WO2018158943A1 - Degradation inhibitor for reverse osmosis membrane and water treatment method - Google Patents

Abstract

The present invention makes it possible to effectively inhibit deterioration of a RO membrane occurring when the oxidation/reduction potential of supply water for the RO membrane is high or when oxidizing substances are included in supply water without lowering the effects of a halogen binding agent used for inhibiting RO membrane fouling. Provided is a degradation inhibitor for a reverse osmosis membrane that is added to supply water when the supply water in which the oxidation/reduction potential exceeds 300 mV or supply water that includes an oxidizing agent is supplied to the reverse osmosis membrane, wherein the degradation inhibitor includes urea and/or a urea derivative. Also provided is a water treatment method wherein reverse osmosis membrane treatment is performed by adding this degradation inhibitor for a reverse osmosis membrane to the supply water for the reverse osmosis membrane.

Description

Reverse osmosis membrane degradation inhibitor and water treatment method

In the present invention, the reverse osmosis (RO) membrane used in the water treatment field has reduced solute inhibition performance such as desalination rate due to the oxidizing substances present in the RO membrane feed water and substances that increase the redox potential. The present invention relates to an agent that is added to the supply water to suppress a decrease in the solute blocking performance of the RO membrane when there is a risk of it. The present invention also relates to a water treatment method for performing RO membrane treatment using this agent.

i) Separation and purification by RO membrane system is an energy-saving process for systems using evaporation and electrodialysis, and is widely used for desalination of seawater and brine, production of industrial water and ultrapure water, and recovery of wastewater. It has been. When the RO membrane is used, fouling occurs in which the RO membrane is contaminated with microorganisms and organic substances. As a countermeasure, hydrogen peroxide, a bonded halogen agent, or an oxidizing agent such as a halogen agent is used to suppress the growth of microorganisms that cause fouling and to decompose organic substances. A representative example of the bound halogen agent is a bound chlorine agent such as chloramine. A representative example of the halogen agent is sodium hypochlorite.
However, these oxidizing substances may cause deterioration of the RO membrane if the amount used is wrong, invalidation immediately before the RO membrane is insufficient, or heavy metals coexist in the supply water.

ii) A reducing agent is added to invalidate the oxidizing substance, but if a heavy metal coexists, even if the reducing agent is added, the oxidation-reduction potential may increase and the RO membrane may be deteriorated. Patent Document 1 describes that when sodium bisulfite is added for dechlorination, the presence of copper ions raises the oxidation-reduction potential and exceeds 300 mV.

iii) Patent Document 2 proposes a method of adding an oxidant as a method of invalidating the oxidizing substance. Patent Document 2 describes that an amino acid that is an oxidant erases a strong oxide without erasing the bonded halogen fungicide.
However, amino acids can eliminate bound halogen fungicides. In addition, there is a risk that amino acids themselves become nutrient sources for microorganisms.

Japanese Patent No. 3399636 Japanese Patent Laying-Open No. 2015-186773

The present invention suppresses the RO membrane deterioration without reducing the fouling suppression effect of the bonded halogen agent or the like when the RO membrane supply water may deteriorate the RO membrane. It is an object to provide an agent and a water treatment method for performing RO membrane treatment using this agent.

The present inventor has intensively studied a mechanism for suppressing the deterioration of the RO membrane, and found that the presence of urea in the RO supply water can suppress the deterioration of the RO membrane.

When a bound halogen agent is used to suppress fouling of the RO membrane, if a non-oxidizing agent such as an amino acid is used, the bound halogen agent is consumed and the function of suppressing fouling is reduced. If it is urea, the deterioration of the RO membrane can be suppressed without consuming the bound halogen agent.
The gist of the present invention is as follows.

[1] A reverse osmosis membrane deterioration inhibitor that is added to a reverse osmosis membrane when supplying supply water having an oxidation-reduction potential exceeding 300 mV to the reverse osmosis membrane, the reverse osmosis membrane containing urea and / or a urea derivative Degradation inhibitor.

[2] A reverse osmosis membrane deterioration inhibitor added to a reverse osmosis membrane when supplying water containing an oxidant to the reverse osmosis membrane, the reverse osmosis membrane deterioration inhibitor containing urea and / or a urea derivative .

[3] The reverse osmosis membrane deterioration inhibitor according to [1] or [2], wherein the supplied water contains at least one of hydrogen peroxide, halogen, stabilized halogen, and sulfite.

[4] The reverse osmosis membrane deterioration inhibitor according to any one of [1] to [3], wherein the reverse osmosis membrane is an aromatic polyamide-based reverse osmosis membrane.

[5] A water treatment method comprising performing reverse osmosis membrane treatment by adding the reverse osmosis membrane deterioration inhibitor according to any one of [1] to [4] to water supplied to the reverse osmosis membrane.

