Microbial fuel cells

Abstract

To provide a microbial fuel cell that has reduced the time until when expected power is obtained even if it is installed in an environment with a large amount of dissolved oxygen.SOLUTION: A microbial fuel cell comprises a negative electrode, a positive electrode, an ion conductor, and an anaerobic condition generating and maintaining layer (anaerobic layer). The negative electrode and the positive electrode are connected with each other with the ion conductor therebetween. The anaerobic layer covers a surface of the negative electrode to which organic matter is supplied. The anaerobic layer transmits the organic matter therethrough, and executing the following experiment results in DO2 / DO1 of 80% or less. Experiment: a connection pipe between a first cell and a second cell is partitioned by the anaerobic layer. The first cell and the second cell include first upper opening and a second upper opening, respectively. The first upper opening is opened and the first cell is constantly exposed to atmospheric air. The second cell is filled with pure water, the second upper opening is opened and the pure water is exposed to atmospheric air, and the amount of dissolved oxygen in the pure water in which oxygen is dissolved in a saturated amount (DO1) is measured. The pure water is bubbled with nitrogen gas, the second upper opening is closed, and after the lapse of 25 hours, the amount of dissolved oxygen in the pure water (DO2) is measured.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present disclosure relates to microbial fuel cells. 【Background Art】 【0002】 Conventionally, microbial fuel cells using anaerobic current-producing microorganisms have been known. In a microbial fuel cell, current-producing microorganisms living near the negative electrode take in organic substances (electron donors) such as sugars and organic acids and water during the metabolic process, generate carbon dioxide, protons, and electrons, and donate electrons to the negative electrode (Reaction Formula 1). Electrons are transmitted from the negative electrode to the positive electrode through an external circuit. At the positive electrode, oxygen (electron acceptor) and protons receive electrons to generate water (Reaction Formula 2). Through these series of reactions, electric power is obtained from the microbial fuel cell. Negative electrode: Organic substance + 2H2O → CO2 + 4H + + 4e - (Reaction Formula 1) Positive electrode: O2 + 4H + + 4e - → 2H2O (Reaction Formula 2) 【0003】 For example, Patent Document 1 discloses a microbial fuel cell in which a negative electrode and a positive electrode are respectively installed at the lower and upper parts of the inner wall surface of a cylindrical holder. The negative electrode of this microbial fuel cell is disposed in a mud layer (sludge layer) containing an organic substance and anaerobic microorganisms, and the positive electrode is disposed in an aqueous layer existing above the mud layer. Further, Patent Document 2 discloses a microbial fuel cell having a cylindrical holder having an opening, a negative electrode provided on the outer surface of the cylindrical holder, and a positive electrode provided inside the cylindrical holder, wherein the negative electrode and the positive electrode are connected via the opening and an ion conductor. This microbial fuel cell can be easily installed simply by driving it into soil or mud containing anaerobic current-generating bacteria (current-producing microorganisms), and can obtain electric power semi-permanently from the natural ecosystem. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2013-84541 [Patent Document 2] Japanese Patent Publication No. 2016-54053 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 In both microbial fuel cells described in Patent Documents 1 and 2, organic matter must be supplied to the current-producing microorganisms near the negative electrode for power generation according to reaction equation 1; therefore, the negative electrode is open to the outside world. 【0006】 When microbial fuel cells are installed in environments with high dissolved oxygen levels, the anaerobic microorganisms that produce electricity may not become active easily, and it may take time before the expected amount of electricity is obtained. 