Water tank water quality management method and water quality management device

Abstract

Provided is a water tank water quality management method in which: an alcohol is added to water in a water tank in which fish are reared; a photocatalyst carrier is brought into contact with the water; a photocatalyst of the photocatalyst carrier is irradiated with ultraviolet rays to synthesize an amino acid by a photocatalytic reaction from the alcohol in the water and at least one substance selected from ammonium ions (NH4 +), nitrate ions (NO3 −), and nitrous acid (NO2 −); and, by doing so, the concentrations of ammonium ions (NH4 +), nitrate ions (NO3 −), and nitrous acid (NO2 −) contained in the water in the water tank are respectively maintained at predetermined values or less. The present invention is capable of providing a water quality management method with which the water quality management of water in a water tank in which fish are reared, in particular, management of the concentrations of ammonia, nitrous acid, and nitric acid, is performed more easily than the conventional method without depending on nitrification treatment and denitrification treatment using nitrifying bacteria and denitrifying bacteria. The present invention is also capable of providing a water quality management device capable of performing said water quality management method.

Description

Water quality control method and water quality control device for aquariums

[0001] The present invention relates to a water quality control method and a water quality control device for an aquarium in which fish are kept.

[0002] Ammonia is generated in aquariums housing fish due to fish waste and feed residues. This ammonia is oxidized to nitrite and nitrate by nitrifying bacteria naturally occurring in the aquarium. However, the oxidation effect of naturally occurring nitrifying bacteria is limited, and over a period of time, ammonia (ammonium ions), nitrite (nitrite salts), and nitrate (nitrate ions) accumulate in the aquarium. Of these, ammonia and nitrite are highly toxic to fish, and nitrate is known to adversely affect fish and other organisms by lowering the pH of the water in the aquarium. Therefore, to remove these substances, it is necessary to periodically replace all or part of the water in the aquarium with fresh water. However, particularly when the volume of the aquarium is large, large amounts of water must be replaced, which requires considerable effort, and furthermore, disposing of water containing a considerable amount of ammonia, nitrite, and nitrate is environmentally undesirable.

[0003] Therefore, in order to promote the oxidation of ammonia and nitrite, which are harmful to fish, to nitrate, nitrification treatment using nitrifying bacteria is carried out on the water in the aquarium, and the nitrate produced by the nitrification treatment is converted into nitrogen (N ２ A method has been proposed for purifying the water in the aquarium by denitrifying it using denitrifying bacteria that reduce CO₂ to CO₂ (Patent Documents 1 and 2).

[0004] In addition, a device has been proposed in which water from an aquarium or water from an aquarium that has been subjected to a nitrification process to produce nitric acid is supplied to a cultivation tank where plants are grown, causing the nitrogen content in the aquarium to be consumed as fertilizer by the plants, and the water from which the nitrogen has been removed is returned to the aquarium (Patent Documents 3 and 4).

[0005] Japanese Patent Application Laid-Open No. 2003-284453 International Publication No. 2019 / 112044 Utility Model Registration No. 3130947 Utility Model Registration No. 3238183

[0006] The methods and devices described in Patent Documents 1 to 4 are believed to be capable of reducing the concentrations of ammonia, nitrite, and nitrate contained in the water of an aquarium where fish are kept. However, because the methods described in Patent Documents 1 to 4 use nitrifying bacteria or denitrifying bacteria, the nitrification and denitrification processes are not necessarily stable, and once unstable, they may require time to stabilize, raising concerns about adverse effects on fish breeding. Therefore, an object of the present invention is to provide a water quality management method and a water quality management device capable of performing this water quality management method that makes it easier to manage the water quality of water in an aquarium where fish are kept, particularly the concentrations of ammonia, nitrite, and nitrate, than conventional methods, without relying on nitrification or denitrification processes using nitrifying bacteria or denitrifying bacteria, or even by using nitrification processes using nitrifying bacteria in combination.

[0007] The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. As a result, when alcohol is added to the water in an aquarium where fish are kept, the water in the aquarium containing this alcohol is brought into contact with a photocatalyst carrier, and ultraviolet light is irradiated onto the photocatalyst, the alcohol contained in the water in the aquarium and ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － ) and at least one selected from the group consisting of ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － The present invention encompasses the following inventions.

[0008] (1) Alcohol is added to the water in an aquarium where fish are kept, and a photocatalyst carrier is brought into contact with the water. The photocatalyst of the photocatalyst carrier is irradiated with ultraviolet light, thereby converting the alcohol in the water into ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２－ ) by a photocatalytic reaction to synthesize amino acids from at least one selected from the group consisting of ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － A method for managing the water quality of an aquarium by maintaining the concentrations of the following substances below a specified value.

[0009] (2) The method for managing the water quality of an aquarium according to (1), in which the water in the aquarium to which alcohol has been added is brought into contact with a photocatalyst carrier installed outside the aquarium, and the photocatalyst in the photocatalyst carrier is irradiated with ultraviolet light. (3) The method for managing the water quality of an aquarium according to (1) or (2), in which the water in the aquarium in which amino acids have been synthesized is used for growing plants. (4) The method for managing the water quality of an aquarium according to (3), in which the water in the aquarium is supplied to a cultivation tank in which the plants are grown, and the water from the cultivation tank is supplied to the aquarium, and the water is circulated between the aquarium and the cultivation tank.

[0010] (5) A method for producing an aquarium for raising fish, in which water containing alcohol is added and a photocatalyst carrier are brought into contact with each other, and ultraviolet light is irradiated onto the photocatalyst of the photocatalyst carrier, thereby converting the alcohol in the water into ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － and an amino acid synthesizer for synthesizing amino acids from at least one selected from the group consisting of ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － (6) The water quality control device for an aquarium according to (5), further comprising a cultivation tank for cultivating plants using the water in the aquarium.

[0011] According to the present invention, it is possible to provide a water quality control method that makes it easier than ever to control the water quality of water in an aquarium where fish are kept, particularly the concentrations of ammonia, nitrite, and nitrate, without relying on nitrification or denitrification processes using nitrifying bacteria or denitrifying bacteria, and a water quality control device that is capable of carrying out this water quality control method.

