Conventionally, purification devices which disinfect/purify water such as bath water, water for a pool, or water for breeding include a water purification device which comprises a filtration means which filtrates a material to be purified and a disinfection means composed of a photocatalyst which is provided so as to be in contact with the water to be purified and a light source which irradiates the photocatalyst (for example, see Patent Document 1).
This water purification device purifies the water to be purified by the photocatalyst and the light source which comprises a fluorescent lamp or an ultraviolet lamp.
Meanwhile, there is a water treatment device in which a large-surface-area material is provided in a reaction container provided in piping through which water to be treated such as bath water flows.
An ultraviolet light source irradiates the large-surface-area material with ultraviolet rays, and an ozone injection means injects ozone to the upstream side of the reaction container (for example, see Patent Document 2).
This water treatment device injects ozone into the water to be treated by the ozone injection means, radiates ultraviolet rays from the outer surface of the reaction container which is formed to be transparent, and forms a photocatalyst on the surface of the large-surface-area material in the reaction container, thereby purifying the water to be treated by the ozone and the photocatalyst.
Moreover, there is a fluid purification device in which a reaction container comprising a double tube having an outer tube and an inner tube is provided at an intermediate position of the piping through which a fluid to be treated such as bath water flows. One electrode is positioned on the entire periphery of the outer tube of the reaction container, and another electrode which is a counterpart of the above described electrode is provided on the transparent inner tube which is spaced from the outer tube by predetermined space. Oxygen or air is supplied to the space between the outer tube and the inner tube while discharge is generated between the electrodes between the outer tube and the inner tube so as to generate ozone. The ozone is mixed with the fluid to be treated so as to purify it (for example, see Patent Document 3).
In the reaction container, the outer tube is formed of stainless steel, while the inner tube is formed of quartz glass or borosilicic acid glass, and one of the electrodes of the outer tube side serves as an earth electrode.
In the fluid purification device, a photocatalyst is installed in the inner tube, the ultraviolet rays generated by the discharge for generating ozone is utilized so as to cause the photocatalyst to be activated and functioned, and the fluid to be treated is purified by the ozone and the photocatalyst.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. H8-89725    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2004-154742    Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2004-223345
However, in the water purification device of Patent Document 1, an attempt is made to improve the disinfection performance by performing disinfection by the photocatalyst and the light source instead of disinfection which is performed merely by an ultraviolet lamp. However, this cannot be considered to have the disinfection performance capable of sufficiently disinfecting the water to be treated.
In the water treatment device of Patent Document 2, since ozone is injected into the water to be treated, the disinfection performance can be enhanced by ozone having high disinfection effects in addition to the photocatalyst. However, in this case, the water treatment device has the structure in which the ozone injection means is provided as another device in the upstream side of the reaction container, and ozone is separately generated by the outside ozone injection means. Therefore, there has been a problem that the entire device becomes complex and large.
The fluid purification device of Patent Document 3 is intended to solve the problem of Patent Document 2 by generating the ozone and the photocatalyst in the reaction container comprising the double tube and purifying the fluid to be treated by a simple structure while the strong disinfection effects of ozone are exerted. However, since this fluid purification device has the structure in which the outer tube of the reaction container is a metal composed of stainless steel, and the inner tube is a dielectric body composed of transparent glass, the following problem have been newly generated.
Specifically, in the fluid purification device, discharge is generated between the electrodes of the reaction container, and, when the electrode is provided on the outer surface side of the inner tube to generate the discharge in the case in which the electrode is provided between the inner tube and the outer tube to generate the discharge, there has been a problem that arc discharge occurs, and a large sound is generated.
On the other hand, when the electrode is caused to be in close contact with the inner surface side of the inner tube, silent discharge occurs, and the problem of generation of the sound can be solved.
However, when the electrode of the inner surface side of the inner tube is charged to be a high-voltage side in this case, and if the fluid that flows within the inner tube is liquid, the liquid is charged to have a high voltage. As a result, there has been a possibility that the pipe connected to the inner tube may be charged to a high voltage, and a dangerous state may be caused. In addition, a protection device is needed when the inner surface side is charged to a high voltage in this manner.
However, attachment of the protection device has been difficult.
Even when the outer tube is caused to be charged to be a high-voltage side, adverse effects may be exerted on the outer side of the outer tube. Therefore, a protection device of a high voltage power supply has been needed.