JP3454622B2 - Method and apparatus for treating organic sewage - 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 capable of significantly reducing the amount of excess biological sludge generated by biological treatment of organic sewage such as sewage.

[0002]

2. Description of the Related Art As a method for reducing the amount of surplus sludge that has been conventionally generated by biological treatment such as activated sludge method, Japanese Patent Publication No.
No. 19719 and JP-A-6-206088 are known. This technique is a technique in which organic sludge is oxidized by ozone to be solubilized and then biologically decomposed into CO ₂ and H ₂ O by aerobic microorganisms. Also known is a technique in which sludge is treated with an alkali, neutralized with an acid, and then returned to an aeration tank.

[0003]

However, when the inventors of the present invention re-tried these conventional techniques, a large amount of ozone, alkali, or acid was required to solubilize sludge, resulting in high running costs. Then, the problem that it was not practical was recognized. An object of the present invention is to provide a technique for reducing the volume of sludge, which overcomes the above-mentioned problems, and the amount of acid chemicals added for neutralization after alkali solubilization can be made smaller than before. .

[0004]

According to the present invention, an organic sewage is purified by a biological treatment step, then solid-liquid separated in a precipitation step, and at least a part of the separated sludge is returned to the biological treatment step. in the processing method of the sewage, alkali sludge withdrawn from another part or biological treatment process of the separation sludge
After the agent is added and allowed to stay under alkaline conditions, it is aerated in the presence of aerobic microorganisms, and the sludge after the aeration is returned to the biological treatment step, and a method for treating organic sewage, and A biological treatment tank for purifying organic wastewater, a settling tank for solid-liquid separation after the purification treatment of the wastewater, and a sludge returning means for returning at least a part of the separated sludge to the biological treatment tank. In an apparatus for treating organic sewage having the above, an alkaline agent adding means for making an alkaline condition the other part of the separated sludge obtained from the settling tank or the sludge drawn from the biological treatment tank, and a retention for retaining the alkaline sludge under the alkaline condition A tank, an aeration tank for aerating sludge accumulated in the retention tank in the presence of aerobic microorganisms, and a sludge returning means for returning the aerated sludge to the biological treatment tank A processor sex sewage.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described with reference to FIG. Raw water 2 such as sewage is supplied to a biological treatment unit (for example, an aeration tank of activated sludge method) 1 to perform biological treatment. Biological treatment department 1
In addition to the standard activated sludge method, a biological nitrification denitrification method and an anaerobic aerobic method can be adopted. The activated sludge slurry 3 flowing out from the biological treatment section 1 is separated in the settling section 4 to obtain the purified treated water 5. Next, most of the separated sludge 6 that has been solid-liquid separated in the settling section 4 is returned to the biological treatment section 1 as return sludge 7. Sludge extracted from the other part of the separated sludge 6 or the biological treatment part 1 (also referred to as biological treatment part extracted sludge)
Alkaline agent for 13 (sodium hydroxide and lime are suitable) 8
Is added, and the mixture is stirred for a predetermined time (about one day) in the retention section 9 under alical conditions of about pH 9 to 11 and then the aeration section 10 is added.
And aeration in the presence of alkali-resistant aerobic microorganisms. Aeration time is good for 3 to 7 days. When aeration is performed in the aeration unit 10, the alkali-resistant aerobic microorganisms naturally proliferate.

As a result, the following interesting phenomenon occurs. That is, when the biological sludge is agitated under alkaline conditions to solubilize the sludge and then aerated in the presence of alkali-resistant aerobic microorganisms, the solubilized sludge is metabolized by the microorganisms, and a large amount of carbon dioxide gas is generated as a product thereof, resulting in pH 8 to 8 It was confirmed that the alkalinity decreased to about 0.5. This results in sulfuric acid,
It was found that the addition of an acid such as hydrochloric acid eliminates the need for artificially lowering the sludge pH. When the biological sludge is stirred under alkaline conditions, the extracellular polymer that protects the cells of the microorganisms that make up the sludge is leached, and the cell walls of the microorganisms are easily destroyed, and the solubilization of the sludge progresses and the aeration part It is considered that by utilizing the sludge in which the aerobic microorganisms in 10 are solubilized, a large amount of carbon dioxide gas is generated and the sludge pH is lowered.

