JP5829956B2 - Method and system for controlling microbial reaction in bottom soil - Google Patents

Description

  The present invention relates to a microbial reaction control method and system for bottom soil, and more particularly, to a method and system for electrochemically controlling a microbial reaction in bottom anaerobic soil.

Carbon dioxide (CO ₂ ), methane (CH ₄ ), nitrous oxide (N ₂ O), and other greenhouse gases (hereinafter sometimes referred to as greenhouse gases) that may increase the Earth's atmospheric temperature Since it may cause floods and abnormal weather that adversely affect human life, it is required to reduce or reduce the amount of such occurrences. For example, for greenhouse gases generated in industrial processes, efforts are made to reduce or reduce the generation amount by optimizing the process operation method (operating time, interval, etc.) in consideration of input energy and productivity. ing. In addition, development of a technique for suppressing the amount of generation from the entire process by decomposing the greenhouse gas generated in the industrial process with, for example, a catalyst or the like is also in progress.

  Greenhouse gases are generated not only from industrial processes, but also from natural waters such as lakes and rivers, agricultural land such as paddy fields, sewage treatment plants, waste disposal sites, landfills, and other natural environments. ing. Warming gases generated in industrial processes are mainly generated by physicochemical reactions such as combustion and reforming, whereas warming gases generated in natural environments are mainly originated from microbial reactions. For example, in lakes, rivers, etc., pollutants (organic matter, nitrogen compounds, etc.) contained in wastewater flowing from the surrounding area are decomposed anaerobically at the bottom of the water to generate greenhouse gases. For this reason, efforts are being made to suppress and reduce the amount of greenhouse gases generated by appropriately treating wastewater flowing into lakes, rivers, etc. to remove pollutants such as organic matter. In paddy fields and the like, organic matter deposited on the anaerobic bottom is decomposed into microorganisms to generate methane. For this reason, a method of reducing the amount of methane generated by adding magnesium oxide powder and / or magnesium hydroxide powder to paddy soil has been proposed (see Patent Document 1).

JP 2010-115572 A JP 2007-227216 A JP 2004-266629 A

Tadashi Watanabe and Seiichiro Nakabayashi "Chemistry of Electron Transfer-Introduction to Electrochemistry", Asakura Shoten, April 25, 1996, pp. 1-73 The Electrochemical Society of Japan “Electrochemical Measurement Manual / Basic”, published by Maruzen, April 5, 2002, pages 3-52

  Warming gas generated in lakes and rivers can be suppressed to some extent by the above-described wastewater treatment. However, in lakes, rivers, etc., organic matter mud such as sludge, bottom mud, and fallen leaves naturally accumulates in addition to pollutants flowing in from the surroundings. Therefore, there is a problem that the warming gas generated from the accumulated mud on the bottom cannot be sufficiently suppressed only by the above-described wastewater treatment. At present, there is no appropriate method to suppress the generation of warming gas from sedimentary mud other than artificial removal by dredging, and no appropriate technology has been developed to suppress the generation of warming gas at the deposited site. . In addition, in recent paddy fields, etc., there is a tendency to apply excess nitrogen fertilizer to improve productivity, and in addition to methane, greenhouse gases such as nitrous oxide are generated from the anaerobic bottom mud of paddy fields. Conventional methane reduction measures have a problem that the generation of nitrous oxide and the like cannot always be suppressed appropriately. In addition, even in sewage treatment plants, waste disposal sites, landfills, etc., considerable amounts of greenhouse gases including methane and nitrous oxide are generated from anaerobic deposits at the bottom of filtration tanks and discharge ponds. ing.

  Conventionally, warming gas generated from bottom sediment in lakes and rivers, bottom sediment in paddy fields, bottom sediment in sewage treatment plants, etc. (hereinafter, these may be collectively referred to as bottom soil) is an industrial process. Compared to the reduction of greenhouse gas emissions due to technological innovation in Japan, it has not been actively controlled or reduced. However, the total amount of greenhouse gases generated from the bottom soil is not always small. For example, if pollutants flowing into lakes and rivers are not properly managed, or organic substances such as garbage are directly disposed in landfills. When dumped, the bottom soil can be a source of huge greenhouse gases. Although the warming gas to be generated varies depending on the properties of the soil, if the microbial reaction in the soil can be appropriately controlled according to the properties of the bottom soil, it can be expected to suppress or reduce the generation of the warming gas.

