JPH06233997A - Ultrapure water production method - Google Patents

Abstract

PURPOSE:To reduce TOC(total organic carbon) in superhigh purity water by allowing untreated water containing urea to pass through a purity water prepara tion device after treating the untreated water biologically. CONSTITUTION:An organic component such as urea is decomposed by a biological treatment device 1 using an organic component in recovered water. This biotreated water is separated by membrane in a UF or MF membrane separation device 2. Next, the pretreated water treated throughout a pretreatment device A is separation-treated using a two-stage RO membrane using a first and a second RO membrane separation device 3, 4 in a primary purity water preparation device B, and is subjected to ion exchange using an ion exchange device 5. Next, TOC contained in the treated water is ionized or decomposed using a low voltage ultraviolet oxidation device 7 in a secondary purity water preparation device C, and the ionized organic substances are removed using an ion exchange device 8. Further, the ionized organic substences are membrane- separated using a UF membrane separation device 9. Thus, it is possible to reduce the TOC level in the superhigh purity water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ultrapure water, and more particularly to a method for producing ultrapure water capable of significantly reducing TOC (total organic carbon) in ultrapure water produced. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, an ultrapure water production system for producing ultrapure water from raw water such as city water, groundwater, and industrial water is basically a pretreatment device, a primary pure water production device, and a secondary water production device. It consists of pure water production equipment. Among them, the pretreatment device is
Floating and filtering equipment. The primary pure water production system has 2
A reverse osmosis membrane separation device and a mixed bed ion exchange device, or an ion exchange pure water device and a reverse osmosis membrane separation device, and the secondary pure water production device is a low pressure ultraviolet oxidation device,
It is composed of a mixed bed type ion exchange device and an ultrafiltration membrane separation device.

Among the unit devices constituting the ultrapure water production system, those for reducing TOC components in raw water by means of separation, adsorption, decomposition, etc. are reverse osmosis membrane separation devices, ion exchange pure water devices, It is a low-pressure UV oxidizer. The TOC reduction mechanism in each unit device is as follows. Reverse osmosis membrane separation device: A filtration method using a reverse osmosis membrane, which removes ionic and colloidal TOC. Ion exchange deionized water device: Removes TOC components adsorbed on or ion exchanged with ion exchange resin. Low-pressure UV oxidizer: 1 emitted from a low-pressure UV lamp
85 nm UV light is used to remove TOC from organic acids and CO ₂
Disassemble until. The decomposed organic matter is removed by the ion exchange resin in the subsequent stage. Particularly, it is used for decomposing volatile organic substances. By the way, TOC exists in about 2 to 5 ppb in the ultrapure water produced by the conventional ultrapure water producing apparatus. As a method for further reducing TOC in the ultrapure water, a means such as multi-stage installation of a reverse osmosis membrane separation device and an increase in the ultraviolet irradiation amount of a low-pressure ultraviolet oxidation device can be considered.
It was confirmed that TOC in the ultrapure water could hardly be further reduced by such means.

As a result of studying the factors that hinder the reduction of TOC, urea (NH ₂ CONH ₂ ) is a component that cannot be removed by the current ultrapure water production equipment, and moreover, it is present in raw water (city water, industrial water, etc.). It was found that urea was present in the range of tens to hundreds of ppb.

The concentration of urea contained in ultrapure water was measured by concentrating (20 to 30 times) the ultrapure water currently obtained, and as a result, 50% or more of TOC of ultrapure water was obtained. It turned out that urea occupies.

As described above, it is difficult for the current ultrapure water producing apparatus to remove urea existing in raw water, and this is because T in the ultrapure water is removed.
It has been clarified that this is a cause of hindering the reduction of OC.
As a result of further studies to remove this urea, it was found that the biological treatment means is suitable as a method for reducing the urea present in the raw water. Based on such knowledge, the applicant of the present invention has stated that in an ultrapure water production system including a raw water pretreatment system, a primary pure water production system and a secondary pure water production system, the pretreatment system includes a biological treatment means. A patent application was previously filed for the “pure water production system”. (Patent application 4
-225681. Hereinafter referred to as "first application". ).

According to the ultrapure water producing apparatus of the above-mentioned prior application, since the biological treatment means is incorporated as a part of the pretreatment apparatus for raw water (city water, groundwater, industrial water, etc.), the conventional pretreatment apparatus is Urea in raw water, which cannot be removed and serves as a TOC source in ultrapure water, can be highly removed, and ultrapure water with a significantly reduced TOC concentration can be obtained.

[0008]

In the apparatus of the above-mentioned prior application, regarding the decomposition rate of urea in the biological treatment means, easily decomposable organic substances (C source) such as acetic acid, sodium acetate, methanol, ethanol, and acetone in raw water are used. It was found that the addition of urea can improve the decomposition rate of urea.

