JP2023103645A - Microalgae culture method and microalgae culture apparatus - Google Patents

Abstract

To provide methods and devices capable of efficiently culturing microalgae while suppressing diffusion of carbon dioxide to the atmosphere.SOLUTION: A method for culturing microalgae and a culture device 1 are disclosed. The culture method comprises a step of removing microalgae from a culture fluid S to obtain a separated solution; and a step of contacting the separated solution to a carbonate substance to obtain a solution W; and a step contacting the solution W to the culture fluid S to supply carbon source to the culture fluid S. The culture device 1 comprises: a culture vessel 10 for containing a culture fluid S; separation means 20 for obtaining a separated solution by removing the microalgae from the culture fluid S; dissolving means 30 for dissolving a carbonate substance into the separated solution to obtain a solution W; and means 40 for supplying carbon source to the culture fluid S by contacting the solution W and the culture fluid S.SELECTED DRAWING: Figure 1

Description

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

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, methods for culturing microalgae have been investigated.
Cultivation of microalgae is generally carried out by supplying carbon dioxide in a gaseous state to a culture medium.

However, when the amount of carbon dioxide supplied becomes excessive, the surplus carbon dioxide that has not been consumed by the microalgae is diffused from the culture solution into the atmosphere, causing global warming.
Therefore, a method of supplying a solution obtained by dissolving carbon dioxide in water to a culture solution has been studied.
As a method for culturing microalgae by dissolving gas in water, for example, Patent Document 1 discloses a method in which gas is converted into microbubbles to generate microbubble water containing microbubbles, and this microbubble water is supplied to a culture solution. A method for doing so is disclosed.

JP 2019-193588 A

However, since the solution obtained by dissolving carbon dioxide in water cannot be supplied in excess of the capacity of the culture tank, the supply amount of carbon dioxide is limited.
An object of the present invention is to provide a microalgae culture method and a microalgae culture apparatus capable of efficiently culturing microalgae while suppressing the diffusion of carbon dioxide into the atmosphere.

The present invention has the following aspects.
[1] A method for culturing microalgae by containing a culture solution in a culture tank,
A separation step of removing the microalgae from the culture solution to obtain a separated solution;
a dissolving step of dissolving a carbonic acid substance in the separation liquid to obtain a solution;
A method for culturing microalgae, comprising a supplying step of bringing the dissolution solution and the culture solution into contact with each other and supplying a carbon source to the culture solution.
[2] The method for culturing microalgae according to [1], wherein the separation step is performed in the culture tank.
[3] The method for culturing microalgae according to [1], wherein the separation step is performed outside the culture tank by extracting part of the culture solution from the culture tank.
[4] The method for culturing microalgae according to any one of [1] to [3], wherein the dissolving step is a step of dissolving gaseous carbon dioxide in the separated liquid to obtain the dissolved liquid.
[5] The method for culturing microalgae according to [4] above, wherein the gaseous carbon dioxide is dissolved in the separated liquid by a method using a non-porous membrane or a method by pressure dissolution.
[6] The method for culturing microalgae according to [5], wherein the non-porous membrane is a polymer membrane.
[7] The method for culturing microalgae according to any one of [4] to [6], wherein the carbon dioxide-containing exhaust gas is used to dissolve the gaseous carbon dioxide in the separated liquid.
[8] The method for cultivating microalgae according to [7] above, 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 factory, and a steel mill.
[9] The method for culturing microalgae according to any one of [1] to [8], wherein the microalgae are one or more selected from Euglena, Pseudocolycystis and Spirulina.
[10] The method for culturing microalgae according to any one of [1] to [9], wherein the culture tank is a photobioreactor type tank.
[11] The method for culturing microalgae according to any one of [1] to [10], further comprising a mixing step of mixing water or an aqueous solution containing useful components other than a carbonate substance with the culture solution or the separated solution. .

