JP2000202210A - Continuous filtering method and filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically improve the quality of treated water while making the most of the advantage of a continuous filter. SOLUTION: The raw water is passed upward through the filter bed 3 of a granular filter medium, the treated water is discharged from above the filter bed 3, the filter medium at the lower part of the bed 3 is drawn off, cleaned and then transferred to the surface of the bed 3, and the filter medium in the bed 3 is successively moved downward by the amt. corresponding to the transferred amt. in this continuous filtering method. In this case, the pressure drop of the bed 3 is detected, and the transfer amount of the filter medium is controlled so that the detected pressure drop is controlled to a previously set value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous filtration method and a filtration apparatus using a filter bed made of granular filter media, and more particularly to a moving bed capable of continuously circulating the filter media while continuously washing the filter media. The present invention relates to a continuous filtration method and a filtration device.

[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 continuous filtration apparatus capable of continuous filtration is known (for example, Japanese Patent Publication No. 3-27242).
Gazette, Japanese Patent Publication No. 56-51808).

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

[0005]

However, in general, it is known that the quality of the treated water is worse in a continuous filtration apparatus as described above than in a fixed-bed filtration apparatus. The biggest reason for this is that in the fixed-bed type filtration device, the 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 cake layer forms fine filtration (surface filtration).
And the quality of the treated water can be kept high,
This is because such a cake layer is not formed or is small in a continuous filtration device.

For this reason, the continuous filtration apparatus as described above is mainly used for treating sewage wastewater and for pretreatment coarse filtration for 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.

Therefore, as described above, the object of the present invention is to provide a continuous filtration apparatus which has an advantage that it can be continuously operated without stopping the apparatus, but has a higher quality than a fixed bed filtration apparatus in terms of the quality of treated water. In view of the fact that it is inferior, it is an object of the present invention to make it possible to greatly improve the quality of treated water in a continuous filtration device by simple improvement.

[0008]

In order to solve the above-mentioned problems, in a continuous filtration method according to the present invention, raw water is passed through a filter bed of granular filter media in an upward flow, and treated water is discharged from above the filter bed. In the continuous filtration method in which the filter medium at the lower part 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 difference between the filter beds is reduced. The method comprises the steps of: detecting a pressure; and controlling a transfer amount of the filter medium so that the detected differential pressure becomes a preset target value.

In this continuous filtration method, the target value of the differential pressure is set to an initial differential pressure, that is, a value larger than the differential pressure in the initial stage of operation when turbid substances such as SS are not trapped in the filter bed. You.

When an air lift pump is used to transfer the filter medium, it is preferable to control the transfer amount of the filter medium by controlling the amount of air supplied to the air lift pump.

[0011] The continuous filtration apparatus according to the present invention comprises a filter bed of a granular filter medium, means for supplying raw water to a lower part of the filter bed, means for discharging treated water filtered by the filter bed from above the filter bed, Means for extracting the filter medium at the bottom of the floor and transferring it to the surface of the filter bed,
In a filtration apparatus having means for washing a transferred filter medium, means for detecting a pressure difference of a filter bed, and transfer of the filter medium so that the pressure difference detected by the detection means becomes a preset target value. Means for controlling the transfer amount of the filter medium in the means.

In this continuous filtration apparatus, the target value of the differential pressure is set to a value larger than the initial differential pressure.

In the case where the means for transferring the filter medium comprises an air lift pump, the means for controlling the transfer amount of the filter medium includes:
It is preferable to include a means for controlling the amount of supplied air in the air lift pump.

In the continuous filtration method and the filtration device according to the present invention, the pressure difference of the filter bed is set to a predetermined target value or to a target value substantially constantly except during the initial operation. The transport amount of the filter medium is controlled so as to approach. The target value of the differential pressure is set to an appropriate value higher than the initial differential pressure. That is, on the raw water inlet side of the filter bed,
An appropriate cake layer is formed, and the differential pressure is controlled so as to be a target value. Therefore, during the continuous filtration operation, an appropriate cake layer is always formed on the raw water inlet side of the filter bed by the differential pressure control of the filter bed, and the cake layer has a stable form, that is, a constant target differential pressure. The resulting stable amount of cake layer is maintained. This cake layer enables finer filtration at all times and improves the quality of treated water.

