Water treatment method and water treatment device

Abstract

To provide a water treatment method capable of removing free chlorine from water to be treated without adversely affecting a surrounding environment.SOLUTION: A water treatment method for removing free chlorine contained in water to be treated includes contacting the water to be treated with fine bubbles comprising a gas containing hydrogen or helium, in which the bubble diameter of the fine bubbles is less than 1000 nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment method and a water treatment device. [Background technology]

[0002] When various types of water or wastewater are treated with chlorine-based disinfectants, residual chlorine such as free chlorine and combined chlorine remains in the treated water. If the treated water containing such residual chlorine is discharged as it is into rivers, lakes, marshes, the sea, etc., there is a risk of adversely affecting the surrounding environment, so the treated water is subjected to treatment to render the residual chlorine harmless.

[0003] Similarly, when seawater to which a chlorine-based disinfectant has been added is discharged into the sea, the residual chlorine content in the discharged seawater is required to be below a certain value to avoid any impact on the environment. Therefore, in facilities that use seawater, the residual chlorine concentration in the seawater is measured at the seawater outlet or the like, and the amount of chlorine-based disinfectant added to the seawater is adjusted so that the measured value is below a predetermined value.

[0004] Regarding such residual chlorine detoxification treatment, for example, Patent Document 1 describes the treatment of drinking water, wash water, sewage, etc. using a residual chlorine remover containing a specific tertiary amino compound and / or a specific guanidino compound. Also, Patent Document 2 describes a ballast water treatment system equipped with a chlorine disinfectant supply device that supplies a chlorine disinfectant to seawater taken in as ballast water to a ship, and a chlorine reducing agent supply device that supplies a chlorine reducing agent to the ballast water when the ballast water to which the chlorine disinfectant has been supplied is discharged into the sea, and describes the use of sulfite, hyposulfite, thiosulfate, etc. as the chlorine reducing agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-144399 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-039680 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when conventional chemicals, such as chlorine-reducing agents such as sulfites, hyposulfites, and thiosulfates, are added to the water to be treated, residual chlorine in the water is removed, but the chemicals may remain in the water. Furthermore, if the excess chemicals added to the water to be treated are released into seawater, they can be harmful. For example, when hypochlorous acid is reduced with sodium thiosulfate, sulfuric acid and hydrochloric acid are produced as by-products. Furthermore, when the water to be treated is seawater, the release of the chlorine-reducing agent into the seawater can cause a reaction between the sulfites and the dissolved oxygen in the seawater, reducing the amount of dissolved oxygen in the seawater and potentially adversely affecting the surrounding environment.

[0007] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a water treatment method and a water treatment device that can remove free chlorine from the water to be treated without discharging harmful components. [Means for solving the problem]

[0008] As a result of extensive research to solve the above problems, the inventors discovered that by generating fine bubbles in the water to be treated, it is possible to reduce the free chlorine contained in the water to be treated without discharging harmful components, and thus completed the present invention.

[0009] That is, the present invention has the following aspects. [1] A water treatment method for removing free chlorine contained in water to be treated, comprising: The method includes contacting the water to be treated with fine bubbles made of a gas containing hydrogen or helium, A water treatment method, wherein the fine bubbles have a bubble diameter of less than 1000 nm. [2] The concentration of the fine bubbles in the water to be treated is 5 × 10 7 ~1.5×10 8 The water treatment method described in [1], wherein the concentration is 1 / ml. [3] The water treatment method according to [1] or [2], wherein the fine bubbles have a bubble diameter of 100 to 600 nm. [4] The water treatment method according to any one of [1] to [3], wherein the water to be treated is brought into contact with the fine bubbles under a pressure of 0.05 to 20 MPa. [5] The water treatment method according to any one of [1] to [4], wherein the hydrogen or the helium is plasma-treated. [6] The water treatment method according to any one of [1] to [5], which includes generating the fine bubbles in the water to be treated. [7] The water treatment method according to any one of [1] to [6], wherein ascorbic acid or hydrogen peroxide is added to the water to be treated before treatment. [8] A pressurized tank for storing fine bubble water containing fine bubbles made of gas containing hydrogen or helium in the water to be treated; an introduction path for introducing the fine bubble water into the pressurized tank; and an outlet path for discharging the fine bubble water from the pressurized tank. [9] The water treatment device according to [8], further comprising a pressurizing mechanism for pressurizing the inside of the pressurized tank to 0.05 to 20 MPa.

[10] Further comprising a fine bubble generator located on the primary side of the pressurized tank, The water treatment device described in [8] or [9], wherein the fine bubble generator generates fine bubbles in the water to be treated to produce fine bubble water, and supplies the fine bubble water to the introduction path. [Effects of the Invention]

[0010] The water treatment method and water treatment device of the present invention can remove free chlorine from the water to be treated without discharging harmful components. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a system diagram schematically illustrating the configuration of a water treatment device according to one embodiment of the present invention. [Figure 2]FIG. 1 is a diagram showing one embodiment of a fine bubble generator used in the water treatment device of this embodiment. [Figure 3] FIG. 2 is a diagram showing one mode of a pressurized tank used in the water treatment device of the present embodiment. [Figure 4] FIG. 2 is a schematic diagram showing the configuration of a water treatment device used in a comparative example of the present invention. [Figure 5] FIG. 2 is a schematic diagram showing the configuration of a water treatment device used in a comparative example of the present invention. [Figure 6] FIG. 10 is a diagram showing the results of the number concentration of ultrafine bubbles before treatment in an example of the present invention. [Figure 7] FIG. 10 is a diagram showing the results of the number concentration of ultrafine bubbles after treatment in an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the present invention, a numerical range expressed using "to" includes both ends of the range. Furthermore, "fine bubbles" refers to bubbles with a diameter of 100 μm or less, of which visible, cloudy bubbles with a diameter of 1 to 100 μm are called "microbubbles," while invisible, colorless, transparent bubbles with a diameter of less than 1 μm are called "ultrafine bubbles (UFB)."

