JP2023103646A - Microalgae culture method and microalgae culture apparatus - Google Patents

Abstract

To provide a microalgae culture method and a microalgae culture apparatus capable of removing dissolved oxygen from a culture solution while efficiently stirring the culture solution.SOLUTION: The microalgae culture method and culture apparatus 1 uses exhaust gas. The microalgae culture method comprises a separation and supply step of separating useful components from exhaust gas and supplying the useful components to a culture solution S, and a stirring step of stirring the culture solution S by using the exhaust gas from which the useful components have been separated as power for stirring the culture solution S. The microalgae culture apparatus 1 includes a culture tank 10 containing a culture solution S, a separation and supply means 20 for separating useful components from exhaust gas and supplying the useful components to the culture solution S, and a stirring means 30 for stirring the culture solution S by using the exhaust gas from which the useful components have been separated as power for stirring the culture solution S.SELECTED DRAWING: Figure 1

Description

The present invention relates to a microalgae culture method and a microalgae culture apparatus.

Coal-fired power plants and the like use fossil fuels, so exhaust gases containing carbon dioxide are emitted. Since greenhouse gases such as carbon dioxide cause global warming, effective utilization of exhaust gas is desired.
In recent years, biofuels produced using photosynthetic microorganisms such as microalgae as raw materials have attracted attention as energy sources that can replace fossil fuels. In addition, some microalgae contain many nutrients, and such microalgae are also used in foods, cosmetics, and the like.
Against this background, it is expected that greenhouse gas emissions will be reduced by using waste gas for culturing microalgae.
When exhaust gas is used for culturing microalgae, it is necessary to separate and recover carbon dioxide from the exhaust gas.

As a method of supplying carbon dioxide to a culture solution using a separation membrane, for example, in Patent Document 1, carbon dioxide generated by mammals is supplied to the separation membrane with a pump for sending, and the carbon dioxide that permeates the separation membrane is cultured. A method for culturing microalgae by supplying a liquid is disclosed.

JP-A-2000-228974

However, in the method described in Patent Document 1, carbon dioxide generated by mammals is supplied to the culture solution, and cultivation of microalgae using exhaust gas has not been studied.
In addition, in the method described in Patent Document 1, the culture solution is stirred while supplying carbon dioxide to the culture solution at the pressure of the blowing pump that supplies carbon dioxide to the separation membrane, and the stirring is not necessarily sufficient. . If the pressure of the air blowing pump is increased, the efficiency of stirring is increased, but energy consumption is increased, which is inefficient.
Furthermore, when carbon dioxide is supplied through a separation membrane, it is difficult for oxygen generated by photosynthesis of microalgae to escape from the culture solution, and dissolved oxygen may inhibit culture.

An object of the present invention is to provide a microalgae culture method and a microalgae culture apparatus capable of removing dissolved oxygen from a culture solution while efficiently stirring the culture solution.

The present invention has the following aspects.
[1] A method for culturing microalgae using exhaust gas,
a separating and supplying step of separating useful components from the exhaust gas and supplying the useful components to the culture solution;
A method for culturing microalgae, comprising a stirring step of stirring the culture solution by using exhaust gas from which the useful components have been separated as stirring power for the culture solution.
[2] The method for culturing microalgae according to [1] above, wherein the useful components are separated from the exhaust gas without separating harmful components from the exhaust gas, and the useful components are supplied to the culture solution.
[3] The method for culturing microalgae according to [2] above, wherein the harmful component is either one or both of dust and heavy metals.
[4] The method for culturing microalgae according to any one of [1] to [3], wherein the useful components are separated from the exhaust gas using a non-porous membrane, and the useful components are supplied to the culture solution.
[5] The method for culturing microalgae according to [4], wherein the non-porous membrane is a polymer membrane.
[6] The microalgae according to any one of [1] to [5], wherein the exhaust gas is exhaust gas emitted from one or more selected from coal-fired power plants, waste incineration plants, cement plants and steelworks. culture method.
[7] The method for culturing microalgae according to any one of [1] to [6], wherein the microalgae are one or more selected from Euglena, Pseudocolycystis and Spirulina.
[8] The method for culturing microalgae according to any one of [1] to [7], wherein the microalgae are cultured in a closed system.
[9] The method for culturing microalgae according to any one of [1] to [8], wherein the agitation step is performed by an aeration method.
[10] The method for culturing microalgae according to any one of [1] to [9] above, wherein the adjusted gas is mixed with the exhaust gas from which the useful components have been separated.
[11] The method for culturing microalgae according to any one of [1] to [10], wherein the stirring step is performed intermittently.

