JP2000271570A - Production of pure water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat concentrated water at low costs in a process for producing pure water by a method in which the alkaline concentrated water discharged from a reverse osmosis apparatus is directly, or after being treated further by a reverse osmosis membrane, neutralized by the acid regeneration drainage of a cation exchange resin column and the exhaust gas of a degasifier. SOLUTION: Raw water, after being passed through an H-type cation exchange resin column 1 to remove scale components such as calcium ions, is supplied to a degasifier 2 to remove carbonate ions and others. The treated water, after being added with an alkali agent to adjust its pH at 9.2 or above, is passed through a reverse osmosis membrane apparatus 3 to be treated. The filtrate is supplied to a deionization column 4 to obtain pure water. Alkaline concentrated water discharged from the apparatus 3 is supplied to a packed column 5 and contacted countercurrentwise with the acid regeneration drainage of the column 1 and the exhaust gas of the degasifier 2 to be neutralized. In this way, the concentrated water is neutralized economically by using acidic substances generated subordinately in a system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a method for producing pure water. More specifically, the present invention provides a process in which raw water is subjected to reverse osmosis membrane treatment under alkaline conditions to produce pure water. The present invention relates to an economical and advantageous method for producing pure water in which a neutralization treatment is performed using an acidic substance generated in water.

[0002]

2. Description of the Related Art As a method for producing pure water or ultrapure water by treating raw water, there is known a method for producing pure water in which the pH is adjusted to 10 or more by adding an alkali, and then the solution is passed through an alkali-resistant reverse osmosis membrane. I have. In such a pure water production method, before the reverse osmosis membrane device, calcium ions and the like in the raw water are removed, and scale components such as calcium are deposited on the reverse osmosis membrane device to prevent the membrane from being clogged. In some cases, a weakly acidic ion exchange resin tower is provided for the purpose of, or a degassing device is provided for the purpose of removing dissolved carbon dioxide gas and reducing the amount of alkali agent added in the subsequent process. Many. Further, a deionization device is generally provided downstream of the reverse osmosis membrane device for the purpose of improving the quality of pure water. In the method for producing pure water using such an alkali-resistant reverse osmosis membrane device, a large amount of alkali needs to be added to increase the pH of the water supplied to the reverse osmosis membrane device. The concentrated water of the apparatus is discharged in a high pH state containing a high concentration of alkali. Therefore, this concentrated water cannot be discharged as it is, but must be discharged after neutralization treatment with hydrochloric acid or the like, and there is a problem that the wastewater treatment cost is inevitably high.

[0003]

SUMMARY OF THE INVENTION Under such circumstances, the present invention provides a process in which raw water is subjected to reverse osmosis membrane treatment under alkaline conditions to produce pure water. The purpose of the present invention is to provide an economically advantageous pure water production method for treating the alkaline concentrated water to be produced at low cost.

