JP2008296172A - Sludge treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sludge treatment method which can reduce the amount of surplus sludge to a minimum level while preventing generation of bad influence on water treatment by efficiently reducing surplus sludge, generated in activated sludge treatment, in an activated sludge treatment system. <P>SOLUTION: In the sludge treatment method where surplus sludge resulting from the activated sludge treatment of organic sewage is reduced by aerobic digestion, an aerobic digestion tank 10 is divided into a plurality of stages in the flow direction of the surplus sludge, the surplus sludge D and a biological activity-promoting agent F are fed into the most upstream, first stage digestion tank 10a to perform aerobic digestion treatment while maintaining the temperature at 25-40°C in the first digestion tank 10a, and a part of the sludge in the most downstream, final stage digestion tank 10b is introduced into an electrolysis tank 12 to be electrolyzed, and then returned to the first stage digestion tank 10a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sludge treatment method for biologically degrading organic sewage such as sewage with activated sludge, and in particular, sludge treatment capable of minimizing the amount of sludge generated by the decomposition treatment of organic matter. It is about the method.

2. Description of the Related Art Conventionally, in order to treat sewage flowing into a sewage treatment plant or the like, an activated sludge method is used in which sewage is introduced into an activated sludge aeration tank, and this is aerated and agitated to perform biological treatment.
Surplus sludge generated in the water treatment process is usually landfilled after concentration and dehydration, but since the disposal site is gradually disappearing, sludge microorganisms are added to the surplus sludge by adding ozone, etc. Has been attempted to reduce the amount of sludge generated by sterilizing and solubilizing and biodegrading in the system, and in particular, the method using electrolysis has attracted attention as a method with low processing costs. .

  However, in these sludge reduction methods, the treated sludge is returned to the aeration tank of the water treatment system and biodegraded by the activated sludge in the aeration tank, which increases the load on the water treatment system and makes the aeration capacity insufficient. Or the quality of treated water deteriorated.

  On the other hand, in order to reduce excess sludge in the sludge treatment system, a method of adding anaerobic digestion or aerobic digestion to the previous stage of conventional concentration / dehydration treatment is also adopted. The rate at which the amount can be reduced is about 40 to 60%, which is not necessarily a sufficient performance, and in recent years, it is not so often employed.

  In view of the problems of the above-described conventional sludge treatment methods, the present invention prevents the adverse effect on water treatment by efficiently reducing excess sludge generated by activated sludge treatment in a sludge treatment system. However, it aims at providing the processing method of the sludge which can reduce excess sludge to the minimum quantity.

  In order to achieve the above object, the sludge treatment method of the present invention is a sludge treatment method for reducing excess sludge generated by activated sludge treatment of organic sludge by aerobic digestion. Divided into multiple stages in the sludge flow direction, surplus sludge and biological activity promoter are introduced into the uppermost first stage digester, and aerobic digestion is maintained while maintaining the inside of the first stage digester at 25-40 ° C. In addition to performing the treatment, a part of the sludge in the final stage digestion tank at the most downstream is guided to the electrolytic treatment tank and subjected to electrolysis, and then returned to the first stage digestion tank.

  In this case, a part of organic sewage flowing into the water treatment facility or a separately cultured microorganism solution can be added as the biological activity promoter.

  Moreover, the amount of sludge solids to be returned after electrolytic treatment can be 2 to 5 times the amount of sludge solids charged into the first stage digestion tank.

  In addition, the sludge in the final digestion tank is concentrated and separated using a solid-liquid separator such as a centrifuge, and the separated water is sent to a water treatment facility, and all or part of the concentrated sludge is transferred to an aerobic digester. Can be returned.

  According to the sludge treatment method of the present invention, an aerobic digestion and electrolytic treatment are rationally combined, and a bioactivity promoter is added to sludge that has been sterilized and partially solubilized and easily decomposed by electrolytic treatment. Since aerobic digestion is performed while maintaining the inside of the first stage digestion tank at 25 to 40 ° C., efficient and stable aerobic digestion can be performed, and the amount of sludge solids discharged out of the field can be concentrated and dehydrated by conventional methods. It can be reduced to 1/3 or less of the case of processing.

