JP6949324B2 - Microbial fuel cell - Google Patents

Description

The present invention relates to a microbial fuel cell that extracts electrical energy from wastewater containing organic pollutants.

Generally, in a microbial fuel cell, an anaerobic microbial film is formed on an electrode (anode), and electrons generated in the process of anaerobic microorganisms decomposing organic pollutants are collected in the anode and taken out to an external circuit. The extracted electrons move to the cathode, which is a counter electrode, via an external circuit. Then, the electrons transferred to the cathode react with oxygen molecules and hydrogen ions, which are electron acceptors, to generate water.

The anode and cathode are separated by a diaphragm such as an ion exchange membrane, and hydrogen ions generated in the process of decomposing organic contaminants of anaerobic microorganisms move from the anode side to the cathode side through the diaphragm. An electric circuit is constructed.

Such a microbial fuel cell includes a two-chamber type having a cathode submerged in water and a one-chamber type having a cathode (air cathode) exposed to air.

Since the two-chamber type has a drawback that aeration is required to supply oxygen, it is generally considered that the one-chamber type is practically advantageous, and research and development are also underway.

Various factors that affect the power generation efficiency of a microbial fuel cell can be considered, and one of the influencing factors is the cathode reaction.

The one-chamber type microbial fuel cell has an advantage that oxygen supply in the cathode reaction can be promoted, but water pressure is applied to the anode chamber side of the ion exchange membrane that separates the anode chamber and the cathode, whereas the cathode side. Since no water pressure is applied to the water pressure, the ion exchange membrane itself supports the water pressure from the anode chamber side, and it is difficult to increase the size.

On the other hand, in the two-chamber type microbial fuel cell, since water pressure is applied to both sides of the ion exchange membrane, there is no need to use a high-strength ion exchange membrane, and there is an advantage that the system can be easily enlarged. Since the supply is by dissolved oxygen, it is difficult to increase the concentration of dissolved oxygen, which is an electron acceptor, due to the limitation of the saturated solubility of dissolved oxygen, and as a result, the cathode reaction has been a factor of lowering the power generation efficiency.

Therefore, for example, as shown in Patent Document 1, iron (III) ions are used as electron acceptors in the cathode solution, and iron (III) chelate compounds are used to improve the solubility near neutral pH. , A technique for increasing the electron acceptor concentration of the cathode solution is known.

In the microbial fuel cell of Patent Document 1, since the iron (III) chelate compound is changed to the iron (II) chelate compound after electron acceptance, the iron (II) chelate compound is sprinkled in a filter bed type iron oxide tank. with ^oxidizer, reacted as shown by the equation ^{_{Fe 2+ -EDTA + 0.25O 2 + H}} + → Fe 3+ -EDTA + 0.5H 2 O, is converted into iron (III) chelate compounds are reused.

Japanese Unexamined Patent Publication No. 2016-162665

^{In the configuration of Patent Document 1 described above, hydrogen ions (H +} ) are consumed when converting an iron (II) chelate compound to an iron (III) chelate compound, as shown by the above formula, when the compound is operated for a long period of time. Therefore, it is necessary to supply ^{the H +} consumed during the conversion to the cathode solution at any time, for example, by supplying an acidic pH adjusting solution to the cathode solution.

However, at that time, there is a problem that anions (salts) contained in the acid are accumulated in the cathode solution and the power generation efficiency is gradually lowered.

Therefore, there has been a demand for a microbial fuel cell in which anions are less likely to accumulate in the cathode solution and can be operated stably for a long period of time.

The present invention has been made in view of these points, and an object of the present invention is to provide a microbial fuel cell which can prevent the accumulation of anions in a cathode solution and can operate stably for a long period of time.

