Sterilization device

Abstract

This invention provides a sterilization device that prevents blockage between electrodes even with small electrode clearances and low applied voltages, and is suitable for personal use. [Solution] A sterilization device comprising electrodes consisting of opposing cathodes and anodes immersed in stored water, and a power supply that applies a voltage between the cathodes and anodes, which sterilizes by anodic oxidation of chloride ions contained in stored water through electrolysis of the stored water and the production of hypochlorous acid, wherein the cathodes and anodes of the electrodes are formed in a plate shape, the cathodes and anodes of the electrodes are housed in a case having a lower opening and an upper opening, and the gap between the cathodes and anodes of the electrodes is 1 to 1.5 times the thickness of the electrode plates.

Description

Technical Field

[0001] The present invention relates to a sterilization device for sterilizing water stored in a water storage tank such as a humidifier, an ice maker, or a water supply tank.

Background Art

[0002] Tap water contains a certain amount of chlorine. However, it is known that while this tap water is being supplied and stored in a storage tank or a water tray, various bacteria multiply in the stored water. In devices that use tap water for water supply, such as the tanks and water trays of ultrasonic humidifiers, the chlorine in the tap water disappears over time due to ultraviolet decomposition, consumption by contact with organic substances, etc. Subsequently, various bacteria multiply, scatter into the air, and there is a risk of causing health damage to the human body.

[0003] In devices that use tap water for water supply, even if tap water is used, the chlorine escapes within 24 hours and general viable bacteria are included. Therefore, there has been a call for attention to always generate a new sterilizing component in the stored water for hygiene management.

[0004] Even if water containing general viable bacteria at a level of 100,000 / cc is taken into the human body, there is no problem with the physical condition. However, if harmful Escherichia coli, Legionella bacteria, or mold is included in the general viable bacteria, it will cause health damage. The more general viable bacteria there are, the more it is evidence that the bacteria are not being controlled, and the risk of the occurrence of harmful bacteria also increases. This is the basis of the concept of environmental safety.

[0005] Generally, as a cause of contamination of stored water, when the stored water comes into contact with the outside air, it is considered to be contaminated by bacteria floating in the space, and when the stored water comes into direct or indirect contact with human skin, the original bacteria present on human skin are considered. These bacteria grow explosively in water without sterilizing power.

[0006] To prevent bacterial contamination, the first thing to consider is to prevent bacteria from entering, that is, to design the storage tank so that it does not come into contact with the outside air. However, although this is theoretically possible, it is often difficult to implement because the operation is left to the user. Secondly, one option is to kill the bacteria that have already invaded, namely by using ultraviolet light. However, this requires irradiation for a certain period of time, areas in the shadow of the ultraviolet light will not be killed, and in some cases, there is a risk of triggering bacterial proliferation. Bacterial proliferation triggering is a phenomenon often seen when sterilization is incomplete, where surviving bacteria sense a threat to their survival and multiply explosively in an attempt to reproduce. Normally, bacteria that are stable at 50,000 / cc can rapidly increase several to tens of times, sometimes reaching 200,000 to 500,000 / cc. Thirdly, as a method to give water itself sterilizing properties, sterilization with ozonated water or hypochlorous acid water can be considered. However, ozone itself is harmful, and the concentration of hypochlorous acid water is limited to below a certain level in order to guarantee safety and sterilizing power.

[0007] Currently, the most effective and safe antibacterial technologies available are either continuously supplying hypochlorous acid water or, as proposed in Patent Document 1, generating hypochlorous acid by electrolysis using electrodes placed in stored water.

[0008] Patent Document 1 describes a drinking water sterilization device in which a pair of chlorine generating electrodes and a chloride ion concentration detection sensor are installed in the water reservoir of a vending machine, and an electrical conductivity measurement cell is installed in the water supply piping, and the amount of electricity supplied to the chlorine generating electrodes is controlled based on the detected chloride ion concentration and electrical conductivity values. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 3-293093 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] In so-called "electrolytic sterilization," which involves inserting electrolytic electrodes into stored water and applying current, as described in Reference 1, there was a problem in that the gap between the electrodes would become clogged due to the deposition of organic matter in the water, preventing the efficient generation of hypochlorous acid. Therefore, efforts have been made to increase the electrode clearance to reduce clogging by organic matter, but this required applying a large voltage between the electrodes, making it difficult to adopt in personal-use devices.

