JPH10202293A - Method and device for biologically nitrating nitrogen-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently nitrate the nitrogen-contg. waste water discharged from the wet process in the production of electronic parts. SOLUTION: The nitrogen-contg. waste water introduced into a raw water tank 1 is neutralized and reduced respectively in the pH neutralization tank 2 and reduction tank 3 and then flocculated in a flocculating and separating tank 4. The nitration inhibitor contained in the waste water is removed by the flocculation. The treated water freed from the inhibitor is introduced into a nitration tank 5 and nitrated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet processing process for manufacturing integrated circuits such as ICs, LSIs and VLSIs, and a manufacturing process for electronic components such as a liquid crystal display device, that is, an electronic device such as a semiconductor wafer. Wastewater discharged from the process of treating the surface of parts with various chemical solutions such as sulfuric acid, hydrogen peroxide, hydrochloric acid, ammonia water and ultrapure water,
More specifically, a cleaning step, an etching step, a developing step,
Furthermore, the present invention relates to a method and an apparatus for nitrifying wastewater containing wastewater discharged from a stripping step and the like, and particularly containing wastewater containing ammoniacal nitrogen.

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs and liquid crystal display devices are manufactured by introducing impurities, depositing insulators, and forming wirings in predetermined regions on a substrate such as a silicon wafer. It is manufactured by repeating the steps described above. In order to perform various processes on such a predetermined area, a photolithography technique is widely adopted. That is, in the photolithography technology, a photoresist is applied on a substrate, and a desired pattern is exposed by a stepper or the like, and then, development,
By performing a so-called wet process such as peeling, etching, or cleaning, only a predetermined region is exposed, and a predetermined process is performed here.

Here, there are two types of photoresists used for photolithography: a negative type resist in which an irradiated portion is insolubilized by exposure, and a positive type resist in which an irradiated portion is solubilized. As a typical positive type photoresist, a novolak resin containing a photosensitive agent such as o-diazonaphthoquinone is known and widely used.

[0004] Ultrapure water, sulfuric acid, hydrogen peroxide, hydrochloric acid, aqueous ammonia, fuming nitric acid, and the like are used in the above-described steps such as development, peeling, etching, and cleaning. And etching, peeling and the like are performed. A process for treating the surface of an electronic component using a liquid such as a chemical solution or ultrapure water is generally called a wet treatment process. Here, these operations such as chemical cleaning, etching, and peeling are usually performed by immersing electronic components in a tank for storing a chemical,
After a certain period of use, the solution is updated to a new one. Therefore, when the chemical solution is updated, the used chemical solution is discharged. The used chemical solution is released after being subjected to a neutralization treatment, a dilution treatment, and other treatments in accordance with the substance contained therein, but various treatments are required in accordance with the regulations of the discharged water.

For example, from the viewpoint of preventing eutrophication in closed water bodies such as lakes and bays, the emission of nitrogen and phosphorus in wastewater is regulated in some areas. Therefore, it is necessary to remove nitrogen contained in wastewater from the above wet treatment process.

Methods for removing nitrogen from wastewater include (i) a microbial method utilizing the nitrification and denitrification of microorganisms, (ii) a discontinuous point chlorination method utilizing the reaction between ammonia and chlorine, and (i)
ii) Ammonia stripping method using release of ammonia at high pH from water, (iv) ion exchange method using ion exchange resin, and the like are known. Here, (ii) and (iii) cover only ammonium salts, and (iv) cover ammonium salts, nitrates and nitrites. On the other hand, in the microbial method (i), in addition to ammonium salts, organic nitrogen, nitrate, and nitrite can be removed, and nitrogen in wastewater can be removed as nitrogen gas without fear of secondary pollution. Another advantage is that the cost is relatively low. Therefore, it has been widely adopted as a method for removing nitrogen from various nitrogen-containing wastewaters.

Here, the nitrogen removal by the microbial method will be briefly described. This microbial method includes a nitrification step of once oxidizing ammonium nitrogen and organic nitrogen in wastewater to nitric acid or nitrous acid, and a denitrifying step of reducing nitric acid or nitrous acid to nitrogen gas. Then, in the nitrification step and the denitrification step, the following reaction proceeds.

