Method for culturing algae

Abstract

To suppress an increase in costs associated with algae cultivation.SOLUTION: A method for culturing algae includes the steps of: spraying fly ash onto the water surface to cause it to float; and attaching algae to the fly ash floating on the water surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to methods for cultivating algae. [Background technology]

[0002] As one method for recovering carbon dioxide, a type of greenhouse gas, from the atmosphere or exhaust gas from a thermal power plant, there is a method of cultivating algae and fixing carbon dioxide by the action of photosynthesis. The algae grown by this method are recovered and processed, and converted into useful substances such as food, medicine, or fuel for use. In order to separate and recover algae dispersed in a culture solution, for example, a method of floating the algae to the surface of the culture solution using a flocculant, or a method of putting the culture solution containing the algae into a centrifuge and centrifuging it, have been used so far in order to separate the algae from the water present in large quantities. In addition, for example, Patent Document 1 discloses a technique for concentrating cultured microalgae, in which light of a wavelength that attracts the cultured microalgae and light of a wavelength that repels the cultured microalgae are combined. In addition, Patent Document 2 discloses a technique for cultivating algae on the water surface to facilitate recovery, in which a mixture of raw materials including an inorganic material, a hardener, and algae culture nutrients is mixed and molded into a molded body, and the molded body is cured to produce an algae culture medium that can float on water. Furthermore, Patent Document 3 discloses a technique for cultivating seaweed or aquatic algae by scattering foam glass carriers that can float on the water surface on the water surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6183825 [Patent Document 2] JP 2000-245278 A [Patent Document 3] JP 2020-000214 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the separation method using a flocculant, the culture liquid cannot be reused because the flocculant remains, and a large amount of waste liquid must be treated. In addition, in the centrifugation method, a large amount of culture liquid must be put into a centrifuge, and a large amount of energy is consumed to operate the centrifuge. The technology described in Patent Document 1 is a method for concentrating algae in an energy-saving manner using light, but the algae to which this method is applied are limited to algae that have the property of being attracted to light. The technology described in Patent Document 2 makes it easy to collect algae by growing them near the water surface using a carrier that has an apparent specific gravity of 1 or less and floats to the water surface, but requires a mixing device for mixing the raw materials for the carrier and curing the mixture, which increases the cost of algae culture. Similarly, the technology described in Patent Document 3 makes it easy to collect algae by using a carrier that has an apparent specific gravity of less than 1 and floats to the water surface. However, the size of the support must be larger than 10 mm due to requirements such as ease of handling, and while this is expected to enable the attachment and growth of large algae such as green laver, it is not suitable for mass production of microalgae.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an algae cultivation method that can suppress increases in costs associated with algae cultivation and algae recovery. [Means for solving the problem]

[0006] In order to achieve the above-mentioned objective, the algae cultivation method of the present disclosure comprises the steps of scattering a floating support on the water surface to cause it to float, and attaching algae to the floating support floating on the water surface. Effect of the Invention

[0007] According to the algae cultivation method of the present disclosure, it is possible to suppress increases in costs associated with algae cultivation and algae harvesting. [Brief description of the drawings]

[0008] [Figure 1] 1 is a flow chart of an algae cultivation method according to one embodiment. [Diagram 2] FIG. 2 is a schematic diagram illustrating the configuration of float ash according to an embodiment. [Figure 3A] FIG. 2 is a diagram showing the state inside a water tank according to an embodiment. [Figure 3B] FIG. 2 is a diagram showing the state inside a water tank according to an embodiment. [Figure 3C] FIG. 2 is a diagram showing the state inside a water tank according to an embodiment. [Figure 3D] FIG. 2 is a diagram showing the state inside a water tank according to an embodiment. [Figure 4] This is a close-up photograph of algae attached to the floating ash. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an algae culture method according to an embodiment of the present disclosure will be described with reference to the drawings. The embodiment shows one aspect of the present disclosure, and does not limit the present disclosure. The embodiment can be arbitrarily modified within the scope of the technical concept of the present disclosure.

