JP2004351353A - Treatment method of sludge - Google Patents

Abstract

An object of the present invention is to provide a sludge solubilization process that incorporates a process for removing phosphorus to prevent deterioration of water treatment and to remove phosphorus only by extracting minimum sludge as surplus sludge. To provide.
SOLUTION: The activated sludge in the aeration tank 2 is used to biologically treat the organic wastewater, solubilize the sludge generated by the biological treatment, and then return the solubilized sludge to the aeration tank 2 for decomposition. In the method for treating sludge, acid is added to the sludge solubilization tank 8 and electrolysis is performed for a predetermined time to promote solubilization of sludge and elution of phosphorus. The sludge floats and separates to perform solid-liquid separation.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for treating sludge that can biologically treat organic wastewater such as sewage with activated sludge and remove organic matter and phosphorus to minimize the amount of generated sludge. It is.
[0002]
[Prior art]
BACKGROUND 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 flows into an activated sludge aeration tank, and is aerated and stirred to perform biological treatment.
Surplus sludge generated in the water treatment process is usually landfilled after dewatering, but since the disposal site is gradually disappearing, ozone is added to the excess sludge to solubilize the sludge. However, a method of reducing the amount of generated sludge to zero by biodegrading in the system has been attempted.
[0003]
[Problems to be solved by the invention]
However, in the above-mentioned conventional method for treating sludge, since the solubilized sludge is returned to the aeration tank as it is, the load on the aeration tank increases, and the capacity of the aeration apparatus becomes insufficient or the water quality deteriorates. There's a problem.
In addition, the technology that eliminates discharged sludge has a drawback in that phosphorus that has been discharged in a form taken into sludge cannot be removed at all.
[0004]
The present invention, in view of the above-mentioned problems of the conventional method for treating sludge, incorporates a process for removing phosphorus in the sludge solubilization process to prevent water treatment from deteriorating and to extract only minimal sludge as surplus sludge. Therefore, an object of the present invention is to provide a method for treating sludge that can also remove phosphorus.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the method for treating sludge of the present invention comprises the steps of biologically treating organic wastewater with activated sludge in an aeration tank and solubilizing sludge generated by biological treatment. In the sludge treatment method in which the sludge was returned to the aeration tank to decompose, an acid was added to the sludge solubilization tank, and an electrolysis treatment was performed for a predetermined time to promote solubilization of the sludge and elution of phosphorus. Thereafter, sludge is floated and separated by fine bubbles generated by the electrolysis treatment to perform solid-liquid separation.
In this case, an alkali agent is added to the separated water obtained by the flotation to insolubilize the phosphorus again, and the inorganic-based sludge containing phosphorus can be separated and discharged.
[0006]
In this activated sludge treatment method, in the activated sludge method, sludge is withdrawn from the final sedimentation tank, guided to a sludge solubilization tank, and subjected to acid addition and electrolysis to promote sterilization of sludge microorganisms and elution of phosphorus. The solubilized sludge is floated and concentrated, returned to the aeration tank for biodegradation, and the separated water obtained by flotation is added with an alkaline agent to adjust the pH, thereby insolubilizing phosphorus again to remove inorganic matter. Because it can be settled and separated as the main sludge, the amount of sludge discharged outside the site can be reduced to about 1/10 of the conventional activated sludge method, and the land required for landfill disposal is small, Even during temporary storage, there is an effect that problems such as anaerobic decay and generation of offensive odor do not occur.
[0007]
Further, a metal salt-based flocculant can be added to the aeration tank.
[0008]
Thereby, the amount of phosphorus recovered per amount of sludge to be treated can be increased.
[0009]
In addition, when the solubilized sludge is floated and separated, flotation separation can be performed after water is poured into the floatation separation tank to dilute the solubilized sludge.
[0010]
As a result, the amount of separated water from which phosphorus is eluted can be increased, so that the amount of phosphorus recovered per amount of sludge to be treated can be increased.
