Method for controlling ultrapure water production device

Abstract

In a method for controlling an ultrapure water production device according to the present invention, a flowmeter 21 and a manual valve 22 are provided to a recovery pipe 13 of a UF membrane 9, a control valve 23 is provided on the downstream side of the manual valve 22, and, on the basis of a value measured by the flowmeter 21, the opening degree of the control valve 23 can be controlled by a control means that is not illustrated. When the flow rate of water supplied to the UF membrane 9 varies, concentrated water W3 increases. By measuring the flow rate of the concentrated water W3 from the UF membrane 9 using the flowmeter 21 and adjusting the opening degree of the control valve 23 so that the flow rate thereof becomes uniform, it is possible to suppress the amount of water that is supplied to the UF membrane 9 and that is excessively discharged to the outside of a system as the concentrated water W3. Such a method for controlling an ultrapure water production device makes it possible to improve the water recovery rate of an ultrafiltration membrane of a pure water production device.

Description

Control method for ultrapure water production equipment

[0001] The present invention relates to a control method for an ultrapure water production apparatus, and more particularly to a control method for the ultrafiltration membrane of an ultrapure water production apparatus.

[0002] Conventionally, in the manufacturing processes of semiconductor devices and liquid crystal devices, ultrapure water, from which impurities have been highly removed, has been used as a cleaning solution for cleaning electronic components such as semiconductor wafers and glass substrates. Ultrapure water is produced, for example, by a pure water production apparatus as shown in Figure 1. In Figure 1, the ultrapure water production apparatus 1 includes a supply pipe 2 that supplies raw water W, which has been treated in a pretreatment system from river water, groundwater, industrial water, etc., to a water to be treated tank 3; a raw water supply pipe 4 that supplies raw water W from the water to be treated tank 3 to a primary pure water system 5; a sub-tank 6 that stores the obtained primary pure water W1; a primary pure water supply pipe 7 that supplies primary pure water W1 from the sub-tank 6 to a secondary pure water system (subsystem) 8; an ultrafiltration membrane (UF membrane) 9 located at the end of the subsystem 8; an ultrapure water supply pipe 10 that supplies the obtained ultrapure water W2 to a use point 11; and a return pipe 12 that returns unused ultrapure water W2 at the use point 11 to the sub-tank 6. The concentrated water W3 from the UF membrane 9 is then sent from the recovery pipe 13 to the treated water tank 3 for reuse. This concentrated water W3 from the UF membrane 9 may be used to produce ultrapure water at around 23°C, or it may be used to produce warm ultrapure water at around 60-75°C.

[0003] In such an ultrapure water production apparatus 1, the pretreatment equipment performs pretreatment of river water, groundwater, and industrial water using methods such as filtration, coagulation and sedimentation, and microfiltration membranes, mainly to remove suspended solids. The primary pure water system 5 includes, for example, a water to be treated tank 3 for storing the pretreated water (raw water) W, a high-pressure pump for supplying the water to be treated W, and an activated carbon tower, a reverse osmosis membrane device, a membrane degasser, an ultraviolet oxidation device, an electrodeionizer, and an ion exchange resin device. This primary pure water system 5 removes most of the electrolytes, fine particles, and live bacteria from the pretreated water (raw water) W, as well as decomposing and removing organic matter.

[0004] Subsystem 8, for example, consists of a sub-pump, heat exchanger, ultraviolet oxidizer, degasser, and non-regenerative mixed-bed ion exchanger located downstream of the sub-tank 6, and has an ultrafiltration membrane (UF membrane) 9 at its end. In this subsystem 8, the ultraviolet oxidizer oxidizes and decomposes trace amounts of organic matter (TOC components) contained in the primary pure water W1, the degasser removes any small amounts of dissolved gas, and then the non-regenerative mixed-bed ion exchanger processes the water to remove residual carbonate ions, organic acids, anionic substances, and even metal ions and cationic substances by ion exchange. Then, the ultrafiltration membrane (UF membrane) 9 removes fine particles to produce ultrapure water W2, which is supplied to the use point 11.

