How to start up a water treatment system

Abstract

To shorten start-up time of a water treatment apparatus without causing elevation of equipment costs.SOLUTION: A start-up method of a water treatment apparatus 1 includes the steps of: performing first treatment for making to-be-treated water pass through the water treatment apparatus 1 including a membrane filtration apparatus 10 under a state in which water can be passed only through a part of a membrane module 11 among a plurality of membrane modules 11-13 of the membrane filtration apparatus 10; taking out a part of the to-be-treated water to be supplied to the membrane filtration apparatus 10 as sample water while executing the first treatment, quantitatively measuring a metal component contained in the sample water with elapse of time, and based on its result, determining whether or not to terminate the first treatment; and performing second treatment for making primary pure water pass through the water treatment apparatus 1 under a state in which a part of the membrane module 11 is exchanged and water can be passed through the plurality of membrane modules 11-13, after terminating the first treatment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for starting up a water treatment device. [Background technology]

[0002] In the manufacturing process of semiconductor devices and liquid crystal devices, ultrapure water, from which impurities have been highly removed, is used for various purposes such as cleaning processes. Ultrapure water is generally produced by sequentially treating raw water (river water, groundwater, industrial water, etc.) in an ultrapure water production system that has a pretreatment system, a primary pure water system, and a secondary pure water system (subsystem). In such ultrapure water production systems, it is known that metal components are eluted from metal components such as pipes and pumps. Since even trace amounts of such metal components have a significant effect on the characteristics of devices, their concentrations must be strictly controlled. In recent years, with the rapid increase in integration and miniaturization of semiconductor devices, the requirements for metal concentrations in ultrapure water are becoming increasingly strict, and ultrapure water with metal concentrations at the pg / L level is being demanded.

[0003] Incidentally, when an ultrapure water production system is newly installed or expanded, residual impurities such as fine particles mixed or generated during the production of the system are removed, and start-up operation is performed until ultrapure water that meets the required water quality is obtained. In order to reduce costs and improve the operating rate, there is a strong demand for shortening the time required for this start-up, but the more strict the requirements for metal concentration in recent years, the longer the start-up time tends to be. In particular, residual impurities such as fine particles are captured and removed by an ultrafiltration (UF) membrane device at the most downstream side of the subsystem, but metal components may be eluted from the captured fine particles, which may require even longer time to obtain ultrapure water that meets the required water quality. In response to this, Patent Document 1 describes a start-up method in which water is passed through a UF membrane device for capturing fine particles installed in parallel with a UF membrane device used during normal operation, and the remaining impurities (particularly fine particles) are captured and removed, and then the water is passed through the UF membrane device used during normal operation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 012248 Summary of the Invention [Problem to be solved by the invention]

[0005] In the method described in Patent Document 1, it is necessary to add a bypass line for installing a UF membrane device for capturing fine particles, but this bypass line is not used during normal operation, which leads to increased equipment costs. In addition, during start-up operation of an ultrapure water production system, the amount of water available is often limited compared to normal operation, and a start-up method that can handle such cases is required.

[0006] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a method for starting up a water treatment device, which is capable of shortening the start-up time without increasing the equipment cost. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the start-up method of a water treatment device of the present invention is a start-up method of a water treatment device that includes a membrane filtration device having a plurality of membrane modules connected in parallel to each other, and treats the water to be treated to produce treated water, and includes the steps of performing a first treatment of passing the water to be treated through the water treatment device by making it possible to pass water through only some of the plurality of membrane modules, taking out a portion of the water to be treated that is supplied to the membrane filtration device as sample water during the performance of the first treatment, quantifying the metal components contained in the sample water over time, and determining whether or not to terminate the first treatment based on the results of the quantification over time, and after the completion of the first treatment, replacing some of the membrane modules, and performing a second treatment of passing the water to be treated through the water treatment device by making it possible to pass water through the plurality of membrane modules.

