JPH1177089A - Treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently treating a waste water to be treated contg. low concn. of org. compd. with a high b.p. such as (CH3 )4 NOH (TMAH) as a main solute ingredient and an inorg washing waste water contg. low concn. of ammonia. SOLUTION: This method for treating waste water comprises an ammonia recovering process wherein a waste water to be treated contg. low concn. or org. compd. with a higher b.p. than that of water as a main solute ingredient and an inorg. washing waste water contg. low concn. of ammonia are mixed and this mixed waste water is distilled to recover ammonia and a concentrating process wherein the mixed waste water from which ammonia is recovered is concentrated to obtain a conc. waste water. It is possible thereby to reduce remarkably the amt. of waste water by treating two kinds of waste water with different properties and to safely and easily recover ammonia. In addition, the recovered ammonia and the conc. waste water can be decomposed into mainly nitrogen, carbon dioxide and water by supercritical water reaction.

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 two types of wastewater which have different properties and are technically difficult to treat independently. The present invention relates to a method for economically treating wastewater by efficiently converting the wastewater into a form that does not cause wastewater.

[0002]

2. Description of the Related Art In a process of manufacturing a semiconductor device, various chemicals are used to finely process a wafer. Therefore, a solution containing various used chemicals is discharged as a waste liquid. For example, in a wafer processing operation such as a developing operation performed in a wafer photolithography process, (CH ₃ ) ₄ NOH
(Hereinafter referred to as TMAH), the wafer is processed with a processing solution containing 0.4 to 1.0% by weight as a main solute component.
The organic alkaline wastewater containing TMAH is discharged. In the wafer cleaning step, NH ₄ OH (30
%), H ₂ O ₂ (30%) and H ₂ O, the wafer is often washed, so that NH 3
₄ OH, H ₂ O ₂ and the washing waste water, each containing about 0.4 to 1.0 wt% is discharged. Treatment of these wastewaters
Due to technical difficulties and the need for specialized knowledge and specialized processing equipment, it is not practical to respond individually at individual semiconductor device manufacturing plants, and is usually collected by processing specialists, It is intensively processed.

[0003]

By the way, as environmental problems are increasing and attention is being paid to the treatment of industrial waste, T
Treatment wastewater containing MAH (hereinafter referred to as TMAH wastewater)
There is a growing demand for reliable and efficient treatment of wastewater at the source of the wastewater under the sufficient control of the source without leaving the treatment of the above-mentioned wastewater such as washing wastewater containing ammonia to a specialized treatment company. ing. Therefore, a method of concentrating wastewater to reduce the volume has been attempted, but there is a problem that concentration is difficult depending on the composition of the wastewater. For example, in wastewater such as washing wastewater containing ammonia, ammonia is generated at the time of heating and concentration, and the concentration treatment is complicated,
The problem is that the cost increases. Although there is a method of concentration by membrane concentration, there is a drawback that the cost is higher than that of heat concentration. There is no suitable method in other conventional wastewater treatment methods, and consequently, the conventional technology includes a low concentration of an organic compound having a higher boiling point than water as a main solute component discharged from a production plant. In fact, there is no method that can easily and surely treat treated wastewater, for example, treated wastewater containing TMAH (hereinafter, referred to as TMAH wastewater) and inorganic cleaning wastewater containing ammonia. I was In the above description, wastewater generated in the process of manufacturing semiconductor devices has been described as an example, but the same problem applies to wastewater discharged from other factories.

Accordingly, an object of the present invention is to provide a method for efficiently treating treated wastewater containing a low concentration of an organic compound having a higher boiling point than water as a main solute component, and inorganic washing wastewater containing a low concentration of ammonia. That is.

