JPWO2009008463A1 - Membrane separator and filtration method - Google Patents

Abstract

Air stagnant in the filtered water piping, which is an obstacle to stable membrane filtration operation, can be reliably discharged from the filtered water piping at the start of backwashing. An object of the present invention is to provide a membrane separation apparatus capable of greatly reducing waste, and a plurality of submerged membrane modules immersed in a treatment tank, and a filtrate water pipe extending from a filtrate outlet of the membrane module. In the membrane separation apparatus provided, in the middle of the filtrate pipe, a trunk pipe is formed by collecting filtrate pipes extending from each submerged membrane module, and an upward branch pipe for exhaust and exhaust means are provided in the trunk pipe. At the same time, a portion of a thick pipe having an inner diameter larger than that of other filtrate water pipes extending in the vertical direction is provided on the trunk pipe below the exhaust means.

Description

  The present invention relates to an apparatus for filtering water using a submerged membrane module. More specifically, the present invention relates to a membrane separation apparatus effective for suppressing an increase in transmembrane pressure difference during filtration.

  The membrane separation method has features such as energy saving, space saving, labor saving, and product quality improvement, and therefore, its use in various fields is expanding. For example, microfiltration membranes and ultrafiltration membranes can be applied to water purification processes for producing industrial water and tap water from river water, groundwater, and sewage treated water.

  The membrane module is roughly classified into a pressure membrane module and an immersion membrane module. The pressurized membrane module is a type of membrane module that introduces pressurized raw water into the module and performs filtration through the membrane surface. On the other hand, the submerged membrane module is a type of membrane module that performs filtration by immersing the membrane module in raw water in a treatment tank that is open to the atmosphere and suctioning the filtered water side.

  The pressure membrane module has the advantage that the filtration pressure can be set higher than that of the immersion type, so the amount of treatment per membrane area increases, so the number of membrane modules required for treatment can be reduced and the installation area can be reduced. Have. On the other hand, the submerged membrane module does not have a pressure-resistant cylindrical case and is used by immersing the membrane in the treated raw water, so it is excellent in discharging turbidity clogged between membranes, and even in highly turbid raw water There is an advantage that it can be filtered. Moreover, since the filtration method is simple and there are few incidental piping, there also exists an advantage which can reduce installation cost.

  As described above, the submerged membrane module performs the filtration by immersing the membrane module in the raw water in the treatment tank opened to the atmosphere and sucking the filtered water side. In the case of suction filtration, the inside of the filtrate pipe from the filtrate outlet of the submerged membrane module to the suction means (suction pump, etc.) that sucks the filtrate water side of the membrane module must be sucked during the filtration process. As a result, a negative pressure state or a state close thereto is obtained. Therefore, the air dissolved in the water in the raw water under atmospheric pressure is partially vaporized in the filtered water pipe that is in a negative pressure state to become a gas, and the air stays in the filtered water pipe.

  In addition, when raw water is membrane filtered using a submerged membrane module, removal objects such as turbidity and organic matter contained in the raw water accumulate on the membrane surface, resulting in membrane clogging phenomenon, increasing membrane filtration resistance. Eventually, filtration cannot be performed. Therefore, in order to maintain the membrane filtration performance, it is common to periodically stop the membrane filtration and perform physical cleaning. Usually, the filtration process and the physical cleaning process described above are automatically and repeatedly performed.

  For physical cleaning, air is blown into the lower part of the membrane module and the membrane is vibrated in water to shake off contaminants adhering to the membrane surface (air washing), or in the direction opposite to the filtration direction of the membrane module That is, there is reverse pressure water washing (back washing) that pushes water (washing water) such as membrane filtration water from the filtrate water side to the supply water side with pressure to eliminate contaminants adhering to the membrane.

  When performing this backwash, the wash water supplied from the filtered water side is press-fitted in the reverse flow direction at a pressure that allows the wash water to pass through the membrane surface of the membrane module. Under this general backwashing pressure level, if air stays in the filtrate piping, only the washing water permeates through the membrane from the inside of the membrane to the outside at the membrane surface of the membrane module. Air staying in the pipe cannot penetrate the membrane. Therefore, air accumulates on the filtered water side in the membrane module, and since the washing water does not permeate and is not backwashed in the portion where the air is accumulated, a membrane area that cannot be cleaned by backwashing is generated and spreads. . For this reason, there exists a problem that physical washing efficiency falls and the raise speed | rate of a membrane filtration differential pressure becomes quick.

  In order to avoid this problem and maintain the stable operation of the membrane module, the air remaining in the filtrate water pipe or the filtrate water side in the membrane module is removed from the filtrate water pipe before backwashing with the washing water. It is effective to discharge to As a specific means, in Patent Document 1, an exhaust means and an air vent valve are provided in communication with the upper end of the suction port of the membrane module, and the air vent valve is opened before backwashing, and the membrane module stays in the filtrate flow path of the membrane module. It is proposed to discharge the gas that is out of the system.

