Solid microbial fuel cell and method for producing the same

Abstract

To provide a simple and safe microbial fuel cell in which liquid leakage is substantially suppressed.SOLUTION: The method for producing a solid microbial fuel cell includes the steps of: preparing a gel-forming material selected from a group consisting of a gelling agent and a water-absorbing polymer; obtaining a gel-like medium containing microorganisms by mixing the gel-forming material, power-generating microorganisms, and a medium including a culture solution inside a fuel cell container; and arranging an anode and a cathode inside the fuel cell container.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid microbial fuel cell comprising a fungus-containing gelled medium and a method for producing the same. [Background technology]

[0002] A microbial fuel cell (MFC) generates electricity by extracting the reducing power (electrons) generated when microorganisms oxidize and decompose (metabolize) organic matter as an electric current. The MFC consists of an anode (negative electrode) and a cathode (positive electrode). At the anode, electrons generated when organic matter is decomposed by microorganisms are collected. The collected electrons are passed through an external circuit to the cathode, where they are converted into O2, electrons, and H + (generated during the decomposition of organic matter at the anode) reacts to become H2O. In an MFC, the potential difference between this anode reaction and cathode reaction generates an electric current, allowing electrical energy to be obtained.

[0003] Attempts being made to develop such microbial fuel cells include a power generation system that generates electricity while performing a purification process in combination with a purification process that uses microorganisms to decompose organic matter in wastewater (see Patent Document 1), a power generation system that enables energy recovery from waste biomass (see Patent Document 2), and a power generation system that uses organisms living in rice paddies, etc. Patent Document 3 also discloses a microbial power generation application device that can raise awareness of ecology.

[0004] The microbial fuel cells described in Patent Documents 1 and 2 are based on the premise of wastewater purification treatment and the utilization of waste biomass, and the source of power-generating microorganisms is a liquid containing organic matter such as waste. Furthermore, the components of the organic matter have not been identified or standardized. In the microbial fuel cell described in Patent Document 3 and the power generation system that uses organisms living in rice paddies, the source of power-generating microorganisms is soil or mud, and mud and soil are required. The need for mud and soil limits its use. Because microbial power generation is a power generation method that is considerate of the global environment, there are hopes for the development of simple microbial fuel cells so that they can be used more widely. To be a simple microbial fuel cell, it is required to be easy to handle, and there are problems with insufficient safety, such as leakage when using liquid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-81963 [Patent Document 2] Japanese Patent Application Publication No. 2023-41694 [Patent Document 3] Japanese Patent Application Publication No. 2018-181581 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a simple microbial fuel cell in which liquid leakage is substantially suppressed and safety is taken into consideration. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have discovered that a microbial fuel cell comprising a gelled medium containing electricity-generating bacteria can solve the above problems, and have arrived at the present invention.

[0008] That is, the present invention includes the following. [1] Providing a gel-forming material selected from the group consisting of a gelling agent and a water-absorbing polymer; a step of mixing the gel-forming material, the electricity-generating fungi, and a medium containing a culture solution in a fuel cell container to obtain a fungi-containing gel-like medium; and placing an anode and a cathode within the fuel cell container. [2] A method for producing a solid microbial fuel cell described in [1], wherein the gel-forming material is at least one selected from the group consisting of alginate, polyvinyl chloride alcohol, polyethylene glycol, sodium acrylate, polyvinylpyrrolidone, carboxymethyl cellulose, hydroxyethyl cellulose, and polyacrylate. [3] A method for producing a solid microbial fuel cell according to [1], which comprises a step of further incorporating a porous material into the fungus-containing gelatinous medium. [4] The method for producing a solid microbial fuel cell according to [3], wherein the porous material is pumice. [5] further disposing a gelled electrolyte solution in the fuel cell container; placing the anode in contact with the fungus-containing gelatinous medium; The method for producing a solid microbial fuel cell described in [1] includes a step of placing the cathode so that it is in contact with the gel electrolyte. [6] A method for producing a solid microbial fuel cell according to [5], comprising a step of placing an electrode support for placing the anode in the fungus-containing gelatinous medium. [7] a fuel cell container; a fungus-containing gel culture medium containing power-generating fungi in the fuel cell container; an anode disposed within the fungus-containing gelatinous medium; and a cathode disposed on the surface of the fungus-containing gelatinous medium. [8] The solid microbial fuel cell according to [7], further comprising a gelled electrolyte solution placed on the fungus-containing gelled medium. [9] The solid microbial fuel cell described in [8], wherein the fungus-containing gelatinous medium further contains a porous material. [Effects of the Invention]

