JP2003094076A - Ozone treating method for water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ozone treating method for water efficiently decomposing an organic matter in the water by improving the contact-efficiency of ozone in a method for decomposing the organic matter in the water in injecting the ozone using an ejector. SOLUTION: This ozone treating method for water is performed by preparing ozone-containing gas in the state of fine air bubbles and jetting it into the water by the ejector. In the method, especially in the ozone decomposition of the organic matter in the water, the outlet part of the ejector is installed in the lower position than the outlet part of the treatment water in a treatment vessel, and downward installed in the position in the water in which the height from the bottom of the treatment vessel satisfies both formulas 1 Q<1/3> /3.5}<=H<= Q<1/3> /1.5} and 2 Q/A}<=H<= 10Q/A} wherein, H is the height (m) of the outlet part of the ejector from the bottom part of the treatment vessel, Q is the amount of flow of water flowing through the ejector (m<3> /hour), and A is the area of a circle (m<2> ) whose radius is the shortest distance between the outlet part of the elector and a side wall of the treatment vessel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for ozone treatment of water, and more particularly to a method for ozone treatment of water which improves the method of injecting ozone into water to efficiently decompose organic substances in water.

[0002]

2. Description of the Related Art A large amount of wastewater containing organic substances is generated from various factories, but from the standpoint of environmental protection, it is not allowed to discharge it into the natural world such as rivers. Required for use. Under such circumstances, there is a growing need to remove organic substances in waste water and reuse water.

Oxidation is one of the methods for removing organic substances in water, and ozone treatment is positioned as one of them. Since ozone is generated and used at the place where it is used, it does not have to store dangerous chemicals, has a strong ability to be oxidatively decomposed, and does not leave harmful substances in the water after decomposition. Therefore, its practical application is expanding.

Ozone is generated from oxygen by silent discharge, electrolysis, light, etc., and is a gas at room temperature. Therefore, in order to decompose the organic matter dissolved in water, it is necessary to dissolve ozone in water or bring it into contact with water containing organic matter.
Ozone is not supplied as ozone gas, but is generated from oxygen by an ozone generator, and the ozone concentration in the gas is usually several percent or less. Therefore, in order to dissolve ozone in water or to bring it into contact with water containing an organic substance, it is desired to use ozone-containing gas having a concentration as high as possible and send it into the water as small bubbles, and let the bubbles stay in the water for a long time. This is because the ozone-containing gas is sucked using the negative pressure that occurs when water is passed through the ejector and passes through the venturi section, and the bubbles are dispersed by the strong turbulent flow in the venturi section, and the diffuser tube made of a porous material is used. Therefore, a method of making fine bubbles is generally put into practical use.

The ejector has the advantages that it has a simple structure and is safe, and that it can be injected by utilizing the negative pressure of the water flow without pressurizing the gas. However, in order to increase the negative pressure, the flow velocity of water has to be increased, and when the flow velocity is increased, the generated bubbles are flowed and the staying time in water is shortened. An ozone generator is more expensive as it generates ozone at a higher concentration, and requires a large amount of electricity to generate it. On the other hand, ozone in bubbles released into water is used for dissolving in water or reacting with organic matter in water, and that is part of it. Will be. Therefore, it is extremely important from an economical point of view to dissolve the generated ozone in water or use it in the reaction as efficiently as possible.

There have already been many reports on a method of dissolving ozone by using an ejector. For example, an ejector is installed in the middle of a line (water pipe) through which water flows, and a gas containing ozone is sucked into the line to cause water and ozone to flow. A method is generally used in which the water containing ozone is connected to the lower part of the reaction tank from the side (Japanese Patent Application Laid-Open No. 2001-2405, Japanese Patent Application Laid-Open No. 10-80691, etc.). As described above, in the ejector installed in the horizontally arranged line, bubbles are generated due to the pressure fluctuation of the ejector nozzle part and the turbulent flow of water, and the generated bubbles move in the water flow, and when they enter the water tank, Immediately rises due to buoyancy in the flow direction and upward. There is an example in which a static mixer is placed in the line after the ejector, but the static mixer has a weak power to make bubbles fine, and it has only an effect of slightly increasing the residence time of bubbles in water.

Further, the ejector is used vertically and a baffle is provided at the ejector outlet, and the gas sucked by the ejector is dispersed into fine bubbles by utilizing the reflection of the water flow to the baffle to disperse the gas component into water. Method of dissolving in
890], but in this case, since the flow of water from the ejector immediately rises, the bubbles containing ozone are also accelerated and rise due to the rising water flow, and the residence time in water cannot be taken sufficiently. There are drawbacks.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to improve the ozone contact efficiency in an ozone treatment method for water, which is carried out by jetting an ozone-containing gas into water in the form of fine bubbles using an ejector. In particular, it is to provide a method of increasing the decomposition efficiency of organic matter in water by ozone treatment.

