WO2017195406A1

WO2017195406A1 - Microbial fuel cell and liquid treatment unit using same

Info

Publication number: WO2017195406A1
Application number: PCT/JP2017/003378
Authority: WO
Inventors: 直毅吉川; 雄也鈴木; 亮釜井; 矢口　充雄
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2016-05-12
Filing date: 2017-01-31
Publication date: 2017-11-16

Abstract

This microbial fuel cell (100) is provided with: an electrolyte solution (70); a positive electrode (10) which is immersed in the electrolyte solution and is composed of a gas diffusion electrode that is at least partially exposed to a gas phase (50); and a negative electrode (20) which is immersed in the electrolyte solution and holds anaerobic microorganisms. With respect to a flow path of the electrolyte solution, the negative electrode is disposed in the electrolyte flow upstream, and the positive electrode is disposed in the downstream of the negative electrode. A liquid treatment unit according to the present invention is provided with the above-described microbial fuel cell.

Description

Microbial fuel cell and liquid processing unit using the same

The present invention relates to a microbial fuel cell and a liquid processing unit using the same. More particularly, the present invention relates to a microbial fuel cell capable of purifying waste water and generating electric energy, and a liquid processing unit using the microbial fuel cell.

In recent years, microbial fuel cells that generate electricity using biomass have attracted attention as sustainable energy. A microbial fuel cell is a battery that oxidizes and decomposes an organic substance while converting the chemical energy of the organic substance contained in domestic wastewater or factory wastewater into electrical energy. The microbial fuel cell is characterized by little generation of sludge and low energy consumption. However, since the power generated by microorganisms is very small and the output current density is low, further improvement is necessary.

As such a microbial fuel cell, a battery having a pair of electrodes (positive electrode, negative electrode), a diaphragm, a reaction tank containing an electrolyte solution, and an external circuit electrically connected to the pair of electrodes is disclosed ( For example, see Patent Document 1). In addition, it is disclosed that a conductive substance having a hole having a predetermined average hole diameter is provided in an electrode substrate constituting the electrode or at least a part of the surface thereof. It is also disclosed that Geobacter sulfurreducens, which is an anaerobic microorganism, is used as a power generation microorganism.

JP2015-82396A

However, since the microbial fuel cell of Patent Document 1 has a positive electrode disposed on one surface of the diaphragm and a negative electrode disposed on the other surface of the diaphragm, oxygen supplied to the positive electrode permeates the diaphragm and becomes a negative electrode. To reach. As a result, there is a problem that the vicinity of the negative electrode becomes aerobic due to the influence of oxygen reaching the negative electrode, and the anaerobic power generation microorganisms do not act effectively.

The present invention has been made in view of such problems of the conventional technology. And the objective of this invention provides the microbial fuel cell which can suppress the influence of oxygen in the negative electrode vicinity, and can perform the electric power generation by an anaerobic microorganism efficiently, and the liquid processing unit using the said microbial fuel cell. There is.

In order to solve the above-described problems, a microbial fuel cell according to the first aspect of the present invention includes an electrolyte, a positive electrode composed of a gas diffusion electrode immersed in the electrolyte and exposed at least partially in the gas phase, A negative electrode which is immersed in the liquid and holds anaerobic microorganisms. And in the flow path of electrolyte solution, a negative electrode is provided in the upstream at the time of electrolyte solution flow, and a positive electrode is provided in the downstream rather than a negative electrode.

A liquid processing unit according to the second aspect of the present invention includes the above-described microbial fuel cell.

FIG. 1 is a perspective view showing an example of a microbial fuel cell according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line AA in FIG. FIG. 3 is an exploded perspective view showing a positive electrode, a cassette base material, and a plate member in the microbial fuel cell. FIG. 4 is a cross-sectional view showing another example of the microbial fuel cell according to the embodiment of the present invention. FIG. 5 is a cross-sectional view showing another example of the microbial fuel cell according to the embodiment of the present invention.

Hereinafter, the microbial fuel cell and the liquid processing unit according to this embodiment will be described in detail. In addition, the dimension ratio of drawing is exaggerated on account of description, and may differ from an actual ratio.

[Microbial fuel cell]
A microbial fuel cell 100 according to this embodiment includes a fuel cell unit 1 as shown in FIGS. 1 and 2. The fuel cell unit 1 includes a positive electrode 10 and a negative electrode 20.

As shown in FIG. 3, the positive electrode 10 is laminated on the cassette base material 30. The cassette base material 30 is a U-shaped frame member along the outer peripheral portion of the surface 10 a of the positive electrode 10, and the upper portion is open. That is, the cassette base material 30 is a frame member in which the bottom surfaces of the two first columnar members 31 are connected by the second columnar members 32. As shown in FIG. 2, the side surface 33 of the cassette base material 30 is joined to the outer peripheral portion of the surface 10 a of the positive electrode 10, and the side surface 34 opposite to the side surface 33 is the outer periphery of the surface 40 a of the plate member 40. It is joined to the part.

As shown in FIG. 2, the fuel cell unit 1 including the positive electrode 10, the negative electrode 20, the cassette base material 30, and the plate member 40 is disposed inside the waste water tank 60 so that a gas phase 50 communicating with the atmosphere is formed. Is done. An electrolytic solution 70 that is a liquid to be treated is held inside the waste water tank 60, and the positive electrode 10 and the negative electrode 20 are immersed in the electrolytic solution 70.

