Water treatment method and water treatment device

Abstract

To provide a water treatment method and a water treatment device that can prevent scale formation in reverse osmosis membrane treatment of target water containing aluminum ions.SOLUTION: A water treatment method includes: an addition step of adding a phosphonic acid compound to target water containing aluminum ions; and a reverse osmosis membrane treatment step of treating the target water having the phosphonic acid compound added thereto through a reverse osmosis membrane to obtain permeated water and concentrated water. The pH of the target water or the concentrated water is less than 5.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, the opportunities for using reverse osmosis membranes, such as in pure water production and water recovery, have been increasing, and the load processed by reverse osmosis membranes has also been increasing. Scaling is one of the most important items in the operation management of reverse osmosis membranes. When scale forms on the surface of the reverse osmosis membrane, it causes an increase in the differential pressure of the membrane, leading to a deterioration in the operation efficiency of the equipment. Therefore, suppressing the generation of these scales is very important for the stable operation of the equipment.

[0003] As a measure against scaling, the addition of a scale inhibitor to the water to be treated is mainly used. Scale inhibitors have structures such as acrylic acid and maleic acid, have a function of capturing cations electrically to suppress the precipitation of scale, and have a dispersing ability due to steric hindrance.

[0004] In addition, as a measure against calcium scale and silica scale, the water to be treated and the concentrated water in reverse osmosis membrane treatment may be acidified to suppress scaling. For example, Patent Document 1 describes a reverse osmosis membrane treatment method in which water to be treated containing at least hardness components and silica is subjected to reverse osmosis membrane treatment and separated into permeated water and concentrated water having a silica concentration equal to or higher than the solubility of silica, and the concentrated water is subjected to reverse osmosis membrane treatment while maintaining the pH at 6 or less.

[0005] Among scales, silica and aluminum often cause problems and are important scale species. Among them, even a small amount of aluminum contained in the water to be treated may cause scaling. However, when an acrylic acid-based scale inhibitor is used under low pH conditions, there is a problem that when the water to be treated contains aluminum, scale is generated and the reverse osmosis membrane is blocked.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a water treatment method and a water treatment apparatus capable of suppressing scale formation in reverse osmosis membrane treatment of water to be treated containing aluminum ions.

Means for Solving the Problems

[0008] The present invention includes an addition step of adding a phosphonic acid compound to water to be treated containing aluminum ions, and a reverse osmosis membrane treatment step of treating the water to be treated to which the phosphonic acid compound has been added with a reverse osmosis membrane to obtain permeated water and concentrated water, and the pH of the water to be treated or the concentrated water is less than 5, which is a water treatment method.

[0009] In the water treatment method, the content of the acrylic acid-based polymer in the water to be treated is preferably 10 mg / L or less.

[0010] In the water treatment method, the phosphonic acid compound is preferably 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0011] In the water treatment method, the content of the aluminum ions in the water to be treated is preferably 0.001 mg / L or more.

[0012] In the water treatment method, the pH of the water to be treated or the concentrated water is preferably 4.5 or less.

[0013] In the water treatment method, the addition concentration of the phosphonic acid compound in the water to be treated is preferably 0.1 mg / L or more as a solid content concentration.

[0014] The present invention provides a water treatment apparatus including: an adding means for adding a phosphonic acid compound to water to be treated containing aluminum ions; a reverse osmosis membrane treatment means for treating the water to be treated to which the phosphonic acid compound has been added with a reverse osmosis membrane to obtain permeated water and concentrated water; and a pH adjusting means for adjusting the pH of the water to be treated or the concentrated water to less than 5.

Effects of the Invention

[0015] According to the present invention, it is possible to provide a water treatment method and a water treatment apparatus capable of suppressing scale generation in the reverse osmosis membrane treatment of water to be treated containing aluminum ions.

Brief Description of the Drawings

[0016]

Figure 1

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Figure 6

Modes for Carrying Out the Invention

[0017] Embodiments 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.