[0005] In this primary pure water system 5 and secondary pure water system 8, water is discharged outside the system in some component units to obtain the required water quality, such as the backwashing process of the filter and activated carbon tower, the concentrated water from the reverse osmosis membrane (RO membrane), the regeneration process of the ion exchange resin device, the concentrated water from the electrodeionizer, and the concentrated water from the ultrafiltration membrane (UF membrane). For example, in the UF membrane 9, as shown in Figure 6, a flow meter 31 and a manual valve 32 are provided in the recovery piping 13 of the UF membrane 9 to control the flow rate of the concentrated water W3 according to the amount of water supplied to the UF membrane 9.

[0006] Since the UF membrane 9 at the end of this ultrapure water production system is supplied with high-purity pure water treated in the primary pure water system 5 and the secondary pure water system 8, it is extremely wasteful in terms of energy utilization to return more than 5% (95% recovery rate) of the water supplied to the UF membrane 9 as concentrated water W3 to the primary pure water system 5 as raw water for operation. Therefore, a method has been adopted in which the concentrated water W3 from the UF membrane 9 is further treated and recovered using a UF membrane, but this has the problem of requiring a large amount of components such as UF membranes, piping, and valves for recovery.

[0007] Furthermore, Patent Document 1 discloses a method for adjusting the flow rate of concentrated water in a UF membrane using a means for adjusting the flow rate of the UF membrane so that fluctuations in the outlet pressure of the UF membrane fall within a predetermined range.

[0008] Japanese Patent Publication No. 2022-017035

[0009] However, the method for controlling the UF membrane in the ultrapure water production apparatus described in Patent Document 1 takes into account the generation of fine particles from the UF membrane, and has the problem that it is not sufficient for improving the water recovery rate by controlling the UF membrane.

[0010] Furthermore, after installation, the UF membrane 9 typically undergoes a process of switching between cleaning and water flow. However, these switching processes are often performed solely by manually adjusting valves. If this process results in an excessive flow load, such as a rapid increase in the concentrated water W3 in the UF membrane 9, it could lead to the rupture of the UF membrane 9, potentially resulting in a deterioration of the ultrapure water quality produced.

[0011] To address these challenges, there is a need for a technology that has a mechanism to avoid applying a sudden flow load to the UF membrane, while simultaneously reducing water production energy by keeping the concentrated water flow rate through the UF membrane to the absolute minimum necessary during normal operation.

[0012] The present invention has been made in view of the above problems, and aims to provide a control method for an ultrapure water production apparatus that can improve the water recovery rate in the ultrafiltration membrane of the ultrapure water production apparatus.

[0013] To achieve the above objective, the present invention first provides a control method for an ultrapure water production apparatus having a primary pure water system, a secondary pure water system, and an ultrafiltration membrane provided at the terminal end of the secondary pure water system for supplying ultrapure water to a point of use, wherein the control method comprises a control mechanism for controlling the concentrated water flow rate of the ultrafiltration membrane and measuring means for measuring one or more of the flow rates of the supply water, treated water, or concentrated water of the ultrafiltration membrane, and the control mechanism controls the flow rate of concentrated water so that the flow rate of concentrated water of the ultrafiltration membrane becomes an arbitrary fixed value (Invention 1).

[0014] According to this invention (Invention 1), by controlling the flow rate of concentrated water in the UF membrane to a fixed value, the amount of UF membrane supply water treated in the primary and secondary pure water systems that is discharged outside the system as concentrated water can be suppressed by fixing the amount. Furthermore, since the amount of concentrated water in the UF membrane does not fluctuate, the risk of UF membrane rupture caused by excessive flow rate load fluctuations of the concentrated water in the UF membrane can be avoided.

