WO2021100726A1

WO2021100726A1 - Sterilization method

Info

Publication number: WO2021100726A1
Application number: PCT/JP2020/042881
Authority: WO
Inventors: 敬祐内藤
Original assignee: ウシオ電機株式会社
Priority date: 2019-11-22
Filing date: 2020-11-18
Publication date: 2021-05-27
Also published as: JP7447442B2; JP2021080147A

Abstract

Provided is a sterilization method which makes it possible to suppress the oxidation of metal ions contained in a liquid fertilizer, and to attain a sterilizing effect.　The present invention pertains to a liquid fertilizer sterilization method. The liquid fertilizer contains metal ions which at least include iron. This sterilization method includes a step (a) for irradiating the liquid fertilizer with ultraviolet light having a principal light emission wavelength in the range of 370-410nm, inclusive.

Description

Sterilization method

The present invention relates to a sterilization method, and particularly to a sterilization method of liquid fertilizer used for growing plants.

Conventionally, a method of growing a plant by using a liquid fertilizer (also referred to as "nutrient solution") without using soil is known (see, for example, Patent Document 1). Specifically, the nutrient solution is sucked up by a pump from the nutrient solution tank containing the nutrient solution, and the nutrient solution is supplied to the cultivation tank in which the plant is placed, so that the plant is grown. .. This nutrient solution is circulated between the cultivation tank and the nutrient solution tank.

By the way, due to circumstances such as the generation of pathogens in the cultivation tank, pathogens may propagate in the nutrient solution in the process of continuing cultivation. Patent Document 1 discloses a method of sterilizing (sterilizing) a nutrient solution by introducing the nutrient solution into a photocatalytic reactor. More specifically, light from a germicidal lamp having a main wavelength of 200 nm to 300 nm is used for a photocatalytic reactor in which a fiber sleeve containing silicon oxide as a main component is used as a base material and a photocatalyst made of titanium oxide is supported on the base material. A method of irradiating the light is disclosed.

Japanese Unexamined Patent Publication No. 2003-274774

Liquid fertilizer (nutrient solution) used for plant growth contains ions composed of metal elements such as iron, copper, zinc and manganese. In particular, iron (II) ion is said to be necessary for the synthesis of chlorophyll, which is indispensable for photosynthesis, and is one of the important elements contained in liquid fertilizer.

However, when ultraviolet light (peak wavelength 185 nm, 254 nm) from a low-pressure mercury lamp generally used as a germicidal lamp is directly applied to liquid fertilizer, iron (II) ions are oxidized and iron (II) is oxidized. III) It changes to ions. This change is considered to be due to the reaction of the following equation (1).
2Fe ²⁺ + (1/2) O ₂ + H ⁺ = 2Fe ³⁺ + H ₂ O (1)

Many plants cannot be absorbed in the state of iron (III) ions. Therefore, when the reaction of the above formula (1) occurs, the amount of absorption of the elements necessary for growing the plant is practically reduced. Therefore, a step of adding (replenishing) the iron (II) ion component to the liquid fertilizer is required.

An object of the present invention is to provide a sterilizing method capable of realizing a bactericidal effect while suppressing oxidation of metal ions contained in liquid fertilizer.

The present invention is a method for sterilizing liquid fertilizer.
The liquid fertilizer contains at least metal ions containing iron, and the liquid fertilizer contains at least iron-containing metal ions.
The liquid fertilizer is characterized by including a step (a) of irradiating the liquid fertilizer with ultraviolet light having a main emission wavelength in the range of 370 nm or more and 430 nm or less.

Through the diligent research of the present inventors, it was confirmed that the light near 254 nm, which is the peak wavelength of ultraviolet light emitted from a low-pressure mercury lamp, has a relatively high absorbance for liquid fertilizer. On the other hand, it was confirmed that the ultraviolet light having a main emission wavelength in the range of 370 nm or more and 430 nm or less has a significantly lower absorbance with respect to the liquid fertilizer than the light in the vicinity of 254 nm.

The high absorbance for liquid fertilizer means that when ultraviolet light is applied to the liquid fertilizer, the light energy is absorbed and the reaction of the above formula (1) is likely to occur. On the other hand, the low absorbance for liquid fertilizer means that when ultraviolet light is applied to the liquid fertilizer, the ultraviolet light easily passes through the nutrient solution, so that the reaction of the above formula (1) is unlikely to occur. To do.

