JP6463656B2 - Water treatment system - Google Patents

Description

  The present invention relates to a water treatment system.

  In a water treatment system equipped with a reverse osmosis membrane used for seawater desalination, control of reverse osmosis membrane contamination is an important issue for stable operation. As a factor that hinders the stable operation of this water treatment system, organic matter accumulated on the reverse osmosis membrane surface and dirt (biofouling) due to biological growth have become major issues. Moreover, a chemical | medical agent is used for suppression of these stain | pollution | contamination, and the excessive use of this chemical | medical agent contributes to the operating cost increase of a water treatment system.

  As a method for grasping the contamination of the reverse osmosis membrane, conventionally, the pressure loss (ΔP) between the inlet and the outlet in the reverse osmosis membrane vessel is measured, and the degree of contamination is evaluated based on the magnitude of the pressure loss. It was. However, with this method, it is difficult to cope with a rapid pressure increase and prevent irreversible contamination of the reverse osmosis membrane. Therefore, for the purpose of more accurate evaluation, a technique described in Patent Document 1 is known. In Patent Document 1, a biofilm-forming base material is arranged, and the amount of biofilm on the biofilm-forming base material is evaluated at a frequency of once a day to six months. Controlling the operating method of the osmosis membrane filtration plant is described.

International Publication No. 2008/038575

  In the technique described in Patent Document 1, the measurement of the amount of biofilm is performed by cutting out the reverse osmosis membrane to which the biofilm is attached and measuring the amount of the biofilm attached (particularly, (See paragraph 0053 of the specification of Patent Document 1). Therefore, the technique described in Patent Document 1 cannot grasp the degree of contamination continuously (in real time).

  The present invention has been made in view of such problems, and the problem to be solved by the present invention is water that can be controlled in accordance with the degree of contamination while continuously grasping the dirt of the reverse osmosis membrane. It is to provide a processing system.

The present inventors have intensively studied to solve the above problems. As a result, it has been found that the above problem can be solved by the following. That is, the gist of the present invention is that a reverse osmosis membrane and a treated water flow path through which the treated water supplied to the reverse osmosis membrane flows are connected in parallel and are one of treated water flowing through the treated water flow path. Is supplied to the reverse osmosis membrane to predict the degree of dirt attached to the reverse osmosis membrane, and during the continuous operation based on the degree of dirt of the reverse osmosis membrane predicted by the dirt prediction device A control unit that controls the supply condition of the treated water supplied to the reverse osmosis membrane, and the contamination prediction device includes an evaluation flow path through which a part of the treated water flowing through the treated water flow path flows. An evaluation member that is disposed so as to be able to come into contact with the treated water flowing through the evaluation flow path, so that dirt adheres along with the flow of the treated water, and a set of electrodes disposed so as to sandwich the evaluation member An AC power source connected in series to the set of electrodes, and the one set Been electrode connected in series, a rectifier for converting alternating current to direct current, characterized in that it is configured with a voltmeter for measuring the output voltage at the rectifier, a water treatment system About.

  ADVANTAGE OF THE INVENTION According to this invention, the water treatment system which can control the driving | operation according to the degree of contamination can be provided, grasping | ascertaining the stain | pollution | contamination of a reverse osmosis membrane continuously.

It is a systematic diagram of the seawater desalination system of a first embodiment. Regarding the reverse osmosis membrane in the seawater desalination system of the first embodiment (present invention) and the conventional seawater desalination system (conventional), (a) change in pressure loss ΔP with respect to continuous operation time, (b) with respect to continuous operation time It is a graph which shows the change of the output value from a foulant sensor. It is a perspective view of the foulant sensor with which the seawater desalination system of a first embodiment is equipped. FIG. 4 is a sectional view taken along line AA in FIG. 3. It is a perspective view of each member which comprises the foulant sensor shown in Drawing 3, (a) is a perspective view from the lower part of an upper member, (b) is the upper part of the state where an evaluation film and a spacer were mounted in a lower member. (C) is a perspective view from above of only the lower member. It is a perspective view about another form of the foulant sensor with which the seawater desalination system of a first embodiment is equipped. It is the BB sectional view taken on the line of FIG. FIG. 7 is a diagram for explaining the principle of the foulant sensor 60 shown in FIG. 6, in which (a) is a circuit diagram for explaining a method for predicting dirt by impedance measurement using the foulant sensor 60 shown in FIG. 6; The state of the foulant sensor 60 when no dirt is attached to the osmotic membrane 16, (c) the state of the foulant sensor 60 when dirt is slightly attached to the reverse osmosis membrane 16, and FIG. It is a figure which shows the foulant sensor 60 when big dirt adheres. It is a perspective view of each member which comprises the foulant sensor shown in FIG. 6, (a) is a perspective view from the downward direction of an upper member, (b) is the upper state of the state which mounted the evaluation film | membrane and the spacer in the lower member. (C) is a perspective view from above of only the lower member. It is a flowchart which shows the control performed in the seawater desalination system of 1st embodiment. It is a systematic diagram of the seawater desalination system of the second embodiment. It is a flowchart which shows the control performed in the seawater desalination system of 2nd embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (this embodiment) will be described with reference to the drawings. In the drawings, the same members are denoted by the same reference numerals, and redundant descriptions are omitted. Moreover, each embodiment can be implemented in combination as appropriate.

