Water treatment device and operation method for water treatment device

Abstract

A water treatment device 1 includes a to-be-treated-water tank 2 that holds water W that is to be treated, a high-pressure pump 3 that pumps this pretreated water W, a first reverse osmosis membrane 4, a concentrate water tank 5 that holds concentrate water W1 from the first reverse osmosis membrane 4, a high-pressure pump 6, and a second reverse osmosis membrane 7 for treating the concentrate water W1 from the first reverse osmosis membrane 4. Permeate water W2 from the second reverse osmosis membrane 7 is returned to the to-be-treated-water tank 2, and concentrate water from the second reverse osmosis membrane 7 is discharged. The first reverse osmosis membrane 4 and the second reverse osmosis membrane 7 have a permeation velocity of 0.5–1.0 m / day at an effective membrane surface pressure of 2 MPa (water temperature 25°C, pure water) or a permeation velocity of 0.5–1.0 m / day at an effective membrane surface pressure of 1.5 MPa (water temperature 25°C, pure water). This water treatment device makes it possible to efficiently concentrate and discharge difficult-to-remove substances without worsening the quality of permeate water from a first reverse osmosis membrane.

Description

Water treatment equipment and method of operating the water treatment equipment

[0001] The present invention relates to a water treatment apparatus having a reverse osmosis membrane for obtaining high-purity treated water and a method for operating the same, and more particularly to a water treatment apparatus and method for operating the same that can reduce difficult-to-remove substances such as low molecular weight organic substances (urea) and boron using a high-pressure reverse osmosis membrane.

[0002] Traditionally, ultrapure water used in the electronics industry, such as semiconductors, is produced by treating raw water in an ultrapure water production system consisting of a pretreatment system, a primary pure water production system (pure water production system), and a subsystem (secondary pure water production system) that processes the primary pure water. In addition, pure water, which is obtained by treating pretreatment water or industrial water with a pure water production system, is used in various industries.

[0003] For example, as shown in Figure 4, the primary pure water apparatus 31, as a water treatment device, includes a water treatment tank 32 for storing pre-treated water (water to be treated) W, a high-pressure pump 33 for supplying the pre-treated water W, a first reverse osmosis membrane 34, a concentrated water tank 35 for storing the concentrated water W1 from the first reverse osmosis membrane 34, a high-pressure pump 36, and a second reverse osmosis membrane 37 for treating the concentrated water W1. The permeate W2 from the second reverse osmosis membrane 37 is returned to the water to be treated tank 32, and the concentrated water from the second reverse osmosis membrane 37 is discharged. On the other hand, the permeate W3 side of the first reverse osmosis membrane 34 includes a pH adjustment means 38, a third reverse osmosis membrane 39, a degassing membrane device 40 for removing dissolved gases, an ultraviolet oxidation device 41, and an electrodeionization device 42. In such a primary pure water apparatus 31, most of the electrolytes, fine particles, live bacteria, etc. in the pre-treated water W are removed, and organic matter is decomposed to obtain pure water W4. In a water treatment apparatus having a first reverse osmosis membrane 34 and a second reverse osmosis membrane 35 for treating the concentrated water W1, the water recovery rate of the first reverse osmosis membrane 34 is 70-85%, and 15-30% is discharged as concentrated water W1. This concentrated water W1 is then used as the water to be treated by the second reverse osmosis membrane 37, thereby obtaining concentrated water and permeate W2 from the second reverse osmosis membrane 37. The water recovery rate of the water treatment apparatus is generally improved by returning this permeate W2 to the water to be treated by the first reverse osmosis membrane (for example, Patent Document 1).

