JP2018023965A - Cleaning method for external pressure type filtration module and filtration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaning method capable of effectively cleaning an external pressure type filtration module having a large average membrane effective length of a hollow fiber membrane.SOLUTION: According to one aspect of the present invention, there is provided a cleaning method for an external pressure type filtration module having a plurality of hollow fiber membranes aligned in one direction and a cylindrical outer cylinder case housing the hollow fiber membranes. The method comprises a filtration stopping process of stopping filtration of treated water, a discharging process of discharging the treated water in the outer cylinder case after the filtration stopping process, a backwash process of cleaning the hollow fiber membranes with backwash water after the discharge process, and a chemical holding process of holding a chemical in the outer cylinder case after the backwash process. An average membrane effective length of the hollow fiber membranes is 2 m or longer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an external pressure filtration module cleaning method and a filtration device.

  2. Description of the Related Art Conventionally, a filtration device including an external pressure filtration module having a plurality of hollow fiber membranes aligned in the vertical direction has been used as a solid-liquid separation treatment device in a manufacturing process such as sewage treatment or medicine. Such a filtration apparatus performs filtration by preventing permeation of impurities contained in the water to be treated by the surface of the hollow fiber membrane and allowing other impurities to permeate inside the hollow fiber membrane.

  However, since such a filtration device prevents the permeation of impurities contained in the water to be treated by the surface of the hollow fiber membrane, impurities that have not been permeated to the inside adhere to the surface of the hollow fiber membrane. Causes fouling. Therefore, there is a possibility that the filtration efficiency of the liquid that should be filtered by the impurities attached to the surface of the hollow fiber membrane is lowered.

  Therefore, in such a filtration apparatus, membrane fouling is prevented by intermittently performing the filtration treatment operation and washing the hollow fiber membrane during the filtration treatment operation. Specifically, for example, the treated liquid is periodically sent into the hollow fiber membrane of the filtration module as backwash water, and the hollow fiber membrane is backwashed (see JP 2010-361183 A). By this reverse cleaning, the solid content and the like deposited on the outer surface of the hollow fiber membrane is wiped off.

JP 2010-361183 A

  However, in the cleaning method described in the above publication, for example, in a filtration module having a large average membrane effective length such that the average membrane effective length of the hollow fiber membrane is 2 m or more, the backwash water is sufficiently distributed throughout the filtration module. Absent. For this reason, in the cleaning method described in the above publication, cleaning near the inflow port of the water to be treated, which is far from the backwashing water inlet and to which impurities easily adhere, tends to be insufficient. Therefore, the cleaning method described in the above publication cannot stably operate a filtration module having a large average membrane effective length with improved filtration efficiency. For this reason, the washing | cleaning method which can wash | clean effectively the filtration module with a large average membrane effective length of a hollow fiber membrane is desired.

  This invention is made | formed based on the above situations, and it aims at provision of the washing | cleaning method and filtration apparatus which can wash | clean effectively the external pressure type | mold filtration module with the large average membrane effective length of a hollow fiber membrane.

  A cleaning method for an external pressure filtration module according to an aspect of the present invention, which has been made to solve the above problems, stores a plurality of hollow fiber membranes aligned in one direction, and the plurality of hollow fiber membranes. A method of cleaning an external pressure filtration module having a cylindrical outer cylinder case, a filtration stopping step for stopping filtration of water to be treated, and discharging the water to be treated in the outer cylinder case after the filtration stopping step The hollow fiber membrane comprises a discharge step, a backwash step for washing the hollow fiber membrane with backwash water after the discharge step, and a chemical solution holding step for holding a chemical solution in the outer cylinder case after the backwash step. The average effective film length is 2 m or more.

  A filtration device according to another aspect of the present invention is an external pressure filtration having a plurality of hollow fiber membranes that are aligned in one direction and a cylindrical outer case that stores the plurality of hollow fiber membranes. A filtration device comprising a module, wherein a filtration stop control for stopping filtration of treated water, a discharge control for discharging treated water in the outer cylinder case after the filtration stop control, and the hollow fiber after the discharge control A control mechanism for performing backwashing control for washing the membrane with backwashing water, and chemical solution holding control for holding the chemical solution in the outer case after the backwashing control, and the average membrane effective length of the hollow fiber membrane is 2 m That's it.

  Since the cleaning effect of the filtration module having a large average membrane effective length is enhanced by using the external pressure filtration module cleaning method and the filtration device according to one aspect of the present invention, the filtration module having a large average membrane effective length is stably operated. can do.

FIG. 1 is a schematic cross-sectional view showing a configuration of a filtration device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a configuration of a filtration device different from the filtration device of FIG.

  A cleaning method for an external pressure filtration module according to an aspect of the present invention includes a plurality of hollow fiber membranes that are aligned in one direction, and a cylindrical outer case that stores the plurality of hollow fiber membranes. A method for cleaning an external pressure filtration module, the filtration stopping step for stopping the filtration of the water to be treated, the discharging step for discharging the water to be treated in the outer cylinder case after the filtration stopping step, and the step after the discharging step A backwashing step for washing the hollow fiber membrane with backwashing water, and a chemical solution holding step for holding a chemical solution in the outer cylinder case after the backwashing step, wherein the average effective membrane length of the hollow fiber membrane is 2 m or more is there.

  In the cleaning method of the external pressure filtration module, after the filtration is stopped in the filtration stop process, the water to be treated in the outer cylinder case is discharged in the discharge process. For this reason, by using the cleaning method of the external pressure filtration module, it is easy to spread backwash water throughout the external pressure filtration module in the backwashing step performed after the discharging step. Moreover, since the washing | cleaning method of the said external pressure type filtration module is equipped with a chemical | medical solution holding process after the said backwashing process, a chemical | medical solution is hold | maintained in the state from which the impurity which can be removed by a backwashing process was removed. For this reason, a chemical | medical solution osmose | permeates a hollow fiber membrane, it is easy to spread over the whole external pressure type filtration module, and the washing | cleaning effect of the inflow port vicinity of the to-be-processed water which an impurity tends to adhere can be heightened. Therefore, by using the cleaning method for the external pressure filtration module, it is possible to effectively wash the filtration module in which the average effective membrane length of the hollow fiber membrane is 2 m or more.

