Operation method of RO membrane system

Abstract

In an RO membrane system that uses a low removal efficiency RO membrane, particularly an ultra-low pressure RO membrane, to treat water requiring slime control, such as organic wastewater, the present invention provides an operating method for an RO membrane system that can evenly sterilize the entire RO system, including the primary and secondary sides. [Solution] An operating method for an RO membrane system in which water to be treated, such as organic wastewater requiring slime control treatment, is passed through a low-removal-rate RO membrane system, characterized in that the primary and secondary sides of the RO membrane are sterilized by including a slime control agent in the water supply to the RO membrane system. The low-removal-rate RO membrane is an RO membrane with an IPA removal rate of 70% or less, an RO membrane with a NaCl removal rate of 93-99%, or an RO membrane with a flux of 2.0 m / d or more at an effective pressure of 1 MPa and a water supply temperature of 25°C.

Description

Technical Field

[0001] The present invention relates to an operation method for an RO membrane device, and particularly relates to an operation method for an RO membrane device with a low removal rate.

Background Art

[0002] In recent years, ultra-low-pressure RO membranes (reverse osmosis membranes) requiring low driving pressure have been increasingly used with the goal of reducing energy consumption and CO₂ emissions. Compared with commonly used ultra-low-pressure RO membranes, such membranes have lower salt removal rates and lower organic matter removal rates. When water to be treated contains low-molecular-weight organic matter, biofouling caused by low-molecular-weight organic matter may occur not only on the primary side (raw water side) but also on the secondary side (permeated water side). In such cases, biofouling countermeasures are required not only on the primary side but also on the secondary side.

[0003] In water treatment methods using reverse osmosis membranes (RO membranes), various bactericides (slime control agents, hereinafter sometimes referred to as slime control agents) are generally used as biofouling countermeasures. Chlorine-based oxidizing agents such as hypochlorous acid are typical bactericides, and are usually added upstream of a reverse osmosis membrane for the purpose of sterilizing the inside of the system. However, since chlorine-based oxidizing agents degrade reverse osmosis membranes, it is generally necessary to reductively decompose the chlorine-based oxidizing agent immediately before the reverse osmosis membrane, and thus such agents are not suitable for sterilizing reverse osmosis membranes.

[0004] Combined chlorine-based slime control agents obtained by reacting a chlorine-based oxidizing agent with sulfamic acid, and combined bromine-based slime control agents obtained by reacting a bromine-based oxidizing agent with sulfamic acid have a low risk of degrading membranes and are suitable for use. However, since such slime control agents are removed by RO membranes, they are unsuitable for sterilization applications on the secondary side a .

[0005] Patent Document 1 describes a method in which, in a system provided with multiple stages of reverse osmosis membranes, a bactericide is newly added as a slime countermeasure to feed water supplied to the second-stage reverse osmosis membrane.

[0006] Patent documents 2 to 4 describe a water treatment system and method for treating water containing ammonia with a reverse osmosis membrane, in which the permeation of a disinfectant containing a chlorine-based oxidizing agent or a bromine-based oxidizing agent and a sulfamic acid compound through the reverse osmosis membrane is suppressed. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2017 / 141717 [Patent Document 2] Japanese Patent Publication No. 2018-183751 [Patent Document 3] Japanese Patent Publication No. 2018-069124 [Patent Document 4] Japanese Patent Publication No. 2018-069120 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to provide an operating method for an RO membrane system that uses a low removal efficiency RO membrane to treat water that requires slime control treatment, such as organic wastewater, and that can evenly sterilize the entire RO system, including the primary and secondary sides. [Means for solving the problem]

[0009] One embodiment of the present invention relates to an operating method for an RO membrane system in which water to be treated, such as organic wastewater requiring slime control treatment, is passed through a low-removal-rate RO membrane system, characterized in that the primary and secondary sides of the RO membrane are sterilized by including a slime control agent in the water supply to the RO membrane system.

[0010] In one aspect of the present invention, the low removal efficiency RO membrane is an RO membrane with an IPA removal rate of 70% or less, an RO membrane with a NaCl removal rate of 93-99%, or an RO membrane with a flux of 2.0 m / d or more at an effective pressure of 1 MPa and a feedwater temperature of 25°C.

[0011] In one aspect of the present invention, the slime control agent is a bound chlorine compound or a bound bromine compound.

