JPWO1999050384A1 - Microalgae culture device - Google Patents

Abstract

(57) [Abstract] This invention relates to a closed dome-shaped, conical, or cylindrical culture device used for culturing microalgae, and a gas discharge device that can be moved freely within the device. The culture device basically consists of a transparent inner member (hemispherical dome, conical peripheral wall, or cylindrical peripheral wall), a transparent outer member, and a bottom that connects the lower ends of both members. A cylindrical opening is provided at the top of the outer member, and a gas inlet and culture solution outlet members are provided at the bottom. The gas discharge device basically consists of two opposing square substrates, a bubble inducer, and a discharge nozzle. This allows the culture solution to be stirred without mechanical stirring, and enables high-concentration culture.

Description

[Detailed Description of the Invention] Microalgae Cultivation Device Technical Field This invention relates to a dome-, cone-, or cylindrical-shaped cultivation device used for culturing photosynthetic organisms such as microalgae, and a gas discharge device movably mounted within the device that supplies gases necessary for cultivation to the culture solution and agitates the culture solution, or to a cultivation device that combines the cultivation device with a gas discharge device.

BACKGROUND ART Large-scale cultivation of microorganisms, including microalgae such as chlorella and spirulina, has been widely studied for the production of useful substances such as vitamins, amino acids, pigments, proteins, polysaccharides, and fatty acids, as well as for the treatment of carbon dioxide, which is considered one of the causes of global warming. Culture products based on the results of this research are commercially available.

Among these microorganisms, most algae absorb carbon dioxide and synthesize useful substances through photosynthesis. Because efficient algae cultivation is crucial, a culture device that allows for efficient photosynthesis is required. For this reason, existing culture devices are being improved and new ones are being developed.

Conventionally, various types of algae culture devices have been widely known, including culture ponds, raceway-type culture devices, tubular-type culture devices, and liquid film-forming culture devices. A culture pond is a type of device in which a culture pond or tank made of concrete is constructed outdoors, a culture solution is poured into the tank, and microalgae such as chlorella are cultivated in the tank using sunlight. However, this type of device requires a pond surface area of, for example, 3,000 ^m² , making it usually quite large.

Furthermore, when microalgae are cultivated using this method, the concentration of microalgae in the culture medium increases as the cultivation progresses, causing the medium to turn a deep green color and preventing sunlight from reaching the bottom of the pond. This phenomenon results in a problem of a decrease in the overall photosynthetic efficiency of the algae unless the microalgae cultivation concentration is reduced.

For this reason, the depth of the liquid cannot exceed 15 cm, and large amounts of land are required for mass cultivation of microalgae. Furthermore, because the concentration of the culture medium cannot be increased, the problem of harvesting the culture medium from the liquid arises: the culture medium must be harvested from a vast amount of low-concentration culture medium.

On the other hand, the culture pond must be agitated to facilitate photosynthesis of the microalgae, but a large amount of energy is required to agitate the large volume of low-concentration liquid.

Furthermore, because the culture ponds are outdoors and open, dust, debris, and other contaminants can easily get into the liquid. Airborne microorganisms and other algae can also get into the ponds and multiply, making it difficult to obtain high-purity, high-quality cultures.

Furthermore, because culture ponds are outdoors, their temperature fluctuates with the weather, making it extremely difficult to maintain a constant temperature. In particular, depending on the region, the temperature can drop too low in winter.

For these reasons, the disadvantage of using ponds to cultivate algae is that it is only suitable for Chlorella, Spirulina, and Dunaliella, which can grow under special conditions such as high pH and high salinity.

A raceway-type culture device divides the interior of a culture tank with baffles, creating a nutrient circulation path. Algae are cultivated by circulating the nutrient through this circulation path using a circulation device. While this method is an improvement over the culture pond method, as with the culture pond method, the algae's photosynthetic rate declines as the culture progresses, resulting in inefficient light utilization. This also creates the problem of low carbon dioxide utilization efficiency. To achieve efficient light utilization, proposals have been made to irradiate the liquid with sunlight via optical fiber. (Japanese Utility Model Application Publication No. 5-43900) However, when culturing algae using this method, mechanical agitation is required to circulate the liquid, which inevitably leads to cell destruction and shear stress (a phenomenon in which algae are broken by shear stress, reducing cell activity and slowing growth).

A tubular culture device is a device for cultivating microalgae and other organisms using a culture tank made of light-transmitting tubes. Cultivating algae using this device prevents contamination of the culture medium with bacteria and allows for high culture concentrations, making it an extremely advantageous method for separating algae from the culture medium and recovering useful substances produced by the algae.

However, when algae are cultivated for a long period of time, the algae adhere to the inner walls of the tubes, dramatically reducing the amount of light that passes through. This phenomenon makes efficient microalgae cultivation difficult, and it is not easy to remove the algae that has adhered to the inner walls of the tubes.

To address these issues, a method has been proposed in which cleaning balls are inserted into the tube and constantly circulated along with the culture solution to clean the inner walls of the tube (Japanese Patent Publication No. 6-90739). However, this method does not consistently remove dirt and algae from the inner walls of the tube, and it requires the balls to be collected and cleaned, as well as constantly circulating them through the tube. Another problem with this method of culturing algae is that because the culture is performed inside the tube, oxygen gas released by the algae during photosynthesis remains within the tube, and this oxygen can actually inhibit photosynthesis (photosynthesis inhibition). Therefore, various devices have been proposed to reduce the adverse effects of oxygen produced by photosynthesis on the culture. (JP Patent Publication No. 9-121835) The liquid film-forming culture device is a device that attaches a light-transmitting dome-shaped lid to the top of a culture tank. Culture medium is sprayed from below onto the inner surface of the dome-shaped lid's top, forming a liquid film of culture medium on the inside of the lid. This liquid film is then irradiated with light. (JP Patent Publication No. 8-38159) However, this proposed method requires a circulation pump to maintain liquid film formation, is not suitable for large-scale culture, and has other problems, such as being unable to utilize sunlight.

