JP5801096B2 - Proteolytic treatment method - Google Patents

Description

  The present invention relates to a proteolytic treatment method. More specifically, the present invention relates to a proteolytic treatment method suitable for use in, for example, food waste containing a large amount of protein.

  As a conventional technique related to a protein processing method, for example, a method described in Patent Document 1 is known. Specifically, it describes that organic waste containing proteins is decomposed in the presence of a thermophilic proteolytic bacterium belonging to the genus Bacillus such as Bacillus stearothermophilus.

  Thus, by using thermophilic proteolytic bacteria, it can be decomposed at a temperature of 50 ° C. or higher, so that vegetable oils and animal fats and oils contained in organic waste can be dissolved and proteolytic The contact area between the bacteria and the protein can be increased, and the protein can be easily decomposed.

JP 2003-274936 A

  However, the conventional proteolytic treatment method using a thermophilic proteolytic bacterium has a problem that the proteolytic proteolytic bacterium itself has a low protein resolution, and the proteolytic treatment cannot be performed efficiently.

  Moreover, in the conventional proteolytic treatment method, although wastes containing proteins can be decomposed, energy cannot be recovered therefrom.

  An object of this invention is to provide the proteolytic processing method which can improve the proteolytic rate by proteolytic bacteria.

  Another object of the present invention is to provide a proteolytic treatment method capable of improving the rate of proteolysis by thermophilic proteolytic bacteria at a temperature of 50 ° C. or higher at which vegetable oils and animal fats are dissolved. .

  Furthermore, an object of the present invention is to provide a method capable of recovering energy while improving the rate of proteolysis by proteolytic bacteria.

  As a result of intensive studies by the inventors of the present invention in order to solve such problems, when a protein is decomposed in a single culture environment of a thermophilic proteolytic bacterium (CT-1 strain: accession number FERM P-21909) Environment of thermophilic proteolytic bacteria (CT-1 strain: accession number FERM P-21909) and Methanothermobacter thermautotrophicus, a thermophilic hydrogen-utilizing methanogen, Methanothermobacter thermautotrophicus It has been found that when protein is decomposed below, the rate of proteolysis is improved and methane gas production ability can be imparted.

  As a result of further investigation based on the above findings, the inventors of the present application have found that a thermophilic proteolytic bacterium (CT-1 strain: accession number FERM P-21909) and a thermophilic hydrogen-assimilating methanogen are methanol. The electrode was brought into contact with the co-culture environment of Thermobacter thermautotrophicus and AQDS (anthraquinone-2,6-disulfonic acid) was added to control the potential of the electrode to -0.8V. We have come to know that by proteolytically degrading proteins in a culture environment, extremely excellent proteolytic processing ability and methane gas production ability are exhibited.

Based on the above findings, the inventors of the present application have developed a thermophilic proteolytic bacterium (CT-1 strain: accession number FERM P-21909) and a thermophilic hydrogen-assimilating methanogen, methanothermobacter sam autotrophicus (Methanothermobacter The electrode is brought into contact with the environment containing thermautotrophicus) and a redox substance is added, and the temperature of the environment is set to 50 ° C. or higher, and the potential of the electrode is controlled to the reduction potential, and the protein is decomposed in this environment. As a result, it has been found that there is a possibility that a large amount of methane gas can be recovered as energy while at the same time making the protein degradation processing ability extremely excellent, and further various studies are repeated. It came to complete.

That is, the proteolytic treatment method of the present invention comprises a thermophilic proteolytic bacterium (CT-1 strain: accession number FERM P-21909) and a thermophilic hydrogen-assimilating methanogen, methanothermobacter sam autotrophicus (Methanothermobacter The electrode is brought into contact with an environment containing thermautotrophicus) and a redox substance is added, and the temperature of the environment is set to 50 ° C. or more, and the potential of the electrode is controlled to the reduction potential while the protein or the protein-containing material is contained in the environment. Is to be disassembled.

  Moreover, the biogas recovery method of the present invention recovers biogas containing methane gas generated during the proteolysis process in the proteolysis processing method of the present invention.

According to the proteolytic treatment method of the present invention, the proteolytic treatment rate by a thermophilic proteolytic bacterium (CT-1 strain: accession number FERM P-21909) can be remarkably improved. Therefore, it is possible to reduce the volume by decomposing organic waste containing a large amount of protein, for example, food waste, etc. more efficiently than conventional methods.

Moreover , according to the proteolytic treatment method of the present invention, a protein produced by a thermophilic proteolytic bacterium (CT-1 strain: accession number FERM P-21909) at a temperature of 50 ° C. or higher at which vegetable oil and animal fat are dissolved. It becomes possible to remarkably improve the decomposition processing speed. Therefore, vegetable oils and animal fats and oils contained in organic waste can be dissolved to increase the contact area between thermophilic proteolytic bacteria (CT-1 strain: accession number FERM P-21909) and proteins. , Protein degradation treatment can be performed more efficiently.

Furthermore, according to the biogas recovery method of the present invention, thermophilic proteolytic bacteria (CT-1 strain: accession number FERM P-21909) and methanothermobacter sam autotrophicus which are thermophilic hydrogen-assimilating methanogens. (Methanothermobacter thermautotrophicus) and so on, the protein is decomposed in the environment including methane gas produced by Methanothermobacter thermautotrophicus , a thermophilic hydrogen-utilizing methanogen, Methanothermobacter thermautotrophicus. Gas can be recovered as energy. In addition, by adding a redox substance to the environment and controlling the potential of the electrode in contact with the environment to the reduction potential, it is simply thermophilic proteolytic bacteria (CT-1 strain: accession number FERM P-21909) and thermophilic The amount of methane gas produced can be improved as compared with the case where the proteolytic treatment is performed in an environment in which the hydrogen-utilizing methanogen, Methanothermobacter thermautotrophicus, is present simultaneously. Accordingly, a large amount of methane gas can be recovered as energy while significantly improving the protein decomposition treatment rate, and efficient and efficient use as a resource of protein or protein-containing material can be achieved.