Generally, for sterilization applications, ultraviolet light of 254 nm, which is close to the peak value of the absorption spectrum of DNA, is often used. On the other hand, as a result of diligent research by the present inventors, the present invention uses ultraviolet light having a main emission wavelength in the range of 370 nm or more and 430 nm or less, which is a wavelength longer than the above-mentioned 254 nm, and is used as a liquid fertilizer. It is an invention made by newly finding that the bactericidal ability can be ensured while suppressing the progress of oxidation of the metal ions contained in. Details will be described later in the section "Modes for Carrying Out the Invention".

It should be noted that preferably, the main emission wavelength of ultraviolet light is 390 nm or more and 410 nm or less, and more preferably, the main emission wavelength of ultraviolet light is 405 nm. Porphyrin, which is a kind of metabolite of bacteria, shows high absorption especially for light in the wavelength range of 390 nm to 410 nm, and it is considered that bactericidal performance is realized by the singlet oxygen generated during this absorption. Be done.

By the way, titanium dioxide, which is generally used as a material for photocatalysts, has a bandgap energy of 388 nm. A low-pressure mercury lamp is used as a light source because the wavelength is sufficiently shorter than 388 nm and is easily available from the viewpoint of surely showing the effect of the photocatalyst. However, when the liquid fertilizer is directly irradiated with ultraviolet light from such a low-pressure mercury lamp, for example, the above equation (1) proceeds, and the elements contained in the liquid fertilizer necessary for plant growth are reduced. It is as described above.

Similarly, manganese, copper, and zinc other than iron also undergo an oxidation reaction when exposed to short-wavelength ultraviolet light. According to the above method, even when a liquid fertilizer containing these metal ions is used, it is possible to similarly exhibit a bactericidal effect while suppressing a decrease in elements necessary for plant growth. Become.

In the present specification, the "main emission wavelength" refers to the total integrated intensity in the emission spectrum when the wavelength region Z (λ) of ± 10 nm with respect to a certain wavelength λ is defined on the emission spectrum. It refers to the wavelength λi in the wavelength region Z (λi) showing an integrated intensity of 40% or more.

The step (a) may be a step of irradiating the ultraviolet light from a light source made of an LED.

As described above, ultraviolet light having a main emission wavelength in the range of 370 nm or more and 430 nm or less has low absorbance with respect to the nutrient solution and high transmittance. Therefore, the ultraviolet light can travel not only in the vicinity of the light source but also in a region away from the light source. Therefore, by realizing the light source with an LED element, it can be easily attached to the wall surface, the bottom surface, the ceiling, or the like of the device in which the liquid fertilizer is stored.

In the sterilization method, the liquid fertilizer after being irradiated with the ultraviolet light in the step (a) is supplied to a growing region of a plant grown using the liquid fertilizer through a pipe (b). It may have.

In this case, the sterilization method further includes a step (c) of delivering the liquid fertilizer from the growing region through a pipe to the region irradiated with the ultraviolet light.
The step (a), the step (b), and the step (c) may be repeatedly executed.

According to this method, the sterilized liquid fertilizer can be constantly supplied to the plant without performing a separate step of replenishing the deficient metal ions.

The step (a) may be a step of irradiating the liquid fertilizer with the ultraviolet light from the outside of the region where the liquid fertilizer is stored.

According to the sterilization method of the present invention, sterilization of liquid fertilizer is realized while suppressing oxidation of metal ions contained in liquid fertilizer.

It is a drawing which shows typically the plant growing system which is an example of the use mode of the sterilization method which concerns on this invention. It is a graph which shows the absorbance of each liquid Q1 to Q4. It is a graph which shows the spectrum of the ultraviolet light used in Example 1. It is a graph which shows the relationship between the exposure amount of the ultraviolet light irradiated by each of the light sources of Example 1 and Comparative Example 1 and the amount of decrease of iron (II) ion contained in liquid Q2. It is a graph which shows the relationship between the exposure amount of ultraviolet light irradiated from the light source of Example 1 and the amount of decrease of the content of Staphylococcus aureus contained in liquid Q2. It is a drawing which shows typically the plant growing system which is another example of the use mode of the sterilization method which concerns on this invention. It is a drawing which shows typically the plant growing system which is another example of the use mode of the sterilization method which concerns on this invention. In the plant growing system shown in FIG. 7, it is a drawing which shows typically the mode of flow of the liquid fertilizer in T1 for a certain period. In the plant growing system shown in FIG. 7, it is a drawing which shows typically the mode of the flow of the liquid fertilizer within a certain period T2. It is a drawing which shows typically the plant growing system which is another example of the use mode of the sterilization method which concerns on this invention.

