Method for cleaning reverse osmosis membranes and apparatus for cleaning reverse osmosis membranes

Abstract

To provide a washing method of a reverse osmosis membrane and a washing device of the reverse osmosis membrane which is excellent in washing property of the reverse osmosis membrane even while suppressing deterioration of the reverse osmosis membrane.SOLUTION: A washing method of a reverse osmosis membrane includes a washing process of washing the reverse osmosis membrane of a reverse osmosis membrane device 10 to which water to be treated is caused to flow to provide concentrate water and permeate water by using washing liquid. Therein, a stabilized hypobromous acid composition which contains a bromine-type oxidizing agent and a sulfamic acid compound in the washing liquid is caused to exist, pH of the washing liquid is in a range of 11 to 13 and the whole chlorine concentration of the washing liquid is 1 mg-Cl2 / L or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for cleaning a reverse osmosis membrane and an apparatus for cleaning a reverse osmosis membrane, which perform cleaning of the reverse osmosis membrane in water treatment using the reverse osmosis membrane.

Background Art

[0002] In a reverse osmosis membrane apparatus that treats raw water using a reverse osmosis membrane to obtain concentrated water and permeated water, as the treatment continues, problems such as deterioration of the quality of the treated water (permeated water) and reduction in flow rate may occur due to contamination of the reverse osmosis membrane. Therefore, currently, for the purpose of cleaning a reverse osmosis membrane contaminated by microorganisms or organic substances, alkaline cleaning using an alkaline agent such as sodium hydroxide or potassium hydroxide is regularly performed.

[0003] In such cleaning of the reverse osmosis membrane, not only an alkaline agent but also a chemical having high detergency and bactericidal properties is added to the cleaning solution, so that the detergency and bactericidal properties are increased, and further recovery of the quality and flow rate of the treated water can be expected.

[0004] Hypochlorous acid is generally cited as a chemical that is very effective in cleaning and sterilizing contaminants, but hypochlorous acid has a problem of deteriorating the reverse osmosis membrane and is not suitable for cleaning the reverse osmosis membrane.

[0005] For example, Patent Document 1 describes that a hypobromous acid stabilizing composition containing a bromine-based oxidizing agent and a sulfamic acid compound is present in the raw water or cleaning water supplied to a membrane separation apparatus provided with a separation membrane. However, Patent Document 1 does not describe the pH, concentration, etc. when the hypobromous acid stabilizing composition is present in the cleaning water.

[0006] Patent Document 2 describes using a strong alkali or a strong acid as a cleaning agent for a reverse osmosis membrane. Although Patent Document 2 describes that stabilized (bonded) bromine and stabilized bromine can be used in addition to a strong alkali or a strong acid as a cleaning agent for a reverse osmosis membrane, the specific usage method, for example, the pH and concentration of the cleaning solution when using stabilized bromine, etc. are not described, and there is no description of the examples used. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2015-062889 [Patent Document 2] Japanese Patent Publication No. 2016-185520 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a reverse osmosis membrane cleaning method and a reverse osmosis membrane cleaning apparatus that have excellent cleaning performance for reverse osmosis membranes while suppressing deterioration of the reverse osmosis membrane. [Means for solving the problem]

[0009] The present invention includes a cleaning step in which a reverse osmosis membrane in a reverse osmosis membrane apparatus, which obtains concentrated water and permeate water by passing water to be treated through it, is cleaned using a cleaning solution, wherein the cleaning solution contains a stabilized hypobromite composition containing bromine and a sulfamic acid compound. Without the presence of chlorine-based oxidizing agents The method for cleaning a reverse osmosis membrane is such that the pH of the cleaning solution is in the range of 11 to 13, and the total chlorine concentration of the cleaning solution is between 1 mg-Cl2 / L and 100 mg-Cl2 / L.

[0010] In the reverse osmosis membrane washing method, the total chlorine concentration is 5 mg-Cl2 / L ~100mg-Cl 2 / L It is preferable that this be the case.

[0011] In the cleaning step of the reverse osmosis membrane cleaning method, it is preferable to stop the flow of the water to be treated to the reverse osmosis membrane apparatus, pass the cleaning solution from the cleaning solution tank that stores the cleaning solution to the reverse osmosis membrane apparatus, and return both the concentrated cleaning water and the permeate obtained to the cleaning solution tank.

