Biogas treatment equipment, biogas treatment methods, methane fermentation treatment systems

Abstract

The object of the present invention is to provide a biogas treatment facility and a biogas treatment method that enable the removal of carbon dioxide contained in biogas generated by methane fermentation in a simple and low-cost manner. [Solution] To solve the above problems, we provide a biogas treatment facility and a biogas treatment method that include a gas-liquid contact section for bringing biogas discharged from a methane fermentation facility into contact with an aqueous solution containing alkaline earth metal ions, wherein a carbonate precipitation reaction proceeds in the gas-liquid contact section. [Effect] According to this invention, for biogas generated by methane fermentation and having a relatively high carbon dioxide content, carbon dioxide can be removed (recovered and fixed) from the biogas by a carbonate precipitation reaction that proceeds without the supply of external energy. This makes it possible to remove carbon dioxide contained in biogas simply and at low cost.

Description

[Technical Field]

[0001] This invention relates to a biogas treatment facility, a biogas treatment method, and a methane fermentation treatment system. [Background technology]

[0002] One known method for treating organic waste (including wastewater and sewage) involves using sludge containing various microorganisms and performing biological treatment under anaerobic conditions (hereinafter referred to as "methane fermentation treatment"). This methane fermentation treatment offers several advantages, including the fact that it does not require aeration power and generates almost no excess sludge.

[0003] Furthermore, methane fermentation treatment using microorganisms that produce methane under anaerobic conditions (hereinafter referred to as "methanogenic bacteria") is widely used due to the high utility of the resulting biogas (methane).

[0004] For example, Patent Document 1 describes a pyrolysis treatment facility that reduces the volume of waste by indirect heating treatment, and uses biogas (digesting gas) obtained by the fermentation of organic substances (methane fermentation) as fuel for a gas engine power generation facility to reduce the total energy running costs. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-310419 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As described in Patent Document 1, biogas obtained by methane fermentation is expected to be used as a new energy source that can reduce the costs associated with facility operation. On the other hand, as also described in Patent Document 1, it is known that biogas contains carbon dioxide in addition to methane.

[0007] Carbon dioxide is considered to have a significant impact on environmental problems such as global warming, and reducing its emissions into the environment is an urgent issue that needs to be addressed. In response to this issue, research is progressing on technologies to reduce carbon dioxide emissions themselves, as well as technologies to capture and sequester emitted carbon dioxide.

[0008] In particular, various methods are being considered as technologies for the capture and sequestration of carbon dioxide. For example, methods for capturing carbon dioxide from carbon dioxide-containing gases include chemical absorption, which involves dissolving carbon dioxide in an absorbent solution such as monoethanolamine; physical adsorption, which involves adsorbing carbon dioxide onto an adsorbent with gas adsorption capacity; and membrane separation, which uses membranes. These methods require energy for capturing and sequestering the carbon dioxide-containing gas produced, which increases the cost of biogas utilization.

[0009] The object of the present invention is to provide a biogas treatment facility and a biogas treatment method that enable the removal of carbon dioxide contained in biogas generated by methane fermentation in a simple and low-cost manner. [Means for solving the problem]

[0010] As a result of diligent research into the above-mentioned problems, the inventors of the present invention have discovered that by contacting biogas generated by methane fermentation with an aqueous solution containing specific ions, and allowing a carbonate precipitation reaction related to carbon dioxide fixation to proceed, it is possible to remove carbon dioxide contained in biogas in a simple and low-cost manner, thereby completing the present invention. In other words, the present invention relates to the following biogas treatment equipment, biogas treatment method, and methane fermentation treatment system.

[0011] The biogas treatment equipment of the present invention, which solves the above problems, is characterized by comprising a gas-liquid contact section that brings biogas discharged from a methane fermentation facility into contact with an aqueous solution containing alkaline earth metal ions, and in which a carbonate precipitation reaction proceeds in the gas-liquid contact section. According to the biogas treatment equipment of the present invention, biogas generated by methane fermentation, which has a relatively high carbon dioxide content, can be treated by contacting it with an aqueous solution containing specific ions to promote a carbonate precipitation reaction related to carbon dioxide fixation, thereby removing carbon dioxide from the biogas as carbonate. Here, the carbonate fixation method, which converts carbon dioxide into carbonate through a chemical reaction (carbonate precipitation reaction), has the advantage that the reaction related to carbonate precipitation proceeds spontaneously, eliminating the need to supply energy from outside for carbon dioxide fixation, and the generated carbonate can be stored stably for a long period of time. In other words, the biogas treatment equipment of the present invention makes it possible to remove carbon dioxide contained in biogas simply and at low cost. This makes it possible to further enhance the usefulness of biogas discharged from methane fermentation equipment as fuel.