  The discharge time of the water to be treated in the discharge step is preferably 0.5 minutes or more and 1 minute or less. By setting the discharge time of the water to be treated in the discharge step within the above range, the liquid to be treated can be sufficiently drained while suppressing an increase in the treatment time. For this reason, it is easy to spread the backwash water throughout the external pressure filtration module in the backwashing process performed after the discharging process. Therefore, the cleaning effect of the filtration module in which the average effective membrane length of the hollow fiber membrane is 2 m or more can be further enhanced.

As the backwash water used in the backwashing step, a chemical solution used in the chemical solution holding step may be used.
Thus, by using the chemical solution used in the chemical solution holding step as the backwash water used in the backwash step, it is not necessary to replace the backwash water with the chemical solution in the chemical solution holding step. Therefore, the cleaning time of the external pressure filtration module can be reduced.

  Air bubbles may be supplied in the chemical solution holding step. Thus, by supplying bubbles in the chemical solution holding step, the chemical solution is agitated and the chemical concentration in the outer cylinder case is made uniform. Thereby, the cleaning effect of the external pressure filtration module can be enhanced.

  Air bubbles may be supplied in the backwashing step. Thus, by supplying bubbles in the backwashing step, impurities attached to the surface of the hollow fiber membrane can be accurately removed, and the effect of preventing membrane fouling can be promoted.

  The chemical solution in the chemical solution holding step may contain sodium hypochlorite or an inorganic acid. By including the inorganic acid in the chemical solution in the chemical solution holding step, the metal is eluted into the inorganic acid, so that the removal efficiency of the metal adhering to the hollow fiber can be improved. Further, the inorganic acid from which the metal is eluted has low toxicity and can be easily treated with waste liquid. Moreover, the removal efficiency of the organic substance adhering to a hollow fiber membrane can be improved by including sodium hypochlorite in the chemical | medical solution of the said chemical | medical solution holding process.

  The hollow fiber membrane is preferably composed mainly of polytetrafluoroethylene. Thus, by using polytetrafluoroethylene as the main component of the hollow fiber membrane, the hollow fiber membrane has a sufficient mechanical strength, so that it is easy to optimize the cleaning conditions without being restricted by the strength of the hollow fiber membrane. Therefore, the cleaning effect of the filtration module can be enhanced.

  A filtration device according to another aspect of the present invention is an external pressure filtration having a plurality of hollow fiber membranes that are aligned in one direction and a cylindrical outer case that stores the plurality of hollow fiber membranes. A filtration device comprising a module, wherein a filtration stop control for stopping filtration of treated water, a discharge control for discharging treated water in the outer cylinder case after the filtration stop control, and the hollow fiber after the discharge control A control mechanism for performing backwashing control for washing the membrane with backwashing water, and chemical solution holding control for holding the chemical solution in the outer case after the backwashing control, and the average membrane effective length of the hollow fiber membrane is 2 m That's it.

  In the said filtration apparatus, after stopping filtration by filtration stop control, the to-be-processed water in an outer cylinder case can be discharged | emitted by discharge control. For this reason, since the backwash water can be controlled by the backwash control after the water to be treated is discharged by the discharge control by using the filtration device, the backwash water can be easily distributed to the entire external pressure filtration module. In addition, by using the filtration device, the chemical solution can be retained by the chemical solution retention control after the backwash water is spread over the entire external pressure filtration module, so that impurities that can be removed by the backwash control are removed. Can hold chemicals. For this reason, a chemical | medical solution osmose | permeates a hollow fiber membrane, it is easy to spread over the whole external pressure type filtration module, and the washing | cleaning effect of the inflow port vicinity of the to-be-processed water which an impurity tends to adhere can be heightened. Therefore, by using the filtration device, it is possible to effectively wash a filtration module in which the average effective membrane length of the hollow fiber membrane is 2 m or more.

  Here, the “main component” means a component having a mass content of 50% or more, preferably 90% or more.

[Details of the embodiment of the present invention]
Embodiments of an external pressure filtration module cleaning method and a filtration device according to the present invention will be described below in detail with reference to the drawings.

  1 includes an external pressure filtration module 2, a filtration operation mechanism 3, a to-be-treated water supply mechanism 4, a discharge mechanism 5, a backwash mechanism 6, a bubble supply mechanism 7, a control mechanism 8, and the like. Is mainly provided.

  The external pressure filtration module 2 mainly has a plurality of hollow fiber membranes 21 aligned in one direction, and a cylindrical outer case 24 for storing the plurality of hollow fiber membranes 21. The average effective membrane length of the hollow fiber membrane 21 is 2 m or more.

  The control mechanism 8 includes a filtration stop control for stopping the filtration of the water to be treated, a discharge control for discharging the water to be treated in the outer cylinder case 24 after the filtration stop control, and the hollow fiber after the discharge control. Back washing control for washing the membrane 21 with back washing water and chemical liquid holding control for holding the chemical liquid in the outer case 24 after the back washing control are performed.