  In this case, digestion efficiency in the aerobic digester can be increased by introducing a part of organic wastewater flowing into the water treatment facility or a separately cultured microorganism solution as the bioactivity promoter.

In addition, the sludge that has been electrolyzed is in a state in which sludge microorganisms are sterilized and solubilized and easily biodegraded, and gradually decomposed by living sludge microorganisms. Since 20 to 50% of the amount of sludge microorganisms grows, a sufficient reduction effect cannot be obtained unless the amount of surplus sludge added is larger than the amount of excess sludge.
Therefore, the amount of sludge solids returned after electrolytic treatment is 2 to 5 times the amount of sludge solids charged into the first digestion tank, so that excess sludge can be efficiently treated and the reduction effect improved. Can be made.

  In addition, the sludge in the final digestion tank is concentrated and separated using a solid-liquid separator such as a centrifuge, and the separated water is sent to a water treatment facility, and all or part of the concentrated sludge is transferred to an aerobic digester. By returning it, electrolytic treatment can be performed on the digestion tank sludge maintained at a high concentration, and the running cost required for electricity bill and electrolyte addition can be reduced.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a sludge treatment method of the present invention will be described based on the drawings.

In FIG. 1, one Example of the processing method of the sludge in this invention is shown.
The sewage A that has flowed into a sewage treatment facility such as a sewage treatment plant is treated with trash and sand in the sewage in the pretreatment facility 1, and then the organic matter in the sewage is biologically carbon dioxide by activated sludge in the aeration tank 2. And decomposed into water.
Further, the treated sludge mixed liquid is guided to the precipitation tank 3 for solid-liquid separation, and the supernatant water is discharged as treated water B.
Most of the settled sludge is returned to the aeration tank by the return sludge pump 4 as return sludge C, but the sludge microorganisms grow by the biological treatment, and surplus sludge is generated.
This surplus sludge D is led to the concentration facility 6 by a sludge treatment system sludge transfer pump 5. Although it is cheap and preferable to use a gravity type concentration tank as the concentration facility 6, it is also possible to use a mechanical concentration facility such as a centrifugal concentrator.

The concentrated excess sludge D is transferred as concentrated sludge E to the aerobic digester 10 by the concentrated sludge pump 7.
The aerobic digestion tank 10 is divided into three stages in the flow direction of the concentrated sludge E, and weirs are provided so as to overflow from the water tanks of each stage and to flow out to the water tanks of the subsequent stages, and the bottoms of the respective water tanks Is provided with an air diffuser for supplying the necessary oxygen.
Note that the number of stages for dividing the aerobic digester 10 is not limited to three stages, and any number of stages can be applied as long as it is two or more stages.

Here, in the process of returning the sludge G in the final stage digestion tank 10b to the first stage digestion tank 10a, a sludge return pump 11 and an electrolytic treatment tank 12 are provided to perform electrolytic treatment.
In addition, in order to perform the electrolytic treatment efficiently in the electrolytic treatment tank 12, an electrolyte storage tank 13 in which an electrolyte such as sodium chloride or potassium chloride is dissolved and an injection pump (not shown) are provided, and a predetermined amount of the aqueous electrolyte solution is supplied. It is configured so that it can be injected into the electrolytic treatment tank 12.

Furthermore, in order to keep the sludge microorganisms in the entire aerobic digestion tank 10 at a high concentration and to stabilize the water level of the aerobic digestion tank 10 by extracting the digested sludge equivalent to the amount of sludge charged into the aerobic digestion tank 10, A mud pump 14 and a centrifugal concentrator 15 for solid-liquid separation are provided.
For the separated water I of the centrifugal concentrator 15, a pipe for supplying water to the aeration tank 2 of the water treatment facility is provided, and for the concentrated centrifugal concentrated sludge H, a pipe and a system for returning to the first stage digestion tank 10a. It is branched into piping for discharging to the outside.
The structure and configuration of the electrolytic treatment tank 12 are not particularly limited, but a stirring and mixing zone is provided such that the injected electrolyte is dispersed in the sludge, or foamed scum generated during the electrolytic treatment is formed on the electrode. It is preferable to provide a structure that does not stick or a device that defoams the foamed scum.

