JP6653934B2 - Power generation method using microbial fuel cell - Google Patents

Description

  The present invention relates to a power generation method using a microbial fuel cell.

  In recent years, the main energy production methods in Japan are thermal power generation and nuclear power generation. On the other hand, due to problems such as generation of greenhouse gases and radioactive contamination, technologies utilizing renewable energy have been receiving attention. One of the uses of renewable energy is energy recovery from biomass waste. One of the technologies for recovering energy from livestock waste such as livestock dung is Microbial Fuel Cells (MFCs). MFCs are devices that use microbial catabolic activity to generate electricity from organic wastewater and renewable biomass (Figure 1).

As shown in FIG. 1, when using a microbial fuel cell, a liquid 101 containing microorganisms and organic substances capable of growing under anaerobic conditions is disposed on the surface of an anode 102. In addition, air is caused to flow on the surface of the cathode 103, and the air is brought into contact with the cathode 103. At the anode 102, hydrogen ions (H ⁺ ) and electrons (e ⁻ ) are generated from the organic substance by the microorganism. The hydrogen ions pass through the ion-permeable membrane 104 and move to the cathode 103 side. When a closed circuit is formed by connecting the anode 102 and the cathode 103 to a load circuit with a conducting wire, a potential difference occurs between the anode 102 and the cathode 103, and power energy is divided by the product of the potential difference and the current flowing through the load circuit. Obtainable.

  Compared to methane fermentation, which is an energy recovery technology using anaerobic treatment like MFCs, MFCs have advantages such as not requiring a generator or gas treatment. However, MFCs also have the disadvantage of lower power output than other energy production technologies. In order to solve such problems, improvements in MFCs and studies using various fuels have been reported.

  For example, Non-Patent Document 1 discloses a method of arranging and operating dairy wastewater containing no solid matter in an annular single-layer microbial fuel cell.

Mardanpour, MM, Mohsen, NE, Tayebeh, B. and Ramin, S.,: Single chamber microbial fuel cell with spiral anode for dairy, Biosensors and Bioelectronics., Vol. 38, No. 1, pp. 264-269, 2012 .

  As shown in Non-Patent Document 1, when an organic waste is used as a fuel in general, by using an organic waste liquid containing only a liquid, a higher output is obtained as compared to a waste liquid containing a solid matter. It is known to be obtained. On the other hand, solid organic matter such as livestock waste has a high content of chemical energy per volume, and thus is considered to have high energy potential. Therefore, there is a need for a technology capable of generating power at high output by a microbial fuel cell using livestock waste such as livestock dung.

  Therefore, an object of the present invention is to provide a power generation method using a microbial fuel cell, which can obtain a relatively high output even when livestock waste is used.

Aspects of the present invention are as follows.
(1) A method for generating power using a microbial fuel cell,
Providing at least a first fuel containing livestock waste, wherein the first fuel has a COD _Cr of 5,000 to 10,000 mg / L, and the microorganism is prepared using the first fuel as a starting fuel. Driving the fuel cell,
Including, methods.
(2) During operation, the second fuel containing at least livestock waste is added to the fuel so that COD _{Cr of the} fuel placed in the fuel reactor of the microbial fuel cell is maintained at 5,000 to 10,000 mg / L. The method according to (1), which comprises adding the compound to a reaction vessel.
(3) The method according to (1) or (2), wherein the first fuel and / or the second fuel is a livestock waste-containing solution containing livestock waste and water.
(4) (1) or (1) wherein the first fuel and / or the second fuel is a livestock waste crushing solution prepared by treating a mixture containing livestock waste and water with a blender. The method according to 2).
(5) A method for generating power using a microbial fuel cell,
Placing at least a fuel containing livestock waste in a fuel reaction tank of the microbial fuel cell, and operating the microbial fuel cell so that COD _{Cr of the} fuel is maintained at 5,000 to 10,000 mg / L. ,
Including, methods.
(6) The method according to (5), wherein the fuel is a livestock waste-containing solution containing livestock waste and water.
(7) The method according to any one of (1) to (6), wherein the livestock waste is livestock dung.

  According to the present invention, it is possible to provide a power generation method using a microbial fuel cell, which can obtain a relatively high output even when using livestock waste.

It is a schematic diagram for explaining the power generation by the microbial fuel cell. FIG. 3 is a schematic exploded perspective view showing a configuration of a cassette electrode. FIG. 2 is a schematic diagram for explaining a configuration of a microbial fuel cell (CE-MFCs) used in the present example.

