentation liquid results in a small amount of carbon dioxide in the methane fermentation liquid, which serves as a substrate for methane production, and it is possible that the amount of methane gas obtained will not be commensurate with the energy required to apply the voltage. Furthermore, although the amount of methane gas obtained by applying a voltage increases, the methane concentration in the biogas cannot be increased, and therefore, when purifying methane gas, the man-hours and costs required for purification cannot be reduced.

[0010] The method of Non-Patent Document 2 requires a constant supply of carbon dioxide and hydrogen, and also requires that the supply ratio of carbon dioxide to hydrogen be maintained at a volume ratio of approximately 1:4, which may result in a large burden on maintenance and management.

[0011] In Patent Document 1, the methane fermentation liquid is simply sprayed onto the carrier-packed tank from above, which means that there will be areas in the carrier-packed layer where the methane fermentation liquid is not sufficiently sprayed, and as biogas passes through these areas, there is a possibility that the amount of methane gas produced will be reduced.In addition, Patent Document 1 tilts the carbon dioxide-methane equilibrium system toward methane production by adjusting the potential and pH, but it is not possible to significantly improve the methane gas concentration.

[0012] In view of this situation, a primary object of the present invention is to provide a biomethanation device and a biomethanation method that can improve the methane gas concentration or increase the amount of methane gas produced, thereby efficiently producing methane gas. [Means for solving the problem]

[0013] A first characteristic configuration of the present invention is a methane fermentation tank for treating organic waste by methane fermentation, a biomethanation tank that performs biomethanation treatment and is disposed downstream of the methane fermentation tank; a supply unit that supplies the methane fermentation liquid from the methane fermentation tank and the biogas obtained by the methane fermentation treatment into the biomethanation tank; The biomethanation tank is provided with a voltage application unit that has an anode and a cathode and applies a voltage to the methane fermentation liquid in the biomethanation tank.

[0014] According to this configuration, the supply unit supplies not only the methane fermentation liquid but also the biogas into the biomethanation tank. By using carbon dioxide in the biogas as a substrate, the amount of methane gas obtained from the biomethanation process can be increased. Furthermore, the methane gas concentration in the gas obtained from the biomethanation process is high, eliminating the need for purification, or reducing the labor and costs required for purification. Furthermore, because the supply unit supplies the methane fermentation liquid and the biogas into the biomethanation tank, the methane fermentation liquid and the biogas can be appropriately contacted under wet conditions, preventing the biogas from passing through the biomethanation tank without contacting the methane fermentation liquid. This increases the residence time of the biogas in the biomethanation tank, thereby increasing the amount of methane gas obtained from the biomethanation process.

[0015] Furthermore, because the system is divided into a methane fermentation tank for methane fermentation and a biomethanation tank for biomethanation, operation can be controlled under conditions suitable for each process, allowing for efficient biomethanation as well as methane fermentation.Furthermore, the biomethanation tank is habituated with archaea that contribute to biomethanation, thereby shortening the reaction time for biomethanation.

[0016] A second characteristic feature of the present invention is that a methane gas concentration detector is provided for detecting the concentration of methane gas obtained from the biomethanation tank.

[0017] According to this configuration, the methane gas concentration detector is provided, which makes it possible to grasp the concentration of methane gas obtained by biomethanation treatment, and therefore the methane gas concentration can be used as an index when managing the operating state of the biomethanation tank, etc. Therefore, it is possible to appropriately confirm whether the methane gas concentration is at a desired concentration, and it is also possible to reliably determine whether to take measures to increase the amount of methane gas produced.

[0018] A third characteristic feature of the present invention is that, in the biomethanation tank, the supply unit is disposed closer to the anode than to the cathode.

[0019] According to this configuration, by arranging the anode in the biomethanation tank closer to the supply unit than the cathode, the anode can be placed in a location where organic matter that serves as a substrate for the organic matter-decomposing bacteria is present, thereby decomposing the organic matter and generating protons. Therefore, at the cathode, methane gas can be appropriately produced using protons and carbon dioxide by the hydrogen-assimilating methanogenic archaea, improving the efficiency of conversion to methane gas.

[0020] A fourth characteristic feature of the present invention is that the biomethanation tank is provided with a biogas retention section for retaining biogas.

[0021] According to this configuration, the biogas retention section retains the biogas in the biomethanation tank, thereby increasing the retention time of the biogas in the biomethanation tank, thereby enabling efficient conversion to methane gas and improving the conversion efficiency to methane gas.

[0022] A fifth characteristic feature of the present invention is that the biogas retention section includes at least a flow direction regulator that regulates the flow direction of the biogas, or a carrier holding section that holds a carrier.

[0023] According to this configuration, biogas can be retained in the biomethanation tank simply by providing a flow direction regulating body or a carrier holding section, so that an appropriate biogas retention section can be provided while simplifying the configuration.

[0024] A sixth characteristic feature of the present invention is that the biogas retention section has retention locations for retaining the biogas around the anode and the cathode.

[0025] According to this configuration, the biogas retention section promotes the retention of biogas around the anode and cathode and the attachment and proliferation of microorganisms that contribute to biomethanation, thereby increasing the retention time of biogas around the anode and cathode. This allows for efficient conversion of carbon dioxide to methane gas using the anode and cathode, improving the efficiency of conversion to methane gas.

