JP4615530B2 - Sludge treatment method - Google Patents

Description

  The present invention relates to a sludge treatment method for biologically decomposing organic sewage such as sewage with activated sludge, and in particular, sludge treatment capable of minimizing the amount of sludge generated by organic substance decomposition. 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 has not been adopted very much (see Non-Patent Document 1).
"Sewerage facility plan, design guidelines and explanation, second part, 1994 edition"

  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. After dividing the sludge into a plurality of stages in the flow direction of the sludge, charging excess sludge into the uppermost first stage digester and conducting the electrolysis treatment by introducing the sludge from the first stage digester into the electrolytic treatment tank In addition to returning to the first stage digestion tank, the sedimentation sludge in the precipitation separation tank provided downstream of the most downstream final stage digestion tank or aerobic digestion tank is returned to the first stage digestion tank for aerobic digestion. It is characterized by performing.

  In this case, the electrolytic treatment can be performed by adding an electrolyte of sodium chloride or potassium chloride to the electrolytic treatment tank.

  Moreover, the amount of sludge to be electrolytically treated in the electrolytic treatment tank can be set to 2 to 5 times the amount of excess sludge charged into the first stage digestion tank.

  Moreover, the amount of precipitation sludge returned to the first stage digestion tank from the final stage digestion tank or the precipitation separation tank can be 2 to 15 times the amount of excess sludge charged into the first stage digestion tank.

According to the sludge treatment method of the present invention, aerobic digestion and electrolytic treatment are rationally combined, and aerobic digestion is performed on sludge that has been sterilized by electrolytic treatment and partially solubilized and easily decomposed. It is possible to perform an efficient and stable aerobic digestion, thereby reducing the amount of sludge discharged outside the field to 1/3 or less of the conventional concentration / dehydration treatment and maintaining a high concentration. By performing the electrolytic treatment by extracting the sludge from the first-stage digestion tank, the running cost required for electricity and electrolyte addition can be reduced.
In this case, if the operation of extracting sludge from the first stage digestion tank, electrolytic treatment and returning it is continued, the highly active sludge microorganisms gradually decrease in the first stage digestion tank and the aerobic digestion reaction proceeds. However, the sludge microorganisms deficient by the electrolytic treatment can be replenished by returning the highly active precipitated sludge precipitated in the final stage digestion tank or the like to the first stage digestion tank.

  In this case, by adding an electrolyte of sodium chloride or potassium chloride to the electrolytic treatment tank and performing the electrolytic treatment, the chloride ions of the electrolyte are converted to hypochlorous acid or hypochlorite ions, and sludge is produced by their oxidizing power. It is possible to sterilize microorganisms efficiently and solubilize a part of them.

In addition, the sludge that has been electrolyzed is in a state in which sludge microorganisms are sterilized and solubilized and are 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 to be electrolyzed in the electrolytic treatment tank is 2 to 5 times the amount of excess sludge that is put into the first stage digestion tank, so that the excess sludge can be efficiently treated and the reduction effect is improved. Can be made.

  In addition, the larger the amount of electrolytically treated sludge, the larger the amount of precipitated sludge that needs to be returned from the precipitation separation zone or precipitation separation tank to the first stage digestion tank, and the first stage digestion from the final stage digestion tank or precipitation separation tank. By setting the amount of precipitated sludge to be returned to the tank to 2 to 15 times the amount of excess sludge to be charged into the first stage digestion tank, the excess sludge can be efficiently treated and the reduction effect can be improved. .