The present inventor has studied and found that in MFCs, the amount of power generation increases as the concentration of livestock waste increases, but if COD _Cr (chemical oxygen demand) of livestock waste is too high, organic matter can be efficiently removed. Was not decomposed and the output tended to decrease. Therefore, the present inventor has studied and found, surprisingly, that a high output can be obtained by using a fuel having COD _{Cr in} the range of 5,000 to 10,000 mg / L. Reached.

That is, one embodiment of the power generation method according to the present invention is to prepare a fuel containing at least livestock waste (also referred to as a first fuel), wherein the COD _{Cr of} the first fuel is 5,000 to 10,000 mg / L and operating the microbial fuel cell using the first fuel as a starting fuel. By using a fuel having a COD _Cr of 5,000 to 10,000 mg / L as a starting fuel (first fuel), a high output can be obtained. Also, the COD (chemical oxygen demand) removal rate can be kept relatively high, and can be set in a suitable range. Preferably, the first fuel is a livestock waste-containing solution (also referred to as a first livestock waste-containing solution) containing livestock waste and water and having a COD _Cr of 5,000 to 10,000 mg / L. That is, the first fuel is preferably a livestock waste-containing solution in which livestock waste is mixed with water so that COD _Cr is in the range of 5,000 to 10,000 mg / L. The livestock waste-containing solution may contain additives as necessary in addition to water as a diluent or suspending agent. Examples of the additives include a nutrient that favors the growth of microorganisms and a pH adjuster.

The COD _Cr of the first fuel (preferably the first livestock waste-containing solution), which is the starting fuel, is 5,000 to 10,000 mg / L, and preferably 6,000 to 9,000 mg / L. As described above, the first fuel can be prepared, for example, by suspending livestock waste (eg, livestock dung) in water such that COD _Cr is in the range of 5,000 to 10,000 mg / L. . If the livestock waste itself has a COD _{Cr in} the range of 5,000 to 10,000 mg / L, the livestock waste itself can be used as a fuel without any need for dilution work. COD _Cr (Chemical Oxygen Demand) is calculated by oxidizing the amount of oxidizable substances in a sample with an oxidizing agent under certain conditions and calculating the amount of oxygen required for oxidation from the amount of oxidizing agent used. (Unit: mg / L). In this example, COD _Cr was measured using a commercially available kit (COD kit (TNT822 and DR2800, manufactured by Hach)).

In addition, a preferred embodiment of the present invention provides at least a fuel cell disposed in the fuel reaction tank of the microbial fuel cell during operation (power generation) so that COD _Cr is maintained in a range of 5,000 to 10,000 mg / L. Adding a second fuel containing livestock waste (for example, a second livestock waste-containing solution) into the fuel reaction tank (adjusting step). That is, the second fuel is supplied such that the COD _{Cr of the} fuel disposed in the fuel reaction tank (for example, the chamber) in which the fuel of the microbial fuel cell is held is always kept in the range of 5,000 to 10,000 mg / L. It can be added into the fuel reactor. In some cases, a predetermined amount (e.g., half the amount of fuel contained in the container) of the fuel already in the fuel reaction tank is removed, and then a predetermined amount (e.g., an amount corresponding to the removed fuel) of the second fuel is removed. Fuel can be added to the fuel reactor. The second fuel may be prepared using a fuel taken out of the fuel reaction tank. For example, the second fuel can be prepared by adding livestock waste to the taken out fuel. As the second fuel, livestock waste itself may be used, or a livestock waste-containing solution prepared as described above may be used. This adjustment step may be performed once or plural times, and the number of times is not particularly limited. Further, as another mode of the adjusting step, for example, while operating the microbial fuel cell, a predetermined amount of COD _Cr of the fuel in the fuel reaction tank is maintained in the range of 5,000 to 10,000 mg / L. It is also conceivable to discharge the second fuel at a predetermined flow rate into the fuel reaction tank while discharging the fuel (the livestock waste-containing solution disposed in the fuel reaction tank) from the fuel reaction tank at a flow rate. As will be understood by those skilled in the art, also in this embodiment, the second fuel may be prepared using the fuel taken out of the fuel reactor.

The COD _Cr of the second fuel is not particularly limited, but is preferably in the range of 5,000 to 10,000 mg / L, and is in the range of 6,000 to 9,000 mg / L, like the first fuel. More preferably, it is within.