[0012] Furthermore, one embodiment of the biogas treatment equipment of the present invention is characterized in that the aqueous solution is wastewater containing calcium ions. This characteristic makes it possible to remove carbon dioxide contained in biogas at a lower cost by using wastewater as the aqueous solution for the carbonate precipitation reaction. Also, according to this feature, calcium carbonate can be obtained as a reaction product reacted with carbon dioxide. Calcium carbonate is a stable compound, easy to recover, and has a wide range of uses, such as being used as an additive (white filler, filler) for rubber, plastics, paints, building materials, etc. Therefore, in addition to enhancing the usefulness of biogas, it has the effect of obtaining a highly useful by-product (calcium carbonate).

[0013] Furthermore, as an embodiment of the biogas treatment facility of the present invention, the wastewater is characterized by containing 100 mg / L or more of calcium ions. It is known that wastewater containing a relatively large amount of calcium ions affects the selection of wastewater treatment methods and the operation of wastewater treatment facilities due to scale formation during the treatment process. According to this feature, in addition to removing carbon dioxide from biogas, calcium ions contained in wastewater with a large impact due to scale formation can be removed with high efficiency, and various subsequent wastewater treatments (especially aerobic treatment) can proceed smoothly.

[0014] The biogas treatment method of the present invention for solving the above problems includes a gas-liquid contact step of contacting an aqueous solution containing alkaline earth metal ions, and in the gas-liquid contact step, a carbonate precipitation reaction is allowed to proceed. According to the biogas treatment method of the present invention, for biogas generated by anaerobic digestion treatment and having a relatively high carbon dioxide content, it is contacted with an aqueous solution containing specific ions to allow a carbonate precipitation reaction related to carbon dioxide immobilization to proceed, so that carbon dioxide in the biogas can be removed as a carbonate, and the removal of carbon dioxide contained in the biogas can be performed simply and at low cost. As a result, the usefulness of the biogas discharged from the anaerobic digestion facility as a fuel can be further enhanced.

[0015] The methane fermentation treatment system of the present invention for solving the above problems is characterized by comprising the above-described biogas treatment facility and a methane fermentation facility. According to the methane fermentation treatment system of the present invention, it becomes possible to easily and at low cost remove carbon dioxide contained in biogas with a relatively high carbon dioxide content ratio generated in the treatment process, and together with the methane fermentation treatment for the object to be treated, it becomes possible to obtain biogas with even higher usefulness as fuel.

[0016] Also, as an embodiment of the methane fermentation treatment system of the present invention, it is characterized by further comprising a solid-liquid separation facility. According to this feature, it becomes possible to easily recover the carbonate deposited in the above-described biogas treatment facility, and together with the methane fermentation treatment for the object to be treated and the acquisition of highly useful biogas, it also becomes easy to effectively utilize the carbonate.

Effects of the Invention

[0017] According to the present invention, it is possible to provide a biogas treatment facility and a biogas treatment method that enable the removal of carbon dioxide contained in biogas generated by methane fermentation treatment easily and at low cost.

[0018] Also, according to the present invention, by applying the above-described biogas treatment facility to a methane fermentation treatment system that performs methane fermentation treatment on an object to be treated, it is possible to provide a methane fermentation treatment system that enables the removal of carbon dioxide contained in biogas generated by methane fermentation treatment easily and at low cost.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic explanatory diagram showing an example of the aspect of a biogas treatment facility and a methane fermentation treatment system according to the first embodiment of the present invention. [Figure 2]This is a schematic diagram illustrating an example of a biogas treatment facility and methane fermentation treatment system according to a second embodiment of the present invention. [Figure 3] This is a schematic diagram illustrating an example of a biogas treatment facility and methane fermentation treatment system according to a third embodiment of the present invention. [Figure 4] This is a schematic diagram illustrating an example of a biogas treatment facility and methane fermentation treatment system according to a fourth embodiment of the present invention. [Modes for carrying out the invention]

[0020] The present invention relates to a biogas treatment facility and biogas treatment method that removes carbon dioxide contained in biogas generated by methane fermentation treatment, which has a relatively high carbon dioxide content, based on a carbonate fixation method. Furthermore, the methane fermentation treatment system of the present invention is equipped with the biogas treatment facility described above, and in conjunction with methane fermentation treatment of the material to be treated, it is possible to obtain biogas with even greater usefulness as a fuel by removing carbon dioxide.

[0021] In this invention, "carbon dioxide" refers not only to gaseous carbon dioxide (CO2), but also to carbonate (H2CO3) and bicarbonate ions (HCO3) in aqueous solutions. - ), carbonate ions (CO3 2- This includes carbon dioxide. Hereafter, when referring specifically to carbon dioxide in its gaseous state, the term "carbon dioxide gas" will be used.

