Microbial fuel battery and concentration method of bacterial liquid

Abstract

To provide a microbial fuel battery in which a decrease in a power generation characteristic is suppressed, and provide a concentration method of a bacterial liquid.SOLUTION: A microbial fuel battery 1 includes a cathode electrode 12, an electrolyte layer 13 that is in contact with the cathode electrode 12 and includes an organic substance and a bacterial liquid containing bacteria of the genus Zobellella, and an anode electrode 11 that is electrically connected to the cathode electrode 12 and is in contact with the electrolyte layer 13 and receives an electron generated by the bacteria. Further, a concentration method of the bacterial liquid used in the microbial fuel battery 1 includes an anode electrode installation step of accommodating brackish water containing the organic substance and bacteria of the genus Zobellella in a container 10 and installing the anode electrode 11, a cathode electrode installation step of installing the cathode electrode 12 on a water surface of brackish water so as to be separated from the anode electrode 11, and a voltage application step of applying a voltage between the anode electrode 11 and the cathode electrode 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a microbial fuel cell and a method for concentrating a bacterial liquid. [Background technology]

[0002] Currently, research is being conducted on microbial fuel cells, and for example, a microbial fuel cell that generates electricity using microorganisms present in the soil of tidal flats and the like is known.

[0003] Patent Documents 1 to 3 disclose microbial fuel cell technologies that generate electricity using bacteria such as Geobacter, Shewanella, Aeromonas, Geothrix, Saccharomyces, and Pseudomonas as current-generating bacteria (electricity-generating bacteria). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-122615 [Patent Document 2] Japanese Patent Publication No. 2021-140988 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-060771 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the bacteria of the genus Geobacter, Shewanella, Aeromonas, Geothrix, and Saccharomyces disclosed in Patent Documents 1 to 3 are hardly capable of generating electricity in brackish water or using brackish water, and there are problems with the power generation characteristics of fuel cells using microorganisms. Furthermore, although Pseudomonas bacteria can generate electricity in brackish water, they have low power generation capacity and cannot grow sufficiently in the power generation environment, so there is a problem that a decline in power generation characteristics cannot be suppressed.

[0006] The present invention was devised in consideration of the above-mentioned problems, and its purpose is to provide a microbial fuel cell that suppresses the deterioration of power generation characteristics, and a method for concentrating a bacterial liquid. [Means for solving the problem]

[0007] The microbial fuel cell of the first invention is characterized by comprising a cathode electrode, an electrolyte layer in contact with the cathode electrode and containing organic matter and a bacterial solution containing bacteria of the genus Zobellella, and an anode electrode electrically connected to the cathode electrode and in contact with the electrolyte layer, receiving electrons produced by the bacteria.

[0008] A microbial fuel cell according to a second aspect of the present invention is the microbial fuel cell according to the first aspect of the present invention, characterized in that the electrolyte layer contains soil, and the anode electrode is buried in the soil.

[0009] The method for concentrating a bacterial liquid in the third invention is a method for concentrating a bacterial liquid used as an electrolyte material for a microbial fuel cell, and is characterized by comprising an anode electrode installation step of storing brackish water containing organic matter and bacteria of the genus Zobellella in a container and installing an anode electrode; a cathode electrode installation step of installing a cathode electrode on the surface of the brackish water so as to be spaced apart from the anode electrode installed in the anode electrode installation step; and a voltage application step of applying a voltage between the anode electrode installed in the anode electrode installation step and the cathode electrode installed in the cathode electrode installation step.

[0010] A fourth aspect of the present invention is a method for concentrating a bacterial liquid according to the third aspect of the present invention, characterized in that the anode electrode installation step further includes placing soil in the container and installing the anode electrode in the soil. [Effects of the Invention]

[0011] According to the first and second inventions, an electrolyte layer containing organic matter and a bacterial solution containing Zobellella bacteria is provided. This allows the Zobellella bacteria to grow sufficiently in the power generation environment. This makes it possible to prevent a decrease in the power generation characteristics of the microbial fuel cell.

