JP2004105782A - High speed filtration method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent rapid rising of filtration resistance and deterioration of quality of filtered water. <P>SOLUTION: The high speed filtration unit 28 is provided with a turbidity sensor 30 for detecting turbidity of raw water after precipitation treatment by a coagulation/precipitation treatment facility 10; a coagulant addition means 32 for adding a polymer coagulant to the raw water; a controller 34; and a granular filter medium layer 38 passing the raw water added with the polymer coagulant. The controller 34 controls an amount of polymer coagulant added by the coagulant addition means 32 according to the detection value of the turbidity sensor 30. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-speed filtration method and apparatus, and more particularly to a high-speed filtration method and apparatus for passing raw water after settling treatment through a packed bed of granular filter media and filtering and separating fine particles contained in the raw water.
[0002]
[Prior art]
The high-speed filtration method is also called a rapid filtration method, and is a method of passing raw water through a granular filter medium layer at a filtration speed of usually 100 m / day or more to filter and separate fine particles in the raw water. The filtration speed is 10 m / day or less. It is distinguished from the slow filtration method. The main purpose of this high-speed filtration method is to restrain fine particles in gaps between filter media forming a granular filter media layer. For this reason, it is important to disperse the fine particles throughout the filter medium layer and to increase the amount of the captured fine particles as much as possible while suppressing an increase in the filtration resistance. The filtration performance is greatly affected by the particle size distribution of the fine particles to be separated by filtration. If the particle size distribution of the fine particles is excessive, most of the fine particles having a large particle size remain in the surface layer on the upstream side of the filter medium layer. The fine particles remaining on the surface layer act similarly to the filter medium to capture the fine particles, exhibiting a phenomenon of surface filtration, leading to instability in operation due to a rapid increase in filtration resistance. Further, if the particle size distribution of the fine particles is too small, the fine particles are liable to remain in the treated water (filtered water) by sewing through the gap between the filter media, resulting in deterioration of the water quality.
For this reason, in this type of high-speed filtration method, it is common practice to subject the water to be treated to a precipitation treatment to remove particles having a large particle diameter in advance. In addition, by performing coagulation and sedimentation treatment, not only particles having a large particle size but also particles having a relatively small particle size are removed by coagulation and sedimentation, thereby reducing the load on a filtration device. Further, a flocculant is added to raw water that has undergone such a precipitation treatment, and fine particles contained in the raw water are aggregated to form fine flocs, which are then passed through a high-speed filtration device. (For example, see Non-Patent Document 1)
[0003]
[Non-patent document 1]
Ide Tetsuo, "Water Treatment Engineering", 4th edition, 1st edition, Gihodo Shuppan Co., Ltd., April 1980, pp. 95-97, 102-105, 127-130
[0004]
[Problems to be solved by the invention]
However, in the conventional high-speed filtration device, sufficient operation management has not been performed even though the particle size distribution of the fine particles to be filtered and separated greatly affects the filtration performance as described above. For example, when purifying river water by high-speed filtration to obtain purified water, if the river water that is turbid due to rainfall is subjected to coagulation sedimentation, the amount of fine particles in the coagulated sedimentation water will be significantly greater than in fine weather, and the fine particles that slide through the filter media Tend to increase. For this reason, if the coagulated sedimentation treated water during rainfall is used as raw water for high-speed filtration, the operation of the high-speed filtration device becomes unstable, and the quality of filtered water deteriorates.
[0005]
The object of the present invention is to improve the above-described problems of the prior art, and even when the amount of fine particles in the raw water and the particle size distribution of the fine particles fluctuate, it is difficult to cause a sudden increase in filtration resistance or deterioration of the quality of the filtered water, An object of the present invention is to provide a high-speed filtration method and apparatus capable of maintaining stable operation.
[0006]
[Means for Solving the Problems]
The high-speed filtration method according to the present invention is a high-speed filtration method in which raw water after the precipitation treatment is passed through a granular filter medium layer to filter and separate fine particles contained in the raw water, wherein the turbidity of the raw water is detected by a turbidity sensor. And adding a predetermined amount of a polymer coagulant to the raw water according to the detection result.