[0022] The embodiments of the biogas treatment equipment, biogas treatment method, and methane fermentation treatment system according to the present invention will be described in detail below. Furthermore, the description of the biogas treatment method according to the present invention will be replaced by the description of the operation of the biogas treatment equipment according to the present invention. The biogas treatment equipment and biogas treatment method described in the embodiments are merely illustrative examples used to illustrate the biogas treatment equipment, biogas treatment method, and methane fermentation treatment system according to the present invention, and are not limited thereto.

[0023] [First Embodiment] Figure 1 is a schematic diagram illustrating a biogas treatment facility and a methane fermentation treatment system in a first embodiment of the present invention. As shown in Figure 1, the methane fermentation treatment system 100A according to this embodiment comprises a biogas treatment facility 10 and a methane fermentation facility 20. Furthermore, as shown in Figure 1, the biogas treatment equipment 10 according to this embodiment includes a biogas introduction unit 11 for introducing biogas G from the methane fermentation equipment 20, and an aqueous solution (in this embodiment, alkaline earth metal ions (Ca)) connected to the biogas introduction unit 11, which mixes biogas G with alkaline earth metal ions. 2+ The system comprises a gas-liquid contact section 12 into which wastewater W) containing ) is introduced, and a biogas discharge section 13 that discharges the biogas G1 after the carbonate precipitation reaction in the gas-liquid contact section 12 has progressed to the outside of the system. In Figure 1, the white arrows indicate the movement of the solution, and the black arrows indicate the movement of the gas.

[0024] (Methane fermentation treatment system) The methane fermentation treatment system 100A of this embodiment is a methane fermentation facility 20 that receives a material to be treated (alkaline earth metal ions (Ca 2+ Organic wastewater OW1) that does not contain ) and an aqueous solution (alkaline earth metal ions (Ca) introduced into the biogas treatment facility 10 2+ This relates to the case where the wastewater W) containing ) is different. In other words, in the methane fermentation treatment system 100A of this embodiment, the methane fermentation equipment 20 and the biogas treatment equipment 10 each function as independent treatments. More specifically, as shown in Figure 1, the methane fermentation equipment 20 in the methane fermentation treatment system 100A of this embodiment receives alkaline earth metal ions (Ca) via line L1. 2+Organic wastewater OW1, which does not contain (etc.), is introduced and undergoes methane fermentation treatment in the methane fermentation facility 20 to produce biogas G containing methane gas and carbon dioxide, and treated water W1. The treated water W1, with reduced organic matter content, is discharged outside the system via line L2, and the biogas G is introduced into the biogas treatment facility 10. In the biogas treatment facility 10 of the methane fermentation treatment system 100A of this embodiment, a carbonate precipitation reaction is carried out to remove carbon dioxide from the biogas G as carbonate, and the biogas G1 with a low carbon dioxide content is discharged outside the system.

[0025] At this time, the methane fermentation equipment 20 includes alkaline earth metal ions (Ca 2+ Any system that can introduce organic wastewater OW1 (hereinafter also simply referred to as "organic wastewater OW1") that does not contain (such as) and perform methane fermentation treatment according to the properties of the organic wastewater OW1 (type of material to be treated, etc.) is acceptable. Specifically, the methane fermentation equipment 20 is equipped with a reaction tank 21 (also called a methane fermentation treatment tank or digester), and anaerobic microorganisms (acid-producing bacteria and methane-producing bacteria) present inside the reaction tank 21 decompose the components contained in the organic wastewater OW1 (methane fermentation treatment), generating biogas G containing methane gas and carbon dioxide (carbonic acid) as products. The reaction tank 21 may consist of a single tank (1 tank) or multiple tanks (for example, a two-tank methane fermentation treatment tank consisting of an acid-producing tank and a methane fermentation tank). In this case, it is preferable that the reaction tank 21 be a closed system and maintain an anaerobic environment.

[0026] In addition to the reaction tank 21 that carries out the methane fermentation process, the methane fermentation equipment 20 in this embodiment may be equipped with various other auxiliary facilities. For example, it may be equipped with means for adjusting the water temperature inside the reaction tank 21, means for adding pH adjusters, and means for adding metals such as nitrogen, phosphorus, cobalt, and nickel, which are nutrients required by microorganisms. Furthermore, the methane fermentation equipment 20 in this embodiment may be equipped with means for recovering and storing biogas G. In this case, the biogas introduction unit 11 in the biogas treatment equipment 10, which will be described later, is not connected to the reaction tank 21 of the methane fermentation equipment 20, but rather to ancillary equipment related to the means for recovering and storing biogas G.