[0013] The clear difference between microbubbles and ultrafine bubbles is that ultrafine bubbles do not scatter visible light and therefore cannot be observed directly with the naked eye, whereas the presence of microbubbles can be confirmed by the appearance of cloudiness. In the present invention, the occurrence of fine bubbles, including microbubbles, was confirmed by visually confirming this cloudiness. Furthermore, the presence of ultrafine bubbles was confirmed by measuring the particle size distribution based on the number distribution using laser diffraction, as described in detail below.

[0014] In the present invention, "millibubbles" refer to bubbles of 1 to 100 mm, and "submillibubbles" refer to bubbles of 100 μm to 1 mm. In the present invention, the generation of these bubbles was confirmed by visual inspection.

[0015] In the present invention, "free chlorine contained in the water to be treated" includes, for example, hypochlorous acid.

[0016] The following is a detailed description of a water treatment method according to an embodiment of the present invention, and the configuration of a water treatment device used therein. Note that the drawings used in the following description may show characteristic parts enlarged for convenience in order to make the characteristics easier to understand, and the dimensional proportions of the components may not necessarily be the same as those in reality.

[0017] <Water treatment equipment> First, an example of the configuration of a water treatment device according to one embodiment of the present invention will be described with reference to the drawings. Here, Fig. 1 is a system diagram that schematically shows the configuration of a water treatment device according to one embodiment of the present invention. As shown in FIG. 1, the water treatment device 1 of this embodiment includes a pump 2, a fine bubble generator 20, a pressurized tank 30, a pressure adjustment nozzle 3, and paths L1 to L5. The water treatment device 1 uses the water to be treated and a required gas to generate fine bubbles in the water to be treated and bring the water to contact with the fine bubbles, thereby removing free chlorine contained in the water to be treated.

[0018] Path L1 is a supply path for water containing free chlorine (water to be treated) to be treated. One end (base end) of path L1 is connected to a supply source (not shown) of water to be treated, and the other end (tip end) is connected to paths L2 and L3. Path L1 is not particularly limited as long as it is airtight and liquidtight. Examples of path L1 include metal piping and flexible resin hoses. The same applies to paths L2 to L5 below.

[0019] The water to be treated is not particularly limited as long as it contains free chlorine. For example, the water to be treated may be water containing free chlorine before being discharged into rivers, lakes, marshes, the sea, etc. Furthermore, water containing free chlorine may be collected from rivers, lakes, marshes, or the sea and used as is. In this case, one end of the path L1 may be placed in the water of the river, lake, marshes, or sea.

[0020] A reducing agent supply mechanism may be provided in path L1 to add a reducing agent to the water to be treated. The reducing agent is not particularly limited as long as it does not produce environmentally hazardous compounds such as sulfuric acid or hydrochloric acid as by-products after the reaction. Examples of such reducing agents include ascorbic acid and hydrogen peroxide, and among these, hydrogen peroxide is particularly preferred from the viewpoint of environmental impact.

[0021] The path L2 is a supply path for raw material gas that turns into fine bubbles in the water to be treated. One end (base end) of the path L2 is connected to a raw material gas supply source (not shown), and the other end (tip end) is connected to the paths L1 and L3.

[0022] The source gas is not particularly limited as long as it is a gas containing hydrogen or helium. Examples include hydrogen gas, helium gas, and a mixed gas containing at least one of these and diluted with another gas. Examples of dilution gases include air, nitrogen gas, and argon gas. Among these, hydrogen gas or helium gas is preferred as the source gas from the viewpoints of safety and simplicity.

[0023] When the raw material gas contains hydrogen and is diluted with another gas, the dilution gas is preferably a gas that does not contain oxygen. The hydrogen concentration in the mixed gas is preferably 30 to 90% by volume, and more preferably 50 to 80% by volume. If the hydrogen concentration is within the above range, free chlorine in the water to be treated can be safely and effectively removed.

[0024] The source of the raw material gas may be selected appropriately depending on the amount of gas used in the water treatment, and may be, for example, a cylinder or tank for each gas type, or a gas generator such as a PSA or electrolysis device.

[0025] The hydrogen or helium in the source gas may be plasma-treated using a plasma treatment device (not shown). By using plasma-treated hydrogen or helium, the effect of improving reduction can be obtained. The plasma treatment conditions can be an electrode distance of 5 mm and an applied voltage of 7 to 12 kV.

[0026] When the hydrogen gas is plasma-treated, the hydrogen concentration in the mixed gas is preferably 30 to 90% by volume, and more preferably 50 to 80% by volume. If the hydrogen concentration is within the above range, free chlorine in the water to be treated can be safely and effectively removed.

