Microbial power generation device and microbial power generation method

Abstract

A microbial power generation device according to the present invention comprises: an anode chamber that holds microorganisms and receives a supply of raw water that includes an organic substance that is an electron donor; and a cathode chamber that is partitioned from the anode chamber by an ion-permeable but non-electroconductive nanoporous or sub-nanoporous film and receives a supply of an oxygen-containing gas an electron acceptor. The microbial power generation device is characterized by comprising a circulation passage that recycles some anode chamber outflow water and supplies the anode chamber outflow water to the anode chamber.

Description

Microbial power generation device and microbial power generation method

[0001] The present invention relates to a microbial power generation device and a microbial power generation method, and more particularly to a microbial power generation device and a microbial power generation method that extract, as electrical energy, the reducing power obtained when organic matter is oxidatively decomposed by microorganisms.

[0002] The microbial power generation device comprises an anode chamber to which raw water containing organic matter that holds microorganisms and acts as an electron donor is supplied, and a cathode chamber separated from the anode chamber by a non-conductive nanoporous or subnanoporous membrane that is ion-permeable and to which an oxygen-containing gas is supplied as an electron acceptor (Patent Documents 1 and 2).

[0003] Patent Document 1 describes the use of a membrane, such as an RO membrane or an NF membrane, with a pore size of 10 nm or less or a divalent valence rejection of 50% or more, as the diaphragm separating the anode chamber and the cathode chamber. The use of such a diaphragm suppresses the permeation of impurities to the cathode while preventing an increase in proton transfer resistance, thereby enabling a high amount of power generation.

[0004] Patent Document 2 describes the introduction of carbon dioxide gas into the oxygen-containing gas supplied to the cathode chamber in an amount of 0.1 to 20% relative to the oxygen. By adding carbon dioxide gas in this way, the pH of the cathode chamber, which becomes highly alkaline, is neutralized, and the Na flow from the anode chamber to the cathode chamber is prevented. ＋ , K. ＋ This will promote the movement of people and improve power generation efficiency.

[0005] JP 2019-504446 A JP 2010-108778 A

[0006] CO in the cathode chamber ２ When a gas containing NaHCO ３ and KHCO ３ There is a risk that bicarbonates with relatively low solubility such as ammonium hydroxide may precipitate and block the flow path of the oxygen-containing gas.

[0007] An object of the present invention is to provide a microbial power generation device and a microbial power generation method in which the precipitation of bicarbonate in the cathode chamber is suppressed.

[0008] The gist of the present invention is as follows.

[0009] [1] A microbial power generation device comprising an anode chamber to which raw water containing microorganisms and organic matter acting as electron donors is supplied, and a cathode chamber separated from the anode chamber by an ion-permeable, non-conductive nanoporous or subnanoporous membrane to which an oxygen-containing gas is supplied as an electron acceptor, characterized in that the microbial power generation device is provided with a circulation flow path that circulates a portion of the anode chamber effluent water and supplies it to the anode chamber.

[0010] [2] A microbial power generation apparatus as described in [1], which has a raw water supply means for supplying raw water to the circulation flow path and a pH adjustment means for adjusting the pH of the inflow water to the anode chamber.

[0011] [3] A microbial power generation device according to any one of [1] to [3], which is equipped with an inorganic carbon concentration adjusting means for adjusting the inorganic carbon concentration of the anode chamber inflow water to 100 to 2,000 mg / L.

[0012] [4] The microbial power generation device of [3], wherein the inorganic carbon concentration adjusting means controls at least one of the flow rate of the anode chamber outflow water circulation flow path and the raw water supply amount.

[0013] [5] A microbial power generation device comprising an anode chamber to which raw water containing microorganisms and organic matter acting as electron donors is supplied, and a cathode chamber separated from the anode chamber by an ion-permeable, non-conductive nanoporous or subnanoporous membrane to which an oxygen-containing gas is supplied as an electron acceptor, characterized in that the microbial power generation device comprises an addition means for adding at least one of carbonate and bicarbonate to the raw water.

