Bioreactor and carbon dioxide recycling system

Abstract

To provide a bioreactor in which the conversion efficiency of a reaction in which a microorganism electrochemically converts carbon dioxide into a resource substance is enhanced, thereby converting carbon dioxide into a resource substance at low cost.SOLUTION: A bioreactor comprising a container having an inlet and an outlet for a fluid and a plurality of plate-shaped electrodes arranged inside the container, unidirectional flow paths being formed inside the container from the inlet to the outlet and the flow paths being formed with the plate-shaped electrodes serving as partition walls and so that opposing flows are adjacent to each other via the partition wall.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bioreactor and a carbon dioxide recycling system. [Background technology]

[0002] Carbon dioxide is a powerful greenhouse gas. Reducing carbon dioxide emissions into the atmosphere is an important issue in combating global warming. As a method for reducing carbon dioxide emissions into the atmosphere, attempts have been made to capture carbon dioxide produced by the combustion of fossil fuels and convert it into resource materials using electrochemical reactions with microorganisms for reuse.

[0003] For example, Patent Document 1 discloses a method for converting carbon dioxide into methane using methanogens through at least one of the following reaction formula (1) and the following reaction formula (3) involving the following reaction formula (2): CO2+8H + +8e - →CH4+2H2O...Formula (1) 2H + +2e - →H2...Equation (2) CO2+4H2→CH4+2H2O...Formula (3) [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-152137 Summary of the Invention [Problem to be solved by the invention]

[0005] It is expected that a low-cost carbon dioxide reuse (recycling) process can be constructed by converting carbon dioxide into resource materials using electrochemical reactions by microorganisms. However, further improvements in conversion efficiency are required for this to be put into practical use.

[0006] An object of the present invention is to provide a bioreactor that increases the conversion efficiency of the reaction in which microorganisms electrochemically convert carbon dioxide into resource substances, thereby enabling carbon dioxide to be converted into resource substances at low cost. Another object of the present invention is to provide a carbon dioxide recycling system that uses the bioreactor. [Means for solving the problem]

[0007] The present invention relates to a bioreactor comprising a vessel having an inlet and an outlet for a fluid, and a plurality of plate-like electrodes disposed inside the vessel, wherein a unidirectional flow path is formed inside the vessel from the inlet to the outlet, and the flow path is formed such that opposing flows are adjacent to each other via the partition wall, with the plate-like electrodes acting as a partition wall.

[0008] Because the bioreactor of the present invention has the above-mentioned configuration, cations (e.g., hydrogen ions) produced at the anode electrode are transported to the cathode electrode by the flow of fluid, and the fluid flows so as to come into contact with both sides of the electrode, thereby increasing the contact efficiency between the fluid and the electrode and reducing the solution resistance to the transport of cations between the electrodes. This increases the current value per electrode area and improves the efficiency of the conversion of carbon dioxide into resource substances (electrochemical reaction by microorganisms). Therefore, by using the bioreactor of the present invention to convert carbon dioxide into resource substances (electrochemical reaction by microorganisms), carbon dioxide can be converted into resource substances at low cost.

[0009] In the bioreactor, the distance between adjacent plate electrodes is preferably 2 cm or less, which further reduces the solution resistance to the transport of cations between the electrodes, thereby increasing the current value per electrode area and further improving the efficiency of the conversion of carbon dioxide into resource substances (electrochemical reaction by microorganisms).

[0010] In the bioreactor, the anode electrodes and cathode electrodes are preferably arranged alternately in the direction of the flow path, which further reduces the solution resistance to the transport of cations between the electrodes.

[0011] The bioreactor may further include a voltage application device connected to the plurality of plate-like electrodes.

[0012] The present invention also relates to a carbon dioxide recycling system comprising a storage section for storing anaerobic groundwater, a reaction section for converting carbon dioxide contained in the anaerobic groundwater into resource materials through an electrochemical reaction by microorganisms, and a transfer section for transferring the anaerobic groundwater from the storage section to the reaction section, wherein the reaction section has the bioreactor according to the present invention described above.

[0013] The recycling system according to the present invention has the bioreactor according to the present invention in the reaction section, which improves the efficiency of conversion of carbon dioxide into resource substances (electrochemical reaction by microorganisms), making it possible to convert carbon dioxide into resource substances at low cost.