It is a figure which shows the time-dependent change of the cell density of Cp (CT-1 strain: accession number FERM P-21909) in a culture test. It is a figure which shows a time-dependent change of the cell density of Mt (Methanothermobacter thermautotrophicus) in a culture test. It is a figure which shows the time-dependent change of the ammonium ion concentration of the culture solution in a culture test. It is a figure which shows the time-dependent change of the organic acid density | concentration of the culture solution in a culture test. It is a figure which shows the structure of the electroculture apparatus used in the culture test. It is a figure which shows the production | generation process of the methane gas from protein. It is sectional drawing which shows an example of the electroculture apparatus concerning 1st Embodiment A. It is sectional drawing which shows an example of the electroculture apparatus concerning 1st Embodiment B. It is sectional drawing which shows an example of the electroculture apparatus concerning 1st Embodiment C. It is sectional drawing which shows an example of the electroculture apparatus concerning 1st Embodiment D. It is sectional drawing which shows an example of the electroculture apparatus concerning 2nd embodiment. It is sectional drawing which shows an example of the other structure of the electroculture apparatus for implementing this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  The potential values in the following description are all values based on the silver / silver chloride electrode potential.

  In the proteolytic treatment method of the present invention, an electrode is brought into contact with an environment containing proteolytic bacteria and methanogens (hereinafter sometimes simply referred to as a culture environment) and a redox substance is added to reduce the potential of the electrode. The protein or protein-containing material is decomposed in the above environment while controlling the potential.

  By decomposing proteins or protein-containing substances in an environment containing proteolytic bacteria and methanogens, hydrogen, lower fatty acids, and carbon dioxide produced by the protein degradation by proteolytic bacteria are consumed by methanogens. As a result, the growth of proteolytic bacteria is promoted, and the proteolytic processing speed is improved.

  Furthermore, by bringing the electrode into contact with the culture environment and adding a redox substance and controlling the potential of this electrode to the reduction potential, the growth of proteolytic bacteria and methanogens is promoted, and the proteolytic processing speed is further improved. To do.

  In the proteolytic treatment method of the present invention, a protein or a protein-containing material is a treatment target. Examples of the protein-containing material include, but are not limited to, organic waste such as food waste containing a lot of protein.

  Here, the proteolytic bacteria and the methanogen are preferably thermophilic. In this case, since the culture environment can be set to 50 ° C. or higher, the vegetable oil or animal oil contained in the protein-containing material such as organic waste is dissolved, and the contact area between the proteolytic bacteria and the protein And the protein can be decomposed more efficiently.

As the thermophilic proteolytic bacterium, a proteolytic bacterium belonging to the genus Coprothermobacter, which is entrusted with the accession number FERM P-21909 is preferable .

As the thermophilic methanogen used in the present invention, Methanothermobacter thermautotrophicus which is a thermophilic hydrogen-utilizing methanogen is preferable.

  Examples of the environment containing proteolytic bacteria and methanogenic bacteria include a culture solution containing proteolytic bacteria and methanogenic bacteria and containing nutrient sources, trace elements, vitamins and the like necessary for these bacteria. In this case, the protein or protein-containing material can be suspended and treated in the culture solution, and the protein or protein-containing material can easily be brought into contact with the proteolytic bacteria. However, the environment containing proteolytic bacteria and methanogens is not limited to the culture solution containing these bacteria, and may be a solid medium such as an agar medium containing these bacteria, or sludge, etc. Good. Moreover, the environment which performs a proteolytic process can also be formed by spraying the culture solution containing a proteolytic microbe and methanogen on a protein or a protein containing material, and making it impregnate. In addition, an environment containing proteolytic bacteria and methanogenic bacteria may be formed by adding methanogenic bacteria to an environment or processing equipment containing proteolytic bacteria. An environment containing proteolytic bacteria and methanogenic bacteria may be formed by adding degrading bacteria.

Here, when thermophilic proteolytic bacteria and thermophilic hydrogen-assimilating methanogens are used, the temperature of the culture environment can be set to 50 ° C. or higher. In some cases, the temperature of the culture environment is preferably 50 ° C to less than 100 ° C, more preferably 50 ° C to 80 ° C, and even more preferably 50 ° C to 70 ° C. Is preferred.

Incidentally, biogas in the proteolytic processing method of the present invention, including methane from the fact that, consuming hydrogen that protein was generated are decomposed by proteolytic bacteria using thermophilic hydrogen-utilizing methanogens Is generated. Therefore, there is an advantage that methane gas can be recovered from the protein as energy.

  In the protein treatment method of the present invention, an electrode is brought into contact with a culture environment and a redox substance is added.

  A reduction potential is applied to the electrode brought into contact with the culture environment. The reduction potential means a potential lower than the oxidation-reduction potential in the culture environment (potential greater on the minus side). When the oxidation-reduction potential in the culture environment is A, the potential X applied to the electrode is preferably X <A (V). More preferably, X ≦ −0.6 (V), and further preferably X ≦ −0.8 (V). However, if the potential X applied to the electrode is too low, electrolysis of water from the culture environment or the like occurs, and electric energy input other than the intended control can be consumed. Therefore, X ≧ −1.4 (V) It is preferable that X ≧ −1.2 (V), and it is more preferable that X ≧ −1.0 (V). These values are all values based on the silver / silver chloride electrode potential.

  The redox substance is added to enhance the potential controllability of the culture environment. By adding the oxidation-reduction substance to the culture environment, the potential applied to the electrode can be reliably reflected in the culture environment, and the proteolytic processing ability by potential control can be reliably improved.

  As the redox substance, a substance that hardly or does not inhibit the metabolism of proteolytic bacteria and methanogenic bacteria can be used as appropriate. Specifically, iron ions, potassium ferrocyanide, quinone compounds such as sodium anthraquinone disulfonate, viologen derivatives such as methyl viologen, and the like can be used. In addition, when using iron ion, it is preferable to coordinate iron ion to a chelating agent so that iron ion can exist stably in a culture environment. Examples of the chelating agent include diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), tetraethylenetriamine (TET), ethylenediamine (EDA), diethylenetriamine (DETA), citric acid, oxalic acid, crown ether, nitrilotetraacetic acid, Mention may be made of any chelating agent capable of coordinating iron ions such as disodium edetate, sodium edetate, trisodium edetate, penicillamine, trisodium pentetate calcium, pentetate, succimer and trientine edetate.

  The amount of the redox substance added is not particularly limited, but is preferably 0.1 to 10 mM, more preferably 0.1 to 5 mM, and 0.1 to 1 mM. Is more preferable.

  The proteolytic treatment method of the present invention is carried out, for example, by an electroculture apparatus shown in FIGS. Hereinafter, the first embodiment will be described based on FIGS. 3 to 6, and the second embodiment will be described based on FIG. 7.

