JP2002192152A - Method and apparatus for water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method which has reverse osmosis membrane devices arranged in two stages or three stages which can obtain high water quality suitable for an apparatus for producing high purity water to be used in a semiconductor production plant, a medicine production plant, a power plant, etc. SOLUTION: A softening device 2, a degassing device through which softened treatment water is passed, an alkali addition device 4 for adjusting the pH of degassed treatment water at 9.0 or above, the first reverse osmosis membrane device 5 through which the treatment water the pH of which is adjusted at 9.0 or above is passed, the second reverse osmosis membrane device 7 through which the treatment water the pH of which is adjusted is passed, the concentrated water of the first reverse osmosis membrane device 5 is passed through the third reverse osmosis membrane device 8, and filtrate from the membrane device is returned to the pre-stage of the first reverse osmosis membrane device 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment method and a water treatment apparatus, and more particularly, to a water treatment method and a water treatment apparatus which require high-purity water quality. The present invention relates to a water treatment method and a water treatment device suitable for producing pure water.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of improving the removal rate of silica and boron by a reverse osmosis membrane device by adding an alkali to the water supplied to the reverse osmosis membrane device to increase the pH.

However, in this method, there is a problem that the chemical added to increase the pH of the water supplied to the reverse osmosis membrane device is not sufficiently removed by the reverse osmosis membrane and leaks into the permeated water. In addition, it is common practice to use used ultrapure water (recovered water) or biologically treated water from another process in the feedwater of the reverse osmosis membrane apparatus. Contains ammonia, and there is a problem that ammonia is leaked into permeated water because it is not sufficiently removed by a reverse osmosis membrane device under alkaline conditions.

As described above, in the method of adding alkali to the feed water of the conventional reverse osmosis membrane apparatus, even if the removal rate of silica or boron can be increased, the added chemical or ammonia leaks into the treated water. It was difficult to obtain treated water of the same quality.

[0005]

As described above, in the method of adding alkali to the feed water of the reverse osmosis membrane apparatus to increase the pH of silica and boron by increasing the pH, the pH of the feed water is increased. The problem that the added drug is not sufficiently removed by the reverse osmosis membrane and leaks into the permeated water, and that the ammonia leaks into the permeated water without being sufficiently removed by the reverse osmosis membrane device under alkaline conditions. There is a need for improvement.

The present invention has been made in view of the above-mentioned conventional problems. In the production of pure water using a reverse osmosis membrane device, silica and boron are removed at a high removal rate.
An object of the present invention is to provide a water treatment method and a water treatment apparatus for removing high-purity pure water used in semiconductor manufacturing plants, pharmaceutical manufacturing plants, power plants, and the like by removing ammonia derived from recovered water and biologically treated water. I do.

[0007]

The water treatment method of the present invention comprises:
In a water treatment method for purifying water to be treated by sequentially passing water through a softening device, a first reverse osmosis membrane device, and a second reverse osmosis membrane device, an alkali is added to water supplied to the first reverse osmosis membrane device. And an acid addition step of adding an acid to the feed water of the second reverse osmosis membrane device (claim 1).

According to the present invention, in the softening step, the hardness component in the feed water that causes scale is removed, and in the alkali addition step, the solubility of silica and boron is increased and removed in the first reverse osmosis membrane treatment step. In the acid addition step, ammonia dissolved in a trace amount in the treated water is transferred to a form of ammonium ions which can be easily removed by the reverse osmosis membrane. High-purity pure water from which boron and also ammonia have been removed is obtained.

Further, in the water treatment method of the present invention, the water to be treated is passed through a softening device, a first reverse osmosis membrane device and a second reverse osmosis membrane device in that order to purify the water, and In the water treatment method, the concentrated water of the reverse osmosis membrane device is passed through a third reverse osmosis membrane device, and the permeated water is refluxed as the supply water of the first reverse osmosis membrane device. It is characterized by comprising an alkali addition step of adding an alkali to the supply water of the apparatus to adjust the pH to 9.0 or higher, and an acid addition step of adding an acid to the supply water of the second reverse osmosis membrane apparatus. Item 2).

