JP2018047406A - Blocking rate improver of reverse osmosis membrane, and blocking rate improvement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blocking rate improver of a RO membrane capable of improving a blocking rate, especially a boron removal rate, without lowering greatly a permeation flux; and to provide a blocking rate improvement method using the blocking rate improver.SOLUTION: A blocking rate improver of a reverse osmosis membrane contains pyrogallol and/or a pyrogallol derivative having a molecular weight below 500. As the pyrogallol derivative, gallic ester having a molecular weight below 300 is especially preferable. In a blocking rate improvement method of the reverse osmosis membrane, the reverse osmosis membrane is processed by the blocking rate improver of the reverse osmosis membrane.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a blocking rate improver that can effectively improve the blocking rate of a reverse osmosis membrane (RO) membrane, particularly an aromatic polyamide-based RO membrane. In view of being used as water, the present invention relates to a RO membrane rejection rate improver, which ensures high desalination rate and improves boron removal rate without significantly reducing the amount of permeate. The present invention also relates to a reverse osmosis membrane rejection rate improving method using the reverse osmosis membrane rejection rate improving agent and a water treatment method using the reverse osmosis membrane subjected to the rejection rate improving process.

  Currently, desalination of seawater and brackish water and water recovery are performed using RO membrane systems in order to make up for the shortage of water supply worldwide. Seawater desalination is used in areas where river water, lake water, or groundwater is not available, such as the Middle East and remote islands, but seawater contains 5-10 mg / L of boron, and WHO drinking water quality guidelines The fourth edition stipulates that the boron concentration be 2.4 mg / L or less. The boron standard was 0.5 mg / L or less in the third edition. According to domestic tap water standards, the boron concentration is 1 mg / L or less.

  Boron in sea water exists mainly in the form of boric acid, but it is hardly dissociated in the neutral region and its molecular weight is as small as 62, so it is difficult to remove with RO membrane. For this reason, the RO membrane is provided in two stages in series, and after the boron concentration is reduced to about 1 to 2 mg / L with the first RO membrane, the pH is increased and boron is further reduced with the second RO membrane. Has been made. Increasing the pH of the second stage RO membrane water supply leads to an increase in processing costs and scale generation risk.

For these reasons, seawater desalination RO membranes are required to improve the boron removal rate as well as the desalination rate.
Even in the ultrapure water production process, if the desalting rate and boron removal rate of the RO membrane are improved, the load on the ion exchange resin and the electric regenerative pure water device downstream of the RO membrane will be reduced, and the processing cost will be reduced. Can do.

On the other hand, in the RO membrane system, in order to suppress biofouling, addition of oxidants such as chlorine (sodium hypochlorite) and hydrogen peroxide to raw water (water to be treated for RO membrane) in the pretreatment process Has been done.
However, since these oxidants have a strong oxidative decomposition action, if these oxidants are added and the raw water is supplied to the RO membrane with insufficient reduction treatment, the RO membrane will deteriorate. It has been known.
In addition, in order to decompose the oxidizing agent in the raw water, a reducing agent such as sodium bisulfite is often added to the raw water and supplied to the RO membrane, but in a reducing environment where sodium bisulfite is excessively added. It is also known that when metals such as Cu and Co coexist in the raw water, the RO membrane deteriorates and the rejection rate decreases (Patent Document 1, Non-Patent Document 1).

  Conventionally, the following methods have been proposed as methods for improving the RO membrane rejection rate.

  Patent Document 2: A method of improving the RO membrane rejection by attaching an anionic or cationic polymer compound to the surface. This method can improve the desalting rate, but it is difficult to improve the removal rate of solutes with low chargeability such as boron.

  Patent Document 3: Nonionic surfactant is brought into contact with and attached to a nanofiltration membrane or reverse osmosis membrane having anion charge, whose permeation flux has increased due to deterioration. A method of reducing membrane contamination and permeated water quality deterioration by reducing it to the range of +20 to -20% at the start of use. The nonionic surfactant used here is known as a membrane contaminant, and there is a risk of greatly reducing the permeation flux when applied to an undegraded RO membrane.

  Patent Document 4: A method of improving the RO membrane rejection by attaching a compound having a polyalkylene glycol chain to the surface. Although this method can improve the desalination rate, it is difficult to improve the boron removal rate.

