JPH07100491A - Operation of natural filter - Google Patents

Abstract

PURPOSE:To provide an operation method for a natural filter wherein a turbid layer suspending above the upper surface of a filter layer can be effectively broken to pieces to effect washing. CONSTITUTION:Raw water in a filter tank is discharged to lower the water level in the filter tank to a level below the upper surface of a filter layer 26, and washing water is sprayed, in the air, against a turbid layer suspending above the filter layer by means of a surface washing device 25 disposed above the filter layer 26, whereby a direct surface washing process, wherein the turbid layer suspending above the filter layer is broken, washed, and removed, is carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for filtering suspended solids contained in groundwater and the like with a filter layer, and utilizing the action of iron bacteria that have been preliminarily grown and supported on the filter layer, thereby making it possible to obtain iron contained in groundwater. , A method for operating a natural filtration device for removing manganese components.

[0002]

2. Description of the Related Art Groundwater is a good water resource, but its raw water often has high iron and manganese concentrations. It is necessary to remove these iron and manganese components in consideration of the need to satisfy the standard value.

Therefore, conventionally, for example, Leptothrix, Sphaerotilus
For example, the utilization of iron bacteria that live in groundwater a lot and have both iron and manganese oxidizing ability has been proposed (“Environmental Technology”, Vol.21, No.2, 1992), and various natural filtration devices are put to practical use. (For example, Japanese Patent Laid-Open No. 1-266897)
No.).

[0004] Generally, this type of device is filled with a granular medium such as a gravel layer, a standard filter sand for water supply, and anthracite, which is arranged in a filter tank, to form a filter layer (filter medium), and ground water etc. The suspended water contained in the raw water is suspended and removed at the upper part of the filter layer by flowing the raw water of the above in a downward flow from above the filter tank, and the action of iron bacteria preliminarily supported on the filter layer is increased. To remove the iron and manganese components contained in the raw water, remove the suspended suspension through the filter layer, and remove the iron and manganese components to collect the treated water from below the filtration tank. Is configured.

By the way, when filtration is carried out for a certain period of time using this kind of apparatus, the suspension suspended matter mainly containing bacteria contained in the raw water is suspended in the upper part of the filter layer due to the continuous filtration. The accumulation causes a film formation, and thus the head loss is gradually increased, and clogging occurs to reduce the filtration effect, which is not preferable.

In order to solve this problem, conventionally, washing water or air is introduced into the filter layer from below the filter layer to remove the suspension accumulated on the surface of the filter layer. However, since the suspended matter is formed into a film on the surface of the filter layer, becomes a mudball, and has tackiness, it may not be completely removed by backwashing which is usually carried out.

For this reason, so-called "surface cleaning" has been conventionally performed, but in this method, as shown in FIG. 4, the upper freeboard portion above the filtration tank is spaced from each other by a predetermined distance. While constructing multiple drainage troughs,
Between the drainage troughs, a surface cleaning device is installed above the filter layer, the raw water is discharged to the top of the drainage trough, and the suspended layer suspended on the upper part of the filter layer is ejected into the water from the nozzle of the surface cleaning device. It is crushed and washed by water spray.

However, in such water injection in water, the shearing force may be insufficient and insufficient for crushing and removing the suspended layer suspended on the upper part of the filter layer. Mud balls were generated due to the tackiness of the product, and the operation was restarted with the filtration effect lowered, which was not preferable.

Therefore, the applicant of the present invention discharges raw water from the filtration tank and exposes (exposes) the surface of the filter layer in the air, so that the surface of the filter layer is exposed in the air from the nozzle of the surface cleaning device. The so-called "direct surface washing", in which the suspended layer suspended on the upper surface of the filter layer is crushed and washed via the jet of water, is extremely effective for the suspended layer accumulated and formed into a film on the surface of the filter layer. The inventors have found that they can be crushed and removed, and have completed the present invention.

[0010]

The present invention has been made in order to solve the problems in the prior art described above, and has the following structures (1) and (2).