[0011] This invention has been made in view of the aforementioned conventional problems, and aims to provide a sterilization device that can prevent blockage between electrodes even when the electrode clearance is small and the applied voltage is low, and that can also be used for personal use. [Means for solving the problem]

[0012] The present invention, as a means for solving the aforementioned problems, (1) Electrodes consisting of opposing cathodes and anodes immersed in stored water, The system includes a power supply that applies a voltage between the cathode and the anode, In a sterilization device that sterilizes by anodic oxidation of chloride ions contained in the stored water through electrolysis of the stored water and uses hypochlorous acid to produce sterilization, The cathode and anode of the electrode are formed in a plate shape. The cathode and anode of the electrode are housed in a case having a lower opening and an upper opening. The gap between the cathode and anode of the electrode is 1 to 1.5 times the thickness of the electrode plate.

[0013] According to the above means (1), the cathode and anode of the electrodes are plate-shaped and housed in a case having a lower opening and an upper opening. As a result, an upward flow of stored water is generated by bubbles between the electrodes, and circulation of stored water by convection, with water flowing in from the lower opening and flowing out from the upper opening, is promoted. The upward flow of stored water between the electrodes causes the precipitates generated on the electrodes to flow, preventing blockage by precipitates between the electrodes. Furthermore, since the gap between the cathode and anode is 1 to 1.5 times the thickness of the electrode plates, the applied voltage between the electrodes can be kept low.

[0014] (2) In means (1) above the electrode, there is an inclined portion that is inclined with respect to the surface of the electrode and promotes convection of the stored water due to the rise of bubbles generated between the cathode and anode of the electrode. According to the means (2) described above, the upward flow of stored water generated between the electrodes flows out to the outside of the case from the upper opening along the inclined portion, thereby promoting convection of the stored water.

[0015] (3) In means (1) or (2), a tray is provided below the electrode to receive deposits falling from the electrode. According to the means (3) described above, even if the precipitates formed on the electrodes peel off and fall off due to drying caused by electrode exposure or when they are submerged in water again and energized, they will be caught in the tray, thus preventing them from falling into the storage tank and being mixed with the water and delivered to the destination.

[0016] (4) In the means (3) above, ribs are provided on the upper surface of the receiving tray parallel to the electrodes. According to the means (3) described above, since the receiving tray is provided with ribs, it is possible to prevent the precipitates accumulated in the receiving tray from being stirred up by the stored water flowing in from the lower opening of the case.

[0017] (5) In any of the means (1) to (4) above, a water level sensor for detecting a predetermined water level of the stored water, The system further includes a control unit that controls the voltage applied between the cathode and the anode according to the water level detected by the water level sensor. According to the means (5) described above, when the water level reaches a point where the electrodes are exposed, the voltage applied between the cathode and anode can be controlled to suppress an increase in the electrode current value and a rise in temperature.

[0018] (6) In means (5), the control unit applies a positive voltage between the cathode and the anode for a first predetermined time, applies a reverse voltage for a second predetermined time, and then repeats a cycle in which no voltage is applied for a third predetermined time. According to the said means (6), after applying a positive voltage between the cathode and the anode for a first predetermined time, and then applying a reverse voltage for a second predetermined time, the electrode surface is cleaned, the adhesion of deposits such as calcium and potassium contained in the stored water between the cathode and the anode is suppressed, and the electrolysis efficiency can be maintained.

[0019] (7) In the said means (5), when the water level drops below the predetermined water level detected by the said water level sensor, the control unit restricts the current flowing between the cathode and the anode to a predetermined current value lower than the current value before detecting the said predetermined water level. According to the said means (7), when the water level drops to a level where the electrodes are exposed, the current is restricted to a low current value, so that an increase in the current value and a temperature rise of the electrodes can be suppressed.

[0020] (8) In the said means (5), when the water level drops below the predetermined water level detected by the said water level sensor, the control unit stops the voltage applied between the cathode and the anode. According to the said means (8), when the water level drops to a level where the electrodes are exposed, the voltage applied between the cathode and the anode is stopped, so that a temperature rise of the electrodes can be suppressed.

