JP2013220384A - Method and apparatus for treating reverse osmosis membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of treating a reverse osmosis membrane which can avoid scale obstacles under neutral to alkaline conditions of target water.SOLUTION: A chelating agent is added intermittently or continuously to target water of reverse osmosis membrane treatment, while the amount of the chelating agent added is increased intermittently. In the operation, the pH of the target water is ≥7, preferably ≥9. A scale preventive agent, together with the chelating agent, is added to the target water, if necessary.

Description

  The present invention relates to a water treatment method and a water treatment apparatus using a reverse osmosis membrane. More specifically, the present invention relates to a technique for avoiding scale failure in reverse osmosis membrane processing.

  In recent years, environmental standards and water quality standards tend to be stricter, and purification by advanced treatment is required for discharged water to rivers and the like. On the other hand, for the purpose of eliminating water shortage, various types of wastewater are being collected and reused without being discharged. Under such circumstances, more advanced water treatment technology is desired. In particular, reverse osmosis membrane (RO) treatment effectively removes impurities such as ions, organic substances and fine particles in water. Since it can be removed, it is used in various fields (see, for example, Patent Documents 1 to 3).

  For example, Patent Document 1 discloses a recovery and reuse method in which wastewater generated in the development process is treated with a reverse osmosis membrane device and the obtained treated water is used again in the development process. Patent Document 2 discloses an ultrapure water production method that efficiently removes organic matter in raw water by combining biological treatment and reverse osmosis membrane treatment to obtain highly pure ultrapure water having a very low concentration of organic matter. It is disclosed. Furthermore, wastewater containing high concentrations of organic substances such as acetone and isopropyl alcohol discharged from electronic device manufacturing factories and the like, and selenium discharged when wet cleaning fossil fuel as described in Patent Document 3 Reverse osmosis membrane treatment is also applied to treatment of wastewater containing fluorines and borons.

  However, the treatment method of passing wastewater after biological treatment as described in Patent Documents 2 and 3 to the reverse osmosis membrane treatment apparatus is based on the membrane surface of the reverse osmosis membrane due to metabolites generated by the decomposition of organic matter by microorganisms. May be blocked and the flux may decrease. On the other hand, when wastewater containing organic matter is directly passed through the reverse osmosis membrane treatment apparatus without performing biological treatment, microorganisms easily propagate in the apparatus. For this reason, in the conventional reverse osmosis membrane treatment, when treating waste water containing organic matter, the growth of microorganisms is suppressed by adding a large amount of a slime control agent.

  In addition, since the slime control agent is expensive, a method of suppressing the growth of microorganisms by adjusting the water to be treated to pass through the reverse osmosis membrane apparatus to pH 9 or higher is currently employed (for example, patent document). 4, 5). In the treatment methods described in Patent Documents 4 and 5, organic matter-containing wastewater whose pH is adjusted to 9.5 or more by adding alkali before, after or simultaneously with the addition of the scale inhibitor is introduced into the reverse osmosis membrane treatment apparatus. Separation process.

  Since microorganisms cannot live in alkaline areas, the treatment method described in Patent Documents 4 and 5 can be applied to create an environment in which microorganisms cannot live without leaving a nutrient source, and an expensive slime control. It is possible to prevent biofouling (slime damage) that occurs due to the propagation of microorganisms without the need to add an agent. In addition, in the treatment methods described in Patent Documents 4 and 5, a decrease in flux (permeation flux) generated when an organic substance such as a nonionic surfactant is adsorbed on the reverse osmosis membrane surface, or an inorganic component such as calcium carbonate. Since the scale failure caused by the precipitation can be prevented, the reverse osmosis membrane treatment can be stably performed.

  Moreover, conventionally, in order to suppress the generation of scale, the pH of the water to be treated is adjusted to 9 or more, and a method for producing pure water by adding a scale dispersant containing a polymer having a carboxyl group in the side chain as an active ingredient Has also been proposed (see Patent Document 6). Furthermore, there is also a technology for temporarily sterilizing a reverse osmosis membrane under acidic conditions of pH 4 or less by intermittently adding sulfuric acid, which is less corrosive than hydrochloric acid, non-volatile and inexpensive, to raw water. It has been proposed (see Patent Document 7).

