Filtration device and filtration method

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

[Technical Field]

[0001] The present invention relates to a downflow filtration device that uses a granular fiber filter medium to filter a liquid to be treated, and to a filtration device and filtration method that perform filtration while removing suspended solids that have peeled off from the filter medium. [Background technology]

[0002] Conventionally, filtration equipment has been known that performs filtration by passing the liquid to be treated through settled irregular filter media in a downward flow. As filtration time passes, suspended solids adhere to the interior and surface of the filter media, causing a decrease in filtration performance, making it necessary to periodically clean the filter media. Filter media cleaning is performed after the filtration process and is typically performed by backwashing water from the wastewater side, aeration, mechanical agitation, or a combination of these.

[0003] For example, Patent Document 1 discloses a filter media cleaning technology in which, during cleaning of a filter media layer, air is supplied from the bottom to fluidize the filter media and release suspended matter, 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 floated and concentrated suspended matter is discharged from the top of the filtration device with cleaning water supplied from the bottom. It also describes a technology in which raw water with fine bubbles introduced is supplied during the filtration process, and suspended matter adhering to the filter media is caused to float and concentrate, and then discharged.

[0004] 7 of Patent Document 2 discloses a filter media cleaning technology in which a cleaning treatment liquid is poured into the bottom of a filtration device, and then the filter media is stirred while a filter media operating member is moved upward through aeration to remove suspended solids adhering to the filter media, which are then discharged from the top of the filtration device. Furthermore, a technology is disclosed in which a filter media operating member is placed inside the filtration device, and the pressure of the flow when draining water at the bottom reduces the gaps in the filter media in order to increase the capture rate of suspended solids during filtration. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5850793 [Patent Document 2] Patent No. 4475924 (Figure 7) Summary of the Invention [Problem to be solved by the invention]

[0006] In conventional filter media cleaning technology, the filter media is agitated and cleaned, which has 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, if the liquid being treated contains a large number of fine particles, the suspended solids contained therein are not sufficiently captured by the filter media layer and are discharged from the bottom, making it impossible to improve filtration accuracy.

[0007] Patent Document 1 discloses a technology in which raw water containing fine bubbles is supplied to a filtration device in the filtration process, causing suspended solids to float and concentrate, resulting in removal. However, because the filter media is not sufficiently compacted, suspended solids cannot be captured efficiently, and the rate of suspended solids removal cannot be reduced. Furthermore, during filter media cleaning, suspended solids detached from the filter media by air supplied through an air supply pipe are floated and concentrated in a fine bubble generator, but there is no description or suggestion that the fine bubble generator can be raised or lowered. Therefore, when the position of the filter media layer changes, fine bubbles cannot be supplied to the desired position, and suspended solids cannot be removed efficiently.

[0008] The technology of Patent Document 2 has a filter medium operating member provided above the filter medium layer, which makes it possible to sufficiently compress the granular fiber filter medium together during the filtration process, but it is difficult to perform stable filtration because the pressing force and opening force of the filter medium operating member depend on the raw water flow rate, the content of suspended solids, the aeration rate, etc. Furthermore, it is not possible to wash the filter medium while the filter medium layer is compressed during the filtration process.

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and provides a filtration device and a filtration method that can continue stable filtration operation by leaving a return prevention member of the filter material layer stationary on the surface layer of the filter material during the filtration process to form a filter material layer with a uniform porosity, and by removing suspended matter that has peeled off the filter material by floating and concentrating it. [Means for solving the problem]

[0010] Before the filtration process The water flow that discharges the consolidated water stored in the filter tank The settling granular fiber filter media is compressed, Placed near the surface of the filter media In a downward flow type filtration device in which a consolidation state is maintained by a return prevention member, A mesh body with water holes was stretched Cylindrical frame Body and , During the filtration process, an agitation fluid jetting device jets an agitation fluid from a jetting part toward the surface of the filter material, and a jetting part jets an agitation fluid upward from the jetting part. a foam separator that ejects fine bubbles; A liftable return prevention member comprising By providing this, the filter layer can be maintained in a compacted state and fine bubbles can be ejected from the desired position, so suspended solids floating up inside the filter tank can be efficiently removed. Furthermore, after the suspended matter is separated from the surface layer of the filter medium by the agitated fluid ejected from the agitated fluid ejection device, the separated suspended matter can be floated and separated by the fine bubbles ejected from the foam separation device.

