Water treatment system, reverse osmosis membrane apparatus operation method, control device, and program

Abstract

This water treatment system provides optimal blockage suppression treatment that can be performed according to the fouling risk of two or more types of raw water. [Solution] The water treatment system 1 includes a reverse osmosis membrane device 6 that separates mixed water, obtained by mixing multiple raw waters of different water qualities, into permeate and concentrated water; a clogging suppression means 9 that suppresses clogging of the reverse osmosis membrane of the reverse osmosis membrane device; a flow rate measuring means 11 that measures the flow rate of each of the multiple raw waters; and a control device 10 that obtains the flow rate ratio of the multiple raw waters based on the measurement value of the flow rate measuring means 11 and controls the clogging suppression operation of the clogging suppression means 9 in stages according to the flow rate ratio.

Description

[Technical Field]

[0001] The present invention relates to a water treatment system, a method for operating a reverse osmosis membrane apparatus, a control device, and a program. [Background technology]

[0002] Pure water and ultrapure water are used as cleaning water and other applications in the manufacturing processes of semiconductor devices and liquid crystal displays. Pure water and ultrapure water are produced by removing impurities (e.g., organic matter, ionic components, fine particles, bacteria, etc.) contained in the raw water. In water treatment systems such as pure water (ultrapure water) production systems, reverse osmosis (RO) membrane treatment is performed to remove organic matter (TOC: total organic carbon) and other substances contained in the raw water.

[0003] In water treatment systems with reverse osmosis (RO) membrane systems, there is a problem of the RO membrane surface becoming clogged with organic matter and scale components. In particular, when the concentrated water from the first-stage RO membrane system is treated in the second-stage RO membrane system, the concentration ratio becomes higher in the second-stage RO membrane system, thus increasing the risk of RO membrane clogging.

[0004] Furthermore, in recent years, in light of the depletion of water resources, efforts are being made to effectively utilize water resources in the production of pure water and ultrapure water by using recycled water, which is produced by treating and reusing groundwater, municipal water, industrial water, and domestic wastewater (sewage), as raw water, or by using recovered water, which is produced by treating and reusing factory wastewater. For this reason, water treatment systems may use two or more water sources with different water qualities (municipal water, industrial water, groundwater, recycled water, recovered water, etc.) as raw water. Normally, a water source with a low fouling risk is used as the raw water for treatment, but if the required amount of treated water increases or if a sufficient amount of raw water cannot be secured due to some trouble, another water source with a high fouling risk may be used as the raw water for treatment. When water with a high fouling risk is used as the raw water, the risk of blockage of the RO membrane (especially the RO membrane of the second-stage RO membrane system) increases accordingly.

[0005] Methods have been proposed to reduce the risk of RO membrane clogging, including adjusting the amount of chemicals added and adjusting the recovery rate of the RO membrane system. Patent Document 1 describes a method for optimizing the recovery rate of treated water by measuring the temperature, electrical conductivity, and flow rate of concentrated water discharged from a reverse osmosis membrane, and controlling the discharge amount of concentrated water based on each measured value. Patent Document 2 describes a method for detecting the water quality of concentrated water from a reverse osmosis membrane module, calculating the Langelier index of the concentrated water based on the detected water quality values, and controlling the recovery rate adjustment and raw water pH adjustment so that the calculated Langelier index is maintained in a range of zero or less. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-984 [Patent Document 2] Japanese Patent Publication No. 2011-147899 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the method described in Patent Document 1 does not provide optimal clogging suppression treatment according to the fouling risk of two or more types of raw water. Therefore, even when the fouling risk is not very high and the risk of RO membrane clogging can be reduced by adding chemicals, there is a problem in that the water recovery rate (recovery rate of the RO membrane system) decreases in order to control the discharge amount of concentrated water. The method described in Patent Document 2 also has the problem that, because it does not provide optimal blockage suppression treatment according to the fouling risk of two or more types of raw water, the water recovery rate tends to decrease and the amount of chemicals used tends to increase.

[0008] The object of the present invention is to provide a water treatment system, a reverse osmosis membrane apparatus, a control device, and a program that can perform optimal blockage suppression treatment according to the fouling risk of two or more types of raw water. [Means for solving the problem]

[0009] The water treatment system of the present invention is A reverse osmosis membrane apparatus that separates a mixed water obtained by mixing multiple raw waters with different water qualities into permeate and concentrated water, A means for suppressing blockage of the reverse osmosis membrane in the reverse osmosis membrane apparatus, A flow rate measuring means for measuring the flow rate of each of the aforementioned multiple raw water sources, The system includes a control device that obtains the flow rate ratios of the plurality of raw waters based on the measured values ​​of the flow rate measuring means, and controls the blockage suppression operation of the blockage suppression means in stages according to the flow rate ratios.

