Reverse osmosis membrane system and control method thereof

Abstract

To provide a reverse osmosis membrane system and its control method that can adjust and control the water supply pH of an RO device even at the time when a pH meter is being calibrated.SOLUTION: A reverse osmosis membrane system in which raw water, after it is subjected to decarbonation treatment by a decarbonation device 4, is passed sequentially through first and second RO devices 9 and 17 to be converted to treated water. Two pH meters 11 and 12 are provided to detect the pH of the feed water to the first RO unit, and a pH adjusting agent is added based on the detection of the pH meter 11 or 12. While the addition of the pH adjusting agent is controlled based on a detection value of one of the pH meters 11 and 12, the other pH meter is calibrated. At the time when the detection is switched from one pH meter to the other pH meter, a difference between a detection value of one meter and a detection value of the other is subtracted from one control condition (set value) to be taken as the other control condition (set value).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a reverse osmosis membrane system, and more particularly to a reverse osmosis membrane system having a water quality measuring means for measuring water supplied to an RO device (reverse osmosis membrane device), and a control method thereof. [Background technology]

[0002] As a method for producing pure water from city water, well water, recycled water, and other water, there is a method in which the water is pretreated (removed turbidity and chlorine), then an acid is added to the water to decarbonate it in a decarbonation tower, a vacuum degassing device, a membrane degassing device, or the like, and the decarbonated water is treated by passing it successively through RO devices arranged in series in multiple stages (Patent Document 1).

[0003] In Patent Document 1, the pH of the feed water to the RO device is adjusted to a pH condition that optimizes the resistivity of the produced water, thereby stably producing high-purity pure water. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-30957 Summary of the Invention [Problem to be solved by the invention]

[0005] In the method of Patent Document 1, it is necessary to periodically calibrate a pH meter for measuring the pH of the feed water of the RO device. Conventionally, the pH of the feed water of the RO treatment device is not adjusted or controlled while the pH meter is being calibrated. Therefore, the quality of the product water of the RO treatment device may deteriorate while the pH meter is being calibrated.

[0006] An object of the present invention is to provide a reverse osmosis membrane system and a control method thereof that are capable of adjusting and controlling the pH of water fed to an RO system even while a pH meter is being calibrated. [Means for solving the problem]

[0007] The present invention is as follows. [1] An RO device that separates RO feed water into permeate and concentrate; A water quality measuring means for RO feed water and RO permeate; A water quality adjusting means for adjusting the water quality of the RO feed water based on the measurement value of the water quality measuring means. In a reverse osmosis system having A plurality of the water quality measuring means are provided, A reverse osmosis membrane system, wherein the water quality adjustment means switches the water quality measurement means employed for water quality adjustment at predetermined time intervals. [2] The reverse osmosis membrane system according to [1], wherein the water quality measuring means is a pH meter and a resistivity meter, and the water quality adjusting means is a pH adjuster adding means.

[0008] [3] A method for controlling a reverse osmosis membrane system according to [1] or [2], characterized in that while the water quality adjustment means is adjusting the water quality based on the measurement value of one water quality measurement means, the other water quality measurement means is calibrated. [4] A control method for a reverse osmosis membrane system according to [3], characterized in that when switching the water quality measurement means, the difference between the detection value of the current measurement means and the detection value of the other measurement means is subtracted from the control condition (set value) of the current measurement means and used as the control condition (set value) of the other measurement means.

[0009] [5] A control method for a reverse osmosis membrane system according to [1] or [2], characterized in that, when switching water quality measurement means, the difference between the detection value of the current measurement means and the detection value of another measurement means is subtracted from the control condition (set value) of the current measurement means, and used as the control condition (set value) of the other measurement means. Effect of the Invention

[0010] According to the present invention, the water quality of the feed water to the RO device can be measured by a plurality of measuring means, and while one measuring means is performing a measurement, the other measuring means is calibrated. When switching to another measuring means, the difference between the detection value of the current measuring means and the detection value of the other measuring means is reflected in the control condition (set value) of the other measuring means. In other words, the control condition (set value) of the other measuring means is set to a value obtained by subtracting the difference in the detection values ​​from the control condition (set value) of the current measuring means. As a result, it is possible to suppress pH fluctuations in the RO feed water. This also makes it possible to stably maintain good water quality of the treated water from the reverse osmosis membrane system. [Brief description of the drawings]

[0011] [Figure 1] 1 is a configuration diagram showing a reverse osmosis system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment will be described with reference to Fig. 1. Raw water is introduced into a raw water tank 1 and sent to a decarbonation device 4 via a feed water pump 2 and a pipe 3. A pH meter 5 for measuring the pH of the water flowing through the pipe 3 is provided in the pipe 3, and an acid such as HCl or H2SO4 is added from a pH adjuster adding means 6 so that the water supplied to the decarbonation device 4 has an acidic pH of 4.0 to 6.0.