  In the said filtration apparatus 1, after stopping filtration by filtration stop control, the to-be-processed water in the outer cylinder case 24 can be discharged | emitted by discharge control. For this reason, since the backwash water can be controlled by the backwash control after the water to be treated is discharged by the discharge control by using the filtration device 1, the backwash water can be easily distributed to the entire external pressure filtration module 2. Further, by using the filtration device 1, the chemical solution can be retained by the chemical solution retention control after the backwash water is spread over the entire external pressure filtration module 2, so that impurities that can be removed by the backwash control are removed. A chemical solution can be held in a state. For this reason, the chemical | medical solution osmose | permeates the hollow fiber membrane 21, and it is easy to spread over the whole external pressure type filtration module 2, and the washing | cleaning effect near the inflow port of the to-be-processed water which an impurity tends to adhere can be improved. Therefore, by using the filtration device 1, it is possible to effectively wash the filtration module in which the average effective membrane length of the hollow fiber membrane 21 is 2 m or more.

  Since the energy consumption per unit area of the hollow fiber membrane is reduced by increasing the average membrane effective length, the filtration device 1 is preferably used particularly for large-scale sewage treatment. be able to.

<External pressure filtration module>
The external pressure filtration module 2 includes a plurality of hollow fiber membranes 21 aligned in one direction, and holding members (an upper holding member 22 and a lower holding member 23) that fix both ends of the plurality of hollow fiber membranes 21. And a cylindrical outer case 24 for storing the plurality of hollow fiber membranes 21.

(Hollow fiber membrane)
The hollow fiber membrane 21 is a porous membrane that allows water to permeate through the inner hollow portion while preventing permeation of particles contained in the liquid to be treated.

  As the hollow fiber membrane 21, a material mainly composed of a thermoplastic resin can be used. Examples of the thermoplastic resin include polyethylene, polypropylene, polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, polyamide, polyimide, polyetherimide, polystyrene, polysulfone, polyvinyl alcohol, polyphenylene ether, polyphenylene sulfide, cellulose acetate, and polyacrylonitrile. And polytetrafluoroethylene (PTFE). Among these, the hollow fiber membrane 21 is preferably composed mainly of polytetrafluoroethylene. As described above, the main component of the hollow fiber membrane 21 is polytetrafluoroethylene, so that the hollow fiber membrane 21 has sufficient mechanical strength. Therefore, the cleaning conditions are optimized regardless of the strength of the hollow fiber membrane 21. Easy to convert. Therefore, the cleaning effect of the external pressure filtration module 2 can be improved. The hollow fiber membrane 21 may appropriately contain other polymers, additives such as a lubricant, and the like.

  The lower limit of the average length (average membrane effective length) of the hollow fiber membrane 21 is 2 m, more preferably 2.5 m, and even more preferably 2.8 m. On the other hand, the upper limit of the average length of the hollow fiber membrane 21 is preferably 4 m, and more preferably 3.5 m. If the average length of the hollow fiber membrane 21 is less than the above lower limit, the filtration processing efficiency may be insufficient. On the other hand, if the average length of the hollow fiber membrane 21 exceeds the above upper limit, the hollow fiber membrane 21 may be excessively bent due to its own weight, or may be handled when the external pressure filtration module 2 is installed. May decrease. The average length of the hollow fiber membrane 21 means the average distance from the upper end portion fixed to the upper holding member 22 to the lower end portion fixed to the lower holding member 23.

  As a minimum of the porosity of hollow fiber membrane 21, 75% is preferred and 78% is more preferred. Moreover, as an upper limit of the porosity of the hollow fiber membrane 21, 90% is preferable and 85% is more preferable. If the porosity of the hollow fiber membrane 21 is less than the above lower limit, the water permeability may be reduced, and the filtration capability of the external pressure filtration module 2 may be reduced. On the other hand, if the porosity of the hollow fiber membrane 21 exceeds the above upper limit, the mechanical strength and scratch resistance of the hollow fiber membrane 21 may be insufficient. The porosity refers to the ratio of the total volume of pores to the volume of the hollow fiber membrane 21 and can be determined by measuring the density of the hollow fiber membrane 21 in accordance with ASTM-D-792.

  The lower limit of the average pore diameter of the hollow fiber membrane 21 is preferably 0.01 μm, and more preferably 0.05 μm. On the other hand, the upper limit of the average diameter of the pores of the hollow fiber membrane 21 is preferably 0.45 μm, and more preferably 0.2 μm. There exists a possibility that water permeability may fall that the average diameter of the void | hole of the said hollow fiber membrane 21 is less than the said minimum. On the contrary, if the average diameter of the pores of the hollow fiber membrane 21 exceeds the upper limit, there is a possibility that the permeation of impurities contained in the liquid to be treated into the hollow fiber membrane 21 cannot be prevented. The average diameter of the pores means the average diameter of the pores on the outer peripheral surface of the hollow fiber membrane 21, for example, a pore diameter distribution measuring device (for example, “Porous Material Automatic Pore Diameter Distribution Measuring System of Porous Materials) )).

(Holding member)
The upper holding member 22 is a member that holds the upper side of the plurality of hollow fiber membranes 21 and is disposed in the outer cylinder case 24. Further, the upper holding member 22 separates the upper and lower portions of the outer cylindrical case 24 from the upper holding member 22. The upper holding member 22 holds the hollow fiber membrane 21 such that the upper ends of the plurality of hollow fiber membranes 21 protrude above the upper holding member 22. As a result, the treated water that has permeated into the plurality of hollow fiber membranes 21 is discharged to a portion above the upper holding member 22 of the outer cylinder case 24.

  The lower holding member 23 is a member that holds the lower side of the plurality of hollow fiber membranes 21 and is disposed below the upper holding member 22 in the outer cylinder case 24. The lower holding member 23 has a plurality of fixing portions 23 a for fixing the lower end portion of the hollow fiber membrane 21. The fixing portion 23a is formed, for example, in a rod shape, and a plurality of the fixing portions 23a are arranged substantially in parallel with a predetermined interval, and a plurality of hollow fiber membranes 21 are provided on the upper side.

  The water to be treated can flow between the upper holding member 22 and the lower holding member 23 in the outer cylinder case 24 through the gaps between the plurality of fixing portions 23 a of the lower holding member 23. The treated water that has flowed in is filtered by the hollow fiber membrane 21 and permeates into the hollow fiber membrane 21.