[0026] A seventh characteristic configuration of the present invention is a discharge fluid circulating unit that supplies at least a portion of the discharge fluid discharged from the biomethanation tank again to the biomethanation tank; a discharge fluid circulation control unit for controlling the discharge fluid circulation unit, When the concentration of methane gas obtained from the biomethanation tank falls below a set concentration, the discharge fluid circulation control unit executes discharge fluid circulation amount increase control to increase the amount of discharge fluid supplied again to the biomethanation tank by the discharge fluid circulation unit.

[0027] According to this configuration, when the concentration of methane gas obtained from the biomethanation tank falls below the set concentration, the discharge fluid circulation control unit executes control to increase the discharge fluid circulation rate, thereby increasing the amount of discharge fluid supplied to the biomethanation tank, thereby increasing the amount of biogas used in the biomethanation process and increasing the amount of methane gas produced. Therefore, even if the concentration of methane gas obtained from the biomethanation tank falls below the set concentration, the discharge fluid circulation control unit executes control to increase the discharge fluid circulation rate, thereby increasing the amount of methane gas produced and obtaining methane gas of a desired concentration higher than the set concentration.

[0028] An eighth characteristic configuration of the present invention is a methane fermentation treatment step of treating organic waste by methane fermentation in a methane fermenter; a biomethanation treatment step in which biomethanation treatment is performed in a biomethanation tank disposed downstream of the methane fermentation tank; a supply step of supplying the methane fermentation liquid from the methane fermentation tank and the biogas obtained by the methane fermentation treatment into the biomethanation tank; and a voltage application step of applying a voltage to the methane fermentation liquid in the biomethanation tank by means of an anode and a cathode.

[0029] According to this configuration, similar to the first characteristic configuration, in the supply step, not only the methane fermentation liquid but also biogas is supplied to the biomethanation tank. Therefore, by using carbon dioxide in the biogas as a substrate, the amount of methane gas obtained from the biomethanation process can be increased. Furthermore, since the methane concentration in the gas obtained from the biomethanation process is high, purification is unnecessary, or the labor and cost required for purification can be reduced. Furthermore, in the supply step, the methane fermentation liquid and biogas are supplied to the biomethanation tank. This allows the methane fermentation liquid and biogas to be appropriately contacted under wet conditions, preventing the biogas from passing through the biomethanation tank without contacting the methane fermentation liquid. This increases the residence time of the biogas in the biomethanation tank, thereby increasing the amount of methane gas obtained from the biomethanation process. Furthermore, because the methane fermentation tank and the biomethanation tank are separated, operation can be controlled under conditions appropriate for each process, allowing both the methane fermentation process and the biomethanation process to be performed efficiently. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a biomethanation device according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing a schematic configuration of a biomethanation device according to a second embodiment. [Figure 3] FIG. 10 is a diagram showing a schematic configuration of a biomethanation device according to a third embodiment. [Figure 4]4A is a side view of a biomethanation tank according to a fourth embodiment, and FIG. 4B is a view taken along the arrows IVB-IVB in FIG. 4A. [Figure 5] Diagram showing the schematic configuration of the biogas retention section [Figure 6] FIG. 10 is a diagram showing a schematic configuration of a biomethanation device according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A biomethanation device and a biomethanation method according to an embodiment of the present invention will be described with reference to the drawings.

[0032] [First embodiment] As shown in Figure 1, this biomethanation device 1 is equipped with a methane fermentation tank 2 that processes organic waste A through methane fermentation to produce biogas D, and a biomethanation tank 3 that processes organic waste A through biomethanation to produce product gas B whose main component is methane gas.

[0033] 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). A methane fermentation liquid C containing organic waste A is stored in the methane fermentation tank 2, and biogas D is produced by carrying out methane fermentation treatment while maintaining the temperature of the methane fermentation liquid C within a predetermined range. To improve the efficiency of biogas generation, a conductive material (activated carbon, etc.) can also be added to the methane fermentation tank 2.

[0034] 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 5 to 30 kg / (m 3 The 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 C in the methane fermentation tank 2.

[0035] 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.

[0036] 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 22 that agitates the methane fermentation liquid C in the methane fermentation tank 2, a heating device (not shown) that heats the methane fermentation liquid C 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.

[0037] Although not shown in the figure, the heating device is equipped with, for example, a circulation path that extracts the methane fermentation liquid C in the methane fermentation tank 2 to the outside and circulates it, a circulation pump that circulates the methane fermentation liquid C in the circulation path, and a heat exchange unit that exchanges heat between the methane fermentation liquid C in the circulation path and a heating medium.

[0038] Biogas D produced by methane fermentation in methane fermentation tank 2 is, for example, approximately 60% methane gas, with carbon dioxide making up the majority of the remainder. Therefore, by providing a biomethanation tank 3 downstream of methane fermentation tank 2 for a biomethanation treatment step that carries out a biomethanation treatment to produce product gas B, product gas B is produced using carbon dioxide.

[0039] In this way, by disposing the biomethanation tank 3 downstream of the methane fermentation tank 2, the biomethanation apparatus 1 can be constructed by retrofitting the biomethanation tank 3 to an existing methane fermentation tank 2. The biomethanation tank 3 can be fixedly installed at a desired location, or, for example, can be portable so that it can be transported. Furthermore, since the biomethanation tank 3 can be installed as needed, the apparatus can usually be operated as a methane fermentation apparatus without installing the biomethanation tank 3, and then, as needed, the biomethanation tank 3 can be installed and the operating method changed to operate as a biomethanation apparatus 1.

[0040] The biomethanation tank 3 has a cylindrical main body 31 with a bottom, and a lid 32 that closes the open upper portion of the main body 31. The main body 31 can have various shapes, such as a circular or polygonal shape in a plan view.