[12] An algae culture apparatus using exhaust gas,
a culture tank containing a culture solution;
Separating and supplying means for separating useful components from the exhaust gas and supplying the useful components to the culture solution;
An apparatus for culturing microalgae, comprising: stirring means for stirring the culture solution by using exhaust gas from which the useful components have been separated as stirring power for the culture solution.
[13] The apparatus for culturing microalgae according to [12], wherein the useful components are separated from the exhaust gas without separating harmful components from the exhaust gas, and the useful components are supplied to the culture solution.
[14] The microalgae culture apparatus of [13], wherein the harmful component is either one or both of dust and heavy metals.
[15] The microalgae culture apparatus according to any one of [12] to [14], wherein the useful components are separated from the exhaust gas using a non-porous membrane, and the useful components are supplied to the culture solution.
[16] The apparatus for culturing microalgae according to [15], wherein the non-porous membrane is a polymer membrane.
[17] The microalgae according to any one of [12] to [16] above, wherein the exhaust gas is exhaust gas emitted from one or more selected from a coal-fired power plant, a waste incineration plant, a cement factory, and a steel mill. culture equipment.
[18] The microalgae culture apparatus according to any one of [12] to [17], wherein the microalgae are one or more selected from Euglena, Pseudocolycystis and Spirulina.
[19] The apparatus for culturing microalgae according to any one of [12] to [18], wherein the culture tank is a photobioreactor type water tank.
[20] The microalgae culture apparatus according to any one of [12] to [19], wherein the stirring means is aeration means.
[21] The apparatus for cultivating microalgae according to any one of [12] to [20], further comprising mixing means for mixing a regulated gas with the exhaust gas after separating the useful components.
[22] The stirring means comprises intermittent supply means for storing the exhaust gas after the separation of the useful components in a storage tank and intermittently supplying the exhaust gas stored in the storage tank to the culture tank. The microalgae culture apparatus according to any one of [12] to [21].

Advantageous Effects of Invention According to the present invention, it is possible to provide a microalgae culture method and a microalgae culture apparatus capable of removing dissolved oxygen from a culture solution while efficiently stirring the culture solution.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic configuration diagram schematically showing an example of a microalgae culture apparatus according to the first aspect of the present invention; FIG. 2 is a schematic configuration diagram schematically showing another example of the microalgae culture apparatus of the first aspect of the present invention. FIG. 2 is a schematic configuration diagram schematically showing an example of a microalgae culture apparatus according to the second aspect of the present invention.

Hereinafter, one embodiment of the microalgae culture method and the microalgae culture apparatus according to the present invention will be described in detail with reference to FIGS. 1 to 3 as appropriate.
In addition, in each drawing used in the following explanation, in order to make the features easier to understand, the characteristic parts may be enlarged for convenience, and the dimensional ratio of each component may differ from the actual one. There is Also, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be implemented with appropriate modifications within the scope of the invention.
In addition, in FIGS. 2 and 3, the same components as in FIG. 1 are denoted by the same reference numerals, and descriptions thereof are omitted.

In the present invention, microalgae refer to single-celled organisms having a synthetic function and having a body length (longer axis of cells) of 100 μm or less.
Microalgae to be cultured in the present invention are not particularly limited, but for example, cyanobacteria, prokaryotic green algae, red algae, gray algae, cryptophytes, dinoflagellates, golden algae, diatoms, brown algae, yellow green algae, and haptoalgae. . Among these, Euglena, Pseudocolycystis, which is a type of green algae, and Spirulina, which is a type of blue-green algae, are preferable from the viewpoint of containing many nutrients and being suitable for use in foods, cosmetics, and the like.

The method for culturing microalgae and the apparatus for cultivating microalgae of the present invention utilize exhaust gas to culture microalgae, and can reduce the emission of greenhouse gases.
Exhaust gases used for culturing microalgae include exhaust gases emitted from facilities that use fossil fuels, such as coal-fired power plants, garbage incinerators, cement plants, and steel mills.
_The exhaust gas contains carbon dioxide (CO ₂ ), oxygen (O ₂ ), nitrogen (N ₂ ), nitrogen oxides (NOx) such as nitrogen dioxide (NO ₂ ), sulfur oxides ( SOx), etc. In addition to these gas components, the exhaust gas may also contain harmful components such as dust and heavy metals.
Carbon dioxide (CO ₂ ), nitrogen oxides (NOx) and sulfur oxides (SOx) are the main useful components of microalgae among the gas components contained in the exhaust gas.

