Methane fermentation treatment system and methane fermentation treatment method

Abstract

To provide a methane fermentation treatment system and a methane fermentation treatment method in which an activity of hydrogen-producing bacteria is increased in a methane fermentation process and a product gas produced by the hydrogen-producing bacteria is added to the methane fermentation tank.SOLUTION: To solve the above problem, in a methane fermentation treatment system, a product gas generated in a hydrogen fermentation tank is supplied to a methane fermentation tank. This has the effect of efficiently generating methane with hydrogen and carbon dioxide, since the product gas containing hydrogen generated in the hydrogen fermentation tank is supplied to the methane fermentation tank.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation treatment system and a methane fermentation treatment method that perform anaerobic treatment. [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] For example, Patent Document 1 describes a method of producing methane by separating hydrogen from the product gas produced in an acid production tank preceding a methane fermentation tank and introducing the separated hydrogen into the methane fermentation tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-157994 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, organic acids are produced in an acid production tank upstream of a methane fermentation tank to facilitate methane fermentation, and the product gas generated during the acid production process is used. The product gas generated in the acid production tank contains hydrogen, but if organic acid production is prioritized, the activity of the hydrogen fermentation bacteria that produce hydrogen decreases, so the product gas generated in the acid production tank has a low hydrogen content, which creates the problem that it cannot be efficiently added to the methane fermentation tank unless the hydrogen is separated before being added.

[0006] Therefore, an object of the present invention is to provide a methane fermentation treatment system and a methane fermentation treatment method that increase the activity of hydrogen-producing bacteria in methane fermentation treatment and generate methane by adding the product gas produced by the hydrogen-producing bacteria to a methane fermentation tank. [Means for solving the problem]

[0007] As a result of extensive research into the above-mentioned problems, the present inventors discovered that by supplying the product gas produced in a hydrogen fermenter to a methane fermenter, methane fermentation can be carried out using the hydrogen and carbon dioxide produced in the hydrogen fermenter, and thus completed the present invention.

[0008] The methane fermentation treatment system of the present invention, which solves the above problems, is characterized in that product gas produced in a hydrogen fermenter is supplied to a methane fermenter. According to the methane fermentation treatment system of the present invention, the product gas containing hydrogen produced in the hydrogen fermentation tank is supplied to the methane fermentation tank, which has the effect of enabling efficient methane production from hydrogen and carbon dioxide.

[0009] Furthermore, one embodiment of the methane fermentation treatment system of the present invention is characterized in that the produced gas is directly supplied to the methane fermentation tank. According to this methane fermentation treatment system, the produced gas can be directly supplied to the methane fermentation tank, which eliminates the need for a separation device and provides the advantage of being a simplified methane fermentation treatment system.

[0010] Furthermore, one embodiment of the methane fermentation treatment system of the present invention is characterized in that the pH of the hydrogen fermenter is 5.5 or less. According to this methane fermentation treatment system, the pH of the hydrogen fermenter is kept at 5.5 or less, which increases the activity of the hydrogen-producing bacteria and enables efficient hydrogen production.

[0011] Furthermore, one embodiment of the methane fermentation treatment system of the present invention is characterized by including a pressurizing unit that pressurizes the produced gas. According to this methane fermentation treatment system, the produced gas is compressed and supplied to the water to be treated, which has the effect of efficiently dissolving the produced gas in the water to be treated.

[0012] The method for treating methane fermentation according to the present invention for solving the above problems is characterized in that product gas produced in a hydrogen fermenter is supplied to a methane fermenter. According to the methane fermentation treatment method of the present invention, hydrogen, which is the product gas produced in the hydrogen fermenter, is supplied to the methane fermenter, which has the effect of enabling efficient methane production from hydrogen and carbon dioxide. [Effects of the Invention]

[0013] According to the present invention, a methane fermentation treatment system and a methane fermentation treatment method can be provided in which methane is produced by increasing the activity of hydrogen-producing bacteria and adding the product gas produced by the hydrogen-producing bacteria to a methane fermentation tank in a methane fermentation treatment. [Brief explanation of the drawings]

