Circulating land-based aquaculture system

Abstract

The objective of the present invention is to provide a new circulating land-based aquaculture system with a reduced water exchange rate. A recirculating land-based aquaculture system for cultivating aquatic organisms, comprising: The invention comprises a breeding system for breeding aquatic organisms, and a water treatment system for extracting a portion of breeding water from the breeding system, treating the water, and returning the water to the breeding system, The water treatment system includes a wastewater storage tank that stores the extracted breeding water, a denitrification tank that uses denitrifying bacteria to denitrify nitrate ions in the breeding water transferred from the wastewater storage tank, and a solid-liquid separation tank that removes solid matter from the breeding water transferred from the denitrification tank, and the problem is solved by a circulating land-based aquaculture system that transfers water containing the solid matter removed in the solid-liquid separation tank to the wastewater storage tank.

Description

[Technical Field]

[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 cultivating fish, shellfish, and the like. [Background technology]

[0002] In a recirculating land-based aquaculture system, water is circulated and reused, so the water quality must be kept constant. In particular, it is necessary to remove ammonia emitted by the aquatic organisms being reared and ammonia generated during the microbial decomposition of organic matter such as feces and leftover food, and to maintain a constant oxygen concentration in the rearing water.

[0003] As a technology for removing ammonia, for example, a system such as that disclosed in Patent Document 1 is known, and as a technology for appropriately controlling the oxygen concentration in breeding water, for example, a system such as that disclosed in Patent Document 2 is known. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-84691 [Patent Document 2] Patent Publication No. 2021-141852 Summary of the Invention [Problem to be solved by the invention]

[0005] The importance of maintaining water quality in recirculating land-based aquaculture systems is recognized, and the above-mentioned technologies have been proposed. However, even in recirculating land-based aquaculture systems, it is said that water supply and discharge per feed amount is limited to 1000 L / kg-feed (hereinafter, the rate of water supply and discharge per feed amount is referred to as the "makeup water ratio"). This is because the concentration of nitrate, a product of ammonia decomposition, must be maintained at an appropriate concentration for the aquatic organisms being raised, and a certain amount of water must be replaced.

[0006] In a recirculating land-based aquaculture system, the energy load and cost associated with water supply, as well as the environmental load associated with wastewater, increase with the scale of the system. Therefore, in large-scale recirculating land-based aquaculture systems, it is important to reduce the water exchange rate. The present disclosure provides a new recirculating land-based aquaculture system with a reduced water exchange rate. [Means for solving the problem]

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

[0008] That is, the present disclosure may include the following. [1] A recirculating land-based aquaculture system for cultivating aquatic organisms, comprising: a breeding system for breeding aquatic organisms; a water treatment system that extracts a portion of the breeding water from the breeding system, treats it, and returns it to the breeding system; The water treatment system is a circulating land-based aquaculture system comprising: a wastewater storage tank for storing the extracted breeding water; a denitrification tank for denitrifying nitrate ions in the breeding water transferred from the wastewater storage tank using denitrifying bacteria; and a solid-liquid separation tank for removing solid matter from the breeding 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 solid-liquid separation tank comprises a solid separation means and a washing means for washing solids adhering to the solid separation means; The circulating land-based aquaculture system described in [1], wherein the water used for cleaning in the cleaning means is transferred to the wastewater storage tank. [3] A recirculating land-based aquaculture system described in [1] or [2], in which solid-liquid separation is performed using one or more devices selected from the group consisting of sedimentation, a screen-type drum filter, a rotary separator, a foam separator, a sand filter, a floating filter media filter, a trickling filter, a rotating disc device, and a fixed-bed biological filter. [4] The circulating land-based aquaculture system according to any one of [1] to [3], wherein the water treatment system includes a sterilization tank that sterilizes the rearing water transferred from the solid-liquid separation tank. [5] A circulating land-based aquaculture system as described in [4], in which the ozone concentration of the rearing water transferred to the sterilization tank is maintained by an ozone dissolution device, and turbidity components and heavy metals are separated by a foam separation device and discharged outside the system. [Effects of the Invention]

[0009] The present disclosure makes it possible to provide a new circulating land-based aquaculture system with a reduced water exchange rate. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flow diagram showing one embodiment of a circulating land-based aquaculture system. DETAILED DESCRIPTION OF THE INVENTION

[0011] The contents of this disclosure will be described in detail below. However, the description of the constituent elements described below is an 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 modifications within the scope of its gist.

