Recirculating land-based aquaculture system

Abstract

The objective is to provide a new recirculating land-based aquaculture system that reduces the water exchange rate. [Solution] A recirculating land-based aquaculture system for cultivating aquatic organisms, The system comprises 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. 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. The water containing the solid matter removed in the solid-liquid separation tank is then transferred to the wastewater storage tank. This circulating land-based aquaculture system solves the problem.

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 raising fish and shellfish.

Background Art

[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, and as a technique for appropriately controlling the oxygen concentration of breeding water, for example, a system such as Patent Document 2 is known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Regarding recirculating land-based aquaculture systems, the importance of maintaining water quality is recognized, and technologies such as those mentioned above have been proposed. On the other hand, even in recirculating land-based aquaculture systems, it is said that, for example, an upper limit of 1000 L / kg-feed is used for water supply and drainage per unit of feed (hereinafter, the ratio of water supply and drainage per unit of feed will be referred to as the "makeup water ratio"). This is because it is necessary to maintain the nitrate concentration, which is a product of ammonia decomposition, at an appropriate level for the aquatic organisms being raised, and therefore a certain amount of water is replaced.

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

[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, A breeding system for raising aquatic organisms, The system includes 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. 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. A recirculating land-based aquaculture system that transfers water containing solid matter to the wastewater storage tank. [2] The solid-liquid separation tank comprises a solid separation means and a cleaning means for cleaning solids adhering to the solid separation means, The circulating land-based aquaculture system according to [1], wherein 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 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 water treatment system comprises a sterilization tank for sterilizing the rearing water transferred from the solid-liquid separation tank, as described in any of [1] to [3]. [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. [Effects of the Invention]

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

[0010] [Figure 1] This is a flow diagram illustrating one form of a recirculating land-based aquaculture system. [Modes for carrying out the invention]

[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 ways 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 will explain it step by step. <Breeding System> The breeding system is a system for breeding aquatic organisms and at least includes a breeding tank. The aquatic organisms are not particularly limited as long as they are aquatic organisms that can be bred in land-based aquaculture. Typically, they include those belonging to the fish and shellfish categories, such as those belonging to the Salmonidae, Palaemonidae, Scombridae, Serranidae, Tetraodontidae, and Veneridae families. The breeding tank has a main water tank and may also include instruments for measuring the quality of the breeding water, and may also be equipped with an oxygen supply device for supplying oxygen to the breeding water. As an example, the main water tank is octagonal. When it is octagonal, spaces are formed in the upper right, lower right, upper left, and lower left respectively, and necessary equipment can be arranged in these spaces. Note that the main water tank may not be octagonal, but may be circular or rectangular.

[0013] The main water tank has an inlet, and breeding water is supplied to the main water tank from the inlet, and mainly the breeding water treated in the water treatment system described later is supplied. The inlet may be provided only one in the main water tank, or two or more may be provided, and it is not particularly limited.

[0014] The main water tank may also be provided with an outlet at approximately the central part of the bottom surface, and the bottom surface of the main water tank may be tapered toward the outlet. The outlet is used for extracting the breeding water and may also be used for removing feces, uneaten feed, and aquatic organisms.

[0015] <Water treatment system> The water treatment system is a system that extracts a part of the breeding water of the breeding system for water treatment and circulates the treated breeding water back to the breeding system. The water treatment system at least includes a drainage storage tank, a denitrification tank, and a solid-liquid separation tank, and may also include other tanks.

[0016] <Drainage storage tank> The drainage storage tank is a tank for temporarily storing water containing breeding water withdrawn from the breeding system, solid organic substances such as feces and uneaten feed, and solids separated and transferred in the solid-liquid separation tank. The drainage storage tank can make the water quality of the withdrawn breeding water as uniform as possible, and can promote the anaerobic process necessary for the denitrification reaction in advance, so that the removal of nitrate ions in the subsequent denitrification tank can proceed smoothly. Furthermore, sand and solids with a high specific gravity mixed in the feed can be precipitated and discharged outside the system. This can save the labor of cleaning sand and the like deposited in the subsequent water tanks. The drainage storage tank may separately include a grit chamber or a desanding device for precipitating and separating sand.

[0017] <Denitrification tank> The denitrification tank is a tank that converts nitrate ions contained in the breeding water into nitrogen gas by denitrifying bacteria and removes them outside the system. Nitrate ions are generated when ammonia discharged from the aquatic organisms to be bred and ammonia generated during the decomposition of organic substances such as feces and uneaten feed by microorganisms are decomposed by the metabolism of nitrifying bacteria. The oxidation of ammonia by nitrifying bacteria may be carried out in a specific area within the circulating land-based aquaculture system, or may be carried out by separately providing a nitrification tank. Since the oxidation of ammonia by nitrifying bacteria needs to be carried out in an aerobic environment, it may be provided with aeration means such as air diffusers and aeration, and stirring means such as stirrers can also be used.

[0018] The denitrification tank may contain a carrier carrying microorganisms. The carrier is not particularly limited, and for example, porous bodies such as ceramics, resins, and sponges are used. Since the denitrification tank stirs these carriers, it may be provided with stirring means such as stirrers.

