Method for treating circulating culture solution in a plant production system, treatment device for circulating culture solution in a plant production system, and plant production system

Abstract

To provide a method for treating circulating culture solution in a plant production system, a device for treating circulating culture solution in a plant production system, and a plant production system that can suppress changes in the components of the circulating culture solution and can safely perform sterilization and purification treatment using a simple device while suppressing the proliferation of bacteria, algae, and the like.SOLUTION: Provided is a method for treating circulating culture solution in a plant production system, comprising: an acid injection step of injecting acid into the circulating culture solution so that the pH of the circulating culture solution is 7 or less; a sterilization and purification treatment step of storing the circulating culture solution after the acid injection in a treatment tank 121, irradiating the circulating culture solution with a first ultraviolet ray having a wavelength range for sterilizing the circulating culture solution, irradiating a gas containing oxygen with a second ultraviolet ray having a wavelength range for generating ozone in the treatment tank 121 to generate ozone, and injecting the ozone and the gas containing oxygen into the circulating culture solution to sterilize the circulating culture solution with ozone, and an adjustment step of adjusting the pH of the circulating culture solution after the sterilization and purification treatment step to a pH suitable for plant growth.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating a circulating culture solution in a plant production system, a treatment device for a circulating culture solution in a plant production system, and a plant production system. [Background technology]

[0002] The circulating nutrient solution used in plant production systems typically consists of water, fertilizer, and pH adjusters. The circulating nutrient solution circulates within the plant production system, providing moisture and nutrients to plants in the cultivation shelves. After being used for plant growth for several weeks to several months, the entire circulating nutrient solution is often discarded and replaced with new circulating nutrient solution. However, replacing the circulating nutrient solution presents several challenges, including the need for large amounts of tap water, the time and labor required to clean the cultivation shelves and the system during the replacement process, and the fact that the fertilizer components contained in the circulating nutrient solution are also discarded when discarding the used circulating nutrient solution. One of the major issues is the proliferation and growth of bacteria and algae caused by the circulation of the circulating nutrient solution within the production system.

[0003] As a measure to suppress the occurrence and proliferation of bacteria and algae in such circulating culture solution, Japanese Patent No. 5802558 (Patent Document 1) describes an example of a hydroponics system in which culture solution, which is liquid fertilizer, is circulated between a nutrient solution tank and a cultivation bed, and which exerts sterilization and organic matter decomposition effects through the synergistic effects of a sterilization and purification unit that has ozone supply functions, ultraviolet radiation functions, and photocatalytic functions.

[0004] Japanese Patent No. 5191782 (Patent Document 2) describes an example of a hydroponics system in which a culture solution, which is liquid fertilizer, is circulated between a solution tank and a cultivation bed. The cultivation bed and the nutrient solution tank are connected by a supply line and a return line to form a circulation line, and a branch circulation line branching off from the supply line has a purified nutrient solution tank and purified cultivation beds, and a sterilization and purification unit is connected to the purified nutrient solution tank in this branch circulation line.

[0005] Various techniques for improving the growth performance of plants in a circulating culture solution have also been reported. JP-A-7-132029 (Patent Document 3) and Japanese Patent No. 4754512 (Patent Document 4) describe examples of hydroponic plant cultivation methods in which fine bubbles are injected into a culture solution for hydroponic plant cultivation in order to increase the amount of dissolved oxygen in the culture solution used for hydroponic plant cultivation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5802558 [Patent Document 2] Patent No. 5191782 [Patent Document 3] Japanese Patent Application Publication No. 7-132029 [Patent Document 4] Patent No. 4754512 Summary of the Invention [Problem to be solved by the invention]

[0007] As described in Patent Documents 1 and 2, ultraviolet treatment, ozone oxidation treatment, pro-oxidation treatment, chemical treatment, and the like are commonly used methods for sterilizing circulating culture solutions. However, ultraviolet treatment may not achieve sufficient sterilization effects due to the turbidity and color of the circulating culture solution. Ozone oxidation treatment involves the supply of ozone gas, and residual ozone in the circulating culture solution or the surrounding gas may wither or discolor plants. In food-grade plant production systems, pro-oxidation treatment and chemical treatment may not be applicable. Furthermore, these ultraviolet treatments, ozone oxidation treatment, pro-oxidation treatment, and chemical treatment have the problem of causing oxidation of metal ion components in the circulating culture solution, resulting in changes in the composition of the circulating culture solution, such as an increase in color.

[0008] In view of the above problems, the present invention provides a method for treating circulating culture solution in a plant production system that can suppress changes in the components of the circulating culture solution and safely perform sterilization and purification treatment using a simple device while suppressing the proliferation of bacteria, algae, etc.; a treatment device for circulating culture solution in a plant production system; and a plant production system. [Means for solving the problem]

[0009] As a result of extensive research aimed at solving the above problems, the present inventors discovered that it is useful to perform a specific sterilization and purification treatment on the circulating culture medium, and arrived at the present invention.

[0010] In one aspect, the present invention, which was completed based on the above findings, provides a method for treating a circulating culture solution in a plant production system, comprising: an acid injection step of injecting acid into the circulating culture solution so that the pH of the circulating culture solution in the plant production system is 7 or less; a sterilization and purification treatment step of placing the circulating culture solution after the acid injection in a treatment tank, irradiating the circulating culture solution with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution, irradiating oxygen-containing gas in the treatment tank with second ultraviolet light having a wavelength range for generating ozone to generate ozone, and injecting the ozone and oxygen-containing gas into the circulating culture solution to sterilize the circulating culture solution with ozone; and an adjustment step of adjusting the pH of the circulating culture solution after the sterilization and purification treatment step to a value appropriate for plant growth.

[0011] In one embodiment, the method for treating a circulating culture solution in a plant production system according to an embodiment of the present invention further includes a bubble injection step of generating oxygen-containing bubbles having a bubble diameter of 100 μm or less and injecting the generated bubbles into the circulating culture solution being treated in the sterilization and purification treatment step.

[0012] In another embodiment, the method for treating a circulating culture solution in a plant production system according to an embodiment of the present invention includes injecting an oxygen-containing gas and bubbles into the circulating culture solution so that the supply ratio of bubbles to oxygen-containing gas into the circulating culture solution is 0.1 or more by volume.

[0013] In yet another embodiment, the method for treating a circulating culture solution in a plant production system according to an embodiment of the present invention comprises injecting oxygen-containing gas and / or bubbles into the circulating culture solution so that the DO of the circulating culture solution treated in the sterilization and purification treatment step is 5 to 20 mg / L.

[0014] In yet another embodiment of the method for treating a circulating culture solution in a plant production system according to an embodiment of the present invention, the sterilization and purification treatment process includes injecting an oxygen-containing gas into a gas circulation section provided between an ultraviolet irradiation means capable of irradiating first and second ultraviolet rays arranged in a treatment tank and a casing arranged around the ultraviolet irradiation means in the treatment tank, irradiating the oxygen-containing gas injected into the gas circulation section with the second ultraviolet light to generate ozone, and injecting the oxygen-containing gas and ozone in the gas circulation section into the circulating culture solution in the treatment tank.

[0015] In yet another embodiment, the method for treating a circulating culture solution in a plant production system according to an embodiment of the present invention comprises generating ozone in a treatment tank so that the ozone concentration in the circulating culture solution in the sterilization and purification treatment step is 0.005 to 0.5 mg O / L of circulating culture solution.

[0016] In yet another embodiment, the method for treating a circulating culture solution in a plant production system according to an embodiment of the present invention further comprises the step of injecting liquid fertilizer into the circulating culture solution.

[0017] In yet another embodiment, the method for treating a circulating culture solution in a plant production system according to an embodiment of the present invention includes a step of adjusting the electrical conductivity of the circulating culture solution to an electrical conductivity appropriate for the growth of the plant to be treated, based on the measurement results of the electrical conductivity of the circulating culture solution.

[0018] In another aspect, the present invention provides a treatment device for a circulating culture solution in a plant production system, comprising: acid treatment means for injecting acid into a circulating culture solution so that the pH of the circulating culture solution in the plant production system is 7 or less; a treatment tank for containing the acid-injected circulating culture solution; ultraviolet irradiation means disposed in the treatment tank for irradiating the circulating culture solution with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution and second ultraviolet light having a wavelength range for generating ozone; and sterilization and purification treatment means including gas injection means for injecting into the treatment tank an oxygen-containing gas that reacts with the second ultraviolet light to promote the generation of ozone; and adjustment means for adjusting the pH of the circulating culture solution treated by the sterilization and purification treatment means to an appropriate pH for plant growth.

[0019] In one embodiment, the treatment device for circulating culture solution in a plant production system according to an embodiment of the present invention further comprises a bubble injection means that is provided between the acid treatment means and the sterilization and purification treatment means and that generates oxygen-containing bubbles with a diameter of 100 μm or less and injects the generated bubbles into the circulating culture solution.

[0020] In another embodiment of the treatment device for circulating culture solution in a plant production system according to an embodiment of the present invention, the external radiation irradiation means includes an ultraviolet lamp capable of irradiating first and second ultraviolet rays and a casing arranged around the ultraviolet lamp, forming a gas circulation section between the ultraviolet lamp and the casing, the gas injection means is connected to the gas circulation section and injects a gas containing oxygen into the gas circulation section, and the circulation section connected to the gas circulation section is configured to circulate and inject the gas containing ozone and oxygen generated in the gas circulation section by irradiation with the second ultraviolet rays into the circulating culture solution in the treatment tank.