Further, in the present invention, in the invention described in each of the above-mentioned claims, by providing a degassing step next to the softening step, carbon dioxide gas (CO ₂ ) which is the other component of scale formation is removed. Thus, pure water with less scale generation can be obtained (claim 3). The acid added in the acid adding step is preferably a divalent or higher polyvalent acid (claim 4).

In the acid addition step, the amount of the acid added is adjusted so that the pH of the treated water to which the acid has been added is 9.0 or less, preferably about 7, and then the conductivity of the water permeated through the second reverse osmosis membrane. Is desirably an amount that sufficiently reduces (claim 5).

In addition, it is more preferable to return the concentrated water discharged from the second reverse osmosis membrane device to the supply water of the first reverse osmosis membrane device from the viewpoint of effective use of the water to be treated. (Claim 6).

[0013]

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

FIG. 1 is a system diagram showing an embodiment of the water treatment method of the present invention.

In the present embodiment, as raw water, city water, well water, industrial water, used ultrapure water (recovered water), biologically treated water in another process, ion exchange treated water, or a mixed water thereof is used. be able to. In general, used ultrapure water (recovered water), biologically treated water from other processes, ion exchange treated water, etc.
Contains trace amounts of ammonia from the decomposition of resins and other organic matter.

These raw waters are passed through a pretreatment device 1 using coagulation sedimentation, membrane filtration, activated carbon treatment, etc., after which a strongly acidic cation exchange resin tower, a weakly acidic cation exchange resin tower, and a hardness component can be removed. Water is passed through a softening device 2 such as a chelate resin tower. In addition, as a pretreatment apparatus, an activated carbon tower is preferable.

The softening device 2 mainly removes calcium, magnesium and the like in raw water, but also removes other cations as a by-product. The softening device 2 is changed to a Na type or an H type by changing the type of the regenerant according to the purpose.

The softened water treated in the softening device 2 is supplied to a degassing device 3 such as a decarbonation tower, a vacuum degassing device or a membrane degassing device.
Is passed through. When the pH of the softened water is 6 or more,
Acids such as HCl and H ₂ SO ₄ are added, and the softened water is adjusted to pH 6 or less, preferably 5 or less, particularly about 3 to 5. Carbon dioxide dissolved as carbonate ions or bicarbonate ions is CO ₂ It is said.

In the degassing device 3, the carbon dioxide gas in the raw water is C
O ₂ is transferred to the gas phase and removed. However, when the concentration of inorganic carbonic acid in the raw water is 5 ppm or less, for example, when treating wastewater discharged from the manufacturing process of a semiconductor factory, the degassing device 3 does not need to be particularly installed.

The treated water degassed by the degassing device 3 includes:
An alkali such as NaOH or KOH is added from the alkali addition device 4 to make alkaline water. The alkali is added in such an amount that the pH of the water treated in the first reverse osmosis membrane device becomes 9.0 or more, preferably 9.5 or more.

The first reverse osmosis membrane device 5 has a pH of 9.0.
The treated water adjusted as described above is passed through, and silica and boron are mainly removed under the high pH condition adjusted by the added alkali. Also, under high pH conditions,
Adjustment with alkali is an effective means for treating raw water such as city water, well water, industrial water, etc., since the contamination resistance to organic substances and microorganisms contained in the raw water is also improved.

The permeated water of the first reverse osmosis membrane device 5 is then added with a divalent or higher polyvalent acid such as H ₂ SO ₄ from an acid addition device 6 to obtain a pH of 9.0 or less, preferably 6 or less. ~ 8,
In particular, the water is adjusted to about 6.5 to 7.5, and then water is passed through the second reverse osmosis membrane device 7. The pH of the second reverse osmosis membrane device 7 in the water to be treated may be adjusted so that the conductivity of the treated water is sufficiently low. Measure and determine the optimal p
It is preferable to adjust the H set value by feedback control.