[0014] In the recycling system, the transfer section preferably has a dissolving means for further dissolving carbon dioxide in the anaerobic groundwater. The bioreactor according to the present invention significantly improves the rate of resource material production by increasing the amount of carbon dioxide contained in the anaerobic groundwater (dissolved carbon dioxide concentration). Therefore, by further dissolving carbon dioxide in the anaerobic groundwater in the transfer section, the rate of resource material production in the reaction section is significantly improved. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a bioreactor that increases the conversion efficiency of the reaction in which microorganisms electrochemically convert carbon dioxide into resource substances, thereby enabling carbon dioxide to be converted into resource substances at low cost.The present invention also provides a carbon dioxide recycling system that uses the bioreactor. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view of a bioreactor according to one embodiment. [Figure 2] FIG. 1 is a front view of a bioreactor according to one embodiment. [Figure 3] FIG. 1 is a side view of a bioreactor according to one embodiment. [Figure 4] FIG. 1 is a plan view of a bioreactor according to one embodiment. [Figure 5] 1 is a schematic diagram of a carbon dioxide recycling system according to one embodiment. [Figure 6] 1A is a graph showing the relationship between applied voltage and current value, and FIG. 1B is a graph showing the relationship between applied voltage and current value per unit area of ​​the electrode. [Figure 7] (A) Graph showing the relationship between the flow rate of anaerobic groundwater and the current value. (B) Graph showing the relationship between the flow rate of anaerobic groundwater and the current value per unit area of ​​the electrode. [Figure 8] 1 is a graph showing the relationship between the anaerobic groundwater supply method and the electromethane production rate. [Figure 9] 1 is a graph showing the relationship between the presence or absence of anaerobic groundwater flow and the electromethane production rate. [Figure 10] FIG. 1 is a front view of a bioreactor of a reference example. [Figure 11] FIG. 1 is a side view of a bioreactor of a reference example. [Figure 12] FIG. 1 is a plan view of a bioreactor of a reference example. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as needed. However, the present invention is not limited to the following embodiments.

[0018] The bioreactor according to this embodiment includes a vessel having an inlet and an outlet for a fluid, and a plurality of plate electrodes disposed inside the vessel. A unidirectional flow path is formed inside the vessel from the inlet to the outlet, and the flow path is formed such that opposing flows are adjacent to each other via the plate electrodes as a partition.

[0019] When a fluid is introduced into the bioreactor through the inlet, a flow of the fluid is generated along the channel formed inside the vessel. Since the channel is formed as a one-way channel from the inlet to the outlet of the vessel, the fluid flows in one direction through the channel. The channel is formed so that opposing streams are adjacent to each other via a partition, with the plate-like electrode acting as a partition. Therefore, cations (e.g., hydrogen ions) produced at the anode electrode are transported to the cathode electrode by the fluid flow, and the fluid flows so as to come into contact with both sides of the electrode, increasing the contact efficiency between the fluid and the electrodes and reducing the solution resistance to the transport of cations between the electrodes.

[0020] The number of plate electrodes placed inside the bioreactor should be at least two, since the plate electrodes must function as both an anode and a cathode. From the viewpoint of further increasing the current value per electrode area, the number of plate electrodes is preferably greater, and may be, for example, 4 or more, 8 or more, 12 or more, or 16 or more. There is no particular upper limit on the number of plate electrodes, but it may be, for example, 32 or less, 28 or less, 24 or less, or 20 or less.

[0021] The plate electrodes placed inside the bioreactor function as anodes and cathodes when connected to a voltage application device (e.g., an external power supply). In this case, the number of anodes and the number of cathodes do not necessarily have to be the same. The anodes and cathodes may be arranged arbitrarily, but from the viewpoint of further reducing the solution resistance to the transport of cations between the electrodes, it is preferable to arrange the anodes and cathodes alternately in the flow path direction (fluid flow direction) from the inlet to the outlet.

[0022] The flow paths formed inside the bioreactor are formed so that opposing flows are adjacent to each other via a partition wall, with the plate electrodes as partition walls. The flow paths are preferably arranged so that each of the plurality of plate electrodes serves as a partition wall, with the opposing flows being adjacent to each other via a partition wall, resulting in a plurality of adjacent flow paths that turn back at one end of each plate electrode. This further increases the contact efficiency between the fluid and the electrodes, and further reduces the solution resistance to the transport of cations between the electrodes.

