Patent Publication Number: US-2020298180-A1

Title: Membrane separation apparatus

Description:
This application is based on and claims the benefit of priority from Japanese Patent Application No. 2019-049892, filed on 18 Mar. 2019, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a membrane separation apparatus. 
     Related Art 
     In manufacturing processes of semiconductor and cleansing of electronic devices and medical instruments, for example, pure water of high purity containing no impurities has been used. In general, this kind of pure water is produced by subjecting raw water, such as groundwater and tap water, to reverse osmosis membrane separation processing in a reverse osmosis membrane module (hereinafter also referred to as “RO membrane module”). 
     A water permeability coefficient of a reverse osmosis membrane made of a high polymer varies in accordance with temperature. The water permeability coefficient of the reverse osmosis membrane also varies due to pore blocking (hereinafter also referred to as “membrane fouling”) and deterioration owing to material oxidation (hereinafter also referred to as “membrane deterioration”). 
     In view of this, to keep a flowrate of permeated water constant in the RO membrane module irrespective of temperature of the raw water and a state of the reverse osmosis membrane, a water quality improving system to perform flowrate feedback water-amount control has been proposed (see, for example, JP-A-2005-296945). 
     In this water quality improving system, a drainage water flowrate regulation valve to regulate a drainage water flowrate and a feedwater pressure regulation valve to regulate a feedwater pressure are employed, and inverter control is performed to control a permeated water flowrate. When control frequency of the drainage water flowrate regulation valve and the feedwater pressure regulation valve is increased, lives of the drainage water flowrate regulation valve and the feedwater pressure regulation valve are shortened. Follow-up control with respect to other PI control is frequently performed to make hunting more liable to occur. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a membrane separation apparatus that can lengthen lives of opening-degree adjustable valves and stabilize various kinds of PI control. 
     According to an aspect of the invention, a membrane separation apparatus includes a reverse osmosis membrane module, a booster pump, a pump controller, an intake water pressure regulation valve, a drainage water flowrate regulation valve, an intake water pressure regulation valve controller, a drainage water flowrate regulation valve controller, and a timing adjustor. The reverse osmosis membrane module is configured to separate feedwater including intake water into permeated water and concentrated water. The booster pump is configured to take in the intake water and discharge the intake water as the feedwater to the reverse osmosis membrane module. The pump controller is configured to control a rotational speed of the booster pump. The intake water pressure regulation valve has an opening degree substantially steplessly adjusted to regulate a pressure of the intake water supplied to the booster pump. The drainage water flowrate regulation valve has an opening degree substantially steplessly adjusted to regulate a drainage water flowrate of the concentrated water to be drained from the apparatus. The intake water pressure regulation valve controller is configured to control the opening degree of the intake water pressure regulation valve. The drainage water flowrate regulation valve controller is configured to control the opening degree of the drainage water flowrate regulation valve. The timing adjustor is configured to adjust timings of control by the pump controller, the intake water pressure regulation valve controller, and the drainage water flowrate regulation valve controller. At the time of supplying water to the membrane separation apparatus, the timing adjustor is configured to provide time lags among a control start timing of the booster pump by the pump controller, a control start timing of the intake water pressure regulation valve by the intake water pressure regulation valve controller, and a control start timing of the drainage water flowrate regulation valve by the drainage water flowrate regulation valve controller. 
     Preferably, at the time of supplying water to the membrane separation apparatus, after starting to control the intake water pressure regulation valve, the timing adjustor is configured to cause the pump controller to start to control the booster pump or configured to cause the drainage water flowrate regulation valve controller to control the drainage water flowrate regulation valve. 
     Preferably, at the time of supplying water to the membrane separation apparatus, the timing adjustor is configured to cause the pump controller to start to control the booster pump after starting to control the intake water pressure regulation valve, and configured to cause the drainage water flowrate regulation valve controller to control the drainage water flowrate regulation valve after starting to control the booster pump. 
     Preferably, the membrane separation apparatus further includes a pressure measurer configured to measure a pressure value of the intake water, and the intake water pressure regulation valve controller is configured to perform feedback control using the pressure value of the intake water as a feedback value. 
     Preferably, the membrane separation apparatus further includes a first flowrate measurer configured to measure a flowrate value of the permeated water, and the pump controller is configured to perform feedback control using the flowrate value of the permeated water as a feedback value. 
     Preferably, the membrane separation apparatus further includes a second flowrate measurer configured to measure a value of the drainage water flowrate, and the drainage water flowrate regulation valve controller is configured to perform feedback control using the value of the drainage water flowrate as a feedback value. 
