FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
WATER TREATMENT APPARATUS AND WATER TREATMENT
METHOD
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION
ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE
ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO
1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

2
SPECIFICATION
Technical Field
[0001] The present application relates to a water treatment apparatus and a
5 water treatment method.
Background Art
[0002] Water treatment techniques are known in which water to be treated is
caused to flow along an electrode facing a dielectric, and active species
10 such as ozone and hydroxy radicals are generated by electric discharge
generated in a space between the water to be treated and the dielectric,
thereby performing treatment such as sterilization of the water to be treated
(refer to, for example, Patent Document 1 and Non-Patent Document 1).
15 Prior Art Document
Patent Document
[0003] Patent Document 1: Japanese Patent Application Laid-Open No.
2013-206767 (paragraphs 0025 to 0038, FIG. 2, FIG. 7)
20 Non-Patent Document
[0004] Non-Patent Document 1: Niels Wardenier et al., Journal of
Hazardous Materials, (USA), 362 (2019) p.238 to 245
Summary of Invention

3
Problems to be Solved by Invention
[0005] However, in the above-described water treatment techniques, when
the flow rate of the water to be treated is increased in order to treat a large
amount of water, part of the water to be treated is scattered in the form of
5 water droplets and adheres to the inner surface of the dielectric. When the
water to be treated adheres to the inner surface of the dielectric, a current
flows on the inner surface of the dielectric, and thus dielectric barrier
discharge cannot be uniformly and stably formed, and the dielectric may be
damaged due to localization of the discharge or the like.
10 [0006] On the other hand, in order to form stable dielectric barrier
discharge, it is necessary to provide a high voltage electrode only in a
region where the water droplets of the water to be treated do not adhere, for
example, in the vicinity of the outlet port, and thus the discharge region is
reduced and the amount of water that can be treated is limited. Further, if
15 high electric power is concentrated on a reduced discharge region in order
to increase the amount of active species to be generated, the temperature of
the dielectric rises, and active species useful for the water treatment are
decomposed, so that the treatment performance is rather lowered.
Furthermore, even if the amount of the active species to be generated can be
20 increased, the active species has a short life, and therefore, the contact area
with the water to be treated is reduced, thereby causing a problem in that
efficient water treatment cannot be performed. As a result, the amount of
water to be treated is limited, and it is difficult to perform efficient water
treatment.

4
[0007] The present application discloses a technique for solving the
above-described problems, and an object of the present application is to
provide a water treatment apparatus and a water treatment method for
efficiently treating water to be treated with a stable operation.
5
Means for Solving the Problems
[0008] A water treatment apparatus disclosed in the present application
includes a first electrode extending in an axial direction, a second electrode
arranged coaxially with the first electrode so as to surround the first
10 electrode from an outside in a radial direction, a dielectric that is formed in
a cylindrical shape, is coaxially arranged and interposed between the first
electrode and the second electrode, forms an annular gap between the
dielectric and one electrode of the first electrode and the second electrode,
and causes to generate dielectric barrier discharge by applying a voltage
15 between the one electrode and the other electrode, and a water-film forming
portion that forms an annular flow path along a circumferential direction
between the water-film forming portion and the one electrode on one end
side in an axial direction with an opening toward the annular gap at a
narrower spacing than the annular gap and causes water to be treated to flow
20 down toward the other end side as a water film covering the one electrode
when the one end side is directed upward to set an axial direction to be
vertical.
[0009] A water treatment method disclosed in the present application using
the water treatment apparatus in which two electrodes and a dielectric

5
arranged between the two electrodes are provided, and a gap extending with
a constant interval is formed between one electrode of the two electrodes
and the dielectric, the water treatment method includes steps of generating
active species by applying a voltage between the two electrodes to cause
5 dielectric barrier discharge, introducing water to be treated from one end
side in an extending direction of the gap, and causing the generated active
species to act on the introduced water to be treated. In the step of
introducing the water to be treated, the one end side is directed upward to
set the extending direction to be vertical, and the water to be treated is made
10 to flow down toward the other end side as a water film that has a thickness
smaller than the constant interval and covers the one electrode.
Advantageous Effect of Invention
[0010] According to the water treatment apparatus or the water treatment
15 method disclosed in the present application, the water to be treated flows in
the form of a water film along an electrode, and thus, destabilization of
dielectric barrier discharge due to adhesion of water droplets to the
dielectric can be suppressed, and the water to be treated can be efficiently
treated with a stable operation.
20
Brief Description of the Drawings
[0011] FIG. 1 is a cross-sectional view along an axis for describing a
configuration of a water treatment apparatus and a water treatment method
according to Embodiment 1.

6
FIG. 2 is an enlarged cross-sectional view along the axis near a
water-film forming portion for describing the configuration of the water
treatment apparatus and the water treatment method according to
Embodiment 1.
5 FIG. 3 is an enlarged cross-sectional view along the axis near a
water-film forming portion for describing a configuration of a water
treatment apparatus and a water treatment method according to Embodiment
2.
FIG. 4 is a cross-sectional view perpendicular to the axis for
10 describing the configuration of the water treatment apparatus and the water
treatment method according to Embodiment 2.
FIG. 5 is a cross-sectional view perpendicular to the axis for
describing a configuration of a water treatment apparatus and a water
treatment method according to a variation of Embodiment 2.
15 FIG. 6 is a cross-sectional view along the axis for describing a
configuration of a water treatment apparatus and a water treatment method
according to Embodiment 3.
FIG. 7 is a cross-sectional view along the axis for describing a
configuration of a water treatment apparatus and a water treatment method
20 according to Embodiment 4.
FIG. 8 is a cross-sectional view along the axis for describing a
configuration of a water treatment apparatus and a water treatment method
according to Embodiment 5.

