Microbial culture tank and microbial culture method

Abstract

A microbial culture tank (10) comprises: a riser tank (11) having a structure for raising a culture liquid (S) that cultures methane-producing bacteria that generate methane (M); a downcomer tank (12) having a structure for lowering the culture liquid (S) overflowing from the riser tank (11); and a recovery section (13) for recovering methane (M) released from the culture liquid (S) in the riser tank (11) and the downcomer tank (12).

Description

Cell culture tank and cell culture method

[0001] The present invention relates to a bacterial cell culture tank and a method for culturing bacterial cells.

[0002] Methanation using microorganisms (referred to as "bacterial cells" where appropriate) is a method in which carbon dioxide and hydrogen are introduced into a culture solution, and methane is produced by methanogens (referred to as "methane bacteria" where appropriate) present in the culture solution.

[0003] JP 2015-057951 A

[0004] However, it is difficult to improve the efficiency of methane production by culturing methanogens. For example, in conventional technologies, fine bubbles of produced methane are discharged together with the culture solution, and methane is desorbed from the culture solution outside the bacterial culture tank, which can reduce the efficiency of methane recovery. Furthermore, in conventional technologies, the culture solution rises slowly, resulting in little flow of methanogens, which reduces the efficiency of contact between hydrogen and methanogens and can reduce the efficiency of methane production.

[0005] The present invention has been made in view of the above, and has as its object to improve the production efficiency of gas generated by bacterial cells.

[0006] A bacterial cell culture tank according to one embodiment of the present invention includes a riser tank having a structure for raising a culture solution for cultivating gas-producing bacterial cells, a descender tank having a structure for lowering the culture solution that has overflowed from the riser tank, and a recovery section for recovering the gas released from the culture solution in the riser tank and the descender tank.

[0007] A bacterial cell culture method according to one embodiment of the present invention is a bacterial cell culture method carried out in a bacterial cell culture tank, and includes an ascending step of ascending a culture solution for cultivating gas-producing bacterial cells, a descending step of descending the culture solution that has overflowed during the ascending step, and a recovery step of recovering the gas released from the culture solution during the ascending step and the descending step.

[0008] According to the present invention, it is possible to improve the production efficiency of the gas generated by the bacterial cells.

[0009] FIG. 1 is a diagram showing an example of a schematic diagram of a bacterial cell culture tank according to an embodiment. FIG. 2 is a block diagram showing an example of the configuration of a bacterial cell culture tank according to an embodiment. FIG. 3 is a diagram explaining a specific example of a bacterial cell culture tank according to a reference technology. FIG. 4 is a diagram showing a specific example 1 of a bacterial cell culture tank according to an embodiment. FIG. 5 is a diagram showing a specific example 2 of a bacterial cell culture tank according to an embodiment. FIG. 6 is a diagram showing a specific example 6 of a bacterial cell culture tank according to an embodiment.

[0010] A bacterial cell culture tank and a bacterial cell culture method according to one embodiment of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiment described below.

[0011] Below, we will explain the outline of the bacterial cell culture tank 10 according to the embodiment, the configuration and functions of the bacterial cell culture tank 10, and finally the effects of the embodiment.

[0012] [1. Overview of bacterial cell culture tank 10] An overview of the bacterial cell culture tank 10 according to an embodiment will be described using Fig. 1. Fig. 1 is a diagram showing an example of a schematic diagram of the bacterial cell culture tank 10 according to an embodiment. Below, the methane production reaction of methanogens, an example of the basic configuration of the bacterial cell culture tank 10, and the effects of the bacterial cell culture tank 10 will be described.

[0013] (1-1. Methane Production Reaction of Methanogens) Methanogens produce methane M through the reaction represented by the following formula (1). ２ " is carbon dioxide C, "H ２ " is hydrogen H, "CH ４ " is methane M, "H ２ O" is water. Also, under normal temperature and pressure conditions, carbon dioxide C, hydrogen H, and methane M are gases, and water is a liquid.

[0014] CO ２ +4H ２ → CH ４ +2H ２ O (1)

[0015] Furthermore, since methanogens are anaerobic bacteria, they cannot produce methane M through the methanogenesis reaction of formula (1) above in an environment where oxygen is present.

[0016] (1-2. Example of Basic Configuration of Bacterial Cell Culture Tank 10) As shown in Fig. 1, the bacterial cell culture tank 10 is composed of an ascending tank 11, a descending tank 12, a collection section 13, an upper surface 14, and a bottom surface 15. The bacterial cell culture tank 10 is a culture tank that produces methane M using carbon dioxide C and hydrogen H as raw materials by culturing methanogens contained in a culture solution S.

[0017] (1-2-1. Rising Tank 11) The rising tank 11 is composed of an outer wall 11a, supply sections 11b (11b-1, 11b-2), and generation sections 11c (11c-1, 11c-2). The rising tank 11 has a double cylindrical outer diameter structure composed of a cylindrical outer wall 11a and a cylindrical inner wall 12a.

[0018] The riser tank 11 uses the supply unit 11b to raise the culture solution S containing methanogens and dissolved carbon dioxide C. For example, the riser tank 11 raises the liquid level of the culture solution S inside the riser tank 11 by continuously supplying a constant amount of culture solution S using the supply unit 11b. The riser tank 11 also generates hydrogen H in the culture solution S as fine bubbles using the generation unit 11c. At this time, the methanogens generate methane M from carbon dioxide C and hydrogen H in the culture solution S through the metabolic reaction represented by the above formula (1).

[0019] Here, the riser tank 11 can adjust the ascending speed of the culture solution S by adjusting the supply amount per unit time of the culture solution S supplied by the supply unit 11b. In this case, the riser tank 11 can increase the ascending speed of the culture solution S by increasing the amount of culture solution S continuously supplied by the supply unit 11b. On the other hand, the riser tank 11 can decrease the ascending speed of the culture solution S by decreasing the amount of culture solution S continuously supplied by the supply unit 11b. For example, the riser tank 11 can cause the methanogens to rise together with the culture solution S by setting the ascending speed of the culture solution S equal to or greater than the settling speed of the methanogens. Here, the settling speed refers to the rate at which the methanogens settle when there is no flow in the culture solution S. On the other hand, the riser tank 11 can cause the methanogens to settle and be separated from the culture solution S by setting the ascending speed of the culture solution S less than the settling speed of the methanogens.

[0020] 1, the supply unit 11b is configured with two units, but the number may be one or three or more units as long as the culture solution S can be uniformly supplied inside the riser tank 11. Also, in FIG. 1, the generation unit 11c is configured with two units, but the number may be one or three or more units as long as hydrogen H can be uniformly generated inside the riser tank 11.

[0021] (1-2-2. Descending Tank 12) The descending tank 12 is composed of an inner wall 12a and a discharge portion 12b. The descending tank 12 has a double cylindrical inner diameter structure composed of a cylindrical outer wall 11a and a cylindrical inner wall 12a.