  However, it is difficult for the device of Patent Document 1 to exhaust all the remaining air out of the system simply by opening the air vent valve. Of course, by opening the air vent valve after the start of backwashing, the air in the filtered water pipe can be pushed out with the washing liquid and discharged out of the system. However, in the apparatus described in Patent Document 1, a plurality of membrane elements are arranged in the vertical direction, and filtered water obtained from these membrane elements is collected laterally. The air mixed in the filtered water obtained does not easily accumulate upward and tends to be dispersed in the filtered water piping. For this reason, it takes a considerable time to discharge the air in the filtered water pipe, and the wash water during that time is discharged outside the system through the air vent valve and is wasted. As a result, there is a problem that the supply amount of cleaning water increases.

  In addition, in the apparatus described in Patent Document 1, since filtered water obtained from a plurality of membrane elements arranged in the vertical direction is collected laterally, the membrane positioned above by the air accumulated during the filtration step The element may not be used for filtration. In that case, only a part of the membrane elements is used for membrane separation, and there is a problem that an efficient and stable membrane filtration operation cannot be performed.

  Therefore, in order to avoid wasting of washing water, which is one of the problems in Patent Document 1, in Patent Document 2, an air venting process is provided before entering the backwash process, and the air in the filtration pipe is stored in the air vent pipe. It has been proposed to discharge out of the system in the subsequent backwashing step.

  However, the apparatus of Patent Document 2 sends the washing water into the filtration membrane through the backwash water pipe in the air venting process, and forms a flow that circulates through the filtrate water pipe to the filtrate water tank. Along with the flow of water, the air is collected from the filtration pipe into the air vent pipe communicating with the air vent valve, and the air collected in the air vent pipe in the subsequent backwashing process is discharged out of the system. That is, by providing an air venting process, the operating rate of the entire operation is reduced, and, as in Patent Document 1, the cleaning water is also discharged out of the system together with the air, resulting in an increase in the supply amount of the cleaning water. There was a problem.

  On the other hand, in Patent Document 3, a T-tube is provided in the filtered water pipe, the lower direction of the T-shaped tube is connected to the filtered water tank, and the upper direction of the T-shaped tube is protruded upward from the immersion tank water surface and mixed into the filtered water. It has been proposed to discharge air out of the system. The apparatus of patent document 3 can isolate | separate the air mixed in filtrate water in the T-shaped tube part in filtrate water piping during a filtration process. However, since all the diameters of the filtrate pipes are the same, depending on the flow rate in the filtrate pipe, air may enter the filtrate pipe side connected to the filtrate tank or in the exhaust pipe connected to the upper part of the T-tube. Is filled with air, and there is a problem that air stays on the filtrate pipe side connected to the filtrate tank.

Moreover, in patent document 4, a falling part is provided in filtered water piping, the falling part is inclined with respect to a vertical line, an air reservoir part is provided, and the air in piping is extracted from the air reservoir part with a suction pump. It has been proposed to discharge out of the system. In the device of Patent Document 4, by inclining the falling part of the filtrate pipe, air mixed in the filtrate gathers on the upper wall surface of the fall pipe, and when it accumulates, it becomes a large bubble, Ascending along the upper wall surface of the downcomer and heading toward the air reservoir, air retention in the downcomer is prevented. However, when the air collected in the air reservoir is sucked by the suction pump, the filtered water in the filtered water pipe may be sucked together, and the filtered water is also discharged out of the system together with the air. There was a problem. In addition, if the suction pump is operated so that the filtrate in the filtrate pipe is not discharged out of the system, there is a possibility that not all the air in the filtrate pipe can be discharged. There was also a problem that hindered driving.
JP-A-8-332354 JP-A-11-207332 JP 2005-161218 A JP 2002-248303 A

  The present invention is a membrane separation apparatus in which a submerged membrane module is installed in a treatment tank to take out filtrated water, and backwashing is started for air staying in the filtrate water pipe which becomes an obstacle when performing stable membrane filtration operation. It is an object of the present invention to provide a membrane separation device that can be reliably discharged from filtered water piping sometimes, and that can greatly reduce waste of washing water when air is discharged from the piping.