However, although this organic substance addition method is a very effective means, it requires a new chemical tank, pump,
There is a drawback that it is necessary to replenish pipes and chemicals. Therefore, it has been desired to develop a method or means for improving treatment efficiency that does not require these facilities and operations.

The present invention has been made in view of the above circumstances, in which city water, ground water, and industrial water are treated as raw water, which is biologically treated and then treated by a primary pure water production apparatus and a secondary pure water production apparatus. In the method for producing ultrapure water by using an organic substance (C
A method for producing ultrapure water capable of producing an ultrapure water having a significantly reduced TOC, by which the urea decomposition rate in the biological treatment process can be improved by means of an alternative to the method of adding a source). The purpose is to do.

[0011]

In the method for producing ultrapure water according to the present invention, raw water is mixed with recovered water for semiconductor cleaning by ultrapure water to perform biological treatment, and then a primary pure water producing apparatus and a secondary pure water are provided. It is characterized by passing water through the manufacturing equipment.

[0012]

[Function] In a factory such as a semiconductor factory, which has conventionally used ultrapure water for cleaning products, the used ultrapure water used for cleaning is recovered again for reuse (hereinafter, It is used as raw water for producing ultrapure water. In the recovered water, organic substances such as isopropyl alcohol, acetic acid, and acetone used for washing are usually contained as TOC of several 100 ppb to several ppm.

Therefore, by mixing such recovered water with raw water containing urea (city water, ground water, industrial water) and performing biological treatment, the organic components present in the recovered water are effective as a C source for biological treatment. It is possible to improve the decomposition efficiency of urea in biological treatment and decompose and remove the organic component.

According to the present invention, the target substances for removal / reduction contained in each of raw water and recovered water can be decomposed and removed at the same time by a single apparatus.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an example of an ultrapure water production apparatus suitable for carrying out the ultrapure water production method of the present invention.

The ultrapure water production system shown in FIG. 1 (a) comprises a biological treatment system and a membrane filter as the pretreatment system A.
That is, the ultrafiltration (UF) or microfiltration (MF) membrane separation device 2 is used as the primary pure water producing device B, and the first reverse osmosis (RO) membrane separation device 3 and the second reverse osmosis (RO) membrane separation device 4 are provided. A mixed bed type ion exchange device 5, a low pressure ultraviolet oxidation device 7 (as a tank 6) as a secondary pure water production device C, a mixed bed type ion exchange device 8 and a UF membrane separation device 9 are provided, and in this order. They are installed in series. 20A is a pipe for introducing raw water, 20B
Indicates a pipe for introducing recovered water.

That is, raw water such as city water, industrial water, and groundwater is first introduced into the biological treatment apparatus 1 for biological treatment to decompose and remove organic substances such as urea. In the present invention, this raw water is introduced. The recovered water is introduced into the pipe 20A through the introduction pipe 20B, and the raw water and the recovered water are mixed and sent to the biological treatment apparatus 1.

In this biological treatment apparatus 1, the decomposition of urea is efficiently progressed by utilizing the organic component in the recovered water, and the organic component in the recovered water is also decomposed. This biologically treated water is introduced into the UF or MF membrane separation device 2 to remove the bacterial cells flowing out from the biological treatment device 1 and subjected to membrane separation.

The pretreated water treated in such a pretreatment device A is then subjected to a two-stage RO membrane separation in the first pure water production device B in the first RO membrane separation device 3 and the second RO membrane separation device 4. It is treated and further ion-exchanged in the mixed bed type ion exchange device 5.

Further, the treated water of the primary pure water producing apparatus B is introduced into the low pressure ultraviolet oxidation apparatus 7 through the tank 6 in the secondary pure water producing apparatus C, and the TOC contained therein is ionized or decomposed. Of these, the ionized organic matter is removed by the mixed bed type ion exchange device 8 in the subsequent stage. The treated water of the mixed bed type ion exchange device 8 is further subjected to a membrane separation treatment by a UF membrane separation device to obtain ultrapure water.

The ultrapure water production system shown in FIG. 1 (b) is shown in FIG. 1 (a) except that the primary pure water production system B is composed of an ion-exchanged pure water system 10 and an RO membrane separation device 11. It has the same structure as the ultrapure water production system.

The ultrapure water producing apparatus used in the present invention is basically the same as the conventional ultrapure water except that raw water and recovered water are directly passed to a pretreatment apparatus provided with a biological treatment apparatus. The same configuration as that of the production apparatus can be used, and the combination and configuration of each apparatus unit such as the RO membrane separation apparatus and the ion exchange pure water apparatus in the primary pure water production apparatus and the secondary pure water production apparatus are the same as the conventional ones. Can be adopted.

