Method and device for sterilizing crops with electric discharge

Abstract

To provide a discharge sterilization method capable of securing safety for workers who perform a sterilization work easily, preventing reduction of a commercial value of fruits being a sterilization object and achieving sufficient sterilization processing, without complicating and increasing a size of a structure of a sterilization device.SOLUTION: At least one of first and second electrodes 11, 13 which face each other sandwiching a space 25 on which sterilization objects 20 such as fruits are arranged, therebetween, is covered with a solid dielectric 12, and a pulse or AC voltage is applied to a space between electrodes 11, 13 by a power source 14. By generating barrier discharge, energy generated by discharge is radiated to the vicinity of a sterilization object region 20a, thereby acquiring a sterilization effect. Since ozone with high density is not generated, safety for workers can be easily secured. A plurality of needle-shaped protrusions are arranged on the first electrode 11, for promoting local electric field concentration and achieving induction of discharge even at a relatively low voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for discharge sterilization of crops. [Background technology]

[0002] It has been known that in fruits such as citrus fruits, stem rot occurs in the fruit after harvest due to the influence of fungi that invade the stems and other parts of the fruit during the growing period. Therefore, in order to prevent stem rot in fruits, it is generally assumed that a chemical agent is used to disinfect the fruit.

[0003] On the other hand, Patent Document 1 shows an ozone generator that can be used for sterilizing drinking water, as an air purifier, a deodorizer, etc. Specifically, it shows a technology for configuring an ozone generator that generates high-concentration ozone by discharging between multiple electrodes and that can be made compact, requires low voltage, and is versatile.

[0004] Patent Document 2 shows a method for sterilizing an item contained in a sealed container. Specifically, the packaging container in which the item to be treated is sealed is brought into close contact with an electrode, and a silent discharge is generated in the packaging by a high AC voltage to eliminate leaking ozone.

[0005] Patent Document 3 shows a sterilization device using barrier discharge, in which the surface of the object to be sterilized is wetted with water or hydrogen peroxide, and then a high voltage is applied between the electrodes to perform the sterilization process, thereby promoting the generation of OH radicals and improving the sterilization effect. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-35855 A [Patent Document 2] JP 2004-209188 A [Patent Document 3] JP 2006-239230 A Summary of the Invention [Problem to be solved by the invention]

[0007] The ozone generator described in Patent Document 1 generates high-concentration ozone, which is expected to have a strong bactericidal and sterilizing effect against various bacteria. Therefore, it is thought that it can also be used to sterilize crops such as fruits and vegetables.

[0008] However, high-concentration ozone is a harmful substance that may adversely affect the human body. Therefore, when using an ozone generator to sterilize crops such as fruits and vegetables, it is necessary to devise a structure for the sterilization device so that workers and other humans do not come into contact with high-concentration OH radicals or ozone, which may lead to a complex and large structure and an increase in the cost of the device.

[0009] In addition, although Patent Document 2 and Patent Document 3 can reduce the generation of ozone, they do not assume the case where an operator sterilizes crops such as fruits. Crops are relatively large objects and vary in size and shape. Furthermore, if the entire crop is sterilized, there is a risk that even parts that do not need sterilization will be sterilized, resulting in a decrease in quality and commercial value. In other words, there is a concern that damage such as surface disorders will occur in the fruit. In addition, promoting the generation of OH radicals as in Patent Document 3 is harmful to the human body.

