JP5828455B2 - Microbial fuel cell and microbial power generation method - Google Patents

Description

  The present invention relates to a microbial fuel cell and a microbial power generation method, and more particularly to a microbial fuel cell and a microbial power generation method using mud containing organic matter and anaerobic microorganisms.

  So-called sludge in which organic substances contained in industrial wastewater and household wastewater accumulate on the riverbed and the seabed together with mud is a big problem. For this reason, various methods for purifying sludge have been studied. A method for effectively utilizing sludge is also being studied. For example, making sludge into concrete or fertilizer is being studied. In addition, the production of methanol or hydrogen from sludge using microorganisms has also been studied.

  One method for effectively utilizing sludge using microorganisms is a microbial fuel cell that generates power by decomposing organic matter in sludge using microorganisms (see, for example, Patent Document 1). A microbial fuel cell causes microorganisms to decompose organic matter and generate electrons and protons. The generated electrons are collected by the negative electrode, transferred to the positive electrode through the circuit, and reacted with protons and oxygen to generate water. By rotating this cycle, power can be taken out. At the same time, organic substances are decomposed by microorganisms, so that sludge can be purified.

JP 2006-114375 A

  However, the conventional microbial battery has the following problems. Sludge is normally in a reduced state where oxygen is consumed, and oxygen must be supplied to the positive electrode. By providing the positive electrode in the aqueous layer, oxygen can be supplied to the positive electrode. In this case, it is necessary to efficiently move protons from the sludge layer to the aqueous layer. For this reason, an ion exchange membrane is usually provided between the sludge layer and the water layer. However, ion exchange membranes are expensive and increase the cost of microbial batteries.

  In addition, the potential difference generated between the positive electrode and the negative electrode is very small. In order to obtain a high voltage, it is conceivable to connect a plurality of microbial fuel cells in series, but simply connecting a plurality of positive electrodes and negative electrodes cannot be connected in series. In order to obtain a high voltage by connecting microbial fuel cells in series, it is necessary to form battery cells in which the positive electrodes and the negative electrodes are independent of each other. In order to obtain an independent battery cell, it is necessary to prepare a plurality of containers having electrodes and to put sludge into the container. Accordingly, it is necessary to collect and transfer sludge from the deposition site and manually put it into a plurality of containers. To automate this, it is necessary to construct a plant. At such a cost, power generation using sludge is not economical.

  In order to put power generation using sludge into practical use, it is not necessary to collect sludge from the deposition site or construct a plant, and it is necessary to make it possible to easily form a microbial fuel cell in a location where sludge is deposited. Is done.

  An object of the present invention is to solve the above-mentioned problems and to realize a microbial fuel cell that does not require operations such as collecting and transferring sludge.

  In order to achieve the above object, the present invention has a configuration in which a microbial fuel cell is embedded in a battery tube having a negative electrode and a positive electrode in a deposited sludge.

  Specifically, a microbial fuel cell according to the present invention comprises a battery body having an insulating holder, a negative electrode provided at the lower part of the holder and a positive electrode provided at the upper part, an organic substance and an anaerobic microorganism. A mud layer containing and a water layer present on the mud layer are provided, the negative electrode is disposed in the mud layer, and the positive electrode is disposed in the water layer.

  The microbial fuel cell of the present invention can be realized by simply burying the lower part of the battery body having the negative electrode and the positive electrode in the sludge depositing. Therefore, operations such as sludge collection and transfer are unnecessary, and a microbial fuel cell can be easily realized.

  In the microbial fuel cell of the present invention, the holding body is cylindrical, and the negative electrode and the positive electrode may be provided on the inner wall surface of the holding body, respectively. In this way, the microbial fuel cell can be easily installed at a place where sludge is accumulated. Further, even if a plurality of microbial fuel cells are installed adjacent to each other where sludge is accumulated, the negative electrodes do not conduct each other and can be connected in series.

  In the microbial fuel cell of the present invention, the water content ratio at the lower end portion of the battery cylinder in the mud layer may be less than 80%.

  In the microbial fuel cell of the present invention, there are a plurality of battery tubes, and the plurality of battery tubes may have a negative electrode and a positive electrode sequentially connected in series.

  In the microbial fuel cell of the present invention, the negative electrode and the positive electrode may each be provided on the outer surface of the holding body. With such a configuration, a microbial fuel cell can be realized at low cost.

  The microbial fuel cell of the present invention may further include carbon particles mixed in a portion where the negative electrode is disposed in the mud layer. In this case, the carbon particles may be bamboo charcoal.