<First embodiment>
In the proteolytic treatment method according to the first embodiment, a proteolytic bacterium and a methanogenic bacterium are added to a culture solution to form a culture environment, and the culture solution and the electrolytic solution are brought into contact with each other through an ion exchange membrane. The working electrode and reference electrode are brought into contact with the liquid, the counter electrode is brought into contact with the electrolyte, the working electrode, the counter electrode and the reference electrode are connected to a constant potential setting device, and the potential of the working electrode is controlled by a three-electrode system. The protein is decomposed. Furthermore, biogas containing methane gas produced by methanogen is recovered.

  The proteolytic treatment method according to the first embodiment is performed by, for example, the electroculture apparatus 1 shown in FIGS. That is, in the electroculture apparatus 1 shown in FIGS. 7 to 10, one of the two tanks partitioned by the ion exchange membrane 6 is a culture tank 7, and the other tank is a counter electrode tank 8. 7 contains the culture solution 4 containing microorganisms and redox substances, and the working electrode 9 and the reference electrode 11 are immersed therein. The counter electrode tank 8 contains the electrolyte solution 4a and the counter electrode 10 is immersed therein. The working electrode 9, the counter electrode 10 and the reference electrode 11 are connected to a constant potential setting device 12, and the constant potential setting device 12 controls the potential of the working electrode 9 in a three-electrode system.

  In this way, by controlling the potential of the working electrode 9 by the three-electrode method, the potential of the working electrode 9 can be strictly controlled to the set potential. Specifically, a potential difference between the working electrode 9 and the reference electrode 11 is measured by a constant potential setting device (potentiostat) 12, and the working electrode 9 and the counter electrode 10 are adjusted so that the potential difference reaches the set potential. A current is passed between them so that no current flows through the reference electrode 11 serving as a reference. The details of the potential control by the three-electrode method are described in, for example, pages 6 to 9 of Electrochemical Measurement Method (above), Technical Bulletin Publishing Co., Ltd., 1st edition 15 printing, published in June 2004. ing. However, when the potential of the working electrode 9 can be controlled only by the voltage between the working electrode 9 and the counter electrode 10, the three-electrode system may not be used.

  Moreover, in the electric culture apparatus 1 shown in FIGS. 7-10, the biogas which retains in the space (head space) above the liquid level of the culture solution 4 in the culture tank 7 is outside the culture tank 7 (electric culture apparatus). The gas in the culture tank 7 is recovered by the gas recovery means 15 provided with a gas exhaust pipe 15a leading to the outside (1), which can be opened and closed by a valve 15b. However, the biogas recovery method is not limited to this method. For example, without providing the gas recovery means 15, an opening is provided in the upper part of the culture tank 7, the opening is closed with an elastic material such as synthetic rubber (for example, silicone rubber or butyl rubber), and gas is applied to the elastic material that closes the opening. You may make it collect | recover biogas from head space by inserting a discharge pipe.

  Furthermore, in the electric culture apparatus 1 shown in FIGS. 7 to 10, the culture solution discharge that guides the culture solution 4 in the culture vessel 7 to the outside of the culture vessel 7 below the liquid level of the culture solution 4 in the culture vessel 7. The culture solution 4 is discharged from the culture tank 7 by the culture solution collecting means 16 provided with a tube 16a and opening and closing the culture solution discharge tube 16a by a valve 16b. Thereby, for example, the reduced protein content (for example, organic waste such as food waste) can be discharged from the culture tank 7 together with the culture solution 4. However, the method for discharging the culture solution 4 is not limited to this method.

  In addition to the gas recovery means 15 and the culture medium collection means 16, a means for adding and supplying substances into the culture tank 7 may be provided. Specifically, an openable and closable substance introduction tube that can add and supply substances to the culture solution 4 from the outside of the culture tank 7 may be provided. In this case, supplementation of the culture solution 4 and necessary substances such as a nutrient source and a neutralizing agent for the culture solution 4 can be added as necessary. Proteolytic bacteria and methanogens can be supplied from this introduction tube, and proteins or protein-containing substances can also be supplied from this introduction tube. Furthermore, gas (nitrogen gas etc.) for making the inside of the culture tank 7 into anaerobic conditions can also be supplied. However, the means for adding and supplying the substance into the culture tank 7 is not limited to such a form and is not necessarily provided. For example, the gas recovery means 15 and the culture solution collection means 16 may be used together as means for adding and supplying substances into the culture tank 7.

  Hereinafter, the case where the electroculture apparatus shown in FIG. 7 is used will be described as a first embodiment A, and the case where the electroculture apparatus shown in FIG. 8 is used will be described as a first embodiment B, which is shown in FIG. The case where the electroculturing apparatus is used will be described as a first embodiment C, and the case where the electroculturing apparatus shown in FIG. 10 is used will be described as a first embodiment D.

(First embodiment A)
The electroculture apparatus 1 shown in FIG. 7 uses a sealed container 20 as a culture tank 7, a closed container 21 that can be accommodated in the container 20 as a counter electrode tank 8, and the small container 21 is at least partially ion-exchanged. In addition to the membrane 6, a gas discharge pipe 22 that discharges gas (gas generated from the counter electrode 10) to the outside of the container 20 is provided. The wiring connecting the counter electrode 10 and the constant potential setting device 12 passes through the gas exhaust pipe 22. In the electroculture device 1 shown in FIG. 7, the wiring connecting the counter electrode 10 and the constant potential setting device 12 passes through the gas exhaust pipe 22, but is not necessarily limited to this configuration. May be connected to the constant potential setting device 12 without passing through the gas discharge pipe 22.

  The sealed container 20 as the culture tank 7 is a container having a size capable of accommodating the small container 21 with the sealed structure as the counter electrode tank 8, and the shape is not particularly limited. Examples of the material of the container include, but are not limited to, glass, plastic, an insulating metal, concrete, and the like. Moreover, you may make it use the container which formed the gas impermeable membrane material in the bag shape by the heat seal etc. as the culture tank 7. FIG.

  The small container 21 having a sealed structure as the counter electrode tank 8 is a container of a size that can be accommodated in the container 20 as the culture tank 7, and includes the ion exchange membrane 6 at least partially. Here, the small container 21 may be a bag-like container formed entirely by the ion-exchange membrane 6, but only one side of the bag-like container may be constituted by the ion-exchange membrane 6, or a part of one surface may be further formed. You may make it comprise only the ion exchange membrane 6. FIG. When the ion exchange membrane 6 is partially used, other portions may be made of the same material as that of the container 20, or may be made of a membrane material other than the ion exchange membrane 6, such as a gas-impermeable membrane material. It may be configured.

