JP2022189838A - Plasma sterilizing water generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma sterilization water generator which produces plasma sterilization water with high sterilization effect.

SOLUTION: A plasma sterilization water generator includes a pressure reducing chamber 1, a box-shaped water tank 2 arranged inside the pressure reducing chamber 1 and storing treated water, a pair of electrodes 3 arranged inside the pressure reducing chamber 1, a power supply 5 for applying an alternating voltage to the pair of electrodes 3. The pair of electrodes 3 has a flat plate electrode 3a provided above the water surface of the treated water stored in the water tank 2, a dielectric 4 provided on the lower side of the flat plate electrode 3a and facing the surface of the treated water stored in the water tank 2 through a space, and a ground electrode 3b provided in the treated water stored in the water tank 2. A pressure reducing pump 1a is connected to the pressure reducing chamber 1 to depressurize the gas phase atmosphere so that the inside of the pressure reducing chamber 1 becomes an extremely low vacuum, a supply pipe D is connected to the water tank 2 to supply plasma sterilization water to the target to be sterilized, and the power supply 5 is configured to input a power of 10 Wh or more per 1 L of the treated water.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to a plasma sterilized water generator for generating plasma sterilized water, which is used, for example, for sterilizing an evaporative humidifier of an outside air processing air conditioner.

In recent years, energy consumption has been greatly reduced by applying the evaporative humidification method, which is more energy-saving than the general steam humidification method, to outdoor air processing air conditioners (external air conditioners) used in factories in the electronics industry. have succeeded in reducing Demands for energy saving are also increasing for facilities with biological clean rooms, including pharmaceutical manufacturing. Therefore, it is desired to perform humidification by the evaporative humidification method even in the biological clean room.

In the evaporative humidification method, an element portion of an evaporative humidifier is impregnated with water for humidification, and conditioned air is ventilated to perform humidification by natural evaporation. Therefore, since the element portion is constantly in a wet state, it becomes an environment in which microorganisms easily propagate. In addition, the propagation of microorganisms is known to cause offensive odors. Especially in biological clean rooms, it is very important to control contamination by microorganisms. Therefore, it was necessary to develop an effective sterilization method for evaporative humidifiers of outdoor air conditioners.

As a sterilization method, there is a method of using chemical solution or functional water with sterilizing power as water supply dripped to the evaporative humidifier. Electrolyzed water, ozonized water, etc. are used as functional water having sterilizing power. However, when ozone water is used, for example, problems such as odor due to residual components and corrosion of peripheral members arise. A method of sterilizing an evaporative humidifier using an ultraviolet lamp has also been proposed. However, since the sterilization range is limited to the irradiation range of ultraviolet rays, it is not suitable for sterilization over a wide area.

In addition, microwave irradiation to an evaporative humidifier and supply of silver ions to humidifying water supply have been proposed. However, the microwave irradiation device is costly and the system is complicated. In addition, the supply of silver ions requires concentration control, and the service life of the electrode, which is the supply source of silver ions, is also a problem.

Against this background, in recent years, a sterilization method using discharge plasma has been proposed as a sterilization method that does not use chemicals or the like. This method sterilizes using the oxidizing power of highly reactive chemically active species and ions generated by discharge plasma. A high sterilization effect can be obtained with only electrical energy, and since there is no persistence unlike methods using chemical solutions, it is applied in various fields.

JP-A-1999-187872 JP-A-2001-252665

Sterilization using plasma includes a method of generating corona discharge using electrodes and performing sterilization with generated radicals. However, since the life of radicals is short and the sterilization range is limited, it is not suitable for sterilizing evaporative humidifiers of outdoor air conditioners. Also proposed is a method of applying a high voltage pulse between electrodes in the water to cause dielectric breakdown in the water to be treated, and sterilizing the water by the generated radicals and shock waves. When the water to be treated is used for sterilization, it is necessary to remove the evaporative humidifier from the outdoor air conditioner and put it into the water tank to be treated, which increases the workload. That is, a sterilization method using plasma suitable for sterilizing an evaporative humidifier of an outdoor air conditioner has not yet been proposed, and its development is eagerly awaited.

The present invention has been proposed to solve the problems of the prior art as described above. It is an object of the present invention to provide a plasma sterilized water generator that generates plasma sterilized water having a high sterilizing effect.

In order to achieve the above objects, the plasma-sterilized water generator of the present invention has the following characteristics.
(1) A decompression chamber, a box-shaped water tank arranged inside the decompression chamber for storing water to be treated, a pair of electrodes arranged inside the decompression chamber, and an AC voltage being applied to the pair of electrodes. and a power supply for applying power, wherein the pair of electrodes are a flat plate-shaped electrode provided so as to be positioned above the water surface of the water to be treated stored in the water tank, and a lower surface side of the flat plate-shaped electrode a dielectric body facing the water surface of the water to be treated stored in the water tank through a space; and a ground electrode provided so as to be positioned in the water to be treated stored in the water tank, A decompression pump is connected to the decompression chamber for decompressing the gas phase atmosphere so that the interior of the decompression chamber becomes an extremely low vacuum, and the water tank is provided with a supply pipe for supplying plasma sterilization water to the sterilization target. The power supply is configured to supply power of 10 Wh or more per 1 L of the water to be treated.

(2) The power supply may be configured to supply power of 20 Wh or more per liter of the water to be treated.

(3) A water supply pipe for supplying pure water may be connected to the water tank.

(4) A sterilization target to which the plasma sterilized water generated by the plasma sterilized water generator is supplied is an evaporative humidifier of an outdoor air conditioner, and the water supply pipe is connected to the evaporative humidifier in the outdoor air conditioner. It may be connected to a humidifying water supply pipe that supplies pure water as drip water.

(5) A sterilization target to which the plasma sterilized water generated by the plasma sterilized water generator is supplied is an evaporative humidifier of an outdoor air conditioner, and the supply pipe is connected to the evaporative humidifier in the outdoor air conditioner. It may be connected to a humidifying water supply pipe that supplies pure water as drip water.

(6) The water tank may be made of metal and grounded to serve as the ground electrode.

(7) The water tank may be provided with a stirring device for stirring the water to be treated stored in the water tank.

(8) The water tank may be provided with a cooling device for cooling the water to be treated, and the water to be treated during the plasma treatment may be cooled to 10° C. or less.

(9) The water tank may be provided with a cooling device for cooling the water to be treated, and the generated plasma sterilized water may be cooled to 7° C. or less.

(10) A space between the dielectric and the surface of the water to be treated stored in the water tank may be 5 mm or more and 10 mm or less.

(11) A space of 50 mm or more may be provided between the inner wall surface of the water tank and the side surface of the flat electrode.

According to the present invention, it is possible to provide a plasma sterilized water generator that generates plasma sterilized water having a high sterilizing effect.

1 is a configuration diagram showing an example of a plasma sterilized water generating device according to a first embodiment; FIG. 1 is a partially enlarged view showing an example of a plasma sterilized water generator according to a first embodiment; FIG. 4 is a flow chart showing a process of generating plasma sterilized water. 5 is a graph showing the sterilization effect of plasma sterilized water generated by the plasma sterilized water generator according to the first embodiment; 5 is a graph showing the sterilization effect of plasma sterilized water and the sterilization effect of electrolyzed water generated by the plasma sterilized water generator according to the first embodiment; 4 is a graph showing the sterilization effect of plasma sterilized water generated while water to be treated is cooled. 4 is a graph showing the sterilization effect of plasma sterilized water generated with an input power amount of 10 Wh/L. 4 is a graph showing the sterilization effect of plasma sterilized water generated with an input power amount of 20 Wh/L. 4 is a graph showing the sterilization effect of plasma sterilized water generated with an input power amount of 20 Wh/L or 17 Wh/L. 4 is a graph showing the sterilization effect of plasma sterilized water generated using 2 L of room temperature water to be treated. 4 is a graph showing the sterilization effect of plasma sterilized water produced using 2 L of water cooled to 2° C.; 4 is a graph showing the sterilization effect of plasma sterilized water generated in a state where the cooling temperature of water to be treated and the amount of electric power supplied are varied. (a) is a graph plotting the storage temperature of plasma sterilized water and the duration of sterilization effect. (b) is a graph showing the result of calculating the storage temperature at which the sterilization effect lasts for 30 minutes or more. (a) is a graph showing the storage time and sterilization effect when the processing temperature and storage temperature of plasma sterilized water are 10°C. (b) is a graph showing storage time and sterilization effect when the treatment temperature and storage temperature of plasma sterilized water are 7°C.

