Water-treating apparatus and water-treating method

Abstract

To provide a water-treating apparatus and water-treating method, capable of inhibiting progression of blockage of reverse osmosis membranes due to scale in reverse osmosis membrane processing.SOLUTION: A water-treating apparatus 1 includes: a reverse osmosis membrane-processing apparatus 12 for passing water to be treated, which includes at least one of calcium and aluminum, through a reverse osmosis membrane to obtain permeate water and concentrated water; and a scale inhibitor-adding pipe 22 for adding a scale inhibitor to the water to be treated; wherein the reverse osmosis membrane is a neutral-charged membrane.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment device and a water treatment method using a reverse osmosis membrane. [Background technology]

[0002] In recent years, reverse osmosis membranes have been increasingly used in water treatment, such as pure water production and water recovery. Scaling, which occurs when solutes in the water being treated are concentrated by the reverse osmosis membrane process and exceed the solubility of the solute, precipitates as scale and clogs the membrane surface of the reverse osmosis membrane, is one of the most common problems with reverse osmosis membranes. Typical scale components include calcium, aluminum, and silica.

[0003] As a countermeasure against scaling, the recovery rate of the reverse osmosis membrane treatment equipment is determined so that the concentration of scale components in the concentrated water from the reverse osmosis membrane treatment does not exceed the solubility of each solute, and the Langelier index (LSI) is less than 0. Here, the LSI (Langelier Saturation Index) is known as an index of the risk of scale including hardness components, and is calculated from the pH, calcium ion concentration, total alkalinity, and soluble substance concentration of the water. The larger this value is, the more likely it is that calcium carbonate will precipitate, and the more likely it is that other scales with similar properties, centered around calcium carbonate, will precipitate or co-precipitate. The LSI can be calculated using the formula (1) described below.

[0004] Generally, the higher the concentration of scale components, the higher the LSI value, so it is recommended to keep LSI<0. Furthermore, as another countermeasure against scaling, it is known to add a scale inhibitor to the feed water for reverse osmosis membrane treatment. For example, Patent Document 1 describes in an example that an agent (scale inhibitor) that disperses scale is added to the feed water for reverse osmosis membrane treatment that uses an anion-charged membrane (ultra-low pressure RO membrane "ES20" manufactured by Nitto Denko Corporation).

[0005] However, lowering the recovery rate by setting LSI<0 leads to an increase in the number of reverse osmosis membranes and an increase in the size of the system, which increases the initial and running costs. Furthermore, in recent years, the concentration of scale components in the water being treated by reverse osmosis membranes has been increasing due to localized water shortages and the spread of water recycling, making it difficult to suppress the progression of membrane blockage caused by scale by adding scale inhibitors alone. Therefore, in addition to scale inhibitors, effective means of suppressing scale are required. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6512322 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a water treatment device and a water treatment method capable of suppressing the progression of clogging of a reverse osmosis membrane caused by scale in reverse osmosis membrane treatment. [Means for solving the problem]

[0008] The present invention is a water treatment device comprising a reverse osmosis membrane treatment means for passing water to be treated, which contains at least one of calcium and aluminum, through a reverse osmosis membrane to obtain permeate water and concentrated water, and a scale inhibitor addition means for adding a scale inhibitor to the water to be treated, wherein the reverse osmosis membrane is a neutrally charged membrane.

[0009] In the water treatment device, it is preferable that the water to be treated further contains silica.

[0010] In the water treatment device, the scale inhibitor preferably contains at least one of a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units, and a phosphonic acid compound.

[0011] In the water treatment device, the neutrally charged membrane is preferably a neutrally charged membrane having a zeta potential on the membrane surface of -10 mV or more and +10 mV or less.

[0012] In the water treatment device, it is preferable that the concentrated water has a Langelier index of more than 0.

[0013] In the water treatment device, the concentrated water preferably has a silica concentration of 120 mg / L or more.

[0014] In the water treatment device, the concentrated water preferably has an aluminum concentration of 0.25 mg / L or more.

[0015] In the water treatment device, it is preferable that the concentrated water has a Langelier index exceeding 0, a silica concentration of 120 mg / L or more, and an aluminum concentration of 0.25 mg / L or more.