JP 2001-276825 A JP 2002-210335 A JP 2011-200848 JP 2005-169372 A JP 2007-253115 A JP 2005-118712 A Japanese Patent Laid-Open No. 2000-300966

  The desalting treatment using a reverse osmosis membrane is generally a concentration treatment performed at a water recovery rate of less than 90%. That is, in the reverse osmosis membrane treatment, about 90% of the amount of water to be treated permeates through the reverse osmosis membrane and is obtained as desalted treated water, but about 10% is condensed water in which the excluded salts are concentrated. Discharged. In this reverse osmosis membrane treatment, in order to suppress the generation of scale itself, a scale inhibitor is allowed to act on all scale-generating components contained in the water to be treated that are sequentially concentrated except for the amount leaked into the permeate. And a large amount of scale inhibitor is required.

  For example, in the treatment methods described in Patent Documents 4 and 5 described above, it is necessary to add a large amount of a scale inhibitor and at least 5 mass times the calcium ion concentration in order to prevent scale failure. For this reason, these conventional processing methods have a problem that the scale inhibitor is costly and increases the operating cost. In addition, when a large amount of scale inhibitor is added to the water to be treated, the scale inhibitor is concentrated in the concentrated water after reverse osmosis membrane treatment, increasing the load in the subsequent wastewater treatment, and the environmental impact of the discharged water There is also a problem that increases.

  On the other hand, the treatment method described in Patent Document 6 is considered effective when the concentration of the scale generation component in the water to be treated is extremely low, but for the water to be treated having a higher concentration of the scale generation component than that, It is presumed that a sufficient scale prevention effect cannot be obtained without the combined use with decarboxylation treatment or ion exchange treatment. Further, in the method described in Patent Document 7, when Ca, Ba, Sr, and the like are contained in the water to be treated (raw water), scales such as calcium sulfate, barium sulfate, and strontium sulfate are generated. When adding sulfuric acid, it is necessary to add a scale inhibitor.

  Therefore, the main object of the present invention is to provide a reverse osmosis membrane treatment method and a reverse osmosis membrane treatment apparatus capable of avoiding scale failure under conditions where the water to be treated is neutral to alkaline.

  As a result of earnest experimental research on an effective method for preventing scale failure in reverse osmosis membrane (RO membrane) treatment, the present inventors added a chelating agent intermittently to the water to be treated. As compared with the case where it is constantly added, it has been found that the same or better performance can be obtained with a smaller addition amount, and the present invention has been achieved.

That is, the reverse osmosis membrane treatment method according to the present invention adds a chelating agent intermittently to a neutral to alkaline treated water of pH 7 or higher, or continuously adds a chelating agent, and the addition Increase the amount intermittently.
In the reverse osmosis membrane treatment method of the present invention, the chelating agent is intermittently added to the water to be treated or the amount of the chelating agent added to the water to be treated is intermittently increased. It can be dissolved and / or peeled off.
As the chelating agent, for example, at least one compound selected from the group consisting of ethylenediaminetetraacetic acid and its salt, gluconic acid and its salt can be used.
In addition to the chelating agent, a scale inhibitor may be added to the water to be treated. In this case, as the scale inhibitor, for example, a phosphate scale inhibitor or a polymer scale inhibitor can be used.
Furthermore, the pH of the water to be treated is preferably 9 or higher.

  A reverse osmosis membrane treatment apparatus according to the present invention includes a reverse osmosis membrane that separates water to be treated into permeate and concentrated water, a chelating agent addition unit that adds a chelating agent to the water to be treated, and a chelate to the water to be treated. A controller for controlling the chelating agent addition unit so that the chelating agent is added intermittently or the chelating agent is continuously added to the water to be treated to increase the amount of the addition intermittently, It is to be prepared.

  According to the present invention, since the chelating agent is intermittently added to the water to be treated or the amount of the chelating agent added to the water to be treated is intermittently increased, the water to be treated is in a neutral to alkaline condition. Even if it exists, a scale failure can be avoided effectively.

It is a figure which shows the structural example of the reverse osmosis membrane processing apparatus to which the reverse osmosis membrane processing method of embodiment of this invention is applied. It is a figure which shows the result of the continuous water flow test in 1st Example of this invention. It is a figure which shows the result of the continuous water flow test in 2nd Example of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

  In the reverse osmosis membrane treatment method according to the embodiment of the present invention, the chelating agent is intermittently added to the water to be treated, or the chelating agent is continuously added to the water to be treated, and the amount added is intermittently increased. Thus, scales such as carbonates and hydroxides formed on the reverse osmosis membrane surface are dissolved and / or peeled off while performing the reverse osmosis membrane treatment. That is, in the reverse osmosis membrane treatment method of this embodiment, rather than avoiding scale failure by suppressing scale generation, partial scale is generated and membrane performance is recovered from a state where scale failure is occurring. This ensures a stable reverse osmosis membrane treatment.

