Methane production method, control device, and methane production system

Abstract

Provided are: a method for producing methane using methanogens, said method having continuously excellent methane production ability even in oxygen (O2) mixing conditions; and a control device and a methane production system that can be used in the production method. Comprising a step of co-culturing methanogens and facultative anaerobic bacteria to produce methane, and a control device and a methane production system that can be used in the production method.

Description

Technical Field

[0001] The present disclosure relates to a method for producing methane, a control device, and a methane production system. Background Art

[0002] In order to meet the recent requirements for clean energy, research is underway to use methane as an energy source and to generate methane using methanogenic bacteria. For example, Patent Document 1 discloses a biogas generation device including: a hydrogen fermentation unit that anaerobically ferments an organic waste liquid using hydrogen-producing bacteria to generate hydrogen and methane raw material organic matter; and a methane fermentation unit that anaerobically ferments the methane raw material organic matter using methanogenic bacteria to generate methane. Patent Document 2 discloses a method for producing methane in which, in the presence of a gas containing carbon dioxide, a red non-sulfur bacterium and a hydrogenotrophic methanogenic bacterium that can be co-cultured using a medium that does not contain an ammonium salt and contains L-cysteine hydrochloride as a reducing agent are co-cultured to obtain methane gas.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-149983

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-192547 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] Methanogenic bacteria that produce methane gas are obligate anaerobic microorganisms, and the presence of oxygen (O 2 ) in the reaction vessel causes a decrease in the activity or death of methanogenic bacteria. When supplying a liquid or a gas from the outside into the reaction vessel that generates methane, oxygen may be mixed in as an impurity, but in any document, no method for countermeasures against oxygen mixing such as oxygen removal is shown. When no countermeasures against oxygen mixing are taken, it may not be possible to generate the expected methane due to the influence of the mixed oxygen.

[0009] Therefore, an object of the present disclosure is to provide a method for producing methane using methanogenic bacteria, a control device, and a methane production system that have a continuously excellent methane generation ability even in an oxygen mixing situation.

[0010] Means for Solving the Problems

[0011] According to some embodiments, the method for producing methane includes a step of co-culturing methanogenic bacteria and facultative anaerobic bacteria to generate methane. Thus, even in an oxygen mixing situation, methane can be generated with a continuously excellent methane generation ability.

[0012] In one embodiment, it may further include:

[0013] a step of monitoring the culture conditions of the culture system;

[0014] a step of determining whether the monitored culture conditions are outside the set threshold range; and

[0015] a step of adjusting the culture conditions to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored culture conditions are outside the set threshold range.

[0016] In one embodiment, the monitored culture condition may be the oxygen concentration, and the controlled culture condition may be the culture temperature.

[0017] In one embodiment, the monitored culture conditions and the controlled culture conditions may be the culture temperature, the pH of the culture solution, the redox potential of the culture solution, or the pressure inside the reaction vessel.

[0018] Some embodiments relate to a control device for controlling the culture conditions for co-culturing methanogens and facultative anaerobic bacteria, comprising the following:

[0019] a sensor unit that monitors the culture conditions of the culture system; and

[0020] a control unit that determines whether the monitored culture conditions are outside the set threshold range, and controls the culture conditions to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored culture conditions are outside the set threshold range.

[0021] Thereby, even in the presence of oxygen mixing, methane can be produced with continuously excellent methane production ability.

[0022] In one embodiment, the monitored culture condition may be the oxygen concentration, and the controlled culture condition may be the culture temperature.

[0023] In one embodiment, the monitored culture conditions and the controlled culture conditions may be the culture temperature, the pH of the culture solution, the redox potential of the culture solution, or the pressure inside the reaction vessel.

[0024] Some embodiments of the methane production system include:

[0025] the above-mentioned control device;

[0026] a reaction vessel for co-culturing methanogens and facultative anaerobic bacteria; and

[0027] a mechanism for adjusting the culture conditions for co-culturing methanogens and facultative anaerobic bacteria,

[0028] In the mechanism for adjusting the culture conditions, the adjustment of the culture conditions is controlled by the control device.

[0029] Thus, even in the case of oxygen mixing, methane can be produced with continuously excellent methane-producing ability.

[0030] Effect of the Invention

[0031] According to the present disclosure, it is possible to provide a methane production method using methanogens, a control device, and a methane production system that can be used for the production method, which have continuously excellent methane-producing ability even in the case of oxygen (O 2 ) mixing. Brief Description of the Drawings

[0032] Figure 1 is a schematic diagram showing an example of the methane production system of the present disclosure.