[0018] The outline of an example of the water treatment apparatus according to an embodiment of the present invention is shown in FIG. 1, and its configuration will be described.

[0019] The water treatment apparatus 1 includes a phosphonic acid compound addition pipe 18 as an addition means for adding a phosphonic acid compound to the water to be treated containing aluminum ions, and a reverse osmosis membrane treatment apparatus 10 as a reverse osmosis membrane treatment means for treating the water to be treated to which the phosphonic acid compound has been added with a reverse osmosis membrane to obtain permeated water and concentrated water.

[0020] In the water treatment apparatus 1 of FIG. 1, a water to be treated pipe 12 is connected to the water to be treated inlet of the reverse osmosis membrane treatment apparatus 10. A permeated water pipe 14 is connected to the permeated water outlet of the reverse osmosis membrane treatment apparatus 10, and a concentrated water pipe 16 is connected to the concentrated water outlet. A phosphonic acid compound addition pipe 18 is connected to the water to be treated pipe 12. A pH adjuster addition pipe 20 may be connected upstream or downstream of the connection point of the phosphonic acid compound addition pipe 18 in the water to be treated pipe 12 as a pH adjustment means for adjusting the pH of the water to be treated or the concentrated water to less than 5. A pH measuring device may be installed in the water to be treated pipe 12 or the concentrated water pipe 16 as a pH measuring means for measuring the pH of the water to be treated or the concentrated water. The water treatment apparatus 1 may include a water to be treated tank for storing the water to be treated upstream of the reverse osmosis membrane treatment apparatus 10.

[0021] The water treatment method and the operation of the water treatment apparatus 1 according to the present embodiment will be described.

[0022] The water to be treated containing aluminum ions is fed into the reverse osmosis membrane treatment apparatus 10 through the water pipe to be treated 12. Here, when the pH of the water to be treated or the concentrated water is measured by the pH measuring device and the pH of the water to be treated or the concentrated water is 5 or more, a pH adjuster may be added through the pH adjuster addition pipe 20 to adjust the pH of the water to be treated or the concentrated water to less than 5 (pH adjustment step). Then, a phosphonic acid compound is added through the phosphonic acid compound addition pipe 18 in the water pipe to be treated 12 (addition step). When the water treatment apparatus 1 is provided with a water tank to be treated in the previous stage of the reverse osmosis membrane treatment apparatus 10, the pH adjuster may be added in the water tank to be treated, and the phosphonic acid compound may be added in the water tank to be treated. The water to be treated to which the phosphonic acid compound is added in the reverse osmosis membrane treatment apparatus 10 is treated with a reverse osmosis membrane to obtain permeated water and concentrated water (reverse osmosis membrane treatment step). The permeated water is discharged through the permeated water pipe 14, and the concentrated water is discharged through the concentrated water pipe 16.

[0023] The inventors of the present invention confirmed that when the reverse osmosis membrane treatment apparatus was operated at a low pH under the condition that aluminum ions were present in the water to be treated, the flux decreased on the reverse osmosis membrane when an acrylic acid polymer was added as an acrylic acid-based scale inhibitor. Therefore, as a result of the study by the inventors of the present invention, it was found that scale generation can be suppressed even when the water to be treated contains aluminum ions by adding a phosphonic acid compound under the condition that the pH of the water to be treated or the concentrated water containing aluminum ions is less than 5.

[0024] The water to be treated to which the water treatment method and the water treatment apparatus according to the present embodiment are applied may be water containing aluminum ions, and there is no particular limitation, and examples thereof include industrial water, wastewater, tap water, and the like. The water to be treated may contain hardness components such as calcium, silica, fluorine, etc. in addition to aluminum ions.