[0021] (9) In the said means (5), when the current value exceeds a predetermined upper limit current value, the control unit reduces the voltage so that the value obtained by multiplying the voltage by the current value becomes constant. According to the said means (9), when the electrodes are exposed and the current value exceeds a predetermined upper limit current value, the voltage is reduced so that the value obtained by multiplying the voltage by the current value becomes constant, so that the current value can be kept within a specified current value. [Advantages of the Invention]

[0022] According to the present invention, even if the electrode clearance is small and the applied voltage is low, a sterilization device that can prevent blockage between electrodes and can be applied to personal use can be provided [Brief Description of the Drawings]

[0023] [Figure 1] A diagram showing the configuration of a sterilization apparatus according to an embodiment of the present invention. [Figure 2] Figure 1 is a perspective view of the electrode section of the sterilization device. [Figure 3] Figure 2 shows an exploded perspective view of the electrode section. [Figure 4] Figure 2 shows a longitudinal cross-sectional view of the electrode section. [Figure 5] Figure 4 shows a cross-sectional view along the VV line. [Figure 6] Figure 5 shows a cross-sectional view along the line VI-VI. [Figure 7] A diagram showing the relationship between the electrode and the water level. [Figure 8] A diagram showing the voltage application pattern to the electrode. [Modes for carrying out the invention]

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0025] Figure 1 shows the configuration of a sterilization device 1 according to an embodiment of the present invention. The sterilization device 1 comprises a storage tank 2, an electrode unit 3, and a control unit 4.

[0026] The storage tank 2 has a suitable shape with a bottom, and its upper end is closed with a lid (not shown) that can be opened. A water supply pipe 6 with a water supply valve 5 is connected to the storage tank 2, and water is supplied from a water source (not shown) by a water supply pump 7, or tap water is supplied directly from a water pipe (not shown). A water distribution pipe 9 with a water distribution valve 8 is connected to the bottom of the storage tank 2, and water is distributed to a consumption destination (not shown). The storage tank 2 is provided with a water level sensor 10, such as a float type or proximity sensor, which detects a predetermined water level of the stored water (i.e., the full water level in this embodiment). The water level sensor 10 turns on when the stored water is above the full water level and turns off when it falls below the full water level. In addition to the water level sensor 10, at least another water level sensor may be provided that detects the water level at which the cathode plates 12a, 12b or anode plate 12c of the electrode section 3 (described later) are exposed from the stored water.

[0027] The electrode unit 3 is mounted on the inner surface of a lid (not shown) of the storage tank 2 so as to be immersed in the stored water. As shown in Figures 2 and 3, the electrode unit 3 comprises a case 11, an electrode plate 12, and a receiving tray 13.

[0028] Case 11 is a rectangular resin container having a front wall 11a, a rear wall 11b, a left side wall 11c, a right side wall 11d, and an upper wall 11e, with a lower opening 14 at its lower end and an electrode housing space 15 inside that communicates with the lower opening 14. The front wall 11a has a front opening 16 that communicates with the electrode housing space 15, and the rear wall 11b has a rear opening 17 that communicates with the electrode housing space 15. The inner surfaces of the left side wall 11c and the right side wall 11d have grooves 18 into which three electrode plates 12a, 12b, and 12c (described later) are fitted, and the outer surfaces have claw portions 19 that support the receiving tray 13 (described later). The upper wall 11e has two electrode mounting portions 20a and 20b. Positive and negative electrode terminals 21a and 21b are attached to each electrode mounting portion 20a and 20b. The upper ends of each electrode terminal 21a and 21b protrude upward from the upper surface of the electrode mounting portion 20, and the lower ends protrude from the inner surface of the upper wall 11e into the electrode housing space 15. As shown in Figure 4, an inclined portion 22 is formed on the inner surface of the upper wall 11e, which slopes diagonally upward toward the front opening 16.

[0029] The electrode plate 12 consists of two cathode plates 12a and 12b and one anode plate 12c. Each electrode plate 12 is made of a titanium plate coated with platinum, ruthenium, or an alloy of ruthenium and iridium. The cathode plates 12a and 12b are roughly T-shaped, with their vertical portions screwed to one of the negative electrode mounting portions 20a with bolts B and nuts N, and their horizontal portions extending toward the left wall 11c and the right wall 11d. The anode plate 12c is L-shaped, in the opposite direction to the cathode plates 12a and 12b, and is located between the two cathode plates 12a and 12b. Its vertical portion is screwed to the positive electrode mounting portion 20b with bolts B and nuts N, and its horizontal portion extends toward the left wall 11c and the right wall 11d. The ends of the horizontal sections of the two cathode plates 12a and 12b, and the ends of the horizontal section of the anode plate 12c, are engaged with the grooves 18 of the case 11.