[0009] Because solid microbial fuel cells are simple and safe, microbial power generation, an environmentally friendly power generation method, can be more widely utilized. Furthermore, because it is a solid fuel cell, there is no need to worry about liquid leakage, and because it is not a liquid, there is less distortion and deformation (less deformation) and it is highly stable. Furthermore, compared to liquid microbial fuel cells, a higher substrate concentration can be maintained, and the microorganisms can be immobilized, i.e., attached to a solid surface and formed into a biofilm, leading to stabilization. Furthermore, since the operation is relatively easy, the complexity of the equipment and facilities is reduced, and productivity is improved. Solid microbial fuel cells are expected to be more durable than liquid microbial fuel cells, improving the long-term stability and sustainability of microbial fuel cells. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a solid microbial fuel cell. [Figure 2] FIG. 2 is a schematic diagram of a solid microbial fuel cell 1A. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes the form for carrying out the invention, but the present invention is not limited to the form for carrying out the invention, and various modifications can be made by a person skilled in the art within the scope that does not detract from the spirit of the invention.

[0012] [Method of manufacturing a solid microbial fuel cell] A method for producing the solid microbial fuel cell 1 will now be described. The method for manufacturing a solid microbial fuel cell 1 includes the steps of preparing a gel-forming material selected from the group consisting of gelling agents and absorbent polymers, mixing the gel-forming material, electricity-generating fungi, and a culture medium containing a culture solution in a fuel cell container 6 to obtain a fungus-containing gel-like culture medium 8, and placing an anode 3A and a cathode 3C in the fuel cell container 6.

[0013] (Gel-forming material) In this specification, the term "gel-forming material" is used to refer to a gelling agent or a water-absorbing polymer, or both. A gelling agent is an additive made of a polymeric substance or colloidal particles that, when added to a liquid, creates a network structure through interaction, causing the liquid to lose its fluidity while retaining a large amount of the liquid solvent or dispersion medium. The gelling agent is not particularly limited as long as it can gel a liquid, but examples include alginate, polyvinyl chloride alcohol, polyethylene glycol, sodium acrylate, polyvinylpyrrolidone, carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylate, carrageenan, agar, gellan gum, collagen, and gelatin. Furthermore, a water-absorbing polymer is a polymer designed to have high water-retaining properties, capable of absorbing 10 to 1000 times its own weight in water. Examples of water-absorbing polymers include sodium polyacrylate. The content of the gel-forming material is not particularly limited, but is preferably 1.0 to 30.0% by weight, more preferably 3.0 to 6.0% by weight, based on the total culture solution. If the content is less than 1.0% by weight, the culture solution will be liquid, and if it exceeds 10.0% by weight, the culture solution will not retain enough moisture for the bacteria. The gel-forming material is mixed with a culture medium containing electricity-generating fungi and a culture solution, and the fungi-containing culture medium is gelled, i.e., solidified, making it less susceptible to leakage and making it safer and easier to handle than microbial fuel cells that use liquid culture media.

[0014] (fuel cell container) The material of the fuel cell container 6 is not particularly limited as long as it is generally non-conductive and can maintain its shape, but examples thereof include plastic and silicone. The shape of the fuel cell container 6 is not particularly limited, but examples include polygonal pillars such as square pillars, and cylindrical pillars, with the square pillars being preferred in order to maximize space efficiency. The fuel cell container 6 has an opening at the top (not shown), and the opening has a lid that can seal the inside of the fuel cell container 6. The fungus-containing gelled medium 8 and the gelled electrolyte 7 can be removed and replaced through the opening.