[0014] [6] A microbial power generation method for generating electricity using a microbial power generation device comprising an anode chamber that holds microorganisms and is supplied with raw water containing organic matter that acts as an electron donor, and a cathode chamber that is separated from the anode chamber by a non-conductive nanoporous or subnanoporous membrane that is ion permeable and is supplied with an oxygen-containing gas as an electron acceptor, characterized in that the inorganic carbon concentration of the inflow water to the anode chamber is set to 100 to 2,000 mg / L.

[0015] [7] The microbial power generation method according to [6], wherein the inorganic carbon concentration is adjusted by adding at least one of carbonate and bicarbonate to the raw water.

[0016] [8] The microbial power generation method according to [6], wherein a portion of the anode chamber effluent water is circulated and supplied to the anode chamber.

[0017] [9] The microbial power generation method according to [8], wherein the anode chamber effluent water circulating in the anode chamber is mixed with raw water, and the pH of the mixed water is adjusted to 6 to 9.

[0018] In one aspect of the present invention, a nanoporous or subnanoporous membrane with low air permeability and a pore size of 0.2 to 10 nm is used as the diaphragm of the microbial power generation device, and carbonate and / or bicarbonate are added to the raw water so that the inorganic carbon concentration of the inflow water to the anode chamber is 100 to 2,000 mg / L. When carbonate and / or bicarbonate are dissolved in water, bicarbonate ions (HCO ３ － ), carbonate ions (CO ３ ２－ ), and non-ionic, undissociated carbonic acid (H ２ CO ３ ) is produced. Undissociated carbonic acid (H ２ CO ３ ) passes through the diaphragm and moves from the anode chamber to the cathode chamber. In the highly alkaline cathode chamber, carbonic acid dissociates and the resulting hydrogen ions (H ＋ ) reduces the pH of the cathode chamber.

[0019] The anode chamber outflow water (treated water) contains CO generated by organic matter decomposition in the anode chamber. ２ In one embodiment of the present invention, instead of adding carbonate and / or bicarbonate to the raw water, a portion of the anode chamber effluent water is circulated to the anode chamber. This increases the inorganic carbon concentration (IC concentration) in the anode chamber, and the amount of undissociated carbonate (H ２ CO ３ ) permeates the membrane and moves from the anode chamber to the cathode chamber, causing a decrease in pH in the cathode chamber.

[0020] According to the present invention, the pH in the cathode chamber can be lowered without introducing carbon dioxide gas into the cathode chamber, and a high amount of power generation can be stably obtained for a long period of time.

[0021] 1 is a schematic cross-sectional view showing an example of a microbial power generation device according to a first embodiment. FIG. 2 is a schematic cross-sectional view showing an example of a microbial power generation device according to a second embodiment.

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0023] [First embodiment] Figure 1 is a schematic cross-sectional view showing an example of a microbial power generation device according to a first embodiment of the present invention.

[0024] The interior of the tank body 1 is divided into a cathode chamber 3 and an anode chamber 4 by a diaphragm (a non-conductive nanoporous or subnanoporous membrane having ion permeability) 2. The nanoporous or subnanoporous membrane that constitutes the diaphragm 2 is preferably a semipermeable membrane having a pore size of 0.2 to 10 nm, such as an RO membrane, NF membrane, or forward osmosis membrane. The thickness of the membrane is preferably about 20 to 500 μm, and is particularly preferably about 50 to 200 μm in order to reduce ion migration resistance while maintaining sufficient strength.