[0012] In particular, according to the second aspect of the present invention, the electrolyte layer contains soil, and the anode electrode is buried in the soil. This means that the anaerobic electricity-generating bacteria around the anode electrode are less likely to be exposed to an aerobic environment. This makes it easier to maintain the voltage of the microbial fuel cell. This further prevents the power generation characteristics of the microbial fuel cell from deteriorating.

[0013] According to the third and fourth inventions, the method includes an anode electrode installation step in which brackish water containing organic matter and Zobellella bacteria is placed in a container and an anode electrode is installed. This allows the Zobellella bacteria to grow sufficiently in the environment during power generation of the microbial fuel cell. This makes it possible to prevent a decrease in the power generation characteristics of the microbial fuel cell that uses a bacterial solution.

[0014] In particular, according to the fourth aspect of the present invention, the anode electrode installation step further includes placing soil in the container and installing the anode electrode in the soil. This means that the anaerobic power-generating bacteria around the anode electrode are less likely to be exposed to an aerobic environment. Therefore, the anaerobic Zobellella bacteria are less likely to decrease when a voltage is applied, and can be easily concentrated. This further prevents a decline in the power generation characteristics of a microbial fuel cell that uses a bacterial solution. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a microbial fuel cell in this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of a method for concentrating a bacterial liquid used in a microbial fuel cell in this embodiment. [Figure 3] FIG. 3 is a graph showing an example of the relationship between the bacterial liquid concentration and the output voltage of the microbial fuel cell in this embodiment. [Figure 4] FIG. 4 is a graph showing an example of the output voltage and elapsed time for each concentration of bacterial liquid in the microbial fuel cell in this embodiment. [Figure 5] FIG. 5 is a graph showing an example of the voltage measurement results at a constant current of the microbial fuel cell in this embodiment. [Figure 6] FIG. 6 is a graph showing an example of the voltage measurement results at a constant current of the microbial fuel cell in this embodiment. [Figure 7] FIG. 7 is a graph showing an example of the measurement results of the output voltage, current density, and power density for each organic matter of the microbial fuel cell in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] An example of a microbial fuel cell 1 according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the configurations in each drawing are shown schematically for the purpose of explanation, and the size of each component and the size comparison between components may differ from those shown in the drawings.

[0017] (Microbial fuel cell 1) An example of a microbial fuel cell 1 according to this embodiment will be described with reference to the drawings.

[0018] The microbial fuel cell 1 is a fuel cell that generates electricity using so-called electricity-generating bacteria. Here, electricity-generating bacteria refers to bacteria that have the function of releasing electrons generated when decomposing organic matter to the outside of their bodies. The microbial fuel cell 1 can generate electricity by filling an exterior material (exterior container) with organic matter as fuel and a bacterial solution containing electricity-generating bacteria. The microbial fuel cell 1 is sealed by the exterior material to prevent air from entering the interior, in order to activate the activity of the electricity-generating bacteria.

[0019] Zobellella bacteria, such as Zobellella denitrificans, are used as the power-generating bacteria of the present invention. Zobellella bacteria can be easily collected from natural environments, such as tidal flat soil or brackish water, and the higher the concentration, the higher the output voltage of the microbial fuel cell 1 obtained. Zobellella bacteria are also suitable for power generation in brackish water areas and using brackish water, which have been difficult to achieve with conventional power-generating bacteria, such as Geobacter bacteria, Shewanella bacteria, Aeromonas bacteria, Geothrix bacteria, and Saccharomyces bacteria. Furthermore, compared to conventional Pseudomonas bacteria that are suitable for power generation in brackish water areas, Zobellella bacteria are less likely to die and can proliferate effectively in the power generation environment. Therefore, applying a voltage to tidal flat soil or brackish water can improve the relative proportion of Zobellella bacteria compared to other bacteria. The power generation characteristics of the microbial fuel cell 1 using Zobellella bacteria and the bacterial composition ratio before and after voltage application will be described in detail in the Examples below.

