JPH09234497A - Method for anaerobically digesting activated sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely reduce the volume of an excess activated sludge by returning most of the sludge separated from liq. to an aerobic digestion stage, ozonating a part of the separated sludge and supplying the whole separated sludge to the aerobic digestion stage. SOLUTION: The excess activated sludge 1 discharged from the activated sludge treating plant of an org. sewage such as sewerage is supplied to an aerobic digestion tank 2, aerated with an oxygen-contg. gas and aerobically digested. The aerobically digested biological sludge is sent to a solid-liq. separation tank 3, the sludge is separated from liq., the deposited sludge 4 is extracted, most of the deposited sludge is returned to the aerobic digestion tank 2 as a return sludge 5, a part of the sludge is transferred to an ozone oxidation tank 7 as a transfer sludge 6, ozone 8 is added to the sludge 6 in the tank 7 to solubilize the sludge 6 by an oxidation reaction, and the solubilized sludge 9 is returned to the aerobic digestion tank 2 along with the return sludge 5. Accordingly, the volume of the activated sludge 1 is completely reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for significantly reducing excess activated sludge discharged from an activated sludge treatment facility for organic wastewater.

[0002]

2. Description of the Related Art A large amount of surplus activated sludge is generated from activated sludge treatment facilities of organic wastewater such as sewage activated sludge treatment facilities, and the treatment and disposal of these surplus activated sludge is the biggest problem at present. . Conventionally, excess activated sludge is difficult to dehydrate, so a large amount of dewatering aid (polymer etc.) is added and dehydrated with a dehydrator and then incinerated.
The cost of the dehydration aid is high, and the dehydrator and incinerator are large-scaled, and the equipment cost and maintenance cost are high. In addition,
Conventionally, there are an anaerobic digestion method and an aerobic digestion method as a sludge reduction method for biologically reducing the excess activated sludge.
Since it requires a long residence time of 0 days or more, the weight reduction rate is inferior, so that it is rarely used these days.
Further, as shown in FIG. 2, ozone is directly added to activated sludge to solubilize the sludge and then aerobic digestion (Japanese Patent Publication No. 57-1).
9719) has been proposed, but it is not practical to apply this method to reduce the amount of surplus activated sludge from the biological treatment facility for organic wastewater because the required ozone addition amount is large and the ozone cost is high. poor.

Further, the above-mentioned technique of solubilizing sludge by directly adding ozone to excess activated sludge has the following problems. That is, if ozone is added directly to excess activated sludge to partially solubilize it and then send it to the aerobic digestion tank for aerobic digestion, there will be a considerable amount of unsolubilized sludge in the supplied activated sludge, which will not be solubilized. Aerobic digestion of sludge is extremely difficult. A large amount of new sludge is produced from the supplied biological sludge containing partially solubilized BOD. Since ozone is not added to this newly generated sludge, aerobic digestion of these sludges is difficult to proceed.

[0004]

DISCLOSURE OF THE INVENTION The present invention has reviewed the above-mentioned treatment method in which ozone is directly added to activated sludge to aerobically digest it, and surplus activated treated sludge generated when aerobically digesting activated sludge at low cost. The challenge is to provide a new technology that can completely reduce the amount of waste. The objective is to streamline the sludge treatment process by eliminating the sludge dehydrator and incinerator.

[0005]

The present invention combines aerobic digestion and solubilization of sludge by ozone oxidation in a novel manner,
Aerobic digestion of activated sludge and ozone oxidation to achieve effective reduction of sludge. That is, the aerobic digestion method of the present invention, excess activated sludge discharged from the activated sludge treatment facility of organic wastewater is subjected to aerobic digestion, solid-liquid separation is performed, and the large amount of separated sludge separated by the solid-liquid separation is used. While returning a part to the aerobic digestion step, ozone is added to a part of the separated sludge for treatment, and the activated sludge is supplied together with most of the separated sludge to the aerobic digestion step. It is an aerobic digestion method. In addition, hereinafter, the sludge generated from the activated sludge treatment facility of organic wastewater is referred to as activated sludge, and the sludge obtained by aerobically digesting the activated sludge is referred to as "biotreatment sludge".