[0012] The present invention provides a cleaning means for cleaning a reverse osmosis membrane in a reverse osmosis membrane apparatus that passes water to be treated through to obtain concentrated water and permeate water, wherein the cleaning means contains a stabilized hypobromite composition containing bromine and a sulfamic acid compound. Without the presence of chlorine-based oxidizing agents The washing device is a reverse osmosis membrane washing apparatus in which the pH of the washing solution is in the range of 11 to 13 and the total chlorine concentration of the washing solution is 1 mg-Cl2 / L to 100 mg-Cl2 / L.

[0013] In the reverse osmosis membrane cleaning apparatus, the total chlorine concentration is 5 mg-Cl2 / L ~100mg-Cl 2 / L It is preferable that this be the case.

[0014] In the reverse osmosis membrane cleaning apparatus, a cleaning liquid tank for storing the cleaning liquid and the cleaning liquid from the cleaning liquid tank liquid The system further includes a return means for returning both the concentrated washing water and the permeate obtained by passing the water through the reverse osmosis membrane apparatus back to the washing liquid tank, and it is preferable to stop the flow of the water to be treated to the reverse osmosis membrane apparatus when the reverse osmosis membrane is being washed by the washing means. [Effects of the Invention]

[0015] The present invention provides a method and apparatus for cleaning reverse osmosis membranes that offer excellent cleaning performance while suppressing deterioration of the reverse osmosis membrane. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram showing an example of a water treatment apparatus equipped with a reverse osmosis membrane cleaning device according to an embodiment of the present invention. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below. This embodiment is just one example of how the present invention can be implemented, and the present invention is not limited to this embodiment.

[0018] Fig. 1 shows a schematic diagram of an example of a water treatment apparatus including a reverse osmosis membrane cleaning apparatus according to an embodiment of the present invention, and its configuration will be described.

[0019] The water treatment apparatus 1 includes a reverse osmosis membrane apparatus 10 as a reverse osmosis membrane treatment means for passing raw water through the reverse osmosis membrane apparatus to obtain concentrated water and permeated water. The water treatment apparatus 1 may include a cleaning liquid tank 12 for storing a cleaning liquid.

[0020] In the water treatment apparatus 1, a pipe 30 is connected to the inlet of the reverse osmosis membrane apparatus 10 via a valve 18 and a feed water pump 14. A pipe 32 is connected to the permeated water outlet of the reverse osmosis membrane apparatus 10 via a valve 20. The cleaning permeated water outlet of the reverse osmosis membrane apparatus 10 and the cleaning permeated water inlet of the cleaning liquid tank 12 are connected by a pipe 36 via a valve 24. A pipe 34 is connected to the concentrated water outlet of the reverse osmosis membrane apparatus 10 via a valve 22. The cleaning concentrated water outlet of the reverse osmosis membrane apparatus 10 and the cleaning concentrated water inlet of the cleaning liquid tank 12 are connected by a pipe 38 via a valve 26. The outlet of the cleaning liquid tank 12 and the downstream side of the feed water pump 14 in the pipe 30 are connected by a pipe 40 via valves 28 and a feed water pump 16. A cleaning agent pipe 42 is connected to the cleaning agent inlet of the cleaning liquid tank 12, and an alkali agent pipe 44 is connected to the alkali agent inlet.

[0021] The reverse osmosis membrane cleaning apparatus according to the present embodiment is configured to include a cleaning liquid tank 12, a feed water pump 16, valves 24, 26, 28, and pipes 30, 36, 38, 40. In the reverse osmosis membrane cleaning apparatus, the cleaning liquid tank 12, the feed water pump 16, the pipe 40, the pipe 30, etc. function as cleaning means. The feed water pump 16, the pipe 36, the pipe 38, etc. function as return means.

[0022] The operation of the water treatment apparatus 1 including the water treatment method including the reverse osmosis membrane cleaning method according to the present embodiment and the reverse osmosis membrane cleaning apparatus will be described.

