JP2011223985A - Method for hydrogen fermentation treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably and efficiently producing hydrogen fermentation liquid for performing hydrogen fermentation treatment with which hydrogen fermentation treatment is stably and efficiently performed.SOLUTION: Electrodes are immersed in a fermentation liquid containing microbial population which perform hydrogen fermentation, and the potential of electrodes are controlled in addition to supplying organic substrate to the fermentation liquid, so that the microbial population performing hydrogen fermentation are preferentially activated. To be concrete, an electrode (working electrode) and a counter electrode, which forms a pair with the working electrode, are immersed in the fermentation liquid, and the potential A of the electrodes (unit: V) is controlled to A≤-1.0 based on a silver-silver chloride electrode potential.

Description

  The present invention relates to a hydrogen fermentation treatment method. More specifically, the present invention relates to a hydrogen fermentation treatment method suitable for recovering biogas containing hydrogen at the same time as decomposing organic waste, and simultaneously decomposing and treating organic waste. Hydrogen fermentation process suitable for recovering biogas containing methane and two-stage fermentation process method of methane fermentation process, as well as hydrogen for decomposing organic waste and simultaneously recovering biogas containing hydrogen The present invention relates to a method suitable for producing a fermentation broth.

  The hydrogen fermentation treatment utilizes the action of anaerobic microorganisms that simultaneously generate hydrogen gas in the process of acid fermentation of an organic substrate. By using organic waste as an organic substrate, hydrogen gas can be recovered as an energy source while decomposing the organic waste, so that it is attracting attention as an extremely useful technology in the industry.

  In recent years, a technique for decomposing organic waste by combining a hydrogen fermentation process and a methane fermentation process has been proposed. For example, Patent Document 1 proposes a technique for simultaneously decomposing raw garbage and paper garbage by combining hydrogen fermentation treatment and methane fermentation treatment. Moreover, in nonpatent literature 1, compared with the case where an organic waste is decomposed | disassembled by a methane fermentation process by decomposing | disassembling an organic waste by combining a hydrogen fermentation process and a methane fermentation process, of biogas. It has been reported that the production rate and biogas yield can be improved.

  Specifically, the two-stage fermentation process that combines the hydrogen fermentation process and the methane fermentation process is performed as follows. That is, as a fermenter for organic waste, two fermenters, a hydrogen fermenter and a methane fermenter, are prepared, and the organic waste is subjected to hydrogen fermentation in the preceding hydrogen fermenter and then fermented. The processing liquid (discharge liquid) which is a thing is sent to a methane fermentation tank of a back | latter stage, and a methane fermentation process is performed. In this way, by performing fermentation treatment in two tanks, a hydrogen fermenter and a methane fermenter, the microbial group involved in hydrogen fermentation and the microbial group involved in methane fermentation are maintained in optimum conditions in the respective treatment tanks. Thus, processing can be performed efficiently.

JP 2006-255537 A

Liu, D., Liu, D., Zeng, R.J., Angelidaki, I. 2006. Hydrogen and methane production from household solid waste in the two-stage fermentation process.Water Res. 40, 2230-2236.

  However, knowledge about the hydrogen fermentation process is still in a poor state, and conditions for carrying out the hydrogen fermentation treatment stably and with high efficiency have not been sufficiently clarified. It cannot be denied that this is one of the obstacles to the practical application of hydrogen fermentation treatment or two-stage fermentation treatment of hydrogen fermentation treatment and methane fermentation treatment.

  Then, an object of this invention is to provide the method which can implement a hydrogen fermentation process stably and highly efficiently.

  Another object of the present invention is to provide a method capable of stably and efficiently carrying out a two-stage fermentation process combining a hydrogen fermentation process and a methane fermentation process.

  Furthermore, an object of this invention is to provide the method of manufacturing the hydrogen fermentation liquid for performing a hydrogen fermentation process stably and efficiently.

  As a result of intensive investigations by the inventors of the present invention in order to solve such problems, two carbon plates were immersed in the methane fermentation liquid, one serving as the working electrode, the other as the counter electrode, and the potential of the working electrode as silver / chloride. By controlling to -1.0 V on the basis of the silver electrode potential, new findings have been obtained that the hydrogen fermentation reaction can proceed in a predominantly stable manner.

  Here, a series of methane fermentation reactions occurring in the methane fermentation liquid includes a hydrolysis reaction, and a part of the hydrolysis reaction is performed by a group of hydrogen-producing bacteria involved in hydrogen fermentation. Therefore, it was considered that the above-described predominance of the hydrogen fermentation reaction was caused by the preferential activation of the microorganism group performing hydrogen fermentation in the methane fermentation broth.

  Based on the above knowledge, the inventors of the present invention are not limited to the methane fermentation broth, but for all fermentation broth including microorganisms that perform hydrogen fermentation, hydrogen fermentation is performed by a very simple method of controlling the potential of the electrode immersed in the fermentation broth. The present inventors have found that the possibility that the microorganism fermentation group to be activated can be preferentially activated to allow the hydrogen fermentation treatment to proceed efficiently and stably, and the present invention has been completed through various studies.

  That is, in the hydrogen fermentation treatment method of the present invention, the electrodes are immersed in a fermentation broth containing microorganisms that perform hydrogen fermentation, an organic substrate is added to the fermentation broth, and the potential of the electrodes is controlled to perform hydrogen fermentation. Is activated preferentially.

  Here, in the hydrogen fermentation treatment method of the present invention, a counter electrode that forms a pair with this electrode is immersed in the fermentation broth, and the potential A (unit: V) of the electrode is A ≦ − on the basis of the silver / silver chloride electrode potential. It is preferable to control to 1.0.

  Moreover, in the hydrogen fermentation treatment method of the present invention, the fermentation liquid is preferably a methane fermentation liquid.

  Furthermore, in the hydrogen fermentation treatment method of the present invention, it is preferable to maintain the pH of the fermentation broth at 5.5-8.

  Next, the two-stage fermentation treatment method of the present invention implements the hydrogen fermentation treatment method of the present invention, and then performs a methane fermentation treatment using a fermented product obtained by the hydrogen fermentation treatment method as a raw material.

Here, in the two-stage fermentation treatment method of the present invention, in the methane fermentation treatment, an electrode is immersed in a methane fermentation solution, and a counter electrode that forms a pair with this electrode is disposed by the following method (1) or (2). The electrode potential B is preferably controlled to B = + 0.3 or B <X (X is the oxidation-reduction potential of the methane fermentation broth itself) on the basis of the silver / silver chloride electrode potential.
(1) Immerse and place in the electrolyte solution in contact with the methane fermentation solution via the ion exchange membrane (2) Place in contact with the methane fermentation solution via the ion exchange membrane

  Next, the method for producing a hydrogen fermentation broth according to the present invention dominates a group of microorganisms that perform hydrogen fermentation by immersing an electrode in a methane fermentation broth, introducing an organic substrate into the fermentation broth, and controlling the potential of the electrode. The step of activating is included.

  Here, in the method for producing a hydrogen fermentation broth according to the present invention, the above-mentioned step includes immersing a counter electrode that forms a pair with the electrode in the methane fermentation broth, and setting the potential A (unit: V) of the electrode to silver / silver chloride. It is preferable to carry out by controlling A ≦ −1.0 on the basis of the electrode potential.

  According to the hydrogen fermentation treatment method of the present invention, the hydrogen fermentation reaction can proceed stably and efficiently with a simple operation and control of controlling the potential of the electrode immersed in the fermentation broth. Therefore, organic waste can be decomposed stably and efficiently, and hydrogen as an energy source can be efficiently recovered.

  According to the two-stage fermentation treatment method of the present invention, the hydrogen fermentation reaction can proceed stably and with high efficiency, and the stability and treatment efficiency of the entire two-stage fermentation process including the methane fermentation process can be improved. . Therefore, it becomes possible to decompose organic waste stably and efficiently, and to efficiently recover hydrogen and methane as energy sources.

  According to the method for producing hydrogen fermented sludge of the present invention, the hydrogen fermented sludge is allowed to proceed predominantly in the methane fermented liquid by a simple operation and control of controlling the potential of the electrode immersed in the methane fermented liquid. Can be manufactured stably and efficiently.

It is a figure which shows the fluctuation | variation of pH of the fermented liquor during the test period in Example 1. FIG. It is a figure which shows the time-dependent change of the biogas production rate in the test period in Example 1. FIG. FIG. 4 is a diagram showing a change with time of a current value of a working electrode during a test period in Example 1. It is a figure which shows an example for the form for implementing the hydrogen-fermentation processing method of this invention. It is a figure which shows the other example of the form for implementing the hydrogen-fermentation processing method of this invention. It is a figure which shows the further another example of the form for implementing the hydrogen-fermentation processing method of this invention. It is sectional drawing which shows an example of the processing apparatus concerning 1st Embodiment A. It is sectional drawing which shows an example of the processing apparatus concerning 1st Embodiment B. It is sectional drawing which shows an example of the processing apparatus concerning 1st Embodiment C. It is sectional drawing which shows an example of the processing apparatus concerning 1st Embodiment D. It is sectional drawing which shows an example of the processing apparatus concerning 2nd embodiment. It is sectional drawing which shows an example of the other form of a processing apparatus. It is sectional drawing which shows the form of the apparatus used in Reference Example 1. It is a figure which shows the driving | running condition (load condition) of the methane fermenter in the reference example 1. FIG. It is a figure which shows the relationship between the setting electric potential obtained in the reference example 1, and a gas production rate. It is a figure which shows the relationship between the setting electric potential obtained in the reference example 1, and a chemical oxygen demand (COD) removal rate. It is a figure which shows the relationship between the setting electric potential obtained in the reference example 1, and floating solid content (SS) removal rate. It is a figure which shows the relationship between the setting potential obtained in Reference Example 1, and a lower fatty acid concentration. It is sectional drawing which shows the form of the apparatus used in Example 1. FIG. It is a figure which shows the driving | running condition (load condition) of the methane fermenter in the reference example 2. FIG. It is a figure which shows the time-dependent change of the gas generation rate in the reference example 2. It is a figure which shows the time-dependent change of the methane gas content rate in the biogas in the reference example 2. FIG. It is a figure which shows the time-dependent change of the VFA density | concentration of the methane fermentation liquid in the reference example 2. FIG. It is a figure which shows the COD removal rate with respect to the organic substance load in the reference example 2. FIG. It is a figure which shows SS removal rate with respect to the organic substance load in the reference example 2. FIG. It is a figure which shows the organic substance load (OLR) and hydraulic residence time (HRT) in Example 2. It is a figure which shows the time-dependent change of the biogas production rate in the test period in Example 2. FIG. It is a figure which shows the hydrogen production | generation rate with respect to the organic substance load amount (OLR) in the test period in Example 2. FIG. It is a figure which shows the fluctuation | variation of pH of the fermented liquor during the test period in Example 2. FIG. It is a figure which shows the VFA density | concentration of the fermented liquor (working electrode tank side) with respect to the organic substance load amount (OLR) in Test 1 of Example 2. FIG. It is a figure which shows the VFA density | concentration in the organic substance load (OLR) 9780 mg / l / day of the fermented liquid in Test 2 of Example 2. FIG. From the results of Test 1 of Example 2, a diagram illustrating the results of calculating the hydrogen recovery rate (gamma _ca) the energy recovery rate (W _H2). It is a figure which shows the organic substance load (OLR) and hydraulic residence time (HRT) in Example 3. It is a figure which shows the biogas production | generation rate with respect to the organic substance load amount (OLR) in the test period in Example 3. FIG. It is a figure which shows the time-dependent change of the biogas production rate in the test period in Example 4. FIG. It is a figure which shows the methane production | generation rate with respect to the organic substance load amount (OLR) in the test period in Example 4. FIG. It is a figure which shows the fluctuation | variation of pH of the fermented liquor during the test period in Example 4. FIG. It is a figure which shows the COD removal rate with respect to organic substance load amount (OLR) in Example 4. FIG. It is a figure which shows SS removal rate with respect to organic substance load amount (OLR) in Example 4. FIG. It is a figure which shows the VFA density | concentration of the fermented liquid with respect to the organic substance load amount (OLR) in Example 4. FIG. In Example 2, it is a figure which shows the hydrogen production rate with respect to organic substance load amount (OLR) at the time of performing the test similar to the test 1 by setting the setting electric potential of a working electrode to -1.2V.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[Hydrogen fermentation treatment method]
In the hydrogen fermentation treatment method of the present invention, an electrode is immersed in a fermentation broth containing a microorganism group that performs hydrogen fermentation, an organic substrate is introduced into the fermentation broth, and the microorganism group that performs hydrogen fermentation by controlling the potential of the electrode is superior. It is trying to activate fortune-telling.

  The fermented liquor containing microorganisms that perform hydrogen fermentation includes methane fermented liquid in a general methane fermenter in which methane fermentation treatment such as organic waste is performed, or sludge collected from the methane fermenter in water or It is preferable to use a methane fermentation solution prepared by diluting with a culture solution or the like, but the methane fermentation solution is not necessarily limited to these, and general hydrogen in which a hydrogen fermentation process such as organic waste is performed. Hydrogen fermentation broth in the fermenter, hydrogen fermented liquor prepared by diluting sludge collected from the hydrogen fermenter with water or a culture solution, and microorganism groups involved in hydrogen fermentation (for example, microorganisms of the genus Clostridium) It is also possible to use a hydrogen fermented solution obtained by adding to a culture solution or the like. Moreover, the sludge collected from the methane fermentation tank can be used as it is without being diluted with water or the like, and the sludge collected from the hydrogen fermentation treatment tank can be used as it is without being diluted with water or the like. Such a sludge itself is also included in the fermented liquid in the present invention.