[0021] In yet another aspect, the present invention provides a plant production system comprising: a cultivation shelf for cultivating plants using a circulating culture solution containing nutrients necessary for plant growth; circulation means for circulating the circulating culture solution discharged from the cultivation shelf back to the cultivation shelf; acid treatment means for injecting acid into the circulating culture solution discharged from the cultivation shelf so that the pH of the circulating culture solution is 7 or less; a treatment tank for containing the acid-injected circulating culture solution; ultraviolet irradiation means disposed in the treatment tank for irradiating the circulating culture solution with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution and second ultraviolet light having a wavelength range for generating ozone in the circulating culture solution; and sterilization and purification treatment means including gas injection means for injecting into the treatment tank an oxygen-containing gas that reacts with the second ultraviolet light to promote the generation of ozone; and adjustment means connected to the sterilization and purification treatment means for adjusting the pH of the circulating culture solution treated by the sterilization and purification treatment means to an appropriate pH for plant growth.

[0022] In one embodiment of the plant production system according to the present invention, the intake point for the circulating culture solution to be supplied to the acid treatment means is located downstream of the cultivation shelf, within the circulation means, or in a culture solution tank that stores the circulating culture solution discharged from the cultivation shelf. [Effects of the Invention]

[0023] According to the present invention, a method for treating circulating culture solution in a plant production system can be provided that can suppress changes in the components of the circulating culture solution and safely perform sterilization and purification treatment using simple equipment while suppressing the growth of bacteria, algae, etc., as well as an apparatus for treating circulating culture solution in a plant production system and a plant production system. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a first modified example of the first embodiment. [Figure 3] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a second modified example of the first embodiment. [Figure 4] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a first modified example of the second embodiment. [Figure 6] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a second modified example of the second embodiment. [Figure 7] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a third embodiment of the present invention. [Figure 8] FIG. 13 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a first modified example of the third embodiment. [Figure 9] FIG. 13 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a second modified example of the third embodiment. [Figure 10] FIG. 13 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a third modified example of the third embodiment. [Figure 11] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to a fourth modified example of the third embodiment. [Figure 12] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 13] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 14] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 15] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 16] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 17] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 18] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 19] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 20] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 21] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 22] FIG. 10 is a schematic diagram showing an example of a treatment device for a circulating culture solution in a plant production system according to another embodiment. [Figure 23] 1 is a schematic diagram showing an example of a treatment device for a circulating culture medium according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] Embodiments of the present invention will be described below with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of component parts to those described below.

[0026] <Plant Production System 100> The plant production system 100 according to this embodiment generally includes a plant factory, a vegetable factory, a seedling production system, a medicinal plant factory, a bio-plant factory, etc., and more specifically includes an artificial light type plant factory, a photosynthetic type plant factory, etc. In particular, the plant production system 100 according to this embodiment can be suitably used in an artificial light type plant factory.

[0027] An artificial light plant factory is an indoor, closed environment that consists of plant cultivation shelves, an air conditioning system (carbon dioxide supply system), a light source, a circulating nutrient solution circulation system (pump, pH regulator, electrical conductivity regulator, etc.), a liquid fertilizer injection system, and a nutrient solution tank (storage tank). An artificial light plant factory is a plant production system 100 that controls artificial light using LED light sources of specific wavelengths, air conditioning, circulating nutrient solution, and other environmental factors necessary for plant growth to maintain constant growth conditions while performing nutrient cultivation. Environmental factors necessary for plant growth include temperature, light intensity, carbon dioxide concentration, water quality (including various nutrients and trace metals), humidity, airflow, and the circulating water volume of the circulating nutrient solution. While the present invention illustrates the cultivation shelves 5, circulation system 4, and nutrient solution tank 10 (see FIG. 3) that constitute part of the plant production system 100 as shown in FIG. 1, the plant production system 100 is not limited to these configurations.

[0028] <Cultivation shelf 5> The cultivation shelf 5 refers to the location in the plant production system 100 where plants are grown. In the cultivation shelf 5, the plants to be grown are held by resin panels or the like. The circulating nutrient solution is typically supplied to the roots of the plants in the cultivation shelf 5, and the circulating nutrient solution that has flowed inside the cultivation shelf 5 is discharged outside the system from the rear of the cultivation shelf 5. Although not shown in the figure, the cultivation shelf 5 is equipped with a light source, a carbon dioxide supply device, a thermometer, a hygrometer, various sensors, and the like, and constant environmental conditions suitable for the growth of each plant are maintained.

[0029] <Circulating culture solution> The circulating nutrient solution circulating through the cultivation shelves 5 is also referred to as a culture solution, cultivation solution, circulating nutrient solution, hydroponic nutrient solution, or nutrient solution. The circulating nutrient solution is recycled within the plant production system 100 and primarily contains water, nutrients (nitrogen, phosphorus), and trace elements such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), and boron (B). It is a liquid that supplies the moisture and nutrients necessary for plant growth. The circulating nutrient solution circulates through the cultivation shelves 5, the circulation means 4, and the nutrient solution tank 10, and its water quality parameters are constantly monitored to maintain a constant pH and electrical conductivity. If any of the water quality parameters of the circulating nutrient solution change, the necessary amounts of pH adjusters (acids and alkalis) or liquid fertilizer are added to maintain the water quality at a constant level.

[0030] <Liquid fertilizer> Liquid fertilizers, commonly referred to as liquid fertilizers or nutrients, are liquid fertilizers used to replenish nutrient salts and trace metal components in circulating nutrient solutions. Liquid fertilizers contain nutrients and trace metal components. Specifically, nutrients and trace metals include nitrogen (N) and its compounds, phosphorus (P) and its compounds, Na, K, Ca, Mg, Fe, B, and hydrates or compounds of each metal. Liquid fertilizers are produced by dissolving the above components according to the purpose in a solvent such as water.

[0031] <Suspended matter> Suspended solids (SS) refer to solid suspended matter floating in wastewater, and refer to the material remaining on filter paper with a pore size of 1 μm when filtered through filter paper. SS includes inorganic and organic materials. Inorganic SS includes components derived from soil and clay components. Organic SS includes components derived from animal, plant, and microbial cells, and from factories. The SS contained in the treated water in this embodiment is not particularly limited, but includes SS derived from components generated in the production process of soft drink manufacturing plants, activated sludge, sludge detached from fluidized carriers, and sludge flocs generated in the coagulation treatment process.

[0032] <General bacteria> In this embodiment, "bacteria" or "general bacteria" refers to bacteria (particularly heterotrophic bacteria) that form colonies on a quasi-agar medium when cultured at 36±1°C for 24±2 hours, and are measured using a method that complies with the Drinking Water Testing Method (published by the Japan Water Works Association, Drinking Water Testing Method) or the Sewage Testing Method (published by the Japan Sewage Works Association, Sewage Testing Method). The number of colonies formed on the medium is expressed as colonies / mL or CFU / mL. Bacteria or general bacteria also include general viable bacteria. Because plant production systems are used for food applications such as vegetables and fruits, certain standard values ​​have been set for bacteria or general bacteria in the culture solution, and they must be kept below a certain concentration.

[0033] <Algae> Algae refers to phytoplankton that grows in the culture medium, on the cultivation shelves, in the channels, in the circulation means for the culture medium, in the culture medium tank, etc. when the circulating culture medium is recycled. Specifically, it refers to green algae, cyanobacteria, golden algae, diatoms, etc., and in particular green algae that contain the photosynthetic pigment (chlorophyll a) in their cells. When algae grow in a plant production system, problems arise, such as the need to change the circulating culture medium more frequently and to clean the channels more frequently.

[0034] (First embodiment) <Circulating culture fluid treatment device> As shown in FIG. 1, the circulating culture solution treatment device of the plant production system 100 according to the first embodiment of the present invention includes an acid treatment means 1 that injects acid into the circulating culture solution of the plant production system 100, a sterilization and purification treatment means 2, and an adjustment means 3 that adjusts the pH of the circulating culture solution treated by the sterilization and purification treatment means 2 to a pH appropriate for plant growth.

[0035] The acid treatment means 1 is a device for injecting acid into the circulating culture solution in the plant production system 100 to adjust the pH of the circulating culture solution to 7 or less, thereby adjusting the circulating culture solution to an acidic state. The acid treatment means 1 is composed of a storage tank, a chemical injection pump, piping, and associated equipment. A pH measurement device (not shown) can be installed upstream or downstream of the acid injection line to control the amount of acid injected depending on the pH. The pH measurement device is not particularly limited, but examples include a pH meter, a pH electrode, and a pH sensor. A total organic carbon meter, a colorimeter, and the like can also be installed. The type of acid is not particularly limited, but examples include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and boric acid. Among these, phosphoric acid, nitric acid, and the like are more preferably used as the acid in order to suppress changes in the properties of the circulating culture solution, such as its color components, over a long period of time and to achieve greater effectiveness in the sterilization and purification treatment by the sterilization and purification treatment means 2.

