JP2009214062A - Operation method of immersion type membrane module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation method which can efficiently improves a water recovery rate, reduce a load on the membrane module, and prevent clogging of a membrane when performing the membrane separation of water by a membrane module installed in an immersion tank. <P>SOLUTION: In a method for producing membrane-filtered water by a water treatment apparatus wherein a filtration membrane module is immersed and installed in the immersion tank storing raw water and a raw water supply port is provide below the upper end of the filtration membrane module, the method includes a water supply and filtration process (a) of extracting the membrane-filtered water by sucking the membrane-filtered water side of the filtration membrane module while supplying the raw water of an amount equal to or more than the amount of extracted membrane-filtered water, and an air cleaning process (c) for cleaning the filtration membrane module by supplying air to the raw water side of the membrane module after stopping membrane filtration are carried out once or repeatedly, and then the water supply and filtration process (a), a filtration process at a lowered liquid level (b) where the liquid level in the immersion tank is lowered by performing the membrane filtration where the supply amount of the raw water is adjusted to zero or an amount less than the amount of the membrane-filtered water, the air cleaning process (c) and a water discharge process (d) of discharging the raw water in the immersion tank to the outside of the tank. The above processes are carried out in this order. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an operation method of a submerged membrane module for performing a membrane filtration treatment of water.

  The membrane separation method by membrane filtration has features such as energy saving, space saving, labor saving, and improvement of filtered water quality, and therefore has been used in various fields. For example, microfiltration membranes and ultrafiltration membranes can be applied to water purification processes that produce industrial water and tap water from river water, groundwater and sewage treated water, and to pretreatment in seawater desalination reverse osmosis membrane treatment processes. can give. Moreover, the filtration membrane module used for membrane separation is classified into a pressurization type and an immersion type irrespective of the processing field. The immersion type membrane module is immersed and installed in an immersion tank, and is used as an immersion type membrane separation means that obtains membrane filtrate from raw water in the immersion tank through a filtration membrane using suction or water head difference as a driving force.

  When water treatment is performed with a submerged membrane module, raw water is continuously or intermittently supplied into the immersion tank, and membrane filtered water is obtained by suction filtration of the membrane module immersed in the immersion tank with a pump or the like. . When raw water is filtered through a membrane, removal objects such as turbidity, organic matter, and inorganic matter contained in the raw water accumulate on the membrane surface, resulting in clogging of the membrane. As a result, the filtration resistance of the membrane increases, and it becomes impossible to continue the filtration over time. Therefore, in order to maintain the membrane filtration performance, it is necessary to periodically wash the membrane. Membrane cleaning can be done by backwashing the membrane filtered water from the secondary side (filtrated water side) to the primary side (raw water side) or by supplying gas to the primary side of the membrane to clean the membrane. There are an air washing step for removing and a draining step for discharging dirt generated in the air washing step and the back washing step from the tank in which the membrane is immersed. In addition, when there is dirt that cannot be removed in the back washing process or the empty washing process, there is a chemical cleaning in which the chemical is brought into contact with the membrane for a certain period of time. Effectively performing these cleaning means is very important for stable operation of membrane filtration.

  Further, in membrane filtration, it is required to increase the ratio of the raw water supplied to the apparatus and the ratio of the membrane filtered water obtained from the apparatus, that is, the recovery rate (membrane filtered water amount / raw water amount), which is important as the performance of the apparatus. For example, when the amount of raw water supplied to the apparatus is 100 and the amount of membrane filtrate obtained from the apparatus is 90, the recovery rate is 90%. In order to increase the recovery rate, it is only necessary to reduce the amount of wastewater drained from the immersion tank by removing the dirt peeled off from the membrane in the backwashing process and the air washing process, but if this drainage amount is reduced, a large amount of dirt will remain in the immersion tank. Therefore, the film tends to be clogged.

