JP2003145169A - Wastewater treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and economically decompose dissolved ozone remaining in waste ozone water after ozone water is used in wet treatment such as washing or the like. SOLUTION: Waste ozone water to which hydrogen peroxide is added is sent to a treatment tank 2 to decompose dissolved ozone in waste ozone water. The amount of hydrogen peroxide added may be a small amount of 1 or less in a molar ratio to dissolved ozone. The emission of dissolved ozone is accelerated by performing aeration in the treatment tank 2. The decomposition of dissolved ozone is accelerated by irradiating waste ozone water with ultraviolet rays along with the addition of hydrogen peroxide. Treated water is reutilized as raw water or the like of ultrapure water supplied to an ozone water making apparatus without being treated as a waste liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste water treatment method and apparatus for decomposing dissolved ozone remaining in waste ozone water after using ozone water in which ozone gas is dissolved, and an ozone water producing apparatus using the apparatus. .

[0002]

2. Description of the Related Art Recently, ozone water has begun to be used in the field of semiconductors, for example, in cleaning treatments of semiconductor substrates and liquid crystal glass substrates, surface modification treatments and the like. The ozone water used here is one in which ozone gas is dissolved in pure water or ultrapure water produced by purifying clean water, contains high-concentration ozone even after use, and is waste ozone water after use. If it is discharged as it is, oxidative deterioration of the material occurs in the drainage process. Therefore, it is necessary to decompose the dissolved ozone remaining in the waste ozone water after use.

Up to now, as a method for treating this waste ozone water, an adsorption treatment with activated carbon or a treatment with an acid waste liquid or an alkali waste liquid has been used.

[0004]

By the way, in the case of ozone water, the cleanliness of the ozone water decreases after it has been used for cleaning due to contaminants removed from the substrate, but it is used as raw water in the process of producing ultrapure water. Compared to tap water, the cleanliness is extremely high. Also, ozone becomes oxygen after decomposition and does not generate harmful substances. Therefore, it is considered that it is better to collect the waste ozone water after use as waste liquid, rather to collect it, purify it, and reuse it as ultrapure water.

In response to such a demand, although the treated water can be recovered by the adsorption treatment with activated carbon, there is a problem of secondary contamination that the treated water is contaminated with activated carbon.
In addition, the activated carbon needs to be replaced regularly, and used activated carbon that is a waste product is generated and needs to be disposed of. On the other hand, in the treatment as an acid waste liquid or an alkali waste liquid, the treated water is discarded and cannot be reused, and the treatment cost is high and the amount of waste water increases.

It is an object of the present invention to provide a wastewater treatment method and apparatus which are low in treatment cost and can obtain treated water with high cleanliness. Further, another object of the present invention is to
An object of the present invention is to provide an ozone water production device having a high commercial value in combination with the wastewater treatment device.

[0007]

In order to achieve the above object, the waste treatment method according to the present invention uses hydrogen peroxide in waste ozone water after ozone water in which ozone gas is dissolved is used for wet treatment such as cleaning. It is added to decompose dissolved ozone remaining in waste ozone water.

Further, the waste water treatment apparatus of the present invention comprises an addition means for adding hydrogen peroxide to the waste ozone water after the ozone water in which ozone gas is dissolved is used for wet treatment such as cleaning.
The contact means for contacting the added hydrogen peroxide with the waste ozone water.

Further, the ozone water producing apparatus of the present invention is an ozone water producing apparatus for producing ozone water using pure water or ultrapure water supplied from the pure water producing apparatus. A treatment that is combined with a wastewater treatment device, and waste ozone water after using the ozone water produced by the ozone water production device is introduced into the wastewater treatment device as water to be treated and discharged from the wastewater treatment device. Water is introduced into the pure water producing apparatus as raw water.

Dissolved ozone remaining in the discharged ozone water is decomposed by the addition of hydrogen peroxide according to the following reaction formula. O ₃ + H ₂ O ₂ → H ₂ O + 2O ₂

According to the above reaction formula, the added amount of hydrogen peroxide required for decomposition of dissolved ozone is theoretically 1 in terms of molar ratio to dissolved ozone, but as a result of experiments, it is actually smaller than that. It was found that dissolved ozone disappeared even with the addition amount. It is considered that this is because not only the dissolved ozone is decomposed and extinguished by the above reaction formula, but also the dissolved ozone is decomposed in a chain by radicals generated by addition of hydrogen peroxide. For this reason, the amount of hydrogen peroxide added can be reduced below the theoretical value. Specifically, the molar ratio to dissolved ozone is preferably 1 or less, 1/30 or more, and particularly 1/5 or less, 1/20 or more. preferable. If the amount of addition is large, the cost of adding hydrogen peroxide increases and the remaining hydrogen peroxide becomes a problem. If it is too small, the decomposition of residual ozone will be insufficient.

The characteristics of dissolved ozone decomposition by the addition of hydrogen peroxide are as follows.