[0033] Figure 2 is a graph showing the change in methane concentration in the gas phase in the reaction vessel of Example 1 over time. The arrow indicates the gas replacement time in the reaction vessel.

[0034] Figure 3 is a graph showing the change in methane concentration in the gas phase in the reaction vessel of Reference Example 1 over time. The arrow indicates the gas replacement time in the reaction vessel.

[0035] Figure 4 is a graph showing the change in methane concentration in the gas phase in the reaction vessel of Comparative Example 1 over time. The arrow indicates the gas replacement time in the reaction vessel. Detailed Description of the Embodiments

[0036] (Methane Production Method)

[0037] The methane production method of the present disclosure includes a step of co-culturing methanogens and facultative anaerobic bacteria to produce methane. In the methane production method of the present disclosure, by supplying the raw materials for methane production in the form of gas or the components of the culture solution, and recovering the gas in the culture system containing the produced methane, methane can be obtained. By co-culturing methanogens and facultative anaerobic bacteria, the facultative anaerobic bacteria consume the mixed oxygen (O 2 ), thereby maintaining the culture system in a low-oxygen state and maintaining the methane-producing activity of methanogens well. Even in the case of oxygen mixing, methane can be produced with continuously excellent methane-producing ability.

[0038] ​​​​In addition, the methane production method of the present disclosure may further include: a step of monitoring the culture conditions of the culture system; a step of determining whether the monitored culture conditions are outside the set threshold range; and a step of adjusting the culture conditions to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored culture conditions are outside the set threshold range. In the methane production method of the present disclosure, the monitored culture condition may be the oxygen concentration, and the controlled culture condition may be the culture temperature. Alternatively, in the methane production method of the present disclosure, the monitored culture condition and the controlled culture condition may be the same, and examples thereof may include the culture temperature, the pH of the culture solution, the oxidation-reduction potential (ORP) of the culture solution, the pressure inside the reaction vessel, etc. By adjusting the culture conditions, the methane production activity of the methanogens can be maintained well, and methane can be produced with continuously excellent methane production ability even in the case of oxygen mixing. For example, by monitoring the oxygen concentration and adjusting the culture temperature, the culture system can be maintained in a low-oxygen state to well maintain the methane production activity of the methanogens, and methane can be produced with continuously excellent methane production ability even in the case of oxygen mixing.

[0039] In addition, in the methane production method of the present disclosure, the gas in the culture system can be periodically replaced, and the gas in the culture system containing the generated methane can be recovered. The replacement of the gas in the culture system can be carried out at regular time intervals or according to the methane concentration in the culture system. In the case of replacing the gas in the culture system according to the methane concentration in the culture system, the methane production method of the present disclosure may further include: a step of monitoring the methane concentration in the culture system; a step of determining whether the methane concentration exceeds the set threshold; and a step of replacing the gas in the culture system when the methane concentration exceeds the set threshold.

[0040] (Control device)

[0041] The control device of the present disclosure is a control device for controlling the culture conditions for co-culturing methanogens and facultative anaerobic bacteria, and includes the following:

[0042] A sensor unit that monitors the culture conditions of the culture system; and

[0043] A control unit that determines whether the monitored culture conditions are outside the set threshold range, and controls the culture conditions to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored culture conditions are outside the set threshold range.

[0044] The control device of the present disclosure can be used in the methane production method of the present disclosure. If the control device of the present disclosure is used in the methane production method, methane can be produced with continuously excellent methane production ability even in the oxygen mixing condition. In the control device of the present disclosure, the monitored culture condition can be the oxygen concentration, and the controlled culture condition can be the culture temperature. Alternatively, in the control device of the present disclosure, the monitored culture condition and the controlled culture condition can be the same, for example, the culture temperature, the pH of the culture solution, the oxidation-reduction potential (ORP) of the culture solution, the oxygen concentration (for example, the dissolved oxygen (DO) of the culture solution, the oxygen concentration in the gas phase part, or both of them, etc.). The description of each component of the control device of the present disclosure will be described later.

