JP6332793B2 - Microbial fuel cell and float - Google Patents

Description

  The present invention relates to a microbial fuel cell and a floating body that can be used in the microbial fuel cell.

  For livestock farmers, the treatment of wastewater from barns is a heavy burden because it requires a great deal of cost and labor. On the other hand, the microbial fuel cell can not only produce electrical energy by the oxidation of organic matter by microorganisms, but can also simultaneously decompose organic waste. For this reason, the microbial fuel cell is expected as a useful new technology in various applications such as wastewater treatment in livestock barns.

  Microbial fuel cells are roughly classified into two tank types and one tank type. The two tank type microbial fuel cell has an anode tank and a cathode tank which are separated from each other by a diaphragm having cation permeability. In the two-cell type microbial fuel cell, a substance capable of accepting electrons such as potassium ferricyanide (iron compound ion), oxygen, iron ion, nitrate ion, and sulfate ion is required in the cathode cell.

  In the one-cell type microbial fuel cell, a cathode having gas permeability, which is also referred to as an air cathode, is used instead of the cathode cell (see, for example, Non-Patent Document 1). FIG. 1 is a schematic cross-sectional view of a single tank type microbial fuel cell in which an anode and a cathode are separate, and FIG. 2 is a schematic cross-sectional view of a single tank type microbial fuel cell in which an anode and a cathode are integrated. . As shown in FIG. 1 and FIG. 2, the microbial fuel cell 10 is in contact with the liquid 11, the liquid 11 (the fuel 11 containing the organic matter and the electron donating microorganisms 12 accommodated in the container 11). The anode 14 disposed, the cation permeable diaphragm 15 disposed so as to be in contact with the liquid 13, and the cathode (air cathode) disposed adjacent to the liquid 13 with the diaphragm 15 interposed therebetween and in contact with the outside air 16). The cathode 16 constitutes a membrane electrode assembly (hereinafter referred to as “MEA”) 17 with the diaphragm 15 and / or the anode 14, and constitutes a part of the wall surface of the container 11. Such a single tank type microbial fuel cell is superior to a two tank type microbial fuel cell in that it does not require a cathode tank different from a tank (anode tank) in which a reaction by microorganisms occurs.

  On the other hand, a microbial fuel cell has been proposed that uses a microorganism in the bottom mud to generate power and decompose organic matter in the bottom mud in places where there is bottom mud such as the sea or rivers (for example, Non-Patent Document 2). reference). The microbial fuel cell described in Non-Patent Document 2 has an anode embedded in bottom mud and a cathode floated on the water surface. The microbial fuel cell described in Non-Patent Document 2 has a cathode floating on the water surface in order to suppress a decrease in output due to a decrease in oxygen concentration in water.

Yanzhen Fan, et al., "Enhanced Coulombic efficiency and power density of air-cathode microbial fuel cells with an improved cell configuration", Journal of Power Sources, Vol. 171, pp. 348-354. Aijie Wang, et al., "Sediment microbial fuel cell with floating biocathode for organic removal and energy recovery", Fromt. Environ. Sci. Eng., Vol. 6, pp. 569-574.

  As shown in FIG. 1 and FIG. 2, in a conventional one tank type (air cathode type) microbial fuel cell 10, the MEA 17 including the cathode 16 constitutes a part of the wall surface of the container 11. For this reason, in the conventional microbial fuel cell 10, since the MEA 17 is required to have a strength that can withstand the pressure of the liquid 13, it is difficult to scale up from a lab scale to a pilot scale or a plant scale. Further, the conventional microbial fuel cell 10 has a problem that when the amount of the liquid 13 is reduced due to evaporation or the like, the contact area between the MEA 17 and the liquid 13 is reduced and the output is reduced.

  The present invention has been made in view of the above points, and provides a microbial fuel cell that is stable in output without being affected by changes in the amount of liquid and that can be easily scaled up, and an MEA used therefor. For the purpose.

  The present inventors have found that the above problem can be solved by floating the anode and the cathode in or on the liquid, and have further studied and completed the present invention.

  That is, the present invention relates to the following microbial fuel cells.

[1] Whether the container, the liquid containing the organic matter and the electron donating microorganisms contained in the container, the anode arranged to contact the liquid, the outside air, and the direct contact with the liquid Or a gas permeable cathode arranged adjacent to each other across a cation permeable membrane, the anode and the cathode floating in or on the liquid Fuel cell.
[2] The anode, the diaphragm and the cathode are integrated to form a membrane electrode assembly, and the membrane electrode assembly has the anode in contact with the liquid and the cathode in contact with the outside air. As described above, the microbial fuel cell according to [1], which floats on the surface of the liquid.
[3] The microbial fuel cell according to [1] or [2], further including a float for floating the anode and the cathode in or on the liquid.