[0016] The present invention provides a water treatment method comprising: a reverse osmosis membrane treatment step of passing water to be treated, which contains at least one of calcium and aluminum, through a reverse osmosis membrane to obtain permeate water and concentrated water; and a scale inhibitor addition step of adding a scale inhibitor to the water to be treated, wherein the reverse osmosis membrane is a neutrally charged membrane.

[0017] In the water treatment method, it is preferable that the water to be treated further contains silica.

[0018] In the water treatment method, the scale inhibitor preferably contains at least one of a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units, and a phosphonic acid compound.

[0019] In the water treatment method, the neutrally charged membrane is preferably a neutrally charged membrane having a zeta potential of the membrane surface of -10 mV or more and +10 mV or less.

[0020] In the water treatment method, it is preferable that the concentrated water has a Langelier index of more than 0.

[0021] In the water treatment method, the concentrated water preferably has a silica concentration of 120 mg / L or more.

[0022] In the water treatment method, the concentrated water preferably has an aluminum concentration of 0.25 mg / L or more.

[0023] In the water treatment method, it is preferable that the concentrated water has a Langelier index of more than 0, a silica concentration of 120 mg / L or more, and an aluminum concentration of 0.25 mg / L or more. Effect of the Invention

[0024] According to the present invention, it is possible to provide a water treatment apparatus and a water treatment method capable of suppressing the progression of clogging of a reverse osmosis membrane caused by scale in reverse osmosis membrane treatment. [Brief description of the drawings]

[0025] [Figure 1] 1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Diagram 2] 1 is a graph showing the transition of flux retention (%) versus operation time (hr) in Example 1 and Comparative Example 1. [Diagram 3] 1 is a graph showing the transition of flux retention (%) versus operation time (hr) in Example 2 and Comparative Example 2. [Figure 4] 1 is a graph showing the transition of flux retention (%) versus operation time (hr) in Example 3 and Comparative Example 3. [Diagram 5] 1 is a graph showing the transition of flux retention (%) versus operation time (hr) in Example 4 and Comparative Example 4. [Figure 6] 1 is a graph showing the transition of flux retention (%) versus operation time (hr) in Example 5 and Comparative Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0027] A water treatment device according to an embodiment of the present invention is a water treatment device comprising a reverse osmosis membrane treatment means for passing water to be treated, which contains at least one of calcium and aluminum, through a reverse osmosis membrane to obtain permeate water and concentrated water, and a scale inhibitor addition means for adding a scale inhibitor to the water to be treated, wherein the reverse osmosis membrane is a neutrally charged membrane.

[0028] An example of a water treatment apparatus according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0029] The water treatment device 1 includes a reverse osmosis membrane treatment device 12 as a reverse osmosis membrane treatment means for passing water to be treated, which contains at least one of calcium and aluminum, through a reverse osmosis membrane to obtain permeate water and concentrated water. The reverse osmosis membrane used in the reverse osmosis membrane treatment device 12 is a neutrally charged membrane. The water treatment device 1 may include a water tank 10 to be treated that stores water to be treated, which contains at least one of calcium and aluminum.

[0030] In the water treatment device 1 in Fig. 1, a water to be treated piping 14 is connected to the water to be treated inlet of the water to be treated tank 10. The water to be treated outlet of the water to be treated tank 10 and the water to be treated inlet of the reverse osmosis membrane treatment device 12 are connected by a water to be treated piping 16. A permeated water outlet of the reverse osmosis membrane treatment device 12 is connected to a permeated water piping 18, and a concentrated water outlet is connected to a concentrated water piping 20. A scale inhibitor addition piping 22 is connected to the chemical inlet of the water to be treated tank 10.

[0031] In the water treatment device 1 of Fig. 1, water to be treated that contains at least one of calcium and aluminum is stored in the water to be treated tank 10 as necessary through the water to be treated piping 14. Here, in the water to be treated tank 10, a scale inhibitor is added to the water to be treated through scale inhibitor addition piping 22 (scale inhibitor addition step). The water to be treated to which the scale inhibitor has been added is sent to the reverse osmosis membrane treatment device 12 through the water to be treated piping 16. The scale inhibitor may be added via a line in the water to be treated piping 14 or the water to be treated piping 16.

