JPH07241576A - Treatment of water using ozone - Google Patents

Abstract

PURPOSE:To accelerate the formation of a hydroxyl free radical (OH.) having high oxidizing power by adding nitrilotriacetic acid to water in order to efficiently remove a very small amt. of an org. substance in water. CONSTITUTION:Nitrilotriacetic acid is injected into water to be treated immediately after introduced into a reaction tank and, thereafter, ozone is diffused in the water to be treated introduced into the reaction tank to make chain reaction consisting of hydroxyl free radical forming reaction due to nitrilotriacetic acid and ozone and hydroperoxy free radical (HO2.) forming reaction due to nitrilotriacetic acid and a hydroxyl free radical (OH.) proceed to form a hydroxyl free radical (OH.) and a very small amt. of an org. substance in water can be efficiently decomposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ozone treatment performed in a water purification process to remove trace organic substances contained in water.

[0002]

2. Description of the Related Art Recently, people's awareness of water is rapidly increasing, and various water treatment methods are used to obtain safe and delicious water in tap water and highly purified treated water in sewage for reuse. Is being considered. In tap water, the problem that the tap water has a musty smell has arisen due to the eutrophication of the rivers and lakes that are the water source. This is a diosmin derived from cyanobacteria,
Or, it is caused by a so-called musty odor substance such as dimethylisoborneol (hereinafter referred to as 2-MIB), and the minimum concentration for musty odor is a very low concentration of about 5 to 20 ng / l. As a countermeasure for this, the water purification plant mainly performs adsorption treatment with activated carbon, but because of the cost increase due to the increase in the amount of activated carbon used and the treatment operation is complicated,
As an alternative method, we are studying advanced treatment such as water treatment using ozone and water treatment by living organisms.
As for sewage, in addition to using it as wash water for toilets and vehicles, or as scenic water such as water in a moat, use water treatment using ozone and membranes from the viewpoint of reducing the load on the water treatment plant and environmental conservation. Advanced treatments such as water treatment have been studied.

Under such circumstances, water treatment using ozone is considered to be an effective means for solving the above-mentioned problems in water treatment. This is because the water treatment using ozone has the advantages that stable treatment can be performed by controlling the electric system and that the injection amount of ozone can be easily controlled. However, there are problems such as an increase in processing cost due to the introduction of equipment and the need for a large land for the construction of a new large reaction tank. Therefore, for a treatment plant that intends to introduce water treatment using ozone,
Not only the construction cost of the equipment but also securing the site is a serious problem. Therefore, in carrying out the water treatment using ozone, various treatment methods have been considered in order to realize the downsizing of the reaction tank, that is, the efficiency of the reaction.

It is well known that, in general, the oxidation reaction of ozone in water is caused by a direct reaction of ozone molecules and a hydroxy radical (OH.) And a hydroperoxy radical (HO _2. ) Generated by the self-decomposition of ozone. In particular, since the hydroxy radical shows a stronger oxidizing power than ozone, increasing the amount thereof will lead to the efficiency of the reaction. The following points can be mentioned as effective methods for improving the efficiency of this reaction. (1) Raise the pH of the water to be treated. (2) Add H ₂ O ₂ . (3) Irradiate with ultraviolet rays. (4) Irradiate with radiation. (5) Irradiate ultrasonic waves. (6) Use catalysts such as metal ions and metal oxides.

[0005]

The above-mentioned methods (1) to (6) for promoting the production of hydroxy radicals (OH.) Are effective in terms of improving the reaction efficiency, but all of them are costly. There are few cases where these methods have been put to practical use because of the high cost, and when treating a large amount of water such as tap water or sewage, the effect will be halved by adding equipment. There is a problem that it ends up. The present invention has been made in view of the above points, and an object thereof is to promote the production of hydroxy radicals (OH.) Having high oxidizing power by the addition of nitrilotriacetic acid, and efficiently decompose trace organic substances. Another object of the present invention is to provide a water treatment method that uses ozone.

[0006]

In order to solve the above-mentioned problems, the method of the present invention comprises adding nitrilotriacetic acid to the water to be treated introduced into the reaction tank or the water just before being introduced into the reaction tank. After the injection, ozone is diffused to perform water treatment.