[0010] <Algae culture method> FIG. 1 is a flow chart of an algae culture method according to an embodiment. As shown in FIG. 1, the algae culture method includes a preparation step S1, a floating step S2, an attachment step S3, a growth step S4, a buoyant body scattering step S5, and a recovery step S6. In an embodiment, the preparation step S1, the floating step S2, the attachment step S3, the growth step S4, the buoyant body scattering step S5, and the recovery step S6 are performed in this order. The algae to be cultured are organisms that perform photosynthesis, excluding mosses, ferns, and seed plants that live on land. The type of algae is not particularly limited, and may be microalgae with a body length of 1 μm or more and 1 mm or less (e.g., Spirulina and Euglena), macroalgae with a body length of more than 1 mm (e.g., Ulva), or freshwater algae that live in freshwater (e.g., Spirogyra, diatoms, and Nostoc commune).

[0011] In the preparation step S1, float ash 2 is prepared as a floating support to which the algae 20 to be cultured is attached while floating on the water surface. Here, the float ash 2 will be described. FIG. 2 is a diagram showing a schematic configuration of the float ash 2 according to one embodiment. The float ash 2 is contained in a small amount (about 1 to 2%) of fly ash generated by coal combustion, and is discharged, for example, from a coal-fired power plant. The float ash 2 is composed of a plurality of particles 4 having a spherical shape and a particle diameter range of 30 μm to 800 μm, and is obtained by gravity sorting of the fly ash. As shown in FIG. 2, each of the plurality of particles 4 has a void 6 formed therein. The particles 4 are white and have a density of 1 g / cm3 or less (they can float in water). The particles 4 are mainly composed of silica (SiO2), and the component having the second highest content is alumina (Al2O3). Furthermore, the particles 4 contain small amounts of components other than silica and alumina, such as iron oxide (Fe2O3), calcium oxide (CaO), and titanium oxide (TiO2). An example of the components of the particles 4 is shown in Table 1 below. In one embodiment, the preparation step S1 is performed by purchasing commercially available float ash 2. The float ash 2 prepared in the preparation step S1 is composed of only particles 4, or the majority of the float ash 2, which is more than 90% of the mass of the float ash 2, is composed of particles 4, and floats to the water surface 3. The particles 4 of the float ash 2 are not limited to being spherical, and may be ovoid. Incidentally, the present disclosure does not limit the floating support to the float ash 2, and any aggregate of particles according to the algae 20 is selected.

[0012] [Table 1]

[0013] In the flotation step S2, the float ash 2 is dispersed on the water surface 3 and suspended. In one embodiment, the float ash 2 is dispersed on the water surface 3 of the culture solution 10 stored in the water tank 8 and suspended thereon. The culture solution 10 is seawater. The amount of the float ash 2 dispersed on the water surface 3 of the culture solution 10 is 330 g / m 2 The amount of the fly ash 2 scattered on the water surface 3 is 1200 g / m 2In the floating step S2, only the floating ash 2 is scattered on the water surface 3, and nothing other than the floating ash 2 is scattered on the water surface 3. Note that, although the present disclosure will be described taking as an example a case in which the algae 20 is contained in seawater, the algae 20 to be cultured may be added to the culture solution 10 before or after the floating ash 2 is scattered on the culture solution 10.

[0014] Each of Figures 3A to 3D is a diagram showing the state inside the water tank 8 according to one embodiment. Time passes in the order of Figures 3A, 3B, 3C, and 3D. In one embodiment, as shown in Figure 3A, the floating step S2 is performed, and the float ash 2 floats on the water surface 3 so as to cover the entire water surface 3. In order to widely float the float ash 2 on the water surface 3, the float ash 2 may be scattered while moving, or the water in the water tank 8 may be pumped up and mixed with the float ash 2 before being returned to the water tank 8, or the float ash 2 floating on the water surface 3 may be stirred.

[0015] In the attachment step S3, the algae 20 is attached to the floating ash 2 floating on the water surface 3. In one embodiment, no treatment is performed on the water tank 8 until a certain period of time has passed since the execution of the floating step S2. Then, as shown in FIG. 3B, after the predetermined period of time has passed, the water surface 3 is covered with a film-like algae 20.