The microbial fuel cell according to claim 1 is a microbial fuel cell that extracts electric energy from wastewater containing an organic pollutant, and has an anode chamber in which the anode is immersed in the wastewater and a cathode in which the cathode is immersed in a cathode solution. A fuel cell body having a chamber, a diaphragm located between the anode chamber and the cathode chamber and capable of transmitting cations from the anode chamber side to the cathode chamber side, and iron ions in the cathode solution of the cathode chamber. It has an oxidizer that oxidizes from divalent to trivalent, and a cathode solution storage unit that stores the cathode solution that oxidizes iron ions by this oxidizer, and circulates the cathode solution from this cathode solution storage unit to the cathode chamber. The circulation means and the hydrogen ion supply means for supplying hydrogen ions to the cathode solution of the cathode solution storage portion are provided, and the hydrogen ion supply means is supplied with the cathode solution and the acid solution, and the acid solution is provided by a cation exchange membrane. It has a diffusion dialysis cell that supplies the hydrogen ions of the above to the cathode solution so that the pH of the cathode solution is 6 or more and 9 or less.

The microbial fuel cell according to claim 2 is the microbial fuel cell according to claim 1, wherein the hydrogen ion supply means includes a diffusion dialysis cell and an acid solution supply unit that supplies an acid solution to the diffusion dialysis cell. The acid solution supply unit has an acid solution storage unit for storing the acid solution and a discharge unit for discharging the excess acid solution from the diffusion dialysis cell to the acid solution storage unit.

The microbial fuel cell according to claim 3 is the microbial fuel cell according to claim 1 or 2, wherein the diffusion dialysis cell includes a cathode solution flow cell through which a cathode solution passes, an acid solution flow cell through which an acid solution passes, and these. It is located between the cathode solution flow cell and the acid solution flow cell, and has a cation exchange film capable of transmitting cations from the acid solution flow cell side to the cathode solution flow cell side.

The microbial fuel cell according to claim 4 is the microbial fuel cell according to any one of claims 1 to 3, wherein the hydrogen ion supply means includes a pH measuring means for measuring the pH of the cathode solution in the cathode solution storage portion. It has a supply adjusting means for adjusting the supply state of the cathode solution and the acid solution to the diffusion dialysis cell according to the measurement result of the pH measuring means, and the supply adjusting means has a pH of 6 or more 9 of the cathode solution. When the value is higher than the predetermined value below, the cathode solution and the acid solution are supplied to the diffusion dialysis cell, and when the pH of the cathode solution is lower than the predetermined value of 6 or more and 9 or less, the diffusion dialysis cell is supplied. The supply of at least one of the cathode solution and the acid solution is stopped, and the stopped supply is discharged from the diffusion dialysis cell.

According to the present invention, since the hydrogen ion supply means has a diffusion dialysis cell that supplies hydrogen ions of the acid solution to the cathode solution using a cation exchange membrane, it is possible to prevent the accumulation of anions in the cathode solution for a long period of time. It can be operated stably over the years.

It is explanatory drawing which shows typically the structure when the pH of the cathode solution is higher than a predetermined value in the microbial fuel cell which concerns on one Embodiment of this invention. It is explanatory drawing which shows typically the structure when the pH of the cathode solution is lower than a predetermined value in the microbial fuel cell of the same as above. It is a graph which shows the time-dependent change of the current density in an Example and a comparative example of a microbial fuel cell. It is a graph which shows the time-dependent change of the electric conductivity in an Example and a comparative example of a microbial fuel cell.

Hereinafter, the configuration of one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a microbial fuel cell, which extracts electrical energy from a wastewater W1 containing an organic pollutant supplied to a fuel cell body 2 via a wastewater supply pump 3. ..

The microbial fuel cell 1 has an anode chamber 5 in which one electrode, the anode 4, is immersed in the drainage W1 supplied via the drainage supply pump 3, and a cathode chamber 7 in which the cathode solution W2 is immersed in the cathode 6, which is the other electrode. And a so-called two-chamber type configuration including a cation exchange film 8 as a diaphragm that is located between the anode chamber 5 and the cathode chamber 7 and allows cations to permeate from the anode chamber 5 side to the cathode chamber 7 side. Is.