[0015] (electricity generating fungi) In the present invention, the electric-generating fungi that can be used are not particularly limited as long as they function as electron donors, and examples thereof include bacteria, filamentous fungi, and yeasts belonging to the genera Saccharomyces, Hansenula, Candida, Micrococcus, Staphylococcus, Streptococcus, Leuconostoa, Lactobacillus, Corynebacterium, Arthrobacter, Bacillus, Clostridium, Neisseria, Escherichia, Enterobacter, Serratia, Achromobacter, Alcaligenes, Flavobacterium, Acetobacter, Moraxella, Nitrosomonas, Nitorobacter, Thiobacillus, Gluconobacter, Pseudomonas, Xanthomonas, Vibrio, Comamonas, Proteus (Proteus vulgaris), Shewanella, and Geobacter. It is more preferable that the bacteria contain at least one of the genus Shewanella and the genus Geobacter.

[0016] The power-generating fungi of the solid microbial fuel cell 1 are isolated by colonizing specific mud containing the power-generating fungi using a serial dilution method, and then cultured in a dedicated medium. This allows for the production of a large number of power-generating fungi. To increase power generation efficiency, the proportion of power-generating fungi relative to the total microorganisms contained is preferably 5% by mass or more, more preferably 50% by mass or more, and even more preferably 80% by mass or more. There are no particular limitations on the method for measuring the proportion (content) of power-generating fungi, but the proportion of power-generating fungi can be measured, for example, by a microbial flora analysis method.

[0017] (Culture medium) The culture medium is an artificial medium that allows the electric-generating bacteria to grow and develop, and in the present invention, it is preferable that the culture medium does not contain mud or the like in which the electric-generating bacteria are naturally present. The type of medium is not particularly limited, but examples include diluted bouillon and synthetic medium. The content of medium components in the medium is preferably about 0.1% to 10% by weight. The medium is prepared by dissolving medium components such as bouillon in water. It is desirable that the medium components and water are sterilized before use. Examples of prepared medium are as follows: 1% bouillon (Maggi Bouillon (Nestlé Japan)), 1% glucose, 1.2% NaCl medium 1% broth, 1% glucose, 1.2% NaCl, 1.5% agar

[0018] A gel-like medium can be formed by mixing a predetermined amount of gel-forming material with the medium described above. When the gel-like medium contains electric-generating bacteria, in the present invention, the electric-generating bacteria, medium, and gel-forming material may be mixed together to form the fungus-containing gel-like medium 8 before forming the fungus-containing gel-like medium 8, or the electric-generating bacteria may be added to the gel-like medium after the gel-like medium is formed to form the fungus-containing gel-like medium 8.

[0019] (inorganic salts) The medium may contain inorganic salts as needed. The inorganic salts are preferably trace amounts of metal compounds having ionic bonds, such as metal salts, to improve the electrical conductivity of the medium. Examples of metal salts include chlorides, phosphates, sulfates, acetates, nitrates, oxides and ions thereof, and conductive polymers. The pH of the medium is not particularly limited, but is preferably 5.5 to 7.5. When the pH is in this range, the electric-generating bacteria can efficiently decompose the following organic matter and generate electrons.

[0020] (organic matter) The medium may contain organic matter as needed. The organic matter serves as a substrate for the metabolism of the electric-generating bacteria, and is preferably used in an amount that allows the growth and survival of the electric-generating bacteria to be maintained. The organic matter is not particularly limited as long as it can be used as a substrate for the metabolism of the electric-generating bacteria, and examples thereof include sugars, amino acids, and complex organic extracts. Examples of sugars include galactose and glucose, with glucose being preferred. Any amino acid can be used depending on the application. Preferred complex organic extracts include peptone, tryptone, and yeast extract.

[0021] (catalyst) The culture medium may contain a catalyst for promoting the transfer of electrons generated by the electricity-generating bacteria. Specifically, promoting the transfer of electrons has the effect of improving the efficiency of power generation. The term "catalyst" as used herein includes enzymes as well as inorganic and organic compounds.

[0022] (surfactant) The culture medium may contain a surfactant. The surfactant enhances the transfer of electrons from the electricity-generating bacteria to the electrodes (anode and cathode) through interaction between the surfactant and the electrodes. This effect is effective for electrode materials with low hydrophilicity. For example, when graphite is used as the electrode material, the hydrophilicity of the graphite is improved, which enhances the adhesion of the electricity-generating bacteria in the culture medium to the graphite surface. Desirable surfactants are nonionic surfactants such as alkyl polyglucosides (APG) and coco glucoside, and amino acid surfactants such as cocamidopropyl betaine and stearoyl glutamic acid. These surfactants are unlikely to have a significant effect on the inactivation of electricity-generating bacteria.

