Method for producing a scale-inhibiting agent for reverse osmosis membranes, scale-inhibiting agent for reverse osmosis membranes, and water treatment method

Abstract

Provided is a method for producing a slime-inhibiting additive for reverse osmosis membranes that contains iodide and inhibits the release of iodine. The method for producing a slime-inhibiting additive for reverse osmosis membranes of the present invention includes an addition step of adding iodide and an alkali agent to water having a free chlorine concentration of 0.2 mg / L or less.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a slime-inhibiting agent for reverse osmosis membranes, the slime-inhibiting agent for reverse osmosis membranes, and a water treatment method using the slime-inhibiting agent for reverse osmosis membranes. Background Technology

[0002] Reverse osmosis (RO) membrane treatment is widely used in processes such as pure water production, wastewater recycling, and seawater desalination. Its application has been particularly increasing in wastewater recycling, especially given the recent water scarcity. RO treatment typically involves pretreatment processes such as sand filtration and membrane filtration. In these pretreatment processes, chlorine-based oxidants such as hypochlorous acid can be used to inhibit sludge formation caused by microbial growth. However, if these oxidants flow into the RO membrane, their performance will significantly deteriorate. Therefore, a reducing agent is added to the feed water to decompose hypochlorous acid and other oxidants, thereby inhibiting membrane degradation.

[0003] However, if water with low inhibition of slime formation is supplied to the reverse osmosis membrane by adding a reducing agent, microorganisms will proliferate on the membrane surface and produce biofouling, sometimes leading to problems such as reduced permeate flow and increased supply pressure.

[0004] Therefore, currently, biofouling agents (sludge inhibitors) that do not easily cause membrane degradation are added to the feed water of reverse osmosis membranes containing reducing agents, such as chloramines, chlorosulfamic acid and other stabilizing chlorine compounds, and stabilizing hypobromoic acid compositions containing bromine oxidants such as bromine and sulfamic acid.

[0005] However, if the amount of reducing agent added is excessive, the bactericide will be reduced and consumed by the reducing agent, resulting in increased dosage and drug costs; if the amount of reducing agent added is too small, there is a problem of membrane deterioration due to residual hypochlorous acid, etc.

[0006] For example, Patent Document 1 describes a process in which sodium metabisulfite, as a reducing agent, is added to the water to be treated, which contains sodium hypochlorite, before the reverse osmosis membrane treatment, and then potassium iodide is added to generate iodine, thereby inhibiting contamination caused by microorganisms.

[0007] However, there is no clear record regarding the amount of potassium iodide required relative to hypochlorous acid, etc. If the amount of potassium iodide added is too small, the reverse osmosis membrane may deteriorate due to the inability to reduce hypochlorous acid, etc.; if the amount of potassium iodide added is excessive, the cost of the reagents will increase.

[0008] On the other hand, it is known that iodide aqueous solutions are oxidized upon contact with air, thereby releasing iodine. Iodine is sublimable and corrosive, therefore the containers for storing iodide aqueous solutions need to be made of expensive materials. Furthermore, iodine has oxidizing power; therefore, when using iodide aqueous solutions to reduce residual chlorine in treated water, the original reducing power is sometimes not achieved. Thus, it is necessary to suppress the release of iodine from iodide aqueous solutions.

[0009] Patent document 2 describes that, in an example, a 1N sodium hydroxide aqueous solution containing 5% by weight potassium iodide remained colorless for one week at room temperature.

[0010] In addition, Patent Document 3 describes that by adding an alkaline compound to a liquid selected from elemental iodine, a compound containing iodine, iodide ions, and ions containing iodine at a concentration of less than 10% by mass, the release of iodine into the air during evaporation and concentration can be suppressed.

[0011] However, the iodide aqueous solutions described in Patent Documents 2 and 3 do not sufficiently suppress iodine release. Therefore, there is a need for a water treatment agent composition that is an iodide aqueous solution that suppresses iodine release and is used for slime suppression in reverse osmosis membranes.

[0012] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 56-033009 Patent Document 2: Japanese Patent Application Publication No. 2010-271141 Patent Document 3: Japanese Patent Application Publication No. 2006-232662 Summary of the Invention

[0013] The technical problem that the invention aims to solve The purpose of this invention is to provide a method for manufacturing a slime-inhibiting agent for reverse osmosis membranes containing iodide and inhibiting the release of iodine, and the slime-inhibiting agent for reverse osmosis membranes.

[0014] In addition, the present invention aims to provide a water treatment method that, in the reverse osmosis membrane treatment of water containing at least one of chlorine-based oxidants and bromine-based oxidants, can suppress the deterioration of the reverse osmosis membrane while suppressing the formation of slime.

[0015] Technical solutions for solving technical problems This invention relates to a method for manufacturing a slime-inhibiting agent for reverse osmosis membranes, which includes an addition step of adding iodide and an alkali agent to water with a free chlorine concentration of less than 0.2 mg / L.

[0016] The present invention is a method for manufacturing a slime inhibitor for reverse osmosis membranes, comprising: a removal step, wherein free chlorine is removed from water with a free chlorine concentration exceeding 0.2 mg / L to reduce the free chlorine concentration to below 0.2 mg / L; and an addition step, wherein an iodide and an alkali are added to the water from which free chlorine has been removed.

[0017] This invention relates to a slime-inhibiting agent for reverse osmosis membranes, comprising iodide, alkali and water, wherein the free iodine concentration is below 0.1 mg / L.

[0018] In the above-mentioned slime-inhibiting agent for reverse osmosis membranes, the iodine ion concentration is preferably 3.8% by mass or more and less than 20% by mass.