[0010] The present invention relates to a reverse osmosis membrane apparatus operation method for separating mixed water, obtained by mixing multiple raw waters with different water qualities, into permeate and concentrated water. A process for calculating the flow rate ratio of the multiple raw waters based on the measured flow rates of each of the multiple raw waters, In accordance with the calculated flow rate ratio, a process is performed to gradually suppress blockage of the reverse osmosis membrane in the reverse osmosis membrane apparatus.

[0011] The present invention is a control device for controlling the operating conditions of a reverse osmosis membrane apparatus that separates mixed water, obtained by mixing multiple raw waters with different water qualities, into permeate and concentrated water. A flow rate ratio acquisition unit that acquires the flow rate ratio of the plurality of raw waters based on the measured flow rate of each of the plurality of raw waters, The system includes a control unit that, according to the flow rate ratio acquired by the flow rate ratio acquisition unit, controls the blockage suppression operation of the blockage suppression means for suppressing blockage of the reverse osmosis membrane of the reverse osmosis membrane apparatus in stages.

[0012] The program of the present invention, On the computer, A procedure for controlling the operating conditions of a reverse osmosis membrane device that separates mixed water obtained by mixing a plurality of raw waters with different water qualities into permeate water and concentrated water, a procedure for calculating the flow rate ratio of the plurality of raw waters based on the measured values of the flow rates of each of the plurality of raw waters; and a procedure for stepwise controlling the blocking suppression operation of blocking suppression means for suppressing blocking of the reverse osmosis membrane of the reverse osmosis membrane device according to the calculated flow rate ratio are executed.

Advantages of the Invention

[0013] According to the present invention, by performing an optimal blocking suppression process according to the fouling risks of two or more types of raw waters, it is possible to suppress the blocking of the RO membrane while reducing the chemical usage amount and improving the water recovery rate.

Brief Description of the Drawings

[0014] [Figure 1] It is a block diagram schematically showing the configuration of a water treatment system according to an embodiment of the present invention. [Figure 2] It is a diagram showing the correspondence relationship between each blocking suppression means, the chemical usage amount, and the flow rate ratio. [Figure 3] It is a diagram showing the correspondence relationship between each blocking suppression means, the water recovery rate, and the flow rate ratio. [Figure 4] It is a block diagram showing the configuration of a control device. [Figure 5] It is a flowchart showing the control procedure of the operating conditions of the brine reverse osmosis membrane device by a control device.

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the embodiments are merely examples, and are not intended to limit the scope of the present invention thereto.

[0016] Figure 1 is a schematic block diagram showing the configuration of a water treatment system according to one embodiment of the present invention. In Figure 1, solid arrows indicate piping (or flow paths), and dashed arrows indicate signal lines (or signals).

[0017] Referring to Figure 1, the water treatment system 1 of this embodiment includes a raw water tank 2 that stores mixed water obtained by mixing two types of raw water with different water qualities. Downstream from the raw water tank 2, there is a pretreatment facility 3, an RO raw water tank 4, a pump 5, and an RO membrane device 6. The raw water tank 2 is connected to the pretreatment facility 3 via piping. The pretreatment facility 3 includes, but is not limited to, a filtration device, an ion exchange device, a decarbonation device, etc. In the pretreatment facility 3, unit devices such as a turbidity removal membrane device or a softening device may be used as needed. Although not shown, a pump may be provided between the raw water tank 2 and the pretreatment facility 3 to supply water from the raw water tank 2 to the pretreatment facility 3. The discharge side of the pretreatment facility 3 is connected to the RO raw water tank 4 via piping. The discharge side of the RO raw water tank 4 is connected to the RO membrane device 6 via piping, and a pump 5 is provided in this piping. By operating the pump 5, the pretreated water stored in the RO raw water tank 4 is supplied to the RO membrane device 6.

[0018] The RO membrane system 6 separates the mixed water (a mixture of two types of raw water with different water qualities) from the RO raw water tank 4 into permeate and concentrated water. The RO membrane system 6 consists of an RO membrane system 61 and a brine reverse osmosis (B-RO) membrane system 62. The RO membrane system 61 is configured to remove impurities from the RO raw water using reverse osmosis, for example, by having one or more reverse osmosis membrane elements. The RO membrane system 61 discharges the permeate that has passed through the reverse osmosis membrane and the concentrated water containing the impurities separated by the reverse osmosis membrane. The B-RO membrane system 62 has a similar configuration to the RO membrane system 61. Other water, such as the permeate from the B-RO membrane system 62, may also be mixed into the RO raw water tank 4. Note that the B-RO membrane system 62 is not a mandatory component and can be omitted.