[0007]
Further, the high-speed filtration device according to the present invention includes a turbidity sensor capable of detecting the turbidity of the raw water after the precipitation treatment, a flocculant adding means for adding a polymer flocculant to the raw water, and detection of the turbidity sensor. Control means for controlling the amount of the polymer flocculant added by the flocculant adding means according to the value, and a granular filter medium layer through which raw water to which the polymer flocculant is added is passed. And In this case, it is preferable that the control means has a function of correcting the amount of the polymer flocculant added by the flocculant adding means according to the temperature of the raw water.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is an apparatus system diagram showing an embodiment of the present invention. The coagulation and sedimentation treatment equipment 10 includes a mixing tank 12, a floc forming tank 14, and a sedimentation tank 15. In the mixing tank 12, the coagulant 18 is added to the inflowing water 16 to be treated, and the water 16 to be treated and the coagulant 18 are mixed by the rapid stirrer 20. In the floc forming tank 14, the water to be treated from the mixing tank 12 is slowly mixed by the slow stirrer 22, and the fine particles in the water to be treated are aggregated by the action of the added coagulant to form flocs. In the sedimentation tank 15, the flocs formed in the floc formation tank 14 settle at the bottom of the tank and are extracted as settled sludge 24. Raw water, which is the supernatant water of the sedimentation tank 15, is supplied to a high-speed filter 28 via a pipe 26. A turbidity meter 30 is disposed in the middle of the pipe 26, and the turbidity meter 30 detects the turbidity of raw water continuously or intermittently.
[0009]
A coagulant adding means 32 is connected to the pipe 26. That is, the turbidity of the raw water detected by the turbidity meter 30 is transmitted to the controller 34, and the controller 34 calculates the amount of the polymer flocculant to be injected into the raw water according to the turbidity of the raw water. The coagulant adding means 32 injects a predetermined amount of the polymer coagulant into the raw water in the pipe 26 according to a signal from the controller 34. Further, a line mixer 36 is provided in the pipe 26, and after the polymer flocculant and the raw water are uniformly mixed in the line mixer 36, the raw water flows into the high-speed filter 28.
[0010]
The injection of the polymer flocculant is expected to have two main effects. The first effect is to aggregate fine particles contained in raw water. The aggregating action of the fine particles need not be completed before the raw water flows the fine particles into the granular filter medium layer 38 of the high-speed filter 28. Rather, it is preferable that the raw water gradually progresses in the process of passing through the granular filter medium layer 38 of the high-speed filter 28. That is, it is preferable that the fine particles in the raw water immediately after flowing into the high-speed filter 28 have a fine particle diameter that easily passes through the gap between the filter media forming the granular filter media layer 38, and in the process of passing through the gap between the filter media. By agglomeration of the fine particles, the fine particles can be restrained in the space between the filter media as flocs of an appropriate size. Such an aggregating action of the fine particles gradually progresses in the entire area of the granular filter medium layer 38, so that the amount of the captured fine particles can be increased as much as possible while suppressing an increase in filtration resistance.
[0011]
The second function of the injection of the polymer flocculant is the action of adhering fine particles. The fine particles flowing into the high-speed filter 28 adhere to the filter medium while passing through the granular filter medium layer 38 by the action of the injected polymer flocculant, and new fine particles are successively linked to the fine particles adhered to the filter medium. Attached. Further, new fine particles adhere to the flocs trapped in the gaps between the filter media, and the flocs gradually increase. Due to such agglomeration of the fine particles inside the gap between the filter media and the adhesion of the fine particles to the filter medium or the floc, when the gap between the filter media is almost completely filled with the fine particles, the water flow resistance in the gap increases. . Then, the raw water changes its flow direction to another void portion having a small water flow resistance, and in the particulate filter medium layer 38, this coagulation action and adhesion action proceed in a complex manner to realize autonomous all-layer filtration. Will be.
The treated water from which the fine particles have been filtered in the process of passing through the granular filter medium layer 38 is discharged out of the system through a pipe 40.
[0012]
The amount of the polymer flocculant to be added is calculated by the controller 34 in accordance with the turbidity of the raw water detected by the turbidimeter 30 as described above, and the calculation formula at this time is usually set based on empirical rules. Is done. FIG. 2 is a graph illustrating a correlation between the turbidity of raw water and a preferable addition amount of a polymer flocculant, which is a basis for setting an arithmetic expression. The solid line A is the case at normal temperature, and the addition amount of the polymer flocculant is a constant amount a until the predetermined turbidity T, and thereafter, as the turbidity increases, the addition amount of the polymer flocculant is increased by a predetermined proportional constant. Increase with c. The dotted line B indicates a case where the temperature of the raw water is low, such as in winter. That is, when the water temperature decreases, the diffusibility of the polymer flocculant deteriorates, and the flocculant effect decreases. Therefore, the addition amount is corrected so as to be relatively increased. The constants T, a, b, c and the like in FIG. 2 are the type and average particle size of the granular filter medium constituting the high-speed filter 28, the layer height of the granular filter medium layer, the flow rate of raw water, and the type of polymer flocculant. An appropriate value is empirically determined according to the performance and the mounting position of the line mixer 36. According to the experimental results of the inventor of the present invention, a sufficient effect is obtained by adding several tens of ppb of the polymer flocculant to the raw water. Therefore, the control of the amount of the polymer flocculant to be added by the controller 34 is usually controlled within the range of this several tens of ppb level.
