JP3821438B2 - Cleaning and dispersing method for floating filter media - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning method when a packed bed of floating filter material filled in a filtration tank is blocked.
[0002]
[Prior art]
[0003]
[Patent Document 1]
JP-A-7-75793 [0004]
In order to filter sewage, return water, factory effluent, garbage leachate, agricultural water, rainwater, clean water, river water, etc., as described in Patent Document 1, it is conventional to use a filtration tank using a floating filter medium. Known from. As the floating filter material, a resin material having a specific gravity (apparent specific gravity) of 0.9 or more is generally used from the viewpoint of strength and durability. Since the specific gravity difference between the water and the floating filter medium is small in this way, when washing water is flowed downward to wash (backwash) the packed bed of the floating filter medium, the floating filter medium is washed away from the lower part of the filtration tank together with the washing water. There is a fear.
Therefore, in general, a screen is stretched under the floating filter medium packed bed to prevent loss during washing, but naturally this screen has an opening smaller than the particle diameter of the floating filter medium, At the time of upward flow filtration, there is a possibility that the lower screen will be blocked first. In this case, it is necessary to clean or replace the screen after removing the packed bed, which requires very large maintenance work and construction.
[0005]
Therefore, the present applicant has developed a filtration method using a packed bed made of a floating filter material having a specific gravity smaller than that of the conventional one, and previously proposed it as Japanese Patent Application No. 2001-347144 as a cleaning method. However, as shown in FIG. 3, the flow of the cleaning water has a weaker peripheral edge than the central part, so that the filter medium at the peripheral part cannot be sufficiently cleaned gradually. There is a problem that the back-washing process is performed only on the portion where water easily escapes, and the efficiency of the filtration process is significantly reduced.
[0006]
[Problems to be solved by the invention]
The present invention solves the above-described conventional problems, and can clean the blocked floating filter material in a short time without increasing the size of the filtration tank or providing a screen at the bottom, and the floating filter medium. The present invention has been made in order to provide a novel method for washing and dispersing a floating filter medium that can reliably wash the whole and maintain high filtration performance for a long period of time.
[0007]
[Means for Solving the Problems]
The method for washing and dispersing a floating filter medium of the present invention, which has been made to solve the above problems, forms a filter medium packed bed made of a floating filter medium having a specific gravity of 0.1 to 0.4 in the filtration tank, and this filter medium packed bed If the filter is clogged with contaminants such as contaminants due to the upward flow filtration treatment, wash water is introduced into the filter medium packed bed from the top in the downward flow, and the entire filter medium packed bed is moved downward away from the screen. Next, air is supplied from the lower side of the filter medium packed bed to disperse the filter medium packed layer solidified into a plug shape, and the packed layer is formed toward the portion without the floating filter medium generated between the filter medium and the screen. thereby sequentially floating a floating filter media from the upper surface when separating the floating filter media contaminants have been trapped between the like at the same time, impurities such as said separated after washing the entire filter medium packed layer by eliminating downwards together with the washing water , The surface of the screen It is characterized in that to form a cleaned floating filter media layer towards.