The anode 4 is formed in a plate shape by a conductive member, and in a state of being immersed in the drainage W1 housed so as to fill the anode chamber 5, one surface is in contact with the cation exchange membrane 8 and the other is in contact with the cation exchange membrane 8. The side surface is installed so as to be a part of the inner surface of the anode chamber 5 accommodating the drainage W1.

Further, on the other side surface of the anode 4, an anaerobic microbial membrane (not shown) that anaerobically decomposes organic pollutants contained in waste water W1 is formed. This anaerobic microbial membrane carries various anaerobic microorganisms and decomposes organic pollutants in wastewater W1.

The cathode 6 is formed of a conductive member in a plate shape, and one surface of the cathode 6 comes into contact with the cation exchange membrane 8 in a state of being immersed in the cathode solution W2 contained so as to fill the cathode chamber 7. The other surface is installed so as to be a part of the inner surface of the cathode chamber 7 containing the cathode solution W2.

The cathode solution W2 is a solution containing trivalent iron ions and a carboxylic acid chelating agent having four or more coordination loci. The carboxylic acid-based chelating agent in the cathode solution W2 combines with trivalent iron ions to form a chelating compound. Further, in order to prevent the formed chelate compound from leaking to the anode chamber 5 side via the cation exchange film, the carboxylic acid chelating agent in the cathode solution W2 has four or more coordination loci. Is preferable, and ethylenediaminetetraacetic acid (EDTA) is particularly preferable. Further, it is preferable to control the pH of the cathode solution W2 so as to be 9 or less.

In the cathode chamber 7, since the cathode 6 needs to be immersed in the cathode solution W2, the cathode solution W2 is not short-circuited, for example, in an upward flow type or a flow path structure.

The anode 4 and the cathode 6 are electrically connected to the external circuit 11. Any circuit can be connected as the external circuit 11.

Then, in the anode chamber 5, the electrons generated in the process of anaerobically decomposing the organic pollutants in the waste water W1 are collected in the anode 4. The collected electrons move from the anode 4 to the cathode 6 through the external circuit 11. Further, hydrogen ions generated in the process of anaerobic decomposition of organic pollutants pass through the cation exchange membrane 8 and move to the cathode chamber 7 side.

In the cathode chamber 7, trivalent iron ions (iron (III) ions) in the cathode solution W2 receive electrons transferred through the external circuit 11 and become divalent iron ions (iron (II) ions).

Here, since the divalent iron ions generated in the cathode chamber 7 do not contribute to the cathode reaction, trivalent iron ions are generated by the cathode solution supply means 12 so as not to reduce the electron acceptor concentration in the cathode chamber 7. The cathode solution W2 in the contained state is continuously supplied.

The cathode solution supply means 12 introduces the outflow liquid W3, which is the cathode solution after the cathode reaction has proceeded from the cathode chamber 7, and oxidizes the divalent iron ions in the liquid. It has a circulation means 14 for circulating a cathode solution W2 containing a trivalent iron ion obtained by oxidizing a valent iron ion to a cathode chamber 7.

The oxidizer 13 is a filter bed layer formed by filling an oxide tank 15 as a tubular oxidizer main body connected to the cathode chamber 7 with a granular filler 16 capable of holding the effluent W3 by surface tension or the like. Has 17.

Further, the outflow liquid W3 from the cathode chamber 7 flows into the oxide tank 15 through the inflow port at the upper part of the oxide tank 15.

Further, the cathode solution W2 oxidized in the oxide tank 15 flows out from the oxide tank 15 through the outlet at the lower part of the oxide tank 15.

