Methane fermentation treatment system, methane fermentation treatment method, and method of using conductive material

Abstract

To provide a methane fermentation treatment system, a methane fermentation treatment method, and a method for using conductive substances to suppress a reaction inhibition of methane fermentation due to an increase in hydrogen concentration in methane fermentation treatment.SOLUTION: To solve the above problem, a methane fermentation treatment system includes a methane fermentation tank and a hydrogen supply part that supplies hydrogen to the methane fermentation tank, and the methane fermentation tank contains conductive substances. According to the present invention, hydrogen is supplied to the methane fermentation tank containing conductive substances, and the conductive substances promote a reaction called DIET (Direct Interspecies Electron Transfer), in which electrons are directly exchanged without hydrogen, which has the effect of suppressing an inhibition of the methane fermentation reaction due to an increase in hydrogen concentration.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation treatment system that performs anaerobic treatment, a methane fermentation treatment method, and a method for using a conductive material. [Background technology]

[0002] One known method for treating wastewater and other water to be treated is biological treatment in an anaerobic environment using sludge containing various microorganisms (hereinafter referred to as "anaerobic treatment"). Anaerobic treatment has many advantages, such as not requiring aeration power and producing almost no excess sludge. Furthermore, it is expected that by using microorganisms to generate methane from carbon dioxide and hydrogen, the carbon dioxide can be consumed, contributing to decarbonization.

[0003] Normally, in methane fermentation reactions, methane is produced along with carbon dioxide as organic acids are decomposed. It is known that a reaction called biomethanation, in which methane is produced from hydrogen and carbon dioxide, occurs in anaerobic digesters, and attempts have been made to produce more methane by adding hydrogen to the anaerobic digester. For example, Patent Document 1 describes the production of methane by supplying hydrogen generated by electrolysis and carbon dioxide emitted and recovered from various industrial fields to a methanation reactor using methanogens. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-33284 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as in Patent Document 1, if hydrogen is simply added to the anaerobic treatment tank in an amount that is too large, the oxidation of propionic acid, butyric acid, etc. becomes difficult to proceed, organic acids tend to accumulate, the overall activity of methane fermentation decreases, and the reaction is inhibited.

[0006] Therefore, an object of the present invention is to provide a methane fermentation treatment system, a methane fermentation treatment method, and a method for using a conductive material that suppress reaction inhibition of methane fermentation due to an increase in hydrogen concentration in methane fermentation treatment. [Means for solving the problem]

[0007] As a result of intensive research into the above-mentioned problems, the inventors discovered that by supplying hydrogen to a methane fermentation tank containing a conductive material, it is possible to suppress the inhibition of the methane fermentation reaction caused by an increase in hydrogen concentration, and thus completed the present invention.

[0008] To solve the above problems, the methane fermentation treatment system of the present invention comprises a methane fermentation tank and a hydrogen supply unit that supplies hydrogen to the methane fermentation tank, and is characterized in that the methane fermentation tank contains a conductive material. According to the methane fermentation treatment system of the present invention, hydrogen is supplied to a methane fermentation tank containing a conductive material, and the conductive material promotes a reaction called DIET (Direct Interspecies Electron Transfer), which directly transfers electrons without using hydrogen, thereby having the effect of suppressing the inhibition of the methane fermentation reaction due to an increase in hydrogen concentration.

[0009] Furthermore, in one embodiment of the methane fermentation treatment system of the present invention, the conductive material is in granular form. In this methane fermentation treatment system, the conductive material is granular, so it acts as a carrier for the methanogens to settle in. This makes it easier to maintain the methanogens in a stable state, and the conductive material and methanogens can be kept in contact with each other, which has the effect of further promoting diet.

[0010] Furthermore, one embodiment of the methane fermentation treatment system of the present invention is characterized in that hydrogen is supplied in a state where it is adsorbed onto a conductive material. According to this methane fermentation treatment system, hydrogen is adsorbed onto the conductive material and then supplied, which has the effect of efficiently supplying hydrogen to the solution in the methane fermentation tank.