[0008] According to this method for starting up a water treatment device, residual impurities such as fine particles that were mixed in or generated during the manufacture of the device and remained in the system can be captured by some of the membrane modules among the multiple membrane modules used during normal operation, and then removed from the system together with the membrane modules. Therefore, the captured fine particles and other residual impurities do not remain in the system and adversely affect the treated water quality, and the time required to obtain treated water that meets the required water quality can be shortened. In addition, since the flow rate required for the first treatment is smaller than that during normal operation, the water treatment device can be started up smoothly even when the amount of water available is limited. Effect of the Invention

[0009] As described above, according to the present invention, the start-up time of a water treatment device can be shortened without increasing the equipment cost. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram of an ultrapure water production apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this specification, the start-up method of the water treatment device of the present invention is illustrated as being applied to an ultrafiltration membrane device included in a subsystem of an ultrapure water production device, but the present invention is not limited thereto and can also be applied to, for example, a reverse osmosis membrane device or a microfiltration membrane device.

[0012] Fig. 1(a) is a schematic diagram showing the configuration of an ultrapure water production apparatus according to one embodiment of the present invention. Fig. 1(b) is a schematic diagram showing the configuration of an ultrafiltration membrane device constituting the ultrapure water production apparatus of this embodiment. Note that the configuration of the ultrapure water production apparatus shown in the figure is merely an example and does not limit the present invention.

[0013] The ultrapure water production apparatus 1 has a primary pure water tank 2, a pump 3, a heat exchanger 4, an ultraviolet oxidation device 5, an ion exchange device 6, and an ultrafiltration (UF) membrane device 10. These are connected in series to a circulation line L1 to constitute a secondary pure water system (subsystem) 20, which sequentially processes primary pure water produced in a primary pure water system (not shown) to produce ultrapure water, and supplies the ultrapure water to a point of use 7.

[0014] The water to be treated (primary pure water) stored in the primary pure water tank 2 is pumped out by a pump 3 and supplied to a heat exchanger 4. The water to be treated, which has passed through the heat exchanger 4 and has been temperature-adjusted, is supplied to an ultraviolet oxidation device 5 and irradiated with ultraviolet light, and total organic carbon (TOC) in the water to be treated is decomposed. Thereafter, the water to be treated is subjected to an ion exchange process in an ion exchange device 6 to remove metals and the like, and fine particles are removed in a UF membrane device 10. The ultrapure water thus obtained is returned to the primary pure water tank 2 through a circulation line L1, and a part of it is supplied to the point of use 7 through a water supply line L2 branched off from the circulation line L1 in response to a water collection request from the point of use 7. A primary pure water supply line L3 is connected to the primary pure water tank 2, and primary pure water is supplied from a primary pure water system as necessary. A blow line L4 is connected to the downstream end of the circulation line L1 via a three-way valve V1, and the three-way valve V1 can be switched between a first position where the downstream side of the circulation line L1 is connected to the primary pure water tank 2 and a second position where the downstream side of the circulation line L1 is connected to the blow line L4. Note that, instead of the three-way valve V1, a plurality of on-off valves (two-way valves) may be provided as a means for switching the connection destination of the circulation line L1. Also, a bypass line that bypasses the ion exchange device 6 may be provided in the circulation line L1.

[0015] The primary pure water tank 2, the pump 3, the heat exchanger 4, the ultraviolet oxidation device 5, and the ion exchange device 6 may be those generally used in the subsystems of ultrapure water production equipment. For example, the ion exchange device 6 may be a non-regenerative mixed-bed ion exchange device (cartridge polisher) filled with a mixed bed of cation exchange resin and anion exchange resin. In this case, the ion exchange device 6 may be a plurality of resin towers connected in parallel, each of which is filled with a mixed-bed ion exchange resin (a mixture of cation exchange resin and anion exchange resin). Meanwhile, the UF membrane device 10 may have any configuration, but in this embodiment, it has the following configuration.