7
Mode for Carrying out Invention
[0012] Embodiment 1
FIG. 1 and FIG. 2 are views for describing a cylindrical water treatment
apparatus and a water treatment method according to Embodiment 1. FIG.
5 1 is a cross-sectional view along an axis for describing a configuration of
the water treatment apparatus, and FIG. 2 is a cross-sectional view of a
water-film forming portion, which is an enlarged view of a portion
corresponding to a region R in FIG. 1.
[0013] The water treatment apparatus of the present application is a water
10 treatment apparatus in a flowing water type using dielectric barrier
discharge. The dielectric barrier discharge refers to a technique in which
one or both of electrodes in a pair facing each other with a gap therebetween
are covered with a dielectric, an AC voltage is applied to the electrodes to
cause discharge in a gas in the gap, and active species generated by the
15 discharge are brought into contact with water to be treated to perform the
treatment.
[0014] As shown in FIG. 1, the water treatment apparatus 10 according to
Embodiment 1 includes a dielectric 1 in a cylindrical shape having a high
voltage electrode 5 on the outer circumferential side, and a ground electrode
20 2 arranged in a column shape on the same axis with the gap relative to an
inner circumferential surface 1fi of the dielectric 1. The dielectric 1 and
the ground electrode 2 are fixed to keep a coaxial relationship by a header
member 3 arranged at one end in the axial direction.
[0015] However, the high voltage electrode 5 is shorter than the dielectric 1

8
in the axial direction, and is arranged in the middle portion of the dielectric
1 excluding both ends of the dielectric in the axial direction. The high
voltage electrode 5 and the ground electrode 2 are electrically connected to
a power supply 80, and are configured to cause dielectric barrier discharge
5 (discharge Dc) between the portion of the dielectric 1 where the high
voltage electrode 5 is arranged and the ground electrode 2 by a high voltage
applied from the power supply 80.
[0016] As the dielectric 1, a material that is excellent in electrical
insulation and chemically stable is suitable. For example, glass, ceramics,
10 or a resin material can be used. A material that is electrically conductive,
chemically stable and has excellent corrosion resistance is suitable for use
as the ground electrode 2. For example, stainless steel, titanium (Ti),
aluminum (Al), graphite, or the like can be used. The high voltage
electrode 5 can be formed, for example, by winding a metal mesh or a metal
15 thin plate around the outer circumferential surface of the dielectric 1and can
also be formed by forming a metal thin film on the outer circumferential
surface of the dielectric 1 by a method such as plating or vapor deposition.
[0017] The header member 3 is provided with a water intake portion 3i for
taking in water to be treated 90 and a water-film forming portion 7 forming
20 an opening along an outer circumferential surface 2fo such that the water to
be treated 90 taken in from the water intake portion 3i flows as a water film
91 along the outer circumferential surface 2fo of the ground electrode 2.
The header member 3 is formed, for example, by resin molding, and when
the ground electrode 2 and the dielectric 1 are fitted in the axial direction,

9
an annular flow path 7c in a ring shape is formed between the outer
circumferential surface 2fo of the ground electrode 2 and the water-film
forming portion 7. At this time, an internal flow path is formed from the
water intake portion 3i to the annular flow path 7c, and one end of the
5 ground electrode 2 is to be exposed for electrical connection.
[0018] As the power supply 80, for example, an AC power supply or a pulse
power supply can be used. The pulse power supply is effective in forming
stable discharge, but is costly. On the other hand, as described later, in the
water treatment apparatus 10 of the present application, since the wetting of
10 the inner circumferential surface 1fi of the dielectric 1 by the water droplets
is suppressed, a relatively low-cost AC power source can be used, and the
cost of the entire apparatus can be suppressed.
[0019] Further, a gap portion 6 in a ring shape formed between the
dielectric 1 in the cylindrical shape and the ground electrode 2 is a place
15 where the discharge Dc is generated, and also functions as a space for
allowing the water to be treated 90 to flow.
[0020] As shown in FIG. 2, the water-film forming portion 7 is interposed
between the dielectric 1 and the ground electrode 2, and it has an inner
circumferential surface 7fi whose inner diameter Di7 is larger than an outer
20 diameter Dx2 of the ground electrode 2 and smaller than the inner diameter
Di1 of the dielectric 1, and an outer circumferential surface in close contact
with the inner circumferential surface 1fi of the dielectric 1, and thus it is
formed in a ring shape. Therefore, the annular flow path 7c is formed
between the inner circumferential surface 7fi of the water-film forming

