JP3383505B2 - Activated sludge treatment method and apparatus for organic wastewater - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new technique for biological treatment of organic wastewater such as sewage, and more particularly to a new technique capable of significantly reducing the amount of excess sludge associated with biological treatment of wastewater.

[0002]

2. Description of the Related Art Conventionally, as a method for reducing the amount of surplus sludge generated by biological treatment such as activated sludge method, Japanese Patent Laid-Open No.
The technique described in Japanese Patent No. 206088 is known. As shown in FIG. 3, after the organic wastewater 11 is subjected to a biological treatment process in the aeration tank 1, biological sludge is drawn out from the settling tank 2 which is a solid-liquid separation device, and a part thereof is an ozone contact tank. 7
After ozone oxidization in the above to solubilize the sludge to reduce SS, the ozone oxidation sludge 15 is returned to the aeration tank 1,
This is a technique for removing BOD eluted from the ozone-oxidizing sludge 15 again by the activated sludge in the aeration tank 1. That is, according to the conventional technique, the sludge reducing action is generated only in the ozone oxidation tank 7, and in the aeration tank 1, B eluted from the sludge by ozone is discharged.
The idea was to remove OD.

[0003]

However, when the present inventor retried this conventional technique, the following serious problems in practical use were recognized. 1. Since the volume of sludge is reduced only by ozone, it is necessary to add a large amount of ozone in order to reduce the excess sludge to zero, resulting in high ozone cost and poor practicability. 2. When ozone is diffused in the ozone contact tank 7, it foams violently and sludge overflows from the ozone contact tank 7. 3. A treatment device for the waste ozone gas discharged from the ozone contact tank 7 is required.

An object of the present invention is to solve all of the above problems, low ozone cost, no overflow of sludge due to foaming, no need for waste ozone gas treatment equipment, and significant elimination of excess sludge. It is intended to provide a method and an apparatus for treating activated sludge of organic sewage which can be used.

[0005]

The present invention is a method and apparatus for treating activated sludge of organic wastewater having the following constitution. (1) In the activated sludge treatment method of performing solid-liquid separation after treating organic sludge with activated sludge and returning the separated sludge obtained by the solid-liquid separation to the activated sludge treatment step, a part of the separated sludge is treated. activated sludge treatment method organic sewage, characterized in that after aeration with oxygen-containing gas is returned to the activated sludge treatment process of the sewage after ozone oxidation. (2) The ozone oxidation is performed in a closed tank,
Oxidized sludge aeration tank for both waste ozone gas and ozone-oxidized sludge
The method for treating activated sludge of organic sewage according to the above (1), characterized in that

(3) A sewage treatment aeration tank for treating activated sludge of organic sewage, a solid-liquid separation means for performing solid-liquid separation after the activated sludge treatment of the sewage, and at least a part of the separated sludge. In an activated sludge treatment device having a sludge returning means for returning to the treatment aeration tank, an ozone oxidation part for ozone-oxidizing a part of the separated sludge and an oxidation for aeration of the ozone-oxidized sludge with an oxygen-containing gas An activated sludge treatment device for organic sewage, comprising: a sludge aeration tank, wherein the sludge digested in the oxidation sludge aeration tank is configured to flow into the wastewater treatment aeration tank. (4) The activated sludge treatment device for organic wastewater according to (3) , wherein the sludge delivery port of the ozone oxidation section is connected to an inlet provided at the bottom of the oxidized sludge aeration tank.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An example of the device of the present invention is shown in FIG. 1, and the present invention will be described with reference to this device. Organic wastewater (hereinafter also simply referred to as sewage) 11 such as sewage is supplied to the sewage treatment aeration section 1B of the aeration tank 1 of the apparatus shown in FIG. To remove it. The activated sludge slurry 12 flowing out from the sewage treatment aeration section 1B is separated in the settling tank 2 which is a solid-liquid separation means, and the treated water 13 from which BOD, COD, SS and the like have been removed is obtained. The precipitated sludge 14 is returned by the sludge return pump 3 to the aeration tank 1 through the sludge return line 4. This sludge return line 4 from the settling tank 2 to the aeration tank 1 is branched into two systems, one of which is
The system is a pipeline 5 for returning sludge to the sewage treatment aeration unit 1B as it is, and the other system is an ozone oxidation unit. The ozone oxidizing section is a closed pipe, and ozone is supplied to the closed pipe 6. Specifically, the ozone contact tank 7 is attached to the closed pipe 6.
Is provided, and ozone 21 is injected into the ozone contact tank 7. The ozone contact tank 7 also has a closed structure.
The retention time of the sludge in the ozone contact tank 7 is about 30 minutes, and the ozone contact tank 7 requires a small volume.

