JP2002035783A - Filtration and separation method and apparatus for biologically treated wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtration and separation method and apparatus for a sludge mixture liquid whereby a uniform dynamic filtration layer is formed in a short time on the surface of a filter, the filtration layer being stable, exhibiting a small decrease in filtration flux with time and always giving clear filtered water. SOLUTION: This method is characterized in that, in a solid-liquid separation method for a sludge mixture liquid wherein a water-permeable filter is used and a dynamic filtration layer of sludge is formed on the surface of the filter to obtain filtered water, a flow straightener is installed at the upper or lower side of the filter to uniformize the flow of the sludge mixture liquid flowing toward the surface of the filter. The speed of descending or ascending of the sludge mixture liquid after passing through the flow straightener is preferably equal to or higher than the sludge settling speed but lower than 0.05 m/s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to sewage treatment by filtration and separation, and more particularly to solid-liquid separation of activated sludge from a mixture of activated sludge generated from biological treatment of sewage and concentration of excess sludge. The present invention relates to a method and an apparatus for solid-liquid separation of activated sludge treated water applicable to the treatment of sewage such as industrial wastewater and domestic wastewater.

[0002]

2. Description of the Related Art Conventionally, in sewage treatment by the activated sludge method,
In order to obtain treated water, solid-liquid separation of the activated sludge from the activated sludge slurry (sludge mixture) from the activated sludge method must be performed. Usually, a method is used in which the activated sludge slurry is introduced into a sedimentation basin, the activated sludge is settled by gravity sedimentation, and the supernatant is discharged from the sedimentation basin as treated water.
In this case, a sedimentation basin that has a sufficient sedimentation area for sedimentation of the activated sludge and can provide a sufficiently long residence time is required, 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 in sedimentation property such as bulking, the sludge flows out of the sedimentation basin, resulting in deterioration of the quality of treated water.

In recent years, instead of a sedimentation basin, a technique of performing solid-liquid separation of activated sludge by membrane separation has been used. In this case, a microfiltration membrane or an ultrafiltration membrane is generally used as a solid-liquid separation membrane. At that time, suction or pressurization by a pump is necessary as filtration and separation means, and usually several tens kPa to
Since the operation is performed at a pressure of several hundred kPa, power consumption by the pump is large, which causes an increase in running cost. In addition, clear treated water without any SS is obtained by membrane separation, while permeation flux (permeation flux) is low, and it is necessary to periodically perform chemical washing in order to prevent membrane contamination.

Recently, as a method of solid-liquid separation of activated sludge instead of a sedimentation basin, a method has been proposed in which a filter made of a breathable sheet such as a nonwoven fabric is immersed in an aeration tank 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 dynamic filtration, a filter for separating activated sludge is immersed in a sludge mixture to form an attached layer of biological sludge on the filter, and the sludge mixture is distributed along the surface of the filter. This is a method of performing solid-liquid separation of a sludge mixture liquid to be filtered. Since the dynamic filtration layer has extremely low filtration resistance, the filtration flux can be obtained ten times higher than the conventional MF membrane and UF membrane, and the required pressure is also reduced to about 1/10. In addition, as a method of forming a dynamic filtration layer, the activated sludge flow rate on the surface of the filtration body is set to an average of 0.05 m / s to 0.4 m / s,
There is an activated sludge filtration method for controlling the flow rate to preferably 0.15 to 0.25 m / s. In the disclosed embodiment of the present filtration method, when the surface velocity of the filter body is 0.2 m / s, the filtration Flu
x is about 2 m / d, and the filtration duration is 2.5 hours or more. On the other hand, the filter body surface flow velocity of the comparative example was 0.03.
At m / s, the filtration flux was initially 4.1 m / d, but dropped to 3.3 m / d after 45 minutes, and the filtration flux was said to decrease in a short time.

