JPH09276887A - Method for treating organic sewage and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new sludge vol. reducing technique capable of markedly reducing the generation amt. of excessive sludge at a low cost without using ozone and alkali and not deteriorating even the quality of treated water. SOLUTION: In this org. sewage treatment method wherein org. sewage is biologically treated in an activated sludge treatment process 1 and sludge is separated in a solid-liquid separation process 2 and at least a part of the separated sludge is returned to the activated sludge treatment process 1, the separated sludge of which the amt. is larger than that of increased sludge is conc. in the activated sludge treatment process 1 and this conc. sludge is heated at 40-100V and the sludge 15 after heating is returned to the activated sludge treatment process 1.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a technique capable of significantly reducing the amount of excess sludge generated in a system for treating organic wastewater such as sewage by an activated sludge method.

[0002]

2. Description of the Related Art The activated sludge method is most widely used as a method for treating organic wastewater, but a large amount of surplus sludge that is difficult to dehydrate is generated. Excess sludge amount is about 50% of removed BOD amount
It is difficult to process. Conventionally, excess sludge is dehydrated,
Although it is disposed of, it is difficult to secure a disposal site, and there is a strong demand for a biological treatment technology with less excess sludge. As a conventional method for reducing the volume of excess sludge, Japanese Patent Application Laid-Open No. 7-88495 discloses a technique in which activated sludge is subjected to ozone oxidation and then introduced into an activated sludge treatment step to perform biological treatment. Also,
JP-A-8-1183 also discloses a sludge volume reduction technique in which activated sludge is subjected to ozone oxidation, then heat-treated, and introduced into an activated sludge treatment step. Furthermore, Japanese Patent Fair 6-6
Japanese Patent No. 1550 discloses a sludge volume reduction method in which an alkali is added to activated sludge, which is heat-treated and introduced into an activated sludge treatment system, and it is shown that the solubilizing effect is also high.

[0003]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 7-8 / 1995
As a result of the inventors' additional tests of the method described in Japanese Patent No. 8495, a large amount of expensive ozone is required for sludge solubilization,
The running cost is too high, and the equipment cost of the ozone generator is also high, and both the operating cost and the equipment cost are extremely high. In addition, foaming troubles in the ozone oxidation tank, the necessity of waste ozone treatment, and ozone Activated sludge B
Since it also has drawbacks such as a decrease in OD removal activity, it has been found that this is not a practical technique except when applied to a fairly small-scale activated sludge treatment facility. In addition, JP-A-8-1183
Although the method described in Japanese Patent Laid-Open Publication No. 7-84952 has a high solubilizing effect, it is not practical because it has a high ozone cost in addition to the heating energy cost and has the same drawbacks as the technique disclosed in Japanese Unexamined Patent Publication No. 7-88495. Furthermore, Japanese Examined Patent Publication 6-615
The method described in JP-A No. 50 has a drawback that a large amount of hardly biodegradable COD and chromaticity (brown) are eluted from sludge by the alkali heat treatment to deteriorate treated water quality. Alkaline cost is also high. The present invention establishes a new technology that solves the drawbacks of conventional sludge volume reduction technology using ozone or alkali, and can reduce the amount of excess sludge generated at a low cost without using ozone and alkali, and also deteriorate the quality of treated water. Providing new technology that does not

[Means for Solving the Problems]

As a result of pursuing a technique capable of effectively reducing the amount of excess sludge generated without using chemicals such as ozone and alkali, the present inventor has obtained a method which has hitherto been a blind spot, that is, a small amount of heat energy and microorganisms. It was found that the activated sludge method that does not generate surplus sludge can be realized only by the action. INDUSTRIAL APPLICABILITY The present invention can realize an “activated sludge method that does not generate excess sludge” with a small amount of heat energy without applying any sludge solubilizing means using chemicals such as ozone and alkali. It cannot break down the volume of sludge unless it is used. " When ozone and alkali are used, the sludge solubilization effect is certainly enhanced, but there is a cost demerit more than the sludge solubilization improvement merit.

The present inventor has found that the conventional sludge solubilization method utilizing ozone and alkali has a significantly poor cost performance, and the solubilization rate is lower than that of the ozone and alkali method, and the sludge is solubilized only by heat treatment. The present invention was completed by finding that the method of the present invention, which covers the lowness by increasing the amount of sludge supplied to the heating treatment, is the best method by comprehensively judging.