  Therefore, an object of the present invention is to provide a method and system capable of appropriately controlling various microbial reactions in various soils according to the bottom soil.

The inventor paid attention to the principle of a microbial fuel cell that recovers electric energy from an organic substance using microorganisms. The microbial fuel cell has, for example, a conductive anode (negative electrode) 31 inserted into a container storing an organic substrate and a conductive material that is brought into contact with air (or an electron acceptor) as indicated by reference numeral 30 in FIG. A cathode (positive electrode) 32 and an ion exchange membrane 33 sandwiched between both electrodes 31 and 32, and the anode 31 and the cathode 32 are connected to each other via an external circuit 34 to form a closed circuit. Formed. An organic substrate (an aqueous solution or gas containing an organic substance) is supplied to the anode 31, and hydrogen ions (H ⁺ ) and electrons (e ⁻ ) are generated from the organic substrate by a microbial reaction on the anode 31. Ions are moved to the cathode 32 side via the ion exchange membrane 33, and electrons are moved to the cathode 32 side via the external circuit 34. On the other hand, air (or an electron acceptor) is supplied to the cathode 32, and hydrogen ions and electrons moved from the anode 31 are combined by oxygen (or electron acceptor) bonding. The microbial fuel cell 30 recovers electrical energy from the organic substrate via the external circuit 34 by this series of reactions.

  For example, a microbial fuel cell 30 is constructed by introducing methanogens or denitrifying bacteria around the anode 31 in FIG. 5 (see Patent Documents 2 and 3). It is similar to the microbial reaction that generates greenhouse gases (methane gas and nitrous oxide) in the soil. In addition, the reaction that occurs on the cathode 32 side of the microbial fuel cell 30 is a reaction that can also occur in the aqueous phase above the bottom soil. Furthermore, the microbial fuel cell 30 performs ion exchange and insulation by sandwiching an ion exchange membrane 33 between both electrodes 31 and 32, but a boundary phase between the bottom soil and the water phase (upper layer of the bottom soil). Can perform the same ion exchange and insulation functions. The microbial fuel cell 30 collects electrical energy corresponding to the oxidation-reduction potential of the microbial reaction. However, since all microbial reactions (biochemical reactions) depend on the oxidation-reduction potential, the two electrodes 31, If an appropriate oxidation-reduction potential is applied between 32 (external circuit 34), it is possible to control the microbial reaction occurring in the bottom soil through the anode 31. The present invention has been completed as a result of research and development based on this idea.

  Referring to the embodiment of FIG. 1, in the method for controlling microbial reaction of a bottom soil according to the present invention, a first electrode 11 is embedded in an anaerobic soil E on the bottom and a second electrode 12 is placed in water W above the bottom electrode. A predetermined microbial reaction (for example, methane gas generation reaction of methane bacteria, reduction reaction of nitrous oxide-reducing bacteria, etc.) in the soil E is performed by the potential controller 20 installed and connected between both electrodes 11 and 12. It is formed by controlling the redox potential V to be suppressed or promoted.

  In addition, referring to the embodiment of FIG. 1, the microbial reaction control system for a bottom soil according to the present invention includes a first electrode 11 embedded in an anaerobic soil E on the bottom and a second electrode installed in water W above the first electrode 11. A predetermined microbial reaction (for example, methane gas generation reaction of methane bacteria, reduction reaction of nitrous oxide reduction bacteria, etc.) in the soil E in the soil E is connected between the electrode 12 and both electrodes 11, 12. A potential control device 20 that controls the redox potential V to be suppressed or promoted is provided.

  Preferably, as shown in FIG. 2, in addition to the potential control device 20, a measurement unit 27 that measures a product generation amount of a predetermined microbial reaction, and a product generation amount of a predetermined microbial reaction while switching the potential of the first electrode 11. And a detecting means 28 for detecting a redox potential V at which a predetermined microbial reaction in the soil E is suppressed or promoted by measuring. In the preferred embodiment, as shown in FIG. 4, an inflow path 7 is provided for allowing the wastewater D containing the predetermined pollutant to flow into the soil E or the water W above the soil E, and the first electrode 11 is contaminated by the potential control device 20. It can be controlled to the redox potential V at which the decomposition microbial reaction of the substance is suppressed or promoted.