As shown in FIG. 2, the sludge prepared by adding sodium hydroxide to the pH 6.8 separated sludge to adjust the pH to 10 (initial pH value 14 after alkali addition) was mechanically stirred for 24 hours, and as a result, the pH became 9.2. As a result of aeration in the presence of alkali-resistant aerobic microorganisms for a further 2 days (pH value after agitation of 15), the sludge pH has decreased to 8.3 (pH value after aeration of 16). It is preferable that the pH of the so-called alkali treatment in which the alkalinization is followed by the retention and stirring in the retention section 9 is 9 to 11.
If the pH is lower than this, the solubilizing effect is small, and if the p
In the case of H, a large amount of brownish chromaticity component (refractory biodegradable COD) is eluted from the biological treatment part and deteriorates the quality of treated water, so it should be avoided.

As means for making the separated sludge 6 alkaline, means for supplying hydroxide ions by electrolysis may be applied. The sludge after aeration is returned to the biological treatment section 1. Sludge (also referred to as post-aeration return sludge) 13 returned to the biological treatment unit 1 after aeration further decomposes in the biological treatment unit 1, and after the alkali agent 8 is added again, it is circulated to the retention unit 9 and the aeration unit 10 to repeatedly decompose. As a result, the decomposition of biological sludge proceeds, and the excess sludge discharged outside the system is significantly reduced. After the addition of the alkaline agent, the amount of sludge supplied to the retention section 9 is within a predetermined range (for example, 4000 to 6000) in the MLSS concentration in the biological treatment section 1.
Controlled so that it is maintained at mg / l) (M in biological treatment unit 1
(Easily possible by installing an LSS automatic measuring device)
To do.

[0009]

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 verification test of the present invention was conducted on sewage based on the process shown in FIG. Table 1 shows the sewage average water quality, and Table 2 shows the test conditions.

[0010]

[Table 1]

[0011]

[Table 2]

After a 10-month test under the above conditions, the quality of the treated water was good as shown in Table 3.

[0013]

[Table 3]

[0014] pH of the sludge aeration tank effluent is 8.3, the excess biological sludge generation amount sewer 1 m ³ per 6.8 to 7.
It was 4g.ss, which was very small. Comparative Example A normal activated sludge treatment test was conducted by omitting the retention tank 9 and the aeration tank 10 in FIG. The quality of treated water was equivalent to that of the present invention, but the amount of excess sludge generated was 45 to 47 g.ss per 1 m ³ of sewage.
That is, a large amount of surplus sludge was generated, which was about 7 times that of the present invention.

[0015]

With the constitution of the present invention, the amount of surplus biological sludge generated from the biological treatment process can be greatly reduced,
Further, it was possible to eliminate the need to add an acid for lowering the pH of the alkali-solubilized sludge.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a method for treating organic wastewater according to the present invention.

FIG. 2 is a graph showing a decrease in pH of alkali-solubilized sludge due to aeration in the presence of aerobic microorganisms.

[Explanation of symbols]

1 biological treatment department 2 Raw water 3 Activated sludge slurry 4 Precipitation part 5 treated water 6 separation sludge 7 Return sludge 8 alkaline agents 9 retention area 10 Aeration section 11 Returned sludge after aeration 12 air 13 Biological treatment department drawing sludge 14 Initial pH value after adding alkali 15 pH value after stirring 16 pH value after aeration

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Claims (2)

(57) [Claims] 1. A method for treating organic sewage, which comprises purifying organic sewage in a biological treatment step, followed by solid-liquid separation in a precipitation step, and returning at least a part of the separated sludge to the biological treatment step. An alkali agent is added to another part of the sludge or sludge extracted from the biological treatment process, and the sludge is retained under alkaline conditions, and then aerated in the presence of aerobic microorganisms, and the sludge after the aeration is subjected to the biological treatment process. A method for treating organic wastewater, which is characterized by returning the wastewater. 2. A biological treatment tank for purifying organic sewage, a sedimentation tank for solid-liquid separation after purification of the sewage, and at least a part of the separated sludge for returning to the biological treatment tank. In an apparatus for treating organic sewage having a sludge returning means, another part of the separated sludge obtained from the settling tank or the sludge drawn from the biological treatment tank is added with an alkaline agent adding means for making the alkaline condition, and an alkaline condition. It has a retention tank to be retained below, an aeration tank for aerating the sludge accumulated in the retention tank in the presence of aerobic microorganisms, and a sludge returning means for returning the aerated sludge to the biological treatment tank. Characteristic organic sewage treatment equipment.