As a method for efficiently increasing the recovery rate and preventing clogging of the membrane, Patent Document 1 describes a method for increasing the recovery rate by collecting dirt in the lower part of the submerged membrane filtration device. . Patent Document 2 describes a method for discharging dirt peeled off from a film in an empty washing process or a back washing process from the upper part of the immersion tank. However, in the method of Patent Document 1, since it is necessary to provide a dirt holding space at the lower part of the immersion tank, there is a problem that a large amount of the chemical solution is required when cleaning the chemical solution. Moreover, the method of Patent Document 2 has a problem that the recovery rate cannot be sufficiently increased.
JP 2006-255587 A Special table 2003-513785 gazette

  The purpose of the present invention is to efficiently increase the water recovery rate and reduce the load on the membrane module when producing membrane filtered water by separating the raw water by the membrane membrane module immersed in the immersion tank, An object of the present invention is to provide an operation method capable of suppressing clogging of a membrane.

In order to achieve the above object, the operation method of the submerged membrane module of the present invention has the following characteristics.
(1) Filtration membrane when membrane filtration water is produced by a water treatment apparatus in which a filtration membrane module is immersed in a dipping tank storing raw water and a raw water supply port is provided below the upper end of the filtration membrane module (A) A feed water filtration step of sucking the membrane filtrate side of the filtration membrane module and taking out the membrane filtrate water while supplying raw water equal to or more than the amount of the membrane filtrate water to be taken out ( c) After the membrane filtration is stopped and the air washing step of supplying air to the raw water side of the membrane module to wash the filtration membrane module once or repeatedly, (a) performing the feed water filtration step, (B) a liquid level lowering filtration step for lowering the liquid level in the immersion tank by performing membrane filtration with the raw water supply amount being zero or less than the amount of membrane filtration water, (c) the air washing step, (d ) Immerse the raw water in the immersion tank The method of operating submerged membrane module and draining process and performing in this order to be discharged to.
(2) In the operation method described in (1) above, (a) the water filtration step is performed for 5 minutes after the start of the (c) air washing step for the water storage volume (V) in the immersion tank below the upper end of the membrane module. The operation method of the submerged membrane module, wherein the ratio (I / V) of the difference (I) between the raw water supply amount and the membrane filtrate water removal amount in the above is 0.5 or more.
(3) In the operation method described in (1) above, when (c) the air washing step is performed during the (a) feed water filtration step, the water storage volume (V) in the immersion tank below the upper end of the membrane module, A method for operating a submerged membrane module, wherein the ratio (H / V) of the amount of raw water (H) in the immersion tank above the upper end of the membrane module is 0.5 or more.
(4) In the operation method described in (2) or (3) above, the membrane filtration flux at the time of (b) the liquid level lowering filtration step is (a) the membrane filtration flux at the time of the feed water filtration step. A method for operating a submerged membrane module, characterized by being low.
(5) In the operation method described in (4) above, (a) the filtration flow rate control means in the feed water filtration step is constant flow filtration, and (b) the filtration flow rate control means in the liquid level lowering filtration step is constant pressure filtration. A method for operating a submerged membrane module, comprising:

  According to the operation method of the submerged membrane module of the present invention, it is possible to operate while efficiently increasing the recovery rate, reducing the load on the membrane module, and suppressing clogging of the membrane.

  The embodiment of the method of the present invention will be described below with reference to FIGS. 1 and 2, taking as an example the case of water treatment using the submerged membrane module filtration device shown in FIG. 1. However, the present invention is not limited to the embodiments described below.

  FIG. 1 is a schematic flow diagram schematically showing an example of a submerged membrane filtration apparatus to which the method of the present invention is applied. A filtration membrane module 2 is immersed in the immersion tank 1. A raw water supply port is provided below the membrane filter module.

  (A) A feed water filtration step (hereinafter referred to as a feed water filtration step (a)) for sucking the membrane filtrate side of the filtration membrane module and taking out the membrane filtrate water while supplying raw water equal to or greater than the amount of the membrane filtrate water taken out )), The raw water is supplied to the immersion tank 1 from the raw water supply port through the raw water pipe 3, and the membrane filtrate is taken out by the suction pump 5 through the membrane module 2, the filtration valve 6, and the membrane filtrate pipe 4. In this step, the liquid level WL of the liquid in the immersion bath is kept constant or gradually rises by setting the amount of raw water supplied to be equal to or more than the amount of filtered water. After performing the feed water filtration step (a) for a predetermined time, the suction pump 5 is stopped, the filtration valve 6 is closed, and the feed water filtration step is stopped. In this step, membrane filtrate is obtained, and at the same time, the suspension in the raw water accumulates on the membrane, and the membrane becomes dirty.

