Algaculture system and algaculture method using same

Abstract

An algaculture system according to the present invention comprises: an algaculture means which is immersed in water and to which algae are fixed; and an adhesion substrate which is provided at an interval below the algaculture means. Here, the shortest distance between the algaculture means and the adhesion substrate is 3.0-14.5 m.

Description

Algae cultivation system and algae cultivation method using the same

[0001] The present invention relates to an algae cultivation system and a method for cultivating algae using the same.

[0002] To solve the problem of global warming, the importance of aiming for "carbon neutrality" - zero greenhouse gas emissions - has been emphasized both domestically and internationally. Possible strategies for achieving carbon neutrality include (i) reducing anthropogenic CO emissions. ２ and (ii) technological development and behavioral changes to reduce CO2 emissions into the environment. ２ These can be broadly divided into two categories: development of negative emission technologies that capture and absorb CO2.

[0003] However, compared with strategy (i), technological development for strategy (ii) has not progressed sufficiently, and drastic research and development is needed.

[0004] On the other hand, low concentrations of CO present in the atmosphere ２ The natural process carried out by macroalgae against CO ２ As shown in Table 1, algal (3G) biomass, which includes macroalgae and microalgae, has higher productivity per year compared to starch-based (1G) and woody (2G) biomass. In particular, macroalgae have a higher CO2 content than other biomass. ２ It is known that the absorption / fixation ratio is extremely high and the biomass energy production process and production conditions are relatively simple (Non-Patent Document 1).

[0005]

[0006] Japan is an island nation surrounded by the sea, and has an exclusive economic zone (EEZ) that is approximately 12 times the size of its land area (the sixth largest in the world). This means that there are many seaweed beds suitable for cultivating large algae.

[0007] However, in order to achieve carbon neutrality, it is important to expand seaweed beds, and it is also desirable to improve the production efficiency of macroalgae in each seaweed bed. Furthermore, the maturation period of macroalgae is limited to certain periods throughout the year. It must be said that we are far from achieving stable carbon neutrality throughout the year.

[0008] Management Sensor, "Industrial Use of Microalgae", Toray Business Research Institute, December 2021, pp. 5-9

[0009] The present invention aims to solve the above problems, and its purpose is to provide an algae cultivation system that can more efficiently cultivate various types of algae, including large algae, and that can accommodate a variety of production scales, as well as an algae cultivation method using the same.

[0010] The present invention is an algae cultivation system comprising: an algae cultivation means immersed in water and having algae fixed thereto; and a settlement substrate provided below the algae cultivation means at a distance, wherein the shortest distance between the algae cultivation means and the settlement substrate is 3.0 m to 14.5 m.

[0011] In one embodiment, the water is natural seawater or artificial seawater.

[0012] In further embodiments, the algae is at least one macroalgae selected from the group consisting of Sargassaceae brown algae and Laminariales brown algae.

[0013] In a further embodiment, the algae cultivation means is fixed in a suspended state in the seawater.

[0014] The present invention also provides a method for cultivating algae, comprising the steps of: immobilizing algae in an algae cultivation means in the algae cultivation system underwater; conjugately cultivating the algae on a settlement substrate in the algae cultivation system through zoospores or fertilized eggs released by the algae; and recovering the algae from both the algae cultivation means and the settlement substrate.

[0015] In one embodiment, the water is natural seawater or artificial seawater.

[0016] In one embodiment, the algae is at least one macroalga selected from the group consisting of Sargassum serrata, Sargassum tamahahakiensis, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum endodonticum, Sargassum yatsumatamoku, kelp, Wakame, Antokume, Eisenia bicolor, Eisenia bicolor (a subspecies of Ecklonia cava), Ecklonia cava, and Sagarame.

[0017] In a further embodiment, the algae is cultivated continuously throughout the year under conditions where the algae species are changed to coincide with the time of maturity.

[0018] The present invention also provides a method for producing a bioethanol feedstock, comprising the steps of: immobilizing algae on an algae cultivation means in an underwater algae cultivation system; conjugately cultivating the algae on a settlement substrate in the algae cultivation system through zoospores or fertilized eggs released by the algae; and recovering the algae from both the algae cultivation means and the settlement substrate as the bioethanol feedstock.