[0019] The concentrated water discharge side of the RO membrane device 61 is connected to the concentrated water tank 7 via piping. The discharge side of the concentrated water tank 7 is connected to the B-RO membrane device 62 via piping 9a. Note that the concentrated water tank 7 is not an essential component and can be omitted. The permeate from the B-RO membrane device 62 is returned via piping 9c to a stage upstream of the B-RO membrane device 62, such as the RO raw water tank 4. The concentrated water discharge side of the B-RO membrane device 62 is connected to piping 9b. The concentrated water may be discharged outside the system via piping 9b, or a portion of the concentrated water may be returned to the concentrated water tank 7 for circulation. The RO membrane device 61 can be called a first reverse osmosis membrane device that separates mixed water into first permeate and first concentrated water. The B-RO membrane device 62 can be called a second reverse osmosis membrane device that separates the concentrated water (first concentrated water) from the RO membrane device 61 into second permeate and second concentrated water.

[0020] In addition to the above configuration, the water treatment system 1 further includes a clogging suppression means 9 for suppressing clogging of the RO membrane of the RO membrane device 6 (in this case, the RO membrane of the B-RO membrane device 62). The clogging suppression means 9 can suppress clogging of the RO membrane in stages. The clogging suppression means 9 includes, for example, automatic pressure regulating valves 91 to 95, a pump 96 equipped with an inverter 96a, a dispersant injection device 97, and pH adjustment devices 98, 99, and these elements constitute a plurality of clogging suppression means for suppressing clogging of the RO membrane of the B-RO membrane device 62. The clogging suppression means 9 may be configured to include at least one of the elements listed herein.

[0021] In the blockage suppression means 9, the pump 96 and the pressure regulating automatic valve 91 are provided in the piping 9a between the B-RO membrane device 62 and the concentrated water tank 7. The pressure regulating automatic valve 91 is located on the B-RO membrane device 62 side of the pump 96. One end of a branch pipe 9d is connected between the pressure regulating automatic valve 91 and the pump 96 in the piping 9a. The other end of the branch pipe 9d is connected to the piping 9b on the concentrated water discharge side of the B-RO membrane device 62. This branch pipe 9d is a bypass pipe and is equipped with a pressure regulating automatic valve 92. A pressure regulating automatic valve 95 is provided in the piping 9b on the concentrated water discharge side of the B-RO membrane device 62. One end of a pipe 9e is connected to the piping 9b on the concentrated water discharge side of the B-RO membrane device 62. The other end of the pipe 9e is connected to the concentrated water tank 7 and is equipped with a pressure regulating automatic valve 93. A pipe 9f is connected to pipe 9b on the concentrated water discharge side of the B-RO membrane device 62, and an automatic pressure regulating valve 94 is installed in this pipe 9f. The arrangement of pipes 9b, 9d to 9f can be changed as needed.

[0022] The dispersant injection equipment 97 is located between the pump 5 and the RO membrane device 61 and adds a dispersant to the water supplied to the RO membrane device 61. The dispersant injection equipment 97 may also be located in the concentration tank 7 or the piping 9a. The pH adjustment equipment 98 may be located immediately before or after the pressure regulating automatic valve 91 in the piping 9a (on the side of the B-RO membrane device 62 than the part where the branch piping 9d is connected) and adds an acid for pH adjustment to the water supplied to the B-RO membrane device 62. Suitable acid agents include, for example, hydrochloric acid, sulfuric acid, citric acid, and oxalic acid, with hydrochloric acid being particularly preferred. The pH adjustment equipment 99 may be installed to add an acid for pH adjustment to the concentrated water of the RO membrane device 61 stored in the concentration tank 7. The acid added by the pH adjustment equipment 99 can be the same as the acid added by the pH adjustment equipment 98. In this embodiment, the system may be configured to include at least one of the branch pipe 9d, pipe 9f, dispersant injection equipment 97, and pH adjustment equipment 98, 99.

[0023] Here, we will specifically describe several means for suppressing blockage of the RO membrane in the B-RO membrane apparatus 62.

[0024] (First blockage suppression means) The first blockage suppression means consists of a dispersant injection device 97. The dispersant injection device 97 suppresses blockage of the RO membranes of the RO membrane device 61 and the B-RO membrane device 62 by adding a dispersant to the water supplied to the RO membrane device 61. The dispersant injection device 97 may be configured to add the dispersant to the concentrated water of the RO membrane device 61 or the water supplied to the B-RO membrane device 62 instead of the water supplied to the RO membrane device 61. The amount of dispersant added should be 5 to 200 mg / L, preferably 10 to 50 mg / L, as a concentration in the concentrated water of the RO membrane. If the amount of dispersant added is too small, the blockage suppression effect will decrease, and if the amount of dispersant added is too large, it will be disadvantageous in terms of chemical costs.

