JP6694374B2 - Filtration device and method of operating the filtration device - Google Patents

Description

  The present invention relates to a filtering device and a method for operating the filtering device.

  In the combined sewer system, rainwater and domestic wastewater (sewage) are collected at the final treatment plant by the same sewer pipe. Therefore, in rainy weather, sewage that exceeds the planned amount of water in fine weather may be collected at the terminal treatment plant. In this case, as one of the measures taken at the terminal treatment plant, it is known that sewage that exceeds the planned amount of water during fine weather is filtered by a filtration device and discharged as simple treated water without undergoing normal water treatment. Has been.

  As such a filtration device, for example, a filtration device including a filtration tank, a filter medium provided in the filtration tank, an air diffusing pipe provided at the bottom of the filtration tank, and a treated water discharge facility provided at the top of the filtration tank. It has been proposed (for example, see Patent Document 1).

  Then, in such a filter device, sewage is introduced from the lower part of the filter tank and passes through the filter medium in an upward flow. At this time, the suspended matter (SS) in the sewage is captured by the filter medium, and the sewage is filtered. Then, the filtered treated water is discharged from the treated water discharge facility.

  Further, the filter medium is appropriately washed in order to maintain its performance. To wash the filter medium, first, the inflow of sewage into the filter tank is stopped. Then, the air diffuser blows air into the filtration tank with the sewage accumulated in the filtration tank. Then, the filter medium is stirred, and the captured SS is separated from the filter medium. As a result, the filter medium is washed. After that, the cleaning wastewater remaining in the filtration tank is discharged from the lower part of the filtration tank.

  Further, as the filtration device, for example, a filtration tank, a filter medium provided in the filtration tank, a cleaning air supply pipe provided in the lower portion of the filtration tank, a raw water supply pipe provided in the lower portion of the filtration tank, and a filtration tank Provided in an upflow filtration device (for example, refer to Patent Document 2) having a treated water outlet provided at an upper portion and a cleaning wastewater outlet provided above the treated water outlet, a filtration tank, and the inside of the filtration tank. A filter device has been proposed that includes a filter medium, an air blowing pipe provided at the bottom of the filtration tank, and a pipe for both treatment water and cleaning drainage, which is provided at the top of the filtration tank and is capable of switching between the treatment water and the cleaning drainage. (See, for example, Patent Document 3).

JP, 2006-35136, A Japanese Patent Publication No. 6-77650 JP, 2004-136197, A

  However, in the case of continuous rainy weather, it is desired that the sewage is continuously filtered by the filtration devices described in Patent Documents 1 to 3. However, if the filtration of the sewage is continuously performed, the performance of the filter medium deteriorates. Therefore, it is necessary to interrupt the filtration of the sewage and wash the filter medium.

  To wash the filter medium, the flow of the sewage into the filter tank is stopped, the filter medium is stirred, and then the entire amount of the cleaning waste water remaining in the filter tank is discharged. Therefore, there is a problem that filtration of sewage is interrupted for a long time and the amount of cleaning wastewater increases.

  Therefore, it is considered to wash the filter medium and let the cleaning waste water flow out from the filtration tank while continuing to flow into the filtration tank.

  However, in the filter device of Patent Document 1, the sewage flows in from the lower part of the filter tank, and the cleaning waste water flows out from the lower part of the filter tank, so that the cleaning waste water in the filter tank cannot efficiently flow out.

  Further, in the filtering devices of Patent Documents 2 and 3, when the filter medium is washed while the inflow of the sewage into the filter tank is continued and the wash drainage is caused to flow out of the filter tank, the flow of the wash drainage flowing out is The filter medium may gather and stick to the vicinity of the outlet. Then, the filter medium cannot be sufficiently stirred, the cleaning of the filter medium becomes insufficient, and the pressure loss increases.

  Therefore, an object of the present invention is to wash the filter medium while continuing the inflow of the sewage into the filter tank, and also to wash the filter medium efficiently even if the cleaning drainage is discharged from the filter tank, thereby reducing the pressure loss. (EN) Provided is a filtration device and an operating method thereof.

  [1] The present invention provides a filtration tank, a filter medium housed in the filtration tank, an inflow section for introducing sewage into the filtration tank, and a trough arranged above the inflow section in the filtration tank. A screen provided in the trough, which partitions the filtration tank and the inner space of the trough, allows water to pass therethrough, and restricts the passage of the filter medium, an outflow portion which communicates with the inner space of the trough, and the filtration. A filtration device having an air supply unit for supplying air to the tank.

  According to such a configuration, the sewage is caused to flow into the filtration tank by the inflow section when the sewage is filtered. Then, the sewage rises in the filter tank, and an upward flow occurs. At this time, the filter medium filters the sewage. Then, the filtered treated water passes through the screen and flows into the trough so as to get over the trough. Then, the treated water passes through the trough and flows out from the outflow section.

  Further, when the filter medium is washed, the air supply unit supplies air to the filter tank while the inflow unit allows the sewage to flow into the filter tank. As a result, the filter medium is agitated and washed. At this time, the cleaning wastewater generated by the cleaning flows through the screen so as to get over the trough while flowing at random by air agitation, and flows into the trough. Then, the cleaning wastewater passes through the trough and is discharged from the outflow portion.

  Therefore, while continuing the inflow of sewage into the filter tank, the filter medium can be washed and the cleaning waste water can be discharged from the filter tank. That is, since the cleaning of the filter medium and the outflow of the cleaning drainage can be performed at the same time, the time required for cleaning the filter medium can be shortened.

  Further, in the trough, only the cleaning wastewater separated from the filter medium flowing in the filtration tank falls from the boundary between the trough and the screen, so that a free water surface different from that in the filtration tank is formed. For this reason, it is possible to suppress the flow of the cleaning drainage from affecting the filter medium in the filtration tank, and it is possible to prevent the filter medium from gathering and sticking to one place near the outflow portion.

  Therefore, it is possible to wash the filter medium while continuing the inflow of sewage into the filter tank, and also to wash the filter medium efficiently even if the cleaning wastewater is discharged from the filter tank, reducing the pressure loss generated during filtration. Can be planned.

  [2] Further, in the present invention, the outflow section causes a first outflow section for causing the treated water filtered by the filter medium to flow out from the filter tank, and a wash drainage generated by cleaning the filter medium to flow out from the filter tank. And a second outflow unit.

