JP2007111638A - Membrane water purification system and membrane water purification method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane water purification system and a membrane water purification method which can inhibit clogging of a filtration membrane while suppressing energy for operation. <P>SOLUTION: The membrane water purification system 1 comprises a fine particle counter 9 for counting the number of fine particles having a specific particle diameter in fine particles of suspended solid in raw water, and a control part 15 for switching the filtration method of the raw water carried out by the filtration membrane 3a between dead end filtration and cross flow filtration based on the number of the counted fine particles having the specific particle diameter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a membrane water purification facility and a membrane water purification method for removing fine particles contained in raw water using a filtration membrane.

Conventionally, a membrane water purification facility described in Patent Document 1 below is known as a technique in such a field. This membrane water purification equipment removes suspended matter in raw water by filtering raw water through a filtration membrane, thereby obtaining membrane filtered water. As a filtration method of the filtration membrane in this type of membrane water purification equipment, dead-end filtration for filtering the entire raw water introduced into the filtration membrane, and a part of the raw water while circulating the raw water through the filtration membrane There is cross-flow filtration that only performs filtration.
Japanese Patent No. 3028447

  However, the filtration by the dead end filtration method has a drawback that it can be operated with a small amount of energy because the circulation amount of the raw water is small, and the filter membrane is easily clogged. On the other hand, the filtration by the cross flow filtration method has a drawback that it is difficult to cause clogging of the filtration membrane, but requires a large amount of energy for circulating a large amount of raw water. In such a membrane water purification facility, in order to achieve both energy saving and suppression of clogging, it is conceivable to operate the membrane water purification facility while appropriately switching between the two methods of dead end filtration and crossflow filtration. . Even in such an operation, further energy saving and suppression of clogging are desired.

  Then, an object of this invention is to provide the membrane water purification equipment and membrane water purification method which can suppress clogging of a filtration membrane, suppressing the energy of driving | operation.

  In the above-described membrane water purification equipment, when the raw water itself containing suspended solids is likely to be clogged in the filtration membrane, it is preferable to select the cross flow filtration as the filtration method to suppress clogging. On the other hand, when the raw water has a property that is relatively difficult to cause clogging, it is preferable to select dead-end filtration to reduce the operation energy. As described above, in order to suppress clogging of the filtration membrane while suppressing operation energy, it is desirable to detect the ease of clogging of the raw water filtration membrane and switch the filtration method at a suitable timing accordingly. It is. In the following description, the property of the raw water as described above indicating the ease of clogging in the filtration membrane is referred to as “easy to clog”.

  Here, as a general index that can express the ease of clogging of the membrane by the raw water, there is a “FI value (Fouling Index)” of the raw water. However, since it is difficult to continuously measure the FI value of raw water continuously, if it is adopted as a criterion for switching the filtration method, continuous operation of the facility becomes difficult. Accordingly, the present inventors have conducted intensive research to find a measurement value that can be used as a reference for switching the filtration method instead of the FI value, with a value that can represent the ease of clogging of raw water. As a result, when the present inventors counted the number of fine particles of suspended solids in raw water separately for each particle size, the particle size shows a high correlation between the number of fine particles and the FI value. The present invention has been found and the present invention has been completed.

  The membrane water purification equipment according to the present invention is a membrane water purification equipment that removes suspended substances contained in raw water using a filtration membrane, and counts the number of fine particles having a specific particle diameter among fine particles of suspended substances in raw water. Control for switching between raw-end filtration and dead-flow filtration based on the number of fine particles having a specific particle size counted by the fine particle counting means Means.