As will be described later, the positive electrode 10 includes a water-repellent water-repellent layer 11, and the plate member 40 is made of a flat plate material that does not transmit the electrolytic solution 70. The side surface 33 of the cassette base material 30 is joined to the outer peripheral portion of the water repellent layer 11, and the side surface 34 is joined to the outer peripheral portion of the plate member 40. Therefore, the electrolytic solution 70 held in the waste water tank 60 is separated from the inside of the cassette base material 30, and the internal space formed by the positive electrode 10, the cassette base material 30 and the plate member 40 becomes a gas phase 50. Yes. The microbial fuel cell 100 is configured such that the gas phase 50 is opened to the outside air, or air is supplied to the gas phase 50 from the outside by, for example, a pump. As shown in FIG. 2, the positive electrode 10 and the negative electrode 20 are electrically connected to an external circuit 80, respectively.

(Positive electrode)
The positive electrode 10 according to this embodiment has a function of causing hydrogen ions and electrons generated by the negative electrode 20 to react with oxygen in the gas phase 50. For this reason, the positive electrode 10 of the present embodiment is not particularly limited as long as it has such a function.

As shown in FIG. 2, the positive electrode 10 according to the present embodiment includes a gas diffusion electrode including a water repellent layer 11 and a gas diffusion layer 12 stacked to be in contact with the water repellent layer 11. By using such a thin plate-like gas diffusion electrode, oxygen in the gas phase 50 can be easily supplied to the catalyst in the positive electrode 10.

The water repellent layer 11 in the positive electrode 10 is a layer having both water repellency and oxygen permeability. The water repellent layer 11 is configured to allow oxygen to move from the gas phase to the liquid phase while favorably separating the gas phase and the liquid phase in the electrochemical system in the fuel cell unit 1. That is, the water-repellent layer 11 can suppress the movement of the electrolytic solution 70 toward the gas phase 50 while allowing oxygen in the gas phase 50 to pass through and moving to the gas diffusion layer 12. In addition, "separation" here means physical interruption | blocking.

The water repellent layer 11 is in contact with the gas phase 50 containing oxygen, and diffuses oxygen in the gas phase 50. In the configuration shown in FIGS. 1 and 2, the water repellent layer 11 supplies oxygen to the gas diffusion layer 12 substantially uniformly. Therefore, the water repellent layer 11 is preferably a porous body so that the oxygen can be diffused. In addition, since the water repellent layer 11 has water repellency, it can suppress that the pores of a porous body are obstruct | occluded by dew condensation etc. and oxygen diffusibility falls. In addition, since the electrolyte solution 70 hardly penetrates into the water-repellent layer 11, oxygen can be efficiently circulated from the surface in contact with the gas phase 50 to the surface facing the gas diffusion layer 12 in the water-repellent layer 11. It becomes.

The water repellent layer 11 is preferably formed in a sheet shape from a woven fabric or a non-woven fabric. The material constituting the water repellent layer 11 is not particularly limited as long as it has water repellency and can diffuse oxygen in the gas phase 50. Examples of the material constituting the water repellent layer 11 include polyethylene, polypropylene, polybutadiene, nylon, polytetrafluoroethylene (PTFE), ethyl cellulose, poly-4-methylpentene-1, butyl rubber, silicone, and polydimethylsiloxane (PDMS). At least one selected from the group consisting of: Since these materials are easy to form a porous body and also have high water repellency, they can suppress clogging of pores and improve gas diffusibility. The water repellent layer 11 preferably has a plurality of through holes in the stacking direction X of the water repellent layer 11 and the gas diffusion layer 12.

The water repellent layer 11 may be subjected to a water repellent treatment using a water repellent as necessary in order to enhance water repellency. Specifically, a water repellent such as polytetrafluoroethylene may be attached to the porous body constituting the water repellent layer 11 to improve water repellency.

The gas diffusion layer 12 in the positive electrode 10 preferably includes a porous conductive material and a catalyst supported on the conductive material. The gas diffusion layer 12 may be composed of a porous and conductive catalyst. By providing the positive electrode 10 with such a gas diffusion layer 12, electrons generated by a local battery reaction described later can be conducted between the catalyst and the external circuit 80. That is, as will be described later, a catalyst is supported on the gas diffusion layer 12, and the catalyst is an oxygen reduction catalyst. Then, the electrons move from the external circuit 80 to the catalyst through the gas diffusion layer 12, whereby the oxygen reduction reaction by oxygen, hydrogen ions, and electrons can be advanced by the catalyst.

In the positive electrode 10, in order to ensure stable performance, it is preferable that oxygen permeate the water-repellent layer 11 and the gas diffusion layer 12 efficiently and be supplied to the catalyst. Therefore, the gas diffusion layer 12 is preferably a porous body having a large number of pores through which oxygen passes from the surface facing the water repellent layer 11 to the opposite surface. The shape of the gas diffusion layer 12 is particularly preferably a three-dimensional mesh. Such a mesh shape makes it possible to impart high oxygen permeability and conductivity to the gas diffusion layer 12.