[0027] When the helium gas is plasma-treated, the helium concentration in the mixed gas is preferably 30 to 90% by volume, and more preferably 50 to 80% by volume. If the helium concentration is within the above range, free chlorine in the water to be treated can be removed effectively and economically.

[0028] The flow rate of the raw material gas supplied to path L2 is preferably 3 to 100 mL / L min, and more preferably 5 to 10 mL / L min. If the flow rate of the raw material gas is within the above range, free chlorine in the water to be treated can be removed effectively and economically.

[0029] The path L3 is located on the primary side of the fine bubble generator 20 and is a mixed fluid supply path that supplies a mixed fluid of the water to be treated and the raw material gas to the fine bubble generator 20. One end (base end) of the path L3 is connected to the paths L1 and L2, and the other end (tip end) is connected to the gas-liquid inlet pipe 21 of the fine bubble generator 20, which will be described later.

[0030] The manner in which paths L1, L2, and L3 are connected is not particularly limited as long as it is possible to generate a mixed fluid of the water to be treated and the raw material gas on the primary side of the fine bubble generator 20. For example, paths L1 and L3 may be an integrated path, with path L2 connected to the path at any position between one end and the other end of the path, or the path may be a double pipe in which path L2 is located inside path L1.

[0031] The pump 2 is located on the path L3 and sends the mixed fluid in the path L3 to the fine bubble generator 20. The pump 2 is not particularly limited as long as it can send the mixed fluid at the required flow rate (or pressure). A centrifugal pump can be used as the pump 2. The pump 2 preferably has a liquid delivery capacity of 5 to 840,000 L / min.

[0032] FIG. 2 is a diagram showing an embodiment of the fine bubble generator 20 used in the water treatment device 1 of this embodiment. As shown in Figure 2(a), the fine bubble generator 20 comprises a gas-liquid inlet pipe 21 for introducing a mixed fluid of water to be treated and raw material gas, a bubble generating mechanism 22 provided on the mixed fluid discharge side of the gas-liquid inlet pipe 21, a cylindrical gas-liquid multiphase flow generating mechanism 25 in which the gas-liquid inlet pipe 21 is positioned at the center of the cylinder, and a discharge pipe 26 provided on the side of the gas-liquid multiphase flow generating mechanism 25 for discharging the water to be treated containing fine bubbles (fine bubble water).

[0033] The gas-liquid multiphase flow generating mechanism 25 has a cylindrical shape. A gas-liquid inlet pipe 21 penetrates from the top of the tube body to the center of the tube. The end of the gas-liquid inlet pipe 21 on the mixed fluid discharge side is positioned with a gap between it and the bottom of the tube body. The interior of the tube body is divided into two sections by a vortex generating mechanism 24: a lower tank section 23a at the bottom of the tube body and an upper tank section 23b at the top of the tube body. The vortex generating mechanism 24 has an upper surface 27a with two to four holes and a lower surface 27b with two to four holes offset from the holes on the upper surface 27a. The holes on the upper surface 27a and the holes on the lower surface 27b correspond to each other. That is, as shown in FIG. 2(b), in the cross section of the vortex generating mechanism 24, each through-hole 28 is obliquely arranged at a certain angle with respect to the surface of the upper surface 27a or the lower surface 27b.

[0034] First, the mixed fluid of the water to be treated and the raw gas introduced into the gas-liquid inlet pipe 21 is introduced into the bubble generation mechanism 22, where it becomes a mixed fluid containing bubbles (air bubbles). The bubble generation mechanism 22 is made of a hollow member having a conical shape, and has a structure in which one or more through-holes 29 are provided in part of the conical surface. The mixed fluid introduced into the gas-liquid inlet pipe 21 passes through the through-holes 29 from the outside of the bubble generation mechanism 22 and is introduced into the interior of the bubble generation mechanism 22, where bubbles are generated. By being equipped with such a bubble generation mechanism 22, the fine bubble generator 20 can generate a sufficient amount of fine bubbles even with a relatively low water pressure and a small amount of water.

[0035] The water to be treated, which has been made into a mixed fluid containing bubbles by the bubble generation mechanism 22, is discharged from the outlet (lower) end of the gas-liquid inlet pipe 21 and introduced into the lower tank section 23a of the gas-liquid multiphase flow generating mechanism 25, and then passes through the through-holes 28 of the vortex generation mechanism 24 and is introduced into the upper tank section 23b of the gas-liquid multiphase flow generating mechanism 25. Because the through-holes 28 are provided obliquely in the cross-sectional direction as described above, when the water to be treated containing bubbles passes through the through-holes 28, a vortex is generated in the upper tank section 23b.

[0036] A vortex is created in the upper tank section 23b around the pipe of the gas-liquid inlet pipe 21, and during this process, the water to be treated, which contains large-diameter bubbles with a low specific gravity, collects inside the upper tank section 23b (toward the center of the cylindrical shape) and is separated into the upper part of the upper tank section 23b. Meanwhile, the water to be treated, which contains small-diameter bubbles, is pushed out of the upper tank section 23b (toward the outer periphery of the cylindrical shape) by centrifugal force. In this way, the fine bubble generator 20 generates water to be treated that contains many small-diameter bubbles, and discharges it through the discharge pipe 26 provided on the side of the gas-liquid multiphase flow generating mechanism 25.