As already mentioned above, when ozone is directly added to activated sludge to chemically solubilize it by ozone oxidation, a large amount of ozone is required. However, activated sludge is preferred in the embodiment of the present invention. The biological treatment sludge is aerobically digested, and ozone is added to the biological treatment sludge that is easily decomposed by the aerobic microorganisms to oxidize and solubilize it to reduce the weight, so that the weight reduction easily proceeds. In addition, when ozone is added to a part of biologically treated sludge to solubilize it, the amount of ozone remaining in the solubilized sludge is small. Is less affected by.

Further, in the aerobic digestion process, maintaining the sludge concentration within an appropriate fixed range makes the digestion process efficient, but in order to maintain this predetermined concentration, a part of the digested sludge is preferable. It is desirable to extract it from the aerobic digestion process. In the present invention, ozone is added to a part of sludge extracted from the system from the aerobic digestion step to solubilize the sludge by chemical oxidation, and excess sludge is returned by returning the solubilized sludge to the aerobic digestion step. While reducing the amount, it is possible to maintain the sludge concentration in the aerobic digestion process within an appropriate fixed range.

The appropriate addition amount of ozone for effectively solubilizing the biotreated sludge is about 10 to 20% based on the solid matter of the biotreated sludge. In the present invention, ozone is added to some of the biologically treated sludge extracted from the aerobic digestion process to oxidize it, so compared with the case where the biologically sludge is directly chemically ozone-oxidized and solubilized. Since the amount of ozone used can be greatly reduced, the ozone cost can also be significantly reduced. The sludge (solubilized sludge) that has been solubilized by chemical oxidation by adding ozone to the biologically treated sludge is then supplied to the aerobic digestion process, where the solubilized sludge is aerated in the presence of aerobic microorganisms, and solubilized. Aerobic microorganisms decompose sludge into carbon dioxide and water.

As another embodiment of the present invention, as the aerobic digestion step of further aerobically digesting the solubilized sludge that has been solubilized by adding ozone to the biologically treated sludge to effect ozone oxidation, the aerobic digestion step of the previous step is used. Instead of directly recirculating to the sewage, a biological treatment process in which an aerobic digestion process such as an activated sludge process of sewage such as another sewage is performed may be used or may be interposed therebetween. In the present invention, as means for solid-liquid separation in the aerobic digestion step, (i) a method of storing in a sedimentation basin and allowing sedimentable sludge to settle, and (i)
i) A method of performing solid-liquid separation by a filter equipped with a separation membrane can be mentioned.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the method for reducing the amount of organic sludge of the present invention will be described below with reference to FIG. Excess activated sludge discharged from activated sludge treatment facility of organic sewage such as sewage 1
Is supplied to the aerobic digestion tank 2, and an oxygen-containing gas (air, etc.)
It is aerated and digested aerobically. The aerobic digestion causes the activated sludge to self-extinguish, and a part (about 30%) of the sludge is decomposed into carbon dioxide and water. However, most of the sludge (about 70%) is difficult to self-extinguish even if it is aerated for a long time, and the weight reduction does not proceed. The biologically treated sludge is sent from the aerobic digestion tank 2 to the solid-liquid separation tank 3. In the present invention, the separated sludge 4 precipitated from the solid-liquid separation tank 3 (for example, a precipitation tank) following the aerobic digestion tank 2 is withdrawn, most of it is returned to the aerobic digestion tank 2 as return sludge 5, and a part of it is returned. Sludge is transferred to the ozone oxidation tank 7 as transfer sludge 6, ozone 8 is added to the sludge in the ozone oxidation tank 7, and the sludge is solubilized by an oxidation reaction,
The solubilized sludge 9 is returned to the aerobic digestion tank 2 together with the returned sludge 5.

In the method of the present invention, a part of the biologically treated sludge obtained by digestion by aerobic digestion is branched, ozone is added to the branched sludge to solubilize it, and the solubilized sludge is aerobically digested. As a result of returning it to the tank 2, it was confirmed that the self-extinguishing of sludge proceeded extremely effectively. The reason for this is considered to be that the oxidative effect of ozone is likely to cause destruction of the polysaccharides and strong microbial cell walls that hinder the progress of autolysis of sludge and facilitate the progress of autolysis.