[0010] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a method and apparatus for discharge sterilization of crops which facilitates ensuring the safety of workers engaged in sterilization work without complicating the structure or increasing the size of the sterilization apparatus, and which is capable of sufficient sterilization treatment while preventing a decrease in the commercial value of the fruits, etc. to be sterilized. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the discharge sterilization method and the discharge sterilization device according to the present invention comprise the following features (1) to ( 4 ) is its feature. (1) A first electrode on a high potential side and a flat second electrode on a low potential side are arranged in a state in which they face each other with a predetermined space therebetween, The first electrode includes a flat plate portion and a plurality of needle-shaped portions protruding from a surface of the flat plate portion facing the second electrode toward the second electrode. 、 covering a surface of the second electrode with a dielectric; Placing a predetermined crop in the space; applying a pulsed voltage or an AC voltage between the first electrode and the second electrode for at least a predetermined time using a predetermined power source to generate discharge plasma, thereby sterilizing the crop; The size of the second electrode is sufficiently larger than the flat portion of the first electrode. Ku , The size of the flat portion of the first electrode is smaller than the overall size of a single crop to be sterilized and is equal to or smaller than the size of an area to be sterilized within the crop; After positioning the area of ​​the plant to be sterilized facing the first electrode, Applying a voltage between the first electrode and the second electrode; A method for sterilizing crops using electrical discharges.

[0012] According to the discharge sterilization method for crops according to the above procedure (1), 2 Since the voltage is applied from the power source while the electrodes are covered with a dielectric, the dielectric, which is an insulator, prevents electric charge from flowing into the electrodes, and no large current flows. Therefore, a barrier discharge, which is a type of discharge plasma, occurs between the first and second electrodes. In the case of a barrier discharge in the air, only a small amount of harmful ozone is generated, and localized discharge energy is generated by the plasma at the discharge point. This discharge energy is irradiated onto the crops placed in the space, and the sterilization process is carried out. In addition, since the discharge energy can be irradiated locally onto the crops, it is possible to sterilize not only the surface but also the inside of the crops. In addition, since high concentrations of ozone are not generated, it is easier to ensure the safety of workers. Furthermore, according to the discharge sterilization method for crops in the above procedure (1), since a plurality of needle-shaped parts are formed on the surface of the flat part of the first electrode facing the second electrode, when a voltage is applied, an electric field is locally concentrated near the first electrode, making it easier to induce a discharge. Therefore, a discharge can be generated even at a relatively low voltage. As a result, an effective sterilization process can be performed without using a large power source. In addition, since the discharge generation is sparse, only a small amount of harmful ozone is generated, making it easier to ensure the safety of workers.

[0014] Furthermore, the above( 1 According to the discharge sterilization method for crops in the procedure of step 1), the first electrode is relatively small, and the area of ​​the crop to be sterilized is positioned facing the first electrode, so that the sterilization treatment can be limited to only the parts of the crop that require sterilization. This makes it possible to prevent the energy from the discharge from being irradiated to parts that do not require sterilization, thereby preventing the quality and commercial value of the crop from being reduced. 1 Because the electrodes are small, discharge can be generated even at a relatively low voltage. As a result, effective sterilization can be performed without using a large power source. In addition, because the first electrode is small, only a small amount of harmful ozone is generated, making it easier to ensure the safety of workers.

[0017] ( 2 ) applying a voltage between the first electrode and the second electrode while the second electrode is connected to earth; The above (1) characterized by the above To The method for sterilizing crops using discharges is described below.

[0018] the above( 2 According to the discharge sterilization method for crops having the procedure of ), even when a relatively large crop is sterilized, the entire area of ​​the crop can be supported by the second electrode. Furthermore, even if the position of the first electrode is moved to match the area of ​​the crop to be sterilized, the first electrode and the second electrode can be maintained facing each other. Furthermore, since the voltage is applied with the second electrode connected to earth, it is easy to prevent electric shock to the worker even when a high voltage is used.

[0019] (3 ) placing a harvested fruit as a crop to be sterilized between the first electrode and the second electrode, and placing the vicinity of the axis of the fruit facing the first electrode; Applying a voltage between the first electrode and the second electrode; The above (1) to ( 2 ) The method for sterilizing crops using electric discharges according to any one of the preceding claims.

[0020] the above( 3 According to the discharge sterilization method for crops using the procedure above, even if bacteria have invaded harvested fruit, they can be sterilized by irradiating them with energy from a localized discharge caused by a barrier discharge, thereby preventing the occurrence of diseases such as stem rot and making it possible to maintain the commercial value of the fruit for a long period of time.

