JPH06170355A - Method for treating waste water containing hydrogen peroxide in semiconductor manufacturing process - Google Patents

Abstract

(57) [Summary] [Objective] Even in wastewater for semiconductor production containing a catalase inhibitor in addition to hydrogen peroxide, catalase effectively acts to decompose and remove hydrogen peroxide easily and efficiently. [Structure] Semiconductor manufacturing wastewater containing hydrogen peroxide has a pH of 8 to
After adjusting the pH to 11, it is contacted with catalase to decompose hydrogen peroxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating semiconductor manufacturing wastewater containing hydrogen peroxide, which decomposes and removes hydrogen peroxide by catalase.

[0002]

2. Description of the Related Art Some waste water discharged from semiconductor manufacturing plants contains hydrogen peroxide. When the wastewater contains hydrogen peroxide, it causes flotation of coagulation sedimentation sludge when the wastewater is treated, and also serves as a COD source.
Hydrogen peroxide needs to be removed from the waste water.

Conventionally, in order to remove hydrogen peroxide in wastewater containing such hydrogen peroxide, a reducing agent such as sodium sulfite and sodium bisulfite, and catalase which is an enzyme that specifically decomposes hydrogen peroxide. Is being processed.

However, in the method using sodium sulfite or sodium bisulfite, since 1 mol of sodium sulfite or sodium bisulfite reacts with 1 mol of hydrogen peroxide, it is necessary to add a large amount of chemicals. Therefore, there is a problem that the cost becomes high and the salt concentration rises. Further, it is difficult to add a necessary amount of chemicals according to the fluctuating hydrogen peroxide concentration, and if added excessively, residual sodium sulfite or sodium hydrogen sulfite raises the COD value of the treated water.

The method using catalase has the advantage that catalase is an excellent biocatalyst and the treatment efficiency at room temperature is very high. However, in the wafer process wastewater discharged from a semiconductor manufacturing plant, fluorine ions, etc. Since it contains the catalase inhibitor, the decomposition rate of hydrogen peroxide may be significantly reduced. As a countermeasure against this, a method of using catalase resistant to fluoride ion or a method of adding an alkaline calcium compound to solid-liquid separate the fluoride ion in the waste water into calcium fluoride and then contacting with catalase is adopted. However, even if the fluoride ion is removed, catalase may not work effectively, and there is a problem that hydrogen peroxide cannot be removed efficiently.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the object of the present invention is to allow catalase to act effectively even in waste water containing a catalase inhibitor so that hydrogen peroxide can be easily and efficiently produced. It is an object of the present invention to propose a method for treating semiconductor manufacturing wastewater containing hydrogen peroxide capable of decomposing and removing hydrogen peroxide.

[0007]

[Means for Solving the Problems] The optimum pH of action of normal catalase is in the vicinity of neutrality ("Chemical Dictionary", Kyoritsu Shuppan Co., Ltd., February 15, 1987, "catalase"). Therefore, when treating wastewater containing no catalase inhibitor, if the pH is adjusted to near neutral, there is almost no difference in enzyme activity, and hydrogen peroxide can be decomposed by catalase. However, in the case of treating semiconductor manufacturing wastewater, catalase may not work effectively even if the wastewater is adjusted to an optimum pH for treating catalase and treated. As a result of investigating the cause, it has been found that such a semiconductor manufacturing wastewater contains a catalase inhibitor, and that this inhibitor inhibits catalase. Furthermore, it was found that the degree of such inhibition was greatly influenced by pH. The present inventors have completed the present invention based on such findings.

That is, according to the present invention, in a method for treating wastewater containing hydrogen peroxide, the wastewater for semiconductor production is contacted with catalase to decompose and remove hydrogen peroxide. A method for treating semiconductor manufacturing wastewater containing hydrogen peroxide, which is characterized in that the method is adjusted.

The waste water to be treated in the present invention is
Wastewater discharged from the semiconductor manufacturing process and containing, in addition to hydrogen peroxide, a catalase inhibitor that inhibits the enzymatic activity of catalase. The catalase inhibitor contained in the wastewater discharged during the semiconductor manufacturing process is recognized as hydroxylamine and other reducing substances. Specific examples of semiconductor manufacturing wastewater containing hydrogen peroxide to which the treatment method of the present invention can be applied include wastewater discharged from semiconductor manufacturing factories such as semiconductor process wastewater.

In the treatment method of the present invention, when the water to be treated is brought into contact with catalase and the hydrogen peroxide in the water to be treated is decomposed by the enzymatic activity of catalase, the pH of the water to be treated is 8 to 1.
The pH is adjusted to 1, preferably 9 to 11. In this way, by performing the catalase treatment within the pH range in which catalase can act and the pH is on the strongly alkaline side, the degree of inhibition by the inhibitor can be greatly reduced. When the pH is less than 8, the degree of inhibition reduction is small, and when it is more than 11, it is usually outside the pH range in which catalase can act.

The pH is adjusted by adding a pH adjusting agent to the water to be treated. This can be performed before the catalase treatment or can be performed simultaneously with the catalase treatment.
Examples of the pH adjusting agent include alkali such as sodium hydroxide, potassium hydroxide and calcium hydroxide; acids such as hydrochloric acid and sulfuric acid; and pH buffer solution.

A known method can be used for the catalase treatment,
For example, in the case of 100,000 units / ml of catalase, it can be carried out by adding about the following amount of catalase. If 1 unit of hydrogen peroxide is 150mg / l,
It is the amount of enzyme that decomposes 1 micromol of hydrogen peroxide per minute at 30 ° C.