[0007]

The method of the present invention is a method based on the viewpoint of efficiently producing a hydroxy radical (OH.) Having an oxidizing power higher than that of ozone. The method according to the present invention is a hydroxy radical producing reaction between nitrilotriacetate and ozone, and nitrilotriacetate. Efficient hydroxy radicals (OH.) By radical chain reaction which has hydroperoxy radical (HO _2. ) Generation reaction by hydroxy radicals (OH.)
To efficiently decompose trace organic substances.

[0008]

EXAMPLES First, the self-decomposition reaction of ozone will be described. Hydroxy radical (OH.) In pure water
It is generated by the autolysis reaction of ozone as shown below. _{O 3 + H 2 O → HO} 3 + + OH - HO 3 + + OH - → 2 HO 2 · O 3 + HO against ₂ · → OH · + 2O ₂ This, hydroxy radicals when there is coexisting materials in water ( The OH.) Formation reaction is based on the radical chain reaction model shown in FIG. 1 and the radical chain reaction formulas shown below. The parts corresponding to the reaction formulas 1 to 3 are also shown in FIG. Here, X is a coexisting substance and represents nitrilotriacetic acid applied to the method of the present invention, and A is a trace organic substance to be removed. In the radical chain reaction formulas (1) to (4), the reaction for producing the hydroxy radical (OH.) Is based on the reaction between nitrilotriacetate X and dissolved ozone O ₃ shown in, and nitrilotriacetate X and the hydroxy radical (OH.) Shown in This is due to the reaction of and due to the hydroperoxy radical (HO _2. ) Generated by and. That is, the water treatment method of the present invention promotes the production of hydroxy radicals (OH.) Having high oxidizing power by the addition of nitrilotriacetic acid, and efficiently decomposes trace organic substances.

The method of the present invention for the removal of musty odor substances, which is a problem in tap water, will be described below with reference to specific examples. FIG. 2 is a schematic view showing a part of the experimental apparatus used for verifying the method of the present invention in section. In FIG. 2, the reaction tank 1 with a lid has a height of 70c.
It has a cylindrical shape of m and an inner diameter of 20 cm, and the baffle plate 2 is provided on the inner wall thereof, and the effective volume is 20 l. The reaction tank 1 has a double structure, and water is circulated by a pump 4 from a constant temperature water tank 3 provided outside to adjust the temperature of the water to be treated. Ozonized air generated by the ozone generator 5 passes through a flow meter 6 and passes through a glass ball diffuser 7 to a reaction tank 1
Air is uniformly diffused inside, and the inside of the reaction tank 1 is stirred by a stirring motor 8 and a stirring blade 9. The ozone gas not used in the reaction is guided from the reaction tank 1 to the exhaust ozone decomposing tower 10, where it is decomposed into oxygen. The ozone gas concentration can be measured by the ozone concentration meter 11, and the measurement sample can be sampled from the sampling port 12.

First, a standard solution prepared by dissolving commercially available 2-MIB in pure water in a phosphate buffer solution adjusted to pH = 7 in the reaction vessel 1 with potassium dihydrogen phosphate and disodium hydrogen phosphate. To give an initial concentration of approximately 300 ng / l
Then, nitrilotriacetic acid is added so that the total organic carbon (hereinafter referred to as TOC) concentration is in the range of 0 to 1 mg / l. By circulating the constant temperature water tank 3 in the reaction tank 1 ,
After the temperature is adjusted to a predetermined temperature, the inside of the reaction tank 1 is uniformly mixed by the stirring motor 8 and the stirring blade 9. After that, the ozone generator 5
15g / m3 of ozonized air with a concentration of 1.7g / Nm ³
Inject it into the reaction tank 1 . Here, the ozone injection rate (ozone gas concentration x gas flow rate x injection time x amount of water to be treated) was constant.