[0025] The content of aluminum ions in the water to be treated only needs to contain aluminum ions and is not particularly limited. For example, it is 0.001 mg / L or more, preferably 0.01 mg / L or more. Since the condition is that the water to be treated contains aluminum ions, there is no particular upper limit to the content of aluminum ions in the water to be treated. For example, it is 100 mg / L or less. When the content of aluminum ions in the water to be treated is more than 100 mg / L, the amount of the required phosphonic acid compound becomes extremely large, and economic problems may become significant.

[0026] The phosphonic acid compound only needs to mainly function as a scale inhibitor and is not particularly limited. For example, it includes at least one compound selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyphosphonoacetic acid, nitrilotrimethylenephosphonic acid, ethylenediamine-N,N,N’,N’-tetramethylenephosphonic acid, or alkali metal salts and alkaline earth metal salts of these phosphonic acids. The phosphonic acid compound may be used alone or in combination of two or more. Among these, the phosphonic acid compound is preferably 2-phosphonobutane-1,2,4-tricarboxylic acid in terms of low decomposability by an oxidizing agent.

[0027] The addition concentration of the phosphonic acid compound in the water to be treated is, for example, 0.1 mg / L or more, preferably 1 mg / L or more, as a solid content concentration. When the addition concentration of the phosphonic acid compound in the water to be treated is less than 0.1 mg / L as a solid content concentration, it may be difficult to obtain a scale inhibition effect. There is no particular upper limit to the addition concentration of the phosphonic acid compound in the water to be treated. For example, it is 1000 mg / L. When the addition concentration of the phosphonic acid compound in the water to be treated exceeds 1000 mg / L, the amount of the chemical added becomes extremely large, resulting in significant economic problems and being unrealistic. When the water to be treated contains metal ions other than aluminum ions, a phosphonic acid compound with a concentration equal to or higher than the above addition concentration may be added to the water to be treated.

[0028] Since the scale inhibition effect of the phosphonic acid compound is exerted, the pH of the water to be treated or the concentrated water is less than 5, preferably 4.5 or less. From the viewpoint of the resistance of the reverse osmosis membrane, etc., the pH of the water to be treated or the concentrated water is preferably 3 or more.

[0029] When the pH of the water to be treated or the concentrated water is 5 or more or less than 3, for example, acids such as hydrochloric acid, sulfuric acid, and nitric acid, and alkalis such as an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution may be used as pH adjusters to adjust the pH of the water to be treated or the concentrated water.

[0030] It is better that the water to be treated does not contain an acrylic acid-based polymer. The content of the acrylic acid-based polymer in the water to be treated is, for example, 10 mg / L or less, preferably 1 mg / L or less, and more preferably 0.1 mg / L or less. The lower the content of the acrylic acid-based polymer in the water to be treated, the better, and there is no particular lower limit.

[0031] The acrylic acid-based polymer, which is an acrylic acid-based scale inhibitor, is a polymer containing acrylic acid as a polymerization component or a copolymerization component. Examples of the acrylic acid-based polymer include polyacrylic acid, a copolymer of acrylic acid and 2-hydroxy-3-allyloxypropanesulfonic acid, a copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, a copolymer of acrylic acid and isoprenesulfonic acid, a copolymer of acrylic acid and 2-hydroxyethyl methacrylate, a copolymer of acrylic acid, 2-hydroxyethyl methacrylate, and isopropylenesulfonic acid, and a terpolymer of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and a substituted acrylamide.

[0032] The phosphonic acid compound may be used in combination with other scale inhibitors; fungicides such as thiazole-based fungicides, 2,2-dibromo-3-nitrilopropionamide (DBNPA), 2,2-dibromo-2-nitroethane (DBNE), 2-bromo-2-nitro-1,3-propanediol (Bronopol), chlorine-based oxidants, bromine-based oxidants, a stabilized hypochlorous acid composition containing a chlorine-based oxidant and a sulfamic acid compound, a stabilized hypobromous acid composition containing a bromine-based oxidant and a sulfamic acid compound; corrosion inhibitors such as heavy metals, phosphates, azole compounds; and the like.