[0016] The UF membrane device 10 has a plurality of UF membrane modules 11-13 (three in the illustrated example) connected in parallel to each other. Each of the UF membrane modules 11-13 is an external pressure type hollow fiber membrane module in which a number of hollow fiber-shaped UF membranes (hereinafter also referred to as "hollow fiber membranes") are bundled and packed in a cylindrical casing, and the water to be treated is supplied from the outside of the hollow fiber membrane and permeated water is taken out from the inside. Each of the UF membrane modules 11-13 adopts a cross-flow method as a filtration method in which the water to be treated is supplied parallel to the membrane surface of the hollow fiber membrane and a part of the water to be treated that does not permeate the membrane is discharged as concentrated water. However, each of the UF membrane modules 11-13 is not limited to an external pressure type hollow fiber membrane module, and may be an internal pressure type in which the water to be treated is supplied from the inside of the hollow fiber membrane and permeated water is taken out from the outside, and a dead-end method in which the entire amount of the water to be treated is filtered may be adopted as a filtration method. The UF membrane may be a flat membrane, and therefore each of the UF membrane modules 11 to 13 may be a pleated type or a spiral type.

[0017] Each of the UF membrane modules 11-13 is connected on the primary side to a circulation line L1 on the upstream side of the UF membrane device 10 via on-off valves V11-V13, and is connected on the secondary side to a circulation line L1 on the downstream side of the UF membrane device 10 via on-off valves V14-V16. A concentrated water line L10 is connected to the UF membrane modules 11-13, which circulates concentrated water separated in the UF membrane modules 11-13 and discharges it outside the system. Sampling lines L11-L13 are connected to the secondary side of each of the UF membrane modules 11-13 to extract treated water from each of the UF membrane modules 11-13 for water quality analysis.

[0018] In addition, the ultrapure water producing apparatus 1 is provided with a first sampling device 8 that collects metal components contained in the treated water from the ion exchange device 6 and a second sampling device 9 that collects metal components contained in the treated water (ultrapure water) from the UF membrane device 10, in order to analyze the metal concentration in the treated water from the ion exchange device 6 and the metal concentration in the treated water (ultrapure water) from the UF membrane device 10.

[0019] Each of the sampling devices 8, 9 is composed of sampling lines L5, L6 and concentration columns 8a, 9a provided on the sampling lines L5, L6. The sampling line L5 is connected to the circulation line L1 between the ion exchange device 6 and the UF membrane device 10 via an on-off valve V2, and the sampling line L6 is connected to the circulation line L1 downstream of the UF membrane device 10 via an on-off valve V3. The concentration columns 8a, 9a capture and concentrate metal components in the sample water (treated water from the ion exchange device 6 or the UF membrane device 10) supplied through the sampling lines L5, L6, and are provided with a porous ion exchanger as a capture member therein. As the porous ion exchanger, for example, an ion adsorption membrane (particularly a porous membrane having a cation exchange ability) can be used, but it is preferable to use a monolithic organic porous ion exchanger in that it allows water to pass at a higher space velocity and shortens the time required for concentration. At least the liquid-contacting parts of each of the sampling devices 8, 9 are preferably made of a non-metal material, for example, a synthetic resin, in particular, a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), or polypropylene (PP).

[0020] Here, we will explain the method for analyzing the metal concentration in the treated water using the above-mentioned sampling devices 8 and 9. Note that although the following will explain the method for analyzing the metal concentration in the treated water using the first sampling device 8, it should be noted that the same applies when the second sampling device 9 is used.