(1) A filter layer is formed by filling a granular medium such as a gravel layer, standard filter sand for water supply, and anthracite above a perforated block which is a support disposed at the bottom of a filtration tank, By passing the raw water in a downward flow from above the filtration tank, suspended suspended matter contained in the raw water is suspended and removed at the upper part of the filter layer, and the action of iron bacteria preliminarily supported on the filter layer is increased. The treated water from which the iron and manganese components contained in the raw water have been removed is collected from below the filtration tank through the perforated block, and the suspended turbid layer above the filter layer is treated as water. This is a method of operating a natural filtration device in which a surface cleaning device is installed above the filter layer for cleaning by jetting, and the raw water in the filtration tank is discharged, and the water level in the filtration tank is discharged below the upper surface of the filter layer. The cleaning water from the surface cleaning device installed above the filter layer. A direct surface washing process is performed to directly spray water into the suspended suspended layer above the air, thereby crushing, washing, and removing the suspended suspended layer above the filter layer. Characteristic natural filtration device operating method.

(2) After the direct surface washing is carried out, in the state where the direct surface washing step is continued, the washing water is passed through the perforated block from the lower side of the filtration tank to the backwash water to the filter layer. The method for operating a natural filtration device according to (1) above, which comprises performing a front-side back-washing step in which the back-washing step is performed at the same time.

In the method, in order to carry out the direct surface washing, the raw water is discharged from the filtration tank, and when the surface of the filter layer is exposed to the air, the raw water is discharged below the surface of the filter layer. If too much, air will be mixed into the inside of the filter layer. Therefore, after the direct surface washing is completed,
When the filtration step is carried out again, the residual air impairs the filtration effect. Therefore, when the direct surface washing is carried out, the drainage is 100 to 2 below the surface of the filter layer.
It is important to stop so that it is about 00 mm.
Such means for controlling drainage include pressure detection and detection by electrodes, and are not particularly limited.

Further, in this case, the distance between the upper surface of the filter layer and the surface washing nozzle, the ejection amount, the time, the nozzle shape and the like are appropriately selected depending on the state of the suspended layer and are particularly limited. It is not something that will be done.

Further, in the case of the surface backwashing step (2) described above, various conditions such as the time for carrying out the surface washing and various conditions such as the time for the subsequent surface backwashing also depend on the state of the suspended layer. Therefore, it is appropriately selected and is not particularly limited.

[0016]

EXAMPLES The operation method of the natural filtration device of the present invention will be described in more detail with reference to the accompanying drawings. First, the structure of the natural filtration device for carrying out the operation method of the present invention will be described below. explain.

FIG. 1 is a schematic view of the whole natural filtration apparatus for carrying out the operating method of the present invention, and FIG. 2 shows a left half of which is an intermediate plan sectional view and a right half of which is a bottom planar sectional view. There is.

In FIG. 1, reference numeral 10 denotes an inflow tank for rectifying raw water such as ground water supplied to the natural filtration device 1 and for evenly distributing the amount of inflow water and supplying it to the filtration chambers 20, 20. belongs to. A plurality of filtration chambers 20 are provided in parallel (in the front-rear direction with respect to FIG. 1) in order to filter the raw water evenly distributed from the inflow tank 10 via the supply pipes 12, 12. (See Figure 2).

Further, the filtration chamber 20 is composed of a filtration tank 22 and a grit 28, and as shown in FIGS. 1 and 4, at the bottom of the filtration tank 22, Japanese Patent Publication No. 60-13724.
So-called "perforated block" as disclosed in Japanese Patent Publication
The perforated block 24 serving as a support is provided by combining and using in parallel to enable uniform water collection and distribution. A filter layer 26 is formed above the perforated block 24. The filter layer 26 is formed by filling granular media such as a gravel layer 26a, high-quality standard reference sand for water supply 26b, and anthracite 26c. Is formed.

Further, as shown in FIGS. 3 and 4, the upper freeboard portion of the filtration tank 22 is provided with a plurality of trough-shaped drainage troughs 29, 29, which are erected at regular intervals. ing. This drainage trough 29 prevents the surface of the filter layer 26 from being disturbed by the impact of the inflowing water.
It has a function of uniformly collecting and discharging cleaning drainage as described later.

Further, as shown in FIGS. 3 and 4, branch pipes 25a, 25a of the conduit 25d of the surface cleaning device 25 are arranged in the gaps between the drainage troughs 29, 29, respectively. Plural sets of surface washing nozzles 25c, 25c are attached to the pipe 25a along the lengthwise direction of the drainage trough 29 so as to be spaced apart from each other at regular intervals and to be located below the drainage trough. There is. The surface washing nozzles 25c, 25c can uniformly wash the entire surface of the filter layer 26 to a deep portion during "direct surface washing" in which the water level in the filtration tank 22 is lowered below the filter layer 26. To do so.