That is, according to the present invention, the organic sludge is biologically treated in the activated sludge treatment step, the sludge is separated in the solid-liquid separation step, and at least a part of the separated sludge is returned to the activated sludge treatment step. In the method for treating sewage, the separated sludge in an amount larger than the amount of multiplied sludge in the activated sludge treatment step is concentrated, the concentrated sludge is heated at 40 to 100 ° C., and the sludge after the heating is activated sludge treatment. A method for treating organic sewage, which is characterized by returning to the process, and an activated sludge treatment tank for treating the activated sewage of the organic sewage, and a solid liquor for solid-liquid separation of the sludge after the activated sludge treatment of the sewage. In an organic wastewater treatment device having a liquid separation device and a sludge returning means for returning at least a part of the separated sludge to an activated sludge treatment tank, a sludge concentrating device for concentrating the separated sludge, and a concentrated sludge 40-100 A processing apparatus of organic sewage, characterized in that in and a heating device for heating processing.

[0007]

FIG. 1 shows a configuration example of the present invention. The organic sludge 11 which is raw water and the return sludge 14 from the solid-liquid separation device 2 are made to flow into the activated sludge treatment tank 1 to perform the activated sludge treatment. Activated sludge is separated by solid-liquid separator 2 and treated water 1
2 and sedimented sludge (sludge concentration about 1%) 13 are obtained. A part of the settled sludge 13 is recycled as it is to the activated sludge treatment tank 1 as the returned sludge 14. The rest of the settled sludge 13
After being concentrated to a sludge concentration of about 3% or more by a sludge concentrating device 3 such as a centrifuge or a flotation concentrator, the temperature is 40 to 100 ° C., preferably 60, while being guided to a warming device 4 and being stirred.
Warm to ~ 80 ° C. It is not necessary to aerate with the heating device 4. Sludge foams when aerated and should be avoided.

If the temperature of the heating device 4 is less than 40 ° C., the sludge solubilizing effect is small. Further, if the temperature exceeds 100 ° C, not only a pressure vessel is required as a heating device but also a temperature of 10
If the temperature exceeds 0 ° C, a large amount of a high-concentration brown chromaticity component is eluted from the sludge and the treated water 12 is markedly colored, which is not preferable. When the temperature is in the range of 50 to 80 ° C., the elution amount of the hardly biodegradable chromaticity component is small, and coloring of the treated water 12 is not particularly problematic. If the temperature is lower than 40 ° C., it takes a considerably long time (4 days or more) to sufficiently solubilize the sludge, so that the preferable range is 40 to 90 ° C., and the most preferable temperature is 50.
~ 70 ° C. It was found that at this temperature, the microorganisms forming the activated sludge were not completely killed, and when they were returned to the activated sludge treatment tank 1, they exhibited BOD removal activity. The reason for further concentrating the sludge by the sludge concentrating device 3 such as centrifugation is to reduce the amount of heating heat and the volume of the heating device 4 and to improve the sludge solubilization speed. Heating sludge 1
It goes without saying that if the heat is recovered from 5, the amount of heat for heating can be further reduced. The heating time may be about 1 to 48 hours.
Higher temperature requires less heating time. Carbohydrate, protein, etc. are eluted from the sludge by the extraction action and hydrolysis action of warm water, and a part of the sludge is solubilized. The heating time of the heating device 4 is experimentally determined in advance so that the sludge solubilization rate is about 20% or more.

Since the warming-treated sludge 15 contains soluble organic matter (BOD) which is easily assimilated by the activated sludge, when added to the activated sludge treatment tank 1, the organic matter is assimilated and removed by the activated sludge. The sludge SS content that has not been solubilized by heating is also decomposed to some extent in the activated sludge treatment tank 1 because the biodegradability by aerobic bacteria is improved. The activated sludge that has proliferated due to the removal of the organic matter (BOD) eluted in the heating device 4 in the activated sludge treatment tank 1 is circulated again in the heating device 4 to be solubilized, and finally the propagated sludge is almost completely carbon dioxide gas. However, depending on the conditions, there is almost no excess sludge to be discharged to the outside of the system.

