JP2001269690A - Filtering and separating method for sewage water treatment and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtering and separating method for sewage water treatment easy in forming a uniform and dynamic filter layer and capable of obtaining a high filter flux at the time when sewage water, etc., are filtered by using a water permeable filter body and to provide water device therefor. SOLUTION: In the filtering and separating method of the sewage water treatment and its device for obtaining filtered water by immersing the water- permeable filter body in a biological reaction tank through a partition plate and subjecting the sewage water to the dynamic filter, an activated sludge solution is circulated to the water permeable filter body so that the average flow velocity on the surface of the water permeable filter body at normal operation may be not lower than sludge sedimentation velocity to lower than 0.05 m/s. The aeration air flow of the biological reaction tank is varied preferably to control the flow velocity on the surface of the water permeable filter.

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 the solid-liquid separation of activated sludge and the concentration of excess sludge, and to the use of 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 sludge separation of activated sludge must be performed after treatment in order to obtain treated water. Normally, a method is used in which activated sludge is introduced into a sedimentation basin, the sludge is settled by gravity sedimentation, and the supernatant is discharged from the sedimentation basin as treated water. In this case, a sedimentation basin having a sufficient sedimentation area and residence time is required for sedimentation of 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 has deteriorated sedimentation properties such as bulking, the sludge flows out of the sedimentation basin, resulting in deterioration of the quality of treated water. In recent years, a technique of performing solid-liquid separation of activated sludge by membrane separation instead of a sedimentation basin has been used. In this case, a microfiltration membrane or an ultrafiltration membrane is generally used as the solid-liquid separation membrane.

Recently, as a solid-liquid separation method of activated sludge instead of a sedimentation basin, the periphery of a water-permeable sheet such as a nonwoven fabric, which is overlapped with a water-permeable porous material for maintaining an interval in an aeration tank, is sealed. There is known a method of immersing a bag-shaped filter body formed in this way to obtain filtered water at a low head pressure. In this case, clear filtered water is obtained by separating the sludge formed on the surface of the filter by the dynamic filtration layer. In addition, as a method for forming a stable dynamic filtration layer, activated sludge filtration in which the activated sludge flow rate on the surface of the filter is controlled to an average of 0.05 m / s to 0.4 m / s, preferably 0.15 to 0.25 m / s. Although a method is known, in this publication, a filter body surface flow velocity of 0.2 m
/ S, the filtration flux is about 2 m / d and the filtration duration is 2.
5 hours or more.

[0004]

However, the present inventors have conducted detailed experiments on the relationship between the filtration flux of the filter and the surface flow rate, and as a result, have found that the flow rate on the filter body surface is 0.05 to 0.4 m.
/ S, particularly preferably 0.15 to 0.25 m / s
In this case, the sludge flow on the surface of the filter body is severe, and it is difficult to form a uniform dynamic filtration layer of the sludge, and an effective filtration area cannot be obtained. In addition, it was found that the filter body surface was quickly blocked by fine sludge flocs, and the effect of washing with water or water was little. The present invention solves the above-mentioned problems, and in filtering sewage or the like using a water-permeable filter, it is easy to form a uniform dynamic filtration layer, and filtration of sewage treatment in which a high filtration flux is obtained. It is an object to provide a separation method and an apparatus therefor.

[0005]

According to the study of the present inventors, it has been found that the filter body is washed in a biological reaction tank where there is no influence from the formation or rupture of air bubbles due to aeration and a vigorous upward movement of the air bubbles. Immediately after that, a more stable dynamic filtration layer is formed in less than 5 minutes when the surface flow velocity of the filter is equal to or higher than the sludge sedimentation velocity and less than 0.05 m / s, and the filtration flux is 5 m / d or higher for 4 hours. The knowledge that it can be continued was obtained. Furthermore, it was confirmed that the dynamic filtration layer formed on the surface of the filter can be easily peeled off only by the empty washing under the condition where the surface flow velocity is less than the sludge sedimentation velocity to 0.05 m / s. The present invention has been completed based on the results of these studies.

