Circulating land-based aquaculture system

Abstract

To provide a circulation type land culture system capable of removing such a risk that growth of aquatic organisms is inhibited.SOLUTION: A circulation type land culture system 100 includes a bottomed cylindrical water tank 10 for storing breeding water A inside, a nanobubble supply device 20 for supplying nanobubbles of oxygen or air into the breeding water A, and a photocatalyst device 30 for irradiating the breeding water A taken from the water tank 10 with ultraviolet light in the presence of a photocatalyst, and thereafter returning the breeding water A into the water tank 10.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a recirculating land-based aquaculture system. [Background technology]

[0002] Land-based aquaculture is the cultivation of aquatic organisms in artificially constructed facilities on land, and can be divided into free-flowing and closed-circulation systems. Free-flowing systems continuously draw in water from the sea, while closed-circulation systems purify the water using water treatment equipment before recycling it.

[0003] The closed circulation system has the advantage that it can be installed inland and is not limited to certain locations, and the rearing environment can be artificially controlled, resulting in rapid growth. However, the closed circulation system requires water treatment facilities.

[0004] When aquatic organisms' excrement and leftover food are decomposed by microorganisms in the breeding water, ammonia nitrogen (NH3 or NH4 + ) is generated. Ammonia nitrogen inhibits the growth of aquatic organisms and must be purified. Closed-loop land-based aquaculture systems have traditionally been equipped with water treatment facilities that purify ammonia nitrogen by combining physical filtration and biological contact filtration (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-23841 [Patent Document 2] Patent No. 5847376 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in biological contact filtration, it takes several weeks or months for the microorganisms to grow sufficiently, and during this period, ammonia nitrogen cannot be sufficiently purified, which may inhibit the growth of aquatic organisms.

[0007] In view of the above, an object of the present invention is to provide a recirculating land-based aquaculture system that can eliminate the risk of inhibiting the growth of aquatic organisms. [Means for solving the problem]

[0008] The circulating land-based aquaculture system of the present invention is characterized by comprising a cylindrical, bottomed aquarium tank containing rearing water, a nanobubble supplying device that supplies oxygen or air nanobubbles to the rearing water, and a photocatalytic device that irradiates the rearing water taken from the aquarium tank with ultraviolet light in the presence of a photocatalyst and then returns the rearing water to the aquarium tank.

[0009] According to the recirculating land-based aquaculture system of the present invention, the oxygen in the nanobubble state supplied from the nanobubble supply device or the oxygen contained in the air is easily dissolved and diffused in the rearing water, thereby creating a highly aerobic environment with a high concentration of dissolved oxygen in the rearing water. Furthermore, by treating the rearing water with a photocatalytic device, ammonia nitrogen in the rearing water can be decomposed into nitrite nitrogen or nitrogen. This contributes to eliminating factors that inhibit the growth of the aquatic organisms being cultivated.

[0010] The circulating land-based aquaculture system of the present invention preferably includes a water current generating device that generates a circumferential water current in the breeding water in the aquarium.

[0011] In this case, the nanobubbles supplied from the nanobubble supply device can be spread throughout the entire aquarium by the water current, making it possible to create a highly aerobic environment throughout the entire aquarium.

[0012] In the circulating land-based aquaculture system of the present invention, it is preferable that the nanobubble supply device supplies the nanobubbles toward the center of the aquarium in a plan view or toward the direction in which the water current is generated.

[0013] When nanobubbles are supplied from the nanobubble supply device toward the center of the tank, the nanobubbles are spread throughout the tank by the water current, which further creates a highly aerobic environment throughout the tank. On the other hand, when nanobubbles are supplied from the nanobubble supply device toward the direction of the water current, the water current can be promoted.

[0014] In the circulating land-based aquaculture system of the present invention, it is preferable that the nanobubble supply device supplies the nanobubbles downward or horizontally in the aquarium tank when viewed from the side.

[0015] In this case, the nanobubbles rise gradually over time, making it possible to dissolve oxygen in the breeding water throughout the entire aquarium, compared to when the nanobubbles are supplied upward in the aquarium.