  FIG. 1 is a system diagram of a seawater desalination system 100 according to the first embodiment. A seawater desalination system 100 (water treatment system) shown in FIG. 1 uses a reverse osmosis membrane 16 to obtain fresh water from seawater (treated water). The seawater desalination system 100 includes a pretreatment device 10 such as a sand filtration tank, a reverse osmosis membrane 16, a supply pump 11 for feeding seawater, and a high-pressure pump 15. Therefore, during normal operation of the seawater desalination system 100, seawater after the foreign matter has been removed by the pretreatment device 10 is provided with the reverse osmosis membrane 16 by the high-pressure pump 15, so that permeated water (freshwater) and concentrated water. And is obtained.

In addition, the seawater desalination system 100 predicts dirt adhering to the reverse osmosis membrane 16 used when obtaining fresh water and prevents contamination of the reverse osmosis membrane 16, a chemical solution, An injection tank 13 (contamination prevention agent tank), a chemical solution injection pump 12 (contamination prevention agent injection pump), and a control unit 50 for controlling them are provided. The “chemical solution” referred to here is an anti-fouling agent having an effect of peeling a foulant that may be generated in the reverse osmosis membrane 16. Further, a pump for supplying the foulant sensor 14 with seawater having a membrane surface flow velocity equal to or higher than the membrane surface flow velocity in the leading membrane of the reverse osmosis membrane 16 (for example, several times). 17 is provided. Since a large amount of seawater is supplied to the foulant sensor 14 by the pump 17, the evaluation membrane 28 constituting the foulant sensor 14 rather than the reverse osmosis membrane 16 (described later with reference to FIG. 4). The adhesion of dirt is promoted. Therefore, the adhesion of dirt to the reverse osmosis membrane 16 can be quickly detected by the foulant sensor 14.
In addition, the membrane surface flow velocity of seawater in the leading membrane of the reverse osmosis membrane 16 and the membrane surface flow velocity of seawater supplied to the foulant sensor 14 are determined by the amount of supplied water on the membrane surface (of the reverse osmosis membrane 16 and the evaluation membrane 28). It can be calculated by dividing by the cross-sectional area of the water passage on the surface.

  The liquid chemical tank 13 is provided with a liquid level sensor 13a for monitoring the amount of liquid chemical stored. When the continuous operation time of the seawater desalination system 100 becomes longer, dirt such as fouling adheres (contaminates) to the reverse osmosis membrane 16, and the desalination efficiency decreases. Therefore, in the seawater desalination system 100, the concentration of the chemical solution contained in the seawater supplied to the reverse osmosis membrane 16 (seawater supply conditions) is controlled by controlling the amount of the chemical solution injected based on the output value of the foulant sensor 14. Thus, contamination of the reverse osmosis membrane 16 is appropriately prevented.

  The detailed configuration of the foulant sensor 14 will be described later with reference to FIG. 3 and the like, but the foulant sensor 14 is provided with an evaluation membrane 28 (evaluation member) that imitates the reverse osmosis membrane 16. Then, when dirt is attached (contaminated) to the evaluation membrane 28, the output value from the foulant sensor 14 changes, and thereby the degree of dirt on the reverse osmosis membrane 16 is predicted. .

  The control unit 50 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), an I / F (interface), etc., although not shown. Configured. The control unit 50 is realized by a predetermined control program stored in the ROM being executed by the CPU.

  FIG. 2 shows (a) change in pressure loss ΔP with respect to continuous operation time for a reverse osmosis membrane in the seawater desalination system 100 of the first embodiment (the present invention) and the conventional seawater desalination system (conventional). ) It is a graph showing the change of the output value from the foulant sensor 14 with respect to the continuous operation time. The plot shown as “Conventional” in FIG. 2B shows values that are considered to have been detected if a conventional seawater desalination system was provided with a foulant sensor.