In the positive electrode 10, the water repellent layer 11 is preferably bonded to the gas diffusion layer 12 via an adhesive in order to efficiently supply oxygen to the gas diffusion layer 12. Thereby, the diffused oxygen is directly supplied to the gas diffusion layer 12, and the oxygen reduction reaction can be performed efficiently. The adhesive is preferably provided on at least a part between the water-repellent layer 11 and the gas diffusion layer 12 from the viewpoint of ensuring the adhesion between the water-repellent layer 11 and the gas diffusion layer 12. However, from the viewpoint of improving the adhesion between the water repellent layer 11 and the gas diffusion layer 12 and supplying oxygen to the gas diffusion layer 12 stably over a long period of time, the adhesive is used as the water repellent layer 11 and the gas diffusion layer. It is more preferable that it is provided on the entire surface between the two.

The adhesive preferably has oxygen permeability, and includes at least one selected from the group consisting of polymethyl methacrylate, methacrylic acid-styrene copolymer, styrene-butadiene rubber, butyl rubber, nitrile rubber, chloroprene rubber, and silicone. Resin can be used.

Here, the gas diffusion layer 12 of the positive electrode 10 in the present embodiment will be described in more detail. As described above, the gas diffusion layer 12 can be configured to include a porous conductive material and a catalyst supported on the conductive material.

The conductive material in the gas diffusion layer 12 can be composed of, for example, one or more materials selected from the group consisting of carbon-based substances, conductive polymers, semiconductors, and metals. Here, the carbon-based material means a material containing carbon as a constituent component. Examples of carbon-based materials include, for example, carbon powder such as graphite, activated carbon, carbon black, Vulcan (registered trademark) XC-72R, acetylene black, furnace black, Denka black, graphite felt, carbon wool, carbon woven cloth, etc. Examples thereof include carbon fibers, carbon plates, carbon paper, carbon disks, carbon cloth, graphite sheets, and carbon-based materials obtained by compression molding carbon particles. Examples of the carbon-based material also include fine-structured materials such as carbon nanotubes, carbon nanohorns, and carbon nanoclusters.

Conductive polymer is a general term for conductive polymer compounds. As the conductive polymer, for example, a single monomer or a polymer of two or more monomers having aniline, aminophenol, diaminophenol, pyrrole, thiophene, paraphenylene, fluorene, furan, acetylene, or a derivative thereof as a structural unit. Can be mentioned. Specifically, examples of the conductive polymer include polyaniline, polyaminophenol, polydiaminophenol, polypyrrole, polythiophene, polyparaphenylene, polyfluorene, polyfuran, and polyacetylene. Examples of the metal conductive material include stainless steel mesh and foam metal. In consideration of availability, cost, corrosion resistance, durability, and the like, the conductive material is preferably a carbon-based substance.

The shape of the conductive material is preferably a powder shape or a fiber shape. Further, the conductive material may be supported by a support. The support means a member that itself has rigidity and can give a certain shape to the gas diffusion electrode. The support may be an insulator or a conductor. When the support is an insulator, examples of the support include glass, plastic, synthetic rubber, ceramics, water-resistant or water-repellent treated paper, plant pieces such as wood pieces, bone pieces, animal pieces such as shells, and the like. . Examples of the porous structure support include porous ceramics, porous plastics, and sponges. When the support is a conductor, examples of the support include carbon materials such as carbon paper, carbon fiber, and carbon rod, metals, conductive polymers, and the like. When the support is a conductor, the support can also function as a current collector by disposing a conductive material carrying a carbon-based material on the surface of the support.

The catalyst in the gas diffusion layer 12 is a platinum-based catalyst, a carbon-based catalyst using iron or cobalt, a transition metal oxide-based catalyst such as partially oxidized tantalum carbonitride (TaCNO) and zirconium carbonitride (ZrCNO), tungsten Alternatively, a carbide catalyst using activated molybdenum, activated carbon, or the like can be used.

The catalyst in the gas diffusion layer 12 is preferably a carbon-based material doped with metal atoms. Although it does not specifically limit as a metal atom, Titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium It is preferably an atom of at least one metal selected from the group consisting of platinum, and gold. In this case, the carbon-based material exhibits excellent performance as a catalyst for promoting the oxygen reduction reaction. What is necessary is just to set suitably the quantity of the metal atom which carbonaceous material contains so that carbonaceous material may have the outstanding catalyst performance.

It is preferable that the carbon-based material is further doped with one or more nonmetallic atoms selected from nitrogen, boron, sulfur, and phosphorus. What is necessary is just to set suitably the quantity of the nonmetallic atom doped by the carbonaceous material so that carbonaceous material may have the outstanding catalyst performance.

The carbon-based material is based on a carbon source material such as graphite and amorphous carbon, for example, and the carbon source material is doped with a metal atom and one or more non-metal atoms selected from nitrogen, boron, sulfur and phosphorus. Can be obtained.

The combination of metal atoms and nonmetal atoms doped in the carbon-based material is appropriately selected. In particular, it is preferable that the nonmetallic atom contains nitrogen and the metallic atom contains iron. In this case, the carbon-based material can have particularly excellent catalytic activity. Note that the nonmetallic atom may be only nitrogen, and the metallic atom may be only iron.