[0011] Furthermore, one embodiment of the methane fermentation treatment system of the present invention is characterized by including a recovery section that recovers conductive materials. According to this methane fermentation treatment system, the conductive material can be recovered by the recovery unit, and therefore the beneficial bacteria adhering to the conductive material can be recovered, which has the effect of helping to maintain the microbial reaction.

[0012] The methane fermentation treatment method of the present invention for solving the above problems is characterized by comprising a step of supplying hydrogen to a methane fermentation tank containing a conductive material. According to the methane fermentation treatment method of the present invention, hydrogen is supplied to a methane fermentation tank containing a conductive material, and the conductive material promotes a reaction known as DIET, which directly exchanges electrons without using hydrogen, thereby suppressing the inhibition of the methane fermentation reaction due to an increase in hydrogen concentration.

[0013] The method for using the conductive material of the present invention to solve the above problems is characterized in that the conductive material is introduced into a methane fermentation tank to which hydrogen is supplied, and promotes the reaction of producing methane from hydrogen and carbon dioxide. According to the method of using the conductive material of the present invention, the conductive material in the methane fermentation tank promotes a reaction called DIET, which directly transfers electrons without using hydrogen, thereby having the effect of suppressing the inhibition of the methane fermentation reaction caused by an increase in hydrogen concentration. [Effects of the Invention]

[0014] According to the present invention, by supplying hydrogen to a methane fermentation tank containing a conductive material, it is possible to suppress the inhibition of the methane fermentation reaction caused by an increase in hydrogen concentration. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic explanatory diagram showing a methane fermentation treatment system according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a schematic explanatory diagram showing a methane fermentation treatment system according to a second embodiment of the present invention. [Figure 3] FIG. 4 is a schematic cross-sectional view showing a methane fermentation treatment system according to a third embodiment of the present invention. [Figure 4] Fig. 1A is a diagram showing the energy state during methane fermentation treatment according to the first embodiment of the present invention, and Fig. 1B is a diagram showing the energy state during conventional methane fermentation. DETAILED DESCRIPTION OF THE INVENTION

[0016] The water to be treated W0 of the present invention corresponds to wastewater containing organic waste, slurry, etc., generated from sewage treatment plants, food factories, etc. However, the water to be treated W0 is not limited to these, and any water containing organic matter that can be anaerobically treated can be treated by the present invention.

[0017] Anaerobic treatment includes methane fermentation by methanogens that produce methane from organic acids, as well as hydrogen-utilizing methanogens that carry out a methane production reaction from hydrogen and carbon dioxide. The present invention produces methane from hydrogen and carbon dioxide, consuming carbon dioxide and promoting methane production (biomethanation).

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a methane fermentation treatment system, a methane fermentation treatment method, and a method for using a conductive material according to the present invention will be described in detail with reference to the drawings. The methane fermentation treatment system described in the embodiment is merely an example for explaining the methane fermentation treatment system according to the present invention, and is not limited thereto. Furthermore, the methane fermentation treatment method and the method of using the conductive material according to the embodiment are replaced by the following description of the configuration and operation of the methane fermentation treatment system.

[0019] [First embodiment] FIG. 1 shows a schematic explanatory diagram of a methane fermentation treatment system according to a first embodiment of the present invention.

[0020] [Methane fermentation treatment system] A methane fermentation treatment system 1A in this embodiment will be described with reference to Figure 1. The methane fermentation treatment system 1A includes a hydrogen supply unit 2 that supplies hydrogen to water to be treated W0, and a methane fermentation tank 3 that performs methane fermentation treatment on the water to be treated W0.

[0021] [Hydrogen supply unit] The hydrogen supply unit 2 supplies hydrogen to the water to be treated W0, which is used for fermentation by hydrogen-assimilating methanogens in the methane fermenter 3. The hydrogen supply unit 2 is not particularly limited as long as it has a function and structure capable of supplying hydrogen to the water to be treated W0. Furthermore, hydrogen may be added to the water to be treated W0 on the line L0 before it is supplied to the methane fermentation tank 3, or hydrogen may be supplied to the liquid inside the methane fermentation tank 3. In this embodiment, the case where hydrogen is added on the line L0 is exemplified. Furthermore, the hydrogen supplied to the water to be treated W0 by the hydrogen supply unit 2 may be any type of hydrogen, including hydrogen generated by a microbial reaction, hydrogen produced by electrolyzing water, or factory exhaust containing hydrogen.

