JPS60125208A - Regeneration of reverse osmosis membrane apparatus - Google Patents

Abstract

PURPOSE:To perform the effective regeneration treatment of a reverse osmosis membrane even when a precipitate caused by polysilicate is precipitated, in preforming desalting treatment after the treatment of soft water, by washing the reverse osmosis membrane with washing water having pH higher than that at the time of desalting before the ratio of a transmitted water amount reaches a specific value or less. CONSTITUTION:Raw water A containing silicate and hardness components is passed through a hard water softening apparatus 1 to remove hardness components. Subsequently, an NaOH solution is added to soft water from an NaH tank 3 to adjust the pH thereof to 8 or more and pH controlled water is introduced into a reverse osmosis membrane apparatus 8 under pressure by a high pressure pump 7 while desalted transmitted water B and untransmitted water C enhanced in the concn. of salts are collected. After desalting treatment is continued until the ratio of a transmitted water amount reaches 0.8 or less, said treatment is interrupted to perform regeneration treatment. A pump 10 is driven to supply transmitted water in a transmitted water tank 9 to the reverse osmosis membrane apparatus 8 as washing water while an NaOH solution is added thereto and the pH of washing water is made higher than that at the time of desalting. Waste washing water is discharged through an untransmitted water line. The polysilicate adhered to the surface of the membrane is dissolved and the ratio of a transmitted water amount is restored to the original state.

Description

[Detailed description of the invention] The present invention softens raw water containing silicic acid and hardness components.
This relates to an improved method of desalination treatment by adjusting the pI-1 of the treated water to 8 or higher and supplying it to a reverse osmosis membrane device using an alkali-resistant reverse osmosis membrane. The purpose of this method is to effectively regenerate when the permeate water tY ratio decreases due to precipitation of polymerized silicic acid on the membrane surface of the reverse osmosis membrane even if this method is used. be.

In the electronics industry, which manufactures LSIs and super LSIs,
The amount of colloidal substances and ions used in cleaning the product
It requires ultrapure water that has been reduced to the PB order. When producing such ultrapure water, reverse osmosis membrane devices are often used in recent years. In other words, raw water that has been subjected to appropriate pretreatment such as turbidity treatment such as coagulation sedimentation filtration and activated carbon filtration is desalted using a reverse osmosis membrane device, and then salts and impurities remaining in the desalted water are removed using a pure water production device and precision filtration. It is generally processed using a device, polisher, etc.

A reverse osmosis membrane device supplies raw water to a reverse osmosis membrane under pressure higher than the osmotic pressure of dissolved salts. Most of the salts are blocked by the reverse osmosis membrane to obtain permeated water with reduced salts as treated water. During this treatment, the colloidal substances contained in the raw water can also be blocked by the reverse osmosis membrane, which is convenient for the production of ultrapure water. . Since reverse osmosis membrane equipment processes raw water through the operations described above, the higher the concentration ratio of raw water, the more permeated water can be barreled from a certain amount of supplied raw water, and the lower the cost. It will be advantageous.

However, when treating raw water that contains large amounts of hard components such as calcium and magnesium, sulfate ions, silicic acid, etc. using a reverse osmosis membrane device, increasing the concentration ratio of the raw water, or in other words, the recovery rate of permeated water, can be compared. Calcium sulfate with low solubility, a complex of hardness components and silicic acid.
Precipitates such as polymerized silicic acid are deposited on the membrane surface of the concentration system, especially reverse osmosis membranes, causing problems such as increased pressure loss and decreased permeate flow rate.

Therefore, conventionally, when raw water containing multiple hardness components is permeated with a reverse osmosis membrane device, a water softening device using, for example, Na-type cation exchange resin is installed at the front stage. This prevents precipitation of hardness and silica complexes from depositing on the membrane surface.

On the other hand, the solubility of silicic acid in water varies greatly as the pH increases; for example, the solubility of silicic acid at 25° C. is as shown in the curve shown in FIG. In other words, when the pH is 7 or less, it is approximately 100 mg a s Si02 /L, but ・p
The more alkaline H exceeds 8.0, the greater the solubility.At pH 9, it is approximately 170■ as S
i02 /L # Approximately 320 mgasS with pl-110
i02/l.

