JP2024046951A - Filtration apparatus and filtration treatment method - Google Patents

Abstract

To provide a filtration apparatus and a filtration treatment method where stable filtration treatment can be continued by keeping the compaction state of a filter medium layer and performing the filtration of suspended matter while separating foams.SOLUTION: In a downflow type filtration apparatus where settleable granular fiber filter medium is compacted at the front stage of a filtration treatment step S4 and compaction state is kept by a return prevention member 9, filtration efficiency is not lowered since filtration can be continued while floating and concentrating suspended matter by that a net body 21 having a flow hole is stretched at a cylindrical frame body 23 and the return prevention member 9 being stood in the vicinity of a filter medium surface layer part 11, keeping the compaction state and moving up and down and a foam separation device 12 being integrated with the return prevention member 9 and jetting fine bubbles are possessed.SELECTED DRAWING: Figure 1

Description

The present invention relates to a downflow filtration device that uses granular fiber filter media to filter the liquid being treated, and to a filtration device and filtration method that performs filtration while removing suspended solids that have detached from the filter media.

Conventionally, filtration devices have been known that perform filtration by passing the liquid to be treated through settled irregular filter media in a downward flow. As filtration time passes, suspended matter adheres to the inside and surface of the filter media, causing a decrease in filtration performance, and so the filter media had to be cleaned periodically. Filter media cleaning is carried out after the filtration process, and is carried out by backwashing water from the wastewater side, aeration, mechanical agitation, or a combination of these.

For example, Patent Document 1 discloses a filter media cleaning technology in which air is supplied from the bottom when cleaning the filter media, the filter media is made to flow and the suspended matter is released, then fine bubbles are supplied from a fine bubble generator provided above the filter media layer to cause the suspended matter to float and concentrate, and the floating and concentrated suspended matter is discharged from the top of the filtration device with cleaning water supplied from the bottom. The document also describes a technology in which raw water with fine bubbles introduced is supplied during the filtration process, and the suspended matter attached to the filter media is caused to float and concentrate, and then discharged.

Figure 7 of Patent Document 2 discloses a filter media cleaning technology in which a cleaning treatment liquid is poured into the bottom of the filtration device, and then the filter media is stirred while being aerated and a filter media manipulation member is moved upward to remove suspended solids adhering to the filter media, which are then discharged from the top of the filtration device. The document also discloses a technology in which a filter media manipulation member is placed inside the filtration device to increase the capture rate of suspended solids during filtration, and the gaps in the filter media are reduced by the pressure of the flow when draining at the bottom.

Patent No. 5850793 Japanese Patent No. 4475924 (Fig. 7)

In conventional filter media cleaning technology, the filter media is agitated and cleaned, which provides a high cleaning effect, but the granular fiber filter media stacked inside the filtration device is not sufficiently compacted during the filtration process, resulting in a high porosity in the filter media layer. As a result, when the treated liquid supplied from above contains a large number of fine particles, the suspended matter contained therein is discharged from the bottom without being sufficiently captured by the filter media layer, making it impossible to improve filtration accuracy.

Patent Document 1 discloses a technology in which raw water containing fine bubbles is supplied to a filtration device in the filtration process, and suspended matter is removed by floating and concentrating it; however, because the filter medium is not sufficiently compacted, suspended matter cannot be captured efficiently, and the rate of suspended matter removal could not be reduced. In addition, when cleaning the filter medium, suspended matter detached from the filter medium by air supplied from an air supply pipe is caused to float and concentrate in a fine bubble generator, but there is no description or suggestion that the fine bubble generator can be raised and lowered. Therefore, when the position of the filter medium layer changes, fine bubbles cannot be supplied to the desired position, and suspended matter cannot be removed efficiently.

The technology of Patent Document 2 provides a filter media manipulation member above the filter media layer, which makes it possible to sufficiently compress the granular fiber filter media during the filtration process. However, since the pressing force and releasing force of the filter media manipulation member depend on the amount of raw water passing through, the content of suspended solids, the amount of aeration, etc., it is difficult to perform a stable filtration process. In addition, it is not possible to wash the filter media while the filter media layer is compressed during the filtration process.

The present invention was made in consideration of these circumstances, and provides a filtration device and filtration method that can continue stable filtration operation by leaving a return prevention member of the filter layer stationary on the surface of the filter during the filtration process to form a filter layer with uniform porosity, and by removing suspended solids that have detached from the filter layer by floating and concentrating them.

