JPH0924379A - Treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method enable to efficiently decompose and treat an org. nitrogen-containing compd. such as quaternary ammonium compd. and an amine similar to the quaternary ammonium compd. within a short period by using a simple treating device without affecting on an environment and enable to efficiently and stably remove a nitrogen component in a waste water. SOLUTION: As first, the concn. of the org. nitrogen-containing compd. in the waste water 1 containing the org. nitrogen-containing compd. such as quaternary ammonium compd. and amine similar to the quaternary ammonium compd is adjusted 2, and after adding peroxodisulfate to this pre-treated waste water 3, the org. nitrogen-containing compd. is decomposed by irradiating UV rays. Then, nitrous acids or hypchlorous acids are added 6 to the primary treated water 5 containing a decomposition product of the org. nitrogen-containing compd., and the nitrogen-containing compd. in the decomposition product is decomposed further to remove nitrogen component as a gaseous nitrogen.

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 waste water containing organic nitrogen-containing compounds such as quaternary ammonium compounds.

[0002]

2. Description of the Related Art Quaternary ammonium compounds have been widely used as organic synthesis reagents, catalysts, surface modifiers, etc. in recent years, but in recent years, they have strong penetrability, little residual property during washing, and are easily Attention has been paid to properties such as high-purity products, and they have come to be used as a developing solution or a cleaning solution in a semiconductor manufacturing process. In particular, it is considered to be an optimum substance for dissolving and removing indenecarboxylic acid generated when a naphthoquinonediazide derivative contained in a high-resolution positive photoresist is photolyzed.

Recently, due to an increase in semiconductor production and a complicated manufacturing process, tetramethylammonium hydroxide (TMAH) and choline ([HOCH ₂ CH ₂ N (CH ₃ ) ₃ ] ⁺ O) are produced.
The amount of quaternary ammonium compounds such as H ⁻ ) is rapidly increasing, and accompanying this, the amount of wastewater containing quaternary ammonium compounds is also increasing. The quaternary ammonium compound contains nitrogen, and if it is directly discharged into a river or the like, it may cause eutrophication in lakes and oceans and cause red tides, so it is necessary to perform some treatment.

As a method for treating the wastewater containing the quaternary ammonium compound as described above, there are known a treatment method using microorganisms such as an activated sludge method and a method of concentrating and incinerating. However, in the former method, the process is complicated and the equipment is too large, and the wastewater cannot be swiftly treated because the treatment reaction is slow.Because microorganisms are handled, it is necessary to pay close attention to the operational management of the wastewater composition and concentration. It has problems such as having to do it. Further, in the latter method, wastewater is concentrated by using a reverse osmosis membrane, an ion exchange resin or the like and then incinerated, but there is a problem that gas treatment of nitrogen oxides generated at this time is required.

[0005]

As described above, the fourth problem
In the treatment of wastewater containing organic nitrogen-containing compounds such as high-grade ammonium compounds, the activated sludge method has problems that the treatment facility is too large and the treatment speed is slow, and that operation management is complicated. The method had problems such as the need for gas treatment.

The present invention has been made in order to solve such a problem, and is capable of treating organic nitrogen-containing compounds such as quaternary ammonium compounds and amines similar thereto with simple treatment equipment and in the surrounding environment. To provide a wastewater treatment method capable of efficiently decomposing in a short time without affecting the environment, etc., and efficiently and stably removing nitrogen components in wastewater. It is an object.

[0007]

Means and Actions for Solving the Problems The method for treating wastewater according to the present invention is, when treating wastewater containing an organic nitrogen-containing compound, irradiating ultraviolet rays after adding peroxodisulfate to the wastewater, A first decomposition step of decomposing the organic nitrogen-containing compound, and a second decomposition step of further decomposing a nitrogen-containing compound among decomposition products of the organic nitrogen-containing compound to remove nitrogen as nitrogen gas. It is characterized by having and.

The wastewater treatment method of the present invention is a method of treating wastewater containing an organic nitrogen-containing compound, and examples of the organic nitrogen-containing compound to be treated include quaternary ammonium compounds and amines similar thereto. At least one selected from the following. Fourth to be processed
Examples of the quaternary ammonium compound include tetramethylammonium hydroxide (TMAH), tetrabutylammonium hydroxide (TBAH), choline ([HOCH ₂ CH ₂ N (CH ₃ )).
_3] ⁺ OH ^-) quaternary ammonium or its sulfate hydroxide such as hydrochloride, inorganic salts nitrate, and organic salts such as acetate salts. The amines to be treated include aliphatic amines such as trimethylamine, dimethylamine, ethylmethylamine and ethanolamine, aromatic amines such as aniline and o-toluidine, and their sulfates, hydrochlorides, nitrates, etc. Inorganic salts, organic salts such as acetate, and the like. The organic nitrogen-containing compound to be treated, such as a quaternary ammonium compound and amines, may be present in the wastewater alone or as a mixture of two or more kinds.

