JP2013123656A - Water quality control device and water quality control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the production efficiency of active species and the reaction efficiency of the active species with organic matter, bacteria, etc contained in treated water by providing plasma generating electrodes in a position of high bubble density in a water quality control device for controlling water quality by generating plasma in the treated water.SOLUTION: The water quality control device includes: a flow passage 1 through which treated water flows; a nozzle part 3 provided in the flow passage 1 and having a throat part 2; a pair of plasma generating electrodes 4 provided with plasma generating parts 41 in the throat part 2; and a gas introduction part 5 having a gas introduction port 51 provided upstream of the plasma generating electrodes 4 and introducing gas to treated water in the flow passage 1.

Description

  The present invention relates to a water quality control apparatus and a water quality control method for controlling water quality by generating plasma in water to be treated.

  2. Description of the Related Art Conventionally, there is a technique for controlling water quality by providing a nozzle in a flow path through which water to be treated flows to generate bubbles, causing plasma discharge in the bubbles, and generating active species such as ions and radicals.

  For example, as shown in Patent Document 1, a nozzle portion having an orifice shape in a flow passage, and a pair of plasma generating electrodes in which a high-voltage side electrode and a ground-side electrode are arranged at intervals on the downstream side of the nozzle portion. There is a water quality control device.

  However, since the pair of plasma generating electrodes is provided on the downstream side where the channel cross-sectional area is large with respect to the channel cross-sectional area of the nozzle portion, the density of bubbles passing through the space between the plasma generating electrodes becomes low. . Then, it becomes difficult to generate plasma between the plasma generating electrodes, and not only the generation efficiency of active species such as ions and radicals generated by bubbles contained in the water to be treated is deteriorated, but also organic substances contained in the water to be treated The contact efficiency between bacteria and the like and plasma and active species also deteriorates. As a result, there is a problem that high water quality control performance cannot be obtained.

JP 2011-41914 A

  Accordingly, the present invention has been made to solve the above-mentioned problems all at once, and in a water quality control apparatus that controls water quality by generating plasma in water to be treated, the bubble density is high and the channel cross-sectional area is small. By providing a plasma generating electrode in the flow channel region, the generation efficiency of active species is improved, and an improvement in reaction efficiency between organic matter and bacteria contained in the water to be treated and plasma and active species To do.

  That is, the water quality control device according to the present invention includes a flow path through which water to be treated is circulated, a minimum flow path provided in the flow path and having a minimum flow path cross-sectional area, or the minimum flow path and the minimum flow path. A nozzle portion having a throat portion composed of a flow passage having a flow passage cross-sectional area of four times or less, a pair of plasma generation electrodes provided with a plasma generation portion in the throat portion, and upstream of the plasma generation electrode And a gas introduction part having a gas introduction port for introducing a gas into the water to be treated in the flow passage.

  If it is such, in the throat part which consists of the minimum flow path where the flow path cross-sectional area is the minimum or the minimum flow path and the flow path which is a flow path cross-sectional area of 4 times or less with respect to the minimum flow path By providing the plasma generating electrode, it is possible to provide the plasma generating electrode in a flow channel region having a high bubble density and a small flow channel cross-sectional area. Accordingly, it is possible to easily generate plasma at the plasma generating electrode, improve the generation efficiency of active species such as ions and radicals generated by bubbles contained in the water to be treated, and be included in the water to be treated. The reaction efficiency of organic matter, bacteria, etc. with plasma and active species can be improved.

  In order to simplify the configuration of the throat part and install the electrode in a region having a high bubble density, and in order to install the electrode in a region having a small cross-sectional area, the throat part may have an equal cross-section flow path. desirable.

  In order to further improve the generation efficiency of active species such as ions and radicals, it is desirable that at least two or more sets of the plasma generating electrodes are provided in the throat portion. In particular, it is desirable that the plurality of sets of plasma generating electrodes be provided along the direction of the central axis of the flow path formed by the throat portion. In this case, the active species generated by the pair of plasma generation electrodes arranged on the upstream side flow to the pair of plasma generation electrodes on the downstream side, and are newly generated by the pair of plasma generation electrodes on the downstream side. Since it reacts with the organic species and bacteria contained in the water to be treated together with the active species, the reaction efficiency with the organic matter and bacteria can be remarkably improved as compared with the case where one set of plasma generating electrodes is provided.