[0012] 1 is a perspective view showing a water quality control device according to a representative embodiment of the present invention. FIG. 1 is an exploded perspective view of an amino acid synthesizer constituting the water quality control device shown in FIG. 1. FIG. 2 is a longitudinal cross-sectional view of the amino acid synthesizer from the side. FIG. 3 is a longitudinal cross-sectional view of the amino acid synthesizer from the front. FIG. 4 is an explanatory diagram showing the procedure for supporting a photocatalytic layer. FIG. 5 is a perspective view of a modified example of the water quality control device shown in FIG. 1. FIG. 6 is an exploded perspective view of an amino acid synthesizer constituting the water quality control device shown in FIG. 7. FIG. 7 is a longitudinal cross-sectional view of the amino acid synthesizer from the side. FIG. 8 is a longitudinal cross-sectional view of the amino acid synthesizer from the front. FIG. 9 is a perspective view of a second embodiment of the water quality control device. FIG. 10 is a longitudinal cross-sectional view of the water control device. FIG. 11 is a perspective view of a third embodiment of the water quality control device. FIG. 12 is a longitudinal cross-sectional view of the water control device. FIG. 13 is a schematic view of a fourth embodiment of the water quality control device. FIG. 14 is a schematic view of a fifth embodiment of the water quality control device. FIG. 15 is a graph showing the change over time in the concentration of ammonium ions in a preliminary test. FIG. 16 is a graph showing the change over time in the concentration of nitrate ions in a preliminary test. ２ － 1 is a graph showing the change in the concentration of ammonium ions over time in Example 1; 2 is a graph showing the change in the concentration of nitrate ions over time in Example 1; ２ － ) concentration over time in Comparative Example 1. FIG. 2 shows the change in ammonium ion concentration over time in Comparative Example 1. FIG. 3 shows the change in nitrate ion concentration over time in Comparative Example 1. FIG. 4 shows the change in nitrite (NO ) concentration over time in Comparative Example 1. ２ － ) concentration over time in Example 2 and Comparative Example 2. FIG. 3 shows the change in ammonium ion concentration over time in Example 2 and Comparative Example 2. FIG. 4 shows the change in nitrate ion concentration over time in Example 2 and Comparative Example 2. FIG. 5 shows the change in nitrite (NO ) concentration over time in Example 2 and Comparative Example 2. ２ － ) concentration over time.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0014] In the water quality management method for an aquarium according to an embodiment of the present invention, alcohol is added to the water in an aquarium in which fish are kept, and a photocatalyst carrier is brought into contact with the water. The photocatalyst of the photocatalyst carrier is irradiated with ultraviolet light, thereby dissolving the alcohol in the water and ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － ) and synthesize amino acids by a photocatalytic reaction, and as a result, ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － The water quality of the aquarium water is controlled by maintaining the concentrations of these elements at or below a predetermined value.

[0015] There are no particular limitations on the fish to which this water quality control method can be applied, as long as they are kept in aquariums. For example, they may be freshwater fish or saltwater fish, ornamental fish, or farmed fish.

[0016] Any alcohol can be used as long as it does not have an adverse effect on the fish being raised and allows for good amino acid synthesis. From the perspective of raising fish, ethanol is preferred.

[0017] Various methods are possible for contacting the photocatalyst carrier with the water from the alcohol-added tank. For example, a photocatalyst layer with a photocatalyst attached thereto may be provided on the contact surface of a container through which the water from the alcohol-added tank flows, or a carrier with a photocatalyst layer formed thereon may be placed so as to be immersed in the water from the tank, or a photocatalyst layer may be formed on the surface of a panel over which water flows. The structures of the photocatalyst carriers used in the water quality control devices 1 (1C), 1A, and 1B described below are merely examples.

[0018] The means for irradiating the photocatalyst of the photocatalyst layer in contact with water with ultraviolet light is not limited to irradiation from the back surface of the glass plate of the photocatalyst carrier 2, as in the water quality control devices 1 (1C), 1A, and 1B described below, and does not necessarily have to be a glass plate. Of course, irradiation may be through water from the front surface side where the photocatalyst layer is present. UV light can be emitted from an LED substrate having an ultraviolet LED light source, but is not limited to this. However, it is necessary to use the UV light in a manner that does not cause harm to fish a and other various organisms.

[0019] The method of adding alcohol to the water in the aquarium includes adding it to the aquarium itself, adding it to the container through which the water in the aquarium flows, etc. The timing of addition is determined by the amount of ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － The amount of alcohol can be determined appropriately taking into consideration the concentration of ammonium ions, etc. (hereinafter collectively referred to as "ammonium ions, etc."), the type of fish a, pH, water temperature, etc. For example, it is generally preferable to maintain ammonium ions at 5 ppm or less, nitrate ions at 20 ppm or less, and nitrite at 1 ppm or less. Since ammonium ions, etc. are typically produced significantly for a certain period after feeding, the supply of alcohol may be started at the same time as feeding. The method of addition may be continuous or intermittent, and can be determined appropriately depending on the concentration of ammonium ions, etc. in the water.

[0020] The amount of alcohol to be added can also be determined appropriately depending on the concentration of ammonium ions, etc.

[0021] The photocatalytic reaction produces alcohol and ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ －The mechanism by which amino acids are produced from at least one selected from the group consisting of ammonium ions (NH ) and ammonium ions (NH ) is not entirely clear, but it is believed that in the presence of OH radicals generated from water by a photocatalyst, alcohols are sequentially oxidized to aldehydes and carboxylic acids, and then the carboxylic acids react with ammonium ions (ammonia) to produce amino acids. In addition, nitrate ions and nitrite ions are reduced to ammonium ions (ammonia), and the ammonium ions (ammonia) derived from these nitrate ions and nitrite ions also react with carboxylic acids derived from alcohols to synthesize amino acids. In this way, ammonium ions (NH ) contained in the water of the aquarium are converted into ammonium ions (NH ). ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － ) is consumed in the synthesis of amino acids, making it possible to maintain their concentrations at or below a predetermined value. Amino acids that can be synthesized are usually of multiple types, such as aspartic acid, threonine, serine, glutamic acid, proline, glycine, alanine, valine, isoleucine, leucine, histidine, and lysine.

[0022] As will be described later, the present inventors have confirmed that various amino acids can be synthesized by photocatalytic reaction by bringing tap water to which alcohol and aqueous ammonia have been added into contact with a photocatalyst carrier and irradiating it with ultraviolet light.

[0023] As mentioned above, alcohol is thought to be oxidized to carboxylic acid and used for amino acid synthesis. Therefore, we considered using carboxylic acid instead of alcohol. However, carboxylic acid significantly lowers the pH of the aquarium water, which raises concerns about its impact on fish. Furthermore, continued addition of carboxylic acid may cause the pH to become neutral, which may result in the generation of suspended solids, leading to concerns about a decline in water quality. On the other hand, by adding alcohol and using it to synthesize amino acids with ammonium ions, etc., it becomes possible to maintain the concentration of ammonium ions, etc. in the water at a predetermined level or below, without the aforementioned concerns associated with adding carboxylic acid.