[First Embodiment]
[1. overall structure]
(Equipment configuration overview)
An embodiment of a plasma-sterilized water generating apparatus according to the present invention will be described with reference to the drawings.
The plasma sterilized water generator A is a device that generates plasma sterilized water to be supplied to an object to be sterilized. Plasma sterilized water is water in which radicals generated by subjecting water to be treated to plasma discharge are dissolved. The sterilization target is sterilized by the sterilization power that the radicals are supposed to have.

In this embodiment, an evaporative humidifier of an outdoor air conditioner is assumed as an example of a sterilization target. The plasma-sterilized water generator A is installed, for example, on or beside the outdoor air conditioner. The plasma sterilized water generator A is connected to the evaporative humidifier of the outdoor air conditioner via a plasma sterilized water supply pipe. A plasma-sterilized water generator A has a decompression chamber 1 , a water tank 2 , a pair of electrodes 3 , a dielectric 4 , and a power supply 5 . Each configuration will be described in detail below with reference to FIG.

(decompression chamber)
The decompression chamber 1 is a vacuum container made of metal or resin and having a pressure-resistant structure. The decompression chamber 1 is connected to an exhaust duct E having a decompression pump 1a and a valve 1b. The exhaust duct E is a duct for discharging the gas inside the decompression chamber 1 . The decompression pump 1 a is a pump for sucking and discharging the gas inside the decompression chamber 1 . The valve 1b is a valve for adjusting the exhaust amount when the gas inside the decompression chamber 1 is exhausted. The decompression pump 1a and the valve 1b are connected to a control device (not shown), and control signals from this control device control the flow rate of the decompression pump 1a and the opening of the valve 1b.

Specifically, the decompression pump 1 a decompresses the gas phase atmosphere in the decompression chamber 1 . Due to the pressure reduction of the gas phase atmosphere by the pressure reduction pump 1a, the applied voltage necessary for generating the dielectric barrier discharge is reduced. Here, the decompression pump 1a may reduce the dielectric strength of the air to some extent and exhaust the gas inside the decompression chamber 1 so as to create an ultra-low vacuum state that facilitates the development of plasma.

Ultra-low vacuum refers to a state in which the degree of pressure reduction is 50 kPa (abs) or less, more preferably about 50 kPa (abs) to 30 kPa (abs), when the power supply voltage is 20 kV/cm. By setting the decompression chamber 1 to an extremely low vacuum, it is possible to reduce the applied voltage required for discharge by about 50%. For example, when the decompression chamber 1 is at atmospheric pressure and an applied voltage of 30 kVpp is required, the required applied voltage is 14 kVpp by setting the decompression chamber 1 to an extremely low vacuum of 30 kPa (abs).

The decompression chamber 1 only needs to have an extremely low vacuum inside, and since the water tank 2 is arranged inside the decompression chamber 1, the gas phase volume of the decompression chamber 1 is relatively small. Therefore, even if a relatively inexpensive pump with an ultimate pressure of about 20 kPa (abs) to 30 kPa (abs) and an exhaust speed of about 10 L/min is used as the decompression pump 1a, the decompression chamber 1 can be brought into an extremely low vacuum state. be able to. Even with a relatively inexpensive and compact decompression pump with a market price of about several tens of thousands of yen, it is possible to bring the gas phase volume of 10 L to the set vacuum state in a few minutes.

(water tank)
The water tank 2 is a metal or resin tank that is arranged inside the decompression chamber 1 and stores the water to be treated. The water tank 2 is a box-shaped member having an opening on its upper surface. The water tank 2 has a size capable of storing, for example, 5 L of water to be treated. The storage amount of the water to be treated may be determined in consideration of the electrode configuration of a pair of electrodes 3 and dielectric 4, which will be described later, the power source capacity of the power source 5, and the like. If the amount of water to be treated is too large for the electrode configuration and power capacity used, plasma sterilized water having sufficient sterilizing power cannot be obtained. In the present embodiment, a configuration capable of imparting sufficient sterilizing power to 5 L of water to be treated will be described as an example.

A water supply pipe S having a valve 2 a is connected to the water tank 2 . The water supply pipe S is a pipe for introducing a liquid to be treated water into the water tank 2 . The valve 2a is a valve for adjusting the amount of liquid introduced. The valve 2a is connected to a control device (not shown), and the opening of the valve 2b is controlled by a control signal from this control device. Water to be treated such as pure water or tap water is supplied from a water supply pipe S to the water tank 2 . Pure water is preferably used as the water to be treated which is supplied to the water tank 2 . This is because the sterilizing power of the generated plasma sterilizing water is improved.

When an outdoor air conditioner to be sterilized is used in a biological clean room, pure water is generally supplied as drip water to the evaporative humidifier of the outdoor air conditioner. Therefore, the water supply pipe S of the water tank 2 may be connected via a valve to the humidification water supply pipe for supplying dripping water to the evaporative humidifier in the outdoor air conditioner. By switching this valve, pure water is supplied to the evaporative humidifier during normal operation of the outdoor air conditioner, and pure water is supplied to the water tank 2 after the operation of the outdoor air conditioner is finished. That is, the pure water used in the outdoor air conditioner can be supplied to the water tank 2 as the water to be treated. With this configuration, it is not necessary to secure a pure water supply line for the plasma sterilized water generator A, which is preferable.

A supply pipe D having a valve 2b and a liquid feed pump 2c is connected to the water tank 2 .
The supply pipe D is a pipe for supplying plasma sterilized water to an object to be sterilized. The supply pipe D may be connected to, for example, a humidifying water supply pipe of the outdoor air conditioner via a valve. By switching this valve, dripping water is supplied to the evaporative humidifier during normal operation of the outdoor air conditioner, and plasma sterilized water is supplied to the evaporative humidifier after the operation of the outdoor air conditioner is finished. When using the humidifying water supply pipe of the outdoor air conditioner, the plasma sterilizing water is supplied to the evaporative humidifier through a humidifying drip header that drips dripping water into the evaporative humidifier. However, the supply pipe D may be connected directly to the evaporative humidifier to be sterilized without being connected to the humidifying water supply pipe of the outdoor air conditioner, and a dedicated supply header may be provided.

The valve 2b is a valve for adjusting the supply amount when plasma sterilizing water is supplied to an object to be sterilized. The liquid feed pump 2c is a pump for adjusting the flow rate of the supplied plasma sterilizing water. The valve 2b and the liquid-sending pump 2c are connected to a control device (not shown), and control signals from the control device control the opening of the valve 2b and the flow rate of the liquid-sending pump 2c.

The faster the supply rate of the plasma sterilized water, the shorter the time required for the sterilization process. However, when using the humidifying water supply piping and humidifying drip header of the external air conditioner to feed plasma sterilized water, the flow rate of the liquid feeding pump must be limited by the piping resistance of the humidifying water supply piping and humidifying drip header. become. In that case, the opening degree of the valve 2b and the flow rate of the liquid transfer pump 2c are controlled so that the maximum flow rate is achieved within the limits of the piping resistance of the humidification water supply pipe and the humidification drip header.

Furthermore, when the amount of water to be treated is large and the water depth is, for example, 100 mm or more, an agitating device for agitating the water to be treated may be provided. Since the surface of the water to be treated is usually swayed by the dielectric barrier discharge, it can be said that the dielectric barrier discharge has a stirring function. However, when the water depth is deep, there is a possibility that the agitation will be insufficient only by shaking due to discharge.

Also, the plasma-sterilized water is generated on the water surface in the vicinity of electrodes 3a, which will be described later. On the other hand, as shown in FIG. 2, the plasma-sterilized water supply pipe D is often provided on the lower side of the water tank 2 due to the structure of the system. Therefore, by providing an agitating device inside the water tank 2, the sterilizing power of the plasma sterilized water supplied to the object to be sterilized can be kept constant.

Furthermore, a cooling device may be provided in the water tank 2 to cool the water to be treated. When the water temperature of the water to be treated rises due to plasma discharge, the sterilization factor may be decomposed and the sterilization effect may be reduced. In particular, when plasma treatment is performed on 2 L or more of water to be treated, the temperature of the water to be treated rises markedly during or after treatment. In addition, the temperature of the water to be treated may rise even if the water to be treated is 2 L or less due to the plasma discharge conditions of the plasma sterilized water generator A and the temperature when the device is used. In such a case, by cooling the water to be treated, the decomposition of the sterilizing factor is suppressed and the sterilizing power of the generated plasma sterilizing water is enhanced.