That is, the present invention has solved the above-mentioned problems by the following means. (1) In a filtration separation method of sewage treatment in which a water-permeable filter is immersed in a biological reaction tank through a partition plate to form a dynamic filtration layer and filtrate water is obtained by filtration, the activated sludge mixture is passed through the water-filter. And separating the water so that the average flow velocity on the surface of the water-permeable filter during normal operation is not less than the sludge settling velocity and less than 0.05 m / s. (2) In obtaining filtered water by filtration for forming a dynamic filtration layer with the water-permeable filter, the amount of aeration air in an aeration section where the water-permeable filter is not immersed is changed, and the flow rate on the surface of the water-permeable filter is changed. The filtration and separation method for sewage treatment according to the above (1), wherein the method is controlled. (3) A filtration / separation device for sewage treatment in which a water-permeable filter is immersed in a biological reactor via a partition plate to obtain filtered water by filtration for forming a dynamic filtration layer, wherein the activated sludge mixture is passed through the water-permeable filter. A filtration apparatus for sewage treatment characterized in that the medium is circulated such that the average flow velocity on the surface of the water-permeable filter during normal operation is not less than the sludge settling velocity and less than 0.05 m / s.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in order to obtain a high filtration flux in a dynamic filtration layer, it is necessary to set the average flow velocity on the surface of the water-permeable filter to be not less than the sludge settling velocity and less than 0.05 m / s. If the water-permeable filter is placed in the aerated biological reaction tank as it is, the liquid is strongly disturbed by the amount of aeration required for the biological reaction to proceed, and it is difficult to obtain such conditions. . for that reason,
By providing a partition plate in the biological reaction tank and separating the aeration unit from the filtration unit, and arranging a water-permeable filter there,
The average flow velocity on the surface of the water-permeable filter can be controlled so as to be within the above-described conditions. The tank may be referred to as a treatment tank, the aeration unit may be referred to as a biological reaction tank, and the filtration unit may be referred to as a filtration tank. At that time, the size and arrangement of the partition plate are appropriately set, and the partition plate is communicated with the aeration section at the upper and lower portions so that the liquid in the biological reaction tank circulates. It is preferable that the distance between the upper end of the partition plate and the liquid surface and the distance between the lower end of the partition plate and the bottom plate be small so that intense water movement caused by aeration in the aeration unit is not transmitted. In addition, the average flow velocity on the surface of the water-permeable filter, including the size and position of the water-permeable filter, can be set to be not less than the sludge settling velocity and less than 0.05 m / s. In addition, various auxiliary members can be used so that the average flow velocity on the surface of the water-permeable filter is not less than the sludge settling velocity and less than 0.05 m / s.

The same effect can be obtained by using any of a nonwoven fabric, a filter cloth, a metal net, and the like as the water-permeable filter. Further, as the filter body shape, any of a flat type, a cylindrical type, and a hollow type can be used, and a plurality of bundles can be used as a module filter body. In carrying out the present invention, the water rises together with the rising air bubbles due to the aeration in the aeration unit, so that the flow of the raised water above the aeration unit passes through the upper end of the partition plate and enters the filtration unit. Will be formed. For this reason, it is common that the activated sludge mixed liquid forms a downward flowing flow in the filtration section.
In that case, the flow differs greatly depending on the distance from the partition plate. Therefore, for the water-permeable filter installed in the filtration section,
In order for the average flow velocity on the surface to be in the above range, it is preferable to provide a rectifying device for averaging the flow of the mixed solution above the filtration unit. It is preferable to use the head pressure as the filtration and separation means of the present invention.

In this case, in the filtration section, a rectifying device is installed at an upper portion thereof, and the activated sludge mixed liquid is introduced into the upper portion of the rectifying device. Therefore, the flow direction of the activated sludge mixed liquid is constant in the filtering section. A dynamic filtration layer of sludge is uniformly formed on a filter provided below the rectifier.
In addition, the sludge sedimentation rate is not less than 0.05
Since the activated sludge mixture flows in a certain direction at a speed of less than m / s, the concentration of sludge flowing on the surface of the filter is almost uniform, and the formation of a dynamic filtration layer is facilitated. In addition, a washing device is installed at the bottom of the filter, and filtration is periodically stopped.
By washing, the sludge layer formed on the surface of the filter can be easily peeled off. This washing method may use one or both of empty washing and water washing. Here, by filtration,
Since a concentrated liquid of activated sludge is formed around the lower part of the water-permeable filter, the concentrated activated sludge is discharged to the outside. In addition, when activated sludge accumulates on the surface of the water-permeable filter, the filtration rate is reduced, and when the air is backwashed, concentrated activated sludge accumulates around the lower part of the water-permeable filter, and is discharged.