  The material of the upper holding member 22 and the lower holding member 23 is not particularly limited, and for example, epoxy resin, ABS resin, silicone resin, or the like can be used.

(Outer cylinder case)
The outer cylinder case 24 is a cylindrical case that houses the plurality of hollow fiber membranes 21. The outer cylinder case 24 can store treated water therein. In addition, the outer cylinder case 24 is provided between the inlet 24a of the water to be treated disposed in the lower portion, the outlet 24b of the treated water disposed in the upper portion, the upper holding member 22 and the lower holding member 23. And the backwashing water discharge port 24 c disposed at a position close to the upper holding member 22.

  The material of the outer case 24 is not particularly limited, and for example, vinyl chloride resin, propylene resin, ethylene resin, ether sulfone resin, epoxy resin, ABS resin, silicone resin, or the like can be used.

<Filtration operation mechanism>
The filtration operation mechanism 3 has a pressurizing pump 3a and controls the operation and stop of the filtration of the treated water X. The pressurizing pump 3 a is disposed on the supply pipe 10 that supplies the water to be treated X to the inlet 24 a of the water to be treated of the external pressure filtration module 2.

  In the said filtration apparatus 1, while the filtration process can be performed by carrying out the pressurized supply of the to-be-processed water X to the inside of the hollow fiber membrane 21 by the driving | operation of the pressurization pump 3a, the filtration process can be stopped by the stop of the pressurization pump 3a.

<Treatment water supply mechanism>
The to-be-treated water supply mechanism 4 has an on-off valve 4a for to-be-treated water, and controls the supply of the to-be-treated water X to the external pressure filtration module 2. The on-off valve 4a for the water to be treated is disposed between the inlet 24a of the water to be treated of the external pressure filtration module 2 of the supply pipe 10 and the pressure pump 3a.

  In the filtration device 1, the on-off valve 4 a for water to be treated is opened during the operation of the pressure pump 3 a of the filtration operation mechanism 3, and the water to be treated X flows into the external pressure filtration module 2. Closed when the pressure pump 3a is stopped, the treated water X is prevented from flowing into the external pressure filtration module 2.

<Discharge mechanism>
The discharge mechanism 5 includes a discharge pipe 5a and a discharge open / close valve 5b, and controls discharge of the water to be treated in the outer cylinder case 24 of the external pressure filtration module 2. The discharge pipe 5a is connected between the inlet 24a of the water to be treated of the external pressure filtration module 2 of the supply pipe 10 and the on-off valve 4a for the water to be treated. The discharge opening / closing valve 5b is disposed in the discharge pipe 5a.

  In the filtration device 1, the water to be treated in the outer cylinder case 24 can be discharged by opening the discharge opening / closing valve 5b.

<Backwash mechanism>
The backwash mechanism 6 includes a backwash water supply pipe 6a, a backwash water supply pump 6b, a backwash water discharge pipe 6c, and a backwash opening / closing valve 6d. Control the cleaning by. The backwash water supply pipe 6 a is connected to the discharge pipe 9. The backwash water supply pump 6b is disposed on the backwash water supply pipe 6a. Further, the backwash water discharge pipe 6 c is connected to the backwash water discharge port 24 c of the external pressure filtration module 2. The backwash opening / closing valve 6d is disposed on the backwash water discharge pipe 6c.

  In the filtration device 1, the backwashing opening / closing valve 6d is opened and the backwashing water supply pump 6b is operated to allow the backwashing water to flow into the external pressure filtration module 2 from the treated water discharge port 24b. The membrane 21 can be cleaned. The backwash water flowing into the external pressure filtration module 2 is discharged through the backwash water discharge pipe 6c, and the hollow fiber membrane 21 is washed by the backwash water flow.

<Bubble supply mechanism>
The bubble supply mechanism 7 includes a bubble supply pipe 7 a and a bubble supplier 7 b and supplies bubbles to the external pressure filtration module 2. One end of the bubble supply pipe 7a is connected between the inlet 24a of the water to be treated of the external pressure filtration module 2 of the supply pipe 10 and the open / close valve 4a for the water to be treated. The other end of the bubble supply pipe 7a is connected to the bubble supply unit 7b.

  The bubble supplier 7b may be any device that can supply bubbles, and for example, a blower, a compressor, or the like can be used.

<Control mechanism>
The control mechanism 8 includes a control device 8a such as a personal computer or a programmable logic controller. The control mechanism 8 controls the operation of the external pressure filtration module 2 and controls the cleaning of the external pressure filtration module 2. Specifically, the control mechanism 8 controls the filtration operation mechanism 3, the treated water supply mechanism 4, the discharge mechanism 5, the backwash mechanism 6, and the bubble supply mechanism 7.

  In the said filtration apparatus 1, the said control mechanism 8 performs filtration operation control which filters the to-be-processed water X using the external pressure type filtration module 2 as operation control. The control mechanism 8 includes, as cleaning control, a filtration stop control for stopping the filtration of the treated water X, a discharge control for discharging the treated water X in the outer cylinder case 24 after the filtration stop control, Backwash control for washing the hollow fiber membrane 21 with backwash water after the discharge control and chemical solution holding control for holding the chemical solution in the outer cylinder case 24 after the backwash control are performed.

<Operation method of filtration device>
Next, an operation method of the filtration device 1 will be described. The operation method of the filtration device 1 includes an operation process and a cleaning process. Although the operation method of the said filtration apparatus 1 may have processes other than the said washing | cleaning process between the said operation process and a washing | cleaning process, it is preferable to repeat the said driving | operation process and a washing | cleaning process alternately. The operation method of the filtration device 1 can promote the effect of preventing membrane fouling and the effect of suppressing the operation cost of the filtration device 1 by repeatedly performing the operation step and the cleaning step.

