JP2001269513A - Method and apparatus for filtering and separating sewage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for filtering and separating sewage, capable of forming an always uniform dynamic filter layer on the surface of a filter without generating the excessive accumulation of sludge accompanied by the elapse of a treatment time and being affected by fluctuations in the flow of sludge in an aeration tank. SOLUTION: In the method and apparatus for filtering and separating sewage, one or a plurality of cylindrical filters each having a water permeable filter sheet bonded to the surface thereof are immersed and arranged in a treatment tank in which sewage flows and treated water is obtained from an intake pipe provided to the axial center part of each cylindrical filter by head pressure difference while each cylindrical filter is rotated around its axial center. It is preferable to be capable of adjusting the rotational speed and rotary direction of the cylindrical filter in the treatment tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of sewage, and more particularly to solid-liquid separation of activated sludge and concentration of excess sludge, and more particularly to sewage that can be used as organic industrial wastewater or domestic wastewater. The present invention relates to a filtration separation method and apparatus.

[0002]

2. Description of the Related Art Conventionally, in water treatment with activated sludge, solid-liquid separation of activated sludge must be performed in order to obtain treated water. Usually, the activated sludge mixture is introduced into the sedimentation basin,
A method is used in which activated sludge is settled by gravity sedimentation, and a supernatant is discharged from a sedimentation tank as treated water. In this case, a sedimentation basin having a sufficient sedimentation area and residence time is required to sediment the activated sludge, which is a factor of increasing the size of the treatment apparatus and increasing the installation volume. In addition, when the activated sludge deteriorates in sedimentation property such as bulking, the activated sludge flows out of the sedimentation basin, resulting in deterioration of the quality of treated water.

In recent years, means for performing solid-liquid separation of activated sludge by membrane separation has been used instead of a sedimentation basin. In this case, a microfiltration membrane or an ultrafiltration membrane is generally used as the solid-liquid separation membrane. At that time, suction or pressurization by a pump is necessary as a filtration / separation means, and the pressure is usually several tens kPa to several hundred kPa. Therefore, power consumption by the pump is large, which causes an increase in running cost. Also,
On the other hand, clear treated water without any SS can be obtained by membrane separation.
The permeation flux (flux) is low, and it is necessary to periodically perform chemical washing to prevent membrane contamination. Recently, as a method of solid-liquid separation of activated sludge instead of a sedimentation basin, a method of immersing a filter made of a water-permeable sheet such as a nonwoven fabric in an aeration tank to obtain filtered water at a low head pressure is known. In this case, the activated sludge passes through at the very beginning of the filtration with the water-permeable sheet, but with a little filtration, a thin layer of activated sludge is formed on the sheet,
The layer is a filtration layer ("Dynamic filtration layer"
), And the sludge formed on the surface of the filter body is separated by the dynamic filtration layer to obtain clear filtered water.

[0004]

However, when the sludge layer is accumulated in the dynamic filtration layer, the filtration resistance increases, and the amount of filtered water decreases. When the filtration resistance becomes high, it is necessary to frequently perform the operation by empty washing or water washing. Furthermore, since the sludge flow in the aeration tank is not uniform, it is difficult to form a uniform dynamic filtration layer on the surface of the filter, and there is a problem that an effective filtration area cannot be obtained. The present invention utilizes filtration separation by a dynamic filtration layer,
Nevertheless, a filtration method for sewage that can always form a uniform dynamic filtration layer on the surface of the filter without causing excessive accumulation of sludge over time and without being affected by fluctuations in the sludge flow in the aeration tank. And an apparatus.

[0005]

In view of the above-mentioned problems, the present inventors have conducted various studies on means for always forming a uniform dynamic filtration layer on the surface of a filter body regardless of the lapse of processing time. According to the research, in order to form a dynamic filtration layer uniformly on the surface of the filter, the flow of sewage to the surface of the filter was adjusted to an appropriate range, and if the filter layer became too thick, the filter layer was formed. It is necessary to increase the flow of sewage to some extent in order to cause it to separate, but rather than changing the flow of sewage each time, it is configured to rotate the filter body, The present invention has been achieved by noting that the flow of sewage relative to the surface of the filter can be relatively changed by changing the rotation speed. By doing so, it is possible to easily maintain an adhering layer of activated sludge particles as a filtration layer on the surface of the filter cloth of the filter so as to have a thickness suitable for filtering activated sludge.