Because microalgae accumulate useful substances in their bodies through photosynthesis, a major challenge is how to efficiently allow microalgae to photosynthesize. Potential factors for efficient photosynthesis include increasing the light-receiving area of the culture device, efficiently stirring the culture solution, adjusting the thickness or depth of the culture solution, making it easy to remove and clean microalgae that adhere to the interior surfaces of the culture device, temperature control, and preventing the intrusion of bacteria, other microalgae, and other contaminants.

The issue of the light-receiving area depends on how large the light-receiving area is and how efficiently the light is directed to the culture solution.

For example, in the case of a culture tank or pond, the surface area is determined by the surface of the tank or pond, so increasing the surface area can only be achieved by increasing the size of the tank or pond; there is no alternative.

Agitation of the culture solution is essential for uniform exposure to light, and is usually achieved by, for example, stirring or moving the solution with a pump, or by mechanical agitation in a tank or pond.

However, such mechanical agitation is undesirable because it can cause cell destruction and shear stress in the microalgae.

Because photosynthetic rates vary depending on the type of microalgae, the depth of the culture solution must be adjusted depending on whether the algae is slow or fast, and also depending on the desired culture concentration. Thus, the thickness or depth of the culture solution must be freely adjustable depending on the conditions, such as the type of microalgae and the desired culture concentration.

Removing and cleaning microalgae that adhere to the interior surfaces of cultivation equipment is not a major problem in open-type cultivation ponds or culture tanks used outdoors. However, in closed cultivation equipment, the adhered microalgae block light, making this removal and cleaning necessary. Furthermore, once cultivation is complete, the equipment must be designed so that the interior surfaces can be easily cleaned and the adhesions removed in order to prepare for the next cultivation.

Temperature control is extremely important, especially in closed systems, because the temperature of the culture medium can rise too high in the summer, causing problems with the culture. One solution to this problem is to add cold water to the culture medium, but this dilutes the medium, and large volumes of diluted medium must be handled in the next step, culture harvesting. This makes this method industrially disadvantageous.

Furthermore, culture devices are typically either designed for outdoor use or for indoor use. Therefore, using outdoor devices indoors can result in low light utilization efficiency, while indoor devices cannot be used outdoors. This has created a need for a simple culture device that can be used indoors or outdoors under standard culture conditions.

Agitation of the culture medium is an essential operation for uniform cultivation.

This is because the culture rate differs between the surface and deeper layers of the liquid medium, so gases such as air and carbon dioxide must be distributed evenly throughout the liquid medium (i.e., the culture solution). Light must be distributed evenly to the microalgae being cultured. Microalgae that tend to form colonies during culture must be prevented from settling and accumulating at the bottom, and must be redispersed throughout the culture solution.

This culture solution must be constantly stirred and supplied with air or carbon dioxide.

Therefore, the present invention aims to provide a closed-type microalgae culture device that overcomes the drawbacks of conventional open-type or closed-type culture devices. The culture device can be dome-shaped, conical, or cylindrical, and offers the following advantages: no contamination by bacteria or other contaminants; easy temperature control of the culture solution; agitation of the culture solution without mechanical stirring prevents destruction of algae cells or shear stress; high culture concentration; easy cleaning of the device; no inhibition of culture by oxygen generated; and high light utilization efficiency.

Another object of the present invention is to provide a gas discharge device for use in a culture apparatus. When this device is used to supply the necessary gas to the culture solution, the device moves and agitates the solution, and the discharged gas also agitates the solution, resulting in excellent contact between the supplied gas and the culture solution, thereby improving culture efficiency.

Furthermore, the present invention relates to a culture apparatus characterized by combining the above-mentioned culture apparatus with a gas discharge device.

Disclosure of the Invention The microalgae culture device of the present invention is a culture device selected from the group consisting of a dome-shaped, conical, and cylindrical shape. The dome-shaped culture device comprises an outer hemispherical dome made of a transparent material, an inner hemispherical dome made of a transparent material, and a bottom connecting the lower ends of the domes. The outer hemispherical dome has a cylindrical opening at the top, and the bottom is equipped with an air and/or carbon dioxide inlet and a culture solution outlet. If necessary, a water sprinkler is provided on the outside of the cylindrical opening, and a water sprinkler receiver is provided around the periphery of the bottom. The conical culture device comprises an outer conical wall made of a transparent material, an inner conical wall made of a transparent material, and a bottom connecting the lower ends of the two walls. The outer conical wall has a cylindrical opening at its top, and the bottom is equipped with an air and/or carbon dioxide gas inlet and a culture medium outlet. If necessary, a water sprinkler is provided on the outside of the cylindrical opening, and a water sprinkler receiver is provided on the outer periphery of the bottom. The cylindrical culture device also comprises an outer cylindrical wall having an upper wall made of a transparent material, an inner cylindrical wall having an upper wall made of a transparent material, and a bottom connecting the lower ends of the two walls. The outer cylindrical wall has a cylindrical opening at its center, and the bottom is equipped with an air and/or carbon dioxide gas inlet and a culture medium outlet. If necessary, a water sprinkler is provided on the outside of the cylindrical opening, and a water sprinkler receiver is provided on the outer periphery of the bottom.

A gas discharge device for use in a microalgae culture system comprises two opposing rectangular substrates, a downwardly open bubble inducer with a U-shaped or inverted U-shaped cross section, and a discharge nozzle. The bubble inducer is inclined relative to the upper surface of the rectangular substrate, and the inclined wall on the upper surface of the bubble inducer is bent at its upper end almost horizontally to form an extending upper wall. The bubble inducer has side walls hanging down from both ends of the inclined wall and the upper wall, and the lower ends of both walls are joined to the upper surface of the rectangular substrate. The discharge nozzle is rotatably attached through a through-hole drilled in the lower portion of the inclined wall. If necessary, at least one of the opposing rectangular substrates is bent in the same direction near its front and/or rear end, and at least one of the rectangular substrates is provided with a weight adjustment means.

The present invention also provides a culture device comprising the above-described culture device and a gas discharge device in combination.

Any transparent material that is transparent, light-transmitting, weather-resistant, and UV-resistant can be used for the culture device. Examples include acrylic resin, polycarbonate, polypropylene, polyethylene, polyvinyl chloride, and glass. However, synthetic resins are preferred for their ease of processing, and acrylic resins are particularly preferred due to their properties.

