JP2009241043A - Backwashing method of membrane filter apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backwashing method of a membrane filter apparatus capable of effectively removing an adhesion substance on the surface of a membrane not perfectly removed by pressure washing and capable of being stably operated for a long period. <P>SOLUTION: The membrane filter apparatus is partitioned into a raw water chamber 1A and a treatment water chamber 1B, has a structure wherein a filter cylinder 7 opened on the side of the treatment water chamber 1B is installed to filter ascending raw water, and is constituted so that a washing water supply pipe 4 is connected to the treatment water chamber 1B and a washing wastewater discharge pipe 6 is connected to the raw water chamber 1A. The backwashing method of this membrane filter apparatus has a first membrane washing process of closing an on-off valve 61 of the washing wastewater discharge pipe 6 in a state that the treatment water chamber 1B is filled with washing water and, after air is injected to pressurize the washing water, opening the on-off valve 61 to transmit the washing water through the membrane at a stroke to backwash the membrane and a second membrane washing process of supplying the washing water to the treatment water chamber 1B in a state that the on-off valve 61 is opened after the first membrane washing process to transmit the same through the membrane at a flow velocity lower than that in the first membrane washing process to backwash the membrane. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for backwashing a membrane filtration device, and more specifically, a membrane capable of effectively removing adhering substances on the membrane surface that cannot be removed even by pressure washing, and capable of stable operation over a long period of time. The present invention relates to a backwashing method for a filtration device.

  Conventionally, the inside of a filtration tank is partitioned into a raw water chamber and a treated water chamber by a partition plate, and a large number of filter cylinders provided with a bag-like membrane that penetrates the partition plate and opens to the treated water chamber side are installed in the raw water chamber. A membrane filtration device having a structure in which raw water entering a raw water chamber is filtered through a membrane and collected as treated water in the treated water chamber is known (Patent Documents 1 and 2).

  In such a membrane filtration apparatus, the clogging substance contained in the raw water clogs the membrane surface over time and causes clogging. For this reason, it is necessary to reverse the washing operation by separating the clogging substances from the membrane surface by flowing the washing water in the direction opposite to that during filtration, and performing the washing operation alternately with the filtration operation to periodically restore the function of the membrane. is there. For example, when seawater is pumped and transferred into a ballast tank of a ship, if the pumped seawater is filtered by a membrane filtration device, particles gradually accumulate on the membrane surface and eventually block the eyes. Most of these particles are inorganic substances such as Si, Al, Fe, etc., and are thought to be derived from the seabed mud. For this reason, it is necessary to exfoliate the particles deposited on the film surface by periodically performing a backwash operation.

On the other hand, in a membrane filtration device that filters seawater into ballast water, the membrane filtration process is performed on a ship, so the amount of washing water during backwash operation is limited. For this reason, it is desirable to backwash effectively with a small amount of washing water.
Japanese Patent Laid-Open No. 5-245313 JP 2006-15296 A

  As a method for effectively performing backwashing of a membrane in such a membrane filtration device with a small amount of washing water, the inventor has introduced air into a treated water chamber filled with washing water with a predetermined pressure in a state where the inside of the filtration tank is sealed. After injecting until it reaches the pressure, the raw water chamber side is opened and the washing water is discharged at once, allowing the washing water to permeate at a high speed in the direction opposite to that during filtration, and removing the adhered substances on the membrane surface. Are trying. This method is extremely effective in removing clogging of the film due to adhered substances with a small amount of washing water.

  However, it has been found that even with this backwashing method, the adhering substance cannot be completely removed, and a part of the adhering substance may remain attached to the film surface. The pressure backwash is usually repeated a plurality of times, and this adhered substance remains without being removed even if the pressure backwash is repeated a plurality of times.

  As shown in FIG. 7, the surface of the film 100 has a pleated shape in which a large number of folds are formed so that peaks and valleys are alternately arranged to increase the surface area. Mud and sand (silt) 200 in the raw water adheres to 101 (portion that becomes a valley when viewed along the filtration direction), and this cannot be removed even by pressure backwashing and is gradually accumulated. There was found.

