Recirculating land-based aquaculture system and method for sterilizing rearing water

Abstract

This disclosure aims to improve the taste of farmed fish. A recirculating land-based aquaculture system for cultivating aquatic organisms, The system comprises a rearing system for raising aquatic organisms, a water treatment system for removing and treating at least a portion of the rearing water from the rearing system and returning it to the rearing system, and a sterilization system for sterilizing the rearing water removed from the rearing system and / or the rearing water treated by the water treatment system. The sterilization system sterilizes the rearing water extracted from the rearing system and / or the rearing water treated in the water treatment system with ozone. The sterilization system comprises a supply means for supplying hydrogen peroxide solution into the sterilization system, and a control means for controlling the amount of hydrogen peroxide solution supplied by the supply means so that the oxidation-reduction potential of the rearing water measured by the measuring means is within an appropriate range for aquatic organisms, in a recirculating land-based aquaculture system.

Description

Technical Field

[0001] The present invention relates to a land-based aquaculture system for culturing aquatic organisms, and more particularly to a recirculating land-based aquaculture system (RAS) for culturing 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 cultured aquatic organisms 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 culture 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 culture water, for example, a system such as Patent Document 2 is known. As a technique for appropriately controlling the alkalinity level in the culture tank, for example, a process such as Patent Document 3 is known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

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 described above have been proposed. On the other hand, since some of the farmed aquatic organisms are consumed by consumers as raw fish without processing, improving the taste of farmed fish is also becoming an important issue. This invention aims to improve the taste of farmed fish. [Means for solving the problem]

[0006] Because recirculating land-based aquaculture systems circulate rearing water during cultivation, they create an environment where certain compounds are easily concentrated. The inventors investigated the causes of taste deterioration in farmed fish in recirculating land-based aquaculture systems and found that the circulation of rearing water generates off-flavor substances, and these compounds degrade the taste of farmed fish. Known off-flavor substances include geosmin (or geosmin, hereinafter referred to as geosmin), 2-methylisoborneol (2-MIB), and tribromoanisole (TBA). To eliminate these off-flavors, we investigated and solved the above problems by adding hydrogen peroxide in addition to ozone sterilization, and by controlling the oxidation-reduction potential of the rearing water within an appropriate range.

[0007] 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, A water treatment system that extracts at least a portion of the rearing water from the aforementioned rearing system, treats it, and returns it to the rearing system, The system includes a sterilization system for sterilizing rearing water extracted from the rearing system and / or rearing water treated in the water treatment system, The aforementioned rearing system comprises a rearing tank and a measuring means for measuring the oxidation-reduction potential of the rearing water in the rearing tank. The sterilization system sterilizes the rearing water extracted from the rearing system and / or the rearing water treated in the water treatment system with ozone. The sterilization system comprises a supply means for supplying hydrogen peroxide solution into the sterilization system, and a control means for controlling the amount of hydrogen peroxide solution supplied by the supply means so that the oxidation-reduction potential of the rearing water measured by the measuring means is within an appropriate range for aquatic organisms, in a recirculating land-based aquaculture system. [2] The sterilization system comprises an ozone dissolving device and a foam separation device, wherein the foam separation device separates the heavy metals from the rearing water and discharges the heavy metals outside the system, as described in [1]. [3] The circulating land-based aquaculture system according to [1] or [2], wherein the supply means supplies hydrogen peroxide water to the ozone dissolving device and / or the foam separation device. [4] A recirculating land-based aquaculture system according to any of [1] to [3] that breaks down off-flavor substances in the rearing water. [5] A method for sterilizing water for rearing aquatic organisms, comprising the step of supplying two or more selected from the group consisting of ozone, ultraviolet light and hydrogen peroxide to the rearing water, A method for sterilizing rearing water, wherein the supply step controls the amount of ozone, ultraviolet light and / or hydrogen peroxide so that the oxidation-reduction potential of the rearing water is within an appropriate range for aquatic organisms. [6] A method for sterilizing aquarium water as described in [5], which decomposes off-flavor substances in the aquarium water. [Effects of the Invention]

[0008] This disclosure provides a new recirculating land-based aquaculture system that can improve the taste of farmed fish. [Brief explanation of the drawing]

[0009] [Figure 1] This is a flow diagram illustrating one form of a recirculating land-based aquaculture system. [Modes for carrying out the invention]

[0010] 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.