[0013] The foam separation device includes a pipe formed along the inner wall of the frame body, and a nozzle hole formed in the pipe. On the top By providing the jetting portion having the above structure, the fluid supplied into the pipe can be jetted out from the jetting portion as fine bubbles.

[0014] In a downward flow filtration method in which suspended solids in a liquid to be treated are captured by a filter layer formed of sedimentary granular fiber filter media, the method includes a consolidated water storage step in which consolidated water is stored in a filter tank up to a predetermined water level, a consolidation step in which the filter layer is consolidated by the water flow when the stored consolidated water is discharged, and a return prevention step in which a return prevention member with a stretched mesh body is placed near the surface of the filter media to maintain the consolidation state of the filter layer.After these steps are performed, 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 filter layer with a uniform and high degree of compaction, and since the suspended solids can be removed efficiently, stable filtration process can be continued. [Effects of the Invention]

[0015] The filtration apparatus and filtration method of the present invention incorporate a foam separation device integrally mounted on a liftable return prevention member. By placing the return prevention member near the surface of the filter medium, operation is possible while maintaining the compaction of the filter medium layer, allowing for stable filtration over long periods of time. Furthermore, since fine bubbles can be ejected from a desired position, suspended solids contained in the supplied treated liquid can be efficiently removed. By performing foam separation during the filtration process, even minute suspended solids that cannot be captured by the filter medium can be removed, improving the suspended solid removal rate. Furthermore, by ejecting an agitating fluid toward the surface of the filter medium using an agitating fluid ejection device, the accumulation of suspended solids on the surface of the filter medium can be prevented, reducing clogging of the surface of the filter medium. This also reduces the time and frequency of cleaning the filter medium after the filtration process. This method is particularly effective for fibrous filter medium with high porosity and compressibility, allowing for continuous operation while maintaining a uniform and high compaction level even during the filtration process. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a longitudinal sectional view of a filtering device according to the present invention. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. 10 is a schematic diagram of the filtration process at the start-up stage. [Figure 5] FIG. 10 is a schematic diagram of the consolidation water storage process. [Figure 6] FIG. [Figure 7] FIG. 10 is a schematic diagram of the return prevention step. [Figure 8] FIG. 10 is a schematic diagram of the filtration process. DETAILED DESCRIPTION OF THE INVENTION

[0017] FIG. 1 is a vertical cross-sectional view of a filtering device according to the present invention. The filtration device 1 has a cylindrical filter tank 2 set upright, filled with fibrous filter media to form a filter media layer 4 on an outflow prevention screen 3 below the filter tank 2. The fibrous filter media is a sedimentary granular fibrous filter media, and is not limited to a specific shape, such as spherical or cylindrical. The liquid to be treated is supplied from an upper treated liquid pipe 5, suspended solids are captured by the filter media layer 4, and the treated water is discharged to the outside through a lower treated liquid pipe 6. If necessary, a screen may be installed above the filter tank 2 to prevent the fibrous filter media from flowing out toward the treated liquid pipe 5.

[0018] Inside the filter tank 2, a return prevention mechanism is provided to prevent the compressed filter layer 4 from loosening in the upward opening direction and causing the porosity of the filter layer 4 to become non-uniform.

[0019] The return prevention mechanism is composed of a driver 7 installed above the filter tank 2, a feed screw member 8 driven by the power of the driver 7, a return prevention member 9 threadedly engaged with the feed screw member 8 to move 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 filter tank 2 to the feed screw member 8, and has a tubular member 34 at its end through which the feed screw member 8 can be inserted. The tubular member 34 functions as a vibration prevention device for the end of the feed screw member 8, which 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 rotate forward and backward, and the remaining ones are configured to be driven by 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 around a drive pulley 31 and a driven pulley 32 provided on each feed screw member 8.