10
portion 7 and the outer circumferential surface 2fo of the ground electrode 2,
the annular flow path 7c being opened in the ring shape at a portion of a
tip-end face 7e in a range not reaching the inner circumferential surface 1fi
of the dielectric 1. As a result, the water to be treated 90 flows out from
5 the water-film forming portion 7 into the gap portion 6 in the form of the
water film 91 along the outer circumferential surface 2fo of the ground
electrode 2.
[0021] The header member 3 is configured to be arranged on the upper side
with the axial direction being vertical such that the water film 91 flowing
10 out from the water-film forming portion 7 flows in the gap portion 6 along
the outer circumferential surface 2fo from one end side of the water-film
forming portion provided with the header member 3 to the other end side in
the axial direction.
[0022] Further, a gas introduction part 4 for introducing a gas into the gap
15 portion 6 is provided in a portion of the dielectric 1 located between the
water-film forming portion 7 and the high voltage electrode 5 in the axial
direction. The gas introduced from the gas introduction part 4 flows in a
space formed between the inner circumferential surface 1fi of the dielectric
1 and the water film 91 in the gap portion 6. Therefore, active species
20 such as ozone, hydrogen peroxide, oxygen atoms, and hydroxy radicals
generated in the supplied gas by the discharge Dc can be caused to act on
the water to be treated 90 (water film 91) to perform water treatment.
[0023] Note that a type of the gas introduced from the gas introduction part
4 can be freely determined according to the application. For example,

11
when a gas containing oxygen (oxygen, air, or the like) is supplied, ozone
and oxygen atoms can be generated by the discharge Dc. Further, when a
rare gas (helium, argon, or the like) is used, hydroxyl radicals (OH) and
hydrogen peroxide can be efficiently generated from water vapor
5 evaporated from the water to be treated 90. Further, when a gas containing
nitrogen (nitrogen, air, etc.) is used, peroxynitrous acid, peroxynitric acid,
etc. having a high sterilization action can be produced.
[0024] Here, the "treatment" of the water to be treated 90 means some
physical, chemical, and biological changes of the water to be treated 90
10 caused by the active species generated by the discharge Dc, and corresponds
to, for example, sterilization of bacteria, inactivation of viruses,
decomposition of organic substances, and the like in the water to be treated
90. Further, for example, it also corresponds to the generation of
functional water by dissolving active species generated by the discharge Dc
15 in the water to be treated 90.
[0025] In the water-film forming portion 7, the water to be treated 90
supplied from the water intake portion 3i passes through a narrow annular
flow path 7c (narrower than the gap portion 6) formed between the
water-film forming portion and the outer circumferential surface 2fo of the
20 ground electrode 2, thereby forming the water film 91 flowing down along
the surface of the ground electrode 2. At this time, it is necessary to form
a space between the water film 91 and the inner circumferential surface 1fi
of the dielectric 1 in the gap portion 6 and to prevent water droplets from
adhering to the inner surface (inner circumferential surface 1fi) of the

12
dielectric 1, and thus the thickness of the water film 91 needs to be
controlled. Therefore, an opening range G7 (= (Di7 – Dx2)/2) in the radial
direction of the water-film forming portion 7, which is defined by the
difference between the inner diameter Di7 of the water-film forming portion
5 7 and the outer diameter Dx2 of the ground electrode 2, is adjusted.
[0026] On the other hand, the size (interval G6 = (Di1 - Dx2)/2) in the
radial direction of the gap portion 6 formed between the ground electrode 2
and the dielectric 1 is set to about 1 mm to 5 mm as shown in Expression (1)
in order to efficiently perform the dielectric barrier discharge.
10 1 mm ≤ (Di1-Dx2)/2 ≤ 5 mm (1)
[0027] If the interval G6 is less than 1 mm, the water to be treated 90 may
adhere to the dielectric 1 due to slight waving of the water film 91, and
stable discharge may not be performed. If the interval G6 is made thicker
than the 5 mm, a very high voltage is required for forming the discharge Dc,
15 which causes problems of an increase in cost of the power supply 80 and an
increase in size of the apparatus due to an increase in the insulating
distance.
[0028] The water film 91 needs to be made thinner than the interval G6 of
the gap portion 6 that is narrow, and is preferably 0.1 mm or more and 3 mm
20 or less. In order to make the film thickness of the film 91 less than 0.1 mm,
the flow rate of the water to be treated 90 must be significantly reduced, and
thus, water treatment in a large flow rate cannot be performed. Further, if
the water film 91 is thicker than 3 mm, waving of the water surface
significantly occurs, and the water droplets may adhere to the inner

13
circumferential surface 1fi of the dielectric 1.
[0029] Further, it is preferable that the water film 91 should be thinner than
the thickness of the space formed between the water film 91 and the inner
circumferential surface 1fi (= interval G6 – thickness of water film 91). If
5 the thickness of the water film 91 is larger than the thickness of the space, a
problem arises in that the water to be treated 90 is electrostatically attracted
to the dielectric 1 side when a voltage is applied to the high voltage
electrode 5, and adheres to the dielectric 1. In contrast, this problem
hardly occurs when the thickness of the water film 91 is smaller than the
10 thickness of the space.
[0030] Therefore, the opening range G7 between the water-film forming
portion 7 and the ground electrode 2 needs to be set to a value smaller than
the interval G6. In particular, the opening range G7 is preferably set to be
0.1 mm or more and 3 mm or less (Expression 2). Further, the inner
15 circumferential surface 7fi of the water-film forming portion 7 is preferably
located closer to the outer circumferential surface 2fo of the ground
electrode 2 than the inner circumferential surface 1fi of the dielectric 1.
0.1 mm ≤ G7 ≤ 3 mm (2)
[0031] As described above, the thicknesses of the water film 91 is
20 controlled using the difference (opening range G7) between the inner
diameter Di7 of the water-film forming portion 7 and the outer diameter
Dx2 of the ground electrode 2, and thus, in the case of achieving the same
opening range G7, the larger outer diameter Dx2 of the ground electrode 2
is preferred. This is because a flow path cross-sectional area (= (Di72
-