【0007】 This disclosure is made in view of the above circumstances, and the purpose of this disclosure is to provide a microbial fuel cell that can be installed in an environment with a high dissolved oxygen content and has a short time required to obtain the expected power. [Means for solving the problem] 【0008】 One aspect of this disclosure is, It comprises a negative electrode, a positive electrode, an ion conductor, and an anaerobic conditions generation and maintenance layer. The negative electrode and the positive electrode are connected via the ion conductor. The anaerobic condition generation and maintenance layer covers at least a portion of the side of the negative electrode where organic matter is supplied, The anaerobic condition generation and maintenance layer is characterized by its permeability of organic matter and, as shown in the experiment below, having a DO2 / DO1 ratio of 80% or less. experiment: The connecting pipe (inner diameter: 3.3 cm) between the first cell and the second cell is separated by the anaerobic condition generation and maintenance layer. The first cell includes a first upper opening, and the second cell includes a second upper opening. The first upper opening is kept open at all times, and the first cell is constantly exposed to the atmosphere. The second cell is filled with pure water with all openings except the second upper opening closed, and the second upper opening is opened so that the pure water is exposed to the atmosphere, and the amount of dissolved oxygen (DO1) in the pure water with a saturated amount of oxygen is measured. The dissolved oxygen in the pure water is removed by bubbling it with nitrogen gas, the second upper opening is closed, and after 25 hours, the amount of dissolved oxygen (DO2) in the pure water is measured. 【0009】 In the above experiment, by creating and maintaining anaerobic conditions where the DO2 / DO1 ratio is 80% or less, covering at least a portion of the side of the negative electrode where organic matter is supplied, the amount of dissolved oxygen in that portion is reduced in a relatively short time, thereby activating the current-producing microorganisms. This allows for the provision of a microbial fuel cell that can be installed in an environment with a high amount of dissolved oxygen, while still providing the expected power in a short time. 【0010】 In one aspect of this disclosure, Preferably, the anaerobic condition generation and maintenance layer includes aerobic microorganisms, oxygen absorbers, oxygen permeation inhibiting filters, water-absorbing polymers, or soil. 【0011】 Dissolved oxygen is consumed by aerobic microorganisms and oxygen absorbers, and oxygen permeation is further inhibited by oxygen permeation-inhibiting filters, water-absorbing polymers, or soil. As a result, the amount of dissolved oxygen in that area is reduced in an even shorter time, activating the current-producing microorganisms and further shortening the time until the expected power is obtained. 【0012】 In one aspect of this disclosure, Preferably, the anaerobic condition generation and maintenance layer covers the entire surface of the negative electrode on the side to which the organic matter is supplied. 【0013】 As the area covered by the anaerobic conditions generation and maintenance layer increases, the amount of dissolved oxygen is reduced in an even shorter time, the current-producing microorganisms are activated, and the time until the expected power is obtained can be further shortened. 【0014】 In one aspect of this disclosure, It further comprises a cylindrical holder, It is preferable that the anaerobic condition generation / maintenance layer, the negative electrode, the ion conductor, and the positive electrode are arranged in order from one end to the other end inside the cylindrical holder. 【0015】 When the cylindrical holder is embedded and installed in soil or the like, organic substances are supplied to the negative electrode through the anaerobic condition generation / maintenance layer from one end of the cylindrical holder, and oxygen is supplied to the positive electrode from the other end of the cylindrical holder, enabling power generation. Since a microbial fuel cell can be handled as a unit housed in the cylindrical holder, installation and wiring are simple. Therefore, it is also easy to increase the electromotive force by connecting a plurality of microbial fuel cells in series or in parallel. 【Brief Description of Drawings】 【0016】 [Figure 1] Shows an embodiment of a microbial fuel cell. [Figure 2] Shows an experimental apparatus. [[ID=1十七]]<0> [Figure 3] Shows an experimental apparatus.<000> [Figure 4] Shows an experimental apparatus. 【Modes for Carrying Out the Invention】 【0017】 Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that the embodiments described below do not unduly limit the content of the present disclosure described in the claims, and not all of the configurations described in the embodiments are essential as the solution means of the present disclosure. 