[0020] Each feed screw member 8 is installed vertically so as to be parallel to the axis of the filter tank 2, and a helical screw thread is formed on the circumferential surface over at least 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 selected appropriately depending on the specifications of the filter device 1 and the lifting speed.

[0021] The return prevention member 9 integrally comprises a foam separation device 12 that separates suspended solids in the liquid being treated that is supplied to the filter media layer 4 by using fine bubbles to float them up and separate them, and discharges them together with the foam from a discharge pipe 20 above the filter tank 2, and an agitation fluid jetting device 13 that jets an agitation fluid (gas or liquid) at the suspended solids that have accumulated on the filter media surface layer 11 to agitate them. 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 separation device 12 and the agitation fluid jetting device 13. A fluid supply source 19 is connected to the supply pipe 18, and a configuration is possible in which fluid can be supplied to the foam separation device 12 and the agitation fluid jetting device 13.

[0022] In this embodiment, the return prevention member 9 is threadedly engaged with a plurality of feed screw members 8, but a single feed screw member 8 may also be installed vertically in the center of the filter tank 2. In this configuration, by installing a guide bar (not shown) vertically at a position eccentric to the axis, it is possible 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 configuration of the lifting mechanism are not limited to those in this embodiment.

[0023] FIG. 2 is a top view of the return prevention member. The return prevention member 9 is a member that is placed near the filter material surface portion 11 to maintain the compacted state of the filter material layer 4, and is made of a mesh body 21 with minute water passage holes stretched inside a cylindrical frame body 23 of a predetermined thickness. The frame body 23 is placed close to the inner wall of the filter tank 2 shown in Figure 1, and is set so that the filter material cannot pass through the gap formed between the frame body 23 and the filter tank 2. If necessary, a sliding member may be provided around the outer periphery of the frame body 23.

[0024] The mesh body 21 is formed of a plate material with minute holes therethrough, a mesh member, etc. The water passage holes of the mesh body 21 have a diameter that allows the water to be treated from the liquid to be treated pipe 5 to pass through to the filter layer 4, and that prevents the filter material from flowing out upward.

[0025] A helical thread groove 27 that screws into each of the feed screw members 8 is formed at a position eccentric to the center of the return prevention member 9. In this embodiment, the thread groove 27 is formed on the inner circumferential surface of a tubular member 35 that has a predetermined height and is placed on the mesh body 21. The tubular member 35 is disposed so as to communicate with an opening (not shown) formed in the mesh body 21, so that the feed screw member 8 can be inserted from above, and by rotating the tubular member 35 with the feed screw member 8 inserted, the return prevention member 9 can be raised and lowered in the vertical direction. The configurations of the thread groove 27, the tubular member 35, etc. in this embodiment are merely examples, and are not limited to these as long as they are capable of engaging with the feed screw member 8.

[0026] If necessary, a reinforcing rib may be added in the vertical direction of the return prevention member 9. Furthermore, when the mesh body 21 is provided in two tiers, upper and lower, with a predetermined gap between them, the fibrous filter material that flows out from the lower mesh body 21 can be captured by the upper mesh body 21.

[0027] In this embodiment, the return prevention member 9 is integrally provided with a foam separation device 12 having a pipe 16A (main pipe 17A, branch pipe 26A) and a jetting portion 15A. The main pipe 17A and branch pipe 26A are formed along 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 branch off vertically from the main pipe 17A. The pipe 16A (main pipe 17A, branch pipe 26A) is fixed to the frame 23 or the mesh body 21 by a known method.

[0028] Piping 16A is fitted with a plurality of ejection parts 15A, each having a large number of ejection holes 14A formed on its upper surface, and ejects compressed air flowing from supply pipe 18 into main pipe 17A and branch pipe 26A upward as fine bubbles. Each ejection part 15A is detachably attached to piping 16A, and if an ejection hole 14A becomes clogged, maintenance can be performed on just the desired ejection part 15A, making maintenance easy.

[0029] Each of the jetting parts 15A generates microscopic bubbles using a known membrane type having a synthetic resin or synthetic rubber membrane on the top surface with numerous microscopic holes (jet holes 14A). The membrane expands due to the compressed air supplied into the pipe 16A, opening the microscopic holes (jet holes 14A), thereby diffusing the air. When the supply of compressed air is stopped, the microscopic holes (jet holes 14A) are in a closed state.