[0025] A positive electrode 5 is disposed in the cathode chamber 3 so as to be in contact with the diaphragm 2. The positive electrode 5 is preferably a plate-shaped positive electrode made of a conductive material (graphite, titanium, stainless steel, etc.). The positive electrode 5 preferably supports an oxygen reduction catalyst such as platinum, for example, by using graphite felt as a substrate. The conductive material of the cathode chamber 3 is preferably water-repellent to prevent its surface from becoming covered with water, which would reduce the oxygen supply rate. A spacer 5a is preferably inserted into the cathode chamber 3, and the positive electrode 5 is pressed against the diaphragm 2 to ensure close contact.

[0026] An oxygen-containing gas such as air is introduced into the cathode chamber 3 from the gas inlet 7 via the inlet pipe 23 , and exhaust gas flows out from the gas outlet 8 through the exhaust pipe 25 .

[0027] An anode 6 made of a conductive porous material is placed in the anode chamber 4. This anode 6 is in contact with the diaphragm 2 directly or via one or two layers of a microbial membrane. The anode is preferably a three-dimensional filler made of a conductive material (graphite, titanium, stainless steel, etc.), and is placed throughout the anode chamber.

[0028] The negative electrode is preferably a porous body with a large surface area, many voids, and water permeability so as to be able to retain many microorganisms.Specific examples include a sheet of a conductive material with at least a roughened surface, or a porous conductor (e.g., graphite felt, foamed titanium, foamed stainless steel, etc.) made of a conductive material in the form of felt or other porous sheets.

[0029] Microorganisms are supported on the negative electrode 6 made of a porous material. The negative electrode solution is introduced into the anode chamber 4 through an inlet 4a and can be discharged through an outlet 4b. Note that the negative electrode solution may not be passed through the anode chamber 4. The inside of the anode chamber 4 is made anaerobic.

[0030] The liquid in the anode chamber 4 is circulated via the outlet 12 , the circulation pipe 10 ( 10 a , 10 b ), the circulation pump 11 and the inlet 9 .

[0031] A discharge pipe branches off from the circulation pipe 10a for discharging a portion of the treated water (water anaerobically treated in the anode chamber 4) to the outside of the system.

[0032] A raw water supply pipe 16 is connected to the circulation pipe 10b so as to add raw water to the circulation water, and a raw water supply pump 17 is provided on the raw water supply pipe 16.

[0033] Further, downstream of the connection point of the raw water supply pipe 16 (towards the inlet 9), this circulation pipe 10b is provided with a pH meter 14 for measuring the pH of the mixed water of raw water and return circulation water, an inorganic carbon concentration meter (IC concentration meter) 15, and an alkali addition means 13 such as an aqueous sodium hydroxide solution is connected, and alkali is added as necessary so that the pH of this mixed water becomes 6 to 9. This mixed water of circulation water and raw water is introduced into the anode chamber 4. It is preferable that the inside of the anode chamber 4 is kept in a state close to a complete mixing state. Note that if the inorganic carbon concentration measured by the inorganic carbon concentration meter 15 is high, an acid is added to lower the pH, and all of the carbonic acid is made undissociated, and then N ２ Generally, carbon is evaporated by bubbling and the amount of evaporated carbon is measured.

[0034] The detection signal from inorganic carbon concentration meter 15 is input to controller 18, which controls the amount of circulating water by circulation pump 11 and the amount of raw water supplied by pump 17 so that the inorganic carbon concentration detected by inorganic carbon concentration meter 15 is preferably 100 to 2000 mg / L, and particularly preferably 400 to 1000 mg / L. Specifically, if the detected concentration is below the lower threshold, the output of circulation pump 11 is increased, and if the detected concentration is still below the lower threshold, the output of raw water supply pump 17 is decreased. Conversely, if the detected concentration is above the upper threshold, the output of circulation pump 11 is decreased, and if the detected concentration is still above the upper threshold, the output of raw water supply pump 17 is increased. Generally, if the amount of circulating water is increased, the inorganic carbon concentration detected by inorganic carbon concentration meter 15 increases, and if the amount of raw water supply is increased, the detected inorganic carbon concentration decreases.