The nonmetallic atom may contain nitrogen, and the metallic atom may contain at least one of cobalt and manganese. Also in this case, the carbon-based material can have a particularly excellent catalytic activity. The nonmetallic atom may be only nitrogen. Further, the metal atom may be only cobalt, only manganese, or only cobalt and manganese.

The shape of the carbon-based material is not particularly limited. For example, the carbon-based material may have a particulate shape or may have a sheet shape. The dimension of the carbon-based material having a sheet-like shape is not particularly limited. For example, the carbon-based material may have a minute dimension. The carbon-based material having a sheet shape may be porous. It is preferable that the porous carbon-based material having a sheet shape has a shape such as a woven fabric shape or a nonwoven fabric shape. Such a carbon-based material can constitute the gas diffusion layer 12 even without a conductive material.

The carbon-based material configured as a catalyst in the gas diffusion layer 12 can be prepared as follows. First, for example, a mixture containing a nonmetallic compound containing at least one nonmetal selected from the group consisting of nitrogen, boron, sulfur, and phosphorus, a metal compound, and a carbon source material is prepared. And this mixture is heated at the temperature of 800 degreeC or more and 1000 degrees C or less for 45 second or more and less than 600 second. Thereby, the carbonaceous material comprised as a catalyst can be obtained.

Here, as the carbon source material, for example, graphite or amorphous carbon can be used as described above. Further, the metal compound is not particularly limited as long as it is a compound containing a metal atom capable of coordinating with a nonmetal atom doped in the carbon source material. Metal compounds include, for example, metal chlorides, nitrates, sulfates, bromides, iodides, fluorides, etc., inorganic metal salts, organic metal salts such as acetates, inorganic metal salt hydrates, and organic metal salts At least one selected from the group consisting of hydrates can be used. For example, when graphite is doped with iron, the metal compound preferably contains iron (III) chloride. Moreover, when graphite is doped with cobalt, the metal compound preferably contains cobalt chloride. When the carbon source material is doped with manganese, the metal compound preferably contains manganese acetate. The amount of the metal compound used is preferably determined so that, for example, the ratio of the metal atom in the metal compound to the carbon source material is in the range of 5 to 30% by mass, and further this ratio is 5 to 20% by mass. More preferably, it is determined to be within the range.

As described above, the nonmetallic compound is preferably at least one nonmetallic compound selected from the group consisting of nitrogen, boron, sulfur and phosphorus. Non-metallic compounds include, for example, pentaethylenehexamine, ethylenediamine, tetraethylenepentamine, triethylenetetramine, ethylenediamine, octylboronic acid, 1,2-bis (diethylphosphinoethane), triphenyl phosphite, benzyldisal At least one compound selected from the group consisting of fido can be used. The amount of the nonmetallic compound used is appropriately set according to the amount of the nonmetallic atom doped into the carbon source material. The amount of the nonmetallic compound used is preferably determined so that the molar ratio of the metal atom in the metal compound to the nonmetallic atom in the nonmetallic compound is in the range of 1: 1 to 1: 2. More preferably, it is determined to be within the range of 1: 1.5 to 1: 1.8.

A mixture containing a nonmetallic compound, a metal compound, and a carbon source material when preparing a carbon-based material configured as a catalyst is obtained, for example, as follows. First, a carbon source material, a metal compound, and a nonmetal compound are mixed, and if necessary, a solvent such as ethanol is added to adjust the total amount. These are further dispersed by an ultrasonic dispersion method. Subsequently, after heating them at an appropriate temperature (for example, 60 ° C.), the mixture is dried to remove the solvent. Thereby, the mixture containing a nonmetallic compound, a metal compound, and a carbon source raw material is obtained.

Next, the obtained mixture is heated, for example, under a reducing atmosphere or an inert gas atmosphere. Thereby, a non-metallic atom is doped to a carbon source raw material, and also a metallic atom is doped by the coordinate bond of a non-metallic atom and a metallic atom. The heating temperature is preferably in the range of 800 ° C. to 1000 ° C., and the heating time is preferably in the range of 45 seconds to less than 600 seconds. Since the heating time is short, the carbon-based material is efficiently produced, and the catalytic activity of the carbon-based material is further increased. In the heat treatment, the temperature rising rate of the mixture at the start of heating is preferably 50 ° C./s or more. Such rapid heating further improves the catalytic activity of the carbonaceous material.

In addition, the carbon-based material may be further acid cleaned. For example, the carbon-based material may be dispersed in pure water with a homogenizer for 30 minutes, and then the carbon-based material may be placed in 2M sulfuric acid and stirred at 80 ° C. for 3 hours. In this case, elution of the metal component from the carbon-based material can be suppressed.

By such a production method, a carbon-based material having a significantly low content of inert metal compound and metal crystal and high conductivity can be obtained.

In the gas diffusion layer 12, the catalyst may be bound to the conductive material using a binder. That is, the catalyst may be supported on the surface of the conductive material and inside the pores using a binder. Thereby, it can suppress that a catalyst detaches | leaves from an electroconductive material and an oxygen reduction characteristic falls. As the binder, for example, at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), and ethylene-propylene-diene copolymer (EPDM) is preferably used. Moreover, it is also preferable to use NAFION (registered trademark) as a binder.