[0010] According to the present invention, in the biological reaction tank, by changing the amount of aeration air, it is possible to change the flow velocity of the surface of the filter body immersed on the opposite side (the filtration section) of the partition plate.
It is possible to form a uniform dynamic filtration layer according to the amount of filtered water and sludge properties. Further, stable filtered water quality can be obtained. In the initial stage of filtration from immediately after washing to the formation of a dynamic filtration layer on the surface of the filter, if the air flow rate is low and the flow rate on the surface of the filter is low, the sludge cohesion in the biological reaction tank is good, and the A filtration layer can be easily formed within a short time. as a result,
The dynamic filtration layer is uniform, and the filtration area can be used effectively. During the steady filtration period from immediately after the formation of the dynamic filtration layer to the filtration body surface cleaning, if the flow velocity on the filtration body surface is increased, the amount of sludge attached to the dynamic filtration layer is reduced, and the decrease in the amount of filtered water due to the increase in filtration pressure is small. As a result, the frequency of empty washing on the filter body surface is reduced. Furthermore, even if sludge is excessively attached to the dynamic filtration layer,
The sludge layer on the surface of the filter can be easily and instantaneously peeled off with a small air volume during the empty washing, and the amount of filtered water at the initial stage of filtration can be obtained again.

Further, in the present invention, when the dynamic filtration layer on the surface of the water-permeable filter is thickened and the filtration resistance is increased, the filtration layer is peeled off by air washing. It is preferable to dispose an air diffuser for introducing air below. In some situations, air may be sent from the air diffuser during filtration.

FIG. 1 is a flow sheet showing an example of a method for treating groundwater according to the present invention. As shown in FIG.
The inflow raw water 1 flows into the biological reaction tank 5 and supplies air by the biological reaction tank supply blower 2 to perform aerobic treatment with activated sludge. The biological reaction tank mixture rising by aeration flows downward from above the partition plate 6 into the filtration tank 7 formed by the partition plate 6, while flowing downward on the surface of the nonwoven fabric filter 8.
The water is filtered from the nonwoven fabric filter 8, passes through the water intake pipe 9, and the treated water 10 is obtained. In addition, the nonwoven fabric filter is aerated from the bottom at regular time intervals from the empty washing blower 11 and the surface is washed by an upward flow method. During this time, the filtration is stopped. Excess sludge is periodically discharged out of the system from the sludge pipe 12. Here, at the time of initial filtration from immediately after washing to the formation of the dynamic filtration layer, and at the time of steady filtration from immediately after the formation of the dynamic filtration layer to the washing, the output of the biological reaction tank supply blower 2 is determined by the electromagnetic flow meter 4 to a predetermined aeration air volume. It is controlled by the blower control device 3 so that Thus, the cleaning is performed at regular time intervals, and the output of the blower 2 is adjusted.

[0013]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A treatment method according to the present invention was performed on the groundwater shown in the flow sheet of FIG. Here, at the time of initial filtration from immediately after washing to the formation of the dynamic filtration layer, and at the time of steady filtration from immediately after the formation of the dynamic filtration layer to the washing, the output of the biological reaction tank supply blower 2 is determined by the electromagnetic flow meter 4 to a predetermined aeration air volume. It is controlled by the blower control device 3 so that Washing was performed at regular time intervals in this manner, the output of the blower 2 was adjusted, and long-term filtration was performed for about two months. Table 1 shows the processing conditions of the biological reaction tank. Table 2 shows the treatment conditions of the filter.