【0018】 Figure 1 shows one embodiment of the microbial fuel cell 10 of this disclosure. The microbial fuel cell 10 comprises a negative electrode 11, a positive electrode 12, an ion conductor 13, an anaerobic condition generation and maintenance layer 14, and a cylindrical holder 15. The anaerobic condition generation and maintenance layer 14, the negative electrode 11, the ion conductor 13, and the positive electrode 12 are arranged sequentially from one end to the other inside the cylindrical holder 15. The negative electrode 11 and the positive electrode 12 are connected via the ion conductor 13, and the anaerobic condition generation and maintenance layer 14 covers the entire surface of the negative electrode 11 on the side to which organic matter is supplied. Note that the anaerobic condition generation and maintenance layer 14 only needs to cover at least a portion of the surface of the negative electrode 11 on the side to which organic matter is supplied. The anaerobic condition generation and maintenance layer 14 is permeable to organic matter, and when the following experiment is performed, the DO2 / DO1 ratio is 80% or less. 【0019】 When one end of the microbial fuel cell 10 is placed in soil or mud, organic matter in the soil or mud is supplied to the negative electrode 11 from one end of the cylindrical holder 15, permeating the anaerobic condition generation and maintenance layer 14, following the flow of water. Current-producing microorganisms living near the negative electrode 11 generate carbon dioxide, protons, and electrons according to reaction equation 1, and donate electrons to the negative electrode 11. The electrons are transmitted from the negative electrode 11 to the external circuit via the negative electrode lead wire 16, and further transmitted from the external circuit to the positive electrode 12 via the positive electrode lead wire 17. The protons generated by the current-producing microorganisms are transmitted to the positive electrode 12 via the ion conductor 13. The other end of the cylindrical holder 15 is open to the atmosphere, and oxygen is supplied to the positive electrode 12 from the other end. At the positive electrode 12, oxygen (electron acceptor) and protons accept electrons, and water is produced according to reaction equation 2. 【0020】 The negative electrode 11 is preferably made of a material that has a surface structure suitable for the habitation of current-producing microorganisms and is electrically conductive. Suitable materials include, for example, carbon, stainless steel, iron, titanium, platinum, gold, silver, copper, nickel, cobalt, ruthenium, and their alloys, as well as biocathodes using enzymes or microorganisms as electrode catalysts, and materials composited with carbon. Suitable forms include, for example, flat surfaces such as sheets, brushes, and meshes, cotton-like materials such as felt and nonwoven fabrics, and rod-like materials such as rods. Current-producing microorganisms may be pre-cultured and accumulated on the surface of the negative electrode 11. 【0021】 The positive electrode 12 is preferably one that has a large contact area with the atmosphere and is electrically conductive. Suitable materials include, for example, carbon, stainless steel, iron, titanium, platinum, gold, silver, copper, nickel, cobalt, ruthenium, and their alloys, as well as non-platinum catalysts such as iron phthalocyanine organometallic complexes, biocathodes using enzymes or microorganisms as electrode catalysts, and materials that combine these with carbon. Suitable forms include flat sheets, brushes, and meshes, cotton-like materials such as felt and nonwoven fabrics, and rod-shaped materials such as rods. 【0022】 The ion conductor 13 transmits protons generated by the current-producing microorganisms to the positive electrode 12. Suitable materials include, for example, porous membranes, ion-exchange polymer membranes such as DuPont's Nafion, aramid nonwovens, cellulose fibers, Japanese paper and glass fibers, electrolyte solutions containing ionic salts such as sodium chloride and potassium chloride, gels (such as agar), soil, and water. 【0023】 The anaerobic condition generation and maintenance layer 14 is permeable to organic matter, and when the following experiment is performed, the DO2 / DO1 ratio is 80% or less, preferably 75% or less, more preferably 65% ​​or less, even more preferably 55% or less, and particularly preferably 51% or less. The smaller the DO2 / DO1 ratio, the faster the dissolved oxygen is reduced on the surface of the negative electrode 11 covered by the anaerobic condition generation and maintenance layer 14, and the more the current-producing microorganisms can be activated. Therefore, even when the microbial fuel cell 10 is installed in an environment with a high dissolved oxygen level, the time it takes to obtain the expected power can be shortened. The anaerobic condition generation and maintenance layer 14 is permeable to organic matter, and when the following experiment is performed, the DO2 / DO1 ratio is small, so the material and form are not particularly limited. Methods for reducing the DO2 / DO1 ratio include oxygen consumption and suppression of oxygen permeation. The former, the