JP2014117639A - Method for decomposing dioxane in water to be treated - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for decomposing dioxane that makes an active species such as radicals efficiently function on water to be treated containing dioxane to decompose the dioxane in the water to be treated.SOLUTION: In a water treatment method, dioxane contained in water W to be treated is decomposed in a discharge space formed by applying high voltage between a cylindrical electrode 3 and a wire electrode 4 disposed in the cylinder of the cylindrical electrode 3 in a treatment chamber 2. The water W to be treated is supplied in a mist state composed of water droplets M of a particle size of 1,500 μm or less.

Description

  The present invention relates to a dioxane decomposition treatment method in water to be treated for decomposing dioxane in water to be treated containing dioxane.

Dioxane, especially 1,4-dioxane, is a chlorinated solvent stabilizer, extraction and reaction solvent (extraction of animal and vegetable oils, pulping, wax, varnish, lacquer, adhesive, moisturizer, rubber, It is used in plastics, pharmaceuticals, cosmetics, herbicides, insecticides, deodorizing fumigants), cleaning solvents and the like.
Since this dioxane has a large possibility of affecting the human body and ecosystem such as carcinogenicity, water quality standards for factory wastewater are established.

On the other hand, ozone has been conventionally used for treatments such as oxidative decomposition, sterilization, and deodorization of organic substances in water in fields such as clean water, sewage, industrial wastewater, and pools (see Patent Document 1).
However, ozone has weak oxidizing power, and dioxane, which is a hardly decomposable substance, takes a very long time even if decomposed, and it is not practical to use a treatment method using only ozone for the decomposition treatment of dioxane.

On the other hand, in order to improve the processing capability, a processing apparatus using an accelerated oxidation process (AOP) method has been proposed (see Patent Document 2).
That is, the accelerated oxidation treatment injects ozone into the water to be treated and irradiates the water to be treated with ultraviolet rays to generate OH radicals, O radicals, and the like having higher oxidizing power than ozone in the water to be treated. In addition, by exposing the water to be treated to radicals, oxidation treatment is performed not only by ozone but also by radicals.

Japanese Patent Laid-Open No. 9-267096 JP 2000-279977 A

However, since the radical has a short lifetime and is likely to disappear, the accelerated oxidation treatment method that generates a small amount of radicals cannot sufficiently exert the oxidizing action by the radical.
In addition, the accelerated oxidation treatment requires additional equipment such as a hydrogen peroxide solution addition device and an ultraviolet irradiation lamp in addition to the ozone generator, and is inherently expensive, so that the equipment cost and running cost are high. .

  In view of the above circumstances, the present invention provides a dioxane decomposition treatment method capable of decomposing dioxane in water to be treated by causing active species such as radicals to efficiently act on water to be treated containing dioxane. It is aimed.

In order to achieve the above object, the method for decomposing dioxane in water to be treated according to the present invention (hereinafter referred to as “treatment method of the present invention”) is a water treatment method for decomposing dioxane contained in water to be treated. Water droplets having a particle diameter of 1500 μm or less in the discharge space generated by applying a high voltage between the cylindrical electrode and the linear electrode arranged so as to face the cylinder of the cylindrical electrode It is characterized by being supplied in a mist state consisting of

In the treatment method of the present invention, the particle size of the water droplets constituting the treated water mist is limited to 1500 μm or less (preferably 10 μm to 1500 μm), because the particle size becomes too large. This is because the surface area per volume contacting the plasma in the discharge space is reduced, and the processing efficiency is degraded.
Examples of the dioxane treated by the treatment method of the present invention include 1,4-dioxane, 1,2-dioxane, and 1,3-dioxane.

  In the present invention, the method for measuring the particle size of the water droplets is based on an immersion method. Water droplets were sprayed onto a petri dish filled with silicon oil from the tip of an injection nozzle installed at the top of the petri dish and collected by a petri dish placed perpendicular to the injection axis. The collected water droplets were quickly imaged, the particle size for each size was counted, and the Sauter average particle size was obtained as the particle size of the water droplets.