[0019] During denitrification by denitrifying bacteria, as a hydrogen donor (hereinafter also referred to as a substrate), methanol, ethanol, sodium acetate, biodegradable resin, glycerin, sugars, etc. are added. As these substrates, those with a high carbon content per molecule, easy degradability, and low cost are more efficient and preferable. On the other hand, solid materials transferred from the solid-liquid separation tank, and solid materials in the wastewater transferred from the recirculating land-based aquaculture system to the wastewater storage tank, include 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 treatment instead of discarding them, the amount of solid material to be discarded can be reduced, thereby reducing the environmental burden on the recirculating land-based aquaculture system.

[0020] <Solid-liquid separation tank> The solid-liquid separation tank receives treated water from which nitrate ions have been removed in the denitrification tank, and separates the solids and liquids contained in the treated water. The separation of solids and liquids can be performed using existing technologies, such as precipitation, microscreen drum filters, swirl separators, foam skimmers, sand separators, and flotation. Floating bead filter, trickling filter, rotating biological contactor, fixed-bed bioreactor These are some examples, but they are not limited to these. 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. The solid material removed in the solid-liquid separation tank contains many organic components that can be used as a denitrification substrate, and therefore can be reused as a substrate in the denitrification tank. Furthermore, by transferring the wash water to the wastewater storage tank as well, the wash water after washing is not discharged but circulated in the land-based aquaculture system, contributing to a low water change rate. While pure water may be used for washing, rearing water may also be used from the perspective of further reducing water change. A storage tank may be provided to temporarily store the solids removed in the solid-liquid separation tank and the washing water used to remove the solids. The solids stored in the storage tank are transferred to a wastewater storage tank and used as substrate for the denitrification tank so that the suspended solids (SS) concentration in the denitrification tank is within an appropriate range. The storage tank may be equipped with a solid material solubilizer. By equipping the storage tank with a solid material solubilizer, 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 methods using a stirrer, solid material crusher, solid material grinder, aeration device, etc., treatment methods such as ozone treatment, alkaline treatment, subcritical water treatment, or a combination thereof can be used.

[0022] <Sterilization tank> The water treatment system may include a sterilization tank. It is preferable that the treated water, from which solid matter has been removed in the solid-liquid separation tank, is transferred to a sterilization tank for further 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 dissolving device and / or a foam separation device to maintain ozone concentration. When the water exchange rate can be significantly 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, potentially rising to concentrations that affect the health of the reared aquatic organisms. Therefore, by discharging these concentrated metal elements from the rearing water as foam outside the system through ozone treatment in the sterilization tank and a foam separation device, the adverse effects of metal elements on aquatic organisms can be eliminated. In addition, turbidity components can also be removed at the same time.

[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 separation device without using an ozone dissolving device. Examples of metal elements that become concentrated include iron, lead, copper, cadmium, mercury, zinc, manganese, tin, nickel, chromium, and aluminum.

[0024] <Crystallization tank> The water treatment system may include a crystallization tank. When 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 above-mentioned metal elements, may become concentrated in the rearing water and rise to concentrations that could 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 by adding an alkali such as sodium hydroxide in the crystallization tank 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. The rearing water to the crystallization tank may be drawn from the wastewater storage tank, the denitrification tank, or the sterilization tank. The crystallized phosphate and / or calcium-containing compounds are removed by a filter or the like, and the decrystallized rearing water is returned to the water treatment system, but it may also be transferred directly to the rearing system.

[0025] As described above, the following inventions are examples of other embodiments of the present invention. A method for removing phosphate and / or calcium in a recirculating land-based aquaculture system, A step in which a portion of the rearing water is removed from the aquaculture system. A crystallization step in which the pH of the extracted rearing water is adjusted to be alkaline to precipitate crystals of a compound containing phosphoric acid and / or calcium, and The method comprises a removal step of removing precipitated compound crystals containing phosphoric acid and / or calcium.

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

[0027] <Low water exchange rate> In this configuration of a 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, by circulating the rearing water, which would conventionally be treated as wastewater, through the water treatment system, a low water replacement rate can be achieved. For example, the daily water replacement rate can be reduced to 10% or less of the total rearing water, preferably 1% or less. Additionally, the water replacement rate per unit of feed can be reduced to 400 L / kg-feed or less, preferably 40 L / kg-feed or less. The inventions described herein contribute to SDG 12: Responsible Consumption and Production, SDG 14: Life Below Water, and SDG 15: Life on Land.

Claims

1. A method for removing phosphate and / or calcium in a recirculating aquaculture system having 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, A step in which a portion of the rearing water is removed from the aquaculture system. A crystallization step in which the pH of the extracted rearing water is adjusted to be alkaline to precipitate crystals of a compound containing phosphoric acid and / or calcium, and A method comprising a removal step of removing precipitated compound crystals.

2. The water treatment system comprises a wastewater storage tank for storing the extracted rearing water and a solid-liquid separation tank for removing solid matter from the extracted rearing water, and the solid matter containing organic matter removed in the solid-liquid separation tank is transferred to the wastewater storage tank, according to claim 1.

3. The method according to claim 1 or 2, wherein the recirculating aquaculture system has a water exchange rate of 400 L / kg-feed or less per unit of feed.

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