  In the microbial fuel cell according to the present invention, the negative electrode comprises a carbon cloth attached to the inner wall surface of the separation cylinder, and the battery cylinder is a carbon layer formed on the inner wall surface of the separation cylinder so as to cover the carbon cloth. It is good also as a structure which has.

  The microbial fuel cell of the present invention may further include an oxygen consuming substance absorbent containing calcium oxide charged into the aqueous layer. In this case, the oxygen-consuming substance absorber may be a coal ash granulated product.

  The microbial fuel cell of the present invention may further include a proton transfer promoting material containing calcium oxide mixed in the mud layer.

  The power supply device according to the present invention includes the microbial fuel cell of the present invention and an auxiliary battery connected in series with the microbial fuel cell. In this way, a higher voltage can be easily obtained than in the case of a microbial fuel cell alone. Also, the life of the battery is much longer than when there is no partial biofuel cell.

  The microbial power generation method according to the present invention includes a step of preparing a battery body having a holding body made of an insulating material, a negative electrode provided at a lower portion of an inner wall surface of the holding body, and a positive electrode provided at an upper portion; In which a negative electrode is buried in a mud layer containing organic matter and anaerobic microorganisms, and the positive electrode is positioned in a water layer present on the mud layer.

  According to the microbial power generation method of the present invention, power generation is performed simply by filling the sludge in which the battery body is deposited, the positive electrode is located in the water layer existing on the sludge, and the negative electrode is buried in the sludge deposited. be able to. Therefore, microbial power generation can be easily performed at a place where sludge is accumulated.

  In the microbial power generation method of the present invention, the holder may be cylindrical, and the negative electrode and the positive electrode may be provided on the inner wall surface of the holder, respectively. In this way, even when a plurality of battery main bodies are embedded in the sludge, since conduction between the negative electrodes can be suppressed, they can be connected in series and a desired voltage can be obtained.

  In the microbial power generation method of the present invention, a plurality of battery tubes may be prepared, and the negative electrode and the positive electrode may be sequentially connected in series in the plurality of battery tubes.

  In the microbial power generation method of the present invention, the negative electrode and the positive electrode may each be provided on the outer surface of the holding body.

  The microbial power generation method of the present invention may have a configuration in which an auxiliary battery and a load are connected in series between the positive electrode and the negative electrode.

  According to the microbial fuel cell of the present invention, it is possible to realize a microbial fuel cell that can easily extract practical electric power.

1 is a perspective view showing a microbial fuel cell according to a first embodiment. It is a perspective view which shows the example of installation of the microbial fuel cell which concerns on 1st Embodiment. It is a graph which shows the relationship between the moisture content of sludge and connection efficiency. It is a graph which shows the relationship between the current density at the time of connecting a microbial fuel cell in series, and a voltage. It is a graph which shows the relationship between the addition amount of the carbon particle in a sludge layer, and the total electric current amount. It is a graph which shows the particle size distribution of the added carbon particle. It is a perspective view which shows the example which provided the carbon layer which covers a negative electrode. It is a perspective view which shows the example which injected | thrown-in the particle | grains containing a calcium oxide in the water layer. It shows the effect of adding particles containing calcium oxide, (a) is a graph showing the concentration of ammonia and hydrogen sulfide, (b) is a graph showing the concentration of (CH _{3) 2} S. It is a graph which shows the increase in the dissolved oxygen concentration by addition of the particle | grains containing a calcium oxide. It is a graph which shows the change of the electrode potential by addition of calcium oxide. It is a table | surface which shows the example of the electromotive force of the obtained microbial fuel cell. It is a perspective view which shows the modification of a battery cylinder. It is a block diagram which shows the power supply device which concerns on 2nd Embodiment. It is a graph which shows the characteristic of the power supply device which concerns on 2nd Embodiment. It is the schematic which shows the LED lamp using a microbial fuel cell.

  In the present disclosure, sludge refers to mud that contains organic matter and anaerobic microorganisms and is in a reduced state. It is common to deposit on the bottom of rivers, swamps, ponds, lakes, seas, etc., but it does not matter where they are deposited. Moreover, the kind of organic substance and anaerobic microorganisms, etc. which are contained are not ask | required. Mud refers to a soil in which fine particles such as clay and silt contain water.