An embodiment of the sterilization method according to the present invention will be described with reference to the drawings.

[System configuration example]
FIG. 1 is a drawing schematically showing a plant growing system, which is an example of the usage mode of the sterilization method according to the present invention. The plant growing system 1 includes an area for growing the plant 10 (cultivation tank 6) and a storage tank 2 in which the liquid fertilizer 3 supplied to the cultivation tank 6 is stored. The liquid fertilizer 3 contains components necessary for growing the plant 10, such as iron, copper, zinc, and manganese, depending on the type of the plant 10. The liquid fertilizer 3 may contain at least iron ions.

The storage tank 2 is provided with a light source unit 4 including a plurality of LED light sources 4a. Each LED light source 4a is configured to be capable of emitting ultraviolet light L1 having a main emission wavelength in the range of 370 nm or more and 430 nm or less. As an example, each LED light source 4a emits ultraviolet light L1 having a main emission wavelength of 405 nm. In the plant growing system 1 shown in FIG. 1, the light source unit 4 is arranged in the storage tank 2 outside the region where the liquid fertilizer 3 is stored.

The storage tank 2 and the cultivation tank 6 are connected by a pipe 5a and a pipe 5b. By driving the pump 7, the liquid fertilizer 3 stored in the storage tank 2 is supplied to the cultivation tank 6 via the pipe 5a, and the liquid fertilizer 3 staying in the cultivation tank 6 is released. It is sent to the storage tank 2 side via the pipe 5b.

The liquid fertilizer 3 stored in the storage tank 2 is irradiated with ultraviolet light L1 from the light source unit 4, so that the liquid fertilizer 3 is sterilized. Therefore, even if the liquid fertilizer 3 accumulated in the cultivation tank 6 contains pathogens, it can be returned to the cultivation tank 6 side again after being sterilized in the storage tank 2. As a result, in the cultivation tank 6, the plant 10 can be grown with the sterilized liquid fertilizer 3.

By setting the main emission wavelength of the ultraviolet light L1 emitted from the light source unit 4 to the range of 370 nm or more and 430 nm or less, sterilization of the liquid fertilizer 3 is performed while suppressing the oxidation of iron ions contained in the liquid fertilizer 3. Can be done. The reason for this will be described below.

[Verification]
<Verification 1>
FIG. 2 shows the absorbance of each liquid of liquid fertilizer (Q1), liquid fertilizer diluted to 1/10 (Q2), aqueous chelated iron solution (Q3), and water (Q4) when irradiated with ultraviolet light of 405 nm. It is a graph which shows the result of having measured. As the liquids Q1 to Q4, those obtained by the following methods were adopted.

[Liquid used]
As the liquid Q1, a fertilizer for hydroponic cultivation "OAT House No. 1" manufactured by OAT Agrio Co., Ltd. was used, and a liquid mixed with tap water under the concentration specified by the A formulation was used. The reason why tap water was used in the liquid Q1 is to simulate the actual plant growing site.

As the liquid Q2, 1 mL of liquid Q1 diluted with 9 mL of ultrapure water was used.

As the liquid Q3, a liquid prepared by the following method was used.
A stock solution was prepared by dissolving 1 g of a fertilizer for making a solution-cultivated fertilizer (product name: EDTA-FE-13, manufactured by Tamagoya Shoten) of 13% chelated iron in 100 mL of ultrapure water. Next, the stock solution was diluted with ultrapure water until the peak absorbance for ultraviolet light at 405 nm could be measured within the range of 0.5 or more and 1.5 or less to obtain liquid Q3. It should be noted that this dilution treatment was performed for the purpose of enabling verification of the wavelength at which the absorbance shows a peak.

