JPH11262771A - Production of pure water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the amperage of a continuous electric generation type pure water apparatus and to obtain high quality without scale hindrance by a method in which the pH of raw water is adjusted at a specified value, the raw water, after being deaerated, is subjected to anion exchange and separated into filtrate and concentrated water by reverse osmosis membrane separation, and the filtrate is converted into pure water by the pure water apparatus. SOLUTION: City water is treated with a clarifying apparatus 1, after its pH being adjusted at 3-5 with HCl, is supplied to a deaerator 2 for deaeration. After the deaerated water being passed through an anion exchange resin column 3, the water, together with the concentrated water of a continuous electric regeneration type pure water apparatus (CEDI) 5 of a post-stage and electrode water, is mixed with HCl, with its pH adjusted at about 6.5-7, and passed through a reverse osmosis membrane separator (RO apparatus) 4 to obtain concentrated water and filtrate. Part of the filtrate is sent to the treated water chamber 5A of the CEDI 5 to be made into pure water. The residual filtrate is sent to a concentrated water chamber 5B to be supplied to an electrode as concentrated water. In this way, high quality treated water is obtained with a reduced power consumption.

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, in the production of pure water used for cleaning water for semiconductors, lenses, liquid crystals, etc., 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 characteristic 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 is reduced.
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) has been provided as a pretreatment means for such CEDI. By installing the RO device, the electrolyte in raw water,
The TOC component can be efficiently removed, the load on CEDI can be reduced, and high-purity treated water can be obtained.

[0005] In the case thus providing a RO device, since the CO ₂ content greatly affects the quality of CEDI process water, in order to reduce the CO _2, the following method has been proposed.

The current value of CEDI is increased.

[0007] The pH of CEDI feed water is increased to 8-9.

[0008] After treatment with a cation exchange resin and a deaerator to reduce Ca ²⁺ and CO ₂ , water is passed through an RO unit.

[0009]

Among the above conventional methods, C
How to increase EDI current and pH of CEDI feedwater
In the method of increasing CO, CO ₂ (HCO ₃ ⁻ ) and a trace amount of Ca
There is a problem that CaCO ₃ scale is generated in the coexistence of ²⁺ . In particular, increasing the pH of the CEDI feedwater will accelerate the generation of scale. Such a phenomenon cannot be eliminated only by RO processing. Further, in the method of increasing the current value, the power cost rises. Besides, T in raw water
OC cannot be removed and the quality of treated water is poor.

In the method of removing the Ca ²⁺ and CO _{2 using} a cation exchange resin and a deaerator, improvement of the specific resistance can be achieved, but TOC or silica (SiO ₂ )
Is not sufficiently reduced, and a sufficiently satisfactory water quality cannot be obtained.

By the way, in the case of removing silica by desalting with CEDI, the amount of current required is greatly increased if the silica removal rate is to be increased. This is because it is necessary to electrically pull the silica with a strong force to move the silica from the treated water chamber to the concentrated water chamber. Therefore, in order to increase the silica removal rate, the amount of current must be increased. become. When the amount of current is increased in this way, water is also decomposed, the current is consumed, and the power cost is further increased.

Also, in desalination by CEDI, if the balance between 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 present invention solves the above-mentioned conventional problems and provides a CE.
An object of the present invention is to provide a method for producing pure water that can obtain treated water of high quality without increasing the current value of DI and preventing scale disturbance.

[0014]

The pure water production method of the present invention comprises a deaeration step in which raw water is adjusted to pH 3 to 5 to deaerate and an anion exchange step in which the raw water is brought into contact with an anion exchange resin. Thereafter, the water is passed through a reverse osmosis membrane separator to obtain permeated water and concentrated water, and the permeated water is supplied to a continuous electric regeneration type pure water apparatus to obtain pure water.

