JP2002035773A - Method and apparatus for treating benzotriazole- containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for treating benzotriazole-containing wastewater capable of efficiently oxidizing and decomposing benzotriazole used as a copper corrosion inhibitor in a semiconductor field for a short time. SOLUTION: In order to treat organic wastewater containing benzotriazole and copper or a copper compound, at first, the wastewater is introduced into an weak acidity adjusting tank 1 for adjusting the pH of the wastewater to weak acidity and the treated liquid flowing out of this adjusting tank is successively passed through an oxidative decomposition tank 2 for bringing the treated liquid into contact with an oxidizing substance, an alkalainity adjusting tank 3 for adjusting the treated liquid flowing out of the tank 2 to alkalinity of pH 10 or more and a sold-liquid separation tank 4 for subjecting formed copper hydroxide to solid-liquid separation, and part of the copper hydroxide-containing slurry formed in the solid-liquid separation tank 4 is returned to the weak acidity adjusting tank 1 through a line 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the treatment of organic wastewater containing benzotriazole, and more particularly to the treatment of organic wastewater containing benzotriazole and copper or copper compounds with oxidizing substances such as ozone and hydrogen peroxide. The present invention relates to a method and an apparatus for oxidative decomposition treatment using the same.

[0002]

BACKGROUND OF THE INVENTION Benzotriazole is widely used as an anticorrosive for copper in the plating and photographic industries.
Further, recently, it has begun to be used in the semiconductor industry, and the importance of treating wastewater containing benzotriazole is increasing. The use of benzotriazole in the semiconductor field is derived from copper wiring processing, and is largely discharged from a copper surface polishing process. Conventionally, benzotriazole-containing wastewater from the plating and photographic industries has often been incinerated as concentrated wastewater, but benzotriazole-containing wastewater from the semiconductor field has a relatively low concentration of tens to hundreds of ppm. Therefore, it cannot be incinerated. Accordingly, wastewater containing benzotriazole in the semiconductor industry must be treated with conventional wastewater treatment equipment. However, benzotriazole is chemically stable, is hardly biodegradable, and contains copper as a coexistent substance, so that it is difficult to treat it with ordinary wastewater treatment equipment. For this reason, benzotriazole-containing wastewater needs to be decomposed with an oxidizing agent such as ozone or hydrogen peroxide. However, as described above, benzotriazole is a relatively chemically stable substance, and therefore has a low oxidative decomposition rate, and poses a significant cost problem in practical use. Further, since the use of benzotriazole is expected to be used in a large amount in the semiconductor field in the future, development of a decomposition technique having excellent treatment performance for benzotriazole-containing wastewater is required.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a benzotriazole-containing wastewater treatment technique which can efficiently and oxidatively decompose benzotriazole used as a copper corrosion inhibitor in the semiconductor field in a short time. .

[0004]