[0025] (Second means of preventing blockage) The second means of preventing blockage consists of a function to flush the RO membrane of the B-RO membrane device 62. Any water can be used as flushing water, but here, from the viewpoint of not requiring additional equipment, the water supplied from the concentration tank 7 (stored water) is used. When flushing is performed, the automatic adjustment valves 92, 93, and 95 are closed, and the automatic pressure adjustment valves 91 and 94 are opened, and water is flowed at low pressure to the primary side of the RO membrane of the B-RO membrane device 62. Flushing is performed to prevent blockage of the RO membrane of the B-RO membrane device 62. The flushing interval is, for example, once every 1 to 24 hours, preferably once every 4 to 12 hours. The flushing time is, for example, in the range of 30 seconds to 15 minutes, preferably in the range of 1 to 5 minutes. If the flushing time is too short, the flushing effect will decrease, and if the flushing time is too long, the recovery rate will decrease. The flushing discharge may consist of only the initial, high-concentration portion, with the later, lower-concentration portion being returned to a separate concentration tank (not shown) via piping.

[0026] (Third means of preventing blockage) The third blockage suppression means consists of a pH adjustment device 98. The pH adjustment device 98 adds an acid agent to the flushing water. In the pH adjustment device 98, the amount of acid agent added may be adjusted so that the flushing water reaches a preset pH value, or a fixed amount of acid agent may be added. The pH value of the flushing water is preferably in the range of 1 to 3. If the pH value of the flushing water is too low, the amount of acid agent used will increase, and if the pH value of the flushing water is too high, the cleaning effect will decrease.

[0027] (Fourth means of preventing blockage) The fourth means of preventing blockage consists of a pH adjustment device 99. The pH adjustment device 99 adds an acid for pH adjustment to the concentrated water of the RO membrane device 61 stored in the concentration tank 7. By passing the pH-adjusted concentrated water through the B-RO membrane device 62, blockage of the RO membrane of the B-RO membrane device 62 is suppressed. In the pH adjustment device 99, the amount of acid added may be adjusted so that the concentrated water stored in the concentration tank 7 reaches a preset pH value, or a fixed amount of acid may be added. The pH value of the concentrated water is preferably in the range of 4 to 6, and particularly preferably in the range of 4.5 to 5.5 from the viewpoint of reducing the solubility of aluminum. If the pH value of the concentrated water is too low, the blocking rate of the RO membrane (the percentage of a specific solute whose permeation is blocked by the RO membrane) will decrease significantly. Note that a pH adjustment device 98 may be used instead of the pH adjustment device 99.

[0028] (Fifth means of preventing blockage) The fifth blockage suppression means consists of a function to adjust the recovery rate of the B-RO membrane device 62. The recovery rate is expressed as the ratio of the amount of treated water discharged from the B-RO membrane device 62 to the amount of water supplied to the B-RO membrane device 62. When the discharge rate of concentrated water increases, the discharge rate of treated water decreases, and as a result, the recovery rate decreases. Conversely, when the discharge rate of concentrated water decreases, the discharge rate of treated water increases, and as a result, the recovery rate increases. Here, the recovery rate is adjusted by closing the automatic adjustment valves 92, 93, and 94 and opening the automatic pressure adjustment valves 91 and 95 to adjust the discharge rate of concentrated water from the B-RO membrane device 62. The automatic pressure adjustment valve 95 may be an automatic valve with adjustable opening degree, and the discharge rate of concentrated water may be adjusted by adjusting the opening degree and opening / closing time, or the pressure of the supplied water may be adjusted by adjusting the opening degree of the inverter 96a of the pump 96 or the automatic valve 91 with adjustable opening degree, and the discharge rate of concentrated water may be adjusted. Alternatively, the recovery rate may be adjusted by adjusting the opening degree of the automatic valve 93 with adjustable opening degree to circulate a portion of the concentrated water. Adjustment using the pressure regulating automatic valve 93 or 95 has the advantage of easy operation adjustment because the amount of water supplied to the B-RO membrane device 62 does not change. On the other hand, adjustment using the inverter 96a of the pump 96 has the advantage of a greater effect in suppressing membrane fouling because the amount of water supplied to the B-RO membrane device 62 and the pressure decrease, which lowers the flow velocity (Flux). The adjustment range for the recovery rate is in the range of 20 to 70%, preferably in the range of 30 to 60%.