[0009]

In order to achieve the above object, the invention of claim 1 is a method of ozone treatment of water, which comprises performing ozone jetting of ozone-containing gas into water in the form of fine bubbles by an ejector. In the method, the ejector outlet portion is located below the treated water outlet portion of the treatment tank, and the height from the treatment tank bottom is expressed by Equation 1 and Equation 2 (where H is the height of the ejector outlet portion from the treatment layer bottom portion ( m), Q is the flow rate of water flowing through the ejector (m ³ / hour), A is the circular area (m ² ) whose radius is the shortest distance between the ejector outlet and the side wall of the processing tank] The feature is that it is installed downward.

[0010]

[Equation 2]

The invention of claim 2 is the ozone treatment method for water according to claim 1, characterized in that the water to be treated is waste water containing organic matter.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The ozone treatment of the present invention mainly decomposes organic substances in water by utilizing the chemical action of ozone, and the fine bubbles of ozone generated at this time are made to stay in water for a long time. It is intended to efficiently decompose the organic substance.

The outline of the method of the present invention is shown in FIG. The water to be treated containing organic substances is sent to the ejector, where ozone-containing gas is sucked to form fine bubbles containing ozone in the water and sent to the treated water tank. Ozone in bubbles is dissolved in water by contact with water, or is used for reaction by gas-liquid contact with organic matter in water at the gas-liquid interface, and the treated water goes out from the outlet at the top of the treatment tank. . On the other hand, the gas that is not dissolved in water and does not participate in the reaction goes out on the water surface and is discharged as exhaust gas from the upper part of the treatment tank. Since the exhaust gas contains ozone that is not dissolved in water, it is usually decomposed into ozone before being released. Further, the treated water discharged from the treatment tank may be partially circulated by returning part of the treated water to the water to be treated and performing ozone treatment again depending on the degree of treatment (the degree to which organic matter in water is decomposed). Exhaust gas treatment and retreatment of treated water are not limited to the present invention and are not shown in FIG.

Ozone is usually generated from air or oxygen by an ozone generator utilizing the action of silent discharge, electrolysis, light, and the like. In the present invention, the method of generating ozone is not limited, but it is preferable that the ozone concentration in the gas is high in order to increase the dissolution rate in water and accelerate the decomposition of organic matter in water which is the object of the present invention. Normally, the ozone concentration is 50-250 g /
Nm ³ , preferably 100 to 150 g / Nm ³ .

The water to be treated is preferably sent to the treatment tank through the ejector while being in contact with the ozone-containing gas at the ejector section. However, a part of the water to be treated can be sent to the treatment tank through a route different from the ejector.

The processing tank usually has a circular or quadrangular cross section, but is not limited to this. Its capacity should be decided in relation to the amount of treated water.

The ejector is not limited in size and shape in the present invention, and may be any one commonly used. Normally, the ejector has a diameter of 15A to 80A (1 /
2 "~ 3 inches), the cross-sectional area of the nozzle part is 5-500 mm
It is ² . The amount of water passing therethrough and the amount of sucked gas are related to the flow velocity of water passing through the nozzle portion, but the amount of water is 0.5 to 50 m ³ / h, and the amount of sucked gas is 0.3 to ³
It is 0 N · m ³ / h.

A feature of the present invention is that the ejector is
It is to be installed at a position specified in relation to the size and shape of the processing tank. That is, the ejector outlet portion should be installed downward at a position below the treated water outlet portion of the treatment tank and at a height from the bottom of the treatment tank that satisfies both [Equation 1] and [Equation 2]. is there.

[Equation 1] and [Equation 2] analyze the flow of water discharged from the ejector, the convection of water in the treatment tank, and the behavior of fine bubbles of ozone in the water. The optimum conditions for the decomposition of organic matter in water by ozone are set. It goes without saying that even if the conditions of [Equation 1] and [Equation 2] are not satisfied, there is a certain effect.

As described above, the ejector is placed downward in the approximate center of the container, and a predetermined distance is provided between the ejector outlet and the bottom of the container in consideration of the total flow rate of water and ozone-containing gas passing through the ejector. Try to keep it. At this time, an obstacle such as a baffle plate is not placed near the exit of the ejector, and the water jetted from the exit of the ejector is directed straight to the bottom of the treatment tank. A plurality of ejectors may be installed in one treatment tank, but in that case, each ejector is installed so as to satisfy the requirements defined in the present invention.

With this arrangement, the water jetted downward from the ejector outlet is weakened in the downward force in the water, or hits the bottom of the treatment tank and goes upward. The rising water flow is weaker than the downward jet water, and the downward strong flow in the tank causes a partial swirling complex movement.

