JP7478373B2 - Sediment improvement method and device using sediment microbial fuel cell - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Published in the Proceedings of the 55th Annual Meeting of the Japan Society on Water Environment (2020)

The present invention relates to a bottom sediment improvement method and device using a sediment microbial fuel cell that utilizes the organic matter metabolism of microorganisms to efficiently improve bottom sediment without requiring additional energy.

Conventionally, in closed or semi-closed water areas such as lakes, marshes, and harbors where water exchange is difficult (hereinafter, these are collectively referred to as closed water areas), there has been a problem that when organic matter contained in the industrial and domestic wastewater that flows into the area accumulates and turns into sludge, it releases nutrients, causing the mass outbreak of blue-green algae and the generation of hydrogen sulfide, resulting in the occurrence of blue tides. The generation of these harmful substances and foul odors, as well as the decrease in dissolved oxygen in the water, have a negative impact on the growth of aquatic organisms and the living environment of surrounding residents, and therefore there has been a demand for environmental improvement in closed water areas. However, not only is dredging work to remove the accumulated sludge (bottom sediment) time-consuming and expensive, but the disposal of the surplus soil has also become a problem. Therefore, there is a demand for technology that can improve the bottom sediment environment at low cost with little environmental impact, and a method of biologically decomposing accumulated sludge by activating microorganisms that exist in nature has attracted attention. For example, microbial fuel cells, including sediment microbial fuel cells (hereinafter also referred to as SMFCs), are a technology that generates electricity by transferring electrons generated by the decomposition (metabolism) of organic matter (sludge, etc.) by anaerobic power-generating bacteria in bottom sediments to a cathode (positive electrode) installed in water via an anode (negative electrode) installed in the bottom sediment, and reacting with dissolved oxygen in the water. In this way, microbial fuel cells are expected to be the next generation of environmental improvement technology for closed water areas because they can decompose and purify bottom sediment sludge while also generating electricity, and improvement proposals have been made, such as those shown in Patent Document 1 and Patent Document 2.

JP 2016-168560 A JP 2018-12086 A JP 2016-175058 A

In Patent Document 1, a first electrode (anode) is placed on the bottom sediment, and a second electrode (cathode) is electrically connected to the second electrode by an external circuit. The second electrode is placed at a different depth above the first electrode, and hydrogen ions, electrons, and oxygen react with each other to efficiently capture hydrogen ions. The oxygen dissolved in the water varies depending on the water depth and environmental changes, and the water-generating reaction is efficiently utilized to improve and stabilize the bottom sediment improvement. However, since the amount of dissolved oxygen in the water is limited, there is a limit to how much the bottom sediment improvement can be improved by simply increasing the number of second electrodes or expanding the area, and there is a problem that sufficient bottom sediment improvement effects cannot be obtained, especially in an oxygen-poor environment.
In addition, Patent Document 2 aims to improve the hypoxic environment around the bottom of the water by irradiating the bottom mud with light using a light irradiator to promote algae growth and improve the hypoxic environment around the bottom of the water through the photosynthesis of the algae, but there is a problem that it takes time for the algae to grow sufficiently, and during that time the hypoxic environment cannot be improved. Furthermore, since the improvement of the hypoxic environment relies on the photosynthesis of the algae, the degree of improvement of the hypoxic environment depends on the growth status of the algae, and there is also a problem that the improvement effect is not stable.
On the other hand, Patent Document 3 proposes an aeration device and an aeration method in which a pump is driven by electricity generated by a biofuel cell in a sludge purification treatment facility, and oxygen is supplied (discharged) from a fine bubble generator disposed in the discharge piping of the pump to a water area (into the water layer) to which dissolved oxygen is to be supplied, thereby performing aeration. However, biofuel cells generate a small amount of electricity, and most of the research to date has been on the use of low-power sensors. In other words, it is difficult to supply sufficient power to drive the pump by simply connecting the pump to the biofuel cell, and even if it can be driven, it is only temporary, and it is impossible to continue driving the pump for a long period of time. Therefore, the operation of the fine bubble generator is unstable, the amount of oxygen that can be supplied is limited, and it is not possible to continuously and stably improve the bottom sediment of a wide range of closed water areas. Therefore, Patent Document 3 describes the use of a charge/discharge control device that charges and discharges the direct current generated by the biofuel cell into a storage battery. However, even if the storage battery is once charged and then discharged, if the battery is continuously discharged, the discharge amount will eventually catch up with the charge amount and the battery will no longer be able to supply power, so some kind of ingenuity is required for the charge/discharge control and operation method. However, Patent Document 3 does not describe the specific configuration and operation of the charge/discharge control device, and it is unclear how to perform stable (continuous) aeration and achieve bottom sediment improvement. In addition, the voltage of the biofuel cell (sediment microbial fuel cell) is low and boosting is essential, but Patent Document 3 does not describe boosting the voltage.
The present invention has been made in consideration of these circumstances, and aims to provide a bottom sediment improvement method and device using a sediment microbial fuel cell that is highly practical and energy-saving, and that can effectively utilize the electricity generated from a sediment microbial fuel cell to steadily supply oxygen to a closed water area that is the target of bottom sediment improvement, thereby increasing the dissolved oxygen concentration, thereby stabilizing the operation of the sediment microbial fuel cell and reliably and efficiently improving the bottom sediment of a wide range of closed water areas.