[0021] ( 4 a first electrode on a high potential side and a flat plate-shaped second electrode on a low potential side, which are arranged to face each other with a predetermined space between them; a power source that generates a discharge plasma between the first electrode and the second electrode, The first electrode includes a flat plate portion and a plurality of needle-shaped portions protruding from a surface of the flat plate portion facing the second electrode toward the second electrode. 、 the surface of the second electrode is covered with a dielectric; the power source applies a pulsed voltage or an AC voltage between the first electrode and the second electrode for at least a predetermined time to generate discharge plasma, thereby sterilizing a predetermined crop placed in the space; The size of the second electrode is sufficiently larger than the flat portion of the first electrode. Ku , The size of the flat portion of the first electrode is smaller than the entire size of a single crop to be sterilized and is equal to or smaller than the size of an area to be sterilized within the crop; The area of ​​the crop to be sterilized is positioned opposite the first electrode. A discharge sterilization device for crops.

[0022] the above( 4 According to the discharge sterilization device having the above configuration, 2Since the electrode is covered with a dielectric material when voltage is applied from the power source, the dielectric material, which is an insulator, prevents charge from flowing into the electrode, and no large current flows. Therefore, a barrier discharge, a type of discharge plasma, occurs between the first and second electrodes. In the case of a barrier discharge, only a small amount of harmful ozone is generated, and localized discharge energy is generated by the plasma at the discharge point. This discharge energy is irradiated onto the crops placed in the space, and the sterilization process is carried out. In addition, since the discharge energy can be irradiated locally onto the crops, it is possible to sterilize not only the surface but also the inside of the crops. In addition, since high concentrations of ozone are not generated, it is easier to ensure the safety of workers. Effect of the Invention

[0023] The discharge sterilization method and discharge sterilization device for crops of the present invention facilitates ensuring the safety of workers engaged in sterilization work without complicating the structure or increasing the size of the sterilization device, and enables sufficient sterilization treatment while preventing a decrease in the commercial value of the fruits and other products to be sterilized.

[0024] The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by reading the following description of the embodiment of the present invention (hereinafter, referred to as "embodiment") with reference to the accompanying drawings. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a block diagram showing the fundamental configuration and usage state of a discharge sterilization device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a front view showing an example of the configuration of a first electrode formed in a needle shape. [Diagram 3] FIG. 3 is a graph showing experimental results in comparison between cases where the method of the present invention was carried out and cases where the method was not carried out. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Specific embodiments of the present invention will be described below with reference to the accompanying drawings. <Example of the fundamental configuration and usage of a discharge sterilization device> FIG. 1 shows the basic configuration and usage state of a discharge sterilization device 10 according to an embodiment of the present invention.

[0027] The discharge sterilization device 10 shown in Fig. 1 comprises a first electrode 11, a solid dielectric 12, a second electrode 13, a power source 14, etc. The first electrode 11 and the second electrode 13 are each formed as, for example, a metal plate having electrical conductivity, and the first electrode 11 and the second electrode 13 are arranged to face each other with a predetermined space 25 interposed therebetween. The periphery of the first electrode 11, particularly the lower surface facing the second electrode 13, is covered with a solid dielectric 12, i.e., an electrical insulator, to prevent the flow of electric charges.

[0028] The power supply 14 can output a high voltage pulse voltage or an AC voltage of, for example, about 15 kV. One output terminal 14a of the power supply 14 is electrically connected to the first electrode 11 via an electric cable 16, and the other output terminal 14b is connected to the earth 15. In addition, the second electrode 13 is connected to the earth 15 via an electric cable 17.

[0029] The space 25 between the first electrode 11 and the second electrode 13 is sufficiently large to accommodate the object to be sterilized 20, which is a crop such as fruit. When sterilizing the object to be sterilized 20, such as fruit, an operator or the like places the object to be sterilized 20 in the space 25 as shown in Fig. 1. The operator or the like then aligns the first electrode 11 and the area to be sterilized 20a so that they face each other.