  It is desirable that the gas inlet is provided on the inner peripheral surface of the throat portion. If it is this, the bubble introduce | transduced by the gas inlet can reach a pair of plasma generation electrode efficiently.

  In order to increase the installation space of the plasma generating electrode in the throat portion and to arrange more plasma generating electrodes in the throat portion, the gas introduction port is provided in the flow passage upstream of the throat portion. It is desirable that

  In order to efficiently generate bubbles in the water to be treated, it is desirable that two or more gas inlets are provided for one throat portion.

  It is desirable that the plasma generating electrode is disposed so as to face the direction perpendicular to the central axis of the flow path formed by the throat portion. In this case, by reducing the facing distance of the plasma generating electrode as much as possible, the flow passage cross-sectional area of the throat portion can be reduced, and plasma is generated in the flow passage region where the bubble density is high and the flow cross-sectional area is small. Not only can the electrodes be arranged, but the area ratio of the plasma generation region to the flow path cross-sectional area can be increased.

  The distribution of bubbles in the flow path formed by the throat portion varies depending on, for example, the position of the gas inlet. Therefore, when there are many bubbles in the vicinity of the central axis of the throat portion, it is desirable that the plasma generation site is disposed at a symmetrical position with respect to the central axis of the flow path formed by the throat portion. Further, when there are many bubbles in the vicinity of the inner peripheral surface of the throat portion, the plasma generation site may be disposed at a symmetrical position with respect to an axis decentered from the central axis of the flow path formed by the throat portion. desirable.

  In order to treat a large amount of water to be treated at the same time without lowering the contact efficiency between the water to be treated and the plasma, the flow path is branched into two or more, and the plasma generation site is arranged in each of the branched paths. It is desirable that the nozzle portion is provided.

  Of the pair of plasma generating electrodes provided in the nozzle portions of the branch paths adjacent to each other, the high-voltage electrode or the ground-side electrode is integrated, so that the number of parts can be reduced and the space can be saved.

  As an electrode that can generate plasma at a low voltage with a small amount of electrode damage in plasma discharge in water, it is preferable that the plasma generating electrode is a needle electrode that has a small electrode surface area and easily generates electric field concentration.

  In order to expand the plasma region and increase the contact efficiency between the water to be treated and the plasma, the pair of plasma generation electrodes are provided with fluid flow holes at corresponding positions of the electrodes, respectively, and the fluid flow holes are formed in the throat portion. May pass through in the same direction as the direction of the central axis of the flow path, and the opening end of the fluid circulation hole may be a plasma generation site. Furthermore, when the opening cross section of the fluid circulation hole has the same shape as the flow path cross section of the throat portion, when there are many bubbles near the side wall surface of the throat portion, the reaction efficiency between the air in the bubbles and the plasma is increased. Can be increased.

  According to the present invention configured as described above, in the water quality control apparatus that controls the water quality by generating plasma in the water to be treated, the plasma generating electrode is provided in the flow channel region having a high bubble density and a small flow channel cross-sectional area. Thus, the generation efficiency of active species can be improved, and the reaction efficiency of the active species with organic matter and bacteria contained in the water to be treated can be improved.

The schematic end elevation which shows the structure of the water quality control apparatus which concerns on 1st Embodiment. The graph which shows the decomposition rate in 1 set, 2 sets, and 3 sets of plasma generating electrodes. The schematic end elevation which shows the structure of the water quality control apparatus which concerns on 2nd Embodiment. The graph which shows the decomposition rate in arrangement | positioning of a plasma generating electrode. The schematic end elevation which shows the structure of the water quality control apparatus which concerns on 3rd Embodiment. The schematic end elevation which shows the structure of the water quality control apparatus which concerns on 4th Embodiment. The graph which shows the decomposition rate in one nozzle part and two nozzle parts. The schematic end elevation which shows the structure of the water quality control apparatus which concerns on 5th Embodiment. The schematic end elevation which shows the structure of the water quality control apparatus in other embodiment. The schematic end elevation which shows the structure of the water quality control apparatus in other embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
As shown in FIG. 1, the water quality control apparatus 100 according to the first embodiment includes a flow passage 1 through which water to be treated is circulated, and a nozzle portion that is provided in the flow passage 1 and in which the throat portion 2 has an equal cross-section flow path. 3 and a pair of plasma generation electrodes 4 in which a plasma generation site 41 is provided in a flow path formed by the throat portion 2, provided upstream of the plasma generation electrode 4, and covered in the flow passage 1. A gas introduction part 5 having a gas introduction port 51 for introducing a gas into treated water and a high voltage power source 6 for applying a voltage to the pair of plasma generating electrodes 4 are provided. Furthermore, an external pipe (not shown) is connected to one end and the other end of the apparatus main body forming the flow passage 1.