[0005]

SUMMARY OF THE INVENTION The present inventors have proposed a filter F
As a result of a detailed experiment on the relationship between lux and the flow and flow rate of the sludge mixture on the surface of the filter, it was found that fluctuations in the surface flow of the filter adversely affect the filtration flux. That is, in the conventional method, the flow direction of the mixed sludge liquid on the surface of the filter body was not uniform, and it was also confirmed that a turbulent flow was caused locally on the surface. Further, it was also recognized that the surface flow velocity was extremely non-uniform and fluctuated up to about 50% of the average flow velocity. It was also found that when the flow and the flow velocity were unstable, it was difficult to form a uniform dynamic filtration layer on the surface of the filter. For this reason, it was also confirmed that fine sludge particles penetrated into the inside of the filter, which increased the filtration resistance and reduced the filtration flux. In addition, since no dynamic filtration layer was formed, it was also confirmed that it was difficult to obtain clear filtered water.

Further, as a result of examining the relationship between the filter body surface flow rate and the filtration flux, it was found that the flow rate of the filter body surface was 0.05 to 0.05.
0.4 m / s, particularly preferably 0.15 to 0.2
In the case of 5 m / s, the sludge flow on the surface of the filter is intense,
It is difficult to form a uniform dynamic filtration layer of sludge,
It was also confirmed that no effective filtration area could be obtained. In this case, it was also found that the filter body surface was quickly clogged by the fine sludge flocs, and that even if washing with water or washing with water was not effective.

The present invention has been made in view of such a conventional problem, and is directed to a liquid-permeable filter for a sludge mixture obtained by biological treatment of sewage (hereinafter also referred to as “biologically treated sewage”). It is an object of the present invention to provide a method and an apparatus for separating a sludge mixture by filtration, in which a reduction in filtration flux with time is small and a clear filtrate is always obtained. In addition, the present invention provides a filtration using a water-permeable filter, in which a uniform dynamic filtration layer is formed within a short period of time on the surface of the filter, and the formed dynamic filtration layer is stabilized, and the filtration with the passage of time is performed. It is an object of the present invention to obtain a method and an apparatus for filtering and separating a sludge mixed solution, in which a decrease in flux is small and clear water can be always obtained. Heretofore, a technique is known in which a MF film or a UF film is immersed in a liquid to be treated, a rectifier is provided below the MF film or a UF film, and the film surface is uniformly dispersed to obtain a good cleaning effect. The above points are fundamentally different from the present invention.

[0008]

In view of the above-mentioned problems, the present inventors have conducted various studies on a method of always forming a uniform dynamic filtration layer on the surface of a filtration body regardless of the lapse of processing time. And immediately after washing the filter,
The surface flow velocity is more than sludge sedimentation velocity and less than 0.05 m / s, a stable dynamic filtration layer is formed within 5 minutes in a very short time, and the filtration flux can be maintained at 5 m / d or more for 4 hours or more. Obtained. Furthermore, it was confirmed that the dynamic filtration layer formed on the surface of the filter can be easily peeled off only by washing under the condition that the surface flow velocity is less than 0.05 m / s. Moreover, it has been found that such a state is easily obtained when the flow of the sludge mixture is uniform with respect to the surface of the filter. That is, by making the flow direction and the surface flow velocity of the biologically treated sewage constant with respect to the filter body surface, a uniform dynamic filtration layer is formed in a short time on the filter body surface, and the formed dynamic filtration layer is stabilized. Focusing on this fact, it has been found that the above problem can be solved by installing a rectifier at the upper or lower part of the filter. The present invention has been made based on such findings.

The present invention has solved the above-mentioned problems by the following constitution. (1) In a solid-liquid separation method of biologically treated sewage using a water-permeable filter to form a dynamic filtration layer of sludge on the surface of the filter to obtain filtered water, a rectifier is installed above or below the filter, A method for filtering and separating a sludge mixture, wherein the sludge mixture flows on the surface of the filter after passing through the flow straightening device, and the flow of the sludge mixture on the surface of the filter is made uniform. (2) The method for filtering and separating a sludge mixture according to the above (1), wherein a falling or rising speed of the sludge mixture having passed through the rectifier is not less than a sludge settling speed and less than 0.05 m / s.

