Culture apparatus of microalgae

Abstract

To provide a culture apparatus of microalgae that can achieve higher productivity of microalgae.SOLUTION: The gist of the present invention is as follows. (1) A culture apparatus of microalgae which carries a microalgae on a culture surface of a carrier to culture the microalgae, and has a gable-roof-like unit structure in which back surfaces of a pair of the carriers face each other, where each culture surface is in a convex shape in a vertical downward direction from a plane surface including an upper side and a lower side of the unit structure. (2) The culture apparatus of microalgae described in (1) where the culture apparatus is in a bellows structure where the gable-roof-like unit structures are connected. (3) The culture apparatus of microalgae described in (1) or (2) where an angle formed by the plane surface and a bottom face of the unit structure is 63 to 76°. (4) The culture apparatus of microalgae described in any one of (1) to (3) where the curvature R of a curved surface formed by the culture surface is 1.0 to 3.0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a microalgae culture device. [Background technology]

[0002] For example, as disclosed in Patent Document 1, there is a technology called solid-phase surface culture (support culture) in which microalgae such as Chlorella and Chlamydomonas are supported on the surface (culture surface) of a support and cultured. This technology can be used in two ways: one that uses sunlight and one that uses artificial lighting. Of these, when sunlight is used, there is a demand for efficient use of sunlight and for increasing the productivity of microalgae per land area.

[0003] The growth rate (productivity) of microalgae on a support increases linearly up to a certain point as the intensity of sunlight hitting the culture surface increases, but once the intensity exceeds a certain level, it becomes constant. Therefore, a technology has been proposed that intentionally reduces the intensity of sunlight hitting a unit area of ​​the culture surface by making the culture surface uneven and increasing the culture area per land area. This technology increases the culture area per land area while reducing the light hitting a unit area of ​​the culture surface until the productivity of the microalgae becomes constant. This allows sunlight to be efficiently converted into microalgae production.

[0004] However, simply increasing the cultivation area per land area is not enough to increase the productivity of microalgae per land area. If the cultivation area is increased too much, the intensity of light hitting the cultivation surface will be too low below the level at which the productivity of microalgae mentioned above becomes constant, and as a result, the productivity of microalgae per land area will actually decrease.

[0005] Another required performance of a culture device is the ability to cultivate microalgae evenly over a wider area of ​​the culture surface. There is an upper limit to the amount of microalgae that can be cultured at one time on each unit surface of the culture surface. Therefore, if the culture of microalgae on the culture surface is uneven, the amount of microalgae cultured on one part of the culture surface will quickly reach the upper limit. For this reason, it is necessary to shorten the period from the start of microalgae cultivation to the harvesting of the microalgae. In this case, because the microalgae are concentrated on one part of the culture surface, the amount of microalgae harvested will be low. Therefore, the productivity of the microalgae will be low.

[0006] On the other hand, if microalgae can be cultivated evenly over a wider area of ​​the culture surface, the growth rate of the microalgae on each unit surface of the culture surface can be kept low, and the microalgae can be cultivated over a wider area of ​​the culture surface, so the period from the start of microalgae cultivation to the harvesting of the microalgae can be extended. In this case, since microalgae can be cultivated over a wider area of ​​the culture surface, the amount of microalgae harvested can be increased. Therefore, the productivity of microalgae can be increased.

[0007] Therefore, two requirements for a solid surface culture device are that it utilizes sunlight to "increase microalgae productivity per land area" and "enable microalgae to be cultivated evenly over a wider area of ​​the culture surface." However, because sunlight's intensity and angle change in complex ways depending on the season, time, and sunlight conditions, there has been little research into what kind of culture device structure would meet these requirements while taking such changes into account.