     Preferably, at the time of supplying water to the membrane separation apparatus, the pump controller is configured to decrease the rotational speed of the booster pump, the intake water pressure regulation valve controller is configured to increase the opening degree of the intake water pressure regulation valve or fully open the intake water pressure regulation valve, and when the rotational speed is decreased and consequently becomes lower than a predetermined value, the intake water pressure regulation valve controller decreases the opening degree of the intake water pressure regulation valve. 
     According to the aspect of the invention, lives of the opening-degree adjustable valves can be lengthened, and various kinds of PI control can be stabilized. 
     The foregoing and other object, features, aspects, and advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating the general arrangement of a membrane separation apparatus according to an embodiment of the invention. 
         FIG. 2  is a graph illustrating a relationship between a pressure and a flowrate concerning a flowrate regulation unit used in a first embodiment of the invention. 
         FIG. 3  is a function block diagram illustrating a controller of the membrane separation apparatus according to the embodiment of the invention. 
         FIG. 4  is a table illustrating exemplary control sequences of components that constitute the membrane separation apparatus according to the embodiment of the invention. 
         FIG. 5  is a table illustrating the exemplary control sequences of the components of the membrane separation apparatus according to the embodiment of the invention, and changes in pressures, flowrates, and a recovery rate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     1. CONFIGURATION OF MEMBRANE SEPARATION APPARATUS 
     A membrane separation apparatus  1  according to an embodiment of the invention will be described with reference to the accompanying drawings.  FIG. 1  is a diagram illustrating the general arrangement of the membrane separation apparatus  1  according to the embodiment of the invention. 
     As illustrated in  FIG. 1 , the membrane separation apparatus  1  according to this embodiment includes a feed pump  12 , a booster pump  2 , a booster-side inverter  3 , an RO membrane module  4  as a reverse osmosis membrane module, a flowrate regulation unit  5 , a check valve  6 , a drainage water flowrate regulation valve  7  as a drainage water flowrate regulator, an intake water pressure regulation valve  14 , an intake water pressure sensor PS 1 , a first flowrate sensor FM 1 , a second flowrate sensor FM 2 , and a controller  30 . In  FIG. 1 , illustration of electrical connection lines between the controller  30  and components to be controlled is omitted. 
     The membrane separation apparatus  1  also includes an intake water line L 1 , a feedwater line L 2 , a permeated water line L 3 , a concentrated water line L 4 , a circulation water line L 5 , and a drainage water line L 6 . In this specification, the term “line” generally refers to a line where a fluid is flowable, such as passages, channels, and piping. 
     The intake water line L 1  is a line to supply intake water W 1  to a junction J 2  to join the feedwater line L 2 . An upstream end of the intake water line L 1  is connected to a supply source (not illustrated) of the intake water W 1 . In the intake water line L 1 , the feed pump  12 , the intake water pressure regulation valve  14 , the intake water pressure sensor PS 1 , and the junction J 2  are disposed in sequence from an upstream side to a downstream side. 
     It should be noted that the intake water W 1  flowing through the intake water line L 1  includes not only raw water directly supplied from the supply source (not illustrated) of the intake water W 1  but also preprocessed water, which is raw water preprocessed by a preprocessor, such as a filtration device (e.g., an iron and manganese removal device and an activated carbon filter), and a water softening device. 
     The feed pump  12  is a device to take in the intake water W 1  that flows through the intake water line L 1  and to send (discharge) the intake water W 1  under pressure to the booster pump  2 . The feed pump  12  is driven at a rotational speed in accordance with a frequency of supplied (input) drive power (hereinafter also referred to as “drive frequency”). 
     The intake water pressure regulation valve  14  is a valve to regulate a pressure of the intake water W 1  that flows through the intake water line L 1 . The intake water pressure regulation valve  14  is electrically connected to the controller  30 . An opening degree of the intake water pressure regulation valve  14  is controlled by the controller  30 . The intake water pressure regulation valve  14  may be, for example, a solenoid valve. 
     The intake water pressure sensor PS 1  measures a pressure of the intake water W 1  that flows through the intake water line L 1 . The intake water pressure sensor PS 1  is electrically connected to the controller  30 . The pressure of the intake water W 1  measured by the intake water pressure sensor PS 1  is transmitted as a detection signal to the controller  30 . 
     The feedwater line L 2  is a line to feed the intake water W 1  as feedwater W 2  to the RO membrane module  4 . An upstream end of the feedwater line L 2  is connected to the junction J 2 . A downstream end of the feedwater line L 2  is connected to a primary inlet port of the RO membrane module  4 . In the feedwater line L 2 , the junction J 2 , the booster pump  2 , and the RO membrane module  4  are disposed in sequence from an upstream side to a downstream side. 