[0011] 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 rearing system is a system for rearing aquatic organisms and comprises at least a rearing tank and a measuring means for measuring the oxidation-reduction potential of the rearing water in the rearing tank. The aquatic organisms are not particularly limited as long as they are aquatic organisms that can be reared in land-based aquaculture, and typically include fish and shellfish, such as those belonging to the Salmonidae, Penaeidae, Mackerelidae, 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, as well as an oxygen supply device for supplying oxygen to the rearing water. For example, the main tank may be octagonal. If it is octagonal, space will be created in the upper right, lower right, upper left, and lower left, and necessary equipment may be placed in these spaces. The main tank does not have to be octagonal; it may also be circular or rectangular.

[0012] 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.

[0013] 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 towards the outlet. The outlet may be used to drain the aquarium water and to remove aquatic organisms.

[0014] In this embodiment, it is provided with measuring means for measuring the oxidation-reduction potential of the breeding water, measures the oxidation-reduction potential of the breeding water, and the measured value is sent to the control means described later. The measuring means is not particularly limited, and a commercially available oxidation-reduction potential measuring instrument may be used.

[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 is not particularly limited as long as it can purify the breeding water. For example, it may be provided with a solid-liquid separation device such as a filter for removing solids in the breeding water, and a nitrification tank for decomposing ammonia in the breeding water by microorganisms. Furthermore, it may be provided with other tanks, such as a storage tank and a denitrification tank.

[0016] <Sterilization system> The sterilization system is a system that sterilizes the breeding water extracted from the breeding system and / or the breeding water treated by the water treatment system with ozone. The sterilization system preferably includes an ozone dissolution device, preferably includes a foam separation device, and more preferably includes both. The breeding water extracted from the breeding system is sterilized with ozone in the sterilization system, and the sterilized breeding water is returned to the breeding system.

[0017] The sterilization system preferably includes an ozone dissolution device and a foam separation device as described above. In recirculating land-based aquaculture, trace metal elements derived from feed and metal elements eluted from metal members used in the equipment of the recirculating land-based aquaculture system are concentrated in the breeding water and may increase to a concentration that affects the health of the cultured aquatic organisms. Therefore, by discharging these metal elements concentrated in the breeding water as bubbles outside the recirculating land-based aquaculture system through ozone treatment and the foam separation device in the sterilization system, the adverse effects of metal elements on aquatic organisms can be eliminated.

[0018] 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, and tin.

[0019] <Hydrogen peroxide supply means and control means> In this configuration, the sterilization system uses ozone for sterilization, as well as hydrogen peroxide for sterilization. In recirculating land-based aquaculture systems, it is necessary to manage the oxidation-reduction potential of the rearing water within an appropriate range to avoid negative impacts on the health of the aquatic organisms being raised. In the recirculating land-based aquaculture system industry, ozone treatment has generally been applied to sterilize the rearing water. When ozone is dissolved in the rearing water, the oxidation-reduction potential of the water increases. As the ozone concentration increases, the sterilization effect and the decomposition effect of difficult-to-decompose substances increase, but at the same time, the oxidation-reduction potential of the rearing water also increases. If the oxidation-reduction potential of the rearing water becomes too high, it can damage the aquatic organisms being raised, potentially leading to their death.