[0033] As the reverse osmosis membrane, for example, a polyamide-based reverse osmosis membrane is used. The reverse osmosis membrane includes a neutral charge membrane, an anion charge membrane, and a cation charge membrane, and any of them may be used. The reverse osmosis membrane is not particularly limited, but a neutral charge membrane is preferred in that it is often used when the water to be treated is wastewater in which inorganic scale and organic fouling are likely to occur.

[0034] In the water treatment method and the water treatment apparatus according to the present embodiment, a device for performing at least one treatment among biological, physical, or chemical pretreatment such as pH adjustment, biological treatment, coagulation treatment, coagulation sedimentation treatment, pressurized flotation treatment, filtration treatment, membrane separation treatment, activated carbon treatment, ozone treatment, ultraviolet irradiation treatment, decarbonation treatment, etc. is provided in the front stage of the reverse osmosis membrane treatment apparatus 10 for treating the water to be treated. For the water to be treated in the reverse osmosis membrane treatment apparatus 10 (reverse osmosis membrane treatment step), at least one treatment among biological, physical, or chemical pretreatment such as pH adjustment, biological treatment, coagulation treatment, coagulation sedimentation treatment, pressurized flotation treatment, filtration treatment, membrane separation treatment, activated carbon treatment, ozone treatment, ultraviolet irradiation treatment, decarbonation treatment, etc. may be performed.

[0035] In the water treatment method and water treatment apparatus according to the present embodiment, at least one device selected from a regenerative ion exchange treatment device, an electro-deionization 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 is provided downstream of the reverse osmosis membrane treatment device 10 to perform treatment on the permeate water of the reverse osmosis membrane treatment device 10. At least one treatment selected from regenerative ion exchange treatment, electro-deionization treatment, non-regenerative ion exchange resin treatment, deaeration membrane treatment, UV sterilization treatment, UV oxidation treatment, particulate removal treatment, and second reverse osmosis membrane treatment may be performed on the permeate water of the reverse osmosis membrane treatment device 10 (reverse osmosis membrane treatment step).

[0036] This specification includes the following embodiments. (1) An addition step of adding a phosphonic acid compound to the water to be treated containing aluminum ions, a reverse osmosis membrane treatment step of treating the water to be treated to which the phosphonic acid compound has been added with a reverse osmosis membrane to obtain permeate water and concentrated water, including, a water treatment method in which the pH of the water to be treated or the concentrated water is less than 5.

[0037] (2) The water treatment method according to (1), wherein the content of the acrylic acid-based polymer in the water to be treated is 10 mg / L or less.

[0038] (3) The water treatment method according to (1) or (2), wherein the phosphonic acid compound is 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0039] (4) The water treatment method according to any one of (1) to (3), wherein the content of the aluminum ions in the water to be treated is 0.001 mg / L or more.

[0040] (5) The water treatment method according to any one of (1) to (4), A water treatment method in which the pH of the water to be treated or the concentrated water is 4.5 or less.

[0041] (6) The water treatment method according to any one of (1) to (5), A water treatment method in which the added concentration of the phosphonic acid compound in the water to be treated is 0.1 mg / L or more as a solid content concentration.

[0042] (7) Adding means for adding a phosphonic acid compound to the water to be treated containing aluminum ions, Reverse osmosis membrane treatment means for treating the water to be treated to which the phosphonic acid compound has been added with a reverse osmosis membrane to obtain permeated water and concentrated water, pH adjustment means for adjusting the pH of the water to be treated or the concentrated water to less than 5, A water treatment apparatus comprising:

[0043] (8) The water treatment apparatus according to (7), A water treatment apparatus in which the content of the acrylic acid-based polymer in the water to be treated is 10 mg / L or less.

[0044] (9) The water treatment apparatus according to (7) or (8), A water treatment apparatus in which the phosphonic acid compound is 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0045] (10) The water treatment apparatus according to any one of (7) to (9), A water treatment apparatus in which the content of the aluminum ions in the water to be treated is 0.001 mg / L or more.