(Negative electrode)
The negative electrode 20 in the present embodiment carries a microbe described later and further has a function of generating hydrogen ions and electrons from at least one of an organic substance and a nitrogen-containing compound in the electrolytic solution 70 by the catalytic action of the microbe. For this reason, the negative electrode 20 of the present embodiment is not particularly limited as long as it has such a function.

The negative electrode 20 of the present embodiment has a structure in which microorganisms are supported on a conductive sheet having conductivity. As the conductor sheet, it is possible to use at least one selected from the group consisting of a porous conductor sheet, a woven conductor sheet, and a nonwoven conductor sheet. The conductor sheet may be a laminate in which a plurality of sheets are laminated. By using such a sheet having a plurality of pores as the conductor sheet of the negative electrode 20, hydrogen ions generated in the local battery reaction described later easily move toward the positive electrode 10, and the rate of the oxygen reduction reaction is increased. It becomes possible to raise. From the viewpoint of improving ion permeability, the conductor sheet of the negative electrode 20 preferably has a space (void) continuous in the stacking direction X, that is, in the thickness direction.

The conductor sheet may be a metal plate having a plurality of through holes in the thickness direction. Therefore, as a material constituting the conductor sheet of the negative electrode 20, for example, at least one selected from the group consisting of conductive metals such as aluminum, copper, stainless steel, nickel and titanium, carbon paper, and carbon felt is used. be able to.

A graphite sheet may be used as the conductor sheet of the negative electrode 20. The negative electrode 20 preferably contains graphite, and the graphene layers in the graphite are preferably arranged along a plane in the direction YZ perpendicular to the stacking direction X. By arranging the graphene layers in this way, the conductivity in the direction YZ perpendicular to the stacking direction X is improved as compared with the conductivity in the stacking direction X. Therefore, the electrons generated by the local battery reaction of the negative electrode 20 can be easily conducted to the external circuit 80, and the efficiency of the battery reaction can be further improved.

The above graphite sheet can be obtained as follows. First, natural graphite is chemically treated with an acid to form an insert between the graphite graphene layers. Next, this is rapidly heated at a high temperature to obtain expanded graphite in which the graphene interlayer is pushed and expanded by the gas pressure due to the thermal decomposition of the intercalated insert. Then, the expanded graphite is pressurized and roll-rolled to obtain a graphite sheet. When the graphite sheet obtained in this way is used as the conductor sheet of the negative electrode 20, the graphene layers in the graphite are arranged along the direction YZ perpendicular to the stacking direction X. Therefore, the conductivity between the negative electrode 20 and the external circuit 80 can be increased, and the efficiency of the battery reaction can be further improved.

The microorganism supported on the negative electrode 20 is not particularly limited as long as it is a microorganism that decomposes an organic substance in the electrolyte solution 70 or a compound containing nitrogen. For example, an anaerobic microorganism that does not require oxygen for growth is used. preferable. Anaerobic microorganisms do not require air for oxidizing and decomposing organic substances in the electrolyte solution 70. Therefore, the electric power required for sending air can be significantly reduced. Moreover, since the free energy which microbes acquire is small, it becomes possible to reduce the amount of sludge generation.

The microorganism held in the negative electrode 20 is preferably an anaerobic microorganism, for example, an electricity producing bacterium having an extracellular electron transfer mechanism. Specifically, examples of the anaerobic microorganism include Geobacter genus bacteria, Shewanella genus bacteria, Aeromonas genus bacteria, Geothrix genus bacteria, and Saccharomyces genus bacteria.

Anaerobic microorganisms may be held on the negative electrode 20 by superimposing and fixing a biofilm containing anaerobic microorganisms on the negative electrode 20. A biofilm generally refers to a three-dimensional structure including a microbial population and an extracellular polymeric substance (EPS) produced by the microbial population. However, the anaerobic microorganisms may be held on the negative electrode 20 without depending on the biofilm. Moreover, the anaerobic microorganisms may be held not only on the surface of the negative electrode 20 but also inside.

The microbial fuel cell 100 includes an external circuit 80 that is electrically connected to the positive electrode 10 and the negative electrode 20 as shown in FIG. The external circuit 80 preferably includes a current control unit that controls a current value flowing between the negative electrode 20 and the positive electrode 10. For example, a resistor can be used as the current control unit.

(Position of positive electrode and negative electrode)
In the microbial fuel cell 100, as shown in FIG. 1, the positive electrode 10 and the negative electrode 20 are disposed so as to be stacked along the stacking direction X in the waste water tank 60. However, the positive electrode 10 and the negative electrode 20 are not in direct contact with each other and have a predetermined interval. The waste water tank 60 is provided with a waste water inlet 61 for supplying the electrolytic solution 70 to the waste water tank 60 and a waste water outlet 62 for discharging the treated electrolytic solution 70 from the waste water tank 60. Yes. The electrolytic solution 70 is continuously supplied through the wastewater inlet 61 and the wastewater outlet 62.

As shown in FIG. 1 and FIG. 2, in the wastewater tank 60, the negative electrode 20 is provided on the upstream side when the electrolyte 70 flows from the wastewater inlet 61 to the wastewater outlet 62. Is also provided downstream. That is, in the microbial fuel cell 100, the electrolytic solution 70 is supplied from the wastewater inlet 61 of the wastewater tank 60 and flows while contacting the surface of the negative electrode 20, and then flows while contacting the positive electrode 10 and then from the wastewater outlet 62. Discharged.