  As shown in the plot of “present invention” in FIG. 2A, in the seawater desalination system 100, the reverse osmosis membrane 16 is prevented from being contaminated based on the output value of the foulant sensor 14. During operation, the pressure loss ΔP in the seawater desalination system 100 hardly changes. On the other hand, in the conventional seawater desalination system, as shown in the “conventional” plot of FIG. 2A, the pressure loss ΔP may increase rapidly as the continuous operation time increases. Therefore, in a conventional seawater desalination system that does not use the foulant sensor 14, the reverse osmosis membrane is prevented from being contaminated based on such a change in the pressure loss ΔP.

  However, since the contamination of the reverse osmosis membrane 16 is considered to progress even in a range where it is not detected as a change in the pressure loss ΔP, the pressure loss ΔP is not a good sensitivity index. That is, although the output value of the foulant sensor 14 gradually increases (“conventional” in FIG. 2B), the pressure loss ΔP does not increase for a while (“conventional” in FIG. 2A). ), Increasing rapidly in a certain operating time. And when pressure loss (DELTA) P changes clearly, since the irreversible dirt has adhered to the reverse osmosis membrane, there exists a possibility that dirt cannot fully be removed.

  Therefore, as shown in the plot of “present invention” in FIG. 2B, the contamination of the reverse osmosis membrane 16 is prevented when the output value from the foulant sensor 14 exceeds a predetermined value. In particular, as shown in the plot of the “present invention” in FIG. 2A, contamination is prevented at a relatively early stage where dirt that cannot be detected by using the pressure loss ΔP as an index is reversed. It is possible to prevent the dirt that is difficult to recover from adhering to the osmotic membrane 16. Thereby, the reverse osmosis membrane 16 is maintained clean, and the lifetime of the reverse osmosis membrane 16 can be extended.

  FIG. 3 is a perspective view of the foulant sensor 14 provided in the seawater desalination system 100 of the first embodiment. In the foulant sensor 14, the lower member 20 and the upper member 21 are fixed so that a space (an evaluation channel, which will be described later with reference to FIG. 4) is formed inside. These are fixed by bolts 33 (not shown in FIG. 4) inserted into the bolt holes 22. In addition, on the upper surface of the foulant sensor 14, an inlet 23 into which seawater flows into a space formed between the lower member 20 and the upper member 21 and an outlet 24 from which seawater flows out are formed. ing. A light receiving element 25 for detecting the light of the LED 27 (not shown in FIG. 3) is provided on the upper surface of the foulant sensor 14.

  4 is a cross-sectional view taken along line AA in FIG. Between the lower member 20 and the upper member 21, there is an evaluation membrane (evaluation member) configured by a reverse osmosis membrane of the same type as the reverse osmosis membrane 16 and imitating the reverse osmosis membrane 16 (see FIG. 1). Has been placed. Accordingly, the seawater that flows in from the inflow port 23 proceeds to the right while contacting the evaluation film 28 and flows out from the outflow port 24 to the outside. The evaluation film 28 is sandwiched between the lower member 20 and the upper member 21, and exposure of seawater to the outside is prevented by the O-rings 29 and 30. The lower member 20 and the upper member 21 are fixed by the bolt holes 22 and 34 and the bolt 33 as described above.

  An LED 27 is disposed below the evaluation film 28. In addition, a light receiving element 25 that receives the light from the LED 27 is disposed above the LED 27 so as to face a space (evaluation flow path) formed between the lower member 20 and the upper member 21. A lens 26 is disposed between the light receiving element 25 and the space. Therefore, the light from the LED 27 passes through the evaluation film 27, is collected by the lens 26, and then received by the light receiving element 25.

  Although not shown, the light receiving element 25 and the LED 27 are connected to an electric signal line connected to the control unit 50 (see FIG. 1). Accordingly, the control of the lighting / extinguishing of the LED 27 and the grasping of the amount of light received by the light receiving element 25 are performed by the control unit 50.

  As described above, the seawater that has flowed in from the inflow port 23 proceeds to the right while contacting the evaluation film 28, and flows out from the outflow port 24 to the outside. Therefore, when the continuous operation time (the time elapsed since the start of operation or the most recent time of the previous CIP cleaning) becomes longer, dirt adheres to the evaluation membrane 28 in the same manner as the reverse osmosis membrane 16. Therefore, if dirt adheres, the light from the LED 27 is blocked by the dirt, thereby reducing the amount of light received by the light receiving element 25. Therefore, the amount of decrease in the amount of light is detected, and the degree of contamination of the reverse osmosis membrane 16 is predicted.

  Although not shown in FIG. 4, a spacer 31 is disposed so as to cover the surface of the evaluation film 28. The spacer 31 will be described later with reference to FIG.