     The booster pump  2  is disposed in the feedwater line L 2 . The booster pump  2  is a device to take in the intake water W 1  and feed (discharge) the intake water W 1  as the feedwater W 2  under pressure to the RO membrane module  4  in the feedwater line L 2 . Drive power having a converted frequency is supplied from the booster-side inverter  3  to the booster pump  2 . The booster pump  2  is driven at a rotational speed in accordance with the frequency of supplied (input) drive power (hereinafter also referred to as “drive frequency”). 
     The booster-side inverter  3  is an electric circuit (or a device including the electric circuit) to supply drive power having a converted frequency to the booster pump  2 . The booster-side inverter  3  is electrically connected to the controller  30 . A command signal is input from the controller  30  to the booster-side inverter  3 . The booster-side inverter  3  outputs drive power having a drive frequency corresponding to a command signal (a current value signal or a voltage value signal) input from the controller  30 . 
     The RO membrane module  4  is a device for membrane separation processing to separate the feedwater W 2  discharged from the booster pump  2  into permeated water W 3  with dissolved salts removed and concentrated water W 4  with the dissolved salts concentrated. The RO membrane module  4  includes a single RO membrane element or a plurality of RO membrane elements (not illustrated). The RO membrane module  4  causes these RO membrane elements to subject the feedwater W 2  to the membrane separation processing to produce the permeated water W 3  and the concentrated water W 4 . 
     The permeated water line L 3  is a line to send the permeated water W 3  separated by the RO membrane module  4 . An upstream end of the permeated water line L 3  is connected to a secondary port of the RO membrane module  4 . A downstream end of the permeated water line L 3  is connected to a device in demand, for example. The first flowrate sensor FM 1  (hereinafter also referred to as “first flowrate detector”) is disposed in the permeated water line L 3 . 
     The first flowrate sensor FM 1  is a device to detect, as a first detection flowrate value, a flowrate of the permeated water W 3  that flows through the permeated water line L 3 . The first flowrate sensor FM 1  is connected to the permeated water line L 3 . The first flowrate sensor FM 1  is electrically connected to the controller  30 . The first detection flowrate value of the permeated water W 3  that has been detected by the first flowrate sensor FM 1  is transmitted to the controller  30  as a detection signal. As the first flowrate sensor FM 1 , for example, a pulse-oscillation flowrate sensor with an axial-flow vane wheel or a tangential vane wheel (not illustrated) disposed in a passage housing may be employed. 
     A first concentrated water line L 41  is a line to send the concentrated water W 4  separated by the RO membrane module  4 . An upstream end of the first concentrated water line L 41  is connected to a primary outlet port of the RO membrane module  4 . A downstream end of the first concentrated water line L 41  is connected to a primary side of the flowrate regulation unit  5 . 
     A second concentrated water line L 42  is a line to send the concentrated water W 4  having a flowrate regulated by the flowrate regulation unit  5 . An upstream end of the second concentrated water line L 42  is connected to a secondary side of the flowrate regulation unit  5 . A downstream side of the second concentrated water line L 42  diverges into the circulation water line L 5  and the drainage water line L 6  at a joint J 1 . 
     Hereinafter, the first concentrated water line L 41  and the second concentrated water line L 42  will be collectively referred to as “concentrated water line L 4 ” on occasion. 
     The flowrate regulation unit  5  includes a constant flowrate element and a proportional element. The constant flowrate element causes the concentrated water W 4  to flow at a substantially constant flowrate irrespective of a differential pressure in the flowrate regulation unit  5 . The proportional element increases a flowrate of the concentrated water W 4  substantially in proportion to the differential pressure in the flowrate regulation unit  5 . Specifically, the differential pressure in the flowrate regulation unit  5  is a difference between a water pressure in the first concentrated water line L 41  and a water pressure in the second concentrated water line L 42 . As the constant flowrate element, a device that maintains a constant flowrate value without requiring auxiliary power and external operation and that is called a water governor, for example, may be employed. As the proportional element, a device called an orifice, for example, may be employed. A flowrate of the concentrated water W 4  flowing from the orifice is in proportion to the differential pressure in the flowrate regulation unit  5 . 
       FIG. 2  is a graph of an exemplary relationship between an inlet pressure of the RO membrane module  4  and a flowrate of the concentrated water W 4  flowing in the flowrate regulation unit  5 . Since the flowrate regulation unit  5  includes the constant flowrate element, the flowrate of the concentrated water W 4  flowing in the flowrate regulation unit  5  sharply increases to a point A when the inlet pressure is generated. That is, approximately, at the same time as generation of the inlet pressure, the concentrated water W 4  at the flowrate as high as the point A flows into the flowrate regulation unit  5 . Because the flowrate regulation unit  5  also includes the proportional element, the flowrate of the concentrated water W 4  flowing in the flowrate regulation unit  5  subsequently increases in a linear function manner as the inlet pressure increases. 
