Recirculating land-based aquaculture system

Abstract

The present invention addresses the problem of providing a novel recirculating land-based aquaculture system having a reduced makeup water ratio.　The problem is solved by a recirculating land-based aquaculture system for culturing an aquatic organism, the recirculating land-based aquaculture system including: a raising system for raising the aquatic organism; and a water treatment system for extracting a portion of cultivation water in the raising system, treating the extracted cultivation water, and returning the treated cultivation water to the raising system. The water treatment system includes: a discharged water storage tank for storing the extracted cultivation water; a denitrification tank for denitrifying nitric acid ions in the cultivation water transported from the discharged water storage tank with a denitrification bacterium; and a solid-liquid separation tank for removing a solid material in the cultivation water transported from the denitrification tank. In the water treatment system, water that contains the solid material removed in the solid-liquid separation tank is transported to the discharged water storage tank.

Description

Recirculating land-based aquaculture system

[0001] The present invention relates to a land-based aquaculture system for raising aquatic organisms, and more particularly to a recirculating land-based aquaculture system (RAS) for raising fish and shellfish.

[0002] In a recirculating land-based aquaculture system, since water is circulated and reused, it is necessary to always keep the water quality constant. In particular, it is necessary to remove ammonia discharged from the aquatic organisms to be raised and ammonia generated during the process of decomposing organic substances such as feces and uneaten feed by microorganisms, and to keep the oxygen concentration in the breeding water constant.

[0003] As a technique for ammonia removal, for example, a system such as Patent Document 1 is known. Also, as a technique for appropriately controlling the oxygen concentration of the breeding water, for example, a system such as Patent Document 2 is known.

[0004] Japanese Patent Application Laid-Open No. 2015-84691 Japanese Patent Application Laid-Open No. 2021-141852

[0005] Regarding recirculating land-based aquaculture systems, the importance of maintaining water quality has been recognized and techniques such as those described above have been proposed. On the other hand, even in a recirculating land-based aquaculture system, for example, it is said that water supply and drainage are carried out at a rate of up to 1000 L / kg-feed per feeding amount (hereinafter, the amount rate of water supply and drainage per feeding amount is referred to as "makeup water ratio"). This is because it is necessary to maintain the nitric acid concentration, which is a product after ammonia decomposition, at an appropriate concentration for the aquatic organisms to be raised, and for this reason, a certain amount of water is replaced.

[0006] In a recirculating land-based aquaculture system, the energy load, cost, and environmental load related to drainage also increase according to the scale. Therefore, in a large-scale recirculating land-based aquaculture system, it is important to reduce the above-mentioned makeup water ratio. The present disclosure provides a new recirculating land-based aquaculture system with a reduced makeup water ratio.

[0007] The inventors of the present invention have investigated the above problems and found that they can be solved by transferring a portion of the wastewater from the solid-liquid separation tank, which removes solid matter from the denitrification treatment water, to a tank further upstream.

[0008] In other words, this disclosure may include the following: [1] A recirculating land-based aquaculture system for cultivating aquatic organisms, comprising: a rearing system for raising aquatic organisms; and a water treatment system that extracts a portion of the rearing water from the rearing system, treats it, and returns it to the rearing system, wherein the water treatment system comprises: a wastewater storage tank for storing the extracted rearing water; a denitrification tank for denitrifying nitrate ions in the rearing water transferred from the wastewater storage tank using denitrifying bacteria; and a solid-liquid separation tank for removing solid matter from the rearing water transferred from the denitrification tank, and the water containing the solid matter removed in the solid-liquid separation tank is transferred to the wastewater storage tank, the recirculating land-based aquaculture system. [2] The recirculating land-based aquaculture system according to [1], wherein the solid-liquid separation tank comprises: a solid matter separation means; and a washing means for washing solid matter attached to the solid matter separation means, and the water used for washing in the washing means is transferred to the wastewater storage tank. [3] The recirculating land-based aquaculture system according to [1] or [2], wherein the solid-liquid separation tank separates solids and liquids using one or more selected from the group consisting of sedimentation, screen-type drum filters, swirling separation devices, foam separation devices, sand filters, floating filter media filters, sprinkler beds, rotating disc devices, and fixed-bed biological filtration tanks. [4] The recirculating land-based aquaculture system according to any one of [1] to [3], wherein the water treatment system comprises a sterilization tank for sterilizing the rearing water transferred from the solid-liquid separation tank. [5] The recirculating land-based aquaculture system according to [4], wherein the rearing water transferred to the sterilization tank has its ozone concentration maintained by an ozone dissolving device, and turbidity components and heavy metals are separated by a foam separation device and discharged outside the system.