Then, in the oxidizing apparatus 13, the effluent W3 from the cathode chamber 7 is dropped from the inflow port, and the effluent W3 flows downward through the filter bed layer 17 while being held so as to propagate along the filler 16. Further, when passing through the filter bed layer 17, an oxidation reaction occurs due to oxygen in the atmosphere, and iron ions in the effluent W3 are oxidized from divalent to trivalent. That is, in the filter bed layer 17 of the oxidation tank 15, the oxidation reaction represented by the formula of ^{4Fe 2+} + O ₂ + 2H ₂ O → 4Fe ³⁺ + 4OH ^{− proceeds.} Further, the cathode solution W2 in which iron ions are trivalently oxidized after passing through the filter bed layer 17 flows out from the outlet and flows into the circulation means 14.

The lower limit of the watering load of the effluent W3 from the cathode chamber 7 to the oxide tank 15 can be determined based on the application conditions of the standard watering filter method that is put into practical use under the low load condition of the watering load. preferable. That is, the watering load of the standard watering filter method is 1 to ³ m 3 / m ² days, and the normal filter bed thickness is 1.5 to 2 m. Therefore, when the RoyukaAtsu to 2m, watering load per volume 1 m ³ of filter bed, because the 0.5~1.5m ³ / ^{m 3} · day, it is preferable to apply the lower limit value.

On the other hand, as the watering load increases, the oxidation efficiency gradually decreases in all cathode solutions having different chelating agents. Therefore, the upper limit of the practical watering load is preferably ^{40 m 3} / m ^{3 days.}

Therefore, the specific watering load on the oxide tank 15 is preferably 0.5 m ³ / m ³ days or more and 40 m ³ / m ³ days or less ^{per 1 m 3 volume of the filter bed layer 17.}

The circulation means 14 transfers the cathode solution storage unit 18, which is a tank for storing the oxidized cathode solution W2 flowing out from the oxide tank 15 through the outlet, and the cathode solution W2 of the cathode solution storage unit 18 to the cathode chamber 7. It has a cathode solution supply pump 19 to supply.

Then, the cathode solution W2 from the oxidizing apparatus 13 is temporarily stored in the cathode solution storage unit 18, and is continuously supplied to the cathode chamber 7 by a predetermined amount by the cathode solution supply pump 19.

Here, since hydroxide ions are also generated in the oxidation reaction in the oxide tank 15, when the cathode solution W2 is supplied from the oxide tank 15 to the cathode solution storage unit 18, hydroxide ions increase in the cathode solution storage unit 18. The pH of the cathode solution W2 gradually rises.

Therefore, by supplying only hydrogen ions to the cathode solution W2 of the cathode solution storage unit 18 to the microbial fuel cell 1, the increase in pH due to hydroxide ions of the cathode solution W2 is prevented, and the cathode due to the above reaction is prevented. A hydrogen ion supply means 21 for preventing the accumulation of anions in the solution storage unit 18 is provided.

The hydrogen ion supply means 21 has a diffusion dialysis cell 23 that selectively supplies hydrogen ions of an acid solution W4 such as hydrochloric acid from the acid solution supply unit 22 to the cathode solution W2 from the cathode solution storage unit 18. ..

The diffusion dialysis cell 23 is located between the cathode solution flow cell 24 through which the cathode solution W2 passes, the acid solution flow cell 25 through which the acid solution W4 passes, and the cathode solution flow cell 24 and the acid solution flow cell 25. It has a cation exchange film 26 that can selectively permeate cations from the side to the cathode solution flow cell 24 side.

Then, the cathode solution W2 and the acid solution W4 are supplied to the diffusion dialysis cell 23 by driving a pump 27 such as a tube pump, the cathode solution W2 passes through the cathode solution flow cell 24, and the acid solution W4 passes through the acid solution flow cell 25. Upon passing through, the hydrogen ions of the acid solution W4 permeate (diffuse and move) through the cation exchange film 26 and are supplied to the cathode solution W2. Further, the cathode solution W2 to which hydrogen ions are supplied is returned to the cathode solution storage unit 18, and the cathode solution W2 in the cathode solution storage unit 18 is agitated by the stirrer 28.

Here, since the hydrogen ion supply means 21 is intended to suppress the accumulation of anions in the cathode solution storage unit 18 during long-term operation and prevent the pH of the cathode solution W2 from rising, the cathode solution is stored. It is preferable to operate according to the pH of the cathode solution W2 of Part 18.