In order to achieve the above object, the present invention has the following configuration.
(1) A membrane separation apparatus comprising a plurality of submerged membrane modules immersed in a treatment tank and a filtrate pipe extending from a filtrate outlet of the membrane module, wherein the membrane separator is in the middle of the filtrate pipe Is provided with a trunk pipe in which filtered water pipes extending from each submerged membrane module are combined, and the trunk pipe is provided with an upward branch pipe for exhaust and exhaust means, and the trunk pipe below the exhaust means is provided in the trunk pipe. A membrane separator provided with a portion of a thick pipe extending in the vertical direction and having a larger inner diameter than other filtrate water pipe portions.
(2) The membrane separation apparatus according to (1), wherein a portion below the exhaust unit in the upward branch pipe is a thick pipe.
(3) The membrane separation apparatus according to (1) or (2), wherein a pipe length of the thick pipe extending in the vertical direction is 0.2 m or more in total length.
(4) The inner diameter of the thick pipe extending in the vertical direction is the inner diameter at which the linear velocity of filtrate passing through the thick pipe portion during filtration is 0.2 m / s or less. ).
(5) The submerged membrane module according to any one of (1) to (4), wherein the submerged membrane module is disposed such that a membrane surface is in a vertical direction.
(6) Furthermore, a suction means for sucking the filtrate water side inside the submerged membrane module, and a water supply means for press-fitting washing water into the membrane module in a direction opposite to the liquid passing direction at the time of filtration are provided. The membrane separator according to any one of (1) to (5).
(7) A method of filtering water with the membrane separator according to any one of (1) to (6), wherein the linear velocity of filtered water passing through the portion of the thick pipe extending in the vertical direction is 0. A filtration method for performing filtration so that the pressure is 2 m / s or less.

    According to the present invention, the air staying in the filtrate water pipe can be reliably discharged from the filtrate water pipe at the start of backwashing in a short time, and the waste of the wash water when discharging the air in the pipe is greatly reduced. Can be reduced. For this reason, an economical membrane separation apparatus capable of stable operation over a long period of time can be provided.

It is a schematic block diagram which shows one embodiment of the membrane separator of this invention. It is a schematic block diagram which shows another one embodiment of the membrane separator of this invention. It is a schematic block diagram which shows one embodiment of the membrane separation apparatus (apparatus which does not have the part of a thick piping) outside this invention.

Explanation of symbols

1 treatment tank 2 membrane module 3 suction means (suction pump)
4 Water supply means (backwash pump)
5 Exhaust means (open / close valve, exhaust valve)
6 Filtrated water pipe 7 Thick pipe part 8 in main pipe Upward branch pipe 31 Filtered water valve 41 Backwash valve 42 Washed water pipe 43 Filtrated water storage tank

  The membrane separation apparatus of the present invention includes, for example, a plurality of submerged membrane modules immersed in a treatment tank, suction means for sucking the filtrate water side inside the membrane module, and a liquid passing direction during filtration. Water supply means for press-fitting the wash water into the membrane module in the reverse direction, and filtrate water piping for communicating between the filtrate outlet of the membrane module and the suction means. The filtrate pipe is provided with a trunk pipe in which the filtrate pipes extending from the respective submersible modules are arranged on the way, and the trunk pipe is provided with an upward branch pipe for exhaust and exhaust means (such as an on-off valve). . Further, the trunk pipe below the exhaust means is provided with a portion such as a thick pipe extending in the vertical direction. This thick pipe portion is a pipe portion in which the linear velocity of filtrate is lower than that of other filtrate water pipe portions. Usually, the pipe diameter (inner diameter) of the filtrate pipe is designed so that the linear velocity of filtrate at the time of filtration is about 1.0 m / s. The inner diameter of the pipe is designed so that the linear velocity of the filtrate passing through the thick pipe portion is a low flow rate of 0.2 m / s or less. As such a thick pipe, it is preferable that the pipe diameter (inner diameter) is obviously larger than the pipe diameter (inner diameter) of the other filtrate water pipe portions.

  Hereinafter, the membrane separation apparatus according to the present invention will be described with reference to FIGS. 1 and 2 schematically showing the membrane separation apparatus of one embodiment. However, the apparatus of the present invention is not limited to these embodiments.

    FIG. 1 is a schematic configuration diagram showing one embodiment of the membrane separation apparatus according to the present invention, and FIG. 2 is a schematic configuration diagram showing another embodiment of the membrane separation apparatus according to the present invention. In FIG. 1 and FIG. 2, there is a difference whether or not a portion below the exhaust means of the upward branch pipe 8 described later is a thick pipe, but the other configurations are the same. FIG. 3 is a schematic configuration diagram showing an embodiment of a membrane separation apparatus other than the present invention shown for comparison.

  The submerged membrane module 2 according to the present invention is a membrane module of a type that is installed by being immersed in a treatment tank 1 that is open to the atmosphere, and is filtered by sucking the filtered water side or by the difference in water level. A plurality of membrane modules (for example, 2 to several hundreds) are installed in the tank.

  The separation membrane applicable to this membrane module is a microfiltration membrane or an ultrafiltration membrane, and its shape is not particularly limited, and a flat membrane, a hollow fiber membrane, a tubular membrane, or any other shape can be used as appropriate. it can. However, it is preferable to use a hollow fiber membrane because membrane damage hardly occurs during backwashing and the membrane area per unit volume is high.

