Microalgae culture method

Abstract

The invention relates to a microalgae culture method which comprises the following steps: culturing microalgae species in the presence of a fat-soluble additive to obtain a culture solution containing floating layer microalgae; and harvesting the microalgae on the floating layer. The fat-soluble additive is introduced in the microalgae culture process, the concentration of a microalgae floating layer can be effectively improved, the viscosity of the microalgae is improved, and therefore the culture efficiency and the harvesting efficiency of the microalgae are remarkably improved.

Description

Technical Field

[0001] The present disclosure relates to the field of microalgae biotechnology, and in particular, to a microalgae cultivation method. Background Art

[0002] Microalgae are ancient single-cell producers on Earth. They are widely distributed and can survive on land, lakes, and oceans. They are small in size, simple in structure, rich in nutrients, and have strong photosynthesis ability to convert light energy into chemical energy. They can convert water, carbon dioxide, and inorganic salts into organic matter and provide their own growth. Microalgae can not only be used directly as food, but also as an important raw material for medicines, health products, feed, and bioengineering products. Some microalgae also have a high ability to produce unsaturated fatty acids and have good application prospects in energy utilization. In today's global energy crisis and increasingly polluted environment, the development and utilization of microalgae biological resources have important social, economic, and environmental benefits.

[0003] At present, industrial cultivation devices for microalgae mainly include open pools and closed photobioreactors. Both types of photobioreactors currently have problems with light utilization and cost. Therefore, it is particularly important to reduce the cost of light sources and improve light utilization efficiency. Among the existing light sources, sunlight is one of the most abundant natural resources on the earth. The use of sunlight not only does not have the problem of power consumption of artificial light sources, but also has a wide wavelength of light, which is very suitable for the cultivation of microalgae. However, when sunlight passes through the algae culture solution, it will be severely attenuated, and the distance that the light can pass is limited, resulting in the formation of dark areas in the deep algae solution due to lack of light, and the light intensity of sunlight staying on the surface of the algae solution often exceeds the saturated light intensity required by the microalgae, resulting in low solar energy utilization, affecting the culture density and yield per unit area of ​​algae, and low breeding efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a microalgae cultivation method to significantly improve the cultivation efficiency and harvesting efficiency of microalgae.

[0005] In order to achieve the above object, the present disclosure provides a microalgae cultivation method, the method comprising:

[0006] Cultivating the microalgae species in the presence of a fat-soluble additive to obtain a culture solution containing floating layer microalgae; wherein the content of the fat-soluble additive is 0.01 to 0.1 volume‰ based on the total volume of the culture solution containing the floating layer microalgae;

[0007] The floating layer microalgae are harvested.

[0008] Optionally, the microalgae species is one or more selected from Spirulina species, Anabaena species, Oscillatoria species and Aphanizomenon species.

[0009] Optionally, based on the total volume of the culture solution containing the floating layer microalgae, the content of the fat-soluble adjuvant is 0.05 to 0.08 volume‰.

[0010] Optionally, the fat-soluble auxiliary agent is one or more selected from fatty compounds, polyether compounds and silicone compounds.

[0011] Optionally, the fatty compound is one or more selected from lauric acid, palmitic acid, animal oil and vegetable oil;

[0012] The polyether compound is polyoxyethylene ether and / or polyoxypropylene ether;

[0013] The organosilicon compound is polydimethylsiloxane and / or organic modified polysiloxane.

[0014] Optionally, the method further comprises: when the concentration of the culture solution containing the floating layer microalgae is 0.05-0.4 g / L, adding the fat-soluble auxiliary agent to carry out the culture.

[0015] Optionally, the culture conditions include: an algae liquid depth of 5 to 100 cm, a temperature of 22 to 28° C., a light intensity of 0 to 25 KLux, and a pH value of 8.5 to 10.5.