The amount of sludge supplied to the heating device 4 is extremely important, and if it is too small, the sludge reducing effect is hardly obtained. That is, when the organic matter eluted by the heating treatment is supplied to the activated sludge treatment tank 1, the organic matter is assimilated and the activated sludge grows. Therefore, simply pull out a large amount of sludge corresponding to the activated sludge treatment system and heat it. But after all, excess sludge is generated. Therefore, the amount of sludge that grows in the activated sludge treatment system (BOD activated sludge treatment tank 1 contained in raw water and warmed sludge
It increases as the amount of influx into the water increases). It is necessary to extract and heat the activated sludge above. For example, after pulling out only the part that was discarded as excess sludge from the conventional activated sludge treatment system and heating it and returning it to the activated sludge treatment system, activated sludge inevitably proliferates and excess sludge is generated. It is important to heat the sludge in excess of the amount that was discarded as excess sludge by the conventional activated sludge method. As a result, the generation of excess sludge can be significantly reduced, and depending on the conditions, the amount of excess sludge to be discarded outside the system can be reduced to zero.
In addition, as a matter of course, the sludge heat treatment step of the present invention can be incorporated into a biological dephosphorization method, a biological nitrification denitrification method, a carrier-added activated sludge method and the like as other examples.

[0011]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. Example 1 Using the process and apparatus shown in FIG. 1, demonstrative tests of the present invention were conducted on sewage having an average water quality shown in Table 1.
Table 2 shows the test conditions.

[0012]

[Table 1]

[0013]

[Table 2]

As a result of the experiment, the average of the quality of the treated water from the solid-liquid separation device 2 after the treatment condition became stable 2 months after the start of treatment was as shown in Table 3, and the average of BOD, SS and COD was high.
Had been removed. In addition, excess sludge is
Not pulled out, but MLSS of activated sludge treatment tank is 365
Since 0-4130 mg / liter was maintained, it was revealed that the generation of excess sludge was almost negligible.

[0015]

[Table 3]

Comparative Example As a result of activated sludge treatment under the same conditions except that the sludge concentration and heating treatment steps in Example 1 were omitted, the amount of excess sludge generated was 0.45 to 0.48 kg / kg of removed BOD. It was a large amount of ss. The treated water quality was BOD and SS were the same as those of the present invention, but CO
D was 11 to 12 mg / liter, and chromaticity was 10 to 12 degrees, which was better than the present invention.

[0017]

EFFECTS OF THE INVENTION As a result of using the method and apparatus of the present invention to heat sludge in a quantity greater than the amount of grown sludge by activated sludge treatment at a specific temperature and then return it to the activated sludge treatment system, ozone and alkali are used. The amount of excess sludge generated can be reduced to almost zero without doing so. Also, it is not necessary to use chemicals such as alkali and ozone to reduce excess sludge,
Since the amount of excess sludge can be reduced with only a small amount of heat energy, operating costs can be reduced. Furthermore, since it is not necessary to use ozone, there is no need for waste ozone treatment equipment, and foaming troubles in the ozone oxidation tank do not occur. Further, since it is not necessary to solubilize with an alkali, the brown chromaticity component is less eluted from the sludge and the treated water is less colored.

[Brief description of drawings]

FIG. 1 is one of the method and apparatus for treating organic wastewater of the present invention.
The figure which shows an example.

[Explanation of symbols]

 1 Activated Sludge Treatment Tank 2 Solid-Liquid Separator 3 Sludge Concentrator 4 Heating Device 5 Sludge Returning Means 11 Organic Sewage 12 Treated Water 13 Settled Sludge 14 Return Sludge 15 Heat Treated Sludge

Claims (2)

[Claims] 1. A method for treating organic sewage, which comprises biologically treating organic sewage in an activated sludge treatment step, separating sludge in a solid-liquid separation step, and returning at least a part of the separated sludge to the activated sludge treatment step. In the above step, the separated sludge in an amount larger than that in the activated sludge treatment step is concentrated, and the concentrated sludge is
A method for treating organic sewage, which comprises heating at 0 to 100 ° C. and returning the heated sludge to an activated sludge treatment step. 2. An activated sludge treatment tank for treating activated sludge of organic sewage, a solid-liquid separation device for solid-liquid separation of sludge after the activated sludge treatment of the sewage, and at least a part of the separated sludge activated. In an organic wastewater treatment device having a sludge returning means for returning the sludge to a sludge treatment tank, a sludge concentrating device for concentrating separated sludge and a concentrated sludge of 40 to 100
An organic wastewater treatment device, comprising: a heating device for heating at ℃.