[0012] Figure 1 is a flow diagram showing one embodiment of a recirculating land-based aquaculture system. <Breeding system> The breeding system is a system for breeding aquatic organisms and includes at least a breeding tank. The aquatic organisms are not particularly limited as long as they are aquatic organisms that can be cultivated on land, and typical examples include fish and shellfish, such as those belonging to the Salmonidae, Penaeidae, Scombridae, Grouper, Tetraodontidae, and Haliotis. The breeding tank has a main tank, and may also be equipped with other instruments for measuring the water quality of the breeding water, and an oxygen supply device for supplying oxygen to the breeding water. One example of an octagonal main tank is octagonal, which leaves spaces at the top right, bottom right, top left, and bottom left, and necessary equipment can be placed in these spaces. The main tank does not have to be octagonal, and may be circular or rectangular.

[0013] The main tank is equipped with an inlet, and breeding water is supplied to the main tank from the inlet, and the breeding water is mainly treated by a water treatment system described below. The main tank may be provided with only one inlet, or may be provided with two or more inlets, and is not particularly limited.

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

[0015] <Water treatment system> The water treatment system is a system in which a portion of the rearing water in the rearing system is extracted, subjected to water treatment, and the treated rearing water is circulated back into the rearing system. The water treatment system includes at least a wastewater storage tank, a denitrification tank, and a solid-liquid separation tank, and may include other tanks.

[0016] <Wastewater storage tank> The wastewater storage tank is a tank that temporarily stores the breeding water extracted from the breeding system, solid organic matter such as feces and leftover food, and water containing solids separated and transferred in the solid-liquid separation tank.The wastewater storage tank makes the quality of the extracted breeding water as uniform as possible, and also advances the anaerobic process necessary to promote denitrification, allowing for smooth removal of nitrate ions in the subsequent denitrification tank. Furthermore, sand and other solids with a high specific gravity that get mixed in with the feed can be allowed to settle and discharged outside the system, which reduces the effort required to clean up sand that accumulates in the downstream tank. The wastewater storage tank may be provided with a separate settling tank or sand removal device for settling and separating sand.

[0017] <Denitrification tank> The denitrification tank is a tank in which nitrate ions contained in the rearing water are converted into nitrogen gas by denitrifying bacteria and removed from the system. Nitrate ions are produced when ammonia emitted by aquatic organisms being raised, or ammonia produced during the microbial decomposition of organic matter such as feces and leftover food, is decomposed by nitrifying bacteria through metabolism. The oxidation of ammonia by nitrifying bacteria can be carried out in a specific area within the recirculating land-based aquaculture system, or in a separate nitrification tank. Because the oxidation of ammonia by nitrifying bacteria must be carried out in an aerobic environment, aeration means such as an aeration pipe or aeration unit may be provided, and agitation means such as an agitator may also be used.

[0018] The denitrification tank may contain a carrier for supporting the microorganisms. The carrier is not particularly limited, and for example, a porous material such as ceramics, resin, or sponge may be used. The denitrification tank may be equipped with a stirring means such as a stirrer to stir the carrier.