Therefore, when raw water containing silicic acid and hardness components is treated with a reverse osmosis membrane device, the raw water is first passed through a water softening device that uses, for example, Na-type cation exchange resin to remove calcium, magnesium, etc. from the raw water. A softening treatment is performed to remove hard components.Next, an alkali such as force nose is added to the treated water to make pi-1 8 or more.This is then fed to a reverse osmosis membrane device using an alkali-resistant reverse osmosis membrane. The applicant has previously proposed a method for desalting.

This method prevents sediments caused by hardness components such as calcium sulfate from depositing on the non-permeated water side by removing hardness components in the water supplied to the reverse osmosis membrane device in advance.
Furthermore, by increasing the pI-1 of the feed water, the solubility of silicic acid is increased, and even if the concentration ratio is increased, the precipitation caused by silicic acid is prevented from being deposited on the non-permeated water side. be.

However, even if the pH of the feed water is increased, it is not preferable to raise the pH of the feed water that much due to salt leakage into the permeated water.The reason is that the solubility of silicic acid increases as the pI-1 increases. Therefore, from the perspective of preventing the precipitation of silicic acid, it is better to make the pl-1 of the feed water as high as possible.On the other hand, the higher the pH, the higher the cation concentration in the feed water, so salts are transferred to the permeate water. leaks in large quantities.

Since a pure water production device using ion exchange resin is usually installed after the reverse osmosis membrane device, it is also necessary to reduce the salt concentration of the permeated water as much as possible. Therefore, the pH of the feed water should be 10 or higher. This is not a good idea; in the above-mentioned method, it is common to adjust the pi-1 of the feed water to 8 to 10.

The present inventors attempted desalination using the above-mentioned method by setting the pH of the supplied water to 8 to 10. Despite taking measures to prevent the precipitation of precipitates caused by hardness components or silicic acid as described above, It was discovered that the permeated water ratio gradually decreased and as the desalination treatment continued, the permeated water ratio finally decreased to 0.8 or less.

As a result of various investigations into the cause of this problem, it was found that it was due to the precipitation of polymerized silicic acid caused by the membrane concentration of the reverse osmosis membrane.

In other words, significant membrane concentration occurs on the membrane surface of the reverse osmosis membrane. Even if the amount of silicic acid in the non-permeated water is calculated from the silicic acid content of the feed water and the concentration ratio of the non-permeated water, the silicic acid concentration in the calculated silicic acid concentration is Even if the pH is adjusted to such a level that it does not precipitate, local concentration occurs in the membrane of the reverse osmosis membrane, which is presumed to cause polymerized silicic acid to precipitate.

Regardless of the cause, if the permeated water amount ratio is less than 8, it is extremely undesirable for industrial equipment.

Therefore, as a result of studying to restore the permeate water ratio,
It has been found that washing the reverse osmosis membrane with washing water with a pLI higher than pH-1 during desalination treatment effectively restores the permeate water ratio.

Generally, precipitates caused by silicic acid adhering to reverse osmosis membranes combine with hardness components to form hard precipitates, which are difficult to remove by washing with alkali.
The hardness components in the raw water are removed in advance and the p of the feed water is
Since 1 is adjusted to 8 to 10, the polymerized silicic acid deposited on the reverse osmosis membrane under such circumstances can be easily removed by alkaline cleaning.

The present invention is based on the above knowledge. Raw water containing silicic acid and hardness components is softened. The pI of the treated water is
In a method of desalination using a reverse osmosis membrane device using an alkali-resistant reverse osmosis membrane by adjusting 1 to 8 or more, the desalination process is carried out at 4 o'clock before the permeated water amount ratio during desalination treatment reaches 0.8 or less. pl
(It is more concerned with a regeneration method for a reverse osmosis membrane device, which is characterized by cleaning the reverse osmosis membrane with cleaning water of high pH.

The present invention will be explained in detail below with reference to the drawings.

FIG. 2 is an explanatory diagram of a flow that is an example of an embodiment of the present invention; 1 is a water softening device filled with Na-type strong acid cation exchange resin; 2 is a hydraulic soda injection pump; 3 is a hydraulic soda tank・4 is the line mixer ・5 is the pH detection unit ・6 is the
+1 controller; 7 is a high-pressure pump; 8" is a reverse osmosis membrane device using an alkali-resistant reverse osmosis membrane; 9 is a permeation water tank; and 10 is a wash water pump.

