JP6666619B2 - 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, attention has been paid to technologies using renewable energy. One of the uses of renewable energy is energy recovery from biomass waste. One of the technologies for recovering energy from food waste is microbial fuel cells (MFCs). MFCs are devices that directly convert the chemical energy of organic substances into electrical energy using microorganisms, and can generate electric current by extracting electrons from the electrodes that are generated in the process of microorganisms decomposing and metabolizing organic substances (Figure 1). ). MFCs can generate electricity from organic wastewater and renewable biomass.

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 do not require a generator or gas treatment, and thus have the advantage of being able to be installed on any scale. 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 using a single-tank microbial fuel cell for wastewater treatment in a beer factory.

Feng, Y., Wang, X., Logan, B.E., and Lee, H .: Brewery wastewater treatment using air-cathode microbial fuel cells Applied Microbiology and Biotechnology, Vol. 78, p. 873-880, 2008.

  As shown in Non-Patent Document 1, wastewater from a factory that manufactures alcoholic beverages such as beer contains a relatively large amount of organic compounds. Can be used as fuel for batteries. Power generation by the microbial fuel cell using wastewater is very useful because wastewater can be treated simultaneously with power generation.

  However, not all wastewater can be used as fuel for microbial fuel cells. In particular, shochu lees generated in the process of producing shochu, which is often produced in the southern part of Japan, has a low pH, and is difficult to use as fuel for microbial fuel cells. Shochu lees are classified as waste acid as industrial waste and must be treated before disposal. As a treatment of shochu lees, a method requiring high energy and cost such as an activated sludge method is generally used. Therefore, a technology capable of processing shochu lees at lower energy cost is required.

  Therefore, an object of the present invention is to provide a power generation method using a microbial fuel cell that can efficiently generate power using shochu lees.

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 shochu lees, wherein the COD _{Cr of} the first fuel is in the range of 5,000 to 20,000 mg / L, and using the first fuel as a starting fuel. Operating the microbial fuel cell,
Including, methods.
(2) During operation, a second liquid containing at least shochu lees so that the COD _{Cr of the} fuel disposed in the fuel reactor of the microbial fuel cell is substantially maintained within the range of 5,000 to 20,000 mg / L. The method according to (1), further comprising adding the fuel described above to the fuel reaction tank.
(3) The method according to (1) or (2), wherein the first fuel and / or the second fuel is a shochu lees-containing solution containing shochu lees and water.
(4) A method for generating power using a microbial fuel cell,
Placing a fuel containing at least shochu lees in a fuel reaction tank of the microbial fuel cell, and the microbial fuel so that COD _{Cr of the} fuel is substantially maintained in the range of 5,000 to 20,000 mg / L. Driving batteries,
Including, methods.
(5) The method according to (4), wherein the fuel is a shochu lees-containing solution containing shochu lees and water.
(6) The method according to any one of (1) to (5), wherein the shochu lees are shochu lees generated in the process of producing shochu of potato, wheat, rice, or buckwheat.

  According to the present invention, it is possible to provide a power generation method using a microbial fuel cell capable of efficiently generating power using shochu lees.

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. It is a graph which shows an experimental result.

The present inventor has studied power generation by MFCs using shochu lees, and found that the use of a fuel obtained by diluting shochu lees so that COD _Cr (chemical oxygen demand) is within a predetermined range is effective. The present inventors have found that organic substances can be decomposed and a high output can be obtained, leading to the present invention.

That is, one embodiment of the power generation method using the microbial fuel cell according to the present invention is to prepare a fuel containing at least shochu lees (also referred to as a first fuel), wherein COD _{Cr of} the first fuel is Operating the microbial fuel cell using 5,000-20,000 mg / L, and using the first fuel as a starting fuel.

By using a fuel having a COD _Cr of 5,000 to 20,000 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 shochu lees-containing solution (also referred to as a first shochu lees-containing solution) containing shochu lees and water and having a COD _Cr of 5,000 to 20,000 mg / L. That is, the first fuel is preferably a shochu lees-containing solution in which shochu lees is mixed with water such that COD _Cr is in the range of 5,000 to 20,000 mg / L. The shochu lees-containing solution may contain additives as necessary in addition to water that functions as a diluent or a suspending agent. Examples of the additives include a nutrient that favors the growth of microorganisms and a pH adjuster.

COD _Cr of the first fuel (preferably the first shochu lees-containing solution containing shochu lees and water) which is the starting fuel is 5,000 to 20,000 mg / L, and may be 7,000 to 12,000 mg / L. preferable. As described above, the first fuel can be prepared, for example, by suspending shochu lees in water such that COD _Cr is in the range of 5,000 to 20,000 mg / L. 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)).

Further, a preferred embodiment of the present invention is arranged such that during operation (power generation), the COD _{Cr of the} fuel disposed in the fuel reaction tank of the microbial fuel cell is substantially maintained in the range of 5,000 to 20,000 mg / L. And adding a second fuel containing at least shochu lees (for example, a second shochu lees-containing solution containing shochu lees and water) into the fuel reaction tank (adjustment step).

That is, during operation, such that the COD _{Cr of the} fuel disposed in the fuel reaction tank (e.g., chamber) in which the fuel of the microbial fuel cell is held is substantially maintained in the range of 5,000 to 20,000 mg / L, A second fuel containing shochu lees 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 shochu lees to the taken out fuel. As the second fuel, shochu lees itself may be used, or a shochu lees-containing solution prepared as described above may be used. This adjustment step may be performed once or a plurality of times, and the number of times is not particularly limited. In another mode of the adjusting step, for example, while operating the microbial fuel cell, the COD _Cr of the fuel in the fuel reaction tank is substantially maintained in the range of 5,000 to 20,000 mg / L. It is also conceivable that the second fuel is allowed to flow into the fuel reaction tank at a predetermined flow rate while the fuel (shochu lees-containing solution disposed in the fuel reaction tank) is discharged from the fuel reaction tank at a predetermined flow rate. . As will be appreciated by those skilled in the art, in this embodiment also, the second fuel may be prepared using fuel removed from the fuel reactor.

