JP3246011B2 - Method for treating semiconductor manufacturing wastewater containing hydrogen peroxide - Google Patents

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 with catalase.

[0002]

2. Description of the Related Art Some wastewater discharged from a semiconductor manufacturing plant contains hydrogen peroxide. If hydrogen peroxide is contained in the wastewater, it may cause the flocculation and settling sludge to float when the wastewater is treated, or it may become a COD source.
It is necessary to remove hydrogen peroxide from wastewater.

Conventionally, in order to remove hydrogen peroxide in wastewater containing hydrogen peroxide, reducing agents such as sodium sulfite and sodium hydrogen sulfite, and catalase, an enzyme that specifically decomposes hydrogen peroxide, have been used. Is performed.

However, in the method using sodium sulfite or sodium bisulfite, one mole of sodium sulfite or sodium bisulfite reacts with respect to 1 mole of hydrogen peroxide, so that it is necessary to add a large amount of a drug. Therefore, there is a problem that the cost increases and the salt concentration increases. In addition, it is difficult to add a required amount of a chemical according to the fluctuating hydrogen peroxide concentration, and there is also a problem that if added excessively, the remaining sodium sulfite or sodium hydrogen sulfite increases the COD value of the treated water.

The method using catalase has the advantage that catalase is an excellent biocatalyst and has a very high treatment efficiency at normal temperature. In some cases, the decomposition rate of hydrogen peroxide may be greatly reduced. As a countermeasure, a method of using catalase which is resistant to fluorine ions or a method of adding an alkaline calcium compound to solid-liquid separation of fluorine ions in waste water as calcium fluoride and then contacting with catalase is adopted. However, even if fluorine ions are removed, catalase may not work effectively, and there is a problem that hydrogen peroxide cannot be removed efficiently.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems by simply making catalase act effectively even in wastewater containing a catalase inhibitor, so that hydrogen peroxide is easily and efficiently obtained. Of the present invention is to propose a method for treating semiconductor manufacturing wastewater containing hydrogen peroxide which can decompose and remove hydrogen.

[0007]

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

[0008] The present invention provides a method of treating a semiconductor manufacturing waste water is contacted with catalase to decompose and remove the hydrogen peroxide wastewater containing hydrogen peroxide, the semiconductor manufacturing waste water containing the hydrogen peroxide, the pH 9 A method for treating semiconductor manufacturing wastewater containing hydrogen peroxide, wherein the pH is adjusted to 11 or less .

The wastewater 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 enzyme activity of catalase. The catalase inhibitor contained in the wastewater discharged in the semiconductor manufacturing process is recognized to be hydroxylamine and other reducing substances. Specific examples of the semiconductor manufacturing wastewater containing hydrogen peroxide to which the treatment method of the present invention can be applied include wastewater discharged from a semiconductor manufacturing plant, 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 to decompose hydrogen peroxide in the water to be treated by the enzymatic activity of catalase, the pH of the water to be treated exceeds 9
In this method, the pH is adjusted to 11 or less . By performing catalase treatment in a pH range within which the catalase can operate and within a strongly alkaline pH range, the degree of inhibition by the inhibitor can be significantly reduced. If the pH is 9 or less , the degree of inhibition reduction is small, and if it exceeds 11, it is usually out of the pH range in which catalase can act, which is not preferable.

The pH is adjusted by adding a pH adjuster to the water to be treated. This can be carried out before the catalase treatment or simultaneously with the catalase treatment.
Examples of the pH adjuster include alkalis such as sodium hydroxide, potassium hydroxide and calcium hydroxide; acids such as hydrochloric acid and sulfuric acid; and pH buffers.

For the catalase treatment, a known method can be adopted.
For example, in the case of catalase of 100,000 units / ml, it can be carried out by adding approximately the following amount of catalase. One unit has a hydrogen peroxide concentration of 150 mg / l.
It is the amount of enzyme that decomposes 1 micromole 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 at 0 mg / l: 50 mg / l, hydrogen peroxide concentration in the water to be treated is 150 to 250 mg / l, addition amount: 100 mg / l, hydrogen peroxide concentration in the water to be treated is 250 to 500 mg / l l when added: 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 increases.