(Operation process)
In the operation process, a filtration process by the external pressure filtration module 2 is performed. The operation process is performed based on the control of the filtration operation mechanism 3 by the control mechanism 8. Specifically, in the above operation process, the water treatment opening / closing valve 4a is opened according to the control of the control mechanism 8 and the pressurizing pump 3a is started to start the filtration process. The filtration process is suspended by closing the valve 4a and stopping the pressurizing pump 3a.

In the above operation process, the filtration process by the external pressure filtration module 2 may be performed continuously, but it is preferable to repeat the filtration process and the cleaning by the discharge mechanism 5 and the backwash mechanism 6. Specifically, the water to be treated in the outer cylinder case 24 of the external pressure filtration module 2 is discharged by the discharge mechanism 5 after the filtration treatment, and then the backwash mechanism 6 performs the backwashing. The operation method of the filtration device 1 is such that the membrane fau is combined with the cleaning effect by the cleaning process described later by repeatedly performing the filtration process by the external pressure filtration module 2 and the cleaning by the backwashing mechanism 6 in the above operation process. Long-term stable operation can be easily and reliably performed while enhancing the ring prevention effect.
In the cleaning in the operation step, cleaning using a chemical solution may be performed. However, since the operation method of the filtration device 1 can perform sufficient cleaning by a cleaning step described later, the chemical solution is used in this operation step. It is preferable not to wash.

  Thus, when performing filtration treatment and washing repeatedly, as a minimum of one filtration treatment time, 20 minutes are preferred and 30 minutes are more preferred. On the other hand, the upper limit of one filtration treatment time is preferably 50 minutes, and more preferably 40 minutes. Moreover, as a minimum of the washing | cleaning time of 1 time of backwashing, 0.3 minute is preferable and 0.5 minute is more preferable. On the other hand, the upper limit of the washing time for one back washing is preferably 2 minutes, and more preferably 1 minute. In addition, one drainage time is determined by the capacity of the external pressure filtration module 2, but is, for example, about 0.5 minutes or more and 1 minute or less.

  The lower limit of the operation time in the operation step is preferably 5 hours, more preferably 8 hours, and even more preferably 10 hours. On the other hand, the upper limit of the operation time in the operation process is preferably 48 hours, more preferably 24 hours, and even more preferably 20 hours. If the operation time in the operation process is less than the lower limit, the filtration efficiency may not be sufficiently improved. On the other hand, when the operation time in the operation process exceeds the upper limit, the amount of impurities attached to the surface of the plurality of hollow fiber membranes 21 may increase and the filtration capacity may be insufficient. In addition, when performing a filtration process and washing | cleaning repeatedly, the said operation time includes the washing | cleaning time performed between filtration processes.

  In the operation step, the operation time of the external pressure filtration module 2 may be controlled based on the filtration processing amount within the time range.

  The upper limit of the transmembrane differential pressure of the hollow fiber membrane 21 in the above operation process is preferably 45 kPa, and more preferably 35 kPa. When the transmembrane pressure difference exceeds the upper limit, the filtration capacity may be insufficient. On the other hand, the lower limit of the transmembrane pressure difference is not particularly limited, but is, for example, about 10 kPa.

  In addition, the permeation flux of the water to be treated in the above operation process is appropriately determined according to the flow rate of the water to be treated and the like.

(Washing process)
In the washing step, the filtration process by the external pressure filtration module 2 is suspended and the external pressure filtration module 2 is washed. Specifically, the cleaning step is started by stopping the pressurizing pump 3a according to the control of the control mechanism 8, and is performed until the pressurizing pump 3a is started again by the control mechanism 8. In this cleaning process, the control mechanism 8 includes a filtration stop control for stopping the filtration of the water to be treated, a discharge control for discharging the water to be treated in the outer cylinder case 24 after the filtration stop control, and after the discharge control. Back washing control for washing the hollow fiber membrane 21 with back washing water and chemical solution holding control for holding a chemical solution in the outer case 24 after the back washing control are performed. Specifically, the cleaning step is performed using a method for cleaning an external pressure filtration module described below.

<Cleaning method of external pressure filtration module>
The cleaning method for the external pressure filtration module includes a filtration stop step for stopping the filtration of water to be treated, a discharge step for discharging the water to be treated in the outer cylinder case 24 after the filtration stop step, and the above-mentioned after the discharge step. A backwashing step for washing the hollow fiber membrane 21 with backwashing water, a chemical solution holding step for holding the chemical solution in the outer cylinder case 24 after the backwashing step, and a chemical solution in the outer cylinder case 24 held in the chemical solution holding step And a flushing process for discharging the water.

  In the external pressure filtration module cleaning method, after the filtration is stopped in the filtration stop process, the water to be treated in the outer cylinder case 24 is discharged in the discharge process. For this reason, by using the cleaning method of the external pressure filtration module, it is easy to spread the backwash water throughout the external pressure filtration module 2 in the backwashing step performed after the discharging step. Moreover, since the washing | cleaning method of the said external pressure type filtration module is equipped with a chemical | medical solution holding process after the said backwashing process, a chemical | medical solution is hold | maintained in the state from which the impurity which can be removed by a backwashing process was removed. For this reason, the chemical | medical solution osmose | permeates the hollow fiber membrane 21, and it is easy to spread over the whole external pressure type filtration module 2, and the washing | cleaning effect near the inflow port of the to-be-processed water which an impurity tends to adhere can be improved. Therefore, by using the method for cleaning the external pressure filtration module, it is possible to effectively clean the filtration module in which the average effective membrane length of the hollow fiber membrane 21 is 2 m or more.