  However, in the filter device of Patent Document 3, the treated water / washing drainage pipe switches between the treating water and the washing drainage and flows out. However, since the common pipe is used for both the outflow of treated water and the outflow of cleaning wastewater, when the treated water flows out, the cleaning wastewater remaining in the pipe mixes with the treated water and May be contaminated.

  On the other hand, according to the above configuration, the outflow section separately includes the first outflow section for outflowing the treated water and the second outflow section for outflowing the cleaning wastewater, so that the treated water is filtered during sewage filtration. Can flow out from the first outflow part without flowing out from the second outflow part, and at the time of cleaning the filter medium, the cleaning drainage can flow out from the second outflow part without flowing out from the first outflow part. .. Therefore, the treated water and the cleaning wastewater can be caused to flow out from the different outflow portions, respectively, so that the cleaning wastewater can be prevented from being mixed into the treated water.

  [3] The present invention also includes the filtration device according to the above [2], wherein the first outflow portion and the second outflow portion are at the same position in the vertical direction.

  However, in the filtration device of Patent Document 2, the cleaning drainage outlet is provided above the treated water outlet. Therefore, in the filtration device of Patent Document 2, when the filter medium is washed subsequent to the filtration of the sewage, the water level in the filtration tank is raised from the position corresponding to the treated water outlet to the position corresponding to the cleaning drainage outlet. There is a need. As a result, there is a problem that it takes time to switch between the sewage filtering operation and the filter material cleaning operation.

  On the other hand, according to the above configuration, since the first outflow portion and the second outflow portion are at the same position in the vertical direction, when switching between the sewage filtering operation and the filter medium cleaning operation, the water level in the filtration tank is changed. Need not be changed. Therefore, the sewage filtering operation and the filter material cleaning operation can be smoothly switched.

  [4] Also, in the present invention, the second outflow portion is disposed above the first outflow portion, the filtering device is disposed at the same position in the vertical direction as the first outflow portion, and the water level is The filter device according to [2], further including a third outflow portion for outflowing the cleaning wastewater so as to be at a position corresponding to the first outflow portion.

  In the filtration device of Patent Document 2, since the cleaning drainage outlet is provided above the treated water outlet, when restarting the filtration of the sewage after cleaning the filter medium, the water level in the filtration tank is set to the cleaning drainage outlet. It is necessary to descend from the corresponding position to the position corresponding to the treated water outlet. In order to lower the water level in the filtration tank, the washing drainage is made to flow out from the drain pipe provided at the bottom of the filtration tank. However, it is difficult to lower the water level in the filtration tank due to the outflow of the cleaning wastewater from the drain pipe while continuing the inflow of sewage from the raw water supply pipe provided at the bottom of the filtration tank.

  On the other hand, according to the above configuration, since the third outflow portion is arranged at the same position in the vertical direction as the first outflow portion, the third outflow portion is changed when switching from the filter medium cleaning operation to the sewage filtering operation. By flowing out the cleaning wastewater from the water, the water level can be lowered to the position corresponding to the first outflow portion.

  [5] The present invention is the method for operating the filtration device according to any one of the above [1] to [4], wherein sewage is caused to flow into the filtration tank from the inflow section to obtain the sewage. A filtration step of filtering the treated water through the outflow section and filtering the treated water, and supplying the air from the air supply section to the filtration tank while continuing the inflow of sewage to wash the filter medium A method of operating the filtration device, including a cleaning step of causing cleaning waste water to flow out from the outflow portion.

  According to such a method, the filter medium is washed while continuing the inflow of sewage. Then, the cleaning wastewater flows into the trough through the screen, then passes through the trough, and is discharged from the outflow portion communicating with the internal space of the trough.

  Therefore, it is possible to suppress the flow of the outflow of cleaning drainage from affecting the filter medium in the filtration tank, and it is possible to prevent the filter medium from gathering and sticking in the vicinity of the outflow portion. As a result, it is possible to wash the filter medium while continuing to flow the sewage into the filter tank, and also to wash the filter medium efficiently even if the cleaning waste water is discharged from the filter tank. Reduction can be achieved.

[6] Further, the present invention is the filtration device according to the above [3], wherein in the step of washing the filter medium, an overflow rate per unit length of the washing drainage with respect to the trough is: The method for operating the filtration device according to the above [5], which is 100 m ³ / m / day or less, is included.

  However, in the process of cleaning the filter media, if the overflow per unit length of the wash drainage per trough exceeds the above value, the filter media gathers and sticks near the trough as the wash drainage overflows into the trough. There are cases.

  On the other hand, according to the above method, the overflow amount per unit length of the cleaning drainage per trough is equal to or less than the above value, so that it is possible to prevent the filter medium from gathering and sticking in the vicinity of the trough. Therefore, the filter medium can be surely washed, and the pressure loss can be surely reduced.

[7] Further, the present invention is the filtration device according to the above [4], wherein in the step of washing the filter medium, a flow velocity of the washing wastewater per unit area to the screen is 3000 m. ^The method for operating the filtration device according to the above [5], which is ³ / m ² / day or less, is included.

  However, in the step of cleaning the filter medium, when the flow velocity of the cleaning wastewater per unit area of the screen exceeds the above value, the filter medium may stick to the screen as the cleaning wastewater passes through the screen.

  On the other hand, according to the above method, since the flow velocity of the cleaning wastewater per unit area of the screen is equal to or less than the above value, the filter medium can be prevented from sticking to the screen. Therefore, the filter medium can be washed more surely and the pressure loss can be reduced more surely.

  In the filtration device and the method for operating the filtration device of the present invention, while continuing to flow into the filtration tank of the sewage, the filter material is washed, and even if the cleaning drainage is allowed to flow out from the filtration tank, the filter material can be efficiently washed, and the pressure is reduced. The loss can be reduced.

FIG. 1 is a schematic configuration diagram of a first embodiment of a filtration device of the present invention. FIG. 2 is a plan view of the filtration device shown in FIG. FIG. 3 is a cross-sectional view taken along the line AA of the filtration device shown in FIG. FIG. 4 is an explanatory diagram for explaining the filtering operation of the filtering device shown in FIG. FIG. 5: is explanatory drawing for demonstrating the washing | cleaning operation | movement of the filtration apparatus shown in FIG. FIG. 6 is a schematic configuration diagram of a second embodiment of the filtration device of the present invention. FIG. 7: is explanatory drawing for demonstrating the filtration operation of the filtration apparatus shown in FIG. FIG. 8: is explanatory drawing for demonstrating the washing | cleaning operation | movement of the filtration apparatus shown in FIG. FIG. 9 is a graph of the water level rise amount of the pressure regulating tank with respect to the elapsed time in Examples 1 and 2. FIG. 10 is a graph of the water level rise amount of the pressure regulating tank with respect to the elapsed time in Examples 3 and 4.