[0029] (Sixth means of preventing blockage) The sixth blockage prevention means consists of a function to bypass the B-RO membrane device 62. When bypassing, the automatic adjustment valves 91, 93, and 94 are closed, and the automatic pressure adjustment valves 92 and 95 are opened, so that the concentrated water from the concentration tank 7 does not flow to the B-RO membrane device 62, but instead flows to pipe 9b via pipe 9d.

[0030] The water treatment system 1 of this embodiment includes a control device 10 and a flow rate measuring means 11 for measuring the flow rate of each raw water to control the blockage suppression means 9 described above. The flow rate measuring means 11 includes flow meters 11a and 11b. The flow meters 11a and 11b measure the flow rates of two raw waters supplied to the raw water tank 2, respectively. The control device 10 obtains the flow rate ratio of the two raw waters based on the measured values ​​of the flow meters 11a and 11b, and controls the blockage suppression operation of the blockage suppression means 9 in stages according to the flow rate ratio. For example, the control device 10 differentially operates the first to sixth blockage suppression means in stages in a predetermined order. The flow rate ratio is, for example, the ratio of the flow rate of the raw water with a higher risk of RO membrane blockage to the total flow rate obtained by summing the flow rates of the two raw waters (the proportion of raw water with a higher risk of RO membrane blockage). The control device 10 controls the operating conditions of the B-RO membrane device 62 so that the blockage suppression means is selected in stages according to the flow rate ratio. Note that the flow rate measuring means 11 is not limited to flow meters 11a and 11b. The flow rate measuring means 11 may be a means of indirectly measuring or calculating the flow rate (for example, a means of calculating the flow rate using a triangular weir).

[0031] The control of operating conditions by the control device 10 will be described in detail below. The water quality of each raw water sample is measured in advance to determine which raw water has a high risk of fouling due to inorganic scales. Here, a raw water sample with a high risk of fouling is one in which, when the concentration ratio of the raw water is gradually increased, the concentration of any component causing fouling (e.g., calcium carbonate, calcium fluoride, calcium sulfate, silica, aluminum, iron, manganese, etc.) exceeds the threshold the fastest compared to other raw water samples. The threshold values ​​(solubility) for each component are as follows. All values ​​are for concentrated water.

[0032] [Calcium carbonate] The value is calculated using the Langelier index and set to >0. The Langelier index is a value that represents the properties of water from a corrosion prevention perspective, and is defined as the difference between the actual pH value and the pH value when calcium carbonate in the water is in equilibrium, neither dissolving nor precipitating. A Langelier index greater than 0 makes scale precipitation more likely. [Calcium fluoride] Calcium fluoride solubility product = [Ca2 + ([F - 2 ) = 4.0×10 -11 (Mol 3 / L 3 ) [Calcium sulfate] Calcium sulfate solubility product = [Ca2 + [SO4 2- = 1.0×10 -5 (Mol 2 / L 2 ) [Silica] Silica solubility = 4T + 20 mg / L (T: water temperature) [Aluminum] Aluminum threshold = 0.1 mg / L [Iron] Iron threshold = 0.2 mg / L [Manganese] Manganese threshold = 0.05 mg / L

[0033] In addition, when it is expected that the pretreatment facility 3 removes the components of the fouling risk substances, except for those components, raw water with a high risk of fouling due to inorganic scale may be determined.

[0034] In this embodiment, the raw water in which the flowmeter 11a is arranged is set as raw water with a high risk of fouling. The control device 10 acquires the ratio (flow rate ratio) of the raw water with a high risk of fouling based on the measured values of the flowmeters 11a and 11b. Let the measured value of the flowmeter 11a be x1 and the measured value of the flowmeter 11b be x2. The ratio (flow rate ratio) X (%) of the raw water with a high risk of fouling is given by X = x1 ÷ (x1 + x2) × 100. The control device 10 controls the operating conditions of the B-RO membrane device 62 using the flow rate ratio X as an index. Specifically, the control device 10 gradually activates the plurality of fouling suppression means 9 of the fouling suppression means 9 in ascending order of the amount of chemicals used to suppress the blockage of the RO membrane or in ascending order of the water recovery rate through the RO membrane based on the flow rate ratio X.

[0035] ​Figure 2 shows the correspondence between each blockage suppression method, the amount of chemical used, and the proportion of high-scale raw water (flow rate ratio X). In Figure 2, the vertical axis represents the amount of chemical used, and the horizontal axis represents the proportion of high-scale raw water (flow rate ratio X) (%). "(1)" to "(6)" shown in Figure 2 represent the first to sixth blockage suppression methods of blockage suppression method 9.

