Microbial fuel cell

Abstract

The purpose of the present invention is to provide a microbial fuel cell which is simple and which uses a power generation method that does not use mud and that considers the global environment.　This microbial fuel cell includes power generating microorganisms, a culture medium, and at least a pair of electrodes. A proportion of the power generating microorganism to contained microorganisms is 5% or more.

Description

microbial fuel cell

[0001] The present invention relates to a microbial fuel cell comprising an electric-power generating microorganism, a culture medium, and at least one pair of electrodes, wherein the proportion of the electric-power generating microorganism relative to the total amount of microorganisms contained therein is 5% or more.

[0002] A microbial fuel cell (MFC) is a microbial power generation device that generates electricity by extracting the reducing power (electrons) generated when microorganisms oxidize and decompose (metabolize) organic matter as an electric current. A microbial fuel cell is explained using Figure 1. An MFC consists of an anode (negative electrode) and a cathode (positive electrode). At the anode, electrons generated as organic matter is decomposed by microorganisms are collected by the electrode. The collected electrons are passed through an external circuit to the cathode, where they are converted into O ２ and electrons, H ＋ (generated during decomposition of organic matter at the anode) reacts with H ２ In the MFC, the potential difference between the anode and cathode reactions generates a current, allowing electrical energy to be obtained.

[0003] Attempts at such microbial power generation devices 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 power generation devices described in Patent Documents 1 and 2 are based on the premise of wastewater purification treatment and utilization of waste biomass, and the source of the 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 power generation device described in Patent Document 3 and the power generation system that uses organisms living in rice paddies, the source of the 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, the development of a simple microbial fuel cell is expected to enable it to be used more widely.

[0005] JP 2006-81963 A JP 2023-41694 A JP 2018-181581 A

[0006] An object of the present invention is to provide a simple and convenient microbial fuel cell.

[0007] In light of the above problems, we conducted extensive research and discovered a microbial fuel cell comprising a power-generating microorganism, a culture medium, and at least one pair of electrodes, in which the proportion of the power-generating microorganisms to the total microorganisms contained is 5% or more, and arrived at the present invention.

[0008] That is, the present invention encompasses the following. [1] A microbial fuel cell comprising an electric-power generating microorganism, a culture medium, and at least a pair of electrodes, wherein the ratio of the electric-power generating microorganisms to all the microorganisms contained is 5% or more. [2] The microbial fuel cell according to [1], wherein the culture medium contains a surfactant. [3] The microbial fuel cell according to [1], wherein the culture medium contains a transition metal ion. [4] The microbial fuel cell according to [1], wherein the culture medium contains a catalyst for promoting the transfer of electrons generated by the electric-power generating microorganism. [5] The pair of electrodes has a diameter of at least 5 cm. ２ [6] The microbial fuel cell according to any one of [1] to [5], wherein the power-generating microorganisms include at least one of bacteria of the genus Shewanella and bacteria of the genus Geobacter.

[0009] The microbial fuel cell of the present invention is simple and easy to use, allowing for more widespread use of microbial power generation, which is an environmentally friendly power generation method.

[0010] FIG. 1 is a conceptual diagram of a microbial fuel cell. FIG. 2 is a schematic diagram of a microbial fuel cell of embodiment 1. (a) shows the state in which the power-generating microorganisms and culture medium are contained, and (b) shows the state in which the power-generating microorganisms and culture medium have been removed and the fuel cell has been folded up and made smaller. FIG. 3 is a schematic diagram of a microbial fuel cell of embodiment 2. FIG. 4 is a relative comparison of the output values ​​of Example 1, Example 2, and Comparative Example 1 (the value of Example 3 is set to 100). FIG. 5 shows actual data for Example 2 and Comparative Example 1. In the figure, the solid line represents the data of Example 2, and the dotted line represents the data of Comparative Example 1.

[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] The present invention is a microbial fuel cell comprising an electric-power generating microorganism, a culture medium, and at least one pair of electrodes, wherein the ratio of the electric-power generating microorganism to all the microorganisms contained therein is 5% or more.