[0035] Condensed water generated in the cathode chamber 3 is discharged from a condensed water outlet (not shown).

[0036] Due to the electromotive force generated between the positive electrode 5 and the negative electrode 6, a current flows through the external resistor 21 via the lead wires 20 and 22.

[0037] By passing an oxygen-containing gas such as air, oxygen-enriched air, or pure oxygen through the cathode chamber 3 and circulating the liquid in the anode chamber 4 while supplying raw water, the following mixture is formed in the anode chamber 4: (organic matter) + H ２ O → CO ２ +H ＋ +e－ The reaction proceeds as follows. － flows through the negative electrode 6 , the lead wire 22 , the external resistor 21 , and the lead wire 20 to the positive electrode 5 .

[0038] In the anode chamber 4, CO is produced by the decomposition reaction of organic matter and water by microorganisms. ２ The pH tends to decrease due to the generation of alkali. Therefore, alkali is added to the circulating water so that the detected pH value of the pH meter 14 is preferably 6 to 9. The alkali adding means 13 is preferably equipped with a tank for an aqueous alkali solution such as sodium hydroxide or potassium hydroxide, and a chemical injection pump.

[0039] In the cathode chamber 3, the positive electrode 5 ２ +4H ＋ +4e － →2H ２ During this reaction, cations move from the anode chamber 4 through the diaphragm 2 to the positive electrode 5 so that the anode chamber 4 and the cathode chamber 3 are kept electrically neutral. The solution in the anode chamber 4, whose pH is adjusted to 6 to 9, is usually ＋ Compared to the concentration, Na from raw water and pH adjuster ＋ Ya K ＋ Concentration is 10 ３ ~10 ５ Since it is twice as expensive, Na ＋ Ya K ＋ The H produced in the positive electrode reaction moves preferentially. ２ The condensed water produced by the condensation of O contains K that has permeated the cation permeable membrane of the diaphragm 2. ＋ , Na ＋ However, since the inorganic carbon concentration in the anode chamber 4 is high at 100 to 2000 mg / L, the pH of the condensed water tends to increase. ２ CO ３ ) moves through the membrane 2 to the cathode chamber 3 by concentration diffusion, and the pH of the condensed water decreases due to the neutralization action of the carbon dioxide. ＋ , K ＋ This promotes the movement of heat and improves power generation efficiency.

[0040] The microorganisms in the anode chamber 4 and the organic matter in the raw water that serves as the electron donor are not particularly limited.

[0041] The organic matter is not particularly limited as long as it can be decomposed by microorganisms, and examples thereof include water-soluble organic matter, organic fine particles that disperse in water, etc. The raw water containing this organic matter may be organic wastewater such as sewage or wastewater from food factories.

[0042] Raw water containing organic matter and preferably microbial nutrients is supplied to the anode chamber after adjusting the pH of the solution to 6 to 9, more preferably 6.5 to 7.5, which is suitable for the growth of electricity-generating bacteria and increases the concentration of undissociated carbonate, and then electrons and protons are generated by the microbial reaction. The temperature condition of the anode chamber is from room temperature to a medium-high temperature, specifically about 20 to 60°C, and particularly preferably about 25 to 45°C.

[0043] The negative electrode solution is a solution that can support microorganisms or cells and has a composition necessary for power generation. For example, when generating power through a respiratory system, a medium containing an energy source and nutrients necessary for respiratory metabolism, such as bouillon medium, M9 medium, L medium, Malt Extract, MY medium, or a nitrifying bacteria selective medium, can be used as the negative electrode solution. Organic waste such as sewage, organic industrial wastewater, or food waste can also be used.

[0044] The negative electrode solution may contain a phosphate buffer, if necessary.

[0045] [Second embodiment] Figure 2 shows an example of a microbial power generation device according to a second embodiment.

[0046] In this embodiment, the circulation pipe 10 and the circulation pump 11 are omitted, and instead, a treated water outflow pipe 10A is connected to an outlet 12.