[0011]
Also, when the solubilized sludge is floated and separated, the separated water obtained by the floatation separation is discharged, water is poured into the remaining concentrated sludge and mixed, and the mixture is allowed to stand still to perform the floatation separation. Can be repeated a plurality of times.
[0012]
As a result, the amount of separated water from which phosphorus is eluted can be increased, so that the amount of phosphorus recovered per amount of sludge to be treated can be increased.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a sludge treatment method of the present invention will be described with reference to the drawings.
[0014]
In this sludge treatment method, a predetermined amount of surplus sludge generated in the activated sludge method is withdrawn, led to a sludge solubilization tank, and an acid is added to perform electrolysis treatment, solubilizing sludge and eluting phosphorus. To promote.
After a predetermined reaction time, this is sent to a flotation separation tank to perform solid-liquid separation, and the separated water is drawn out by a pump and led to a precipitation separation tank. In order to increase the amount of separated water collected at this time, it is effective to repeat the operation of injecting water to dilute the solubilized sludge or injecting water to float and separate a plurality of times.
[0015]
To the separated water from which phosphorus has been eluted, an alkaline agent is added and mixed in a precipitation separation tank or a pH adjustment tank provided immediately before the precipitation separation tank to insolubilize phosphorus contained in the separation water again, and the precipitation separation tank To precipitate.
In order to recover more phosphorus, it is effective to add a metal salt-based flocculant to the aeration tank to increase the concentration of phosphorus contained in excess sludge.
The precipitated sludge mainly containing inorganic matter containing phosphorus is taken out of the plant after temporary storage, and the supernatant water is returned to the aeration tank for biological treatment.
On the other hand, the solubilized sludge that has floated in the flotation tank has been sterilized by electrolysis, and can be biodegraded by returning to the aeration tank.
[0016]
In the activated sludge method, of the phosphorus contained in the sewage, solid substances are adhered or adsorbed to the activated sludge, and the soluble phosphoric acid is partially absorbed into the microorganisms, so Some phosphorus is removed from it.
In addition, since the remaining soluble phosphorus flows out with the treated water, if a metal salt-based coagulant such as iron salt is added to the inflow portion to the aeration tank or the final sedimentation tank, it is insolubilized as a phosphoric acid compound and the wastewater Phosphorus removal performance can be improved.
[0017]
Solid phosphorus and phosphate compounds contained in the sludge led from the final sedimentation tank to the sludge solubilization tank can be eluted from the microorganisms by adding acid to lower the pH to 2 or less, It is in a state of being dissolved inside. At this time, if the electrolysis treatment is performed, the sludge microorganisms are killed, and a part of the cell wall and the cell membrane is destroyed, and the components in the microorganisms are dissolved in the liquid.
[0018]
Next, when the solubilized sludge is guided to the flotation tank and allowed to stand still, fine bubbles of oxygen and hydrogen generated by the electrolysis adhere to the sludge surface, so the sludge floats and is concentrated, and the sludge layer is concentrated. Separated water is generated under
After standing for a predetermined time, the separated water is guided to a precipitation separation tank. At this time, after injecting and mixing the water such as the treated water into the flotation tank, and performing flotation or performing the operation of injecting and mixing the water and performing flotation a plurality of times, the sludge exists between the particles of the sludge. Since phosphorus can be recovered as separated water, the amount of phosphorus recovered per solubilization treatment amount can be increased.
[0019]
By adding an alkaline agent to the separated water containing the eluted phosphorus or phosphoric acid in a precipitation separation tank or a pH adjustment tank provided immediately before and raising the pH to 3 or more, most of the phosphorus is again in a solid state. And phosphoric acid can also react with the metal salt to be insolubilized.
At this time, since the inorganic matter dissolved by the acid also returns to a solid matter as the pH increases, the sludge precipitated in the sedimentation separation tank becomes sludge mainly composed of an inorganic substance such as a phosphate compound.
In addition, since the supernatant water of the sedimentation separation tank contains eluted easily decomposable organic substances due to the solubilization treatment, it is returned to the aeration tank as a sedimentation separation liquid to perform biological treatment.