[0013] [Microbial Fuel Cell] A microbial fuel cell 1 according to a first embodiment of the present invention will be described with reference to FIG. 2(a). One embodiment of the microbial fuel cell 1 of the present invention has a housing 2, which contains therein power-generating microorganisms 3, a culture medium 4, a pair of electrodes 5 (negative electrode 51, positive electrode 52), and a partition (ion exchange membrane) 10. While the power-generating microorganisms 3 are not shown in FIG. 2, the housing 2 is provided with a USB port 6 on the outside and a conductor 7 inside connecting the electrode 5 to the USB port 6. The top of the housing 2 is provided with an opening 8 and a lid 9. Note that FIG. 2(a) shows a state in which an electronic device D equipped with a storage battery, such as a smartphone, is being charged. FIG. 3 shows a microbial fuel cell 11 according to a second embodiment of the present invention, in which a pair of electrodes 5 (51 and 52) are arranged alternately. Note that the ion exchange membrane 10 and conductor 7 described in the first embodiment are omitted from FIG. 3.

[0014] The microbial fuel cells 1, 11 can be used for long periods of time by replacing the culture medium 4 and adding power-generating microorganisms 3 as needed. While mud has traditionally been used in microbial fuel cells, the microbial fuel cells 1, 11 use the culture medium 4 instead of mud. The culture medium 4 in the microbial fuel cells 1, 11 can be prepared by adjusting a medium source with a predetermined composition and adding water to the medium source. The culture medium can be prepared by preparing a powder of the dry solids of the medium source with a predetermined composition in advance, adding the powder to the housing 2, and then adding water. Preparing a powder of the dry solids of the medium source with a predetermined composition in advance makes it easy to handle, and since it is a powder, it has excellent storage stability. Because of its excellent storage stability, the microbial fuel cells 1, 11 can also be used as disaster prevention supplies. In some cases, a gelling agent can be added to the culture medium to prepare a solid culture medium.

[0015] The power density of the microbial fuel cell 1 of the present invention is 20 W / m ３ Preferably, it is 40 W / m ３ That's all.

[0016] (Electricity-generating microorganism 3) The electric power-generating microorganism 3 is not particularly limited as long as it has a function as an electron donor. For example, Saccharomyces, Hansenula, Candida, Micrococcus, Staphylococcus, Streptococcus, Leuconostoa, Lactobacillus, Corynebacterium, Arthrobacter, Bacillus, Clostridium, Neisseria, Escherichia, Enterobacter, Serratia, Achromobacter, Alc Examples of suitable bacteria include bacteria, filamentous fungi, and yeasts belonging to the genera Aligenes, Flavobacterium, Acetobacter, Moraxella, Nitrosomonas, Nitorobacter, Thiobacillus, Gluconobacter, Pseudomonas, Xanthomonas, Vibrio, Comamonas, Proteus (Proteus vulgaris), Shewanell, and Geobacter. It is more preferable to include at least one type of bacteria belonging to the genus Shewanella and Geobacter.

[0017] To increase power generation efficiency, the ratio of the power-generating microorganisms 3 to the total microorganisms contained is preferably 5% or more, more preferably 50% or more, and even more preferably 80% or more. If the ratio of the power-generating microorganisms 3 to the total microorganisms contained is less than 5%, the power generation capacity may decrease. Note that the power-generating microorganisms 3 can grow if conditions such as the state of the culture medium 4 in the microbial fuel cells 1, 11 and the presence or absence of organic matter are favorable.

[0018] The method for measuring the proportion (content) of power-generating microorganisms 3 is not particularly limited, and the proportion of power-generating microorganisms 3 can be measured, for example, by a microbiome analysis method. Specifically, a sample is taken from the used culture medium containing the power-generating microorganisms 3, and the V4-V5 region (420 bp) of the 16S rRNA gene (16S rDNA) of the power-generating microorganisms 3 is amplified by PCR, and the base sequence is determined by sequence analysis. The obtained 16S rDNA base sequence can be classified by clustering analysis to identify the type of bacteria contained and determine the content. To improve the accuracy of the content, it is preferable to mix several sampled samples and perform the analysis, or to average the data obtained by analyzing several samples separately.

[0019] By using cultured power-generating microorganisms, the ratio of power-generating microorganisms 3 to the total microorganisms contained can be increased.