In the treatment method of the present invention, as a method for supplying the water to be treated in a mist state composed of water droplets having a particle diameter of 1500 μm or less, the water to be treated can be made into a mist state comprising water droplets having a particle diameter of 1500 μm or less. Although not particularly limited, for example, a method of injecting from an injection nozzle, a method of supplying by steaming with a steam generator such as a heating type or an ultrasonic type, and the like, and a method of injecting from an injection nozzle are preferable in terms of cost.
As described above, when the water mist to be treated is ejected from the ejection nozzle, for example, the discharge space from the upper side to the lower side of the discharge space, the upper side from the lower side of the discharge space to the discharge space, and the discharge space from the side of the discharge space. However, since water droplets can be supplied into the discharge space more efficiently, it is preferable to spray from the top to the bottom.

Moreover, it is preferable to adjust the injection angle of the injection nozzle so that the outermost edge of the to-be-treated water mist injected from the injection nozzle is along the outermost edge of the discharge space.
That is, even if it is sprayed so as to spread to the outside from the outermost edge of the discharge space, the efficiency is lowered, and it may hit the inner wall surface of the container, become large water droplets and flow down along the inner wall surface, and there is a possibility that the efficiency becomes worse.

  In the present invention, the spray angle (spray angle) means that the water droplets in the treated water mist ejected from the nozzle fall while marking the parabola, and therefore the treated water mist immediately after coming out of the nozzle ejection port. Means the spread angle.

Furthermore, in the processing method of the present invention, the number of spray nozzles is not particularly limited, and it is sufficient that one or more spray nozzles are provided.
In addition, when two or more pairs of cylindrical electrodes and linear electrodes are provided, two or more spray nozzles may be provided. However, when a plurality of pairs of cylindrical electrodes and linear electrodes are provided, the number of spray nozzles is set. In order to minimize and efficiently disassemble the cylindrical electrode, the cylindrical electrode is arranged so that the central axis of each cylindrical electrode is parallel to the injection axis direction of the injection nozzle and located far from the injection axis of the injection nozzle. It is preferable that the injection nozzle side end face is provided at a position farther from the injection nozzle than the injection nozzle side end face of the cylindrical electrode arranged at a position close to the injection axis.

  The material of the cylindrical electrode and the linear electrode is not particularly limited as long as it is conductive and excellent in corrosion resistance, but stainless steel is preferable.

Moreover, it is preferable that the cylindrical electrode is equipped with the opening of the magnitude | size which can pass the water droplet which a cylindrical electrode comprises to-be-processed water mist in a surrounding wall.
As described above, when the opening is provided, the opening ratio of the cylindrical electrode is preferably 50% or more of the entire peripheral wall in consideration of the processing efficiency.

The cylindrical electrode provided with the opening as described above is not particularly limited. For example, a wire mesh, a punching metal formed into a cylindrical shape, a spiral having a linear material wound in a coil shape, and the like. The thing etc. which formed the clearance gap connected in the shape are mentioned.
When a large number of holes are provided in the peripheral wall of the cylindrical electrode, the size of the hole is not particularly limited as long as the cylindrical shape can be maintained and water droplets injected from the injection nozzle can pass through. Is about 0.01 mm 2 to 625 mm 2.

In consideration of processing efficiency, it is preferable that two or more pairs of cylindrical electrodes and linear electrodes are provided in one processing chamber.
In addition, when two or more pairs of cylindrical electrodes and linear electrodes are provided and water droplets are supplied from one spray nozzle to a discharge space generated between each cylindrical electrode and the linear electrode, The cylindrical electrode in which the central axis of each cylindrical electrode is parallel and the end surface on the injection nozzle side of the cylindrical electrode arranged at a position far from the injection axis of the injection nozzle is arranged at a position close to the injection axis. It is preferable to arrange a plurality of electrode pairs so as to be provided at a position far from the injection nozzle as compared with the end surface on the injection nozzle side.

  The charging voltage applied between the cylindrical electrode and the linear electrode is not particularly limited as long as it is a voltage at which streamer discharge occurs.

  Further, in the treatment method of the present invention, a water storage tank that receives and stores mist, and a pump that sends the water stored in the water storage tank as treated water to the treated water mist supply means are provided to circulate the treated water. You may be made to process it.

Further, in the treatment method of the present invention, in order to increase the generation amount of active species and increase the treatment capacity, in order to dissolve a large amount of air in the treated water compared to other organic substances, the air is forced into the treated water. It is preferable to supply air from the outside or forcibly supply air from outside to ensure a sufficient amount of air in the processing chamber.
The method of supplying air into the water to be treated is not particularly limited, but a method of previously bubbling in the water to be treated water or a method of bubbling in the water storage tank in the above circulating type, etc. Is mentioned.