[0016] In addition, in the circulating land-based aquaculture system of the present invention, it is preferable that a filter medium is placed on the bottom or side of the aquarium, and microorganisms are supported on the filter medium to form a biological contact filtration device.

[0017] In this case, the biological contact filtration device can purify the ammonia nitrogen in the breeding water. As described above, the aquarium is a highly aerobic environment, which promotes the growth of microorganisms, especially aerobic bacteria, and shortens the period required for the microorganisms to grow and purify a sufficient amount of ammonia nitrogen. This contributes to eliminating factors that inhibit the growth of aquatic organisms.

[0018] In addition, in the circulating land-based aquaculture system of the present invention, it is preferable that the filter medium is divided into a plurality of compartments, and the compartments are arranged with gaps between them.

[0019] In this case, the area of ​​contact between the filter media and the water flow increases, so that the oxygen dissolved in the breeding water carried by the water flow is efficiently supplied to the microorganisms supported on the filter media, which promotes the growth of microorganisms, especially aerobic bacteria, and makes it possible to increase the purification capacity of ammonia nitrogen.

[0020] In addition, in the circulating land-based aquaculture system of the present invention, it is preferable that the rearing water taken from the aquarium is supplied to the photocatalyst device via a filter or a settling tank.

[0021] In this case, the suspended matter can be separated by a filter or a settling tank, so it is possible to prevent a decrease in the purification capacity of the photocatalytic device for ammonia nitrogen due to the intrusion of the suspended matter.

[0022] In addition, in the circulating land-based aquaculture system of the present invention, it is preferable that the rearing water is taken from the top or bottom of the aquarium and returned to the aquarium from the top via the photocatalyst device.

[0023] When breeding water is taken from the top of the tank, suspended matter is relatively absent in the upper part of the tank, making it possible to prevent a decrease in the purification capacity of the photocatalytic device for ammonia nitrogen due to suspended matter entering the tank. On the other hand, when breeding water is supplied to the photocatalytic device through a filter or settling tank, suspended matter is relatively abundant in the lower part of the tank, so a filter or settling tank can be used to separate most of the suspended matter, making it possible to reduce the amount of suspended matter in the tank.

[0024] In the circulating land-based aquaculture system of the present invention, it is preferable that the rearing water taken from the aquarium is supplied to the photocatalyst device via a membrane filtration device that filters out ammonia nitrogen.

[0025] In this case, since the ammonia nitrogen is filtered by the membrane filtration device, it is possible to reduce the amount of ammonia nitrogen that needs to be purified in the photocatalyst device.

[0026] In addition, in the circulating land-based aquaculture system of the present invention, it is preferable to further include a drain outlet provided on the bottom of the aquarium for draining the rearing water.

[0027] In this case, the breeding water containing a large amount of sediment, such as suspended matter, accumulated on the bottom of the aquarium can be discharged to the outside through the drain outlet, thereby reducing the amount of suspended matter in the aquarium.

[0028] In addition, in the circulating land-based aquaculture system of the present invention, it is preferable that the drain outlet is provided in the center of the funnel-shaped sloping bottom of the aquarium.

[0029] In this case, the funnel-shaped slope at the bottom of the tank causes suspended solids and other sediments to gather toward the outlet, allowing these sediments to be efficiently discharged to the outside through the outlet, thereby further reducing suspended solids in the tank. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic top view of a circulating land-based aquaculture system according to a first embodiment of the present invention. [Figure 2] 1 is a schematic longitudinal sectional view of a circulating land-based aquaculture system according to a first embodiment of the present invention. [Figure 3] FIG. 5 is a schematic top view of a circulating land-based aquaculture system according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a schematic longitudinal sectional view of a circulating land-based aquaculture system according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] Recirculating land-based aquaculture systems (hereinafter simply referred to as aquaculture systems) 100, 200 according to embodiments of the present invention will be described with reference to Figures 1 to 4. The aquaculture systems 100, 200 are facilities for cultivating aquatic organisms such as fish, shellfish, and crustaceans on land.

[0032] Figures 1 and 2 are diagrams for schematically explaining an aquaculture system 100 according to a first embodiment, and Figures 3 and 4 are diagrams for schematically explaining an aquaculture system 200 according to a second embodiment. Note that in Figures 1 to 4, the shapes and dimensions of the components are exaggerated for ease of understanding.