     It should be noted that in the flowrate regulation unit  5 , the constant flowrate element and the proportional element may be integrally provided or provided as separate members. When the constant flowrate element and the proportional element are integrally provided, for example, a flow direction of the proportional element may coincide with a longitudinal axis direction of the flowrate regulation unit  5 , and a flow direction of the constant flowrate element may be perpendicular to the longitudinal axis direction of the flowrate regulation unit  5 . Alternatively, the flow direction of the proportional element may be perpendicular to the longitudinal axis direction of the flowrate regulation unit  5 , and the flow direction of the constant flowrate element may coincide with the longitudinal axis direction of the flowrate regulation unit  5 . Alternatively, both of the flow direction of the constant flowrate element and the flow direction of the proportional element may coincide with the longitudinal axis direction of the flowrate regulation unit  5 . 
     The circulation water line L 5  diverges from the concentrated water line L 4  and is a line to return circulation water W 41  to the junction J 2 . The circulation water W 41  is part of the concentrated water W 4  separated by the RO membrane module  4 . An upstream end of the circulation water line L 5  is connected to the concentrated water line L 4  at the joint J 1 . A downstream end of the circulation water line L 5  is connected to the intake water line L 1  at the junction J 2 . The check valve  6  is disposed in the circulation water line L 5 . 
     The drainage water line L 6  diverges from the concentrated water line L 4  at the joint J 1  and is a line to drain drainage water W 42  from the apparatus (out of the system). The drainage water W 42  is the rest of the concentrated water W 4  separated by the RO membrane module  4 . In the drainage water line L 6 , the second flowrate sensor FM 2  (hereinafter also referred to as “second flowrate detector”) and the drainage water flowrate regulation valve  7  as a drainage water flowrate regulator are disposed from an upstream side to a downstream side. 
     The second flowrate sensor FM 2  is a device to detect, as a second detection flowrate value, a drainage water flowrate of the drainage water W 42  to be drained from the apparatus via the drainage water line L 6 . The second flowrate sensor FM 2  is connected to the drainage water line L 6 . The second flowrate sensor FM 2  is electrically connected to the controller  30 . The second detection flowrate value of the drainage water W 42  that has been detected by the second flowrate sensor FM 2  is transmitted to the controller  30  as a detection signal. As the second flowrate sensor FM 2 , for example, a pulse-oscillation flowrate sensor with an axial-flow vane wheel or a tangential vane wheel (not illustrated) disposed in a passage housing may be employed. 
     The drainage water flowrate regulation valve  7  is capable of regulating the drainage water flowrate of the drainage water W 42  to be drained from the apparatus via the drainage water line L 6 . The drainage water flowrate regulation valve  7  is electrically connected to the controller  30 . A valve opening degree of the drainage water flowrate regulation valve  7  is controlled in accordance with a drive signal transmitted from the controller  30 . The controller  30  transmits a current value signal (e.g., 4 mA to 20 mA) to the drainage water flowrate regulation valve  7  and controls the valve opening degree to regulate the drainage water flowrate of the drainage water W 42 . The drainage water flowrate regulation valve  7  may be, for example, a solenoid valve. 
     2. FUNCTION BLOCKS OF CONTROLLER 
     The controller  30  includes components such as a CPU, a ROM, a RAM, and a CMOS memory, which are communicable with one another via buses, and is known to those skilled in the art. 
     The CPU is a processor to totally control the membrane separation apparatus  1 . The CPU reads various kinds of programs stored in the ROM via the buses and controls the whole membrane separation apparatus  1  in accordance with the various kinds of programs. Consequently, as illustrated in a function block diagram of  FIG. 3 , the controller  30  implements functions of a pump controller  31 , an intake water pressure regulation valve controller  32 , a drainage water flowrate regulation valve controller  33 , and a timing adjustor  34 . The RAM stores various kinds of data, such as temporary calculation data and display data. The CMOS memory is a non-volatile memory, which is backed up by a battery (not illustrated) and retains a memory state even when the membrane separation apparatus  1  is powered off. 
     The pump controller  31  controls the rotational speed of the booster pump  2 . More specifically, the pump controller  31  controls a frequency of the booster pump  2  via the booster-side inverter  3  so as to regulate a flowrate of the feedwater W 2  discharged by the booster pump  2 . The pump controller  31  may perform feedback control using a flowrate value of the permeated water W 3  detected by the first flowrate sensor FM 1 . 