[0005]

Means for Solving the Problems The present inventor firstly stated that:
First, ammonia was recovered from the inorganic cleaning wastewater, then mixed with the treated wastewater, mixed and concentrated to reduce the volume of the wastewater, and the first invention method was completed. Secondly, attention was paid to the application of the supercritical water reaction in order to achieve complete treatment of the mixed and concentrated wastewater. By the way, the TM including
In order to directly apply the supercritical water reaction to the treatment of wastewater such as AH wastewater and washing wastewater, there is a problem that the calorific value of the wastewater is low. That is, the organic matter in the TMAH-containing wastewater is mainly T
Although it is MAH and the cleaning wastewater mainly contains ammonia, the concentration of both is low, so simply sending wastewater to the supercritical water region of the supercritical water reactor will cause supercritical water reaction. It is difficult to sufficiently supply the heat for maintaining the fuel, and it is necessary to separately inject the fuel into the supercritical water reactor in order to supplement the heat and maintain the supercritical water reaction. In this case, the advantage of the supercritical water reaction cannot be fully utilized, which results in an increase in fuel cost.
Even if an attempt is made to apply a supercritical water reaction to the treatment of wastewater such as MAH wastewater and washing wastewater, it has been difficult to commercialize it because the cost is high and it is not economically feasible. As described above, although the supercritical water reaction is directly applied to the raw wastewater, there is a problem of calorific value, but the concentrated wastewater mixed and concentrated by the method of the first invention contains organic substances at a relatively high concentration. Speaking of
It has been found that the supercritical water reaction can be applied to the concentrated wastewater by concentrating the organic substance to a concentration of an organic substance which can be used for the supercritical water reaction by the first invention method. That is, the second invention method of completely treating the concentrated wastewater concentrated by the first invention method by a supercritical water reaction has been completed. Thirdly, as another method of completely treating wastewater by a supercritical water reaction, the treated wastewater is concentrated, ammonia is recovered from the washing wastewater, and then the concentrated wastewater and ammonia are completely treated by a supercritical water reaction. With the idea of processing, the method of the present invention was completed.

[0006] The supercritical water reaction is a method of decomposing organic substances by utilizing the high reactivity of supercritical water. For example, it decomposes hard-to-decompose harmful organic substances into harmless carbon dioxide and water. In order to convert the compound into a useful low-molecular compound by decomposing a high-molecular compound that is hardly decomposable, the practical use of the compound has been actively studied. Supercritical water refers to water that is in a supercritical state, that is, water that is beyond the critical point of water, and more specifically, has a critical temperature, that is, a temperature of 374.1 ° C. or higher, and a critical pressure of water. That is, water in a state under a pressure of 22.04 MPa or more. Supercritical water has a high dissolving power to dissolve organic substances and can completely dissolve non-polar substances that are abundant in organic compounds.Supercritical water is mixed with gases such as oxygen and nitrogen at an arbitrary ratio. To form a single phase.

The supercritical water reaction means a reaction in supercritical water or a reaction using supercritical water as a medium. For example, a hardly decomposable organic substance containing a salt-forming substance such as chlorine or sulfur is converted into a supercritical water region. Examples thereof include an oxidation reaction in which oxidizing and decomposing by an oxidizing agent, for example, air, and a decomposing reaction in which high-molecular organic matter is decomposed into low molecular weight in supercritical water. In these supercritical water reactions, supercritical water may function only as a solvent that dissolves a reactant, for example, an organic substance and oxygen, that is, may function only as a reaction field, or when supercritical water reacts with a reactant. Yes, the manner in which supercritical water contributes to the reaction is complex and various.

In order to achieve the above object, a method for treating wastewater according to the present invention (hereinafter referred to as a first invention method) comprises: an alkaline treatment wastewater containing an organic compound having a higher boiling point than water as a main solute component; A treatment method for treating an inorganic cleaning wastewater containing ammonia in the same process, wherein an ammonia recovery step of recovering ammonia by distilling a mixed wastewater obtained by mixing the treated wastewater and the cleaning wastewater, and recovering the ammonia A concentration step of concentrating the mixed wastewater to obtain a concentrated wastewater.

In order to further treat the concentrated wastewater, the method for treating wastewater according to the present invention (hereinafter referred to as the second invention method) comprises:
It is characterized by having a supercritical water reaction step of decomposing the obtained concentrated wastewater and ammonia into nitrogen, carbon dioxide gas and water mainly by a supercritical water reaction, following the concentration step.

