KR20180100223A - Water treatment system and water treatment method using reverse osmosis membrane - Google Patents

Abstract

A water treatment system and a water treatment method capable of reducing the amount of the bactericide added in water treatment using two or more reverse osmosis membranes. The second reverse osmosis membrane device (14) for treating the permeated water of at least the first reverse osmosis membrane device (12) and the first reverse osmosis membrane device (12) In the water treatment system 1 for performing the reverse osmosis membrane treatment, the concentrated water of the second reverse osmosis membrane device 14 in the second stage is circulated to the feed water of the first reverse osmosis membrane device 12 in the first stage And adding a bactericide having a blocking rate of 70% or more in the reverse osmosis membrane to the water supplied from the second reverse osmosis membrane unit 14, and a water treatment method.

Description

Water treatment system and water treatment method using reverse osmosis membrane

The present invention relates to a water treatment system and a water treatment method using a reverse osmosis membrane.

The occurrence of slime in the water treatment using a reverse osmosis membrane (RO membrane) is a frequent problem, and it is now dealt with by the addition of an organic disinfectant or the addition of a chlorine disinfectant and a bromine disinfectant (See, for example, Patent Document 1 and Patent Document 2). In order to improve the quality of the treated water of the reverse osmosis membrane, it is preferable that the inhibition rate of these bactericides by the reverse osmosis membrane is high.

Also, as in Patent Document 3, the water treatment may be carried out using a reverse osmosis membrane of two stages. In the method of Patent Document 3, since most of the bactericide is blocked in the first reverse osmosis membrane, it is necessary to add a sanitizer again to the slime countermeasure of the second reverse osmosis membrane, The chlorine-based disinfectant in the membrane and the alkaline disinfectant in the second-stage reverse osmosis membrane are applied. However, since the injection point of the preparation becomes two places and the amount of the bactericide added tends to increase, the apparatus becomes complicated and the operation cost rises.

JP 2006-263510 A JP 2015-062889 A JP 5050605 B

An object of the present invention is to provide a water treatment system and a water treatment method capable of reducing the amount of the bactericide added in water treatment using a reverse osmosis membrane having two or more stages.

The present invention relates to a water treatment system using two or more reverse osmosis membranes, comprising a reverse osmosis membrane apparatus of at least a first stage and a reverse osmosis membrane apparatus of a second stage for treating permeated water of a first reverse osmosis membrane apparatus, And a circulation means for circulating the concentrated water of the second-stage reverse osmosis membrane device to the feed water of the first-stage reverse osmosis membrane device, wherein the feed water of the second- Is added to the water treatment system.

In the water treatment system, the bactericide having a retardation rate of 70% or more in the reverse osmosis membrane is preferably at least one of a hypobromic acid stabilizing composition, chlorosulfamic acid, hypochlorous acid, hypobromic acid, isothiazolone compound, and halothioacetamide compound It is preferable to use one type.

It is preferable that the water treatment system further comprises a deaeration membrane for performing deaeration of the feed water of the reverse osmosis membrane at the second stage at the downstream end to which a sterilizing agent having a retardation rate of 70% or more in the reverse osmosis membrane is added.

In the water treatment system, it is preferable that the sterilizing agent having an inhibition rate of 70% or more in the reverse osmosis membrane is an anionic bactericide, and the reverse osmosis membrane device in the second stage has an anion charging membrane.

In the water treatment system, it is preferable that the first reverse osmosis membrane device has a neutral membrane.

The present invention also provides a water treatment method for carrying out a reverse osmosis membrane treatment at two or more stages using a reverse osmosis membrane at least in a first stage and a reverse osmosis membrane in a second stage for treating permeated water of a reverse osmosis membrane in the first stage , The concentrated water of the reverse osmosis membrane at the second stage is circulated to the feed water of the reverse osmosis membrane at the first stage to use the water of reverse osmosis membrane at the second stage at a rate of 70% It is a water treatment method in which a bactericide is added.

In the water treatment method, the bactericide having a retardation rate of 70% or more in the reverse osmosis membrane is preferably at least one of a hypobromic acid stabilizing composition, chlorosulfamic acid, hypochlorous acid, hypobromous acid, isothiazolone compound and halothioacetamide compound It is preferable to use one type.

In the water treatment method, it is preferable to perform deaeration of the feed water of the reverse osmosis membrane at the second stage by using a deaeration membrane at the end of the step of adding a sterilizing agent having a retardation of 70% or more in the reverse osmosis membrane.

In the water treatment method, it is preferable that the bactericide having a retardation rate of 70% or more in the reverse osmosis membrane is an anionic bactericide, and the reverse osmosis membrane in the second step is an anion-lower membrane.

In the water treatment method, the first reverse osmosis membrane is preferably a neutral membrane.

According to the present invention, it is possible to provide a water treatment system and a water treatment method capable of reducing the addition amount of the bactericide in water treatment using two or more reverse osmosis membranes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of a water treatment system according to an embodiment of the present invention; FIG.
2 is a schematic structural view showing another example of a water treatment system according to an embodiment of the present invention;
3 is a schematic view showing a conventional water treatment system;
4 is a schematic block diagram of a flat membrane testing apparatus used for evaluation of a blocking ratio in a reverse osmosis membrane in an embodiment.