[0027] The organic wastewater OW1 to be treated by the methane fermentation equipment 20 in the methane fermentation treatment system 100A of this embodiment is not particularly limited, but it is acceptable as long as it is treated water W1 that is discharged after undergoing methane fermentation treatment in the reaction tank 21, with a reduced content of the substances to be treated (organic matter). Specific examples of substances to be treated include wastewater containing organic matter. Here, wastewater containing organic matter refers to industrial wastewater discharged from various factories such as food processing plants, chemical plants, and pulp and paper mills, as well as domestic wastewater such as sewage. However, wastewater containing organic matter is not limited to these; any wastewater containing organic matter that can be biologically treated under anaerobic conditions is subject to treatment in the methane fermentation facility 20. Examples of such wastewater include organic wastewater containing livestock manure and sludge (excess sludge).

[0028] The biogas G emitted from the methane fermentation facility 20 mainly contains methane gas, with a methane content of approximately 60-80% by volume. It is known to also contain 20-40% by volume of carbon dioxide and trace amounts (less than 1% by volume) of hydrogen sulfide. Therefore, when seeking to effectively utilize the biogas G discharged from the methane fermentation facility 20, it is preferable to remove components other than methane gas that function as fuel, particularly carbon dioxide. In removing carbon dioxide, it is desirable that, considering environmental issues such as global warming, carbon dioxide be captured and sequestered rather than released into the atmosphere. Furthermore, it is desirable to reduce the energy required for carbon dioxide capture and sequestering, thereby lowering the costs associated with biogas utilization. Therefore, the methane fermentation treatment system 100A of this embodiment shall be equipped with a biogas treatment facility 10.

[0029] (Biogas treatment facility) The biogas treatment facility 10 in this embodiment removes carbon dioxide contained in biogas G (biogas with a relatively high carbon dioxide content) discharged from the methane fermentation facility 20 based on the carbonate fixation method. More specifically, the biogas treatment facility 10 of this embodiment is for carrying out a gas-liquid contact step in which biogas G discharged from the methane fermentation facility 20 is brought into contact with an aqueous solution containing alkaline earth metal ions. In this gas-liquid contact step, a carbonate precipitation reaction is carried out to remove carbon dioxide (recover and fixate carbon dioxide) based on the carbonate fixation method. The following describes the various components of the biogas treatment facility 10.

[0030] The biogas introduction section 11 is for introducing biogas G produced in the methane fermentation facility 20 to the gas-liquid contact section 12. Specifically, as shown in Figure 1, it consists of piping connecting the methane fermentation facility 20 (reaction tank 21) and the gas-liquid contact section 12. However, the biogas introduction section 11 is not limited to being directly connected to the methane fermentation facility 20. For example, if the biogas G discharged from the methane fermentation facility 20 is temporarily stored in another facility (such as a gas storage facility), the biogas introduction section 11 may be connected to this gas storage facility to introduce the biogas G to the gas-liquid contact section 12.

[0031] The gas-liquid contact section 12 is for bringing biogas G, introduced via the biogas introduction section 11, into contact with an aqueous solution containing alkaline earth metal ions, in order to carry out a carbonate precipitation reaction related to the fixation of carbon dioxide in the biogas G. As the gas-liquid contact part 12, any structure can be used as long as it can bring the carbon dioxide in the biogas G into contact with an aqueous solution containing alkaline earth metal ions that react with carbon dioxide to form carbonates, thereby precipitating carbonates. The specific means and apparatus structure related to the gas-liquid contact part 12 are not particularly limited.

[0032] In this embodiment, the gas-liquid contact part 12 is composed of, for example, a reaction tank 12a capable of storing the aqueous solution containing alkaline earth metal ions supplied through the line L3. Biogas G is introduced into the reaction tank 12a through the biogas introduction part 11, and gas-liquid contact occurs inside the reaction tank 12a. As a result, carbon dioxide (carbonate ions (CO3 2- )) in the biogas G reacts with alkaline earth metal ions (calcium ions (Ca 2+ )) in this embodiment, and the formation (precipitation) of carbonates proceeds. Thus, the carbon dioxide contained in the biogas G is removed from the biogas G as carbonates (calcium carbonate, denoted as "CaCO3" in FIG. 1).

[0033] At this time, the aqueous solution containing alkaline earth metal ions introduced through the line L3 may be any aqueous solution in which alkaline earth metal ions capable of reacting with carbon dioxide (carbonate ions (CO3 2- )) exist (the carbonate precipitation reaction can proceed), and its origin is not particularly limited. For example, it is also possible to use an aqueous solution containing alkaline earth metal ions in nature, such as seawater or river water. However, from the perspective of the reaction efficiency of the carbonate precipitation reaction, it is preferable to use an aqueous solution in which alkaline earth metal ions are artificially (as a result of human activities) contained, such as drainage / wastewater from factories or leachate from landfill sites, and the content rate of alkaline earth metal ions tends to be high. In particular, by using drainage (wastewater) as the aqueous solution containing alkaline earth metal ions, it becomes possible to remove the carbon dioxide contained in the biogas G at a lower cost.