  The bottom soil microbial reaction control method and system according to the present invention includes a potential control device 20 between the first electrode 11 embedded in the bottom anaerobic soil E and the second electrode 12 installed in the water W thereabove. Are connected, and the first electrode 11 is controlled by the potential control device 20 to the oxidation-reduction potential V at which a predetermined microbial reaction in the bottom soil E is suppressed or promoted.

(B) Conventionally, warming gas generated from bottom sediments (bottom soil E) of lakes, rivers, etc. for which there was no appropriate control method other than dredging, was installed in the in-situ electrode pairs 11, 12 By simply controlling the oxidation-reduction potential V in the soil E, it can be suppressed / reduced by suppressing or promoting the microbial reaction that produces or consumes the greenhouse gas.
(B) In addition, by providing a measurement means 27 for measuring the amount of product generated by the predetermined microbial reaction in the bottom soil E, the product generation amount of the predetermined microbial reaction is measured while switching the oxidation-reduction potential V. An appropriate oxidation-reduction potential V corresponding to E can be selected to suppress the generation of warming gas stably and efficiently.
(C) By appropriately selecting the redox potential V according to the bottom soil E, various microbial reactions occurring in the soil E can be suppressed or promoted, not only methane, nitrous oxide, etc. It can also be applied and used in the case of simultaneous suppression including greenhouse gases.

(D) Not only microbial reactions that produce or consume greenhouse gases, but also other microbial reactions that occur in the bottom soil E can be used to suppress or promote microbial reactions that decompose toxic substances and various nutrients. It can also be expected to contribute to purification of the bottom soil E and improvement of the surrounding water quality by suppressing or promoting the above.
(E) For example, wastewater containing predetermined pollutants flows into the bottom soil E, and the bottom soil E is controlled to a redox potential V at which the degradation microbial reaction of the pollutants is suppressed or promoted. Can be used for processing.
(F) Underwater soil such as lakes, rivers, and paddy fields that have not been previously targeted for controlling or reducing greenhouse gases can be included in the target by applying the present invention. It can also be used for emissions trading (CDM) and corporate social contribution (CSR).

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the accompanying drawings.
These are the block diagrams of one Example of the microbial reaction control method of the bottom soil by this invention. These are explanatory drawings of the experiment which confirms the effect of the microorganisms reaction control method by this invention. These are an example of the graph which shows the experimental result of FIG. These are explanatory drawings of other Examples of the microbial reaction control method of the bottom soil by this invention. These are explanatory drawings which show the principle of a conventional microbial fuel cell.

  FIG. 1 shows an embodiment in which the microbial reaction control system of the present invention is applied to bottom soil E such as lakes, rivers, paddy fields, etc., in which the generation of greenhouse gases is to be suppressed. The system of the illustrated example includes a first electrode 11 embedded in an anaerobic soil E on the bottom of the water, a second electrode 12 installed in the water W above the first electrode 11, and a potential control device 20 connected between both electrodes 11, 12. And have. In general, the bottom soil E is anaerobic except for the oxide layer on the surface in contact with the upper water W, and organic substances are decomposed by anaerobic microorganisms in the anaerobic layer to generate methane and other warming gases. In the illustrated example, the first electrode 11 is embedded in the anaerobic layer below the oxide layer of the bottom soil E. For example, as shown in FIG. 2, the second electrode 12 is supported away from the bottom soil E by an appropriate support member 15. However, if the insulation with the first electrode 11 can be secured, the second electrode 12 is directly placed on the surface of the bottom soil E. May be.

  The electrodes 11 and 12 in the illustrated example can be made of, for example, carbon fiber, carbon plate, graphite or other conductive material, or can be made of a metal material. The potential control device 20 connected between the electrodes 11 and 12 controls the potential of the first electrode 11 to supply oxidizing power or reducing power into the bottom soil E to produce or consume warming gas in the soil E. By suppressing or promoting a predetermined microbial reaction, the microbial flora or microbial metabolism in the soil E is modified to suppress the generation of warming gas. As described above, since all microbial reactions (biochemical reactions) depend on the redox potential, by controlling the redox potential V of the first electrode 11, the metabolic pathway of the microbial reaction in the bottom soil E and Changes in metabolic rate can be effected.

