JP2004290752A - Method for filtering confluent sewage at high speed - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for filtering confluent sewage at a high speed, by which the majority of a filthy solid substance can be removed even when a large quantity od rainwater is flowed and a backwashing operation can be performed quickly. <P>SOLUTION: The confluent sewage is introduced into a plurality of upward stream type filtration tanks 1 the top surface of each of which is used as a common treated water tank 5 and filtered at a high filtration speed of 1,000-1,200 m/day by using a floating filter medium 4 which is packed in each of the tanks 1 and has 0.1-0.4 bulk density. When the medium 4 is clogged in any of the tanks 1, the supply of an original water to the tank 1 to be washed is stopped and the tank 1 to be washed is backwashed by making the treated water in the tank 5 flow downward into the tank 1 to be washed at the speed of 1.2-4.0 m/minute. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed filtration method that does not rely on microbial purification of combined sewage and is applied to a combined sewage system where sewage and rainwater are combined as sewage.
[0002]
[Prior art]
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2001-219193 [0003] In a combined sewer system of sewage and rainwater as disclosed in Patent Document 1, the flow rate between fine weather and rainy weather changes significantly. Generally, in a combined sewage treatment plant, the maximum amount of water flowing into the sewage treatment plant during rainy time is restricted to 3Q which is three times the design water amount Q. Of these, Q can be subjected to the same normal processing as in fine weather, but over Q to 3Q exceeds the normal processing capacity of the treatment plant reaction tank, so simple processing using the first sedimentation tank as it is I do. When the amount of water further increases and exceeds 3Q, the water is discharged to rivers and the like without any treatment.
[0004] Therefore, when the amount of combined sewage exceeds Q during rainy weather, most pollutants are discharged to rivers and the like as they are, resulting in environmental pollution. Especially in large cities where sewerage has spread very quickly, combined sewerage is often used, and this environmental problem is becoming more apparent with the development of the waterfront.
[0005] In order to deal with such a problem, a high-speed filtration device for physically treating rainwater is being actively developed. However, the high-speed rainwater filtration system currently under study requires a filter media thickness of 2 m or more and requires a filter media outflow prevention screen at the bottom, or a coagulant is added to improve the treatment efficiency. In practical use, it is impossible to use civil engineering facilities such as the existing first sedimentation basin with a water depth of 2.5 to 4 m, and it is necessary to construct a new civil engineering structure. It was a technology that required a lot of cost. In addition, there is also a problem that the backwashing takes a long time when the filter medium layer is clogged, so that the backwash cannot catch up, and the filter layer is clogged when a large amount of rainwater flows.
[0006] In addition, a purifying apparatus using a filter medium that does not require a filter medium outflow prevention screen at the lower portion has been developed, but this is performed for the purpose of immobilizing microorganisms on the filter medium to purify organisms, and is mainly used in a septic tank or the like. The technology applied. The processing speed is generally 100 m / day or less in consideration of the biological reaction, and when the technology is used for high-speed filtration as described in the present invention, the compression strength of the filter medium is insufficient, so that the filter medium is deformed. Therefore, there is a drawback that clogging is immediately caused and stable filtration cannot be performed.
[0007]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and is applicable to a case where rainwater exceeding Q flows in during rainy weather or a large amount of rainwater flowing further exceeding 3Q flows in rainy weather. Can be installed at a low cost by simply remodeling the existing primary sedimentation basin and rainwater storage basin, and can perform the backwashing operation quickly. To provide an efficient high-speed filtration method.
[0008]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a method in which combined sewage, which is raw water, is guided to a plurality of upward-flow-type filtration tanks each having an upper surface serving as a common treatment water tank. High-speed filtration is performed at a filtration speed of 1000 to 1200 m / day by the floating filter medium filled in the filter tank, and when the floating filter medium is blocked, supply of raw water to the filter tank to be cleaned is stopped and common The backwash in which the treated water in the treated water tank is flowed downward to the filtration tank to be washed is sequentially performed for each filtration tank. The backwashing speed is preferably set to 1.2 to 4.0 m / min, and it is preferable to use a floating filter medium having a bulk density of 0.1 to 0.4. Furthermore, in order to avoid consolidation, it is preferable to use a floating filter medium having a 50% compression hardness of 0.1 MPa or more.