[0010] Another method of treating wastewater by supercritical water reaction according to the present invention (referred to as the third invention method) is a treated wastewater containing an organic compound having a higher boiling point than water as a main solute component and an inorganic containing ammonia. This is a treatment method for treating system washing wastewater, in which the treatment wastewater is concentrated to obtain concentrated treatment wastewater, and the pH is adjusted to 7 or more by adding alkali to the washing wastewater, and then ammonia is recovered by distillation. And a supercritical water reaction step in which the obtained concentrated wastewater and ammonia are mainly decomposed into nitrogen, carbon dioxide and water by a supercritical water reaction.

The first, second and third invention methods are produced when a wafer is processed in the process of manufacturing a semiconductor device, and are treated wastewater mainly containing (CH ₃ ) ₄ NOH at a low concentration as an organic compound; and The present invention can be suitably applied to treatment of cleaning wastewater generated when a wafer is cleaned with cleaning water containing NH ₄ OH and H ₂ O ₂ at a low concentration in a manufacturing process of a semiconductor device. Here, a semiconductor device or the like refers to a semiconductor element such as a transistor, a diode, or a laser element formed on a silicon semiconductor substrate or a compound semiconductor substrate and an integrated circuit element thereof.

The distillation operation performed in the first and third invention methods may be a simple distillation method or a rectification method in which a part of the ammonia is refluxed from the top of the column, as long as ammonia can be recovered at a high recovery rate. The reason for adjusting the pH to neutral or alkaline by adding alkali to the washing wastewater in the third invention method is to prevent the production of ammonia chloride and to facilitate the recovery of ammonia, and the pH value is preferably Is 7 or more, and more preferably 10 to 12. In the step of obtaining the concentrated wastewater or the concentrated wastewater of the first and third invention methods,
It is preferable to concentrate at a concentration rate as high as possible, but practically, the concentration is 60 to 70 times. The method of concentration is not particularly limited as long as concentrated wastewater or concentrated wastewater can be obtained. For example, a heat concentration method for evaporating water or a membrane concentration method using a reverse osmosis membrane or the like may be used. In the case of the heat concentration method, the mixture is heated to a temperature lower than the decomposition degree of the organic compound and concentrated, and if necessary, heated under reduced pressure.
The supercritical water reactor for carrying out the supercritical water reaction in the second and third invention methods may be a known supercritical water reactor, and the concentrated wastewater or concentrated wastewater is mainly subjected to nitrogen and carbon dioxide gas by the supercritical water reaction. There is no restriction on the type and composition as long as it can be decomposed into water and water.

[0013] The first method of the present invention comprises the following two methods having different properties.
It has the effect of mixing the treated wastewater and washing wastewater and treating them in the same process to greatly reduce the volume of wastewater.Furthermore, when distilling to recover ammonia, the alkaline treated wastewater and washing water Since the mixed solution obtained by mixing with the wastewater is distilled, there is an advantage that it is not necessary to separately add an alkali to adjust the pH as in the second invention method. The concentrated wastewater obtained in the concentration step can be further treated by evaporation to dryness, wet combustion, or the like. The second invention method has an advantage that the concentrated wastewater can be completely converted to harmless substances by a supercritical water reaction. The third invention method is the second invention method.
As in the method of the invention, the concentrated wastewater can be completely converted into a harmless substance by the supercritical water reaction.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Embodiment 1 This embodiment is an example of an embodiment of the method of the first invention, and FIG. 1 is a flowchart showing a flow of a process of a wastewater treatment method of this embodiment. The TMAH-containing wastewater to which the present method is applied is 0.4 to 1.0 TMAH generated when a wafer is treated with treated water in the process of manufacturing a semiconductor device.
It is treated wastewater containing at a concentration of% by weight. APM is cleaning wastewater containing ammonia (NH ₃ ) and hydrogen peroxide (H ₂ O ₂ ) of about 0.4 to 1.0%, respectively, generated when a wafer is cleaned in the process of manufacturing a semiconductor device. . In this example, as shown in FIG. 1, mixed wastewater obtained by mixing TMAH-containing wastewater and APM is fed into a distillation column and continuously distilled to recover ammonia as ammonia vapor or an aqueous ammonia solution. Examples of distillation conditions are shown below. Supply temperature of mixed wastewater: normal temperature Pressure of distillation column: 0.12 MPa Column bottom temperature of distillation column: 103 ° C. Column top temperature of distillation column: 48 ° C. Reflux ratio: 2.4

