Cleaning method for a downward flow filtration system using fiber filter media

Abstract

This invention provides a cleaning method for a downward-flow filtration system using fibrous filter media, which prevents suspended solids from reattaching to the filter media by discharging the cleaning wastewater after cleaning the filter media at a rate faster than the sedimentation rate of the filter media layer. [Solution] In a cleaning method for a downward-flow type filtration device, in which a cleaning step S2 is performed in which a cleaning liquid is stored up to a predetermined height in a filtration tank 2 in which a filter media layer 4 composed of amorphous filter media is formed, the filter media 15 is agitated and cleaned, and then the cleaning drainage liquid is discharged from below, the cleaning time for the filter media can be shortened by performing a depressurization step S3 in which the pressure inside the filtration tank 2 is reduced to a predetermined pressure using a depressurization pump 8 to make the filter media 15 float, after the cleaning step S2 is performed, or simultaneously with the cleaning step S2, and then performing a discharge step S5 in which the cleaning drainage liquid is discharged from the bottom of the filtration tank 2 at a speed faster than the settling speed of the floated filter media layer 4.

Description

Technical Field

[0006] , , ,

[0001] The present invention relates to a method for cleaning a downward-flow filtration device using a fiber filter medium, which can shorten the cleaning time and reduce the cleaning water volume during the filter medium cleaning process in a filtration device using a fiber filter medium.

Background Art

[0002] Conventionally, a downward-flow filtration device using an amorphous fiber filter medium with a specific gravity greater than 1 captures impurities in the liquid to be treated supplied from above during the filtration process using the filter medium. However, as the filtration operation continues, the impurities captured by the filter medium accumulate, and the filtration performance gradually deteriorates. To maintain the performance of the filtration device, a cleaning fluid such as cleaning liquid or compressed air is periodically supplied from below the filtration tank to perform agitation cleaning of the filter medium.

[0003] Patent Document 1 discloses a filter medium cleaning technique in which fine bubbles supplied from a gas-liquid mixing nozzle installed at the bottom of a filter medium layer are attached to the fiber filter medium to increase the buoyancy of the filter medium, and then air is supplied from the lower part of the filtration device to peel off suspended substances from the filter medium.

[0004] Patent Document 2 discloses a filter medium cleaning technique in which reverse washing water supplied with compressed air is decompressed to generate water containing a large amount of fine bubbles, and the generated water is supplied to the filter layer to expand the filter layer by the fine bubbles to peel off suspended substances from the filter medium.

[0005] Patent Document 3 discloses a filter medium cleaning technique in which the pressure inside a container housing a hollow fiber membrane filter is reduced by a vacuum pump to peel off fine particles attached to the filter by bubbles of carbon dioxide gas.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] Conventionally, downward-flow filtration systems have a filter media outflow prevention screen installed below them to prevent the filter media from flowing out to the treated liquid discharge side. However, when discharging the wash water after cleaning the filter media, the filter media would settle before or at the same time as the wash water, sometimes blocking the filter media outflow prevention screen. This reduced the efficiency of the wash water drainage, leading to longer washing times and increased wash water usage. There was also the problem of suspended solids in the wash water reattaching to the filter media that settled before the wash water.

[0008] Patent Document 1 describes a method of increasing the buoyancy of a fibrous filter media by attaching fine bubbles to it before supplying compressed air from below the filtration device. However, the filtration device is open at the top, and the inside of the device is under atmospheric pressure. As a result, the filter media to which the fine bubbles have attached does not easily settle downwards after agitation and washing, leading to problems such as the time required for the filter media layer to be reformed.

[0009] Patent Document 2 describes a method in which water mixed with microbubbles is supplied to the filter layer, causing the microbubbles to adhere to the filter media, which then expands and detaches suspended solids. However, similar to Patent Document 1, microbubbles adhere to the fibrous filter media during cleaning, making it difficult for the filter media to settle after agitation and cleaning. Furthermore, while compressed air is mixed into the water to generate water with microbubbles and the pressure is reduced, there is no description or suggestion of reducing the pressure inside the filtration tank.