1. Filtration Device As shown in FIG. 1, the filtration device 1 includes a pressure regulating tank 2 and a filtration tank 3. The pressure regulation tank 2 and the filtration tank 3 share the partition wall 4 and are arranged adjacent to each other. The partition wall 4 has an inflow port 5 as an example of an inflow section. The inflow port 5 is arranged at the lower end of the partition wall 4. The inflow port 5 penetrates the partition wall 4 along a first horizontal direction which is a direction adjacent to the pressure regulating tank 2 and the filtration tank 3, and the inner space of the pressure regulating tank 2 and the inside of the filtration tank 3 are penetrated. It communicates with the space.

  Further, the filtration tank 3 includes a first side wall 3A and a second side wall 3B that are arranged at intervals in a second horizontal direction that intersects both the vertical direction and the first direction (see FIG. 2). ). The first side wall 3A is arranged at one end of the filtration tank 3 in the second direction, and the second side wall 3B is arranged at the other end of the filtration tank 3 in the second direction (FIG. 2). reference).

  The filtration device 1 further includes a sewage supply pipe 6, an air diffusing pipe 7 as an example of an air supply unit, a support floor 8, a filter medium 9, a trough unit 10, and an outflow unit 11 (see FIG. 2). There is.

  The sewage supply pipe 6 is a pipe for supplying sewage to the filtration device 1. One end of the sewage supply pipe 6 is located above the inflow port 5 and is opened above the pressure regulating tank 2. The other end of the sewage supply pipe 6 is connected to a sand basin or the like at an end treatment plant (not shown).

The air diffuser 7 is a member for supplying air to the filtration tank 3, and can discharge air. The air diffuser 7 is arranged in the lower part of the filtration tank 3. In the present embodiment, a plurality (three) of air diffusers 7 are provided. As shown in FIG. 3, the air diffuser 7 extends in the second direction. The plurality of air diffusers 7 are arranged in parallel in the first direction at intervals so that they are located at the same position in the vertical direction (see FIG. 1). The air diffuser 7 is supported by the first side wall 3A. A pipe 12 (see FIG. 3) is connected to the air diffuser 7 so that air can be supplied from the outside of the filtration tank 3. A plurality of air diffusers 7A are opened in the air diffuser 7 along the second direction at intervals (see FIG. 3).
The air diffuser 7 is not particularly limited in its arrangement and number as long as it can uniformly diffuse the entire filter tank 3. For example, the plurality of air diffusers 7 may extend in the first direction and may be arranged in parallel in the second direction with a space therebetween.

  As shown in FIG. 1, the support floor 8 is a member for supporting the filter medium 9. The support bed 8 is arranged above the plurality of air diffusers 7 in the filtration tank 3. The support floor 8 extends in the horizontal direction and is formed over the entire filtration tank 3. The support floor 8 is fixed to the filtration tank 3. The support floor 8 is formed of a screen that allows water to pass therethrough and restricts the passage of filter media.

  The filter medium 9 is a member for filtering sewage and is capable of removing SS components in sewage. Further, the filter medium 9 is configured so as to float in the sewage and the cleaning drainage. The filter medium 9 is housed in the filtration tank 3 and is provided in plurality. The material of the filter medium 9 is not particularly limited, and examples thereof include polyester fibers, polyolefin fibers, polystyrene fibers and the like. The filter medium 9 can be used alone or in combination of two or more kinds. Further, in order to reduce the specific gravity, it is possible to use a filter medium obtained by mixing fibers. The filter medium 9 is preferably a polyolefin fiber filter medium, and more preferably the fiber filter medium described in JP-A-2006-035135.

  The trough unit 10 is arranged in the upper portion of the filtration tank 3. The trough unit 10 is arranged above the support floor 8 with a space therebetween. In this embodiment, a plurality (three) of trough units 10 are provided. The number of trough units 10 is the same as the number of air diffusers 7. The trough unit 10 is arranged above the corresponding air diffusing tube 7 with a space therebetween. The trough unit 10 is arranged so as to overlap the corresponding air diffusing pipe 7 when viewed in the vertical direction.

  The arrangement and the number of trough units 10 are not particularly limited and may not correspond to the air diffuser 7. Further, the number of trough units 10 is appropriately changed according to the design water amount during the filtration operation.

  As shown in FIG. 2, the trough unit 10 extends in the second direction. The plurality of trough units 10 are arranged in parallel in the first direction at intervals so that they are at the same position in the vertical direction. Both ends of the trough unit 10 in the second direction are fixed to the first side wall 3A and the second side wall 3B.

  As shown in FIG. 1, the trough unit 10 includes a trough 15 and a screen 16. The trough 15 is arranged above the inflow port 5 in the filtration tank 3. The trough 15 has a concave cross-section whose upper side is open and extends in the second direction. Specifically, the trough 15 integrally includes a bottom wall 15A and two side walls 15B. The bottom wall 15A has a flat plate shape extending in the second direction. The two side walls 15B extend upward from both ends of the bottom wall 15A in the first direction.

  The screen 16 is provided on the trough 15. Specifically, a plurality of (two) screens 16 are provided in each trough unit 10, and one screen 16 is provided for each of the two side walls 15B. The screen 16 extends upward from the side wall 15B. Further, the screen 16 extends over the entire trough 15 in the second direction (see FIG. 3). The screen 16 partitions the filtration tank 3 and the internal space of the trough 15. The screen 16 is configured to allow the passage of water and regulate the passage of the filter medium 9.

  As shown in FIG. 2, the outflow portion 11 is a member for letting out treated water (described later) and cleaning drainage (described later) from the filtration tank 3. The outflow portion 11 communicates with the internal space of the trough 15 of each trough unit 10. Specifically, the outflow unit 11 includes a first outflow unit 18 and a second outflow unit 19.

  The first outflow unit 18 is a member for outflowing treated water (described later) from the filtration tank 3. A plurality (three) of the first outflow units 18 are provided corresponding to the plurality of trough units 10. As shown in FIG. 3, the first outflow unit 18 includes a first outflow port 24, which is an example of a first outflow portion, a first pipe 20, and a first valve 21.