[0009] This disclosure enables the provision of a new recirculating land-based aquaculture system that reduces the water exchange rate.

[0010] This is a flow diagram illustrating one form of a recirculating land-based aquaculture system.

[0011] The contents of this disclosure will be described in detail below, but the description of the constituent elements described below is just one example (representative example) of an embodiment of the invention, and the invention in this disclosure is not limited to these contents, and can be implemented in various modified forms within the scope of its gist.

[0012] Figure 1 is a flow chart showing one form of a recirculating land-based aquaculture system. The following is a step-by-step explanation. <Aquaculture System> The aquaculture system is a system for raising aquatic organisms and is equipped with at least a rearing tank. The aquatic organisms are not particularly limited as long as they are aquatic organisms that can be raised in land-based aquaculture, and typically include fish and shellfish, such as those belonging to the Salmonidae, Penaeidae, Scombridae, Serranidae, Tetraodontidae, and Haliotidae families. The rearing tank has a main tank and may also be equipped with instruments for measuring the water quality of the rearing water, and may also be equipped with an oxygen supply device for supplying oxygen to the rearing water. The main tank is octagonal as an example, and if it is octagonal, spaces will be created in the upper right, lower right, upper left, and lower left, and necessary equipment may be placed in these spaces. Note that the main tank does not have to be octagonal, but may be circular or rectangular.

[0013] The main tank is equipped with an inlet, through which aquarium water is supplied. This water is primarily treated by the water treatment system described later. The main tank may have only one inlet, or it may have two or more; there are no particular limitations.

[0014] The main tank may also have an outlet located approximately in the center of its bottom, and the bottom of the main tank may be tapered toward the outlet. The outlet may be used to drain the aquarium water and to remove feces, leftover food, and aquatic organisms.

[0015] <Water Treatment System> The water treatment system is a system that extracts a portion of the rearing water from the rearing system, treats it, and then recirculates the treated rearing water back into the rearing system. The water treatment system comprises at least a wastewater storage tank, a denitrification tank, and a solid-liquid separation tank, and may also include other tanks.

[0016] <Wastewater Storage Tank> The wastewater storage tank is a tank for temporarily storing water containing rearing water, solid organic matter such as feces and leftover feed, and solid matter separated and transferred in the solid-liquid separation tank, which is removed from the rearing system. The wastewater storage tank helps to homogenize the water quality of the removed rearing water as much as possible, and also allows for the anaerobic conditions necessary for the denitrification reaction to proceed first, thus facilitating the removal of nitrate ions in the subsequent denitrification tank. Furthermore, it allows for the sedimentation of sand and other solid matter with high specific gravity that may be mixed in with the feed, and discharged outside the system. This reduces the effort required to clean the sand and other matter that accumulates in the subsequent tanks. The wastewater storage tank may also be equipped with a separate sand sedimentation tank or sand removal device for sedimentation and separation of sand.

[0017] <Denitrification Tank> A denitrification tank is a tank that converts nitrate ions contained in rearing water into nitrogen gas using denitrifying bacteria and removes them from the system. Nitrate ions are produced when ammonia, which is excreted from the aquatic organisms being reared, and ammonia produced during the decomposition of organic matter such as feces and leftover feed by microorganisms, are decomposed by nitrifying bacteria. The oxidation of ammonia by nitrifying bacteria may be carried out in a specific area within the recirculating land-based aquaculture system, or it may be carried out by providing a separate nitrification tank. Since the oxidation of ammonia by nitrifying bacteria must be carried out in an aerobic environment, aeration means such as diffusers and aeration may be provided, and stirring means such as agitators may also be used.

[0018] The denitrification tank may contain a carrier that holds microorganisms. The carrier is not particularly limited, and porous materials such as ceramics, resins, and sponges can be used. The denitrification tank may be equipped with stirring means such as a stirrer to agitate these carriers.