Moreover, this invention relates to the following floating bodies for microbial fuel cells.
[4] An anode, a gas permeable cathode, a cation permeable membrane joined to one surface of the cathode, and the anode, the membrane and the cathode for floating in or on a liquid A floating body for a microbial fuel cell having a float.
[5] The floating body for a microbial fuel cell according to [4], wherein the anode is joined to a surface of the diaphragm where the cathode is not disposed.

  According to the present invention, it is possible to provide a microbial fuel cell that is stable in output without being affected by a change in the amount of liquid (fuel) and that can be easily scaled up, and an MEA used therefor.

It is a cross-sectional schematic diagram of the conventional microbial fuel cell in which an anode and a cathode are separate bodies. It is a cross-sectional schematic diagram of a conventional microbial fuel cell in which an anode and a cathode are integrated. 1 is a schematic cross-sectional view showing a configuration of a microbial fuel cell according to Embodiment 1. FIG. 4 is a schematic cross-sectional view showing a configuration of a microbial fuel cell according to Embodiment 2. FIG. 6 is a schematic cross-sectional view showing a configuration of a microbial fuel cell according to a modification of Embodiment 2. FIG. It is a graph which shows the result of the voltage measurement in an Example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
FIG. 3 is a schematic cross-sectional view showing the configuration of the microbial fuel cell 100 according to the first embodiment. As shown in FIG. 3, the microbial fuel cell 100 includes a vessel 110, a liquid 130 containing an organic substance (fuel) and an electron donating microorganism 120, an anode 140, a membrane electrode assembly (MEA) including a diaphragm 150 and a cathode 160. ) 170 and float 180. In the microbial fuel cell 100 according to the present embodiment, the anode 140 is not joined to the diaphragm 150.

  The container 110 constitutes a main body portion of the microbial fuel cell 100 and accommodates the liquid 130. The material, shape, and size of the container 110 are not particularly limited, and can be set as appropriate according to the application. In the microbial fuel cell 100 according to the present embodiment, unlike the conventional one-tank type microbial fuel cell (see FIGS. 1 and 2), the cathode 160 (or the MEA 170 including the cathode 160) is a part of the wall surface of the container 110. It does not constitute a part. Therefore, the container 110 can be enlarged, that is, the microbial fuel cell 100 can be scaled up without considering the destruction of the cathode 160 due to the increase in the pressure of the liquid 130.

The liquid 130 contains an organic substance serving as a fuel and the electron donating microorganism 120. Usually, the liquid 130 is an aqueous solution containing one or more electrolytes. The type of electrolyte is not particularly limited as long as it is a substance that can be ionized in water. Examples of the electrolyte include NaH ₂ PO ₄ / Na ₂ HPO ₄ , KH ₂ PO ₄ / K ₂ HPO ₄ , NaCO ₃ / NaHCO ₃ , NaCl, KCl, NH ₄ Cl and the like. Further, the liquid 130 may be further added with an electron-transmitting intervening substance such as an electron mediator or conductive fine particles as necessary.

  There may be one kind of electron-donating microorganism 120, or two or more kinds. When organic wastewater or sludge is used as fuel, electron-donating microorganisms that inhabit them can be used as they are without adding electron-donating microorganisms from the outside. For example, Pseudomonas, Geobacter, etc. inhabit every part of the natural environment such as soil, fresh water, seawater, etc., so if organic wastewater or sludge is used as fuel, they can be used without being added from the outside.

  The kind of the organic substance serving as the fuel is not particularly limited as long as the electron donating microorganism 120 can be metabolized. As organic materials to be used as fuel, not only useful resources such as alcohol, monosaccharides and polysaccharides but also unused resources (organic waste) such as agricultural and industrial waste, organic waste liquid, human waste, sludge and food residues are used. be able to. An organic substance serving as a fuel is added as necessary to maintain and grow the electron-donating microorganism 120 and to continuously operate the microbial fuel cell 100.