[0023] During normal operation, valves 18, 20, and 22 are open, valves 24, 26, and 28 are closed, and the water supply pump 14 is activated to send the water to be treated through piping 30 to the reverse osmosis membrane device 10. In the reverse osmosis membrane device 10, reverse osmosis treatment is performed using a reverse osmosis membrane, and permeate water and concentrated water are obtained (reverse osmosis treatment process). The permeate water is discharged through piping 32, and the concentrated water is discharged through piping 34.

[0024] During the cleaning operation, a stabilized hypobromite composition is supplied to the cleaning solution tank 12 through the cleaning agent piping 42, and an alkaline agent is supplied through the alkaline agent piping 44, preparing a cleaning solution containing the stabilized hypobromite composition. Valves 18, 20, and 22 are closed, the water supply pump 14 is stopped, valves 24, 26, and 28 are opened, and the water supply pump 16 is activated, sending the cleaning solution through piping 40 and piping 30 to the reverse osmosis membrane device 10. In the reverse osmosis membrane device 10, the reverse osmosis membrane is cleaned, and cleaning permeate and cleaning concentrate are obtained (cleaning step). The cleaning permeate may be returned to the cleaning solution tank 12 through piping 36, and the cleaning concentrate may be returned to the cleaning solution tank 12 through piping 38 (return step).

[0025] In the water treatment method and water treatment apparatus 1 comprising a reverse osmosis membrane cleaning device according to this embodiment, a stabilized hypobromous acid composition containing a brominated oxidizing agent and a sulfamic acid compound is present in the cleaning solution as a cleaning agent for the reverse osmosis membrane, the pH of the cleaning solution is in the range of 11 to 13, and the total chlorine concentration of the cleaning solution is 1 mg-Cl2 / L or higher.

[0026] The inventors have found that stabilized hypobromite compositions exhibit excellent cleaning and sterilizing power under alkaline conditions, and are effective for cleaning and sterilizing dirt on reverse osmosis membranes. In particular, they have found that the cleaning effect of stabilized hypobromite compositions at a predetermined total chlorine concentration under alkaline conditions is extremely effective. Cleaning with this stabilized hypobromite composition at a predetermined total chlorine concentration under alkaline conditions has a cleaning power superior to that of alkaline cleaning or stabilized (bound) chlorine bromite.

[0027] In the washing process, it is preferable to stop the flow of the water to be treated to the reverse osmosis membrane apparatus 10. Then, it is preferable to provide a separate washing liquid tank 12, pass the washing liquid from the washing liquid tank 12 to the reverse osmosis membrane apparatus 10 to perform washing, and return both the resulting concentrated washing water and washing permeate to the washing liquid tank 12.

[0028] By stopping the flow of water to be treated to the reverse osmosis membrane device 10, the effects of suppressing contamination originating from the water to be treated and the decrease in pH during washing can be obtained. By returning both the concentrated washing water and the permeate from washing to the washing solution tank 12, the effects of enabling treatment with a small amount of water and at a stable pH can be obtained.

[0029] The pH of the cleaning solution should be in the range of 11 to 13, preferably 12 to 13. If the pH of the cleaning solution is below 11, the cleaning power will decrease, and if it exceeds 13, it may degrade the reverse osmosis membrane.

[0030] The total chlorine concentration of the cleaning solution is 1 mg-Cl2 / L or higher, preferably 5 mg-Cl2 / L or higher, more preferably 10 mg-Cl2 / L or higher, and even more preferably in the range of 10 to 100 mg-Cl2 / L. If the total chlorine concentration of the cleaning solution is less than 1 mg-Cl2 / L, the cleaning power will decrease, and if it exceeds 100 mg-Cl2 / L, it may degrade the reverse osmosis membrane. If the total chlorine concentration of the cleaning solution is 5 mg-Cl2 / L or higher, the cleaning power will be higher.

[0031] There are no particular restrictions on the temperature of the cleaning solution, but it is preferable to set it to, for example, around 30-40°C.

[0032] In the cleaning process, it is preferable to pass the cleaning solution through the reverse osmosis membrane for a predetermined time, then stop the flow of the cleaning solution and immerse the membrane in the cleaning solution (immersion process). There are no particular restrictions on the immersion time, but for example, it may be about 10 to 15 hours. There are no particular restrictions on the immersion temperature, but for example, it is preferable to set it to about 30 to 40°C.