[0004] Japanese Patent Application Publication No. 9-206749

[0005] In a water treatment apparatus that processes concentrated water W1 from a first reverse osmosis membrane 34 with a second reverse osmosis membrane 37, as described above, if the water W being treated by the first reverse osmosis membrane 34 contains difficult-to-remove substances such as urea, a problem arises when the removal rate of these difficult-to-remove substances by the first reverse osmosis membrane 34 is low. In this case, the difficult-to-remove substances leak into the permeate water W3, increasing the load on the downstream water treatment equipment and affecting the quality of the resulting pure water W4. On the other hand, if the removal rate (removal capacity) of the first reverse osmosis membrane 34 is high, the difficult-to-remove substances are concentrated in the concentrated water W1, and high-purity pure water W4 can be obtained in the permeate water W3. However, if the removal rate of these difficult-to-remove substances by the second reverse osmosis membrane 37 that treats this concentrated water W1 is low, the difficult-to-remove substances leak into the permeate water W2 of the second reverse osmosis membrane 35, and this permeate water W2 is returned to the water W being treated by the first reverse osmosis membrane 34. If this effect becomes significant, there is a risk that the concentration of difficult-to-remove substances will occur within the pure water production device 31, leading to a deterioration in the water quality of the permeate W3 from the first reverse osmosis membrane 34.

[0006] The present invention has been made in view of the above problems, and aims to provide a water treatment apparatus and a method for operating the same that can efficiently concentrate and discharge difficult-to-remove substances from the system without deteriorating the water quality of the permeate from the first reverse osmosis membrane.

[0007] In view of the above objectives, the present invention first provides a water treatment apparatus comprising a first reverse osmosis membrane and a second reverse osmosis membrane for treating the concentrated water from the first reverse osmosis membrane, wherein the permeate from the second reverse osmosis membrane is returned as water to be treated by the first reverse osmosis membrane, and the first and second reverse osmosis membranes are reverse osmosis membranes having a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less at an effective membrane surface pressure of 2 MPa (water temperature 25°C, pure water), or a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less at an effective membrane surface pressure of 1.5 MPa (water temperature 25°C, pure water) (Invention 1).

[0008] According to the above invention (Invention 1), even when the water quality of the water to be treated fluctuates or when the water to be treated contains substances that are difficult to remove, high-purity treated water can be obtained without leaking the substances that are difficult to remove to the permeate side of the first reverse osmosis membrane. Furthermore, even when the permeate from the second reverse osmosis membrane is returned as the water to be treated by the first reverse osmosis membrane, it is possible to make the concentration of substances that are difficult to remove in the permeate from the second reverse osmosis membrane lower than the concentration of substances that are difficult to remove in the water to be treated, thereby preventing the concentration of substances that are difficult to remove within the system.

[0009] Secondly, the present invention provides a water treatment apparatus comprising a first reverse osmosis membrane and a second reverse osmosis membrane for treating the concentrated water from the first reverse osmosis membrane, wherein the permeate from the second reverse osmosis membrane is returned as treated water from the first reverse osmosis membrane, and the first and second reverse osmosis membranes are reverse osmosis membranes having a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less at an effective membrane surface pressure of 2 MPa (water temperature 25°C, pure water), or a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less at an effective membrane surface pressure of 1.5 MPa (water temperature 25°C, pure water), wherein the first reverse osmosis membrane is operated with a recovery rate of 70-85%, and the second reverse osmosis membrane is operated with a recovery rate of 50-75% (Invention 2).

[0010] According to the above invention (Invention 2), even when the water quality of the water to be treated fluctuates or when the water to be treated contains difficult-to-remove substances, high-purity treated water can be obtained without leaking difficult-to-remove substances to the permeate side of the first reverse osmosis membrane. Furthermore, by operating the first reverse osmosis membrane with a recovery rate of 70-85% and the second reverse osmosis membrane with a recovery rate of 50-75%, even when the permeate from the second reverse osmosis membrane is returned as treated water to the first reverse osmosis membrane, the concentration of difficult-to-remove substances in the permeate from the second reverse osmosis membrane can be made lower than the concentration of difficult-to-remove substances in the water to be treated, thereby preventing the concentration of difficult-to-remove substances within the system.