DISCLOSURE OF THE INVENTION The present invention focuses on the fact that benzotriazole-containing wastewater contains a trace amount of copper, and utilizes the catalytic action of copper to improve the rate of oxidative decomposition, thereby improving the efficiency of wastewater. It has been found that good processing can be performed, and the present invention has been completed. That is, the present invention provides a method for treating an organic wastewater containing benzotriazole and copper or a copper compound, wherein a weakly acidic adjustment step of adjusting the pH of the wastewater to a slightly acidic, and a treatment solution flowing out of this step is treated with an oxidizing substance. The process comprises an oxidative decomposition step of bringing into contact, an alkalinity adjusting step of adjusting the treatment liquid flowing out of this step to an alkali of pH 10 or more, and a solid-liquid separation step of solid-liquid separation of the produced copper hydroxide. A method for treating benzotriazole-containing wastewater is provided. The present invention
Further, in a treatment apparatus for an organic wastewater containing benzotriazole and copper or a copper compound, a weakly acidic adjustment tank for adjusting the pH of the wastewater to slightly acidic, and an oxidizing method for bringing the treatment liquid flowing out of the adjustment tank into contact with an oxidizing substance. A benzotriazole-containing solution comprising: a decomposition tank; an alkali adjustment tank for adjusting a treatment liquid flowing out of the tank to an alkali of pH 10 or more; and a solid-liquid separation tank for solid-liquid separation of the produced copper hydroxide. An object of the present invention is to provide a wastewater treatment device. Further, in the present invention, when the copper concentration coexisting in the benzotriazole-containing wastewater is less than the equivalent of the benzotriazole concentration, a part of the copper hydroxide-containing slurry generated in the solid-liquid separation tank is weakly acidified. It is preferable that a copper hydroxide-containing slurry be returned by providing a line for returning the copper hydroxide to make the copper concentration equal to or more than the equivalent.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the decomposition rate of benzotriazole in the coexistence state of copper is preferably further improved in the weakly acidic range of pH 5 to 6, and therefore, in the present invention, oxidizing agents such as ozone and hydrogen peroxide are used. A weakly acidic adjusting tank is provided before the oxidative decomposition tank using the substance, and the pH of the liquid to be treated is previously adjusted to a weakly acidic, that is, pH 5 to 6. In the present invention, the pH of the discharged wastewater may be about 4 depending on the type of the wastewater to be treated. In this case, it is not necessary to adjust the pH by adding an acid to the weakly acidic adjusting tank, so that a more inexpensive treatment can be expected.

[0006] Decomposition efficiency of benzotriazole varies greatly depending on the copper concentration in the wastewater, and when the coexisting copper concentration is equal to or higher than the benzotriazole concentration, the benzotriazole decomposition rate by oxidizing substances such as ozone is increased. Is improved. Therefore, as a measure for realizing this, it is preferable to return the copper-containing slurry from a solid-liquid separation tank provided at the latter stage of the apparatus. At this time, the copper concentration in the oxidative decomposition tank can be arbitrarily set by controlling the rate of returning the copper-containing slurry from the subsequent solid-liquid separation tank.

[0007]

Next, the present invention will be described more specifically with reference to the drawings. FIG. 1 is a system diagram of an apparatus for treating benzotriazole-containing wastewater showing one embodiment of the present invention. In FIG. 1, raw water, that is, benzotriazole (hereinafter, referred to as benzotriazole)
BTA) and organic wastewater containing copper are adjusted to a weakly acidic region of pH 5 to 6 in the weakly acidic adjusting tank 1 and then contacted with oxidizing substances such as ozone and hydrogen peroxide. Water is sent to the oxidative decomposition tank 2 in order to cause the oxidation. As described above, when the raw water is already weakly acidic and does not require pH adjustment, the raw water can be directly sent to the oxidative decomposition tank 2. Benzotriazole in raw water is oxidatively decomposed in the oxidative decomposition tank 2. The treated water flowing out of the oxidative decomposition tank 2 is introduced into the alkalinity adjusting tank 3 and adjusted to pH 10 or more by adding an alkaline agent. As a result, the copper ions contained in the treated water are precipitated as copper hydroxide Cu (OH) _2, and solid-liquid separated in the solid-liquid separation tank 4. The supernatant liquid of the solid-liquid separation tank 4 is supplied to the downstream equipment as treated water.

On the other hand, a copper-containing slurry is discharged from the bottom of the solid-liquid separation tank 4, a part of which is returned to the weakly acidic adjusting tank 1 by a copper-containing slurry return line 5, and the remainder is discharged as sludge discharged outside the system. Is done. It is preferable that the copper concentration of the water to be treated in the oxidative decomposition tank 2 be maintained at several times to several tens times the copper concentration contained in the raw water by returning the copper-containing slurry to the weakly acidic adjusting tank 1. . By returning the copper-containing slurry, copper is present in the oxidative decomposition tank 2 in an amount equivalent to or more than the BTA concentration, so that oxidative decomposition by ozone or hydrogen peroxide is promoted, and BTA in the wastewater is quickly removed.