14
Dx22
) × π/4) of the water-film forming portion 7 is increased, and the flow
rate of the water to be treated 90 can be increased. However, when the
flow rate is increased, the water droplets are likely to scatter, and therefore,
the interval G6 of the gap portion 6 needs to be set to be wider.
5 [0032] On the premise of the above-described configuration, the operation
of the water treatment apparatus 10, that is, a water treatment method will
be described. A gas is supplied at a predetermined flow rate from the gas
introduction part 4, and the power supply 80 is operated to apply a high
voltage between the high voltage electrode 5 and the ground electrode 2.
10 Thus, the discharge Dc is formed in the range where the high voltage
electrode 5 is arranged in the axial direction in the gap portion 6.
[0033] On the other hand, the water to be treated 90 supplied to the water
intake portion 3i passes through the internal flow path formed in the header
member 3, and is discharged from the annular flow path 7c in the ring shape
15 in the water-film forming portion 7 toward the gap portion 6. At this time,
the water to be treated 90 flows down along the axial direction on the outer
circumferential surface 2fo of the ground electrode 2 as the water film 91 in
the gap portion 6. Therefore, active species such as ozone, hydrogen
peroxide, oxygen atoms, and hydroxy radicals generated by the discharge
20 Dc act on the water to be treated 90 in the form of the water film 91,
whereby the water to be treated 90 is processed.
[0034] Since the water to be treated 90 covers the outer circumferential
surface 2fo of the ground electrode 2 as the water film 91, the contact area
between the active species and the water to be treated 90 can be increased,

15
and even short-lived active species such as oxygen atoms and hydroxy
radicals can be effectively utilized to enhance the efficiency in the water
treatment. Further, since the water to be treated 90 is prevented from
scattering in the form of water droplets, a wide discharge area can be
5 formed in the direction in which the water to be treated 90 flows down.
This suppresses a local temperature rise and suppresses thermal
decomposition of ozone, hydrogen peroxide, and the like that are useful for
the water treatment, thereby enabling efficient water treatment.
[0035] Note that, also in the following embodiments, the gas introduction
10 part 4 is not necessarily formed in the dielectric 1 as shown in FIG. 1, but
may be formed in the header member 3. In this case, for example, an gas
outlet port to the gap portion 6 should be arranged downstream to the
opening of the water-film forming portion 7 or along the inner
circumferential surface 1fi of the dielectric 1. This can prevent the
15 generation of water droplets due to the mixing of the gas and the water to be
treated 90.
[0036] Embodiment 2
In a water treatment apparatus according to Embodiment 2, an example in
which a protruded portion having a rectifying action is formed on a portion
20 of the outer circumferential surface of the ground electrode facing the inner
circumferential surface of the water-film forming portion will be described.
FIG. 3 and FIG. 4 are for describing a configuration of a water treatment
apparatus according to Embodiment 2, FIG. 3 is a cross-sectional view
corresponding to FIG. 2 of Embodiment 1, showing a water-film forming

16
portion in an enlarged manner for describing the configuration of the water
treatment apparatus, and FIG. 4 is a cross-sectional view that is taken along
a line A-A of FIG. 3 and is perpendicular to the axis of the water treatment
apparatus. FIG. 5 is a cross-sectional view of a water treatment apparatus
5 according to a variation, which is perpendicular to the axis and corresponds
to FIG. 4.
[0037] Note that Embodiment 2 is the same as Embodiment 1 except that the
ground electrode is provided with the protruded portion and the description
of the same portions will be omitted, and the configuration including the
10 power supply in FIG. 1 used in the description in Embodiment 1, the
opening range of the water-film forming portion in FIG. 2, and the like will
be referred to.
[0038] As shown in FIG. 3 and FIG. 4, the water treatment apparatus 10
according to Embodiment 2 is provided with a protruded portion 2p at a
15 position of the outer circumferential surface 2fo of the ground electrode 2
with which the annular flow path 7c is formed by facing the inner
circumferential surface 7fi of the water-film forming portion 7 in the axial
direction. The protruded portion 2p has a plurality of rib-like structures
radially protruding from the outer circumferential surface 2fo of the ground
20 electrode 2.
[0039] In Embodiment 1, the water film 91 is formed by the flow of the
water to be treated 90 in the narrow annular flow path 7c formed between
the outer circumferential surface 2fo of the ground electrode 2 and the inner
circumferential surface 7fi of the water-film forming portion 7. However,

17
when the flow rate (flow velocity) of the water to be treated 90 is high,
waving of the surface of the water film 91 may occur due to a pressure
change between the inside and the outside of the water-film forming portion
7, etc., and the water to be treated 90 may adhere to the dielectric 1.
5 [0040] In contrast, in Embodiment 2, the flow of the water to be treated 90
is rectified by the presence of the protruded portion 2p in the annular flow
path 7c, and thus the waving of the water film 91 is suppressed. Therefore,
even at a higher flow rate of the water to be treated 90, the discharge Dc can
be stably formed and the treatment can be performed.
10 [0041] Note that the protruded portion 2p is not limited in the shape to a
plurality of radially protruding rib-like structures shown in FIG. 4. For
example, as shown in a water treatment apparatus 10 according to a
variation of FIG. 5, the protruded portion 2p may be formed by a plurality
of mountain-shaped protruded portions radially protruding from the outer
15 circumferential surface 2fo of the ground electrode 2. Further, an
appropriate design can be made as far as the flow regulation effect of the
water to be treated 90 can be obtained. Furthermore, the protruded portion
2p is not necessarily formed integrally with the ground electrode 2, and may
be formed by fastening or joining a separate member to the ground electrode
20 2.
[0042] Embodiment 3
In Embodiment 1 and Embodiment 2, the examples have been described in
which only the path along the outer circumferential surface of the columnar
ground electrode is provided as the flow path of the water to be treated in