[0032] In the reverse osmosis membrane treatment device 12, the water to be treated is passed through a reverse osmosis membrane to perform reverse osmosis membrane treatment to obtain permeated water and concentrated water (reverse osmosis membrane treatment step). The permeated water is discharged through a permeated water pipe 18, and the concentrated water is discharged through a concentrated water pipe 20.

[0033] Until now, it was believed that the deposition of scale in reverse osmosis membrane treatment was caused by the solute concentration of the concentrated water, particularly the solute concentration near the surface of the reverse osmosis membrane, and that the type of reverse osmosis membrane had no effect. However, the present inventors have found that the type of reverse osmosis membrane affects the progression of scaling.

[0034] The present inventors have found that when a neutrally charged membrane is used as a reverse osmosis membrane, clogging of the reverse osmosis membrane by scale is less likely to progress than when an anion-charged membrane is used. This is thought to be because cations such as calcium and aluminum, which are typical scale components, are attracted to the vicinity of the membrane in an anion-charged membrane and concentrated to a high concentration, whereas this phenomenon is less likely to occur in a neutrally charged membrane. Although silica is anionic, it is known that precipitation is promoted by cations such as calcium and aluminum. Therefore, it is thought that the use of a neutrally charged membrane is effective for the purpose of suppressing silica precipitation.

[0035] Neutral charged membranes are mainly used in the field of wastewater treatment. Normally, the surface of a reverse osmosis membrane is anion-charged, but by neutralizing the surface by coating or other surface treatment, it has the effect of suppressing membrane surface contamination, mainly caused by organic matter. On the other hand, due to the surface treatment, the amount of permeated water is lower than that of an anion-charged membrane, and there is a disadvantage that the operating pressure of the pump and power consumption increase when trying to obtain the same amount of water production. Therefore, unless there is a special reason, it is common to use an anion-charged membrane. For example, in applications where pure water is produced from groundwater, an anion-charged membrane is used together with a scale inhibitor. For example, in applications where pure water is produced from groundwater and the concentration of scale components in the groundwater is high, the use of a neutral charged membrane makes it difficult for the reverse osmosis membrane to become clogged, making it possible to suppress power consumption during long-term operation.

[0036] Reverse osmosis membranes include neutrally charged membranes, anion-charged membranes, and cation-charged membranes. In this specification, a membrane having a zeta potential at pH 7.0 in the range of -10 mV to 10 mV, as determined by the method for measuring the zeta potential described in the Examples below, is defined as a neutrally charged membrane, a membrane having a zeta potential of more than 10 mV as a cation-charged membrane, and a membrane having a zeta potential of less than -10 mV as an anion-charged membrane. Organic substances that tend to contaminate reverse osmosis membranes are often anionic, and in order to suppress their adhesion, the zeta potential of the neutral membrane is preferably in the range of -10 to 0 mV.

[0037] Examples of commercially available neutrally charged membranes include BW30XFR (manufactured by The Dow Chemical Company), LFC3 (manufactured by Nitto Denko Corporation), TML20 (manufactured by Toray Industries, Inc.), and OFR625 (all manufactured by Organo Corporation).

[0038] An example of a commercially available cation-charged membrane is ES10C (manufactured by Nitto Denko Corporation).

[0039] Examples of commercially available anion-charged membranes include ES15, ES20, CPA3, CPA5 (all manufactured by Nitto Denko Corporation), and RE-8040BLN (manufactured by Woongjin Co., Ltd.).

[0040] The water to be treated contains at least one of calcium and aluminum. The water to be treated may further contain silica, magnesium, etc. The water to be treated containing at least one of calcium and aluminum may be water containing at least one of calcium and aluminum, and is not particularly limited, but examples thereof include coagulation treated water, membrane filtration treated water, industrial water, etc.

[0041] The pH of the water to be treated is, for example, in the range of 4.0 to 10.0, and preferably in the range of 5.5 to 9.0. If the pH of the water to be treated is less than 4.0, the rejection rate of the reverse osmosis membrane may drop sharply and the permeated water quality may deteriorate, whereas if the pH exceeds 10.0, the reverse osmosis membrane may deteriorate due to hydrolysis.