Therefore, the hydrogen ion supply means 21 includes a pH measuring means (not shown) for measuring the pH of the cathode solution W2 in the cathode solution storage unit 18, and a cathode solution W2 and an acid solution to the diffusion dialysis cell based on the pH measured by the pH measuring means. It has a control unit as a supply adjusting means (not shown) for adjusting the supply state of W4.

Further, the acid solution supply unit 22 has an acid solution storage unit 31 for storing the acid solution W4 and a discharge unit 32 for discharging the excess acid solution W4 from the diffusion dialysis cell 23 to the acid solution storage unit 31. ing.

The discharge unit 32 has a three-way solenoid valve 33 as a route switching means provided between the pump 27 and the acid solution flow cell 25, and the acid from the acid solution flow cell 25 to the acid solution storage unit 31 via the three-way solenoid valve 33. It has a discharge line 34 that serves as a route for discharging the solution.

Then, when the pH of the cathode solution W2 of the cathode solution storage unit 18 is higher than a predetermined value (for example, pH 7), the supply adjusting means controls the three-way electromagnetic valve 33 by the control unit as shown in FIG. The path from the pump 27 to the acid solution flow cell 25 is opened, and the discharge line 34 from the acid solution flow cell 25 to the acid solution storage unit 31 is closed. In this supply state, the pump 27 operates to supply both the cathode solution W2 and the acid solution W4 to the diffusion dialysis cell 23, so that hydrogen ions are supplied from the acid solution W4 to the cathode solution W2 via the cation exchange membrane 26. The pH is lowered by returning the cathode solution W2 to which the hydrogen ions are supplied to the cathode solution storage unit 18.

On the other hand, when the pH of the cathode solution W2 of the cathode solution storage unit 18 is lower than a predetermined value (for example, pH 7), the supply adjusting means controls the three-way electromagnetic valve 33 by the control unit as shown in FIG. The path from the pump 27 to the acid solution flow cell 25 is blocked, and the discharge line 34 from the acid solution flow cell 25 to the acid solution storage unit 31 is opened. That is, in the discharge state, the pump 27 is stopped, the supply of the acid solution W4 to the acid solution flow cell 25 is stopped, and the acid solution W4 remaining in the acid solution flow cell 25 is passed through the discharge line 34 by gravity to acid. Discharge to the solution storage unit 31.

Further, in such a discharge state, the acid solution W4 is discharged into the acid solution flow cell 25, so that excess hydrogen ions from the acid solution W4 are discharged with respect to the cathode solution W2 whose pH is lower than a predetermined value. The supply is cut off.

It should be noted that the predetermined value of the above pH, which serves as a reference for switching the supply state to the diffusion dialysis cell 23, is that the pH is not biased toward acidity from the viewpoint of preventing the back diffusion of hydrogen ions from the cathode solution W2 to the anode chamber 5. Since it is appropriate and it is inappropriate that the pH is biased toward alkaline from the viewpoint of suppressing the formation of hydroxide precipitate of iron ions, the range of 6.0 or more and 9.0 or less is preferable, and it is 7.0. The closer it is, the more preferable.

The supply adjusting means is not limited to the configuration in which the supply of the acid solution W4 to the diffusion dialysis cell 23 is stopped when the pH of the cathode solution W2 in the cathode solution storage unit 18 is lower than a predetermined value as described above, and the diffusion dialysis is performed. The supply of the cathode solution W2 to the cell 23 may be stopped, or the supply of both the cathode solution W2 and the acid solution W4 to the diffusion dialysis cell 23 may be stopped.

Further, the discharge unit 32 is not limited to the configuration in which the three-way solenoid valve 33 is provided, and may be a configuration that can discharge the excess acid solution W4 of the diffusion dialysis cell 23 to the acid solution storage unit 31.