[0019] In one embodiment, the water is natural seawater or artificial seawater.

[0020] In one embodiment, the algae is at least one macroalga selected from the group consisting of Sargassum serrata, Sargassum tamahahakiensis, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum endodonticum, Sargassum yatsumatamoku, kelp, Wakame, Antokume, Eisenia bicolor, Eisenia bicolor (a subspecies of Ecklonia cava), Ecklonia cava, and Sagarame.

[0021] In a further embodiment, the algae is cultivated continuously throughout the year under conditions where the algae species are changed to coincide with the time of maturity.

[0022] According to the present invention, it is possible to efficiently cultivate algae, such as macroalgae, by increasing productivity per unit area of ​​the seaweed bed. Furthermore, no special machinery is required for this cultivation. Furthermore, it is possible to cultivate algae almost continuously throughout the year, and the resulting algae can be provided more stably as a raw material for, for example, ethanol.

[0023] Fig. 1 is a schematic diagram showing an example of an algae cultivation system of the present invention. Fig. 2 is a schematic diagram showing another example of an algae cultivation system of the present invention. Fig. 3 is a schematic diagram showing yet another example of an algae cultivation system of the present invention. Fig. 4 is a diagram showing a relationship between the types of macroalgae that can be cultivated using the algae cultivation system of the present invention and their maturation times (times of maximum biomass) in Japan.

[0024] The algae cultivation system of the present invention will now be described with reference to the accompanying drawings, in which like reference numerals are used throughout the following drawings to designate components that are similar to those shown in the other drawings.

[0025] 1 is a schematic diagram showing an example of an algae cultivation system of the present invention. The algae cultivation system (hereinafter sometimes simply referred to as the "system") 100 comprises an algae cultivation means 110 and a settlement substrate 120.

[0026] The algae cultivation means 110 is immersed in water and has algae fixed thereon in advance. The algae cultivation means 110 may have, for example, a net-like, rope-like, or wire-like form and may be made of materials such as chemical fibers (e.g., nylon and polyester and combinations thereof), natural fibers (e.g., hemp, cotton, silk, and straw and combinations thereof), and metals (e.g., stainless steel, tungsten, aluminum, and copper and combinations thereof). A preferred example of the algae cultivation means 110 is a fishing net. When the algae cultivation means 110 is a fishing net, there are no limitations on the thickness (size), mesh size (mesh size), number of vertical meshes (hatch), or horizontal mesh size (space), and a fishing net of any number or size may be selected by a person skilled in the art.

[0027] The algae 106 to be cultivated are fixed to the algae cultivation means 110. The algae 106 may be of the same species, or two or more species may be fixed. For example, the algae 106 are attached to threads (e.g., Cremona threads) known to those skilled in the art and then fixed by winding the threads around the algae cultivation means 110.

[0028] The algae 106 may grow in freshwater, brackish water, or seawater. The type of algae 106 to be cultivated can be selected according to the water 142 in the cultivation environment. In the present invention, it is preferable that the algae 106 be algae that can grow in seawater, because this allows for mass cultivation using a marine environment. In addition, as described above, CO ２ Preferably, the algae 106 is a macroalgae because of its high immobility ratio.

[0029] When the environment in which the algae 106 grow (i.e., the surrounding water) is seawater, the seawater may be either natural seawater or artificial seawater. For example, when the environment in which the algae 106 grow is natural seawater, the algae cultivation system of the present invention is placed in the sea. Alternatively, when the environment in which the algae 106 grow is artificial seawater, the algae cultivation system of the present invention does not have to be placed in the sea. For example, it can also be used as a land-based cultivation system on land, such as in a factory.

[0030] The algae 106 belonging to the macroalgae are not particularly limited, but examples thereof include brown algae belonging to the Sargassaceae family and brown algae belonging to the Laminaria family.

[0031] The algae 106 belonging to the macroalgae are not particularly limited, but examples thereof include Sargassum horneri, Sargassum muticum, Sargassum micracanthum, Sargassum thunbergii, Sargassum siliguastrum, Sargassum piluliferum, Sargassum autumnale, Sargassum macrocarpum, Sargassum ringgoldianum ssp. coreanum, Sargassum yendoi, Sargassum patens, Saccharina japonica, Undaria pinnatifida, and Eckloniopsis radicosa, Eisenia bicyclis, Ecklonia cava, Ecklonia cava ssp. kurome (a subspecies of Ecklonia), Eisenia nipponica, Heribaudiella fluviatilis, Sargassum thunbergii, Batrachospermum gelatinosum, Prasiola japonica, and combinations thereof.