Although it does not specifically limit as an air supply means, When bubbling in to-be-processed water, it is preferable to supply it in a tank as a bubble as fine as possible.
The method of making fine bubbles is not particularly limited, but is a diffuser equipped with a hard porous body that generates fine bubbles by sintering a synthetic resin such as ABS resin, polymethyl methacrylate, polyethylene, or polypropylene, or ceramic, and the like. High-speed swirl shear method, Venturi decompression foaming method, high-speed agitation method, and a method of installing a microbubble nozzle (for example, a product name Nano Planet M2 type microbubble generator) at the tip of the air supply pipe piped in the receiving tank Can be mentioned.

Moreover, the supply amount of air when bubbling into the water to be treated is not particularly limited, but is preferably 500 to 1000 L / min per 1 m3 of the water to be treated. Incidentally, in the case of other organic substances, less than 500 L / min is sufficient.
On the other hand, the supply amount of air when supplying air into the processing chamber is not particularly limited, but is preferably 500 to 2000 L / min. Incidentally, in the case of other organic substances, less than 500 L / min is sufficient.
Note that only one of the supply of air into the water to be treated and the supply of air into the treatment chamber may be performed.

As described above, the treatment method of the present invention is a water treatment method for decomposing dioxane contained in water to be treated, and is a cylindrical electrode and a linear electrode arranged so as to face the inside of the cylindrical electrode. Since the water to be treated is supplied in a mist state composed of water droplets having a particle size of 1500 μm or less in the discharge space generated by applying a high voltage between them, a long discharge space is formed in a cylindrical shape. In addition, water droplets having a fine particle size of 1500 μm or less are exposed to the discharge space for a long time in the cylindrical long discharge space.
Accordingly, dioxane in the water droplets of the water mist to be treated is efficiently decomposed by active species such as ozone, OH radicals and O radicals generated by discharge.

  In addition, if a spray nozzle is used as the treated water mist supply means and the spray angle of the spray nozzle is adjusted so that the outermost edge of the treated water mist sprayed from the spray nozzle is along the outermost edge of the discharge space, The treated water can be efficiently supplied to the discharge space in accordance with the diameter of the cylindrical electrode, and the treatment can be performed more efficiently.

  In addition, if the cylindrical electrode is provided with a large number of holes on the wall surface through which water droplets constituting the treated water mist can pass, the discharge space can be discharged even if the treated water mist is sprayed from the side of the cylindrical electrode. Water droplets can be supplied inside.

If two or more pairs of cylindrical electrodes and linear electrodes are provided in one processing chamber, processing can be performed more efficiently.
In addition, when two or more pairs of cylindrical electrodes and linear electrodes are arranged and the central axes of the cylindrical electrodes are arranged in parallel, the cylindrical electrodes are large enough to pass the water droplets constituting the water mist to be treated as described above. If the peripheral wall is provided with a large number of holes and openings, water drops once inside the cylindrical electrode come out through the holes and enter the adjacent cylindrical electrode. Therefore, processing can be performed efficiently.

  Further, in the case of the configuration including two or more pairs of cylindrical electrodes and linear electrodes as described above, the injection axis direction of the injection nozzle and the central axis of each cylindrical electrode are parallel to each other, The injection nozzle side end face of the cylindrical electrode arranged at a position far from the injection axis is arranged at a position farther from the injection nozzle than the injection nozzle side end face of the cylindrical electrode arranged at a position close to the injection axis. If a cylindrical electrode is arrange | positioned, to-be-processed water mist can be supplied to discharge space without waste, and it can process more efficiently.

  Furthermore, a water-reserving water circulation structure comprising a water storage tank that receives and stores water droplets in the water-to-be-treated mist and a pump that sends the water stored in the water storage tank to the water-to-be-treated mist supply means as the water to be treated. For example, the decomposition rate of the organic matter in the water to be treated can be improved.