[0020] (Method for isolating and culturing the power-generating microorganisms 3) The power-generating microorganisms 3 used are isolated by colonizing them using a serial dilution method from a specific mud containing the power-generating microorganisms 3. The isolated power-generating microorganisms 3 are then cultured in a dedicated medium. By doing so, a large number of power-generating microorganisms 3 can be obtained, and the proportion of power-generating microorganisms 3 relative to the total microorganisms contained in the microbial fuel cells 1, 11 at the initial start-up can be made 5% or more.

[0021] In conventional microbial power generation devices, power-generating microorganisms are supplied using sludge, waste, or soil generated during sewage treatment as inoculum. Meanwhile, in microbial fuel cells 1 and 11, the power-generating microorganisms 3 can be supplied in an easy-to-handle form, such as a power-generating microorganism-containing powder. The amount or ratio of the power-generating microorganisms in the power-generating microorganism-containing powder is set so as to obtain practical power, and the components of the power-generating microorganism-containing powder are adjusted and standardized. The ratio and type of power-generating microorganisms 3 may be selected to achieve high power generation efficiency and high power density, and microorganisms that interfere with power generation may be reduced or removed. In addition to the power-generating microorganisms 3, the power-generating microorganism-containing powder may also contain organic matter, inorganic salts, sugars, etc.

[0022] (Culture medium 4) The culture medium 4 is an artificial medium that can grow and develop the power-generating microorganisms 3, and in the present invention, it is preferable that the culture medium 4 does not contain mud or the like in which the power-generating microorganisms 3 naturally exist. There are no particular limitations on the type of culture medium 4, but examples include diluted bouillon and synthetic media.

[0023] The culture medium 4 can be liquid with a solvent such as water, or can be made into a gel by adding a gelling agent. There are no particular limitations on the gelling agent as long as it can thicken or solidify the culture medium 4, and it is preferable to use gelatin, agar, etc. The content of these components is preferably 0.5 to 2.5% by weight of the total culture medium. The content of the culture components in the culture medium 4 is preferably approximately 0.1 to 10% by weight. It 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 culture media are as follows: ・1% bouillon (Maggi Bouillon (Nestle Japan)) ・1% bouillon, 1% agar medium ・1% bouillon, 1M NaCl medium ・1% bouillon, 1M NaCl, 1% agar medium

[0024] (Inorganic Salt) The culture medium 4 may contain an inorganic salt. The inorganic salt is preferably a trace amount of a metal compound having an ionic bond, such as a metal salt, in order to improve the electrical conductivity of the culture medium 4. Examples of the metal salt include NaCl, KCl, and CaCl. ２ Examples of suitable chloride salts include chloride salts such as the above. The pH of the culture medium 4 is not particularly limited, but is preferably 5.5 to 7.5. When the pH is in this range, the power-generating microorganisms 3 can efficiently decompose the following organic matter and generate electrons.

[0025] (Organic matter) The culture medium 4 may contain organic matter as needed. The organic matter serves as a substrate for the metabolism of the power-generating microorganisms 3, and is preferably used in an amount sufficient to maintain the growth and survival of the power-generating microorganisms 3. The organic matter is not particularly limited as long as it can be used as a substrate for the metabolism of the power-generating microorganisms 3, and examples thereof include sugars, amino acids, and complex organic extracts. Examples of sugars include galactose and glucose, with glucose being preferred. Examples of amino acids include glutamic acid, alanine, glycine, and cystine. Examples of complex organic extracts include peptone, tryptone, and yeast extract.

[0026] (Catalyst) The culture medium 4 may contain a catalyst for promoting the transfer of electrons generated by the power-generating microorganisms 3. Specifically, promoting the transfer of electrons has the effect of improving power generation efficiency. The catalyst referred to here includes enzymes in addition to inorganic compounds and organic compounds.

[0027] (Surfactant) The culture medium 4 may contain a surfactant. The inclusion of a surfactant can enhance the transfer of electrons from the power-generating microorganisms 3 to the electrode 5 due to the interaction between the surfactant and the electrode. 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 can be improved, thereby increasing the adhesion of the power-generating microorganisms 3 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 significantly affect the inactivation of the power-generating microorganisms 3.

