JP2016091805A - Microbial fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a one-tank type microbial fuel cell high in decomposition ability of an organic material and also capable of removing nitrogen.SOLUTION: A microbial fuel cell includes: a container; a liquid which is received in the container and includes an organic material and electron-donating microorganisms; an anode arranged to be in contact with the liquid; a cathode which is arranged to be in contact with the ambient air and to be in direct contact with the liquid or to be adjacent to the liquid through a diaphragm having cation permeability, and has gas permeability; and an aeration device feeding oxygen-containing gas into the liquid. The aeration device preferably feeds the gas into the liquid intermittently.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a 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. Similarly, the treatment of sewage in urban areas is very costly and labor intensive. 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 and sewage purification treatment in urban areas.

  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.

  On the other hand, in a 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 the diaphragm 15, or the diaphragm 15 and the anode 14 and the membrane electrode assembly 17, 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.

  The microbial fuel cell utilizes the use of the anode as the final electron acceptor when the electron donating microorganism decomposes organic matter under anaerobic conditions. As described above, since the microbial fuel cell uses anaerobic treatment by electron-donating microorganisms, it is considered essential that the container of the single tank type microbial fuel cell be maintained in an anaerobic state.

Hong Liu, and Bruce E. Logan, "Electricity Generation Using an Air-Cathode Single Chamber Microbial Fuel Cell in the Presence and Absence of a Proton Exchange Membrane", Environ. Sci. Technol., Vol. 38, pp. 4040-4046 .

  As described above, the microbial fuel cell is expected not only to generate electricity but also to perform purification treatment by decomposing organic substances in the wastewater. However, conventional microbial fuel cells have a lower ability to decompose organic matter than the activated sludge method. Therefore, development of a microbial fuel cell having a high ability to decompose organic substances is expected. Furthermore, removal of nitrogen in wastewater is also important for purification of wastewater, but conventional microbial fuel cells cannot be removed because they are operated in an anaerobic state.

  This invention is made | formed in view of this point, and it aims at providing the 1 tank type microbial fuel cell which has high decomposition | disassembly capability of organic substance, and can also remove nitrogen.

  The present inventors have surprisingly found that power generation can be continued even if aeration is carried out in a single tank type microbial fuel cell. Furthermore, the present inventors have found that the ability of decomposing organic substances is remarkably increased by performing aeration in a single tank type microbial fuel cell, and nitrogen removal is also performed. The inventors further studied these findings 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 A microbial fuel cell comprising: a cathode having gas permeability and an aeration apparatus for sending a gas containing oxygen to the liquid, which are arranged adjacent to each other with a cation-permeable diaphragm interposed therebetween.
[2] The microbial fuel cell according to [1], wherein the aeration apparatus intermittently sends the gas into the liquid.
[3] The aeration apparatus intermittently sends the gas to the liquid, whereby an aerobic state and an anaerobic state are repeated in the liquid, and nitrogen in the liquid is removed. Microbial fuel cell.
[4] The microbial fuel cell according to any one of [1] to [3], wherein the gas is air.
[5] The microbial fuel cell according to any one of [1] to [4], wherein the aeration apparatus adjusts an amount of the gas fed in accordance with a current flowing between the anode and the cathode.
[6] The microbial fuel cell according to any one of [1] to [5], wherein the aeration apparatus is driven by a current flowing between the anode and the cathode.
[7] The microbial fuel cell according to any one of [1] to [6], wherein the cathode floats on a surface of the liquid.
[8] The diaphragm and the cathode are integrated to form a membrane electrode assembly, and the membrane electrode assembly is configured so that the diaphragm contacts the liquid and the cathode contacts the outside air. The microbial fuel cell according to [7], which floats on a surface of the liquid, and the anode floats in the liquid.
[9] 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 [7], which floats on the surface of the liquid.
[10] The microbial fuel cell according to [8] or [9], wherein the membrane electrode assembly is disposed so as to be inclined with respect to a surface of the liquid.
[11] The microbial fuel cell according to any one of [7] to [10], further including a float for floating the anode and the cathode in or on the liquid.

  ADVANTAGE OF THE INVENTION According to this invention, the microbial fuel cell which has high decomposition | disassembly capability of organic substance and can also remove nitrogen can be provided.