[0036] In the acid treatment means 1, it is preferable to inject acid into the circulating culture solution so that the pH of the circulating culture solution is 6 or less, preferably 5.5 or less, and even more preferably 5 or less. The circulating culture solution contains trace metals as fertilizer components, and the ultraviolet irradiation and oxidation promotion treatment by the sterilization and purification treatment means 2 described below may cause oxidation of metal ions, potentially increasing the chromaticity of the circulating culture solution. In this embodiment, the provision of the acid treatment means 1 can suppress an increase in the chromaticity of the circulating culture solution due to oxidation of metal components in the circulating culture solution, particularly iron and manganese, and therefore effectively suppress changes in the components of the circulating culture solution.

[0037] The sterilization and purification treatment means 2 is a device for sterilizing and purifying the circulating culture solution discharged from the cultivation shelf 5. The sterilization and purification treatment means 2 includes a treatment tank 21 that contains the circulating culture solution after the acid has been injected by the acid treatment means 1, an ultraviolet irradiation means 22 that is disposed in the treatment tank 21 and irradiates the circulating culture solution with ultraviolet light, and a gas injection means 23 that injects an oxygen-containing gas into the treatment tank 21 to promote the generation of ozone in the treatment tank 21 by reacting with the ultraviolet light irradiated from the ultraviolet irradiation means 22.

[0038] The configuration of the ultraviolet irradiation means 22 is not particularly limited. The ultraviolet irradiation means 22 includes, for example, an ultraviolet lamp 122, a casing 25 arranged around the ultraviolet lamp 122 to cover the periphery of the ultraviolet lamp 122, a power source, wiring (not shown), and the like, and is configured to form a gas flow section 126 between the ultraviolet lamp 122 and the casing 25. There are no particular limitations on the type of ultraviolet lamp 122, but hot cathode or cold cathode lamps are preferably used. The casing 25 functions to protect the ultraviolet lamp 122 while allowing oxygen-containing gas injected from the gas injection means 23 to flow between the ultraviolet lamp 122 and the casing 25. There are no limitations on the material of the casing 25, but it is preferable that the casing 25 is colorless and transparent, such as acrylic resin, vinyl chloride resin, or glass resin, and that it does not absorb or reflect ultraviolet light in the wavelength range emitted by the ultraviolet irradiation means 22 and is not easily deteriorated by ultraviolet light.

[0039] The ultraviolet irradiation means 22 is a device that irradiates the circulating culture medium with first ultraviolet light having a wavelength range for sterilizing the circulating culture medium and second ultraviolet light having a wavelength range for generating ozone in the circulating culture medium. In the example shown in FIG. 1, the ultraviolet irradiation means 22 is provided with a first ultraviolet light irradiation means 22A (first ultraviolet lamp) that irradiates the first ultraviolet light and a second ultraviolet light irradiation means 22B (second ultraviolet lamp) that irradiates the second ultraviolet light, respectively, but is not limited to this example. Preferably, the ultraviolet irradiation means 22 can be configured to irradiate the first ultraviolet light and the second ultraviolet light, which have different wavelength ranges, using a single ultraviolet lamp, thereby achieving miniaturization and simplification of the device.

[0040] The wavelength range of the first ultraviolet light is not limited as long as it is a wavelength range that can sterilize the circulating culture solution, but is typically a wavelength range of 240 to 300 nm, more typically 240 to 260 nm. The wavelength range of the second ultraviolet light is not limited as long as it is a wavelength range that can generate ozone by ultraviolet irradiation, but is typically a wavelength range of 180 to 190 nm, more typically 185 nm.

[0041] The gas injection means 23 is composed of, for example, an air compressor, an air pressure gauge, an air flow meter, a pressure reducing valve, piping, and associated devices. Air is most preferably used as the oxygen-containing gas from the viewpoints of ease of handling, availability, and economy. Furthermore, the oxygen-containing gas may further contain any gas other than oxygen, such as ozone, carbon dioxide, or hydrogen, or two or more of these gases may be introduced simultaneously. The gas injection means 23 is connected to a gas flow section 126 formed between the ultraviolet lamp 122 and the casing 25. The gas injection means 23 injects an oxygen-containing gas, typically air, into the gas flow section 126 through an inlet 231 provided in the casing 25.

[0042] The sterilization and purification treatment means 2 is an apparatus for killing general bacteria and algae in the circulating culture solution by irradiating the circulating culture solution with first ultraviolet light using ultraviolet light irradiation means 22. In the sterilization and purification treatment means 2, oxygen-containing gas such as air is injected into the gas flow section 126 around the ultraviolet light irradiation means 22 using gas injection means 23, and then second ultraviolet light is irradiated. Ozone is generated from a portion of the injected oxygen in the gas flow section 126. Furthermore, hydroxyl radicals are generated in the circulating culture solution by the small amount of ozone generated by the irradiation of the second ultraviolet light and the irradiation of the first ultraviolet light by the first ultraviolet light irradiation means 22A. As a result, the sterilization and purification treatment means 2 performs an accelerated oxidative decomposition reaction (AOP treatment) using ultraviolet light, ozone, and hydroxyl radicals. This AOP treatment efficiently decomposes general bacteria, algae, suspended solids (SS), dissolved organic matter, etc. in the circulating culture solution.

[0043] Advanced Oxidation Process (AOP) treatment is also known as accelerated oxidation treatment or accelerated oxidation treatment. This AOP treatment promotes oxidative decomposition reactions by generating more hydroxyl radicals than a single oxidation treatment through the reaction of several oxidants with water. Examples of oxidants used in AOP treatment include ozone and hydrogen peroxide. Unlike treatment methods using chemicals, AOP treatment is useful because it leaves no residue after treatment and has excellent decolorization properties. Therefore, by applying it to the sterilization and purification treatment of circulating culture solution used for plant growth, such as in the plant production system 100, it is possible to safely perform sterilization and purification treatment using simple equipment while suppressing changes in the composition of the circulating culture solution and the proliferation of bacteria and algae. In this embodiment, among AOP treatments, ultraviolet (UV) treatment using ultraviolet light is combined with AOP treatment to promote oxidation treatment, organic matter treatment, sterilization treatment, etc., thereby achieving a sterilization and purification treatment effect that is even greater than that of UV treatment, ozone treatment, or AOP treatment alone.

[0044] There are no particular limitations on the amount of gas injected by gas injection means 23, but if the amount injected is too large, the reaction between air and ultraviolet light will be insufficient, resulting in insufficient ozone production, while if the amount injected is too small, the circulating culture solution may not have a sufficient amount of oxygen (dissolved oxygen concentration: DO) necessary for plant growth, and the amount of ozone produced for the AOP treatment performed by sterilization and purification treatment means 2 may be insufficient, resulting in a reduced sterilization and purification treatment effect. To obtain a stable and higher sterilization and purification treatment effect, although not limited to the following, oxygen-containing gas and / or bubbles are preferably injected into the circulating culture solution in the sterilization and purification treatment step so that the DO of the circulating culture solution is 5 to 20 mg / L, more preferably so that the DO is 6 to 15 mg / L, and even more preferably so that the DO is 6 to 12 mg / L.

[0045] When air is supplied as the oxygen-containing gas, it is preferably supplied at 0.005 to 1 L / L, and more preferably 0.01 to 0.5 L / L, of the circulating culture medium supplied to the treatment tank 21. Although not limited thereto, when air is supplied as the oxygen-containing gas, the gas-liquid ratio of the circulating culture medium to the injected gas (volume ratio of circulating culture medium / oxygen-containing gas) is preferably 1 to 200, and more preferably 3 to 100.

[0046] The gas containing ozone and oxygen generated in the gas flow section 126 of the ultraviolet irradiation means 22 is injected via the circulation section 24 connected to the gas flow section 126 into the circulating culture medium flowing through the circulating liquid flow section 127 outside the casing 25 in the treatment tank 21. This allows the small amount of ozone generated by ultraviolet irradiation to be effectively utilized, making the AOP treatment more efficient. It is preferable to install a pretreatment device (not shown), such as a filter for removing floating and suspended components, upstream of the sterilization and purification treatment means 2, in order to further enhance the purification effect of the circulating culture medium.

[0047] If too much ozone is generated in the circulating culture solution in the treatment tank 21, ozone may remain in the circulating culture solution circulating to the cultivation shelf 5, causing discoloration of plants. In the present invention, instead of supplying ozone from an external source to the treatment tank 21, air is injected into the treatment tank 21 and into the gas flow section 126 of the ultraviolet irradiation means 22. Oxygen and ultraviolet light react in the gas flow section 126 to generate trace amounts of ozone, which then reacts with the ultraviolet light to generate highly oxidizing hydroxyl radicals. The circulating culture solution is treated by the acid treatment means 1 to a pH of 7 or less, preferably 6 or less, and even 5.5 or less, thereby efficiently dissolving ozone in the circulating culture solution. Furthermore, the amount of ozone in the circulating culture solution is so small that it is decomposed to a level that does not adversely affect plants, etc., by pH adjustment using the adjustment means 3 described below, eliminating the need for special treatments for decomposing ozone dissolved in the circulating culture solution. Furthermore, since no ozone is supplied from the outside, the device configuration is simple and running costs can be reduced. Therefore, according to the present invention, the circulating culture solution can be sterilized and purified using simpler and smaller equipment.

[0048] Although not limited to the following, in this embodiment, after the sterilization and purification treatment step in the sterilization and purification treatment means 2, specifically, the ozone treatment in the sterilization and purification treatment step is preferably carried out so that the ozone concentration in the circulating culture medium discharged from the sterilization and purification treatment means 2 is 0.005 to 0.5 mg-O3 / L-circulating culture medium, more typically 0.01 to 0.4 mg-O3 / L-circulating culture medium, and even more typically 0.01 to 0.3 mg-O3 / L-circulating culture medium.