  Non-Patent Document 2: A method of improving the desalination rate by attaching tannic acid or the like to a deteriorated film. It cannot be said that the improvement effect of the rejection rate by this method is large. For example, the permeated water conductivity of ES20 (manufactured by Nitto Denko) and SUL-G20F (manufactured by Toray Industries), which are deteriorated RO membranes, are measured before and after the treatment. They are 82% → 88% and 92% → 94%, respectively, and the rejection rate cannot be increased until the solute concentration of the permeated water is halved.

  Non-Patent Document 3: A method of improving the RO membrane rejection by adding polyvinyl methyl ether (PVME) to tannic acid. Although this method can improve the desalination rate, no study has been made on improving the boron removal rate.

JP-A-7-308671 JP 2006-110520 A JP 2008-86945 A JP 2007-289922 A

Fujiwara et al., Desalination, Vol.96 (1994), 431-439 Sato, Tamura, Chemical Engineering, Vol.34 (2008), 493-498 S.T.Mitrouli, A.J.Karabelas, N.P.Isaias, D.C.Sioutopoulos, and A.S.Al Rammah, Reverse Osmosis Membrane Treatment Improves Salt-Rejection Performance, IDA Journal I Second Quarter 2010, p22-34

The above prior art has the following problems.
(1) The recovery and improvement of desalination rate is the main, and improvement of boron removal rate has not been studied.
(2) The effect of improving the rejection rate is small.
(3) The permeation flux is greatly reduced.

  The present invention solves these problems, and an RO membrane rejection rate improver that can improve the rejection rate, particularly the boron removal rate, without significantly reducing the permeation flux, and this rejection rate improver. An object of the present invention is to provide a method for improving the rejection rate using the.

  As a result of intensive studies to solve the above problems, the present inventors have found that pyrogallol or a low molecular weight pyrogallol derivative can solve the above problems, and have completed the present invention.

  That is, the gist of the present invention is as follows.

[1] A reverse osmosis membrane rejection rate improver comprising pyrogallol and / or a pyrogallol derivative having a molecular weight of less than 500.

[2] The reverse osmosis membrane rejection rate improver according to [1], comprising at least the pyrogallol derivative, wherein the pyrogallol derivative has a molecular weight of less than 300.

[3] The reverse osmosis membrane rejection rate improver according to [1] or [2], which contains at least the pyrogallol derivative, and the pyrogallol derivative is a gallic acid ester.

[4] The reverse osmosis membrane rejection rate improver according to any one of [1] to [3], wherein the reverse osmosis membrane is a polyamide-based reverse osmosis membrane.

[5] The reverse osmosis membrane rejection improving agent according to any one of [1] to [4], wherein the reverse osmosis membrane is a reverse osmosis membrane for seawater desalination.

[6] A reverse osmosis membrane rejection rate improving method comprising treating a reverse osmosis membrane with the reverse osmosis membrane rejection rate improving agent according to any one of [1] to [5].

[7] A water treatment method characterized by using a reverse osmosis membrane treated by the inhibition rate improving method according to [6].

According to the RO membrane rejection rate improver of the present invention, the rejection rate, particularly the boron removal rate, can be improved without greatly reducing the permeation flux.
According to the present invention, the following effects can be industrially obtained by improving the RO membrane rejection rate, particularly the boron removal rate.
That is, conventionally, when producing drinking water by desalination of seawater, a process such as assembling a multi-stage RO to raise the pH of the second stage RO supply water has been required. This process can be reduced to a lower cost. Also in the ultrapure water production process, the RO membrane rejection rate can be improved, reducing the load on the ion exchange resin and the electric regenerative pure water device in the subsequent stage of the RO membrane, thereby reducing the processing cost.

It is a schematic diagram which shows the flat film test apparatus used by the test example.

  Hereinafter, embodiments of the present invention will be described in detail.

[mechanism]
The examination process that the inventor has conceived of the present invention is as follows.