[0028] (Transition metal ions) The culture medium 4 can contain transition metal ions. The transition metal ions can be iron ions (Fe ２＋ and Fe ３＋ ), vanadium ions (V ２＋ and V ３＋ ), manganese ions (Mn ２＋ and Mn ４＋) and other transition metal ions with low environmental impact are preferred, and iron ions (Fe ２＋ and Fe ３＋ ) Such transition metal ions are preferred because they promote extracellular electron transfer in the power-generating microorganism 3. 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.

[0029] (Regarding replacement) The culture medium 4 can be removed from the housing 2 and replaced. If the metabolism of the power-generating microorganisms 3 decreases and the voltage drops due to a decrease in organic matter in the culture medium or changes in other conditions, the culture medium 4 containing the power-generating microorganisms 3 can be removed from the housing 2 and replaced with power-generating microorganisms 3 with high metabolism and fresh culture medium. When replacing the culture medium 4, a new culture medium 4 containing the power-generating microorganisms 3 can be used. Furthermore, the power-generating microorganisms to be added at this time can be a portion of the culture medium 4 containing the power-generating microorganisms 3 that was previously used, added to the new culture medium 4, thereby supplying the power-generating microorganisms 3 to the new culture medium-containing water 4. In this way, long-term use is possible by successively cultivating the power-generating microorganisms 3. In the microbial fuel cells 1, 11, the culture medium supplies organic matter that serves as a metabolic substrate for the power-generating microorganisms, making microbial power generation easy and enabling the microbial power generators 1, 11 to be used in a wide variety of applications.

[0030] The culture medium 4 can be replaced by removing the lid 9 on the top of the housing 2 and taking it out through the opening 8. For new culture medium 4, dried or concentrated medium components can be dissolved or diluted with a liquid such as water, or a gelling agent can be added to form a gel.

[0031] (Electrode 5) One or both of the pair of electrodes 5 is made of a substrate coated with a conductive material. Examples of the conductive material include carbon electrodes such as graphite, carbon cloth, and carbon paper, and electrodes formed using metals, etc.

[0032] The pair of electrodes 5 is such that one of the negative electrode 51 or the positive electrode 52 of the electrode 5 is at least 5 cm ２The surface area is 5 cm or more. ２ If the distance is less than 1 / 2, the power generation efficiency may decrease. The shape of the pair of electrodes 5 of the microbial fuel cell 1 of the present invention may be flat as in the first and second embodiments, or may be a solid or hollow cylindrical, cylindrical, polygonal prism, or the like.

[0033] The negative electrode 51 of the microbial fuel cells 1, 11 receives electrons from the power-generating microorganisms 3 that decompose organic matter in an anaerobic or aerobic environment. The negative electrode 51 is disposed, for example, near the bottom of the housing 2 and is connected to the USB port 6 via a lead wire 7. The positive electrode 52 of the microbial fuel cells 1, 11 is connected to the USB port 6 via a lead wire 7, and the electrons collected at the negative electrode 51 and transferred via the lead wire 7 and the USB port 6 are converted to O at the positive electrode 52. ２ And reacted with H ２ O, a part or all of the positive electrode 52 comes into contact with the culture medium-containing water 4.

[0034] (Housing 2) The housing 2 of the microbial fuel cell 1 is made of a flexible material that can be folded and expanded. The material constituting the housing 2 is not particularly limited as long as it is a flexible material, and examples thereof include plastic and silicone. The shape of the housing 2 is not particularly limited, and examples thereof include polygonal pillars such as square pillars, cylindrical pillars, etc., and a square pillar shape is preferred to maximize space efficiency.

[0035] The housing 2 has an opening 8 at the top, and the opening 8 has a lid 9 that can seal the inside of the housing. The culture medium 4 can be removed and replaced through the opening 8.

[0036] The housing 2 has a partition 10 therein that separates the culture medium 4. The material that constitutes the partition 10 is not particularly limited as long as it is an ion exchange membrane.

[0037] (Isolation of Electric-Generating Microorganism 3) Soil was collected from the vicinity of the Tama River in Tachikawa City, Tokyo, and a portion of the soil was cultured overnight at room temperature in a 1% bouillon solution. The soil in the culture solution was allowed to settle, and a portion of the culture supernatant was seeded on a 1% bouillon / 1% agar medium to allow colonies to form. Each colony that formed was cultured on a 1% bouillon / 1% agar medium. Each colony was cultured on a 1% bouillon medium, and the voltage of the culture solution was measured to isolate and select electric-generating microorganisms.