Embodiments of the present invention will be described below. The present embodiment is an example of carrying out the present invention, and the present invention is not limited to this embodiment.

<Water Treatment System and Water Treatment Method>

An outline of an example of the water treatment system according to the embodiment of the present invention is shown in Fig. 1, and the structure thereof will be described. The water treatment system 1 includes a first reverse osmosis membrane device 12 at the first stage and a second reverse osmosis membrane device 14 at the second stage. The water treatment system 1 may be provided with the raw water tank 10 at the front end of the first reverse osmosis membrane device 12. [

1, the pipe 16 is connected to the raw water inlet of the raw water tank 10, and the outlet of the raw water tank 10 and the inlet of the first reverse osmosis membrane device 12 are connected to a pipe (not shown) 18). The permeate outlet of the first reverse osmosis membrane device 12 and the inlet of the second reverse osmosis membrane device 14 are connected by a pipe 20 and the pipe 24 is connected to the second reverse osmosis membrane device 14 And is connected to the permeated water outlet. The pipe 22 is connected to the concentrated water outlet of the first reverse osmosis membrane unit 12 and the concentrated water outlet of the second reverse osmosis membrane unit 14 and the concentrated water inlet of the raw water tank 10 are connected to each other through circulation And is connected by a pipe 26. A sterilant addition pipe 28 as a sterilant addition means is connected to the pipe 20.

The operation of the water treatment method and the water treatment system 1 according to the present embodiment will be described.

The raw water to be treated is stored in the raw water tank 10 as necessary through the pipe 16 and then sent to the first reverse osmosis membrane device 12 in the first stage through the pipe 18. [ In the first reverse osmosis membrane device 12, the first reverse osmosis membrane treatment is performed (first reverse osmosis membrane treatment step). The first permeated water from the first reverse osmosis membrane unit 12 is fed to the second reverse osmosis membrane unit 14 through the pipe 20 and the first concentrated water is passed through the pipe 22 .

Here, the second reverse osmosis membrane device 14 is fed through the sterilizing agent addition pipe 28 in the front end of the second reverse osmosis membrane device 14, for example, in the pipe 20, , A microbicide having a blocking ratio of 70% or more in the reverse osmosis membrane is added (microbicide addition step). Although it is not necessary to add a sterilizing agent to the feed water of the first reverse osmosis membrane device 12 in the first stage, it is preferable that no sterilizing agent is added. Since the sterilizing agent is not added to the water supplied to the first reverse osmosis membrane device 12 in the first stage, the addition amount of the sterilizing agent can be further reduced.

In the second reverse osmosis membrane device 14, the second reverse osmosis membrane treatment is performed (second reverse osmosis membrane treatment step). The second permeated water from the second reverse osmosis membrane device 14 is discharged as treated water through the piping 24 and the second concentrated water flows through the circulating pipeline 26 to the first reverse osmosis membrane For example, to the raw water tank 10 (circulation process). In the circulation process, the second concentrated water may be circulated in the pipe 16, the pipe 18, and the like.

The sterilizing agent to be added to the feed water of the second reverse osmosis membrane device 14 has a blocking ratio of not less than 70% in the reverse osmosis membrane. Therefore, most of the sterilizing agent is blocked by the reverse osmosis membrane in the second stage, . In the flow of circulating the second concentrated water of the second reverse osmosis membrane unit 14 of the second stage to the front end of the first reverse osmosis membrane unit 12 of the first stage, The sterilizing agent derived from the second concentrated water of the second reverse osmosis membrane unit 14 is mixed with the supplied water (raw water). This makes it possible to reduce the amount of the bactericide added in the water treatment using the reverse osmosis membrane of two or more stages.

Although the reverse osmosis membrane of two stages is used in the example of Fig. 1, the present invention is not limited thereto. In the water treatment method and the water treatment system using two or more reverse osmosis membranes, the concentration of the reverse osmosis membrane in the second stage is set to 1 The amount of the sterilizing agent added can be reduced by circulating the feed water of the reverse osmosis membrane at the first stage and adding a sterilizing agent at a rate of 70% or higher in the reverse osmosis membrane to the feed water of the second reverse osmosis membrane.

The isothiazolone compound, which is a typical organic-based disinfectant, permeates the reverse osmosis membrane by about 20%, and the second concentrated water of the second reverse osmosis membrane unit 14 is supplied to the front end of the first reverse osmosis membrane unit 12 The amount of circulation to the front end of the first reverse osmosis membrane device 12 is reduced even in the circulating flow. Therefore, it is more preferable to use a sterilizing agent in which 90% or more, preferably 99% or more, is blocked with a reverse osmosis membrane.

Since the second reverse osmosis membrane device 14 immediately after the addition of the sterilizing agent has better circulation of the sterilizing agent component, it is preferable to use an anion-based reverse osmosis membrane (anion sub-membrane) Good. On the other hand, in the first reverse osmosis membrane device (12) upstream of the bactericide addition point, the sterilizing agent component remains at the rear end of the neutral membrane having a relatively low inhibition rate of the sterilizing agent.

