JPH11244853A - Production of pure water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain treated water of high quality by controlling feed water to a specified pH, passing the water through a first reverse osmosis membrane separator of a low desalting rate, deaerating the first permeated water thus obtd., then passing the treated water through a second reverse osmosis membrane separator, and supplying the second permeated water to a purifying device to obtain pure water. SOLUTION: The feed water is first treated in a device 1 to remove suspended substances, and then concentrated water from a RO device 4 and an acid are added to the water to control the pH to 4 to 5 to prevent gelation of silica in a RO device 2. The concentrated water in the RO device 2 is discharged to the outside of the system, while the permeated water is deaerated in a deaerating device 3. To the deaerated water, concentrated water from a pure water device (CEDI) 6 and an alkali are added to control the pH to 7 to 11. The water after pH control is supplied to a RO device 4 to remove silica as well as to remove a carbonic acid component to obtain a permeated water of high quality. The permeated water from the RO device 4 is supplied to a treated water room 6A of the CEDI 6, while a part of the concentrated water is supplied to a concentrated water room 6B. Thus, pure water is obtd. from the treated water room 6A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverse osmosis membrane separation apparatus (RO apparatus) for raw water and a continuous electric regeneration type pure water apparatus (CED).
I) and the method for producing pure water.
The present invention relates to a method for producing pure water, which increases the water recovery rate and improves the quality of pure water obtained when producing pure water by combining an O apparatus and CEDI.

[0002]

2. Description of the Related Art Conventionally, for the production of pure water used for cleaning water for semiconductors, lenses, liquid crystals and the like, and medical water, a plurality of anion exchange membranes 21 and cation exchange membranes 22 are alternately arranged as shown in FIG. A continuous electric regeneration type pure water device (CEDI) in which concentrated water chambers 23 and treated water chambers 24 are alternately formed and mixed with an anion exchange resin and a cation exchange resin in the treated water chamber 24 and filled are used frequently. Have been. CEDI has an excellent feature that it can perform an effective deionization treatment, does not require regeneration like an ion-exchange resin, can completely continuously sample water, and can obtain water of extremely high purity.

In CEDI, ions in feed water (water to be treated) flowing into a treated water chamber 24 move in the resin 20 in the direction of the gradient of the potential of the anode 25 and the cathode 26 based on affinity, concentration and mobility. And the treated water chamber 24 and the concentrated water chamber 23
Exchange membrane 22 or anion exchange membrane 21 that separates
And charge neutralization is maintained in all chambers. Then, due to the semi-osmotic characteristics of the ion exchange membranes 21 and 22 and the directionality of the gradient of the potential, the ions in the supply water are reduced in the treated water chamber 24 and the adjacent concentrated water chamber 23
Then it will be concentrated. Therefore, pure water (deionized water) is recovered from the treated water chamber 24. In addition, 27 is an anode room and 28 is a cathode room.

Conventionally, a reverse osmosis membrane separation device (RO device) is sometimes provided as a pretreatment means for such CEDI. By disposing the RO device, the electrolyte and TOC components in the raw water can be efficiently removed, and the CED
The load on I can be reduced, and high-purity treated water can be obtained.

[0005] In the case where the RO apparatus is provided as described above, Japanese Patent Application Laid-Open No. 9-29 aims to increase the deionization efficiency of CEDI and efficiently produce high-quality treated water.
No. 0271 discloses a high desalination rate RO apparatus and a low desalination rate RO apparatus.
For example, as shown in FIG. 2, raw water is passed through a high desalination ratio RO device 11 and the permeated water is supplied to a treated water chamber 12A of the CEDI 12, and the concentrated water is subjected to low desalination, as shown in FIG. Through the RO device 13 and the permeated water
It has been proposed to supply water to twelve concentrated water chambers 12B. The technology described in Japanese Patent Application Laid-Open No. 9-290271
The CEDI concentrated water is based on the finding that the higher the salt concentration to some extent, the higher the current efficiency and the higher the deionization efficiency.