  Thus, by accommodating the small container 21 in the container 20, the small container 21 is immersed in the culture solution 4 accommodated in the container 20, and the ion exchange membrane 6 provided in at least a part of the small container 21. Comes into contact with the culture medium 4. In other words, the culture solution 4 comes into contact with the electrolyte solution 4 a through the ion exchange membrane 6. And by this structure, the oxidation-reduction substance contained in the culture solution 4 is blocked by the ion exchange membrane 6, and stays in the culture solution 4 without transferring to the electrolyte solution 4a. Thereby, the electric potential controllability of the culture solution 4 can be made excellent.

  Here, in the first embodiment A, it is preferable that the small container 21 has a sealed structure. In this case, when a useful gas is generated from the counter electrode 10 by providing a gas discharge pipe that discharges the gas generated in the small container 21 to the outside of the container 20, the gas is recovered without omission. Can do. However, the small container 21 does not necessarily have a sealed structure.

  Moreover, it is preferable that the culture tank 7 (container 20) has a sealed structure. In this case, it is easy to control the culture tank 7 to anaerobic conditions. Moreover, the entire amount of the biogas can be easily recovered by the above-described gas recovery means 15 and the like without preventing the biogas from leaking out of the container 20 while preventing the increase in pressure in the container 20 due to the biogas.

  The working electrode 9 that can be used in the present embodiment is not particularly limited, and an electrode capable of causing a reduction reaction on the surface thereof, such as a carbon electrode or a platinum electrode, can be used as appropriate. As the counter electrode 10, an electrode capable of causing an oxidation reaction that complements the reduction reaction in the working electrode 9, such as a carbon electrode or a platinum electrode, can be used as appropriate.

(First embodiment B)
The electric culture apparatus 1 shown in FIG. 8 has two tanks opened by partitioning a container 23 whose upper side is opened by an ion exchange membrane 6, and an upper open part of one tank as the culture tank 7 is formed. The gas impervious film or the gas impervious member 24 is used. That is, the electroculture apparatus 1 shown in FIG. 8 has substantially the same configuration as that of FIG. 7 except for the partition configuration of the culture tank 7 and the counter electrode tank 8 by the ion exchange membrane 6, and the electroculture shown in FIG. The same effects as when using the apparatus can be achieved.

  In the electric culture apparatus 1 shown in FIG. 8, the counter electrode tank 8 may remain open, but it has a sealed structure like the culture tank 7, and the gas generated in the counter electrode tank 8 is discharged outside the counter electrode tank 8. A gas discharge pipe for discharging may be provided. By comprising in this way, when useful gas generate | occur | produces from the counter electrode 10, this can be collect | recovered without a leak.

  Further, in the electric culture apparatus 1 shown in FIG. 8, the head space of the culture tank 7 and the head space of the counter electrode tank 8 may be communicated with each other, or may be separated from each other by a partition wall or the like.

  Moreover, it is preferable that the culture tank 7 has a sealed structure and includes the gas recovery means 15 and the like, as in the first embodiment A.

  In the electroculture apparatus 1 shown in FIG. 8, as the gas impermeable membrane or the gas impermeable member 24, those generally used in various fields can be appropriately used. For example, examples of the gas impermeable member include, but are not limited to, glass, plastic, an insulating metal, concrete, and the like. Further, as the gas impermeable membrane, for example, the ion exchange membrane 6 can be used, but is not limited thereto.

  The material of the container 23 that can be used in this embodiment is the same as that of the first embodiment A. The working electrode 9 and the counter electrode 10 that can be used in this embodiment are the same as those in the first embodiment A.

(First embodiment C)
The electroculture apparatus 1 shown in FIG. 9 has a U-shaped container in which two containers 25a and 25b each having an opening below the liquid level of the liquid to be stored are connected via the ion exchange membrane 6 at the opening. 25, one container 25a is used as a culture tank 7 with a sealed structure, and the other container 25b is opened as a counter electrode tank 8. In this case, the culture solution 4 and the electrolyte solution 4a are in contact with each other through the ion exchange membrane 6, and the space above the liquid level of the culture solution 4 in the culture tank 7 and the liquid level of the electrolyte solution 4a in the counter electrode tank 8 are used. Also, the upper space is spaced apart by the U-shaped structure of the container 25 itself. That is, the electroculture apparatus 1 shown in FIG. 9 has substantially the same configuration as that of FIG. 8 except for the configuration of the container 25. Therefore, the same effect as that obtained when the electroculture apparatus shown in FIG. 8 (and FIG. 7) is used can be obtained.

  Here, the opening of the other container 25b of the electroculture apparatus 1 in the first embodiment C is, for example, when the end of the other container 25b is completely opened, as shown in FIG. This means that the case includes a gas discharge pipe 22 that discharges the gas generated in the counter electrode tank 8 outside the counter electrode tank 8 while having a sealed structure like the one container 25a. By providing the gas discharge pipe 22, when useful gas is generated from the counter electrode tank 8, it can be easily recovered without leakage.

  Moreover, it is preferable that the culture tank 7 has a sealed structure and includes the gas recovery means 15 and the like, as in the first embodiment A.

  The material of the container 25 that can be used in this embodiment is the same as that of the first embodiment A. The working electrode 9 and the counter electrode 10 that can be used in this embodiment are the same as those in the first embodiment A.

(First embodiment D)
The electroculture apparatus 1 shown in FIG. 10 has an H-shaped container in which two containers 26a and 26b each having an opening below the liquid level of the liquid to be accommodated are connected via the ion exchange membrane 6 at the opening. 26 is formed, one container 26a is used as a culture tank 7 with a sealed structure, and the other container 26b is opened as a counter electrode tank 8. Also in this case, the culture solution 4 and the electrolyte solution 4a are in contact with each other through the ion exchange membrane 6, and the space above the liquid level of the culture solution 4 in the culture vessel 7 and the solution of the electrolyte solution 4a in the counter electrode vessel 8 are also shown. The space above the surface is separated by the H-shaped structure of the container 26 itself. That is, the electroculture apparatus 1 shown in FIG. 10 has substantially the same configuration as that of FIG. 8 except for the configuration of the container 25. Therefore, the same effect as that obtained when the electroculture apparatus shown in FIG. 8 (and FIG. 7) is used can be obtained.