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. It is a cross-sectional schematic diagram which shows the structure of the microbial fuel cell which concerns on embodiment. It is a cross-sectional schematic diagram which shows the structure of the microbial fuel cell which concerns on the modification of embodiment. FIG. 5A is a graph showing the change over time of the oxidation-reduction potential (ORP) in the microbial fuel cell according to the embodiment, and FIG. 5B is a graph showing the change over time of the oxidation-reduction potential in the intermittent aeration activated sludge tank. It is. FIG. 6 is a graph showing a change with time of the output density per unit area of the cathode in the microbial fuel cell according to the embodiment. FIG. 7 is a graph showing the measurement results of the chemical oxygen demand of the mixed solution in the microbial fuel cell and the intermittent aeration activated sludge tank according to the embodiment. FIG. 8 is a graph showing measurement results of the nitrogen concentration of the mixed liquid in the microbial fuel cell and the intermittent aeration activated sludge tank according to the embodiment. FIG. 9 is a graph showing a change with time of the output density per unit area of the cathode in the microbial fuel cell according to the embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, a membrane electrode assembly (MEA) including a diaphragm and a cathode floats on a liquid containing organic matter (fuel) and electron donating microorganisms, and an anode floats in the liquid Will be described.

(Configuration of microbial fuel cell)
FIG. 3 is a schematic cross-sectional view showing the configuration of the microbial fuel cell 100 according to one embodiment of the present invention. As shown in FIG. 3, the microbial fuel cell 100 includes a container 110, a liquid 120, an anode 130, a membrane electrode assembly 140, a float 150, and an aeration device 160. The liquid 120 includes an organic substance and an electron donating microorganism 122. The membrane electrode assembly 140 includes a diaphragm 142 and a cathode 144. The aeration apparatus 160 includes a pump 162, an air diffuser 164, and a control unit 166. Further, the anode 130 and the cathode 144 are electrically connected by a conducting wire 170 constituting an external circuit, and the pump 162 is electrically connected to the conducting wire 170 via the control unit 166.

  The container 110 constitutes the main body of the microbial fuel cell 100 and contains the liquid 120. 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 144 (or the membrane electrode assembly 140 including the cathode 144) is the container 110. It does not constitute a part of the wall surface. For this reason, the container 110 can be enlarged, that is, the microbial fuel cell 100 can be scaled up without considering the destruction of the cathode 144 due to the increase in the pressure of the liquid 120.

The liquid 120 is accommodated in the container 110 and contains an organic substance serving as a fuel and an electron donating microorganism 122. Usually, the liquid 120 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 120 may further contain an electron-transmitting intermediary material such as an electron mediator or conductive fine particles as necessary.

  Among the electron donating microorganisms 122 in the liquid 120, at least some of the electron donating microorganisms 122 are supported on the anode 130. That is, the anode 130 also functions as a carrier that holds the electron-donating microorganism 122 at a high density. There may be one kind of electron-donating microorganism 122, 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 122 can be metabolized. Organic materials used as fuel include not only useful resources such as alcohol, monosaccharides, polysaccharides, and proteins, but also unused resources (organic waste) such as agricultural and industrial waste, organic waste liquid, human waste, sludge, and food residues. Can be used. The organic matter serving as the fuel is added as necessary to maintain and grow the electron-donating microorganism 122 and to continuously operate the microbial fuel cell 100.

  The anode 130 is disposed so as to contact the liquid 120. In the present embodiment, the anode 130 is supported by the float 150 via the conducting wire 170 and floats (immersed) in the liquid 120. The material and shape of the anode 130 are not particularly limited, and can be appropriately selected according to the adhesion of the electron donating microorganism 122, the degree of electron transfer from the electron donating microorganism 122, and the like. Examples of the material of the anode 130 include carbon and metal. Examples of the shape of the anode 130 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 130 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 140 includes a diaphragm 142 having cation permeability and a cathode 144 having gas permeability. The diaphragm 142 and the cathode 144 are integrated to form a membrane electrode assembly 140. The membrane electrode assembly 140 is disposed such that the diaphragm 142 is in contact with the liquid 120 and the cathode 144 is in contact with the outside air. In the present embodiment, the diaphragm 142 is fixed to the lower side of the float 150 so as to block the through hole of the annular float 150, and the cathode 144 is laminated on the diaphragm 142 in the through hole of the float 150. Yes. As a result, the membrane electrode assembly 140 floats on the surface of the liquid 120. The membrane electrode assembly 140 may be arranged so as to be parallel to the surface (liquid level) of the liquid 120, but the surface (liquid level) of the liquid 120 may be suppressed in order to prevent bubbles from remaining below the diaphragm 142. It is preferable that it is arrange | positioned so that it may incline with respect to (refer FIG. 3).