     The intake water pressure regulation valve controller  32  controls the opening degree of the intake water pressure regulation valve  14 . In particular, in accordance with a timing adjusted by the timing adjustor  34 , described later, the intake water pressure regulation valve controller  32  controls the opening degree of the intake water pressure regulation valve  14 . The intake water pressure regulation valve controller  32  may perform feedback control using a pressure value of the intake water W 1  detected by the intake water pressure sensor PS 1 . 
     The drainage water flowrate regulation valve controller  33  controls the opening degree of the drainage water flowrate regulation valve  7 . In particular, in accordance with a timing adjusted by the timing adjustor  34 , described later, the drainage water flowrate regulation valve controller  33  controls the opening degree of the drainage water flowrate regulation valve  7 . The drainage water flowrate regulation valve controller  33  may perform feedback control using a flowrate value of the drainage water W 42  detected by the second flowrate sensor FM 2 . 
     The timing adjustor  34  adjusts timings of control by the pump controller  31 , the intake water pressure regulation valve controller  32 , and the drainage water flowrate regulation valve controller  33 . In particular, at the time of supplying water to the membrane separation apparatus  1 , the booster pump  2 , the intake water pressure regulation valve  14 , and the drainage water flowrate regulation valve  7  that are operated at once affect one another so that phenomena may occur, such as hunting and increases in the number of operations of the intake water pressure regulation valve  14  and the drainage water flowrate regulation valve  7 . In view of this, to prevent hunting and decrease the number of operations of the intake water pressure regulation valve  14  and the drainage water flowrate regulation valve  7 , the timing adjustor  34  provides time lags among a control start timing of the booster pump  2  by the pump controller  31 , a control start timing of the intake water pressure regulation valve  14  by the intake water pressure regulation valve controller  32 , and a control start timing of the drainage water flowrate regulation valve  7  by the drainage water flowrate regulation valve controller  33  at the time of supplying water to the membrane separation apparatus  1 . The time lags are set considering factors, such as time until the intake water pressure is stabilized, a maximum frequency of the booster pump  2 , and operation time of the intake water pressure regulation valve  14  and the drainage water flowrate regulation valve  7 . 
     At the time of supplying water to the membrane separation apparatus  1 , the timing adjustor  34  provides time lags among the control start timing of the booster pump  2  by the pump controller  31 , the control start timing of the intake water pressure regulation valve  14  by the intake water pressure regulation valve controller  32 , and the control start timing of the drainage water flowrate regulation valve  7  by the drainage water flowrate regulation valve controller  33 . This results in six possible control sequences in controlling the booster pump  2 , the intake water pressure regulation valve  14 , and the drainage water flowrate regulation valve  7 . Furthermore, considering whether to close the intake water pressure regulation valve  14  at a preparatory stage of supplying water to the membrane separation apparatus  1  or whether to open the intake water pressure regulation valve  14  itself while the passage can be opened and closed by an ON-OFF valve upstream of the intake water pressure regulation valve  14 , twelve control sequences are possible. 
       FIG. 4  is a table illustrating these twelve control sequences. 
     Referring to the table of  FIG. 4 , as illustrated in the row No. 1, suppose that the intake water pressure regulation valve  14  is first operated, that the booster pump  2  is operated next, and that the drainage water flowrate regulation valve  7  is finally operated. In this case, after the booster pump  2  is operated and when the intake water pressure is stabilized, the opening degree of the drainage water flowrate regulation valve  7  is adjusted so that unstable operation is less likely to occur. 
     As illustrated in the row No. 2, suppose that the intake water pressure regulation valve  14  is first operated, that the drainage water flowrate regulation valve  7  is operated next, and that the booster pump  2  is finally operated. In this case, when the booster pump  2  is operated, the intake water pressure decreases. Accordingly, the opening degree of the drainage water flowrate regulation valve  7  that has been adjusted once is to be readjusted so that the intake water pressure regulation valve  14  and the drainage water flowrate regulation valve  7  are operated at once to make hunting more liable to occur. Depending upon follow-up performance of the drainage water flowrate regulation valve  7 , the drainage water flowrate may exceed a target drainage water flowrate, which may cause an amount of water supplied to the membrane separation apparatus  1  to exceed an allowable supplied water amount. 
     Control sequences illustrated in the rows Nos. 3 to 6 are inoperable modes in which the intake water pressure regulation valve  14  is not operated at a control start, and no water is supplied to the membrane separation apparatus  1 . 