[0030] Any device capable of generating fine bubbles may be used, and other fine bubble generating mechanisms may be used instead of the air diffusion type. The material of the piping 16 may be selected appropriately depending on the conditions, such as metal, synthetic resin, or ceramic.

[0031] FIG. 3 is a bottom view of the return prevention member. In this embodiment, the agitated fluid jetting device 13 having the piping 16B (main pipe 17B, branch pipe 26B) and jetting portion 15B is installed integrally with the lower part of the return prevention member 9 described in detail in Fig. 2. The main pipe 17B and branch pipe 26B are formed along the inner wall 30 of the frame. As with the foam separation device 12, the piping 16B (main pipe 17B, branch pipe 26B) is fixed to the frame 23 or the mesh 21 by a known method.

[0032] The pipe 16B has a plurality of downward jets. Out Hole 14B of The main pipe 17B may be omitted and the supply pipe 18 may be directly connected to the branch pipe 26B. Although the agitation fluid jetting device 13 is configured with a plurality of pipes 16B, the present invention is not limited to this as long as it is a mechanism that can agitate the suspended solids deposited on the surface layer portion 11 of the filter medium.

[0033] It is desirable that the pipes 16A and 16B constituting the foam separator 12 and the agitated fluid jetting device 13 are installed at a predetermined distance from the mesh body 21. This prevents the installed pipes 16A and 16B from blocking the water passage holes of the mesh body 21 and reducing the water passage efficiency. Furthermore, 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 pipe 26B may be laid over the main pipe 17B to communicate with it.

[0034] When using fine bubbles as the agitated fluid, the main pipe 17 that constitutes the foam separation device 12 and the agitated fluid jetting device 13 may be shared, and the jetting section 15A may be provided above the main pipe 17 and the jetting section 15B may be provided below it.

[0035] The number and positions of the ejection portions 15A and 15B constituting the foam separator 12 and the agitated fluid ejection device 13, the diameter, shape and ejection angle of the ejection holes 14A and 14B, etc. are also appropriately selected according to design conditions. [Example]

[0036] In this embodiment, after the steps shown in FIGS. 4 to 7 described below are performed, the filtration step shown in FIG. 8 is performed. conduct. FIG. 4 is a schematic diagram of the filtration process at the start-up stage. When new filter media is added to the filter tank 2, or when the water in the filter tank 2 is drained after the filtration treatment step S4 and the fibrous filter media has been washed, the fibrous filter media ends up piled up on the outflow prevention screen 3. The return prevention member 9 is raised above the filter tank 2 and is placed in a position where it will not get in the way when replacing the fibrous filter media or during the filter media washing step S5.

[0037] The filter layer 4 is in a state of natural settling, with large voids between the fibrous filter media. If the liquid to be treated is passed through this state, 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 for consolidating the filter layer 4 are carried out prior to the filtration treatment step S4.

[0038] <Consolidated water storage process S1> Figure 5 is a schematic diagram of the consolidation water storage process. In the compressed water storage step S1, compressed water is stored in the filter tank 2. Compressed water is supplied into the filter tank 2 from the treated liquid pipe 5. Valve V2 installed in the treated liquid pipe 6 is closed, and the compressed water is stored in the filter tank 2. At this time, valve V3 installed in the discharge pipe 20 is open, allowing air to be drawn in and discharged from above the filter 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 surface layer 11 of the filter material.

[0039] In this embodiment, the consolidated water is newly supplied to the filtration tank 2 from the outside, but the cleaning liquid stored in the filtration tank 2 after the filter media cleaning step S5 may also be used as the consolidated water.

[0040] <Consolidation process S2> Figure 6 is a schematic diagram of the consolidation process. In the consolidation step S2, the fiber filter medium is consolidated to form the filter medium layer 4. The consolidation water is poured up to a predetermined water level. After storing the water, the valve V2 installed in the treated liquid pipe 6 is opened, and the consolidated water is discharged downwards in one go. At this time, the water flow toward the bottom of the filter tank 2 consolidates the fibrous filter material above the outflow prevention screen 3, forming a filter material layer 4 with a sufficient degree of compaction. When the consolidation step S2 is performed, the gaps between the fibrous filter material become smaller, and the height of the filter material 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 filter tank 2 and then discharged, may be performed multiple times.