[0022] The descending tank 12 allows the culture solution S that has overflowed the inner wall 12a from the ascending tank 11 to descend. For example, the descending tank 12 allows the culture solution S, whose liquid level has risen by continuously supplying a constant amount of culture solution S via the supply unit 11b of the ascending tank 11, and whose liquid level has exceeded the inner wall 12a, i.e., the overflowing culture solution S, to descend into the descending tank 12. When the ascending culture solution S overflows the inner wall 12a, or when the descending culture solution S comes into contact with the inner wall 12a or falls against and collides with the bottom surface 15, methane M contained in the culture solution S is released as a gas. Here, methane M may be a gas remaining in the liquid in the form of fine bubbles, or may be a gas dissolved in the liquid. Furthermore, the descending tank 12 discharges the culture solution S that has descended to the bottom surface 15 to the outside of the bacterial cell culture tank 10 via the discharge unit 12b.

[0023] Here, if a descending step P (not shown), which is a stepped structure described below, is installed on the inner wall 12a of the descending tank 12, the contact time and frequency of the culture solution S with the inner wall 12a can be increased, thereby accelerating the release of methane M dissolved in the culture solution S. Furthermore, if a collection membrane F (not shown), described below, is installed on the inner wall 12a of the descending tank 12, the methanogens can be collected from the descending culture solution S. At this time, by withdrawing the methanogens from the upper side of the collection membrane F and returning them to the ascending tank, the outflow of the methanogens to the outside can be prevented.

[0024] (1-2-3. Recovery unit 13) The recovery unit 13 is installed in the center of the upper surface 14, and recovers methane M released from the culture solution S in the ascending tank 11 and the descending tank 12. Here, the recovery unit 13 sends the recovered methane M to an airtight storage tank through piping.

[0025] (1-2-4. Upper surface 14) The upper surface 14 has a circular structure, and its circumference is joined to the upper part of the outer wall 11a. On the other hand, the upper surface 14 is not joined to the inner wall 12a, and a gap is formed between the upper surface 14 and the inner wall 12a, which allows the culture solution S and gas to move from the ascending tank 11 to the descending tank 12. The upper surface 14 has a structure common to the ascending tank 11 and the descending tank 12, and has a recovery section 13 in the center.

[0026] (1-2-5. Bottom surface 15) The bottom surface 15 has a circular structure, the circumference of which is joined to the lower part of the outer wall 11a, and the center of which is joined to the lower part of the inner wall 12a. The bottom surface 15 has a structure common to the ascending tank 11 and the descending tank 12, and has supply portions 11b (11b-1, 11b-2) near the circumference corresponding to the region of the ascending tank 11, and a discharge portion 12b in the center corresponding to the region of the descending tank 12.

[0027] (1-3. Effects of the Bacterial Cell Culture Tank 10) Below, an overview of methanation, an overview of the reference technology and problems therewith will be described, followed by an overview and effects of the bacterial cell culture tank 10 according to the embodiment.

[0028] (1-3-1. Overview of Methanation) Carbon dioxide (C) emissions from manufacturing processes such as steel, chemicals, automobiles, and electricity, as well as from power plants using coal and natural gas, are urgently needed to prevent global warming. Against this backdrop, research and development into the effective utilization of carbon dioxide (C) as a resource has been actively conducted to reduce greenhouse gas emissions. Examples include the synthesis of biofuels through photosynthesis using algae, the synthesis of chemical raw materials using microorganisms, and the synthesis of methane (M) from carbon dioxide (C) and hydrogen (H) (methanation). By synthesizing methane (M) using carbon dioxide (C) in factory exhaust gas, carbon dioxide (C) can be recycled as a resource. Methane (M) is the main component of city gas and has a higher volumetric energy density than hydrogen (H) and ammonia. Furthermore, it can be supplied through existing pipelines and gas pipes. Natural gas, the mainstream fuel, generates carbon dioxide (C) when burned, so a carbon-neutral synthetic gas is desired.

[0029] Methanation methods include catalytic methods and microbial methods. Methanation using microorganisms is a technique in which carbon dioxide (C) and hydrogen (H) are introduced into a culture solution (S) and methane (M) is synthesized by methanogens present in the culture solution (S). In methods using microorganisms, synthesis is possible in a relatively mild environment of 100°C or less, and complex reaction control is not required, making maintenance easy and enabling the equipment to be made larger. As described above, in order to effectively utilize carbon dioxide (C) as a resource against the backdrop of preventing global warming, there is an urgent need to develop technologies that can be used for methanation using microorganisms, the synthesis of chemical raw materials, the synthesis of biofuels, etc.

[0030] (1-3-2. Overview of the Reference Technology) In the Reference Technology, methane M is produced using a bacterial cell culture tank 10P with a single-tank structure as follows. First, in the Reference Technology, a culture solution S in which carbon dioxide C is dissolved is supplied to a bacterial cell culture tank 10P in which methanogens exist. Second, in the Reference Technology, fine bubbles of hydrogen H are generated in the culture solution S by a bubbling method, causing the methanogens to produce methane M. Third, in the Reference Technology, the produced methane M released as a gas is collected.

[0031] (1-3-3. Problems with the Reference Technology) First, in the reference technology, fine bubbles of the produced methane M are discharged together with the culture solution S, and the methane M is desorbed from the culture solution S outside the bacterial culture tank 10P, which may reduce the recovery efficiency of the methane M.

[0032] Secondly, in the reference technology, the flow of methanogens is low, which reduces the contact efficiency between hydrogen H and methanogens, and may reduce the production efficiency of methane M.

[0033] (1-3-4. Overview) As described above, the bacterial cell culture tank 10 has a two-tank structure and is composed of the riser tank 11, the descender tank 12, the collection unit 13, and the like. First, the riser tank 11 causes the culture solution S containing methanogens and dissolved carbon dioxide C to rise. At this time, the riser tank 11 continuously supplies a constant amount of culture solution S via the supply unit 11b, thereby raising the liquid level of the culture solution S inside the riser tank 11. The riser tank 11 can also adjust the rate at which the culture solution S rises by adjusting the amount of culture solution S supplied per unit time. At this time, the riser tank 11 can increase or decrease the rate at which the culture solution S rises by increasing or decreasing the amount of culture solution S continuously supplied via the supply unit 11b. Second, the riser tank 11 generates hydrogen H in the culture solution S as fine bubbles, causing the methanogens to produce methane M. Third, the descender tank 12 causes the culture solution S that overflows from the riser tank 11 to descend. At this time, the descending tank 12 is the culture solution S whose liquid level has risen by continuously supplying a constant amount of the culture solution S from the supply unit 11b of the ascending tank 11, and the culture solution S whose liquid level has exceeded the inner wall 12a, i.e., the overflowing culture solution S, is allowed to descend into the descending tank 12. Fourth, the recovery unit 13 recovers methane M released from the culture solution S in the ascending tank 11 and the descending tank 12.

