Methods for cultivating algae for bait and cultivation of algae for food

Abstract

To provide an algae culture method for bait and an algae medium, which do not require a special light radiation unit when culturing at high density, algae for bait, and by ingenuity about the medium, can reduce culture cost.SOLUTION: An algae culture method comprises: a culture solution production step 1 for producing a culture solution by mixing, an algae medium using potassium nitrate, and artificial sea water obtained by dissolving a raw material of artificial sea water in city water; an algae mixing step (2) for bait for mixing algae for bait with the culture solution obtained in the culture solution production step 1 after executing the same step; a light radiating step (3) for radiating light as independent nutrient, to the algae mixed culture solution obtained in the algae mixing step (2) for bait, for causing photosynthesis for growing the algae for bait at high density, where the light radiating step (3) is configured so that, when a growth ratio of the algae for bait is reduced, an organic carbon source charging step (4) for charging an organic carbon source, is executed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for culturing algae for feed and a culture medium for algae. Specifically, it relates to a method for culturing algae for feed such as diatoms, for which the demand is expected to increase as feed for bivalves, fish larvae, etc., and a culture medium for algae.

Background Art

[0002] As a method for culturing algae, the technique described in Patent Document 1 is known. [[ID=1,3]] Patent Document 1 describes a continuous culturing method for algae using a closed-type microalgae continuous culturing device equipped with a light-emitting body or a light irradiation device having an optical waveguide using the light-emitting body as a light source. The light irradiation device irradiates light having a light quality and a light quantum necessary for photosynthesis of microalgae in the culture solution at center wavelengths of 430 to 480 nm, 560 to 620 nm, and 675 to 685 nm, and a ratio of the light quantum amount based on the short wavelength of 0.5 to 5 and 4 to 10, respectively, toward the culture solution from at least one of the side wall surface, the upper surface, and the lower surface of the culture solution. And, a heating device for subjecting the culture solution containing a water-soluble carbohydrate as a carbon source of the microalgae to heat sterilization treatment is held inside or outside, and a sterile supply device or a filtration sterilization device for introducing contents into the culture solution is provided.

[0003] The technique described in Patent Document 1 provides a heterotrophic / photoautotrophic coexistence type system that realizes rapid growth of microalgae by generating wavelengths that reinforce photosynthesis by carotenoids by forming a chip in which a light-emitting diode chip and a fluorescent substance are integrated. To achieve this objective, the technology described in Patent Document 1 proposes: (1) a system for balancing the amount and concentration of oxygen required under heterotrophic conditions for microalgae and the concentration of carbon dioxide generated by the respiration of microalgae; (2) an improvement of a photoluminescent material that enables a combination of light quality effective for photosynthesis and the required amount of photon energy; (3) the construction of a light irradiation system that can uniformly and efficiently supply this light into a microalgae culture apparatus; and (4) a system that can be performed without impairing the performance of the light irradiation system and the photoluminescent material when heating and sterilizing a culture medium containing carbon sources and nutrients for organisms. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-183002 [Overview of the project] [Problems that the invention aims to solve]

[0005] The technology described in Patent Document 1 requires a light irradiation device that irradiates the microalgae in the culture medium with light quality and photons necessary for photosynthesis at central wavelengths of 430-480 nm, 560-620 nm, and 675-685 nm, with short-wavelength-based photon quantum ratios of 0.5-5 and 4-10, respectively, in order to achieve high-density cultivation. This is a factor that increases cultivation costs. Furthermore, Patent Document 1 does not describe any innovative ideas regarding the culture medium, which accounts for a large portion of the cultivation cost when cultivating algae for feed. Therefore, the problem that the present invention aims to solve is to provide a method for cultivating algae for feed and a culture medium for algae that eliminates the need for a special light irradiation device when cultivating algae for feed at high density, and makes it possible to reduce cultivation costs by making creative improvements to the culture medium. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows.