The bubbles containing ozone generated in the ejector section are in the flow of water and are suddenly released into the processing tank at the exit of the ejector, and are rapidly decelerated with the flow of water. Will work and be miniaturized. Furthermore, the fine bubbles turn to rise due to the flow of water and buoyancy, but at this time, the rise is not linear due to the downward flow of water from the ejector and the partial swirling flow of water, and it takes time to reach the water surface. Therefore, as a result, the contact time between ozone in the bubbles and water becomes long. If the cross-sectional area of the treatment tank is too small for the total flow rate of the water to be treated and the gas containing ozone, the rising flow velocity will be too fast and ozone bubbles will escape from the water without taking sufficient time, and the cross-sectional area of the treatment tank will be too large. Since the ascending flow in the tank is not entrained in the strong downward flow, the ozone bubbles will also escape from the water without taking sufficient time.

When ozone is injected into water to decompose organic substances in the water, hydrogen peroxide is allowed to coexist in the water or the pH of the water is changed.
It is known that the higher the value, the better the decomposition by ozone. The present invention does not prevent such modification of the water to be treated so that it is convenient for ozonolysis.

[0024]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

[Ejector used for test] Driving water diameter: 15A Suction side diameter: 15A Liquid nozzle diameter: 3.5mm Gas nozzle / throat diameter: 6.2mm Supply water amount: 0.75m ³ / hour

[Treatment tank used for the test] Cylindrical column [Diameter: 2
0, 36, 72 cm (A = 0.031, 0.1, 0.4
(M ^Two)) Three types are used]] From the center and bottom of the treatment tank
Install the ejector outlet at a fixed height (H) and
Water to be treated at a flow rate (Q), and ozone-containing gas [O
Done concentration: 120 g / Nm^Three] Was sucked.

[Test method] 10 pp of isopropanol
20ppm of hydrogen peroxide was added to the aqueous solution to make test water.
A volume of treated water (water discharged from the treatment tank outlet) is returned to this test water by mixing and flowing to an ejector, that is, a part of the treated water is circulated, and the pH of the treatment tank outlet is 7 to 8
Sodium hydroxide aqueous solution was added so that Since acetic acid generated from isopropanol is hard to be decomposed by ozone, in this experiment, attention was paid only to the first-step decomposition by isopropanol, and the TOC value was measured after removing the acetic acid from the treated water through the ion exchange resin.
Ion-exchange resin treatment uses treated water at a flow rate of 250 L / h,
Duolite C-20 (strongly acidic ion exchange resin) and Duolite A-116 (strongly basic ion exchange resin) were mixed at a volume ratio of 4: 6 and passed through 7 liters.

[Results] The results are shown in Table 1.

[Table 1] From these results, it was confirmed that TOC was removed well and ozone treatment could be efficiently performed in the range satisfying both [Equation 1] and [Equation 2] shown in the present invention.

[Test-2] A cylindrical tank used in Test-1 [diameter: 36 cm (A = 0.1 (m ² )] for comparison with the case where ozone fine bubbles were sent laterally from the side of the processing tank. ], When the ejector is placed vertically outside the treatment tank and the water to be treated discharged from the ejector is sent slightly below the water surface of the treatment tank, (2) the ejector is placed horizontally outside the treatment tank. The test was conducted when the water to be treated that had been installed and discharged from the ejector was fed from the side near the bottom of the treatment tank, and (3) when the ejector was laid horizontally near the bottom of the treatment tank. Water flow rate, ozone concentration [Ozone concentration: 120 g
/ Nm ³ ], etc., the experiment number 4 (No.
Same as 4).

The results are shown in Table 2.

[Table 2] From this result, it was confirmed that vertically installing the ejector in water enables more efficient ozone treatment than horizontally installing the ejector which is generally used conventionally. Also,
Even when the ejector is installed vertically, it is more efficient to install the ejector part in the water rather than putting it out of the water.

[0031]

EFFECTS OF THE INVENTION According to the method of the present invention, water containing organic matter such as waste water can be efficiently treated with ozone, and can be effectively used for setting ejector conditions and designing equipment.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a treatment tank, an ejector installation position, and a water flow according to the method of the present invention.

Claims (2)

[Claims] 1. A method for ozone treatment of water, which comprises ejecting an ozone-containing gas into water in the form of fine bubbles by an ejector, wherein the ejector outlet portion is located below the treated water outlet portion of the treatment tank and from the bottom of the treatment tank. The height is Equation 1 and Equation 2 [wherein, H is the height (m) from the bottom of the treatment layer at the exit of the ejector, and Q is the flow rate of water flowing through the ejector (m ³ /
And A is a circular area (m ² ) whose radius is the shortest distance between the ejector outlet and the lateral wall of the treatment tank]. . [Equation 1] 2. The method for ozone treatment of water according to claim 1, wherein the water to be treated is waste water containing an organic substance.