It is sectional drawing of 1st Embodiment of the water treatment apparatus used for the processing method of this invention. It is the figure which represented typically 2nd Embodiment of the water treatment apparatus used for the processing method of this invention. It is the figure which represented typically 3rd Embodiment of the water treatment apparatus used for the processing method of this invention. It is the figure which represented typically 4th Embodiment of the water treatment apparatus used for the processing method of this invention. It is the figure which represented typically 5th Embodiment of the water treatment apparatus used for the processing method of this invention. It is the figure which represented typically the state which looked at the cylindrical electrode and linear electrode of 6th Embodiment of the water treatment apparatus concerning this invention used for the processing method of this invention from the upper surface side. It is the figure which represented typically the water treatment apparatus of the ozone simple substance process used for the 1, 4- dioxane containing water treatment implemented in the comparative example 1. It is the figure which showed the processing time of 1, 4- dioxane containing water processing implemented in Example 1 and Comparative Example 1, and the residual 1, 4- dioxane density | concentration.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
FIG. 1 shows a first embodiment of a water treatment apparatus used in the treatment method of the present invention.

As shown in FIG. 1, the water treatment apparatus 1a includes a treatment chamber 2, a cylindrical electrode 3, a linear electrode 4, a water tank 5 to be treated, a pump 6, and an injection nozzle 7 that is an injection nozzle. The water supply hose 71 to be treated, the pulse power generator 8 which is a high voltage power source, and the water tank storage box 9 to be treated are provided.
The processing chamber 2 is formed of, for example, an insulating material such as acrylic resin, and is provided so as to close the cylindrical processing chamber main body 21 and the lower end of the processing chamber main body 21 except for the water passage hole 22a. The lower cover part 22 and the upper cover part 23 provided so that the upper end of the process chamber main body 21 may be closed except the injection nozzle installation hole 23a part are provided, and the lower cover part 22 is the to-be-processed water tank accommodation box 9. The opening 91 of the to-be-processed water tank storage box 9 is received by the periphery of the opening 91 in a state in which the opening 91 is closed.

The cylindrical electrode 3 is obtained by, for example, processing a stainless steel 1 to 100 mesh 0.35 mm thick net into a cylindrical shape, and the outer diameter is slightly smaller than the inner diameter of the processing chamber body 21. .
The linear electrode 4 is formed of, for example, a stainless steel wire having a diameter of 0.28 mm, and is provided along the central axis of the cylindrical electrode 3.

The treated water tank 5 is accommodated in the treated water tank accommodation box 9 so that the water passage hole 22a of the lower lid portion 22 faces from below.
The pump 6 is provided adjacent to the treated water tank 5 in the treated water tank storage box 9, and the treated water W in the treated water tank 5 is supplied to the injection nozzle 7 via the treated water supply hose 71. To send.

The spray nozzle 7 sprays the treated water sent via the treated water supply hose 71 in a mist state composed of water droplets having a particle size of 1500 μm or less toward the upper opening of the cylindrical electrode 3. ing.
Moreover, the injection angle of the injection nozzle 7 is adjusted to an angle along the inner wall surface of the cylindrical electrode 3 that is the outermost edge of the discharge space at the maximum spread portion of the water Mist M to be injected.

The pulse power generator 8 is connected to the cylindrical electrode 3 and the linear electrode 4 so that the cylindrical electrode 3 is a cathode and the linear electrode 4 is an anode, and between the cylindrical electrode 3 and the linear electrode 4. A high voltage is applied in a pulse shape to cause streamer discharge between the cylindrical electrode 3 and the linear electrode 4.

In the treatment method of the present invention, treated water W containing dioxane is charged into the treated water tank 5 and a high voltage is applied between the cylindrical electrode 3 and the linear electrode 4 by the pulse power generator 8. Is applied in a pulse shape to form a streamer discharge space in the cylindrical electrode 3 that is cylindrical in the vertical direction.
Then, the pump 6 is driven so that the water to be treated W in the water tank 5 to be treated is sent to the spray nozzle 7 through the hose 71 and directed from above the cylindrical electrode 3 toward the central axis of the cylindrical electrode 3. The water to be treated W is treated while being circulated.

  That is, active species such as ozone, OH radicals, and O radicals are generated in the discharge space by the streamer discharge, and water droplets in the water mist M to be treated, which is sprayed from the spray nozzle 7 fall in the cylindrical discharge space. In the meantime, these active species are contacted and dioxane in each water droplet is efficiently oxidized and decomposed.

FIG. 2 shows a second embodiment of the water treatment apparatus used in the treatment method of the present invention.
As shown in FIG. 2, this water treatment apparatus 1 b is the same as the above water treatment except that the cylindrical electrode 3 and the linear electrode 4 of the same size are arranged in the horizontal direction in the 4-pair treatment chamber 2. It is the same as the apparatus 1a.

