Raceway-type water tank and method for cleaning same

Abstract

[Problem] In seaweed cultivation using a raceway-type water tank, seaweed is typically harvested by means of a filter in a drainage channel or the like provided in the bottom surface of the tank. However, due to the size and structure of seaweed, by simply draining the water, the seaweed remains in the water tank without flowing and moving to the drainage channel. As a result, the seaweed remains scattered on the bottom surface of the water tank without reaching the drainage channel, causing the problem in which recovery work becomes complicated and inefficient. [Solution] A raceway-type water tank for culturing seaweed according to the present invention, the bottom surface of the water tank including two or more inclined surfaces, each inclined surface being inclined in the longitudinal direction of the water tank, each inclined surface having an upper end portion and a lower end portion, the gradient of the upper end portion relative to the lower end portion being 0.3 to 2.0%, the upper end portions of adjacent inclined surfaces forming a hill portion or the the lower end portions thereof forming a valley portion, and a drainage channel being provided at the lower end portion of each inclined surface or in the vicinity thereof.

Description

Raceway-type water tank and cleaning method thereof

[0001] The present invention relates to a raceway-type water tank and a cleaning method thereof.

[0002] In recent years, land-based aquaculture of fish and algae has attracted attention toward the establishment of a sustainable fisheries industry. Among them, raceway-type water tanks that can efficiently utilize limited water resources are applied to the cultivation and culturing of various biological species due to their structural characteristics. For example, for fish, by using a raceway-type water tank, the water flow can be maintained in one direction, and the circulation of water is promoted to efficiently supply dissolved oxygen, so that healthy growth can be expected (Non-Patent Document 1). Also, in the cultivation of microalgae, the same tank has excellent light irradiation efficiency due to its shallow and wide shape, and enables the formation of a uniform growth environment by stirring, thus contributing to the stable production of algae used as raw materials for health foods and biofuels (Patent Document 1). The inventors of the present application have developed a land-based aquaculture technology for seaweeds such as Porphyra using this raceway-type water tank (Patent Document 2).

[0003] WIKIPEDIA, Raceway (aquaculture), [retrieved on Apr. 18, 2025], Internet, <URL: https: / / en.wikipedia.org / wiki / Raceway_(aquaculture)>

[0004] JP 2023-023581 A, Japanese Patent Application No. 2025-067172

[0005] Raceway-type aquariums are widely used in land-based aquaculture of fish and microalgae, and the construction of the cultivation environment and wastewater treatment are relatively easy. In the case of fish, the organisms are moved out of the tank before wastewater treatment, so it is sufficient to simply drain the water. In the case of microalgae, individual cells are tiny and dispersed colloidally in the water, so it is possible to efficiently harvest them by draining the water along with them. On the other hand, when cultivating seaweed in raceway-type aquariums, a new challenge arises that is different from these. Namely, it is difficult to efficiently collect the cultivated seaweed during the wastewater treatment process. Seaweed is generally harvested by using a filter to drain a channel installed at the bottom of the tank, but due to its size and structure, seaweed does not naturally flow to the drain when water is simply drained, and may be left behind in the tank. As a result, the seaweed does not reach the drain and remains scattered at the bottom of the tank, resulting in a complicated and inefficient collection process. This problem is particularly pronounced in large raceway-type aquariums. Figure 10 shows an overall view of a conventional raceway-type aquarium. The bottom surface is parallel to the horizontal plane. The drain channel for discharging water from the aquarium can be placed at any position on the bottom surface. Figure 11 is a photograph showing the state after draining a raceway-type aquarium in which Porphyra has been cultivated, and it can be seen that a large amount of seaweed remains on the bottom of the aquarium even after draining is complete. This is because, with conventional drainage methods, the seaweed does not move sufficiently to the drain channel and remains in the aquarium, which hinders the efficient collection of seaweed. In view of these problems, the present invention aims to provide a novel raceway-type aquarium with a configuration that enables smooth guidance of seaweed to the drain channel and efficient collection.