Next, the ammonia-free mixed wastewater obtained from the bottom of the distillation column is fed into a multi-stage evaporator, and TM
Continuous evaporation and concentration at a temperature at which AH does not decompose.
Examples of conditions for evaporation concentration are shown below. Number of stages of evaporator: 2 stages Pressure of evaporator: 150 to 200 Torr Temperature of evaporator: 60 ° C to 70 ° C Concentration of TMAH in concentrated TMAH-containing wastewater: 18% by weight

In this embodiment, TMAH-containing wastewater and AP
The mixed wastewater obtained by mixing M and M is treated as described above,
The volume of concentrated wastewater could be reduced to about 2% of the original wastewater amount. The concentrated wastewater obtained can be further evaporated to dryness to reduce its volume, or can be completely treated by wet combustion.

Second Embodiment The second embodiment is the same wastewater as that of the first embodiment, that is, contains TM.
FIG. 2 is a flowchart showing a process flow of a wastewater treatment method according to an embodiment of the present invention, which is one example of an embodiment in which the second invention method is applied to the treatment of AH wastewater and APM.
In this example, as shown in FIG. 2, first, in the same manner as in Embodiment 1, mixed wastewater obtained by mixing TMAH-containing wastewater and APM is fed into a distillation column, and continuously distilled to obtain ammonia. Is recovered as ammonia vapor. Next, the mixed wastewater containing no ammonia obtained from the bottom of the distillation column is fed into a multi-stage evaporator and continuously evaporated and concentrated at a temperature at which TMAH is not decomposed.

Next, the recovered mixed wastewater mixed with ammonia is transferred to a supercritical water reactor, where it is decomposed into nitrogen, carbon dioxide and water by a supercritical water reaction. Examples of conditions for the supercritical water reaction are shown below. Reactor temperature: 600 ° C. Reactor pressure: 25 MPa On the other hand, in order to condense and recover the water vapor evaporated in the process of evaporating and concentrating, for example, to use it as raw water for producing pure water required in the semiconductor device manufacturing process. , And water is sent to the pure water production equipment.

The supercritical water reaction is performed by various types of supercritical water reactors. The supercritical water reactor 10 used in the present embodiment will be described with reference to FIG. The supercritical water reactor 10 is an example of a modal process type supercritical water reactor which is one of the basic types of the supercritical water reactor, and includes a vertical reaction vessel 12.
A supercritical water region 14 in which a condition equal to or higher than the critical point of water, that is, a supercritical condition is maintained, is located above the water, and a fluid to be treated is introduced into the supercritical water region 14. In the present embodiment, the fluid to be treated is a mixed fluid of ammonia and concentrated wastewater. Chlorine compounds in organic matter contained in the fluid to be treated,
When an acid-forming substance such as a sulfur compound is contained, an acid is generated by the supercritical water reaction and corrodes the reaction vessel 12, so that the acid is neutralized by a neutralizing agent and converted into a salt. In this case, usually, a subcritical water region 18 maintained at a temperature lower than the critical temperature of water is formed at a lower portion of the reaction vessel 12 through an interface 16 with the supercritical water region 14, and the generated salt is formed. Transfer from the supercritical water region 14 to the subcritical water region and redissolve it,
It is discharged together with subcritical wastewater as described below. Supercritical water is retained in the supercritical water region 14 of the reaction vessel 12, and subcritical water is retained in the subcritical water region 18 via the interface 16.