[0034] (1-3-5. Effects) First, the bacterial cell culture tank 10 promotes gas-liquid separation by overflow, contact, falling, etc. of the culture solution S by lowering the liquid level in the descending tank 12 below the liquid level in the ascending tank 11, thereby releasing methane M into the air and improving the recovery efficiency of methane M. Second, the bacterial cell culture tank 10 increases the ascending speed of the culture solution S and increases the flow of methanogens, thereby improving the contact efficiency between hydrogen H and the methanogens and improving the production efficiency of methane M. Third, the bacterial cell culture tank 10 utilizes the sedimentation properties of methanogens to prevent the outflow of methanogens from the bacterial cell culture tank 10, thereby maintaining the bacterial cell density in the bacterial cell culture tank 10 and improving the production efficiency of methane M.

[0035] 2. Configuration and Function of Bacterial Cell Culture Tank 10 The configuration and function of the bacterial cell culture tank 10 shown in FIG. 1 will be described using FIG. 2. FIG. 2 is a block diagram showing an example configuration of the bacterial cell culture tank 10 according to an embodiment. The bacterial cell culture tank 10 is composed of a rising tank 11, a descending tank 12, a collection section 13, an upper surface 14, and a bottom surface 15. Below, examples of the configuration and function of the bacterial cell culture tank 10 will be described in detail, in the order of the rising tank 11, the descending tank 12, the collection section 13, the upper surface 14, and the bottom surface 15, after explaining an example structure of the bacterial cell culture tank 10 and specific examples of bacterial cells.

[0036] (2-1. Structural Example of the Bacterial Cell Culture Tank 10) The bacterial cell culture tank 10 has a riser tank 11, which is structured to raise the culture solution S for cultivating gas-producing bacteria. The bacterial cell culture tank 10 also has a descender tank 12, which is structured to lower the culture solution S that has overflowed from the riser tank 11. For example, the bacterial cell culture tank 10 has a circular upper surface 14, a circular bottom surface 15, a cylindrical outer wall 11a, and a cylindrical inner wall 12a attached to the bottom surface 15, and has a double cylindrical structure with a gap between the upper surface 14 and the inner wall 12a that allows the culture solution S to overflow. In this case, as will be described later in [3. Specific Examples of the Bacterial Cell Culture Tank 10] (3-2. Specific Example 1 of the Bacterial Cell Culture Tank 10), the bacterial cell culture tank 10 may have a structure in which the riser tank 11 is the outer diameter side of the double cylindrical structure and the descender tank 12 is the inner diameter side of the double cylindrical structure. Also, [3. As will be described later in (3-3. Specific Example of the Bacterial Cell Culture Tank 10) (Specific Example 2 of the Bacterial Cell Culture Tank 10), the bacterial cell culture tank 10 may have a structure in which the ascending tank 11 is the inner diameter side of a double cylindrical shape, and the descending tank 12 is the outer diameter side of the double cylindrical shape.

[0037] Furthermore, the bacterial cell culture tank 10 may have a double rectangular cylindrical structure having a square upper surface 14, a square bottom surface 15, a square cylindrical outer wall 11a, and a square cylindrical inner wall 12a attached to the bottom surface 15, with a gap between the upper surface 14 and the inner wall 12a that allows the culture solution S to overflow. Alternatively, the bacterial cell culture tank 10 may have a two-tank structure or a double structure that includes an ascending tank 11 and a descending tank 12 and allows the culture solution S to overflow from the ascending tank 11 to the descending tank 12.

[0038] (2-2. Specific Examples of Bacterial Cells) The bacterial cells are, for example, methanogens that produce methane M as a gas, but the type of gas and the bacterial cells are not particularly limited. The methanogens are archaea that synthesize methane M under anaerobic conditions, such as those classified into the genus Methanobacterium or Methanococcus, but the type of methanogen is not particularly limited. The bacterial cells use, for example, carbon dioxide C and hydrogen H as gas substrates, but the gas substrates are not particularly limited. The gas produced by the bacterial cells is not limited to methane M, and may be a volatile hydrocarbon (e.g., ethane, ethylene, acetylene), etc.

[0039] (2-3. Configuration and Functionality Examples of the Rising Tank 11) A configuration and functionality example of the rising tank 11 will be described. The rising tank 11 is composed of an outer wall 11a, a supply section 11b, and a generation section 11c. The following description will be given in the order of the outer wall 11a, the supply section 11b, and the generation section 11c.

[0040] (2-3-1. Exterior wall 11a) The exterior wall 11a is made of a metal such as austenitic stainless steel or other iron-based steel formed into a cylindrical shape. The exterior wall 11a may also be made of materials such as reinforced concrete, glass, plastic, stone, or wood, and is not particularly limited in terms of material or shape as long as it has corrosion resistance and airtightness.

[0041] (2-3-2. Supply unit 11b) The supply unit 11b is realized by, for example, a delivery port and piping equipped with a check valve and having a delivery function to the inside of the bacterial cell culture tank 10. The supply unit 11b is installed, for example, on the bottom surface 15 corresponding to the area of ​​the riser tank 11, but may also be installed below the outer wall 11a, and there are no particular restrictions on the installation position.

[0042] The supply unit 11b supplies a culture solution S containing a substance used by the bacterial cells as a gaseous substrate. For example, the supply unit 11b supplies a culture solution S containing carbon dioxide C used by the bacterial cells as a gaseous substrate. The supply unit 11b also supplies a culture solution S containing carbon dioxide C used by the methanogens as a substrate for producing methane M. In this case, the supply unit 11b can also supply a culture solution S containing carbon dioxide C and hydrogen H used by the methanogens as substrates for producing methane M.

[0043] Regarding the rate at which the culture solution S is supplied, as will be described later in [3. Specific Examples of the Bacterial Cell Culture Tank 10] (3-6. Specific Example 5 of the Bacterial Cell Culture Tank 10), the supply unit 11b supplies the culture solution S at an ascending rate equal to or greater than the settling rate of the bacterial cells. That is, when it is desired to improve the efficiency of methane M production, the supply unit 11b increases the flow of the methanogens to improve the contact efficiency between hydrogen H and the methanogens, thereby adjusting the supply amount of the culture solution S per unit time so that the ascending rate of the culture solution S is equal to or greater than the settling rate of the methanogens. Furthermore, as will be described later in [3. Specific Examples of the Bacterial Cell Culture Tank 10] (3-7. Specific Example 6 of the Bacterial Cell Culture Tank 10), the supply unit 11b supplies the culture solution S at an ascending rate less than the settling rate of the bacterial cells. That is, when it is desired to prevent the outflow of methanogens to the outside or to remove dead methanogens, the supply unit 11b adjusts the amount of culture solution S supplied per unit time to decrease so that the ascending speed of the culture solution S becomes less than the settling speed of the methanogens. At this time, by adjusting the ascending speed of the culture solution S to maintain an appropriate ascending speed that is less than the settling speed of the methanogens, the supply unit 11b increases the residence time of carbon dioxide C dissolved in the culture solution S in the tank, increases the opportunity for contact between the carbon dioxide C and the methanogens, reduces the outflow of methanogens to the descending tank 12, and maintains the bacterial density, thereby improving the efficiency of methane M production.

