JP2000202209A - Filtering method and filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To greatly enhance water quality of treated water and also to greatly reduce a discharge quantity of generated washing water for a filter medium by intermittently stopping transfer of the filter medium with respect to a continuous filtering device. SOLUTION: The filter medium A at the lower end part of a filter bed 3 is pulled out through a filter medium transfer pipe 7 and is transferred to a washing device 8 with air fed into the filter medium transfer pipe 7 from an air feed pipe 10. The feed of the air is controlled with an electromagnet valve 11. Here, a pressure sensor 17 for detecting differential pressure at a time when raw water passes through the filter bed 3, is provided in the vicinity of a feed pipe 5 of the raw water. A detection signal of the differential pressure from the pressure sensor 17 is transferred to a control device 18, and a working signal is outputted to the electromagnet valve 11 for controlling feed of the air, and a stop of the feed and a start of the feed are controlled. Like this, by intermittently stopping the transfer of the filter medium, a preferred cake layer is adequately formed on a filter bed inlet side, and filtering accuracy can be enhanced and leakage of the treated water to SS, etc., can be prevented, while the raw water is continuously filtered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration method and a filtration apparatus using a filter bed made of a particulate filter medium,
The present invention relates to an operation control technique of a moving bed type continuous filtration device capable of continuously circulating a filter medium of a filter bed while washing the same.

[0002]

2. Description of the Related Art A filtration method and a filtration apparatus are known in which a fixed filter bed is formed with a granular filter medium, for example, filter sand having a predetermined particle diameter, and raw water (water to be treated) is filtered through the filter bed. ing. In such a fixed-bed filtration device,
As the operating time elapses, the SS accumulates on the filter bed surface and the pressure difference of the filter bed rises. When the pressure difference reaches a certain level, it is necessary to perform backwashing to wash and regenerate the filter medium of the filter bed. There is.
During this backwash, the process must be stopped. If the SS concentration of the raw water is high, the differential pressure rises quickly, so that the frequency of backwashing increases and the amount of washing wastewater increases.

[0003] In a fixed bed type filtration device, raw water is passed through the filter bed in an upward flow, the treated water filtered out from the upper part of the filter bed is discharged, and the filter material at the lower part of the filter bed is transferred by a transfer means such as an air lift pump. After being continuously extracted and washed, it is transferred (circulated) to the surface of the filter bed, and the filter medium in the filter bed corresponding to the amount of the transferred filter medium is sequentially moved downward in a countercurrent direction to the raw water passage direction. A moving bed type filtration device capable of continuous filtration is known (for example, Japanese Patent Publication No. 3-27242, Japanese Patent Publication No. 56-51808).

In such a filtration apparatus, since the extracted filter medium is continuously washed and returned to the filter bed, it can be operated without stopping the apparatus, and even when the SS concentration of the raw water is high, the extraction of the filter medium is performed. By increasing the speed, the speed of discharging SS accumulated in the filter bed can be increased,
A large increase in the differential pressure of the filter bed can be prevented.

[0005]

However, it is generally known that the quality of the treated water is worse in the continuous filtration apparatus as described above than in the fixed bed type filtration apparatus. One of the reasons is that it is difficult to make the movement of the filter medium in the filter bed downward uniformly, and there are parts where the movement speed is slow and part where it is fast, and SS gradually accumulates in the filter bed. This is because it gradually leaks into the treated water.

Another reason is that, in a fixed-bed type filtration device, SS filtered on the surface of the filter bed on the raw water inlet side adheres and accumulates to form a cake layer, and the fine filtration by the cake layer ( Although surface filtration can occur and the quality of the treated water can be kept high, this is because such a cake layer is not formed or small in a continuous filtration device.

[0007] Further, as another reason,
In the cleaning method using a filtration device described in Japanese Patent Publication No. 27242 or Japanese Patent Publication No. 56-51808, it is difficult to completely clean the filter medium. Leakage in the treated water.

For this reason, the continuous filtration apparatus as described above is mainly used for the treatment of sewage wastewater and the coarse filtration for pretreatment of a fixed-bed filtration apparatus when the water to be treated has a high SS (eg, river water). A water treatment device using an ion exchange resin, which is only used as a device and requires relatively high water quality, an ultrafiltration device,
It was not used as a pretreatment device such as a reverse osmosis membrane filtration device.