[0013]
When the polymer coagulant is quantitatively added irrespective of the turbidity of the raw water, the following adverse effects mainly occur due to excess or deficiency of the added amount. That is, if the addition amount is too small, the aggregating action and the adhering action of the fine particles in the raw water will be insufficient, and the fine particles will easily leak into the treated water discharged from the pipe 40, and the water quality will be deteriorated. If the amount of addition is excessive, most of the fine particles in the raw water aggregate before the raw water flows into the high-speed filter 28. The floc coarsened by the aggregation is captured by the surface layer of the granular filter medium layer 38 of the high-speed filter 28, so that a so-called surface filtration phenomenon is exhibited, and it is difficult to continue full-layer filtration, which is the original purpose of the high-speed filter 28. It becomes. For this reason, the flow resistance of the granular filter medium layer 38 is increased, and unstable operation such as the frequency of backwashing of the filter medium layer is increased.
[0014]
As described above, feedforward control based on the turbidity of raw water is effective for controlling the amount of the polymer flocculant to be added. A turbidity meter for detecting the turbidity of the treated water is installed in the pipe line 40, and based on the turbidity of the treated water detected by the turbidity meter, the polymer flocculant is added to the raw water flowing into the high-speed filter 28. It is also conceivable to feedback control the amount of addition. However, this method is effective for preventing a situation in which the water quality is deteriorated due to an insufficient amount of the polymer flocculant, but for preventing unstable operation when the amount of the polymer coagulant is excessive. Does not work effectively. It is also conceivable that the control responsiveness is reduced by a time lag due to the passage time of the raw water in the filter medium layer. On the other hand, according to the feedforward control based on the turbidity of the raw water according to the present invention, the amount of the polymer flocculant added can be controlled to an appropriate amount without causing a time lag according to the turbidity of the raw water. This can avoid both deterioration of water quality due to turbidity and unstable operation due to excess. If the feedback control of the amount of the polymer flocculant added based on the turbidity of the treated water is supplementarily combined with the feedforward control described above, finer control becomes possible, and the reliability of the high-speed filter is improved. The performance is improved.
[0015]
In the description of the above embodiment, the polymer flocculant from the flocculant adding means 32 is injected into the raw water in the pipe 26, and the polymer flocculant and the raw water are mixed by the line mixer 36. The case where it is made to flow into was shown. However, the mixing means of the polymer flocculant and the raw water according to the present invention is not limited to this, and a mixing tank is disposed in the middle of the pipe 26, and the polymer flocculant is injected into the raw water flowing into the mixing tank. It may be configured to mix and stir. Further, the turbidity meter of the raw water need not be provided in the middle of the pipe 26. For example, the turbidity of the supernatant water in the settling tank 15 is detected, and the detection result is input to the controller 34 as the turbidity of the raw water. Is also good.
[0016]
【The invention's effect】
According to the present invention, the turbidity of the raw water after the precipitation treatment is detected by a turbidity sensor, and a predetermined amount of a polymer flocculant is added to the raw water according to the detection result. Even when the amount or the particle size distribution of the fine particles fluctuates, a rapid increase in filtration resistance in a high-speed filter or deterioration of the quality of filtered water is hardly caused, and stable operation can be maintained.
[Brief description of the drawings]
FIG. 1 is an apparatus system diagram showing an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between raw water turbidity and the amount of coagulant added.
[Explanation of symbols]
10 Coagulation / sedimentation treatment equipment 26 (supply of raw water) Pipe 28 High-speed filter 30 Turbidity meter 32 Polymer addition means 34 Controller 36 Line mixer 38 Granular filter medium Layer 40 ... (Discharge of treated water) Pipe line

Claims (3)

In a high-speed filtration method of passing raw water after the precipitation treatment through a granular filter medium layer and filtering and separating fine particles contained in the raw water, the turbidity of the raw water is detected by a turbidity sensor, and the raw water is filtered in accordance with the detection result. A high-speed filtration method, comprising adding a predetermined amount of a polymer flocculant to the mixture. A turbidity sensor capable of detecting the turbidity of the raw water after the precipitation treatment, a flocculant adding means for adding a polymer flocculant to the raw water, and a flocculant adding means in accordance with the detection value of the turbidity sensor A high-speed filtration device comprising: a control unit for controlling the amount of the polymer flocculant to be mixed; and a granular filter medium layer through which raw water to which the polymer flocculant is added passes. The high-speed filtration device according to claim 2, wherein the control means has a function of correcting the amount of the polymer flocculant added by the flocculant adding means according to the temperature of the raw water.

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