As shown in Fig. 2, there is additionally provided between the first reverse osmosis membrane device 12 of the first stage and the second reverse osmosis membrane device 14 of the second stage a unit operation (For example, a degassing film 30 for degassing carbon dioxide gas or the like), a germicide is added between the first reverse osmosis membrane device 12 and the degassing film 30 at the first stage, It is possible to suppress bio-contamination of the unit operation. That is, by providing the demineralization membrane 30 for deaerating the water supplied to the second reverse osmosis membrane unit 14 at the second stage, and the like, at the downstream end of the addition of the microbicide having a retardation rate of 70% or more in the reverse osmosis membrane, It is possible to suppress biological contamination of the membrane 30 and the like.

As the reverse osmosis membrane used in the first reverse osmosis membrane device (12) and the second reverse osmosis membrane device (14), a polyamide based polymer membrane is used as a mainstream, and there are a neutral membrane, an anion subbing membrane and a cationic charge membrane. The neutral membrane indicates that the zeta potential at pH 7.0 is in the range of -15 to 5 (㎷), as determined by the zeta potential measurement method described later in Examples, and the negative ion charge membrane shows the zeta potential at pH 7.0 And the dislocation is less than -15 (.). A cellulose acetate polymer membrane may be used for the reverse osmosis membrane of the first reverse osmosis membrane unit 12 and a polyamide series polymer membrane may be used for the reverse osmosis membrane of the second reverse osmosis membrane unit 14. [ In this case, a sterilizing agent such as hypochlorous acid is added to the feed water of the first reverse osmosis membrane device 12 at the first stage, and the rate of rejection in the reverse osmosis membrane to the feed water of the second reverse osmosis membrane device 14 is 70 % &Lt; / RTI &gt;

Examples of the commercially available neutral film include OFR-625 (product of Organo Corporation), BW30XFR (product of Dow Chemical Company), LFC3 (product of Nitto Denko Corporation) TML20 (manufactured by Toray Industries, Inc.), and the like.

Examples of commercially available negative ion charge-controlling membranes include ES15, ES20, CPA3 (manufactured by Nitto Denko Corporation) and RE-8040BLN (manufactured by Woongjin Co., Ltd.).

In the water treatment method and the water treatment system according to the embodiment of the present invention, the first reverse osmosis membrane device 12 of the first stage has the neutral membrane, the second reverse osmosis membrane device 14 of the second stage has the neutral membrane, Membrane, and the bactericide having a rate of blocking in the reverse osmosis membrane of 70% or more is an anionic bactericide, the anionic bactericide is more likely to be inhibited from the second reverse osmosis membrane device 14 (anion sub-membrane) It is likely to be circulated to the first reverse osmosis membrane device 12 (neutral membrane) in the first stage. Since the anionic germicide easily permeates through the first reverse osmosis membrane device 12 in the first stage and the bactericide component remains in the water supplied from the second reverse osmosis membrane device 14 in the second stage, .

Examples of the target water (raw water) include electronic industrial wastewater such as an alcohol-containing water containing an alcohol such as methanol, ethanol, isopropyl alcohol and the like. Since the electronic industrial wastewater such as alcohol-containing water has a high risk of occurrence of slime, the water treatment method and the water treatment system according to the present embodiment can be suitably applied to the desalination process of the electronic industrial wastewater.

Examples of the bactericide having a retardation rate of 70% or more in the reverse osmosis membrane include a hypobromic acid stabilizing composition, an anionic bactericide such as chlorosulfamic acid, hypochlorous acid and hypobromic acid, 5-chloro-2-methyl- Thiazolin-3-one, isothiazolone compounds such as 2-methyl-4-isothiazolin-3-one and halothioacetamide compounds such as 2,2-dibromo-3-nitrilopropionamide And a neutral bactericide, and a hypobromous acid stabilizing composition, chlorosulfamic acid, isothiazolone compound and halothioacetamide compound having a blocking ratio of not less than 80% in the reverse osmosis membrane is preferable, More preferably at least one of hypobromic acid stabilizing composition, chlorosulfamic acid and halothioacetamide compound having a blocking ratio of 90% or more, particularly 99% or more. In this specification, the term "retardation" in the reverse osmosis membrane refers to a lowering rate in the case where the anion lower film "ES15" (aromatic polyamide-based anion lowering film, manufactured by Nitto Denko Corporation) is used as a reverse osmosis membrane Lt; / RTI &gt;

The halocyanoacetamide compound is, for example, a compound represented by the following general formula:

(Wherein X ₁ and X ₂ each independently represent a halogen atom or a hydrogen atom such as F, Cl, Br or I, and R ₁ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)

&Lt; Hypobromic acid stabilizing composition >

The hypobromic acid stabilizing composition contains a &quot; bromine-based oxidizing agent &quot; and a &quot; sulfamic acid compound &quot;, and may further contain an alkali.

