Liquid treatment device, liquid treatment method, and plasma treatment liquid

The present disclosure provides a liquid treatment device, a liquid treatment method, and a plasma treatment liquid each capable of efficiently generating plasma and treating a liquid in a short time period. A liquid treatment device according to the present disclosure includes a first electrode, a second electrode disposed in a liquid to be treated, an insulator disposed around the first electrode with a space between the first electrode and the insulator, the insulator has an opening portion in a position in contact with the liquid to be treated, a power supply that applies voltage between the first electrode and the second electrode, and a supply device supplying a liquid to the space before the power source applies the voltage.

DESCRIPTION OF THE RELATED ART

The present disclosure relates to a plasma treatment device a liquid treatment method, and a plasma treatment liquid which generate plasma in a liquid to treat the liquid or particularly to treat water.

Conventional liquid treatment devices include a device using high-voltage pulse discharge (see, e.g., Patent Literature 1 (Japanese Patent No. 4784624)). FIG. 8 is a configuration diagram of a conventional liquid treatment device (a sterilizing device). A sterilizing device 1 shown in FIG. 8 includes a discharge electrode 6 which is paired a bar-shaped high voltage electrode 2 with a plate-shaped grounding electrode 3. The high voltage electrode 2 is coated with an insulator 4 except an end surface of a tip portion 2a to form a high voltage electrode portion 5. The tip portion 2a of the high voltage electrode 2 and the grounding electrode 3 are immersed in a liquid to be treated 8 in a treatment tank and are oppositely disposed to each other at a predetermined electrode interval. The high voltage electrode 2 and the grounding electrode 3 are connected to a power source 9 generating a high voltage pulse. A negative-polarity high voltage pulse of 2 to 50 kV at 100 Hz to 20 kHz is applied between the both electrodes to cause a discharge. Evaporation of water due to the energy thereof and vaporization associated with shock waves generate air bubbles 10 composed of water vapor (a flash boiling phenomenon). Plasma generated in the vicinity of the high voltage electrode 2 generates OH, H, O, O2−, O−, and H2O2for sterilization of microorganisms and bacteria.

Another conventional liquid treatment device supplies a gas from a tube type electrode to a treatment tank to create a state in which a liquid to be treated and air bubbles are interposed between electrodes, and a high voltage pulse is applied between the electrodes to generate plasma for treating the liquid (see, e.g., Patent Literature 2 (Japanese Patent No. 4041224)). This liquid treatment device can generate plasma for treating liquid even when the high voltage pulse applied between the electrodes is a low voltage and therefore can reduce a power consumption. A liquid contamination removal device is disclosed that has a series of pulsed electric arc generating electrodes arranged in a liquid to promote arcs in the liquid by injecting a gas through one of the electrodes (see, e.g., Patent Literature 3 (Japanese Patent No. 3983282)).

SUMMARY

The devices of the conventional configurations described above, however, have a problem that a long time is taken for treatment of liquid because of a low plasma generation efficiency.

Therefore, one non-limiting and exemplary embodiment provides a liquid treatment device and a liquid treatment method each capable of generating plasma efficiently and treating a liquid within a short period of time, and a plasma treatment liquid being treated by the liquid treatment device or the liquid treatment method.

In one general aspect, a liquid treatment device according to the present disclosure includes:

a first electrode;

a second electrode disposed in a liquid to be treated;

an insulator disposed around the first electrode with a space between the first electrode and the insulator, wherein the insulator has an opening portion in a position in contact with the liquid to be treated;

a power source applying voltage between the first electrode and the second electrode so as to generate plasma in the vicinity of the opening portion of the insulator; and

a supply device supplying a liquid through a path which is different from the opening portion to the space before the power source applies the voltage.

These general and specific aspects may be implemented using a liquid treatment device, a liquid treatment method, and any combination of liquid treatment devices and liquid treatment methods.

The liquid treatment device, the liquid treatment method, and the plasma treatment liquid, plasma according to the present disclosure are capable of treating a liquid in a short time by generating plasma effectively.

DETAILED DESCRIPTION

A liquid treatment device according to a first aspect of the present disclosure includes:

a first electrode;

a second electrode disposed in a liquid to be treated;

an insulator disposed around the first electrode with a space between the first electrode and the insulator, wherein the insulator has an opening portion in a position in contact with the liquid to be treated;

a power source applying voltage between the first electrode and the second electrode so as to generate plasma in the vicinity of the opening portion of the insulator; and

a supply device supplying a liquid through a path which is different from the opening portion to the space before the power source applies the voltage.

With such a configuration, since the plasma can efficiently be generated and long-life OH radicals can be generated as compared to a conventional device, the liquid to be treated can be treated within a short period of time. A product generated by the plasma can be controlled by the liquid supplied from the supply device, and a substance in the liquid to be treated can be decomposed by the product efficiently within a short period of time.

In a liquid treatment device according to a second aspect of the present disclosure,

the supply device according to the first aspect supplies the liquid to the space to form a state in which the space is filled with the liquid,

the power source applies voltage between the first electrode and the second electrode after the space is filled with the liquid to evaporate the liquid in the space so as to generate a gas, and to discharge in the gas when the gas is released from the opening portion of the insulator into the liquid to be treated so as to generate the plasma.