  FIG. 5 is a perspective view of each member constituting the foulant sensor 14 shown in FIG. 3, (a) is a perspective view from below the upper member 21, and (b) is an evaluation film 28 on the lower member 20. A perspective view from above of the state in which the spacer 31 is placed, (c) is a perspective view from above of only the lower member 20. FIG. 5 also shows a spacer 31 not shown in FIG. As shown in FIG. 5A, a mesh-like spacer 31 is attached so as to cover the lens 26. In addition, as shown in FIG. 5B, the mesh spacer 31 is placed on the surface of the evaluation film 28. By arranging the spacer 31, the environment in the vicinity of the evaluation membrane 28 can be made similar to the environment on the membrane surface of the reverse osmosis membrane 16 that predicts the degree of adhesion of dirt, and the adhesion of dirt to the reverse osmosis membrane 16. This state is also reproduced well on the evaluation film 28. Although a part of the lens 26 may be covered with the spacer 31, the degree of contamination is predicted based on the amount of change in the amount of light as described above, so there is no effect unless the position of the spacer 31 is shifted.

  Further, as shown in FIG. 5C, a plurality of LEDs 27 are arranged below the evaluation film 28 so as to be covered with the evaluation film 28 (see FIG. 5B). A groove in which O-rings 29 and 30 (see FIG. 4) (not shown) are arranged is formed in a raceway shape so as to surround the LED 27.

  Furthermore, the size of the evaluation membrane 28 is such that the flow passage width is the same as the flow passage width when the reverse osmosis membrane 16 permeates seawater. Therefore, the evaluation membrane 28 provided in the foulant sensor 14 is made of the same material and the same flow path width as the reverse osmosis membrane 16, so that the state of contamination of the reverse osmosis membrane 16 can be accurately predicted. It becomes.

  FIG. 6 is a perspective view of another form of the foulant sensor 14 provided in the seawater desalination system 100 of the first embodiment. The upper surface of the foulant sensor 60 according to the embodiment shown in FIG. 6 is not provided with a light receiving element or the like, and the inflow port 23 for allowing seawater to flow into the internal space (evaluation channel) and the internal seawater Only the outlet 24 for discharge is formed.

  7 is a cross-sectional view taken along line BB in FIG. The foulant sensor 60 includes a pair of electrodes 61 and 62 so as to sandwich the evaluation film 28 (evaluation member). The details will be described later with reference to FIG. 8, but the foulant sensor 60 produces an action like a capacitor having this pair of electrodes 61 and 62, thereby the degree of contamination attached to the evaluation film 28. Judging. Although not shown, the electrodes 61 and 62 are connected to an electric signal line connected to the control unit 50 (see FIG. 1). Although not shown in FIG. 7 as in FIG. 4, a spacer 32 is disposed on the surface of the evaluation film 28.

  In addition, seawater flows in the direction indicated by the solid line arrow above the evaluation membrane 28. Further, pure water or salt water flows through the lower side of the evaluation film 28 in the direction indicated by the broken line arrow. By passing pure water or salt water below the evaluation film 28, the space between the electrode 61 and the electrode 62 is filled with pure water or salt water, and electrical measurement becomes possible. Moreover, depending on the case, it is possible to operate while generating a filtration flux without applying mechanical pressure to the evaluation membrane 28 by passing salt water having a higher osmotic pressure than seawater. In other words, the passage of water between the upper side and the lower side of the evaluation film 28 can be controlled by the osmotic pressure difference of the liquid flowing through the upper side and the lower side of the evaluation film 28.

  Here, a method for predicting dirt attached to the reverse osmosis membrane 16 by the foulant sensor 60 will be described.

  FIG. 8 is a diagram for explaining the principle of the foulant sensor 60 shown in FIG. 6, and FIG. 8A is a circuit diagram for explaining a method for predicting dirt by impedance measurement using the foulant sensor 60 shown in FIG. b) State of the foulant sensor 60 when no dirt is attached to the reverse osmosis membrane 16, (c) State of the foulant sensor 60 when the dirt is slightly attached to the reverse osmosis membrane 16, and FIG. It is a figure which shows the foulant sensor 60 when big dirt adheres to the osmosis membrane 16. FIG. As shown in FIG. 8A, an impedance measurement circuit is configured by including a foulant sensor 60, an AC power supply 71, a resistor 72, and a rectifier circuit 73.

  The rectifier circuit 73 converts alternating current into direct current. The AC power supply 71 and the resistor 72 are connected in series with the foulant sensor 60, and the rectifier circuit 73 is connected in parallel with the foulant sensor 60. A voltmeter (not shown) measures the potential difference between the output terminals V1 and V2 of the rectifier circuit 73 (the output voltage of the rectifier circuit 73 and the inter-terminal voltage between the terminals V1 and V2). . That is, in this embodiment, the impedance of the CR series circuit is measured from the voltage change when an AC voltage is applied at a constant current to the CR series circuit using the foulant sensor 60 as a capacitor, and a pair of electrodes 61, The capacitance between 62 is measured.