[0044] To explain the origin of the carbon dioxide C used by the bacterial cells as a substrate, the supply unit 11b supplies the culture solution S containing carbon dioxide C produced by the combustion of a carbon-containing fuel. That is, the supply unit 11b can be used to convert carbon dioxide C produced by the combustion of petroleum, coal, or the like, into methane M. The supply unit 11b also supplies the culture solution S containing carbon dioxide C produced by the combustion of methane M produced by the bacterial cells. That is, the supply unit 11b can supply the methane M produced by the methanogens to an apparatus such as a boiler, and recover the carbon dioxide C produced by the combustion of methane M in the apparatus and use it to convert it back into methane M.

[0045] (2-3-3. Generation section 11c) The generation section 11c is realized, for example, by a delivery port and piping having micropores and a delivery function to the inside of the bacterial cell culture tank 10. The generation section 11c is installed, for example, at the bottom of the outer wall 11a, but may also be installed on the bottom surface 15 corresponding to the area of ​​the riser tank 11, and there are no particular limitations on the installation position.

[0046] The generating unit 11c generates, as bubbles, a substance that the bacterial cells use as a gas substrate. For example, the generating unit 11c generates, as bubbles, hydrogen H that the bacterial cells use as a gas substrate. The generating unit 11c also generates, as bubbles, hydrogen H that the methanogens use as a reaction substrate for methane M. At this time, the generating unit 11c can also generate, as bubbles, a mixed gas containing carbon dioxide C and hydrogen H that the methanogens use as reaction substrates for methane M.

[0047] Regarding the origin of hydrogen H used as the substrate, the generator 11c generates hydrogen H as bubbles produced by electrolysis using renewable energy. For example, the generator 11c can be used to convert hydrogen H produced by electrolysis using electrical energy generated by sunlight into methane M. The generator 11c also generates hydrogen H as bubbles that is by-produced in the production process. For example, the generator 11c can be used to convert hydrogen H that is by-produced in the caustic soda production process into methane M. The generator 11c can also be used to convert hydrogen H produced by city gas reforming into methane M.

[0048] (2-4. Configuration and Function Examples of the Descending Tank 12) A configuration and function example of the descending tank 12 will be described. The descending tank 12 is composed of an inner wall 12a and a discharge portion 12b. Below, the inner wall 12a and the discharge portion 12b will be described in that order.

[0049] (2-4-1. Inner Wall 12a) The inner wall 12a is made of a metal such as austenitic stainless steel or other iron-based steel formed into a cylindrical shape. The inner wall 12a may also be made of a material such as reinforced concrete, glass, plastic, stone, or wood, and is not particularly limited in terms of material or shape as long as it has corrosion resistance and airtightness.

[0050] (2-4-2. Discharge section 12b) The discharge section 12b is realized by, for example, a delivery port and piping equipped with a check valve and having a function of delivering to the outside of the bacterial cell culture tank 10. The discharge section 12b is installed, for example, on the bottom surface 15 corresponding to the area of ​​the descending tank 12, but may also be installed on the lower part of the internal wall 12a, and the installation position is not particularly limited. The discharge section 12b discharges the culture solution S that has descended to the bottom surface 15 of the descending tank 12.

[0051] (2-4-3. Other) As will be described later in [3. Specific Examples of the Bacterial Cell Culture Tank 10] (3-4. Specific Example 3 of the Bacterial Cell Culture Tank 10), the descending tank 12 may have one or more stepped structures on the inner wall 12a that retain the descending culture solution S for a predetermined period of time. That is, the descending tank 12 has a stepped structure, which increases the overflow length, prevents the liquid level in the ascending tank 11 from rising, and prevents the overflow portion of the inner wall 12a from being submerged. Furthermore, as will be described later in [3. Specific Examples of the Bacterial Cell Culture Tank 10] (3-5. Specific Example 4 of the Bacterial Cell Culture Tank 10), the descending tank 12 may have a structure that captures bacterial cells from the descending culture solution S. For example, the descending tank 12 may have a membrane that is installed parallel to the bottom surface 15 and has a pore size smaller than the size of the bacterial cells as a structure for capturing bacterial cells.

[0052] (2-5. Configuration and Functional Examples of the Collection Unit 13) Configuration and functional examples of the collection unit 13 will be described. The collection unit 13 is realized, for example, by a delivery port and piping equipped with a check valve and having a function of delivering to the outside of the bacterial cell culture tank 10. The collection unit 13 is installed, for example, on the upper surface 14, but may also be installed on the upper part of the outer wall 11a, and there are no particular limitations on the installation position.

[0053] The recovery unit 13 recovers gases released from the culture solution S in the ascending tank 11 and the descending tank 12. For example, the recovery unit 13 recovers methane M produced by methanogens contained in the culture solution S using carbon dioxide C and hydrogen H as substrates, and sends the methane M to an airtight storage tank through piping.

[0054] (2-6. Examples of the Structure and Function of the Upper Surface 14) Examples of the structure and function of the upper surface 14 will be described. The upper surface 14 is made of, for example, a circular metal such as austenitic stainless steel or other iron-based steel. The upper surface 14 may also be made of materials such as reinforced concrete, glass, plastic, stone, or wood, and is not particularly limited in terms of material or shape as long as it is corrosion-resistant and airtight. The upper surface 14 has, for example, a collection section 13 in the center and is joined to the outer wall 11a at its periphery. The upper surface 14 is not joined to the inner wall 12a, and there is a gap between the upper surface 14 and the inner wall 12a that allows the culture solution S and gas to move from the ascending tank 11 to the descending tank 12.

[0055] (2-7. Examples of the structure and function of the bottom surface 15) Examples of the structure and function of the bottom surface 15 will be described. The bottom surface 15 is made of, for example, a metal such as austenitic stainless steel or other iron-based steel formed in a circular shape. The bottom surface 15 may also be made of materials such as reinforced concrete, glass, plastic, stone, wood, etc., and is not particularly limited in terms of material or shape as long as it is corrosion-resistant and airtight. The bottom surface 15 has, for example, a discharge portion 12b in the center, is joined to the lower part of the outer wall 11a at its periphery, and is joined to the lower part of the inner wall 12a near its center.

[0056] 3. Specific Examples of Bacterial Cell Culture Tank 10 A specific example of the bacterial cell culture tank 10P according to the reference technology will be described with reference to FIGS. 3 to 9, and then a specific example of the bacterial cell culture tank 10 will be described.

[0057] (3-1. Specific Example of Bacterial Cell Culture Tank 10P) A specific example of the bacterial cell culture tank 10P according to the reference technology will be described with reference to FIG. 3. FIG. 3 is a diagram illustrating a specific example of the bacterial cell culture tank 10P according to the reference technology. Below, a specific example of a bacterial cell culture tank 10P having a single-tank structure will be described.