That is, the present invention has solved the above-mentioned problems by the following means. (1) In a treatment tank into which sewage flows, one or a plurality of cylindrical filters having a water-permeable filter sheet attached to the surface are immersed and arranged, and the shaft is rotated while rotating the cylindrical filter about the axis. A method for filtering and separating sewage, characterized in that treated water is obtained from a central intake pipe with a head pressure difference. (2) The method for filtering and separating sewage according to (1), wherein the rotation speed and the rotation direction of the cylindrical filter are adjusted in the treatment tank. (3) One or a plurality of cylindrical filters having a water-permeable filter sheet attached to the surface, which are immersed and disposed in a treatment tank into which sewage flows, and a rotation for rotating the cylindrical filters about an axis. Means, and a water intake pipe drawn out of the water tank from the center of the axis of the cylindrical filter for extracting filtered water with a low suction force due to a lower head difference than the cylindrical filter. Sewage filtration and separation equipment. (4) The filtration and separation apparatus for sewage according to (3), wherein in the treatment tank, the rotating means is capable of adjusting a rotation speed and a rotation direction of the cylindrical filter.

[0007]

According to the present invention, in a sewage treatment tank, if a cylindrical filter having a water-permeable filter sheet attached to the surface is immersed in the treatment tank, filtered water can be obtained with a small pressure. it can. In this case, if the cylindrical filter is rotated at an appropriate speed, a uniform dynamic filtration layer is formed on the surface of the water-permeable filtration sheet in a short time, and clear filtered water can be obtained. In this case, the filter is preferably cylindrical. Since the formed dynamic filtration layer is formed during rotation, the thickness of the layer is uniform and smooth, so the filtration pressure rise due to the adhesion of sludge is small, and a stable amount of filtered water can be obtained for a relatively long time. It is possible to get. Furthermore, when the adhesion layer of the sludge becomes thicker and the filtration pressure increases, by increasing the rotation speed, the flow velocity on the surface of the water-permeable filtration sheet becomes higher, and the adhered sludge can be easily separated.

[0008] By thus forming a dynamic filtration layer again, it is possible to always obtain clear filtered water.
Depending on the properties of the sludge, if the rotation direction is reversed, the attached sludge can be similarly easily peeled off. As described above, by rotating the cylindrical filter body and periodically adjusting the rotation speed or the rotation direction, it is possible to obtain a stable filtration flux and clear filtered water, and perform empty washing or backwashing. There is the advantage that there is no need to do it at all. In the rotation of the cylindrical filter, it is easy to rotate around the axis of the cylindrical filter when there is only one cylindrical filter. In the case where there are a plurality of filter bodies, the rotation structure becomes complicated to rotate each cylindrical filter body around its axis, so a plurality of cylindrical filter bodies are attached to one support, for example, an annular body. It is easy to rotate the support around its axis.

A non-woven fabric is preferred as the water-permeable filtration sheet used in the present invention. The nonwoven fabric can be used without any limitation as long as it can be generally used for filtering wastewater. The material is preferably made of synthetic resin fiber, for example, polyester fiber is suitably used. Since the water permeability changes depending on the thickness of the fiber, the thickness of the nonwoven fabric and the basis weight, a suitable one is selected. Further, since they are also related to the strength of the nonwoven fabric, those having as high a strength as possible in relation to the filtration pressure are used. When the strength of the nonwoven fabric is not large, it is preferable to use a reinforcing material. The thickness of the non-woven fabric may be, for example, about 0.4 mm,
Low filtration resistance. In some cases, a similar effect can be obtained by using a water-permeable filter such as a filter cloth or a metal net in place of the nonwoven fabric. The diameter of the cylinder, which is the shape of the filter, is appropriately selected. If the length of the cylinder is large, the filtration area can be increased. Further, even if the cylindrical filter is immersed in the treatment tank either vertically or horizontally and rotated, a uniform dynamic filtration layer can be formed and the same effect can be obtained.