In a downflow filtration device that compresses settleable granular fiber filter media in the first stage of the filtration process and maintains the compressed state with a return prevention member, a mesh body with water holes is stretched over a cylindrical frame, and the return prevention member that can be raised and lowered is placed near the surface of the filter media to maintain the compressed state, and a foam separation device that is integral with the return prevention member and sprays fine bubbles is provided. This allows the filter media layer to be maintained in a compressed state and fine bubbles to be sprayed from the desired position, allowing suspended solids that float up in the filter tank to be efficiently removed.

The foam separation device is equipped with a spray section that sprays fine bubbles toward the surface of the filter medium, so that the fine bubbles sprayed toward the surface of the filter medium can detach suspended matter from the surface of the filter medium and cause it to float and be separated.

The return prevention member is equipped with an agitation fluid ejection device that agitates the suspended matter captured on the surface of the filter medium, and the ejection portion of the foam separation device is arranged facing upwards, so that the suspended matter can be peeled off from the surface of the filter medium by the agitation fluid ejected from the agitation fluid ejection device, and then the peeled suspended matter can be floated and separated by fine air bubbles ejected from the foam separation device.

The foam separation device is equipped with a pipe formed along the inner wall of the frame body, and an ejection section formed in the pipe and having fine ejection holes, so that fluid supplied into the pipe can be ejected as fine bubbles from the ejection section.

In a downward flow filtration method in which suspended solids in the liquid being treated are captured by a filter layer formed of a settling granular fiber filter medium, the method includes a compressed water storage process in which compressed water is stored in a filter tank up to a specified water level, a consolidation process in which the filter layer is consolidated by the water flow when the stored compressed water is discharged, and a return prevention process in which a return prevention member with a stretched mesh body is placed near the surface of the filter medium to maintain the consolidation state of the filter layer. After this, the filtration process is started, and during the filtration process, fine bubbles are sprayed from a foam separation device attached integrally to the return prevention member to foam-separate the suspended solids, making it possible to perform the filtration process while maintaining a uniform and highly compacted filter layer, and since the suspended solids can be removed efficiently, stable filtration process can be continued.

The filtration device and filtration method of the present invention are provided with a foam separation device integrally attached to a return prevention member that can be raised and lowered. By placing the return prevention member near the surface layer of the filter medium, operation is possible while maintaining the compaction of the filter medium layer, so stable filtration can be continued for a long time. In addition, since fine bubbles can be ejected from a desired position, suspended matter contained in the supplied liquid to be treated can be efficiently removed. By performing foam separation during the filtration process, even fine suspended matter that cannot be captured by the filter medium is removed, so the removal rate of suspended matter can be improved. Furthermore, by ejecting the agitated fluid toward the surface layer of the filter medium using the agitation fluid ejection device, the accumulation of suspended matter on the surface layer of the filter medium can be prevented, so clogging of the surface layer of the filter medium is unlikely to occur. As a result, it is also possible to reduce the time and frequency of cleaning the filter medium after the filtration process. This is particularly effective for fibrous filter medium with high porosity and high compressibility, and it is possible to continue operation while maintaining a uniform and high compaction degree even during the filtration process.

1 is a vertical cross-sectional view of a filtering device according to the present invention. FIG. FIG. FIG. 13 is a schematic diagram showing the start-up of a filtration process. FIG. 2 is a schematic diagram of the consolidation water storage process. FIG. FIG. FIG.

FIG. 1 is a vertical sectional view of a filtering device according to the present invention.
The filtration device 1 has a cylindrical filtration tank 2 set upright, and a fibrous filter medium is filled inside to form a filter medium layer 4 on an outflow prevention screen 3 below the filtration tank 2. The fibrous filter medium is a sedimentary granular fibrous filter medium, and the shape is not limited to a spherical or columnar shape. The liquid to be treated is supplied from an upper treated liquid pipe 5, suspended solids are captured by the filter medium layer 4, and the treated water is discharged to the outside from a lower treated liquid pipe 6. If necessary, a screen may be installed above the filtration tank 2 to prevent the outflow of the fibrous filter medium toward the treated liquid pipe 5.