First, as described above, the amount of hydrogen peroxide used can be reduced below the theoretical value. Therefore, the running cost is low and the amount of hydrogen peroxide remaining in the recovered water after the decomposition treatment is also reduced. Second, in the reaction of ozone and hydrogen peroxide, water and oxygen are produced, and no harmful substances are produced. Even if hydrogen peroxide remains, the amount is very small and eventually decomposed into water and oxygen. Therefore, there is no secondary contamination of treated water such as activated carbon. Thirdly, regular replacement is unnecessary and no waste is generated.

In order to increase the removal efficiency of dissolved ozone,
In addition to the addition of hydrogen peroxide, it is effective to perform aeration with air or nitrogen gas. According to aeration, the discharge of dissolved ozone remaining in the discharged ozone water is promoted,
The efficiency of removing dissolved ozone is improved. In addition to the addition of hydrogen peroxide, irradiation with ultraviolet rays is also effective. The irradiation of ultraviolet rays accelerates the decomposition of dissolved ozone remaining in the exhaust ozone water, thereby improving the efficiency of removing dissolved ozone.

By increasing the efficiency of removing dissolved ozone in this way, it becomes possible to further reduce the required amount of hydrogen peroxide. Further, it becomes possible to remove or reduce the excess hydrogen peroxide contained in the recovered water after the decomposition treatment.

If only ultraviolet rays are irradiated without adding hydrogen peroxide in order to decompose dissolved ozone, the apparatus becomes large and the power consumption becomes large. When ultraviolet rays are used as the light source, an increase in size of the device and an increase in power consumption can be avoided as much as possible.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of a wastewater treatment device showing an embodiment of the present invention.

This wastewater treatment equipment is an equipment suitable for carrying out the wastewater treatment method of the present invention, and is combined with an ozone water producing equipment for producing ozone water using ultrapure water. This ozone water producing apparatus produces ozone water by dissolving ozone gas generated by an ozonizer in ultrapure water supplied from the pure water producing apparatus. Ozone water produced by the ozone water production equipment is used for cleaning treatment of semiconductor substrates and liquid crystal glass substrates, surface modification treatment, etc., and the waste ozone water after use is introduced into this wastewater treatment equipment as treated water. To be done.

The pure water producing apparatus purifies raw water to produce ultrapure water. The produced ultrapure water is used not only in the ozone water producing apparatus but also in the semiconductor substrate and the glass substrate for liquid crystal. It is supplied to all processing steps.

In this wastewater treatment equipment, the water to be treated consisting of waste ozone water is introduced into the treatment tank 2 via the mixer 1.
On the upstream side of the mixer 1, hydrogen peroxide is added to the water to be treated. The amount of addition is determined based on the amount of dissolved ozone remaining in the water to be treated. A sensor 3 for measuring the amount of dissolved ozone is provided further upstream of the hydrogen peroxide addition point.

The mixer 1 agitates the water to be treated to which hydrogen peroxide has been added to promote the reaction. The treatment tank 2 is a contact means for bringing the added hydrogen peroxide into contact with the water to be treated. The inside of the processing tank 2 is divided by a partition wall 4 into a retention tank on the upstream side and an aeration tank on the downstream side. Clean air is introduced into the aeration tank through the filter 5. The exhaust gas discharged from the processing tank 2 with the introduction of clean air is discharged into the atmosphere through the filter 6 and the exhaust ozone decomposer 7.

The treated water discharged from the treatment tank 2 is sent to the pure water producing apparatus described above and used as a part of the raw water for producing ultrapure water.

In this wastewater treatment equipment, hydrogen peroxide is added to the water to be treated. The water to be treated to which hydrogen peroxide has been added is
After being stirred by the mixer 1, the treatment tank 2 moves from the retention tank to the aeration tank. In this process, dissolved ozone existing in the water to be treated and hydrogen peroxide keep contacting with each other. As a result, dissolved ozone is decomposed and its disappearance is promoted. Further, by injecting clean air into the water to be treated in the aeration tank, the dissolved ozone remaining in the water to be treated is removed to the outside of the water to be treated.

Dissolved ozone in the water to be treated is efficiently removed by such double treatment (decomposition by addition of hydrogen peroxide and elimination by aeration). When the specific treatment water is irradiated with ultraviolet rays in the treatment tank 2, the removal efficiency is further improved.

The treated water discharged from the treatment tank 2 does not contain dissolved ozone. As for hydrogen peroxide, excessive addition can be avoided by appropriately selecting the addition amount according to the ozone concentration. However, the cleanliness of the semiconductor substrate and the glass substrate for liquid crystal is slightly lowered by being used for cleaning treatment, surface modification treatment, and the like. However, the cleanliness is much higher than that of clean water used as raw water for ultrapure water production in pure water production equipment. Therefore, the treated water can be reused as raw water for ultrapure water production in the pure water production system without any trouble, and the reuse reduces the burden on the pure water production system and simplifies the purification process. .

In addition to this, since the efficiency of removing dissolved ozone is high, the amount of hydrogen peroxide used is reduced as much as possible. Further, new secondary contamination of treated water, which is a problem in adsorption treatment with activated carbon, regular chemical replacement work, and generation of waste are avoided.

The exhaust gas discharged from the processing tank 2 contains ozone, but the ozone is removed by passing through the exhaust ozone decomposer 7, detoxified and discharged into the atmosphere.