[0012] In one aspect of the present invention, the slime control agent concentration on the primary side is adjusted so that a slime control agent of 0.1 mg / L as Cl2 or more is present as an active ingredient on both the primary and secondary sides of the RO membrane.

[0013] In one aspect of the present invention, the slime control agent is added to the primary and secondary sides of the RO membrane apparatus.

[0014] In one aspect of the present invention, the permeate from the RO membrane apparatus is passed through a high-removal-efficiency RO membrane apparatus.

[0015] In one aspect of the present invention, a mixture of at least a portion of the permeate from the RO membrane apparatus and other water is passed through the high-removal-efficiency RO membrane apparatus.

[0016] In one aspect of the present invention, the NaCl removal rate of the RO membrane in the high-removal-rate RO membrane apparatus is 99% or higher.

[0017] In one aspect of the present invention, the other water is river water, lake water, well water, municipal water, industrial water, or recovered water. [Effects of the Invention]

[0018] The inventors, while working to solve the problem of slime control in treated water systems such as organic wastewater that require slime control treatment, found that in the case of RO membranes with low removal rates, the removal rate of slime control agents is also low. According to the present invention, it is possible to sterilize both the primary and secondary sides of a low-removal-rate RO membrane, and by sterilizing the entire RO system including the primary and secondary sides evenly, biofouling can be efficiently prevented.

[0019] In one aspect of the present invention, biofouling of the high-rejection RO membrane is suppressed by passing permeated water containing the slime control agent obtained after sterilization of the secondary side through the high-rejection RO membrane. Furthermore, by treating this permeated water containing the slime control agent with the high-rejection RO membrane, the slime control agent and low-molecular-weight organic substances remaining in the permeated water of the low-rejection RO membrane are removed.

[0020] The required concentration of the slime control agent for suppressing biofouling varies depending on factors such as the organic matter concentration. Therefore, in one aspect of the present invention, when the organic matter concentration is high, an additional slime control agent is added to the secondary side. This suppresses biofouling on the secondary side.

Mode for Carrying Out the Invention

[0021] An operation method for an RO membrane device according to one aspect of the present invention is an operation method for an RO membrane device in which water to be treated that requires slime control, such as organic wastewater, is passed through a low-rejection RO membrane device, wherein the primary side and secondary side of the RO membrane are sterilized by causing the feed water for the RO membrane device to contain a slime control agent.

[0022] Examples of the low-rejection RO membrane (including membranes with low operating pressure) include RO membranes having an IPA (isopropyl alcohol) rejection rate of 0 to 70%, RO membranes having a NaCl rejection rate of 93 to 99%, or RO membranes having a flux of 2.0 to 10.0 m / d at an effective pressure of 1 MPa and a feed water temperature of 25°C.

[0023] As the low-rejection RO membrane, a polyamide-based RO membrane having a low IPA rejection rate can be suitably used. The IPA rejection rate can be calculated by measuring the IPA concentration in the feed water, concentrated water, and treated water. Membranes with a low NaCl rejection rate and membranes with a large amount of permeated water per pressure have a low organic matter rejection rate, so if the IPA concentration cannot be measured, suitability as a low-rejection RO membrane is determined from the NaCl rejection rate or the amount of permeated water per pressure.

[0024] RO membranes with low removal rates include, but are not limited to, Kurita Water Industries' K-RO-A-20P3-FX00, Aquaporin's Clear Ultra 8040, and LG Chemical's BW-MOST.

[0025] Furthermore, the RO membrane is not limited to new membranes; it may also be a membrane whose salt removal rate and organic matter removal rate have decreased due to long-term use, cleaning, or oxidation such as hypochlorite, resulting in a higher water volume. In that case, the RO membrane model with the lower removal rate may be one other than those mentioned above.

[0026] Examples of water to be treated that require slime control treatment using the method of the present invention include organic wastewater, inorganic wastewater, effluent, river water, industrial water, tap water, recovered water, general wastewater, and process wastewater. The TOC of this treated water is preferably 0.5 mg / L or higher, and particularly preferably around 1 to 500 mg / L.

[0027] Suitable slime control agents include bound chlorine compounds or bound bromine compounds, that is, reaction products of a chlorine-based oxidizing agent and a sulfamic acid compound, or reaction products of a bromine-based oxidizing agent and a sulfamic acid compound.