[0034] Furthermore, suitable examples of alkaline earth metal ions contained in this aqueous solution include calcium ions and barium ions, with calcium ions being a particularly suitable example. This results in the acquisition of calcium carbonate as a reaction product when it reacts with carbon dioxide. Calcium carbonate is a stable compound that is easy to recover and has a wide range of applications, such as being used as an additive (white filler) for rubber, plastics, paints, and building materials. Therefore, in addition to enhancing the usefulness of biogas, it also provides the effect of obtaining a highly useful by-product (calcium carbonate).

[0035] Furthermore, the amount of alkaline earth metal ions contained in this aqueous solution is preferably such that the carbonate precipitation reaction upon contact with carbon dioxide in biogas G can proceed sufficiently. Specifically, it is preferable that it contains 100 mg / L or more of calcium ions. It is known that wastewater containing relatively high levels of calcium ions can lead to scale formation during the treatment process, which can affect the selection of wastewater treatment methods and the operation of wastewater treatment facilities. On the other hand, the aqueous solution introduced to the biogas treatment equipment 10 of this embodiment via line L3 is calcium ion (Ca 2+ By using wastewater W containing ), in addition to removing carbon dioxide from biogas G, calcium ions can be removed with high efficiency from calcium ion-containing wastewater W, which is greatly affected by scale formation, thus enabling smoother subsequent wastewater treatment. In this embodiment, the aqueous solution containing alkaline earth metal ions introduced via line L3 is defined as calcium ions (Ca 2+ This explanation will focus on, but is not limited to, the use of wastewater W containing ) (hereinafter also simply referred to as "wastewater W").

[0036] Here, specific means and structures for promoting the carbonate precipitation reaction in the gas-liquid contact section 12 include, for example, providing a blower and a diffuser (not shown) as a biogas introduction section 11 and dispersing biogas G into the wastewater W contained in the reaction tank 12a, or performing countercurrent contact by introducing biogas G from the lower part of the reaction tank 12a while introducing wastewater W from the upper part of the reaction tank 12a. In this case, biogas G may be introduced as fine bubbles (fine bubbles, microbubbles, etc.) into the wastewater W contained in the reaction vessel 12a to form an extremely small gas-liquid interface reaction field and promote the carbonate precipitation reaction. Alternatively, a structure may be provided in the reaction vessel 12a to improve the countercurrent contact efficiency between biogas G and wastewater W. Furthermore, means to promote the carbonate precipitation reaction in the gas-liquid contact section 12 may be provided separately. Means to promote the carbonate precipitation reaction include, for example, providing means to concentrate the aqueous solution (wastewater W) in the reaction vessel 12a, or adjusting the pH in the reaction vessel 12a.

[0037] The reaction that proceeds in the gas-liquid contact section 12 is based on a carbonate fixation method (carbonate precipitation reaction) that converts carbon dioxide into carbonate through a chemical reaction. Since the reaction related to carbonate precipitation proceeds spontaneously, there is no need to supply energy from an external source for carbon dioxide fixation, and the generated carbonate has the advantage of being able to be stored stably for a long period of time.

[0038] The biogas G introduced into the gas-liquid contact section 12 is then discharged out of the system via the biogas discharge section 13 as biogas G1, from which carbon dioxide has been removed. Here, biogas G1 consists mainly of methane gas, which increases its usefulness as a fuel. On the other hand, alkaline earth metal ions (Ca) are found in the wastewater W. 2+ ) will be removed, and alkaline earth metal ions (Ca 2+The treated water W2, with a reduced content of ), is discharged outside the system via line L4. At this time, the treated water W2 contains carbonate (calcium carbonate) produced by the carbonate precipitation reaction in the gas-liquid contact section 12. Therefore, the carbonate (calcium carbonate) is also discharged outside the system via line L4. Here, the treated water W2 may be used for separate wastewater treatment, or it may be discharged as is. Furthermore, since the scale formation of the treated water W2 is suppressed compared to wastewater W, it is possible to carry out smooth treatment when it is used for various treatments (especially aerobic treatment).

[0039] As described above, the biogas treatment facility 10 in this embodiment treats biogas G, which is discharged from the methane fermentation facility 20 and has a relatively high carbon dioxide content, with an aqueous solution containing alkaline earth metal ions, particularly alkaline earth metal ions (Ca 2+ This method removes carbon dioxide from biogas as carbonate by bringing it into contact with wastewater containing carbon dioxide and allowing the carbonate precipitation reaction related to carbon dioxide fixation to proceed. Furthermore, the carbonate precipitation reaction that takes place within the biogas treatment facility 10 is a reaction that proceeds spontaneously, and therefore does not require the supply of external energy for carbon dioxide fixation. In other words, it is possible to remove carbon dioxide contained in biogas G simply and at low cost. In addition, the carbonate produced by the carbonate precipitation reaction can be stored stably for a long period of time and can be used for various purposes, thus having the advantage of high utility.