[0021] First, the on-off valve V2 is opened, and a part of the treated water from the ion exchanger 6 is supplied to the sampling line L5 as sample water and passed through the concentration column 8a, where the metal components in the sample water are captured and concentrated by the porous ion exchanger. The water passing time (concentration time) at this time depends on the amount of water passing through the concentration column 8a, but is not particularly limited as long as the metal components to be analyzed are concentrated to a degree that can be quantified with sufficient accuracy, and is, for example, several days. After a predetermined water passing time has elapsed, the on-off valve V2 is closed, and the water passing through the concentration column 8a is stopped. Then, the concentration column 8a is removed from the sampling line L5, the porous ion exchanger filled inside is recovered, and the metal components captured by the recovered porous ion exchanger are eluted into an eluent (for example, nitric acid diluted to a predetermined concentration). Thereafter, the metal components in the eluent are quantified, and the metal concentration in the sample water is calculated from the obtained metal amount. As a method for quantifying metal components, for example, an inductively coupled plasma mass spectrometer (ICP-MS) can be used, and the metal concentration in the sample water can be calculated by dividing the obtained amount of metal by the concentration factor of the eluent.

[0022] There is no particular limit to the type of metal component to be analyzed here, and at least one of Na, K, Ca, Mg, Fe, Cu, Al, Zn, Ni, Cr, and Pb can be analyzed. For example, it is known that Na and Ca can be eluted from ion exchange resins, Al, Cr, Fe, Ni, and Cu can be eluted from metal components such as pipes and pumps, and Zn can be eluted from UF membranes, and metal components that can be eluted can be analyzed as necessary. Note that the metal components referred to here include both metal ion and metal particle (fine particle) forms.

[0023] The quantitative analysis of metal components is preferably performed as an operation management for supplying ultrapure water of stable quality to the point of use 7 during normal operation of the ultrapure water production system 1. When the ultrapure water produced by the ultrapure water production system 1 is used for cleaning semiconductor devices, liquid crystal devices, and the like, as described above, it is required to strictly manage the metal concentration in the ultrapure water. The metal concentration at this time is greatly influenced by the performance of the ion exchange resin filled in the ion exchange device 6. That is, when the performance of the ion exchange resin is deteriorated, the metal components contained in the water to be treated are not removed by the ion exchange device 6 and leak into the ultrapure water, and the water quality of the ultrapure water does not meet the required level. Therefore, the analysis result of the metal concentration in the treated water from the ion exchange device 6 can be used to evaluate the performance of the ion exchange resin and, based on the evaluation, to determine whether or not the ion exchange resin needs to be replaced. In addition, by comparing the analysis results of the metal concentration in the treated water from the ion exchange device 6 with the analysis results of the metal concentration in the treated water (ultrapure water) from the UF membrane device 10, it is possible to identify the cause, for example, when the water quality of the ultrapure water supplied to the point of use 7 no longer meets the required level.

[0024] In addition, the above-mentioned quantitative analysis of metal components is also performed during start-up operation when a new or additional ultrapure water production system 1 is installed. The start-up operation of the ultrapure water production system 1 is performed in the order of a sterilization cleaning process, a flushing process, a water-flow cleaning process, and a finishing process after each device of the subsystem 20 is in an operational state, and the above-mentioned quantitative analysis of metal components is performed to determine the timing to end the water-flow cleaning process. Each process of the start-up operation of the ultrapure water production system 1 will be described below.

[0025] (Sterilization and cleaning process) The sterilizing and cleaning process is a process in which hydrogen peroxide is added to the primary pure water stored in the primary pure water tank 2 to generate sterilizing water (hydrogen peroxide water), the generated sterilizing water is circulated along the circulation line L1, and in some cases, the inside of the system is then immersed in the sterilizing water. By performing the sterilizing and cleaning process, the sterilizing water containing hydrogen peroxide is passed through the subsystem 20, and the subsystem 20 is sterilized and cleaned.

[0026] In the sterilizing and cleaning process, first, the primary pure water in the primary pure water tank 2 is pumped out by the pump 3 and returned to the primary pure water tank 2 through a return line (not shown) connected downstream of the pump 3. In this state, a predetermined amount of hydrogen peroxide is added to the circulation line L1 between the primary pure water tank 2 and the pump 3, and mixed with the circulating primary pure water, to prepare sterilizing water of a uniform concentration in the primary pure water tank 2. Then, after disconnecting the return line, the sterilizing water in the primary pure water tank 2 is circulated along the circulation line L1, so that the sterilizing water is passed through the subsystem 20, and the subsystem 20 is sterilized and cleaned. Thereafter, if necessary, the circulation of the sterilizing water is stopped, and the inside of the system is immersed in the sterilizing water.

