JP6329007B2 - Cleaning method for floating filter media layer - Google Patents

Description

  The present invention relates to a method for backwashing a floating filter medium layer in a filtration system that filters raw water using a floating filter medium layer composed of a large number of floating filter media.

  Conventionally, as a filtration system that filters raw water such as sewage to obtain filtered water, it is placed above the floating filter media layer made of a large number of foamed filter media made of foamed polymer, and prevents the floating filter media from flowing out. An upward-flow filtration system having a screen, a raw water inlet and a backwash drainage outlet disposed below the floating filter material layer, and a filtration tank having a filtrate storage part located above the screen. It is known (see, for example, Patent Document 1).

  In the above filtration system using the floating filter medium, the raw water flowing in from the raw water inlet is passed upward through the floating filter medium layer, so that impurities (for example, garbage, foreign substances, etc.) and suspended suspended solids are flown. The filtered water is removed. In the above filtration system, for example, when the filtration resistance of the floating filter medium layer increases, the filtrate layer stored in the filtrate storage section is allowed to flow down naturally, so that the floating filter medium layer is backwashed (hereinafter referred to as “backwash”). Sometimes called). Specifically, in the above filtration system, the floating filter medium constituting the floating filter medium layer is developed downward by the downward flow of the filtered water, and impurities and floating suspensions trapped in the floating filter medium layer as filtration continues. The material is being removed.

  Here, in the above-described backwashing of the floating filter medium layer, the backwash drainage generated when the filtered water is allowed to flow naturally and the floating filter medium is expanded downward is discharged from the backwash drainage outlet to the outside of the filtration tank. ing. Therefore, when the floating filter material developed downward reaches the backwash drainage outlet, there arises a problem that the floating filter material flows out of the filtration tank. Therefore, in the filtration system using the floating filter medium layer, it is required to backwash the floating filter medium layer while suppressing the outflow of the floating filter medium to the outside of the filtration tank.

  Therefore, for example, in Patent Document 2, as a method of avoiding the outflow of the floating filter medium when backflushing the floating filter medium layer while promoting the flow of the floating filter medium by aeration from below the floating filter medium layer, one end is located above the filter medium layer. An air bypass pipe that communicates and opens at the other end under atmospheric pressure outside the filtration tank is provided, and a water-repellent gas permeable membrane that allows only gas to pass through is provided in the air bypass pipe so that aerated air is effectively removed. A technology has been proposed to prevent the filter medium from flowing out of the discharge pipe of the backwash drainage by balancing the flow rate of the backwash water with the flow rate of the backwash drainage by allowing it to escape outside the filtration tank. .

Japanese Patent No. 3853738 JP 11-47782 A

  However, the technique described in Patent Document 2 is a filter medium that is generated due to the fact that air is stored in the filtration tank and the flow rate of backwash water inflow and the drainage flow rate of backwash wastewater cannot be balanced. However, no attention has been paid to the magnitude of the inflow flow rate of the backwash water and the drainage flow rate of the backwash drainage. Therefore, in the technique described in Patent Document 2, for example, when the flow rate of the downward flow is increased in order to effectively wash the floating filter layer by deploying the floating filter material further downward, the floating filter medium flows out. It was not possible to suppress it.

  On the other hand, in the backwashing of the floating filter material layer of the filtration system, it is required to efficiently expand the floating filter material downward and efficiently perform the backwash while suppressing the outflow of the floating filter material.

  Therefore, the present invention is a filtration system that filters raw water using a floating filter medium layer composed of a large number of floating filter media, and effectively backwashes the floating filter media layer while suppressing the floating filter medium from flowing out of the filtration tank. It is an object of the present invention to provide a method for cleaning a floating filter medium layer that makes it possible.

An object of the present invention is to advantageously solve the above problems, and the method of cleaning a floating filter medium layer according to the present invention includes a floating filter medium layer made of a floating filter medium, and an upper side of the floating filter medium layer. A filtration system having a filtration tank comprising a screen for preventing the floating filter material from flowing out, a filtrate storage part provided on the upper side of the screen, and a backwash drainage outlet disposed below the floating filter material layer. A method for cleaning a floating filter material layer in
A first backwashing step of discharging the water in the filtration tank from the backwash drainage outlet at a flow rate at which the floating filter medium descends;
When the floating filter material reaches a predetermined position above the backwash drainage outlet, the flow rate of the backwash drainage discharged from the backwash drainage outlet is the flow rate at which the floating filter stagnates or rises. A second backwashing step to be changed to
It is characterized by including.
Thus, in the first backwashing step, if the water in the filtration tank is discharged at a flow rate at which the floating filter medium descends, the floating filter medium can be expanded further downward, so that the floating filter medium layer is effectively reversed. Can be washed. In addition, if the floating filter medium is stagnated or raised at the timing when the floating filter medium reaches a predetermined position, the floating filter medium can be sufficiently developed by moving the floating filter medium downward and the floating filter medium is effectively washed. It can suppress flowing out.
In the present invention, the “predetermined position” is between the lower end of the floating filter material layer and the backwash drainage outlet before the start of backwashing, and can suppress the outflow of the floating filter material at a desired level. For example, “allowable amount of floating filter flow out”, “desired backwash efficiency”, “time required to change backwash drain valve opening”, etc. Can be determined.