[0042] To adjust the pH of the water to be treated, a pH adjuster such as an acid, for example, hydrochloric acid, sulfuric acid, or nitric acid, or an alkali, for example, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide, may be used.

[0043] The calcium concentration in the water to be treated is in the range of, for example, 0.1 to 500 mg / L, the aluminum concentration is in the range of, for example, 0.25 to 5 mg / L, and the silica concentration is in the range of, for example, 120 to 400 mg / L.

[0044] Examples of the scale inhibitor used include a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as structural units, a phosphonic acid compound, and a polymer having a tert-butyl group. From the viewpoint of a large anionic charge, for example, a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as structural units and a phosphonic acid compound are preferred.

[0045] Examples of copolymers containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as constituent units include a copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, a terpolymer of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and a substituted acrylamide, and a terpolymer of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and a monomer having a tert-butyl group.

[0046] The weight average molecular weight of the copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units is not particularly limited, but is, for example, in the range of 2000 to 11000, and preferably in the range of 4000 to 5000. If the weight average molecular weight of this copolymer is less than 2000, the steric hindrance effect in scale inhibition may be insufficient, and if it exceeds 11000, the reverse osmosis membrane may be clogged. The molar ratio of acrylic acid to 2-acrylamido-2-methylpropanesulfonic acid in this copolymer is not particularly limited, but is, for example, in the range of 80:20 to 70:30, and preferably in the range of 78:22 to 72:28. If the amount of acrylic acid in the copolymer is less than 70:30 in terms of the molar ratio of acrylic acid to 2-acrylamido-2-methylpropanesulfonic acid, the ability to chelate cations may become insufficient, and if the amount of 2-acrylamido-2-methylpropanesulfonic acid is less than 80:20, the dispersion force due to charge repulsion of the scale inhibitor polymer itself may become insufficient.

[0047] Examples of the phosphonic acid compound include phosphonic acid compounds that mainly function as scale dispersants, such as 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyphosphonoacetic acid, nitrilotrimethylenephosphonic acid, ethylenediamine-N,N,N',N'-tetramethylenephosphonic acid, and at least one compound selected from the group consisting of alkali metal salts and alkaline earth metal salts of these phosphonic acids.

[0048] One or more types of copolymers containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as constituent units may be used, one or more types of phosphonic acid compounds may be used, or one or more types of copolymers containing acrylic acid and AMPS as constituent units and one or more types of phosphonic acid compounds may be used in combination. When using in combination, for example, a copolymer containing a predetermined amount of acrylic acid and AMPS as constituent units and a predetermined amount of phosphonic acid compound may be mixed and added to the water to be treated, or a copolymer containing a predetermined amount of acrylic acid and AMPS as constituent units and a predetermined amount of phosphonic acid compound may be added separately to the water to be treated.

[0049] The amount of the scale inhibitor in the water to be treated may be, for example, in the range of 0.1 to 50 mg / L relative to the amount of the water to be treated, and is preferably in the range of 1 to 20 mg / L. If the amount of the scale inhibitor is less than 0.1 mg / L relative to the amount of the water to be treated, the scale inhibition effect may not be obtained, whereas if it exceeds 50 mg / L, the scale inhibition effect relative to the chemical ratio may be small and the running costs may increase.

[0050] The Langelier Saturation Index (LSI) of the concentrated water is preferably greater than 0, and more preferably 0.16 or more. If the Langelier Saturation Index of the concentrated water is 0 or less, membrane clogging due to scale may not occur even if a neutrally charged membrane is not used for the reverse osmosis membrane. There is no particular upper limit to the Langelier Saturation Index of the concentrated water, but it is, for example, 3.0.

[0051] The LSI can be calculated by the following formula (1), and can be calculated, for example, by desk calculation or using calculation software provided by a separation membrane manufacturer or a scale inhibitor manufacturer. LSI = pH - pHs + 1.5 × 10 -2 ×(T-25) Formula (1) pH = 8.313-log(Ca 2+ )-log(A)+S where pH is the pH of the water, T is the water temperature [℃], (Ca 2+ ) is Ca 2+ (A) is the milliequivalent concentration of total alkalinity [meq / L], (B) is the milliequivalent concentration of total alkalinity [meq / L], and S is the correction value (S=(2×√μ) / (1+√μ), μ: 2.5×10 -5 × sd), where sd refers to the soluble substance concentration [mg / L].