  Here, the opening of the other container 26b of the electroculture apparatus 1 in the first embodiment D is, for example, when the upper part of the other container 26b is completely opened, as shown in FIG. This means that the case includes a gas discharge pipe 22 that discharges the gas generated in the counter electrode tank 8 outside the counter electrode tank 8 while having a sealed structure like the one container 25a. By providing the gas discharge pipe 22, when useful gas is generated from the counter electrode tank 8, it can be easily recovered without leakage.

  Moreover, it is preferable that the culture tank 7 has a sealed structure and includes the gas recovery means 15 and the like, as in the first embodiment A.

  The material of the container 26 that can be used in the present embodiment is the same as that in the first embodiment A. The working electrode 9 and the counter electrode 10 that can be used in this embodiment are the same as those in the first embodiment A.

<Second Embodiment>
In the proteolytic treatment method according to the second embodiment, a proteolytic bacterium and a methanogen are introduced into a culture solution to form a culture environment, the working electrode and the reference electrode are brought into contact with the culture solution, and the culture solution and the counter electrode are contacted. Are contacted via an ion exchange membrane, the working electrode, the counter electrode, and the reference electrode are connected to a constant potential setting device, and the potential of the working electrode is controlled by a three-electrode system to decompose the protein. Yes. Furthermore, biogas containing methane gas produced by methanogen is recovered. That is, it differs from the proteolytic treatment method in the first embodiment only in that the counter electrode is brought into direct contact with the ion exchange membrane without using an electrolytic solution.

  However, since the ion current flows between the working electrode 9 and the counter electrode 10 via the ion exchange membrane 6 without using the electrolyte solution 4a as in the first embodiment, the protein according to the second embodiment. According to the decomposition processing method, it is possible to obtain the same effect by controlling the potential of the working electrode 9 as in the first embodiment.

  The proteolytic treatment method according to the second embodiment is performed by, for example, an electroculture apparatus shown in FIG. In the electroculture apparatus 1 shown in FIG. 11, the working electrode 9 and the reference electrode 11 are arranged in a sealed container 5 having at least a part of the ion exchange membrane 6, and the counter electrode 10 is arranged outside the container 5. The culture solution 4 is accommodated in the container 5, the working electrode 9 and the reference electrode 11 are immersed in the culture solution 4, and the ion exchange membrane 6 of the container 5 is at least a part when the culture solution 4 is accommodated in the container 5. Is provided at a position where it can come into contact with the ion exchange membrane 6, and the counter electrode 10 is arranged in contact with at least a part of the surface of the ion exchange membrane 6 opposite to the contact surface of the culture solution 4. . In the electric culture apparatus 1 shown in FIG. 11, an opening 5 a is provided below the liquid level of the culture solution 4 in the container 5, the opening 5 a is closed with the ion exchange membrane 6, and ion exchange outside the container 5 is performed. It is assumed that the counter electrode 10 is disposed in contact with at least a part of the surface of the film 6. That is, in the electric culture apparatus 1 shown in FIG. 11, the entire container 5 functions as the culture tank 7.

  Therefore, according to the electroculture apparatus 1 shown in FIG. 11, since the container 5 has a sealed structure, biogas does not leak from the container 5. Further, as in the first embodiment, there is an advantage that the inside of the container 5 can be easily controlled to an anaerobic condition.

  In addition, although the electric culture apparatus 1 shown in FIG. 11 is provided with the gas recovery means 15 and the culture solution collection means 16 as in the first embodiment, as described above, the gas recovery method and the culture solution collection are performed. The method is not limited to those using these means. Further, as in the first embodiment, a means for adding and supplying a substance may be provided.

  Hereinafter, the details of the electroculture apparatus 1 shown in FIG. 11 will be described. However, configurations other than those described below are substantially the same as those in the first embodiment, and a description thereof will be omitted.

  The container 5 has a sealed structure including at least a part of the ion exchange membrane 6. Examples of the material of the container 5 include, but are not limited to, glass, plastic, metal subjected to insulation treatment, concrete, and the like. In FIG. 11, the opening 5 a provided below the liquid level of the culture solution 4 of the sealed container 5 is closed by the ion exchange membrane 6, but the form and structure of the container 5 are particularly limited. Not. For example, the entire container 5 may be a bag-shaped container formed of the ion-exchange membrane 6, or only one surface of the bag-shaped container may be formed of the ion-exchange membrane 6, or a part of one surface may be ion-exchanged. You may make it comprise only with the film | membrane 6. FIG. When the ion exchange membrane 6 is partially used, the other portions may be made of the above-mentioned material such as glass, or other membrane materials other than the ion exchange membrane 6, such as the culture solution 4 and the components in the culture solution 4. You may comprise by the film | membrane material which does not permeate | transmit both. In short, the culture solution 4 accommodated in the container 5 may be a container having a structure that can come into contact with the ion exchange membrane 6 constituting at least a part of the container 5.

  The counter electrode 10 is brought into contact with at least a part of the surface opposite to the contact surface of the ion exchange membrane 6 with the culture solution 4. In the present embodiment, the counter electrode 10 is a plate-like carbon electrode, but the shape and material of the counter electrode 10 are not limited to this, and the shape is that the contact with the ion exchange membrane 6 is essential. The material may be made of a material capable of causing an oxidation reaction that complements the exchange of electrons to the reduction reaction at the working electrode 9. In the present embodiment, the counter electrode 10 has a larger area than the ion exchange membrane 6 so that the entire ion exchange membrane 6 is completely covered with the counter electrode 10, and the ion exchange membrane 6 and the counter electrode 10 are covered. If the counter electrode 10 is brought into contact with at least a part of the surface opposite to the contact surface of the ion exchange membrane 6 with the culture solution 4, the culture solution 4 is passed through the ion exchange membrane 6. Therefore, it is not always necessary to bring the ion exchange membrane 6 and the counter electrode 10 into contact with each other so that the entire ion exchange membrane 6 is completely covered with the counter electrode 10. However, by completely covering the entire ion exchange membrane 6 with the counter electrode 10, the counter electrode 10 can function as a protective material for the ion exchange membrane 6, and the ion transmission surface from the culture solution 4 increases. As a result, there is an advantage that the potential controllability of the culture solution 4 can be improved, which is preferable. As a method of completely covering the entire ion exchange membrane 6 with the counter electrode 10, for example, ion exchange is performed by closing the opening 5 a by applying an adhesive around the opening 5 a of the container 5 and bonding the counter electrode 10. The entire membrane 6 and the counter electrode 10 may be brought into contact with each other, or an ion exchange membrane formed by applying an adhesive around the opening 5a of the container 5 and applying it to at least a part of the surface of the counter electrode 10 By bonding 6, the counter electrode 10 may be brought into contact with the entire ion exchange membrane 6 that closes the opening 5 a while closing the opening 5 a with the ion exchange membrane 6. Examples of the agent for coating and forming the ion exchange membrane 6 include a Nafion dispersion, but are not limited thereto. Alternatively, a Nafion dispersion may be applied to the surface of the counter electrode 10 and the ion exchange membrane 6 may be attached before the Nafion dispersion is dried. In this case, the adhesion and contact properties of the ion exchange membrane 6 to the surface of the counter electrode 10 can be made sufficient.