  The diaphragm 142 is a film that can selectively permeate cations, and is disposed between the liquid 120 and the cathode 144. As described above, in the present embodiment, the diaphragm 142 is fixed to the lower side of the float 150 so as to close the through hole of the annular float 150. The type of the diaphragm 142 is not particularly limited as long as it can selectively permeate cations. Examples of the diaphragm 142 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) 144 is disposed adjacent to the liquid 120 with the diaphragm 142 interposed therebetween. As described above, in this embodiment, the cathode 144 is laminated on the diaphragm 142 in the through hole of the annular float 150. The material and shape of the cathode 144 are not particularly limited as long as both gas permeability and conductivity can be achieved. Examples of the material of the cathode 144 include carbon and metal. Examples of the cathode 144 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 150 floats on the surface (liquid level) of the liquid 120 and directly or indirectly supports the anode 130, the diaphragm 142, and the cathode 144. As a result, the anode 130 floats in the liquid 120, and the diaphragm 142 and the cathode 144 float on the surface of the liquid 120. That is, the anode 130, the diaphragm 142 and the cathode 144, and the float 150 constitute one floating body. The material and shape of the float 150 are not particularly limited as long as the anode 130, the diaphragm 142, and the cathode 144 can float in or on the liquid 120. For example, the float 150 is a foamed plastic such as polystyrene foam, a hollow structure made of resin, metal, or the like. In the present embodiment, the float 150 is a ring-shaped foamed plastic.

  The aeration apparatus 160 includes a pump 162, an air diffuser 164, and a control unit 166. The aeration apparatus 160 sends a gas containing oxygen into the liquid 120. In the present embodiment, the aeration apparatus 160 sends air 168 into the liquid 120. The aeration apparatus 160 may be driven by electric power supplied from the outside, or may be driven by electric power obtained by power generation of the microbial fuel cell 100. In the present embodiment, aeration apparatus 160 is driven by a current flowing between anode 130 and cathode 144 (that is, electric power obtained by power generation of microbial fuel cell 100).

  The aeration apparatus 160 may continuously send the air 168 into the liquid 120. However, from the viewpoint of easily adjusting the balance between the power generation ability and the organic substance decomposition ability, the air 168 may be intermittently sent into the liquid 120. preferable. When the aeration apparatus 160 intermittently sends the air 168 to the liquid 120, the time of the aeration state and the time of the non-aeration state are the power generation capability of the microbial fuel cell 100, the decomposition capability of organic matter, the concentration of the organic matter contained in the liquid 120, etc. It adjusts suitably according to. For example, when the concentration of the organic matter contained in the liquid 120 is high, the aeration time per time is about 30 minutes to 4 hours, and the non-aeration time per time is about 1 to 12 hours. When the organic matter is sufficiently decomposed and the liquid 120 is purified, the electric power obtained by the power generation of the microbial fuel cell 100 decreases. That is, the concentration of the organic substance in the liquid 120 can be detected by a current flowing between the anode 130 and the cathode 144. Therefore, the aeration apparatus 160 may adjust the amount of air 168 that is fed in accordance with the current flowing between the anode 130 and the cathode 144. For example, when the current corresponding to the biochemical oxygen demand (BOD) of the liquid 120 is more than 2000 mg / L, the aeration time per time is about 3 hours, and the non-aeration time per time is 3 hours. It should be about. In the case of a current corresponding to a BOD of 500 to 2000 mg / L, the aeration time per time may be about 2 hours, and the non-aeration time per time may be about 4 hours. In the case of a current corresponding to a BOD of 50 to 500 mg / L, the aeration time per time may be about 1 hour, and the non-aeration time per time may be about 5 hours. In addition, in the case of a current corresponding to when the BOD is less than 500 mg / L, aeration does not have to be performed. However, if the nitrogen concentration is high, the nitrification reaction may be promoted by aeration. In this case, after the nitrification reaction, nitrogen can be removed by introducing a small amount of raw sewage water as an electron donor into the container 110 to cause a denitrification reaction.