[0058] As shown in Figure 3, first, the bacterial cell culture tank 10P is supplied with a culture solution S containing dissolved carbon dioxide C from the bottom of the bacterial cell culture tank 10P, and fine bubbles of hydrogen H are generated from the lower part of the wall of the bacterial cell culture tank 10P, causing the methanogens to produce methane M while the culture solution S rises. Second, the bacterial cell culture tank 10P collects the methane M released as a gas from the upper surface of the bacterial cell culture tank 10P. Third, the bacterial cell culture tank 10P discharges the culture solution S to the outside of the bacterial cell culture tank 10P from the upper part of the wall of the bacterial cell culture tank 10P.

[0059] In this case, in the bacterial cell culture method using the bacterial cell culture tank 10P, fine bubbles of the produced methane M are discharged to the outside together with the culture solution S, which may reduce the efficiency of recovery of the methane M. Furthermore, in the bacterial cell culture method using the bacterial cell culture tank 10P, the rising speed of the culture solution S is slow and the flow of the methanogens is small, which may reduce the efficiency of contact between the hydrogen H and the methanogens, thereby reducing the efficiency of production of methane M.

[0060] (3-2. Specific Example 1 of Bacterial Cell Culture Tank 10) Specific Example 1 of the bacterial cell culture tank 10 according to the embodiment will be described with reference to FIG. 4. FIG. 4 is a diagram showing Specific Example 1 of the bacterial cell culture tank 10 according to the embodiment. Below, Specific Example 1 of the bacterial cell culture tank 10 having a double cylindrical structure, with an ascending tank 11 on the outer diameter side and a descending tank 12 on the inner diameter side, will be described.

[0061] As shown in FIG. 4 , first, in the bacterial cell culture tank 10, the culture solution S containing dissolved carbon dioxide C is supplied from two locations on the bottom surface 15 of the riser tank 11 on the outer diameter side. Microscopic bubbles of hydrogen H are generated from two locations near the bottom surface 15 of the riser tank 11, causing the methanogens to produce methane M while the culture solution S rises. Second, in the bacterial cell culture tank 10, the methane M contained in the culture solution S is released as a gas by overflowing from the riser tank 11 on the outer diameter side into the descender tank 12 on the inner diameter side. Third, in the bacterial cell culture tank 10, a recovery unit 13 installed on the upper surface 14 recovers the methane M released as a gas from the culture solution S in the riser tank 11 and the descender tank 12. Fourth, the bacterial cell culture tank 10 discharges the culture solution S to the outside of the bacterial cell culture tank 10 from a discharge unit 12b installed on the bottom surface 15 of the descender tank 12.

[0062] In the specific example 1 of the bacterial cell culture tank 10, the ascending culture solution S overflows the inner wall 12a, the descending culture solution S comes into contact with the inner wall 12a, or falls to the bottom surface 15 and collides with it. This facilitates binding of the microscopic bubbles of methane M that remain in the liquid by adhering to the solids or the solids in the culture solution S, and makes it easier for the methane M to be released as a gas from the culture solution S, thereby improving the recovery efficiency of methane M.

[0063] (3-3. Specific Example 2 of Bacterial Cell Culture Tank 10) Specific Example 2 of the bacterial cell culture tank 10 according to the embodiment will be described with reference to FIG. 5. FIG. 5 is a diagram showing Specific Example 2 of the bacterial cell culture tank 10 according to the embodiment. Below, Specific Example 2 of the bacterial cell culture tank 10 having a double cylindrical structure, with an ascending tank 11 on the inner diameter side and a descending tank 12 on the outer diameter side, will be described.

[0064] As shown in Figure 5, first, in the bacterial cell culture tank 10, the culture solution S containing dissolved carbon dioxide C is supplied from the bottom 15 of the riser tank 11 on the inner diameter side, and fine bubbles of hydrogen H are generated near the bottom 15 of the riser tank 11, causing the methanogens to produce methane M while the culture solution S rises. Second, in the bacterial cell culture tank 10, the methane M contained in the culture solution S is released as a gas by overflowing from the riser tank 11 on the inner diameter side into the descender tank 12 on the outer diameter side. Third, in the bacterial cell culture tank 10, the collection unit 13 installed on the upper surface 14 collects the methane M released as a gas from the culture solution S in the riser tank 11 and the descender tank 12. Fourth, the bacterial cell culture tank 10 discharges the culture solution S to the outside of the bacterial cell culture tank 10 from discharge units 12b installed at two locations on the bottom 15 of the descender tank 12.

[0065] In the specific example 2 of the bacterial cell culture tank 10, similarly to the specific example 1 of the bacterial cell culture tank 10, the bacterial cell culture tank 10 facilitates binding of each of the methane M bubbles that remain in the liquid by adhering to fine bubbles or solids in the culture solution S, and facilitates release of the methane M as a gas from the culture solution S, thereby improving the recovery efficiency of the methane M.

[0066] (3-4. Specific Example 3 of Bacterial Cell Culture Tank 10) Specific Example 3 of the bacterial cell culture tank 10 according to the embodiment will be described with reference to FIG. 6. FIG. 6 is a diagram showing Specific Example 3 of the bacterial cell culture tank 10 according to the embodiment. Below, Specific Example 3 of the bacterial cell culture tank 10 will be described, which has a double cylindrical structure, an ascending tank 11 on the outer diameter side, a descending tank 12 on the inner diameter side, and a descending stage P of a stepped structure installed in the descending tank 12.

[0067] As shown in Figure 6, first, in the bacterial cell culture tank 10, in the outer diameter riser tank 11, a culture solution S containing dissolved carbon dioxide C is supplied from two locations on the bottom surface 15 of the riser tank 11, and fine hydrogen H bubbles are generated from two locations near the bottom surface 15 of the riser tank 11, causing the methanogens to produce methane M while the culture solution S rises. Second, in the inner diameter descender tank 12 of the bacterial cell culture tank 10, the culture solution S overflowing from the outer diameter riser tank 11 descends by contacting or colliding with a stepped descending step P, and the methane M dissolved in the culture solution S is released as a gas. Third, in the bacterial cell culture tank 10, a recovery unit 13 installed on the upper surface 14 recovers the methane M released as a gas from the culture solution S in the riser tank 11 and the descender tank 12. Fourth, the bacterial cell culture tank 10P discharges the culture solution S to the outside of the bacterial cell culture tank 10 at the discharge part 12b installed on the bottom surface 15 of the descending tank 12.

[0068] In the specific example 3 of the bacterial cell culture tank 10, the bacterial cell culture tank 10 has a stepped structure, which increases the overflow length, prevents the liquid level in the riser tank 11 from rising, and prevents the overflow portion of the inner wall 12a from being submerged. In addition, by increasing the contact time and frequency of the culture solution S with the inner wall 12a, the methane M bubbles that remain in the liquid by adhering to fine bubbles and solids in the culture solution S are more likely to bind to each other, and are more likely to be released as a gas from the culture solution S, thereby further improving the recovery efficiency of methane M.