[0020] According to such a microbial fuel cell 1, Zobellella bacteria can be sufficiently grown in the power generation environment. This makes it possible to suppress a decrease in the power generation characteristics of the microbial fuel cell 1. In the following description, the term "bacterial solution" also refers to a bacterial solution containing Zobellella bacteria.

[0021] 1, the microbial fuel cell 1 includes an anode electrode 11, a cathode electrode 12, and an electrolyte layer 13. The microbial fuel cell 1 can be electrically connected to an external circuit 2 to supply power to the external circuit 2, similar to a conventional battery.

[0022] <Anode electrode 11> The anode electrode 11 is electrically connected to the cathode electrode 12 via a conductor such as a titanium wire and an external circuit 2. The anode electrode 11 is in contact with the electrolyte layer 13 and receives electrons generated when the power-generating bacteria in the electrolyte layer 13 oxidize and decompose organic matter. Here, since the power-generating bacteria used in the present invention are anaerobic bacteria, maintaining the anode electrode 11 in an anaerobic environment makes it difficult for the decomposition efficiency of organic matter to decrease, which in turn makes it difficult for the power generation characteristics to decrease.

[0023] For example, when the electrolyte layer 13 contains soil, the anode electrode 11 may be buried in the soil. In other words, the anaerobic power-generating bacteria around the anode electrode 11 are less likely to be exposed to an aerobic environment. In this case, the voltage of the microbial fuel cell 1 is more likely to be maintained. This makes it possible to further prevent a decrease in the power generation characteristics of the microbial fuel cell 1.

[0024] A weight 111 may be attached to the anode electrode 11 to prevent it from floating upward and coming into contact with the cathode electrode 12. As the weight 111, for example, a glass flat ball or the like may be used.

[0025] The anode electrode 11 may be, for example, a carbon felt or a metal oxide catalyst electrode.

[0026] <Cathode electrode 12> The cathode electrode 12 is electrically connected to the anode electrode 11 via a conductor such as a titanium wire and an external circuit 2. The cathode electrode 12 consumes the electrons received via the external circuit 2 through a reduction reaction.

[0027] The cathode electrode 12 may be, for example, a platinum catalyst electrode or carbon felt.

[0028] <Electrolyte layer 13> The electrolyte layer 13 is in contact with the anode electrode 11 and the cathode electrode 12. The electrolyte layer 13 contains an organic matter and a bacterial solution containing bacteria of the genus Zobellella.

[0029] An electrolyte solution containing, for example, an organic liquid, a bacterial solution, and a buffer solution (pH adjuster) may be used for the electrolyte layer 13. The dissolved oxygen concentration of the electrolyte layer 13 may be reduced by blowing nitrogen gas into the layer, for example, in order to activate the activity of the electricity-generating bacteria near the anode electrode 11.

[0030] The electrolyte layer 13 may contain, for example, brackish water from a tidal flat, soil, etc. in addition to the bacterial solution. That is, the electrolyte layer 13 may be in a liquid state, a muddy state, or a semi-solid state in which the liquid and solid are separated.

[0031] (Method for concentrating bacterial solution used in microbial fuel cell 1) Next, an example of a method for concentrating the bacterial liquid used in the microbial fuel cell 1 of this embodiment will be described with reference to the drawings. The bacterial liquid produced by the following concentration method can be used as the bacterial liquid for the microbial fuel cell 1. In the method for concentrating the bacterial liquid, each step may be performed by a person, for example, or each step may be performed via a program installed in a known computer.

[0032] The method for concentrating a bacterial liquid includes an anode electrode installation step, a cathode electrode installation step, and a voltage application step.

[0033] <Anode electrode installation process> 2, the anode electrode installation step involves placing organic matter and brackish water 131 containing Zobellella bacteria in a container as an electrolyte layer 13, and installing an anode electrode 11. Here, the container may be a container for concentrating a bacterial solution that is separate from a battery exterior container, which is the exterior material of the battery, or the battery exterior container may be used.