[0052] The calcium concentration in the concentrated water is preferably 0.1 mg / L or more, more preferably 1 mg / L or more. If the calcium concentration in the concentrated water is less than 0.1 mg / L, membrane clogging due to scale may not occur even if a neutrally charged membrane is not used for the reverse osmosis membrane. There is no particular upper limit for the calcium concentration in the concentrated water, but it is, for example, 500 mg / L.

[0053] The silica concentration in the concentrated water is preferably 120 mg / L or more, more preferably 150 mg / L or more. If the silica concentration in the concentrated water is less than 120 mg / L, membrane clogging due to scale may not occur even if a neutrally charged membrane is not used for the reverse osmosis membrane. The upper limit of the silica concentration in the concentrated water is not particularly limited, but is, for example, 400 mg / L.

[0054] The aluminum concentration in the concentrated water is preferably 0.25 mg / L or more, more preferably 5 mg / L or more. If the aluminum concentration in the concentrated water is less than 0.25 mg / L, membrane clogging due to scale may not occur even if a neutrally charged membrane is not used for the reverse osmosis membrane. There is no particular upper limit for the aluminum concentration in the concentrated water, but it is, for example, 10 mg / L.

[0055] In the water treatment method according to this embodiment, in addition to the above-mentioned scale inhibitor and pH adjuster, other agents such as a slime control agent and an anticorrosive agent such as a heavy metal, a phosphate or an azole compound may be used.

[0056] This specification includes the following embodiments. [1] A reverse osmosis membrane treatment means for passing water to be treated, which contains at least one of calcium and aluminum, through a reverse osmosis membrane to obtain permeated water and concentrated water; A scale inhibitor adding means for adding a scale inhibitor to the water to be treated, The water treatment device, wherein the reverse osmosis membrane is a neutrally charged membrane.

[0057] [2] The water treatment device according to [1], The water to be treated further contains silica.

[0058] [3] A water treatment device according to [1] or [2], The scale inhibitor in the water treatment device includes at least one of a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units, and a phosphonic acid compound.

[0059] [4] A water treatment device according to any one of [1] to [3], The water treatment device, wherein the neutrally charged membrane has a zeta potential of the membrane surface of -10 mV or more and +10 mV or less.

[0060] [5] A water treatment device according to any one of [1] to [4], The water treatment device, wherein the concentrated water has a Langelier Index of more than 0.

[0061] [6] A water treatment device according to any one of [1] to [5], The water treatment device, wherein the concentrated water has a silica concentration of 120 mg / L or more.

[0062] [7] A water treatment device according to any one of [1] to [6], The water treatment device, wherein the concentrated water has an aluminum concentration of 0.25 mg / L or more.

[0063] [8] A water treatment device according to any one of [1] to [4], The water treatment device, wherein the concentrated water has a Langelier index exceeding 0, a silica concentration of 120 mg / L or more, and an aluminum concentration of 0.25 mg / L or more.

[0064] [9] A reverse osmosis membrane treatment step in which water to be treated containing at least one of calcium and aluminum is passed through a reverse osmosis membrane to obtain permeate and concentrated water; A scale inhibitor adding step of adding a scale inhibitor to the water to be treated; Including, The method for treating water, wherein the reverse osmosis membrane is a neutrally charged membrane.

[0065]

[10] [9] The water treatment method according to the present invention, The water treatment method, wherein the water to be treated further contains silica.

[0066]

[11] The water treatment method according to [9] or

[10] , The water treatment method, wherein the scale inhibitor comprises at least one of a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units, and a phosphonic acid compound.

[0067]

[12] The water treatment method according to any one of [9] to

[11] , The water treatment method, wherein the neutrally charged membrane has a zeta potential of the membrane surface of -10 mV or more and +10 mV or less.