"First aspect"
[Microalgae culture device]
FIG. 1 shows an example of a microalgae culture apparatus according to the first aspect of the present invention.
A microalgae culture apparatus 1 shown in FIG.

The culture tank 10 is a tank containing the culture solution S.
As the culture tank 10, a closed system culture tank may be used when microalgae are cultured in a closed system, and an open system culture tank may be used when microalgae are cultured in an open system.
Here, the term "closed system" means that the environment inside the culture tank is isolated from the environment outside the culture tank. Useful components such as carbon dioxide supplied to the culture solution S are less likely to be released from the water surface into the gas phase, culture of microalgae is less likely to be affected by the environment outside the culture tank, and foreign matter such as dust can be prevented from entering. For these reasons, it is preferable to culture microalgae in a closed system.

Examples of closed-system culture tanks include photobioreactor-type water tanks.
Examples of photobioreactor-type water tanks include flat-plate-type water tanks, tube-type water tanks, sunlight-collecting water tanks, and internal irradiation-type water tanks.
Examples of the open culture tank include a raceway type water tank. Further, instead of the culture tank 10, microalgae may be cultured in a pond or the like.

The culture solution S contained in the culture tank 10 may be appropriately determined according to the type of microalgae to be cultured.

The separating and supplying means 20 is means for separating useful components from the exhaust gas and supplying the culture solution S with the useful components separated from the exhaust gas.
The separation supply means 20 shown in FIG. 1 includes a gas separation membrane 211 .
The gas separation membrane 211 is not particularly limited as long as it can separate useful components from the exhaust gas, and may be a porous membrane or a non-porous membrane. Moreover, it may be a polymer membrane, or a separation membrane made of an inorganic material such as ceramics or metal. Among them, as the gas separation membrane 211, a porous polymer membrane or a non-porous polymer membrane is preferable.
In particular, if the gas separation membrane 211 is a non-porous membrane, when the exhaust gas contains harmful components, the harmful components are not separated from the exhaust gas, that is, without permeating the harmful components to the culture solution S side. A useful component can be separated from the exhaust gas and supplied to the culture solution S.
If the exhaust gas does not contain harmful components, or if the exhaust gas contains harmful components but the pore size is smaller than the size of the harmful components (such as the particle size), the gas separation membrane 211 Porous membranes may also be used.

The non-porous film is preferably a polymer film made of a material containing one or more selected from polymer materials such as polyolefin resins, polyurethane resins, fluorine resins and silicone resins. In particular, a material containing one or more selected from polyolefin-based resins, polyurethane-based resins, and silicone-based resins from the viewpoint of efficiently separating useful components from exhaust gas and supplying a sufficient amount of useful components to the culture medium S. It is preferable to consist of
The porous membrane is preferably a polymer membrane made of a polymer material, for example, a material containing one or more selected from polyolefin resins, polyurethane resins and fluorine resins.

The gas separation membrane 211 may have a single-layer structure or a multi-layer structure. When the gas separation membrane 211 has a multi-layer structure, it preferably has a multi-layer structure including, for example, two porous layers and one non-porous layer provided therebetween.

The average film thickness of the gas separation membrane 211 is preferably 0.7-1.3 μm, more preferably 0.8-1.2 μm. If the average film thickness of the gas separation membrane 211 is equal to or greater than the above lower limit, it is possible to stably produce without causing defects during production. If the average film thickness of the gas separation membrane 211 is equal to or less than the above upper limit, good permeability of useful components can be maintained.
The average film thickness of the gas separation membrane 211 is obtained by observing the cross section of the gas separation membrane 211 with a scanning electron microscope (SEM) and analyzing the image to determine the film thickness of the gas separation membrane 211 at a plurality of locations (five or more locations). It is obtained by measuring and calculating the average value.

The shape of the gas separation membrane 211 is not particularly limited, and may be a hollow fiber membrane, a flat membrane, or the like depending on the application. Among them, hollow fiber membranes are preferred.
Moreover, the gas separation membrane 211 may be provided with a support (for example, a fibrous material such as a braided cord or braid) for reinforcing the gas separation membrane 211 . For example, when the form of the gas separation membrane 211 is a hollow fiber membrane, the gas separation membrane 211 may be formed by forming a non-porous membrane or a porous membrane on a hollow support.