By the way, normally, as a biological treatment means for treating organic wastewater, there is an activated sludge method and the like. However, this method is applicable to low concentration organic-containing water such as city water, groundwater and industrial water used as raw water for producing ultrapure water. Even if such a method is applied, it is impossible to retain the bacterial cells and it cannot be used as a TOC reduction method.

On the other hand, the upward flow type biodegrading device for fluidizing the special carrier in the upward flow to immobilize the bacterial cells on the surface of the carrier is effective as a biological treatment means for preventing the bacterial cells from flowing out. In this case, activated carbon or anthracite, sand, zeolite, ion exchange resin provided in the biodegradation tank,
Bacteria are retained on the surface of the carrier so that the components eluted into raw water such as plastic molded products can be ignored, and upward by the raw water and recovered water from the bottom of the biodegradation tank and the effluent of the aeration tank separately provided. The biological treatment may be carried out by flowing in a stream.

The biological treatment apparatus is not limited to the upward circulating water system, but may be the downward circulating water system.

The ultrapure water producing apparatus shown in the figure is an example of an apparatus suitable for carrying out the present invention, and the method of the present invention is not limited to the one shown in the figure as long as the gist thereof is not exceeded.
For example, the raw water and the recovered water can be mixed by separately providing a mixing tank. However, in the normal case, a direct supply to the pipe is sufficient. In addition, a coagulation sedimentation device or a coagulation filtration device may be provided in a front stage or a rear stage of the biological treatment device.

Further, as a means for removing the bacterial cells flowing out from the biological treatment device provided in the latter stage of the biological treatment device, a sand filter or the like may be used in addition to the membrane filter.

In the method of the present invention, as long as raw water and recovered water are mixed and treated, the mixing ratio is not particularly limited. Is preferably mixed in an amount of 40 to 80% by volume.

The present invention will be described in more detail below with reference to specific examples and comparative examples.

Example 1 Raw water (Atsugi city water (October to December 1992)) was treated by the ultrapure water production system shown in FIG. 1 (a). As the biological treatment device, an upflow-type biodegradation device in which activated carbon was used to support cells was used, and a UF membrane separation device was provided at the subsequent stage. Raw water retention time (H
RT) was 15 minutes. In addition, cleaning and recovery water discharged in the semiconductor manufacturing process was mixed with this raw water at a ratio of 50% by volume with respect to the raw water. The TOC of the obtained ultrapure water is shown in Table 1.
Shown in.

Comparative Example 1 Sodium acetate (CH ₃ COONa) was added to the above-mentioned upflow biodegradation apparatus at 1 mg / l (C
The same treatment as in Example 1 was carried out except that the addition was performed. Table 1 shows the TOC of the obtained ultrapure water.

[0033]

[Table 1]

As is clear from Table 1, according to the method for producing ultrapure water of the present invention, it is possible to achieve the same excellent treatment efficiency as in the case of adding the organic substance without adding the organic substance in the biological treatment step. , TOC can be remarkably reduced to obtain ultrapure water.

If it is attempted to produce ultrapure water equivalent to the ultrapure water obtained in the above-mentioned Example 1 and Comparative Example 1 without adding any organic substance and without mixing the recovered water, the biological The HRT of the decomposition device had to be about 30 minutes.

[0036]

As described in detail above, according to the method for producing ultrapure water of the present invention, after the city water, groundwater, and industrial water containing urea are biologically treated as raw water, the primary pure water producing apparatus and the secondary water are used. When water is passed through the next pure water producing apparatus to produce ultrapure water, the rate of urea decomposition can be improved in the biological treatment process without injecting new organic matter (C source). Better processing efficiency, TOC of ultrapure water obtained
Can be further reduced. A single device can decompose and reduce not only the TOC source (urea) in raw water but also the TOC source in recovered water. With such an effect, it is possible to efficiently manufacture ultrapure water of extremely high purity.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of an ultrapure water production apparatus suitable for carrying out the ultrapure water production method of the present invention.

[Explanation of symbols]

 A Pretreatment device B Primary pure water production device C Secondary pure water production device 1 Biological treatment device 2 UF or MF membrane separation device 3 First RO membrane separation device 4 Second RO membrane separation device 5, 8 Mixed bed ion exchange device 6 Tank 7 Low-pressure UV oxidizer 9 UF membrane separator 10 Ion-exchange pure water device 11 RO membrane separator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C02F 3/10 ZAB A

Claims (1)

[Claims] 1. A method for producing ultrapure water, comprising mixing raw water with semiconductor cleaning and recovery water using ultrapure water for biological treatment and then passing the water through a primary pure water production apparatus and a secondary pure water production apparatus. Production method.