JP3784002B2 - Bulking suppression type continuous activated sludge process - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a continuous activated sludge method for biologically treating organic wastewater, and more particularly to a continuous activated sludge method that does not cause sludge sedimentation inhibition (bulking) due to growth of filamentous bacteria.
[0002]
[Prior art]
At present, the continuous activated sludge method is most widely used as a method for treating organic wastewater such as industrial wastewater and domestic wastewater. In this method, as shown in FIG. 1, waste water (raw water 1) adjusted to a constant flow rate by a flow rate adjusting tank 10 is continuously introduced into an aeration tank 20 and subjected to an aeration process with activated sludge. 30 separates sludge and treated water. In this case, the precipitated sludge is usually returned to the aeration tank. However, in order to keep the sludge concentration in the aeration tank constant, a part of the precipitated sludge is withdrawn and disposed of appropriately.
[0003]
As described above, the continuous activated sludge method is a biological treatment method that is most often adopted in domestic wastewater treatment facilities such as sewage treatment plants and industrial wastewater treatment facilities. There has been a major drawback that a phenomenon called bulking is likely to occur. When the above bulking occurs, sludge separation in the sedimentation tank becomes insufficient, and sludge is mixed into the treated water, so that the quality of the treated water is remarkably deteriorated.
[0004]
Conventionally, in order to maintain the quality of treated water within an acceptable range, when bulking occurs, it has been practiced to introduce drugs that inhibit the growth of filamentous bacteria such as enzymes and microbial preparations. However, this method is symptomatic and cannot be a radical solution, and has the disadvantage of increasing the cost of the drug. Therefore, from the standpoint of preventing the growth of filamentous bacteria by increasing the initial BOD concentration and decreasing the BOD concentration sequentially, the extrusion flow method makes the aeration tank longer in the shape of a flow path rather than a complete mixing method. However, due to the strong stirring by aeration and the BOD adsorption rate of sludge being fast, the actual apparatus cannot obtain a sufficient concentration change, and to solve the bulking Not reached.
[0005]
Also, for the purpose of obtaining the same effect as the above-described extrusion flow method, an attempt was made to divide the aeration tank into a number of series tanks by dividing it into many partitions, but in order to obtain a sufficient BOD concentration change, Has to be divided into many tanks and has proved unrealistic. Therefore, the aeration tank is divided into a plurality of tanks, a membrane module is incorporated in the final aeration tank instead of the precipitation tank, and the liquid filtered through the membrane is drained as treated water. In this case, since a UF or MF membrane is used as the membrane, an extremely clear treated water can be obtained regardless of the presence or absence of filamentous bacteria. However, regular cleaning is required to clog the membrane. Further, since membrane replacement is required, there is a disadvantage that not only the initial cost but also the running cost is increased.
[0006]
Therefore, usually designed BOD volume load of a continuous activated sludge method is kept below ^3-days 0.5 kg / m, in the industrial wastewater treatment facilities, exceed the design load due to an increase in production volume, bulking You may be bothered by. Such a drawback is that an adsorption tank having a small volume consisting of one tank to several tanks is provided in the front stage of a normal aeration tank so that BOD concentration is sufficiently high and BOD can be sufficiently adsorbed by sludge. However, the quality of the treated water may be slightly deteriorated. In such a case, SS (floating solids) increased, and the SS concentration sometimes exceeded 100 mg / liter.
[0007]
By the way, in the case of organic wastewater treatment employing the conventional activated sludge method, the sludge squeezer in the sedimentation tank is usually designed to operate at the lowest possible speed so as not to disturb the sediment. For example, according to “Sewage Sewerage Facility Planning and Design Guidelines and Explanation” (edited by the Japan Sewerage Association), “The speed of the sludge collector in the final sedimentation basin (= sedimentation tank) Smaller than the pond, preferably with a variable speed function, preferably 30cm for the chain flight type (type in which the scraping plate moves in one direction with the chain). The outer peripheral speed of the plate should not exceed 2.5 m / min. "
[0008]
Thus, in the case of a general activated sludge method, since the sedimentation compaction property of sludge is not so good (SVI is around 200), it was necessary to operate the scraper so as not to stir as much as possible. The SVI is an index indicating the sedimentation / consolidation property of sludge and is obtained from the following equation.
SVI = SV ₃₀ / MLSS × 10,000 (ml / g)
Here, SV ₃₀ is the ratio (%) of the volume that sludge settled and concentrated after taking the sludge mixed liquid in a graduated cylinder and allowing it to stand for 30 minutes. MLSS is the solid content concentration (mg / l) in the sludge mixed solution, and the smaller the SVI, the better the sludge settling / consolidation. The normal value in the continuous method is about 100 to 200, but may be 100 or less in the batch method.
[0009]
On the other hand, in the case of the above-described bulking-suppressed continuous activated sludge method provided with an adsorption tank, the sedimentation / consolidation property of the sludge is improved (around 50 when the SVI is low), so the scraper is slow. And the sludge becomes consolidated at the bottom of the sedimentation tank, and the fluidity is almost lost. Accordingly, it has been found that it is effective to prevent the increase in the SS concentration as described above by appropriately stirring with a scraper to such an extent that the sludge does not become a compacted state.