[0014] [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. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] Anaerobic treatment includes methane fermentation using methanogens that produce methane from organic acids, as well as hydrogen-utilizing methanogens that produce methane from hydrogen and carbon dioxide. During normal methane fermentation, carbon dioxide is produced along with methane. Therefore, by adding hydrogen from an external source, it is possible to consume carbon dioxide and produce methane from hydrogen and carbon dioxide (a process called biomethanation). In the present invention, attention is focused on this reaction, and biomethanation can be promoted.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a methane fermentation treatment system and a methane fermentation treatment method 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. The methane fermentation treatment method of this embodiment is replaced by the following description of the configuration and operation of the methane fermentation treatment system.

[0018] [First embodiment] FIG. 1 is a schematic diagram illustrating a methane fermentation treatment system 1A according to a first embodiment of the present invention.

[0019] [Methane fermentation treatment system] A methane fermentation treatment system 1A according to this embodiment will be described with reference to Figure 1. The methane fermentation treatment system 1A of the present invention includes a hydrogen fermenter 2 that supplies hydrogen to water to be treated W1, which undergoes methane fermentation, and a methane fermenter 3 that performs methane fermentation treatment on the water to be treated W1.

[0020] [Hydrogen fermenter] The hydrogen fermentation tank 2 produces hydrogen from the water to be treated W0 to be used for methane fermentation in the methane fermentation tank 3, and the product gas G1 produced by hydrogen fermentation of the water to be treated W0 is sent to the methane fermentation tank 3. The hydrogen fermenter 2 is not particularly limited as long as it has the function and structure to perform hydrogen fermentation treatment using hydrogen-producing bacteria within the tank and to supply hydrogen-containing product gas G1 to the water to be treated W1. The hydrogen-containing product gas G1 may be supplied to the water to be treated W1 on line L1 before being supplied to the methane fermenter 3, or may be supplied to the liquid inside the methane fermenter 3. In this embodiment, the case where the product gas G1 is added to the water to be treated W1 on line L1 through line L2 is exemplified.

[0021] Furthermore, the hydrogen fermenter 2 preferably undergoes anaerobic treatment, and the pH is adjusted to activate the hydrogen fermentation bacteria so as to promote hydrogen production by the hydrogen fermentation bacteria. Specifically, the pH of the hydrogen fermenter 2 is preferably adjusted and maintained in the range of 5.5 to 5.0. This pH range can suppress fermentation by anaerobic bacteria other than the hydrogen fermentation bacteria, allowing the product gas G1 generated in the hydrogen fermenter 2 to be hydrogen gas with a high hydrogen content. By producing hydrogen gas with a high hydrogen content, there is no need to separate the product gas G1 generated in the hydrogen fermenter 2, and it can be added directly to the water to be treated W1. This is also advantageous in that a separation device for separating hydrogen from the product gas G1 is not required, thereby simplifying the methane fermentation treatment system 1A. Note that the product gas G1 also contains carbon dioxide in addition to hydrogen.

[0022] [Methane fermentation tank] The methane fermentation tank 3 is not particularly limited as long as it is capable of performing anaerobic treatment and methane fermentation by methanogens. The methane fermentation tank 3 is not particularly limited as long as it can store the water to be treated W2 supplied with hydrogen produced in the hydrogen fermentation tank 2 and can produce methane from the supplied hydrogen and carbon dioxide. Note that carbon dioxide includes both that contained in the product gas G1 and that produced in the methane fermentation tank 3. The methane fermenter 3 may also simultaneously produce organic acids by acid-producing bacteria, which are the source of methane production.