[0016] In the growth step S4, after the attachment step S3 and before the recovery step S6, the algae 20 is grown until at least a part of the upper surface of the float ash 2 is covered with the algae 20. In one embodiment, the water tank 8 is not treated until a certain period of time has passed since the attachment step S3 was performed. Then, as shown in FIG. 3C, after a certain period of time has passed from the state shown in FIG. 3B, a plurality of clumps 30 of the algae 20 are formed on the water surface 3. The process of forming the clumps 30 of the algae 20 will be described. The algae 20 grows thicker along the direction of gravity, and as it grows, it aggregates the particles 4 of the float ash 2. Therefore, gaps 40 that are not covered by the algae 20 or the particles 4 are formed on the water surface 3, and the clumps 30 of the algae 20 are formed. The clumps 30 of the algae 20 are supplemented with oxygen bubbles generated by the algae 20 through photosynthesis, and float on the water surface 3 due to the buoyancy of the aggregated particles 4 of the float ash 2 and the bubbles. As shown in FIG. 3C, each of the multiple clumps 30 of algae 20 may be spaced apart from one another.

[0017] In the buoyant body scattering step S5, after the floating step S2 and before the collecting step S6, a buoyant body 42 that provides buoyancy to the algae 20 is scattered on the water surface 3. In one embodiment, the buoyant body scattering step S5 is performed after the growing step S4 and before the collecting step S6. The buoyant body 42 is scattered so as to fill the gap portion 40, and the clumps 30 of the algae 20 take up the buoyant body 42, acquire buoyancy, and grow into larger clumps. The buoyant body 42 includes at least one of perlite particles, vermiculite particles, and biochar particles generated by carbonizing plants through incomplete combustion. In some embodiments, the buoyant body scattering step S5 is performed after the floating step S2 and before the attachment step S3. In some embodiments, the buoyant body scattering step S5 is performed after the attachment step S3 and before the growth step S4.

[0018] In some embodiments, the method for cultivating algae further includes the additional step of scattering additional float ash 2 onto the water surface 3 when gaps 40 that are not covered by the algae 20 or particles 4 are formed on the water surface 3 after the attachment step S3. According to such a method, the gaps 40 can be utilized to cultivate the algae 20, thereby increasing the yield of the algae 20.

[0019] After a certain period of time has passed from the state shown in Fig. 3C, the algae 20 continues to grow, and the clump 30 of the algae 20 becomes heavier than the buoyancy of the particles 4 and bubbles of the flocculated fly ash 2. Then, as shown in Fig. 3D, one of the clumps 30 of the multiple algae 20 sinks below the water surface 3.

[0020] In the recovery step S6, the algae 20 attached to the float ash 2 scattered on the water surface 3 are recovered while floating on the water surface 3. In one embodiment, the recovery step S6 is executed when the area in which the algae 20 are visible when the water surface 3 of the culture solution 10 is visually observed from above becomes larger than a set value. For example, the area in which the algae 20 are visible is determined by utilizing the difference in color between the particles 4 (white) and the algae 20 (green).

[0021] (Action and effect) The action and effect of an algae cultivation method according to one embodiment will be described. According to one embodiment, by simply scattering floating ash 2 on the water surface 3 and floating it, algae 20 are allowed to attach to the floating floating ash 2 and cultivated. Therefore, it is not necessary to install treatment equipment such as an addition device for adding additives to the floating ash 2 or an agitation device for agitating the culture solution 10. This makes it possible to suppress an increase in the cost of algae cultivation.