[0045] (Methane production system)

[0046] The methane production system of the present disclosure includes: the above-mentioned control device of the present disclosure; a culture tank for co-culturing methanogens and facultative anaerobic bacteria; and a mechanism for adjusting the culture conditions for co-culturing methanogens and facultative anaerobic bacteria, in which the adjustment of the culture conditions is controlled by the control device. If the methane production system of the present disclosure is used, methane can be produced with continuously excellent methane production ability even in the oxygen mixing condition.

[0047] (Description of each component)

[0048] Hereinafter, each component of the methane production method, control device, and methane production system of the present disclosure will be described.

[0049] <Methanogen>

[0050] As methanogens, examples include: Methanobacterium alcaliphilum, Methanobacterium bryantii, Methanobacterium congolense, Methanobacterium defluvii, Methanobacterium espanolae, Methanobacterium formicicum, Methanobacterium ivanovii, Methanobacterium palustre, Methanobacterium thermaggregans, Methanobacterium uliginosum, Methanobrevibacter acididurans, Methanobrevibacter arboriphilicus, Methanobrevibacter gottschalkii, Methanobrevibacter olleyae, Methanobrevibacter ruminantium, Methanobrevibacter smithii, Methanobrevibacter woesei, Methanobrevibacter wolinii, Methanothermobacter marburgensis, Methanothermobacter thermoautotrophicus, Methanobacterium thermoautotrophicus, Methanothermobacter thermoflexus, Methanothermobacter thermophilics, Methanothermobacter wolfeii, Methanothermussociabilis), Methanocorpusculum bavaricum, Methanocorpusculum parvum, Methanoculleus chikuoensis, Methanoculleus submarinus, Methanogenium frigidum, Methanogenium liminatans, Methanogenium marinum, Methanomicrobium mobile, Methanocaldococcus jannaschii, Methanococcus aeolicus, Methanococcus maripaludis, Methanococcus vannielii, Methanococcus voltaei, Methanothermococcus thermolithotrophicus, etc.

[0051] <Facultative anaerobic bacteria>

[0052] As facultative anaerobic bacteria, examples include: Caldilineaceae (such as Caldilineaceae aerophila), Staphylococcus genus (Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus), Corynebacterium genus (such as Corynebacterium glutamicum (Corynebacterium glutamicum)), Listeria genus (such as Listeria monocytogenes), Escherichia coli genus (such as Escherichia coli), etc.

[0053] <Raw materials for methane production>

[0054] As raw materials for methane production, for example, a combination of hydrogen (H 2 ) and carbon dioxide (CO 2 ) can be listed. As the reaction for methane production by methanogens, examples include:

[0055] CO 2 + 4H 2 → CH 4 + 2H 2 O

[0056] <Monitored and controlled culture conditions>

[0057] As the monitored culture conditions, for example, oxygen concentration (such as the amount of dissolved oxygen (DO) in the culture solution, etc.), culture temperature, pH of the culture solution, oxidation-reduction potential (ORP) of the culture solution, pressure inside the reaction vessel, etc. can be cited.

[0058] As the controlled (adjusted) culture conditions, for example, culture temperature, pH of the culture solution, oxidation-reduction potential (ORP) of the culture solution, pressure inside the reaction vessel, etc. can be cited.

[0059] - Oxygen concentration -

[0060] The oxygen concentration can be monitored, for example, using the amount of dissolved oxygen (DO) in the culture solution, the oxygen concentration in the gas phase part, or both of them as indicators. Methanogens are obligate anaerobic microorganisms, and the presence of oxygen (O 2 ) leads to a decrease in activity, inhibition of proliferation, and death. Therefore, it is necessary to minimize the oxygen concentration (for example, the DO amount in the culture solution, the oxygen concentration in the gas phase part, or both of them). When the monitored oxygen concentration exceeds a preset threshold, the culture conditions are adjusted to increase the activity of facultative anaerobic bacteria, so that oxygen (O 2 ) is consumed and removed by facultative anaerobic bacteria. As the adjusted culture conditions, for example, culture temperature can be cited. If the temperature increases, the solubility of gas in the liquid decreases. Therefore, the temperature can be increased to reduce the DO amount, but it may also lead to the death of the cells. Therefore, it is preferable to adjust the culture temperature so that it does not become too high.

[0061] The culture temperature can be adjusted for optimizing the oxygen concentration by feeding back the monitored oxygen concentration. For example, such feedback can be performed using a control device that includes: a sensor part (such as a dissolved oxygen sensor, an oxygen sensor in the gas phase part, etc.) that monitors the oxygen concentration in the culture system (such as the DO amount in the culture solution, the oxygen concentration in the gas phase part, or both of them); and a control part that determines whether the monitored oxygen concentration exceeds a set threshold, and controls the culture temperature to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored oxygen concentration exceeds the set threshold.