  In the hydrogen fermentation treatment method of the present invention, when a methane fermentation broth is used as a fermentation broth containing a microorganism group that performs hydrogen fermentation, the microorganism group that performs the hydrogen fermentation existing in the methane fermentation liquid is preferentially activated. Thus, the hydrogen fermentation reaction can proceed predominantly and stably in the fermentation broth. In addition, when a hydrogen fermentation broth is used as a fermentation broth that includes a microorganism group that performs hydrogen fermentation, the microorganism group that performs the hydrogen fermentation existing in the hydrogen fermentation broth is activated, and the hydrogen fermentation reaction is performed in the fermentation broth. It can proceed stably.

  As an electrode immersed in the fermentation broth, it is preferable to use a hydrophobic electrode, and it is particularly preferable to use a carbon electrode such as a carbon plate, but it is not necessarily limited to these electrodes, Various electrodes that do not inhibit the hydrogen fermentation reaction can be used. Conventionally, a method using electrolysis is well known as a general technique for producing hydrogen, and in the electrolysis method, a noble metal (catalyst) electrode such as platinum is generally used as an electrode. Although the present invention is a technique capable of producing hydrogen in the same manner as the electrolysis method, a low-cost material such as a carbon plate can be used as an electrode, and this is also extremely advantageous compared to the conventional technique. In addition, when an electrode capable of supporting microorganisms such as a carbon plate is used, microorganisms adhere to the electrode surface at the initial stage of potential control, and current easily flows on the electrode surface. The effect of promoting the predominance of the fermentation reaction can also be expected.

  Examples of organic substrates include, but are not limited to, organic waste such as livestock waste, garbage, wastewater treatment sludge, various biomass (eg, rice cakes), and paper waste. . For example, for the purpose of simply generating hydrogen gas, an organic substrate that can be easily used by the hydrogen-producing bacteria group may be added to the fermentation broth. In addition, it is suitable for an organic substrate such as organic waste to be subjected to a hydrogen fermentation treatment after appropriately performing pretreatment such as crushing and separation as necessary depending on its properties. Here, according to the experiments by the inventors of the present application, by energizing the electrode (working electrode), the hydrogen fermentation reaction is preferentially stabilized even when the simulated garbage slurry including the dog food is used as the organic substrate. As a result, it is possible to cause hydrogen fermentation to proceed in a predominantly stable manner using a wide variety of organic substrates by energizing the electrode (working electrode). obtain.

  The potential control method of the electrode is not particularly limited as long as the microorganism group that performs hydrogen fermentation can be activated preferentially. However, the potential control method is not particularly limited. It is preferable to immerse a counter electrode that forms a pair with the working electrode together with the working electrode to control the potential A (unit: V) of the working electrode. The potential A of the working electrode may be set to A ≦ −1.0 on the basis of the silver / silver chloride electrode potential, but is preferably set to −1.4 <A ≦ −1.0. More preferably, 3 ≦ A ≦ −1.0, and even more preferably −1.2 ≦ A ≦ −1.0. When this potential control method is adopted, if A> −1.0, the hydrogen fermentation reaction does not dominate. Further, if A ≦ −1.4, the amount of electric power to be input becomes large and the hydrogen production efficiency may be reduced, or the sulfate reducing bacteria may dominate in the fermenter and hydrogen may be consumed. Further, when the working electrode is a carbon electrode, hydrogen generation by water splitting becomes dominant.

  The dominant activation of the microorganism group that performs hydrogen fermentation means either or both of improvement of the function of the microorganism group that performs hydrogen fermentation and improvement of the function of the microorganism itself that performs hydrogen fermentation. ing.

  Here, in the hydrogen fermentation treatment method of the present invention, if the pH of the fermentation solution is excessively biased to the acidic side or the alkaline side, the hydrogen fermentation reaction may be inhibited, as in many microbial reaction systems. . Therefore, it is preferable to maintain the pH of the fermentation broth in a common-sense pH range in the microbial reaction system. Specifically, it is preferable to maintain the pH of the fermentation broth at 5.5-8, and pH 6-8. It is more preferable to maintain the degree. As the hydrogen fermentation reaction proceeds, lower fatty acids (lactic acid, acetic acid, propionic acid, butyric acid, etc.), which are products of hydrogen fermentation, dissolve in the fermentation liquid, and the pH of the fermentation liquid may be biased to the acidic side. It is preferable to maintain a pH in the above range by adding a pH adjuster such as sodium hydroxide to the fermentation broth periodically or optionally. In addition, by maintaining the pH of the fermentation broth in the above range in this way, in a two-stage fermentation treatment method that combines a hydrogen fermentation treatment and a methane fermentation treatment described later, a fermented product (treatment) that is sent to the methane fermentation treatment tank Since the pH of the liquid is near neutral, it is possible to prevent a decrease in methane fermentation treatment efficiency due to the acid shift of the methane fermentation liquid.

  According to the hydrogen fermentation treatment method of the present invention, hydrogen can be generated using an organic substrate such as organic waste as a raw material, and the volume of organic waste can be reduced. In other words, organic waste can be recovered by converting it to hydrogen. Therefore, it can be utilized as a hydrogen recovery method capable of giving added value as a hydrogen generation source to organic waste.

  Next, a specific example of an apparatus for carrying out the hydrogen fermentation treatment method of the present invention will be described.

  An example of an apparatus for carrying out the hydrogen fermentation treatment method of the present invention is shown in FIG. In this hydrogen fermentation apparatus 1, two containers 26 a and 26 b each having an opening below the liquid level of the liquid to be stored are connected at the opening to form an H-shaped container 26. The working electrode tank 7 is used as a sealed structure, and the other container 26b is also used as a counter electrode tank 8 as a sealed structure. Then, the fermented liquid 4 is accommodated in each tank of the container 26, the working electrode 9 and the reference electrode 11 are contacted (immersed) in the fermented liquid 4 in the working electrode tank 7, and the fermented liquid 4 in the counter electrode tank 8 is contacted. The counter electrode 10 is in contact (immersion). The working electrode 9, the counter electrode 10, and the reference electrode 11 are connected to a constant potential setting device 12, and the potential of the working electrode 9 is controlled by a three-electrode system.

  In this way, by controlling the potential of the working electrode 9 by the three-electrode method, the potential of the working electrode 9 can be strictly controlled to the set potential. Specifically, a potential difference between the working electrode 9 and the reference electrode 11 is measured by a constant potential setting device (potentiostat) 12, and the working electrode 9 and the counter electrode 10 are adjusted so that the potential difference reaches the set potential. A current is passed between them so that no current flows through the reference electrode 11 serving as a reference. The details of the potential control by the three-electrode method are described in, for example, pages 6 to 9 of Electrochemical Measurement Method (above), Technical Bulletin Publishing Co., Ltd., 1st edition 15 printing, published in June 2004. ing.

  However, when the potential of the working electrode 9 can be controlled only by the voltage between the working electrode 9 and the counter electrode 10, the three-electrode system may not be used.

  The counter electrode 10 can be appropriately made of a material that can cause a reaction that complements the oxidation-reduction reaction that occurs at the working electrode 9. For example, a carbon electrode such as a carbon plate is preferably used.

  Examples of the material of the container 26 include, but are not limited to, glass, plastic, metal subjected to insulation treatment, concrete, and the like.

  As described above, the fermentation liquid 4 accommodated in the container 26 is obtained by using a methane fermentation liquid in a general methane fermentation tank in which a methane fermentation process such as organic waste is performed, or sludge collected from the methane fermentation tank. It is preferable to use a methane fermentation solution prepared by diluting with water or a culture solution, but is not necessarily limited to this, and a general hydrogen fermentation treatment of organic waste or the like is performed. Hydrogen fermentation broth in a simple hydrogen fermenter, hydrogen fermented liquor prepared by diluting sludge collected from the hydrogen fermenter with water or a culture solution, and microorganism groups involved in hydrogen fermentation (for example, microorganisms of the genus Clostridium) It is also possible to use a hydrogen fermented solution obtained by adding the above to a culture solution or the like. Moreover, the sludge collected from the methane fermentation tank can be used as it is without being diluted with water or the like, and the sludge collected from the hydrogen fermentation treatment tank can be used as it is without being diluted with water or the like.

  What is necessary is just to set the temperature of the container 26 (temperature of the fermentation broth 4) suitably according to the optimal temperature of the microorganism group which performs the hydrogen fermentation which exists in the fermentation broth 4. FIG. Specifically, for example, the temperature may be 4 ° C to less than 100 ° C, but is preferably 40 ° C to 70 ° C, more preferably 50 ° C to 60 ° C, and even more preferably 55 ° C.

  Here, the redox material 3 may be added to the fermentation broth 4. Thereby, the controllability of the solution potential of the fermentation broth 4 is improved, and the solution potential of the fermentation broth 4, particularly the solution potential in the vicinity of the working electrode 9 can be easily brought close to the potential of the working electrode 9. Stable progression may be promoted.

  The redox material 3 is a material that can reversibly generate a redox reaction with the working electrode 9 immersed in the fermentation broth 4 and that is not toxic to microorganisms living in the fermentation broth 4 Can be used. For example, a general iron ion is mentioned as a soil component. Here, in order to allow iron ions to stably exist in the fermentation broth, it is preferable to coordinate the iron ions to the chelating agent and add them to the fermentation broth. As the chelating agent, any chelating agent capable of coordinating iron ions can be used. For example, diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), tetraethylenetriamine (TET), ethylenediamine (EDA), diethylenetriamine (DETA), citric acid, oxalic acid, crown ether, nitrilotetraacetic acid, disodium edetate, sodium edetate, trisodium edetate, penicillamine, trisodium pentetate calcium, pentetate, succil and edet Mention may be made of acid trientine. In addition to iron ions, quinone compounds such as potassium ferrocyanide and sodium anthraquinone disulfonate, and methyl viologen can be used. These substances also reversibly change into an oxidized form and a reduced form by an oxidation-reduction reaction. In particular, a quinone compound is a substance known as one of the soil components and is preferable. In other words, by adding the soil itself to the fermentation broth, the redox potential of the fermentation broth can be controlled by the redox material 3 contained in the soil. However, the oxidation-reduction substance 3 is not limited to the above-described substances.

  In addition, since the methane fermentation liquid and hydrogen fermentation liquid that can be used as the fermentation liquid 4 usually contain a redox substance, it is originally included in the fermentation liquid without adding the redox substance 3 separately. You may make it utilize the oxidation-reduction substance currently being used. In addition, since it has been confirmed by experiments by the present inventors that hydrogen fermentation proceeds predominately and stably without the addition of the redox substance 3, the addition of the redox substance 3 is an essential condition. Absent.

  Here, in the hydrogen fermentation apparatus 1 shown in FIG. 4, the gas discharge pipe which guides the biogas containing hydrogen gas which stays in the space (head space) above the liquid level of the fermentation liquid 4 in the container 26a to the outside of the container 26a. The biogas inside the container 26a is recovered by a gas recovery means 15 provided with a gas exhaust pipe 15a that can be opened and closed by a valve 15b. However, the biogas recovery method is not limited to this method. For example, without providing the gas recovery means 15, an opening is provided in the upper part of the container 26 a and the opening is closed with an elastic material such as synthetic rubber (for example, silicone rubber), and the injection needle of the syringe is attached to the elastic material that closes the opening. You may make it collect | recover biogas from head space by inserting. The elastic material such as synthetic rubber closes the hole when the injection needle is pulled out. Therefore, when the biogas is not collected, the biogas does not leak from the container 26a even if the injection needle is pulled out. Moreover, since carbon dioxide is mixed in the biogas, a means for removing carbon dioxide may be provided in the gas recovery means 15 or the subsequent stage. Specifically, for example, only hydrogen gas may be taken out by passing biogas through a sodium hydroxide solution and dissolving carbon dioxide in the sodium hydroxide solution.

  Moreover, in the hydrogen fermentation apparatus 1 shown in FIG. 4, the fermentation liquid discharge pipe 16a which guides the fermentation liquid 4 in the container 26a out of the container 26a is provided below the liquid level of the fermentation liquid 4 in the container 26a. The fermentation solution 4 is collected from the container 26a by the fermentation solution collection means 16 that allows the solution discharge pipe 16a to be opened and closed by a valve 16b. However, the method for collecting the fermentation broth 4 is not limited to this method. For example, without providing the fermented liquid collecting means 16, an opening may be provided in the container 26a, closed with an elastic material such as synthetic rubber, and the fermented liquid 4 may be collected by inserting a syringe needle. Or you may make it connect to the syringe of one end of the pipe | tube with which both ends were opened, and soak the other end in the fermentation broth 4 and extract | collect the fermentation broth 4 through a pipe | tube. Also in these cases, biogas does not leak from the container 26a.

  Furthermore, a means for adding and supplying substances to the fermentation broth 4 may be provided separately from the gas recovery means 15 and the fermentation broth collection means 16. Specifically, an openable / closable substance introduction tube that can add and supply substances to the fermentation broth 4 from the outside of the container 26a may be provided. In this case, substances such as nutrient sources, neutralizing agents, and fermented sludge can be added to the fermentation broth as necessary. Of course, an organic substrate such as organic waste can also be supplied from this introduction tube. Gas can also be supplied to keep the environment anaerobic. In addition, since the hydrogen fermentation apparatus 1 shown in FIG. 4 has the container 26 as a sealed structure, it is easy to control the inside of the container 26 to an anaerobic environment. However, it is not always necessary to provide means for adding and supplying substances to the fermentation broth 4, and the gas recovery means 15 and the fermentation liquid collecting means 16 may be used together as means for adding and supplying substances to the fermentation broth 4. . Further, as described above, the injection needle of the syringe may be inserted into the elastic material, and the substance may be added and supplied to the fermentation broth 4.

