Plasma microbubble generator, water treatment device using same, and water treatment method

Abstract

Provided is a water treatment apparatus and method that purifies polluted water or the like that is contaminated with difficult-to-decompose organic substances such as organic fluorine compounds, and that has a simple structure and is easy to operate. [Solution] The water treatment device 1 is composed of a treatment tank 10, a plasma micro-bubble generator 20 and a high-voltage power supply unit 30. A high voltage is applied from the high-voltage power supply unit 30 to a fluid F containing micro-bubbles FB flowing out from the plasma micro-bubble generator 20 to generate discharge plasma inside the micro-bubbles FB, which is then mixed with the water to be treated WD contained in the treatment tank 10, thereby decomposing difficult-to-decompose organic substances present in the water to be treated WD.

Description

[Technical field]

[0001] The present invention relates to a water treatment device and a water treatment method, and more particularly to a plasma fine bubble generator for treating contaminated water containing persistent organic substances such as organic fluorine compounds, and a water treatment device and a water treatment method using the same. [Background technology]

[0002] In recent years, the harmfulness and accumulation of organic fluorine compounds have come to light, and as a result, their manufacture and use have been restricted. 8 F 17 SO 3 H, PFOS) and Perfluorooctanoic Acid (C 7 F 15 Long-chain organic fluorine compounds such as COOH and PFOA are very stable chemical substances, and are difficult to decompose in the natural environment after being released into the environment. In addition, it is known that if PFOS and PFOA are ingested into the human body, they remain in the body for a long time and bioaccumulate. In recent years, contamination of well water and tap water in Japan with PFOS and PFOA has been confirmed, and the Ministry of the Environment has positioned PFOS and PFOA as items requiring monitoring for the protection of human health, and has set provisional target values ​​for public water bodies and groundwater.

[0003] For the treatment of PFOS and PFOA, methods such as decomposition by photocatalysis and adsorption by adsorbents have been proposed, while a method of purifying the liquid by generating fine bubbles in the liquid to be treated and generating plasma within the fine bubbles has been proposed. It has been reported that this method can rapidly decompose refractory organic substances such as organic fluorine compounds that could not be decomposed even by accelerated oxidation treatment using OH radicals, which act as the strongest oxidizing agent except for fluorine. Furthermore, this method can significantly reduce the breakdown voltage required for plasma formation by introducing fine bubbles into the liquid, so it is expected that the efficiency of radical generation will be dramatically improved, which will lead to the solution of the problems of underwater plasma treatment methods.

[0004] A liquid treatment device disclosed in Patent Document 1 has been proposed for liquid purification by decomposition treatment in which plasma is generated in such fine bubbles. In this liquid treatment device, a plurality of openings are provided at the bottom of a treatment tank containing the liquid to be treated, and gas is sent from a bubble generating unit through the openings into the inside of the treatment tank. Meanwhile, the bubble generating unit controls the flow rate of the gas to a constant value, and generates periodic pressure fluctuations in the gas to send it into the openings of the treatment tank. Then, a high voltage synchronized with the pressure fluctuations is generated between a plurality of anode electrodes provided at positions overlapping the plurality of openings and a cathode electrode provided inside the treatment tank, to treat the liquid to be treated.

[0005] According to the above-mentioned liquid treatment device, by subjecting the gas to periodic pressure fluctuations, bubbles can be generated intermittently, continuously, and reliably from multiple openings, and by generating a high voltage at the optimal timing in synchronization with the pressure fluctuations, plasma can be generated within the bubbles generated at each opening. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-128909 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the above liquid treatment device, since the multiple openings provided at the bottom of the treatment tank function as bubble generation sources and also as plasma generation sites, the openings must be small enough to prevent the liquid in the treatment tank from leaking out, and large enough to ensure that plasma is generated within the bubbles, so the diameter of the openings is set to 0.3 to 0.5 mm. However, since the diameter of the openings cannot be changed, it is difficult to adjust the bubble size when the type or flow rate of the bubble gas changes, and the change in bubble size may change the energy state in the plasma generated within the bubbles, resulting in a decrease in treatment efficiency. [Means for solving the problem]

[0008] The present invention has been made in consideration of the above-mentioned object, and has an object to provide a plasma micro-bubble generator that is simple in structure and easy to operate, and that can purify groundwater, tap water, or contaminated water that is contaminated with persistent organic fluorine compounds such as PFOS and PFOA, as well as a water treatment device and water treatment method using the same.