The water to be treated is preferably cooled not only during plasma discharge, but also when the plasma sterilized water generated in the plasma treatment is stored. By cooling the water to be treated after plasma treatment, the sterilizing power of the plasma sterilizing water can be maintained for a long time. By setting the cooling temperature of the water to be treated by the cooling mechanism to 10° C. or less, plasma sterilized water having strong sterilizing power is generated. In order to maintain the sterilizing effect of plasma sterilized water after generation for a longer period of time, the storage temperature of plasma sterilized water is preferably 7° C. or lower.

From the above, as a cooling mechanism, it is preferable to use a chiller with a capacity of about 700 W, which can cool 5 to 10 L of treated water to 10° C. or less in about 10 to 15 minutes. By installing a metal tube heat exchanger in the water tank 2 as ancillary to this chiller, the water to be treated in the water tank 2 can be cooled. The metal tube heat exchanger of the cooling mechanism may also be used as the ground electrode 3b described below.

(a pair of electrodes and a dielectric)
Inside the decompression chamber 1, an electrode 3a corresponding to a pair of electrodes 3 and a ground electrode 3b are arranged so as to face each other. A dielectric 4 is installed between the electrode 3a and the ground electrode 3b.

The electrode 3a is a plate-like electrode and is made of metal. As metals, corrosion-resistant metals such as nickel, various stainless steels, aluminum, and copper can be used. Alternatively, Kovar may be used because of compatibility with glass, which is an example of the dielectric 4 . The size of the electrode 3a in the horizontal direction is set to be smaller than the opening of the water tank 2 so that it can be accommodated inside the water tank. That is, the area of the plane of the electrode 3a is approximately the same as the area of the water surface. As a result, a planar dielectric barrier discharge having an area approximately equal to that of the water surface is generated.

The flat plate-like electrode 3a is preferably in the shape of a disc or a square with rounded corners. Concentration of electric field on the edge portion and development of spark discharge can be prevented by forming the shape without corners. As described above, the electrode 3a can have a disk shape of φ150 mm, for example. Note that the heat generated by the application of the AC voltage is conducted to the metal portion of the electrode 3a. Therefore, a heat sink made of metal may be installed on the upper surface of the electrode 3a to promote heat dissipation.

The electrode 3 a is arranged on the upper side of the water tank 2 . Specifically, as shown in FIG. 2, the electrode 3a is provided so as to be positioned above the surface of the water to be treated when the water to be treated is supplied to fill the tank 2 with the water to be treated. That is, a space is created between the surface of the water to be treated and the electrode a.

In this embodiment, the lower surface side of the electrode 3a is covered with the dielectric 4. As shown in FIG. Therefore, the dielectric 4 faces the water surface of the water to be treated stored in the water tank 2 via a space. Therefore, the space between the electrode 3a and the surface of the water to be treated actually means the space between the dielectric 4 and the surface of the water to be treated.

The narrower the space between the dielectric 4 and the surface of the water to be treated, the lower the resistance and the easier the discharge. However, the plasma-sterilized water generator A may be placed in a place where slight shaking occurs, such as the upper part of an outdoor air conditioner. Therefore, when the water to be treated is undulated due to vibration or the like, the dielectric 4 may come into contact with the water to be treated. Therefore, the space between the dielectric 4 and the surface of the water to be treated is preferably 5 mm or more and 10 mm or less. In particular, it was confirmed that by setting the space to 8 mm, it is possible to discharge with an appropriate applied voltage and prevent contact between the dielectric 4 and the water to be treated.

Preferably, the dielectric 4 has a relatively large dielectric constant (εr), a small dielectric loss tangent (tan δ), and a good dielectric strength (KV/mm). However, when a ferroelectric material such as barium titanate having a dielectric constant exceeding several thousand is used, the heat generated by the dielectric effect due to the application of AC voltage may reach a high temperature. In that case, it is preferable to provide the electrode 3a with a heat dissipation mechanism such as a heat sink to dissipate heat. As for the thickness of the dielectric 4, the thinner it is, the easier it is to discharge. However, it is necessary to consider the balance between the applied voltage of the power supply 5 and the dielectric strength of the dielectric 4, which will be described later. Also, the thickness of the dielectric 4 is determined in consideration of the durability and mechanical strength of the electrode 3a.

Considering the above conditions, materials for the dielectric 4 include glass (εr: 3 to 10, tan δ: 0.003), polyethylene (εr: 2 to 2.5, tan δ: ~0.0005), polypropylene ( εr: 2 to 2.3, tan δ: ~0.0005), polytetrafluoroethylene (εr: 2.0, tan δ: ~0.0002), alumite (oxalic acid alumite; εr: 6 to 10, tan δ: ~0 .001) or silicon nitride (εr: 7-8, tan δ: 0.0005). For example, a glass plate or a ceramic plate having a thickness of about 2 to 3 mm can be used as the dielectric 4 so as to have sufficient strength, and a metal layer of about 50 μm can be vapor-deposited thereon as the electrode 3a. Nickel or titanium, for example, may be used as the metal to be vapor-deposited. In particular, glass and nickel are compatible with each other and can be vapor-deposited uniformly so as not to cause holes or the like in the nickel layer. It is also possible to use kovar sealing glass for the dielectric and fuse it with kovar.

The ground electrode 3 b is arranged on the lower side of the water tank 2 . In the example of FIG. 1 , the water tank 2 is made of resin, and the ground electrode 3 b is provided at a position submerged in the water to be treated stored in the water tank 2 . The discharge current of the dielectric barrier discharge is configured to flow through the water to be treated to the ground electrode 3b.

The material of the ground electrode 3b may be metal, and its shape can be freely changed. However, it is constructed so that the discharge current of the dielectric barrier discharge can be surely led to the ground. As will be described later, experiments have shown that the pH of the water to be treated is about 3 due to the influence of nitric acid generated by the plasma. Therefore, when the ground electrode 3b is submerged in the untreated water of the water tank 2, it is preferable to use, for example, stainless steel as a metal that is excellent in corrosion resistance in water and relatively resistant to nitric acids.

When the water tank 2 is made of metal, the water tank 2 may be grounded so that the water tank 2 functions as the ground electrode 3b. That is, the ground electrode 3b arranged in the water to be treated 2 includes the water tank 2 itself. However, when the water tank 2 is made of metal, spark discharge toward the inner wall surface of the water tank 2 occurs when the inner wall surface of the water tank 2 exposed to the gas phase side from the surface of the water to be treated becomes extremely close to the electrode 3a. can be considered.

Therefore, as shown in FIG. 2, it is preferable to secure a predetermined distance between the side surface of the electrode 3a and the inner wall surface of the water tank 2. FIG. This distance varies depending on the voltage applied to the electrode 3a, the thickness of the dielectric 4, and the atmospheric pressure of the decompression chamber 1. Considering that the insulation of air is 30 kV per 1 cm, a spark discharge of 50 mm or more is required. can be prevented. Also, the portion of the inner wall surface of the water tank 2 exposed to the gas phase may be covered with an insulating resin coating 2d.

(power supply)
The power source 5 is a high-voltage power source that applies an AC voltage for generating dielectric barrier discharge to the pair of electrodes 3 . The power source 5 may have an AC alternating frequency of several kHz to several tens of kHz, a maximum applied voltage of approximately 10 kV _0-p (2 to 3 kV/cm), and a power source capacity of approximately 500 VA. For the power source 5, a power source that can obtain the peak sterilizing power of the plasma sterilizing water when the voltage application time is 30 minutes or less may be appropriately selected in consideration of the capacity of the water to be treated. A power supply 5 is provided outside the decompression chamber 1 and connected to the electrode 3a.

The circuit configuration of the power supply device may be one that can generate an alternating voltage of about 10 kV _0-p (2 to 3 kV/cm) with a sine wave, triangular wave, or pulse wave of several kHz to several tens of kHz. The higher the applied _voltage , the higher the processing efficiency. can develop plasma.