[0023] (transition metal ions) The medium may contain transition metal ions. The transition metal ions include iron ions (Fe 2+ and Fe 3+ ), vanadium ions (V 2+ and V 3+), manganese ions (Mn 2+ and Mn 4+ ), and more preferably, iron ions (Fe 2+ and Fe 3+ ) Such transition metal ions are preferred because they promote extracellular electron transport in the electric-generating bacteria. When adding transition metal ions, transition metal salts can be added, such as chloride compounds, nitrate compounds, and sulfate compounds of the above transition metal ions, and it is preferable to satisfy the above pH.

[0024] (anode and cathode) The anode 3A of the semi-solid biofuel cell 1 receives electrons from electricity-generating bacteria that decompose organic matter in an anaerobic or aerobic environment. The anode 3A is placed in a fungus-containing gelatinous medium 8. The electrons collected at the anode 3A and transported via the leads (cathode connecting lead 5 and anode connecting lead 4) react with O2 at the cathode 3C to form HO, so that part or all of the cathode 3C comes into contact with the gelatinous electrolyte 7. A cathode in which part of the cathode 3C comes into contact with air and utilizes oxygen in the air is called an air cathode. An advantage of the air cathode is that it is only necessary to circulate air through the air cathode; there is no need to aerate the fungus-containing gelatinous medium 8 or the gelatinous electrolyte 7.

[0025] The anode 3A and the cathode 3C are made of a substrate coated with a conductive material. Examples of conductive materials include carbon electrodes such as graphite, carbon cloth, and carbon paper, and metal electrodes. For example, the anode 3A can be made of flat graphite, and the cathode 3C can be made of a flat metal plate made of aluminum.

[0026] The shape of the anode 3A and cathode 3C of the solid microbial fuel cell can be a flat plate as in the embodiment, or alternatively, a solid or hollow cylindrical, columnar, polygonal columnar, or the like.

[0027] The manufacturing method for the solid microbial fuel cell 1 may further include a step of incorporating a porous material into the fungus-containing gelled medium 8. Adding a porous material to the fungus-containing gelled medium 8 is advantageous in terms of reducing the weight of the device and stably culturing the fuel cell. Porous materials are not particularly limited as long as they are porous, but examples include activated carbon, diatomaceous earth, silica gel, zeolite, sponge, porous ceramic, porous plastic, pumice, etc. Furthermore, aerogels composed of silica, organic polymers, carbon, alumina, titania, etc. are also considered to be porous materials. They have a low apparent specific gravity and are expected to reduce the weight of the device. Pumice (e.g., pumice that floats on water) and activated carbon are particularly preferred. Furthermore, by including a porous material, the culture medium can enter the pores, making it possible to produce a microbial fuel cell that is resistant to drying.

[0028] The step of arranging the anode 3A and the cathode 3C includes a step of arranging the anode 3A so that it contacts the fungus-containing gelled medium 8, and a step of arranging the cathode 3C so that it contacts the gelled electrolyte solution 7.

[0029] (gel electrolyte) The electrolyte contained in the gelled electrolyte solution 7 is not particularly limited as long as it is a substance that is electrolyzed into anions and cations when dissolved in a solvent, and examples thereof include bases, acids, and salts. Examples of substances contained in the electrolyte solution include chloride ions, phosphate ions, sulfate ions, acetate ions, nitrate ions, conductive polymers, etc. The gel electrolyte 7 is an electrolyte made of a gel containing water. The gel-forming material contained in the gel electrolyte 7 can be the same gel-forming material used in the process of obtaining the fungus-containing gel culture medium 8, and the same gel-forming material or a different gel-forming material can be used.

[0030] A partition membrane 9 made of an ion exchange membrane such as a cation exchange membrane or a plastic with multiple through-holes may be provided at the boundary between the gelled electrolyte solution 7 and the fungus-containing gelled medium 8. There are no particular limitations on the material of this partition membrane 9 as long as it allows ions to pass through. By providing such a partition membrane 9, it is possible to prevent the gelled electrolyte solution 7 and the fungus-containing gelled medium 8 from mixing with each other.