FIG. 3 is a diagram showing the effect of addition of nitrilotriacetic acid on the decomposition of 2-MIB. The abscissa shows the TOC concentration of nitrilotriacetic acid, and the ordinate shows the relative reaction rate constant. Here, the relative reaction rate constant is a relative value when the reaction rate constant of the musty odorous substance in the absence of an additive substance (here, nitrilotriacetic acid) is 1. Therefore, when the relative reaction rate constant is larger than 1, it indicates that the additive substance promotes the decomposition of musty odor substance. According to this result, it is understood that the reaction rate of 2-MIB is increased by the addition of a small amount of nitrilotriacetic acid, and the TOC concentration of 0.7 mg / l has an about 19-fold accelerating effect. FIG. 4 shows the results of an experiment conducted similarly for diosmin, in which the horizontal axis represents the TOC concentration of nitrilotriacetic acid,
It is a relationship diagram which showed the vertical axis as a relative reaction rate constant.
It can be seen from FIG. 4 as well as in the case of 2-MIB that the decomposition is promoted by the addition of nitrilotriacetic acid. As shown in FIGS. 3 and 4, the degree of the effect of the present invention is
The concentration of nitrilotriacetic acid in the water to be treated has a great influence. Therefore, in order to obtain the target treatment performance, it is necessary to add nitrilotriacetic acid before contact with ozone to make the concentration of nitrilotriacetic acid constant.

As described above, the method of the present invention comprises the reaction of producing hydroxy radicals (OH.) By nitrilotriacetic acid and ozone,
And nitrilotriacetic acid and hydroxy radical (OH.)
The radical chain reaction having a hydroperoxy radical (HO ₂ ·) generation reaction by OH efficiently generates hydroxy radical (OH), and efficiently decomposes trace organic substances such as musty odor substances. Is not specified, and there is no need to adjust the pH of the water to be treated. That is, the method of the present invention has the advantage that the treatment can be carried out without the need for pretreatment and posttreatment.

In the examples, the case of tap water was described, but since the method of the present invention is intended for trace organic substances such as musty odor substances, it has the same effectiveness when applied to sewage. , COD, BOD, etc. can be reduced. The effect of adding nitrilotriacetic acid is also expected to be affected by raw water, so it is necessary to select an effective concentration as described above. Further, since the method of the present invention utilizes the reaction between nitrilotriacetic acid and ozone when injecting nitrilotriacetic acid, it is injected into raw water before the treatment with ozone, and the raw material at the time of nitrilotriacetic acid injection is used. It is important that the oxidizing agent does not remain in the water and that the raw water into which the nitrilotriacetic acid has been injected is not subjected to oxidation treatment or adsorption treatment before the ozone treatment.

[0014]

As described above, according to the method of the present invention, a facility for injecting nitrilotriacetic acid is added to a water treatment system using ozone, and nitrilotriacetic acid is injected into raw water to coexist. Therefore, musty odorous substances etc.
Sewage makes it possible to accelerate the decomposition of unspecified trace amounts of organic substances such as COD and BOD. As a result, the reaction tank can be downsized, and the site area of the facility can be made smaller.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a radical chain reaction in the presence of coexisting substances.

FIG. 2 is a schematic diagram of an experimental apparatus used to verify the method of the present invention.

FIG. 3 is a relationship diagram of nitrilotriacetic acid and relative reaction rate constants for 2-MIB.

FIG. 4 is a diagram showing the relationship between nitrilotriacetic acid and relative reaction rate constants for diosmin.

[Explanation of symbols] 1 reaction tank 2 baffle plate 3 constant temperature water tank 4 pump 5 ozone generator 6 flow meter 7 ball diffuser 8 stirring motor 9 stirring blade 10 exhaust ozone decomposition tower 11 ozone concentration meter 12 sampling port

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takayuki Morioka 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 inside Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. Ozone is diffused into the water to be treated to oxidatively decompose a trace amount of organic substances contained in the water to be treated, and nitrilotriacetic acid is injected into the water to be treated. The water treatment method used. 2. The method of claim 1, wherein nitrilotriacetic acid is injected into the water to be treated introduced into the reaction tank. 3. The water treatment method using ozone according to claim 1, wherein nitrilotriacetic acid is injected into the water to be treated immediately before introducing the water to be treated into the reaction tank.