JP3447028B2 - How to reduce organic sludge - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for significantly reducing the amount of organic sludge such as sewage raw sludge, surplus activated sludge, and mixed raw sludge.

[0002]

2. Description of the Related Art A large amount of sewage sludge, surplus activated sludge and organic sludge (hereinafter also referred to as "raw sludge") are generated from sewage activated sludge treatment facilities. The amount of generation is increasing with the expansion of sewerage facilities, and the treatment and disposal of the increasing amount of organic sludge is currently the biggest problem. Conventionally, organic sludge has been dehydrated with a dehydration aid (organic polymer, etc.) and then incinerated after being dehydrated. However, if a large amount of sludge is used, the dehydrator and incinerator are large. It becomes a large scale, equipment cost,
Due to the large amount of maintenance costs, incineration is economically difficult.

As one of the means for solving this problem, there has been a biological sludge weight reduction method, which is conventionally known as an anaerobic digestion method or an aerobic digestion method. However, these biological sludge reduction methods have problems that the reduction rate is inferior for a long residence time and that hardly-dewatering sludge is produced. The reality is that there is none. A method has also been proposed in which the activated sludge is directly ozone-treated without anaerobic digestion, solubilized, and then returned to the aeration tank (JP-A-7-116685). There are drawbacks such as high ozone oxidation cost and poor practicality from an economical point of view.

[0004]

DISCLOSURE OF THE INVENTION It is an object of the present invention to review a biological sludge reduction method such as an anaerobic digestion method or an aerobic digestion method, and to provide a new technique for effectively reducing activated sludge. It is an issue. The present invention also aims to rationalize the entire sludge treatment process by effectively and economically reducing the amount of organic sludge, thereby greatly reducing the amount of sludge brought into the sludge dehydrator and incinerator. is there.

[0005]

The present invention combines biological anaerobic digestion, aerobic digestion and solubilization treatment of sludge by ozone oxidation in a novel manner to provide an effective and economical treatment of organic sludge. It is possible to reduce the amount of waste. That is, the present invention was able to solve the above problems by the means shown below. (1) After anaerobically digesting organic sludge in an anaerobic digestion step, ozone is added to the digested sludge to solubilize it, and the solubilized sludge is further aerated with sewage in the presence of aerobic microorganisms. A method for reducing the amount of organic sludge, which is characterized by: (2) After the organic sludge is anaerobically digested in the anaerobic digestion step, solid-liquid separation is performed by the membrane separation means, ozone is added to the separated digested sludge to solubilize it, and the solubilized sludge is further aerobic A method for reducing the amount of organic sludge, which comprises performing aeration treatment with sewage in the presence of microorganisms.

As already mentioned above, when the raw sludge is directly chemically ozone-oxidized to be solubilized, a large amount of ozone is required. However, in the embodiment of the present invention, the raw sludge is anaerobically digested and anaerobic digested. The part that is easily decomposed by the active microorganisms (usually sludge SS
About 60% of the weight). The hydraulic retention time in the anaerobic digestion tank may be about 7 to 14 days. Maintaining an appropriate sludge concentration in the anaerobic digestion process makes the digestion process efficient, but it is desirable to extract a part of the digested sludge from the anaerobic digestion process in order to maintain this predetermined concentration. . Ozone is added to a part of the sludge extracted from the anaerobic digestion process outside the system (the amount required to maintain the sludge concentration in the anaerobic digestion tank at a specified value) to solubilize the sludge by chemical oxidation. . The appropriate addition amount of ozone for effectively solubilizing sludge is about 10 to 20% based on the sludge solid matter. In the present invention, as a result of anaerobic digestion, the amount of sludge is significantly reduced, so that the amount of ozone used is significantly smaller than that in the case of solubilizing the raw sludge directly by chemical ozone oxidation. Therefore, the ozone cost can be reduced significantly.

The sludge solubilized by chemical oxidation by adding ozone is then supplied to an aerobic digestion process in which the solubilized sludge is aerated in the presence of aerobic microorganisms, and the solubilized sludge is treated by the aerobic microorganisms. Decomposes into carbon dioxide and water. As a result, 90% or more of the original sludge weight is reduced. As an aerobic digestion process after ozone oxidation, a biological treatment process such as an activated sludge process of sewage and other sewage can be used.

In a preferred embodiment of the present invention, means for solid-liquid separation of the digested sludge in the anaerobic digestion process by membrane separation is provided, and the sludge reduced in weight by anaerobic digestion is solid-liquid separated. The anaerobic digestion process is more effective by discharging it to the outside, transferring a part of the solidified sludge to the anaerobic digestion process, extracting the rest, adding ozone to the extracted digested sludge and solubilizing it by ozone oxidation. And can be economical.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method for reducing the amount of organic sludge of the present invention will be described below with reference to FIG. Figure 1 shows the case of solid-liquid separation of sludge reduced by anaerobic digestion. However, a part of sludge is extracted and ozone-oxidized without solid-liquid separation of sludge reduced by anaerobic digestion. Alternatively, the present invention is not limited by the description of the embodiments below.

