JPH08103603A - Upflow filtration method - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the concentration of suspended matter in the treated water obtained at the beginning of the filtration process after the washing process. [Structure] A filter layer 3 of a floating filter medium is provided in the treatment tank 1,
In the up-flow filtration method, in which raw water is passed through the filter layer in an upward flow to perform the filtration step, and washing water is passed in a downward flow to perform the washing step, A circulation pipe 9 for supplying water to the bottom of the tank to circulate is provided, and after washing, the water in the treatment tank is circulated by the above circulation pipe to pass upward through the filter layer for a predetermined time, and then the raw water is raised. The filtration process is carried out by passing water in a stream.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating an upflow filtration device having a filter layer of a floating filter material in a treatment tank.

[0002]

2. Description of the Related Art A levitation filter medium having a spherical shape and an indefinite shape and a specific gravity of 1 or less is foam-molded from polystyrene, polyethylene, urethane resin or the like, and the levitation filter medium is placed under a screen 2 in a treatment tank 1 as shown in FIG. , The floating filter medium is collected under the screen by buoyancy to form the filter layer 3, and raw water is supplied to the bottom of the treatment tank by the water supply pipe 4 and the pump P1 to flow upward into the filter layer in the tank. To pass SS in the raw water to the filter layer,
An upflow filtration device that drains treated water from a drain pipe 5 at the upper part of a treatment tank to perform a filtration process has been conventionally known. In addition, a biofilm of microorganisms is attached to the surface of the flotation filter material that constitutes the filter layer, and raw water is passed through the filter layer in an upward flow and aeration is performed from the diffuser pipe 6 at the bottom of the tank to filter SS in the raw water. Biofilm filtration is known in the art, in which not only is it trapped in a layer, but also dissolved organic substances contained in raw water are decomposed into microorganisms to be removed and reduced.

When the filtration process is continued, the trapped SS and the excessively grown biofilm block the gap between the floating filter media and the pressure loss increases. When the pressure loss increases to a predetermined value, the valve of the water supply pipe 4 and the valve of the drainage pipe 5 are closed to interrupt the filtration process, and the sprinkling pipe 7 supplies the wash water to the filter layer from above and the drain at the bottom of the tank. The valve of the pipe 8 is opened, the drain pipe discharges the water in the tank and the washing water flowing downward causes the floating filter medium to flow, and the valve of the drain pipe is closed to stop the supply of the washing water, and the diffuser pipe. By ejecting air from 6 and repeating air washing in which the floating filter medium is caused to flow by air bubbles, SS and sludge are separated from the floating filter medium, and finally washing water is supplied from the sprinkler pipe 7 and the valve of the drain pipe 8 is turned on. Open to wash out SS and sludge from the drain pipe together with the wash water, and when SS and sludge are no longer observed in the wash water discharged from the drain pipe, stop the supply of wash water from the sprinkler pipe and close the drain pipe valve. , The washing process is completed. As the wash water, treated water obtained from the drainage pipe 5 at the time of the filtration step or industrial water is used.

[0004]

After the cleaning process is completed as described above, raw water is supplied to the bottom of the treatment tank by the water supply pipe 4 and the pump P1, and the water is passed upward through the filter bed 3 in the tank. When the filtration step is restarted, SS and sludge are mixed and discharged into the treated water obtained in the drain pipe 5 at the beginning of the filtration step. this is,
While the washing water during the washing step flows downward in the filter layer,
Since the raw water in the filtration step flows upward in the filter layer in the reverse direction, the buoyant filter medium is disturbed until the filter layer is consolidated by the upward flowing water of the raw water in the filtration step immediately after washing. A small amount of SS and sludge existing in the bed is mixed with the treated water and discharged. For this reason, the treated water discharged to the drainage pipe 5 is returned to the raw water tank for a certain period of time at the beginning of the filtration step, and thereafter, treated water in which SS and sludge are not mixed is obtained. However, if so, it is necessary to make the tank for raw water large.

[0005]

The present invention was developed for the purpose of solving the above-mentioned problems, and a circulation pipe for supplying water on the filter layer to the bottom of the tank and circulating it in the treatment tank is provided. After the cleaning, the water in the treatment tank is circulated through the circulation pipe after washing and is passed through the filter layer in an upward flow for a predetermined time, and then raw water is passed in an upward flow to perform a filtration step. To do.