Ultrapure water was used as the liquid Q4.

[Measuring method]
Using an ultra-trace spectrophotometer "NanoDrop One" (registered trademark) manufactured by Thermo Fisher Scientific, each of the sample liquids Q1 to Q4 was dropped onto the measurement port to measure the absorbance.

[result]
FIG. 2 is a graph showing the absorbance of each liquid Q1 to Q4. According to FIG. 2, the liquid Q4, which is water (ultrapure water), has extremely low absorbance with respect to light having a wavelength in a wide band of 240 nm to 430 nm, including the vicinity of 254 nm, which is the main peak wavelength of a low-pressure mercury lamp, that is, It can be seen that it shows high transmittance.

It can be seen that liquid Q1, which is a liquid fertilizer, has high absorbance for light having a wavelength of 254 nm, which is the main peak wavelength of a low-pressure mercury lamp, while has low absorbance for light having a wavelength in the range of 370 nm or more and 430 nm or less. Specifically, the liquid Q1 has an absorbance of 2.8 (au) for light having a wavelength of 254 nm, and an average absorbance of 0.2 (au. U.) for light having a wavelength in the range of 370 nm or more and 430 nm or less. ) About. That is, the liquid Q1 transmits light having a wavelength in the range of 370 nm or more and 430 nm or less about 14 to 15 times as much as light having a wavelength of 254 nm. In other words, it can be seen that the liquid Q1 which is a liquid fertilizer absorbs a large amount of ultraviolet light in the vicinity of 254 nm, which is the main peak wavelength of the low-pressure mercury lamp, and generally transmits ultraviolet light in the range of 370 nm or more and 430 nm or less.

From the results shown in FIG. 2, when the liquid fertilizer is irradiated with ultraviolet light near 254 nm, the amount absorbed by the liquid fertilizer is high. It is expected that the ultraviolet light will be absorbed and the ultraviolet light will not travel over a wide area in the storage tank. In other words, when sterilizing liquid fertilizer using ultraviolet light in such a wavelength band, the depth of the storage tank should be extremely shallow or at a high flow velocity in order to irradiate the entire liquid fertilizer with ultraviolet light. It is hypothesized that it is necessary to irradiate ultraviolet light while moving and stirring liquid fertilizer.

<Verification 2>
The degree of fluctuation in the amount of iron (II) ions contained in the liquid fertilizer when the liquid fertilizer was irradiated with ultraviolet light of different wavelengths was compared. Specifically, when liquid Q2, which is a liquid fertilizer diluted to 1/10, is used and the liquid Q2 is irradiated with ultraviolet light having a main emission wavelength of 405 nm (Example 1), the main emission wavelength The degree of fluctuation in the amount of iron (II) ions before and after irradiation with ultraviolet light was compared for both cases of irradiation with ultraviolet light of 254 nm (Comparative Example 1).

[Used light source]
FIG. 3 is a graph showing the spectrum of ultraviolet light used in Example 1. As the light source of Example 1, an LED irradiator having a wavelength of 405 nm (UniFiled SF150, manufactured by Ushio, Inc.) was used.

Further, as Comparative Example 1, among the ultraviolet light emitted from the low-pressure mercury lamp, the ultraviolet light obtained by passing through a filter that blocks ultraviolet light of 300 nm or more is used, so that only the wavelength in the vicinity of 254 nm is substantially emitted. Ultraviolet light, which appears as spectral intensity, was used.

[Measuring method]
The liquid Q2 was housed in a petri dish of φ30, and the iron (II) ion content concentration before irradiation was measured by a digital pack test (manufactured by Kyoritsu Rikagaku Kenkyusho Co., Ltd.). Next, from an irradiation distance of 50 mm, ultraviolet light emitted from each of the light sources of Example 1 and Comparative Example 1 was irradiated, and the concentration of iron (II) ions after irradiation was measured by the same method. The above measurement was performed a plurality of times with different exposure amounts.

[result]
FIG. 4 is a graph showing the relationship between the exposure amount of the irradiated ultraviolet light and the decrease amount of iron (II) ions contained in the liquid Q2 in each of Example 1 and Comparative Example 1. The amount of decrease in iron (II) ions is the ratio of the amount of iron (II) ions contained in the liquid Q2 after irradiation to the amount of iron (II) ions contained in the liquid Q2 before irradiation. Calculated by value.