  Conventionally, chemical cleaning is generally used as a performance recovery method when a scale failure occurs in a reverse osmosis membrane. However, when the scale is dissolved and / or removed by chemical cleaning, it is necessary to replace the primary side (treated water side) of the reverse osmosis membrane with a chemical solution and circulate the chemical solution in the system or immerse the membrane in the chemical solution. There is. And when performing these operations, the reverse osmosis membrane treatment must be stopped, and an alternative machine must be prepared to continue the treatment. On the other hand, the reverse osmosis membrane treatment method of the present embodiment can dissolve and / or remove the generated scale without stopping the reverse osmosis membrane treatment and restore the performance of the reverse osmosis membrane.

[PH of water to be treated]
In the reverse osmosis membrane treatment method of this embodiment, the water to be treated is not acidified by adding sulfuric acid or the like. That is, the water to be treated in the reverse osmosis membrane treatment method of the present embodiment is neutral to alkaline at pH 7 or higher. Moreover, it is preferable that the pH of to-be-processed water is 9 or more, and it becomes possible not only to avoid a scale failure but also to prevent biofouling (slime failure). In addition, the adjustment method of pH of to-be-processed water is not specifically limited, It can carry out using well-known alkaline agents, such as sodium hydroxide.

[Chelating agent]
The chelating agent used in the reverse osmosis membrane treatment method of the present embodiment is not particularly limited. For example, nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriamine Pentaacetic acid (DTPA), triethylenetetraamine hexaacetic acid (TTHA), citric acid, oxalic acid, gluconic acid, or a salt thereof can be used. In addition, although these chelating agents can also be used independently, you may use it in combination of 2 or more type.

  In particular, when the pH of the water to be treated is 9 or more, it is preferable to use ethylenediaminetetraacetic acid or a salt thereof, gluconic acid or a salt thereof. These chelating agents react with the scale components generated in the reverse osmosis membrane and are unlikely to become a gel or precipitate that is difficult to re-dissolve. There is little risk of deteriorating performance. On the other hand, citric acid and oxalic acid do not exhibit sufficient effects under alkaline conditions, and therefore these compounds are unsuitable when the pH of the water to be treated is 9 or more.

[Chelating agent addition conditions]
In the reverse osmosis membrane treatment method of the present embodiment, the addition frequency or increase frequency of the chelating agent is not particularly limited, and is appropriately set according to the scale component concentration in the water to be treated and the operating conditions of the reverse osmosis membrane treatment. However, it is preferable to perform addition or increase for 2 to 12 hours per time, about once / day to once / week. As a result, the performance recovery effect of the reverse osmosis membrane can be obtained with a low concentration and a short time treatment as compared with general chemical cleaning performed by stopping the reverse osmosis membrane treatment.

  In the reverse osmosis membrane treatment method of the present embodiment, the chelating agent is not always added, and even when always added, scale is generated on the concentrated water and reverse osmosis membrane surface generated by the reverse osmosis membrane treatment in order to suppress the addition to a small amount. . The scale of the reverse osmosis membrane surface is amorphous at the time of generation and is easily dissolved and peeled, but it is expected to grow and become stronger as the operation of the reverse osmosis membrane treatment continues. The

  In fact, at the beginning of scale generation, it is possible to restore the performance of the reverse osmosis membrane to the state before scale generation by simple cleaning with a low concentration chemical solution in a short time. It is necessary to perform cleaning for a long time with this chemical solution, and even if such cleaning is performed, the original state may not be recovered. On the other hand, at a frequency of once / day to once / week, add a chelating agent to the water to be treated for 2 to 12 hours, or increase the amount of the chelating agent added to the water to be treated. By this, it can melt | dissolve and / or peel before the scale produced | generated on the reverse osmosis membrane surface becomes strong.

  Further, the amount of the chelating agent added to the water to be treated is not particularly limited, but in the reverse osmosis membrane treatment method of the present embodiment, the already generated scale is redissolved to restore the differential pressure. The concentration of the chelating agent in the water to be treated during intermittent addition or intermittent increase is set to a relatively high concentration. Specifically, the chelating agent is intermittently added so that the concentration in the water to be treated is 10 mg / L or more, or the chelating agent is intermittently added so that the concentration is constantly twice or more of the concentration at the time of addition. It is preferable to increase the amount.