[0062] - Culture temperature -

[0063] Each microbial strain has an inherent growth temperature range. Outside this range, the microorganism cannot proliferate. Additionally, when the culture temperature deviates from the optimum growth temperature, its activity decreases. When the culture temperature is lower than the growth temperature for a long time, it takes time to recover the activity. When the culture temperature is higher than the growth temperature, the bacterial cells may die.

[0064] When the optimum growth temperatures of methanogens and facultative anaerobic bacteria are different, the operation is usually carried out at the optimum growth temperature of methanogens. In the case of excessive oxygen concentration, oxygen (O 2 ) can be removed more actively by changing the culture temperature to the optimum growth temperature of facultative anaerobic bacteria.

[0065] Therefore, the culture temperature can be adjusted by feedback based on the monitored oxygen concentration to be, for example, the optimum growth temperature of facultative anaerobic bacteria. Additionally, by monitoring and feeding back the culture temperature itself, the culture temperature can be adjusted (for example) to a temperature that will not become too high to cause the death of the bacterial cells. In the case of monitoring and feeding back the culture temperature itself, for example, such feedback can be performed using a control device that includes: a sensor unit that monitors the culture temperature of the culture system; and a control unit that determines whether the monitored culture temperature is outside a set threshold range, and controls the culture temperature to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored culture temperature is outside the set threshold range. As the control unit for controlling the culture temperature, for example, a temperature adjustment device capable of heating or cooling the reaction vessel can be cited.

[0066] - pH of the culture solution-

[0067] Each microbial strain has an inherent growth pH range. Outside this range, the microorganism does not proliferate. When deviating from the optimum growth pH, the activity of the microorganism decreases. The pH of the culture solution can be adjusted, for example, by monitoring and feeding back the pH of the culture solution. When deviating from the optimum growth pH, by adding an alkali or an acid to the culture solution to restore it to the range, the growth states of methanogens and facultative anaerobic bacteria can be maintained well, and continuous excellent methane production ability can be achieved to produce methane.

[0068] For example, such feedback can be performed using a control device that includes: a sensor unit that monitors the pH of the culture solution of the culture system; and a control unit that determines whether the monitored pH of the culture solution is outside a set threshold range, and controls the pH of the culture solution to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored pH of the culture solution is outside the set threshold range. As the control unit for controlling the pH of the culture solution, for example, an alkaline solution injection device and an acidic solution injection device can be cited.

[0069] - Redox potential (ORP) of the culture medium -

[0070] Methanogens are active under anaerobic conditions and are active in a reducing environment where the redox potential shows a negative value. The value of the redox potential at which they are active varies depending on the type of microorganism. In an environment where facultative anaerobic bacteria are present, although methane can be produced by allowing time to pass, in order to more actively improve the environment, it is preferable to adjust the redox potential (ORP) of the culture medium so that the activity state of the microorganisms is good. Such adjustment can be carried out, for example, by adding a reducing agent (sodium sulfide nonahydrate, cysteine hydrochloride monohydrate, etc.) to the culture medium. It should be noted that oxygen (O 2 ) is the main cause of the increase in ORP, so it can be considered that oxygen (O 2 ) may be mixed in when the ORP increases.

[0071] For example, the ORP of the culture medium can be adjusted by monitoring and feedback of the redox potential of the culture medium. For example, such feedback can be performed using a control device that includes: a sensor unit that monitors the redox potential of the culture medium in the culture system; and a control unit that determines whether the monitored redox potential of the culture medium is outside a set threshold range, and controls the redox potential of the culture medium to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored redox potential of the culture medium is outside the set threshold range. As a control unit for controlling the redox potential of the culture medium, for example, a reducing agent injection device can be cited.

[0072] - Pressure inside the reaction vessel -

[0073] Each microbial strain has an inherent growth pressure range, and outside the growth pressure range, the microorganisms do not proliferate until they die. The pressure inside the reaction vessel (for example) can be adjusted to the optimal growth pressure of the microorganisms by monitoring and feedback of the pressure inside the reaction vessel. When the pressure inside the reaction vessel is outside the growth pressure range of the microorganisms, for example, by discharging the gas phase inside the reaction vessel from the gas outlet to return it to the range, the growth states of methanogens and facultative anaerobic bacteria can be maintained well, and an excellent and continuous methane production ability can be achieved to produce methane.