On the other hand, a bioactivity promoter storage tank 8 and an injection pump 9 are provided to enhance the decomposition effect of the electrolytically treated return sludge.
As a biological activity promoter, it is possible to use a part of organic sewage flowing into a water treatment facility by piping.
It is also possible to separately cultivate microbial cells such as Bacillus and periodically use this microbial solution while replenishing the biological activity promoter storage tank 8.

Next, the operation of this embodiment will be described.
Sludge extracted by the sludge return pump 11 from the last stage digestion tank 10 b of the aerobic digestion tank 10 is sent to the electrolytic treatment tank 12.
In the electrolytic treatment tank 12, a predetermined amount of the aqueous electrolyte solution is injected and mixed into the sludge from the electrolyte storage tank 13, and the electrolytic treatment is performed by flowing a direct current.
That is, chlorine ions in the electrolyte injected by passing a direct current are converted into hypochlorous acid and hypochlorite ions, so that sludge microorganisms are sterilized and partly solubilized by their oxidizing power.
As the conditions for the electrolytic treatment, the injection amount of the electrolyte is 0.3 to 1% with respect to the sludge, and a metal electrode in which platinum and iridium are coated on the titanium substrate is used as the electrode, and the current density is 5 to 40 mA / cm ² . It is desirable to treat the energization amount per 1 g of sludge solids as 0.05 to 0.3 A · hr.
In addition, if a small amount of acid is injected at the time of electrolytic treatment and electrolysis is performed in a weakly acidic region around pH = 5, only hypochlorous acid having a higher oxidizing power than hypochlorite ions can be generated. Electrolytic treatment can be performed more efficiently.

The electrolytically treated sludge is returned to the first stage digestion tank 10a, but efficiently while the sterilized or partially solubilized sludge microorganisms move from the first stage digestion tank 10a to the final stage digestion tank 10b. In order to biodegrade, it is necessary to maintain a high concentration of highly active microorganisms.
That is, the concentrated sludge E introduced into the first stage digestion tank 10a by the concentrated sludge pump 7 contains a large amount of living microorganisms, but is not necessarily highly active sludge.
For this reason, organic sewage containing organic matter that is easily decomposable for sludge microorganisms, or a culture solution containing highly active microorganisms is stored in the bioactivity promoter storage tank 8, and this bioactivity promotion is performed in accordance with the input of concentrated sludge. Add a small amount of Agent F.
At the same time, by keeping the entire aerobic digester 10 at 25 to 40 ° C., the activity of the microorganism having the highest biological activity in this temperature region can be dramatically increased.

  In addition, sludge that has been electrolyzed is in a state in which sludge microorganisms are sterilized and solubilized and easily biodegraded, and gradually decomposed by living sludge microorganisms. Since 20 to 50% of the amount of sludge microorganisms grows, a sufficient weight reduction effect cannot be obtained unless the electrolytic treatment is performed more than the amount of the concentrated sludge E that has been input. 2-5 times the amount of sludge G is electrolyzed.