[0041] In order to carry out biomethanation treatment in the biomethanation tank 3, a supply unit 4 is provided which performs a supply step of supplying the methane fermentation liquid C from the methane fermentation tank 2 and the biogas D obtained by the methane fermentation treatment into the biomethanation tank 3. The supply unit 4 is equipped with a biogas supply unit 41 which extracts the biogas D from the methane fermentation tank 2 and supplies it into the biomethanation tank 3, and a methane fermentation liquid supply unit 42 which extracts the methane fermentation liquid C from the methane fermentation tank 2 and supplies it to the biomethanation tank 3.

[0042] The biogas supply unit 41 extracts biogas D from the gas phase of the methane fermentation tank 2 and supplies the biogas D from the lower side of the main body 31 in the biomethanation tank 3. The methane fermentation liquid supply unit 42 extracts methane fermentation liquid C from the liquid phase of the methane fermentation tank 2 and supplies it to the lower part of the biomethanation tank 3. The biogas supply unit 41 supplies all of the biogas D obtained by the methane fermentation process to the biomethanation tank 3, and the methane fermentation liquid supply unit 42 supplies all or part of the methane fermentation liquid C in the methane fermentation tank 2 to the biomethanation tank 3.

[0043] In this way, biogas D is supplied to the biomethanation tank 3 by the biogas supply unit 41, and methane fermentation liquid C is supplied by the methane fermentation liquid supply unit 42, so that no raw materials (e.g., carbon dioxide and hydrogen) other than the methane fermentation liquid C and biogas D are supplied to the biomethanation tank 3. Therefore, without producing hydrogen separately, it is possible to generate product gas B while saving energy and reducing costs.

[0044] The biomethanation tank 3 receives and stores the methane fermentation liquid C from the methane fermentation liquid supply unit 42. For this reason, in the biomethanation tank 3, more than half of the height (vertical direction) of the biomethanation tank 3 is a liquid phase section 33 in which the methane fermentation liquid C is stored, and the remaining upper portion is a gas phase section 34 in which the methane fermentation liquid C is not stored.

[0045] The biogas supply unit 41 does not simply supply the biogas D from the lower side of the biomethanation tank 3, but rather sprays the biogas D from a spray unit 43 disposed at the bottom of the biomethanation tank 3, thereby supplying the biogas D in a bubbled (fine-bubble) state to the methane fermentation liquid C stored in the biomethanation tank 3. When the biogas D is bubbled (fine-bubbled), it is preferable that the bubble diameter be small, and can be, for example, 10 μm to 3 mm.

[0046] The biomethanation tank 3 is equipped with a voltage application unit 5 that has an anode 51 and a cathode 52 and that performs a voltage application step of applying a voltage to the methane fermentation liquor C stored in the biomethanation tank 3. The anode 51 and cathode 52 are formed in an elongated shape that is longer in the vertical direction than in the horizontal direction. The anode 51 and cathode 52 are disposed spaced apart in the horizontal direction while being supported by being removed from the lid 32 of the biomethanation tank 3. In the vertical direction, the anode 51 and cathode 52 are disposed so that their entirety is located within the liquid phase section 33 of the biomethanation tank 3. Incidentally, the voltage application unit 5 applies a voltage and supplies a current, for example, from an external power source, and it is possible to change whether to supply AC or DC as appropriate.

[0047] When a positive voltage (potential) is applied to the anode 51, an oxidation reaction occurs on the surface of the electron donor (organic substance) attached to the anode surface. As a result, electrons (e - ) flows into the external power supply via the anode 51. Meanwhile, protons (H + ) moves through the liquid toward the cathode 52. On the surface of the organic matter attached to the cathode region, a reduction reaction occurs between electrons supplied from an external power source, protons that have moved through the liquid, and carbon dioxide in the liquid, producing methane and water. The electron donor is organic matter, for example, that was not decomposed in the methane fermentation tank 2. In addition, methane and water are also produced from the carbon dioxide and hydrogen in the liquid. The anode region and cathode region are equivalent to the periphery of the anode 51 and the periphery of the cathode 52, and can be, for example, a range whose radius is the short-side length of the anode 51 and the cathode 52 from the central axis in the longitudinal direction of the anode 51 and the cathode 52, or a range sandwiched between the anode 51 and the cathode 52.

[0048] In this way, in the biomethanation tank 3, the methane fermentation liquid C and the biogas D are brought into contact under wet conditions, and a biomethanation process is performed by applying a voltage to the methane fermentation liquid C using the voltage application unit 5, thereby using the carbon dioxide in the biogas D as a substrate to produce product gas B. By bubbling the biogas D (forming fine bubbles) and bringing the methane fermentation liquid C and the biogas D into contact under wet conditions, the residence time of the biogas D can be extended, and the amount of product gas B produced can be increased. Carbon dioxide dissolved in the liquid phase other than that derived from the biogas D is also used as a substrate.

[0049] The residence time of biogas D in the biomethanation tank 3 may be set appropriately between 10 and 1,440 minutes, but is preferably 10 minutes or longer, more preferably 30 minutes or longer, even more preferably 60 minutes or longer, and particularly preferably 120 minutes or longer. Setting the residence time of biogas D in this way increases the residence time of biogas D in the biomethanation process, thereby efficiently utilizing carbon dioxide in the biogas D as a substrate and improving the conversion efficiency to product gas B. Here, the residence time is calculated as the value obtained by dividing the effective volume of the biomethanation tank 3 by the flow rate of biogas D. Furthermore, when exhaust gas E is circulated in the exhaust fluid circulation unit 6, the residence time is calculated as the value obtained by dividing the sum of the effective volume of the biomethanation tank 3 and the effective volume of the circulation path 61 by the flow rate of biogas D. The effective volume is the volume of the methane fermentation liquid C stored in the biomethanation tank 3 or the circulation path 61 during normal operation.