[0024] In an embodiment of the aquarium water quality management method of the present invention, aquarium water containing synthesized amino acids can be used for plant growth. It is known that amino acids can be directly absorbed by plants and serve as fertilizers that promote plant growth. In this embodiment, synthesized amino acids are effectively utilized as plant fertilizer. Furthermore, because amino acids synthesized from ammonium ions and other ions in the aquarium water are consumed outside the aquarium, the total amount of nitrogen sources in the aquarium can be reduced, allowing for better management of the aquarium water quality. The type of plant is not particularly limited, and examples include edible plants such as vegetables and fruits, and ornamental plants such as flowers, but those suitable for hydroponic cultivation are preferred. The cultivation tank for growing plants is not limited to the one shown in FIG. 14 (described below), and any known structure can be used. Furthermore, if a cultivation tank is provided, it is preferable to supply water from the aquarium to the cultivation tank, use that water for plant cultivation, and then supply the cultivation tank water to the aquarium repeatedly, thereby circulating water between the cultivation tank and the aquarium. This allows for repeated water use, conserving water, while better maintaining and managing the water quality of the aquarium water where fish are kept.

[0025] In the aquarium water quality management method according to an embodiment of the present invention, good water quality management is possible without nitrification treatment using nitrifying bacteria or denitrification treatment using denitrifying bacteria. However, depending on the type of fish and breeding conditions, it may be possible to efficiently synthesize amino acids and make water quality management easier by using biological filtration such as nitrification and denitrification treatment using microorganisms, or physical filtration to physically remove fish droppings and feed residues, as pretreatment, and then use the treated water after these pretreatments for amino acid synthesis. Even with these pretreatments, ammonium ions and the like remain in the pretreated water. However, by returning the water after amino acid synthesis to the aquarium, the concentration of ammonium ions and the like in the water in the aquarium can be maintained below a predetermined value. While this type of biological filtration and physical filtration is commonly performed, using them in combination with amino acid synthesis reduces the concentration of ammonium ions and the like to a predetermined value and maintains good water quality.

[0026] Examples of this type of biological filtration method include methods using various filter media to which microbial flora such as nitrifying bacteria can adhere. The filter media is not particularly limited, and known filter media such as silicate mineral filter media can be used. The physical filtration method is not particularly limited, and includes methods using filters, foam separators (skimmers), etc. The skimmer is not particularly limited, and known skimmers such as Venturi types can be used. For example, when raising saltwater fish, a skimmer may be used to remove organic matter such as protein to a certain extent. Furthermore, biological filtration may be performed using filter media to which microbial flora such as nitrifying bacteria are attached, thereby nitrifying ammonia ions in seawater to a certain extent.

[0027] Next, an embodiment of a water quality control device for realizing the above-described water quality control method for an aquarium will be described.

[0028] As shown in Figures 1 to 4, an aquarium water quality control device 1 according to a first embodiment of the present invention comprises an aquarium 30 in which fish a are kept, and an amino acid synthesizer 8. The amino acid synthesizer 8 comprises a photocatalyst carrier 2 and a light irradiator 9 that irradiates ultraviolet light onto the photocatalyst in the photocatalyst carrier 2. In this embodiment, the amino acid synthesizer 8 comprises a container 7 for bringing the photocatalyst carrier 2 into contact with water 14 of the aquarium 30 to which alcohol has been added, and a photocatalyst layer 5 made of a photocatalyst that undergoes a photocatalytic reaction in response to ultraviolet light is provided on the inner surface (contact surface) of the container 7 that comes into contact with the water. Water is stored or circulated in the container 7, and ultraviolet light is irradiated onto the photocatalyst layer 5 by the light irradiator 9, thereby converting the alcohol in the water into ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － ) by a photocatalytic reaction to synthesize amino acids from at least one selected from the group consisting of ammonium ions, ammonium ions, and ammonium ions contained in the water of the aquarium 30. By converting the ammonium ions and ammonium ions contained in the water of the aquarium 30 into amino acids in this way, the concentration of the ammonium ions and ammonium ions in the water of the aquarium 30 can be maintained at a predetermined value or lower that does not affect the breeding of the fish a.

[0029] The amino acid synthesizer 8 according to this embodiment will be described in detail below.

[0030] At least a portion of the inner surface of the container 7 that comes into contact with the water to be treated is made of a glass substrate 4, and a photocatalyst layer 5 carrying a photocatalyst is provided on the inner surface side of the glass substrate 4. The light irradiating unit 9 is provided on the outer surface of the glass substrate 4 opposite the contact surface, and is configured to irradiate ultraviolet light through the glass substrate 4 to the photocatalyst in the photocatalyst layer 5. The photocatalyst layer 5 has good adhesion to the glass substrate 4, and is preferably made of an aggregate of titanium oxide crystals formed by thermal hydrolysis of titanium (IV) tetrabutoxide on the surface, and titanium oxide particles having an average particle size of 1 μm or less that are carried on the surface together with the aggregate of titanium oxide crystals, using the aggregate of titanium oxide crystals as a binder.

[0031] The aggregates of titanium oxide crystals in titanium (IV) tetrabutoxide adhere to the surface 4a of an unroughened glass substrate 4. Titanium oxide particles have high photocatalytic reactivity, but when used alone, they have low adhesion to the surface 4a of an unroughened glass substrate 4. By combining the two, their mutual affinity allows the titanium oxide crystals in titanium (IV) tetrabutoxide to function as a binder supporting the titanium oxide particles, and the titanium oxide particles also penetrate between the titanium (IV) tetrabutoxide crystals, functioning as a binder to strengthen the bonds between the crystals and preventing peeling off of the crystal units.

[0032] As shown in Figure 5, the photocatalytic layer 5 is formed by first preparing a mixed solution by mixing titanium oxide particles with an average particle size of 1 μm or less with an alcohol-diluted solution of titanium(IV) tetrabutoxide (S101). The concentration of titanium(IV) tetrabutoxide in the mixed solution is 2% to 5%. The particle size of the titanium oxide particles is preferably 7 to 100 nm, and more preferably 20 to 70 nm. If the particle size is too small, ultraviolet light, decomposition substances, and adsorption substances will not reach the interior of the photocatalytic layer 5, and improved catalytic function will not be expected. The weight ratio of titanium(IV) tetrabutoxide to titanium oxide particles in the mixed solution is 0.5 to 3.