  Therefore, after the feed water filtration step (a), (c) the membrane filtration is stopped and air is supplied to the raw water side of the membrane module to wash the filtration membrane module (hereinafter referred to as the “air washing step (c)”. .)I do. At this time, it is preferable to stop the water supply. In this air washing step (c), air supplied from the blower 10 is diffused as bubbles from the air diffuser disposed below the membrane module 2 through the air washing valve 12 and the air washing air pipe 11. At the same time before or after the air washing step (c), the backwash valve 9 is opened, and the backwash water is sent to the secondary side of the membrane module 2 through the backwash water pipe 7 by the backwash pump 8 to perform the backwash. You may implement the process (henceforth a backwashing process) to perform. By these, air and water collide with the membrane surface, the filtration membrane is swung, and suspended substances accumulated on the membrane surface and between the membranes are peeled off and removed. Are uniformly dispersed as a suspended substance.

  In this invention method, an air washing process (c) is performed after a feed water filtration process (a). The feed water filtration step (a) and the air washing step (c) may be repeated (repetition A in FIG. 2).

  After the feed water filtration step (a) and the air washing step (c), the feed water filtration step (a) is performed again, and then (b) the raw water supply amount is zero or less than the amount of membrane filtrate water. A liquid level lowering filtration step (hereinafter referred to as a liquid level lowering filtration step (b)) for lowering the liquid level in the immersion tank is performed by membrane filtration. In this step, the liquid level WL in the immersion tank is lowered by stopping the supply of the raw water or performing membrane filtration while supplying the raw water in an amount smaller than the amount of membrane filtration water.

  After the liquid level lowering filtration step (b), after performing the above-described air washing step (c), (d) a draining step (hereinafter referred to as draining step (d)) for discharging the raw water in the immersion bath to the outside of the immersion bath. ). In this step, the drain valve 14 is opened, and the liquid in the tank is drawn out of the immersion tank through the drain pipe 13. Due to the drainage of the liquid in the tank, the suspended matter dispersed in the liquid in the tank is discharged together with the liquid in the tank. After completion of the drainage step (d), in order to perform the feed water filtration step (a) again, a feed water step for feeding the raw water into the immersion tank through the raw water pipe 3 is performed, and then the feed water filtration step (a) Is resumed.

  An example of the process sequence of the operation process implemented by the method of the present invention is shown in FIG. 2 (process flow diagram). In the embodiment of FIG. 2, after repeatedly performing the feed water filtration step (a) and the air washing step (c), the feed water filtration step (a), the liquid level lowering filtration step (b), and the air washing step (c). The drainage step (d) is performed in this order. After that, water is supplied, the process returns to the water supply filtration step (a), and the operation is repeated (repeat B).

  The feed water filtration step (a) and the air washing step (c) may be performed once or repeatedly (repetition A). Moreover, you may perform a liquid level fall filtration process (b) between the feed water filtration process (a) and an air washing process (c). When the liquid level lowering filtration step (b) is performed in this manner, it is more preferable because a space for storing water above the upper end of the membrane module of the immersion tank can be minimized. The number of repetitions in the repetition A is preferably in the range of at most about several tens of times. By performing the air washing step (c) after the feed water filtration step (a), dirt accumulated in the membrane is once peeled off from the membrane, so that the dirt on the membrane is less than when the air washing step (c) is not performed. Accumulation can be reduced.