[0006] The raceway-type tank for cultivating seaweed according to the present invention has two or more inclined surfaces on the bottom of the tank, each inclined surface is sloped along the longitudinal direction of the tank, each inclined surface has an upper end and a lower end, the slope of the upper end relative to the lower end is 0.3% to 2.0%, adjacent inclined surfaces form a peak with their upper ends or a valley with their lower ends, and drainage grooves are provided at or around the lower end of each inclined surface.

[0007] In the raceway-type aquarium of the present invention, seaweed can be smoothly guided to the drain when the aquarium is drained, and collected efficiently. This improves the efficiency of aquarium cleaning.

[0008] Photograph of seaweed. Example of a raceway-type aquarium (overhead view) Example of a raceway-type aquarium (overhead view) Example of a raceway-type aquarium (overhead view) Example of a raceway-type aquarium (overhead view) About the inclined surface Example of a raceway-type aquarium (schematic diagram from the side of the aquarium) Example of a raceway-type aquarium (schematic diagram from the side of the aquarium) Example of a raceway-type aquarium (schematic diagram from the side of the aquarium) Example of a raceway-type aquarium (schematic diagram from the side of the aquarium) Example of a raceway-type aquarium (schematic diagram from the side of the aquarium) Example of a raceway-type aquarium (schematic diagram from the side of the aquarium) Example of a raceway-type aquarium (schematic diagram from the side of the aquarium) Variations of the inclined surface Variations of the inclined surface Variations of the drainage channel Variations of the drainage channel Variations of the drainage channel Photograph of the drainage channel Manufacturing method of the present invention Differences from comparative examples Conventional type raceway-type aquarium with a horizontal bottom Conventional type raceway-type aquarium with a large amount of seaweed remaining on the bottom of the aquarium.

[0009] 50 Drainage channel 100 Raceway-type tank 110 Paddle 120 Inner wall of the raceway-type tank

[0010] Hereinafter, several embodiments of the present invention will be described in detail with reference to the drawings. With respect to the matters described in the embodiments of the present invention, the design can be appropriately modified without changing the scope of the present invention. <About the seaweed of the present invention> In the present invention, the seaweed can be any kind of seaweed, such as green laver, sea lettuce, monostroma, Caulerpa lentillifera, seaweed, kelp, wakame seaweed, akamoku seaweed, Sargassum, hijiki seaweed, mozuku seaweed, kuromo, matsumo, tsurumo, arame, kurome, antotono, kayamonori, amanori, tosakanori, ogonori, mirin, furigusa, tsurushiramo, fusanori, sujikonori, funori, tengusa, ginkgo, tsunomata, centipede, fudaraku, tsurutsuru, tsuzuregusa, kirinsai, kagikenori, dulse, suginori, umizomen, yuna, shikinori, etc. The length of the seaweed should preferably be 3 cm or more. This length limitation is intended to clarify that the seaweed targeted by this invention is a large seaweed, which is significantly different from microalgae of a few microns in size. More preferably, the length of the seaweed should be 5 cm or more, and more preferably 7 cm or more. The larger the seaweed, the more likely it is that it will not be guided to the drain when the raceway-type tank is drained, and will remain on the bottom of the tank. Figure 1 shows actual photographs of seaweed of various lengths. As shown in Figure 1, the length of the seaweed can be measured by stretching it in a specific direction.

[0011] <First Embodiment> Figure 2a is an overhead view of a raceway-type water tank according to one embodiment of the present invention. In Figure 2a, the front side of the water tank is omitted in order to clearly show the structure of the bottom surface of the water tank. The paddles installed in the water tank and the water in the water tank are also omitted from the description (the same applies to other embodiments). The bottom surface of the water tank is composed of a first inclined surface, a second inclined surface, and a third inclined surface. The first inclined surface has a downward slope from the lower left to the upper right in Figure 2a, the second inclined surface has an upward slope from the lower left to the upper right, and the third inclined surface has a downward slope from the lower left to the upper right, similar to the first inclined surface. In other words, all of the inclined surfaces are inclined along the longitudinal direction of the water tank. Each inclined surface has two ends formed along a direction intersecting the longitudinal direction of the tank. Of these two ends, the one located higher in the vertical direction is called the "upper end," and the one located lower is called the "lower end."