[12] A microalgae culture apparatus,
a culture tank containing a culture solution;
Separation means for removing the microalgae from the culture solution to obtain a separated solution;
a dissolving means for dissolving a carbonate substance in the separation liquid to obtain a solution;
An apparatus for culturing microalgae, comprising supply means for bringing the dissolution solution and the culture solution into contact with each other and supplying a carbon source to the culture solution.
[13] The apparatus for culturing microalgae according to [12], wherein the separating means is present in the culture tank.
[14] The separating means is a means for extracting a part of the culture solution from the culture tank and removing the microalgae to obtain the separated solution, and is present outside the culture tank. Microalgae culture equipment.
[15] The microalgae culture apparatus according to any one of [12] to [14], wherein the dissolving means is means for obtaining the dissolved liquid by dissolving gaseous carbon dioxide in the separated liquid.
[16] The apparatus for culturing microalgae according to [15] above, wherein the gaseous carbon dioxide is dissolved in the separated liquid by a method using a non-porous membrane or a method by pressurized dissolution.
[17] The apparatus for culturing microalgae according to [16], wherein the non-porous membrane is a polymer membrane.
[18] The apparatus for cultivating microalgae according to any one of [15] to [17], wherein the gaseous carbon dioxide is dissolved in the separated liquid using exhaust gas containing carbon dioxide.
[19] The apparatus for cultivating microalgae according to [18] above, wherein the exhaust gas is exhaust gas discharged from one or more selected from a coal-fired power plant, an incinerator, a cement factory, and a steel mill.
[20] The microalgae culture apparatus according to any one of [12] to [19], wherein the microalgae are one or more selected from Euglena, Pseudocolycystis and Spirulina.
[21] The apparatus for culturing microalgae according to any one of [12] to [20], wherein the culture tank is a photobioreactor type water tank.
[22] The apparatus for culturing microalgae according to any one of [12] to [21], further comprising mixing means for mixing water or an aqueous solution containing useful components other than a carbonate substance into the culture solution or the separated solution. .

ADVANTAGE OF THE INVENTION According to this invention, the culture|cultivation method of microalgae and the culture|cultivation apparatus of microalgae which can culture|cultivate microalgae efficiently can be provided, suppressing the diffusion of the carbon dioxide to the atmosphere.

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 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.
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 FIG. 2, 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.

In the present invention, the carbonate substance is a general term for carbon dioxide (CO ₂ ), carbonic acid (H ₂ CO ₃ ), hydrogen carbonate ion (bicarbonate ion) (HCO ₃ ⁻ ), and carbonate ion (CO ₃ ²⁻ ). is.

In the method for culturing microalgae and the apparatus for culturing microalgae of the present invention, it is preferable to culture microalgae using exhaust gas containing carbon dioxide from the viewpoint of reducing greenhouse gas emissions.
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 separation means 20 is means for removing microalgae from the culture solution S to obtain a separation solution.
The separation means 20 shown in FIG. 1 comprises a first separation membrane module 21 arranged in the culture tank 10 . That is, the separating means 20 shown in FIG. 1 exists in the culture tank 10 .
By using the first separation membrane module 21, microalgae can be removed from the culture solution S with high separation performance, and a separated liquid from which the microalgae are sufficiently removed can be obtained.

The first separation membrane module 21 includes a filtration membrane (solid-liquid separation membrane) such as a microfiltration membrane and an ultrafiltration membrane. Examples of microfiltration membranes include hollow fiber membranes, flat membranes, tubular membranes, monolithic membranes, and the like. Ultrafiltration membranes include hollow fiber membranes, flat membranes, tubular membranes and the like. Among these membranes, hollow fiber membranes are preferably used because of their high volume filling ratio.

When a hollow fiber membrane is used as the filtration membrane of the first separation membrane module 21, examples of the material include cellulose, polyolefin, polysulfone, polyvinylidene difluoride (PVDF), and polytetrafluoroethylene (PTFE). be done. Among these, polyvinylidene difluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferable as the material for the hollow fiber membrane because of their chemical resistance and resistance to pH changes.
When a monolithic membrane is used as the filtration membrane of the first separation membrane module 21, it is preferable to use a ceramic membrane.

The average pore size of micropores formed in the microfiltration membrane or ultrafiltration membrane is preferably 0.01 to 1.0 μm, more preferably 0.05 to 0.45 μm. If the average pore diameter of the micropores is at least the above lower limit, the pressure required for solid-liquid separation can be kept sufficiently low. If the average pore diameter of the micropores is equal to or less than the above upper limit, microalgae are less likely to leak into the separated liquid.

A separated liquid supply line 22 is connected to the first separation membrane module 21 shown in FIG.
The separated liquid supply line 22 is a pipe that supplies the permeated liquid that has passed through the filtration membrane of the first separation membrane module 21 , that is, the separated liquid from which microalgae have been removed from the culture solution S to the dissolving means 30 .
A pump 23 is installed in the separated liquid supply line 22 . Thereby, the separated liquid can be discharged from the culture tank 10 and supplied to the dissolving means 30 .