[0050] The temperature inside the biomethanation tank 3 is not particularly limited as long as the reaction proceeds, but is preferably set to 25°C to 60°C in consideration of microbial activity.

[0051] The biomethanation tank 3 is provided with a methane gas extraction unit 35 that extracts the produced gas B from the discharge fluid discharged from the biomethanation tank 3 by extracting the produced gas B from the upper part of the biomethanation tank 3. The produced gas B extracted by the methane gas extraction unit 35 can be supplied to an external device such as a methane gas utilization device. A methane fermentation liquid discharge unit 36 ​​that discharges the methane fermentation liquid C is provided at the lower part of the biomethanation tank 3.

[0052] The biomethanation tank 3 is equipped with an exhaust fluid circulation section 6 that not only extracts the product gas B generated in the methane gas extraction section 35, but also supplies at least a portion of the exhaust gas E (e.g., a mixed gas of product gas B and biogas D) that becomes part of the exhaust fluid discharged from the biomethanation tank 3 back to the biomethanation tank 3.

[0053] The exhaust fluid circulation unit 6 is equipped with a circulation path 61 that supplies exhaust gas E discharged from the upper part of the biomethanation tank 3 to the lower part of the biomethanation tank 3 and circulates the exhaust gas E. The circulation path 61 merges with the biogas supply unit 41 and supplies the exhaust gas E to the ejection unit 43. This allows the exhaust gas E to be supplied in a bubbled state to the methane fermentation liquid C stored in the biomethanation tank 3 in the ejection unit 43, and the exhaust gas E can be brought into contact with the methane fermentation liquid C under wet conditions.

[0054] The system is equipped with a discharge fluid circulation control unit 7 that controls the discharge fluid circulating unit 6. When the concentration of product gas B obtained from the biomethanation tank 3 falls below a set concentration, the discharge fluid circulation control unit 7 executes a discharge fluid circulation amount increase control that increases the amount of discharge fluid supplied again to the biomethanation tank 3 by the discharge fluid circulating unit 6. Here, the set concentration is not particularly limited as long as it is a value of 70% or more, and can be set preferably to 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0055] For example, a methane gas concentration detection unit 10 is provided that detects the concentration of product gas B obtained from the biomethanation tank 3, and the methane gas concentration is obtained by outputting the detection information of this methane gas concentration detection unit 10 to the discharge fluid circulation control unit 7. There are no particular restrictions on the location where the methane gas concentration detection unit 10 is installed, but it is preferable to install it, for example, in the gas phase unit 34 of the biomethanation tank 3 (see FIG. 1), the methane gas extraction unit 35, or somewhere along the circulation path 61.

[0056] For example, when exhaust gas E is not being supplied to the biomethanation tank 3 by the exhaust fluid circulation unit 6, the exhaust fluid circulation control unit 7 starts operating pumps and the like disposed in the circulation path 61, etc., during the gas circulation rate increase control, to start supplying exhaust gas E to the biomethanation tank 3 by the exhaust fluid circulation unit 6. When exhaust gas E is being supplied to the biomethanation tank 3 by the exhaust fluid circulation unit 6, the exhaust fluid circulation control unit 7 increases the rotation speed of pumps and the like disposed in the circulation path 61, etc., to increase the amount of exhaust gas E supplied to the biomethanation tank 3 by the exhaust fluid circulation unit 6. In this way, during the gas circulation rate increase control, the exhaust fluid circulation control unit 7 controls the operating state of pumps and the like disposed in the circulation path 61, etc., to increase the amount of exhaust gas supplied again to the biomethanation tank 3 by the exhaust fluid circulation unit 6. In the gas circulation rate increase control, when the concentration of the generated gas B discharged from the biomethanation tank 3 recovers to or exceeds the set concentration, the amount of exhaust gas E supplied to the biomethanation tank 3 by the exhaust fluid circulation unit 6 is reduced, or the supply of exhaust gas E to the biomethanation tank 3 by the exhaust fluid circulation unit 6 is stopped.

[0057] In managing the operating state of the biomethanation tank 3, the methane gas concentration detected by the methane gas concentration detection unit 10 is used as an index. As described above, when the concentration of product gas B obtained from the biomethanation tank 3 falls below the set concentration, the discharge fluid circulation control unit 7 executes control to increase the amount of discharge fluid circulated, thereby ensuring that the concentration of product gas B obtained from the biomethanation tank 3 is equal to or greater than the set concentration. In addition, for example, the residence time of biogas D in the biomethanation tank 3 can be set so that the concentration of product gas B obtained from the biomethanation tank 3 is equal to or greater than the set concentration. In this way, by using the methane gas concentration detected by the methane gas concentration detection unit 10 as an index, it is possible to obtain product gas B having a concentration equal to or greater than the set concentration.

[0058] In the biomethanation tank 3, any one of the first to third treatment methods can be adopted as the treatment method for the methane fermentation liquid C and the biogas D.