[0046] (11) The water treatment apparatus according to any one of (7) to (10), A water treatment apparatus in which the pH of the water to be treated or the concentrated water is 4.5 or less.

[0047] (12) The water treatment apparatus according to any one of (7) to (11), A water treatment apparatus in which the addition concentration of the phosphonic acid compound in the water to be treated is 0.1 mg / L or more as a solid content concentration.

Example

[0048] Hereinafter, examples and comparative examples will be given to explain the present invention more specifically and in detail. However, the present invention is not limited to the following examples.

[0049] <Reference Example 1, Comparative Reference Example 1> [Beaker Test] The beaker test was conducted under the following test conditions.

[0050] (Test Conditions) Test water: Pure water Aluminum ion (Al) concentration: 1 mg / L (Reference Example 1), no Al addition (Comparative Reference Example 1) Copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AA / AMPS copolymer, weight average molecular weight 4500): 12.9 mg / L as solid Test water pH: 3, 3.5, 4, 4.5, 5, 5.5

[0051] (Evaluation Method) Aluminum chloride hexahydrate was added to the test water so that the aluminum ion concentration was as described above, and further, an AA / AMPS copolymer was added as an acrylic acid-based polymer so that the concentration was as described above. The pH of the test water was adjusted to the above pH with hydrochloric acid. After 72 hours, the mixed solution was filtered through a 0.45 μm filter, and then Lovibond KS255 and KS256, which are reagents for measuring polyacrylic acid, were added. The turbidity was measured as the absorbance of polyacrylic acid (PAA absorbance) at an absorbance of 660 nm using a spectrophotometer (Hach, DR-3900 type). The results are shown in Figure 2.

[0052] As can be seen from Figure 2, compared with Comparative Reference Example 1 in which the test water does not contain aluminum, in Reference Example 1, the PAA absorbance is low at a pH of less than 5, suggesting that the AA / AMPS copolymer precipitates as the pH decreases.

[0053] <Reference Examples 2 and 3> [Beaker Test] The beaker test was conducted under the following test conditions.

[0054] (Test Conditions) Test water: Pure water Concentration of aluminum ion (Al): 1 mg / L Copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AA / AMPS copolymer, weight average molecular weight 4500) (Reference Example 2) or polyacrylic acid (PAA, weight average molecular weight 4500) (Reference Example 3): 12.9 mg / L as solid pH of test water: 4

[0055] (Evaluation Method) Aluminum chloride hexahydrate was added to the test water so that the concentration of aluminum ion became the above value, and further, AA / AMPS copolymer (Reference Example 2) or polyacrylic acid (Reference Example 3) was added as an acrylic acid-based polymer so that the concentration became the above value. The pH of the test water was adjusted to pH 4 with hydrochloric acid, respectively. After 72 hours, the mixed solution was filtered through a 0.45 μm filter, and then Lovibond KS255 and KS256, which are reagents for measuring polyacrylic acid, were added. Then, the turbidity was measured as the absorbance of polyacrylic acid (PAA absorbance) at 660 nm using an absorptiometer (Hach, DR-3900 type), and the ratio of the measured value to the theoretical value of PAA absorbance was defined as the PAA residual rate (%). The PAA theoretical value was defined as the PAA absorbance when all of the polyacrylic acid or AA / AMPS copolymer was dissolved. The results are shown in Figure 3.

[0056] As can be seen from Figure 3, for polyacrylic acid as well, the PAA absorbance was low at pH 4, suggesting that the influence of aluminum and pH on polyacrylic acid is greater than that on the AA / AMPS copolymer.

[0057] <Example 1, Comparative Example 1> [Comparison between Acrylic Acid-Based Polymer and Phosphonic Acid Compound] A water permeation test was conducted on the reverse osmosis membrane under the following test conditions. The results are shown in Figure 4.