For example, in the bottom soil E, the organic compound is hydrolyzed to be reduced in molecular weight, then first decomposed into an organic acid by the acid-producing bacteria group, and then the organic acid is hydrogen, carbon dioxide, acetic acid, etc. by the hydrogen-producing bacteria. And finally, acetic acid (CH ₃ COO ⁻ ) is reduced by methane bacteria to generate methane (CH ₄ ) (see formula (1)). In order to advance the microbial reaction of the formula (1) to the right side, the redox potential needs to be −240 mV or less, and methane is not generated at a higher redox potential than that from acetic acid by microorganisms such as iron reduction reaction. Acetic acid is oxidized to carbon dioxide by an electron emission reaction (formula (2)) or an oxygen respiration reaction (formula (3)). That is, in the illustrated example, if the first electrode 11 is controlled to −240 mV or more by the potential control device 20, the microbial reaction of the formula (1) in the bottom soil E is theoretically suppressed, and the methane from the bottom soil E is suppressed. Release can be suppressed. Although carbon dioxide is generated by the microbial reaction of formulas (2) to (3) instead of methane, the global warming potential of carbon dioxide (the intensity of the greenhouse effect that raises the Earth's atmospheric temperature) is about 1/20 of that of methane. Therefore, even if carbon dioxide is released instead of methane, the impact on global warming is small.

CH ₃ COO ⁻ + 9H ⁺ + 8e ⁻ → 2CH ₄ + 2H ₂ O (1)
CH ₃ COO ⁻ + 2H ₂ O → 2CO ₂ + 7H ⁺ + 8e ⁻ (2)
CH ₃ COO ⁻ + O ₂ → 2CO ₂ + 3H ⁺ + 4e ⁻ …………………………… (3)
2H ₂ O → 4H ⁺ + 4O ₂ + 4e ⁻ ……………………………………………… (4)
4H ⁺ + 4O ₂ + 4e ⁻ → 2H ₂ O ……………………………………………… (5)

As can be seen from a comparison between the formula (1) and the formulas (2) to (3), in the illustrated system, the first electrode 11 and the second electrode are controlled by controlling the oxidation-reduction potential V of the first electrode 11. 12, the moving direction of the electrons (e ⁻ ) can be switched. That is, if the oxidation-reduction potential is −240 mV or less, reducing power is supplied from the second electrode 12 to the first electrode 11 (electrons are released from the second electrode 12 to the first electrode 11), and methane is generated ( If the oxidation-reduction potential is controlled to −240 mV or more, the oxidizing power is supplied to the first electrode 11 (electrons are emitted from the first electrode 11 to the second electrode 12). ) Carbon dioxide is generated (see formulas (2) to (3) and (5)). Acetic acid consumed in the vicinity of the first electrode 11 is appropriately supplemented by the fermentation reaction of the surrounding organic matter, and H ⁺ consumed in the vicinity of the second electrode 12 is appropriately supplemented from the surrounding water W. A large amount of electrolyte (ie, salt) is dissolved in seawater, and various electrolytes are also dissolved in fresh water. In general, various electrolytes are dissolved from the bottom soil E. Although the reaction of the formulas (1) to (5) can be advanced without dissolving the electrolyte or the like in the water W, an appropriate electrolyte (inorganic salt or the like) may be added to the water W as necessary. It is valid.

  The potential control device 20 in the illustrated example controls the oxidation-reduction potential V of the first electrode 11 so that the above-described expression (1) and the expressions (2) to (3) are switched. Generally, in electrolysis, a potential difference is provided between the first electrode 11 and the second electrode 12 to cause the decomposition reaction to proceed. However, since only the two electrodes 11 and 12 cause the oxidation reaction and the reduction reaction to proceed simultaneously, Therefore, it is difficult to control one electrode 11 to a specific oxidation-reduction potential (for example, −240 mV or higher). In the illustrated example, a three-electrode potentiostat having a reference electrode 14 that always shows a constant redox potential is used together with the first electrode (working electrode) 11 and the second electrode (auxiliary electrode) 12 as the potential control device 20. ing. The three-electrode potential control device 20 can specify and control the exact potential of the first electrode 11 from the potential difference (voltage) between the reference electrode 14 and the first electrode 11. However, the potential control device 20 used in the present invention is not limited to a potentiostat, and may be a galvanostat.