  Moreover, in the hydrogen fermentation apparatus 1 shown in FIG. 4, the gas discharge pipe 22 which discharges | emits the gas generated in the counter electrode tank 8 out of the container 26b shall be provided. In the processing apparatus 1 shown in FIG. 4, the wiring for connecting the counter electrode 10 and the constant potential setting device 12 passes through the gas exhaust pipe 22, but the wiring is not necessarily limited to this configuration. The constant potential setting device 12 may be connected without passing through the gas discharge pipe 22. Here, since the gas staying in the head space of the counter electrode tank 8 contains hydrogen, in addition to the gas generated in the working electrode tank 7, the gas generated in the counter electrode tank 8 is recovered as an energy source. It is preferable.

  Here, the apparatus for implementing the hydrogen fermentation treatment method of the present invention is not limited to the apparatus in the form of FIG.

  For example, as shown in FIG. 5, the fermentation solution 4 may be stored in a sealed container 20, and the working electrode 9, the counter electrode 10, and the reference electrode 11 may be immersed in the fermentation solution 4. Further, as shown in FIG. 6, an opening 20 a is provided below the surface of the fermentation liquid 4 in the container 20, and this opening is closed with the counter electrode 10. Also good. Even in these forms, the hydrogen fermentation treatment method of the present invention can be stably carried out by controlling the potential of the working electrode 9 to a predetermined value.

  As described above, the hydrogen fermentation treatment method of the present invention employs a very simple potential control method in which the working electrode 9 and the counter electrode 10 (and also the reference electrode 11) are immersed in the fermentation broth 4. It has the feature that it can be implemented by controlling the potential. If the hydrogen fermentation treatment method of the present invention is carried out using the fermentation solution 4 as the methane fermentation solution, the hydrogen fermentation reaction is dominant in the fermentation reaction that proceeds in the methane fermentation solution. That is, the methane fermentation liquid becomes a hydrogen fermentation liquid for decomposing organic waste and recovering hydrogen. Therefore, by applying the hydrogen fermentation treatment method of the present invention to the methane fermentation broth, a hydrogen fermentation broth can be produced from the methane fermentation broth, and the hydrogen fermentation collected from this hydrogen fermentation broth or this hydrogen fermentation broth. The sludge can be subjected to the hydrogen fermentation treatment method of the present invention or other hydrogen fermentation treatment methods.

[Two-stage fermentation process]
The fermented product (treatment liquid) discharged by the hydrogen fermentation treatment method of the present invention may be subjected to methane fermentation treatment in a general methane fermentation tank, but a fixed bed type methane fermentation in which a hydrophobic carrier is added to the methane fermentation liquor. It is preferable to perform methane fermentation treatment in a tank. As the hydrophobic carrier, for example, carbon fibers are preferably used, carbon fibers having a porosity of 25% to 98%, preferably carbon fibers having a porosity of 50 to 98%, and more preferably a porosity. 98% carbon fiber can be used, but the hydrophobic carrier is not limited to carbon fiber, and for example, a carrier such as a fiber made of polyethylene or polypropylene may be used. Carbon fiber is easy to ensure a high porosity, and for example, a carbon fiber nonwoven fabric is particularly suitable because it can easily ensure a high porosity (98%) and can be obtained at low cost. And, by adopting the methane fermentation treatment method using energization described below, the methane fermentation treatment can be further efficiently advanced, and the two-stage fermentation treatment combining the hydrogen fermentation treatment and the methane fermentation treatment is extremely efficient. It can be well progressed and is extremely suitable.

  The methane fermentation treatment method using energization is carried out by immersing an electrode in a methane fermentation solution and controlling the potential of the electrode to preferentially activate the methane producing bacteria group in the methane fermentation solution.

Specifically, the counter electrode that forms a pair with the working electrode is arranged by the following method (1) or (2), and the potential B of the working electrode is set to B = + 0.3 or B on the basis of the silver / silver chloride electrode potential. The methane fermentation treatment is carried out by controlling to <X (X is the oxidation-reduction potential of the methane fermentation liquor itself).
(1) Immerse and place in the electrolyte solution in contact with the methane fermentation solution via the ion exchange membrane (2) Place in contact with the methane fermentation solution via the ion exchange membrane

  By setting the potential B of the working electrode to B <X, a reduction reaction occurs on the working electrode, and electrons are given to the microorganism group involved in methane fermentation and activated. Thereby, methane fermentation is accelerated | stimulated. Therefore, the methane fermentation reaction can be promoted by increasing the potential B of the working electrode to the minus side of X. However, if the potential of the potential B of the working electrode is excessively increased to the minus side, Electrolysis is likely to occur and may inhibit methane fermentation. Therefore, the potential of the working electrode B is preferably −1.4 <B <−0.5, more preferably −1.2 ≦ B ≦ −0.6, and −1. 0.0 ≦ B ≦ −0.6 is more preferable, −1.0 ≦ B ≦ −0.8 is still more preferable, and B = −0.8 is most preferable. It is. When B ≧ −0.5, the reduction reaction hardly proceeds at the working electrode, and the promotion of methane fermentation hardly occurs. However, in B = + 0.3, promotion of methane fermentation can occur exceptionally.

  Hereinafter, the methane fermentation treatment method according to the counter electrode arrangement form of (1) will be specifically described as the first embodiment, and the methane fermentation treatment method according to the counter electrode arrangement form of (2) will be described as the second embodiment. This will be specifically described.

<First embodiment>
In the methane fermentation treatment method according to the first embodiment, the working electrode, the counter electrode, and the reference electrode are connected to a constant potential setting device, the methane fermentation solution and the electrolytic solution are contacted via an ion exchange membrane, and the methane fermentation solution The reference electrode is brought into contact with the working electrode, the counter electrode is brought into contact with the electrolytic solution, and the potential of the working electrode is controlled within the above range by a three-electrode system.

  The methane fermentation treatment method according to the first embodiment is performed by, for example, the processing apparatus 101 illustrated in FIGS. That is, in the processing apparatus 101 shown in FIGS. 7 to 10, one of the two tanks partitioned by the ion exchange membrane 106 is a processing tank 107, and the other tank is a counter electrode tank 108. Contains the methane fermentation solution 4 and the working electrode 109 and the reference electrode 111 are immersed therein. The counter electrode tank 118 contains the electrolytic solution 114a and the counter electrode 110 is immersed therein, and the working electrode 109 and the counter electrode 110 are immersed therein. Is connected to a constant potential setting device 112 so that the potential of the working electrode 109 is controlled by a three-electrode system. However, when the potential of the working electrode 109 can be controlled only by the voltage between the working electrode 109 and the counter electrode 110, the three-electrode method may not be used.

  Moreover, in the processing apparatus 101 shown in FIGS. 7-10, the biogas containing the methane gas which retains in the space (head space) above the liquid level of the methane fermentation liquid 104 in the processing tank 107 is outside the processing tank 107 ( A gas exhaust pipe 115a that leads to the outside of the processing apparatus 1 is provided, and biogas in the processing tank 107 is recovered by gas recovery means 115 that can be opened and closed by a valve 115b. However, the biogas recovery method is not limited to this method. For example, without providing the gas recovery means 115, an opening is provided in the upper part of the processing tank 107, and the opening is closed with an elastic material such as synthetic rubber (for example, silicone rubber), and the syringe is injected into the elastic material that closes the opening. You may make it collect | recover biogas from a head space with a needle. The elastic material such as synthetic rubber closes the hole when the injection needle is pulled out. Therefore, when the biogas is not collected, the biogas does not leak from the processing tank 107 even if the injection needle is pulled out.

  Furthermore, in the processing apparatus 101 shown in FIGS. 7 to 10, methane fermentation that guides the methane fermentation solution 104 in the treatment tank 107 to the outside of the treatment tank 107 below the liquid level of the methane fermentation solution 104 in the treatment tank 107. A methane fermentation broth 4 is collected from the processing tank 107 by a methane fermentation broth collecting means 116 that includes a liquid discharge pipe 116a and that can be opened and closed by a valve 116b. However, the method for collecting the methane fermentation broth 104 is not limited to this method. For example, without providing the methane fermentation broth sampling means 116, the processing tank 107 may be provided with an opening, closed with an elastic material such as synthetic rubber, and the injection needle of a syringe may be inserted to collect the methane fermentation broth 104. . Or you may make it connect to the syringe of one end of the pipe | tube with which both ends were opened, and immerse the other end in the methane fermentation liquid 104, and extract | collect the methane fermentation liquid 104 through a pipe | tube. Also in these cases, biogas does not leak from the processing tank 107.

  In addition to the gas recovery means 115 and the methane fermentation broth collection means 116, means for adding and supplying substances to the methane fermentation broth 104 may be provided. Specifically, an openable / closable substance introduction pipe that can add and supply substances to the methane fermentation broth 104 from the outside of the treatment tank 107 may be provided. In this case, substances such as nutrient sources, neutralizing agents, and methane fermentation sludge can be added to the methane fermentation broth as necessary. Of course, paper waste can also be supplied from this introduction tube. Gas can also be supplied to keep the environment anaerobic. However, it is not always necessary to provide means for adding and supplying substances to the methane fermentation broth 4, and the gas recovery means 115 and the methane fermentation liquid collecting means 116 may be used together as means for adding and supplying substances to the methane fermentation broth 104. May be. Further, as described above, the injection needle of the syringe may be inserted into the elastic material to add and supply the substance to the methane fermentation liquid 104.

  Hereinafter, the case where the processing apparatus shown in FIG. 7 is used will be described as a first embodiment A, the case where the processing apparatus shown in FIG. 8 is used will be described as a first embodiment B, and the processing apparatus shown in FIG. Will be described as the first embodiment C, and the case where the processing apparatus shown in FIG. 10 is used will be described as the first embodiment D.

(First embodiment A)
In the processing apparatus 101 shown in FIG. 7, a sealed container 120 is used as a processing tank 107, a sealed small container 121 that can be accommodated in the container 120 is used as a counter electrode tank 108, and the small container 121 is at least partly an ion exchange membrane. 106 and a gas discharge pipe 122 for discharging gas (gas generated from the counter electrode 110) to the outside of the container 120. In the processing apparatus 101 shown in FIG. 7, the wiring for connecting the counter electrode 110 and the constant potential setting device 112 passes through the gas exhaust pipe 122. However, the wiring is not necessarily limited to this configuration. The constant potential setting device 112 may be connected without passing through the gas discharge pipe 122.

  Therefore, according to the processing apparatus 101 shown in FIG. 7, biogas does not leak from the processing tank 107. In addition, since the gas generated from the counter electrode tank 108 does not leak into the processing tank 107, the gas generated from the counter electrode tank 108 is mixed with the biogas to reduce the methane concentration of the biogas, or the counter electrode tank The gas generated from 108 does not dissolve in the methane fermentation solution 104 and does not adversely affect the growth and function of the microorganism group involved in methane fermentation. Furthermore, since the processing tank 107 has a sealed structure, there is an advantage that the processing tank 107 can be easily controlled in an anaerobic environment.

  Further, by accommodating the small container 121 in the container 120, the small container 121 is immersed in the methane fermentation solution 104 accommodated in the container 120, and the ion exchange membrane 6 provided in at least a part of the small container 121 is Contact with methane fermentation solution 4. In other words, the methane fermentation solution 104 comes into contact with the electrolytic solution 104a through the ion exchange membrane 106.

  The sealed container 120 as the processing tank 107 is a container of a size that can accommodate the sealed small container 121 as the counter electrode tank 108, and the shape is not particularly limited. Examples of the material of the container include, but are not limited to, glass, plastic, metal subjected to insulation treatment, concrete, and the like. Further, a container in which a gas-impermeable film material is formed in a bag shape by heat sealing or the like may be used as the processing tank 107.

  The small container 121 having a sealed structure as the counter electrode tank 108 is a container of a size that can be accommodated in the container 120 as the processing tank 107, and includes the ion exchange membrane 106 at least in part. Here, the small container 121 may be a bag-like container formed entirely by the ion exchange membrane 106, but only one side of the bag-like container may be constituted by the ion exchange membrane 106, or a part of one surface may be further formed. You may make it comprise only the ion exchange membrane 106. FIG. When the ion exchange membrane 106 is partially used, other portions may be made of the same material as that of the container 120, or may be made of a membrane material other than the ion exchange membrane 106, for example, a gas impermeable membrane material. The gas from the small container 121 (gas generated from the counter electrode tank 108) may be configured not to leak into the container 120.

  The methane fermentation liquid 104 accommodated in the treatment tank 107 is prepared by using methane fermentation liquid in a general methane fermentation tank in which methane fermentation processing such as organic waste is performed, or sludge collected from the methane fermentation tank with water or Although what was prepared by diluting with a culture solution is mentioned, It is not limited to these. For example, the sludge itself collected from the methane fermentation tank may be used.

  The fermented product (treatment liquid) obtained by the hydrogen fermentation treatment of the present invention is added to the treatment tank 107. That is, the fermented product (treatment liquid) obtained by the hydrogen fermentation treatment is put into a methane fermentation tank in which methane fermentation treatment is performed.

  The electrolytic solution 104a accommodated in the counter electrode tank 108 may include, for example, sodium ions or potassium ions. Since the methane fermentation solution 104 usually contains sodium ions, potassium ions, and the like, the methane fermentation solution 104 can also be used as the electrolytic solution 104a.

  As the working electrode 109 and the counter electrode 110, for example, a conductive material such as a carbon plate can be used as appropriate. At the counter electrode 110, a reaction that complements the exchange of electrons with respect to the redox reaction at the working electrode 109 proceeds.

