JP2023073688A - Water treatment method and silica-base scale inhibitor - Google Patents

Abstract

To provide a water treatment method capable of suppressing formation of silica-base scales in a reverse osmosis membrane under neutral condition even when silica content in a target water is high concentration, and a silica-base scale inhibitor used in the water treatment method.SOLUTION: A water treatment method includes: an addition step of adding a scale inhibitor to a silica-containing target water; and a reverse osmosis membrane treatment step of conducting the scale inhibitor-added target water to a reverse osmosis membrane for separation into permeated water and concentrated water. The scale inhibitor comprises a copolymer including a bisphenol S monomer unit having a specified structure and a phenolsulfonic acid monomer unit having a specified structure.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a water treatment method that performs reverse osmosis membrane treatment, and a silica-based scale inhibitor that can be used in the water treatment method.

In recent years, there have been increasing opportunities to use reverse osmosis membranes for purposes such as pure water production and water recovery. Scaling is one of the most important operational control items for reverse osmosis membranes. When scale is generated on the surface of the reverse osmosis membrane, it causes an increase in differential pressure and leads to deterioration in the operating efficiency of the facility. Therefore, it is very important to suppress the generation of such scale for stable operation of the facility.

Among various types of scale, it is particularly difficult to suppress generation of silica-based scale. This is because the silica scale is accelerated by other ion components and the silica scale is uncharged.

As a countermeasure against scaling, the main measure is to add a scale dispersant to the water to be treated. Scale dispersants have structures such as acrylic acid, maleic acid, and phosphonic acid, and have the function of trapping cations in an electrically charged manner to suppress scale deposition, and obtain dispersibility due to steric hindrance. However, as described above, since silica is a non-charged substance, there are few effective silica-based scale dispersants. It is limited to indirect scaling measures that physically and sterically hinder the growth of silica scale, such as periodic film flushing and the use of multi-branched polymers with a structure similar to tert-butyl groups ( For example, see Patent Document 1).

Therefore, when taking measures against silica scale, silica scaling is suppressed by making the water to be treated acidic and controlling the deposition time of silica (for example, see Patent Document 2), or making the water to be treated alkaline and silica Reverse osmosis membranes have been operated by increasing the solubility of silica to suppress precipitation of silica.

However, when the water to be treated is acidified, the rejection rate of the reverse osmosis membrane is seriously lowered, resulting in deterioration of the treated water quality. When the water to be treated is made alkaline, the risk of scale precipitation of hardness components becomes extremely high, so it was necessary to add a dispersant for hardness components and install pretreatment equipment such as softening treatment.

In addition, although the above-mentioned silica-based scale dispersant is effective against silica at relatively low concentrations, it could not exhibit a sufficient inhibitory effect at high concentrations (for example, 200 mg/L or more).

Japanese Patent No. 6512322 Japanese Patent No. 3187629

An object of the present invention is to provide a water treatment method capable of suppressing the generation of silica-based scale in a reverse osmosis membrane under neutral conditions even when the silica content of the water to be treated is high, and the water treatment method. An object of the present invention is to provide a silica-based scale inhibitor that can be used in the method.

（１）

（２） The present invention comprises an addition step of adding a scale inhibitor to treated water containing silica, and passing the treated water to which the scale inhibitor has been added through a reverse osmosis membrane to separate into permeated water and concentrated water. and a reverse osmosis membrane treatment step, wherein the scale inhibitor comprises a bisphenol S monomer unit represented by the following chemical formula (1) and a phenolsulfonic acid monomer unit represented by the following chemical formula (2). It is a water treatment method containing a copolymer containing.

(1)

(2)

In the water treatment method, the pH of the water to be treated is preferably 6.5 or higher.

In the water treatment method, it is preferable that the concentrated water has a silica concentration of 150 mg/L or more.

In the water treatment method, the molecular weight of the copolymer is preferably in the range of 1,000 to 100,000 as weight average molecular weight.

In the water treatment method, the concentration of the scale inhibitor added to the water to be treated is preferably 5 mg/L or more as a solid content concentration.

（１）

（２） The present invention provides a silica-based scale inhibitor containing a copolymer containing a bisphenol S monomer unit represented by the following chemical formula (1) and a phenolsulfonic acid monomer unit represented by the following chemical formula (2). is.