The gas separation membrane 211 is immersed in the culture solution S contained in the culture tank 10 .
The gas separation membrane 211 in the illustrated example is a hollow fiber membrane, and is immersed in the culture solution S in the state of the separation membrane module 21 .
The illustrated separation membrane module 21 includes a sheet 212 composed of a plurality of gas separation membranes 211 and a pair of housings 213 .

The sheet 212 has a plurality of gas separation membranes 211 arranged at regular intervals. A plurality of gas separation membranes 211 may be bundled to form a separation membrane bundle, and the plurality of separation membrane bundles may be spaced apart from each other to form a sheet 212 .
Both longitudinal ends of the sheet 212 are inserted into and supported by a pair of housings 213 .
The pair of housings 213 are substantially hollow members into which both ends of the sheet-like material 212 are inserted and fixed, and in the example shown in FIG. That is, the sheet 212 is held between the first housing 213a and the second housing 213b.

The exhaust gas line 22 is connected to the first housing 213a so that the exhaust gas is supplied to the inside of the first housing 213a. On the other hand, the discharge line 32 described later is connected to the second housing 213b, and the exhaust gas after the useful components have been separated, that is, the remaining gas components that have not been separated from the exhaust gas and have not permeated the gas separation membrane 211 (hereinafter referred to as , also referred to as “off-gas”) is discharged.
The separation membrane module 21 is configured such that the exhaust gas is sent into the hollow portions of the plurality of gas separation membranes 211 through the first housing 213a, the useful components are separated from the exhaust gas, and the useful components are supplied to the culture solution S. configured to That is, as shown in FIG. 1, useful components (CO ₂ , NOx, SOx, etc.) contained in the exhaust gas permeate the gas separation membrane 211 and diffuse into the culture solution S. As shown in FIG. By using the gas separation membrane 211, useful components such as gaseous carbon dioxide contained in the exhaust gas are dissolved in the culture solution S and diffused.

The agitating means 30 is means for agitating the culture solution S by using exhaust gas (off-gas) after separation of useful components as power for agitating the culture solution S.
The agitation means 30 shown in FIG. 1 is an aeration means comprising an aeration pipe 31 arranged substantially horizontally near the bottom of the culture tank 10 and a discharge line 32 .
The air diffuser 31 of this example consists of a circular tube having a circular cross section perpendicular to the longitudinal direction, and a plurality of circular air diffusion holes 311 for ejecting gas are formed in the upper part of the peripheral wall of the air diffuser 31 along the longitudinal direction. are formed in a row.
Here, the “upper portion of the peripheral wall” is the peripheral wall located above the axis of the diffuser tube 31 when the diffuser tube 31 is arranged so that its longitudinal direction is substantially horizontal.

The discharge line 32 is a pipe for discharging off-gas from the separation membrane module 21 . One end of the discharge line 32 is connected to the second housing 213b, and the other end is connected to the diffuser pipe 31. As shown in FIG.
In the stirring means 30, the off-gas that has not been separated from the exhaust gas by the separating/supplying means 20, i.e., that has not permeated the gas separation membrane 211, is supplied to the diffuser tube 31 via the second housing 213b and the discharge line 32, and diffused. It is configured to be discharged into the culture solution S from the pores 311 . The release of the off-gas into the culture solution S causes the culture solution S to be aerated and agitated.
Off-gases are mainly N ₂ and O ₂ .

If the exhaust gas contains harmful components, using a non-porous membrane as the gas separation membrane 211 or using a porous membrane having pores smaller in pore diameter than the size of the harmful components (particle size, etc.) will reduce the harmful components. is also discharged from the separation membrane module 21 together with the off-gas and supplied to the diffuser pipe 31 . Therefore, in such a case, it is preferable to provide a filter (not shown) for separating the off-gas and harmful components in the middle of the discharge line 32 to supply only the off-gas to the diffuser pipe 31 .

The mixing means 40 is means for mixing the adjusted gas with the exhaust gas (off-gas) from which useful components have been separated.
The mixing means 40 shown in FIG. 1 comprises a tank 41 and a regulated gas supply line 42 .
A tank 41 is a tank that contains the adjustment gas.
The regulated gas supply line 42 is a pipe that supplies the regulated gas contained in the tank 41 to the offgas, and is configured to join the offgas in the discharge line 32 to mix the regulated gas with the offgas in the discharge line 32. It is
Conditioning gases include, for example, air, N ₂ , O ₂ , and the like.