  The pump 162 feeds air taken from outside under the control of the control unit 166 to the diffuser pipe 164. The type of the pump 162 is not particularly limited, and can be appropriately selected according to the required air discharge amount.

  The air diffuser 164 discharges the air sent from the pump 162 into the liquid 120. When it is desired to increase the efficiency of dissolving oxygen in the liquid 120, the air diffuser 164 releases fine bubbles. The shape and configuration of the air diffuser 164 are not particularly limited as long as the above object can be achieved. Examples of the air diffuser 164 include a tube attached with a mesh, a membrane tube, and the like.

  The control unit 166 controls the operation of the pump 162 so that aeration is performed under preset conditions. For example, when aeration is intermittently performed, the control unit 166 controls the pump 162 so as to operate only for a predetermined time. Further, as described above, the control unit 166 may control the pump 162 according to the current flowing between the anode 130 and the cathode 144. Aeration by the aeration apparatus 160 is performed in order to promote the decomposition of the organic matter in the liquid 120. Therefore, when the concentration of the organic matter in the liquid 120 is reduced, it is not necessary to aerate, and anaerobic from the viewpoint of improving the power generation capacity. In some cases, it may be preferable not to perform aeration to obtain a state. In such a case, the control unit 166 may stop the operation of the pump 162 when detecting a decrease in current. In this way, power consumption by the pump 162 can be suppressed.

(Operation of microbial fuel cell)
Next, the operation of the microbial fuel cell 100 according to the present embodiment will be described.

  When the microbial fuel cell 100 according to the present embodiment is operated, hydrogen ions and electrons are generated when an organic substance (for example, acetic acid) is decomposed into carbon dioxide by the electron donating microorganism 122 in the container 110. Hydrogen ions generated by the decomposition of the organic matter pass through the diaphragm 142 and move to the surface of the cathode 144. On the other hand, the electrons generated by the decomposition of the organic matter are collected by the anode 130 and move to the cathode 144 via an external circuit. Further, since the cathode 144 has air permeability, oxygen is also present on the surface of the cathode 144. In such a situation, water is generated on the surface of the cathode 144 as hydrogen ions and electrons react 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.

  The microbial fuel cell 100 according to the present embodiment is mainly characterized by aeration during operation. Since power generation by the above mechanism uses anaerobic treatment, the conventional microbial fuel cell is designed to be in an anaerobic state (a state in which there is almost no dissolved oxygen) in the liquid. On the other hand, in the microbial fuel cell 100 according to the present embodiment, the dissolved oxygen concentration in the liquid 120 is increased to some extent by aeration continuously, preferably intermittently, in order to improve the decomposition ability of organic matter. By aeration in this way, in addition to power generation and an organic matter decomposition by anaerobic treatment, the organic matter can also be decomposed by an aerobic treatment. As a result, organic substances can be decomposed more efficiently than a conventional microbial fuel cell or an activated sludge method using intermittent aeration (intermittent aeration activated sludge method) (see FIG. 7). In addition, as shown in the examples below, according to the experiments of the present inventors, in addition to being able to continue power generation without killing the electron-donating microorganism 122 even if intermittent aeration is performed (see FIG. 6), It is known that the power generation capacity may be improved by aeration depending on aeration conditions (see FIG. 9).

  In addition, since the microbial fuel cell 100 according to the present embodiment also uses aerobic treatment, it is possible to remove nitrogen, which was impossible with a conventional microbial fuel cell using only anaerobic treatment (see FIG. 8). ). For example, when the aeration apparatus 160 intermittently sends air 168 to the liquid 120, the aerobic state and the anaerobic state are repeated in the liquid 120. In an aerobic state, ammonia contained in the liquid 120 is oxidized to nitric acid. In an anaerobic state, the reaction from nitric acid to gaseous nitrogen is promoted using electrons supplied from organic matter, and denitrification occurs. Therefore, the microbial fuel cell 100 according to the present embodiment can also be used as a deodorizing device by aeration using air containing bad odors from barns or compost. When aeration is performed using air containing malodor, malodorous components such as ammonia move to the liquid 120 and are converted to odorless nitrogen gas and deodorized by a cycle of aerobic treatment and anaerobic treatment.

(effect)
As described above, in the microbial fuel cell 100 according to the present embodiment, the aerobic treatment and the aerobic treatment are used by aeration to maintain the power generation capability, and improve the decomposition ability of organic matter and nitrogen. Removal is realized. That is, the microbial fuel cell 100 according to the present embodiment has higher purification performance than the conventional microbial fuel cell in addition to the power generation capability.

