JP2002028660A - Desalting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desalting device for operating an electric deionizing device stably for a long period with suppressed maintenance cost, and stably manufacturing high purity of treated water, as the desalting device using the electric deionizing device. SOLUTION: In the desalting device where a membrane type turbidity- removing device, a reverse osmosis membrane treating device, a sodium type strong acidic cation exchange resin device and an electric deionizing device are arranged along a flow path in order, an alkali chemical addition means with which pH of water fed to the electric deionizing device is adjusted to >=7.5 and <=11.0, or an alkali chemical addition means to adjust pH of a circulation system of concentrated water in the electric deionizing device to >=9.0, is installed in a circulation flow path of concentrated water in the electric deionizing device. By addition of the alkali chemical, the number of bacteria in concentrated water of the electric deionizing device can be brought close to 0 pieces/ml, thus the problem of operational unbalance due to decrease in the flow rate of a concentrated room due to bacteria and the problem of lowering in the quality of treated water caused by this unbalance are dissolved, and water quality stabilized for a long period is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to industrial water, city water,
The present invention relates to a desalination unit that treats raw water such as well water with a reverse osmosis membrane treatment unit and an electric deionization unit. In particular, the desalination unit can be operated stably over a long period of time and with low maintenance costs. Further, the present invention relates to a desalination apparatus capable of stably producing high-purity treated water.

[0002]

2. Description of the Related Art In recent years, as an apparatus for producing demineralized water, a desalination apparatus provided with an electric deionization apparatus at the subsequent stage of a reverse osmosis membrane treatment apparatus has been widely used.

In general, as shown in FIG. 1, an electric deionization apparatus comprises a plurality of anion exchange membranes 3 and cation exchange membranes 4 arranged alternately between an anode 1 and a cathode 2 to form an anion exchange membrane 3 Desalting chambers 5 and concentrating chambers 6 separated by a cation exchange membrane 4 are formed alternately, and the desalting chamber 5 to which water to be treated is supplied is filled with a mixture 7 of an anion exchange resin and a cation exchange resin. The DC voltage is applied between the anode 1 and the cathode 2. Reference numeral 8 denotes an anode chamber, 9 denotes a cathode chamber, and 10 denotes a circulation pump for circulating water flowing to the concentration chamber 6 in order to increase the rate of concentration of ion components from the water to be treated.

[0004] In the electric deionization apparatus configured as described above, the ionic components in the feed water are adsorbed by the mixture 7 of the anion exchange resin and the cation exchange resin in the desalting chamber 5. The adsorbed ion component is transferred to the concentration chamber 6 by the action of the direct current, and the mixture 7 of the anion exchange resin and the cation exchange resin is continuously regenerated.

That is, in the electric deionization apparatus, adsorption and regeneration of ions are performed in parallel.

[0006]

As described above, in a conventional desalination apparatus composed of a reverse osmosis membrane treatment apparatus and an electric deionization apparatus, an anion exchange resin and a cation exchange resin of an electric deionization apparatus are used. Since the mixture 7 is continuously regenerated, the mixture 7 is inherently capable of operating stably for a long period of time. However, it is often the case that the bacteria ( Bacteria) proliferate, thereby decreasing the flow rate of the enrichment chamber. Eventually, there is a problem that the operation balance of the electric deionization apparatus is lost and the quality of treated water is reduced.

[0007] In such a desalination apparatus in which a reverse osmosis membrane treatment apparatus and an electric deionization apparatus are used, most of the hardness components (Ca, Mg, etc.) are removed in the reverse osmosis membrane treatment apparatus. Some leak and flow into the electric deionizer, generating a hardness scale in the electric deionizer,
There is also a problem that the quality of the treated water deteriorates and the cost increases due to frequent chemical cleaning.

Further, in a desalination apparatus composed of such a reverse osmosis membrane treatment apparatus and an electric deionization apparatus, the reverse osmosis membrane treatment apparatus may be clogged by turbidity components in raw water. When clogging occurs, depending on the cause, cleaning of the reverse osmosis membrane treatment device is required,
Alternatively, there is a problem in that the quality of the treated water of the reverse osmosis membrane treatment device is deteriorated, and the stable operation of the subsequent electric deionization device is hindered.