anaerobic condition generation and maintenance layer 14, may contain, for example, aerobic microorganisms or oxygen absorbers. The latter anaerobic condition generation and maintenance layer 14 may include, for example, soil deaerated by blowing nitrogen gas or carbon dioxide gas, an oxygen permeability inhibiting filter, a water-absorbing polymer, or soil (humic substances / humic substances). Aerobic microorganisms and deoxidizing agents may be included in the anaerobic condition generation and maintenance layer 14 individually, or they may be included in the anaerobic condition generation and maintenance layer 14 after being added to soil, a solution, or a gel. As deoxidizing agents, for example, divalent iron ions (FeO), reducing agents such as ascorbic acid and oxalic acid can be used. As an oxygen permeability inhibiting filter, for example, a dialysis tube can be used. 【0024】 The details of the experiment will be explained using Figures 2-4. The experimental apparatus 20 comprises a first cell 21, a second cell 22, a connecting pipe 23 with an inner diameter of 3.3 cm, and an anaerobic condition generation and maintenance layer 14. The first cell 21, the second cell 22, and the connecting pipe 23 constitute a so-called H-shaped cell, and the connecting pipe 23 between the first cell 21 and the second cell 22 is separated by the anaerobic condition generation and maintenance layer 14. The first cell 21 includes a first upper opening 24, and the second cell 22 includes a second upper opening 25. The first upper opening 24 is always open, and the first cell 21 is always exposed to the atmosphere. The second cell 22 is filled with pure water 26, with all openings except the second upper opening 25 closed. The second upper opening 25 is opened, and the pure water 26 is exposed to the atmosphere (Figure 2). The amount of dissolved oxygen (DO1) in the pure water 26, which has reached a saturation point, is measured using a dissolved oxygen meter. Subsequently, the pure water 26 is bubbling with nitrogen gas to remove the dissolved oxygen (Figure 3), and the second upper opening 25 is closed with a lid 27 (Figure 4). The atmosphere comes into contact with the anaerobic condition generation and maintenance layer 14 through the first upper opening 24, the first cell 21, and the connecting pipe 23, so oxygen permeates through the anaerobic condition generation and maintenance layer 14 and gradually dissolves into the pure water 26 in the second cell 22. After 25 hours, the amount of dissolved oxygen (DO2) in the pure water 26 is measured using a dissolved oxygen meter. 【0025】 As examples of the above experiment, Table 1 shows the results when a dialysis tube with nothing inside was used as the anaerobic condition generation and maintenance layer 14 (Example 1), and when a dialysis tube containing soil with aerobic microorganisms was used as the anaerobic condition generation and maintenance layer 14 (Example 2). As a comparative example, Table 1 shows the results when the connecting tube 23 was shielded with an impermeable lid, and the second upper opening 25 of the second cell 22 was kept open at all times, that is, not closed with the lid 27 (Comparative Example). [Table 1] 【0026】 In the comparative example, oxygen permeated through the second upper opening 25 and dissolved into the pure water 26 in the second cell 22, causing the dissolved oxygen level to rise to 96% of the saturation level after 25 hours. On the other hand, in Example 1, the dissolved oxygen level after 25 hours was kept to about 74% of the saturation level. This is thought to be because oxygen gradually diffused into the pure water 26 in the second cell 22 by permeating through the dialysis tube. In Example 2, the dissolved oxygen level after 25 hours was kept to about 50% of the saturation level. This is thought to be because the aerobic microorganisms contained in the anaerobic condition generation and maintenance layer 14 consumed the oxygen. Because this anaerobic condition generation and maintenance layer 14 uses a dialysis tube, it can permeate organic matter supplied to the current-producing microorganisms and retain aerobic microorganisms. Therefore, by using a microbial fuel cell 10 in which at least a portion of the side of the negative electrode 11 that is supplied with organic matter is covered with this anaerobic condition generation and maintenance layer 14, the amount of dissolved oxygen in that portion can be reduced in a relatively short time, the current-producing microorganisms can be activated, and the time it takes to obtain the expected power can be shortened even when installed in an environment with a high amount of dissolved oxygen. 