  Preferably, the first fuel and / or the second fuel is a livestock waste crushing solution prepared by treating a mixture containing livestock waste and water with a blender. By suspending livestock waste while crushing it in water with a blender, a uniform and easily decomposable organic substance suspension can be obtained. The rotation speed of the blender is not particularly limited, and can be appropriately selected.

In another embodiment of the power generation method according to the present invention, a fuel containing at least livestock waste (for example, a livestock waste-containing solution) is placed in a fuel reaction tank of a microbial fuel cell, and COD _{Cr of the} fuel is used. Operating the microbial fuel cell such that is maintained between 5,000 and 10,000 mg / L. The present invention is based on the finding that a high output can be obtained when the COD _{Cr of} the fuel is maintained in the range of 5,000 to 10,000 mg / L, as described above. As a method for maintaining the COD _{Cr of the} fuel (for example, a solution containing livestock waste) at 5,000 to 10,000 mg / L, as described in the above-described embodiment, a method in which the fuel is already in the fuel reaction tank is used. There is a method in which a predetermined amount of the second fuel is added to the fuel reaction tank after a fixed amount of the fuel is taken out. Alternatively, while operating the microbial fuel cell, while discharging the fuel from the fuel reaction tank at a predetermined flow rate, so that the COD _Cr of the fuel in the fuel reaction tank is maintained in the range of 5,000 to 10,000 mg / L, There is a method in which the second fuel is newly introduced into the fuel reaction tank at a predetermined flow rate. As described above, the second fuel added to the fuel reaction tank may be prepared using the fuel taken out of the fuel reaction tank. The COD _Cr of the fuel at the start of operation may not be in the range of 5,000 to 10,000 mg / L, and may be more than 10,000 mg / L. However, as much as possible, the COD _Cr of the fuel at the start of operation is preferably in the range of 5,000 to 10,000 mg / L.

  During operation of the microbial fuel cell, it is preferable to stir the fuel in order to maintain a uniform suspension of the fuel.

  Livestock waste is waste discharged in the livestock industry and the livestock product processing industry, and includes, for example, livestock dung, livestock carcass, demolition residues of livestock, internal organs, and feathers. Among these, livestock dung is preferred. The livestock droppings are not particularly limited, but include, for example, livestock droppings such as cows, horses, pigs, sheep, goats, and chickens. The livestock dung is preferably cow dung, pig dung or chicken dung, and more preferably cow dung. Livestock dung may include urine. Also, livestock waste (eg, livestock dung) may be dried. The livestock waste-containing solution (for example, a livestock dung-containing solution) is preferably a blended livestock dung crushing solution, and more preferably a cow dung crushing solution.

  The microorganism that supplies the electrons by decomposing the livestock waste is not particularly limited, but includes, for example, an anaerobic microorganism and an aerobic microorganism. The microorganism is preferably an anaerobic microorganism, and the operation is preferably performed under anaerobic conditions using an anaerobic microorganism. As the microorganism, a microorganism contained in livestock waste may be used, or may be added to fuel from outside.

  As the microorganism, a microorganism that does not terminate the electron transfer system in the cell membrane of the microorganism is desirable, and a microorganism that easily captures electrons outside the cell membrane with the negative electrode and catalyzes the electron transfer to the negative electrode is desirably used. Preferred microorganisms are sulfur-reducing bacteria, iron-reducing bacteria, manganese dioxide-reducing bacteria, and dechlorinating bacteria. As the microorganism, the genus Geobacter and the genus Shewanella are preferable.

  The microbial fuel cell used for power generation is not particularly limited, and for example, a conventionally known microbial fuel cell can be used. As the microbial fuel cell, for example, cassette-electrode microbial fuel cells (CE-MFCs) can be used. A cassette electrode (Cassette Electrode, CE) has a feature that its size can be easily changed, and large-scale power generation is possible by using a plurality of CEs at the same time. FIG. 2 shows a configuration example of the cassette electrode. The cassette electrode has a structure in which a cathode 203 and an anode 202 are integrated with an ion-permeable membrane (proton exchange membrane) 204 interposed therebetween. In FIG. 2, reference numeral 205 denotes an external resistor. A plurality of cassette electrodes can be inserted into the fuel reaction tank.