Here, the power source 5 is configured to apply power of 10 Wh or more, preferably 20 Wh or more, to 1 L of water to be treated. For example, by treating 3 L of water to be treated at 180 W for 20 minutes, 20 Wh of electric power can be supplied to 1 L of water to be treated. When the same amount of power is applied, even if the power and the time of application are different, the same sterilization effect can be obtained as long as the total amount of power is the same. In the plasma-sterilized water generator A of the present embodiment, when power of 10 Wh/L or more is supplied, plasma-treated water having a sterilizing effect is generated. The sterilization effect of the generated plasma sterilized water is improved by setting the power to be supplied to 20 Wh/L or more. The input power amount can be monitored by installing a power meter in the power supply system.

[2. Sterilized water generation process]
As shown in FIG. 3, the plasma-sterilized water generator A having the above configuration generates plasma-sterilized water through the following steps.
(1) Process of supplying water to be treated to water tank 2 (2) Process of depressurizing decompression chamber 1 (3) Process of plasma treatment by dielectric barrier discharge (4) Process of releasing decompression chamber 1 to atmospheric pressure (5) Supply of plasma sterilized water process

The evaporative humidifier to be sterilized in this embodiment is a humidifier that humidifies gas by blowing air to an element part such as a humidifying filter that absorbs water. This humidifying filter absorbs about 5 to 15 liters of liquid. A typical outdoor air conditioner is often provided with two humidifying filters. Therefore, in the sterilized water generation step below, a configuration and conditions suitable for generating 30 L of plasma sterilized water will be described as an example.

In addition, it is assumed that the sterilization of the evaporative humidifier with plasma sterilization water is performed at night after the operation of the outdoor air conditioner is finished. Therefore, the 30 L of plasma-sterilized water need not necessarily be generated at once. It is preferable that the plasma sterilized water is divided into several liters and generated a plurality of times and supplied to the vaporization type humidifier each time. The following description details the process of producing 30L of plasma-sterilized water by producing 6 times 5L of plasma-sterilized water.

The power capacity required to generate 5 L of plasma-sterilized water is 500 VA to 1000 VA. Further, it is preferable to use a disk-shaped electrode 3a having a diameter of about 150 mm and to use glass as the dielectric 4. FIG. Considering the electrode capacitance, the thickness of the glass as the dielectric 4 was set to 2 to 3 mm to provide sufficient strength.

(Process for supplying water to be treated)
In the water-to-be-treated supply step, 5 L of pure water, which is water to be treated, is supplied to the water tank 2 . That is, the valve 2a of the water tank 2 is opened by the control signal from the control device. By opening the valve 2a, pure water is supplied to the water tank 2 through the water supply pipe S of the water tank 2 connected to the humidifying water supply pipe of the outdoor air conditioner. Here, when 5 L of pure water is supplied to the water tank 2, the valve 2a is returned to the closed state by the control signal from the control device.

(Decompression process)
In the decompression step, the gas inside the decompression chamber 1 is discharged to create a decompressed state. That is, the control signal from the control device opens the valve 1b of the decompression chamber 1 . When the valve 1b is opened, the decompression pump 1a is activated by a control signal from the control device. The decompression pump 1a sucks and discharges the gas inside the decompression chamber 1 until the decompression chamber 1 reaches an extremely low vacuum state. Here, the ultra-low vacuum means a state in which the degree of pressure reduction is 50 kPa or less. The controller stops the decompression pump 1a and closes the valve 1b after the decompression chamber 1 is in an extremely low vacuum state.

(Plasma treatment process)
In the plasma treatment step, plasma is generated by dielectric barrier discharge in the space between the electrode 3a coated with the dielectric 4 and the surface of the water to be treated. That is, when a high voltage is applied from the power supply 5 to the electrode 3a, plasma is generated in the space between the surface of the water to be treated and the dielectric 4. FIG. Since the water to be treated is electrically connected to the ground electrode 3b, plasma is generated in the space between the surface of the water to be treated and the dielectric 4. FIG. Radicals are generated in the water to be treated by the plasma generated in the gas phase, so plasma-sterilized water can be obtained.

(Atmospheric pressure release process)
In the atmospheric pressure release step, the pressure in the decompression chamber 1 is released to the atmospheric pressure. That is, the valve 1b of the decompression chamber 1 is opened by a control signal from the control device.

(Plasma sterilized water supply step)
In the plasma sterilized water supply step, the generated plasma sterilized water is supplied to the evaporative humidifier of the outdoor air conditioner. That is, the valve 2b of the water tank 2 is opened by the control signal from the control device. When the valve 2b is opened, the liquid transfer pump 2c is activated by a control signal from the control device. The liquid feed pump 2c sucks and discharges the plasma sterilized water inside the water tank 2 until the 5 L of plasma sterilized water stored in the water tank 2 is discharged. Since the plasma sterilized water supply pipe D is connected to the humidifying water supply pipe of the outdoor air conditioner, the plasma sterilized water discharged from the water tank 2 is supplied to the evaporative humidifier of the outdoor air conditioner. Sterilize. Then, when all the plasma-sterilized water inside the water tank 2 is discharged, the valve 2b is returned to the closed state by the control signal from the control device.

By repeating the above plasma-sterilized water generation process six times, a total of 30 L of plasma-sterilized water is generated and supplied to the evaporative humidifier of the outdoor air conditioner. A drain pan is provided below the evaporative humidifier of the outdoor air conditioner. Therefore, the plasma sterilized water dropped from the evaporative humidifier is discharged to the outside of the outdoor air conditioner through this drain pan. Although the pH of the plasma sterilized water is low, it is sufficiently diluted with the pure water supplied to the evaporative humidifier during normal operation, so that it does not corrode the outdoor air conditioner.

[3. About the sterilization principle of plasma sterilization water]
Hereinafter, the principle of sterilizing the object to be sterilized by the plasma sterilized water generated by the plasma sterilized water generator of the present embodiment will be described.

First, representative examples of radicals generated by gas-phase plasma include hydroxyl radicals (OH.), superoxide anion radicals ( _O.sub.2- .), ^and hydroperoxy radicals (HOO.). These radicals are dissolved and diffused in the plasma sterilization water to exhibit sterilization power. According to previous studies, hydroxy radicals (OH.), which have high sterilizing power, have a very short lifespan and hardly diffuse into liquids to be sterilized. On the other hand, the superoxide anion radical (O ₂ ⁻ .) can exist in water for several seconds, and as shown in formula (1), it reacts with hydrogen ions (H ⁺ ) in the liquid, resulting in hydroperoxy It is said to form a radical (HOO.). It is believed that this hydroperoxy radical (HOO.) kills bacteria in the liquid.
[O ₂ ^-・] + [H ⁺ ] ⇔ [HOO・] (1)

The acid dissociation constant for this equilibrium reaction is pKa 4.8. Therefore, when the pH of the liquid is lower than 4.8, the reaction of formula (1) proceeds to the right, and hydroperoxy radicals (HOO.) increase. Therefore, in the conventional plasma-sterilized water generator, plasma-sterilized water having a desired sterilization power was obtained by adjusting the pH of the liquid to 4.8 or less in advance.

In the plasma-sterilized water obtained in the present embodiment, it is considered that the radicals generated by gas-phase dielectric barrier discharge are dissolved and diffused in the water to be treated to obtain the sterilizing power. The bactericidal factor is believed to be the hydroperoxy radical (HOO.). Here, in the plasma sterilized water generator A of the present embodiment, the dielectric barrier discharge acts on the gas phase inside the decompression chamber 1, thereby oxidizing the nitrogen contained in the gas phase, and finally entering the water to be treated. It has been confirmed that it dissolves as nitric acid in Therefore, as shown in Table 1, it was confirmed from the experimental data that the pH automatically decreased to around 3.

表１からも明らかな通り、プラズマ殺菌水生成装置Ａにて３０分間誘電体バリア放電を作用させたプラズマ殺菌水には、５００ｐｐｍ以上の硝酸が含有しており、ｐＨは３．１前後まで低下していた。以上の測定結果より、本実施形態のプラズマ殺菌水生成装置Ａでは、被処理水のｐＨが４．８以下となるため、あらかじめｐＨを調整する手順を取らずとも高い殺菌効果が得られる状態にすることができる。

As is clear from Table 1, plasma sterilized water subjected to dielectric barrier discharge for 30 minutes in plasma sterilized water generator A contains 500 ppm or more of nitric acid, and the pH drops to around 3.1. Was. From the above measurement results, in the plasma sterilized water generator A of the present embodiment, the pH of the water to be treated is 4.8 or less, so a high sterilization effect can be obtained without taking a procedure to adjust the pH in advance. can do.