  The material of the membrane used for the microfiltration membrane and the ultrafiltration membrane is not particularly limited, but polyacrylonitrile, polyphenylene sulfone, polyphenylene sulfide sulfone, polyvinylidene fluoride, polypropylene, polyethylene, polysulfone, polyvinyl alcohol, cellulose acetate, ceramic, etc. It is preferable that at least one selected from the group consisting of these inorganic materials is included. Further, from the viewpoint of film strength and chemical resistance, a resin film mainly composed of polyvinylidene fluoride is more preferable.

  The pore diameter on the membrane surface is not particularly limited, but can be appropriately selected within the range of 0.001 μm to 1 μm.

  The hollow fiber membrane module is a membrane module having a structure in which ends of hollow fiber membrane bundles in which several hundred to tens of thousands of hollow fiber membranes are bundled are bonded, and is roughly divided into the following two types. First, the hollow fiber membranes are bonded to each other with the end surfaces of the hollow fiber membranes open at one end, and the hollow fiber membranes are bonded to each other with the end surfaces of the hollow fiber membranes closed at the other end. Type. The other is a type in which the hollow fiber membranes are bonded to each other with both end surfaces of the hollow fiber membranes open. Any type of module may be used in the present invention. In addition, the immersion type membrane module 2 shown in FIG. 1 adheres and fixes the hollow fiber membranes in a state where the end surfaces of the hollow fiber membranes are opened at one end (upper end side in the figure), and the other end (see FIG. 1). The bottom end side of each of the hollow fiber membranes is bonded in a closed state. Furthermore, in the embodiment shown in FIG. 1, the hollow fiber membrane is not bonded integrally on the lower end side of the module, but the hollow fiber membrane is divided into a plurality of small bundles and separated from each other. Each is glued. By configuring in this way, the hollow fiber membrane can be shaken moderately up and down and left and right during the filtration process, and the suspension substance can be prevented from adhering to the membrane surface. Can be improved.

  There are no particular restrictions on the adhesive used to bond and fix the both ends of the hollow fiber membrane bundle with an adhesive, but thermosetting resins such as epoxy resins and urethane resins are generally used.

  In addition, the adhesive fixing portions formed on both ends of the hollow fiber membrane bundle are connected via a large number of hollow fiber membrane portions existing between the hollow fiber membrane bundles, and the hollow fiber membranes are connected to the multiple hollow fiber membrane portions. The membranes are arranged in parallel, and the membrane filtration function is exhibited in this part. The multiple hollow fiber membrane bundles may have a structure in which no reinforcing member is interposed, or may have a structure in which a reinforcing means is interposed. As a structure including the reinforcing means, for example, about 1 to 30 cylindrical stays (metal rods, etc.) are arranged on the outer periphery or inside of the hollow fiber membrane bundle, and the adhesive fixing parts are also connected by the stays. Structure. Further, a porous plate material such as a net may be installed so as to cover the outer periphery of the hollow fiber membrane bundle.

  The submerged membrane module may be placed vertically, that is, the membrane filtration operation may be performed by arranging the membrane surface in the vertical direction (in the case of a hollow fiber membrane module, the longitudinal direction of the hollow fiber membrane is substantially vertical). However, the membrane filtration operation may be performed by placing horizontally, that is, the membrane surface is in the horizontal direction (in the case of a hollow fiber membrane module, the longitudinal direction of the hollow fiber membrane is substantially horizontal). However, it is preferable to install the membrane module vertically so that the filtrate outlet is on the upper side in that the amount of air required for air washing (air washing) can be reduced.

  A suction means 3 is connected to the submerged membrane module 2 as described above in order to suck the filtrate side in the module. A suction pump is generally used as the suction means 3. Further, in order to backwash the submerged membrane module 2, a water supply means 4 for press-fitting the washing water into the membrane module in the direction opposite to the liquid passing direction at the time of filtration is also provided. As the water supply means 4, a backwash pump is generally used.

  The suction means 3 is connected by a filtrate water pipe 6 so as to communicate with the filtrate water side of the membrane module 2. The filtrate water pipe 6 is connected to the filtrate water outlet of the submerged membrane module 2 and includes a trunk pipe that collects the filtrate water pipes extending from each membrane module. The trunk pipe is connected with an upward branch pipe and an exhaust means 5 (open / close valve, exhaust valve) for discharging the gas remaining in the filtrate pipe 6 to the outside of the piping system at the start of backwashing. In addition, the main pipe below the exhaust means 5 is provided with a thick pipe portion 7 extending in the vertical direction. In the present invention, the vertical direction includes not only a completely vertical (vertical) vertical direction but also a slightly inclined vertical direction (substantially vertical direction). The inclination angle at this time is preferably up to 45 degrees. If the pipe is provided at an inclination angle greater than this, since the movement of the air that is separated from the filtrate water at the thick pipe portion 7 and directed to the upward branch pipe 8 is hindered, the separation of the filtrate water and the air at the thick pipe portion 7 is prevented. Does not proceed efficiently. Moreover, the part of thick piping means the part with a relatively large internal diameter in filtrate water piping.