     In a control sequence illustrated in the row No. 7, adjustment of the intake water pressure regulation valve  14  is first performed to make the intake water pressure a target intake water pressure. Then, in a similar manner to the mode illustrated in the row No. 1, after the booster pump  2  is operated and when the intake water pressure is stabilized, the opening degree of the drainage water flowrate regulation valve  7  is adjusted so that unstable operation is less likely to occur. 
     In a control sequence illustrated in the row No. 8 as well, adjustment of the intake water pressure regulation valve  14  is first performed to make the intake water pressure the target intake water pressure. Then, in a similar manner to the mode illustrated in the row No. 2, when the booster pump  2  is operated, the intake water pressure decreases. Accordingly, the opening degree of the drainage water flowrate regulation valve  7  that has been initially adjusted is to be readjusted so that the intake water pressure regulation valve  14  and the drainage water flowrate regulation valve  7  are operated at once to make hunting more liable to occur. Depending upon follow-up performance of the drainage water flowrate regulation valve  7 , the drainage water flowrate may exceed a target drainage water flowrate, which may cause the amount of water supplied to the membrane separation apparatus  1  to exceed the allowable supplied water amount. 
     In a control sequence illustrated in the row No. 9, after operating the booster pump  2 , adjustment of the intake water pressure regulation valve  14  is performed to make the intake water pressure a target intake water pressure. Since operation of the booster pump  2  causes the intake water pressure to change moment by moment to make operation more liable to be unstable. During this time, because a time lag is set, the drainage water flowrate regulation valve  7  is not operated so that an intake water amount may exceed an allowable intake water amount, and that excessive concentration may occur. 
     In a control sequence illustrated in the row No. 10, after starting to operate the drainage water flowrate regulation valve  7 , operation of the intake water pressure regulation valve  14  is started with the drainage water flowrate regulation valve  7  kept operated so as to regulate the intake water pressure. Thus, all the components to be controlled are operated at once to make hunting more liable to occur. 
     In a control sequence illustrated in the row No. 11, after adjusting the opening degrees of the drainage water flowrate regulation valve  7  and the intake water pressure regulation valve  14 , the booster pump  2  is operated so that readjustment of the opening degrees of the drainage water flowrate regulation valve  7  and the intake water pressure regulation valve  14  will be needed and take more time until operation is stabilized. 
     In a control sequence illustrated in the row No. 12, after starting to operate the drainage water flowrate regulation valve  7 , operation of the intake water pressure regulation valve  14  is started with the drainage water flowrate regulation valve  7  kept operated. Thus, in operating the intake water pressure regulation valve  14 , all the components to be controlled are operated at once to make hunting more liable to occur. 
     That is, according to this embodiment, to prevent hunting and decrease the number of operations by the intake water pressure regulation valve  14  and the drainage water flowrate regulation valve  7 , preferably, control of the intake water pressure regulation valve  14  is started first. More preferably, after starting to control the intake water pressure regulation valve  14  first, control of the booster pump  2  is started next, and finally, control of the drainage water flowrate regulation valve  7  is started. 
     At the time of supplying water to the membrane separation apparatus  1 , the pump controller  31  decreases the rotational speed (frequency) of the booster pump  2 , and the intake water pressure regulation valve controller  32  increases the opening degree of the intake water pressure regulation valve  14  or fully opens the intake water pressure regulation valve  14 . When the rotational speed is decreased and consequently becomes lower than a predetermined value, the intake water pressure regulation valve controller  32  may decrease the opening degree of the intake water pressure regulation valve  14 . 
     When the frequency of the booster pump  2  becomes lower than a predetermined value, the booster pump  2  is not cooled enough. This makes it necessary to set a minimum frequency of the booster pump  2  in operation. When the frequency of the booster pump  2  becomes lower than the minimum frequency in operation, the opening degree of the intake water pressure regulation valve  14  is gradually decreased to enable such control as to prevent, to the utmost, the frequency of the booster pump  2  from becoming lower than the minimum frequency in operation. 
     3. EXAMPLES 
       FIG. 5  is a table illustrating operation examples of the membrane separation apparatus  1  according to this embodiment. More specifically, the table of  FIG. 5  illustrates changes in the opening degree of the intake water pressure regulation valve  14 , the opening degree of the drainage water flowrate regulation valve  7 , and control details of the frequency of the booster pump  2 . The table of  FIG. 5  also illustrates changes in the intake water pressure, a membrane inlet pressure, the drainage water flowrate, a processed water flowrate (the flowrate of the permeated water W 3 ), and an actual recovery rate in accordance with those changes. An arrow slanting upward to the right, an arrow straight to the right, and an arrow slanting downward to the right respectively represent increasing, constant, and decreasing. It should be noted that in this table, the “actual recovery rate” refers to a rate of a flowrate of the feedwater W 2  to the processed water flowrate (the flowrate of the permeated water W 3 ). The flowrate of the feedwater W 2  is calculated from the sum of the drainage water flowrate and the processed water flowrate (the flowrate of the permeated water W 3 ). In the table of  FIG. 5 , time elapses from an upper row to a lower row. 