In the present invention, any of the above degassing step and anion exchange step may be performed first. In this degassing step, the (bi) carbonic acid component in the water is brought into a CO ₂ state by setting the pH to 3 to 5 under acidic conditions, and is easily removed by degassing.

In the anion step, the pH of the influent water becomes alkaline by treating the influent water with an anion exchange resin. Under alkaline conditions, the silica ionizes and the residual CO ₂ also ionizes into (bi) carbonate ions.
The ionized silica and (bi) carbonate ions are adsorbed and removed by the anion exchange resin. Further, a part of the TOC in the water is ionized in the alkaline state, and thus is adsorbed and removed by the anion exchange resin.

As described above, in the treatment of raw water by the degassing step and the anion exchange step, the raw water may be treated in the order of the degassing step and the anion exchange step, or the raw water may be treated in the order of the anion exchange step and the degassing step. Is also good. The treated water obtained by treating the raw water in the two steps as described above is introduced into the RO device. This RO
Since almost neutral water (water obtained by treating raw water) having a pH of 6 to 9.5 is supplied to the apparatus, an ordinary RO membrane having a high desalination rate can be used. The feed water (water obtained by treating raw water) of this RO device is one from which scale components such as carbonate ions and silica have been removed by degassing and anion exchange treatment. And high-quality permeated water can be obtained at a high recovery rate.

In the CEDI process, since the substances causing the scale, such as silica and carbonate ions, have been removed in the preceding steps, the generation of scale in the CEDI can be prevented, and the CEDI can be operated stably for a long time. .

Further, as described above, when the silica is removed by the CEDI, the power cost rises. However, in the present invention, the silica is removed before the CEDI.
In CEDI, there is no need to particularly consider the removal of silica, and an increase in current value can be suppressed.

Further, in the preceding stage of CEDI, the carbonic acid component is sufficiently removed by degassing and treatment with an anion exchange resin, so that the inflow of the carbonic acid component into CEDI is extremely small.
Therefore, there is no problem of the deterioration of the water quality of the CEDI treated water caused by the above-mentioned CO ₂ , and a good water quality can be obtained stably.

[0021]

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 the embodiment of the present invention.

In the present invention, as 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 waste water from a semiconductor manufacturing process using ultrapure water can be used. Can be subjected to biological treatment to a TOC of 1 ppm or less according to a conventional method, and further subjected to RO treatment and ion exchange treatment as needed to obtain raw water. In the case where the biologically treated water is used as raw water, the biologically treated water may be supplied to the entrance side of the anion exchange resin tower 3.

The 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 the turbidity treatment is led to a deaeration step. In this deaeration step, a mineral acid such as HCl or H ₂ SO ₄ is added to adjust the pH to 3 to 5, and deaeration is performed by the deaerator 2.

In the deaerator 2, since the pH of the feed water is acidic at 5 or less, the (bi) 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 2, an ordinary deaerator such as a decarboxylation (air contact method) device, a N ₂ deaerator, a vacuum deaerator, and a film deaerator can be used.

The degassed water from the degassing device 2 is then led to an anion exchange step and passed through an anion exchange resin tower 3. In the anion exchange resin tower 3, as described above, the alkaline condition is reached, the silica is ionized, and the residual CO ₂ is also ionized to form (bi) carbonate ions. By adsorption. Further, a part of the TOC in the water is ionized in the alkaline state, and thus is adsorbed and removed by the anion exchange resin. The anion exchange resin of the anion exchange resin tower 3 may be a weakly basic anion exchange resin or a strongly basic anion exchange resin, and specifically, “Levatit MP64” (manufactured by Bayer AG) (Basic anion exchange resin), "LEVATIT MP500" (strongly basic anion exchange resin), and the like can be used.

The effluent of the anion exchange resin tower 3 is usually p
H 9.5 to 10.5 alkaline.

In FIG. 1, the raw water is treated in the order of the degassing step and the anion exchange step. However, in the present invention, the raw water can be treated in the order of the anion exchange step and the degassing step. A trace amount of oxygen may be dissolved in the anion exchange step. However, if the degassing step is provided after the anion exchange step, such oxygen can also be removed.