(Nitrification step) NH ₄ ⁺ +1.5 O ₂ → No ₂ ⁻ + H ₂₀ + 2H ⁺ (1) NO ₂ ⁻ +0.5 O ₂ → NO ₃ ⁻ (2) (Denitrification step) 2NO ₂ ⁻ + 6H ⁺ ( (Hydrogen donor) → N ₂ + 2H ₂ O + 2OH ⁻ (3) 2NO ₃ ⁻ + 10H ⁺ (hydrogen donor) → N ₂ + 4H ₂ O + 2OH ⁻ (4) Here, the reactions (1) and (2) in the nitrification step described above. Is a reaction that proceeds under aerobic conditions, and (1)
Nitrosom is a representative bacterium involved in the reaction (2).
onas and Nitrobacter, respectively.

On the other hand, the reactions (3) and (4) in the denitrification step proceed under anaerobic conditions, and the reactions are facultative anaerobic bacteria Pseudomonas and Micrococcu.
s, Hyphomicrobium, Thiobacillus and the like.

Here, the above-mentioned bacteria involved in the nitrification reaction of (1) and (2) are autotrophic bacteria and grow without an organic carbon source. When an organic carbon source is present in wastewater, the organic carbon source is usually oxidatively decomposed by aerobic bacteria. On the other hand, in the (3) and (4) denitrification reactions, a hydrogen donor (organic carbon source) is required to reduce nitric acid and nitrous acid. As a method for supplying the hydrogen donor, a method utilizing organic matter in wastewater, a method of adding a chemical such as methanol, and a method utilizing endogenous respiration of microorganisms are known.

Since the nitrogen removal method using such microorganisms is superior in various points as compared with other removal methods as described above, it can be used for semiconductor integrated circuits such as ICs, LSIs, VLSIs, and liquid crystal display devices. It has also been conventionally used for wastewater containing nitrogen discharged in a wet treatment process in production. Since these wastewaters often have very low pH or contain oxidizing substances such as hydrogen peroxide, they are subjected to pretreatment such as neutralization and reduction of oxidizing substances before being treated with microorganisms. Has been provided.

[0012]

As described above, the nitrogen removal method using microorganisms has various merits, but the treatment of wastewater discharged from the wet treatment process in the production of electronic components, which is the object of the present invention. It was found that the efficiency was not high enough. That is, according to the study of the present inventors, the nitrification rate in the nitrification step is:
For example, it was found that the nitrification rate of ammonia nitrogen in sewage was significantly lower. In recent years, there has been a demand for more efficient nitrogen removal in accordance with stricter emission regulations and the like, and there is a problem that it is desired to more efficiently and stably remove nitrogen in wastewater.

The present inventors conducted various experiments on this point, and as a result, the nitrogen-containing wastewater discharged from the wet treatment process for electronic components as described above, particularly the wastewater from the cleaning step using ammonia, When treating wastewater including wastewater from a washing step using a chemical solution in which sulfuric acid and hydrogen peroxide are mixed, nitrification of ammonia nitrogen is inhibited even if pH neutralization and hydrogen peroxide reduction treatment are performed. It became clear. That is, it has been found that the wastewater discharged from such a wet treatment process contains a substance that inhibits the nitrification reaction, and thus the nitrification efficiency is reduced.

The present invention has been made based on the above recognition, and a method for biologically nitrifying nitrogen-containing wastewater capable of performing effective nitrification treatment on nitrogen-containing wastewater discharged from a wet treatment process in the production of electronic components. It is intended to provide the device.

[0015]

SUMMARY OF THE INVENTION The present invention relates to a method for biologically nitrifying nitrogen-containing wastewater discharged from a wet treatment process in the production of electronic components. The method is characterized in that a biological nitrification treatment is carried out after a nitrification inhibitor contained in waste water is removed by performing a coagulation separation treatment. In this way, by subjecting the wastewater to the coagulation separation treatment, the nitrification inhibitor contained in the wastewater is effectively separated and removed. Therefore, the nitrification rate in the subsequent nitrification treatment can be made sufficiently high, and the effective nitrification treatment can be stably performed.

Further, the wastewater contains ammonia nitrogen.

Further, the wastewater includes a wastewater obtained by treating the above electronic component with a solution containing sulfuric acid and hydrogen peroxide. Further, the wastewater contains a substance having a thiophene structure.