Accordingly, an object of the present invention is to provide a desalination apparatus for producing desalinated water from raw water such as industrial water, city water and well water, and more particularly, to a desalination apparatus using an electric deionization apparatus. It is an object of the present invention to provide a desalination apparatus which can operate a deionization apparatus stably for a long period of time and at a low maintenance cost, and can stably produce high-purity treated water.

[0010]

According to the first aspect of the present invention, there is provided a desalination apparatus.
Membrane clarifier and reverse osmosis membrane treatment device, sodium (Na)
In a device for desalinating water to be treated by sequentially disposing a type strongly acidic cation exchange resin device and an electric deionization device along a flow path, an alkali agent is added to the water supplied to the electric deionization device, and PH of the water supplied to the deionizer is 7.5
As mentioned above, it is characterized by having an alkali agent adding means for adjusting the concentration to 11.0 or less.

According to a second aspect of the present invention, there is provided a desalination apparatus in which a membrane type opacity apparatus, a reverse osmosis membrane treatment apparatus, a sodium (Na) type strongly acidic cation exchange resin apparatus, and an electric deionization apparatus are sequentially arranged along a flow path. In the apparatus for desalinating the water to be treated, an alkaline agent is added to the concentrated water circulation channel in the electric deionization apparatus to adjust the pH of the concentrated water circulation system in the electric deionization apparatus to 9.0 or more. Characterized in that it has a means for adding alkali.

The desalination apparatus according to claim 3 is the desalination apparatus according to claims 1 and 2, wherein the added alkaline agent is
It is characterized in that it does not substantially contain a cation having a valency or higher.

[0013]

FIG. 2 is a block diagram showing an embodiment of the present invention.
FIG. Note that the desalination apparatus of the present invention is not limited to these embodiments, and it is also possible to arrange another device between each component device.

The membrane-type clarifier used in the present invention is for removing suspended substances (SS), fouling substances and the like from raw water such as industrial water, city water and well water. Although an apparatus using an external filtration membrane or a microfiltration membrane can be used, an internal pressure type total filtration apparatus using a hollow fiber type module is particularly suitable for the present invention.

The raw water is treated with a membrane type clarifier to remove the turbidity, thereby reducing the load on the reverse osmosis membrane treatment unit at the subsequent stage.
The quality of treated water can be improved.

The reverse osmosis membrane used in the reverse osmosis membrane treatment apparatus used in the present invention is not particularly limited, but an aramid-based membrane, a polyamide-based membrane, a cellulose acetate membrane and the like are exemplified as usable in the present invention. . In particular, a spiral crosslinked aramid-based composite membrane is more suitable for the present invention because the effect of the present invention is more easily exhibited.

The reverse osmosis membrane treatment device has the function of separating and removing ions and other impurities including carbonate ions and silica in the treated water of the membrane type clarifier. In the electric deionizer described below, it is possible to separate and remove these ions, silica and the like, but if these impurities are removed only by the electric deionizer, the processing cost becomes high. It is important to reduce the load on the electric deionizer by desalting with an osmosis membrane treatment device. Since the reverse osmosis membrane treatment device also removes fine particles, organic matter, viable bacteria, and the like in water, it is possible to prevent contamination of the electric deionization device due to the inflow thereof, and to realize a stable electric deionization device. Enable driving.

The sodium (Na) type strongly acidic cation exchange resin apparatus used in the present invention is for removing hardness components (Ca, Mg, etc.) from water to be treated supplied to an electric deionization apparatus in advance. is there.

Most of the Ca ions, Mg ions and the like are also removed in the reverse osmosis membrane treatment apparatus. In the present invention, the sodium (Na) type strongly acidic cation exchange resin apparatus is provided separately for the following reason. by.