Here, in the method for cleaning a floating filter material layer of the present invention, the filtration system has a backwash drain valve that adjusts the flow rate of backwash drainage discharged from the backwash drainage outlet.
In the first backwashing step and the second backwashing step, the floating filter medium layer is washed by natural flow of filtrate in the filtrate storage part by opening the backwash drain valve,
In the second back washing step, it is preferable that the opening degree of the back washing drain valve is made smaller than that in the first back washing step. Thus, if the filtered water in the filtrate storage part is allowed to flow naturally after the opening degree of the backwash drain valve in the second backwash process is made smaller than that in the first backwash process, the floating filter medium is outside the filtration tank. This is because the floating filter medium layer can be washed with energy saving by suppressing the flow to the bottom.

  Moreover, the washing | cleaning method of the floating filter material layer of this invention further includes the 3rd backwash process which makes the opening degree of the said backwash drain valve larger than the said 2nd backwash process after the said 2nd backwash process. Is preferred. In the case where the floating filter material layer is backwashed by the natural flow of filtered water in the filtrate storage section, the flow of backwash drainage gradually decreases as the water level in the filtrate storage section decreases. This is because if the step is provided after the second backwashing step, it is possible to suppress or prevent a decrease in the flow rate of the backwash wastewater and to continue the effective cleaning of the floating filter material layer.

  Furthermore, the method for cleaning a floating filter material layer of the present invention may increase the degree of opening of the backwash drain valve in the third backwash process in response to a decrease in the level of filtrate water in the filtrate storage part. preferable. If the opening of the backwash drain valve is increased in response to a decrease in the water level in the filtered water reservoir, the flow rate of the backwash drainage can be reduced even if the floating filter layer is backwashed by the natural flow of filtered water. This is because the floated filter material layer can be more effectively washed and more effectively cleaned.

  In the method for cleaning a floating filter medium layer of the present invention, it is preferable to detect the arrival of the floating filter medium at the predetermined position using a contact sensor, an optical sensor, or an ultrasonic sensor. This is because if a contact sensor, an optical sensor, or an ultrasonic sensor is used, the arrival at a predetermined position can be detected more reliably even if properties such as the density of the floating filter medium change due to continuation of filtration. .

  Furthermore, in the method for cleaning a floating filter medium layer of the present invention, it is also preferable to detect the arrival of the floating filter medium at the predetermined position using a change in the water level of the filtrate storage section. This is because if the change in the water level of the filtrate storage part is used, the arrival of the floating filter medium at the predetermined position can be detected more stably.

  According to the method for cleaning a floating filter medium layer of the present invention, in a filtration system that filters raw water using a floating filter medium layer made of a large number of floating filter media, the floating filter medium is effectively prevented from flowing out of the filtration tank. The floating filter material layer can be backwashed.

It is explanatory drawing explaining schematic structure of the typical filtration system with which the washing | cleaning method of the floating filter material layer of this invention is performed. It is explanatory drawing which shows the state in the filtration tank at the time of wash | cleaning a floating filter material layer using an example of the washing | cleaning method of the floating filter material layer of this invention, and shows the state immediately after a 1st backwashing process start. It is explanatory drawing which shows the state in the filtration tank at the time of wash | cleaning a floating filter material layer using an example of the washing | cleaning method of the floating filter material layer of this invention, and shows the state at the time of a 2nd backwash process start. It is explanatory drawing which shows the state in the filtration tank at the time of wash | cleaning a floating filter material layer using an example of the washing | cleaning method of the floating filter material layer of this invention, and shows the state at the time of a 3rd backwash process start. It is a graph which shows the time-dependent change of the flow volume of backwashing drainage, and the opening degree of a backwashing drainage valve in washing | cleaning operation of the floating filter media layer using an example of the washing | cleaning method of the floating filter media layer of this invention. It is explanatory drawing which shows the cross section of punching metal etc. which can be used for the screen of the filtration system in which the washing | cleaning method of the floating filter material layer of this invention is performed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, what attached | subjected the same code | symbol in each figure shall show the same component.
The filtration system in which the method for washing a floating filter material layer of the present invention is performed is not particularly limited, and can be used for sewage treatment, industrial wastewater treatment, water treatment, water treatment, and the like. Specifically, the filtration system can be used, for example, when filtering sewage at a sewage treatment plant.