[0010] Patent Document 3 describes a method for generating a large amount of bubbles by reducing the pressure inside a hollow fiber membrane storage container with a vacuum pump in order to remove fine particles adhering to the hollow fiber membrane filter. However, the filter media used is a hollow fiber membrane filter, not an amorphous filter media. Therefore, there is no need to allow the filter media to settle to the bottom of the container after cleaning. The purpose of reducing the pressure is also not to adjust the settling speed of the filter media.

[0011] The present invention provides a method for cleaning a downward flow filtration apparatus using fibrous filter media, which prevents the re-adhesion of suspended matter to the filter media by reducing the pressure inside the filtration tank containing the cleaned filter media to make the filter media layer float, and then discharging the cleaning wastewater at a speed faster than the settling speed of the filter media layer. [Means for solving the problem]

[0012] The present invention relates to a cleaning method for a downward-flow type filtration apparatus, which involves storing a cleaning solution up to a predetermined height in a filtration tank forming a filter media layer composed of amorphous filter media, stirring and cleaning the filter media, and then discharging the cleaning wastewater from below. In this method, a depressurization step is performed after the cleaning process, or simultaneously with the cleaning process, in which the pressure inside the filtration tank is reduced to a predetermined pressure using a depressurization pump to float the filter media. After this depressurization step is performed, the cleaning wastewater is discharged from the bottom of the filtration tank at a speed faster than the settling speed of the floating filter media layer, thereby preventing suspended solids from reattaching to the filter media layer.

[0013] During the aforementioned discharge process, the inside of the filtration tank is pressurized, and a water absorption process is carried out to allow the filter media to absorb the cleaning solution, causing the filter media layer that has absorbed the cleaning solution to settle. [Effects of the Invention]

[0014] This invention prevents suspended solids detached from the filter media from reattaching to the filter media by reducing the pressure inside the filtration tank containing the washed filter media to make the filter media layer float, and then discharging the washing drainage at a speed faster than the settling speed of the filter media layer. This eliminates the need to repeatedly wash the filter media, thereby reducing washing time and the amount of washing water used. Furthermore, by discharging the washing drainage before the filter media layer, the filter media outflow prevention screen is not blocked by the filter media, thus preventing a decrease in washing efficiency. [Brief explanation of the drawing]

[0015] [Figure 1] This is a longitudinal cross-sectional side view of the downward flow type filtration device according to the present invention. [Figure 2] Similarly, this is a schematic diagram of the filter media cleaning process S1. [Figure 3] Similarly, this is a schematic diagram of the depressurization process S2. [Figure 4] It is also a schematic diagram of the water absorption step S3 and the discharge step S4. [Figure 5] It is also a schematic diagram of the filter medium in each step.

Embodiments for Carrying Out the Invention

[0016] FIG. 1 is a longitudinal side view of a downward flow filtration device. The filtration device 1 vertically installs a cylindrical filtration tank 2, fills it with an amorphous fiber filter medium 15 (FIG. 5) inside, and forms a filter medium layer 4 on a filter medium outflow prevention screen 3A stretched below the filtration tank 2. The fiber filter medium 15 is a sedimentable granular fiber filter medium with a specific gravity greater than 1, and its shape is not limited, such as spherical or columnar. The liquid to be treated is supplied from the upper supply pipe 5, and the suspended substances contained in the liquid to be treated are captured in the filter medium layer 4, and the treated liquid is discharged from the lower discharge pipe 6. A filter medium outflow prevention screen 3B is also stretched above the filtration tank 2 to prevent the outflow of the filter medium 15 to the supply pipe 5 side.

[0017] [[ID=第十九]]

[0018] A cleaning pipe 7 is provided below the filtration tank 2. When cleaning the filter medium, compressed air is injected into the filter medium layer 4 through the cleaning pipe 7 from an air supply source (not shown) such as a blower to stir and clean the filter medium 15. Thereby, the suspended substances attached to the filter medium 15 are removed, and the filter medium 15 is regenerated. As a stirring means for the filter medium 15, a known mechanical stirring device may be used instead of the cleaning pipe 7, and it can be appropriately modified and implemented.

