JPH0985299A - Method for decreasing quantity of organic sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively and economically decrease the quantity of org. sludge by anaerobically digesting org. sludge in an anaerobic digestion process and adding ozone or hydrogen peroxide to the digested sludge to solubilize the sludge and further anaerobically digesting the solubilized sludge. SOLUTION: Org. sludge 1 such as sewage raw sludge or excessive activated sludge is anaerobically digested in an anaerobic digestion process 2 at first and a part easily decomposable biologically is decreased in quantity. About 60wt.% of SS of raw sludge is digested herein. The remaining digested sludge is drawn out to a chemical oxidizing process 3 and ozone or hydrogen peroxide is added to the sludge to solubilize the same. Next, the solubilized sludge is further anaerobically digested by anaerobic bacteria in a second anaerobic digestion process 4 to be decomposed to carbon dioxide and water. By this method, 90wt.% or more of raw sludge can be decreased in quantity. The digested sludge of the second anaerobic digestion process 4 is subjected to solid-liquid separation and the separated soln. 5 is drained and the solid is treated as sludge residue 6.

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 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. Further, the activated sludge is directly ozone-treated to solubilize it, and then returned to the aeration tank (JP-A-7-1166).
No. 85) is also proposed, but it has drawbacks such as high ozone oxidation cost and poor practicability from the economical aspect.

[0004]

[Problems to be Solved] In order to efficiently carry out the activated sludge treatment method of organic wastewater, the organic sludge produced therefrom can be efficiently reduced, that is, the long-term reduction can be achieved. It is necessary to develop a technology that can be performed without requiring a lot of time and heat energy. The present invention reviews biological sludge reduction methods such as anaerobic digestion method and aerobic digestion method, makes the biological reduction method effective, and makes the reduction by the chemical oxidation method more economical. To provide a new technology that is targeted. An object of the present invention is to reduce the amount of organic sludge effectively and economically, thereby greatly reducing the amount of sludge brought into a sludge dehydrator and an incinerator and rationalizing the entire sludge treatment process. .

[0005]

The present invention combines biological anaerobic digestion and solubilization treatment by chemical oxidation in a novel manner to realize an effective and economical reduction of organic sludge. It was done. That is, the present invention was able to solve the above problems by the means shown below. (1) An organic sludge is anaerobically digested in an anaerobic digestion step, and then ozone or hydrogen peroxide is added to the digested sludge to solubilize it, and the solubilized sludge is further anaerobically digested. A method for reducing the amount of organic sludge, which comprises (2) anaerobically digesting organic sludge in an anaerobic digestion step, followed by solid-liquid separation by a membrane separation means, and separating solid digested sludge with ozone or hydrogen peroxide. A method for reducing the amount of organic sludge, which comprises adding and solubilizing the solubilized sludge and further anaerobic digesting the solubilized sludge.

As described above, when the raw sludge is directly chemically oxidized to be solubilized, a large amount of ozone and hydrogen peroxide are required, but after the raw sludge is anaerobically digested, the digestion is performed. When ozone or hydrogen peroxide is added to the sludge to solubilize it, the anaerobic digestion makes it easy to decompose into anaerobic microorganisms in the original sludge (usually 60% of the sludge SS weight).
The amount of ozone required for solubilization can be greatly reduced. Furthermore, maintaining an appropriate sludge concentration in the anaerobic digestion process makes the digestion process efficient, but in order to maintain this predetermined concentration, a part of the digested sludge must be extracted from the anaerobic digestion process. Therefore, if ozone or hydrogen peroxide is added to the extracted digested sludge to solubilize it, the amount of ozone and hydrogen peroxide required for solubilization will be small, and the digestion process will be complete. As effective and economical as. Then, the solubilized digested sludge is supplied to a step for further anaerobic digestion, and the solubilized sludge is decomposed into carbon dioxide gas and water by microorganisms. As a result, 90% or more of the original sludge weight is reduced.

Furthermore, a means for solid-liquid separation of digested sludge by membrane separation is provided in the anaerobic digestion process to perform solid-liquid separation of biologically reduced sludge, and the separated liquid is allowed to flow out of the system. The anaerobic digestion process becomes more effective and economical by using a method in which a part of the sludge is transferred to the digestion process and the rest is extracted and chemically oxidized to be solubilized.

[0008]

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 the drawings. In FIG. 1, the organic sludge 1 is first anaerobically digested in the first anaerobic digestion step 2 to reduce the amount of the portion that is easily biologically decomposed. 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. Anaerobic digestion step 2 from the first anaerobic digestion step 2
The sludge concentration inside should be kept at about 6% or less, where sludge can be sufficiently stirred. The remaining digested sludge is extracted outside the system (chemical oxidation step 3) and ozone or hydrogen peroxide is added to solubilize the sludge in the chemical oxidation step 3. The solubilized sludge is transferred to the second anaerobic digestion step 4 and further anaerobicly digested by anaerobic microorganisms to decompose into carbon dioxide gas and water. As a result, about 90% or more of the weight of the original sludge is reduced in the sludge sent to the solubilization treatment. Second anaerobic digestion step 4
Digested sludge is separated into solid and liquid, and the separated liquid 5 is drained out of the system,
The solid content is treated as residual sludge 6 (reduced sludge).