[0015] Secondly, the present invention provides a control method for an ultrapure water production apparatus having a primary pure water system, a secondary pure water system, and an ultrafiltration membrane provided at the terminal end of the secondary pure water system for supplying ultrapure water to a point of use, the method comprising a control mechanism for controlling the concentrated water flow rate of the ultrafiltration membrane, and measuring means for measuring one or more of the flow rates of the supply water, treated water, or concentrated water of the ultrafiltration membrane, wherein the control mechanism controls the flow rate of concentrated water of the ultrafiltration membrane so that the flow rate of concentrated water of the ultrafiltration membrane becomes a predetermined ratio to the supply flow rate of the ultrafiltration membrane (Invention 2).

[0016] According to the present invention (Invention 2), by setting the flow rate of concentrated water for the UF membrane to a predetermined ratio with respect to the feedwater flow rate for the UF membrane and controlling the flow rate of concentrated water, the amount of UF membrane feedwater treated in the primary and secondary pure water systems that is discharged outside the system as concentrated water for the UF membrane can be suppressed by setting it to a predetermined ratio. Furthermore, by varying the flow rate ratio of concentrated water according to the feedwater flow rate for the UF membrane, it is possible to suppress the excessive discharge of concentrated water outside the system even if the allowable feedwater for the UF membrane increases rapidly. Moreover, since the amount of concentrated water for the UF membrane is predetermined, the risk of UF membrane rupture caused by excessive flow rate fluctuations of concentrated water for the UF membrane can also be avoided.

[0017] In the above inventions (Inventions 1 and 2), it is preferable to control the flow rate of concentrated water through the ultrafiltration membrane to be 5% or less of the supply flow rate of the ultrafiltration membrane (Invention 3).

[0018] According to this invention (Invention 3), it is possible to effectively suppress the excessive discharge of the feedwater for the UF membrane, which has been treated in the primary pure water system and the secondary pure water system, as concentrated water for the UF membrane.

[0019] In the above invention (Invention 3), it is preferable that the control mechanism for controlling the concentrated water flow rate of the ultrafiltration membrane is provided in the piping of the ultrafiltration membrane (Invention 4).

[0020] According to this invention (Invention 4), by controlling the concentrated water flow rate of the ultrafiltration membrane for each ultrafiltration membrane, it is possible to optimize the suppression of excessive discharge of the UF membrane's supply water, which has been treated in the primary pure water system and the secondary pure water system, as concentrated water from the UF membrane.

[0021] In the above invention (Invention 3), it is preferable that the ultrafiltration membranes are arranged in parallel, and the control mechanism for controlling the concentrated water flow rate of the ultrafiltration membranes is provided in the confluence pipe of the concentrated water from the multiple ultrafiltration membranes (Invention 5).

[0022] According to this invention (Invention 5), when multiple ultrafiltration membranes are provided in parallel, the control of the concentrated water flow rate is performed after the concentrated water from each ultrafiltration membrane has merged. This reduces the number of control mechanisms that prevent the supply water for the UF membranes, which has been treated in the primary and secondary pure water systems, from being excessively discharged outside the system as concentrated water for the UF membranes, thereby simplifying the control process.

[0023] According to the control method for the ultrapure water production apparatus of the present invention, the flow rate of concentrated water from the ultrafiltration membrane is controlled so that the flow rate of concentrated water from the ultrafiltration membrane is set to an arbitrary fixed value or to a predetermined ratio to the supply flow rate of the ultrafiltration membrane. This suppresses the excessive discharge of the supply water from the UF membrane, which has been treated in the primary and secondary pure water systems, as concentrated water from the UF membrane. Furthermore, since the concentrated water from the UF membrane does not fluctuate rapidly, the risk of UF membrane rupture due to excessive flow load on the concentrated water from the UF membrane can be avoided.