An inflow pipe 20 is connected to an upper portion of the reaction vessel 12, and a fluid for performing a supercritical water reaction flows into the supercritical water region 14. The inflow pipe 20 has a fluid line 22 for supplying a fluid to be treated having an organic substance to be treated by a supercritical water reaction, an air line 24 for supplying air as an oxidizing agent for oxidizing the organic substance, and supercritical water. A supercritical water line 26 for supplying supercritical water to the region joins. Reaction vessel 1
2, a processing fluid line 30 is further connected to
The organic matter in the fluid to be treated mainly becomes water and carbon dioxide by the supercritical water reaction, and flows out from the supercritical water region 14 through the treatment fluid line 30 together with the treatment fluid. When the organic substance has a chlorine-based compound or the like that generates an acid, a neutralizing agent line 28 for adding an alkali neutralizer to the processing target fluid is connected to the processing target fluid line 22 in order to neutralize the generated acid. In addition, a subcritical water region 18 for transferring the salt generated by the neutralization is formed. Subcritical water area 1
When forming 8, the subcritical water line 32 and the subcritical drainage line 34 are connected to the lower part of the reaction vessel 12, and the subcritical water line 32 supplies subcritical water to the subcritical water region 18,
The subcritical drain line 34 discharges the subcritical water in which the salt generated by the supercritical water reaction and the neutralization reaction is dissolved or suspended from the subcritical water region 18 as subcritical drainage.

In order to maintain the supercritical water reaction stably,
It is necessary to maintain the supercritical water region 14 of the reaction vessel 12 at a temperature of about 600 ° C. and a pressure of about 25 MPa. Therefore, in order to maintain the temperature and pressure conditions, as shown in FIG.
And a gas-liquid separation tank 40 are sequentially provided, and a pressure reducing valve 38 is provided.
Adjusts the flow rate while reducing the processing fluid while the valve opening is adjusted by the pressure control device 42. Further, although not shown, the fluid to be treated, air and supercritical water are supplied to the fluid line 22, the air line 24, and the supercritical water line 26 to a predetermined temperature, and the pressure is increased to a predetermined pressure. A heating device, a compressor and a booster pump are provided.

Embodiment 3 This embodiment is the same as the wastewater of Embodiment 1, that is, TM-containing water.
FIG. 4 is one example of an embodiment in which the third invention method is applied to the treatment of AH wastewater and APM, and FIG. is there. In this method, the pH of the APM is adjusted by adding an alkali, for example, an aqueous solution of NaOH, and the pH-adjusted APM is sent to a distillation column, and is continuously distilled to recover ammonia as ammonia vapor. Examples of distillation conditions are shown below. APM pH value: 11 to 12 APM supply temperature: normal temperature Distillation column pressure: 0.12 MPa Distillation column bottom temperature: 103 ° C. Distillation column top temperature: 48 ° C. Reflux ratio: 2.4 Ammonia was recovered The remainder flows out from the bottom of the distillation column as water containing inorganic impurities, and is treated by an ordinary wastewater treatment device.

On the other hand, the TMAH-containing wastewater is fed into a multistage evaporator-type concentrator, and is continuously evaporated and concentrated at a temperature at which TMAH is not decomposed. Examples of conditions for evaporation concentration are shown below. Number of stages of evaporator: 2 stages Pressure of evaporator: 150 to 200 Torr Temperature of evaporator: 60 ° C to 70 ° C Concentration of TMAH in concentrated TMAH-containing wastewater: 18% by weight

Next, the recovered ammonia and the concentrated TMAH-containing wastewater are mixed and transferred to a supercritical water reactor 10 having the same configuration as that of the second embodiment.
Decomposes into nitrogen, carbon dioxide and water. Examples of conditions for the supercritical water reaction are shown below. Reactor temperature: 600 ° C. Reactor pressure: 25 MPa On the other hand, water vapor evaporated in the process of evaporating and condensing is condensed and recovered and used, for example, as raw water for producing pure water required in the process of manufacturing semiconductor devices. For this purpose, water is sent to a pure water production system.