For example, after subjecting the water to be treated after coagulation and sedimentation to gravity filtration with a fixed bed type filtration device, the turbidity is 0.1 degrees or less, SDI (FI in JIS) is 2-3, and inorganic water is used in industrial water. When a coagulant is added and the mixture is filtered with a direct pressure filtration device, the turbidity is 0.1 degrees or less and the SDI is 5 to 7,
Such a high-quality water could not be obtained with the continuous filtration device as described above.

Therefore, an object of the present invention is to improve the operation method and operation control means in a continuous filtration apparatus while taking advantage of the fact that the apparatus can be continuously operated without stopping the apparatus, thereby improving the quality of treated water. Is to be able to greatly increase.

Another object of the present invention is to significantly reduce the discharge amount of filter medium washing water generated in a continuous filtration device.

[0012]

In order to solve the above-mentioned problems, a filtration method according to the present invention comprises passing raw water through a filter bed of granular filter media in an upward flow, discharging treated water from above the filter bed, In a filtration method in which the filter medium at the bottom of the filter bed is extracted, washed, and then transferred to the surface of the filter bed, and the filter medium in the filter bed corresponding to the amount of the transferred filter medium is sequentially moved downward, the transfer of the filter medium is intermittently stopped. The method comprises the steps of:

In this filtering method, when the transfer of the filter medium is stopped, it is preferable that the supply of the washing water used for washing the transferred filter medium is also stopped.

As a control method for intermittently stopping the transfer of the filter medium, at least one of the stop and the start of the transfer of the filter medium is controlled based on the pressure difference of the filter bed, or the stop and the start of the transfer of the filter medium. A method of controlling at least one based on a predetermined time or a control method combining these methods can be adopted.

[0015] In the above method, particularly when treating raw water having a high SS concentration, it is preferable to add a flocculant to the raw water and pass the raw water directly to a filtration device for filtration.

The filter device according to the present invention comprises a filter bed of granular filter material, a means for supplying raw water to the lower part of the filter bed, a means for discharging treated water filtered by the filter bed from above the filter bed, and a lower part of the filter bed. Means for extracting the filter medium and transferring it to the filter bed surface, and a filter device having means for washing the transferred filter medium,
Control means for intermittently stopping the transfer of the filter medium is provided.

This filter device preferably has control means for stopping the washing means when the transfer of the filter medium is stopped.

As a control means for intermittently stopping the transfer of the filter medium, the filter device has a means for detecting a pressure difference of the filter bed,
Further, the control means may be configured to control at least one of stop and start of the transfer of the filter medium based on the detected pressure difference of the filter bed. Alternatively, the stop control means of the transfer of the filter medium may be configured to control at least one of the stop and the start of the transfer of the filter medium based on a time predetermined by a timer. Further, the control may be made by appropriately combining both the differential pressure and the time by the timer.

In the filtering method and the filtering device according to the present invention, the transfer of the filter medium is intermittently stopped, and the stop of the transfer causes the SS filtered at the raw water inlet side of the filter bed.
They adhere to each other and are accumulated in an appropriate amount to form a cake layer. By this cake layer, cake filtration occurs, the accuracy of filtration is improved, and the quality of treated water is improved. In addition, when the transfer of the filter medium is stopped, there is no SS leak that is likely to occur when the filter medium is returned to the filter bed surface side, so that high treated water quality is secured from this surface.

In addition, when the transfer of the filter medium is stopped intermittently, when the pressure difference in the filter bed rises to a certain level, the rise in the pressure difference is detected directly or by a timer. By controlling the stop time, transfer of the next filter medium is started so that the differential pressure does not excessively increase, and the filter medium extracted from the lower part of the filter bed is intermittently washed and returned to the surface of the filter bed. Therefore, the operation of stopping the transfer of the filter medium, restarting the transfer, washing the filter medium being transferred, and returning it to the surface of the filter bed while performing continuous feed of the raw water are repeated at an appropriate timing. Become.

As a result, while ensuring high treated water quality,
Raw water can be continuously filtered. By improving the quality of treated water, it can be used as a pretreatment device for a water treatment device using an ion exchange resin, an ultrafiltration device, or a reverse osmosis membrane filtration device, despite being a continuous filtration device.