[Microalgae culture method]
An example of the method for culturing microalgae according to the first aspect of the present invention will be described below. The microalgae culture method described below is an example of the microalgae culture method using the microalgae culture apparatus 1 shown in FIG.
The method for culturing microalgae of the present embodiment includes a separation and supply step of separating useful components from exhaust gas and supplying the useful components to the culture solution S, and stirring the culture solution S with the exhaust gas (off-gas) after separating the useful components. and a stirring step of stirring the culture solution S using the power as power.
Specifically, it is as follows.

First, exhaust gas emitted from facilities that use fossil fuels, such as coal-fired power plants, waste incinerators, cement plants, and steel plants, is introduced into the hollow portion of the gas separation membrane 211 through the exhaust gas line 22 and the first housing 213a. send to
The exhaust gas sent to the gas separation membrane 211 is separated by the gas separation membrane 211 . Specifically, useful components contained in the exhaust gas are separated from the exhaust gas by the gas separation membrane 211, and the separated useful components are supplied into the culture solution S (separation supply step).
Since the gas separation membrane 211 is immersed in the culture solution S contained in the culture tank 10 , the useful components that permeate the gas separation membrane 211 are diffused directly into the culture solution S. At that time, useful components such as gaseous carbon dioxide are easily dissolved in the culture solution S because air bubbles are less likely to be generated.

Exhaust gas from which useful components have been separated, that is, remaining gas components (off-gas) that have not been separated from the exhaust gas and have not permeated the gas separation membrane 211 are sent to the air diffuser 31 via the second housing 213b and the discharge line 32. It is supplied and discharged into the culture medium S from the air diffusion holes 311 (stirring step). In the present embodiment, the off-gas is released into the culture solution S, so that the off-gas serves as a stirring power for the culture solution S, and the culture solution S is aerated and stirred.
When the supply amount of the offgas is small and the stirring power of the culture solution S is weak, the adjustment gas is mixed with the offgas by the mixing means 40 to adjust the supply amount of the offgas (stirring power of the culture solution S). is preferred.

The conditions for culturing microalgae are not particularly limited, and may be determined according to the type of microalgae to be cultured.
Microalgae may be cultured in a closed system or in an open system. The useful components supplied to the culture solution S are less likely to be released from the water surface into the gas phase, the culture of microalgae is less likely to be affected by the environment outside the culture tank, and foreign matter such as dust can be prevented from entering. Cultivation of microalgae is preferably carried out in a closed system.
Further, when the exhaust gas contains harmful components, the useful components are separated from the exhaust gas into the culture solution S without separating the harmful components from the exhaust gas, that is, without permeating the harmful components to the culture solution S side. preferably supplied to In this case, it is preferable to provide a filter (not shown) for separating the off-gas and harmful components in the middle of the exhaust line 32 to supply only the off-gas to the diffuser pipe 31 .
The culture temperature is preferably 4 to 40°C, more preferably 15 to 35°C.
The light applied to the microalgae may be sunlight or artificial light.

[Effect]
In the method for cultivating microalgae and the apparatus for culturing microalgae of the first aspect of the present invention as described above, waste is discharged from facilities that use fossil fuels such as coal-fired power plants, garbage incineration plants, cement plants, and ironworks. Since the exhaust gas from the fuel cell is used as a source of carbon dioxide, greenhouse gas emissions can be reduced. Moreover, since the exhaust gas (off-gas) after separating the useful components from the exhaust gas is used as power for stirring the culture solution, the culture solution can be stirred efficiently. In addition, since the culture solution is aerated by supplying off-gas to the culture solution, oxygen generated by photosynthesis of microalgae is easily removed from the culture solution, and culture inhibition due to dissolved oxygen is less likely to occur. Carbon dioxide dissolved in the culture solution is consumed by the microalgae before being removed from the culture solution by aeration.

Microalgae cultured according to the present invention are used, for example, in foods, cosmetics, biofuels, and the like.
In particular, when exhaust gas containing harmful components is used for culturing microalgae, the useful components are separated from the exhaust gas without separating the harmful components from the exhaust gas, that is, without permeating the harmful components to the culture solution side. Microalgae cultured in a culture solution are suitable as raw materials for foods, cosmetics, and the like.

Although the microalgae culture apparatus 1 of the illustrated example includes one culture tank 10, a plurality of culture tanks may be installed to simultaneously culture microalgae.
When installing a plurality of culture tanks, the same type of microalgae or different types of microalgae may be cultured in each culture tank. Alternatively, culture may be performed in a closed system in at least one of the culture tanks and in an open system in the remaining culture tanks.
In addition, in the microalgae culture apparatus 1 of the illustrated example, one separation membrane module 21 is immersed in one culture tank 10, but a plurality of separation membrane modules 21 may be used depending on the size of the culture tank 10. It can be immersed.

