JP2004130164A - Method and apparatus for filtering aqueous suspension - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filtering method for filtering suspended particles in raw water of every kind such as sewage or the like at a high speed by a simple and compact filter apparatus while markedly reducing a rise in loss head, and the filter apparatus using the same. <P>SOLUTION: A sucked water stream forming pipe is rotatably provided in close vicinity to the surface layer of the filter medium packed bed provided in the filter apparatus to form sucked water streams while performing the filtering treatment of water to be treated and rotating the sucked water stream forming pipe, and the filtered matter on the surface layer of the filter medium packed bed is excluded while discharging the washing wastewater containing the excluded filtered matter. It is preferable to make the rotary speed of the sucked water stream forming pipe variable and to use a floatable filter medium as the filter medium. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for high-speed filtration of suspended water (hereinafter also referred to as “raw water”) containing suspended particles such as sewage and industrial effluent, and relates to a technique capable of high-speed filtration of suspended particles in raw water with a low head loss. .
Further, the present invention is an innovation which is particularly suitable as a high-speed solid-liquid separation technology for rainwater overflow (abbreviated as CSO) of a combined sewer system containing organic suspended particles or sewage flowing into a sewage treatment facility. Technology.
[0002]
[Prior art]
Recently, the pollution load of public water bodies due to rainfall overflow (CSO) in a combined sewer has become a major problem. There is a long-awaited demand for a new technology that can separate solid-liquid CSOs with as compact equipment as possible.
Conventionally, as a technique for filtering and removing SS from a suspension, deep bed filtration using granular materials such as sand and anthracite as a filter material is known, but organic SS such as sewage is removed at a large filtration rate. Attempts to remove it were severely clogged and impractical.
[0003]
Filtration methods using various granular solids (eg, granular plastic) other than anthracite and sand as filter media are also being studied. However, if the filter media size is increased to reduce clogging, the SS removal rate will deteriorate. (Patent Documents 1 and 2). In particular, since organic SS contained in sewage and the like has a strong adhesive force, a technology capable of satisfying the conflicting demands of high sewage removal rate, low clogging, and small increase in filtration resistance for such sewage is practical. Had not been converted.
[0004]
[Patent Document 1]
JP-A-4-187294 [0005]
[Patent Document 2]
JP-A-4-363105
[Problems to be solved by the invention]
The present invention provides a new technology that enables high-speed filtration of suspended particles in various raw waters such as sewage by using a simple and compact device while significantly reducing the rise in the head loss.
[0007]
[Means for Solving the Problems]
The present invention has solved the above problems by the following means.
(1) A suction water flow generating tube is rotatably provided near the surface of the filter medium packed layer provided in the filtration device, and suction is performed while rotating the suction water flow generating tube while filtering the water to be treated. A method for filtering suspended water, comprising: causing a water flow to remove a filtrate on a surface layer of a filter medium-packed layer; and discharging washing wastewater containing the removed filtrate.
(2) A filter medium filling layer is provided in the filtration device, and a suction water flow generating pipe having a suction port is rotatably provided near the surface of the packing layer, and the suction is performed while performing the filtration of the water to be treated. A device for filtering suspended water, wherein a suction water flow is generated while rotating a water flow generating tube, and washing wastewater containing a filtrate on the surface of the packed bed is discharged from the suction port.
(3) The filtration device according to (2), wherein a rotation speed of the suction water flow generating tube is variable.
(4) The filtering device according to (2) or (3), wherein the filter medium is a floating filter medium.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a configuration diagram showing one embodiment of the high-speed filtration device of the present invention. In the figure, 1 is a filtration device, 2 is raw water, 3 is raw water inflow section, 4 is filter medium packed layer, 5 is filtered water, 6 is filtered water outflow section, 7 is suction water flow generating pipe, 8 is slit, and 9 is motor Reference numeral 10 is a suction pump, and 12 and 14 are nets.