With such a configuration, since a space formed between the first metal electrode and the insulator is filled with the liquid, air in the space can be removed. As a result, as compared to the case of filling the space with air, an amount of a nitrogen compound generated by the plasma can be reduced. In other words, an amount of the nitrogen compound generated by the plasma can be controlled by using the liquid, for example, the liquid to be treated, supplied from the supply device. By reducing the generated nitrogen compound in this way, the energy of the plasma is not consumed by a process of generating the nitrogen compound and the OH radicals can efficiently be generated. As a result, the liquid to be treated can be treated within a short period of time.

In a liquid treatment device according to a third aspect of the present disclosure, the liquid treatment device according to the first aspect further includes a holding block holding the first electrode and connected to the insulator,

wherein the holding block has a structure sealing the first electrode.

With such a configuration, liquid or gas can be restrained from leaking from inside the space to the outside in a connecting portion connecting the holding block and the first electrode. As a result, since the gas can be discharged from the opening portion of the insulator, the plasma can certainly be generated in the gas present in the opening portion of the insulator to treat the liquid to be treated efficiently within a short period of time.

In a liquid treatment device according to a fourth aspect of the present disclosure, the holding block according to the third aspect includes a flow channel connecting the space formed between the first electrode and the insulator to the supply device.

With such a configuration, the supply device can be attached to the holding block and liquid or gas can easily be supplied through the flow channel to the space between the first electrode and the insulator. Since the holding block can be made of an easily processable material, a process cost for disposing the flow channel can be reduced.

In a liquid treatment device according to a fifth aspect of the present disclosure, the first electrode according to a first aspect has therein a flow channel connecting the space formed between the first electrode and the insulator to the supply device.

With such a configuration, the supply device can be attached to the first electrode and liquid or gas can easily be supplied through the flow channel to the space between the first electrode and the insulator.

In a liquid treatment device according to a sixth aspect of the present disclosure, the opening portion of the insulator according to the first aspect is disposed in an opening direction that is a vertically upper direction relative to a side surface of the insulator.

With such a configuration, since bubble clogging of air bubbles can be suppressed in the vicinity of the opening portion, the plasma can efficiently be generated.

In a liquid treatment device according to an seventh aspect of the present disclosure, a plurality of the opening portions of the insulator according to the first aspect are arranged at the insulator.

With such a configuration, since the plasma can be generated from a plurality of the opening portions, the plasma can more efficiently be generated.

In a liquid treatment device according to an eighth aspect of the present disclosure, the liquid treatment device according to the first aspect further includes a first tank storing the liquid to be treated.

With such a configuration, the liquid treatment device with improved usability can be provided.

In a liquid treatment device according to a ninth aspect of the present disclosure, the treatment device according to the eighth aspect further includes a second tank connected to the first tank by a circulating pump and pipe.

With such a configuration, the liquid treatment device can treat a larger volume of the liquid to be treated.

In a liquid treatment device according to a tenth aspect of the present disclosure, the second tank according to the ninth aspect is connected to ground.

With such a configuration, the liquid treatment device of the present disclosure can suppress an electric shock.

A system according to an eleventh aspect of the present disclosure with a cleaning or purifying function includes the liquid treatment device according to the first aspect.

With such a configuration, the liquid to be treated can be treated efficiently within a short period of time in a system with a cleaning or purifying function including the liquid treatment device of the present disclosure.

A liquid treatment method according to a twelfth aspect of the present disclosure includes:

supplying a liquid to a space formed between a first electrode and an insulator having an opening portion through a path which is different from an opening portion, wherein the insulator is disposed around the first electrode through the space, and the opening portion is disposed in contact with a liquid to be treated; and

applying voltage between the first electrode and a second electrode to generate plasma in the opening portion of the insulator, wherein the second electrode is disposed in the liquid to be treated.

With such a configuration, since the plasma can efficiently be generated and long-life OH radicals can be generated, the liquid to be treated can be treated within a short period of time. The product generated by the plasma can be controlled by supplying a liquid to a space formed by the first electrode and the insulator. As a result, since the product can be generated depending on the liquid to be treated, a substance in the liquid to be treated can efficiently be decomposed.

In a liquid treatment method according to a thirteenth aspect of the present disclosure, after the space is filled with the liquid by supplying the liquid according to the twentieth aspect, the voltage is applied between the first electrode and the second electrode to evaporate the liquid in the space so as to generate a gas, and to discharge in the gas when the gas is released from the opening portion of the insulator into the liquid to be treated so as to generate the plasma in the gas.

With such a configuration, since the plasma can efficiently be generated and long-life OH radicals can be generated, the liquid to be treated can be treated within a short period of time. Since a space formed between the first metal electrode and the insulator is filled with the liquid, air in the space can be removed. As a result, as compared to the case of filling the space with air, an amount of the nitrogen compound generated by the plasma can be reduced. In other words, an amount of the nitrogen compound generated by the plasma can be controlled by the liquid treatment method of the present disclosure.