The gas introduced into the culture system must contain carbon dioxide. However, air may be mixed with carbon dioxide to increase the carbon dioxide concentration, or air and carbon dioxide may be introduced into the system separately.

Carbon dioxide is best used in combination with air. As the carbon dioxide-mixed air rises through the culture solution while stirring, the carbon dioxide is dispersed and absorbed into the solution, while the air acts to remove oxygen generated by the culture from the solution. However, if carbon dioxide is introduced alone into the culture solution, the rate of introduction is low, which inevitably slows the rate at which carbon dioxide diffuses into the solution.

The cylindrical opening functions to release air injected into the culture medium, unused carbon dioxide, and generated oxygen into the atmosphere. However, open openings are prone to the ingress of dust and other contaminants. To prevent the ingress of such substances, it is preferable to install a filter element over the opening or to install a cover element over the opening that functions similarly to a filter element.

This opening may be molded integrally with the upper wall of the outer hemispherical dome, outer conical wall, or outer cylindrical wall, or it may be molded separately and then attached.

The dome-, conical-, or cylindrical-shaped culture device used as the main body of the culture device may have an outer and inner component formed as a single unit, or one may be formed as a single unit and the other may be assembled from appropriately divided components, such as two or four pieces, or both may be assembled from divided components. The method of construction of the culture device can be determined based on the size and shape of the culture device.

Furthermore, the water receiver may be made of any material and structure, including metal and plastic, as long as it can receive the water flowing down the outer surface of the device.

The trickle receiver may be formed separately from the culture device body, or may be formed by extending the lower end of the outer culture device member horizontally around the periphery and bending the tip upward, or may be formed by extending the lower end of the inner culture device member horizontally around the periphery and bending the tip upward.

Preferably, the water receiver is made of a separate component molded from the main body of the culture device.

The air and/or carbon dioxide gas introducing member provided at the bottom may be a tubular member having a large number of gas discharge holes formed therein, or may be a member having gas discharge holes formed at the bottom.

The gas introduced into the culture medium through this introduction element agitates the medium as it rises through the medium, eliminating the need for mechanical agitation. This method therefore prevents cell destruction and shear stress caused by mechanical agitation.

Furthermore, as the gas level rises, oxygen gas produced by photosynthesis can be released more efficiently and quickly from the culture solution.

There are two methods for supplying the culture medium to the culture device. One is to provide a supply member (e.g., a supply hole) at the bottom and supply the culture medium through this supply member.

The second method is to supply the culture medium through a cylindrical opening at the top.

Providing various supply and introduction components to the device increases the complexity of the device, and at the same time, contamination problems arise when attempting to change the type of microalgae being cultivated.

Therefore, the second method is the most preferred.

Both the inner and outer components of the culture device are made of transparent materials. By providing an artificial light source inside the device, outdoor cultivation is possible even at night. In indoor cultivation, efficient continuous cultivation can be achieved by using two artificial light sources, one inside and one outside the device.

The dome-shaped culture device has a small footprint but a large surface area, resulting in a large light-receiving area. Furthermore, this device provides excellent agitation of the culture medium.

Furthermore, when this device is made of plastic, it can be easily formed by vacuum forming and is the most inexpensive to manufacture.

For these reasons, a dome-shaped culture device is the most preferred microalgae culture device.

In order to control and monitor the culture conditions, it is preferable to provide the culture device with various sensors such as a temperature sensor, a liquid level sensor, a pH sensor, and a dissolved oxygen sensor. These sensors are provided through the cylindrical opening or the outer wall of the device.

The gas discharge device of the present invention discharges gas, such as air, diagonally downward toward the bottom of the culture device, causing the algae to hop forward inside the device like a frog. This action vigorously agitates the culture solution, and the released gas also agitates the culture solution as it rises. In particular, if the microalgae being cultured tend to form colonies, the gas discharged from the gas discharge device destroys the colonies, dispersing the microalgae throughout the culture solution and improving culture efficiency.

The gas discharge device is usually made of plastic, and a weight adjustment means is provided to adjust the weight of the device.

Microalgae that can be cultured using the culture device of the present invention include not only the commercially successful Chlorella, Spirulina, and Dunaliella, but also a variety of other microalgae. Examples include highly valuable microalgae that produce useful substances, such as Haematococcus pluviaris, which produces β-ketocarotenoids (astaxanthin), Isocrysis galvana, which is used as live feed for marine fish farming and produces polyunsaturated fatty acids (DHA), and Nannochloropsis oculata, which is also used as live feed for marine fish farming and produces polyunsaturated fatty acids (EPA). The culture device of the present invention allows these microalgae to be cultured at high concentrations with high light utilization efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a dome-shaped culture device of the present invention. Figure 2 is a partial schematic diagram showing the state of culture using the dome-shaped culture device shown in Figure 1. Figure 3 is a front view of the dome-shaped culture device shown in Figure 1. Figure 4 is an explanatory diagram showing a mass culture system for microalgae using the dome-shaped culture device shown in Figures 1-3. Figure 5 is a cross-sectional view of a conical culture device of the present invention. Figure 6 is a front view of the conical culture device of Figure 5. Figure 7 is a cross-sectional view of a cylindrical culture device of the present invention. Figure 8 is a front view of the cylindrical culture device of Figure 7. Figure 9 is a perspective view of a gas discharge device. Figure 10 is a side view of the gas discharge device of Figure 9. Figure 11 is a plan view of the gas discharge device of Figure 9. Figure 12 is a cross-sectional view of the gas discharge device of Figure 9, Figure 13 is an enlarged cross-sectional view of the discharge nozzle of the gas discharge device of Figure 9, Figure 14 is a cross-sectional explanatory diagram showing the state when the gas discharge device discharges gas into the culture solution, Figure 15 is a cross-sectional explanatory diagram of a culture device combining a dome-shaped culture device itself with a gas discharge device, Figure 16 is a partially cut-away top view of Figure 15, Figure 17 is a cross-sectional explanatory diagram of a culture device combining a conical-shaped culture device itself with a gas discharge device, Figure 18 is a cross-sectional explanatory diagram of a culture device combining a cylindrical-shaped culture device itself with a gas discharge device, Figure 19 is a perspective view showing another example of the gas discharge device of the present invention, Figure 20 is a perspective view showing another example of the gas discharge device of the present invention, Figure 21 is a perspective view showing yet another example of the gas discharge device of the present invention, Figure 22 is a cross-sectional view taken along the X-X' line in Figure 21.