  This is because, in the pressure cleaning that instantaneously permeates high-pressure cleaning water during backwashing, instantaneous cleaning water is provided near the tip of the pleat peak 102 (the peak when viewed along the filtration direction). Since the flow of water concentrates and the film surface in the valley portion 101 of the pleat becomes a plane substantially parallel to the flow of the washing water, the cleaning passes through the holes in the vertical direction from the film surface in the valley portion 101. This is probably because the water flow is not sufficiently formed, the force for removing the adhered substances at this site is insufficient, and the silt 200 does not completely escape. Therefore, when a normal filtration operation is performed in a state where such a silt 200 is accumulated, the membrane is rapidly clogged, resulting in an increase in the transmembrane pressure difference, and a long-term stable operation cannot be performed. was there.

  Accordingly, the present invention provides a method for backwashing a membrane filtration device that can effectively remove adhered substances on the membrane surface that cannot be removed even by pressure washing, and can perform stable operation over a long period of time. This is the issue.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
The inside of the filtration tank is partitioned into a raw water chamber and a treated water chamber by a partition plate, and a number of filter cylinders provided with a bag-like membrane that penetrates the partition plate and opens to the treated water chamber side in the raw water chamber. The raw water that has been installed and enters the raw water chamber is filtered by the membrane while flowing upward in the raw water chamber, and has a structure in which the raw water rises in the filter cylinder as treated water and is collected in the treated water chamber, In the backwashing method of the membrane filtration apparatus, the cleaning water supply pipe is connected to the treated water chamber via an on-off valve, and the cleaning water discharge pipe is connected to the raw water chamber via the on-off valve.
After the treatment water chamber is filled with washing water, the on-off valve of the washing drainage pipe is closed, air is injected into the treatment water chamber to pressurize the washing water, and then the on-off valve of the washing drainage discharge pipe is opened. A first membrane cleaning step for performing reverse cleaning of the membrane by opening the pressurized cleaning water through the membrane at a stretch by opening,
After the first membrane cleaning step, by supplying cleaning water from the cleaning water supply pipe to the treated water chamber with the opening / closing valve of the cleaning drainage pipe opened, the first membrane cleaning step And a second membrane cleaning step of performing reverse cleaning of the membrane by allowing the cleaning water to pass through the membrane at a low flow rate.

(Claim 2)
The backwashing method for a membrane filtration device according to claim 1, wherein a flow rate of the washing water in the second membrane washing step is 1 to 3 m / s.

(Claim 3)
The backwashing method for a membrane filtration device according to claim 1 or 2, wherein the cleaning water supply time in the second membrane cleaning step is 10 to 90 seconds.

(Claim 4)
4. The method of backwashing a membrane filtration device according to claim 1, wherein the membrane is a pleated membrane.

(Claim 5)
The backwashing method for a membrane filtration device according to any one of claims 1 to 4, wherein in the first membrane cleaning step, fine bubbles are introduced into the cleaning water in the treated water chamber.

(Claim 6)
The method for backwashing a membrane filtration device according to any one of claims 1 to 5, wherein the raw water is ballast water to be supplied to a ballast tank of a ship.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view showing an example of a membrane filtration apparatus suitable for carrying out the backwashing method of the present invention.

  In the figure, 1 is a filtration tank. The filtration tank 1 is preferably formed in a cylindrical bowl shape, and the inside is partitioned by a partition plate 11 into a raw water chamber 1A into which raw water is introduced and a treated water chamber 1B in which treated water after filtration is collected. Has been. A raw water supply port 12 is provided at the lower side of the raw water chamber 1A, and a treated water discharge port 13 is provided at the upper portion of the treated water chamber 1B.