Next, according to conventional studies, pernitric acid (peroxynitric acid: HOONO ₂ ) is shown as a source of hydroperoxy radicals (HOO.) with high sterilizing power. Pernitric acid (HOONO ₂ ) synthesized by a chemical reaction or the like is hydrogen ions (H ⁺ ), superoxide anion radicals (O ₂ ⁻ ·), nitrogen dioxide (NO ₂・), etc., and the resulting superoxide anion radical (O ₂ ^-・) is said to produce hydroperoxy radicals (HOO・) with high bactericidal activity under strongly acidic conditions, resulting in bactericidal activity. It is
[HOONO ₂ ] ⇔ [H ⁺ ] + [O ₂ ^- .] + [NO _2. ] (2)

In addition, the mechanism for producing pernitric acid (HOONO ₂ ) is said to be as shown in formulas (3) to (5). That is, nitrous acid (HNO ₂ ) and hydrogen peroxide (H ₂ O ₂ ) react to form peroxynitrite (HOONO). Then, it reacts with hydrogen ions (H ⁺ ) under acidic conditions to produce nitronium ions (NO ₂ ⁺ ) and water (H ² O). Furthermore, the reaction of nitronium ions (NO ₂ ⁺ ) with hydrogen peroxide (H ₂ O ₂ ) to produce pernitric acid (HOONO ₂ ) and hydrogen ions (H ⁺ ) is believed to proceed under strongly acidic conditions. ing.
[HNO ₂ ] + [H ₂ O ₂ ] → [HOONO] (3)
[HOONO] + [H ⁺ ] ⇔ [NO ₂ ⁺ ] + [H ² O] (4)
[NO ₂ ⁺ ] + [H ₂ O ₂ ] ⇔ [HOONO ₂ ] + [H ⁺ ] (5)

Here, in general, various reaction products are generated in the discharge field of atmospheric pressure plasma, and it has been reported that these include hydrogen peroxide (H ₂ O ₂ ) and nitrous acid (HNO ₂ ). there is As shown in Table 1 above, hydrogen peroxide (H ₂ O ₂ ) and nitric acid (HNO ₃ ) are confirmed to be contained in the plasma sterilized water produced by the plasma sterilized water generator A of the present embodiment. . Therefore, when the dielectric barrier discharge acts on the water to be treated, nitrous acid (HNO ₂ ) and hydrogen peroxide (H ₂ O ₂ ), which are precursors of pernitric acid (HOONO ₂ ), are generated. It is considered that pernitric acid (HOONO ₂ ) is generated in the water to be treated due to the generation of this precursor.

As described above, the pH of the plasma sterilized water generated by the plasma sterilized water generator A is strongly acidic at around 3.1. Therefore, pernitric acid (HOONO ₂ ) is generated from nitrous acid (HNO ₂ ) and hydrogen peroxide (H ₂ O ₂ ) by dielectric barrier discharge and dissolved in the water to be treated. These substances are considered to be the supply sources of hydroperoxy radicals (HOO.) with high bactericidal activity.

[4. experiment]
(1) Experiment using Plasma Sterilized Water at Normal Temperature The result of verifying the sterilization effect of the plasma sterilized water generated by the plasma sterilized water generator A of the present embodiment is shown below. Plasma sterilized water used in the experiment was generated using 1 L of pure water at room temperature (approximately 25° C.) as water to be treated. The degree of pressure reduction in the pressure reduction chamber 1 was 50 kPa (abs), the alternating frequency of the power source 5 was 20 kHz, and the applied voltage was 10 kV _0-p (18 kV _pp ) to generate a sine wave, thereby generating a dielectric barrier discharge. . The voltage application time, that is, the plasma generation time was 30 minutes.

The experiment was performed by preparing four ampoules each containing 1 mL of an E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. 9 mL of pure water was added to one of the ampoules and diluted 10-fold to obtain a control sample having a concentration of about 10 ⁸ CFU/mL. To the remaining 3 ampoules, 9 mL of plasma-sterilized water was added and diluted 10-fold to prepare test samples. Three types of plasma-sterilized water were used as test specimens: plasma-sterilized water immediately after generation, plasma-sterilized water 30 minutes after generation, and plasma-sterilized water 60 minutes after generation. After culturing the control specimen and three test specimens, the number of colonies was counted.

The results of counting the number of colonies are shown in FIG. From Fig. 4, the number of viable bacteria in the test specimen using plasma sterilized water immediately after plasma treatment is reduced by more than 6 orders of magnitude compared to the control specimen, indicating that the plasma sterilized water immediately after plasma treatment has a strong sterilizing power. I know there is. Also, in the test specimen using the plasma-sterilized water 30 minutes after the plasma treatment, the number of viable bacteria was reduced by more than 5 orders of magnitude compared to the control specimen, demonstrating sufficiently high sterilizing power. On the other hand, it can be seen that the test specimen using the plasma-sterilized water 60 minutes after the plasma treatment has lower sterilizing power than the other two types of plasma-sterilized water.

From the above results, it was confirmed that the normal-temperature plasma-sterilized water produced by the plasma-sterilized water generator A of the present embodiment maintained its sterilizing effect for about 30 minutes after the plasma treatment was finished.

(2) Experiment on sterilization effect of plasma sterilized water The sterilization effect of plasma sterilized water generated by the plasma sterilized water generator A of the present embodiment was compared with the sterilization effect of commercially available electrolyzed water used for sterilization. The electrolyzed water used for comparison is also used for sterilizing evaporative humidifiers of outdoor air conditioners, and is slightly acidic hypochlorous acid water (HCLO) around pH 6. Plasma sterilized water used in the following experiments was generated using 500 mL of pure water. The conditions of decompression chamber 1 are the same as in experiment (1) above. The voltage application time, that is, the plasma generation time was set to 10 minutes.

The experimental method is the same as the above two experiments, 1 mL of E. coli (ATCC 13706) suspension, 9 mL of pure water as a control sample, and plasma sterilized water generated by the plasma sterilized water generator A of this embodiment as a test sample. 9 mL, and 9 mL of electrolyzed water (slightly acidic hypochlorous acid water) was used for the comparative sample, and each was diluted 10 times. These three specimens were cultured and colony counts were performed.

From FIG. 5, the number of viable bacteria in the test sample and comparative sample decreased by 6 digits or more compared to the control sample, reaching the detection limit. From this, the plasma sterilized water generated by the plasma sterilized water generator A of the present embodiment is as strong as the commercially available electrolyzed water (slightly acidic hypochlorous acid water) that is also used for sterilizing vaporization humidifiers. It has been proven to have a bactericidal effect.

(3) Experiment using low-temperature water to be treated Plasma sterilization water generated using water to be treated at room temperature (about 25°C) and plasma sterilization generated using water to be treated in a cooled state (about 5°C) We compared the sterilizing power of water. The plasma-sterilized water used in the experiment was generated using 500 mL of pure water. The conditions of decompression chamber 1 are the same as in experiment (1) above. The voltage application time, that is, the plasma generation time was set to 10 minutes.

The experiment was conducted by preparing eight ampoules each containing 1 mL of an E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. A control specimen was prepared in the same manner as in (1) above. The same sample was prepared with cooled pure water and used as a control sample when cooled. In addition, 9 mL of plasma-sterilized water was added to the three ampoules, diluted 10-fold, and used as test samples. Three types of plasma-sterilized water were used as test specimens: plasma-sterilized water immediately after generation, plasma-sterilized water 30 minutes after generation, and plasma-sterilized water 60 minutes after generation. Further, three ampoules were prepared with various plasma-sterilized waters produced by cooling the same ampules, and used as test specimens when cooled. After culturing 2 types of control specimens and 6 types of test specimens, the number of colonies was counted.

The result of counting the number of colonies is shown in FIG. FIG. 6 shows the results when the water to be treated was normal temperature and when the water was cooled. First, the plasma sterilized water produced using the water to be treated at normal temperature had a high sterilizing power for about 30 minutes after the plasma treatment, but the sterilizing effect significantly decreased after 60 minutes. On the other hand, in the plasma-sterilized water produced using the water cooled to about 5°C, the number of bacteria decreased by more than 5 orders of magnitude compared to the control sample even after 60 minutes from the plasma treatment.