Further, if the supply of the washing water is stopped together with the transfer of the filter medium, the discharge amount of the washing water is greatly reduced as compared with the case of the continuous washing, so that the washing is facilitated and the apparatus is downsized. (Especially, downsizing of the washing water storage tank) can be achieved.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. 1 and 2 each show a schematic configuration of a continuous filtration device to which the present invention can be applied, and FIG. 3 shows an operation control example of the filtration device according to the present invention.

FIG. 1 shows a filtration device according to a first embodiment of the present invention.
2 shows a case where the present invention is applied to a filtration device equivalent to the one disclosed in No. 2. In FIG. 1, reference numeral 1 denotes an entire filtration apparatus, and a filter bed 3 of granular filter material, for example, filter sand having a predetermined particle size, is formed in a tower 2. Raw water is tower 2
The raw water is supplied to a raw water flow path 4 extending vertically along the side wall of the filter bed, and is supplied to a lower part of the filter bed 3 from a supply pipe 5 provided at a lower part of the raw water flow path 4. The supplied raw water passes through the filter bed 3 in an upward flow, is filtered, and is discharged as treated water from above the filter bed 3 through a treated water outlet 6.

In the raw water flow path 4, there is provided a filter medium transfer pipe 7 extending to the lower end of the filter bed 3 and opening at the lower end.
The filter medium transfer pipe 7 extends to above the tower 2 and communicates with a washing device 8. The washing device 8 returns the washed filter medium to the surface (upper surface) of the filter bed 3 via the return path 9. The filter medium transfer pipe 7 draws out the filter medium at the lower end of the filter bed 3 and removes the filter medium.
In this embodiment, an air lift pump mechanism is used for this transfer, and the filter medium transfer pipe 7 is connected from the air supply pipe 10.
The filter medium is transferred by the air supplied to the inside. The supply of air is controlled by the solenoid valve 11.

In the cleaning device 8, the separated filter medium is lifted obliquely upward while stirring and separating the transferred filter medium and turbid substances such as SS adhering to the filter medium by rotating the screw 12. It is returned to the surface of the filter bed 3 via the return path 9. At this time, cleaning water is supplied from the cleaning water supply pipe 13 through the nozzle 14, and the separated turbidity is washed out and discharged from the drain pipe 15 as cleaning wastewater. The supply of cleaning water is controlled by a solenoid valve 16. As this cleaning water, a part of the treated water from the treated water outlet 6 can be used, or water from another supply source can be used.

The filter medium is extracted from the lower portion of the filter bed 3 and the transfer operation of returning the washed filter medium to the surface of the filter bed 3 is repeated, so that the filter medium in the filter bed 3 corresponding to the amount of the transferred filter medium is sequentially reduced. Moved down.

In the vicinity of the feed pipe 5 of the raw water in the tower 2, the pressure difference between the raw water passing through the filter bed 3, that is, the pressure P ₁ corresponding to the rise in the pressure loss through the filter bed 3 with respect to the initial pressure P ₀ . Is provided. Pressure sensor 17
Is sent to the control device 18. The control device 18 outputs operation signals to the electromagnetic valve 11 for controlling the supply of air and the electromagnetic valve 16 for controlling the supply of cleaning water, and controls the supply stop and the supply start thereof.

In the present embodiment, the tower 2 is shown in FIG.
The filter medium transfer pipe 7, the air supply pipe 10, and the washing device 8 are horizontally moved by a driving means (not shown), which extends in a direction perpendicular to the paper surface of FIG. It is configured to be able to reciprocate (in a vertical direction).

FIG. 2 shows a filtration device 21 according to a second embodiment of the present invention.
1 shows a case where the present invention is applied to a filtering device equivalent to that disclosed in Japanese Patent Publication No. 1808. In FIG. 2, a filter bed 23 of a granular filter medium is formed in a tower 22, and raw water is supplied to a lower part of the filter bed 23 from a raw water flow path 24. The supplied raw water passes through the filter bed 23 in an upward flow and is filtered.
Through the treated water outlet 25 and discharged as treated water.

At the center of the tower 22, a filter bed 2
A filter medium transfer pipe 26 extending to the lower end of the filter medium 3 is provided, and an upper end of the filter medium transfer pipe 26 communicates with a washing device 27. The filter medium transfer pipe 26 extracts the filter medium at the lower end of the filter bed 23 and transfers it to the washing device 27. In this embodiment, an air lift pump mechanism is used for this transfer, and the air supply pipe 2
The filter medium is transferred by the air supplied from 8 into the filter medium transfer pipe 26. The supply of air is controlled by a solenoid valve 29.