That is, it is widely used that a circuit pattern is formed on a wafer by using a novolak resin as a photoresist in the above-described photolithography process, and then the wafer is washed with a cleaning solution containing sulfuric acid and hydrogen peroxide. Cleaning method. The wastewater by this method often contains a thiophene-structured substance which is considered to be derived from a novolak resin remaining in a very small amount on the wafer. It was presumed to be a nitrification inhibitor. Thus, it has been found that by performing the coagulation separation treatment on such wastewater in advance, the subsequent nitrification treatment can be made efficient and stable.

Further, the present invention is characterized in that the coagulant added to and mixed with the waste water is an iron or aluminum coagulant. It has been experimentally confirmed that the nitrification inhibitor is effectively removed by the coagulation treatment using such an inorganic coagulant.

The present invention is also a biological nitrification apparatus for nitrogen-containing wastewater discharged from a wet treatment process in the production of electronic components, wherein a coagulant is added to the wastewater, mixed, and then solid matter is separated. It is characterized by including a coagulation / separation means for removing a nitrification inhibitor, and a nitrification treatment means for performing a nitrification treatment in aerobic atmosphere on a liquid from which solids are separated by the coagulation / separation means.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the embodiment. Raw water containing cleaning wastewater containing ammonia and cleaning wastewater containing sulfuric acid and hydrogen peroxide discharged from a wet processing process in an LSI or liquid crystal display device manufacturing factory is introduced and stored in the raw water tank 1. Usually, the wastewater contains a substance having a thiophene structure which is considered to be derived from the novolak resin used in the photolithography process. In addition, the wastewater may be further mixed with other wastewater.

Since the wastewater in the raw water tank 1 usually exhibits acidity, the acidic wastewater is introduced into the pH neutralization tank 2 by a raw water pump or the like, and first subjected to a neutralization treatment. That is, this p
A sodium hydroxide (NaOH) solution is supplied to the H neutralization tank 2 to adjust the pH of the waste water to near neutrality. The wastewater neutralized in the pH neutralization tank 2 is then introduced into the reduction tank 3. The reducing tank 3 is supplied with a reducing agent (for example, sodium sulfite or sodium bisulfite), whereby oxidizing substances such as hydrogen peroxide in waste water are reduced. In addition, you may employ | adopt an activated carbon tank as the reduction tank 3, and may remove an oxidizing substance with activated carbon.

The wastewater subjected to such neutralization and reduction treatment is introduced into the coagulation / separation tank 4, where the coagulation / separation treatment is performed. In the present embodiment, PAC (polyaluminum chloride) is added as a flocculant to form flocculated flocs, and then the flocs formed are, for example, precipitated and separated. Not only coagulation sedimentation, coagulation flotation separation,
Coagulation filtration and the like can also be employed. As the coagulant, an iron salt such as ferric chloride or an aluminum salt such as aluminum sulfate is preferably used. In addition, a polymer flocculant is added,
It is also suitable to enhance the agglutination reaction.

In the flocculation / separation tank 4, the treated water from which flocs have been flocculated and separated is introduced into a nitrification tank 5. The nitrification tank 5 includes an aeration tank, a sedimentation separation tank, and a return line for settling sludge, and performs the oxidation treatment (nitrification treatment) of ammonia nitrogen by the aerobic bacteria described above. It is also preferable that the nitrification reaction tank is formed by a fixed bed such as an immersion filter bed or a rotating disk, and the return line is omitted.

The treated water in the nitrification tank 5 is introduced into a denitrification tank 6. The denitrification tank 6 includes a stirring tank in which methanol is added and mixed as a hydrogen donor, a settling tank, and a return line for settling sludge, and oxidizes methanol to reduce nitric acid to nitrogen gas. It is also preferable to cover the denitrification tank 6 to reduce the contact with the atmosphere. Further, it is also preferable that the denitrification tank 6 is filled with a filler, and a fixed bed for growing microorganisms is filled therein. This eliminates the need for a return line. Furthermore, instead of the addition of methanol, endogenous respiration of bacteria or organic matter in wastewater may be used.

As described above, in the present embodiment, the coagulation / separation tank 4 is disposed before the nitrification tank 5. Then, in this coagulation separation tank 4, the nitrification inhibitor contained in the wastewater is removed. Therefore, there is no nitrification inhibitor in the wastewater flowing into the nitrification tank 5, and efficient nitrification can be performed. Although the mechanism of aggregation of the nitrification inhibitor is not clear,
It is considered to be the same as the usual organic or heavy metal removal mechanism. In addition, the nitrification inhibitor, sulfuric acid / novolak resin
It is generated by causing a chemical change in a cleaning step using hydrogen peroxide, and is presumed to be a substance having a thiophene structure.