As described above, the plasma sterilized water generated by the plasma sterilized water generator A contains pernitric acid as a sterilizing factor. Since this pernitric acid disappears as the temperature rises, it is thought that cooling the water to be treated could prolong the life of the sterilizing factor. From the above results, it was found that the durability of the sterilizing effect of the generated plasma sterilizing water can be improved by performing the plasma treatment while keeping the temperature of the water to be treated low.

(4) Experiment on the amount of power input to water to be treated The results of verification of the relationship between the amount of power input by the plasma sterilized water generator A of this embodiment and the sterilization effect of the generated plasma sterilized water are shown below. The plasma sterilized water used in the first experiment was generated using 4 L of cooled pure water as the water to be treated. The conditions of decompression chamber 1 are the same as in experiment (1) above. Then, the power source 5 applied 240 W of electric power to 4 L of the water to be treated for 10 minutes. That is, the input power amount in the first experiment was 10 Wh/L.

The experiment was conducted by preparing 10 ampoules each containing 1 mL of an E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. 9 mL of pure water was added to the five halves of the ampules and diluted 10-fold to obtain control samples having a concentration of about 10 ⁸ CFU/mL. To the remaining 5 ampules, 9 mL of plasma-sterilized water was added to dilute 10-fold to prepare test samples. As for test specimens, plasma-sterilized water immediately after production was used to prepare each test specimen. After culturing the control sample and the test sample, the number of colonies was counted.

The results of counting the number of colonies are shown in FIG. From FIG. 7, although the sterilization effect varies, the number of viable bacteria is reduced by 3 to 6 digits, indicating that it has sterilization power. From the above results, plasma sterilized water having sterilizing power can be generated by configuring the power supply 5 of the plasma sterilized water generator A of the present embodiment to supply 10 Wh of power to 1 L of water to be treated. One thing has been confirmed.

Next, a second experiment was conducted by increasing the amount of power supplied by the power supply 5 . The plasma sterilized water used in the second experiment was generated using 3 L of cooled pure water as the water to be treated. The conditions of decompression chamber 1 are the same as in experiment (1) above. Then, the power supply 5 applied 180 W of electric power to 3 L of the water to be treated for 20 minutes. That is, the input power amount in the second experiment was 20 Wh/L.

The experiment was conducted by preparing 14 ampoules each containing 1 mL of an E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. 9 mL of pure water was added to the seven halves of the ampules to dilute them 10-fold to obtain control samples having a concentration of about 10 ⁸ CFU/mL. To the remaining 7 ampoules, 9 mL of plasma-sterilized water was added to dilute 10-fold to prepare test samples. As for test specimens, plasma-sterilized water immediately after production was used to prepare each test specimen. After culturing the control sample and the test sample, the number of colonies was counted.

The results of counting the number of colonies are shown in FIG. From FIG. 8, in the second experiment, viable bacteria decreased by 6 digits or more in almost all the samples except one, indicating that the sample has extremely high bactericidal activity. From the above results, by configuring the power source 5 of the plasma-sterilized water generator A of the present embodiment to supply 20 Wh of power to 1 L of the water to be treated, plasma-sterilized water with higher sterilizing power can be reliably produced. It was confirmed that it is possible to generate

(5) Investigation of amount of electric power supplied to water to be treated A study was conducted on the power supplied by the power source 5 of the plasma-sterilized water generator A of the present embodiment and the influence of the input time on the generated plasma-sterilized water. Specifically, as plasma sterilized water A, sterilized water was prepared by applying electric power of 180 W for 20 minutes to 3 L of cooled pure water as water to be treated. The amount of power input for plasma sterilized water A is 20 Wh/L. Further, as plasma sterilized water B, sterilized water was prepared by applying electric power of 400 W for 10 minutes to 4 L of cooled pure water as water to be treated. The amount of power input for plasma sterilized water B is 17 Wh/L.

The experiment was conducted by preparing 10 ampoules each containing 1 mL of an E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. 9 mL of pure water was added to each of the five ampoules and diluted 10-fold to obtain a control sample having a concentration of about 10 ⁸ CFU/mL. Of the remaining ampules, 9 mL of plasma-sterilized water A was added to 3 ampules, diluted 10-fold, and used as test samples. In addition, 9 mL of plasma sterilized water B was added to the two ampoules and diluted 10-fold to prepare test samples. As for test specimens, plasma-sterilized water immediately after production was used to prepare each test specimen. After culturing the control sample and the test sample, the number of colonies was counted.

The results of counting the number of colonies are shown in FIG. From FIG. 9, it can be seen that both the cases of using plasma sterilized water A and the case of using plasma sterilized water B have reduced viable bacteria by more than 6 orders of magnitude, and have extremely high sterilizing power. . In other words, it was confirmed that plasma sterilized water having a sterilizing power based on the total amount of electric power can be generated if substantially the same amount of electric power is applied, even if the electric power and the input time are different.

(6) Experiments on the amount of water to be treated and water temperature As in the experiment described in (1) above, when the amount of water to be treated is 1 L or less, the plasma sterilized water has sterilizing power even when the plasma treatment is performed at room temperature. It was possible to generate Therefore, in this experiment, the sterilizing power of room temperature plasma sterilized water produced by increasing the amount of pure water at room temperature (approximately 25° C.) to 2 L as the water to be treated was verified.

The conditions of decompression chamber 1 are the same as in experiment (1) above. First, normal temperature plasma sterilized water C was obtained by applying power of 180 W to 2 L of room temperature water to be treated by the power supply 5 for 20 minutes. Next, the power source 5 applied a power of 180 W to 2 L of water to be treated at room temperature for 30 minutes to obtain plasma sterilized water D at room temperature.

The experiment was performed by preparing five ampoules each containing 1 mL of an E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. A control specimen was prepared in the same manner as in (1) above. To the remaining four ampules, 9 mL each of plasma-sterilized water C and D left standing for 1 minute after generation and plasma-sterilized water C and D left standing for 30 minutes after generation were added and diluted 10-fold, and the test sample and did. After culturing the control sample and the test sample, the number of colonies was counted.

The results of counting the number of colonies are shown in FIG. In addition, in FIG. 10, the number of colonies of the control specimen is indicated by a dotted line at the top of the graph. From FIG. 10, neither the plasma sterilized water C nor the plasma sterilized water D had sufficient sterilizing power regardless of the standing time. Even if the plasma sterilizing water was generated with the input power of 330 W×20 minutes and 330 W×30 minutes with respect to 2 L of the water to be treated, no sterilizing effect could be obtained. It was considered that this result was caused by the fact that when the amount of water to be treated increases, the plasma power needs to be increased, and the temperature of the water to be treated rises. In the above experiment, the temperature of the water to be treated was about 20.degree. It was expected that the bactericidal factor was decomposed due to the water temperature rise caused by the plasma discharge, and the bactericidal effect was lost.

Therefore, a similar experiment was conducted by cooling 2 L of pure water to 2° C. during the plasma treatment process. First, the power source 5 applied a power of 180 W to the water to be treated for 10 minutes to obtain plasma sterilized water E at room temperature. Next, plasma sterilized water F at room temperature was obtained by applying power of 180 W to the water to be treated by the power source 5 for 20 minutes. Lastly, the power source 5 applied a power of 180 W to the water to be treated for 30 minutes to obtain normal temperature plasma sterilized water G.

The experiment was conducted by preparing 13 ampoules containing 1 mL of E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. A control specimen was prepared in the same manner as in (1) above. Of the remaining 12 ampoules, 9 mL of plasma-sterilized water E left to stand for 1 minute after production was added to 2 ampoules, diluted 10-fold, and used as test samples. To the other two ampules, 9 mL of plasma-sterilized water F, which had been left standing for 1 minute after generation, was added and diluted 10-fold to prepare test samples. To the other two ampoules, 9 mL of plasma-sterilized water G, which had been left standing for 1 minute after generation, was added and diluted 10-fold to prepare test specimens. Furthermore, for the remaining six amplifiers, test specimens were prepared in the same manner using plasma-sterilized water E, F, and G that had been allowed to stand for 30 minutes after generation. After culturing the control sample and the test sample, the number of colonies was counted.