FIG. 3 shows a third embodiment of the water treatment apparatus used in the treatment method of the present invention.
As shown in FIG. 3, the water treatment apparatus 1c is the same as the water treatment apparatus 1b except that the spray nozzle 7 is provided below the cylindrical electrode 3 and the water mist to be treated is sprayed vertically upward. It has become.

  According to the water treatment apparatus 1c, the water mist M to be treated is sprayed from the lower side of the discharge space toward the discharge space, so that each water droplet in the water mist M to be treated once rises, and then due to its gravity. By descending, the residence time in the discharge space is increased, and the treatment can be performed more efficiently.

FIG. 4 shows a fourth embodiment of the water treatment apparatus used in the treatment method of the present invention.
As shown in FIG. 4, this water treatment apparatus 1 d is provided with an injection nozzle 7 on the side of the cylindrical electrode and injects water to be treated from the side surface of the cylindrical electrode 3 in the horizontal direction. It is the same as that of the said water treatment apparatus 1a.

FIG. 5 shows a fifth embodiment of the water treatment apparatus used in the treatment method of the present invention.
As shown in FIG. 5, the water treatment device 1 e has a length in the central axis direction of two cylindrical electrodes 3 b farther than the two cylindrical electrodes 3 a closer to the injection axis C of the injection nozzle 7. And the upper end surface of the short cylindrical electrode 3b is arranged at a position away from the injection nozzle 7 from the upper end surface of the long cylindrical electrode 3a, that is, positioned below, and is injected from the injection nozzle 7. The water treatment apparatus 1b is the same as the water treatment apparatus 1b except that the outermost edge of the treated water mist M is adjusted so as to be surely stored in the short cylindrical electrode 3b.

FIG. 6 shows a sixth embodiment of the water treatment apparatus used in the treatment method of the present invention.
As shown in FIG. 6, the water treatment device 1 f includes six electrode pairs each formed of a cylindrical electrode 3 and a linear electrode 4, and the linear electrode 4 serves as a central axis of the processing chamber body 21. The water treatment apparatus 1a is the same as the water treatment apparatus 1a except that the other five electrode pairs are arranged at equal intervals on the same circumference so as to radially surround the periphery of the other electrode pairs.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the water to be treated may contain organic substances other than dioxane.
In the above embodiment, the water to be treated containing dioxane is stored in the water tank to be treated and is circulated to be treated. However, the water is made to drop through one treatment chamber and passed once. If dioxane can be reduced to a specified concentration or less, it is not necessary to circulate it. Further, the treatment chambers may be provided in multiple stages, and the treatment water treated with one treatment water may be further treated in the downstream treatment chamber.
The water treatment device of the sixth embodiment has a double structure in which the periphery of one electrode pair is surrounded by five electrode pairs, but a large number of electrode pairs are further arranged in triples and quadruples on the outside. The upper end surface of the cylindrical electrode disposed on the outer side of the container main body may be positioned below the upper end surface of the cylindrical electrode disposed on the inner side as in the water treatment apparatus of the fifth embodiment. You may make it provide in.

Specific examples of the present invention will be described below in comparison with comparative examples.
Example 1
Except for providing the microbubble nozzle connected to the air pipe in the water storage tank and providing the air pipe for supplying air into the treatment chamber, the water treatment apparatus 1a shown in FIG. Water to be treated containing 4-dioxane at a concentration of about 100 ppm is sampled at a treatment time of 0 hour, 1 hour, 2 hours, and 4 hours, and the concentration of dioxane is measured using a gas chromatograph mass spectrometer (GC MS).
[Experimental conditions]
Water to be treated: 7 liters Water to be treated (circulation speed): 14 L / min Charging voltage: 27 kV
Number of discharges: 100 times / second Cylindrical electrode: 4 mesh, wire diameter 1.0 mm, aperture ratio 80%, inner diameter of plain mesh stainless steel wire mesh cylindrical electrode: 40 mm
Length of cylindrical electrode (length in the central axis direction): 500 mm
Linear electrode: diameter of stainless steel wire treated water mist having a wire diameter of 0.28 mm: 750 to 970 μm
Injection angle of injection nozzle: 30 °
Distance from spray nozzle to cylindrical electrode: The outermost edge of the water mist to be treated was adjusted to be the upper end of the outer edge of the cylindrical electrode located at the outermost part.
Air supply amount to water storage tank: adjusted to 700 L / min per 1 m3 of water to be treated.
Air supply amount to treatment chamber: adjusted to 1000 L / min per 1 m3 of water to be treated.