Further, the hypobromic acid stabilizing composition contains "a reaction product of a bromine-based oxidizing agent and a sulfamic acid compound", and may further contain an alkali.

The ratio of the equivalent amount of the "sulfamic acid compound" to the equivalent of the "bromine-based oxidizing agent" is preferably 1 or more, and more preferably 1 or more and 2 or less. When the equivalent ratio of the "sulfamic acid compound" to the equivalent amount of the "bromine-based oxidizing agent" is less than 1, there is a possibility that the reverse osmosis membrane will deteriorate, and when it exceeds 2, the production cost may increase.

Examples of the bromine-based oxidizing agent include bromine (liquid bromine), bromine chloride, bromine acid, bromate, and hypobromous acid. Also, the "reaction product of a bromine compound and a chlorine-based oxidizing agent" obtained by reacting a bromine compound with a chlorine-based oxidizing agent such as hypochlorite is also included in the "bromine-based oxidizing agent".

Among them, the preparation of "a mixture of bromine and a sulfamic acid compound (a mixture of a bromine and a sulfamic acid compound)" or "a reaction product of a bromine and a sulfamic acid compound" using bromine is described in "Preparation of hypochlorous acid, Hydrochloric acid and sulfamic acid ", the chloride ion is less and the possibility of corrosion of the metal material such as the piping is low without deteriorating the reverse osmosis membrane, and is more preferable.

Examples of the bromine compound include sodium bromide, potassium bromide, lithium bromide, ammonium bromide and hydrobromic acid. Among them, sodium bromide is preferable in terms of preparation cost and the like.

The chlorine-based oxidizing agent includes, for example, chlorine gas, chlorine dioxide, hypochlorous acid or its salt, chlorous acid or its salt, chloric acid or its salt, perchloric acid or its salt, chlorinated isocyanuric acid or its salt . Among them, examples of the salt include alkali metal hypochlorite such as sodium hypochlorite, potassium hypochlorite, alkali hypochlorite such as calcium hypochlorite and barium hypochlorite, sodium chlorite such as sodium chlorite and potassium chlorite, Alkaline earth metal salts such as alkali metal salts and barium chlorites, other metal chlorites such as nickel chlorite, alkali metal chlorides such as ammonium chlorate, sodium chlorate and potassium chlorate, alkaline earth metal chlorides such as calcium chlorate and barium chlorate, etc. . These chlorine-based oxidizing agents may be used singly or in combination of two or more kinds. As the chlorine-based oxidizing agent, sodium hypochlorite is preferably used from the viewpoint of handleability and the like.

The sulfamic acid compound is a compound represented by the following general formula (1)

R ₂ NSO ₃ H (1)

(Wherein R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms)

Examples of the sulfamic acid compound include, in addition to sulfamic acid (amide sulfuric acid) in which both R groups are hydrogen atoms, N-methylsulfamic acid, N-ethylsulfamic acid, N-propylsulfamic acid, N- Sulfamic acid and N-butylsulfamic acid, and the other is an alkyl group having 1 to 8 carbon atoms, N, N-dimethylsulfamic acid, N, N-diethyl The two R groups such as sulfamic acid, N, N-dipropylsulfamic acid, N, N-dibutylsulfamic acid, N-methyl-N-ethylsulfamic acid and N-methyl- A sulfamic acid compound in which one of two R groups, i.e., a sulfamic acid compound and an N-phenylsulfamic acid, which are alkyl groups of 1 to 8, is a hydrogen atom and the other is an aryl group of 6 to 10 carbon atoms, have. Examples of the sulfamates include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts, strontium salts and barium salts, manganese salts, copper salts, zinc salts, iron salts, cobalt salts, Other metal salts, ammonium salts, and guanidine salts. The sulfamic acid compound and salts thereof may be used singly or in combination of two or more kinds. As the sulfamic acid compound, sulfamic acid (amide sulfuric acid) is preferably used in view of environmental load and the like.

Examples of the alkali include alkali hydroxides such as sodium hydroxide and potassium hydroxide. Sodium hydroxide and potassium hydroxide may be used in combination in view of the stability of the product at low temperatures and the like. The alkali may be used not as a solid but as an aqueous solution.

As the hypobromic acid stabilizing composition, it is preferable to use a solution containing bromine and a sulfamic acid compound (such as bromine and iodine) because the polyamide-based reverse osmosis membrane and the like are not deteriorated further and the leakage amount of effective halogen to RO permeated water is smaller. For example, a mixture of bromine and a sulfamic acid compound, an alkali and water, or a reaction product of a bromine and a sulfamic acid compound, such as those containing a mixture of bromine and sulfa A mixture of a reaction product of a phosphoric acid compound, an alkali and water is preferable.

The hypobromic acid stabilizing composition has a germicidal effect and hardly causes film deterioration such as hypochlorous acid or the like. At the normal use concentration, the influence on the film deterioration can be substantially ignored. Therefore, it is the most suitable as a bactericide.

Unlike hypochlorous acid and the like, the hypobromic acid stabilizing composition scarcely permeates the reverse osmosis membrane and the like, and therefore hardly affects the quality of treated water. In addition, since concentration can be measured in the field such as hypochlorous acid, more accurate concentration control is possible.