[0033] The aquaculture systems 100 and 200 are cylindrical and include an aquarium tank 10 that contains breeding water A, a nanobubble supplying device 20 that supplies oxygen or air nanobubbles to the breeding water A in the aquarium tank 10, and a photocatalytic device 30 that irradiates the breeding water A taken from the aquarium tank 10 with ultraviolet light in the presence of a photocatalyst and then returns the water to the aquarium tank 10.

[0034] The aquarium 10 has a cylindrical shape with a bottom, and contains breeding water A made of seawater, freshwater, or the like, suitable for breeding aquatic organisms such as fish, shellfish, and crustaceans. The aquarium 10 may have any shape as long as it has a cylindrical outer shape, and may also have an annular cylindrical shape (doughnut shape) without a center. Because the aquarium 10 has a cylindrical outer shape, it can withstand high water pressure and can be made large. It is also suitable for generating a water current in the breeding water A, which will be described later.

[0035] The aquaculture systems 100 and 200 further include a water current generator 40 that generates a water current (circulating current) that circulates the culture water A in the aquarium 10 in a predetermined circumferential direction, here, clockwise as indicated by the white arrow in Figures 1 and 3. The water current generator 40 is, for example, a circulation pump or a circulator, but any type of pump can be used as long as it is capable of generating an appropriate water current. The aquaculture system 100 may also include the water current generator 40. Furthermore, the drive unit of the water current generator 40 does not necessarily need to be installed inside the aquarium 10. For example, the water current generator 40 may be configured by installing a water intake and a water supply inlet at different positions on the plane of the aquarium 10 and installing a pump in the piping between the two.

[0036] The aquaculture systems 100, 200 may also be connected to a culture water supply device 50, such as a water storage tank or water truck, that supplies culture water A from the outside into the aquarium 10. This allows culture water A to be added to the aquarium 10 from the outside, making it possible to maintain a predetermined amount of culture water A contained in the aquarium 10 even if it decreases due to evaporation, sampling, purification treatment operations, etc. Furthermore, it is also possible to dilute high-concentration culture water A as a fail-safe in case the concentration of growth inhibitors for aquatic organisms, such as ammonia nitrogen (described below), exceeds the treatment range due to a problem or the like.

[0037] In the aquaculture systems 100 and 200, the nanobubble supply device 20 is disposed in the aquarium 10. The nanobubble supply device 20 supplies a large amount of high-oxygen nanobubbles to the breeding water A in the aquarium 10 and is, for example, a commercially available nanobubble generator that generates nanobubbles using high-concentration oxygen supplied from a high-concentration oxygen supply device 21. The high-concentration oxygen supply device 21 is, for example, a commercially available device that extracts oxygen at a high concentration, such as approximately 90%, from the atmosphere. However, the nanobubble supply device 20 may also supply nanobubbles using oxygen that is not a high concentration, for example, oxygen with a concentration less than 90%. Alternatively, the nanobubble supply device 20 may supply nanobubbles made of air taken in from the atmosphere by, for example, an air intake means (not shown). The nanobubble supply device 20 may also take in oxygen from an oxygen source, such as an oxygen cylinder (not shown).

[0038] When nanobubbles are supplied to breeding water A, oxygen in the nanobubble state dissolves and diffuses in breeding water A, making it possible to create a highly aerobic environment in breeding water A with a large amount of dissolved oxygen. This makes it possible to promote the decomposition of organic matter such as excrement and leftover food of aquatic organisms by microorganisms, especially aerobic bacteria, present in breeding water A. In addition, the growth of microorganisms is promoted, and ammonia nitrogen (NH3 or NH4 + It is also possible to increase the decomposition ability of

[0039] 2 and 4, the nanobubble supply device 20 is installed in the lower part of the aquarium 10. As a result, the nanobubbles supplied by the nanobubble supply device 20 rise gradually over time, and this, together with the generation of a water current, makes it possible to dissolve oxygen in the breeding water A in nanobubbles throughout the aquarium 10. However, since nanobubbles rise much more slowly than normal air bubbles, the nanobubble supply device 20 may be installed in the middle or upper part of the aquarium 10 in the vertical direction.