(3) A solid-liquid separation device for biologically treated sewage, which uses a water-permeable filter to form a dynamic filtration layer of sludge on the surface of the filter to obtain filtered water. A rectifying device arranged, and an intake pipe led out of the treatment tank or the solid-liquid separation tank from the top of the filter body for extracting filtered water with a low suction force due to a low head pressure difference from the filter body. A solid-liquid separation device for a sludge mixture, comprising: (4) The rectifying device is characterized in that the falling or rising speed of the sludge mixture passing therethrough is set to be not less than the sludge settling speed and less than 0.05 m / s.
A solid-liquid separator for a mixed sludge liquid according to the above.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, there is provided a solid-liquid separation method for biologically treated sewage using a water-permeable filter, forming a dynamic filtration layer of sludge on the surface of the filter to obtain filtrate.
If a rectifier is installed on the upper or lower part of the filter, the sludge mixture that has passed through the rectifier can flow in the same direction with respect to the surface of the filter, and fluctuations in flow velocity are small,
It can be fairly uniform. As a result, the flow of sludge on the surface of the filter becomes extremely uniform,
An almost uniform dynamic filtration layer is formed within a short time, and clear filtered water can be obtained. Since the formed dynamic filtration layer is stable, the filtration flux over time
Less decrease.

The rectifying device used in the present invention is provided on the upstream side with respect to the water permeable filter because the sludge mixture flows through the water permeable filter. Specifically, when the water-permeable filter is immersed in the activated sludge tank and filtration is performed, the sludge mixture liquid flows upward from below the water-permeable filter by aeration and passes through the surface of the filter as a rising flow. Therefore, a rectifier is installed below the water-permeable filter. In addition, another filtration tank is provided next to the aeration tank, and when the sludge mixture flows out of the upper part of the aeration tank and flows into the upper part of the filtration tank, the sludge mixture is placed above the water-permeable filter. Since the sludge mixture passes through the surface of the filter as a downward flow, a rectifier is installed above the water-permeable filter. As for the size of the rectifying device, it is preferable that the width thereof correspond to the entire width of the filter body surface so that the sludge mixture liquid flows uniformly over the entire width of the filter body surface.
In addition, as a form of the rectifying device, a rectifying device in which a plurality of rectifying plates are arranged in parallel, a rectifying device provided with a distribution plate in front of the rectifying plates, a grid (rectifying grid), or the like can be used.

The sludge mixture passed through the rectifier flows in a fixed direction at a flow velocity along the filter body surface of not less than 0.05 m / s and less than 0.05 m / s, so that the sludge concentration flowing on the filter body surface is substantially uniform. Yes, the formation of a dynamic filtration layer is facilitated. If a washing device is installed below the filter and the filtration is periodically stopped and the filter is washed, 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. Non-woven fabric, filter cloth,
Similar effects can be obtained by using any of metal nets and the like. 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. The pore size of the water-permeable filter is about 10 μm or more,
400 μm is preferred.

As the sludge to be filtered and separated by the water-permeable filter, any of activated sludge, coagulated sludge, primary sludge and the like can be used. It can also be used for solid-liquid separation of wastewater with high SS, river water, and the like. When used for solid-liquid separation of activated sludge, a method in which activated sludge is supplied from an aeration tank to a filtration / separation tank equipped with a water filter, and filtered, a method in which a filter is directly immersed in an aeration tank and filtered, and aeration The same effect can be obtained by using a method in which the tank is partitioned by a partition plate, divided and communicated with an aeration section and a filtration section, and a water-permeable filter is installed in the filtration section and filtration is performed. As a device, a filtration device for performing each of the above methods can be formed. In this case, it is preferable to appropriately manage the BOD load of the aeration tank so that no BOD remains in the activated sludge mixture. When used for solid-liquid separation of coagulated sludge, filtration may be performed by directly immersing the water-permeable filter in the coagulation tank,
It is preferable that the organic matter in the sewage is agglomerated by the addition of a flocculant, and the agglomerated sludge after good floc formation is introduced into a filtration separation tank provided with a water-permeable filter to be filtered. Further, since the filtration flux becomes more stable as the sludge floc becomes larger, a more stable treatment can be expected by using a mixed sludge to which a polymer is added after the coagulation treatment.