Further, as shown in FIGS. 1 and 2, the water that has passed through the filter layer 26 and has been filtered is collected in the water collecting tank 30 through the perforated block 24. In addition,
A plurality of water collecting tanks 30 are provided in parallel so as to correspond to each filtering tank 22. The filtered water collected in the water collecting tank 30 flows into the water purifying tank 40 that is in communication with the filtered siphon pipe 90 connected to the upper portion of the water collecting tank 30. In addition, the water purification tank 40 is all the filtration tanks 22.
It is a single water purification tank 40 common to all. Then, the filtered water collected and merged from each water collecting tank 30 into the water purification tank 40 is
After passing through the weir 42 at the outlet of the water purification tank provided in the water purification tank 40, the water is recovered by the water purification recovery path 44 provided below the water purification auxiliary tank 43, and after chlorine injection, it will be used as water purification.

On the other hand, a reverse U-shaped backwash siphon pipe 100 is connected to the upper part of the water collection tank 30, and the other end is arranged in a backwash water storage tank 70 provided above the water collection tank 30. It is set up. The backwash siphon pipe 100 utilizes the water stored in the backwash water storage tank 70 to remove the filter layer 26.
In order to carry out the washing, the washing water is sent from the backwash water storage tank 70 to the water collecting tank 30. Further, a backwash flow controller (damper) 110 is connected to the upper end of the backwash siphon pipe 100. By adjusting the backwash flow controller 110, the backwashing area is changed to change the backwash flow rate. It is possible to adjust the flow rate at the time. The backwash water storage tank 70 is a single backwash water storage tank 70 common to all the filtration tanks 22 (see FIG. 2).

Further, a waste water siphon pipe 120 is provided so as to branch from the filtration siphon pipe 90, and the waste water tank 6
0 and the water collection tank 30 are connected. This is for discharging the filtered water of unstable water quality immediately after backwashing to the waste water tank 60 via the waste water siphon pipe 120. The waste water tank 60 is also a single waste water tank 60 common to all the filtration tanks 22 (see FIG. 2).

Further, a makeup water pump 170 is provided in the water purification tank 40 described above, and is connected to the backwash water storage tank 70 via a pipe line 172. This is for preliminarily storing backwash water for backwash in the backwash water storage tank 70. Further, in the water purification tank 40, a surface washing pump 160 is arranged and connected to a conduit 25d of the above-mentioned surface cleaning device 25 via a pipe 162 to supply washing water for surface washing. Is configured to.

On the other hand, a drain valve 28a is provided at the lower end of the gallite 28 of the filtration chamber 20, and water such as raw water is drained to a drain tank 50 provided below the inflow tank 10. ing. The drain tank 50 is also a single drain tank 50 common to all the filtration tanks 22 (FIG. 2).
reference).

A pipe line 132 for direct surface drainage is provided at the bottom of the filtration tank 22, and the drain tank 5 is provided at the other end.
It has reached 0. Further, in the case of this embodiment, the pipeline 13
2 or a water collecting tank 30 is provided with a pressure detection device (not shown), and the water level of the filtering tank 22 is 100 to below the filter layer surface from the upper surface of the filter layer 26 during drainage when performing direct surface washing.
The drainage is configured to stop below about 200 mm. As such means for controlling drainage, in addition to the pressure detection as in the present embodiment, detection by electrodes is conceivable, and is not particularly limited.

The operation of the natural filtration device thus constructed will be described in detail with reference to FIG. 5 to FIG. 14, particularly the block diagram showing the operating state of FIG. In addition, FIG.
In FIG. 14, in order to show the state of water, the part where water is present is shown slightly dark.

(1) Filtration Step (See FIG. 5) First, the raw water uniformly distributed from the inflow tank 10 through the supply pipes 12, 12 flows into the filtration chamber 20 and is provided in the upper freeboard section. While flowing into the filter tank 22 through the drainage troughs 29, 29 and passing through the filter layer 26, suspended suspended matter, which is a turbidity component, is removed, and the suspended suspended matter is suspended above the filter layer 26. By the action of bacteria, iron and manganese in raw water are oxidized and removed.