  In this membrane water purification equipment, the number of fine particles having a specific particle size among the fine particles of suspended substances in raw water is counted. Based on the counted number of fine particles, the system is operated while switching the filtration method performed in the filtration membrane, and dead-end filtration and cross-flow filtration are performed. By adopting the number of fine particles having a particle size having a high correlation with the FI value of the raw water as a reference for switching the filtration method in this case, the ease of clogging of the raw water is recognized without measuring the FI value of the raw water. Thus, it is possible to switch the filtration method following the ease of clogging. That is, according to this membrane water purification equipment, it becomes possible to switch the filtration method in a timely manner following the ease of clogging of the raw water, so it is possible to suppress clogging of the filtration membrane while suppressing the energy of operation. it can.

  In addition, when the number of fine particles having a specific particle size is less than the threshold, the control means sets the filtration method to dead-end filtration, and when the number of fine particles having the specific particle size is greater than or equal to the threshold, the control means It is preferable that the filtering method is switched and the threshold value is variable so that the above method is cross flow filtration. By adopting such a configuration, even when performing high flux operation with a relatively high raw water treatment speed or low flux operation with a relatively low raw water treatment speed, select an appropriate threshold value for each. Therefore, the filtration method can be switched according to the processing speed.

  Further, the membrane water purification method of the present invention is a membrane water purification method for removing suspended substances contained in raw water using a filtration membrane, wherein the number of fine particles having a specific particle size among fine particles of suspended substances in raw water is determined. Based on the fine particle counting step to count and the number of fine particles having a specific particle size counted by the fine particle counting step, the raw water filtration method performed in the filtration membrane is between dead-end filtration and cross-flow filtration. And a control step for switching.

  In this membrane water purification method, the number of fine particles having a specific particle size among the fine particles of suspended substances in raw water is counted. Based on the counted number of fine particles, the system is operated while switching the filtration method performed in the filtration membrane, and dead-end filtration and cross-flow filtration are performed. By adopting the number of fine particles having a particle size having a high correlation with the FI value of the raw water as a reference for switching the filtration method in this case, the ease of clogging of the raw water is recognized without measuring the FI value of the raw water. Thus, it is possible to switch the filtration method following the ease of clogging. That is, according to this membrane water purification method, it becomes possible to switch the filtration method in a timely manner following the ease of clogging of the raw water, so it is possible to suppress clogging of the filtration membrane while suppressing operation energy. it can.

  According to the membrane water purification equipment and the membrane water purification method of the present invention, clogging of the filtration membrane can be suppressed while suppressing operation energy.

  Hereinafter, a preferred embodiment of a membrane water purification facility and a membrane water purification method according to the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the membrane water purification facility 1 is a facility that removes suspended substances from the introduced raw water to obtain membrane filtered water, and includes a raw water tank 2 and a membrane filtration device 3. In this membrane water purification equipment 1, raw water containing suspended substances is introduced through a line L 1 and temporarily stored in the raw water tank 2. And the raw | natural water of the raw | natural water tank 2 is introduce | transduced from the inlet_port | entrance of the membrane filtration apparatus 3 through the line L2 and the line L11 with the raw | natural water pump P2.

  The membrane filtration device 3 has a filtration membrane 3a for filtering the raw water, and the introduced raw water is filtered by the filtration membrane 3a. And the membrane filtration apparatus 3 discharges | emits a liquid component from an exit through the line L12 while capturing the solid component after filtration of raw | natural water with the filtration membrane 3a. The liquid discharged from the line L12 is temporarily stored in the water purification basin 5 as membrane filtrate and sent to a subsequent process (not shown). Further, a line L13 is connected to the membrane filtration device 3 on the upstream side of the filtration membrane 3a, and a part of the raw water introduced from the line L11 is discharged from the line L13 by opening the valve V13 on the line L13. can do. The raw water discharged from the line L13 is introduced into the membrane filtration device 3 from the inlet side through the line L11 again by the circulation pump P13. Here, the filtration membrane 3a is made of cellulose acetate, and is constituted by an internal pressure type hollow fiber UF membrane having a nominal pore diameter of 0.01 μm.