[0030] The gap between electrodes in the electrode plate 12 is set to be 1 to 1.5 times the thickness of the electrode plate 12. If the gap between electrodes 12 is less than 1 times the thickness of the electrode plate 12, the generation of upward flow of stored water due to bubbles generated between electrodes is suppressed, and circulation of stored water by convection is not promoted. Also, if the gap between electrodes 12 exceeds 1.5 times the thickness of the electrode plate 12, a large voltage must be applied between electrodes, making it unsuitable for personal use equipment. In this embodiment, the thickness of the electrode plate 12 is 0.8 mm, and the gap between electrodes 12 is set to approximately 1 mm. The effective area of ​​each electrode plate 12 is 200 mm² on one side. 2 Front and back are preferred, and in the embodiment, the dimensions are 0.8 mm thick, 29 mm wide, and 8 mm high, but are not limited to these.

[0031] The tray 13 has a front wall 13a, a rear wall 13b, a left side wall 13c, a right side wall 13d, and a bottom wall 13e, and is a rectangular container the same size as the case 11 so as to be able to cover the lower opening 14 of the case 11 from below. The left side wall 13c and the right side wall 13d of the tray 13 have projections 24 formed therein, each having an engagement hole 23 that engages with the claw portion 19 of the case 11. The projections 24 have stepped portions 25 that abut against the edge of the lower opening 14 of the case 11. When the tray 13 is attached to the case 11, the stepped portions 25 abut against the edge of the lower opening 14 of the case 11 so that an inlet 21 communicating with the electrode housing space 15 is formed between the upper end of the tray 13 and the lower end of the case 11. On the upper surface of the bottom wall 13e of the tray 13, ribs 27 are provided below the two cathode plates 12a and 13b, parallel to the cathode plates 12a and 13b.

[0032] As shown in Figure 1, the control unit 4 is provided between the electrode unit 3 and the DC power supply 28 that applies voltage to the electrode unit 3. If there is a water supply pump 7, the control unit 4 adjusts the water level by turning the water supply pump 7 on and off based on the detected water level detected by the water level sensor 10. It also switches the positive and negative voltage applied to the electrode unit 3 and controls the current flowing through the electrode unit 3 based on the detected water level detected by the water level sensor 10, thereby controlling or turning on the voltage applied to the electrode unit 3.

[0033] Next, the operation of the sterilization device 1, which has the above configuration, will be described.

[0034] With water to be sterilized (tap water) stored in the storage tank 2 and the electrode plates 12 of the electrode unit 3 immersed in the water, a DC voltage of 6 to 24V is applied from the DC power supply 28 via the control unit 4 between the cathode plates 12a and 12b and the anode plate 12c of the electrode unit 3. The stored water is electrolyzed by a voltage applied between the cathode plates 12a and 12b and the anode plate 12c of the electrode section 12. Hydrogen is produced at the cathode, oxygen is produced at the anode, and chlorine gas is generated from chloride ions in the stored water. This chlorine gas then reacts with H2O to produce hypochlorous acid (HOCl) and hydrochloric acid (HCl). The generated hypochlorous acid (HOCl) allows the stored water to maintain its bactericidal properties. The energizing voltage and energizing time are set according to the capacity of the storage tank 2 and the number of bacteria present.

[0035] While a voltage is applied between the cathode plates 12a, 12b and the anode plate 12c of the electrode section 3, the hydrogen generated at the cathode plates 12a, 12b and the oxygen generated at the anode plate 12c rise as bubbles, causing an upward flow in the water stored between the cathode plates 12a, 12b and the anode plate 12c. This upward flow of water causes convection to occur, where the water stored between the cathode plates 12a, 12b and the anode plate 12c flows out of the case 11 through the inclined section 22 of the case 11 and the front opening 16 of the case 11, moves downward within the storage tank 2, enters the electrode housing space 15 through the inlet 26 between the upper end of the receiving tray 13 and the lower end of the case 11, and returns to the space between the cathode plates 12a, 12b and the anode plate 12c. Due to this convection of the stored water, the hypochlorous acid (HOCl) generated between the cathode plates 12a and 12b and the anode plate 12c spreads throughout the stored water in the storage tank 2, and the distributed stored water contains hypochlorous acid (HOCl), becoming highly disinfectant water.