[0007] Firstly, After the culture medium production process, in which a culture medium is prepared by mixing an algal culture medium using potassium nitrate with artificial seawater, In the culture medium manufacturing process, feed algae are added to the culture medium and mixed in a feed algae mixing process. A method for cultivating algae for feed, characterized by performing a light irradiation step, in which the algae mixed culture medium obtained by the feed algae mixing step is irradiated with light to perform photosynthesis and grow the feed algae at high density. Here, the production of the culture medium is not limited to the case where artificial seawater mix and an algal growing medium using potassium nitrate are dissolved in water simultaneously, but also includes the case where artificial seawater mix has been prepared in advance by dissolving the artificial seawater mix in water, and then the algal growing medium using potassium nitrate is mixed in afterward. In other words, in the culture medium manufacturing process, the order in which artificial seawater and the algal culture medium using potassium nitrate are mixed does not matter, as long as they can be mixed. Secondly, The method for cultivating feed algae according to the first description, characterized in that when the growth rate of feed algae decreases in the light irradiation step, the growth rate is improved by performing an organic carbon source input step, in which an organic carbon source is introduced. Thirdly, The method for cultivating algae for feed according to the second claim, characterized in that the organic carbon source used in the light irradiation step is glucose. Fourth, The method for cultivating algae for feed according to any one of the first to third claims, characterized in that the artificial seawater used in the culture medium manufacturing process is prepared by dissolving an artificial seawater base in tap water. Fifth, A method for culturing feed algae according to any one of the first to third claims, characterized in that the feed algae used in the feed algae mixing step is an alga of the genus Chaetoceros. Sixth, A method for culturing feed algae according to any one of the first to third claims, characterized in that the feed algae used in the feed algae mixing step is an alga of the genus Chaetoceros, specifically Tenuissimus or Gracilis. Seventh, A culture medium used when cultivating algae for feed, A culture medium for algae, characterized by containing potassium nitrate. Eighth, A culture medium used when cultivating algae for feed, A culture medium for algae, characterized by having nitrate as the main component, derived from potassium nitrate, and containing the components of phosphoric acid, silicon, manganese, iron, and selenium. Ninth, A culture medium used when cultivating algae for feed, A culture medium for algae, characterized by containing 100,000 to 990,000 mg of potassium nitrate, 3,000 to 30,000 mg of dipotassium hydrogen phosphate, 3,000 to 30,000 mg of Fe(III)-EDTA, 0,100 to 1,000 mg of thiamine hydrochloride, 0,001 to 0,010 mg of biotin, 0,001 to 0,010 mg of vitamin B12, 0,100 to 0,900 mg of manganese(II) chloride tetrahydrate, 0,050 to 8,000 mg of sodium silicate, and 0,001 to 0,010 mg of sodium selenite per liter of water. Tenth, A culture medium used when cultivating algae for feed, A culture medium for algae, characterized by containing 200,000 to 900,000 mg of potassium nitrate, 4,000 to 20,000 mg of dipotassium hydrogen phosphate, 4,000 to 20,000 mg of Fe(III)-EDTA, 0.150 to 0.800 mg of thiamine hydrochloride, 0.001 to 0.008 mg of biotin, 0.001 to 0.008 mg of vitamin B12, 0.150 to 0.700 mg of manganese(II) chloride tetrahydrate, 0.100 to 6,000 mg of sodium silicate, and 0.001 to 0.008 mg of sodium selenite per liter of water. Eleventh, A culture medium used when cultivating algae for feed, A culture medium for algae, characterized by containing 220,000 to 600,000 mg of potassium nitrate, 4,500 to 10,000 mg of dipotassium hydrogen phosphate, 4,500 to 10,000 mg of Fe(III)-EDTA, 0.150 to 0.600 mg of thiamine hydrochloride, 0.001 to 0.006 mg of biotin, 0.001 to 0.006 mg of vitamin B12, 0.150 to 0.500 mg of manganese(II) chloride tetrahydrate, 0.120 to 4,000 mg of sodium silicate, and 0.001 to 0.006 mg of sodium selenite per liter of water. Twelfth, A culture medium used when cultivating algae for feed, A culture medium for algae, characterized by containing 230,000 to 250,000 mg of potassium nitrate, 4,700 to 5,500 mg of dipotassium hydrogen phosphate, 4,500 to 6,000 mg of Fe(III)-EDTA, 0.150 to 0.400 mg of thiamine hydrochloride, 0.001 to 0.004 mg of biotin, 0.001 to 0.004 mg of vitamin B12, 0.160 to 0.230 mg of manganese(II) chloride tetrahydrate, 0.120 to 1,000 mg of sodium silicate, and 0.001 to 0.004 mg of sodium selenite per liter of water.