  As shown in FIG. 1, the first outlet 24 is formed on the first side wall 3A and penetrates the first side wall 3A in the second direction. Specifically, the first outlet 24 is disposed above the bottom wall 15A of the trough 15 and between the two side walls 15B when viewed from the second direction, and is located at the same position in the vertical direction as the side wall 15B. It is arranged. Thereby, the 1st outflow port 24 is open for free passage with the internal space of the end of one side of trough 15 in the 2nd direction.

  The first pipe 20 is connected to the first side wall 3A so as to communicate with the first outlet 24. The first valve 21 is provided in the first pipe 20. The first valve 21 can open and close the first pipe 20. Note that, as shown in FIG. 2, the plurality of first pipes 20 are joined to each other and then connected to a discharge port (not shown).

  The second outflow unit 19 is a member for outflowing cleaning wastewater (described later) from the filtration tank 3. A plurality of (three) second outflow units 19 are provided corresponding to the plurality of trough units 10. As shown in FIG. 3, the second outflow unit 19 includes a second outflow port 25, which is an example of a second outflow portion, a second pipe 22, and a second valve 23.

  The second outlet 25 is formed in the second side wall 3B and penetrates the second side wall 3B in the second direction. Specifically, the second outlet 25 is disposed above the bottom wall 15A of the trough 15 and between the two side walls 15B when viewed from the second direction, and is located at the same position in the vertical direction as the side wall 15B. It is arranged. As a result, the second outlet 25 communicates with the internal space of the other end of the trough 15 in the second direction. The first outlet 24 and the second outlet 25 are at the same position in the vertical direction. The first outlet 24 and the second outlet 25 are arranged so as to sandwich the trough 15, and are arranged on opposite sides of the trough 15.

  The second pipe 22 is connected to the second side wall 3B so as to communicate with the second outlet 25. The second valve 23 is provided in the second pipe 22. The second valve 23 can open and close the second pipe 22. In addition, as shown in FIG. 2, the plurality of second pipes 22 are joined to each other and then connected to a storage unit (not shown).

2. Operation Method of Filtration Device Next, an operation method (continuous operation method) of the filtration device 1 will be described. The operating method of the filtering device 1 includes a step of preparing the filtering device 1, a filtering step of filtering sewage, and a washing step of washing the filter medium 9.

  Specifically, in the method of operating the filtering device 1, the filtering device 1 is prepared as shown in FIGS. 1 and 3 (preparing step). Then, the sewage is filtered by the filtering device 1 (filtering step).

In the filtration process of the filtration device 1, first, the first valve 21 opens the first pipe 20, and the second valve 23 closes the second pipe 22. Then, the sewage is caused to flow from the sewage supply pipe 6 into the pressure regulating tank 2. The flow rate of sewage in the filtration step is, for example, 500 m ³ / day or more.

  Then, the sewage passes through the inflow port 5 at the above-mentioned flow rate and flows into the filtration tank 3 from the pressure regulating tank 2. That is, the inflow port 5 allows the sewage to flow into the filtration tank 3. Then, as shown in FIG. 4, the sewage rises in the filtration tank 3 and an upward flow occurs. At this time, the filter medium 9 floats in the sewage and rises, and removes the SS component in the sewage. As a result, the sewage is filtered.

  As shown in the enlarged view of FIG. 1, the filtered treated water passes through the screen 16 so as to get over the side wall 15B of the trough 15. Then, the treated water flows (overflows) into the trough 15.

  Further, in the filtration step, the first pipe 20 is opened and the second pipe 22 is closed, so that the treated water that has flowed into the trough 15 flows out from the first outlet 24. That is, the first outlet 24 causes the treated water filtered by the filter medium 9 to flow out from the filtration tank 3.

  As a result, the sewage is filtered by the filtering device 1. In the sewage filtering operation, since the filter medium 9 removes the SS component in the sewage, the pressure loss of the filtering device 1 increases and the water level of the pressure regulating tank 2 rises as the filtering operation is continued.

  Therefore, as shown in FIG. 5, in the filtering device 1, when the pressure loss exceeds a predetermined value, the sewage filtering operation is switched to the cleaning operation of the filter medium 9. Specifically, in the filtering device 1, when the water level of the sewage in the pressure regulating tank 2 rises from the water level at the time of still water to a predetermined amount or more (for example, 0.5 m or more), the sewage filtering operation is changed to the cleaning operation of the filter medium 9. Switch. In the first embodiment, the water level of the sewage (treated water and cleaning waste water) is located at the upper end of the side wall 15B (lower end of the screen 16) in the filtration tank 3.

  In order to switch from the sewage filtering operation to the filter material 9 cleaning operation, first, the first valve 21 closes the first pipe 20, and the second valve 23 opens the second pipe 22. Then, following the filtration step, air is supplied from the air diffuser 7 to the filtration tank 3 while continuing the inflow of sewage into the filtration tank 3 (cleaning step). That is, the air diffuser 7 supplies air to the filtration tank 3.

  Then, the upper part of the support floor 8 is agitated by the bubbles, and the filter medium 9 flows. At this time, the SS component removed by the filter medium 9 is separated from the filter medium 9 and dispersed in the sewage. As a result, the filter medium 9 is washed.

  As shown in the enlarged view of FIG. 1, the cleaning wastewater generated by the cleaning passes through the screen 16 so as to get over the side wall 15B of the trough 15 while flowing randomly by the air stirring. Then, the wash drainage flows (overflows) into the trough 15.

At this time, the overflow rate (overflow load) per unit length of the wash drainage to the trough 15 is, for example, 150 m ³ / m / day or less, preferably 100 m ³ / m / day or less, for example, 80 m ³ / m. / Day or more. The overflow rate (overflow load) per unit length of the cleaning wastewater with respect to the trough 15 can be calculated as follows.
Formula (1):
Overflow load [m ³ / m / day] = flow rate of sewage in washing process [m ³ / day] / (total side wall length of each trough 15 (trough overflow length) [m] × trough 15 (Number)
Further, in the cleaning process, the first pipe 20 is closed and the second pipe 22 is opened, so the cleaning wastewater that has flowed into the trough 15 flows out from the second outlet 25. That is, the second outflow port 25 causes the cleaning drainage generated by cleaning the filter medium 9 to flow out from the filtration tank 3. Further, the trough 15 is used for both outflow of treated water and outflow of cleaning waste water.