The dissolving means 30 is means for obtaining the solution W by dissolving the carbonate substance in the separation liquid.
The dissolving means 30 shown in FIG. 1 is a means for obtaining a solution W by using an exhaust gas containing carbon dioxide and dissolving the carbon dioxide contained in the exhaust gas into a separated liquid.
The dissolution means 30 shown in FIG. 1 includes a dissolution tank 31 and a gas separation membrane 321 .

The dissolution tank 31 is a tank for obtaining the solution W. FIG. The separated liquid supplied from the separating means 20 is stored in the dissolving tank 31 before the flue gas is supplied, and the dissolving liquid W is obtained by dissolving carbon dioxide in the separated liquid stored in the dissolving tank 31. be done.

The gas separation membrane 321 is a supply means for separating useful components from the exhaust gas and supplying the useful components separated from the exhaust gas to the separated liquid.
The gas separation membrane 321 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. Further, 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 321, a porous polymer membrane or a non-porous polymer membrane is preferable.
In particular, if the gas separation membrane 321 is a non-porous membrane, when the exhaust gas contains harmful components, the exhaust gas can A useful component can be separated from the liquid and supplied to the separated liquid.
If the exhaust gas does not contain harmful components, or even if the exhaust gas contains harmful components, if the pore diameter of the pores is smaller than the size of the harmful components (particle size, etc.), the gas separation membrane 321 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, from the viewpoint of efficiently separating useful components from exhaust gas and supplying a sufficient amount of useful components into the separated liquid, materials containing one or more selected from polyolefin-based resins, polyurethane-based resins and silicone-based resins. It is preferable to be
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 321 may have a single-layer structure or a multi-layer structure. When the gas separation membrane 321 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 321 is preferably 0.7-1.3 μm, more preferably 0.8-1.2 μm. If the average film thickness of the gas separation membrane 321 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 321 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 321 is obtained by observing the cross section of the gas separation membrane 321 with a scanning electron microscope (SEM) and analyzing this image to determine the film thickness of the gas separation membrane 321 at multiple locations (five locations or more). It is obtained by measuring and calculating the average value.

The shape of the gas separation membrane 321 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 321 may be provided with a support (for example, a fibrous material such as a braided cord or braid) for reinforcing the gas separation membrane 321 . For example, when the form of the gas separation membrane 321 is a hollow fiber membrane, the gas separation membrane 321 may be formed by forming a non-porous membrane or a porous membrane on a hollow support.

The gas separation membrane 321 is immersed in the separated liquid stored in the dissolution tank 31 . Note that the gas separation membrane 321 is immersed in the solution W after the solution W is obtained.
The gas separation membrane 321 in the illustrated example is a hollow fiber membrane, and in the state of the second separation membrane module 32, is immersed in the separated liquid (or the dissolved liquid W obtained in the dissolution tank 31).
The second separation membrane module 32 of the illustrated example includes a sheet-like object 322 composed of a plurality of gas separation membranes 321 and a pair of housings 323 .

The sheet-like object 322 has a plurality of gas separation membranes 321 arranged at regular intervals. A plurality of gas separation membranes 321 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 322 .
Both longitudinal ends of the sheet 322 are inserted into and supported by a pair of housings 323 .
The pair of housings 323 are substantially hollow members into which both ends of the sheet-like material 322 are inserted and fixed, and in the example shown in FIG. That is, the sheet 322 is held between the first housing 323a and the second housing 323b.

An exhaust gas line 331 is connected to the first housing 323a so that the exhaust gas is supplied to the inside of the first housing 323a. On the other hand, a discharge line 332 is connected to the second housing 323b to discharge the remaining gas components that have not been separated from the exhaust gas, that is, that have not permeated the gas separation membrane 321 (hereinafter also referred to as "off gas"). is configured as
Then, the second separation membrane module 32 separates useful components from the exhaust gas through the first housing 323a into the hollow portions of the plurality of gas separation membranes 321, and supplies the useful components to the separated liquid. 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 321 and are diffused into the separated liquid to obtain the dissolved liquid W. As shown in FIG. By using the gas separation membrane 321, useful components such as gaseous carbon dioxide contained in the exhaust gas are dissolved in the separated liquid and diffused.
In addition, the second separation membrane module 32 is arranged so that the off-gas that has not been separated from the exhaust gas, i.e., that has not permeated the gas separation membrane 321, is discharged out of the system of the dissolution tank 31 through the second housing 323b. Configured. Off-gases are mainly N ₂ and O ₂ . When the exhaust gas contains harmful components, if a non-porous membrane is used as the gas separation membrane 321, or a porous membrane with a pore size smaller than the size (particle size, etc.) of the harmful components is used, the harmful components will also be offgassed. It is discharged out of the system of the dissolving tank 31 together.