[0036] In the example in Figure 2, the amount of chemicals used is given by the following relationship: [6th blockage suppression means] < [1st and 2nd blockage suppression means] < [3rd blockage suppression means] < [4th and 5th blockage suppression means]. Normal operation is performed when the flow rate ratio X is less than 20%. The 1st blockage suppression means is selected when the flow rate ratio X is between 20% and 30%. The 2nd blockage suppression means is selected when the flow rate ratio X is between 30% and 50%. The 3rd blockage suppression means is selected when the flow rate ratio X is between 50% and 60%. The 4th blockage suppression means is selected when the flow rate ratio X is between 60% and 80%. The 5th blockage suppression means is selected when the flow rate ratio X is between 80% and 90%. The 6th blockage suppression means is selected when the flow rate ratio X is 90% or more. Furthermore, the sixth blockage suppression means is a bypass, and the B-RO membrane device 62 is shut down, so it is selected as the final blockage suppression means regardless of the amount of chemicals used.

[0037] Furthermore, the range of the flow rate ratio X(%) set for each blockage suppression means is not limited to the range shown in Figure 2. The range of the flow rate ratio X(%) can be set in any way as long as the operating conditions of the B-RO membrane system 62 can be appropriately controlled according to the fouling risk of the two raw waters, and the amount of chemicals used can be reduced while suppressing RO membrane blockage.

[0038] Figure 3 shows the correspondence between each blockage suppression means, the water recovery rate, and the proportion of high-scale raw water (flow rate ratio X). In Figure 3, the vertical axis represents the water recovery rate, and the horizontal axis represents the proportion of high-scale raw water (flow rate ratio X) (%). "(1)" to "(6)" shown in Figure 3 represent the first to sixth blockage suppression means of blockage suppression means 9.

[0039] In the example in Figure 3, the water recovery rate is given the relationship [First blockage suppression means] > [Second, third, and fourth blockage suppression means] > [Fifth blockage suppression means] > [Sixth blockage suppression means]. Normal operation is performed when the flow rate ratio X is less than 20%. The first blockage suppression means is selected when the flow rate ratio X is between 20% and 30%. The second blockage suppression means is selected when the flow rate ratio X is between 30% and 50%. The third blockage suppression means is selected when the flow rate ratio X is between 50% and 60%. The fourth blockage suppression means is selected when the flow rate ratio X is between 60% and 80%. The fifth blockage suppression means is selected when the flow rate ratio X is between 80% and 90%. The sixth blockage suppression means is selected when the flow rate ratio X is 90% or more. Furthermore, the sixth blockage suppression means is a bypass, and the B-RO membrane device 62 is shut down, so it is selected as the final blockage suppression means regardless of the water recovery rate.

[0040] Furthermore, the range of the flow rate ratio X(%) set for each clogging suppression means is not limited to the range shown in Figure 3. The range of the flow rate ratio X(%) can be set in any way as long as the operating conditions of the B-RO membrane system 62 can be appropriately controlled according to the fouling risk of the two raw waters, and the water recovery rate can be improved while suppressing clogging of the RO membrane.

[0041] Figure 4 is a block diagram showing the configuration of the control device 10. The control device 10 is composed of a computer such as a CPU (Central Processing Unit) that operates according to a computer program (hereinafter referred to as "program") that describes the processing content as a procedure, and has a control unit 14, a flow rate ratio acquisition unit 12, and a storage unit 13.

[0042] The storage unit 13 holds programs and data necessary for controlling the blockage suppression means 9 and the RO membrane device 6 (RO membrane device 61 and B-RO membrane device 62). For example, the storage unit 13 holds the correspondence between the amount of chemicals used and the ratio of each blockage suppression means to high-scale raw water (flow rate ratio X) shown in Figure 2, and the correspondence between the water recovery rate and the ratio of each blockage suppression means to high-scale raw water (flow rate ratio X) shown in Figure 3, as data necessary for processing. The storage unit 13 may be, for example, a memory such as ROM (Read Only Memory) or RAM (Random Access Memory), or an HDD (Hard Disk Drive).

[0043] Alternatively, the program may be recorded on a recording medium readable by the control device 10, and the program recorded on this recording medium may be read by the control device 10 and executed. The recording medium includes, for example, portable recording media such as floppy disks, magneto-optical disks, DVDs (Digital Versatile Discs), CDs (Compact Discs), Blu-ray (Registered Trademark) Discs, USB (Universal Serial Bus) memory, and SD cards.

[0044] The flow rate ratio acquisition unit 12 acquires the flow rate ratio X based on the measured values ​​of the flow meters 11a and 11b. The control unit 14 operates according to the program stored in the storage unit 13 and controls the operating conditions of the B-RO membrane apparatus 62 by the control device 10 by sequentially activating each of the blockage suppression means 9 in a predetermined order according to the flow rate ratio X acquired by the flow rate ratio acquisition unit 12.