On the other hand, in the sludge that has been floated and concentrated in the flotation tank, microorganisms that retain the cell form remain in addition to the cell walls and cell membrane fragments of the microorganisms. If returned to the tank, it can be decomposed by activated sludge.
As described above, the sludge that increases in the aeration tank is decomposed by adding a solubilization treatment step, and is settled in the sedimentation separation tank, and the sludge that is transported out of the plant is agglomerated phosphate compound and the like. Since the sludge is mainly composed of inorganic substances, the amount of discharged sludge can be reduced to about 1/10 of the conventional sludge.
[0020]
【Example】
FIG. 1 shows an embodiment of the sludge treatment method of the present invention.
The sewage A flowing into a sewage treatment facility such as a sewage treatment plant is sent to the aeration tank 2 after removing sand and residue by the pretreatment facility 1, and is biologically treated by activated sludge. The sewage treated in the aeration tank 2 is sent to the final sedimentation tank 3 as a mixed sludge, separated into solid and liquid, and overflows as treated water B.
In this case, although not shown in the figure, if it is desired to enhance the phosphorus removal performance for the purpose of advanced treatment, a coagulant supply device is added, and an iron or aluminum-based material that reacts with phosphoric acid in wastewater to generate a compound is added. The coagulant is added to the aeration tank 2.
The settled sludge is withdrawn intermittently or continuously by the sludge return pump 4 and returned to the aeration tank 2 as returned sludge C.
[0021]
Part of the settled sludge withdrawn from the final settling tank 3 is transferred as excess sludge D to the gravity thickening tank 6 by the sludge transfer pump 5 and concentrated, and then the sludge supply pump 7 is started periodically to concentrate the sludge. The sludge E is put into the sludge solubilization tank 8.
In the sludge solubilization tank 8, phosphorus is eluted by an acid such as sulfuric acid supplied from the acid supply device 7, and an electrolytic treatment is performed by flowing a direct current between electrodes immersed in the tank.
The solubilized sludge F staying for a predetermined time and sterilized and partially solubilized is guided to the flotation tank 10 and allowed to stand still, and the sludge is floated and separated by fine bubbles generated by the electrolysis treatment to solidify. Separate the liquid and float and concentrate the sludge solids.
[0022]
While the separated water H from the flotation tank 10 is guided to the sedimentation separation tank 14 by the distribution transfer pump 11, the pH is adjusted by injecting an alkali agent such as caustic soda by the alkali supply device 13 in the pH adjustment tank 12. Is done.
The pH may be adjusted in the pipe or in the sedimentation separation tank 14. However, since it is more reliable to control the injection of the alkali agent while stirring, the pH is adjusted in the pH adjustment tank 12 provided separately as shown in the figure. It is appropriate to do.
[0023]
Since the liquid led to the sedimentation / separation tank 14 contains precipitated sludge solids, the sludge is settled by allowing the liquid to stand still, and is periodically drawn into the sludge storage tank 16 by the sludge drawing pump 15. And store temporarily.
The stored sludge K is carried out of the treatment plant by a vacuum truck or the like, but it is also possible to provide a dewatering machine or the like and periodically perform a dewatering treatment.
In addition, the supernatant water J of the sedimentation separation tank 14 is returned to the aeration tank 2. However, since the supernatant liquid is also generated during the temporary storage in the sludge storage tank 15, a pipe for returning the supernatant water must be provided. Is desirable.
[0024]
On the other hand, the sludge G that has floated in the flotation tank 10 can be returned to the aeration tank 2 through a separately provided floating sludge scraping device or a sludge pump. The method of returning to the aeration tank 2 by switching the valve of the branch pipe provided on the side is simple.
[0025]
Next, the operation of the present embodiment will be described.
The concentrated sludge E supplied to the sludge solubilization tank 8 by the sludge supply pump 7 contains phosphoric acid taken into microorganisms, a phosphoric acid compound insolubilized by a coagulant, and solid phosphorus. .