The water to be treated to which catalase has been added is reacted with stirring for 5 to 30 minutes, preferably 10 to 15 minutes, so that 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 is efficiently decomposed and removed.

After decomposing and removing hydrogen peroxide with catalase, for example, an inorganic coagulant such as a calcium compound, an aluminum compound or an iron compound and / or a polymer coagulant such as polyacrylamide are added to remove metals. To carry out the coagulation sedimentation process. When an aluminum salt, an iron salt, or the like is used as a coagulant, the coagulation and precipitation treatment is usually performed at a pH of 6.5 to 7.5, so it is necessary to readjust the pH. Since the coagulation treatment is performed in a higher pH range, it is not necessary to readjust the pH.

[0017]

Next, an embodiment 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 value shown in Table 1 with a phosphate buffer and a carbonate buffer. Catalase manufactured by Kurita Water Industries Ltd.
Krivata K300 (registered trademark, enzyme activity 100000)
Unit / ml, optimal pH 6 to 11) was added at 50 mg / l, and hydrogen peroxide was decomposed at 30 ° C. The reaction rate (K) after 5 minutes was determined by the following equation. Table 1 shows the results. ln (C / C ₀ ) = − Kt C ₀ : initial hydrogen peroxide concentration C: hydrogen peroxide concentration after t minutes K: reaction rate t: time (minutes)

[0018]

[Table 1]

From Table 1, the optimum pH of the enzyme for tap water
The reaction rate is high (enzyme activity is high) in the range of pH 6 to 11, which is particularly high.
It can be seen that there is not much difference in the reaction rate in the range of ~ 11. In the case of pH 5.5 and 11.5, the reaction rate is low because it is outside the range of the optimum pH of the enzyme.

Example 1 Instead of tap water, semiconductor manufacturing wastewater (having a hydrogen peroxide content of 15
0 mg / l, pH 2.5) in the same manner as in Comparative Example 1. The pH was adjusted with hydrochloric acid or sodium hydroxide. Table 2 shows the results.

[0021]

[Table 2]

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

When the results in Tables 1 and 2 are compared, pH 8 to
In the range of 11, the results in Table 2 were smaller than those in Table 1, and the inhibition was not completely removed. However, the degree was smaller than the drop at pH 6 to 7, and the degree was particularly small, particularly 10 to 11 It can be seen that the extent of inhibition was significantly reduced in the range of.

Example 2 Another commercially available catalase was added to the same semiconductor production waste water as in Example 1 at 5000 units / liter, and the reaction rate was determined in the same manner as in Comparative Example 1. Table 3 shows the results.

[0025]

[Table 3]

[0026]

As described above, according to the present invention, the semiconductor manufacturing wastewater containing hydrogen peroxide is brought into contact with catalase by adjusting the pH to more than 9 to 11 or less. Hydrogen peroxide can be decomposed and removed well.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Takao Numakura 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd. (56) References JP-A-63-270595 (JP, A) JP-A-2-222773 (JP, A) JP-A-60-175504 (JP, A) JP-A-6-63531 (JP, A) JP-A-6-86988 (JP, A) JP-A-58-6299 (JP, A) JP-A-64-11689 (JP, A) JP-A-3-143598 (JP, A) JP-A-3-86297 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C02F 1/00 C02F 1/58

Claims (1)

(57) [Claims] 1. A method for treating wastewater that decomposes and removes hydrogen peroxide by bringing the semiconductor production wastewater containing hydrogen peroxide into contact with catalase, wherein the semiconductor production wastewater containing hydrogen peroxide has a pH of more than 9.
A method for treating semiconductor manufacturing wastewater containing hydrogen peroxide, wherein the pH is adjusted to 11 or less .