(1)

(2)

In the silica-based scale inhibitor, the molecular weight of the copolymer is preferably in the range of 1,000 to 100,000 as weight average molecular weight.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a water treatment method capable of suppressing generation of silica-based scale in a reverse osmosis membrane under neutral conditions even if the water to be treated has a high silica content, and a water treatment method therefor. A silica-based scale inhibitor that can be used can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows an example of the water treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows the water treatment apparatus used in the Example. 4 is a graph showing the flux retention rate (%) with respect to the water flow time (hr) in Example 1 and Comparative Example 1. FIG. 4 is a graph showing the behavior of Flux _t=t /Flux _t=0 (−) when pH is changed in Example 1. FIG. 4 is a graph showing the flux retention rate (%) at each additive concentration after 40 hours of water passage in Example 2. FIG. 10 is a graph showing the results of evaluating the dispersibility of hardness components (Ca dispersion ratio (%)) in Example 3. FIG.

An embodiment of the present invention will be described below. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

<Water treatment method>
The water treatment method according to the present embodiment comprises an addition step of adding a scale inhibitor to water to be treated containing silica, and passing the water to be treated to which the scale inhibitor has been added through a reverse osmosis membrane to form permeate. and a reverse osmosis membrane treatment step for separating into concentrated water, and the scale inhibitor is a bisphenol S monomer unit represented by the following chemical formula (1) and a phenolsulfonic acid unit represented by the following chemical formula (2). A water treatment method containing a copolymer containing a mer unit.

（１）

（２）

(1)

(2)

An outline of an example of a water treatment apparatus for performing the water treatment method according to the present embodiment is shown in FIG. 1, and the configuration thereof will be described.

The water treatment apparatus 1 shown in FIG. 1 is a reverse osmosis membrane treatment means for passing water to be treated to which a scale inhibitor has been added through a reverse osmosis membrane to separate permeated water and concentrated water. 10. The water treatment apparatus 1 may include a scale inhibitor addition pipe 18 as an addition means for adding the scale inhibitor to the water to be treated containing silica.

In the water treatment apparatus 1 , a water pipe 12 to be treated is connected to the inlet of the reverse osmosis membrane treatment apparatus 10 . A permeated water pipe 14 is connected to a permeated water outlet of the reverse osmosis membrane treatment apparatus 10, and a concentrated water pipe 16 is connected to a concentrated water outlet. A scale inhibitor addition pipe 18 is connected to the water pipe 12 to be treated.

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

Water to be treated containing silica (silica-containing water) is sent to the reverse osmosis membrane treatment apparatus 10 through the water to be treated pipe 12 . Here, a scale inhibitor is added to the water to be treated containing silica in the water to be treated pipe 12 through the scale inhibitor addition pipe 18 (adding step). A water tank to be treated that stores water to be treated may be installed upstream of the reverse osmosis membrane treatment apparatus 10, and the scale inhibitor may be added in the water tank to be treated.

In the reverse osmosis membrane treatment apparatus 10, the water to be treated to which the scale inhibitor has been added is passed through the reverse osmosis membrane and separated into permeated water and concentrated water (reverse osmosis membrane treatment step). Permeate is discharged through permeate line 14 and concentrate is discharged through concentrate line 16 .

The scale inhibitor used in this water treatment method is a copolymer containing bisphenol S monomer units represented by the above chemical formula (1) and phenolsulfonic acid monomer units represented by the above chemical formula (2). It is a scale inhibitor contained.

The present inventors have found that even if the content of silica in the water to be treated is high, as a means for suppressing the generation of silica-based scale in a reverse osmosis membrane under neutral conditions, a sulfonic acid-based polymer is added to silica. It was discovered that silica scaling in a reverse osmosis membrane can be reduced by adding it to the water to be treated. By using a scale inhibitor containing a copolymer containing bisphenol S monomer units and phenolsulfonic acid monomer units, silica scaling is inhibited under neutral conditions and at high silica contents (e.g., Even if the silica content is 200 mg/L or more), silica scale can be suppressed and stable operation can be realized.

Silica is an uncharged substance, but its surface is slightly anionically charged. Therefore, it is believed that the strong anionic charge of the sulfonic acid group of the sulfonic acid-based polymer can disperse silica. Here, when this sulfonic acid-based polymer further has a bisphenol S structure, the bisphenol S structure and the surface of the reverse osmosis membrane attract each other by the action of hydrogen bonding, so that the sulfonic acid-based polymer stays in the vicinity of the membrane, It is considered that silica scale deposition on the film surface can be suppressed more effectively.