  The anode 140 is disposed so as to contact the liquid 130. In the present embodiment, the anode 140 is supported by the float 180 via the conducting wire 190, and is floated (immersed) in the liquid 130. The material and shape of the anode 140 are not particularly limited, and can be appropriately selected according to the adhesion of the electron donating microorganism 120, the degree of electron transfer from the electron donating microorganism 120, and the like. Examples of the material of the anode 140 include carbon and metal. Examples of the shape of the anode 140 include a planar shape such as a cloth, and a three-dimensional shape such as a brush shape, a rod shape, and a granular shape. Examples of the anode 140 include carbon paper, graphite plate, carbon cloth, carbon mesh, graphite particles, activated graphite particles, carbon felt, reticulated vitrified carbon, carbon brush, stainless steel mesh, and the like.

  The membrane electrode assembly (MEA) 170 includes a diaphragm 150 and a gas permeable cathode 160. The diaphragm 150 and the cathode 160 are joined to each other. The MEA 170 is arranged such that the diaphragm 150 contacts the liquid 130 and the cathode 160 contacts the outside air. In this embodiment, the diaphragm 150 is fixed to the lower side of the float 180 so as to block the through hole of the annular float 180, and the cathode 160 is laminated on the diaphragm 150 in the through hole of the float 180. Yes.

  The diaphragm 150 is a film that can selectively permeate cations, and is disposed between the liquid 130 and the cathode 160. As described above, in the present embodiment, the diaphragm 150 is fixed to the lower side of the float 180 so as to block the through hole of the annular float 180. The kind of the diaphragm 150 is not particularly limited as long as it can selectively permeate cations. Examples of the diaphragm 150 include a proton exchange membrane. The proton exchange membrane is a membrane made of a proton conductive ion exchange polymer electrolyte. Examples of the material of the proton exchange membrane include perfluorosulfonic acid-based fluorine ion exchange resins and organic / inorganic composite compounds. The perfluorosulfonic acid-based fluorine ion exchange resin includes, for example, a copolymer containing a polymer unit based on a perfluorovinyl ether having a sulfo group and / or a carboxyl group and a polymer unit based on tetrafluoroethylene. Including. Nafion (registered trademark) is known as such a fluorine ion exchange resin. The organic / inorganic composite compound is a substance composed of a compound in which a hydrocarbon polymer (for example, polyvinyl alcohol) and an inorganic compound (for example, tungstic acid) are combined. Membranes made of these materials are commercially available.

  The cathode (air cathode) 160 is disposed so as to be adjacent to the liquid 130 with the diaphragm 150 interposed therebetween. As described above, in this embodiment, the cathode 160 is stacked on the diaphragm 150 in the through hole of the annular float 180. The material of the cathode 160 is not particularly limited as long as it has gas permeability and conductivity. Examples of the material of the cathode 160 include carbon and metal. Examples of the cathode 160 include carbon paper, carbon cloth, carbon mesh, graphite particles, activated graphite particles, carbon felt, reticulated vitrified carbon, stainless steel mesh, and the like. Further, an oxygen reduction catalyst such as platinum or activated carbon may be supported on these surfaces.

  The float 180 floats on the surface of the liquid 130 and directly or indirectly supports the anode 140, the diaphragm 150 and the cathode 160. As a result, the anode 140 floats in the liquid 130, and the diaphragm 150 and the cathode 160 float on the surface of the liquid 130. That is, the anode 140, the diaphragm 150, the cathode 160, and the float 180 constitute one floating body. The material and shape of the float 180 are not particularly limited as long as the anode 140 and the cathode 160 can float in or on the liquid 130. For example, the float 180 is a foamed plastic such as polystyrene foam, a hollow structure made of resin, metal, or the like. In the present embodiment, the float 180 is a ring-shaped foamed plastic.

  In the microbial fuel cell 100 according to the present embodiment, hydrogen ions and electrons are generated when an organic substance (for example, acetic acid) is decomposed into carbon dioxide by the electron donating microorganism 120 in the container 110. Hydrogen ions generated by the decomposition of the organic matter pass through the diaphragm 150 and move to the surface of the cathode 160. On the other hand, the electrons generated by the decomposition of the organic matter are collected by the anode 140 and move to the cathode 160 via an external circuit. Further, since the cathode 160 has air permeability, oxygen is also present on the surface of the cathode 160. Under such circumstances, water is generated on the surface of the cathode 160 by the reaction of hydrogen ions and electrons with oxygen. Therefore, by supplying the organic substance into the container 110, the above cycle can be maintained and electric power can be continuously supplied to the external circuit.