[0030] The area and size of the second electrode 13 are formed to be sufficiently larger than the presumed size of the object to be sterilized 20. The area of ​​the first electrode 11 is approximately the same as the area to be sterilized 20a (sufficiently smaller than the entire object to be sterilized 20 and the second electrode 13), and the shape of the first electrode 11 is, for example, circular. The area to be sterilized 20a corresponds to the area around the stem or the stem of the fruit.

[0031] <Sterilization procedure> An operator places an object to be sterilized 20 in space 25 as shown in Fig. 1, and after determining the position of first electrode 11 and area to be sterilized 20a, starts up power supply 14 by operating the operator in the state shown in Fig. 1. As a result, a pulse voltage or AC voltage output by power supply 14 is applied between first electrode 11 and second electrode 13.

[0032] As a result, in an atmospheric pressure environment, a discharge occurs between the first electrode 11 and the second electrode 13. Here, because the first electrode 11 is covered with the solid dielectric 12, the flow of charges is prevented and no large current flows during the discharge. Therefore, a barrier discharge, which is a type of discharge plasma, occurs.

[0033] In addition, plasma is formed near the first electrode 11 due to the barrier discharge, and this plasma generates energy due to local discharge. In addition, the amount of ozone generated at this time is very small, so it does not affect the human body of the worker or the like. The energy due to the generated discharge is irradiated to the sterilization target area 20a of the sterilization target object 20 located at a position opposite the first electrode 11. This provides a sterilization effect. In particular, since the discharge sterilization device 10 can locally apply energy due to discharge, it can sterilize not only the surface but also the inside of the sterilization target area 20a. In addition, since the energy due to discharge is not irradiated to unnecessary parts other than the sterilization target area 20a opposite the first electrode 11, deterioration of the quality of fruits, etc. can be prevented.

[0034] In addition, since the first electrode 11 is formed to be relatively small and the second electrode 13 is connected to the earth 15, electric shock due to the high voltage output from the power source 14 is unlikely to occur. The sterilization process of the sterilization target area 20a is carried out, for example, continuously for a certain period of time or intermittently, and after the certain period of time has elapsed, the output of the power source 14 is shut off to terminate the discharge.

[0035] <Example of the configuration of the first electrode formed in a needle shape> An example of the configuration of the first electrode 11A formed in a needle shape is shown in Fig. 2. The first electrode 11A has needle-shaped parts 11a extending in the thickness direction on a thin metal base material. In other words, a large number of metal needles are arranged so as to protrude from the surface of the metal base material.

[0036] When the first electrode 11A in Fig. 2 is used as the first electrode 11 in Fig. 1, the tip side of the needle-shaped portion 11a is arranged to face the second electrode 13 and the object 20 to be sterilized. This makes it possible to promote electric field concentration in the vicinity of the needle-shaped portion 11a when the voltage output by the power source 14 is applied to the first electrode 11A. As a result, a state is created in which discharge is easily induced, so that discharge is possible even when the voltage output by the power source 14 is relatively low. Therefore, effective sterilization treatment is possible even when the power source 14 is made smaller.

[0037] On the other hand, the second electrode 13 is assumed to be made of a conductive metal material such as a copper plate, but the surface of the electrode may be covered with a dielectric. In order to prevent an operator from getting an electric shock, the second electrode 13 must be connected to the earth 15 before the power source 14 outputs a voltage.

[0038] When an operator manually sterilizes objects 20 to be sterilized, such as fruits, it is assumed that the second electrode 13 is placed on the housing of the device or on a table, and each object 20 to be sterilized is manually placed on the second electrode 13. The operator then operates a handle having suitable insulation properties to position the first electrode 11 together with the electric cable 16 so that it faces the area to be sterilized 20a, and turns on the start switch of the power source 14. The object 20 to be sterilized may be moved to align the first electrode 11 with the area to be sterilized 20a.