[0012] Here, the inclined surface of the present invention will be described in detail with reference to Figure 3. Figure 3 is a schematic diagram of an inclined surface viewed from a direction perpendicular to the longitudinal direction of the water tank (i.e., the side direction). In Figure 3, the upper end, lower end, length of the inclined surface in the longitudinal direction of the water tank, and vertical length of the inclined surface are shown. The distance between the two ends in the horizontal plane when the upper end and lower end of the inclined surface are projected vertically onto a horizontal plane is defined as the "length of the inclined surface in the longitudinal direction of the water tank." On the other hand, the distance between the two ends in the vertical plane when the upper end and lower end of the inclined surface are projected vertically along the horizontal direction is defined as the "length of the inclined surface in the vertical direction." The gradient of the inclined surface (i.e., the ratio of the inclination of the upper end to the lower end) is defined as "vertical length of the inclined surface" ÷ "length of the inclined surface in the longitudinal direction of the water tank." The gradient ratio of the inclined surface according to the present invention is preferably 0.3% or more and 2.0% or less. The lower limit of the gradient is more preferably 0.4% or more, and even more preferably 0.5% or more. The upper limit of the gradient is more preferably 1.6% or less, and more preferably 1.2% or less (the same applies to other embodiments). For example, a gradient of 1% means that when the length of the inclined surface in the longitudinal direction of the tank is 100m, the length of the inclined surface in the vertical direction is 1m. The gradient of each inclined surface may be different for each inclined surface. The length of each inclined surface in the longitudinal direction of the tank may be different for each inclined surface. The length of each inclined surface in the vertical direction may be different for each inclined surface. Furthermore, it is desirable that the length of each inclined surface in the vertical direction is 5cm or more and 80cm or less. More preferably 70cm or less. More preferably 60cm or less. More preferably 50cm or less. More preferably 40cm or less. More preferably 30cm or less. Since the water depth when cultivating seaweed in a raceway-type tank is generally 80cm or less, it is undesirable for the length of the inclined surface in the vertical direction to be close to the water depth.

[0013] In the raceway-type water tank shown in Figure 2a, a valley is formed between the two inclined surfaces by the adjacent placement of the lower ends of the first and second inclined surfaces. Similarly, a peak is formed between the two inclined surfaces by the adjacent placement of the upper ends of the second and third inclined surfaces. A common drainage channel is provided at the lower ends of the first and second inclined surfaces, and a separate drainage channel is provided at the lower end of the third inclined surface. In Figure 2a, this drainage channel is provided along the inside of the arc-shaped side wall of the raceway-type water tank, but the shape of the drainage channel is arbitrary, as will be described in detail later. Note that the lower ends of each inclined surface and the drainage channels do not necessarily need to be physically adjacent; they only need to be located around the lower ends. In other words, it is sufficient that the water flowing down along the inclined surface is guided to the drainage channels via the lower ends. By equipping the tank with multiple inclined surfaces and drainage channels in this manner, it becomes possible to efficiently guide the seaweed in the raceway-type tank into the drainage channels along with the water when the water is drained from the tank, thereby achieving smooth and efficient collection.

[0014] Figure 2b is an overhead view of a raceway-type water tank according to one embodiment of the present invention. In Figure 2b, the front side of the water tank is omitted in order to clearly show the structure of the bottom surface of the water tank. The bottom surface of the water tank is composed of a first inclined surface and a second inclined surface. The first inclined surface has an upward slope that slopes from the lower left to the upper right in Figure 2b, and the second inclined surface has a downward slope that slopes from the lower left to the upper right. A peak is formed between the two inclined surfaces by the adjacency of the upper end of the first inclined surface and the upper end of the second inclined surface. Drainage channels are provided around the lower end of the first inclined surface and the lower end of the second inclined surface, respectively. These drainage channels are provided along the inside of the arc-shaped side wall of the raceway-type water tank.