The concentration of the organic nitrogen-containing compound in the wastewater is
It is preferably in the range of 0.5 to 10 g / l. In particular, if the concentration of the organic nitrogen-containing compound is too low, the proportion of nitrogen oxides, especially nitrate ions in the decomposition products after the ultraviolet irradiation treatment becomes large, and the subsequent decomposition step (second decomposition step) becomes difficult. At the same time, since the treatment efficiency is lowered and the treatment equipment and the treatment cost are increased, it is preferable to concentrate to the above concentration range by using a separation membrane such as a reverse osmosis membrane or an ion exchange resin. The material of the reverse osmosis membrane to be used depends on the properties of drainage, but examples thereof include acetyl cellulose type and aromatic polyamide type. If the wastewater to be treated interferes with the concentration operation by a reverse osmosis membrane or the like, or if there are substances that reduce the concentration efficiency, such as colloidal organic substances or inorganic substances, the substances are aggregated and precipitated, Pretreatment such as removal by a coagulation filtration method or an ultrafiltration membrane method may be performed. Further, when the pH of the wastewater affects the concentration operation by the reverse osmosis membrane or the like, the pH of the wastewater may be adjusted in advance.

In the wastewater treated according to the present invention,
Components other than the organic nitrogen-containing compound as described above, for example, an organic solvent such as alcohol, a compound such as indenecarboxylic acid derived from a photosensitive resin such as a naphthoquinonediazide derivative may coexist and can be decomposed at the same time. In some cases, if these other components interfere with the decomposition treatment of the organic nitrogen-containing compound, it is preferable to remove them in advance.

In the wastewater treatment method of the present invention, first, as a first decomposition step, wastewater containing an organic nitrogen-containing compound such as the above-mentioned quaternary ammonium compound and amines,
For example, after adding peroxodisulfates such as potassium peroxodisulfate (K ₂ S ₂ O ₈ ) and sodium peroxodisulfate (Na ₂ S ₂ O ₈ ), ultraviolet rays emitted from an ultraviolet lamp or the like are irradiated. Thus, when ultraviolet rays are irradiated after adding peroxodisulfuric acid, peroxodisulfuric acid produces active species rich in oxidation reaction as described below, and this active species removes organic nitrogen-containing compounds in wastewater. It oxidizes and decomposes the organic substances it contains.

[0012]

Embedded image The amount of the above-mentioned peroxodisulfate added to the wastewater is
The amount is preferably 2.5 to 20 times the mol of the organic nitrogen-containing compound in the waste water. When the amount of peroxodisulfate added is within the above range, the proportion of ammonia, low molecular weight amines, etc. in the decomposition products generated by the ultraviolet irradiation treatment becomes very large, and the decomposition step (second step) thereafter. Can be easily implemented. That is, in the wastewater treatment method of the present invention, it is important to mainly produce ammonia, low molecular weight amines or the like as a decomposition product of the organic nitrogen-containing compound in the first decomposition step.

For example, if the amount of peroxodisulfate added exceeds 20 times the molar amount of the organic nitrogen-containing compound, the nitrogen oxide NO _x occupies the decomposition products generated by the ultraviolet irradiation treatment.
Ratio increases. Nitrogen oxide NO _x can be reduced to nitrogen gas by using a strong reducing agent, but this causes an increase in processing cost and processing time. On the other hand, ammonia, low molecular weight amines and the like can be chemically decomposed, and the nitrogen content can be easily removed as nitrogen gas. If the amount of peroxodisulfate added is less than 2.5 times the molar amount of the organic nitrogen-containing compound, the treatment rate of the organic nitrogen-containing compound will be reduced.