  The three-electrode potential control device 20 in the illustrated example passes most of the current between the working electrode (first electrode) 11 and the auxiliary electrode (second electrode) 12, so that the working electrode 11 and the reference electrode 14 A potential control circuit 21 that determines the potential of the working electrode 11 by passing a minute current therebetween is provided. The potential of the working electrode 11 can be switched by the variable voltage circuit 22 of the potential control circuit 21, and the potential of the working electrode 11 is controlled based on the measured value of the voltmeter 23 and the potential of the reference electrode 14 (Non-Patent Documents 1 and 2). reference). For example, a target value of the redox potential (for example, the redox potential of the equation (1)) is set in the memory 24 of the potential control circuit 21, and the operating electrode 11 is accurately set to the target potential by the variable voltage circuit 22 and the voltmeter 23. Match. The potential control device 20 in the illustrated example includes a current measurement circuit 25 and an ammeter 26 between the working electrode 11 and the auxiliary electrode 12, and controls the potential of the working electrode 11 based on the measurement value of the ammeter 26. It is also possible.

  However, it is known that the microbial reaction that generates methane in the bottom soil E is not limited to the formula (1) but involves a plurality of methane bacteria. In addition, the environment of microbial reaction in the bottom soil E is not constant, the material constituting the soil E (the composition ratio of silt, sand, etc.), the gas phase, the liquid phase, the ratio of the solid phase that determines the physical properties of the soil E Depending on the aggregate formation state, the microstructure, pH, and water content change, and the oxidation-reduction potential V can vary due to the influence thereof. For example, there is a report that an oxidation-reduction potential of −150 mV or more is necessary to suppress methane production in the bottom soil E. In order to suppress the generation of greenhouse gases stably and efficiently, it is necessary to set the oxidation-reduction potential V in accordance with the constituent materials and physical properties of the in-situ bottom soil E. It is desirable to detect the oxidation-reduction potential V (for example, the oxidation-reduction potential V of the formula (1) in the original position) at which generation of a warming gas is suppressed and use it for control.

  FIG. 2 shows an embodiment of the potential control device 20 that detects the oxidation-reduction potential V corresponding to the original bottom soil E and uses it for control. The potential control apparatus 20 in the illustrated example includes a measuring unit 27 that measures a product generation amount (for example, methane concentration) of a microbial reaction. In addition, while switching the potential of the first electrode 11 embedded in the underwater soil E at the original position, the measured value of the product generation amount (for example, methane generation amount) of the microbial reaction is input, and the microbial reaction is actually performed at the original position. It has a detecting means 28 for detecting the oxidation-reduction potential V to be suppressed (for example, the oxidation-reduction potential V at which the microbial reaction of the formula (1) is suppressed in the original position and switched to the microbial reaction of the formulas (2) to (3)). doing. As shown in Experimental Example 1 to be described later, an oxidation-reduction potential V at which generation of a warming gas is suppressed is detected at each original position by the potential control device 20 in the illustrated example. For example, the detected potential V is detected by the potential control device 20. By setting the target value and controlling the first electrode 11, it is possible to stably and efficiently suppress the generation of warming gas.

[Experimental Example 1]
In order to confirm the effect of the microbial reaction control method according to the present invention, an experiment was performed to confirm the effect by creating an experimental apparatus shown in FIG. In this experiment, simulated bottom mud was prepared by mixing the bottom mud sampled from a freshwater fish farm and the soil purchased at a horticultural store as the original bottom soil E. About 2 liters of a container 5 with a lid (made of PET bottle) was filled, and a first electrode with a conducting wire (graphite plate, length 6 cm × width 5 cm × thickness 0.8 cm) was embedded at the bottom of the simulated bottom mud E. Moreover, about 0.4 liters of water W is put on the upper part of the simulated bottom mud E, and is supported by the support member 15 in the water W, and the second electrode 12 with a lead wire having the same size as the first electrode (graphite plate, vertical 6 cm × 5 cm wide × 0.8 cm thick). The conductors of the first electrode 11 and the second electrode 12 are connected to a three-electrode type potential control device 20 (potentiostat) to form a circuit, and the reference electrode 14 of the potential control device 20 is connected to the underwater near the first electrode 11. The oxidation-reduction potential V in the simulated bottom mud E can be arbitrarily set by the potential control device 20.