[0020] As described above, ozone-only treatment, which involves dissolving ozone in the rearing water, can lead to the oxidation-reduction potential of the rearing water exceeding the appropriate range for the aquatic organisms being reared if the ozone concentration is increased in an attempt to achieve a higher effect. However, the inventors have found that by adding a certain amount of hydrogen peroxide simultaneously with dissolving ozone in the rearing water, it is possible to suppress the rise in the oxidation-reduction potential of the rearing water, thereby significantly improving the sterilization effect of the rearing water while reducing damage to the aquatic organisms being reared. Furthermore, we discovered that by supplying ozone and hydrogen peroxide to the rearing water in the sterilization system, off-flavors such as geosmin (or geosmin, hereafter geosmin), 2-methylisoborneol (2-MIB), and tribromoanisole (TBA) can be broken down and removed by hydroxyl radicals with stronger oxidizing power generated by the oxidation-reduction reaction between ozone and hydrogen peroxide. These hydroxyl radicals are generated not only by the redox reaction between ozone and hydrogen peroxide, but also by the redox reaction between ozone and ultraviolet light (UV), and by the redox reaction between hydrogen peroxide and ultraviolet light, and can similarly decompose and remove off-flavors.

[0021] The following are the experimental results of off-flavor decomposition. <Experiment> Geosmin was added to a tank containing 20 L of water and thoroughly stirred to prepare an aqueous solution with a geosmin concentration of 57 ng / L. Ozone was dissolved in the aqueous solution to a concentration of 2 mg / L, and when the geosmin concentration was measured, it decreased to 37 ng / L, indicating a geosmin decomposition rate of 35%. The oxidation-reduction potential of the aqueous solution at this time was 300 mV. Next, hydrogen peroxide was added to the geosmin-containing solution to achieve an effective concentration of 4 mg / L, and ozone was dissolved to an ozone concentration of 6 mg / L. When the geosmin concentration was measured in this state, it decreased to 12 ng / L, indicating a geosmin decomposition rate of 79%. The oxidation-reduction potential of the aqueous solution at this time was 300 mV. From the above experimental results, it can be understood that even with an increased ozone concentration, the coexistence of ozone and hydrogen peroxide allows the oxidation-reduction potential to be maintained at a level that does not affect the aquatic organisms being raised, and also enables the decomposition of geosmin.

[0022] In other words, the sterilization system of this embodiment includes a supply means for supplying hydrogen peroxide solution into the sterilization system, and a control means for controlling the amount of hydrogen peroxide solution supplied so that the oxidation-reduction potential of the rearing water measured by the measuring means of the rearing system is within an appropriate range for aquatic organisms. The hydrogen peroxide solution supplied by the supply means may be supplied to, for example, an ozone dissolving device or to a foam separation device. Alternatively, ozone and hydrogen peroxide solution may be supplied directly to the foam separation device without using an ozone dissolving device. The control means may also control the amount of ozone supplied to the ozone dissolving device by the ozone generator. As described above, if the amount of ozone supplied is too much, the oxidation-reduction potential of the rearing water will rise, so it is preferable to control the amount of ozone supplied together with the supply control of hydrogen peroxide.

[0023] The supply amount of hydrogen peroxide solution is controlled by adjusting the ozone injection rate (mg-O3 / L) and the molar ratio of ozone to hydrogen peroxide within an appropriate range in the sterilization system, such as in an ozone dissolving device or foam separation device. Specifically, the oxidation-reduction potential of the rearing water is measured using the aforementioned oxidation-reduction potential measuring means, and the supply amount of hydrogen peroxide solution to the sterilization system is controlled so that the oxidation-reduction potential is in the range of approximately 100mV to 500mV, preferably approximately 200mV to 350mV. Note that the appropriate ozone injection rate and the appropriate molar ratio of ozone to hydrogen peroxide will vary depending on the degree of contamination of the rearing water. Measuring the oxidation-reduction potential of rearing water involves measuring the oxidation-reduction potential of the rearing water within the rearing system. Typically, this involves measuring the oxidation-reduction potential of the rearing water in the rearing tank, but if the oxidation-reduction potential of the rearing water in the rearing system can be measured, the oxidation-reduction potential of the rearing tank may also be measured in the piping connecting the rearing tanks.