[0032] Of the above, the macroalgae 106 that can be immobilized in the algae cultivation means 110 may be one type or a combination of two or more types depending on their maturity period.

[0033] For example, from January to May in Japan, Sargassum horneri and Sargassum tamahahakiensis may be used alone or in combination as the algae 106 .

[0034] Alternatively, in March to May in Japan, Akamoku, Tamahahakimoku, and Togemoku may be used as the algae 106, either alone or in combination.

[0035] Alternatively, in June to August in Japan, the algae 106 may be selected from the group consisting of Scutellaria baicalensis, Scutellaria baicalensis, Scutellaria japonica, Scutellaria japonica, Scutellaria baicalensis, and Scutellaria baicalensis, either singly or in combination.

[0036] Alternatively, in July to September in Japan, as the algae 106, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum antokume, Eisenia bicolor, Eisenia bicolor, Ecklonia cava, and Sargassum serrata may be used alone or in combination.

[0037] Alternatively, in September to November in Japan, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum antokume, Eisenia bicolor, Eisenia bicolor, Ecklonia cava, and Sargassum serrata may be used as the algae 106, either alone or in combination.

[0038] Alternatively, from September to December in Japan, Akiyoremoku may be used as the algae 106 .

[0039] 1, the algae cultivation means 110 has ends 112, 114 fixed to a float 130 floating on the water surface 140, with the ends 112, 114 fixed to the float 130 at an arbitrary interval, and is arranged in a suspended state in the water 142 so that the float 130 is bent, for example, into a gentle U-shape as a whole. The float 130 may be fixed using, for example, a wire 132 and an anchor 134 to prevent it from moving in any direction on the water surface 140.

[0040] The algae cultivation means 110 may also have a tubular (e.g., cylindrical or rectangular) net 145 (e.g., a fishing net) arranged around its periphery and extending vertically in the water. The cylindrical net 145 protects the algae 106 from water movement such as tidal currents, and creates a gentle cultivation environment within the net 145. The bottom end 146 of the net 145 may not be in contact with the water bottom 147 so that it floats in the water 142, or it may be in contact with the water bottom 147.

[0041] The adhesion substrate 120 is an artificial object placed on the bottom surface 150 of the water 142, and is composed of a relatively thin member having a predetermined plane, such as a fabric, sheet, or plate having a predetermined thickness. Specifically, the adhesion substrate 120 may be a woven, knitted, or nonwoven fabric made of chemical fibers such as nylon and polyester; natural fibers such as hemp, cotton, silk, and straw; metal filaments such as stainless steel, tungsten, aluminum, and copper; or a combination thereof; a sheet made of a thermoplastic resin (e.g., nylon and polyester and a combination thereof), elastomer, rubber, or a combination thereof; or a plate (including, for example, a hollow plate) made of a thermoplastic resin (e.g., nylon and polyester and a combination thereof), elastomer, rubber, stainless steel, tungsten, aluminum, copper, wood, concrete, mortar, and glass, or a combination thereof.

[0042] The thickness of the adhesion substrate 120 is not particularly limited, but is preferably 30 cm to 100 cm, and more preferably 50 cm to 70 cm. If the thickness of the adhesion substrate 120 is less than 30 cm, disadvantages may arise, such as insufficient strength and being easily washed away by water currents such as tidal currents. If the thickness of the adhesion substrate 120 exceeds 100 cm, it becomes heavy overall, which may increase the difficulty of placing it on the water bottom surface 150 and / or removing it from the water 142 and recovering it.

[0043] In the present invention, the attachment substrate 120 may be a combination of a plurality of appropriately cut pieces of the above fabric, sheet and / or plate material placed on the water bottom surface 150 .

[0044] The size of the adhesion substrate 120 is not particularly limited, but is designed to be larger than the algae cultivation means 110 suspended above, or to be the same size as or larger than the horizontal cross section of the vertically extending cylindrical net 145.