The washing device 27 is provided with an inner tube 30 and an outer tube 31. The inner tube 30 transfers the filter medium by inverting the flow direction of the filter medium ejected from the upper end opening of the filter medium transfer pipe 26. The obtained filter medium and turbid substances such as SS adhering to the filter medium are transferred into the outer tube 31 while being stirred and separated. In the outer tube 31, the separated filter medium having a large specific gravity sinks downward, and the turbid matter having a small specific gravity floats up and is discharged from the drain port 32 as washing wastewater together with washing water. Washing,
The separated filter medium is returned to the surface side of the filter bed 23. In the present embodiment, a part of the treated water that has passed through the filter bed 23 is used as washing water for washing the transferred filter medium. The transfer operation of extracting the filter medium from the lower portion of the filter bed 23 and returning the washed filter medium to the surface of the filter bed 23 is repeated, so that the filter medium 23 to be transferred is separated.
The inner filter media is sequentially moved downward.

In the vicinity of the connecting portion of the raw water flow path 24 of the tower 22,
A pressure sensor 33 that detects a pressure difference when the raw water passes through the filter bed 23 is provided. The differential pressure detection signal from the pressure sensor 33 is sent to the control device 34. The control device 34
An operation signal is output to a solenoid valve 29 that controls the supply of air,
Controls the stop and start of the transfer of the filter media by the air lift.

In the filtration apparatus according to the first and second embodiments, when the SS concentration of raw water, for example, sewage or river water, or industrial water before treatment is high, the filtration apparatus 1, If a flocculant or the like is added in advance before the water is supplied to 21 to make the turbid matter flocculate so as to be easily filtered, it is possible to obtain treated water of higher quality. The flocculant is not particularly limited, and for example, polyaluminum chloride (PAC), a sulfate band, or the like can be used.

In the filter device according to the first and second embodiments, the intermittent stop of the transfer of the filter medium is controlled as follows. The control can be performed based on the differential pressure of the filter bed and the time set in advance by a timer. Examples of typical control methods are shown in FIGS. 3 (a) to 3 (e). For example, a combination of the differential pressure and time control other than that shown in FIG. 3 is also possible.

[0036] In the control shown in FIG. 3 (a), the transport of the filter medium when setting the differential pressure to start the transfer of the filter medium to P _1, the differential pressure detected by the pressure sensor 17 and 33 reaches P ₁ To start. The differential pressure for stopping the transfer of the filter medium is the initial differential pressure P
_0, and it stops the transport of the filter medium when it reaches the initial differential pressure P _0, continues the stopped state until the differential pressure reaches P _1. This operation is repeatedly controlled by the control devices 18 and 34, and when the transfer is stopped, a cake layer is formed on the raw water inlet side of the filter bed to improve the quality of the treated water. To prevent leaks to In addition, in the filtration device 1 shown in FIG. 1, the supply of the cleaning water is stopped at the same time as the transfer is stopped, so that the amount of the cleaning drainage is greatly reduced.

In the control shown in FIG.
The transfer stop time T ₁ and the transfer time T ₂ are set in advance by the timers incorporated in 8, 34, and the transfer is started after the elapse of T ₁ and stopped after the elapse of T ₂ , and these operations are repeated. Let it do. When the differential pressure of the filter bed returns to P ₀ during the time T ₂ , the transfer is started from the state of the initial differential pressure P ₀ even when the transfer is started after the lapse of T ₂ . In this control, the same operation and effect as described with reference to FIG.

In the control shown in FIG. 3C, only the transfer time is controlled by the time T ₂ set by the timer.
Continue until the pressure difference of the filter bed reaches P _1, the timer is started starts the transfer when it reaches P _1.
3 in the control shown in (d) is controlled by the transfer stopping time only time T ₁ set by the timer, the operation of the transfer is T with starting at ₁ elapsed time, the initial differential pressure P ₀ pressure differential filter bed , The transfer stop is started, and this operation is repeated. The control shown in FIG. 3E is a composite control example in which the transfer stop time is controlled by T ₁ set by a timer, the transfer is started when T _{1 has} elapsed, and the differential pressure of the filter bed is initially increased. to continue the transfer after reduced to the differential pressure P ₀ to the timer set time T ₃ has elapsed. T ₃ starts transfer stop from the elapsed time.