[0019] In addition, the intake pipe 9 is equipped with a pressure gauge 11, and the pressure inside the filtration tank 2 can be measured when the vacuum pump 8 is operating. Note that the equipment used for vacuum reduction is not limited to this as long as it is a mechanism capable of creating a vacuum state inside the filtration tank 2. Regarding the connection position of the intake pipe 9, it is not specified in this embodiment, and it may be any position where the immersion liquid inside the filtration tank 2 is not sucked.

[0020] Generally, in the latter stage of the filtration process step, a filter medium cleaning step is carried out to remove the suspended substances adhering to the filter medium and regenerate the filter medium. When the cleaning step is carried out by the batch cleaning method, after storing the cleaning liquid up to a predetermined height inside the filtration tank 2, the filter medium 15 is stirred inside the filtration tank 2, and after a predetermined time has elapsed, the cleaning drain liquid is discharged from below the filtration tank 2. In this embodiment, after floating the filter medium when discharging the cleaning drain liquid, the cleaning drain liquid is discharged at a speed faster than the sedimentation speed of the filter medium layer 4. Hereinafter, the specific methods of the filtration process step S1 and the filter medium cleaning step S1 to the cleaning drain liquid discharge step S4 carried out after the filtration process step S1 in this embodiment will be described in detail based on FIGS. 1 to 5.

[0021] <Filtration process step S1> In the filtration process step S1, after opening the supply valve 12 shown in FIG. 1, the liquid to be treated is supplied from the supply pipe 5 into the filtration tank 2. When the supplied liquid to be treated passes through the filter medium layer 4 filled in the filtration tank 2, the suspended substances are captured and discharged to the outside as the treated liquid through the discharge pipe 6. At this time, the discharge valve 13 is in the open state, and the intake valve 10 and the air vent valve 14 are in the closed state. It shifts to the cleaning step S2 under predetermined conditions such as after a predetermined treatment time has elapsed.

[0022] FIG. 2 is a schematic diagram of the filter medium cleaning step S2. <Cleaning step S2> In the washing process S2, after closing the discharge valve 13 interposed in the discharge pipe 6, the supply of washing liquid is started. After the washing liquid is stored in the filtration tank 2 to a predetermined height, compressed air is injected from the washing pipe 7 to agitate and wash the filter media 15. The filter media 15 moves while repeatedly rotating and colliding due to the compressed air continuously injected from below, and suspended matter attached to the filter media 15 is detached. In this embodiment, a batch washing method is adopted, and the washing liquid is stored in the filtration tank 2 and the filter media 15 is agitated and washed for a predetermined time. After performing the washing process S2 for a predetermined time, the process moves to the depressurization process S3.

[0023] Figure 3 is a schematic diagram of the depressurization process S3. <Depressurization process S3> In the depressurization process S3, the depressurization pump 8 connected to the filtration tank 2 is activated to reduce the pressure inside the filtration tank 2 to a predetermined level. After closing the supply valve 12 and the air vent valve 14 to create a seal and opening the intake valve 10, the depressurization pump 8 is activated to draw in air from inside the filtration tank 2, causing the pressure inside the filtration tank 2 to gradually decrease. The drawn-in air is discharged to the outside through the intake pipe 9.

[0024] Each filter medium 15, which has been cleaned in the cleaning step S2 preceding the depressurization step S3, is in an immersed state and holds cleaning solution and a small amount of air bubbles 16 (Figure 5(a)) inside the voids between the fibers. When a depressurization action is applied to the filter medium 15 in this state, the air bubbles 16 held inside the voids of the filter medium expand, as shown in Figure 5(b). At this time, the air bubbles attached to the periphery of the filter medium and the air bubbles dissolved in the cleaning solution in the filtration tank 2 also expand.