[0039] When sterilization of objects 20 to be sterilized, such as fruits, is performed automatically, it is assumed that a large number of objects 20 to be sterilized are sequentially sent onto the second electrode 13 using, for example, a conveyor belt or a robot. Then, for each object 20 to be sterilized, the object 20 to be sterilized or the first electrode 11 is moved to align the two, and then the supply of voltage from the power source 14 to the first electrode 11 and the second electrode 13 is started. After a certain time has elapsed, the supply of voltage is stopped and the object 20 to be sterilized is replaced with the next object.

[0040] <Explanation of Experimental Results> In order to confirm the effect of the discharge sterilization method of the present invention, an experiment was carried out under the following conditions. Condition of sterilization target 20: Harvested fruit 12 hours after inoculation of stem rot fungus into the stem Sterilization conditions: Frequency of AC voltage applied between electrodes 11 and 13: 10 [kHz] Applied voltage: 15[kVp-p] Sterilization time: 0.5[min] Conditions for observation of results: The state of the sterilization target 20 after sterilization treatment and the state of the non-sterilized sterilization target 20 were observed every day.

[0041] The results of this experiment are shown in Figure 3. In Figure 3, disease incidence data D1 shows the change in disease incidence over time for fruits that were not sterilized, and disease incidence data D2 shows the change in disease incidence over time for fruits that were sterilized under the above conditions. In Figure 3, the horizontal axis shows the number of days that have passed, and the vertical axis shows the disease incidence [%].

[0042] As shown as disease incidence data D1 in Fig. 3, for fruits that were not sterilized, the disease incidence reached 100% 8 days after inoculation with stem rot fungi. In contrast, as shown as disease incidence data D2 in Fig. 3, for fruits that were sterilized using the method of the present invention, no disease was observed 8 days after inoculation with stem rot fungi. In other words, it was confirmed that sterilizing fruits using the method of the present invention can effectively sterilize them, and therefore can prevent the onset of stem rot.

[0043] <Advantages of discharge sterilization method> By using the above-mentioned discharge sterilization method for crops for sterilization of fruits, the onset of stem rot can be effectively prevented as shown in Figure 3. In particular, since the discharge energy generated by the plasma can sterilize not only the surface but also the inside of the sterilization target 20, effective sterilization is possible.

[0044] Moreover, since sterilization is performed using barrier discharge, which generates little harmful ozone due to discharge, no special configuration is required to protect workers from ozone, and the size and cost of the sterilization device can be suppressed. Also, since only the sterilization target area 20a can be sterilized, it is possible to prevent the quality and commercial value of fruits and the like from decreasing due to the sterilization process.

[0045] Furthermore, by combining a first electrode 11 having a relatively small area with a second electrode 13 having a large area as shown in FIG. 1 and connecting the second electrode 13 to earth 15, it becomes easier to prevent electric shock and also easier to handle the object to be sterilized 20, such as by positioning it. 2, discharge can be initiated even at a relatively low voltage, facilitating miniaturization of the power source 14. Note that, instead of the multiple needle-shaped protrusions (needle-shaped portions 11a), multiple cylindrical protrusions made of a conductive solid or liquid material may be formed on the surface of the first electrode 11A.

[0046] Here, the features of the discharge sterilization method and the discharge sterilization device according to the above-mentioned embodiments of the present invention are briefly summarized and listed in the following [1] to [6]. [1] A first electrode (11) and a second electrode (13) are arranged to face each other with a predetermined space (25) therebetween, At least one surface of the first electrode and the second electrode is covered with a dielectric (solid dielectric 12); A predetermined crop (object to be sterilized 20) is placed in the space, applying a pulsed voltage or an AC voltage between the first electrode and the second electrode for at least a predetermined time using a predetermined power source (14) to generate discharge plasma, thereby sterilizing the crop. A method for sterilizing crops using electrical discharges.

[0047] [2] The size of the first electrode (11) is smaller than the overall size of the crop (object 20) to be sterilized and is equal to or smaller than the size of the area (20a) to be sterilized in the crop; After positioning the area of ​​the plant to be sterilized facing the first electrode, Applying a voltage between the first electrode and the second electrode; The method for discharge sterilization of crops according to the above [1].