[0040] In the aquaculture system 100, the nanobubble supplying device 20 supplies nanobubbles in the horizontal direction. Here, two nanobubble supplying devices 20 are arranged in the aquarium 10, and supply nanobubbles in the circumferential direction in accordance with the direction of the water current generated by the water current generating device 40. This allows the nanobubbles to be distributed throughout the entire aquarium 10 in the planar direction. In addition, the nanobubbles can also promote the water current.

[0041] On the other hand, in the aquaculture system 200, the nanobubble supply device 20 supplies nanobubbles toward the center of the aquarium 10 in a plan view. As a result, the nanobubbles supplied from the nanobubble supply device 20 spread in the radial direction of the aquarium 10 and are further diffused by the water current around the circumference.

[0042] In either case, nanobubbles are present throughout the aquarium 10, and since oxygen in the nanobubble state is easily dissolved in the breeding water A, it is possible to create a highly aerobic environment in which a high concentration of oxygen is dissolved in the breeding water A.

[0043] The aquaculture systems 100 and 200 may not include the water current generating device 40. In this case, the nanobubble supply device 20 supplies nanobubbles in the circumferential direction, thereby forming a water current in the rearing water A in the circumferential direction.

[0044] Furthermore, it is preferable that the nanobubble supply device 20 supplies the nanobubbles downward or horizontally in the vertical direction in a side view of the water tank 10. This is because, as described above, the nanobubbles gradually rise over time.

[0045] Depending on the specifications of the nanobubble supply device 20, it may be placed outside the water tank 10. In this case, it is sufficient that the supply port for nanobubbles supplied by the nanobubble supply device 20 is located inside the water tank 10 or communicates with the inside of the water tank 10.

[0046] In the aquaculture systems 100 and 200, the photocatalytic device 30 is disposed outside the aquarium 10. The breeding water A is taken from the aquarium 10 via a pump 31, and the breeding water A is passed through the photocatalytic device 30 and returned to the aquarium 10.

[0047] Although the photocatalytic device 30 is not shown in detail, the rearing water A is supplied to the inside of a reaction tube filled with a photocatalyst such as titanium oxide, and ultraviolet light is irradiated onto the rearing water passing through the reaction tube. The rearing water A that has passed through the reaction tube is then returned to the aquarium 10. By passing the rearing water A through the photocatalytic device 30, its strong oxidizing action can decompose (denitrify) the ammonia nitrogen in the rearing water A into nitrite nitrogen or nitrogen (N2). The photocatalytic device 30 may be a device having a known configuration. The rearing water A that has passed through the photocatalytic device 30 is returned to the aquarium 10. In this way, in this embodiment, the rearing water A is circulated through the photocatalytic device 30.

[0048] In the aquaculture systems 100 and 200, a bypass flow path is provided in the flow path that takes in culture water A from the aquarium 10 and supplies it to the photocatalyst device 30, and this bypass flow path is provided with a membrane filtration device 60. When the concentration of ammonia nitrogen in the culture water A taken from the aquarium 10 is high, it is preferable to supply the water to the photocatalyst device 30 via the membrane filtration device 60 by operating a switching valve 90.

[0049] The membrane filtration device 60 is a device equipped with a filtration membrane such as a microfiltration membrane or an ultrafiltration membrane that can separate ammonia nitrogen. By removing ammonia nitrogen to a certain extent in advance using the membrane filtration device 60 in this way, the concentration of ammonia nitrogen to be decomposed in the photocatalytic device 30 can be reduced, making it possible to reduce the load on the photocatalytic device 30.

[0050] Furthermore, the breeding water A contains suspended matter consisting of organic matter such as excrement and leftover food from aquatic organisms, and if such suspended matter gets into the photocatalytic device 30, it may reduce the decomposition ability of the photocatalytic device 30. Although it is possible to separate suspended matter using the membrane filtration device 60, this is not preferable because adhesion of suspended matter to the filtration membrane reduces separation performance.