  In the experiment of FIG. 2, after diluting an inorganic salt medium (main components are sodium phosphate and trace salts) in water W above the simulated bottom mud E, it was added as an electrolyte. Further, a photoacoustic multi-gas monitor 27 is connected to the upper opening of the container 5 to continuously measure the methane concentration (methane generation amount) in the gas phase gas generated in the simulated bottom mud E by the microbial reaction in the container 5. In addition to the measurement, the detection means 28 for switching the target potential is connected to the potential control device 20, the control potential V of the first electrode 11 in the simulated bottom mud E is set, and the change in the methane concentration in the gas phase is measured. . The experimental results are shown in the graph of FIG.

  In the graph of FIG. 3, “Blank” indicates the methane generation concentration when no electrode is installed, and “Uncontrolled” indicates that electrodes 11 and 12 are embedded and installed, but a resistor is connected between the electrodes 11 and 12. The methane generation concentration in a state where no potential is applied to the electrode 11 (uncontrolled state) is shown. When the current flowing through the circuits of both electrodes 11 and 12 was monitored by the potential control device 20 in the uncontrolled state, the current value gradually increased over about 120 days, and it was recognized that a constant current was generated thereafter. It was. Since this current production is thought to be due to the decomposition of organic matter in the simulated bottom mud E, the microbial distribution of the genus Geobacter in the simulated bottom mud E was confirmed by quantitative PCR. This microorganism was unevenly distributed at a concentration of about 3 times that of other parts and about 15 times the concentration of the first electrode 11 itself. Similarly, when the number of methane bacteria was measured, it was reduced to about 1/7 in the vicinity of the first electrode 11 as compared with other parts. Furthermore, when the simulated bottom mud E in the vicinity of the first electrode 11 was sampled and the simulated bottom mud E in a part away from the electrode 11 was compared with the methane generation activity, the activity was reduced to about 1/25. From these facts, it was confirmed that the oxidizing power was supplied from the upper water W to the simulated bottom mud E through the circuit of the electrodes 11 and 12 even in the uncontrolled state, and the amount of methane generated was suppressed to some extent. It was. However, as shown in FIG. 3, in the uncontrolled state, although it is slightly lower than the methane gas concentration of Blank, about 7 ppm of methane is detected in the gas phase in the container 5, and the methane generation amount is stably and efficiently suppressed. Not done.

  From the above, it was confirmed that the oxidizing power was supplied into the bottom soil E only by the natural potential difference. However, the graph of FIG. 3 shows the oxidation-reduction of the first electrode 11 more actively using the potential control device 20. It shows that the methane concentration in the gas phase in the container 5 changes by switching the potential V. FIG. 3 shows the redox potential V using the silver / silver chloride electrode as the reference electrode 14. When the redox potential V is −200 mV or less, about 7 ppm of methane is generated, whereas the redox potential V is It shows that by setting it to -100 mV or more, the amount of methane generated is suppressed to 3 ppm or less, which is about half. From this experimental result, the oxidation-reduction potential V that suppresses the methane gas production reaction of methane bacteria in the simulated bottom mud E used in this experiment (the microbial reaction of the expression (1) is suppressed, and the expressions (2) to (3) The oxidation-reduction potential V) for switching to the microbial reaction is -100 mV or more, and the potential control device 20 causes the first electrode 11 with respect to the reference electrode (silver / silver chloride electrode) 14 to have an oxidation-reduction potential V of -100 mV or more. By controlling it, it was confirmed that the oxidation-reduction potential of sludge from the vicinity of the electrode to the surroundings was raised widely, and the generation of methane could be suppressed stably and efficiently.