[0010] The treatment by filtration and separation according to the present invention will be described with reference to the drawings. FIG. 1 schematically shows an example of filtration and separation of wastewater. As shown in FIG.
Flows into the aeration tank 3, is aerated by the air supply pipe 2,
Perform aerobic treatment with activated sludge. The activated sludge mixture in the aeration tank 3 flows into the filtration tank 6 formed by the partition plate 4,
Filtration is performed by the rotating nonwoven fabric filtration module 7, and the treated water 9 is obtained through an intake pipe 8. In FIG. 1, ΔH
Indicates the head difference at the time of removal of the treated water. In addition, since the activated sludge accumulates in the filtration tank 6, the excess sludge is periodically discharged out of the system through the sludge pipe 10. Here, at the time of filtration of the filtration tank 6, the filtration module 7 is always rotated at a low speed by the stirrer 5. In the filtration operation using a nonwoven fabric, the filtration is temporarily stopped after a predetermined filtration time, the rotation speed of the stirrer 5 is increased, and the sludge layer on the filtration module 7 is separated. Start. Thus, long-term filtration can be performed by adjusting the speed of the stirrer 5 at predetermined time intervals.

[0011]

The present invention will be described below in detail with reference to examples. However, the present invention is not limited to only the following examples.

Example 1 Groundwater (raw water) was subjected to the treatment method shown in FIG. 1, and filtration and separation were performed using the method of the present invention.
Table 3 shows the quality of the treated raw water. In the treatment method shown in FIG. 1, the inflow raw water 1 was flowed into the aeration tank 3 to be aerated, and aerobic treatment with activated sludge was performed. Aeration tank mixed liquid is partition wall 4
Into the filtration tank 6 formed by the above, filtered by the nonwoven fabric filtration module 7, passed through the intake pipe 8, and obtained treated water 9. In the filtration tank 6, the thickened activated sludge settled, and the excess sludge was periodically discharged from the sludge pipe 10 to the outside of the system.
Here, at the time of filtration in the aeration tank, the filtration module 7 is always rotated at a low speed by the stirrer 5. In the filtration operation with non-woven fabric,
After a predetermined filtration time, the filtration is temporarily stopped, and the rotation speed of the stirrer 5 is increased. Then, the stirring speed is again set to the filtration speed, and the filtration is started. Thus, the speed of the stirrer 5 was adjusted at predetermined time intervals, and a long-term filtration of about 2 months was performed.

FIG. 2 shows the shape of the cylindrical module 11 used in this embodiment. (A) is a side view, (b) is a plan view. In this example, three filter modules were used as one filter unit, fixed to the filter housing 12, and the water intake pipes 13 of each module 11 were collectively collected to collect water. However, the present invention is not limited to this, and the same effect can be obtained with any number of filter bodies as long as the filter body housing 12 is a cylinder and the arrangement of the filter body modules 11 is uniform inside. Table 1 shows the processing conditions of the aeration tank in this example. Table 2 shows the processing conditions of the filtration module.

[0014]

[Table 1]

As shown in Table 1, the amount of raw water flowing into the aeration tank is 10 m ³ / d, and the amount of aeration air is about 0.1 m ³ / m.
² / min. The aeration air volume here was the air volume per aeration tank cross-sectional area. The aeration tank MLSS is about 2
It was 500 mg / liter, and the BOD load of the entire tank was about 0.15 kg / kg · d.

[0016]

[Table 2]

Table 2 shows the processing conditions of the filtration module. In this example, a total of 30 cylindrical filter modules having a diameter of 5 cm and a length of 100 cm were used. The nonwoven fabric filtration module 7 used a nonwoven fabric of polyester fiber.
The effective area of the filter is 4.7 m ² . The average head pressure during filtration is about 10 cm. Further, the module rotation speed during filtration was kept constant at 15 rpm. The rotation speed when the filtration was stopped was set to 300 rpm. Processing was continued at intervals of 240 minutes of filtration and 3 minutes of stop. Table 3 shows the average values of the raw water and the treated water after the continuous treatment for about two months.