[0023] The distance between adjacent plate electrodes (the distance in the out-of-plane direction of the plate electrodes) is preferably 2 cm or less, more preferably 1.5 cm or less, and even more preferably 1 cm or less, which can further reduce the solution resistance to the transport of cations between the electrodes.

[0024] The plate electrode may have a member to support its shape, but in order to allow direct contact between the fluid and the electrode, it is preferable that at least a portion of the electrode surface is exposed, and it is more preferable that the entire electrode surface is exposed.

[0025] The plate electrode may be an electrode formed in a plate shape. The electrode material is not particularly limited as long as it functions as an electrode, and examples thereof include carbon, stainless steel, and titanium. When the plate electrode has a member that supports the shape, the member is preferably formed of an insulating material, and specific examples thereof include polystyrene, vinyl chloride, and acrylic plates.

[0026] The container constituting the bioreactor is preferably made of an insulating material, specific examples of which include vinyl chloride, acrylic resin, etc. The shape of the container is not particularly limited, but a rectangular parallelepiped shape is preferred because it allows plate electrodes to be densely arranged, thereby increasing the contact efficiency between the fluid and the electrodes.

[0027] In one embodiment of the bioreactor, plate electrodes arranged so as to contact the bottom surface and first side wall inside the container and plate electrodes arranged so as to contact the bottom surface and second side wall opposite the first side wall inside the container are alternately arranged, thereby forming a unidirectional flow path from the inlet to the outlet inside the container, and the flow path is formed so that opposing flows are adjacent to each other via the partition, with the plate electrodes acting as a partition.

[0028] FIG. 1 is a perspective view of a bioreactor according to one embodiment. FIG. 2 is a front view of a bioreactor according to one embodiment. FIG. 3 is a side view of a bioreactor according to one embodiment. FIG. 4 is a plan view of a bioreactor according to one embodiment. The bioreactor 100 shown in FIGS. 1 to 4 includes a rectangular parallelepiped container 10 and a plurality of plate electrodes 20 disposed inside the container 10. The rectangular parallelepiped container 10 has an inlet 11 for introducing a fluid (e.g., anaerobic groundwater) into the container 10 and an outlet 12 for discharging the fluid to the outside of the container 10. The plate electrodes 20 are connected to a voltage application device (not shown) via conductive wires 30 and function as anode electrodes and cathode electrodes. The bioreactor 100 shown in FIGS. 1 to 4 is configured such that the plate electrodes 20 are connected to a voltage application device (not shown) via conductive wires 30, and the anode electrodes and cathode electrodes are arranged alternately. The distance D between the plate electrodes 20 of the bioreactor 100 (the distance in the out-of-plane direction of the plate electrodes 20) is, for example, 1 cm.

[0029] In the bioreactor 100, plate electrodes 20 arranged so as to contact the interior bottom surface and first side wall of the container 10 and plate electrodes 20 arranged so as to contact the interior bottom surface and a second side wall opposite the first side wall are alternately arranged, thereby forming a unidirectional flow path from the inlet 11 to the outlet 12 inside the container 10. Note that in the bioreactor 100, the outlet 12 is formed at a position lower than the top of the plate electrode 20, so that the fluid does not flow beyond the plate electrode 20. This flow path is formed so that opposing fluid flows are adjacent to each other via the plate electrode 20 as a partition.

[0030] The bioreactor of this embodiment can be used by introducing anaerobic water, carbon dioxide, and microorganisms capable of converting carbon dioxide into resource substances through an electrochemical reaction (hereinafter also referred to as "electron-utilizing microorganisms") into the bioreactor, and by using the electrochemical reaction of the electron-utilizing microorganisms to convert carbon dioxide into resource substances.

[0031] Anaerobic water is water that lacks oxygen. Anaerobic water is in a reducing state due to the lack of oxygen, and electrons (e - ) can be released. Anaerobic water may be, for example, naturally occurring anaerobic water (anaerobic groundwater) such as water present in an anaerobic underground aquifer or brine remaining in an oil or gas field, or may be anaerobic water obtained by subjecting water to anaerobically treatment. Examples of anaerobic treatment methods for producing anaerobic water include a method of expelling dissolved oxygen by bubbling inert gas through the water, and a method of removing dissolved oxygen by adding a reducing agent such as sodium sulfide or titanium chloride to the water. Anaerobic groundwater contains dissolved carbon dioxide and underground microorganisms (for example, brine remaining in an oil or gas field contains methanogens), and therefore can be preferably used as the fluid to be introduced into the bioreactor according to this embodiment.