[0022] Furthermore, according to one embodiment, as the algae 20 grow, the mucous membrane of thickening polysaccharides (such as carrageenan, fucoidan, and alginic acid) secreted from the algae 20 takes in the particles 4 of the floating ash 2 while continuing to grow on the water surface 3, and the algae 20 aggregates to form a mass 30 of the algae 20. The mass 30 of the algae 20 continues to float on the water surface 3 due to the buoyancy of the particles 4 of the floating ash 2 and the oxygen bubbles generated by the photosynthesis of the algae 20. In this process, the algae bodies dry on the water surface 3, so that the mass 30 of the algae 20 with a low water content can be collected, improving the collection efficiency of the algae 20 and suppressing the increase in the collection cost of the algae 20. Furthermore, since the algae 20 are located on the water surface 3, they can use sunlight for photosynthesis without attenuation by water, and can almost directly take in carbon dioxide from the atmosphere. Therefore, a higher growth rate can be achieved compared to when the algae 20 is submerged in the culture solution 10.

[0023] In one embodiment, the algae 20 is cultured in the water tank 8, but the present disclosure is not limited to this form. In some embodiments, the floating step S2 involves uniformly scattering the floating ash 2 on the water surface 3 of the ocean or lake to float it. According to this method, the culture area can be easily expanded and a large amount of algae 20 can be cultured. In addition, special machinery and power are not required in the stage of culturing the algae 20. Furthermore, the clumps 30 of the algae 20 floating on the water surface 3 can be collected by a suction machine or the like, which not only reduces the power and labor required for collection, but also allows the collected clumps 30 of the algae 20 to be obtained in a solid state with a moisture content of approximately 80 to 90%, so that the conventional process of separating the culture solution 10 containing the algae 20 with a chemical or dehydrating the pumped culture solution 10 with a centrifuge can be omitted.

[0024] According to one embodiment, the particle diameter of the particles 4 is in the range of 30 μm to 800 μm, so that each of the particles 4 moves with the flow of the culture solution 10. This suppresses collisions between the particles 4 floating on the water surface 3, and the algae 20 proliferate in the gaps between the particles 4, and the algae 20 are prevented from falling off the floating ash 2 due to waves. In the case of particles 4 larger than 800 μm, the particles 4 move and rotate due to waves, etc., and when the particles 4 are dispersed in the early stage of the cultivation of the algae 20, the proliferation of the algae 20 is limited to the surface of the particles 4, and a large yield cannot be obtained. In addition, particles smaller than 30 μm do not have sufficient buoyancy, so they easily sink due to surface dirt and adhesion of the algae 20 immediately after dispersion, and cannot maintain a state of floating on the water surface 3. In some embodiments, the particle size of the particles 4 is 30 μm or more and 200 μm or less, and collisions between the particles 4 are further suppressed, and the falling off of the algae 20 from the fly ash 2 can be further suppressed.

[0025] According to one embodiment, the particles 4 have pores 6 formed therein and a density of 1 g / cm 3 Since the above properties are as follows, the particles 4 can be used as a support for floating on the water surface 3 and culturing the algae 20. By using such particles 4, it is possible to grow microalgae, which are the algae 20 having a size of about 5 to 20 μm, on the surface of the particles 4, and to grow large algae 20 such as filamentous algae that do not have buoyancy by themselves by incorporating the particles 4. Furthermore, according to one embodiment, the particles 4 contain iron, which can promote the growth of the algae 20.

[0026] If the amount of float ash 2 scattered on the water surface 3 is too small, the algae 20 will not form a mat-like mass covering the entire water surface 3, but will instead be scattered on the water surface 3 in the form of granules with a diameter of about 5 mm, and no yield will be obtained. 2As a result, the water surface 3 can be completely covered by the floating ash 2, maximizing the amount of algae 20 recovered. The algae 20 grow by attaching to the floating ash 2 and proliferating, so that a mat of the algae 20 covers the water surface 3, thereby increasing the amount of algae 20 recovered.

[0027] If an excessive amount of float ash 2 is scattered on the water surface 3, the amount of float ash 2 that does not float on the water surface 3 increases. The float ash 2 that is not floating on the water surface 3 will be blown away by the wind. In addition, the excess float ash 2 casts shade and inhibits the photosynthesis of the algae 20, and the float ash 2 that is not in contact with the water surface 3 is dry and has a dehydrating effect, causing the algae 20 to die. In contrast, according to one embodiment, the amount of float ash 2 scattered on the water surface 3 of the culture solution 10 is 1200 g / m 2 Since this is the case, the amount of floating ash 2 that is wet but does not float on the water surface 3 can be reduced, and consumption of the floating ash 2 and inhibition of the growth of algae 20 by the floating ash 2 can be suppressed.