[0008] The culture medium using potassium nitrate described above has a component composition that supplements any missing components, based on a comparison between the components of a commercially available culture medium dissolved in natural seawater and the components of Aquarium Systems' artificial seawater mix (Instant Ocean: product name) dissolved in tap water. In other words, the culture medium using potassium nitrate mainly consists of nitrate produced by potassium nitrate, and also contains phosphoric acid, silicon, manganese, iron, and selenium. Specifically, the following composition is preferred. It is preferable to use 237.905 mg of potassium nitrate, 5.000 mg of dipotassium hydrogen phosphate, 5.200 mg of Fe(III)-EDTA, 0.200 mg of thiamine hydrochloride, 0.002 mg of biotin, 0.002 mg of vitamin B12, 0.180 mg of manganese(II) chloride tetrahydrate, 0.144 mg of sodium silicate, and 0.002 mg of sodium selenite per liter of water.

[0009] As the organic carbon source, in addition to glucose, vitamins, preferably vitamin B12, can be used.

[0010] As the algae for feed, it is preferable to use algae of the genus Chaetoceros, which are known to have a high growth rate. As the algae of the genus Chaetoceros, tenuissimus, gracilis, and calcitrans can be used alone, or two or more species can be mixed and used.

[0011] In the light irradiation step, the growth rate can also be increased by injecting carbon dioxide in the minimum required amount.

Effects of the Invention

[0012] According to the present invention, the following effects can be achieved.

[0013] The method for culturing algae for feed according to the present invention uses a medium containing low-cost potassium nitrate, so it is possible to reduce the culture cost. In addition, when the growth rate of the algae for feed decreases, by adding an organic carbon source, it is possible to suppress the influence of bacterial growth and improve the growth rate without using a special light irradiation device, enabling high-density culture.

Brief Description of the Drawings

[0014] [Figure 1] It is an explanatory diagram of the method for culturing algae for feed according to the present invention. [Figure 2]This graph shows the results of Test Example 1. [Figure 3] This graph shows the results of Test Example 2. [Figure 4] This graph shows the results of Test Example 3. [Figure 5] This graph shows the results of Test Example 4. [Figure 6] This graph shows the results of Test Example 5. [Figure 7] This graph shows the results of Test Example 6. [Figure 8] This graph shows the results of Test Example 7. [Figure 9] This graph shows the results of Test Example 8. [Figure 10] This graph shows the results of Test Example 9. [Figure 11] This graph shows the results of Test Example 10. [Figure 12] This graph shows the results of Test Example 11. [Modes for carrying out the invention]

[0015] Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings. In the attached drawings, identical components are denoted by the same reference numeral, and redundant explanations have been omitted. The description herein represents only one embodiment of the present invention, and therefore the present invention is not limited to this embodiment. [Examples]

[0016] The method for cultivating algae for feed according to this embodiment is as shown in Figure 1, and consists of (1) a culture medium manufacturing step, (2) a feed algae mixing step, (3) a light irradiation step [autotrophic culture step], and (4) an organic carbon source input step [heterotrophic culture step]. The details are explained below.

[0017] (1)Culture solution manufacturing process This process involves mixing an artificial culture medium using potassium nitrate (hereinafter referred to as the original culture medium) with artificial seawater prepared by dissolving artificial seawater concentrate in tap water to produce a culture medium. Since tap water is used as is, the process can be simplified. The original culture medium using potassium nitrate was developed by comparing the components of commercially available culture media dissolved in natural seawater with the components of Aquarium Systems' artificial seawater mix (Instant Ocean: product name) dissolved in tap water, and supplementing the missing components.

[0018] In other words, the original culture medium using potassium nitrate has nitrate as its main component, and also contains phosphoric acid, silicon, manganese, iron, and selenium. Thus, the original culture medium utilizes the fact that artificial seawater contains more mineral components such as metals than natural seawater. By reducing the amount of metal components, which are present in large quantities in conventional artificial culture media, to the bare minimum, it is possible to achieve lower costs.

[0019] The component compositions of natural seawater, artificial seawater (instant ocean), commercially available culture media, and original culture media are shown in the following table. Note that vitamins common to all culture media are not listed.