[0032] The carbon dioxide used may be the carbon dioxide originally contained in the anaerobic water (dissolved carbon dioxide), or may be carbon dioxide dissolved in the anaerobic water by blowing carbon dioxide gas into the anaerobic water. Methods for dissolving carbon dioxide in anaerobic water include, for example, blowing carbon dioxide gas into the anaerobic water, adding dry ice to the anaerobic water, and spraying anaerobic water into a carbon dioxide gas atmosphere (for example, using a high-concentration CO2 dissolving device (product name: high-concentration oxygen dissolving device, manufactured by Tomoe Shokai Co., Ltd.)). Carbon dioxide may also be dissolved in anaerobic water containing dissolved carbon dioxide.

[0033] The electron-utilizing microorganisms can be any microorganism capable of converting carbon dioxide into resource substances through an electrochemical reaction. Examples of electron-utilizing microorganisms include microorganisms capable of converting carbon dioxide into hydrocarbons such as methane through an electrochemical reaction (e.g., methanogens), microorganisms capable of converting carbon dioxide into organic acids such as acetic acid through an electrochemical reaction (e.g., acetogens), and microorganisms capable of converting carbon dioxide into biodegradable polymers such as polyhydroxyalkanoates (PHAs) through an electrochemical reaction (e.g., PHA-producing bacteria).

[0034] More specific examples of electron-utilizing microorganisms include, for example, methanogens belonging to the class Methanobacteria, methanogens belonging to the class Methanomicrobia, methanogens belonging to the class Methanococci, methanogens belonging to the class Methanopyri, acetogens belonging to the class Clostridia, acetogens belonging to the class Negativicutes, and PHA-producing bacteria belonging to the class Betaproteobacteria.

[0035] The method for introducing anaerobic water, carbon dioxide, and electron-utilizing microorganisms into the bioreactor is not particularly limited. Specifically, for example, a fluid containing anaerobic water, carbon dioxide, and electron-utilizing microorganisms may be prepared and introduced into the bioreactor, or a cathode electrode on which electron-utilizing microorganisms are immobilized may be placed in the bioreactor in advance, and the fluid containing anaerobic water and carbon dioxide may be introduced into the bioreactor, or these methods may be used in combination.

[0036] Anaerobic water, carbon dioxide, and electron-utilizing microorganisms are introduced into the bioreactor. First, electrons (e - ) are released, and counter ions (cations, e.g., hydrogen ions) are generated. The cations then flow along the flow path with the fluid and reach the cathode electrode. The electrons reach the cathode electrode via an external power source (voltage application device). At the cathode electrode, electron-utilizing microorganisms use the electrons (and cations, if necessary) to carry out a reaction that converts carbon dioxide into a resource substance. For example, if the resource substance is methane, the conversion reaction is CO2 + 8H + +8e - →CH4 + 2H2O. The voltage applied by the voltage application device may be set appropriately within the range of, for example, 0.1 to 5.0 V. The voltage applied by the voltage application device may be within the range of 0.2 to 3.0 V, 0.3 to 2.0 V, 0.4 to 1.5 V, or 0.5 to 1.2 V. The generated resource substance may be recovered as a gas from the gas phase of the bioreactor, for example, or may be recovered from the fluid discharged from the outlet.

[0037] The bioreactor according to this embodiment can be incorporated into a carbon dioxide recycling system for use.

[0038] The carbon dioxide recycling system according to this embodiment includes at least a storage section that stores anaerobic groundwater, a reaction section that converts the carbon dioxide contained in the anaerobic groundwater into resource materials through an electrochemical reaction by microorganisms, and a transfer section that transfers the anaerobic groundwater from the storage section to the reaction section. Here, the reaction section includes a bioreactor according to the present invention. Because the recycling system according to this embodiment includes a bioreactor according to the present invention in the reaction section, the efficiency of conversion of carbon dioxide into resource materials (electrochemical reaction by microorganisms) is improved, and carbon dioxide can be converted into resource materials at low cost.