[0049] The adjusting means 3 is a device that adjusts the pH of the circulating culture solution to a pH appropriate for plant growth by injecting a pH adjuster into the circulating culture solution that has passed through the sterilization and purification treatment means 2. The adjusting means 3 typically comprises a storage tank for storing the pH adjuster, a chemical injection pump, piping, and associated equipment. The adjusting means 3 may have a treatment tank or the like that mixes the circulating culture solution with the pH adjuster, or may be a type in which the pH adjuster is directly injected into the piping through which the circulating culture solution flows.

[0050] The pH adjuster used in the adjusting means 3 is typically an alkaline agent. Examples of alkaline agents include sodium hydroxide, magnesium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, calcium carbonate, potassium carbonate, magnesium carbonate, sodium bicarbonate, ammonium hydroxide, ammonium carbonate, and hydrates thereof. Liquid fertilizer can also be used as the pH adjuster. In this case, efficient treatment can be achieved by using an aqueous solution or hydrate of potassium hydroxide as the liquid fertilizer. The amount of pH adjuster injected is not particularly limited as long as it maintains the appropriate pH of the circulating culture solution. In the adjusting means 3, the pH adjuster is injected into the circulating culture solution to adjust the pH to 5 to 7, more typically 5.5 to 6.5. Furthermore, adding the pH adjuster to adjust the pH to 5 to 7 in the adjusting means 3 promotes ozone radicalization, thereby adjusting the pH to an appropriate level for plant growth on the cultivation shelves 5 while decomposing soluble organic matter in the circulating culture solution.

[0051] A pH measuring device for measuring the pH of the circulating culture solution may be placed upstream or downstream of the adjusting means 3. This makes it possible to control the amount of pH adjuster injected depending on the measurement results of the pH measuring device. Acids such as phosphoric acid, nitric acid, and sulfuric acid may be injected into the circulating culture solution depending on the measurement results of the pH measuring device. Examples of pH measuring devices include, but are not limited to, a pH meter, a pH electrode, and a pH sensor. A total organic carbon meter, a color meter, and the like may also be installed to measure the water quality of the circulating culture solution after the pH adjustment treatment by the adjusting means 3.

[0052] The circulating culture solution, the pH of which has been adjusted by the adjusting means 3, is circulated to the cultivation shelves 5 by the circulating means 4, which circulates the circulating culture solution discharged from the cultivation shelves 5 to the cultivation shelves 5. The circulating means 4 is composed of a pump, piping, and associated equipment that circulates the circulating culture solution within the plant production system 100. Although not shown in FIG. 1 , the circulating means 4 can be equipped with a flow meter for the circulating culture solution, a pressure meter, a pH meter, an electrical conductivity meter, a colorimeter, a total organic carbon (TOC) meter, an oxidation-reduction potential (ORP) meter, a dissolved oxygen concentration (DO) meter, a camera for image interpretation, and sensors related to these, which can be installed at any location.

[0053] According to the first embodiment of the present invention, ultraviolet rays of two wavelength ranges are irradiated via ultraviolet irradiation means 22 of sterilization and purification treatment means 2, and simultaneously, oxygen-containing gas is injected from gas injection means 23 into gas circulation section 126 of ultraviolet irradiation means 22 to irradiate with the second ultraviolet light, thereby generating a small amount of ozone, and hydroxyl radicals are generated by irradiating with the first ultraviolet light in the presence of ozone. As a result, the AOP treatment by ultraviolet rays and ozone is promoted, and this promotion effect can enhance the sterilization effect in the circulating culture solution, thereby suppressing the growth of bacteria and algae for a long period of time.

[0054] Furthermore, according to the first embodiment of the present invention, unlike conventional systems, ozone is not supplied from an external source, and no sterilizing chemicals are used, thereby providing a chemical-free, low-ozone-concentration sterilization and purification treatment. As a result, the circulating culture solution contains almost no residual chemicals or residual ozone, and does not inhibit the growth of plants on the cultivation shelves 5. Furthermore, the circulating culture solution treatment device according to the embodiment of the present invention, which is equipped with the acid treatment means 1 and the adjustment means 3, can also suppress an increase in color due to the oxidation of metal ions in the circulating culture solution during the oxidation promotion treatment in the sterilization and purification treatment step. This suppresses changes in the components of the circulating culture solution, enabling safe sterilization and purification treatment using a simple device while suppressing the growth of bacteria, algae, and the like for a long period of time.

[0055] As shown in FIG. 2, the intake point for the circulating culture solution is located in the circulation line (piping) of the circulation means 4 downstream of the cultivation shelves 5 of the plant production system 100. At least a portion of the circulating culture solution taken from the circulation means 4 may be subjected to acid treatment by acid treatment means 1, sterilization and purification treatment by sterilization and purification treatment means 2, and pH adjustment treatment by adjustment means 3. The circulating culture solution that has passed through adjustment means 3 is returned to the upstream side of the cultivation shelves 5 in the circulation line of the circulation means 4. The treatment device shown in FIG. 2 allows at least a portion of the circulating culture solution to be taken. When the occurrence of organic matter, bacteria, algae, etc. in the circulating culture solution is low, a portion of the circulating culture solution can be taken, sterilized, and purified, and then returned to the circulation means 4. This allows for simpler and more efficient sterilization and purification treatment compared to treating the entire amount of the circulating culture solution.

[0056] As shown in FIG. 3 , the circulating culture solution is taken from a culture solution tank 10 connected downstream of the cultivation shelves 5 of the plant production system 100. At least a portion of the circulating culture solution taken from the culture solution tank 10 may be subjected to acid treatment by acid treatment means 1, sterilization and purification treatment by sterilization and purification treatment means 2, and pH adjustment treatment by adjustment means 3. The circulating culture solution that has passed through adjustment means 3 is returned to the culture solution tank 10 or the circulation means 4. The treatment device shown in FIG. 3 allows at least a portion of the circulating culture solution to be taken and returned to the culture solution tank 10 or the circulation means 4, thereby achieving more efficient treatment than when the entire amount of circulating culture solution is taken and treated. Furthermore, by temporarily returning the circulating culture solution after sterilization and purification treatment to the culture solution tank 10, the component concentrations of the circulating culture solution within the culture solution tank 10 can be uniformized. This allows for a stable supply of circulating culture solution with minimal fluctuations in component concentrations to the cultivation shelves 5.

[0057] (Processing method) A circulating culture solution can be sterilized and purified using a circulating culture solution treatment device in a plant production system 100 according to a first embodiment of the present invention, as shown in Figures 1 to 3. That is, the method for treating a circulating culture solution in the plant production system 100 according to the first embodiment of the present invention includes an acid injection step of injecting an acid into the circulating culture solution so that the pH of the circulating culture solution in the plant production system 100 is 7 or less; a sterilization and purification treatment step of storing the circulating culture solution after the acid injection in a treatment tank 21, irradiating the circulating culture solution with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution, irradiating an oxygen-containing gas in the treatment tank 21 with second ultraviolet light having a wavelength range for generating ozone to generate ozone, and injecting the ozone and oxygen-containing gas into the circulating culture solution to sterilize the circulating culture solution with ozone; and an adjustment step of adjusting the pH of the circulating culture solution after the sterilization and purification treatment step to a pH appropriate for plant growth.

[0058] According to the method for treating a circulating culture solution in the plant production system 100 of the first embodiment, the circulating culture solution is irradiated with first and second ultraviolet rays in the presence of oxygen to perform an AOP treatment using ultraviolet rays and ozone (UV-AOP treatment). This makes it possible to obtain a circulating culture solution that suppresses the proliferation of bacteria, algae, and the like for a long period of time and does not inhibit the growth of plants on the cultivation shelves 5 even after undergoing a sterilization and purification treatment.

[0059] (Second embodiment) As shown in FIG. 4, the circulating culture solution treatment device of the plant production system 100 according to the second embodiment of the present invention includes an acid treatment means 1, a sterilization and purification treatment means 2, an adjustment means 3, and a bubble injection means 6 that is provided between the acid treatment means 1 and the sterilization and purification treatment means 2 and that generates oxygen-containing bubbles with a bubble diameter of 100 μm or less and injects the generated bubbles into the circulating culture solution.

[0060] In the bubble injection means 6, a portion of the oxygen-containing gas supplied from the gas injection means 23 is injected into the bubble injection means 6 to generate minute bubbles, which are then dissolved in the circulating culture medium, and the circulating culture medium containing the bubbles is then sent to the sterilization and purification treatment means 2. The smaller the diameter of the bubbles generated by the bubble injection means 6, the longer it takes for the bubbles to dissolve in the circulating culture medium. Therefore, by reducing the diameter of the bubbles generated by the bubble injection means 6, more bubbles remain in the circulating culture medium, thereby adjusting the DO of the circulating culture medium to a more suitable range.

[0061] The air bubble injection means 6 is not particularly limited, and various devices can be used, such as an ejector type, an injector type, a swirl flow type, a Venturi type, a two-phase critical flow type, a self-priming type using negative pressure of a rotor blade (static mixer), an Aura Jet type, or other device that uses shear force or swirl flow caused by water flow, a device that uses cavitation, a device that uses pressurized dissolution, or a device that uses a porous membrane.