Further, although the pump 27 independently supplies both the cathode solution W2 and the acid solution W4 to the diffusion dialysis cell 23, it may be configured to be supplied by two independent pumps.

Next, the operation and the like of the above-described embodiment will be described.

In the microbial fuel cell 1, the wastewater W1 containing the organic pollutants flows into the anode chamber 5 by the wastewater supply pump 3, and the organic pollutants are anaerobically decomposed by the anaerobic microbial film formed on the anode 4. Further, the electrons generated by the anaerobic decomposition are collected by the anode 4 and moved to the cathode 6 via the external circuit 11.

In the cathode chamber 7, trivalent iron ions, which are electron acceptors in the cathode solution W2, become divalent iron ions by receiving electrons from the anode 4. Further, the hydrogen ions permeated from the anode chamber 5 react with the hydroxide ions generated by the oxidation reaction in the oxide tank 15 to generate water.

Further, hydrogen ions generated by anaerobic decomposition in the anode chamber 5 pass through the cation exchange membrane 8 and move to the cathode chamber 7 side to form an electric circuit.

The effluent W3, which is the cathode solution after the cathode reaction proceeds after receiving electrons, is introduced from the cathode chamber 7 into the oxidizing device 13 to oxidize the divalent iron ions in the liquid, and the cathode having the trivalent iron ions. It is supplied as the solution W2 to the cathode solution storage unit 18.

In such an oxidation reaction in the oxidizing apparatus 13, hydroxide ions are also generated, so that the pH of the cathode solution W2 in the cathode solution storage unit 18 gradually rises with the lapse of the operating time.

When the pH of the cathode solution W2 in the cathode solution storage unit 18 is higher than 7, the hydrogen ion supply means 21 connected to the cathode solution storage unit 18 is set to the supply state shown in FIG. The pH is lowered by selectively supplying the hydrogen ions in the acid solution W4 to the solution W2 and returning the cathode solution W2 to which the hydrogen ions are supplied to the cathode solution storage unit 18.

When hydrogen ions are supplied from the acid solution W4 to the cathode solution W2 in this way, cations such as sodium ions and potassium ions diffuse and move from the cathode solution W2 to the acid solution W4, so that the ions in the acid solution W4 Balance is maintained.

Further, the cations in the cathode solution W2 are supplied by the cations in the wastewater W1 being diffused and moved to the cathode solution in the fuel cell main body 2.

As for the acid solution W4, the hydrogen ion concentration decreases and the salt accumulates as the diffusion dialysis cell 23 moves, so that the acid solution W4 in the acid solution storage portion 31 elapses after a predetermined period of time. However, compared to the chelating agent of Patent Document 1, for example, the acid solution W4 itself is extremely cheap, and when neutralized, it becomes a harmless neutral salt solution, and the cost of obtaining and disposing of it is also high. Can be minimized.

On the other hand, when the pH of the cathode solution W2 in the cathode solution storage unit 18 is lower than 7, it is not necessary to supply hydrogen ions to the cathode solution W2, so that the hydrogen ion supply means connected to the cathode solution storage unit 18 21 is set to the discharge state shown in FIG. 2, and the supply of the acid solution W4 to the diffusion dialysis cell 23 is stopped.

Even when the pH is lower than 7, for example, if the pump 27 is simply stopped, the diffusion movement of hydrogen ions continues between the cathode solution W2 and the acid solution W4 remaining in the diffusion dialysis cell 23. As the pH of the cathode solution W2 in the diffusion dialysis cell 23 drops, the cathode solution W2 in the diffusion dialysis cell 23 flows into the cathode solution storage unit 18 at the next operation when the pump 27 is operated, which is more than expected. The pH in the cathode solution reservoir 18 may drop.

Therefore, when the pH of the cathode solution storage unit 18 is lower than 7, and it is not necessary to diffuse and move hydrogen ions, the path from the pump 27 to the acid solution flow cell 25 is blocked, and the acid solution flow cell 25 to the acid solution 25 is blocked. It is preferable that the discharge line 34 to the storage unit 31 is opened and the excess acid solution W4 remaining in the diffusion dialysis cell 23 is discharged to the acid solution storage unit 31 by the discharge unit 32.