[0045] Figure 5 is a flowchart showing the control procedure for the operating conditions of the B-RO membrane apparatus 62 by the control device 10. First, the flow rate ratio acquisition unit 12 acquires the flow rate ratio X based on the measured values ​​of the flow meters 11a and 11b (step S10). Next, the control unit 14 determines whether the flow rate ratio X is less than 20% (step S11).

[0046] If the determination in step S11 is "Yes", the control unit 14 causes the B-RO membrane apparatus 62 to operate normally (step S12). If the determination in step S11 is "No", the control unit 14 determines whether the flow rate ratio X is less than 30% (step S13). If the determination in step S13 is "Yes", the control unit 14 causes the first blockage suppression means to add the dispersant (step S14). If the determination in step S13 is "No", the control unit 14 determines whether the flow rate ratio X is less than 50% (step S15).

[0047] If the determination in step S15 is "Yes", the control unit 14 causes the second blockage suppression means to perform a flushing operation (step S16). If the determination in step S15 is "No", the control unit 14 determines whether the flow rate ratio X is less than 50% (step S17). If the determination in step S17 is "Yes", the control unit 14 causes the third blockage suppression means to perform acid flushing operation (step S18). If the determination in step S17 is "No", the control unit 14 determines whether the flow rate ratio X is less than 80% (step S19).

[0048] If the determination in step S19 is "Yes", the control unit 14 causes the pH adjustment operation using the fourth blockage suppression means (step S20). If the determination in step S19 is "No", the control unit 14 determines whether the flow rate ratio X is less than 90% (step S21). If the determination in step S21 is "Yes", the control unit 14 is instructed to perform recovery rate adjustment operation using the fifth blockage suppression means (step S22). If the determination in step S21 is "No", the control unit 14 is instructed to perform bypass operation using the sixth blockage suppression means (step S23).

[0049] After processing steps S11, S14, S16, S18, S20, S22, and S23 described above, the process returns to step S10. The series of processes from step S10 to steps S11, S14, S16, S18, S20, S22, and S23 may be repeated continuously, or they may be repeated at predetermined time intervals using a timer.

[0050] By controlling the operating conditions of the B-RO membrane system 62 as described above, multiple clogging suppression means can be activated in stages, allowing processing without excessively reducing the water recovery rate or increasing the amount of chemicals used when the risk of RO membrane clogging is relatively low. For example, if the risk of RO membrane clogging is not very high, clogging can be suppressed by adding a dispersant alone, and processing can be performed without reducing the water recovery rate. In this way, optimal clogging suppression treatment can be performed according to the fouling risk of the raw water, making it possible to suppress RO membrane clogging while reducing the amount of chemicals used and improving the water recovery rate.

[0051] Furthermore, since only flow meters are used to measure the flow rate of each raw water source, without using measuring instruments to measure water quality, the number of instruments can be reduced, and costs can be lowered.

[0052] In this embodiment, mixed water is treated by mixing two raw waters with different water qualities, but the mixed water may be a mixture of three raw waters with different water qualities. In this case, a flow meter is provided for each raw water. Then, the flow rate ratio X is obtained for the raw water with the highest risk of fouling due to inorganic scale, and the operating conditions of the B-RO membrane device 62 described above are controlled based on this flow rate ratio X. This makes it possible to perform optimal blockage suppression treatment according to the fouling risk of two or more types of raw water.

[0053] Furthermore, although the first to sixth clogging suppression means are selected in stages in this embodiment, the system is not limited thereto. The operating conditions of the B-RO membrane apparatus 62 may be controlled using one or more of the first to sixth clogging suppression means. As shown in Figures 2 and 3, the clogging suppression means listed on the graph have lower chemical usage and lower water recovery rates as they are moved to the left of the graph. Therefore, it is preferable to use two or more clogging suppression means listed on the left side of the graph. The more clogging suppression means used, the more gradually clogging of the RO membrane can be suppressed, optimizing chemical usage and water recovery rates.

[0054] Furthermore, two or more of the first to fifth blockage suppression means may be used in combination. For example, when the flow rate ratio X is 50% or more and less than 60%, the first to third blockage suppression means may be used in combination.

[0055] Furthermore, at least one of the first to sixth blockage suppression means may be divided into two or more means. For example, the first blockage suppression means may be divided into multiple means with different amounts of dispersant added (specifically, means with a small amount and means with a large amount). Also, the second blockage suppression means may be divided into multiple means with different flushing frequencies or durations (specifically, means with a high flushing frequency and means with a low flushing frequency, or means with a long flushing duration and means with a short flushing duration, etc.).