[0033] Next, this mixture is applied to the surface 4a of a glass substrate 4 (S102), and the titanium(IV) tetrabutoxide in the mixture is hydrolyzed by heating at 150°C or higher (S103). By applying the mixture to the surface of the glass substrate, which has been preheated to 150°C or higher, the titanium(IV) tetrabutoxide in the mixture can be efficiently hydrolyzed. This hydrolysis converts the titanium(IV) tetrabutoxide into aggregates of titanium oxide crystals, and together with the aggregates, forms a photocatalytic layer 5 carrying titanium oxide particles (S104).

[0034] As shown in FIG. 2 , a pair of photocatalyst carriers 2 each comprising such a glass substrate 4 and a photocatalyst layer 5 are provided on a front and rear side of a frame 6 for a housing, which is made up of an upper plate 61, side plates 62 and 63, and a bottom plate 64, so as to close the front and rear openings 6 a and 6 b, and each photocatalyst carrier 2 is attached to the openings 6 a and 6 b with the front side on which the photocatalyst layer 5 is formed facing the inside of the frame 6 for a housing.

[0035] Water 14 is circulated and supplied inside the housing frame 6 to which each photocatalyst carrier 2 is attached, and amino acids are produced from the ammonium ions and the like contained in the water 14 in the water tank 30 and the added alcohol by photocatalytic reaction in the photocatalytic layer 5 of the front and rear photocatalyst carriers 2 facing the internal space S1. In other words, the internal space S1 of the housing frame 6 serves as the main processing space of the amino acid synthesizer 8.

[0036] As shown in Figure 1, an aquarium 30 in which fish a are kept is provided below the container 7, and between the two is provided a pumping passage 33 consisting of a pumping pipe 32 whose upper end is connected to an opening 64a formed in the bottom plate 64 of the housing frame 6 of the container 7 and whose lower end is connected to a pumping pump 31 arranged in the aquarium 30, and a return passage 35 consisting of a return pipe 34 whose one end is connected to openings 62a, 63a formed in the left and right side plates 62, 63 of the frame 6 at a position above the internal space S1 and whose other end extends into the aquarium 30, for returning the water 14 supplied to the internal space S1 through the pumping passage 33 back to the aquarium 30.

[0037] Water 14 supplied to the lower part of the internal space S1 of the container 7 through the pumping path 33 flows upward through the internal space S1, producing amino acids through a photocatalytic reaction caused by the photocatalyst carrier 2 in the process, and is then returned to the water tank 30 from an upper position through the return path 35 and supplied again to the internal space S1 of the container 7 through the pumping path 33, thereby repeatedly producing amino acids through a photocatalytic reaction. The opening 61a in the upper plate 61 is an open hole that opens the upper space of the internal space S1 to the atmosphere and is configured to take in and discharge air, thereby maintaining a constant water pressure and allowing the water 14 to circulate smoothly through the pumping path 33 and the return path 35.

[0038] The supply of water 14 through the pumping channel 33 may be continuous or intermittent. The supply speed and timing can be appropriately set by controlling the pumping pump 31. In this embodiment, water is supplied to the internal space S1 from below and returned from above, but this is not limiting. Water may be supplied from above and returned from below, or an appropriate wall may be provided in the internal space S1 to form a longer return flow path, with the pumping channel and return flow path connected at both ends of the path.

[0039] In this embodiment, the container 7 made of the housing frame 6 having the photocatalyst carrier 2 is supported above by the support frame 11, and water is circulated between the container 7 and the water tank 30 provided below, but the present invention is not limited to this positional relationship. Also, although the water circulates vertically in the internal space S1, it is of course possible to turn the housing frame 6 sideways and have the water flow horizontally.

[0040] The light irradiation unit 9 is configured such that LED substrates 90 each having an ultraviolet LED light source 91 are arranged in parallel at intervals on the back side (outside opposite the internal space S1) of each photocatalyst carrier 2, and ultraviolet light is irradiated from the back side through the glass substrate 4 of the photocatalyst carrier 2 to the photocatalyst in the photocatalyst layer 5 on the front side. The LED substrates 90 are attached to the contact surface facing the photocatalyst carrier 2 of a vertically extending metal support plate 92 with a bent U-shaped cross section, and are configured so that heat generated by the ultraviolet LED light source 91 can be dissipated to the outside from the support plate 92. As the ultraviolet light source, an ultraviolet LED capable of emitting ultraviolet light of a predetermined wavelength is used from the viewpoint of using a wavelength that is less harmful to fish a and various other living organisms and from the viewpoint of simplifying the device configuration. However, this is not necessarily limited to this, and various ultraviolet light sources can be adopted by configuring the device in a way that can prevent irradiation of ultraviolet light of harmful wavelengths to the outside. In this embodiment, the container 7 having the photocatalyst carrier 2 is placed outside the aquarium 30 together with the light irradiating unit 9 so that the device is configured so that ultraviolet rays are not irradiated onto the fish a.

[0041] To further promote heat dissipation, a metal cover plate 80, also bent in a U-shaped cross section and extending vertically, is provided on the outside of the light emitting unit 9. A vertically extending gap S2 is formed between the cover plate 80 and the surface opposite the contact surface of the support plate 92, allowing outside air to be introduced / exhausted through upper and lower openings 80a, 80b. A through-hole 80c is formed in the approximate center of the cover plate 80, allowing outside air to be introduced / exhausted from the gap S2, and an electric fan 82 is provided to introduce / exhaust air through the through-hole 80c. This allows the heat generated by the light emitting unit 9 to be efficiently dissipated to the outside.

[0042] In this embodiment, air is supplied to the water 14 in the aquarium 30 to provide oxygen to the fish a. This air supply is achieved through an air passage 16, which is composed of an aeration pipe 160 with one end connected to an air pump 161 and the other end installed at the bottom of the aquarium 30. However, if the end of the return pipe 34 extending into the aquarium 30 is positioned above the surface of the water 14 in the aquarium 30, air can be taken in when the returning water 14 reaches the water surface. Therefore, the air passage 16 is not necessarily provided as long as the oxygen concentration in the water can be maintained within an acceptable range for the fish a. On the other hand, if the end of the return pipe 34 extending into the aquarium 30 is positioned below the surface of the water 14 in the aquarium 30, as in the example shown in FIG. 1 , air is not taken in by the returning water 14 at the water surface, so the provision of the air passage 16 is preferable. Furthermore, if it is expected that water will be circulated intermittently between the water tank 30 and the amino acid synthesizer 8, it is preferable to provide an air passage 16.

[0043] In this embodiment, the alcohol used for amino acid synthesis in the amino acid synthesizer 8 (container 7) may be supplied to the aquarium 30 or to the container 7. The supply of alcohol can be carried out according to the concentrations of ammonium ions and the like contained in the water 14 in the aquarium 30, but it may also be carried out periodically in conjunction with feeding the fish a. The supply of food and alcohol to the aquarium 30 can be carried out, for example, through a through-hole 303 provided at a predetermined position in the cover plate 302 of the aquarium 30.