According to the above-mentioned microbial fuel cell, the hydrogen ion supply means 21 can prevent the accumulation of anions in the cathode solution W2, so that the decrease in power generation efficiency due to the accumulation of anions can be prevented and the operation is stable for a long period of time. It is possible.

Further, since the acid solution supply unit 22 has a discharge unit 32 for discharging the excess acid solution W4 remaining in the diffusion dialysis cell 23, the diffusion dialysis cell is used when it is not necessary to supply hydrogen ions to the cathode solution W2. The diffusion movement of hydrogen ions in 23 can be stopped more accurately as needed, and the pH in the cathode solution reservoir 18 can be adjusted more appropriately by the hydrogen ion supply means 21.

Further, the hydrogen ion supply means 21 supplies the cathode solution W2 and the acid solution W4 to the diffusion dialysis cell 23 when the pH of the cathode solution W2 of the cathode solution storage unit 18 is higher than 7, and the cathode solution of the cathode solution storage unit 18 Since the supply of at least one of the cathode solution W2 and the acid solution W4 to the diffusion dialysis cell 23 is stopped when the pH of W2 is lower than 7, it is more efficient to operate according to the pH in the cathode solution storage unit 18. Accumulation of anions can be prevented.

Hereinafter, this example and a comparative example will be described.

With respect to the microbial fuel cell 1 (Example) having the configuration shown in FIGS. 1 and 2 and the microbial fuel cell (Comparative Example) having the conventional configuration in which the diffusion dialysis cell 23 is not provided, the generated current density according to the elapsed days and the generated current density and The change in electrical conductivity was measured to confirm the power generation status.

In both the examples and the comparative examples, for the fuel cell main body 2, the anode chamber 5 side has a volume of 867 mL, and the supply amount of the raw water (Ryukoku University actual sewage) of the drainage model to be supplied is 3.6 mL / min. The residence time was 4 hours, and the cathode chamber 7 side was operated so that the volume was 70.1 mL and the watering load on the oxide tank 15 was 6.88 m ³ / m ³ days.

The effective electrode areas of the anode 4 and the cathode 6 of the fuel cell body 2 are both 200 cm ² .

The diffusion dialysis cell 23 contains a cathode solution W2 (FeCl ₃ : 5 mM, Na ₂ EDTA 10 mM, NaOH) via a single cation exchange membrane 26 (Nafion® Ne-1110, effective area 32.2 cm ^2). The pH is adjusted to 7) and the acid solution W4 (hydrochloric acid 20 mM) are in contact with each other, and hydrogen ions move from the acid solution W4 to the cathode solution W2 by concentration diffusion.

The volumes of the cathode solution storage unit 18 and the acid solution storage unit 31 are both 800 mL.

Further, the cathode solution flow cell 24 and the acid solution flow cell 25 of the diffusion dialysis cell 23 have a width of 2.8 cm, a height of 11.5 cm and a thickness of 0.5 cm (effective volume 16.1 cm ³ ), and are a tube pump pump 27. The cathode solution W2 and the acid solution W4 were each passed at a flow rate of 1.5 mL / min.

In the comparative example in which the diffusion dialysis cell 23 was not used, the pH was adjusted by directly adding an acid (10N sulfuric acid) to the cathode solution storage unit 18 by a pump based on the pH sensor.

FIG. 3 shows changes in current density over time with respect to the power generation status in these Examples and Comparative Examples. From the experimental results shown in FIG. 3, it can be confirmed that the current density of the examples is higher than that of the comparative examples, and stable power generation continues even after the lapse of a predetermined period.

Further, FIG. 4 shows the change over time in the electrical conductivity of the cathode solution W2. As shown in FIG. 4, in the comparative example, the electric conductivity increased with time and the influence of the accumulation of anions was confirmed, but in the example, the electric conductivity remained low and the anions were maintained. The effect of the accumulation of was not confirmed.