[0037] If desired, the discharge pipe 26 may be configured to have a bubble generation mechanism 22 installed inside the pipe, similar to the gas-liquid inlet pipe 21. When the bubble generation mechanism 22 is installed in the discharge pipe 26, the water to be treated containing small-diameter bubbles passes through the bubble generation mechanism 22, thereby making the water to be treated contain even smaller-diameter bubbles. If desired, two or more bubble generation mechanisms 22 may be arranged in parallel in the discharge pipe 26, and by providing three or more bubble generation mechanisms in the entire apparatus 20, it is possible to improve the efficiency of fine bubble generation. If desired, it is preferable to install one bubble generation mechanism 22 in the gas-liquid inlet pipe 21 and one to four bubble generation mechanisms 22 in the discharge pipe 26.

[0038] The above-described configuration of the fine bubble generator 20 is an example and is not intended to be limiting. The water treatment device 1 of the present invention can be any conventionally known fine bubble generator disclosed in prior art documents (e.g., Japanese Patent No. 6353936, Japanese Patent No. 6118544, etc.). Furthermore, the water treatment device 1 of the present invention can also be a fine bubble generator that utilizes a method known in the art for generating fine bubbles, such as the ejector method, cavitation method, gas-liquid shear (swirl flow) method, or pressurized dissolution method.

[0039] The ejector method is a method in which pressurized liquid is sent to an ejector, and the countless "separated flows" generated inside the ejector atomize the self-primed gas to generate bubbles. In this method, water is flowed from a wide flow path to a narrow flow path, and then back to the wide flow path again, causing the pressure to be suddenly released, which breaks up the self-primed air, and the flow velocity in the narrow flow path increases rapidly, causing the self-primed air to break up due to the flow velocity, which turns the self-primed air into bubbles.

[0040] The cavitation method involves sending pressurized liquid into a generator with a cavitation structure, and using the cavitation phenomenon (cavity phenomenon) that occurs in the structure to precipitate dissolved gas contained in the liquid and generate bubbles.

[0041] The gas-liquid shear (swirl flow) method is a method in which pressurized liquid is sent from an eccentric direction into a generator with a cylindrical structure, inducing swirl inside the cylinder, and the shear stress cuts through the air to generate bubbles.

[0042] The pressurized dissolution method is a method in which gas is forcibly dissolved under pressure, and then bubbles are precipitated by reducing the pressure (releasing to the atmosphere). In other words, by applying pressure, gas is dissolved in the liquid to an excessive degree beyond the saturation value according to Henry's law, and then the pressure is released to re-bubble the gas that was dissolved above the saturation value.

[0043] Path L4 is located between the fine bubble generator 20 and the pressurized tank 30, and is a fine bubble water introduction path that supplies the water to be treated (fine bubble water) containing fine bubbles delivered from the fine bubble generator 20 to the pressurized tank 30. One end (base end) of path L4 is connected to the discharge pipe 26 of the fine bubble generator 20, and the other end (tip end) is connected to the introduction pipe 32 of the pressurized tank 30, which will be described later.

[0044] FIG. 3 is a diagram showing one embodiment of the pressurized tank 30 used in the water treatment device 1 of this embodiment. As shown in Figure 3, the pressurized tank 30 comprises a main body 31, which is a cylindrical, pressure-resistant container, an inlet pipe 32 for introducing the water to be treated (fine bubble water) containing fine bubbles into the main body 31, and an outlet pipe 33 provided on the lower side of the main body 31 for discharging the fine bubble water to the outside of the main body 31.

[0045] The main body 31 is installed so that its longitudinal axis is vertical, from the viewpoint of the residence time of the fine bubble water. The volume of the main body 31 is not particularly limited and can be selected appropriately depending on the amount of water to be treated. The volume of the main body 31 can be 0.2 to 500,000 L, and preferably 0.5 to 500,000 L.

[0046] The introduction pipe 32 has a horizontal section 32A extending horizontally and a vertical section 32B extending vertically, with these ends joined to form an L-shape. The horizontal section 32A penetrates the lower part of the side surface of the main body 31, and is positioned so that the vertical section 32B is at the center of the tube. The vertical section 32B extends vertically inside the main body 31, and its tip (upper end) is positioned with a gap between it and the upper part of the main body 31. As a result, one end (base end) of the introduction pipe 32 is connected to the path L4, and the tip (upper end) opens upward into the space inside the main body 31.

[0047] First, the water to be treated (fine bubble water) containing fine bubbles introduced into the inlet pipe 32 from path L4 is transported horizontally by the horizontal section 32A and reaches the inside of the main body 31. Next, the fine bubble water rises from the bottom to the top of the vertical section 32B and is discharged into the space inside the main body 31 from the opening at the tip (top end) of the vertical section 32B. Here, by flowing the fine bubble water upward in the vertical section 32B, the coarse gas contained in the fine bubble water is separated from the fine bubble water containing many small bubbles. The separated gas is stored in the gas phase inside the main body 31, and the fine bubble water is stored in the liquid phase inside the main body 31.

[0048] Thus, the water treatment device 1 of this embodiment, equipped with the pressurized tank 30, allows the fine bubble water generated by the fine bubble generator 20 to remain inside the inlet pipe 32 and main body 31 for a long period of time. Furthermore, the pressurized tank 30 has a flow path (i.e., vertical section 32B) through which the fine bubble water flows from bottom to top and which opens at the top, allowing coarse gases to be separated from the fine bubble water along the flow path of the fine bubble water. Therefore, the water treatment device 1 of this embodiment ensures sufficient time for the water to be treated and the fine bubbles to come into contact with each other.