  A raw water supply pipe 2 is connected to the raw water supply port 12, and a supply path of the raw water can be opened and closed by an on-off valve 21. In the present invention, as raw water, ballast water (seawater or fresh water) for supplying to a ballast tank of a ship is preferably used. When seawater is used as the ballast water, the substances to be filtered include zooplankton, phytoplankton, microorganisms, elements such as Si, Al, and Fe, inorganic substances such as oxides and chlorides, and other matters. There are suspended substances (SS), gel-like substances and the like.

  A treated water discharge pipe 3 is connected to the treated water discharge port 13, and a discharge path for treated water can be opened and closed by an on-off valve 31.

  Further, the treated water discharge port 13 is connected with a washing water supply pipe 4 for supplying washing water for backwashing the filtration membrane, and a supply path for the washing water can be opened and closed by an on-off valve 41. A cleaning water supply pump 42 is interposed in the cleaning water supply pipe 4 to supply cleaning water in the cleaning water tank 43 from the processing water discharge port 13 to the processing water chamber 1B in the filtration tank 1.

  Furthermore, the pressurized water supply pipe 5 for supplying air to the treated water discharge port 13 in a state where the treated water chamber 1B is filled with the washing water during backwashing and pressurizing the treated water chamber 1B. Is connected, and the supply path of the pressurizing air can be opened and closed by the on-off valve 51. The other end of the pressurizing air supply pipe 5 is connected to a pressurizing air supply source 52 for supplying pressurized air. For example, a compressor can be used as the pressurizing air supply source 52. The pressurizing air supply pipe 5 is provided with a pressure gauge 53 for measuring the pressure of the pressurized air sent into the treated water chamber 1B.

  A washing drain discharge port 14 is provided at the bottom of the raw water chamber 1A. A cleaning drainage discharge pipe 6 is connected to the cleaning drainage outlet 14, and a cleaning drainage discharge path can be opened and closed by an on-off valve 61.

  The wash water supply pipe 4 and the pressurizing air supply pipe 5 may be connected to the treated water chamber 1B separately from the treated water discharge port 13 so that they can be supplied.

  Reference numeral 7 denotes a filtration cylinder suspended from the partition plate 11, and the filtration cylinder 7 is composed of a porous cylindrical support 71 and a filtration membrane 72.

  For example, polyethylene can be used as the material of the support 71. The support 71 has an upper opening 73 that opens toward the treated water chamber 1B so that treated water can be fed to the treated water chamber 1B. The surface of the support 71 may be formed in a mesh shape or may be formed with a large number of holes. The opening ratio on the surface of the support 71 is preferably in the range of 40% to 70%, more preferably in the range of 45% to 65%, and still more preferably in the range of 50% to 65%.

  The filtration membrane 72 can be a microfiltration membrane or an ultrafiltration membrane, but a microfiltration membrane is preferred. The microfiltration membrane that can be preferably used in the present invention can be obtained as a commercial product, for example, “Yumicron membrane filter” manufactured by Yuasa Membrane System Co., Ltd. can be used.

  The filtration membrane 72 is formed in a bag shape, and is coated on the outer periphery of the support 71 as shown in FIG. As shown in the figure, the filtration membrane 72 is preferably a pleated filtration membrane that is pleated in the length direction.

  A large number of filter cylinders 7 are suspended from the partition plate 11 and arranged in the raw water chamber 1A. The number is appropriately determined according to the size of the filtration tank 1 and the amount of raw water treated.

  Reference numeral 8 denotes a fine bubble discharge unit, which is disposed in the treated water chamber 1B of the filtration tank 1. A porous member can be used for the fine bubble discharge portion 8. The fine bubble discharge unit 8 is connected to an air supply source 82 via an air supply pipe 81. By operating the air supply source 82, fine bubbles are introduced into the treated water chamber 1B. A compressor can be used as the air supply source 82.