(Circumstances Leading to One Embodiment According to the Present Disclosure)

As described in the section of “DESCRIPTION OF THE RELATED ART”, the sterilizing device of Patent Literature 1 shown in FIG. 8 instantaneously vaporizes a liquid by using the flash boiling phenomenon and causes a discharge between the bar-shaped high voltage electrode 2 and the plate-shaped grounding electrode 3 disposed oppositely to each other, thereby generating plasma. However, since an energy for vaporizing the liquid must be applied to cause the flash boiling phenomenon, the device has a problem that a long time is taken for treatment of liquid because the plasma cannot efficiently be generated.

The device of Patent Literature 2 or Patent Literature 3 generates air bubbles in a liquid by supplying a gas into the liquid for generating plasma and applies a high voltage between the electrodes to cause a discharge in the air bubbles, thereby generating the plasma. The device of Patent Literature 2 or Patent Literature 3, however, has a problem that a liquid treatment cannot efficiently be performed because products (such as electrons, ions, or radicals) generated by the plasma are not generated in accordance with a substance contained in a liquid that should be treated (a liquid to be treated).

Therefore, the present inventors found a configuration having a supply device supplying a fluid controlling a product generated by plasma into a space formed between a first metal electrode and an insulator. In this configuration, a fluid can be supplied from the supply device to the space between the first metal electrode and the insulator to control the product generated by plasma depending on a liquid that should be treated (a liquid to be treated). As a result, the liquid treatment can be performed efficiently within a short period of time.

Embodiments of the present disclosure are described with reference to the drawings. In all the following figures, the same or equivalent portions are denoted by the same reference numerals and are not redundantly be described.

First Embodiment

Overall Configuration

An overall configuration of a liquid treatment device100according to a first embodiment of the present disclosure is described.

FIG. 1shows a schematic of an overall configuration of the liquid treatment device100according to the first embodiment of the present disclosure. As shown inFIG. 1, the liquid treatment device100according to the first embodiment includes a first metal electrode101, a second metal electrode102, an insulator103, a power source104, and a supply device105. The liquid treatment device100according to the first embodiment may further include a first tank106and a second tank107. In the first embodiment of the following description, the liquid treatment device100includes the first tank106and the second tank107, and the first tank106and the second tank107are connected through a pipe109to a circulating pump108.

As shown inFIG. 1, the first tank106and the second tank107are filled with a liquid that is treated (a liquid to be treated)110and are connected through the pipe109to the circulating pump108. One wall of the first tank106is disposed with the first metal electrode101and the second metal electrode102penetrating through the wall. A portion of each of the first metal electrode101and the second metal electrode102is located in the liquid to be treated110in the first tank106. An insulator103having an opening portion112and a holding block113holding the first metal electrode101are disposed such that a space111is formed around the first metal electrode101. A flow channel114is disposed inside the holding block113, and the supply device105and the space111are connected via this flow channel114. A power source104is disposed between the first metal electrode101and the second metal electrode102for applying high voltage to cause a discharge at the opening portion112of the insulator103so as to generate plasma115. As described above, the liquid treatment device100according to the first embodiment of the present disclosure is configured such that the supply device105supplies a fluid controlling the product generated by the plasma115into the space111between the first metal electrode101and the insulator103.

An electrode configuration around the first metal electrode101in the liquid treatment device100according to the first embodiment is described. An electrode configuration around the first metal electrode101in the first embodiment includes the first metal electrode101, the insulator103, the supply device105, and the holding block113.

FIG. 2shows a cross-sectional view of the electrode configuration around the first metal electrode101in the first embodiment. As shown inFIG. 2, the insulator103is disposed around the first metal electrode101such that the space111is formed therebetween. The insulator103has the at least one opening portion112to allow the inside of the first tank106to communicate with the space111. The holding block113holding the first metal electrode101is disposed at the end portion of the insulator103. The holding block113is provided with the flow channel114connecting the supply device105supplying the fluid and the space111. The flow channel114bent at a right angle is disposed in the holding block113by way of example inFIG. 2, but not limited to this. The flow channel114may have any shape capable of supplying the fluid from the supply device105to the space111between the first metal electrode101and the insulator103.

FIG. 3shows a cross-sectional view of an electrode configuration around another first metal electrode101in the first embodiment. As shown inFIG. 3, the first metal electrode101may have the flow channel114disposed within the first metal electrode101. For example, the first metal electrode101may be in a hollow shape having an opening end. The supply device105may be connected to an end portion of the first metal electrode101to supply the fluid from the supply device105via the flow channel114of the first metal electrode101to the space111between the first metal electrode101and the insulator103.

As described above, the electrode configuration of the first embodiment is configured such that the supply device105supplies the fluid via the flow channel114disposed in the holding block113or the first metal electrode101to the space111between the first metal electrode101and the insulator103. With this configuration, for example, the fluid can be easily be supplied from the supply device105disposed outside the first tank106to the space111between the first metal electrode101and the insulator103. Since an easily processable member can be used for the holding block113in the electrode configuration shown inFIG. 2, a process cost for disposing the flow channel114can be reduced.