According to FIG. 4, in both Example 1 and Comparative Example 1, it is confirmed that the amount of iron (II) ions contained in the liquid Q2 decreases as the exposure amount (irradiation dose) increases. ..

More specifically, when compared with the amount of exposure required for the amount of decrease in iron (II) ion concentration to reach −0.95 (Log), it is 1.8 J / cm for ultraviolet light having a wavelength of 254 nm (Comparative Example 1). ^In ^{contrast to 2,} it was 2160 J / cm 2 in ultraviolet light having a wavelength of 405 nm (Example 1). From this, it is said that the degree of decrease in the iron (II) ion concentration associated with the irradiation of the liquid fertilizer with ultraviolet light having a wavelength of 405 nm is about 1/1200 with respect to the ultraviolet light having a wavelength of 254 nm. Estimated. That is, it can be seen that when the liquid fertilizer is irradiated with ultraviolet light having a wavelength of 405 nm, the amount of decrease in the iron (II) ion concentration is significantly smaller than that when the liquid fertilizer is irradiated with ultraviolet light having a wavelength of 254 nm at the same exposure amount. ..

As a result of the verification 1, as shown in FIG. 2, the liquid Q3 composed of the aqueous chelated iron solution has high absorbance for ultraviolet light in the wavelength band of 240 nm to 280 nm, and has high absorbance for ultraviolet light in the wavelength band of 370 nm to 430 nm. Consistent with low absorbance results.

The reason why the liquid Q2 diluted to 1/10 was adopted instead of the liquid Q1 which is the liquid fertilizer itself in the verification 2 is as follows. As described above with reference to FIG. 2, in the case of liquid Q1, it hardly transmits ultraviolet light of 254 nm in the first place. Therefore, even if the liquid Q1 is irradiated with the ultraviolet light (254 nm) of Comparative Example 1, most of the ultraviolet light is absorbed on the surface thereof, and as a result, under the same conditions as the ultraviolet light (405 nm) of Example 1. , Due to the inability to compare the degree of decrease in iron (II) ion concentration.

<Verification 3>
The point that the sterilization performance can be realized even by the ultraviolet light having a wavelength of 405 nm was verified below.

[Used light source]
The same light source as in Example 1 of Verification 2 was used.

[Measuring method]
The liquid Q1 (liquid manure), the bacterial solution 3mL of Staphylococcus aureus (NBRC.12732), was added to a 10 ⁷ CFU / mL. This liquid was housed in a petri dish of φ30 and irradiated with the light source of Example 1 from an irradiation distance of 50 mm. The illuminance on the irradiated surface at this time was 150 mW / cm ² . This illuminance value was measured with an ultraviolet integrated light meter (UIT-250 / UVD-S405 manufactured by Ushio, Inc.).

The exposure amount was adjusted by changing the time during which the ultraviolet light from the light source was irradiated, and the degree of decrease in the amount of Staphylococcus aureus contained in the liquid Q1 was compared before and after the irradiation. The amount of Staphylococcus aureus after being irradiated with ultraviolet light was measured by smearing it on a standard agar medium, culturing at 37 ° C. for 48 hours, and then counting the generated colonies.

[result]
FIG. 5 is a graph showing the relationship between the exposure amount of ultraviolet light emitted from the light source of Example 1 and the decrease amount of the content of Staphylococcus aureus contained in the liquid Q2. The "inactivation rate" on the vertical axis is calculated by the Log value of the content of Staphylococcus aureus contained in the liquid Q1 after irradiation with respect to the content of Staphylococcus aureus contained in the liquid Q1 before irradiation. It was.

According to the results of FIG. 5, ^{it can be seen that when ultraviolet light having a wavelength of 405 nm is irradiated with an exposure amount of 50 J / cm 2} , Staphylococcus aureus contained in the liquid Q1 can be reduced to about 1/10. Furthermore, by setting the exposure amount to 100 J / cm ² , the Staphylococcus aureus contained in the liquid Q1 can be reduced to almost 1/100, ^{and by setting the exposure amount to 280 J / cm 2} , it is contained in the liquid Q1. It can be seen that the amount of Staphylococcus aureus can be reduced to almost 1/10000. That is, it can be seen that the bactericidal effect is exhibited by irradiating with ultraviolet light having a wavelength of 405 nm. It is considered that the reason for this is that, as described above in Verification 1, the ultraviolet light having a wavelength of 405 nm exhibits the property of transmitting through the liquid fertilizer, so that the ultraviolet light travels throughout the liquid fertilizer.