[0020] [Table 1]

[0021] "Instant Ocean," used as artificial seawater, has been found to have an extremely high content of metallic elements compared to natural seawater. In particular, Mo, Cu, Zn, and Co were thought to be present in sufficient quantities in the artificial culture medium. Furthermore, commercially available culture media have an uneven distribution of components; for example, boron (B) is included in culture medium B but not in the other two types of culture media, suggesting that it is likely unnecessary. Based on these considerations, the original culture medium was formulated with the following composition. Per liter of water, the following amounts are present: potassium nitrate 237.905 mg, dipotassium hydrogen phosphate 5.000 mg, Fe(III)-EDTA 5.200 mg, thiamine hydrochloride 0.200 mg, biotin 0.002 mg, vitamin B12 0.002 mg, manganese(II) chloride tetrahydrate 0.180 mg, sodium silicate 0.144 mg, and sodium selenite 0.002 mg.

[0022] The following table shows the compositions when combining commonly known culture media A (Daigo IMK medium), culture media B (Modified SWM-3 (mSWM-3) medium), and culture media C (f / 2 medium) with natural seawater, and when combining the original culture media with Instant Ocean.

[0023] [Table 2]

[0024] According to the table above, the combination of the original culture medium and Instant Ocean was found to have no missing atoms compared to the combination of commercially available culture medium and artificial seawater, and was confirmed to be well-balanced.

[0025] The original culture medium, as shown in the molar concentration, is shown in the following table in terms of weight concentration (unit: mg / L). Here, while all commercially available culture media use sodium nitrate (NaNO3) for nitrogen, the original culture medium uses potassium nitrate (KNO3), which is widely used in agriculture and is significantly cheaper.

[0026] [Table 3]

[0027] (2) Algae mixing process for feed This step involves adding a Chaetoceros strain, which has a fast growth rate and is used as feed algae, to the culture medium obtained in the culture medium manufacturing step and mixing it. In this example, and in each of the following test examples, either Chaetoceros tenuissimus or Chaetoceros gracilis was used as the Chaetoceros strain.

[0028] (Test Example 1) Using Chaetoceros strain gracilis, we conducted a comparative study of growth under different culture media using sodium nitrate and potassium nitrate as nitrogen sources, with all other conditions being the same. The results are shown in Figure 2. As shown in Figure 2, it was confirmed that a culture medium using potassium nitrate exhibits almost the same effect as a culture medium using sodium nitrate.

[0029] (Test Example 2) Using Chaetoceros gracilis as the strain, we cultured the original medium (with sodium selenite (Na2SeO3) removed from the original medium shown in the weight concentration above) and medium C under the same conditions of water temperature 25°C, LED irradiation, and aeration, and confirmed the growth status. The culture was performed using 500 ml bottles, with 2 conditions × 3 bottles = 6 bottles, and the average value of the 3 bottles was used to compare the two conditions. The results are shown in Figure 3. As shown in Figure 3, although there was no significant difference in growth rate, the original medium resulted in a slightly lower final yield. However, it was confirmed that it was possible to grow cells to a practically sufficient cell density.

[0030] (Test Example 3) Using Chaetoceros tenuissimus as the strain, the original medium and medium A, as indicated by the weight concentrations, were cultured under the same conditions of 25°C water temperature, LED irradiation, and aeration, and the growth status was confirmed. Culturing was performed using 500 ml bottles, with three bottles for the original medium and one bottle for medium A. The average value of the three bottles was then compared to that of medium A. The results are shown in Figure 4. As shown in Figure 4, the initial density of culture medium A was not measured, but from the second day onward, it was confirmed that the growth rate was comparable to that of commercially available culture media.

[0031] The original culture medium used in the culture medium manufacturing process according to this embodiment is optimized for Chaetoceros strains and can be reduced to less than half the cost of known culture medium combinations (reagent-based). In other words, the cost of commercially available Daigo IMK medium is 1,330 yen per 250 liters, and even if you prepare the individual components yourself, it will cost 370 yen, whereas this can be reduced to about 50 yen.

[0032] (3) Light irradiation process This process involves growing feed algae at high density by irradiating a culture medium, which contains feed algae mixed in the feed algae mixing process, with light to perform photosynthesis as an autotroph.