[0027] In addition, hydrogen peroxide contained in the sterilizing water may deteriorate the ion exchange resin filled in the ion exchange device 6, and may decrease its performance. Therefore, the sterilizing cleaning process is performed before the ion exchange resin is filled in the ion exchange device 6, that is, in a state where the ion exchange resin is not filled. Alternatively, if the sterilizing water is configured to bypass the ion exchange device 6 through the above-mentioned bypass line, the sterilizing cleaning process may be performed after the ion exchange resin is filled in the ion exchange device 6. In addition, the sterilizing cleaning process is performed in a state where water can be passed from the ion exchange device 6 only to the first UF membrane module 11 among the three UF membrane modules 11 to 13 constituting the UF membrane device 10, that is, in a state where the on-off valves V11 and V14 are opened and the on-off valves V12 to V13 and V15 to V16 are closed. This is because, in the water passing cleaning process described later, the first UF membrane module 11 is used to capture and remove impurities, particularly fine particles, that are mixed in or generated during the manufacture of the device and remain in the system.

[0028] The hydrogen peroxide concentration in the sterilizing water is not particularly limited, but is preferably 0.1 to 5 mass %. The time for carrying out the sterilizing and cleaning step depends on the hydrogen peroxide concentration in the sterilizing water, but is not particularly limited as long as it does not deteriorate the UF membrane of the first UF membrane module 11. For example, the circulation time of the sterilizing water is 0.5 to 8 hours, and the immersion time in the sterilizing water is 2 hours or more.

[0029] (Flushing process) The flushing process is a process in which the sterilizing water remaining in the subsystem 20 is replaced with primary pure water after the sterilizing and cleaning process is completed.

[0030] After the sterilizing and cleaning process has been performed for a certain period of time, the sterilizing water in the primary pure water tank 2 is discharged outside the system, and primary pure water is supplied from a primary pure water system (not shown) to the primary pure water tank 2 and stored therein, and then the flushing process is started. In the flushing process, the three-way valve V1 is switched from the first position in the sterilizing and cleaning process to the second position, and the sterilizing water in the subsystem 20 is pushed out of the system from the circulation line L1 through the blow line L4 by the primary pure water passed by the operation of the pump 3. In this way, the sterilizing water remaining in the subsystem 20 is replaced with the primary pure water.

[0031] The flushing step is performed until it is confirmed that the sterilizing water has been sufficiently discharged outside the system and replaced with primary pure water, that is, until it is confirmed that almost no hydrogen peroxide remains in the system. The absence of hydrogen peroxide remaining in the system can be confirmed, for example, by detecting the hydrogen peroxide concentration in the wastewater from the blow line L4 during the flushing step and finding that the detected value is equal to or lower than a predetermined value (e.g., 0.5 mg / L).

[0032] (Water passing cleaning process) The water passing cleaning process is a process in which primary pure water is passed through the subsystem 20 to treat it, and the treated water is circulated along the circulation line L1 to clean the subsystem 20. The water passing cleaning process (first treatment) is performed following the germicidal cleaning process and the flushing process, in a state in which water from the ion exchange device 6 can be passed only through the first UF membrane module 11.

[0033] When it is confirmed that almost no hydrogen peroxide remains in the system, the supply of water to the subsystem 20 is stopped, and the flushing process is completed. Then, after the ion exchange device 6 is filled with ion exchange resin, or after the bypass line is disconnected, the supply of water to the subsystem 20 is resumed, and the water-passing cleaning process is started. In the water-passing cleaning process, the three-way valve V1 is switched to the first position, and the treated water treated in the subsystem 20 is returned to the primary pure water tank 2 through the circulation line L1. In this way, the subsystem 20 is passed through and cleaned by circulating the treated water, and as a result, impurities, particularly fine particles, that were mixed in or generated during the manufacture of the device and remained in the system are captured and removed by the first UF membrane module 11.