[0024] This is a flow diagram showing an ultrapure water production apparatus to which the first embodiment of the present invention can be applied. This is a schematic diagram showing the control method of the ultrafiltration membrane in the first embodiment. This is a schematic diagram showing the control method of the ultrafiltration membrane in the second embodiment of the present invention. This is a schematic diagram showing the control method of the ultrafiltration membrane in the third embodiment of the present invention. This is a flow diagram showing a fourth embodiment of an ultrapure water production apparatus to which the present invention can be applied. This is a schematic diagram showing the control method of the ultrafiltration membrane in Comparative Example 1 (conventional example).

[0025] The control method for the ultrapure water production apparatus of the present invention will be described in detail below.

[0026] [First Embodiment] <Ultrapure Water Production Apparatus> Figure 1 shows an ultrapure water production apparatus to which the control method for the ultrapure water production apparatus of the present invention can be applied. Since this ultrapure water production apparatus has been described above, a detailed explanation will be omitted.

[0027] <Control Mechanism for UF Film> In this embodiment, the control mechanism for the UF film has the configuration shown in Figure 2. In Figure 2, the recovery pipe 13 for the UF film 9 has a flow meter 21 as a measuring means, and further, a manual valve 22 and a control valve 23 as a control mechanism are provided downstream of the manual valve 22. The opening degree of this control valve 23 can be controlled based on the measured value of the flow meter 21 by a control means (not shown).

[0028] <Control Method for Ultrapure Water Production Equipment> Next, we will explain the control method for the ultrapure water production equipment described above.

[0029] (Urpure Water Production Process) In the ultrapure water production apparatus 1 shown in Figure 1, the primary pure water system 5 includes, for example, a water to be treated tank 3 for storing pre-treated water (raw water) W, a high-pressure pump for supplying the water to be treated W, an activated carbon tower, a reverse osmosis membrane device, a membrane degasser, an ultraviolet oxidation device, an electrodeionizer, an ion exchange resin device, and the like. This primary pure water system 5 removes most of the electrolytes, fine particles, live bacteria, etc. from the water to be treated W, and also decomposes organic matter.

[0030] In subsystem 8, trace amounts of organic matter (TOC components) contained in primary pure water W1 are oxidized and decomposed by an ultraviolet oxidation device, the small amount of dissolved gas is removed by a degasser, and then the remaining carbonate ions, organic acids, anionic substances, and even metal ions and cationic substances are removed by ion exchange through a non-regenerative mixed-bed ion exchange device. Then, fine particles are removed by an ultrafiltration membrane (UF membrane) 9 to obtain ultrapure water W2, which is supplied to the use point 11.

[0031] As shown in Figure 2, by providing a flow meter 21, a manual valve 22, and a control valve 23 in the recovery piping 13 for the UF membrane 9, when the flow rate of the supply water for the UF membrane 9 increases, the amount of concentrated water W3 would normally also increase. However, in this embodiment, the flow rate of the concentrated water W3 for the UF membrane 9 is measured by the flow meter 21, and the opening of the control valve 23 is adjusted so that the flow rate remains constant. This makes it possible to suppress the amount of the supply water for the UF membrane 9, which has been treated in the primary pure water system 5 and the secondary pure water system 8, that is excessively discharged outside the system as concentrated water W3 to a constant amount. The fixed value of the flow rate of the concentrated water W3 for the UF membrane 9 is preferably an arbitrary fixed value within the range of 5% or less of the flow rate of the supply water for the UF membrane 9, and particularly 3% or less (recovery rate of the UF membrane 9 is 95% or more, particularly 97% or more). This ensures that the excessive discharge of the supply water for the UF membrane 9 as concentrated water W3 outside the system is reliably suppressed. Furthermore, since the flow rate of concentrated water W3 does not fluctuate rapidly, the risk of the UF membrane 9 rupturing due to excessive flow load of concentrated water W3 can be avoided. This control can also be applied to flow rate fluctuations during processes such as cleaning after installation of the UF membrane 9, and disconnection for water flow or replacement.

[0032] [Second Embodiment] <Ultrapure Water Production Apparatus> The ultrapure water production apparatus of the second embodiment is the same as that of the first embodiment described above.