[0039] In the carbon dioxide recycling system according to this embodiment, the transfer unit may include a dissolving means for further dissolving carbon dioxide in the anaerobic groundwater. By further dissolving carbon dioxide in the anaerobic groundwater in the transfer unit, the rate at which resource materials are produced in the reaction unit is significantly improved.

[0040] Fig. 5 is a schematic diagram of a carbon dioxide recycling system according to one embodiment. The carbon dioxide recycling system 1000 shown in Fig. 5 includes a storage unit 500 that stores anaerobic groundwater, a reaction unit 300 that converts the carbon dioxide contained in the anaerobic groundwater into resource materials through an electrochemical reaction using microorganisms, and a transfer unit that transfers the anaerobic groundwater from the storage unit to the reaction unit.

[0041] The storage unit 500 may be configured as, for example, a natural gas separation tank. In this case, anaerobic groundwater pumped up from the ground is temporarily stored in the natural gas separation tank, and natural gas is separated in the natural gas separation tank. The anaerobic groundwater from which natural gas has been separated is transferred to the reaction unit 300 via a transfer unit.

[0042] The transfer unit includes a pump 510 and a conduit 430 that pumps the anaerobic groundwater from the storage unit 500, and the conduit 430 is connected to the inlet 11 of the bioreactor 100. In the carbon dioxide recycling system 1000, the transfer unit also includes a dissolving means 400 that further dissolves carbon dioxide in the anaerobic groundwater. In response to the opening and closing (On / Off) of electromagnetic valves 410 and 420 provided along the conduit 430, the anaerobic groundwater being transferred through the conduit 430 is guided to the dissolving means 400, where the carbon dioxide is further dissolved by the dissolving means 400. The dissolving means 400 may be, for example, a high-concentration gas dissolving device (e.g., a CO2 high-concentration dissolving device (product name: high-concentration oxygen dissolving device, manufactured by Tomoe Shokai Co., Ltd.)), but is not limited thereto. The dissolving means 400 may also be configured as a device that injects carbon dioxide gas into anaerobic groundwater or a device that adds dry ice to anaerobic groundwater.

[0043] The reaction section 300 includes a bioreactor 100. The bioreactor 100 is configured as the bioreactor according to the present invention described above. The bioreactor 100 may be operated to circulate anaerobic groundwater therein via a conduit 330, a pump 350, and a conduit 340. The bioreactor 100 may be equipped with a water level meter, a pH sensor, a hygrometer, an oxidation-reduction potential (ORP) meter, a potentiostat, or the like, as needed, to monitor the reaction. The reaction section 300 may further include a means for recovering the generated resource material (e.g., methane). When the generated resource material is methane, the generated gas (methane gas) may be recovered, for example, from the top of the bioreactor 100 via a gas recovery conduit. In this case, a methane sensor 310 or a gas logger 320 for monitoring the amount of methane produced may be provided in the conduit. The reaction section 300 may be configured, for example, as a geobioelectric reactor. The external power supply (voltage application device) connected to the bioreactor 100 may be, for example, a power supply derived from renewable energy (electricity generated by solar power generation, wind power generation, marine power generation, hydroelectric power generation, etc.) or nighttime standby power. [Example]

[0044] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples. In the following examples, groundwater (brine water) pumped from a natural gas well (South Kanto Gas Field) was used as the anaerobic groundwater. The anaerobic groundwater contained subsurface microorganisms (e.g., methanogens). The dissolved carbon dioxide concentration of the anaerobic groundwater was 28.5 mM.

[0045] Test Example 1: Measurement of current value when voltage applied to bioreactor is changed Using a bioreactor of the example having the configuration shown in Figures 1 to 4 (reactor volume 10 L, anaerobic groundwater volume 8 L, plate electrode size: width 9.4 cm × length 23 cm, 9 cathode electrodes, 9 anode electrodes, distance between adjacent plate electrodes 1 cm), current values ​​were measured when the applied voltage was changed. The bioreactor of the example is configured such that the plate electrodes are connected to a voltage application device, and the cathode electrodes and anode electrodes are arranged alternately. Hereinafter, the bioreactor of the example is also referred to as an "interdigitated 18-electrode bioreactor."