Accordingly, an object of the present invention is to provide a continuous activated sludge method capable of suppressing the occurrence of bulking and the generation of suspended solids in treated water.
[0010]
[Means for Solving the Problems]
The above object of the present invention is a continuous activated sludge process for biologically treating organic wastewater, comprising an aeration tank, an adsorption tank provided in the front stage of the aeration tank, and a sedimentation tank, The adsorption tank comprises at least one aeration tank having a small capacity of 1/200 to 1/15 of the total aeration tank volume, and the peripheral speed of the precipitation tank exceeds 2.5 m / min, and 8 m / min. and wherein the agitation to Turkey at a rotational speed equal to or less than was achieved by bulking inhibitory continuous activated sludge method.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a conceptual diagram of a facility for carrying out the bulking-suppressing continuous activated sludge method of the present invention.
Reference numeral 7 in the figure is an adsorption tank provided in the front stage of the aeration tank 20 in the present invention. In the case of this figure, a three-tank configuration having the aeration apparatus 3 is provided by an internal partition. Yes. Reference numeral 8 denotes a stirring blade provided in the sedimentation tank 30. A known contact material 21 can be appropriately disposed in the aeration tank 20. The aeration tank 20 may have a plurality of tanks, and sludge may be returned from the final aeration tank to the adsorption tank. In addition, when the aeration tank 20 has a plurality of configurations, the contact material 21 may be disposed in all the tanks, or the contact material may be disposed in only some of the tanks. The contact material 21 can be appropriately selected and used from known contact materials such as a string-like contact material, a corrugated contact material, and a floating carrier.
[0012]
In order to further enhance the effect of the adsorption tank 7 in the present invention, the adsorption tank has a supernatant BOD concentration of 30 mg / l or more and a BOD adsorption amount of 50% or more at the time of volume loading assumed at the time of design. It is preferable to design so that If the supernatant BOD in the adsorption tank is less than 30 mg / l, the growth of filamentous bacteria in the adsorption tank may not be sufficiently suppressed, and even if the supernatant BOD is 30 mg / l or more, the adsorption If the BOD adsorption rate up to the tank is less than 50%, the growth of filamentous bacteria in the subsequent aeration tank may not be sufficiently suppressed. When the adsorption tank has a multi-stage structure composed of a plurality of tanks or a multi-tank structure separated by internal partition walls, the supernatant BOD concentration is 30 mg / l or more in any of the tanks. And the total BOD adsorption rate until then may be 50% or more. In this case, a situation occurs in which the above conditions are satisfied before the final tank of the installed adsorption tank.
[0013]
The adsorption tank 7 in the present invention is an extremely small capacity aeration tank, and its structure is basically the same as that of a conventional aeration tank. However, since the inside of the adsorption tank 7 is always in a high load state, the contact material. Preferably, 21 is not present. The volume of the adsorption tank 7 in the present invention is required to be 1/15 to 1/200 of the total aeration tank volume, and particularly preferably about 1/30 to 1/100. The adsorption tank 7 can be configured as a single tank or a multi-tank structure as shown in FIG. 2, but there are factors such as the BOD concentration of raw water, the sludge concentration, the nature of the sludge, and the temperature that cannot be avoided. In order to disperse these fluctuation factors and maintain the conditions as the adsorption tank, it is preferable that the adsorption tank 7 has a series multi-tank configuration, and it is particularly preferable to use 2 to 4 tanks in terms of design. In this case, the volume of the first adsorption tank (most upstream tank) is preferably 1/30 to 1/100 of the total aeration tank volume.
[0014]
The greatest feature of the present invention is that the settling tank 30 is stirred at a normal speed or higher. In the case of the rotary type, stirring is performed so that the outer peripheral speed of the stirring blade 8 exceeds 2.5 m / min and is 8 m / min or less .
In the case of the bulking-suppressing continuous activated sludge method having the adsorption tank 7 as in the present invention, if the agitation is performed at low speed, the sludge becomes compacted at the bottom of the sedimentation tank, and the fluidity is almost lost. The SS concentration is increased, but the SS concentration can be prevented from increasing by carrying out stirring more than usual as in the present invention.
[0015]
The whole amount of the raw water and the returned sludge 4 from the settling tank 30 may be put into the adsorption tank 7, but it is not impossible to put a part into the aeration tank. The shape of the aeration tank in the present invention can be appropriately selected from known ones such as a complete mixing type, an extrusion flow type, and a deep layer type. The aeration tank does not have to be a single tank, and may be composed of a plurality of tanks as described above. As described above, a contact material for attaching sludge is installed in the aeration tank. Also good.
In the present invention, in order to perform biological denitrification and dephosphorization, known means can be appropriately combined depending on the purpose, such as combining an anaerobic tank.