A return prevention mechanism is provided inside the filter tank 2 to prevent the compressed filter layer 4 from loosening in the upward opening direction, causing the porosity of the filter layer 4 to become uneven.

The return prevention mechanism is composed of a driver 7 installed above the filtration tank 2, a feed screw member 8 driven by the power of the driver 7, a return prevention member 9 that is screwed into the feed screw member 8 and moves up and down, and a support rod 10 that rotatably supports the end of the feed screw member 8. The support rod 10 extends from the inner wall of the filtration tank 2 to the feed screw member 8, and has a cylindrical member 34 at its end through which the feed screw member 8 can be inserted. The cylindrical member 34 functions as a vibration prevention device for the end of the feed screw member 8 that extends downward through the return prevention member 9. In this embodiment, three feed screw members 8 are used, one of which is connected to the driver 7 and configured to be able to rotate forward and backward, and the remaining ones are configured to be driven by the power transmitted from the driver 7. The power of the driver 7 is transmitted by a drive transmission member 33 such as a timing belt suspended on a drive pulley 31 and a driven pulley 32 provided on each feed screw member 8.

Each feed screw member 8 is installed vertically so as to be parallel to the axis of the filtration tank 2, and a helical screw thread is formed on the periphery at least over the lifting range of the return prevention member 9. The pitch of the screw thread and the connection method with the driver 7 (direct connection, worm gear, etc.) are appropriately selected according to the specifications of the filtration device 1 and the lifting speed.

The return prevention member 9 is integrally equipped with a foam separator 12 that separates suspended matter in the treated liquid supplied to the filter layer 4 by using fine air bubbles to float and separate the suspended matter and discharges it together with the foam from a discharge pipe 20 above the filtration tank 2, and an agitation fluid jetting device 13 that jets an agitation fluid (gas or liquid) onto the suspended matter accumulated on the filter surface layer 11 to agitate it. A flexible supply pipe 18 that can expand and contract in response to the lifting and lowering action of the return prevention member 9 is connected to the foam separator 12 and the agitation fluid jetting device 13. A fluid supply source 19 is connected to the supply pipe 18, and the structure is such that fluid can be supplied to the foam separator 12 and the agitation fluid jetting device 13.

In this embodiment, the return prevention member 9 is screwed to multiple feed screw members 8, but a single feed screw member 8 may be installed vertically in the center of the filtration tank 2. In this configuration, a guide bar (not shown) can be installed vertically at a position eccentric to the axis to prevent the return prevention member 9 from wobbling forward, backward, left, or right. As long as there is a mechanism that can raise and lower the return prevention member 9 in this way, the number of feed screw members 8 and the form of the lifting mechanism are not limited to this embodiment.

FIG. 2 is a top view of the anti-return member.
The return prevention member 9 is a member that is placed near the filter media surface portion 11 to maintain the compressed state of the filter media layer 4, and is made of a mesh body 21 having minute water passage holes stretched inside a cylindrical frame body 23 having a predetermined thickness. The frame body 23 is placed close to the inner wall of the filtration tank 2 shown in Fig. 1, and is set so that the filter media cannot pass through the gap formed between the frame body 2 and the filtration tank 2. If necessary, a sliding member may be provided around the outer periphery of the frame body 23.

The mesh body 21 is formed from a plate material with tiny holes drilled through it, a mesh member, etc. The water passage holes of the mesh body 21 are of a diameter that allows the water to be treated from the treated liquid pipe 5 to pass through to the filter layer 4, and prevents the filter material from flowing out upwards.

At a position eccentric to the center of the return prevention member 9, a helical screw groove 27 that screws into each feed screw member 8 is formed. In this embodiment, the screw groove 27 is formed on the inner peripheral surface of a tubular member 35 having a predetermined height that is installed on the net body 21. The tubular member 35 is arranged so as to communicate with an opening (not shown) formed in the net body 21, so that the feed screw member 8 can be inserted from above, and the return prevention member 9 can be raised and lowered in the vertical direction by rotating the feed screw member 8 with it inserted. The configuration of the screw groove 27 and the tubular member 35 in this embodiment is one example, and is not limited to this as long as it is a configuration that can engage the feed screw member 8.

If necessary, reinforcing ribs may be added in the vertical direction of the return prevention member 9. Also, if the mesh body 21 is provided in two levels, upper and lower, with a specified distance between them, the fiber filter material that flows out from the lower level mesh body 21 can be captured by the upper level mesh body 21.