The supply means 40 is means for bringing the solution W and the culture medium S into contact with each other and supplying the carbon source to the culture medium S in the culture tank 10 .
The supply means 40 comprises a solution supply line 41 .
The solution supply line 41 is a pipe for supplying the solution W obtained in the dissolution tank 31 to the culture tank 10 .

The mixing means 50 shown in FIG. 1 is means for mixing the separated liquid with water (X1) or an aqueous solution (X2) containing useful components other than the carbonate substance. In the present invention, water (X1) and aqueous solution (X2) are also collectively referred to as "liquid (X)".
Mixing means 50 comprises a tank 51 and a liquid supply line 52 .
The tank 51 is a tank that contains liquid (X).
The liquid supply line 52 is a pipe for supplying the liquid (X) contained in the tank 51 to the separation liquid. (X) can be supplied.
Useful ingredients other than carbonates include, for example, trace elements such as phosphorus, nitrogen, and potassium.

[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 step of removing microalgae from the culture solution S to obtain a separation liquid, a dissolution step of dissolving a carbonate substance in the separation liquid to obtain a solution W, and a solution W is brought into contact with the culture solution S to supply the carbon source to the culture solution S, and a mixing step of mixing the liquid (X) with the separation solution.
Specifically, it is as follows.

First, the pump 23 provided in the middle of the separation liquid supply line 22 is driven, and the culture liquid S is subjected to membrane filtration through the filtration membrane of the first separation membrane module 21. The separated liquid from which the algae have been removed is discharged from the culture tank 10 and supplied to the dissolving tank 31 of the dissolving means 30 (separation step).

After the amount of the separated liquid to immerse the second separation membrane module 32 is stored in the dissolution tank 31, it is discharged from facilities that use fossil fuels such as coal-fired power plants, garbage incineration plants, cement plants, and ironworks. The discharged exhaust gas is fed into the hollow portion of the gas separation membrane 321 through the exhaust gas line 331 and the first housing 323a.
The exhaust gas sent to the gas separation membrane 321 is separated by the gas separation membrane 321 . Specifically, the useful components contained in the exhaust gas are separated from the exhaust gas by the gas separation membrane 321, and the separated useful components are dissolved in the separated liquid in the dissolving tank 31 to obtain the dissolved liquid W (dissolving step). Since the gas separation membrane 321 is immersed in the separated liquid stored in the dissolution tank 31, the useful components that permeate the gas separation membrane 321 are diffused directly into the separated liquid. At that time, bubbles are less likely to be generated, so useful components such as gaseous carbon dioxide are easily dissolved in the separated liquid.
The remaining gas component (off-gas) that has not been separated from the exhaust gas, that is, has not permeated the gas separation membrane 321, is discharged out of the system of the dissolving tank 31 through the second housing 323b.

Next, by adding the solution W to the culture tank 10 via the solution supply line 41, the solution W and the culture solution S are brought into contact, and the carbon source is supplied to the culture solution S in the culture tank 10 ( supply process). The supply step may be carried out continuously or intermittently depending on the progress of culture.
When the culture progresses and the concentration of microalgae in the culture solution S increases, it is preferable to withdraw the culture solution S from the culture tank 10 . When the culture solution S is extracted from the culture tank 10, the amount of the culture solution S in the culture tank 10 decreases. It is preferred to adjust the amount (mixing step).