[0074] For example, such feedback can be performed using a control device that includes: a sensor unit that monitors the pressure inside the reaction vessel in the culture system; and a control unit that determines whether the monitored pressure inside the reaction vessel is outside a set threshold range, and controls the pressure inside the reaction vessel to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored pressure inside the reaction vessel is outside the set threshold range. As a control unit for controlling the pressure inside the reaction vessel, for example, a gas outlet can be cited.

[0075] <Reaction vessel>

[0076] The reaction vessel may be any container that can hold the culture solution and the gas phase and perform liquid culture of microorganisms in the culture solution, and is not particularly limited. Hereinafter, with reference to Figure 1 , an example of the reaction vessel 100 and the methane (CH 4 ) production system 300 including the reaction vessel 100 will be described. The reaction vessel 100 can be connected to a hydrogen (H 2 ) gas supply unit 101, a carbon dioxide (CO 2 ) gas supply unit 102, a gas discharge unit 103, a gas analysis device 104, a temperature sensor 105, and a pressure sensor 106 in the gas accommodation area. In addition, the reaction vessel 100 can be connected to a temperature sensor 105, a dissolved oxygen (DO) sensor 107, a pH sensor 108, an oxidation-reduction potential (ORP) sensor 109, a temperature adjustment mechanism 110, an oxidation-reduction potential (ORP) adjustment mechanism 111, and a pH adjustment mechanism 112 in the culture solution accommodation area. The reaction vessel 100 can also be connected to a methane (CH 4 ) storage tank 200 via a gas discharge port 103. The methane (CH 4 ) production system 300 may include some or all of the reaction vessel 100 and the above components other than the reaction vessel 100.

[0077] Examples

[0078] Hereinafter, the present invention will be described in more detail using examples, but the technical scope of the present invention is not limited to these.

[0079] (Example 1)

[0080] (1) Inject a culture solution having the same composition as Medium No. 398 (https: / www.nite.go.jp / nbrc / catalogue / NBRCMediumDetailServl et?NO=398) described in the NBRC online catalog into the reaction vessel. (2) Seal the container and fill the gas phase part with a H 2 / CO 2 mixed gas (mixing ratio H 2 :CO 2 = 80:20 vol.%). (3) Inject a microbial population containing hydrogenotrophic methanogens and facultative anaerobic bacteria into the culture solution. (4) Add air to the gas phase part so that the oxygen (O 2) The content is 1 vol.%. (5) The inside of the container is pressurized to the set pressure at the start of cultivation using the reaction gas. (6) Cultivation is carried out under the condition that the temperature is kept constant at a specified value. (7) It is confirmed that the supplied CO 2 is converted into methane, and using H 2 / CO 2 as the reaction gas to displace the generated methane gas, after adding air in such a way as to become the same conditions as in (4) above, it is pressurized to the set pressure using the reaction gas and cultivation is continued.

[0081] The culture solution contains hydrogenotrophic methanogens of the genus Methanothermobacter and facultative anaerobic bacteria of the genus Caldilinea.

[0082] The results of the change over time of the methane concentration (index of methane production amount) in the reaction vessel are as Figure 2 shown. The arrow indicates the moment when the generated methane gas is displaced using the H 2 / CO 2 mixed gas as the reaction gas. According to Figure 2 the results shown, even in the presence of O 2 which has the activity inhibition characteristic of hydrogenotrophic methanogens, methane was continuously and favorably produced.

[0083] (Reference Example 1)

[0084] Methane production is carried out using standard cultivation with only methanogens of the genus Methanothermobacter. Specifically, as the microorganism, a culture solution containing only methanogens of the genus Methanothermobacter and not containing facultative anaerobic bacteria is used, and air is not added to the gas phase during cultivation. Except for this, cultivation is carried out in the same manner as in Example 1.

[0085] The results of the change over time of the methane concentration (index of methane production amount) in the reaction vessel are as Figure 3 shown. The arrow indicates the moment when the generated methane gas is displaced using the H 2 / CO 2 mixed gas as the reaction gas. According to Figure 3 the results shown, since O 2 which has the activity inhibition characteristic of hydrogenotrophic methanogens was not added, even if the culture solution does not contain facultative anaerobic bacteria, methane was continuously and favorably produced.