[0034] <Cathode electrode installation process> In the cathode electrode installation step, the cathode electrode 12 is installed on the surface of the brackish water 131 so as to be spaced apart from the anode electrode 11 installed in the anode electrode installation step. Here, the cathode electrode 12 may be installed on one or more supports 14 provided in a substantially vertical direction on the upper surface of the anode electrode 11. Here, the supports 14 may be made of wood.

[0035] <Voltage application process> In the voltage application step, after the cathode electrode installation step, the container is sealed and the pressure inside the container is reduced using a vacuum pump 3 to create an anaerobic environment.

[0036] Thereafter, in the voltage application step, a voltage is applied between the anode electrode 11 installed in the anode electrode installation step and the cathode electrode 12 installed in the cathode electrode installation step via the power generation characteristic evaluation device 4. In this case, Zobellella bacteria can be sufficiently grown in the environment during power generation of the microbial fuel cell 1. This makes it possible to suppress a decrease in the power generation characteristics of the microbial fuel cell 1 that uses a bacterial solution.

[0037] The anode electrode 11 is preferably fixed below the surface of the brackish water 131 to prevent contact with the cathode electrode 12, which will be installed later. The anode electrode installation step may involve, for example, further placing soil 132 as the electrolyte layer 13 in a container and installing the anode electrode 11 in the soil. In other words, the anaerobic power-generating bacteria around the anode electrode 11 are less likely to be exposed to an aerobic environment. In this case, the anaerobic Zobellella bacteria are less likely to decrease due to voltage application, and can be easily concentrated. This further prevents a decline in the power generation characteristics of the microbial fuel cell 1 that uses a bacterial solution.

[0038] According to this embodiment, the electrolyte layer 13 includes organic matter and a bacterial solution containing Zobellella bacteria. Therefore, Zobellella bacteria can grow sufficiently in the power generation environment. This makes it possible to suppress a decrease in the power generation characteristics of the microbial fuel cell 1.

[0039] Furthermore, according to this embodiment, the electrolyte layer 13 includes soil 132, and the anode electrode 11 is buried in the soil 132. In other words, the anaerobic power-generating bacteria around the anode electrode 11 are less likely to be exposed to an aerobic environment. This makes it easier to maintain the voltage of the microbial fuel cell 1. This makes it possible to further prevent a decline in the power generation characteristics of the microbial fuel cell 1.

[0040] Furthermore, according to this embodiment, an anode electrode installation step is provided in which brackish water 131 containing organic matter and Zobellella bacteria is placed in a container and an anode electrode 11 is installed. This allows Zobellella bacteria to grow sufficiently in the environment during power generation of the microbial fuel cell 1. This makes it possible to prevent a decrease in the power generation characteristics of the microbial fuel cell 1 that uses a bacterial solution.

[0041] Furthermore, according to this embodiment, the anode electrode installation step further includes placing soil 132 in the container and installing the anode electrode 11 in the soil 132. In other words, the anaerobic power-generating bacteria around the anode electrode 11 are less likely to be exposed to an aerobic environment. Therefore, the anaerobic Zobellella bacteria are less likely to decrease due to voltage application, and can be easily concentrated. This further prevents a decrease in the power generation characteristics of the microbial fuel cell 1 that uses a bacterial solution. [Example]

[0042] The results of experiments using the above-described embodiment will be specifically described below, taking examples of the present invention and comparative examples.

[0043] <Experiment 1: Verification of the power generation characteristics of Zobellella bacteria> In this experiment, the output voltage of the microbial fuel cell 1 containing a bacterial solution containing Zobellella bacteria was confirmed, and the power generation characteristics of Zobellella bacteria were verified.

[0044] The bacterial solution containing Zobellella bacteria used in this experiment was prepared by the following method.

[0045] First, a mixture of Zobellella bacteria stored at -80°C and a glycerol stock was streaked onto LB agar medium and cultured for 16 hours in an incubator at 29°C. Then, colonies that appeared on the agar medium were transferred to 2 mL of LB liquid medium using a platinum loop and cultured with shaking in a water bath at 29°C for 16 hours (step 1).