[0056] The water treatment system 1 of this embodiment is not limited to the illustrated configuration. Unit operating devices that constitute a pure water production system or an ultrapure water production system may be applied to the water treatment system 1 as needed. An ultrapure water production system, for example, consists of a primary pure water system that produces pure water and a subsystem that further removes impurities from the pure water produced by the primary pure water system. The primary pure water system mainly consists of an activated carbon unit, a 2B3T (two-bed, three-column ion exchange system), a reverse osmosis membrane system, an ultraviolet irradiation unit, a multi-bed pure water system (SBP), and a degasser, while the subsystem mainly consists of an ultraviolet irradiation unit, an ion exchange unit, a degasser, and an ultrafiltration membrane system. These components (unit operating devices) may be applied to the water treatment system 1 as needed. [Explanation of Symbols]

[0057] 1. Water treatment system 2 Raw water tank 3. Pre-treatment equipment 4 RO raw water tanks 5 pumps 6, 61 RO membrane equipment 62 B-RO membrane equipment 7. Concentration tank 9 Blockage suppression means 10 Control device 11 Flow measurement means 11a, 11b flowmeter

Claims

1. A reverse osmosis membrane apparatus that separates a mixed water obtained by mixing multiple raw waters with different water qualities into permeate and concentrated water, A means for suppressing blockage of the reverse osmosis membrane in the reverse osmosis membrane apparatus, A flow rate measuring means for measuring the flow rate of each of the aforementioned multiple raw water sources, A water treatment system comprising: a control device that acquires the flow rate ratio of a plurality of raw waters based on the measurement value of the flow rate measuring means, and controls the blockage suppression operation of the blockage suppression means in stages according to the flow rate ratio.

2. The aforementioned blockage suppression means comprises a plurality of blockage suppression means for suppressing blockage of the reverse osmosis membrane of the reverse osmosis membrane apparatus. The water treatment system according to claim 1, wherein the control device differentially controls the plurality of blockage suppression means in a predetermined order in steps according to the flow rate ratio of the plurality of raw waters.

3. The water treatment system according to claim 2, wherein the control device operates the plurality of clogging suppression means in a stepwise manner, in order of decreasing amount of chemicals used to suppress clogging of the reverse osmosis membrane, or in order of increasing water recovery rate through the reverse osmosis membrane.

4. The water treatment system according to claim 2, wherein the plurality of blockage suppression means comprises two or more means from among means of adding a dispersant to the water supplied to the reverse osmosis membrane, means of flushing the reverse osmosis membrane, means of adding an acid to the flushing water used for flushing, means of adding an acid to the water supplied to the reverse osmosis membrane, means of adjusting the recovery rate of the reverse osmosis membrane device, and means of bypassing the reverse osmosis membrane device.

5. The reverse osmosis membrane apparatus is, A first reverse osmosis membrane apparatus for separating the mixed water into a first permeate and a first concentrated water, The first reverse osmosis membrane apparatus is supplied with the first concentrated water, and the second reverse osmosis membrane apparatus separates the first concentrated water into a second permeate and a second concentrated water, The water treatment system according to any one of claims 1 to 4, wherein the blockage suppression means is configured to suppress blockage of the reverse osmosis membrane of the second reverse osmosis membrane apparatus.

6. A method for operating a reverse osmosis membrane apparatus that separates mixed water, obtained by mixing multiple raw waters with different water qualities, into permeate and concentrated water, A process for calculating the flow rate ratio of the multiple raw waters based on the measured flow rates of each of the multiple raw waters, A method for operating a reverse osmosis membrane apparatus, comprising performing a process to gradually suppress blockage of the reverse osmosis membrane in the reverse osmosis membrane apparatus according to the calculated flow rate ratio.

7. A control device for controlling the operating conditions of a reverse osmosis membrane apparatus that separates mixed water, obtained by mixing multiple raw waters with different water qualities, into permeate and concentrated water, A flow rate ratio acquisition unit that acquires the flow rate ratio of the plurality of raw waters based on the measured flow rate of each of the plurality of raw waters, A control device comprising: a control unit that controls the blockage suppression operation of a blockage suppression means for suppressing blockage of the reverse osmosis membrane of the reverse osmosis membrane apparatus in stages according to the flow rate ratio acquired by the flow rate ratio acquisition unit.

8. On the computer, A procedure for controlling the operating conditions of a reverse osmosis membrane apparatus that separates mixed water, obtained by mixing multiple raw waters with different water qualities, into permeate and concentrated water, A procedure for calculating the flow rate ratio of the plurality of raw waters based on the measured flow rates of each of the plurality of raw waters, A program for executing a procedure to control, in stages, the blockage suppression operation of a blockage suppression means that suppresses blockage of the reverse osmosis membrane of the reverse osmosis membrane apparatus, according to the calculated flow rate ratio.

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