[0015]

The present invention will be described below in more detail with reference to examples. However, the present invention is not limited to only these examples. In all the drawings for describing the embodiments, components having the same function are denoted by the same reference numerals, and their repeated description will be omitted.

Embodiment 1 An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic explanatory view of an apparatus to which a treatment method according to the present invention is applied to a group groundwater. As shown in FIG. 1, the inflow raw water 1 flows into the biological treatment tank 2, and performs aerobic treatment with activated sludge in the biological treatment tank 2. The activated sludge mixture is supplied from the biological reaction tank outlet 3 to the solid-liquid separation tank 5 by the sludge supply pump 4. The activated sludge mixed liquid that has flowed into the solid-liquid separation tank 5 passes through the rectifier 6, flows through the water-permeable filter 7 in a uniform flow, and is separated into solid and liquid by the water-permeable filter 7. The treated water 9 is obtained from the intake pipe 8 of the water-permeable filter 7 with a head pressure difference ΔH. Further, the cleaning of the filter body 7 is periodically stopped by the cleaning device 11 provided below the rectifier 6. The concentrated sludge after the filtration is returned to the biological reaction tank 2 from the concentrated sludge return line 10. The excess sludge is periodically discharged from the sludge discharge line 12 to the outside of the system.

Table 1 shows the processing conditions of the biological treatment tank in Example 1. Table 2 shows the processing conditions of the solid-liquid separation tank provided with the filter. As shown in Table 1, the amount of raw water flowing into the biological reaction tank was 15 m ³ / d, and the amount of sludge returned from the solid-liquid separation tank was 7.5 m ³ / d. Further, the MLSS of the biological treatment tank was set to about 3500 mg / liter. In this case, the BOD load of the entire tank was about 0.10 kg / kg · d.

[0018]

[Table 1]

The BOD is completely decomposed and removed in the biological treatment tank, and the activated sludge mixture flowing into the solid-liquid separation tank has no residual undecomposed BOD. It is possible to suppress the accompanying biological contamination of the filter body surface. As a result, the life of the filter body is prolonged, and a stable amount of filtered water can be secured for a long period of time. In order to obtain the above-described treatment effects, it is preferable that the BOD load of the biological treatment tank is 0.3 kg / kg · d or less. BOD such as anaerobic / aerobic method, digestion and denitrification method
Not only that, but also biological methods for removing N and P can be applied.

Table 2 shows the processing conditions of the solid-liquid separation tank. In this embodiment, the effective area is 0.2 m ² and the effective volume is 0.4 m ³
Was used. At the bottom of the solid-liquid separation tank, a pore size of 10
mm rectifying grid was installed. As the rectifying grating, one having the shape shown in FIG. 5 was used. Material: SUS304 Surface area: 0.2 m ² (width 20 cm × width 100 cm) Height: 40 cm As the inflow-portion perforated plate, one in which 20 holes each having a diameter of 10 mm were uniformly arranged was used. Outlet porous plate has a diameter of 15
mm and holes having a pitch interval of 20 mm were uniformly arranged. Four planar nonwoven fabric filters having an effective area of 1.6 m ² were installed as filter modules as the water-permeable filters immediately above the straightening grid. As a material of the nonwoven fabric, a polyester material having a basis weight of 60 g / m ² , a thickness of 0.4 mm, and a pore diameter of about 50 to 100 μm was used.

The average head pressure during filtration was about 10 cm, and the amount of filtered water was 15 m ³ / d. The flow rate of the activated sludge mixture passed through the rectifying grid was adjusted to about 0.025 by passing through the filter.
The sludge supply amount was controlled so as to be m / s. In addition, the washing of the filter body was performed by air-washing the surface by aeration, and the aeration air flow rate was 50 liter / min. At the time of washing, filtration is stopped, and after washing, filtration is started again.
Processing continued at time intervals of minutes.