According to the present invention, a large amount of combined sewage flowing into a sewage treatment plant in rainy weather is guided to a plurality of upward-flow type filtration tanks, and the floating filter material filled in each of the filtration tanks is used for 1000 to 1200 m. High speed filtration at a filtration rate of / day. Therefore, even when rainwater exceeding Q or a large amount of rainwater exceeding 3Q flows, most of the polluted solid substances can be removed. Also, since part of the existing initial sedimentation basin and rainwater storage basin can be divided and installed, it is not necessary to construct new civil engineering equipment and secure the installation space. Further, backwashing of each filtration tank can be performed quickly and sequentially.
[0010]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.
FIG. 1 is a sectional view showing an apparatus used for high-speed filtration of combined sewage of the present invention, and FIG. 2 is an A-A sectional view thereof. This device is constructed by modifying a conventional first sedimentation basin or rainwater storage tank provided in a combined sewage treatment plant. In this embodiment, three filtration tanks 1 partitioned by partition walls 2 are provided. If the number of tanks is plural, the number is arbitrary.
These filtration tanks 1 are upward-flow type filtration tanks, each having a vertical raw water inflow section 3 for each tank as shown in FIG. The combined rainwater is supplied to the lower part of the tank from the raw water inflow section 3, the SS is captured while passing through the packed bed of the floating filter medium 4, and the treated water flows upward. As shown in FIG. 1, the upper surface of each filtration tank 1 is a common treatment water tank 5, and the treated water is taken out from its end (the right end in the drawing) and discharged to a river or the like. In order to prevent the floating filter medium 4 from flowing out, a net 6 is provided on the upper surface of the packed layer of the floating filter medium 4.
The floating filter medium 4 used in the present invention is preferably made of a foamed polymer having a bulk density of 0.1 to 0.4. If the bulk density exceeds 0.4, it may flow downward during backwashing. Examples of the foamed polymer having such physical properties include foamed polypropylene, foamed polystyrene, foamed polyethylene, and the like. Further, as the floating filter medium 4 used in the present invention, an irregular or cylindrical one having a size of 4 to 10 mm is preferable. Here, the uneven shape is not intended to adhere the purifying microorganisms, but is intended to catch or detain the polluted solid substance at the uneven portion so that it can be easily removed. Instead of such a simple shape, it means a different shape having some irregularities on the outer surface. The thickness of the filling layer of the floating filter medium 4 can be reduced to about 1 m, which is half or less than that of the conventional case.
The filtration tank 3 filled with such a floating filter medium 4 can capture a large amount of SS without compaction of the filter medium. Therefore, in the present invention, high-speed filtration is performed at a filtration speed of 1000 to 1200 m / day. Actual equipment that can perform high-speed filtration of 1000 m / day or more without adding a flocculant has not been known. By performing such high-speed filtration, even when a large amount of rainwater intensively flows into the sewage, the entire amount can be filtered at an SS removal rate of about 70%. However, if it exceeds 1200 m / day, the SS removal rate decreases, which is not preferable.
In the present invention, since such high-speed filtration is possible, a large amount of combined sewage can be treated at high speed. However, as the amount of trapped SS increases, the layer of the floating filter medium 4 becomes clogged, the pressure loss increases, and the filtration capacity decreases, so that backwashing is required. At this time, in the present invention, the supply of raw water to the filtration tank 1 to be washed is stopped, and the treated water in the common treated water tank 5 is caused to flow downward to the filtration tank 1 to be washed to perform backwashing.
In order to stop the supply of the raw water to the filtration tank 1 to be cleaned in this way, a slide gate is provided at the raw water supply port 7 for supplying the raw water to the raw water inflow section 3 of each filtration tank 1 as shown in FIG. It is preferable to mount 8 so that it can be opened and closed. In addition, an opening / closing valve can be used instead of the slide gate 8.
The procedure for backwashing is as follows.