(First embodiment)
As shown in FIG. 1, the microbial fuel cell 100 according to this embodiment includes a battery main body 111, and a sludge layer 113 and a water layer 114 that fill the inside of the battery main body 111. The battery body 111 includes a cylindrical holder 121 made of an insulating material, a negative electrode (anode) 122 attached to the lower part of the inner wall surface of the holder 121, and a positive electrode (an anode) attached to the upper part of the inner wall surface ( Cathode) 123. The negative electrode 122 is disposed in the sludge layer 113, and the positive electrode 123 is disposed in the aqueous layer 114. Conductive wires 125 are connected to the negative electrode 122 and the positive electrode 123, respectively. The conducting wire 125 may be nickel or platinum. The electric power generated by the microbial fuel cell 100 can be used in the load 101 connected to the conducting wire 125.

  The negative electrode 122 and the positive electrode 123 which are electrodes may be formed using a conductive material, but carbon is preferable because of its high effect of collecting electrons. In the case of using carbon as the negative electrode 122 and the positive electrode 123, it is easy to increase the surface area, so that a carbon cloth made of carbon fiber or the like may be used. In the case of using a carbon cloth, there is an advantage that the conductive wire 125 can be sewn and the connection becomes easy.

  The holding body 121 may be any material as long as it is an insulating material. For example, the holding body 121 may be a resin pipe such as vinyl chloride, acrylic, polyethylene, or polypropylene. In particular, a vinyl chloride pipe is preferable because it is durable and inexpensive.

  The battery body 111 of the present embodiment has a cylindrical shape with an open lower end. Therefore, as shown in FIG. 2, the battery body 111 is embedded so that the negative electrode 122 is embedded in the sludge 103 deposited on the riverbank or the coast, and the upper part of the battery body 111 is filled with water so that the positive electrode 123 is immersed. Only by this, the microbial fuel cell 100 can be realized. The water filling the upper part of the battery body 111 may be fresh water or salt water.

  In the microbial fuel cell 100 of the present embodiment, the water layer 114 is in contact with the sludge layer 113, and no ion exchange membrane or the like is provided between the sludge layer 113 and the water layer 114. However, since ion exchange is efficiently performed at the interface between the sludge layer 113 and the water layer 114, protons can be efficiently moved from the sludge layer 113 into the water layer 114 without providing a proton exchange membrane.

  The electromotive voltage that can be generated by one microbial fuel cell 100 is about 0.3 V to about 0.6 V when viewed from the redox potential of sludge. However, if a plurality of battery main bodies 111 are arranged as shown in FIG. 2 and the negative electrode 122 and the positive electrode 123 are sequentially connected, a voltage necessary for driving the load 101 can be obtained.

  Since the holding body 121 has a cylindrical shape with the lower end opened, when the moisture content of sludge in the lower part of the battery main body 111 is high and the conductivity is high, the negative electrodes 122 are connected to each other, and the microbial fuel cell 100 is connected in series. Even if connected, the voltage cannot be increased. However, as a result of examination by the inventors of the present application, if the water content ratio in the lower part of the battery body 111 is lower than at least about 80%, the microbial fuel cells 100 can be made independent by the cylindrical holders 121, respectively. It became clear that the voltage can be added by connecting the batteries 100 in series.

  FIG. 3 shows the relationship between the moisture content of sludge at the lower end of the battery body 111 and the connection efficiency when the microbial fuel cells 100 are connected in series. The connection efficiency W is W = Vsum / (V1 + V2). However, Vsum is a voltage obtained when two microbial fuel cells 100 are connected in series, and V1 and V2 are voltages obtained by a single microbial fuel cell 100, respectively.

  As shown in FIG. 3, even when the water content ratio is 70%, an increase in voltage is recognized and the connection efficiency is not high, but it is clear that the microbial fuel cells 100 can be connected in series. When the water content is lower than about 50%, the connection efficiency exceeds 80%. Therefore, in the case of series connection, the water content is preferably about 50% or less.

  The moisture content of the accumulated sludge tends to be higher at the surface and lower as it becomes deeper. For this reason, the moisture content of sludge in the lower part of the battery main body 111 can be controlled by adjusting the depth in which the battery main body 111 is embedded.

  Actually, when the moisture content of the accumulated sludge was measured, it was about 82% at a position 25 cm from the surface and about 54% at a position 40 cm. The microbial fuel cell 100 was created by embedding the battery body 111 in this sludge, and it was verified whether serial connection was possible. The holding body 121 was an acrylic pipe having an inner diameter of 15 cm and a height of 50 cm. Each of the negative electrode 122 and the positive electrode 123 is a 10 cm square carbon cloth, the negative electrode 122 is provided so that the lower end is about 2 cm above the lower end of the holding body 121, and the upper end of the positive electrode 123 is about 2 cm below the upper end of the holding body 121 It was provided so that.