On the other hand, the filtered water that has passed through the filter layer 26 and is filtered is collected in the water collecting tank 30 via the perforated block 24, and the filter siphon pipe 9 connected to the upper portion of the water collecting tank 30.
After passing through 0, the water flows into the water purification tank 40 and is collected by a water purification recovery path 44 provided below the water purification auxiliary tank 43 beyond the weir 42 at the water purification tank outlet provided in the water purification tank 40 and after chlorine injection. Used as clean water.

Further, by continuing the filtration, suspended suspended matter is suspended on the upper surface of the filter layer 26, and the head loss is gradually increased, and accordingly, the water level in the filtration chamber 20 is gradually increased. Become. Therefore, after the filtration is continued for a certain period of time, the following washing step, particularly the "surface washing step" is required.

(2) Washing Step Filtration Drainage Step (See FIG. 6) As described above, when the head loss in the filtration chamber 20 increases and reaches a certain level, the inflow distribution valve 14 is closed to perform filtration. Draining, that is, the filtration siphon tube 90 is operating, the above-described filtration process is continued, and only the above-mentioned filtration is performed. The purpose of this drainage of filtered water is to reduce the amount of discharged water by effectively utilizing the raw water stored in the upper part of the filter layer 26.

Water Draining Step (See FIG. 7) After the water level above the filter layer 26 has dropped to some extent by the above-described filtered water drainage, the siphon break valve 91 of the filter siphon tube 90 is opened to stop the water flow of the filter siphon tube 90. (Break), and open the drain valve 28a provided at the lower end of the grit 28 of the filtration chamber 20 to open the drain tank 50.
First, the raw water is drained, and the water level in the filtration chamber 20 is adjusted to the drainage trough 2
Drain up to the top of 9.

Direct surface washing water draining step (see FIG. 8) After the water draining step is completed, the direct surface washing water draining valve 133 at the bottom of the filtration tank 22 is opened, and the filtered water purified through the filter layer 26 is directly washed by the direct surface washing. The water is drained to the drain tank 50 through the drainage pipe 132.

A pressure detecting device (not shown) provided in the conduit 132 or the water collecting tank 30 detects the water level in the filtration tank 22 to stop the drainage, whereby the water level after draining The filter layer 26 is accurately stopped so that it is about 100 to 200 mm below the surface.

Direct surface washing step (see FIG. 9) After the direct surface washing draining step is completed, the water purifying tank 4
0, the surface cleaning pump 160 is operated to open the surface cleaning valve 164, and the surface cleaning apparatus 2 is opened via the pipe 162.
The washing water for surface washing is supplied to the conduit 25d of No. 5 and each branch pipe 25a. A plurality of surface washing nozzles 25c are provided along the longitudinal direction of the drainage trough 29 and are arranged at regular intervals.
As a result, washing water is ejected, and the suspended layer on the surface of the filter layer 26 is crushed and washed uniformly in the air to remove the suspended layer.

In this case, the distance between the upper surface of the filter layer 26 and the surface washing nozzle 25c is not particularly limited,
It is appropriately selected depending on the ejection amount, the nozzle shape, the state of the suspended layer, etc., and is not particularly limited.

Back-flushing process (see FIG. 10) After the direct back-flushing process is completed, the back-flushing siphon pipe 100 is operated in a state where the above-mentioned front-flushing process is continued to be stored in the back-flushing water storage tank 70. The stored water is sent as backwash water from the backwash water storage tank 70 to the water collection tank 30, and the filtration tank 22
Backwash water is ejected through the perforated block 24 at the bottom of the filter layer 26 to wash the filter layer 26.

Thus, by simultaneously performing the surface washing from above and the back washing from below, the filter layer 26 can be efficiently and effectively washed by the synergistic effect (in particular, the filter layer 26).
It is possible to remove the turbid layer film on the upper surface and to clean the clogging of the filter layer 26).

At this time, the cleaning wastewater overflowing from the filtration tank 22 is drained to the drain tank 50 through the drain trough 29 and the drain valve 28a provided at the lower end of the gallite 28 of the filtration chamber 20. .