[0009] The plasma microbubble generator according to the present invention comprises: A plasma micro-bubble generator that receives a fluid and generates plasma inside micro-bubbles contained in the fluid, the plasma micro-bubble generator comprises a fluid holder for receiving the fluid, an impact receiving body disposed at a predetermined gap from the fluid holder, and a high-voltage power supply device; a flange is formed at one end of the fluid holder, a first metal electrode is provided on a surface of the flange opposite to a surface facing the impact receiver, and a second metal electrode is provided on a surface of the impact receiver opposite to a surface facing the fluid holder, This plasma micro-bubble generator is characterized in that a voltage is applied between the first metal electrode and the second metal electrode by the high-voltage power supply device, thereby generating plasma inside micro-bubbles contained in the fluid flowing out from the gap between the fluid holder and the impact receiver.

[0010] In addition, the water treatment device according to the present invention includes: a treatment tank in which the water to be treated is stored; one or more plasma micro-bubble generators that are disposed within the treatment tank and receive a fluid from outside the treatment tank and generate plasma inside micro-bubbles contained in the fluid; A water treatment device comprising a high-voltage power supply device, the plasma micro-bubble generator is comprised of a fluid holder for receiving the fluid, and an impact receiving body disposed at a predetermined gap from the fluid holder, a flange is formed at one end of the fluid holder, a first metal electrode is provided on a surface of the flange opposite to a surface facing the impact receiver, and a second metal electrode is provided on a surface of the impact receiver opposite to a surface facing the fluid holder, This water treatment device is characterized in that plasma is generated inside fine bubbles contained in the fluid flowing out from the gap between the fluid holder and the impact receiver by applying a voltage between the first metal electrode and the second metal electrode using the high-voltage power supply device.

[0011] In addition, the water treatment method according to the present invention comprises the steps of: A treatment tank for storing water to be treated received from the outside; One or more plasma micro-bubble generators are disposed in the treatment tank, receive the water to be treated stored in the treatment tank, and generate plasma inside micro-bubbles contained in the water to be treated; A high voltage power supply device; A water treatment method comprising: the plasma micro-bubble generator comprises a first metal electrode and a second metal electrode, the first metal electrode and the second metal electrode are disposed on either side of a flow path through which the micro-bubbles flow out, and the first metal electrode and the second metal electrode are electrically insulated; This water treatment method is characterized in that a voltage is applied between the first metal electrode and the second metal electrode by the high-voltage power supply device, thereby generating plasma inside fine bubbles contained in the water to be treated that flows out from the gap between the fluid holder and the impact receiver. Effect of the Invention

[0012] According to the present invention, plasma is efficiently generated within fine bubbles by the plasma fine bubble generator, so that water to be treated that contains persistent organic matter can be efficiently treated. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a flow diagram of a water treatment device according to an embodiment of the present invention. [Diagram 2] 2 is a schematic cross-sectional view showing a plasma fine bubble generator constituting a part of the water treatment device. FIG. [Diagram 3] 3(a) is a schematic vertical cross-sectional view showing another plasma fine-bubble generator constituting a water treatment device, and FIG. 3(b) is a view taken along the line AA in FIG. 3(a). [Figure 4] FIG. 4 is a flow diagram of a water treatment device according to a first modified example of the embodiment of the present invention. [Diagram 5] FIG. 11 is a flow diagram of a water treatment device according to a second modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Embodiment of Water Treatment Device) Hereinafter, an embodiment of a water treatment device according to the present invention will be described. Fig. 1 is a flow diagram of a water treatment device according to an embodiment of the present invention, and Fig. 2 is a cross-sectional schematic diagram showing a plasma micro-bubble generator constituting the water treatment device. Note that the present invention is not limited to only these embodiments.