[0069] In Fig. 6 , the descending step P is installed at an upper position where the culture solution S comes into contact with or falls onto the bottom surface 15 immediately after overflow, but it may also be installed at a lower position where the culture solution S comes into contact with or falls onto the bottom surface 15 just before falling onto the bottom surface 15, and the installation position of the descending step P is not particularly limited. Also, in Fig. 6 , the descending step P has a one-step structure, but it may have two or more steps, and the number of steps of the descending step P is not particularly limited. Also, in Fig. 6 , the descending step P has a mortar-shaped step structure with a slope, but it may be installed on a part of the inner wall 12a or may be a step structure perpendicular to the inner wall 12a, and the shape of the descending step P is not particularly limited.

[0070] (3-5. Specific Example 4 of the Bacterial Cell Culture Tank 10) A specific example 4 of the bacterial cell culture tank 10 according to the embodiment will be described with reference to FIG. 7. FIG. 7 is a diagram showing a specific example 4 of the bacterial cell culture tank 10 according to the embodiment. Below, a specific example 4 of the bacterial cell culture tank 10 will be described, which has a double cylindrical structure, an ascending tank 11 on the outer diameter side and a descending tank 12 on the inner diameter side, and in which a collection membrane F that captures methanogens is installed in the descending tank 12.

[0071] As shown in FIG. 7 , first, in the bacterial cell culture tank 10, the culture solution S containing dissolved carbon dioxide C is supplied from two locations on the bottom surface 15 of the riser tank 11 on the outer diameter side. Microbubbles of hydrogen H are generated from two locations near the bottom surface 15 of the riser tank 11, causing the methanogens to produce methane M while the culture solution S rises. Second, in the bacterial cell culture tank 10, the culture solution S overflowing from the riser tank 11 on the outer diameter side descends in the descender tank 12 on the inner diameter side, causing the methane M dissolved in the culture solution S to be released as a gas. Third, in the bacterial cell culture tank 10, a recovery unit 13 installed on the upper surface 14 recovers the methane M released as a gas from the culture solution S in the riser tank 11 and the descender tank 12. Fourth, in the bacterial cell culture tank 10, a capture membrane F installed on the inner wall 12a of the descender tank 12 captures the methanogens from the culture solution S. At this time, the methanogens can be prevented from leaking out by withdrawing them from the upper side of the collection film F and returning them to the ascending tank 11. Fifth, the bacterial cell culture tank 10 discharges the culture solution S to the outside of the bacterial cell culture tank 10 at the discharge part 12b installed on the bottom surface 15 of the descending tank 12.

[0072] In the above-described specific example 4 of the bacterial cell culture tank 10, the bacterial cell culture tank 10 collects methanogens from the culture solution S in the descending tank 12 and returns them to the culture solution S, thereby preventing the outflow of methanogens from the bacterial cell culture tank 10 and maintaining the bacterial cell density in the bacterial cell culture tank 10, thereby further improving the efficiency of producing methane M. Furthermore, by collecting methanogens from the culture solution S in the descending tank 12, the bacterial cell culture tank 10 can prevent pipe clogging due to methanogens.

[0073] In Figure 7, the trapping membrane F is installed at an upper position where it filters the culture solution S immediately after overflow, but it may also be installed at a lower position where it filters the culture solution S immediately before it falls to the bottom surface 15, and there is no particular limitation on the installation position of the trapping membrane F. Also, in Figure 7, there is one trapping membrane F, but there may be two or more, and there is no particular limitation on the number of trapping membranes F. Also, in Figure 7, the trapping membrane F has a rod-like shape that filters a certain range of the culture solution S descending in the descending tank 12, but there is no particular limitation on the shape of the trapping membrane F.

[0074] (3-6. Specific Example 5 of Bacterial Cell Culture Tank 10) Specific Example 5 of the bacterial cell culture tank 10 according to the embodiment will be described with reference to FIG. 8. FIG. 8 is a diagram showing Specific Example 5 of the bacterial cell culture tank 10 according to the embodiment. Below, we will describe Specific Example 5 of the bacterial cell culture tank 10 in which the riser tank 11 supplies the culture solution S so that the rising speed of the culture solution S is equal to or greater than the settling speed of the methanogens.

[0075] As shown in FIG. 8 , when the culture solution S containing dissolved carbon dioxide C is supplied from the bottom surface 15 of the riser tank 11 in the bacterial cell culture tank 10, the supply amount of the culture solution S per unit time is adjusted to increase so that the ascending speed of the culture solution S becomes equal to or greater than the settling speed of the methanogens.

[0076] In the specific example 5 of the bacterial cell culture tank 10, the bacterial cell culture tank 10 allows the methanogens to rise together with the culture solution S, thereby increasing the rate at which the culture solution S rises, increasing the flow of the methanogens, and improving the contact efficiency between the hydrogen H and the methanogens, thereby further improving the production efficiency of methane M.

[0077] (3-7. Specific Example 6 of Bacterial Cell Culture Tank 10) Specific Example 6 of the bacterial cell culture tank 10 according to the embodiment will be described with reference to FIG. 9. FIG. 9 is a diagram showing Specific Example 6 of the bacterial cell culture tank 10 according to the embodiment. Below, we will describe Specific Example 6 of the bacterial cell culture tank 10 in which the riser tank 11 supplies the culture solution S so that the rising speed of the culture solution S is less than the settling speed of the methanogens.

[0078] As shown in FIG. 9 , when the culture solution S containing dissolved carbon dioxide C is supplied from the bottom surface 15 of the riser tank 11 in the bacterial cell culture tank 10, the amount of culture solution S supplied per unit time is adjusted to decrease so that the ascending speed of the culture solution S becomes less than the settling speed of the methanogens.

[0079] In the above-described specific example 6 of the bacterial cell culture tank 10, the bacterial cell culture tank 10 allows live methanogens to settle and separate them from the culture solution S, thereby preventing the outflow of live methanogens from the bacterial cell culture tank 10 and maintaining the bacterial cell density in the bacterial cell culture tank 10, thereby further improving the production efficiency of methane M. In addition, the bacterial cell culture tank 10 allows dead methanogens to settle and separate them from the culture solution S, thereby increasing the proportion of live methanogens in the bacterial cell culture tank 10 and maintaining the bacterial cell density in the bacterial cell culture tank 10, thereby further improving the production efficiency of methane M. Furthermore, by maintaining an appropriate rising speed, the bacterial cell culture tank 10 increases the residence time of carbon dioxide C dissolved in the culture solution S in the tank, increasing the opportunity for contact between the carbon dioxide C and the methanogens, thereby improving the production efficiency of methane M.

[0080] 4. Effects of the embodiment Finally, effects of the embodiment will be described below. Effects 1 to 19 corresponding to the configurations and functions of the embodiment will be described below.

[0081] (4-1. Effect 1) In the above-described embodiment, the bacterial cell culture tank 10 includes the riser tank 11 having a structure for raising the culture solution S for cultivating gas-producing bacterial cells, the descender tank 12 having a structure for lowering the culture solution S that has overflowed from the riser tank 11, and the recovery unit 13 for recovering the gas released from the culture solution S in the riser tank 11 and the descender tank 12. Therefore, in the embodiment, the production efficiency of the gas produced by the bacterial cells can be improved.