[0046] After the first step, the translucent yellow LB liquid medium in the area where the bacteria had grown began to turn cloudy yellow. After confirming that the LB liquid medium had turned cloudy yellow, 0.5 mL of LB liquid (culture medium) was added to 150 mL of LB liquid medium, and the mixture was again cultured with shaking in a thermostatic water bath at 29°C for 16 hours (second step).

[0047] After the second step, the LB liquid medium was confirmed to be yellow and cloudy, and then centrifuged at 3500 rpm for 35 minutes using a centrifuge. The supernatant was discarded (third step).

[0048] After the third step, 5.0 × 10 glucose (organic matter) was added to remove the LB solution. -3 10 mL of fuel buffer solution, which was a mixture of 9.995 mL of PBM (Phosphate Buffer Medium) and 10 mL of ethanol, was added, and the precipitate at the bottom of the tube was stirred using a vortex mixer. The tube was then centrifuged again at 3500 rpm for 30 minutes. The supernatant liquid generated by this centrifugation was discarded (Step 4).

[0049] After the fourth step, glucose 2.5 x 10 -3 5 mL of fuel buffer solution containing 4.9975 mL of PBS and 4.9975 mL of PBM was added, and the precipitate at the bottom of the tube was stirred using a vortex mixer (fifth step).

[0050] A bacterial solution containing Zobellella bacteria was prepared using the above method. In addition, by adding the above bacterial solution to a fuel buffer solution, several electrolyte solutions with different bacterial solution concentrations (volume of bacterial solution per mL of fuel buffer solution) were prepared.

[0051] The electrolyte used in this experiment was prepared as follows.

[0052] An electrolyte solution obtained by adding 0.03 mL of bacterial solution to 30 mL of fuel buffer solution to give a bacterial solution concentration of 1 μL / mL was designated Example 1 of the present invention. An electrolyte solution obtained by adding 0.3 mL of bacterial solution to 30 mL of fuel buffer solution to give a bacterial solution concentration of 10 μL / mL was designated Example 2 of the present invention. An electrolyte solution obtained by adding 1.5 mL of bacterial solution to 30 mL of fuel buffer solution to give a bacterial solution concentration of 50 μL / mL was designated Example 3 of the present invention. An electrolyte solution obtained by adding 3.0 mL of bacterial solution to 30 mL of fuel buffer solution to give a bacterial solution concentration of 100 μL / mL was designated Example 4 of the present invention. An electrolyte solution obtained by adding no bacterial solution to 30 mL of fuel buffer solution to give a bacterial solution concentration of 0 μL / mL was designated Comparative Example 1. Each fuel buffer solution was adjusted to 30 mL by mixing 29.985 mL of glucose and 0.015 mL of PBM.

[0053] For ease of comparison, the bacterial solution concentration of Invention Example 2 was used as the standard, and Invention Example 1 (bacterial solution concentration 1 μL / mL) was designated "1 / 10×," Invention Example 2 (bacterial solution concentration 10 μL / mL) was designated "1×," Invention Example 3 (bacterial solution concentration 50 μL / mL) was designated "5×," and Invention Example 4 (bacterial solution concentration 100 μL / mL) was designated "10×." Comparative Example 1 (bacterial solution concentration 0 μL / mL) was designated "no bacteria added."

[0054] The anode electrode 11 was made of carbon felt manufactured by Nippon Carbon Co., Ltd., and the cathode electrode 12 was made of platinum-supported carbon manufactured by Chemix Co., Ltd. (Pt amount: 1.0 mg / cm). 2 ) and titanium wire was used for the lead wire.

[0055] Furthermore, an "HJ1020mSD8" manufactured by Hokuto Denko Corporation was used as the power generation characteristic evaluation device 4 to measure OCV (open circuit voltage), and the voltage value was recorded 72 hours after the start of measurement.

[0056] The results of this experiment are shown in FIG.

[0057] 3, the output voltage of the microbial fuel cell 1 was approximately 130 [mV] for Inventive Example 1, approximately 220 [mV] for Inventive Example 2, approximately 290 [mV] for Inventive Example 3, and approximately 380 [mV] for Inventive Example 4. The output voltage of Comparative Example 1 was 0 [mV].