(Filtering stop process)
In the filtration stop process, the filtration of the water to be treated is stopped using the filtration operation mechanism 3. Specifically, under the control of the control mechanism 8, the pressurizing pump 3a is stopped, and the on-off valve 4a for water to be treated is closed. As a result, the treated water X is prevented from flowing into the external pressure filtration module 2.

(Discharge process)
In the discharging step, the water to be treated in the outer cylinder case 24 is discharged after the filtering stop step using the discharging mechanism 5. Specifically, according to the control of the control mechanism 8, the discharge opening / closing valve 5 b is opened to discharge substantially the entire amount of water to be treated in the outer cylinder case 24. Note that “substantially the entire amount is discharged” means that the amount of water to be treated remaining in the outer cylinder case 24 after discharging is 5% by volume or less, preferably 1 volume with respect to the amount of water to be treated in the outer case 24 at the time of filtration operation. It means that it discharges so that it may become less than%.

  The time required for the discharging step is determined by the capacity of the external pressure filtration module 2, and is, for example, about 0.5 minutes to 1 minute. As a minimum of discharge time (time required for a discharge process) of treated water in a discharge process, 0.6 minutes are more preferred. On the other hand, the upper limit of the discharge time of the water to be treated in the discharge step is more preferably 0.8 minutes. If the discharge time of the water to be treated in the discharge step is less than the lower limit, the liquid to be treated cannot be sufficiently drained and the cleaning effect of the filtration module may be insufficient. Conversely, if the discharge time of the water to be treated in the discharge process exceeds the above upper limit, the time required for the discharge process becomes unnecessarily long, and the cleaning efficiency of the filtration module may be reduced.

(Backwash process)
In the backwashing process, the hollow fiber membrane 21 is washed with backwashing water using the backwashing mechanism 6 after the discharging process. Specifically, according to the control of the control mechanism 8, the backwash opening / closing valve 6 d is opened, and the backwash water is caused to flow into the external pressure filtration module 2 from the treated water discharge port 24 b by the operation of the backwash water supply pump 6 b. Thus, the hollow fiber membrane 21 is cleaned. The backwash water that has flowed into the external pressure filtration module 2 is discharged through the backwash water discharge pipe 6c.

  Air bubbles may be supplied in the backwashing step. Thus, by supplying air bubbles in the backwashing step, impurities attached to the surface of the hollow fiber membrane 21 can be accurately removed, and the effect of preventing membrane fouling can be promoted. The bubble supply can be performed by the bubble supply mechanism 7.

  The backwash water is not particularly limited as long as the hollow fiber membrane 21 can be washed. For example, treated water or city water can be used, but as the backwash water used in the backwash step, a chemical solution holding described later is used. A chemical used in the process may be used. Thus, by using the chemical solution used in the chemical solution holding step as the backwash water used in the backwash step, it is not necessary to replace the backwash water with the chemical solution in the chemical solution holding step. Therefore, the cleaning time of the external pressure filtration module 2 can be reduced.

  As a minimum of the discharge pressure of backwash water by backwash water supply pump 6b, 20 kPa is preferred and 100 kPa is more preferred. On the other hand, the upper limit of the discharge pressure of the backwash water is preferably 200 kPa, and more preferably 150 kPa. There exists a possibility that the washing | cleaning effect by backwashing water may be insufficient that the discharge pressure of the said backwashing water is less than the said minimum. Conversely, if the discharge pressure of the backwash water exceeds the upper limit, the backwash water supply pump 6b having a high discharge pressure and the external pressure filtration module 2 having a high pressure resistance are required, which may increase the cost of manufacturing equipment. There is.

  As a minimum of backwashing time, 0.3 minutes are preferred and 0.5 minutes are more preferred. On the other hand, the upper limit of the backwash time is preferably 2 minutes, and more preferably 1 minute. If the backwash time is less than the lower limit, impurities attached to the surface of the hollow fiber membrane 21 may not be sufficiently removed. On the other hand, if the backwash time exceeds the upper limit, the filtration time is relatively decreased, and thus the filtration efficiency may not be sufficiently improved. Here, the backwash time refers to the time from the start of inflow of backwash water to the external pressure filtration module 2 until the inflow is stopped. In addition, when performing backwash intermittently several times continuously, it is set as the time from the start of inflow of the backwash water of the first backwash to the stop of inflow of the last backwash.

(Chemical solution holding process)
In the chemical solution holding step, the chemical solution is held in the outer cylinder case 24 after the back washing step. In the chemical solution holding process, the control mechanism 8 has an on-off valve 4a for the filtration operation mechanism 3, a discharge on-off valve 5b of the discharge mechanism 5, a backwash water supply pipe 6a of the backwash mechanism 6, and a backwash water supply. This can be done by controlling the pump 6b and the backwash opening / closing valve 6d. Specifically, the chemical solution supplied to the external pressure filtration module 2 is held by closing the open / close valve 4a for water to be treated, the open / close valve 5b for discharge, and the open / close valve 6d for backwashing according to the control of the control mechanism 8. To do. In addition, when using the chemical | medical solution used at a chemical | medical solution holding | maintenance process as backwashing water, the backwashing water used for backwashing at the time of completion | finish of a backwashing process is not discharged | emitted, but it retains as it is. When the chemical solution used in the chemical solution holding step is not used as the backwash water, the backwash mechanism 6 is used before closing the on-off valve 4a, the discharge on-off valve 5b, and the backwash on-off valve 6d. The chemical solution is supplied from the backwash water supply pipe 6a to the external pressure filtration module 2 using the backwash water supply pump 6b. The chemical solution supply time is determined by the capacity of the external pressure filtration module 2 and is, for example, about 0.5 minutes to 2.0 minutes.

  Air bubbles may be supplied in the chemical solution holding step. Thus, by supplying bubbles in the chemical solution holding step, the chemical solution is agitated and the chemical concentration in the outer case 24 is made uniform. Thereby, the cleaning effect of the filtration module can be enhanced. The bubble supply can be performed by the bubble supply mechanism 7.