[0062] In particular, the bubble injection means 6 used in the second embodiment is preferably a bubble generator equipped with a porous membrane, which allows for a more compact and simplified device. In a bubble generator equipped with a porous membrane, gas is supplied to the porous membrane, and microbubbles generated on the surface of the porous membrane are swept away by the shear force of the water flow, generating microbubbles in the water. The bubble injection means 6 can inject gas into the bubble injection means 6 via a branch line branched from a gas supply line that supplies gas from a compressor or the like to the gas injection means 23. By adjusting the amount of gas branched from the branch line, the ratio of the amount of gas injected by the bubble injection means 6 into the circulating culture solution to the amount of gas supplied by the gas injection means 23 to the sterilization and purification treatment means 2 can be adjusted.

[0063] Although not limited thereto, in the present invention, the ratio of the amount of gas injected into the circulating culture medium by the bubble injection means 6 to the amount of gas supplied to the sterilization and purification treatment means 2 by the gas injection means 23, i.e., the supply ratio of bubbles to oxygen-containing gas supplied to the circulating culture medium (supply amount from the bubble injection means 6 / supply amount from the gas injection means 23), is greater than 0.0 and less than 1.0 in volume ratio. Preferably, the oxygen-containing gas and bubbles are injected so that the supply ratio of bubbles to oxygen-containing gas to the circulating culture medium is 0.1 or greater in volume ratio. The supply ratio is more preferably 0.2 or greater, and more preferably 0.3 or greater. The supply ratio is more preferably 0.9 or less, even more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.6.

[0064] The bubbles generated by the bubble injection means 6 are preferably microbubbles with a diameter of 100 μm or less, more preferably 10 μm or less, and even more preferably ultrafine bubbles with a diameter of 1000 nm or less. Microbubbles slowly rise due to buoyancy while contracting in the circulating culture medium. Therefore, when the second ultraviolet light is irradiated by the ultraviolet irradiation means 22, the ultraviolet irradiation time can be longer compared to millibubbles with a diameter of approximately 1 mm, thereby increasing the amount of ozone generated.

[0065] Ultrafine bubbles, also known as ultrafine bubbles or nanobubbles, are bubbles with diameters ranging from several tens of nanometers to 1,000 nanometers (1 μm). Ultrafine bubbles are distinct from microbubbles or microfine bubbles, which are known as fine bubbles with diameters ranging from 1 μm to 100 μm. The main physical properties of ultrafine bubbles are reported to be their extremely small diameter and slow rising speed, which allows them to remain in liquid for long periods of time; the generation of hydroxyl radicals when the bubbles collapse; their extremely high dissolution efficiency; their negative surface charge; and the repulsion of other bubbles when they come close to each other.

[0066] Ultrafine bubbles, due to their small diameter and low buoyancy, can remain in water for extended periods of time, from several weeks to several months, even longer than microbubbles. The long-term retention of ultrafine bubbles in the circulating culture solution without dissipation allows for the supply of high-concentration oxygen from the bubble injection means 6 to the cultivation shelves 5. Furthermore, ozone-containing bubbles generated from ultrafine bubbles, known as ozone ultrafine bubbles, remain in the circulating culture solution for extended periods of time and react with the collapse of the bubbles or the second ultraviolet light emitted from the ultraviolet irradiation means 22 to generate hydroxyl radicals. Because ultrafine bubbles have a high dissolution efficiency, their oxidizing, sterilizing, and decolorizing effects are enhanced compared to external injection of ozone gas, which is less soluble in the solution. The bubble injection means 6 may simultaneously generate millibubbles with diameters of approximately 1 μm to 1 mm as a by-product when generating microbubbles or ultrafine bubbles. By generating and injecting various types of bubbles with different diameters into the circulating culture medium, it is possible to efficiently maintain the DO in the circulating culture medium and perform sterilization and purification treatment.

[0067] To generate ultrafine bubbles or microbubbles using a device with a porous membrane as the bubble injection means 6, the pressure of the injected gas is preferably 0.1 MPa or higher, and more preferably 0.5 MPa or higher. If the gas pressure is too high, it may not be efficient from the viewpoints of maintaining the device and performing high-pressure processing, so the upper limit of the gas pressure can be set to, for example, 1 MPa or lower.

[0068] The gas supplied to the bubble injection means 6 is preferably air, but any gas, such as oxygen, ozone, carbon dioxide, or hydrogen, may also be added, or two or more types of gases may be introduced simultaneously. A filter for removing suspended components may be installed upstream of the bubble injection means 6. Injecting bubbles into the circulating culture solution using the bubble injection means 6 allows bubbles to remain in the circulating culture solution at a high concentration for a long period of time, thereby improving the ozone concentration during ozone generation. This results in improved AOP treatment. Furthermore, a secondary effect of having bubbles remaining in the circulating culture solution at a high concentration is that the circulating culture solution can be sent to the cultivation shelves 5 with a high DO concentration, thereby promoting the growth of plants on the cultivation shelves 5.

[0069] According to the second embodiment, the provision of the air bubble injection means 6 allows bubbles with a diameter of 100 μm or less, preferably 1000 nm or less, to be dissolved in the circulating culture solution, thereby supplying the circulating culture solution containing the bubbles to the sterilization and purification treatment means 2. When small bubbles, for example, bubbles with a diameter of 1000 nm or less, are dissolved in the circulating culture solution, they remain in the treatment tank 21 of the sterilization and purification treatment means 2 for a long period of time. Irradiation with the second ultraviolet light generates trace amounts of ozone from the oxygen in the bubbles. The reaction of the generated ozone with ultraviolet light and hydroxyl radicals increases the efficiency of the AOP treatment in the sterilization and purification treatment means 2. Furthermore, since the air bubbles remain in the circulating culture solution for a long period of time even after the sterilization and purification treatment, the DO of the circulating culture solution can be improved, thereby producing a circulating culture solution suitable for plant growth. Furthermore, the provision of the air bubble injection means 6 improves the DO of the circulating culture solution, thereby reducing the amount of air injected into the sterilization and purification treatment means 2. This reduces the overall amount of air injected into the circulating culture medium, thereby reducing the power required for injecting bubbles, allowing for more economical and efficient processing.

[0070] 5, the intake point for the circulating culture solution is provided in the circulation line of the circulation means 4 downstream of the cultivation shelves 5 of the plant production system 100, and at least a portion of the circulating culture solution taken from the circulation means 4 may be subjected to acid treatment by the acid treatment means 1, air bubble injection treatment by the air bubble injection means 6, sterilization and purification treatment by the sterilization and purification treatment means 2, and pH adjustment treatment by the adjustment means 3. The circulating culture solution that has passed through the adjustment means 3 is returned to the circulation line of the circulation means 4 upstream of the cultivation shelves 5.

[0071] 6, the intake point for the circulating culture solution is provided in a culture solution tank 10 connected downstream of the cultivation shelf 5 of the plant production system 100, and at least a portion of the circulating culture solution taken from the culture solution tank 10 may be subjected to acid treatment by acid treatment means 1, sterilization and purification treatment by sterilization and purification treatment means 2, and pH adjustment treatment by adjustment means 3. The circulating culture solution that has passed through adjustment means 3 is returned to the culture solution tank 10 or to the circulation means 4 without passing through the culture solution tank 10.

[0072] (Processing method) The circulating culture solution can be sterilized and purified using the treatment device for the circulating culture solution in the plant production system 100 according to the second embodiment shown in FIGS. That is, the method for treating a circulating culture solution in the plant production system 100 according to the second embodiment of the present invention includes an acid injection step in which acid is injected into the circulating culture solution so that the pH of the circulating culture solution in the plant production system 100 is 7 or less; a bubble injection step in which oxygen-containing bubbles having a bubble diameter of 100 μm or less, or even 1000 nm or less, are generated and the generated bubbles are injected into the circulating culture solution to be treated in the sterilization and purification treatment step; a sterilization and purification treatment step in which the circulating culture solution after the acid injection is placed in a treatment tank 21, the circulating culture solution is irradiated with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution, and an oxygen-containing gas is irradiated with second ultraviolet light having a wavelength range for generating ozone in the treatment tank 21 to generate ozone, and the ozone and oxygen-containing gas are injected into the circulating culture solution to sterilize the circulating culture solution; and an adjustment step in which the pH of the circulating culture solution after the sterilization and purification treatment step is adjusted to an appropriate pH for plant growth.

[0073] According to the second embodiment of the method for treating a circulating culture solution in the plant production system 100, microbubbles or ultrafine bubbles are generated in the bubble injection means 6 and injected into the circulating culture solution. Compared to larger bubbles with a diameter exceeding 1 mm, microbubbles or ultrafine bubbles rise more slowly within the treatment tank 21, allowing them to be irradiated with the second ultraviolet light from the ultraviolet irradiation means 22 for a longer period of time. As a result, more ozone can be generated from the oxygen in the bubbles in the circulating culture solution than when a gas containing ozone and oxygen is injected into the circulating culture solution only from the gas injection means 23. This increases the amount of ozone generated in the sterilization and purification means 2, enabling more efficient AOP treatment in the sterilization and purification means 2. Furthermore, because the ultrafine bubbles of oxygen-containing gas remain in the solution for a longer period of time, more oxygen can be supplied to the plants on the cultivation shelves 5.