[0047] Furthermore, a raw water supply pipe 16 is directly connected to the inlet 9, and the raw water supply pump 17, pH meter 14, inorganic carbon concentration meter 15, and alkali addition means 13 are provided in this pipe 16. Furthermore, in this embodiment, carbonate or bicarbonate addition means 19 is connected to this pipe 16. In this embodiment, the carbonate or bicarbonate addition means is provided between the raw water supply pump 17 and the alkali addition means 13, but is not limited to this.

[0048] The detection signal from the inorganic carbon concentration meter 15 is input to a controller 18, which controls the raw water supply pump 17 and the chemical injection pump (not shown) of the carbonate or bicarbonate adding means 19 so that the concentration detected by the inorganic carbon concentration meter 15 is 100 to 2000 mg / L, preferably 400 to 1000 mg / L. Specifically, if the detected concentration is below the lower threshold, the output of the chemical injection pump is increased, and if the detected concentration is still below the lower threshold, the output of the raw water supply pump 17 is decreased. Conversely, if the detected concentration is above the upper threshold, the output of the chemical injection pump is decreased, and if the detected concentration is still above the upper threshold, the output of the raw water supply pump 17 is increased. Suitable carbonates or bicarbonates are sodium salts, potassium salts, and ammonium salts. The carbonate or bicarbonate adding means 19 preferably includes a tank for an aqueous solution of a carbonate or bicarbonate, such as sodium carbonate or sodium bicarbonate, and a chemical injection pump.

[0049] The other configurations of the microbial power generation device of the second embodiment are the same as those of the microbial power generation device of the first embodiment, and in Figure 2, the same reference numerals as in Figure 1 indicate the same parts.

[0050] Comparative Examples and Examples will be described below.

[0051] Comparative Example 1 The microbial power generation device shown in FIG. 2 was configured as follows.

[0052] An anode chamber (volume 175 mL) 4 measuring 25 cm in length, 7 cm in width, and 1 cm in thickness was filled with 1 cm thick graphite felt to form a negative electrode 6. A cathode chamber 3 was formed between this anode chamber 4 and an RO membrane (ES-20 manufactured by Nitto Denko) as a diaphragm 2. The cathode chamber 3 measured 25 cm in length, 7 cm in width, and 0.5 cm in thickness (volume 87.5 mL). A gas diffusion electrode was placed in the cathode chamber 3 as a positive electrode. A 0.4 cm thick polyethylene lattice molded body was filled in order to closely contact the positive electrode with the support layer side of the RO membrane. The gas diffusion electrode was formed by dispersing Pt-loaded carbon black (Pt content 50 wt%) in Nafion® solution at a concentration of 0.5 mg-Pt / cm on one side of 160 μm thick carbon paper treated with water repellency using PTFE. ２ The coating was applied so that the thickness was 130° C., and the resulting coating was used.

[0053] Stainless steel wires were attached to the graphite felt anode and carbon paper cathode using conductive paste to form lead wires 20 and 22, respectively, and connected across an external resistor 21. The external resistance was set to 100 Ω at start-up and gradually decreased depending on the power output. This microbial power generation device was placed in a room controlled at 35°C.

[0054] Raw water containing 600 mg / L of ethanol, 100 mg / L of yeast extract, 50 mM phosphate buffer, and ammonium chloride (COD Ｃｒ 1,400 mg / L, pH 7.2) was supplied at 3 mL / min in an upflow manner (HRT 1 hr, COD Ｃｒ Tank load 34kg / m ３ / d).

[0055] No carbonate and / or bicarbonate was added to the raw water.

[0056] Prior to the introduction of raw water, the effluent from another microbial power generation device was introduced as an inoculum. Air was supplied to the cathode chamber in a downward flow at a flow rate of 300 mL / min. No negative electrode solution was introduced through the inlet 4a or outlet 4b.