[0019] In the above-mentioned slime-inhibiting agents for reverse osmosis membranes, a pH of 8 or higher is preferred.

[0020] This invention is a water treatment method comprising: a reverse osmosis membrane treatment step, wherein, for water to be treated containing at least one of a chlorine-based oxidant and a bromine-based oxidant, a reverse osmosis membrane is used to obtain concentrated water and permeate water, wherein the reverse osmosis membrane is provided with a slime-inhibiting agent such that iodine ions are present in the water to be treated in such a manner that 1 mol of iodine ions is 2 mol or more relative to the free chlorine and free bromine content of the water to be treated.

[0021] This invention is a water treatment method comprising: a membrane filtration treatment step, wherein the water to be treated, containing at least one of a chlorine-based oxidant and a bromine-based oxidant, is subjected to membrane filtration treatment using a separation membrane; and a reverse osmosis membrane treatment step, wherein the membrane-filtered water obtained in the above membrane filtration treatment step is used to obtain concentrated water and permeate water using a reverse osmosis membrane, wherein the reverse osmosis membrane is provided with a slime-inhibiting agent such that iodine ions are present in the water to be treated in such a manner that 1 mol of iodine ions is 2 mol or more relative to the free chlorine and free bromine content of the water to be treated in the above membrane filtration treatment step.

[0022] Invention Effects According to the present invention, a method for manufacturing a slime-inhibiting agent for reverse osmosis membranes containing iodide and inhibiting the release of iodine, and a slime-inhibiting agent for reverse osmosis membranes, are provided.

[0023] In addition, according to the present invention, a water treatment method can be provided that, in the reverse osmosis membrane treatment of water containing at least one of a chlorine-based oxidant and a bromine-based oxidant, can suppress the deterioration of the reverse osmosis membrane while suppressing the formation of slime. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating an example of a water treatment apparatus used to implement a water treatment method employing a slime-inhibiting agent for reverse osmosis membranes according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram illustrating another example of the composition of a water treatment apparatus for implementing a water treatment method using a slime-inhibiting agent for a reverse osmosis membrane according to an embodiment of the present invention.

[0026] Figure 3 This is a graph representing the reactivity in Example 4.

[0027] Figure 4 This is a graph showing the redox potential (ORP) of the products in Example 4, Reference Examples 3 and 4. Detailed Implementation

[0028] The following describes embodiments of the present invention. These embodiments are examples of implementing the present invention, and the present invention is not limited to these embodiments.

[0029] <Water Treatment Equipment and Methods> A schematic example of a water treatment apparatus for implementing a water treatment method using the slime-inhibiting agent for reverse osmosis membranes according to embodiments of the present invention is shown below. Figure 1 .

[0030] The water treatment apparatus 1 includes a reverse osmosis membrane unit 14 as a reverse osmosis membrane treatment unit. This unit uses a reverse osmosis membrane to obtain concentrated water and permeate water from the treated water containing at least one of a chlorine-based oxidant and a bromine-based oxidant. The water treatment apparatus 1 may also include a treated water tank 10 for storing the treated water. The water treatment apparatus 1 may also include a membrane filtration unit 12 upstream of the reverse osmosis membrane unit 14 as a membrane filtration treatment unit. This unit uses a separation membrane to perform membrane filtration treatment on the treated water containing at least one of a chlorine-based oxidant and a bromine-based oxidant.

[0031] exist Figure 1 In the water treatment apparatus 1, a treated water pipe 18 is connected to the treated water inlet of the treated water tank 10. The treated water outlet of the treated water tank 10 is connected to the treated water inlet of the membrane filtration device 12 via a treated water pipe 20. The membrane filtration treated water outlet of the membrane filtration device 12 is connected to the membrane filtration treated water inlet of the reverse osmosis membrane device 14 via a pump 16 and a membrane filtration treated water pipe 22. A permeate water pipe 24 is connected to the permeate outlet of the reverse osmosis membrane device 14, and a concentrate water pipe 26 is connected to the concentrate outlet. At least one of the following locations—before the pump 16 in the treated water pipe 18, the treated water tank 10, the treated water pipe 20, and the membrane filtration treated water pipe 22, and after the pump 16 in the membrane filtration treated water pipe 22—can be connected as a slime inhibitor addition unit for adding slime inhibitors for the reverse osmosis membrane. Figure 2As shown, a reducing agent addition pipe 30 can be connected to at least one of the treated water pipe 18, the treated water tank 10, the treated water pipe 20, and the membrane filtration treated water pipe 22 as a reducing agent addition unit.

[0032] The operation of the water treatment method and water treatment apparatus 1 involved in this embodiment will be described.

[0033] exist Figure 1 In the water treatment apparatus 1, treated water containing at least one of a chlorine-based oxidant and a bromine-based oxidant is stored in a treated water tank 10 as needed via treated water piping 18, and then conveyed to a membrane filtration apparatus 12 via treated water piping 20. In the membrane filtration apparatus 12, the treated water is subjected to membrane filtration treatment using a separation membrane (membrane filtration process). The membrane-filtered water obtained in the membrane filtration process is conveyed to a reverse osmosis membrane apparatus 14 via membrane-filtered water piping 22. Reverse osmosis membrane treatment is performed in the reverse osmosis membrane apparatus 14 (reverse osmosis membrane treatment process), wherein the membrane-filtered water is treated using a reverse osmosis membrane to obtain concentrated water and permeate. The permeate is discharged via permeate piping 24, and the concentrated water is discharged via concentrated water piping 26.