With any of the control methods described above, it is possible to repeatedly stop the desired intermittent transfer of the filter medium. By such intermittent transfer stop control of the filter media,
In addition to the functions and effects described above, the following functions and effects can be obtained.

That is, in general, in a continuous filtration device, filter media washing,
Changing the transfer speed (air lift amount) is most preferable in terms of filtration performance. However, the control amount by the air lift can usually be changed only in the range of about 30 to 100%, and the fluctuation of the SS concentration of the raw water is usually much larger than that. Control is difficult.

However, in the present invention, FIGS.
As shown in (e), by simply changing the operation rate (time interval) of intermittent transfer and washing, it is possible to substantially freely follow the variation ratio of the SS concentration of the raw water (that is, a very large ratio). Therefore, it is possible to control the amount of the filter medium to be desirably washed and transferred in accordance with the state of the raw water described above.

[0042]

EXAMPLE Using the filtration device shown in FIG. 1, PAC (polyaluminum chloride) as a flocculant and kaolin as a turbid component were injected into a raw water line, and the differential pressure increased from the initial filter bed differential pressure. Minute (rising pressure difference), treated water turbidity, treated water SDI (Silt Density Index: AS)
TM-D4189-82). The experimental conditions are shown below. <Experimental conditions> Raw water flow rate: 11.25 m ³ / h Filtration speed: 7.5 m / h Filter material: Filter sand (effective diameter = 0.5 mm, uniformity coefficient = 1.4) Kaolin addition amount: 10 degrees as raw water turbidity (About 5 mg / l) PAC addition amount: 5 mg / l

Example 1 Under the above conditions, the operation was carried out by an operation method of controlling the upper and lower limits of the rising differential pressure shown in FIG. Specifically, the transfer of the filter medium and the washing of the filter medium are stopped until the rising differential pressure becomes 10 cmAq. When the rising differential pressure becomes 10 cmAq, the transfer of the filtering medium and the washing of the filtering medium are started, and the rising differential pressure becomes 0 cmAq.
When the flow returned to Aq, the transfer of the filter medium and the washing of the filter medium were stopped, and these were repeated to carry out the experiment. The amount of sand circulation and the amount of washing water at this time are as follows. Sand circulating volume: Stopped = 0.0 L / min Transfer: 1.5 L / min Wash water: Stopped = 0.0 L / min Transfer: 9.0 L / min

Example 2 An operation was performed under the above-described conditions by a driving method controlled by a timer shown in FIG. More specifically, the experiment was carried out by setting the stop time of the transfer of the filter medium and the washing of the filter medium to 120 minutes, and the operation time of the transfer of the filter medium and the washing of the filter medium to 20 minutes. The amount of sand circulation and the amount of washing water at this time are as follows. Sand circulating volume: Stoppage time = 0.0 L / min Transfer time: 1.5 L / min Wash water volume: Stoppage = 0.0 L / min Transfer time: 9.0 L / min

Embodiment 3 Under the above conditions, a control method using a rising differential pressure value and a timer as shown in FIG. Specifically, the transfer of the filter medium and the washing of the filter medium were stopped until the rising differential pressure became 10 cmAq, and when the rising differential pressure became 10 cmAq, the transfer of the filtering medium and the washing of the filter medium were performed for 20 minutes, and these were repeated, and the experiment was repeated. Was carried out. The amount of sand circulation and the amount of washing water at this time are as follows. Sand circulating volume: Stopped = 0.0 L / min Transfer: 1.5 L / min Wash water: Stopped = 0.0 L / min Transfer: 9.0 L / min

Comparative Example 1 As a comparative example, an experiment of constantly transferring and washing the filter medium was performed under the following conditions. Sand circulation volume: 1.5 liter / min Wash water volume: 9.0 liter / min

Experimental Results FIGS. 4 to 6 show changes over time of the differential pressure, turbidity and SDI of Example 1 and Comparative Example 1. Table 1 shows the turbidity of the treated water, the average value of the SDI, and the amount of the washing water discharged in Examples 1 to 3 and Comparative Example 1. In each of the methods of Examples, the turbidity of treated water and SDI were better than Comparative Example 1. In particular, the SDI of the treated water could be significantly reduced. Further, at this time, the amount of washing wastewater was smaller in Examples 1 to 3 than in Comparative Example 1.