[0057] After the start of operation, the average power generation amount and COD for 10 days from the 10th to the 20th day ＣｒThe average removal rate and the observation results of the operating conditions are shown in Table 1. Table 2 shows the pH of the anode chamber influent (raw water for Comparative Examples 1 to 3 and Example 1, and raw water and circulated water for Examples 2 to 4 in which treated water circulation was performed), anode chamber effluent (treated water), and cathode chamber effluent, as well as the IC concentrations of the anode chamber influent and effluent, on the 10th to 20th days after the start of operation. Note that an InnovOx Lab model manufactured by Veolia was used as the IC concentration meter 15.

[0058] Comparative Example 2 The procedure was the same as Comparative Example 1, except that 2% of carbon dioxide gas was introduced into the air supplied to the cathode chamber. The results are shown in Tables 1 and 2.

[0059] Comparative Example 3 The procedure was the same as Comparative Example 1, except that 2.4 g / L of NaCl was added to the raw water. The results are shown in Tables 1 and 2.

[0060] [Example 1] NaHCO ３ The same procedure as in Comparative Example 1 was carried out except that 3.5 g / L of was added. The results are shown in Table 1.

[0061] [Example 2] In Comparative Example 1, instead of the pipes 10A and 16, circulation pipes 10 (10a and 10b) and a circulation pump 11 were provided as shown in Figure 1, and pipe 10b was connected to pipe 16. The other configurations were the same as those of Comparative Example 1.

[0062] In this device, as shown in Figure 1, a portion of the water effluent from the anode chamber was circulated at 32 mL / min, mixed with raw water, and then the pH was adjusted to 7.2 by adding 1N NaOH before being supplied to the anode chamber. Other operating conditions were the same as in Comparative Example 1. The results are shown in Tables 1 and 2.

[0063] [Example 3] A portion of the anode chamber effluent water was circulated at 32 mL / min, mixed with raw water, and then the pH was adjusted to 6.2 by adding 1N NaOH or 1N HCl before being supplied to the anode chamber. The rest of the procedure was the same as in Example 2. The results are shown in Tables 1 and 2.

[0064] [Example 4] The same device configuration as in Comparative Example 1 was used, but a portion of the anode chamber effluent water was circulated at 32 mL / min, mixed with raw water, and then the pH was adjusted to 8.2 by adding 1N NaOH before being supplied to the anode chamber. The rest of the procedure was the same as in Example 2. The results are shown in Tables 1 and 2.

[0065]

[0066]

[0067] [Discussion] In all of Comparative Examples 1 to 3 and Examples 1 to 4, the amount of power generated began to increase 2 to 3 days after the start of operation, and the amount of power generated and removal rate reached their peaks around the 10th day, after which the performance was almost maintained, except for Comparative Example 2. As shown in Table 1, the amount of power generated was 220 W / m for Comparative Examples 1 and 3. ３ , 250 W / m ３ In contrast, in Examples 1 to 4, it was 290 to 420 W / m ３ The removal rate was also improved to 58-72%, which was equal to or greater than the 52-60% in Comparative Examples 1 and 3. The amount of power generation was 100-200 W / m in Comparative Examples 1 and 3 for the next three months. ３ In contrast, in Examples 3 and 4, the ３ In Examples 1 and 2, the ３ That was all.

[0068] In Comparative Example 2, the average power generation amount from 10 to 20 days after the start of operation was 430 W / m ３ Although the removal rate was also the highest at 78%, NaHCO ３ and KHCO ３ These substances precipitated and blocked the air, making it impossible to ventilate.