  Then, the supply of air from the air diffuser 7 is stopped. With the above, the cleaning operation of the filter medium 9 is completed. The cleaning time of the filter medium 9 (from the start of air supply to the air diffuser 7 to the stop) is calculated from the product of the vertical distance from the support floor 8 to the trough 15 and the projected area of the filtration tank 3, Also, with respect to the amount of water in the upper part, for example, the total amount of cleaning wastewater becomes equal to or more than the amount of water, for example, equal to or less than twice the amount of water, preferably 1.5 times the amount of water Less than an hour.

  Then, if necessary, the washing drainage is caused to flow out from the second outlet 25 for a predetermined time while continuing the inflow of the sewage into the filtration tank 3 (water draining step). The predetermined time is appropriately changed depending on the flow rate of waste water, but is, for example, 1 minute or more, for example, 10 minutes or less, and preferably 5 minutes or less.

  Then, as shown in FIG. 4, the first pipe 20 is opened by the first valve 21 and the second pipe 22 is closed by the second valve 23 to switch from the cleaning operation of the filter medium 9 to the sewage filtering operation. As a result, the above filtering operation is restarted. That is, the filtering device 1 can repeat the filtering operation of the sewage and the cleaning operation of the filter medium 9.

3. Action and effect [1] As shown in FIG. 4, in the filtration device 1, the sewage is caused to flow into the filtration tank 3 by the inflow port 5 when the sewage is filtered. Then, the sewage rises in the filtration tank 3 and an upward flow occurs. At this time, the filter medium 9 filters the sewage. Thereafter, the filtered treated water passes through the screen 16 and flows into the trough 15 so as to get over the trough 15. Then, the treated water passes through the trough 15 and flows out from the first outlet 24.

  Further, as shown in FIG. 5, when the filter medium 9 is washed, the air diffuser pipe 7 supplies air to the filter tank 3 while the inflow port 5 allows the sewage to flow into the filter tank 3. As a result, the filter medium 9 is stirred and washed. At this time, the cleaning wastewater generated by the cleaning flows through the screen 16 and flows into the trough 15 so as to get over the trough 15 while flowing randomly by the air agitation. Then, the cleaning wastewater passes through the trough 15 and flows out from the second outlet 25.

  Therefore, while continuing the inflow of the sewage into the filter tank 3, the filter medium 9 can be washed and the cleaning waste water can be discharged from the filter tank 3. That is, the cleaning of the filter medium 9 and the outflow of the cleaning drainage can be performed at the same time, so that the time required for cleaning the filter medium 9 can be shortened.

  Immediately after the start of the cleaning process, the cleaning waste water containing the high-concentration SS component can be efficiently discharged from the filtration tank 3. Therefore, the amount of cleaning drainage can be reduced.

  Further, in the trough 15, only the cleaning waste water separated from the filter medium 9 flowing in the filtration tank 3 falls (flows in) from the boundary portion between the trough 15 and the screen 16, so that it is separated from the inside of the filtration tank 3. A free water surface is formed. For this reason, it is possible to suppress the flow of the outflow of cleaning waste water from affecting the filter medium 9 in the filter tank 3, and it is possible to prevent the filter medium 9 from gathering and sticking to one place in the vicinity of the second outlet 25.

  Therefore, the filter medium 9 can be efficiently washed even when the cleaning medium 9 is washed while the inflow of the sewage into the filtration tank 3 is continued, and the pressure loss is reduced. Can be planned.

  [2] As shown in FIG. 4, in the filtration device 1, when the sewage is filtered, the treated water can flow out from the first outlet 24 without flowing out from the second outlet 25. Further, as shown in FIG. 5, in the filtering device 1, when the filter medium 9 is washed, the cleaning drainage can be made to flow out from the second outlet 25 without flowing out from the first outlet 24. Therefore, the treated water and the cleaning wastewater can be caused to flow out from the different outflow portions, respectively, so that the cleaning wastewater can be prevented from being mixed into the treated water. Moreover, since the 1st outflow port 24 and the 2nd outflow port 25 are formed separately, compared with the case where processing water and washing | cleaning wastewater switch out from a common outlet, and flow out, treated water flows out. It is possible to smoothly perform switching between the cleaning drainage and the outflow of the cleaning wastewater, and it is possible to shorten the switching time.

  [3] As shown in FIGS. 4 and 5, the first outlet 24 and the second outlet 25 are at the same position in the vertical direction. Therefore, when switching between the filtering operation of the sewage and the cleaning operation of the filter medium 9, it is not necessary to change the water level in the filtration tank 3. As a result, the sewage filtering operation and the filter medium 9 cleaning operation can be smoothly switched.

[4] In the step of washing the filter medium 9, the overflow rate per unit length of the washing drainage to the trough 15 is preferably 100 m ³ / m / day or less. In this case, it is possible to prevent the filter material 9 from gathering near the trough 15 and sticking to it. Therefore, the filter medium 9 can be reliably washed, and the pressure loss can be surely reduced.

4. Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. 6 to 8. In the second embodiment, the same members as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted.

  In the filtering device 30 of the second embodiment, as shown in FIG. 6, the second outlet 25 is arranged above the first outlet 24. Specifically, the second outlet 25 is arranged above the side wall 15B of the trough 15 with a space therebetween. The 2nd outflow port 25 is arrange | positioned with the space | interval S on the upper side with respect to the side wall 15B. That is, the second outlet 25 and the upper edge of the side wall 15B are arranged with a space S therebetween in the vertical direction. The second outlet 25 is arranged between the lower edge and the upper edge of the screen 16.

  The filtering device 30 further includes a third outflow unit 31. Although not shown, the third outflow unit 31 is provided in plurality (three) corresponding to the plurality of trough units 10. The third outflow unit 31 includes a third outflow port 37 as an example of a third outflow portion, a third pipe 32, and a third valve 33.

  The third outlet 37 is formed on the second side wall 3B and penetrates the second side wall 3B in the second direction. Specifically, the third outlet 37 is disposed above the bottom wall 15A of the trough 15 and between the two side walls 15B when viewed from the second direction, and is located at the same position in the vertical direction as the side wall 15B. It is arranged. As a result, the third outlet 37 communicates with the internal space of the other end of the trough 15 in the second direction. The third outlet 37 is arranged at the same position as the first outlet 24 in the vertical direction.