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
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 microalgae culture method and the microalgae culture apparatus of the first aspect of the present invention described above, carbon dioxide is dissolved in the separated liquid obtained by removing the microalgae from the culture solution, and the obtained solution is Since the carbon dioxide is returned to the culture medium, the necessary amount of carbon dioxide can be supplied to the culture medium without exceeding the capacity of the culture tank. Moreover, the concentration of carbon dioxide dissolved in the culture solution can be adjusted according to the progress of the culture, and the optimal amount of carbon dioxide can be supplied to the culture solution, so the amount of carbon dioxide supplied is less likely to be excessive. In addition, since the carbon dioxide is dissolved in the separation liquid and supplied to the culture medium, the separation liquid and the solution are mixed, and the carbon dioxide is dissolved in the solution. Therefore, even if the carbon dioxide is not completely consumed, surplus carbon dioxide is dissolved in the culture solution, so the carbon dioxide is less likely to diffuse into the atmosphere.
Therefore, with the method for culturing microalgae and the apparatus for culturing microalgae of the first aspect of the present invention, it is possible to efficiently culture microalgae while suppressing the diffusion of carbon dioxide into the atmosphere.
In particular, greenhouse gas emissions can be reduced by using exhaust gases emitted from facilities that use fossil fuels, such as coal-fired power plants, garbage incinerators, cement plants, and steel mills, as a source of carbon dioxide.

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 first separation membrane module 21 is immersed in one culture tank 10, but depending on the size of the culture tank 10, a plurality of first separation membrane modules of the separation membrane module 21 may be immersed.

In the first embodiment, gaseous carbon dioxide is dissolved in the separated liquid using the gas separation membrane 321 such as a non-porous membrane to prepare the solution W. Alternatively, the solution W may be prepared by dissolving carbon dioxide in the form of carbon dioxide in the separated liquid. Specifically, the gas phase portion of the dissolution tank 31 is filled with carbon dioxide, the dissolution tank 31 is sealed, and the inside of the dissolution tank 31 is pressurized to dissolve the gaseous carbon dioxide in the separated liquid to obtain the dissolved liquid W may be prepared.
Further, instead of the exhaust gas, gaseous carbon dioxide may be directly supplied to the dissolving tank 31 to prepare the solution W, or carbonates (such as sodium carbonate, potassium carbonate, etc.) and bicarbonates (such as sodium bicarbonate, potassium bicarbonate, etc.) may be supplied directly or in the form of an aqueous solution to the dissolution tank 31 to prepare the solution W. However, from the viewpoint of easily controlling the concentration of the carbonate substance in the solution W, it is preferable to prepare the solution W by dissolving gaseous carbon dioxide in the separation liquid. Among them, the method using the gas separation membrane 321 such as a non-porous membrane is particularly preferable from the viewpoint of efficiently dissolving carbon dioxide into the separated liquid.

In addition, in the microalgae culture apparatus 1 of the illustrated example, the liquid supply line 52 joins the separation liquid supply line 22 in the middle, and the liquid (X) is supplied to the separation liquid in the separation liquid supply line 22. However, the liquid (X) may be added directly to the culture solution S in the culture tank 10 and mixed.

"Second aspect"
[Microalgae culture device]
FIG. 2 shows an example of a microalgae culture apparatus according to the second aspect of the present invention.
The microalgae culture apparatus 2 shown in FIG.
The culture tank 10, the dissolving means 30, the supplying means 40, and the mixing means 50 are the same as those in the first embodiment, and thus descriptions thereof are omitted.

The separation means 20 shown in FIG. 2 includes a first separation membrane module 21 arranged outside the culture vessel 10 . That is, the separation means 20 shown in FIG. 2 is a means for extracting a part of the culture solution S from the culture tank 10 and removing microalgae from the extracted culture solution S to obtain a separated liquid. exist.
Examples of the first separation membrane module 21 include the first separation membrane module exemplified above in the description of the first embodiment.

A separated liquid supply line 22, a culture medium supply line 24, and a concentrated liquid return line 25 are connected to the first separation membrane module 21 shown in FIG.
The separation liquid supply line 22 is the same as in the first embodiment, and therefore the description thereof is omitted.
The culture solution supply line 24 is a pipe that extracts part of the culture solution S from the culture tank 10 and supplies the extracted culture solution S to the first separation membrane module 21 . One end of the culture solution supply line 24 is connected to the culture tank 10 and the other end is connected to the first separation membrane module 21 .
The concentrated solution return line 25 is a pipe for returning to the culture tank 10 the concentrated solution in which the microalgae are concentrated without passing through the filtration membrane of the first separation membrane module 21 . One end of the concentrate return line 25 is connected to the first separation membrane module 21 and the other end is connected to the culture tank 10 . As a result, the microalgae in the culture solution S extracted from the culture tank 10 can circulate between the culture tank 10 and the separating means 20 .
A concentrated liquid discharge line 26 is connected in the middle of the concentrated liquid return line 25 so that at least part of the concentrated liquid can be discharged.