As described above, at least a part of the positive electrode 10 is exposed to the gas phase 50, and the water repellent layer 11 supplies oxygen to the gas diffusion layer 12 substantially uniformly. Therefore, the electrolytic solution 70 that has flowed in the vicinity of the positive electrode 10 comes into contact with oxygen, and oxygen is dissolved. If the positive electrode 10 is provided on the upstream side of the electrolytic solution 70 and the negative electrode 20 is provided on the downstream side of the positive electrode 10 in the waste water tank 60, the electrolytic solution 70 in which oxygen is dissolved by the positive electrode 10 reaches the negative electrode 20. Therefore, the vicinity of the negative electrode 20 becomes aerobic. As a result, the action of the anaerobic microorganisms supported on the negative electrode 20 becomes insufficient, which may reduce the power generation efficiency.

However, in the microbial fuel cell 100 of the present embodiment, in the flow path of the electrolyte solution 70, the negative electrode 20 is provided on the upstream side when the electrolyte solution 70 flows, and the positive electrode 10 is provided on the downstream side of the negative electrode 20. . Therefore, the electrolytic solution 70 in which oxygen is dissolved is difficult to reach the negative electrode 20, and the vicinity of the negative electrode 20 becomes anaerobic. As a result, the anaerobic microorganisms carried on the negative electrode 20 act effectively, and the power generation efficiency can be improved.

As described above, the positive electrode 10 and the negative electrode 20 are not in direct contact with each other and are arranged with a predetermined interval. That is, a predetermined interval is provided so that the electrolytic solution 70 in which oxygen is dissolved by the positive electrode 10 does not reach the negative electrode 20. Thus, the negative electrode 20 can be kept more anaerobically by separating the positive electrode 10 and the negative electrode 20 and moving the negative electrode 20 away from the positive electrode 10. Thereby, anaerobic power-generating bacteria can be fully utilized, and it is possible to efficiently generate electric energy while reducing the amount of generated sludge.

In order to make the vicinity of the negative electrode more anaerobic, as shown in FIG. 2, the shortest distance D between the positive electrode 10 and the negative electrode 20 is preferably 30 mm or more. The shortest distance D between the positive electrode 10 and the negative electrode 20 is more preferably 50 mm or more. Furthermore, the shortest distance D between the positive electrode 10 and the negative electrode 20 is particularly preferably 100 mm or more. When the distance of the closest part between the positive electrode 10 and the negative electrode 20 is 30 mm or more, the negative electrode 20 can be separated from the positive electrode 10 far away. As a result, since the vicinity of the negative electrode can be made more anaerobic, anaerobic power-generating bacteria can be effectively utilized.

Next, the operation of the microbial fuel cell 100 of this embodiment will be described. When the positive electrode 10 and the negative electrode 20 are immersed in the electrolytic solution 70, the gas diffusion layer 12 and the negative electrode 20 of the positive electrode 10 are immersed in the electrolytic solution 70, and at least a part of the surface 10 a of the water repellent layer 11 is exposed to the gas phase 50. To do.

During operation of the microbial fuel cell 100, an electrolyte solution 70 containing at least one of an organic substance and a nitrogen-containing compound is supplied to the negative electrode 20, and air or oxygen is supplied to the positive electrode 10. At this time, the air is continuously supplied through an opening provided in the upper part of the cassette base material 30.

In the positive electrode 10 shown in FIG. 2, air diffuses through the water repellent layer 11 and the gas diffusion layer 12. In the negative electrode 20, hydrogen ions and electrons are generated from at least one of the organic substance and the nitrogen-containing compound in the electrolytic solution 70 by the catalytic action of microorganisms. The generated hydrogen ions move to the positive electrode 10 side through the electrolytic solution 70. Further, the generated electrons move to the external circuit 80 through the conductor sheet of the negative electrode 20, and further move from the external circuit 80 to the gas diffusion layer 12 of the positive electrode 10. Hydrogen ions and electrons are combined with oxygen by the action of the catalyst supported on the gas diffusion layer 12 and consumed as water.

In the microbial fuel cell 100 of the present embodiment, the negative electrode 20 is installed upstream of the flow of the electrolyte solution 70, and the positive electrode 10 is installed downstream. This prevents the electrolytic solution 70 in which oxygen mixed from the positive electrode 10 is dissolved from reaching the negative electrode 20. Furthermore, by separating the negative electrode 20 far from the positive electrode 10, the vicinity of the negative electrode 20 can be made more anaerobic. Therefore, it is possible to obtain a microbial fuel cell 100 that can effectively use anaerobic power-generating bacteria and reduce the amount of generated sludge.

The negative electrode 20 according to this embodiment may be modified with, for example, an electron transfer mediator molecule. Alternatively, the electrolytic solution 70 in the waste water tank 60 may contain electron transfer mediator molecules. Thereby, the electron transfer from an anaerobic microorganism to the negative electrode 20 is accelerated | stimulated, and more efficient liquid processing is realizable.