[0040] Furthermore, in the methane fermentation treatment system 100A of this embodiment, by providing the biogas treatment equipment 10 described above, it becomes possible to remove carbon dioxide contained in biogas that has a relatively high carbon dioxide content generated during the treatment process in a simple and low-cost manner. Combined with the methane fermentation treatment of the material to be treated (organic wastewater OW1), it becomes possible to obtain biogas with even greater usefulness as fuel. Furthermore, in the methane fermentation treatment system 100A of this embodiment, the biogas treatment equipment 10 and the methane fermentation equipment 20 perform processing independently, which has the advantage that factors that could inhibit the methane fermentation treatment reaction (such as oxygen) are less likely to be introduced into the methane fermentation equipment 20.

[0041] [Second Embodiment] Figure 2 is a schematic diagram illustrating a biogas treatment facility in a second embodiment of the present invention. The methane fermentation treatment system 100B according to this embodiment differs from the methane fermentation treatment system 100A in the first embodiment described above in the arrangement (connection route) of the biogas treatment equipment 10 and the methane fermentation equipment 20. More specifically, the biogas treatment equipment 10 and the methane fermentation equipment 20 are connected in series. Note that, of the components of the methane fermentation treatment system 100B in this embodiment that are the same as those of the methane fermentation treatment system 100A in the first embodiment, the explanation will be omitted. In particular, the structure of the biogas treatment equipment 10 and the methane fermentation equipment 20, as well as the treatment content and treatment means carried out in the biogas treatment equipment 10 and the methane fermentation equipment 20, will be treated as the same as those described above for the methane fermentation treatment system 100A.

[0042] In this embodiment, the methane fermentation treatment system 100B is configured such that the material to be treated introduced into the methane fermentation equipment 20 and the aqueous solution introduced into the biogas treatment equipment 10 are the same (alkaline earth metal ions (Ca 2+ This relates to organic wastewater OW2) containing (etc.). In other words, the methane fermentation treatment system 100B of this embodiment functions as a system in which the biogas treatment equipment 10 and the methane fermentation equipment 20 perform treatment in succession. More specifically, as shown in Figure 2, in the methane fermentation treatment system 100B of this embodiment, a biogas treatment facility 10 is located upstream of the methane fermentation equipment 20, and the biogas treatment facility 10 and the methane fermentation equipment 20 are connected via line L6. Furthermore, alkaline earth metal ions (Ca) are supplied to the biogas treatment facility 10 via line L5. 2+ Organic wastewater OW2 containing (etc.) will be introduced. Here, alkaline earth metal ions (Ca 2+ Organic wastewater OW2 containing (etc.) is defined as the above-mentioned organic wastewater OW1 with alkaline earth metal ions (Ca 2+ It differs in that it contains (etc.), and as for the other components, it is sufficient that they are discharged as treated water W1 after undergoing methane fermentation treatment in the reaction tank 21, similar to organic wastewater OW1, and alkaline earth metal ions (Ca 2+ Examples include industrial and domestic wastewater containing organic matter (such as [specific examples of organic matter]).

[0043] Furthermore, in the biogas treatment facility 10, alkaline earth metal ions (Ca) in organic wastewater OW2 are removed. 2+ While the amount of unreacted organic matter (CO2) decreases through reaction with carbon dioxide (carbonate ions) in biogas G, the treatment of organic matter does not proceed. Therefore, the organic wastewater OW2 that has passed through the biogas treatment facility 10, along with the unreacted organic matter, is introduced into the methane fermentation facility 20 via line L6 as a solution (solution S1) further containing carbonate (calcium carbonate). Then, through methane fermentation treatment in the methane fermentation facility 20, biogas G containing methane gas and carbon dioxide and treated water W3 are produced. At this time, the treated water W3, with reduced levels of organic matter and alkaline earth metal ions, is discharged from the system via line L7. In addition, the treated water W3 contains carbonate (calcium carbonate). Therefore, the carbonate (calcium carbonate) is also discharged from the system via line L7. The treated water W3 discharged from the system via line L7 may be further subjected to various wastewater treatments (especially aerobic treatment). Meanwhile, biogas G is introduced into the biogas treatment facility 10. In the biogas treatment facility 10 of the methane fermentation treatment system 100B of this embodiment, a carbonate precipitation reaction is carried out between alkaline earth metal ions in organic wastewater OW2 and carbon dioxide (carbonate ions) in biogas G. This removes carbon dioxide from biogas G as carbonate, and the resulting biogas G1 with a reduced carbon dioxide content is discharged outside the system.