[0028]

EXAMPLE Exhausted ozone water having a dissolved ozone concentration of 45 ppm was dissolved in ozone at a molar ratio of 0.5, 0.2, 0.
After contacting with 1 hydrogen peroxide, the dissolved ozone concentration in the exhaust ozone water was measured. Contact time 0.4 seconds, 5 seconds, 13
There are 3 types of seconds. Table 1 shows the measurement results of the dissolved ozone concentration.

[0029]

[Table 1]

When the molar ratio of hydrogen peroxide is 0.5,
Dissolved ozone concentration from 45ppm to 30pp in 4 seconds contact
m. The contact time for 5 seconds reduces to 7 ppm, and the contact time for 13 seconds reduces to 2 ppm.

When the molar ratio of hydrogen peroxide is 0.2,
Dissolved ozone concentration from 45 ppm to 36 after contact for 0.4 seconds
Reduce to ppm. After contacting for 5 seconds, 15ppm, 13
In the second contact, it is reduced to 6 ppm.

When the molar ratio of hydrogen peroxide is 0.1,
Dissolved ozone concentration from 45 ppm to 42 after contact for 0.4 seconds
Reduce to ppm. After contacting for 5 seconds, 23ppm, 13
With second contact, it is reduced to 13 ppm.

As can be seen from the above, even if the molar ratio of hydrogen peroxide is lowered from 0.5 to 0.2, the same decomposition efficiency can be secured by increasing the contact time from 5 seconds to 13 seconds. . Even when the molar ratio of hydrogen peroxide is reduced from 0.2 to 0.1, the same decomposition efficiency can be secured by increasing the contact time from 5 seconds to 13 seconds. Although depending on the contact time, even if the molar ratio of hydrogen peroxide is less than 1, dissolved ozone can be sufficiently decomposed. The decrease in the molar ratio can be sufficiently compensated by increasing the contact time (increasing the size of the processing tank).

In the above-described embodiment, the ozone concentration in the water to be treated (exhausted ozone water) was measured on the upstream side and the amount of hydrogen peroxide was determined based on the measured ozone concentration. It may be added only to the extent not present. It is also possible to omit aeration.

The target field of the present invention is not limited to the above-mentioned semiconductor field, but is applicable to fields where clean water is required and the degree of contamination of water after use is comparatively small.

[0036]

As described above, the wastewater treatment method and apparatus of the present invention can effectively decompose the waste ozone water by the addition of hydrogen peroxide, and can prevent secondary pollution of the treated water. Enables its reuse. Moreover, the running cost is low, and it is not necessary for regular replacement and waste disposal.

Further, the ozone water producing apparatus of the present invention is not limited to simply producing ozone water, but is equipped with the above-mentioned highly efficient and economical wastewater treatment apparatus for waste ozone water after use. There is no concern about environmental problems, and the product value is extremely high. Also, by using the treated water discharged from the wastewater treatment equipment as the raw water in the pure water production equipment that is the source of pure water or ultrapure water used for the production of ozone water, the pure water production equipment can be simplified. It is possible to improve the economic efficiency.

[Brief description of drawings]

FIG. 1 is a system diagram of a wastewater treatment apparatus showing an embodiment of the present invention, showing a schematic configuration of an apparatus suitable for carrying out the wastewater treatment method of the present invention.

[Explanation of symbols]

1 mixer 2 processing tanks 3 sensors 4 partitions 5,6 filter 7 Waste ozone decomposer

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D037 AA13 AB11 BA18 BB05 BB09                       CA02 CA09                 4D038 AA08 AB27 BA02 BA04 BB07                       BB15                 4D050 AA13 AB32 BA04 BC09 BD02                       BD06                 4G042 CE01

Claims (6)

[Claims] 1. A method for decomposing dissolved ozone remaining in waste ozone water by adding hydrogen peroxide to waste ozone water after the ozone water in which ozone gas is dissolved is used for wet treatment such as cleaning. Wastewater treatment method. 2. The wastewater treatment method according to claim 1, wherein the amount of hydrogen peroxide added is 1/30 or more and 1 or less in terms of molar ratio to dissolved ozone. 3. The wastewater treatment method according to claim 1, wherein the discharge of dissolved ozone is promoted by performing aeration in addition to the addition of hydrogen peroxide. 4. The decomposition of dissolved ozone is promoted by irradiation with ultraviolet rays in addition to the addition of hydrogen peroxide.
The wastewater treatment method according to 2 or 3. 5. Addition means for adding hydrogen peroxide to waste ozone water after using ozone water in which ozone gas is dissolved for wet treatment such as cleaning, and contact for contacting the added hydrogen peroxide with waste ozone water. A wastewater treatment device comprising: 6. An ozone water production apparatus for producing ozone water using pure water or ultrapure water supplied from the pure water production apparatus, which is combined with the wastewater treatment apparatus according to claim 5. The waste ozone water after using the ozone water produced by the ozone water producing apparatus is introduced into the wastewater treatment apparatus as water to be treated, and the treated water discharged from the wastewater treatment apparatus is raw water to the pure water producing apparatus. The ozone water production device is characterized by being introduced as.