  As described above, the foulant sensor 60 operates like a capacitor. That is, as shown in FIG. 7, in the foulant sensor 60, a pair of electrodes 61 and 62 are arranged so as to sandwich the evaluation film 28 (see FIG. 7). Therefore, the seawater and the evaluation film 28 existing between the electrode 61 and the electrode 62, and when fouling is attached, all of the foulant and the like are considered as “one dielectric”, and the change in the dielectric constant is measured, whereby the evaluation film The dirt adhering to 28 can be evaluated. The change in dielectric constant can be evaluated by measuring the potential difference between the terminals V1 and V2 of the circuit shown in FIG.

  For example, as shown in FIG. 8B, the state in which the dirt is not attached to the evaluation film 28 can be considered as a constant state between the electrode 61 and the electrode 62, and the potential difference between V1 and V2 is also constant. It becomes. However, when the continuous operation time becomes longer and dirt starts to adhere to the evaluation film 28 as shown in FIG. 8C, a change starts to occur in the potential difference between V1 and V2. When further dirt adheres to the evaluation film 28 as shown in FIG. 8D, the potential difference between V1 and V2 greatly changes from the potential difference shown in FIG. 8B where dirt has not adhered. . As described above, since the potential difference changes depending on the degree of dirt adhering to the evaluation membrane 28, the degree of dirt on the reverse osmosis membrane 16 is predicted based on this change.

  9 is a perspective view of each member constituting the foulant sensor 60 shown in FIG. 6, (a) is a perspective view from below of the upper member 21, and (b) is an evaluation film 28 on the lower member 20. A perspective view from above of the state in which the spacer 31 is placed, (c) is a perspective view from above of only the lower member 20. As shown in FIG. 9A, the electrode 61 is fixed to the lower surface of the upper member between the inflow port 23 and the outflow port 24. Further, as shown in FIG. 9B, a spacer 31 is placed on the surface of the evaluation film 28 as in the case of the foulant sensor 14 described above. Further, as shown in FIG. 9C, an electrode 62 is fixed on the upper surface of the lower member 20 between the pure water inlet 63 and the outlet 64.

  FIG. 10 is a flowchart showing the control performed in the seawater desalination system 100 of the first embodiment. In the seawater desalination system 100, the injection amount of a chemical solution (contamination inhibitor) for preventing contamination of the reverse osmosis membrane 16 is controlled based on the output value of the foulant sensor 14 during continuous operation. The flow shown in FIG. 10 is executed by the control unit 50 shown in FIG. 1 unless otherwise specified.

  During the continuous operation, the control unit 50 monitors the output value from the foulant sensor 14. The “output value” here is a difference from the light amount at the time of initial operation, which is calculated based on the light amount measured by the light receiving element 25 (see FIG. 4). Then, the control unit 50 determines whether or not the sensor output value S exceeds a predetermined chemical injection start threshold value S1 at predetermined time intervals during monitoring (step S101). And when it is judged that sensor output value S exceeded the chemical | medical solution injection start threshold value S1 (Yes direction of step S101), the control part 50 controls the chemical | medical solution injection pump 12, and supplies the chemical | medical solution to the seawater provided to the reverse osmosis membrane 16 Injection is started (step S102). The injection amount at this time is an amount that becomes R1 as the injection rate (concentration) of the chemical into seawater.

  After the start of the chemical injection, the control unit 50 continuously monitors the output value from the foulant sensor 14. Then, it is determined whether or not the sensor output value S exceeds a predetermined chemical solution injection stop threshold S2 every predetermined time during the monitoring (step S103). When the sensor output value S does not exceed the chemical solution injection stop threshold value S2 (including the case where the sensor output value S and the chemical solution injection stop threshold value S2 are equal to each other in Step S103), the reverse osmosis membrane is obtained by the chemical solution injection. The controller 50 determines that the contamination prevention of 16 is sufficiently performed, and stops the chemical solution injection (step S109). Thereafter, the steps after step S101 are repeated.