[0011] The water treatment apparatus of the present invention has a first reverse osmosis membrane and a second reverse osmosis membrane for treating the concentrated water from the first reverse osmosis membrane, and has a water treatment facility that returns the permeate from the second reverse osmosis membrane as the water to be treated by the first reverse osmosis membrane. Since the first and second reverse osmosis membranes are reverse osmosis membranes with an effective membrane pressure of 2 MPa (water temperature 25°C, pure water) and a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less, or an effective membrane pressure of 1.5 MPa (water temperature 25°C, pure water) and a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less, high-purity treated water can be obtained without leaking difficult-to-remove substances to the permeate side of the first reverse osmosis membrane, even when the water quality of the water to be treated fluctuates or when the water to be treated contains difficult-to-remove substances. Furthermore, even when the permeate from the second reverse osmosis membrane is returned as the treated water from the first reverse osmosis membrane, it is possible to make the concentration of difficult-to-remove substances in the permeate from the second reverse osmosis membrane lower than the concentration of difficult-to-remove substances in the treated water, thereby preventing the concentration of difficult-to-remove substances within the system.

[0012] This is a flow diagram showing a water treatment apparatus according to one embodiment of the present invention. This is a flow diagram showing a water treatment apparatus for Comparative Example 1. This is a flow diagram showing a water treatment apparatus for Comparative Example 2. This is a flow diagram showing a pure water production apparatus to which the water treatment apparatus of the present invention can be applied.

[0013] The water treatment apparatus of the present invention will be described below with reference to the attached drawings.

[0014] [Water Treatment Device] The water treatment device of this embodiment, for example, constitutes a pure water production device as shown in Figure 4, and has a first reverse osmosis membrane and a second reverse osmosis membrane for treating the concentrated water from the first reverse osmosis membrane, and the permeate from the second reverse osmosis membrane is returned as the water to be treated by the first reverse osmosis membrane. Furthermore, as the pure water production device, a primary pure water production device in an ultrapure water production device is preferred.

[0015] In this embodiment, the water treatment apparatus has the configuration shown in Figure 1. Specifically, the water treatment apparatus 1 includes a water treatment tank 2 for storing pre-treated water (water to be treated) W, a high-pressure pump 3 for supplying the pre-treated water W, a first reverse osmosis membrane 4, a concentrated water tank 5 for storing the concentrated water W1 from the first reverse osmosis membrane 4, a high-pressure pump 6, and a second reverse osmosis membrane 7 for treating the concentrated water W1 from the first reverse osmosis membrane 4. The permeate W2 from the second reverse osmosis membrane 7 is returned to the water treatment tank 2, and the concentrated water from the second reverse osmosis membrane 7 is discharged.

[0016] (First Reverse Osmosis Membrane) In this embodiment, the following performance is used as the first reverse osmosis membrane 4. Reverse osmosis membrane (1) - Permeation flux of 0.5 m under the conditions of effective membrane pressure of 2.0 MPa (water temperature 25°C, pure water (RO permeate)) ３ / (m ２ - 1.0m (days) or more ３ / (m ２ - Below 25°C - Salt removal rate: 99% or more (effective membrane pressure 2.0 MPa (water temperature 25°C, feedwater 500 mg / L at NaCl) - IPA (isopropyl alcohol) removal rate: 90% or more (effective membrane pressure 2.0 MPa (water temperature 25°C, feedwater 500 mg / L at IPA) or reverse osmosis membrane (2) - Permeation flux 0.5 m under conditions of effective membrane pressure 1.5 MPa (water temperature 25°C, pure water (RO permeate)) ３ / (m ２ - 1.0m (days) or more ３ / (m ２ • (Days) or less • Salt removal rate: 99% or more (effective pressure on membrane surface 2.0 MPa (water temperature 25°C, water supply 500 mg / L at NaCl) • IPA (isopropyl alcohol) removal rate: 90% or more (effective pressure on membrane surface 2.0 MPa (water temperature 25°C, water supply 500 mg / L at IPA))

[0017] (Second reverse osmosis membrane) The second reverse osmosis membrane 7 is the same as the first reverse osmosis membrane 4. Here, both the first reverse osmosis membrane 4 and the second reverse osmosis membrane 7 may be reverse osmosis membrane (1) or reverse osmosis membrane (2), or one may be reverse osmosis membrane (1) and the other reverse osmosis membrane (2), but it is preferable to use reverse osmosis membrane (2) for both in terms of power consumption.