[0008] To date, structures such as a flat panel type (Patent Document 2) in which supports with culture surfaces perpendicular to the ground are arranged in a row, and a solar panel type in which supports with inclined culture surfaces are arranged in a row have been proposed. However, all of these have had the problem of low productivity of the microalgae obtained and uneven cultivation of the microalgae on the culture surface (high productivity in the upper part where light is more likely to reach, and low productivity in the lower part). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2022-87852 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-175964 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a microalgae culture device that can achieve higher microalgae productivity. [Means for solving the problem]

[0011] The gist of the present invention is as follows. (1) A culture device for culturing microalgae by supporting them on a culture surface of a support, A microalgae cultivation device characterized in that a pair of the supports have gable-roof-shaped unit structures with their backs facing each other, and each of the cultivation surfaces has a convex shape that is vertically downward from a plane containing the upper and lower edges of the unit structures. (2) The microalgae culture device according to (1), characterized in that the culture device is a bellows structure in which the gable roof-shaped unit structures are connected. (3) The microalgae culture device according to (1) or (2), wherein the angle formed between the plane and the bottom surface of the unit structure is 63 to 76°. (4) The microalgae culture device according to any one of (1) to (3), wherein the curvature R of the curved surface formed by the culture surface is 1.0 to 3.0. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a microalgae culture device and a microalgae culture method that can achieve higher productivity of microalgae. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view showing the overall configuration of a culture device according to an embodiment of the present invention. [Figure 2A] FIG. 2 is an explanatory diagram for explaining the definition of curvature R. [Figure 2B] FIG. 2 is an explanatory diagram for explaining the definition of curvature R. [Figure 3] FIG. 2 is an explanatory diagram showing the structures of various unit structures used in the examples. [Figure 4] 1 is a graph showing the relationship between the height to base ratio and the annual microalgae production (g / m 2 / y) for each type of unit structure. [Figure 5] 1 is a graph showing the relationship between the height to base ratio and the annual microalgae production (g / m2 / y) for each type of bellows structure. [Figure 6] 1 is a graph showing the relationship between the height to base ratio and the standard deviation (g / m 2 / y) of microalgae production on the culture surface for each type of bellows structure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0015] <1. Findings of the Inventor> The present inventors thought that by performing simulations using the characteristics of sunlight and microalgae productivity in solid-phase surface culture, it might be possible to identify a culture device structure that would result in high microalgae productivity. As a result of diligent simulations, the present inventors identified a novel device structure that would result in high microalgae productivity.

[0016] The inventors have determined that a culture device with a bellows-shaped culture surface (i.e., a bellows structure) in particular leads to high biomass productivity. The reason for this is thought to be that in addition to being able to secure a large culture surface per land area, the angle of the culture surface relative to sunlight can be appropriately adjusted, and in many cases the light intensity on the culture surface can be appropriately adjusted under the various light conditions observed in real environments.

[0017] The inventors have found that, among bellows structures, a bellows structure in which each gable roof portion (unit structure of the bellows structure) has a convex shape in the vertical downward direction relative to a plane including its upper side (ridge line) and lower side (valley bottom) is more suitable. In this bellows structure, the culture surface of each gable roof portion has a convex shape in the vertical downward direction.

[0018] The upper part of the gable roof near the top edge is more susceptible to light, while the lower part near the bottom edge of the gable roof is less susceptible to light. Therefore, with a simple bellows structure, productivity in the upper part is high and that in the lower part is low. Therefore, by making the gable roof part convex in the vertical downward direction, light is more likely to reach the lower part and the intensity of light reaching the upper part is reduced. This corrects the unevenness in the way light hits, allowing more uniform light to hit the entire bellows structure (light of an intensity that results in high microalgae production efficiency), reducing productivity unevenness and improving productivity of the entire device. The present invention was made based on the above findings.

[0019] <2. Overall configuration of the culture device> Next, the overall configuration of the culture device 1 according to this embodiment will be described with reference to Figures 1 to 2B. Figure 1 is a perspective view showing the overall configuration of the culture device 1 according to this embodiment, and Figures 2A and 2B are explanatory diagrams for explaining the definition of the curvature R.

[0020] The culture device 1 has a bellows structure in which multiple unit structures 1a are connected by sharing a lower side 1c. Each unit structure 1a has a gable roof shape with a pair of supports 10, 20 with their back surfaces 11b, 21b facing each other. The surfaces of the supports 10, 20 serve as culture surfaces 11a, 21a for microalgae, allowing microalgae to be cultured on the culture surfaces.

