JPH10461A - Drainage treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the quantity of injected acid for decarbonation and to enable the prevention of the propagation of bacteria in a system by a method in which COD-containing drainage, after being added with hydrogen peroxide, is oxidized by being irradiated with ultraviolet rays and treated with active carbon. SOLUTION: Hydrogen peroxide is injected into COD-containing drainage, the COD components are oxidation-decomposed by being irradiated with ultraviolet rays. The treated water, after being added with acid, is decoarbonated and then contacted with active carbon to remove residual hydrogen peroxide. Water without COD components, carbonic acid components generated by the decomposition of the COD components, and residual hydrogen peroxide is supplied to a primary water purifying apparatus, etc., as required to be treated further. As drainage applicable to the method, low-TOC drainage such as semiconductor washing drainage and high-TOC drainage such as fuel electrode condensate of a fuel cell are named.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wastewater treatment method, and more particularly to a wastewater treatment method suitable for collecting and reusing wastewater from a semiconductor manufacturing process and fuel cell wastewater. More specifically, the present invention relates to a method for decomposing and removing COD components by subjecting COD-containing wastewater to ultraviolet (UV) oxidation treatment.

[0002]

2. Description of the Related Art Hydrogen peroxide is added to COD-containing wastewater such as organic matter-containing wastewater discharged from a semiconductor manufacturing process and methanol-containing wastewater (fuel electrode condensed water) discharged from a fuel cell, and then a UV oxidation tank is added. Wastewater treatment method in which COD components are decomposed into carbon dioxide gas and water by UV irradiation, and then passed through an activated carbon tower to decompose and remove excess hydrogen peroxide remaining in the UV oxidized water (FIG. 2). Is known.

In the treatment of waste water from the semiconductor manufacturing process, the treated water thus obtained is usually treated as recovered water through a primary pure water apparatus and further treated in a secondary pure water producing apparatus, and Water is produced.

[0004] The pH of the UV oxidized water is about 5.5 due to the total dissolved carbonic acid (carbon dioxide gas generated by UV oxidation and hydrogen carbonate ions and carbonate ions generated from carbon dioxide gas). I have. At the outlet of the activated carbon tower, the pH rises to about 6.7 due to a change in ion balance.

[0005]

In the above-mentioned conventional processing method, carbon dioxide gas generated by UV oxidation and hydrogen carbonate ions and carbonate ions generated from the carbon dioxide gas flow into the recovered water treatment water tank as they are, There is a problem that the ion load of the ion exchange device of the primary pure water device is caused.

[0006] In the UV oxidation tank, aeration may be performed to mix the liquid. A part of the carbon dioxide gas is released to the atmosphere by this aeration, but most of the carbon dioxide component is removed. Flows into the primary pure water tank without any change.

[0007] In order to reduce the load on the ion exchange unit of the primary pure water production system, it is conceivable to provide a decarbonation tower after the activated carbon tower to reduce the total carbonic acid content. The following problems occur.

That is, as described above, the pH of the UV oxidized water is
Although the pH is relatively low, the pH of the effluent of the activated carbon tower flowing into the primary pure water tank has increased to near neutral,
For decarboxylation, it is necessary to add an acid to lower the pH again. Therefore, there arises a problem that the ion load increases due to the addition of the acid.

Further, there is another problem that bacteria are easily propagated because the inside of the decarbonation tower is not sterilized. In particular, since a large amount of air is introduced into the decarbonation tower by a fan, bacteria easily propagate.

[0010] The present invention solves the above-mentioned conventional problems and provides CO 2
Provided is a wastewater treatment method capable of reducing the amount of acid injected for decarboxylation treatment and preventing the propagation of bacteria in the system when UV-treating D-containing wastewater to decompose and remove COD components. The purpose is to:

[0011]

The wastewater treatment method of the present invention is characterized in that hydrogen peroxide is added to COD-containing wastewater, then oxidation treatment is performed by ultraviolet irradiation, decarboxylation treatment, and activated carbon treatment. And

In the present invention, the UV oxidized water is subjected to a decarboxylation treatment before the activated carbon treatment. As described above, since the water having a relatively low pH after the UV oxidation is subjected to the decarboxylation treatment, the injection amount of the acid necessary for the pH adjustment for the decarboxylation can be reduced.

[0013] Further, since hydrogen peroxide remains in the UV oxidized water flowing into the decarbonation tower, the inside of the decarbonation tower is kept in a sterilized state by the hydrogen peroxide, and the propagation of bacteria is prevented. You.

[0014]

FIG. 1 is a system diagram showing a wastewater treatment method according to the present invention.

As shown, in the method of the present invention, C
After injecting hydrogen peroxide into the OD-containing wastewater, UV irradiation is performed to oxidatively decompose the COD component. Then, after injecting the acid into the UV oxidation treatment water, decarboxylation treatment is performed. Next, the decarbonated water is brought into contact with activated carbon to remove residual hydrogen peroxide.

The water from which the COD component, the carbonic acid component generated by the decomposition of COD, and the residual hydrogen peroxide have been removed by UV oxidation, decarboxylation, and activated carbon treatment, may be removed as necessary.
It is sent to the next pure water device and the like and further processed.

Wastewater to be treated by the method of the present invention is low TOC such as semiconductor cleaning wastewater (for example, TOC is 2.0 pp.
m or less) High TOC such as waste water and fuel cell condensate
(For example, about 300 ppm of TOC) wastewater.