  When introducing the fine bubbles, it is necessary to discharge the fine bubbles from the air supply source 82 at a pressure higher than the pressurized air supplied from the pressurization air supply source 52 via the pressurization air supply pipe 5. The bubble discharge pressure is preferably set 50 to 100 kPa higher than the pressure in the pressurized state of the treatment water chamber 1B in order to discharge the bubbles well. The diameter of the fine bubbles is preferably about the same as the pore diameter of the filtration membrane 72 from the viewpoint of allowing the filtration membrane 72 to permeate. This diameter is defined by the pore diameter of the porous member. The configuration for introducing these fine bubbles is preferably provided in the present invention.

  In such a membrane filtration apparatus, during a filtration operation in which raw water is treated, raw water is introduced from the raw water supply pipe 2 into the raw water chamber 1A via the raw water supply port 12, and flows upward in the raw water chamber 1A, so that the filtration membrane Filter by passing through 72. The treated water filtered by the filtration membrane 72 proceeds further upward in the filter cylinder 71, is collected into the treated water chamber 1 </ b> B from the upper opening 73, and passes through the treated water discharge pipe 3 from the treated water discharge port 13. Discharged.

  If the raw water treatment by the filtration membrane 72 is continued in this manner, the filtration membrane 72 is gradually clogged, so that the filtration membrane 72 needs to be back-washed. In the present invention, the backwashing operation is performed in two stages of a first film cleaning process and a second film cleaning process. Hereinafter, each step will be described.

  The first membrane cleaning step is a step of allowing the pressurized cleaning water to pass through the membrane all at once from the treated water chamber 1B side toward the raw water chamber 1A side. In this step, the on / off valve 21 of the raw water supply pipe 2 is closed to stop the supply of raw water, and then cleaning water for backwashing is supplied from the cleaning water supply pipe 4 to the treated water chamber 1B. The cleaning water is supplied from the cleaning water tank 43 by driving the cleaning water supply pump 42. At this time, the on-off valve 61 of the cleaning / drainage pipe 6 and the on-off valve 31 of the treated water discharge pipe 3 are closed, and the inside of the treated water chamber 1B is filled with washing water. By injecting pressurized air from the pressurized air supply pipe 5 into the treated water chamber 1B filled with the washed water, the washed water in the treated water chamber 1B is pressurized.

  At this time, it is preferable to generate fine bubbles from the fine bubble discharge unit 8 by operating the air supply source 82. That is, by supplying cleaning water from the cleaning water supply pipe 4 into the treatment water chamber 1B and operating the air supply source 82 in a state where the treatment water chamber 1B is filled with the cleaning water, the fine bubble discharge unit 8 is operated. To produce fine bubbles.

  When the inside of the treated water chamber 1B is filled with cleaning water, the open air valve 51 is opened and the pressurized air supply source 52 is operated to supply pressurized air into the treated water chamber 1B. Pressurize the wash water. The cleaning water is pressurized by opening the on-off valve 61 of the cleaning drainage discharge pipe 16 and passing the cleaning water in the treated water chamber 1B through the filter membrane 72 when the cleaning water is discharged from the cleaning drainage outlet 14 to the outside. This is to move the raw water chamber 1A to the raw water chamber 1A at a stretch and remove the adhered substances on the filtration membrane 72.

  The pressure at the time of pressurization is preferably a pressure equal to or higher than the bubble point of the filtration membrane 72. The pressure can be measured by a pressure gauge 53 provided in the pressurizing air supply pipe 5. By pressurizing the inside of the treatment water chamber 1B at a pressure higher than the bubble point of the filtration membrane 72, the fine bubbles B introduced into the treatment water chamber 1B pass through the holes 72a of the filtration membrane 72 as shown in FIG. To do. At this time, most of the adhered substances (including gel-like substances) X on the surface of the filtration membrane 72 are removed together.

  Further, as shown in FIG. 4, the fine bubbles B that have passed through the filtration membrane 72 and exited toward the raw water chamber 1 </ b> A rise while hitting the membrane surface of the filtration membrane 72, thereby further removing the adhered substances on the surface. Encourage.