(1) In order to enhance the removal effect of uncharged low molecules to which charge repulsion such as boron cannot be applied, the present inventor adsorbs low molecular substances in the gaps of the dense layer of the RO membrane, and opens the gaps. I thought it was necessary to make it smaller.
(2) As described in Non-Patent Documents 2 and 3, tannic acid is known to have an effect of improving the desalination rate, and is considered to be a substance having a high affinity with the RO membrane. However, since tannic acid has a high molecular weight of 500 or more, it is difficult to adsorb in the gap between the dense layers of the RO membrane. As a result, it is difficult to improve the removal rate of uncharged small molecules such as boron.
(3) Therefore, by using the low molecular weight constituting the tannic acid as the low molecular weight adsorbing material, the low molecular weight material with high affinity to the RO membrane is adsorbed in the gap of the dense layer of the membrane, It was hypothesized that the effect of removing small non-charged molecules such as boron can be increased by reducing the size.
(4) Based on this hypothesis, the present inventor focused on the pyrogallol skeleton in which three hydroxy groups were added to the benzene ring as a component of tannic acid that has increased affinity for the membrane. It has been found that by adsorbing to the RO membrane, there is an effect of improving the desalting rate, and further, not only the desalting rate but also the boron removal rate can be improved.

  The structural formulas of the types of tannic acid (hydrolyzed type and condensed type) and the bilgarol structure constituting it are shown below.

  Structural formulas of pyrogallol and typical pyrogallol derivatives used in the present invention are shown below. Examples of pyrogallol derivatives include methyl gallate (MW: 184) and ethyl gallate (MW: 198) in which the propyl group of propyl gallate shown below is replaced with a methyl group, an ethyl group, a butyl group, an octyl group, and a lauryl group, respectively. ), Butyl gallate (MW: 226), octyl gallate (MW: 282), gallic acid alkyl esters such as lauryl gallate (MW: 338).

  In addition, catechol and catechol derivatives in which two hydroxy groups are added to the benzene ring represented by the following structural formula are also low molecular weight organic compounds having a high affinity for RO membranes, and an improvement in blocking rate can be obtained. The effect is low compared to pyrogallol and its derivatives.

The mechanism for improving the rejection rate and the boron removal rate according to the present invention is as follows.
(1) Tannic acid has an effect of improving the desalination rate and has a high affinity for the membrane.
(2) Three hydroxy groups are added to pyrogallol constituting tannic acid, which increases the affinity for the membrane.
(3) Since tannic acid is a substance having a molecular weight of 500 or more, it is difficult to adsorb in the gap between the dense layers of the film. Thus, the polymer gap in the film can be filled.
(4) As a result, not only the desalting rate but also the boron removal rate can be improved.

[Rejection rate improver]
The RO membrane rejection rate improver of the present invention is characterized by containing pyrogallol (molecular weight: 126) and / or a pyrogallol derivative having a molecular weight of less than 500.

  The pyrogallol derivative having a molecular weight of less than 500 is not particularly limited, but the aforementioned gallic acid (molecular weight: 170), methyl gallate (molecular weight: 184), ethyl gallate (molecular weight: 198), propyl gallate (molecular weight: 212). ), Butyl gallate (molecular weight: 226), octyl gallate (molecular weight: 282), gallic acid alkyl esters such as lauryl gallate (molecular weight: 338) (the carbon number of the alkyl group is preferably 1-12), epigallo Catechin (molecular weight: 306), epigallocatechin gallate (molecular weight: 458), methyl 3,4,5-trimethoxybenzoate (molecular weight: 226) and the like, among these, particularly affinity for RO membranes, From the standpoint of improving the desalination rate and improving the boron removal rate, pyrogallol or a pyrogallow with a molecular weight of less than 300 Derivatives are preferred, in particular, gallic acid esters are preferred.

  These pyrogallol and pyrogallol derivatives may be used alone or in combination of two or more.

[Prevention rate improvement method]
The RO membrane rejection rate improving method of the present invention is to perform the RO membrane rejection rate improving treatment using the rejection rate improving agent of the present invention. Specifically, the RO membrane aqueous solution of the rejection rate improving agent of the present invention is applied to the RO membrane. This is a method of improving the desalination rate of the deteriorated RO membrane and improving the boron removal rate by passing water. Hereinafter, the aqueous solution of the blocking rate improver that passes through the RO membrane for the RO membrane blocking rate improving process is referred to as “blocking rate improving treated water”.

  In the rejection rate improving method of the present invention, the concentration of the aforementioned pyrogallol and / or pyrogallol derivative, which is an active ingredient of the rejection rate improving agent in the rejection rate improving treated water, is preferably 0.01 to 100 mg / L, 0 More preferably, it is 1-10 mg / L. If the concentration of the active ingredient in the treatment rate improvement treated water is lower than the lower limit, a sufficient improvement effect of the rejection rate cannot be obtained. If the concentration is higher than the upper limit, the permeation flux decreases greatly, and the treatment cost also increases. To do.