The results of counting the number of colonies are shown in FIG. As shown in FIG. 11, the plasma sterilized water left standing for 1 minute after generation reduced viable bacteria by five orders of magnitude or more, and sufficient sterilization effect was obtained. In particular, in the plasma-sterilized water F and G, in which the amount of power input is 30 Wh/L or more, viable bacteria are reduced by six orders of magnitude or more, indicating that the plasma-sterilized water having a strong sterilizing effect is obtained. It was confirmed that plasma sterilizing water having a sterilizing effect can be generated by cooling the water to be treated when the volume of the water to be treated is 2 L or more.

Further, from FIG. 11, the plasma sterilized water left standing for 30 minutes after generation did not have a sterilizing effect. In this experiment, since the water to be treated was cooled only during the plasma treatment, the water temperature of the plasma sterilized water rose during standing, and the sterilization factors were decomposed.

(7) Experiment on Cooling Temperature and Input Power Amount In the plasma sterilizing water generator A of the present embodiment, the effect of the cooling temperature by the cooling mechanism and the input power amount on the generated plasma sterilizing water was examined. The conditions of decompression chamber 1 are the same as in experiment (1) above. Plasma sterilized water H was obtained by applying a power of 180 W to 3 L of water cooled to 2° C. for 10 minutes by a power source 5 . Plasma sterilized water I was obtained by applying a power of 180 W for 20 minutes to 3 L of water to be treated cooled to 2° C. by the power source 5 . Plasma sterilized water J was obtained by applying power of 180 W for 30 minutes to 3 L of water to be treated cooled to 2° C. by the power source 5 .

Plasma sterilized water K was obtained by applying power of 180 W to 3 L of water cooled to 10° C. for 10 minutes by the power source 5 . The plasma sterilized water L was obtained by applying a power of 180 W to 3 L of the water to be treated cooled to 10° C. for 20 minutes by the power source 5 . The plasma sterilized water M was obtained by applying power of 180 W to 3 L of the water to be treated cooled to 10° C. for 30 minutes by the power source 5 .

The experiment was performed by preparing seven ampoules each containing 1 mL of an E. coli (ATCC13706) suspension adjusted to a concentration of about 10 ⁸ CFU/mL. A control specimen was prepared in the same manner as in (1) above. To the remaining 6 ampoules, 9 mL each of plasma sterilized water H and K with a discharge time of 10 minutes, plasma sterilized water I and L with a discharge time of 20 minutes, and plasma sterilized water J and M with a discharge time of 30 minutes were added. It was diluted 10 times and used as a test sample. As for test specimens, plasma-sterilized water immediately after production was used to prepare each test specimen. After culturing the control sample and the test sample, the number of colonies was counted.

The results of counting the number of colonies are shown in FIG. In addition, in FIG. 12, the number of colonies of the control specimen is indicated by a dotted line at the top of the graph. From FIG. 12, comparing plasma sterilized water H and G with a power input of 15 Wh/L, the plasma sterilized water H, in which the water to be treated is cooled to 2°C, has a five-digit reduction in viable bacteria. , had a bactericidal effect. On the other hand, the plasma sterilized water K in which the water to be treated was cooled to 10°C did not provide a sufficient sterilization effect.

On the other hand, in plasma sterilized water I, L, J, and M, which have power inputs of 20 Wh/L or more, viable bacteria are reduced by six orders or more regardless of the cooling temperature, and an excellent sterilization effect is obtained. rice field. From the above results, it was confirmed that a lower cooling temperature of 10° C. or lower is preferable. It was also found that plasma sterilized water with high sterilizing power can be generated by setting the power input amount to 20 Wh/L.

(8) Experiment on Storage Temperature of Plasma Sterilized Water From the experiment (6) above, it was found that the sterilization effect was reduced when the plasma treatment was performed after cooling for 30 minutes. Therefore, we further investigated the storage temperature of the plasma sterilized water. FIG. 13(a) shows the results of measuring the duration of the sterilizing effect of plasma sterilized water at storage temperatures of 5° C., 12° C., 14° C., and 20° C. for the same plasma sterilized water. From this result, it was found that the lower the cooling temperature, the longer the duration of the sterilization effect.

From the results of FIG. 13(a), the graph of FIG. 13(b) was created to determine the relationship between the duration of the sterilization effect and the storage temperature. I found that I needed to. The plasma sterilized water generated by the plasma sterilized water generator A needs to maintain its sterilizing effect to some extent in consideration of the supply speed to the object to be sterilized. It was found that by setting the storage temperature of the plasma sterilized water to 7° C. or lower, it is possible to take the supply time into account.

(9) Experiment on Cooling Temperature and Storage Temperature During Plasma Processing From the experiment (7) above, it was found that the cooling temperature during plasma processing is preferably 10° C. or less. Also, from the experiment (8) above, it was found that the storage temperature of the generated plasma-sterilized water is preferably 7° C. or lower. In order to standardize the cooling energy for generation and storage, the processing temperature and storage temperature were standardized at 10°C and 7°C for verification.

FIG. 14(a) is a graph showing the relationship between storage time and sterilization effect when the treatment temperature and storage temperature are both 10°C. From FIG. 14(a), it was found that under the conditions of 10° C. treatment and 10° C. storage, although a high sterilization effect was obtained after plasma treatment, there was variation, and the sterilization effect weakened over time. FIG. 14(b) is a graph showing the relationship between storage time and sterilization effect when the treatment temperature and storage temperature are both 7°C. From FIG. 14(b), under the conditions of 7°C treatment and 7°C storage, even after 30 minutes from immediately after plasma treatment, viable bacteria decreased by more than 6 orders of magnitude, indicating that the sterilization effect of plasma sterilization water is high. found to persist. From the above, it was confirmed that when the processing temperature and the storage temperature are shared, it is preferable to set the cooling temperature for both to 7° C. or lower with the storage temperature as the standard.

[5. Action effect]
The effects of the plasma sterilized water generator of the present embodiment as described above are as follows.
(1) A decompression chamber 1, a box-shaped water tank 2 arranged inside the decompression chamber 1 for storing water to be treated, a pair of electrodes 3 arranged inside the decompression chamber 1, and a pair of electrodes 3 and a power supply 5 for applying an AC voltage, and the pair of electrodes 3 are a flat electrode 3a provided so as to be positioned above the water surface of the water to be treated stored in the water tank 2, and a flat electrode 3a. A dielectric 4 provided on the lower surface side of the water tank 2 and opposed to the water surface of the water to be treated stored in the water tank 2 via a space, and a ground electrode provided so as to be positioned in the water to be treated stored in the water tank 2. 3b, and the decompression chamber 1 is connected to a decompression pump 1a for decompressing the gas phase atmosphere so that the inside of the decompression chamber 1 becomes an extremely low vacuum.

With the above configuration, plasma can be generated by dielectric barrier discharge in the space between the electrode 3a coated with the dielectric 4 and the surface of the water to be treated. Radicals are generated in the water to be treated by the plasma generated in the gas phase, so plasma sterilized water having a high sterilizing effect can be obtained.

In addition, the decompression pump 1a decompresses the gas phase atmosphere in the decompression chamber 1, thereby reducing the applied voltage necessary for generating the dielectric barrier discharge. Since the gas-phase atmosphere can be decompressed as long as the decompression chamber 1 is in an extremely low vacuum state, the decompression chamber 1 can be brought into an extremely low vacuum state even by using a relatively inexpensive pump.

(2) The power supply 5 is configured to supply power of 10 Wh or more per liter of water to be treated.

Plasma sterilized water having a sterilizing effect can be obtained by setting the input power of the power supply 5 to 10 Wh/L. Even if the input power and input time are different, if the total amount of power input is the same, plasma sterilized water having the same sterilization effect can be obtained. Therefore, it is possible to control the sterilization effect of the obtained plasma sterilized water by the input power.

(3) A water supply pipe S for supplying pure water is connected to the water tank 2 .

By using pure water as the water to be treated, the sterilization effect of the generated plasma sterilized water can be enhanced.

(4) The sterilization target to which the plasma sterilized water generated by the plasma sterilized water generator A is supplied is the evaporative humidifier of the outdoor air conditioner, and the water supply pipe S is connected to the evaporative humidifier in the outdoor air conditioner with pure water. is connected to a humidifying water supply pipe that supplies water as drip water.

By connecting the water supply pipe S to the humidifying water supply pipe, the pure water used in the outdoor air conditioner can be supplied to the water tank 2 as the water to be treated. Therefore, since it is not necessary to secure a pure water supply line for the plasma sterilized water generator A, it is possible to provide the plasma sterilized water generator A with a cheaper and simpler structure.