[0044] The alcohol supply method may be manual or automatic, and may be continuous or intermittent. When it is done manually, for example, a predetermined amount of alcohol measured into a pipette or measuring container can be dropped into the water tank 30 or the container 7. When it is done manually, it can be done intermittently at a predetermined time, for example, by adding alcohol when feeding the fish a. When it is done automatically, for example, an appropriate pump can be selected depending on the flow rate of the alcohol to be added, and the pump can be operated continuously or intermittently to supply the alcohol to the water tank 30 or the container 7.

[0045] When supplying alcohol to the container 7, for example, as in the modified examples shown in Figures 6 to 9, a tube 150 can be inserted and fixed from the upper plate 61 of the housing of the container 7 of the amino acid synthesizer 8 to the interior, and an alcohol supply unit 15 can be provided that supplies alcohol from a container filled with alcohol to the water 14 in the container 7 through the tube 150 using a pump 151. This allows alcohol to be supplied to the water 14 in the container 7 and used for the amino acid synthesis reaction, which is thought to reduce the impact on the environment of the aquarium, such as fish, caused by adding alcohol to the aquarium 30. Note that in the modified examples shown in Figures 6 to 9, the same components as those in Figures 1 to 4 are designated by the same reference numerals.

[0046] The concentration of ammonium ions and the like in the water of the aquarium 30 can be measured at an appropriate frequency depending on the type of fish, the breeding density, etc. Measurements can be performed by sampling water from the aquarium 30 and using test paper, a measurement kit, an ion chromatograph, a concentration measurement sensor, etc. For example, when a concentration measurement sensor is used, the concentration of ammonium ions and the like can be measured automatically.

[0047] For example, fish a are fed at predetermined times and raised while the concentrations of ammonium ions and the like are measured at predetermined frequencies, and when any of these concentrations exceed a predetermined value, a predetermined amount of alcohol is added to the aquarium 30 or container 7, and amino acids are synthesized from the alcohol and ammonium ions and the like using the amino acid synthesizer 8, consuming the ammonium ions and the like, thereby maintaining the concentration of ammonium ions and the like in the water 14 of the aquarium 30 at or below a predetermined value, thereby managing the water quality of the water in the aquarium 30.

[0048] A control unit may be provided that can control the operation of the alcohol supply pump 151, the water pump 31 of the amino acid synthesizer 8, and the light irradiation unit 9 based on the measurement results of the concentration of ammonium ions, etc. Also, a temperature regulator that can adjust the water temperature of the aquarium 30 may be provided depending on the type of fish.

[0049] 10 and 11 show a second embodiment of a water quality control device according to the present invention. The water quality control device 1A of this second embodiment includes an aquarium 30A in which fish a are kept, and an amino acid synthesizer 8A configured such that a photocatalyst carrier 2 is formed by providing a photocatalyst layer 5 on the outer peripheral surface of a peripheral wall 41 of a glass substrate 4 having a bottom plate and a cylindrical portion continuous with the bottom plate and opening at the water surface, and a light irradiator 9 is provided inside the glass substrate 4 for irradiating ultraviolet light toward the inner peripheral surface of the peripheral wall 41. In this second embodiment, because ultraviolet light is irradiated toward the water 14 side of the aquarium 30A, the light source used for the light irradiator 9 is limited to one that does not affect the fish a.

[0050] Then, this photocatalyst carrier 2 is immersed in an aquarium 30A in which fish a are kept, with the upper opening 12 above the water surface, and alcohol is added to the aquarium 30A in accordance with the concentration of ammonium ions and the like in the water within the aquarium 30A, whereby amino acids are synthesized from the alcohol and ammonium ions and the like contained in the water 14 within the aquarium 30A that comes into contact with the photocatalyst layer 5 on the outer peripheral surface, and the concentration of ammonium ions and the like in the water 14 within the aquarium 30A is maintained at or below a predetermined value, thereby controlling the water quality of the water within the aquarium 30A.

[0051] In the second embodiment, an air passage 16 is provided for the purpose of supplying oxygen to the fish a. In the example shown in Figures 10 and 11, one air passage 16 is provided, but multiple air passages may be provided depending on the size of the aquarium 30A and the density of the fish a. The alcohol may be added manually or automatically. If added automatically, the alcohol supply unit 15 shown in Figures 6 to 9 may be applied to the aquarium 30A. A temperature regulator capable of adjusting the water temperature may also be provided.

[0052] 12 and 13 show a third embodiment of the water quality control device according to the present invention. The water quality control device 1B of this third embodiment includes a water tank 30 and an amino acid synthesizer 8B, which is configured such that a slider 13 having a U-shaped cross section and a photocatalyst carrier 2 as a bottom plate is provided on a cover plate 301 of the water tank 30, the slider 13 being inclined at an appropriate angle as a water channel for water 14, and the water 14 is supplied to the top of the slider 13 by a water pump 31 and a water pumping pipe 32, and the water falls from the bottom into the water tank 30 and is returned.

[0053] As shown in FIG. 13 , the photocatalyst carrier 2 has a photocatalyst layer 5 formed on the upper surface of a plate-shaped glass substrate 4, and a light irradiation unit 9 for irradiating ultraviolet light is disposed parallel to the back surface of the photocatalyst carrier 2. The photocatalyst layer 5 forming the bottom surface of the slider 13 synthesizes amino acids from alcohol and ammonium ions, etc., contained in the water 14 as it flows over it, thereby maintaining the concentration of ammonium ions, etc., in the water 14 in the water tank 30A below a predetermined value, thereby managing the water quality of the water in the water tank 30A. In this embodiment 3, ultraviolet light is irradiated toward the side opposite the water tank 30B. Therefore, depending on the light source used for the light irradiation unit 9, it is preferable to provide a cover that covers the upper side of the slider 13 and can prevent ultraviolet light from radiating to the outside.

[0054] In the third embodiment, air is taken into the water 14 by the water falling from the slider 13, so an air passage 16 for supplying oxygen to the fish a is not provided, but may be provided if necessary. The alcohol may be added manually or automatically. If added automatically, the alcohol supply unit 15 shown in Figures 6 to 9 may be applied to the aquarium 30B. A temperature regulator capable of adjusting the water temperature may also be provided.