  The nozzle part 3 includes a convergent part 31 whose sectional area gradually decreases from the upstream side to the downstream side, a divergent part 32 whose sectional area gradually increases from the upstream side to the downstream side, and a gap between them. And the throat portion 2 having the smallest channel cross-sectional area.

  The throat part 2 is an equal cross-section flow path and has a predetermined length. Further, the throat portion 2 is provided with three sets of two gas introduction portions 5 and a pair of plasma generation electrodes 4 provided with plasma generation portions 41 in order from the upstream.

  The two gas introduction parts 5 are constituted by through holes formed in the side wall of the flow passage 1. The two gas introduction portions are provided to face each other in a direction orthogonal to the central axis direction of the flow path formed by the throat portion 2. And the opening in the inner peripheral surface of the throat part 2 of the gas introduction part 5 becomes the gas introduction port 51. That is, the two gas introduction ports 51 are disposed to face each other on the inner peripheral surface of the throat portion 2. Further, these gas inlets 51 are located on the upstream side of the plasma generating electrode 4 on the most upstream side. The external air that has passed through the gas introduction part 5 configured as described above and has been sucked into the throat part 2 from the gas introduction port 51 becomes bubbles in the water to be treated.

  Each set of plasma generating electrodes 4 is constituted by a needle electrode whose tip is a plasma generating portion 41. Each set of plasma generating electrodes 4 is disposed so as to face the direction orthogonal to the central axis direction of the flow path formed by the throat portion 2. Further, the three plasma generation sites 41 in each set of plasma generation electrodes 4 are arranged at symmetrical positions with respect to the central axis C of the flow path formed by the throat portion 2. In the present embodiment, the opposing directions of the plasma generating electrodes 4 in each group are the same as each other, but are not limited thereto.

  Next, the water quality control method of the water quality control apparatus 100 will be described.

  When the water to be treated flows through the flow passage 1, the water to be treated flows into the throat portion 2 while increasing the flow velocity by the convergent portion 31 of the nozzle portion 3. And the to-be-processed water which flowed into the throat part 2 falls in pressure because the flow velocity became large. Therefore, a pressure difference is generated between the external air and the throat portion 2 with respect to the gas introduction portion 5, and the external air is sucked into the throat portion 2 from the gas introduction port 51 through the gas introduction portion 5. Bubbles are generated in the treated water.

  The water to be treated containing bubbles flows to the downstream plasma generation electrode 4. A plasma discharge is generated in the bubble between the two plasma generation sites 41 facing each other, and active species such as ions and radicals are generated in the bubble. This active species decomposes organic substances and bacteria in the water to be treated.

  Next, FIG. 2 shows the experimental results of the organic matter decomposition performance in the water quality control device when one set of plasma generating electrodes 4 is provided, when two sets are provided, and when three sets are provided. When one set of plasma generating electrodes 4 is used, when the liquid to be treated containing indigo carmine is passed through the water quality control device for 30 minutes, the decomposition rate of the indigo carmine is 25%. It was. On the other hand, when two sets of plasma generating electrodes 4 were used, the decomposition rate of indigo carmine was improved to 70%. As described above, it was found that two sets of samples exhibited double or more decomposition performance compared to one set. This is because the active species generated by the first set of plasma generating electrodes 4 reach the second set of plasma generating electrodes 4 and react with indigo carmine in the water to be treated together with the active species generated by the second set. Conceivable. Furthermore, when three sets of plasma generating electrodes 4 were used, the decomposition rate of indigo carmine was improved to 85%. As described above, it was found that three sets exhibited three times or more decomposition performance compared to one set.