The copolymer contained in the scale inhibitor is a copolymer containing bisphenol S monomer units represented by the above chemical formula (1) and phenolsulfonic acid monomer units represented by the above chemical formula (2). be. The copolymer contained in the scale inhibitor is represented by the following chemical formula (3), a bisphenol S monomer unit represented by the above chemical formula (1) and a phenolsulfonic acid represented by the above chemical formula (2) It may be a copolymer composed of monomer units. A copolymer containing a monomer unit represented by the chemical formula (1) and a monomer unit represented by the chemical formula (2), or a monomer unit represented by the chemical formula (1) and the chemical formula The monomer unit (m) represented by the chemical formula (1) in the copolymer consisting of the monomer unit represented by (2) and the monomer unit (n ) is not particularly limited. preferably, and more preferably m>>n.

（３）

(3)

A copolymer containing a monomer unit represented by the above chemical formula (1) and a monomer unit represented by the above chemical formula (2) is a monomer unit represented by the above chemical formula (1) and the above chemical formula A monomer unit other than the monomer unit represented by (2) may be included. The monomers constituting the monomer units other than the monomer units represented by the chemical formula (1) and the monomer units represented by the chemical formula (2) are not particularly limited, but for example, acrylic acid , maleic acid, methacrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and the like.

The molecular weight of the copolymer is not particularly limited, but the weight average molecular weight is preferably in the range of 1000 to 100000, more preferably in the range of 1000 to 25000, further preferably in the range of 4000 to 25000. preferable. The weight average molecular weight of the copolymer can be measured, for example, by gel permeation chromatography (GPC), which is a general measurement method. When the weight-average molecular weight of the copolymer is less than 1000, the effect of suppressing scale may be insufficient. The coalescence is highly viscous and may be difficult to handle.

The pH of the water to be treated is not particularly limited, but is preferably 6.5 or higher, more preferably 6.6 or higher. The upper limit of the pH is preferably 11 or less from the standpoint of film deterioration, and more preferably less than pH 9, since a pH of 9 or more may increase the silica solubility. If the pH of the water to be treated is less than 6.5, the permeation flux (flux) of the reverse osmosis membrane may decrease. The pH of the water to be treated is the pH of the water to be treated after the scale inhibitor has been added.

The concentration of silica in the concentrated water is not particularly limited, but is preferably 150 mg/L or more, more preferably 200 mg/L or more. The upper limit of the silica concentration of the concentrated water is, for example, 400 mg/L, preferably 300 mg/L. That is, the concentration of silica in concentrated water is particularly effective in the range of 200-300 mg/L. The silica concentration here refers to the concentration of ionic silica. If the silica concentration of the concentrated water is less than 150 mg/L, the scale inhibitor is superior, but the scale can be suppressed even with existing chemicals. may be seen, but may not have long-term effects.

The concentration of the scale inhibitor added to the water to be treated is not particularly limited, but the solid content concentration is preferably in the range of 1 to 1000 mg/L, more preferably in the range of 1 to 100 mg/L, and more preferably in the range of 5 to 25 mg/L. is more preferred. If the concentration of the scale inhibitor added to the water to be treated is less than 1 mg/L as a solid concentration, a sufficient scale inhibitory effect may not be obtained. , economic problems are large and unrealistic.

The above polymer may be used in combination with other "scale inhibitors", "bactericides", "anticorrosives" and the like.

Other scale inhibitors include polymer electrolytes and phosphonic acid compounds.

Examples of polymer electrolytes include anionic polymers, amphoteric polymers, and cationic polymers.

Examples of anionic polymers include polyacrylic acid, polymaleic acid, phosphinic acid polymers, copolymers of acrylic acid and 2-hydroxy-3-allyloxypropanesulfonic acid, acrylic acid and 2-acrylamide-2- Copolymers of methylpropanesulfonic acid, copolymers of acrylic acid and isoprenesulfonic acid, copolymers of acrylic acid and 2-hydroxyethyl methacrylate, acrylic acid and 2-hydroxyethyl methacrylate and isopropylene sulfone Copolymers with acids, copolymers of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and substituted acrylamides, copolymers of maleic acid and pentene, alkali metal salts and alkalis of these anionic polymers Earth metal salts and the like can be mentioned. One of these anionic polymers and salts thereof may be used alone, or two or more thereof may be used in combination.