  When performing the feed water filtration step (a), it is important to supply raw water from the raw water supply port below the membrane module into the tank and supply a raw water amount equal to or greater than the amount of membrane filtered water. When the feed water filtration step (a) is performed after the air washing step (c), the liquid in the bath (w2) in the immersion bath below the upper end of the membrane module is again drawn to the membrane module side and filtered. At the same time, the suspended substance suspended in the liquid (w2) in the tank again adheres to the filtration membrane in the membrane module. However, since the raw water supply amount is equal to or greater than the membrane filtration water amount, the liquid (w1) in the immersion tank above the upper end of the membrane module is hardly attracted to the membrane module side, and the suspended suspension in the liquid (w1). The turbid substance remains floating in the immersion tank liquid (w1) above the upper end of the membrane module without being filtered.

  If the feed water filtration step (a) is continued, the liquid in the immersion tank near the membrane module below the upper end of the membrane module will eventually have a water quality equivalent to the raw water supplied. Suspended substances suspended in the immersion tank liquid (w1) above the upper end of the membrane module are turbid substances that have been peeled off by the air washing process and become very fine suspended substances. It keeps floating as it is. As a result, it is possible to perform membrane filtration with the dirt that should be accumulated on the membrane surface of the membrane module suspended in the upper part of the membrane module, so that the dirt load on the membrane surface can be reduced. It is possible to operate while preventing clogging of the membrane.

  In the liquid level lowering filtration step (b), the water accumulated in the immersion tank liquid (w1) above the upper end of the membrane module in the feed water filtration step (a) is stopped or the feed water amount is less than the membrane filtration water amount. As a result, the liquid level WL in the immersion bath is gradually lowered. By carrying out this step, the amount of drainage discharged from the immersion tank can be reduced and the recovery rate can be improved during the subsequent drainage step (d). At this time, since the liquid level WL in the immersion tank is lowered, water containing a large amount of suspended matter accumulated in the immersion tank above the upper end of the membrane module falls to the vicinity of the membrane module and is filtered by the membrane surface of the membrane module. Therefore, the load on the membrane temporarily increases. Therefore, in the liquid level lowering filtration step (b), it is preferable to lower the membrane filtration flux and temporarily reduce the membrane load as compared to the feed water filtration step (a).

  Since the time for performing the liquid level lowering filtration step (b) is as short as 1/10 compared with the time for the feed water filtration step (a), even if the membrane filtration flux is temporarily lowered, the average amount of membrane filtration water in the device is Since it does not significantly decrease, it is possible to realize efficient operation. As a method for lowering the membrane filtration flux, a constant flow rate that keeps the membrane filtration flow rate constant by using an inverter of the suction pump 5 or a constant flow valve installed in the middle of the filtrate piping 4 during the feed water filtration step (a). By filtering and maintaining the control value of the inverter and the constant flow valve at the control value at the end of the feed water filtration step (a) in the liquid level lowering filtration step (b), constant pressure filtration is performed. A method of naturally reducing the filtration flow rate is preferable because it can be most easily performed. By performing constant pressure filtration, it is possible to operate stably without increasing the operating differential pressure even in the liquid level lowering filtration step (b) in which water containing a large amount of suspended substances is filtered. The operation can be performed without the filtration differential pressure exceeding the limit differential pressure of the membrane module.

  Subsequent to the liquid level lowering filtration step (b), the air washing step (c) is performed, the suspended substance is suspended in the entire liquid in the immersion bath, and then in the immersion bath from the immersion bath in the drainage step (d). Drain the suspended material of 1a in the liquid.

  When performing the feed water filtration step (a), in order to operate while accumulating suspended substances in the tank above the upper end of the membrane module, compared with the water storage volume (V) in the immersion tank below the upper end of the membrane module. The ratio (I / V) of the difference (I) between the raw water supply amount and the membrane filtrate removal amount in 5 minutes from the start of the feed water filtration step (a) after the air washing step (c) is performed is 0.5 or more. It is preferable. Here, the amount of raw water supply and the amount of membrane filtrate removal are expressed by volume. The larger the volume of the difference (I), the faster the suspended material can be pushed up to the upper part of the membrane, the amount of suspended material filtered by the membrane module can be reduced, the load on the membrane module is reduced, and the membrane It becomes possible to suppress fouling. In particular, when the feed water filtration step (a) is started, suspended substances are dispersed throughout the immersion tank, so a large amount of raw water is fed immediately after the feed water filtration step (a) is started, and then the raw water feed amount It is also preferable to reduce the amount of water to the same level as the amount of membrane filtration water. However, if the amount (I) obtained by subtracting the amount of membrane filtration water from the amount of raw water supplied is too large, the liquid level rises too rapidly and the liquid in the tank tends to overflow from the immersion tank. A large amount is required, and the immersion tank becomes too large, which is not preferable in terms of apparatus cost. Therefore, compared with the water storage volume (V) in the immersion tank below the upper end of the membrane module, the feed water filtration step (a) after the start of the air washing step (c) The ratio (I / V) to the difference (I) is preferably at most 2 or less.