18
the gap portion. In Embodiment 3, an example will be described in which
a ground electrode formed of a porous material in a circular tube is used and
a flow path of the water to be treated is formed also inside the ground
electrode.
5 [0043] FIG. 6 is a cross-sectional view along an axis for describing a
configuration of a water treatment apparatus according to Embodiment 3.
Note that Embodiment 3 is the same as Embodiment 1 except that the
ground electrode is formed of a porous material in a circular tube, and
therefore, the description of the same portions will be omitted, and the
10 opening range of the water-film forming portion in FIG. 2, and the like used
in Embodiment 1 will be referred to.
[0044] As shown in FIG. 6, the water treatment apparatus 10 according to
Embodiment 3 is such that the ground electrode 2 of a porous material is
configured in a circular tube in which a water conduit 2c is formed to
15 penetrate the ground electrode in the axial direction. The other
configurations and the operation are the same as those of Embodiment 1.
As a porous material forming the ground electrode 2, for example, a
member obtained by molding a metal mesh, a punching metal, or the like (in
a plate material or a sheet material) into a circular tube shape can be used.
20 Alternatively, the ground electrode 2 can be formed by making a plurality of
through holes in the radial direction in a metal tube or can be formed of a
sintered metal.
[0045] In Embodiment 3, the water to be treated 90 supplied from the water
intake portion 3i to the internal flow path of the header member 3 not only

19
flows down along the annular flow path 7c but also enters the water conduit
2c through pores in a tube wall 2w of the ground electrode 2 and flows
down in the water conduit 2c.
[0046] When the discharge Dc is generated in the gap portion 6 in such a
5 configuration, the short-lived active species such as oxygen atoms and
hydroxy radicals among the active species generated by the discharge Dc
locally act on the water to be treated 90 in the vicinity of the surface of the
water film 91. On the other hand, long-lived active species such as ozone
and hydrogen peroxide are dissolved in the water to be treated 90 from the
10 surface of the water film 91 and diffused into the water to be treated 90
flowing in the water conduit 2c through the pores of the porous material
forming the ground electrode 2, whereby a wide range of treatment is
performed.
[0047] When the columnar ground electrode 2 is used as in Embodiment 1
15 and Embodiment 2, the region where the water to be treated 90 flows is
limited to the surface (outer circumferential surface 2fo) of the ground
electrode 2. Although this is effective in efficiently causing the
short-lived active species to act on the water to be treated, there is a
problem in that the flow rate of the water to be treated 90 is relatively low.
20 In contrast, in Embodiment 3, the water to be treated 90 flows not only on
the surface of the ground electrode 2 but also flows the inside thereof (water
conduit 2c), and therefore the flow rate can be increased. At this time, the
water to be treated 90 flowing inside the ground electrode 2 can also be
efficiently treated by the action of the long-lived active species.

20
[0048] Embodiment 4
In Embodiment 1 to Embodiment 3, the examples have been described in
which the outer diameter of the ground electrode is constant along the axial
direction. In Embodiment 4, an example will be described in which an
5 inclined portion where the outer diameter of the ground electrode changes
along the axial direction is provided.
[0049] FIG. 7 is a cross- sectional view along the axis for describing a
configuration of a water treatment apparatus according to Embodiment 4.
Note that Embodiment 4 is the same as Embodiment 1 except that the
10 ground electrode is provided with the inclined portion, and the description
of the same portions is omitted, and FIG. 2 used in Embodiment 1 is also
referred to.
[0050] As shown in FIG. 7, in the water treatment apparatus 10 according to
Embodiment 4, the ground electrode 2 has, in the region where the high
15 voltage electrode 5 is formed in the axial direction, an inclined portion 2t in
which the outer diameter Dx2 of the ground electrode 2 decreases along the
direction in which the water to be treated 90 flows down. Other structures
and the operation are the same as those of Embodiment 1.
[0051] For example, when the ground electrode 2 having a constant outer
20 diameter Dx2 as exemplified in Embodiment 1 to Embodiment 3 is used, the
water film 91 becomes thicker toward the downstream side (lower side in
the figure) due to fluid resistance action when the water to be treated 90
flows down along the outer circumferential surface 2fo of the ground
electrode 2. Therefore, a gap (discharge distance) of the space formed

21
between the water film 91 and the inner circumferential surface 1fi of the
dielectric 1 is narrowed toward the downstream side, and the discharge Dc
may be nonuniform between the upstream side and the downstream side.
In addition, when the region (discharge region) in which the discharge Dc is
5 generated in the axial direction is extended, the water to be treated 90
adheres to the dielectric 1 on the downstream side where the gap is
narrowed, and thus the possibility that normal discharge cannot be
performed increases.
[0052] In contrast, according to Embodiment 4, the inclined portion 2t in
10 which the outer diameter Dx2 decreases toward the downstream side is
provided in a portion corresponding to the discharge region in the ground
electrode, so that the change in the thickness of the water film 91 along the
flow direction is compensated to be able to keep the discharge distance
constant in the discharge region. Therefore, the discharge Dc can be
15 stably formed in a wider region, and the increase in the treatment flow rate
can be achieved.
[0053] Note that the range (length in the axial direction) and inclination of
the inclined portion 2t can be appropriately designed in accordance with the
range of the discharge region and the flow rate of the water to be treated 90.
20 In addition, the formation of the inclined portion 2t is not limited to the
portion facing the high voltage electrode 5 as shown in FIG. 7, and may be
appropriately designed as long as the stable discharge Dc can be formed.
That is, the setting range of the inclined portion 2t in the axial direction
may be longer or shorter than that of the high voltage electrode 5.