[0058] Therefore, according to Examples 1 to 4 of the present invention, it was confirmed that the higher the concentration of the bacterial solution containing Zobellella bacteria, the higher the output voltage obtained. This indicates that Zobellella is a power-generating bacterium involved in power generation. As a result, the microbial fuel cell 1 containing the bacterial solution containing Zobellella bacteria can generate power. Furthermore, the higher the concentration of the bacterial solution containing Zobellella bacteria, the more the discharge characteristics of the microbial fuel cell 1 can be improved.

[0059] <Experiment 2: OCV measurement of a fuel cell containing Zobellella bacteria> In this experiment, the reliability of the microbial fuel cell 1 containing Zobellella bacteria was confirmed by comparing the time course of OCV measurements for microbial fuel cell 1 with each concentration of bacterial solution containing Zobellella bacteria. Note that a description of the same conditions as in Experiment 1 will be omitted.

[0060] The electrolyte solutions used in this experiment were prepared as follows. First, 6.0 mL of bacterial solution (same as in Experiment 1, the same applies below) was added to 30 mL of fuel buffer solution to give an electrolyte solution with a bacterial solution concentration of 200 μL / mL, which was designated as Example 5 of the present invention. Next, 9.0 mL of bacterial solution was added to 30 mL of fuel buffer solution to give an electrolyte solution with a bacterial solution concentration of 300 μL / mL, which was designated as Example 6 of the present invention. Next, 12.0 mL of bacterial solution was added to 30 mL of fuel buffer solution to give an electrolyte solution with a bacterial solution concentration of 400 μL / mL, which was designated as Example 7 of the present invention. Next, 15.0 mL of bacterial solution was added to 30 mL of fuel buffer solution to give an electrolyte solution with a bacterial solution concentration of 500 μL / mL, which was designated as Example 8 of the present invention.

[0061] For ease of comparison, the bacterial solution concentration of Inventive Example 2 was used as the standard, and Inventive Example 5 (bacterial solution concentration 200 μL / mL) was designated as "20×", Inventive Example 6 (bacterial solution concentration 300 μL / mL) was designated as "30×", Inventive Example 7 (bacterial solution concentration 400 μL / mL) was designated as "40×", and Inventive Example 8 (bacterial solution concentration 500 μL / mL) was designated as "50×".

[0062] The results of this experiment are shown in FIG.

[0063] According to FIG. 4, the output voltage of the microbial fuel cell 1 144 hours after the start of discharge was highest in Example 8 of the present invention, followed by Example 7 of the present invention, Example 5 of the present invention, and Example 6 of the present invention.

[0064] According to Examples 5 to 8 of the present invention, it was confirmed that the higher the concentration of the bacterial solution containing Zobellella bacteria, the more likely it is that high reliability can be obtained. As a result, the higher the concentration of the bacterial solution containing Zobellella bacteria, the more the reliability of the microbial fuel cell 1 can be improved.

[0065] <Experiment 3: Constant current load test of a fuel cell containing Zobellella bacteria> In this experiment, the continuous operating time of the microbial fuel cell 1 containing Zobellella bacteria was confirmed by comparing the time course of the output voltage under constant current operation for the microbial fuel cell 1 with each bacterial solution concentration containing Zobellella bacteria. Note that a description of the same conditions as in Experiment 1 will be omitted.

[0066] The electrolyte used in this experiment was prepared as follows. First, 1 mL of fuel buffer solution was added to the liquid obtained after completing the fourth step of Experiment 1, and the precipitate at the bottom of the tube was stirred with a vortex mixer to prepare a new bacterial solution. Then, 15.0 mL of this bacterial solution was added to 30 mL of the same fuel buffer solution as in Experiment 2 to prepare an electrolyte. The amount of fuel buffer added in the bacterial solution prepared in this experiment was 1 / 5, and the concentration was 25 times higher than that of the bacterial solution prepared in Experiment 2, resulting in a bacterial solution concentration of 12,500 μL / mL. This electrolyte was designated Example 9 of the present invention.