In this embodiment, the return prevention member 9 is integrally provided with the piping 16A (main pipe 17A, branch pipe 26A) and the foam separator 12 having the ejection section 15A. The main pipe 17A and the branch pipe 26A are formed across the inner wall 30 of the frame. Specifically, the main pipe 17A connected to the supply pipe 18 is bridged to the frame 23, and multiple branch pipes 26A are branched vertically from the main pipe 17A. The piping 16A (main pipe 17A, branch pipe 26A) is fixed to the frame 23 or the mesh 21 by a known method.

The pipe 16A is fitted with multiple ejection parts 15A with numerous ejection holes 14A formed on the upper surface, and ejects compressed air flowing from the supply pipe 18 into the main pipe 17A and the branch pipe 26A upward as fine bubbles. Each ejection part 15A is detachably attached to the pipe 16A, and in the event that an ejection hole 14A becomes clogged, maintenance can be performed on only the desired ejection part 15A, making it easy to maintain.

Each nozzle 15A generates microscopic bubbles using a known membrane type nozzle with a synthetic resin or synthetic rubber membrane on the upper surface and numerous microscopic holes (emission holes 14A). The membrane expands due to the compressed air supplied into the pipe 16A, opening the microscopic holes (emission holes 14A), thereby dispersing the air. When the supply of compressed air is stopped, the microscopic holes (emission holes 14A) are in a closed state.

Note that any device capable of generating fine bubbles may be used, and other fine bubble generating mechanisms may be used instead of the aeration type. The material of the pipe 16 may be selected appropriately depending on the conditions, such as metal, synthetic resin, or ceramic.

FIG. 3 is a bottom view of the anti-return member.
In this embodiment, the agitating fluid jetting device 13 having the piping 16B (main pipe 17B, branch pipe 26B) and the jetting portion 15B is integrally installed at the lower part of the return prevention member 9 described in detail in Fig. 2. The main pipe 17B and the branch pipe 26B are formed across the inner wall 30 of the frame. The piping 16B (main pipe 17B, branch pipe 26B) is fixed to the frame 23 or the mesh 21 by a known method, similar to the foam separation device 12.

The pipe 16B has an ejection section 15B having a plurality of downwardly facing ejection holes 14B, and can eject the agitated fluid introduced from a supply pipe 18 connected to the circumferential surface of the main pipe 17B. The main pipe 17B may be omitted, and the supply pipe 18 may be directly connected to the branch pipe 26B. In this embodiment,
Although the agitating fluid jetting device 13 is configured with a plurality of pipes 16B, the present invention is not limited to this as long as the mechanism is capable of agitating the suspended solids accumulated on the filter media surface portion 11.

The pipes 16A and 16B constituting the foam separator 12 and the agitated fluid ejection device 13 are preferably installed at a predetermined distance from the mesh body 21. This prevents the installed pipes 16 from blocking the water passage holes of the mesh body 21, which would otherwise reduce the water passage efficiency. As long as they can be raised and lowered together with the return prevention member 9, the pipes 16A and 16B may be bridged to the inner wall 30 of the frame, or may be spaced apart from the inner wall 30 of the frame. Furthermore, the branch pipes 26B branching off from the main pipe 17B may branch out radially or concentrically, or may further branch off from the branch pipe 26B. The branch pipes 26B may be laid over the main pipe 17B to communicate with it.

When using fine bubbles as the agitated fluid, the main pipe 17 constituting the foam separation device 12 and the agitated fluid ejection device 13 may be shared, with the ejection section 15A provided above the main pipe 17 and the ejection section 15B provided below.

The number and positions of the ejection sections 15A and 15B constituting the foam separation device 12 and the agitated fluid ejection device 13, as well as the diameter, shape, and ejection angle of the ejection holes 14A and 14B, are also appropriately selected according to the design conditions.

In this embodiment, after the steps shown in FIGS. 4 to 7 described below are performed, the filtration process step shown in FIG. 8 is carried out.
FIG. 4 is a schematic diagram of the filtration process at the start-up stage.
When new filter media is added to the filtration tank 2, or when the water in the filtration tank 2 is drained after the filtration treatment step S4 and the fibrous filter media is washed, the fibrous filter media is piled up on the outflow prevention screen 3. The return prevention member 9 is raised above the filtration tank 2 and is left in a position where it does not get in the way when replacing the fibrous filter media or during the filter media washing step S5.