[0059] The first treatment method is a transient method in which produced gas B is extracted from the biomethanation tank 3 without circulating the mixed fluid containing the methane fermentation liquid C and biogas D, the discharge fluid, etc., to the biomethanation tank 3. The second treatment method is a circulation method in which produced gas B is extracted from the biomethanation tank 3 while a portion of the mixed fluid containing the methane fermentation liquid C and biogas D, the discharge fluid, etc., is circulated to the biomethanation tank 3. The third treatment method is a batch method in which, when the methane fermentation liquid C and biogas D are supplied to the biomethanation tank 3 by the supply unit 4, the supply of the methane fermentation liquid C and biogas D to the biomethanation tank 3 is stopped, the supply suspension state is maintained for the reaction time required for the biomethanation treatment reaction, and then the supply of the methane fermentation liquid C and biogas D to the biomethanation tank 3 is resumed. In this batch method, extraction of produced gas B from the biomethanation tank 3 can be started when the methane gas concentration detected by the methane gas concentration detection unit 10 reaches or exceeds a set concentration.

[0060] The treatment method to be adopted for the methane fermentation liquid C and biogas D can be changed as appropriate, and any of treatment methods 1 to 3 can be selected and adopted depending on various operating conditions, etc. Among treatment methods 1 to 3, it is preferable to adopt treatment method 1, but even if treatment method 2 or 3 is adopted, it is possible to obtain product gas B with a methane gas concentration equal to or higher than the set concentration.

[0061] Second Embodiment The second embodiment is an embodiment different from the first embodiment in terms of the locations of the anode 51 and the cathode 52. Other configurations are the same as those of the first embodiment, so the same reference numerals and symbols are used to denote the same components, and the description thereof will be omitted. The description will focus on the locations of the anode 51 and the cathode 52, with reference to FIG.

[0062] As shown in FIG. 2 , the anode 51 and the cathode 52 are disposed vertically spaced apart in the biomethanation tank 3, with the anode 51 positioned on the lower side. The anode 51 and the cathode 52 have a length spanning both opposing left-right wall portions of the main body 31 of the biomethanation tank 3, and are formed into an elongated shape that is longer in the left-right direction than in the up-down direction. Both left-right ends of the anode 51 and the cathode 52 are attached to both side walls of the main body 31, and the anode 51 and the cathode 52 are disposed across both side walls of the main body 31. In the vertical direction, the anode 51 is disposed in a lower portion of the main body 31 near the ejection portion 43, and the cathode 52 is disposed at the upper end of the liquid phase portion 33 of the biomethanation tank 3. The anode 51 and the cathode 52 are disposed so that their entirety is located within the liquid phase portion 33 of the biomethanation tank 3. The ejection parts 43 are not limited to being arranged at intervals in the vertical direction, as long as they are arranged closer to the anode 52 than to the cathode 52 .

[0063] Incidentally, the anode 51 and the cathode 52 can be disposed not only at a distance in the vertical direction but also at a distance in the width direction (horizontal direction) or diagonal direction of the biomethanation tank 3. In this case, in the biomethanation tank 3, the supply unit 4 (ejection unit 43) can be disposed at a position closer to the anode 51 than to the cathode 52.

[0064] Third Embodiment The third embodiment is an embodiment different from the first embodiment in terms of the locations of the anode 51 and the cathode 52. Other configurations are the same as those of the first embodiment, so the same reference numerals are used and the description thereof is omitted, and the description will focus on the locations of the anode 51 and the cathode 52 with reference to FIG.

[0065] As shown in FIG. 3 , the anode 51 and the cathode 52 are disposed at a distance from each other in the left-right direction, but are disposed so as to protrude from the liquid phase portion 33 toward the gas phase portion 34 of the biomethanation tank 3 in the up-down direction. The anode 51 and the cathode 52 are formed in an elongated shape that is longer in the up-down direction than in the left-right direction, and are set to a length in the up-down direction that is shorter by a predetermined length than the overall length of the main body portion 31 of the biomethanation tank 3. The anode 51 and the cathode 52 are affixed to the side wall portion of the main body portion 31. The anode 51 and the cathode 52 can be removed by removing the lid portion 32 and grasping the portions of the anode 51 and the cathode 52 that protrude into the gas phase portion 34. This facilitates maintenance work, such as replacement of the anode 51 and the cathode 52.

[0066] [Fourth embodiment] The fourth embodiment is a variation of the biomethanation tank 3 in the first embodiment. Other configurations are the same as those in the first embodiment, so the same reference numerals are used to denote the same components, and the description will be omitted. The description will be centered on the biomethanation tank 3, based on FIG. 4.

[0067] As shown in Figure 4, the biomethanation tank 3 is formed in a cylindrical shape and is provided with a cylindrical covering 8 that surrounds the biomethanation tank 3. The covering 8 is formed with a larger diameter than the biomethanation tank 3 and is disposed at a predetermined distance from the outer wall 37 of the biomethanation tank 3. This results in a double-tube configuration of the biomethanation tank 3 and the covering 8, and as shown in Figure 4(B), a water passage section 81 that serves as a hollow space is formed between the outer wall 37 of the biomethanation tank 3 and the covering 8.

[0068] 4(A), a water supply unit 82 that supplies water F to the water passage unit 81 is provided at a lower portion of the water passage unit 81, and a water discharge unit 83 that discharges the water F from the water passage unit 81 is provided at an upper portion of the water passage unit 81. Although not shown, the water F discharged from the water discharge unit 83 is supplied to the water supply unit 82, and is then supplied again from the water supply unit 82 to the water passage unit 81. In this way, by circulating and supplying water F (e.g., warm water at 37°C) to the water passage unit 81 by the water supply unit 82 and the water discharge unit 83, it is possible to adjust the temperature of the biomethanation tank 3, for example by keeping the biomethanation tank 3 warm.