[0045] In the aquaculture system 100 of the present invention, algae 106' are fixed (attached) to the settlement substrate 120 via temporary roots (appressorium). These algae 106' are not artificially placed, but have grown naturally on the settlement substrate 120 due to zoospores or fertilized eggs 160 released from the algae 106 suspended from the algae cultivation means 110. The algae 106' may be of the same species as the algae 106 suspended from the algae cultivation means 110, or may have grown naturally due to other zoospores or fertilized eggs provided from outside while floating in the water 142.

[0046] FIG. 2 is a schematic diagram showing another example of an algae cultivation system of the present invention.

[0047] In the algae cultivation system 200 shown in Figure 2, the growth substrate 120' has a plurality of folds 122'. Because the growth substrate 120' has such a configuration, the algae 106' that have grown naturally on the growth substrate 110 can be easily collected by a person skilled in the art by using the folds 122' of the growth substrate 110 to pull the algae 106' above the water surface 140.

[0048] Referring again to FIG. 1, the algae 106 fixed in the algae cultivation means 110 release reproductive cells or fertilized eggs 160 into the water 142 as they grow.

[0049] For example, if the algae 106 is a brown algae of the Laminariaceae family, the sporophyte will release zoospores and gametophytes, which are reproductive cells. If the algae 106 is a brown algae of the Sargassaceae family, the adult algae will release fertilized eggs.

[0050] In the present invention, zoospores (reproductive cells) and fertilized eggs released from such algae 106 can be used to reach the settlement substrate 110. After that, algae 106' are grown "conjugatedly" with the algae 106 through the reproductive cells or fertilized eggs 160 that have reached the settlement substrate 110, and as a result, algae 106, 106' can be cultivated both in the algae cultivation means 110 and in the settlement substrate 120 disposed below it.

[0051] The minimum distance between the algae cultivation means 110 and the settlement substrate 120 is not particularly limited, as it varies depending on the type of seaweed being cultivated and the degree of water movement, such as tidal currents, at the cultivation site, etc., but is generally between 3.0 m and 14.5 m, preferably between 4.0 m and 10 m. If the minimum distance between the algae cultivation means 110 and the settlement substrate 120 is less than 3.0 m, the algae may be affected by tidal currents, for example, and zoospores (reproductive cells) or fertilized eggs 160 released from the algae 106 may be excessively swept away by tidal currents or other water currents before reaching the settlement substrate 120 below, making it difficult to conjugately cultivate the algae 106′ on the settlement substrate 120. If the minimum distance between the algae cultivation means 110 and the settlement substrate 120 exceeds 14.5 m, the amount of sunlight necessary for cultivating the algae 106′ may not reach the settlement substrate 120 at such a depth.

[0052] FIG. 3 is a schematic diagram showing another example of an algae cultivation system of the present invention.

[0053] In the algae cultivation system 300 shown in Figure 3, the algae cultivation means 110 are fixed to a number of buoys 330 instead of the floats 130 shown in Figure 1. By fixing the algae cultivation means 110 to such buoys 330 instead of to floats, the resulting algae cultivation system 300 can have a simpler or more compact configuration.

[0054] The algae cultivation system 300 shown in Figure 3 also allows reproductive cells or fertilized eggs 160 released from the algae 106 suspended in the algae cultivation means 110 to move to the settlement substrate 120, and algae 106' can be cultivated conjugately on the settlement substrate 120 together with the algae 106.

[0055] FIG. 4 is a schematic diagram showing yet another example of an algae cultivation system of the present invention.

[0056] In the algae cultivation system 400 shown in Figure 4, the algae cultivation device 110 is secured to a number of buoys 330 instead of the floats 130 shown in Figure 1. In addition, ends 412, 414 of the algae cultivation device 110 are secured to a frame 430 that floats on the water surface 140, and the frame 430 is secured to anchors 134 located in the water 142 via a number of rigid struts 432.

[0057] This configuration limits the movement of the frame 430 on the water surface 140. This reduces the possibility that the algae cultivation system 400 will be washed away elsewhere due to, for example, strong winds.