  On the other hand, when the sensor output value S exceeds the chemical solution injection stop threshold value S2 in Step S103 (Yes direction of Step S103), the control unit 50 determines that the sensor output value S exceeds the chemical solution injection rate increase threshold value S3. It is determined whether or not (step S104). As a result of the determination, when the sensor output value S does not exceed the chemical solution injection rate increase threshold value S3 (including the case where the sensor output value S and the chemical solution injection rate increase threshold value S3 are equal), the reverse osmosis membrane 16 Although the contamination still exists, it is determined that sufficient contamination prevention has been performed by the chemical injection at the chemical injection rate R1, and the steps after step S103 are repeated. On the other hand, when the sensor output value S exceeds the chemical solution injection rate increase threshold value S3 (Yes direction in step S104), the control unit 50 sufficiently removes dirt on the reverse osmosis membrane 16 in the chemical solution injection at the chemical solution injection rate R1. Judge that it is not possible. Therefore, the control unit 50 controls the chemical solution injection pump 12 to increase the injection rate of the chemical solution from R1 to R2 (step S105).

  The control unit 50 continues to monitor the output value from the foulant sensor 14 even after the chemical liquid injection is started at the chemical liquid injection rate R2. Then, it is determined whether or not the sensor output value S exceeds the chemical solution injection stop threshold S2 at predetermined time intervals during the monitoring (step S106). As a result of this determination, when the sensor output value S does not exceed the chemical solution injection stop threshold value S2 (including the case where the sensor output value S is equal to the chemical solution injection stop threshold value S2), the above step S103 and Similarly, the controller 50 stops the chemical solution injection (step S1110). Thereafter, the steps after step S101 are repeated.

  On the other hand, when the sensor output value S exceeds the chemical injection stop threshold value S2 (Yes direction in step S106) in step S106, the control unit 50 determines that the sensor output value S exceeds the CIP cleaning execution threshold value S4. It is determined whether or not (step S107). As a result of the determination, if the sensor output value S does not exceed the CIP cleaning execution threshold value S4 (No direction in step S107), the reverse osmosis membrane 16 is still contaminated, but the chemical injection with the chemical injection rate R2 is sufficient. It is determined that prevention of contamination is possible, and the steps after step S106 are repeated again.

  On the other hand, when the sensor output value S exceeds the CIP cleaning execution threshold value S4 (Yes direction in step S107), the control unit 50 cannot sufficiently remove the dirt of the reverse osmosis membrane 16 by the chemical injection at the chemical injection rate R2. Judge. That is, it is determined that the prevention of contamination of the reverse osmosis membrane 16 is insufficient only by the injection of the chemical solution. Therefore, the control unit 50 stops the seawater desalination operation by stopping the supply pump 11, and then performs CIP cleaning of the reverse osmosis membrane 16 using a CIP cleaning agent stored in a CIP cleaning agent tank (not shown) (step) S108).

  In the flow shown in FIG. 10, a change in the injection rate of the chemical solution and the timing of CIP cleaning are determined while predicting the degree of contamination of the reverse osmosis membrane 16. Therefore, seawater desalination can be performed continuously while optimizing the injection amount and injection timing of the chemical solution, and excessive injection of the chemical solution can be suppressed. In addition, by injecting the chemical solution from the stage where the degree of contamination is not so large, irreversible contamination is prevented from being attached and the life can be extended. Moreover, it is possible to prevent the CIP cleaning from being performed even though the degree of contamination is not so large, and it is possible to suppress the unnecessary use of the CIP cleaning agent and the long-time shutdown due to the CIP cleaning.

  FIG. 11 is a system diagram of the seawater desalination system 200 of the second embodiment. In the seawater desalination system 100 described above, the injection amount and the injection timing of the chemical solution are determined based on the output value from the foulant sensor 14, but the seawater desalination system 200 shown in FIG. Based on the above, whether or not the preprocessing device 81 (corresponding to “preprocessing device” in the claims) is connected is switched. Specifically, the control unit 50 switches the three-way valve 80 based on the output value from the foulant sensor 14. As a result, the treated water flow path from the pretreatment device 10 to the reverse osmosis membrane 16 is branched to form a branched flow passage. After the seawater is passed through the branched flow passage, the treated water flow path is processed by the pretreatment device 10. The seawater is further supplied to the pretreatment device 81.

  Depending on the place where the seawater is taken, the season, the time zone, etc., the size of the foreign matter contained in the seawater differs, and it may not be possible to remove the foreign matter sufficiently with only the pretreatment device 10 such as a sand filtration tank. For example, since the water quality of seawater in which red tide has occurred is poor, only the pretreatment device 10 during normal operation is insufficient, and as a result, foreign matter cannot be sufficiently removed, so that the reverse osmosis membrane 16 is likely to be contaminated. That is, the speed at which dirt adheres to the reverse osmosis membrane 16 is increased. Therefore, in the seawater desalination system 200, in addition to the pretreatment device 10 such as a sand filtration tank based on the output value from the foulant sensor 14, for example, an ultrafiltration membrane (UF) or the like capable of performing finer filtration. A pretreatment device 81 such as a microfiltration membrane (MF) is used together.