The constituent components in the first embodiment will be described.

The first metal electrode101is at least partially disposed in the first tank106filled with the liquid to be treated110. The first metal electrode101is held by the holding block113. The first metal electrode101in the first embodiment has a column shape with a diameter of 0.95 mm. These are a diameter and a shape as an example of the first metal electrode101. The diameter of the first metal electrode101may be any diameter as long as the plasma115is generated, and may be equal to or less than 2 mm. The shape of the first metal electrode101is not limited to the column shape and may be any shape such as a rectangular parallelepiped shape or a planar shape, for example. The first metal electrode101may be made of material such as iron, tungsten, copper, aluminum, platinum, or an alloy containing one or a plurality of metals selected from these metals. Yttrium oxide having an electrical resistivity of 1 to 30 Ωcm due to addition of a conductive substance may be thermally sprayed to a portion of the surface of the first metal electrode101. The thermal spray of yttrium oxide has an effect of extending an electrode life. The first metal electrode101is disposed in the first tank106in the configuration described in the first embodiment, but the position of the first metal electrode101is not limited thereto. An electrode made of metal material is used as the first metal electrode101in the first embodiment, but not limited to this. The first metal electrode may be used that includes a material other than metal material, such as carbon.

As shown in an electrode configuration depicted inFIG. 3, the first metal electrode101may be provided with a flow channel114through which the fluid supplied from the supply device105flows. For example, the first metal electrode101may be in a hollow shape having an opening end.

The second metal electrode102is also at least partially disposed in the first tank106filled with the liquid to be treated110. The second metal electrode102is not limited in terms of the disposed position and may be disposed at any position in the first tank106. The second metal electrode102may be made of any conductive metal material. For example, as is the case with the first metal electrode101, the second metal electrode102may be made of material such as iron, tungsten, copper, aluminum, platinum, or an alloy containing one or a plurality of metals selected from these metals. The second metal electrode102is disposed in the first tank106in the configuration described in the first embodiment, but the position of the second metal electrode102is not limited thereto. For example, the second metal electrode102needs to have at least a portion disposed in the liquid to be treated110. An electrode made of metal material is used as the second metal electrode102in the first embodiment, but not limited to this. The second metal electrode may be used that includes a material other than metal material, such as carbon.

The insulator103is disposed such that the space111is formed around the first metal electrode101. The insulator103is provided with the opening portion112to allow the inside of the first tank106to communicate with the space111. Therefore, the insulator103is disposed around the first metal electrode101with the space111therebetween and has the opening portion112in a position in contact with the liquid to be treated110. The position in contact with the liquid to be treated110may be any portion of the insulator103disposed (immersed) in the liquid to be treated110, for example. The opening portion112has a function of generating an air bubble116in the liquid to be treated110in the first tank106. The insulator103of the first embodiment has, by way of example, a cylindrical shape with an inner diameter of 1 mm and an outer diameter of 2 mm and is provided with the one opening portion112with a diameter of 0.7 mm. The insulator103is not limited to the size or the shape described above and may have any size or shape as long as the space111can be formed around the first metal electrode101. For example, the diameter of the opening portion112is 0.7 mm in the first embodiment, but not limited to this, the diameter may be an arbitrary size equal to or less than 2 mm. The insulator103may include a plurality of the opening portions112. The position of the opening portion112is not particularly limited and can be provided in a vertically upper direction (an upper direction ofFIGS. 1 to 3) relative to a side surface of the insulator103. By setting the opening direction of the opening portion112upward, the bubble clogging of the air bubbles116generated in the opening portion112can be prevented. The opening portion112may be disposed in an end surface of the insulator103. The insulator103may be made of a material such as aluminum oxide, magnesium oxide, yttrium oxide, insulating plastic, glass, and quartz, for example.

The power source104is disposed between the first metal electrode101and the second metal electrode102. The power source104can apply pulse voltage or AC voltage between the first metal electrode101and the second metal electrode102. The voltage waveform may have a pulse shape, a half sine wave shape, or a sine wave shape, for example.

The supply device105is disposed on the holding block113or the first metal electrode101as shown inFIG. 2 or 3. The supply device105supplies a fluid via the flow channel114disposed in the holding block113or the first metal electrode101to the space111formed between the first metal electrode101and the insulator103. The fluid is liquid or gas for controlling the product generated by the plasma115. The liquid is, for example, tap water or the liquid to be treated110. The gas is, for example, He,02, or air. The liquid or gas is arbitrarily selected for generating a product corresponding to a substance contained in the liquid to be treated110. The supply device105can be implemented by using a syringe shown inFIG. 2 or 3as well as a pump, for example.

The first tank106is used for storing the liquid to be treated110. The volume of the first tank106and the second tank107is about 600 milliliters in total. The liquid to be treated110in the first tank106is circulated by the circulating pump108and the pipe109as described above. The circulating speed of the liquid to be treated110is set to an appropriate value from a decomposition rate of a substance to be decomposed by the plasma115and the volume of the first tank106.