[0049] Next, after the water to be treated and the fine bubbles have been sufficiently brought into contact in the pressurized tank 30, the fine bubble water is discharged from the pressurized tank 30 through the outlet pipe 33 provided below the side of the main body 31.

[0050] The outlet pipe 33 may be configured to have a bubble generation mechanism 22 installed inside the pipe, similar to the gas-liquid inlet pipe 21 of the bubble generator 20 described above. When the bubble generation mechanism 22 is installed in the outlet pipe 33, the fine bubble water passes through the bubble generation mechanism 22, thereby making the water to be treated contain even smaller bubbles, thereby promoting contact between the water to be treated and the fine bubbles.

[0051] Path L5 is located on the secondary side of the pressurized tank 30 and is a fine bubble water outlet path that discharges the fine bubble-containing water (fine bubble water) that has been discharged from the pressurized tank 30 to the outside of the system. One end (base end) of path L5 is connected to the outlet pipe 33 of the pressurized tank 30, and the other end (tip) is open. When water from rivers, lakes, and oceans that contains free chlorine is collected and used as the water to be treated as is, the other end (tip) of path L5 can be placed in the water of the river, lake, or ocean, and the water to be treated from which the free chlorine has been removed can be returned.

[0052] The pressure adjustment nozzle 3 is located at the end of the path L5 and discharges the water to be treated from which free chlorine has been removed at a required flow rate (or pressure). The pressure adjustment nozzle 3 is not particularly limited as long as it can discharge the fluid at the required flow rate (or pressure). For example, a ball valve can be used as the pressure adjustment nozzle 3. Furthermore, the discharge capacity of the pressure adjustment nozzle 3 is preferably such that it can discharge at a flow rate of 5 to 840,000 L / min.

[0053] In a continuous fluid path such as paths L3 to L5, the pump 2 is disposed on the primary side and the pressure adjustment nozzle 3 is disposed on the secondary side, so the fluid path from the secondary side of the pump 2 to the primary side of the pressure adjustment nozzle 3 is pressurized to a required pressure. Accordingly, the fine bubble generator 20 and the pressurized tank 30 located on paths L3 to L5 are also pressurized. That is, in the water treatment device 1 of this embodiment, the pump 2 and the pressure adjustment nozzle 3 constitute a pressurizing mechanism.

[0054] According to the water treatment device 1 of this embodiment, the fluid path including the fiber bubble generator 20 and the pressurized tank 30 is pressurized to the required pressure by the pressurizing mechanism, which increases the residence time in the pressurized tank 30 and promotes contact (reaction) between the water to be treated and the fine bubbles. In addition, the pressurizing mechanism suppresses the flow rate in the fluid path including the fiber bubble generator 20 and the pressurized tank 30, which increases the density of fine bubbles in the water to be treated and promotes contact (reaction) between the water to be treated and the fine bubbles.

[0055] In the water treatment device 1 of this embodiment, a configuration using the pump 2 and the pressure adjustment nozzle 3 as a pressurizing mechanism has been described as an example, but the configuration is not limited to this as long as it can pressurize the fluid path including the fiber generator 20 and the pressurizing tank 30 to the required pressure. For example, instead of or simultaneously with the pressure adjustment nozzle 3, a pressure adjustment valve or a back pressure valve may be arranged in the path L5.

[0056] <Water treatment method> Next, the water treatment method of the present invention will be described. The water treatment method of the present invention removes free chlorine contained in the water to be treated by contacting the water to be treated with fine bubbles consisting of a gas containing hydrogen or helium and having a bubble diameter of less than 1000 nm.

[0057] Hereinafter, as one embodiment of the water treatment method of the present invention, a case where a water treatment device 1 shown in FIG. 1 is used will be described as an example. The water treatment method of this embodiment is roughly composed of the steps of preparing water to be treated and a gas (raw material gas) containing hydrogen or helium, generating a mixed fluid containing the water to be treated and the raw material gas, generating fine bubbles in the water to be treated, and discharging the water to be treated after free chlorine has been removed.

[0058] (preparation) In the water treatment method of this embodiment, first, water to be treated and a raw material gas are prepared. Specifically, water containing free chlorine is selected as the water to be treated and introduced into the water treatment device 1 via path L1. For example, seawater or freshwater containing hypochlorous acid as free chlorine can be used as the water to be treated. If the free chlorine concentration in the water to be treated is extremely high, a reducing agent may be added to the water to be treated to enhance the effect. From the perspective of environmental load, it is particularly preferable to use hydrogen peroxide as the reducing agent. It is preferable to appropriately select the amount of reducing agent added to the water to be treated within a range that does not cause harm when excess is discharged.

[0059] At the same time, a gas containing hydrogen or helium at a required concentration is prepared as a raw material gas and introduced into the water treatment device 1 via path L2. The hydrogen or helium used as the raw material gas may be plasma-treated. Using a gas containing plasma-treated hydrogen or helium as the raw material gas is expected to improve reactivity.

[0060] (Generation of mixed fluid) Next, a mixed fluid containing the water to be treated and the raw material gas is generated. Specifically, a mixed fluid is generated by supplying the water to be treated and the raw material gas to the path L3. Here, it is preferable that the contents of the water to be treated and the raw material gas in the mixed fluid are appropriately adjusted by the amount of the raw material gas discharged through the path L1 and the discharge rate of the pump 2 provided in the path L3.