In the sludge solubilization tank 8, the acid is supplied by the acid supply device 9, or the pH is adjusted to a predetermined value of 5 or less, preferably 2 or less based on the indicated value of the pH sensor provided in the sludge solubilization tank 6. Inject the acid until.
Electrodes for electrolysis treatment are arranged in the sludge solubilization tank 8, and a stirrer and a circulating pump are provided to mix the inside of the tank sufficiently and to pass a DC current between the electrodes while allowing the sludge between the electrodes to flow sufficiently. .
At this time, since hypochlorous acid is generated by the electrolysis, the microorganisms in the sludge are sterilized by the hypochlorous acid. In order to generate hypochlorous acid more efficiently, it is preferable to add salt to the acid to be added or to add salt separately. Further, due to the action of the acid, phosphorus is eluted from the microorganisms, phosphorus is dissolved in the liquid from the phosphate compound, and most of the phosphorus is transferred from sludge and solids into water.
That is, microorganisms are killed mainly by the effect of electrolysis, and cell walls and cell membranes constituting the microorganisms are partially damaged and cytoplasm in the cells is eluted, while phosphorus added to solids is mainly caused by the action of acid addition. Elutes into the water of the solubilized sludge.
[0026]
The time of the electrolysis treatment varies depending on the concentration and the current value of the sludge. However, depending on the conditions, the solubilized sludge F subjected to the electrolysis treatment contains fine oxygen and hydrogen bubbles generated by the electrolysis. Is attached to the flotation / separation tank 10 by overflow or a pump, and when it is allowed to stand, sludge solids float and concentrate.
At this time, it is desirable to stop the sludge supply pump 7 and control so that the solubilized sludge does not flow into the floating concentration tank 10.
[0027]
After a predetermined standing time has elapsed, the distribution transfer pump 11 is started, the valve to the pH adjustment tank 12 of the branch pipe is opened, and the separated water collected in the lower part is drawn out to the pH adjustment tank 12. The valve is switched at the stage when the separated water is almost drawn out, and the sludge G that has floated and concentrated is returned to the aeration tank 2.
At this time, since dissolved phosphorus remains in the water between the particles of the floating sludge G, in order to lead more soluble phosphorus to the pH adjusting tank, the dissolved phosphorus is treated in the floating separation tank. After injecting water or water such as separation water from a gravity concentration tank to dilute the solubilized sludge, perform flotation separation, or discharge only the separated water obtained by flotation separation, and drain the remaining concentrated sludge with water. It is appropriate to use a method in which a series of flotation separation operations of injecting, mixing, standing again to carry out flotation, and discharging separated water are repeated a plurality of times.
By performing the operation of increasing the amount of separated water in this manner, the amount of phosphorus recovered per solubilization treatment amount can be increased.
[0028]
Next, when alkali is injected into the separation water H in the pH adjustment tank 12 and the pH is raised to 3 or more, preferably 5 or more, most of the dissolved phosphorus becomes solid again, and phosphoric acid is also removed. It reacts with the metal salt of the coagulant and becomes a phosphoric acid compound and is insolubilized.
At this time, since the inorganic matter dissolved by the acid also returns to the solid matter with the increase in pH, the sludge 1 precipitated in the sedimentation separation tank 14 at the subsequent stage becomes sludge mainly composed of an inorganic substance such as a phosphate compound.
Since the supernatant water J of the sedimentation separation tank 14 contains easily decomposable organic substances eluted by the solubilization treatment, it is returned to the aeration tank 2 and biologically treated with activated sludge.
[0029]
On the other hand, in the sludge G that has floated in the flotation tank 8, fragments of the cell walls and cell membranes of the microorganisms, and microorganisms that have maintained the form of the cells remain. When returned, sludge microorganisms gradually lower the molecular weight and eventually break down into water and carbon dioxide.
[0030]
In the above embodiments, a general water treatment flow has been described. However, instead of the final sedimentation tank 3, a membrane separation device is provided in the aeration tank 2, and a membrane such as a microfiltration membrane or an ultrafiltration membrane is used. Alternatively, a membrane separation activated sludge method for filtering the treated water B may be employed.