The bottom sediment improvement method according to the present invention, which is in line with the first object, comprises a first electrode (anode) buried in the bottom sediment of a closed body of water to be improved, and a second electrode (cathode) electrically connected to the first electrode and placed in the water immediately above the bottom sediment, and organic matter contained in the bottom sediment is decomposed by microorganisms in the bottom sediment, and electrons generated by the decomposition move through the first electrode to the second electrode, thereby generating electricity.
The electricity generated by one or more of the sediment microbial fuel cells is stored and, while being boosted, is intermittently supplied to a motor-driven aeration pump, which intermittently aerates the above-mentioned water.

In the bottom sediment improvement method using a sediment microbial fuel cell according to the first invention, it is preferable to increase the dissolved oxygen concentration of the immediately above water to 2 mg/L or more by aeration using the aeration pump.

The bottom sediment improvement device using a sediment microbial fuel cell according to the present invention, which is in line with the second object, comprises a first electrode (anode) that is buried in the bottom sediment of a closed body of water that is to be improved, and a second electrode (cathode) that is electrically connected to the first electrode and placed in the water immediately above the bottom sediment, and generates electricity by electrons generated when organic matter contained in the bottom sediment is decomposed by microorganisms in the bottom sediment and the electrons move through the first electrode to the second electrode in the bottom sediment improvement device using a sediment microbial fuel cell,
The system comprises a power generation unit having one or more of the sediment microbial fuel cells, a charge/discharge boost unit having multiple capacitors, a motor-driven aeration pump, and a control unit that controls the charge/discharge boost unit, and the control unit switches between charging the charge/discharge boost unit by the power generation unit and discharging to the aeration pump by the charge/discharge boost unit, thereby intermittently aerating the immediately above water using the aeration pump.

In the bottom sediment improvement device using a sediment microbial fuel cell according to the second invention, the charge/discharge boost unit has a switching means for connecting each of the capacitors to one or more of the sediment microbial fuel cells during charging, and for disconnecting each of the capacitors from one or more of the sediment microbial fuel cells during discharging, and for connecting the multiple capacitors in series, and it is preferable that the control unit has an automatic switching circuit that operates the switching means at a predetermined time interval to switch between the charging and discharging.

In the bottom sediment improvement device using a sediment microbial fuel cell according to the second invention, it is further preferable that the automatic switching circuit has a charge/discharge time setting means, and that the switching means switches between the charging and discharging in accordance with the charging time and discharging time set by the charge/discharge time setting means.

In the bottom sediment improvement device using a sediment microbial fuel cell according to the second invention, the charge/discharge time setting means may have a variable resistor, and the charge time and the discharge time may be adjusted by changing the resistance value of the variable resistor.

The bottom sediment improvement method using a sediment microbial fuel cell according to the first invention stores and boosts the electricity generated by one or more sediment microbial fuel cells while intermittently supplying it to a motor-driven aeration pump, which then intermittently aerates the water directly above it. This makes effective use of the electricity generated by the sediment microbial fuel cell to reliably and efficiently improve the bottom sediment, and is highly energy-saving.