  Here, as shown in FIG. 1, the filtration system 100 which can implement an example of the washing | cleaning method of the floating filter material layer of this invention is equipped with the filtration tank 10 for filtering raw | natural water and obtaining filtered water. And in the filtration tank 10, the floating filter medium layer 12 which consists of the screen 11, many floating filter media supported by the screen 11, the raw | natural water inflow port 13 installed in the lower side of the floating filter medium layer 12, and the floating filter medium layer A plurality of backwash drainage outlets 14 disposed below 12, a filtrate storage unit 15 provided on the upper side of the screen 11, and a filtrate outlet 16 provided on the upper side of the screen 11 are arranged. Yes.

  Further, the filtration system 100 includes a first sensor 18 that detects that the floating filter medium has reached a predetermined position in the filtration tank 10, a second sensor 19 that measures the water level of the filtrate storage part 15, and from these sensors. And a control device 70 that receives the information and controls the opening degree of the backwash drain valve 62 described later. The filtration system 100 includes an air ejection part 51, a blower 54 as an air supply source for supplying air to the air ejection part 51, an air supply pipe 52 that connects the blower 54 and the air ejection part 51, and an air supply It has a filter medium dispersing mechanism 55 configured by an air supply pipe valve 53 provided in the pipe 52 to improve the fluidity of the floating filter medium by aeration during the backflow cleaning of the floating filter medium layer 12.

  Here, the floating filter medium constituting the floating filter medium layer is a filter medium having a specific gravity smaller than that of the raw water (that is, floating in the raw water). And in this filtration system 100, well-known floating filter media, such as the particulate floating filter material made from a foaming polymer of patent document 1, can be used as a floating filter material.

Further, the screen 11 disposed on the upper side of the floating filter medium layer 12 is not particularly limited as long as it is a screen that can prevent the floating filter medium from flowing out from the filtered water outlet 16. For example, the cross section shown in FIG. A punching metal having a large number of openings 200 or the like can be used.
Here, as shown to Fig.4 (a), as for the general punching metal, the surface of the non-opening part is planar. Therefore, when such punching metal is used as the screen 11, when fine sand particles pass through the screen 11 due to aeration at the time of backwashing of the floating filter material layer 12, the passed sand particles and the like are deposited on the screen 11. May stay in the filtrate storage part 15. Therefore, as the screen 11, for example, it is preferable to use a plastic plate having a mortar-shaped opening portion whose opening diameter on the lower surface is smaller than that on the upper surface (FIG. 4B). If such a plate is used as the screen 11 with the larger opening diameter on the upper side, sand particles can be prevented from staying in the filtrate storage part 15 due to the inclination of the mortar-shaped opening, and the floating filter medium The sand particles can be easily passed through the screen 11 and discharged when the layer is backwashed.

  The floating filter medium layer 12 is formed by placing a large number of floating filter media 12A in a filtration tank 10 filled with water up to a predetermined height, and then placing a screen 11 on the upper side of the input floating filter medium 12A. Can be provided inside.

The 1st sensor 18 is used in order to control the outflow of a floating filter medium at the time of backwashing of the floating filter material layer 12, and the lower end of the floating filter medium layer 12 and the backwash drainage outlet 14 before the start of backwashing. It is installed at a predetermined position (in the illustrated example, a position having a height h ₁ upward from the installation position of the backwash drainage outlet 14). Specifically, the first sensor 18 considers “acceptable amount of floating filter outflow”, “desired backwash efficiency”, “time required for changing the opening degree of the backwash drain valve 62”, and the like. It is provided at a position determined in advance by experiment or simulation. The content detected by the first sensor 18 is sent to the control device 70.
The first sensor 18 is not particularly limited, and a known sensor that can detect that the floating filter medium has reached a predetermined position in the filtration tank 10 can be appropriately selected and used. It is preferable to use a type sensor, an optical sensor, or an ultrasonic sensor (hereinafter, these may be collectively referred to as a “physical sensor”). Normally, properties such as the density of floating filter media change over time as filtration continues, so it is possible to accurately detect the arrival of a floating filter medium at a specified position based on the flow rate of backwash wastewater and the time spent on backwashing. Difficult to do. However, if a contact sensor, an optical sensor, or an ultrasonic sensor (physical sensor) is used, the arrival at a predetermined position can be detected more reliably even if the characteristics such as the density of the floating filter change over time. Can do. Here, as the contact-type sensor, for example, it has a float that can move downward as the floating filter material descends in the filtration tank 10, and the float is moved to a predetermined position by a magnet or the like in the float. A float sensor can be used to detect arrival. As an optical sensor, for example, a laser light source that emits a laser beam having an intensity that does not scatter significantly with contaminants or suspended suspended solids but scatters with a floating filter medium, and a detector that detects the scattering intensity of the laser beam, A light scattering sensor using can be used. As an ultrasonic sensor, for example, an ultrasonic transmitter / receiver that transmits / receives ultrasonic waves in the height direction in the filtration tank 10, an ultrasonic transmitter / receiver and a floating filter medium using the time from transmission to reception of such ultrasonic waves, It is possible to use a sensor that uses a calculator that calculates the distance.
In addition, the 1st sensor 18 can be attached to the arbitrary positions in the filtration tank 10, if it can detect that the floating filter medium reached | attained the predetermined position in the filtration tank 10. FIG.