  According to the water quality control apparatus 100 configured as described above, the plasma generation electrode 4 is provided in the throat portion 2 that is an equal cross-section flow path, so that plasma is generated in a flow path area having a high bubble density and a small cross-sectional area. An electrode 4 can be provided. Thereby, the area ratio of the plasma area | region with respect to the flow-path cross-sectional area of the throat part 2 can be enlarged, and the contact efficiency of the bubble and plasma contained in to-be-processed water can be improved. Therefore, it is possible to easily generate plasma at the plasma generating electrode 4 and to improve the generation efficiency of active species such as ions and radicals generated by bubbles contained in the water to be treated, so that the organic matter contained in the water to be treated And the reaction efficiency of bacteria and bacteria with plasma and active species can be improved.

Second Embodiment
Next, a second embodiment will be described with reference to FIG. In the second embodiment, the same reference numerals are used for members that are the same as or correspond to those in the first embodiment.

  The water quality control apparatus 100 according to the second embodiment differs from the first embodiment in the arrangement of the plasma generating electrodes 4. As shown in FIG. 3, the plasma generation site 41 of the plasma generation electrode 4 in the present embodiment is disposed so as to be symmetric with respect to an axis that is eccentric from the central axis C of the throat portion 2. Further, the plasma generation sites 41 of the present embodiment are arranged in a staggered pattern so as to be staggered in the vertical direction. More specifically, the plasma generation sites 41 of the plasma generation electrodes 4 of each set are arranged so as to be positioned in the vicinity of the inner peripheral surface of the throat portion 2.

  Next, refer to FIG. 4 for the effects of the case where the plasma generation site 41 is arranged opposite to the central axis C of the flow path formed by the throat portion 2 and the case where the plasma generation site 41 is arranged eccentrically from the central axis C. I will explain. When arranged opposite to the central axis C, the decomposition rate of indigo carmine was 85%, but when arranged opposite to the center axis C, the decomposition rate of indigo carmine was 100%. In the configuration of the present embodiment, many bubbles are generated in the vicinity of the inner peripheral surface of the throat portion 2, so it is considered that a higher decomposition rate was obtained when the plasma generation site 41 was arranged eccentrically than when it was arranged centrally. It is done.

  According to the water quality control apparatus 100 according to the second embodiment configured as described above, the gas introduction port 51 is provided on the inner peripheral surface of the throat portion 2, and many bubbles are generated near the inner peripheral surface of the throat portion 2. In this case, by arranging the plasma generation site 41 at a symmetrical position with respect to the axis decentered from the central axis C of the throat portion 2, plasma can be generated in a portion where there are many bubbles in the throat portion 2. . As a result, it is possible to easily generate plasma at the plasma generating electrode 4 and to improve the generation efficiency of active species such as ions and radicals generated by bubbles contained in the water to be treated, and to be included in the water to be treated. The reaction efficiency of the active species with organic matter and bacteria can be improved.

<Third Embodiment>
Next, a third embodiment will be described with reference to FIG. In the third embodiment, the same reference numerals are used for members that are the same as or correspond to those in the first and second embodiments.

  As shown in FIG. 5, the water quality control device 100 according to the third embodiment has the opening end of the gas introduction part 5 provided in the same direction as the flow direction of the water to be treated. Specifically, the opening end of the gas introduction part 5 is provided coaxially with the central axis C of the flow passage 1 on the upstream side of the throat part 2. That is, the gas inlet 51 opens in the same direction as the flow direction of the water to be treated on the same axis as the central axis C of the flow passage 1.

  According to the water quality control apparatus 100 according to the third embodiment configured as described above, the gas introduction port 51 is on the upstream side of the throat portion 2 and is coaxial with the central axis C of the flow path 1 in the flow direction of the water to be treated. Therefore, many bubbles are generated in the vicinity of the central axis C of the throat portion 2. Since all the plasma generation sites 41 in the three sets of plasma generation electrodes 4 are arranged symmetrically with respect to the central axis C of the throat portion 2, plasma is generated in a portion where there are many bubbles in the throat portion 2. be able to. As a result, it is possible to easily generate plasma at the plasma generating electrode 4 and to improve the generation efficiency of active species such as ions and radicals generated by bubbles contained in the water to be treated, and to be included in the water to be treated. The reaction efficiency of the active species with organic matter and bacteria can be improved.

<Fourth embodiment>
Next, a fourth embodiment will be described with reference to FIG. In the fourth embodiment, the same reference numerals are used for members that are the same as or correspond to those in each of the embodiments.