  What is necessary is just to set the temperature (temperature of the methane fermentation liquid 4) of the processing tank 107 suitably according to the optimal temperature of the microorganism group which performs the methane fermentation which exists in the methane fermentation liquid 4. FIG. Specifically, for example, the temperature may be 4 ° C to less than 100 ° C, but is preferably 40 ° C to 70 ° C, more preferably 50 ° C to 60 ° C, and even more preferably 55 ° C.

  Here, as in the present embodiment, by providing the ion exchange membrane 106, the microorganisms present in the methane fermentation liquid 104 can be retained on the processing tank 107 side without being moved (diffused) to the counter electrode tank 108. . Therefore, since the electrons can be supplied from the working electrode 109 to the microorganism while preventing the electrons from being extracted from the microorganism due to the oxidation reaction of the counter electrode 110, the effect of the present invention can be more easily obtained. Furthermore, by putting the electrolytic solution in the counter electrode tank 108, the electron extraction reaction by the counter electrode tank 108 is completed with the electrolytic solution, so that the extraction of electrons from the microorganisms is reliably prevented.

  Also, by providing the ion exchange membrane 106, when the potential of the working electrode 109 is controlled, the flow of ion current between the methane fermentation broth 104 and the electrolytic solution 104a is allowed. The potential of the working electrode 109 can be continuously controlled while maintaining the charge balance.

  Furthermore, by adding the oxidation-reduction substance 103 to the methane fermentation broth 104, the controllability of the solution potential of the methane fermentation broth 104 is improved, and the solution potential of the methane fermentation broth 104 is easily brought close to the potential of the working electrode 109. And by providing the ion exchange membrane 106, permeation | transmission to the electrolyte solution 104a of the oxidation reduction material 103 contained in the methane fermentation liquid 104 can be prevented. For example, by using a Nafion membrane that is a membrane that transmits only monovalent cations as the ion exchange membrane 106, when the redox material 103 is an iron ion, a divalent iron ion or a trivalent iron ion is used. Does not permeate the ion exchange membrane 106, and therefore, the redox material can be allowed to remain in the methane fermentation broth 104 without permeating the electrolyte 104a. Therefore, when the potential of the working electrode 109 is controlled, the concentration ratio of the oxidized form and reduced form of the redox substance 103 in the methane fermentation solution 104 changes accordingly, and the solution potential of the methane fermentation solution 104 by the potential of the working electrode 109 is changed. The followability of is improved. Therefore, it becomes easy to activate the microorganisms present in the methane fermentation broth 104 to improve its function.

  The redox substance 103 is a substance that can reversibly cause a redox reaction with the working electrode 109 immersed in the methane fermentation broth 104, and is toxic to microorganisms living in the methane fermentation broth 104. Substances that do not work can be used. For example, a general iron ion is mentioned as a soil component as mentioned above. Here, in order to allow iron ions to stably exist in the methane fermentation broth, it is preferable that iron ions be coordinated with the chelating agent and added to the methane fermentation broth. As the chelating agent, any chelating agent capable of coordinating iron ions can be used. For example, diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), tetraethylenetriamine (TET), ethylenediamine (EDA), diethylenetriamine (DETA), citric acid, oxalic acid, crown ether, nitrilotetraacetic acid, disodium edetate, sodium edetate, trisodium edetate, penicillamine, trisodium pentetate calcium, pentetate, succil and edet Mention may be made of acid trientine. In addition to iron ions, quinone compounds such as potassium ferrocyanide and sodium anthraquinone disulfonate, and methyl viologen can be used. These substances also reversibly change into an oxidized form and a reduced form by an oxidation-reduction reaction. In particular, a quinone compound is a substance known as one of the soil components and is preferable. In other words, by adding the soil itself to the methane fermentation solution, the oxidation-reduction potential of the methane fermentation solution may be controlled by the oxidation-reduction substance 103 contained in the soil. However, the redox material 103 is not limited to the above-described materials.

  Note that the methane fermentation broth 104 normally contains a redox material, and thus the above redox material may not be added. In particular, in the methane fermentation treatment method according to the present embodiment, if at least the solution potential of the methane fermentation solution 104 in the vicinity of the working electrode 109 can be controlled, the supply of electrons from the working electrode 109 to the microorganism occurs and the effect of the present invention is obtained. Therefore, the addition of the redox material 103 is not essential.

(First embodiment B)

  In the processing apparatus 101 shown in FIG. 8, two tanks opened by partitioning a container 123 whose upper side is opened by an ion exchange membrane 106 are formed, and the upper open part of one tank as the processing tank 107 is a gas. It is assumed that it is blocked by an impermeable film or a gas impermeable member 124. That is, the processing apparatus 101 shown in FIG. 8 has the same configuration as that of FIG. 7 except that the gas generated from the counter electrode tank 108 does not leak into the processing tank 107. Therefore, the same effect as when the processing apparatus shown in FIG. 7 is used can be obtained.

  As the gas impermeable film or the gas impermeable member 124, those generally used in various fields can be appropriately used. For example, examples of the gas impermeable member include, but are not limited to, glass, plastic, an insulating metal, concrete, and the like. As the gas impermeable membrane, for example, an ion exchange membrane 106 can be used, but is not limited thereto.

  The counter electrode tank 108 may be left open, but has a sealed structure similar to the processing tank 107 and includes a gas discharge pipe for discharging the gas generated in the counter electrode tank 108 to the outside of the counter electrode tank 108. It may be. In this case, since the gas generated from the counter electrode tank 108 can be discharged from a desired position, it can be recovered and reused in some cases.

(First embodiment C)
In the processing apparatus 101 shown in FIG. 9, two containers 125 a and 125 b each having an opening below the liquid level of the liquid to be stored are connected to each other through the ion exchange membrane 6 through the opening to form a U-shaped container 125. The one container 125a is used as a processing tank 107 with a sealed structure, and the other container 125b is opened as a counter electrode tank 108. In this case, the methane fermentation solution 104 and the electrolyte solution 104a are in contact with each other through the ion exchange membrane 106, and the space above the liquid surface of the methane fermentation solution 104 in the treatment tank 107 and the solution of the electrolyte solution 104a in the counter electrode tank 108 are used. The space above the surface is separated by the U-shaped structure of the container 125 itself. Since one container 125a has a sealed structure, the biogas generated from the processing tank 107 leaks from the processing tank 107 while preventing the gas generated from the counter electrode tank 108 from entering the processing tank 107. Can be prevented. Therefore, the same effect as when the processing apparatus shown in FIG. 7 is used can be obtained.

  In addition, the opening of the other container 125b in the processing apparatus 101 shown in FIG. 9 is, for example, when the end of the other container 125b is completely opened, while having a sealed structure like the one container 125a, This also includes the case where a gas discharge pipe for discharging the gas generated in the counter electrode tank 108 to the outside of the counter electrode tank 108 is provided. In the case where the gas discharge pipe is provided, the gas generated from the counter electrode tank 108 can be discharged from a desired position, so that it can be easily recovered and reused.

(First embodiment D)
In the processing apparatus 1 shown in FIG. 10, two containers 126 a and 126 b each having an opening below the liquid level of the liquid to be stored are connected through the ion exchange membrane 106 at the opening to connect the H-shaped container 126. The one vessel 126a has a sealed structure as the processing tank 107, and the other vessel 126b is opened as the counter electrode tank 108. Also in this case, the methane fermentation solution 104 and the electrolytic solution 104a are in contact with each other through the ion exchange membrane 106, and the space above the liquid surface of the methane fermentation solution 104 in the treatment tank 107 and the electrolytic solution 104a in the counter electrode tank 108. The space above the liquid level is separated by the H-shaped structure of the container 126 itself. Since one container 126a of the H-shaped container 126 has a sealed structure, the processing tank 107 has a sealed structure. Therefore, it is possible to prevent the biogas generated from the processing tank 107 from leaking from the processing tank 107 while preventing the gas generated from the counter electrode tank 108 from entering the processing tank 107. Therefore, the same effect as when the processing apparatus shown in FIG. 7 is used can be obtained.

  Note that the opening of the other container 126b in the present embodiment is not limited to the case where the container 126 is completely opened, but the gas generated in the counter electrode tank 108 is controlled in the same manner as the one container 126a. This also includes the case where a gas discharge pipe for discharging outside the electrode tank 108 is provided. In the case where the gas discharge pipe is provided, the gas generated from the counter electrode tank 108 can be discharged from a desired position, so that it can be easily recovered and reused.

<Second Embodiment>
In the methane fermentation treatment method according to the second embodiment, the working electrode, the counter electrode, and the reference electrode are connected to a constant potential setting device, and the methane fermentation solution and the counter electrode are brought into contact with each other through an ion exchange membrane. The working electrode and the reference electrode are brought into contact with each other, and the potential of the working electrode is controlled within the above range. That is, it differs from the methane fermentation treatment method in the first embodiment only in that the counter electrode is brought into direct contact with the ion exchange membrane without using an electrolyte.

  However, an ionic current flows between the working electrode 109 and the counter electrode 110 via the ion exchange membrane 106 without using the electrolytic solution 104a as in the first embodiment. In addition, the effect of retaining the microorganisms in the methane fermentation liquid 104 in the treatment tank 107 without moving (diffusing) to the counter electrode 110 side is also obtained. Furthermore, an effect of not allowing the redox material 103 in the methane fermentation broth 104 to permeate the counter electrode 110 side is also obtained. Therefore, according to the methane fermentation treatment method according to the second embodiment, the same effect can be obtained under the same potential control conditions as in the first embodiment.

  The methane fermentation treatment method according to the second embodiment is performed by, for example, a processing apparatus shown in FIG. In the processing apparatus 101 shown in FIG. 11, a working electrode 109 and a reference electrode 111 are disposed in a sealed container 105 having at least a part of an ion exchange membrane 106, and a counter electrode 110 is disposed outside the container 105. The methane fermentation broth 104 is accommodated in 105 and the working electrode 109 and the reference electrode 111 are immersed in the methane fermentation broth 104, and the ion exchange membrane 106 of the container 104 is at least when the methane fermentation broth 104 is accommodated in the container 105. The counter electrode 110 is arranged in contact with at least a part of the surface of the ion exchange membrane 106 opposite to the contact surface of the methane fermentation broth 104. It is supposed to be. In the processing apparatus 101 shown in FIG. 11, an opening 105 a is provided below the liquid level of the methane fermentation solution 104 in the container 105, the opening 105 a is closed with the ion exchange membrane 106, and ion exchange outside the container 105 is performed. It is assumed that the counter electrode 110 is disposed in contact with at least a part of the surface of the film 106. That is, in the processing apparatus 101 shown in FIG. 11, the entire container 105 functions as the processing tank 107.

  Therefore, according to the processing apparatus 101 shown in FIG. 11, biogas does not leak from the container 105. In addition, since the gas generated from the counter electrode 110 does not leak into the container 105, the gas generated from the counter electrode 110 is mixed into the biogas to reduce the methane concentration of the biogas, or from the counter electrode 110. The dissolved gas does not dissolve in the methane fermentation solution 104 and does not adversely affect the growth and function of the microorganism group involved in methane fermentation. Furthermore, since the container 105 has a sealed structure, there is an advantage that the inside of the container 105 can be easily controlled in an anaerobic environment.

  In addition, although the processing apparatus 101 shown in FIG. 11 includes the gas recovery means 115 and the methane fermentation liquid collection means 116 as in the first embodiment, as described above, the gas recovery method, the methane fermentation liquid The collection method is not limited to those using these means. Further, as in the first embodiment, means for adding and supplying a substance to the methane fermentation broth 104 may be provided.

  Details of the processing apparatus 101 shown in FIG. 11 will be described below. However, configurations other than those described below are substantially the same as those in the first embodiment, and a description thereof will be omitted.

  The container 105 has a sealed structure including at least a part of the ion exchange membrane 106. Examples of the material of the container 105 include, but are not limited to, glass, plastic, metal subjected to insulation treatment, concrete, and the like. In FIG. 11, the opening 105 a provided below the liquid surface of the methane fermentation solution 104 of the sealed container 5 is closed by the ion exchange membrane 106, but the form and structure of the container 105 are particularly It is not limited. For example, the entire container 105 may be a bag-like container formed by the ion-exchange membrane 106, or only one surface of the bag-like container may be constituted by the ion-exchange membrane 106, or a part of one surface may be ion-exchanged. You may make it comprise only with the film | membrane 106. FIG. When the ion exchange membrane 106 is partially used, the other portions may be made of the above-described material such as glass, or other membrane materials other than the ion exchange membrane 106, for example, in the methane fermentation broth 104 and the methane fermentation broth 104 You may comprise with the film | membrane material which does not permeate | transmit both of the component (including microorganisms). In short, the methane fermentation liquid 104 accommodated in the container 105 may be a container having a structure that can come into contact with the ion exchange membrane 106 constituting at least a part of the container 105.