[0028] The ratio of the equivalent amount of the sulfamic acid compound to the equivalent amount of the brominated or chlorinated oxidizing agent is preferably 1 or more, and more preferably in the range of 1 to 3. If the ratio is less than 1, it may degrade the film, and if it exceeds 3, it may increase manufacturing costs.

[0029] Examples of bromine-based oxidizing agents include bromine (liquid bromine), bromine chloride, bromate, bromate salts, and hypobromous acid. Hypobromous acid may also be produced by reacting a bromide such as sodium bromide with a chlorine-based oxidizing agent such as hypochlorous acid.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] For the analysis of stabilized chlorine compositions, stabilized bromine compositions, and monochloramine, methods such as free chlorine analysis and total chlorine analysis using the DPD method can be applied. Measuring instruments employing the DPD method (for example, HACH's Pocket Residual Chloride Meter DR300) can measure the active ingredient reacted with the reagent as free chlorine or total chlorine concentration. In the case of bromine compounds, the concentration of the active ingredient reacting with the reagent can be determined, but the unit of measurement is mg / L as Cl2. For convenience, in this patent, even for bromine compounds, the concentration will be expressed as mg / L as Cl2 concentration (concentration measured by DR300). Instead of using such residual chlorine measuring instruments, one may use measuring instruments for bromine, or one may create a calibration curve and measure and quantify using the DPD method.

[0034] In one aspect of the present invention, the amount of sludge agent added to the feedwater on the primary side is adjusted so that a sludge agent of 0.1 mg / L as Cl2 or more is present as an active ingredient on both the primary and secondary sides of the RO membrane.

[0035] The sludge agent may be added only to the feedwater of the RO membrane, or it may be added to both the primary and secondary sides of the RO membrane.

[0036] In one aspect of the present invention, after treating the primary and secondary sides of the RO membrane with a slurry-retaining agent, all or part of the RO membrane permeate, or a mixture of it with other water, may be treated in a separate RO membrane apparatus.

[0037] Other examples of water include river water, lake water, well water, municipal water, industrial water, and recycled water.

[0038] As another RO membrane system, a high-removal-efficiency RO membrane system is preferred.

[0039] For high-removal-efficiency RO membranes, those with a NaCl removal rate of 99% or higher are preferred.

[0040] Commercially available high-removal-efficiency RO membranes include, but are not limited to, Nitto Denko's ES20, NTR-759-HR, ESPA2, CPA5, SWC4, SWC5; Toray's SUL-G, SU-720, TM720D, TM820V, TBW; Dupont's BW30, SW30; and LG Chemical's MaxRO, BW 400 R GS2.

[0041] There are no particular restrictions on the size of the RO membrane system, but 4-inch and 8-inch systems are preferred.

[0042] The method of the present invention can be applied to a variety of uses, including water treatment, wastewater recovery treatment, concentration, and polishing of treated water, but it is particularly suitable for wastewater recovery treatment. [Examples]

[0043] The following three types of slurry-retaining agents were prepared and used in the examples and comparative examples.

[0044] [Preparation of stabilized chloric acid composition] A stabilized chloric acid composition was prepared by mixing 50 parts by weight of a 12% sodium hypochlorite aqueous solution, 12 parts by weight of sodium sulfamate, 8 parts by weight of sodium hydroxide, and 30 parts by weight of water while cooling.

[0045] [Preparation of stabilized bromate composition] An aqueous solution of sodium bromide was prepared by dissolving 5.2 parts by weight of sodium bromide in 7.3 parts by weight of water. This solution was added to 30 parts by weight of an aqueous sodium hypochlorite solution containing 12% by weight of available chlorine (Cl2 equivalent), and stirred at room temperature (20°C) for 10 minutes to prepare an aqueous hypobromous acid solution. Next, an aqueous sodium sulfamate solution was prepared by adding 8.3 parts by weight of sulfamic acid to 8.6 parts by weight of water, and then adding 8.6 parts by weight of 48% sodium hydroxide while cooling. This solution was added to the aqueous hypobromous acid solution, and stirred at room temperature (20°C) for 10 minutes to obtain a stabilized bound bromate, which is an aqueous solution of a bound bromine compound. composition I obtained it.

[0046] [Preparation of monochloramine] A monochloramine aqueous solution was prepared by mixing an aqueous solution of 5.35 g of ammonium chloride dissolved in 494.65 g of water with an aqueous solution of sodium hypochlorite containing 12% by weight of available chlorine (Cl2 equivalent) dissolved in 450.5 g of water, while cooling the mixture.