Further, even if the water quality of the raw water fluctuates, since the pressure difference of the filter bed is constantly controlled so as to reach the target value, the optimum cake layer is automatically formed in response to the fluctuation of the water quality of the raw water. And the quality of the treated water is always kept high.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show schematic configurations of a continuous filtration apparatus to which the present invention can be applied, respectively. FIG. 1 shows a continuous filtration device according to a first embodiment of the present invention.
242 shows a case where the present invention is applied to a continuous filtration device equivalent to that disclosed in Japanese Patent No. 242. In FIG. 1, reference numeral 1 denotes the entire continuous filtration apparatus, in which a filter bed 3 of granular filter material, for example, filter sand having a predetermined particle size is formed in a tower 2. The raw water is supplied to a raw water flow path 4 extending vertically along the side wall of the tower 2, 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 is used for this transfer, and the filter medium is transferred by the air supplied from the air supply pipe 10 into the filter medium transfer pipe 7. The supply amount of air is controlled by an electromagnetic flow control valve 11.

In the cleaning device 8, by rotating the screw 12, the transported filter medium and the suspended matter such as SS adhering to the filter medium are stirred and separated, and the separated filter medium is lifted obliquely upward. 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 amount of cleaning water is controlled by an electromagnetic flow control 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 continuously performed. Moved to

In the vicinity of the feed pipe 5 of the raw water in the tower 2, a pressure difference when the raw water passes through the filter bed 3, that is, a pressure (differential pressure) corresponding to an increase in the pressure loss passing through the filter bed 3 with respect to the initial differential pressure. ) Is provided. Pressure sensor 1
The detection signal of the differential pressure from 7 is sent to the control device 18. In the control device 18, the target value of the differential pressure is set in advance,
The control device 18 outputs an operation signal to the electromagnetic flow control valve 11 that controls the air supply amount so that the differential pressure detected by the pressure sensor 17 becomes a set target value, and the detected differential pressure is substantially reduced. The transfer amount of the filter medium by the air lift pump is controlled so as to always reach the set target value. The preset differential pressure target value is set to a value higher than the initial differential pressure. The amount of washing water can be controlled to be a constant amount, and the amount of supplied water can be varied according to conditions.

In the present embodiment, the tower 2 is the one 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 continuous filtration apparatus 21 according to a second embodiment of the present invention.
This shows a case where the present invention is applied to a continuous filtration device equivalent to that disclosed in JP-A-6-51808. 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, is filtered, and is discharged as treated water from above the filter bed 23 through a treated water outlet 25.

At the center of the tower 22, a filter bed 2 is arranged vertically.
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 is used for this transfer, and the filter medium is supplied from the air supply pipe 28 into the filter medium transfer pipe 26. The filter medium is transferred by the air thus blown. The supply amount of air is controlled by an electromagnetic flow control 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 filter medium is withdrawn from the lower portion of the filter bed 23 and the transfer operation of returning the washed filter medium to the surface of the filter bed 23 is continuously performed. Be moved.

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. In the control device 34, a target value of the differential pressure higher than the initial differential pressure is set in advance, and the control device 34 outputs an operation signal to the electromagnetic flow control valve 29 for controlling the amount of supplied air to detect the detected differential pressure. The transfer amount of the filter medium by the air lift pump is controlled so that the pressure substantially always reaches the set target value.

In the continuous filtration apparatus according to the first and second embodiments, raw water such as sewage or river water,
Alternatively, when the SS concentration of the industrial water or the like before the treatment is high, a coagulant or the like is added in advance before being supplied to the continuous filtration devices 1 and 21, so that the turbid matter is flocculated and easily filtered. By doing so, it becomes possible to obtain treated water of higher quality. The flocculant is not particularly limited,
For example, polyaluminum chloride (PAC), a sulfate band, or the like can be used.

In the continuous filtration apparatus according to each of the above-described embodiments, when continuously filtering raw water, the pressure difference of the filter bed substantially always becomes a set target value higher than the initial pressure difference. Thus, the transfer amount of the filter medium is controlled. The transfer amount of the filter medium is controlled by changing the supply air amount of the air lift pump. By setting the target value of the differential pressure to an appropriate value, an appropriate cake layer is always formed on the raw water inlet side of the filter bed, and the presence of the cake layer enables fine filtration at all times. Water quality is improved.

It is considered that the value of the pressure difference of the filter bed and the amount of the cake layer formed are substantially proportional to each other. Therefore, by always controlling the differential pressure to an appropriate set target value, a desired cake layer is always automatically obtained. Will be formed. Therefore, the quality of the treated water is also stably maintained at a high level.
In particular, as shown in Examples described later, the SDI (Si
lt Density Index: ASTM-D41
89-92) are greatly reduced.

[0029]

EXAMPLE Using a continuous filtration apparatus 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 pressure difference from the initial filter bed pressure difference was measured. Rise (differential pressure rise), treated water turbidity,
The treated water SDI was measured. 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 Wash water amount: 9.0 liter / min

Under the above conditions, the set target value of the rising differential pressure is 2c
mAq and 10 cmAq, and as a comparative example, the sand circulating amount (transfer amount of the filter medium) was fixed at 0.4 and 1.5 liter / min so as not to cause an increase in the differential pressure with respect to the initial differential pressure. . In addition, the sand circulation amount (transfer amount of the filter medium) of the example, and the turbidity and SDI of the example and the comparative example were measured. Example 1: Setting value of rising differential pressure = 2 cmAq Example 2: Setting value of rising differential pressure = 10 cmAq Comparative Example 1: Sand circulating amount = 0.4 liter / min Comparative Example 2: Sand circulating amount = 1.5 liter / min

The results are shown in Table 1. In Example 1, the rising differential pressure (set value) was 2 cmAq, and in Example 2, the rising differential pressure was 10 cmAq.
The operation was performed at cmAq, and in Comparative Examples 1 and 2, there was no increase in the differential pressure. As shown in Table 1, the average values of the turbidity of the treated water and the SDI were higher in the example than in the comparative example.
In particular, the effect of reducing SDI was great.

[0032]

[Table 1]

[0033]

As described above, according to the continuous filtration method and the filtration apparatus of the present invention, the differential pressure of the filter bed is detected,
Since the transfer amount of the filter medium is controlled so that the differential pressure becomes an appropriate target value set in advance, and an almost optimal cake layer can be stably formed substantially constantly on the raw water inlet side, the cake layer is formed. By the filtration in the presence of water, the quality of the treated water can always be kept at a high level, and in particular, the SDI of the treated water can be greatly reduced, and the quality of the treated water can be greatly 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. .

Further, by controlling the pressure difference of the filter bed to a target value, it is possible to always form and maintain an optimum cake layer even if the water quality of the raw water fluctuates, and to automatically maintain a good water quality at all times. Can be secured.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 1,21 Continuous 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 Pipes 11, 16, 29 Electromagnetic flow control valve 12 Screw 13 Cleaning water supply pipe 14 Nozzle 15 Drain pipe 17, 33 Pressure sensor 18, 34 Control device 30 Inner pipe 31 Outer pipe 32 Drain outlet

Claims (6)

[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. In a continuous filtration method in which the filter medium in the filter bed corresponding to the amount of the filter medium is sequentially moved downward, a differential pressure of the filter bed is detected,
A continuous filtration method characterized by controlling a transfer amount of a filter medium so that the detected differential pressure becomes a preset target value. 2. The continuous filtration method according to claim 1, wherein the target value of the differential pressure is set to a value larger than an initial differential pressure. 3. The transfer amount of the filter medium is controlled by using an air lift pump for transferring the filter medium and controlling the amount of air supplied to the air lift pump.
Continuous filtration method. 4. A filter bed of granular filter medium, means for supplying raw water to the lower part of the filter bed, means for discharging treated water filtered by the filter bed from above the filter bed, and extraction of the filter medium at the lower part of the filter bed for filtration. In a filtration device having a means for transferring to a floor surface and a means for washing a filter medium to be transferred, a means for detecting a pressure difference of a filter bed, and a pressure difference detected by the detection means is set to a predetermined target value. Means for controlling the transfer amount of the filter medium in the transfer means for the filter medium so as to provide a continuous filtration apparatus. 5. The continuous filtration device according to claim 4, wherein the target value of the differential pressure is set to a value larger than the initial differential pressure. 6. The continuous filtration apparatus according to claim 4, wherein said filter medium transfer means has an air lift pump, and said filter medium transfer amount control means includes means for controlling an amount of air supplied to said air lift pump.