  The counter electrode 110 is brought into contact with at least a part of the surface opposite to the contact surface of the ion exchange membrane 106 with the methane fermentation solution 104. In the present embodiment, the counter electrode 110 is a plate-like carbon electrode, but the shape and material of the counter electrode 110 are not limited to this, and the shape is that the contact with the ion exchange membrane 106 is essential. And a material capable of proceeding with a reaction that complements the exchange of electrons with respect to the oxidation-reduction reaction at the working electrode 109, that is, the oxidation reaction can proceed when the reduction reaction occurs at the working electrode 109. A material electrode may be used. In the present embodiment, the counter electrode 110 has a larger area than the ion exchange membrane 106 so that the entire ion exchange membrane 106 is completely covered with the counter electrode 110, and the ion exchange membrane 106 and the counter electrode 110 are covered. Although it is made to contact, if the counter electrode 110 is made to contact at least one part of the surface on the opposite side to the contact surface of the ion exchange membrane 106 with the methane fermentation liquid 104, methane fermentation will be carried out via the ion exchange membrane 106. Since ions are transmitted from the liquid 104 to the counter electrode 110, the ion exchange membrane 106 and the counter electrode 110 may not necessarily be in contact with each other so that the entire ion exchange membrane 6 is completely covered with the counter electrode 110. However, by completely covering the entire ion exchange membrane 106 with the counter electrode 110, the counter electrode 110 can function as a protective material for the ion exchange membrane 106, and the surface for transmitting ions from the methane fermentation broth 104 increases. As a result, there is an advantage that the potential controllability of the methane fermentation liquid 104 can be improved, which is preferable. As a method of completely covering the entire ion exchange membrane 106 with the counter electrode 110, for example, an ion exchange that closes the opening 105 a by applying an adhesive around the opening 105 a of the container 105 and bonding the counter electrode 110 is performed. The entire membrane 106 and the counter electrode 110 may be brought into contact with each other, or an ion exchange membrane formed by applying an adhesive around the opening 105 a of the container 105 and applying it to at least a part of the surface of the counter electrode 110. The counter electrode 110 may be brought into contact with the entire ion exchange membrane 106 that closes the opening 105 a while the opening 105 a is closed with the ion exchange membrane 106 by adhering 106. Examples of the agent for forming the ion exchange membrane 106 include, but are not limited to, a Nafion dispersion. Alternatively, a Nafion dispersion may be applied to the surface of the counter electrode 110, and the ion exchange membrane 106 may be attached before the Nafion dispersion is dried. In this case, the adhesion and contact of the ion exchange membrane 106 to the surface of the counter electrode 110 can be made sufficient.

  Here, the counter electrode 110 is preferably a porous body. In this case, the gas generated on the contact surface between the ion exchange membrane 106 and the counter electrode 110 can easily pass through the surface opposite to the contact surface. In addition, the counter electrode 110 is made a porous body, and the ion exchange membrane 106 is attached using a Nafion dispersion liquid, so that the ion exchange membrane 106 and the counter electrode 110 are separated by the penetration of the Nafion dispersion liquid into the pores of the porous body. The contact area can be increased to facilitate the progress of the electrochemical reaction, which is preferable.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

  For example, when performing a methane fermentation process, as shown in FIG. 12, the methane fermentation solution 104 and the electrolyte 104a are separated by an impermeable member 140 that does not allow ions or microorganisms to permeate, instead of the ion exchange membrane 106, or the process. The tank 107 and the counter electrode tank 108 are formed in separate containers, and the methane fermentation broth 104 and the electrolyte 104a are brought into contact (liquid junction) via a salt bridge 141 (agar or the like containing a saturated electrolyte solution such as KCl). You may do it. Also in this case, the movement of microorganisms in the methane fermentation broth 104 to the counter electrode tank 108 can be prevented, so that the extraction of electrons from the counter electrode 110 can be prevented, and the flow of ion current is caused by the salt bridge. Is acceptable. Further, since the redox substance 103 contained in the methane fermentation broth 104 does not pass through the counter electrode tank 108, the controllability of the solution potential of the methane fermentation broth 104 is also ensured.

  Moreover, when performing a methane fermentation process, it is preferable that the working electrode 109 is a carrier holding electrode provided with a hydrophobic carrier on at least a part of its surface. As the hydrophobic carrier, for example, carbon fibers are preferably used, carbon fibers having a porosity of 25% to 98%, preferably carbon fibers having a porosity of 50 to 98%, and more preferably a porosity. 98% carbon fiber can be used, but the hydrophobic carrier is not limited to carbon fiber, and for example, a carrier such as a fiber made of polyethylene or polypropylene may be used. Carbon fiber is easy to secure a high porosity, and for example, a carbon fiber nonwoven fabric is suitable because it is easy to ensure a high porosity (98%) and can be obtained at low cost. The carrier holding electrode used in the present invention may be provided with a carrier on at least a part of the electrode surface, but is preferably provided on one side of the electrode surface and provided on the entire electrode surface. Most preferably. The higher the carrier holding area on the electrode surface, the easier it is to support microorganisms. Examples of the method of providing the carrier on the electrode surface include adhesion by an adhesive, and a method of covering the electrode by covering the electrode with a bag or cylinder, but is not limited thereto. Here, it is preferable that the carrier capable of supporting the microorganism has liquid permeability capable of ensuring contact between the electrode and the methane fermentation broth. In this case, the microorganisms can be sufficiently loaded up to the vicinity of the electrode of the carrier, and the controllability of the potential in the vicinity of the electrode can be ensured to sufficiently activate the microorganism on the carrier. In other words, even if the carrier material is a conductive material such as carbon, if the porosity is increased in order to increase the amount of microorganisms supported, the conductivity performance will be substantially reduced and substantially reduced. If the carrier does not flow, but the carrier has liquid permeability that can ensure contact between the electrode and the methane fermentation broth, the potential of the methane fermentation broth that fills the gap in the carrier is controlled, and the potential environment of the carrier is reduced to microorganisms. Can be controlled within the optimum range.

  Also, when performing methane fermentation treatment, as described above, the carrier holding electrode provided with the hydrophobic carrier on at least a part of the surface of the working electrode 109 is used, and the hydrophobic carrier is dispersed in the methane fermentation solution 104 as well. Is preferred. Alternatively, the hydrophobic carrier may be dispersed only in the methane fermentation broth 104 without providing the hydrophobic carrier on the electrode surface.

  When performing methane fermentation treatment, a counter electrode that forms a pair with the working electrode is immersed in the methane fermentation solution, and the potential C (unit: V) of the working electrode is -1. By controlling to 0 <B <X (X is a redox potential of the methane fermentation liquid itself), methane fermentation may be promoted. That is, methane fermentation may be promoted by using an apparatus having the same basic configuration as the above-described hydrogen fermentation apparatus without providing an ion exchange membrane as in the above-described embodiment. When B ≧ −0.5, the reduction reaction hardly proceeds at the working electrode, and the promotion of methane fermentation hardly occurs. Moreover, in B <=-1.0, predominance of hydrogen fermentation is accelerated | stimulated and methane fermentation will be deactivated conversely.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  The potential values described in the examples mean potential values based on the silver / silver chloride electrode potential reference unless otherwise specified.

[Example 1]
<Experimental equipment>
FIG. 19 shows a cross-sectional view of the experimental apparatus used in this example. Two glass vials each having a volume of 250 mL (manufactured by Duran) were connected to each other through a lower opening to form an H-shaped container 26. One of the glass vials was a working electrode tank 26a, and the other was a counter electrode tank 26b. A discharge part 51 and a supply part 52 are provided in the working electrode tank 26a. The working electrode tank 26a was covered, and a silicone rubber plug was provided on the upper surface of the lid to ensure hermeticity when wiring and electrodes penetrated from the outside to the inside of the working electrode tank 26a. Further, the tube 33 is passed through a silicone rubber stopper under the condition of the lid, and the gas in the space (head space) above the liquid level of the liquid contained in the working electrode tank 26a is discharged from one end of the tube 33, The gas was collected in the bag 34 connected to the other end.

  In the working electrode tank 26a and the counter electrode tank 26b, plate-like carbon electrodes (2.5 cm × 7.5 cm × 0.2 cm) were arranged, respectively, to obtain a working electrode 9 and a counter electrode 10. Moreover, the fermented liquid 4 was accommodated in the container 26, and was made to contact with the working electrode 9 and the counter electrode 10. FIG.

  The counter electrode tank 26b was also covered, and a silicone rubber plug was provided on the upper surface of the cover, and the gas discharge pipe 22 was passed through the silicone rubber plug. Then, a wiring 31 for connecting the counter electrode 10 and the constant potential setting device 12 was passed through the gas exhaust pipe 22. Both ends of the gas discharge pipe 22 are opened, and the gas generated in the counter electrode tank 26b is arranged so that one end is disposed inside the counter electrode tank 26b and the other end is disposed outside the counter electrode tank 26b. It was made to discharge to the outside of 26b.

  The wiring from the working electrode 9 of the working electrode tank 26a to the constant potential setting device 12 was drawn out of the processing tank 26a through a silicone rubber plug. The reference electrode 11 (silver / silver chloride electrode, HS-205C, manufactured by Toa DKK Corporation) was inserted into the silicone rubber plug from the outside of the working electrode tank 26a and brought into contact with the fermentation broth 4. The working electrode 9, the counter electrode 10, and the reference electrode 11 were connected to a three-electrode constant potential setting device (potentiostat, PS-08P, manufactured by Toho Giken) 12 to control the potential of the working electrode 9.

<Fermentation liquid composition and operation method>
Fermentation liquid 4 was prepared by adding 2 mL of sludge accumulated by performing methane fermentation (55 ° C.) with simulated raw garbage to 250 mL of a solution having the following composition. The inside of the container 26 was filled with nitrogen. The yeast extract manufactured by Wako Pure Chemical Industries, Ltd. is used, and DSMZ Medium 131 trace element solution (hereinafter referred to as trace element solution) and DSMZ Medium 141 vitamin solution (hereinafter referred to as vitamin solution) are DSMZ ( Deutsche Sammlung von Mikroorganismen and Zellkulturen) was used. During the experiment, the temperature of the fermentation broth 4 was set to 55 ° C. Moreover, during the experiment period, the fermented liquid 4 was continuously stirred by the stirring bar.
(Solution composition)
KH ₂ PO ₄ : 0.8 g / L
K ₂ HPO ₄ : 1.6 g / L
NH ₄ Cl: 1 g / L
NaHCO ₃ : 2 g / L
MgCl ₂ · 6H ₂ O: 0.1 g / L
CaCl ₂ · 2H ₂ O: 0.2 g / L
NaCl: 0.8 g / L
Yeast extract: 1 g / L
Trace element solution: 10 mL / L
Vitamin solution: 10mL / L

  In addition, 2,6-anthraquinone disulfonate (AQDS) was added to the fermentation broth 4 to a concentration of 0.2 mM.

  Furthermore, 1N sodium hydroxide aqueous solution was added to the fermented liquid 4 and pH was adjusted to 7.8.

  The driving method was a fill and draw method. That is, the operation was performed in such a manner that a certain amount of the fermentation broth 4 was discarded and the same amount of substrate was added. As the substrate, a simulated garbage substrate in which a dog food (Vita-one, manufactured by Nippon Pet Foods Co., Ltd.) was turbid at 100 g / L (10% by weight) in the solution having the above composition was used.

  In the container 26, 500 mL of the fermented liquid 4 having the above composition was accommodated for experiments.

<Analysis method>
The composition (methane, hydrogen, carbon dioxide) in the product gas was measured by gas chromatography equipped with a thermal conductivity detector (GC390B, manufactured by GL Science) and an activated carbon packed stainless steel column (manufactured by GL Science).

  Analysis of VFA (volatile fatty acid) was performed by liquid chromatography (GL Science, GL-7400).

  The analysis of COD (chemical oxygen demand) was performed by JIS K 0102-20 (analyzer: manufactured by HACH, DR800).

<Test conditions>
The test was performed for 14 days with the set potential of the working electrode 9 set to -1.0V. The organic load (OLR) during the test period was 2445 mg / L / day until the 8th day, and then 4890 mg / L / day. The hydraulic residence time (HRT) was 50 days until the 8th day and 25 days thereafter.

<Test results>
(1) pH
FIG. 1 shows the pH fluctuation results during the test period. The change in pH was only observed between 7.8 and 6.6, confirming that the pH was maintained in the neutral region during the test period.

(2) Biogas production rate and biogas composition FIG. 2 shows the change over time in the biogas production rate during the test period. There was a tendency that the biogas production rate gradually decreased from the start of the test to the 8th day and then gradually increased until the final day.

Moreover, when the biogas composition of the 4th day and the last day was analyzed, hydrogen gas that was not produced at all on the 4th day was produced in a large amount on the last day as shown below. It became clear that almost no methane gas was produced on the last day.
(Gas composition on the 4th day)
・ H ₂ : 0vol%
・ CH ₄ : 52.27vol%
・ CO ₂ : 47.73 vol%
(Last day gas composition)
・ H ₂ : 35.20vol%
・ CH ₄ : 1.40vol%
・ CO ₂ : 63.39 vol%

  Here, as described above, since the pH during the test period fluctuated in the neutral region, methane production by methane fermentation should normally be observed. However, since almost no methane production was seen on the last day, it was considered that methane fermentation was almost stopped. On the other hand, hydrogen production was observed on the last day instead of methane, suggesting the possibility that hydrogen fermentation predominates.

  In addition, the biogas production rate gradually decreased from the start of the test to the 8th day and then gradually increased to the final day, so that the methane fermentation gradually started from the start of the test to the 8th day. It was thought that hydrogen fermentation occurred and the biogas production rate gradually increased until the last day.

(3) Current Value of Working Electrode 9 A change with time of the current value of the working electrode 9 is shown in FIG. It became clear that the current value (absolute value) gradually increased on the 7th to 8th days.

  The hydrogen conversion efficiency on the 14th day was calculated using Faraday's law based on the current values shown in FIG. Specifically, in order to generate 1 mole of hydrogen, an electric amount twice as much as the Faraday constant is required, and the theoretical hydrogen generation amount was calculated on the assumption that all currents were used for hydrogen generation. The actual hydrogen generation amount relative to the theoretical hydrogen generation amount was defined as the hydrogen conversion efficiency. As a result, the hydrogen conversion efficiency was 87.6%.

(4) COD removal rate and COD removal rate The COD removal rate and the COD removal rate were determined for the 8th to 14th days.

The COD removal rate was determined by the following equation (1).
_{X = (d / 250) [} S-C 0 - (C n -C 0) / {1- (1-d / 250) n}] ···· (1)
Here, X is the COD removal rate per day (mgCOD / L / day), d is the exchange amount of the methane fermentation broth, and S is the substrate COD (mg / L). C ₀ is the COD (mg / L) on the 0th day, and C _n is the COD (mg / L) on the nth day.