The second tank107is connected, for example, via the circulating pump108and the pipe109to the first tank106. The second tank107may be used for a water clarification device, an air conditioner, a humidifier, a washing machine, an electric razor washer, or a dish washer, for example. The second tank107may be connected to ground so as to suppress an electric shock.

The holding block113is connected to one end portion of the insulator103. The holding block113holds the first metal electrode101. The holding block113may have a structure of sealing so as to prevent leakage of the fluid supplied from the supply device105into the space111in the portion connecting to the first metal electrode101. For example, the structure may be achieved such that the first metal electrode101is screwed to the holding block113. The sealing structure is not limited thereto and may be any structure.

As shown inFIG. 2, the flow channel114may be disposed inside the holding block113. With this configuration, the fluid may be supplied from the supply device105via the flow channel114disposed in the holding block113to the space111.

A liquid treatment method using the liquid treatment device100according to the first embodiment is described.

Before starting the liquid treatment, the fluid controlling the product generated by the plasma115is supplied from the supply device105via the flow channel114to the space111formed between the first metal electrode101and the insulator103. The case of using liquid and the case of using gas as the fluid supplied from the supply device105are separately be described.

<Case of Using Liquid as Supplied Fluid>

The case of using liquid as the supplied fluid will be described.

If the fluid supplied from the supply device105is liquid, the supply device105supplies the liquid via the flow channel114to the space111to achieve a state of the space111filled inside with the liquid. In particular, before the power source104applies voltage between the first metal electrode101and the second metal electrode102, the state of the space111filled inside with the liquid is formed. The state of the space111filled inside with the liquid is not limited to a state of the space111filled inside with the liquid supplied from the supply device105and includes a state of the space111filled inside with liquid in which the liquid supplied from the supply device105is mixed with the liquid to be treated110of the first tank106.

The power source104applies voltage between the first metal electrode101and the second metal electrode102.

The electric power input from the first metal electrode101increases the temperature of the liquid in the space111. Because of this temperature increase, the liquid in the space111is evaporated to generate a gas. The generated gas gathers in the space111and is discharged due to a pressure difference between the pressure inside the space111and the pressure of the first tank106from the opening portion112disposed in the insulator103to the liquid to be treated110in the first tank106.

When this gas passes through the opening portion112, the gas replaces the liquid in the vicinity of the opening portion112with gas, insulating the first metal electrode101and the second metal electrode102conducted through the liquid. At this point, the high voltage from the power source104is applied to the gas present in the opening portion112and a discharge occurs due to electric field concentration. As a result, the plasma115is generated in the gas present in the opening portion112. Once the plasma115is generated, the plasma115is continuously and serially generated and the gas containing the plasma115is discharged from the opening portion112of the insulator103into the liquid to be treated110in the first tank106. The plasma115is put into a state of projecting from the opening portion112of the insulator103into the liquid to be treated110in the first tank106. Therefore, the first embodiment achieves a state in which the plasma115is generated in the opening portion112of the insulator103.

Moreover, the gas containing the plasma115projecting from the opening portion112is partially separated to generate a plurality of the air bubbles116. The air bubbles116are dispersed in the liquid to be treated110in the first tank106. The plurality of the air bubbles116contains electrons, ions, or radicals generated by the plasma115. The plurality of the air bubbles116sterilizes the liquid to be treated110and/or decomposes a chemical substance contained in the liquid to be treated110. The generation of electrons, ions, or radicals contained in the plurality of the air bubbles116can be controlled by the liquid (fluid) supplied by the supply device105.

<Case of Using Gas as Supplied Fluid>

The case of using gas as the supplied fluid is described.

If the fluid supplied from the supply device105is gas, the supply device105supplies the gas via the flow channel114to the space111to achieve a state of the space111filled inside with the gas. In particular, before the power source104applies voltage between the first metal electrode101and the second metal electrode102, the state of the space111filled inside with the gas is formed. The state of the space111filled inside with the gas is not limited to a state of the space111filled inside with the gas supplied from the supply device105and includes a state of the space111filled inside with gas in which the gas supplied from the supply device105is mixed with gas originally present in the space111(e.g., air, or gas generated by vaporization of the liquid to be treated110).

The power source104applies voltage between the first metal electrode101and the second metal electrode102.

The high voltage from the power source104is applied to the gas present in the opening portion112and a discharge occurs in the gas due to electric field concentration. As a result, the plasma115is generated in the gas. Once the plasma115is generated, the plasma115is continuously and serially generated and the gas containing the plasma115is discharged from the opening portion112of the insulator103toward the liquid110in the first tank106. The plasma115is put into a state of projecting from the opening portion112of the insulator103into the liquid to be treated110in the first tank106. Therefore, the first embodiment achieves a state in which the plasma115is generated in the vicinity of the opening portion112of the insulator103. The vicinity of the opening portion112means the opening portion112and a region in the gas extended from the opening portion112into the liquid to be treated110.

Moreover, the gas containing the plasma115projecting from the opening portion112is partially separated to generate a plurality of the air bubbles116. The air bubbles116are dispersed in the liquid to be treated110in the first tank106. The plurality of the air bubbles116contains electrons, ions, or radicals generated by the plasma115. The plurality of the air bubbles116sterilizes the liquid to be treated110and/or decomposes a chemical substance contained in the liquid to be treated110. The generation of electrons, ions, or radicals contained in the plurality of the air bubbles116can be controlled by the liquid (fluid) supplied by the supply device105.