[0016] Optionally, the culturing includes alternating illumination culturing and non-illumination culturing;

[0017] The light culture comprises a first stirring section and a first non-stirring section which are performed alternately;

[0018] The non-lighting culture includes a second non-agitation section and an optional second agitation section;

[0019] On each culture day, the total duration of the first stirring stage and the second stirring stage is 2 to 12 hours.

[0020] Optionally, the harvesting is at least one of filtering-type harvesting, scraper-type harvesting and suction-cup-type harvesting.

[0021] Optionally, the method further comprises: after harvesting the floating layer microalgae, using the remaining culture solution for cyclic culture.

[0022] Through the above technical solution, the present invention introduces a fat-soluble additive during the microalgae cultivation process, which can effectively increase the concentration of the microalgae floating layer and increase the viscosity of the microalgae, thereby significantly improving the cultivation efficiency and harvesting efficiency of the microalgae.

[0023] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0024] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0025] The present disclosure provides a microalgae cultivation method, which comprises: cultivating microalgae species in the presence of a fat-soluble auxiliary agent to obtain a culture solution containing floating layer microalgae; wherein the content of the fat-soluble auxiliary agent is 0.01 to 0.1 volume‰ based on the total volume of the culture solution containing the floating layer microalgae; and harvesting the floating layer microalgae.

[0026] According to the present disclosure, the microalgae is a microalgae with floating characteristics, that is, in an undisturbed state, the microalgae tend to float on the surface of the culture solution to form a floating layer of a certain thickness, and the thickness of the floating layer is usually between 0.1 and 5 mm. Specifically, the microalgae species can be one or more selected from Spirulina species, Anabaena species, Oscillatoria agardhii species and Aphanizomenon species, preferably Spirulina species and Anabaena species.

[0027] According to the present disclosure, the lipophilic additive refers to a substance that can be dissolved in a non-polar solvent. By introducing the lipophilic additive, the concentration of microalgae in the floating layer can be effectively increased and the viscosity of the microalgae can be increased during the microalgae cultivation process, thereby significantly improving the cultivation efficiency of microalgae.

[0028] The fat-soluble additive can be one or more selected from fatty compounds, polyether compounds and organosilicon compounds. The above-mentioned fat-soluble additives also have a defoaming effect, which can reduce the foam in the culture solution during the breeding process.

[0029] Furthermore, the fatty compound may be one or more selected from lauric acid, palmitic acid, animal oil and vegetable oil; the polyether compound may be polyoxyethylene ether and / or polyoxypropylene ether; the organosilicon compound may be polydimethylsiloxane and / or organic modified polysiloxane, wherein the polydimethylsiloxane may be, for example, dimethyl silicone oil.

[0030] In a preferred embodiment, the fat-soluble adjuvant is dimethyl silicone oil and / or edible vegetable oil. The use of the above-mentioned fat-soluble adjuvant is conducive to maximizing the cultivation efficiency of microalgae.

[0031] In a preferred embodiment, based on the total volume of the culture solution containing the floating layer microalgae, the content of the fat-soluble additive is 0.05 to 0.08 volume‰, so as to further improve the cultivation efficiency of microalgae.

[0032] According to the present disclosure, there is no special restriction on the timing of applying the fat-soluble adjuvant. For example, it can be directly added to the culture medium, or it can be added to the algae liquid at any stage of the culture. In one embodiment, the fat-soluble adjuvant is added when the concentration of the algae liquid is in a suitable range to effectively improve the cultivation efficiency of microalgae. Specifically, the method includes: when the concentration of the culture solution containing the floating layer microalgae is 0.05-0.4 g / L, the fat-soluble adjuvant is added for the culture; preferably, when the concentration of the culture solution containing the floating layer microalgae is 0.15-0.3 g / L, the fat-soluble adjuvant is added for the culture. The fat-soluble adjuvant can be added all at once or in batches, as long as the total amount meets the above-mentioned dosage range.