[0055] FIG. 14 is a schematic diagram illustrating a fourth embodiment of the water quality control device according to the present invention. The water quality control device 1C of this fourth embodiment includes an aquarium 30, an amino acid synthesizer 8, and a cultivation tank 70 for cultivating plants. Specifically, the cultivation tank 70 is provided in addition to the water quality control device 1 of the first embodiment. Therefore, the method for synthesizing amino acids from alcohol and ammonium ions contained in the water in the aquarium 30 is the same as that of the first embodiment. In this fourth embodiment, hydroponic cultivation is performed using the water in the aquarium 30 that contains water treated by the amino acid synthesizer 8. By utilizing the amino acids synthesized by the amino acid synthesizer 8 as plant fertilizer, the nitrogen source containing the amino acids contained in the water in the aquarium 30 can be used for hydroponic cultivation, thereby reducing the total amount of nitrogen sources in the aquarium 30 and enabling better water quality management in the aquarium 30.

[0056] As shown in Figure 14, the cultivation tank 70 has a planter 71 serving as a cultivation bed for the plant b, a cultivation water supply channel 72 that supplies water 14 from the aquarium 30 to the planter 71, and a cultivation return channel 73 that returns the water supplied to the planter 71 to the aquarium 30, thereby enabling water to circulate between the aquarium 30 and the cultivation tank 70. The cultivation water supply channel 72 comprises a water supply pump 75 and a water supply pipe 74 that has a first end (lower end) connected to the water supply pump 75 located in the aquarium 30 and a second end (upper end) that opens toward the planter 71. The cultivation return channel 73 has an opening 77 that is open to receive water discharged from the planter 71, and a return pipe 76 that has a first end (lower end) that opens toward the aquarium 30 and a second end (upper end) connected to the opening 77. As shown in Figure 14, if the lower end of the return pipe 76 is located above the water surface of the water tank 30, air can be taken in when the returning water reaches the water surface, so it is not necessarily necessary to provide the air vent 16 as shown in Figure 1.

[0057] When fish a are reared and the concentration of ammonium ions and other ions in the water in the aquarium 30 exceeds a predetermined value, alcohol is added to the aquarium 30 or the container 7, and the amino acid synthesizer 8 is activated to synthesize amino acids from the alcohol and ammonium ions and return the amino acid-containing water to the aquarium 30. Furthermore, the water from the aquarium 30, to which the water treated by the amino acid synthesizer 8 is returned, is supplied by a water supply pump 75 from the upper end of a water supply pipe 74 to a planter 71 in which a plant b is grown. The amino acids and nitrate ions contained in the water are consumed by the plant b, thereby reducing the nitrogen content in the water. The water used for hydroponic cultivation is then discharged from the planter 71 and returned to the aquarium 30 through the cultivation return path 73, thereby maintaining the concentration of ammonium ions and other ions in the water in the aquarium 30 below a predetermined value. Repeated circulation of the water from the aquarium 30 between the amino acid synthesizer 8 and the cultivation tank 70 further reduces the nitrogen content in the water, thereby maintaining and managing the water quality of the aquarium 30. It also makes it possible to raise fish with fewer water changes.

[0058] The cultivation tank 70 may be provided with a pH adjusting device to adjust the pH to a level suitable for cultivating the desired plants, or a nutrient supplying device to add necessary nutrients to the extent that the water quality of the aquarium 30 is not affected. In addition, in the fourth embodiment, the water quality control device 1 of the first embodiment is combined with the cultivation tank 70, but the water quality control devices 1A and 1B of the second and third embodiments may also be combined with the cultivation tank 70. Furthermore, in the fourth embodiment, water from the aquarium 30 is supplied to the cultivation tank 70, but it may also be configured so that the water is supplied from the reflux pipe 34 of the amino acid synthesizer 8.

[0059] FIG. 15 is a schematic diagram of a fifth embodiment of the water quality control device according to the present invention. The water quality control device 1D of this fifth embodiment includes a water tank 30C, an amino acid synthesizer 8, and a pretreatment tank 50 for biological filtration and physical filtration. In this fifth embodiment, the water in the water tank 30C is first subjected to pretreatment for biological filtration and physical filtration in the pretreatment tank 50. The resulting pretreated water is then supplied to the container 7 of the amino acid synthesizer 8, and water containing amino acids synthesized in the presence of alcohol is returned to the water tank 30C. In the pretreatment tank 50 of this fifth embodiment, biological filtration and physical filtration are performed in this order, but the pretreated water contains ammonium ions and the like. The method of synthesizing amino acids from ammonium ions and the like contained in the pretreated water and a separately added alcohol is the same as in the first embodiment.

[0060] This fifth embodiment is an example of rearing saltwater fish C in seawater 14a. When rearing saltwater fish C, it is effective to perform a physical filtration process using a skimmer 57 to physically remove saltwater fish C feces and feed residues, but this does not directly remove ammonium ions and the like from the seawater 14a. It may also be effective to perform a biological filtration process to nitrify ammonium ions in the seawater 14a using a filter medium to which microbial flora such as nitrifying bacteria are attached. However, as mentioned above, nitrification by nitrifying bacteria is not always stable. On the other hand, in this fifth embodiment, by using the amino acid synthesizer 8 in combination, amino acids are synthesized from ammonium ions and alcohol in the seawater 14a, and the seawater 14a containing this amino acid is returned to the aquarium 30C, so that the concentration of ammonium ions and the like in the seawater 14a in the aquarium 30C can be maintained below a predetermined value. Therefore, by using these physical filtration processes and biological filtration processes in combination with the amino acid synthesizer 8, water quality management according to the type of fish, such as saltwater fish, and the rearing conditions, can be more easily performed.

[0061] The configuration of the water quality control device 1D according to the fifth embodiment is described in detail below. As shown in Fig. 15, a drain outlet 38 is provided on the bottom of the aquarium 30C. A drain pipe 37 is provided that connects the drain outlet 38 to the interior of the aquarium 30C and extends downward. A cylindrical overflow pipe 36 is provided that surrounds the entire periphery of the drain outlet 38 and extends toward the water surface, allowing seawater 14a in the aquarium 30C to overflow from the opening 36 on the water surface side. The overflowed seawater 14a in the aquarium 30C flows down the overflow pipe 36 toward the bottom of the aquarium 30C, passes through the drain outlet 38, further flows down the drain pipe 37, and flows into the biological filtration section 51 of the pretreatment tank 50 through an opening 37a below.