The bottom sediment improvement device using the sediment microbial fuel cell of the second invention has a control unit that switches between charging the charge/discharge boost unit using the power generation unit and discharging to the aeration pump using the charge/discharge boost unit. Even if the voltage generated by the sediment microbial fuel cell of the power generation unit is low, the charge/discharge boost unit can be charged and boosted for use to supply the power needed to drive the aeration pump. This allows the aeration pump to intermittently aerate the water just above it, increasing the dissolved oxygen concentration in the water just above it, without requiring additional energy, and thus enabling bottom sediment improvement to be performed efficiently and at low cost.

1 is a schematic front view showing the configuration of a sediment microbial fuel cell in a bottom sediment improvement method using a sediment microbial fuel cell according to one embodiment of the present invention. FIG. FIG. 2 is a circuit diagram showing the operation of a bottom sediment improvement device using a sediment microbial fuel cell during charging according to one embodiment of the present invention. FIG. 2 is a circuit diagram showing the operation of the bottom sediment improvement device using the same sediment microbial fuel cell during discharging. FIG. 2 is a circuit diagram showing the configuration of a control unit of the bottom sediment improvement device using the same sediment microbial fuel cell. (A) and (B) are graphs showing the time change in inter-electrode voltage of a sediment microbial fuel cell in a bottom sediment improvement device using the same sediment microbial fuel cell, and graphs showing the time change in voltage applied to a motor driving an aeration pump, respectively. 13 is a graph showing the time change in the dissolved oxygen concentration in the immediately upstream water in a closed water area to which the bottom sediment improvement device using the same sediment microbial fuel cell has been applied.

Next, with reference to the attached drawings, an embodiment of the present invention will be described for better understanding of the present invention.
As shown in Figure 1, a sediment microbial fuel cell 10 in a bottom sediment improvement method using a sediment microbial fuel cell according to one embodiment of the present invention (hereinafter simply referred to as the bottom sediment improvement method) has a first electrode (anode) 14 buried in bottom sediment 12 in a closed water area 11 that is the target of bottom sediment improvement, and a second electrode (cathode) 16 electrically connected to the first electrode 14 and installed in the water 15 directly above the bottom sediment 12, and generates electricity by electrons generated when organic matter contained in the bottom sediment 12 is decomposed by microorganisms (anaerobic microorganisms) in the bottom sediment 12 moving through the first electrode 14 to the second electrode 16.

The first electrode 14 and the second electrode 16 are connected by an electrical connection wire 18 having electrical conductivity, such as titanium, iron, or stainless steel, and the power generated by the sediment microbial fuel cell 10 can be supplied to a motor (DC motor, not shown) for driving an aeration pump 19. However, the voltage generated by the sediment microbial fuel cell 10 is small, and the aeration pump 19 (motor) cannot be driven stably and continuously.
Therefore, in the bottom sediment improvement method according to the present invention, the electricity generated by the multiple sediment microbial fuel cells 10 is stored and boosted while being intermittently supplied to a motor-driven aeration pump 19, which intermittently aerates the immediately upstream water 15. In particular, by increasing the dissolved oxygen concentration (DO) of the immediately upstream water 15 to 2 mg/L or more through aeration by the aeration pump 19, the effect of suppressing elution of nutrients can be enhanced, and bottom sediment improvement can be performed efficiently.

The material of the first electrode 14 is a conductive material such as a metal material and a carbon material, but is not particularly limited as long as it can receive electrons generated by the decomposition of organic matter by microorganisms. Specifically, iron, stainless steel, titanium, aluminum, copper, platinum, etc. are used as the metal material, and graphite, carbon fiber, etc. are used as the carbon material. In FIG. 1, the first electrode 14 is a rectangular flat plate, but the shape of the first electrode is not particularly limited and can be selected from various shapes such as mesh, lattice, block, and porous, and the outer shape is not limited to a rectangular shape but can be appropriately selected from various shapes such as a circle, a polygon, and others. In addition, when the first electrode is formed of carbon fiber, carbon cloth, carbon mat, carbon felt, carbon paper, etc. can be used as the first electrode.
The second electrode 16 is made of the same material as the first electrode 14, but is preferably made of a carbon material that has high electrical conductivity and is resistant to corrosion. The second electrode is made of the same shape as the first electrode, but the shape may be bent or curved, or may have an uneven surface.