On the other hand, even if such a reduction treatment is performed, the amount of sludge cannot normally be reduced to zero. Therefore, the sludge G is guided from the final stage digestion tank 10b to the centrifugal concentrator 15 for solid-liquid separation, and the separated water is separated. The water level of the aerobic digestion tank 10 is stabilized by sending water to the water treatment facility, and an appropriate amount of concentrated sludge, for example, about 20% of the solid content of the concentrated sludge E put into the aerobic digestion tank 10, is solid. Drain things out of the system.
Considering the sludge concentration in the aerobic digester 10, the aerobic digester 10 can be stabilized by electrolytically treating an appropriate amount of sludge and discharging the appropriate amount of centrifugal concentrated sludge H to the outside of the system. It becomes possible.
Instead of discharging the centrifugal concentrated sludge H, the sludge in the aerobic digestion tank 10 can be directly discharged by the sludge pump 14. In this case, since the water level of the aerobic digestion tank 10 gradually rises only by discharging a small amount of sludge after reduction, the sludge G is solid-liquid separated using the centrifugal concentrator 15 and separated. It is necessary to send water to the water treatment facility, return the entire amount of concentrated sludge to the aerobic digester 10, and operate the centrifugal concentrator 15 until the water level reaches a predetermined water level.

As described above, the sludge treatment method of the present example is a combination of aerobic digestion and electrolytic treatment, and bioactive promoters are targeted for sludge that has been sterilized and partially solubilized and easily decomposed by electrolytic treatment. Addition and aerobic digestion while maintaining the inside of the tank at 25 to 40 ° C, so that efficient and stable aerobic digestion can be performed, and the amount of sludge solid matter discharged out of the field is the case of conventional concentration and dehydration treatment Can be reduced to 1/3 or less.
In addition, solid-liquid separation is performed with a solid-liquid separation device such as a centrifuge, and the whole or part of the concentrated sludge is returned to the aerobic digester, so that the digestion tank sludge maintained at a high concentration can be electrolyzed. Since the treatment is performed, there is an effect that the running cost required for electricity bill and electrolyte addition can be reduced.

  As mentioned above, although the processing method of the sludge of this invention was demonstrated based on the Example, this invention is not limited to the structure described in the said Example, In the range which does not deviate from the meaning, the structure is suitably used. Can be changed.

  The sludge treatment method of the present invention has a negative effect on water treatment by rationally combining aerobic digestion and electrolytic treatment and efficiently reducing excess sludge generated by activated sludge treatment in a sludge treatment system. In addition to sewage treatment plants that treat living sewage with activated sludge, organic wastewater generated at factories and other facilities has the property of reducing excess sludge to a minimum amount while preventing wastewater. Can also be suitably applied to wastewater treatment facilities that treat activated carbon with activated sludge.

It is a flowchart which shows one Example of the processing method of the sludge of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pretreatment equipment 2 Aeration tank 3 Settling tank 4 Return sludge pump 5 Sludge transfer pump 6 Concentration equipment 7 Concentrated sludge pump 8 Bioactivity promoter storage tank 9 Injection pump 10 Aerobic digester 10a First stage digester 10b Final stage digestion Tank 11 Sludge return pump 12 Electrolytic treatment tank 13 Electrolyte storage tank 14 Feeding pump 15 Centrifugal concentrator A Sewage B Treated water C Return sludge D Surplus sludge E Concentrated sludge F Bioactivity promoter G Digested sludge H Centrifugal concentrated sludge I Separated water

Claims (4)

  In the sludge treatment method that reduces the excess sludge generated by the activated sludge treatment of organic sludge by aerobic digestion, the aerobic digester is divided into multiple stages in the flow direction of the excess sludge, Surplus sludge and biological activity promoter are introduced into the first stage digestion tank, and aerobic digestion treatment is performed while maintaining the inside of the first stage digestion tank at 25 to 40 ° C. A method for treating sludge, wherein the part is guided to an electrolytic treatment tank and electrolyzed, and then returned to the first stage digestion tank.   The method for treating sludge according to claim 1, wherein a part of the organic sewage flowing into the water treatment facility or a separately cultured microorganism solution is added as the bioactivity promoter.   The method for treating sludge according to claim 1 or 2, wherein the amount of sludge solids returned after electrolytic treatment is 2 to 5 times the amount of sludge solids charged into the first stage digestion tank.   The final stage digester sludge is concentrated and separated using a solid-liquid separator such as a centrifuge, and the separated water is sent to a water treatment facility, and all or part of the concentrated sludge is returned to the aerobic digester. The method for treating sludge according to claim 1, 2, or 3.

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