[Other Configurations] In the process of manufacturing semiconductor integrated circuits and liquid crystal display devices, fluorine-based wastewater is generated in addition to the above-mentioned wastewater containing nitrogen (nitrogen-based wastewater). This is because hydrogen fluoride is often used for etching and the like. For the removal of fluorine, a coagulation treatment using calcium ions is usually employed.

Although the fluorine-based wastewater and the nitrogen-based wastewater containing ammonia are generated from separate steps, they may be treated as a mixed wastewater obtained by mixing these wastewaters. However, the treatment of fluorine with calcium ions removes fluorine by crystallizing calcium fluoride. Therefore, the higher the fluorine concentration in the wastewater, the better the treatment efficiency.

Therefore, the wastewater generated from the wet treatment process in the production of electronic components is more likely to be removed than by mixing fluorine-based wastewater and nitrogen-based wastewater to reduce the fluorine concentration in the wastewater by dilution and then removing fluorine. It is preferable to collect the wastewater separately and perform crystallization treatment with calcium ions only on the fluorine-based wastewater.

That is, as shown in FIG. 2, only the fluorine-based wastewater is introduced into the crystallization tank 12 through the raw water tank 11, where fluorine is removed as calcium fluoride. And
This treated water is introduced into, for example, a coagulation / separation tank 4 for nitrogen-based wastewater, and then treated together. By such processing,
Both fluorine-based wastewater and nitrogen-based wastewater can be effectively treated.

When a relatively large amount of organic matter is contained in the wastewater, an aerobic biological treatment for removing the organic matter is performed on the wastewater after the coagulation treatment, followed by a nitrification treatment. Good.

[0033]

【Example】

Example 1 A nitrification experiment by a batch test was performed using wastewater discharged from a washing process of an LSI manufacturing plant having the following water quality.

PH: 1.5 NH ₄ —N: 50 mg / L NO ₃ —N: 50 mg / L TOC: 1 mg / L H ₂ O ₂ : 3000 mg / L H ₂ SO ₄ : 6000 mg / L After adjusting and performing reduction treatment with sodium bisulfite, NaHC was used as a pH buffer.
O ₃ : 2000 mg / L was added to prepare a sample for the nitrification treatment experiment.

This sample was directly used for the nitrification treatment (without aggregation), and the supernatant liquid after aggregation treatment under the following conditions was used for the nitrification treatment (with aggregation).

Addition amount of 10% PAC solution: 200 mg / L Aggregation pH: 7 Rapid stirring time: 5 minutes Addition amount of polymer flocculant (Orfloc AP-1 (trade name of Organo Corporation)): 4 mg / L Slow stirring Time: 15 minutes Standing time: 30 minutes Sample 5 thus obtained (without aggregation) (with aggregation)
00 mL was placed in a beaker, and sludge from a nitrification tank treating sewage was added to the beaker and seeded so as to be 200 mg SS / L. Then, this was aerated, the ammonia nitrogen concentration was measured every hour, and the nitrification rate per unit SS (suspended solid matter = microorganism) per hour was determined from the decrease rate of ammonia nitrogen. Shown in

[0037]

[Table 1] Maximum nitrification rate (mg-N / g-ss / h) No aggregation 0.97 With aggregation 9.3 From this, it can be seen that the nitrification rate in the nitrification treatment can be increased almost 10 times by performing the aggregation treatment. Recognize.

The floc separated when the waste water was coagulated by PAC was subjected to infrared absorption analysis, and it was confirmed that the floc contained a thiophene-structured substance.

Example 2 Using a fixed-bed nitrification reactor having an effective volume of 0.3 m ³ , a biological nitrification experiment of wastewater discharged from a washing process in an LSI manufacturing plant was performed. The filler is a flat non-woven fabric described in JP-A-8-164400, in which a corrugated non-woven fabric is adhered onto the flat non-woven fabric so that the opening is in the vertical direction. Using. Raw water and aerated air were supplied from the lower part of the reactor, and the amount of aerated air was 50 NL (normal liter) / min.

The water quality of the waste water was as follows.