There is no restriction | limiting in particular as the 2nd sensor 19, The known water level meter which can measure the water level of the filtrate water storage part 15 can be selected suitably, and can be used. Then, the measured value of the second sensor 19 is sent to the control device 70.
In addition, the 2nd sensor 19 can be attached to the arbitrary positions in the filtration tank 10, if the water level of the filtrate water storage part 15 can be measured.

The filter medium dispersing mechanism 55 is for dispersing the floating filter medium 12A and improving the cleaning efficiency of the floating filter medium layer 12 during backflow cleaning of the floating filter medium layer 12 described in detail below. Specifically, the air supply pipe valve 53 is opened and the blower 54 is operated at an arbitrary timing during the backwashing of the floating filter material layer 12, so that air is ejected upward from the air ejection part 51, and floats. The filter medium 12A is dispersed.
In addition, if the air ejection part 51 which comprises the filter-medium dispersion | distribution mechanism 55 can spray air with respect to the floating filter medium of the lower side of the screen 11, it can be installed in arbitrary positions, and arbitrary shape and can do. The control device 70 can also control the opening and closing of the air supply piping valve 53 and the activation and stop of the blower 54.

  Further, in this filtration system 100, a plurality of (six in FIG. 1) backwash drainage outlets 14 located in the lower part of the filtration tank 10 discharge backwash drainage from the filter tank 10 when the floating filter material layer 12 is backwashed. The backwash drainage pipe 61 is connected to a backwash drainage treatment facility (not shown). The backwash drainage pipe 61 has a backwash drainage valve 62 whose opening degree can be adjusted.

Therefore, in this filtration system 100, the water in the filtration tank 10 can be sent out of the filtration tank 10 through the backwash drainage pipe 61 by opening the backwash drain valve 62.
The path and pipe diameter of the backwash drain pipe 61 and the valve diameter of the backwash drain valve 62 are determined when the backwash drain valve 62 is opened when the water level of the filtrate storage section 15 is at the filtered water outlet 16. When sending the water in the filtration tank 10 at a degree of 100%, it is necessary that at least the floating filter medium constituting the floating filter medium layer 12 is lowered in the filter tank 10.

  Moreover, the control apparatus 70 of the filtration system 100 controls the opening degree of the backwash drain valve 62 based on the signal from a 1st sensor or a 2nd sensor.

  And in this filtration system 100, raw | natural water is filtered with the floating filter material layer 12 of the filtration tank 10 as follows. Moreover, in this filtration system 100, when the filtration resistance rises to a predetermined value or more, the first backwashing process, the second backwashing process, and the third backwashing process described in detail below are performed. As a result, the floating filter medium layer 12 in the filtration tank 10 is washed.

<Raw water filtration operation>
As shown in FIG. 1, in the filtration system 100, the raw water piping valve 42 is opened, the raw water is fed to the lower part of the filtration tank 10 with the air supply piping valve 53 and the backwash water distribution valve 62 closed, and the floating filter medium is supplied. Raw water is passed through the layer 12 in an upward flow to obtain filtered water. Then, after the filtrate water obtained flows through the filtrate water storage unit 15 in an upward flow, it is discharged to a river or the like via the filtrate water outlet 16.

<Cleaning operation of floating filter material layer>
And in the filtration system 100, when filtration resistance rises more than predetermined value regularly or by continuing filtration of raw | natural water, the raw | natural water piping valve 42 is closed and filtration of raw | natural water by the floating filter material layer 12 is complete | finished. To do. Thereafter, the floating filter material layer 12 in the filtration tank 10 is washed through the following steps.

(First backwash process)
In this filtration system 100, after the filtration of the raw water is finished, the opening degree of the backwash drain valve 62 is set to 100% as a predetermined opening degree (first opening degree), and the water in the filtration tank 10 flows down naturally. Then, such water is discharged as backwash drainage from the backwash drainage outlet 14 (FIG. 2A). At this time, the water in the filtration tank 10 that passes from the upper part to the lower part of the floating filter medium layer 12 functions as washing water (back washing water) for the floating filter medium layer 12, and the floating filter medium layer by the washing water. 12 is washed. In the present specification, “backwash drainage” refers to water discharged from the filtration tank 10 to the outside of the filtration tank 10 via the backwash drainage outlet 14.
Specifically, as shown in FIG. 3, the cleaning operation of the floating filter material layer 12 is started by changing the opening degree of the backwash drain valve 62 which was 0% at the end of the raw water filtering operation. Start raising to 100%. At time t ₁ , the floating filter medium 12A starts to descend in the filtration tank 10, and the first backwash process is started from here. Then, the time T _1, the opening degree of the backwash drain valve 62 reaches 100 percent of the first opening. Thereafter, the first backwashing process is continued until the floating filter medium 12A reaches a predetermined position described later.