  As described above, in the microbial fuel cell 100 according to the present embodiment, the anode 140 and the MEA 170 (cathode 160) float in or on the liquid 130 without forming part of the wall surface of the container 110. Therefore, the container 110 can be enlarged, that is, the microbial fuel cell 100 can be scaled up without considering the destruction of the anode 140 and the MEA 170 due to the increase in the pressure of the liquid 130. Moreover, since the entire surface of the anode 140 and the MEA 170 (cathode 160) is always in contact with the liquid 130 regardless of the amount of the liquid 130, power can be stably supplied to the external circuit without being affected by the change in the amount of the liquid 130. Can be output.

  In addition, the microbial fuel cell 100 according to the present embodiment can be easily installed or removed simply by floating or removing the float 180 (floating body) attached with the anode 140 and the MEA 170 on the surface of the liquid 130. . Therefore, it is easy to introduce the microbial fuel cell 100 according to the present embodiment into an existing facility.

  In the present embodiment, the microbial fuel cell 100 having the diaphragm 150 has been described, but the diaphragm 150 is not an essential component. That is, the cathode 160 should not be in contact with the anode 140, but may be in direct contact with the liquid 130. However, considering the practicality of the battery, it is preferable that the diaphragm 150 is present.

[Embodiment 2]
FIG. 4 is a schematic diagram showing the configuration of the microbial fuel cell 200 according to Embodiment 2. As shown in FIG. As shown in FIG. 4, the microbial fuel cell 200 includes a container 110, a liquid 130 containing organic matter and electron donating microorganisms 120, an MEA 270 including an anode 240, a diaphragm 150 and a cathode 160, and a float 180.

  The microbial fuel cell 200 according to the second embodiment is different from the microbial fuel cell 100 according to the first embodiment in that the anode 240 is included in the MEA 270 and is joined to the diaphragm 150. Therefore, the same components as those in the microbial fuel cell 100 according to Embodiment 1 are denoted by the same reference numerals, and description thereof is omitted.

  The MEA 270 includes an anode 240 having liquid permeability, a diaphragm 150 and a cathode 160 having gas permeability. The anode 240, the diaphragm 150, and the cathode 160 are joined together and integrated. The MEA 270 is arranged such that the anode 240 is in contact with the liquid 130 and the cathode 160 is in contact with the outside air. In the present embodiment, the anode 240 and the diaphragm 150 are fixed to the lower side of the float 180 so as to close the through hole of the annular float 180, and the cathode 160 is placed on the diaphragm 150 in the through hole of the float 180. Are stacked.

  The anode 240 is disposed in contact with the liquid 130. As described above, in this embodiment, the diaphragm 150 is fixed to the lower side of the float 180 so as to block the through hole of the annular float 180, and further, the lower side of the diaphragm 150 (the cathode 160 is disposed). The anode 240 is laminated on the non-exposed surface. The material of the anode 240 is not particularly limited as long as it has liquid permeability and conductivity. Examples of the material of the anode 240 include carbon and metal. Further, the shape of the anode 240 is not particularly limited. For example, as shown in FIG. 4, the anode 240 may have a planar shape. Further, as shown in FIG. 5, the anode 240 may further have a three-dimensional shape such as a brush shape or a rod shape in addition to the planar shape portion. By doing in this way, since the contact area of the anode 240 and the liquid 130 (electron-donating microorganism 120) increases, the output of the microbial fuel cell 200 can be improved. In addition, when the anode 240 is joined only to a part of the diaphragm 150, the anode 240 may not have liquid permeability.

  In addition to the effects of the microbial fuel cell 100 according to the first embodiment, the microbial fuel cell 200 according to the present embodiment can be installed more easily because the anode 240, the diaphragm 150, and the cathode 160 are integrated. Has an effect.

  In each of the above embodiments, the microbial fuel cells 100 and 200 having the float 180 for floating the anodes 140 and 240 and the cathode 160 in or on the liquid 130 have been described. However, the float 180 is an indispensable constituent element. Absent. For example, if the anodes 140 and 240, the diaphragm 150, or the cathode 160 are made to have a hollow structure so that they float themselves, the float 180 may be omitted. However, when the practicality of the battery is taken into consideration, it is preferable that the float 180 is present.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

  In this example, a microbial fuel cell according to Embodiment 1 (see FIG. 3) was produced and its voltage characteristics were measured.

1. Production of Microbial Fuel Cell (1) Production of Anode An anode was produced by fixing one 10 × 9 cm carbon cloth and two 10 × 3 cm carbon cloths to a conducting wire using a binding band.

