JP3210077B2 - Activated sludge settling improver and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical for improving the sedimentation of activated sludge in activated sludge wastewater treatment and a method for producing the same.

[0002]

2. Description of the Related Art Activated sludge is the most widely used method for treating organic wastewater containing organic substances such as general household wastewater and industrial wastewater. The activated sludge method blows air into wastewater containing pollutants to increase the activated sludge, which is a collection of microorganisms, to absorb and decompose and remove organic matter. It consists of a "precipitation step" in which sedimentation is separated from treated water by utilizing.
Part of the settled activated sludge is extracted outside the system as surplus sludge, and the rest is returned to the aeration tank. If these two processes do not work well, the activated sludge treatment will not be performed smoothly.

In actual wastewater treatment, an abnormal phenomenon of activated sludge called “bulking” sometimes occurs due to fluctuations in the flow rate of inflow wastewater and fluctuations in the organic matter composition in the wastewater.
When the activated sludge bulking phenomenon occurs, the flocs of the activated sludge are difficult to separate from the treated water, the sludge flows out together with the treated water, the water quality of the treated water is significantly deteriorated, and the sludge concentration in the aeration tank decreases. Processing efficiency becomes poor.

[0004] The bulking phenomenon of activated sludge is roughly classified into the following three types. Poor sedimentation due to abnormal growth of filamentous bacteria. Poor sedimentation due to accumulation of highly viscous substances. Poor sedimentation due to miniaturization of flocs such as sludge dismantling.

Various methods have been proposed to eliminate the bulking phenomenon of activated sludge, for example, a method of adding bentonite, cristobalite, etc.
60-175599), a method of adding an inorganic agent and a cationic organic polymer flocculant (JP-A-62-186997, JP-A-2-186997)
17998 publication) is known. Since these methods involve a specific gravity difference between the added inorganic agent and other agents, there is a drawback that only the inorganic agent precipitates at the bottom without being retained by the sludge floc. Further, the same phenomenon occurs when a cationic organic polymer flocculant is used in combination, and there is a disadvantage that the duration of the effect is shortened.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an improving agent capable of imparting a long-lasting sedimentation property to activated sludge having a bulking phenomenon.

[0007]

In view of such circumstances, the inventors of the present invention have conducted various tests and researches on various activated sludges which have caused a bulking phenomenon. By forming a coating of a water-soluble metal salt and further using a sedimentation improver of activated sludge having a film of a cationic polymer flocculant or a cationic inorganic flocculant formed on its surface, the activated sludge can be efficiently treated with this improver. It was found that it adhered to the surface and formed a floc, good sedimentation properties were obtained, and that the duration was long, thereby completing the present invention.

The inorganic porous particles used in the present invention are preferably irregular particles having a large water-insoluble supporting surface area. Representative examples thereof include calcium silicate, kaolin,
Examples include bentonite, activated clay, natural zeolite, colloidal earth, magnesia, and diatomaceous earth. The particle size of these porous particles is desirably in the range of 50 to 500 μm. If the diameter is less than 50 μm, it becomes difficult to perform the coating treatment. If the diameter exceeds 500 μm, the activated sludge adheres to the modifier. It is not practical because it precipitates before.

Representative examples of the water-soluble metal salt used in the present invention include metal salts such as ferrous sulfate, ferric sulfate, and aluminum sulfate, which form hydroxide flocs near neutrality. Are preferred.

A typical cationic polymer flocculant used in the present invention is dialkylaminoethyl (meth)
Examples include quaternary salts of acrylate polymers, quaternary salts of dialkylaminopropyl (meth) acrylamide polymers, and quaternary salts of polyamines. The higher the degree of polymerization of these polymer flocculants, the better, and particularly those having a molecular weight of 2,000,000 to 6,000,000 are suitable. In order to obtain good cohesiveness, it is preferable that the cation equivalent value is 2.5 meq / g or more, which is strong cationic. On the other hand, a typical cationic inorganic flocculant used in the present invention is an inorganic salt polymer such as polyaluminum chloride and polyiron chloride.