[0024] For more precise control of the oxidation-reduction potential of the rearing water, in addition to measuring the oxidation-reduction potential of the rearing water in the rearing system, the oxidation-reduction potential of the rearing water at other locations may be measured, and these measurements may be used to control the hydrogen peroxide solution. Preferably, these other locations are foam separators, and may include, for example, the rearing water flowing into the foam separator and the rearing water flowing out of the foam separator. By sending the continuously measured values ​​from these two locations to the control means, the oxidation-reduction potential of the rearing water can be managed more precisely, enabling accurate control of the hydrogen peroxide solution supply. For example, the oxidation-reduction potential of the rearing water flowing out of the foam separator can be controlled to be between 0 and 800 mV, preferably between 300 and 500 mV.

[0025] As described above, the amount of ozone in the rearing water is not particularly limited as long as the oxidation-reduction potential of the rearing water can be kept within an appropriate range, but it is usually 0.005 to 50 mg / L, and preferably 0.01 to 20 mg / L. Furthermore, as long as the oxidation-reduction potential of the rearing water can be kept within an appropriate range, the amount of hydrogen peroxide in the rearing water is not particularly limited, but it is usually 0.01 to 100 mg / L, and preferably 0.1 to 50 mg / L.

[0026] As described above, the following inventions are examples of other embodiments of the present invention. A method for sterilizing water used for raising aquatic organisms, comprising the step of supplying two or more elements selected from the group consisting of ozone, ultraviolet light, and hydrogen peroxide to the water used for raising aquatic organisms. A method for sterilizing rearing water, wherein the supply step controls the amount of ozone, ultraviolet light and / or hydrogen peroxide solution so that the oxidation-reduction potential of the rearing water is within an appropriate range for aquatic organisms.

[0027] <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.

[0028] The invention disclosed herein allows for the decomposition and removal of off-flavors from the rearing stage rather than the harvest stage, thereby improving the taste of farmed fish. 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 recirculating land-based aquaculture system for cultivating aquatic organisms, A breeding system for raising aquatic organisms, A water treatment system that extracts at least a portion of the rearing water from the aforementioned rearing system, treats it, and returns it to the rearing system, The system includes a sterilization system for sterilizing rearing water extracted from the rearing system and / or rearing water treated in the water treatment system, The aforementioned rearing system comprises a rearing tank and a measuring means for measuring the oxidation-reduction potential of the rearing water in the rearing tank. The sterilization system sterilizes the rearing water extracted from the rearing system and / or the rearing water treated in the water treatment system with ozone. The sterilization system includes a supply means for supplying hydrogen peroxide solution into the sterilization system, and a control means for controlling the amount of hydrogen peroxide solution supplied by the supply means so that the oxidation-reduction potential of the rearing water measured by the measuring means is within an appropriate range for aquatic organisms. A recirculating land-based aquaculture system that uses ozone and hydrogen peroxide to suppress the rise in oxidation-reduction potential in the rearing water while decomposing off-flavor substances.

2. The sterilization system comprises an ozone dissolving device and a foam separation device, wherein heavy metals are separated from the rearing water by the foam separation device and discharged outside the system, as described in claim 1.

3. The circulating land-based aquaculture system according to claim 2, wherein the supply means supplies hydrogen peroxide water to the ozone dissolving device and / or the foam separation device.

4. A method for sterilizing water used for raising aquatic organisms, comprising the step of supplying ozone and hydrogen peroxide solution to the water used for raising aquatic organisms, The step of supplying ozone and hydrogen peroxide to the rearing water is performed so that the oxidation-reduction potential of the rearing water is within an appropriate range for aquatic organisms. A method for sterilizing aquarium water that controls the amount of [unclear] and suppresses the rise in oxidation-reduction potential of the aquarium water while breaking down off-flavor substances in the aquarium water.

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