[0051] Therefore, in the aquaculture system 100, the culture water A taken from the top of the aquarium 10 is supplied to the photocatalyst device 30 and the membrane filtration device 60. This is because suspended solids tend to settle to the bottom of the aquarium, so by taking the culture water A from the top of the aquarium 10 where suspended solids are relatively unlikely to be present, it is possible to prevent the photocatalyst device 30 and the membrane filtration device 60 from becoming contaminated by the presence of suspended solids, which would reduce the decomposition and removal performance.

[0052] In the aquaculture system 100, sludge-like sediment such as leftover food accumulated in the lower part of the aquarium 10 is discharged to the outside through a discharge outlet 11 provided at the bottom of the aquarium 10. Here, the entire bottom of the aquarium 10 is inclined in a funnel shape (cone shape), and the discharge outlet 11 is provided at the lowest part of the slope, which is the center of the bottom. Note that the bottom of the aquarium 10 may be partially inclined in a funnel shape, including the center.

[0053] Furthermore, the discharge of sediment from the discharge outlet 11 may be performed continuously, or may be performed as needed by providing a water stop valve (not shown) or the like, which is operated automatically by a control device or manually by an operator.

[0054] On the other hand, in the aquaculture system 200, the breeding water A taken from the aquarium 10 is supplied to the photocatalytic device 30 and the membrane filtration device 60 via a sedimentation tank 71 that settles and separates suspended matter in the breeding water A, and further via filters 72 and 73 that separate suspended matter, such as strainers and filters.

[0055] Specifically, breeding water A taken from the aquarium 10 is supplied to a settling tank 71, which is a water storage tank, via a pump 74. This settling tank 71 is what should be called a water storage tank, and suspended matter sinks and accumulates at the bottom of the water storage tank 71, and the supernatant liquid is supplied to a filter 72, which is a filter, via a pump 75. This filter 72 separates even finer suspended matter, and the purified breeding water A is supplied to the photocatalyst device 30 and the membrane filtration device 60. Here, the settling tank 71 and the filter 72 constitute a solid-liquid separation device as a physical filtering means.

[0056] The water intake 12 is formed at the bottom of the aquarium 10, and a filter 73 made of a strainer is disposed upstream (above) of the water intake 12. This filter 73 separates suspended matter and sediment, and the purified culture water A is supplied to the settling tank 71. The water intake 12 is provided in the center of the horizontal bottom of the aquarium 10. However, the water intake 12 may also be provided at the bottom of the funnel-shaped sloping bottom of the aquarium 10, like the outlet 11 of the aquaculture system 100. The culture water A containing sediment and the like is constantly discharged from the water intake 12 and supplied to the settling tank 71.

[0057] In the aquaculture system 200, the filter 73 consisting of a strainer, the sedimentation tank 71 consisting of a water storage tank, and the filter 72 are arranged in this order. However, the arrangement order is not limited to this, and some of these may be omitted, or a physical filter device with a different configuration may be provided additionally or in place of the other.

[0058] As described above, in the aquaculture system 200, the culture water A is taken from the bottom of the aquarium 10 and returned to the top of the aquarium 10. This is because the culture water A containing sediments that tend to be present at the bottom of the aquarium 10 is taken, and by removing the sediments and suspended solids contained therein using the settling tank 71 and filters 72 and 73, a decrease in the decomposition ability of the photocatalyst device 30 and the membrane filtration device 60 is suppressed, and the culture water A in the aquarium 10 can be purified, making it possible to establish a closed circulation aquaculture system.

[0059] Furthermore, the aquaculture systems 100 and 200 are equipped with a biological contact filtration device 80 in which filter media 81 and 82 are placed in the aquarium 10 and microorganisms are supported at high concentrations on the filter media 81 and 82. The biological filtration device 80 supports aerobic ammonia-oxidizing bacteria and nitrite-oxidizing bacteria on the filter media 81 and 82. These microorganisms oxidize the ammonia nitrogen in the breeding water A to nitrite nitrogen (nitrogen contained in nitrite ions (NO2-) or nitrite), and further oxidize the nitrite nitrogen to nitrate (NO3). These changes can be carried out quickly (efficiently) due to the high concentration of microorganisms.

[0060] The biological filtration device 80 may further include a filter medium supported by anaerobic denitrifying bacteria. In this case, the microorganisms can be supported in the portions of the filter medium 81, 82 that are less in contact with the water flow. This allows nitric acid to be converted into nitrogen gas (N2) and released into the atmosphere.