[0058] The algae cultivation system 4 shown in Figure 4 also allows reproductive cells or fertilized eggs 160 released from the algae 106 suspended in the algae cultivation means 110 to move to the settlement substrate 120, and algae 106' can be cultivated conjugately on the settlement substrate 120 together with the algae 106.

[0059] The algae cultivation system of the present invention allows for the cultivation of a larger amount of algae within a limited area seen from the water surface. In particular, the algae 106 suspended from the algae cultivation means 110 can be grown conjugately with the algae 106' on the settlement substrate 120, and both the algae 106 and 106' can be easily harvested.

[0060] (Method for Cultivating Algae) Next, the method for cultivating algae of the present invention will be described.

[0061] In the method of the present invention, algae are first immobilized in water (e.g., freshwater, brackish water, or seawater) on an algae cultivation means in the algae cultivation system.

[0062] The algae immobilized in the algae cultivation means are preferably juveniles that have been grown in advance using methods known to those skilled in the art. In the present invention, it is preferable to appropriately increase the cultivation density to prevent the algae from becoming food for fish and shellfish that cause seaweed erosion. By controlling the cultivation density, algae such as macroalgae secrete bromophenols, such as 2,4-dibromophenol and 2,4,6-tribromophenol, outside the algae. These bromophenols function as chemical defense substances (repellents) against marine herbivorous animals such as fish and shellfish, thereby preventing the above-mentioned seaweed erosion.

[0063] The algae are then conjugated to a substrate in an algae cultivation system through the reproductive cells or fertilized eggs released by the algae.

[0064] When cultivating algae in the ocean, the release of reproductive cells or fertilized eggs from the algae is achieved by releasing the algae (juveniles) fixed to the algae cultivation means into the ocean (when cultivating in the ocean), and then allowing a predetermined period of time for the algae to naturally initiate maturation. This predetermined period varies depending on the type of algae being cultivated, the time of year, and the cultivation environment (e.g., water temperature and cultivation density), and is therefore not necessarily limited. For example, it is preferably 150 to 360 days after fixation (or release) to the algae cultivation means. Furthermore, the period from when the released reproductive cells or fertilized eggs are received by the settlement substrate until conjugate breeding begins also varies depending on the type of algae being cultivated, the time of year, and the cultivation environment (e.g., water temperature and cultivation density), and is therefore not necessarily limited. For example, it is preferably 30 to 60 days after the release of the reproductive cells or fertilized eggs from the algae.

[0065] The algae are then harvested from both the algae cultivation means and the growth substrate.

[0066] In other words, in the method of the present invention, the target algae can be recovered not only from the algae cultivation means but also from the adhesion substrate, so the amount of algae recovered is certainly greater than when the algae cultivation means is used alone.

[0067] In this way, algae can be cultivated more efficiently.

[0068] Algae cultivated by the above method can be used as a raw material for bioethanol, which can be obtained, for example, using the method described below. When using such algae as a bioethanol raw material, it is desirable to constantly obtain a predetermined amount of the raw material regardless of the season. In the present invention, to enable such a constant supply of bioethanol raw material, it is preferable to select different algae to be cultivated depending on the season.

[0069] FIG. 5 is a diagram showing the relationship between the types of macroalgae that can be cultivated using the algae cultivation system of the present invention and their maturation times (times of maximum biomass) in areas south of Tohoku in Japan.

[0070] The macroalgae that can be cultivated in the waters around Japan mature at different times depending on the species, and as a whole, any type of algae can be obtained from January to December.

[0071] As shown in FIG. 5 , for example, January to May in Japan corresponds to the maturation period for Sargassum horneri and Sargassum tamahahaki. Furthermore, March to May in Japan corresponds to the maturation period for Sargassum horneri, Sargassum tamahahaki, and Sargassum tamahahaki. Furthermore, June to August in Japan corresponds to the maturation period for Sargassum serrata, Sargassum yolki, Sargassum mametawara, Sargassum endo, and Sargassum yatsumataku. Furthermore, July to September in Japan corresponds to the maturation period for Sargassum yolki, Sargassum yanagi, and Sargassum antokume. Furthermore, September to November in Japan corresponds to the maturation period for Sargassum akiyoremoku, Eisenia bifida, Sargassum kuromensis, Sargassum kajime, and Sargassum sagarame. Furthermore, September to December in Japan corresponds to the maturation period for Sargassum akiyoremoku.