2 and 3 described above are not only for detecting methane but also for detecting a redox potential V effective for suppressing the generation of other warming gases such as nitrous oxide in the bottom soil E. Available. In the natural environment, ammonia (for example, ammonia originating from human waste such as protein or animals) produces nitric acid and nitrous acid by nitrification and denitrification processes involving single or multiple microbial reactions in the bottom soil E. After being decomposed into nitric oxide from nitric acid (see formula (11)), it is finally broken down into nitrogen and released into the atmosphere (see formula (12)). While the reaction for producing nitric acid and nitrous acid from ammonia proceeds under absolute aerobic conditions requiring oxygen, the reduction reaction of the nitrous oxide reducing bacterium of formula (12) is anaerobic conditions, that is, the oxidation-reduction potential V. Proceeds low.
2HNO ₃ + 8H ⁺ + 8e ⁻ → 5H ₂ O + N ₂ O (11)
N ₂ O + 2H ⁺ + 2e ⁻ → N ₂ + H ₂ O …………………………………… (12)

  For example, in the experiment of FIG. 2, ammonia or nitric acid is added to the bottom soil E, and the nitrous oxide concentration in the gas phase gas is continuously measured by a gas concentration measuring device (photoacoustic multi-gas monitor) connected to the opening of the container 5. The change in the amount of nitrous oxide generated is measured while switching the oxidation-reduction potential V in the bottom soil E by the potential control device 20. When the redox potential V of the soil E is high, the reduction reaction of the nitrous oxide-reducing bacteria (denitrification reaction of the formula (12)) does not proceed, and the reducing power is reduced to supply the reducing power into the soil E. This promotes the decomposition of nitrous oxide and increases denitrification. From this increase / decrease in nitrous oxide concentration, an oxidation-reduction potential V at which the reduction reaction of nitrous oxide-reducing bacteria is promoted according to the soil E is detected, and the detected potential V is set as a target value of the potential control device 20. By controlling the oxidation-reduction potential V of the soil E, generation of nitrous oxide having a warming coefficient about 300 times that of carbon dioxide can be stably and efficiently suppressed.

  Thus, the “method and system capable of appropriately controlling various microbial reactions in various soils according to the bottom soil”, which is an object of the present invention, can be achieved.

  As described above, the method for suppressing or promoting the microbial reaction that produces or consumes the greenhouse gas in the bottom soil E has been described. However, the system of the present invention suppresses or promotes another microbial reaction that occurs in the bottom soil E. Also available in cases. For example, as shown in Table 1, the oxidation-reduction potential V of a microbial reaction that decomposes or generates nitrate nitrogen, hydrogen sulfide, and other harmful substances, phosphorus, and other nutrient salts is known. By controlling the oxidation-reduction potential V, decomposition of harmful substances and nutrients in the soil E can be promoted or production can be suppressed. Further, in the experimental apparatus of FIG. 2, instead of measuring the reaction product (methane, etc.) in the gas phase, by measuring the reaction product (hazardous substances, nutrients, etc.) in the soil E by the measuring means 27, Detecting an optimum redox potential V that can promote or suppress the decomposition of harmful substances and nutrients in accordance with the properties of the underwater soil E, and controls the first electrode 11 based on the detected potential V. Therefore, it is possible to stabilize and increase the efficiency of decomposition or generation of harmful substances and nutrients.

  FIG. 4 shows an embodiment in which the microbial reaction control system of the present invention is used for wastewater treatment. In the illustrated example, the first electrode 11 is embedded in the bottom soil E of a filtration tank (or an open pond such as an open pond) 6 of a wastewater treatment facility, and the second electrode 12 is installed in the water W above it. For example, waste water D containing pollutants (for example, organic substances such as acetic acid or nitrate nitrogen) is introduced into the soil E or the water W above it from the inflow path 7 of the filtration tank 6. By controlling the oxidation-reduction potential V at which the microbial reaction of the contaminants in the soil E is suppressed or promoted by the connected potential control device 20, the contaminants that have penetrated into the soil E are decomposed. The oxidation-reduction potential V at which the degradation microorganism reaction of the pollutant is suppressed or promoted can be determined in the same manner as in the above-described methane gas production reaction of methane bacteria or the reduction reaction of nitrous oxide-reducing bacteria. The waste water D after decomposing the pollutants is slowly filtered through the soil E and aerobized, and then discharged from the discharge channel 8 (from the discharge channel 9 when aerobicization is not required).