In order to produce the sedimentation improver of the present invention, the inorganic porous particles are put into a stirrer having a rotating blade having a rotation speed of 500 to 1000 rpm, and the inorganic porous particles are stirred and suspended. A saturated aqueous solution of a water-soluble metal salt is sprayed on the mixture, and the mixture is continuously stirred for 10 to 20 minutes to uniformly adhere the water-soluble metal salt to the particle surface. And dry.

Then, 1-5% of the separately prepared cationic coagulant is added to the system in which the hot air is continuously blown while stirring.
An aqueous solution may be sprayed to form a layer of a cationic coagulant on the surface of the particles coated with the water-soluble metal salt, and then dried.

A preferred composition of the sedimentation improver of the present invention is:
50 to 85% by weight of inorganic porous particles in a dry state;
5 to 20% by weight of metal salt and 10 to 10% of cationic coagulant
It is blended at a ratio of 45% by weight.

In the use of the sedimentation improver of the present invention, the method of adding the activated sludge to the activated sludge is not particularly limited, but it is preferable to uniformly charge the activated sludge in the aeration tank. 0.05-1 per 1 g dry weight
g is preferable.

[0015]

The sediment improver of the activated sludge of the present invention is added to the aeration tank because it has two layers consisting of a water-soluble metal salt layer and a cationic coagulant layer on the surface of the inorganic porous particles. At the same time, the activated sludge quickly adheres to the surface of the sedimentation improver, and forms large flocs mainly of particles, so that excellent sedimentation can be obtained. In addition, since the aggregate component gradually elutes from the surface of the porous particles, the floc forming ability is maintained for a long time.

[0016]

【Example】

(Example 1) 2 kg of calcium silicate particles (average particle size: 50 μm) were charged into a container of a super mixer (manufactured by Kawata Co., Ltd.) having a capacity of 20 liters, and the rotation speed was 700 rpm.
Using a high-pressure pump, 600 g of an aqueous solution of aluminum sulfate (28 wt%) was sprayed into a vessel in which the particles were suspended and fluidized by rotating the stirring blades, to uniformly adhere the particles to the surfaces of the particles. Then, using a hot air generator (manufactured by Taketsuna Seisakusho), hot air at a temperature of 120 ° C. and a flow rate of 20 liters / min was blown into the container to evaporate and dry the attached moisture of the particles. When the attached water content becomes about 1%, 2% of acrylamide-modified quaternary salt polymer flocculant (molecular weight 6 million, cation equivalent value 3.2 meq / g) is blown while blowing warm air.
Inject 35 kg of the aqueous solution into the container using a high pressure pump,
The surface of the particles is coated with a polymer flocculant while evaporating water, and dried until the attached water content becomes about 3%.
2.8 kg of a sedimentation improver were obtained.

On the other hand, dry solid content (hereinafter referred to as MLSS)
Is 1800 ppm, the sludge index value (hereinafter SVI: Slug
10 liters of activated sludge from a sewage treatment plant having an e Volume Index of 250 is placed in an aeration tank having a capacity of 12.5 liters, and while aeration is performed at an air amount of 7 liters / minute, glucose 0.36 g / liter and polypeptone 0 .12
g / liter of synthetic sewage was continuously added to the aeration tank at a rate of 10 liters per day using a metering pump, and the activated sludge was cultured.
And the filamentous bacteria II-7 proliferated, and on the fourth day, the filamentous bulking activated sludge had an MLSS of 1900 ppm and an SVI of 480.

When 2.2 g of the above sedimentation improver was put into the aeration tank, activated sludge adhered immediately after the addition of the sedimentation improver, and a large floc having the sedimentation improver as a core was formed. Was. Thereafter, the culture is continued, and SVI is
When the value was measured, it was SVI which was 480 before introduction.
The value changed to 110 after 1 day, 120 after 3 days, 100 after 5 days, 140 after 7 days, 120 after 10 days, 190 after 15 days, and 215 after 20 days. The activated sludge maintained a state in which a good floc was formed for a long period of time, maintained an SVI value of 150 or less for about two weeks, and showed good sedimentation.