[0068]

[13] The water treatment method according to any one of [9] to

[12] , The water treatment method, wherein the Langelier Index of the concentrated water is greater than 0.

[0069]

[14] The water treatment method according to any one of [9] to

[13] , The water treatment method, wherein the silica concentration in the concentrated water is 120 mg / L or more.

[0070]

[15] The water treatment method according to any one of [9] to

[14] , The water treatment method, wherein the aluminum concentration in the concentrated water is 0.25 mg / L or more.

[0071]

[16] The water treatment method according to any one of [9] to

[12] , The water treatment method, wherein the concentrated water has a Langelier index of more than 0, a silica concentration of 120 mg / L or more, and an aluminum concentration of 0.25 mg / L or more. EXAMPLES

[0072] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0073] [RO flat membrane water flow test] An RO flat membrane water flow test was carried out. A specified amount of each solute was dissolved in pure water to prepare raw water. The ionic silica concentration was adjusted to a specified concentration using sodium metasilicate, the aluminum ion concentration was adjusted to a specified concentration using aluminum chloride, the calcium ion concentration was adjusted to a specified concentration using calcium chloride, the magnesium ion concentration was adjusted to a specified concentration using magnesium chloride, and the bicarbonate ion was adjusted to a specified concentration using sodium bicarbonate. The concentration of the soluble substances was a specified concentration of 500 to 1000 [mg / L]. The pH of the raw water was adjusted to pH 7.5 using hydrochloric acid or sodium hydroxide. The water flow was carried out at a room temperature of 25 ± 2 ° C. The raw water for this flat membrane water flow test was simulated as RO concentrated water when water was flowed through a reverse osmosis membrane element.

[0074] In the RO flat membrane water flow test, raw water was used as the water to be treated and was fed to the reverse osmosis membrane using a pump, where it was separated into permeated water and concentrated water. The permeated water was sampled on an electronic balance, and the concentrated water was returned to the raw water tank. Pure water was replenished to make up for the permeated water that had left the system. The operating pressure of the pump was 0.75 MPa or 1.22 MPa. The amount of concentrated water was 100 mL / min, ensuring a sufficient amount for the amount of permeated water. After starting the water flow, it was waited for about 30 minutes to confirm that the entire system had become almost uniform, and the flux at that point was recorded as the initial value. Flux refers to the permeation flux, and is calculated as the amount of permeated water [g] / density of water [g / mL] / membrane area [m 2 Thereafter, the flux was measured over time, and the ratio [%] of the flux at each time to the initial flux was recorded as the flux retention [%].

[0075] In addition, when water is passed through a typical reverse osmosis membrane element, the water to be treated is separated into permeate water and concentrated water by the reverse osmosis membrane, and the recovery rate is, for example, about 50% to 90%, which is equivalent to a concentration rate of about 2 to 10 times. On the other hand, the recovery rate of a flat membrane water flow test is, for example, about 0.01% to 0.05%, and the raw water quality is approximately equal to the concentrated water quality. This is because the flat membrane water flow test is an investigation method used at the laboratory level, and the purpose is to reduce the amount of sample water required to conduct the test. In the flat membrane water flow test, the risk of clogging is evaluated by passing water simulating concentrated water, which has the highest concentration of clogging substances, through the reverse osmosis membrane.

[0076] [Measurement of zeta potential of reverse osmosis membrane] The zeta potential of each reverse osmosis membrane was measured by plate electrophoresis using a 10 mM NaCl aqueous solution of pH 4 to 6 as the measurement solution, and a reverse osmosis membrane measuring 15 mm x 33 mm (thickness 5 mm or less) was immersed in the measurement solution.

[0077] The zeta potential of the reverse osmosis membrane was determined using a zeta potential / particle size measurement system ELSZseries manufactured by Otsuka Electronics Co., Ltd. The zeta potential of the reverse osmosis membrane was calculated from the measured electroosmosis plot using the Mori-Okamoto formula and the Smoluchowski formula below.