[0025]

According to the first method of the present invention, treated wastewater containing a low concentration of an organic compound having a higher boiling point than water such as TMAH as a main solute component and cleaning wastewater containing a low concentration of ammonia are mixed. By collecting and further concentrating, two types of wastewater having different properties can be treated in the same process to greatly reduce the volume, and wastewater containing ammonia can be treated safely and easily. Further, according to the second invention method, the concentrated wastewater obtained by concentration according to the first invention method is efficiently and completely treated by a supercritical water reaction to be converted into a safe substance which does not cause a problem of environmental pollution. Can be. Further, according to the third invention method, TMAH is used as the main solute component.
By separately pretreating treated wastewater containing organic compounds having a higher boiling point than water at a low concentration and washing wastewater containing ammonia at a low concentration, the wastewater is completely treated efficiently by supercritical water reaction, It can be converted to a safe substance that does not cause pollution problems. By applying the method of the present invention to wafer processing wastewater and wafer cleaning wastewater each having a low concentration and dissolving an organic solute component discharged in the process of manufacturing a semiconductor device, no secondary waste treatment is required. To a level, wastewater can be treated efficiently.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a process flow of a first embodiment of a wastewater treatment method according to the present invention.

FIG. 2 is a flowchart showing a process flow of a second embodiment of the wastewater treatment method according to the present invention.

FIG. 3 is a flow sheet showing a configuration of an example of a supercritical water reactor.

FIG. 4 is a flowchart showing a process flow of a third embodiment of the wastewater treatment method according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 supercritical water reactor 12 vertical reaction vessel 14 supercritical water region 16 interface 18 subcritical water region 20 inflow pipe 22 fluid line to be treated 24 air line 26 supercritical water line 28 neutralizer line 30 treatment fluid line 32 Supercritical water line 34 subcritical drainage line 36 cooler 38 pressure reducing valve 40 gas-liquid separation tank 42 pressure controller

Claims (5)

[Claims] 1. A treatment method for treating an alkaline treatment wastewater containing an organic compound having a higher boiling point than water as a main solute component and an inorganic washing wastewater containing ammonia in the same process, wherein the treatment wastewater and the washing wastewater are separated. A method for treating wastewater, comprising: an ammonia recovery step of recovering ammonia by distilling mixed wastewater formed by mixing; and a concentrating step of concentrating the mixed wastewater from which ammonia has been recovered to obtain concentrated wastewater. 2. The method according to claim 1, further comprising a supercritical water reaction step of decomposing the obtained concentrated wastewater and ammonia into nitrogen, carbon dioxide gas and water mainly by a supercritical water reaction, following the concentration step. Wastewater treatment method as described. 3. A method for treating treated wastewater containing an organic compound having a higher boiling point than water as a main solute component and inorganic cleaning wastewater containing ammonia, wherein the treated wastewater is concentrated to obtain concentrated treated wastewater. Process, adding alkali to the washing wastewater to adjust the pH to 7 or more,
Wastewater characterized by having an ammonia recovery step of recovering ammonia by distillation, and a supercritical water reaction step of mainly decomposing the obtained concentrated wastewater and ammonia into nitrogen, carbon dioxide and water by a supercritical water reaction Processing method. 4. The treatment wastewater is mainly composed of (C) as an organic compound generated when a wafer is treated in a semiconductor device manufacturing process.
H ₃ ) ₄ Wastewater containing NOH, and inorganic cleaning wastewater
NH wafer in the manufacturing process of the semiconductor device ₄ OH and H ₂ O ₂
The wastewater treatment method according to any one of claims 1 to 3, wherein the wastewater is wastewater generated by washing with washing water containing: 5. The method according to claim 1, wherein in the step of obtaining the concentrated wastewater or the concentrated wastewater, the mixed wastewater in which the treated wastewater or the ammonia is recovered is concentrated by an evaporation method, and the evaporated water is recovered. The method for treating wastewater according to any one of the preceding claims.