According to the present invention, when the redox potential of the RO membrane feed water is high or the oxidizing substance in the feed water without reducing the effect of the bonded halogen agent used for suppressing the fouling of the RO membrane. It is possible to effectively suppress the deterioration of the RO membrane caused when it is contained.

6 is a graph showing the change over time in free chlorine concentration and combined chlorine concentration after addition of a deterioration inhibitor in Example I-1 and Comparative Example I-1. 6 is a graph showing changes with time in the TOC concentration after addition of a deterioration inhibitor in Example I-1 and Comparative Example I-1. FIG. 3a is a schematic diagram showing the configuration of the flat membrane test apparatus used in Experiment II. FIG. 3b is a cross-sectional view showing the structure of the closed container of the flat membrane test apparatus. 2 is a graph showing the change over time in the desalting rate in Example II-1 and Comparative Examples II-1 and II-2. 2 is a graph showing the change over time in the desalting rate in Example III-1 and Comparative Example III-1.

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

Hereinafter, “urea and / or urea derivative” may be referred to as “urea (derivative)”.

[Action mechanism]
(1) Urea (derivatives), particularly urea (H ₂ N—CO—NH ₂ ) has a structure close to the amide bond of the aromatic polyamide RO membrane, and has a strong affinity for the amide bond portion. By adsorbing to the amide bond portion of the membrane, it is considered that the attack on the amide bond of the oxidizing substance in the oxidizing environment is prevented, and the amide bond cleavage is suppressed. Therefore, by being oxidized, it works differently from an oxidizable substance that reduces the oxidizable substance and reduces the influence of the oxidizable substance.

(2) Urea (derivatives), particularly urea, is a low carbon source and is structurally unlikely to decompose due to attack of oxidizing substances. For this reason, the bound halogen agent is hardly consumed, and the fouling suppression effect by the bound halogen agent is not lowered.

[RO membrane]
In the present invention, the RO membrane to be cleaned may be an aromatic polyamide RO membrane or a cellulose acetate RO membrane. The present invention is particularly effective in suppressing deterioration of the aromatic polyamide RO membrane in terms of the adsorption action of urea (derivative) to the amide bond portion of the aromatic polyamide RO membrane.

[Urea (derivative)]
The urea (derivative) used in the present invention is preferably a low molecular compound having a molecular weight of 300 or less. Urea (derivative) Examples of the urea derivative include those represented by the following general formula (I), specifically urea (H ₂ N—CO—NH ₂ ), biuret (H ₂ N—CO—NH—CO). —NH ₂ ), polyurea, others, semicarbazide, allantoin, citrulline, thiourea, thiosemicarbazide, thiourea derivatives and the like.

(R ¹ ) (R ² ) NC (O) —N (R ³ ) (R ⁴ ) (I)
(Wherein R ¹ , R ² , R ³ , and R ⁴ each independently represents a hydrogen atom, an alkyl group, an aryl group, or —R ⁵ CONH ₂ (wherein R ⁵ represents a single bond or an alkylene group) Represents an amidoacyl group having

Urea (derivative) may be used alone or in combination of two or more.

Of urea (derivatives), urea and biuret are preferable in terms of RO membrane protection effect, solubility, and availability, and urea is particularly preferable.

[Supply water]
The RO membrane supply water targeted in the present invention (hereinafter sometimes referred to as “RO supply water”) is:
(1) Redox potential (ORP) exceeds 300 mV (including substances that increase ORP)
Or (2) Supply water that may reduce the solute blocking performance such as the desalination rate of the RO membrane by passing water by containing an oxidizing agent (oxidizing substance).

The present invention is particularly effective for feed water having an ORP of 400 mV or higher and high RO membrane deterioration.

As such supply water, for example, water containing alkali metal ions and transition metal ions such as copper ions and manganese ions such as seawater is added with an oxidizing agent such as sodium hypochlorite to suppress fouling. Furthermore, there may be mentioned feed water (pH 5 to 9) to which a reducing agent such as sodium bisulfite is added for dechlorination.

Oxidizing agents contained in the feed water containing oxidizing agents include hydrogen peroxide, stabilizing halogens (bonded halogen agents), halogen oxo acids such as peracetic acid, percarbonate, sulfurous acid, hypochlorous acid and their salts (for example, , Alkali metal salts, alkaline earth metal salts), halogens such as chlorine, bromine and iodine, peroxides, and the like. Of these, hydrogen peroxide, halogen, stabilized halogen (bonded halogen agent), or one or more of sulfites are preferred. In particular, in order to effectively obtain the effect of the present invention that the fouling suppressing effect by the bonded halogen agent is not lowered, the bonded halogen agent is preferable.

Examples of the bonded halogen agent include bonded chlorine agents such as chloramine and monochlororosulmic acid.