[0021] Furthermore, each of the culture surfaces 11a, 21a has a shape that is convex in the vertically downward direction relative to a plane 30 that includes the upper side 1b and the lower side 1c of the unit structure 1a. The curvature R of the culture surfaces 11a, 21a is preferably 1.0 to 3.0. This further enhances the productivity of microalgae. Here, a method for determining the curvature R will be explained using Figures 2A and 2B.

[0022] In a cross section perpendicular to the longitudinal direction of the unit structure 1a, an ellipse (e.g., ellipse 40, 50, etc.) is defined that passes through the upper side 1b and one lower side 1c of the unit structure 1a and whose axes coincide with the horizontal and vertical directions of space. Here, the ellipse in this embodiment also includes a perfect circle. Furthermore, the ratio of the length (= b) of the vertical axis (e.g., vertical axis 42, 52) of the ellipse to the length (= a) of the horizontal axis (e.g., horizontal axis 41, 51) of the ellipse is twice the ratio of the height (= d) to the length (= c) of the base side 1d' of the unit structure 1a. In this case, the ratio of the length (= a) of the horizontal axis of the ellipse to the length (= c) of the base side 1d' of the unit structure 1a is defined as the curvature R.

[0023] For example, in the example shown in FIG. 2(A), the length (= c) of the base 1d' of unit structure 1a is 1, and the height (= d) is 0.5. In this case, d / c = 0.5, so the ratio b / a of the length of the vertical axis to the length of the horizontal axis of the ellipse is 2 × d / c = 2 × 0.5 = 1. Therefore, the ellipse is a perfect circle. The length of the horizontal axis 41 of ellipse 40 is equal to the length of the vertical axis 42, and the curvature R defined by ellipse 40 is 1.0. In other words, the length (= a) of the horizontal axis 41 of ellipse 40 is equal to the length (= c) of the base 1d' of unit structure 1a. The length of the horizontal axis 51 of ellipse 50 is equal to the length (= c) of the vertical axis 52, and the curvature R defined by ellipse 50 is 1.5. In other words, the length (= a) of the horizontal axis of ellipse 50 is 1.5 times the length (= c) of the base 1d' of unit structure 1a.

[0024] In the example shown in FIG. 2(B), the length (= c) of the base 1d' of unit structure 1a is 1, and the height (= d) is 1. In this case, d / c = 1, so the ratio b / a of the length of the vertical axis of the ellipse to the length of the horizontal axis is 2 × d / c = 2 × 1 = 2. Therefore, the length of the vertical axis of the ellipse is twice the length of the horizontal axis. In other words, the horizontal axis is the minor axis of the ellipse, and the vertical axis is the major axis of the ellipse. The length of vertical axis 42 of ellipse 40 is twice the length of horizontal axis 41, and the curvature defined by ellipse 40 is 1.0. The length of vertical axis 52 of ellipse 50 is twice the length of horizontal axis 51, and the curvature defined by ellipse 50 is 1.5.

[0025] Furthermore, the angle θ between the plane 30 and the bottom surface 1d of the unit structure 1a (the side formed when the bottom surface 1d is cut in a cross section perpendicular to the longitudinal direction is the base side 1d') is 63 to 76°, which can further increase the productivity of microalgae.

[0026] As described above, the growth rate (productivity) of microalgae increases linearly up to a certain point as the intensity of sunlight striking the culture surfaces 11a, 21a increases, but once the intensity exceeds a certain level, the growth rate (productivity) becomes constant. Therefore, it is preferable that the uneven structure of the culture device 1 is adjusted so that sunlight of an amount that causes the growth rate of the microalgae to become constant strikes the uneven structure of the culture device 1. Such adjustments can be made using a simulation, which will be described later.

[0027] In addition, a water supply mechanism (not shown) capable of supplying water to each unit structure 1a is disposed above each unit structure 1a. The water supplied from the water supply mechanism can be a liquid culture medium containing components necessary or useful for the growth of microalgae. The culture surface of each unit structure is composed of a water-absorbent porous carrier (not shown), and the water supplied from the water supply mechanism is absorbed by the porous carrier and flows down through it. Microalgae are cultured on this porous carrier. Furthermore, a recovery mechanism (not shown) for recovering the water supplied to each unit structure 1a is disposed below each unit structure 1a. The culture device 1 is preferably installed in an atmosphere with a higher CO2 concentration than the atmosphere. This can further increase the productivity of microalgae.