  The voltage when the lower end portion of the battery body 111 was 25 cm deep from the surface of the accumulated sludge was about 0.41 V, and the voltage when the height was 40 cm was about 0.39 V. In this case, the connection efficiencies were about 50% and about 85%, respectively. Therefore, the individual microbial fuel cells 100 can be made independent and connected in series by embedding the battery body 111 in the sludge deposited so that the moisture content of the sludge at the lower end of the battery body 111 is at least less than 80%. It becomes possible. It is preferable that the lower end portion of the battery main body 111 is at a deeper position and the moisture content of the sludge at the lower end portion of the battery main body 111 is about 50% or less because the connection efficiency can be improved.

  FIG. 4 shows the relationship between current density and voltage when a predetermined number of microbial fuel cells 100 created under the same conditions are connected in series. It is clear that the voltage can be added and the current can be taken out by connecting the microbial fuel cells 100 in series. For example, when lighting a light emitting diode, electric power of 0.2 W or more is required. Even in such a power region, the voltage can be added by serial connection.

  Electric power can be taken out if the negative electrode 122 is disposed in the sludge layer 113, but in order to obtain a microbial fuel cell that can be connected in series, it is necessary to provide it above the lower end of the holding body 121. Further, it is preferable that the portion near the negative electrode 122 in the sludge layer 113 has a high water content to some extent. For this reason, the negative electrode 122 is preferably provided at a position where the lower end is separated from the lower end of the holding body 121 by about 2 cm or more. The positive electrode 123 is preferably provided at a position where the oxygen concentration is high in the aqueous layer 114, and is preferably provided near the upper end of the aqueous layer 114. For this reason, when the holder 121 is filled with water, it is disposed so that the upper end of the positive electrode 123 is positioned about 2 cm from the upper end of the holder 121 so that the holder 121 is completely submerged in water and positioned as high as possible. That's fine.

  The sludge layer 113 can be used as it is deposited. However, an additive may be added to the sludge layer 113. For example, by adding carbon particles to the sludge layer 113, the effective area of the negative electrode 122 can be increased, and the current that can be extracted from the microbial fuel cell 100 can be improved. Any carbon particles may be added to the sludge layer 113, but pulverized bamboo charcoal is preferable in consideration of handling and cost.

  FIG. 5 shows the relationship between the mixing ratio of bamboo charcoal into sludge and the total amount of current extracted from the microbial fuel cell 100. In FIG. 5, the horizontal axis indicates the ratio (wt%) of the added weight of bamboo charcoal to the dry weight of sludge. The vertical axis represents the total amount of current when the load resistance is 100Ω and the current is supplied for one week. Bamboo charcoal used was pulverized with a mortar. The result of measuring the particle size distribution of the added bamboo charcoal with a laser diffraction particle size distribution system is shown in FIG.

  As shown in FIG. 5, the total current amount increased greatly by adding carbon particles. By adding about 10 wt% of carbon particles, the total amount of current increased to about double that when no carbon particles were added. Furthermore, when about 30 wt% was added, the total current amount could be improved to about four times that when no addition was made.

  When the microbial fuel cell 100 is directly installed in a place where sludge is deposited, it may be difficult to mix carbon particles in the sludge. In this case, as shown in FIG. 7, a carbon layer 126 made of carbon particles may be formed on the inner wall surface of the holding body 121 so as to cover the negative electrode 122. Also in this case, the effective area of the negative electrode 122 can be increased. The carbon layer 126 may be formed by any method. For example, the carbon layer 126 may be formed by attaching carbon particles to the inner wall surface of the holding body 121 via a double-sided tape or an adhesive layer. Note that the carbon layer 126 may be provided even when carbon particles are mixed in the sludge.

  The effective area of the negative electrode 122 can also be increased by embedding massive or rod-like carbon in the sludge layer 113 around the negative electrode 122 so as to be in contact with the negative electrode 122. The lump or rod-shaped carbon may be bamboo charcoal that has not been crushed. It is also possible to use a porous bamboo charcoal block or the like obtained by crushing bamboo charcoal and then solidifying it into a block shape again. Since the porous bamboo charcoal block has a large surface area, the effect of increasing the effective area of the negative electrode 122 is increased.