  FIG. 12 is a flowchart showing the control performed in the seawater desalination system 200 of the second embodiment. The flow shown in FIG. 12 is also executed by the control unit 50 shown in FIG. 11 unless otherwise specified.

  In the seawater desalination system 200, pretreatment of seawater supplied to the reverse osmosis membrane 16 is performed only by the pretreatment device 10 during continuous operation. That is, seawater from the pretreatment device 10 is directly supplied to the reverse osmosis membrane 16. Further, during continuous operation, the control unit 50 monitors the output value from the foulant sensor 14. The output value is recorded in an HDD (not shown). The “output value” here is a difference from the light amount at the time of initial operation, which is calculated based on the light amount measured by the light receiving element 25 (see FIG. 4).

  Then, the control unit 50 determines whether or not the sensor output value S exceeds a predetermined CIP cleaning execution threshold value S5 at predetermined time intervals during monitoring (step S201). When it is determined that the sensor output value S exceeds the CIP cleaning execution threshold value S5 (Yes direction in step S201), it is determined that the degree of contamination attached to the reverse osmosis membrane 16 is large, and the flow shown in FIG. In the same manner as above, CIP cleaning is performed (step S108).

  On the other hand, when it is determined in step S201 that the sensor output value S does not exceed the CIP cleaning execution threshold value S5 (when the sensor output value S is equal to the CIP cleaning execution threshold value S5, the No direction in step S201), the control unit 50 Determines whether the change speed ΔS of the sensor output value S exceeds the preprocessing device switching threshold value ΔS6 (including the case where the changing speed ΔS and the preprocessing device switching threshold value ΔS6 are equal, step S202). The change rate ΔS is calculated by using the output value from the foulant sensor 14 for each time recorded in the HDD. When the change rate ΔS of the sensor output value S exceeds the preprocessing device switching threshold value ΔS6 (Yes direction in step S202), the control unit 50 determines that the dirt deposition rate is too high, and further increases the amount of seawater. It is determined that preprocessing is necessary. Therefore, the control unit 50 switches the three-way valve 80 (step S203), and in addition to the preprocessing device 10, the preprocessing by the preprocessing device 81 is started (step S204). As a result, seawater from the pretreatment device 10 is supplied to the reverse osmosis membrane 16 via the pretreatment device 81.

  Thereafter, even during the execution of the preprocessing by the preprocessing device 81 in addition to the preprocessing device 10, the control unit 50 continuously monitors the output value from the foulant sensor 14 and calculates the change rate ΔS. Then, the controller 50 determines whether or not the change speed ΔS of the sensor output value S exceeds a predetermined emergency stop threshold ΔS7 at predetermined time intervals during the monitoring (step S205). When it is determined that the change rate ΔS of the sensor output value S exceeds the predetermined emergency stop threshold ΔS7 (Yes direction in step S205), the control unit 50 may use both the preprocessing devices 10 and 81. It is determined that the dirt adhesion rate cannot be suppressed. Therefore, the control unit 50 stops the supply pump 11 and performs CIP cleaning in the same manner as the flow shown in FIG. 10 (step S108).

  With the flow shown in FIG. 12, seawater desalination can be performed continuously while predicting the deposition rate of dirt on the reverse osmosis membrane 16. Therefore, compared with the case where only the single pretreatment device 10 is used, the adhesion rate of dirt to the reverse osmosis membrane 16 can be slowed, and the frequency of CIP cleaning can be suppressed. Thereby, the increase in the use cost of the CIP cleaning agent accompanying CIP washing | cleaning and the freshwater preparation cost accompanying the stop of the seawater desalination system 200 can be suppressed.

  Moreover, in the seawater desalination system 200 of 2nd embodiment, the adhesion of the stain | pollution | contamination with respect to the foulant sensor 14 is promoted like the said seawater desalination system 100. FIG. Therefore, even when the water quality of seawater is rapidly deteriorated due to red tide or the like, the degree of contamination on the reverse osmosis membrane 16 can be predicted quickly by using the foulant sensor 14. Thereby, it is possible to prevent irreversible dirt from adhering to the reverse osmosis membrane 16 and prevent the reverse osmosis membrane 16 from being suddenly blocked.

  Although the present embodiment has been described above with reference to the drawings as appropriate, the present embodiment is not limited to the contents described above.