  In the membrane water purification equipment 1, the flow path of the raw water can be changed by opening / closing the valve V13 and turning on / off the circulation pump P13, thereby selectively switching the filtration method in the membrane filtration device 3 and operating. can do. That is, when the valve V13 is closed and the circulation pump P13 is turned off, the entire amount of raw water introduced from the inlet of the membrane filtration device 3 is filtered by the filtration membrane 3a. That is, in this case, the raw water filtration method performed by the filtration membrane 3a is dead-end filtration. When the membrane water purification facility 1 is operated by this dead end filtration, since the circulation amount of the raw water is small, it can be operated with a small amount of energy, but there is a disadvantage that the filtration membrane 3a is easily clogged.

  On the other hand, when the valve V13 is opened and the circulation pump P13 is turned on, the raw water introduced from the inlet of the membrane filtration device 3 passes through the membrane surface of the filtration membrane 3a and circulates, while part of the raw water is circulated. Is filtered through the filtration membrane 3a, and the remainder is again introduced into the inlet of the membrane filtration device 3 through the line L13 and circulated. That is, in this case, the raw water filtration method performed by the filtration membrane 3a is cross flow filtration. When the membrane water purification facility 1 is operated by this cross flow filtration, the membrane surface is washed by the flow of raw water generated along the membrane surface of the filtration membrane 3a, and suspended substances adhering to the membrane surface are washed away. It is difficult to cause clogging of the film 3a. On the other hand, the operation by the cross flow filtration has a drawback that a large amount of energy is required for circulating a large amount of raw water.

  For this reason, in the membrane water purification facility 1, in order to suppress clogging of the filtration membrane 3a while suppressing operation energy, the above two types of filtration methods are switched in a timely manner in accordance with the ease of clogging of raw water. It is preferable to drive. That is, when the raw water is not easily clogged, the filtration method is set to dead end filtration in order to give priority to saving energy of operation, and when the raw water is easily clogged, clogging of the filter membrane 3a is suppressed. In order to prioritize the above, it is desired that the filtration method is cross flow filtration. And in order to switch this filtration system at a good timing, it is important to correctly detect the clogging ease of raw water that changes from time to time depending on various conditions such as season and weather.

  Here, the FI value is generally used as an index indicating the properties of raw water containing suspended solids, and this FI value is an index directly indicating the ease of clogging. It can also be a standard. However, since the FI value cannot be continuously and automatically measured, if the FI value of the raw water is used as the switching reference, smooth continuous operation of the membrane water purification facility 1 becomes difficult.

  Therefore, the present inventors have found that most of the suspended particulates involved in the clogging of the filtration membrane 3a have a specific particle size corresponding to the pore size of the filtration membrane 3a. It has been found that the number of fine particles having a specific particle size (hereinafter referred to as “specific fine particles”) can be used as an index of clogging ease. And in the membrane water purification equipment 1, the specific fine particle number contained per unit volume of raw | natural water is employ | adopted as a switching reference | standard of a filtration system instead of FI value. That is, in this membrane water purification equipment 1, when the number of the specific fine particles is less than the threshold, the filtration method is dead-end filtration, and when the number of the specific fine particles is greater than or equal to the threshold, the filtration method is the cross flow filtration. Driving.

  In order to switch the filtration method based on the number of specific fine particles as described above, the membrane water purification facility 1 includes a turbidity sensor 7 and a fine particle counter 9. The turbidity sensor 7 measures the turbidity of the raw water in the raw water tank 2, converts the result into an electrical signal, and transmits it to the control unit 15. The fine particle counter 9 measures the number of fine particles of the suspended substance contained per unit volume of the raw water in the raw water tank 2 for each particle diameter, converts the result into an electric signal, and transmits the electric signal to the control unit 15. In addition, the control unit 15 processes these electrical signals and transmits the electrical signals to the valve V13 and the circulation pump P13 to switch between opening and closing of the valve V13 and ON / OFF of the circulation pump P13.