  Examples of the chemical used in the chemical solution include sodium hypochlorite, inorganic acid, organic acid, sodium hydroxide, and surfactant. Of these, sodium hypochlorite and inorganic acids are preferred.

  By including sodium hypochlorite in the chemical solution, the removal efficiency of organic substances adhering to the hollow fiber membrane 21 can be improved. When sodium hypochlorite is used, the lower limit of the concentration of sodium hypochlorite is preferably 1 mg / L, and more preferably 10 mg / L. On the other hand, the upper limit of the concentration of sodium hypochlorite is preferably 500 mg / L, and more preferably 100 mg / L. There exists a possibility that the washing | cleaning effect of the hollow fiber membrane 21 may become inadequate that the density | concentration of the said sodium hypochlorite is less than the said minimum. In addition, the cleaning effect can be enhanced by using sodium hydroxide together. In this case, from the viewpoint of the cleaning effect, the ratio of sodium hypochlorite to the total amount of sodium hypochlorite and sodium hydroxide is preferably 85% by mass or more.

  Moreover, since the metal is eluted in the inorganic acid by including the inorganic acid in the chemical solution, the removal efficiency of the metal adhering to the hollow fiber can be improved. Further, the inorganic acid from which the metal is eluted has low toxicity and can be easily treated with waste liquid. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, sodium bisulfite and the like. When using an inorganic acid, the lower limit of the concentration of the inorganic acid is preferably 10 mg / L, more preferably 50 mg / L. On the other hand, the upper limit of the concentration of the inorganic acid is preferably 1000 mg / L, and more preferably 500 mg / L. There exists a possibility that the washing | cleaning effect of the hollow fiber membrane 21 may become inadequate that the density | concentration of the said inorganic acid is less than the said minimum. Further, from the viewpoint of the cleaning effect, an inorganic acid may be added so that the pH of the chemical solution is 2 or less.

  The lower limit of the chemical solution retention time is preferably 15 minutes, and more preferably 30 minutes. On the other hand, the upper limit of the chemical solution holding time is preferably 90 minutes, and more preferably 60 minutes. If the chemical solution retention time is less than the lower limit, impurities attached to the surface of the hollow fiber membrane 21 may not be sufficiently removed. On the other hand, if the chemical solution retention time exceeds the upper limit, the filtration time is relatively reduced, and thus the filtration efficiency may not be sufficiently improved.

(Flushing process)
In the flushing step, the hollow fiber membrane 21 is subjected to forward cleaning using forward cleaning water such as water to be treated, and the chemical solution in the outer cylinder case 24 held in the chemical solution holding step is discharged. The flushing process can be performed by the control mechanism 8 controlling the pressurizing pump 3a of the filtration operation mechanism 3 and the on-off valve 4a for water to be treated. Specifically, according to the control of the control mechanism 8, the open / close valve for treated water 4a is opened and the pressurizing pump 3a is operated. Further, the flush water is supplied to the supply pipe 10.

  The lower limit of the flushing time is preferably 0.5 minutes, and more preferably 1 minute. On the other hand, the upper limit of the flushing time is preferably 10 minutes, and more preferably 5 minutes. When the flushing time is less than the lower limit, impurities attached to the surface of the hollow fiber membrane 21 may not be sufficiently removed or the chemical solution may not be sufficiently discharged. On the other hand, if the flushing time exceeds the upper limit, the filtration time is relatively reduced, and thus the filtration efficiency may not be sufficiently improved.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  In the above embodiment, the case where the backwashing mechanism is used for supplying the chemical solution has been described. However, as shown in FIG. 2, the outer cylinder case 24 of the filtration device 11 further includes a chemical solution supply port 24d for supplying the chemical solution. You may further provide the chemical solution supply mechanism 12 comprised by the chemical solution supply pipe | tube 12a connected to the supply port 24d, and the chemical solution supply pump 12b arrange | positioned on the said chemical solution supply pipe | tube 12a. In the case of such a configuration, the chemical liquid supply port 24 d is preferably disposed at a position close to the lower holding member 23 between the upper holding member 22 and the lower holding member 23. By arranging the chemical solution supply port 24d in the above position in this way, the chemical solution can be supplied to the inflow side of the water to be treated where impurities easily adhere to the hollow fiber membrane 21, so that the cleaning effect of the hollow fiber membrane 21 is improved. Enhanced.

  Further, the number of external pressure filtration modules of the filtration device is not limited to one, and may be plural. When the said filtration apparatus has a some external pressure type filtration module, these some external pressure type filtration modules may be controlled collectively, and each may be controlled separately.

  In the external pressure filtration module cleaning method, supply of bubbles in the backwashing step and the chemical solution holding step is not essential, and supply of bubbles can be omitted in either or both steps. In addition, when bubbles are not supplied in both the backwashing step and the chemical solution holding step, the bubble supply mechanism of the filtration device can be omitted.

  Further, in the method for cleaning the external pressure filtration module, the flushing step is not essential and can be omitted.

  The external pressure filtration module may have a configuration in which the upper holding member holds both ends of the hollow fiber membrane, and the lower holding member bends the hollow fiber membrane by bending it into a U shape. In this case, the average length of the hollow fiber membrane refers to the length from the lower end portion of the curved portion fixed by the lower holding member to the upper end portion fixed to the upper holding member.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Processing Example 1]
Using the filtration apparatus, 35 minutes of filtration, 0.75 minutes of drainage of water to be treated, and 0.75 minutes of backwashing were performed in this order as one operation step. The washing process was performed every time the above operation process was performed 20 times (operation time 12 hours). As said washing | cleaning process, drainage of the to-be-processed water for 0.75 minutes, backwashing for 0.75 minutes, chemical | medical solution supply for 1 minute, chemical | medical solution holding | maintenance for 40 minutes, and flushing for 3 minutes were performed in this order. In addition, treated water was used for backwash water and normal wash water, and a sodium hypochlorite aqueous solution having a concentration of 200 mg / L was used for the chemical solution. Moreover, the average membrane effective length of the hollow fiber membrane of the said filtration apparatus is 3 m.