  The on-off valve and the exhaust valve provided as the exhaust means 5 are opened only for a certain time from the start of the reverse destination where the wash water is pressed in the reverse flow direction for backwashing. The exhaust unit 5 may be an exhaust unit that exhausts only air during pressurization instead of the on-off valve and the exhaust valve. Examples of the exhaust means for discharging only air at the time of pressurization include a check valve that closes when the inside of the pipe is decompressed and opens when the inside of the pipe is pressurized and discharges only air, and a hydrophobic membrane. However, if the pressure loss at the time of air discharge is high, air staying in the filtered water pipe at the start of backwashing will easily flow to the membrane module side. preferable.

  The air generated by the negative pressure in the filtered water pipe during the filtration process stays in the filtered water pipe at the start of the reverse flow. The water is pressed into the branch pipe 8 upward from the branch portion and discharged through the exhaust means 5.

  Here, in the conventional submerged membrane filtration apparatus shown in FIG. 3 (when there is no part of the thick pipe), the air staying in the filtrate pipe moves along with the flow of the filtrate, and the whole filtrate pipe It diffuses and stays. Therefore, in order to exhaust most of the air in the filtrate water pipe from the filtrate water pipe 6 through the upward branch pipe 8 and the exhaust means 5 at the start of the backwashing process, the exhaust means 5 is left for a considerable time (for example, (It must be open for about 10 seconds). Further, since the cleaning water is discharged from the exhaust means 5 simultaneously with the air when the exhaust means 5 is open, the wash water injected at this time does not contribute to the cleaning of the membrane module and is wasted. As a result, a large amount of cleaning water is required to clean the submerged membrane module 2.

  On the other hand, in the submerged membrane filtration apparatus of the present invention shown in FIGS. 1 and 2, the thick pipe portion 7 is provided on the trunk pipe extending in the substantially vertical direction on the lower side of the exhaust means 5. In the case of FIG. 1, the upward branch pipe 8 below the exhaust means 5 is also a thick pipe. The thick pipe has a larger pipe diameter (inner diameter) than the pipe diameter (inner diameter) of other filtrate water pipes, like the thick pipe portion 7 provided in the main pipe.

  In the membrane filtration device of the present invention having such a structure, air generated by the negative pressure in the pipe during the filtration step moves in the filtrate water pipe 6 in accordance with the flow of the filtrate water. When passing, the flow velocity in the pipe temporarily decreases, the air and filtered water are separated in the vertical direction, and most of the gas in the pipe gathers and stays in the upward branch pipe 8 below the exhaust means 5. Therefore, when the exhaust means 5 is opened at the start of the backwash process and the washing water is started to be press-fitted, the staying air in the filtrate water pipe is quickly discharged from the filtrate water pipe. Can be greatly shortened. At this time, since air and filtered water are separated and air is concentrated in the vicinity of the exhaust means 5, the air is preempted from the exhaust means 5, and the washing water is discharged following the air discharge. Can be minimized.

  When the thick pipe portion 7 is not a vertically extending pipe, that is, in a horizontal direction or an oblique direction close thereto, the filtered water flowing through the thick pipe portion 7 flows vertically in the pipe during the filtration process. Even if the filtered water and the air are separated in the direction, the separated air is not easily concentrated in the upward branch pipe 8 below the exhaust means 5. For this reason, the time required for exhausting the air by opening the exhaust means 5 cannot be sufficiently shortened, and as a result, the amount of washing water flowing out through the exhaust means 5 tends to increase.

  Furthermore, in the aspect shown in FIG. 1, FIG. 2, it is the structure which returns the discharged | emitted wash water to a processing tank. With such a configuration, it is possible to prevent the wash water that is injected to wash the membrane module from being discharged out of the system, and to greatly reduce the amount of wasted wash water.

  Moreover, in the submerged membrane filtration apparatus shown in FIGS. 1 and 2, filtered water and air are separated in the vertical direction at the thick pipe portion 7, and the separated air is accumulated in the upward branch pipe 8 during the filtration process. At this time, when the volume of the separated air exceeds the pipe internal volume in the upward branch pipe 8, the air stays in the thick pipe portion 7 and diffuses throughout the main pipe. Therefore, as shown in FIG. 1, it is preferable that the upward branch pipe 8 below the exhaust means 5 is also a thick pipe. By providing a thick pipe portion in the upward branch pipe 8 as well, a sufficient volume for storing the air separated in the thick pipe portion 7 is secured, and air can be prevented from staying in the thick pipe portion 7. . In this case, the thick pipe portion 7 and the upward branch pipe 8 of the filtrate water pipe may be a continuous thick pipe.