[0031] The method for producing the solid microbial fuel cell 1 may include the step of providing an electrode support 10 for placing the anode 3A in the fungus-containing gelatinous medium 8. The electrode support 10 is not particularly limited as long as it can place the anode 3A in the fungus-containing gelatinous medium 8, but examples include non-conductive nonwoven fabric, sponge, porous plate, etc., and sponge is preferred because it is thought to increase the contact area between the fungus and the electrode.

[0032] Another embodiment, a solid microbial fuel cell 1A, is shown in Figure 2. The solid microbial fuel cell 1A is made of the same materials as the solid microbial fuel cell 1, but the fungus-containing gelled medium 8 and the gelled electrolyte 7 are arranged side by side in the horizontal direction in Figure 2, and a partition membrane 9 is provided between the fungus-containing gelled medium 8 and the gelled electrolyte 7. The anode 3A and cathode 3C are inserted into the fungus-containing gelled medium 8 and the gelled electrolyte 7, respectively. The plate-shaped anode 3A and cathode 3C are inserted so that they are approximately parallel to the partition membrane 9. This configuration makes it easy to manage the fungus-containing gelled medium and the gelled electrolyte from the top of the housing. In other words, it is possible to add additional electricity-generating bacteria, gel-forming materials, medium, water, etc.

[0033] The power density of solid microbial fuel cell 1 is 20 W / m 3 More than 40W / m 3 That's all. [Example]

[0034] A solid microbial fuel cell was fabricated with the configuration shown in Figure 2. The constituent materials are as follows: Cathode: Zinc and conductive carbon fiber Anode: graphite Electricity-generating bacteria: Shewanella genus bacteria Media formulation: 1% broth, 1% glucose, 1.2% NaCl Gel material: sodium acrylate (gelling agent) Type of pumice: Horticultural burnt pumice (used in granular form, containing SiO2 and Al2O3 as its main components) Partition film: plastic plate

[0035] When the fuel cell having the above configuration was operated to generate electricity, it was confirmed that stable power generation was possible for several days.

[0036] [Explanation of symbols] 1 Solid microbial fuel cell 2 Power Generation Department 3A anode 3C cathode 4 Anode connection wire 5 Cathode connecting wire 6 Fuel cell container 7. Gel electrolyte 8. Fungal-containing gel medium 9 Partition membrane 10 Electrode support

Claims

1. providing a gel-forming material selected from the group consisting of gelling agents and water-absorbing polymers; a step of mixing the gel-forming material, the electricity-generating fungi, and a medium containing a culture solution in a fuel cell container to obtain a fungi-containing gel-like medium; and placing an anode and a cathode within the fuel cell container.

2. 2. The method for producing a solid microbial fuel cell according to claim 1, wherein the gel-forming material is at least one selected from the group consisting of alginate, polyvinyl chloride alcohol, polyethylene glycol, sodium acrylate, polyvinylpyrrolidone, carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylate, carrageenan, agar, gellan gum, collagen, gelatin, etc.

3. The method for producing a solid microbial fuel cell according to claim 1, further comprising a step of adding a porous material to the fungus-containing gelatinous medium.

4. The method for producing a solid microbial fuel cell according to claim 3, wherein the porous material is pumice.

5. further disposing a gelled electrolyte solution within the fuel cell container; placing the anode in contact with the fungus-containing gelatinous medium; The method for producing a solid microbial fuel cell according to claim 1, further comprising the step of: placing the cathode in contact with the gel electrolyte.

6. 6. The method for producing a solid microbial fuel cell according to claim 5, further comprising the step of providing an electrode support for placing the anode in contact with the fungus-containing gelatinous medium.

7. a fuel cell container; a fungus-containing gel culture medium containing power-generating fungi in the fuel cell container; an anode disposed within the fungus-containing gelatinous medium; and a cathode disposed on the surface of the fungus-containing gelatinous medium.

8. 8. The solid microbial fuel cell of claim 7, further comprising a gelled electrolyte solution disposed on top of the fungus-containing gelled medium.

9. The solid microbial fuel cell of claim 8 , wherein the fungus-containing gelatinous medium further comprises a porous material.

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