[0069] Fifth Embodiment The fifth embodiment is an embodiment different from the first embodiment in terms of the anode 51 and the cathode 52. Other configurations are the same as those of the first embodiment, so the same reference numerals are used and the description thereof is omitted. The following description will focus on the anode 51 and the cathode 52 with reference to FIG. 5.

[0070] As shown in FIG. 5(A), a biogas retention section 9 is provided around the anode 51 and the cathode 52, where the biogas D is retained. The biogas retention section 9 retains the biogas D by filling a first carrier 91 between the anode 51 and the cathode 52, which are arranged at a distance in the left-right direction. A first carrier filling and holding section 92 (corresponding to a carrier holding section) that fills and holds the first carrier 91 is provided between the anode 51 and the cathode 52. The first carrier filling and holding section 92 is formed to be porous, and the diameter of the pores is larger than the diameter of organic waste particles such as sludge particles. This allows the organic waste particles to pass through the first carrier filling and holding section 92, preventing the first carrier filling and holding section 92 from being clogged with the organic waste particles. Here, the periphery of the anode 51 and the cathode 52 can be, for example, a range whose radius is the short-side length of the anode 51 and the cathode 52 from the central axis of the longitudinal direction of the anode 51 and the cathode 52, or a range sandwiched between the anode 51 and the cathode 52.

[0071] The biogas retention section 9 is not limited to being filled with a first carrier 91 as shown in Fig. 5(A), but can also retain biogas D by fixing a second carrier 94 to the surface (corresponding to the carrier holding section) of the anode 51 or the cathode 52 as shown in Fig. 5(B). As shown in Fig. 5(B), a magnet 93 is embedded in the anode 51 or the cathode 52, and a second carrier 94 containing a magnetic material (e.g., black iron tetroxide) is fixed to the surface of the anode 51 or the cathode 52 by magnetic force. The first carrier 91 and the second carrier 94 are not particularly limited, but are preferably conductive, and most preferably are activated carbon, carbon felt, or carbon brush.

[0072] The biogas retention section 9 retains the biogas D around the anode 51 and the cathode 52, but the retention location for the biogas D is not limited to the area around the anode 51 and the cathode 52, and the location of the retention location can be changed as appropriate as long as it is within the biomethanation tank 3.

[0073] In addition to what is shown in Figure 5, the biogas retention section 9 can also be equipped with, for example, a flow direction regulator (not shown) that regulates the flow direction of the biogas D within the biomethanation tank 3. As shown in Figure 1, the flow direction of the biogas D within the biomethanation tank 3 is vertical, from the bottom to the top, but by using the flow direction regulator to change the flow direction of the biogas D to the left or right, for example, the biogas D can be made to meander, and the retention time of the biogas D within the biomethanation tank 3 can be increased.

[0074] Sixth Embodiment The sixth embodiment is a modification of the first embodiment in which the methane fermentation liquid C and biogas D are supplied to the biomethanation tank 3. Other configurations are the same as those of the first embodiment, and therefore the same reference numerals are used to denote the same components, and the description thereof will be omitted. The following description will focus on the supply of the methane fermentation liquid C and biogas D to the biomethanation tank 3, with reference to FIG. 6 .

[0075] 1 , in the first embodiment, the biogas supply unit 41 supplies the biogas D extracted from the methane fermentation tank 2 from the lower side of the main body 31 in the biomethanation tank 3, and the methane fermentation liquid supply unit 42 supplies the methane fermentation liquid C extracted from the methane fermentation tank 2 to the lower part of the biomethanation tank 3. In this way, the supply unit 4 supplies the methane fermentation liquid C and the biogas D to the lower side of the biomethanation tank 3.

[0076] 6 , a biogas supply unit 41 supplies biogas D extracted from the methane fermentation tank 2 to the upper side of the biomethanation tank 3, and a methane fermentation liquid supply unit 42 supplies methane fermentation liquid C extracted from the methane fermentation tank 2 to the upper part of the biomethanation tank 3. In this way, the supply unit 4 supplies the methane fermentation liquid C and biogas D to the upper side of the biomethanation tank 3.

[0077] The biomethanation tank 3 is configured as a sealed tank in which fluids such as methane fermentation liquid C and biogas D are stored throughout its interior. As in the first embodiment, the biogas supply unit 41 supplies the biogas D in a bubbled (finely bubbled) state to the methane fermentation liquid C in the biomethanation tank 3 by spraying the biogas D from a spray unit 43 disposed at the top of the biomethanation tank 3.

[0078] As shown in Figure 6, a storage tank 101 is provided downstream of the biomethanation tank 3 to store the discharge fluid G discharged from the biomethanation tank 3. The discharge fluid G can be a mixed fluid of a liquid such as a methane fermentation liquid C and a gas such as a mixed gas of produced gas B and biogas D. A discharge fluid supply unit 102 is provided to remove the discharge fluid G from the bottom side of the biomethanation tank 3 and supply it from above the storage tank 101. Incidentally, the storage tank 101 can also be omitted.