That is, it is known that the silica component (SiO ₂ ) and carbonic acid (CO ₂ ) are easily ionized under alkaline conditions.
The removal rate of silica components (SiO ₂ ) and carbonic acid (CO ₂ ) is expected to be improved by an electric deionization apparatus, but desalination with an electric deionization apparatus provided after the conventional reverse osmosis membrane treatment apparatus In the apparatus, even if the electric deionization apparatus is operated under alkaline conditions, the quality of the treated water is not stable for a long time.

After examining the cause, the hardness component (C) remaining in the supply water introduced into the electric deionizer was determined.
a, Mg, etc.) are precipitated under alkaline conditions, and a hardness scale is generated in the concentration chamber in the electric deionization apparatus, resulting in electric resistance, thereby deteriorating the quality of treated water from the electric deionization apparatus. Do you get it. That is, Ca ions, Mg ions, etc. are mostly removed in the reverse osmosis membrane treatment device, but leak a small amount, and when they flow into the alkaline electric deionization device, they cause a hardness scale,
This has had a significant effect on the quality of the treated water, such as a drop in the specific resistance of the treated water in the electric deionizer.

The sodium (Na) type strongly acidic cation exchange resin device according to the present invention substantially completely removes the hardness components that could not be removed by the reverse osmosis membrane treatment device, and forms scale in the electric deionization device. It acts to prevent.

In the present invention, a strongly acidic cation exchange resin of Na type is used as the cation exchange resin for the following reason.

That is, it is possible to remove the hardness components (Ca, Mg, etc.) by using a strongly acidic cation exchange resin regenerated to H-type instead of Na-type strongly acidic cation-exchange resin. When the strongly acidic cation exchange resin regenerated is used, sodium ions (Na ⁺ ) can be easily removed from the water to be treated by an electric deionizer.
Since such monovalent ions are also removed at the same time, the frequency of regeneration of the strongly acidic cation exchange resin is increased, and the running cost of the desalting apparatus is significantly increased.

When a weakly acidic cation exchange resin regenerated to the Na type is used, the ion exchange rate is lower than that of the strongly acidic cation exchange resin, and the water to be treated supplied to the electric deionizer is reduced. Hardness component (Ca, Mg, etc.)
It is extremely difficult to reduce the residual amount of the steel to about 0.25 ppm (asCaCO ₃ ) or less, and it is not possible to achieve the effect of preventing the generation of a hardness scale in an electric deionization apparatus.

In the desalination apparatus of the present invention, since a reverse osmosis membrane treatment apparatus is provided before the strongly acidic cation exchange resin apparatus of Na type, maintenance of the strongly acidic cation exchange resin apparatus of Na type can be remarkably reduced. .

The means for adding an alkaline agent in the desalination apparatus according to the first aspect of the present invention is characterized in that:
The pH of the water supplied to the electric deionization device is adjusted to 7.5 or more and 11.0 or less by adding an alkali agent to the treated water of the type strongly acidic cation exchange resin device.

The pH adjustment by the alkali agent adding means is performed to make the number of bacteria (bacteria) in the feed water close to 0 / ml. The pH adjustment is from 7.5 to about 11.0, preferably the pH is 7 0.5 to 10.0, more preferably 7.5 to 9.0. When the pH is 7 or less, the number of bacteria (bacteria) in the supply water of the electric deionizer is 1 ml.
By adding an alkaline agent, the cell membrane of bacteria (bacteria) in the supply water of the electric deionization device is broken to inactivate live bacteria in the supply water. 0 bacteria /
ml. By this effect, in the electric deionization device, the problem of the operation balance collapse due to the decrease in the flow rate of the concentration chamber due to bacteria (bacteria) and the problem of the decrease in the treated water quality due to it can be solved, and the stable water quality can be obtained for a long time. In addition, high-purity water quality can be obtained. However, when the pH exceeds about 11, the ionic load in the feed water of the electric deionization apparatus is remarkably increased, so that it is not economical, and in some cases, the treatment water quality of the electric deionization apparatus may be deteriorated. It is not preferable.