  When carbon particles are added to the sludge, oxygen-consuming substances such as hydrogen sulfide may be generated from the sludge. When the oxygen consuming substance is generated, the dissolved oxygen concentration in the water layer 114 is lowered, so that the amount of oxygen supplied to the positive electrode 123 is lowered and the power generation efficiency is lowered. For this reason, as shown in FIG. 8, it is preferable to introduce an oxygen-consuming substance absorber 116 for absorbing the oxygen-consuming substance into the water layer 114. The oxygen-consuming substance absorbing material 116 may be any material that can absorb oxygen-consuming substances such as hydrogen sulfide, but may be particles containing calcium. Coal ash granulate is in the form of beads containing about 15 wt% calcium oxide, and is preferable from the viewpoint of handling and cost.

FIGS. 9A and 9B show ammonia (NH _3), which is an oxygen consuming substance contained in the water layer, in the case where coal ash granulate is not used as the oxygen consuming substance absorbent in the water layer. ), Hydrogen sulfide (H ₂ S) and methyl sulfide ((CH ₃ ) ₂ S). In the experiment, sewage sludge was used, and a coal ash granule having a particle size of 5 mm to 40 mm was put on the sewage sludge so as to have a thickness of about 10 cm. When coal ash granulate was put into the water layer, the concentrations of ammonia, hydrogen sulfide and methyl sulfide in the water layer were greatly reduced.

  FIG. 10 shows the result of measuring the dissolved oxygen concentration in the water layer 114 before and after the coal ash granule having a particle size of 5 mm or less was charged on the sludge layer 113 to a thickness of about 10 mm. Yes. The dissolved oxygen concentration increased greatly after 1 day had passed since the coal ash granulation was added.

  By introducing the coal ash granulated material into the water layer 114, oxygen consuming substances such as hydrogen sulfide generated from the sludge layer 113 are absorbed, and consumption of dissolved oxygen in the water layer 114 is suppressed. It is thought that the dissolved oxygen concentration increased. The input amount of the coal ash granulated product needs to be adjusted depending on the particle size, but when the average particle size is about 5 mm, the thickness may be about several mm to 20 mm. Even when carbon is not added to the sludge layer 113, it is preferable to introduce an oxygen-consuming substance absorbent into the water layer 114 because the dissolved oxygen concentration can be improved.

By mixing calcium ions in the sludge layer 113, it is possible to promote the movement of protons generated by the activity of microorganisms from the sludge layer 113 to the water layer 114. Protons generated in the sludge layer 113 are easily trapped by an inorganic substance or the like present in the sludge layer 113, so that only a part of the generated protons move into the water layer 114. However, it is considered that by adding calcium ions, protons and calcium ions are replaced, and the movement of protons into the water layer 114 is promoted. Therefore, it is preferable to supply calcium ions (Ca ²⁺ ) into the system to suppress the generation of hydrogen sulfide. For supplying calcium ions, for example, calcium oxide (CaO) may be added to the sludge.

  FIG. 11 shows the relationship between the electrode potential and the current density when 20 wt% of calcium oxide is added as a proton transfer promoter in the sludge layer 113 and when it is not added. As shown in FIG. 11, the potential difference between the electrodes could be increased by about 1.5 times by adding calcium oxide. This is considered to be because the protons in the sludge layer 113 easily move to the water layer 114 due to calcium ions generated from calcium oxide. In addition to an increase in electromotive voltage, a large voltage can be extracted even in a region where the current density is large.

  The proton transfer promoting material does not need to be pure calcium oxide, and coal ash granulated material or steel slag containing calcium oxide may be used. In particular, steel slag has a high calcium oxide content of about 25 wt% to 40 wt%, and is preferable as a proton transfer promoter in terms of handling and cost. Increasing the amount of steel slag mixed increases the effect of promoting proton movement, but it is difficult to mix a large amount of steel slag into the sludge. For this reason, in the case of steel slag containing about 35 wt% of calcium oxide, it may be added so that the sludge layer 113 contains about 10 wt% to 30 wt%, preferably about 20 wt%.

  Even if the proton transfer promoting material is mixed only in the shallow portion of the sludge layer, an effect of suppressing proton trapping can be obtained, and the voltage and current can be improved.

  When 20 microbial fuel cells 100 were actually formed, the electromotive force of each microbial fuel cell 100 was as shown in FIG. When the 20 microbial fuel cells 100 were connected in series, the electromotive voltage was 12.275 V. When 6 light emitting diodes were connected in series, they could be lit. Moreover, it was able to light continuously for 3 days or more. In addition, the upper part of the sludge layer 113 used the tidal flat sediment mud of the Enami district of Hiroshima-shi, and the lower part used sludge which added bamboo charcoal and steel slag. The ratio of each component in this case was bamboo charcoal 2 wt%, steel slag 33 wt%, organic mud 30 wt%, and pore water 35 wt%. In addition, coal ash granulated material having a particle size of 5 mm or less was introduced into the water layer 114 as an oxygen consuming substance absorbing particle so as to have a thickness of about 10 mm.