[0067] For ease of comparison, Invention Example 9 (bacterial solution concentration 12,500 μL / mL) was designated "1250×" based on the bacterial solution concentration of Invention Example 2. Invention Example 9 was also compared with Invention Example 8 (50×).

[0068] The results of this experiment are shown in Figures 4 and 5. The graph in Figure 4 and the graph of "50x" in Figure 5 show the same values.

[0069] 4, the continuous operation time of Inventive Example 8 was approximately 5.3 [h]. According to Fig. 5, the continuous operation time of Inventive Example 9 was approximately 24 [h].

[0070] According to Examples 8 and 9 of the present invention, it was confirmed that the higher the concentration of the bacterial solution containing Zobellella bacteria, the longer the continuous operation time that can be obtained. Therefore, the higher the concentration of the bacterial solution containing Zobellella bacteria, the more the convenience of the microbial fuel cell 1 can be improved.

[0071] <Experiment 4: Comparison of power generation characteristics between Zobellella bacteria and types of organic matter> In this experiment, the voltage, current density, and power density of the microbial fuel cell 1 for each combination of a bacterial solution containing Zobellella bacteria and several different organic substances were compared to confirm the power generation characteristics of the microbial fuel cell 1 containing Zobellella bacteria for each type of organic substance. Note that a description of the same conditions as in Experiment 1 will be omitted.

[0072] The electrolyte used in this experiment was prepared by adding the same bacterial solution as in Experiment 1 to three types of organic matter: glucose, acetic acid, and lactic acid. The bacterial solution concentration was 12,500 μL / mL in each case.

[0073] In addition, Example 10 of the present invention is referred to as "electrolyte solution containing glucose," Example 11 of the present invention is referred to as "electrolyte solution containing acetic acid," and Example 12 of the present invention is referred to as "electrolyte solution containing lactic acid." Compared to.

[0074] The results of this experiment are shown in Figures 7(a) to 7(c). Figure 7(a) shows an example using "glucose," Figure 7(b) shows an example using "acetic acid," and Figure 7(c) shows an example using "lactic acid."

[0075] According to FIG. 7(a), the power density of the microbial fuel cell 1 of Example 11 of the present invention was approximately 3.5 mW / m at most. 2 Furthermore, according to FIG. 7(b), the power density of the microbial fuel cell 1 of Example 12 of the present invention was a maximum of approximately 2.5 mW / m 2 According to FIG. 7(c), the power density of the microbial fuel cell 1 of Example 13 of the present invention was a maximum of about 3.5 mW / m 2 It was.

[0076] <Experiment 5: Ratio of Zobellella bacteria before and after voltage application> In this experiment, to verify the proportion of Zobellella bacteria before and after the power generation experiment, we checked how the proportion of Zobellella bacteria in brackish water or soil collected from Yatsu tidal flats (Chiba Prefecture, Japan) changed before and after voltage application. Note that explanations of conditions similar to those in Experiment 1 will be omitted.

[0077] The electrolyte used in this experiment was collected soil 132 and brackish water 131. A commercially available plastic container (volume approximately 900 cm) was used as the outer packaging. 3 Carbon felt manufactured by Nippon Carbon Co., Ltd. was used for both electrodes, and titanium wire was used for the lead wire.

[0078] The cell for this experiment was prepared in the following manner. First, as shown in Figure 2, soil 132 was poured into the exterior material to a height of 4 cm from the bottom, and the anode electrode 11 was buried in the center. Then, brackish water 131 was poured into the exterior material to a height of 8 cm from the bottom, and one or more supports 14 were erected on the top surface of the anode electrode 11. The cathode electrode 12 was then placed on the water surface so as to be supported by the supports 14. Each electrode 11, 12 had a radius of 5.0 cm and a surface area of ​​approximately 157 cm. 2Before being installed inside the exterior packaging, each of the electrodes 11 and 12 was acclimatized in brackish water 131 for several seconds. In addition, in order to reproduce the environment (low oxygen state) in the Yatsu tidal flat soil inside the exterior packaging, degassing was performed for about 1 minute using a vacuum pump 3.