At this time, the strong oxidizing power of ozone destroys the cell walls of the microorganisms constituting the biological sludge, solubilizes the sludge, reduces SS, and produces soluble BOD. Ozone oxidation is sealed in a closed pipeline 6 and an ozone contact tank 7
Since it is carried out in-house, there is no occurrence of "a trouble of overflow of foamed sludge in the ozone contact tank" as in the prior art shown in FIG. The ozone oxidizing sludge 15 delivered from the closed pipe 6 flows out to the bottom of the oxidizing sludge aeration unit 1A of the aeration tank 1. The unabsorbed residual ozone bubbles flowing out from the closed pipe 6 to the bottom of the oxidized sludge aeration unit 1A are
Ozone is almost completely absorbed in the treatment liquid while rising inside the container toward the liquid surface, and the conventional waste ozone treatment equipment is no longer required.

The ozone-oxidizing sludge 15 is an oxidizing sludge aeration unit 1A.
Inside is aerated with an oxygen-containing gas such as air for a long time (about 5 to 7 days), and BOD eluted from the ozone oxidation sludge 15 is removed during this period. In addition, SS is highly self-extinguished and is greatly reduced. The self-extinguishing sludge 16 flowing out from the oxidative sludge aeration unit 1A is aerated in the sewage treatment aeration unit 1B on the downstream side of the aeration tank 1 along with the return sludge 17 that returns the sewage 11 and the separated sludge 14 as they are, and the BOD of the sewage 11 is increased. Along with the removal, the BOD of the self-digesting sludge 16 is removed. Oxidized sludge aeration unit 1 on the upstream side of the aeration tank 1.
The self-extinguishing sludge 16 flowing out of A is further self-extinguished in the wastewater treatment aeration section 1B, and finally excess sludge is not generated. When the existing activated sludge aeration tank can be used, the front stage of the aeration tank 1 can be diverted to a self-digestion tank for ozone-oxidized sludge, that is, an oxidized sludge aeration unit 1A as shown in FIG. In case of plug flow type aeration tank, aeration tank 1
Since there is a flow similar to that of a river inside, sewage 11 and self-extinguishing sludge 16 do not mix even without providing partition wall 8 that separates oxidation sludge aeration unit 1A and sewage treatment aeration unit 1B. Therefore, it is not necessary to clearly separate the oxidizing sludge aeration unit 1A and the sewage treatment aeration unit 1B by the partition wall 8.

The amount of ozone added is 1 to the weight of sludge SS.
About 4% is sufficient, and the generation of excess sludge can be reduced to zero with a smaller amount of ozone than in the conventional technique shown in FIG. On the contrary,
In the prior art, the ozone addition amount is required to be 5 to 15% because there is no self-extinguishing process of ozone-oxidized sludge. The reason why the amount of ozone added in the present invention is small is that the sludge treated with ozone is aerated for a long time to effectively promote the self-extinguishing of ozone-oxidized sludge. That is, in the present invention, the reduction of sludge SS proceeds in both the ozone oxidation tank 7 and the oxidized sludge aeration unit 1A which is a self-digestion tank. The sludge flow rate in the closed pipe line 6 for performing ozone oxidation may be set so that the amount of solid matter is usually 2 to 3 times the amount of surplus activated sludge generated during conventional activated sludge treatment in which ozone is not added. ,
Since it changes depending on the properties of sludge and the amount of ozone added, it must be determined experimentally accurately.

[0011]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. [Example] A demonstration test of the method of the present invention was conducted on sewage using the apparatus of FIG. Table 1 shows the water quality of the sewage to be treated.

[0012]

[Table 1]

Table 2 shows the test conditions.

