Sterilizing rearing water

Abstract

The present disclosure addresses the problem of improving the taste of cultured fish that have been cultured.　Provided is a land-based recirculating aquaculture system for culturing aquatic organisms, the system comprising: a rearing system that rears the aquatic organisms; a water treatment system that extracts and treats at least a portion of the rearing water of the rearing system and returns the water to the rearing system; and a sterilization system that sterilizes the rearing water extracted from the rearing system and / or the rearing water treated by the water treatment system. The rearing water extracted from the rearing system and / or the rearing water treated by the water treatment system are ozone-sterilized in the sterilization system, and the sterilization system comprises: a supply means that supplies hydrogen peroxide water into the sterilization system; and a control means that controls the amount of the hydrogen peroxide water supplied by the supply means so that an oxidation-reduction potential of the rearing water measured by a measurement means falls within an appropriate range for the aquatic organisms.

Description

Circulating land-based aquaculture system and method for sterilizing breeding water

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

[0002] In a circulating 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 bred and ammonia generated during the decomposition of organic substances such as feces and residual 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 breeding water, for example, a system such as Patent Document 2 is known. As a technique for appropriately controlling the alkalinity level in the aquaculture tank, a process such as Patent Document 3 is known.

[0004] Japanese Patent Application Laid-Open No. 2015-84691, Japanese Patent Application Laid-Open No. 2021-141852, WO2023 / 131960

[0005] Regarding the circulating land-based aquaculture system, the importance of maintaining water quality is recognized and the above-mentioned techniques have been proposed. On the other hand, some of the aquatic organisms to be cultured are consumed by consumers as raw fish without being processed. Therefore, improving the taste of the cultured fish has become an important issue. The present invention aims to improve the taste of the cultured fish.

[0006] Because recirculating land-based aquaculture systems circulate rearing water for aquaculture, they create an environment where certain compounds are easily concentrated. The inventors investigated the causes of deterioration in the taste of farmed fish in recirculating land-based aquaculture systems and found that the circulation of rearing water generates off-flavor substances, and these compounds deteriorate the taste of farmed fish. Known off-flavors include geosmin (or geosmin, hereinafter referred to as geosmin), 2-methylisoborneol (2-MIB), and tribromoanisole (TBA). In order to remove these off-flavors, the inventors investigated and solved the above problem by adding hydrogen peroxide in addition to ozone sterilization and 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, comprising: a rearing system for rearing 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, wherein the rearing system comprises rearing tanks and measuring means for measuring the oxidation-reduction potential of the rearing water in the rearing tanks; the sterilization system sterilizes the rearing water removed from the rearing system and / or the rearing water treated by the water treatment system with ozone; and the sterilization system comprises supply means for supplying hydrogen peroxide solution into the sterilization system, and 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. [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 out of the system, as described in [1]. [3] The supply means supplies hydrogen peroxide to the ozone dissolving device and / or the foam separation device, as described in [1] or [2]. [4] The sterilization system of land-based aquaculture according to any one of [1] to [3], which decomposes off-flavor substances in rearing water. [5] A method for sterilizing rearing water for 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, 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] The method for sterilizing rearing water according to [5], which decomposes off-flavor substances in rearing water.

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

[0009] This is a flow diagram illustrating one form of a recirculating land-based aquaculture system.

[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 ways 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 describes it in order. <Aquaculture System> The aquaculture system is a system for raising 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 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.

[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, a measuring means for measuring the oxidation-reduction potential of the rearing water is provided, and the measured value is sent to a control means described later. The measuring means is not particularly limited, and a commercially available oxidation-reduction potential meter may be used.

[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 is not particularly limited as long as it is a system that can purify the rearing water. For example, it may be equipped with a solid-liquid separation device such as a filter to remove solid matter from the rearing water, a nitrification tank to decompose ammonia in the rearing water with microorganisms, and may also be equipped with other tanks, such as a storage tank or a denitrification tank.

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

[0017] As mentioned above, the sterilization system preferably includes an ozone dissolving device and a foam separation device. In recirculating land-based aquaculture, trace amounts of metal elements derived from feed and metal elements leached from metal components used in the equipment of the recirculating land-based aquaculture system can become concentrated in the rearing water, potentially rising to concentrations that affect the health of the aquatic organisms being reared. Therefore, by discharging these concentrated metal elements from the rearing water as foam outside the recirculating land-based aquaculture system through ozone treatment and a 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 can be concentrated include iron, lead, copper, cadmium, mercury, zinc, manganese, and tin.

[0019] <Means for supplying and controlling hydrogen peroxide> In this embodiment, in addition to sterilization by ozone, hydrogen peroxide is supplied to the sterilization system for further 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 affecting the health of the aquatic organisms being raised. In the industry of recirculating land-based aquaculture systems, ozone treatment has generally been applied to sterilize rearing water. When ozone is dissolved in rearing water, the oxidation-reduction potential of the rearing water increases, and the higher the ozone concentration, the greater the sterilization effect and the decomposition effect of difficult-to-decompose substances, 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, and they may die.

[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, they have found that by supplying ozone and hydrogen peroxide solution to the rearing water in the sterilization system, off-flavors such as geosmin (or geosmin, hereinafter geosmin), 2-methylisoborneol (2-MIB), and tribromoanisole (TBA) can be decomposed 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 for off-flavor decomposition. <Experiment> Geosmin was added to a tank containing 20 L of water and stirred well 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 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 above geosmin-containing solution to an effective concentration of 4 mg / L, and ozone was dissolved to a 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 measurement 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 an 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 amount of hydrogen peroxide solution supplied.

[0023] The supply rate of hydrogen peroxide solution is controlled in the sterilization system to which it is supplied, for example, in the ozone dissolution device or foam separation device, by controlling the ozone injection rate (mg-O ３This is done by setting the ozone injection rate ( / L) within an appropriate range and the molar ratio of ozone to hydrogen peroxide within an appropriate range. Specifically, the oxidation-reduction potential of the rearing water is measured using the aforementioned oxidation-reduction potential measuring means, and the amount of hydrogen peroxide solution supplied to the sterilization system is controlled so that the range is approximately 100 mV to 500 mV, preferably approximately 200 mV to 350 mV. 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. The oxidation-reduction potential of the rearing water is measured in the rearing system. Typically, the oxidation-reduction potential of the rearing water in the rearing tank is measured, 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 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. Also, 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 invention is an alternative embodiment of the present invention: 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, 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.

[0027] <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.

[0028] The invention described 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 invention described 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 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, wherein the 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 removed from the rearing system and / or the rearing water treated by the water treatment system with ozone; and 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.

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 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 recirculating land-based aquaculture system according to any one of claims 1 to 3, which decomposes 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, 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 rearing water according to claim 5, which decomposes off-flavor substances in the rearing water.

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