JP2957464B2 - Treatment method for wastewater containing hydrogen peroxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a waste water treatment method for obtaining a harmless water is removed as a precipitate by insolubilization soluble chemicals in the industrial wastewater, in particular, hydrogen peroxide in the waste water (H ₂ The present invention relates to a wastewater treatment method for decomposing O ₂ ).

[0002]

2. Description of the Related Art Manufacturing processes for semiconductor devices include processes such as etching, polishing, and cleaning. In these processes, various chemicals such as hydrofluoric acid, phosphoric acid, and hydrogen peroxide are used. Therefore, when discarding these wastewaters,
Processing is required to prevent pollution. FIG. 4 is a configuration diagram schematically showing a conventional wastewater treatment system used for this purpose.

[0003] Waste water a discharged from each manufacturing process is first collected in a raw water tank 1 and stays there for a predetermined time. The concentration of the chemical in the waste water a may temporarily increase depending on the state of the process operation. If the chemical concentration is too high, the wastewater treatment may be incomplete. Therefore, the chemical is temporarily stored in the raw water tank to make the concentration uniform. In order to make the concentration uniform, air is introduced into the raw water tank 1 by the air pump 2, and the waste water is gently stirred. The drainage a contains fluorine ions and phosphate ions, and has an average pH of about 2 to 3. If an abnormality occurs in the wastewater treatment system, it is necessary to store the wastewater until the repair is completed. To this end, the larger the raw water tank is, the better, but the space is large enough to store 5 to 6 hours of wastewater due to space limitations. Therefore, the time during which the drainage a stays in the raw water tank 1 is about 5 to 6 hours.

The waste water from the raw water tank 1 is sent to the reaction tank 3 as waste water b. In the reaction tank 3, a stirrer 4 is used to promote the reaction.
The wastewater is vigorously stirred. The following reaction is performed in this reaction tank. The wastewater is neutralized by mixing an alkaline neutralizing agent (such as calcium hydroxide or sodium hydroxide) 5. By adding Ca salt 7 such as calcium carbonate, fluorine ion (F ⁻ ) and phosphate ion (PO ₄ ⁻ , P ₂ O ₅ ⁻ )
To a Ca salt that is hardly soluble in water. Catalase 6a is added to decompose hydrogen peroxide into water and oxygen.

[0005] Here, the amount of catalase added is about 30 ppm with respect to the wastewater b. Catalase is a general term for enzymes that decompose hydrogen peroxide into water and oxygen. There are countless types derived from living organisms. Optimal pH for enzymatic action
Is estimated to be around neutral for liver, erythrocytes and bacteria, and 5.3 to 8.6 for plants (edited by the Chemical Dictionary Editor's Committee, "Chemical Dictionary" Kyoritsu Shuppan, pp. 425- 42
6) Therefore, in the reaction tank, catalase was added after adding the neutralizing agent. The time during which the waste water b stays in the reaction tank 3 is about 30 minutes.

The wastewater from the reaction tank 3 is sent to the coagulation tank 8 as wastewater c. The water-insoluble substances generated in the reaction tank 3 and contained in the wastewater c are so fine that they hardly precipitate. Therefore,
In the flocculation tank 8, a flocculant 10 such as a high-molecular polymer is added to grow the fine water-insoluble substance into a large floc 11 that can easily precipitate. In the coagulation tank 8, the wastewater is gently stirred by the stirrer 9 in order to promote the coagulation. Aggregation grows to the desired size in about 30 minutes, although not as rapidly as the neutralization reaction.

The wastewater from the coagulation tank 8 is used as wastewater d as the sedimentation tank 12
Sent to The sedimentation tank 12 is a tank for sedimenting the flocs 11 grown in the coagulation tank 8 and separating them into solid and liquid. The time required for precipitation is about 5 to 6 hours. Separated sediment 13 and drainage e are taken out from different outlets, and the treatment is completed. If waste water with unreacted hydrogen peroxide mixed therein is sent to the sedimentation tank 12, bubbles are generated by decomposition of the hydrogen peroxide, and the bubbles are combined with the flocs, so that the flocs float. Would. For this reason,
The solid-liquid separation in the sedimentation tank becomes incomplete, and the drainage e is discharged while containing the flocs. In order to avoid this inconvenience, it is said that the concentration of hydrogen peroxide in the waste water d needs to be 10 ppm or less. Conventionally, a large amount of catalase has been introduced into the reaction tank in order to reduce the concentration to below this level. In addition, the wastewater treatment method to add catalase,
For example, Japanese Patent Publication No. Hei.
0595).