[0033] <UF Membrane Control Mechanism> In this embodiment, the UF membrane control mechanism has the configuration shown in Fig. 3. In Fig. 3, a flow meter 21 is provided in the recovery pipe 13 of the UF membrane 9. Further, a manual valve 22 and a control valve 23 as a control mechanism are provided on the downstream side of the manual valve 22. Furthermore, the primary pure water supply pipe 7 has a flow meter 24 as a measuring means for measuring the supply water flow rate of the UF membrane 9. The control valve 23 can be controlled based on the measured value of the flow meter 24 by control means not shown.

[0034] <Control Method of Ultra-Pure Water Manufacturing Apparatus> Next, the control method of the ultra-pure water manufacturing apparatus as described above will be explained.

[0035] (Ultra-Pure Water Manufacturing Process) The ultra-pure water manufacturing process is the same as that of the first embodiment described above.

[0036] And, as shown in Fig. 3, by providing a control valve 23 in the recovery pipe 13 of the UF membrane 9 and a flow meter 24 for measuring the supply water flow rate of the UF membrane 9 in the primary pure water supply pipe 7, when the supply water flow rate of the UF membrane 9 fluctuates, with respect to the supply water flow rate of the UF membrane 9 measured by the flow meter 24, the concentrated water flow rate is controlled by setting a predetermined ratio, for example, 5% as the concentrated water flow rate, so that the UF membrane 9 can be stably operated. Also, it is possible to set the ratio to the supply flow rate of this UF membrane 9 to be even smaller (less than 5%), and it is also possible to suppress excessive discharge outside the system as the concentrated water W3 of the UF membrane 9. As the ratio of the flow rate of the concentrated water W3 of this UF membrane 9, it is preferably an arbitrary fixed value within the range of 5% or less of the supply water flow rate of the UF membrane 9, particularly 3% or less (the recovery rate of the UF membrane 9 is 95% or more, particularly 97% or more). Note that this control can be similarly applied to flow rate fluctuations during processes such as cleaning, water passing, and separation for replacement after the installation of the UF membrane 9.

[0037] [Third Embodiment] <Ultra-Pure Water Manufacturing Apparatus> The ultra-pure water manufacturing apparatus of the third embodiment is the same as that of the first embodiment described above.

[0038] <UF Membrane Control Mechanism>In this embodiment, the UF membrane control mechanism has the configuration as shown in FIG. 4. In FIG. 4, the recovery pipe 13 of the UF membrane 9 has a flow meter 21, and further a manual valve 22 and a control valve 23 as a control mechanism are provided on the downstream side of this manual valve 22. Furthermore, the ultra-pure water supply pipe 10 has a flow meter 25 as a control mechanism for measuring the flow rate of the treated water of the UF membrane 9. The control valve 23 can be controlled based on the measured value of the flow meter 25 by control means not shown.

[0039] <Control Method of Ultra-Pure Water Production Device> Next, the control method of the ultra-pure water production device as described above will be explained.

[0040] (Ultra-Pure Water Production Process) The ultra-pure water production process is the same as that of the first embodiment described above.

[0041] And, as shown in FIG . 4, by providing a control valve 23 in the recovery pipe 13 of the UF membrane 9 and a flow meter 25 for measuring the flow rate of the treated water of the UF membrane 9 in the ultra-pure water supply pipe 10, when the flow rate of the supply water of the UF membrane 9 fluctuates, with respect to the flow rate of the treated water of the UF membrane 9 measured by the flow meter 25, the concentration water flow rate such that the recovery rate of the UF membrane 9 from the flow rate of the treated water of the UF membrane becomes a predetermined value, for example, 5% is calculated (concentration water flow rate [m ３ / h] = treated water flow rate [m ３ / h] / 0.95 - treated water flow rate [m ３ / h]), and by controlling based on this, the operation of the UF membrane 9 can be stably performed. Also, it is possible to set the ratio to the supply flow rate of this UF membrane 9 to be even smaller (less than 5%), and it is also possible to suppress excessive discharge outside the system as the concentrated water W3 of the UF membrane 9. As the ratio of the flow rate of the concentrated water W3 of this UF membrane 9, it is preferably an arbitrary fixed value within the range of 5% or less of the flow rate of the supply water of the UF membrane 9, particularly 3% or less (the recovery rate of the UF membrane 9 is 95% or more, particularly 97% or more). Note that this control can be similarly applied to flow rate fluctuations during processes such as cleaning, water passing, and separation for replacement after the installation of the UF membrane 9.