[0044] As described above, in the methane fermentation treatment system 100B of this embodiment, by connecting the biogas treatment equipment 10 and the methane fermentation equipment 20 in series, it becomes possible to perform methane fermentation treatment and biogas treatment in an integrated and coordinated manner on an aqueous solution (organic wastewater OW2) containing organic matter and alkaline earth metal ions. Furthermore, similar to the methane fermentation treatment system 100A described above, the methane fermentation treatment system 100B in this embodiment makes it possible to remove carbon dioxide contained in biogas, which has a relatively high carbon dioxide content generated during the treatment process, in a simple and low-cost manner. Combined with methane fermentation treatment of the materials to be treated contained in organic wastewater OW2, it becomes possible to obtain biogas with even greater usefulness as fuel.

[0045] [Third Embodiment] Figure 3 is a schematic diagram illustrating a biogas treatment facility in a third embodiment of the present invention. The methane fermentation treatment system 100C according to this embodiment further includes a solid-liquid separation facility 30 compared to the methane fermentation treatment system 100A in the first embodiment described above. More specifically, as shown in Figure 3, the solid-liquid separation facility 30 is provided downstream of the biogas treatment facility 10. Note that the configuration of the methane fermentation treatment system 100C in this embodiment that is the same as the configuration of the methane fermentation treatment system 100A in the first embodiment will not be described.

[0046] The solid-liquid separation equipment 30 of this embodiment contains carbonates produced by the carbonate precipitation reaction in the biogas treatment equipment 10, and alkaline earth metal ions (Ca 2+ The treated water W2, in which the content of ) has decreased, is introduced via line L8 and subjected to a separation treatment that separates it into liquid and solid components. While there are no particular limitations on the specific means or structure of the solid-liquid separation equipment 30, a sedimentation separation system is a preferred example from the viewpoint of using less energy (lower power consumption).

[0047] In the solid-liquid separation equipment 30 of this embodiment, the introduced treated water W2 is separated into a liquid component (treated water W2) and a solid component, which is sludge W3. The liquid component (treated water W2) separated in the solid-liquid separation equipment 30 is then discharged outside the system via line L9. Meanwhile, the sludge W3 is discharged outside the system via line L10. At this time, the sludge W3 contains carbonate (calcium carbonate), and the carbonate (calcium carbonate) is also discharged outside the system via line L10. It is preferable to recover the carbonate (calcium carbonate) discharged outside the system and use it for other purposes.

[0048] Furthermore, the treated water W2 introduced from the biogas treatment facility 10 via line L8 may contain some biogas G1 in addition to carbonates. Therefore, as shown in Figure 3, the solid-liquid separation equipment 30 of this embodiment is preferably equipped with a recovery means (line L11) for recovering biogas G1 contained in the treated water W2 introduced from the biogas treatment equipment 10, and by connecting this recovery means (line L11) to the biogas discharge section 13, it is preferable to ensure the reliable recovery of biogas G1 with a reduced carbon dioxide content. In this case, in order to suppress the diffusion of biogas G1 into the atmosphere, it is preferable that the solid-liquid separation equipment 30 be constructed in a way that can form a sealed state.

[0049] As described above, the methane fermentation treatment system 100C of this embodiment can easily recover carbonates precipitated (generated) in the biogas treatment equipment 10, and together with methane fermentation treatment of the material to be treated in organic wastewater OW1 and the acquisition of highly useful biogas G1, it facilitates the effective utilization of carbonates.

[0050] [Fourth Embodiment] Figure 4 is a schematic diagram illustrating a biogas treatment facility in a fourth embodiment of the present invention. The methane fermentation treatment system 100D according to this embodiment is further equipped with a solid-liquid separation facility 30 compared to the methane fermentation treatment system 100B in the second embodiment described above. More specifically, the solid-liquid separation facility 30 is placed between the biogas treatment facility 10 and the methane fermentation facility 20. Note that the configuration of the methane fermentation treatment system 100D in this embodiment that is the same as the configuration of the methane fermentation treatment system 100B in the second embodiment will not be described.

[0051] The solid-liquid separation equipment 30 provided in the methane fermentation treatment system 100D of this embodiment separates alkaline earth metal ions (Ca) through the carbonate precipitation reaction in the biogas treatment equipment 10. 2+ While the content of ) has decreased, solution S1 containing carbonate (calcium carbonate) produced by the carbonate precipitation reaction and unreacted organic matter is introduced via line L12 for separation treatment to separate it into liquid and solid components.