[0033] In the cleaning process, for example, a cleaning solution tank 12 can be installed, a stabilized hypobromous acid composition can be added to the cleaning solution tank, and then an alkaline agent can be added to adjust the pH to 11-13.

[0034] If the pH of the cleaning solution falls below 11 during the cleaning process, an alkaline agent can be added to the cleaning solution tank 12 to adjust the pH of the cleaning solution to a range of 11 to 13. A pH measuring device may be installed in the cleaning solution tank 12 as a pH measuring means, and valves, pumps, etc., may be installed in the alkaline agent piping 44 as a means of adjusting the amount of alkaline agent added, and a control device may be provided as a control means, and the pH measuring device and the valves, pumps, etc., of the alkaline agent piping 44 may be connected by wired or wireless electrical connections. Based on the pH measured by the pH measuring device, the control device may control the valves, pumps, etc., of the alkaline agent piping 44 to adjust the amount of alkaline agent added, and the pH of the cleaning solution may be automatically adjusted to a range of 11 to 13.

[0035] If the total chlorine concentration of the cleaning solution falls below 1 mg-Cl2 / L during the cleaning process, a stabilized hypobromous acid composition can be added to the cleaning solution tank 12 to adjust the total chlorine concentration of the cleaning solution to 1 mg-Cl2 / L or higher. A total chlorine concentration measuring device may be installed in the cleaning solution tank 12 as a means of total chlorine concentration, valves or pumps may be installed in the cleaning agent piping 42 as a means of adjusting the amount of cleaning agent added, and a control device may be provided as a control means. The total chlorine concentration measuring device and the valves or pumps of the cleaning agent piping 42 may be connected by wired or wireless electrical connections. Based on the total chlorine concentration measured by the total chlorine concentration measuring device, the control device may control the valves or pumps of the cleaning agent piping 42 to adjust the amount of stabilized hypobromous acid composition added, and automatically adjust the total chlorine concentration of the cleaning solution to 1 mg-Cl2 / L or higher.

[0036] The cleaning solution tank 12 may be installed temporarily or permanently.

[0037] The water treatment method and water treatment apparatus comprising a reverse osmosis membrane cleaning method and a reverse osmosis membrane cleaning apparatus according to this embodiment are suitably applied, for example, to the production of pure water, seawater desalination, wastewater recovery, and the like.

[0038] The pH of the treated water is preferably in the range of 2 to 12, and more preferably in the range of 4 to 11. The lower limit of the pH of the treated water is preferably 5.5 or higher, more preferably 6.0 or higher, and even more preferably 6.5 or higher. The upper limit of the pH of the treated water is preferably 9.0 or lower, and more preferably 8.0 or lower.

[0039] Examples of reverse osmosis membranes include anion-charged membranes, cation-charged membranes, and neutral membranes, and any of these membranes may be used.

[0040] The "stabilized hypobromous acid composition containing a brominated oxidizing agent and a sulfamic acid compound" may be a stabilized hypobromous acid composition containing a mixture of the "brominated oxidizing agent" and the "sulfamic acid compound," or it may be a stabilized hypobromous acid composition containing the "reaction product of the brominated oxidizing agent and the sulfamic acid compound."

[0041] The "stabilized hypobromous acid composition" can be prepared by injecting, for example, a "brominated oxidizing agent" and a "sulfamic acid compound" into the cleaning solution tank 12 using a chemical injection pump or the like. The "brominated oxidizing agent" and the "sulfamic acid compound" may be added to the cleaning solution tank 12 separately, or they may be mixed together as undiluted solutions before being added to the cleaning solution tank 12.

[0042] Examples of bromine-based oxidizing agents include bromine (liquid bromine), bromine chloride, bromate, bromate salts, and hypobromous acid. Hypobromous acid may be produced by reacting a bromine compound such as sodium bromide with a chlorine-based oxidizing agent such as hypochlorous acid. When the bromine-based oxidizing agent is bromine, there is no chlorine-based oxidizing agent present, resulting in significantly lower degradation of the reverse osmosis membrane. In other words, a stabilized hypobromous acid composition containing bromine and a sulfamic acid compound is preferred, as it suppresses the degradation of the reverse osmosis membrane.