[0079] As shown in Fig. 6, gas-liquid separation is performed in the storage tank 101 to separate the discharge fluid G into gas and liquid. The storage tank 101 is provided with a methane gas extraction unit 104 that extracts the produced gas B that has been gas-liquid separated in the storage tank 101, thereby obtaining the produced gas B from the discharge fluid G discharged from the biomethanation tank 3. The produced gas B extracted by the methane gas extraction unit 104 can be supplied to an external device such as a methane gas utilization device. Although not shown, the storage tank 101 may be provided with a methane fermentation liquid discharge unit that discharges the methane fermentation liquid C from a lower portion thereof.

[0080] As in the first embodiment, the biomethanation tank 3 is provided with an exhaust fluid circulation unit 6 that supplies at least a portion of the exhaust fluid G discharged from the biomethanation tank 3, i.e., fluid H, back to the biomethanation tank 3, as shown in FIG.

[0081] As shown in Fig. 6, the discharge fluid circulation unit 6 is provided with a circulation path 103 that supplies at least a portion of the discharge fluid G discharged from the biomethanation tank 3, that is, fluid H, to the upper part of the biomethanation tank 3 to circulate the fluid H. When supplying fluid H to the biomethanation tank 3, the circulation path 103 can not only be connected to the upper part of the storage tank 101, but can also branch off from a midpoint of the discharge fluid supply unit 102, as shown by the dashed dotted line in Fig. 6.

[0082] When circulating and supplying the fluid H to the biomethanation tank 3, any one of the first to fourth circulation forms can be adopted to circulate and supply the fluid H to the biomethanation tank 3, or a combination of the first to fourth circulation forms can be adopted to circulate and supply the fluid H to the biomethanation tank 3.

[0083] In the first circulation mode, a liquid and a gas are extracted from the liquid phase and the gas phase, respectively, of the storage tank 101, and the extracted liquid and gas are mixed in the circulation path 103, and the mixed fluid can be supplied to the biomethanation tank 3 as fluid H. In this case, a line mixing mode in which the liquid and gas extracted in the circulation path 103 are mixed, or a tank mixing mode in which a mixing tank or the like is provided on the circulation path 103 and the extracted liquid and gas are mixed in the mixing tank can be adopted.

[0084] In the second circulation mode, the liquid and gas can be extracted from the liquid phase and gas phase, respectively, of the storage tank 101, and the extracted liquid and gas can be separately supplied to the biomethanation tank 3. In this case, although not shown in the figures, a liquid circulation path that supplies the liquid extracted from the liquid phase of the storage tank 101 to the biomethanation tank 3 and a gas circulation path that supplies the gas extracted from the gas phase of the storage tank 101 to the biomethanation tank 3 can be provided separately.

[0085] In the third circulation mode, a gas-liquid mixing device such as an agitator or a pump is provided in the storage tank 101, and the mixed fluid of liquid and gas mixed in the gas-liquid mixing device can be supplied as fluid H to the biomethanation tank 3 via the circulation path 103.

[0086] 6, at least a part of fluid H of the discharge fluid G discharged from the biomethanation tank 3 can be supplied to the biomethanation tank 3 via a branch path branched off from an intermediate portion of the discharge fluid supply unit 102, via the circulation path 103. In this case, for example, a three-way valve or the like can be provided at the junction of the branch path branched off from an intermediate portion of the discharge fluid supply unit 102 and the circulation path 103, and the three-way valve can be used to switch between a state employing any of the first to third circulation modes and a state employing the fourth circulation mode.

[0087] When the concentration of product gas B obtained from the biomethanation tank 3 falls below the set concentration, the discharge fluid circulation control unit 7, which controls the discharge fluid circulation unit 6, executes discharge fluid circulation rate increase control, which increases the amount of discharge fluid supplied to the biomethanation tank 3 again in the discharge fluid circulation unit 6. Here, the control content and set concentration of the discharge fluid circulation rate increase control are the same as those in the first embodiment, so a description thereof will be omitted.

[0088] The installation location of the methane gas concentration detection unit 10 is not particularly limited, but for example, when using any of the first, third, and fourth circulation modes to circulate and supply the fluid H to the biomethanation tank 3, it is preferable to install the unit in the gas phase section of the storage tank 101 (see FIG. 6) or at an intermediate location on the circulation path 103. When using the second circulation mode to circulate and supply the fluid H to the biomethanation tank 3, it is preferable to install the unit in an intermediate location on the circulation path for gas. When the methane gas concentration detection unit 10 is installed at an intermediate location on the circulation path 103, a gas-liquid separation unit may be provided as necessary to enable measurement of the methane gas concentration, and a pump or the like may also be provided to supply the separated liquid and gas to the biomethanation tank 3.

[0089] This sixth embodiment is provided with a discharge fluid circulation unit 6, and therefore, like the first embodiment, any one of the first to third treatment methods can be adopted as the treatment method for the methane fermentation liquid C and biogas D in the biomethanation tank 3.

[0090] In the sixth embodiment, the first treatment method is a transient method in which the produced gas B is extracted from the storage tank 101 without circulating the discharge fluid G to the biomethanation tank 3. The second treatment method is a circulation method in which the produced gas B is extracted from the storage tank 101 while circulating a portion of the discharge fluid G to the biomethanation tank 3. The third treatment method is a batch method in which, when the methane fermentation liquid C and biogas D are supplied to the biomethanation tank 3 by the supply unit 4, the supply of the methane fermentation liquid C and biogas D to the biomethanation tank 3 is stopped, the supply suspension state is maintained for the reaction time required for the biomethanation treatment reaction, and then the supply of the methane fermentation liquid C and biogas D to the biomethanation tank 3 is resumed. In this batch method, as in the first embodiment, when the methane gas concentration detected by the methane gas concentration detection unit 10 reaches or exceeds a set concentration, the extraction of the produced gas B from the storage tank 101 can be started.