     As illustrated in  FIG. 5 , according to this embodiment, after starting to control the intake water pressure regulation valve  14  at timing T 1 , operation of the booster pump  2  is started at timing T 5 , and finally, control of the drainage water flowrate regulation valve  7  is started at timing T 7 . 
     At timing T 1 , control of the intake water pressure regulation valve  14  is started. This causes the opening degree of the intake water pressure regulation valve  14  to increase between timing T 1  and timing T 2  to increase the intake water pressure whereas other attribute values are not changed. In particular, no change is found in the membrane inlet pressure because the intake water pressure is not high enough. 
     Between timing T 2  and timing T 3 , in addition to the increase in the intake water pressure, the membrane inlet pressure increases to raise the drainage water flowrate and the intake water flowrate. 
     Between timing T 3  and timing T 4 , the opening degree of the intake water pressure regulation valve  14  is kept constant. This makes the intake water pressure constant in a manner different from the period between timing T 1  and timing T 2 . 
     Between timing T 4  and timing T 5 , the membrane inlet pressure, the drainage water flowrate, and the intake water flowrate that have been increasing between timing T 3  and timing T 4  are made constant. 
     At timing T 5 , operation of the booster pump  2  is started. This causes the pump frequency of the booster pump  2  to increase between timing T 5  and timing T 6  to increase the membrane inlet pressure so as to raise the processed water flowrate and the intake water flowrate. Thus, the actual recovery rate is increased. 
     Between timing T 6  and timing T 7 , the pump frequency of the booster pump  2  is made constant. This causes the membrane inlet pressure that has been increasing between timing T 5  and timing T 6  to be constant, and the processed water flowrate and the intake water flowrate that have been raised to be constant. Consequently, the actual recovery rate becomes constant. 
     At timing T 7 , control of the drainage water flowrate regulation valve  7  is started. This causes the opening degree of the drainage water flowrate regulation valve  7  to decrease between timing T 7  and timing T 8  to lower the drainage water flowrate and the intake water flowrate. Thus, the actual recovery rate is increased. 
     Between timing T 8  and timing T 9 , the opening degree of the drainage water flowrate regulation valve  7  is made constant. This causes the drainage water flowrate and the intake water flowrate that have been lowered between timing T 7  and timing T 8  and the actual recovery rate to be constant. 
     4. EFFECTS OF THIS EMBODIMENT 
     The membrane separation apparatus  1  according to the above-described embodiment can provide the following effects, for example. 
     The membrane separation apparatus  1  includes the pump controller  31 , the intake water pressure regulation valve  14 , the drainage water flowrate regulation valve  7 , the intake water pressure regulation valve controller  32 , the drainage water flowrate regulation valve controller  33 , and the timing adjustor  34 . The pump controller  31  controls the rotational speed of the booster pump  2 . The intake water pressure regulation valve  14  has the opening degree substantially steplessly adjusted to regulate the pressure of the intake water W 1  supplied to the booster pump  2 . The drainage water flowrate regulation valve  7  has the opening degree substantially steplessly adjusted to regulate the drainage water flowrate of the concentrated water W 4  to be drained from the apparatus. The intake water pressure regulation valve controller  32  controls the opening degree of the intake water pressure regulation valve  14 . The drainage water flowrate regulation valve controller  33  controls the opening degree of the drainage water flowrate regulation valve  7 . The timing adjustor  34  adjusts the timings of control by the pump controller  31 , the intake water pressure regulation valve controller  32 , and the drainage water flowrate regulation valve controller  33 . The timing adjustor  34  provides time lags among the control start timing of the booster pump  2  by the pump controller  31 , the control start timing of the intake water pressure regulation valve  14  by the intake water pressure regulation valve controller  32 , and the control start timing of the drainage water flowrate regulation valve  7  by the drainage water flowrate regulation valve controller  33  at the time of supplying water to the membrane separation apparatus  1 . 
     The control start timings of the booster pump  2 , the intake water pressure regulation valve  14 , and the drainage water flowrate regulation valve  7  are deviated from one another to decrease a possibility of hunting. Moreover, this decreases time until the flowrates are stabilized. 