[0004]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor passed raw water through an H-type cation exchange resin tower, and then degassed by a degassing device. In the process of producing pure water by passing water through a reverse osmosis membrane device under alkaline conditions, and then directly or further reverse osmosis membrane treatment of the alkaline concentrated water discharged from the reverse osmosis membrane device It has been found that the object can be achieved by neutralizing the obtained concentrated water with the acid regeneration wastewater of the H-type cation exchange resin tower or the exhaust gas of the degassing device, and based on this finding, the present invention Was completed. That is, in the present invention, (1) raw water is passed through an H-type cation exchange resin tower, degassed by a degassing device, and then passed through a reverse osmosis membrane device under alkaline conditions of pH 9.2 or more. In producing pure water by water, neutralizing the alkaline concentrated water discharged from the reverse osmosis membrane device with the acid regeneration wastewater of the H-type cation exchange resin tower or the exhaust gas of the degassing device. And (2) passing the raw water through an H-type cation exchange resin tower, degassing with a degassing device, and then reverse osmosis under alkaline conditions of pH 9.2 or more. In producing pure water by passing water through the membrane device, alkaline concentrated water discharged from the reverse osmosis membrane device is passed through a separately provided reverse osmosis membrane device, and the permeated water is subjected to H-type cations. Return to the exchange resin tower or degassing unit and A method for producing pure water, comprising neutralizing an alkaline concentrated water discharged from a provided reverse osmosis membrane device with an acid regeneration wastewater of the H-type cation exchange resin tower or an exhaust gas of a degassing device. , Is provided.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention is characterized in that raw water is passed through an H-type cation exchange resin tower, degassed by a degassing device, and then subjected to reverse osmosis membrane under alkaline conditions of pH 9.2 or more. This is a method for producing pure water by passing water through the device. The raw water used in the method of the present invention preferably has a water quality suitable for raw water of a so-called primary pure water apparatus, which is subjected to treatment such as coagulation sedimentation and activated carbon treatment to remove turbidity and the like. In the method of the present invention, first, the raw water is passed through an H-type cation exchange resin tower. By this water flow, scale components such as calcium ions and magnesium ions in the raw water are removed, and scale components are deposited in a reverse osmosis membrane device at a later stage to prevent membrane blockage and prevent a decrease in water production. it can. In the H-type cation exchange resin tower, it is preferable to regenerate using an acid such as hydrochloric acid or sulfuric acid, and then pass an alkali agent to partially convert the cation exchange resin into Na type. By regenerating the cation exchange resin with hydrochloric acid and further converting a part of the cation exchange resin to Na type with sodium hydroxide, both the H type resin and the Na type resin are present in the cation exchange resin tower. By _{R 2 -Ca + 2HCl → 2R-} H + CaCl 2 R-H + NaOH → R-Na + H 2 O H type resin and Na-type resin are both present,
Calcium can be removed according to the following formula regardless of the form of calcium ions in the raw water. Ca (HCO ₃ ) ₂ + 2R−H → R ₂ −Ca + 2H ₂ C
O ₃ CaCl ₂ + 2R-Na → R ₂ -Ca + 2NaCl In the method of the present invention, the treated water from which scale components such as calcium ions have been removed in this way is supplied to a degassing device, and degassed. Is done. In this degassing device, carbonate ions in water are removed as carbon dioxide. The degassing apparatus is not particularly limited, and examples thereof include a decarbonation tower, a vacuum degassing tower, a nitrogen degassing tower, and a membrane degassing apparatus. Among these apparatuses, particularly, treated water and air A decarbonation tower and a membrane deaerator by countercurrent contact with water are preferred. Next, the degassed water is adjusted to pH 9.2 or higher, and then passed through a reverse osmosis membrane device. There is no particular limitation on the method of adjusting the pH, and examples thereof include a method of adding an alkaline aqueous solution such as sodium hydroxide and potassium hydroxide, a method of contacting with a strongly basic anion exchange resin, and an electrolytic method. . As a method of adding an alkaline aqueous solution, for example, it is advantageous to provide a pH adjusting tank with a stirrer, to provide an alkaline aqueous solution injection port in a water flow line, and to install a static mixer or the like on the downstream side thereof. . It is particularly preferable to adjust this pH to the range of 9.5 to 11.

The reverse osmosis membrane used in the reverse osmosis membrane device is preferably an alkali-resistant reverse osmosis membrane which is not deteriorated even if the pH becomes 10 or more for a long term. In this case, since the concentrated water has a higher pH than the supply water under alkaline conditions, it is important to select an alkali-resistant reverse osmosis membrane in consideration of the concentrated water pH. Examples of such an alkali-resistant reverse osmosis membrane include, for example, those manufactured by Film Tec, which are commercially available as those having long-term durability up to pH 11;
Nitto Denko, which is commercially available as FILMTEC type FT30 or the like, and has long-term durability up to pH 10
ES20, ES10, NTR759 manufactured by Toray Industries, Inc.
And a polyamide-based film such as SU700. In this reverse osmosis membrane device, the reverse osmosis membrane may be provided in one stage, or may be provided in multiple stages. When the reverse osmosis membrane is provided in multiple stages, the permeated water of the first stage reverse osmosis membrane is used as the supply water of the second stage reverse osmosis membrane. In the method of the present invention, the treated water (permeated water) obtained by passing water through the reverse osmosis membrane device can be passed through a deionization device to finish pure water. There is no particular limitation on the deionizer, for example, a regenerative or non-regenerative mixed bed ion exchanger,
An electric regeneration type deionization device, a positively charged reverse osmosis membrane, or the like can be used. Examples of the regenerated or non-regenerated mixed bed ion exchange device include an ion exchange device filled with a known regenerative or non-regeneration type strongly acidic cation exchange resin and a strongly basic anion exchange resin. As the electric regeneration type deionization apparatus, a known apparatus can be used. This apparatus does not require regeneration by a chemical, has a small size, has a large capacity, and can economically produce pure water. . The positively charged reverse osmosis membrane is a reverse osmosis membrane obtained by cationizing a polyamide skin layer on the membrane surface. As such a positively charged reverse osmosis membrane, for example, a commercially available Nitto Denko Corporation E
S10C, SU900 of Toray Industries, Inc. and the like can be used. In the method of the present invention, there are two modes for treating the alkaline concentrated water discharged from the reverse osmosis membrane device, namely, (1) the alkaline concentrated water is directly used as the acid in the H-type cation exchange resin tower. (2) the alkaline concentrated water is passed through a separately provided reverse osmosis membrane device, and the permeated water is subjected to H-type cation exchange resin. The alkaline concentrated water discharged from the separately provided reverse osmosis membrane device while being returned to the tower or the degassing device is subjected to acid regeneration wastewater from the H-type cation exchange resin tower or exhaust gas from the degassing device. There is a method of summing. By employing the method (2), the recovery rate of pure water can be improved.