[0082] (4-2. Effect 2) In the above-described embodiment, the bacterial cell culture tank 10 has the ascending tank 11 having the supply part 11b that supplies the culture solution S containing a substance that the bacterial cells use as a substrate for gas, and the descending tank 12 having the discharge part 12b that discharges the culture solution S that has descended to the bottom surface 15 of the descending tank 12. Therefore, in the embodiment, in the process of continuously culturing the bacterial cells and generating gas, it is possible to improve the production efficiency of the gas generated by the bacterial cells.

[0083] (4-3. Effect 3) In the above-described embodiment, the riser tank 11 of the bacterial cell culture tank 10 has a generation section 11c that generates bubbles from a substance that the bacterial cells use as a substrate for gas. Therefore, in this embodiment, by effectively introducing the substrate for bacterial cell production, it is possible to improve the production efficiency of the gas produced by the bacterial cells.

[0084] (4-4. Effect 4) In the above-described embodiment, the supply unit 11b of the bacterial cell culture tank 10 supplies the culture solution S at an ascending speed equal to or greater than the settling speed of the bacterial cells. Therefore, in this embodiment, the ascending speed of the culture solution S and the flow of the bacterial cells are increased, and the contact efficiency between the bacterial cells and the substrate is improved, thereby improving the production efficiency of the gas generated by the bacterial cells.

[0085] (4-5. Effect 5) In the above-described embodiment, the supply unit 11b supplies the culture solution S at an ascending speed that is less than the settling speed of the bacterial cells in the bacterial cell culture tank 10. Therefore, in the embodiment, by preventing the outflow of live bacteria to the outside or removing dead bacteria, the bacterial cell density in the bacterial cell culture tank 10 is maintained, thereby improving the production efficiency of the gas generated by the bacterial cells.

[0086] (4-6. Effect 6) In the above-described embodiment, the descending tank 12 of the bacterial cell culture tank 10 has a structure with one or more steps that holds the descending culture solution S for a predetermined period of time. Therefore, in the embodiment, the contact time or number of times of the culture solution S with the wall surface is increased, making it easier to release gas from the culture solution S, thereby improving the production efficiency of gas produced by the bacterial cells.

[0087] (4-7. Effect 7) In the above-described embodiment, the bacterial cell culture tank 10 has a structure in which the descending tank 12 collects bacterial cells from the descending culture solution S. Therefore, in the embodiment, the bacterial cells are prevented from leaking out and are reused, thereby maintaining the bacterial cell density in the bacterial cell culture tank 10, thereby improving the production efficiency of the gas generated by the bacterial cells.

[0088] (4-8. Effect 8) In the above-described embodiment, the descending tank 12 of the bacterial cell culture tank 10 has a structure for capturing bacterial cells, which is a membrane placed parallel to the bottom surface and has a pore size smaller than the size of the bacterial cells. Therefore, in this embodiment, the trapping membrane F is used to prevent the bacterial cells from leaking out and the bacterial cells are reused, thereby maintaining the bacterial cell density in the bacterial cell culture tank 10 and improving the production efficiency of the gas generated by the bacterial cells.

[0089] (4-9. Effect 9) In the above-described embodiment, the bacterial cell culture tank 10 has a double cylindrical structure having a circular top surface 14, a circular bottom surface 15, a cylindrical outer wall, and a cylindrical inner wall attached to the bottom surface 15, with a gap between the top surface 14 and the inner wall that allows the culture solution S to overflow. Therefore, in the embodiment, the contact efficiency between the bacterial cells and the substrate is improved, improving the gas production efficiency, and the gas is released from the culture solution S, improving the gas recovery efficiency, thereby improving the production efficiency of the gas produced by the bacterial cells.

[0090] (4-10. Effect 10) In the above-described embodiment, the bacterial cell culture tank 10 has the ascending tank 11 configured as the outer diameter side of a double cylindrical structure, and the descending tank 12 configured as the inner diameter side of the double cylindrical structure. Therefore, in the embodiment, the culture solution S is allowed to overflow from the ascending tank 11 on the outer diameter side to the descending tank 12 on the inner diameter side, thereby improving the gas production efficiency and gas recovery efficiency, thereby improving the production efficiency of the gas produced by the bacterial cells.

[0091] (4-11. Effect 11) In the above-described embodiment, the bacterial cell culture tank 10 has the ascending tank 11 configured as the inner diameter side of a double cylindrical structure, and the descending tank 12 configured as the outer diameter side of the double cylindrical structure. Therefore, in the embodiment, the culture solution S is allowed to overflow from the ascending tank 11 on the inner diameter side to the descending tank 12 on the outer diameter side, thereby improving the gas production efficiency and gas recovery efficiency, thereby improving the production efficiency of the gas produced by the bacterial cells.

[0092] (4-12. Effect 12) In the above-described embodiment, the bacterial cells are methanogens that produce gaseous methane M. Therefore, in the embodiment, the production efficiency of methane M produced by the methanogens can be improved.

[0093] (4-13. Effect 13) In the above-described embodiment, the bacterial cells use carbon dioxide (C) and hydrogen (H) as gas substrates. Therefore, in the embodiment, the production efficiency of the gas generated by the bacterial cells using carbon dioxide (C) and hydrogen (H) as substrates can be improved.

[0094] (4-14. Effect 14) In the above-described embodiment, the supply unit 11b of the bacterial cell culture tank 10 supplies the culture solution S containing carbon dioxide C, which the bacterial cells use as a gaseous substrate. Therefore, in the embodiment, it is possible to improve the production efficiency of the gas generated by the bacterial cells using carbon dioxide C as a substrate.

[0095] (4-15. Effect 15) In the above-described embodiment, the supply unit 11b of the bacterial cell culture tank 10 supplies the culture solution S containing carbon dioxide C produced by combustion of a carbon-containing fuel. Therefore, in the embodiment, the production efficiency of the gas produced by the bacterial cells using carbon dioxide C as a substrate can be improved, and the carbon dioxide C emitted by the combustion of the fuel can be effectively utilized.

[0096] (4-16. Effect 16) In the above-described embodiment, the supply unit 11b of the bacterial cell culture tank 10 supplies the culture solution S containing carbon dioxide C produced by combustion of methane M produced by the bacterial cells. Therefore, in the embodiment, the production efficiency of the gas produced by the bacterial cells using carbon dioxide C as a substrate can be improved, and the carbon dioxide C emitted by combustion of methane M produced by the methanogens can be effectively utilized.

[0097] (4-17. Effect 17) In the above-described embodiment, the generation unit 11c of the bacterial cell culture tank 10 generates hydrogen H, which is used as a gaseous substrate by the bacterial cells, as bubbles. Therefore, in the embodiment, it is possible to improve the production efficiency of the gas generated by the bacterial cells using hydrogen H as a substrate.

[0098] (4-18. Effect 18) In the above-described embodiment, the generating unit 11c of the bacterial cell culture tank 10 generates hydrogen H as bubbles by electrolysis using renewable energy. Therefore, in the embodiment, the production efficiency of the gas generated by the bacterial cells using hydrogen H as a substrate can be improved, and the hydrogen H generated by renewable energy can be effectively utilized.