[0018]

[Table 3]

As shown in Table 3, the pH of the raw water was 7.
1, turbidity 150 degrees, SS86mg / liter, whereas treated water has pH 7.6, turbidity 5.5 degrees, SS
8.6 mg / l, the filtered water obtained by the nonwoven fabric filtration module was found to be clear. Also, CO
Regarding D and S-COD, and BOD and S-BOD, in raw water, 75 mg / L and 42 mg / L and 110 mg / L and 65 mg / L, respectively, whereas in treated water, 15.0 mg / L and 11 mg / L, respectively. 0.0 mg / liter, 7.8 mg / liter, and 5 mg / liter or less, and it was recognized that the quality of the treated water was good.

FIG. 3 shows the progress of the filtration flux in the embodiment. During a continuous treatment period of about 1500 hours, the filtration Flu
x was constant at about 2.2 m / d, and stable processing was obtained. FIG. 4 shows the turbidity progress of the filtered water. During the treatment period, the turbidity of the filtered water was about 3 to 10 degrees, no large fluctuation was observed, and it was recognized that a stable treatment could be performed by the dynamic filtration layer filtration of the sludge.

[0021]

According to the present invention, in a sewage treatment tank,
If the cylindrical filter having the nonwoven fabric attached to the surface is immersed in a treatment tank, filtered water can be obtained with a small pressure. In this case, if the cylindrical filter is rotated at an appropriate speed, a uniform dynamic filtration layer is formed on the surface of the nonwoven fabric in a short time, and clear filtered water can be obtained. The formed dynamic filtration layer has a small increase in filtration pressure due to adhesion of sludge, and can obtain a stable amount of filtered water for a relatively long time. Furthermore, when the adhesion layer of sludge becomes thicker and the filtration pressure increases, by increasing the rotation speed, the flow velocity on the surface of the nonwoven fabric increases, and it is possible to easily remove the adhered sludge. A dynamic filtration layer is formed again, and it is possible to always obtain clear filtered water. Depending on the properties of the sludge, if the rotation direction is reversed, the attached sludge can be similarly easily peeled off. As described above, it is possible to obtain a stable filtration flow rate and clear filtration by rotating the cylindrical filter body and periodically adjusting the rotation speed or the rotation direction. There is no at all.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a filtration / separation apparatus for wastewater of the present invention.

2A and 2B are explanatory views of the shape of a cylindrical module according to the present invention, wherein FIG. 2A is a side view and FIG. 2B is a plan view.

FIG. 3 is a graph showing a relationship between elapsed time and filtration flux according to one embodiment of the present invention.

FIG. 4 is a graph showing a relationship between elapsed time and turbidity of filtered water in one example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inflow raw water 2 Air supply pipe 3 Aeration tank 4 Partition wall 5 Stirrer 6 Filtration tank 7 Filtration module 8 Intake pipe 9 Treated water 10 Drainage pipe 11 Cylindrical filtration module 12 Filtration body hosing 13 Intake pipe 14 Treated water

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D026 BA03 BB01 BC23 BC26 BC29 BC31 4D059 AA03 BA01 BE11 BE13 BE14 BE21 CA22

Claims (4)

[Claims] In a treatment tank into which sewage flows, one or a plurality of cylindrical filters having a water-permeable filtration sheet attached to the surface are immersed and arranged, and the cylindrical filter is rotated around an axis. And a method for filtering and separating sewage, wherein treated water is obtained from a water intake pipe at the center of the shaft with a head pressure difference. 2. The method for filtering and separating wastewater according to claim 1, wherein the rotation speed and the rotation direction of the cylindrical filter are adjusted in the treatment tank. 3. One or a plurality of cylindrical filters having a water-permeable filter sheet attached to the surface, immersed and disposed in a treatment tank into which sewage flows, and rotating about the cylindrical filters. A rotating means for causing the filter to have a water head drawn out of the water tank from the center of the shaft of the cylindrical filter for extracting filtered water with a low suction force due to a lower head difference than the cylindrical filter. A filtration / separation device for sewage. 4. The filtration / separation apparatus for sewage water according to claim 3, wherein the rotating means is capable of adjusting a rotation speed and a rotation direction of the cylindrical filter in the treatment tank.