  The microbial fuel cell 100 according to the present embodiment has a very simple structure, and can easily generate power in a place where sludge is accumulated. In addition, by connecting a plurality of microbial fuel cells 100 in series, voltages can be added and an arbitrary voltage can be obtained. Furthermore, since sludge is decomposed by microorganisms by performing power generation, sludge can be purified. For example, if the microbial fuel cell 100 of the present embodiment is provided in a side groove or the like where sludge is accumulated and a light emitting diode (LED) is turned on by the obtained electric power, it can be used as a streetlight and the side groove can be purified. it can.

  When the moisture content of the accumulated sludge is high, a battery body 111A as shown in FIG. 13 may be used. The battery body 111A has a movable lid 127 at the lower end. After the battery main body 111 is pierced into the accumulated sludge, the water supplied from below to the sludge layer 113 can be reduced by closing the lid 127. For this reason, the conductivity of the sludge layer 113 in the lower part of the battery body 111A can be kept low. It is only necessary to reduce the supply of water from below, and the lower portion of the holding body 121 does not need to be sealed when the lid 127 is closed. In FIG. 13, a plurality of triangular movable plates are connected to the lower end portion of the holding body 121, and a lid portion 127 that closes the distal end portion is provided by bringing the distal end portion of the movable plate inward after being embedded in the sludge. An example is shown. However, the structure of the lid 127 is not limited to this. For example, a structure may be adopted in which a lid portion made of a disk-like plate having one end connected to the lower end portion of the holding body is provided, and the lid portion is pulled up after being embedded in the sludge.

  The diameter, length, and the like of the electrode cylinder shown in the present embodiment are examples, and may be appropriately changed according to the conditions of the installation location. Moreover, although the example in which the negative electrode and the positive electrode are the same material and size has been shown, they may be different. Although an example in which an electrode cylinder having a lower end opened so that it can be directly installed in a place where sludge is deposited has been shown, a configuration may be adopted in which sludge is introduced into an electrode cylinder having a lower end sealed. Depending on the conditions such as the deposition location, the kind and amount of organic matter and anaerobic microorganisms contained in sludge, the supply state of oxygen, and the like change, and the oxidation-reduction potential also changes. For this reason, the voltage obtained by the microbial fuel cell varies somewhat. However, since any number of microbial fuel cells of this embodiment can be connected in series, a desired voltage can be easily obtained by adjusting the number of connections.

(Second Embodiment)
In the first embodiment, the case where the load is driven only by the microbial fuel cell is shown. However, the load may be driven by a power supply device in which a microbial fuel cell and an auxiliary battery are connected in series. In this way, a voltage sufficient to drive the load can be obtained without connecting a large number of microbial fuel cells in series. In addition, it is possible to continue driving the load for a much longer time than in the case of only a battery other than the microbial fuel cell.

  FIG. 14 shows a configuration of a power supply apparatus 200 according to the second embodiment. As shown in FIG. 14, in a power supply device 200 that supplies power to a load 251, a microbial fuel cell 260 and an auxiliary battery 270 are connected in series to the load 251. By connecting the microbial fuel cell 260 and the auxiliary battery 270 in series, the load 251 can be driven for a much longer time than in the case of the auxiliary battery 270 alone.

  FIG. 15 shows a change in the output voltage of the power supply apparatus 200 when a red LED is used for the load 251. In FIG. 15, as the microbial fuel cell 260, two cylindrical ones having an inner diameter of 15 cm and a height of 50 cm were used in series as in the first embodiment. A 10 cm square carbon cloth was used for the positive electrode and the negative electrode, and the amount of sludge layer was about 100 g. Moreover, bamboo charcoal was added to the sludge layer as carbon particles, and about 10 mm of coal ash granulated material was deposited on the sludge layer as an oxygen consuming substance absorbent. As the auxiliary battery 270, two commercially available AA alkaline batteries were used in series.

  In the case of a power supply device in which only two AA alkaline batteries are connected in series without connecting a microbial fuel cell, the voltage, which was about 3 V immediately after the LED was turned on, gradually decreased, and about 28 days passed. Later, it became 0V and the LED stopped emitting light. Further, in the case of the power supply device in which the microbial fuel cell and the auxiliary battery are connected in parallel, the voltage, which was about 3V immediately after the LED was turned on, rapidly decreased to about 0.7V and once stabilized. However, the voltage dropped again from the 23rd day, and after about 28 days, the voltage became about 0.1V and the LED stopped emitting light. On the other hand, in the case of the power supply apparatus 200 of the present embodiment, the initial voltage was about 1.6 V, but the voltage remained almost unchanged after about 70 days, and the LED continued to emit light.