[0019] During denitrification using denitrifying bacteria, methanol, ethanol, sodium acetate, biodegradable resins, glycerin, sugars, etc., are added as hydrogen donors (hereinafter also referred to as substrates). For these substrates, it is preferable to use those with a high carbon content per molecule, that are easily decomposable, and inexpensive, as this improves efficiency. On the other hand, solid materials transferred from solid-liquid separation tanks and solid materials in wastewater transferred from recirculating land-based aquaculture systems to wastewater storage tanks contain leftover feed, feces, sludge, etc., which can be used as substrates in denitrification. Therefore, such solid organic materials may be reused as substrates in the denitrification tank. In this way, by reusing the solid materials removed in the solid-liquid separation tank for denitrification instead of discarding them, the amount of discarded solid material can be reduced, thereby lowering the environmental burden of the recirculating land-based aquaculture system.

[0020] <Solid-Liquid Separation Tank> In the solid-liquid separation tank, treated water from which nitrate ions have been removed in the denitrification tank is transferred, and the solids and liquids contained in the treated water are separated. Existing technologies can be used to separate the solids and liquids, and examples include, but are not limited to, precipitation, microscreen drum filters, swirl separators, foam skimmers, sand separators, floating bead filters, trickling filters, rotating biological contactors, and fixed-bed bioreactors. These devices may be used individually or in combination.

[0021] The solid material removed in the solid-liquid separation tank is transferred to the wastewater storage tank, containing a small amount of treated water. If the solid-liquid separation tank is equipped with a washing device, the washing water used to remove the solid material is also transferred to the wastewater storage tank along with the removed solid material. Since the solid material removed in the solid-liquid separation tank contains many organic components that can be used as a denitrification substrate, it can be reused as a substrate in the denitrification tank. Furthermore, by transferring the washing water to the wastewater storage tank as well, the washing water after washing is not discharged but circulated in the land-based aquaculture system, contributing to a low water change rate. Pure water may be used as the washing water, but from the perspective of further reducing water change, rearing water may also be used. A storage tank may be provided to temporarily store the solid material removed in the solid-liquid separation tank and the washing water used to remove the solid material. The solid material stored in the storage tank is transferred to the wastewater storage tank so that the suspended solids concentration (SS concentration) in the denitrification tank is within an appropriate range, and is used as a substrate in the denitrification tank. The storage tank may be equipped with a solid material solubilization device. By equipping the storage tank with a solid material solubilization device, the denitrification efficiency when using solid materials as substrates in the denitrification tank can be improved. The method for solubilizing solid materials is not particularly limited as long as it can solubilize the solid material, and can be methods using a stirrer, a solid material crusher, a solid material grinder, aeration device, etc., or treatment methods such as ozone treatment, alkaline treatment, subcritical water treatment, or a combination thereof.

[0022] <Sterilization Tank> The water treatment system may include a sterilization tank. It is preferable that treated water from which solid matter has been removed in the solid-liquid separation tank is transferred to a sterilization tank for purification. In the sterilization tank, sterilization is typically performed using ozone or ultraviolet light, and the purified treated water is returned to the rearing system. It is preferable that the sterilization tank be equipped with an ozone dissolving device and / or a foam separation device to maintain the ozone concentration. When the water exchange rate can be greatly reduced by denitrification in the denitrification tank and return of treated water in the solid-liquid separation tank, trace metal elements derived from the feed of aquatic organisms and metal elements leached from metal components used in the equipment of the recirculating land-based aquaculture system may become concentrated in the rearing water and rise to a concentration that may affect the health of the reared aquatic organisms. Therefore, by discharging these concentrated metal elements in the rearing water as foam outside the system using ozone treatment and a foam separation device in the sterilization tank, the adverse effects of metal elements on aquatic organisms can be eliminated. In addition, it is also possible to remove turbidity components.

[0023] The method of dissolving ozone is not particularly limited; for example, ozone dissolving devices such as ejectors, oxygen cones, LHOs (Low Head Oxygenators), and deep shafts can be used. Alternatively, ozone may be supplied directly to the foam separator without using an ozone dissolving device. Examples of metal elements that can be concentrated include iron, lead, copper, cadmium, mercury, zinc, manganese, tin, nickel, chromium, and aluminum.