FIG. 2 is a graph showing the change over time in the residual concentration of BTA when oxidative decomposition treatment is performed on wastewater having a BTA content of 20 ppm and a copper concentration of 2.5 ppm under various conditions. The copper / BTA molar ratio of this wastewater is 0.24
And the content of copper has not reached the equivalent concentration of BTA. Then, copper was added to this wastewater and the effect of oxidative decomposition with ozone was examined.
Under the conditions of 0 and 1.5, a significant improvement in the BTA decomposition rate was confirmed. That is, it was found that the oxidative decomposition rate of the BTA-containing wastewater changes depending on the concentration of coexisting copper, and that the performance is significantly improved if the Cu / BTA molar ratio is 1 or more.

Further, as shown in FIG. 2, Cu / BT
It was clarified that the decomposition performance was further improved by setting the pH at the time of oxidative decomposition to a weakly acidic region even when the A molar ratio was the same. It is thought that this phenomenon is caused by the stabilization of ozone gas due to a decrease in pH, the concentration of copper ions in the liquid, and the like, but the detailed mechanism is not necessarily clear. Further, based on the above results, a continuous water flow test was performed in a 20-liter reactor. as a result,
The BTA-containing wastewater shown above was treated with a residence time of 30 minutes in the ozone oxidation tank, and it was confirmed that the BTA could be removed to 1.0 mg / L or less. While the required residence time in the normal ozone oxidative decomposition method was 2.5 hours, the method of the present invention can improve the performance by about 5 times, and can greatly reduce the required amount of ozone and the scale of the apparatus. Was.

[0011]

The use of the BTA oxidative decomposition method according to the present invention enables high-performance oxidative decomposition that cannot be obtained with a normal oxidizer, and contains benzotriazole used as a copper anticorrosive in the field of semiconductors and the like. Wastewater can be efficiently treated in a short time.

[Brief description of the drawings]

FIG. 1 is a system diagram of an apparatus for treating benzotriazole-containing wastewater showing one embodiment of the present invention.

FIG. 2 is a graph showing the change over time in the residual concentration of benzotriazole due to oxidative decomposition.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Weak acid adjustment tank 2 Oxidation decomposition tank 3 Alkalinity adjustment tank 4 Solid-liquid separation tank 5 Copper-containing slurry return line

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Claims (4)

[Claims] 1. A method for treating an organic wastewater containing benzotriazole and copper or a copper compound, comprising the steps of: adjusting a pH of the wastewater to a weak acidity; and contacting a treatment liquid flowing out of the step with an oxidizing substance. Oxidative decomposition step
A method for treating benzotriazole-containing wastewater, comprising: an alkalinity adjusting step of adjusting the treatment liquid flowing out of this step to an alkali having a pH of 10 or more; and a solid-liquid separation step of solid-liquid separation of the produced copper hydroxide. . 2. The method for treating benzotriazole-containing wastewater according to claim 1, wherein a part of the copper hydroxide-containing slurry generated in the solid-liquid separation step is returned to the weakly acidic adjustment step. 3. An apparatus for treating an organic wastewater containing benzotriazole and copper or a copper compound, comprising: a weakly acidic adjusting tank for adjusting the pH of the wastewater to slightly acidic; It is characterized by comprising an oxidative decomposition tank to be brought into contact, an alkali adjustment tank for adjusting the treatment liquid flowing out of this tank to an alkali of pH 10 or more, and a solid-liquid separation tank for solid-liquid separation of the produced copper hydroxide. Treatment equipment for wastewater containing benzotriazole. 4. The apparatus for treating benzotriazole-containing wastewater according to claim 3, further comprising a line for returning a part of the copper hydroxide-containing slurry generated in the solid-liquid separation tank to the weakly acidic adjusting tank.