According to the present invention, the amount of activated sludge is reduced almost completely and almost no sludge is generated outside the system from the process of FIG. Therefore, a sludge dewatering machine, a sludge incinerator, etc. are not required or the scale can be significantly reduced. The hydraulic retention time of the aerobic digestion tank in the present invention may be about 7 days, which is reduced to about 1/2 of the required retention days of the conventional aerobic digestion method. The proper addition amount of ozone in the present invention is as small as 3 to 5% per 1 kg of the solid matter of the branched biologically treated sludge, which is sufficient. Since the present invention applies a method of adding a small amount of ozone during aerobic digestion to reduce the factors that inhibit digestion, the known technique shown in FIG. Compared with the method of aerobic digestion after solubilization), less ozone is required.

In the method for reducing the amount of activated sludge according to the present invention, an interesting effect was observed when the biologically treated sludge digested in the aerobic digestion tank was subjected to solid-liquid separation by the membrane separation means. That is, it was confirmed that the membrane contamination was reduced in the membrane separation. Therefore, in the conventionally known excess sludge treatment step, it is necessary to perform solid-liquid separation by a precipitation method, whereas in the present invention, even if solid-liquid separation is performed by a more efficient membrane separation means, it is almost unnecessary to replace the separation membrane. The advantage of being fully usable was recognized.

[0014]

EXAMPLES Table 1 shows the experimental conditions based on the process of FIG. Excess activated sludge (solid concentration 5.0 g / liter) of sewage was treated according to the treatment flow shown in FIG.
The sludge treatment amount is 10 liters / day (50 g / day).
The aerobic digester 2 used in the aerobic digestion process has a volume of 70.
The digestion tank 2 is aerated with air, the dissolved oxygen amount in the liquid to be treated in the tank is maintained at 5 to 6 mg / l, the temperature in the digestion tank 1 is 25 ° C., and the sludge concentration is 5 to 6 g. / Liter. The biologically treated sludge produced by the aerobic digestion is subjected to solid-liquid separation by a precipitation method, and the separated water separated there is discharged to the outside of the system, and most of the separated sludge 4 is returned sludge 5 to the aerobic digestion tank 2. Send it back. A part of the separated sludge is used as the transfer sludge 6 and has an ozone oxidation tank 7 having the specifications shown in Table 1 below.
Then, ozone 8 is added to the sludge, the sludge is solubilized by an oxidation reaction, and the solubilized sludge 9 is returned to the aerobic digestion tank 2 together with the returned sludge 5.

[0015]

[Table 1]

As a result of continuing the test for 9 months under these conditions, 96% of the total weight of the excess activated sludge (9 kg) supplied was decomposed, and the amount of sludge discharged to the outside of the system was very small.

[0017]

【The invention's effect】

1. The effect of reducing excess activated sludge is extremely large, and the sludge treatment and disposal process is rationalized. The amount of sludge discharged to the outside of the system can be made minute. 2. Ozone addition costs are reduced because the amount of ozone used for activated sludge is significantly reduced.

[Brief description of drawings]

FIG. 1 shows a process flow of sludge reduction of the present invention in which activated sludge is aerobically digested and then part of the separated sludge is oxidized with ozone.

FIG. 2 shows a conventional sludge reduction process flow in which activated sludge is directly ozone-oxidized.

[Explanation of symbols] 1 supplied activated sludge 2 aerobic digestion tank 3 solid-liquid separation tank 4 separation sludge 5 return sludge 6 transfer sludge 7 ozone oxidation tank 8 ozone 9 solubilized sludge 10 supply biological sludge 11 ozone oxidation tank 12 aerobic digestion Tank 13 Settling tank 14 Return sludge

Claims (1)

[Claims] 1. Excessive activated sludge discharged from the activated sludge treatment facility for organic wastewater is subjected to aerobic digestion and then solid-liquid separated,
Most of the separated sludge separated by the solid-liquid separation is returned to the aerobic digestion step, and ozone is added to a part of the separated sludge for treatment, and most of the separated sludge is treated with the aerobic digestion. An aerobic digestion method for activated sludge, which is characterized in that it is supplied to a process.