[0033] The culture can be carried out under conventional microalgae culture conditions in the art, using a culture medium well known in the art. Specifically, the culture conditions may include: an algae liquid depth of 5 to 100 cm, a temperature of 22 to 28°C, a light intensity of 0 to 25 Klux, and a pH value of 8.5 to 10.5. The culture medium used in the culture may be a Z's medium (Zarrouk medium), a BG11 medium, etc., preferably a Z's medium. The culture can be carried out in a bioreactor, which may be an open reactor or a closed reactor with an artificial light source. The culture time can be adjusted as needed. For example, the culture time can be 5 to 21 days, i.e., 120 to 504 hours, where every 24 hours is a culture day.

[0034] In one embodiment, the culture may include alternating illumination culture and non-illumination culture to promote floating culture of microalgae. The illumination intensity of the illumination culture may be 5-25Klux, and the light-dark cycle ratio in each culture day (24h) is 12h / 12h.

[0035] Furthermore, the light culture includes a first stirring section and a first non-stirring section that are performed alternately, and the non-light culture includes a second non-stirring section and an optional second stirring section to further promote the generation of floating layer microalgae. The first stirring section and the second stirring section refer to the process in which the culture solution containing microalgae is disturbed, and the stirring method of the first stirring section and the second stirring section can be airlift bubbling or turbine stirring, preferably airlift bubbling. The first non-stirring section and the second non-stirring section refer to the process in which the culture solution containing microalgae is left to stand. Specifically, in each culture day (24 hours), the conditions of the first stirring section may include: the stirring method is airlift bubbling, the ventilation volume is 0.02 to 0.2 L / min relative to 1L of the culture solution containing the floating layer microalgae, and the ventilation time is 2 hours to 12 hours; the conditions of the first non-stirring section may include: the temperature is 22 to 28°C, and the time is 1 hour to 8 hours; the conditions of the second stirring section may include: the stirring method is airlift bubbling, the ventilation volume is 0.02 to 0.2 L / min relative to 1L of the culture solution containing the floating layer microalgae, and the time is 0 hours to 5 hours; the conditions of the second non-stirring section may include: the temperature is 22 to 28°C, and the time is 5 hours to 16 hours; the total duration of the first stirring section and the second stirring section may be 2 to 12 hours. When the lipophilic additive is added during the culture process, the lipophilic additive can be added to the algae solution at any one or more stages of the first stirring stage, the first non-stirring stage, the second stirring stage, and the second non-stirring stage. When a floating layer of microalgae has been formed in the culture solution, the lipophilic additive is preferably added to the floating layer of microalgae.

[0036] Through the above-mentioned cultivation, the algae liquid in the obtained culture liquid is naturally stratified, wherein a large amount of floating layer microalgae and a small amount of suspended layer microalgae are contained, and the floating layer microalgae are mature microalgae to be harvested. The thickness of the floating layer microalgae can be 0.1-5 mm.

[0037] According to the present disclosure, the method for harvesting the floating layer microalgae can be conventional in the art. Specifically, the harvesting can be at least one of filtration-type harvesting, scraper-type harvesting and suction cup-type harvesting. Among them, the filtration-type harvesting is a method of filtering the culture solution with a filtration device to obtain the floating layer microalgae. The scraper-type harvesting is a method of scraping the floating layer microalgae in the culture solution with a scraper device, which can be a mechanical automated scraper harvesting or a manual scraper harvesting. The scraper device may include a connected scraper head and a connecting rod, wherein the angle between the scraper head and the connecting rod may be 90 to 135°, the thickness of the scraper head may be no more than 0.5 cm, and the shape of the scraper head may be a horizontal V-shape (the inner angle of the V-shape does not exceed 45°). The material of the scraper head is not particularly limited. The suction cup harvesting is a method for harvesting floating layer microalgae in the culture solution by the suction of a suction cup device, the suction cup device can be a mobile suction cup (the moving speed can be 0.5-5m / min) or a fixed suction cup, the center of the suction cup is provided with a channel, the channel is connected to a peristaltic pump, the area of ​​the channel is 1 / 100-1 / 10 of the total area of ​​the suction cup, the material of the suction cup is not particularly limited, it can be metal or non-metal, preferably stainless steel or plastic. When the harvesting is scraper harvesting and / or suction cup harvesting, it is beneficial to improve the harvesting efficiency of the floating layer microalgae.

