JP2001029752A - Manufacture of high-purity water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the proliferation of bacteria in a system to prevent a slime contamination from occurring by adjusting untreated water to a specific pH value range and running the pH value-adjusted water through a reverse osmosis membrane device and a deoxidation device of a front stage and further, running the pH value-readjusted water through an electric deionizing device with the passage of deionized water through an osmosis membrane of a rear stage. SOLUTION: Untreated water originating from a plant as waste water is previously treated using a turbidity removing device 1 and a specified acid is added to the treated water to adjust its pH value to 4-6. At the same time, the pH value-adjusted water is treated by means of a reverse osmosis membrane device 2 and a deoxidation device 3 of a front stage respectively. That is, oxygen and a carbon dioxide gas are removed by adjusting the pH value and at the same time, the proliferation of slime (live bacteria) is inhibited by lowering the dissolved oxygen concentration of the treated water to 100 ppb or less by a deoxidation process. Next the pH value of the treated water is adjusted to 7-8 by adding alkali and at the same time, the treated water is further treated using an electric deionizing device 4. In succession, the deionized water is treated with the help of a reverse osmosis device 5 of a rear stage. Thus it is possible to remove an organic matter, silica and the like included in the treated water to enhance its purity and deliver it as high-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 and an apparatus for producing ultrapure water, and in particular, suppresses the generation of slime (live bacteria) in a reverse osmosis (RO) membrane apparatus and stabilizes high-purity water for a long period of time. And a method and an apparatus for producing ultrapure water.

[0002]

2. Description of the Related Art Conventionally, the following system is provided as a system for producing pure water by treating recovered water from industrial water, city water, well water, semiconductor manufacturing processes or the like.

After treating with a multi-bed ion exchange resin,
Method of treating with RO membrane device After treating with RO membrane device, treating with mixed bed tower ion exchange resin, and further treating with RO membrane device After treating with RO membrane device, treating with electrodialysis device,
Further processing method with RO membrane equipment

[0004]

In any of the above methods (1) to (4), the growth of bacteria in the system cannot be suppressed.
Since slime (bacterium) accumulates on the O membrane surface, resulting in deterioration of water quality and decrease in permeation flux of the membrane, there is a drawback in that it is necessary to periodically sterilize and wash the RO membrane device.

[0005] In particular, in the method (1), there is also a problem of contamination of the RO membrane device in the latter stage due to the eluted substances from the ion exchange resin after regeneration.

The electrodialysis apparatus used in the above method is provided for removing CO ₂ , and is constituted only by an ion exchange membrane, and has a deionizing ability but a weak sterilizing action. In order to obtain a bactericidal action with an electrodialysis machine,
It is necessary to supply a current higher than the limit current density, which is economically disadvantageous.

[0007] The present invention solves the above-mentioned conventional problems, suppresses the growth of bacteria in the system, prevents slime contamination of the RO membrane device, and continuously and stably obtains high-purity water for a long period of time. It is an object of the present invention to provide a method and an apparatus for producing ultrapure water.

[0008]

According to the method for producing ultrapure water of the present invention, raw water is adjusted to pH 4 to 6, and then passed through a first-stage reverse osmosis membrane device and a deoxygenation device. Is adjusted to 7 to 8, and then passed through an electrodeionization apparatus, and the obtained deionized water is passed through a second-stage reverse osmosis membrane apparatus.

[0009] The apparatus for producing ultrapure water of the present invention converts raw water to pH.
First pH adjusting means for adjusting the pH to 4 to 6, and the first pH adjusting means;
A first-stage reverse osmosis membrane device and a deoxygenation device for treating the water whose pH has been adjusted by the adjusting means, and the water treated by the first-stage reverse osmosis membrane device and the deoxygenation device to a pH of 7 to 8. Second pH adjusting means for adjusting, an electrodeionization apparatus for treating water whose pH has been adjusted by the second pH adjustment means, and a reverse osmosis membrane for treating deionized water obtained by the electrodeionization apparatus And a device.

[0010] As described above, in an electrodialysis apparatus comprising only an ion exchange membrane and having no conductive substance between the ion exchange membranes, only an electric current flows depending on the electric conductivity of water. However, there is no germicidal action at a current of about the ion removal level. It is said that an electrodialysis apparatus can achieve a bactericidal action at a current density equal to or higher than the limit current density. However, for this purpose, a high current density of 30 A / m ² or more is usually required, which is economically disadvantageous.