[0074] (Third embodiment) As shown in FIG. 7, the circulating culture solution treatment device of the plant production system 100 according to the third embodiment of the present invention differs from the treatment device shown in FIG. 1 in that it includes an electrical conductivity meter 7 that measures the electrical conductivity of the circulating culture solution, a liquid fertilizer means 8 that injects liquid fertilizer into the circulating culture solution, and pH meters 9a and 9b that measure the pH of the circulating culture solution.

[0075] FIG. 7 shows an example in which an electrical conductivity meter 7 is connected to the circulation means 4 downstream of the adjustment means 3. The measurement results of the electrical conductivity of the circulating nutrient solution by the electrical conductivity meter 7 are output to a control means (not shown). Based on the measurement results of the electrical conductivity of the circulating nutrient solution, the control means outputs a predetermined control signal to, for example, supply liquid fertilizer, a pH adjuster, or the like to the circulating nutrient solution so as to adjust the electrical conductivity of the circulating nutrient solution to an electrical conductivity appropriate for the growth of the target plant. Alternatively, based on the measurement results of the electrical conductivity of the circulating nutrient solution, an operator may manually adjust the amount of liquid fertilizer or pH adjuster added to the circulating nutrient solution to adjust the electrical conductivity of the circulating nutrient solution to an appropriate value.

[0076] The liquid fertilizer means 8 is a device for injecting liquid fertilizer into the circulating culture solution to maintain a constant concentration of fertilizer components in the circulating culture solution. The liquid fertilizer means 8 is composed of a storage tank, a chemical injection pump, piping, and associated equipment. In the example of Figure 7, the liquid fertilizer means 8 is connected to the acid treatment means 1, the adjustment means 3, and the circulation means 4 downstream of the adjustment means 3.

[0077] The residual value of fertilizer components in the circulating culture solution can be monitored by an electrical conductivity meter 7. Therefore, the electrical conductivity meter 7 may be installed before or after the liquid fertilizer means 8, and the required amount of liquid fertilizer may be injected by automatic control. The range of electrical conductivity is preferably 130 mS / m or more, more preferably 140 mS / m or more, and even more preferably 150 mS / m or more. The upper limit of electrical conductivity is preferably, for example, 300 mS / m or less, and more preferably 250 mS / m or less.

[0078] pH meters 9a and 9b are located downstream of the acid treatment means 1 and the adjustment means 3, respectively. By measuring and monitoring the pH of the circulating culture solution downstream of the acid treatment means 1 using pH meter 9a, it is possible to confirm whether the pH of the circulating culture solution supplied to the sterilization and purification treatment means 2 is within the appropriate range. If the pH of the circulating culture solution supplied to the sterilization and purification treatment means 2 is not within the appropriate range (pH 7 or less, preferably 5 or less), the pH can be adjusted, for example, by adding a pH adjuster, and then supplying the pH-adjusted circulating culture solution to the sterilization and purification treatment means 2. This prevents oxidation of trace metal components in the circulating culture solution and prevents an increase in chromaticity of the circulating culture solution. Furthermore, by measuring the pH of the circulating culture solution after the adjustment means 3 using pH meter 9b, the pH of the circulating culture solution supplied to the cultivation shelves 5 can be adjusted to the appropriate range. This allows for stable plant growth on the cultivation shelves 5.

[0079] 8, the intake point for the circulating culture solution is provided in the circulation line of the circulation means 4 downstream of the cultivation shelves 5 of the plant production system 100, and at least a portion of the circulating culture solution taken from the circulation means 4 may be subjected to acid treatment by the acid treatment means 1, sterilization and purification treatment by the sterilization and purification treatment means 2, pH adjustment treatment by the adjustment means 3, and liquid fertilizer supply to the circulating culture solution by the liquid fertilizer means 8. The circulating culture solution that has passed through the adjustment means 3 is returned to the circulation line of the circulation means 4 upstream of the cultivation shelves 5.

[0080] 9, the intake point for the circulating culture solution is provided in a culture solution tank 10 connected downstream of the cultivation shelf 5 of the plant production system 100, and at least a portion of the circulating culture solution taken from the culture solution tank 10 may be subjected to acid treatment by an acid treatment means 1, sterilization and purification treatment by a sterilization and purification treatment means 2, pH adjustment treatment by an adjustment means 3, and liquid fertilizer supply to the circulating culture solution by a liquid fertilizer means 8. The circulating culture solution that has passed through the adjustment means 3 is returned to the circulation means 4.

[0081] As shown in Fig. 10, the treatment apparatus of Fig. 8 may further be provided with an air bubble injection means 6 connected between the acid treatment means 1 and the sterilization and purification treatment means 2. Also, a liquid fertilizer means 8 may be further provided after the inlet through which the circulating culture solution whose pH has been adjusted by the adjustment means 3 is returned to the circulation means 4, so that liquid fertilizer is supplied to the circulating culture solution flowing within the circulation means 4. As shown in Fig. 11, the treatment apparatus of Fig. 9 may further be provided with an air bubble injection means 6 connected between the acid treatment means 1 and the sterilization and purification treatment means 2.

[0082] (Processing method) A circulating culture solution can be sterilized and purified using a circulating culture solution treatment device in a plant production system 100 according to a third embodiment shown in Figures 7 to 11. That is, the circulating culture solution treatment method in the plant production system 100 according to the third embodiment of the present invention further includes the steps of measuring the electrical conductivity of the circulating culture solution, injecting liquid fertilizer into the circulating culture solution, and measuring the pH of the circulating culture solution, in addition to the treatment method according to the first embodiment. The treatment method according to the third embodiment includes an electrical conductivity meter 7, liquid fertilizer means 8, and pH meters 9a and 9b, thereby enabling more accurate adjustment of the properties of the circulating culture solution.

[0083] (Other embodiments) The example shown in Figure 12 includes an acid injection section 11 instead of the acid treatment means 1 in Figures 1 to 11, an alkali injection section 31 instead of the adjustment means 3 in Figures 1 to 11, and a culture solution tank 10 for storing the circulating culture solution downstream of the alkali injection section 31. An electric conductivity meter 7, liquid fertilizer means 8, and pH meters 9, 9a, and 9b are connected to the circulation means 4 downstream of the culture solution tank 10, allowing the water quality of the circulating culture solution to be measured.

[0084] The acid injection unit 11 is composed of an acid storage tank, a chemical injection pump, piping, and associated equipment, and injects acid into the circulating culture solution from an injection point provided in the circulation means 4. The alkali injection unit 31 is composed of an alkali storage tank, a chemical injection pump, piping, and associated equipment, and injects alkali into the circulating culture solution treated by the sterilization and purification treatment means 2 from an injection point provided in the circulation means 4. In FIG. 12, multiple cultivation shelves 5 are provided. The multiple cultivation shelves 5 are connected in parallel to the circulation means 4. The treatment device shown in FIG. 12 can circulate and supply a circulating culture solution composed of more uniform and appropriate components to the multiple cultivation shelves 5. As shown in FIG. 13, a pump 41 may be further provided in the circulation means 4 connected between the cultivation shelves 5 and the acid injection unit 11.

[0085] 14 shows a configuration in which the circulating culture solution discharged from a plurality of cultivation shelves 5 is stored in the culture solution tank 10 via the circulation means 4, and the circulating culture solution stored in the culture solution tank 10 is returned to the plurality of cultivation shelves 5 via the circulation means 4. The intake and return points for the circulating culture solution are provided in the culture solution tank 10 or the circulation means 4.

[0086] As shown in Fig. 15, a bubble injection means 6 may be provided between the acid injection section 11 and the sterilization and purification treatment means 2. As shown in Fig. 16, the intake point and return point for the circulating culture solution may be provided in the circulation line of the circulation means 4 connected to the cultivation shelves 5 of the plant production system 100. As shown in Fig. 17, the intake point for the circulating culture solution may be provided in the culture solution tank 10 connected to the cultivation shelves 5 of the plant production system 100. The return point for the circulating culture solution may be connected directly to the circulation means 4 without passing through the culture solution tank 10.

[0087] The treatment device shown in FIG. 18 may include a liquid fertilizer injection unit 81 that injects liquid fertilizer into an injection unit (not shown) provided in the piping of the circulation means 4. The liquid fertilizer injection unit 81 is composed of a liquid fertilizer storage tank, a chemical injection pump, piping, and associated equipment. The type and number of liquid fertilizers are not particularly limited. For example, as shown in FIG. 19, liquid fertilizer injection units 81a and 81b may be provided at multiple locations before and after the culture solution tank 10. As shown in FIG. 20, the liquid fertilizer injection units 81a and 81b may be connected to an injection point provided in the return piping for the circulating culture solution to the culture solution tank 10 and to an injection point provided in the circulation means 4 downstream of the culture solution tank 10. The return point for the circulating culture solution may be provided in the culture solution tank 10 or in the circulation means 4 downstream of the culture solution tank 10.

[0088] As shown in Figure 21, the intake point of the circulating culture solution to be supplied to the acid injection section 11 in Figure 15 may be located in the circulation means 4 subsequent to the cultivation shelf 5 in the plant production system 100, and the circulating culture solution may be returned to the cultivation shelf 5 via the pump 41, the acid injection section 11, the air bubble injection means 6, the sterilization and purification treatment means 2, the alkali injection section 31, and the culture solution tank 10.