[0028] According to one embodiment, the algae 20 is harvested while the algae 20 is floating on the water surface 3 as clumps 30, so that less energy is required to remove water from the harvested algae 20 compared to when the algae 20 is cultured underwater. Also, compared to when the algae 20 is cultured underwater, the algae 20 proliferates as high-density clumps 30 floating on the water surface 3, so that the algae 20 can be harvested easily and is concentrated at the time of harvesting.

[0029] In some embodiments, the collection step S6 is performed when the algae 20 floating on the water surface 3 starts to partially sink. Specifically, the collection step S6 is performed when one of the multiple clumps 30 of the algae 20 starts to sink, as shown in Fig. 3D. In other words, the collection step S6 is performed when the weight of the clump 30 of the algae 20 becomes greater than the buoyancy due to proliferation of the algae 20. According to such a method, it is possible to increase the amount of algae 20 collected while reducing the energy required to remove water from the collected algae 20.

[0030] According to one embodiment, by carrying out the growth step S4, it is possible to increase the amount of algae 20 collected, compared to the case where the algae 20 is collected before covering the upper surface of the floating ash 2. According to one embodiment, by carrying out the buoyancy body scattering step S5, the buoyancy body 42 provides buoyancy to the clumps 30 of the algae 20. Therefore, it is possible to increase the amount of the algae 20 that can float on the water surface 3.

[0031] <Example 1> The inventors of the present disclosure have found that by using particles 4 of floating ash 2 as a support for algae 20, it is possible to realize the cultivation of algae 20 at low cost. Example 1 is a case where floating ash 2 composed of particles 4 in Table 1 above is spread on the water surface 3. The volume of the water tank 8 used for cultivation is 80 L, and when 60 L of seawater collected in Kure City, Hiroshima Prefecture was poured in, the area of ​​the water surface 3 was 0.3 m 2 100 g of the fly ash 2 was scattered in the water tank 8. This corresponds to a scattering density of 330 g / m 2 No other nutrients were added, and the culture period was two months, from early February to the end of March.

[0032] Ten days after the floating ash 2 was spread, the water surface 3 was covered with a thin green film of algae 20, which gradually grew thicker and formed a mat-like mass (see FIG. 3B). After 25 days, the mat-like algae 20 separated, and many island-like masses 30 of algae 20 were floating on the water surface 3 (see FIG. 3C). This is thought to be because the masses 30 of algae 20 captured oxygen bubbles produced by photosynthesis and were floating on the water surface 3 due to the buoyancy of the oxygen bubbles in addition to the buoyancy of the floating ash 2. Even after 35 days, it was seen that each of the multiple masses 30 of algae 20 had grown even thicker. After 50 days, partial settling of the masses 30 of algae 20 was observed, so the algae 20 was collected from the water tank 8. It is thought that the best time to collect the masses 30 of algae 20 is just before they can no longer be supported by buoyancy and begin to settle.

[0033] With reference to Fig. 4, the results of enlarged observation of a piece of the clump 30 of algae 20 by an optical microscope will be described. Fig. 4 is an enlarged photograph of algae 20 attached to the fly ash 2. As shown in Fig. 4, the diameter of the particle 4 was about 150 µm. This particle 4 had granular microalgae 20A (20) and fibrous microalgae 20B (20) that are thought to be blue-green algae and have a diameter of about 5 to 10 µm attached to its surface. Granular microalgae 20A and fibrous microalgae 20B were also present between the particles 4, and the particles 4 were loosely bound to each other by the granular microalgae 20A and fibrous microalgae 20B.