  As described above, in the reverse osmosis membrane treatment method of the present embodiment, a chelating agent is added to the water to be treated or the amount of the chelating agent is added in a state where scale is generated on the concentrated water or the reverse osmosis membrane surface. Increase the amount. In this case, the chelating agent acts on the scale component in the concentrated water, but preferentially acts on the scale component on the reverse osmosis membrane surface present at a higher concentration. When a small amount of chelating agent is constantly added and the amount added is increased intermittently to increase the concentration of the chelating agent in the water to be treated, the reaction efficiency between the chelating agent and the scale components increases, and the scale obstacle avoidance effect Will improve.

  Thus, in the reverse osmosis membrane treatment method of the present embodiment, by adjusting the addition frequency and concentration of the chelating agent, it is possible to add a small amount of the scale inhibitor and the chelating agent in a smaller amount than when always adding a constant amount, It is possible to obtain a scale obstacle avoidance effect equal to or greater than that.

[Scale inhibitor]
Moreover, in the reverse osmosis membrane treatment method of this embodiment, a scale inhibitor can be added to the water to be treated as necessary. In general, the above-mentioned “chelating agent” may also be treated as a “scale inhibitor”. However, in the present invention, in order to clearly distinguish between “chelate” and “scale inhibitor”, The “scale inhibitor” does not include those that form a chelate complex with a metal ion.

  In addition, the scale inhibitor used in the reverse osmosis membrane treatment method of the present embodiment is not particularly limited, but an excellent scale prevention effect can be obtained even in water to be treated with a pH of 7 or higher, so 1-hydroxyethylidene. Phosphoric acid scale inhibitors such as -1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), or acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid ( Polymeric scale inhibitors such as AMPS are preferred. In addition, although these scale inhibitors can also be used independently, you may use it in combination of 2 or more type.

  However, when the pH of the water to be treated is 9 or more, a substance that decomposes under alkaline conditions to produce normal phosphoric acid such as sodium hexametaphosphate is not suitable. The scale inhibitor can be added intermittently in the same manner as the chelating agent, but it is preferable that a specific amount is always added to the water to be treated.

[Reverse osmosis membrane treatment equipment]
FIG. 1 is a diagram illustrating a configuration example of a reverse osmosis membrane treatment apparatus to which the reverse osmosis membrane treatment method of the present embodiment is applied. As shown in FIG. 1, the reverse osmosis membrane treatment method of the present embodiment includes a chelating agent addition unit 2 that adds a chelating agent to water to be treated and a control unit 4 that controls the chelating agent addition unit 2. It can be implemented by a processing device.

  In this reverse osmosis membrane treatment apparatus, the chelating agent addition unit 2 is provided in a flow path that connects the tank 1 in which treated water is stored and the reverse osmosis membrane 5. In addition, the control unit 4 controls the addition amount, addition time, addition frequency, and the like of the chelating agent in the chelating agent addition unit 2. Specifically, when the chelating agent is not constantly added to the treated water, the chelating agent is constantly added to the treated water so that the chelating agent is intermittently added to the treated water. In the case, the chelating agent addition unit 2 is controlled so that the addition amount is intermittently increased.

  Moreover, the reverse osmosis membrane treatment apparatus can be provided with a scale inhibitor addition unit 3 for adding a scale inhibitor to the water to be treated as necessary. The addition amount, addition time, and addition frequency of the scale inhibitor by the scale inhibitor addition unit 3 can be controlled independently, but may be controlled by the control unit 4 together with the chelating agent addition unit 2. Further, in the reverse osmosis membrane treatment apparatus, if necessary, a pH adjusting unit (not shown) for adjusting the pH of the water to be treated downstream of the chelating agent adding unit 2 and the scale inhibitor adding unit 3. Can also be provided.

  As described above in detail, in the reverse osmosis membrane treatment method of the present embodiment, a chelating agent is intermittently added to the water to be treated having a pH of 7 or more, or the chelating agent is continuously added. Since the amount added is intermittently increased, the scale generated on the film surface can be easily dissolved and peeled off by the chelating action. As a result, the occurrence of scale failure in the reverse osmosis membrane treatment can be effectively avoided.