Formula (1) will be described in detail. First, COD (C ₁ ) of the first day, COD (C ₂ ) of the second day, COD (C _n ) of the n day, and COD (C _{n + 1} ) of the ( _{n + 1} ) day have a constant COD removal rate. Assuming that there is, it can be expressed as: X × 1 means COD (mg / L) removed in one day.
C ₁ = (1−d / 250) C ₀ + (d / 250) S−X × 1 (2)
C ₂ = (1−d / 250) C ₁ + (d / 250) S−X × 1 (3)
C _n = (1−d / 250) C _n−1 + (d / 250) S−X × 1 (4)
C _{n + 1} = (1−d / 250) C _n + (d / 250) S−X × 1 (5)

When the equation (4) is subtracted from the equation (5), the following equation is obtained.
_{C n + 1 -C n = (} 1-d / 250) (C n -C n-1) ···· (6)

Here, the equation (6) can be transformed into the following equation.
^{_{C n + 1 -C n = (}} 1-d / 250) n (C 1 -C 0) ···· (7)

Therefore, Expression (7) in the case of n = n−1, n−2,..., 1, 0 is expressed as follows.
^{_{C n -C n-1 = (}} 1-d / 250) n-1 (C 1 -C 0) ···· (8)
C _n-1 −C _n−2 = (1−d / 250) ⁿ⁻² (C ₁ −C ₀ ) (9)
_{C 2 -C 1 = (1-} d / 250) (C 1 -C 0) ···· (10)
C ₁ -C ₀ = (1-d / 250) ⁰ (C ₁ -C ₀ ) (11)

Therefore, regarding the equation (7), when the sum is taken as n = n−1, n−2,..., 1, 0, the following equation is derived.
^{_{C n -C 0 = {(1}} -d / 250) n-1 + (1-d / 250) n-2 + ···· + (1-d / 250) +1} (C 1 -C 0) (12)

Then, by substituting equation (2) into equation (12), by organizing erase the _{C 1,} formula (1) it is derived.

In this example, the COD of the methane fermentation liquid on the 8th day was 32200 mg / L. The COD of the methane fermentation liquid on the 14th day was 49100 mg / L. The substrate COD was 122250 mg / L. And from the 8th day, 10 mL of methane fermentation broth was taken out and 10 mL of substrate was newly added. Therefore, when the COD removal rate X was calculated with S = 122250, d = 10, C _n = 49100, and C ₀ = 32200, X = 882 (mg / L / day) was obtained.

  Here, since the daily organic load was 4890 mg / L / day, the calculated value of X was divided by this value to calculate the COD removal rate. As a result, the COD removal rate was 18%.

  From this calculation result, it was revealed that the substrate-derived COD was reliably removed from the 8th day to the 14th day.

(5) VFA concentration As a result of measuring the VFA concentration of the methane fermentation solution on the 14th day, it was revealed that the acetic acid was 82 mM, propionic acid 9 mM, butyric acid 25 mM, and the VFA concentration was 115 mM. When this is converted into COD, it becomes 10961 mg / L. Since the COD of the methane fermentation liquid on the 14th day was 49100 mg / L, it was considered that most of the substrate remained as VFA. In addition, as a result of measuring the VFA density | concentration of a methane fermentation liquid on the 4th day, they were acetic acid 47 mM, propionic acid 3.3 mM, butyric acid 3.6 mM, and VFA density | concentration was 54 mM.

(6) Summary As described above, from day 8 to day 14, COD derived from the substrate is surely removed, and accumulation of VFA (especially accumulation of acetic acid and butyric acid, which are main metabolites in hydrogen fermentation) is also seen. Therefore, it was considered that hydrogen was generated as a result of removal of substrate-derived COD by hydrogen fermentation. On the fourth day, since no hydrogen was generated, the electrolysis of water hardly occurred at the voltage applied in this example, and hydrogen generation occurred as a result of the input electric energy promoting hydrogen fermentation. It was thought that.

[Example 2]
Based on the experimental results of Example 1, further detailed examination was performed.

<Experimental equipment>
The basic configuration was the same experimental apparatus as in Example 1. However, the gas generated in the counter electrode tank 26b was collected in a bag, and both the gas from the working electrode tank 26a (cathode gas) and the gas from the counter electrode tank 26b (anode gas) were collected for analysis. .

<Fermentation liquid composition and operation method>
Fermentation liquid 4 used 500 mL of sludge accumulated by performing methane fermentation (55 ° C.) with simulated raw garbage. The inside of the container 26 was filled with nitrogen. AQDS functioning as a redox material was not used in this example. Further, sodium hydroxide (5N) was added to adjust the initial pH of the fermentation broth 4 to 7.2.

The operation method was the same as in Example 1. However, as a substrate, a simulated garbage substrate in which a dog food (Vita-one, manufactured by Nippon Pet Foods Co., Ltd.) was turbid at 100 g / L (10% by weight) in a solution having the following composition was used.
(Solution composition)
KH ₂ PO ₄ : 1.1 g / L
K ₂ HPO ₄ : 1.7 g / L
NiCl ₂ · 6H ₂ O: 0.004 g / L
CoCl ₂ · 6H ₂ O: 0.005 g / L

  The simulated garbage substrate had a CODcr (dichromate chemical oxygen demand) of 122.3 g CODcr / L and an SS (suspended solid) of 53.3 g / L.

  Moreover, during the test period, sodium hydroxide (5N) was added to the fermentation broth once a day to adjust the pH to 7.2.

  Furthermore, when operating by the fill and draw system, the fermented liquid for waste is extracted from each of the working electrode tank 7 and the counter electrode tank 8 in an equal amount, and this is mixed to prepare a methane fermentation treatment of Example 4 described later. As a substrate.

<Analysis method>
Same as Example 1.

<Test conditions>
(1) Test 1
The test was conducted for 64 days with the set potential of the working electrode 9 set to -1.0V. The organic load (OLR) and hydraulic residence time (HRT) during the test period were as shown in FIG. Specifically, 5 mL / day of simulated garbage is introduced on the 1st to 9th days (HRT: 50 days, OLR: 2445 mg / l / day), and 10 mL / day of simulated garbage is introduced on the 10th to 17th days. (HRT: 25 days, OLR: 4890 mg / l / day) On the 18th to 24th days, 20 mL / day of simulated garbage was introduced (HRT: 12.5 days, OLR: 9780 mg / l / day), 25-38 On the day, 40 mL / day of simulated garbage was introduced (HRT: 6.25 days, OLR: 19560 mg / l / day), and on the 39th to 47th days, 60 mL / day of simulated garbage was introduced (HRT: 4.17). Day, OLR: 29340 mg / l / day), 48 to 54 days, mock-up garbage was introduced at 80 mL / day (HRT: 3.13 days, OLR: 39120 mg / l / day), 55 to 59 days simulated 100ml / day of garbage (HRT: 2.5 days, OLR: 48900 mg / l / day) On the 60-64th day, 120 mL / day of simulated food waste was added (HRT: 2.1 days, OLR: 58680 mg / l / day). The test was carried out in triplicate, and the test result was shown by an error bar of the average value and standard deviation.

(2) Test 2 (Comparative test A)
The same fermentation broth as in Test 1 was housed in a 250 mL container, filled with nitrogen and sealed, and the test was conducted without conducting electricity. This was designated as Comparative Test A. However, hydrochloric acid (1N) was added to adjust the initial pH to 5.5, and then the test was conducted without adjusting the pH. Biogas was recovered from the headspace in the container.

(3) Test 3 (Comparative test B)
Microorganisms present in the fermentation broth 4 were deactivated, and an energization test in the absence of the microorganisms was performed as comparative test B. Specifically, autoclave treatment (120 ° C., 15 minutes) is performed for each experimental apparatus in a state where 5 mL of simulated garbage substrate is added under the same conditions as in Test 1, and the set potential of the working electrode 9 is set to −1.0 V or −1. The cathode gas was recovered at .4V. Each energization period was 1 day.

<Test results>
(1) Biogas production rate FIG. 27 shows the change over time of the biogas production rate during the test period. In FIG. 27, ● represents the biogas production rate based on the cathode gas production amount in Test 1, ■ ■ represents the biogas production rate based on the anode gas production amount in Test 1, and x represents the biogas production rate in Test 2 The biogas production rate is shown. In test 1 in which the working electrode 9 was energized at −1.0 V, the biogas generation rate tended to increase as the organic load (OLR) increased, and this trend was observed until the last day. It was. On the other hand, in Test 2 in which no energization was performed, generation of biogas was not observed after the 24th day.

(2) Hydrogen production rate Based on the measurement result of the hydrogen content in the biogas, the result of obtaining the hydrogen production rate with respect to the organic load (OLR) is shown in FIG. In FIG. 28, ● represents the hydrogen production rate based on the cathode gas production amount in Test 1, ■ represents the hydrogen production rate based on the anode gas production amount in Test 1, and ▲ represents hydrogen based on the biogas production amount in Test 2. The generation rate is shown. In Test 1 in which the working electrode 9 was energized at −1.0 V, the hydrogen generation rate tended to increase gradually as the organic load (OLR) increased, and this trend continued to the end. It was. The final hydrogen production rate (organic load: 58680 mg / l / day) is 2445 mL / L / day on the working electrode tank side (cathode tank side) and 2130 mL / L on the counter electrode tank side (anode tank side). / Day. On the other hand, in Test 2 in which no current was supplied, almost no hydrogen was generated.

(3) pH
FIG. 29 shows the change in pH of the fermentation broth during the test period. In FIG. 29, ● represents the pH of the fermented liquid on the working electrode tank side (cathode tank side) in Test 1, ■ represents the pH of the fermented liquid on the counter electrode tank side (anode tank side) in Test 1, and x represents The pH of the fermentation liquid of test 2 is shown. In Test 1, pH measurement was performed immediately before pH adjustment once a day by adding sodium hydroxide. From the results shown in FIG. 29, in Test 1, in the operation after the 25th day for both the working electrode tank side and the counter electrode tank side fermented liquid (organic substance loading: 19560 mg / l / day or more), the pH is 1 day. There was a tendency to decrease from 7.2 to about 5.5 to 6.4. In Test 2 in which no current was applied, the pH was maintained at about 4.7 to 5.5, and the pH at which hydrogen fermentation could occur was maintained, but almost no hydrogen production was seen as described above. .

(4) VFA concentration FIG. 30A and FIG. 30B show the change over time of the VFA concentration of the fermentation broth during the test period. 30A is the VFA concentration with respect to the organic load (OLR) of the fermented liquid on the working electrode tank side (cathode tank side) of Test Example 1, and FIG. 30B is the organic load (OLR) of the fermented liquid of Test 2 at 9780 mg / l. VFA concentration per day. In the figure, ■ indicates total VFA concentration (lactic acid + acetic acid + propionic acid + butyric acid), x indicates lactic acid concentration, ○ indicates acetic acid concentration, Δ indicates propionic acid concentration, and ● indicates butyric acid concentration. Is shown. In Test Example 1, the fermented liquid on the working electrode tank side (cathode tank side) had almost the same VFA concentration and VFA composition (lactic acid, acetic acid, propionic acid and butyric acid as the fermented liquid on the counter electrode tank (anode tank side). Of the composition).

  From the results shown in FIG. 30A, in the fermentation liquid of Test 1, mainly the production of acetic acid and butyric acid was seen, and the production of lactic acid was hardly seen. On the other hand, from the results shown in FIG. 30B, production of lactic acid was mainly observed in the fermentation liquid of Test 2. In addition, it was thought that the fall of pH of a fermented liquid was produced by the production | generation of a VFA component.

Here, hydrogen fermentation is a reaction system in which hydrogen, carbon dioxide, acetic acid and butyric acid are generated in the process of decomposing a substrate such as glucose as shown in the following formula (Reference 1: Liu, D. , Liu, D., Zeng, RJ, Angelidaki, I. 2006. Water Res. 40, 2230-2236., Reference 2: Ueno, Y., Sasaki, D., Fukui, H., Haruta, S., Ishii, M., Igarashi, Y. 2006. J. Appl. Microbiol. 101, 331-343.)
C ₆ H ₁₂ O ₆ + 2H ₂ O → 4H ₂ + 2CH ₃ COOH + 2CO ₂ ... (Chemical Formula 1)
C ₆ H ₁₂ O ₆ → 2H ₂ + CH ₃ CH ₂ CH ₂ COOH + 2CO ₂ ... (Chemical formula 2)
In addition, there are two types of lactic fermentation, homolactic fermentation and heterolactic fermentation.
In homolactic fermentation, a substrate such as glucose is decomposed according to the following formula to produce lactic acid. At this time, almost no by-products are produced (Tokyo Chemical Doujin, Biochemical Dictionary, 3rd edition).
C ₆ H ₁₂ O ₆ → 2CH ₃ CH (OH) COOH (Chemical formula 3)
In heterolactic fermentation, in addition to lactic acid, ethanol, acetic acid, glycerol, carbon dioxide gas and the like are generated. The production ratio of by-products is not necessarily constant, but representative examples include the following two mass balance formulas.
C ₆ H ₁₂ O ₆ → CH ₃ CH (OH) COOH + C ₂ H ₅ OH + CO ₂ ... (Chemical formula 4)
2C ₆ H ₁₂ O ₆ + H ₂ O → 2CH ₃ CH (OH) COOH + CH ₃ COOH + C ₂ H ₅ OH + 2CO ₂ + 2H ₂ (chemical formula 5)
Considering the above fermentation process, from the above test results, hydrogen fermentation is predominantly progressing in the fermentation liquid of Test 1 in which the production of acetic acid and butyric acid was mainly seen, and the production of lactic acid was mainly seen. It was considered that lactic acid fermentation proceeded predominately in the fermented liquid obtained in Test 2. That is, in Test 1, it was considered that hydrogen fermentation, which is a more advantageous fermentation mode for producing hydrogen, is proceeding predominantly.