[0034] In the absence of a membrane filtration device 12 in the water treatment device 1, the water to be treated, containing at least one of a chlorine-based oxidant and a bromine-based oxidant, is fed to a reverse osmosis membrane device 14, where reverse osmosis membrane treatment (reverse osmosis membrane treatment process) is performed, wherein the water to be treated is treated using a reverse osmosis membrane to obtain concentrated water and permeate water.

[0035] In the water treatment method and water treatment apparatus 1 according to this embodiment, the water treatment apparatus 1 includes a membrane filtration device 12. During the membrane filtration treatment process, in the water to be treated in the membrane filtration treatment process containing at least one of a chlorine-based oxidant and a bromine-based oxidant, a slime inhibitor for reverse osmosis membranes is added through a slime inhibitor addition pipe 28 to achieve a free chlorine and free bromine content of 2 mol or more relative to 1 mol of the water to be treated (slime inhibitor addition process). If the water treatment apparatus 1 does not include a membrane filtration device 12, in the water to be treated in the reverse osmosis membrane treatment process containing at least one of a chlorine-based oxidant and a bromine-based oxidant, at least 2 mol of slime inhibitor is added through a slime inhibitor addition pipe 28 relative to 1 mol of the free chlorine and free bromine content of the water to be treated (slime inhibitor addition process). It should be noted that in this specification, "at least one of a chlorine-based oxidant and a bromine-based oxidant" is sometimes abbreviated as "chlorine-based oxidant, etc." It should be noted that at least one of the chlorine-based and bromine-based oxidants can be added before or after adding a slime-inhibiting agent to treated water that does not contain chlorine-based or bromine-based oxidants, and at least one of the chlorine-based and bromine-based oxidants can be added additionally before or after adding a slime-inhibiting agent to treated water that contains at least one of the chlorine-based and bromine-based oxidants. In this case, one or more oxidant addition pipes for adding at least one of the chlorine-based and bromine-based oxidants can be provided.

[0036] By adding a slime inhibitor for reverse osmosis membranes to the water being treated using reverse osmosis membranes containing chlorine-based oxidants, the chlorine-based oxidants and other substances that may cause reverse osmosis membrane degradation can be reduced. Through the chlorine-based oxidants, the slime inhibitor is oxidized into iodine, which has bactericidal properties, becoming a slime inhibitor that hardly degrades the reverse osmosis membrane and inhibits slime formation. Therefore, by adding a slime inhibitor for reverse osmosis membranes to the water being treated containing chlorine-based oxidants, the degradation of the reverse osmosis membrane and the formation of slime can be inhibited.

[0037] The location for adding a slime-inhibiting agent for reverse osmosis membranes to the treated water containing chlorine-based oxidants can be any of the following: the treated water piping 18, the treated water tank 10, the treated water piping 20 before the membrane filtration device 12, or the membrane filtration treated water piping 22 after the membrane filtration device 12. Considering the need to inhibit the deterioration of the membrane filtration device 12 using chlorine-based oxidants, the preferred location for adding the slime-inhibiting agent is the treated water in the membrane filtration process, i.e., the treated water tank 10 or the treated water piping 20 before the membrane filtration device 12.

[0038] As chlorine-based and bromine-based oxidants, any oxidant with a higher redox potential (ORP) than iodine is acceptable. Even a stabilized hypobromic acid composition containing chlorine or bromine-based oxidants such as bromine and aminosulfonic acid compounds can achieve the same effect. However, considering factors such as reaction rate, an oxidant that can be detected in the form of free chlorine is preferred. Examples of oxidants that can be detected in the form of free chlorine include hypochlorous acid, hypobromic acid, or their salts.

[0039] In this specification, the oxidizing power of the oxidant is expressed as total chlorine or free chlorine based on the DPD method. In this specification, "total chlorine" refers to the concentration determined by spectrophotometry using N,N-diethyl-p-phenylenediamine sulfate (DPD), as described in "JIS K 0120:2013, 33. Residual Chlorine". For example, 2.5 mL of 0.2 mol / L potassium dihydrogen phosphate solution is added to a 50 mL colorimetric tube, along with 0.5 g of DPD dilution powder (a powder obtained by crushing 1.0 g of N,N-diethyl-p-phenylenediamine sulfate and mixing it with 24 g of sodium sulfate), 0.5 g of potassium iodide, and an appropriate amount of sample. Water is added to the mark and dissolved, and the mixture is allowed to stand for approximately 3 minutes. Quantification is performed based on the absorbance near a wavelength of 510 nm (or 555 nm) for a pink to pink color development. Furthermore, in this specification, "free chlorine" refers to the oxidizing power of the oxidant determined by the above-mentioned "total chlorine" determination method without the addition of potassium iodide.

[0040] DPD is oxidized by oxidizing agents, such as chlorine, bromine, iodine, hydrogen peroxide, and ozone, which can be used as analytes. Chlorine that can be quantified as total chlorine includes all oxidizing forms such as hypochlorous acid, hypochlorite ions, chlorine, chloramine, dichloramine, and other bound chlorine. Similarly, all oxidizing forms of bromine and iodine can also be measured. Free chlorine that can be quantified as total chlorine is the form that can be measured without the addition of potassium iodide in the above-mentioned methods for determining total chlorine, such as hypochlorous acid, hypobromous acid, chlorine, bromine, and iodine.

[0041] Furthermore, "total chlorine" can be converted to "total iodine". Specifically, the conversion is based on the molecular weight of chlorine and the molecular weight of iodine. That is, "total chlorine" × (253.8 / 70.9) ≒ "total chlorine" × 3.58 = "total iodine". "Free chlorine" can also be converted to "free iodine".