[0047] <Reference example 1> Sample water prepared by adding 10 mg / L of IPA (reagent-grade isopropyl alcohol) and the above-mentioned solvent as available chlorine at a concentration of 1 mg / L as Cl2 to ultrapure water was passed through a flat-membrane RO test apparatus equipped with either a high-removal-efficiency RO membrane (Nitto Denko ES20) or a low-removal-efficiency RO membrane (Kurita Water Industries K-RO-A-20P3-FX00), and the removal rate was measured.

[0048] The operating conditions were a flux of 0.65 m / d and a recovery rate of 60%. The concentration of the solvent in the permeate was measured using the DR300 mentioned above. The results of the removal rate measurement are shown in Table 1.

[0049] [Table 1]

[0050] Evaluation water, prepared by dissolving NaCl to 500 mg / L in ultrapure water, was passed through a flat-membrane RO test apparatus equipped with a low-removal-efficiency RO membrane (Kurita Water Industries K-RO-A-20P3-FX00), and the NaCl removal rate was measured. The NaCl concentration in the permeate was measured using a conductivity meter. The operating conditions and the measured NaCl removal rates are shown in Table 2.

[0051] [Table 2]

[0052] ultra pure water of A flat-membrane RO test apparatus equipped with a low-removal-efficiency RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) was used to test water flow, and the flux was measured. Flux was calculated by dividing the treated water volume measured by a flow meter by the membrane area. The operating conditions and flux measurement results are shown in Table 3.

[0053] [Table 3]

[0054] <Example 1-1> In the wastewater recovery treatment of an electronic device factory containing IPA 1 mg / L (TOC concentration = 0.7 mg / L), when a recovery RO system using a low removal efficiency RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.5 mg / L.

[0055] When a stabilized hypochlorous acid composition was added as a slurry treatment agent at a concentration of 1 mg / L as Cl2, a concentration of 0.15 mg / L as Cl2 of the stabilized hypochlorous acid composition was detected in the secondary treated water (persemate from recovered RO measurement; the same applies hereinafter). As both the primary and secondary sides were treated with the slurry treatment agent, no biofouling was observed, and stable operation was possible.

[0056] <Example 1-2> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a low removal rate RO membrane (Aquaporin Clear Ultra 8040, IPA removal rate approximately 50-60%) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.4 mg / L.

[0057] When a stabilized hypobromite composition was added as a slurry-retaining agent at a concentration of 1 mg / L as Cl2, a concentration of 0.18 mg / L as Cl2 of the stabilized hypobromite composition was detected in the secondary treated water. Because both the primary and secondary sides were treated with the slurry-retaining agent, no biofouling was observed, and stable operation was possible.

[0058] <Examples 1-3> In the same wastewater recovery treatment at the same electronic device factory as in Example 1-1, when a recovery RO system using a low removal rate RO membrane (LG Chemical BW-MOST, IPA removal rate approximately 50-60%) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.4 mg / L.

[0059] When monochloramine was added as a slurry treatment agent at a concentration of 1 mg / L as Cl2, 0.9 mg / L as Cl2 of monochloramine was detected in the secondary treated water. Because both the primary and secondary sides were treated with the slurry treatment agent, no biofouling was observed, and stable operation was possible.

[0060] <Comparative Example 1-1> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a high-removal-efficiency RO membrane (ES20 manufactured by Nitto Denko) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.2 mg / L.

[0061] When a stabilized hypochlorous acid composition was added as a slurry-conditioning agent at a concentration of 1 mg / L as Cl2, the stabilized hypochlorous acid composition was not detected in the secondary treated water. This result indicates that the secondary slurry-conditioning treatment was insufficient.

[0062] <Comparative Example 1-2> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a high-removal-efficiency RO membrane (Toray SU-720) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.15 mg / L.

[0063] When a stabilized hypobromous acid composition was added as a slurry-conditioning agent at a concentration of 1 mg / L as Cl2, 0.03 mg / L as Cl2 of the stabilized hypobromous acid composition was detected in the secondary treated water. However, this result was insufficient for secondary slurry-conditioning treatment.

[0064] <Reference example 1-3> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a high-removal-efficiency RO membrane (Dupont BW30HRLE-440) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.1 mg / L.