[0043] Examples of bromine compounds include sodium bromide, potassium bromide, lithium bromide, ammonium bromide, and hydrobromic acid. Of these, sodium bromide is preferred from the standpoint of formulation cost and other factors.

[0044] Examples of chlorine-based oxidizing agents include chlorine gas, chlorine dioxide, hypochlorous acid or its salts, chlorous acid or its salts, chloric acid or its salts, perchloric acid or its salts, chlorinated isocyanuric acid or its salts, etc. Among these, examples of salts include alkali metal hypochlorite salts such as sodium hypochlorite and potassium hypochlorite, alkaline earth metal hypochlorite salts such as calcium hypochlorite and barium hypochlorite, alkali metal hypochlorite salts such as sodium chlorite and potassium chlorite, alkaline earth metal hypochlorite salts such as barium chlorite, other metal hypochlorite salts such as nickel chlorite, alkali metal chlorite salts such as ammonium chlorate, sodium chlorate, and potassium chlorate, alkaline earth metal chlorite salts such as calcium chlorate and barium chlorate, etc. These chlorine-based oxidizing agents may be used individually or in combination of two or more. From the viewpoint of handling, etc., sodium hypochlorite is preferred as the chlorine-based oxidizing agent.

[0045] Sulfamic acid compounds are compounds represented by the following general formula (1). R2NSO3H (1) (In the formula, R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

[0046] Examples of sulfamic acid compounds include sulfamic acid (amidosulfuric acid), in which both R groups are hydrogen atoms; sulfamic acid compounds in which one of the two R groups is a hydrogen atom and the other is an alkyl group having 1 to 8 carbon atoms, such as N-methylsulfamic acid, N-ethylsulfamic acid, N-propylsulfamic acid, N-isopropylsulfamic acid, and N-butylsulfamic acid; sulfamic acid compounds in which both of the two R groups are alkyl groups having 1 to 8 carbon atoms, such as N,N-dimethylsulfamic acid, N,N-diethylsulfamic acid, N,N-dipropylsulfamic acid, N,N-dibutylsulfamic acid, N-methyl-N-ethylsulfamic acid, and N-methyl-N-propylsulfamic acid; sulfamic acid compounds in which one of the two R groups is a hydrogen atom and the other is an aryl group having 6 to 10 carbon atoms, such as N-phenylsulfamic acid; or salts thereof. Examples of sulfamate salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts, strontium salts and barium salts, other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts and nickel salts, ammonium salts and guanidine salts. Sulfamate compounds and their salts may be used individually or in combination of two or more. From the standpoint of environmental impact, sulfamic acid (amidosulfate) is preferred as the sulfamate compound.

[0047] The stabilized hypobromite composition may further contain an alkali. Examples of alkalis include sodium hydroxide, potassium hydroxide, and other alkali hydroxides. Sodium hydroxide and potassium hydroxide may be used in combination from the viewpoint of product stability at low temperatures. The alkali may also be used as an aqueous solution rather than a solid.

[0048] <Cleaning agent for reverse permeability membranes> The reverse osmosis membrane cleaning agent used in the reverse osmosis membrane cleaning method and reverse osmosis membrane cleaning apparatus according to this embodiment contains a stabilized hypobromous acid composition containing a "brominated oxidizing agent" and a "sulfamic acid compound," and may further contain an alkali.

[0049] Furthermore, the reverse permeable membrane cleaning agent may contain a stabilized hypobromous acid composition containing a "reaction product of a brominated oxidizing agent and a sulfamic acid compound," and may also contain alkali.

[0050] Brominated oxidizing agents, brominated compounds, chlorine-based oxidizing agents, and sulfamic acid compounds are as described above.

[0051] The stabilized hypobromous acid composition according to this embodiment is preferably one that contains bromine and a sulfamic acid compound (or a mixture of bromine and a sulfamic acid compound) in order to further degrade the reverse osmosis membrane, for example, a mixture of bromine, a sulfamic acid compound, alkali and water, or one that contains a reaction product of bromine and a sulfamic acid compound, for example, a mixture of a reaction product of bromine and a sulfamic acid compound, alkali and water.