Effects (a product and a decomposition rate) of the liquid treatment device100of the first embodiment of the present disclosure are described. Two cases are discussed. One is the case of filling the space111formed between the first metal electrode101and the insulator103with air117before the treatment of the liquid to be treated110. The other is the case of filling the space111with the liquid to be treated110before the treatment of the liquid to be treated110. The case of filling the space111with the air117supplied from the supply device105is described as Example 1 and the case of filling the space111with the liquid to be treated110supplied from the supply device105is described as Example 2. Also, a difference in the product due to power consumption is described as a reference by using Reference Examples 1 and 2.

Examples 1 and 2 are described.

In Example 1, the liquid treatment was performed in the liquid treatment device100in the first embodiment shown inFIG. 1in the state of filling the space111formed between the first metal electrode101and the insulator103with the air117supplied from the supply device105.FIG. 4shows the state of filling the space111formed between the first metal electrode101and the insulator103with the air117supplied from the supply device105in the first embodiment. As shown inFIG. 4, the space111was filled with the air117supplied from the supply device105in Example 1. The liquid to be treated110of Example 1 was at a CH3COOH concentration of 1 ppm and an electric conductivity of 19.2 mS/m. In Example 1, the power source104applies pulse voltage with power consumption of 300 W, a pulse width of 1 μs, and a frequency of 30 kHz.

In Example 2, the liquid treatment was performed in the state of filling the space111with the liquid to be treated110supplied from the supply device105.FIG. 5shows the state of filling the space111formed between the first metal electrode101and the insulator103with the liquid to be treated110supplied from the supply device105in the first embodiment. As shown inFIG. 5, the space111was filled with the liquid to be treated110supplied from the supply device105to remove air in Example 2. The other conditions are the same as Example 1.

Reference Examples 1 and 2 are described.

Reference Example 1

Reference Example 1 is different from Example 1 in that the power consumption is 30 W. The other conditions are the same as Example 1. Therefore, in the Reference Example 1, the power source104applied the pulse voltage with power consumption of 30 W, a pulse width of 1 μs, and a frequency of 30 kHz in the state of filling the space111with the air117supplied from the supply device105as shown inFIG. 4. The liquid to be treated110of Reference Example 1 was at a CH3COOH concentration of 1 ppm and an electric conductivity of 19.2 mS/m as is the case with Examples 1 and 2.

Reference Example 2

Reference Example 2 is different from Example 2 in that the power consumption is 30 W. The other conditions are the same as Example 2. Therefore, in the Reference Example 2, the power source104applied the pulse voltage with power consumption of 30 W, a pulse width of 1 μs, and a frequency of 30 kHz in the state of filling the space111with the liquid to be treated110supplied from the supply device105as shown inFIG. 5. The liquid to be treated110of Reference Example 2 was at a CH3COOH concentration of 1 ppm and an electric conductivity of 19.2 mS/m as is the case with Examples 1 and 2.

Products generated by the plasma treatment (liquid treatment) in Examples 1 and 2 and Reference Examples 1 and 2 are discussed. Also, generation amounts thereof are discussed.

To measure concentrations of various ions contained in the liquid having undergone the plasma treatment (the liquid treatment) in Examples 1 and 2 and Reference Examples 1 and 2, ion chromatography (DX-500, manufactured by Dionex) was used for the measurement.

FIG. 6shows time dependency of concentration of NO3−contained in the plasma treatment liquid in Examples 1 and 2 and Reference Examples 1 and 2. As shown inFIG. 6, in the plasma treatment liquid of Example 1 from the liquid treatment performed in the state of filling the space111with the air117supplied from the supply device105, the concentration of NO3−is higher as compared to Example 2. The generation rate of NO3−of Example 1 is 8×10−5g/(min·W) or more. On the other hand, in the plasma treatment liquid of Example 2 from the liquid treatment performed in the state of filling the space111with the liquid to be treated110supplied from the supply device105, the concentration of NO3−is lower as compared to Example 1 and the generation rate of NO3−is 8×10−5g/(min·W) or less. From the above, it is understood that when the liquid treatment is performed in the state of filling the space111with the air117supplied from the supply device105, NO3−is likely to be generated as the product. On the other hand, it is understood that when the liquid treatment is performed in the state of filling the space111with the liquid to be treated110supplied from the supply device105, the generation amount of NO3−is reduced as compared to Example 1. This is because the energy of the plasma is preferentially consumed by the process of generating a nitrogen compound through activation of N2contained in the air117in the space111in a place where the plasma is generated (a plasma generation field) in Example 1. Although NO3−was generated in Example 2 since N2dissolved in the liquid to be treated110exists, NO3−is not generated if N2is not dissolved in the liquid to be treated110.