[0034] After culturing the algae 20 for two months, the algae 20 in the water tank 8 was collected using a sieve with 425 μm mesh. After draining, 730 g of algae bodies were obtained. After collecting the algae 20, floating ash 2 with no algae 20 attached remained on the water surface 3 in the water tank 8, but for calculation purposes it was assumed that the collected algae bodies contained 100 g of floating ash 2. As a result of the calculation, the collected amount of algae was approximately 2.1 kg / m 2 If the moisture content of algae 20 is assumed to be 85%, the dry weight is 0.3 kg / m 2 The yield was 18.9 t / ha·year when converted to a 1-hectare culture pond and a 1-year period. Note that the period during which Algae 20 was cultured was under low temperature and low light conditions in mid-winter, and it is expected that a greater yield would be obtained if Algae 20 were cultured during a warmer period.

[0035] <Example 2> Next, the effects of different carriers floating on the water surface 3 will be described. Example 2 will be a case where float ash 2 (particle size range 30-200 μm) is spread on the water surface 3, and as comparative examples, the cases where fly ash (particle size range 20-500 μm), perlite (particle size range 500 μm-2 mm), crushed and gravity-separated particles of perlite (particle size range 50-800 μm), vermiculite (particle size range 1-8 mm), unburned particles derived from woody biomass (major axis dimension 2-5 mm), rice husk charcoal (major axis dimension 3-6 mm), and stearic acid particles (approximately 2 mm) are each spread on the water surface 3 will also be described. In the experiment, as in Example 1, seawater collected in Kure City, Hiroshima Prefecture was individually injected into the water tank 8 as the culture solution 10. If a mat of algae 20 was obtained within three weeks, a circle was marked in the "algae growth" column. If growth of algae 20 was observed on the surface of the scattered particles without forming a mat, a triangle was marked. If no growth of algae 20 was observed, a cross was marked. In addition to the above experiment, an experiment was conducted in which the mat-like algae obtained in Example 1 was cut into 10 mm x 10 mm pieces, and the scattered particles and the mat of algae 20 were placed in the water tank 8. In this experiment, if a mat of algae 20 covering the water surface was obtained within two weeks, a circle was marked in the "algae growth" column. If no change was observed, a cross was marked. The water tank 8 was installed in a sunny location indoors. Each of the eight types of particles was scattered so as to cover the entire water surface 3 in the water tank 8. Then, the state of the algae 20 in the water tank 8 was confirmed after 20 days had passed. Incidentally, of the eight types of particles, those that settle quickly are dispersed in an amount that covers the bottom surface of the water tank 8.

[0036] As shown in Table 2 below, the float ash 2 continued to float on the water surface 3, and the attachment and growth of algae 20 was observed over time. In contrast, the fly ash (derived from coal) quickly settled after being spread, and the growth of algae 20 was observed on the surface of the settled fly ash. The perlite continued to float on the water surface 3, but the growth of algae 20 was limited to the gaps between the perlite particles and on the surface of the perlite, and it did not grow to cover the water surface 3. However, in an experiment in which a mat of algae 20 was also added, the mat of algae 20 absorbed the perlite particles and continued to grow on the water surface 3. Crushed perlite, like the float ash 2, continued to float on the water surface 3, and both the generation and growth of algae 20 were observed. Vermiculite, unburned particles derived from woody biomass, and rice husk charcoal floated on the water surface 3 immediately after spreading, but after three days, almost all of them settled due to water absorption, and no generation of algae 20 was observed. In contrast, in an experiment in which a mat of algae 20 was also added, the mat of algae 20 took in the coarse perlite particles and continued to float. Although the stearic acid particles continued to float on the water surface 3, neither the emergence nor growth of algae 20 was observed.

[0037] [Table 2]

[0038] From the above results, it is considered that the particles suitable for the growth of algae 20 are the fly ash 2 and crushed perlite particles, and the particle size is in the range of 20 to 800 μm. Furthermore, at the growth stage of algae 20, even particles of a few mm in size can be incorporated into the mat of algae 20. This increases the buoyancy of the mat of algae 20, and it was found that it can float on the water surface 3 for a longer period of time and continue to grow. Note that although unburned particles and rice husk charcoal contain potassium and phosphorus, which are elements necessary for the growth of algae 20, they are considered not to have affinity for them at the growth stage of algae 20. In addition, it is considered that the stearic acid particles are water repellent, and therefore the adhesion of algae 20 is suppressed.