[0022] [Methane fermentation tank] The methane fermentation tank 3 is capable of performing anaerobic treatment, and methane fermentation by methanogens is carried out in the methane fermentation tank 3. There are no particular limitations on the methane fermentation tank 3, as long as it can store water to be treated W2 containing a conductive material 4 therein and can produce methane from hydrogen supplied by the hydrogen supply unit 2 and carbon dioxide.

[0023] The conductive substance 4 in the water to be treated W2 containing the conductive substance 4 is shown as being contained in the water to be treated W0 in advance, but it may also be added at any time before the hydrogen supply unit 2, between the hydrogen supply unit 2 and the line L0 of the methane fermentation tank 3, or when the conductive substance 4 is added in the methane fermentation tank 3.

[0024] <Conductive material> The conductive substance 4 is added for the purpose of promoting a phenomenon called DIET (Direct Interspecies Electron Transfer), in which microorganisms directly exchange electrons with each other without using hydrogen to promote methane fermentation. DIET has the effect of promoting the methane production reaction from organic acids, a reaction known as a symbiotic reaction, during the methane fermentation reaction process. The principle is that when microorganisms attach to the conductive material 4, electron transfer between microorganisms can proceed with a small energy gap, which is thought to promote the methane fermentation reaction. Conventionally, as shown in Figure 4(B), when hydrogen is supplied to carry out a methane fermentation reaction without containing a conductive substance, the hydrogen concentration increases, making it difficult for the oxidation reaction of organic matter to occur, and methane fermentation does not proceed. Therefore, in the present invention, as shown in Fig. 4(A), the addition of a conductive material 4 promotes the methane fermentation reaction without the use of hydrogen. Therefore, even if hydrogen is added to the water to be treated W2 in the methane fermentation tank and the hydrogen partial pressure increases, oxidation of organic matter occurs and methane fermentation occurs, thereby suppressing reaction inhibition caused by an increase in hydrogen partial pressure.

[0025] As the conductive material 4, a magnetic material or a porous material can be used, and specific examples include activated carbon, coal coke, graphite, magnetite, iron sulfide minerals, reduced iron, manganese ferrite, nickel ferrite, and cobalt ferrite. Furthermore, there are no particular limitations on the shape and size of the conductive material 4. Examples of the shape of the conductive material 4 include powder, granules, plates, sponges, etc. In consideration of the contact efficiency with anaerobic bacteria (such as methanogens), powder or granules, which have a large surface area, are preferred.

[0026] When the conductive material 4 is in powder form, this is preferable in terms of increasing the dispersion efficiency in the water to be treated W2 and improving the contact efficiency with anaerobic bacteria (such as methanogens).

[0027] Furthermore, when the conductive material 4 is granular, it can be used as a carrier, and methanogens can be fixed on the surface of the conductive material 4, making it easier to maintain the methanogens in a stable state. Furthermore, the conductive material 4 and the methanogens can be maintained in contact with each other, which further promotes diet. Activated carbon is preferably used as the granular conductive material 4, as it is porous and easily available.

[0028] Furthermore, when the granular conductive material 4 is used as a carrier, either a fluidized bed or a fixed bed may be used. A fluidized bed provides good contact efficiency with the water to be treated W2, while a fixed bed is less likely to flow out to a subsequent process together with the treated water W1, making it easier to maintain methanogens inside the methane fermentation tank 3, which is preferable. For the above reasons, in the case of methane fermentation treatment involving solid matter (slurry), it is preferable that the conductive material 4 is in powder or granular form, and in the case of methane fermentation treatment involving wastewater containing organic waste, it is preferable that the conductive material 4 is in granular form.

[0029] [Other configurations] As another configuration, the methane fermentation treatment system 1A has lines L0, L1, L2, and L3. Line L0 is a pipe for supplying water to be treated W0 to the methane fermentation tank 3. Line L1 is a pipe for supplying hydrogen gas G1 from the hydrogen supply unit 2. L2 is a pipe for sending treated water W1, which is water to be treated W2 treated in the methane fermentation tank 3, to a subsequent process. L3 is a pipe for sending methane gas G2 produced in the methane fermentation tank 3 to the outside.