22
[0054] Embodiment 5
In Embodiment 1 to Embodiment 4, the examples have been described in
which the high voltage electrode is continuously present in the axial
direction. In Embodiment 5, an example will be described in which the
5 high voltage electrodes are intermittently arranged along the axial direction.
[0055] FIG. 8 is a cross-sectional view along the axis for describing a
configuration of a water treatment apparatus according to Embodiment 5.
Note that Embodiment 5 is the same as Embodiment 1 except that the high
voltage electrodes are intermittently arranged along the axial direction, and
10 therefore, the description of the same portions will be omitted and FIG. 2
used in Embodiment 1 will be referred to.
[0056] In the water treatment apparatus 10 according to Embodiment 5, as
shown in FIG. 8, three electrodes (first electrode 51, second electrode 52,
and third electrode 53) are intermittently arranged as the high voltage
15 electrode 5 on the outer circumferential surface of the dielectric 1 along the
flow direction (axial direction: vertical direction in FIG. 8) of the water to
be treated 90. That is, the multiple electrodes (first electrode 51, second
electrode 52, and third electrode 53) are arranged at intervals to each other
in order from the upstream side of the flow of the water to be treated 90.
20 [0057] Thus, a discharge Dc1, a discharge Dc2, and a discharge Dc3 are
formed at respective positions corresponding to the first electrode 51, the
second electrode 52, and the third electrode 53. The other structures and
operation are the same as those of Embodiment 1.
[0058] For example, when the high voltage electrode 5 continuous in the

23
axial direction as exemplified in Embodiment 1 to Embodiment 4 is used to
extend the installation range in the axial direction, the water film 91 is
disturbed by the influence of the external electric field for forming the
discharge Dc, and the water surface is likely to wave as the water film flows
5 downstream. As a result, it is considered that water droplets are likely to
adhere to the dielectric 1.
[0059] In contrast, in Embodiment 5, since the multiple electrodes (first
electrode 51, second electrode 52, and third electrode 53) are intermittently
arranged along the flow direction of the water to be treated 90, the
10 installation range per electrode is narrower than in the case of using the
continuous high voltage electrode 5. Therefore, even when the water film
91 is disturbed at each electrode, the water surface of the water film 91 is
stabilized again in the region where the high voltage electrode 5 is not
arranged, that is, in the region where no external electric field exists. This
15 effect makes it possible to suppress adhesion of the water to be treated 90 to
the dielectric 1 and form a stable discharge Dc even when a dielectric
barrier discharge is generated in a wide region as the discharge Dc
(discharge Dc1 + discharge Dc2 + discharge Dc3).
[0060]Furthermore, although various exemplary embodiments and examples
20 are described in the presentapplication, various features, aspects, and
functions described in one or more embodiments are not inherent in an
application of the contents disclosed in a particular embodiment, and can be
applicable alone or in their various combinations to each embodiment.
Accordingly, countless variations that are not illustrated are envisaged

24
within the scope of the art disclosed in the specification of the present
application. For example, the case where at least one component is
modified, added or omitted, and the case where at least one component is
extracted and combined with a component disclosed in another embodiment
5 are included.
[0061] For example, in the present application, the examples have been
shown in which the high voltage electrode 5 is arranged on the outer
circumferential side so as to surround the ground electrode 2 arranged at the
axial center, but this is not a limitation. The high voltage electrode may be
10 on the axial center side and the ground electrode may be on the outer
circumferential side. Further, the examples have been shown in which the
dielectric 1 is arranged on the inner circumferential surface side of the outer
circumferential side electrode (high voltage electrode 5 in the above
example), and the water film 91 is formed along the outer circumferential
15 surface (outer circumferential surface 2fo) of the axial center side electrode
(ground electrode 2 in the above example), but this is not a limitation. The
dielectric may be arranged along the outer circumferential surface of the
electrode on the axial center side, and the water film 91 may be formed
along the inner circumferential surface of the electrode on the outer
20 circumferential side.
[0062] Further, a dielectric may be arranged on each of the both pole
electrodes, and the water film 91 may be formed on at least a side facing
one of the dielectrics. Further, in the case where the dielectric is arranged
along the inner circumferential surface of the electrode on the outer

25
circumferential side, when a transparent material such as quartz is used, the
formation state of the water film 91 and the scattering state of the water
droplets can be easily observed from the outside of the apparatus.
Therefore, for example, by adjusting the amount of water while checking
5 the state of the water film 91, the treatment amount of the water to be
treated 90 can be readily increased to an upper limit at which water droplets
do not scatter.
[0063] Further, as the water treatment method, the example of using the
water treatment apparatus 10 in the cylindrical shape capable of achieving
10 the flow control of water and gas in a simple configuration has been
described, but this is not a limitation. In its essence, the water film 91
thinner than the interval G6 is formed on the electrode (ground electrode 2)
facing the dielectric 1 that is spaced apart with the interval G6 and causes to
generate the dielectric barrier discharge, and the water film 91 is made to
15 flow along the surface (outer circumferential surface 2fo) of the electrode.
Therefore, when the active species generated by the dielectric barrier
discharge is caused to act on the water to be treated 90, the flow control of
water and gas may be complicated, but the water treatment method of the
present application can be applied regardless of the electrode shape such as
20 a parallel plate.
[0064]As described above, the water treatment apparatus 10 of the present
application includes the first electrode (for example, ground electrode 2)
extending in the axial direction, the second electrode (for example, high
voltage electrode 5) arranged coaxially with the first electrode so as to