[0015] Figure 2c is an overhead view of a raceway-type water tank according to one embodiment of the present invention. In Figure 2c, the front side of the water tank is omitted in order to clearly show the structure of the bottom surface of the water tank. The bottom surface of the water tank is composed of a first inclined surface and a second inclined surface. The first inclined surface has a downward slope that slopes from the lower left to the upper right in Figure 2b, and the second inclined surface has an upward slope that slopes from the lower left to the upper right as well. A valley is formed between the two inclined surfaces by the proximity of the lower ends of the first inclined surface and the lower ends of the second inclined surface. A common drainage channel is provided at the lower ends of the first inclined surface and the lower ends of the second inclined surface. The drainage channel is arranged along the boundary between the lower ends of the first inclined surface and the second inclined surface, i.e., the valley, but it is sufficient for the drainage channel to be provided at any position in the valley, and it is not necessarily required to be precisely positioned on the boundary line. Figure 2d is an overhead view of the same embodiment as Figure 2a, with simplified explanatory text to improve visibility.

[0016] Figures 4a to 4c are schematic diagrams of variations of the raceway-type water tank of the present invention, all viewed from the side of the tank (i.e., perpendicular to the longitudinal direction). Figure 4a has a configuration that is generally the same as the raceway-type water tank shown in Figure 2c, and has two inclined surfaces, the lower ends of which are adjacent to each other to form a valley. A common drainage channel is provided in this valley. The upper ends of the first inclined surface and the upper ends of the second inclined surface are adjacent to the ends of the raceway-type water tank. However, as in the embodiment of Figure 2c, the upper ends of the first inclined surface and the upper ends of the second inclined surface do not have to be adjacent to the ends of the raceway-type water tank. In the embodiment of Figure 2c, the semicircular portions at both ends of the water tank are not inclined surfaces. Figure 4b shows an example in which the valley has a certain width, and a gap is provided between the lower end of the first inclined surface and the lower end of the second inclined surface. With such a configuration, the design freedom of the drainage mechanism is improved, such as arranging the drainage channel within a predetermined width of the valley.

[0017] Figure 4c has a configuration that is generally similar to the raceway-type tank shown in Figure 2b, and has two inclined surfaces, the upper ends of which are adjacent to each other to form a raised section. Drainage channels are provided around the lower ends of each. The raised section at the bottom of the raceway-type tank in Figure 4c is wider than the raised section in Figure 2b.

[0018] Figure 5a shows a configuration that is generally similar to the raceway-type water tank shown in Figure 2a, and has three inclined surfaces. The lower end of the first inclined surface and the lower end of the second inclined surface are adjacent to each other, forming a valley. A drainage channel is provided in the valley. The upper end of the second inclined surface and the upper end of the third inclined surface are adjacent to each other, forming a peak. A drainage channel is also provided around the lower end of the third inclined surface. Figures 5b and 5c show an example of an embodiment having four inclined surfaces. The number of inclined surfaces in the present invention is two or more. The number of inclined surfaces can be set appropriately according to the longitudinal length of the raceway-type water tank. Although not specifically shown, it may be not only four or more inclined surfaces, but also five or more inclined surfaces, or six or more inclined surfaces.

[0019] Figure 5d shows another variation, illustrating a configuration with three inclined surfaces. In this example, the lower ends of the first and second inclined surfaces are at the same vertical height, while the lower end of the third inclined surface is at a different height. The upper ends of the second and third inclined surfaces are at the same height, but the upper end of the first inclined surface is at a different height. Furthermore, the lengths of the first, second, and third inclined surfaces in the longitudinal direction of the tank are all different, resulting in a configuration where each inclined surface has its own individual inclination conditions. Although Figure 5d shows an example configuration with three inclined surfaces, the present invention is not limited to this, and similar modifications are possible with two inclined surfaces or with four or more inclined surfaces.

[0020] <Further Variations of the Embodiments> The inclined surface in the present invention is not limited to flat surfaces as shown above, but may be composed of a smooth curved surface. In addition to a configuration in which the entire inclined surface has a constant angle of inclination, a configuration in which the angle of inclination changes continuously is also acceptable. For example, a shape in which the angle of inclination gradually becomes steeper or gradually gentler along the middle of the inclined surface is also in line with the spirit of the present invention. Furthermore, a configuration in which multiple inclined surfaces having different angles of inclination are connected in a continuous manner is also acceptable. However, shapes that involve steps or abrupt bends that hinder the smooth flow of fluid, or stepped shapes, are not suitable for the purpose of the present invention and are therefore not included.