[0089] As shown in Figure 22, the intake point for the circulating culture solution is provided in a culture solution tank 10 connected downstream of the cultivation shelf 5 of the plant production system 100, and at least a portion of the circulating culture solution taken from the culture solution tank 10 may be subjected to acid injection treatment, air bubble injection treatment, sterilization and purification treatment, and pH adjustment treatment, and then returned to the culture solution tank 10 or the circulation means 4.

[0090] According to an embodiment of the present invention, a small amount of ozone is generated by simultaneously irradiating the circulating culture solution with ultraviolet light in two wavelength ranges and supplying air, thereby accelerating the AOP treatment using ultraviolet light and ozone. This promotion effect enhances the sterilization effect and is effective in suppressing the growth of bacteria and algae. Furthermore, according to an embodiment of the present invention, by providing the air bubble injection means 6, the oxygen dissolution efficiency of the bubbles (ultrafine bubbles) generated by the air bubble injection means 6 is very high, making it possible to maintain a high DO concentration in the circulating culture solution for a long period of time. As a result, the DO concentration in the circulating culture solution supplied to the cultivation shelves 5 can be adjusted to an appropriate concentration. Furthermore, by irradiating the ultrafine bubbles with a second ultraviolet light to generate ozone (ultrafine ozone bubbles), the dissolution of ozone is promoted, thereby enhancing the sterilization effect. [Example]

[0091] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0092] <Device configuration> A schematic diagram of the circulating culture solution treatment device used in the test is shown in Figure 23. This treatment device comprises a raw water tank 101 that contains the circulating culture solution, a culture solution circulation line 104 that takes the circulating culture solution from the raw water tank 101, sterilizes and purifies it, and then returns it to the raw water tank 101, a sterilization and purification treatment means 120 connected to the culture solution circulation line 104, and an air bubble injection means 106 connected to the culture solution circulation line 104 that injects air bubbles into the circulating culture solution.

[0093] An air compressor 128 was connected to the air bubble injection means 106 to inject air as an oxygen-containing gas into the air bubble injection means 106. To inject air as an oxygen-containing gas into the sterilization and purification treatment means 120, an air pump (not shown) was provided attached to the operation panel 110, a flow meter and an air drain were provided on the air injection line 123, and air was injected into the treatment tank 121 by the air pump attached to the operation panel 110. A single ultraviolet lamp capable of emitting ultraviolet rays in the wavelength ranges of 185 nm and 254 nm was installed in the center of the treatment tank 121 of the sterilization and purification treatment means 120, and a glass casing 125 was provided outside the ultraviolet lamp. Air was injected from the air injection line 123 into a gas flow section 126 formed in the casing 125. Ozone gas was generated from a portion of the air supplied into the casing 125 from the air injection line 123 by irradiation with ultraviolet rays in the wavelength range of 185 nm. The air and ozone gas were circulated through the circulation section 124 to the circulating liquid flow section 127, which was the liquid phase section in the treatment tank 121 of the sterilization and purification treatment means 2, and injected into the circulating culture solution. A stirrer 142 was installed in the raw water tank 101, and the circulating culture solution was fed to the culture solution circulation line 104 from a circulation pump 141 connected to the raw water tank 101.

[0094] <Test conditions> Table 1 shows the test conditions. The raw water used was circulating culture medium collected from plant factory A, with a total volume of 50 L, with a circulating water volume of 15 L / min, a circulation time of 10 minutes, and a water temperature of 20-30°C (unadjusted). The raw water pH was adjusted to a range of 5-8. The UV lamp output was 110 W, the UV irradiation dose was 0.37 Wh / L, and the UV irradiation time was 10 minutes. The UV irradiation dose was calculated using the formula: UV irradiation dose = (UV output × UV irradiation time) ÷ (circulating water volume × circulation time).

[0095] In Test 1, no gas was injected, and only ultraviolet light was irradiated. In Tests 2 to 8, gas was supplied into the casing 125 of the sterilization and purification means 120. In Tests 6 to 8, ultrafine bubbles were generated by the air bubble injection means 106 and injected into the circulating culture solution. Air was used as the injected gas, and the total injection volume was adjusted within the range of 0.38 to 1.9 L / min. The air injection volume (air bubble injection volume) into the air bubble injection means 106 was 0.19 L / min in Test 7 and 0.1 L / min in Test 8. In Table 1, the "gas-liquid ratio" refers to the volume ratio of the injected air volume to the circulating water volume of the circulating culture solution (circulating water volume / injected air volume). Here, the ratios were 7:40 in Tests 2 to 5, 7.9 in Test 6, and 38 in Test 8.

[0096] [Table 1]

[0097] <Measurement items> Tables 2 and 3 show the water quality analysis results for the raw water and treated water. The measured items were pH, water temperature, DO (dissolved oxygen concentration), electrical conductivity, color, turbidity, general bacterial count, total manganese (Mn), soluble Mn, total iron (Fe), soluble Fe, general bacterial reduction rate, and color increase rate. These water quality analysis items were measured in accordance with the drinking water testing method (published by the Japan Water Works Association, drinking water testing method) or the sewage testing method (published by the Japan Sewage Works Association, sewage testing method), and JIS-K0102 (Japanese Industrial Standards). Electrical conductivity was measured for the raw water and treated water using a conductivity meter.

[0098] The general bacteria reduction rates in Tables 2 and 3 were calculated based on the formula: general bacteria reduction rate = (raw water concentration - treated water concentration) ÷ raw water concentration × 100. The "color increase rate" was calculated based on the formula: color increase rate = (treated water concentration - raw water concentration) ÷ treated water concentration × 100. The sample for measuring the soluble components was filtered using glass filter paper with a pore size of 1 mm, and the filtrate after filtration was used.

[0099] [Table 2]

[0100]

Table 3

[0101] <Effect on sterilization and purification treatment> The reduction rates of general bacteria are as follows: Test 1: 94.8%, Test 2: 97.8%, Test 3: 98.7%, Test 4: 99.1%, Test 5: 98.8%, Test 6: 97.4%, Test 7: 96.7%, Test 8: 97.0%. The sterilization and purification treatment effects of Tests 2 - 8 with injection of air and ultraviolet light in two wavelength regions are better than those of Test 1 with irradiation of only ultraviolet light in two wavelength regions during the sterilization and purification treatment. That is, it can be seen that the number of general bacteria is reduced when air is injected compared to only ultraviolet irradiation. Therefore, it can be seen that when air is injected into the sterilization and purification treatment means 120, the treatment effect is improved compared to only ultraviolet irradiation.

[0102] <Effect by pH adjustment> The color increase rates are as follows: Test 1: 11%, Test 2: 50%, Test 3: 26%, Test 4: Unable to measure due to high - concentration turbidity, Test 5: 5.6%, Test 6: 50%, Test 7: 40%, Test 8: 32%. Also, for Tests 3, 4, and 5 where pH adjusters were added to the raw water to adjust the test conditions to pH 7 (Test 3), pH 8 (Test 4), and pH 5 (Test 5), the results were Test 3: 1.5 degrees, Test 4: 50 degrees, Test 5: 1.0 degrees. The turbidity increased rapidly when the raw water before sterilization and purification treatment was made greater than 7 and closer to 8. Also, when the raw water was adjusted to pH 8, the raw water became turbid and white precipitates were deposited. This is considered to be because the metal ions of the fertilizer components in the circulating culture solution precipitated as hydroxides under alkaline conditions. In order to suppress component changes such as color increase, the pH condition should be 7 or less, further 6 or less, even further 5.5 or less, and even further 5 or less. In order to prevent the precipitation of fertilizer components, it was found that the final treated water needs to be pH 7 or less.

[0103] <Effect of bubble injection treatment> Comparing Test 2 and Test 7, which used the same total gas injection amount without adjusting the pH of the circulating culture solution, the general bacteria reduction rate in Test 2, where no bubbles were injected, was 97.8%, while in Test 7, where bubbles were injected, it was 96.7%, achieving sufficiently high general bacteria reduction rates of above 95%. Meanwhile, the DO in the treated water was 7.7 mg / L in Test 2 and 8.7 mg / L in Test 7, indicating that the DO in the circulating culture solution in Test 7, where ultrafine bubbles were injected, was higher than in Test 2. Furthermore, although the total gas injection amount in Test 7 was approximately one-fifth that of Test 6, the DO of the treated water in Tests 6 and 7 was maintained at a similar high level. In other words, by optimizing the gas injection amount by combining the injection of gas into the sterilization and purification treatment means 120 via the air injection line 123 in Figure 23 and the injection of bubbles such as ultrafine bubbles using the air bubble injection means 106, it is possible to maintain a high DO of the treated water while reducing the total gas injection amount. Furthermore, the results of Tests 7 and 8, which combined the injection of gas into the sterilization and purification treatment means 120 and the injection of bubbles such as ultrafine bubbles into the circulating culture solution by the air bubble injection means 106, showed that a higher DO of the treated water can be maintained by increasing the proportion of air bubbles injected. Thus, it can be seen that this embodiment can maintain a high DO of the treated water, which is suitable for promoting plant growth, while suppressing the growth of general bacteria.