The high-speed filtration device of the present invention shown in FIG. 1 has, for example, a specific gravity close to 1 (or floats on its own or rises above) inside a filtration tower provided with a raw water inflow portion at a lower portion and a filtered water outflow portion at an upper portion. The specific gravity pushed up by the countercurrent is preferably about 0.9 to 1.1.) Plastic (such as polypropylene) granules are filled. The shape of the granular material is arbitrary, and platelets, star-shaped particles, hollow cylinders, and the like are preferable because the filling porosity increases. A filter media particle size of about 5 to 20 mm is suitable. The thickness of the filling layer is preferably about 1 to 2 m.
[0009]
The raw water or raw water to which a flocculant (a polymer flocculant alone or a combination of an inorganic flocculant and a polymer flocculant) has been added is flown upward or downward in the raw water. Are trapped in the voids of the filler and removed by filtration. The example shown in FIG. 1 is for upflow filtration. In the present invention, the filtration can be performed by downward filtration.
In a conventional filtration device, if the operation of passing raw water through such a packed bed is continued, SS is most caught in the surface layer A of the packed bed. SS trapping progresses to the whole layer, and finally SS trapping capacity reaches the limit, SS of treated water increases rapidly or filtration resistance reaches a predetermined value. At this point, the inflow of raw water was stopped and the filter medium was washed.
[0010]
On the other hand, in the present invention, a suction water flow generating pipe (simply referred to as “suction water flow pipe”) having a suction port in the radial direction of the tank is rotatably provided near the horizontal plane of the surface layer portion A of the packed bed. The suction water flow generating pipe is provided at a portion close to the packed bed, and a suction pump generates a suction water flow having a flow velocity of several meters / second at the suction port. The shape of the suction port can take various shapes, but is preferably a slit portion because it can widely contact the surface layer portion.
The slit width is made smaller than the filter medium particle size so that the filter medium does not flow into the suction pipe. There is a method of setting a net in the slit, but it is not recommended because the net is easily clogged. A porous pipe may be used instead of the slit. When the suction water flow generating tube is provided at the center of the packed bed, the length of the slit is preferably the diameter or radius of the packed bed.
The suction water flow generating tube can be rotated by a motor, and the rotation speed is variable. An appropriate rotation speed is several to several tens of RPM.
[0011]
An operation mode of such a filtration device of the present invention in the case of upward flow filtration will be described.
The raw water 2 flows into the filtration device 1 in an upward flow. The raw water SS is mainly captured in the surface layer portion A below the filter medium packed layer 4, and the amount of trapped SS in the surface layer portion A increases, and the filtration resistance increases. However, if the suction pump 10 is operated intermittently while the raw water 2 is being filtered, a strong suction water flow is generated in the slit 8 of the suction water flow generation pipe 7.
[0012]
As a result, the filter medium at the surface layer portion of the packed bed 4 has a small specific gravity, so it is easily pulled downward and developed, and the SS trapped in the packed bed 4 is also sucked at the same time. The water is sucked, and the surface washing water 11 is discharged out of the tank via the pipe. The operation of the suction pump 10 is usually performed intermittently, but may be always performed.
By such a mechanism, in the present invention, most of the SS trapped in the surface layer A is discharged out of the system during the filtration step, and the amount of SS trapped in the surface layer A hardly increases. The rise in filtration resistance is very small. As a result, the increase in filtration resistance of the entire packed bed is reduced, and long-time filtration can be performed even at a high filtration rate and a high raw water SS concentration.
[0013]
However, if filtration is continued for a long time, the amount of trapped SS at a higher position (deeper position) than the surface layer increases, so that the filtration resistance gradually increases and reaches a predetermined value. Stop the filtration and wash the entire packed bed.
The filter medium washing of the entire packed bed 4 is performed, for example, as follows. That is, when the suction water flow pipe 7 is rotated at several tens of RPM while diffusing the air 17 from the air diffusion member, for example, the air diffusion device 13 for several minutes, the suction water flow pipe 7 shows an action of a stirring blade, and the filter medium is strongly strengthened. Because of the disturbance, the turbidity adhering to the filter medium is peeled off. Thereafter, the water in the tank is quickly drained from the washing drainage pipe 16 and taken out as the washing drainage 15. As a result, the suspended matter trapped in the filler is discharged, and the packed layer 4 is cleaned.