[0061] The filter media 81 and 82 are filled with carriers of tubular, spherical, granular, honeycomb, porous, etc., made of, for example, activated carbon, porous ceramics, synthetic fiber, zeolite, etc., and are capable of supporting a high concentration of microorganisms due to their large surface area.

[0062] In the aquaculture systems 100 and 200, the filter media 81 and 82 are placed at the bottom of the aquarium 10. In the aquaculture system 100, the filter media 81 is divided into a plurality of compartments and placed with gaps between the compartments.

[0063] Specifically, as shown in Fig. 1, filter medium 81 is divided into a plurality of compartments and arranged in the circumferential direction of aquarium 10. Filter medium 81 is arranged in an annular cylindrical shape (doughnut shape) as a whole. Filter medium 81 is arranged by, for example, placing it on a multi-tiered rack installed in aquarium 10. Although not shown, filter medium 81 may also be divided into a plurality of compartments and arranged in the radial direction of aquarium 10. Furthermore, as shown in Fig. 2, filter medium 81 is divided into a plurality of compartments and arranged in the depth direction of aquarium 10.

[0064] In this way, by dividing and arranging the filter medium 81 into multiple compartments, the area of ​​the filter medium 81 that comes into contact with the water flow is increased, and oxygen dissolved in the rearing water A carried by the water flow is efficiently supplied to the microorganisms held in the filter medium 81. This allows the microorganisms, especially aerobic bacteria, to grow well, and makes it possible to increase the ability of the microorganisms to decompose ammonia nitrogen.

[0065] On the other hand, in the aquaculture system 200, the filter media 82 are arranged at a predetermined height across the entire bottom of the aquarium 10. By arranging the filter media 82 across the entire bottom of the aquarium 10 in this way, it is possible to arrange a large number of filter media 82 while ensuring space for the aquatic organisms in the aquarium 10 to grow. In addition, the lower layer of the filter media 82 has little contact with oxygen and can support anaerobic denitrifying bacteria, which can promote denitrification, which is the final treatment of ammonia nitrogen.

[0066] 2, the filter medium 83 may be divided into a plurality of pieces and hung in the water tank 10. In this case, the area of ​​the filter medium 83 that comes into contact with the water flow increases, and the ability to decompose ammonia nitrogen can be improved.

[0067] Although not shown, a filter medium may be placed on the side of the aquarium 10. In this case, for example, the filter medium may be placed around the entire inner periphery of the aquarium 10, or the filter medium may be partitioned in the circumferential or radial direction of the aquarium 10 and placed on the inner periphery of the aquarium 10 or with a gap between the inner periphery and the inner periphery.

[0068] Furthermore, it is preferable to supply nanobubbles from the nanobubble supply device 20 described above toward the filter media 81 to 83. This allows oxygen in the nanobubble state to be supplied to the microorganisms supported on the filter media 81 to 83, thereby enabling the proliferation of the microorganisms to be improved.

[0069] As described above, according to the aquaculture systems 100 and 200, the oxygen in the nanobubble state supplied from the nanobubble supply device 20 dissolves in the breeding water A and easily diffuses, creating a highly aerobic environment with a high concentration of dissolved oxygen in the breeding water A. Activating the aerobic microorganisms in the breeding water A not only facilitates the decomposition of excrement and leftover food from aquatic organisms, but also promotes the decomposition of ammonia nitrogen. Furthermore, treating the breeding water A in a circulatory manner using the photocatalytic device 30 allows the decomposition of ammonia nitrogen in the breeding water A into nitrite nitrogen or nitrogen. These actions enable efficient and stable decomposition of ammonia nitrogen, which inhibits the growth of aquatic organisms, and promote the growth of aquatic organisms.

[0070] Furthermore, the aquaculture systems 100 and 200 can also decompose ammonia nitrogen in the breeding water A by the organism contact filtration device 80. This can further promote the growth of aquatic organisms.