[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 2 shown in FIG.
The method for culturing microalgae of the present embodiment includes a separation step of removing microalgae from the culture solution S to obtain a separation liquid, a dissolution step of dissolving a carbonate substance in the separation liquid to obtain a solution W, and a solution W is brought into contact with the culture solution S to supply the carbon source to the culture solution S, and a mixing step of mixing the liquid (X) with the separation solution.
Specifically, it is as follows.

First, the pump 23 provided in the middle of the separation liquid supply line 22 is driven to extract part of the culture medium S from the culture tank 10, and the culture medium S extracted through the culture medium supply line 24 is transferred to the separating means 20. It is supplied to the first separation membrane module 21 . Subsequently, the culture solution S is subjected to membrane filtration through the filtration membrane of the first separation membrane module 21, and the separated solution that has passed through the filtration membrane, that is, the culture solution S from which microalgae have been removed is supplied to the dissolution tank 31 of the dissolution means 30. (separation process).
The concentrated liquid in which the microalgae are concentrated without passing through the filtration membrane of the first separation membrane module 21 is returned to the culture tank 10 via the concentrated liquid return line 25 . When the culture progresses and the concentration of microalgae in the culture solution S increases, at least part of the concentrated solution is discharged through the concentrated solution discharge line 26 .

The dissolution step and supply step following the separation step are the same as those in the first embodiment, and thus descriptions thereof are omitted.
In addition, as described above, when the culture progresses and at least part of the concentrated solution is discharged, the amount of the culture solution S in the culture tank 10 decreases. It is preferable to adjust the amount of the culture solution S in the culture tank 10 by supplying (mixing step).
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 microalgae culture method and the microalgae culture apparatus of the second aspect of the present invention described above, carbon dioxide is dissolved in the separated liquid obtained by removing the microalgae from the culture solution, and the obtained solution is Since the carbon dioxide is returned to the culture medium, the necessary amount of carbon dioxide can be supplied to the culture medium without exceeding the capacity of the culture tank. Moreover, the concentration of carbon dioxide dissolved in the culture solution can be adjusted according to the progress of the culture, and the optimal amount of carbon dioxide can be supplied to the culture solution, so the amount of carbon dioxide supplied is less likely to be excessive. In addition, since the carbon dioxide is dissolved in the separation liquid and supplied to the culture medium, the separation liquid and the solution are mixed, and the carbon dioxide is dissolved in the solution. Therefore, even if the carbon dioxide is not completely consumed, surplus carbon dioxide is dissolved in the culture solution, so the carbon dioxide is less likely to diffuse into the atmosphere.
Therefore, with the method for culturing microalgae and the apparatus for culturing microalgae of the first aspect of the present invention, it is possible to efficiently culture microalgae while suppressing the diffusion of carbon dioxide into the atmosphere.
In particular, greenhouse gas emissions can be reduced by using exhaust gases emitted from facilities that use fossil fuels, such as coal-fired power plants, garbage incinerators, cement plants, and steel mills, as a source of carbon dioxide.
In addition, in the microalgae culture apparatus of the second aspect of the present invention, since the separation means exists outside the culture tank, maintenance of the first separation membrane module 21 (for example, cleaning of the filtration membrane, etc.) is easy. is.

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 microalgae culture apparatus 2 of the illustrated example, one first separation membrane module 21 is immersed in one culture tank 10, but depending on the size of the culture tank 10, a plurality of first separation membrane modules of the separation membrane module 21 may be immersed.

Further, in the second embodiment, the solution W is prepared by dissolving gaseous carbon dioxide in water using the gas separation membrane 321 such as a non-porous membrane. The solution W may be prepared by dissolving carbon dioxide in water. A specific method is the same as in the first aspect.
Further, instead of the exhaust gas, gaseous carbon dioxide may be directly supplied to the dissolving tank 31 to prepare the solution W, or carbonates (such as sodium carbonate, potassium carbonate, etc.) and bicarbonates (such as sodium bicarbonate, potassium bicarbonate, etc.) may be supplied directly or in the form of an aqueous solution to the dissolution tank 31 to prepare the solution W.