On the other hand, in an electrodeionization apparatus in which a conductive substance (ion exchanger) is filled between ion exchange membranes, a sterilizing action can be obtained at a low current using the surface of the ion exchanger as a medium. be able to.

According to the present invention, the water treated with an RO membrane device and a deoxidizer to reduce dissolved oxygen (DO) is treated with an electric deionizer so that the electric deionizer has low current and good current. Sterilization action is obtained, slime contamination of the RO membrane device at the subsequent stage is prevented, and high water quality can be maintained for a long period of time to maintain stable operation. In the RO membrane device subsequent to the electrodeionization device, fine particles, TOC, silica, and the like in deionized water from the electrodeionization device are efficiently removed. As described above, by combining the electrodeionization apparatus and the RO membrane apparatus, the non-regeneration type ion exchange resin equipment usually provided in the ultrapure water production system can be eliminated, and the equipment cost can be reduced. Can be achieved.

[0013]

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

FIGS. 1A to 1C are system diagrams showing an embodiment of a method and an apparatus for producing ultrapure water according to the present invention.

In the present invention, the raw water to be treated is
Industrial water, municipal water, well water, or recovered water from a manufacturing process, for example, washing wastewater from a manufacturing process for semiconductors, liquid crystals, or the like. In the case where recovered water from a manufacturing process such as recovered water for semiconductor manufacturing is used as raw water, and when the concentration of organic matter (TOC) in the recovered water is high, as shown in FIG. ,
It is preferable to preliminarily treat the catalyst with a decomposition means using a catalyst or a TOC removing device 6 such as an RO membrane device to reduce the TOC to 0.5 mg / L or less.

Raw water such as industrial water, city water, well water, etc., is preferably pre-treated as necessary by a clarifier 1. The clarifier 1 generally has an ultrafiltration (UF) filter. Membrane equipment,
Although a microfiltration (MF) membrane device or the like is used, a TOC removal device such as a biological treatment device or an RO membrane device may be used.
Further, with respect to water containing hardness components such as industrial water, city water, and well water, the hardness components may be removed by a softening device.

Raw water or its turbidity-treated water (or TOC-removed water) is prepared by adding a mineral acid such as HCl or H ₂ SO ₄ to pH.
After the adjustment to 4 to 6, processing is performed by the first-stage RO film apparatus (hereinafter, referred to as “first RO film apparatus”) 2 and the deoxidizer 3.

Here, the adjusted pH is used to remove carbon dioxide gas together with oxygen, and reduces the load on the subsequent desalination apparatus. If the pH exceeds 6, the bacteriostatic effect deteriorates,
If it is less than 4, the influence of corrosion becomes remarkable.
Is 4 to 6.

There is no particular limitation on the processing order of the first RO membrane device 2 and the deoxidizing device 3, and as shown in FIGS. 1 (a) and 1 (c), the first RO membrane device 2 is desalted. Rear deoxygenator 3
Alternatively, as shown in FIG. 1B, the first RO film apparatus 2 may perform the first oxygen treatment after the first oxygen treatment. In any case, it is preferable to perform the deoxidizing treatment by the deoxidizing device 3 so that the DO of the treated water becomes 100 ppb or less. If the DO exceeds 100 ppb, a sufficient effect of suppressing the growth of viable bacteria cannot be obtained even if sterilization is performed in the subsequent electrodeionization apparatus 4.

The deoxidizer 3 includes a membrane deaerator,
A vacuum deaerator, a nitrogen gas deaerator, or the like can be used.

The RO film of the first RO film device 2 is not particularly limited, and an RO film of polysulfone, polyamide, polyvinyl acetate, or the like can be used.
Inlet pressure 7.0-15.0 kg / cm ² , water recovery 70-
The RO film is processed under the condition of 85%.

The water treated in the first RO membrane device 2 and the deoxidizer 3 is added to an alkali such as NaOH to adjust the pH to 7.
After the adjustment to 処理 8, the treatment is performed by the electrodeionization apparatus 4 and then by the second stage RO membrane apparatus (hereinafter, referred to as “second RO membrane apparatus”) 5. From the standpoint of silica removal efficiency, the higher the adjusted pH, the better. However, if the adjusted pH is excessively high, the characteristics required as ultrapure water will not be satisfied, so the adjusted pH is 7-8, preferably 7-7. .5.