The content of the oxidizing agent in the feed water is not particularly limited, but is about 0.01 to 1 mg / L for halogen and about 0.1 to 100 mg / L for stabilized halogen.

RO feed water preferably has a pH of 6 to 9 from the standpoint of maintaining the blocking performance and suppressing the scale.

In the present invention, urea (derivative) is added to the RO supply water that lowers the solute inhibition performance such as the desalination rate of the RO membrane to suppress the degradation of the solute inhibition performance. If the amount of urea (derivative) added to the RO supply water is too small, the effect of suppressing deterioration due to the addition of urea (derivative) cannot be sufficiently obtained. If the amount of urea (derivative) added to the RO supply water is too large, it may become a carbon source for microorganisms or may leak in a large amount to the RO permeate. The amount of urea (derivative) added is in the range of 0.01 to 100 mg / L, particularly 0.1 to 10 mg / L, and is appropriately set according to the degree of ORP of the RO supply water, the type and content of the oxidizing agent It is preferable to do.

The water treatment method of the present invention can be carried out according to a conventional method except that urea (derivative) is added to the RO supply water as an RO membrane deterioration inhibitor.
Addition of urea (derivative) to the RO supply water may be continuous or intermittent, but it is preferable to add continuously.

Hereinafter, the present invention will be described more specifically with reference to examples.

[Experiment I]
An experiment was conducted to investigate the non-consumability of chlorinating agents by the following procedures 1) to 3).

1) 0.9 mg / L of sulfamic acid was added to an aqueous solution of 500 mg / L sodium chloride and 20 mg / L sodium bicarbonate, and after adjusting the pH to 6.5 with hydrochloric acid and sodium hydroxide, the effective chlorine concentration was 1.75 mg. Sodium hypochlorite was added so as to be / L. Thereafter, manganese chloride (MnCl ₂ ) was added so that the manganese concentration was 0.6 mg / L, and copper chloride (CuCl ₂ ) was added so that the copper concentration was 0.02 mg / L. Simulated feed water (ORP 600 mV) was prepared by fine adjustment to pH 6.5 with sodium hydroxide.

2) Free chlorine concentration, combined chlorine concentration, and TOC of the simulated feed water were measured.

3) After the deterioration inhibitor was added to the simulated water supply, the free chlorine concentration, combined chlorine concentration, and TOC were measured over time.

Comparative Example I-1: The above 1) to 3) were performed using 1 mg / L of aspartic acid as a deterioration inhibitor.
Example I-1: 1 mg / L of urea was used as a deterioration inhibitor, and the above 1) to 3) were carried out.

Fig. 1 shows the changes over time in the free chlorine concentration and the combined chlorine concentration after the deterioration inhibitor was added. In Comparative Example I-1 to which aspartic acid was added, the free chlorine concentration was decreased, but the bound chlorine concentration was also decreased, indicating that the bound chlorine agent was consumed. On the other hand, in Example I-1 to which urea was added, both the free chlorine concentration and the combined chlorine concentration decreased slowly.

FIG. 2 shows the change with time in the TOC concentration after the addition of the deterioration inhibitor. This TOC concentration excludes the TOC concentration before adding the deterioration inhibitor as a blank. In Comparative Example I-1 to which aspartic acid was added, the initial TOC concentration was higher than that in Example I-1 to which urea was added, and decreased with time. This means that aspartic acid is decomposed by free chlorine or combined chlorine. In the case of urea, there is almost no change, and it can be seen that urea is hardly affected by free chlorine and bound chlorine.

[Experiment II]
An experiment was conducted to investigate the effect of suppressing deterioration by the following procedures 1) to 4).

1) 0.9 mg / L of sulfamic acid was added to an aqueous solution of 500 mg / L sodium chloride and 20 mg / L sodium bicarbonate, and the pH was adjusted to 6.5 with hydrochloric acid and sodium hydroxide. Thereafter, sodium hypochlorite was added so that the effective chlorine concentration was 1.75 mg / L. Thereafter, manganese chloride (MnCl ₂ ) was added so that the manganese concentration was 0.6 mg / L, and copper chloride (CuCl ₂ ) was added so that the copper concentration was 0.02 mg / L. Simulated feed water (ORP 600 mV) was prepared by fine adjustment to pH 6.5 with sodium hydroxide.

2) A deterioration inhibitor was added to the simulated supply water to obtain RO supply water.