(2) Preparation of MEA 16 mg of conductive carbon powder (Vulcan XC-72; CABOT) having a particle size of 30 to 40 nm, 16 mg of platinum powder (Tanaka Kikinzoku Co., Ltd.) having a particle size of 2 to 3 nm, an ion conductive polymer solution ( A solution containing 5% by mass of Nafion (registered trademark) (0.32 mL) was mixed to prepare a paste. The obtained paste was uniformly applied on the surface of a Teflon (registered trademark) sheet (7.0 cm in diameter) and dried to form a catalyst layer. The catalyst layer on the Teflon sheet is pressed using a hot press machine in a state where the Teflon sheet is laminated on the proton exchange membrane so that the catalyst layer is in contact with the proton exchange membrane (Nafion-117; diameter 11 cm) (120 The catalyst layer (thickness: about 100 μm) was transferred to the proton exchange membrane by performing 10 ° C.

  Next, 0.8 mL of the above-described ion conductive polymer solution was applied to a Teflon-processed carbon cloth (diameter: 7.0 cm). Further, the above-described proton exchange membrane is laminated on the ion conductive polymer solution so that the catalyst layer is in contact therewith, and is pressed and pressure-bonded under the same conditions as described above, whereby the MEA including the cathode and the membrane is included. Was made.

(3) Preparation of culture medium Additives shown in the following table were added to distilled water to prepare a culture medium (electrolyte solution).

(4) Production of microbial fuel cell As a container, a glass cylinder having one of its openings closed was prepared. The inner space of the container has a diameter of 10.5 cm and a height of 15 cm. The aforementioned medium was mixed with the electron-donating microorganism and activated sludge as fuel in a ratio of 9: 1. 0.8 L of the obtained mixed solution was introduced into the container.

  The anode and MEA (proton exchange membrane and cathode) were fixed to a ring-shaped float (outer diameter 10 cm × inner diameter 7 cm × height 5 cm) made of polystyrene foam. At this time, each member was arranged so that the anode, the proton exchange membrane, and the cathode were arranged in this order from the bottom.

  The anode and MEA were installed in the container by floating the liquid in the container. The anode was immersed in the liquid, and the cathode was in contact with the outside air. There was a proton exchange membrane between the cathode and the liquid. The anode and cathode were connected to an external voltmeter.

2. Measurement of voltage characteristics of microbial fuel cell A microbial fuel cell was prepared and operated while stirring the liquid in the container for the first 5 days. After that, it was operated without stirring, and the voltage was measured every minute at room temperature. did. The external resistance was 4.3 kΩ.

  FIG. 6 is a graph showing a change with time of voltage after stirring is stopped. From this graph, it can be seen that the microbial fuel cell according to the present invention can stably generate power.

  For example, when an organic waste liquid is used as a fuel, the microbial fuel cell and MEA according to the present invention can not only recover electrical energy from the organic waste liquid but also perform a purification process of the organic waste liquid. Therefore, the microbial fuel cell and MEA according to the present invention are useful in wastewater treatment in livestock barns, sewage treatment in urban areas, and the like.

DESCRIPTION OF SYMBOLS 10 Microbial fuel cell 11 Container 12 Electron donating microorganism 13 Liquid 14 Anode 15 Diaphragm 16 Cathode (air cathode)
17 Membrane electrode assembly (MEA)
100,200 Microbial fuel cell 110 Container 120 Electron donating microorganism 130 Liquid 140,240 Anode 150 Diaphragm 160 Cathode (air cathode)
170,270 Membrane electrode assembly (MEA)
180 float 190 conductor

Claims (2)

A container,
A liquid containing organic matter and electron-donating microorganisms contained in the container;
A float floating on the surface of the liquid;
An anode which is directly or indirectly supported by said float so as to extend substantially along the vertical direction in the liquid,
It is directly or indirectly supported by the float so as to float on the surface of the liquid, and is in contact with the outside air, directly in contact with the liquid, or adjacent to the liquid with a cation-permeable membrane interposed therebetween. A gas permeable cathode disposed;
Have
The inner surface of the container and the anode face each other only through the liquid,
Microbial fuel cell. A float to float on the surface of the liquid,
An anode supported directly or indirectly by the float so as to extend in a substantially vertical direction in the liquid when the float is floated on the liquid ;
A gas that is directly or indirectly supported by the float so as to float on the surface of the liquid when the float is floated on the liquid, and is arranged to come into contact with outside air when the float is floated on the liquid. A permeable cathode;
A cation permeable membrane joined to one side of the cathode so as to be positioned between the cathode and the liquid when the float is floated on the liquid ;
I have a,
The anode is not surrounded by other members in the horizontal direction perpendicular to the vertical direction.
A floating body for microbial fuel cells.

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