[0018] [Operation Method of Water Treatment Equipment] The operation method of the pure water production equipment described above will be explained based on Figure 1.

[0019] First, the high-pressure pump 3 is driven to supply the water to be treated W from the water to be treated tank 2 to the first reverse osmosis membrane 4. This first reverse osmosis membrane 4 removes salts from the water to be treated W, as well as ionic components, TOC, etc. At this time, the first reverse osmosis membrane 4 is operated at a recovery rate of 70-85%. Since the first reverse osmosis membrane 4 is a membrane with high removal performance, the recovery rate is set so that difficult-to-remove substances such as urea are concentrated in the concentrated water W1 to 2 to 5 times, especially 2.5 to 4.5 times, compared to the water to be treated W. On the other hand, the treated water (permeate) W3 has a high removal rate (removal capacity) of difficult-to-remove substances, so high-purity treated water W3 can be obtained.

[0020] Next, the concentrated water W1 from the first reverse osmosis membrane 4 is stored in the concentrated water tank 5, and the high-pressure pump 6 is driven to supply the concentrated water W1 to the second reverse osmosis membrane 7. This second reverse osmosis membrane 7 is operated at a recovery rate of 50-75%. Although difficult-to-remove substances are highly concentrated in this concentrated water W1, in this embodiment, the second reverse osmosis membrane 7 is also a membrane with high removal performance, so the recovery rate is set such that the concentration of difficult-to-remove substances such as urea in the permeate W2 from the second reverse osmosis membrane 7 is lower than the concentration in the water to be treated W. Then, this permeate W2 is returned to the water to be treated tank 2, and the concentrated water is discharged outside the system.

[0021] As a result, even if the permeate W2 from the second reverse osmosis membrane 7 is returned as the treated water W from the first reverse osmosis membrane 4, difficult-to-remove substances are not concentrated within the system, and continuous operation does not lead to deterioration of the water quality of the permeate W3 from the first reverse osmosis membrane 4.

[0022] As described above, the water treatment apparatus of the present invention has been described with reference to the accompanying drawings. The present invention only needs to use a membrane having a membrane surface effective pressure greater than a predetermined value as the first reverse osmosis membrane 4 and the second reverse osmosis membrane 7 for recovery that treats the concentrated water W1 thereof, and various modifications can be implemented. For example, in FIG. 1, an activated carbon tower may be provided in front of the second reverse osmosis membrane 7. Further, chemical injection equipment such as a slime control agent, a scale dispersant, and a pH adjuster may be provided in the water to be treated W of the first reverse osmosis membrane 4. Similarly, chemical injection equipment such as a slime control agent, a scale dispersant, and a pH adjuster may be provided in the water to be treated (concentrated water W2 of the first reverse osmosis membrane) of the second reverse osmosis membrane 7.

[0023] Hereinafter, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

[0024] [Example 1] In the water treatment apparatus 1 shown in FIG. 1, as the first reverse osmosis membrane 4 and the second reverse osmosis membrane 7, a reverse osmosis membrane having a membrane surface effective pressure of 1.5 MPa was used, and the water to be treated (raw water) W obtained by adding 100 μg / L of urea to pure water was supplied to the first reverse osmosis membrane 4 at 100 m ３ / h, and the first reverse osmosis membrane 4 was operated at a recovery rate of 75% and the second reverse osmosis membrane 7 was operated at a recovery rate of 66%. At this time, the urea removal rate of the first reverse osmosis membrane 4 was about 80%, and the urea removal rate of the second reverse osmosis membrane 7 was also about 80%.