In addition, in the stirring means 30 shown in FIG. 1, the discharge line 32 is directly connected to the air diffuser 31, and the off-gas is continuously supplied to the culture tank S. For example, as shown in FIG. The means 30 includes an intermittent supply means 33 for storing the exhaust gas (off-gas) after separating useful components in a storage tank 331 and intermittently supplying the exhaust gas (off-gas) stored in the storage tank 331 to the culture tank 10. may be
The intermittent supply means 33 shown in FIG. 2 includes a storage tank 331 , an offgas supply line 332 , and a valve 333 provided in the offgas supply line 332 .

The storage tank 331 is a tank that stores off-gas.
The offgas supply line 332 is a pipe that supplies the offgas stored in the storage tank 331 to the diffuser pipe 31 . One end of the offgas supply line 332 is connected to the storage tank 331 and the other end is connected to the diffuser pipe 31 .
Examples of the valve 333 include an electromagnetic valve, an electric valve, an air-driven valve, a manual valve, and the like.

When culturing microalgae using the microalgae culture apparatus 2 shown in FIG. Then, when a certain amount of off-gas is stored, it is preferable to open the valve 333 to supply the exhaust gas to the diffuser tube 31 at once, thereby intermittently stirring the culture solution S. By performing the stirring step intermittently in this way, the off-gas is released into the culture solution S in the form of larger bubbles, so that the stirring efficiency is further enhanced.
Note that the adjustment gas supply line 42 of the mixing means 40 shown in FIG.

"Second aspect"
[Microalgae culture device]
FIG. 3 shows an example of a microalgae culture apparatus according to the second aspect of the present invention.
The microalgae culture apparatus 3 shown in FIG.
The culture tank 10, the stirring means 30, and the mixing means 40 are the same as those in the first embodiment, and thus descriptions thereof are omitted.

The separation supply means 20 shown in FIG. 3 includes a dissolution tank 23 and a gas separation membrane 211 .
The dissolution tank 23 is a tank for obtaining a solution W by dissolving the active ingredient separated from the exhaust gas in the culture solution S supplied from the culture tank 10 .
A culture solution supply line 24 and a solution supply line 25 are connected to the dissolution tank 23 .
The culture fluid supply line 24 is a pipe that extracts part of the culture fluid S from the culture tank 10 and supplies the extracted culture fluid S to the dissolving tank 23 . One end of the culture solution supply line 24 is connected to the culture tank 10 and the other end is connected to the dissolution tank 23 .
The solution supply line 25 is a pipe for supplying the solution W obtained in the dissolution tank 23 to the culture tank 10 . One end of the solution supply line 25 is connected to the dissolution tank 23 and the other end is connected to the culture tank 10 .

The dissolution tank 23 is supplied with the culture solution S from the culture tank 10 via the culture solution supply line 24 . The carbon dioxide in the culture solution supplied to the dissolution tank 23 is consumed by the microalgae, so the carbon dioxide concentration is relatively low.
A solution W is obtained by dissolving the active ingredient separated from the exhaust gas in the culture solution S supplied to the dissolving tank 23 . The solution W is a culture solution with a relatively high carbon dioxide concentration.
By supplying the solution W thus obtained, that is, the culture solution having a relatively high carbon dioxide concentration to the culture tank 10 through the solution supply line 25, the culture solution S flows between the culture tank 10 and the dissolution tank 23. It circulates so that the culture medium S in the culture tank 10 can be supplied with useful components separated from the exhaust gas.

As the gas separation membrane 211, the gas separation membranes exemplified above in the explanation of the first aspect can be mentioned.
The gas separation membrane 211 is immersed in the culture solution previously supplied to the dissolution tank 23 . Note that the gas separation membrane 211 is immersed in the solution W after the solution W is obtained.
The gas separation membrane 211 in the illustrated example is a hollow fiber membrane, and in the state of the separation membrane module 21, it is immersed in the culture solution previously supplied to the dissolution tank 23 (or the solution W obtained in the dissolution tank 23). ing.
The illustrated separation membrane module 21 includes a sheet 212 composed of a plurality of gas separation membranes 211 and a pair of housings 213 .
The sheet-like object 212 and the pair of housings 213 are the same as the sheet-like object 212 and the pair of housings 213 exemplified above in the description of the first aspect, respectively, so description thereof will be omitted.