  Further, as described above, the microbial fuel cell 100 according to the present embodiment can also adjust the aeration time according to the organic substance concentration in the liquid 120. In addition, since the anode 130 carries the electron donating microorganism 122 at a high concentration in the microbial fuel cell 100 according to the present embodiment, the organic matter is more efficiently obtained than the intermittent aeration activated sludge method without a member that carries the microorganism. It can also be disassembled (see FIG. 7). Moreover, since the microbial fuel cell 100 which concerns on this Embodiment utilizes not only an aerobic process but an anaerobic process, it can also reduce the generation amount of an excess sludge rather than the activated sludge method which does not use an anaerobic process. Moreover, the microbial fuel cell 100 according to the present embodiment can also perform nitrogen removal and deodorization treatment (see FIG. 8).

  Further, in the microbial fuel cell 100 according to the present embodiment, the anode 130, the diaphragm 142, and the cathode 144 float in or on the liquid 120 without constituting a 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 130, the diaphragm 142, and the cathode 144 due to the increase in the pressure of the liquid 120. In addition, regardless of the amount of the liquid 120, the entire surface of the anode 130 and the cathode 144 is always in contact with the liquid 120 directly or through the diaphragm 142, so that the external circuit is not affected by the change in the amount of the liquid 120. Can be output stably.

  Furthermore, in the microbial fuel cell 100 according to the present embodiment, the aeration apparatus 160 that sends the air 168 into the liquid 120 is installed, and the float 150 attached with the anode 130, the diaphragm 142, and the cathode 144 is attached to the surface of the liquid 120. The microbial fuel cell 100 according to the present embodiment can be easily installed or removed simply by floating or taking it out. 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 in which the membrane electrode assembly 140 including the diaphragm 142 and the cathode 144 is floating on the surface of the liquid 120 and the anode 130 is floating in the liquid 120 has been described. The positions of the anode 130, the diaphragm 142, and the cathode 144 are not limited to this. For example, a liquid permeable anode 130, a diaphragm 142, and a cathode 144 are integrated to form a membrane electrode assembly. The membrane electrode assembly is in contact with the liquid 120, and the cathode 144 is exposed to the outside air. You may float on the surface of the liquid 120 so that it may contact. Also in this case, it is preferable that the membrane electrode assembly is disposed so as to be inclined with respect to the surface (liquid level) of the liquid 120. Further, as shown in FIG. 4, an anode 130 and a cathode 144 may be arranged on the wall surface of the container 110 in the same manner as a conventional one-tank type microbial fuel cell. Also in this case, the aeration apparatus 160 does not change that the gas (for example, air 168) containing oxygen is sent to the liquid 120 in the container 110.

  In the present embodiment, the microbial fuel cell 100 having the float 150 for floating the anode 130 and the cathode 144 in or on the liquid 120 has been described. However, the float 150 is not an essential component. For example, if the anode 130, the diaphragm 142, or the cathode 144 are made to float by making them have a hollow structure, the float 150 may be eliminated. However, when the practicality of the battery is taken into consideration, it is preferable that the float 150 is present.

  In the present embodiment, the microbial fuel cell 100 having the diaphragm 142 has been described. However, the diaphragm 142 is not an essential component. That is, the cathode 144 should not be in contact with the anode 130, but may be in direct contact with the liquid 120. However, when the practicality of the battery is taken into consideration, the diaphragm 142 is preferably provided.

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

[Experiment 1]
In this experiment, a microbial fuel cell (see FIG. 3) according to the above embodiment was produced, and its power generation characteristics and organic matter decomposition characteristics were evaluated. In this experiment, aeration was performed intermittently.

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) Production of membrane electrode assembly 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 Kogyo Co., Ltd.) having a particle size of 2 to 3 nm, ion conductivity A polymer solution (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. In a state where the Teflon sheet on which the catalyst layer is formed is laminated on the proton exchange membrane so that the catalyst layer comes into contact with the proton exchange membrane (Nafion-117; diameter 11 cm), press (120 ° C., 10 ° C.) Minutes), the catalyst layer (thickness: about 100 μm) was transferred to the proton exchange membrane.