  Moreover, it is preferable from a viewpoint of the adsorptivity of a rejection rate improving agent that pH of the rejection rate improvement process water is about 5-10.

  In addition, to the rejection rate improving treated water, an inorganic electrolyte such as sodium chloride (NaCl), a neutral organic substance such as isopropyl alcohol and glucose, a low molecular polymer such as polymaleic acid, and the like may be added as a tracer. The treatment effect can be confirmed by analyzing the degree of permeation of salt and glucose into the permeated water of the RO membrane.

  If the water supply pressure when the treated water with improved rejection rate is passed through the RO membrane is excessively high, the adsorption to the membrane gap proceeds too much, and if it is too low, the adsorption to the membrane gap does not advance. It is preferably 20 to 150%, particularly 50 to 130% of the normal operating pressure. When the RO membrane is an ultra-low pressure membrane, the inlet pressure of the apparatus is preferably 0.1 to 1.0 MPa. When the RO membrane is a low-pressure membrane, the inlet pressure of the apparatus is preferably 0.1 to 2.0 MPa. When the RO membrane is a seawater desalination membrane, the inlet pressure of the apparatus is preferably 0.1 to 7.0 MPa.

The linear velocity of RO membrane permeated water during the rejection improvement process is related to pressure, water temperature, membrane shape, and the like, but is preferably a permeation flux of 0.1 to ⁵ m ³ / (m ² · d). The reason is that, like the feed water pressure, if the pressure is excessively high, the adsorption proceeds too much, and if the pressure is excessively low, the contact efficiency to the membrane gap deteriorates.

  Moreover, the water temperature of the rejection improvement processing water at the time of rejection improvement processing is normal temperature, for example, about 10-35 degreeC is preferable. If the water temperature is too low, the amount of permeated water is lowered and the contact efficiency is deteriorated. If the temperature of the water for improving the rejection rate is too high, the membrane material may be denatured.

  It is preferable that the time for passing the treated water for improving the rejection rate is a time for which the pyrogallol and / or the pyrogallol derivative, which is an active ingredient, sufficiently permeate through the RO membrane. When the RO membrane apparatus is not operated in a steady state, it is preferable to pass water for about 0.5 to 500 hours, particularly about 1 to 150 hours, when the treated water with improved rejection rate is passed. If the water passage time is excessively short, the treatment is terminated without sufficiently fixing the active ingredient, and the attached active ingredient may be peeled off.

  The rejection rate improvement process may be performed during the steady operation of the RO membrane device, for example, by adding an aqueous solution prepared from the rejection rate improvement treatment agent to the RO water supply during the steady operation of the RO membrane device. The time for adding the aqueous solution of the rejection improving agent to the RO water supply is preferably about 0.5 to 500 hours, but the aqueous solution of the rejection improving agent may be constantly added to the RO water supply.

  When the RO membrane device is operated for a long time and the membrane contamination occurs and the permeation flux is reduced, the rejection rate improving process may be performed after the membrane cleaning.

  Examples of the membrane cleaning agent used in this case include mineral acids such as hydrochloric acid, nitric acid and sulfuric acid, and organic acids such as citric acid and oxalic acid. Examples of the alkali cleaning include sodium hydroxide and potassium hydroxide. In general, the pH is about 2 for acid cleaning and about 12 for alkali cleaning.

[RO membrane]
In the present invention, examples of the membrane structure of the RO membrane to be subjected to the rejection improvement processing include polymer membranes such as asymmetric membranes and composite membranes. Examples of the RO membrane material include aromatic polyamides, aliphatic polyamides, polyamide materials such as composite materials thereof, and cellulose materials such as cellulose acetate. Among these, the RO membrane made of an aromatic polyamide material has high affinity with the blocking rate improver of the present invention, and therefore the blocking rate improver and blocking rate improving method of the present invention are particularly preferably applied. Can do.

  There is no restriction | limiting in particular in the form of RO membrane module, For example, a tubular membrane module, a plane membrane module, a spiral membrane module, a hollow fiber membrane module etc. can be mentioned.

  In addition, this invention may be applied to a new RO membrane, and may be applied to an RO membrane having a reduced rejection rate due to use.