In the illustrated separation membrane module 21, the exhaust gas is fed into the hollow portions of the plurality of gas separation membranes 211 through the first housing 213a, and useful components are separated from the exhaust gas and supplied to the dissolution tank 23 in advance. It is configured to supply useful components into the culture medium. That is, as shown in FIG. 3, the useful components (CO ₂ , NOx, SOx, etc.) contained in the exhaust gas are diffused into the culture solution previously supplied to the dissolution tank 23, and the solution W is obtained. By using the gas separation membrane 211 , useful components such as gaseous carbon dioxide contained in the exhaust gas are dissolved in the culture solution previously supplied to the dissolution tank 23 and diffused.

[Microalgae culture method]
An example of the method for culturing microalgae according to the second aspect of the present invention will be described below. The microalgae culture method described below is an example of the microalgae culture method using the microalgae culture apparatus 3 shown in FIG.
The method for culturing microalgae of the present embodiment includes a separation and supply step of separating useful components from exhaust gas and supplying the useful components to the culture solution S, and stirring the culture solution S with the exhaust gas (off-gas) after separating the useful components. and a stirring step of stirring the culture solution S using the power as power.
Specifically, it is as follows.

First, a pump (not shown) provided in the middle of the culture solution supply line 24 is driven to extract part of the culture solution S from the culture tank 10, and the culture solution S extracted through the culture solution supply line 24 is separated. It is supplied to the dissolving tank 23 of the supply means 20 .
Next, the exhaust gas emitted from facilities that use fossil fuels, such as coal-fired power plants, waste incinerators, cement plants, steel plants, etc., is introduced into the hollow portion of the gas separation membrane 211 through the exhaust gas line 22 and the first housing 213a. send to
The exhaust gas sent to the gas separation membrane 211 is separated by the gas separation membrane 211 . Specifically, the useful components contained in the exhaust gas are separated from the exhaust gas by the gas separation membrane 211, and the separated useful components are dissolved in the culture solution in the dissolution tank 23 to obtain the solution W. Since the gas separation membrane 211 is immersed in the culture solution previously supplied to the dissolution tank 23, the useful components permeating through the gas separation membrane 211 are directly diffused into the water. At that time, since air bubbles are less likely to be generated, the useful components are easily dissolved in the culture medium.
Next, by supplying the solution W to the culture tank 10 via the solution supply line 25, the culture solution S in the culture tank 10 is supplied with useful components separated from the exhaust gas (separation supply step).

Exhaust gas from which useful components have been separated, that is, remaining gas components (off-gas) that have not been separated from the exhaust gas and have not permeated the gas separation membrane 211 are sent to the air diffuser 31 via the second housing 213b and the discharge line 32. It is supplied and discharged into the culture medium S from the air diffusion holes 311 (stirring step). In the present embodiment, the off-gas is released into the culture solution S, so that the off-gas serves as a stirring power for the culture solution S, and the culture solution S is aerated and stirred.
When the supply amount of the offgas is small and the stirring power of the culture solution S is weak, the adjustment gas is mixed with the offgas by the mixing means 40 to adjust the supply amount of the offgas (stirring power of the culture solution S). is preferred.
The conditions for culturing the microalgae and the like are the same as those in the first embodiment, so the description thereof is omitted.

[Effect]
In the method for culturing microalgae and the apparatus for cultivating microalgae of the second aspect of the present invention described above, waste from facilities that use fossil fuels such as coal-fired power plants, garbage incineration plants, cement plants, and steel plants Since the exhaust gas from the fuel cell is used as a source of carbon dioxide, greenhouse gas emissions can be reduced. Moreover, since the exhaust gas (off-gas) after separating the useful components from the exhaust gas is used as power for stirring the culture solution, the culture solution can be stirred efficiently. In addition, since the culture solution is aerated by supplying off-gas to the culture solution, oxygen generated by photosynthesis of microalgae is easily removed from the culture solution, and culture inhibition due to dissolved oxygen is less likely to occur. Carbon dioxide dissolved in the culture solution is consumed by the microalgae before being removed from the culture solution by aeration.

Although the microalgae culture apparatus 2 of the illustrated example includes one culture tank 10, a plurality of culture tanks may be installed to simultaneously culture microalgae.
When installing a plurality of culture tanks, the same type of microalgae or different types of microalgae may be cultured in each culture tank. Alternatively, culture may be performed in a closed system in at least one of the culture tanks and in an open system in the remaining culture tanks.