Backwashing Process (See FIG. 11) After the above-mentioned backwashing process is carried out for a certain period of time, the backwash valve 164
Is closed, the surface washing pump 160 is stopped, the backwash siphon pipe 100 is activated, and only the backwash is performed. At this time, the suspended components completely peeled from the filter sand by the direct surface washing step and the surface backwashing step are filtered through the drainage trough 29 as washing sewage overflowing from the filtration tank 22 by this step. The water is drained to the drain tank 50 through the drain valve 28a provided at the lower end of the galluit 28 of the chamber 20.

Water-filling step (see FIG. 12) After completion of the series of washing steps described above, the drain valve 28 a and the backwash siphon pipe 100 are stopped, the inflow distribution valve 14 is opened, and the supply pipe 12 from the inflow tank 10 is opened. Through
Raw water is supplied into the filtration chamber 20, water filling is performed up to the top of the drainage trough 29, and preparations are made for shifting to the next filtration process. However, at this time, the filter siphon tube 9
0 remains inactive.

Disposal process (see FIG. 13) As the final stage of the cleaning process, the disposal siphon pipe 1 is used so that the cleaning waste water remaining in the filter layer 26 is not mixed with the filtered water.
20 is started. As a result, the filtered water of unstable water quality immediately after backwashing is discharged to the waste water tank 60 through the waste water siphon pipe 120 for a certain period of time.

Replenishment water step (see FIG. 14) The washing step is completed by the above-mentioned waste water step, the filter siphon pipe 90 is activated, and the water is collected from the water collecting tank 30 to the water purifying tank 40 via the filter siphon tube 90. It flows in, is collected, and after chlorine injection, it is used as purified water. After that, the procedure proceeds to the filtration step (1), and a series of cycles is repeated. However, during this filtration step, in order to secure the next backwash water and store it in the backwash water storage tank 70 in advance, the makeup water pump 170 is operated and the water purification tank 40 is operated.
A part of the filtered water in the backwash water storage tank 7 is passed through a pipe 172.
0, and the makeup water pump 170 is stopped while the backwash water storage tank 70 is filled with the washing water.

Comparative Example 1 As the surface washing method, so-called "normal surface washing" is carried out in a state where the filtration layer is filled with water (draining to the trough), and direct surface washing of the present invention (draining to the filter surface). ), The surface washing amount is 0.2 to 0.
3m3 / min, backwash amount 0.6-0.7m3 / min, nozzle position 5-18cm, surface wash 1-3 minutes, table backwash 1-3
Minutes and backwashing were performed for 1 to 3 minutes to compare the cleaning rates. The results are shown in Table 1 below. As is clear from the results shown in Table 1, the direct cleaning of the present invention is far superior to the ordinary cleaning in terms of the cleaning effect.

[0046]

[Table 1]

[0047]

According to the method of operating the natural filtration device of the present invention, the raw water in the filtration tank is discharged, the water level in the filtration tank is discharged below the upper surface of the filter layer, and the surface disposed above the filter layer. The washing water is sprayed directly from the washing device to the suspended layer above the filter layer in the air, thereby crushing, washing and removing the suspended layer above the filter layer. Therefore, the suspended layer accumulated and filmed on the surface of the filter layer can be crushed and removed very effectively.

Further, in the method for operating the natural filtration device of the present invention, after the direct surface washing is carried out, the washing water is passed through the perforated block from the lower side of the filtration tank to reverse the washing water. Since the backwashing process is performed by simultaneously performing the backwashing process in which washing water is passed to the filter layer, by performing the surface washing from above and the backwashing from below at the same time, a synergistic effect is achieved efficiently and effectively. It is possible to remove the turbid layer film on the upper surface of the filtration layer and clean the clogging of the filtration layer.

[Brief description of drawings]

FIG. 1 is a schematic view of an entire natural filtration device for carrying out an operating method of the present invention.

FIG. 2 is a plan sectional view of a natural filtration device for carrying out the operating method of the present invention, in which the left half shows an intermediate plan sectional view and the right half shows a bottom planar sectional view.

FIG. 3 is a top view of a filtration chamber of a natural filtration device for carrying out the operation method of the present invention.

FIG. 4 is a vertical cross-sectional view of a filtration chamber of a natural filtration device for carrying out the operating method of the present invention.

[Fig. 5] Fig. 5 is a view similar to Fig. 1, showing a filtration step in an operating state of a natural filtration device for carrying out the operation method of the present invention.