Here, the first opening degree of the backwash drain valve 62 is an opening degree at which the floating filter medium 12 </ b> A constituting the floating filter medium layer 12 has a flow rate so as to descend in the water of the filtration tank 10. Accordingly, in the first backwashing process in the filtration system 100, the floating filter medium 12A develops further downward in the water of the filtration tank 10 while the washing water passes from the upper part to the lower part of the floating filter medium layer 12, so that the floating filter medium layer 12 can be backwashed effectively.
In this specification, “the floating filter medium descends” means that the force generated by the downward flow of water in the filtration tank 10 exceeds the buoyancy of the floating filter medium 12A, and thus the floating filter medium layer 12 made of the floating filter medium 12A. It includes that at least the height from the bottom of the filtration tank 10 at the lower end is lowered.

  Further, the first opening degree of the backwash drain valve 62 in the first backwash process is not particularly limited as long as the floating filter medium 12A continues to descend, and is determined in consideration of the time until the floated filter medium reaches a predetermined position. can do. Specifically, the first opening degree of the backwash drain valve 62 in the first backwash process is from the viewpoint of fully utilizing the pipe diameter of the backwash drainage pipe 61 and increasing the backwash efficiency of the floating filter medium 12A. It is preferably 80 to 100%, more preferably 100% in terms of the cross-sectional area ratio of the flow channel when fully open is 100%.

Here, in this filtration system 100, during filtration, raw water is passed through the floating filter material layer 12 in an upward flow, so the floating filter material 12A constituting the floating filter material layer 12 is consolidated toward the screen 11 side, and the first At the start of the backwashing process, the floating filter medium 12A can be expanded downward while remaining in a lump shape. Therefore, in this filtration system 100, immediately after the start of the first backwashing process, air is sprayed from the air ejection part 51 to the floating filter medium 12A for a predetermined time, and is consolidated toward the screen 11 side by the filtration process. The floating filter medium 12A can be dispersed to improve the cleaning efficiency of the floating filter medium layer 12.
In addition, it is preferable to complete | finish the blowing of the air from the air ejection part 51 by the time the floating filter medium 12A reaches | attains the below-mentioned predetermined position.

(Second backwash process)
Floating filter media 12A to continue to lower the filtration tank 10 in the first backflushing step, any, as a predetermined position, reaches a position of a height h ₁ above the installation position of the backwashing water discharge outlet 14 (FIG. 2B ). At that time, the backwash drain valve 62 is opened at a predetermined opening (second opening) so that the floating filter medium 12A constituting the floating filter medium layer 12 is changed to a flow rate that stagnates or rises in the water of the filtration tank 10. Then, the water in the filtration tank 10 is discharged from the backwash drain outlet 14 as backwash drainage. Also at this time, the water in the filtration tank 10 that passes from the upper part to the lower part of the floating filter medium layer 12 functions as washing water (back washing water) for the floating filter medium layer 12, and the floating filter medium by the washing water. Layer 12 is cleaned.
Specifically, as shown in FIG. 3, the time t ₂ after the opening of the backwash drain valve 62 becomes 100%, the first sensor 18 detects that the floating filter medium 12A reaches a predetermined position . And based on the detection by the said 1st sensor 18, the control apparatus 70 begins to reduce the opening degree of the backwash drain valve 62 toward 70%, and a 2nd backwash process is started. Then, at time T ₂ after time t ₂ , the opening degree of the backwash drain valve 62 reaches 70% as the second opening degree. Here, since the opening degree of the backwash drain valve 62 is reduced after the start of the second backwash process, and the water level of the filtrate storage unit 15 continues to decrease, the flow rate of the backwash drainage is reduced. Will be. Then, at a time (not shown) between time t ₂ and time t ₃ to be described later, the floating filter medium 12A constituting the floating filter medium layer 12 stagnates in the water or starts to rise.

The “predetermined position” is between the lower end of the floating filter medium layer 12 and the backwash drainage outlet 14 before the start of backwashing, and can prevent the floating filter medium 12A from flowing out at a desired level. It is a position determined in advance as a position. In addition, the “predetermined position” was previously tested in consideration of “allowable flow rate of floating filter medium 12A”, “desired backwash efficiency”, “time required to change the opening degree of the backwash drain valve 62”, and the like. Alternatively, it can be determined by simulation, for example, a position 10 to 50% higher than the interval between the lower end of the screen 11 and the installation position of the backwash drainage outlet 14 above the installation position of the backwash drainage outlet 14. Preferably, the position can be 10 to 20% high.
Therefore, in the 2nd back washing process in the filtration system 100, it can suppress that 12A of floating filter media flows out of the filtration tank 10, washing | cleaning the floating filter material layer 12 effectively.
Here, in this specification, “the floating filter medium stagnates or rises” means that the force generated by the downward flow of water in the filtration tank 10 balances with the buoyancy of the floating filter medium 12A or the buoyancy of the floating filter medium 12A. It is included that at least the height from the bottom of the filtration tank 10 at the lower end of the floating filter medium layer 12 made of the floating filter medium 12A is maintained or increased.