That is, the decomposition efficiency and the type of decomposition products of the organic nitrogen-containing compound by the ultraviolet irradiation treatment largely depend on the concentration of the organic nitrogen-containing compound in the wastewater and the added amount of peroxodisulfate, and When both the organic nitrogen-containing compound concentration and the peroxodisulfate concentration in the product are high, the decomposition efficiency of the organic nitrogen-containing compound can be increased and the proportion of ammonia and low molecular weight amines in the decomposition products Can be made larger, in contrast to nitrogen oxides
The proportion of NO _x decreases. Therefore, it is desirable to satisfy the concentration of the organic nitrogen-containing compound in the wastewater and the amount of the peroxodisulfate added in the wastewater within the above-mentioned range.

In the first decomposition step of the present invention, as described above, the organic nitrogen-containing compound in the waste water is mainly composed of low molecular weight amines such as monomethylamine and ammonia, and lower alcohols such as methanol. Be disassembled. Among these decomposition products, nitrogen-containing compounds such as low molecular weight amines and ammonia are further decomposed in the second decomposition step, and the nitrogen content is removed as nitrogen gas.

The above-mentioned decomposition treatment of nitrogen-containing compounds such as low molecular weight amines and ammonia uses at least one of nitrous acid (nitrous acid and its salt) and hypochlorous acid (hypochlorous acid and its salt). It is preferable to carry out. For example, since the waste water after the irradiation with ultraviolet rays is in an acidic state of about pH 0 to 7, when a nitrite salt such as sodium nitrite is added thereto, a reaction occurs and nitrous acid is produced. This nitrous acid decomposes low molecular weight amines such as monomethylamine to produce nitrogen gas, lower alcohol, water and the like. Similarly, when a hypochlorite such as sodium hypochlorite is added, ammonia is oxidatively decomposed to generate nitrogen gas and the like.

Since the products produced by the decomposition of the organic nitrogen-containing compound are mainly low molecular weight amines and ammonia, it is preferable to add nitrites and hypochlorous acid together. Further, the nitrites and the hypochlorous acid may be added at the same time, but it is preferable to add them separately. The amount of nitrites and hypochlorous acid added is based on the low molecular weight amines and ammonia generated by the decomposition of organic nitrogen-containing compounds.
It is preferably about 2 to 25 equivalents.

In the above-mentioned second decomposition step, the nitrogen gas generated by the addition of nitrites and hypochlorous acid may be removed by natural deaeration. For example, aeration such as bubbling with air may be used. By doing so, it is possible to quickly remove it from the wastewater.

As described above, according to the method for treating wastewater of the present invention, the organic nitrogen-containing compound such as a quaternary ammonium compound or amine similar to the quaternary ammonium compound contained in the wastewater is used as the first component.
In the decomposition step of, the low molecular weight amines, ammonia, etc. are mainly converted, and then the low molecular weight amines, ammonia, etc. are removed as nitrogen gas in the second decomposition step, so that the nitrogen content in the wastewater can be easily treated. It can be efficiently reduced with equipment in a short time.

[0020]

EXAMPLES Next, examples of the present invention will be described.

Example 1 The process of treating wastewater according to this example will be described with reference to FIG. In this example, wastewater in the semiconductor manufacturing process mainly containing TMAH used in the developing process of the silicon wafer was treated. The property of this drainage is that the TMAH concentration is 0.1
The concentration was 2g / l, total nitrogen concentration was 0.018g / l, and pH was 9.3. In addition to TMAH, the wastewater to be treated contained organic substances and 2-propanol which are considered to be derived from the photosensitive resin. First, the TMAH concentration of the wastewater 1 to be treated is 1.1 g / l and the total nitrogen concentration is 0.17 g in a concentration tank 2 using a reverse osmosis membrane.
It concentrated so that it might become / l. Next, 3500 ml of this pretreated (concentrated) treated wastewater was introduced into the ultraviolet decomposition tank 4. A low-pressure mercury lamp with an output of 30 W is installed inside the ultraviolet decomposition tank 4 so that it can irradiate ultraviolet rays having a main wavelength of 254 nm. In the ultraviolet decomposition tank 4, first, 9 g of potassium peroxodisulfate was added to the pretreated wastewater 3, that is, TM in the pretreated wastewater 3
Five times the amount of AH moles was added and the treated wastewater 3 was irradiated with the above ultraviolet rays for 1 hour while stirring.

Next, 1 was decomposed in the ultraviolet decomposition tank 4
Transfer the next treated water 5 to the chemical denitrification tank 6, and add 5g of sodium nitrite.
Was added, and the mixture was stirred while bubbling with air. about
After bubbling for 15 minutes, sodium hypochlorite was added.
5 g was added and stirred for 15 minutes while bubbling with air. Then, the treated water 7 was discharged from the chemical denitrification tank 6.