BEST MODE FOR CARRYING OUT THE INVENTION To explain the present invention in more detail, the incubation device and gas discharge device of the present invention will be described with reference to the accompanying drawings.

1 to 3 show a dome-shaped culture device 1.

Figure 3 is a front view of the dome-shaped culture apparatus 1. A cylindrical opening 4 is provided at the top of the outer hemispherical dome 8. A sprinkler member 3 for cooling the dome 8 is provided outside the cylindrical opening 4. A sprinkler receiver 11 for water sprinkled from the sprinkler member 3 is provided below the dome 8. The apparatus 1 is supported by multiple fixing members 16. A gas inlet member 6 and a culture medium outlet member 7 are attached to the bottom 14 of the culture apparatus.

Figure 1 is a cross-sectional view of the apparatus 1. The apparatus 1 is composed of an outer hemispherical dome 8, an inner hemispherical dome 9, and a base 14 connecting the lower ends of the two domes. A separate cylindrical opening 4 is provided at the top of the dome 8, and a sprinkler member 3 is provided outside the cylindrical opening 4. Cooling water 15 is sprinkled onto the surface of the dome 8 from the sprinkler member 3, and falls down to a sprinkler receiver 11 while covering the surface of the dome 8 in the form of a film.

The temperature of the culture solution 5 is controlled by this cooling water 15 (see FIG. 2).

The domes 8, 9, bottom 14, cylindrical opening 4, and trickle receptacle 11 are each made of a transparent material. An acrylic resin is typically used as the transparent material. Metal materials such as stainless steel can also be conveniently used for the trickle receptacle 11. The cooling water drains from the trickle receptacle 11 through a drainage member (not shown). The drained water is stored and reused as cooling water.

A gas inlet member 6 for supplying air and/or carbon dioxide to the culture solution 5 and an outlet member 7 for removing the culture solution 5 from the culture device 1 are attached to the bottom 14. A plurality of gas inlet pipes 10 with multiple inlets drilled on the upper surface of the bottom 14 are arranged on the upper surface of the bottom 14 and constitute part of the gas inlet member 6. The gas supplied by the gas inlet member 6 is preferably air mixed with carbon dioxide, but air alone may also be used.

An artificial light source 2 is installed inside the inner hemispherical dome. This allows microalgae to photosynthesize even during outdoor cultivation at night. Furthermore, for indoor cultivation, photosynthesis can be performed using artificial light sources simultaneously from both the inside and outside of the cultivation device, allowing for greater depth or thickness of the culture solution.

Figure 2 shows a schematic diagram of the culture process. Gas bubbles 12 released into the culture solution 5 from the gas injection pipe 10 rise through the culture solution 5 along the inner wall of the outer hemispherical dome 8 due to their buoyancy. This upward movement of the bubbles 12 promotes the upward movement of the culture solution, and carbon dioxide contained in the bubbles 12 is supplied to the culture solution. Oxygen generated by photosynthesis of the microalgae is absorbed by the bubbles 12. The bubbles 12 are released into the atmosphere at the surface of the culture solution. The culture solution flow 17 that rose along the inner wall of the dome 8 descends along the wall of the inner hemispherical dome 9.

In this way, gases such as air supplied to the culture solution from near the bottom not only supply carbon dioxide to the culture solution, but also absorb the oxygen gas that is generated and release it into the atmosphere, while simultaneously agitating the culture solution uniformly.

In summer, if the temperature of the culture medium rises too high and cultivation becomes difficult, cooling water 15 can be supplied from the sprinkler member 3 onto the surface of the outer hemispherical dome 8 to regulate the temperature of the culture medium. The water used for cooling is collected via the sprinkler receiver 11 and reused.

In the case of outdoor cultivation, if cultivation is to be continued at night, continuous cultivation for 24 hours can be achieved by using an artificial light source 2 provided in the inner space of the inner hemispherical dome 9.

During the day, microalgae actively photosynthesize in the sunlight and grow, producing and accumulating useful substances such as proteins, polysaccharides, fatty acids, pigments, and vitamins. However, at night, such photosynthesis does not occur, and the substances synthesized during the day are lost due to the microalgae's own energy consumption. In summer, for example, up to about 20% of the weight of the algae body is lost compared to daytime, resulting in a significant loss.

To prevent this loss, artificial light sources can be used to stimulate photosynthesis and compensate for this loss. Therefore, an artificial light source with enough light to stimulate minimal photosynthesis is sufficient, but more light than this is acceptable. Examples of artificial light sources include fluorescent lamps, incandescent lamps, and halogen lamps.

For indoor cultivation, artificial light sources can be used both inside and outside the cultivation device 1. Using artificial light source 2 in this way enables efficient continuous cultivation 24 hours a day.

To monitor the culture status, it is necessary to constantly measure the temperature, liquid level, pH, and dissolved oxygen (DO) of the culture medium and maintain these values within optimal ranges. Therefore, it is desirable to attach these sensors to the device, preferably through the cylindrical opening 4 at the top, or through either dome 8 or dome 9, or both. Since dome installation increases the device's complexity and makes cleaning more difficult, installation through the cylindrical opening 4 is most preferable.

This dome-shaped culture device 1 can be freely combined with two types of hemispherical domes with different radii to change the volume of the space formed between the two domes and the distance between the domes. This means that the volume of culture medium and the thickness or depth of the culture medium can be freely set.

Furthermore, because microalgae adhere to the surfaces of the device that come into contact with the culture medium, when removing and cleaning this adhesion, the outer hemispherical dome 8 of the two hemispherical domes can be removed and washed separately, or both can be removed and washed in separate locations.