[0062] The pretreatment tank 50 includes a biological filtration section 51 that receives seawater 14a from the water tank 30C via the drain pipe 37 and performs biological filtration, a physical filtration section 52 that receives the seawater 14a flowing out from the biological filtration section 51 and performs physical filtration, and a pretreated water storage section 53 that receives the seawater 14a flowing out from the physical filtration section 52 and temporarily stores it as pretreated water. In this fifth embodiment, the biological filtration section 51 is surrounded on all sides by a sidewall 54 that is higher than the sidewalls of the physical filtration section 52 and the pretreated water storage section 53, and a perforated plate 55 is installed horizontally at a predetermined height below the water surface from the bottom. A filter medium 56 is installed above the perforated plate 55. The filter medium 56 is installed to cover all or part of the upper surface of the perforated plate 55 (in this fifth embodiment, it is installed to cover only part of the upper surface). In addition, a drain outlet 54a connecting the biological filtration section 51 and the physical filtration section 52 is provided at a position below (toward the bottom surface of) the perforated plate 55 in the portion of the side wall 54 that serves as a partition between the biological filtration section 52 and the physical filtration section 52. The biological filtration section 51 is provided with a cover plate 51a having a hole through which the drain pipe 37 can pass. The physical filtration section 52 is partitioned by a partition 58 so that it can receive and retain seawater 14a flowing out from the biological filtration section 51, and the water surface side is open so that the seawater 14a can overflow from the upper side of the partition 58 into the pretreated water storage section 53. A skimmer 57 is provided in the physical filtration section 52, and the skimmer 57 removes feces of marine fish C, feed residue, and the like that may be contained in the seawater 14a flowing in from the biological filtration section 51 via the drain outlet 54a. A lifting pump 31 is provided in the pretreated water storage section 53, and seawater 14a that overflows from a partition wall 58 and is temporarily stored therein is supplied from a lifting pipe 32 into the container 7 of the amino acid synthesizer 8. Then, for example, when the concentration of ammonium ions or the like in the water tank 30C exceeds a predetermined value, the ammonium ions or the like contained in the seawater 14a (pretreated water) can be reacted with a separately added alcohol in the container 7 to synthesize amino acids, as described above, and the seawater 14a can be refluxed to the water tank 30C through a pair of reflux pipes 34. When the concentration of ammonium ions or the like in the water tank 30C is equal to or lower than a predetermined value, the seawater can be refluxed without amino acid synthesis.In this case, the photocatalytic reaction may be stopped by stopping the irradiation of ultraviolet light by the light irradiation unit 9, or a branch pipe directly communicating with the water tank 30C may be provided in the middle of the water pumping pipe 32 together with a valve, so that the seawater 14a (pretreated water) in the pretreated water storage unit 53 is directly supplied to the water tank 30C by the water pumping pump 31. The arrows in Figure 15 indicate the flow of seawater 14a when seawater 14a is supplied into the container 7 of the amino acid synthesizer 8.

[0063] In this fifth embodiment, the supply of alcohol, the water quality management including the measurement of the concentration of ammonium ions and the like in the seawater 14a in the water tank 30C, and the control of various devices can be performed in the same manner as in the first embodiment.

[0064] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples and can be embodied in various forms without departing from the gist of the present invention.

[0065] (Preliminary Experiment) Using the water quality control device 1 shown in Figures 1 to 4 (however, no fish were kept), an experiment was conducted to confirm that amino acids were produced by a photocatalytic reaction by circulating tap water to which ethanol and aqueous ammonia had been added through the amino acid synthesizer 8.

[0066] First, photocatalyst carrier 2 was prepared as follows. Titanium (IV) tetrabutoxide and 100 ml of monomer were diluted with ethanol to obtain a 2% diluted solution. To this was added 4 g of a slurry containing titanium oxide particles ("ST-01" manufactured by Ishihara Sangyo Kaisha, Ltd., containing 3% titanium oxide particles with an X-ray particle size of 7 nm) to obtain a mixed solution. Two borosilicate glass plates (300 mm x 60 mm) were heated to 150-350°C and the mixed solution was sprayed onto them. As a result, the ethanol evaporated from the mixed solution on the glass plate surface, and the organic groups of the titanium (IV) tetrabutoxide decomposed to form titanium oxide crystals. At the same time, the relatively small titanium oxide particles became entrapped in the titanium oxide crystals and were supported on the glass surface. Through the above process, two photocatalyst carriers 2 were obtained, each of which had a photocatalyst layer 5 supported on the glass plate. Using the obtained photocatalyst carrier 2, a water quality control device 1 was assembled, which includes an amino acid synthesizer 8 and a water tank 30, as shown in Figures 1 to 4. However, air (oxygen) was not supplied to the water in the water tank using an air pump. A temperature regulator was used to maintain the water temperature at 25°C. The light irradiation unit 9 used 36 ultraviolet LEDs (18 on each side) with a wavelength of 375 nm. The current to the LEDs was 700 mA.

[0067] The tank was filled with approximately 20 L of tap water, and the amino acid synthesizer 8 was operated. Ethanol (purity 99.5%) was manually added to the tank once a day. The amount of ethanol added was 1 mL from the start of the test until the 11th day, and 0.8 mL from the 12th day onwards. Four days after the start of the test, 1 mL of ammonia water (ammonia concentration 1.8 ppm) was added to the tank. The types and concentrations of amino acids in the water were measured on the 24th day after the start of the test. The results are shown in Table 1. The changes over time in the concentrations of ammonium ions, nitrate ions, and nitrite in the water during the test are also shown in Figures 16 to 18.

[0068] Example 1 Using a water quality control device 1 (water temperature controlled at 25°C, no air supply via an air pump) with the same configuration as in the preliminary experiment, the aquarium 30 was filled with approximately 60 L of ultrapure water and five goldfish were reared. The amino acid synthesizer 8 was operated simultaneously with the start of rearing. Food (Tetra Corporation, product name: Tetrafin) was provided once a day, and ethanol (99.5% purity) was manually added. The amount of food added was an amount that could be consumed within 2-3 minutes. The amount of alcohol added was 1 mL from the start of the test until the 26th day, and 0.8 mL from the 27th day onwards. The concentrations of ammonium ions, nitrate ions, and nitrite in the water were measured during the test, and their changes over time were confirmed. The results are shown in Figures 19-21. Additionally, the type and concentration of amino acids in the water were measured on the 39th day from the start of the test. The results are shown in Table 1. Additionally, the free amino acid concentration in a solution in which 0.7 g of food was added to 1,000 mL of water was measured, and the results are shown in Table 1.

[0069] Comparative Example 1 Using a water quality control device 1 (temperature controlled at 26°C, no air supply) with the same configuration as in the preliminary experiment, the aquarium 30 was filled with approximately 15 L of ultrapure water and three goldfish were reared. The amino acid synthesizer 8 was operated simultaneously with the start of rearing. The light irradiator 9 used 36 ultraviolet LEDs (18 on each side) with a wavelength of 375 nm. The current to the LEDs was 700 mA. Food (Tetrafin, manufactured by Tetra Corporation) was provided twice a day (9:00 AM and 3:00 PM) in an amount that could be consumed in 2-3 minutes. No alcohol was added. The concentrations of ammonium ions, nitrate ions, and nitrite in the water were measured during the test, and their changes over time were confirmed. The results are shown in Figures 22 to 24.