The filter layer 4 is in a naturally settled state, with large gaps between the fibrous filter media. If the liquid to be treated is passed through in this state, the suspended matter in the liquid to be treated will not be captured by the fibrous filter media, but will pass through the filter layer 4 and be discharged together with the treated liquid. Therefore, steps S1 to S3 are carried out prior to the filtration process S4 to consolidate the filter layer 4.

<Compressed water storage step S1>
FIG. 5 is a schematic diagram of the consolidation water storage process.
In the compressed water storage step S1, compressed water is stored in the filtration tank 2. Compressed water is supplied into the filtration tank 2 from the treated liquid pipe 5. The valve V2 installed in the treated liquid pipe 6 is closed, and the compressed water is stored in the filtration tank 2. At this time, the valve V3 installed in the discharge pipe 20 is open, allowing air to be sucked in and exhausted from above the filtration tank 2. When the compressed water has been stored up to a predetermined water level, the supply of compressed water is stopped. At this time, it is desirable to position the return prevention member 9 close to the vicinity of the surface layer 11 of the filter medium.

In this embodiment, the consolidated water is newly supplied from outside to the filtration tank 2, but the cleaning liquid stored in the filtration tank 2 after the filter media cleaning process S5 may also be used as the consolidated water.

<Consolidation step S2>
FIG. 6 is a schematic diagram of the consolidation process.
In the consolidation step S2, the fibrous filter media is consolidated to form the filter media layer 4. After the consolidated water is stored up to a predetermined water level, the valve V2 installed in the treatment liquid pipe 6 is opened, and the consolidated water is discharged downwards in one go. At this time, the fibrous filter media is consolidated above the outflow prevention screen 3 by the water flow toward the bottom of the filtration tank 2, forming a filter media layer 4 with a sufficient degree of compaction. When the consolidation step S2 is performed, the gaps between the fibrous filter media become smaller, and the height of the filter media layer 4 becomes lower compared to when natural settling occurs. If necessary, the consolidation step S2, in which the consolidated water is stored in the filtration tank 2 and then discharged, may be performed multiple times.

<Return prevention process S3>
FIG. 7 is a schematic diagram of the anti-return process.
In the return prevention step S3, the return prevention member 9 is placed near the filter media surface layer 11 to maintain the consolidated state of the filter media layer 4. Simultaneously with the consolidation step S2, the driver 7 is driven to rotate the feed screw member 8 connected to the driver 7 in the forward direction. The return prevention member 9 starts to descend while being screwed into the feed screw member 8.

When it is detected that the return prevention member 9 has descended to the surface layer 11 of the filter medium, which has been appropriately compressed by the compressed water, the driver 7 is stopped and the return prevention member 9 is left stationary in that position. The descent of the return prevention member 9 is detected, for example, by a tachometer 24 or a position detector 25 disposed in the filtration tank 2, or a torque meter 28 disposed at the connection part of the driver 7, etc.

The tachometer 24 measures the number of rotations of the feed screw member 8 or the driver 7, and sends a stop signal to the driver 7 when a predetermined number of rotations is reached.

The position detection device 25 also uses a known contact or non-contact type device to send a stop signal to the drive machine 7 when the return prevention member 9 reaches a predetermined position.

Furthermore, the torque meter 28 measures the sudden increase in torque when the return prevention member 9 reaches the filter media surface layer 11, and sends a stop signal to the driver 7 when the torque measurement exceeds a predetermined measurement value. Note that the method of detecting the descent is not limited to the above method, but can be determined appropriately depending on the conditions.

It is desirable to set the descent speed of the return prevention member 9 slower than the descent speed of the fibrous filter medium caused by the consolidation water during the consolidation step S2. If the fibrous filter medium is compressed by the return prevention member 9 before being compressed by the consolidation water, only the compression ratio of the upper part of the filter medium layer 4 will increase, preventing the formation of a filter medium layer 4 with a uniform porosity. Depending on the conditions, if a speed faster than the descent speed of the fibrous filter medium is set, it is adjusted so as not to overtake the descending filter medium surface portion 11.