In this verification 3, ultraviolet light having a wavelength of 254 nm (Comparative Example 2) is not used because the ultraviolet light in this wavelength band does not pass through the liquid fertilizer in the first place, so that it has a sufficient bactericidal action over the entire liquid fertilizer. This is because it is not possible to show.

<Summary of verification>
From the above verification, it can be seen that the ultraviolet light having a wavelength of 405 nm can realize a bactericidal action on the liquid fertilizer while suppressing the decrease of iron (II) ions contained in the liquid fertilizer. From the results of FIG. 2, it can be seen that the absorbance of the liquid fertilizer (Q1) is low even for ultraviolet light in the wavelength band of 370 nm or more and 430 nm or less, as in the case of the wavelength of 405 nm. In addition, porphyrins show high absorbance for ultraviolet light in the wavelength band. Therefore, it can be seen that the same effect can be achieved by ultraviolet light having a main emission wavelength in the range of 370 nm or more and 430 nm or less.

However, in view of the absorbance of ultraviolet light for porphyrins, the main emission wavelength of ultraviolet light used for sterilizing liquid fertilizers is more preferably 390 nm or more and 410 nm or less.

As described above, the light source unit 4 is composed of the LED light source 4a that emits the ultraviolet light L1 having a main emission wavelength of 370 nm or more and 430 nm or less, so that the ultraviolet light L1 is contained in the storage tank 2. It proceeds through the stored liquid fertilizer 3. Therefore, it is not always necessary to install the light source unit 4 in the liquid fertilizer 3, and as shown in FIG. 1, the light source unit 4 can be installed at a position away from the liquid fertilizer 3. In this case, the waterproof design for the light source unit 4 is not always necessary.

Note that filters may be installed at the storage tank 2, the cultivation tank 6, the pipes (5a, 5b), the inlet or the outlet of the pump 7, and the like.

[Another system configuration example]
The mode of utilizing the liquid fertilizer sterilization method according to the present invention is not limited to the system as shown in FIG. Hereinafter, another system configuration example will be described.

<1> As shown in FIG. 6, the liquid fertilizer 3 may be sterilized in a sterilization treatment tank 9 provided separately from the storage tank 2. The sterilization treatment tank 9 has a light source unit 4 arranged inside a mantle tube designed to be waterproof. The liquid fertilizer 3 stored in the storage tank 2 is sent to the sterilization treatment tank 9 by the pump 7 via the pipe 5a. The liquid fertilizer 3 is sterilized by the ultraviolet light L1 emitted from the light source unit 4 arranged in the sterilization tank 9. The sterilized liquid fertilizer 3 is sent to the cultivation tank 6 via the pipe 5c. Further, the liquid fertilizer 3 that has remained in the cultivation tank 6 for a certain period of time is sent to the storage tank 2 via the pipe 5b.

The inside of the sterilization treatment tank 9 may be completely filled with the liquid fertilizer 3, or the liquid level of the liquid fertilizer 3 may be accommodated in a state of being in contact with the atmosphere.

<2> As shown in FIG. 7, the plant growing system 1 may include a plurality of storage tanks 2 (2a, 2b) in which the light source unit 4 is built. In this case, it is possible to supply the liquid fertilizer 3 which has already been sterilized in advance to the cultivation tank 6 while performing the sterilization treatment on the liquid fertilizer 3. In the example shown in FIG. 7, the pipe 5b and the pipe 5d are connected via the check valve 11, and the pipe 5a and the pipe 5c are connected via the check valve 12.

An example of a specific processing method will be explained. First, as shown in FIG. 8A, the sterilized liquid fertilizer 3 is supplied to the cultivation tank 6 via the pipe 5a from the storage tank 2a in which the liquid fertilizer 3 that has already been sterilized is stored. To. At this time, the liquid fertilizer 3 kept in the cultivation tank 6 for a certain period of time is sent out to the storage tank 2a through the pipe 5b. In FIG. 8A, the flow of the liquid fertilizer 3 at this time is illustrated by the broken line arrow d1.