[0070]

[0071] As shown in Table 1, in Example 1, amino acids other than the free amino acids derived from the feed were present, and amino acids common to those in the preliminary test were also present, indicating that amino acids were synthesized by a photocatalytic reaction between the added ethanol and ammonium ions, etc., derived from the fish, etc., in Example 1. Furthermore, from Figures 19 to 24, it can be seen that by adding ethanol as in Example 1, the concentration of ammonium ions, etc., in the aquarium was maintained lower than in Comparative Example 1.

[0072] Example 2 Using the water quality control device 1D shown in FIG. 15 (water temperature controlled at 25°C, no air supply via an air pump), the aquarium 30C was filled with approximately 60 L of breeding water (SEALIFE, artificial seawater, manufactured by Marine Tech Co., Ltd.), and 12 blue-green damselfish were reared. The amino acid synthesizer 8 used in Preliminary Experiment 1 was the same as that shown in FIGS. 1 to 4, except that the configuration of the water pumping pipe 35 and the return pipe 34 was changed to that shown in FIG. 15. The filter media 56 used were the Powerhouse Basic Hard Type (Wollastonite, cylindrical), M size, manufactured by Taiheiyo Cement Corporation, and Gokujo Sango No. 15, manufactured by JUN Co., Ltd. The skimmer 57 used was a Mantis Skimmer (Venturi type) manufactured by Volks Japan Co., Ltd. Simultaneously with the start of breeding, the amino acid synthesizer 8 was operated to synthesize amino acids via photocatalytic reaction. The fish were given food (SEALIFE SURE, manufactured by Marine Tech Co., Ltd.) twice a day, approximately 0.06 ml each time. Ethanol (purity 99.5%) was added to the tank twice a day (9:00 a.m. and 3:00 p.m., with a 6-hour interval), 1 ml each time. The concentrations of ammonium ions, nitrate ions, and nitrite (NO ) in the seawater 14a of the test tank 30C were ２ － The concentration of amino acids was measured and their change over time was confirmed. In the case of seawater, amino acids cannot be measured, so they were not measured.

[0073] Comparative Example 2 In the water quality control device 1D shown in FIG. 15, a branch pipe that directly communicates with the water tank 30C together with a valve is provided midway on the water pumping pipe 32, and the seawater 14a (pretreated water) in the pretreated water storage section 53 is directly supplied to the water tank 30C by the water pumping pump 31. In this comparative example, 12 blue-green damselfishes were reared in the same manner as in Example 2, except that no photocatalytic reaction was performed. The ammonium ions, nitrate ions, and nitrite (NO ) in the seawater 14a in the water tank 30C under test were measured. ２ － ) concentration was measured and its change over time was confirmed.

[0074] The measurement results for Example 2 and Comparative Example 2 are shown in Figures 25 to 27. As shown in these figures, even when rearing saltwater fish, by adding ethanol and synthesizing amino acids through a photocatalytic reaction as in Example 2, the concentrations of ammonium ions and the like in the aquarium are maintained low even after the rearing time has passed, compared to Comparative Example 2, in which no photocatalytic reaction was performed.

[0075] DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C, 1D Water quality control device for aquarium 2 Photocatalyst carrier 4 Glass substrate 5 Photocatalyst layer 6 Housing frame 6a, 6b Opening 7 Container 8, 8A, 8B Amino acid synthesizer 9 Light irradiation unit 11 Support frame 12 Opening 13 Slider 14 Water 14a Seawater 15 Alcohol supply unit 150 Tube 151 Pump 16 Ventilation path 160 Ventilation pipe 161 Air pump 30, 30A, 30B, 30C Aquarium 31 Water pumping pump 32 Water pumping pipe 33 Water pumping path 34 Return pipe 35 Return path 36 Overflow pipe 36a, 37a Opening 37 Drain pipe 38 Drain outlet 41 Peripheral wall 50 Pretreatment tank 51 Biological filtration unit 51a Cover plate 52 Physical filtration section 53 Pretreated water storage section 54 Side wall 55 Perforated plate 56 Filter material 57 Skimmer 58 Partition wall 61 Upper plate 61 Housing upper plate 61a Opening 62, 63 Side plates 62a, 63a Opening 64 Bottom plate 64a Opening 70 Cultivation tank 71 Planter 72 Cultivation water supply channel 73 Cultivation return channel 74 Water supply pipe 75 Water supply pump 76 Return pipe 77 Opening 80 Cover plate 80a, 80b Opening 80c Through hole 82 Electric fan 90 LED board 91 Light source 92 Support plate 301, 302 Cover plate 303 Through hole S1 Internal space S2 Gap a Fish b Plants c saltwater fish

Claims

1. Add alcohol to the water in an aquarium where fish are kept, bring it into contact with a photocatalyst carrier, and irradiate the photocatalyst of the photocatalyst carrier with ultraviolet light. This allows the alcohol in the water to react with ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － ) by a photocatalytic reaction to synthesize amino acids from at least one selected from the group consisting of ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － A method for managing the water quality of an aquarium by maintaining the concentrations of the following substances below a specified value.

2. A method for managing the water quality of an aquarium as described in claim 1, in which the water in the aquarium to which alcohol has been added is brought into contact with a photocatalyst carrier installed outside the aquarium, and ultraviolet light is irradiated onto the photocatalyst in the photocatalyst carrier.

3. The method for managing water quality in an aquarium according to claim 1 or 2, wherein the water from the aquarium in which amino acids have been synthesized is used for growing plants.

4. A method for managing the water quality of an aquarium as described in claim 3, wherein water from the aquarium is supplied to a cultivation tank in which the plants are cultivated, water from the cultivation tank is supplied to the aquarium, and water is circulated between the aquarium and the cultivation tank.

5. An aquarium for raising fish, and a photocatalyst carrier are brought into contact with the water of the aquarium to which alcohol has been added, and ultraviolet light is irradiated onto the photocatalyst of the photocatalyst carrier, thereby converting the alcohol in the water into ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － and an amino acid synthesizer for synthesizing amino acids from at least one selected from the group consisting of ammonium ions (NH ４ ＋ ), nitrate ions (NO ３ － ) and nitrite (NO ２ － A water quality control device for an aquarium that maintains the concentrations of these substances below a specified value.

6. The water quality control device for an aquarium according to claim 5, further comprising a cultivation tank for cultivating plants using the water in the aquarium.

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