[0078] (Mori-Okamoto formula) U obs (z) = AU0(z / b) 2 +ΔU0(z / b)+(1-A)U0+U p Where: z: Distance from the cell center position U obs (z): Apparent mobility at z position in the cell A: 1 / [(2 / 3)-(0.420166 / K)] K=a / b: 2a and 2b are the horizontal and vertical lengths of the cell cross section, a>b U p : the true mobility of the particle U0: Average mobility on the top and bottom of the cell ΔU0: Difference in mobility between the top and bottom surfaces of the cell

[0079] (Smoluchowski's formula) ζ=4πηU / ε Where: U: Electrical mobility ε: Dielectric constant of the solvent η: viscosity of the solvent

[0080] The physical properties of the solvent were those of pure water at 25° C. (refractive index: 1.3328, viscosity: 0.8878, dielectric constant: 78.3).

[0081] <Example 1, Comparative Example 1> The raw water was adjusted so that the concentration of each solute was the value shown in Table 1. The LSI of the raw water of the water quality in Table 1 was calculated to be 0.17. The pump operating pressure was set to 0.75 MPa, and an RO flat membrane water flow test was carried out. As the scale inhibitor, a binary copolymer polymer (weight average molecular weight: 4500) of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) mixed with 2-phosphonobutane-1,2,4-tricarboxylic acid as a phosphonic acid compound was used. The amount of the scale inhibitor in the treated water was added so that the binary copolymer polymer was 11.5 mg / L and the phosphonic acid compound was 4.3 mg / L relative to the amount of raw water. In Example 1, a neutrally charged membrane (BW30XFR) manufactured by Film Tec was used as the reverse osmosis membrane. The zeta potential of BW30XFR was measured to be -7.9 mV. In Comparative Example 1, an anion-charged membrane (ES20) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane. The zeta potential of ES20 was measured and found to be −35 mV.

[0082] [Table 1]

[0083] The change in flux retention rate (%) versus operation time (hr) is shown in Figure 1. In Example 1, compared to Comparative Example 1, it was possible to maintain a high flux retention rate.

[0084] <Example 2, Comparative Example 2> The raw water was adjusted so that the concentration of each solute was the value shown in Table 2. The LSI of the raw water of the water quality in Table 2 was calculated to be 0.21. The pump operating pressure was set to 0.75 MPa, and an RO flat membrane water flow test was performed. The above-mentioned binary copolymer of acrylic acid and AMPS was used as the scale inhibitor. The amount of the scale inhibitor in the water to be treated was added so that the binary copolymer was 46 mg / L relative to the amount of raw water. In Example 2, a neutrally charged membrane (LFC3) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane. The zeta potential of LFC3 was measured and found to be -1.3 mV. In Comparative Example 2, an anion-charged membrane (ES20) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane.

[0085] [Table 2]

[0086] The change in flux retention rate (%) versus operation time (hr) is shown in Figure 2. In Example 2, compared to Comparative Example 2, it was possible to maintain a high flux retention rate.

[0087] <Example 3, Comparative Example 3> The raw water was adjusted so that the concentration of each solute was the value shown in Table 3. The LSI of the raw water of the water quality in Table 3 was calculated to be 0.49. The pump operating pressure was set to 0.75 MPa, and an RO flat membrane water flow test was carried out. As the scale inhibitor, a mixture of the binary copolymer of acrylic acid and AMPS and the phosphonic acid compound was used. The amount of the scale inhibitor in the water to be treated was the same as in Example 2. In Example 3, a neutrally charged membrane (LFC3) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane. In Comparative Example 3, an anion-charged membrane (ES20) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane.

[0088] [Table 3]

[0089] The change in flux retention rate (%) versus operation time (hr) is shown in Figure 3. In Example 3, compared to Comparative Example 3, it was possible to maintain a high flux retention rate.

[0090] <Example 4, Comparative Example 4> The raw water was adjusted so that the concentration of each solute was the value shown in Table 4. The LSI of the raw water of the water quality in Table 4 was calculated to be -0.84. The pump operating pressure was set to 0.75 MPa, and an RO flat membrane water flow test was performed. The above-mentioned binary copolymer of acrylic acid and AMPS was used as the scale inhibitor. The amount of the scale inhibitor in the water to be treated was added so that the binary copolymer was 13.8 mg / L relative to the amount of raw water. In Example 4, a neutral charged membrane (LFC3) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane. In Comparative Example 4, an anion charged membrane (ES20) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane.