The pH of the hypobromic acid stabilizing composition is, for example, more than 13.0 and more preferably more than 13.2. When the pH of the composition is 13.0 or less, the effective halogen in the composition sometimes becomes unstable.

The concentration of bromic acid in the hypobromic acid stabilizing composition is preferably less than 5 mg / kg. If the concentration of bromic acid in the hypobromic acid stabilizing composition is 5 mg / kg or more, the concentration of bromic acid ions such as RO permeated water may be increased.

&Lt; Preparation method of hypobromic acid stabilizing composition >

The hypobromic acid stabilizing composition may be obtained by mixing a bromine-based oxidizing agent and a sulfamic acid compound, or may be mixed with an alkali.

As a method of preparing a hypobromic acid stabilizing composition containing bromine and a sulfamic acid compound or a hypobromic acid stabilizing composition containing a reaction product of bromine and a sulfamic acid compound, a mixed solution containing water, an alkali and a sulfamic acid compound And adding bromine to the mixed solution containing water, an alkali and a sulfamic acid compound under an inert gas atmosphere. The reaction is carried out in the presence of an inert gas atmosphere or under an inert gas atmosphere, whereby the concentration of bromic acid ions in the composition is lowered and the concentration of bromic acid ions in RO permeated water or the like is lowered.

The inert gas to be used is not limited, but at least one of nitrogen and argon is preferable in terms of production and the like, and nitrogen is preferable from the viewpoint of production cost and the like.

The concentration of oxygen in the reactor during the addition of bromine is preferably 6% or less, more preferably 4% or less, still more preferably 2% or less, and particularly preferably 1% or less. When the oxygen concentration in the reactor at the time of the bromine reaction exceeds 6%, the amount of the generated bromic acid in the reaction system sometimes increases.

The addition amount of bromine is preferably 25% by weight or less, more preferably 1% by weight or more and 20% by weight or less with respect to the total amount of the composition. If the addition ratio of bromine exceeds 25 wt% with respect to the total amount of the composition, the amount of the generated bromic acid in the reaction system may increase. If it is less than 1% by weight, the reforming effect may be poor.

The reaction temperature at the time of bromine addition is preferably controlled within the range of 0 占 폚 to 25 占 폚, but from the viewpoint of production cost and the like, it is more preferable to control the reaction temperature within the range of 0 占 폚 to 15 占 폚. When the reaction temperature at the time of bromine addition exceeds 25 DEG C, the amount of the produced bromic acid in the reaction system sometimes increases. When the reaction temperature is lower than 0 DEG C, the reaction may be frozen.

Example

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

&Lt; Example 1 and Comparative Examples 1 and 2 >

The water treatment system of Fig. 1 was used in Example 1, and the conventional water treatment system of Fig. 3 was used in Comparative Example 1. In the conventional water treatment system 5 of Fig. 3, a sterilizing agent addition pipe 32 for adding a sterilizing agent to the feed water of the first reverse osmosis membrane device 12 at the first stage is connected to the pipe 18. (Injection) of the sterilizing agent at one point (injection point 2) from the sterilizing agent addition pipe 28 as shown in Fig. 1 and two points from the sterilizing agent addition pipe 32 and the sterilizing agent addition pipe 28 as shown in Fig. 3 (Medicament) was added while changing the kinds of the sterilizing agent as shown in Table 1 with respect to the case where the sterilizing agent was added (injected) at the injection point 1 and the injection point 2, respectively. The sterilizing agent was allowed to be at least 3 mg / L in front of the reverse osmosis membrane. As the reverse osmosis membrane in the first and second stages, a reverse osmosis membrane "ES15" manufactured by Nitto Denko Corporation, which is an anion sub-membrane, was used. The feed quantity Q was 200 liters / h of pure water, the recovery rate of the reverse osmosis membrane at the first stage was 50%, and the recovery rate of the reverse osmosis membrane at the second stage was 90%.

[Measurement of zeta potential of reverse osmosis membrane]

The zeta potential of the reverse osmosis membrane was determined using a zeta dislocation / particle size measurement system ELS series manufactured by Otsuka Electronics Co., Ltd. The zeta potential of the reverse osmosis membrane was calculated from the measured electro-osmotic plot from the Mori-Okamoto equation and the Smoluchowski equation.

(Expression of Mori-Okamoto)

_{U obs (z) = AU 0} (z / b) 2 + ΔU 0 (z / b) + (1-A) U 0 + U p

From here,

z: Distance from the center of the cell

U _obs (z): the apparent mobility at the z-position in the cell

A: 1 / [(2/3) - (0.420166 / K)]

K = a / b: 2a and 2b are the lengths of the cross section of the cell cross section, and a> b

U _p : true mobility of particles

U ₀ : Average mobility on the upper and lower surfaces of the cell

ΔU ₀ : Difference in mobility on the upper and lower surfaces of the cell

(Expression of small ruchowski)

ζ = 4πηU / ε

From here,

U: Electricity mobility

ε: permittivity of solvent

η: viscosity of solvent

A 10 mM aqueous NaCl solution (pH of about 5.4) was used as the assay solution. Two pairs of the aqueous solution and the sample were prepared for each sample, one of which was acidic (pH 2, 3, 4, 5, 6, 7) and the other was alkaline (pH 8, 9) And the zeta potential at each pH was measured. The physical properties of the solvent were pure water (refractive index: 1.3328, viscosity: 0.8878, dielectric constant: 78.3) at 25 캜.