[0025] As a result, the buoyancy of the filter media 15 increases, causing the filter media 15, which was swimming in the filtration tank 2, to float upward and form a filter media layer 4 near the filter media outflow prevention screen 3B. At this time, bubbles 16, which are formed by the deposition of gas dissolved in the immersion liquid in the filtration tank 2, also help the filter media 15 float. As the filter media 15 floats, the suspended matter that has detached from the filter media 15 sinks downward in the filtration tank 2. The bubbles 16 that have expanded inside the filter media (Figure 5(b)) are released into the washing liquid from the voids inside the filter media and then discharged to the outside through the intake pipe 9.

[0026] In this embodiment, the depressurization process S3 is continued until the pressure measured by the pressure gauge 11 installed in the intake pipe 9 reaches a predetermined pressure, and then continues for a predetermined time. After the predetermined time has elapsed, the depressurization process S3 is terminated and the process moves to the water intake process S4 (described later). The depressurization process S3 may also be terminated when the pressure in the filtration tank 2 reaches a predetermined pressure.

[0027] Furthermore, in this embodiment, the depressurization process S3 is started after the cleaning process S2 is completed, but the cleaning process S2 may be performed simultaneously during the depressurization process S3. In this case, after accumulating cleaning liquid to a predetermined height in the filtration tank 2 at the start of the cleaning process S2, the depressurization pump 8 is started to reduce the pressure inside the filtration tank 2, and then the cleaning process S2 is started. By performing agitation cleaning of the filter media 15 while reducing the pressure, it is possible to detach suspended solids from the filter media 15 while the filter media 15 is floating. Compressed air may be supplied from the cleaning pipe 7 while reducing the pressure in the filtration tank 2, but since air is taken into the filtration tank 2 by opening a valve interposed in the compressed air supply line (not shown) connected to the cleaning pipe 7, a compressed air supply source such as a blower can be omitted. In this embodiment, the timing of starting the supply of compressed air is after the start of the depressurization pump 8, but it may be before the start of the depressurization pump 8.

[0028] Figure 4 is a schematic diagram of the water absorption process S4 and the discharge process S5. <Water absorption process S4 and discharge process S5> In the water intake process S4, after the depressurization process S3 is completed, the depressurization pump 8 is stopped and the intake valve 10 is closed, and the air vent valve 14 installed in the filtration tank 2 is opened to open the filtration tank 2 to the atmosphere. Opening the air vent valve 14 increases the pressure inside the filtration tank 2, bringing it to atmospheric pressure.

[0029] By opening the filtration tank 2 to the atmosphere, the cleaning liquid stored in the filtration tank 2 is repressurized, causing the expanded air bubbles 16 within the filter media 15 to contract and become extremely small. At this time, as shown in Figure 5(c), the cleaning liquid surrounding the filter media is drawn into the filter media, and the air bubbles 16 held in the voids inside the filter media are replaced by the cleaning liquid, resulting in all of the filter media 15 becoming saturated with water.

[0030] In this embodiment, the water intake process S4 is started to open the inside of the filtration tank 2 to the atmosphere, and the discharge process S5 is started. In the discharge process S5, the discharge valve 13 is opened to discharge the cleaning wastewater inside the filtration tank 2 from the bottom of the filtration tank 2. The supply valve 12 is kept closed.

[0031] As the water absorption process S4 removes air bubbles from the voids of the filter media, it loses buoyancy and its tendency to settle increases. As a result, the filter media layer 4 gradually settles from the position indicated by the dashed line in the diagram and eventually accumulates on the filter media outflow prevention screen 3A below the filtration tank 2.

[0032] As the filter media layer 4 settles, the washing wastewater remaining in the filtration tank 2 is discharged to the outside through the discharge pipe 6 located below the filtration tank 2. In this embodiment, the washing wastewater is discharged at a speed faster than the settling speed of the filter media layer 4. Specifically, the settling speed of the filter media layer 4 is calculated in advance through testing, and the discharge speed of the washing wastewater is set so that it is discharged at a speed faster than the calculated settling speed. The opening of the discharge valve 13 and the diameter of the discharge pipe 6 are adjusted so that the washing wastewater is discharged at a predetermined speed, and then the washing wastewater is discharged. When discharging the washing wastewater, the discharge speed of the washing wastewater is measured using a flow meter (not shown) installed in the discharge pipe 6. Note that operations such as adjusting the opening of the discharge valve 13 while visually confirming the settling filter media layer 4 in the filtration tank 2 may also be performed, and as long as the washing wastewater is discharged at a speed faster than the settling speed of the filter media layer 4, the embodiment is not limited to this one.