In the desalination apparatus according to the second aspect of the present invention, the alkaline agent adding means adds an alkaline agent to a concentrated water circulation flow path in the electric deionization apparatus to add an alkali agent to the concentrated water in the electric deionization apparatus. The pH of the concentrated water circulation system is constantly adjusted to 9.0 or more, whereby the number of bacteria (bacteria) in the concentrated water can be drastically reduced. The added alkaline agent decomposes the cell membrane of bacteria (bacteria) in the concentrated water of the electric deionization device, inactivates the viable bacteria existing in the concentrated water circulation system, and thereby concentrates the electric deionization device. It is possible to prevent the operation balance from being lowered due to the decrease in the room flow rate and the reduction in the treated water quality due to the reduction, and to obtain a stable water quality for a long period of time.

The alkaline agent added to the feed water of the electric deionizer or the alkaline agent added to the circulating system of the concentration chamber of the electric deionizer includes NaOH,
Alkaline agents substantially free of divalent or higher cations, such as KOH, NH ₄ OH and NH ₃ gas, are used. When the alkali agent to be added contains cations having two or more valencies, the risk of hardness scaling occurring in the electrodeionization device increases.

Next, an embodiment of the present invention will be described.

(Examples 1 to 4) FIG. 4 is a system diagram of a desalination apparatus of the present invention used in Examples 1 to 4.

The apparatus of this embodiment is constituted by sequentially arranging a membrane type turbidity removing apparatus, a reverse osmosis membrane treating apparatus, a Na type strongly acidic cation exchange resin, and an electric deionizing apparatus along the flow of the water to be treated. ing.

The alkaline agent added to the feed water of the electric deionizer is NaOH. 6. Adjust the pH of the feed water to 7.
It adjusted to 7, 8.7, 9.8, and 10.8, and each ran continuously for 30 days.

Table 1 shows the flow rate ratio of the enrichment chamber 30 days after the operation when the flow rate of the enrichment chamber of the electric deionization apparatus was set to 1.0 in the initial stage of the operation under each test condition. Table 1 also shows the treated water quality of the electric deionizer and the viable cell count in the concentrated water after 30 days. The raw water used was water from Atsugi City, Kanagawa Prefecture, and the equipment used and the operating conditions were as follows.

Membrane-type clarifier: NML-E2HS-4 (manufactured by Nomura Micro Science) Reverse osmosis membrane: SU-710 (manufactured by Toray) Water recovery (65%), water temperature (20 to 25 ° C.) sodium Type strongly acidic cation exchange resin: Duolite C
-20 (manufactured by Rohm & Haas) Electric deionizer: EDI-50 (manufactured by Ionic) Water recovery rate (95%), DC voltage (450 to 600 V) Supply water flow rate (11.4 m ³ / h) ( Comparative Examples 1-2) A test was performed in the same manner as in Example 1 except that the pH of the water supplied to the electric deionization apparatus was changed to 6.0 and 7.3. Table 1 shows the results.

[Table 1]

(Examples 5 to 7) FIG. 5 is a system diagram of a desalination apparatus of the present invention used in Examples 5 to 7.

The apparatus of this embodiment is constructed by sequentially arranging a membrane type turbidity removing apparatus, a reverse osmosis membrane treating apparatus, a Na type strongly acidic cation exchange resin, and an electric deionizing apparatus along the flow of the water to be treated. ing. The alkaline agent added to the concentrated water circulation system of the electric deionizer is NaOH. The pH of the concentrated water was adjusted to 9.3, 10.7, and 12.1 and each was continuously operated for 30 days. Table 2 shows the flow rate ratio of the enrichment chamber and the number of viable bacteria 30 days after the operation, when the flow rate of the enrichment chamber of the electric deionization apparatus was set to 1.0 in the initial operation of each test condition.

[Table 2]

(Comparative Examples 3 and 4) A test was conducted in the same manner as in Example 5 except that the pH of the circulating system of the concentrated water in the electric deionization apparatus was changed to 7.3 and 8.7. Table 2 shows the results.