[0034] As described above, in the process of producing ultrapure water, metal components are eluted from metal members such as the pipes and pump 3 constituting the circulation line L1. However, since such metal components are removed by the ion exchanger 6, they have almost no effect on the quality of the ultrapure water. On the other hand, in the resin tower constituting the ion exchanger 6, some members (e.g., a collector screen for preventing the outflow of ion exchange resin) are made of metal materials such as stainless steel (SUS) from the viewpoint of mechanical strength. Therefore, it is known that metal components may be eluted from the ion exchanger 6 itself. In order to meet the recent strict requirements for the metal concentration in ultrapure water, it is necessary to suppress the elution of such metal components from the ion exchanger 6. For this purpose, it is preferable to carry out a water passing cleaning process to sufficiently elute the metal components from the ion exchanger 6 in advance. In other words, it is preferable to carry out the water passing cleaning process until the elution of metal components from the ion exchanger 6 is almost completely eliminated.

[0035] Therefore, in this embodiment, the above-mentioned quantitative analysis of the metal components is performed over time using the first sampling device 8 while the water-flow cleaning process is being performed. Then, from the results of the quantitative analysis, the change over time of the metal concentration in the treated water from the ion exchange device 6 (i.e., the water to be treated supplied to the UF membrane device 10) is calculated, and based on the calculated change over time, it is determined whether or not to end the water-flow cleaning process. Specifically, it is determined whether or not the above-mentioned metal concentration has reached a steady state, and when the steady state has been reached, it is determined that there is almost no elution of the metal components from the ion exchange device 6, and it is determined that the water-flow cleaning process should be ended.

[0036] The predetermined value at this time is not particularly limited, and is appropriately set according to the type of metal component to be analyzed and the required water quality of the ultrapure water to be produced. In addition, whether or not the metal concentration in the treated water from the ion exchange device 6 has reached a steady state can be determined, for example, by comparing two pieces of time-series data of metal concentration that are continuous in time and determining whether or not they match within the error range of the above-mentioned quantitative analysis. That is, when the two pieces of data match within the quantitative error range, it can be determined that the metal concentration in the treated water from the ion exchange device 6 has reached a steady state. It is preferable to select Fe (iron) as the metal component to be analyzed here. This is because more iron is eluted from SUS, which is preferable as the metal material for the resin tower of the ion exchange device 6, than from other metal components.

[0037] During the water passing cleaning process, metal components may be eluted from the fine particles captured in the first UF membrane module 11, and there is a high possibility that such elution of metal components from the fine particles will occur steadily. As a result, the metal concentration in the treated water from the UF membrane device 10 reaches a steady state at a higher value, which may cause a delay in the start-up of the ultrapure water production system 1. However, in this embodiment, regardless of the presence or absence of elution of such metal components, the first UF membrane module 11 is replaced after the water passing cleaning process is completed. Therefore, the influence of the fine particles captured in the first UF membrane module 11 does not adversely affect the start-up of the ultrapure water production system 1 thereafter. In addition, in order to monitor the behavior of the metal concentration in the treated water from the UF membrane device 10, the above-mentioned quantitative analysis of the metal components may be performed over time using the second sampling device 9 during the water passing cleaning process.

[0038] (Finishing process) The finishing process is a process in which primary pure water is passed through the subsystem 20 for treatment to produce ultrapure water, and is performed until ultrapure water that meets the required water quality is obtained. The finishing process (second treatment) is performed in a state in which water can be passed from the ion exchange device 6 to the three UF membrane modules 11-13 that make up the UF membrane device 10, as described below.