[0030] [About the operation of the methane fermentation treatment system] The process flow and operation of the methane fermentation treatment system 1A will be described with reference to FIG.

[0031] First, the water to be treated W0 passes through a line L0 and is supplied to a methane fermentation tank 3. The water to be treated W0 is water to be treated that contains a conductive substance 4. The hydrogen supply unit 2 supplies hydrogen gas G1 via line L1 to the water to be treated W0 flowing inside line L0, thereby supplying hydrogen to the water to be treated W2 in the methane fermentation tank 3. This process is referred to as the step of supplying hydrogen to the methane fermentation tank containing the conductive material.

[0032] Next, water to be treated W2 containing a conductive material and hydrogen is supplied to a methane fermentation tank 3, where methane fermentation takes place. A methane fermentation reaction involving DIET occurs inside the methane fermentation tank 3, resulting in methane fermentation by organic acids and methane fermentation by hydrogen and carbon dioxide, producing methane gas, which is discharged to the outside through line L3. The water to be treated W2 is treated and passes through line L2, where it is sent as treated water W1 to the subsequent process. This process is referred to as the methane fermentation step. The above steps complete the operation of the methane fermentation treatment system 1A of the present invention.

[0033] [Second embodiment] A methane fermentation treatment system 1B according to a second embodiment of the present invention will be described with reference to Figure 2. The methane fermentation treatment system 1B of this embodiment differs from the methane fermentation treatment system 1A in that it includes a conductive material supply unit 5, and hydrogen from the hydrogen supply unit 2 is adsorbed onto the conductive material 4 before being supplied to the methane fermentation tank 3.

[0034] [Conductive material supply section] The conductive material supply unit 5 is not particularly limited as long as it has the function and structure to supply the conductive material 4 to the methane fermentation tank 3. In this embodiment, the conductive material supply unit 5 is installed on the line L0 and supplies the conductive material 4 to the water to be treated W0, but the conductive material supply unit 5 may also be connected to the methane fermentation tank 3 and supply the conductive material 4.

[0035] The conductive material supply unit 5 supplies the conductive material 4 onto which hydrogen supplied from the hydrogen supply unit 2 has been adsorbed to the water to be treated W0, and the water to be treated W0 passes through line L0 and is sent to the methane fermentation tank 3, thereby becoming water to be treated W2. If hydrogen gas is added directly to the water to be treated W0 or W2, there is a risk that incomplete dissolution of hydrogen gas will occur. Therefore, by adding the conductive material 4 with hydrogen adsorbed to it to the water to be treated W0 or W2, hydrogen can be efficiently supplied into the solution in the methane fermentation tank. In this embodiment, the conductive material 4 is preferably activated carbon because it adsorbs hydrogen.

[0036] [About the operation of the methane fermentation treatment system] The process flow and operation of the methane fermentation treatment system 1B will be described with reference to FIG.

[0037] First, hydrogen gas G1 supplied from the hydrogen supply unit 2 through the line L1 is adsorbed by the conductive material 4. This step is referred to as a hydrogen adsorption step.

[0038] Next, the water to be treated W0 passes through line L0 and is supplied to the methane fermentation tank 3. The water to be treated W0 may or may not contain a conductive substance 4. At this time, the conductive substance supply unit 5 supplies the conductive substance 4 to which hydrogen has been adsorbed through line L4 to the water to be treated W0 flowing inside line L0. This operation causes the hydrogen supply unit 2 to supply hydrogen to the water to be treated W0 via the conductive substance 4, thereby supplying hydrogen to the water to be treated W2 in the methane fermentation tank 3. This process is referred to as the step of supplying hydrogen to the methane fermentation tank containing a conductive substance.

[0039] Next, the methane fermentation step of the methane fermentation treatment system 1A is carried out, and the operation of the methane fermentation treatment system 1B of the present invention is completed. [Third embodiment] A methane fermentation treatment system 1C according to a third embodiment of the present invention will be described with reference to Figure 3. The methane fermentation treatment system 1C of this embodiment differs from the methane fermentation treatment system 1A in that it includes a conductive material recovery unit 6 that recovers conductive materials 4 contained in treated water W1 treated in the methane fermentation tank 3 and returns the recovered conductive materials 4 to the methane fermentation tank 3.