[0025] As a result, with respect to the urea concentration of 100 μg / L in the water to be treated W, the urea concentration in the permeated water W3 of the first reverse osmosis membrane 4 was 32 μg / L, and high-quality treated water was obtained. On the other hand, the urea concentration in the concentrated water W1 of the first reverse osmosis membrane 4 was 303 μg / L. The concentrated water W1 of the first reverse osmosis membrane 4 was treated with the second reverse osmosis membrane 7 to obtain permeated water W2. The urea concentration in the permeated water W2 of the second reverse osmosis membrane 7 was 89 μg / L, which was lower than the urea concentration of 100 μg / L in the water to be treated (raw water) W. In the concentrated water of the second reverse osmosis membrane 7, the urea concentration was 719 μg / L and was discharged out of the system. From these facts, it was confirmed that even if the permeated water W2 of the second reverse osmosis membrane 7 was returned to the water to be treated W of the first reverse osmosis membrane 4 and stored in the water treatment tank 2, no internal concentration would occur, and it was possible to prevent the deterioration of the water quality of the permeated water W3 of the first reverse osmosis membrane 4.

[0026] [Comparative Example 1] As shown in Figure 2, in the water treatment apparatus 1 shown in Figure 1, the first reverse osmosis membrane 4A and the second reverse osmosis membrane 7A are: - Under the conditions of an effective membrane pressure of 0.75 MPa (water temperature 25°C, pure water (RO permeate)), the permeation flux is 0.5 m ３ / (m ２ - 1.0m (days) or more ３ / (m ２ The water treatment apparatus 1 was constructed in the same manner as above, except that the following conditions were used: • Salt removal rate: 98% or more (effective membrane pressure 0.75 MPa (water temperature 25°C, feedwater 500 mg / L at NaCl) • IPA removal rate: 80% or more (effective membrane pressure 0.75 MPa (water temperature 25°C, feedwater 500 mg / L at IPA)

[0027] In this water treatment apparatus 1, the water to be treated (raw water) W, which is pure water to which 100 μg / L of urea has been added, is 100 ml ３ The first reverse osmosis membrane 4A was supplied at a rate of / h, and the first reverse osmosis membrane 4A was operated with a recovery rate of 75%, while the second reverse osmosis membrane 7A was operated with a recovery rate of 66%. At this time, the urea removal rate of the first reverse osmosis membrane 4A was approximately 30%, and the urea removal rate of the second reverse osmosis membrane 7A was also approximately 30%.

[0028] As a result, while the urea concentration of the treated water W was 100 μg / L, the urea concentration of the permeate W3 from the first reverse osmosis membrane 4A was 83 μg / L, and a high level of treated water quality could not be obtained. On the other hand, the urea concentration of the concentrated water W1 from the first reverse osmosis membrane 4A was 152 μg / L, and this concentrated water W1 from the first reverse osmosis membrane 4A was treated with the second reverse osmosis membrane 7A to obtain permeate W2. The urea concentration of the permeate W2 from the second reverse osmosis membrane 7A was 122 μg / L, which was higher than the urea concentration of the treated water (raw water) W, which was 100 μg / L. The concentrated water from the second reverse osmosis membrane 7 had a urea concentration of 209 μg / L and was discharged outside the system. From these findings, it was confirmed that returning the permeate W2 from the second reverse osmosis membrane 7A to the treated water tank 2 as the treated water W from the first reverse osmosis membrane 4A would cause urea concentration within the system, which could lead to a deterioration in the water quality of the permeate W3 from the first reverse osmosis membrane 4A.