[0052] The stabilized hypobromite composition according to this embodiment, particularly the stabilized hypobromite composition containing bromine and a sulfamic acid compound, has a good cleaning effect compared to chlorine-based oxidizing agents such as hypochlorous acid, while hardly causing the significant membrane degradation of reverse osmosis membranes that chlorine-based oxidizing agents such as hypochlorous acid do. At normal usage concentrations, the effect on membrane degradation is substantially negligible. For this reason, it is ideal as a cleaning agent for reverse osmosis membranes.

[0053] The stabilized hypobromous acid composition according to this embodiment can be measured on-site in the same way as hypochlorous acid, allowing for more accurate concentration control.

[0054] The pH of the stabilized hypobromite composition is, for example, greater than 13.0, and more preferably greater than 13.2. If the pH of the stabilized hypobromite composition is 13.0 or lower, the effective halogen in the stabilized hypobromite composition may become unstable.

[0055] The bromate concentration in the stabilized hypobromous acid composition is preferably less than 5 mg / kg. If the bromate concentration in the stabilized hypobromous acid composition is 5 mg / kg or higher, the bromate ion concentration in the washing solution may become high.

[0056] <Method for manufacturing a cleaning agent for reverse permeability membranes> The reverse osmosis membrane cleaning agent used in the reverse osmosis membrane cleaning method and reverse osmosis membrane cleaning apparatus according to this embodiment is obtained by mixing a brominated oxidizing agent and a sulfamic acid compound, and an alkali may be further mixed in.

[0057] A method for producing a reverse permeable membrane cleaning agent containing bromine and a sulfamic acid compound preferably includes a step of adding bromine to a mixture containing water, alkali, and a sulfamic acid compound under an inert gas atmosphere and allowing it to react, or a step of adding bromine to a mixture containing water, alkali, and a sulfamic acid compound under an inert gas atmosphere. Adding and reacting under an inert gas atmosphere, or adding under an inert gas atmosphere, lowers the concentration of bromate ions in the stabilized hypobromous acid composition.

[0058] While there are no limitations on the inert gas used, at least one of nitrogen and argon is preferred from the standpoint of manufacturing and other factors, and nitrogen is particularly preferred from the standpoint of manufacturing cost and other factors.

[0059] The oxygen concentration in the reactor during bromine addition is preferably 6% or less, more preferably 4% or less, even more preferably 2% or less, and particularly preferably 1% or less. If the oxygen concentration in the reactor during the bromine reaction exceeds 6%, the amount of bromate produced in the reaction system may increase.

[0060] The bromine addition rate is preferably 25% by weight or less relative to the total amount of the stabilized hypobromous acid composition, and more preferably 1% by weight or more and 20% by weight or less. If the bromine addition rate exceeds 25% by weight relative to the total amount of the stabilized hypobromous acid composition, the amount of bromate produced in the reaction system may increase. If it is less than 1% by weight, the cleaning power may be inferior.

[0061] The reaction temperature during bromine addition is preferably controlled within the range of 0°C to 25°C, but from the standpoint of manufacturing costs, it is more preferable to control it within the range of 0°C to 15°C. If the reaction temperature during bromine addition exceeds 25°C, the amount of bromate produced in the reaction system may increase, and if it is below 0°C, freezing may occur. [Examples]

[0062] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0063] (1) Preparation of stabilized hypobromite composition Under a nitrogen atmosphere, a stabilized hypobromite composition was prepared by mixing liquid bromine: 16.9 wt%, sulfamic acid: 10.7 wt%, sodium hydroxide: 12.9 wt%, potassium hydroxide: 3.94 wt%, and water: the remainder. The pH of the stabilized hypobromite composition was 14, and the total chlorine concentration was 7.5 wt%. The total chlorine concentration was measured using the total chlorine measurement method (DPD (diethyl-p-phenylenediamine) method) with a HACH DR / 4000 multi-parameter water quality analyzer (mg-Cl2 / L). The detailed preparation method of the stabilized hypobromite composition is as follows.