[0046] For comparison, similar measurements were performed using a bioreactor of a reference example having the configuration shown in Figures 10 to 12 (reactor volume: 10 L, anaerobic groundwater volume: 8 L, plate electrode size: 9.5 cm wide x 29 cm long, two cathode electrodes, two anode electrodes, distance between adjacent plate electrodes: 4 cm). Figure 10 is a front view of the bioreactor of the reference example. Figure 11 is a side view of the bioreactor of the reference example. Figure 12 is a plan view of the bioreactor of the reference example. The bioreactor 200 shown in Figures 10 to 12 includes a cylindrical container 10 and four plate electrodes 20 arranged inside the container 10. The bioreactor 200 is configured such that the plate electrodes 20 are connected to a voltage application device (not shown) via conductive wires 30, and the cathode electrodes 20a and anode electrodes 20b are arranged alternately. Cylindrical vessel 10 is formed with an inlet 11 for introducing anaerobic groundwater into the vessel and an outlet 12 for discharging the anaerobic groundwater to the outside of the vessel. In bioreactor 200 shown in Figures 10 to 12, anaerobic groundwater introduced from inlet 11 can freely move between plate electrodes 20 and between plate electrodes 20 and the inner wall of vessel 10. Hereinafter, the bioreactor of the reference example will also be referred to as a "cylindrical four-electrode bioreactor."

[0047] Anaerobic groundwater was introduced into each of the interdigitated 18-electrode bioreactor and cylindrical 4-electrode bioreactor, and the flow rate was maintained at 2 L / min. The volume of anaerobic groundwater inside the vessels at steady state was 8 L in both cases. Acetic acid was added to the anaerobic groundwater introduced into the bioreactors to a concentration of 10 mM. In steady state, the current value was measured when a voltage ranging from 0 V to 0.6 V was applied using a voltage application device (external power supply).

[0048] The results are shown in Figure 6. Figure 6(A) is a graph showing the relationship between applied voltage and current value. Figure 6(B) is a graph showing the relationship between applied voltage and current value per unit electrode area. The 18-electrode interdigital bioreactor was able to obtain a larger current value than the 4-electrode cylindrical bioreactor (Figure 6(A)), and the current value per unit electrode area was also larger (Figure 6(B)). The larger the current value, the more efficiently the electrochemical reaction can be carried out by the microorganisms. Furthermore, the 18-electrode interdigital bioreactor responded by increasing the applied voltage, and the current value also increased in a straightforward manner, suggesting that no unnecessary side reactions were occurring. This is also thought to be the reason why a larger current value was obtained than with the 4-electrode cylindrical bioreactor.

[0049] [Test Example 2: Measurement of current value when changing the flow rate of anaerobic groundwater] Using the comb-type 18-electrode bioreactor and cylindrical-type 4-electrode bioreactor described in Test Example 1, the current value was measured while changing the flow rate of anaerobic groundwater.

[0050] Anaerobic groundwater was introduced into each of the interdigitated 18-electrode bioreactor and cylindrical 4-electrode bioreactor, and maintained at a specific flow rate (within the range of 0 to 3 L / min). The volume of anaerobic groundwater inside the vessels at steady state was 8 L in both cases. Acetic acid was added to the anaerobic groundwater introduced into the bioreactor to a concentration of 10 mM. In the steady state, the current value was measured when a voltage of 0.6 V (600 mV) was applied using a voltage application device (external power supply).

[0051] The results are shown in Figure 7. Figure 7(A) is a graph showing the relationship between the flow rate of anaerobic groundwater and the current value. (B) is a graph showing the relationship between the flow rate of anaerobic groundwater and the current value per unit area of ​​the electrode. The interdigitated 18-electrode bioreactor was able to obtain a larger current value than the cylindrical 4-electrode bioreactor at all measured flow rates (Figure 7(A)), and the current value per unit area of ​​the electrode was also larger (Figure 7(B)). The larger the current value, the more efficiently the electrochemical reaction can be carried out by the microorganisms. It was also confirmed that the current value increased in proportion to the flow rate of the anaerobic groundwater. This is thought to be because the solution resistance to the transport of cations between the electrodes decreases as the flow rate of anaerobic groundwater increases.