[0008]

In the above-mentioned conventional wastewater treatment method, catalase is charged into the reaction tank 3, so that the reaction time before flowing into the precipitation tank 12 is as short as about 1 hour, In order to sufficiently reduce the concentration of hydrogen peroxide in the waste water d, it was necessary to add a large amount of catalase. As a means for reducing the amount of catalase to be charged, a method of increasing the residence time in the reaction tank 3 or the flocculation tank 8 or charging catalase together with the neutralizing agent into the raw water tank 1 can be considered. However, the former method is not realistic because a large capacity is required for a stirrer that vigorously stirs external wastewater that requires a large space in a reaction tank or a coagulation tank. Also, the latter is difficult to realize because a stirrer that vigorously stirs the wastewater from the raw water tank is required. Therefore,
The problem to be solved by the present invention is to make it possible to reduce the amount of catalase to be added without increasing the scale of the processing apparatus.

[0009]

According to the wastewater treatment method of the present invention, in order to solve the above-mentioned problems, catalase is used in a raw water tank using a catalase of a type capable of decomposing hydrogen peroxide even in an acidic solution. The following two methods are adopted.

As described in the "Chemical Dictionary", conventional catalase is active at about pH 5.3 to 8.6, and cannot be directly introduced into wastewater of pH 3 or lower to be treated in the present invention. Did not. However, recently catalase, mainly extracted from mold, has been obtained which still shows activity even at low pH values. As such a catalase, Ask Super 25 (trade name: manufactured by Mitsubishi Gas Chemical Co., Ltd.) can be mentioned. In the present invention, this type of catalase is used.

FIG. 2 shows a solution of pH 2.5 and an initial hydrogen peroxide concentration of 250 ppm, and 12 ppm of Asksuper 25 and catalase (hereinafter referred to as a conventional product) which has been conventionally used and derived from bovine or porcine liver. 6) shows the transition of the concentration of hydrogen peroxide when (2) is added. As shown in the figure, when Ask Super 25 was added, hydrogen peroxide could be almost completely decomposed after 300 minutes, but when the conventional product catalase was added, a low level was obtained. Since the activity is lost due to the pH, the hydrogen peroxide concentration hardly changes even after a long time. An experiment similar to that of FIG. 2 was performed by changing the pH value. That is, 12 ppm of catalase was added to 250 ppm of hydrogen peroxide having different pH values, and after 5 hours, how much hydrogen peroxide could be decomposed was measured. FIG. 3 shows that the amount of decomposition at pH 7 was 1
It is a graph illustrated as 00. From this graph, it can be seen that the conventional product has little ability to decompose hydrogen peroxide at pH 4 or less. The wastewater treatment method of the present invention,
Catalase which does not lose its activity even in an acidic solution is used and is charged in a raw water tank. By using this means, the above-mentioned problem can be solved.

[0012]

FIG. 1 is a block diagram showing the outline of a treatment system for carrying out a wastewater treatment method according to the present invention. Unlike the conventional treatment method shown in FIG. 4, catalase 6 is charged into the raw water tank 1. The catalase used does not lose its activity even in an acidic solution. As in the conventional example, the waste water a discharged from the various places in the factory is first collected in a large-capacity raw water tank 1, where catalase 6 is charged and stays there for a predetermined time. The waste water is gently stirred by the air sent by the air pump 2. The residence time of the wastewater in this raw water tank is about 5 to 6 hours. Most of the hydrogen peroxide is decomposed during this residence. The waste water from the raw water tank 1 is sent to the reaction tank 3 as waste water b, and the neutralizing agent 5 and C
a salt 7 is added to form a Ca salt that is hardly soluble in water. In the reaction tank 3, vigorous stirring is performed by a stirrer 4 to promote the reaction. The time during which the waste water b stays in the reaction tank 3 is about 30 minutes.

The waste water from the reaction tank 3 is sent to the coagulation tank 8 as waste water c. The coagulant 10 added here causes the reaction tank 3
The water-insoluble substance produced in the step (1) grows into a large floc 11 which tends to precipitate. In the coagulation tank 8, the wastewater is gently stirred by the stirrer 9. The residence time in the coagulation tank 8 is about 30 minutes. The wastewater from the coagulation tank 8 is sent to the sedimentation tank 12 as wastewater d, where the floc 11 grown in the coagulation tank 8 is settled to perform solid-liquid separation. The residence time in the settling tank 12 is about 5 to 6 hours. According to the wastewater treatment method of the present invention, the time from the introduction of catalase to the settling tank can be greatly extended from 6 to 7 hours, which is 1 hour in the conventional example. Therefore, even if the amount of catalase added is smaller than in the case of the conventional example, the concentration of hydrogen peroxide can be sufficiently reduced before reaching the precipitation tank.