In addition, regarding the arrival of the floating filter medium 12A at a predetermined position, in the above example, the first sensor 18 detects, but the second sensor 19 measures the water level of the filtrate storage part 15 and detects it using the change in the water level. You can also That is, for example, after the backwash drain valve 62 is opened and the first backwash process is started, the filtered water storage section until the floating filter medium 12A starts to flow out of the filtration tank 10 through the backwash drainage outlet 14. It is also possible to preliminarily detect that the flotation filter 12A has reached a predetermined position based on the result of the analysis by previously analyzing the change of the 15 water levels over time. Thus, if the change of the water level of the filtrate storage part 15 is used, the arrival of the floating filter medium 12A to the predetermined position can be detected more stably.
In particular, from the viewpoint of more reliably detecting the arrival of the floating filter medium 12A at a predetermined position, both the first sensor 18 as a physical sensor and the second sensor 19 that measures the water level of the filtrate storage unit 15 are used. In any case, it is more preferable to detect the arrival of the floating filter medium 12A at a predetermined position in accordance with the method described above. In this case, for example, after starting to use the new floating filter medium 12A, a period (for example, 12 to 24 months) arbitrarily determined as a period during which the density of the floating filter medium 12A can be changed by continuing the filtration has elapsed. Until then, the detection result by the first sensor 18 as a physical sensor is preferentially adopted, and during that time, the relationship between the detection result and the change in the water level of the filtrate storage part 15 measured by the second sensor 19 is obtained. Analyze, and after the period has elapsed, the detection result by the second sensor 19 is preferentially adopted based on the result of the analysis, and the physical sensor prevents the floating filter medium 12A from flowing out in large quantities. Therefore, the control device 70 can be appropriately configured so as to function as a safety device.

  In addition, the second opening degree of the backwash drain valve 62 in the second backwashing process is an opening degree at which the floating filter medium 12A that has reached a predetermined position in the filtration tank 10 has a flow rate that stagnates or rises. And it is necessary that the opening is smaller than the final opening of the first backwashing step. For example, the second opening degree is analyzed in advance by experiment or simulation while considering the water level of the filtrate water storage unit 15 while the second backwashing process is started, and the opening degree at which the floating filter medium 12A stagnates. , And can be determined based on the results of such analysis. Specifically, the second opening degree of the backwash drain valve 62 in the second backwash process can be set to 70 to 90%, for example, in the cross-sectional area ratio of the flow path when the full opening is 100%.

(Third backwashing process)
Here, when the opening degree of the backwash drain valve 62 in the second backwashing process is held at the second opening degree, the pressure (water head pressure) is reduced as the water level of the filtrate storage unit 15 is lowered. The flow rate of backwash drainage gradually decreases. On the other hand, at the time of backwashing, the speed at which the water in the filtration tank 10 passes through the floating filter medium layer 12 should be fast as long as the floating filter medium 12A does not flow out. Therefore, in this filtration system 100, after setting the backwash drain valve 62 to the second opening, as the third backwash process, the opening of the backwash drain valve 62 is set within a range where the floating filter 12A does not reach the predetermined position. The floated filter medium layer 12 is washed by the natural flow of the filtrate in the filtrate storage part 15 by making it larger than the second opening.
More specifically, the time t ₃ when shown in Figure 3, the opening of the backwash drain valve 62 was 70% starting raised towards 100%, the third backwash step is started.
Thus, if the opening degree of the backwash drain valve 62 is made larger than that at the time of the second backwash process after the second backwash process in which the water level of the filtrate water storage unit 15 is lowered to a certain extent, the flow rate of the backwash drainage is reduced. The decrease is suppressed or prevented, and the effective cleaning of the floating filter material layer 12 can be continued.

  In addition, the reduction | decrease in the flow volume of the backwash waste_water | drain accompanying the fall of a head pressure is the maximum of the filtrate water storage part 15 with respect to the volume below the screen 11 in the filtration tank 10, especially when the storage volume of the filtrate water storage part 15 is small. This is conspicuous when the ratio of the storage volumes (the maximum storage volume of the filtrate storage section / the volume below the screen) is 1.0 or less. Therefore, when the ratio is 1.0 or less, it is particularly preferable to perform the third backwashing step.