(Examples 2 to 6) Using a predetermined amount of an inorganic porous particle, a saturated metal salt solution and a cationic coagulant as shown in Table 1, a sedimentation improver was prepared in exactly the same manner as in Example 1. Prepared. Next, this sedimentation improver was added to the same activated sludge continuous treatment system as in Example 1, and the SVI value was measured over time. The results were as shown in Table 2.

[0020]

[Table 1]

[0021]

[Table 2]

Example 7 An on-site test was conducted using a processing apparatus having an aeration tank volume of 150 m ³ and a sedimentation tank volume of 30 m ³ in which wastewater treatment was performed in an actual slaughterhouse. In the activated sludge of this treatment apparatus, the flocs were disintegrated, and the sludge was discharged together with the treated water without the fine sludge settling. The MLSS value was 1800 ppm and the SVI value was 500. 70 kg of the sedimentation improver produced in the same manner as in Example 6 was put into an aeration tank, and the change with time of the sedimentation was measured. The SVI value was 500 before the addition, 105 after the addition, and 105 after the addition. 110 days later, 1 day after 3 days
It changed to 110 after 20, 7 days, 170 after 10 days, and 280 after 16 days. The fine sludge which was in a dispersed state before the introduction was formed, and after the introduction, formed flocs having a modifier as a nucleus to improve the sedimentation property, and this effect was maintained for about 2 weeks.

Example 8 Aeration tank volume 2 of a confectionery manufacturer
An actual in-situ test was performed using a wastewater treatment apparatus having a capacity of 70 m ³ and a settling tank capacity of 70 m ³ . Since this factory manufactures gummy candy, wastewater contains a lot of gelatin, activated sludge causes high viscosity bulking, and sludge flows out with treated water without sedimentation at all. , MLSS value is 2800 ppm, SVI value is 35
It was 0. 68 kg of the sedimentation improver produced in the same manner as in Example 1 was put into an aeration tank, and the secular change with time was measured. The SVI value was 350 before the addition, 140 after the addition, and 1 after the addition. 140 days later, 150 days later, 150,5
180 days later, 210 days later, 210 days later, 280 days later, 1 day later
Five days later, it changed to 340. Immediately after the introduction, the fine sludge which had been dispersed before the introduction was formed into flocs with the improver as a nucleus to improve the sedimentation property, and this effect was maintained for about 10 days.

(Comparative Example 1) When exactly the same treatment was performed as in Example 1 except that the sedimentation improving agent was not added, the SVI value which was 480 before charging was changed to
490 days, 510 days, 510 days, 470 days, 520 days, 520 days, 470 days, 470 days, 460 days, 15 days
After 0 day, the value was 470, indicating that no effect of improving sedimentation was observed.

Comparative Example 2 Except that calcium silicate particles, an aqueous solution of aluminum sulfate and an acrylamide-modified quaternary salt polymer flocculant were separately added in place of the settling improver used in Example 1, respectively. When exactly the same processing was performed, the SVI value was 480 before the introduction, but 110 after 1 day, 440 after 3 days, and 440 after 5 days.
It shows 490 after 80 and 7 days, 520 after 10 days, 480 after 15 days, and 460 after 20 days. It was found that about 3 days after the addition, the sedimentation effect disappeared and the duration was poor.

[0026]

By using the sedimentation improver of the present invention, an activated sludge floc having good sedimentation can be formed, so that the poor sedimentation of activated sludge caused by various causes can be eliminated. Due to the long duration, efficient activated sludge treatment is possible in actual wastewater treatment.

Claims (2)

(57) [Claims] 1. Activated sludge characterized in that a coating of a water-soluble metal salt is formed on the surface of inorganic porous particles, and a coating of a cationic polymer coagulant or a cationic inorganic coagulant is formed on the surface. Sedimentation improver. 2. An aqueous solution containing a water-soluble metal salt is sprayed onto the stirred inorganic porous particles and coated, followed by drying, and then a cationic polymer flocculant is applied to the treated stirred inorganic porous particles. Alternatively, a method for producing a sedimentation improver for activated sludge, which comprises spraying an aqueous solution containing a cationic inorganic coagulant, coating and drying.