[0042] In the process of adding slime inhibitors to the treated water, the method of adding the slime inhibitor for reverse osmosis membranes to the treated water can be either continuous addition of the slime inhibitor or intermittent addition, which involves setting periods during which the slime inhibitor is added and periods during which it is not added. From the perspective of chemical costs, intermittent addition is preferred.

[0043] In the process of adding slime inhibitors, it is preferable to add them intermittently for more than 10 seconds and less than 12 hours during the addition period, and for more than 5 seconds and less than 320 hours during the no-addition period.

[0044] Alternatively, it is preferable to add a reducing agent during this additive-free period. For example... Figure 2 As shown, the reducing agent is added to the treated water in the membrane filtration process or the treated water (membrane-filtered treated water) in the reverse osmosis membrane treatment process via the reducing agent addition pipe 30 (reducing agent addition step). During the no-addition period, the reducing agent can be added to the treated water via the treated water pipe 18, the treated water tank 10, the treated water pipe 20 before the membrane filtration device 12, or the membrane-filtered treated water pipe 22 after the membrane filtration device 12. The reducing agent can be added before or after the slime-inhibiting agent addition, but preferably before the slime-inhibiting agent addition.

[0045] Without the addition of a reducing agent during the non-addition period, the reverse osmosis membrane may sometimes deteriorate. Examples of reducing agents include sulfites such as sodium sulfite, bisulfites such as sodium bisulfite, thiosulfates such as sodium thiosulfate, hydrazine, hydroxylamine, and hydrogen sulfide. From a safety perspective, sulfites, bisulfites, and thiosulfates are preferred, with thiosulfates being more preferred.

[0046] In the case of sulfites and bisulfites, as shown in equations (1) and (2) below, free iodine reacts with an equimol of the reducing agent, while in the case of thiosulfates, as shown in equation (3) below, free iodine reacts with a 1 / 2mol of the reducing agent. In the case of adding and retaining a reducing agent during the period without addition, the reducing agent reduces the free iodine generated during the addition period. However, by using thiosulfates, the reduction is more effectively suppressed compared to sulfites and bisulfites.

[0047] I₂ + SO₃ 2- +H₂O→H₂SO₄+2I - Equation (1) I₂ + HSO₃ - +H₂O→2I - +3H + +SO4 2-Equation (2) I₂ + 2S₂O₃ 2- →2I - +S4O6 2- Equation (3) The amount of iodide ions added is preferably controlled so that the oxidation-reduction potential (ORP) of the water treated by the reverse osmosis membrane reaches 800 mV or less after adding 2 mol or more of iodide ions per mol of free chlorine and free bromine relative to the amount of chlorine-based oxidants or the like in the treated water. This ORP is preferably 750 mV or less, more preferably 700 mV or less. If the ORP exceeds 800 mV, it can sometimes lead to deterioration of the reverse osmosis membrane. The amount of iodide ions added to the treated water can be easily managed by pH and ORP. For example, when iodide ions are added as a slime-inhibiting agent for reverse osmosis membranes containing water and iodides, the amount of iodide ions added to the treated water can be managed by pH and ORP even if the amount of free chlorine in the treated water is unstable.

[0048] As a slime inhibitor added to the treated water for reverse osmosis membranes, it is sufficient to add the slime inhibitor in such a way that the amount of iodine ions reaches more than 2 mol per mol of free chlorine and free bromine. If the amount of slime inhibitor added to the treated water is less than 2 mol per mol of free chlorine and free bromine, the reverse osmosis membrane may deteriorate.

[0049] As a slime-inhibiting agent for reverse osmosis membranes, it can be added in the form of solid iodides such as sodium iodide or potassium iodide, or in the form of an aqueous solution pre-dissolved in sodium iodide or potassium iodide, or in the form of an aqueous solution containing free iodine. From the viewpoint of processability, it is preferable to add it in the form of an aqueous solution; from the viewpoint of storageability, it is more preferable to add it in the form of an aqueous solution that does not contain free iodine.

[0050] <Slime Inhibiting Agent for Reverse Osmosis Membranes> The reverse osmosis membrane slime inhibitor used in the water treatment method of this embodiment is a composition containing iodide, alkali and water, and having a free iodine concentration of 0.1 mg / L or less.

[0051] The slime-inhibiting agent for reverse osmosis membranes involved in this embodiment contains iodide, alkali and water, and the concentration of iodide ions in the slime-inhibiting agent for reverse osmosis membranes is preferably 3.8% or more and less than 20%, and the pH of the slime-inhibiting agent for reverse osmosis membranes is preferably 8 or more.

[0052] The slime-inhibiting agent for reverse osmosis membranes involved in this embodiment is a composition containing iodide with a free iodine concentration of 0.1 mg / L or less, and the free iodine is inhibited. The free iodine concentration of the slime-inhibiting agent for reverse osmosis membranes is preferably 0.05 mg / L or less, and the lower the better. If the free iodine concentration of the slime-inhibiting agent for reverse osmosis membranes exceeds 0.1 mg / L, attention should be paid to the material of the tank used and the piping used for adding it.

[0053] The color of the slime-inhibiting agent for reverse osmosis membranes involved in this embodiment is, for example, 5 degrees or less, preferably below the detection limit.

[0054] The iodides contained in the slime-inhibiting agents for reverse osmosis membranes are inorganic salts of iodine, such as potassium iodide, sodium iodide, lithium iodide, copper iodide, and zinc iodide. From a cost perspective, potassium iodide or sodium iodide is preferred. The slime-inhibiting agents for reverse osmosis membranes may contain one or more iodides.