[0052] [Test Example 3: Measurement of electromethane production rate when changing the anaerobic groundwater supply method] Using the comb-type 18-electrode bioreactor described in Test Example 1, the electromethane production rate was measured when the method of supplying anaerobic groundwater was changed.

[0053] Figure 8 is a graph showing the relationship between the anaerobic groundwater supply method and the electromethane production rate. Details of each condition in Figure 8 are as follows.

[0054] <Test 1: 900mV groundwater batch supply> Anaerobic groundwater was introduced into an 18-electrode interdigitated bioreactor, and the flow of anaerobic groundwater was internally circulated (flow rate 2 L / min), and the electrochemical methane production rate was measured. The volume of anaerobic groundwater inside the vessel was 8 L. A voltage of 0.9 V (900 mV) was applied using a voltage application device (external power source), and the amount of gas (methane) produced was measured using a methane sensor (BCP-CH4, BlueSens) and a gas logger (milligas counter, Nippon Flow Control).

[0055] <Test 2: 900mV groundwater batch supply + dry ice> Anaerobic groundwater was introduced into an 18-electrode interdigital bioreactor, and the flow of the anaerobic groundwater was internally circulated (flow rate 2 L / min), and the electrochemical methane production rate was measured. The volume of anaerobic groundwater inside the vessel was 8 L. Approximately 1 g / L of dry ice was added to the anaerobic groundwater introduced into the bioreactor (this changed the pH of the anaerobic groundwater from 8 to 6.8). A voltage of 0.9 V (900 mV) was applied using a voltage application device (external power supply), and the amount of gas (methane) produced was measured using a methane sensor (BCP-CH4, BlueSens) and a gas logger (milligas counter, Nippon Flow Control).

[0056] <Test 3: 900mV continuous groundwater supply> Anaerobic groundwater was introduced into an 18-electrode interdigitated bioreactor and maintained at a flow rate of 400 mL / min. The volume of anaerobic groundwater inside the vessel at steady state was 8 L. At steady state, a voltage of 0.9 V (900 mV) was applied using a voltage application device (external power supply), and the amount of gas (methane) produced was measured using a methane sensor (BCP-CH4, BlueSens) and a gas logger (milligas counter, Nippon Flow Control).

[0057] <Test 4: Continuous supply of 900mV CO2-dissolved groundwater> Anaerobic groundwater was introduced into an 18-electrode interdigital bioreactor and maintained at a flow rate of 400 mL / min. At steady state, the volume of anaerobic groundwater inside the vessel was 8 L. A high-concentration CO2 dissolution device (product name: High-concentration Oxygen Dissolution Device, manufactured by Tomoe Shokai Co., Ltd.) was used to dissolve the anaerobic groundwater into carbon dioxide (gas) before introducing it into the bioreactor. The dissolved carbon dioxide concentration in the anaerobic groundwater after passing through the high-concentration CO2 dissolution device was 57.1 mM. At steady state, a voltage of 0.9 V (900 mV) was applied using a voltage application device (external power supply), and the amount of gas (methane) produced was measured using a methane sensor (BCP-CH4, manufactured by BlueSens) and a gas logger (milligas counter, manufactured by Nippon Flow Control Co., Ltd.).

[0058] <Test 5: 2V Continuous groundwater supply> The amount of gas (methane) generated was measured in the same procedure as in Test 3, except that the approval voltage was changed from 0.9 V (900 mV) to 2 V.

[0059] <Test 6: Continuous supply of 2V CO2 dissolved groundwater> The amount of gas (methane) generated was measured in the same procedure as in Test 4, except that the approval voltage was changed from 0.9 V (900 mV) to 2 V.

[0060] As shown in Fig. 8, by increasing the amount of carbon dioxide (dissolved carbon dioxide concentration) contained in anaerobic groundwater, the methane production rate (electro-methane production rate) correspondingly improves significantly (comparison between Test 1 and Test 2, Test 3 and Test 4, Test 5 and Test 6). In particular, by using a high-concentration CO2 dissolution device to increase the dissolved carbon dioxide concentration from 28.5 mM to 57.1 mM, the electro-methane production rate increased by about 50 times (comparison between Test 3 and Test 4, Test 5 and Test 6). Also, since the electro-methane production rate does not increase significantly even when the applied voltage is increased above 900 mV, it can be seen that a sufficient electro-methane production rate can be obtained at an applied voltage (~1.5 V) that is not so high, and it can be operated at low cost.