[0048] [3] The first electrode (11A) has a surface on which a plurality of needle-shaped or cylindrical protrusions (needle-shaped portions 11a) made of a conductive solid material or liquid material are formed, the needle-shaped or cylindrical protrusions being arranged in a direction facing the crop. 3. The method for sterilizing crops using electrical discharges according to any one of [1] to [2] above.

[0049] [4] The second electrode is formed to be sufficiently larger than the first electrode; A voltage is applied between the first electrode and the second electrode while the second electrode is connected to earth (15). 4. The method for sterilizing crops using electrical discharges according to any one of [1] to [3] above.

[0050] [5] A harvested fruit is placed between the first electrode and the second electrode as a crop to be sterilized, and the vicinity of the axis of the fruit (the region to be sterilized 20a) is placed facing the first electrode; Applying a voltage between the first electrode and the second electrode; 5. The method for discharge sterilization of crops according to any one of [1] to [4] above.

[0051] [6] A first electrode (11) and a second electrode (13) arranged opposite each other with a predetermined space therebetween; a power source (14) for generating a discharge plasma between the first electrode and the second electrode; At least one surface of the first electrode and the second electrode is covered with a dielectric (solid dielectric 12), The power source applies a pulsed voltage or an AC voltage between the first electrode and the second electrode for at least a predetermined time to generate discharge plasma, and sterilizes a predetermined crop (a sterilization target 20) placed in the space. A discharge sterilization device for crops. [Explanation of symbols]

[0052] 10 Electric discharge sterilizer 11,11A 1st electrode 11a Needle-like part 12 Solid Dielectrics 13 Second electrode 14 Power supply 14a, 14b output terminals 15 Earth 16,17 Electrical cables 20 Sterilization objects 20a Sterilization target area 25 Space D1, D2 Incidence Data

Claims

1. A first electrode on a high potential side and a flat second electrode on a low potential side are disposed in a state of facing each other with a predetermined space therebetween; the first electrode includes a flat portion and a plurality of needle-shaped portions protruding from a surface of the flat portion facing the second electrode toward the second electrode, covering a surface of the second electrode with a dielectric; A predetermined crop is placed in the space; applying a pulsed voltage or an AC voltage between the first electrode and the second electrode for at least a predetermined time using a predetermined power source to generate discharge plasma, thereby sterilizing the crop; The size of the second electrode is sufficiently larger than the flat portion of the first electrode, The size of the flat portion of the first electrode is smaller than the entire size of a single crop to be sterilized and is equal to or smaller than the size of an area to be sterilized within the crop; After positioning the area of ​​the plant to be sterilized facing the first electrode, Applying a voltage between the first electrode and the second electrode; A method for sterilizing crops using electrical discharges.

2. A voltage is applied between the first electrode and the second electrode while the second electrode is connected to earth.

2. The method for sterilizing crops using electrical discharges according to claim 1.

3. A harvested fruit is placed between the first electrode and the second electrode as a crop to be sterilized, and the vicinity of the axis of the fruit is placed facing the first electrode; Applying a voltage between the first electrode and the second electrode; 3. The method for sterilizing crops using electrical discharges according to claim 1 or 2.

4. a first electrode on a high potential side and a flat plate-shaped second electrode on a low potential side, the first electrode and the second electrode being disposed opposite each other with a predetermined space therebetween; a power source that generates a discharge plasma between the first electrode and the second electrode, the first electrode includes a flat portion and a plurality of needle-shaped portions protruding from a surface of the flat portion facing the second electrode toward the second electrode, the surface of the second electrode is covered with a dielectric; the power source applies a pulsed voltage or an AC voltage between the first electrode and the second electrode for at least a predetermined time to generate discharge plasma, thereby sterilizing a predetermined crop placed in the space; The size of the second electrode is sufficiently larger than the flat portion of the first electrode, The size of the flat portion of the first electrode is smaller than the entire size of a single crop to be sterilized and is equal to or smaller than the size of an area to be sterilized within the crop; The area of ​​the crop to be sterilized is positioned opposite the first electrode. A discharge sterilization device for crops.

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