Control method for ultrapure water production equipment

Abstract

A method for controlling an ultrapure water production system is provided that can improve the water recovery rate in the ultrafiltration membrane of the pure water production system. [Solution] A flow meter 21 and a manual valve 22 are provided in the recovery pipe 13 of the UF membrane 9, and a control valve 23 is provided downstream of the manual valve 22, and the opening of the control valve 23 can be controlled by a control means (not shown) based on the measurement value of the flow meter 21. If the flow rate of the feed water to the UF membrane 9 fluctuates, the amount of concentrated water W3 increases, but by measuring the flow rate of the concentrated water W3 from the UF membrane 9 with the flow meter 21 and adjusting the opening of the control valve 23 so that the flow rate remains constant, it is possible to suppress the amount of feed water to the UF membrane 9 that is excessively discharged outside the system as concentrated water W3.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling an ultrapure water production system, and more particularly to a method for controlling an ultrafiltration membrane of an ultrapure water production system. [Background technology]

[0002] Conventionally, ultrapure water, from which impurities have been highly removed, has been used as a cleaning liquid for cleaning electronic components such as semiconductor wafers and glass substrates in the manufacturing processes of semiconductor devices and liquid crystal devices. Ultrapure water is produced, for example, by a pure water production system such as the one shown in FIG. 1. In FIG. 1, the ultrapure water production system 1 includes a supply pipe 2 that supplies raw water W (e.g., river water, groundwater, or industrial water) treated in a pretreatment system to a water tank 3 to be treated, a raw water supply pipe 4 that supplies the raw water W from the water tank 3 to a primary pure water system 5, a subtank 6 that stores the resulting primary pure water W1, a primary pure water supply pipe 7 that supplies the primary pure water W1 from the subtank 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 resulting ultrapure water W2 to a point of use 11, and a return pipe 12 that returns unused ultrapure water W2 from the point of use 11 to the subtank 6. The concentrated water W3 from the UF membrane 9 is then sent to the treated water tank 3 through the recovery pipe 13 and reused. This concentrated water W3 from the UF membrane 9 may be used to produce ultrapure water at about 23°C, or may be used to produce warm ultrapure water at about 60 to 75°C.

[0003] In this type of ultrapure water production system 1, the pretreatment device performs pretreatment on river water, groundwater, and industrial water using filtration, coagulation sedimentation, microfiltration membranes, etc., primarily to remove suspended solids. The primary pure water system 5 includes, for example, a water tank 3 for storing pretreated water (raw water) W, a high-pressure pump for transporting the water W, an activated carbon tower, a reverse osmosis membrane device, a membrane degasser, an ultraviolet oxidation device, an electrodeionization device, an ion exchange resin device, etc. This primary pure water system 5 removes most of the electrolytes, fine particles, live bacteria, etc. from the pretreated water (raw water) W, and also decomposes and removes organic matter.

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

[0005] In the primary pure water system 5 and the secondary pure water system 8, to obtain the required water quality, water is discharged from some of the components, such as the backwash process for the filter and activated carbon tower, the concentrated water from the reverse osmosis membrane (RO membrane), the regeneration process for the ion exchange resin device, the concentrated water from the electrodeionization device, 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 installed in the recovery pipe 13 for the UF membrane 9, and the flow rate of the concentrated water W3 is controlled to vary depending on the amount of feedwater supplied to the UF membrane 9.

[0006] Highly purified water treated in the primary pure water system 5 and secondary pure water system 8 is supplied to the UF membrane 9 at the end of this ultrapure water production equipment, so operating the system by returning 5% or more (recovery rate of 95%) of the water supplied to the UF membrane 9 as concentrated water W3 and using it as raw water for the primary pure water system 5 is extremely wasteful in terms of effective energy utilization. Therefore, a method has been used in which the concentrated water W3 from the UF membrane 9 is further treated with a UF membrane and recovered, but this has the problem of requiring many components such as UF membranes, piping, and valves for recovery.

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

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-017035 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the method of controlling the UF membrane in the ultrapure water production apparatus described in Patent Document 1 takes into consideration the generation of fine particles from the UF membrane, and there is a problem in that the improvement of the water recovery rate by controlling the UF membrane is insufficient.

[0010] Furthermore, after the UF membrane 9 is installed, it is usually subjected to processes such as switching between cleaning and water flow. However, these processes are often switched only by adjusting the valves manually. If the operation is subjected to an excessive flow rate load, such as a sudden increase in the concentrated water W3 of the UF membrane 9, this may lead to the rupture of the UF membrane 9, which may result in a deterioration in the quality of the ultrapure water being produced.