Examples of amphoteric polymers include copolymers of diallylamine hydrochloride and maleic acid, copolymers of diallylamine amide sulfate and maleic acid, and copolymers of diallyldimethylammonium chloride and maleic acid. These amphoteric polymers and salts thereof may be used singly or in combination of two or more.

Examples of cationic polymers include polydiallylamine and polydiallyldimethylammonium chloride. These cationic polymers and salts thereof may be used singly or in combination of two or more.

Phosphonic acid compounds include, for example, 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyphosphonoacetic acid, nitrilotrimethylenephosphonic acid, salts of the phosphonic acids, and the like. is mentioned. Phosphonic acid compounds may be used as free acids or as salts. Phosphonic acid salts include, for example, alkali metal salts such as lithium salts, sodium salts and potassium salts, and alkaline earth metal salts such as magnesium salts and calcium salts. The salt of phosphonic acid may be either a normal salt or an acid salt. These phosphonic acids and salts thereof may be used singly or in combination of two or more.

Examples of disinfectants include hypochlorite, chloramine, chlorosulfamic acid, hypobromous acid, halogen compounds such as stabilized hypobromous acid compositions, isothiazolone compounds, 2,2-dibromo-3- Nitrilopropionamide (DBNPA), organic nitrogen compounds such as 2,2-dibromo-2-nitriethanol (DBNE), quaternary ammonium compounds and the like can be mentioned. Examples of the stabilized hypobromous acid composition include a stabilized hypobromous acid composition containing a mixture of a "bromine-based oxidizing agent" and a "sulfamic acid compound", and a "reaction between a brominated oxidizing agent and a sulfamic acid compound and a stabilized hypobromous acid composition containing "product".

Examples of anticorrosive agents include azole compounds such as benzotriazole and tolyltriazole, phosphates, molybdates, zinc salts, and nitrites.

Applications of the reverse osmosis membrane treatment in the water treatment method according to the present embodiment include, for example, pure water production, seawater desalination, wastewater recovery, and the like.

The water to be treated includes industrial water, well water, surface water, tap water, water discharged from the semiconductor manufacturing process, such as wastewater from the abatement system, acid-alkali neutralization wastewater, etc. Cooling tower blow water and the like can be mentioned. The water to be treated may be seawater or brackish water.

In the water treatment method and water treatment apparatus according to the present embodiment, the reverse osmosis membrane treatment apparatus 10 is preceded by pH adjustment, biological treatment, coagulation treatment, coagulation sedimentation treatment, pressure flotation treatment, and Equipped with a device for performing at least one of biological, physical, or chemical pretreatments such as filtration, membrane separation, activated carbon, ozonation, ultraviolet irradiation, and decarboxylation, and a reverse osmosis membrane For the water to be treated in the treatment device 10 (reverse osmosis membrane treatment process), pH adjustment, biological treatment, coagulation treatment, coagulation sedimentation treatment, pressure flotation treatment, filtration treatment, membrane separation treatment, activated carbon treatment, ozone treatment, and ultraviolet irradiation treatment At least one of biological, physical or chemical pretreatments such as decarboxylation may be performed.

In addition, in the water treatment method and the water treatment apparatus according to the present embodiment, a regenerative ion exchange treatment apparatus, an electric At least one of a salt treatment device (EDI), a non-regenerative ion exchange resin device, a deaeration membrane treatment device, a UV sterilization treatment device, a UV oxidation treatment device, a particulate removal treatment device, and a second reverse osmosis membrane treatment device Equipped with a device, the permeated water of the reverse osmosis membrane treatment device 10 (reverse osmosis membrane treatment step) is treated, regenerative ion exchange treatment, electrical desalination treatment, non-regenerative ion exchange resin treatment, degassing membrane treatment, At least one of UV sterilization treatment, UV oxidation treatment, fine particle removal treatment, and second reverse osmosis membrane treatment may be performed.

<Silica-based scale inhibitor>
The silica-based scale inhibitor according to the present embodiment is a copolymer containing a bisphenol S monomer unit represented by the above chemical formula (1) and a phenolsulfonic acid monomer unit represented by the above chemical formula (2). A silica-based scale inhibitor to suppress the formation of silica-based scale in an aqueous system.

The copolymer is as described in <Water treatment method> above.