As described above, since the H-type cation exchange resin tower performs regeneration using an acid such as hydrochloric acid or sulfuric acid, an acid regeneration effluent is generated. Therefore, the concentrated aqueous alkaline solution is neutralized using the acid regeneration wastewater as in the methods (1) and (2). This neutralization treatment has a pH of 5
It is better to make it to be about 8.5. In the degassing device, an acidic gas containing carbon dioxide and the like is discharged, and the exhaust gas is used to neutralize the alkaline concentrated water as in the methods (1) and (2). In the neutralization treatment, it is preferable to use a packed tower filled with a suitable filler and bring the concentrated water and the exhaust gas into countercurrent contact. In the countercurrent contact, it is advantageous to flow the concentrated water downward and to flow the mixed gas of the exhaust gas and the air used as needed upward. At this time, the LV of the concentrated water is usually 10 to 1
00 m / hr, preferably 20 to 50 m / hr, and the gas / liquid ratio is preferably 10 to 30. Further, this neutralization treatment is preferably performed so that the pH becomes about 5 to 8.5. If necessary, the neutralization treatment with the exhaust gas and the neutralization treatment with the acid regeneration effluent are used in combination. be able to. Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 1 to 4 are process flow charts of different examples for carrying out the method of the present invention. In FIG. 1, raw water is passed through an H-type cation exchange resin tower 1 to remove calcium ions and the like. After the scale components have been removed, it is supplied to the degassing device 2 to remove carbonate ions and the like in the water. Next, the treated water is adjusted to a pH of 9.2 or more by adding an alkali agent, and then passed through a reverse osmosis membrane device 3, and the permeated water is further supplied to a deionization tower 4 provided as necessary, and purified. Finished with water. The alkaline concentrated water discharged from the reverse osmosis membrane device 3 is supplied to the packed tower 5 and countercurrently contacts the degassed exhaust gas discharged from the degassing device 2 and air used as necessary, thereby being neutralized. In FIG. 2, the alkaline concentrated water discharged from the reverse osmosis membrane device 3 is neutralized in the neutralization tank 6 by an acid regeneration effluent discharged during regeneration of the H-type cation exchange resin tower 1. Otherwise, it is the same as the case of FIG. On the other hand, in FIG. 3, raw water is passed through an H-type cation exchange resin tower 1 to remove scale components such as calcium ions, and then supplied to a degassing device 2 to remove carbonate ions and the like in the water. You. Next, the treated water is adjusted to a pH of 9.2 or more by adding an alkali agent, and then passed through a reverse osmosis membrane device 3, and the permeated water is further supplied to a deionization tower 4 provided as necessary, and purified. Finished with water. The alkaline concentrated water discharged from the reverse osmosis membrane device 3 is passed through the reverse osmosis membrane device 7, and the permeated water is H
It is returned to the cation exchange resin tower 1 of the type or the degassing device 2. On the other hand, the alkaline concentrated water discharged from the reverse osmosis membrane device 7 is supplied to the packed tower 5, countercurrently contacts the acidic exhaust gas discharged from the degassing device 2 and air used as necessary, and is neutralized. In FIG. 4, the alkaline concentrated water discharged from the reverse osmosis membrane device 7 is supplied to the neutralization tank 6.
It is neutralized by the acid regeneration effluent discharged at the time of regeneration of the H-type cation exchange resin tower 1. Otherwise, it is the same as the case of FIG.