[0086] (Comparative Example 1)

[0087] As the microorganism, a culture solution containing only hydrogenotrophic methanogens belonging to the genus Methanothermobacter and not containing facultative anaerobic bacteria was used, and cultivation was carried out in the same manner as in Example 1 except for this.

[0088] The results of the change over time in the methane concentration (index of methane production amount) in the reaction vessel are as Figure 4 shown. The arrow indicates the time when the generated methane gas was replaced with the H 2 / CO 2 mixed gas used as the reaction gas. According to Figure 4 the results shown, since facultative anaerobic bacteria were not contained, the added O 2 was not consumed and accumulated, the growth state of the hydrogenotrophic methanogens deteriorated, the methane production ability decreased with the passage of the cultivation time, and finally methane production almost stopped.

[0089] (Results)

[0090] In Example 1 of the methane production method according to the present invention, even in the presence of oxygen (O 2 ) having the activity inhibition characteristic of hydrogenotrophic methanogens, methane was continuously and favorably produced to the same extent as in Reference Example 1 showing methane production by standard cultivation using hydrogenotrophic methanogens. On the other hand, in Comparative Example 1 in which cultivation was carried out using a culture solution not containing facultative anaerobic bacteria, the methane production ability decreased with the passage of the cultivation time, and finally methane production almost stopped. This result shows that, according to the methane production method of the present invention, methane can be favorably produced even in the presence of oxygen having the activity inhibition characteristic of hydrogenotrophic methanogens.

[0091] [Table 1]

[0092]

[0093] Industrial Applicability

[0094] According to the present disclosure, it is possible to provide a methane production method using methanogens, a control device, and a methane production system that can be used in the method, which have a continuously excellent methane production ability even in a situation where oxygen (O 2 ) is mixed.

[0095] Explanation of Signs

[0096] 100 Reaction vessel

[0097] 101 Hydrogen (H 2 ) gas supply section

[0098] 102 Carbon dioxide (CO 2 ) gas supply section

[0099] 103 Gas discharge port

[0100] 104 Gas analysis device

[0101] 105 Temperature sensor

[0102] 106 Pressure sensor

[0103] 107 Dissolved oxygen (DO) sensor

[0104] 108 pH sensor

[0105] 109 Oxidation-reduction potential (ORP) sensor

[0106] 110 Temperature adjustment mechanism

[0107] 111 Oxidation-reduction potential (ORP) adjustment mechanism

[0108] 112 pH adjustment mechanism

[0109] 113 Oxygen sensor

[0110] 200 Methane (CH 4 ) Gas storage tank

[0111] 300 Methane (CH 4 ) Manufacturing system

Claims

1. A method for producing methane, comprising the step of co-culturing methanogenic bacteria and facultative anaerobic bacteria to produce methane.

2. The production method according to claim 1, further comprising: a step of monitoring the culture conditions of the culture system; a step of determining whether the monitored culture conditions are outside a set threshold range; and a step of adjusting the culture conditions to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored culture conditions are outside the set threshold range.

3. The production method according to claim 2, wherein the monitored culture condition is the oxygen concentration, and the controlled culture condition is the culture temperature.

4. The production method according to claim 2, wherein the monitored culture condition and the controlled culture condition are the culture temperature, the pH of the culture solution, the redox potential of the culture solution, or the pressure inside the reaction vessel.

5. A control device, which is a control device for the culture conditions for co-culturing methanogenic bacteria and facultative anaerobic bacteria, and has the following: a sensor unit that monitors the culture conditions of the culture system; and a control unit that determines whether the monitored culture conditions are outside a set threshold range, and controls the culture conditions to increase the oxygen consumption activity of the facultative anaerobic bacteria when the monitored culture conditions are outside the set threshold range.

6. The control device according to claim 5, wherein the monitored culture condition is the oxygen concentration, and the controlled culture condition is the culture temperature.

7. The control device according to claim 5, wherein the monitored culture condition and the controlled culture condition are the culture temperature, the pH of the culture solution, the redox potential of the culture solution, or the pressure inside the reaction vessel.

8. A methane production system, comprising: the control device according to any one of claims 5 to 7, a reaction vessel for co-culturing methanogenic bacteria and facultative anaerobic bacteria, and a mechanism for adjusting the culture conditions for co-culturing methanogenic bacteria and facultative anaerobic bacteria, in the mechanism for adjusting the culture conditions, the adjustment of the culture conditions is controlled by the control device.

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