[0064] To maintain an oxygen concentration of 1% in the reaction vessel, nitrogen gas was continuously injected into a 2L four-necked flask using a mass flow controller. 1436g of water and 361g of sodium hydroxide were added and mixed, followed by 300g of sulfamic acid and mixing. While maintaining a cooling temperature of 0-15°C, 473g of liquid bromine was added, followed by 230g of 48% potassium hydroxide solution. The resulting stabilized hypobromous acid composition was obtained with a weight ratio of 10.7% sulfamic acid and 16.9% bromine relative to the total volume of the composition, and an equivalent ratio of sulfamic acid to bromine of 1.04. The pH of the resulting solution was measured by the glass electrode method and found to be 14. The bromine content of the resulting solution was measured by converting bromine to iodine with potassium iodide and then performing a redox titration with sodium thiosulfate and found to be 16.9%, which was 100.0% of the theoretical content (16.9%). Furthermore, the oxygen concentration in the reaction vessel during the bromine reaction was measured using the "Oxygen Monitor JKO-02 LJDII" manufactured by Jiko Co., Ltd. The bromate concentration was less than 5 mg / kg.

[0065] The pH was measured under the following conditions. Electrode type: Glass electrode type pH meter: Toa DKK Corporation, IOL-30 model Electrode calibration was performed using two-point calibration with Kanto Chemical Co., Ltd.'s neutral phosphate pH (6.86) standard solution (Type 2) and Kanto Chemical Co., Ltd.'s borate pH (9.18) standard solution (Type 2). Measurement temperature: 25℃ Measurement value: The electrode is immersed in the measuring solution, and the value after stabilization is taken as the measurement value. The average of three measurements is then taken.

[0066] (2) Preparation of bacterial suspension The bacterial strain used was Pseudomonas fluorescens (National Institute of Technology and Evaluation). This bacterium was spread onto Trypticase Soy Agar agar (BD Japan), cultured, and then colonies were collected using a platinum loop and cultured in liquid medium prepared with Soybean-Casein Digest Broth DAIGO (Nippon Pharmaceutical Co., Ltd.).

[0067] (3) Biofilm formation 750 μL of the prepared bacterial suspension was added to each of the 96-well deep plates. Then, the protrusions of the PCR plate (96 wells) were placed on top so that they were immersed in the bacterial suspension in the deep plate. The plates were then sealed at the top and bottom and incubated at 30°C for 18 hours while shaking to form a biofilm on the surface of the protrusions of the PCR plate.

[0068] (4) Evaluation of cleanability 750 μL each of a stabilized hypobromite composition at a predetermined pH and concentration was added to a new 96-well deep plate. A PCR plate with a biofilm formed on its protrusion surface was then placed in contact with the plate, and the attached biofilm was washed off at 25±5°C for 3 hours while shaking, with the plate sealed at both ends. pH adjustment was performed using sodium hydroxide solution or hydrochloric acid.

[0069] After the washing process was complete, the PCR plate was washed with phosphate buffer to remove any washing solution adhering to its surface. Next, 900 μL of crystal violet staining solution (Kanto Chemical) was added to a new 96-well deep plate, and the washed PCR plate was immersed on top of it for 5 minutes. After that, any staining solution adhering to the surface of the PCR plate other than the biofilm was thoroughly washed off with pure water.

[0070] Next, 900 μL of ethanol (95%) was added to a new 96-well deep plate, and the washed PCR plate was placed on top of it. The staining solution adhering to the biofilm was extracted for 5 minutes while shaking. 200 μL of the extracted staining solution was dispensed into 96-well microplates (Nunc® Immuno TSP Lids / Thermo Fisher), and the absorbance of these plates at a wavelength of 595 nm was measured using a Multiskan Sky absorbance microplate reader (Thermo Fisher).