It is very convenient to assemble the outer hemispherical dome in two separate pieces. In any case, the two domes do not have to be molded as a single unit; they can be molded in multiple separate pieces and then assembled.

The hemispherical dome shape may be a hemispherical dome formed by cutting a sphere at an appropriate position, but from the standpoint of light utilization efficiency and light reception, a hemispherical shape is most preferable.

Furthermore, the present invention is not limited to spherical shapes, but also encompasses deformed spherical shapes such as oval shapes.

Dome sizes can range from about 50 cm to 200 cm in diameter, but the appropriate size can be selected as the culture device depending on the type of microalgae to be cultured, the culture conditions, and the purpose of the culture.

The distance between the two domes depends on the type of microalgae, the cultivation conditions, and the purpose of cultivation, but should be set so as to obtain maximum photosynthetic efficiency. Generally, it is preferably 2.5 to 10 cm, and more preferably about 5 cm.

Next, a dome-shaped culture device 1 was assembled, consisting of an outer hemispherical dome 8 with a radius of approximately 50 cm and an inner hemispherical dome with a radius of approximately 45 cm, with a dome-to-dome distance of 5 cm. At the top of the dome 8, a cylindrical opening 4 with a diameter of 6 cm was formed separately from the dome 8.

When the microalga Spirulina platensis was cultivated using this culture device, a culture concentration of 10-20 g/L and a productivity of 2.0-5.0 g/L/day were achieved. In contrast, the conventional culture pond method achieved a culture concentration of 0.3-0.5 g/L and a productivity of 0.1-0.2 g/L/day. This demonstrated an approximately 10-fold improvement in productivity compared to conventional cultivation methods.

Additionally, in the cultivation of Haematococcus pluvialis, which produces the red pigment astaxanthin, it was found possible to produce algal biomass containing astaxanthin at a high concentration of 4% to 8% by culturing at a concentration of 5-10 g/L. Cultivating this red pigment-producing Haematococcus pluvialis is extremely difficult using conventional pond culture methods. Furthermore, the marine alga Nannochloropsis oculata was also successfully cultivated at a concentration of approximately 5-10 g/L, compared with a conventional method limit of 0.2-0.4 g/L.

Figure 4 shows a system for simultaneously culturing large quantities of microalgae by arranging multiple closed outdoor cultivation devices according to the present invention. Each device may contain the same type of microalgae for cultivation simultaneously, or different types of microalgae may be cultivated separately. Each device is equipped with various sensors to control the cultivation conditions.

This is extremely effective because it allows for independent control of the various culture conditions of each device, even if the types of microalgae being cultured in each device are different.

Furthermore, even if individual devices are arranged relatively densely, the light utilization rate or the light receiving area per occupied area is large, making it very convenient, suitable for large-scale culture, and extremely productive.

5 and 6 show a conical shaped culture device 21.

FIG. 6 is a front view of the conical culture device 21. The outer conical peripheral wall 28 is made of a transparent material and has a cylindrical opening 24 at the top. A sprinkler member 23 for cooling the peripheral wall 28 is provided outside the opening 24. A sprinkler receiver 31 for cooling water sprinkled from the sprinkler member 23 is provided at the bottom of the peripheral wall 28. The device 21 is supported by multiple fixing members 36.

A gas inlet member 26 and a culture medium outlet member 27 are attached to the bottom 14 of the device 21.

Figure 5 is a cross-sectional view of the device 21. The device 21 is composed of an outer conical peripheral wall 28 made of a transparent material, an inner conical peripheral wall 29 also made of a transparent material, and a bottom 34 connecting the lower ends of both peripheral walls. A cylindrical opening 24 is provided separately at the top of the outer conical peripheral wall 28, and a sprinkler member 23 is provided outside the opening 24. Cooling water is sprinkled from the sprinkler member 23 onto the surface of the peripheral wall 28, covering the surface of the peripheral wall 28 as a film, and then falls to the sprinkler receiver 31. The temperature of the culture medium 25 is controlled by the cooling water.

The peripheral wall 28, the peripheral wall 29, the bottom 34, the cylindrical opening 24, and the water spray receiver 31 are each made of a transparent material such as acrylic resin.

The cooling water is drained from the water spray receiver 31 through a drain member (not shown).

Attached to the bottom 34 are a gas inlet 26 for supplying air and/or carbon dioxide to the culture solution 25 and an outlet 27 for removing the culture solution 25 from the device 21. A plurality of gas inlet pipes 30 with multiple gas inlets drilled into their upper surfaces are located on the upper surface of the bottom 14, forming part of the gas inlet 26. Furthermore, an artificial light source 22 is provided in the interior space of the peripheral wall 29, allowing continuous photosynthesis during outdoor cultivation at night.

7 and 8 show a cylindrical culture device 41.

Figure 8 is a front view of a cylindrical culture device 41. The outer cylindrical peripheral wall 48 has a top wall 57 made of a transparent material. A cylindrical opening 44 is provided near the center of the top wall. A sprinkler member 43 for cooling the top wall 57 and peripheral wall 48 is provided outside the opening 44. A sprinkler receiver 51 for cooling water sprinkled from the sprinkler member 43 is provided at the bottom of the peripheral wall 48. The device 41 is supported by multiple fixing members 56.

A gas inlet member 46 and a culture medium outlet member 47 are attached to the bottom 54 of the device 41.

Figure 7 is a cross-sectional view of the device 41. The device 41 is composed of an outer cylindrical peripheral wall 48 having an upper wall 57, an inner cylindrical peripheral wall 49 having an upper wall 58, and a bottom 54 connecting the lower ends of the two peripheral walls. A cylindrical opening 44 is integrally formed near the center of the upper wall 57, and a sprinkler member 43 is provided outside the opening 44. Cooling water is sprinkled from the sprinkler member 43 onto the upper wall 57, forming a film that covers the surface of the peripheral wall 48, and reaches the sprinkler receiver 51.

The temperature of the culture solution 45 is controlled by cooling water.

The peripheral wall 48, the peripheral wall 49, the upper wall 57, the upper wall 58, the cylindrical opening 44, and the water spray receiver 51 are each made of a transparent material such as acrylic resin.