As the electrodeionization apparatus 4, a plurality of anion exchange membranes and cation exchange membranes are alternately arranged between an anode chamber having an anode and a cathode chamber having a cathode to form a concentration chamber and a desalination chamber. It is possible to use a general one formed alternately and filled in a desalting chamber with an ion exchanger such as a mixed resin of anion exchange resin and cation exchange resin or ion exchange fiber. If it is 4, the sterilization effect can be obtained together with the deionization treatment at a relatively low current density of 4 to 20 A / m ² , preferably 6 to 10 A / m ² .

The deionized water of the electrodeionization apparatus 4 is then treated in the second RO membrane apparatus 5 to remove the remaining traces of TOC, silica, etc., thereby increasing the purity. (Pure water).

In the second RO membrane device 5, the sterilization treatment under the low DO condition in the preceding electrodeionization device 4 suppresses the growth of viable bacteria, and extends to the membrane surface for a long time. Stable treatment can be performed without causing problems such as a decrease in the permeation flux of the membrane due to the accumulation of the slime and a deterioration in the quality of the treated water, so that high-quality treated water can be obtained.

The RO membrane of the second RO membrane apparatus 5 is not particularly limited, and an RO membrane of polysulfone, polyamide, polyvinyl acetate, or the like can be used. In a normal case, the inlet pressure is 7.0 to 15.0 kg. / Cm ² , water recovery rate 80-90%
The RO film is processed under the following conditions.

In the present invention, as shown in FIG. 1C, the concentrated water of the electrodeionization device 4 and the concentrated water of the second RO membrane device 5 are supplied to the inlet side of the first RO membrane device 2. Returning and circulating is preferred in terms of improving the water recovery rate. Also in this case, the electrodeionization device 4 and the second RO
Since the water supply of the membrane device 5 is sufficiently enhanced by the treatment by the first RO membrane device 2 and the deoxidizer 3 in the preceding stage,
By returning these concentrated waters to the inlet side of the first RO membrane device 2, there is almost no problem of deterioration in the quality of treated water, and good treatment can be performed.

[0028]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 By the method shown in FIG. 1B, ultrapure water was produced using city water as raw water.

The equipment used and the processing conditions are as follows.

Denaturation device: UF membrane device (Preblocks manufactured by Kurita Industries Co., Ltd., fractional molecular weight: 20,000) Deoxygenation device: Membrane deaerator (Liquicel 4 manufactured by Hoechst)
Pressure, 30 Torr Sweep gas = N ₂ (0.2 N-m ³ / hr) Treated water amount = 1.0 m ³ / hr First RO membrane device: RO membrane (Nippon Denko “ES- 20
-D "4 inch, 2 pieces series) Inlet pressure = 9 kg / cm ² Water recovery = 70% Electrodeionizer: Electrodeionizer (Kurita Kogyo Co., Ltd.)
"M-10 type" (2 units) Treated water volume = 120 L / hr Water recovery rate = 70% Second RO membrane device: RO membrane (Nippon Denko "NTR-7"
59 "2.5 inches, 1 line) Inlet pressure = 7 kg / cm ² Water recovery rate = 90% HCl was added to the water supply of the deoxidizer (membrane deaerator) to adjust the pH to 5.0. D of treated water of this membrane deaerator
O was 50 ppb. NaOH was added to the water supplied to the electrodeionization apparatus to adjust the pH to 7 to 7.5. The concentrated water of the electrodeionization device and the concentrated water of the second RO membrane device were returned to the inlet side of the first RO membrane device.

The current density of the electrodeionization apparatus is 3 A / m ²
Or 6 A / m ² , the number of viable bacteria in the water at the outlet of the electrodeionization apparatus (deionized water, that is, water supply to the second RO membrane apparatus) and the permeation flux of the RO membrane apparatus after continuous operation for 4 months When,
The quality of the treated water of the RO membrane device was examined, and the results are shown in Table 1.

Comparative Example 1 In Example 1, an electrodialysis device (“CS-O type” Selemion membrane, 2 manufactured by Asahi Glass Co., Ltd.) was used instead of the electrodeionization device.
), And the operation was performed in the same manner as in Example 1 except that operation was performed at a current density of 10 A / m ² or 30 A / m ² , a treated water amount of 120 L / hr, and a water recovery rate of 70%. , The electrodialyzer outlet water (deionized water, ie the second RO
Number of viable bacteria in water supply to membrane device) and RO after continuous operation for 4 months
The permeation flux of the membrane device and the quality of the treated water of the RO membrane device were examined, and the results are shown in Table 1.