[0039] <Example 3> Next, a case where freshwater algae of algae 20 is cultured using floating ash 2 will be described as Example 3. As the freshwater algae, star jelly (algae 20), which is relatively easy to obtain, was used. Star jelly collected in Kure city, Hiroshima prefecture was used. Since star jelly was in a dry state when collected, its weight was used as the weight before culture. The water tank 8 had a capacity of 300 mL and the area of ​​the water surface 3 was about 8000 mm 2 Mineral water was used as the culture solution 10, and the culture solution 10 was maintained at 250 mL including 2 g of dried star jelly. No other substances that could become nutrients were added. Two water tanks 8 were installed in a sunny location indoors, and 5 g (spreading density 640 g / m2) of floating ash 2 was spread on the water surface 3 in the first water tank 8A (8), and floating ash 2 was not spread on the water surface 3 in the second water tank 8B (8). In both the first water tank 8A and the second water tank 8B, the star jelly was floating on the water surface 3. Then, after 30 days, the star jelly was taken out from each of the first water tank 8A and the second water tank 8B. The floating ash 2 was separated from the taken out star jelly by suction filtration, and the mass was measured after a drying process at 40 ° C for 5 hours using a hot air drying oven. In addition, since it was difficult to separate the floating ash 2 from the star jelly in the first water tank 8A, the evaluation was based on the combined value of the star jelly and the floating ash 2.

[0040] As shown in Table 3, the mass of the star jellyfish in the first tank 8A where floating ash 2 was scattered (the mass of floating ash 2 was added) increased from 7.0 g to 8.3 g (the weight of the star jellyfish alone increased from 2.0 g to 3.1 g). In contrast, the mass of the star jellyfish in the second tank 8B where floating ash 2 was not scattered increased from 2.0 g to 2.2 g. In this way, the scattering of floating ash 2 had the effect of multiplying the star jellyfish.

[0041] [Table 3]

[0042] Moreover, while the color of the star jelly in the first tank 8A was dark green, the color of the star jelly in the second tank 8B became lighter over the course of days, and the amount of oxygen bubbles produced by photosynthesis also decreased. For this reason, it is believed that the float ash 2 has a fertilizing effect on the star jelly in addition to providing buoyancy.

[0043] The contents described in each of the above embodiments can be understood, for example, as follows.

[0044] [1] The method for cultivating algae according to the present disclosure comprises: A step (S2) of scattering the floating support (2) on the water surface (3) to make it float; and a step (S3) of attaching algae (20) to the floating support floating on the water surface.

[0045] According to the configuration described in [1] above, the floating supports are dispersed on the water surface to make them float, and the algae are cultured by attaching them to the floating supports, so there is no need to install treatment devices such as an additive device for adding additives to the floating supports or a stirring device for stirring the culture solution, which makes it possible to suppress increases in the costs of algae culture.

[0046] Furthermore, according to the configuration described in [1] above, as the algae grow, the particles constituting the floating support aggregate with each other. The algae continue to float on the water surface due to the buoyancy of the aggregated floating support particles and bubbles generated by photosynthesis. As a result, the algae aggregate and dry on the water surface, making it possible to obtain algae with a low moisture content, and thus suppressing the increase in the cost of collecting the algae.

[0047] [2] In some embodiments, in the method according to [1] above, The floating support is composed of a plurality of particles (4) having a particle diameter in the range of 30 μm to 800 μm.

[0048] According to the method described in [2] above, each of the particles moves with the flow of the culture solution, so that collisions between the particles are suppressed, and therefore, it is possible to suppress the algae from falling off the floating support.

[0049] [3] In some embodiments, in the method according to [2] above, Each of the plurality of particles has a void formed therein and a density of 1 g / cm 3 The following is the result.

[0050] According to the method described in [3] above, the floating support particles can be applied as a support for algae.