The effluent from the anion exchange step or degassing step is led to a RO device after pH adjustment. In the example of FIG. 1, the effluent of the anion exchange resin tower 3 is the
An acid is added as necessary together with the concentrated water of pH 5 to adjust pH 6 to
After being adjusted to 9.5, water is passed through the RO device 4.

In this RO device 4, since almost neutral water having a pH of 6 to 9.5 is supplied, the NaCl removal rate is 98%.
An ordinary RO membrane having a high desalination ratio as described above, for example, an RO membrane of polyamide type or cellulose acetate type can be used.
Specifically, “NTR759HR” manufactured by Nitto Denko Corporation, [E
S-20] or [SU-700] manufactured by Toray Industries, Inc. can be used.

In the RO device 4, as described above, the water supply is obtained by removing scale components such as carbonate ions and silica by the treatment of the deaerator 2 and the anion exchange resin tower 3, so that the water recovery rate is reduced. Even if the concentration is increased, scale disturbance is not caused, and high-quality permeated water can be obtained at a high recovery rate of about 85 to 95%.

The permeated water of the RO device 4 is supplied to a later stage CEDI.
The concentrated water is supplied to the treated water chamber 5A and the concentrated water chamber 5B, and the concentrated water is discharged out of the system.

As shown in FIG. 2, in the CEDI 5, the concentrated water chamber 23 and the treated water chamber 24 are separated from the anode chamber 27 and the cathode chamber 28 by the anion exchange membrane 21 and the cation exchange membrane 22. 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 5, deionization is performed according to the above-described principle, and pure water is obtained from the treated water chamber 5A, and concentrated water is discharged from the concentrated water chamber 5B. In addition, the permeated water of the RO device 4 is supplied to the electrode chambers (the anode chamber and the cathode chamber) of the CEDI 5.

The pure water from the treated water chamber 5A 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 5B is returned to the preceding stage of the RO device 4 and supplied to the RO device 4. Further, the effluent from the electrode chamber is also returned to the preceding stage of the RO device 4.

In the present invention, by the previous stage of CEDI5, scale-causing substances such as silica and carbonate ions in the raw water are highly removed, so that the generation of scale in CEDI5 is prevented, and CEDI5 itself is 85%. ~ 9
It can be operated stably for a long period of time with a high water recovery rate of about 5%. In particular, carbonic acid is highly removed by degassing and adsorption removal in the anion exchange resin tower 3, so that the inflow of (bi) carbonate ions into the CEDI 5 is extremely small, and the ion balance caused by the above-mentioned 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.

Further, since silica is previously removed before the CEDI 5, it is not necessary to pay particular attention to the removal of the silica in the CEDI 5, and an increase in the current value can be suppressed.

The permeated water of the RO device 4 serving as the water supply to the treated water chamber 5A and the concentrated water chamber 5B of the CEDI 5 is obtained by removing the scale components to a high degree by the deaerator 2 and the anion exchange resin tower 3 at the preceding stage. Therefore, even if the concentrated water of the CEDI 5 is returned and supplied to the RO device 4, the RO device 4 does not cause a scale failure or the like, and can stably perform the processing.

In the embodiment shown in FIG. 1, the only water discharged to the outside of the system is the concentrated water of the RO device 4, and the water recovery rate of the entire system is set to a high water recovery rate of 80% or more. In addition, high quality treated water can be obtained.

[0042]

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.

First, 500 L / hr of city water was treated with a turbidity separator (external pressure type hollow fiber UF membrane separator) 1, adjusted to pH 4 with HCl, and supplied to a deaerator 2. As the deaerator 2, an air counterflow type (air volume: 10 m ³ / hr) decarbonation tower filled with 5 L of a filler (net ring) is used.
Treated at 30 m / hr.