[0023] [Other configurations] Other components of the methane fermentation treatment system 1A include lines L0, L1, L2, L3, and L4. Line L0 is a pipe for supplying the water to be treated W0 to the hydrogen fermentation tank 2. L1 is a pipe for sending the water to be treated W1 after hydrogen fermentation tank 2, in which the water to be treated W0 has been treated in the hydrogen fermentation tank 2, to the methane fermentation tank 3. Line L2 is a pipe for supplying the produced gas G1 from the hydrogen fermentation tank 2 to the water to be treated W1. Line L3 is a pipe for sending the methane gas G2 produced in the methane fermentation tank 3 to the outside. Line L4 is a pipe for sending the treated water W2 treated in the methane fermentation tank 3 to a subsequent process.

[0024] [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.

[0025] First, the water to be treated W0 passes through line L0 and is supplied to the hydrogen fermenter 2. This process is referred to as the supply step.

[0026] The hydrogen-producing bacteria produce product gas G1 from the water to be treated W0 supplied to the hydrogen fermenter 2. This process is referred to as the hydrogen production step.

[0027] The product gas G1 passes through line L2 and is supplied to the water to be treated W1 sent from the hydrogen fermenter 2 to a subsequent process. This process is defined as a step in which the product gas G1 produced in the hydrogen fermenter 2 is supplied to the methane fermenter 3. The water to be treated W1 is supplied to a methane fermentation tank 3 through a line L1.

[0028] Next, methane fermentation is carried out in the methane fermenter 3. This process is referred to as the methane fermentation step. Methane gas G2 is produced from the supplied hydrogen and carbon dioxide through methane fermentation. The produced methane gas G2 is discharged to the outside through line L3. The water to be treated W1 is also treated, and the treated water W2 is sent to the subsequent process through line L4. The above steps complete the operation of the methane fermentation treatment system 1A of the present invention.

[0029] [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 pressurizing unit 4, which pressurizes the product gas G1 produced in the hydrogen fermentation tank 2 and supplies it to the water to be treated W1, thereby supplying the water to be treated W3 containing the product gas G1 to the methane fermentation tank 3.

[0030] [Pressure section] The pressurizing unit 4 is not particularly limited as long as it can pressurize the product gas G1 produced in the hydrogen fermenter 2 and supply it to the water to be treated W1 as compressed gas. The pressurizing section 4 compresses the product gas G1 and supplies it to the water to be treated W1, which acts as a microvalve inside the methane fermentation tank 3, making it easier to dissolve hydrogen, which is poorly soluble in water, and has the effect of enabling the product gas G1 to be efficiently supplied to the methane fermentation bacteria. In addition, in this embodiment, an example is given in which the pressurizing unit 4 supplies the product gas G1 to the water to be treated W1 on line L1 to produce water to be treated W3, which is then supplied to the methane fermentation tank 3 through line L5, but the product gas G1 compressed by the pressurizing unit 4 may also be supplied to the methane fermentation tank 3. In the case of an upward flow type in which the water to be treated passes from the bottom to the top of the methane fermentation tank 3, by supplying the product gas G1 from the bottom of the methane fermentation tank 3, the carbon dioxide contained in the product gas G1 can be supplied from the bottom of the methane fermentation tank 3, which has the effect of enabling methane fermentation to be carried out efficiently.

[0031] [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.

[0032] Similar to the methane fermentation treatment system 1A, a supply step, a hydrogen production step, and a hydrogen generation step are performed.

[0033] The generated product gas G1 passes through line L2 and is supplied to the water to be treated W1 sent from the hydrogen fermenter 2 to a subsequent process. At this time, the product gas G1 is supplied to the pressurizing section 4, and the product gas G1 is supplied to the water to be treated W1. This process is referred to as the pressurized supply step.

[0034] Thereafter, the water to be treated W3 is supplied to the methane fermentation tank 3 through the line L5, and the product gas G1 produced in the hydrogen fermentation tank 2 is supplied to the methane fermentation tank 3.

[0035] Thereafter, a methane fermentation step is carried out, and methane gas G2 is discharged to the outside through line L3. In addition, treated water W2 is sent to the subsequent process through line L4. The above steps complete the operation of the methane fermentation treatment system 1B of the present invention.