Cooling water is drained from the trickle receiver 51 through a drainage member (not shown). A gas inlet member 46 for supplying gas to the culture solution and a drainage member 47 for removing the culture solution 45 from the device 41 are attached to the bottom 54. A plurality of gas inlet pipes 50 with multiple gas inlets drilled into their upper surfaces are arranged on the upper surface of the bottom 54, forming part of the gas inlet member 46.

Furthermore, an artificial light source 42 is provided in the inner space formed by the upper wall 58 and the peripheral wall 49, allowing photosynthesis to occur even at night.

9-12 show a perspective view, a side view, a plan view, and a cross-sectional view, respectively, of the gas delivery device 100, and FIG. 13 shows an enlarged cross-sectional view of the delivery nozzle of the gas delivery device.

Gas discharge device 100 consists of opposing rectangular substrates 101, 101', a bubble guide member 102 with a U-shaped cross section that opens downward, and a discharge nozzle 103. Bubble guide member 102 is inclined relative to the upper surfaces 107, 107' of the rectangular substrates, and has an inclined wall 104 on its upper surface, an upper wall 105 whose upper end extends approximately horizontally, and side walls 106, 106' depending from both ends of inclined wall 104 and upper wall 105, with the lower ends of both side walls 106, 106' joined to the upper surfaces 107, 107' of both rectangular substrates 101, 101'. Both substrates are fixed by fixing members 108, 108'.

The discharge nozzle 103 is rotatably provided through a through-hole 109 drilled in the lower part of the inclined wall 104. To prevent the nozzle 103 from slipping out of the through-hole 109, stoppers 110 and 110' are provided on the outer periphery of the nozzle 103 at opposing positions across the through-hole 109.

Whether the culture device body is dome-shaped, triangular pyramidal, or cylindrical, the inner and outer edges of its bottom are concentric circles, creating a circular shape with a circular hole cut out from the center of the plate. To facilitate easy movement of this hollowed-out circular bottom, the leading and trailing ends of the rectangular base plates 101, 101' are bent in the same direction, as shown in Figure 11.

The angle of inclination of the inclined wall 104 with respect to the upper surface of the square substrate should be designed to be 45° to 60°.

FIG. 14 is an explanatory diagram showing the state when gas is discharged into the culture solution by the gas discharge device.

Gas, such as air or air mixed with carbon dioxide, travels from a gas supply device (not shown) installed separately from the culture device through a gas inlet pipe 111 to an outlet nozzle 103 and is released from its tip toward the bottom 112 of the culture device. After hitting the bottom 112, the released gas 113 turns into bubbles 114 and rises along the inside of the bubble guide member 102, i.e., along the inclined wall 104 and upper wall 105, and is discharged from the edge of the upper wall 105 into the culture solution 115. The discharged bubbles 114 rise through the solution and are released into the atmosphere at the surface of the culture solution. While the gas is in contact with the culture solution, carbon dioxide is absorbed into the culture solution, while oxygen, generated by algae photosynthesis and dissolved in the culture solution as bubbles, is absorbed into the gas. As the bubbles 114 rise through the culture solution, they simultaneously push the liquid upward, generating convection currents in the liquid.

The gas and bubbles 114 released from the tip of the discharge nozzle 103 create buoyancy within the gas discharge device itself, generating a propulsive force in the direction indicated by the arrow. This causes the gas discharge device 100 to move in a floating state in the direction indicated by the arrow. As it moves, the device 100 repeatedly lands on the bottom due to its own weight, then floats up and moves forward, resulting in significant agitation of the culture medium. The movement of this gas discharge device in the culture medium is similar to the movement of a frog hopping forward.

The components that make up gas discharge device 100 are typically plastic. However, since plastic itself is often quite light and buoyant in the culture medium, they are often molded to add a heavy filler to give them a certain amount of weight. Alternatively, they may be molded to resemble artificial stone by laminating rock powder or filler powder bonded to rectangular substrates 101, 101' with synthetic resin such as epoxy resin. Alternatively, rectangular substrates 101, 101' may have their lower portions made of an artificial stone-like material and their upper portions made of plastic. Alternatively, metal weights such as lead may be attached and detached to any desired locations on the opposing surfaces of rectangular substrates 101, 101' to adjust the overall weight of gas discharge device 3. The most preferable configuration is one that allows for adjustment of the overall weight.

FIG. 15 is a cross-sectional view of a culture device 150 formed by combining a gas discharge device 100' and a dome-shaped culture device main body 151, and FIG. 16 is a top view thereof, with a portion cut away.

Here, the culture device body 151 comprises an outer hemispherical dome 153, an inner hemispherical dome 152, and a bottom 154 connecting the lower ends of the two domes. A cylindrical opening 155 is provided at the top of the dome 153; other components are not shown.

All of these materials are transparent materials, such as acrylic resin.

The gas discharge device 100′, to which the gas inlet pipe 157 is connected, is inserted through the cylindrical opening 155 of the culture device main body 151 and placed on the bottom 154.

The gas introduction pipe 157 is made of a material such as polyurethane, silicone, or synthetic rubber, and is in contact with the surface of the inner hemispherical dome 152.

When a gas such as air is supplied to the gas discharge device 100', the device 100' moves forward in the direction of the arrow while splashing through the culture solution. At this time, the culture solution is sufficiently agitated by the discharged gas and the movement of the gas discharge device.

As the gas discharge device 100' advances over the annular bottom 154, the gas inlet pipe 157 connected thereto, as shown in FIG. 16, scrubs, i.e., cleans, the surface of the inner hemispherical dome 152 as the device 100' moves circularly over the bottom 154. In other words, the gas inlet pipe 157 scrubs, i.e., cleans, the surface of the dome 152 as the device 100' moves circularly over the bottom 154. In other words, the gas inlet pipe 157 prevents algae from adhering to the surface of the dome 152 and also cleans the surface.

Furthermore, since the gas discharge device 100' moves the culture solution 156 while stirring it, any algae that form colonies are destroyed and dispersed again in the culture solution, resulting in extremely efficient culture.