In Comparative Example 1, the current density was 30 A / m
Operating conditions such as ² are too high in voltage and are economically disadvantageous.

[0035]

[Table 1]

The decrease in the quality of the treated water after the continuous operation in Example 1 and Comparative Example 1 is considered to be due to the eluate from the number of viable bacteria attached to the RO membrane surface and the outflow of CO ₂ . Although the operation was stopped and the RO membrane was sterilized and washed with 0.3% by weight of H ₂ O ₂ water, the quality of the treated water could be restored to the same level as at the beginning of the operation. Did not recover well.

COMPARATIVE EXAMPLE 2 In Example 1, a 1-inch net ring was used instead of the membrane deaerator, and a decarbonation tower through which air of 10 N-m ² / m ² · min flowed upward was used. Water LV through this decarbonation tower
= Deionized water after operation for 2 months (exit water of the electrodeionization device, ie, water supply to the second RO membrane device) except that the countercurrent treatment was performed at 40 m ³ / m ² · hr. Was examined and the results are shown in Table 2.

Table 2 also shows the viable cell count of deionized water (outlet water of the electrodeionization apparatus, ie, water supply to the second RO membrane apparatus) after two months of operation in Example 1.

[0039]

[Table 2]

From the above results, it can be seen that long-term continuous operation can be performed while maintaining high water quality by removing DO, treating with an electrodeionization apparatus, and then treating with an RO membrane apparatus.

[0041]

As described in detail above, according to the method and apparatus for producing ultrapure water of the present invention, the growth of bacteria in the system is suppressed,
It is possible to prevent a decrease in the quality of treated water and a decrease in permeation flux of the membrane due to slime contamination of the RO membrane device, and to obtain high-purity water continuously and stably for a long period of time.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method and an apparatus for producing ultrapure water according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 turbidity device 2 first RO membrane device 3 deoxygenation device 4 electrodeionization device 5 second RO membrane device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 9/00 502 C02F 9/00 502Z 502L 502K 503B 503 504B 504 504E 1/46 103 F Term (Reference) 4D006 GA03 KB01 KB17 MA13 MA14 MC21 MC54 MC62 PA01 PB02 PB05 PB23 PC02 4D037 AA03 AB11 BA23 BB05 BB07 CA03 CA04 CA14 4D061 DA02 DB02 EA09 EB01 EB13 EB19 EB37 FA03 FA09 FA11 GA30 GC01

Claims (6)

[Claims] 1. After adjusting the pH of raw water to 4 to 6, the solution is passed through a first-stage reverse osmosis membrane device and a deoxygenation device, and then the pH is adjusted to 7 to 8 and then passed through an electrodeionization device. A method for producing ultrapure water, characterized in that the ultrapure water is passed through a second-stage reverse osmosis membrane device. 2. The method for producing ultrapure water according to claim 1, wherein the raw water is industrial water, city water, well water, or water recovered from a production process. 3. The method according to claim 1, wherein the concentration of dissolved oxygen in the inflow water of the electrodeionization apparatus is 100 ppb or less.
Or 2) a method for producing ultrapure water. 4. The concentrated water discharged from the electrodeionization apparatus and the concentrated water discharged from the second-stage reverse osmosis membrane device are returned to the preceding stage of the first-stage reverse osmosis membrane device. The method for producing ultrapure water according to any one of claims 1 to 3, wherein 5. A first pH for adjusting raw water to pH 4 to 6.
Adjusting means; a first-stage reverse osmosis membrane device and a deoxygenation device for treating the water whose pH has been adjusted by the first pH adjustment device; and a first-stage reverse osmosis membrane device and a deoxygenation device. A second pH adjusting means for adjusting the pH of the treated water to 7 to 8, an electrodeionization apparatus for treating the water whose pH has been adjusted by the second pH adjustment means, and an electrodeionization apparatus obtained by the electrodeionization apparatus. An apparatus for producing ultrapure water, comprising: a reverse osmosis membrane device for treating deionized water. 6. A means for feeding concentrated water discharged from the electrodeionization device to a stage preceding the first stage reverse osmosis membrane device, and means for supplying concentrated water from the second stage reverse osmosis membrane device to the first stage. 6. An apparatus for producing ultrapure water according to claim 5, further comprising means for feeding the water to a stage preceding the reverse osmosis membrane device of the eye.