[0022]

[Table 2]

FIG. 2 shows the change over time of the filtration flux in Example 1. In a continuous process of about 1500 hours,
The average filtration flux was about 2.3 to 2.5 m / d, and stable processing was obtained.

Comparative Example FIG. 6 shows the course of the average filtration flux when the rectifying grid was not installed under the same operating conditions as in Example 1. The average filtration flux was 2.8 m / d, almost the same as in Example 1, at the start of the treatment. However, the filtration flux gradually decreased with the progress of the treatment, and the filtration flux after 1500 hours.
x became 1/3 of the initial value and decreased to 1 m / d or less. From the above results, it was recognized that the installation of the rectifying grid contributed to the stability of the filtration flux. The turbidity of the filtered water was always 10 degrees or less, and no significant difference from the example was observed. FIG. 3 shows the progress of the filtration turbidity during this period. In the continuous treatment for about 1500 hours, the turbidity of the filtered water was about 3 to 5 degrees, no large fluctuation was observed, the dynamic filtration layer of sludge was formed stably, and good water quality was obtained. . Table 3 shows the average values of raw water and treated water after continuous treatment for about 1500 hours.

[0025]

[Table 3]

Raw water pH 7.1, turbidity 150 degrees, SS
86 mg / liter, whereas treated water has p
H7.6, turbidity was 3.5 degrees, SS was 1 mg / liter or less, and it was recognized that the filtered water obtained by the nonwoven fabric filter was clear. COD and S-COD are 75 mg / L and 42 mg / L for raw water, respectively, whereas 11.5 mg / L and 10.0 mg / L for treated water, BOD and S-BOD, respectively.
Are raw water and 110 mg / liter and 65 mg / liter, respectively.
In the case of treated water, it was 6.3 mg / liter and 5 mg / liter or less, and it was recognized that the treated water quality was good.

Embodiment 2 Another embodiment of the present invention will be described below in detail with reference to the drawings. In FIG. 4, in the same way as in the first embodiment,
The schematic explanatory drawing of the apparatus at the time of immersing a water-permeable filter body directly in an aeration tank is shown. As shown in FIG. 4, the inflow raw water 1 flows into the biological treatment tank 2, and the aeration blower 14 in the biological treatment tank 2.
The aerobic treatment with the activated sludge is performed by aerating the lower air diffuser 13 using a gas. Here, the activated sludge flow in the aeration section rises with the rise of the air bubbles from the aeration of the air diffuser 13 and flows into the flow straightening device 6 through the partition plate 15. The activated sludge flow that has passed through the rectifier 6 is converted into a uniform flow through the water-permeable filter 7.
Circulates in a downward flow over the surface. The activated sludge flow to the surface of the filter 7 is of a cross-flow type.

The filtered water from the water-permeable filter 7 has a head difference Δ
H is obtained as treated water 9 through an intake pipe 8. Also,
The filtering of the filter 7 is periodically stopped by stopping the filtration and aeration from the cleaning blower 11 to the cleaning diffuser 16 provided below the water-permeable filter 7. The processing conditions of the biological treatment tank are as follows:
Same as Example 1. Further, the same water-permeable filter 7 as in Example 1 was used. Table 4 shows the filtration conditions of the water-permeable filter 7.

[0029]

[Table 4]

A continuous treatment was performed under the above conditions for about two months.
The filtration flux during that period averages 2.5 m / d,
The results were almost the same as those shown in FIG. In addition, the turbidity of the treated water was always 5 degrees or less, and the same result as that of FIG. 3 was obtained. Thus, the water-permeable filter 7 is immersed directly in the aeration tank,
Similarly, a good dynamic filtration layer can be obtained stably even if activated sludge that has passed through the rectifier 6 creates a swirling flow through the rectifier 6 and circulates downward on the surface of the filter body 7. Clear filtered water could be obtained.