[0065] When monochloramine was added as a slurry agent at a concentration of 1 mg / L as Cl2, 0.9 mg / L as Cl2 of monochloramine was detected in the secondary treated water.

[0066] <Example 2-1> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a low removal rate RO membrane (Aquaporin Clear Ultra 8040) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.4 mg / L.

[0067] This treated water was returned to the raw water in the ultrapure water production process, and when a 7:3 mixture of the treated water and the raw water was operated in a primary RO system using a high-removal-efficiency RO membrane (ESPA2 manufactured by Nitto Denko) at a recovery rate of 60%, the TOC of the treated water in the primary RO system was less than 0.1 mg / L.

[0068] When a stabilized hypochlorous acid composition at a concentration of 5 mg / L as Cl2 was added as a slurry control agent to the feedwater of the above-mentioned RO recovery system, a concentration of 0.8 mg / L as Cl2 of the stabilized hypochlorous acid composition was detected in the secondary treated water of the RO recovery system.

[0069] In the primary RO system feedwater, which consisted of a 7:3 mixture of treated water and raw water, a stabilized hypochlorous acid composition at 0.5 mg / L as Cl2 was detected. However, no stabilized hypochlorous acid composition was detected on the secondary side of the primary RO system, allowing for stable operation.

[0070] <Example 2-2> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a low removal rate RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.4 mg / L.

[0071] When this treated water was returned to the raw water in the ultrapure water production process, and a 7:3 mixture of the treated water and the raw water was operated in a primary RO system using a high-removal-efficiency RO membrane (CPA5 manufactured by Nitto Denko) at a recovery rate of 60%, the TOC of the treated water in the primary RO system was less than 0.1 mg / L.

[0072] When a stabilized hypobromite composition was added at a concentration of 5 mg / L as Cl2 as a slurry converter to the feedwater of the above-mentioned RO recovery system, a concentration of 0.9 mg / L as Cl2 of the stabilized hypobromite composition was detected in the secondary treated water of the RO recovery system.

[0073] In the primary RO system feedwater, which consisted of a 7:3 mixture of treated water and raw water, a stabilized hypobromite composition was detected at a concentration of 0.5 mg / L as Cl2. However, in the secondary side of the primary RO system, stabilized hypobromite was detected. bromine No acidic components were detected, and stable operation was achieved.

[0074] <Comparative Example 2-3> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a low removal rate RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.4 mg / L.

[0075] This treated water was returned to the raw water in the ultrapure water production process, and when the 7:3 mixture of recovered water and raw water was operated in a primary RO system using a low-removal-efficiency RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) at a recovery rate of 60%, the TOC of the treated water in the primary RO system was 0.3 mg / L.

[0076] When stabilized chloramine at 1 mg / L as Cl2 was added as a slurry-containing agent to the feedwater of the above-mentioned RO recovery system, 0.9 mg / L as Cl2 of chloramine was detected in the secondary treated water of the RO recovery system.

[0077] In the primary RO system feedwater, which consisted of a 7:3 mixture of treated water and raw water, chloramine was detected at a concentration of 0.7 mg / L as Cl2, and 0.6 mg / L of chloramine was detected on the secondary side of the primary RO system. The permeated organic components increased the load on the downstream UV oxidizer, and the permeated chloramine damaged the anion exchange resin, resulting in a decrease in neutral salt decomposition capacity and ion exchange capacity.

[0078] <Comparative Example 2-4> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a low removal rate RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.5 mg / L.

[0079] This treated water was returned to the raw water in the ultrapure water production process, and a 5:5 mixture of the recovered water and raw water was operated in a primary RO system using a low-removal-efficiency RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) at a recovery rate of 60%. The TOC of the treated water in the primary RO system was 0.3 mg / L.

[0080] When a stabilized hypochlorous acid composition at a concentration of 2 mg / L as Cl2 was added to the feedwater of the above-mentioned RO recovery system as a solvent, a concentration of 0.2 mg / L as Cl2 of the stabilized hypochlorous acid composition was detected in the secondary treated water of the RO recovery system.

[0081] In the primary RO system feedwater, which consisted of a 5:5 mixture of treated water and raw water, a stabilized hypochlorous acid composition at 0.1 mg / L as Cl2 was detected, while no stabilized hypochlorous acid composition was detected on the secondary side of the primary RO system. Furthermore, the permeated organic components increased the load on the subsequent UV oxidizer.