[0069] As shown in Table 2, the pH of the cathode chamber outflow water was high at 12.5 and 12.8 in Comparative Examples 1 and 3, but it dropped to 10.5 in Comparative Example 2, where carbon dioxide gas was introduced into the cathode chamber. Ｃｒ This appears to have led to an improvement in the removal rate, but on the other hand, the amount of NaHCO in the cathode chamber ３ and KHCO ３ In contrast, in Examples 1 to 4, NaHCO ３By adding carbon dioxide or circulating the treated water, the pH of the water effluent from the cathode chamber is reduced to 10.3 to 11.6 without introducing carbon dioxide gas into the cathode chamber, and the amount of power generation and COD are improved. Ｃｒ The removal rate was improved. In addition, unlike Comparative Example 2, the carbon dioxide concentration in the cathode chamber did not increase excessively, so NaHCO ３ and KHCO ３ It is believed that this allowed stable operation for three months.

[0070] In this way, it was found that the present invention makes it possible to lower the pH in the cathode chamber of a microbial power generation device without introducing carbon dioxide gas into the cathode chamber, thereby enabling a high amount of power generation to be obtained stably over a long period of time.

[0071] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of the effects of the invention. This application is based on Japanese Patent Application No. 2024-067635 filed on April 18, 2024, the entire contents of which are incorporated by reference.

[0072] REFERENCE SIGNS LIST 1 Tank body 2 Diaphragm 3 Cathode chamber 4 Anode chamber 5 Positive electrode 6 Negative electrode 10 (10a, 10b) Circulation pipe 10A Treated water outflow pipe 13 Alkali addition means 15 Inorganic carbon concentration meter 16 Raw water supply pipe 18 Controller 19 Carbonate or bicarbonate addition means 21 External resistance

Claims

1. A microbial power generation device comprising an anode chamber that holds microorganisms and is supplied with raw water containing organic matter that acts as an electron donor, and a cathode chamber that is separated from the anode chamber by a non-conductive nanoporous or subnanoporous membrane that is ion-permeable and is supplied with an oxygen-containing gas as an electron acceptor, characterized in that the microbial power generation device is equipped with a circulation flow path that circulates a portion of the water effluent from the anode chamber and supplies it to the anode chamber.

2. A microbial power generation apparatus as described in claim 1, further comprising a raw water supply means for supplying raw water to the circulation flow path, and a pH adjustment means for adjusting the pH of the inflow water into the anode chamber.

3. A microbial power generation device according to any one of claims 1 to 3, comprising an inorganic carbon concentration adjusting means for adjusting the inorganic carbon concentration of the anode chamber inflow water to 100 to 2,000 mg / L.

4. A microbial power generation apparatus according to claim 3, wherein the inorganic carbon concentration adjusting means controls at least one of the flow rate of the anode chamber outflow water circulation flow path and the amount of raw water supplied.

5. A microbial power generation device comprising an anode chamber to which raw water containing microorganisms and organic matter acting as electron donors is supplied, and a cathode chamber separated from the anode chamber by an ion-permeable, non-conductive nanoporous or subnanoporous membrane to which an oxygen-containing gas is supplied as an electron acceptor, characterized in that the microbial power generation device comprises an addition means for adding at least one of carbonate and bicarbonate to the raw water.

6. A microbial power generation method for generating electricity using a microbial power generation device comprising an anode chamber that holds microorganisms and is supplied with raw water containing organic matter that acts as an electron donor, and a cathode chamber that is separated from the anode chamber by an ion-permeable, non-conductive nanoporous or subnanoporous membrane and is supplied with an oxygen-containing gas as an electron acceptor, wherein the inorganic carbon concentration of the water flowing into the anode chamber is set to 100 to 2,000 mg / L.

7. The microbial power generation method according to claim 6, wherein the inorganic carbon concentration is adjusted by adding at least one of carbonate and bicarbonate to the raw water.

8. The microbial power generation method according to claim 6, wherein a portion of the anode chamber effluent water is circulated and supplied to the anode chamber.

9. The microbial power generation method according to claim 8, wherein the anode chamber effluent water circulating in the anode chamber is mixed with raw water, and the pH of the mixed water is adjusted to 6-9.

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