[0024] <Crystallization Tank> The water treatment system may be equipped with a crystallization tank. When the water exchange rate can be significantly reduced by denitrification in the denitrification tank or by transferring treated water from the solid-liquid separation tank to the wastewater storage tank, phosphorus and calcium, in addition to the above-mentioned metal elements, may become concentrated in the rearing water and rise to concentrations that may affect the health of the aquatic organisms being reared. For this reason, it is preferable to transfer the rearing water to a crystallization tank and crystallize phosphoric acid and / or calcium. Crystallization of phosphoric acid and / or calcium can be carried out in the crystallization tank by adding an alkali such as sodium hydroxide to adjust the pH to alkaline, specifically by raising the pH to about 8 to 14, preferably about 9 to 10, but alkali may also be added in an upstream tank to which the rearing water is transferred to the crystallization tank. Rearing water may be transferred to the crystallization tank by drawing it from the wastewater storage tank, drawing it from the denitrification tank, or drawing it from the sterilization tank. The crystallized phosphoric acid and / or calcium-containing compounds are removed by a filter or the like, and the rearing water from which the crystals have been removed is returned to the water treatment system, but it may also be transferred to the rearing system as is.

[0025] As described above, the following invention is another embodiment of the present invention: A method for removing phosphate and / or calcium in a recirculating land-based aquaculture system, comprising: an extraction step of removing a portion of the rearing water from the aquaculture system; a crystallization step of adjusting the pH of the removed rearing water to alkaline to precipitate crystals of a compound containing phosphate and / or calcium; and a removal step of removing the precipitated crystals of the compound containing phosphate and / or calcium.

[0026] <Other Equipment> In addition to the above, this water treatment system may be equipped with other equipment that can be provided in a typical water treatment system.

[0027] <Low Water Replacement Rate> In this embodiment of the recirculating land-based aquaculture system, the solid material removed in the solid-liquid separation tank is transferred to the wastewater storage tank while containing a small amount of rearing water. Furthermore, if the solid-liquid separation tank is equipped with a washing device, the washing water used to remove the solid material is also transferred to the wastewater storage tank along with the removed solid material. In this way, a low water replacement rate can be achieved by circulating the rearing water, which was conventionally treated as wastewater, through the water treatment system. In one example, the daily water replacement rate can be set to 10% or less of the total rearing water, preferably 1% or less. Furthermore, the amount of water replaced per unit of feed can be set to 400 L / kg-feed or less, preferably 40 L / kg-feed or less. The invention according to this disclosure contributes to SDG 12: Responsible Consumption and Production, SDG 14: Life Below Water, and SDG 15: Life on Land.

Claims

1. A recirculating land-based aquaculture system for cultivating aquatic organisms, comprising: a rearing system for raising aquatic organisms; and a water treatment system that extracts a portion of the rearing water from the rearing system, treats it, and returns it to the rearing system, wherein the water treatment system comprises: a wastewater storage tank for storing the extracted rearing water; a denitrification tank for denitrifying nitrate ions in the rearing water transferred from the wastewater storage tank using denitrifying bacteria; and a solid-liquid separation tank for removing solid matter from the rearing water transferred from the denitrification tank, and the water containing the solid matter removed in the solid-liquid separation tank is transferred to the wastewater storage tank.

2. The circulating land-based aquaculture system according to claim 1, wherein the solid-liquid separation tank comprises a solid separation means and a washing means for washing solids adhering to the solid separation means, and the water used for washing in the washing means is transferred to the wastewater storage tank.

3. The recirculating land-based aquaculture system according to claim 1 or 2, wherein the solid-liquid separation tank is separated by one or more selected from the group consisting of sedimentation, screen drum filters, swirling separation devices, foam separation devices, sand filters, floating filter media filters, sprinkler beds, rotating disc devices, and fixed-bed biological filtration tanks.

4. The recirculating land-based aquaculture system according to claim 1 or 2, wherein the water treatment system comprises a sterilization tank for sterilizing the rearing water transferred from the solid-liquid separation tank.

5. The recirculating land-based aquaculture system according to claim 4, wherein the rearing water transferred to the sterilization tank has its ozone concentration maintained by an ozone dissolving device, and turbidity components and heavy metals are separated by a foam separation device and discharged outside the system.

6. A method for removing phosphate and / or calcium in a recirculating land-based aquaculture system, comprising: an extraction step of removing a portion of the rearing water from the aquaculture system; a crystallization step of adjusting the pH of the removed rearing water to alkaline to precipitate crystals of a compound containing phosphate and / or calcium; and a removal step of removing the precipitated compound crystals.

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