  The said effect is show | played in the part 7 of the thick piping of the trunk piping from which filtered water flows down at the time of filtration. For this function and effect, it is preferable that the thick pipe portion 7 extends in the substantially vertical direction without being bent horizontally in the middle of a distance of less than 0.2 m. That is, the length of the thick pipe portion 7 extending in the vertical direction is preferably 0.2 m or more, and more preferably 0.5 m or more continuously in the pipe direction.

  Certainly, even when the length of the thick pipe portion 7 is as short as less than 0.2 m, or even when the pipe is folded in the horizontal direction with a length of less than 0.2 m, filtered water and air in the thick pipe portion 7. Can be separated. However, in order to reduce the water production cost, it is required to increase the filtration flux. When the filtration flux increases, the air easily moves along with the flow of the filtrate. Therefore, it becomes difficult to completely separate the air and the filtered water, the air moves to the entire trunk pipe, and it becomes difficult to sufficiently collect the air in the pipe. Therefore, in the present invention, the length of the thick pipe portion 7 is set to 0.2 m or more, and further to 0.5 m or more in order to achieve the above-described effects even in an operation where the filtration flux is large. preferable. The same applies to the case where the linear velocity of the filtered water at the filtration step in the thick pipe portion 7 is faster than 0.2 m / s.

  On the other hand, the portion extending vertically from the branch point (the position where the upward branch tube branches) in the filtrate pipe 6 is a thick pipe, and the air generated by the negative pressure during the filtration process is passed vertically with the filtrate water. It may be separated. However, the length of the thick pipe in the vertical direction is sufficient if it has the required length in the system. Therefore, if the length of pipe is longer than necessary, the disadvantage is that the equipment cost increases by making the pipe thicker. There is. Therefore, the upper limit is preferably 2 m or less.

  In the present invention, it is only necessary to provide a vertical pipe portion 7 in the filtrate pipe on the lower side of the exhaust means 5, so that the thick pipe extending in the lateral direction follows the thick pipe portion in the vertical direction. In addition, a pipe having a normal diameter extending in the horizontal direction or the vertical direction may be provided. However, as described above, if the portion other than the thick pipe portion 7 disposed for separating the filtrate and air is made a thick pipe, there is a demerit that the equipment cost is increased by making the pipe thick, It is preferable to arrange a pipe having a normal diameter.

  On the other hand, the vertical pipe length of the upward branch pipe 8 is preferably 0.15 m or more and 0.5 m or less. When the length of the upward branch pipe 8 is as short as less than 0.15 m, it is not possible to secure a sufficient volume for storing the air separated from the filtrate in the thick pipe portion 7, so that air is It is mixed and diffuses and stays in the whole trunk pipe. Further, if the length of the upward branch pipe 8 is longer than 0.5 m, it is possible to secure a sufficient volume for storing the air separated from the filtrate in the thick pipe portion 7, but the exhaust means at the start of the backwash process When 5 is opened and the washing water is started to be injected, an extra pressure is required to exhaust air from the exhaust means 5 by the amount of the head pressure applied in the pipe. Furthermore, by making the length of the upward branch pipe 8 to be 0.5 m or more, the exhaust means 5 is opened at the start of the backwash process, the washing water starts to be injected, and the air accumulated in the upward branch pipe 8 at the filtration process As a result, the distance for discharging the air through the exhaust means 5 becomes longer, and extra cleaning water for discharging the air is used, so that the membrane cannot be sufficiently cleaned within the specified time.

  Further, as shown in FIG. 1, when the upward branch pipe 8 is also made of a thick pipe and connected to the thick pipe portion 7, the total length in the pipe direction (the length of the upward branch pipe 8 + the thick pipe portion 7) is 0. .35 m or more is preferable, and 0.65 m or more is more preferable. In addition, it is preferable that the internal diameter of these thick piping is a diameter from which the linear velocity of the filtered water which passes the part 7 of thick piping at the time of filtration will be 0.2 m / s or less.

  Furthermore, in order to make sure that air and filtered water are reliably separated in the thick pipe portion 7, a part or all of the thick pipe portion 7 is made of a transparent material, and the flow in the pipe is reduced. It is preferable to be visible from the outside. Examples of the transparent member include transparent resin and transparent glass. The upward branch pipe 8 below the exhaust means 5 is also preferably made of a transparent material.

  Next, a method of performing filtration and then backwashing in the membrane separation apparatus of the present invention will be described taking the case of using the membrane separation apparatus of FIG. 1 as an example.