[0061] (Fine bubble water generation) Next, fine bubbles are generated in the water to be treated to produce fine bubble water. Specifically, as shown in Figure 2, by introducing the mixed fluid into the fine bubble generator 20 through path L3, fine bubbles with a bubble diameter of less than 1000 nm are generated in the water to be treated, producing water to be treated containing fine bubbles (fine bubble water).

[0062] The fine bubbles preferably contain a large amount of ultrafine bubbles (UFB) with a bubble diameter of less than 1000 nm, more preferably a large amount of UFB with a bubble diameter of 50 to 800 nm, and particularly preferably a large amount of UFB with a bubble diameter of 100 to 600 nm. Here, UFB with a bubble diameter of 100 to 600 nm are excellent in free chlorine removal efficiency, as shown in the examples described below. Note that the water to be treated containing fine bubbles may also contain microbubbles with a bubble diameter of 1 to 100 μm.

[0063] Furthermore, as will be shown in the examples below, the number concentration of fine bubbles in the water to be treated is 5 × 10 7 ~1.5×10 8 It is preferable to use cells / mL.

[0064] The diameter of the fine bubbles generated in the water to be treated and the concentration of fine bubbles in the water to be treated can be adjusted appropriately depending on factors such as the shape, size, number, and arrangement of the bubble generation mechanism 22 of the fine bubble generator 20.

[0065] In the water treatment method of this embodiment, fine bubbles are generated in the water to be treated to produce fine bubble water, which brings the water to be treated into contact with the fine bubbles. Fine bubbles with a diameter of less than 1000 nm can remain in the water to be treated for a long time, allowing them to effectively remove free chlorine from the water to be treated. In this respect, this method is fundamentally different from the method of aerating raw material gas into the water to be treated.

[0066] The contact time between the water to be treated and the fine bubbles can be adjusted appropriately by installing a pressurized tank 30 on the secondary side of the fine bubble generator 20 and lengthening the flow path of the fiber-bubble water, as shown in Figures 1 and 3. In this case, it is preferable to pressurize the flow path of the fine bubble water to 0.05 to 20 MPa by adjusting the discharge flow rate of the pump 2 and the pressure adjustment nozzle 3, and bring the water to be treated and the fine bubbles into contact. By appropriately pressurizing the flow path of the fine bubble water, the fine bubbles can be retained in the water to be treated for a long time, thereby improving the efficiency of free chlorine removal.

[0067] (Discharge of untreated water) Next, the water to be treated after the treatment to remove free chlorine is discharged. Specifically, as shown in Figure 1, the water to be treated is discharged from the system through a pressure adjustment nozzle 3 provided at the end of path L5. The concentration of free chlorine in the discharged water to be treated is significantly reduced compared to the value before treatment. Furthermore, although the water to be treated contains unreacted fine bubbles, even if it is discharged, it is ultimately released into the atmosphere, so it does not affect the surrounding environment.

[0068] As described above, according to the water treatment device 1 and water treatment method of this embodiment, by contacting the water to be treated with fine bubbles consisting of a gas containing hydrogen or helium and having a bubble diameter of less than 1000 nm, free chlorine in the water to be treated can be removed without discharging harmful components.

[0069] The technical scope of 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. For example, in the water treatment method of the above-described embodiment, a configuration in which fine bubble water is generated using the fine bubble generator 20 has been described as an example, but this is not limiting. The water treatment method of the present invention may also be configured to generate fine bubble water using well-known methods for generating fine bubbles, such as the ejector method, cavitation method, gas-liquid shear (swirl flow) method, and pressurized dissolution method. [Example]

[0070] The present invention will be specifically described based on the following examples, but the present invention is not limited to these examples. Examples 1 to 3 are working examples, and Examples 4 to 10 are comparative examples.

[0071] <Verification Test 1> (Adjustment of treated water) Free chlorine was generated in seawater, and the concentration was adjusted to 0.33±0.03 ppm to prepare the water to be treated.

[0072] (Method for measuring free chlorine concentration) The free chlorine concentration in the treated water was measured by the DPD (N,N-diethylparaphenylenediamine) method. Specifically, this was measured using a DR300 pocket colorimeter (manufactured by HACH). The free chlorine concentration of the treated water before treatment is shown in Table 1.

[0073] (Example 1) The water to be treated was passed once through the water treatment device 1 shown in Figures 1 to 3. The operating conditions of the device were as follows. Raw material gas: Hydrogen gas (100% by volume) Gas flow rate: 50mL / min Gas supply rate to treated water: 8.3mL / L · Raw gas supply form: Ultra-fine bubbles Pump 2 discharge flow rate: 6 l / min Pump outlet to pressure adjusting nozzle outlet pressure: 0.5MPa Pressure of the pressurized tank: 0.3 MPa

[0074] Next, the water to be treated discharged from the water treatment device 1 was collected, and the free chlorine concentration of the water to be treated after the free chlorine removal test was measured. The initial value of the free chlorine concentration in the treated water was set to 100%, and the decay rate was calculated from the free chlorine concentration in the treated water after the free chlorine removal test. The free chlorine concentration in the treated water after treatment and the decay rate are shown in Table 1.