[0029] [Comparative Example 2] As shown in Figure 3, in the water treatment apparatus 1 shown in Figure 1, the second reverse osmosis membrane 7A is: - Under the conditions of an effective membrane pressure of 0.75 MPa (water temperature 25°C, pure water (RO permeate)), the permeation flux is 0.5 m ３ / (m ２ - 1.0m (days) or more ３ / (m ２ The water treatment apparatus 1 was constructed in the same manner as above, except that the following conditions were used: • Salt removal rate: 98% or more (effective membrane pressure 0.75 MPa (water temperature 25°C, feedwater 500 mg / L at NaCl) • IPA removal rate: 80% or more (effective membrane pressure 0.75 MPa (water temperature 25°C, feedwater 500 mg / L at IPA)

[0030] In this water treatment apparatus 1, the water to be treated (raw water) W, which is pure water to which 100 μg / L of urea has been added, is 100 ml ３ The first reverse osmosis membrane 4 was supplied at a rate of / h, and the first reverse osmosis membrane 4 was operated with a recovery rate of 75%, while the second reverse osmosis membrane 7A was operated with a recovery rate of 66%. At this time, the urea removal rate of the first reverse osmosis membrane 4 was approximately 80%, and the urea removal rate of the second reverse osmosis membrane 7A was approximately 30%.

[0031] As a result, while the urea concentration of the treated water W was 100 μg / L, the urea concentration of the permeate W3 from the first reverse osmosis membrane 4 was 32 μg / L, achieving a high level of treated water quality. On the other hand, the urea concentration of the concentrated water W1 from the first reverse osmosis membrane 4A was 303 μg / L, and this concentrated water W1 from the first reverse osmosis membrane 4 was treated with the second reverse osmosis membrane 7A to obtain permeate W2. The urea concentration of the permeate W2 from the second reverse osmosis membrane 7A was 244 μg / L, which was higher than the urea concentration of the treated water (raw water) W, which was 100 μg / L. The concentrated water from the second reverse osmosis membrane 7 had a urea concentration of 419 μg / L and was discharged outside the system. From these findings, it was confirmed that returning the permeate W2 from the second reverse osmosis membrane 7A to the treated water tank 2 as the treated water W from the first reverse osmosis membrane 4 could lead to urea concentration within the system, potentially causing a deterioration in the water quality of the permeate W3 from the first reverse osmosis membrane 4.

[0032] 1. Water treatment device 2. Water to be treated tank 3. High-pressure pump 4. First reverse osmosis membrane 5. Concentrated water tank 6. High-pressure pump 7. Second reverse osmosis membrane W. Water to be treated (pre-treated water) W1. Concentrated water from the first reverse osmosis membrane W2. Permeate from the second reverse osmosis membrane W3. Treated water (permeate) from the first reverse osmosis membrane

Claims

1. A water treatment apparatus comprising a first reverse osmosis membrane and a second reverse osmosis membrane for treating the concentrated water from the first reverse osmosis membrane, wherein the permeate from the second reverse osmosis membrane is returned as treated water from the first reverse osmosis membrane, the first and second reverse osmosis membranes being reverse osmosis membranes having a permeation velocity of 0.5 m / day or more and 1.0 m / day or less at an effective membrane pressure of 2 MPa (water temperature 25°C, pure water), or a permeation velocity of 0.5 m / day or more and 1.0 m / day or less at an effective membrane pressure of 1.5 MPa (water temperature 25°C, pure water).

2. A water treatment apparatus comprising a first reverse osmosis membrane and a second reverse osmosis membrane for treating the concentrated water from the first reverse osmosis membrane, wherein the permeate from the second reverse osmosis membrane is returned as treated water from the first reverse osmosis membrane, and the first and second reverse osmosis membranes are reverse osmosis membranes having a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less at an effective membrane pressure of 2 MPa (water temperature 25°C, pure water), or a permeate flow rate of 0.5 m / day or more and 1.0 m / day or less at an effective membrane pressure of 1.5 MPa (water temperature 25°C, pure water), wherein the first reverse osmosis membrane is operated with a recovery rate of 70-85%, and the second reverse osmosis membrane is operated with a recovery rate of 50-75%.

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