  The bubble point of the filtration membrane 72 is the lowest pressure at which bubbles pass through the filtration membrane 72, and this bubble point is determined by the pore diameter of the membrane, the surface tension of the membrane, and the like. In the experimental example of the present invention, bubbles were passed through the membrane by applying a pressure of 110 to 160 kPa to the microfiltration membrane 72 having a pore diameter in the range of 0.4 to 0.9 μm. Generally, it is preferable that the pressurization force by pressurized air shall be 300-500 kPa.

  On the other hand, the second film cleaning step is performed after the first film cleaning step. In the second membrane cleaning step, after the cleaning water that has been pressurized and passed through the filter membrane 72 in the first membrane cleaning step is discharged from the cleaning drainage discharge pipe 6, the on-off valve 61 of the cleaning drainage discharge pipe 6 is used. In the state where is opened, the cleaning water is further supplied from the cleaning water supply pipe 4 to the treated water chamber 1B, and the cleaning water is permeated through the filtration membrane 72. The cleaning water at this time is only supplied by the operation of the cleaning water supply pump 42 and is not pressurized by the pressurizing air supply source 52. Therefore, the filtration membrane 72 is reversely cleaned by slowly allowing the cleaning water to permeate from the treated water chamber 1B side to the raw water chamber 1A side at a lower flow rate than in the first membrane cleaning step.

  Thus, the flow rate when the washing water permeates the filtration membrane 72 is preferably 1 to 3 m / s.

  The time for supplying the cleaning water in the second film cleaning step is preferably 10 to 90 seconds.

  Thus, unlike the first membrane cleaning step in which the cleaning water instantaneously passes through the filtration membrane 72, the cleaning water slowly and gradually passes through the pores of the filtration membrane 72. This washing water does not concentrate on the pleat crests (portions that are crested when viewed along the filtration direction) as in pressure washing, but on the almost entire surface of the pleated filtration membrane 72. Since it is going to pass in the vertical direction, the cleaning water also passes through the valley of the pleat (the part that becomes a valley when viewed along the filtration direction) and cannot be removed even by the first film cleaning process. Deposited substances such as silt remaining and accumulated in the valleys of the pleats gradually peel off from the membrane surface by the slowly flowing wash water flow and flow out into the raw water chamber 1A together with the wash water.

  Therefore, by performing the second membrane cleaning step after the first membrane cleaning step in the backwash operation, the filtration membrane 72 can be restored to a state equivalent to a new membrane without adhesion of silt or the like. In addition, it is possible to suppress a rise in transmembrane pressure and perform a stable filtration operation for a long time.

  In the present invention, the first film cleaning step and the second film cleaning step are preferably repeated a plurality of times in one backwash operation. In this case, the first film cleaning process and the second film cleaning process are not limited to being alternately repeated a plurality of times, but only the first film cleaning process is repeated a plurality of times, and then the second film cleaning process is performed. It is good also as an aspect to do.

  FIG. 5 and FIG. 6 show an embodiment (FIG. 5) in which only the first membrane cleaning step is performed when seawater is membrane filtered by a membrane filtration device having the same filtration membrane, and after the first membrane cleaning step. It is the graph which investigated the change of the transmembrane differential pressure in the mode (Drawing 6) which performed the 2nd membrane washing process. Here, two towers of membrane filtration devices are prepared, and while one side is performing a filtration operation, the other is back-washed, and an operation for waiting is performed.

  In the aspect of FIG. 5, only the 1st film | membrane washing | cleaning process which sends to the treated water chamber which filled the pressurized air of 500 kPa with washing water at each backwash operation, and discharges at a stretch was implemented. As a result, immediately after the backwash operation is performed, the transmembrane pressure difference temporarily decreases, but increases immediately, gradually increases with an increase in the cumulative operation time, and the overall inclination increases.