[0019] When denitrifying using denitrifying bacteria, hydrogen donors (hereinafter also referred to as substrates) such as methanol, ethanol, sodium acetate, biodegradable resins, glycerin, and sugars are added. For these substrates, substrates with a high carbon content per molecule, which are easily degradable and inexpensive, are preferred for efficiency. On the other hand, the solids transferred from the solid-liquid separation tank and the solids in the wastewater transferred from the recirculating land-based aquaculture system to the wastewater storage tank include residual feed, feces, sludge, etc., which can be used as substrates for denitrification. Therefore, such solid organic matter may be reused as substrates for the denitrification tank. In this way, by reusing the solids removed in the solid-liquid separation tank for denitrification treatment rather than discarding them, the amount of solids to be discarded can be reduced, and the environmental impact of the recirculating land-based aquaculture system can be reduced.

[0020] <Solid-liquid separation tank> The treated water from which nitrate ions have been removed in the denitrification tank is transferred to the solid-liquid separation tank, where solids and liquids contained in the treated water are separated. The separation of solids and liquids can be achieved using existing technologies, such as, but 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 alone or in combination.

[0021] The solids removed in the solid-liquid separation tank are transferred to a wastewater storage tank together with 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 solids is also transferred to the wastewater storage tank together with the removed solids. The solids removed in the solid-liquid separation tank contain many organic components that can be used as denitrification substrates, so they can be reused as substrates 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 exchange rate. While purified water can be used as the washing water, aquaculture water can also be used to further reduce water exchange rates. A storage tank may be provided to temporarily store the solids removed in the solid-liquid separation tank and the wash water used to remove the solids. The solids stored in the storage tank are transferred to the wastewater storage tank and used as a substrate for the denitrification tank so that the suspended solids concentration (SS concentration) in the denitrification tank is within an appropriate range. The storage water tank may be equipped with a solid solubilization device. By providing the storage water tank with a solid solubilization device, the denitrification efficiency can be improved when solids are used as substrates in the denitrification tank. The solid solubilization method is not particularly limited as long as it can solubilize solids, and methods that use a stirrer, solid crusher, solid pulverizer, aeration device, etc., treatment methods such as ozone treatment, alkali treatment, and subcritical water treatment, or combinations thereof, can be used.

[0022] <Sterilization tank> The water treatment system may include a sterilization tank. The treated water from which solids have been removed in the solid-liquid separation tank is preferably transferred to the 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. The sterilization tank is preferably equipped with an ozone dissolution device and / or a foam separation device to maintain the ozone concentration. When the water exchange rate can be significantly reduced by denitrification in the denitrification tank and by returning treated water in the solid-liquid separation tank, trace metal elements derived from the feed of aquatic organisms and metal elements eluted from metal components used in the recirculating land-based aquaculture system can become concentrated in the rearing water and potentially reach concentrations that affect the health of the rearing aquatic organisms. Therefore, by using ozone treatment in the sterilization tank and a foam separation device to remove these concentrated metal elements from the rearing water as foam and discharge them outside the system, the adverse effects of the metal elements on aquatic organisms can be eliminated. In addition, turbidity components can also be removed.

[0023] The method for dissolving ozone is not particularly limited, and for example, an ozone dissolving device such as an ejector, an oxygen cone, an LHO (Low Head Oxygenator), a deep shaft, etc. Alternatively, ozone may be directly supplied to a foam separator without using an ozone dissolving device. The metal elements to be concentrated include iron, lead, copper, cadmium, mercury, zinc, manganese, tin, nickel, chromium, and aluminum.

[0024] <Crystallization tank> The water treatment system may also include a crystallization tank. If the water exchange rate can be significantly reduced by denitrification in a denitrification tank or by transferring treated water from a solid-liquid separation tank to a wastewater storage tank, phosphorus and calcium, in addition to the metal elements mentioned above, may become concentrated in the rearing water, potentially increasing to concentrations that affect the health of the reared aquatic organisms. Therefore, it is preferable to transfer the rearing water to a crystallization tank and crystallize phosphate and / or calcium. Crystallization of phosphate and / or calcium can be achieved by adding an alkali such as sodium hydroxide to the crystallization tank to adjust the pH to alkaline, specifically by raising the pH to about 8 to 14, preferably about 9 to 10. However, alkali addition may also be performed in a tank upstream of the tank rearing water being transferred to the crystallization tank. The rearing water may be transferred to the crystallization tank by withdrawing it from a wastewater storage tank, a denitrification tank, or a sterilization tank. The crystallized phosphate and / or calcium-containing compound crystals are removed using 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 directly to the rearing system.