  Judging from the capacity of AA alkaline batteries and the power consumption of red LEDs, it is considered reasonable that the LED does not emit light in about four weeks when only two AA alkaline batteries are connected in series. It is done. In addition, since the electromotive force of the microbial fuel cell is about 0.6 V, when two microbial fuel cells connected in series and two dry cells connected in series are connected in parallel, the microbial fuel cell Current will also flow to the fuel cell, and the voltage may have fallen more rapidly than in the case of a single dry cell.

  On the other hand, when two microbial fuel cells 260 and two dry cells are connected in series, the reason why the voltage is stable for a long time at about 1.6 V is not clear. However, almost the same voltage was obtained when two microbial fuel cells 260 and one dry cell were connected in series. In addition, when one microbial fuel cell 260 and one dry cell were connected in series, a voltage of about 1.59 V was stably obtained. Furthermore, when the number of dry batteries connected in series was three and four, voltages of about 1.81 V and about 1.98 V were obtained, respectively. From these facts, it is presumed that one of the following phenomena occurs. First, the microbial fuel cell 260 acts as an internal resistance, so that the amount of current of the auxiliary battery 270 is adjusted to lower the output voltage, and the voltage from the microbial fuel cell 260 is superimposed and stabilized for a long period of time. It can be considered that voltage can be output. It is also conceivable that a stable voltage can be output over a long period of time due to the charging effect from the microbial fuel cell 260 to the auxiliary battery 270. It is considered that the auxiliary battery 270 hardly outputs, and there is a possibility that the output can be continued until the auxiliary battery 270 deteriorates due to rust or the like.

  Although an example in which two microbial fuel cells 260 and two dry cells are connected in series is shown, one auxiliary battery 270 may be used, or three or more may be connected in series. Moreover, not only an alkaline battery but a manganese battery, a lithium battery, or a silver oxide battery may be used. Moreover, it is not necessary to be a primary battery, and a secondary battery such as a nickel cadmium, nickel metal hydride or lithium ion battery may be used. Further, the battery need not be a dry battery, and may be a lead storage battery or the like. If the red LED emits light, it can be used as the auxiliary battery 270 if a voltage of about 1 V is generated.

  One microbial fuel cell 260 or three or more microbial fuel cells 260 may be connected in series. Further, similarly to the first embodiment, the negative electrode may be covered with a carbon layer, or a proton transfer promoter may be added to the sludge layer. Moreover, it is not necessary to add the carbon particles to the sludge layer and dispose the oxygen consuming substance absorber. When there is one microbial fuel cell 260, a negative electrode and a positive electrode may be provided on the outer surface of the holding body. When the negative electrode and the positive electrode are provided on the outer surface of the holding body, the holding body does not need to have a thick cylindrical shape, and can have a cylindrical shape with a small inner diameter or a rod shape. For this reason, the microbial fuel cell main body can be easily pierced into the accumulated sludge, and installation of the microbial fuel cell is further facilitated. If the lower end portion of the holding body is pointed, the installation becomes easier.

  FIG. 16 shows an LED lamp 300 using a microbial fuel cell main body 311 in which a positive electrode and a negative electrode are provided on the outer surface of a holding body. A negative electrode 322 and a positive electrode 323 made of carbon cloth are affixed to the outer surface of a cylindrical holder 321 having a thickness that can accommodate an AA battery. An LED 351 serving as a load is provided at the end of the holding body 321 on the positive electrode 323 side, and the end of the holding body 321 on the negative electrode side is sealed. Inside the holding body 321, two AA batteries 371 are accommodated as auxiliary batteries 370. The negative electrode 322 is connected to the positive electrode of the auxiliary battery 370, the positive electrode 323 is connected to the anode of the LED 351, and the cathode of the LED 351 is connected to the negative electrode of the auxiliary battery 370 by a conducting wire 325 such as a nickel wire. In addition, although the example which accommodates the auxiliary | assistant battery 370 in the inside of the holding body 321 was shown for the holding body 321 as a cylinder shape, the holding body 321 should just hold | maintain the negative electrode 322 and the positive electrode 323, and may be rod-shaped.