     At the time of supplying water to the membrane separation apparatus  1 , after starting to control the intake water pressure regulation valve  14 , the timing adjustor  34  causes the pump controller  31  to start to control the booster pump  2  or causes the drainage water flowrate regulation valve controller  33  to start to control the drainage water flowrate regulation valve  7 . 
     When control of the booster pump  2  is started first, the booster pump  2  is to be controlled again after starting to control the intake water pressure regulation valve  14 . By starting to control the intake water pressure regulation valve  14  first, such complicated control can be avoided. 
     At the time of supplying water to the membrane separation apparatus  1 , after starting to control the intake water pressure regulation valve  14 , the timing adjustor  34  causes the pump controller  31  to start to control the booster pump  2 , and after starting to control the booster pump  2 , the timing adjustor  34  causes the drainage water flowrate regulation valve controller  33  to start to control the drainage water flowrate regulation valve  7 . 
     When the intake water pressure regulation valve  14  is opened after closing the drainage water flowrate regulation valve  7 , there is a possibility of increasing the recovery rate. More specifically, when the drainage water flowrate regulation valve  7  is operated first, the subsequent operation of the booster pump  2  changes the intake water pressure. Thus, the intake water pressure regulation valve  14  and the drainage water flowrate regulation valve  7  are operated at once and may cause hunting and exceeding the allowable intake water amount. After starting to control the intake water pressure regulation valve  14 , the booster pump  2  is operated, and after the intake water pressure is stabilized, the drainage water flowrate regulation valve  7  is controlled so that stable operation can be implemented without exceeding an allowable recovery rate. 
     The membrane separation apparatus  1  further includes the intake water pressure sensor PS 1  to measure a pressure value of the intake water W 1 . The intake water pressure regulation valve controller  32  performs feedback control using the pressure value of the intake water W 1  as a feedback value. 
     When the intake water pressure is not kept constant, an inverter of the booster pump  2  and the drainage water flowrate regulation valve  7  are operated in accordance with a change in the intake water pressure so frequently that hunting is more liable to occur. Moreover, depending upon the follow-up performance, exceeding the allowable supplied water amount and increasing the recovery rate may occur. When the intake water pressure regulation valve  14  is controlled using the pressure value of the intake water W 1  as a feedback value, the pressure value of the intake water W 1  is kept constant so that the possibility of hunting can be decreased. Furthermore, possibilities of exceeding the allowable supplied water amount and excessive concentration can be decreased. The drainage water flowrate regulation valve  7  has a type capable of continuous operation and a type incapable of continuous operation. In the case of requiring frequent control of the drainage water flowrate regulation valve  7 , the type incapable of continuous operation cannot be employed. However, by keeping the pressure of the intake water W 1  constant, the drainage water flowrate regulation valve  7  of the type incapable of continuous operation can be used. 
     The membrane separation apparatus  1  further includes the first flowrate sensor FM 1  to measure a flowrate value of the permeated water W 3 . The pump controller  31  performs feedback control using the flowrate value of the permeated water W 3  as a feedback value. 
     Regulation to make the permeated water amount a target permeated water amount prevents the permeated water amount from changing due to a water temperature change so that the flowrate can be kept constant. 
     The membrane separation apparatus  1  further includes the second flowrate sensor FM 2  to measure a drainage water flowrate value. The drainage water flowrate regulation valve controller  33  performs feedback control using the drainage water flowrate value as a feedback value. 
     Regulation to make the drainage water flowrate a target drainage water flowrate enables operation with a recovery rate as close as possible to a set recovery rate. 
     At the time of supplying water to the membrane separation apparatus  1 , the pump controller  31  decreases the rotational speed of the booster pump  2 , and the intake water pressure regulation valve controller  32  increases the opening degree of the intake water pressure regulation valve  14  or fully opens the intake water pressure regulation valve  14 . When the rotational speed is decreased and consequently becomes lower than the predetermined value, the intake water pressure regulation valve controller  32  decreases the opening degree of the intake water pressure regulation valve  14 . 
     The rotational speed of the booster pump  2  is decreased, and the opening degree of the intake water pressure regulation valve  14  is increased or the intake water pressure regulation valve  14  is fully opened so that a raw water pressure can be utilized to the maximum to implement energy saving operation. 
     5. MODIFICATION 
     In the above-described embodiment, the membrane separation apparatus  1  is an RO membrane apparatus including the RO membrane module  4 . This, however, should not be construed in a limiting sense. The membrane separation apparatus  1  may be, for example, an NF (loose RO) membrane apparatus. 
     Various modifications and alterations of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention, and it should be understood that this is not limited to the illustrative embodiments set forth herein.