The silica-based scale inhibitor according to the present embodiment may further contain the above-mentioned "scale inhibitor", the above-mentioned "bactericide", the above-mentioned "corrosion inhibitor", etc., in addition to the above-mentioned polymer.

The silica-based scale inhibitor according to the present embodiment suppresses the generation of silica-based scale in a water system, for example, by being present in a water system such as water treatment including a reverse osmosis membrane treatment process (reverse osmosis membrane treatment apparatus). can do. In particular, even if the content of silica in the aqueous system is high, the generation of silica-based scale in the aqueous system can be suppressed under neutral conditions.

The water system to be treated is not particularly limited, but for example, cooling water system, reverse osmosis membrane (RO membrane), nanofiltration membrane (NF membrane), ultrafiltration membrane (UF membrane), microfiltration membrane (MF membrane ), etc., and can suppress scale generation on the heat transfer surface of the heat exchanger, the separation membrane surface of the membrane separation device, and the like.

The pH of the aqueous system during the treatment is not particularly limited, but is preferably pH 6.5 or higher, more preferably pH 6.6 or higher. The upper limit of the pH is preferably 11 or less from the standpoint of film deterioration, and more preferably less than pH 9, since a pH of 9 or more may increase the silica solubility. If the pH of the aqueous system during treatment is less than 6.5, the permeation flux (flux) of the reverse osmosis membrane may decrease. The pH of the aqueous system during treatment is the pH after the addition of the scale inhibitor.

The aqueous silica concentration is not particularly limited, but is preferably 150 mg/L or more, more preferably 200 mg/L or more. The upper limit of the aqueous silica concentration is, for example, 400 mg/L, preferably 300 mg/L. That is, the concentration of silica in the aqueous system is particularly effective in the range of 200-300 mg/L. The silica concentration here refers to the concentration of ionic silica. If the silica concentration in the aqueous system is less than 150 mg/L, the present scale inhibitor is superior, but it is within the range where even existing chemicals can suppress scale. long-term effects may not be seen.

The concentration of the silica-based scale inhibitor added to the aqueous system is not particularly limited, but the solid content concentration is preferably in the range of 1 to 1000 mg/L, more preferably in the range of 1 to 100 mg/L, and more preferably in the range of 5 to 25 mg/L. is more preferred. If the concentration of the silica-based scale inhibitor added to the aqueous system is less than 1 mg/L as a solid concentration, a sufficient scale inhibitory effect may not be obtained. , economic problems are large and unrealistic.

EXAMPLES 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.

<Example 1>
In the flow shown in FIG. 2, the polymer represented by the above chemical formula (3) having a weight average molecular weight of 15200 (m:n=1:9 to 9:1), reverse osmosis membrane treatment was performed under the following test conditions, and the flux retention rate was measured. The flux retention rate is a value indicating the ratio when the initial flux (permeation flow rate m ³ /d/(membrane area m ² × transmembrane pressure MPa) × temperature correction) is 100%. For the stability of the test system, the water flow time was set to 0 hours after 1 hour from the start of water flow. FIG. 3 shows the flux retention rate (%) with respect to the water flow time (hr).

<Comparative Example 1>
As a silica-based scale inhibitor, a conventional terpolymer of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and substituted acrylamide (weight average molecular weight: 5000) was used, reverse osmosis membrane treatment was performed in the same manner as in Example 1, and the flux retention rate was measured. FIG. 3 shows the flux retention rate (%) with respect to the water flow time (hr).

(Test condition)
・Test water (water to be treated): pure water SiO ₂ : 400 mg/L
Ca, Mg: 300 mg _CaCO3 /L
Al: 0.25 mg/L
HCO ₃ ⁻ : 150 mg CaCO ₃ /L
・Water temperature: 25℃
・pH: 7.5
・Reverse osmosis membrane: ES20 flat membrane manufactured by Nitto Denko ・Silica-based scale inhibitor concentration: 25 mg/L as solid

From FIG. 3, it can be seen that the polymer of the chemical formula (3) of Example 1 has a higher flux retention rate and a higher silica scale dispersibility.

[Examination of pH conditions]
In the flow shown in FIG. 2, in order to evaluate changes in behavior due to pH, the pH of the water to be treated was gradually lowered from pH 7, reverse osmosis membrane treatment was performed under the following test conditions, and the flux retention rate was confirmed. FIG. 4 shows the behavior of Flux _t=t /Flux _t=0 (−) when the pH is changed.