[0048]

[Table 1]

[0049]

As described above, according to the filtering method and the filtering device of the present invention, the transfer of the filter medium is intermittently stopped in the continuous filtering device, so that the preferable cake layer is provided on the inlet side of the filter bed. By appropriately forming the raw water, the filtration accuracy can be improved while the raw water is continuously filtered, and the leakage of the treated water such as SS can be prevented. In particular, the SDI of the treated water is greatly reduced to improve the quality of the treated water. Can be improved. Improvement of treated water quality makes it possible to use a continuous filtration device as a pretreatment device for a water treatment device using an ion exchange resin, an ultrafiltration device, and a reverse osmosis membrane filtration device. .

If the supply of the filter medium washing water is stopped at the same time as the transfer of the filter medium is stopped, the amount of washing drainage can be greatly reduced, and a large drain tank is not required. Thus, cost can be reduced.

Further, when an air lift pump or the like is used for circulating and transferring the filter medium, the operation of stopping and starting the transfer of the filter medium is repeated so that the operation rate of the transfer means can be controlled merely by controlling the operation rate of the transfer means. It is possible to freely control the transfer amount of the filter medium. As a result, water quality fluctuations of a wide range of raw water (for example, S
It is possible to follow up the control of the transfer speed of the filter medium in accordance with the variation of the S load amount), and it is possible to always control the operating conditions to be optimal according to the state of the raw water.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a filtration device according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a filtration device according to a second embodiment of the present invention.

FIG. 3 shows an operation control example of the filtration device according to the present invention.
It is a relational diagram of the pressure difference of a filter bed, and time.

FIG. 4 is a characteristic diagram of a rising differential pressure in Example 1 and Comparative Example 1.

FIG. 5 is a characteristic diagram of treated water turbidity in Example 1 and Comparative Example 1.

FIG. 6 is a characteristic diagram of SDI in Example 1 and Comparative Example 1.

[Explanation of symbols]

 1, 21 Filtration device 2, 22 Tower 3, 23 Filter bed 4, 24 Raw water flow path 5 Supply pipe 6, 25 Treated water outlet 7, 26 Filter material transfer pipe 8, 27 Washing device 9 Return path 10, 28 Air supply pipe 11 , 16, 29 Solenoid valve 12 Screw 13 Cleaning water supply pipe 14 Nozzle 15 Drain pipe 17, 33 Pressure sensor 18, 34 Controller 30 Inner pipe 31 Outer pipe 32 Drain outlet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 29/38 580Z

Claims (10)

[Claims] Claims 1. Raw water is passed upward through a filter bed of granular filter medium, treated water is discharged from above the filter bed, the filter medium at the bottom of the filter bed is extracted, washed, and then transferred to the surface of the filter bed. A filter method for sequentially moving a filter medium in a filter bed corresponding to an amount of a filter medium to be moved downward, wherein the transfer of the filter medium is intermittently stopped. 2. The method according to claim 1, wherein when the transfer of the filter medium is stopped, the supply of the washing water used for cleaning the transferred filter medium is also stopped. 3. The filtration method according to claim 1, wherein at least one of the stop and the start of the transfer of the filter medium is controlled based on the pressure difference of the filter bed. 4. The filtering method according to claim 1, wherein at least one of the stop and the start of the transfer of the filter medium is controlled based on a predetermined time. 5. The filtration method according to claim 1, wherein a filtration is performed after adding a flocculant to the raw water. 6. A filter bed of a granular filter medium, a means for supplying raw water to the lower part of the filter bed, a means for discharging treated water filtered by the filter bed from above the filter bed, and a filter medium for extracting the filter medium at the lower part of the filter bed to filter. A filter device comprising: means for transferring to a floor surface; and means for washing a transferred filter medium, comprising a control means for intermittently stopping the transfer of the filter medium. 7. The filtering apparatus according to claim 6, further comprising control means for stopping the washing means in accordance with the stop of the transfer of the filter medium. 8. A means for detecting a pressure difference of the filter bed, wherein the control means for stopping the transfer of the filter medium determines at least one of the stop and the start of the transfer of the filter medium based on the detected pressure difference of the filter bed. The filtration device according to claim 6, wherein the filtration device controls the pressure. 9. The filter medium transfer stop control means controls at least one of a stop and a start of transfer of the filter medium based on a predetermined time by a timer. A filtration device according to any one of the above. 10. The filtering device according to claim 6, wherein the filter medium transferring means and the filter medium washing means are configured to be movable integrally with the filter bed in a horizontal direction.