[0028] Such a structure can be realized by the following means. The culture surface can be constructed by laminating a water-absorbent porous body onto a water-impermeable substrate. Plate-shaped materials such as metal, wood, and plastic can be used as the substrate, processed into a curved surface as necessary. Alternatively, a curved surface can be constructed using a water-impermeable sheet material such as rubber, vinyl, or waterproof cloth. Thin plate- or sheet-shaped polyvinyl alcohol sponges or cellulose sponges can be used as the porous body. If necessary, a sheet-shaped member can be attached to the surface of the porous body. This member serves to retain microalgae and prevent their escape. It is preferable that the material be water-permeable and impermeable to microalgae cells. Suitable materials for this purpose include glass fiber filter paper, or dense cloth or nonwoven fabric made of natural or chemical fibers. The structure can also be easily realized by fabricating a platform out of metal tubes such as iron or aluminum and attaching the above-described culture surface to it. The effects of the present invention can be achieved as long as the shape of the culture surface of the unit structure satisfies the structural requirements, and the means for achieving this are not limited to the methods described herein.

[0029] The culture apparatus 1 has the above-described configuration, which can further increase the productivity of microalgae. That is, the culture apparatus 1 according to this embodiment does not have a simple bellows structure, but each unit structure 1a has a convex shape in the vertically downward direction, which corrects unevenness in the way light hits, allowing more uniform light to hit the entire culture apparatus 1 (light of an intensity that provides high microalgae production efficiency), reducing unevenness in productivity and improving productivity throughout the apparatus.

[0030] Here, algae is a general term for organisms that perform oxygenic photosynthesis, excluding terrestrial plants. Microalgae refers to unicellular algae or those that form tiny colonies. Microalgae include some green algae, some red algae, some heteroknots, and cyanobacteria. Examples of microalgae to which the present invention is expected to be applicable include Chlorella (Chlorella sp.), Parachlorella (Parachlorella sp.), Chlamydomonas (Chlamydomonas sp.), Scenedesumus sp., Desmodesmus sp., Botryococcus (Botriococcus sp.), Nannochloropsis sp., and Spirulina (Arthrospira sp., Spirulina sp.). The present invention is expected to be applicable to not only the microalgae exemplified here, but also any microalgae that can be cultured on a solid surface. [Example]

[0031] <1. Example 1> Next, examples of this embodiment will be described. In Example 1, a suitable basic structure of the culture device 1 was specified. The specific processing is as follows.

[0032] In Example 1, a suitable basic structure of the culture device 1 was identified by performing a simulation. The simulation was performed using the 3D-CAD software Rhino7. Rhino7 has a function called Grasshopper implemented for metaprogramming. In addition, Ladybug was used as open-source plug-in software for Rhino7. Ladybug is capable of performing various solar radiation simulations based on weather data.

[0033] Ladybug has sample code called Radiation Analysis that runs on Grasshopper and can simulate how light hits structures in natural environments, created on Rhino 7. The inventors performed the simulation by adding their own code (which converts how light hits structures into the productivity of microalgae) to this sample code.

[0034] The light conditions in the simulation were defined by loading a weather conditions file. The weather conditions file Ladybug can use as input is an ep file, a format used by energy analysis software called EnergyPlus. For this study, we downloaded a solar radiation data file from the New Energy and Industrial Technology Development Organization (NEDO)'s annual solar radiation database (MONSOLA-20, solar radiation database browsing system (https: / / appww2.infoc.nedo.go.jp / appww / )) and converted it to ep format. The only items actually used in the calculation were the latitude, longitude, time zone, altitude, and hourly intensity of direct and scattered light on the horizontal plane for each day of the measurement point. Blank values ​​were entered for the other items included in the ep format. The other items were not used in the simulation.