In the present invention, in the treatment of such a two-stage reverse osmosis membrane device, the concentrated water of the first reverse osmosis membrane device 5 is supplied to the third reverse osmosis membrane device.
And the resulting permeated water is returned to the stage preceding the first reverse osmosis membrane device, whereby the water to be treated can be effectively used. In this case, the alkali is not added to the supply water of the first reverse osmosis membrane device 5 but to the supply water of the third reverse osmosis membrane device 8. Also in this case, the pH is adjusted to be 9.0 or more. Further, if necessary, alkali may be added to both the supply water of the first reverse osmosis membrane device 5 and the supply water of the third reverse osmosis membrane device 8. The concentrated water in the third reverse osmosis membrane device 8 is discharged out of the system.

In the present invention, as the reverse osmosis membrane of the first, second, and third reverse osmosis membrane devices 5, 7, and 8, "SU-700" and "SUL-G" manufactured by Toray Industries, Inc., Nitto Denko Corporation Reverse osmosis membranes such as “NTR759” and “ES20” manufactured by Company and “BW-30” manufactured by Filmtec can be used. However, as the reverse osmosis membrane of the second reverse osmosis membrane device 5,
It is also possible to use a positively charged film such as “SU-900” manufactured by Toray Industries, Inc., “ES20C” manufactured by Nitto Denko Corporation.

According to the method of the present invention, the treated water (the permeated water of the second reverse osmosis membrane device 7) has an electric conductivity of 1.0 μS
/ Cm or less of high quality treated water can be obtained.

The concentrated water of the first reverse osmosis membrane device 5 is treated with the third reverse osmosis membrane device 8 to obtain the permeated water and the concentrated water of the second reverse osmosis membrane device 7 and the first reverse osmosis membrane device By returning the water to the preceding stage of the device 5, the water recovery rate can be greatly increased.

The third reverse osmosis membrane device 8 is different in type from the first reverse osmosis membrane device 5, and in particular, in order to optimize the flow rate per module of the concentrated water, the first reverse osmosis membrane device 8 is tentatively used. Assuming that the diameter of the nozzle is 8 inches, it can be made smaller, such as 4 inches.

The third reverse osmosis membrane device 8 desalinates the concentrated water of the first reverse osmosis membrane device 5, so that the salt concentration of the supplied water increases, which is a factor of deteriorating the quality of permeated water. Therefore, the third reverse osmosis membrane device 8 includes a module having a higher desalination rate than the first reverse osmosis membrane device 5, for example, the first reverse osmosis membrane device 5 includes "SU-700" manufactured by Toray Industries, Inc. The third reverse osmosis membrane device 8 may be “SU-700R” manufactured by Toray Industries, Inc.

[0029]

The present invention will be described in more detail with reference to the following examples.

Example 1 Water treatment was carried out by the process shown in FIG. 1 by using a mixture of well water and recovered water from a semiconductor factory as raw water. First, after passing water through a pretreatment device 1 consisting of an activated carbon tower, water was passed through a softening device 2 consisting of an ion exchange tower filled with a weakly acidic cation exchange resin [Bayer, Lewatit CNP80] to perform a softening treatment. Then, after passing water through a degassing device (decarbonation tower) 3 to perform degassing treatment, NaO
H was added to pH 10.5, and the first reverse osmosis membrane device 5
Water.

H ₂ SO ₄ is added to the permeated water of the first reverse osmosis membrane device (reverse osmosis membrane: “SU-700” manufactured by Toray Industries, Inc.) 5 from the acid addition device 6 to adjust the pH to 6.5. 2 Reverse osmosis membrane device (reverse osmosis membrane: "SUL-G" manufactured by Toray Industries, Inc.)
7 was passed.

The concentrated water of the first reverse osmosis membrane device 5 is supplied to a third reverse osmosis membrane device (reverse osmosis membrane: “SU-70” manufactured by Toray Industries, Inc.).
0 "), and the concentrated water was discharged out of the system. The permeated water of the third reverse osmosis membrane device 8 and the concentrated water of the second reverse osmosis membrane device 7 were returned to the preceding stage of the first reverse osmosis membrane device 5.