[0039] When it is determined that the water passing cleaning process is completed, the on-off valves V12-V13, V15-V16 are opened, and water starts to pass from the ion exchange device 6 to the second and third UF membrane modules 12, 13. At the same time, the on-off valves V11, V14 are closed, and water passing through the first UF membrane module 11 is stopped. After the first UF membrane module 11 is replaced, the on-off valves V11, V14 are opened to resume water passing through the first UF membrane module 11, and the finishing process is started. In the finishing process, a circulation operation similar to that of the normal operation is performed, and the treated water from the UF membrane device 10 is returned to the primary pure water tank 2 through the circulation line L1, thereby accelerating the purification of ultrapure water. When the flow of water to the first UF membrane module 11 is resumed, the treated water from the first UF membrane module 11 is discharged outside the system without being merged with the treated water from the second and third UF membrane modules 12, 13 until it is confirmed that the treated water has the same water quality (metal concentration) as the treated water from the second and third UF membrane modules 12, 13. Whether the metal concentrations in the treated waters have become approximately the same can be confirmed by analyzing the metal concentrations in the treated waters collected from the sampling lines L11 to L13 using a procedure similar to that of the quantitative analysis of metal components described above.

[0040] As described above, the finishing process is performed until ultrapure water that satisfies the required water quality is obtained. For this purpose, during the execution of the finishing process, the above-mentioned quantitative analysis of the metal components is performed using the second sampling device 9, and the metal concentration in the treated water (ultrapure water) from the UF membrane device 10 is calculated. Then, based on the calculated metal concentration, it is determined whether or not the finishing process is to be terminated, that is, whether or not the start-up operation of the ultrapure water production system 1 can be terminated and normal operation can be started. Specifically, when the metal concentration in the treated water from the UF membrane device 10 becomes equal to or lower than a predetermined value, it is determined that the finishing process is to be terminated, that is, it is determined that the start-up operation of the ultrapure water production system 1 can be terminated and normal operation can be started. The predetermined value at this time is not particularly limited, and is appropriately set according to the type of metal component to be analyzed and the required water quality of the ultrapure water to be produced. In addition, the metal component to be analyzed here is not particularly limited, and at least one of the above-mentioned types of metal components, i.e., for example, Na, K, Ca, Mg, Fe, Cu, Al, Zn, Ni, Cr, and Pb, can be selected as the analysis target.

[0041] As described above, the first UF membrane module 11 is replaced prior to the finishing step regardless of whether metal components are eluted from the captured particles in the water passing cleaning step. Therefore, as the first UF membrane module 11, it is not necessary to install a new one when assembling the ultrapure water production system 1, as long as it has been confirmed in advance that the performance of the module has not deteriorated.

[0042] As described above, according to the start-up operation of this embodiment, impurities, particularly fine particles, that were mixed in or generated during the manufacture of the device and remained in the system are captured and removed by the first UF membrane module 11, but this first UF membrane module 11 is to be replaced during the start-up operation. That is, in this embodiment, after the fine particles are captured by a part of the UF membrane modules 11 of the UF membrane device 10 used during normal operation, the captured fine particles can be removed outside the system of the ultrapure water production system 1 together with the UF membrane module 11. Therefore, during the start-up operation, the fine particles captured by the UF membrane device 10 do not remain in the system as they are, and metal components are not eluted from such fine particles to adversely affect the treated water quality. As a result, the time required to obtain ultrapure water that meets the required water quality can be shortened.

[0043] In addition, since the water passing cleaning process of this embodiment is performed in a state where water can pass only through the first UF membrane module 11 from the ion exchange device 6, the flow rate required in this process can be less than the flow rate (rated flow rate) during normal operation. Therefore, for example, even if the primary pure water system is also started up at the same time, and the amount of primary pure water supplied from the primary pure water system is small and the amount of available water is limited, the water passing cleaning process can be performed without difficulty. In addition, in the finishing process of this embodiment, since the fine particles captured in the water passing cleaning process are removed from the UF membrane device 10, sufficient treatment performance can be achieved even if water is passed through the UF membrane device 10 at a flow rate less than the rated flow rate. Note that, if there is a margin in the amount of available water, the water passing cleaning process may be performed at a smaller flow rate, and then the finishing process may be performed at the rated flow rate.