PH: 0.5 to 1.5 NH ₄ —N: about 50 mg / L on average NO ₃ —N: about 50 mg / L on average TOC: 0.5 to 2.0 mg / L H ₂ O ₂ : 30 to 5000 mg / L H ₂ SO ₄ : 1500 to 6000 mg / L This wastewater was previously neutralized with pH and passed through the activated carbon layer at an SV (space velocity) of 5 h ⁻¹ to confirm that H ₂ O ₂ was removed. did. The pH was adjusted so that the treated water at the outlet of the reactor was around 7. For Run 1, the waste water after passing through the activated carbon layer was directly used, and for Run 2, the supernatant liquid was used after the waste water after passing through the activated carbon layer was aggregated under the following conditions.

Addition amount of 10% PAC solution: 200 mg / L Aggregation pH: 7 Rapid stirring time: 5 minutes Addition amount of polymer flocculant (Orfloc AP-1 (trade name of Organo Corporation)): 4 mg / L Slow stirring Time: 15 minutes Standing time: 30 minutes The flow rate of the treated water was gradually increased, and the change in the ammonia nitrogen concentration of the treated water was measured. FIG. 2 shows the relationship between the volumetric load of ammonia nitrogen and the nitrification rate based on the results.

The volume load and the nitrification rate were determined as follows.

(Volume load) = (raw water ammonia nitrogen concentration) × (raw water supply amount) ÷ (reactor effective volume) (nitrification rate) = {(raw water ammonia nitrogen concentration) − (treatment water ammonia nitrogen concentration)} × (Raw water supply) ÷
(Reactor effective volume) In FIG. 3, ● represents the result of Run 1 and １ represents the result of Run 2. In Run 1, since the nitrification rate of ammoniacal nitrogen was not stable, the plots varied, but it was determined that the maximum nitrification rate was about 0.2 kg-N (nitrogen) / m ³ / d. On the other hand, in Run2, 0.6 kg-N
The plot varies with a high load of / m ³ / d or more, but is stable below that. The maximum nitrification rate is 0.
It is determined to be 7 kg-N / m ³ / d. Than this,
It was confirmed that the nitrification rate was increased by about 3.5 times by performing the aggregation treatment.

The floc separated during the aggregation treatment in Run 2 was subjected to infrared absorption analysis.
It was confirmed that this floc contained a substance having a thiophene structure.

[0046]

As described above, according to the present invention,
By subjecting waste water from a wet treatment process in the production of electronic components to a coagulation treatment to remove a nitrification inhibitor, the subsequent nitrification treatment can be made efficient.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of an embodiment.

FIG. 2 is a block diagram showing another configuration.

FIG. 3 is a diagram showing the relationship between the volumetric load of ammonia nitrogen and the nitrification rate.

[Explanation of symbols]

1 Raw water tank, 2 pH neutralization tank, 3 Reduction tank, 4 Coagulation separation tank, 5 Nitrification tank, 6 Denitrification tank.

Claims (6)

[Claims] 1. A biological nitrification method for nitrogen-containing wastewater discharged from a wet treatment process in the production of electronic components, wherein a coagulant is added to and mixed with the wastewater, and thereafter, a coagulation separation process for separating a solid substance is performed. A biological nitrification method for nitrogen-containing wastewater, wherein a biological nitrification treatment is performed after removing a nitrification inhibitor contained therein. 2. The method according to claim 1, wherein said wastewater includes wastewater obtained by treating electronic components with a solution containing sulfuric acid and hydrogen peroxide. . 3. The method according to claim 1, wherein the wastewater contains ammonia nitrogen as a nitrogen component. 4. The method according to claim 1, wherein said wastewater contains a thiophene-structured substance. 5. The method according to claim 1, wherein the coagulant added to and mixed with the wastewater is an iron- or aluminum-based coagulant. Nitrification method. 6. A biological nitrification apparatus for nitrogen-containing wastewater discharged from a wet treatment process in the production of electronic components, comprising adding and mixing a flocculant to the wastewater, and thereafter separating a solid substance to remove a nitrification inhibitor. A biological nitrification apparatus for nitrogen-containing wastewater, comprising: a coagulation / separation means for removing; and a nitrification treatment means for performing nitrification treatment in an aerobic atmosphere on a liquid from which solids have been separated by the coagulation / separation means.