[0011] To address these issues, there is a need for technology that has a mechanism that prevents a sudden flow rate load from being placed on the UF membrane, and that can also reduce the energy required for water production by keeping the concentrated water flow rate of the UF membrane to the minimum necessary during normal operation.

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

[0013] In order to achieve the above-mentioned object, 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 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 a measuring means for measuring the flow rate of one or more of the supply water, treated water, and concentrated water through the ultrafiltration membrane, and the control mechanism controls the flow rate of concentrated water so that the flow rate of concentrated water through the ultrafiltration membrane becomes an arbitrary fixed value (Invention 1).

[0014] According to this invention (Invention 1), by controlling the flow rate of the concentrated water through the UF membrane to a fixed value, the amount of UF membrane feed water treated in the primary and secondary pure water systems that is discharged to the outside of the system as concentrated water through the UF membrane can be controlled by keeping it at a fixed value. In addition, because the amount of concentrated water through the UF membrane does not fluctuate, the risk of UF membrane rupture due to excessive fluctuations in the flow rate load of the concentrated water through the UF membrane can be avoided.

[0015] Secondly, the present invention provides a method for controlling an ultrapure water production apparatus having a primary pure water system, a secondary pure water system, and an ultrafiltration membrane provided at the 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 flow rate of concentrated water through the ultrafiltration membrane, and a measuring means for measuring one or more of the flow rates of supply water, treated water, and concentrated water through the ultrafiltration membrane, the control mechanism controlling the flow rate of concentrated water 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 (Invention 2).

[0016] According to this invention (Invention 2), by setting the flow rate of the UF membrane concentrate to a predetermined ratio relative to the UF membrane feedwater flow rate and controlling the concentrate flow rate, the amount of UF membrane feedwater treated in the primary and secondary pure water systems that is discharged outside the system as UF membrane concentrate can be controlled by setting it to a predetermined ratio. Also, by varying the flow rate ratio of the concentrate according to the UF membrane feedwater flow rate, it is possible to prevent excessive discharge outside the system as concentrate even if the UF membrane's allowable feedwater suddenly increases, and further, because the UF membrane concentrate is at a predetermined ratio, the risk of UF membrane rupture due to excessive fluctuations in the flow rate load of the UF membrane concentrate can be avoided.

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

[0018] According to this invention (Invention 3), it is possible to effectively prevent the excess discharge of UF membrane feed water treated in the primary and secondary pure water systems from the system as concentrated water from the UF membrane.

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

[0020] According to this invention (Invention 4), by controlling the flow rate of concentrated water from each ultrafiltration membrane for each ultrafiltration membrane, it is possible to optimize the prevention of excessive discharge of the UF membrane feed water treated in the primary and secondary pure water systems out of the 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 flow rate of concentrated water from the ultrafiltration membranes is provided in a confluence pipe for the concentrated water from the plurality of ultrafiltration membranes (Invention 5).

[0022] According to this invention (Invention 5), when multiple ultrafiltration membranes are provided in parallel, the concentrate flow rate is controlled after the concentrates from each ultrafiltration membrane are joined together, thereby reducing the number of control mechanisms that prevent the UF membrane feed water treated in the primary and secondary pure water systems from being excessively discharged outside the system as UF membrane concentrate, thereby simplifying control. [Effects of the Invention]

[0023] According to the method for controlling an ultrapure water production system of the present invention, the flow rate of the concentrate from the ultrafiltration membrane is controlled so that the flow rate of the concentrate from the ultrafiltration membrane is an arbitrary fixed value or a predetermined ratio to the supply flow rate from the ultrafiltration membrane, which makes it possible to prevent the UF membrane feed water treated in the primary and secondary pure water systems from being excessively discharged outside the system as the UF membrane concentrate. Furthermore, because the UF membrane concentrate does not fluctuate suddenly, the risk of the UF membrane breaking due to an excessive flow rate load on the UF membrane concentrate can be avoided. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a flow diagram showing an ultrapure water production system to which a first embodiment of the present invention can be applied. [Figure 2] FIG. 2 is a schematic diagram showing a method for controlling an ultrafiltration membrane in the first embodiment. [Figure 3] FIG. 4 is a schematic diagram showing a method for controlling an ultrafiltration membrane in a second embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram showing a method for controlling an ultrafiltration membrane in a third embodiment of the present invention. [Figure 5] FIG. 10 is a flow chart showing a fourth embodiment of an ultrapure water production system to which the present invention can be applied. [Figure 6] FIG. 1 is a schematic diagram showing a method for controlling an ultrafiltration membrane in Comparative Example 1 (conventional example). DETAILED DESCRIPTION OF THE INVENTION

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

[0026] [First Embodiment] <Ultra-pure Water Production Apparatus> FIG. 1 shows an ultra-pure water production apparatus to which the control method of the ultra-pure water production apparatus of the present invention can be applied. Since this ultra-pure water production apparatus has been described above, its detailed description will be omitted.