[0044] In this embodiment, the UF membrane device 10 is composed of three UF membrane modules 11-13, but the number of UF membrane modules constituting the UF membrane device 10 is not limited to this and may be two, or four or more. Furthermore, when the number of UF membrane modules is four or more, the number of UF membrane modules through which water is passed in the water passing cleaning step is not limited to one, so long as it is not all of the four or more UF membrane modules, and may be two or more depending on the amount of water available during start-up operation. [Explanation of symbols]

[0045] 1 Ultrapure water production equipment 2 Primary pure water tank 3. Pump 4 Heat exchanger 5. UV oxidation equipment 6. Ion exchange device 7 Use Points 8,9 Sampling Device 8a,9a Concentration columns 10. Ultrafiltration Membrane Device 11~13 Ultrafiltration Membrane Module L1 Circulation Line L2 Water supply line L3 Primary pure water supply line L4 Blow Line L5, L6, L11~L13 sampling lines L10 Concentrated water line V1 Three-way valve V2, V3, V11~V16 On-off valve

Claims

1. A start-up method for a water treatment device including a membrane filtration device having a plurality of membrane modules connected in parallel to each other, which treats water to be treated to produce treated water, comprising: A step of performing a first process of passing water to be treated through the water treatment device while allowing water to pass through only some of the membrane modules among the plurality of membrane modules; During the execution of the first treatment, a part of the water to be treated that is supplied to the membrane filtration device is taken out as a sample water, the metal components contained in the sample water are quantified over time, and based on the result of the quantification over time, it is determined whether or not to terminate the first treatment; and after completion of the first treatment, replacing some of the membrane modules and enabling water to pass through the plurality of membrane modules, thereby performing a second treatment in which the water to be treated is passed through the water treatment device.

2. The start-up method for a water treatment device as described in claim 1, wherein the step of determining whether to terminate the first treatment includes calculating the change in concentration of the metal component in the sample water over time from the results of the quantitative determination over time, and determining whether to terminate the first treatment based on the calculated change over time.

3. The start-up method for a water treatment device as described in claim 2, wherein determining whether or not to terminate the first treatment includes determining whether or not the concentration of the metal component in the sample water has reached a steady state, and determining to terminate the first treatment if the steady state has been reached.

4. The start-up method for a water treatment device as described in claim 3, wherein determining whether the concentration of the metal component in the sample water has reached a steady state includes determining that the concentration of the metal component has reached a steady state when two temporally consecutive data among the time series data of the concentration of the metal component match within the range of error when quantifying the metal component.

5. A method for starting up a water treatment device as described in any one of claims 1 to 4, further comprising the steps of: extracting a portion of the treated water from the membrane filtration device as sample water during execution of the second treatment, quantifying the metal components contained in the sample water, and determining whether or not to transition from the second treatment to normal operation based on the results of the quantification.

6. 6. The method for starting up a water treatment device according to claim 1, further comprising the step of allowing water to pass through only some of the membrane modules before performing the first treatment, and passing the water to be treated, to which hydrogen peroxide has been added, through the water treatment device to sterilize the water treatment device.

7. A method for starting up a water treatment device as described in any one of claims 1 to 6, wherein quantifying the metal components includes passing the sample water through a porous ion exchanger to capture the metal components in the sample water with the porous ion exchanger, eluting the captured metal components into an eluent, and quantifying the metal components in the eluent.

8. 8. A method for starting up a water treatment device according to claim 1, wherein the water treatment device is an ultrapure water production device equipped with a subsystem that treats primary pure water as the treated water to produce ultrapure water, and the subsystem includes an ultrafiltration membrane device having a plurality of ultrafiltration membrane modules connected in parallel to each other as the membrane filtration device.

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