[0091] [Table 4]

[0092] Figure 4 shows the change in flux retention (%) versus operating time (hr). Although the conditions were such that LSI<0, a slight decrease in flux was observed. This is thought to be due to scale from silica or aluminum, not hardness components. Even in this case, Example 4 was able to maintain a higher flux retention than Comparative Example 4.

[0093] <Example 5, Comparative Example 5> The raw water was adjusted so that the concentration of each solute was the value shown in Table 5. The LSI of the raw water of the water quality in Table 5 was calculated to be 0.17. The scale inhibitor was a mixture of the binary copolymer of acrylic acid and AMPS and the phosphonic acid compound. The amount of the scale inhibitor in the treated water was added so that the binary copolymer was 100 mg / L relative to the amount of raw water. In Example 5, a neutral charge membrane (LFC3) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane. In Comparative Example 5, an anion charge membrane (ES20) manufactured by Nitto Denko Corporation was used as the reverse osmosis membrane. The operating pressure of the pump was 1.22 MPa for LFC3 and 0.75 MPa for ES20. In Example 5 and Comparative Example 5, the permeation rates [g / min] of LFC3 and ES20 were made equal to each other, and an RO flat membrane water flow test was performed.

[0094] [Table 5]

[0095] The change in flux retention rate (%) versus operation time (hr) is shown in Fig. 5. In Example 5, compared to Comparative Example 5, it was possible to maintain a high flux retention rate.

[0096] In this way, the device and method of the embodiment were able to suppress the progression of clogging of the reverse osmosis membrane due to scale during reverse osmosis membrane treatment. [Explanation of symbols]

[0097] 1 water treatment device, 10 treated water tank, 12 reverse osmosis membrane treatment device, 14, 16 treated water piping, 18 permeated water piping, 20 concentrated water piping, 22 scale inhibitor addition piping.

Claims

1. a reverse osmosis membrane treatment means for passing water to be treated, which contains at least one of calcium and aluminum, through a reverse osmosis membrane to obtain permeated water and concentrated water; A scale inhibitor adding means for adding a scale inhibitor to the water to be treated, 2. A water treatment device according to claim 1, wherein the reverse osmosis membrane is a neutrally charged membrane.

2. The water treatment device according to claim 1, The water treatment device according to claim 1, wherein the water to be treated further contains silica.

3. The water treatment device according to claim 1, The water treatment device is characterized in that the scale inhibitor contains at least one of a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units, and a phosphonic acid compound.

4. The water treatment device according to claim 1, The water treatment device is characterized in that the neutrally charged membrane is a neutrally charged membrane having a zeta potential of the membrane surface of -10 mV or more and +10 mV or less.

5. a reverse osmosis membrane treatment step of passing the water to be treated, which contains at least one of calcium and aluminum, through a reverse osmosis membrane to obtain a permeate and a concentrated water; A scale inhibitor adding step of adding a scale inhibitor to the water to be treated; Including, A water treatment method, wherein the reverse osmosis membrane is a neutrally charged membrane.

6. The water treatment method according to claim 5, The water treatment method, wherein the water to be treated further contains silica.

7. The water treatment method according to claim 5, The water treatment method is characterized in that the scale inhibitor contains at least one of a copolymer containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units, and a phosphonic acid compound.

8. The water treatment method according to claim 5, The water treatment method is characterized in that the neutrally charged membrane is a neutrally charged membrane having a zeta potential of the membrane surface of -10 mV or more and +10 mV or less.

9. The water treatment method according to claim 5, A water treatment method, characterized in that the concentrated water has a Langelier index of more than 0.

10. The water treatment method according to claim 5, A water treatment method characterized in that the silica concentration in the concentrated water is 120 mg / L or more.

11. The water treatment method according to claim 5, A water treatment method characterized in that the aluminum concentration in the concentrated water is 0.25 mg / L or more.

12. The water treatment method according to claim 5, The water treatment method is characterized in that the concentrated water has a Langelier index of more than 0, a silica concentration of 120 mg / L or more, and an aluminum concentration of 0.25 mg / L or more.

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