[0055] The concentration of iodide ions in the slime-inhibiting agent for reverse osmosis membranes is preferably less than 20% by mass, more preferably 1% by mass or more and less than 20% by mass, even more preferably 3.8% by mass or more and less than 20% by mass, even more preferably 10% by mass or more and less than 20% by mass, particularly preferably 15% by mass or more and less than 20% by mass, and particularly preferably 15% by mass or more and less than 19% by mass. When the concentration of iodide ions is less than 1% by mass, the increased dosage may lead to increased costs associated with the transportation, storage, and addition of the drug. If the concentration exceeds 20% by mass, especially exceeding 19% by mass, free iodine is easily generated under high-temperature storage conditions, sometimes requiring an increased amount of alkali to prevent the generation of free iodine.

[0056] As an alkaline agent contained in a slime-inhibiting agent, any agent capable of adjusting the pH of the solution is acceptable. Examples include hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, and tetramethylammonium hydroxide; carbonates such as sodium carbonate and potassium carbonate; and bicarbonates such as sodium bicarbonate and potassium bicarbonate. Among these, from the perspectives of safety and formulation cost, hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide are preferred, with sodium hydroxide or potassium hydroxide being more preferred.

[0057] Furthermore, from the viewpoint of storage stability, the slime-inhibiting agent for reverse osmosis membranes preferably contains 0.01% by mass or more of an alkaline agent, more preferably 0.02% by mass or more of an alkaline agent. The upper limit of the alkaline agent content is, for example, less than 10% by mass, preferably less than 1% by mass.

[0058] The pH of the slime-inhibiting agent for reverse osmosis membranes is preferably 8 or higher, more preferably 12 or higher. When the pH of the slime-inhibiting agent for reverse osmosis membranes is less than 8, free iodine may sometimes be generated. The upper limit of the pH of the slime-inhibiting agent for reverse osmosis membranes is, for example, 14 or lower.

[0059] As for water, for example, water with a free chlorine concentration of less than 0.2 mg / L, examples include pure water and ultrapure water.

[0060] The slime-inhibiting agent for reverse osmosis membranes described in this embodiment can be suitable as a water treatment agent for reducing residual chlorine in treated water and for disinfecting treated water. The iodide ions contained in the slime-inhibiting agent for reverse osmosis membranes can effectively reduce residual chlorine, rendering it harmless. The slime-inhibiting agent for reverse osmosis membranes described in this embodiment is particularly suitable as a disinfection agent in reverse osmosis membrane treatment.

[0061] In water treatment systems, oxidants such as hypochlorous acid and hypobromic acid are typically added for sterilization and to inhibit slime formation. However, it is known that these oxidants remain in the treated water without being consumed, in order to achieve the desired sterilization and slime inhibition. This residue can then flow into downstream water treatment systems, negatively impacting them. It is generally believed that the inflow of residual chlorine and other pollutants can cause corrosion in cooling towers, performance degradation of reverse osmosis membranes in reverse osmosis systems, and significant oxidative degradation in resin towers and electrodeionization (EDI) systems.

[0062] The slime inhibitor for reverse osmosis membranes described in this embodiment can suppress the effects on downstream water treatment equipment, such as corrosion in cooling towers, performance degradation of reverse osmosis membranes in reverse osmosis membrane units, and oxidative degradation in resin towers or electro-deionization (EDI) systems.

[0063] When using the above-mentioned sludge-inhibiting agent for reverse osmosis membranes for water treatment, for example, the agent can be added to the treated water containing at least one of a chlorine-based oxidant and a bromine-based oxidant. Furthermore, in a water treatment method that uses a reverse osmosis membrane to treat water containing at least one of a chlorine-based oxidant and a bromine-based oxidant, the above-mentioned sludge-inhibiting agent for reverse osmosis membranes can be added to the treated water treated by the reverse osmosis membrane.

[0064] By adding iodide to water treated by reverse osmosis membrane treatment containing at least one of chlorine-based and bromine-based oxidants, the chlorine-based oxidants that may cause deterioration of the reverse osmosis membrane can be reduced. Through the chlorine-based oxidants, the sludge inhibitor for reverse osmosis membranes is oxidized to iodine, which has bactericidal properties, and becomes a sludge inhibitor that hardly deteriorates the reverse osmosis membrane and inhibits sludge formation. Therefore, by adding the aforementioned sludge inhibitor for reverse osmosis membranes to water containing chlorine-based oxidants, the deterioration of the reverse osmosis membrane and the formation of sludge can be inhibited.

[0065] <Preparation method of slime inhibitor for reverse osmosis membranes> The reverse osmosis membrane slime inhibitor used in the water treatment method of this embodiment can be manufactured by a method including the following steps: an addition step, wherein an iodide and an alkali are added to water with a free chlorine concentration of 0.2 mg / L or less. Alternatively, the reverse osmosis membrane slime inhibitor used in the water treatment method of this embodiment can be manufactured by a method including the following steps: a removal step, wherein free chlorine is removed from water with a free chlorine concentration exceeding 0.2 mg / L to bring the free chlorine concentration to 0.2 mg / L or less; and an addition step, wherein an iodide and an alkali are added to the water from which the free chlorine has been removed.

[0066] There are no particular limitations on the methods for removing free chlorine from water with a free chlorine concentration exceeding 0.2 mg / L and reducing the free chlorine concentration to below 0.2 mg / L. For example, methods using activated carbon or reducing agents such as sodium bisulfite can be cited. However, when using reducing agents, an excess of reducing agent needs to be added to cope with changes in the free chlorine concentration. Therefore, it is preferable to use activated carbon to remove free chlorine.