(5) Test 3 As a result of performing Test 3, even when the set potential of the working electrode 9 was set to −1.0 V, almost no hydrogen was generated in both the cathode gas and the anode gas. From this, the result obtained in Test 1 does not result from hydrogen generated by electrolysis of water, but is produced by dominantly activating the microorganism group that performs hydrogen fermentation existing in the fermentation broth. It was revealed that this was due to hydrogen. When the set potential of the working electrode 9 is −1.4 V, a large amount of hydrogen is recovered from the working electrode tank side (cathode tank side) (110.9 mL / L / day), and the water is electrolyzed. It has been confirmed that this occurs. However, if the potential is smaller than -1.4V on an absolute value basis (for example, -1.3V or -1.2V), water electrolysis hardly occurred.

(6) Hydrogen recovery rate and energy recovery rate The hydrogen recovery rate (γ _cat ) on the cathode cell side is shown in Reference 3 (Call, D., Logan, BE 2008. Environ. Sci. Technol. 42, 3401-3406.). Based on the calculation. Specifically, the calculation was performed using the following equation.
γ _cat = n _{H 2} / n _CE (a)
In formula (a), n _H2 is the number of moles of hydrogen recovered, and n _CE is the number of moles of hydrogen that can be generated from the measured current value (I).

The energy recovery rate was calculated based on the electrical input shown in the following equation.
η ^W = W _H2 / W _in (b)
In formula (b), W _H2 (unit: J) is the heat of combustion of the produced hydrogen (amount of heat of 285.83 kJ per mole of hydrogen), and W _in (unit: J) is determined by the following formula: Electrical input.
W _in = IE _ap (c)
In formula (c), E _ap is a voltage applied using a potentiostat.

  The results calculated for the hydrogen recovery rate and energy recovery rate are shown in FIG. In FIG. 31, ◆ indicates the hydrogen recovery rate, and ■ indicates the energy recovery rate.

  From the results shown in FIG. 31, it was found that the hydrogen recovery rate increases as the organic load (OLR) increases. If all the electrons from the working electrode are used for electrolysis for hydrogen production, the hydrogen recovery rate is 100%. However, in the calculation result of this example, the organic substance loading amount is 58680 mg / Since the hydrogen recovery rate at 1 / day was 4987%, it was also found that most of the produced hydrogen was derived from the simulated garbage substrate introduced into the fermentation broth.

  From the results shown in FIG. 31, the energy recovery rate increased with an increase in organic matter load (OLR), and the energy recovery rate was 3887% at an organic matter load of 58680 mg / l / day.

  From the above results, it was revealed that most of the hydrogen generated in Test 1 was not directly generated from the electrochemical reaction.

(7) Summary From the above results, it became clear that hydrogen fermentation can be preferentially advanced using methane fermentation sludge collected from a methane fermentation tank. Further, as shown in FIG. 40 (in the figure, ● is a cathode gas and □ is an anode gas), the potential of the working electrode is -1.2V, and -1.0V. Similarly, it was confirmed that hydrogen fermentation can be preferentially advanced. From this, it was considered that hydrogen fermentation could be preferentially advanced if the potential A (unit: V) of the working electrode was A ≦ −1.0. However, if the potential A of the working electrode is excessively increased to the negative side, the amount of electric power to be input increases, resulting in a decrease in hydrogen production efficiency, deterioration of the electrode due to vigorous electrolysis of water, Since hydrogen may be consumed by sulfate-reducing bacteria due to the predominance of reducing bacteria, −1.4 <A ≦ −1.0 is preferable, and −1.2 ≦ A ≦. It was considered that -1.0 was more preferable.

[Example 3]
Instead of an H-type device in which two containers are connected as used in Examples 1 and 2, 250 mL of the fermentation liquid 4 is accommodated in one container 20, and the working electrode 9, the counter electrode 10, and the reference electrode are contained in the fermentation liquid. The test was carried out under the same conditions as in Test 1 of Example 2 except that an apparatus of a type immersed in 10 (see FIG. 5) was used. Whether or not can be preferentially advanced. The organic load (OLR) and hydraulic retention time (HRT) in the test of Example 3 are shown in FIG.

  Similar to Example 2, FIG. 33 shows the result of obtaining the hydrogen generation rate with respect to the organic load (OLR) based on the measurement result of the hydrogen content in the biogas. Similar to Example 2, there was a tendency for the hydrogen production rate to gradually increase with an increase in organic matter loading (OLR), and this trend was observed until the end. The final hydrogen production rate (organic load: 58680 mg / l / day) was 2288 mL / L / day. In addition, when no current was supplied, almost no hydrogen was generated. From the above results, it was confirmed that the hydrogen fermentation reaction proceeded predominantly in the test of Example 3 as in Example 2.

  Therefore, it was confirmed that the hydrogen fermentation reaction can be preferentially advanced by energization regardless of the shape of the apparatus used. In addition, if the apparatus having a simple configuration as in Example 3 can dominate the hydrogen fermentation reaction, the main point is to immerse the working electrode and the counter electrode in the fermentation broth, so that the potential of the working electrode It has also been clarified that the hydrogen fermentation reaction can be preferentially advanced without being limited to the apparatus configuration if is controlled within a certain range.

[Reference Example 1]
The effect of potential control on the methane fermentation reaction was investigated.

<Experimental apparatus and experimental method>
A sectional view of the experimental apparatus used in this reference example is shown in FIG. One of two 250 mL glass vials (manufactured by Duran) is a methane fermentation tank 126a, the other is a counter electrode tank 126b, and two vials are passed through a cation exchange membrane (Nafion K) 106 at the lower opening. A bottle was connected to form an H-shaped container 126. Moreover, the discharge part 152 and the supply part 151 were provided in the methane fermentation tank 126a. The methane fermentation tank 126a was covered, and a silicone rubber stopper was provided on the upper surface of the lid to ensure a sealed product when wiring and electrodes were passed. Further, the tube 133 is passed through the silicone rubber stopper on the upper surface of the lid, and the gas in the space (head space) above the liquid surface of the fermentation liquid 104 of the methane fermentation tank 126a is discharged from one end of the tube 133, and the other end of the tube Gas was collected in a bag 134 connected to the.

  The counter electrode tank 126b accommodated the electrolytic solution 104a and also accommodated the counter electrode 110 (2.5 cm × 7.5 cm × 0.2 cm plate-like carbon electrode) and immersed in the electrolytic solution 104a. The counter electrode tank 126b was also covered, and a silicone rubber plug was provided on the upper surface of the cover, and the gas discharge pipe 122 was passed through the silicone rubber plug. Then, a wiring 131 for connecting the counter electrode 110 and the potential control device 112 was passed through the gas exhaust pipe 122. The gas discharge pipe 122 is open at both ends, and the gas generated in the counter electrode tank 126b is arranged so that one end is disposed inside the counter electrode tank 126b and the other end is disposed outside the counter electrode tank 126b. It was made to discharge outside 126b.

  The working electrode 109 (2.5 cm × 7.5 cm × 0.2 cm plate carbon electrode) is housed in the methane fermentation tank 126a and immersed in the fermentation broth 104, and the wiring from the working electrode 109 to the potential control device 112 is silicone. It was pulled out of the methane fermentation tank 126a through a rubber stopper. The reference electrode 111 (silver / silver chloride electrode) was inserted into a silicone rubber stopper from the outside of the methane fermentation tank 126a and brought into contact with the fermentation broth 104. The working electrode 109, the counter electrode 110, and the reference electrode 111 were connected to a three-electrode potential controller (potentiostat) 112 to control the potential of the working electrode 109.

The composition of the fermented liquid 104 accommodated in the methane fermenter 126a is as follows: KH ₂ PO ₄ 1.135 g / l, K ₂ HPO ₄ 1.740 g / l, NiCl ₂ · 6H ₂ O 0.403 mg / l, CoCl ₂ · 6H ₂ O 0.484 mg / l. Anthraquinone-2,6-disulfonic acid (AQDS) was added to a final concentration of 0.2 mM. The composition of the electrolytic solution 104a was NaCl 5.844 g / l.

  To the fermentation liquid 104, a microbial community obtained from seed sludge accumulated by performing methane fermentation (55 ° C.) with simulated raw garbage was added. During the experiment, the pH of the fermentation broth 4 was maintained at 7.4 to 7.9, and the temperature was maintained at 55 ° C. Moreover, the fermented liquid 104 and the electrolyte solution 104a continued stirring with the stirring bar.

Further, in this reference example, the operation was performed while applying the load shown in FIG. 14 (organic matter load amount OLR, hydraulic retention time HRT). The operation of the methane fermentation tank was performed by the fill and draw method. In other words, a certain amount of fermentation broth was discarded and the operation was performed by adding the same amount of substrate. The substrate is 100g / l (10% by weight) of dog food (Nippon Pet Food, Vita-one), KH ₂ PO ₄ 1.135 g / l, K ₂ HPO ₄ 1.740 g / l, NiCl ₂ · 6H ₂ O 0.403 A simulated garbage substrate containing mg / l, CoCl ₂ · 6H ₂ O 0.484 mg / l was used.

  The potential of the working electrode 109 is + 0.6V, + 0.3V, -0.3V, -0.6V, -0.8V based on the potential of the silver / silver chloride electrode as the reference electrode 111. It was. As a comparative experiment, methane fermentation treatment was performed without energizing the working electrode 109. The fermented liquid 104 to which the working electrode 109 and the microbial community had been added was brought into contact several days before the start of the experiment, and a few microbial communities were supported on the working electrode 109 in advance before the experiment.

  In addition, since the potential of the methane fermentation broth 104 was about −0.5 V, when the potential of the working electrode 109 is +0.6 V, +0.0 V, +0.3 V, and −0.3 V, the working electrode 109 In this case, an oxidation reaction occurs, and a reduction reaction occurs at -0.6V and -0.8V. This means that the cathode current flows through the working electrode 109 at −0.6 V and −0.8 V, and the anode current flows through the working electrode 109 at +0.6 V, +0.3 V, +0.0 V, and −0.3 V. I was able to confirm it.

<Analysis method>
(1) Chemical analysis method The composition analysis of the gas discharged from the methane fermentation tank 126a was performed by gas chromatography (manufactured by Agilent, apparatus name: 6890N).

  The lower fatty acid concentration analysis of the fermentation broth 4 was performed by an analysis method: liquid chromatography (product name: GL-7400, manufactured by GL Science).

  The analysis of COD (chemical oxygen demand) was performed according to the analysis method: Japanese Industrial Standard (JIS) K 0102-20 (HACH, apparatus name: DR800).

  The analysis of SS (floating solid content) was performed by an analysis method: JIS K 0102-14.1 (manufactured by Yamato, apparatus name DN63).

<Experimental result>
(1) Relationship between set potential and gas generation rate FIG. 15 shows changes with time in the gas generation rate at various set potentials. In FIG. 15, x is a plot of the results of three experiments under the condition of no energization. ○ is a plot of the average of three experimental results under the condition of -0.8 V. For data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. □ is a plot of the average of three experimental results under the condition of −0.6 V. For the data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. Δ is + 0.0V, ◇ is −0.3V, ◆ is + 0.3V, and ▲ is + 0.6V.

  Regarding the conditions of + 0.3V, -0.6V and -0.8V, no decrease in gas generation rate was observed during the operation period. In particular, under the conditions of -0.6 V and -0.8 V, no decrease in gas generation rate was observed even when the organic load was increased to 31.8 g / l / day.

(2) Relationship between set potential and COD removal rate FIG. 16 shows changes over time in the COD removal rate at various set potentials. In FIG. 16, “x” is a plot of the average value of three experimental results under no-energization conditions, and the standard deviation is indicated by an error bar. ○ is a plot of the average of three experimental results under the condition of -0.8 V. For data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. □ is a plot of the average of three experimental results under the condition of −0.6 V. For the data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. Δ is + 0.0V, ◇ is −0.3V, ◆ is + 0.3V, and ▲ is + 0.6V.

  With respect to the conditions of +0.3 V, −0.6 V, and −0.8 V, the COD removal rate continued to increase without decreasing as the organic load increased. In particular, for the conditions of −0.6 V and −0.8 V, the COD removal rate continued to increase without decreasing even when the organic load was increased to 31.8 g / l / day.

(3) Relationship between set potential and SS removal rate FIG. 17 shows changes with time in the SS removal rate at various set potentials. In FIG. 17, “x” is a plot of the average value of three experimental results under no-energization conditions, and the standard deviation is indicated by an error bar. ○ is a plot of the average of three experimental results under the condition of -0.8 V. For data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. □ is a plot of the average of three experimental results under the condition of −0.6 V. For the data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. Δ is + 0.0V, ◇ is -0.3V, and ◆ is + 0.3V.

  Regarding the conditions of +0.3 V, −0.6 V, and −0.8 V, the SS removal rate continued to increase without decreasing as the organic load increased. In particular, under the conditions of −0.6 V and −0.8 V, the SS removal rate continued to increase without decreasing even when the organic load was increased to 31.8 g / l / day.

(4) Relationship between set potential and lower fatty acid concentration FIG. 18 shows changes with time in lower fatty acid concentration at various set potentials. In FIG. 18, x is a plot of average values of three experimental results under the condition of no energization. ○ is a plot of the average of three experimental results under the condition of -0.8 V. For data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. □ is a plot of the average of three experimental results under the condition of −0.6 V. For the data before increasing the organic load to 31.8 g / l / day, the standard deviation is the error bar. It showed in. Δ is + 0.0V, ◇ is −0.3V, ◆ is + 0.3V, and ▲ is + 0.6V.