[0061] 〔Test Example 4: Measurement of electro-methane production rate when the flow of anaerobic groundwater is changed〕 Using the comb-type 18-electrode bio-reactor described in Test Example 1, the electro-methane production rate was measured when the flow of anaerobic groundwater was changed.

[0062] Fig. 9 is a graph showing the relationship between the presence or absence of the flow of anaerobic groundwater and the electro-methane production rate. The details of each condition in Fig. 9 are as follows.

[0063] <CO2 dissolved groundwater with flow> Anaerobic groundwater was introduced into the comb-shaped 18-electrode bioreactor and maintained at a flow rate of 400 mL / min. The volume of anaerobic groundwater inside the container in the steady state was 8 L. For the anaerobic groundwater introduced into the bioreactor, a CO2 high-concentration dissolution device (trade name: High-concentration Oxygen Dissolution Device, manufactured by Hoppo Shokai Co., Ltd.) was used to further dissolve carbon dioxide by passing the anaerobic groundwater through carbon dioxide (gas). The dissolved carbon dioxide concentration in the anaerobic groundwater after passing through the CO2 high-concentration dissolution device was 57.1 mM. In the steady state, a voltage of 0.9 V (900 mV) was applied with a voltage application device (external power supply), and the amount of gas (methane) generated was measured with a methane sensor (BCP-CH4, manufactured by BlueSens) and a gas logger (milligas counter, manufactured by Nippon Flow Control Co., Ltd.).

[0064] <Dissolved CO2 in groundwater · No flow> Anaerobic groundwater was introduced into the comb-shaped 18-electrode bioreactor, and the rate of electro-methane generation was measured without the flow (flow rate 0 L / min) of anaerobic groundwater. The volume of anaerobic groundwater inside the container was 8 L. For the anaerobic groundwater introduced into the bioreactor, a CO2 high-concentration dissolution device (trade name: High-concentration Oxygen Dissolution Device, manufactured by Hoppo Shokai Co., Ltd.) was used to further dissolve carbon dioxide by passing the anaerobic groundwater through carbon dioxide (gas). The dissolved carbon dioxide concentration in the anaerobic groundwater after passing through the CO2 high-concentration dissolution device was 57.1 mM. A voltage of 0.9 V (900 mV) was applied with a voltage application device (external power supply), and the amount of gas (methane) generated was measured with a methane sensor (BCP-CH4, manufactured by BlueSens) and a gas logger (milligas counter, manufactured by Nippon Flow Control Co., Ltd.).

[0065] As shown in Fig. 9, due to the flow (flow rate) of anaerobic groundwater, the methane generation rate (electro-methane generation rate) increases by approximately 20 times.

Explanation of symbols

[0066] 10...container, 11...inlet, 12...outlet, 20...plate electrode, 20a...cathode electrode, 20b...anode electrode, 30...conductive wire, 100, 200...bioreactor, 300...reaction section, 400...dissolution means, 500...storage section, 1000...carbon dioxide recycling system.

Claims

1. a vessel having an inlet and an outlet for a fluid, and a plurality of plate electrodes disposed inside the vessel; a unidirectional flow path extending from the inlet to the outlet is formed inside the container, The flow paths are formed such that opposing flows are adjacent to each other via the plurality of plate-like electrodes, each serving as a partition.

2. 2. The bioreactor according to claim 1, wherein the distance between adjacent plate electrodes is 2 cm or less.

3. 3. The bioreactor according to claim 1, wherein the anode electrodes and the cathode electrodes are arranged alternately in the direction of the flow path.

4. The bioreactor according to any one of claims 1 to 3, further comprising a voltage application device connected to the plurality of plate-like electrodes.

5. The system comprises a storage section for storing anaerobic groundwater, a reaction section for converting carbon dioxide contained in the anaerobic groundwater into resource materials through an electrochemical reaction by microorganisms, and a transfer section for transferring the anaerobic groundwater from the storage section to the reaction section, A carbon dioxide recycling system, wherein the reaction section has the bioreactor according to any one of claims 1 to 4.

6. The recycling system according to claim 5 , wherein the transfer section has a dissolving means for further dissolving carbon dioxide in the anaerobic groundwater.

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