In the present invention, first, raw water is passed through a water softening device 1 to remove hardness components from the raw water.

Next, an aqueous sodium hydroxide solution is added to the soft water from the hydric soda tank 3 using the injection pump 2, and the PL-1 of the soft water is adjusted to 8 or more, preferably around 9. In addition, during this injection, the pH is detected by a pH detection unit attached after the line mixer 4, and the force-injection of soda solution 111 from the injection pump 2 is instrumented to 1 so that a predetermined pH value is obtained. Adjustment is made using the tears controller 6. Through these operations, the hardness components of the raw water A have been removed and the pH has been made alkaline, and the soft water is forced into the reverse osmosis membrane device 8 using the high-pressure pump 7. Collect water C. Although not shown, the soft water is passed through a reverse osmosis membrane device 8.
It is preferable to remove suspended solids using a precision filter before pressurizing.

If such desalting treatment is continued, the permeated water amount ratio gradually decreases, but before the permeated water amount ratio reaches 0.8 or less, the following regeneration treatment is performed.

That is, the drive of the high-pressure pump 7 is stopped to interrupt the desalination process, the washing water pump 10 is driven to supply the permeated water in the permeated water tank 9 to the reverse osmosis membrane device as washing water, and the washing water is supplied with force. Aqueous sodium hydroxide solution is added from the sodium chloride tank 3 using the injection pump 2, and the pH of the washing water is adjusted to ρII, preferably 10 or more, which is higher than the pH during the desalination treatment described above.

Furthermore, during this injection, the pH is detected by the PL + detection unit attached after the line mixer 4, and the amount of the aqueous sodium hydroxide solution injected from the injection pump 2 is instrumented so that it reaches a predetermined value of 1. Needless to say, the pH value is adjusted using the standard FC pH controller 6. Washing waste water is blown to the outside via the non-permeable water line. If this type of washing is performed for one hour, the polymerized silicic acid adhering to the membrane surface of the reverse osmosis membrane will be effectively dissolved, and the permeate water amount ratio will be the same as before. The state will be restored. Although the washing may be carried out at room temperature, it is more effective to heat the washing water to 30°C to 40°C.

In addition, in this embodiment, permeated water is used as the washing water.
Although the desalination process is interrupted while performing the regeneration process, it is also possible to perform the regeneration process while continuing the desalination process by using soft water as the wash water.

In other words, when the permeate water ratio decreases, - Increase the amount of injected water solution from the injection pump 2 - Continue desalination by setting the pH of the soft water to a higher pH than the pH at the time of desalination - Desalination This method dissolves polymerized silicic acid adhering to the membrane surface of the reverse osmosis membrane while performing the treatment. However, if regeneration treatment is performed while continuing desalination treatment in this way, the salt concentration of the permeated water will increase during this time, so this point needs to be taken into consideration.

When the above-mentioned cleaning is completed and the value of the permeated water amount ratio returns to the original value, the desalination process described above is continued.

In addition, the permeated water amount ratio in the present invention is - The permeated water amount Qt as the desalination treatment time t passes - The permeated water amount Q at the initial stage of the desalination treatment
Indicates the number divided by o. For example, a permeated water ratio of 0.8 indicates that the permeated water amount decreases to 80% under the same conditions compared to the permeated water amount at the initial stage of desalination treatment.

In addition, the alkali-resistant reverse osmosis membrane used in the present invention is different from the conventionally used cellulose acetate membrane, and includes recent membranes such as polyetheramide composite membranes, polyvinyl alcohol composite membranes, aromatic polyamide membranes, and polybenzimidazolo membranes. refers to an alkali-resistant reverse osmosis membrane developed in

As explained above, the present invention prevents precipitates caused by hardness components from precipitating in non-permeable daffodils by removing the hardness components in advance, even if the raw water contains large amounts of silicic acid and hardness components. Furthermore, since the solubility of silicic acid is increased by increasing the pH of the feed water, even if the concentration ratio is increased, the precipitation of silicic acid-induced precipitates on the non-permeated water side is suppressed, and such treatment is If a precipitate caused by polymerized silicic acid is still deposited on the membrane surface of the reverse osmosis membrane due to membrane concentration even after desalination treatment, the pI is higher than I)H during desalination treatment.
-Since the reverse osmosis membrane can be treated effectively with the washing water in step 1 - When using a reverse osmosis membrane to treat water that contains a large amount of silicic acid and hardness components - The recovery rate of permeated water can be increased at low cost. The economic benefits are great.