[0035] The meteorological condition file used as the input file is average annual data for Omishima, Ehime Prefecture. Average annual data is artificial data created using the following procedure. First, the average monthly solar radiation amount was calculated from actual meteorological measurement data from 1981 to 2009. Next, the year closest to the average monthly value was selected, and the data for the selected 12 months was combined to create one-year data. This was used as the average annual data, i.e., the meteorological condition file. Note that this meteorological condition file is provided by the NEDO annual solar radiation database. In this example, the data provided by the NEDO annual solar radiation database was used. This data can be considered to represent average annual solar radiation data at the measurement location. In the simulation described below, the analysis period was set to one year of the average year. During the analysis, the direction, altitude, and intensity of direct and scattered sunlight in the simulation changed hourly based on the contents of this input file.

[0036] Ladybug's standard function is to output the integrated value of the amount of light energy on the surface of a structure over a specified period as the simulation result. In this case, to calculate the productivity of microalgae, the inventor added his own code to the Ladybug calculation process. The method for converting the amount of light energy into microalgae productivity is described in detail below.

[0037] Every hour, the amount of light energy (E) perpendicular to each surface element on the culture surface (described below) of the unit structure 1a being calculated was converted into the average photosynthetic photon flux density (hereinafter referred to as PPFD) for each hour using equation (1). The conversion was performed assuming that the proportion of photosynthetically active radiation in the solar energy at the ground surface was 46% and the average photon energy in photosynthetically active radiation was 225.3 [KJ / mol]. Equation (1): E [kWh / m 2 / h] × 2041.7 = PPFD [μmol / m 2 / s] Next, the photosynthetic photon flux density was converted to the biomass productivity of microalgae using equation (2). In equation (2), I is PPFD, and P [g / m 2 / h] is the biomass productivity of microalgae. Equation (2): P=[f·I+P max -√{(f·I+P max ) 2 -4f I q P max}] / 2q-R

[0038] Equation (2) is a partially modified equation based on the approximation equation for the light-photosynthesis curve (an equation showing the relationship between photosynthetic photon flux density and photosynthetic rate). Since biomass productivity can be considered as the sum of the individual photosynthetic rates of the microalgae cells contained in the biomass, it is reasonable to use the approximation equation for the light-photosynthesis curve as the equation for the relationship between photosynthetic photon flux density and biomass productivity. f, q, R, and P in equation (2) max To determine the value of , we used a further modification of equation (2) to obtain equation (3). In equation (3), I is PPFD, and ΣP [g / m 2 / d] is the biomass productivity of microalgae. Equation (3): ΣP = 14[f·I + P max -√{(f·I+P max ) 2 -4f I q P max}] / 2q-24R This equation was fitted to the experimental values ​​obtained under 1% CO2 addition conditions from the results of the culture experiment shown in Reference 1 (Nippon Steel Technical Report No. 417), and the best fitting parameter combination was obtained. Among the experimental values, PPFD was 1,357 [μmol / m 2 / s] and biomass productivity was 18.1 [g / m 2 The plot of [ / d] is considered an outlier and is not used in fitting. The parameters to be fitted are f, q, and R in equation (3), and P maxwas determined using the constraint of 20R. Note that f is a parameter corresponding to the initial gradient in the light-photosynthesis curve, q is a parameter corresponding to the convexity in the light-photosynthesis curve, and R is the respiration rate of the microalgae. In addition, a constraint was imposed that none of the parameters take negative values. The meaning of equation (3) is as follows: In the above culture experiment, the light period (time when light is irradiated) was 14 hours and the dark period (time when light is not irradiated) was 10 hours. Therefore, the daily biomass productivity ΣP shown in the culture experiment was determined by adding up the 14-hour term related to photosynthesis and the 24-hour term related to respiration in equation (2). As a result of fitting, the obtained parameters were used to construct equation (2), and a relationship equation expressing the photosynthetic photon flux density and the productivity of the microalgae was obtained. Note that the obtained parameter values ​​are as follows: f: 0.004587, q: 0.967, R: 0.062, P max :1.24. Using the above relational expression, the amount of light energy per hour on each surface element on the unit structure 1a was converted into the productivity of microalgae per hour. For each surface element, the productivity of microalgae was integrated over the calculation period of one year to determine the annual productivity of microalgae for each surface element. In this case, surface elements with negative productivity of microalgae were treated as having a productivity of zero. This is rational, as a situation in which the amount of biomass present in a certain area is negative does not actually exist. For each surface element, the integrated value of the productivity of microalgae and the area was calculated, and these values ​​were added up for all surface elements to obtain the annual production amount of microalgae for each unit structure 1a. This was then multiplied by 1m2, which is the area occupied by the unit structure 1a. 2 Dividing by this, the annual productivity (production amount) of microalgae per unit structure 1a (g / m 2 / y) was obtained.