[Fig. 6] Fig. 6 is a view similar to Fig. 5, showing a filtered water draining step in an operating state of the natural filtration device for carrying out the operating method of the present invention.

FIG. 7 is a view similar to FIG. 5, showing a draining step in an operating state of a natural filtration device for carrying out the operating method of the present invention.

FIG. 8 is a view similar to FIG. 5, showing a direct surface wash draining step in an operating state of a natural filtration device for carrying out the operating method of the present invention.

FIG. 9 is a view similar to FIG. 5, showing the direct surface washing process in the operating state of the natural filtration device for carrying out the operating method of the present invention.

FIG. 10 is a view similar to FIG. 5, showing a surface backwashing step in an operating state of a natural filtration device for carrying out the operating method of the present invention.

FIG. 11 is a view similar to FIG. 5, showing the backwashing step of the operating state of the natural filtration device for carrying out the operating method of the present invention.

FIG. 12 is a view similar to FIG. 5, showing the water filling step in the operating state of the natural filtration device for carrying out the operating method of the present invention.

FIG. 13 is a view similar to FIG. 5, showing a draining process in an operating state of a natural filtration device for carrying out the operating method of the present invention.

FIG. 14 is a view similar to FIG. 5, showing the makeup water process in the operating state of the natural filtration device for carrying out the operating method of the present invention.

FIG. 15 is a block diagram showing an operating state of a natural filtration device for carrying out the operating method of the present invention.

[Explanation of symbols]

 1 ... Natural filtration device 10 ... Inflow tank 12 ... Supply pipe 14 ... Inflow distribution valve 20 ... Filtration chamber 22 ... Filtration tank 24 ... Perforated block 25 ... Surface cleaning device 25a ... Branch pipe 25c ... Surface washing nozzle 25d ... Conduit 26 ... Filter layer 26a ... Gravel layer 26b ... Standard filter sand for water supply 26c ... Anthracite 28 ... Galit 28a ... Drainage valve 29 ... Drainage trough 30 ... Water collection tank 40 ... Water purification tank 42 ... Weir 43 ... Water purification auxiliary tank 44 ... Water purification recovery path 50 ... Drainage tank 60 ... Waste water tank 70 ... Backwash water storage tank 90 ... Filtration siphon pipe 91 ... Siphon break valve 100 ... Backwash siphon pipe 110 ... Backwash flow controller (damper) 120 ... Wastewater siphon pipe 132 ... Direct surface wash Drainage line 133 ... Direct surface wash water drain valve 160 ... Surface wash pump 162 ... Pipe line 164 ... Surface wash valve 170 ... Make-up water pump 172 ... Pipe Road

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Horii 22 Yamashiro-cho, Soraku-gun, Kyoto Prefecture Kami-Komako-inui 22 (72) Inventor Yutaka Ishimaru 5-9-6 Tsukigaoka, Nishi-ku, Kobe-shi, Hyogo

Claims (2)

[Claims] 1. A filter layer is formed by filling a granular medium such as a gravel layer, a standard sand filter for water supply, and anthracite above a perforated block, which is a support disposed at the bottom of a filtration tank,
By passing the raw water downward from above the filtration tank,
Suspended suspended matter contained in raw water is suspended and removed at the upper part of the filter bed, and iron and manganese components contained in the raw water are removed by the action of iron bacteria that have been preliminarily carried on the filter bed. Water is configured to be collected from the lower side of the filtration tank through the perforated block, and a surface cleaning device is arranged above the filter layer in order to clean the suspended layer suspended above the filter layer by water injection. The method of operating the installed natural filtration device is that the raw water in the filtration tank is discharged, the water level in the filtration tank is discharged below the upper surface of the filter layer, and the cleaning water is discharged from the surface cleaning device installed above the filter layer. Directly jetting water into the suspended suspended layer above the filter layer in the air, thereby crushing suspended suspended layer above the filtered layer.
A method for operating a natural filtration device, which comprises performing a direct surface washing step of washing and removing. 2. After performing the direct surface washing, in a state where the direct surface washing step is continued, the washing water is passed through the perforated block from the lower side of the filtration tank to the backwashing water to pass it to the filtration layer. The method for operating a natural filtration device according to claim 1, wherein a front-side backwashing step in which the washing step is performed at the same time is performed.