  One end of the third pipe 32 is connected to the second side wall 3B so as to communicate with the third outlet 37. The other end of the third pipe 32 is connected to the second pipe 22. The third valve 33 is provided in the third pipe 32. The third valve 33 can open and close the third pipe 32.

  The filtering device 30 further includes a drain section 34. The drain portion 34 includes a drain port 38, a drain pipe 35, and a valve 36. The drain port 38 is formed in the lower portion of the filtration tank 3. The drain port 38 is arranged below the support floor 8. Specifically, the drain port 38 is formed in the first side wall 3A and penetrates the first side wall 3A in the second direction. One end of the drain pipe 35 is connected to the first side wall 3A so as to communicate with the drain port 38. The other end of the drain pipe 35 is connected to a storage unit (not shown). The valve 36 is provided in the drain pipe 35. The valve 36 can open and close the drain pipe 35.

  The connection position of the drain portion 34 with the filtration device 30 is not particularly limited as long as it is below the support floor 8. For example, the drain port 38 may be formed in the bottom wall of the filtration tank 3, and one end of the drain pipe 35 may be connected to the bottom wall of the filtration tank 3.

  Such a filtering device 30 filters sewage as in the filtering device 1 of the first embodiment (filtering step). Specifically, in the filtering operation of the filtering device 30, first, the first pipe 21 opens the first pipe 20, the second valve 23 closes the second pipe 22, and the third valve 33 opens the third pipe. 32 is closed. The drain pipe 35 is always closed by a valve 36.

  Then, the sewage is caused to flow into the filtration tank 3 at the above flow rate, as in the first embodiment. Then, as shown in FIG. 7, the sewage rises in the filtration tank 3. At this time, the filter medium 9 removes the SS component in the sewage and filters the sewage.

  The filtered treated water passes through the screen 16 and flows (overflows) into the trough 15 so as to get over the side wall 15B of the trough 15. After that, the treated water that has flowed into the trough 15 is discharged from the first outlet 24. In the filtering operation of the filtering device 30, the water level of the treated water is located at the upper end of the side wall 15B (the lower end of the screen 16) in the filtration tank 3.

  After that, as shown in FIG. 8, when the water level of the sewage in the pressure regulating tank 2 (see FIG. 1) rises above a predetermined amount from the water level at the time of still water, in the filtering device 30, the filtering operation from the sewage filtering operation to the cleaning operation of the filter medium 9 is performed. Switch to.

  In order to switch from the sewage filtration operation to the cleaning operation of the filter medium 9, first, with the third valve 33 closing the third pipe 32, the first valve 21 closes the first pipe 20 and the second valve 23. Thus, the second pipe 22 is opened.

  Then, following the filtration step, air is supplied from the air diffusing pipe 7 to the filtration tank 3 while continuing the inflow of sewage into the filtration tank 3.

  At this time, since the sewage is continuously flowing into the filtration tank 3, the water level of the sewage gradually rises to a position corresponding to the second outlet 25 in the vertical direction (water level raising step). Thereby, the water level of the sewage (cleaning wastewater) is located between the lower end and the upper end of the screen 16 in the filtration tank 3. Further, the filter medium 9 is agitated and washed.

  The cleaning drainage generated by cleaning passes through the screen 16 and flows into the space partitioned by the screen 16 and the trough 15.

At this time, the flow velocity of the cleaning wastewater per unit area of the screen 16 is, for example, 3500 m ³ / m ² / day or less, preferably 3000 m ³ / m ² / day or less. The flow velocity of the cleaning wastewater per unit area of the screen 16 can be calculated as follows.
Formula (2):
Flow velocity [m ³ / m ² / day] = flow rate of sewage in washing process [m ³ / day] / (length of screen 16 in predetermined direction [m] × second outlet 25 and screen 16 in vertical direction (The length of the space S from the bottom edge [m] x number of screens 16)
Then, the cleaning wastewater that has passed through the screen 16 is discharged from the second outlet 25. Then, the supply of air from the air diffuser 7 is stopped. Then, if necessary, the outflow of the cleaning wastewater from the second outlet 25 is continued.

  Next, in the filtering device 30, the cleaning operation of the filter medium 9 is switched to the filtering operation of the sewage. In order to switch the washing operation of the filter medium 9 to the sewage filtering operation, the third valve 32 is opened by the third valve 33 while the first valve 20 is closed by the first valve 21. In addition, the valve 36 opens the drain pipe 35.

  Then, the cleaning wastewater (sewage) flows out from the third outlet 37 and the drain port 38. The drain of the cleaning drainage from the drain port 38 may be a natural flow, but is preferably sucked by a pump.

  At this time, as shown in FIG. 7, the water level of the cleaning drainage gradually falls to a position corresponding to the third outlet 37 in the vertical direction. That is, the third outlet 37 flows out the cleaning wastewater so that the water level of the cleaning wastewater (sewage) is at a position corresponding to the first outlet 24 in the vertical direction.

  After that, the first pipe 20 is opened by the first valve 21, the third pipe 32 is closed by the third valve 33, and the drain pipe 35 is closed by the valve 36. As a result, the switching from the cleaning operation of the filter medium 9 to the sewage filtering operation is completed, and the above filtering operation is restarted.

  As shown in FIG. 7 and FIG. 8, in the filtering device 30, the second outlet 25 is arranged above the first outlet 24, so that the filtering medium is different from the filtering device 1 of the first embodiment. In the cleaning step of No. 9, it is possible to improve the area of the portion of the screen 16 through which the cleaning drainage passes, and consequently reduce the flow velocity of the cleaning drainage per unit area with respect to the screen 16. Therefore, it is possible to prevent the filter medium 9 from sticking to the screen 16 in the step of cleaning the filter medium 9.

More specifically, in the step of cleaning the filter medium 9, the flow velocity of the cleaning wastewater per unit area of the screen 16 is preferably 3000 m ³ / m ² / day or less. Therefore, it is possible to reliably prevent the filter medium 9 from sticking to the screen 16. As a result, the filter medium 9 can be washed more reliably, and the pressure loss can be reduced more reliably.

  Further, in the filtration device 30, the third outlet 37 is arranged at the same position as the first outlet 24 in the vertical direction. Therefore, when the cleaning operation of the filter medium 9 is switched to the sewage filtering operation, the cleaning drainage can be caused to flow out from the third outlet 37, and the sewage water level can be changed from the position corresponding to the second outlet 25 to the first outlet. It can be lowered to a position corresponding to the outlet 24.