  Here, the counter electrode 10 is preferably a porous body. In this case, the gas generated at the contact surface between the ion exchange membrane 6 and the counter electrode 10 can easily pass through the surface opposite to the contact surface. In addition, the counter electrode 10 is made a porous body, and the ion exchange membrane 6 is attached using a Nafion dispersion liquid, whereby the ion exchange membrane 6 and the counter electrode 10 are separated by the penetration of the Nafion dispersion liquid into the pores of the porous body. The contact area can be increased to facilitate the progress of the electrochemical reaction, which is preferable.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, as shown in FIG. 12, the culture solution 4 and the electrolyte 4a are separated not by the ion exchange membrane 6 but by the impervious member 40 that does not allow any ions or microorganisms to pass through, or the culture vessel 7 and the counter electrode vessel 8 are separated. It may be formed in a separate container, and the culture solution 4 and the electrolyte 4a may be brought into contact (liquid junction) via the salt bridge 41 (agar or the like containing a saturated electrolyte solution such as KCl). Also in this case, the flow of ion current is allowed by the salt bridge 41, and the same effect as the above-described embodiment can be obtained.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  In the following description, all potential values are based on the silver / silver chloride electrode.

(Example 1)
Various studies were made on the proteolytic processing ability of the proteolytic bacteria and methanogenic bacteria in the co-culture environment.

1. Experimental Method (1) Proteolytic Bacteria Proteolytically decomposes the CT-1 strain, a strain deposited with the accession number FERM P-21909 on February 9, 2010 at the Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology. Used as a fungus. The CT-1 strain is a microorganism belonging to the genus Coprothermobacter, and is a thermophilic proteolytic bacterium exhibiting protein resolution at 50 ° C. to 80 ° C., most preferably 55 ° C. The base sequence of 16S rRNA gene of CT-1 strain is shown in SEQ ID NO: 1 in the sequence listing. In the following description, the CT-1 strain may be referred to as “Cp”.

(2) Methane-producing bacteria Methanothermobacter thermautotrophicus (JCM1004), a thermophilic hydrogen-assimilating methane-producing bacterium, was used. In the following description, the Methanothermobacter sum autotrophic may be referred to as “Mt”.

(3) Electroculture apparatus The experiment was performed using the electroculture apparatus 1 shown in FIG. The culture vessel 5 was a 250 mL glass vial (manufactured by Duran), and a circular opening 5 a having a diameter of 2.0 cm was provided at the bottom of the culture vessel 5. The opening 5a was closed with a counter electrode 10 (porous plate-like carbon electrode) through an ion exchange membrane 6 (proton exchange membrane, N117, manufactured by DuPont). More specifically, a 20% Nafion dispersion (DE2021, manufactured by DuPont) is applied to the lower half of one surface of a porous plate-like carbon electrode, an ion exchange membrane 6 is attached to the Nafion dispersion application part, and a culture vessel The ion exchange membrane 6 was adhered and fixed to the opening 5a so that the entire opening 5a of the 5 was covered with the ion exchange membrane 6.

  The culture vessel 4 was accommodated in the culture vessel 5 until about the eighth minute, and a head space was secured above the liquid surface. The culture vessel 5 was covered with a lid 18 and provided with a butyl rubber stopper as an elastic material on the upper surface 18a of the lid 18 to ensure hermeticity when wiring and electrodes were passed.

  The working electrode 9 (plate-like carbon electrode (7.5 cm × 2.5 cm × 0.2 cm)) is housed in the culture vessel 5 and immersed in the culture solution 4, and the wiring from the working electrode 9 is passed through the butyl rubber plug to the culture vessel 5. Pulled out outside. Furthermore, the reference electrode 11 (silver / silver chloride electrode (RE-1B, BAS Co., Ltd.)) was inserted into the butyl rubber stopper from the outside of the culture vessel 5 and brought into contact with the culture solution 4. Then, the working electrode 9, the counter electrode 10 and the reference electrode 11 were connected to a three-electrode type constant potential setting device (potentiostat) so that the potential of the working electrode 9 could be strictly controlled.

  Gas generated during the culture period is collected in an aluminum sampling bag (manufactured by GL Sciences, trade name: aluminum bag, 1 L) with a tube 22 passed through a butyl rubber stopper, one end of which is placed in the head space, and the other end did.

(4) Culture solution The culture solution was added with 3.0 g / L of casein (manufactured by Sigma) and 1.0 g / L of yeast extract (manufactured by Wako Pure Chemical Industries, Ltd.) in a basic medium having the following composition. A thing was used. In the following description, this liquid medium is referred to as casein medium. In the casein medium, 0.5 g / L of cysteine-HCl · H ₂ O and 0.5 g / L of Na ₂ S · 9H ₂ O were added as reducing agents. Moreover, the medium 131 trace element solution made from DSMZ (Deutsche Sammlung von Mikroorganismen and Zellkulturen) was used for the trace element solution, and the medium 141 vitamin solution made from DSMZ was used for the vitamin solution.
[Composition of basic medium (composition in 1 L of distilled water)]
・ KH ₂ PO ₄ : 0.1 g
・ K ₂ HPO ₄ : 0.2 g
・ NH ₄ Cl: 1.0 g
・ NaHCO ₃ : 2.0 g
MgCl ₂ · 6H ₂ O: 0.1 g
・ CaCl ₂ · 2H ₂ O: 0.1 g
・ NaCl: 0.6g
・ Resazurin: 0.1mg
Trace element solution: 10 mL
・ Vitamin solution: 1mL

(5) Culture test conditions The culture test was carried out under the following 10 conditions.
<Co-culture conditions>
(A) Cp + Mt, −0.8 V, oxidation-reduction substance added (b) Cp + Mt, no potential control, oxidation-reduction substance addition (c) Cp + Mt, −0.8 V, no oxidation-reduction substance added (d) Cp + Mt, no potential control No addition of redox substances <Single culture conditions>
(E) Cp, -0.8 V, oxidation-reduction substance added (f) Cp, no potential control, oxidation-reduction substance addition (g) Cp, -0.8 V, no oxidation-reduction substance added (h) Cp, no potential control No addition of redox substances <control conditions>
(I) No microorganism added, -0.8 V, redox substance added (j) No microorganism added, no potential control, no redox substance added

  As the redox material, AQDS (anthraquinone-2,6-disulfonic acid) was used and added so that the AQDS concentration of the culture solution 4 was 0.2 mM.