[0006]

The above RO device and C
In the method of producing pure water in combination with EDI,
In order to obtain high-quality treated water, it is necessary to install an ion-exchange resin tower that requires regeneration treatment as a pretreatment device, or install a mixed-bed ion-exchange resin tower that also requires regeneration treatment at the subsequent stage. There is such a problem. There is also a problem that the water recovery rate cannot be increased due to the problem of scaling due to Ca or silica. For example, in the RO apparatus, the water recovery rate is set so that the silica concentration of the concentrated water is 100 to 120 ppm or less, and the water recovery rate is usually 70 to 80%. Further, the water recovery rate of CEDI is also set at about 70 to 80%. Conventionally, the concentrated water of CEDI is returned as feed water to the RO device to increase the water recovery rate of the entire system to 70 to 80%, but it cannot be said that the water recovery rate is sufficiently satisfactory.

In the desalination using CEDI, if the balance between the cations and anions in the raw water is lost, more ions may remain in the treated water, but if there is carbonic acid (CO ₂ ) in the raw water. , cause collapsing this balance, the presence of carbonate since it will affect the quality of the treated water CEDI, there is also a problem of quality degradation due to CO _2.

The technique described in Japanese Patent Application Laid-Open No. 9-290271 does not take into account the removal of silica and carbonic acid and the improvement of the water recovery rate.
Silica flows out of the system, and this becomes a load on the CEDI 12, which leads to a decrease in the quality of the treated water and an increase in the amount of current in the CEDI 12. There is also a problem of water quality deterioration caused by carbonic acid.

In order to prevent the silica from flowing out of the low-desalting-ratio RO apparatus 13, a RO apparatus having a normal desalting rate is used instead of the low-desalting-ratio RO apparatus as the second-stage RO apparatus. However, in this case, the silica will be further concentrated in the second-stage RO apparatus,
There is a problem of scale hindrance due to gelation of silica. There is also the problem of CaCO ₃ scale.

[0010] The present invention solves the above-mentioned conventional problems, increases the water recovery rate without causing scale disturbance, prevents water quality deterioration due to carbonic acid, and prevents leakage of silker, thereby obtaining high quality treated water. An object is to provide a method for producing pure water.

[0011]

According to the method for producing pure water of the present invention, after adjusting the pH of raw water to pH 4 to 5, the water is passed through a first reverse osmosis membrane separation device (first RO device) having a low desalination ratio. To obtain a first permeated water and a first concentrated water, degassing the first permeated water, adjusting the pH to 7 to 11, and then a second reverse osmosis membrane separation device (second RO device) Through the second permeate and the second
And the second permeated water is supplied to a treated water chamber of a continuous electric regeneration water purifier (CEDI) to obtain pure water from the treated water chamber.

In the present invention, the water supply to the first RO device is adjusted to pH 4
By adjusting the value to ５5, gelation of silica can be prevented, and precipitation of silica can be suppressed up to a silica concentration of about 200 mg / L. Therefore, in the first RO device, the silica passes through the low desalting rate RO membrane without being scaled. The first RO device having a low desalting rate removes Ca ions, and other salts do not necessarily have to be removed. Since the first RO apparatus has a low desalination rate, it can be operated at a low water pressure with a high water recovery rate, and the decrease in membrane flux is small.

[0013] The permeated water of the first RO device is sent to a deaeration step.

In the degassing step, since the pH in the system is 5 or less, the carbonic acid in the water is in the state of CO ₂ and is easily removed.

The removal of Ca ions in the first RO device and the removal of CO ₂ in this deaeration step can prevent the subsequent stage of CaCO ₃ scale.

The degassed water is then adjusted to a pH of 7 to 11, and then introduced into the second RO device. Thus, the second R
By making the water supply to the O device alkaline, it is possible to prevent silica leakage and scale disturbance. That is, the silica gel causes a scale hindrance such as clogging of the RO film. However, in the case of alkalinity, the silica is ionized and does not gel and does not cause a scale hindrance. Since the ionized silica is eliminated by the RO film without clogging the RO film, the leakage of silica to the permeated water side is suppressed. In addition, carbonic acid remaining in water also becomes (bi) carbonate ion, is eliminated by the RO membrane together with other ions, and leakage to the permeated water side is suppressed. Therefore, in the second RO device, even if the water recovery rate is increased, no scale disturbance is caused, and high-quality permeated water from which scaled components are highly removed can be obtained.