[Evaluation of the inhibition rate in the reverse osmosis membrane of bactericide]

For each bactericide having the composition shown in Table 1, the inhibition rate of the bactericide in the reverse osmosis membrane was evaluated by the flat membrane testing apparatus under the following conditions.

(Exam conditions)

Test apparatus: Flat membrane test apparatus (see Fig. 4)

Membrane Master Membrane Master C70-F Flow Membrane Test Cell

Flat membrane type: Negative ion lower membrane &quot; ES15 &quot; (aromatic polyamide-based negative ion anion membrane, low-pressure RO membrane, manufactured by Nitto Denko Corporation)

Plate diameter: 75 mm in diameter

Test Number: Ultrapure Water

Test water pH: 7.0 (The following sterilizing agent was added and adjusted to hydrochloric acid and sodium hydroxide)

Test quantity: 50ℓ

Test water temperature: 25 ° C ± 1 ° C

Supply pressure: 0.75MPa

Test quantity: 5 L / min

Evaluation Fungicides: See Table 1

Disinfectant concentration: 3 mg / l

(Test Methods)

Each bactericide was added to the test water, the pH was adjusted, and the mixture was circulated for 30 minutes. After each permeated water was sufficiently blown, raw water and permeated water were sampled and the concentration of the bactericide was measured, And the blocking rate was calculated. The bactericide was added directly to the tank to a concentration of 3 mg / l.

The inhibition rate of each bactericide in the reverse osmosis membrane was determined by the following equation.

(%) = (Bactericidal concentration of feed water - bactericidal concentration of permeated water) / (bactericidal concentration of feed water) x 100

[Preparation of hypobromic acid stabilizing composition]

Under the nitrogen atmosphere, a mixture of liquid bromine: 16.9 wt%, sulfamic acid: 10.7 wt%, sodium hydroxide: 12.9 wt%, potassium hydroxide: 3.94 wt%, and water were mixed to prepare a hypobromic acid stabilizing composition Was prepared. The pH of the hypobromic acid stabilizing composition was 14, and the effective halogen concentration (effective chlorine conversion concentration) was 7.5% by weight. A detailed preparation method of the hypobromic acid stabilizing composition is as follows.

1436 g of water and 361 g of sodium hydroxide were added to a 2 L four-necked flask sealed with continuous injection while the flow rate of nitrogen gas was controlled by a mass flow controller so that the oxygen concentration in the reaction vessel was maintained at 1% And then 300 g of sulfamic acid was added and mixed. 473 g of liquid bromine was added while maintaining the temperature of the reaction solution at 0 to 15 캜 while cooling was continued, and then 230 g of a 48% potassium hydroxide solution was added. The desired hypobromic acid stabilizing composition was obtained in which the sulfamic acid was 10.7% by weight, bromine was 16.9%, and the equivalent ratio of sulfamic acid to the equivalent amount of bromine was 1.04. The pH of the obtained solution was 14 as measured by a glass electrode method. The bromine content of the obtained solution was 16.9% as determined by a method of converting bromine to iodine by potassium iodide and then performing redox titration using sodium thiosulfate. The bromine content was 100.0% of the theoretical content (16.9%). The oxygen concentration in the reaction vessel at the time of the bromine reaction was measured using "Oxygen Monitor JKO-02 LJDII" manufactured by Jikco Ltd. Also, the concentration of bromic acid was less than 5 mg / kg.

[Example 1-1 and Comparative Example 1-1]

In Example 1-1 and Comparative Example 1-1, a hypobromic acid stabilizing composition (anionic) was added as a bactericide. At this time, the inhibition ratio (RO blocking ratio) of the hypobromous membrane of the hypobromic acid stabilizing composition was measured and found to be 99.1%.

In Comparative Example 1-1, when the bactericide was added so that the bactericide concentration C1 from the injection point 1, the bactericide concentration C2 from the injection point 2 to the bactericide concentration C2, and the bactericide concentrations C1 and C2 were all 3 mg / l, the addition amount of the bactericide X1 + X2 = 21.5 g / d. Next, in Example 1-1, when a bactericide was added so that the bactericidal concentration C1 in the water supplied to the first reverse osmosis membrane device 12 was 3 mg / l from the injection point 2, the addition amount of the bactericide X2 And the fungicide concentration C2 was 6.1 mg / l (> 3 mg / l). Compared with Comparative Example 1-1, the addition amount of the bactericide was reduced by 7.0 g / d in Example 1-1. The results are shown in Table 2.