[0025] As explained above, other aspects of the present invention include the following inventions. A method for removing phosphate and / or calcium in a recirculating land-based aquaculture system, comprising: A step of extracting a portion of the rearing water from the aquaculture system; a crystallization step of adjusting the pH of the extracted rearing water to alkaline to precipitate crystals of a compound containing phosphate and / or calcium; and and a removal step of removing the precipitated crystals of a compound containing phosphate and / or calcium.

[0026] <Other facilities> In addition to the above, the water treatment system of this embodiment may also be provided with other equipment that can be provided in a normal water treatment system.

[0027] <Low water exchange rate> In this embodiment of the circulating land-based aquaculture system, the solids removed in the solid-liquid separation tank are transferred to the wastewater storage tank together with a small amount of rearing water. If the solid-liquid separation tank is equipped with a washing device, the washing water used to remove the solids is also transferred to the wastewater storage tank along with the removed solids. By circulating rearing water, which was previously treated as wastewater, through the water treatment system, a low water exchange rate can be achieved. For example, the daily water exchange rate can be reduced to 10% or less, preferably 1% or less, of the total rearing water. Furthermore, the amount of water exchanged per feed can be reduced to 400 L / kg-feed or less, preferably 40 L / kg-feed or less. The invention disclosed herein 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 breeding system for breeding aquatic organisms; a water treatment system that extracts a portion of the breeding water from the breeding system, treats it, and returns it to the breeding system; The water treatment system is a circulating land-based aquaculture system comprising: a wastewater storage tank for storing the extracted breeding water; a denitrification tank for denitrifying nitrate ions in the breeding water transferred from the wastewater storage tank using denitrifying bacteria; and a solid-liquid separation tank for removing solid matter from the breeding water transferred from the denitrification tank, and the solid matter, including organic matter, removed in the solid-liquid separation tank is transferred to the wastewater storage tank.

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

3. 3. The recirculating land-based aquaculture system according to claim 1 or 2, wherein solid-liquid separation is performed in the solid-liquid separation tank using one or more devices selected from the group consisting of settling, a screen-type drum filter, a swirl-type separator, a foam separator, a sand filter, a floating filter media filter, a trickling filter, a rotating disc device, and a fixed-bed biological filter.

4. 3. The circulating land-based aquaculture system according to claim 1, wherein the water treatment system includes a sterilization tank that sterilizes the rearing water transferred from the solid-liquid separation tank.

5. 5. The circulating land-based aquaculture system according to claim 4, wherein the ozone concentration of the rearing water transferred to the sterilization tank is maintained by an ozone dissolution device, and turbidity components and heavy metals are separated by a foam separation device before being discharged outside the system.

6. A circulating aquaculture system having a breeding system for breeding aquatic organisms and a water treatment system for extracting and treating a portion of the breeding water from the breeding system and returning it to the breeding system.

1. A method for removing phosphate and / or calcium, comprising: The water treatment system comprises a wastewater storage tank for storing the extracted breeding water, a denitrification tank for denitrifying nitrate ions in the breeding water transferred from the wastewater storage tank using denitrifying bacteria, and a solid-liquid separation tank for removing solid matter in the breeding water transferred from the denitrification tank, and transfers the solid matter, including organic matter, removed in the solid-liquid separation tank to the wastewater storage tank; A step of extracting a portion of the rearing water from the aquaculture system; a crystallization step of adjusting the pH of the extracted 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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