  In the filtration step, the filtrate water valve 31 is opened, the filtrate water is taken out from the membrane module 2 by the suction action by the suction means 3, and is sent to the filtrate water storage tank 43 through the filtrate water pipe 6. Here, in the apparatus according to the present invention, when the filtrate passes through the thick pipe portion 7 in the trunk pipe, the linear velocity of the filtrate becomes a low flow rate. Therefore, the air mixed in the filtered water is separated from the downward flow of the filtered water and rises, and moves to the upward branch pipe 8 below the exhaust means 5. As a result, air concentrates and stays in the upward branch pipe 8 below the exhaust means 5.

  In order to stop the filtration, the suction means 3 is stopped and the filtered water valve 31 is closed.

  Subsequently, the exhaust means 5 is opened, and at the same time, the backwash valve 41 in the middle of the wash water pipe 42 is opened, and the water feed means 4 is operated to feed the wash water in the reverse flow direction. By this pumping of the washing water, the air concentrated in the upward branch pipe 8 below the exhaust means 5 is discharged from the filtrate pipe through the exhaust means 5. Therefore, the time during which the exhaust means 5 is opened can be greatly shortened (for example, can be shortened to about 3 seconds), and most of the gas discharged first through the exhaust means 5 is air. In addition, if the upward branch pipe 8 below the exhaust means 5 is transparent, the point in time when the air has escaped from the exhaust means 5 can be visually recognized from outside the pipe, so that the exhaust means 5 can be quickly closed. An operation in which no cleaning water is discharged from the exhaust means 5 is also possible. Moreover, since the front-end | tip part of the upward branch pipe 8 is opened above the processing tank, the wash water discharged | emitted from filtrate water piping is supplied in a processing tank. In addition, if the exhaust means 5 is closed after the time which can discharge the air in piping passes, cleaning liquid will be sent to the filtrate side of a membrane module, and the back washing in a membrane module will be performed.

The present invention will be described in detail using the following examples. In Examples 1 to 4, a membrane separation apparatus in which the upward branch pipe 8 shown in FIG. On the other hand, in Comparative Example 1, the membrane separation apparatus shown in FIG. 3 was used. Each membrane separator was constructed by connecting and immersing five immersion membrane modules (effective membrane length 1 m, effective membrane area 25 m ² ) having the following structure in series in a treatment tank.

Immersion membrane module:
-8000 hollow fiber membranes and hollow fiber membranes made of polyvinylidene fluoride with an outer diameter of 1.0 mm and a nominal pore diameter of 0.01 mm are bonded and fixed to the module components at the upper end and divided into a plurality of small bundles at the lower end While separating them from each other, each small bundle is bonded.Each hollow fiber membrane is open on the upper bonding end side and sealed on the lower bonding end side.A module cap with a permeate outlet is provided on the upper bonding portion. Arrangement <Example 1>
Using the membrane separation apparatus in which the length of the thick pipe portion 7 (inner diameter: 2.5 times the inner diameter of the other filtrate water pipe 6 portion) of the membrane separation apparatus shown in FIG. The membrane module was filtered at a filtration flux of 0.5 m / d. As a result, the linear velocity of the filtrate water in the trunk pipe (the upstream part of the thick pipe part 7 of the filtrate water pipe 6) was 1.2 m / s, but when it flowed into the thick pipe part 7 As a result, the linear velocity of filtered water became 0.08 m / s. Moreover, as a result of visually confirming the flow of filtrate and air, the air dissolved in the filtrate was separated at the thick pipe portion 7 and accumulated in the upward branch pipe 8. Therefore, it can be seen that if the wash water is pressed in the reverse flow direction at the start of the back wash, the air accumulated in the upward branch pipe 8 can be discharged by the press-fitting of the wash water. However, since the pipe length of the thick pipe portion 7 for separating the filtered water and the air was short, there was air that flowed downstream along with the filtered water, which was dispersed in the downstream pipe. It stayed.

<Example 2>
The filtration operation was performed in the same manner as in Example 1 except that the length of the thick pipe portion 7 was 0.2 m. As a result, the linear velocity of filtered water in the trunk pipe was 1.2 m / s, but when it flowed into the portion 7 of the thick pipe, the linear velocity of filtered water became 0.08 m / s. Moreover, as a result of visually confirming the flow of filtrate and air, the air dissolved in the filtrate was separated at the thick pipe portion 7 (and separated and accumulated in the upward branch pipe 8. On the other hand, the downstream pipe Therefore, when the washing water was injected in the reverse flow direction at the start of the backwashing, the air accumulated in the upward branch pipe 8 was efficiently removed by the injection of the washing water. It turns out that it can discharge.

  And since the air dissolved in the filtered water was separated at the thick pipe portion 7 and accumulated only in the upward branch pipe 8, even if the filtration flux was 0.5 m / d, It was found that if the portion 7 was at least 0.2 m, the filtered water and air were reliably separated.