[0038] The floating layer microalgae obtained by the harvesting can be directly stored as microalgae products, or sent to a next-stage processing device for further processing. The next-stage processing device can be, for example, a separation device, preferably a centrifugal device and / or a filtration device.

[0039] In one embodiment, the method further comprises: after harvesting the floating layer microalgae, the remaining culture solution is used for cyclic culture. The cyclic culture means that after harvesting, the remaining culture solution can be subjected to ion measurement and appropriate nutrients can be optionally supplemented according to the measurement results, and then the above-mentioned culture is repeated, thereby realizing cyclic cultivation of microalgae.

[0040] The technical solution disclosed in the present invention is simple and easy to implement, can significantly improve the cultivation efficiency of microalgae, is compatible with the optimization of other cultivation conditions, can be easily embedded in existing microalgae production technology, and has good prospects for promotion and application.

[0041] The present disclosure is further described in detail below in conjunction with embodiments, but the present disclosure is not limited thereto.

[0042] The Spirulina platensis and Anabaena sp. strain PCC used in the examples were purchased from the Institute of Hydrobiology, Chinese Academy of Sciences.

[0043] Calculation method for microalgae culture solution concentration: Absorb a certain volume of microalgae solution (V, L), filter it with a 400-mesh filter cloth, dry the filter residue in a 60°C constant temperature drying oven for 48 hours, weigh it (m, g), and calculate the culture solution concentration (m / V, g / L).

[0044] The proportion of breeding efficiency and harvesting efficiency is calculated according to the following formula:

[0045] Breeding efficiency (g / m 2 / D) = (final culture solution concentration - initial culture solution concentration) × algae culture depth / culture time

[0046] Harvest efficiency ratio (%) = weight of dry algae powder collected after harvesting / (final culture solution concentration × algae culture volume) × 100%

[0047] Example 1

[0048] The Spirulina algae were inoculated into a 60 L (1 m × 0.4 m × 0.15 m) open box photobioreactor using Z's medium. The concentration of the culture solution after inoculation was 0.18 g / L, and 0.05‰ (v / v) dimethyl silicone oil was added to the algae solution. The depth of the algae liquid was 10 cm, the temperature was 22-28°C, and the pH value was 8.5-10.5. In each culture day (24 h), light culture (light intensity 12 KLux) and non-light culture (light intensity 0 KLux) were carried out alternately. The light-dark cycle ratio was 12 h / 12 ​​h. In the light culture, the first stirring stage (temperature 22-28°C, airlift bubbling, relative to 1 L of algae liquid, the ventilation volume was 0.1 L / min, and the ventilation time was 6 h) and the first non-stirring stage (temperature 22-28°C, 6 hours) were carried out alternately. In the non-light culture, the second non-stirring stage (temperature 22-28°C, 12 h) was carried out. The algae liquid in the reactor was naturally stratified, and the thickness of the floating layer of algae liquid was about 0.5 mm.

[0049] A circular suction cup with a diameter of 5 cm and a central opening radius of 0.5 cm was placed in the reactor. The suction cup was inserted into the algae liquid surface by about 1 to 2 mm. The suction cup was made of PVC and connected to a peristaltic pump through a hose. The flow rate of the peristaltic pump used was 5 L / min. The floating layer microalgae were harvested by manually moving the suction cup. The suction cup moved at a speed of about 3 m / min, and the harvesting was completed after 0.3 min. After the harvesting was completed, the suction cup was removed, the remaining microalgae culture solution in the reactor was stirred, and the elemental composition was detected and the required nutrients were added to continue the cyclic cultivation of microalgae.

[0050] After 5 days of cultivation, when the concentration of the culture medium was 0.42 g / L, the floating layer was harvested, and about 1.5 L of floating layer microalgae were collected, accounting for 3.75% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 11.9 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0051] Example 2

[0052] The microalgae were cultured according to the method of Example 1, except that edible vegetable oil was used as a fat-soluble adjuvant instead of the dimethyl silicone oil in Example 1.