[0021] The method for counting inclined surfaces in this invention will be explained. Even if the inclined surface is composed of a smooth curved surface, or if multiple inclined surfaces with different inclination angles are connected in a continuous manner, if the water flows towards the same drainage channel (valley) when water is poured from the top of the inclined surface, then these can be considered to function as inclined surfaces with the same function. Therefore, in such cases, they are counted together as one inclined surface. Even if the surface of such an inclined surface is not flat, the gradient of the inclined surface is considered in the same way as in previous embodiments. That is, the distance between the two ends in the horizontal plane when the upper end and lower end of the inclined surface are projected vertically along the horizontal direction is defined as the "length of the inclined surface in the longitudinal direction of the water tank". On the other hand, the distance between the two ends in the vertical plane when the upper end and lower end of the inclined surface are projected vertically along the horizontal direction is defined as the "length of the inclined surface in the vertical direction". The gradient of the inclined surface (i.e., the ratio of the inclination of the upper end to the lower end) is defined as "length of the inclined surface in the vertical direction" ÷ "length of the inclined surface in the longitudinal direction of the water tank".

[0022] Figures 6a and 6b are schematic diagrams of the inclined bottom surface of a raceway-type water tank as seen from the side of the tank. Since water flows towards the same drain channel from each of these inclined surfaces, they are counted as a single inclined surface. The "vertical length of the inclined surface" and the "length of the inclined surface in the longitudinal direction of the tank" for each inclined surface are defined as shown in the figures. The gradient of the inclined surface is defined as "vertical length of the inclined surface" ÷ "length of the inclined surface in the longitudinal direction of the tank," as in the previously shown embodiment. Figure 6a is an example of an inclined surface formed by continuously connecting multiple inclined surfaces with different inclination angles. Figure 6b is an example of an inclined surface composed of a smooth curved surface.

[0023] Figures 7a, 7b, and 7c are schematic diagrams showing examples of drainage channel installation locations. Drainage channels can be installed in any shape at any position at or around the lower end of each inclined surface. Basically, drainage channels are provided at or around the lower end of each inclined surface to receive water and seaweed flowing down the lower end. Figure 7a shows a configuration in which drainage channels are provided along the boundary between the lower end of the first inclined surface and the lower end of the second inclined surface, i.e., the valley, which is a characteristic of this example. Furthermore, it is desirable that the ends of this drainage channel in the longitudinal direction extend to near the side walls of the raceway-type tank. By making the drainage channels placed in the valleys wide in this way, it becomes possible to efficiently collect and recover seaweed and water flowing down the first and second inclined surfaces. Similarly, drainage channels of the same shape are placed along the lower end of the third inclined surface. These drainage channels can also efficiently collect and recover seaweed and water flowing down the third inclined surface. Figure 7b shows an example in which a drainage channel is provided around the lower end of the third inclined surface. The drainage channel is located in the center of the semicircular part of the raceway-type tank and has an elongated shape along the longitudinal direction of the tank. With this configuration, seaweed and water flowing down the third inclined surface are efficiently guided to the drainage channel, and it is expected to have the effect of suppressing the stagnation and retention of water and seaweed, especially in the semicircular part. Figure 7c shows an example in which a drainage channel is provided around the lower end of the third inclined surface. This drainage channel is arranged along the inner wall of the semicircular part of the raceway-type tank and has an arc shape. With this structure, seaweed and water flowing down the inclined surface in the semicircular part naturally collect along the inner wall and are efficiently guided to the arc-shaped drainage channel, thus enabling smooth drainage while suppressing the stagnation of seaweed and water. Figure 7d is a photograph of an actual drainage channel. As shown in Figure 7a, this is an embodiment in which a drainage channel is provided along the boundary between the lower ends of the two inclined surfaces, i.e., the valley. This drainage channel has a groove running along the valley, with holes at the ends of the groove for draining water to the outside. A filter can be installed in the drainage channel to separate and collect seaweed from the water.