[0015] The water treatment device 1 according to the present invention comprises a treatment tank 10, a plasma bubble generator 20, and a high-voltage power supply unit 30. The treatment tank 10 is a container for accommodating the water to be treated WD, which is the target of treatment, and is desirably formed from a material that is stable with respect to the water to be treated WD accommodated therein, such as plastic. A plurality of plasma micro-bubble generators 20 are disposed inside the treatment tank 10, and a fluid F is supplied to each plasma micro-bubble generator 20 from the outside via a supply pipe 11. An opening / closing valve 12 is disposed at the inlet of the fluid F to each plasma micro-bubble generator 20.

[0016] As shown in FIG. 2, the plasma micro-bubble generator 20 is formed of a fluid holder 21 and an impact receiver 22. The fluid holder 21 is formed of a body 211, a ceiling 212, a fluid introduction section 213, and a flange 214. The body 211 is substantially cylindrical, and a substantially hemispherical ceiling 212 is formed at one end of the body 211, and a circular tube-shaped fluid introduction section 213 for receiving a fluid F is formed from the center of the ceiling 212 toward the outside. A brim-shaped flange 214 is formed at the other end of the body 211 so as to expand radially outward, and the impact receiver 22 is disposed opposite the flange 214 with a narrow gap G between them. A first metal electrode 215 is disposed in an annular shape on the surface of the flange 214 opposite the impact receiver 22. The fluid holder 21 is formed of an insulating material such as ceramics.

[0017] The impact receiver 22 is a substantially circular flat plate, and a second metal electrode 221 is disposed in an annular shape on the surface of the impact receiver 22 opposite the flange portion 214 of the fluid holder 21. The outer diameter of the impact receiver 22 and the outer diameter of the flange portion 214 are substantially the same, and a substantially uniform narrow gap G is maintained between the impact receiver 22 and the flange portion 214 over the entire circumference thereof in order to provide a large flow resistance to the fluid F when it flows out of the gap G, thereby reducing the pressure and causing cavitation, as will be described later. The impact receiver 22 is formed from an insulating material such as ceramics.

[0018] Since the first metal electrode 215 disposed on the flange portion 214 and the second metal electrode 221 disposed on the impact receiver 22 need to be electrically insulated as described later, the fluid holder 21 and the impact receiver 22 are supported by separate means in the treatment tank 10. In order to control the pressure loss of the fluid F when the fluid flows out from the gap G between the flange portion 214 of the fluid holder 21 and the impact receiver 22, at least one of the fluid holder 21 and the impact receiver 22 may be supported in the treatment tank 10 via a slide mechanism (not shown) so that the position in the height direction can be adjusted. For example, the impact receiver 22 is disposed near the bottom of the treatment tank 10, and the fluid holder 21 is supported relative to the impact receiver 22 via a slide mechanism, so that the position in the height direction can be adjusted. By changing the pressure loss received by the fluid F, the size and number of fine bubbles FB generated in the fluid F can be changed.

[0019] A case where water WD to be treated containing refractory organic matter is treated using the water treatment device 1 having the above configuration will be described. First, a fluid F is supplied from the supply pipe 11 through the on-off valve 12 to each plasma fine-bubble generator 20 disposed in the treatment tank 10 filled with the water WD to be treated. The fluid F then flows into the plasma fine-bubble generator 20 from the fluid inlet 213 of the fluid holder 21, and is temporarily held in the space S surrounded by the body 211, the ceiling 212, and the impact receiver 22. The fluid F then flows out of the narrow gap G between the flange 214 of the fluid holder 21 and the impact receiver 22, but at that time, it receives a large flow resistance and the pressure drops significantly, causing cavitation. Therefore, fine bubbles FB are generated in the fluid F.

[0020] When the fluid F containing the fine bubbles FB flows out of the gap G, a high voltage is applied between the first metal electrode 215 arranged on the flange portion 214 of the fluid holder 21 and the second metal electrode 221 arranged on the impact receiver 22 by the high-voltage power supply device 30. On the other hand, since the fluid holder 21 including the flange portion 214 and the impact receiver 22 are made of an insulator, the flange portion 214 and the impact receiver 22 act as a dielectric barrier. Therefore, a dielectric barrier discharge occurs in the fine bubbles FB contained in the fluid F, and high-speed electrons present in the discharge plasma and active species in a high-energy excited state are generated in the fine bubbles FB. Then, the fluid F containing the fine bubbles FB in which these active species have been generated flows out into the water WD to be treated and is mixed therewith, whereby the organic fluorine compounds and other refractory organic matter contained in the water WD are decomposed. The treated water WE after the treatment is discharged to the outside through the drain pipe 13.