26
surround the first electrode from the outside in the radial direction, the
dielectric 1 that is formed in a cylindrical shape, is coaxially arranged and
interposed between the first electrode and the second electrode, forms an
annular gap (gap portion 6) between the dielectric and the one electrode (for
5 example, ground electrode 2) of the first electrode and the second electrode,
and causes to generate dielectric barrier discharge by applying a voltage
between the one electrode and the other electrode, and the water-film
forming portion 7 that forms the annular flow path 7c along a
circumferential direction between the water-film forming portion and the
10 one electrode (for example, ground electrode 2) on one end side in an axial
direction with an opening toward the annular gap (gap portion 6) at a
narrower spacing (opening range G7) than the annular gap (gap portion 6)
and causes water to be treated 90 to flow down toward the other end side as
the water film 91 covering the one electrode (outer circumferential surfaces
15 2fo of the grand electrode 2) when the one end side is directed upward to set
the axial direction to be vertical. Therefore, since the water to be treated
90 flows down along the surface of the electrode (outer circumferential
surface 2fo) as the water film 91 thinner than the interval G6 of the gap
portion 6, the instability of the dielectric barrier discharge due to the
20 adhesion of the water droplets to the dielectric 1 can be suppressed, and the
water to be treated 90 can be efficiently processed by the stable operation.
[0065] When the interval G6 between the one electrode (for example,
ground electrode 2) and the dielectric 1 is equal to or larger than 1 mm and
equal to or smaller than 5 mm, it is not necessary to apply an excessive

27
voltage, and it is possible to effectively suppress the scattering of water
droplets to the dielectric 1, and thus a stable and efficient dielectric barrier
discharge (Dc) can be formed.
[0066] In particular, when a spacing of the opening (opening range G7) is
5 equal to or larger than 0.1 mm and equal to or smaller than 3 mm, the
thickness of the water film 91 can be controlled to be 0.1 mm or more and 3
mm or less. As a result, the water droplets are not scattered on the
dielectric 1, and the water to be treated 90 can be processed with a high
throughput.
10 [0067] Further, the other electrode (for example, high voltage electrode 5)
is arranged to be spaced apart from the water-film forming portion 7 in the
axial direction, and the gas introduction part 4 for supplying a gas to the
space formed between the water film 91 and the dielectric 1 is provided
between the water-film forming portion 7 and the other electrode (high
15 voltage electrode 5) in the axial direction, and thus the type of active
species to be generated can be controlled by the type of gas to be
introduced.
[0068] Further, if the one electrode (ground electrode 2) is provided with
the protruded portion 2p protruding toward the annular flow path 7c in the
20 region where the annular flow path 7c is formed, even if the flow rate of the
water to be treated 90 increases, the waving of the water film 91 is
suppressed by the rectifying action of the protruded portion 2p, and the
scattering of the water droplets to the dielectric 1 can be more efficiently
suppressed.

28
[0069] Alternatively, in the region of the one electrode (ground electrode 2)
facing the other electrode (high voltage electrode 5), when the inclined
portion 2t whose diameter changes along the axial direction is provided
such that the interval G6 between the one electrode and the dielectric
5 increases along the flow direction, the increase in the thickness of the water
film 91 along the flow direction is compensated to be able to keep the
discharge distance constant in the discharge region. Therefore, the
discharge Dc can be stably formed in a wider region, and the increase in the
treatment flow rate can be achieved.
10 [0070] In addition, when the other electrode (high voltage electrode) is
configured with multiple electrodes (first electrode 51 to third electrode 53)
spaced apart from each other in the axial direction, even when the water
film 91 is disturbed by the electric field at each of the electrodes, the water
surface of the water film 91 is stabilized again in a region where no external
15 electric field exists before the water film 91 passes by the next electrode.
This effect makes it possible to suppress the adhesion of the water to be
treated 90 to the dielectric 1 and form the stable discharge Dc even when
the dielectric barrier discharge is generated in a wide region as the
discharge Dc (discharge Dc1 + discharge Dc2 + discharge Dc3).
20 [0071] Here, if the above-described one electrode (the electrode facing the
dielectric 1 with the interval therebetween) is the first electrode (for
example, the ground electrode 2) located on the axial center side, the water
film 91 covers the outer circumferential surface 2fo. Therefore, when a
transparent dielectric 1 such as quartz glass is used, the surface of the water