[Water treatment method]
The water treatment method of the present invention uses the RO membrane that has been subjected to the rejection rate improvement treatment by the rejection rate improvement method of the present invention, and is highly discharged in the electronic device manufacturing field, semiconductor manufacturing field, and other various industrial fields. Effectively applied to water treatment for recovery and reuse of wastewater containing TOC or low-concentration TOC, desalination of seawater and brine, ultrapure water production from industrial water and city water, and water treatment in other fields .

  In particular, according to the present invention, not only the desalination rate of the RO membrane but also the boron removal rate can be improved, so the water treatment method of the present invention is effective for seawater desalination processes where boron removal is important. Applied.

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

In the following test examples, the flat membrane test apparatus shown in FIG. 1 was used as the test apparatus.
This flat membrane test apparatus is provided with a flat membrane cell 2 at an intermediate position in the height direction of a cylindrical container 1 having a bottom and a lid, and the inside of the container is divided into a raw water chamber 1A and a permeated water chamber 1B, and the container 1 is divided into a stirrer. 3, water to be treated is supplied to the raw water chamber 1 </ b> A via the pipe 11 by the pump 4, and the stirrer 5 in the container 1 is rotated to stir the raw water chamber 1 </ b> A so that the permeated water passes through the permeated water. While taking out from the chamber 1B through the pipe 12, the concentrated water is taken out from the raw water chamber 1A through the pipe 13. The concentrated water outlet pipe 13 is provided with a pressure gauge 6 and an opening / closing valve 7.

[Test Example I]
Using the following RO membrane and the flat membrane test apparatus shown in FIG. 1, the feed water (1) was passed under the following operating conditions, and then the feed water (2) was passed (the test water of the feed water (2) was passed. Water time is 4.5 hours).

RO membrane: Aromatic polyamide ultra-low pressure RO membrane "ES20" manufactured by Nitto Denko Corporation
Feed water (1) (blank): An aqueous solution in which boric acid (Kishida Chemical) was added to pure water so that the boron concentration was 5 mg / L to pH 6.5. Feed water (2) (test water): blank A 10 mg / L additive was added to the aqueous solution to adjust the pH to 6.5. Operating conditions: Permeation flux 1 m ³ / (m ² · d), recovery rate 80%, temperature 24 ° C. ± 2 ° C.

From the above water flow test, the boron removal rate, the decrease rate of the boron permeability, and the permeation flux ratio were determined by the following formulas (1) to (4).
Boron permeability = boron concentration in permeated water / boron concentration in concentrated water (1)
Boron removal rate = 1-boron permeability (2)
Decrease rate of boron permeability = 1-boron permeability of test water / boron permeability of blank (3)
Permeation flux ratio = blank operating pressure / test water operating pressure (4)

<Additives>
The following were used as the additive in each case.
Comparative Example I-1: Catechol (Molecular weight 110, manufactured by Kishida Chemical Co., Ltd.)
Comparative Example I-2: Chlorogenic acid (molecular weight 354, manufactured by Tokyo Chemical Industry Co., Ltd.)
Example I-1: pyrogallol (molecular weight 126, manufactured by Wako Pure Chemical Industries, Ltd.)
Example I-2: Propyl gallate (molecular weight 212, manufactured by Kishida Chemical Co., Ltd.)
Example I-3: Ethyl gallate (molecular weight 198, manufactured by Tokyo Chemical Industry Co., Ltd.)
Example I-4: Methyl gallate (molecular weight 184, manufactured by Tokyo Chemical Industry Co., Ltd.)
Example I-5: Methyl 3,4,5-trimethoxybenzoate (molecular weight 226, manufactured by Wako Pure Chemical Industries, Ltd.)
Example I-6: Epigallocatechin gallate (molecular weight 458, manufactured by Wako Pure Chemical Industries, Ltd.)

Table 1 shows the test results.
As is apparent from Table 1, in the examples, the decrease rate of the boron permeability exceeds 0.1. On the other hand, the permeation flux ratio can maintain 0.8 or more.

[Test Example II]
Using the following RO membrane and the flat membrane test apparatus shown in FIG. 1, the feed water (1) was passed under the following operating conditions, and then the feed water (2) was passed (the test water of the feed water (2) was passed. Water time is 1 hour).