[0058] (Test conditions) Test water: Pure water Concentration of aluminum ions (Al): 1 mg / L Copolymer of AA / AMPS (weight average molecular weight 4500), or 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC): 12.9 mg / L as solid pH of test water: 3, 3.5 Reverse osmosis membrane: LFC3-LD-4040 manufactured by Nitto Denko (polyamide-based neutral charged membrane) Water temperature: 25 °C

[0059] As can be seen from Figure 4, even under the conditions where membrane fouling progresses in Comparative Example 1 using the AA / AMPS copolymer as the acrylic acid-based polymer, it was confirmed that in Example 1, membrane fouling was suppressed by using PBTC as the phosphonic acid compound.

[0060] (Example 2, Comparative Example 2) [Element test under composite scale] A water permeation test was conducted on the reverse osmosis membrane under the following test conditions. The results of Example 2 are shown in Figure 5, and the results of Comparative Example 2 are shown in Figure 6.

[0061] (Test conditions) Test water: Water obtained by sterilizing Sagamihara well water with hypochlorous acid, followed by sand filtration and then activated carbon treatment Concentration of calcium ions (Ca): 300 mg / L Concentration of magnesium ions (Mg): 60 mg / L Concentration of aluminum ions (Al): 2 mg / L Copolymer of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and t-butyl-substituted acrylamide (AA / AMPS / t-BAM terpolymer, weight average molecular weight 5000), PBTC: 7.65 mg / L as solid pH of test water: 3.5 Reverse osmosis membrane: LFC3-LD-4040 manufactured by Nitto Denko Corporation (polyamide-based neutrally charged membrane)

[0062] As can be seen from FIG. 6, in Comparative Example 2 using an AA / AMPS / t-BAM terpolymer as the acrylic acid-based polymer, the change rate of the permeation coefficient decreased to 90% after 200 hours. However, as can be seen from FIG. 5, in Example 2 using PBTC as the phosphonic acid compound, the change rate of the permeation coefficient showed a gradual decrease, and the change rate of the permeation coefficient still maintained almost 100% even after 200 hours.

[0063] Thus, in the examples, scale generation could be suppressed in the reverse osmosis membrane treatment of the water to be treated containing aluminum ions.

Explanation of symbols

[0064] 1 Water treatment apparatus, 10 Reverse osmosis membrane treatment apparatus, 12 Water to be treated pipe, 14 Permeate water pipe, 16 Concentrated water pipe, 18 Phosphonic acid compound addition pipe, 20 pH adjuster addition pipe.

Claims

1. An addition step of adding a phosphonic acid compound to the water to be treated containing aluminum ions, A reverse osmosis membrane treatment step of treating the water to be treated to which the phosphonic acid compound has been added with a reverse osmosis membrane to obtain permeated water and concentrated water, comprising, A water treatment method characterized in that the pH of the water to be treated or the concentrated water is less than 5.

2. The water treatment method according to Claim 1, characterized in that the content of the acrylic acid-based polymer in the water to be treated is 10 mg / L or less.

3. The water treatment method according to Claim 1, characterized in that the phosphonic acid compound is 2-phosphonobutane-1,2,4-tricarboxylic acid.

4. The water treatment method according to Claim 1, characterized in that the content of the aluminum ions in the water to be treated is 0.001 mg / L or more.

5. The water treatment method according to Claim 1, characterized in that the pH of the water to be treated or the concentrated water is 4.5 or less.

6. The water treatment method according to Claim 1, characterized in that the addition concentration of the phosphonic acid compound in the water to be treated is 0.1 mg / L or more as a solid content concentration.

7. An addition means for adding a phosphonic acid compound to the water to be treated containing aluminum ions, A reverse osmosis membrane treatment means for treating the water to be treated to which the phosphonic acid compound has been added with a reverse osmosis membrane to obtain permeated water and concentrated water, A pH adjustment means for adjusting the pH of the water to be treated or the concentrated water to less than 5, A water treatment apparatus characterized by comprising.

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