With regard to Reference Examples 1 and 2 of the plasma treatment performed at power consumption of 30 W, it is understood that the concentration of NO3−is drastically reduced as compared to Examples 1 and 2 of the plasma treatment performed at power consumption of 300 W. A comparison is then be made between Reference Examples 1 and 2, i.e., between the state of filling the space111with the air117supplied from the supply device105and the state of filling the space111with the liquid to be treated110supplied from the supply device105. It is understood that the concentration of NO3−is higher in the state of filling the space111with the air117supplied from the supply device105(Reference Example 1) as compared to the state of filling the space111with the liquid to be treated110supplied from the supply device105(Reference Example 2). From the above, it is understood that while the space111is filled with the air117supplied from the supply device105, the energy of the plasma is preferentially consumed by the process of generating a nitrogen compound through activation of N2contained in the air117in the place where the plasma is generated (the plasma generation field) also in the case of the power consumption of 30 W.

The decomposition rate of the plasma treatment liquid of Examples 1 and 2 is described by taking decomposition of CH3COOH as an example.

FIG. 7shows time dependency of concentration of CH3COO−contained in the plasma treatment liquid in Examples 1 and 2. As shown inFIG. 7, comparing Example 1 with Example 2, it is understood that the concentration of CH3COO−is lower in the Example 2 in the state of filling the space111with the liquid to be treated110supplied from the supply device105. It is also understood fromFIG. 7that while the decomposition rate of CH3COOH of Example 2 is 1.3×10−9g/min or more, the decomposition rate of CH3COOH of Example 1 is 1.3×10−9g/min or less. This is because less N2is present in the place where the plasma is generated (the plasma generation field) in Example 2 as compared to Example 1 and, therefore, the energy of the plasma is efficiently consumed by the decomposition reaction of CH3COOH without being consumed by the process of producing the nitrogen compound.

As described above, the air117can be removed from the space111by achieving the state of filling the space111formed between the first metal electrode101and the insulator103with the liquid to be treated110supplied from the supply device105. This enables provision of control such that the nitrogen compound generated by the plasma115is reduced as compared to when the air111is present in the space111. As a result, the energy of the plasma115is efficiently consumed by a reaction of decomposition of the substance in the liquid to be treated110without being consumed by the process of producing the nitrogen compound.

The case of using He (helium) as the fluid supplied by the supply device105is described. It is found that when the liquid treatment is performed in the state of filling the space111formed between the first metal electrode101and the insulator103with He by the supply device105, H2O2is generated by the plasma115. In the case of filling the space111with He, the generation rate of H2O2in the plasma treatment liquid is about 7.5 times greater as compare to the case of filling the space117with the air117supplied from the supply device105. Using He as the supplied fluid can accelerate the generation rate of H2O2in this way and is therefore useful for bleaching or sterilization, for example.

The case of using O2as the fluid supplied by the supply device105is described. It is found that when the liquid treatment is performed with the space111filled with O2by the supply device105, H2O2is generated by the plasma115. In the case of filling the space111with O2, the generation rate of H2O2in the plasma treatment liquid is about 9.2 times greater as compare to the case of filling the space117with the air117supplied from the supply device105. Using O2as the supplied fluid can accelerate the generation rate of H2O2in this way and is therefore useful for bleaching or sterilization, for example.

If the liquid treatment is performed with the space111filled with tap water by the supply device105, H2O2is generated by the plasma115.

As described above, by using arbitrary liquid or gas as the fluid supplied by the supply device105, the generation rate of the product such as H2O2can be controlled.

An OH radical generation rate during the liquid treatment in Example 2 is described.

OH radicals are generated in the liquid treated in Example 2. The concentration of OH radicals in the plasma treatment liquid of Example 2 was measured by using an electron spin resonance spectrometer (JES-FA 300, JEOL Ltd.) with an ESR (electron spin resonance) method. To measure OH radicals with the ESR method, the OH radicals must be bound to a spin trapping agent called DMP. In this measurement, DMPO (5.5-dimethyl-1-pyrroline N-oxide, manufactured by Dojindo Laboratories) was used.

In Example 2, the time dependency of OH radicals was measured after the generation of the plasma115was started by applying the pulse voltage. As a result, it was found that the OH radical generation rate during the plasma treatment (liquid treatment) was 1×10−8mol/(min·W) or more. The time dependency is also measured after the generation of the plasma115was terminated by turning off the pulse power source. As a result, it was found that the life of the OH radicals was 5 minutes or longer and was about 10 minutes.

As described above, in the plasma treatment liquid having undergone the liquid process by the liquid treatment device100according to the first embodiment, OH radicals can continuously exist even after the stop of energization (discharge). As a result, a substance to be decomposed can efficiently be decomposed even after the stop of energization of the liquid treatment device100according to the first embodiment of the present disclosure.

As described above, if a liquid is treated by plasma (hereinafter, in-liquid plasma) generated in the liquid that should be treated (the liquid to be treated)110and has the NO3−generation rate of 8×10−5g/(min·W) or less and the OH radical generation rate of 1×10−8mol/(min·W) or more, OH radicals can continuously exist even after the stop of energization (discharge). As a result, a substance in the liquid to be treated110can efficiently be decomposed.