  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 2 by the return sludge pump 4 as return sludge C, but the sludge microorganisms grow along with the biological treatment, and surplus sludge is generated.
In order to transfer the surplus sludge D to the sludge treatment system, the sludge transfer pump 5 first leads to the concentration facility 6.
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 intermittently transferred to the aerobic digester 8 by the concentrated sludge pump 7 as the concentrated sludge E.
As shown in FIG. 2, the aerobic digester 8 is divided into three stages in the flow direction of the concentrated sludge E, and an aeration tube 81 is provided for each.
The concentrated sludge E is introduced into the most upstream first stage digestion tank 8a, and the concentrated sludge E in the first stage digestion tank 8a is guided to the electrolytic treatment tank 10 to be described later and electrolyzed, and then the first stage. While returning to the digester tank 8a, the sedimentation sludge G of the most downstream final stage digester tank 8c is extracted and returned to the first stage digester tank 8a.
In addition, the number of stages for dividing the aerobic digester 8 is not limited to three, and can be applied if it is two or more.
The final-stage digestion tank 8c is a tank for forming a precipitation separation zone. The air diffuser 81 at the bottom is provided with an electrically operated valve 82 so that aeration can be stopped, and an overflow weir 83 at the top. Is provided.
Furthermore, a sedimentation sludge return pump 9 is provided for returning the sedimentation sludge G precipitated at the bottom of the final stage digestion tank 8c to the first stage digestion tank 8a.
When the final stage digestion tank 8c for forming the precipitation separation zone is provided, operation control as will be described later is required, so that the precipitation separation is performed in the subsequent stage of the aerobic digestion tank 8 instead of the final stage digestion tank 8c. It is also possible to use a method of providing a tank and returning the precipitated sludge to the first stage digestion tank 8a.

On the other hand, an electrolytic treatment tank 10 is provided in the vicinity of the aerobic digestion tank 8, and sludge in the tank is guided from the first stage digestion tank 8a to the electrolytic treatment tank 10 by the sludge supply pump 11, and the electrolytic treatment after the treatment is performed. The sludge H is connected by piping so as to return the sludge H to the first stage digestion tank 8a.
Further, the adjacent electrolyte storage tank 12 is configured such that a predetermined amount of an electrolyte aqueous solution in which an electrolyte of sodium chloride or potassium chloride is dissolved can be injected into the electrolytic treatment tank 10.
The configuration of the electrolytic treatment tank 10 is 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 fixed to the electrode. It is preferable to provide an apparatus that does not defoam the foamed scum.

Next, the operation of this embodiment will be described.
The concentrated sludge E introduced into the first stage digestion tank 8a of the aerobic digestion tank 8 by the concentrated sludge pump 7 is withdrawn by the sludge supply pump 11 while staying in the first stage digestion tank 8a, and sent to the electrolytic treatment tank 10 And mud is sent.
In the electrolytic treatment tank 10, a predetermined amount of the aqueous electrolyte solution is injected and mixed into the sludge from the electrolyte storage tank 12, and electrolytic treatment is performed by flowing a direct current. That is, by flowing a direct current, chlorine ions in the injected electrolyte are converted into hypochlorous acid and hypochlorite ions, so that sludge microorganisms are sterilized by these oxidizing powers and partly solubilized. .
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 amount of energization 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 H is returned to the first stage digestion tank 8a, but if the operation of extracting the sludge from the first stage digestion tank 8a and electrolytically returning it is performed, highly active sludge microorganisms will be returned. Since it gradually decreases and the aerobic digestion reaction does not proceed, the highly active precipitated sludge G precipitated in the final digestion tank 8c is returned to the first digestion tank 8a.
In addition, the electrolytically treated sludge H is in a state in which sludge microorganisms are sterilized and solubilized and easily biodegraded, and gradually decomposed by living sludge microorganisms. As the sludge microorganisms of 20 to 50% of the reduced amount proliferate, sufficient reduction effect cannot be obtained unless the electrolytic treatment is performed more than the surplus amount of the added sludge.
For this reason, the amount of electrolytic treatment per day is preferably 2 to 5 times the amount of sludge charged per day, and the larger the amount of sludge treated, the greater the amount of precipitated sludge G returned from the precipitation separation zone 8c. It is necessary to set the amount of precipitation sludge G returned to about 2 to 15 times the amount of input sludge.

On the other hand, with the addition of new concentrated sludge, the sludge in the first stage digestion tank 8a overflows into the second stage digestion tank 8b and further to the final stage digestion tank 8c.
In this case, the staying days in the first stage digestion tank 8a is preferably about 2 to 10 days, and the staying days after the second stage digestion tank 8b is preferably about 5 to 20 days, during which the electrolytic treatment sludge gradually biodegrades. In order to reduce the amount, the amount of solids decreases and the sludge concentration decreases as the later stage.
Therefore, the final stage digestion tank 8c is operated as a precipitation separation zone, and the aeration stirring is stopped by closing the valve 82 of the air diffusion pipe 81 of the final stage digestion tank 8c with a timer or the like, and the sludge having a low concentration is left. To accumulate a high concentration of sludge at the bottom.
Then, after the sludge is allowed to settle for a predetermined time, the concentrated sludge pump 7 is started, and new concentrated sludge E is caused to flow from the first stage digestion tank 8a of the aerobic digestion tank 8, and from the final stage digestion tank 8c, The digested sludge F containing a slight amount of sludge solids is caused to overflow from the overflow weir 83.
The sedimentation sludge G precipitated in the final stage digestion tank 8c is returned to the first stage digestion tank 8a by operating the sedimentation sludge return pump 9, and high-activity and high-density sludge microorganisms are returned to the first stage digestion tank. Replenish 8a.
In the case where a separate sedimentation tank is provided after the aerobic digestion tank 8 and the precipitated sludge G is returned to the first digestion tank 8a, the installation space and equipment become large, but the valve 82, the concentrated sludge pump 7 and the intermittent operation control of the settled sludge return pump 9 become unnecessary.