[0052] The solid-liquid separation equipment 30 provided in the methane fermentation treatment system 100D can use the same configuration (structure and treatment means) as the methane fermentation treatment system 100C described above. In the solid-liquid separation equipment 30 of this embodiment, the introduced solution S1 is separated into a liquid component, solution S2, and a solid component, sludge W5.

[0053] The sludge W5 separated in the solid-liquid separation equipment 30 is discharged outside the system via line L14. At this time, the sludge W5 contains carbonate (calcium carbonate), and the carbonate (calcium carbonate) is also discharged outside the system via line L14. It is preferable to recover the carbonate (calcium carbonate) discharged outside the system and use it for other purposes, similar to the methane fermentation treatment system 100C described above.

[0054] The liquid component (solution S2 containing organic matter) separated in the solid-liquid separation equipment 30 is introduced into the methane fermentation equipment 20 via line L13. Through methane fermentation treatment in the methane fermentation equipment 20, biogas G containing methane gas and carbon dioxide, and treated water W4 with reduced levels of organic matter and alkaline earth metal ions are produced. The treated water W4 is discharged outside the system via line L7, and the biogas G is introduced into the biogas treatment equipment 10.

[0055] Furthermore, in the methane fermentation treatment system 100D of this embodiment, it is preferable to provide a recovery means (line L15) for recovering biogas G1 contained in the solution S1 introduced from the biogas treatment equipment 10, similar to the methane fermentation treatment system 100C described above, and connect it to the biogas discharge section 13, thereby ensuring reliable recovery of biogas G1 with a reduced carbon dioxide content.

[0056] As described above, the methane fermentation treatment system 100D of this embodiment can easily recover the carbonate precipitated (generated) in the biogas treatment equipment 10, and together with methane fermentation treatment of the material to be treated in organic wastewater OW2 and the acquisition of highly useful biogas G1, it facilitates the effective utilization of carbonate.

[0057] The embodiments described above are merely examples of biogas treatment equipment, biogas treatment methods, and methane fermentation treatment systems. The biogas treatment equipment, biogas treatment methods, and methane fermentation treatment systems according to the present invention are not limited to the embodiments described above, and the biogas treatment equipment, biogas treatment methods, and methane fermentation treatment systems according to the embodiments described above may be modified without changing the gist of the claims. [Industrial applicability]

[0058] The biogas treatment equipment and biogas treatment method of the present invention can produce biogas with low environmental impact and high usefulness as fuel. In particular, it is suitable for use with biogas generated by methane fermentation and having a relatively high carbon dioxide content, as it enables the removal of carbon dioxide contained in the biogas in a simple and low-cost manner. Furthermore, the methane fermentation treatment system of the present invention is suitably used as a methane fermentation treatment system that, in conjunction with methane fermentation treatment of the material to be treated, can obtain biogas with even greater usefulness as a fuel by removing carbon dioxide. [Explanation of Symbols]

[0059] 100A, 100B, 100C, 100D Methane fermentation treatment system, 10 Biogas treatment equipment, 11 Biogas introduction section, 12 Gas-liquid contact section, 12a Reaction tank, 13 Biogas discharge section, 20 Methane fermentation equipment, 21 Reaction tank, 30 Solid-liquid separation equipment, L1~L15 Line, G Biogas containing methane gas and carbon dioxide, G1 Biogas with reduced carbon dioxide content, OW1 Organic wastewater without alkaline earth metal ions, OW2 Organic wastewater containing alkaline earth metal ions, S1 Solution containing organic matter and carbonate, S2 Solution containing organic matter, W Wastewater containing alkaline earth metal ions, W1 Treated water with reduced organic matter content, W2 Treated water with reduced alkaline earth metal ion content, W3 Sludge containing carbonate, W4 Treated water with reduced organic matter and alkaline earth metal ion content, W5 Sludge containing carbonate

Claims

1. It includes a gas-liquid contact section that brings biogas discharged from a methane fermentation facility into contact with an aqueous solution containing alkaline earth metal ions, A biogas treatment facility characterized in that a carbonate precipitation reaction proceeds in the gas-liquid contact area.

2. The biogas treatment apparatus according to claim 1, characterized in that the aqueous solution is wastewater containing calcium ions.

3. The biogas treatment facility according to claim 2, characterized in that the wastewater contains 100 mg / L or more of calcium ions.

4. The system includes a gas-liquid contact step in which biogas discharged from a methane fermentation facility is brought into contact with an aqueous solution containing alkaline earth metal ions. A biogas treatment method characterized by allowing a carbonate precipitation reaction to proceed in the aforementioned gas-liquid contact step.

5. The biogas treatment equipment according to claim 1, A methane fermentation treatment system characterized by comprising a methane fermentation facility.

6. The methane fermentation treatment system according to claim 5, further comprising a solid-liquid separation facility.

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