[0091] The treatment method to be adopted for the methane fermentation liquid C and biogas D can be changed as appropriate, and any of treatment methods 1 to 3 can be selected and adopted depending on various operating conditions, etc. Of treatment methods 1 to 3, it is most preferable to adopt treatment method 1, but even if treatment method 2 or 3 is adopted, it is possible to obtain product gas B with a methane gas concentration equal to or higher than the set concentration.

[0092] In this sixth embodiment, only the supply form to the biomethanation tank 3 is different, and therefore the second to fifth embodiments can also be adopted for the biomethanation tank 3 in the sixth embodiment. Incidentally, when the second embodiment is adopted, the anode 51 is disposed in an upper portion of the biomethanation tank 3 close to the ejection part 43 in the vertical direction, and the cathode 52 is disposed in a lower portion of the biomethanation tank 3 farther from the ejection part 43 than the anode 51.

[0093] [Another embodiment] Other embodiments of the present invention will be described below. Note that the configurations of the embodiments described below are not limited to being applied independently, but can also be applied in combination with the configurations of other embodiments.

[0094] (1) In the above embodiment, the supply unit 4 includes the biogas supply unit 41 and the methane fermentation liquid supply unit 42, and the biogas D and the methane fermentation liquid C are supplied separately into the biomethanation tank 3. However, for example, the biogas D can be injected into the methane fermentation liquid C before it is supplied to the biomethanation tank 3, and the mixture can be stirred and mixed using an in-line mixer or the like before being supplied to the biomethanation tank 3. In this case, the flow path for supplying the biogas D into the biomethanation tank 3 and the flow path for supplying the methane fermentation liquid C into the biomethanation tank 3 can be a common flow path.

[0095] (2) In the above embodiment, the surface areas of the anode 51 and the cathode 52 in the longitudinal direction are the same. However, for example, the surface area may be made larger toward the bottom of the biomethanation tank 3 where the biogas D is abundant, or may have a zigzag or wave shape that changes the surface area.

[0096] (3) In the first to third embodiments described above, the methane gas extraction section 35 and the circulation path 61 in the exhaust fluid circulation section 6 are provided separately. However, for example, the circulation path 61 may be branched off from a midpoint of the methane gas extraction section 35, and a part of the methane gas extraction section 35 may also be used as the circulation path 61.

[0097] (4) In the above embodiment, a biomethanation device 1 having a methane fermentation tank 2 is exemplified. However, by omitting the methane fermentation tank 2 and providing a supply unit that supplies carbon dioxide, hydrogen, and organic waste to the biomethanation tank 3, biomethanation treatment can be performed in the biomethanation tank 3 having the voltage application unit 5. [Explanation of symbols]

[0098] 1. Biomethanation equipment 2. Methane fermentation tank 3 Biomethanation tank 4 Supply section 5. Voltage application section 6 Discharge fluid circulation section 7. Discharge fluid circulation control section 9 Biogas storage area 10 Methane gas concentration detector 51 Anode 52 cathode 92 First carrier filling and holding section (carrier holding section) A. Organic waste B. Methane gas C. Methane fermentation liquid D. Biogas E Exhaust gas (exhaust fluid) G Discharge fluid

Claims

1. a methane fermentation tank for treating organic waste through methane fermentation; a biomethanation tank that performs biomethanation treatment and is disposed downstream of the methane fermentation tank; a supply unit that supplies the methane fermentation liquid from the methane fermentation tank and the biogas obtained by the methane fermentation treatment into the biomethanation tank; A biomethanation device having an anode and a cathode, and equipped with a voltage application unit that applies a voltage to the methane fermentation liquid in the biomethanation tank.

2. 2. The biomethanation device according to claim 1, further comprising a methane gas concentration detector that detects the concentration of methane gas obtained from the biomethanation tank.

3. 3. The biomethanation device according to claim 1, wherein the supply unit is disposed in the biomethanation tank closer to the anode than to the cathode.

4. 3. The biomethanation device according to claim 1, further comprising a biogas retention section for retaining biogas in the biomethanation tank.

5. The biomethanation device according to claim 4, wherein the biogas retention section includes at least a flow direction regulator that regulates the flow direction of the biogas, or a carrier holding section that holds a carrier.

6. The biomethanation device according to claim 4 , wherein the biogas retention section has retention locations for retaining the biogas around the anode and the cathode.

7. a discharged fluid circulating unit that supplies at least a portion of the discharged fluid discharged from the biomethanation tank back to the biomethanation tank; a discharge fluid circulation control unit that controls the discharge fluid circulation unit, 3. The biomethanation device according to claim 1, wherein the exhaust fluid circulation control unit executes exhaust fluid circulation amount increase control to increase the amount of exhaust fluid supplied again to the biomethanation tank by the exhaust fluid circulation unit when the concentration of methane gas obtained from the biomethanation tank becomes less than a set concentration.

8. a methane fermentation treatment step of subjecting organic waste to methane fermentation treatment in a methane fermentation tank; a biomethanation treatment step in which biomethanation treatment is performed in a biomethanation tank disposed downstream of the methane fermentation tank; a supply step of supplying the methane fermentation liquid from the methane fermentation tank and the biogas obtained by the methane fermentation treatment into the biomethanation tank; a voltage application step of applying a voltage to the methane fermentation liquid in the biomethanation tank using an anode and a cathode.

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