Specifically, in the metabolic mechanism by anaerobic microorganisms, electrons are transferred between cells or with the final electron acceptor. When a mediator molecule is introduced into the electrolytic solution 70, the mediator molecule acts as a final electron acceptor of metabolism, and delivers received electrons to the negative electrode 20. As a result, it is possible to increase the rate of oxidative decomposition of the organic substance or the like in the electrolytic solution 70. Such an electron transfer mediator molecule is not particularly limited. As the electron transfer mediator molecule, for example, at least one selected from the group consisting of neutral red, anthraquinone-2,6-disulfonic acid (AQDS), thionine, potassium ferricyanide, and methylviologen can be used.

In the fuel cell unit 1 shown in FIG. 3, the cassette base 30 is open at the entire top, but may be partially opened if air (oxygen) can be introduced into the interior, It may also be closed.

In the microbial fuel cell 100 of this embodiment, as shown in FIG. 2, the positive electrode 10 and the negative electrode 20 can be electrically connected to an external circuit 80, respectively, and electric energy can be taken out. However, when there is no need to extract electric energy, the external circuit 80 may not be provided. That is, in the microbial fuel cell 100A, the positive electrode 10 and the negative electrode 20 may be short-circuited.

Specifically, in the microbial fuel cell 100A shown in FIG. 4, the positive electrode 10 and the negative electrode 20 are not in direct contact with each other and are arranged with a predetermined interval. Further, the negative electrode 20 is provided on the upstream side when the electrolytic solution 70 flows from the waste water inlet 61 to the waste water outlet 62, and the positive electrode 10 is provided on the downstream side of the negative electrode 20. A conductive member 90 is provided between a surface 10 b of the positive electrode 10 facing the negative electrode 20 and a surface 20 a of the negative electrode 20 facing the positive electrode 10, and the positive electrode 10 and the negative electrode 20 are separated by the conductive member 90. Electrically connected. In this way, also by short-circuiting the positive electrode 10 and the negative electrode 20, electrons generated in the negative electrode 20 move to the positive electrode 10, and an oxygen reduction reaction can be caused in the positive electrode 10.

The conductive member 90 is not particularly limited as long as the positive electrode 10 and the negative electrode 20 can be electrically connected in the state of being immersed in the electrolytic solution 70. For example, a carbon material can be used. As the carbon material, for example, at least one selected from the group consisting of graphite sheet, carbon paper, carbon cloth, and carbon felt can be used.

As described above, the

microbial fuel cells

100 and 100A of the present embodiment include the electrolytic solution 70, the positive electrode 10 including the gas diffusion electrode that is immersed in the electrolytic solution 70 and at least a part of which is exposed to the gas phase 50, and the electrolytic solution 70. And a negative electrode 20 that retains anaerobic microorganisms. In the flow path of the electrolytic solution 70, the negative electrode 20 is provided on the upstream side when the electrolytic solution 70 flows, and the positive electrode 10 is provided on the downstream side of the negative electrode 20. With such a configuration, the electrolyte solution 70 in which oxygen is dissolved becomes difficult to reach the negative electrode 20 and the vicinity of the negative electrode 20 becomes anaerobic. Therefore, the anaerobic microorganisms carried on the negative electrode 20 act effectively, and power generation Efficiency can be improved. As a result, it is possible to obtain a microbial fuel cell that can efficiently generate electrical energy while reducing the amount of generated sludge.

The microbial fuel cell of the present embodiment is not limited to the above-described configuration, and for example, as shown in FIG. 5, a configuration in which the positive electrode 10 and the negative electrode 20 are arranged in separate wastewater tanks may be used. Specifically, the microbial fuel cell 100B includes a first waste water tank 60A and a second waste water tank 60B. The first wastewater tank 60A is provided with a wastewater inlet 61 for supplying the electrolyte solution 70 to the first wastewater tank 60A, and the treated electrolyte solution 70 is supplied to the second wastewater tank 60B. A waste water outlet 62 for discharging from the two waste water tanks 60B is provided. A communication pipe 63 is provided between the first wastewater tank 60A and the second wastewater tank 60B so that the electrolytic solution 70 can flow.

The negative electrode 20 is disposed inside the first wastewater tank 60A, and the positive electrode 10 is disposed inside the second wastewater tank 60B. Further, the positive electrode 10 and the negative electrode 20 are electrically connected to the external circuit 80. In the configuration shown in FIG. 5, the two positive electrodes 10 face each other with a space therebetween, and further, a cassette base material 30 is provided between the positive electrodes 10 to hold them apart, so that a gas phase is formed inside. 50 is formed. That is, the side surface 33 and the side surface 34 of the cassette base material 30 are joined to the outer peripheral portion of the water repellent layer 11 in the positive electrode 10, thereby forming the gas phase 50 inside. The gas phase 50 is not filled with the electrolyte solution 70 and is open to the outside air, so that the air can be supplied to the water repellent layer 11.

In the microbial fuel cell 100B having the above-described configuration, first, the electrolytic solution 70 is continuously supplied from the wastewater inlet 61 of the first wastewater tank 60A and contacts the surface of the negative electrode 20. In the negative electrode 20, hydrogen ions and electrons are generated from at least one of the organic substance and the nitrogen-containing compound in the electrolytic solution 70 by an anaerobic microorganism. The generated hydrogen ions move together with the electrolytic solution 70 to the second wastewater tank 60B through the communication pipe 63. Further, the generated electrons move to the external circuit 80 through the conductor sheet of the negative electrode 20, and further move from the external circuit 80 to the gas diffusion layer 12 of the positive electrode 10. Hydrogen ions and electrons are combined with oxygen by the action of the catalyst supported on the gas diffusion layer 12 and consumed as water. Further, the electrolytic solution 70 purified by microorganisms is discharged to the outside through the waste water outlet 62.