In the CEDI, up to the previous step, C
Since scale-causing substances such as a ions, silica, and carbonate ions are removed, generation of scale in CEDI can be prevented, and CEDI can be operated stably for a long time. In particular, since carbonic acid is removed as much as possible by removal by degassing and removal by treatment in a second RO apparatus under alkaline conditions, the flow of (bi) carbonate ions into CEDI is extremely small. For this reason, the CE caused by the aforementioned CO ₂
There is no problem of deterioration in the water quality of the DI treated water, and good water quality can be obtained stably.

[0018]

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 embodiment of the present invention.

In the present invention, as the raw water, water used as ordinary raw water for producing pure water, such as industrial water, city water, and well water, can be used, and wastewater from a semiconductor manufacturing process using ultrapure water can be used. Is subjected to biological treatment, RO treatment, and ion exchange treatment according to a conventional method to obtain raw water.

Raw water is preferably first treated with a turbidity removing device 1 in order to remove turbidity in the raw water and dissolved substances that can be insolubilized. A turbidity membrane separation (for example, microfiltration (MF) membrane or ultrafiltration (UF) membrane) can be used. By providing the turbidity removing device 1, the load at the subsequent stage can be reduced, and the quality of treated water can be improved.

The raw water subjected to turbidity treatment is then subjected to the second stage
An acid such as HCl or H ₂ SO ₄ is added together with the concentrated water of the RO device 4 to adjust the pH to ₄ to 5. By adjusting the feed water of the first RO device 2 to pH 4-5, the first RO device 2
The gelation of silica at the step can be prevented, and the silica scale can be prevented. That is, conventionally, from the viewpoint of the silica scale, the operation is performed at a silica concentration of 100 to 120 ppm or less. However, by setting the pH to 4 to 5, the silica scale can be prevented up to a silica concentration of about 200 ppm, and the water recovery rate can be reduced. And the operation with a water recovery rate of 90% or more becomes possible.

In the present invention, as the first RO device 2, a RO film having a low desalting rate, preferably an RO film having a NaCl removal rate of about 85 to 95% (hereinafter referred to as a "loose RO apparatus"). May be called.) With such a loose RO apparatus, the silica removal rate is low, but Ca ²⁺ can be removed by 99% or more.

In addition, a loose RO apparatus can be operated at a low pressure, and has the advantage that the decrease in film flux is small.

The concentrated water in the first loose RO device 2 is discharged out of the system, and the permeated water is deaerated in a deaerator 3.

In the deaerator 3, since the pH of the feedwater is acidic at 5 or less, the carbonic acid component in the water is in a CO ₂ state and is efficiently removed. In addition, dissolved oxygen in water can be removed at the same time. As the deaerator 3,
Decarboxylation (air contact method) apparatus, N ₂ deaerator, vacuum degasser, it is possible to use a conventional deaerator such as a membrane degasifier.

The deaerated water from the deaerator 3 is supplied to the C
An alkali such as NaOH or KOH is injected together with the concentrated water of EDI6 to adjust the pH to 7-11. This adjusted pH
The value is preferably higher from the viewpoint of ionization of silica,
If the temperature is too high, the problem of deterioration of the RO film of the second RO device 4 occurs, so the adjusted pH value is particularly 8 to 10.5, especially 9.
5 to 10 are preferred.

The RO film of the second RO device 4 to which the water whose pH has been adjusted as described above is supplied is preferably made of NaCl.
An RO film with a high desalination rate of 99% or more, for example, an RO film of polyamide type or cellulose acetate type is used.

As described above, since the second RO device 4 is operated under alkaline conditions, there is no fear of silica scale. Also, since Ca ²⁺ is removed by the first loose RO device 2 and CO ₂ is removed by the deaerator 3,
The water recovery rate can be increased without fear of CaCO ₃ scale, and the operation can generally be performed at a water recovery rate of 80 to 90%. In the second RO device 4, the ionized silica is removed, and the remaining carbonic acid component also becomes (bi) carbonate ion and is removed together with other ions, so that high-quality permeated water is obtained.

The permeated water of the second RO device 4 is supplied to the subsequent CE
The DI 6 is supplied to the treated water chamber 6A, a part of the concentrated water is supplied to the concentrated water chamber 6B of the CEDI 6, and the remainder is supplied to the first loose RO device 2.