[0036] In the sterilization apparatus 1 of this embodiment, the cathode plates 12a, 12b and anode plate 12c of the electrode section 3 are plate-shaped and housed in a case 11 having a lower opening 14 and an upper front opening 16. As a result, an upward flow of stored water is generated by bubbles between the electrodes, and circulation by convection of the stored water flowing in from the lower opening 14 and flowing out from the upper front opening 16 is promoted. The upward flow of stored water between the electrodes causes the precipitates generated on the electrodes to flow, preventing blockage by precipitates between the electrodes. Furthermore, since the gap between the cathode plates 12a, 12b and the anode plate 12c is 1 to 1.5 times the thickness of the electrode plates, the applied voltage between the electrodes can be kept low.

[0037] Furthermore, the upward flow of stored water generated between the electrodes flows out of the case 11 through the upper opening 14 along the inclined section 22, thereby promoting convection of the stored water.

[0038] Furthermore, even if the precipitates formed on the electrodes peel off and fall due to drying caused by electrode exposure or when they are submerged in water again and energized, they can be caught by the receiving tray 13, preventing them from falling into the storage tank 2 and being mixed with the water and delivered to the destination. The receiving tray 13 is provided with ribs 27, which prevents the precipitates accumulated on the receiving tray 13 from being stirred up by the stored water flowing in from the lower opening 14 of the case 11.

[0039] Next, we will explain the current control by the control unit 4 of the sterilization device 1.

[0040] It is anticipated that the water level in the storage tank 2 will temporarily drop due to water distribution, exposing the electrode plate 12. Therefore, the inventors investigated the relationship between the water level relative to the electrode plate 12, the current value, and the electrode temperature.

[0041] (1) When the electrode plate is completely submerged (Figure 7(a)) Due to the upward flow of water stored between the cathode plates 12a, 12b and the anode plate 12c, the water stored between the cathode plates 12a, 12b and the anode plate 12c is constantly replaced, and the current value and electrode temperature remain stable. (2) When the electrode plate is submerged in water up to its upper edge (Figure 7(b)) Since no upward flow of stored water occurs between cathode plates 12a and 12b and anode plate 12c, and the same stored water continues to be electrolyzed, the current value and electrode temperature gradually increase. (3) When the electrode plate is partially submerged in water (Figure 7(c)) The water stored between the cathode plates 12a and 12b and the anode plate 12c is retained up to the upper end of the electrode plate 12 by capillary action, but because there is no water exchange, the current value gradually increases. (4) When the electrode plate is submerged in water up to its lower end (Figure 7(d)) Because the lower end of the electrode plate 12 is in contact with the liquid, the water stored between the cathode plates 12a and 12b and the anode plate 12c is retained up to the upper end of the electrode plate 12 by capillary action, similar to the case of partial submersion. However, since there is no exchange of water, the current value gradually increases, and a very slight rise in the electrode temperature is observed. (5) When the electrode plate is completely exposed after being submerged in water (Figure 7(e)) There is a high probability that water is retained between the cathode plates 12a and 12b and the anode plate 12c, causing the current value and electrode temperature to rise. (6) When the electrode plate is fully exposed and dry (Figure 7(f)) There is a high possibility that water remains between the cathode plates 12a and 12b and the anode plate 12c, causing the current value and electrode temperature to rise. As described above, it was found that the relationship between the electrode plate 12 and the water level of the stored water causes changes in the current value and temperature, resulting in differences in the ability to generate hypochlorous acid (HOCl) by electrolysis and its safety.

[0042] Therefore, the control unit 4 controls the voltage applied between the cathode plates 12a and 12b and the anode plate 12c according to the water level detected by the water level sensor 10. As a result, when the water level reaches a point where the electrode plate 12 is exposed, the voltage applied between the cathode and anode can be controlled to suppress an increase in the electrode current and a rise in temperature.

[0043] Furthermore, as shown in Figure 8(a), the control unit 4 applies a positive voltage between the cathode and anode for a first predetermined time (t1), applies a reverse voltage for a second predetermined time (t2), and then repeats a cycle in which no voltage is applied for a third predetermined time. In this embodiment, the first predetermined time (t1) for applying the positive voltage is 15 seconds, the second predetermined time (t2) for applying the reverse voltage is 15 seconds, and the time in which no voltage is applied is 59 minutes, so that a 1-hour cycle is repeated, but this is not the only configuration. In this way, by applying a positive voltage between the cathode and anode for a first predetermined time, and then applying a reverse voltage for a second predetermined time, the electrode surfaces are cleaned, the adhesion of precipitates such as calcium and potassium contained in the water stored between the cathode and anode is suppressed, and electrolysis efficiency can be maintained.