[0082] <Example 3> In the wastewater recovery treatment of the same electronic device factory as in Example 1-1, when a recovery RO system using a low removal rate RO membrane (Kurita Water Industries K-RO-A-20P3-FX00) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.5 mg / L.

[0083] When this treated water was returned to the raw water in the ultrapure water production process, and then a 7:3 mixture of the recovered water and the raw water was operated in a primary RO system using ES20 with a recovery rate of 60%, the TOC of the treated water in the primary RO system was less than 0.1 mg / L.

[0084] When a stabilized hypochlorous acid composition at 2 mg / L as Cl2 was added as a slurry control agent to the feedwater of the above-mentioned RO recovery system, a stabilized hypochlorous acid composition at 0.35 mg / L as Cl2 was detected in the secondary treated water of the RO recovery system.

[0085] Considering dilution due to mixing with raw water, a stabilized hypochlorous acid composition at a concentration of 0.3 mg / L as Cl2 was added to the feedwater of the primary RO system, resulting in a total stabilized hypochlorous acid composition concentration of 0.5 mg / L as Cl2. When treatment was carried out, the stabilized hypochlorous acid composition was not detected on the secondary side of the primary RO system, and stable operation was achieved.

[0086] <Example 4> In the same wastewater recovery treatment at the electronic device factory as in Example 1-1, when a recovery RO system using a high-removal-efficiency RO membrane (ES20 manufactured by Nitto Denko) with reduced organic matter removal performance (IPA removal rate decreased to 60%) was operated at a recovery rate of 75%, the TOC concentration in the treated water was approximately 0.4 mg / L.

[0087] This treated water was returned to the raw water in the ultrapure water production process, and when the recovered water and the raw water were mixed in a 7:3 ratio and operated in a primary RO system using a new high-efficiency RO membrane (Nitto Denko ES20) at a recovery rate of 60%, the TOC of the treated water in the primary RO system was less than 0.1 mg / L.

[0088] When a stabilized hypochlorous acid composition at 1 mg / L as Cl2 was added as a slurry control agent to the feedwater of the above-mentioned RO recovery system, a stabilized hypochlorous acid composition at 0.2 mg / L as Cl2 was detected in the secondary treated water of the RO recovery system.

[0089] In the primary RO system feedwater, which consisted of a 7:3 mixture of treated water and raw water, a stabilized hypochlorous acid composition at 0.14 mg / L as Cl2 was detected. However, no stabilized hypochlorous acid composition was detected on the secondary side of the primary RO system, allowing for stable operation.

Claims

1. In an operating method for an RO membrane system that passes water to be treated through a low-removal-efficiency RO membrane system, A method for operating an RO membrane system, wherein the primary and secondary sides of the RO membrane are sterilized by adding a slime control agent to the water supply of the RO membrane system, The low removal efficiency RO membrane is an RO membrane with an IPA removal rate of 70% or less, an RO membrane with a NaCl removal rate of 93-99%, or an RO membrane with a flux of 2.0 m / d or more at an effective pressure of 1 MPa and a feedwater temperature of 25°C. A method for operating an RO membrane apparatus, characterized in that the slime control agent is a reaction product of a chlorine-based oxidizing agent and a sulfamic acid compound, or a reaction product of a bromine-based oxidizing agent and a sulfamic acid compound.

2. The primary and secondary sides of the aforementioned RO membrane contain 0.1 mg / L as Cl as the active ingredient. ２ A method for operating an RO membrane apparatus according to claim 1, wherein the concentration of the slime control agent on the primary side is adjusted so that the above-mentioned slime control agent is present.

3. A method for operating an RO membrane apparatus according to claim 1, wherein the slime control agent is added to the primary and secondary sides of the RO membrane apparatus.

4. A method for operating an RO membrane apparatus according to claim 1, wherein the permeate from the RO membrane apparatus is passed through a high-removal-efficiency RO membrane apparatus.

5. A method for operating an RO membrane apparatus according to claim 1, wherein a mixture of at least a portion of the permeate from the RO membrane apparatus and other water is passed through the high-removal-efficiency RO membrane apparatus.

6. A method for operating an RO membrane apparatus according to claim 4 or 5, wherein the NaCl removal rate of the RO membrane of the high-removal-rate RO membrane apparatus is 99% or more.

7. The method for operating an RO membrane apparatus according to claim 6, wherein the other water is river water, lake water, well water, city water, industrial water, or recovered water.

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