During the period T1 in which the liquid fertilizer 3 is flowing between the storage tank 2a and the cultivation tank 6, in the storage tank 2b, the ultraviolet light L1 from the light source unit 4 is emitted to the stored liquid fertilizer 3. The sterilization process is performed by being irradiated. During this period T1, the light source unit 4 in the storage tank 2a may be turned off, may be turned on with the same output as during the sterilization process, or may be turned on in a dimmed state. You can leave it.

Next, after a certain period of time has passed, as shown in FIG. 8B, the cultivation tank 6 is sterilized from the storage tank 2b in which the liquid fertilizer 3 that has already been sterilized is stored, via the pipe 5c. The treated liquid fertilizer 3 is supplied. At this time, the liquid fertilizer 3 kept in the cultivation tank 6 for the above period is sent out to the storage tank 2b through the pipe 5d. In FIG. 8B, the flow of the liquid fertilizer 3 at this time is illustrated by the broken line arrow d2.

During the period T2 in which the liquid fertilizer 3 is flowing between the storage tank 2b and the cultivation tank 6, in the storage tank 2a, the ultraviolet light L1 from the light source unit 4 is emitted to the stored liquid fertilizer 3. The sterilization process is performed by being irradiated. During this period T2, the light source unit 4 in the storage tank 2b may be turned off, may be turned on with the same output as during the sterilization process, or may be turned on in a dimmed state. You can leave it.

Hereafter, the same process is repeatedly executed. As a result, the fully sterilized liquid fertilizer 3 can be continuously supplied to the cultivation tank 6.

<3> As shown in FIG. 9, the sterilization light source unit 4 may be arranged in the liquid of the liquid fertilizer 3 stored in the storage tank 2. In this case, the light source unit 4 may be arranged in the mantle tube designed to be waterproof, as in the configuration described above with reference to FIG.

<4> In the above-described embodiment, the light source unit 4 includes a plurality of LED light sources 4a. However, the structure of the light source unit 4 is not limited as long as it has a configuration capable of emitting ultraviolet light L1 whose main emission wavelength is in the range of 370 nm or more and 430 nm or less. However, from the viewpoint of irradiating the stored liquid fertilizer 3 with light having a spread in the surface direction, it is preferable to use a surface light source.

1: Plant growing system 2: Storage tank 2a: Storage tank 2b: Storage tank 3: Liquid fertilizer 4: Light source 4a: LED light source 5a: Piping 5b: Piping 5c: Piping 5d: Piping 6: Cultivation tank 7: Pump 9: Sterilization treatment tank 10: Plant 11: Check valve 12: Check valve L1: Ultraviolet light

Claims

It is a method of sterilizing liquid fertilizer.
The liquid fertilizer contains at least metal ions containing iron, and the liquid fertilizer contains at least iron-containing metal ions.
A sterilization method comprising the step (a) of irradiating the liquid fertilizer with ultraviolet light having a main emission wavelength in the range of 370 nm or more and 430 nm or less.
The sterilization method according to claim 1, wherein the metal ion is an iron (II) ion.
The sterilization method according to claim 1 or 2, wherein the step (a) is a step of irradiating the ultraviolet light from a light source made of an LED.
The sterilization method according to any one of claims 1 to 3, wherein the ultraviolet light has a main emission wavelength of 405 nm.
It is characterized by having a step (b) of supplying the liquid fertilizer after being irradiated with the ultraviolet light by the step (a) to a growing region of a plant grown using the liquid fertilizer through a pipe. The sterilization method according to any one of claims 1 to 4.
It has a step (c) of sending out the liquid fertilizer from the growing area through a pipe to the area irradiated with the ultraviolet light.
The sterilization method according to claim 5, wherein the step (a), the step (b), and the step (c) are repeatedly executed.
Any one of claims 1 to 6, wherein the step (a) is a step of irradiating the liquid fertilizer with the ultraviolet light from the outside of the region in which the liquid fertilizer is stored. The sterilization method described in the section.