(Comparative Examples 5 to 6) In Example 5, Ca (OH) ₂ containing a divalent cation was used as a pH adjuster for the recirculating system of the concentrated water of the electric deionization apparatus. Example 5 except that 9.5 and 10.4 were used.
The test was performed in the same manner as described above. However, the flow rate of the concentration chamber and the viable cell count in the concentrated water were lower because the flow rate of the concentration chamber decreased sharply.
The value 10 days after the start of operation was used. Table 3 shows the results.

[Table 3]

(Embodiment 8) FIG. 6 shows the change over time in the difference (differential pressure) between the feed water pressure and the concentrated water pressure in the reverse osmosis membrane treatment apparatus in Example 1. Similarly, FIG. 7 shows a change with time of the specific resistance of the water treated by the electric deionization apparatus in Example 1.

(Comparative Example 7) A test was carried out in the same manner as in Example 8 except that the membrane type turbidizer and the sodium-type strongly acidic cation exchange resin were bypassed, as shown by the dotted line in FIG. . FIGS. 6 and 7 show the difference (pressure difference) between the feed water pressure and the concentrated water pressure of the reverse osmosis membrane treatment apparatus and the temporal change of the treated water specific resistance of the electric deionization apparatus, respectively. In Comparative Example 7, since the treated water specific resistance of the electric deionization apparatus decreased in a short time, the concentrated water circulation system of the apparatus was cleaned (maintenance) with HCl.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a configuration of an example of an electric deionization apparatus used in the present invention.

FIG. 2 is a system diagram of an embodiment of the desalination apparatus according to claim 1 of the present invention.

FIG. 3 is a system diagram of another embodiment of the desalination apparatus according to claim 2 of the present invention.

FIG. 4 is a system diagram of a desalination apparatus used in Examples 1 to 4.

FIG. 5 is a system diagram of a desalination apparatus used in Examples 5 to 7.

FIG. 6 is a graph showing the change over time of the difference (differential pressure) between the feed water pressure and the concentrated water pressure of the reverse osmosis membrane treatment device of Example 1.

FIG. 7 is a graph showing the change over time in the water resistivity of the electric deionization apparatus in Example 1.

[Explanation of symbols]

1 ... Anode, 2 ... Cathode, 3 ... Anion exchange membrane, 4 ...
... Cation exchange membrane, 5 ... Desalination room, 6 ... Concentration room, 7 ...
... mixture of anion exchange resin and cation exchange resin, 8
… Anode chamber, 9… Cathode chamber, 10… Circulation pump.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/44 C02F 9/00 502E 9/00 502 502F 502K 502M 503A 503 504D 504 504E 1/46 103F Term (Reference) 4D006 GA03 GA06 GA07 HA01 HA61 HA95 KA02 KA52 KA55 KA57 KA72 KB01 KB11 MA01 MC18 MC54 MC56 PA01 PB02 PB05 PB06 PB15 PB23 PB24 PB27 PB28 4D025 AA01 AB19 BA09 BB02 BB07 DA05 DA04 4EB06 EB01 EB02 EB02 EB02 FA09 GC05

Claims (3)

[Claims] 1. A water treatment apparatus comprising a membrane type turbidity removing apparatus, a reverse osmosis membrane treatment apparatus, a sodium (Na) type strongly acidic cation exchange resin apparatus and an electric deionization apparatus arranged in this order along a flow path to desalinate the water to be treated. An alkaline agent is added to the water supplied to the electric deionization device to adjust the pH of the water supplied to the electric deionization device to 7.5 or more;
A desalination apparatus comprising an alkali agent adding means for adjusting the concentration to 1.0 or less. 2. A method for desalinating water to be treated by sequentially arranging a membrane type clarifier, a reverse osmosis membrane treatment unit, a sodium (Na) type strongly acidic cation exchange resin unit and an electric deionization unit along a flow path. An apparatus for adding an alkali agent to a concentrated water circulation flow path in the electric deionization apparatus to adjust the pH of the concentrated water circulation system in the electric deionization apparatus to 9.0 or more. A desalination apparatus characterized by the above-mentioned. 3. The desalination apparatus according to claim 1, wherein the added alkaline agent does not substantially contain a cation having a valency of 2 or more.