[0044] The control unit 4 turns off when the water level sensor 10 detects a predetermined water level, and when the water level drops, it limits the current to a predetermined value that is lower than the current value at the time before the water level sensor 10 detected the predetermined water level, i.e., when the water level was full.

[0045] For example, the current can be limited by reducing the voltage applied during the first predetermined time (t1) and the voltage applied during the second predetermined time (t2), or by narrowing the interval between the first predetermined time (t1) and the second predetermined time (t2). In this way, when the water level drops to a level where the electrode 12 is exposed, the current is limited to a low value, thereby suppressing an increase in the current value and temperature rise of the electrode 12.

[0046] Alternatively, as shown in Figure 8(b), the control unit 4 turns off at time A when the water level sensor 10 detects a predetermined water level, and stops applying voltage between the cathode and anode when the water level drops. Then, when the water supply pump 7 turns on and water is supplied to the storage tank 2 from the water supply pipe 6, and the water level rises and the water level sensor 10 turns on at time B, it starts applying voltage between the cathode and anode again. In this way, when the water level drops to a level where electrode 12 is exposed, the voltage applied between the cathode and anode is stopped, thereby suppressing the temperature rise of electrode 12.

[0047] The control unit 4 has a constant current constant voltage charging circuit, and when the current value exceeds a predetermined upper limit current value due to voltage fluctuations, electrode exposure, etc., it reduces the voltage so that the value obtained by multiplying the current value by the voltage becomes constant. This ensures that even if control as shown in Figure 8(b) becomes impossible due to a malfunction of the water level sensor 10, the current value can be kept within the specified current value.

[0048] The present invention is not limited to the embodiments described above, and various modifications and changes can be made. [Explanation of symbols]

[0049] 1...Sterilizer 2…Storage tank 3...Electrode part 4…Control Unit 5…Water supply valve 6…Water supply pipe 7…Water supply pump 8…Water distribution valve 9…Water pipe 10...Water level sensor 11… Case 12...Electrode plate 12a...Cathode plate 12b...Cathode plate 12c…Anode plate 13... Saucer 14…Lower opening 15… Electrode housing space 16…Front opening 17...Rear opening 18...Groove 19… Nail area 20a, 20b... Electrode mounting section 21a, 21b...electrode terminal 22…Slope part 23…Engagement hole 24...projection piece 25...Double part 26…Inlet 27... Rib 28…Power supply

Claims

1. An electrode consisting of opposing cathodes and anodes immersed in stored water, The system includes a power supply that applies a voltage between the cathode and the anode, In a sterilization device that sterilizes by anodic oxidation of chloride ions contained in the stored water through electrolysis of the stored water and uses hypochlorous acid to produce sterilization, The cathode and anode of the electrode are formed in a plate shape. The cathode and anode of the electrode are housed in a case having a lower opening and an upper opening. A sterilization device in which the gap between the cathode and anode of the electrode is 1 to 1.5 times the thickness of the electrode plate.

2. The sterilization apparatus according to claim 1, further comprising above the electrode, an inclined portion that is inclined with respect to the surface of the electrode and promotes convection of the stored water due to the rise of bubbles generated between the cathode and anode of the electrode.

3. The sterilization apparatus according to claim 1, wherein a tray is provided below the electrode to receive precipitates falling from the electrode.

4. The sterilization apparatus according to claim 3, wherein ribs parallel to the electrodes are provided on the upper surface of the receiving tray.

5. A water level sensor that detects a predetermined water level of the stored water, The sterilization apparatus according to any one of claims 1 to 4, further comprising a control unit that controls the voltage applied between the cathode and the anode according to the water level detected by the water level sensor.

6. The sterilization apparatus according to claim 5, wherein the control unit repeats a cycle of applying a positive voltage between the cathode and the anode for a first predetermined time, applying a reverse voltage for a second predetermined time, and then not applying any voltage for a third predetermined time.

7. The sterilization apparatus according to claim 5, wherein the control unit, when the water level falls below the predetermined water level detected by the water level sensor, limits the current flowing between the cathode and the anode to a predetermined current value lower than the current value before the detection of the predetermined water level.

8. The sterilization apparatus according to claim 5, wherein the control unit stops applying the voltage between the cathode and the anode when the water level falls below the predetermined water level detected by the water level sensor.

9. The sterilization apparatus according to claim 5, wherein the control unit reduces the voltage so that the value obtained by multiplying the current value by the voltage becomes constant when the current value exceeds a predetermined upper limit current value.

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