  When the LED lamp 300 is embedded in the sludge layer such that the negative electrode 322 is buried in the sludge layer deposited and the positive electrode 323 is located in the water layer above the sludge layer, the LED 351 is lit. Once the LED lamp 300 is embedded in the sludge layer, it can continue to emit light for at least several months to one year. In addition, a plurality of LED lamps 300 can be installed if an interval is provided so that the negative electrodes 322 or the positive electrodes 323 do not contact each other. Characters or images can be displayed by arranging a plurality of LED lamps 300.

  FIG. 16 shows a configuration in which a dry battery as an auxiliary battery and an LED as a load and a microbial fuel cell main body are integrated, but at least one of the auxiliary battery and the load may be arranged in another place. Is possible. The auxiliary battery is not limited to an AA dry battery, and any battery may be used. The load is not limited to the LED. It is also possible to use the microbial fuel cell body alone.

  The microbial fuel cell according to the present invention can be easily installed in a place where sludge is accumulated, and is useful as a method for effectively using sludge.

DESCRIPTION OF SYMBOLS 100 Microbial fuel cell 101 Load 103 Deposition sludge 111 Battery main body 111A Battery main body 113 Sludge layer 114 Water layer 121 Holder 121A Holder 122 Negative electrode 123 Positive electrode 125 Conductive wire 126 Carbon layer 127 Lid part 200 Power supply device 251 Load 260 Microbial fuel cell 270 Auxiliary Battery 300 LED lamp 311 Microbial fuel cell body 321 Holding body 322 Negative electrode 323 Positive electrode 325 Conductor 351 LED
370 Auxiliary battery 371 Dry battery

Claims (17)

A microbial fuel cell at least partially disposed in a mud layer containing organic matter and anaerobic microorganisms,
E Bei an insulating holder, a battery body having a positive electrode provided on an anode and an upper provided in a lower portion of the holding member,
The negative electrode is disposed in the mud layer;
The microbial fuel cell, wherein the positive electrode is disposed in a water layer existing on the mud layer . The holding body is cylindrical,
The microbial fuel cell according to claim 1, wherein the negative electrode and the positive electrode are respectively provided on an inner wall surface of the holding body.   3. The microbial fuel cell according to claim 2, wherein a moisture content in a lower end portion of the holding body in the mud layer is less than 80%. The battery body is plural,
The microbial fuel cell according to claim 2, wherein the negative electrode and the positive electrode are sequentially connected in series.   The microbial fuel cell according to claim 1, wherein the negative electrode and the positive electrode are each provided on an outer surface of the holding body.   The microbial fuel cell according to any one of claims 1 to 3, further comprising carbon particles mixed in a portion of the mud layer where the negative electrode is disposed.   The microbial fuel cell according to claim 6, wherein the carbon particles are made of bamboo charcoal.   The microbial fuel cell according to any one of claims 1 to 7, wherein the negative electrode includes a carbon cloth attached to the holding body and a carbon layer covering the carbon cloth.   The microbial fuel cell according to any one of claims 1 to 8, further comprising an oxygen-consuming substance absorber containing calcium oxide introduced into the water layer.   The microbial fuel cell according to claim 9, wherein the oxygen-consuming substance absorbent is a coal ash granulated material.   The microbial fuel cell according to any one of claims 1 to 10, further comprising a proton transfer promoting material containing calcium oxide mixed in the mud layer. The microbial fuel cell according to any one of claims 1 to 11,
A power supply device comprising: the microbial fuel cell; and an auxiliary battery connected in series. A method for power generation of a microbial fuel cell, wherein at least a part thereof is disposed in a mud layer containing organic matter and anaerobic microorganisms,
Preparing a battery body having a holding body made of an insulating material, a negative electrode provided at a lower portion of the holding body, and a positive electrode provided at an upper portion;
It said battery body, said the mud layer in the negative electrode is filled, microbial power generation method, wherein the positive electrode in the aqueous layer is present and a step of arranging so as to be located on the mud layer . The holding body is cylindrical,
The microbial power generation method according to claim 13, wherein the negative electrode and the positive electrode are each provided on an inner wall surface of the holding body. Preparing a plurality of battery bodies;
The microbial power generation method according to claim 14, wherein the negative electrode and the positive electrode are sequentially connected in series in the plurality of battery main bodies.   The microbial power generation method according to claim 13, wherein the negative electrode and the positive electrode are each provided on an outer surface of the holding body.   The microbial power generation method according to any one of claims 13 to 16, wherein an auxiliary battery and a load are connected in series between the positive electrode and the negative electrode.

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