  In the reverse osmosis membrane treatment, the conventional scale failure avoidance method that suppresses the generation of scale itself by using a scale inhibitor makes stable treatment taking into account fluctuations in the quality of the water to be treated. However, in the reverse osmosis membrane treatment method of the present embodiment, scale obstacles can be efficiently avoided with the addition of a small amount of chelating agent. In addition, the reverse osmosis membrane treatment method of the present embodiment does not need to stop the reverse osmosis membrane treatment or prepare an alternative machine like conventional chemical cleaning, and even when an unintentional scale failure occurs. It is possible to restore the membrane performance without stopping the reverse osmosis membrane treatment.

  Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention.

(First embodiment)
In the first example, a continuous water flow test for about one month was performed, and a case where a chelating agent was intermittently added to the water to be treated (Example 1) and a case where a constant amount was constantly added (Comparative Example 1). , 2) and the stability in reverse osmosis membrane treatment were compared. FIG. 2 is a diagram showing the results of a continuous water flow test in the first example.

<Example 1>
As the raw water, simulated waste water having a calcium concentration of about 0.1 mg / L, an M alkalinity of about 50 mg / L (as CaCO ₃ ), and an iron concentration of about 0.1 mg / L was used. And the residual chlorine was removed from raw | natural water with the activated carbon filter filled with granular activated carbon (Kurita Kogyo Co., Ltd. cricol WG160), and it was set as the to-be-processed water.

Next, the pH of the water to be treated was adjusted to 10 to 10.5 with sodium hydroxide, and this was supplied to a reverse osmosis membrane (ES20 manufactured by Nitto Denko Corporation) to perform a reverse osmosis membrane treatment. The reverse osmosis membrane treatment was performed in a constant permeation flux operation with a permeation flux of 0.7 m ³ / m ² · d under conditions of a water temperature of about 25 ° C. and a water recovery rate of 85%.

  Then, ethylenediaminetetraacetic acid tetrasodium as a chelating agent was added to the water to be treated at a frequency of 1/7 days so that the concentration of the water to be treated was 10 mg / L. . In addition, in FIG. 2, the chelating agent addition time is shown by the arrow. This continuous water flow test was conducted for about one month, and the change with time of the reverse osmosis differential pressure (osmotic pressure 0, converted to 25 ° C.) was confirmed. As a result, as shown in FIG. 2, the reverse osmosis differential pressure was maintained at 0.5 MPa or less.

<Comparative Example 1>
Continuous water flow test under the same conditions as in Example 1 above, except that ethylenediaminetetraacetic acid tetrasodium as a chelating agent was constantly added to the water to be treated so that the concentration of the water to be treated was 1 mg / L. Carried out. As a result, as shown in FIG. 2, the reverse osmosis differential pressure exceeded 0.6 MPa in the third week from the start of the test, and stable performance was not obtained. The amount of chelating agent used in Comparative Example 1 was 2.8 times the amount used in Example 1.

<Comparative example 2>
Continuous water flow test under the same conditions as in Example 1 above, except that ethylenediaminetetraacetic acid tetrasodium as a chelating agent was always added to the water to be treated so that the concentration of the water to be treated was 5 mg / L. Carried out. As a result, as shown in FIG. 2, in the continuous water flow test for about one month, the differential pressure between reverse osmosis membranes was maintained at 0.5 MPa or less, and stable performance was obtained. However, the amount of chelating agent used in Comparative Example 2 was 14 times the amount used in Examples.

(Second embodiment)
In the second example, a continuous water flow test for about one month was carried out, the scale inhibitor was constantly added to the water to be treated, and the chelating agent was added intermittently (Example 2). The stability in the reverse osmosis membrane treatment was compared between the case where both the chelating agent and the chelating agent were constantly added (Comparative Example 3). FIG. 3 is a diagram showing the results of a continuous water flow test in the second example.

<Example 2>
As the raw water, simulated waste water having a calcium concentration of about 1 mg / L, an M alkalinity of about 100 mg / L (as CaCO ₃ ), and iron, copper, nickel, and zinc concentrations of about 0.1 mg / L was used. And the residual chlorine was removed from raw | natural water with the activated carbon filter filled with granular activated carbon (Kurita Kogyo Co., Ltd. cricol WG160), and it was set as the to-be-processed water.