[0016]
【The invention's effect】
In the continuous activated sludge method of the present invention, bulking hardly occurs because the growth of filamentous bacteria is suppressed. Therefore, since the design volume load can be increased as compared with the conventional case, not only the operation management becomes easy, but also the processing capacity is improved. For this reason, if the quality of the treated wastewater is the same as before, the installation area of the treatment facility can naturally be reduced. Further, since the occurrence of SS is small and the quality of treated water is not deteriorated, the present invention is extremely significant.
[0017]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in full detail, this invention is not limited by this. In addition, as a processing apparatus, the thing similar to the processing facility shown in FIG. 2 was used. However, no contact material was used. The adsorption tank is 0.25 liter x 2 tanks, the aeration tank is 9.5 liters, the precipitation tank is 1.3 liters, the inner diameter of the precipitation tank is 95 mm, the stirrer is a flat plate with a width of 85 mm and a height of 15 mm (stirring blade) ) Was rotated by an upper motor through a shaft (the rotation radius of the stirring blade was 42.5 mm). Two sets of the same structure were used for comparison.
[0018]
Examples and Comparative Examples When the rotation speed of the stirring blade is “A: always 2.5 rpm”, “B: 5 rpm (0 to 13 days), 10 rpm (13 to 21 days), 20 rpm (21 to 35) Day)) ”.
The outer peripheral speed of the stirring blade at 2.5 rpm is 0.67 m / min, 1.3 m / min at 5 rpm, 2.7 m / min at 10 rpm, and 5.3 m / min at 20 rpm.
[0019]
As raw water, artificial waste water (BOD 100,000 mg / liter) was diluted with tap water so as to have a predetermined BOD concentration and treated at 25 to 28 ° C. so that the aeration tank residence time was 24 hours. The artificial drainage was prepared by adding and dissolving the following reagents in 1 liter of distilled water, and stored refrigerated until use.
110g glucose
Polypeptone 40g
KH ₂ PO ₄ 4.8 g
NaCl 3.2g
MgSO ₄ · 7H ₂ O 1.0g
[0020]
The concentration of the raw water was 600 mg / liter during the 0-28th day and 800 mg / liter during the 28-35th day. Moreover, as seed sludge, sludge trained by the activated sludge method using the raw water was used. Further, oxygen was supplied by aeration to the adsorption tank and the aeration tank so that the dissolved oxygen concentration in each tank was 0.2 mg / liter or more. In addition, the produced | generated sludge was suitably extracted so that MLSS in an aeration tank may not exceed 4,500 mg / liter.
[0021]
The change in the SS concentration of the treated water after the treatment as described above is as shown in FIG.
In the case of A with a constant stirring rotation speed of 2.5 rpm, when the raw water BOD concentration was 600 mg / liter (BOD volumetric load 0.6 kg / m ³ · day), it was somewhat cloudy. When the raw water BOD concentration was 800 mg / liter (BOD volumetric load 0.8 kg / m ³ · day) (after the 28th day), the turbidity increased and the SS concentration reached about 100 mg / liter.
On the other hand, in the case of B where the number of revolutions was increased from 5 rpm to 20 rpm, although some turbidity was observed around the first 10 days, the turbidity disappeared thereafter, and the raw water BOD concentration was 800 mg / liter (BOD volume load 0.8 kg). / M ³ · day), the SS concentration was always 10 mg / liter or less, and the quality of the treated water could be maintained well. These results demonstrate the effectiveness of the present invention.
[Brief description of the drawings]
FIG. 1 is an example of a treatment facility in a conventional continuous activated sludge process.
FIG. 2 is an example of a treatment facility in the bulking-suppressing continuous activated sludge method of the present invention, which comprises an aeration tank equipped with an adsorption tank and a sedimentation tank.
FIG. 3 is a graph demonstrating the stirring effect in the settling tank.
[Explanation of symbols]
1 Raw water (drainage)
2 Treated water 3 Aeration device 4 Return sludge 5 Extracted sludge 6 Blower 7 Adsorption tank 8 Stirring blade 10 Flow rate adjustment tank 20 Aeration tank 21 Contact material 30 Precipitation tank

Claims (4)

A continuous activated sludge method for biologically treating organic wastewater, comprising an aeration tank, an adsorption tank provided in the preceding stage of the aeration tank, and a sedimentation tank, wherein the adsorption tank is a whole aeration tank The tank is composed of at least one aeration tank having a small volume of 1/200 to 1/15 of the volume, and the precipitation tank is agitated at a rotation speed at which the peripheral speed exceeds 2.5 m / min and is 8 m / min or less. It characterized the Turkey, bulking inhibitory continuous activated sludge method.   The bulking suppression type continuous activated sludge method according to claim 1, wherein the adsorption tank is an adsorption tank having partition walls therein so that the adsorption tank is substantially composed of two or more tanks.   The bulking-suppressing continuous activity according to claim 1 or 2, wherein the adsorption tank is arranged so that the supernatant BOD concentration in the adsorption tank is 30 mg / l or more and the BOD adsorption rate up to that is 50% or more. Sludge method.   The bulking suppression type continuous activated sludge method according to any one of claims 1 to 3, wherein a contact material is present in the aeration tank.

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