Examples will be described below to clarify the effects of the present invention.

Example Raw water having the composition shown in Table 1 was softened in accordance with the flow of the present invention shown in Figure 1. First, it was softened in a water softening device filled with Na-type strongly acidic cation exchange resin. The pH was adjusted to 9 with the addition of
The treatment was carried out using a reverse osmosis membrane device using a 7199 membrane (trade name) under conditions of a permeate recovery rate of 75 cm and a supply pressure of 30 kg/ci. In addition, by continuing such treatment, when the permeated water amount ratio of the reverse osmosis membrane device decreased to 0.94, the pH was adjusted to 11 by adding sodium hydroxide to the permeated water according to the method of the present invention, and the washing water was was supplied to a reverse osmosis membrane device for 1 hour at a supply pressure of 5 kg/ah for regeneration treatment.

The results are shown in Figure 3. Figure 3 shows the change in the amount of permeated water Qt with the passage of operating time t.The permeated water amount ratio (Q t/Q, o
) is calculated, and this is shown on the vertical axis, and the processing time is shown on the horizontal axis.

The results obtained when the regeneration process of the present invention was not performed are also shown in FIG. 3.

As seen in Figure 3, when the regenerative treatment of the present invention is performed, the permeated water volume ratio returns to its original state, but in the conventional method without regenerative treatment, the permeated water volume ratio decreases as the treatment time continues. did.

Table 1

[Brief explanation of drawings]

Figure 1 is a graph showing the solubility of silicic acid at a water temperature of 25°C. The vertical axis shows r (dissolved melon) and the horizontal axis shows KpH. Figure 2 shows a flow chart showing an example of an embodiment of the present invention. It is an explanatory diagram. Fig. 3 shows the decrease in the permeated water amount ratio with respect to the treatment time in the example. The vertical axis shows the permeated water -
[ii Ratio/The processing time is shown on the horizontal axis. 1. Water softener 2. Soda injection pump 3. Soda tank 463.・Line mixer 5, --, pl+detection section 6,,,,p
i-1 controller 7, high pressure pump 8, reverse osmosis membrane device 90.・、Permeated water tank 10 、、・・Washing water pump Fig. 1 3 4 5 6 7 8 9 10 H1213□ P
H Figure 2 Figure 3 OIoo 200 300 400 500 600<
14. Saki fj1 (hr)' Procedural amendment (voluntary) March 8, 1985 Manabu Shiga, Commissioner of the Patent Office1, Indication of the case 1981 Patent Application No. 2314712, Name of the invention Regeneration of reverse osmosis membrane device Method 3: Relationship with the person making the amendment Patent applicant address 5-5-16 Hongo, Bunkyo-ku, Tokyo Name (
440) Organo Co., Ltd. Representative Kunio Nagai 4, Agent Address: 113, 812-5151 6 Contents of amendment 7 Please amend the following matters in the specification as shown in the attached sheet. 1. On page 3, line 10, replace "calcium sulfate" with "
Calcium carbonate, calcium sulfate.'' 2. On page 3, line 15, insert the following sentence after "When performing transparency processing." ``A method for preventing the precipitation of calcium carbonate by adding an acid in the first stage and a method for reducing the recovery rate of water.'' 3. On page 3, line 18, ``with calcium sulfate'' is replaced with ``calcium carbonate''. I am corrected. 4. From the bottom line of page 4 to the first line of page 5, the words "calcium sulfate, etc." are corrected to "calcium carbonate, etc." 5. On the 4th line of page 13, replace "Figure 1" with "Figure 2"
I am corrected. that's all

Claims (1)

[Claims] In a method in which raw water containing silicic acid and hardness components is softened, the pI-1 of the treated water is adjusted to 8 or more, and desalination is performed using a reverse osmosis membrane device using an alkali-resistant reverse osmosis membrane.Desalination treatment 1. A regeneration method for a reverse osmosis membrane device, characterized in that the reverse osmosis membrane is washed with wash water having a pH higher than pl-1 during desalination before the permeated water amount ratio reaches 0.8 or less.