[Example 1-2 and Comparative Example 1-2]

In Example 1-2 and Comparative Example 1-2, isothiazolone (neutral) was added as a fungicide. KATHON (registered trademark) WT (manufactured by Dow Chemical Company), which is a disinfectant containing an isothiazolone compound, was used in the preparation. At this time, the inhibition rate of isothiazolone in the reverse osmosis membrane was measured and found to be 81.8%.

In Comparative Example 1-2, when the bactericide was added so that the bactericide concentration C1 from the injection point 1, the bactericide concentration C2 from the injection point 2 to the bactericide concentration C2, and the bactericide concentrations C1 and C2 were all 3 mg / liter, the addition amount of the bactericide X1 + X2 = 20.3 g / d. Next, in Example 1-2, a bactericide was added from the injection point 2 so that the bactericidal concentration C1 in the water supplied to the first reverse osmosis membrane device 12 was 3 mg / l, and the addition amount of the bactericide X2 And the fungicide concentration C2 was 7.3 mg / L (> 3 mg / L). Compared with Comparative Example 1-2, the addition amount of the bactericide was reduced by 4.2 g / d in Example 1-2. The results are shown in Table 2.

[Example 1-3 and Comparative Example 1-3]

In Examples 1-3 and Comparative Examples 1-3, hypochlorous acid (anionic) was added as a bactericide. At this time, the inhibition rate of hypochlorous acid in the reverse osmosis membrane was measured to be 71.0%.

In Comparative Example 1-3, when the fungicide was added so that the fungicide concentration C1 from the injection point 1, the fungicide concentration C2 to the fungicide concentration C2, and the fungicide concentrations C1 and C2 were all 3 mg / l, the addition amount of the fungicide X1 + X2 = 19.5 g / d. Next, in Example 1-3, when a bactericide was added so that the bactericidal concentration C1 in the water supplied to the first reverse osmosis membrane device 12 was 3 mg / l from the injection point 2, the addition amount of the bactericide X2 Was 17.8 g / d, and the bactericidal concentration C2 was 8.3 mg / L (> 3 mg / L). Compared with Comparative Example 1-3, the addition amount of the bactericide was reduced by 1.7 g / d in Example 1-3. The results are shown in Table 2.

[Examples 1-4 and Comparative Examples 1-4]

In Examples 1-4 and Comparative Examples 1-4, a halothioacetamide compound was used as a bactericide. At this time, the inhibition rate of the halothioacetamide compound in the reverse osmosis membrane was measured and found to be 97.0%.

In Comparative Example 1-4, when the bactericide was added from the injection point 1 to the bactericide concentration C1, from the injection point 2 to the bactericide concentration C2 and to the bactericide concentrations C1 and C2 of 3 mg / l, the addition amount of the bactericide X1 + X2 = 21.4 g / d. Next, in Example 1-4, a bactericide was added so that the bactericidal concentration C1 in the water supplied to the first reverse osmosis membrane device 12 was 3 mg / l from the injection point 2, and the addition amount of the bactericide X2 (14.6 g / d) and the bactericidal concentration C2 was 6.2 mg / l (> 3 mg / l). Compared with Comparative Example 1-4, the amount of the bactericide added in Example 1-4 was reduced by 6.8 g / d. The results are shown in Table 2.

[Comparative Example 2-1 and Comparative Example 2-2]

In Comparative Example 2-1 and Comparative Example 2-2, chloramine (anionic) was added as a bactericide. At this time, the inhibition rate of chloramine in the reverse osmosis membrane was measured to be 10.2%.

In Comparative Example 2-2, when the bactericide was added so that the bactericide concentration C1 from the injection point 1, the bactericide concentration C2 to the bactericide concentration C2 from the injection point 2, and the bactericide concentrations C1 and C2 were all 3 mg / l, the addition amount of the bactericide X1 + X2 = 15.1 g / d. Next, in Comparative Example 2-1, when the bactericide was added from the injection point 2 so that the bactericidal concentration C1 in the water supplied to the first reverse osmosis membrane device 12 was 3 mg / l, the addition amount of the bactericide X2 was 91.5 g / d, and the bactericidal concentration C2 was 40.8 mg / L (> 3 mg / L). Compared with Comparative Example 2-2, the addition amount of the bactericide was increased by 76.4 g / d in Comparative Example 2-1. The results are shown in Table 2.

&Lt; Example 2 and Comparative Example 3 >

1 was used in Example 2, the conventional water treatment system in Fig. 3 was used in Comparative Example 3, and chlorosulfamic acid (anionic) was used as a bactericide.

[Example 2-1 and Comparative Example 3-1]

In Example 2-1 and Comparative Example 3-1, a reverse osmosis membrane "ES20" manufactured by Nitto Denko Corporation, which is an anion sub-membrane, was used as the first and second-stage reverse osmosis membranes. At this time, the inhibition rate of chlorosulfamic acid in the reverse osmosis membrane was measured and found to be 99.6%.