[0042] Although the present invention has been described above based on the embodiments described above, the present invention is not limited to the embodiments described above, and various modifications are possible. For example, the configuration of the ultrapure water production apparatus 1 is not particularly limited and can be applied to an ultrapure water production apparatus 1 having a primary pure water system 5 and subsystem 8 of various configurations. Also, as shown in Figure 5, a recycling tank 13A may be provided in the middle of the recovery piping 13, and the concentrated water W3 may be temporarily stored in the recycling tank 13A and supplied to the concentrated water of the electrodeionizer, the regeneration water of the regenerative ion exchanger, the sealing water of the vacuum pump, the heat exchanger, etc., which constitute the primary pure water system 5. Furthermore, the control mechanism for the concentrated water W3 of the UF membrane 9 may be installed in the recovery piping 13 of each UF membrane 9, but if there are multiple series of UF membranes 9 in parallel, it may be installed in the confluence piping of the concentrated water W3 of each UF membrane 9. In addition, the flow rate of the ultrapure water production apparatus 1 itself may be controlled by the rated operation of the pump or manual valve adjustment, but inverter control operation may be adopted and linked to this control.

[0043] The present invention will be described in more detail based on the following specific examples.

[0044] [Comparative Example 1] In the ultrapure water production apparatus 1 shown in Figure 1, the water supply flow rate to the UF membrane 9 is 200 m³ as shown in Figure 6. ３ For each hour, the flow rate of concentrated water W3 is set to 10 m³ to achieve a recovery rate of 95%. ３ / h (treated water flow rate 190m ３ The manual valve 32 was adjusted to 300 m / h. Then, the water supply flow rate of the UF membrane 9 was set to 300 m ３ The flow rate was increased or decreased up to / h. Because the adjustment was made by a manual valve 32, the flow rate of the treated water (ultrapure water) W2 of the UF membrane 9 and the flow rate of the concentrated water W3 could not be precisely controlled, resulting in a haphazard operation. This haphazard operation meant that there was a possibility of excessive flow to the concentrated water W3 side during sudden fluctuations in the water supply flow rate of the UF membrane 9 or when the UF membrane 9 was replaced, which carried the risk of the UF membrane 9 rupturing. In addition, the amount of concentrated water W3 returned to the return destination for the UF membrane was more than necessary.

[0045] [Example 1] In the ultrapure water production apparatus 1 shown in Figure 1, the water supply flow rate to the UF membrane 9 is set to 200 to 300 m³ as shown in Figure 2. ３Varied to / h, measured the concentrated water flow rate of the UF membrane 9 with the flow meter 21, and when the flow rate of the concentrated water W3 was 10 m ３ / h, controlled the flow rate of the treated water (ultrapure water) W2 to be 190 - 290 m ３ / h (supply water flow rate - flow rate of the concentrated water W3). As a result, compared with Comparative Example 1, since the concentrated water W3 of the UF membrane 9 was controlled at a fixed value of 10 m ３ / h, the concentrated water W3 of the UF membrane 9 did not become excessive. Also, it became possible to avoid the breakage risk of the UF membrane 9 due to the flow rate load variation of the excessive flow rate variation of the concentrated water W3 of the UF membrane 9.