[0036] [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 an acid production tank 5, produces water to be treated W4 containing organic acids from water to be treated W1, and supplies the water to be treated W4 to the methane fermentation tank 3.

[0037] [Acid generation tank 5] The acid production tank 5 performs anaerobic treatment using acid-producing bacteria on the treated water W1 that has been treated in the hydrogen fermentation tank 2, and is not particularly limited as long as it can produce treated water W4 to be used in the methane fermentation tank 3 from the treated water W1. The acid production tank 5 is supplied with the water to be treated W1 from the line L1, and the pH of the pH-adjusted water to be treated W1 is preferably adjusted so as to promote fermentation by the acid-producing bacteria. Specifically, the pH of the liquid in the acid production tank 5 is preferably adjusted and maintained in the range of 6.0 to 8.0, which is higher than the pH of the hydrogen fermenter 2. If the pH is within this range, fermentation by the hydrogen fermentation bacteria can be suppressed, and acid production can be carried out efficiently in the acid production tank 5. The pH of the acid production tank 5 may be adjusted by supplying treated water W5 from the methane fermentation tank 3 through a line L7. Furthermore, although the example has been given in which the product gas G1 is supplied to the water to be treated W4 on the line L6 via the line L2, it may also be supplied to the line L1 or to the methane fermentation tank 3.

[0038] [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.

[0039] Similar to the methane fermentation treatment system 1A, a supply step, a hydrogen production step, and a hydrogen generation step are performed.

[0040] The generated product gas G1 passes through line L2 and is supplied to the water to be treated W4 sent from the hydrogen fermenter 2 to a subsequent process. This process is defined as a step in which the product gas G1 generated in the hydrogen fermenter 2 is supplied to the methane fermenter 3. The water to be treated W1 is supplied to the acid generation tank 5 through a line L1.

[0041] Acid production is performed by acid-producing bacteria in the water to be treated W4 supplied to the acid production tank 5. This process is referred to as the acid production step. The water to be treated W4 treated by the acid-producing bacteria is supplied to the methane fermentation tank 3 through a line L6.

[0042] Thereafter, a methane fermentation step is carried out, and the treated water W5 from the methane fermentation tank 3 is returned to the acid production tank 5 through a line L7. This process is referred to as a return step. Then, methane gas G2 is discharged to the outside through line L3, and treated water W2 is sent to the subsequent process through line L4. The above steps complete the operation of the methane fermentation treatment system 1C of the present invention.

[0043] In this embodiment, the acid production tank 5 is provided in the methane fermentation treatment system 1A, but the acid production tank 5 may be provided in the methane fermentation treatment system 1B. [Industrial Applicability]

[0044] The methane fermentation treatment system and methane fermentation treatment method of the present invention are used for water to be treated that can be treated anaerobically, such as wastewater containing organic waste generated from sewage treatment plants and food factories, and slurries that can be treated with methane fermentation. [Explanation of symbols]

[0045] 1A, 1B, 1C Methane fermentation treatment system 2 Hydrogen fermenter 3. Methane fermentation tank 4 Pressurizing section 5 Acid generation tank

Claims

1. A pressurizing unit is provided to pressurize the product gas produced in the hydrogen fermenter, A methane fermentation treatment system, characterized in that the gas pressurized by the pressurizing unit is supplied to a methane fermentation tank.

2. 2. The methane fermentation treatment system according to claim 1, wherein the gas is directly supplied to a methane fermentation tank.

3. 3. The methane fermentation treatment system according to claim 1, wherein the pH of the hydrogen fermenter is 5.5 or less.

4. An acid production tank for anaerobic treatment of the water to be treated in the hydrogen fermentation tank using acid-producing bacteria, 2. The methane fermentation treatment system according to claim 1, wherein the treated water anaerobically treated in the acid production tank is supplied to a methane fermentation tank.

5. pressurizing the product gas produced in the hydrogen fermenter; and a step of supplying the gas pressurized in the step to a methane fermentation tank.

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