The return prevention member 9, which is placed stationary near the filter media surface layer 11, is screwed into the feed screw member 8 and does not move upward due to the repulsive force of the compressed filter media layer 4. Similarly, when the liquid to be treated is passed through during the filtration process S4, the lower filter media layer 4 is not pressed.

In this embodiment, the consolidation step S2 and the return prevention step S3 are performed simultaneously, but it is sufficient that the return prevention member 9 is lowered to the filter surface layer 11 immediately after the filter layer 4 is consolidated. For example, if the return prevention step S3 is started before the consolidation step S2, the filter layer 4 may be consolidated with compressed water while the return prevention member 9 is slowly lowered, so that the return prevention member 9 reaches the filter surface layer 11 before the compressed filter layer 4 loosens in the upward opening direction.

The filter layer 4 is compressed with compressed water, and a water-permeable return prevention member 9 is brought into sliding contact with the filter surface layer 11 to prevent the compressed filter layer 4 from loosening in the opening direction, and the filtration process S4 is started. The filter layer 4 is formed by the compressed water in a uniform and highly compressed form, allowing for stable filtration from the beginning of operation.

<Filtration process S4>
FIG. 8 is a schematic diagram of the filtration process.
In the filtration process S4, the liquid to be treated is supplied into the filtration tank 2 for filtration. The liquid to be treated is supplied into the filtration tank 2 from the treated liquid pipe 5 and passed through the filter media layer 4 filled in the filtration tank 2. At this time, the valve V2 installed in the treated liquid pipe 6 is opened so that the treated liquid after passing through the filter media layer 4 can be discharged. The valve V3 installed in the discharge pipe 20 is also opened, and since air supplied into the tank causes air to accumulate, the air is removed to adjust the pressure in the filtration tank 2 so that it does not rise too much.

After the supply of the liquid to be treated is started and the liquid to be treated rises to a predetermined water level, the fluid supply source 19 connected to the foam separation device 12 is driven to supply compressed air from the supply pipe 18 toward the pipe 16A. The compressed air flows into the main pipe 17A (pipe 16A) shown in FIG. 2, and then passes through each branch pipe 26A (pipe 16A) and is sprayed upward as fine bubbles from the nozzle holes 14A formed in each spray section 15A. In this embodiment, fine bubbles are constantly sprayed during the filtration process S4, so suspended solids generated during filtration can be efficiently floated and separated. The timing of starting the supply of compressed air is determined appropriately depending on the conditions.

The many fine bubbles ejected adsorb suspended matter mixed in the treated liquid supplied from above, and suspended matter that has naturally detached from the filter media layer 4 due to the effects of water pressure, etc., and rise to the water surface. The bubbles adsorbing the suspended matter that rise one after another then gather at the water surface, forming foam on the water surface. The foam formed on the water surface is discharged from the discharge pipe 20 above the filtration tank 2.

After a predetermined time has elapsed since the start of the filtration process S4, suspended matter contained in the treated liquid passing through the filter layer 4 gradually accumulates on the filter surface layer 11. In this embodiment, the return prevention member 9 is placed stationary on the filter surface layer 11, and the filtration process is performed while maintaining a uniform compaction state, so suspended matter can be efficiently captured between the filter media. However, as the filtration time passes, suspended matter accumulates on the filter surface layer 11, causing the filtration pressure to rise in a short period of time, which can cause a decrease in filtration efficiency.

Therefore, in this embodiment, during the filtration process S4, an agitated fluid is sprayed toward the filter media surface layer 11, and filtration is performed while peeling off the suspended matter that has accumulated on the filter media surface layer 11.

The filter media surface layer 11 is stirred when a predetermined gap X is formed between the stirred fluid ejection device 13 provided at the bottom of the return prevention member 9 and the filter media surface layer 11. The predetermined gap X is several centimeters to several tens of centimeters, and is formed when the filter media surface layer 11 is gradually consolidated by the supply pressure of the liquid being treated during the filtration process. In this embodiment, a highly compressible fibrous filter media is used, so the filter media layer 4 is consolidated by the water pressure of the liquid being treated, forming the predetermined gap X.

After the specified gap X is formed, the fluid supply source 19 connected to the agitating fluid ejection device 13 is driven to supply the agitating fluid from the supply pipe 18 toward the main pipe 17B (piping 16B) shown in FIG. 3. The agitating fluid supplied to the main pipe 17B (piping 16B) is ejected toward the filter media surface layer 11 from the ejection holes 14B formed in multiple branch pipes 26B that communicate with the main pipe 17B (piping 16B).