First, as shown in FIG. 3, the supply of raw water to the filtration tank 1 to be cleaned is stopped, and the cleaning drain valve 9 provided at the bottom of the filtration tank 1 is opened. Then, the treated water in the common treated water tank 5 flows downward through the packed bed of the floating medium 4, and is discharged to the cleaning drain tank 11 via the cleaning drain pipe 10. At this time, the packed bed of the floating filter medium 4 is backwashed. The backwash speed is set to 1.2 to 4.0 m / min. If the backwash speed is slower than this, the backwash effect becomes insufficient, and if it is faster than this, the floating filter medium 4 may flow out together with the backwash water.
In the present invention, the reason for stopping the supply of the raw water to the filtration tank 1 to be washed and performing the backwashing is to secure the above-mentioned backwashing speed. That is, backwashing is possible by opening the washing / draining valve 9 even while the supply of the raw water is continued, but a part of the raw water is discharged to the cleaning / drain tank 11 via the cleaning / drain pipe 10 as it is. Therefore, the amount of true backwash water that passes through the packed bed of the floating filter medium 4 is omitted by that amount, and the backwash speed is reduced. If the supply of the raw water to the filtration tank 1 to be cleaned is stopped and the backwashing is performed as in the present invention, such a fear does not occur.
[0018]
Due to such backwashing, the packed bed of the floating filter medium 4 that has been closed is agitated and expanded, and the SS is separated from the floating filter medium 4. The floating filter medium 4 having a low bulk density floats up against the downward flow for backwashing, so that it stays almost at the original position, and does not run off even if no net is provided below. The separated SS flows down to the lower part of the tank together with the backwash water and is discharged from the washing drainage pipe 10. The washing wastewater is guided to a sewage inflow channel or a conventional first sedimentation basin by a drainage pump 12 provided in a washing drainage tank 11 for treatment.
The above-mentioned backwashing is sequentially performed for each of the filtration tanks 1. However, in the filtration tanks 1 other than the filtration tank 1 to be washed, the high-speed filtration processing continuously proceeds. Processed water is always supplied. The time required for backwashing in one tank is about 2 minutes, which is about 1/10 of the conventional backwashing time. For this reason, even when a large amount of combined sewage exceeding 3Q flows, there is an advantage that backwashing can be performed while performing high-speed filtration.
[0020]
As described above, according to the high-speed filtration method for combined sewage of the present invention, even when rainwater exceeding Q flows in during rainy weather, or even when large amounts of rainwater exceeding 3Q flow, Most of the polluted solid substances can be removed by the high-speed filtration, and the conventional environmental pollution can be prevented. Further, according to the high-speed filtration method of combined sewage of the present invention, the backwash operation can be sequentially and rapidly performed on each filtration tank while the filtration is continued. Moreover, according to the present invention, since the thickness of the floating filter medium can be reduced and a large area is not required, it can be installed at a low cost by modifying an existing first sedimentation tank or rainwater storage tank.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a rainwater treatment apparatus according to an embodiment of the present invention.
FIG. 2 is a sectional view taken along line AA of FIG.
FIG. 3 is a cross-sectional view illustrating a backwash state.
[Explanation of symbols]
1 Filtration tank, 2 bulkhead, 3 Raw water inlet, 4 Floating filter material, 5 Common treatment water tank, 6 net, 7 Raw water supply port, 8 Slide gate, 9 Wash drain valve, 10 Wash drain pipe, 11 Wash drain tank, 12 Drain pump

Claims (4)

The combined sewage, which is raw water, is guided to a plurality of upward-flow-type filtration tanks each having an upper surface serving as a common treatment water tank, and is subjected to high-speed filtration at a filtration speed of 1000 to 1200 m / day by a floating filter material filled in each filtration tank. At the same time, when the clogging of the floating filter material occurs, the supply of raw water to the filtration tank to be cleaned is stopped, and backwashing in which the treated water in the common treatment water tank flows downward to the filtration tank to be washed is performed for each filtration tank. A high-speed filtration method for combined sewage, which is performed sequentially. The method for high-speed filtration of combined sewage according to claim 1, wherein the backwashing speed is 1.2 to 4.0 m / min. The high-speed filtration method for combined sewage according to claim 1, wherein a floating filter medium having a bulk density of 0.1 to 0.4 is used. The high-speed filtration method for combined sewage according to claim 1, wherein a floating filter medium having a 50% compression hardness of 0.1 MPa or more is used.

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