29
film 91 can be observed from the outside in the radial direction through the
dielectric 1, and adjusting of the thickness of the water film 91 can be
readily performed.
[0072] In this case, when the configuration is such that the first electrode
5 located on the axial center side is formed in a circular tube by forming the
water conduit 2c that passes through in the axial direction on the inner side
in the radial direction, and at least part of the tube wall 2w is formed of a
porous material from the outer circumferential surface 2fo to the water
conduit 2c, long-lived active species such as ozone and hydrogen peroxide
10 are dissolved in the water to be treated 90 from the surface of the water film
91 and diffused into the water to be treated 90 flowing in the water conduit
2c through the pores of the porous material forming the ground electrode 2.
Thus, the long-lived active species can be effectively used to perform a
wide range of treatment, and the flow rate of the water to be treated 90, that
15 is, the treatment amount can be increased.
[0073] As described above, the water treatment method of the present
application is a water treatment method using the water treatment apparatus
10 in which two electrodes (grand electrode 2 and high voltage electrode 5)
and the dielectric 1 arranged between the two electrodes are provided, and
20 the gap (gap portion 6) extending with a constant interval is formed between
the one electrode (for example, outer circumferential surface 2fo of the
grand electrode 2) of the two electrodes and the dielectric 1. The water
treatment method includes steps of generating active species by applying a
voltage between the two electrodes to cause dielectric barrier discharge

30
(discharge Dc), introducing the water to be treated 90 from the one end side
in the extending direction of the gap, and causing the generated active
species to act on the introduced water to be treated 90. In the step of
introducing the water to be treated 90, the one end side is directed upward
5 to set the extending direction to be vertical, and the water to be treated 90 is
made to flow down toward the other end side as the water film 91 that has a
thickness smaller than the constant interval G6 and covers the one electrode
(outer circumferential surface 2fo). Therefore, the water to be treated 90
flows along the outer circumferential surface 2fo in the form of the water
10 film, and thus, it is possible to suppress instability of the dielectric barrier
discharge due to adhesion of the water droplets to the dielectric 1 and to
efficiently treat the water to be treated 90 with a stable operation.
Description of Reference Numerals and Signs
15 [0074] 1: dielectric, 1fi: inner circumferential surface, 2: ground electrode,
2c: water conduit, 2fo: outer circumferential surface, 2p: protruded portion,
2t: inclined portion, 3: header member, 3i: water intake portion, 4: gas
introduction part, 5: high voltage electrode, 6: gap portion, 7: water-film
forming portion, 7c: annular flow path, 10: water treatment apparatus, 80:
20 power supply, 90: water to be treated, 91: water film, Dc: discharge, Di1:
inner diameter (of dielectric), Di7: inner diameter (of water-film forming
portion), Dx2: outer diameter (of ground electrode), G7: opening range, G6:
gap

We Claim:
[Claim 1] A water treatment apparatus comprising:
a first electrode extending in an axial direction;
5 a second electrode arranged coaxially with the first electrode so as to
surround the first electrode from an outside in a radial direction;
a dielectric that is formed in a cylindrical shape, is coaxially arranged
and interposed between the first electrode and the second electrode, forms
an annular gap between the dielectric and one electrode of the first
10 electrode and the second electrode, and causes to generate dielectric barrier
discharge by applying a voltage between the one electrode and the other
electrode; and
a water-film forming portion that forms an annular flow path along a
circumferential direction between the water-film forming portion and the
15 one electrode on one end side in an axial direction with an opening toward
the annular gap at a narrower spacing than the annular gap and causes water
to be treated to flow down toward the other end side as a water film
covering the one electrode when the one end side is directed upward to set
an axial direction to be vertical.
20
[Claim 2] The water treatment apparatus according to claim 1, wherein an
interval between the one electrode and the dielectric is equal to or larger
than 1 mm and equal to or smaller than 5 mm.

32
[Claim 3] The water treatment apparatus according to claim 2, wherein a
spacing of the opening is equal to or larger than 0.1 mm and equal to or
smaller than 3 mm.
5 [Claim 4] The water treatment apparatus according to any one of claims 1 to
3, further comprising a gas introduction part provided between the
water-film forming portion and the other electrode in the axial direction,
and configured to supply a gas to a space formed between the water film and
the dielectric, the other electrode being arranged to be spaced apart from the
10 water-film forming portion in the axial direction.
[Claim 5] The water treatment apparatus according to any one of claims 1 to
4, wherein the one electrode is provided with a protruded portion protruding
toward the annular flow path in a region where the annular flow path is
15 formed.
[Claim 6] The water treatment apparatus according to any one of claims 1 to
5, wherein, in a region of the one electrode facing the other electrode, an
inclined portion whose diameter changes along the axial direction is
20 provided such that the interval between the one electrode and the dielectric
increases along a flow direction.
[Claim 7] The water treatment apparatus according to any one of claims 1 to
6, wherein the other electrode is configured with a plurality of arranged

33
electrodes spaced apart from each other in the axial direction.
[Claim 8] The water treatment apparatus according to any one of claims 1 to
7, wherein the one electrode is the first electrode.
5
[Claim 9] The water treatment apparatus according to claim 8, wherein the
first electrode is formed in a circular tube by forming a water conduit that
passes through in an axial direction on an inner side in a radial direction,
and at least part of a wall of the tube is formed of a porous material from an
10 outer circumferential surface to the water conduit.
[Claim 10] A water treatment method using a water treatment apparatus in
which two electrodes and a dielectric arranged between the two electrodes
are provided, and a gap extending with a constant interval is formed
15 between one electrode of the two electrodes and the dielectric, the water
treatment method comprising steps of:
generating active species by applying a voltage between the two
electrodes to cause dielectric barrier discharge;
introducing water to be treated from one end side in an extending
20 direction of the gap; and
causing the generated active species to act on the introduced water to
be treated, wherein,
in the step of introducing the water to be treated, the one end side is
directed upward to set the extending direction to be vertical, and the water

34
to be treated is made to flow down toward the other end side as a water film
that has a thickness smaller than the constant interval and covers the one
electrode.