[0027] <Control Mechanism of UF Membrane> In the present embodiment, the control mechanism of the UF membrane has a configuration as shown in FIG. 2. In FIG. 2, the recovery pipe 13 of the UF membrane 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 on the downstream side of this manual valve 22. This control valve 23 can control its opening degree based on the measured value of the flow meter 21 by a control means (not shown).

[0028] <Control Method of Ultra-pure Water Production Apparatus> Next, the control method of the ultra-pure water production apparatus as described above will be described.

[0029] (Ultra-pure Water Production Process) In the ultra-pure water production apparatus 1 shown in FIG. 1, the primary pure water system 5 includes, for example, a treated water tank 3 for storing pretreated water (raw water) W, a high-pressure pump for feeding this treated water W, an activated carbon tower, a reverse osmosis membrane device, a membrane degassing device, an ultraviolet oxidation device, an electric deionization device, an ion exchange resin device, and the like. In this primary pure water system 5, most of the electrolytes, fine particles, live bacteria, etc. in the treated water W are removed and organic substances are decomposed.

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

[0031] Then, as shown in Fig. 2, by providing a flow meter 21, a manual valve 22, and a control valve 23 in the recovery pipe 13 of the UF membrane 9, when the flow rate of the feed water to the UF membrane 9 increases, usually the concentrate water W3 also increases. However, in this embodiment, the flow rate of the concentrate water W3 of the UF membrane 9 is measured by the flow meter 21, and the opening degree of the control valve 23 is adjusted so that the flow rate becomes constant. Therefore, it is possible to suppress the amount of the feed water to the UF membrane 9 treated by the primary pure water system 5 and the secondary pure water system 8 and discharged outside the system as the concentrate water W3 to a certain amount. As the fixed value of the flow rate of the concentrate water W3 of the UF membrane 9, it is preferably any fixed value within the range of 5% or less, particularly 3% or less (the recovery rate of the UF membrane 9 is 95% or more, particularly 97% or more) of the flow rate of the feed water to the UF membrane 9. Thereby, it is possible to reliably suppress the excessive discharge of the feed water to the UF membrane 9 outside the system as the concentrate water W3. Further, since the flow rate of the concentrate water W3 does not fluctuate rapidly, it is also possible to avoid the risk of breakage of the UF membrane 9 due to an excessive flow rate load of the concentrate water W3. Note that this control can be similarly applied to the flow rate fluctuations during processes such as cleaning, water passing, and separation for replacement after the installation of the UF membrane 9.

[0032] [Second Embodiment] <Ultra-pure Water Production Apparatus> The ultra-pure water production apparatus of the second embodiment is the same as the aforementioned first embodiment.

[0033] <Control Mechanism of UF Membrane> In this embodiment, the control mechanism of the UF membrane has a configuration as shown in Fig. 3. In Fig. 3, 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. Further, the primary pure water supply pipe 7 has a flow meter 24 as a measuring means for measuring the flow rate of the feed water to 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 Production Apparatus> Next, a control method of the ultra-pure water production apparatus as described above will be described.

[0035] (Ultra-pure water production process) The ultra-pure water production process is the same as that of the first embodiment described above.

[0036] Then, as shown in FIG. 3, a control valve 23 is provided 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 is provided in the primary pure water supply pipe 7. When the supply water flow rate of the UF membrane 9 fluctuates, the control valve 23 controls the concentrated water flow rate so that the concentrated water W3 becomes a predetermined ratio, for example, 5% of the supply water flow rate measured by the flow meter 24. Thus, the operation of the UF membrane 9 can be stabilized. 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 any fixed value within the range of 5% or less, particularly 3% or less (the recovery rate of the UF membrane 9 is 95% or more, particularly 97% or more) of the supply water flow rate of the UF membrane 9. Note that this control can be similarly applied to flow rate fluctuations during processes such as cleaning, water passing, and disconnection for replacement after the installation of the UF membrane 9.

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

[0038] <Control mechanism of UF membrane> In this embodiment, the control mechanism of the UF membrane has a 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 downstream 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 apparatus> Next, a method for controlling the above-described ultrapure water production system will be described.