As described above, since the liquid treatment device100according to the first embodiment of the present disclosure can efficiently generate the plasma115and can generate long-life OH radicals as compared to a conventional device, the liquid to be treated110can be treated within a short period of time. The liquid treatment device100according to the first embodiment has the configuration capable of supplying the fluid controlling the product generated by the plasma115to the space111between the first metal electrode101and the insulator103before treatment of the liquid to be treated110. With this configuration, the liquid treatment device100according to the first embodiment can achieve the state of filling the space111with the fluid supplied from the supply device105before the liquid treatment and generate the product corresponding to the substance in the liquid to be treated110by the plasma115. Therefore, the liquid treatment device100according to the first embodiment can use the fluid supplied by the supply device105to control the product generated by the plasma115. The liquid treatment device100according to the first embodiment can treat the liquid to be treated110with the product efficiently within a short period of time.

When the fluid supplied from the supply device105in the first embodiment is the liquid to be treated110, the space111formed between the first metal electrode101and the insulator103is filled with the liquid to be treated110supplied from the supply device105. Therefore, the air in the space111can be removed before the liquid treatment. As a result, an amount of the nitrogen compound generated by the plasma115can be reduced as compared to the case of filling the space111with the air117. Therefore, when the liquid to be treated110is used as the fluid supplied from the supply device105, an amount of the nitrogen compound generated by the plasma115can be controlled.

When the fluid supplied from the supply device105in the first embodiment is gas, such as He, and O2, the plasma115generates H2O2. H2O2is useful for bleaching or sterilization, for example. As described above, by using arbitrary gas as the gas supplied from the supply device105depending on the liquid to be treated110, the product generated by the plasma115can be controlled. As a result, the substance in the liquid to be treated110can be decomposed efficiently within a short period of time.

The liquid treatment device100according to the first embodiment has the holding block113at the end portion of the insulator103to hold the first metal electrode101. The connecting portion between the first metal electrode101and the holding block113preferably has a sealing structure, such as a screwing structure. Such a structure can prevent the fluid from leaking to the outside in the connecting portion between the first metal electrode101and the holding block113. The gas is released from the opening portion112of the insulator103and the plasma115can certainly be generated in the gas present in the opening portion112.

The flow channel114in the first embodiment is disposed inside the holding block113or the first metal electrode101. With this configuration, the fluid can easily be supplied from the supply device105via the flow channel114to the space111between the first metal electrode101and the insulator103. Since the holding block113can be made of an easily processable material, the process cost for providing with the flow channel114can be reduced.

Since the opening direction of the opening portion112of the insulator103in the first embodiment is set to the vertically upper direction relative to the side surface of the insulator103, the bubble clogging of the air bubbles116can be prevented in the vicinity of the opening portion112. A plurality of the opening portions112can be arranged at the insulator103. As a result, the plasma115can efficiently be generated from the opening portions112.

The liquid treatment device100according to the first embodiment has the first tank106and the second tank107connected through the pipe109to the circulating pump108therefore can treat a large volume of the liquid to be treated110. The second tank107can be connected to ground to prevent an electric shock.

By using the second tank107in the first embodiment for a water clarification device, an air conditioner, a humidifier, a washing machine, an electric razor washer, a dish washer, a toilet, or water for hydroponic culture/a nutrient solution circulation device, the liquid treatment device100can be used for various electrical products etc. A system with a cleaning or purifying function including the liquid treatment device100of the first embodiment can be achieved.

The liquid treatment device100according to the first embodiment may be implemented in any embodiments. For example, embodiments include a liquid treatment method. According to this liquid treatment method, since the plasma115can efficiently be generated and long-life OH radicals can be generated, the liquid to be treated110can be treated within a short period of time. According to this liquid treatment method, any liquid or gas can be used depending on the liquid to be treated110as the fluid supplied from the supply device105to the space111to control the product generated by the plasma115. For example, an amount of the nitrogen compound generated by the plasma115can be controlled. The liquid to be treated110may be used as the fluid supplied from the supply device105so as to reduce the nitrogen compound. The air117may be used as the fluid supplied from the supply device105so as to increase the nitrogen compound. He (helium) and O2may be used as the fluid supplied from the supply device105so as to generate H2O2, as described above, the liquid treatment method according to the first embodiment can control the product generated by the plasma115depending on the liquid to be treated110and, therefore, the liquid to be treated110can be treated within a short period of time.

The liquid (plasma treatment liquid) treated by the liquid treatment device100according to the first embodiment and the liquid treatment method has long-life OH radicals continuously existing after the stop of energization (discharge). As a result, the liquid to be treated110can be treated efficiently within a short period of time.

The liquid treated by the liquid treatment device100according to the first embodiment, i.e., the liquid treated by the plasma (the in-liquid plasma) generated in the liquid, has long-life OH radicals continuously existing after the stop of energization (discharge). As a result, the liquid to be treated110can be treated efficiently within a short period of time.

The liquid treatment device, the liquid treatment method, and the plasma treatment liquid according to the present disclosure can control a type of a product generated by plasma while efficiently generating the plasma so as to treat a liquid to be treated within a short period of time and, therefore, is useful as a water purifier for sewage treatment etc.