[0053] After 6 days of cultivation, when the concentration of the culture medium was 0.44 g / L, the floating layer was harvested, and about 1.95 L of floating layer microalgae were collected, accounting for 4.88% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 12.43 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0054] Example 3

[0055] Microalgae were cultured according to the method of Example 1, except that dimethyl silicone oil was added when the concentration of the culture solution after inoculation was 0.05 g / L.

[0056] After 11 days of cultivation, when the concentration of the culture medium was 0.42 g / L, the floating layer was harvested, and about 1 L of floating layer microalgae was collected, accounting for 2.5% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 10.12 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0057] Example 4

[0058] The microalgae were cultured according to the method of Example 1, except that dimethyl silicone oil was added when the culture solution concentration reached 0.4 g / L.

[0059] After 7 days of cultivation, when the concentration of the culture medium was 0.44 g / L, the floating layer was harvested, and about 1.25 L of floating layer microalgae was collected, accounting for 3.13% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 10.53 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0060] Example 5

[0061] The microalgae were cultured according to the method of Example 1, except that 0.01‰ (v / v) dimethyl silicone oil was added to the algae solution.

[0062] After 8 days of cultivation, when the concentration of the culture medium was 0.45 g / L, the floating layer was harvested, and about 1.15 L of floating layer microalgae were collected, accounting for 2.88% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 9.66 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0063] Example 6

[0064] The microalgae were cultured according to the method of Example 1, except that 0.1‰ (v / v) dimethyl silicone oil was added to the algae solution.

[0065] After 7 days of cultivation, when the concentration of the culture medium was 0.45 g / L, the floating layer was harvested, and about 1.3 L of floating layer microalgae were collected, accounting for 3.25% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 10.24 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0066] Example 7

[0067] The microalgae were cultured according to the method of Example 1, except that palmitic acid was used as a fat-soluble adjuvant to replace the dimethicone in Example 1.

[0068] After 7 days of cultivation, when the concentration of the culture medium was 0.46 g / L, the floating layer was harvested, and about 1.4 L of floating layer microalgae were collected, accounting for 3.5% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 11.78 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0069] Example 8

[0070] The microalgae were cultured according to the method of Example 1, except that the algae species used were Anabaena species.

[0071] After 7 days of cultivation, when the concentration of the culture medium was 0.47 g / L, the floating layer was harvested, and about 1.55 L of floating layer microalgae were collected, accounting for 3.88% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 12.13 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0072] Example 9

[0073] Microalgae were cultured according to the method of Example 1, except that only the first stirring stage (temperature 22-28°C, airlift bubbling, aeration volume of 0.1 L / min relative to 1 L of algae liquid, and aeration time of 12 h) was performed in the light culture, and the second stirring stage (temperature 22-28°C, airlift bubbling, aeration volume of 0.1 L / min relative to 1 L of algae liquid, and aeration time of 12 h) was performed in the non-light culture.

[0074] After 5 days of cultivation, when the concentration of the culture medium was 0.35 g / L, the floating layer was harvested, and about 0.9 L of floating layer microalgae was collected, accounting for 2.25% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 8.33 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0075] Comparative Example 1

[0076] The microalgae were cultured according to the method of Example 1, except that dimethicone was not added.

[0077] After 8 days of cultivation, when the concentration of the culture medium was 0.41 g / L, about 0.85 L of floating layer microalgae was collected, accounting for 2.13% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 7.6 g of dry algae powder, and the proportion of breeding efficiency and harvesting efficiency was calculated and listed in Table 1.

[0078] Comparative Example 2

[0079] The microalgae were cultured according to the method of Example 1, except that 0.001‰ (v / v) dimethyl silicone oil was added to the algae solution.