During this process, the gas inlet tube becomes twisted. However, as shown in Figure 13, the discharge nozzle is rotatable, so the nozzle rotates within the through-hole, eliminating the twist.

FIG. 17 is an explanatory cross-sectional view of a culture device 160 formed by combining a gas discharge device 100″ and a conical culture device main body 161.

Here, the culture device body 161 comprises an outer conical peripheral wall 163 made of a transparent material, an inner conical peripheral wall 162 made of a transparent material, and a bottom 164 connecting the lower ends of the two peripheral walls, and a cylindrical opening 165 made of a transparent material is provided at the top of the peripheral wall 163. Other components are not shown here.

The gas discharge device 100″ connected to the gas inlet pipe 167 is inserted through the cylindrical opening 165 and placed on the bottom 164.

When a gas such as air is supplied to the gas discharge device 100", the device 100" repeats forward movement while splashing through the culture solution. This movement is as described for the culture device in Figures 15 and 16.

FIG. 18 is a cross-sectional view of a culture device 170 formed by combining a gas discharge device 100''' and a cylindrical culture device main body 171.

Here, the culture device body 171 comprises an outer cylindrical peripheral wall 173 having an upper wall made of a transparent material, an inner cylindrical peripheral wall 172 having an upper wall made of a transparent material, and a bottom 174 connecting the lower ends of both peripheral walls. A cylindrical opening 175 made of a transparent material is provided in the center of the upper wall of the outer cylindrical peripheral wall 173. Other components are not shown here.

Gas discharge device 100''' connected to gas inlet pipe 177 is inserted through cylindrical opening 175 and placed on bottom 174.

When a gas such as air is supplied to the gas discharge device 100''', the device 100''' repeatedly moves forward while hopping through the culture medium. This movement is as described for the culture device in Figures 15 and 16.

FIG. 19 is a perspective view showing another embodiment of the gas discharge device of the present invention.

This gas discharge device 200 differs from the gas discharge device 100 shown in Figure 9 in that, of the opposing rectangular substrates 201 and 201', one rectangular substrate 201 is shorter than the other rectangular substrate 201' and its leading and trailing ends are not bent, but otherwise is the same. Also, 202 denotes a bubble guide member, 203 denotes a discharge nozzle, 211 denotes a gas introduction pipe, 201 and 201' denote rectangular substrates, 204 denotes an inclined wall, 205 denotes an upper wall, 206 denotes a side wall, 207 and 207' denote upper surfaces, and 208 and 208' denote fixing members.

In addition, weights (not shown) serving as weight adjustment means are detachably attached to the rectangular base plates 201 and 201'.

FIG. 20 is a perspective view showing another embodiment of the gas discharge device of the present invention.

This gas discharge device 300 differs from the gas discharge device 100 shown in Figure 9 in that the leading and trailing ends of the opposing rectangular substrates 301, 301' are not bent, but are otherwise the same. Also, 302 denotes a bubble guide member, 303 denotes a discharge nozzle, 311 denotes a gas introduction pipe, 301, 301' denote rectangular substrates, 304 denotes an inclined wall, 305 denotes an upper wall, 306 denotes a side wall, 307, 307' denote upper surfaces of the rectangular substrates, and 308, 308' denote fixing members.

In addition, weights (not shown) serving as weight adjustment means are detachably attached to the rectangular base plates 301 and 301'.

Figure 21 is a perspective view showing yet another embodiment of the gas discharge device of the present invention. Figure 22 shows a cross-sectional view of the gas discharge device shown in Figure 21 taken along line X-X'.

This gas discharge device 400 comprises opposing rectangular base plates 401, 401', a V-shaped bubble guide member 402 with an inverted U-shaped cross section that opens downward, and a discharge nozzle 403 connected to a gas inlet pipe 411. The bubble guide member 402 is inclined relative to the upper surfaces 407, 407' of the rectangular base plate, and has a semicircular inclined wall 404 on its upper surface, the upper end of which is bent almost horizontally while maintaining its semicircular shape to form an extending upper wall 405. The inverted U-shaped cross section has two side walls (composed of a side wall 406 and another side wall (not shown)) that hang down from the semicircular side end, and the lower ends of both side walls are joined to the upper surfaces 407, 407' of the rectangular base plate. The discharge nozzle 403 is rotatably mounted through a through-hole 409 bored in the semicircular top portion below the inclined wall 404 of the bubble guide member 402, which has an inverted U-shaped cross section. To prevent the discharge nozzle 403 from slipping out of the through-hole 409, two stoppers 410, 410' are provided on the outer periphery of the discharge nozzle 403 at opposing positions across the through-hole 409.

The ends formed by the top wall 405 and both side walls are open, and the rectangular substrates 401, 401′ are fixed by fixing members 408, 408′.

In this example, the two rectangular substrates are not bent at their leading and trailing ends, but the leading and trailing ends of the two rectangular substrates may be bent in the same direction, or only one rectangular substrate may be bent at its leading and/or trailing end.

In addition, weights (not shown) serving as weight adjustment means are detachably attached to the rectangular base plates 401 and 401'.

INDUSTRIAL APPLICABILITY As described above, the culture apparatus, gas discharge device, or culture apparatus combining the culture apparatus and gas discharge device according to the present invention is suitable for culturing microalgae at high concentrations, eliminating the need for mechanical stirring of the culture solution. Furthermore, by installing an artificial light source within the device's interior, continuous culture can be performed 24 hours a day outdoors, and indoors, light can be irradiated from both inside and outside the device, enabling continuous culture.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (18)