[0051] [4] In some embodiments, in the method according to any one of [1] to [3] above, The amount of the floating carrier to be spread on the water surface is 330 g / m 2 That's all.

[0052] According to the method described in [4] above, it is possible to prevent the formation of areas on the water surface where the floating support is not floating, and to prevent a reduction in the amount of algae recovered.

[0053] [5] In some embodiments, in the method according to any one of [1] to [4] above, The method further includes a step (S4) of collecting the algae attached to the floating support dispersed on the water surface while the algae are floating on the water surface.

[0054] According to the method described in [5] above, the energy required to remove water from the harvested algae can be reduced.

[0055] [6] In some embodiments, in the method according to [5] above, The step of harvesting the algae is carried out when the algae floating on the water surface starts to partially sink.

[0056] According to the method described in [6] above, it is possible to increase the amount of algae recovered while reducing the energy required to remove water from the recovered algae.

[0057] [7] In some embodiments, in the method according to [5] or [6] above, After the step of attaching the algae to the floating support and before the step of recovering the algae, the method further comprises the step of growing the algae until at least a portion of the upper surface of the floating support is covered by the algae.

[0058] According to the method described in [7] above, the yield of algae can be increased.

[0059] [8] In some embodiments, in the method according to any one of [5] to [7] above, The method further includes a step of scattering a buoyant body on the water surface that provides buoyancy to the algae, after the step of scattering the floating support on the water surface to float it and before the step of recovering the algae.

[0060] According to the method described in [8] above, the amount of algae that can be suspended on the water surface can be increased by providing buoyancy to the algae.

[0061] [9] In some embodiments, in the method according to [8] above, The buoyant body includes at least one of perlite particles, vermiculite particles, and biochar particles produced by carbonizing plant matter through incomplete combustion.

[0062] According to the method described in [9] above, it is possible to easily impart buoyancy to algae.

[0063]

[10] In some embodiments, in the method according to any one of [1] to [9] above, The floating support is fly ash.

[0064] According to the method described in

[10] above, the floating support can be easily prepared. [Explanation of symbols]

[0065] 2 floating ash 3 water surface 4 particles 6 Vacancies 8. Aquarium 8A First Tank 8B Second tank 10 Culture solution 20 Algae 20A Granular microalgae 20B Filamentous microalgae 30 Algae mass 40 Gap area 42 Buoyancy body S1 Preparation Steps S2 Floating Step S3 Adhesion step S4 Growth step S5 Buoyancy scattering step S6 Collection step

Claims

1. A step of scattering the floating carrier on the water surface to make it float; and attaching algae to the floating support floating on the water surface. Algae culture method.

2. The floating support is composed of a plurality of particles having a particle diameter range of 30 μm to 800 μm. The method for cultivating algae according to claim 1 .

3. Each of the plurality of particles has a void formed therein and a density of 1 g / cm ３ Below is the The method for cultivating algae according to claim 2.

4. The amount of the floating carrier to be spread on the water surface is 330 g / m ２ That's all. The method for cultivating algae according to any one of claims 1 to 3.

5. The method further includes a step of collecting the algae attached to the floating support dispersed on the water surface while the algae is floating on the water surface. The method for cultivating algae according to any one of claims 1 to 3.

6. The step of collecting the algae is carried out when the algae floating on the water surface starts to partially settle. The method for cultivating algae according to claim 5.

7. After the step of attaching the algae to the floating support and before the step of collecting the algae, the method further comprises the step of growing the algae until at least a portion of the upper surface of the floating support is covered with the algae. The method for cultivating algae according to claim 5.

8. The method further includes a step of scattering a buoyant body on the water surface to provide buoyancy to the algae after the step of scattering the floating support on the water surface to float it and before the step of collecting the algae. The method for cultivating algae according to claim 5.

9. The buoyant body includes at least one of perlite particles, vermiculite particles, and biochar particles produced by carbonizing plants through incomplete combustion. The method for cultivating algae according to claim 8.

10. The floating support is float ash. The method for cultivating algae according to any one of claims 1 to 3.

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