A preferred method for reducing the amount of organic sludge of the present invention will be described with reference to FIG. In the weight reduction step,
The digested sludge produced by the first anaerobic digestion step 2 is subjected to solid-liquid separation in a solid-liquid separation step 7 such as membrane separation or centrifugation to obtain a separation solution 5 having almost zero SS. Most of the membrane separation sludge 8 (reflux sludge 9) is refluxed to the first anaerobic digestion step 2. The remaining portion of the membrane separation sludge (transfer sludge 10) is sent to the chemical oxidation step 3 and chemically solubilized by adding ozone or hydrogen peroxide. The solubilized sludge is transferred to the second anaerobic digestion step 4 and decomposed into carbon dioxide gas and water by anaerobic microorganisms. By such an operation, the weight of the original sludge is 95
% Or more is reduced. Since about 5% by weight of the original sludge is not decomposed in many cases, it is supplied as a residue 6 (reduced sludge) to the sludge dehydrator for disposal. A more preferable method for reducing the amount of organic sludge is shown in FIG. The difference between the sludge reduction method of FIG. 3 and the method of FIG. 2 is that the solubilized sludge is returned to the first anaerobic digestion step 2 instead of being transferred to the second anaerobic digestion step 4. The second anaerobic digestion step 4 is also performed by the anaerobic digestion step 2.

In the method for reducing the amount of organic sludge according to the present invention, the following interesting effects were recognized. That is, in the weight reduction method shown in FIG. 1, solid-liquid separation of digested sludge in the final step, and in the weight reduction method shown in FIGS. 2 and 3, membrane separation in the anaerobic digestion step. Was found to be less. The reason seems to be that the membrane pollutants are oxidatively decomposed by the chemical oxidation of digested sludge by ozone or hydrogen peroxide. Further, in the second anaerobic digestion step in FIGS. 1 and 2 and the anaerobic digestion step in which the solubilized sludge is circulated in FIG. 3, the effect that hydrogen sulfide in the digestion gas is slightly reduced was recognized. This is probably because the sulfate-reducing bacteria are killed by chemical oxidation with ozone or hydrogen peroxide.

[0011]

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. 3: Sewage mixed raw sludge (solids concentration 2
5.0 g / liter) was processed according to the processing flow shown in FIG. In addition, in FIG. 3, since there is only one anaerobic digestion step, only the anaerobic digestion step was used. The volume of the digestion tank used in the anaerobic digestion step is 150 liters, the temperature of the anaerobic digestion is 35 ° C., the sludge concentration is 4.1 to 4.5%, and the retention days are 15 days. A membrane separation method was applied to the solid-liquid separation, and a UF membrane having a cut-off molecular weight of 100,000 was used as the membrane. The linear velocity of the flux passing through the UF membrane is 0.1 m / day. The method of cleaning when the film is contaminated is by chemical cleaning with sodium hypochlorite.

Solubilization of the solid-liquid separated digested sludge was carried out by the ozone oxidation method. The digested sludge solid matter that has been solid-liquid separated is supplied at a rate of 1.4 liters / day to an ozone oxidation tank having a volume of 1 liter, and 12% of ozone based on the weight of the digested sludge solid matter is supplied to oxidize it. . As a result of continuing the treatment for 1 year under these conditions, the amount of solid residue that cannot be decomposed is 1
It was extremely low at 3 to 14.6 g / day, and about 95% of the sludge supplied to the solubilization step was decomposed.

Further, the membrane-separated water generated when the digested sludge was subjected to solid-liquid separation was in an SS zero state and was extremely clear. It was confirmed that the linear velocity of the membrane-permeating flux in the solid-liquid separation step could be maintained at 0.1 m / day during the treatment for one year, and there was no membrane contamination that would not be recovered by washing. Also, when hydrogen peroxide is used instead of ozone oxidation and the amount of hydrogen peroxide added is 50% per chemical oxidation tank inflow sludge, the amount of solid residue that cannot be decomposed is 67 to 73 g / day. Although it is inferior to the ozone oxidation method, it is not inferior to practical use.

[0014]

According to the present invention, the effect of reducing the amount of organic sludge is large, the treatment time for biological sludge reduction is shortened, and the addition cost of ozone and hydrogen peroxide in solubilization by chemical oxidation is reduced. Can be significantly reduced compared to the case where the biological sludge reduction method is not used together. Also,
Membrane contamination in the membrane separation step can be almost eliminated.

[Brief description of drawings]

FIG. 1 shows a case of a method of carrying out a first anaerobic digestion step, a chemical oxidation step and a second anaerobic digestion step in the present invention.

FIG. 2 shows a case where a membrane separation step is inserted after the first anaerobic digestion step in the present invention shown in FIG.

FIG. 3 shows a case in which the second anaerobic digestion step is combined with the first anaerobic digestion step in the present invention shown in FIG. 2 to be an anaerobic digestion step.

[Explanation of symbols]

 1 Organic Sludge 2 First Anaerobic Digestion Process 3 Chemical Oxidation Process 4 Second Anaerobic Digestion Process 5 Separation Liquid 6 Residual Sludge 7 Solid-Liquid Separation Process 8 Membrane Separation Sludge 9 Reflux Sludge 10 Transfer Sludge 11 Anaerobic Digestion Process

Claims (2)

[Claims] 1. An organic sludge is anaerobically digested in an anaerobic digestion step, and then ozone or hydrogen peroxide is added to the digested sludge to solubilize it, and the solubilized sludge is further anaerobically digested. Method for reducing organic sludge. 2. The organic sludge is anaerobically digested in an anaerobic digestion step, and then solid-liquid separated by a membrane separation means, and ozone or hydrogen peroxide is added to the separated digested sludge to solubilize it.
A method for reducing the amount of organic sludge, characterized by further anaerobically digesting the solubilized sludge.