The water supply, permeated water and concentrated water amounts of the reverse osmosis membrane devices 5, 7, and 8 are as follows. First reverse osmosis membrane device 5: Water supply amount = 750 liter / h Permeate amount = 500 liter / h Concentrated water amount = 250 liter / h Second reverse osmosis membrane device 7: Water supply amount = 500 liter / h Permeate amount = 450 1 liter / h Concentrated water amount = 50 liter / h Third reverse osmosis membrane device 8: Water supply amount = 250 liter / h Permeated water amount = 190 liter / h Concentrated water amount = 60 liter / h Comparative Example 1 First Example H in the reverse osmosis membrane device 5
_The treatment was performed in the same manner as in Example 1 except that ₂ SO ₄ was not added.

Table 1 shows the results of Example 1 and Comparative Example 1.

[0035]

[Table 1] As is clear from Table 1, the treated water obtained by adding an acid to the permeated water of the first reverse osmosis membrane device has higher water quality than the treated water not added, and the first and second reverse osmosis membranes are used. Even after reusing the concentrated water of the apparatus, it was possible to obtain treated water having an electric conductivity of 0.3 μS / cm. Also, the amount of sodium leaked into the treated water (the permeated water of the second reverse osmosis membrane device) could be reduced.

Further, by reusing the concentrated water, a water recovery rate of 92.0% can be achieved, and the water recovery rate is 60.0% when the concentrated water is not reused. Could be greatly increased.

Example 2 In the process shown in FIG. 1, the concentrated water of the second reverse osmosis membrane device 7 was used as wastewater, and water treatment was performed using well water mixed with recovered water from a semiconductor factory as raw water. . Others were the same as Example 1.

Comparative Example 2 In Example 2, the permeated water of the first reverse osmosis membrane device 5 was H
Water treatment was carried out in the same manner as in Example 1 except that ₂ SO ₄ was not added.

The results of Example 2 and Comparative Example 2 are shown in Table 2. In particular, the results are shown focusing on ammonia which is remarkably contained in the recovered water of the semiconductor factory.

[0040]

[Table 2] As is clear from Table 2, the treated water obtained by adding an acid to the permeated water of the first reverse osmosis membrane device has higher water quality than the treated water not added, and the treated water of ammonia (the second reverse osmosis water) is used. The amount of leakage into the permeable membrane device (permeated water) could be reduced.

Example 3 In the case where ammonia is not contained and the conductivity of the treated water may be high, other than the second reverse osmosis membrane apparatus in the steps shown in FIG. When water treatment was performed under the same conditions as in 1, the treated water could be obtained with a high desalination rate and a high recovery rate.

Example 4 In the process shown in FIG. 1, the third reverse osmosis membrane device 8 was operated under alkaline conditions of pH 9.0 or more, with the alkali addition position being the supply water for the third reverse osmosis membrane device 8. Then, water treatment was performed using recovered water from a semiconductor factory as raw water. At this time,
The reverse osmosis membrane of the second reverse osmosis membrane device 7 used in Example 1 was changed from “SUL-G” manufactured by Toray Industries, Inc. to “ES20C” manufactured by Nitto Denko Corporation, and the other conditions were the same as in Example 1. .

Example 5 In Example 4, N was added to the permeated water of the first reverse osmosis membrane device 5.
Except that aOH was added, the amount of sodium leakage due to the difference in the addition position was compared in the same manner as in Example 4.

Table 3 shows the results of Examples 4 and 5. In particular, the results focusing on the Na amount of NaOH for pH adjustment are shown.