[Claims] 1. A microalgae culture device, the device being selected from the group consisting of a dome-shaped, conical, and cylindrical shape. The dome-shaped culture device comprises an outer hemispherical dome made of a transparent material, an inner hemispherical dome made of a transparent material, and a bottom connecting the lower ends of the two domes. The outer hemispherical dome has a cylindrical opening at the top, and the bottom is provided with an air and/or carbon dioxide inlet and a culture medium outlet. The cone-shaped culture device comprises an outer conical peripheral wall made of a transparent material, a transparent inner conical peripheral wall, and a bottom connecting the lower ends of the two peripheral walls. The outer conical peripheral wall has a cylindrical opening at the top, and the bottom is provided with an air and/or carbon dioxide inlet and a culture medium outlet. Alternatively, the cylindrical culture device may comprise an outer cylindrical peripheral wall having an upper wall made of a transparent material, an inner cylindrical peripheral wall having an upper wall made of a transparent material, and a bottom connecting the lower ends of both peripheral walls, the outer cylindrical peripheral wall having a cylindrical opening in the center of the upper wall, and the bottom having an air and/or carbon dioxide gas inlet member and a culture medium outlet member. 2. The culture device according to claim 1, wherein the culture device is dome-shaped. 3. The culture device according to claim 1, wherein the culture device has a conical shape. 4. The culture device according to claim 1, wherein the culture device has a cylindrical shape. 5. The culture device according to any one of claims 1 to 4, wherein the transparent material is an acrylic resin. 6. The culture device according to any one of claims 1 to 5, further comprising a water sprinkler member disposed on the outside of the cylindrical opening and a water sprinkler receiver disposed on the outer periphery of the bottom. 7. The culture device according to any one of claims 1 to 6, further comprising an artificial light source disposed within the interior space of the inner hemispherical dome, the inner conical wall, or the inner cylindrical wall. 8. A gas discharge device for use in a microalgae culture apparatus, the gas discharge device comprising two opposing rectangular base plates, a bubble inducing member with a U-shaped cross section and opening downward, and a discharge nozzle, the bubble inducing member being provided at an angle relative to the upper surfaces of the rectangular base plates, the inclined wall on the upper surface of the bubble inducing member being bent at its upper end to a substantially horizontal position to form an extending upper wall, the inclined wall having side walls hanging down from both ends of the inclined wall and the upper wall, the lower ends of both walls being joined to the upper surfaces of the rectangular base plates, and the discharge nozzle being rotatably attached through a through-hole drilled in the lower portion of the inclined wall. 9. A gas discharge device for use in a culture apparatus, comprising two opposing rectangular base plates, a bubble inducer member with an inverted U-shaped cross section that opens downward, and a discharge nozzle; the bubble inducer member is disposed at an angle relative to the upper surface of the rectangular base plate, and the upper end of the semicircular inclined wall on the bubble inducer member is bent approximately horizontally while maintaining its semicircular shape to form an extending upper wall; the bubble inducer has side walls that hang down from both ends of the inclined wall and the upper wall, and the lower ends of both walls are joined to the upper surface of the rectangular base plate; and the discharge nozzle is rotatably attached through a through-hole drilled in the lower part of the inclined wall. 10. A gas discharge device selected from claims 8 or 9, wherein at least one of two opposing rectangular substrates has a structure in which the leading end and/or the trailing end are bent in the same direction. 11. A gas discharge device selected from claims 8 through 10, characterized in that a weight adjustment means is provided on at least one of the two opposing rectangular base plates. 12. A microalgae culture device comprising a culture device main body and a gas discharge device, wherein the culture device main body is a dome-shaped, conical, or cylindrical culture device, wherein the dome-shaped culture device comprises an outer hemispherical dome made of a transparent material, an inner hemispherical dome made of a transparent material, and a bottom connecting the lower ends of the domes, wherein a cylindrical opening is provided at the top of the outer hemispherical dome and an air and/or carbon dioxide gas inlet and a culture medium outlet at the bottom, wherein the conical culture device comprises an outer conical peripheral wall made of a transparent material, an inner conical peripheral wall made of a transparent material, and a bottom connecting the lower ends of the outer conical peripheral wall, wherein a cylindrical opening is provided at the top of the outer conical peripheral wall and an air and/or carbon dioxide gas inlet and a culture medium outlet at the bottom, wherein a conical culture device comprises an outer conical peripheral wall made of a transparent material, an inner conical peripheral wall made of a transparent material, and a bottom connecting the lower ends of the outer conical peripheral wall, wherein a cylindrical opening is provided at the top of the outer conical peripheral wall and an air and/or carbon dioxide gas inlet and a culture medium outlet at the bottom, Alternatively, the cylindrical culture device may comprise an outer cylindrical peripheral wall having an upper wall made of a transparent material, an inner cylindrical peripheral wall having an upper wall made of a transparent material, and a bottom connecting the lower ends of both peripheral walls, with a cylindrical opening in the center of the upper wall of the outer cylindrical peripheral wall, and an air and/or carbon dioxide inlet member and a culture medium outlet member provided at the bottom. The gas discharge device is comprised of two opposing rectangular base plates, a bubble guide member with a U-shaped or inverted U-shaped cross section that opens downward, and a discharge nozzle; the bubble guide member is provided at an angle relative to the upper surface of the rectangular base plate, and the inclined wall on the upper surface of the bubble guide member is bent at its upper end to form an extending upper wall that is approximately horizontal, and the bubble guide member has side walls that hang down from both ends of the inclined wall and the upper wall, and the lower ends of both side walls are joined to the two upper surfaces of the rectangular base plate; and the discharge nozzle is attached to the rotor by passing through a through-hole drilled in the lower portion of the inclined wall. 13. The culture device according to claim 12, wherein the transparent material of the culture device body is acrylic resin. 14. The culture device according to claim 12 or 13, further comprising an air and/or carbon dioxide gas introduction member at the bottom of the culture device body. 15. The culture apparatus according to any one of claims 12 to 14, wherein the culture apparatus body further comprises a water sprinkler member on the outside of the cylindrical opening and a water sprinkler receiver on the outer periphery of the bottom. 16. The culture device according to any one of claims 12 to 15, wherein the culture device main body further comprises an artificial light source provided in the inner space of the inner hemispherical dome, the inner conical peripheral wall, or the inner cylindrical peripheral wall. 17. The culture device according to any one of claims 12 to 16, wherein at least one of the rectangular base plates of the gas discharge device is bent in the same direction at the front end and/or rear end. 18. The culture device according to any one of claims 12 to 17, wherein a weight adjustment means is provided on at least one of the two rectangular base plates of the gas discharge device.