[0013] The decarbonation device 4 may be, but is not limited to, a decarbonation tower, a membrane type decarbonation device, or the like.

[0014] The water decarbonated in the decarbonation device 4 is supplied to a first RO device 9 via a pipe 7 and a pump 8.

[0015] A first pH meter 11 and a second pH meter 12 are provided in the pipe 7 to measure the pH of the water flowing through the pipe 7. An aqueous solution of an alkali such as NaOH or KOH is added from a pH adjuster adding means 13 so that the pH measured by the first pH meter 11 or the second pH meter 12 becomes a pH condition (e.g., 7.0 to 8.5) that optimizes the resistivity of the treated water in the second RO device 17.

[0016] The detection signals of the first pH meter 11 and the second pH meter 12 are also transmitted to the control device 14 .

[0017] The permeated water from the first RO device 9 is sent to the second RO device 17 via a pipe 15 and a pump 16. The permeated water from the second RO device 17 is taken out as treated water via a pipe 18.

[0018] A resistivity meter 19 is provided to measure the resistivity of the water flowing inside the pipe 17, and a detection signal from the resistivity meter 19 is transmitted to the control device 14. An electric conductivity meter may be provided instead of the resistivity meter.

[0019] The concentrated water from the first RO device 9 is discharged outside the system, but a part of it may be returned to the raw water tank 1 or the pipe 3 (or the pipe 7). The concentrated water from the second RO device 17 is returned to the raw water tank 1.

[0020] In this embodiment, the pH adjuster adding means 13 controls the addition of the pH adjuster for a predetermined time (for example, 1 to 10 days, particularly 2 to 3 days) based on a signal from one of the two pH meters 11 and 12 (in this case, the first pH meter 11). During this predetermined time, the control device 14 calibrates the second pH meter 12.

[0021] During the next predetermined time, the pH adjuster adding means 13 controls the addition of the pH adjuster based on the signal from the second pH meter 12, and the control device 14 calibrates the first pH meter during this time.

[0022] Thereafter, similarly, the pH meter 11, 12 used for pH control is switched at predetermined time intervals, and the pH meter not used for pH control is calibrated.

[0023] In this embodiment, when the control device 14 switches the pH meter used for pH control from the first or second pH meter 11 to the second or first pH meter 12, it compares the detected pH of the pH meter previously used with the detected pH of the pH meter to be used going forward, and if there is a difference ΔpH, it changes the pH control conditions by the amount of that difference ΔpH (for example, if the detected pH of the first pH meter before the switch is 7.80 and the detected pH of the second pH meter after the switch is 7.70, it lowers the pH control conditions (set value) by 0.10).

[0024] By doing this, there will be no time period when the pH of the feed water from the RO treatment device is not adjusted or controlled. Also, when switching between the first and second pH meters 11 and 12 used for control, fluctuations in the control conditions (set values) can be suppressed.

[0025] It also prevents control instability when switching pH meters.

[0026] In this way, deterioration of the water quality produced by the RO treatment device can be prevented while the pH meter is being calibrated.

[0027] In the above embodiment, the water quality measuring means is a pH meter, but other water quality measuring means (for example, an electric conductivity meter) may also be used. [Explanation of symbols]

[0028] 1 Raw water tank 4 Decarboxylation device 6,13 Means for adding pH adjuster 9 1st RO device 17 2nd RO device

Claims

1. An RO device that separates the RO feed water into a permeate and a concentrate; A water quality measuring means for the RO feed water and the RO permeate water; A water quality adjusting means for adjusting the water quality of the RO water supply based on the measurement value of the water quality measuring means. In a reverse osmosis system having A plurality of the water quality measuring means are provided, A reverse osmosis membrane system, wherein the water quality adjustment means switches the water quality measurement means employed for water quality adjustment at predetermined time intervals.

2. 2. The reverse osmosis membrane system according to claim 1, wherein the water quality measuring means is a pH meter and a resistivity meter, and the water quality adjusting means is a pH adjusting agent adding means.

3. 3. A method for controlling a reverse osmosis membrane system according to claim 1 or 2, characterized in that while the water quality adjustment means is adjusting the water quality based on the measurement value of one water quality measurement means, the other water quality measurement means is calibrated.

4. 4. The control method for a reverse osmosis membrane system according to claim 3, wherein, when switching the water quality measurement means, the difference between the detection value of the current measurement means and the detection value of the other measurement means is subtracted from the control condition (set value) of the current measurement means to set the control condition (set value) of the other measurement means.

5. 3. A control method for a reverse osmosis membrane system according to claim 1 or 2, characterized in that, when switching the water quality measurement means, the difference between the detection value of the current measurement means and the detection value of another measurement means is subtracted from the control condition (set value) of the current measurement means and used as the control condition (set value) of the other measurement means.

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