[0024] <Manufacturing Method of the Present Invention> As an example of a manufacturing method for a raceway-type water tank according to the present invention, a method using a deformable material for the outer wall of the water tank will be described. 1. First, as shown in Figure 8(1), a structure having an inclined surface is constructed on the ground surface in advance so that the bottom surface of the water tank has a desired inclined structure. 2. Next, the deformable material that will become the outer wall of the water tank is placed along the surface shape of the inclined structure and molded (see Figure 8(2)). This method makes it possible to flexibly manufacture raceway-type water tanks with various bottom surface shapes by adjusting the ground surface shape at the site where the water tank is installed. An example of a deformable material used for the bottom surface of the water tank is a polypropylene sheet. The thickness of the sheet is appropriately selected according to the type of material used and the size of the water tank, for example, about 3 to 10 mm is a guideline. The bottom surface shape of the raceway-type water tank manufactured in this way will be substantially the same as the shape of the water tank's contact surface. As shown in Figure 8(2), when formed on a contact surface with an inclined surface, the bottom surface of the water tank will also be molded to have two inclined surfaces. In other words, when the tank's contact surface has multiple inclined surfaces, the tank's bottom deforms to follow them, and the desired structure is naturally formed. Here, "tank contact surface" refers to the ground structure including the aforementioned inclined structure, and it is also possible to form the inclined structure by, for example, piling up soil on the ground. In any case, a raceway-type tank manufactured by this method has a bottom surface that is molded along a contact surface having a predetermined inclined structure and is configured to follow the inclined shape of the contact surface. To put it another way, a raceway-type tank manufactured by this method has a bottom surface made of a deformable material and is placed in close contact with a contact surface having a predetermined inclined structure, so that the inclined shape of the tank's bottom surface is formed to be substantially the same as the inclined shape of the contact surface. To put it yet another way, a raceway-type tank manufactured by this method has a bottom surface that includes a structure directly molded onto a ground surface having a predetermined inclined structure, and this structure functions as the inclined surface of the tank's bottom surface. Furthermore, this manufacturing method can be summarized as follows.A method for manufacturing a raceway-type water tank, comprising: (1) creating a ground surface having a desired inclined structure on the ground surface; and (2) arranging and shaping a deformable material that constitutes the outer wall or bottom surface of the water tank along the inclined shape of the ground surface. Or, a method for manufacturing a raceway-type water tank, comprising laying a deformable material on the ground surface so as to follow the shape of the ground surface having an inclined structure, and shaping the bottom surface of the water tank with the material. Note that the method for manufacturing a raceway-type water tank according to the present invention is not limited to the method using a deformable material as described above. For example, other manufacturing means can be adopted, such as a method of directly forming the desired bottom surface structure by pouring concrete using a formwork, or a method of assembling and installing pre-formed modular members on site. This allows for flexible selection of the optimal manufacturing method according to the topographical conditions of the installation site and the purpose of use of the water tank.

[0025] <Comparison with Conventional Technology> The structural features of the present invention will be explained using Figure 9. Comparative Example 1 in Figure 9(1) is a conventional raceway-type tank with a flat bottom. As mentioned earlier, the problem with raceway-type tanks with a flat bottom is that it is difficult to smoothly guide seaweed to the drain and efficiently collect it. Comparative Example 2 in Figure 9(2) is an example where there is only one inclined surface on the bottom of the tank. Compared to a general pond-type tank (circular tank), a raceway-type tank is longer in the longitudinal direction. Therefore, if there is only one inclined surface on the bottom, the vertical length (height) of the inclined surface becomes large. For example, even if the gradient of the bottom surface is 1%, if the longitudinal size of the raceway-type tank is 80m, the vertical length (height) of the inclined surface will be 80cm. It is difficult to manufacture and install a tank with such a structure, and it is undesirable considering that the water depth when cultivating seaweed in a raceway-type tank is generally about 80cm. On the other hand, by having two or three inclined surfaces on the bottom of the tank, as shown in Figure 9(3) Example A and Figure 9(4) Example B, even if the gradient of the inclined surfaces is the same 1%, the vertical length (height) of the inclined surfaces can be reduced to half or one-third. In other words, the effects of the present invention tend to become more pronounced as the length in the longitudinal direction of the raceway-type tank increases. Therefore, in the present invention, it is preferable that the length in the longitudinal direction of the tank be 20 m or more, and more preferably 30 m or more, 40 m or more, or 50 m or more.