The amount of hydrogen peroxide added to this wastewater is T
8.5 ppm or more to OC1 ppm, especially 10 to 12
It is preferably set to ppm.

The amount of UV irradiation applied to the waste water after the addition of hydrogen peroxide is preferably 0.1 wh or more, and more preferably about 0.15 to 0.3 wh, per 1 ppm of the TOC in the methanol state to be removed.

As the decarbonation means, a decarbonation tower, a degassing membrane device or the like can be used.

The excess hydrogen peroxide treatment is preferably performed by passing water through an activated carbon tower.

A primary pure water tank may be provided between the UV oxidation tank and the decarbonation tower. In this case, city water, industrial water, or the like may be introduced into the primary pure water tank and mixed with UV oxidized water for treatment.

According to the wastewater treatment method of the present invention, CO washing water such as semiconductor washing waste water and fuel electrode condensed water of a fuel cell is used.
The amount of acid required for the decarboxylation treatment of the D-containing wastewater can be reduced, and the ionic load and bacterial load of the subsequent device can be significantly reduced.

[0024]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 Methanol containing 810 ppm, TOC 310 ppm,
The fuel electrode condensed water of the phosphoric acid fuel cell having a pH of 4.0 was used as raw water, and was treated according to the procedure shown in FIG.

First, hydrogen peroxide is added to the fuel electrode condensed water.
The hydrogen peroxide concentration in the fuel electrode condensate after the addition is 340
It was added so as to be 0 ppm.

Then, the mixture was introduced into a UV oxidation tank and irradiated with UV at 0.17 wh per 1 mg of methanolic TOC.

Next, when the pH of the water was higher than 5.5, H ₂ SO ₄ was added so that the pH became 5.5, and the mixture was introduced into a decarbonation tower to be decarbonated. Thereafter, the water was introduced into an activated carbon tower, and brought into contact with activated carbon to decompose residual hydrogen peroxide. Table 1 shows the water quality (average over time) of raw water and water collected in each part. In addition, at the inlet side of the decarbonation tower, if necessary, H is adjusted for pH adjustment for decarbonation.
₂ SO ₄ is injected to adjust the pH at the inlet of the decarbonation tower to 5.5 or less. In this embodiment, H ₂ SO _{4 is used.}
Indicates that the H ₂ SO ₄ concentration in the added water to be treated is 1 p.
Since the pH was reduced to 5.5 or less by injecting the solution to a concentration of pm or less, the consumption of the acid was extremely small.

[0029]

[Table 1]

Comparative Example 1 As shown in FIG. 2, hydrogen peroxide was added to the same condensate of the fuel electrode as in Example 1 at the same ratio as in Example 1, and then UV-oxidized in the same UV oxidation tank as in Example 1. Thereafter, water was passed through the activated carbon tower, H ₂ SO ₄ was injected, and decarbonation was performed in the decarbonation tower. Table 2 shows the quality of the water sampled in each part. The same activated carbon tower and decarbonation tower as in Example 1 were used.

In Comparative Example 2, in order to adjust the pH to 5.5 or lower suitable for decarboxylation at the inlet side of the decarbonation tower,
It was necessary to inject H ₂ SO ₄ to 18 ppm.

[0032]

[Table 2]

Example 2 The same conditions as in Example 1 were used except that semiconductor cleaning wastewater having a TOC of 1.2 ppm and a pH of 4.8 was used as raw water, the amount of hydrogen peroxide added was 13 ppm, and the amount of UV irradiation was 0.25 wh per mg of TOC. Processed.

Treatment water quality, H ₂ SO ₄ at the inlet of the decarbonation tower
Table 3 shows the addition amount and the number of bacteria in the effluent of the activated carbon tower.

Comparative Example 2 Hydrogen peroxide was added to the same raw water as in Example 2 in the same manner as in Example 2.
After UV irradiation with addition of 3 ppm, water was first passed through the activated carbon tower as shown in FIG. 2, and then H ₂ SO ₄ was added to adjust the pH to 5.0.
It was set to 5 or less, and then water was passed through a decarbonation tower.

Treatment water quality, H ₂ SO ₄ at the inlet of the decarbonation tower
Table 3 shows the addition amount and the number of bacteria in the effluent of the activated carbon tower.

[0037]

[Table 3]

As is apparent from the above results, the method of the present invention can greatly reduce the amount of acid injection required for decarboxylation, and can prevent the growth of bacteria in the system. Therefore, it is possible to reduce the ion load and the bacterial load of the subsequent primary water purification device.

[0039]

As described above in detail, the wastewater treatment method of the present invention is such that COD-containing wastewater is added with hydrogen peroxide, subjected to UV oxidation treatment, decarbonated, and then activated carbon treated. In addition, the amount of acid required for decarboxylation can be significantly reduced. In addition, for this reason, the ion load of the secondary pure water device installed at the latter stage of the process of the present invention is reduced. Furthermore, since the inside of the decarbonation facility is kept in a sterilized state by the residual hydrogen peroxide, the growth of bacteria in the decarbonation facility is prevented, and the bacterial load on the secondary water purification device at the subsequent stage is reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a wastewater treatment method of the present invention.

FIG. 2 is a system diagram showing a conventional example.

Claims (1)

[Claims] 1. A wastewater treatment method comprising adding hydrogen peroxide to COD-containing wastewater, performing an oxidation treatment by irradiation with ultraviolet rays, performing a decarboxylation treatment, and further performing an activated carbon treatment.