[0045]

[Table 3] As is apparent from Table 3, a reverse osmosis membrane device having a large number of positive charges in the functional membrane was used as the second reverse osmosis membrane device 7, and the position of the alkali addition was changed to the supply water of the third reverse osmosis membrane device 8. Example 4 in which water was supplied to the first reverse osmosis membrane device 5 in the position where the alkali was added in Example 1
When compared with Example 4, the treated water of Example 4 was more treated with Na (second
It can be seen that the amount of leakage from the reverse osmosis membrane device 5 to the permeated water) is reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a water treatment method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pretreatment tower 2 ... Softening apparatus 3 ... Degassing apparatus 4 ... Alkali addition apparatus 5 ... 1st reverse osmosis membrane apparatus 6 ... Acid addition apparatus 7 ... 2nd reverse osmosis membrane apparatus 8 .... 3rd reverse osmosis membrane device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) C02F 1/42 C02F 1/42 BA (72) Inventor Motonori Yanagi 2-9-1 Okada, Atsugi-shi, Kanagawa No. 8 Nomura Micro Science Co., Ltd. (72) Inventor Takayuki Jimaru 2-9-8 Okada, Atsugi-shi, Kanagawa F-term Nomura Micro Science Co., Ltd. 4D006 GA03 KA02 KA03 KA52 KA53 KA54 KA55 KA63 KA64 KB11 KB12 KB13 KD11 KD17 KE15Q KE15R PA01 PB06 PB07 PC02 PC31 PC42 4D025 AA02 AA04 AA07 AB34 BA09 BA17 DA01 DA03 DA05 DA10 4D037 AA03 AB11 BA23 BB07 CA03 CA14 CA15

Claims (10)

[Claims] 1. A water treatment method for purifying water to be treated by passing it through a softening device, a first reverse osmosis membrane device, and a second reverse osmosis membrane device in order, wherein the supply of the first reverse osmosis membrane device is performed. A water treatment method comprising: an alkali addition step of adding an alkali to water to adjust the pH to 9.0 or higher; and an acid addition step of adding an acid to water supplied to the second reverse osmosis membrane device. 2. The water to be treated is sequentially passed through a softening device, a first reverse osmosis membrane device and a second reverse osmosis membrane device to be purified, and the concentrated water of the first reverse osmosis membrane device is removed. In a water treatment method wherein water is passed through a third reverse osmosis membrane device and the permeated water is refluxed as supply water for the first reverse osmosis membrane device, wherein an alkali is added to the supply water of the third reverse osmosis membrane device A water treatment method, comprising: an alkali addition step of adjusting the pH to 9.0 or higher; and an acid addition step of adding an acid to water supplied to the second reverse osmosis membrane device. 3. The water treatment method according to claim 1, further comprising a degassing step of passing treated water from the softening device through a degassing device to degas. 4. The method according to claim 1, wherein the acid added to the feed water of the second reverse osmosis membrane device is a divalent or higher polyvalent acid. Water treatment method. 5. The water treatment method according to claim 1, wherein the pH of the supply water of the second reverse osmosis membrane device to which the acid is added is lower than 9.0. . 6. The apparatus according to claim 1, wherein the concentrated water discharged from the second reverse osmosis membrane device is returned to the supply water of the first reverse osmosis membrane device. Water treatment method. 7. A water treatment apparatus comprising a softening device, a first reverse osmosis membrane device, and a second reverse osmosis membrane device arranged along a flow path for purifying water to be treated, wherein the first reverse osmosis is provided. A water treatment apparatus comprising: an alkali addition device for adding an alkali to water supplied to a membrane device; and an acid addition device for adding an acid to water supplied to the second reverse osmosis membrane device. 8. A softening device, a first reverse osmosis membrane device, and a second reverse osmosis membrane device are arranged along a flow path for purifying the water to be treated, and the concentrated water of the first reverse osmosis membrane device is provided. In a water treatment apparatus provided with a third reverse osmosis membrane device for passing water therethrough and refluxing the permeated water as supply water for the first reverse osmosis membrane device, the supply of the third reverse osmosis membrane device A water treatment apparatus comprising: an alkali addition device for adding an alkali to water; and an acid addition device for adding an acid to water supplied to the second reverse osmosis membrane device. 9. The water treatment apparatus according to claim 7, wherein a degassing device is provided between the softening device and the first reverse osmosis membrane device. 10. The water treatment according to claim 7, wherein the concentrated water of the second reverse osmosis membrane device is returned to the supply channel of the first reverse osmosis membrane device. apparatus.