Thus, in the microbial fuel cell 100B of this embodiment, the positive electrode 10 and the negative electrode 20 are arranged in separate wastewater tanks, the negative electrode 20 is installed upstream of the flow of the electrolytic solution 70, and the positive electrode 10 is installed downstream. is doing. Thereby, for example, a lid portion for preventing oxygen in the atmosphere from being dissolved in the electrolytic solution 70 can be provided on the upper portion of the first waste water tank 60A. As a result, since the vicinity of the negative electrode 20 can be made more anaerobic, it is possible to further activate the anaerobic microorganisms and further increase the power generation efficiency.

[Liquid processing unit]
Next, the liquid processing unit according to this embodiment will be described. The liquid processing unit of this embodiment includes the microbial fuel cell 100 described above.

As described above, the microbial fuel cell 100 of the present embodiment obtains electric energy by decomposing an organic compound with microorganisms. Therefore, using such a function, the microbial fuel cell 100 can be used as a liquid treatment unit for purifying waste water.

Specifically, in the microbial fuel cell 100, an electrolytic solution 70 containing at least one of an organic substance and a nitrogen-containing compound is supplied to the negative electrode 20 as a liquid to be treated. Then, carbon dioxide or nitrogen is generated together with hydrogen ions and electrons from at least one of the organic matter and the nitrogen-containing compound in the electrolytic solution 70 by metabolism of the microorganisms supported on the negative electrode 20.

For example, when the electrolytic solution 70 contains glucose as an organic substance, carbon dioxide, hydrogen ions, and electrons are generated by the following local battery reaction.
Negative electrode 20: C ₆ H ₁₂ O ₆ + 6H ₂ O → 6CO ₂ + 24H ⁺ + 24e ⁻
・ Positive electrode 10: 6O ₂ + 24H ⁺ + 24e ⁻ → 12H ₂ O
Moreover, when the electrolyte solution 70 contains ammonia as a nitrogen-containing compound, nitrogen, hydrogen ions, and electrons are generated by the following local battery reaction.
Negative electrode 20: 4NH ₃ → 2N ₂ + 12H ⁺ + 12e ⁻
Positive electrode 10: 3O ₂ + 12H ⁺ + 12e ⁻ → 6H ₂ O

Thus, by using the microbial fuel cell 100 as the liquid processing unit, the organic matter and the nitrogen-containing compound in the electrolytic solution 70 come into contact with the negative electrode 20 and are oxidatively decomposed, so that the electrolytic solution 70 can be purified. In addition, as described above, the electrolytic solution 70 is supplied to the wastewater tank 60, and further, the wastewater inlet 61 and the wastewater outlet 62 for discharging the treated electrolytic solution 70 from the wastewater tank 60 are provided. 70 can be continuously supplied to the wastewater tank 60. Therefore, the electrolytic solution 70 can be continuously brought into contact with the negative electrode 20 so that the electrolytic solution 70 can be processed efficiently.

The microbial fuel cell and the liquid processing unit of the present embodiment have been described above. However, the present embodiment is not limited to these, and various modifications are possible within the scope of the gist of the present embodiment. Specifically, in the drawing, the positive electrode 10 and the negative electrode 20 provided with the water repellent layer 11 and the gas diffusion layer 12 are formed in a rectangular shape. However, these shapes are not particularly limited, and can be arbitrarily changed depending on the size of the microbial fuel cell, desired purification performance, and the like. Further, the area of each layer can be arbitrarily changed as long as a desired function can be exhibited.

The entire contents of Japanese Patent Application No. 2016-096066 (application date: May 12, 2016) are incorporated herein by reference.

ADVANTAGE OF THE INVENTION According to this invention, the influence of the oxygen in the negative electrode vicinity can be suppressed, and the microbial fuel cell which can perform the electric power generation by an anaerobic microorganism efficiently, and the liquid processing unit using the said microbial fuel cell can be obtained. .

10 Positive electrode 20 Negative electrode 50 Gas phase 70

Electrolyte

100, 100A, 100B Microbial fuel cell D Shortest distance

Claims

An electrolyte,
A positive electrode comprising a gas diffusion electrode immersed in the electrolyte and at least partially exposed to the gas phase;
A negative electrode immersed in the electrolyte and holding anaerobic microorganisms;
With
In the electrolytic solution flow path, the negative electrode is provided on the upstream side when the electrolytic solution flows, and the positive electrode is provided on the downstream side of the negative electrode.
The microbial fuel cell according to claim 1, wherein the shortest distance between the positive electrode and the negative electrode is 30 mm or more.
The microbial fuel cell according to claim 1 or 2, wherein the shortest distance between the positive electrode and the negative electrode is 50 mm or more.
The microbial fuel cell according to any one of claims 1 to 3, wherein a shortest distance between the positive electrode and the negative electrode is 100 mm or more.
The microbial fuel cell according to any one of claims 1 to 4, wherein the positive electrode and the negative electrode are short-circuited.
A liquid processing unit comprising the microbial fuel cell according to any one of claims 1 to 5.