Here, as a timing for making the opening degree of the backwash drain valve 62 larger than the second opening degree in the second backwashing process (t ₃ in FIG. ₃ ), the floating filter medium 12A has reached a predetermined position. As long as it is not detected by the first sensor 18, there is no particular limitation. For example, the filtrate storage part measured by the second sensor 19 when the predetermined execution time of the second backwashing process has elapsed. When the water level of 15 falls below a predetermined water level (this water level is indicated as h ₂ in FIG. 2C), or the like. Here, as the “predetermined water level” in the filtered water storage unit 15, for example, a position having a height of 50 to 100 cm from the upper surface of the screen 11 can be used.
And in this filtration system 100, the control apparatus 70 can perform the change of the opening degree from the 2nd opening degree of the backwash drain valve 62 by a timer function or based on the detection by a sensor.

  Here, the opening degree of the backwash drain valve 62 in the third backwashing process is larger than the second opening degree in the second backwashing process, and is within a predetermined range as long as the floating filter medium 12A does not reach the predetermined position again. The opening (third opening) may be constant. Specifically, for example, the third opening degree can be set to 80 to 100% in terms of the cross-sectional area ratio of the flow path when fully opened is set to 100%.

Alternatively, in the third backwashing step, the opening degree of the backwash drain valve 62 is increased to 100% in response to a decrease in the filtrate water level in the filtrate storage part 15 measured by the second sensor 19. Also good. As a method of increasing the opening degree of the backwash drain valve 62 in response to a decrease in the filtrate water level in the filtrate storage unit 15, for example, even if the filtrate water level in the filtrate storage unit 15 decreases. There is a method of adjusting the opening degree of the backwash drainage valve 62 so that the flow rate of the backwash drainage is within the range of the last flow rate ± 15% of the second backwash process. More specifically, the control device 70 stores in advance the relationship between the filtrate water level in the filtrate storage unit 15, the opening degree of the backwash drain valve 62, and the flow rate of the backwash drainage. 2 Based on the correlation between the water level of the filtrate measured by the sensor 19 and the opening degree of the backwash drain valve 62 and the flow rate of the backwash drainage at the measured water level, the flow rate of the backwash drainage is determined in the second backwash process. A method of selecting the opening degree of the backwash drain valve 62 so as to be within the range of the final flow rate ± 15% can be mentioned. The above correlation can be obtained by, for example, the Torrichelli's theorem (in a container containing a liquid with a small hole on its side, g acceleration of gravity, h of the height difference between the liquid level and the hole, and v of the liquid outflow velocity). In some cases, the correction coefficient obtained by actual measurement or the like can be taken into consideration while using a law that satisfies the relationship of v = (2gh) ^1/2 .
Thus, if the opening degree of the backwash drain valve 62 is increased in response to a decrease in the level of the filtrate water, the drainage flow rate of the water in the filtration tank is made more uniform, and the floating filter material layer 12 is more effective. Can be washed.

And in this filtration system 100, the backwash drain valve 62 is closed and a series of washing operation of the floating filter material layer 12 is completed.
Specifically, as shown in FIG. 3, at a predetermined timing t _4, the third backwash step is completed by the opening of the backwash drain valve 62 was 100% begins to reduce. When the opening degree of the backwash drain valve 62 is fully closed, the flow of backwash drainage becomes zero, and a series of washing operations of the floating filter material layer 12 is completed. Thereafter, the raw water filtration operation and the floating filter material layer 12 washing operation are optionally repeated.

Here, the timing for ending the third backwashing step (t ₄ in FIG. 3) is not particularly limited. For example, the water level of the filtrate storage unit 15 measured by the second sensor 19 is a predetermined limit water level. And so on when: In this case, in FIG. 3, after the time t ₃ , for example, by the method described above, the opening degree of the backwash drain valve 62 is started to increase in response to the decrease in the filtrate water level in the filtrate storage part 15, to T _3, the opening degree of the backwash drain valve 62 reaches 100 percent. Next, at time t ₄ , the second sensor 19 detects that the water level of the filtrate storage part 15 has reached a predetermined limit water level. Then, based on the detection by the second sensor 19, the control device 70 starts to lower the opening degree of the backwash drain valve 62 toward 0%, and the third backwash process is ended.

  The “predetermined limit water level” at the water level of the filtrate storage unit 15 is preferably as low as possible. In the first backwashing step, the foreign matter trapped in the floating filter material layer 12 by the blowing of air from the air jetting part 51 constituting the filter medium dispersing mechanism 55 is applied to the screen 11 so as to counter the downward flow. The final water level of the filtered water storage unit 15 in the backwash operation may be as low as possible, for example, lower than the upper surface of the screen 11. It is because it can remove effectively and the deterioration of the quality of the filtrate water which flows out from the filtrate outlet 16 at the time of filtration operation can be suppressed.