[0008]
In the present invention, since a floating filter medium having a specific gravity (apparent specific gravity) of 0.1 to 0.4 and a large specific gravity difference with water is used, the washing water is fed into the packed bed with a high-speed downward flow of 1 m / min or more. Even if backwashing is carried out after the introduction, the floating filter medium will not be washed away, and a screen for preventing the washing away from the bottom of the packed bed is unnecessary. In addition, the wash water is introduced into the filter medium packed bed in a downward flow from the upper part to move the filter medium packed bed downward, and air is supplied from the lower side of the filter medium packed bed in the initial stage so that the plug is solidified. Disperse a certain filter medium packed bed separately, thereby separating SS, contaminants, etc. from the floating filter medium, which has become sparse throughout, and removing the separated SS, contaminants, etc. together with the washing water. In addition, by performing the cleaning by a special mechanism of cleaning the entire filter medium packed bed, the blocked floating filter medium can be efficiently cleaned in a short time without deepening the filtration tank.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a filtration tank, and a packed bed 2 of floating filter media is formed in the middle part thereof. The floating filter used here has a specific gravity (apparent specific gravity) of 0.1 to 0.4, and is made of a closed porous polymer porous material such as expanded polyethylene or expanded polystyrene. This floating filter medium is preferably made of a material having a 50% compression hardness of 0.1 MPa or more in order to avoid compaction during filtration. 50% compression hardness means the pressure required to crush the particles of the floating filter medium until the height is halved. If the specific gravity of the floating filter medium is less than 0.1, the strength will be insufficient and it will be easy to consolidate. If it exceeds 0.4, the specific gravity difference with water will gradually decrease, and there will be a risk of filter medium loss due to high-speed downflow backwashing. Arise.
[0010]
The size of the floating filter medium is not particularly limited, but it is preferably about 4 to 10 mm in consideration of filtration performance, trapping amount of impurities, SS, etc., possibility of loss, and washability. Further, when the floating filter medium is formed by punching from a foamed polymer sheet, it is preferably punched and formed into a size of 4 to 10 mm using a sheet having a thickness of 2 mm or more. In addition, it is preferable to make the shape different from a simple rectangular parallelepiped or sphere, such as a star shape or a windmill shape having protrusions on the outside, particularly in order to improve the amount of impurities, SS, and the like.
[0011]
The height of the packed bed 2 of the floating filter medium is preferably 0.5 m or more, and the depth of the filtration tank 1 is preferably 2 m or more. A raw water inflow passage (not shown) is formed on the side of the packed bed 2, and the raw water is supplied to the lower part of the filtration tank 1, and while passing through the packed bed 2 as an upward flow, impurities and SS Etc. are trapped in the floating filter medium. Note that a screen 4 is provided on the upper portion of the packed bed 2 to prevent the floating filter medium from being lost during filtration. However, since this screen 4 is located on the upper portion of the packed bed 2, there is almost no clogging. Easy to clean. The filtered water is discharged through the filtered water layer 5 formed on the top of the packed bed 2.
[0012]
When a large amount of foreign matter, SS, etc. is captured in the packed bed 2 and the blockage proceeds, this is caught by, for example, a change in the water level of the raw water inflow channel, and the filtration is performed when the water level reaches a predetermined height. The tank 1 is automatically cleaned. In this embodiment, for example, a drain valve for cleaning is provided at the bottom of the filtration tank 1, and cleaning is started by opening the drain valve.
[0013]
When washing, first, the drain valve is opened to discharge the raw water in the filtration tank 1 from the lower part of the packed bed 2. At the same time, the filtered water flows from the upper part into the packed bed 2 as washing water. The flow rate of the washing water at this time is a high speed of 1 m / min or more. In this way, when washing water is introduced into the packed bed 2 at a considerably higher speed than before, the packed bed 2 of the floating filter medium, which is solidified in a plug shape due to the blockage of SS and impurities by filtration, is shown in the left of FIG. As a whole, the whole moves instantaneously downward, and the upper surface is separated from the screen 4.
[0014]
Then, at the same time as the cleaning water is introduced into the packed bed 2, air is supplied for a short time (for example, about 5 seconds) from the air supply pipe 7 provided below in the initial stage (for example, about 5 to 10 seconds). Then, air is applied from the lower part to the packed bed of the floating filter medium solidified in a plug shape. Then, as shown in the right diagram of FIG. 2, the solidified floating filter medium is dispersed apart, and thereby the floating filter medium from the upper surface of the packed bed 2 toward the portion without the floating filter medium generated between the screen 4. Begins to rise one after another, and at the same time, foreign matter, SS, and the like trapped between the floating filter media are separated.