[0080] After 8 days of cultivation, when the concentration of the culture medium was 0.42 g / L, about 0.9 L of floating layer microalgae was collected, accounting for 2.25% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 7.9 g of dry algae powder, and the proportion of breeding efficiency and harvesting efficiency was calculated and listed in Table 1.

[0081] Comparative Example 3

[0082] Microalgae were cultured according to the method of Example 1, except that dimethyl silicone oil was not added, and only the first stirring stage was performed in the light culture (temperature 22-28°C, airlift bubbling, aeration volume of 0.1 L / min relative to 1 L of algae liquid, and aeration time of 12 h), and the second stirring stage was performed in the non-light culture (temperature 22-28°C, airlift bubbling, aeration volume of 0.1 L / min relative to 1 L of algae liquid, and aeration time of 12 h).

[0083] After 10 days of cultivation, when the concentration of the culture medium was 0.45 g / L, about 0.75 L of floating layer microalgae was collected, accounting for 1.88% of the total culture medium volume; the harvested floating layer microalgae were separated and dried to obtain 6.94 g of dry algae powder, and the cultivation efficiency and harvesting efficiency ratio were calculated and listed in Table 1.

[0084] Table 1

[0085] Example <![CDATA[Breeding efficiency (g / m 2 / day)]]> Recovery efficiency ratio (%) Example 1 4.80 70.83 Example 2 4.33 70.63 Example 3 3.36 60.24 Example 4 3.71 59.83 Example 5 3.38 53.67 Example 6 3.86 56.89 Example 7 4.00 64.02 Example 8 4.14 64.52 Example 9 3.40 59.50 Comparative Example 1 2.88 46.34 Comparative Example 2 3.00 47.02 Comparative Example 3 2.70 38.56

[0086] As can be seen from Table 1, the cultivation of microalgae using the disclosed method has higher cultivation efficiency and harvesting efficiency.

[0087] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0088] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0089] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for cultivating microalgae, characterized in that: The method includes: Cultivating the microalgae species in the presence of a fat-soluble additive to obtain a culture solution containing floating layer microalgae; wherein the content of the fat-soluble additive is 0.01 to 0.1 volume‰ based on the total volume of the culture solution containing the floating layer microalgae; The floating layer microalgae are harvested.

2. The method according to claim 1, wherein: The microalgae species are one or more species selected from Spirulina, Anabaena, Oscillatoria axolotl and Aphanizomenon.

3. The method according to claim 1, wherein: Based on the total volume of the culture solution containing the floating layer microalgae, the content of the fat-soluble auxiliary agent is 0.05 to 0.08 volume‰.

4. The method according to claim 1, wherein: The fat-soluble auxiliary agent is one or more selected from fatty compounds, polyether compounds and organosilicon compounds.

5. The method according to claim 4, wherein: The fatty compound is one or more selected from lauric acid, palmitic acid, animal oil and vegetable oil; The polyether compound is polyoxyethylene ether and / or polyoxypropylene ether; The organosilicon compound is polydimethylsiloxane and / or organic modified polysiloxane.

6. The method according to claim 1, wherein: The method further comprises: when the concentration of the culture solution containing the floating layer microalgae is 0.05-0.4 g / L, adding the fat-soluble auxiliary agent to carry out the culture.

7. The method according to claim 1, wherein: The culture conditions include: algae liquid depth of 5 to 100 cm, temperature of 22 to 28° C., light intensity of 0 to 25 Klux, and pH value of 8.5 to 10.

5.

8. The method according to claim 1, wherein: The culturing includes alternating light culturing and non-light culturing; The light culture comprises a first stirring section and a first non-stirring section which are performed alternately; The non-lighting culture includes a second non-agitation section and an optional second agitation section; On each culture day, the total duration of the first stirring stage and the second stirring stage is 2 to 12 hours.

9. The method according to claim 1, wherein: The harvesting is at least one of filtering harvesting, scraper harvesting and suction cup harvesting.

10. The method according to claim 1, wherein: The method further comprises: after harvesting the floating layer microalgae, using the remaining culture solution for cyclic culture.