[0041] <Return prevention process S3> FIG. 7 is a schematic diagram of the return prevention process. In the return prevention step S3, the return prevention member 9 is placed near the filter material surface layer 11 to maintain the consolidated state of the filter material 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 begins to descend while threadedly engaging with the feed screw member 8.

[0042] 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 consolidated 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 arranged in the filter tank 2, or a torque meter 28 arranged at the connection part of the driver 7, etc.

[0043] The tachometer 24 measures the number of revolutions of the feed screw member 8 or the driver 7, and sends a stop signal to the driver 7 when the number of revolutions reaches a predetermined number.

[0044] Furthermore, the position detector 25 uses a known contact or non-contact type device and sends a stop signal to the driver 7 when the return prevention member 9 reaches a predetermined position.

[0045] Furthermore, the torque meter 28 measures the sudden increase in torque when the return prevention member 9 reaches the filter material surface layer portion 11, and if the torque measured exceeds a predetermined measurement value, it sends a stop signal to the driver 7. Note that the method of detecting descent is not limited to the above method and can be determined appropriately depending on the conditions.

[0046] The speed at which the return prevention member 9 descends is preferably slower than the speed at which the fibrous filter medium is descended 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 descending speed of the fibrous filter medium is set, the speed should be adjusted so as not to overtake the descending surface layer 11 of the filter medium.

[0047] The return prevention member 9 placed near the filter media surface layer 11 is threadedly engaged with the feed screw member 8, and therefore 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 treatment step S4, the lower filter media layer 4 is not pressed.

[0048] 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 material surface layer portion 11 immediately after the filter material layer 4 is consolidated. For example, if the return prevention step S3 is started before the consolidation step S2, the return prevention member 9 may be slowly lowered while the filter material layer 4 is consolidated with compressed water, so that the return prevention member 9 reaches the filter material surface layer portion 11 before the compressed filter material layer 4 begins to loosen upward in the opening direction.

[0049] 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 loosening in the opening direction due to the compressed filter layer 4, and the filtration process S4 is started in this state. The filter layer 4 is formed with a uniform and highly compacted density by the compressed water, so stable filtration can be performed from the beginning of operation.

[0050] <Filtration process step 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 through 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 can be discharged after passing through the filter media layer 4. 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 bled to adjust the pressure in the filtration tank 2 so that it does not rise too much.

[0051] 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, then passes through each branch pipe 26A (pipe 16A) and is sprayed upward as fine bubbles from the nozzle holes 14A formed in each nozzle section 15A. In this embodiment, fine bubbles are constantly sprayed during the filtration treatment step S4, allowing suspended solids generated during filtration to be efficiently floated and separated. The timing for starting the supply of compressed air is determined appropriately depending on the conditions.

[0052] The many fine bubbles ejected adsorb suspended solids present in the treated liquid supplied from above, as well as suspended solids that have naturally separated from the filter layer 4 due to the influence of water pressure, and rise to the water surface. The bubbles adsorbing the suspended solids that rise one after another then gather on 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 filter tank 2.

[0053] After a predetermined time has elapsed since the start of the filtration process step S4, suspended matter contained in the liquid to be treated passing through the filter media layer 4 gradually accumulates on the filter media surface layer 11. In this embodiment, the return prevention member 9 is left stationary on the filter media surface layer 11, and the filtration process is performed while maintaining a uniformly compacted state, so suspended matter can be efficiently captured between the filter media, but as the filtration time passes, suspended matter accumulates on the filter media surface layer 11, causing the filtration pressure to increase in a short period of time and possibly causing a decrease in filtration efficiency.

[0054] Therefore, in this embodiment, an agitating fluid is jetted toward the filter surface layer portion 11 during the filtration treatment step S4, and filtration is performed while peeling off the suspended solids deposited on the filter surface layer portion 11.