[0071] <Example 1, Comparative Example 1> In Example 1, the pH of the stabilized hypobromite composition was adjusted to 12, and the total chlorine concentrations were adjusted to 0, 1, 5, 10, 50, and 100 mg-Cl2 / L, respectively. In Example 2, the pH of the stabilized hypobromite composition was adjusted to 11, and the total chlorine concentrations were adjusted to 0, 1, 5, 10, 50, and 100 mg-Cl2 / L, respectively. In Comparative Example 1, the pH was adjusted to 10, and the total chlorine concentrations were adjusted to 0, 1, 5, 10, 50, and 100 mg-Cl2 / L, respectively. The absorbance (wavelength 595 nm) of the staining solution extracted after washing was measured for each measurement. In the washing step of each measurement, the absorbance when the sample was in contact with pure water only for 3 hours (not alkali or chemicals) was set to 100%, and the ratio (%) of the absorbance at other concentrations to this value, i.e., the biofilm retention rate (%), is shown in Table 1.

[0072] [Table 1]

[0073] Thus, at pH 10, the biofilm was hardly reduced regardless of the concentration used for washing, but at pH 11 and 12, the biofilm washing performance improved when the total chlorine concentration was 1 mg-Cl2 / L or higher. At pH 11 and 12, the biofilm washing performance improved particularly at a total chlorine concentration of 5 mg-Cl2 / L or higher.

[0074] As described above, the reverse osmosis membrane cleaning method of the example was found to be excellent in cleaning the reverse osmosis membrane while suppressing the deterioration of the reverse osmosis membrane. [Explanation of Symbols]

[0075] 1 water treatment device, 10 reverse osmosis membrane device, 12 cleaning solution tank, 14, 16 water supply pumps, 18, 20, 22, 24, 26, 28 valves, 30, 32, 34, 36, 38, 40 piping, 42 cleaning agent piping, 44 alkaline agent piping.

Claims

1. The reverse osmosis membrane apparatus, which obtains concentrated water and permeate water by passing water to be treated through it, includes a cleaning step in which the reverse osmosis membrane is cleaned using a cleaning solution. The cleaning solution contains a stabilized hypobromous acid composition comprising bromine and a sulfamic acid compound, and does not contain a chlorine-based oxidizing agent. The pH of the cleaning solution is in the range of 11 to 13, and the total chlorine concentration of the cleaning solution is 1 mg-Cl ２ / L~100mg-Cl ２ A method for cleaning a reverse osmosis membrane, characterized by being / L.

2. A method for cleaning a reverse osmosis membrane according to claim 1, The total chlorine concentration is 5 mg-Cl ２ / L~100mg-Cl ２ A method for cleaning a reverse osmosis membrane, characterized by being / L.

3. A method for cleaning a reverse osmosis membrane according to claim 1 or 2, A method for cleaning a reverse osmosis membrane, characterized in that, in the cleaning step, the flow of the water to be treated to the reverse osmosis membrane apparatus is stopped, the cleaning solution is passed from a cleaning solution tank that stores the cleaning solution to the reverse osmosis membrane apparatus, and both the resulting concentrated cleaning water and the cleaning permeate are returned to the cleaning solution tank.

4. A reverse osmosis membrane apparatus, which obtains concentrated water and permeate water by passing water to be treated through it, is equipped with a cleaning means for cleaning the reverse osmosis membrane using a cleaning solution. The cleaning solution contains a stabilized hypobromous acid composition comprising bromine and a sulfamic acid compound, and does not contain a chlorine-based oxidizing agent. The pH of the cleaning solution is in the range of 11 to 13, and the total chlorine concentration of the cleaning solution is 1 mg-Cl ２ / L~100mg-Cl ２ A reverse osmosis membrane cleaning device characterized by being / L.

5. A reverse osmosis membrane cleaning apparatus according to claim 4, The total chlorine concentration is 5 mg-Cl ２ / L~100mg-Cl ２ A reverse osmosis membrane cleaning device characterized by being / L.

6. A reverse osmosis membrane cleaning apparatus according to claim 4 or 5, A cleaning liquid tank for storing the cleaning liquid, A return means for returning both the concentrated cleaning water and the permeate obtained by passing the cleaning liquid from the cleaning liquid tank through the reverse osmosis membrane apparatus to the cleaning liquid tank, Furthermore, A reverse osmosis membrane cleaning apparatus characterized in that, when cleaning the reverse osmosis membrane using the cleaning means, the flow of the water to be treated to the reverse osmosis membrane apparatus is stopped.

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