JP7625960B2 - Reverse osmosis membrane system and control method thereof - Google Patents

Description

The present invention relates to a reverse osmosis membrane system, and in particular to a reverse osmosis membrane system having a water quality measurement means for the water supplied to an RO device (reverse osmosis membrane device), and a control method thereof.

One method for producing pure water from city water, well water, reclaimed water, and other water is to pretreat the water (removing turbidity and chlorine), add acid, and decarbonate it in a decarbonation tower, vacuum degassing device, or membrane degassing device, and then pass the decarbonated water through multiple stages of RO equipment arranged in series for treatment (Patent Document 1).

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.

Japanese Patent Application Publication No. 10-30957

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

The present invention aims to provide a reverse osmosis membrane system and a control method thereof that can adjust and control the pH of the water supplied to an RO device even when the pH meter is being calibrated.

The present invention is as follows.
[1] An RO device that separates RO feed water into permeate and concentrated water;
A water quality measuring means for the RO feed water and the RO permeate water;
and a water quality adjustment means for adjusting the water quality of the RO feed water based on the measurement value of the water quality measurement means.
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.

[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.

[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.

According to the present invention, the water quality of the RO system's feed water can be measured by multiple 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 current measuring means minus the difference in the detection values is set as the control condition (set value) of the other 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 in the treated water from the reverse osmosis membrane system.

1 is a configuration diagram showing a reverse osmosis system according to an embodiment.

An embodiment will be described below 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 pH of the water supplied to the decarbonation device 4 becomes acidic, between 4.0 and 6.0.

The decarbonation device 4 may be, but is not limited to, a decarbonation tower, a membrane decarbonation device, etc.

The water decarbonated in the decarbonation device 4 is supplied to the first RO device 9 via piping 7 and pump 8.

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 is at a pH condition (e.g., 7.0 to 8.5) that optimizes the resistivity of the treated water in the second RO device 17.

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

The permeate from the first RO device 9 is sent to the second RO device 17 via piping 15 and pump 16. The permeate from the second RO device 17 is taken out as treated water via piping 18.

A resistivity meter 19 is installed to measure the resistivity of the water flowing through the pipe 17, and the detection signal of the resistivity meter 19 is transmitted to the control device 14. An electrical conductivity meter may be installed instead of the resistivity meter.

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

In this embodiment, the pH adjuster addition means 13 controls the addition of the pH adjuster for a predetermined time (e.g., 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.

During the next specified time, the pH adjuster addition 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.

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.

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 used up until that point 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 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).

By doing this, there will be no time periods when the pH of the feedwater to the RO treatment plant is not adjusted or controlled. In addition, fluctuations in the control conditions (set values) can be suppressed when switching between the first and second pH meters 11, 12 used for control.

It also prevents control instability when switching pH meters.

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

In the above embodiment, the water quality measuring means is a pH meter, but other water quality measuring means (e.g., an electrical conductivity meter) may also be used.

Reference Signs List 1 raw water tank 4 decarbonation device 6, 13 pH adjuster adding means 9 first RO device 17 second RO device

Claims (5)

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