[0033] (4) Organic carbon source input process This process is carried out during the light irradiation process. When the growth of feed algae progresses through photosynthesis and the growth rate decreases due to high density, glucose is introduced as an organic carbon source, similar to heterotrophic culture, to support photosynthetic culture under light irradiation and promote further growth. By implementing this process, it becomes possible to further enhance the growth effect of feed algae compared to simply performing only steps (1) to (3) above in sequence. Here, the effect of bacterial growth is suppressed solely by controlling the timing of glucose addition, eliminating the need for sterilization equipment and allowing for the easy maintenance of a high growth rate.

[0034] (Test example 4) Using Chaetoceros gracilis as the strain, we conducted culture tests under identical conditions, comparing the growth rate and final yield when 0.1 g / liter of glucose was added as an organic carbon source and when it was not added, after the growth rate of feed algae increased and the density became high during the light irradiation process. The common test conditions were a water temperature of 25°C, LED irradiation, and aeration. For the first four days of the experiment, the plants were propagated using only inorganic carbon sources and normal photosynthesis. From day 4 onward, the growth rates were compared between treatments with and without glucose supplementation.

[0035] The test was conducted using 500 ml bottles, with 2 conditions × 3 bottles = 6 bottles, and the average value of the 3 bottles was used to compare the two conditions. Furthermore, the cell density of algae was determined by counting under a microscope using a Thoma hemocytometer. The results are shown in the following table.

[0036] [Table 4]

[0037] The growth rate data is shown in Figure 5. As shown in Figure 5, it was confirmed that adding glucose increased the rate of acceleration. The average data for growth rate and final yield are shown in the following table.

[0038] [Table 5]

[0039] Regarding growth rate, we defined the rate with the highest determination coefficient as the rate obtained by performing exponential regression on three or more data points after glucose addition, and compared them. As a result, the average growth rates of the three plants in each treatment group differed statistically significantly (t-test: P<0.05), confirming the effect of glucose addition. The final yield was defined as the average of the last two points where cell growth stopped and the cell count leveled off, and this was used for comparison. As a result, the average final yield of the three plants in each treatment group differed statistically significantly (t-test: P<0.05), confirming the effect of glucose supplementation.

[0040] (Examples 5-7 of the test) Using Chaetoceros gracilis as the strain, we investigated the phenomenon in which the final yield significantly increases when an organic carbon source is added after reaching high density and the growth rate has decreased through photosynthetic culture using only an inorganic carbon source. This was done in a small 4.5-liter test chamber under the same conditions, with a water temperature of 27°C, LED irradiation, aeration, and the addition of 1 g / liter of glucose as the organic carbon source, with only the test day being changed. Three tests were conducted under the same conditions. Example Test 5 is for a test that began on May 10, 2021. Test example 6 is for a test that began on May 30, 2021. Test example 7 is for a test that began on July 5, 2021. In all of the tests, the carbon content was increased using only an inorganic carbon source for a period of time from the start of the experiment. Glucose was added during the later stages of culture when the growth rate plateaued, and the subsequent growth status was monitored.

[0041] The results of Test Example 5 are shown in Figure 6. The results of Test Example 6 are shown in Figure 7. The results of Test Example 7 are shown in Figure 8.

[0042] In all three experiments, it was confirmed that when the plants were grown using only an inorganic carbon source through normal photosynthesis, the growth rate plateaued in the later stages of cultivation. In other words, with photosynthesis using only inorganic carbon sources, the growth rate slows down in the later stages of cultivation, and the yield plateaus early on. However, when glucose, an organic carbon source, was added afterward, further growth was confirmed in all three experiments. By promoting the use of inorganic carbon sources during the later stages of cultivation, when the growth rate slows down, heterotrophic growth can be promoted, thereby increasing the final yield. The reason the growth rate is lower in the initial stages of cultivation is that the culture medium is diluted during the initial stages (which makes growth easier), and additional culture medium is added (top dressing) after a certain amount of growth is achieved to allow the plants to grow to the density required for the final yield.