  Next, 0.8 mL of the above-described ion conductive polymer solution was applied to a Teflon-processed carbon cloth (diameter: 7.0 cm). Furthermore, the above 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 membrane including the cathode and the diaphragm An electrode assembly was produced.

(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 A plastic 2K beaker was prepared as a container. An air diffuser connected to a pump (air discharge rate: 1.7 to 2.0 L / min) was disposed at the bottom of the beaker. The aforementioned medium was mixed with the electron-donating microorganism and activated sludge as fuel in a ratio of 4: 1. 1.5 L of the obtained mixed solution was introduced into a beaker.

  The anode and membrane electrode assembly (proton exchange membrane and cathode) were fixed to an annular float made of expanded polystyrene (outer diameter 10 cm × inner diameter 7 cm × height 5 cm). The anode was fixed to the float via a conducting wire (see FIG. 3).

  The anode and the membrane electrode assembly were placed in the beaker by floating the mixed solution in the beaker. The anode was in a floating state in the mixed solution, and the cathode was in contact with the outside air. Moreover, the membrane electrode assembly was inclined with respect to the liquid level of the mixed solution. The anode and cathode were connected to an external wattmeter.

2. Evaluation of Microbial Fuel Cell The power generation characteristics and purification characteristics of the prepared microbial fuel cell according to the above embodiment were evaluated. In addition, for comparison, a reaction tank (hereinafter referred to as “intermittent aeration activated sludge tank”) that performs the intermittent aeration activated sludge process using the same container, pump, diffuser tube, and mixed solution was prepared, and the purification characteristics were evaluated. .

  At room temperature, the microbial fuel cell according to the embodiment was operated in a cycle of aeration for 1 hour and non-aeration for 5 hours, the power was measured every minute, and the output density per unit area of the cathode was calculated. At the same time, the redox potential (ORP) of the mixed solution was also measured. Further, the chemical oxygen demand (COD) of the mixed solution was measured every day. In addition, the total nitrogen (TN) concentration of the mixed solution was measured on the fourth day after the operation. For comparison, the chemical oxygen demand and the total nitrogen concentration of the liquid mixture were also measured for the microbial fuel cell that was operated without aeration.

  Similarly, at room temperature, an intermittent aeration activated sludge tank was operated in a cycle of aeration for 1 hour and non-aeration for 5 hours, and the oxidation-reduction potential of the mixed solution was measured every minute. In addition, the chemical oxygen demand of the mixed solution was measured every day. Further, on the fourth day after the operation, the total nitrogen concentration of the mixed solution was measured.

  FIG. 5A is a graph showing the change over time of the oxidation-reduction potential (ORP) in the microbial fuel cell according to the embodiment, and FIG. 5B is a graph showing the change over time of the oxidation-reduction potential in the intermittent aeration activated sludge tank. It is. From these graphs, it can be seen that in both the microbial fuel cell and the intermittent aeration activated sludge tank according to the embodiment, the oxidation-reduction potential has increased to a positive value due to aeration and is in an aerobic state. .

  FIG. 6 is a graph showing a change with time of the output density per unit area of the cathode in the microbial fuel cell according to the embodiment. From this graph, it can be seen that the microbial fuel cell according to the embodiment can continue power generation even when intermittent aeration is performed. It can also be seen that the output density decreases and the output waveform changes due to the decrease in the concentration of the organic substance over time.

  FIG. 7 is a graph showing the measurement results of the chemical oxygen demand of the mixed solution in the microbial fuel cell and the intermittent aeration activated sludge tank according to the embodiment. This graph also shows the measurement result of the microbial fuel cell operated without performing the aeration process. From this graph, it can be seen that the microbial fuel cell according to the present invention can decompose organic matter faster than the intermittent aeration activated sludge tank. This is because various microorganisms including electron donating microorganisms adhere to the anode at a high density, so that the microorganisms are kept at a high concentration in the container, and further, organic matter and electron donating microorganisms in the mixed solution are aerated by aeration. It is thought that it was possible to contact efficiently. It can also be seen that the microbial fuel cell according to the present invention can decompose organic matter significantly faster than the microbial fuel cell operated without aeration treatment.