[0072] Therefore, by appropriately selecting the algae to be cultivated throughout the year from January to December, it is possible to consistently produce the above algae that can be used as a raw material for bioethanol.

[0073] Algae (e.g., macroalgae) that can be obtained by the above method are rich in sugars such as cellulose, hemicellulose, alginic acid, mannitol, laminaran, etc. Ethanol (i.e., bioethanol) can be produced from the sugars contained in the algae.

[0074] (Method for Producing Bioethanol) Methods for producing bioethanol using cultivated algae as a bioethanol raw material are known. For example, bioethanol can be produced using arming yeast that displays specific enzymes on the cell surface.

[0075] Examples of enzymes displayed on the cell surface of arming yeast include endoglucanase, β-glucosidase, cellobiohydrolase, xylanase, β-xylosidase, xylose isomerase, exo- / endo-alginate lyase, and laminarin-degrading enzyme (Gly5M).

[0076] Specific examples of arming yeast include cellulose-degrading arming yeast (Fujita et al., Appl. Environ. Microbiol., 68, 5136-5141 (2002); Bae et al., Appl. Environ. Microbiol.,81, 59-66 (2015)), hemicellulose-degrading arming yeast (Fujita et al., J. Mol. Catalys. 17,189-195 (2002); Ota, et al., Biotechnol. Progress, 29, 346-351 (2013); Sasaki, et al., Biotechnol. Progress, 33, 1068-1076 (2017)), and alginate / mannitol-degrading arming yeast (Takagi et al., Appl. Microbiol., Biotechnol., 101, 6627-6636 (2017), and laminaran-degrading arming yeast (Motone et al., J. Biotechnol., 231, 129-135 (2016)).

[0077] Bioethanol obtained by this method can be used, for example, as an automobile fuel to replace gasoline. Furthermore, since the bioethanol is produced through algae cultivation as described above, there is no competition with food production.

[0078] According to the present invention, since algae can be constantly produced as described above, the resulting bioethanol can be stably supplied to the market. ２ It is possible to cultivate large algae with a high absorption and fixation ratio, which reduces CO2 emitted into the environment. ２ As a result, the present invention can contribute to the realization of carbon neutrality.

[0079] The present invention will be described in detail below with reference to examples, although the present invention is not limited to these examples.

[0080] Example 1: Preparation of algae cultivation system (R1) The algae cultivation system (R1) shown in FIG. 1 was prepared as follows.

[0081] Specifically, in December 2021, the algae 106 was seeded with Cremona thread (36 strands, left-handed triple twist, 5 m long), which was then wound around a 12 mm diameter poly rope with a left twist to create the algae cultivation means 110. Ten of these were prepared and hung on a float 130, a fishing net (net 145) was placed around it, and the algae was secured with anchors 134 to a location (cultivation site) approximately 100 m offshore from Obama Port, Toba City, Mie Prefecture, Japan. The seabed at the cultivation site was covered with a 50 cm thick adhesion substrate 120 made of a fabric combining chemical and natural fibers, and its end was secured to the seabed surface 150 to prevent the adhesion substrate 120 from moving due to tidal currents. The shortest distance between the algae cultivation means 110 and the adhesion substrate 120 at this cultivation site was approximately 8 m. This resulted in the creation of the titled algae cultivation system (R1).

[0082] Example 2: Cultivation of macroalgae Using the algae cultivation system (R1) prepared in Example 1, brown algae of the Laminariaceae family were cultivated as follows.

[0083] First, free gametophytes subcultured in the laboratory were crushed in a mixer and sprayed onto Cremona thread. The Cremona thread was then submerged in a container filled with seawater and cultured at 18 to 20°C. This culture was continued until the juveniles (sporophytes) reached a size visible to the naked eye. The Cremona thread was then wrapped around a poly rope as described above and released into the ocean. After approximately six months of culture near the sea surface, the brown algae of the Laminariaceae family, Ecklonia cava ssp. kurome (a subspecies of Ecklonia cava), which had been seeded in the algae cultivation means 110, grew large. It was confirmed that similar brown algae of the Laminariaceae family were also growing conjugatively on the settlement substrate 120 located below the algae cultivation means 110. Approximately 20 kg of dry weight of Ecklonia cava ssp. kurome was subsequently obtained from the algae cultivation means 110 and the settlement substrate 120.