[0014]

[Table 2]

As a result of conducting a test for one year under the above conditions,
The average quality of treated water is SS5, BOD6, COD7mg / l
Very good water quality was obtained. In addition, excess biological sludge
Did not occur. The sludge index (SVI) of activated sludge is
It is as small as 80-110 and the sedimentation of activated sludge is good.
Luking was not recognized. Also, the processing liquid level of the aeration tank 1
The ozone concentration emitted from the plant was negligible. [Comparative Example] Acid for self-extinguishing ozone-oxidized sludge 15
Omission of the chemical sludge aeration section 1A and O ₃Absorb the activated sludge
Example except that the ratio was set to 20 mg per 1 g
The experiment was conducted under the same experimental conditions as in 1. As a result, excess sludge generation
The amount of raw material cannot be reduced to zero, and sewage is 1 m³Per 25
-30 g of excess sludge was generated.

FIG. 2 shows the results of an experiment in which ozone-oxidized sludge was self-digested. FIG. 2 shows the reducing effect of sludge SS when ozone is absorbed at a ratio of 20 mg per 1 g of activated sludge and then aerated with air for 5 days. When a small amount of ozone is absorbed by sludge and then aerated, SS of sludge is
Is effectively reduced. On the other hand, in order to obtain the same SS reduction effect with ozone alone, ozone is sludge 1
It was necessary to add 68 mg per gram.

[0017]

Since the present invention incorporates a self-digesting step for ozone-oxidized sludge, the amount of surplus activated sludge generated from the biological treatment step can be significantly reduced by adding a small amount of ozone. Further, by performing the ozone oxidation in a sealed state, it is possible to eliminate the sludge foaming trouble in the ozone contact tank. Further, by sending the ozone-oxidized sludge into the treatment liquid which is aerated with the oxygen-containing gas, residual ozone bubbles are effectively absorbed in the treatment liquid, so that waste ozone treatment equipment is not required. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an activated sludge treatment device of organic sewage according to the present invention.

FIG. 2 is a graph showing the sludge volume reduction effect of the present invention.

FIG. 3 is a diagram showing an example of a conventional activated sludge treatment device for organic sewage.

[Explanation of symbols]

1 aeration tank 1A Oxidized sludge aeration section 1B Sewage treatment aeration section 2 settling tank 3 Sludge return pump 4 Sludge return line 6 closed pipe 7 Ozone contact tank 8 partitions 9 Air diffuser 11 dirty water 12 Activated sludge slurry 13 Treated water 14 Separation sludge 15 Ozone-oxidizing sludge 16 Self-extinguishing sludge 17 Return sludge 21 Ozone 22 air

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Claims (4)

(57) [Claims] 1. An activated sludge treatment method, wherein solid waste separation is performed after treating organic wastewater with activated sludge, and the separated sludge obtained by the solid waste separation is returned to the activated sludge treatment step.
Activated sludge treatment method organic wastewater characterized by returning part of the separated sludge from the aerated with an oxygen-containing gas after ozone oxidation in the activated sludge treatment process of the sewage. 2. The ozone oxidation is carried out in a closed tank, and the ozone is closed.
Both the exhaust ozone gas from the tank and the ozone-oxidizing sludge are oxidized and polluted.
The activated sludge treatment method according to claim 1, wherein the activated sludge is caused to flow into the mud aeration tank . 3. A sewage treatment aeration tank for treating activated sewage of organic sewage, a solid-liquid separation means for performing solid-liquid separation after sewage treatment of activated sewage, and at least a part of the separated sludge. In an activated sludge treatment device having a sludge returning means for returning to an aeration tank, an ozone oxidation part for ozone-oxidizing a part of the separated sludge and an oxidizing sludge for aeration of ozone-oxidized sludge with an oxygen-containing gas An activated sludge treatment device for organic sewage, comprising an aeration tank, and configured so that sludge digested in the oxidation sludge aeration tank flows into the sewage treatment aeration tank. 4. The organic sewage activated sludge treatment apparatus according to claim 3, characterized in that connected to the inlet provided at a lower portion of the sludge feed the oxidizing sludge aeration tank the outlet of the ozone oxidation unit.