[0040] [Conductive Material Recovery Department] The conductive material recovery unit 6 is not particularly limited as long as it has the function and structure to separate and recover the conductive material 4 contained in the treated water W1 treated in the methane fermentation tank 3 and return it to the methane fermentation tank 3. Note that, although the present embodiment illustrates a case in which the recovered conductive material 4 is returned to the methane fermentation tank 3 through line L6, line L6 may also be connected to line L0.

[0041] The conductive material recovery section 6 may be any method or device that separates and recovers the conductive material 4, and specifically, sedimentation separation is an example. When a magnetic material such as magnetite, iron sulfide mineral, reduced iron, manganese ferrite, nickel ferrite, or cobalt ferrite is used as the conductive material, a magnetic separation device can be used. The recovered conductive material 4 is returned to the methane fermentation tank 3 via line L6, which prevents the methanogens attached to the conductive material from escaping, allowing for more stable methane fermentation.

[0042] [About the operation of the methane fermentation treatment system] The process flow and operation of the methane fermentation treatment system 1C will be described with reference to FIG.

[0043] First, a hydrogen supply step and a methane fermentation step are performed in the methane fermentation treatment system 1A.

[0044] Next, the treated water W1 treated in the methane fermentation tank 3 is sent to the conductive material recovery unit 6 through line L2. The conductive material recovery unit 6 then separates the conductive material 4. This process is referred to as the separation step.

[0045] Next, the separated and recovered conductive material 4 is returned through line L6 to the methane fermentation tank 3. This process is referred to as a return step. The methanogens attached to the conductive material 4 are returned to the inside of the methane fermentation tank 3, thereby enabling stable methane fermentation to be carried out continuously. Furthermore, treated water W4 from which the conductive material 4 has been separated by the conductive material recovery section 6 is sent to the subsequent process via line L5.

[0046] In this embodiment, the case where the conductive material recovery unit 6 is provided in the methane fermentation treatment system 1A has been exemplified, but the conductive material recovery unit 6 may also be provided in the methane fermentation treatment system 1B. [Industrial Applicability]

[0047] The methane fermentation treatment system, methane fermentation treatment method, and method of using the conductive material of the present invention are used for water to be treated that can be anaerobically treated, such as wastewater containing organic waste generated from sewage treatment plants, food factories, etc., and slurry that can be methane fermented. [Explanation of symbols]

[0048] 1A, 1B, 1C Methane fermentation treatment system 2 Hydrogen supply unit 3. Methane fermentation tank 4 Conductive materials 5 Conductive material supply section 6. Conductive material recovery section

Claims

1. A methane fermentation tank supplied with a conductive material; a hydrogen supply unit that supplies hydrogen to the methane fermentation tank, A methane fermentation treatment system, wherein the conductive material is in the form of powder, granules, plates or sponge.

2. 2. The methane fermentation treatment system according to claim 1, wherein the conductive material promotes DIET (Direct Interspecies Electron Transfer) to suppress inhibition of methane fermentation due to an increase in hydrogen concentration.

3. A methane fermentation treatment system as described in claim 1 or 2, characterized in that it is provided with a conductive material supply unit that supplies the conductive material to the methane fermentation tank.

4. A methane fermentation treatment system described in any one of claims 1 to 3, characterized in that the conductive material is activated carbon.

5. The methane fermentation treatment system according to any one of claims 1 to 4, further comprising a recovery unit that recovers the conductive material.

6. A method for producing methane fermentation using a methane fermenter, comprising: supplying hydrogen to the methane fermenter to which the conductive material has been supplied; A method for treating methane fermentation, characterized in that the conductive substance is in the form of powder, granules, plates or sponge.

7. A powdery, granular, plate-like, or spongy conductive material, A method for using a conductive material, characterized in that the conductive material is introduced into a methane fermentation tank to which hydrogen is supplied, to promote a reaction for producing methane from hydrogen and carbon dioxide.

Images