[0040] (Ultrapure water manufacturing process) The process for producing ultrapure water is the same as that in the first embodiment described above.

[0041] As shown in FIG. 4, a control valve 23 is provided in the recovery pipe 13 of the UF membrane 9, and a flow meter 25 for measuring the flow rate of the treated water from the UF membrane 9 is provided in the ultrapure water supply pipe 10. When the flow rate of the feed water to the UF membrane 9 fluctuates, the concentrated water flow rate is calculated from the treated water flow rate of the UF membrane 9 measured by the flow meter 25 so that the recovery rate of the UF membrane 9 becomes a predetermined value, for example, 5% (concentrated water flow rate [m 3 / h] = treated water flow rate [m 3 / h] / 0.95-treated water flow rate [m 3 / h]) and controlling it based on this allows for stable operation of the UF membrane 9. It is also possible to set this ratio to the supply flow rate of the UF membrane 9 even smaller (less than 5%), thereby preventing excessive discharge of the UF membrane 9 concentrate W3 from the system. The ratio of the flow rate of the UF membrane 9 concentrate W3 to the flow rate of the UF membrane 9 is preferably set to an arbitrary fixed value within a range of 5% or less, particularly 3% or less, of the flow rate of the supply water to the UF membrane 9 (recovery rate of the UF membrane 9 of 95% or more, particularly 97% or more). This control can also be applied to flow rate fluctuations during processes such as cleaning after installation of the UF membrane 9, or when the UF membrane 9 is disconnected for water flow or replacement.

[0042] Although the present invention has been described above based on the above-described embodiments, it is not limited to these embodiments and various modifications are possible. For example, the ultrapure water production system 1 may be configured to have various primary pure water systems 5 and subsystems 8. As shown in FIG. 5 , a recycle tank 13A may be provided in the recovery pipe 13, and the concentrated water W3 may be temporarily stored in the recycle tank 13A and supplied to the primary pure water system 5, such as the concentrated water for the electrodeionization device, the regeneration water for the regenerative ion exchange device, the fill water for the vacuum pump, or a heat exchanger. The control mechanism for the concentrated water W3 from the UF membrane 9 may be installed in the recovery pipe 13 for each UF membrane 9. However, if multiple UF membranes 9 are connected in parallel, the control mechanism may be installed in the confluence pipe for the concentrated water W3 from each UF membrane 9. Furthermore, the flow rate of the ultrapure water production system 1 itself may be controlled by rated pump operation or manual valve adjustment, or it may be controlled by inverter-controlled operation and linked to this control. [Example]

[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 system 1 shown in FIG. 1, the flow rate of the water supplied to the UF membrane 9 is 200 m 3 / h, the flow rate of concentrated water W3 was set to 10m to achieve a recovery rate of 95%. 3 / h(treated water flow rate 190m 3 / h) by the manual valve 32. The flow rate of the water supply to the UF membrane 9 was adjusted to 300 m 3 / h. Because the adjustment was made using the manual valve 32, the flow rate of the treated water (ultrapure water) W2 from the UF membrane 9 and the flow rate of the concentrated water W3 could not be precisely controlled, resulting in a run-of-the-mill operation. This run-of-the-mill operation could result in an excessive flow rate flowing into the concentrated water W3 side when the feedwater flow rate of the UF membrane 9 suddenly fluctuated or when the UF membrane 9 was being replaced, posing a risk of rupture of the UF membrane 9. In addition, the amount of concentrated water W3 from the UF membrane that was returned to the return destination was greater than necessary.

[0045] [Example 1] In the ultrapure water production system 1 shown in FIG. 1, the flow rate of the water supplied to the UF membrane 9 is set to 200 to 300 m 3 / h, and the flow rate of the concentrated water through the UF membrane 9 is measured by the flow meter 21. When the flow rate of the concentrated water W3 is 10 m 3 / h, treated water (ultrapure water) W2 flow rate 190-290m 3 / h (feed water flow rate - flow rate of concentrated water W3). 3 / h, there was no excess of concentrated water W3 in the UF membrane 9. It was also possible to avoid the risk of rupture of the UF membrane 9 due to flow rate load fluctuations caused by excessive flow rate fluctuations of the concentrated water W3 in the UF membrane 9.