[0006]

EXAMPLE The treatment tank 1 is provided with a circulation pipe 9 having a circulation pump P2 for circulating the water above the filter layer 3 to the bottom of the tank. Then, after the washing step is completed, the circulation pump P2 is operated before the filtration step is restarted, and the water on the filter layer in the treatment tank is supplied to the bottom of the tank through the circulation pipe 9 so that water flows upward in the filter layer. And circulate. As a result, at the beginning of circulation, the floating filter medium flows,
Eventually, the levitation filter material was tightly gathered under the screen 2 due to buoyancy and the filter layer was consolidated, and S contained in the circulating water was added.
S and sludge are captured by the compacted filter bed and are not present in the circulating water.

If necessary, the treatment tank is provided with a turbidity concentration detector 10 for detecting the turbidity of water above the filter layer, and if it is detected that SS or sludge is not present in the water above the filter layer, it is circulated. Stop the pump P2, close the valve of the circulation pipe, stop the circulation process,
The valves of the water supply pipe and the drainage pipe are opened, and the pump P1 is operated to restart the filtration process. As a result, treated water containing less SS and sludge can be obtained.

Nitrification and denitrification operation was performed by the biofilm filtration apparatus of FIG. 1 using a treatment tank having a diameter of 400 mm and a height of 5200 mm. Floating filter media has a particle size of 3.5 mm and a specific gravity of 0.03
Made of expanded polystyrene, and the height of the filter layer is 3
000 mm. Nitrogen was removed by a circulation method in which part of the treated water in the upper part of the filter bed was circulated to the raw water for denitrification. In raw water, NH ₄ -N = 50 mg / stand, BOD 170 mg /
Vertical, SS = 8 mg / vertical industrial wastewater was used.

A test (conventional method) in which raw water is immediately passed through the filter layer in an upward flow after washing to carry out a filtering step, and after the washing step, 1
A test (the method of the present invention) was conducted in which the circulation step was carried out for 0 minutes without passing the raw water, and then the raw water was passed through the filter layer in an upward flow to perform the filtration step. Upward circulation water LV of raw water in the filtration process
Was 4 m / hour. The upward flowing water LV in the circulation step of the method of the present invention was 10 m / hour in order to quickly consolidate the filter layer and accelerate the capture of SS and sludge. The results of the test are shown in Fig. 2, and in the conventional method, the SS concentration of the treated water 5 minutes after starting the passage of the raw water was about 50 mg / stand, and after that, the SS concentration was reduced, but 20 minutes after the passage of water. Later treated water SS
The concentration was still 10 mg / cubic. On the other hand, in the method of the present invention, the SS concentration of the treated water 5 minutes after starting the passage of the raw water is 10 mg / stand, and the SS concentration decreases thereafter, and the SS concentration of the treated water 20 minutes after the start of the passage of water. Was 5 mg / stand, which was far lower than that of the conventional method.

[0010]

As is apparent from the above, according to the present invention, the washing step is performed after the washing step is performed by the biofilm filtration in which the biofilm is attached to the flotation filter or the simple filtration in which the biofilm is not attached to the flotation filter. When restarted, treated water containing very little SS and sludge can be obtained. Therefore, it is not necessary to return the treated water at the beginning of the filtration process to the raw water storage tank, and there is no need to upsize the storage tank.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an upflow filtration device that can perform the filtration method of the present invention.

FIG. 2 is a graph showing changes over time in the turbidity concentration in treated water when the filtration according to the conventional method and the filtration according to the method of the present invention are performed.

[Explanation of symbols]

 1 Treatment tank 2 Screen 3 Filter layer by floating filter material 4 Raw water supply pipe 5 Treated water drain pipe 6 Diffuser pipe 7 Wash water sprinkler pipe 8 Drain pipe 9 Circulation pipe 10 Turbidity concentration detector P1 Raw water supply pump P2 Circulation pump

Claims (1)

[Claims] 1. A filter layer comprising a floating filter material is provided in a treatment tank,
In the up-flow filtration method, in which raw water is passed through the filter layer in an upward flow to perform the filtration step, and washing water is passed in a downward flow to perform the washing step, A circulation pipe for supplying water to the bottom of the tank to circulate is provided, and after washing, the water in the treatment tank is circulated by the above circulation pipe to flow upward through the filter layer for a predetermined time, and then the raw water flows upward. An upflow filtration method, characterized in that the filtration step is carried out by passing water through.