[0015]

[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 0.02 m ³ / m.
² / min and 0.1 m ³ / m ² / min. In addition,
The aeration air volume here was the air volume per aeration tank cross-sectional area.
At the time of regular filtration of the filter, the aeration air volume is approximately 0.1 m ³ / m ²
/ Min. During the initial filtration from immediately after the filter body washing to the formation of the dynamic filtration layer, the amount of aerated air was set to about 0.02 m ³ / m ² / min. The aeration tank ML
SS was about 2500 mg / liter, the flocculation of the sludge was good, and the floc was large. Also, the BOD of the entire tank
The load became about 0.15 kg / kg · d. Note that this embodiment is merely an example of the present invention. The effect of the present invention can be further enhanced by using the BOD load in which the inflowing raw water BOD is completely decomposed and removed in the biological reactor. The BOD load of the biological reaction tank excluding the filtration tank in which the filter was immersed was 0.3
It is preferably set to not more than kg / kg / d. In this case, since the BOD of the raw water does not remain at all in the activated sludge mixture flowing into the filtration tank, no biofilm is formed on the surface of the filter, and a stable amount of filtered water can be secured for a long term. In this experiment, activated sludge was used as raw water from the group groundwater.

[0017]

[Table 2]

Table 2 shows the treatment conditions of the filter. In this example, four flat nonwoven fabric filters having an effective filtration area of 0.5 m ² were used as the filter module. As the filter, a polyester non-woven fabric having a thickness of 0.4 mm and an opening of about 20 to 30 μm was used. The basis weight was 60 g / m ² . The average head pressure during filtration is about 10 cm. The period from immediately after the washing to the formation of the dynamic filtration layer, in this case, the period during which the turbidity of the filtered water was 10 degrees or less was defined as the initial filtration. During this time, the aeration air volume of the biological reaction tank was adjusted at about 0.02 m ³ / m ² / min so that the average flow velocity on the surface of the filter was 0.01 m / s. In addition, if the filter body surface flow velocity at the time of initial filtration is more than sludge sedimentation velocity and less than 0.05 m / s, a favorable dynamic filtration layer will be formed. Usually, the sedimentation velocity of the activated sludge is about 0.002 m / s at the maximum, and at the time of initial filtration, the filter body surface flow velocity is 0.002 m / s to 0.01 m / s.
If s, a favorable dynamic filtration layer can be formed within a relatively short time. In this experiment, the surface flow velocity was made as uniform as possible. As a specific method, the air was uniformly supplied from the air diffuser, and the swirling flow was made uniform. The distance between the partition plate and the air diffuser and the distance between the partition plate and the filter were almost the same.

At the time of steady filtration, in this case, from the time immediately after the formation of the dynamic filtration layer to the time when the filter is washed, the air flow rate of the biological reaction tank is set to about 0.1 m so that the average flow velocity on the filter is about 0.03 m / s. ³ / m ² / min. Further, the amount of air washes was set such that the average flow velocity of the filter surface during the air-washing was 0.5 m / s. During the empty washing, the filtration was stopped. The initial filtration time, the steady filtration time, and the emptying (stop) time interval were set to 5 minutes, 12 hours, and 3 minutes, respectively. So about 2
Table 3 shows the average values of raw water and treated water after continuous treatment for months.

[0020]

[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 4.1 degrees, SS
It was 5.0 mg / liter, and the filtered water obtained by the nonwoven fabric filter module was found to be clear.
For COD and S-COD, and for BOD and S-BOD, in raw water, 75 mg / liter and 42 m
g / l, 110 mg / l and 65 mg / l, whereas the treated water has 13.5 m / l
g / liter and 11.0 mg / liter, 5.8 mg / liter
Liter and 5 mg / liter or less, and it was recognized that the quality of the treated water was good.

FIG. 2 shows the time course of the filtration flux in this embodiment. Filtration F about 5 hours after initial filtration
The lux was little reduced, about 5 m / d or more could be maintained, and stable treatment was obtained. FIG. 3 shows the turbidity of the filtered water. After 5 minutes of initial filtration, the turbidity of the filtered water becomes 10 degrees or less,
Thereafter, the temperature was about 5 degrees, no large fluctuation was observed, and a dynamic filtration layer of sludge was formed in a short time, and it was recognized that stable treatment was possible.