[0046] [Example 2] In the ultrapure water production system 1 shown in FIG. 1, the flow rate of the water supplied to the UF membrane 9 is set to 200 to 300 m as shown in FIG. 3 / h, and the flow rate of the feed water to the UF membrane 9 is measured by the flow meter 24. The flow rate of the concentrated water W3 is set to 5% (10 to 15 m) of the feed water flow rate. 3 / h), treated water (ultrapure water) W2 flow rate 190-285m 3 / h (feed water flow rate - flow rate of concentrated water W3). As a result, the concentrated water W3 in the UF membrane 9 did not become excessive compared to Comparative Example 1. In addition, it became possible to avoid the risk of breakage of the UF membrane 9 due to flow load fluctuations caused by excessive flow rate fluctuations of the concentrated water W3 in the UF membrane 9.

[0047] [Example 3] In the ultrapure water production system 1 shown in FIG. 1, the flow rate of the treated water from the UF membrane 9 is 190 to 285 m 3 / h, the flow rate of the concentrated water W3 at which the recovery rate becomes 5% from the flow rate of the treated water of the UF membrane 9 was calculated using the following formula: Concentrated water flow rate [m 3 / h]= Treated water flow rate〔m 3 / h) / 0.95-treated water flow rate [m 3 / h Based on this calculated value, the flow rate of the concentrated water W3 is set to 5% (10-15 m 3 / h), the flow rate of the feed water to the UF membrane 9 is 200 to 300 m3 / h (treated water flow rate / 0.95). As a result, the concentrated water W3 of the UF membrane 9 did not become excessive compared to Comparative Example 1. In addition, it became possible to avoid the risk of breakage of the UF membrane 9 due to flow rate load fluctuations caused by excessive flow rate fluctuations of the concentrated water W3 of the UF membrane 9. [Explanation of symbols]

[0048] 1 Ultrapure water production equipment 2 Supply pipe 3. Treated water tank 4 Raw water supply pipe 5 Primary pure water system 6 Subtank 7 Primary pure water supply pipe 8 Secondary pure water system (subsystem) 9 Ultrafiltration membrane (UF membrane) 10 Ultrapure water supply pipe 11 Use Points 12 Return piping 13 Recovery piping 13A Recycling Tank 21 Flow meter (measurement means) 22 Manual valve 23 Control valve (control means) 24 Flowmeter (Measuring means) 25 Flowmeter (Measuring means) W Raw Water W1 Primary pure water W2 Ultrapure water (secondary pure water) W3 Concentrated water

Claims

1. 1. A method for controlling an ultrapure water production apparatus having a primary pure water system, a secondary pure water system, and an ultrafiltration membrane provided at a terminal side of the secondary pure water system for supplying ultrapure water to a point of use, comprising: The ultrapure water production apparatus includes a control mechanism for controlling the flow rate of concentrated water through the ultrafiltration membrane, and a first flow meter for measuring the flow rate of feed water through the ultrafiltration membrane or a second flow meter for measuring the flow rate of treated water through the ultrafiltration membrane; When the ultrapure water production apparatus has the first flow meter, the flow rate of the concentrated water is controlled by the control mechanism based on the flow rate measured by the first flow meter so that the flow rate of the concentrated water through the ultrafiltration membrane becomes an arbitrary fixed value; A control method for an ultrapure water production apparatus, in which, when the ultrapure water production apparatus has the second flow meter, the flow rate of the concentrated water through the ultrafiltration membrane is controlled by the control mechanism based on the measured flow rate of the second flow meter so that the flow rate of the concentrated water becomes an arbitrary fixed value.

2. 1. A method for controlling an ultrapure water production apparatus having a primary pure water system, a secondary pure water system, and an ultrafiltration membrane provided at a terminal side of the secondary pure water system for supplying ultrapure water to a point of use, comprising: The ultrapure water production apparatus includes a control mechanism for controlling the flow rate of concentrated water through the ultrafiltration membrane, and a first flow meter for measuring the flow rate of feed water through the ultrafiltration membrane or a second flow meter for measuring the flow rate of treated water through the ultrafiltration membrane; When the ultrapure water production apparatus has the first flow meter, the control mechanism controls the flow rate of the concentrated water of the ultrafiltration membrane based on the flow rate measured by the first flow meter so that the flow rate of the concentrated water of the ultrafiltration membrane becomes a predetermined ratio to the supply flow rate of the ultrafiltration membrane; When the ultrapure water production apparatus has the second flow meter, the control mechanism controls the flow rate of the concentrated water through the ultrafiltration membrane based on the flow rate measured by the second flow meter so that the flow rate of the concentrated water is a predetermined ratio to the supply flow rate of the ultrafiltration membrane.

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

4. 4. The method for controlling an ultrapure water production system according to claim 3, wherein the control mechanism for controlling the flow rate of concentrated water through the ultrafiltration membrane is provided in a pipe for the ultrafiltration membrane.

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

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