Next, a bottom sediment improvement device (hereinafter, also simply referred to as a bottom sediment improvement device) 20 using a sediment microbial fuel cell according to one embodiment of the present invention shown in Figures 2 and 3 will be described. In this example, the bottom sediment improvement device 20 includes a power generation unit 21 having a plurality (seven in this case) of sediment microbial fuel cells 10, a charge/discharge boost unit 23 having a plurality (seven in this case) of capacitors 22, a motor-driven aeration pump 19, and a control unit 25 that controls the charge/discharge boost unit 23. The control unit 25 switches between charging the charge/discharge boost unit 23 (each capacitor 22) by the power generation unit 21 and discharging (power supply) to the aeration pump 19 by the charge/discharge boost unit 23, so that the aeration pump 19 intermittently aerates the immediately upstream water 15.
In other words, by charging the multiple capacitors 22 for a predetermined time with the power generated by the multiple sediment microbial fuel cells 10 to store sufficient power, boosting the voltage, and then discharging, it becomes possible to apply a voltage equal to or higher than the motor's operating voltage to the motor to drive the aeration pump 19 for a predetermined time, and by repeating charging and discharging, aeration of the upstream water 15 is performed intermittently. This aeration is performed by inserting the tip (outlet) of the discharge pipe 26 connected to the discharge port of the aeration pump 19 into the upstream water 15 and blowing in air (oxygen), as shown in Figure 1.

The bottom sediment improvement device 20 will be described in detail below.
The charge/discharge boost unit 23 has a switching means 27 that connects each capacitor 22 to each sediment microbial fuel cell 10 corresponding to each capacitor 22 during charging, as shown in FIG. 2, and disconnects each capacitor 22 from each sediment microbial fuel cell 10 and connects multiple (all) capacitors 22 in series during discharging, as shown in FIG. 3. The control unit 25 operates the switching means 27 at a predetermined time interval to switch between charging and discharging. Here, a charging circuit 28 is provided between the power generation unit 21 (each sediment microbial fuel cell 10) and the charge/discharge boost unit 23 (each capacitor 22), and a discharging circuit 29 is provided between the charge/discharge boost unit 23 (each capacitor 21) and the aeration pump 19. Therefore, during charging, the charging circuit 28 is selected by the switching means 27, and each capacitor 22 is connected to each sediment microbial fuel cell 10 corresponding to each capacitor 22 via the charging circuit 28, and each capacitor 22 is independently charged by each sediment microbial fuel cell 10 (multiple capacitors 22 are charged in parallel). During discharge, the discharging circuit 29 is selected by the switching means 27, so that the multiple (all) capacitors 22 are connected in series via the discharging circuit 29, and discharge is performed to the aeration pump 19 (motor) in a boosted state. Note that the signal lines (wiring) connecting the control unit 25 and the switching means 27 are omitted in Figures 2 and 3.

The switching means 27 uses a relay switch (one example of a switching element) 30, and the control unit 25 includes an automatic switching circuit 31 that operates the switching means 27 at a predetermined time interval to switch between charging and discharging using an astable multivibrator circuit shown in FIG. 4, and a power source 32 for operating the automatic switching circuit 31. The automatic switching circuit 31 has a charge/discharge time setting means 33, and switching between charging and discharging is performed by the switching means 27 according to the charge time and discharge time set by the charge/discharge time setting means 33. Specifically, the charge/discharge time setting means 33 has a variable resistor 34, and the charge time and discharge time are adjusted by changing the resistance value of the variable resistor 34, but is not limited to this and can be selected as appropriate. The configuration of the switching means is not limited to this embodiment and can be selected as appropriate. The configuration of the control unit (automatic switching circuit) is also not limited to this embodiment and can be selected as appropriate depending on the configuration of the switching means, the charging circuit, and the discharging circuit, etc.

In this embodiment, the case where seven capacitors are used in one bottom sediment improvement device to correspond to seven sediment microbial fuel cells has been described, but the number of sediment microbial fuel cells can be selected as appropriate, and may be one if sufficient electrode area can be secured. In addition, the number of capacitors is selected as appropriate, as long as there are multiple capacitors for boosting the voltage, and the number does not need to be the same as the number of sediment microbial fuel cells. Furthermore, the method of connecting the sediment microbial fuel cells and the capacitors during charging is selected as appropriate depending on the respective numbers of sediment microbial fuel cells and capacitors. For example, multiple capacitors may be charged with one sediment microbial fuel cell, or multiple capacitors may each be charged with multiple sediment microbial fuel cells.

