JPH091177A - Improvement of activated sludge - Google Patents

Abstract

PURPOSE: To efficiently prevent bulking at a low cost by respectively specifying the grain sizes and addition ratio of floatable synthetic resin granular materials in a method for adding these granular materials as the contents of an activated sludge aeration tank to this aeration tank. CONSTITUTION: The waste water subjected to a primary treatment is introduced through a pipe 3 into the aeration tank 1 in which the floatable synthetic resin granular materials 5 and the activated sludge 6 are housed. The waste water is aerated by an aerator 4, by which the molds generated from the activated sludge 6 are destroyed. The waste water mixture composed of the treated granular materials and the activated sludge moves to a granular material separating section 7 where only the activated sludge 6 settles and the granular materials 5 having the floating property are pushed back again into the aeration tank 1. At this time, the synthetic resin granular materials 5 made of ordinarily used synthetic resins, such as polypropylene and polyethylene, having the floating property are used. The grain size of the granular state is specified to 1 to 4mm and more particularly about 2mm. The amt. of the synthetic resin granular materials 5 to be used is specified to 10 to 40vol.%, more preferably 30vol.% of the total volume of the contents in the aeration tank 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater by the activated sludge method.

[0002]

The activated sludge method is one of the most typical methods for aerobically treating wastewater with microorganisms. In the activated sludge method, wastewater is treated in an aeration tank under aerobic conditions while blowing air from the bottom of the tank. In this process, the organic matter in the wastewater is assimilated and decomposed by microorganisms, part of which becomes microbial cells and forms sludge. Next, the treated liquid containing sludge from the aeration tank is transported to the sedimentation tank,
It is left to stand. In this settling tank, the sludge is settled and separated from the supernatant, and the supernatant is often discharged or reused.

On the other hand, a part of the activated sludge is returned to the aeration tank and reused as microbial bodies for the treatment of new waste water, and the remaining sludge which is not returned is used as fertilizer etc. after draining and drying. It In the above-mentioned activated sludge method, filamentous fungi may grow in the aeration tank, the mycelia may be entangled with each other to form a solid, and floating in the liquid, so-called bulking may occur. When bulking occurs, the sludge settling in the settling tank is hindered and the wastewater treatment efficiency is greatly reduced.

As a method for preventing this bulking, a method of adding a chemical substance such as thiophosphoric acid ester (Japanese Patent Publication No. 56-34352), a method of using a cationic organic polymer flocculant (JP-A-2-17998) and bisbiguanide Method of adding compound (Japanese Patent Application Laid-Open No. 55-17719)
6) is known, and as a method for mechanically destroying a mycelial mass of a filamentous fungus, a method of ejecting a fluid by an ejector into an aeration tank (JP-A-55-155796) and destruction of the filamentous fungus by ultrasonic waves Method (JP-A-5-34519)
2) is known. However, it has not been known that the addition of the synthetic resin granules destroys the mycelium of the filamentous fungus to prevent bulking.

[0005]

DISCLOSURE OF THE INVENTION As a result of various studies on a new method for preventing bulking which can be carried out at a low cost, the present invention can be used under a specific condition where a synthetic resin granule satisfying a specific condition is added to an aeration tank. By doing so, they found that bulking can be efficiently prevented at low cost, and completed the present invention.

[0006]

In order to achieve the above object, the present invention uses an activated sludge aeration tank in which a floatable synthetic resin granule having an average particle diameter of 1 to 4 mm is added to the aeration tank. Provided is a wastewater treatment method, which comprises adding 10 to 40% by volume to the total amount of the product.

[0007]

[Detailed Description] The activated sludge method in the present invention is an activated sludge method which has been widely used in the past, and is not particularly limited. The synthetic resin granules added to the aeration tank in the present invention are polypropylene, polyethylene or other commonly used synthetic resin having a floating property, especially those made of plastic, and are made of polypropylene from the viewpoint of hardness of the granules, cost, etc. Those are particularly preferable. The shape of the granular body is not particularly limited, but a spherical body, a tetrahedron, a hexahedron, for example, a rectangular parallelepiped or a cube can be used, and from the viewpoint of mechanically cutting and destroying the hyphae of filamentous fungi, a rectangular parallelepiped or a cube is preferable. Particularly preferred.

The diameter of the granules is preferably 1 to 4 mm, especially 2
-3 mm, especially about 2 mm is preferred. If the particle size is too small,
Also, if it is too large, the bulking prevention effect is reduced. Here, the diameter of the granular body means the diameter when the granular body is a sphere, the average of the lengths of six edges in the case of a tetrahedron, and the average length of 12 edges in the case of a hexahedron. It means the average length of the ridge.

The amount of the synthetic resin particles used in the present invention is 10 to 40 with respect to the total volume of the contents in the aeration tank.
% By volume, with 30% by volume being particularly preferred. If the amount of the particulates is too small, the bulking prevention effect is not sufficient, and if the amount of the particulates is too large, the amount of treated water in the aeration tank is reduced and the treatment efficiency is reduced.