(Test condition)
・Test water: Sagamihara well water sterilized with hypochlorous acid, sand-filtered, and treated with activated carbon HCO ₃ ⁻ : 8 mg CaCO ₃ /L
Nitrate ion: 10mg/L
Sulfate ion: 6mg/L
Chloride ion: 33mg/L
Na: 4 mg/L
Ca: 13 mg/L
Mg: 6mg/L
_SiO2 : 22 mg/L
・Water temperature: 25℃
・pH: starting at 7.0, changing to 6.9, 6.8, 6.7, 6.6, 6.5 ・Silica-based scale inhibitor concentration: 30mg/L as product
・Reverse osmosis membrane: ES20 element manufactured by Nitto Denko ・pH adjuster: hydrochloric acid

From FIG. 4, almost no decrease in flux retention rate was observed up to pH 6.6, but a slight decrease was confirmed at pH 6.5. Therefore, it can be seen that the preferable pH range is pH 6.6 or higher.

<Example 2>
[Confirmation of appropriate density]
Appropriate additive concentrations of silica-based scale inhibitors when used for reverse osmosis membranes were evaluated. FIG. 5 shows the flux retention rate (%) at each additive concentration after 40 hours of water passage. The test conditions are the same as in Example 1.

From FIG. 5, it can be seen that all have high flux retention rates compared to the blank. Since the performance is almost the same when 5.25 to 15 mg/L is added, it can be said that sufficient performance can be exhibited even when 5 mg/L is added. In addition, since the scale dispersibility is high with the addition of 20 mg/L or more, it can be said that the addition of 20 mg/L or more is desirable when applying to the water to be treated which has a relatively high ion load.

<Example 3>
[Formulation with 2-phosphonobutane-1,2,4-tricarboxylic acid]
The dispersibility of the hardness component (Ca dispersion ratio (%)) was evaluated by a beaker test under the following test conditions. The results are shown in FIG.

(Test condition)
・Test water: pure water ・Ca: 400 mg CaCO ₃ /L
・M-Alk: 400 mg CaCO ₃ /L
・pH: 8
・Immersion time: 18h
・Water temperature: 70℃

From FIG. 6, it was found that hardness dispersibility was low without PBTC. A silica-based scale inhibitor is usually blended with a polymer for dispersing hardness. Here, when PBTC was blended and the same test was conducted, high hardness dispersibility was obtained. Therefore, when used as a chemical for reverse osmosis membranes, it can be said that scaling is further suppressed by blending a hardness scale dispersant such as PBTC.

As described above, by using the silica-based scale inhibitor of the example, even if the content of silica in the water to be treated is high, the generation of silica-based scale in the reverse osmosis membrane is suppressed under neutral conditions. I was able to

1 water treatment equipment, 10 reverse osmosis membrane treatment equipment, 12 treated water pipe, 14 permeated water pipe, 16 concentrated water pipe, 18 scale inhibitor addition pipe.

Claims (7)

an adding step of adding a scale inhibitor to water to be treated containing silica;
a reverse osmosis membrane treatment step of passing the water to be treated to which the scale inhibitor has been added through a reverse osmosis membrane to separate the permeated water and the concentrated water;
including
The scale inhibitor is characterized by containing a copolymer containing a bisphenol S monomer unit represented by the following chemical formula (1) and a phenolsulfonic acid monomer unit represented by the following chemical formula (2): water treatment method.

(1)

(2) The water treatment method according to claim 1,
A water treatment method, wherein the pH of the water to be treated is 6.5 or higher. The water treatment method according to claim 1 or 2,
A water treatment method, wherein the concentrated water has a silica concentration of 150 mg/L or more. The water treatment method according to any one of claims 1 to 3,
A water treatment method, wherein the molecular weight of the copolymer is in the range of 1,000 to 100,000 as a weight-average molecular weight. The water treatment method according to any one of claims 1 to 4,
A water treatment method, wherein the concentration of the scale inhibitor added to the water to be treated is 5 mg/L or more as a solid content concentration. A silica-based scale inhibitor comprising a copolymer containing a bisphenol S monomer unit represented by the following chemical formula (1) and a phenolsulfonic acid monomer unit represented by the following chemical formula (2): .

(1)

(2) The silica-based scale inhibitor according to claim 6,
A silica-based scale inhibitor, wherein the molecular weight of the copolymer is in the range of 1,000 to 100,000 as weight average molecular weight.

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