  For example, in the form shown in FIG. 1, the pump 17 is provided to promote the adhesion of dirt to the evaluation film 28 constituting the foulant sensor 14. However, the pump 17 is replaced with or together with the pump 17 at a high temperature (for example, 37 A heating device may be provided for supplying seawater at about 0 ° C. to the evaluation membrane 28. By allowing seawater having a temperature at which microorganisms that cause biofouling to propagate easily to flow through, propagation of microorganisms on the evaluation membrane 28 can be further promoted.

  Furthermore, in the above-described embodiment, when the membrane surface flow rate of seawater supplied to the foulant sensor 14 and the membrane surface flow rate of seawater supplied to the reverse osmosis membrane 16 are compared, they are supplied to the foulant sensor 14. Although the pump 17 was controlled so that the membrane surface flow rate of the seawater was faster, if the adhesion of dirt to the evaluation membrane 28 constituting the foulant sensor 14 can be promoted, even if it is not the flow rate relative to the membrane surface, The pump 17 may be controlled using a simple flow rate as an index. Specifically, for example, driving of the pump 17 provided immediately before the foulant sensor 14 to accelerate the flow velocity can also promote the adhesion of dirt to the evaluation film 28.

  Further, from the viewpoint of further promoting the contamination of the evaluation film 28, the surface charge of the evaluation film 28 may be changed to create an environment in which microorganisms can be easily propagated. As a method of changing the surface charge, for example, there is a method of applying a polysaccharide or the like to the surface of the evaluation film 28.

  Furthermore, in the form shown in FIG. 11, the pretreatment device 81 is installed together with the pretreatment device 10, but the pretreatment device 10 may not be used. That is, although it is supplied directly to the reverse osmosis membrane 16 without passing through the pretreatment device during normal operation, the pretreatment device 81 may be connected by switching the three-way valve 80.

  Moreover, in the said embodiment, seawater was used as treated water, However, Treated water is not restricted to seawater, What kind of thing may be sufficient.

10,81 Pretreatment device 12 Chemical solution injection pump (contamination inhibitor injection pump)
13 Chemical tank (Anti-pollution agent tank)
14,60 Foulant sensor (dirt prediction device)
16 Reverse osmosis membrane 28 Evaluation membrane (evaluation member)
61, 62 One set of electrodes 50 Control unit 71 AC power supply 73 Rectifier 100, 200 Seawater desalination system

Claims (4)

A reverse osmosis membrane,
It is connected in parallel to the treated water flow path through which the treated water supplied to the reverse osmosis membrane flows, and a part of the treated water flowing through the treated water flow path is supplied to the reverse osmosis membrane. A dirt prediction device for predicting the degree of dirt attached;
A control unit that controls the supply condition of the treated water supplied to the reverse osmosis membrane based on the degree of contamination of the reverse osmosis membrane predicted by the soil prediction device during continuous operation ,
The dirt prediction device includes:
An evaluation channel through which a part of the treated water flowing through the treated water channel flows;
By being disposed so as to be able to come into contact with the treated water flowing through the evaluation flow path, an evaluation member to which dirt adheres along with the flow of treated water,
A set of electrodes arranged so as to sandwich the evaluation member;
An AC power source connected in series to the set of electrodes;
A rectifier connected in series to the set of electrodes and converting alternating current into direct current;
A water treatment system, comprising: a voltmeter that measures an output voltage of the rectifier . A pollution control agent tank for storing a pollution control agent for preventing contamination of the reverse osmosis membrane;
A pollution inhibitor injection pump for injecting the pollution inhibitor stored in the pollution inhibitor tank into the treated water supplied to the reverse osmosis membrane,
The control unit changes the amount of the antifouling agent to be injected into the treated water supplied to the reverse osmosis membrane based on the degree of contamination of the reverse osmosis membrane predicted by the stain prediction device. The water treatment system according to claim 1, wherein the pollution control agent injection pump is controlled. A pretreatment device for treating the seawater supplied to the reverse osmosis membrane before being supplied to the reverse osmosis membrane;
A branch channel branched from the treated water channel and connected to the pretreatment device,
Based on the degree of dirt of the reverse osmosis membrane predicted by the dirt prediction device, the control unit flows directly through the treated water flow path to the reverse osmosis membrane or via the pretreatment device. The water treatment system according to claim 1, wherein a flow path of the treated water is controlled so that the treated water is supplied to the reverse osmosis membrane. The soil prediction apparatus is configured to include an evaluation member that is disposed so as to be able to contact the supplied treated water, so that the soil adheres as the treated water flows.
The evaluation member is supplied with the treatment water so that the flow rate of the treated water supplied to the stain prediction device is faster than the flow rate of the treatment water supplied to the reverse osmosis membrane. The water treatment system according to any one of claims 1 to 3 , wherein adhesion of dirt to the water is promoted.

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