In Comparative Example 3-1, when the bactericide was added so that the bactericide concentration C1 from the injection point 1, the bactericide concentration C2 to the bactericide concentration C2 from the injection point 2, and the bactericide concentrations C1 and C2 were all 3 mg / l, the addition amount of the bactericide X1 + X2 = 21.6 g / d. Next, in Example 2-1, when a bactericide was added so that the bactericidal concentration C1 in the water supplied to the first reverse osmosis membrane device 12 was 3 mg / l from the injection point 2, the addition amount of the bactericide X2 (14.4 g / d), and the fungicide concentration C2 was 6.0 mg / l (> 3 mg / l). Compared with Comparative Example 3-1, the addition amount of the bactericide was reduced by 7.2 g / d in Example 2-1. The results are shown in Table 3.

[Example 2-2 and Comparative Example 3-2]

In Example 2-2 and Comparative Example 3-2, the reverse osmosis membrane "ES20" manufactured by Nitto Denko Corporation, which is an anion sub-membrane, was used as the reverse osmosis membrane in the first stage, "LFC3" manufactured by Nitto Denko Co., Ltd. was used. At this time, the inhibition rate of chlorosulfamic acid in the reverse osmosis membrane was measured to be 97.9%.

In Comparative Example 3-2, when a bactericide was added so that the bactericide concentration C1 from the injection point 1, the bactericide concentration C2 to the bactericide concentration C2 from the injection point 2, and the bactericide concentrations C1 and C2 were all 3 mg / l, the addition amount of the bactericide X1 + X2 = 21.4 g / d. Then, in Example 2-2, the bactericide was added so that the bactericidal concentration C1 in the water supplied to the first reverse osmosis membrane device 12 was 3 mg / l from the injection point 2, X2 was 14.5 g / d, and the fungicide concentration C2 was 6.1 mg / l (> 3 mg / l). Compared with Comparative Example 3-2, the addition amount of the bactericide was reduced by 6.9 g / d in Example 2-2, and the reduction width was smaller than that in Comparative Examples 3-1 and 2-1. The results are shown in Table 3.

From the above test, the amount of the bactericide reduced in the Examples was larger than that in the Comparative Examples.

Thus, by the water treatment system and the water treatment method of the embodiment, the amount of the bactericide added can be reduced in the water treatment using the reverse osmosis membrane of two or more stages.

1, 3, 5: water treatment system 10: raw water tank
12: first reverse osmosis membrane device 14: second reverse osmosis membrane device
16, 18, 20, 22, 24: piping 26: circulation piping
28, 32: Disinfectant-added piping 30:

Claims (10)

A water treatment system using a reverse osmosis membrane of two or more stages,
A reverse osmosis membrane device of at least a first stage and a reverse osmosis membrane device of a second stage for treating permeated water of the first reverse osmosis membrane device; And
And circulation means for circulating the concentrated water of the second-stage reverse osmosis membrane device to the feed water of the first-stage reverse osmosis membrane device,
Wherein a sterilizing agent having a rejection ratio of 70% or more in the reverse osmosis membrane is added to the feed water of the second reverse osmosis membrane. The method according to claim 1,
The bactericide having a retardation rate of 70% or more in the reverse osmosis membrane is at least one of a hypobromic acid stabilizing composition, chlorosulfamic acid, hypochlorous acid, hypobromic acid, isothiazolone compound and halothioacetamide compound Water treatment system. 3. The method according to claim 1 or 2,
And a deaeration membrane for deaerating the feed water of the reverse osmosis membrane at the second stage after the addition of a sterilizing agent having a retardation rate of 70% or more in the reverse osmosis membrane. 4. The method according to any one of claims 1 to 3,
Wherein the bactericide having an inhibition rate of 70% or more in the reverse osmosis membrane is an anionic bactericide, and the second reverse osmosis membrane device has an anion charging membrane. 5. The method of claim 4,
Wherein the first reverse osmosis membrane device comprises a neutral membrane. There is provided a water treatment method for performing a reverse osmosis membrane treatment at two or more stages by using a reverse osmosis membrane at least at a first stage and a reverse osmosis membrane at a second stage for treating permeated water of a reverse osmosis membrane at the first stage,
The concentrated water of the reverse osmosis membrane at the second stage is circulated to the feed water of the reverse osmosis membrane at the first stage and a sterilizing agent having a blocking ratio at the reverse osmosis membrane of not less than 70% is added to the feed water of the reverse osmosis membrane at the second stage And water. The method according to claim 6,
The bactericide having a retardation rate of 70% or more in the reverse osmosis membrane is at least one of a hypobromic acid stabilizing composition, chlorosulfamic acid, hypochlorous acid, hypobromic acid, isothiazolone compound and halothioacetamide compound Water treatment method. 8. The method according to claim 6 or 7,
Characterized in that deaeration of the feed water of the second reverse osmosis membrane is performed by using a deaeration membrane at the downstream end of the addition of the microbicide having a retardation rate of 70% or more in the reverse osmosis membrane. 9. The method according to any one of claims 6 to 8,
Wherein the bactericide having an inhibition rate of 70% or more in the reverse osmosis membrane is an anionic bactericide, and the reverse osmosis membrane in the second step is an anion subbing membrane. 10. The method of claim 9,
Wherein the first reverse osmosis membrane is a neutral membrane.

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