  As shown in FIG. 6, in the water quality control apparatus 100 according to the fourth embodiment, the flow passage 1 is branched into two, and the nozzle portions 3 are provided in the respective branch paths 1A and 1B. Further, a plasma generating electrode 4 is provided in the throat portion 2 of the nozzle portion 3 in each branch path 1A, 1B. The plasma generating electrodes 4 provided in each throat portion 2 are provided so as to be at the same position. And one electrode (a high voltage electrode or a ground side electrode) is united among the pair of plasma generation electrodes 4 provided in the throat part 2 of each branch path 1A, 1B. Specifically, of the pair of plasma generating electrodes 4 provided on the throat portion 2 of one branch passage 1A, the electrode on the other branch passage 1B side and the throat portion 2 of the other branch passage 1B are provided. Of the pair of plasma generating electrodes 4, the electrode on the one branch path 1A side is a common electrode.

  Next, the effects of the case where one nozzle portion is formed without branching the flow passage and the case where two nozzle portions are provided by branching the flow passage will be described with reference to FIG. When it was not branched, the decomposition rate of indigo carmine was 25%, but when it was branched, the decomposition rate of indigo carmine was 100%. Thus, when controlling the water quality of the same amount of water to be treated, by dividing the flow passage 1, the flow passage cross-sectional area of the throat portion of each branch passage is reduced, and the plasma with respect to the flow passage cross-sectional area of the throat portion is reduced. Since the area ratio of the region can be increased, it is considered that a high decomposition rate can be obtained.

  According to the water quality control apparatus 100 according to the fourth embodiment configured as described above, the flow passage 1 is branched into two, and the nozzle portion 3 is provided in each of the branch passages 1A and 1B. Even if the flow passage cross-sectional area of the throat portion is reduced and the area ratio of the plasma region to the flow passage cross-sectional area of the throat portion is increased, the same amount of water to be treated can be controlled. As a result, it is possible to easily generate plasma at the plasma generating electrode 4 and to improve the generation efficiency of active species such as ions and radicals generated by bubbles contained in the water to be treated, and to be included in the water to be treated. The reaction efficiency of organic matter, bacteria, etc. with plasma and active species can be improved. Moreover, since the high-voltage side electrode or the ground-side electrode is shared by one electrode among the pair of plasma generation electrodes provided in each branch path, the number of parts can be reduced, and the water quality control device 100 can be reduced in size. Can be

<Fifth Embodiment>
Next, a fifth embodiment will be described with reference to FIG. In the fifth embodiment, the same reference numerals are used for members that are the same as or correspond to those in each of the embodiments.

  The water quality control apparatus 100 according to the fifth embodiment is different from the above embodiments in the configuration of the plasma generating electrode 4. As shown in FIG. 8, the plasma generating electrode 4 of the present embodiment has a fluid circulation hole 42 at a corresponding position of each electrode 4, and the fluid circulation hole 42 is a flow path formed by the throat portion 2. It arrange | positions at the throat part 2 so that it may penetrate in the same direction as a center axis direction. The opening end of the fluid circulation hole 42 becomes the plasma generation site 41. The opening cross section of the fluid circulation hole 42 has the same shape as the flow path cross section of the throat portion 2, and the pair of plasma generating electrodes 4 has the opening end portion of the fluid circulation hole 42 flush with the inner peripheral surface of the throat portion 2. It is arranged to be. In this water quality control device 100, plasma is generated over the entire circumference at the opening end of the fluid circulation hole 42 of each electrode 4, and the plasma region can be enlarged.

  According to the water quality control apparatus 100 according to the fifth embodiment configured as described above, plasma can be generated over the entire circumference on the inner peripheral surface of the throat portion 2, and organic matter, bacteria, etc. contained in the water to be treated And the reaction efficiency of plasma and active species can be further improved.

<Other modified embodiments>
The present invention is not limited to the above embodiment.

  For example, as shown in FIG. 9, only one set of plasma generating electrodes 4 may be arranged for one throat portion 2, or two sets or four or more sets are arranged for one throat portion. It may be a thing.

  Further, a plurality of nozzle portions may be provided along the downstream side from the upstream side in one flow passage, and one or a plurality of sets of plasma generating electrodes may be arranged for each nozzle portion.