[0031]

According to the present invention, in a method for solid-liquid separation of biologically treated sewage in which a dynamic filtration layer of sludge is formed on the surface of a water-permeable filter to obtain filtered water, a rectifying device is provided above or below the filter. By installing the sludge mixture, the sludge mixture that has passed through the rectifier can flow in the same direction with respect to the surface of the filter body, and the fluctuation of the flow velocity is small and can be fairly uniform. As a result, the flow of sludge on the surface of the filter becomes extremely uniform, and almost uniform dynamic filtration is formed on the surface of the filter within a short time, so that clear filtered water is obtained. Since the formed dynamic filtration layer is stable, there is little decrease in filtration flux with time. In addition, the present invention applies a rectifier to the dynamic filtration, and is one time less than those using a conventional UF membrane or MF membrane.
A filtration flux almost 0 times is obtained, and the pressure is reduced to nearly 1/10.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a filtration / separation apparatus for wastewater in which a biological treatment tank and a solid-liquid separation tank of the present invention are separately provided.

FIG. 2 shows elapsed time and average filtration Flu of Example 1 of the present invention.
6 is a graph showing a relationship with x.

FIG. 3 is a graph showing a relationship between elapsed time and turbidity of filtered water in Example 1 of the present invention.

FIG. 4 is a schematic explanatory diagram of an apparatus for filtering and separating biologically treated sewage provided in the biological treatment tank of the present invention.

FIG. 5 is a side view of a rectifying grid used in the present invention.

FIG. 6 is a graph showing the relationship between elapsed time and average filtration flux in a comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Inflow raw water 2 Biological treatment tank 3 Biological treatment tank outlet 4 Sludge supply pump 5 Solid-liquid separation tank 6 Rectifier 7 Water-permeable filter 8 Intake pipe 9 Treated water 10 Concentrated sludge return line 11 Cleaning device 12 Sludge line 13 Aeration tube 13 14 Aeration blower 15 Partition plate 16 Air diffuser for cleaning

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuya Hirata 4-2-1 Motofujisawa, Fujisawa-shi, Kanagawa Prefecture Ebara Research Institute, Ltd. (72) Shunsuke Shimizu 4-chome Motofujisawa, Fujisawa-shi, Kanagawa 2-1 Inside Ebara Research Institute, Inc. (72) Inventor Masanori Goto 4-2-1 Motofujisawa, Fujisawa-shi, Kanagawa Prefecture In-house Ebara Research Institute, Inc. (72) Inventor Katsunori Ichiki, Fujisawa-shi, Kanagawa 4-2-1 Fujisawa, Ebara Research Institute, Inc. (72) Inventor Daichi Sakashita 4-2-1, Motofujisawa, Fujisawa-shi, Kanagawa Prefecture F-term in Ebara Research Institute, Inc. 4D006 HA93 KA13 KB22 KC14 KE02Q MA16 PA02 PB08 PC64 4D028 BC11 BC17 BD11 BD17 CA00 CB02 4D059 AA04 AA05 AA06 BE02 BE13 BE51 CB17 EB11

Claims (4)

[Claims] 1. A solid-liquid separation method for biologically treated sewage using a water-permeable filter and forming a dynamic filtration layer of sludge on the surface of the filter to obtain filtered water, wherein a rectifying device is installed above or below the filter. A method for separating and filtering a sludge mixture, wherein the sludge mixture flows on the surface of the filter after passing through the flow straightening device, and the flow of the sludge mixture on the surface of the filter is made uniform. 2. The method for filtering and separating a sludge mixture according to claim 1, wherein the descending or rising speed of the sludge mixture passed through the rectifier is not less than the sludge settling speed and less than 0.05 m / s. 3. A solid-liquid separation device for biologically treated sewage, which uses a water-permeable filter to form a dynamic filtration layer of sludge on the surface of the filter and obtains filtered water, which is disposed above or below the filter. And a water intake pipe drawn out of the treatment tank or the solid-liquid separation tank from the top of the filter body for extracting filtered water with a low suction force by a low head pressure difference from the filter body. A solid-liquid separation device for a sludge mixed solution, characterized in that: 4. The rectifying device according to claim 1, wherein said sludge mixture has a lowering or rising speed of at least 0.05 sludge settling speed.
4. The apparatus for separating solid and liquid sludge mixtures according to claim 3, wherein the apparatus is configured to be less than m / s.