  Another way to operate while accumulating suspended substances in the upper part of the membrane is as follows: in the immersion tank below the upper end of the membrane module when the air washing step (c) is performed during the feed water filtration step (a). The ratio (H / V) of the liquid volume (H) in the immersion tank above the upper end of the membrane module to the water storage volume (V) is preferably 0.5 or more. The larger the ratio (H / V), the higher the liquid (w1) above the upper end of the membrane module, even when the suspended substance is uniformly suspended throughout the liquid in the immersion tank during the air washing step (c). Since more suspended solids migrate inside, when the feed water filtration step (a) is started, the suspended solids present in the liquid (w2) below the upper end of the membrane module are relatively less. Suspended substances in the liquid filtered by the module are reduced, and the load can be reduced. The larger the ratio (H / V), the more the load on the film can be reduced. However, if the ratio is too large, a large space above the immersion tank is required, which increases the immersion tank and is not preferable in terms of apparatus cost. Therefore, the ratio (H / V) described above is preferably 5 or less at most.

  The position of the raw water supply port for supplying raw water into the immersion tank may be lower than the upper end of the membrane module. In order to prevent the water supplied into the tank from being mixed with the immersion tank liquid (w1) above the upper end of the membrane module, it is not located near the upper end of the membrane module, but near or lower than the lower end position of the membrane module. It is also preferable that the raw water supply port is provided near the lowermost part of the immersion tank. Further, it is more preferable that a rectifying cylinder is provided at the water supply port so that the entire liquid in the immersion tank does not become a mixed flow by water supply, and the water supply is dispersed and supplied.

  Here, the water storage volume (V) in the immersion tank below the upper end of the membrane module is determined based on the volume of the immersed membrane module and the piping, members, and scattering in the tank from the volume in the immersion tank below the upper end of the membrane module. The volume excluding the volume of the trachea and the like, that is, the volume in the immersion tank where the raw water accumulates. Further, the raw water amount (H) in the immersion tank above the upper end of the membrane module is a volume obtained by removing the piping and members in the tank from the immersion tank volume above the upper end of the membrane module, that is, the raw water is accumulated. It is the amount of liquid in the immersion tank of the part.

  The upper end of the membrane module immersed in the immersion tank is the highest position in the vertical direction of the filtration membrane part where the filtration membrane is arranged as a membrane module and actually performs the filtration function in the membrane module It is. In the case of FIG. 1, the symbol P corresponds to the height of the upper end of the membrane module. Here, the filtration membrane disposed in the membrane module may be a hollow fiber membrane or a flat membrane, but the hollow fiber membrane is more preferable from the viewpoint of the cleaning property of the membrane and the membrane area ratio per installation area. The hollow fiber membranes are preferably arranged vertically, but may be arranged horizontally.

  Here, the membrane filtration flux is the amount of membrane filtration water per membrane area, and increasing the membrane filtration flux is important in increasing the efficiency of the membrane filtration device.

  The submerged membrane module device used in the present invention requires a space for storing water above the upper end of the membrane module. Further, the space in the immersion tank below the upper end of the membrane module is more preferably as small as possible without the membrane module, and the density of the membrane module per volume in the immersion tank is preferably higher. For this reason, it is more preferable not to provide a space at the lower part of the membrane module and to install the membrane module as close to the lower part of the immersion bath as possible.