In the present embodiment, the permeated water of the second RO unit 4 is irradiated with an ultraviolet ray oxidizing device (hereinafter referred to as "UV oxidizing device").
After processing in step 5, feed to CEDI6. Thus U
By treating with the V oxidizer 5, treated water with higher water quality can be obtained, which is preferable.

That is, RO devices 2 and 4, deaerator 3, CE
The DI6 alone cannot remove a very small amount of TOC in raw water, but as shown in FIG. 1, by providing a UV oxidizer 5, TOC in raw water is decomposed into small molecules by UV oxidative decomposition and ionized. Can be easily separated by the subsequent CEDI 6, and the water quality can be further improved.

When a UV oxidizing device is provided, there is no particular limitation on the place of the UV oxidizing device, and it can be installed at any position. In particular, the TOC component ionized by UV oxidative decomposition is provided immediately before CEDI. Is preferred in that it can be quickly removed.

It is preferable that the UV oxidizing apparatus 5 be capable of irradiating UV having a high oxidizing ability at a low wavelength of 180 to 220 nm, particularly 180 to 190 nm.

The treated water of the UV oxidizer 5 is supplied to the treated water chamber 6A of the CEDI 6.

As shown in FIG. 3, the concentrated water chamber 23 and the treated water chamber 24 are separated from the CEDI 6 by the anion exchange membrane 21 and the cation exchange membrane 22, and the anode chamber 27 and the cathode chamber 28. Alternatively, a general commercially available CEDI in which a mixed bed of a cation exchange resin and an anion exchange resin is filled in the treated water chamber 24 and the concentrated water chamber 23 can be used.

In the CEDI 6, deionization is performed according to the principle described above, pure water is obtained from the treated water chamber 6A, and concentrated water is discharged from the concentrated water chamber 6B. The electrode chamber (anode chamber, cathode chamber) of the CEDI 6 is supplied with the concentrated water of the second RO device 4.

The pure water from the treated water chamber 6A is discharged out of the system and sent to the place of use.

On the other hand, the concentrated water from the concentrated water chamber 6B is supplied to the second R
The water is returned to the preceding stage of the O device 4 and supplied to the second RO device 4.

In the present invention, substances causing scale, such as Ca ²⁺ ions, silica, and carbonate ions, in the raw water have been highly removed by the preceding stage of CEDI6.
The occurrence of scale in DI6 is prevented and CEDI6
The device itself can operate stably for a long period of time with a high water recovery rate of about 85 to 95%. In particular, carbonic acid is highly removed by the removal by degassing and the elimination in the second RO device under alkaline conditions, so that the inflow of (bi) carbonate ions into CEDI 6 is extremely small, and the ion balance caused by the aforementioned CO ₂ is reduced. There is no decrease in the water quality of the CEDI treated water due to the displacement, and the treated water with good water quality can be obtained stably.

As described above, since the second RO device 4 is processed under alkaline conditions, even if the concentrated water of CEDI 6 is returned and supplied, it is possible to perform the processing stably without causing scale disturbance or the like. Can be.

In the embodiment shown in FIG. 1, the only water discharged to the outside of the system is the concentrated water of the first loose RO device 2.
A high water recovery rate of 80% to 90% or more can be obtained, and high-quality treated water can be obtained.

[0043]

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

Example 1 City water was treated by the method shown in FIG. 1 to produce pure water. However, the UV oxidation device 5 is not provided, and the second RO device 4
Was directly supplied to CEDI6.

First, 270 L / hr of city water is treated by a turbidity removing device (external pressure type hollow fiber UF membrane separation device) 1, and then concentrated with 10 L / hr of concentrated water of a second RO device 4 at the subsequent stage using HCl.
The water was adjusted to H4 and passed through the first loose RO device 2. As the first loose RO device 2, "N" manufactured by Nitto Denko Corporation
TR-729HF "(polyamide-based synthetic composite membrane, NaC
(1 removal rate: 90%) Using one (4 inches) loaded, operation was performed at a water supply pressure of 10 kg / cm ² and a water recovery rate of 90%.

The concentrated water in the first loose RO device 2 was discharged out of the system, and the permeated water was supplied to the deaerator 3. As the deaerator 3, a membrane deaerator (manufactured by Hoechst Japan: Liq-C)
EL, 2 inch 1 pc.), Vacuum degree 40 Torr, N
_Two volumes were treated at 1 L / min.