After the stirring fluid is sprayed, the surface portion 11 of the filter layer is stirred, and suspended matter is separated from the surface portion 11. The separated suspended matter passes through the water passage holes opened in the mesh body 21 of the return prevention member 9 and floats upward. After being adsorbed by fine air bubbles constantly supplied from the foam separator 12 into the filter tank 2, it continues to rise toward the water surface. Then, the air bubbles that rise one after another form foam on the water surface.

The predetermined gap X may be confirmed, for example, by a sensor capable of measuring the position through an inspection window provided in a part of the filtration tank 2, or by photographing and confirming using an imaging device. Alternatively, the pressure in the filtration tank 2 may be continuously measured, and when the measured value reaches a predetermined value, the thickness of the filter layer 4 is recognized as having changed. In this embodiment, the return prevention member 9 is stationary near the filter tank surface layer 11, so the filter layer 4 does not move upward or downward. However, for example, when it is desired that the distance from the filter surface layer 11 to the agitation fluid ejection device 13 is equal to or greater than the predetermined gap X, the agitation fluid ejection device 13 may be moved to eject the filter agitation fluid from any position.

The foam formed on the water surface is discharged from the discharge pipe 20 together with the fine bubbles constantly sprayed upward from the aeration section 15. Since the valve V3 interposed in the discharge pipe 20 is always open during the filtration process, the foam formed on the water surface in the filtration tank 2 is discharged together with the fine bubbles constantly discharged from the aeration section 15 toward the discharge pipe 20.

At this time, the opening degree of the valve V3 is appropriately adjusted according to the value of the level gauge 29 that measures the water level in the filtration tank 2 and is provided in the discharge pipe 20. In this embodiment, in order to perform filtration while maintaining the water level in the filtration tank 2 constant, the level gauge 29 is provided in the discharge pipe 20 and the water level is constantly measured. If the measured water level deviates from a predetermined value, the opening degree of the valve V3 is adjusted. For example, if the measured water level is lower than the predetermined value, the opening degree of the valve is increased, and the amount of foam and fine bubbles discharged is increased to raise the water level to a predetermined value. If a large amount of air remains above the filtration tank 2, it will lead to a drop in the water level in the filtration tank 2, so the above operation is performed based on the measurement value of the level gauge 29. Note that the method of discharging the foam is not limited to this embodiment, and it may be a form in which the foam is constantly overflowing and discharged from the discharge pipe 20.

After the filtration process S4 is completed, the supply of the liquid to be treated is stopped and valve V1 is closed. At the same time, the operation of the fluid supply source 19 is stopped and the foam separation operation is terminated. The supply of the liquid to be treated is continued not only during foam separation but also during stirring of the filter media surface layer 11, and is terminated when a predetermined time, a predetermined time, a predetermined pressure, etc. is reached.

The timing of starting and ending the ejection of the stirred fluid is also determined based on a predetermined time, a predetermined time, a predetermined pressure, etc. The stirred fluid may be ejected continuously or intermittently.

In this embodiment, the agitation fluid jetting device 13 is installed below the return prevention member 9, and the foam separation device 12 is installed above it, so that fine air bubbles can be supplied to the suspended matter immediately after it has been detached by the agitation fluid supplied from the agitation fluid jetting device 13. This allows the suspended matter to be adsorbed onto the fine air bubbles before it rises to the water surface, allowing for efficient foam generation. In addition, because the foam separation device 12 and the agitation fluid jetting device 13 can be raised and lowered, the agitation fluid jetting device 13 can be disposed near the filter media surface layer 11, preventing suspended matter from accumulating on the filter media surface layer 11.

The filter surface layer 11 during the filtration process S4 is constantly cleaned, so the filtration efficiency does not decrease. By constantly cleaning the filter surface layer 11 while continuing filtration in this way, it is possible to prevent an early rise in filtration pressure, extend the duration of filtration, and reduce the time and frequency of cleaning the filter.