[0075] (Examples 2 to 5) The water to be treated was passed through once under the same operating conditions as in Example 1, except that the raw material gas was replaced with 100% hydrogen gas by volume and the gas species (100% by volume) shown in Table 1 were used. The plasma treatment conditions in Example 3 were as follows. The results are shown in Table 1. ·Distance between electrodes: 5mm Applied voltage: 10kV Processing time: 0.079 seconds

[0076] (Example 6) The water to be treated was passed through once under the same operating conditions as in Example 1, except that no raw material gas was used. The results are shown in Table 1.

[0077] (Example 7) 1, the water to be treated was passed through the pressurized tank 30 once without operating the fine bubble generator 20. The operating conditions of the apparatus were as follows: Raw material gas: Hydrogen gas (100% by volume) Gas flow rate: 50mL / min Gas supply rate to treated water: 8.3mL / L · Raw gas supply form: Microbubbles Pump 2 discharge flow rate: 6 l / min Pump outlet to pressure adjusting nozzle outlet pressure: 0.5MPa Pressure of the pressurized tank: 0.5MPa

[0078] Next, the water to be treated discharged from the water treatment device 1 was collected, and the free chlorine concentration of the water to be treated after the free chlorine removal test was measured. Table 1 shows the free chlorine concentration value of the water to be treated after treatment and the decay rate.

[0079] (Example 8) FIG. 4 is a schematic diagram showing the configuration of a water treatment device used as a comparative example of the present invention. As shown in Figure 4, a water treatment device was prepared that included a pressurized tank for storing seawater as the water to be treated, and a millibubble generator with porous ceramic attached to the tip of a gas outlet pipe. Using this water treatment device, the tip of the gas outlet pipe was immersed in the water to be treated stored in a pressurized tank, and air bubbles were supplied to the water to be treated under the following conditions. ·Water to be treated: 5L Raw material gas: Hydrogen gas (100% by volume) Operating time: 1 min Gas flow rate: 50mL / min Gas supply rate for treated water: 10mL / L · Raw material gas supply form: Millibubble Pressure of the pressurized tank: atmospheric pressure

[0080] Next, the treated water was collected from the pressure tank after the water treatment, and the free chlorine concentration of the treated water after the free chlorine removal test was measured. The free chlorine concentration of the treated water after treatment and the decay rate are shown in Table 1.

[0081] (Example 9) Bubbles were supplied to the water to be treated in the same manner as in Example 9, except that the gas flow rate of the raw material gas and the gas supply rate to the water to be treated were changed as follows under the operating conditions of Example 8. The results are shown in Table 1. Gas flow rate: 500mL / min Gas supply rate for treated water: 100mL / L

[0082] (Example 10) FIG. 5 is a schematic diagram showing the configuration of a water treatment device used as a comparative example of the present invention. As shown in Figure 5, a water treatment device was prepared that included a sealable pressurized tank, an inlet pipe for introducing seawater, which is the water to be treated, into the pressurized tank, an outlet pipe for discharging the water to be treated from the pressurized tank, and an on-off valve located in the outlet pipe. First, the inside of the pressure vessel was replaced with hydrogen gas. Next, seawater was sent from the inlet pipe to the pressure vessel at a pressure of 0.5 MPa while the valve on the outlet pipe was closed and the vessel was left to stand for one minute, thereby allowing hydrogen to be pressure-dissolved in the seawater inside the pressure vessel. Pressurized tank: 5L Raw material gas: Hydrogen gas (100% by volume) · Raw gas supply form: Dissolved Pressure of the pressurized tank: 0.5MPa

[0083] Next, to prevent the generation of microbubbles in the pressure tank, the on-off valve of the outlet pipe was gradually opened to return the pressure to atmospheric pressure. After the treatment, the treated water was sampled from the pressure tank, and the free chlorine concentration of the treated water after the free chlorine removal test was measured. The post-treatment values ​​of the free chlorine concentration of the treated water and the decay rate are shown in Table 1.

[0084] [Table 1]

[0085] (result) As shown in Table 1, in Examples 1 to 3, hydrogen gas, helium gas, and plasma-treated helium gas were supplied in the form of ultrafine bubbles (UFB) with a bubble diameter of less than 1000 nm and brought into contact with the seawater to be treated. As a result, it was confirmed that the attenuation rate of the free chlorine concentration was 70% or more in all cases, demonstrating an extremely excellent removal effect.

[0086] In Examples 4 and 5, the water to be treated was brought into contact with ultrafine bubbles with a bubble diameter of less than 1000 nm. However, because the raw material gas was not hydrogen gas or helium gas, the attenuation rate of the free chlorine concentration was about 50%, and sufficient removal effect was not obtained. In Example 6, the water to be treated was simply passed through the treatment facility without contacting it with fine bubbles, and therefore the attenuation rate of the free chlorine concentration was 30%, meaning that a sufficient removal effect was not achieved. In Examples 7 to 9, the water to be treated was brought into contact with hydrogen gas bubbles, but because the bubbles were not ultrafine bubbles with a diameter of less than 1000 nm, the attenuation rate of the free chlorine concentration was 60% or less, and sufficient removal effect was not achieved. In Example 10, the water to be treated was brought into contact with dissolved hydrogen, but the attenuation rate of the free chlorine concentration was only about 60%, and a sufficient removal effect was not obtained.