[0079] The experimental conditions were as follows: the microbial fuel cell 1 was connected to the power generation characteristic evaluation device 4, and after confirming that the OCV had stabilized by OCV measurement, a predetermined current was passed under IV measurement. The current value was sampled in increments of 20 μA every 4 minutes, ultimately reaching 160 μA.

[0080] To confirm the proportion of Zobellella bacteria, 30 to 50 DNA samples extracted from each colony of soil 132 before the addition of the exterior material were sequenced using a commercially available DNA extraction kit to identify the bacteria from which each DNA sample was derived. The number of samples identified as Zobellella bacteria by this method was divided by the total number of samples to determine the proportion of Zobellella bacteria. The proportion of Zobellella bacteria was also calculated using the same method for soil 132' after the current had been drawn up to 160 μA.

[0081] The results of this experiment are shown in Table 1.

[0082] [Table 1]

[0083] According to Table 1, the proportion of Zobellella bacteria was undetectable in soil 132 before voltage application (it was not observed as being low compared to the proportion of other bacteria), but increased to 30% in soil 132' after voltage application. This is thought to be due to the proliferation of Zobellella bacteria due to their involvement in power generation, and the relative increase in their proportion due to the death of fungi that are unsuitable for the environment during power generation (electric potential, pH, etc.).

[0084] For reference, the proportion of Pseudomonas bacteria, which accounted for the majority of the soil 132 before voltage application, was also confirmed. This was 93% in soil 132 before voltage application, but decreased to 45% in soil 132' after voltage application.

[0085] According to this experiment, by using at least one of the soil 132′ and the brackish water 131′ after voltage application, a bacterial solution or an electrolyte solution rich in Zobellella bacteria can be prepared, which can be used as the bacterial solution or the electrolyte solution for the microbial fuel cell 1. In other words, the technique used in this experiment can be used as a method for concentrating the bacterial solution used as the electrolyte material for the microbial fuel cell 1.

[0086] Furthermore, this experiment confirmed that the proportion of Pseudomonas bacteria decreased before and after voltage application, while the proportion of Zobellella bacteria increased. This indicates that Zobellella bacteria proliferated more than Pseudomonas bacteria under the power generation environment. Therefore, by providing an electrolyte layer 13 containing a bacterial solution containing Zobellella bacteria, it is possible to suppress a decrease in the power generation characteristics of the microbial fuel cell 1.

[0087] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0088] 1 Microbial fuel cell 10 containers 11 Anode electrode 111 Weight 12 cathode electrode 13 Electrolyte layer 131 Brackish water 132 Soil 14 Posts 2 External circuit 3. Vacuum pump 4. Power generation characteristic evaluation device

Claims

1. A cathode electrode; an electrolyte layer in contact with the cathode electrode and containing an organic substance and a bacterial solution containing Zobellella bacteria; an anode electrode electrically connected to the cathode electrode and in contact with the electrolyte layer to receive electrons produced by the bacteria; To be prepared A microbial fuel cell characterized by:

2. the electrolyte layer includes soil; The anode electrode is buried in the soil. The microbial fuel cell according to claim 1, characterized in that

3. A method for concentrating a bacterial liquid used as an electrolyte material for a microbial fuel cell, comprising: an anode electrode installation step of storing brackish water containing organic matter and bacteria of the genus Zobellella in a container and installing an anode electrode; a cathode electrode installation step of installing a cathode electrode on the surface of the brackish water so as to be spaced apart from the anode electrode installed in the anode electrode installation step; a voltage applying step of applying a voltage between the anode electrode installed in the anode electrode installing step and the cathode electrode installed in the cathode electrode installing step; Having A method for concentrating a bacterial liquid, characterized by:

4. The anode electrode installation step further includes placing soil in the container and installing the anode electrode in the soil.

4. The method for concentrating a bacterial liquid according to claim 3,

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