[0043] The test results statistically confirmed that adding heterotrophic growth using an organic carbon source, a different mechanism, to normal photosynthesis using an inorganic carbon source increased the growth rate and ultimately increased the final yield. Furthermore, while the growth rate slows down in the later stages of cultivation when using only inorganic carbon sources for normal photosynthesis, it has been confirmed through multiple trials that by utilizing organic carbon sources at that point, further growth can occur, thereby increasing the final yield.

[0044] Furthermore, since organic carbon sources can also be utilized by bacteria, competition between algae and bacteria will occur after their addition. Therefore, it is necessary to devise culture conditions that prevent the massive proliferation of bacteria. It was thought that adding an organic carbon source in the later stages of cultivation shortened the time it took for bacteria to grow (the time from the addition of organic carbon to harvest) and helped to maintain a sufficiently low bacterial biomass so as not to affect the final yield of algae.

[0045] (Test Example 8) Using Chaetoceros strain gracilis, a 4.5-liter small test chamber employing a batch culture method was used. Under conditions of a water temperature of 25°C, LED irradiation, and aeration, Daigo IMK medium was used. The culture was autoclaved, and initially, no organic carbon source was added. When the growth rate began to decrease, the organic carbon source (glucose 1g / liter) was added. On each measurement day, we examined the cell density of algae and bacteria. At that time, the number of bacteria was counted using nucleic acid fluorescence staining with DAPI. Note that the bacterial density is quite low at the start of cultivation. The photosynthetic cultivation was continued without using an organic carbon source. Once the algae reached a certain density, an organic carbon source was added, and the cultivation was then carried out in a cycle of short-term harvesting. The results are shown in Figure 9.

[0046] Looking at the results of test example 8, the bacteria were 200 × 10 4 The density remained lower than cells / ml and increased after the addition of an organic carbon source. The algae proliferated well before the introduction of the organic carbon source, and further proliferation was observed some time after the introduction of the organic carbon source. This suggests that the number of bacterial cells was suppressed to a degree that did not affect the growth of algae.

[0047] (Test Example 9) Using Chaetoceros strain gracilis, and employing a batch culture method similar to that in Test Example 8, a 4.5-liter small test chamber was used. Under conditions of a water temperature of 25°C, LED irradiation, and aeration, Daigo IMK medium was used. Autoclave sterilization was not performed, and the culture was initially carried out without the addition of an organic carbon source. The organic carbon source (glucose 0.5 g / liter) was added the day before the planned harvest date. On each measurement day, we examined the cell density of algae and bacteria. At that time, the number of bacteria was counted using nucleic acid fluorescence staining with DAPI. The results are shown in Figure 10.

[0048] Looking at the results of Test Example 9, similar to the sterilization case, the period from the beginning until the introduction of the organic carbon source was 200 × 10 4 The density remained lower than cells / ml and increased after the addition of an organic carbon source. Although the algae showed a decrease in cell number due to the decrease in salinity, they generally proliferated well before the introduction of the organic carbon source, and further proliferation was observed after the introduction of the organic carbon source. This suggests that even without sterilization, the number of bacterial cells was suppressed to a degree that did not affect the growth of algae.

[0049] By adding an organic carbon source, which serves as food for bacteria, towards the end of the algae cultivation process, it is possible to suppress the rapid proliferation of bacteria while promoting the healthy growth of algae. Furthermore, this effect was observed even without sterilization procedures, just as it was with sterilization. This indicates that by optimizing the timing of adding an organic carbon source in a batch culture system, high-density cultivation of algae can be achieved without aseptic techniques.

[0050] (Test Example 10) To determine the culture medium concentration at which the feed algae proliferate at the highest density, tests were conducted under different culture medium concentrations and the following conditions. The experiment was conducted using Chaetoceros gracilis as the culture medium, with LED irradiation at a water temperature of 25°C and under aeration conditions, using the original culture medium described in the table in paragraph

[0026] from which sodium selenite (Na2Se03) had been removed. The experiment involved culturing algae to a density of 1.6 million cells / mL and then adding the original culture medium at 1x (indicated as Kyuei 1x), 3x (indicated as Kyuei 3x), and 5x (indicated as Kyuei 5x) concentrations to promote growth. In this study, three 500 mL bottles were used for each concentration, and the culture conditions were compared by measuring the cell density after culturing for six days. The results are shown in Figure 11.