[0055] The filter material surface layer 11 is stirred when a predetermined gap X is formed between the stirred fluid jetting device 13 provided below the return prevention member 9 and the filter material surface layer 11. The predetermined gap X is several centimeters to several tens of centimeters, and is formed by the filter material surface layer 11 being gradually consolidated by the supply pressure of the liquid to be treated during the filtration process. In this embodiment, a highly compressible fibrous filter material is used, so the filter material layer 4 is consolidated by the water pressure of the liquid to be treated, and the predetermined gap X is formed.

[0056] After the predetermined gap X is formed, the fluid supply source 19 connected to the agitated fluid jetting device 13 is driven to supply the agitated fluid from the supply pipe 18 toward the main pipe 17B (piping 16B) shown in Fig. 3. The agitated fluid supplied to the main pipe 17B (piping 16B) is jetted toward the filter medium surface layer portion 11 from the jetting holes 14B formed in a plurality of branch pipes 26B communicating with the main pipe 17B (piping 16B).

[0057] After the stirring fluid is ejected, the filter layer surface portion 11 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, rises upward, and is adsorbed by fine air bubbles constantly supplied into the filter tank 2 from the foam separation device 12, after which it continues to rise toward the water surface. Then, foam is formed on the water surface by the air bubbles that rise one after another.

[0058] The predetermined gap X may be confirmed, for example, by a sensor capable of measuring the position through an inspection window provided in part of the filter tank 2, or by photographing using an imaging device. Alternatively, the pressure inside the filter tank 2 may be continuously measured, and when the measurement value reaches a predetermined value, it is recognized that the thickness of the filter medium layer 4 has changed. In this embodiment, the anti-return member 9 is stationary near the filter tank surface layer 11, so the filter medium layer 4 does not move upward or downward. However, if, for example, the distance from the filter medium surface layer 11 to the agitation fluid jetting device 13 is desired to be equal to or greater than the predetermined gap X, the agitation fluid jetting device 13 may be moved to jet the filter medium agitation fluid from any position.

[0059] The foam formed on the water surface is discharged from the discharge pipe 20 together with the fine bubbles that are constantly sprayed upward from the aeration unit 15. Since the valve V3 installed in the discharge pipe 20 is always open during the filtration process, the foam formed on the water surface in the filter tank 2 is discharged together with the fine bubbles that are constantly discharged from the aeration unit 15 toward the discharge pipe 20.

[0060] At this time, the opening of valve V3 is adjusted appropriately according to the value of a level gauge 29 installed in the discharge pipe 20, which measures the water level in the filtration tank 2. In this embodiment, in order to perform filtration while maintaining a constant water level in the filtration tank 2, a level gauge 29 is installed in the discharge pipe 20 and constantly measures the water level. If the measured water level deviates from a predetermined value, the opening of valve V3 is adjusted. For example, if the measured water level is lower than the predetermined value, the opening of the valve is increased, increasing the amount of foam and fine bubbles discharged and raising the water level to the predetermined value. Because a large amount of air remaining above the filtration tank 2 leads to a drop in the water level in the filtration tank 2, the above operation is performed based on the measurement value of the level gauge 29. Note that the method of discharging foam is not limited to this embodiment, and may be a form in which foam is constantly overflowed and discharged from the discharge pipe 20.

[0061] After the filtration process S4 is completed, the supply of the liquid to be treated is stopped and the 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 agitation of the filter surface layer 11, and is terminated when a predetermined time, a predetermined time, a predetermined pressure, etc. is reached.

[0062] Furthermore, the timing of starting and ending the jetting of the agitated fluid is determined based on a predetermined time, a predetermined time, a predetermined pressure, etc. The agitated fluid may be jetted continuously or intermittently.

[0063] In this embodiment, the agitated fluid jetting device 13 is installed below the return prevention member 9, and the foam separation device 12 is installed above it. This allows fine bubbles to be supplied to the suspended matter immediately after it has been separated by the agitated fluid supplied from the agitated fluid jetting device 13. This allows the suspended matter to be adsorbed onto the fine bubbles before it rises to the water surface, thereby efficiently generating foam. Furthermore, because the foam separation device 12 and the agitated fluid jetting device 13 can be raised and lowered, the agitated fluid jetting device 13 can be disposed near the filter material surface layer 11, preventing suspended matter from accumulating on the filter material surface layer 11.