  Based on the above configuration, a membrane water purification method performed in the membrane water purification facility 1 will be described with reference to FIG.

  First, the turbidity of the raw water stored in the raw water tank 2 is measured by the turbidity sensor 7 (S102), and the control unit 15 performs a predetermined operation until the turbidity exceeds a predetermined reference value. (S110 described later). In addition, when the turbidity of the raw water exceeds the reference value, the following processing is performed. That is, the fine particle counter 9 counts the number of fine particles of suspended solids contained per unit volume of raw water stored in the raw water tank 2 for each particle size, and sends it to the control unit 15 as an electric signal. The control unit 15 counts the number of fine particles having a preset specific particle size (here, for example, a particle size of 5 μm or less) among the number of fine particles counted separately for each particle size, that is, the specific number of fine particles. P is acquired (S104). Thus, the fine particle counter 9 and the control unit 15 constitute a fine particle counting means for counting the specific fine particle number P. The setting of the “specific particle size” will be described later.

  Here, when the operation state of the membrane water purification facility 1 is a high flux operation (“high flux operation” will be described later) (S106), the filtration format switching threshold is set to n1 (S108). If the number P of specific fine particles per unit volume of the raw water is less than the threshold value n1, the control unit 15 transmits an electrical signal to the valve V13 and the circulation pump P13, closes the valve V13, and turns off the circulation pump P13. Thus, the filtration format is switched to dead-end filtration (S110). Thereby, since the amount of water circulating in the membrane water purification facility 1 is reduced, efficient filtration can be performed while suppressing energy related to operation when the ease of clogging of the raw water is relatively low. On the other hand, if the specific particle number P is equal to or greater than the threshold value n1, the control unit 15 opens the valve V13 and turns on the circulation pump P13 to switch the filtration type to cross flow filtration (S112). Thereby, clogging of the filtration membrane 3a can be suppressed when clogging ease of raw water is relatively high.

  Moreover, in step S106, when the operation state of the membrane water purification facility 1 is other than the high flux operation, the threshold value for switching the filtration format is set to n2 larger than the n1 (S114). Then, similarly to S108, the control unit 15 switches the filtration format to dead-end filtration if the specific particle count P is less than the threshold value n2 (S110), and if the particulate count P is greater than or equal to the threshold value n2, the filtration format. Is switched to cross flow filtration (S112). Thus, the threshold value is variable depending on whether the setting of the operation state of the membrane water purification facility 1 is high flux operation or other operation.

  In this membrane water purification equipment 1, a water pressure difference (transmembrane differential pressure) between the upstream side and the downstream side of the filtration membrane 3a is detected by a sensor (not shown), and the control unit 15 changes the transmembrane pressure difference (transmembrane difference). The pressure trend is constantly monitored. When the controller 15 determines that the transmembrane pressure difference trend is abnormal (S114), the controller 15 performs an abnormal process such as chemical cleaning of the filtration membrane 3a (S116). The process described above is repeated by the control unit 15 during the operation of the membrane water purification facility 1, so that clogging of the filtration membrane 3 a is suppressed while suppressing operation energy, and continuous operation with stable transmembrane pressure is possible. It becomes.

  Here, the setting of the “specific particle size” related to the specific fine particle number P in the processing will be described. The particle size with which the fine particles become the main factor of clogging of the filtration membrane 3a varies depending on various conditions such as the components of suspended substances in the raw water. Therefore, it is necessary to make a setting corresponding to the raw water to be treated by the membrane water purification facility 1 to determine what particle size fine particles should be counted as the filtration method switching reference. Therefore, in setting a specific particle size, the raw water to be treated is previously determined by experiment to determine the relationship between the FI value and the number of fine particles for each particle size, and the particle size having the highest correlation with the FI value is determined. The specific particle size in the raw water is set. That is, there is a correlation that if the number of fine particles having a certain particle size in the raw water increases, the FI value of the raw water also increases. Set as.