A method for reducing the amount of the organic sludge of the present invention will be described with reference to FIG. In FIG. 1, the organic sludge 1 is first anaerobically digested in an anaerobic digestion step 2 to reduce a portion that is easily biodegraded. The treatment of anaerobic digestion is performed by a conventionally known method of anaerobic digestion, and normally, about 60% of the SS weight in the raw sludge is digested by the anaerobic digestion. By this anaerobic digestion step 2, the organic sludge becomes a low molecular weight soluble organic compound, and as a result, the amount of the organic sludge is reduced accordingly. The organic sludge 1 is anaerobically digested in the anaerobic digestion step 2, and then the digested sludge is subjected to solid-liquid separation by membrane separation by the UF membrane 3 to obtain a separation liquid 4 with almost zero SS.
The separated liquid 4 is discharged outside the system.

On the other hand, most of the membrane separation sludge 5 is reflux sludge 8.
Is refluxed to the anaerobic digestion step 2. The remaining part of the membrane separation sludge (transfer sludge 6) is supplied to the chemical oxidation tank 7 with ozone and is solubilized by ozone oxidation. Ozone has a strong oxidizing power, destroys the cell wall of microorganisms, solubilizes sludge and turns it into BOD. The appropriate amount of ozone added to effectively solubilize sludge is about 10 to sludge solids.
20%. The solubilized sludge 10 is guided to the aerobic digestion tank 9, where it is decomposed into carbon dioxide gas and water by various aerobic microorganisms. The sludge flowing out from the aerobic digestion tank 9 is separated into concentrated sludge and supernatant water by the solid-liquid separation means 11, the supernatant water is discharged out of the system, and the concentrated sludge is refluxed to the chemical oxidation tank 7 or the aerobic digestion tank 9. It By such operation, 95% to 100% of the sludge weight of the original sludge is extinguished, so that almost no residual sludge is generated. In the method for reducing the amount of organic sludge according to the present invention, the following interesting effects were observed in the membrane separation of aerobic digested sludge. That is, it was confirmed that the membrane contamination in the membrane separation was reduced in the membrane reduction method shown in FIG. The reason seems to be that the membrane contaminants are oxidatively decomposed by the chemical oxidation of digested sludge by ozone.

[0012]

EXAMPLE An example of the method for reducing the amount of organic sludge of the present invention will be described below with reference to FIG. However, the present invention is not limited to the examples below. Example 1 Sewage mixed raw sludge (solid concentration 25.0 g / liter)
Was processed according to the processing flow shown in FIG. The sludge treatment amount is 10 liters / day (250 g / day). The volume of the anaerobic digestion tank 1 used in the anaerobic digestion process is 70 liters, the temperature of anaerobic digestion is 35 ° C., and the sludge concentration is 41.
~ 45 g / l. A membrane separation method was applied to the solid-liquid separation means, and a UF membrane with a cut-off molecular weight of 100,000 was used as the membrane. U
The linear velocity of the flux passing through the F membrane is 0.1 m / day. The method of cleaning when the film is contaminated is by chemical cleaning with sodium hypochlorite.

The solubilization of the solid-liquid separated digested sludge was carried out by the ozone oxidation method. Membrane-separated solids of digested sludge are supplied at a rate of 1.6 liters / day to an ozone oxidizer having a volume of 1 liter, and 12% of ozone based on the weight of the solids of digested sludge is supplied thereto for ozone oxidation. The solubilized sludge solubilized by the ozone oxidation method is then transferred to the aerobic digestion tank 9,
It is aerobically digested by various aerobic microorganisms. The volume of the aerobic digestion tank 9 is 16 liters, the water temperature is 25 ° C., and the residence time is 10 days. As a result of continuing the treatment for 1 year under these conditions, the amount of solid residue that cannot be decomposed is 11 to 12 g.
/ 95 days of sludge supplied to the solubilization process
% Has been decomposed. The membrane-separated water had an SS content of zero and was extremely clear.

The linear velocity of the flux permeating through the membrane in the solid-liquid separation step can be maintained at 0.1 m / day for one year of treatment, and it was confirmed that there is no membrane contamination that cannot be recovered by washing. It was

[0015]

According to the present invention, the effect of reducing the amount of organic sludge is great, the treatment time for biological sludge reduction is shortened, and the ozone addition cost in solubilization by chemical oxidation is biological It is possible to significantly reduce the amount compared with the case where the different sludge reduction methods are not used together. Further, it is possible to almost eliminate the membrane contamination in the membrane separation step.

[Brief description of drawings]

FIG. 1 shows a process flow of the present invention in which an anaerobic digestion step, a chemical oxidation step and an aerobic digestion step are performed.

[Explanation of symbols]

1 organic sludge 2 Anaerobic digester 3 Membrane separation unit 4 Membrane separation liquid 5 Membrane separation sludge 6 Transfer sludge 7 Ozone oxidation tank 8 Reflux sludge 9 aerobic digester 10 Solubilized sludge 11 Solid-liquid separation means

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) C02F 11/00-11/20 C02F 3/12

Claims (2)

(57) [Claims] 1. An organic sludge is anaerobically digested in an anaerobic digestion step, and then ozone is added to the digested sludge to solubilize it, and the solubilized sludge is further mixed with sewage in the presence of aerobic microorganisms.
A method for reducing the amount of organic sludge, which is characterized by performing aeration treatment. 2. The organic sludge is anaerobically digested in an anaerobic digestion step, then solid-liquid separated by a membrane separation means, and ozone is added to the separated digested sludge to solubilize the solubilized sludge. A method for reducing the amount of organic sludge, which comprises aeration-treating with sewage in the presence of aerobic microorganisms.