  When waste water D containing contaminants such as acetic acid is introduced into the filtration tank 6 in the illustrated example, microorganisms that decompose acetic acid and pass electrons to the electrode 11 in the surrounding area A of the first electrode 11 in the bottom soil E Aerobic microorganisms that inhabit and grow electrons in the area C around the second electrode 12 in the water W, and pass oxygen ions while consuming oxygen in the soil upper layer area between the two. Is formed. When the surfaces of the electrodes 11 and 12 become dirty and current becomes insufficient, for example, the potential control device 20 can apply a reverse potential to remove the dirt on the electrode surface. Moreover, when clogging etc. generate | occur | produce in the bottom soil E, a wastewater after a process can be made to flow back to the soil E from the drainage channel 8 and wash | clean (backwash) as shown by a dashed line in the figure.

5 ... Container 6 ... Filtration tank (release pond)
DESCRIPTION OF SYMBOLS 7 ... Inflow channel 8 ... Discharge channel 9 ... Discharge channel 11 ... 1st electrode 12 ... 2nd electrode 14 ... Reference electrode 15 ... Support member 20 ... Potential control device 21 ... Potential control circuit 22 ... Variable voltage circuit 23 ... Voltmeter 24 ... Memory 25 ... Current measuring circuit 26 ... Ammeter 27 ... Measuring means 28 ... Detection means 30 ... Microbial fuel cell 31 ... Anode (negative electrode)
32 ... Cathode (positive electrode) 33 ... Ion exchange membrane 34 ... Circuit D ... Waste water E ... Bottom soil W ... Water

Claims (11)

The first electrode is embedded in the anaerobic soil on the bottom of the water and the second electrode is installed in the water above the first electrode. The potential control device connected between the two electrodes suppresses the first electrode from causing a predetermined microbial reaction in the soil. A method for controlling a microbial reaction in a submerged soil, which is controlled to promote an oxidation-reduction potential. 2. The redox potential according to claim 1, wherein a predetermined microbial reaction in the soil is suppressed or promoted by measuring a product generation amount of the predetermined microbial reaction while switching the potential of the first electrode by the potential control device. And controlling the first electrode at the detected potential to control the microbial reaction in the bottom soil. 3. The control method according to claim 1, wherein a predetermined pollutant-containing wastewater is allowed to flow into the soil or water above the soil, and the first electrode is set to a redox potential at which a degradation microbial reaction of the pollutant is suppressed or promoted. A method for controlling a microbial reaction in a submerged soil. The control method according to any one of claims 1 to 3, wherein the first electrode is controlled to an oxidation-reduction potential at which a methane gas production reaction of methane bacteria is suppressed. 4. The control method according to claim 1, wherein the first electrode is controlled to an oxidation-reduction potential that promotes a reduction reaction of nitrous oxide-reducing bacteria. A first electrode embedded in anaerobic soil at the bottom of the water, a second electrode installed in the water above the first electrode, and an oxidation that is connected between both electrodes to suppress or promote a predetermined microbial reaction in the soil A bottom soil microbial reaction control system comprising a potential control device for controlling to a reduction potential. 7. The control system according to claim 6, wherein a measuring means for measuring a product generation amount of the predetermined microbial reaction and a product generation amount of the predetermined microbial reaction while switching a potential of the first electrode, A microbial reaction control system for underwater soil, comprising detection means for detecting an oxidation-reduction potential at which a predetermined microbial reaction is suppressed or promoted. 8. The control system according to claim 6 or 7 , wherein an inflow path through which waste water containing a predetermined pollutant flows into the soil or the water above the ground is provided, and the first electrode is suppressed by the potential control device from decomposing microbial reaction of the pollutant. Or the microbial reaction control system of the bottom soil which controls to the oxidation-reduction potential promoted. The control system according to any one of claims 6 to 8, wherein the first electrode is controlled to an oxidation-reduction potential at which a methane gas generation reaction of methane bacteria is suppressed. 9. The control system according to claim 6, wherein the first electrode is controlled to an oxidation-reduction potential that promotes a reduction reaction of nitrous oxide-reducing bacteria. 11. The control system according to claim 6, wherein the potential control device is connected to the first electrode and the second electrode, and has a reference electrode that always shows a constant redox potential. Microbial reaction control system for bottom soil as a control device.