  The feed water filtration step (a) is usually about 5 to 60 minutes, and the air washing step (c) is preferably about 5 to 120 seconds. In the draining step (d), it is preferable to discharge the entire amount of the liquid in the immersion tank, but a part of the liquid in the immersion tank may be discharged. In the liquid level lowering filtration step (b), the lower the liquid level, the higher the recovery rate, which is preferable. However, the liquid level is usually between 50 cm above the upper end of the membrane module and the center of the membrane module. It is preferable to reduce the surface.

  Here, the filtration membrane used in the membrane module is not particularly limited as long as it is a porous membrane having a filtration function, but is not limited to inorganic materials such as ceramics, polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer. , Polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, chlorotrifluoroethylene-ethylene copolymer, polyfluoride Examples thereof include a porous membrane containing at least one polymer selected from the group consisting of vinylidene chloride, polysulfone, cellulose acetate, polyvinyl alcohol, polyethersulfone, and vinyl chloride. Furthermore, a polyvinylidene fluoride (PVDF) porous film is preferable from the viewpoint of film strength and chemical resistance, and a polyacrylonitrile porous film is preferable from the viewpoint of high hydrophilicity and strong stain resistance. The pore diameter on the membrane surface is not particularly limited and may be a microfiltration membrane or an ultrafiltration membrane.

Example 1
The flow shown in FIG. 1 is obtained by using an apparatus in which one immersion type membrane module CFU-1015V (manufactured by Toray Industries, Inc.) provided with an external pressure PVDF ultrafiltration hollow fiber membrane is immersed in an immersion tank. The water treatment experiment was conducted under the following conditions. In this apparatus, the water storage volume (V) in the immersion tank below the upper end of the membrane module was 25 liters, and the raw water supply port was disposed below the lower end of the membrane module.

The water treated at the sewage treatment plant is supplied as raw water, and after performing the feed water filtration step (a) for 10 minutes by a constant flow rate filtration method with a filtration flow rate of 1.5 m ³ / (m ² · d), an air washing step (C) was carried out for 15 seconds, the feed water filtration step (a) was again carried out for 10 minutes, the air washing step (c) was carried out for 15 seconds, and the feed water filtration step (a) was carried out for 10 minutes. In the feed water filtration step (a), water was supplied in an amount 3 liters / minute greater than the amount of filtered water.

  After the final feed water filtration step (a), a liquid level lowering filtration step (b) was performed to lower the liquid level in the immersion tank to the upper end of the membrane module. During the liquid level lowering filtration step (b), the raw water was stopped, and constant pressure filtration was performed at the filtration pressure at the end of the feed water filtration step (a). After completion of the liquid level lowering filtration step (b), an air washing step (c) was performed for 30 seconds. At this time, a backwashing step was simultaneously performed. After the air washing step (c), the drainage step (d) was performed, and all the water in the immersion tank was discharged out of the immersion tank. Thereafter, the raw water was supplied into the immersion tank, and the raw water was filled up to the upper end of the membrane module. Then, a series of operation was repeated in the procedure of returning to the feed water filtration step (a) again.

  The initial membrane differential pressure after starting operation is 20 kPa at 25 ° C temperature corrected differential pressure, and the membrane differential pressure after operating for one month is 30 kPa at 25 ° C temperature corrected differential pressure. I was able to. The difference between the minimum differential pressure and the maximum differential pressure during the membrane filtration operation from the end of the drainage process (d) to the end of the next drainage process (d) was 5 kPa on average. The recovery rate was 95%.

  In this embodiment, the membrane filtration from the raw water supply volume for 5 minutes from the start of the feed water filtration step (a) after the air washing step (c) is performed on the water storage volume (V) in the immersion tank below the upper end of the membrane module. The ratio (I / V) of volume (I) minus water volume was 0.6.

(Comparative Example 1)
Using the same raw water and apparatus as in Example 1, the feed water filtration step (a) was performed for 30 minutes by a constant flow rate filtration method with a filtration flow rate of 1.5 m ³ / (m ² · d), and then the air washing step ( c) was carried out for 60 seconds. At the same time, a backwashing step was performed. After the air washing step (c), the drainage step (d) was performed, and all the liquid in the immersion tank was discharged out of the immersion tank. Thereafter, the raw water was supplied into the immersion tank, and the raw water was filled up to the upper end of the membrane module. Then, it returned to the feed water filtration step (a) again and repeated this series of operations. In the feed water filtration step (a), the same amount of filtered water was supplied.