  In the second embodiment, when the cleaning operation of the filter medium 9 is switched to the sewage filtering operation, the drain pipe 35 is opened and the third pipe 32 is opened to clean the drain port 38 and the third outlet 37. Drainage is drained to lower the sewage level, but is not limited to this.

  The filtering device 30 may not include the drain portion 34. In this case, when switching from the cleaning operation of the filter medium 9 to the filtering operation of the sewage, the third pipe 32 can be opened, and the cleaning drainage can be caused to flow only from the third outlet 37 to lower the water level of the sewage. ..

5. Modifications In the first embodiment and the second embodiment, the trough 15 has a concave shape whose upper side is opened, but the shape of the trough 15 is not particularly limited, and the V-shaped that the upper side is opened. It may be (semi-circular).

  In 1st Embodiment and 2nd Embodiment, although the outflow part 11 is equipped with the 1st outflow port 24 and the 2nd outflow port 25, it is not limited to this, and the outflow part 11 is the outflow of process water and cleaning drainage. It can be switched between outflow and outflow of both treated water and washing wastewater.

  In the first embodiment and the second embodiment, the outflow portion 11 (the first outflow unit 18, the second outflow unit 19, and the third outflow unit 31) includes a pipe and a valve for opening and closing the pipe. Is not particularly limited. Examples of the opening / closing mechanism include a gate that divides the opening into upper and lower parts in a shutter shape. When the opening / closing mechanism is a gate, an open water channel can be used instead of the pipe.

  In the first embodiment and the second embodiment, the washing step is carried out while continuing the inflow of the sewage following the filtering step, but the present invention is not limited to this, and the sewage may be inserted between the filtering step and the washing step. The inflow can be stopped for a short time (for example, 5 minutes or less).

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Specific numerical values such as a blending ratio (content ratio), physical property values, parameters, etc. used in the following description are described in the above-mentioned "Mode for carrying out the invention", and a corresponding blending ratio (content ratio). ), Physical property values, parameters, etc., can be replaced by the upper limit values (values defined as “below” or “less than”) or lower limit values (values defined as “greater than or equal to”).

Examples 1 and 2
The filtering device (1st Embodiment) shown in FIGS. 1-3 was prepared. The filtration tank has a length of 3 m, a width (predetermined direction): 1 m, and a depth when still water (vertical direction): 3 m, and a water tank has a length: 0.5 m, a width: 1 m, and a depth when still water: It was 3 m (total volume at still water: 10.5 m ³ ). The filter medium was formed into a columnar shape from a non-woven sheet made of polyolefin fibers. The diameter of the filter medium was 8 mm, and the length of the filter medium was 8 mm. Next, the first pipe was opened by the first valve and the second pipe was closed by the second valve. Then, the sewage was caused to flow into the filtration tank at the flow rate shown in Table 1 to filter the sewage (filtration step). The filtered treated water flowed out from the first outlet.

  After that, when the water level in the pressure regulating tank rose 0.5 m above the still water level, the sewage filtration step was switched to the filter medium washing step. Specifically, the first valve closed the first pipe and the second valve opened the second pipe to start the supply of air from the air diffuser 7. In addition, in the washing process of the filter medium, the sewage was continuously flowed into the filtration tank at the flow rate shown in Table 1. The cleaning wastewater generated by cleaning flowed out from the second outlet. After the washing time shown in Table 1, the air supply from the air diffuser was stopped and the washing of the filter medium was completed.

  Next, while continuing the inflow of the sewage into the filtration tank 3 at the flow rates shown in Table 1, the cleaning drainage was caused to flow out from the second outlet (discharging step). Then, the 1st piping was opened with the 1st valve, the 2nd piping was closed with the 2nd valve, and the filtration process was restarted.

  In addition, Table 1 shows the amount of cleaning wastewater (= flow rate of sewage in the cleaning process x cleaning time + flow rate of sewage in the draining process x draining time + head loss of the pressure adjusting tank) and the amount of water remaining in the cleaning and draining process The amount of treated water (= flow rate of sewage in filtration step × (washing time + draining time)) is shown.

  The degree of recovery of pressure loss before and after the cleaning process is shown in FIG. In FIG. 9, the degree of recovery of the pressure loss before and after the cleaning process is shown using the amount of water level rise from the stationary water level in the pressure regulating tank as an index. In FIG. 9, the horizontal axis is the elapsed time, and the vertical axis is the water level rise amount from the stationary water level in the pressure regulating tank.

As shown in FIG. 9, in Example 1 (overflow load: 100 m ³ / m / day), the amount of water level rise in the pressure regulating tank decreased from 50 cm to 1 cm in the cleaning process. After the filtration process was restarted, the amount of water level rise in the pressure regulating tank was 5 cm, which was almost equal to the state in which water was passed through the filter medium that did not hold the SS component.

On the other hand, in Example 2 (overflow load: 133 m ³ / m / day), in comparison with Example 1, due to the phenomenon that a part of the filter material sticks (is pressed) to the screen surface in the cleaning process, the pressure loss The reduction amount has decreased. Specifically, in the cleaning step, the amount of rise in the water level in the pressure regulating tank dropped from 50 cm to 14 cm and then gradually increased to 21 cm. After the filtration process was restarted, the amount of rise in the water level from the static water level in the pressure regulating tank was 23 cm (+18 cm compared with Example 1).

Examples 3 and 4
The filtering device (2nd Embodiment) shown in FIGS. 6-8 was prepared. The dimensions of the filtration tank and the water conditioning tank were the same as in Example 1, and the distance between the second pipe and the lower edge of the screen was 0.1 m. The filter medium was the same as in Example 1.

  Next, the first valve opened the first pipe, the second valve closed the second pipe, and the third valve closed the third pipe. Then, the sewage was caused to flow into the filtration tank at the flow rate shown in Table 1 to filter the sewage (filtration step). The filtered treated water flowed out from the first outlet.

  Then, when the water level in the pressure regulating tank rises 0.5 m above the static water level, the first valve closes the first pipe while the third valve closes the third pipe, and the second valve closes. The valve opened the second pipe. As a result, the water level of the sewage rose to the position corresponding to the second outlet.

  Then, the supply of air from the air diffuser was started, and the cleaning process of the filter medium was started. In addition, in the washing process of the filter medium, the sewage was continuously flowed into the filtration tank at the flow rate shown in Table 1. The cleaning wastewater generated by cleaning flowed out from the second outlet. After the washing time shown in Table 1, the air supply from the air diffuser was stopped and the washing of the filter medium was completed.