[0008]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 A column filled with 50 liters of H-type cation exchange resin “H-type SP112” (manufactured by Bayer AG) was charged with Atsugi-shi water (pH
7.6, an electric conductivity of 150 μS / cm, and a calcium concentration of 40 mg / liter in terms of calcium carbonate) were passed at a rate of 1 m ³ / hr. At the time of passing water for 160 hours, calcium ions and magnesium ions leaked.
The cation exchange resin was regenerated with hydrochloric acid having a concentration of% by weight to obtain 250 liters of regenerated wastewater having a pH of 1.4. next,
This treated water was degassed with a membrane under the conditions of a pressure of 50 Torr and a displacement of an extraction pump of 0.04 m ³ / min [Liqui-Cel (registered trademark) (4 inch) 2 manufactured by Hoechst Japan Ltd.] 2
Use a book linked to a series]. After adding sodium hydroxide to the membrane deaerated water and adjusting the pH to 10, it is supplied to a reverse osmosis membrane device [using a reverse osmosis membrane “ES-20” (4 inches) manufactured by Nitto Denko Corporation). did. At this time, processing water 0.8 m ³ / hr, the recovery rate of 80% and a discharging concentrated water 0.2m ³ /hr(pH10.5~10.6). When the discharged concentrated water was neutralized with the regenerated effluent, the concentrated effluent was adjusted to pH 8 using 21 cc / hr of the regenerated effluent.
It could be adjusted to ~ 8.5. Example 2 A tower diameter of 0.092 m in which a net ring was packed to a height of 1 m
Of the concentrated water obtained in Example 1 in
While flowing in at a flow rate of 2 m ³ / hr, the exhaust gas from the membrane deaeration treatment in Example 1 was flowed from the bottom at a flow rate of 2.4 m ³ / hr (gas / liquid ratio: 12). As a result, the pH of the concentrated water was 8.
It became 4. Example 3 Example 2, except that shed membrane degassing treated flue gas 2.4 m ³ / hr and a gas mixture of air 3.0 m ³ / hr from the packed column bottom was subjected to the same procedure as in Example 2 (Liquid / gas ratio 2
7). As a result, the pH of the concentrated water became 8.2. Comparative Example 1 In Example 1, when a neutralization treatment was performed using hydrochloric acid instead of the regenerated effluent, 18 ppm or more of HCl was required to neutralize to the same pH as in Example 1. Was. Comparative Example 2 The same operation as in Example 2 was performed, except that air of 6 m ³ / hr (gas / liquid ratio: 30) was flowed from the lower part of the packed tower in place of the exhaust gas from the membrane deaeration treatment. As a result, the pH of the concentrated water dropped only to 8.8.

[0009]

According to the present invention, in the process of producing pure water by subjecting raw water to reverse osmosis membrane treatment under alkaline conditions, alkaline concentrated water discharged by the reverse osmosis membrane treatment is treated in a system. Pure water can be produced economically and advantageously by performing a neutralization treatment using an acidic substance generated as a by-product.

[Brief description of the drawings]

FIG. 1 is a flow chart of an example for carrying out the method of the present invention.

FIG. 2 is a process flow chart of another example for carrying out the method of the present invention.

FIG. 3 is a process flow chart of another example for carrying out the method of the present invention.

FIG. 4 is a process flow chart of another example for carrying out the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 H-type cation exchange resin tower 2 Degassing apparatus 3 Reverse osmosis membrane apparatus 4 Deionization tower 5 Packing tower 6 Neutralization tank 7 Reverse osmosis membrane apparatus

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/66 522 C02F 1/66 522R 530 530B 540 540C 540Z F-term (Reference) 4D006 GA03 KA02 KA52 KA63 KA72 KB11 KB17 KE15Q KE15R MA11 MC54 PB06 PB27 PC03 PC04 4D025 AA04 AB19 BA09 BA11 BA14 BB04 DA01 DA05 4D037 AA03 AB11 BA23 BB05 BB07 CA03 CA14 CA15

Claims (2)

[Claims] (1) After passing raw water through an H-type cation exchange resin tower, the raw water is degassed by a degasser, and then has a pH of 9.2.
In producing pure water by passing water through the reverse osmosis membrane device under the above alkaline conditions, the alkaline concentrated water discharged from the reverse osmosis membrane device is subjected to acid regeneration effluent of the H-type cation exchange resin tower. Alternatively, a method for producing pure water, wherein neutralization treatment is performed with exhaust gas from a degassing device. 2. After passing the raw water through an H-type cation exchange resin tower, the raw water is degassed by a degasser, and then the pH is adjusted to 9.2.
In producing pure water by passing water through the reverse osmosis membrane device under the above alkaline conditions, alkaline concentrated water discharged from the reverse osmosis membrane device is passed through a separately provided reverse osmosis membrane device, The permeated water is returned to the H-type cation exchange resin tower or the degassing device, and the alkaline concentrated water discharged from the separately provided reverse osmosis membrane device is subjected to acid regeneration in the H-type cation exchange resin tower. A method for producing pure water, wherein neutralization treatment is performed with waste water or exhaust gas from a degassing device.