  The initial membrane differential pressure when the operation was started was 20 kPa at a temperature corrected differential pressure of 25 ° C., and the differential pressure after one month of operation was 50 kPa at a temperature corrected differential pressure of 25 ° C., compared with Example 1. The differential pressure increased rapidly. Further, the difference between the minimum differential pressure and the maximum differential pressure during the membrane filtration operation from the end of the drainage step (d) to the end of the next drainage step (d) was 10 kPa on average. The recovery rate was 94%.

  The method of the present invention is applied when operating a water treatment apparatus in which a filtration membrane module is immersed in an immersion tank. More specifically, in the field of drinking water production in waterworks, industrial water, industrial ultrapure water, industrial water production such as food and medicine, sewage treatment fields such as municipal sewage purification and industrial wastewater treatment, and in front of seawater desalination reverse osmosis membranes Although it applies to the water treatment method using the immersion type membrane module used for a process etc., it is not restricted to these.

It is an apparatus general | schematic flowchart which shows an example of the immersion type membrane filtration apparatus with which this invention method is applied. It is a process flow figure showing one preferred embodiment of a process order which carries out the method of the present invention.

Explanation of symbols

1: immersion tank w1: liquid in immersion tank above upper end of membrane module w2: liquid in immersion tank below upper end of membrane module WL: liquid level (water level) of liquid in immersion tank
P: Horizontal plane at the upper end of the membrane module 2: Membrane module 3: Raw water piping 4: Membrane filtration water piping 5: Suction pump 6: Filtration valve 7: Backwash water piping 8: Backwash pump 9: Backwash valve 10: Blower 11: Air washing air pipe 12: Air washing valve 13: Drain piping 14: Drain valve

Claims (5)

  Operation of the filtration membrane module when the membrane filtration water is produced by the water treatment device in which the filtration membrane module is immersed in the immersion tank storing the raw water and the raw water supply port is provided below the upper end of the filtration membrane module (A) A feed water filtration step of sucking the membrane filtrate side of the filtration membrane module and taking out the membrane filtrate water while supplying raw water equal to or greater than the amount of the membrane filtrate water taken out, and (c) the membrane After the filtration is stopped and the air washing step of supplying air to the raw water side of the membrane module to wash the filtration membrane module is performed once or repeatedly, the (a) feed water filtration step is performed, and then (b) A liquid level lowering filtration step for lowering the liquid level in the immersion tank by performing membrane filtration with the raw water supply amount being zero or less than the amount of membrane filtration water, (c) the washing step, and (d) the immersion tank. The raw water inside is drained out of the immersion tank The method of operating submerged membrane module and draining process and performing in this order to.   The operation method according to claim 1, wherein the water supply volume (V) in the immersion tank below the upper end of the membrane module is (c) after the air washing step (a) the raw water supply amount in 5 minutes from the start of the feed water filtration step. The operation method of the submerged membrane module, wherein the ratio (I / V) of the difference (I) between the amount of the filtered water and the amount of the membrane filtrate is 0.5 or more.   2. The operation method according to claim 1, wherein (a) during the feed water filtration step, (c) when performing the air washing step, from the upper end of the membrane module with respect to the water storage volume (V) in the immersion tank below the upper end of the membrane module. A method for operating a submerged membrane module, wherein the ratio (H / V) of the amount of raw water (H) in the upper immersion tank is 0.5 or more.   The operation method according to claim 2 or 3, characterized in that (b) the membrane filtration flux at the time of carrying out the liquid level lowering filtration step is lower than the membrane filtration flux at the time of (a) carrying out the feed water filtration step. Operation method of submerged membrane module.   5. The operation method according to claim 4, wherein (a) the filtration flow rate control means in the feed water filtration step is constant flow filtration, and (b) the filtration flow rate control means in the liquid level lowering filtration step is constant pressure filtration. A method for operating the submerged membrane module.

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