[0039] Here, the unit structure 1a to be calculated is a plane, a gable roof, a pyramid, a flat panel, and a solar panel, as shown in Figure 3. The base area of ​​the unit structure 1a (the exclusive area in the top view (plan view)) is 1 m 2The culture device 1 has a structure in which such unit structures 1a are repeated in the horizontal direction (up, down, left, and right directions). In this simulation, mathematically similar unit structures are equivalent (giving the same results), so the absolute value of the length has no meaning, but the productivity of the microalgae is expressed as g / m 2 To express the unit of / y, the base area of ​​unit structure 1a is 1m 2 Therefore, the height of the unit structure 1a indicates the height of the unit structure 1a when the length of one side of the base area is 1 m. Each unit structure 1a will be described in detail below.

[0040] The unit structure 1a, which has a planar structure, is a square structure with a surface of 1m square that is horizontal to the ground, and the entire top surface of the plane is defined as the culture surface. This structure is isotropic in terms of direction and has a height of 0, so only one condition was set.

[0041] The gable roof structure is a structure consisting of two rectangular faces that share a common top edge 1b. The length of the shared top edge 1b is 1m, and it is parallel to the bottom edge 1d and located at the center and above the bottom edge 1d. Furthermore, the opposite side of each rectangle to the top edge 1b coincides with the two opposing sides of the base (bottom edge 1c). The top surfaces of the two rectangles are defined as the cultivation surface. Three conditions were set: 0° when the top edge 1b faces north-south, 90° when the top edge 1b faces east-west, and 45° when the top edge 1b faces northeast. The distance between the bottom edge 1d and the top edge 1b is defined as the height. Note that a structure in which gable roof structures are connected becomes a bellows structure.

[0042] The pyramid structure is a regular square pyramid with the base 1d measuring 1m square, with the apex 1e located above the center of the base 1d. The top surfaces of the four sides are defined as the culture surface. Two conditions were set: a condition where the culture surface faces north, south, east, and west, and a condition where the hypotenuse 1f faces north, south, east, and west, respectively, is defined as 0°, and a condition where the hypotenuse 1f faces north, south, east, and west, is defined as 45°. The distance from the base 1d to the apex 1e is defined as the height.

[0043] The flat panel structure is a rectangle with a width of 1 m, perpendicular to the ground, and two horizontal sides of the base, located at the center of the base 1d. One side of this plane 1g is defined as the culture surface. Only structures with a culture surface facing south were considered. The distance between the base 1d and the top side 1h of the rectangle was defined as the height.

[0044] The solar panel structure consists of a rectangle (hereafter referred to as the back surface) 1i perpendicular to one side of the bottom surface 1d, and a rectangle (hereafter referred to as the slope) 1l connecting the top side 1j of the back surface 1i and the opposite side 1k of the bottom side. The top surface of slope 1l was defined as the cultivation surface. Only structures with slopes facing south were considered. The distance between the bottom surface 1d and the top side 1j of the slope was defined as the height.

[0045] In both structures, 81 of the above-mentioned unit structures 1a were arranged horizontally in 9 columns and 9 rows in the same orientation, with no gaps between them. The central one was designated as the calculation target, and the other unit structures were designated as shields. The results are shown in Figure 4. Graph L1 corresponds to the planar structure, graphs L2 to L4 correspond to the bellows structure at 0°, 45°, and 90°, respectively, graphs L5 and L6 correspond to the pyramid structure at 0° and 45°, respectively, graph L7 corresponds to the flat panel structure, and graph L8 corresponds to the solar panel structure. The bellows structure provided the highest productivity. Therefore, the bellows structure was further examined in Example 2.