COMPARATIVE EXAMPLE 1 In the same processing flow as in Example 1, the same filtration module was used, and when the surface flow rate was set to 0.2 m / s, the progress of the filtration flux and the filtration water turbidity were respectively shown in FIG. Shown in FIG. At a surface flow velocity of 0.2 m / s, the filtration flux was about 7 m / d at the initial stage, whereas about 1 m / d after 30 minutes.
d or less, and a good dynamic filtration layer was not formed on the surface of the filter, and it was recognized that sludge adhered and filtration Flux was reduced. As shown in FIG. 5, the turbidity of the filtered water at the start of the initial filtration was slightly higher than that of the example of about 34 degrees, but was about 10 degrees or less thereafter, and was about the same as that of example 1.

[0024]

According to the present invention, the average flow velocity on the surface of the water-permeable filter provided through the biological reaction tank and the partition plate is set to be not less than the sludge settling velocity and less than 0.05 m / s. It is possible to form a uniform dynamic filtration layer corresponding to the amount of filtered water and the sludge property, and it is possible to perform filtration while maintaining the filtration flux high. Further, stable filtered water quality can be obtained. In addition, by changing the aeration air volume in the biological reaction tank, it is possible to change the flow velocity of the surface of the filter body immersed on the opposite side of the partition plate, and it is possible to respond to the amount of filtered water and the sludge properties, and to obtain a uniform dynamic filtration layer. Can be formed. Further, stable filtered water quality can be obtained.

In the initial filtration up to the formation of the dynamic filtration layer on the surface of the filter, if the amount of aeration air is small and the flow velocity on the surface of the filter is low, the sludge cohesion in the biological reaction tank is good and the dynamic filtration on the surface of the filter is good. Layers can be easily formed in a short time. Also, the dynamic filtration layer is uniform,
The filtration area can be used effectively. Once the dynamic filtration layer is formed, increasing the flow rate on the surface of the filter during the filtration period will reduce the amount of sludge adhering to the dynamic filtration layer,
There is little decrease in filtered water volume due to increased filtration pressure. As a result,
The frequency of empty washing on the filter body surface is reduced. Further, when the sludge is excessively adhered to the dynamic filtration layer, the sludge layer on the surface of the filter can be easily peeled off by empty washing with a small amount of air, and the amount of filtered water at the initial stage of filtration can be obtained again.

[Brief description of the drawings]

FIG. 1 shows a flow sheet of an example of the processing method of the present invention.

FIG. 2 is a graph showing a lapse of time of a filtration flux in Example 1.

FIG. 3 shows a graph of the turbidity of filtered water over time in Example 1.

FIG. 4 is a graph showing the lapse of time of a filtration flux in Comparative Example 1.

FIG. 5 shows a graph of the turbidity of filtered water over time in Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inflow raw water 2 Biological reaction tank supply blower 3 Blower control device 4 Electromagnetic flowmeter 5 Biological reaction tank 6 Partition plate 7 Filtration tank 8 Filtration body 9 Intake pipe 10 Treatment water 11 Empty washing blower 12 Drainage pipe 13 Diffusion pipe 14 Diffusion pipe

Claims (3)

[Claims] 1. A filtration method for sewage treatment in which a water-permeable filter is immersed in a biological reaction tank via a partition plate to obtain filtered water by filtration for forming a dynamic filtration layer. On the other hand, the average flow velocity on the surface of the water-permeable filter during normal operation is not less than the sludge settling velocity to 0.05 m
/ S flow rate of less than / s. 2. When obtaining filtered water by filtration for forming a dynamic filtration layer with the water-permeable filter, varying the amount of aeration air in an aeration section where the water-permeable filter is not immersed, and The method according to claim 1, wherein the flow rate is controlled. 3. A filtration / separation apparatus for sewage treatment in which a permeable filter is immersed in a biological reaction tank through a partition plate to obtain filtered water by filtration for forming a dynamic filtration layer, wherein the activated sludge mixed liquid is permeable. For the filter, the average flow velocity on the surface of the water-permeable filter during normal operation is equal to or higher than the sludge settling velocity to 0.05 m.
Sewage treatment filtration / separation apparatus characterized by being distributed so as to be less than / s.