  Then, while continuing the state in which the first pipe was closed by the first valve, the second pipe was closed by the second valve and the third pipe was opened by the third valve (water draining step). In addition, the drain pipe was opened by the valve. Then, the water level of the cleaning drainage dropped to a position corresponding to the third outlet (first outlet).

  After that, the first pipe was opened by the first valve, the third pipe was closed by the third valve, and the drain pipe was closed by the valve. Then, the filtration process was restarted.

  In addition, Table 1 shows the amount of cleaning wastewater and the amount of untreated water in the cleaning and draining process. Further, the degree of recovery of pressure loss before and after the cleaning process is shown in FIG.

As shown in FIG. 10, in Example 3 (screen passing speed: 3000 m ³ / m ² / day), after restarting the filtration step, the water level increase in the pressure regulating tank was 5 cm as in Example 1. there were.

On the other hand, in Example 4 (screen passage speed: 3333 m ³ / m ² / day), the amount of rise in water level from the static water level in the pressure regulating tank was 24 cm after the filtration step was restarted (compared with Example 3). And +19 cm).

Comparative Example 1
The filtration step was carried out in the same manner as in Example 1. Then, when the water level in the pressure regulating tank rose 0.5 m above the still water level, the inflow of sewage was stopped. Next, the sewage was caused to flow out from a drain pipe provided at the bottom of the filtration tank so that the water level of the sewage was located 10 cm below the trough. The outflow time was 1 minute.

Next, the air supply from the air diffuser was started, and after 3 minutes, the air supply from the air diffuser was stopped. Then, the entire amount of the cleaning waste water in the filtration tank was allowed to flow out from the drain pipe at a flow rate of 1800 m ³ / day (required time: 8.4 minutes).

Then, the inflow of sewage (flow rate 1800 m ³ / day) was restarted, the water level of the sewage was raised to the position corresponding to the first valve (required time: 8.4 minutes), and the filtration process was restarted.

  In addition, in Table 1, the amount of washing wastewater (= total volume of the filtration device when still water) and the amount of untreated water in the washing / draining process (= flow rate in the filtering process × (washing time + draining time + switching time)) Indicates.

  As shown in Table 1, Examples 1 to 4 were confirmed to be capable of reducing the time required for cleaning the filter medium and reducing the amount of cleaning waste water, as compared with Comparative Example 1.

DESCRIPTION OF SYMBOLS 1 Filtration device 3 Filtration tank 5 Inflow port 7 Air diffuser pipe 9 Filter medium 11 Outflow part 15 Trough 16 Screen 24 First outflow port 25 Second outflow port 30 Filtration device 37 Third outflow port

Claims (10)

A filtration tank,
A filter material housed in the filtration tank,
An inflow section for inflowing sewage into the filtration tank,
A trough disposed above the inflow portion in the filtration tank,
A screen provided in the trough, which partitions the filtration tank and the inner space of the trough, allows the passage of water, and restricts the passage of the filter medium,
An outflow portion communicating with the internal space of the trough,
An air supply unit for supplying air to the filtration tank ,
The filtration tank includes a first side wall and a second side wall that are arranged at intervals in the horizontal direction that intersects the vertical direction,
The trough is
Disposed between the first side wall and the second side wall,
Extending in a direction in which the first side wall and the second side wall face each other,
The filtering device , wherein the screen extends upward from the trough .   The trough is
    A bottom wall extending in a direction in which the first side wall and the second side wall face each other;
    Two side walls extending upward from both ends of the bottom wall in a direction intersecting with the extending direction of the bottom wall,
  The screen is
    One on each of the two sidewalls,
    The filtering device according to claim 1, wherein the filtering device extends upward from each of the side walls. Both ends of the trough in the facing direction of the first side wall and the second side wall are fixed to the first side wall and the second side wall,
The outflow portion is
A first outflow section for outflowing the treated water filtered by the filter medium from the filtration tank;
The 2nd outflow part which flows out the washing | cleaning waste_water | drain produced by washing | cleaning of the said filter medium from the said filtration tank is provided, The filtration apparatus of Claim 2 characterized by the above-mentioned. The filtration device according to claim 3 , wherein the first outflow portion and the second outflow portion are at the same position in the vertical direction. The first outflow portion is a first outflow port formed in the first side wall, and is located above the bottom wall and when viewed from the direction in which the first side wall and the second side wall face each other. Placed between the side walls,
  The second outflow portion is a second outflow port formed in the second side wall, and is located above the bottom wall and when viewed from a direction in which the first side wall and the second side wall face each other. The filtering device according to claim 4, characterized in that it is arranged between the side walls. The second outflow portion is disposed above the first outflow portion,
The filtration device further includes a third outflow portion that is disposed at the same position in the vertical direction as the first outflow portion, and that causes the wash drain to flow out so that the water level corresponds to the position of the first outflow portion. The filtration device according to claim 3 , wherein The first outflow portion is a first outflow port formed in the first side wall, and is located above the bottom wall and when viewed from the direction in which the first side wall and the second side wall face each other. Placed between the side walls,
The second outflow portion is a second outflow port formed in the second side wall, is disposed above the two side walls with a space therebetween, and has a lower end edge and an upper end edge of the screen. Placed between
  The third outflow portion is a third outflow port formed on the second side wall, and is located above the bottom wall and when viewed from the direction in which the first side wall and the second side wall face each other. 7. Filtering device according to claim 6, characterized in that it is arranged between the side walls. A method of operating a filtering device according to any one of claim 1 to 7
A filtering step of causing sewage to flow into the filtration tank from the inflow section, filtering the sewage with the filter medium, and causing treated water to flow out from the outflow section,
While continuing the inflow of sewage, air is supplied from the air supply unit to the filtration tank, the filter medium is washed, and a cleaning wastewater generated by cleaning is caused to flow out from the outflow unit. How to operate the filtration device. The filtration device is the filtration device according to claim 4 or 5 ,
The method for operating a filtration device according to claim 8 , wherein, in the step of washing the filter medium, an overflow rate of the washing waste water per unit length with respect to the trough is 100 m ³ / m / day or less. .. The filtration device is the filtration device according to claim 5 or 6 ,
The method for operating a filtration device according to claim 8 , wherein, in the step of cleaning the filter medium, a flow velocity of the cleaning wastewater per unit area with respect to the screen is 3000 m ³ / m ² / day or less. ..

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