  Under the conditions of +0.3 V, -0.6 V, and -0.8 V, accumulation of lower fatty acids is hardly observed. In particular, for the conditions of -0.6 V and -0.8 V, the organic load is 31. Even when increased to 8 g / l / day, accumulation of lower fatty acids was hardly observed. From this result, in addition to the case where the set potential is set to +0.3 V and −0.6 V, also in the case of −0.8 V, it is possible to prevent the methane fermenter from being oxidized and to carry out the methane fermentation treatment over a long period of time. It became clear.

(5) Summary Based on the above results, the potential of the working electrode 109 is set to + 0.3V, -0.6V, and -0.8V based on the silver / silver chloride electrode potential standard as the reference electrode 111, thereby increasing the load. Under the conditions (organic load 26.9 g COD / l / day), a series of methane fermentation treatments were performed without reducing the gas production rate, COD removal rate, SS removal rate, and without accumulating lower fatty acids. It has become clear that the microbial reaction process can proceed. In particular, by setting the potential of the working electrode 109 to −0.6 V or −0.8 V based on the reference potential of the silver / silver chloride electrode serving as the reference electrode 111, an even higher load condition (organic load 31.8 g COD / 1 / day), it is possible to proceed with a series of microbial reaction processes of methane fermentation without reducing the gas generation rate, COD removal rate, SS removal rate, and without accumulating lower fatty acids. It became clear that there was.

  In addition, almost the same result was obtained when the set potential was set to -0.6V and -0.8V, and therefore the set potential was a value between -0.6V and -0.8V. It is estimated that almost the same result can be obtained even when set to. From this, by setting the set potential to +0.3 V or −0.6 V to −0.8 V, it is possible to proceed a series of microbial reaction processes of methane fermentation treatment even under high load conditions. I understood. And by making setting potential into -0.6V--0.8V, it becomes easy to acquire the improvement effect of SS removal rate, and the accumulation suppression effect of a lower fatty acid, and a series of microbial reaction processes of a methane fermentation process are advanced. It has been found suitable above. Further, since a reduction reaction occurs at the working electrode 109 at −0.6 V to −0.8 V, it was suggested that methane fermentation can be promoted by controlling the working electrode 109 to a potential at which the reduction reaction can occur. . However, if the potential of the working electrode 109 is excessively increased to the minus side, water electrolysis may occur and methane fermentation may be inhibited. Therefore, the potential B (unit: V) of the working electrode 109 is Y (electricity of water). It is preferable that the potential at which decomposition occurs) <B <X (the potential of the fermentation broth itself). Specifically, −1.4 <B <−0.5 is preferable.

[Reference Example 2]
Adhering carbon fiber nonwoven fabric (carbon fiber nonwoven fabric (type: pitch, porosity: about 98%, diameter: 30.0 mm, height: 70.0 mm, thickness: 2.4 mm) to one side of the carbon plate of the working electrode 109 The same experiment as in Reference Example 1 was performed, except that AQDS, which is a redox substance, was not added to the methane fermentation broth 4. Therefore, the methane fermentation broth was used. The controllability of the solution potential of No. 4 is inferior to that of Reference Example 1. In addition, the composition of the substrate is 100 g / L for dog food (Vita-one, manufactured by Nippon Pet Food), 0.8 g / L of rice straw. L, KH ₂ PO ₄ 1.135 g / l, K ₂ HPO ₄ 1.740 g / l, NiCl ₂ .6H ₂ O 0.403 mg / l, CoCl ₂ .6H ₂ O 0.484 mg / l.

  The operating conditions (temperature, pH, operating method) were the same as in Reference Example 1. The organic load and the hydraulic residence time were as shown in FIG.

  The set potential was set to -0.8V and -1.0V. For comparison, an experiment was also conducted for the case where no potential control was performed (control).

  FIG. 21 shows the change over time in the gas generation rate. As for the control, when the organic load was 27.8 g CODcr / L / day, the gas generation rate started to decrease, whereas at -0.8 V, the gas generation rate did not decrease even at this organic load. It was confirmed that methane fermentation was in progress. Moreover, when it was set to -1.0V, it was confirmed that a high gas production | generation rate is obtained even if an organic substance load is 32.7gCODcr / L / day.

  Next, the methane gas content is shown in FIG. As for the control, when the organic load was 27.8 g CODcr / L / day, the methane gas content was greatly reduced. On the other hand, at -0.8V and -1.0V, the methane gas content does not decrease even at this organic load, and at -1.0V, the organic load is 32.7 g CODcr / L / day. No decrease in content was observed.

  Next, FIG. 23 shows changes with time in the VFA (lower fatty acid) concentration. For the control, when the organic load was 27.8 g CODcr / L / day, a significant increase in VFA concentration was observed. On the other hand, at −0.8 V and −1.0 V, no significant increase in VFA concentration was observed even with this organic loading, and for −1.0 V, the organic loading was 32.7 g CODcr / L / day. It was also confirmed that the VFA concentration could be maintained at a low concentration.

  Next, the COD removal rate is shown in FIG. Regarding the control, the COD removal rate is small compared to the cases of −0.8 V and −1.0 V, and when the organic load is 27.8 g CODcr / L / day, the COD removal rate tends to be greatly reduced. It was seen. On the other hand, at -0.8 V and -1.0 V, no decrease in COD removal rate was observed even at this organic load, and for -1.0 V, the organic load was 32.7 g CODcr / L / day. No reduction in COD removal rate was observed.

  Next, the SS removal rate is shown in FIG. Regarding the control, the SS removal rate is small compared to the cases of −0.8 V and −1.0 V, and when the organic load is 27.8 g CODcr / L / day, the SS removal rate tends to decrease. It was. On the other hand, at -0.8 V and -1.0 V, the SS removal rate of 40% or more can be maintained even at this organic load, and for -1.0 V, the organic load is 32.7 g CODcr / L / Even on a day, an SS removal rate of 40% or more was maintained.

  As described above, by providing a hydrophobic carrier capable of supporting microorganisms on the electrode surface, an organic load amount as high as 27.8 g CODcr / L / day, and further 32.7 g CODcr without adding a redox substance to the methane fermentation solution. It was revealed that the methane fermentation treatment can be stably performed even at an extremely high organic load of / L / day. That is, in this reference example, even when the amount of organic load is equal to or higher than that of the reference example 1 in spite of the low controllability of the solution potential due to the absence of the redox substance. The methane fermentation process could be performed stably. Furthermore, it became clear that an organic substrate containing lignocellulosic biomass that is difficult to be decomposed, such as rice straw, can be efficiently decomposed.

  The above effect is that the microbial group adheres to the surface of the carrier in a large amount as a result of the potential around the carbon fiber provided on the surface of the working electrode being controlled to a potential very close to the set potential. This is considered to be obtained as a result of the electron being easily supplied to the group.

  Further, even when a hydrophobic carrier capable of supporting microorganisms is provided on the electrode surface, it is presumed that the same effect can be obtained by the potential at which an excellent effect is obtained in Reference Example 1.

[Example 4]
A two-stage process combining hydrogen fermentation and methane fermentation was studied.

<Experimental equipment>
A 250 mL glass vial manufactured by Duran was used as the reactor. 250 mL of sludge collected from the thermophilic anaerobic digestion tank (methane fermentation tank) in which stable gas generation from garbage was performed was placed in this glass bottle. Two carbon fiber nonwoven fabrics (type: pitch, porosity: about 98%, length: 70 mm, width: 30 mm, thickness: 2.4 mm) were placed in a glass bottle. The glass bottle contained a stir bar for operating the reactor while stirring. After putting all the contents in the glass bottle, the gas bottle was replaced with nitrogen gas, sealed with a lid, and an anaerobic environment in the glass bottle was secured. Then, a gas collecting tube was inserted into the silicone rubber provided on the upper surface of the lid, and a bag was provided at the outer end of the glass bottle of the gas collecting tube, and biogas generated from the inside of the glass bottle was collected in the bag. And the gas generation amount was measured by the water displacement method.

<Driving method>
The operation was performed while stirring at a temperature (fermentation liquid temperature) of 55 ° C. The reactor is operated by a fill-and-draw method, and a certain amount of the fermented liquid is discarded once a day, and the fermented liquid collected in the test 1 of Example 2 as a discarded portion once a day (in the working electrode tank). The test was carried out by adding half the amount of the fermentation broth and the mixture of the fermentation broth in the counter electrode tank. Therefore, in accordance with the organic load (OLR) of the second embodiment, the organic load (OLR) also increases stepwise in the present embodiment. During the test, it was operated while stirring the fermentation broth with a stir bar.

<Analysis method>
Same as Example 2. SS was the same as in Reference Example 1.

<Experimental result>
(1) Biogas production rate FIG. 34 shows changes with time in the biogas production rate during the test period. The biogas production rate tended to increase gradually over time, and this trend continued until the last day.

(2) Methane production rate Based on the measurement result of the methane content in the biogas, the result of obtaining the methane production rate with respect to the organic load (OLR) is shown in FIG. The methane production rate tended to gradually increase with an increase in organic load (OLR), and this trend continued to the end. The final methane production rate (organic load: 58680 mg / l / day) was 6493 mL / L / day.

(3) pH
FIG. 36 shows the change in pH of the fermentation broth during the test period. During the test period, the pH was maintained at 7-8.

(4) COD removal rate and SS removal rate The COD removal rate and SS removal rate during the test period are shown in FIGS. 37 and 38, respectively.

  From the results shown in FIG. 37, the COD removal rate gradually decreased with an increase in the organic load, and at an organic load of 58680 mg / l / day, the COD removal rate was 50%.

  Further, from the results shown in FIG. 38, the SS removal rate gradually decreased with an increase in the organic load, and at an organic load of 58680 mg / l / day, the SS removal rate was 43.1%.

In addition, in the two-stage process of the hydrogen fermentation process in Test Example 1 of Example 2 and the methane fermentation process in this example, the CODcr recovery rate including the CODcr remaining in the solution with respect to the charged CODcr was calculated (formula As a result, the CODcr recovery rate was 74.6% or more at an organic load of 19560 mg / l / day or more. From this, it was confirmed that the experimental method was valid as an evaluation method for the two-stage treatment of the hydrogen fermentation treatment in Test Example 1 of Example 2 and the methane fermentation treatment in this Example.
(CODcr recovery rate) = (CODcr of fermentation liquid + CODcr of biogas) / input CODcr × 100 (d)

(5) VFA concentration FIG. 39 shows the VFA concentration of the fermented liquid relative to the organic load (OLR). Corresponding to the increase in organic load, the VFA concentration also increased over time, but it was confirmed that methane fermentation proceeded well.

(6) Summary From the above results, the effluent from the hydrogen fermentation process using electricity is subjected to the methane fermentation process, so that the final organic load is 58680 mg / l / day, even under high load conditions. It was possible to make the production proceed well. From this, it was confirmed that the two-stage fermentation process can be carried out by subjecting the effluent of the hydrogen fermentation process using electricity to the methane fermentation process. Moreover, from this result, possibility that a two-stage fermentation process could be implemented more efficiently was shown by using the waste liquid of the hydrogen fermentation process using electricity for the methane fermentation process using electricity further.

4 Fermentation liquid 9 Electrode (working electrode)
DESCRIPTION OF SYMBOLS 10 Counter electrode 104 Methane fermentation liquid 106 Ion exchange membrane 109 Working electrode 110 Counter electrode 111 Reference electrode 112 Constant potential setting apparatus

Claims (9)

  Immerse the electrode in a fermentation broth containing a group of microorganisms that perform hydrogen fermentation, add an organic substrate to the fermentation broth, and control the potential of the electrode to preferentially activate the group of microorganisms that perform the hydrogen fermentation. A hydrogen fermentation treatment method.   The counter electrode which makes a pair with the electrode together with the electrode is immersed in the fermentation broth, and the potential A (unit: V) of the electrode is controlled to A ≦ −1.0 based on the silver / silver chloride electrode potential reference. The hydrogen fermentation treatment method as described in 2.   The hydrogen fermentation treatment method according to claim 1 or 2, wherein the fermentation broth is a methane fermentation broth.   The hydrogen fermentation treatment method according to any one of claims 1 to 3, wherein the pH of the fermentation broth is maintained at 5.5 to 8.   A two-stage fermentation treatment method, wherein the hydrogen fermentation treatment method according to any one of claims 1 to 4 is carried out, and then a methane fermentation treatment is performed using a fermentation product obtained by the hydrogen fermentation treatment method as a raw material. .   The said methane fermentation process is implemented by immersing an electrode in a methane fermentation liquid, controlling the electric potential of the said electrode, and activating the methanogenic bacteria group in the said methane fermentation liquid preferentially. The two-stage fermentation treatment method described. The electrode is immersed in the methane fermentation broth, and a counter electrode that forms a pair with the electrode is disposed by the following method (1) or (2), and the potential B of the electrode is B based on the silver / silver chloride electrode potential reference. = + 0.3 or B <X, wherein X is the oxidation-reduction potential of the methane fermentation broth itself.
(1) Immerse in an electrolyte solution in contact with the methane fermentation solution via an ion exchange membrane, and (2) Arrange it in contact with the methane fermentation solution via an ion exchange membrane   A step of immersing an electrode in a methane fermentation broth, introducing an organic substrate into the fermentation broth, and controlling the potential of the electrode to preferentially activate a group of microorganisms that perform the hydrogen fermentation, A method for producing a hydrogen fermentation broth.   In the step, a counter electrode paired with the electrode is immersed in the methane fermentation broth, and the potential A (unit: V) of the electrode is set to A ≦ −1.0 based on the silver / silver chloride electrode potential. The manufacturing method of the hydrogen fermentation liquid of Claim 8 implemented by controlling.