3) FIG. RO treatment was performed using the flat membrane test apparatus shown to 3a, 3b. The RO membrane used was “ES20” manufactured by Nitto Denko Corporation, and the recovery rate was 80%.
In this flat membrane test apparatus, RO membrane supply water is supplied from a pipe 11 to a raw water chamber 1A below the flat membrane cell 2 in which the RO membrane of the sealed container 1 is set by a high-pressure pump 4. FIG. As shown in 3b, the sealed container 1 is composed of a lower case 1a on the raw water chamber 1A side and an upper case 1b on the permeate water chamber 1B side, and a flat membrane cell between the lower case 1a and the upper case 1b. 2 is fixed through an O-ring 8. The flat membrane cell 2 is configured such that the permeate side of the RO membrane 2A is supported by the porous support plate 2B. The raw water chamber 1 </ b> A below the flat membrane cell 2 is stirred by rotating the stirring bar 5 with a stirrer 3. The RO membrane permeated water is taken out from the pipe 12 through the permeated water chamber 1B on the upper side of the flat membrane cell 2. The concentrated water is taken out from the pipe 13. The pressure in the sealed container 1 is adjusted by a pressure gauge 6 provided in the water supply pipe 11 and a pressure adjusting valve 7 provided in the concentrated water outlet pipe 13.

4) The desalting rate was calculated by the following formula, and the change with time of the desalting rate was determined.
Desalination rate [-] = 1-conductivity of permeated water / conductivity of concentrated water

Comparative Example II-1: 1) to 4) were carried out without using a deterioration inhibitor.
Comparative Example II-2: 1 mg / L of aspartic acid was used as a deterioration inhibitor and 1) to 4) were carried out.
Example II-1: 1 mg / L of urea was used as a deterioration inhibitor, and 1) to 4) were carried out.

Fig. 5 shows the change over time in the desalting rate. In Comparative Example II-1 in which no deterioration inhibitor was used, the desalting rate was the lowest. In Comparative Example II-2 using aspartic acid as the deterioration inhibitor, the decrease in the desalting rate can be suppressed, but as shown in Experiment I, it is considered that bound chlorine is consumed. In Example II-1 using urea as a deterioration inhibitor, the decrease in the desalting rate was suppressed, and as shown in Experiment I, bound chlorine was not consumed. It is considered that the effect of suppressing the decrease in the desalination rate can be improved by changing the amount of urea added.

[Experiment III]
An experiment was conducted to investigate the effect of suppressing deterioration by the following procedures 1) to 4).

1) Sodium hypochlorite is added to an aqueous solution of sodium chloride 500 mg / L and sodium bicarbonate 20 mg / L so that the effective chlorine concentration is 100 mg / L, and the pH is adjusted to 6.5 with hydrochloric acid and sodium hydroxide. Thus, simulated supply water (ORP 900 mV) was prepared.

2) A deterioration inhibitor was added to the prepared simulated feed water to obtain RO feed water.

3) FIG. RO treatment was performed using the flat membrane test apparatus shown to 3a, 3b. The RO membrane used was “ES20” manufactured by Nitto Denko Corporation, and the recovery rate was 80%.

4) The desalting rate was calculated in the same manner as in Experiment II, and the change over time in the desalting rate was determined.

Comparative Example III-1: 1) to 4) were carried out without using a deterioration inhibitor.
Example III-1: 100 mg / L of urea was used as a deterioration inhibitor, and 1) to 4) were carried out.

Fig. 5 shows the change over time in the desalting rate. In Comparative Example III-1 in which no deterioration inhibitor is used, the desalination rate is greatly reduced over time, but in Example III-1 in which urea is used as the deterioration inhibitor, reduction in the desalination rate can be suppressed. .

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2016-035931 filed on Feb. 26, 2016, which is incorporated by reference in its entirety.

DESCRIPTION OF SYMBOLS 1 Container 2 Flat membrane cell 2A RO membrane 2B Porous support plate 3 Stirrer 4 High pressure pump 5 Stirrer 6 Pressure gauge 7 Pressure adjustment valve 8 O-ring

Claims (5)

A reverse osmosis membrane deterioration inhibitor added to a reverse osmosis membrane when supply water having a redox potential exceeding 300 mV is supplied to the reverse osmosis membrane, the reverse osmosis membrane degradation inhibitor containing urea and / or a urea derivative . A reverse osmosis membrane deterioration inhibitor added to a reverse osmosis membrane when supplying supply water containing an oxidizing agent to the reverse osmosis membrane, the reverse osmosis membrane degradation inhibitor containing urea and / or a urea derivative. 3. The reverse osmosis membrane deterioration inhibitor according to claim 1 or 2, wherein the supplied water contains at least one of hydrogen peroxide, halogen, stabilized halogen, and sulfite. 4. The reverse osmosis membrane deterioration inhibitor according to any one of claims 1 to 3, wherein the reverse osmosis membrane is an aromatic polyamide reverse osmosis membrane. 5. A water treatment method, wherein the reverse osmosis membrane deterioration inhibitor according to any one of claims 1 to 4 is added to water supplied to the reverse osmosis membrane to perform reverse osmosis membrane treatment.

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