[0021] In the above, it is preferable that the high-voltage power supply 30 generates a pulsed voltage. By generating a pulsed voltage, the current flowing through the fluid F is made pulsed, reducing the conductor loss of the fluid F, and the fluid F is capacitively coupled, enabling highly efficient treatment.

[0022] The fluid F supplied from the outside to the plasma micro-bubble generator 20 may be a liquid alone, or may be a gas-liquid mixture fluid containing bubbles such as micro-bubbles FB in the liquid. In the case of a liquid, water is mainly used, but is not limited to this. In the case of a gas, it is not limited to air, and may be a gas containing oxygen. By using a gas containing oxygen, dissociated oxygen atoms and excited oxygen molecules are generated, which facilitates the decomposition of organic fluorine compounds such as PFOS and PFOA.

[0023] The time for which the high voltage is applied between the first metal electrode 215 and the second metal electrode 221 can be changed depending on the flow rate of the fluid F, the generation state of the fine bubbles FB, or the width of the gap G between the flange portion 214 and the impact receiver 22. These can be adjusted according to the type and concentration of poorly soluble organic matter contained in the to-be-treated water WD to be treated, as well as the physical properties and composition of the to-be-treated water WD, the type of chemical reaction induced by the plasma, and the like.

[0024] The plasma micro-bubble generator 20 is not limited to the structure shown in Fig. 2, and may have a structure like the plasma micro-bubble generator 20a shown in Fig. 3. The plasma micro-bubble generator 20a is configured by attaching an outlet flow path 231 for the micro-bubbles FB made of an insulator to the outlet of a micro-bubble generator 23 that generates micro-bubbles FB by ultrasonic waves or the like, and arranging a first metal electrode 215a on the outer periphery of the outlet flow path 231. A disk-shaped impact receiver 22a made of an insulator is disposed with a narrow gap G from the end of the outlet flow path 231, and a second metal electrode 221a is disposed on the surface opposite to the impact receiver 22a that faces the end of the outlet flow path 231.

[0025] With such a plasma micro-bubble generator 20a, by applying a high voltage between the first metal electrode 215a and the second metal electrode 221a, the outlet flow path 231 and the impact receiver 22a act as a dielectric barrier. As a result, when the fluid F passes through the narrow gap G, a dielectric barrier discharge occurs in the micro-bubbles FB generated in the fluid F, generating high-speed electrons and active species in a high-energy excited state. These are then mixed into the water WD to decompose the refractory organic matter in the water WD. As the micro-bubble generator 23, various types such as an ultrasonic type, a swirling flow type, a pressurized dissolution type, and a micro-hole type can be used.

[0026] In the plasma micro-bubble generator 20a, in order to control the flow resistance applied to the fluid F by adjusting the width of the gap G between the end of the outlet flow path 231 and the impact receiver 22a, at least one of the micro-bubble generator 23 and the impact receiver 22a may be supported in the treatment tank 10 so that the position in the height direction can be adjusted via a slide mechanism (not shown). For example, the impact receiver 22a may be disposed near the bottom of the treatment tank 10 and the micro-bubble generator 23 may be supported via a slide mechanism, or conversely, the micro-bubble generator 23 may be disposed near the bottom of the treatment tank 10 and the impact receiver 22a may be supported via a slide mechanism.

[0027] (First Modification of the Embodiment) As a first modification of the water treatment device, a water treatment device 1A including a circulation pump 14 for circulating water to be treated WD as shown in Fig. 4 may be used. In the water treatment device 1A, while circulating a part of the water to be treated WD by the circulation pump 14, the water to be treated is mixed with a fluid F supplied from the outside and supplied as a mixed fluid WM to a plasma fine-bubble generator 20. Then, plasma is generated in the fine bubbles FB generated in the mixed fluid WM by the plasma fine-bubble generator 20 to treat the persistent organic matter contained in the mixed fluid WM, and the treated water to be treated WD is discharged from a drain pipe 13 as wastewater WE.