Furthermore, when the iron concentration in the cathode solution W2 after the completion of the above experiment was measured by ICP emission spectroscopic analysis, it was 244 mg / L in the comparative example, whereas it was 257 mg / L in the example.

The iron concentration at the beginning of the experiment was 5 mM (279 mg / L), and considering the dilution effect due to the permeation of the added acid and water, it is considered that almost no iron outflow occurred.

Therefore, in the examples, it was confirmed that the microbial fuel cell 1 can be continuously and stably operated while suppressing the accumulation of anions in the cathode solution W2 by controlling the pH by the diffusion dialysis cell 23.

1 Microbial fuel cell 2 Fuel cell body 4 Anode 5 Anode chamber 6 Cathode 7 Cathode chamber 8 Cation exchange membrane as diaphragm
13 Oxidizer
14 Circulation means
18 Cathode solution reservoir
21 Hydrogen ion supply means
22 Acid solution supply unit
23 Diffusion dialysis cell
24 Cathode solution flow cell
25 Acid Solution Flow Cell
26 Cation exchange membrane
31 Acid solution reservoir
32 Discharge
W1 drainage
W2 cathode solution
Outflow as W3 cathode solution
W4 acid solution

Claims (4)

A microbial fuel cell that extracts electrical energy from wastewater containing organic pollutants.
It is located between the anode chamber in which the anode is immersed in the drainage, the cathode chamber in which the cathode is immersed in the cathode solution, and the anode chamber and the cathode chamber, and can permeate cations from the anode chamber side to the cathode chamber side. The main body of the fuel cell having a cathode and
An oxidizing device that oxidizes iron ions in the cathode solution of the cathode chamber from divalent to trivalent.
A circulation means that has a cathode solution storage unit that stores a cathode solution obtained by oxidizing iron ions in this oxidizing device and circulates the cathode solution from the cathode solution storage unit to the cathode chamber.
A hydrogen ion supply means for supplying hydrogen ions to the cathode solution of the cathode solution storage unit is provided.
The hydrogen ion supply means is a diffusion dialysis cell to which a cathode solution and an acid solution are supplied and the hydrogen ions of the acid solution are supplied to the cathode solution by a cation exchange membrane so that the pH of the cathode solution is 6 or more and 9 or less. A microbial fuel cell characterized by having. The hydrogen ion supply means includes a diffusion dialysis cell and an acid solution supply unit that supplies an acid solution to the diffusion dialysis cell.
The acid solution supply unit includes an acid solution storage unit for storing the acid solution and a discharge unit for discharging the excess acid solution from the diffusion dialysis cell to the acid solution storage unit. Item 1. The microbial fuel cell according to Item 1. The diffusion dialysis cell is located between the cathode solution flow cell through which the cathode solution passes, the acid solution flow cell through which the acid solution passes, and the cathode solution flow cell and the acid solution flow cell, and is located from the acid solution flow cell side to the cathode solution flow cell side. The microbial fuel cell according to claim 1 or 2, further comprising a cathode exchange film capable of transmitting a cathode ion. The hydrogen ion supply means adjusts the supply state of the cathode solution and the acid solution to the diffusion dialysis cell according to the pH measuring means for measuring the pH of the cathode solution in the cathode solution storage portion and the measurement result of the pH measuring means. Has a supply adjustment means,
When the pH of the cathode solution is higher than a predetermined value of 6 or more and 9 or less , the supply adjusting means supplies the cathode solution and the acid solution to the diffusion dialysis cell.
When the pH of the cathode solution is lower than a predetermined value of 6 or more and 9 or less, the supply of at least one of the cathode solution and the acid solution to the diffusion dialysis cell is stopped, and the stopped supply of the solution is supplied to the diffusion dialysis cell. The microbial fuel cell according to any one of claims 1 to 3, wherein the microbial fuel cell is discharged from.

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