Next, an example of carrying out the method of the present invention will be described with reference to the drawings. 1 represents the aeration tank and 2 represents the precipitation tank. The wastewater that has been subjected to the primary treatment by microbial treatment or the like enters the aeration tank 1 through the pipe 3. The aeration tank 1 contains buoyant synthetic resin particles 5 and activated sludge 6, and the air pipe 1
The air from 3 is aerated by the aeration device 4 attached to the lower part of the aeration tank. In the aeration tank, the activated sludge and the particulate matter are agitated by aeration, and the filamentous fungus generated from the activated sludge is physically destroyed.

A granular material separating section 7 is attached to a side portion of the aeration tank 1, and the treated granular material / activated sludge mixed waste water is moved to the granular material separating section 7. In the granular material separating section, only the activated sludge settles, and the floating granular material is pushed back into the aeration tank. The treated water containing activated sludge is sent to the settling tank 2 through the pipe 8. Since the liquid is not stirred in the settling tank 2, the liquid is naturally separated into the supernatant liquid 9 and the sludge 10. The treated supernatant liquid is discharged through the discharge pipe 11, and the sludge is discharged through the discharge pipe 12. The sludge thus discharged is subjected to dewatering, drying, etc. and finally processed. Further, the sludge may be returned to the aeration tank 1 again and recycled.

In the above method, since the floatable resin granules 5 are added to the aeration tank 1, the hyphae of the filamentous fungus are cut, the growth of the filamentous fungus is suppressed, and bulking is prevented. Precipitation is very easy to carry out.
Further, since the granular material does not need to be added again and is used semipermanently, the processing cost is extremely low.

[0013]

Next, the present invention will be described more specifically with reference to examples. Embodiment 1 FIG . Effect of particle size of granules on sludge sedimentation To investigate sludge sedimentation, SVI (sludge capacity index,
Measurement of the Sludge Volume Index) was performed. SVI is the volume occupied by 1 g of activated sludge suspended matter in ml when the mixed solution in the aeration tank is allowed to stand for 30 minutes. Usually, it is considered desirable that the SVI is around 100. For sludge in bulking state, S
The VI value is 400 to 500. SVI is calculated by the following equation.

[0014]

(Equation 1) Here, SV ₃₀ is the activated sludge sedimentation rate, and shows the amount of sedimented sludge when the material is allowed to stand for 30 minutes in a graduated cylinder having a volume of 1 L, as a percentage of the material amount.

Organic wastewater (BOD 180 ppm) was put into an aeration tank with an actual capacity of 500 L, and the MLSS concentration was 2500 mg /
It was controlled to be constant at L. The particle size of the modified polypropylene granules added to the aeration tank at 30% by volume is 1 mm.
Square, 2 mm square, 3 mm square, 4 mm square were changed, and SV _{30 in} each case was measured, and SVI was calculated. The value of SVI with respect to the particle size of the granular material is shown in FIG. As shown in Fig. 2, the particle size is 2 mm
It can be seen that in the case of, the SVI is the lowest and the sedimentation property is good.

Embodiment 2 . Granules for sludge sedimentation
Effect of addition amount As in Example 1, in order to investigate the sedimentation property of sludge, SV
I was measured. Put the organic waste water (BOD 180ppm) into the aeration tank with the actual capacity of 500L and set the MLSS concentration to 250.
It was controlled to be constant at 0 mg / L. Then, the addition amount of the modified polypropylene granules having a particle diameter of 2 mm added to the aeration tank is 10% by volume, 20% by volume, 30% by volume, 40% by volume.
Then, SV _{30 in} each case was measured, and SVI was calculated. FIG. 3 shows the SVI value with respect to the added amount of the granular material. As shown in FIG. 3, when the addition amount is 30% by volume to 40% by volume, the SVI is low and the sedimentation property is good.

Example 3 Activated sludge from phenol-containing wastewater
Treated high-concentration wastewater containing phenol (phenol content 500pp
m; BOD 200 ppm) was subjected to the primary treatment by the entrapping immobilization gel method, and the primary treated water (phenol content 0.1 ppm;
BOD of 180 ppm) was obtained. This was continuously supplied to an aeration tank having an actual volume of 500 l at a flow rate of 190 l / hr, extracted at the same flow rate, and sent to a precipitation tank having a total volume of 300 l. To the aeration tank, 2 mm square (average particle size 2 mm) modified polypropylene granules were added in an amount of 30% by volume. Ventilation is 0.5L / L
It was done at the speed of a minute. No bulking occurred in the aeration tank and precipitation occurred very easily in the precipitation tank. No phenol was detected in the supernatant of the precipitation tank, and the BOD was 2 ppm.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an apparatus used for carrying out an activated sludge method of the present invention.

FIG. 2 is a graph showing the relationship between the particle size of a granular material and the sedimentation property of sludge.

FIG. 3 is a graph showing the relationship between the amount of granular material added and the sludge settling property.

[Explanation of symbols]

 1 ... Aeration tank 2 ... Sedimentation tank 3 ... Treatment wastewater 4 ... Aeration device 5 ... Synthetic resin granules 10 ... Precipitate 11 ... Treated wastewater (supernatant)

Claims (1)

[Claims] 1. In the activated sludge method, a floatable synthetic resin granular material having an average particle diameter of 1 to 4 mm is added to the activated sludge aeration tank in an amount of 10 to 40% by volume based on the total amount of the contents of the aeration tank. A characteristic wastewater treatment method.