[0028] In this case, a flow control valve 16 may be provided on the outlet pipe 15 of the circulation pump 14. By controlling the flow rate of the circulating water WD to be treated with the flow control valve 16, it is possible to adjust the pressure loss of the mixed fluid WM passing through the gap G between the flange portion 214 of the fluid holder 21 and the impact receiver 22 in the plasma fine-bubble generator 20. For example, when the concentration of persistent organic matter in the water to be treated WD is high, the circulation flow rate from the circulation pump 14 is increased and the amount of fine bubbles FB generated is increased by adjusting the gap G between the flange portion 214 of the fluid holder 21 and the impact receiver 22 in the plasma fine-bubble generator 20, thereby promoting the decomposition of the persistent organic matter.

[0029] By configuring the water treatment device 1A in such a manner that the water to be treated WD is circulated, it becomes possible to operate the water treatment device 1A in accordance with the type and concentration of the persistent organic matter contained in the water to be treated WD.

[0030] (Modification 2 of the embodiment) 5, the water treatment device 1A may be configured as a water treatment device 1B in which only the water to be treated WD is continuously supplied without supplying a fluid F from the outside, the water to be treated WD is treated by a plasma fine bubble generator 20 while being circulated by a circulation pump 14, and the treated water WE is continuously discharged from a drain pipe 13. According to such a water treatment device 1B, the water to be treated WD can be continuously treated, and therefore the persistent organic matter in the water to be treated WD can be efficiently treated.

[0031] The embodiments disclosed above are merely examples, and the scope of the present invention is indicated by the claims rather than the above embodiments, and includes all modifications and variations within the meaning and scope of the claims. [Explanation of symbols]

[0032] 1,1A,1B Water treatment equipment 11 Supply piping 12. On-off valve 13 Drain pipe 14 Circulation pump 15 (Circulation pump) outlet piping 16 Flow Control Valve 20,20a Plasma Microbubble Generator 21 Fluid retainer 211 Torso 212 Ceiling 213 Fluid introduction section 214 Flange part 215,215a 1st metal electrode 22,22a receptor 221,221a Second metal electrode 23 Microbubble Generator 231 Outlet Channel 30 High Voltage Power Supply F fluid FB Microbubbles G gap S space WD Treated water WE Drainage WM mixed fluid

Claims

1. A plasma micro-bubble generator that receives a fluid and generates plasma inside micro-bubbles contained in the fluid, the plasma micro-bubble generator comprises a fluid holder for receiving the fluid, an impact receiving body disposed at a predetermined gap from the fluid holder, and a high-voltage power supply device; a flange is formed at one end of the fluid holder, a first metal electrode is disposed on a surface of the flange opposite to a surface facing the impact receiver, and a second metal electrode is disposed on a surface of the impact receiver opposite to a surface facing the fluid holder, a plasma micro-bubble generator characterized in that a voltage is applied between the first metal electrode and the second metal electrode by the high-voltage power supply device, thereby generating plasma inside micro-bubbles contained in the fluid flowing out from the gap between the fluid holder and the impact receiver.

2. a treatment tank in which the water to be treated is stored; one or more plasma micro-bubble generators disposed within the treatment tank, receiving a fluid from outside the treatment tank, and generating plasma inside micro-bubbles contained in the fluid; A water treatment device comprising a high-voltage power supply device, the plasma micro-bubble generator is comprised of a fluid holder for receiving the fluid, and an impact receiving body disposed at a predetermined gap from the fluid holder, a flange is formed at one end of the fluid holder, a first metal electrode is disposed on a surface of the flange opposite to a surface facing the impact receiver, and a second metal electrode is disposed on a surface of the impact receiver opposite to a surface facing the fluid holder, a high-voltage power supply device that applies a voltage between the first metal electrode and the second metal electrode to generate plasma inside fine bubbles contained in the fluid flowing out from the gap between the fluid holder and the impact receiver.

3. 3. The water treatment device according to claim 2, 1. A water treatment device comprising: a circulation pump that circulates a portion of the water to be treated in the treatment tank to an inlet of the plasma fine bubble generator.

4. The water treatment device according to claim 2 or 3, A water treatment device characterized in that one of a fluid holder and an impact receiver constituting the plasma fine-bubble generator is arranged to be movable relative to the other, and a gap between the fluid holder and the impact receiver is adjustable.

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