In the unlikely event that the floating filter medium moves downward while being hardened without being dispersed apart even by the air supply, the block hits the air supply pipe 7 and the block is broken and dispersed, There is no risk of lumps remaining. Moreover, since the specific gravity of the separated contaminants and SS is approximately 0.5 or more and is heavier than the specific gravity of the floating filter medium, the contaminants and SS flow downward along with the washing water flow. On the other hand, the floated filter medium that has risen gradually forms a washed filter medium layer below the screen 4.
[0015]
During this time, the downward washing water flow continues, so that the unwashed floating filter material layer below is gradually moved and dispersed downward while being disturbed by the water flow. Therefore, a layer in which the floating filter medium is sparse is always formed between the upper washed floating filter layer and the lower unwashed floating filter layer. In this sparse layer, the specific gravity is as described above. Due to the difference, the rising of the floating media and the separation of impurities and SS proceed rapidly. During this time, the separated contaminants and SS move to the lower part of the filtration tank 1, and the entire cleaning is completed when reaching the lower end of the packed bed 2 while being gradually concentrated with the contaminants and SS. Of course, the separated impurities and SS gather at the lower part of the filtration tank 1 and are discharged via the drain valve.
[0016]
If the above-described washing of the floating filter medium according to the present invention is performed, for example, at a downward flow of 2 m / min, it can be completed within one minute if the height of the packed bed is about 2.0 m. As a result, the entire surface becomes a washed floating filter material layer, and the pressure loss is recovered. Thereafter, the drain valve is closed and the filtration is resumed.
[0017]
In the present invention, it is preferable to set the flow rate of the washing water to 1 m / min or more. This allows the above-described unique washing mechanism to be expressed, and efficient washing can be performed in a short time. Of course, although there is an influence of the size of the filtration tank 1, if the flow rate of the washing water is less than 1 m / min, the above-described unique washing mechanism is not exhibited, and the washing time is prolonged, which is not preferable.
[0018]
【The invention's effect】
As described above, according to the method for washing and dispersing a floating filter medium of the present invention, the closed floating filter medium can be efficiently washed in a short time without increasing the size of the filtration tank or providing a screen at the bottom. In addition, the entire floating filter medium can be reliably washed, and high filtration performance can be maintained over a long period of time.
Further, since the downward expansion of the packed bed is about 40% at the maximum, there is an advantage that it is not necessary to increase the size of the filtration tank, and it is not necessary to provide a screen for preventing loss at the lower part.
Therefore, the present invention greatly contributes to the development of industry as a method for washing and dispersing floating filter media that has solved the conventional problems.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a state before cleaning according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a cleaning process of a floating filter medium.
FIG. 3 is a cross-sectional view showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Filtration tank 2 Packing layer of floating filter material 4 Screen 5 Filtration water layer 7 Pipe for air supply

Claims (2)

When a filter medium packed bed made of floating filter medium with a specific gravity of 0.1 to 0.4 is formed in the filtration tank, and this filter medium packed bed is clogged with contaminants such as contaminants by upward flow filtration, The washing water is introduced into the filter medium packed bed in a downward flow, the entire filter medium packed bed is moved away from the screen , and then air is supplied from the lower side of the filter medium packed bed to solidify into a plug shape. The filter medium packed bed in the above is dispersed apart, and the floating filter medium is lifted one after another from the upper surface of the packed bed toward the part where there is no floating filter medium generated between the screen and at the same time, the impurities trapped between the floating filter medium Etc., and the separated contaminants etc. are removed downward together with the washing water to wash the entire filter medium packed bed , and then a floated filter medium layer is formed below the screen with the floated float filter medium. Characteristic washing of floating filter media Method.   The floating filter medium according to claim 1, wherein a pipe for air supply is provided below the filter medium packed bed of the filtration tank, and when the packed bed moves downward during cleaning, the packed bed hits the pipe and is dispersed apart. Washing and dispersing method.

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