The culture temperature was 55 ° C., and the head space was replaced with N ₂ —CO ₂ (80:20). Further, the stirrer 15 was placed in the culture vessel 5 and the culture solution 4 was stirred at 200 rpm.

The amount of inoculation was as follows.
<Co-culture conditions>
・ Cp: 7.2 × 10 ⁵ cells / mL
Mt: 2.4 × 10 ⁵ cells / mL
・ Cp: Mt = 3: 1
<Single culture conditions>
・ Cp: 7.2 × 10 ⁵ cells / mL

(6) Measurement item The culture solution 4 was extract | collected on the 1st day, the 3rd day, the 5th day, and the 7th day from the culture | cultivation start, and the microbial cell density, the ammonium ion density | concentration, and the organic acid density | concentration were measured.

  The cell density was measured as follows. First, the total number of bacteria in the collected culture solution 4 was counted by microscopic observation. The number of Mt bacteria was determined from the ratio of autofluorescence from coenzyme F420 to fluorescence of DAPI (4 ′, 6-diamino-2-phenylindole) using a fluorescence microscope. The number of Cp bacteria was determined by subtracting the number of Mt bacteria from the total number of bacteria. These values were converted into the number of bacteria per volume of the collected culture solution 4 to calculate the cell density.

  The ammonium ion concentration was measured by ion exchange chromatography (ICS-1500, manufactured by Dionex) equipped with a CS16 cation column after filtering the culture solution 4 through a membrane having a pore size of 0.2 μm.

  The organic acid concentration was measured by high-pressure liquid chromatography (GL Science, GL-7400) after filtering the culture solution 4 through a membrane having a pore size of 0.2 μm.

  In addition, the insoluble carbon concentration, the soluble carbon concentration, and the evolved gas composition were measured after completion of the culture (7th day).

  The insoluble carbon concentration was measured as follows. First, the SS (floating solid content) concentration of the culture solution 4 was analyzed according to JIS K 0102-14.1. Then, the amount of carbon in the SS is obtained from the SS concentration of the culture solution 4 at the start of the culture test and the organic matter (casein) constituting the SS. Using this as an index, the insoluble carbon concentration is determined from the analysis value of the SS concentration. Asked.

  The soluble carbon concentration was measured by centrifuging the culture solution 4 (15,000 rpm, 1 min) and measuring the total carbon concentration of the supernatant with a TOC analyzer (manufactured by Toray, TNC-6000).

  The generated gas composition was obtained by analyzing the gas collected in the aluminum sampling bag by gas chromatography (manufactured by GL Science, GC390B). The amount of gas generated was measured by water displacement.

2. Experimental result (1) Cell density The time-dependent change of the cell density of Cp is shown in FIG. Moreover, the time-dependent change of the microbial cell density of Mt is shown in FIG.

  From the results shown in FIG. 1, it is clear that the cell density of Cp is more likely to increase in the co-culture condition groups (a) to (d) than in the single culture condition groups (e) to (h). . In addition, among the co-culture condition groups, it became clear that the cell density of Cp was most likely to increase under the conditions (a) (Cp + Mt, −0.8 V, oxidation-reduction substance added), and the cell density on day 7 In comparison, the cell density was increased 1.4 times as compared with the condition (d) (Cp + Mt, no potential control, no addition of redox substance).

  From the results shown in FIG. 2, it is clear that the cell density of Mt is most likely to increase under the conditions (a) (Cp + Mt, −0.8 V, oxidation-reduction substance added). Then, the cell density increased 3.6 times as compared with the condition of (d) (Cp + Mt, no potential control, no oxidation-reduction substance added).

  From the above results, it has been clarified that the cell density of both Cp and Mt is most likely to increase under the conditions (a) (Cp + Mt, −0.8 V, addition of redox substance).

(2) Ammonium ion concentration The time-dependent change of the ammonium ion concentration is shown in FIG.

  From the results shown in FIG. 3, it has been clarified that the co-culture condition groups (a) to (d) are more likely to have higher ammonium ion concentrations than the single culture condition groups (e) to (h). In addition, among the co-culture condition groups, it was revealed that the ammonium ion concentration is most likely to increase under the conditions (a) (Cp + Mt, −0.8 V, oxidation-reduction substance added).

  Here, since ammonium ions are generated in the culture solution 4 due to the degradation of protein (casein), the higher the ammonium ion concentration, the more proteolysis is promoted. Therefore, from the results shown in FIG. 3, the co-culture condition groups (a) to (d) are more likely to promote proteolysis than the single culture condition groups (e) to (h). Among the condition groups, it was revealed that proteolysis is most easily promoted particularly under the conditions (a) (Cp + Mt, −0.8 V, addition of redox substance).

(3) Organic Acid Concentration The change with time of the organic acid concentration is shown in FIG.

  From the results shown in FIG. 4, it was revealed that the co-culture condition groups (a) to (d) are more likely to have higher organic acid concentrations than the single culture condition groups (e) to (h). Moreover, it became clear that the organic acid concentration is most likely to be increased under the condition (a) (Cp + Mt, −0.8 V, addition of redox substance) among the co-culture condition groups.

  Here, since the organic acid is also generated in the culture solution 4 due to the decomposition of the protein (casein) like the ammonium ion, the higher the concentration of the organic acid, the more the proteolysis is promoted. become. Therefore, from the results shown in FIG. 4, the co-culture condition groups (a) to (d) are more likely to promote proteolysis than the single culture condition groups (e) to (h). Among the condition groups, it was revealed that proteolysis is most easily promoted particularly under the conditions (a) (Cp + Mt, −0.8 V, addition of redox substance). This tendency was consistent with the proteolysis promoting tendency shown in FIG.