  The operation was performed for 10 days with the permeation flux of the water to be treated in the operation process in the range of 40 LMH to 60 LMH in the above operation procedure. The intermembrane | transmembrane differential pressure of the hollow fiber membrane in the operation process in the meantime was 30 kPa on average.

[Processing Example 2]
In the said processing example 1, the said filtration apparatus was drive | operated like the processing example 1 except not having drained in the washing | cleaning process. The intermembrane | transmembrane differential pressure of the hollow fiber membrane in the operation process in the meantime was 50 kPa on average.

  Comparing the results of treatment example 1 and treatment example 2, the average transmembrane pressure difference of treatment example 1 is lower than the average transmembrane pressure difference of treatment example 2. In other words, it can be seen that by draining the water to be treated in the washing step, the transmembrane pressure difference can be reduced, and the hollow fiber membrane having an average membrane effective length of 2 m or more can be effectively washed.

[Processing Example 3]
In the said processing example 1, the said filtration apparatus was drive | operated similarly to the processing example 1 except draining the to-be-processed water for 0.25 minutes in the washing | cleaning process. The intermembrane | transmembrane differential pressure of the hollow fiber membrane in the operation process in the meantime was 45 kPa on average.

  Comparing the results of treatment example 3 and treatment example 2, the average transmembrane pressure difference in treatment example 3 is lower than the average transmembrane pressure difference in treatment example 2. It can be seen that by draining the water to be treated in the washing step, the transmembrane pressure difference can be reduced and the hollow fiber membrane can be effectively washed.

  Comparing the results of treatment example 1 and treatment example 3, the average transmembrane pressure difference of treatment example 1 is lower than the average transmembrane pressure difference of treatment example 3. In the processing example 1, by setting the discharge time of the water to be treated in the discharge process to 0.5 minutes or more and 1 minute or less, the drainage of the liquid to be processed further proceeds. As a result, the discharge time is less than 0.5 minutes. It is considered that the transmembrane pressure difference is lower than in the case of certain treatment example 3. That is, it can be seen that the hollow fiber membrane having an average membrane effective length of 2 m or more can be more effectively washed by setting the discharge time of the treated water in the discharge step to 0.5 minutes or more and 1 minute or less.

  Since the cleaning effect of the filtration module having a large average membrane effective length is enhanced by using the external pressure filtration module cleaning method and the filtration device according to one aspect of the present invention, the filtration module having a large average membrane effective length is stably operated. can do.

DESCRIPTION OF SYMBOLS 1, 11 Filtration apparatus 2 External pressure type filtration module 21 Hollow fiber membrane 22 Upper holding member 23 Lower holding member 23a Fixed part 24 Outer cylinder case 24a Inlet 24b Outlet 24c Backwash water outlet 24d Chemical solution supply port 3 Filtration operation mechanism 3a Pressurized pump 4 Untreated water supply mechanism 4a Untreated water open / close valve 5 Discharge mechanism 5a Discharge pipe 5b Discharge open / close valve 6 Backwash mechanism 6a Backwash water supply pipe 6b Backwash water supply pump 6c Backwash water discharge pipe 6d Open / close valve for backwash 7 Bubble supply mechanism 7a Bubble supply pipe 7b Bubble supply device 8 Control mechanism 8a Control device 9 Discharge pipe 10 Supply pipe 12 Chemical liquid supply mechanism 12a Chemical liquid supply pipe 12b Chemical liquid supply pump

Claims (8)

A method of cleaning an external pressure filtration module having a plurality of hollow fiber membranes that are aligned in one direction and a cylindrical outer tube case that stores these hollow fiber membranes,
A filtration stopping step for stopping filtration of the water to be treated;
A discharge step of discharging the treated water in the outer case after the filtration stop step;
A backwashing step of washing the hollow fiber membrane with backwashing water after the discharging step;
A chemical solution holding step for holding the chemical solution in the outer cylinder case after the backwashing step,
A method for cleaning an external pressure filtration module, wherein the average effective membrane length of the hollow fiber membrane is 2 m or more.   The method for cleaning an external pressure filtration module according to claim 1, wherein the discharge time of the treated water in the discharge step is 0.5 minutes or more and 1 minute or less.   The method for cleaning an external pressure filtration module according to claim 1 or 2, wherein the chemical solution used in the chemical solution holding step is used as the backwash water used in the backwashing step.   The method for cleaning an external pressure filtration module according to claim 1, 2 or 3, wherein bubbles are supplied in the chemical solution holding step.   The method for cleaning an external pressure filtration module according to any one of claims 1 to 4, wherein bubbles are supplied in the backwashing step.   The cleaning method for an external pressure filtration module according to any one of claims 1 to 5, wherein the chemical solution in the chemical solution holding step contains sodium hypochlorite or an inorganic acid.   The method for cleaning an external pressure filtration module according to any one of claims 1 to 6, wherein the hollow fiber membrane contains polytetrafluoroethylene as a main component. A filtration apparatus comprising an external pressure filtration module having a plurality of hollow fiber membranes that are aligned in one direction and a cylindrical outer cylinder case that stores the plurality of hollow fiber membranes,
Filtration stop control for stopping filtration of the water to be treated;
Discharge control for discharging the treated water in the outer cylinder case after the filtration stop control,
Backwash control for washing the hollow fiber membrane with backwash water after the discharge control;
A control mechanism for performing a chemical solution holding control for holding a chemical solution in the outer cylinder case after the backwash control,
A filtration device wherein the average effective membrane length of the hollow fiber membrane is 2 m or more.

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