[0064] Furthermore, since the filter surface layer 11 is constantly cleaned during the filtration treatment step S4, the filtration efficiency does not decrease. By continuing filtration while constantly cleaning the filter surface layer 11 in this way, it is possible to prevent an early rise in filtration pressure, extend the filtration duration, and reduce the time and frequency of cleaning the filter medium.

[0065] In this embodiment, the ejection portion 15 of the foam separation device 12 is configured to face upward, but the ejection portion 15 may be configured to face downward and installed on the return prevention member 9, allowing a single device to perform both surface agitation of the filter medium and foam separation. In this configuration, 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, agitation of the surface of the filter medium can be performed before the predetermined gap X is formed due to consolidation of the treated liquid. Alternatively, a configuration may be adopted in which only the foam separation device 12 with its ejection port facing upward is installed integrally with the return prevention member 9, allowing only foam separation to be performed during the filtration treatment step S4.

[0066] <Filter cleaning process S5> In the filter media cleaning step S5, as shown in Figure 4, the return prevention member 9, which is 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 filter tank 2 to clean the fiber filter media. After cleaning the filter media, the waste cleaning liquid is discharged from the discharge pipe 20. At this time, valves V2 and V3 are in an open state. In this embodiment, the filter media is cleaned using a known method, but because filtration is performed while removing suspended matter prior to the filter media cleaning step S5, clogging of the filter media surface layer 11 is unlikely to occur. This makes it possible to reduce the time and frequency of filter media cleaning.

[0067] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention. [Industrial Applicability]

[0068] The present invention performs filtration while removing suspended solids that accumulate on the surface of the filter media while maintaining the compacted state of the filter media layer, making it less likely for the filter media layer to become clogged and allowing for stable filtration to continue. Furthermore, because suspended solids are removed prior to the filter media cleaning process, filtration can be continued for extended periods of time, reducing the time and frequency of filter media cleaning. Fiber media with high capture rates can be used for coagulation filtration, which tends to result in surface filtration, or for highly turbid water, or for special applications requiring high clarity, such as pools. By performing deep filtration, this is a beneficial filtration method that allows for long filtration processes with less frequent cleaning. [Explanation of symbols]

[0069] 1. Filtration equipment 2 Filtration tank 4 Filter media layer 9. Return prevention member 11 Filter material surface 12 Foam separator 13 Agitation fluid jetting device 14A spout hole 15A spout part 16A piping 21 net body 23 Frame 30 Frame inner wall S1 Consolidation water storage process S2 Consolidation process S3 Return prevention process S4 Filtration process

Claims

1. In a downward flow filtration device, a settling granular fiber filter medium is compressed by a water flow that discharges compressed water stored in a filtration tank (2) in the preceding stage of a filtration treatment step (S4), and the compressed state is maintained by a return prevention member (9) that is stationary in the vicinity of the surface layer (11) of the filter medium. a cylindrical frame (23) on which a mesh body (21) having water passage holes is stretched; an agitating fluid jetting device (13) that jets an agitating fluid from a jetting portion (15B) toward the surface layer portion (11) of the filter material during the filtration treatment step (S4); a foam separator (12) that ejects fine bubbles upward from an ejection portion (15A); The liftable return prevention member (9) is provided. A filtration device characterized by:

2. The foam separation device (12) includes a pipe (16A) formed along the inner wall (30) of the frame (23); a jetting part (15A) formed in the pipe (16A) and having fine jetting holes (14A) on the upper surface thereof; 2. The filtration device according to claim 1.

3. 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 the water flow when the stored consolidation 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 surface layer (11) of the filter material to maintain the compressed state of the filter material layer (4), a filtration treatment step (S4) is started, During the filtration treatment step (S4), A foam separator (12) integrally attached to the return prevention member (9) ejects fine bubbles to separate suspended matter by foam separation. A filtration treatment method characterized by:

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