[0026] <Regarding the method for cleaning the aquarium and collecting seaweed> The raceway-type aquarium of the present invention has a bottom surface composed of multiple inclined surfaces, each inclined surface having a predetermined gradient along the longitudinal direction of the aquarium. By utilizing this configuration, when draining water, it is possible to flow water along the inclined surfaces, effectively washing away seaweed attached to the inclined surfaces and naturally guiding it to the drainage channel. Conventionally, it was necessary to manually collect the seaweed scattered in the aquarium after draining, making the cleaning work complicated and inefficient. According to the present invention, it is possible to achieve automatic collection of seaweed in conjunction with the draining operation, thereby reducing the workload and shortening the working time. Specifically, when draining water, by flowing water from the upper end of the inclined surface, the water flow moves the seaweed attached to or settled on the inclined surface toward the lower end. The drainage channel provided at or around the lower end of the inclined surface is structured to receive the seaweed and water thus guided, making it possible to collect the seaweed in the drainage channel and collect it all at once. This method is characterized not only as a means of cleaning the inside of the aquarium, but also as a collection method for efficiently collecting seaweed. In particular, the configuration of the present invention is extremely effective when dealing with seaweed species that are relatively large and do not easily drift downstream. Specifically, the raceway-type tank of the present invention can also be applied to a method of collecting seaweed in which seaweed attached to the bottom surface is guided down the inclined surface and collected in a drainage channel when the tank is drained. This method can be flexibly applied according to the gradient and number of inclined surfaces, the shape and size of the tank, and will be a useful means in various land-based aquaculture sites.

[0027] While several embodiments of the present invention have been described, these are merely illustrative and do not limit the technical scope of the invention. The present invention is not limited to the specific configurations, shapes, dimensions, and processes described, and can be modified, improved, substituted, and applied as appropriate by those skilled in the art, and these are also included in the technical scope as long as they do not depart from the spirit of the invention. In the description, a raceway-type water tank is mainly illustrated as an elliptical structure with semicircular ends, but it is not limited to this, and the present invention can also be applied to rectangular water tanks, for example. Furthermore, the number of inclined surfaces and the gradient of each inclination can be appropriately adjusted within the scope of the present invention depending on the longitudinal length and overall size of the water tank. Moreover, the lengths, angles, and shapes of the inclined surfaces shown in the drawings are schematic representations for ease of understanding and do not necessarily accurately reflect the actual dimensions and structure. In particular, the inclination angles may be exaggerated in the drawings for the sake of visibility and clarity of explanation.

Claims

1. A raceway-type tank for cultivating seaweed, characterized in that the bottom surface of the tank has two or more inclined surfaces, each inclined surface is sloped along the longitudinal direction of the tank, each inclined surface has an upper end and a lower end, the slope of the upper end relative to the lower end is 0.3% or more and 2.0% or less, adjacent inclined surfaces form a peak with their upper ends or a valley with their lower ends, and drainage channels are provided at or around the lower end of each inclined surface.

2. The raceway-type water tank according to claim 1, having three or more inclined surfaces.

3. The raceway-type water tank according to claim 1, wherein the length in the longitudinal direction is 20 m or more.

4. The raceway-type aquarium according to claim 1, wherein the vertical length of each inclined surface is 5 cm or more and 80 cm or less.

5. The raceway-type aquarium according to claim 1, wherein the shape of the bottom surface of the aquarium is substantially the same as the shape of the surface that the aquarium is in contact with.

6. A method for cleaning a raceway-type aquarium according to any one of claims 1 to 5, wherein seaweed attached to the bottom surface of the aquarium is washed away by flowing water along the inclined surface during drainage and guided to the drain.

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