As described above, it is possible to increase the sludge concentration by using the membrane, and to perform solubilization treatment using acid and electrolysis on the sludge drawn directly from the aeration tank.
[0031]
【The invention's effect】
According to the method for treating sludge of the present invention, in the activated sludge method, sludge is extracted from the final sedimentation tank, guided to a sludge solubilization tank, and subjected to acid addition and electrolysis to sterilize sludge microorganisms and elute phosphorus. The solubilized sludge is floated and concentrated, returned to the aeration tank for biodegradation, and the separation water obtained by flotation separation is added with an alkaline agent to adjust the pH, thereby re-phosphorizing phosphorus. Since it can be insolubilized and sedimented and separated as inorganic-based sludge, the amount of sludge discharged out of the plant can be reduced to about 1/10 of the conventional activated sludge method, and the land required for landfill disposal is reduced. There is an effect that problems such as anaerobic decay and generation of offensive odor do not occur even during temporary storage during the temporary storage.
[0032]
Also, by adding a metal salt-based flocculant to the aeration tank, the amount of phosphorus recovered per sludge amount to be treated can be increased.
[0033]
Also, when floatation separation of the solubilized sludge, after diluting the solubilized sludge by pouring water into the floatation separation tank, by performing floatation separation, it is possible to increase the amount of separated water from which phosphorus is eluted, The amount of phosphorus recovered per sludge amount to be treated can be increased.
[0034]
In addition, when the solubilized sludge is floated and separated, the separated water obtained by the floatation separation is discharged, water is poured into the remaining concentrated sludge and mixed, and the mixture is allowed to stand still to perform the floatation separation. By repeating a series of flotation operations for discharging wastewater a plurality of times, the amount of separated water from which phosphorus has been eluted can be increased, so that the amount of phosphorus recovered per sludge amount to be treated can be increased.
[Brief description of the drawings]
FIG. 1 is a sewage treatment flow chart showing one embodiment of a method for treating sludge of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pretreatment equipment 2 Aeration tank 3 Final sedimentation tank 4 Sludge return pump 5 Sludge transfer pump 6 Gravity concentration tank 7 Sludge supply pump 8 Sludge solubilization tank 9 Acid supply device 10 Floating separation tank 11 Distribution transfer pump 12 pH adjustment tank 13 Alkaline Feeding device 14 Sedimentation separation tank 15 Sludge extraction pump 16 Sludge storage tank A Sewage B Treatment water C Returned sludge D Excess sludge E Condensed sludge F Solubilized sludge G Floating sludge H Separation water I Extraction sludge J Superficial water K Discharged sludge

Claims (5)

A method for treating sludge, in which organic sludge is biologically treated by activated sludge in an aeration tank and sludge generated by the biological treatment is solubilized, and the solubilized sludge is returned to the aeration tank for decomposition. In addition to adding acid to the sludge solubilization tank and performing electrolysis treatment for a predetermined time to promote solubilization of the sludge and elution of phosphorus, the sludge is floated and separated by fine bubbles generated by the electrolysis treatment. A method for treating sludge, wherein solid-liquid separation is performed. The sludge treatment according to claim 1, wherein an alkali agent is added to the separated water obtained by the flotation to insolubilize phosphorus again, and the sludge mainly containing inorganic substances containing phosphorus is separated and discharged. Method. 3. The method for treating sludge according to claim 1, wherein a metal salt-based flocculant is added to the aeration tank. 4. The method for treating sludge according to claim 1, wherein when the solubilized sludge is floated and separated, water is poured into the floatation separation tank to dilute the solubilized sludge and then floatation separation is performed. At the time of flotation separation of solubilized sludge, drain the separated water obtained by flotation separation, pour water into the remaining concentrated sludge, mix, and stand still again to perform flotation separation and discharge the separated water. 5. The method for treating sludge according to claim 1, wherein a series of flotation operations is repeated a plurality of times.

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