[0038] (Production of Culture Medium 4) Sugar, salt, dextrin, beef tallow, starch (including wheat), powdered soy sauce, onion, yeast extract, vitamin C, and citric acid were mixed to obtain a culture medium raw material.

[0039] Example 1 (Power Density and Power Generation Efficiency) 0.05 g of culture medium raw material, the above-obtained power-generating microorganisms, and 50 mL of tap water were added to a housing 2 equipped with a pair of electrodes 5 (both electrodes 5 were made of graphite) connected to a USB port 6 via a lead wire 7. Furthermore, iron (III) nitrate as a transition metal ion and Triton X-100 as a surfactant were added so that the content was 0.1 wt % relative to the total weight of the anode side (total of gel weight, culture medium, power-generating microorganisms, and surfactant). The current and voltage were measured for 7 days. Output decreased on the third day, so water was added. High power generation was observed after 1 to 2 days. Long-term use is possible by subculture of the power-generating microorganisms 3 in the culture medium 4 and preventing drying. Furthermore, power was calculated from the measured current and voltage. The power density was 40 W / m ３ It was.

[0040] Example 2: 0.05 g of culture medium raw material, the above-obtained power-generating microorganisms, and 50 mL of tap water were added to a housing 2 equipped with a pair of electrodes 5 (electrodes 5 made of graphite and zinc plate) connected to a USB port 6 via a lead wire 7. Manganese dioxide (transition metal ion) and Triton X-100 (surfactant) were then added, with a concentration of 0.1 wt % relative to the total weight of the anode side (total of gel weight, culture medium, power-generating microorganisms, and surfactant). The current and voltage were measured for 7 days. Output decreased on the third day, so culture medium was added. High power generation was observed after 1-2 days. Long-term use is possible by subculture of power-generating microorganisms 3 in the culture medium 4 and preventing drying. The power was calculated from the measured current and voltage. The power density was 300 W / m ３ The output values ​​for 6 hours, 12 hours, and 24 hours in Example 3 (described later) are set to 100, and a comparison with Example 2 and Comparative Example 1 (described later) is shown in FIG.

[0041] Example 3 Current and voltage were measured using the same device and under the same conditions as in Example 2, except that no surfactant was used in Example 1. The results are shown in Figure 5. The actual measurement data is shown in Figure 4.

[0042] Comparative Example 1: Current and voltage were measured using the same device and under the same conditions as in Example 2, except that the surfactant and the electricity-generating bacteria were not included in Example 1. The results are shown in Figure 5. The actual measurement data are shown in Figure 4.

[0043] The present invention is a microbial fuel cell that is an environmentally friendly power generation method and is also a simple microbial fuel cell, and therefore contributes to the utilization, production, and sale of microbial fuel cells, and has industrial applicability.

[0044] REFERENCE SIGNS LIST 1 Microbial fuel cell 2 Housing 3 Power-generating microorganism 4 Culture medium 5 Electrode 51 Negative electrode 52 Positive electrode 6 USB port 7 Conductor 8 Opening 9 Lid 10 Ion exchange membrane A1 Organic matter A2 Catalyst A3 Water-repellent treatment agent A4 Culture medium (medium) dedicated to power-generating microorganisms

Claims

1. A microbial fuel cell comprising: an electricity-generating microorganism; a culture medium; and at least a pair of electrodes, the ratio of the electricity-generating microorganism to the total microorganisms being 5% or more.

2. The microbial fuel cell of claim 1, wherein the culture medium comprises a surfactant.

3. The microbial fuel cell of claim 1, wherein the culture medium contains transition metal ions.

4. The microbial fuel cell according to claim 1, wherein the culture medium contains a catalyst for promoting the transfer of electrons generated by the electricity-generating microorganisms.

5. The pair of electrodes is at least 5 cm apart. ２ The microbial fuel cell according to claim 1, having a surface area of ​​at least 100 nm.

6. A microbial fuel cell according to any one of claims 1 to 5, wherein the power-generating microorganisms include at least one type of bacteria from the genus Shewanella and the genus Geobacter.

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