As described above, the sludge treatment method of the present invention divides the aerobic digestion tank 8 into a plurality of stages in the flow direction of the excess sludge D, and inputs the excess sludge D into the first-stage digestion tank 8a of the uppermost stream. The sludge in the first stage digestion tank 8a is guided to the electrolytic treatment tank 10 and electrolyzed, and then returned to the first stage digestion tank 8a, and the most downstream final stage digester tank 8c or aerobic digester tank 8 is returned. The settling sludge G in the settling tank provided in the latter stage is returned to the first stage digesting tank 8a to perform aerobic digestion.
In this way, aerobic digestion and electrolytic treatment are rationally combined, and aerobic digestion is performed on sludge that has been sterilized by electrolytic treatment and partially solubilized and easily decomposed. It is possible to perform aerobic digestion, thereby reducing the amount of sludge discharged outside the field to 1/3 or less of the conventional concentration / dehydration treatment, and the sludge of the first stage digestion tank 8a maintained at a high concentration By performing the electrolytic treatment by extracting the metal, there is an effect that the running cost required for electricity and electrolyte addition can be reduced.
In this case, if the operation of extracting the sludge from the first stage digestion tank 8a, performing electrolytic treatment and returning it is continued, the highly active sludge microorganisms gradually decrease in the first stage digestion tank 8a, and the aerobic digestion reaction. However, the sludge microorganisms deficient by the electrolytic treatment can be replenished by returning the highly active precipitated sludge G precipitated in the final stage digestion tank 8c or the like to the first stage digestion tank 8a.

  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 performs efficient and stable aerobic digestion on sludge easily decomposed by electrolytic treatment, and extracts the sludge from the first stage digestion tank maintained at a high concentration for electrolytic treatment. In addition to the sewage treatment plant that treats domestic sewage with activated sludge, organic wastewater generated in factories, etc. can be reduced. The present invention can also be suitably applied to wastewater treatment facilities that are treated with activated sludge.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pretreatment equipment 2 Aeration tank 3 Precipitation tank 4 Return sludge pump 5 Sludge transfer pump 6 Concentration equipment 7 Concentrated sludge pump 8 Aerobic digester 8a First stage digester 8b Second stage digester 8c Final stage digester 81 Aeration pipe 82 Valve 83 Overflow weir 9 Precipitation sludge return pump 10 Electrolytic treatment tank 11 Sludge supply pump 12 Electrolyte storage tank A Waste water B Treated water C Return sludge D Surplus sludge E Concentrated sludge F Digested sludge G Precipitated sludge

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, After surplus sludge is introduced into the first stage digestion tank, the sludge from the first stage digestion tank is guided to the electrolytic treatment tank and electrolyzed, and then returned to the first stage digestion tank, and the most downstream final stage A method for treating sludge, characterized in that a settling sludge in a settling tank provided downstream of a digestion tank or an aerobic digestion tank is returned to the first stage digestion tank for aerobic digestion.   The method for treating sludge according to claim 1, wherein the electrolytic treatment is performed by adding an electrolyte of sodium chloride or potassium chloride to the electrolytic treatment tank.   The sludge treatment method according to claim 1 or 2, wherein the amount of sludge to be electrolyzed in the electrolytic treatment tank is 2 to 5 times the amount of surplus sludge charged into the first stage digestion tank.   The amount of precipitated sludge to be returned from the final stage digestion tank or the precipitation separation tank to the first stage digestion tank is 2 to 15 times the amount of excess sludge charged into the first stage digestion tank. 2. The method for treating sludge according to 2 or 3.

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