[0014]

Next, an embodiment of the present invention will be described.
The present invention is not limited to this. Raw water tank (residence time 310
Min), a reaction tank (residence time 30 minutes), a coagulation tank (residence time 30 minutes), and a sedimentation tank (residence time 310 minutes), and a residual hydrogen peroxide decomposition test was performed. Experimental wastewater was used by drawing wastewater from a production line into a raw water tank. Lime milk was used for pH adjustment in the reaction tank. Ask Super 25 20p for drainage of raw water tank
pm was added. pH 2.8, hydrogen peroxide concentration 123
When AskSuper 25 was added to the wastewater from the raw water tank of ppm, the concentration of hydrogen peroxide in the wastewater flowing into the sedimentation tank after 6 hours was 5 ppm. When AskSuper 25 was added to the wastewater from the raw water tank having a pH of 3.1 and a hydrogen peroxide concentration of 206 ppm, the concentration of hydrogen peroxide in the wastewater flowing into the sedimentation tank after 6 hours had passed was 4 ppm.

[Comparative Example 1] In the same processing apparatus, 30 ppm of Ask Super 25 was quantitatively added to the waste water of the reaction tank. When the pH of the wastewater flowing into the reaction tank was 2.3 and the concentration of hydrogen peroxide was 220 ppm, the concentration of hydrogen peroxide in the wastewater flowing into the precipitation tank after one hour had passed was 24 ppm.

[Comparative Example 2] In the same treatment apparatus, 30 ppm of a conventional catalase was quantitatively added to wastewater from a raw water tank. The pH in the raw water tank is 2.6 and the concentration of hydrogen peroxide is 1
When it was 90 ppm, the concentration of hydrogen peroxide in the wastewater flowing into the sedimentation tank after 6 hours was 25 ppm.

[0017]

As described above, the wastewater treatment method according to the present invention involves adding catalase, which does not decrease its activity even in an acidic solution, to the wastewater from a raw water tank, so that a conventional wastewater treatment system can be used almost as it is. Thus, the amount of catalase used to decompose residual hydrogen peroxide can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a wastewater treatment system used in an embodiment of the present invention.

FIG. 2 is a graph showing the time course of decomposition of hydrogen peroxide when the catalase used in the present invention and a conventional catalase are used.

FIG. 3 is a graph showing pH values and activities of catalase used in the present invention and conventional catalase.

FIG. 4 is a schematic configuration diagram of a conventional wastewater treatment system.

[Explanation of symbols]

 Reference Signs List 1 raw water tank 2 air pump 3 reaction tank 4, 9 stirrer 5 neutralizer 6, 6a catalase 7 Ca salt 8 coagulation tank 10 coagulant 11 floc 12 sedimentation tank 13 sediment

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 1/00-1/78

Claims (5)

(57) [Claims] 1. A method for uniforming the concentration in a method for treating a wastewater containing hydrogen peroxide, including a treatment for uniforming the concentration by storing the solution for 5 to 6 hours , a pH adjustment treatment to be performed thereafter, and a treatment for insolubilizing the content. Concentration by adding catalase to the wastewater without losing the activity even in acidic solution
Method of processing the hydrogen peroxide-containing wastewater, which comprises carrying out reduction with hydrogen peroxide and a decomposition treatment to water and oxygen at the same time. 2. Hydrogen peroxide which is stored in a raw water tank for storing the raw waste water for 5 to 6 hours to make the concentration uniform and a reaction tank in which waste water is supplied from the raw water tank to adjust pH and perform a predetermined reaction. In the method for treating the wastewater containing water, catalase that does not lose its activity even in an acidic solution is added to the wastewater in the raw water tank to equalize the concentration and decompose hydrogen peroxide.
A method for treating hydrogen peroxide-containing wastewater, which is carried out at times . 3. A raw water tank for storing the raw waste water for 5 to 6 hours for uniform concentration, a reaction tank for supplying waste water from the raw water tank to perform pH adjustment and a predetermined reaction, and a waste water for supplying water from the reaction tank. Of a hydrogen peroxide-containing wastewater performed using a flocculation tank in which the reaction product is flocculated in the reaction tank, and a sedimentation tank in which wastewater is supplied from the flocculation tank and sedimentation of the flocculate in the flocculation tank is performed. In the treatment method, catalase that does not lose its activity even in an acidic solution is added to the wastewater in the raw water tank to simultaneously perform the concentration uniformization and the decomposition treatment of hydrogen peroxide.
Method of processing the hydrogen peroxide-containing wastewater, characterized in that the Hare. 4. The method for treating wastewater containing hydrogen peroxide according to claim 2, wherein the raw water tank has a capacity several times or more the capacity of the reaction tank. 5. The method for treating wastewater containing hydrogen peroxide according to claim 2, wherein gentle stirring is performed in the raw water tank and vigorous stirring is performed in the reaction tank.