In addition, in the microalgae culture apparatus 2 of the illustrated example, the liquid supply line 52 joins the separation liquid supply line 22 in the middle, and the liquid (X) is supplied to the separation liquid in the separation liquid supply line 22. However, the liquid (X) may be added directly to the culture solution S in the culture tank 10 and mixed. Alternatively, the liquid supply line 52 may be merged with the culture solution supply line 24 in the middle to supply the culture solution S extracted from the culture tank 10 in the culture solution supply line 24 .

1 microalgae culture apparatus 2 microalgae culture apparatus 10 culture tank 20 separation means 21 first separation membrane module 22 separated liquid supply line 23 pump 24 culture liquid supply line 25 concentrated liquid return line 26 concentrated liquid discharge line 30 dissolving means 31 dissolution tank 32 second separation membrane module 321 gas separation membrane 322 sheet 323 housing 323a first housing 323b second housing 331 exhaust gas line 332 discharge line 40 supply means 41 solution supply line 50 mixing means 51 tank 52 Liquid supply line S culture solution W dissolution solution

Claims (22)

A method for culturing microalgae by storing a culture solution in a culture tank,
A separation step of removing the microalgae from the culture solution to obtain a separated solution;
a dissolving step of dissolving a carbonic acid substance in the separation liquid to obtain a solution;
A method for culturing microalgae, comprising a supplying step of bringing the dissolution solution and the culture solution into contact with each other and supplying a carbon source to the culture solution. The method for culturing microalgae according to claim 1, wherein the separation step is performed in the culture tank. The method for culturing microalgae according to claim 1, wherein the separation step is performed outside the culture tank by extracting a part of the culture solution from the culture tank. The method for culturing microalgae according to any one of claims 1 to 3, wherein the dissolving step is a step of dissolving gaseous carbon dioxide in the separated liquid to obtain the dissolved liquid. The method for culturing microalgae according to claim 4, wherein the gaseous carbon dioxide is dissolved in the separated liquid by a method using a non-porous membrane or a method by pressure dissolution. The method for culturing microalgae according to claim 5, wherein the non-porous membrane is a polymer membrane. The method for cultivating microalgae according to any one of claims 4 to 6, wherein the gaseous carbon dioxide is dissolved in the separated liquid using exhaust gas containing carbon dioxide. The method for cultivating microalgae according to claim 7, 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 factory and a steel mill. The method for culturing microalgae according to any one of claims 1 to 8, 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 9, wherein the culture tank is a photobioreactor-type water tank. The method for culturing microalgae according to any one of claims 1 to 10, further comprising a mixing step of mixing water or an aqueous solution containing useful components other than a carbonate substance with the culture solution or the separated solution. A microalgae culture apparatus,
a culture tank containing a culture solution;
Separation means for removing the microalgae from the culture solution to obtain a separated solution;
a dissolving means for dissolving a carbonate substance in the separation liquid to obtain a solution;
An apparatus for culturing microalgae, comprising supply means for bringing the dissolution solution and the culture solution into contact with each other and supplying a carbon source to the culture solution. 13. The apparatus for cultivating microalgae according to claim 12, wherein the separating means is present in the culture tank. 13. The microalgae according to claim 12, wherein the separation means extracts a part of the culture solution from the culture tank and removes the microalgae to obtain the separated liquid, and is present outside the culture tank. culture equipment. The apparatus for culturing microalgae according to any one of claims 12 to 14, wherein said dissolving means is means for obtaining said solution by dissolving gaseous carbon dioxide in said separated liquid. The apparatus for culturing microalgae according to claim 15, wherein the gaseous carbon dioxide is dissolved in the separated liquid by a method using a non-porous membrane or a method by pressurized dissolution. The microalgae culture device according to claim 16, wherein the non-porous membrane is a polymer membrane. The apparatus for cultivating microalgae according to any one of claims 15 to 17, wherein the gaseous carbon dioxide is dissolved in the separated liquid by using exhaust gas containing carbon dioxide. 19. The apparatus for cultivating microalgae according to claim 18, wherein the exhaust gas is exhaust gas discharged from one or more selected from a coal-fired power plant, an incinerator, a cement factory and a steel mill. The microalgae culture apparatus according to any one of claims 12 to 19, 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 20, wherein the culture tank is a photobioreactor type water tank. The apparatus for culturing microalgae according to any one of claims 12 to 21, further comprising mixing means for mixing water or an aqueous solution containing useful components other than a carbonate substance with the culture solution or the separated solution.

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