Here, in the third backwashing step, the opening degree of the backwash drainage valve 62 is set or adjusted so that the floating filter medium 12A does not reach a predetermined position until the end of the third backwashing step. Therefore, it is preferable to take measures to prevent the floating filter medium 12A from flowing out of the filtration tank 10 in case it is detected that the floating filter medium 12A has reached the predetermined position. As such a countermeasure, for example, the backwash drain valve 62 is changed to the first on the basis of detection of the floating filter 12A reaching the predetermined position by the first sensor 18 after the opening degree of the backwash drain valve 62 is set to the third opening. The second backwashing process is repeated again after setting the opening to 2 degrees, and after a predetermined time has elapsed (for example, after 2 to 10 seconds have elapsed since the setting of the backwash drain valve 62 to the second opening was completed). The control device 70 can be configured in advance so as to shift to the third back washing step.
In addition, even if it is the time of a 2nd backwash process and the time of the 2nd backwash process repeated after a 3rd backwash process, if it becomes the timing mentioned above, a 2nd backwash process will be complete | finished and a series of floating filter media The controller 70 can be configured to complete the cleaning operation of the layer 12.

  As mentioned above, although the washing | cleaning method of the floating filter material layer of this invention was demonstrated using an example, the filtration system in which the washing | cleaning method of the floating filter material layer of this invention is performed is not limited to the said example, and adds a change suitably. be able to.

  In the filtration system 100 of the above example, switching between the steps in the washing operation of the floating filter material layer 12 is controlled by the control device 70. However, the floating filter material of the present invention can be manually operated without using the control by the control device 70. A cleaning method for the layer 12 can also be implemented. Specifically, for example, after the raw water filtration operation is completed, the backwash drain valve 62 is set to the first opening, and when the first sensor 18 detects that the floating filter medium 12A has reached a predetermined position. The backwash drain valve 62 is manually set to the second opening. For example, when the water level of the filtrate water storage unit 15 measured by the second sensor 19 falls below a predetermined water level, the backwash drain valve 62 is manually set to the second opening. The backwash drain valve 62 is manually closed when the second sensor 19 detects that the water level of the filtrate water storage unit 15 measured by the second sensor 19 has reached a predetermined limit water level. However, the floating filter medium layer of the present invention can be washed.

  According to the present invention, in a filtration system that filters raw water using a floating filter medium layer composed of a large number of floating filter media, the floating filter medium layer is effectively backwashed while suppressing the floating filter medium from flowing out of the filtration tank. be able to.

DESCRIPTION OF SYMBOLS 10 Filtration tank 11 Screen 12 Floating filter material layer 12A Floating filter material 13 Raw water inlet 14 Backwash drainage outlet 15 Filtrated water storage part 16 Filtration water outlet 18 First sensor 19 Second sensor 41 Raw water piping 42 Raw water piping valve 51 Air ejection part 52 Air supply pipe 53 Air supply pipe valve 54 Blower 55 Filter medium dispersion mechanism 61 Backwash drainage pipe 62 Backwash drainage valve 70 Controller 100 Filtration system 200 Opening

Claims (6)

A floating filter layer made of a floating filter medium, a screen disposed above the floating filter medium layer to prevent the floating filter medium from flowing out, a filtered water storage section provided on the upper side of the screen, and a lower layer than the floating filter medium layer A method for cleaning a floating filter material layer in a filtration system having a filtration tank with a backwash drainage outlet arranged on the side,
A first backwash that discharges water in the filtration tank from the backwash drainage outlet until the floated filter medium reaches a predetermined position above the backwash drainage outlet at a flow rate at which the floating filter medium descends. Process,
When the floating filter medium has reached the predetermined position of the upper than the backwashing water discharge outlet, the flow rate of the backwash waste water discharged from the backwashing water discharge outlet, the floating filter media or increases stagnant A second backwashing step to reduce the flow rate;
A method for cleaning a floating filter medium layer. The filtration system has a backwash drain valve that adjusts the flow rate of backwash drainage discharged from the backwash drain outlet,
In the first backwashing step and the second backwashing step, the floating filter medium layer is washed by natural flow of filtrate in the filtrate storage part by opening the backwash drain valve,
The cleaning method according to claim 1, wherein in the second backwashing step, the opening degree of the backwash drain valve is made smaller than that in the first backwashing step.   The washing | cleaning method of Claim 2 which further includes the 3rd backwashing process which makes the opening degree of the said backwash drain valve larger than the said 2nd backwashing process after the said 2nd backwashing process.   The washing | cleaning method of Claim 3 which makes the opening degree of the said backwash drainage valve correspond to the fall of the water level of the filtrate water in the said filtrate water storage part at a said 3rd backwash process.   The washing | cleaning method in any one of Claims 1-4 which detects the arrival of the said floating filter medium to the said predetermined position using a contact-type sensor, an optical sensor, or an ultrasonic sensor.   The washing | cleaning method in any one of Claims 1-4 which detects the arrival of the said floating filter medium to the said predetermined position using the change of the water level of the said filtrate water storage part.

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