Note that "COD _Cr is substantially kept within a predetermined range during operation" means that COD _Cr is always within the predetermined range during the entire operation period from the start of operation to the stop of operation. However, it does not mean that COD _Cr is kept within a predetermined range during a period in which high efficiency, which is an effect of the present invention, can be obtained. Specifically, the COD _Cr can preferably be kept within a predetermined range in more than 80% of the duration of the operating period, COD _Cr in more than 90% of the period of operation time is kept within a predetermined range Is more preferable, and it is further preferable that COD _Cr be kept within a predetermined range during 100% of the operation period. The time when COD _Cr deviates from the predetermined range includes, for example, before and after replenishing the second fuel.

The COD _Cr of the second fuel is not particularly limited, but is preferably in the range of 5,000 to 20,000 mg / L, and is in the range of 7,000 to 12,000 mg / L, like the first fuel. More preferably, it is within.

  It is preferable that the first fuel and / or the second fuel is a mixture containing shochu lees and water. By adjusting the shochu lees to an appropriate dilution ratio, an organic suspension suitable for processing and power generation can be obtained.

In another embodiment of the power generation method according to the present invention, a fuel containing at least shochu lees (for example, a solution containing shochu lees) is disposed in a fuel reaction tank of a microbial fuel cell, and COD _{Cr of the} fuel is 5,000. Operating the microbial fuel cell to be substantially maintained in the range of 20,00020,000 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 substantially kept in the range of 5,000 to 20,000 mg / L, as described above. As a method of operating so that the COD _{Cr of the} fuel (eg, shochu lees-containing solution) is kept in the range of 5,000 to 20,000 mg / L, as described in the above-described embodiment, for example, A method of adding a second fuel to the fuel reaction tank, and in some cases, a method of removing a predetermined amount of fuel already in the fuel reaction tank and then adding a predetermined amount of the second fuel to the fuel reaction tank. No. 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 within the range of 5,000 to 20,000 mg / L, There is also a method of newly flowing the second fuel 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 20,000 mg / L, and may be more than 20,000 mg / L. However, as much as possible, it is preferable that the COD _Cr of the fuel at the start of operation also falls within the range of 5,000 to 20,000 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.

  The raw material of shochu is not particularly limited, but is, for example, potato, barley, rice, or soba. That is, the shochu lees are, for example, shochu lees generated in the process of producing shochu of potato, wheat, rice or buckwheat. The type of shochu lees is not particularly limited, and examples thereof include mashed lees (raw lees, saccharified lees), excess yeast, and the like. Among these, raw lees are preferable. The shochu lees may be dried.

  The microorganism that supplies the electrons by decomposing the shochu lees is not particularly limited, and examples thereof include 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 microorganisms, microorganisms contained in shochu lees 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 sulfate-reducing bacteria, nitrate-reducing bacteria, 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. The cassette electrode (Cassette Electrode, CE) has a feature that the size can be easily changed, and large-scale power generation is possible by simultaneously using a plurality of CEs. 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 (shochu lees solution) Shochu lees of potato shochu collected from a brewery in the prefecture were used. Using ultrapure water, shochu lees was adjusted so that COD _Cr became 500mg / L, 1,000mg / L, 5,000mg / L, 10,000mg / L, 20,000mg / L, 70,000mg / L (stock solution). . COD _Cr was measured using a COD kit (TNT822 and DR2800, manufactured by Hach) (see Table 1 below).

(2) Preparation of cassette electrode The cassette electrode is shown in FIG. 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 shochu lees solution as a starting fuel was placed in a chamber (550 mL in internal volume as a battery), and then a cassette electrode was placed 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 the operation, the fuel (shochu lees 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 for a predetermined number of days. Thereafter, the COD _Cr removal rate (%) was calculated from the measurement results.

3. Results The above-described experiment was performed on six types of shochu lees-containing solutions, and the results (maximum power density) obtained are shown in Table 1. As shown in Table 1, in samples of Nos. 3 to 5, high maximum power densities were obtained. Regarding the COD removal efficiency, as shown in FIG. 4, high treatment efficiency was obtained in Nos. 3 to 5.

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 (6)

A method for generating power using a microbial fuel cell,
Providing at least a first fuel containing shochu lees, wherein the COD _{Cr of} the first fuel is in the range of 5,000 to 20,000 mg / L, and using the first fuel as a starting fuel. Operating the microbial fuel cell,
Including, methods. During operation, the second fuel containing at least shochu lees is provided so that COD _{Cr of the} fuel disposed in the fuel reaction tank of the microbial fuel cell is substantially maintained within the range of 5,000 to 20,000 mg / L. The method of claim 1, comprising adding into the fuel reactor.   The method according to claim 1 or 2, wherein the first fuel and / or the second fuel is a shochu lees-containing solution containing shochu lees and water. A method for generating power using a microbial fuel cell,
Placing a fuel containing at least shochu lees in a fuel reaction tank of the microbial fuel cell, and the microbial fuel so that COD _{Cr of the} fuel is substantially maintained in the range of 5,000 to 20,000 mg / L. Driving batteries,
Including, methods.   The method according to claim 4, wherein the fuel is a shochu lees-containing solution containing shochu lees and water.   The method according to any one of claims 1 to 5, wherein the shochu lees are shochu lees generated in the process of producing shochu of potato, wheat, rice, or buckwheat.

Images