【0027】 Although this embodiment has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novelty and effects of this disclosure. Therefore, all such modifications are included within the scope of this disclosure. For example, any term that appears at least once in the specification or drawings together with a broader or synonymous term may be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration of this embodiment is not limited to that described herein, and various modifications are possible. [Explanation of symbols] 【0028】 10 Microbial fuel cell, 11 Negative electrode, 12 Positive electrode, 13 Ion conductor, 14 Anaerobic condition generation / maintenance layer, 15 Cylindrical holder, 16 Negative electrode lead wire, 17 Positive electrode lead wire, 20 Experimental apparatus, 21 First cell, 22 Second cell, 23 Connecting tube, 24 First upper opening, 25 Second upper opening, 26 Pure water, 27 Lid

Claims

[Claim 1] It comprises a negative electrode, a positive electrode, an ion conductor, an anaerobic condition generation and maintenance layer, and a cylindrical holder. The anaerobic condition generation and maintenance layer, the negative electrode, the ion conductor, and the positive electrode are arranged in order from one end to the other inside the cylindrical holder. The negative electrode and the positive electrode are connected via the ion conductor by contacting the surface on one end and the surface on the other end of the cylindrical holder of the ion conductor, respectively. The anaerobic condition generation and maintenance layer covers the entire surface of the negative electrode on the side to which organic matter is supplied from one end of the cylindrical holder. The anaerobic condition generation and maintenance layer is permeable to the organic matter, and the microbial fuel cell is characterized in that, when the following experiment is performed, the DO2 / DO1 ratio is 80% or less. experiment: The connecting pipe (inner diameter: 3.3 cm) between the first cell and the second cell is separated by the anaerobic condition generation and maintenance layer. The first cell includes a first upper opening, and the second cell includes a second upper opening. The first upper opening is kept open at all times, and the first cell is constantly exposed to the atmosphere. The second cell is filled with pure water with all openings except the second upper opening closed, and the second upper opening is opened so that the pure water is exposed to the atmosphere, and the amount of dissolved oxygen (DO1) in the pure water with a saturated amount of oxygen is measured. The pure water is degassed by bubbling it with nitrogen gas to remove dissolved oxygen, the second upper opening is closed, and after 25 hours, the amount of dissolved oxygen (DO2) in the pure water is measured. [Claim 2] In the microbial fuel cell according to claim 1, A microbial fuel cell characterized in that the anaerobic condition generation and maintenance layer includes aerobic microorganisms, an oxygen scavenger, an oxygen permeation inhibiting filter, a water-absorbing polymer, or soil. [Claim 3] It comprises a negative electrode, a positive electrode, an ion conductor, and an anaerobic conditions generation and maintenance layer. The negative electrode and the positive electrode are connected via the ion conductor by contacting one surface of the ion conductor with the other surface of the ion conductor, respectively. The aforementioned anaerobic condition generation and maintenance layer covers the entire surface of the negative electrode on the side where organic matter is supplied from the outside. The aforementioned anaerobic condition generation and maintenance layer comprises aerobic microorganisms, soil, and one or more selected from oxygen absorbers, oxygen permeation inhibiting filters, and water-absorbing polymers. The anaerobic condition generation and maintenance layer is permeable to the organic matter, and the microbial fuel cell is characterized in that, when the following experiment is performed, the DO2 / DO1 ratio is 80% or less. experiment: The connecting pipe (inner diameter: 3.3 cm) between the first cell and the second cell is separated by the anaerobic condition generation and maintenance layer. The first cell includes a first upper opening, and the second cell includes a second upper opening. The first upper opening is kept open at all times, and the first cell is constantly exposed to the atmosphere. The second cell is filled with pure water with all openings except the second upper opening closed, and the second upper opening is opened so that the pure water is exposed to the atmosphere, and the amount of dissolved oxygen (DO1) in the pure water with a saturated amount of oxygen is measured. The pure water is degassed by bubbling it with nitrogen gas to remove dissolved oxygen, the second upper opening is closed, and after 25 hours, the amount of dissolved oxygen (DO2) in the pure water is measured.

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