In this embodiment, the ejection part 15 of the foam separation device 12 is configured to face upward, but the ejection part 15 may be configured to face downward and installed on the return prevention member 9, so that one device can perform surface stirring of the filter medium and foam separation. In this case, it is desirable to provide a predetermined gap between the mesh body 21 and the foam separation device 12, so that fine bubbles can be ejected from above the mesh body 21. By providing a predetermined gap above the mesh body 21, it is possible to perform stirring of the surface of the filter medium before the predetermined gap X is formed by the consolidation of the treated liquid. In addition, it is also possible to provide a configuration in which only the foam separation device 12 with an ejection port facing upward is installed integrally with the return prevention member 9, so that only foam separation is performed during the filtration process S4.

<Filter cleaning process S5>
In the filter media cleaning step S5, as shown in Fig. 4, the return prevention member 9 in sliding contact with the filter media surface layer 11 is raised to a predetermined position, and cleaning liquid is supplied from the treatment liquid pipe 6 into the filtration tank 2 to clean the fiber filter media. The cleaning waste liquid after cleaning the filter media is discharged from the discharge pipe 20. At this time, the valves V2 and V3 are in an open state. In this embodiment, the filter media is cleaned by a known method, but since filtration is performed while removing suspended matter in the preliminary stage of the filter media cleaning step S5, clogging of the filter media surface layer 11 is unlikely to occur. Therefore, the time and frequency of cleaning the filter media can be reduced.

The present invention is not limited to the embodiment described above. Modifications can be made as appropriate without departing from the spirit of the present invention.

The present invention performs filtration while removing suspended matter that accumulates on the surface of the filter media while maintaining the compacted state of the filter media layer, making it difficult for the filter media layer to become clogged, and stable filtration processing can be continued. In addition, because suspended matter is removed prior to the filter media cleaning process, filtration operation can be continued for long periods of time, reducing the time and frequency of filter media cleaning. Fiber filter media with a high capture rate can be used for coagulation filtration and highly turbid water that are prone to surface filtration, or for special applications that require high clarity, such as pools, and by performing deep layer filtration, it is a useful filtration method that allows for a long filtration process with less frequent cleaning.

Reference Signs List 1 Filtration device 2 Filtration tank 4 Filter layer 9 Return prevention member 11 Filter surface layer 12 Foam separator 13 Agitation fluid ejection device 14A Ejection hole 15A Ejection part 16A Pipe 21 Mesh body 23 Frame body 30 Frame body inner wall S1 Consolidated water storage step S2 Consolidation step S3 Return prevention step S4 Filtration treatment step

Claims (5)

In a downflow filtration device, a sedimentary granular fiber filter medium is compressed in a stage prior to a filtration treatment step (S4) and the compressed state is maintained by a return prevention member (9),
a cylindrical frame (23) having a mesh body (21) with water holes stretched thereon, and a liftable return prevention member (9) that is placed near the surface layer (11) of the filter medium to maintain a compressed state;
A filtration device comprising: a foam separator (12) integrally formed with a return prevention member (9) and adapted to eject fine bubbles. 2. The filtering device according to claim 1, wherein the foam separation device (12) is provided with an ejection section (15A) that ejects fine bubbles toward a surface portion (11) of the filter medium. The return prevention member (9) is provided with an agitating fluid ejection device (13) for agitating the suspended matter captured by the surface layer portion (11) of the filter medium,
2. The filtering device according to claim 1, wherein the foam separator (12) has a jet portion (15A) facing upward. The foam separation device (12) includes a pipe (16A) formed along the inner wall (30) of the frame (23);
4. The filtering device according to claim 1, further comprising: a jetting portion (15A) formed in the pipe (16A) and having fine jetting holes (14A). A downward flow filtration method in which suspended solids in a liquid to be treated are captured by a filter layer (4) formed of a sedimentary granular fiber filter medium,
A consolidated water storage step (S1) of storing consolidated water in a filtration tank (2) up to a predetermined water level;
A consolidation step (S2) of consolidating the filter layer (4) by a water flow when the stored consolidated water is discharged;
After a return prevention step (S3) is performed in which a return prevention member (9) with a mesh body (21) stretched thereon is placed near the filter medium surface portion (11) to maintain the compressed state of the filter medium layer (4), a filtration treatment step (S4) is started, and
During the filtration process (S4),
A filtration treatment method characterized in that fine bubbles are ejected from a foam separator (12) attached integrally to a return prevention member (9) to separate suspended matter by foam separation.

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