[0067] Water with a free chlorine concentration exceeding 0.2 mg / L, used as a raw material in the removal process, can be exemplified by tap water.

[0068] The free chlorine concentration of the water used in the addition process, or the free chlorine concentration of the water obtained by removing or reducing free chlorine in the removal process, should be below 0.2 mg / L, preferably below 0.1 mg / L, and the lower the better.

[0069] In the additive process, iodide and alkali can be added to the water after free chlorine has been removed, for example, at a temperature of 0–50°C. There are no particular restrictions on the order of addition of iodide and alkali. If necessary, the water can be stirred using a stirring device after the iodide and alkali have been removed. The resulting reverse osmosis membrane slime inhibitor should be stored at a temperature of, for example, -5–50°C.

[0070] By means of manufacturing this reverse osmosis membrane slime inhibitor, a reverse osmosis membrane slime inhibitor containing iodide and inhibiting the release of iodine can be obtained.

[0071] This specification includes the following implementation methods.

[0072] [1] A method for manufacturing a slime inhibitor for reverse osmosis membranes, comprising an addition step of adding iodide and alkali to water with a free chlorine concentration of less than 0.2 mg / L.

[0073] [2] A method for manufacturing a slime-inhibiting agent for reverse osmosis membranes, comprising: The removal process includes removing free chlorine from water with a free chlorine concentration exceeding 0.2 mg / L, reducing the free chlorine concentration to below 0.2 mg / L; and The process involves adding iodide and an alkali to the water from which free chlorine has been removed.

[0074] [3] A slime-inhibiting agent for reverse osmosis membranes, comprising an iodide, an alkali and water, Furthermore, the free iodine concentration is below 0.1 mg / L.

[0075] [4] According to the reverse osmosis membrane slime inhibitor described in [3], wherein, The iodide ion concentration is above 3.8% and less than 20%.

[0076] [5] The slime-inhibiting agent for reverse osmosis membranes according to [3] or [4], wherein, The pH of the slime-inhibiting agent used in the reverse osmosis membrane is above 8.

[0077] [6] A water treatment method comprising a reverse osmosis membrane treatment step, wherein, for water to be treated containing at least one of a chlorine-based oxidant and a bromine-based oxidant, a reverse osmosis membrane is used to obtain concentrated water and permeate. The reverse osmosis membrane slime inhibitor mentioned in any one of [3] to [5] is present in the water to be treated, so that the amount of iodine ions relative to the amount of free chlorine and free bromine in the water to be treated reaches more than 2 mol per mol.

[0078] [7] A water treatment method comprising: A membrane filtration treatment process, wherein, for the water to be treated containing at least one of chlorine-based oxidants and bromine-based oxidants, membrane filtration is performed using a separation membrane; and The reverse osmosis membrane treatment process, wherein the membrane-filtered water obtained in the membrane filtration process is further treated using a reverse osmosis membrane to obtain concentrated water and permeate water. The reverse osmosis membrane slime inhibitor mentioned in any one of [3] to [5] is present in the water to be treated in the membrane filtration process, so that the amount of iodine ions relative to the amount of free chlorine and free bromine in the water to be treated reaches more than 2 mol per mol.

[0079] Example The present invention will be described in more detail below with examples and comparative examples, but the present invention is not limited to the following examples.

[0080] <Example 1> The free iodine concentration of the slime-inhibiting agent for reverse osmosis membranes was determined under different free chlorine concentrations in the water used in the preparation of the slime-inhibiting agent. Since the free iodine in the composition increases the color, the color was also measured.

[0081] A specified amount of sodium hypochlorite was added to ultrapure water with a free chlorine concentration of less than 0.02 mg / L to adjust the free chlorine concentration to a specified level. Potassium iodide (20% by mass) was added as an iodide to the water (80% by mass) after the residual chlorine concentration was adjusted. It should be noted that no alkali agent as a pH adjuster was included. The ultrapure water was prepared using Sagamihara well water from Japan with a free chlorine concentration of less than 0.02 mg / L, using desalination units such as ion exchange resin and reverse osmosis membrane.

[0082] The colorimetric properties of the obtained composition were determined using the method described in the URL (https: / / www.toadkk.co.jp / support / hach / runbook / f6idue00000036jm-att / 8025_Pt-Co.pdf).

[0083] Free iodine was quantified using the DPD method.

[0084] The results are shown in Table 1.

[0085] [Table 1]

[0086] When the water used to prepare the slime inhibitor for reverse osmosis membranes contains a free chlorine concentration of less than 0.2 mg / L, the free iodine concentration is below the detection limit (<0.05 mg / L), and the color is also below 5 degrees.

[0087] <Example 2> [Evaluation of long-term storage stability] Using the proportions shown in Tables 2, 3, 4, and 5, potassium iodide was added as the iodide in ultrapure water with a free chlorine concentration of less than 0.02 mg / L at 25°C. The pH of the composition was adjusted using hydrochloric acid or sodium hydroxide aqueous solution. The resulting composition (sludge inhibitor for reverse osmosis membranes) had a free iodine concentration of less than 0.05 mg / L. The free iodine content after 30 days at 25°C and 30 days at 50°C was quantified using DPD. The results are shown in Tables 6 and 7, respectively.

[0088] [Table 2]

[0089] [Table 3]

[0090] [Table 4]

[0091] [Table 5]

[0092] [Table 6]

[0093] [Table 7]

[0094] When stored at 25°C for 30 days, the composition exhibits good stability at pH 8 and above. When stored at 50°C for 30 days, the composition exhibits good stability at pH 12 and above.