  With such a setting, the particle size of the fine particles, which is a main factor of clogging of the filtration membrane 3a in the raw water, is set as the specific particle size. Then, by setting the specific particle size in this way, the ease of clogging of the raw water is accurately determined by the specific fine particle count P that is relatively easy to measure without measuring the FI value. be able to. Therefore, in the membrane water purification facility 1, it becomes possible to switch the filtration method with good timing in conjunction with the ease of clogging of the raw water. As a result, it is possible to perform continuous operation while suppressing the energy of operation of the membrane water purification facility 1 and suppressing clogging of the filtration membrane 3a. The membrane water purification facility 1 is provided with a setting means for setting a specific particle size, and the specific particle size as described above is referred to with reference to various conditions (for example, rainfall information) that can change the properties of the raw water. The setting may be automatically performed.

  In the above process, the reason why the threshold value n1 during high flux operation is set lower than the threshold value n2 during low flux operation is as follows. When performing high flux operation, clogging is more likely to occur, so it is necessary to switch to cross-flow filtration as soon as possible even if the number of particles is relatively small in order to prioritize the suppression of clogging. is there. Here, an operation in which the filtration flow rate at the filtration membrane 3a is 2.5 m / day or more is referred to as “high flux operation”, and an operation in which the filtration flow rate is less than 1.5 m / day is referred to as “low flux operation”. The operation of 5 m / day or more and less than 2.5 m / day is referred to as “normal flux operation”. In addition, as threshold value n1, n2, it is preferable to set the value corresponding to 2.5-4 of FI value of raw | natural water.

  In addition, this invention is not limited to embodiment mentioned above. For example, changes in the turbidity of raw water, the rate of increase in turbidity of raw water, the number of fine particles having a particle size close to the pore size of the filtration membrane 3a, FI value, rainfall information, dam discharge information, and transmembrane pressure difference Switching between dead-end filtration and crossflow filtration may be performed using a switching criterion that combines one or more of other conditions such as rate.

  Moreover, in the said embodiment, although the internal pressure type | formula hollow fiber membrane with the high washing | cleaning effect of a membrane surface was used as the filtration membrane 3a in the case of crossflow filtration, you may use an external pressure type | formula hollow fiber membrane for this invention. The filtration membrane 3a is not limited to a UF membrane, and may be an MF membrane. The material of the filtration membrane 3a is not limited to an organic membrane, and may be an inorganic membrane.

It is the schematic which shows embodiment of the membrane water purification equipment which concerns on this invention. It is a flowchart of the membrane water purification method performed with a membrane water purification equipment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Membrane water purification equipment, 3 ... Membrane filtration apparatus, 3a ... Filtration membrane, 9 ... Fine particle counter (fine particle counting means), 15 ... Control part (control means).

Claims (3)

In membrane water purification equipment that removes suspended matter contained in raw water using a filtration membrane,
Fine particle counting means for counting the number of fine particles having a specific particle size among the fine particles of the suspended substance in the raw water;
Control means for switching the raw water filtration method performed by the filtration membrane between dead-end filtration and cross-flow filtration based on the number of fine particles having the specific particle diameter counted by the fine particle counting means; Membrane water purification equipment characterized by comprising The control means includes
When the number of fine particles having the specific particle size is less than a threshold, the filtration method is dead-end filtration, and when the number of fine particles having the specific particle size is greater than or equal to the threshold, the filtration method Switch the filtration method so that the method is cross flow filtration,
The membrane water purification facility according to claim 1, wherein the threshold value is variable. In a membrane water purification method for removing suspended substances contained in raw water using a filtration membrane,
A fine particle counting step for counting the number of fine particles having a specific particle size among the fine particles of the suspended matter in the raw water;
A control step of switching the raw water filtration method performed by the filtration membrane between dead-end filtration and cross-flow filtration based on the number of fine particles having the specific particle diameter counted by the fine particle counting step. And a membrane water purification method.

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