[0071] In the biological contact filtration device 80, it takes several weeks to several months for the microorganisms to grow sufficiently and become able to purify a large amount of ammonia nitrogen. However, even during this period, ammonia nitrogen can be purified by supplying nanobubbles and the photocatalyst device 30. Even if the amount of ammonia nitrogen increases as aquatic organisms grow, the biological contact filtration device 80 can still purify it sufficiently.

[0072] Furthermore, the nanobubbles supplied from the nanobubble supply device 20 create a highly aerobic environment in the breeding water A, which promotes the growth of microorganisms, particularly aerobic bacteria, and can also shorten the period. Furthermore, the nanobubbles also facilitate the decomposition of organic matter such as leftover food, making it possible to suppress the generation of ammonia nitrogen.

[0073] It is sufficient for the circulating land-based aquaculture system of the present invention to be equipped with components equivalent to the water tank 10, the nanobubble supply device 20, and the photocatalyst device 30, respectively.

[0074] The present invention is not limited to the above-described circulating land-based aquaculture systems 100 and 200, and modifications can be made as appropriate. For example, the circulating land-based aquaculture systems 100 and 200 may be partially combined as appropriate. Furthermore, a biological contact filtration tank having a configuration equivalent to or similar to the biological contact filtration device 80 may be installed outside the aquarium 10. Furthermore, various physical and biological treatment devices, such as an ozone treatment device and an electrolytic treatment device, may also be additionally provided. Furthermore, the circulating land-based aquaculture system of the present invention can be applied not only to commercial aquaculture systems, but also to systems for cultivating aquatic organisms in aquariums and the like. [Explanation of symbols]

[0075] 10...aquarium, 11...outlet, 12...water intake, 20...nanobubble supply device, 21...high-concentration oxygen supply device, 30...photocatalytic device, 31...pump, 40...water flow generator, 50...breeding water supply device, 60...membrane filtration device, 71...sedimentation tank, water storage tank, 72...filter, 73...filter, strainer, 74, 75...pump, 80...biological contact filtration device, 81-83...filter media, 90...switching valve, A...breeding water, 100, 200...circulating land-based aquaculture system, aquaculture system.

Claims

1. a cylindrical aquarium with a bottom, containing breeding water therein; a pair of nanobubble supply devices disposed inside the aquarium and supplying nanobubbles of oxygen or air to the breeding water; a water current generating device that generates a circumferential water current in the breeding water in the aquarium; a photocatalytic device disposed outside the aquarium, which takes water from the aquarium, irradiates the water with ultraviolet light in the presence of a photocatalyst, and then returns the water to the aquarium; Equipped with the pair of nanobubble supply devices are arranged point-symmetrically with respect to the center position of the water tank along the inner circumferential surface of the water tank, The water flow generating device is disposed along the inner circumferential surface of the water tank, A circulating land-based aquaculture system, wherein the pair of nanobubble supply devices supply the nanobubbles toward the center position of the aquarium tank in a plan view or toward the direction in which the water flow is generated.

2. A circulating land-based aquaculture system as described in Claim 1, characterized in that the water flow generating device is arranged on a line that is perpendicular to the line connecting the pair of nanobubble supply devices and passes through the center position.

3. 3. The recirculating land-based aquaculture system according to claim 1, wherein the nanobubble supply device supplies the nanobubbles downward or horizontally in the aquarium tank when viewed from the side.

4. A circulating land-based aquaculture system as described in any one of claims 1 to 3, characterized in that a filter material is placed on the bottom or side of the aquarium, and microorganisms are supported on the filter material to form a biological contact filtration device.

5. 5. A recirculating land-based aquaculture system as described in claim 4, characterized in that the filter medium is divided into a plurality of compartments, and the compartments are arranged with gaps between them.

6. 6. The circulating land-based aquaculture system according to claim 1, wherein the breeding water taken from the aquarium is supplied to the photocatalyst device via a filter or a sedimentation tank.

7. A circulating land-based aquaculture system as described in any one of claims 1 to 6, characterized in that the breeding water is taken from the top or bottom of the aquarium and returned to the aquarium from the top of the aquarium via the photocatalytic device.

8. 8. A circulating land-based aquaculture system according to any one of claims 1 to 7, characterized in that the breeding water taken from the aquarium is supplied to the photocatalyst device via a membrane filtration device that filters out ammonia nitrogen.

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