<Example 3>
Example 1 except that the length of the thick pipe portion 7 (inner diameter: 2.5 times the inner diameter of the other filtrate water pipe 6 portion) is 0.3 m and the filtration flux is 1.0 m / d. The filtration operation was performed in the same manner. As a result, the linear velocity of filtered water in the trunk pipe was 2.42 m / s, but when it flowed into the thick pipe portion 7, the linear velocity of filtered water became 0.17 m / s. Moreover, as a result of visually confirming the flow of filtrate and air, the air dissolved in the filtrate was separated at the thick pipe portion 7 and accumulated in the upward branch pipe 8. Therefore, it can be seen that if the wash water is pressed in the reverse flow direction at the start of the back wash, the air accumulated in the upward branch pipe 8 can be discharged by the press-fitting of the wash water. However, because the pipe length of the thick pipe portion 7 for separating the filtered water and air was short, there was air that flowed downstream along with the filtered water, which was dispersed in the downstream pipe. It stayed.

<Example 4>
A filtration operation was performed in the same manner as in Example 3 except that the length of the thick pipe portion 7 was 0.5 m. As a result, the linear velocity of filtered water in the trunk pipe was 2.42 m / s, but when it flowed into the thick pipe portion 7, the linear velocity of filtered water became 0.17 m / s. Moreover, as a result of visually confirming the flow of filtrate and air, the air dissolved in the filtrate was separated at the thick pipe portion 7 and accumulated in the upward branch pipe 8. On the other hand, air dispersed and staying in the downstream piping was not observed. Therefore, it can be seen that if the wash water is press-fitted in the back flow direction at the start of the back wash, the air accumulated in the upward branch pipe 8 can be efficiently discharged by the press-fitting of the wash water.

  And since the air dissolved in the filtered water was separated at the portion 7 of the thick pipe and accumulated only in the upward branch pipe 8, even if the filtration flux was 1.0 m / d, It has been found that if the portion 7 is at least 0.5 m, the filtered water and air are reliably separated.

<Comparative example 1>
Using the membrane separation apparatus shown in FIG. 3 having no thick pipe portion, the filtration operation of the submerged membrane module was performed at a filtration flux of 0.5 m / d. As a result, the linear velocity of filtrate in the filtrate pipe 6 was constant at 1.2 m / s. Moreover, as a result of visually confirming the flow of filtrate and air, a part of the air dissolved in the filtrate was collected in the upward branch pipe 8, but the filtrate and air were separated in the filtrate pipe. It was not performed, and most of the air was accompanied by the filtered water and flowed downstream, and was dispersed and stayed in the downstream piping. Therefore, even if the washing water is pressed in the reverse flow direction at the start of the backwashing, the air cannot be discharged efficiently, and the membrane surface cleaning by the backwashing is not sufficiently performed, which makes it difficult to perform a stable filtration operation. .

  The membrane separation apparatus provided with the submerged membrane module of the present invention can be applied to water treatment, sewage treatment, pretreatment for seawater desalination, industrial wastewater treatment, and the like. The scope of application is not limited to these.

Claims (7)

  A membrane separation apparatus comprising a plurality of submerged membrane modules immersed in a treatment tank and a filtrate water pipe extending from a filtrate outlet of the membrane module, each in the middle of the filtrate water pipe, The main pipe is provided with a main pipe that collects filtrate water pipes extending from the submerged membrane module, and the main pipe is provided with an upward branch pipe for exhaust and exhaust means, and the main pipe on the lower side of the exhaust means has a vertical direction. The membrane separation apparatus is provided with a thick pipe portion having an inner diameter larger than that of other filtrate water pipe portions.   The membrane separation apparatus according to claim 1, wherein a portion below the exhaust unit in the upward branch pipe is a thick pipe.   The membrane separation apparatus according to claim 1 or 2, wherein a pipe length of the thick pipe extending in the vertical direction is 0.2 m or more in total length.   The internal diameter of the said thick piping extended in the said up-down direction is an internal diameter in which the linear velocity of the filtrate water which passes through the part of this thick piping at the time of filtration becomes 0.2 m / s or less. Membrane separator.   The membrane separator according to any one of claims 1 to 4, wherein the submerged membrane module is arranged such that a membrane surface is in a vertical direction.   The apparatus further comprises suction means for sucking the filtrate water side inside the submerged membrane module, and water supply means for press-fitting wash water into the membrane module in a direction opposite to the liquid flow direction during filtration. The membrane separation apparatus in any one of 1-5.   A method for filtering water with the membrane separation device according to any one of claims 1 to 6, wherein a linear velocity of filtered water passing through a portion of the thick pipe extending in the vertical direction is 0.2 m / s or less. Filtration processing method to perform filtration.

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