Next, the pH of the water to be treated was adjusted to 10 to 10.5 with sodium hydroxide, and this was supplied to a reverse osmosis membrane (ES20 manufactured by Nitto Denko Corporation) to perform a reverse osmosis membrane treatment. The reverse osmosis membrane treatment was performed in a constant permeation flux operation with a permeation flux of 0.7 m ³ / m ² · d under conditions of a water temperature of about 25 ° C. and a water recovery rate of 85%.

  Then, Byhibit AM (containing 50% by mass of PBTC manufactured by Lanxess) as a scale inhibitor was constantly added to the water to be treated so that the concentration of the water to be treated was 1 mg / L. Further, sodium gluconate is constantly added as a chelating agent so that the concentration of the water to be treated is 1.5 mg / L, and tetrasodium ethylenediaminetetraacetate is added so that the concentration of the water to be treated is 20 mg / L. Was added at a frequency of once every 7 days for 6 hours. In addition, in FIG. 3, the addition time of ethylenediaminetetraacetic acid tetrasodium is shown by the arrow.

  This continuous water flow test was conducted for about one month, and the change with time of the reverse osmosis differential pressure (osmotic pressure 0, converted to 25 ° C.) was confirmed. As a result, as shown in FIG. 3, the reverse osmosis differential pressure could be maintained at 0.4 MPa or less.

<Comparative Example 3>
To the water to be treated, ethylenediaminetetraacetic acid tetrasodium was not continuously added but continuously added so that the concentration of the water to be treated was 5 mg / L. A water test was performed. As a result, as shown in FIG. 3, the reverse osmosis differential pressure exceeded 0.5 MPa during one month, and stable performance was not obtained. In addition, the amount of ethylenediaminetetraacetic acid tetrasodium used in Comparative Example 3 was 7 times the amount used in Example 2.

  As described above, the reverse osmosis membrane treatment methods of Examples 1 and 2 maintain the reverse osmosis membrane differential pressure of 0.5 MPa or less (Δ0.1 MPa / month or less) in a continuous water flow test for one month. Stable operation was possible. This result indicates that the reverse osmosis membrane treatment can be recovered without stopping the reverse osmosis membrane treatment, and the reverse osmosis membrane performance can be recovered continuously.

  On the other hand, the reverse osmosis membrane treatment methods of Comparative Examples 1 and 3 have stable performance compared to Examples 1 and 2 despite the use of a large amount of chelating agents and scale inhibitors. I couldn't. On the other hand, in the reverse osmosis membrane treatment method of Comparative Example 2 in which stable performance was obtained, a larger amount of chelating agent was required than in Example 1 in order to obtain stable performance.

  From the above results, according to the reverse osmosis membrane treatment method of the present invention, stable membrane performance can be obtained with a smaller amount of chelating agent, so that it is stable without performing reverse osmosis membrane performance recovery treatment such as chemical cleaning. It was confirmed that the reverse osmosis membrane treatment can be carried out over a long period of time, and the operating cost due to the chelating agent can be reduced.

DESCRIPTION OF SYMBOLS 1 Tank 2 Chelating agent addition part 3 Scale inhibitor addition part 4 Control part 5 Reverse osmosis membrane

Claims (7)

  A reverse osmosis membrane treatment method in which a chelating agent is intermittently added to neutral to alkaline treated water having a pH of 7 or more, or a chelating agent is continuously added, and the amount added is intermittently increased.   The reverse osmosis membrane treatment method according to claim 1, wherein the chelating agent is at least one compound selected from the group consisting of ethylenediaminetetraacetic acid or a salt thereof and gluconic acid or a salt thereof.   The reverse osmosis membrane treatment method according to claim 1, wherein a scale inhibitor is further added to the water to be treated.   The reverse osmosis membrane treatment method according to claim 3, wherein the scale inhibitor is phosphoric acid type or polymer type.   The reverse osmosis membrane treatment method according to any one of claims 1 to 4, wherein the pH of the water to be treated is 9 or more.   6. The reverse osmosis membrane treatment method according to any one of claims 1 to 5, wherein the chelating inhibitor is added or increased at a frequency of once / day to once / week. A reverse osmosis membrane for separating treated water into permeate and concentrated water;
A chelating agent addition unit for adding a chelating agent to the water to be treated;
The chelating agent addition unit is controlled so that the chelating agent is intermittently added to the water to be treated, or the chelating agent is continuously added to the water to be treated to increase the amount of the addition intermittently. A control unit;
A reverse osmosis membrane treatment apparatus.

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