[0046] [Example 2] In the ultrapure water production apparatus 1 shown in FIG. 1, as shown in FIG. 3, the supply water flow rate to the UF membrane 9 was varied to 200 - 300 m ３ / h, measured the flow rate of the supply water to the UF membrane 9 with the flow meter 24, and when the flow rate of the concentrated water W3 was 5% of the supply water flow rate (10 - 15 m ３ / h), controlled the flow rate of the treated water (ultrapure water) W2 to be 190 - 285 m ３ / h (supply water flow rate - flow rate of the concentrated water W3). As a result, compared with Comparative Example 1, the concentrated water W3 of the UF membrane 9 did not become excessive. Also, it became possible to avoid the breakage risk of the UF membrane 9 due to the flow rate load variation of the excessive flow rate variation of the concentrated water W3 of the UF membrane 9.

[0047] [Example 3] In the ultrapure water production apparatus 1 shown in FIG. 1, as shown in FIG. 4, when the treated water flow rate of the UF membrane 9 varied to 190 - 285 m ３ / h, calculated the concentrated water flow rate [m ３ / h] of the concentrated water W3 with a recovery rate of 5% from the treated water flow rate of the UF membrane 9 by the following formula: Concentrated water flow rate [m ３ / h] = Treated water flow rate [m ３ / h] - Treated water flow rate [m ３ / h] / 0.95. Based on this calculated value, controlled the flow rate of the concentrated water W3 to be 5% (10 - 15 m ３ / h) and the supply water flow rate of the UF membrane 9 to be 200 - 300 m

[0048] 1 Ultrapure water production apparatus 2 Supply pipe 3 Water to be treated tank 4 Raw water supply pipe 5 Primary pure water system 6 Sub-tank 7 Primary pure water supply pipe 8 Secondary pure water system (subsystem) 9 Ultrafiltration membrane (UF membrane) 10 Ultrapure water supply pipe 11 Use point 12 Return piping 13 Recovery piping 13A Recycling tank 21 Flow meter (measuring means) 22 Manual valve 23 Control valve (control means) 24 Flow meter (measuring means) 25 Flow meter (measuring means) W Raw water W1 Primary pure water W2 Ultrapure water (secondary pure water) W3 Concentrated water

Claims

1. A control method for an ultrapure water production apparatus having a primary pure water system, a secondary pure water system, and an ultrafiltration membrane provided at the terminal end of the secondary pure water system for supplying ultrapure water to a point of use, the control method comprising: a control mechanism for controlling the flow rate of concentrated water through the ultrafiltration membrane; and measuring means for measuring one or more of the flow rates of the supply water, treated water, or concentrated water through the ultrafiltration membrane, wherein the control mechanism controls the flow rate of concentrated water through the ultrafiltration membrane to an arbitrary fixed value.

2. A control method for an ultrapure water production apparatus having a primary pure water system, a secondary pure water system, and an ultrafiltration membrane provided at the terminal end of the secondary pure water system for supplying ultrapure water to a point of use, the control method comprising: a control mechanism for controlling the flow rate of concentrated water through the ultrafiltration membrane; and measuring means for measuring one or more of the flow rates of the supply water, treated water, or concentrated water through the ultrafiltration membrane, wherein the control mechanism controls the flow rate of concentrated water through the ultrafiltration membrane so that the flow rate of concentrated water through the ultrafiltration membrane is a predetermined ratio to the supply flow rate of the ultrafiltration membrane.

3. A control method for an ultrapure water production apparatus according to claim 1 or 2, wherein the flow rate of concentrated water through the ultrafiltration membrane is controlled to be 5% or less of the supply flow rate of the ultrafiltration membrane.

4. The control mechanism for controlling the concentrated water flow rate of the ultrafiltration membrane is provided in the piping of the ultrafiltration membrane, the control method for an ultrapure water production apparatus according to claim 3.

5. A control method for an ultrapure water production apparatus according to claim 3, wherein a plurality of ultrafiltration membranes are arranged in parallel, and the control mechanism for controlling the concentrated water flow rate of the ultrafiltration membranes is provided in the confluence pipe of the concentrated water from the plurality of ultrafiltration membranes.

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