(Comparative Example 1)
Using the water treatment apparatus 100 shown in FIG. 7, treated water containing 1,4-dioxane at a concentration of about 100 ppm in purified water under the following experimental conditions is treated with water, and the treatment time is 0 hours, 1 hour, 2 hours. Sampling was performed for 4 hours, and the dioxane concentration was measured using a gas chromatograph mass spectrometer (GC-MS manufactured by Shimadzu Corporation).
[Experimental conditions]
Amount of water to be treated: 7 liters Circulation speed of water to be treated: 14 L / min Ozone generator: Oxygen gas supply flow rate manufactured by Ecodesign: 10 L / min
Generated ozone gas flow rate: 10L / min
Generated ozone gas concentration: 100g / Nm3 (50000ppm)
Injection nozzle: Nano bubble nozzle

The 1,4-dioxane concentration for each treatment time measured in Example 1 and Comparative Example 1 is plotted, the relationship between the treatment time and 1,4-dioxane concentration is determined, and shown in FIG. In FIG. 8, the vertical axis represents 1,4-dioxane concentration (mg / L), and the horizontal axis represents treatment time (hours).
As shown in FIG. 8, it can be seen that the treatment method of the present invention (Example 1) can efficiently decompose dioxane in a shorter time than the ozone treatment method (Comparative Example 1).
In addition, according to the treatment method of the present invention, a sufficient decomposition treatment effect can be obtained without providing additional equipment such as a hydrogen peroxide solution addition device and an ultraviolet irradiation lamp, and the equipment cost can be reduced.

  Although the processing method of this invention is not specifically limited, For example, it can use for the purification | cleaning of the waste_water | drain containing a hardly decomposable substance, such as a dioxane, and the disinfection of contaminated water.

1a, 1b, 1c, 1d, 1e, 1f Water treatment device 2 Treatment chamber 21 Treatment chamber body 3, 3a, 3b Cylindrical electrode 4 Linear electrode 5 Water tank 6 Pump 7 Injection nozzle 8 Pulse power generator (high pressure) Power supply)
W Treated water M Treated water mist

Claims (7)

  A water treatment method for decomposing dioxane contained in water to be treated, which is generated by applying a high voltage between a cylindrical electrode and a linear electrode arranged to face the inside of the cylindrical electrode. A method for decomposing dioxane in water to be treated, characterized in that the water to be treated is supplied into the discharge space in a mist state comprising water droplets having a particle size of 1500 μm or less.   The dioxane decomposition | disassembly method in the to-be-processed water of Claim 1 which injects from an injection nozzle and makes to-be-processed water a mist state.   The dioxane decomposition treatment method of to-be-processed water of Claim 2 which adjusts the injection angle of an injection nozzle so that the outermost edge of the to-be-processed water mist injected from an injection nozzle may follow the outermost edge of discharge space.   The dioxane decomposition treatment method in to-be-processed water in any one of Claims 1-3 which equips a wall surface with many holes of the magnitude | size which the cylindrical electrode can pass the water droplet which comprises to-be-processed water mist.   The method for decomposing dioxane in water to be treated according to any one of claims 1 to 4, wherein the open area ratio of the cylindrical electrode is 50% or more.   A plurality of pairs of cylindrical electrodes and linear electrodes are provided in one processing chamber, and water to be treated is supplied from a single spray nozzle into a discharge space generated between each pair of cylindrical electrodes and linear electrodes. The dioxane decomposition | disassembly processing method in the to-be-processed water in any one of Claims 1-5.   A plurality of pairs of cylindrical electrodes and linear electrodes are arranged such that the central axis of each cylindrical electrode is parallel to the injection axis direction of the injection nozzle, and the cylindrical electrodes are arranged at positions far from the injection axis of the injection nozzle 7. The method for decomposing dioxane in water to be treated according to claim 6, wherein the injection nozzle side end face is provided at a position farther from the injection nozzle than the injection nozzle side end face of the cylindrical electrode disposed at a position close to the injection axis. .

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