[0095] <Example 3, Reference Examples 1 and 2> [Evaluation of sterilization effect] The reverse osmosis membrane slime-inhibiting agent (potassium iodide (KI) aqueous solution) and sodium hypochlorite (NaClO), as well as sodium hypochlorite as a reference example and an iodine-based oxidant (the oxidant described in International Publication No. 2021 / 192582) were added to simulated water at the following concentrations, and the bactericidal effects were compared. The simulated water was prepared by adding broth to dechlorinated raw well water from Sagami, resulting in a viable bacteria count of 10-1. 7 The viable count was determined using a San-ai bio-checker TTC (manufactured by San-ai Petroleum). The results are shown in Table 8.

[0096] Sodium hypochlorite (Reference Example 1): 1.0 mg / L Sodium hypochlorite: 1.0 mg / L; and a mixture of a reverse osmosis membrane slime inhibitor (potassium iodide aqueous solution) with a free iodine concentration of less than 0.05 mg / L: 4.5 mg / L potassium iodide (as an additive, equivalent to 22.5 mg / L) (Example 3). Iodine-based oxidizing agent (Reference Example 2): 1.0 mg / L as Cl2 (International Publication No. 2021 / 192582) [Table 8]

[0097] When using the reverse osmosis membrane slime inhibitor (potassium iodide aqueous solution) and sodium hypochlorite in the examples, the bactericidal effect is superior to that of sodium hypochlorite and is the same as that of the iodine-based oxidant described in International Publication No. 2021 / 192582.

[0098] <Example 4, Reference Examples 3 and 4> Determination of redox potential (ORP) Figure 3 , Figure 4 )] In the example, a slime-inhibiting agent (potassium iodide (KI) aqueous solution) and sodium hypochlorite (NaClO) were added to ultrapure water, and the redox potential (ORP) was measured. Figure 3 The results shown are as follows: at pH 4, 7, and 10, sodium hypochlorite was added first, followed by a reverse osmosis membrane slime inhibitor (potassium iodide aqueous solution) (solid line), and sodium hypochlorite was added first, followed by a reverse osmosis membrane slime inhibitor (potassium iodide aqueous solution) (dashed line). Figure 4 The results show the effects of adding the reverse osmosis membrane of the embodiment with a slime-inhibiting agent and sodium hypochlorite, sodium hypochlorite as a reference example, and an iodine-based oxidant (the oxidant described in International Publication No. 2021 / 192582) at pH 4, 7, and 10 in the following concentrations.

[0099] Sodium hypochlorite (Reference Example 3): 1.0 mg / L Sodium hypochlorite: 1.0 mg / L; and a mixture of a reverse osmosis membrane slime inhibitor (potassium iodide aqueous solution) with a free iodine concentration of less than 0.05 mg / L: 4.5 mg / L potassium iodide (as an additive, equivalent to 22.5 mg / L) (Example 4). Iodine-based oxidizing agent (Reference Example 4): 1.0 mg / L as Cl2 (International Publication No. 2021 / 192582) • Solid line: Add NaClO first, then add KI • Dashed line: Add KI first, then NaClO It can be seen that as long as the amount of iodine ions added is controlled so that the oxidation-reduction potential (ORP) of the treated water reaches below 800mV, it is sufficient.

[0100] <Example 5, Comparative Example 1> [Effects on membranes] The effects of using the slime-inhibiting agent (potassium iodide aqueous solution (KI)) and sodium hypochlorite (NaClO) in the reverse osmosis membrane examples were evaluated. The results are shown in Table 9.

[0101] (Experimental Procedure) 1. Measure the Flux and EC rejection rate of the reverse osmosis membrane before contact with the reagent. 2. Bring the drug into contact with the reverse osmosis membrane to achieve a CT value of 30,000 (mg / L as Cl2). h) is used as a theoretical value.

[0102] 3. After contact with the reagent, measure the flux and EC rejection rate of the reverse osmosis membrane. Flux is calculated by dividing the permeate flow rate per unit specified time at 25°C by the membrane area and operating pressure. EC rejection rate is calculated by measuring the conductivity of the permeate and the supply water using a conductivity meter, and by (100 - [permeate conductivity / supply water conductivity] × 100).

[0103] (Experimental conditions) • Reverse osmosis membrane test apparatus • Reverse osmosis membrane: Manufactured by Nitto Denko, reverse osmosis flat sheet membrane (ESPA2, LFC3) Water supply: pure water + NaCl, water temperature: 25℃, pressure: 0.75MPa, water flow rate: 5L / min • NaCl: 500 mg / L • Sodium hypochlorite (Comparative Example 1): 0.30 g / L • Sodium hypochlorite: 0.30 g / L; and a mixture of a reverse osmosis membrane slime inhibitor (potassium iodide aqueous solution) with a free iodine concentration of less than 0.05 mg / L: 1.35 g / L potassium iodide (as an additive, equivalent to 6.75 g / L) (Example 5) [Table 9]

[0104] When using the reverse osmosis membrane slime inhibitor (potassium iodide aqueous solution) and sodium hypochlorite in the example, the reverse osmosis membrane showed almost no degradation.

[0105] <Example 6, Reference Examples 5-7> [The effect of iodine ion addition on residual free chlorine concentration] (Experimental Procedure) A sodium hypochlorite aqueous solution was prepared using dechlorinated raw well water from Sagami Province to achieve a concentration of 5 mg / L as Cl2. Potassium iodide was added to prepare a mixed solution to achieve a free chlorine concentration of iodide ions per mol of sodium hypochlorite of 0, 0.5, 1.0, and 2.0 mol. The concentration of free chlorine as hypochlorous acid residue in the mixed solution was then measured.