In addition, in the stirring means 30 shown in FIG. 3, the discharge line 32 is directly connected to the air diffuser 31, and the off-gas is continuously supplied to the culture tank S, but as described in the first embodiment, In addition, the stirring means 30 is provided with intermittent supply means for storing the exhaust gas (off-gas) after separating the useful components in the storage tank and intermittently supplying the exhaust gas (off-gas) stored in the storage tank to the culture tank. may Since the intermittent supply means is the same as in the first aspect, its explanation is omitted.

1 microalgae culture device 2 microalgae culture device 3 microalgae culture device 10 culture tank 20 separation supply means 21 separation membrane module 211 gas separation membrane 212 sheet 213 housing 213a first housing 213b second housing 22 Exhaust gas line 23 dissolution tank 24 culture solution supply line 25 solution supply line 30 stirring means 31 air diffusion pipe 311 diffusion hole 32 discharge line 33 intermittent supply means 331 storage tank 332 offgas supply line 333 valve 40 mixing means 41 tank 42 regulated gas supply line S culture solution W solution

Claims (22)

A method for culturing microalgae using exhaust gas,
a separating and supplying step of separating useful components from the exhaust gas and supplying the useful components to the culture solution;
A method for culturing microalgae, comprising a stirring step of stirring the culture solution by using exhaust gas from which the useful components have been separated as stirring power for the culture solution. The method for culturing microalgae according to claim 1, wherein the useful components are separated from the exhaust gas without separating harmful components from the exhaust gas, and the useful components are supplied to the culture solution. The method for culturing microalgae according to claim 2, wherein the harmful component is either one or both of dust and heavy metals. The method for culturing microalgae according to any one of claims 1 to 3, wherein a non-porous membrane is used to separate the useful components from the exhaust gas and supply the useful components to the culture solution. The method for culturing microalgae according to claim 4, wherein the non-porous membrane is a polymer membrane. The culture of microalgae according to any one of claims 1 to 5, wherein the exhaust gas is exhaust gas discharged from one or more selected from a coal-fired power plant, a waste incineration plant, a cement plant and a steel mill. Method. The method for culturing microalgae according to any one of claims 1 to 6, wherein the microalgae are one or more species selected from Euglena, Pseudocolycystis and Spirulina. The method for culturing microalgae according to any one of claims 1 to 7, wherein the microalgae are cultured in a closed system. The method for culturing microalgae according to any one of claims 1 to 8, wherein the stirring step is performed by a method using aeration. The method for cultivating microalgae according to any one of claims 1 to 9, wherein a regulated gas is mixed with the exhaust gas after separating the useful components. The method for culturing microalgae according to any one of claims 1 to 10, wherein the stirring step is performed intermittently. An algae culture apparatus using exhaust gas,
a culture tank containing a culture solution;
Separating and supplying means for separating useful components from the exhaust gas and supplying the useful components to the culture solution;
An apparatus for culturing microalgae, comprising: stirring means for stirring the culture solution by using exhaust gas from which the useful components have been separated as stirring power for the culture solution. The apparatus for culturing microalgae according to claim 12, wherein the useful components are separated from the exhaust gas without separating harmful components from the exhaust gas, and the useful components are supplied to the culture solution. The apparatus for cultivating microalgae according to claim 13, wherein the harmful component is one or both of soot and heavy metals. The apparatus for culturing microalgae according to any one of claims 12 to 14, wherein a non-porous membrane is used to separate the useful components from the exhaust gas and supply the useful components to the culture solution. The microalgae culture device according to claim 15, wherein the non-porous membrane is a polymer membrane. The cultivation of microalgae according to any one of claims 12 to 16, wherein the exhaust gas is exhaust gas discharged from one or more selected from a coal-fired power plant, a waste incineration plant, a cement plant and a steel mill. Device. The microalgae culture apparatus according to any one of claims 12 to 17, wherein the microalgae are one or more species selected from Euglena, Pseudocolycystis and Spirulina. The apparatus for culturing microalgae according to any one of claims 12 to 18, wherein the culture tank is a photobioreactor-type water tank. The apparatus for culturing microalgae according to any one of claims 12 to 19, wherein the stirring means is aeration means. The apparatus for culturing microalgae according to any one of claims 12 to 20, further comprising mixing means for mixing a regulated gas with the exhaust gas after separating the useful components. 12 to 12, wherein the stirring means comprises intermittent supply means for storing the exhaust gas after the separation of the useful components in a storage tank and intermittently supplying the exhaust gas stored in the storage tank to the culture tank. 22. The apparatus for culturing microalgae according to any one of 21.

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