[0033] Since the discharged cleaning wastewater contains suspended solids detached from the filter media 15, completing the discharge of the cleaning wastewater before the filter media 15 reaches the filter media outflow prevention screen 3A prevents the suspended solids from reattaching to the filter media 15. This eliminates the need to repeatedly clean the filter media, thus reducing the amount of cleaning water used. Furthermore, by discharging the cleaning wastewater before the filter media 15 reaches the screen, the filter media 15 prevents the filter media outflow prevention screen 3A from becoming blocked, thus maintaining the efficiency of the cleaning wastewater discharge. As the cleaning efficiency can be maintained from start to finish, the cleaning time can be shortened.

[0034] In this embodiment, after the filter media layer 4 is floated in the depressurization step S3, the water absorption step S4 is performed to settle the filter media layer 4. However, the water absorption step S4 may be omitted, and the depressurization pump 8 may be stopped at the end of the depressurization step S3, and the discharge valve 13 may be opened without returning the inside of the filtration tank 2 to atmospheric pressure to discharge the cleaning wastewater. In this case, a separate drain pump 17 for discharging the cleaning wastewater is prepared and connected to the discharge pipe 6, and the cleaning wastewater in the filtration tank 2 is sucked out and forcibly discharged. Alternatively, when the drain pump 17 is driven, the air vent valve 14 may be opened to draw in air from above the filtration tank 2, and the cleaning wastewater may be discharged by the suction force of the drain pump 17. Discharging the cleaning wastewater while drawing in air from above improves the efficiency of the cleaning wastewater discharge. Note that the drain pump 17 may be an existing one, such as a stock solution supply pump (not shown). When using a drain pump, the opening of the discharge pipe 6 and the discharge valve 13 is set so that the cleaning drainage is discharged at a rate faster than the pre-calculated settling velocity of the filter media layer 4.

[0035] The present invention is not limited to the embodiments detailed above. It can be modified and implemented as appropriate without departing from the spirit of the invention. [Industrial applicability]

[0036] This invention prevents suspended solids detached from the filter media after cleaning from reattaching to the filter media, thereby improving the efficiency of subsequent filtration processes. Furthermore, by discharging the cleaning wastewater at a speed faster than the sedimentation rate of the filter media layer, the filter media outflow prevention screen is not blocked by the filter media, thus preventing a decrease in cleaning efficiency. Consequently, filtration and filter media cleaning can be performed in a short time, reducing the overall operating time of the equipment and contributing to energy savings. [Explanation of Symbols]

[0037] 2. Filtration tank 4. Filter media layer 8. Pressure reducing pump 15 filter media S2 cleaning process S3 Depressurization Process S4 Water absorption process S5 Discharge Process

Claims

1. In a cleaning method for a downward-flow type filtration apparatus, a cleaning step (S2) is performed in which a cleaning liquid is stored up to a predetermined height in a filtration tank (2) that has formed a filter media layer (4) composed of amorphous filter media, the filter media (15) is agitated and cleaned, and then the cleaning drainage liquid is discharged from below, A depressurization step (S3) is performed after the cleaning step (S2), or simultaneously with the cleaning step (S2), in which the pressure inside the filtration tank (2) is reduced to a predetermined level using a depressurization pump (8) to float the filter media (15). A discharge process (S5) is performed in which the washing wastewater is discharged from the bottom of the filtration tank (2) at a speed faster than the settling speed of the floating filter media layer (4). A method for cleaning a downward flow filtration apparatus using a fibrous filter material, characterized by the following features.

2. During the discharge process (S5), the filtration tank (2) is pressurized, and a water absorption process (S4) is performed to allow the cleaning solution to be absorbed into the filter media (15). A method for cleaning a downward flow type filtration apparatus using a fibrous filter material as described in feature 1.

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