[0106] For the determination of the free chlorine concentration as a hypochlorous acid residue, referring to the "Indophenol Blue Spectrophotometric Method (JIS K102)," a specified amount of ammonia was added to the mixture to generate chloramine. Then, sodium phenolate solution was added and mixed. After standing for 30 minutes, the absorbance at approximately 630 nm was measured to quantify the generated chloramine. The quantified chloramine concentration was calculated as the amount of free chlorine in the mixture as a hypochlorous acid residue. The results are shown in Table 10.

[0107] [Table 10]

[0108] When 2 mol or more of iodide ions are added relative to 1 mol of free chlorine, free chlorine is not detected (below the detection limit). On the other hand, when the amount of iodide ions added is 1.0 mol relative to 1 mol of free chlorine, free chlorine is slightly detected. Free chlorine derived from hypochlorous acid can degrade the reverse osmosis membrane, so it is preferable that free chlorine is undetectable in the water treated by the reverse osmosis membrane. Therefore, the amount of iodide ions added is preferably 2.0 mol or more.

[0109] <Examples 7-9, Reference Examples 8-13> [Effect of Iodide Ion Addition on Redox Potential (ORP)] (Experimental Procedure) Sodium hypochlorite aqueous solution was added to ultrapure water with the pH adjusted to a specified value at a concentration of 1 mg / L as Cl2. Potassium iodide was then added, and the mixture was stirred for 3 minutes before measuring the oxidation-reduction potential (ORP). Potassium iodide was added to achieve a free chlorine concentration of iodide ions relative to sodium hypochlorite of 0, 1.0, and 2.0 mol per mol. The ORP was measured using an ORP meter (RM-20P) from Toa DKK Corporation. The results are shown in Table 11.

[0110] [Table 11]

[0111] The more iodide ions are added, the lower the oxidation-reduction potential (ORP) becomes. Especially at pH 4, when the amount of iodide ions added is more than 2 mol relative to 1 mol of free chlorine, the oxidation-reduction potential (ORP) is significantly reduced, falling below the standard of 700 mV for oxidation-reduction potential that can negligibly affect the reverse osmosis membrane.

[0112] As shown in the examples, a sludge-inhibiting agent for reverse osmosis membranes containing iodide and inhibiting the release of iodine was obtained. Furthermore, by using the sludge-inhibiting agent for reverse osmosis membranes of the examples, in the treatment of water containing at least one of a chlorine-based oxidant and a bromine-based oxidant, it is possible to inhibit sludge formation while simultaneously inhibiting reverse osmosis membrane degradation.

[0113] Explanation of reference numerals in the attached figures 1 Water treatment unit, 10 Treated water tank, 12 Membrane filtration unit, 14 Reverse osmosis membrane unit, 16 Pump, 18, 20 Treated water piping, 22 Membrane filtration treated water piping, 24 Permeate water piping, 26 Concentrated water piping, 28 Sludge inhibitor addition piping, 30 Reducing agent addition piping.

Claims

1. A method for manufacturing a slime-inhibiting agent for reverse osmosis membranes, characterized in that, include: The process involves adding iodide and an alkaline agent to water with a free chlorine concentration below 0.2 mg / L. The reverse osmosis membrane uses a slime-inhibiting agent: It contains iodide, alkali and water. The free iodine concentration is below 0.1 mg / L. The iodide ion concentration is 3.8% by mass or more and less than 20% by mass. pH above 8 Iodine is generated in the treated water containing at least one of chlorine-based and bromine-based oxidants.

2. A method for manufacturing a slime-inhibiting agent for reverse osmosis membranes, characterized in that, include: The removal process includes removing free chlorine from water with a free chlorine concentration exceeding 0.2 mg / L, reducing the free chlorine concentration to below 0.2 mg / L; and In the process of adding iodide and alkali, iodide and alkali are added to the water from which free chlorine has been removed. The reverse osmosis membrane uses a slime-inhibiting agent: It contains iodide, alkali and water. The free iodine concentration is below 0.1 mg / L. The iodide ion concentration is 3.8% by mass or more and less than 20% by mass. pH above 8 Iodine is generated in the treated water containing at least one of chlorine-based and bromine-based oxidants.

3. A slime-inhibiting agent for reverse osmosis membranes, characterized in that, The reverse osmosis membrane uses a slime-inhibiting agent: It contains iodide, alkali and water. The free iodine concentration is below 0.1 mg / L. The iodide ion concentration is 3.8% by mass or more and less than 20% by mass. pH above 8 Iodine is generated in the treated water containing at least one of chlorine-based and bromine-based oxidants.

4. A water treatment method, characterized in that, include: The reverse osmosis membrane treatment process, wherein for water to be treated containing at least one of chlorine-based oxidants and bromine-based oxidants, a reverse osmosis membrane is used to obtain concentrated water and permeate. The treated water contains the slime-inhibiting agent for reverse osmosis membranes as described in claim 3, so that the amount of iodine ions relative to the amount of free chlorine and free bromine in the treated water reaches more than 2 mol per mol.

5. A water treatment method, characterized in that, include: A membrane filtration treatment process, wherein, for the water to be treated containing at least one of chlorine-based oxidants and bromine-based oxidants, membrane filtration is performed using a separation membrane; and The reverse osmosis membrane treatment process, wherein, for the membrane-filtered water obtained in the membrane filtration treatment process, a reverse osmosis membrane is used to obtain concentrated water and permeate water. The reverse osmosis membrane slime inhibitor as described in claim 3 is present in the water being treated in the membrane filtration process, so that the amount of iodine ions relative to the amount of free chlorine and free bromine in the water being treated reaches more than 2 mol per mol.

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