(4) Insoluble carbon concentration, soluble carbon concentration, evolved gas composition Table 1 shows insoluble carbon concentration, soluble carbon concentration, and evolved gas composition. In Table 1, the unit “mg-C / L” of CH ₄ and CO ₂ means the weight in terms of carbon per 1 L of the reactor (culture vessel). The unit “mmol / L” of H ₂ means the number of moles per liter of the reactor (culture vessel).

  From the results shown in Table 1, it is clear that the co-culture condition groups (a) to (d) have a lower insoluble carbon concentration than the single culture condition groups (e) to (h). became. Moreover, it became clear that the insoluble carbon concentration was the lowest among the co-culture condition groups, particularly under the condition (a) (Cp + Mt, −0.8 V, addition of redox substance).

  In addition, from the results shown in Table 1, the soluble carbon concentration is higher in the co-culture condition groups (a) to (d) than in the single culture condition groups (e) to (h). It became clear. Moreover, it became clear that the soluble carbon concentration was highest among the co-culture condition groups, particularly under the conditions (a) (Cp + Mt, −0.8 V, addition of redox substance).

  Here, since the insoluble carbon concentration is reduced by protein decomposition, and the soluble carbon concentration is increased by protein decomposition, the lower the insoluble carbon concentration is, the lower the insoluble carbon concentration is. Also, the higher the soluble carbon concentration, the more proteolysis is promoted. Therefore, from the results shown in Table 1, from the results shown in FIG. 4, the co-culture condition groups (a) to (d) promote the proteolysis more than the single culture condition groups (e) to (h). It was revealed that proteolysis is most easily promoted under the condition (a) (Cp + Mt, −0.8 V, addition of redox substance), among the co-culture condition groups. This tendency was consistent with the proteolysis-promoting tendency shown in FIGS.

  From the results shown in Table 1, in the co-culture condition groups (a) to (d), the amount of methane gas generated is the largest under the conditions (a) (Cp + Mt, −0.8 V, addition of redox substance). Became clear.

In addition, compared to the single culture condition groups (e) to (h), the CO ₂ generation amount and the H ₂ generation amount were decreased in the coculture condition groups (a) to (d). In the group, it was confirmed that H ₂ and CO ₂ were consumed by Mt as raw materials for methanogenesis.

(5) Summary As described above, from the results of changes in cell density over time in the single culture condition groups (e) to (h) and the coculture condition groups (a) to (d), It was revealed that the growth can be promoted, and the co-culture condition group can promote the proteolysis. This effect was very remarkable under the condition (a) of the co-culture conditions (Cp + Mt, −0.8 V, oxidation-reduction substance added). Moreover, under the condition (a), the methane gas production ability was also significantly improved.

It is reported that methane production from hydrogen-utilizing methane bacteria is based on the following reaction formula (Cheng S, Xing D, Call DF, and Logan BE (2009) Direct biological conversion of electrical current into methane by electromethanogenesis. Environ Sci Technol 43: 3953-3958.).
_{^{CO 2 + 8H + + 8e -}} → CH 4 + 2H 2 O
From this reaction formula, it can be seen that 8 electrons (771882C, 8 times the Faraday constant) are required to produce 1 mole of methane. In the condition (a) of this example, 77.4 C (1.28 × 10 ⁻⁴ A (average value) × 604,800 sec) was used for 7 days. If all of the average current energy that flowed for 7 days in culture is used for methane production, the amount of methane gas that can be produced by the above reaction formula is 4.81 mg-C / L. On the other hand, 113.5 mg-C / L methane gas far exceeding this value was generated under the condition (a) of this example. From this, it was clarified that methane gas more than the input energy can be recovered by the effect of symbiosis of microorganisms by energization.

  Here, in the main culture test, it was confirmed that a reduction current flows to the working electrode 9 when a potential is applied. Therefore, the electrode is brought into contact with the co-culture environment of Cp and Mt, and an oxidation-reduction substance for increasing the potential controllability of the culture solution 4 is added, and the potential of the electrode is controlled to the reduction potential. The effect was thought to be achieved.

  In addition, in the present example, it was confirmed that the above effect was exhibited in a co-culture environment of Cp and Mt. Therefore, it was considered that the same effect was also exhibited in an environment containing Cp and Mt. .

Furthermore, in this example, a culture test was conducted using the CT-1 strain (Cp), which is a thermophilic proteolytic bacterium, and the methanothermobacter sam autotrophicus (Mt), which is a thermophilic hydrogen-assimilating methanogen. It was. Thus, the co-culture environment of these microorganisms, organic acids via peptides and amino acids from the protein from the protein by Cp (lower fatty: _VFA), NH 3, CO ₂ and _{H 2} are generated, the CO ₂ and _{H 2} Methane gas is produced by the thermophilic hydrogen-assimilating methanogen as a raw material. This reaction mechanism from proteolysis to methane production (see Fig. 6) is not unique when thermophilic proteolytic bacteria and thermophilic hydrogen-utilizing methane bacteria are used. This can occur in the same way when using general (hydrogen-utilizing methane bacteria, acetic acid-assimilating methane bacteria, etc.). Therefore, by bringing the electrode into contact with the co-culture environment of proteolytic bacteria and methanogenic bacteria, adding a redox substance for enhancing the potential controllability of the culture solution 4, and controlling the potential of the electrode to the reduction potential, It was considered that the same effect as described above was exhibited. Furthermore, the electrode is brought into contact with an environment containing proteolytic bacteria and methanogens, and a redox substance for increasing the potential controllability of this environment is added, and the potential of the electrode is controlled to the reduction potential. It was thought that the same effect was exhibited.

Claims (2)

Environment including microorganisms of the genus Coprothermobacter (Coprothermobacter) entrusted with the thermophilic proteolytic accession number FERM P-21909 and Methanothermobacter thermautotrophicus (thermophilic methanogen) Contacting the electrode with an oxidation-reduction substance, setting the temperature of the environment to 50 ° C. or higher, and decomposing the protein or protein-containing material in the environment while controlling the potential of the electrode at the reduction potential. Proteolytic treatment method characterized. A biogas recovery method comprising recovering biogas containing methane gas generated during proteolytic treatment by the method according to claim 1 .