[0084] (Reference Examples 1 to 4: Ethanol production from macroalgae) 1 kg of the kurome obtained in Example 2 was cut into 5-50 mm pieces and added to a normal yeast culture solution. Next, arming yeast (Murai et al., Appl. Environ. Microbiol., 63, 1362-1366 (1997)) displaying specific enzymes on the cell surface shown in Table 2 was added to this culture solution at an equal ratio (OD 20-30), and the culture was anaerobically cultured at 30°C for 24-48 hours, yielding 150 g to 200 g of ethanol from each culture solution.

[0085]

[0086] Macroalgae such as Kurome (a subspecies of Ecklonia cava) contain polysaccharides such as cellulose, hemicellulose, alginic acid, mannitol, and laminaran, and the Kurome cultivated in Example 2 also contained abundant polysaccharides. Therefore, when cultured using each arming yeast shown in Table 2, the desired ethanol could be produced efficiently.

[0087] The present invention is useful for obtaining raw materials for, for example, bioethanol production.

[0088] 100, 200, 300, 400 Algae cultivation system 106, 106' Algae 110 Algae cultivation means 112, 114, 412, 414 End 120, 120' Settling substrate 122' Fold 130 Float 132 Wire 134 Anchor 140 Water surface 142 Underwater 145 Net 146 Bottom 147 Water bottom 150 Water bottom surface 160 Zoospores or fertilized eggs 330 Buoy 430 Frame 432 Support

Claims

1. An algae cultivation system comprising: an algae cultivation means that is immersed in water and to which the algae are fixed; and a settlement substrate provided below the algae cultivation means with a gap therebetween, wherein the shortest distance between the algae cultivation means and the settlement substrate is between 3.0m and 14.5m.

2. The algae cultivation system of claim 1, wherein the water is natural seawater or artificial seawater.

3. The algae farming system of claim 2, wherein the algae is at least one macroalgae selected from the group consisting of brown algae of the Sargassaceae family and brown algae of the Laminaria family.

4. The algae cultivation system according to claim 2, wherein the algae cultivation means is fixed in a suspended state in the seawater.

5. A method for cultivating algae, comprising the steps of: fixing algae in water to an algae cultivation means in an algae cultivation system described in any one of claims 1 to 4; conjugately cultivating the algae on a settlement substrate in the algae cultivation system through zoospores or fertilized eggs released by the algae; and recovering the algae from both the algae cultivation means and the settlement substrate.

6. The method of claim 5, wherein the water is natural seawater or artificial seawater.

7. The method according to claim 6, wherein the algae is at least one type of macroalgae selected from the group consisting of Sargassum serrata, Sargassum tamahahakiensis, Sargassum tschonoskii, Sargassum umbellata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum pea ...japonica, Laminaria japonica, Laminaria kombu, Wakame, Antokume, Eisenia bicolor, Eisenia bicolor, Ecklonia cava, and Sagarame.

8. The method of claim 7, wherein the algae is cultivated continuously throughout the year under conditions in which the species is changed according to the time of maturation.

9. A method for producing a bioethanol raw material, comprising the steps of: fixing algae in water to an algae cultivation means in an algae cultivation system described in any one of claims 1 to 4; conjugately cultivating the algae on a substrate in the algae cultivation system through zoospores or fertilized eggs released by the algae; and recovering the algae from both the algae cultivation means and the substrate as the bioethanol raw material.

10. The method of claim 9, wherein the water is natural seawater or artificial seawater.

11. The method of claim 10, wherein the algae is at least one type of macroalgae selected from the group consisting of Sargassum serrata, Sargassum tamahahakiensis, Sargassum tschonoskii, Sargassum umbellata, Sargassum serrata, Sargassum serrata, Sargassum serrata, Sargassum pea, Sargassum serrata, Sargassum pea, Sargassum japonica, Laminaria ...

12. The method of claim 11, wherein the algae is cultivated continuously throughout the year under conditions in which the species is changed according to the time of maturation.

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