(5) The object to be sterilized to which the plasma sterilized water generated by the plasma sterilized water generator A is supplied is the evaporative humidifier of the outdoor air conditioner. The supply pipe D is connected, and the supply pipe D is connected to a humidification water supply pipe that supplies pure water as drip water to an evaporative humidifier in the outdoor air conditioner. Plasma sterilized water generator.

By connecting the supply pipe D to the humidifying water supply pipe, plasma sterilized water can be supplied to the evaporative humidifier, which is sterilized water, using the structure of the outdoor air conditioner including the humidifying drip header. Since there is no need to provide a pipe for supplying plasma-sterilized water on the outdoor air conditioner side, it is possible to provide a plasma-sterilized water generator that is less expensive and has a simpler structure.

(6) The water tank 2 is made of metal and grounded to form a ground electrode 3b.

With the configuration as described above, the need to separately provide the ground electrode 3b inside the water tank 2 is eliminated. Therefore, it is possible to provide a plasma sterilized water generator that is less expensive and has a simpler structure.

(7) The water tank 2 is provided with a stirring device so as to be positioned in the water to be treated stored in the water tank 2 .

By providing an agitating device inside the water tank 2, even when the amount of water to be treated is large and the water depth is deep, dielectric barrier discharge can be applied to the entire water to be treated. Therefore, plasma sterilized water having a high sterilization effect can be produced. Also, the sterilizing power of the plasma sterilizing water supplied to the object to be sterilized can be kept constant.

(8) The water tank 2 is provided with a cooling device for cooling the water to be treated, and cools the water to be treated to 10° C. or less during the plasma treatment.

By cooling the water to be treated to 10° C. or less during the plasma treatment with the cooling device, it is possible to generate plasma sterilized water having strong sterilizing power.

(9) The water tank 2 is provided with a cooling device for cooling the water to be treated, and cools the generated plasma sterilized water to 7°C or less.

By cooling the produced plasma-sterilized water to 7° C. or less by the cooling device and storing it, the sterilizing effect of the plasma-sterilized water can be maintained for a long period of time.

(10) The space between the dielectric 4 and the surface of the water to be treated stored in the water tank 2 is 5 mm or more and 10 mm or less.

By setting the space between the dielectric 4 and the water to be treated to 5 mm or more and 10 mm or less, it is possible to discharge with an appropriate applied voltage. Moreover, contact between the dielectric 4 and the water to be treated due to vibration or the like is prevented.

(11) A space of 50 mm or more is provided between the inner wall surface of the water tank 2 and the side surface of the flat electrode 3a.

When the water tank 2 is made of metal, spark discharge toward the inner wall surface of the water tank 2 occurs when the inner wall surface of the water tank 2 exposed to the gas phase side from the water surface of the water to be treated is extremely close to the electrode 3a. can be considered. Spark discharge can be prevented by securing a space of 50 mm or more between the inner wall surface of the water tank 2 and the side surface of the flat electrode 3a.

[Other embodiments]
(1) In the above embodiment, the water tank 2 is provided with a cooling device for cooling the water to be treated. However, cold water for air conditioning (usually about 7° C.), which is used as a refrigerant for the cooling coil of the outdoor unit, may be used as the water to be treated. That is, the water supply pipe S of the water tank 2 can be connected to the air conditioning cold water supply pipe of the outdoor air conditioner. By lowering the water temperature at the start of the plasma treatment, it is possible to keep the water temperature of the plasma sterilized water low. Therefore, the sterilizing power of the generated plasma sterilizing water can be maintained for a long time.

(2) The control of the plasma sterilized water generator A using the input power amount described in the above embodiment may be configured such that the control device calculates and controls the voltage application time based on the amount of water to be treated and the power. good. In the above embodiment, it is assumed that the controller is built in the plasma sterilized water generator A, but an external controller may be connected to the plasma sterilized water generator A. The controller can be realized by controlling a computer with a predetermined program or by a dedicated electronic circuit. It should be noted that the amount of water to be treated, the amount of electric power supplied, and the voltage application time can also be configured to be input by the user.

(3) When the object to be sterilized is the evaporative humidifier of the outdoor air conditioner, it is preferable to perform the drying operation of the evaporative humidifier after stopping the air conditioning operation of the outdoor air conditioner. The plasma sterilized water generated by the plasma sterilized water generator can easily permeate the humidifying element, and the sterilization effect of the plasma sterilized water can be improved.

(4) In the above embodiment, the object to be sterilized is the evaporative humidifier of the outdoor air conditioner, but the object to be sterilized is not limited to this. For example, it can be applied to household evaporative humidifiers, household evaporative humidifying air cleaners, and the like. Many of these devices have a structure in which a part of the evaporative humidification element (filter material, filter) is in contact with the water in the humidification water reservoir at all times or while rotating. Therefore, by applying a dielectric barrier discharge to the water in the humidifying reservoir, the humidifying water is sterilized, and the evaporative humidifier element (filter material, filter) impregnated with the humidifying water is sterilized. It becomes possible.

A Plasma sterilized water generator 1 Decompression chamber E Exhaust duct 1a Decompression pump 1b Valve 2 Water tank S Water supply pipe 2a Valve D Supply pipe 2b Valve 2c Liquid transfer pump 3a Electrode 3b Ground electrode 4 Dielectric 5 Power supply

Claims (11)

a vacuum chamber;
a box-shaped water tank arranged inside the decompression chamber for storing the water to be treated;
a pair of electrodes arranged inside the decompression chamber;
a power supply that applies an alternating voltage to the pair of electrodes,
the pair of electrodes,
a plate-shaped electrode provided so as to be positioned above the water surface of the water to be treated stored in the water tank;
a dielectric provided on the lower surface side of the flat electrode and facing the water surface of the water to be treated stored in the water tank with a space therebetween;
a ground electrode provided so as to be positioned in the water to be treated stored in the water tank;
A decompression pump is connected to the decompression chamber for decompressing the gas phase atmosphere so that the inside of the decompression chamber becomes an extremely low vacuum,
A supply pipe for supplying plasma sterilized water to a sterilization target is connected to the water tank,
The plasma sterilized water generating apparatus, wherein the power supply is configured to supply power of 10 Wh or more per liter of the water to be treated. 2. The plasma sterilized water generating apparatus according to claim 1, wherein said power supply is configured to supply power of 20 Wh or more per liter of said water to be treated. 3. The plasma sterilized water generator according to claim 1, wherein a water supply pipe for supplying pure water is connected to said water tank. The object to be sterilized to which the plasma sterilized water generated by the plasma sterilized water generator is supplied is an evaporative humidifier of an outdoor air conditioner,
4. The plasma sterilized water generating apparatus according to claim 3, wherein said water supply pipe is connected to a humidification water supply pipe for supplying pure water as drip water to said evaporative humidifier in said outdoor air conditioner. The object to be sterilized to which the plasma sterilized water generated by the plasma sterilized water generator is supplied is an evaporative humidifier of an outdoor air conditioner,
The plasma sterilized water generating apparatus according to any one of claims 1 to 4, wherein the supply pipe is connected to a humidification water supply pipe that supplies pure water as drip water to the evaporative humidifier in the outdoor air conditioner. . The plasma sterilized water generating apparatus according to any one of claims 1 to 5, wherein the water tank is made of metal and is grounded to serve as the ground electrode. The plasma sterilized water generating apparatus according to any one of claims 1 to 6, wherein the water tank is provided with a stirring device for stirring the water to be treated stored in the water tank. The plasma sterilized water generating apparatus according to any one of claims 1 to 7, wherein the water tank is provided with a cooling device for cooling the water to be treated and cools the water to be treated to 10°C or less during the plasma treatment. The plasma sterilized water generating apparatus according to any one of claims 1 to 8, wherein the water tank is provided with a cooling device for cooling the water to be treated, and cools the generated plasma sterilized water to 7°C or less. The plasma sterilized water generator according to any one of claims 1 to 9, wherein the space between the dielectric and the water surface of the water to be treated stored in the water tank is 5 mm or more and 10 mm or less. The plasma sterilized water generating apparatus according to any one of claims 1 to 10, wherein a space of 50 mm or more is provided between the inner wall surface of the water tank and the side surface of the flat electrode.

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