[0046] <2. Example 2> In Example 2, a suitable bellows structure was identified. Specifically, a convex bellows structure and a concave bellows structure were prepared by changing the culture surface to a curved surface using the bellows structure of Example 1 as the basic structure. In the convex bellows structure, the culture surface is convex in the vertically upward direction, and in the concave bellows structure, the culture surface is convex in the vertically downward direction. The concave bellows structure corresponds to this embodiment.

[0047] In these structures, the cross section of the culture surface is an elliptical arc. For both the bellows convex structure and the bellows concave structure, structures with curvature R of 1.0, 2.0, and 3.0 were prepared. The definition of curvature R for the bellows concave structure is as described above. The curvature R of the bellows convex structure is the curvature R of the bellows concave structure, inverted upside down. The practical lower limit of curvature R is 1.0. This is because when curvature R is less than 1.0, it is impossible to achieve both a curve that passes through two points (top and bottom edges) and two adjacent culture surfaces that do not overlap. Furthermore, when curvature R is infinite, both the bellows convex structure and the bellows concave structure converge to a simple bellows structure (discussed in Example 1). Other simulation conditions were the same as in Example 1.

[0048] The results are shown in Figure 5. Graph L10 corresponds to a simple bellows structure, graphs L11 to L13 correspond to bellows concave structures (curvature R = 1.0, 2.0, 3.0), and graphs L14 to L16 correspond to bellows convex structures (curvature R = 1.0, 2.0, 3.0). As is clear from Figure 5, the bellows concave structure, i.e., the structure of the culture device 1 according to this embodiment, increases the productivity of microalgae. Furthermore, it can be seen that the productivity of microalgae is particularly high when the curvature R is 1.0 to 3.0. The value in parentheses on the horizontal axis is the angle θ formed between the plane including the upper and lower sides of the bellows concave structure (i.e., plane 30) and the bottom surface 1d. It can be seen that the productivity of microalgae is particularly high when the angle θ is 63 to 76°.

[0049] 3. Example 3 The variation in productivity of microalgae on the culture surface of each structure was evaluated for the simulation performed in Example 2. A weighted standard deviation was calculated using the annual biomass production per area of ​​each surface element and the area of ​​the surface element obtained when calculating the annual biomass productivity value for each unit structure 1a, and this was defined as the variation in biomass productivity for each unit structure 1a.

[0050] The results are shown in Figure 6. Graph L20 corresponds to a simple bellows structure, graphs L21 to L23 correspond to bellows concave structures (curvature R = 1.0, 2.0, 3.0), and graphs L24 to L26 correspond to bellows convex structures (curvature R = 1.0, 2.0, 3.0). As is clear from Figure 6, the bellows concave structure, i.e., the structure of the culture device 1 according to this embodiment, reduces the variation in microalgae productivity. Furthermore, it can be seen that the variation in microalgae productivity is particularly low when the curvature R is 1.0 to 3.0. The value in parentheses on the horizontal axis is the angle θ formed between the plane including the upper and lower edges of the bellows concave structure (i.e., plane 30) and the bottom surface 1d. It can be seen that the variation in microalgae productivity is particularly low when the angle θ is 63 to 76°.

[0051] As described above, the culture device 1 according to this embodiment makes it possible to culture microalgae with little variation on the culture surface and with high productivity.

[0052] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0053] 1 Culture device 1a Unit structure 1b Top 1c bottom edge 1d bottom 10, 20 Support 11a, 21a Culture surface 11b, 21b back 30 planes 40, 50 oval R curvature

Claims

1. A culture device for culturing microalgae by supporting them on a culture surface of a support, A microalgae cultivation device characterized in that a pair of the supports have gable-roof-shaped unit structures with their backs facing each other, and each of the cultivation surfaces has a convex shape that is vertically downward from a plane containing the upper and lower edges of the unit structures.

2. The microalgae culture device according to claim 1 , wherein the culture device is a bellows structure in which the gable roof-shaped unit structures are connected.

3. The microalgae culture device according to claim 1 or 2, characterized in that the angle formed between the plane and the bottom surface of the unit structure is 63 to 76 degrees.

4. The microalgae culture device according to claim 1 or 2, characterized in that the curvature R of the curved surface formed by the culture surface is 1.0 to 3.0.

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