The concentration of hydrogen peroxide in the water to be treated is 10 to 15
Addition amount when 0 mg / l: 50 mg / l, hydrogen peroxide concentration in the water to be treated is 150 to 250 mg / l: 100 mg / l, hydrogen peroxide concentration in the water to be treated is 250 to 500 mg / l Addition amount when 1: 300 mg /
l or more.

When adding catalase, the water temperature is preferably 0 to 50 ° C, preferably 25 to 37 ° C. Under such conditions, the enzymatic activity of catalase becomes high.

The treated water added with catalase is reacted for 5 to 30 minutes, preferably 10 to 15 minutes with stirring, whereby hydrogen peroxide is decomposed and removed by catalase. At this time, since the pH of the water to be treated is adjusted to the above range, the degree of inhibition by the inhibitor is greatly reduced, and therefore, hydrogen peroxide can be decomposed and removed efficiently.

After decomposing and removing hydrogen peroxide with catalase, for example, in order to remove metals, inorganic flocculants such as calcium compounds, aluminum compounds and iron compounds and / or polymer flocculants such as polyacrylamide are added. Aggregation treatment can be performed. When aluminum salt, iron salt, etc. are used as the coagulant, the coagulation-sedimentation treatment is usually performed at pH 6.5 to 7.5, so it is necessary to readjust the pH, but when using lime etc. as the coagulant. Since the coagulation treatment is performed in a higher pH range, it is not necessary to readjust the pH.

[0017]

EXAMPLES Next, examples of the present invention will be described. Comparative Example 1 Hydrogen peroxide was dissolved in tap water to a concentration of 150 mg / l, and the pH was adjusted to the values shown in Table 1 with a phosphate buffer solution and a carbonate buffer solution. Catalase manufactured by Kurita Water Industries Ltd.
Krivata K300 (registered trademark, enzyme activity 100000
Unit / ml, optimum pH 6-11) was added so as to be 50 mg / l, and hydrogen peroxide was decomposed at 30 ° C. The reaction rate (K) after 5 minutes was calculated from the following formula. The results are shown in Table 1. ln (C / C ₀ ) = − Kt C ₀ : initial hydrogen peroxide concentration C: hydrogen peroxide concentration after t minutes Kt: reaction rate after t minutes

[0018]

[Table 1]

From Table 1, in the case of tap water, the optimum pH of the enzyme
The reaction rate is high in the range of pH 6 to 11 (enzyme activity is high), and the reaction rate is high even at pH 6 to 7,
It can be seen that there is not much difference in reaction rate in the range of -11. At pH 5.5 and 11.5, the reaction rate is slow because it is outside the optimum pH range of the enzyme.

Example 1 Wastewater from semiconductor manufacturing (hydrogen peroxide content: 15
The reaction rate was determined in the same manner as in Comparative Example 1 using 0 mg / l, pH 2.5). The pH was adjusted with hydrochloric acid or sodium hydroxide. The results are shown in Table 2.

[0021]

[Table 2]

From Table 2, it can be seen that in the case of semiconductor manufacturing wastewater, the reaction rate is slow and the enzyme is inhibited at pH 6 to 7 even within the optimum pH range of the enzyme. However, in the pH range of 8 to 11, the reaction rate is faster than in the pH range of 6 to 7, and the degree of inhibition is significantly reduced.

Comparing the results of Table 1 and Table 2, pH 8 to
In the range of 11 as well, the results of Table 2 are smaller than the results of Table 1, and although the inhibition was not completely removed, the degree was smaller than the drop at pH 6 to 7, and that of pH 8 to 11 was small. It can be seen that the degree of inhibition is greatly reduced in the range.

Example 2 Another unit of commercial catalase was added to the same semiconductor production wastewater as in Example 1 at 5000 units / liter, and the reaction rate was determined in the same manner as in Comparative Example 1. The results are shown in Table 3.

[0025]

[Table 3]

[0026]

As described above, according to the present invention, since the semiconductor manufacturing wastewater containing hydrogen peroxide is adjusted to pH 8 to 11 and brought into contact with catalase, hydrogen peroxide can be easily and efficiently produced. Can be disassembled and removed.

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[Procedure amendment]

[Submission date] December 3, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

EXAMPLES Next, examples of the present invention will be described. Comparative Example 1 Hydrogen peroxide was dissolved in tap water to a concentration of 150 mg / l, and the pH was adjusted to the values shown in Table 1 with a phosphate buffer solution and a carbonate buffer solution. Catalase manufactured by Kurita Water Industries Ltd.
Krivata K300 (registered trademark, enzyme activity 100000
Unit / ml, optimum pH 6-11) was added so as to be 50 mg / l, and hydrogen peroxide was decomposed at 30 ° C. The reaction rate (K) after 5 minutes was calculated from the following formula. The results are shown in Table 1. ln (C / C ₀ ) = − Kt C ₀ : initial hydrogen peroxide concentration C: hydrogen peroxide concentration after t minutes K: reaction rate t: time (minutes)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Numakura 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd.

Claims (1)

[Claims] 1. A method for treating wastewater, which comprises removing hydrogen peroxide containing semiconductor by contacting it with catalase to decompose and remove hydrogen peroxide, wherein the pH of semiconductor production wastewater containing hydrogen peroxide is adjusted to pH 8-11. A method for treating semiconductor manufacturing wastewater containing hydrogen peroxide, comprising: