JP4763670B2 - Filtration device - Google Patents

Description

  The present invention relates to a filtration apparatus for aggregating suspended substances and performing filtration treatment in water treatment.

Coagulation filtration is widely used for removing suspended solids in industrial process water, river water, etc., as raw water for manufacturing processes in plants, water treatment for producing tap water, wastewater treatment, and the like. In the coagulation filtration treatment, for example, an aluminum-based coagulant or the like is added to and mixed with raw water to flock suspended substances in the raw water. The suspended flocs are removed by capturing the generated floc with a filter medium. In this way, clear filtered water is obtained.
In the filtration device, when the filter medium captures a predetermined amount of suspended solids, the filtration resistance increases and the outflow of flocs increases. For this reason, cleaning for regenerating the filter medium is performed. This washing is performed by allowing washing water (usually filtered water) to flow back through the filtration device and removing the trapped suspended matter. However, immediately after this washing is performed, suspended substances in the filtered water increase and sufficient filtration cannot be performed in many cases. This is because the flocculant on the surface of the filter medium is removed by washing, and after the filtration process is resumed, the suspended substance and flocculant are introduced into the filtration device without the flocculant being sufficiently coated on the filter medium surface. It is thought that the flocculant and the filter medium cannot be bound well.
On the other hand, in industrial water treatment facilities, industrial water may be subjected to a coagulation filtration followed by reverse osmosis membrane filtration (RO membrane filtration). As raw water for RO membrane filtration, a water quality of about 3.0 to 4.0 is required by SDI (Silt Density Index). For this reason, it is desired that even an aggregating filtration apparatus supplies water with an SDI of less than 3.0 from the beginning of the filtration process.
Generally, rapid sand filtration basins with a filtration rate of about 5 m / h are often used in water purification plants, but in order to prevent deterioration of water quality at the initial stage of the filtration process, the filtration rate is reduced, waste water, etc. is used. In the treatment of industrial water, treatment at a faster filtration rate is required. For example, when the filtration rate is 20 m / h or more, as described above, suspended substances, flocculants, and filter media cannot be bound well at the beginning of the filtration process, and the turbid component is converted to SDI at the initial stage of the filtration process. It becomes more difficult to make it less than 0.
As measures to prevent deterioration of water quality at the beginning of filtration treatment, slowing the filtration rate, discarding water at the beginning of filtration treatment, returning water to the raw water tank at the beginning of filtration treatment, adding flocculant at the end of the washing process of the filtration pond (For example, Patent Document 1), additional aggregation in the filter basin or in the filter medium layer (for example, Patent Document 2).
JP 2001-259313 A JP 2001-137616 A

However, the above-mentioned measures have the problem that the quality of filtered water can be improved, but the operation control is complicated and the addition of a flocculant injection facility is required.
In this invention, it aims at provision of the filtration apparatus from which the filtered water whose SDI is less than 3.0 is obtained from the filtration treatment initial stage.

  The filtration apparatus of the present invention is a filtration apparatus having a means for adding a flocculant to a suspension in water to be treated and a filtration tower for removing the suspension, and the repose angle of the filtration tower is 18 to 30. It has one or more filter media layers made of granular filter media at 0 °. The filtration tower is defined by the following equation (1) when the porosity before the start of filtration treatment is 40 to 60% and the filter medium layer is passed through a filter medium layer having a height of 1000 mm at a filtration rate of 20 m / h. It is preferable to have a filter medium layer with a compaction rate of 0.5 to 5.0%.

  ADVANTAGE OF THE INVENTION According to this invention, the filtration apparatus from which the filtered water whose SDI is less than 3.0 can be obtained from the early stage of a filtration process can be provided.

Hereinafter, an example is given and explained about the filtration device of the present invention. However, the present invention is not limited to the following embodiments.
FIG. 1 is a schematic view of a filtration device 10 according to an embodiment of the present invention. The filtration apparatus 10 stores a treated tank (hereinafter referred to as raw water) that is raw water before purification, a receiving tank 12 that temporarily stores, a flocculant tank 14, an acid tank 16, a filtration tower 20, and filtered water. A water tank 28 is provided.
The receiving tank 12 has a pump 30 inside, and a pipe 50 a connected to the pump 30 is connected to the line mixer 18 via a valve 42 a and a flow meter 32. The pipe 50d on the secondary side of the line mixer 18 reaches the branch 60a via the valve 42b. The branch 60a branches to a pipe 50f and a pipe 50e. The pipe 50e is connected to a discharge port (not shown) via a valve 42c. On the other hand, the pipe 50 f is connected to the upper part of the filtration tower 20.
The filtration tower 20 includes a first filter medium layer 24, a second filter medium layer 26, and a differential pressure gauge 38. A support material having an opening smaller than the particle size of the granular filter medium used for the second filter medium layer 26 is installed at the bottom of the filtration tower 20, and the second filter medium layer 26 is formed by filling the granular filter medium thereon. ing. An upper portion of the second filter medium layer 26 is further filled with a granular filter medium used for the first filter medium layer 24 to form the first filter medium layer 24. A free board is provided above the first filter medium layer 24.
The pipe 50g connected to the lower part of the filtration tower 20 is branched into pipes 50h and 50i by a branch 60b. The pipe 50i is connected to the water tank 28 via the valve 42d. The pipe 50h connected to the water tank 28 merges with the pipe 50g at the branch 60b via the pump 40 and the valve 42e. The flocculant tank 14 is joined to the pipe 50a via the pump 34 and the acid tank 16 is joined to the pipe 50a on the primary side of the line mixer 18 via the pump 36 and the pipe 50c.

At least one of the first filter medium layer 24 and the second filter medium layer 26 included in the filtration tower 20 is formed by being filled with a granular filter medium having an angle of repose of 18 to 30 °. Here, the angle of repose is an angle obtained by the injection method (JIS R9301-2-2) (the same applies hereinafter).
In the granular filter medium, when the angle of repose is the same material and the same average particle diameter, the angle of repose is large. It is considered that the frictional force between the granular materials is large, that is, the surface has many irregularities and corners. The granular filter medium having a large angle of repose has a relatively high ratio of contact between convex portions and corners, and the porosity in the filter medium layer is high. This void is an unstable space with a small contact area between the particulate filter media. Therefore, when pressure due to water flow is applied to the filter medium layer or an impact due to external vibration or the like is applied, the contact area between the granular filter media is small, and the voids are likely to collapse.
In the granular filter medium in the present invention, the angle of repose is 18 to 30 °. If the angle of repose is less than 18 °, both the initial void ratio and the consolidation ratio before passing water are too low, and the filter medium at the start of the filtration treatment This is because contact with the flocculant is insufficient, and the suspended solids cannot be sufficiently removed at the beginning of the filtration process. On the other hand, if the angle of repose exceeds 30 °, both the initial void ratio and the consolidation ratio are too high, the filtration time is shortened, and the suspended solids cannot be captured sufficiently.

The initial porosity of the filter medium layer in the present invention is preferably 40 to 60%. If the initial porosity is less than 40%, the differential pressure increases from the beginning of the filtration process, and as a result, the filtration duration time is shortened. Further, if it exceeds 60%, the gap or opening of the filter medium becomes large, and it becomes difficult to capture particularly minute ones of the generated flocks between the filter mediums.
Here, the initial porosity means the porosity in the first filter medium layer 24 and the second filter medium layer 26 before the start of the filtration treatment, and is obtained by the following formula (2). Specifically, it is the volume obtained by subtracting the volume of the particulate filter medium from the volume of the filter medium layer, that is, the ratio of the voids to the volume of the filter medium layer. The volume of the granular filter medium can be determined by dividing the mass of the granular filter medium by the specific gravity of the granular filter medium.

The consolidation rate of the filter medium having an angle of repose of 18 to 30 ° in the present invention is preferably 0.5 to 5.0%.
When the consolidation rate is less than 0.5%, the flocculant contact with the filter medium is insufficient at the start of the filtration process, and the suspended solids cannot be flocked at the beginning of the filtration process, and the suspended solids cannot be removed sufficiently. . On the other hand, if the consolidation ratio exceeds 5.0%, the filtration time is shortened and the suspended substances cannot be removed sufficiently.
The consolidation ratio in the present invention is the degree of decrease of the filter medium when water is passed through a filter medium layer having a height of 1000 mm at a filtration rate of 20 m / h, and is a consolidation ratio (%) defined by the above formula (1). expressed. It should be noted that when the filtration rate is slowed down after passing water at a filtration rate of 20 m / h, the compaction rate does not need to be reduced according to the filtration rate.

The material of the filter medium in the present invention is not particularly limited, and examples thereof include silica sand, anthracite, polyester granular fiber filter medium, and the like.
The particulate filter media used for the first filter media layer 24 and the second filter media layer 26 may be the same material or different materials, and are determined according to the quality of raw water and the quality required for filtered water. be able to. For example, the first filter medium layer 24 is filled with anthracite, and the second filter medium layer 26 is filled with silica sand.
However, at least one of the first filter 24 and the second filter medium layer 26 is filled with a filter medium having an angle of repose of 18 to 30 °.

The height D1 of the first filter medium layer 24 and the height D2 of the second filter medium layer 26 are not particularly limited and can be determined in consideration of the contamination state of the raw water, the treatment amount, etc., but D1 and D2 are respectively It is preferable that it is 400-1200 mm. This is because when the thickness is less than 400 mm, the time during which the raw water comes into contact with the particulate filter medium is shortened, and the suspended matter in the raw water may not be sufficiently removed. On the other hand, if it exceeds 1200 mm, it is necessary to use a large amount of washing water, and the water recovery rate is greatly reduced.
Moreover, the ratio of the height D1 of the first filter medium layer 24 and the height D2 of the second filter medium layer 26 is not particularly limited, and is required for contaminants in raw water and water after filtration (hereinafter referred to as filtered water). It can be determined in consideration of cleanliness and the like.

The raw water filtration method by the filtration device 10 will be described.
First, the raw water A flows into the receiving tank 12. The valves 42c and 42e are closed, and the valves 42a, 42b and 42d are opened. The flocculant is fed from the flocculant tank 14 by the pump 34 and the acid solution is fed from the acid tank 16 by the pump 36 to the primary side of the line mixer 18. The fed flocculant and acid solution flow into the upper part of the filtration tower 20 via the line mixer 18. The flocculant and the acid solution that flowed in flow while diffusing in the filter medium of the first filter medium layer 24 and the second filter medium layer 26, and a film of the flocculant is formed on the surface of the filter medium.
Subsequently, while monitoring with the flow meter 32, the raw water in the receiving tank 12 is fed at a predetermined flow rate using the pump 30. The fed raw water is mixed with the flocculant and the acid solution by the line mixer 18 and flows into the upper portion of the filtration tower 20. The raw water that has flowed into the filtration tower 20 flows through the first filter medium layer 24 and then flows through the second filter medium layer 26. During this time, the suspended substance in the raw water is flocked by the flocculant, and the suspended substance that has been flocked flows while being captured by the filter medium filled in the first filter medium layer 24 and the second filter medium layer 26. The filtered water from which suspended substances have been removed flows out from the lower part of the filtration tower 20. The filtered water that flows out is stored in the water tank 28. And it sends as filtered water B as needed.

When the above filtration process is continued, the suspended substances trapped in the first filter medium layer 24 and the second filter medium layer 26 gradually increase, and the filter medium is saturated and the suspended substances cannot be trapped. Therefore, the filtration resistance is monitored by the differential pressure gauge 38 installed in the filtration tower 20, and the filter medium is regenerated by washing before the filter medium is completely saturated. The filter medium is regenerated by so-called backwashing.
Specifically, the pump 30 is stopped, the feed of raw water is stopped, and the above-described filtration process is finished. Next, the valves 42a, 42b, and 42d are closed, and the valves 42c and 42e are opened. The filtrate in the water tank 28 is fed by the pump 40, and the fed filtrate is circulated in the filtration tower 20 from the lower part of the filtration tower 20 through the pipe 50h, the branch 60b, and the pipe 50g. Is done. The filtered water that has become an upward flow is discharged from the upper part of the filtration tower 20 while removing suspended substances trapped in the granular filter medium of the first filter medium layer 24 and the second filter medium layer 26 from the surface of the granular filter medium, and the pipe 50f. The gas is discharged from a discharge port (not shown) via the branch 60a and the pipe 50e. After the backwashing is completed, the above filtration process is started again.

The flocculant is not particularly limited and can be selected according to the application. Examples thereof include inorganic aluminum-based and iron-based flocculants. Of these, inorganic aluminum-based flocculants are preferable, and polyaluminum chloride (PAC) is particularly preferable.
Moreover, although the addition amount of a flocculant is not specifically limited, It is preferable to add so that it may become 2-30 mg / l with respect to raw | natural water. If it is less than 2 mg / l, the film formation on the surface of the particulate filter medium becomes insufficient at the beginning of the filtration treatment, and there is a possibility that the suspended substances in the raw water cannot be sufficiently flocculated and removed. On the other hand, when the concentration exceeds 30 mg / l, the flocculant may flock at the upper part of the first filter medium layer 24 or the second filter medium layer 26 to block the filter medium.

  The acid solution is not particularly limited as long as the raw water can have a target pH, and examples thereof include aqueous solutions such as hydrochloric acid and sulfuric acid.

  The raw water is not particularly limited and may be any of river water, seawater, groundwater, tap water, industrial wastewater, and the like.

  The filtration rate by the filtration device of the present invention is represented by LV (linear velocity) and is a value represented by m / h. Although the filtration processing speed is not particularly limited, LV = 10 to 40 m / h is preferable, and 20 to 30 m / h is more preferable. If the filtration rate is less than 10 m / h, the filtration area must be increased in order to obtain a large amount of filtered water, and if it exceeds 40 m / h, suspended substances may not be sufficiently removed. is there. Furthermore, LV = 20 to 30 m / h is more preferable because suspended substances can be reliably removed while keeping the filtration area small.

The water flow rate at the time of backwashing is represented by LV as with the filtration rate. The water flow rate for backwashing is limited by the particle size and density of the filter medium, that is, the sedimentation rate, but is preferably 20 to 50 m / h from the viewpoint of washing accuracy and efficiency.
Moreover, it is preferable that the amount of water flow is 1.5 to 5 times the volume ratio of the total void volume of the first filter medium layer 24 and the second filter medium layer 26. If the amount is less than 1.5 times, the cleaning may be insufficient. If the amount exceeds 5 times, a large amount of washing water is required, and the amount of waste liquid increases, which is not preferable.

  The timing of cleaning the first filter medium layer 24 and the second filter medium layer 26 may be set by setting a filtration resistance by the differential pressure gauge 38 or by setting a timer based on an empirically obtained time. Furthermore, backwashing can be performed in combination with surface washing or air washing in addition to backwashing using filtered water. The surface cleaning is a cleaning method in which water is sprayed on the upper surface of the first filter medium layer 24 so that suspended substances attached to the filter medium on the first filter medium layer 24 are separated by a water flow. The air cleaning is a cleaning method in which air is circulated from the lower part of the filtration tower 20 and the suspended substances attached to the filter medium in the filtration tower 20 are peeled off by a shearing force when the air passes through the surface of the filter medium.

The present invention is not limited to the above-described embodiment, and can be modified without departing from the object of the present invention.
In the above-described embodiment, the filtration tower 20 has the first filter medium layer 24 and the second filter medium layer 26, but the filter medium layer may be only one layer or three or more layers. Moreover, the granular filter material to be used may be a mixture of two or more granular filter media. Here, when mixing 2 or more types of granular filter media, the repose angle of the mixed granular filter media needs to be 18-30 degrees.
In the above-described embodiment, the first filter medium layer 24 is formed by filling the particulate filter medium directly used for the first filter medium layer 24 on the second filter medium layer 26. A support may be provided on the boundary surface of the filter medium layer 26.
In the above-described embodiment, the acid solution is used for pH adjustment. However, when the pH of the raw water is acidic or when the pH is greatly reduced by the addition of the flocculant, the alkaline water is added to the raw water. You may adjust pH of.

  According to the filtration device of the present invention, since the filter medium layer has an appropriate gap, each filter medium can sufficiently come into contact with the flocculant at the beginning of the filtration treatment, and a film of the flocculant is formed. In addition, since the filter medium layer has an appropriate compaction rate, the gap between the granular filter media is reduced after the liquid flow, and the filtration time can be made appropriate. As a result, immediately after the start of the filtration treatment, it is possible to obtain filtered water having a high removal ability with respect to suspended substances in raw water and having an SDI of less than 3.0.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, it is not limited to an Example.
(Measurement of SDI)
The filtered water was filtered under a pressure of 206 kPa using a membrane filter having a diameter of 47 mm and a pore diameter of 0.45 μm. The time T1 required for the first 500 ml filtration was measured, followed by filtration for 15 minutes, and then the time T2 required for filtering 500 ml of filtered water was further measured, and the SDI value was determined by the following formula.

(Differential pressure measurement)
With the pressure on the secondary side of the filtration tower kept constant, the pressure on the primary side of the filtration tower was measured to obtain a differential pressure (gauge pressure).

Example 1
Silica sand 1 as a filter medium (standard product for water supply, effective diameter: 0.6 mm, uniformity coefficient: 1.1, angle of repose: 18 °) in a column (filtration area = 0.0314 m ² ) having an inner diameter of 200 mm and a height of 4000 mm To obtain a filter medium layer. The filter medium layer was backwashed (air washing speed: 40 m / h × 10 minutes, water backwashing speed: 36 m / h × 12 minutes), and then naturally settled, so that the height of the filter medium layer was 1000 mm. Subsequently, industrial water (turbidity: 1, pH: 7.2 to 7.5) was passed through for 12 hours at a filtration rate of 30 m / h. At this time, PAC was added so as to be 10 mg / l. At the same time, hydrochloric acid was added to adjust the pH of the raw water to 6.5. The SDI of filtered water measured between 15 and 720 minutes after the start of liquid flow is shown in FIG. 2, and the differential pressure measurement result of the filtration tower is shown in FIG. Table 1 shows the specifications of the filter medium and the consolidation ratio.

(Example 2)
The silica sand 1 of the filter medium was the same as Example 1 except that the anthracite 1 (standard product for water supply, effective diameter: 0.8 mm, uniformity coefficient: 1.2, angle of repose: 22 °) was used. The SDI measurement results are shown in FIG. 2, the differential pressure of the filtration tower is shown in FIG. 3, and the specifications of the filter media and the consolidation ratio are shown in Table 1.

(Example 3)
The silica sand 1 of the filter medium was carried out in the same manner as in Example 1 except that the anthracite 2 (standard product for water supply, effective diameter: 0.8 mm, uniformity coefficient: 1.2, angle of repose: 25 °) was used. The SDI measurement results are shown in FIG. 2, the differential pressure of the filtration tower is shown in FIG. 3, and the specifications of the filter media and the consolidation ratio are shown in Table 1.

Example 4
The same operation as in Example 1 was conducted except that the silica sand 1 of the filter medium was changed to a polyester granular fiber filter medium 1 (repose angle: 30 °). The SDI measurement results are shown in FIG. 2, the differential pressure of the filtration tower is shown in FIG. 3, and the specifications of the filter media and the consolidation ratio are shown in Table 1.

(Comparative Example 1)
The filtration was performed in the same manner as in Example 1 except that the silica sand 1 was changed to silica sand 2 (standard water supply product, effective diameter: 0.6 mm, uniformity coefficient: 1.4, angle of repose: 15 °). The SDI measurement results are shown in FIG. 2, the differential pressure of the filtration tower is shown in FIG.

(Comparative Example 2)
This was performed in the same manner as in Example 1 except that the silica sand 1 of the filter medium was a polyester granular fiber filter medium 2 (rest angle: 40 °). The SDI measurement results are shown in FIG. 2, the differential pressure of the filtration tower is shown in FIG. 3, and the specifications of the filter media and the consolidation ratio are shown in Table 1.

From Table 1, the filter media of Examples 1 to 4 have a compaction rate at LV = 20 m / h in the range of 0.6 to 3.0%, and Comparative Example 1 is less than 0.5%. The comparative example 2 exceeded 5.0%.
FIG. 2 is a graph showing changes over time in the SDI of filtered water in Examples 1 to 4 and Comparative Examples 1 and 2. Each legend represents the results of (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Comparative Example 1, and (f) Comparative Example 2, respectively. Yes. From the results of FIG. 2, in Examples 1 to 4, the SDI was less than 3.0 in the measurement 15 minutes after the start of water flow. On the other hand, in Comparative Example 1, it was found that it took 1 hour and 30 minutes or more for the SDI to be less than 3.0. Moreover, in the comparative example 2, it turned out that SDI cannot be less than 3.0 irrespective of filtration continuation time. In Example 1, compared with Examples 2 to 4, the SDI was a low value over 12 hours until the water flow treatment was completed. From this, when water quality evaluation by SDI is performed, it can be said that silica sand is preferable compared to anthracite and fiber filter media.
FIG. 3 is a graph showing the change over time in differential pressure (filtration resistance) in Examples 1 to 4 and Comparative Examples 1 and 2. The legend is the same as in FIG. From the results shown in FIG. 3, the differential pressure of each filter medium is 15 to 240 minutes after the start of the filtration treatment. Comparative Example 2 (polyester granular fiber filter medium 2) <Example 4 (polyester granular fiber filter medium 1) <Example 3 (Anthracite 2) <Example 2 (Anthracite 1) <Example 1 (Silica Sand 1) <Comparative Example 1 (Silica Sand 2) In this order, the pressure difference tends to increase. From this, it was found that when the effective differential pressure was the same, in the initial stage after the start of the filtration treatment, the filtration duration was longer for the fiber filter medium and for the silica sand.
Therefore, it is possible to reduce the frequency of washing the filtration tower and improve the quality of the filtered water by selecting an appropriate filter medium in consideration of the quality of the raw water, the passing time and the filtered water quality. For example, if the two-layer filtration is performed by combining the quartz sand 1 and the anthracite 2, it is possible to extend the filtration duration or improve the filtered water SDI as compared with the case where each is single.

It is a mimetic diagram of a filtration device concerning one embodiment of the present invention. It is a graph showing the time-dependent change of SDI of an Example and a comparative example. It is a graph showing the time-dependent change of the differential pressure | voltage in an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Filtration apparatus 14 Coagulant tank 20 Filtration tower 24 1st filter medium layer 26 2nd filter medium layer

Claims (2)

  A filtration apparatus having means for adding a flocculant to a suspension in water to be treated and a filtration tower for removing the suspension, wherein the filtration tower is made of a granular filter medium having an angle of repose of 18 to 30 °. A filtration apparatus comprising one or more layers. The filtration tower is defined by the following formula (1) when the porosity before the start of filtration treatment is 40 to 60% and the filter medium layer is passed through a filter medium layer having a height of 1000 mm at a filtration rate of 20 m / h. The filtration apparatus according to claim 1, further comprising a filter medium layer having a consolidation ratio of 0.5 to 5.0%.

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