Next, 250 L / hr of degassed water was adjusted to pH 9.5 by adding NaOH together with 40 L / hr of the concentrated water of CEDI 6 at the subsequent stage, and then passed through the second RO device 4.

As the second RO device 4, a single (4 inch) RO film “NTR-759HR” (manufactured by Nitto Denko Corporation) (polyamide-based synthetic composite film, NaCl removal rate 99.5%)
Was treated at a water supply pressure of 12 kg / cm ² and a water recovery rate of 83%. 240 L / hr of permeated water of the second RO device 4 is supplied to the treated water chamber 6A of CEDI (“Pure Ace PA240” manufactured by Kurita Kogyo Co., Ltd.) 6, and 40 L / hr of the concentrated water is concentrated water chamber of CEDI6. 6B
Water.

The obtained treated water (pure water from CEDI6)
Was examined for water quality and water recovery, and the results are shown in Table 1.

Example 2 In Example 1, a UV oxidizing device 5 for irradiating UV of 185 nm was provided, and the permeated water of the second RO device 4 was treated with the UV oxidizing device 5 under the condition of 0.2 KWH / m ^3. Other than the above, the treatment was carried out in the same manner, and the quality and water recovery of the obtained treated water were examined. The results are shown in Table 1.

[0051]

[Table 1]

Comparative Example 1 The same procedure as in Example 1 was carried out except that the deaerator was not provided.
O ₃ skewing occurred, causing a decrease in the amount of permeated water of the second RO device and an increase in the differential pressure.

Comparative Example 2 The procedure of Example 1 was repeated, except that the pH was not adjusted on the inlet side of the first loose RO apparatus 2 but the pH was adjusted to 7.0, and the same procedure was performed 5 to 7 times. As a result, a scourge of CaCO ₃ was generated, resulting in a decrease in the amount of permeated water of the second RO device and an increase in the differential pressure.

Comparative Example 3 The procedure of Example 1 was repeated, except that the pH was not adjusted on the inlet side of the second RO device 4 and the process was carried out at pH 6.9. Silica scale was generated in the apparatus, and the amount of permeated water was reduced.

[0055]

As described in detail above, according to the method for producing pure water of the present invention, the water recovery rate when producing pure water by combining an RO device and CEDI is 10 to 10 times that of the conventional method.
In addition to being able to improve by as much as 20%, high quality treated water can be obtained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of an embodiment of the present invention.

FIG. 2 is a system diagram showing a conventional example.

FIG. 3 is a schematic configuration diagram showing the structure of CEDI.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 turbidity device 2 first loose RO device 3 deaerator 4 second RO device 5 UV oxidation device 6 CEDI 6A treated water room 6B concentrated water room 11 high desalination ratio RO device 12 CEDI 12A treated water room 12B concentrated water room 13 Low Desalination RO Device 20 Ion Exchange Resin 21 Anion Exchange Membrane 22 Cation Exchange Membrane 23 Concentrated Water Room 24 Treated Water Room 25 Anode 26 Cathode 27 Anode Room 28 Cathode Room

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[Procedure amendment]

[Submission date] March 12, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction contents]

[0052] In Comparative Example 1 Example 1, where except that no provided deaerator was treated in the same manner, CaC 10-12 days
Scale of O ₃ is generated, lowering the permeate flow of the 2RO device, resulting in a rise in differential pressure.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction contents]

Comparative Example 2 The procedure of Example 1 was repeated, except that the pH was not adjusted on the inlet side of the first loose RO apparatus 2 but the pH was adjusted to 7.0, and the treatment was performed for 5 to 7 days. in <br/> scale of CaCO ₃ occurs, decrease in permeate flow rate of the 2RO device, resulting in a rise in differential pressure.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/469 C02F 1/46 103

Claims (1)

[Claims] 1. After adjusting the pH of raw water to 4 to 5, the water is passed through a first reverse osmosis membrane separation device having a low desalination rate to obtain a first permeated water and a first concentrated water. After degassing the first permeate, the pH is adjusted to 7 to 11 and then passed through a second reverse osmosis membrane separator to obtain a second permeate and a second concentrated water. A method for producing pure water, comprising supplying permeated water to a treated water chamber of a continuous electric regeneration type pure water apparatus to obtain pure water from the treated water chamber.