RO membrane: Toray Industries aromatic polyamide seawater desalination RO membrane "TM820V"
Feed water (1) (blank): An aqueous solution to which pH is 8 by adding boric acid to pure water so that the boron concentration is 5 mg / L and adding 32 g / L NaCl (Kishida Chemical). 2) (Test water): Aqueous solution in which 10 mg / L of added drug was added to the blank to adjust the pH to 8 Operating conditions: Operating pressure 5.5 MPa, temperature 24 ° C. ± 2 ° C.

In the same manner as in Test Example I, the boron removal rate and the decrease rate of the boron permeability were determined from the above formulas (1) to (3). The permeation flux ratio was determined by the following equation (5).
Permeation flux ratio = test water permeation flux / blank permeation flux (5)

<Additives>
The following were used as the additive in each case.
Comparative Example II-1: Catechin (molecular weight 110, manufactured by Sigma-Aldrich)
Comparative Example II-2: Ploidy tannin (molecular weight of 500 or more, manufactured by Fuji Chemical Industry Co., Ltd.)
Comparative Example II-3: Mimosatanine (molecular weight of 500 or more, manufactured by Kawamura Tsusho)
Example II-1: Propyl gallate (molecular weight 212, manufactured by Kishida Chemical Co., Ltd.)

Table 2 shows the test results.
As is clear from Table 2, in the examples, the decrease rate of the boron permeability exceeds 0.2. On the other hand, the permeation flux ratio can also be maintained at 0.95 or more.

[Test Example III]
Using the following RO membrane and the flat membrane test apparatus shown in FIG. 1, the feed water (1) was passed under the following operating conditions, and then the feed water (2) was passed (the test water of the feed water (2) was passed. Water time is 2 hours).

RO membrane: Aromatic polyamide-based seawater desalination RO membrane “SWC5-MAX” manufactured by Nitto Denko Corporation
Feed water (1) (blank): An aqueous solution to which pH is 8 by adding boric acid to pure water so that the boron concentration is 5 mg / L and adding 32 g / L NaCl (Kishida Chemical). 2) (Test water): Aqueous solution in which 2 mg / L of added drug was added to the blank to adjust the pH to 8 Operating conditions: Operating pressure 5.5 MPa, temperature 24 ° C. ± 2 ° C.

From the above water flow test, the boron removal rate and the reduction rate of the transmittance were obtained from the formulas (1) to (3) in the same manner as in Test Example I. The permeation flux ratio was determined from Equation (5) in the same manner as in Test Example II. Moreover, the removal rate of NaCl and the decrease rate of the transmittance were obtained by the following formulas (6) to (8).
NaCl permeability = NaCl concentration in permeated water / NaCl concentration in concentrated water (6)
NaCl removal rate = 1-NaCl permeability (7)
Decrease rate of NaCl permeability = 1-NaCl permeability of test water / NaCl permeability of blank
... (8)

<Additives>
The following were used as the additive in each case.
Example III-1: Propyl gallate (molecular weight 212, manufactured by Kishida Chemical Co., Ltd.)
Example III-2: Butyl gallate (molecular weight 226, manufactured by Wako Pure Chemical Industries, Ltd.)

Table 3 shows the test results.
As can be seen from Table 3, even when 2 mg / L of propyl gallate or butyl gallate was added, the removal rate of boron and NaCl was improved, and the permeation flux decreased slightly.

1 container 1A raw water chamber 1B permeate water chamber 2 flat membrane cell 3 stirrer

Claims (7)

  A reverse osmosis membrane blocking rate improver comprising pyrogallol and / or a pyrogallol derivative having a molecular weight of less than 500.   The reverse osmosis membrane blocking rate improver according to claim 1, comprising at least the pyrogallol derivative, wherein the pyrogallol derivative has a molecular weight of less than 300.   The inhibitor of a reverse osmosis membrane according to claim 1 or 2, wherein the pyrogallol derivative contains at least the pyrogallol derivative, and the pyrogallol derivative is a gallic acid ester.   The reverse osmosis membrane blocking rate improver according to any one of claims 1 to 3, wherein the reverse osmosis membrane is a polyamide-based reverse osmosis membrane.   The reverse osmosis membrane blocking rate improver according to any one of claims 1 to 4, wherein the reverse osmosis membrane is a reverse osmosis membrane for seawater desalination.   A reverse osmosis membrane rejection rate improving method comprising treating a reverse osmosis membrane with the reverse osmosis membrane rejection rate improving agent according to any one of claims 1 to 5.   A water treatment method using a reverse osmosis membrane treated by the inhibition rate improving method according to claim 6.

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