[0051] The results of Test Example 10 show that when culture media of each concentration was added as supplemental fertilizer, the maximum cell density was 5.07 million cells / mL (day 6) with a 1x fertilizer, 5.61 million cells / mL (day 6) with a 3x fertilizer, and 4.34 million cells / mL (day 4) with a 5x fertilizer. Therefore, since using five times the amount of fertilizer may have resulted in the growing medium being too concentrated and reducing the plant's ability to grow, it was determined that one to three times the amount of fertilizer would be appropriate. Based on the above considerations, it was determined that the appropriate amount of culture medium to be added to the artificial seawater, including the amount used for prior cultivation, is 1 to 4 times the amount of the standard original culture medium.

[0052] (Test Example 11) To determine the optimal culture medium concentration for the highest density of algae growth, tests were conducted under different sodium silicate concentrations and the following conditions. The experiment was conducted under an aerated environment with LED irradiation at a water temperature of 25°C, using the original culture medium described in the table in paragraph

[0026] as the reference medium, and Chaetoceros gracilis as the Chaetoceros strain. In the experiment, algae were cultured in three stages, varying only the sodium silicate content of the standard culture medium: 1 / 10th the amount (0.072 mg / L), 1x the amount (0.72 mg / L), and 10x the amount (7.2 mg / L). For each concentration, three 500 mL bottles were used for incubation for 5 days, and the culture conditions were compared by measuring the cell density. The results are shown in Figure 12.

[0053] The results of Test Example 11 showed that the maximum cell density was reached on day 4 of culture under all conditions. The densities were 5.81 million cells / mL with 1 / 10 the amount of sodium silicate, 7.56 million cells / mL with 1x the amount, and 7.16 million cells / mL with 10x the amount. Since the algal yield decreased when the amount was reduced to 1 / 10th, it was determined that the appropriate amount of sodium silicate to add to the original culture medium is 1 to 10 times the standard amount (0.144 to 1.44 mg / L).

[0054] Based on the results of Test Examples 10 and 11 above, the preferred range of additive amounts in the original culture medium composition is shown in the following table. [Table 6] [Explanation of Symbols]

[0055] 1 Culture solution manufacturing process 2 Algae mixing process for feed 3 Light irradiation process 4. Organic carbon source input process

Claims

1. After the culture medium manufacturing process, which involves mixing an algal culture medium, primarily composed of nitrate from potassium nitrate and containing phosphate, silicon, manganese, iron, and selenium, with artificial seawater prepared by dissolving an artificial seawater base (which has a higher content of metal elements including Mo, Cu, Zn, and Co compared to natural seawater) in tap water, a culture medium is produced. In the culture medium manufacturing process, feed algae are added to the culture medium and mixed in a feed algae mixing process. A method for cultivating algae for feed, characterized by performing a light irradiation step, in which the algae mixed culture medium obtained by the feed algae mixing step is irradiated with light to perform photosynthesis and grow the feed algae at high density.

2. The method for cultivating feed algae according to claim 1, characterized in that when the growth rate of feed algae decreases in the light irradiation step, the growth rate is improved by performing an organic carbon source input step, in which an organic carbon source is introduced.

3. The method for cultivating algae for feed according to claim 2, characterized in that the organic carbon source used in the light irradiation step is glucose.

4. A method for culturing algae for feed according to any one of claims 1 to 3, characterized in that the algae used in the aforementioned algae mixing step for feed are algae of the genus Chaetoceros.

5. A method for culturing feed algae according to any one of claims 1 to 3, characterized in that the feed algae used in the feed algae mixing step is an alga of the genus Chaetoceros, specifically Tenuissimus or Gracilis.

6. A culture medium used when cultivating algae for feed, A culture medium for algae, characterized by containing 100,000 to 990,000 mg of potassium nitrate, 3,000 to 30,000 mg of dipotassium hydrogen phosphate, 3,000 to 30,000 mg of Fe(III)-EDTA, 0,100 to 1,000 mg of thiamine hydrochloride, 0,001 to 0,010 mg of biotin, 0,001 to 0,010 mg of vitamin B12, 0,100 to 0,900 mg of manganese(II) chloride tetrahydrate, 0,050 to 8,000 mg of sodium silicate, and 0,001 to 0,010 mg of sodium selenite per liter of water.

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