JP3417740B2 - Method and apparatus for reducing organic sludge - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus 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 Organic sludge such as sewage sludge, excess activated sludge and raw sludge (hereinafter,
A lot of "raw sludge" is generated,
The amount of those generated is increasing with the expansion of sewerage facilities, and the treatment and disposal of the increasing organic sludge is now 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, the equipment cost, the maintenance cost, etc. are large, and the incineration becomes economically difficult.

One of the means for solving this problem is to reduce the amount of organic sludge, and various means have been proposed for that purpose. As one of means for reducing sludge, there has been a biological biological method for reducing sludge, and an anaerobic digestion method and an aerobic digestion method are known. 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. In addition, a method is also known in which all of the organic sludge is subjected to alkali treatment and heat treatment and then subjected to anaerobic digestion, but the chemical cost and heating cost are high, and it is not practical from the economical aspect. There are drawbacks such as scarcity. Further, a method has also been proposed in which activated sludge is directly subjected to ozone treatment, solubilized, and then returned to an aeration tank (JP-A-7-116685), but the cost of ozone production is high and economical. There are drawbacks such as poor practicality in terms of aspects.

[0004]

[Problems to be solved] In order to efficiently carry out the activated sludge treatment method of organic wastewater, reduction of the amount of organic sludge generated therefrom does not require long-term treatment,
In addition, it is necessary to develop technology that can be performed without requiring much heat energy. An object of the present invention is to review the anaerobic digestion method and provide a new technique for effectively reducing the amount of organic sludge in combination with other reductions. Further, the present invention aims to significantly reduce the amount of sludge brought into the sludge dehydrator and incinerator by effectively reducing the amount of organic sludge, and to further rationalize the sludge treatment process as a whole. Is.

[0005]

The present invention combines the effects of organic sludge in a novel manner by combining biological anaerobic digestion, alkaline heat treatment and solubilization treatment by biological aerobic digestion. This is a real reduction. That is, the present invention was able to solve the above problems by the means shown below. (1) The organic sludge is subjected to anaerobic digestion and membrane separation in a membrane separation type anaerobic digestion step, the membrane separation liquid is drained to the outside of the system, and most of the solid digested sludge membrane separated is subjected to the anaerobic digestion step. The method is a method for reducing the amount of organic sludge, which comprises the steps of: refluxing to, and transferring the rest to a solubilization tank, subjecting to alkali heat treatment for solubilization, and then transferring to an aerobic digestion step for further aerobic digestion. (2) Introduce organic sludge, perform anaerobic digestion and membrane separation,
Membrane separation type anaerobic digester, membrane that drains the membrane separation liquid to the outside of the system
Most of the separated solid digested sludge is anaerobic digester.
Means for refluxing into the tank
And aerobically digest the solubilized sludge from the solubilizer.
Sludge reduction equipment characterized by having a digester for performing
Place Here, an aeration tank for biological treatment of wastewater can be used as a means for aerobic digestion. A treatment method of incorporating a membrane separation means in the anaerobic digestion step and performing membrane separation and solid-liquid separation in the anaerobic digestion step is called membrane separation type anaerobic digestion.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Organic sludge weight reduction method of the present invention
The apparatus will be described with reference to FIG. In FIG. 1, organic sludge 1 is first anaerobically digested in anaerobic digestion step 2,
Reduce the amount of biodegradable parts. The anaerobic digestion process is performed by a conventionally known anaerobic digestion method, and about 60% of the SS weight in the raw sludge is digested. 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.

During the anaerobic digestion step 2, the membrane separation means 3 (U
(F membrane unit etc.) is incorporated, solid-liquid separation of digested sludge is carried out, and separation liquid 4 having almost zero SS is obtained. Further, most of the separated solid membrane separation sludge 5 is refluxed to maintain the sludge concentration in the anaerobic digestion step 2 at a predetermined concentration. The sludge concentration in the anaerobic digestion step 2 should be kept to about 6% or less at which sludge can be sufficiently stirred. If the sludge concentration is too high, the viscosity becomes too large and the sludge cannot be sufficiently stirred. The remaining portion 6 of the membrane separation sludge is taken out to a solubilization tank 7 outside the system and heated and treated with an alkali to solubilize the sludge. After that, the solubilized sludge 9 is supplied to the aerobic digestion step 8, and the solubilized sludge is decomposed into carbon dioxide gas and water by aerobic microorganisms.
Instead of supplying the solubilized sludge 9 to the aerobic digestion step 8, the solubilized sludge may be sent to the aeration tank of the activated sludge treatment step for biological treatment with aerobic microorganisms. When solubilized sludge 9 is biologically treated in aerobic digestion step 8, 90% by weight of the original sludge
Is reduced.

The heating temperature for solubilizing digested sludge is 50.
~ 100 ° C, heating time 1 ~ 6 hours, alkali treatment p
H is preferably about 10 to 13. The alkaline agent is preferably caustic soda. As a result of anaerobic digestion, the amount of sludge decreases,
In addition, since only a part of the raw sludge needs to be subjected to the alkali heat treatment, the heating cost and the alkali agent cost are greatly reduced as compared with the method of subjecting the raw sludge to the alkali heat treatment. An anaerobic digestion time of about 15 to 30 days is sufficient. Alkali heat treatment of raw sludge as in the past causes some organic matter that promotes membrane closure to elute from the sludge.
Subsequent membrane separation results in membrane closure. In the present invention, since the raw sludge is anaerobically digested and then the membrane is separated, there are few substances causing the membrane closure, and the present invention is advantageous. It is an essential factor in the present invention to incorporate membrane separation in the anaerobic digestion process and completely prevent the sludge from flowing out to the separation liquid side. This is because if solid-liquid separation means such as precipitation separation or centrifugation is adopted instead of membrane separation, a large amount of sludge will leak to the separation liquid side, and the sludge will flow out of the system without being solubilized. Is. FIG. 1 shows one embodiment of the process flow of the present invention.

[0009]

EXAMPLES Examples of the method for reducing the amount of organic sludge of the present invention will be shown below. However, the present invention is not limited to the examples below. Example based on FIG. 1: Sewage mixed raw sludge (solids concentration 2
4.0 g / liter) was treated according to the treatment flow shown in FIG. The volume of the digestion tank used in the anaerobic digestion step is 150 liters, the anaerobic digestion temperature is 35 ° C., and the amount of raw sludge supplied is 10 liters / day (240 g / day). Membrane separation method is applied for solid-liquid separation, and the molecular weight of the membrane is 1
50,000 UF membranes were used.

The solid matter of the digested sludge, which had been solid-liquid separated, was supplied to a solubilization tank having a volume of 10 liters and subjected to an alkali heat treatment. The heating temperature is 80 ° C. and the pH is 12. afterwards,
The solubilized sludge is supplied to the aerobic digestion process, and the solubilized sludge is biologically treated by aerobic microorganisms. Residence time is 7
No particular heating is performed during the day. When the reduction treatment of the mixed raw sludge generated from the sewage treatment process was performed under these conditions, the amount of residual sludge generated was 18 to 20 g / day, which was 90% of that of the original sludge.
% Or more decomposed and disappeared. For comparison, when the alkali heat treatment and the subsequent aerobic digestion were deleted and the same treatment as in the above example was performed, the amount of residual sludge generated was 86 to 90 g / day, which was compared to the present invention. The efficiency of weight loss was significantly inferior.

[0011]

According to the present invention, since the sludge reduction is not performed only by the biological sludge reduction, the biological sludge reduction time can be shortened and the biological sludge reduction can be performed first. Since the sludge volume is reduced, the separated water is removed, and a part of the solid digested sludge is solubilized, the heating cost and alkali consumption can be significantly reduced, and the organic sludge volume reduction effect is great. Furthermore, the scale of the sludge dewatering machine could be greatly reduced compared to the case where the entire raw sludge was heat-treated with alkali without using the biological sludge reduction method.

[Brief description of drawings]

FIG. 1 shows a case of a method of performing an anaerobic digestion step, a membrane separation step, an alkali heat treatment step and an aerobic digestion step in the present invention.

[Explanation of symbols]

1 organic sludge 2 Anaerobic digestion process 3 Membrane separation means 4 Separation liquid 5 Solid separation sludge 6 Solid separation sludge 7 Solubilization tank 8 Aerobic digestion process 9 Solubilized sludge

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Claims (2)

(57) [Claims] 1. An organic sludge is subjected to anaerobic digestion and membrane separation in a membrane separation type anaerobic digestion step, and the membrane separation liquid is discharged to the outside of the system,
Most of the membrane-separated solid digested sludge is refluxed to the anaerobic digestion step, the rest is transferred to a solubilization tank and alkali-heated for solubilization, and then transferred to the aerobic digestion step for further aerobic digestion. A method for reducing the amount of organic sludge, which comprises: 2. Anaerobic digestion and membrane separation by introducing organic sludge
Membrane-separated anaerobic digestion that drains the membrane separation liquid to the outside of the system
Most of the equipment and membrane-digested solid digested sludge are anaerobic
Means for refluxing to digester, heat treatment with alkali
Aerobic solubilizer and solubilized sludge from the solubilizer
Sludge characterized by having a digester for sexual digestion
Weight reduction device.