The degassed water is then passed through an anion exchange resin tower (strongly basic anion exchange resin “LEVATIT MP500”).
After passing through SV (10 L / hr) 3 with SV = 10 / hr, the pH was adjusted to 6.5 to 7 by adding HCl together with the concentrated water of CEDI 5 and the electrode water in the latter stage, and passed through the RO device 4.

As the RO device 4, an RO film loaded with one (4 inch) “NTR-759HR” (polyamide-based synthetic composite film, 98% NaCl removal rate) manufactured by Nitto Denko Corporation is used. 500L / hr, water supply pressure 12
The treatment was performed at kg / cm ² and a water recovery rate of 40%.

Of the 230 L / hr of permeated water of the RO device 4, 150 L / hr was supplied to the treated water chamber 5 A of CEDI (“Pure Ace PA120” manufactured by Kurita Kogyo Co., Ltd.) 5, and 60 L / hr was concentrated water. Water is supplied to room 5B, and 20L / h
r was supplied to the electrode chamber.

The obtained treated water (pure water from CEDI5)
The water quality of CEDI5 and the voltage and current value of CEDI5 were examined.
It was shown to.

COMPARATIVE EXAMPLE 1 The procedure of Example 1 was repeated except that the degassing apparatus and the anion exchange resin tower were omitted, and the turbid raw water (pH 6.5 to 7) was passed directly to the RO apparatus. went. That is,
The clarified raw water is supplied to the RO device at a water supply amount of 500 L / hr and a water supply pressure of 12 kg / cm ² , and 150 L / hr of the permeated water of 230 L / hr is supplied to the treated water chamber of CEDI.
60 L / hr was supplied to the concentrated water chamber, and 20 L / hr was supplied to the electrode chamber.

[0050] The quality of the obtained treated water and the voltage of CEDI,
The current value was examined, and the results are shown in Table 1.

Comparative Example 2  In Example 1, the anion exchange resin tower was omitted, and
And a cation exchange resin tower before the deaerator (decarbonation tower).
(50 L of “Levatit SP112” manufactured by Bayer AG
) And treated through a cation exchange resin tower and a decarbonation tower.
After adjusting the pH to 6.5 to 7 by adding an alkali to the water,
Except that the water passed through the RO device and CEDI
Processing was performed.

The quality of the obtained treated water and the voltage of CEDI,
The current value was examined, and the results are shown in Table 1.

[0053]

[Table 1]

As is clear from Table 1, according to the present invention, high-quality treated water can be obtained with a small amount of power consumption.

In the first embodiment, the RO device was operated at a water recovery rate of 46%.
Even with operation at a high recovery rate of 0%, there was no problem such as scale disturbance, and the treated water quality almost equivalent to that of Example 1 could be obtained.

[0056]

As described above in detail, according to the method for producing pure water of the present invention, in a method for producing pure water by combining an RO device and CEDI, the current value of CEDI is not increased, and Thus, high quality treated water can be obtained by preventing scale disturbance.

[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 schematic configuration diagram showing the structure of CEDI.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 turbidity device 2 degassing device 3 anion exchange resin tower 4 RO device 5 CEDI 5A treated water chamber 5B concentrated water chamber 20 ion exchange resin 21 anion exchange membrane 22 cation exchange membrane 23 concentrated water chamber 24 treated water chamber 25 anode 26 cathode 27 Anode compartment 28 Cathode compartment

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/44 C02F 1/44 J 9/00 502 9/00 502Z 502J 502F 502L 503 503B 504 504B 504E

Claims (1)

[Claims] 1. A process in which raw water is subjected to a degassing process of adjusting the pH to 3 to 5 and degassing, and an anion exchange process of bringing the raw water into contact with an anion exchange resin. A method for producing pure water, comprising obtaining water and concentrated water, and supplying the permeated water to a continuous electric regeneration type pure water apparatus to obtain pure water.