[0087] (Consideration) Here, in Examples 1 to 5, ultrafine bubbles with a bubble diameter of less than 1000 nm were used in contact, and it was confirmed that using hydrogen gas as the contact gas is advantageous for removing free chlorine from seawater, the water to be treated. The reason why using hydrogen is advantageous is thought to be the reactivity between hydrogen and free chlorine. On the other hand, when helium gas is used as the contact gas, it was confirmed that the effect of attenuating the free chlorine concentration is greater than that of other gases, although helium gas is inert. Hydrogen gas and helium gas have one thing in common: they are both positively charged. That is, hydrogen gas and helium gas have a positive surface potential, which is thought to make them more likely to capture free chlorine.

[0088] Although the detailed mechanism is uncertain, it is believed that ultrafine hydrogen gas bubbles may be showing a significant removal effect due to two mechanisms at work: the reactivity of hydrogen gas and the mechanism related to the charge of the ultrafine bubbles.It is likely that the reduction effect of free chlorine can be obtained by simply aerating with hydrogen, but it is thought that the fact that the bubbles are made into ultrafine bubbles, behave like ions, and remain in water for a longer period of time than bubbles with a particle size of millibubbles or larger contributes greatly to this effect.

[0089] In addition, in Examples 1 and 7 to 10, the water to be treated was contacted with hydrogen gas, and it was confirmed that the free chlorine removal effect of hydrogen gas was improved by using ultrafine bubbles with a bubble diameter of less than 1000 nm. Therefore, the water treatment method of the present invention is safe and economical because it can remove free chlorine with a small amount of hydrogen gas used by contacting the water with ultrafine bubbles.

[0090] <Verification Test 2> (Method for measuring the number concentration of ultrafine bubbles) The number concentration of ultrafine bubbles (particle diameter: 10 nm to 1000 nm) in the water to be treated was measured at a temperature of 25°C using an NS300 manufactured by Malvern Panalytical.

[0091] First, the treated water was sampled after passing through once under the same conditions as in Example 1 of Verification Test 1 described above, except that seawater containing no free chlorine was used as the treated water, and the concentration and number concentration of ultrafine bubbles were measured. The concentration of ultra-fine bubbles is 1.28 x 10 8 ±5.28×10 6 It was. The results for the number concentration of ultrafine bubbles are shown in Figure 6. In Figure 6, the X axis represents the bubble diameter (nm) and the Y axis represents the bubble concentration (bubbles / ml).

[0092] Next, in Example 1 of the above-described Verification Test 1, the water to be treated was sampled after passing through once, and the concentration and number concentration of ultra-fine bubbles were measured. The concentration of ultra-fine bubbles is 2.33 x 10 7 ±4.81×10 6 It was. The results for the number concentration of ultrafine bubbles are shown in Figure 7. In Figure 7, the X axis represents the bubble diameter (nm) and the Y axis represents the bubble concentration (bubbles / mL).

[0093] (result) From the results of the ultrafine bubble concentration, the number of ultrafine bubbles consumed to treat 6 L of water (amount treated per minute) with a free chlorine concentration of 0.33 ppm was 78 million to 100 million. Therefore, the number concentration of fine bubbles in the water to be treated was 5 x 10 7 ~1.5×10 8 It was confirmed that a concentration of 1000 / mL is preferable.

[0094] 6 and 7, it was confirmed that the number of fine bubbles with a diameter of 100 to 600 nm decreased. Therefore, it was confirmed that it is preferable that the fine bubbles in the water to be treated contain many bubbles with a diameter of 100 to 600 nm.

[0095] <Verification Test 3> Using the same method as in Example 1, it was confirmed that when the free chlorine reached 0 ppm, the total chlorine also reached 0 ppm. Initial value: Free chlorine 0.08 ppm, total chlorine 0.09 ppm After treatment: Free chlorine 0 ppm (below detection limit), total chlorine 0 ppm (below detection limit) [Explanation of symbols]

[0096] 1...water treatment device, 2...pump, 3...pressure adjustment nozzle, 20...fine bubble generator, 30...pressurized tank, L1 to L5...paths

Claims

1. A water treatment method for removing free chlorine contained in water to be treated, comprising: The method includes contacting the water to be treated with fine bubbles made of a gas containing hydrogen or helium, The fine bubbles have a bubble diameter of 100 to 600 nm, The water treatment method comprises adjusting the concentration of the fine bubbles in the water to be treated to 5×10 7 to 1.5×10 8 bubbles / ml.

2. The water treatment method according to claim 1 , wherein the hydrogen or the helium is plasma-treated.

3. The water treatment method according to claim 1 , further comprising generating the fine bubbles in the water to be treated.

4. The water treatment method according to claim 3, further comprising pressurizing the water to be treated containing the fine bubbles to 0.05 to 20 MPa after generating the fine bubbles in the water to be treated.

5. The water treatment method according to claim 1, wherein ascorbic acid or hydrogen peroxide is added to the water to be treated before the water to be treated is brought into contact with the fine bubbles.

6. A water treatment device used in the water treatment method according to any one of claims 1 to 5, a fine bubble generator that generates fine bubble water containing fine bubbles made of gas containing hydrogen or helium in the water to be treated; a pressurized tank for storing the fine bubble water; an introduction path for introducing the fine bubble water from the fine bubble generator into the pressurized tank; and an outlet path for discharging the fine bubble water from the pressurized tank.

7. The water treatment device according to claim 6, further comprising a pressurizing mechanism for pressurizing the inside of the pressurized tank to 0.05 to 20 MPa.

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