  On the other hand, in the mode of FIG. 6, at the time of each backwash operation, the first membrane cleaning step of sending the pressurized air of 500 kPa to the treated water chamber filled with the cleaning water and discharging it at once, and the flow rate at 1.5 m / s The second film cleaning step of supplying cleaning water was repeated alternately. As a result, the transmembrane pressure difference is significantly reduced as compared with the embodiment of FIG. 5, the transmembrane pressure difference after 24 hours of cumulative operation is reduced by 60%, and the overall inclination is reduced. In comparison with the above, it was possible to stably perform the filtration operation for a long time.

The schematic sectional drawing which shows an example of the membrane filtration apparatus suitable for enforcing the backwashing method of this invention Cross section of filter tube A figure explaining how fine bubbles pass through a filtration membrane A figure explaining how fine bubbles pass through a filtration membrane The graph which shows the relationship between the accumulation operation time at the time of performing only a 1st film | membrane washing | cleaning process, and transmembrane differential pressure | voltage The graph which shows the relationship between the accumulation operation time at the time of performing a 1st film | membrane washing | cleaning process and a 2nd film | membrane washing | cleaning process, and transmembrane pressure difference The figure explaining the state of the film surface after the conventional backwashing

Explanation of symbols

1: Filtration tank 1A: Raw water chamber 1B: Treated water chamber 11: Partition plate 12: Raw water supply port 13: Treated water discharge port 14: Washing drain discharge port 2: Raw water supply pipe 21: On-off valve 3: Treated water discharge pipe 31 : On-off valve 4: Wash water supply pipe 41: On-off valve 42: Wash water supply pump 43: Wash water tank 5: Pressurization air supply pipe 51: On-off valve 52: Pressurization air supply source 53: Pressure gauge 6: Wash drainage Discharge pipe 61: On-off valve 7: Filter cylinder 71: Support body 72: Filtration membrane 72a: Hole 73: Upper opening 8: Fine bubble discharge part 81: Air supply pipe 82: Air supply source

Claims (6)

The inside of the filtration tank is partitioned into a raw water chamber and a treated water chamber by a partition plate, and a number of filter cylinders provided with a bag-like membrane that penetrates the partition plate and opens to the treated water chamber side in the raw water chamber. The raw water that has been installed and enters the raw water chamber is filtered by the membrane while flowing upward in the raw water chamber, and has a structure in which the raw water rises in the filter cylinder as treated water and is collected in the treated water chamber, In the backwashing method of the membrane filtration apparatus, the cleaning water supply pipe is connected to the treated water chamber via an on-off valve, and the cleaning water discharge pipe is connected to the raw water chamber via the on-off valve.
After the treatment water chamber is filled with washing water, the on-off valve of the washing drainage pipe is closed, air is injected into the treatment water chamber to pressurize the washing water, and then the on-off valve of the washing drainage discharge pipe is opened. A first membrane cleaning step for performing reverse cleaning of the membrane by opening the pressurized cleaning water through the membrane at a stretch by opening,
After the first membrane cleaning step, by supplying cleaning water from the cleaning water supply pipe to the treated water chamber with the opening / closing valve of the cleaning drainage pipe opened, the first membrane cleaning step And a second membrane cleaning step of performing reverse cleaning of the membrane by allowing the cleaning water to pass through the membrane at a low flow rate.   The backwashing method for a membrane filtration device according to claim 1, wherein a flow rate of the washing water in the second membrane washing step is 1 to 3 m / s.   The backwashing method for a membrane filtration device according to claim 1 or 2, wherein the cleaning water supply time in the second membrane cleaning step is 10 to 90 seconds.   4. The method for backwashing a membrane filtration device according to claim 1, wherein the membrane is a pleated membrane.   The backwashing method for a membrane filtration device according to any one of claims 1 to 4, wherein in the first membrane cleaning step, fine bubbles are introduced into the cleaning water in the treated water chamber.   The method for backwashing a membrane filtration device according to any one of claims 1 to 5, wherein the raw water is ballast water to be supplied to a ballast tank of a ship.

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