Next, the results of experiments conducted to confirm the effects of the present invention will be described.
Example 1
The performance of the bottom sediment improvement device 20 shown in Figures 2 to 4 was evaluated. In this example, in order to reproduce the state of the closed water area 11 shown in Figure 1, a tank with a width of 30 cm, a depth of 17 cm, and a height of 25 cm was used. The bottom sediment 12 collected from a eutrophic pond was spread in the tank to a height of 10 cm, and the surface water collected from the same pond was filled on top of the bottom sediment 12 to a depth of 10 cm (a position 20 cm above the bottom of the tank) as the directly above water 15. The directly above water 15, which was reduced by evaporation during the experiment, was replenished with distilled water. As the first electrode 14, seven pieces of carbon felt measuring 4 cm x 10 cm were embedded in the bottom sediment 12 at intervals of 5 cm. As the second electrode 16, seven pieces of carbon felt measuring 8 cm x 10 cm (twice the area of the first electrode 14) were arranged in the directly above water 15 (above the first electrode 14). At this time, the top of the second electrode 16 was set to be above the surface of the directly above water 15. The first electrodes 14 and the paired second electrodes 16 were connected one by one with electrical connection wires 18 made of stainless steel wire to form seven sediment microbial fuel cells 10, which served as power generation units 21 (see Figures 2 and 3). The rest of the configuration, including the charge/discharge boost unit 23 (switching means 27), the control unit 25 (automatic switching circuit 31), the charging circuit 28, and the discharging circuit 29, was the same as that of the bottom sediment improvement device 20 (see Figures 2 to 4).

The bottom sediment improvement device 20 (sediment microbial fuel cell 10) constructed as above was acclimated for about three months, and then its operation was checked. The water temperature of the upstream water 15 was adjusted to 26° C. by a heater driven by external electricity.
In this example, the charge (standby) time was adjusted to about 88 seconds and the discharge (aeration) time to about 1 second using the charge/discharge time setting means 33 (variable resistor 34) of the control unit 25 (automatic switching circuit 31 using a non-stable multivibrator circuit) shown in Figure 4, and charging and discharging were repeated. The inter-electrode voltage of each sediment microbial fuel cell 10 and the voltage applied to the motor driving the aeration pump 19 were measured at 1 second intervals using a voltage logger, and the results are shown in Figures 5 (A) and (B). Note that Figure 5 (A) shows a representative value of the inter-electrode voltage of seven sediment microbial fuel cells 10.

From Fig. 5(A), it can be seen that the capacitor 22 connected to each sediment microbial fuel cell 10 stably repeats a cycle of gradually charging and suddenly discharging in a cycle of about 1.5 minutes. Also, from Fig. 5(B), it can be seen that during charging, no voltage is applied to the motor driving the aeration pump 19, and at the timing of discharging, which occurs in a cycle of about 1.5 minutes, a voltage equal to or higher than the motor's operating voltage (here, 1.5 V) is applied to the motor.
Therefore, according to the bottom sediment improvement device 20 of the present invention, the control unit 25 switches between charging the charge/discharge boost unit 23 by the power generation unit 21 and discharging to the aeration pump 19 by the charge/discharge boost unit 23, so that even if the amount of power generated by each sediment microbial fuel cell 10 of the power generation unit 21 is small, the charge/discharge boost unit 23 can be charged and the electricity required to drive the aeration pump 19 can be stored, and it has been confirmed that the aeration pump 19 can be driven stably and intermittently (intermittently) without requiring additional energy.

Example 2
Next, in order to confirm the bottom sediment improvement effect of the bottom sediment improvement device 20, changes in the dissolved oxygen concentration (DO) of the immediately upstream water 15 were examined when the bottom sediment improvement device 20 was operating and when it was not operating (non-operating) under the same configuration and conditions as in Example 1. The dissolved oxygen concentration (DO) of the immediately upstream water 15 was measured at approximately hourly intervals using a DO meter with a logger, and the results are shown in Figure 6. In this example, the bottom sediment improvement device 20 was operated for three days, then non-operated for four days, and then operated for three days again before being non-operated.
From Figure 6, it can be seen that while the bottom sediment improvement device 20 is operating, the DO of the immediately above water 15 gradually increases and reaches 2 mg/L or more, which is an effective level for suppressing the leaching of nutrients, and while the bottom sediment improvement device 20 is not operating, the DO of the immediately above water 15 tends to gradually decrease.
Therefore, it was confirmed that the bottom sediment improvement method and bottom sediment improvement device 20 of the present invention can intermittently aerate the immediately above water 15 with the aeration pump 19 to increase the dissolved oxygen concentration of the immediately above water 15, thereby enhancing the effect of suppressing the elution of nutrients, and enabling efficient bottom sediment improvement at low cost. It is considered that by scaling up the configuration of this bottom sediment improvement device 20, it is possible to suppress the elution of nutrients over a wide range in an actual closed water area.

Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the above embodiments, and also includes other embodiments and variations that can be considered within the scope of the matters described in the claims.
The water in the closed water area to be improved may be fresh water or sea water. The number, size and arrangement of the first and second electrodes used in one bottom sediment improvement device are appropriately selected. The number and arrangement of bottom sediment improvement devices installed in one closed water area are appropriately selected according to the size of the closed water area and the environment (pollution state, etc.). The time interval for intermittent operation of the aeration pump is also appropriately selected.

10: Sediment microbial fuel cell, 11: Closed water area, 12: Bottom sediment, 14:, First electrode, 15: Overflow water, 16: Second electrode, 18: Electrical connection line, 19: Aeration pump, 20: Bottom sediment improvement device, 21: Power generation unit, 22: Capacitor, 23: Charge/discharge boost unit, 25: Control unit, 26 Discharge pipe, 27: Switching means, 28: Charging circuit, 29: Discharging circuit, 30: Relay switch, 31: Automatic switching circuit, 32: Power source, 33: Charge/discharge time setting means, 34: Variable resistor

Claims (6)

A method for improving bottom sediment using a sediment microbial fuel cell includes an anode buried in the bottom sediment of a closed water area to be improved, and a cathode electrically connected to the anode and installed in the water immediately above the bottom sediment, and organic matter contained in the bottom sediment is decomposed by microorganisms in the bottom sediment, and electrons generated by the decomposition move through the anode to the cathode to generate electricity, the method comprising the steps of:
A bottom sediment improvement method using a sediment microbial fuel cell, characterized in that the electricity generated by one or more of the sediment microbial fuel cells is stored and boosted while intermittently supplying the electricity necessary to drive a motor-driven aeration pump, which intermittently aerates the water immediately above where the cathode is installed using the aeration pump to increase the dissolved oxygen concentration of the water immediately above, thereby improving the bottom sediment . A bottom sediment improvement method using a sediment microbial fuel cell according to claim 1, characterized in that the dissolved oxygen concentration of the immediately above water is increased to 2 mg/L or more by aeration using the aeration pump. A bottom sediment improvement device using a sediment microbial fuel cell has an anode buried in the bottom sediment of a closed water area to be improved, and a cathode electrically connected to the anode and installed in the water immediately above the bottom sediment, and generates electricity by electrons generated by decomposition of organic matter contained in the bottom sediment by microorganisms in the bottom sediment and moving through the anode to the cathode ,
A bottom sediment improvement device using a sediment microbial fuel cell comprising a power generation unit having one or more of the sediment microbial fuel cells, a charge/discharge boost unit having multiple capacitors, a motor-driven aeration pump, and a control unit that controls the charge/discharge boost unit, wherein the control unit switches between charging the charge/discharge boost unit by the power generation unit and discharging to the aeration pump by the charge/discharge boost unit to intermittently supply the power necessary to drive the aeration pump, and the aeration pump intermittently aerates the water immediately above where the cathode is installed using the aeration pump to increase the dissolved oxygen concentration of the water immediately above, thereby improving the bottom sediment . A bottom sediment improvement device using a sediment microbial fuel cell as described in claim 3, characterized in that the charge/discharge boost unit has a switching means for connecting each of the capacitors to one or more of the sediment microbial fuel cells during charging, and for disconnecting each of the capacitors from one or more of the sediment microbial fuel cells during discharging, and for connecting the multiple capacitors in series, and the control unit has an automatic switching circuit that operates the switching means at a predetermined time interval to switch between the charging and discharging. A bottom sediment improvement device using a sediment microbial fuel cell according to claim 4, characterized in that the automatic switching circuit has a charge/discharge time setting means, and the switching means switches between the charging and discharging in accordance with the charging time and discharging time set by the charge/discharge time setting means. A bottom sediment improvement device using a sediment microbial fuel cell according to claim 5, characterized in that the charge/discharge time setting means has a variable resistor, and the charge time and the discharge time are adjusted by changing the resistance value of the variable resistor.

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