  FIG. 8 is a graph showing measurement results of the nitrogen concentration of the mixed liquid in the microbial fuel cell and the intermittent aeration activated sludge tank according to the embodiment. This graph also shows the measurement result of the microbial fuel cell operated without performing the aeration process. From this graph, it can be seen that the microbial fuel cell according to the present invention can remove nitrogen in the mixed solution in the same manner as the intermittent aeration activated sludge tank. It can also be seen that microbial fuel cells operated without aeration treatment cannot remove nitrogen. This is considered to be because a microbial fuel cell operated without performing aeration treatment is always in an anaerobic state, and does not generate an ammonia oxidation reaction (nitrification) that occurs in an aerobic state and does not cause a denitrification reaction. . This shows that nitrogen removal is promoted by performing (intermittent) aeration in the microbial fuel cell.

[Experiment 2]
In this experiment, the power generation characteristics of the microbial fuel cell when operated under conditions different from those in Experiment 1 were evaluated.

1. Production of microbial fuel cell In this experiment, the same configuration as that of the microbial fuel cell produced in Experiment 1 was used except that a pump with an air discharge rate of 1.1 L / min was used and a medium having a different composition was used. A microbial fuel cell was prepared. The medium (electrolyte solution) was prepared by adding the additives shown in the following table to distilled water.

2. Evaluation of Microbial Fuel Cell At room temperature, the microbial fuel cell according to the embodiment is operated in a cycle of 2 hours of aeration and 4 hours of non-aeration, and the power is measured every minute, and the output density per unit area of the cathode is calculated. Calculated.

  FIG. 9 is a graph showing a change with time of the output density per unit area of the cathode in the microbial fuel cell according to the embodiment. In this graph, the time when aeration was performed is indicated by an arrow. From this graph, it can be seen that the output of power generation is increased by aeration depending on the composition of the organic matter contained in the culture medium and the conditions of aeration. The reason for this is unknown, but one possibility is that the liquid mixture was appropriately stirred by weak aeration, or that the inhibitor attached to the anode was removed.

  Since the microbial fuel cell according to the present invention has a high ability to decompose organic matter while maintaining power generation capacity, it is useful in, for example, wastewater treatment in livestock barns or sewage purification treatment in urban areas.

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)
DESCRIPTION OF SYMBOLS 100 Microbial fuel cell 110 Container 120 Liquid 122 Electron donating microorganism 130 Anode 140 Membrane electrode assembly (MEA)
142 Diaphragm 144 Cathode (Air Cathode)
150 Floating 160 Aeration device 162 Pump 164 Air diffuser 166 Control unit 168 Air 170 Conductor

Claims (11)

A container,
A liquid containing organic matter and electron-donating microorganisms contained in the container;
An anode disposed in contact with the liquid;
A gas permeable cathode disposed in contact with the outside air and in direct contact with the liquid, or adjacent to a cation permeable membrane;
An aeration apparatus for sending a gas containing oxygen to the liquid;
Having
Microbial fuel cell.   The microbial fuel cell according to claim 1, wherein the aeration apparatus intermittently sends the gas into the liquid.   The microbial fuel cell according to claim 2, wherein the aeration apparatus intermittently feeds the gas into the liquid, whereby the aerobic state and the anaerobic state are repeated in the liquid, and nitrogen in the liquid is removed. .   The microbial fuel cell according to any one of claims 1 to 3, wherein the gas is air.   The microbial fuel cell according to any one of claims 1 to 4, wherein the aeration apparatus adjusts an amount of the gas fed in accordance with a current flowing between the anode and the cathode.   The microbial fuel cell according to any one of claims 1 to 5, wherein the aeration apparatus is driven by a current flowing between the anode and the cathode.   The microbial fuel cell according to any one of claims 1 to 4, wherein the cathode floats on a surface of the liquid. The diaphragm and the cathode are integrated to form a membrane electrode assembly,
The membrane electrode assembly floats on the surface of the liquid so that the diaphragm is in contact with the liquid and the cathode is in contact with outside air,
The anode floats in the liquid;
The microbial fuel cell according to claim 7. The anode, the diaphragm and the cathode are integrated to form a membrane electrode assembly,
The membrane electrode assembly floats on the surface of the liquid so that the anode contacts the liquid and the cathode contacts the outside air,
The microbial fuel cell according to claim 7.   The microbial fuel cell according to claim 8 or 9, wherein the membrane electrode assembly is disposed so as to be inclined with respect to a surface of the liquid.   The microbial fuel cell according to any one of claims 7 to 10, further comprising a float for floating the anode and the cathode in or on the surface of the liquid.

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