[0104] <Impact of ozone generation> For the circulating culture solution of Tests 5 and 6 after irradiation with ultraviolet light in the wavelength ranges of 185 nm and 254 nm, the gas inside the casing of the sterilization and purification treatment means 120 was sampled, and the ozone concentration in the gas was measured. In Table 4, the "airborne ozone concentration" was measured in accordance with the Sewage Testing Method (published by the Japan Sewage Works Association, Sewage Testing Method). In Table 4, the "air injection rate" indicates the air injection flow rate from the air injection line 123 in Figure 23, and the "circulating water volume" indicates the supply flow rate of the circulating culture solution introduced into the sterilization and purification treatment means 120. In Table 4, the "ozone supply rate" was calculated by multiplying the airborne ozone concentration by the air inflow rate, and the ozone concentration was evaluated based on the ozone supply rate relative to the circulating water volume of the circulating culture solution. The airborne ozone concentration was 0.6 mg O3 / L air in Test 5 and 0.3 mg O3 / L air in Test 6, and the ozone supply rate was 0.014 g O3 / h in Test 5 and 0.034 g O3 / h in Test 6. The ozone supply concentration was 0.015 mg O3 / L circulating culture solution in Test 5 and 0.038 mg O3 / L circulating culture solution in Test 6. The ozone concentrations were lower than those in typical ozone oxidation treatments.

[0105] [Table 4]

[0106] Thus, this study demonstrated that a sterilization and purification process combining UV irradiation (irradiating the circulating culture solution with first and second UV rays) and gas injection (injecting oxygen-containing gas) into the circulating culture solution reduced general bacteria compared to Test 1, which did not include a gas injection process, and also tended to reduce soluble organic matter. Furthermore, the color increase rate in Test 5 (pH 5) was lower than in Tests 2-4 (pH 6-8), confirming the effectiveness of this device in suppressing color increase under acidic conditions. Furthermore, Tests 7 and 8 demonstrated that the infusion of air bubbles, such as ultrafine bubbles, into the circulating culture solution can maintain a higher DO with a smaller air injection volume overall, potentially promoting plant growth in the downstream cultivation shelves. Furthermore, although the ozone concentrations generated in Tests 5 and 6 were low, the reduction in general bacteria and soluble organic matter was greater than that achieved by UV alone, confirming the effectiveness of this treatment method and treatment device.

[0107] Although the present invention has been described using the above embodiments, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. While the present invention has been described using the sterilization and purification treatment of a circulating culture solution in a plant production system as an example, the present invention can be applied to various types of water to be treated that are suitable for sterilization and purification treatment using ultraviolet light and ozone instead of a circulating culture solution. Thus, the present disclosure is not limited to the above embodiments, and components can be combined and modified to achieve specific embodiments without departing from the spirit and scope of the present disclosure. [Explanation of symbols]

[0108] 1... Acid treatment means 2... Disinfection and purification treatment means 3…Adjustment means 4…Circulation means 5…Cultivation shelf 6...Air bubble injection means 7...Electrical conductivity meter 8…Liquid fertilizer means 9,9a,9b…pH meter 10…Culture solution tank 11...Acid injection part 21...Treatment tank 22...Ultraviolet irradiation means 22A...First ultraviolet irradiation means 22B...Second ultraviolet irradiation means 23...Gas injection means 24...Circulation section 25...Casing 31...Alkali injection section 41...Pump 81,81a,81b…Liquid fertilizer injection part 100...Plant production system 101...Raw water tank 104...Culture solution circulation line 106...Air bubble injection means 110...Operation panel 120... Disinfection and purification treatment means 121... Treatment tank 122...Ultraviolet lamp 123...Air injection line 124...Circulation section 125...Casing 126...Gas flow section 127…Circulating fluid distribution section 128...Air compressor 141...Circulation pump 142...Agitator 231…Inlet

Claims

1. An acid injection step of injecting acid into the circulating culture solution in the plant production system so that the pH of the circulating culture solution is 7 or less; a sterilization and purification treatment step of storing the circulating culture solution after the acid has been injected into a treatment tank, irradiating the circulating culture solution with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution, irradiating an oxygen-containing gas with second ultraviolet light having a wavelength range for generating ozone in the treatment tank to generate ozone, and injecting the ozone and the oxygen-containing gas into the circulating culture solution to sterilize the circulating culture solution using ozone; an adjusting step of adjusting the circulating culture solution after the sterilization and purification treatment step to a pH appropriate for plant growth; A method for treating a circulating culture solution in a plant production system having the above structure.

2. A method for treating a circulating culture solution of a plant production system as described in claim 1, further comprising a bubble injection step of generating oxygen-containing bubbles having a bubble diameter of 100 μm or less after the acid injection step and before the sterilization and purification treatment step, and injecting the generated bubbles into the circulating culture solution to be treated in the sterilization and purification treatment step.

3. 3. The method for treating a circulating culture solution in a plant production system according to claim 2, further comprising injecting the oxygen-containing gas and the air bubbles so that a supply ratio of the air bubbles to the oxygen-containing gas into the circulating culture solution is 0.1 or more in terms of volume ratio.

4. 4. The method for treating a circulating culture solution in a plant production system according to claim 2 or 3, comprising injecting the oxygen-containing gas and / or bubbles into the circulating culture solution so that the DO of the circulating culture solution treated in the sterilization and purification treatment step is 5 to 20 mg / L.

5. The sterilization and purification treatment step includes: injecting the oxygen-containing gas into a gas circulation section provided between an ultraviolet irradiation means capable of irradiating the first and second ultraviolet rays, which is disposed in the treatment tank, and a casing disposed around the ultraviolet irradiation means in the treatment tank; irradiating the oxygen-containing gas injected into the gas flow portion with the second ultraviolet light to generate the ozone; The method for treating a circulating culture solution of a plant production system according to any one of claims 1 to 3, comprising injecting the oxygen-containing gas and the ozone in the gas circulation section into the circulating culture solution in the treatment tank.

6. The ozone concentration in the circulating culture solution in the sterilization and purification treatment step is 0.005 to 0.5 mg-O 3 The method for treating a circulating culture solution of a plant production system according to any one of claims 1 to 3, further comprising generating the ozone in the treatment tank so as to obtain a circulating culture solution of 1 / L / L.

7. A method for treating a circulating culture solution of a plant production system described in any one of claims 1 to 3, further comprising a step of injecting liquid fertilizer into the circulating culture solution after adjusting the pH to a level suitable for plant growth.

8. A method for treating a circulating culture solution of a plant production system described in any one of claims 1 to 3, comprising a step of adjusting the electrical conductivity of the circulating culture solution to an electrical conductivity appropriate for the growth of the plant to be treated based on the measurement results of the electrical conductivity of the circulating culture solution after adjusting it to a pH appropriate for plant growth.

9. an acid treatment means for injecting an acid into the circulating culture solution of the plant production system so that the pH of the circulating culture solution is 7 or less; a sterilization and purification treatment means including: a treatment tank containing the circulating culture solution into which the acid has been injected; an ultraviolet irradiation means disposed in the treatment tank and irradiating the circulating culture solution with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution and second ultraviolet light having a wavelength range for generating ozone; and a gas injection means for injecting into the treatment tank an oxygen-containing gas that reacts with the second ultraviolet light to promote the generation of the ozone; an adjusting means for adjusting the pH of the circulating culture solution treated by the sterilization and purification means to a pH suitable for plant growth; A treatment device for circulating culture solution in a plant production system comprising:

10. 10. The treatment device for a circulating culture solution of a plant production system according to claim 9, further comprising: a bubble injection means provided between the acid treatment means and the sterilization and purification treatment means, which generates oxygen-containing bubbles having a bubble diameter of 100 μm or less and injects the generated bubbles into the circulating culture solution.

11. the ultraviolet irradiation means includes an ultraviolet lamp capable of irradiating the first ultraviolet light and the second ultraviolet light, and a casing disposed around the ultraviolet lamp, and a gas flow section is formed between the ultraviolet lamp and the casing; the gas injection means is connected to the gas flow section and injects the oxygen-containing gas into the gas flow section; 11. The device for treating a circulating culture solution of a plant production system according to claim 9 or 10, further comprising: a circulation unit connected to the gas circulation unit configured to circulate and inject the gas containing the ozone and the oxygen generated in the gas circulation unit by irradiation with the second ultraviolet light into the circulating culture solution in the treatment tank.

12. a cultivation shelf for cultivating plants using a circulating culture solution containing nutrients necessary for plant growth; a circulation means for circulating the circulating culture solution discharged from the culture shelf to the culture shelf; an acid treatment means for injecting acid into the circulating culture solution discharged from the cultivation shelf so that the pH is 7 or less; a sterilization and purification treatment means including: a treatment tank containing the circulating culture solution into which the acid has been injected; an ultraviolet irradiation means disposed in the treatment tank, which irradiates the circulating culture solution with first ultraviolet light having a wavelength range for sterilizing the circulating culture solution and second ultraviolet light having a wavelength range for generating ozone in the circulating culture solution; and a gas injection means which injects into the treatment tank an oxygen-containing gas that reacts with the second ultraviolet light to promote the generation of the ozone; an adjusting means connected to the sterilization and purification treatment means for adjusting the pH of the circulating culture solution treated by the sterilization and purification treatment means to a pH appropriate for plant growth; A plant production system comprising:

13. 13. The plant production system according to claim 12, wherein the intake point of the circulating culture solution to be supplied to the acid treatment means is a culture solution tank that is downstream of the cultivation shelf and is within the circulation means or that stores the circulating culture solution discharged from the cultivation shelf.

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