Treated water 7 obtained by such a two-step treatment
Was examined by using an ion chromatography method or the like.
As a result, the TMAH concentration was 0.095 g / l, which was about 9% of the concentration before treatment (concentration after pretreatment). The total nitrogen concentration was 0.025 g / l, which was about 15% of the concentration before treatment (concentration after pretreatment), confirming that the nitrogen content was significantly reduced.

Example 2 In Example 1 above, TMA after concentration of the wastewater 1 to be treated is performed.
Wastewater treatment was performed in the same manner as in Example 1 except that the H concentration (and total nitrogen concentration) and the addition amount of potassium peroxodisulfate were changed. Table 1 shows the TMAH concentration, the amount of potassium peroxodisulfate added, and the reduction rate of the total nitrogen concentration after the treatment in the combination thereof, that is, the TMAH decomposition efficiency and the decomposition product removal efficiency. The reduction rate of the total nitrogen concentration was calculated according to the following formula.

[0025]

[Equation 1]

[Table 1] As is clear from Table 1, particularly excellent treatment efficiency is obtained when the TMAH concentration in the waste water and the addition amount of potassium peroxodisulfate are both high within a predetermined range. Further, it is understood that if the amount of potassium peroxodisulfate added is too large, the reduction rate of the nitrogen content decreases. This is because the proportion of nitrogen oxides in the decomposition products in the first decomposition step increases.

Example 3 First, wastewater mainly containing trimethylamine (N (CH ₃ ) ₃ ) was treated. The properties of this wastewater are as follows: trimethylamine concentration 0.20g / l, total nitrogen concentration 0.051g / l, pH
8.0. Such treated wastewater was concentrated in a concentration tank using a reverse osmosis membrane so that the trimethylamine concentration was 1.6 g / l and the total nitrogen concentration was 0.41 g / l. Next, 500 ml of this pretreated (concentrated) treated wastewater was introduced into the ultraviolet decomposition tank. In the ultraviolet decomposition tank, first, 19 g of potassium peroxodisulfate was added to the pretreated wastewater, that is, 5 times the number of moles of trimethylamine in the pretreated wastewater was added, and the treated wastewater was agitated as in Example 1. The same ultraviolet light was irradiated for 1 hour.

Next, the primary treated water decomposed in the ultraviolet decomposition tank was transferred to a chemical denitrification tank, 10 g of sodium nitrite was added thereto, and the mixture was stirred while bubbling with air. After bubbling for about 15 minutes, sodium hypochlorite 10g
Was added and the mixture was stirred for 15 minutes while bubbling with air.
Then, the treated water was discharged from the chemical denitrification tank.

The properties of the treated water obtained by such a two-step treatment were investigated by using an ion chromatography method or the like. As a result, the trimethylamine concentration was 0.096 g / l, which was about 6% of the concentration before treatment (concentration after pretreatment). In addition, the total nitrogen concentration was 0.040 g / l, which was about 10% of the concentration before treatment (concentration after pretreatment), confirming that the nitrogen content was significantly reduced.

In each of the above embodiments, TMAH
Although the treatment of the wastewater mainly containing trimethylamine and the wastewater mainly containing trimethylamine has been described as an example, the wastewater containing other quaternary ammonium compounds and amines can be similarly treated.

[0030]

As described above, according to the wastewater treatment method of the present invention, the organic nitrogen-containing compound such as a quaternary ammonium compound or similar amines can be efficiently treated with a simple treatment facility / apparatus. In addition, the decomposition treatment can be carried out stably and inexpensively without affecting the surrounding environment and the nitrogen content in the wastewater can be efficiently and stably removed. Therefore, the total nitrogen concentration, which is one of the important indicators of water quality, can be made extremely low, so that it can be safely discharged to rivers and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a wastewater treatment process according to an embodiment of the present invention.

[Explanation of symbols]

 1 ... Treated wastewater 2 ... Concentration tank 3 ... Pretreated wastewater 4 ... UV decomposition tank 5 ... Primary treated water 6 ... Chemical denitrification tank 7 ... Treated water

Claims (1)

[Claims] 1. When treating wastewater containing an organic nitrogen-containing compound, a first decomposition step of decomposing the organic nitrogen-containing compound by irradiating with ultraviolet rays after adding peroxodisulfate to the wastewater, A second decomposition step of further decomposing the nitrogen-containing compound among the decomposition products of the organic nitrogen-containing compound to remove the nitrogen content as nitrogen gas.