[0099] (4-19. Effect 19) In the above-described embodiment, the generating unit 11c of the bacterial cell culture tank 10 generates hydrogen H, which is generated secondarily in the production process, as bubbles. Therefore, in the embodiment, the production efficiency of the gas generated by the bacterial cells using hydrogen H as a substrate is improved, and the hydrogen H generated secondarily in the production process can be effectively utilized.

[0100] [5. System] Information including processing procedures, control procedures, specific names, various data and parameters shown in the above documents and drawings may be changed as desired unless otherwise specified.

[0101] Furthermore, the components of each device shown in the figure are conceptual functional components and do not necessarily have to be physically configured as shown. In other words, the specific form of distribution and integration of each device is not limited to that shown. In other words, all or part of the devices can be functionally or physically distributed or integrated in any unit depending on various loads, usage conditions, etc.

[0102] [6. Others] Some examples of combinations of the disclosed technical features are described below.

[0103] (1) A bacterial cell culture tank comprising: a riser tank having a structure for raising a culture solution for cultivating gas-producing bacterial cells; a descender tank having a structure for lowering the culture solution that has overflowed from the riser tank; and a recovery section for recovering the gas released from the culture solution in the riser tank and the descender tank.

[0104] (2) The bacterial cell culture tank according to (1), wherein the ascending tank has a supply section for supplying the culture solution containing a substance used by the bacterial cells as a substrate for the gas, and the descending tank has a discharge section for discharging the culture solution that has descended to the bottom of the descending tank.

[0105] (3) The bacterial cell culture tank according to (2), wherein the riser tank has a generating section that generates bubbles of a substance that the bacterial cells use as a substrate for the gas.

[0106] (4) The bacterial cell culture tank according to (2) or (3), wherein the supply unit supplies the culture medium at an ascending speed equal to or greater than the settling speed of the bacterial cells.

[0107] (5) The bacterial cell culture tank according to (2) or (3), wherein the supply unit supplies the culture medium at an ascending speed that is less than the settling speed of the bacterial cells.

[0108] (6) The bacterial cell culture tank according to any one of (2) to (5), wherein the descending tank has one or more stepped structures that retain the descending culture solution for a predetermined period of time.

[0109] (7) The bacterial cell culture tank according to any one of (2) to (6), wherein the descending tank has a structure for collecting the bacterial cells from the descending culture solution.

[0110] (8) The bacterial cell culture tank according to (7), wherein the descending tank has a membrane, which is arranged parallel to the bottom surface and has a pore size smaller than the size of the bacterial cells, as a structure for capturing the bacterial cells.

[0111] (9) The bacterial cell culture tank according to any one of (1) to (8), which has a double cylindrical structure having a circular upper surface, a circular bottom surface, a cylindrical outer wall, and a cylindrical inner wall attached to the bottom surface, with a gap between the upper surface and the inner wall that allows the culture solution to overflow.

[0112] (10) The bacterial cell culture tank according to (9), wherein the ascending tank is an outer diameter side structure of the double cylindrical structure, and the descending tank is an inner diameter side structure of the double cylindrical structure.

[0113] (11) The bacterial cell culture tank according to (9), wherein the ascending tank is an inner diameter side structure of the double cylindrical structure, and the descending tank is an outer diameter side structure of the double cylindrical structure.

[0114] (12) The bacterial cell culture tank according to any one of (1) to (11), wherein the bacterial cells are methanogens that produce methane as the gas.

[0115] (13) The bacterial cell culture tank according to any one of (1) to (12), wherein the bacterial cells use carbon dioxide and hydrogen as the gaseous substrates.

[0116] (14) A bacterial cell culture method carried out in a bacterial cell culture tank, comprising: an ascending step of ascending a culture solution for cultivating gas-producing bacterial cells; a descending step of descending the culture solution that has overflowed during the ascending step; and a recovery step of recovering the gas released from the culture solution during the ascending step and the descending step.

[0117] 10 Microbial cell culture tank 11 Rising tank 11a External wall 11b Supply part 11c Generation part 12 Descending tank 12a Internal wall 12b Discharging part 13 Collection part 14 Top surface 15 Bottom surface

Claims

1. A bacterial cell culture tank comprising: a riser tank having a structure for raising a culture solution for cultivating gas-producing bacterial cells; a descender tank having a structure for lowering the culture solution that has overflowed from the riser tank; and a recovery unit for recovering the gas released from the culture solution in the riser tank and the descender tank.

2. The bacterial cell culture tank according to claim 1, wherein the ascending tank has a supply section for supplying the culture solution containing a substance used by the bacterial cells as a substrate for the gas, and the descending tank has a discharge section for discharging the culture solution that has descended to the bottom of the descending tank.

3. The bacterial cell culture tank according to claim 2, wherein the riser tank has a generation section that generates bubbles of a substance that the bacterial cells use as a substrate for the gas.

4. The bacterial cell culture tank according to claim 2, wherein the supply unit supplies the culture medium at an ascending speed equal to or greater than the settling speed of the bacterial cells.

5. The bacterial cell culture tank according to claim 2, wherein the supply unit supplies the culture medium at an ascending speed that is less than the settling speed of the bacterial cells.

6. The bacterial cell culture tank according to claim 2, wherein the descending tank has one or more stepped structures for retaining the descending culture solution for a predetermined period of time.

7. The bacterial cell culture tank according to claim 2, wherein the descending tank has a structure for collecting the bacterial cells from the descending culture solution.

8. The bacterial cell culture tank according to claim 7, wherein the descending tank has a structure for capturing the bacterial cells, the membrane being placed parallel to the bottom surface and having a pore size smaller than the size of the bacterial cells.

9. The bacterial cell culture tank according to any one of claims 1 to 8, wherein the bacterial cell culture tank has a double cylindrical structure having a circular top surface, a circular bottom surface, a cylindrical outer wall, and a cylindrical inner wall attached to the bottom surface, with a gap between the top surface and the inner wall that allows the culture medium to overflow.

10. A bacterial cell culture tank according to claim 9, wherein the ascending tank is an outer diameter side structure of the double cylindrical structure, and the descending tank is an inner diameter side structure of the double cylindrical structure.

11. A bacterial cell culture tank according to claim 9, wherein the ascending tank is an inner diameter side structure of the double cylindrical structure, and the descending tank is an outer diameter side structure of the double cylindrical structure.

12. The bacterial cell culture tank according to any one of claims 1 to 8, wherein the bacterial cells are methanogens that produce methane as the gas.

13. The bacterial cell culture tank according to any one of claims 1 to 8, wherein the bacterial cells use carbon dioxide and hydrogen as the gaseous substrates.

14. A bacterial cell culture method carried out in a bacterial cell culture tank, comprising: an ascending step of ascending a culture solution in which gas-producing bacterial cells are cultured; a descending step of descending the culture solution that has overflowed during the ascending step; and a recovery step of recovering the gas released from the culture solution during the ascending step and the descending step.

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