  Furthermore, a structure in which the gas introduction port 51 is provided on the side wall surface of the convergent portion 31 may be employed.

  In addition, the gas introduction unit 5 may have a bubble generator, and the bubbles generated by the bubble generator may be introduced into the water to be treated.

In the above-described embodiment, the throat portion 2 is an equal cross-section flow path including only the minimum flow path having the minimum flow path cross-sectional area. However, as illustrated in FIG. 10, the throat section 2 includes the minimum flow path 21 and the minimum flow path. You may have the flow path 22 which is a flow-path cross-sectional area 4 times or less with respect to the flow path 21. FIG. That is, when the cross-sectional area of the minimum flow path 21 is A _min , the maximum cross-sectional area that the flow path 22 can take is 4 A _min , and the cross-sectional area A _electrode of the flow path in which the plasma generating electrode 4 is provided is A _min ≦ A _electrode ≦ 4 A _min .
In FIG. 10, the minimum flow path 21 is formed on the upstream side of the throat portion 2, and the plasma generating electrode 4 is provided in the flow path 22 on the downstream side of the minimum flow path 21. The minimum flow path 21 is provided with a gas inlet 51 of the gas inlet 5. Moreover, in FIG. 10, although the flow path 22 is shown as an equal cross-section flow path, it is not restricted to an equal cross-section flow path.

  In addition, it goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Water quality control apparatus 1 ... Flow path 2 ... Throat part 3 ... Nozzle part 4 ... Plasma generation electrode 41 ... Plasma generation part 5 ... Gas introduction part 51 ... Gas inlet 6 ・ ・ ・ High voltage power supply

Claims (16)

A flow passage for circulating the water to be treated;
A throat portion provided in the flow passage and including a minimum flow path having a minimum flow path cross-sectional area or a flow path having a flow path cross-sectional area not more than four times the minimum flow path and the minimum flow path. A nozzle part;
A pair of plasma generation electrodes provided with a plasma generation site in the throat portion;
A water quality control apparatus comprising: a gas introduction unit provided upstream of the plasma generation electrode and having a gas introduction port for introducing gas into the water to be treated in the flow passage.   The water quality control apparatus according to claim 1, wherein the throat portion is an equal cross-section flow path.   The water quality control device according to claim 1 or 2, wherein at least two sets of the pair of plasma generating electrodes are provided in the throat portion.   The water quality control device according to claim 3, wherein the plurality of sets of plasma generating electrodes are provided along a central axis direction of a flow path formed by the throat portion.   The water quality control device according to claim 1, wherein the gas introduction port is provided on an inner peripheral surface of the throat portion.   The water quality control device according to claim 1, wherein the gas introduction port is provided in the flow passage upstream of the throat portion.   The water quality control device according to claim 1, wherein two or more gas introduction ports are provided for one throat portion.   The pair of plasma generating electrodes are disposed so as to face each other in a direction orthogonal to a central axis direction of a flow path formed by the throat portion. The water quality control device described.   The water quality according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the pair of plasma generation sites are disposed symmetrically with respect to a central axis of a flow path formed by the throat portion. Control device.   The plasma generation site according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the plasma generation site is disposed symmetrically with respect to an axis decentered from a central axis of a flow path formed by the throat portion. Water quality control device. The flow passage is branched into two or more, and the nozzle portion is provided in each branch passage;
The water quality control apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein each of the nozzle portions is provided with the pair of plasma generating electrodes.   The water quality control apparatus according to claim 11, wherein a high-voltage electrode or a ground-side electrode is integrated with each other among a pair of plasma generation electrodes provided in nozzle portions of adjacent branch paths.   The water quality control device according to claim 1, wherein the pair of plasma generating electrodes are needle electrodes.   The pair of plasma generating electrodes are provided with fluid circulation holes at corresponding positions of the electrodes, respectively, and the fluid circulation holes penetrate in the same direction as the central axis direction of the flow path formed by the throat portion. The water quality control apparatus according to claim 1, wherein an opening end portion of the fluid circulation hole is a plasma generation site.   The water quality control device according to claim 14, wherein an opening cross section of the fluid circulation hole has the same shape as a flow path cross section of the throat portion.   A water quality control method for controlling the quality of water to be treated using the water quality control device according to claim 1.