Since the filter medium packed bed is easily washed by the mechanism as described above, the raw water is supplied again and the upward flow filtration is started.
[0014]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples. The scope of the present invention is not limited to these.
[0015]
Example 1 (Filtration test of combined sewage sewer stormwater overflow)
A sewage filtration test was performed using the apparatus of the present invention shown in FIG. The filtration tank is a layer (filled layer porosity of 94%) in which a cylindrical container having an inner diameter of 30 cm is filled with a polypropylene square filter medium (size: 4 × 4 × 2 mm) having a specific gravity of 0.91 to a thickness of 2 m. Sewage having an SS of 130 mg / liter was passed through the filtration tank at a filtration speed of 1440 m / d.
The suction water flow pipe has a pipe diameter of 15 mm, a slit length of 15 cm, and a slit width of 1.8 mm. The slit portion was arranged so as to be located 25 mm from the lower surface of the filling layer. The flow rate of the suction water flow at the slit was 0.5 m / sec. The rotation speed is 10 rpm. The suction water flow was generated by operating a suction pump installed outside the tank. While filtering the raw water at a filtration speed of 1440 m / d, a suction water flow was generated at intervals of 5 minutes for 1 minute to wash the surface layer portion.
[0016]
As a result of performing such an operation, the filtration resistance was 0.6 m head even after the elapse of 2:00, and the time required for the filtration resistance to rise to the 2 m head was 7:00 and 25 minutes later. The average value of the filtered water SS was 26 mg / liter.
[0017]
Comparative Example 1
As a comparative test, ordinary upward flow filtration was performed using the same filter medium packed bed as in Example 1 without using a suction water flow generating tube.
Water was passed through the sewage (130 mg / liter) in an upward flow at a filtration speed of 1440 m / d. As a result, the average value of the filtered water SS up to 2 hours after the start of the operation was 23 mg / liter, and the filtration resistance increased to 2 m head after 2 hours and 20 minutes, and the filtered water SS deteriorated to 85 mg / liter.
[0018]
【The invention's effect】
According to the present invention, the following effects can be obtained.
(1) Since the surface layer portion of the packed bed where clogging progresses fastest can be effectively washed while filtering the raw water, the rate of increase of the filtration resistance of the entire packed bed is much smaller than that of the conventional apparatus. Since the frequency of “washing the entire packed bed by stopping the inflow of raw water” is reduced, the operation rate of the filtration device is greatly improved.
(2) Even if the filtration speed is very high, the increase in filtration resistance is small, so that raw water having a large amount of SS such as sewage CSO can be filtered at a high speed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing one embodiment of a high-speed filtration device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Filtration apparatus 2 Raw water 3 Raw water inflow part 4 Filter material packed bed 5 Filtration water 6 Filtration water outflow part network 7 Suction water flow generating tube motor 8 Slit 9 Motor 10 Suction pump 11 Surface part washing drainage 12 Net 13 Air diffuser 14 Net 15 Cleaning Drainage 16 Cleaning drainage pipe 17 Air A Surface layer

Claims (4)

A suction water flow generating pipe is rotatably provided in the vicinity of the surface of the filter medium packed layer provided in the filtration device, and a suction water flow is generated while rotating the suction water flow generating pipe while filtering the water to be treated. A method of filtering suspended water, comprising: removing a filtrate on the surface of the filter medium-filled layer; and discharging washing wastewater containing the removed filtrate. In the filtration device, a filter medium-filled layer is provided, and a suction water flow generating pipe having a suction port is rotatably provided near the surface of the packed layer, and the suction water flow generating pipe is provided while performing a filtration treatment of the water to be treated. A suspension water filtration device characterized by causing a suction water flow while rotating the water, and discharging washing wastewater containing a filtrate on the surface of the packed layer from the suction port. 3. The filtering device according to claim 2, wherein a rotation speed of the suction water flow generating tube is variable. The filtering device according to claim 2 or 3, wherein the filter medium is a floating filter medium.

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