1. Experimental Method (1) Preparation of Fuel (Cow Dung Solution) Cow dung was collected at the Sumiyoshi field of Miyazaki University. 350 mL of ultrapure water was added to a predetermined amount of the collected cow dung, and crushed at a rotation speed of “High” for 120 seconds using a blender (Waring Blender 7011HS, manufactured by WARINGH). Thereafter, the mixture after the blender treatment was collected using 150 mL of ultrapure water while washing the blender to prepare a cow dung crushing solution. As the cow dung crushing solution, four types of samples prepared using different amounts of cow dung were respectively prepared (two samples per one type of concentration). When the COD _Cr of each cow dung crushing solution was measured with a COD kit (TNT822 and DR2800, manufactured by Hach), they were respectively 2938 mg / L, 6108 mg / L, 8625 mg / L, and 20900 mg / L (average of n = 2). (See Table 1 below).

(2) Preparation of cassette electrode The cassette electrode is shown in Fig. 2 with reference to the literature (Electricity generation from model organic wastewater in a cassette-electrode microbial fuel cell, Appl Microbiol Biotechnol, DOI 10.1007 / s00253-008-1516-0). The thing of the structure shown was produced. The cathode box is made of a plastic frame (4.2 x 22.5 cm, inner frame 3.0 x 19.5 cm). Further, the cathode box has two air holes (diameter: 3 mm), so that air can be taken into the cathode box. Cathodes (air cathodes) 203 are arranged on both sides of the cathode box, and the cathode 203 is bonded to the cathode box using epoxy resin. On the surface of the cathode 203 opposite to the cathode box, an anode (graphite felt anode) 202 (4.5 × 22.5 cm) is disposed via an ion-permeable membrane (proton exchange membrane) 204 (4.5 × 22.5 cm). .

(3) Operation of CE-MFCs A cow manure crushing solution as a starting fuel was placed in a chamber (550 mL internal volume as a battery), and then a cassette electrode was installed in the chamber. Next, the head space in the chamber was replaced with a mixed gas of N ₂ and CO ₂ (80:20), and the operation of CE-MFCs was started at 30 ° C. During operation, the fuel (cattle manure crushing solution) was constantly stirred (600 rpm). As a seeding source, 1.0 mL of MFCs fuel which had been used in operation of another apparatus in advance was used. Microorganisms that catalyze the transfer of electrons to the negative electrode grow in the fuel. Note that the external resistance was set to 470Ω during the running operation. The operation was performed for 11 days.

2. Analysis method (1) Maximum power density
The maximum power density of MFCs was calculated from the current value using a potentiostat.

(2) COD _Cr (chemical oxygen demand)
For the measurement of COD _Cr , a COD kit (TNT822 and DR2800, manufactured by Hach) was used. COD _Cr was measured before the operation of CE-MFCs (day 0) and after the operation was completed (day 11). Thereafter, the COD _Cr removal rate (%) was calculated from the measurement results.

3. Results The above experiment was performed on four types of cow dung crushing solutions, and the obtained results (maximum power density, COD removal rate) are shown in Table 1. As shown in Table 1, high maximum power densities were obtained in the samples of Nos. 2 and 3.

101 Liquid containing microorganisms and organic substances 102 Anode 103 Cathode 104 Ion-permeable membrane (proton exchange membrane)
202 Anode 203 Cathode 204 Ion permeable membrane (proton exchange membrane)
205 External resistance

Claims (8)

A method for generating power using a microbial fuel cell,
Providing at least a first fuel containing livestock dung , wherein the first fuel has a COD _Cr of 5,000 to 10,000 mg / L, and the microbial fuel using the first fuel as a starting fuel. Driving batteries,
Including, methods. During operation, a second fuel containing at least livestock dung is introduced into the fuel reactor so that COD _{Cr of the} fuel disposed in the fuel reactor of the microbial fuel cell is maintained at 5,000 to 10,000 mg / L. The method of claim 1, comprising adding. The method according to claim 1 or 2, wherein the first fuel and / or the second fuel is a livestock dung- containing solution containing livestock dung and water. The method according to claim 1 or 2, wherein the first fuel and / or the second fuel is a livestock dung crushing solution prepared by treating a mixture containing livestock dung and water with a blender. A method for generating power using a microbial fuel cell,
Placing at least a fuel containing livestock dung in the fuel reaction tank of the microbial fuel cell, and operating the microbial fuel cell so that COD _{Cr of the} fuel is maintained at 5,000 to 10,000 mg / L,
Including, methods. COD of fuel in the fuel reactor _Cr The method according to claim 5, wherein the microbial fuel cell is operated by adding further fuel containing at least livestock dung into the fuel reactor so that is maintained at 5,000 to 10,000 mg / L. Wherein the fuel is a livestock manure containing solution containing livestock manure and water, the method according to claim 5 or 6. The method according to any one of claims 1 to 7 , wherein the livestock dung is cow dung .

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